JP2003086871A - Excited light source unit, raman amplifier, and optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such an excited light source unit for Raman amplification or the like that is provided with a structure for adjusting an output signal light spectrum in an amplified wavelength bandwidth. SOLUTION: This excited light source unit (LU) is provided with N sets of excited light sources (11 to 14) to output excited lights with N (>=2) channels having different wavelengths to each other, a multiplexer (2) for multiplexing the excited lights having N channels, and an output structure (3) for supplying the excited light outputted from the multiplexer (2) to an optical fiber (L) for Raman amplification. Especially, at least one of the light sources (11 to 14) is provided with a wavelength variable excited light source that can change the channel wavelength of excited light to be outputted, and such a structure allows for adjustment of the excited light spectrum, thus improving the controllability of the spectrum of outputted signal light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pumping light source unit for Raman amplification used as a light source for supplying pumping light in a Raman amplifier, a Raman amplifier using the same, and an optical transmission system.

[0002]

2. Description of the Related Art An optical fiber amplifier is an optical component that amplifies the power of signal light propagating in an optical fiber transmission line constituting an optical transmission system so as to compensate for transmission loss generated in the optical fiber transmission line. An optical fiber amplifier installed on an optical fiber transmission line includes an optical amplification optical fiber that also functions as a part of the optical fiber transmission line, and a pumping light source that supplies pumping light to the optical amplification optical fiber. When the signal light is input to the optical amplification optical fiber to which the pumping light is supplied, the signal light is amplified in the optical amplification optical fiber.

An example of such an optical fiber amplifier is E
A rare earth element-doped fiber amplifier doped with a rare earth element such as r (erbium) and a Raman amplifier that utilizes a Raman amplification phenomenon by stimulated Raman scattering are used.

Here, a rare earth element-doped fiber amplifier (for example, EDFA: Erbium-Doped Fiber Amplifier, E) is used.
The r-doped fiber amplifier) uses an optical fiber doped with a rare earth element (for example, EDF: Erbium-Doped Fiber, Er-doped optical fiber) as an optical fiber for optical amplification.
On the other hand, the Raman amplifier uses a silica-based optical fiber or the like forming an optical fiber transmission line as a Raman amplification optical fiber.

[0005]

DISCLOSURE OF THE INVENTION As a result of detailed examination of the conventional Raman amplifier, the inventors have found the following problems. That is, among the conventional optical fiber amplifiers, the Raman amplifier has an advantage that an arbitrary wavelength band can be used as an amplification wavelength band by appropriately selecting the wavelength of the pumping light. Further, if a pumping light source unit composed of a plurality of pumping light source units that output pumping lights of a plurality of channels having different wavelengths is used as the pumping light source unit for Raman amplification, a plurality of pumping light source units are supplied from the pumping light source unit. The signal light can be amplified in a wider amplification wavelength band determined by the pumping light of the channel.

Here, when a pumping light source unit including a plurality of pumping light sources is applied to realize a Raman amplifier having a wider amplification wavelength band, in general, a gain spectrum within the amplification wavelength band (gain-wavelength dependence Characteristics) or flattening of the power spectrum of the amplified signal light (wavelength dependence of output signal light power). On the other hand, US Pat. No. 6,115,174 discloses a Raman amplifier to which a plurality of pumping light sources are applied. In this Raman amplifier, the wavelength and power of the pumping light supplied from each pumping light source are set so that the power spectrum of the output signal light is substantially flattened within the amplification wavelength band. In this way, by adjusting the pumping light power in each pumping light source, the pumping light spectrum in the entire pumping channel is adjusted, and as a result, the power spectrum of the output signal light can be adjusted.

However, in such a configuration in which the pumping light spectrum in the entire pumping channel is adjusted only by the pumping light power, the pumping light spectrum and the output signal light spectrum corresponding thereto cannot be sufficiently controlled. For example, when the output signal light spectrum in the amplification wavelength band changes significantly, in the conventional Raman amplifier,
There has been a problem that the output signal light spectrum cannot be adjusted sufficiently to cope with such a change.

Further, in Japanese Patent Laid-Open No. 2000-208840, an optical multiplexer for multiplexing lights from a plurality of pumping light sources and a plurality of optical reflectors provided corresponding to these pumping light sources are disclosed. It is made of a material whose center wavelength change derivative with respect to temperature change in the operating wavelength band is approximately equal, and at the specified temperature within the operating environment temperature range, the optimum wavelength of the input port of the optical multiplexer causes each optical reflection. A configuration approximately equal to the center reflection wavelength of the vessel is disclosed. However,
In the above-mentioned configuration, the optimum wavelengths of the light reflector and the optical multiplexer similarly change with respect to the change of the environmental temperature. As a result, the transmission loss of the excitation light is kept almost constant,
The pumping light power can be maintained, but since wavelength fluctuations are allowed, the Raman amplifier that depends on the pumping light wavelength has a problem that the wavelength shift of the gain spectrum occurs.

The present invention has been made to solve the above problems, and improves the controllability of the pumping light spectrum so that the output signal light spectrum in the amplification wavelength band of the Raman amplifier can be adjusted sufficiently. It is an object of the present invention to provide a pumping light source unit having a structure for performing the above, a Raman amplifier including the pumping light source, and an optical transmission system including the Raman amplifier.

[0010]

A pumping light source unit according to the present invention is a pumping light source for Raman amplification applied as a light source for supplying pumping lights of N (≧ 2) channels having different wavelengths to a Raman amplifier. It is a unit. The pumping light unit includes N pumping light sources, a pumping light multiplexer,
It has an output structure. The N pumping light sources output N-channel pumping lights having different wavelengths. The pumping light multiplexer outputs N pumping light from each of the N pumping light sources.
The pump lights of the channels are combined. The output structure supplies the pumping light multiplexed by the multiplexer to the Raman amplification optical fiber. In particular, the pumping light unit according to the present invention is characterized in that at least one of the N pumping light sources includes a variable wavelength pumping light source capable of changing the channel wavelength of the pumping light to be output.

The pumping light source unit that functions as pumping light supply means in the Raman amplifier includes N pumping light sources that respectively output pumping lights of a plurality of channels, and at least one of the pumping light sources has a wavelength. A variable excitation light source is included. With such a configuration, when adjusting the spectrum of the pumping light supplied from the pumping light source unit, not only the pumping light power of each channel but also the channel wavelength output from the wavelength tunable pumping light source as needed. Can also be adjusted. Therefore, the pumping light source with improved controllability of the pumping light spectrum so as to be able to sufficiently cope with various changes, including the case where the pumping light spectrum in all channels of the output pumping light changes significantly. The unit is realized. Further, by applying such a pumping light source unit to a Raman amplifier, it becomes possible to sufficiently adjust the power spectrum of the output signal light within the amplification wavelength band in the Raman amplifier.

The variable wavelength pumping light source capable of controlling the channel wavelength of the pumping light output includes a pumping laser, a resonance grating and a channel adjusting system as the variable wavelength pumping light source. The resonance grating reflects the light output from the pump laser toward the pump laser. The channel wavelength adjustment system adjusts the reflection wavelength of the resonance grating. As described above, according to the external resonator type laser that uses the resonance grating provided outside the pumping laser, the channel wavelength of the pumping light to be output is efficiently adjusted by adjusting the reflection wavelength of the resonance grating. Controllable.

In the external resonator type, it is preferable that the resonance grating is a Bragg grating that reflects light having a Bragg wavelength. Further, as a specific example of the Bragg grating, a fiber Bragg grating in which at least a core region of the optical fiber has a periodic refractive index change along the longitudinal direction of the optical fiber is applicable. According to such a fiber Bragg grating, both the structure of the external resonance in the wavelength tunable laser and the structure of the optical waveguide for outputting the pumping light from the wavelength tunable laser to the pumping light multiplexer can be realized with a simple structure.

The channel wavelength adjusting system for adjusting the reflection wavelength of the fiber Bragg grating includes stress applying means and heating means. The stress applying means changes the grating period by applying a predetermined stress to the fiber Bragg grating,
Adjust the wavelength of reflected light. The heating means heats the fiber Bragg grating to change the refractive index of the core region portion in which the Bragg grating is formed, and adjust the wavelength of the reflected light.

When the Bragg grating is formed in an optical waveguide made of a material having an electro-optical effect, the channel wavelength adjusting system may include an electric field applying means. The electric field applying means changes the refractive index of the optical waveguide by applying an electric field of a predetermined intensity to the optical waveguide in which the Bragg grating is built. With such a channel tuning system,
Both the structure of external resonance in the wavelength tunable laser and the structure of the optical waveguide that outputs the pumping light from the wavelength tunable laser to the pumping light multiplexer can be realized with a simple structure.

The variable wavelength pumping light source may include a semiconductor laser and heating means for changing the oscillation wavelength of the semiconductor laser by adjusting the chip temperature of the semiconductor laser. Alternatively, the wavelength tunable pumping light source may include a wavelength tunable laser provided with a pumping laser and a wavelength tunable bandpass filter capable of changing the wavelength of the transmitted light. With any of these configurations, it is possible to efficiently control the channel wavelength of the pumping light to be output, as in the external resonator type wavelength tunable laser using the above-mentioned resonance grating.

Further, the pumping light multiplexer may include a transmission characteristic adjusting means for adjusting the transmission wavelength characteristic. Thereby, even when the channel wavelength of the pumping light from each pumping light source multiplexed by the pumping light multiplexer changes, the transmission characteristics in the pumping light multiplexer are adjusted according to the wavelength change, The pumping light of each channel can be appropriately combined.

The pumping light multiplexer is, for example, a plurality of polarization multiplexers for respectively polarization-mixing pumping lights of mutually adjacent channels for each pumping light of two channels having adjacent wavelengths. It is possible to configure a wavelength multiplexer that further wavelength-multiplexes the pumping light output from the polarization multiplexer. Thus, when the polarization multiplexer is applied to the pumping light multiplexer, it is not necessary to adjust the transmission characteristics even if the channel wavelength of the pumping light changes during the polarization multiplexing of the pumping light. Therefore, by combining the polarization multiplexer and the wavelength multiplexer, the excitation light can be easily combined.

It is preferable that the pumping light multiplexer configured as described above further includes a depolarizer provided between the polarization multiplexer and the wavelength multiplexer. By providing the depolarizer in this manner, the influence of the polarization dependence of the amplification gain in Raman amplification when the pumping light source unit is applied to a Raman amplifier is reduced.

Further, the pumping light multiplexer may include an arrayed waveguide type diffraction grating, an interleaver, or a combination thereof. Since the pumping light multiplexer is composed of the arrayed waveguide type diffraction grating and the interleaver, it is possible to favorably cope with the change in the channel wavelength of the pumping light.

Each of the N pumping light sources includes an external resonator type laser having a pumping laser and a resonance grating. At least one of the N external resonator type lasers is a resonance grating. It is preferable that the external cavity type tunable laser further includes a channel wavelength adjusting system for changing the reflection wavelength of the laser. At this time, it is preferable that the pumping light multiplexer includes at least one circulator device and a reflection grating. The circulator device multiplexes the pumping light output from each of the N external resonator type lasers. Each of the reflection gratings is installed between the resonance grating of each external cavity laser and the optical circulator. Further, these reflection gratings have a reflection characteristic of reflecting the excitation light of any channel output from the optical circulator device to the resonance grating toward the optical circulator device. As described above, the pumping lights from the plurality of pumping light sources can be combined by the configuration to which the optical circulator device is applied.

Specifically, the pumping light multiplexer to which the optical circulator device is applied is designed to sequentially combine the N-channel pumping lights outputted from each of the N external resonator type lasers (N -1) connected to stage (N-1)
Includes three 3-port optical circulators. Alternatively, the pumping light multiplexer may include one (N + 1) -port optical circulator that multiplexes N-channel pumping light output from each of the N external resonator type lasers. Furthermore, the pumping light multiplexer may include one (N + 2) -port optical circulator that multiplexes N-channel pumping light output from each of the N external resonator type lasers. In this case, the return light caused by Rayleigh scattering or the like generated in the Raman amplification optical fiber can be effectively blocked, and the output of each of the N pumping light sources can be stabilized.

Further, the pumping light multiplexer may further include an optical isolator provided between the resonance grating and the reflection grating of each of the N external resonator type lasers. As a result, light of a plurality of wavelengths is prevented from externally resonating in the external resonator type laser due to the influence of the reflection grating.

In the channel wavelength adjusting system, the reflection wavelength of the reflection grating, which reflects the pumping light from the external resonator type wavelength tunable laser corresponding to the reflection grating, is changed to the corresponding external resonator wavelength tunable wavelength. It is changed in synchronization with the reflection wavelength of the laser resonance grating. As a result, even when the channel wavelength of the pumping light output from the external resonator type wavelength tunable laser is changed, the pumping light can be reliably reflected by the corresponding reflection grating.

In the pump optical multiplexer to which the optical circulator device is applied, it is preferable that the resonance grating and the reflection grating include a Bragg grating that reflects light having a Bragg wavelength. Specifically, it is preferable that the Bragg grating includes a fiber Bragg grating in which at least a core region of the optical fiber has a periodic refractive index change along the longitudinal direction of the optical fiber. The reflection wavelength of the fiber Bragg grating is changed in the channel wavelength adjusting system, which includes stress applying means, heating means or electric field applying means. The stress applying unit changes the grating period by applying a predetermined stress to the fiber Bragg grating. The heating means is
Heating the fiber Bragg grating changes the index of refraction in the core region. Further, when the Bragg grating is formed on an optical waveguide made of a material having an electro-optical effect, the electric field applying means as the channel wavelength adjusting system applies an electric field of a predetermined intensity to the optical waveguide on which the Bragg grating is formed. The application changes the refractive index of the optical waveguide.

The output structure outputs the pumping light multiplexed by the pumping light multiplexer to the optical transmission line through which the signal light to be Raman-amplified propagates, so that the pumping light is multiplexed with the signal light. Including a multiplexer. However, such an output multiplexer
The output optical fiber of the pumping light source unit may be connected to a multiplexer provided on the optical transmission line side instead of being provided on the pumping light source unit side.

Even if the output of any of the plurality of pumping light sources is reduced, the flatness of the power spectrum of the output signal light (the gain spectrum of the Raman amplifier) is maintained, so that the channel wavelengths of the remaining pumping light sources are maintained. In the above-described configuration in which the pumping light spectrum is adjusted by changing the above, some deterioration of the gain spectrum cannot be avoided.
Therefore, the pumping light source unit according to the present invention, together with the main pumping light supply system that constantly outputs pumping light of a plurality of channels, reduces the output of any one of the pumping light sources included in the main pumping light supply unit. A preliminary pumping light supply system for preventing the deterioration of the pumping light spectrum due to this may be provided.

That is, the pumping light source unit comprises a main pumping light supply system, a multiplexer, an output structure, a preliminary pumping light source system, and an optical switch. The main pumping light supply system includes N pumping light sources that respectively output N (≧ 2) channels of pumping light having different wavelengths in a steady state. The multiplexer multiplexes N-channel pumping light output from each of the N pumping light sources. The output structure outputs the excitation light multiplexed by the multiplexer. The preliminary pumping light supply system includes one or more spare pumping light sources, and at least one of the spare pumping light sources is a variable wavelength pumping light source capable of changing a channel wavelength of pumping light to be output. is there. The optical switch is arranged on the optical path between the main pumping light supply system and the multiplexer. In addition, the optical switch has a configuration in which when the output from any of the N pumping light sources included in the main pumping light supply system is reduced, the output of the pumping light source that has decreased and the output from the preliminary pumping light source are output. Function to switch.

As described above, the main pumping light supply system and the preliminary pumping light supply system are provided, and the channels from the pumping light supplied to the Raman amplification optical fiber are provided by switching the output from these by an optical switch. The wavelength of
Since it is maintained even in the event of a failure of any of the N pumping light sources, the effect on the gain spectrum is small.

It is preferable that the optical switch includes an optical switch utilizing an optical interference effect in order to avoid instantaneous interruption of the pumping light guided to the multiplexer.

Further, the pumping light source unit is provided between the optical switch and the backup pumping light supply system in order to reduce the number of backup pumping light sources included in the backup pumping light supply system and improve cost performance. It is preferable to further include a 1 × M (≧ 2) -port optical switch arranged on the optical path of the above. The pumping light source unit may include an M (≧ 2) port output demultiplexer arranged on the optical path between the optical switch and the preliminary pumping light supply system.

Further, the pumping light source unit may further include a resonance grating arranged on an optical path between the optical switch and the 1 × M port optical switch. The resonance grating has a central reflection wavelength that is substantially equal to the wavelength of the pumping light output from the pumping light source that should be switched via the optical switch among the N pumping light sources. This is because it is possible to prevent reliability deterioration due to the conventional wavelength tunable method.

The pumping light source unit may further include a channel wavelength adjusting system for changing the wavelength of the light reflected by the resonance grating,
In this case, it is possible to effectively reduce the number of preliminary excitation light sources. The channel wavelength adjusting system may include a stress applying unit that changes the grating period by applying a predetermined stress to the resonance grating. Further, the channel wavelength adjusting system may include heating means for changing the refractive index in the core region by heating the resonance grating. When the resonance grating is formed in the optical waveguide made of a material having an electro-optical effect, the channel wavelength adjusting system is configured to apply an electric field of a predetermined intensity to the optical waveguide in which the resonance grating is formed. An electric field applying means for changing the refractive index of the optical waveguide may be included.

A Raman amplifier according to the present invention comprises a Raman amplification optical fiber and a pumping light source unit having the above structure. The Raman amplification optical fiber is supplied with pumping light for Raman amplification and Raman-amplifies the signal light within a predetermined amplification wavelength band. Also, the pumping light source unit supplies pumping light to the Raman amplification optical fiber. With this configuration, the output signal light spectrum in the amplification wavelength band can be sufficiently adjusted. Therefore, it is possible to realize a Raman amplifier with improved controllability of the amplification gain so as to be able to sufficiently cope with various changes including the case where the output signal light spectrum largely changes within this amplification wavelength band. .

The Raman amplifier preferably includes an input power measuring system for measuring the power of the input signal light and a control section. Based on the measurement result of the input power measurement system, the control unit controls the N-channel output from each of the N pumping light source units included in the pumping light source unit so that the output signal light spectrum becomes substantially flat. Controls the power or wavelength of the excitation light.
On the other hand, the Raman amplifier may include an output power measurement system that measures the power of the Raman-amplified output signal light, and a control unit. In this case, the control unit outputs each of the N pumping light sources included in the pumping light source unit so that the output signal light spectrum becomes substantially flat based on the measurement result of the output power measuring system. Controls the power or wavelength of the excitation light. Further, the Raman amplifier may include an instruction signal input system for receiving an instruction signal from the outside and a control unit. In this configuration, the control unit controls each of the N pumping light source units included in the pumping light source unit so that the output signal light spectrum becomes substantially flat on the basis of the instruction signal taken in by the instruction signal input system. It controls the power or wavelength of the pumping light output from the.

In this way, by controlling the pumping light output based on the measurement result of the input signal light power, the measurement result of the output signal light power, or the control instruction by the instruction signal,
The pumping light spectrum of all channels supplied from the pumping light source unit and the power spectrum of the signal light output from the Raman amplifier can be appropriately controlled according to the state of the signal light.

As a concrete control method, the control section controls the power or wavelength of the pumping light so that the output signal light spectrum becomes substantially flat. Also,
The control unit controls the frequency at which the signal light power is minimum in the output signal light spectrum from the frequency to 13
It is preferable to control at least one channel wavelength of the pumping light so as to approach a frequency higher than THz to 15 THz.

Further, the control unit is arranged to such an extent that the power of the pumping light output from one or more pumping light sources of the N pumping light sources included in the pumping light source unit cannot contribute to Raman amplification. When the power is decreased, the power of the pumping light output from the remaining pumping light sources other than the pumping light source whose power has been lowered is controlled so that the power variation of each channel of the Raman-amplified signal light becomes 2 dB or less. preferable.

The optical transmission system according to the present invention comprises a plurality of repeater sections, and the average variation of the output signal light power per repeater section is 2 dB or less. Such an optical transmission system is generally composed of 6 repeater sections,
In particular, the dynamic range of receivable optical power of the avalanche photodiode used in the receiver is -17.
Considering that the output power is about −32 dB, it is necessary to suppress the power variation of the output signal light per relay section to 2 dB, and the total power of the 6 relay sections to about 12 dB.

The optical transmission system according to the present invention is
An optical transmission line through which a signal light within a predetermined signal wavelength band propagates,
The Raman amplifier having the above-described structure is provided at a predetermined position on the optical transmission line. In particular, the Raman amplifier may have a configuration in which a part of the optical transmission line is used as a Raman amplification optical fiber and pumping light is supplied to the optical transmission line. In this case, with respect to the signal light transmitted through the optical transmission line such as the optical fiber transmission line, the optical signal including the distributed constant type optical amplifier capable of sufficiently controlling the power spectrum of the signal light within the signal light wavelength band. A transmission system is realized.

On the other hand, the Raman amplifier included in the optical transmission system according to the present invention may include an optical fiber for Raman amplification separately from the optical transmission line, and the optical fiber for Raman amplification is optically provided in the optical transmission line. Are connected to each other and form a part of the optical transmission line. In this case, for the signal light propagating in the optical transmission line such as the optical fiber transmission line, the power spectrum of the signal light in the signal light wavelength band can be sufficiently controlled.
An optical transmission system including a lumped constant optical amplifier is realized.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a pumping light source unit, a Raman amplifier, and an optical transmission system according to the present invention will be described in detail below with reference to FIGS. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Further, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is a diagram showing the configuration of a first embodiment of an excitation light source unit according to the present invention. The pumping light source unit LU according to the first embodiment is a light source unit applied to a Raman amplifier for Raman-amplifying a plurality of channels of signal light (WDM signals) propagating in a Raman amplification optical fiber. A plurality of channels of pumping light having different wavelengths are supplied to the Raman amplification optical fiber.

The pumping light source unit LU is a pumping light supply system 1 for supplying pumping light of a plurality of channels.
And a pumping light multiplexer 2 that multiplexes the pumping lights of these multiple channels, and an output structure 3 for outputting the multiplexed pumping light to an external optical transmission line L. The pumping light supply system 1 for generating pumping lights of a plurality of channels is composed of a plurality of pumping light sources that respectively output pumping lights having different wavelengths.

In the first embodiment shown in FIG. 1,
The pumping light supply system 1 includes a first pumping light source 11 that outputs pumping light of wavelength λ ₁ , a second pumping light source 12 that outputs pumping light of wavelength λ ₂ (λ ₂ > λ ₁ ), and a wavelength λ ₃ ( a third pumping light source 13 for outputting pumping light of λ ₃ > λ ₂ ) and a wavelength λ
_Fourth pumping light source 14 that outputs pumping light of ₄ (λ ₄ > λ ₃ ).
It is equipped with four excitation light sources. Further, each of these pumping light sources 11 to 14 is a wavelength tunable pumping light source configured such that the wavelengths λ _{1 to} λ ₄ of the pumping light to be output can be variably controlled within a predetermined wavelength range.

The pumping light of the wavelengths λ _{1 to} λ ₄ (four-channel pumping light) output from each of the four wavelength tunable pumping light sources 11 to 14 is combined in the pumping light multiplexer 2, and the predetermined as a whole. The excitation light has a power spectrum of.
Then, the multiplexed pumping light is output to the optical transmission line L through which the signal light propagates via the output structure 3. The output structure 3 is
An output optical waveguide 31 and an output multiplexer 32 are included. As a result, the pumping light multiplexed by the pumping light multiplexer 2 passes through the output optical waveguide 31 and is then multiplexed by the output multiplexer 32 with the signal light propagating in the optical transmission line L.

The pumping light supply system 1 in the pumping light source unit LU which functions as the pumping light source of the Raman amplifier is composed of a plurality of pumping light sources 11 to 14 which respectively output pumping lights of channel wavelengths λ _{1 to} λ _4. To be done. These pumping light sources 11 to 14 are variable wavelength pumping light sources, respectively. With this configuration, the excitation light source unit LU
When adjusting the entire pumping light spectrum supplied from, it is possible to adjust not only the power of each pumping light but also the wavelength of the pumping light output from the tunable pumping light sources 11 to 14 as necessary. it can.

That is, when the pumping light source unit composed of a plurality of pumping light sources is applied to the Raman amplifier, the gain spectrum or the power spectrum of the output signal light is generally flattened within the amplification wavelength band which is a wide band. Is required. The power spectrum of the signal light output from the Raman amplifier to be adjusted is determined by the power spectrum of the pump light supplied from the pump light source unit. Therefore, in order to adjust the power spectrum of the signal light output from the Raman amplifier, it is necessary to adjust the power spectrum of the pump light output from the pump light source unit.

For such adjustment of the excitation light spectrum, there is a method of adjusting the excitation light power of each channel output from each excitation light source included in the excitation light source unit. However, such an adjusting method cannot obtain sufficient controllability of the excitation light spectrum. For example, when the power of one of the plurality of pumping light sources included in the pumping light source unit is down, the vicinity of the signal light wavelength corresponding to the channel wavelength of the pumping light supplied by the down pumping light source is close. Therefore, the power spectrum of the output signal light drops significantly. In such a case, even if the power of the pumping light supplied by the remaining pumping light sources excluding the pumping light source that is down is adjusted, it is not possible to sufficiently compensate for the dip in the power spectrum of the output signal light. Can not.

On the other hand, according to the pumping light source unit LU having a plurality of pumping light sources 11 to 14 each of which is a variable wavelength pumping light source, the power spectrum of the pumping light to be output in the entire channel In order to be able to fully respond to various changes, including the case where
A pumping light source unit LU with improved controllability of the pumping light spectrum is realized. Further, if such a pumping light source unit LU is applied to a Raman amplifier, it becomes possible to sufficiently adjust the power variation of the output signal light within the amplification wavelength band in the Raman amplifier.

Adjustment of the pumping light spectrum and flattening of the output signal light spectrum in the pumping light source unit LU shown in FIG. 1 will be described with reference to FIGS. 2 and 3.

FIG. 2 shows the power spectrum of the pumping light supplied from the pumping light source unit LU shown in FIG. 1, and the horizontal axis shows the pumping light wavelength λ. During normal operation of the pumping light source unit LU, four wavelength tunable pumping light sources 11 to 14 are used to pump four channels of pumping light having wavelengths λ _{1 to} λ ₄ indicated by broken lines in FIG. Is supplied.

Here, when the power of the third pumping light source (wavelength variable pumping light source) 13 out of the four pumping light sources 11 to 14 is lowered and the pumping light of the wavelength λ ₃ is no longer supplied. think about. At this time, in the Raman amplifier to which the pumping light source unit LU is applied, the power spectrum of the output signal light drops significantly near the signal light wavelength corresponding to the pumping light wavelength λ ₃ .

FIG. 3 is an output signal light spectrum in a Raman amplifier to which the pump light source unit LU shown in FIG. 1 is applied, and the horizontal axis represents the channel wavelength (nm) of the signal light amplified by the pump light. Shows. Moreover, the vertical axis represents the signal light output power (0.5 dBm / div) at each channel wavelength of the signal light.

In the normal operation of the pumping light source unit LU, which is supplied with the four-channel pumping light of wavelengths λ _{1 to} λ ₄ ,
By optimizing the power of the pumping light supplied from each of the pumping light sources 11 to 14, as indicated by the broken line S, the power spectrum of the signal light output from the Raman amplifier is substantially flattened. At this time, if the pumping light source 13 goes down and the pumping light of the channel wavelength λ ₃ is no longer supplied,
As shown by the broken line Sd, the power spectrum of the output signal light shows that the amplification gain and the signal light output power are large near the signal light wavelength corresponding to the pumping light wavelength λ ₃ (near wavelength 1565 nm in FIG. 3). I am depressed.

On the other hand, in the pumping light source unit LU according to the first embodiment, the wavelengths λ ₁ supplied from the three tunable pumping light sources 11, 12 and 14 remaining without being downed, The pumping light of the three channels of λ ₂ and λ ₄ is
As shown by the solid lines in FIG. 2, the pumping light wavelengths are changed in the wavelength axis directions approaching the wavelength λ ₃ , respectively, and adjusted to λ ₁ ′, λ ₂ ′, and λ ₄ ′, respectively. This allows
The power spectrum of the pump light supplied from the pump light source unit LU viewed from the entire channel is adjusted, and the power spectrum of the signal light output from the Raman amplifier is as flat as possible, as shown by the solid line S ′ in FIG. Be converted. Specifically, the three wavelength tunable pumping light sources 11, 12 and 14 remaining without being down-shifted are wavelength-controlled so that the power variation for each channel of the Raman-amplified signal light is 2 dB or less. Is preferred.

The pumping light source unit LU according to the first embodiment utilizing a plurality of variable wavelength pumping light sources 11 to 14 is
As described above, it has excellent controllability with respect to the adjustment of the output signal light spectrum changed within the amplification wavelength band. Further, such a pumping light source unit LU is also effective for various adjustments to the output signal light spectrum other than flattening the power spectrum of the output signal light.

For example, when the output signal light spectrum in two or more different wavelength bands is flattened and used as an amplification wavelength band (two or more Raman amplifiers of the same configuration are used), a pumping light source unit having the above-mentioned structure. L
If it is U, it is possible to change the amplification wavelength band, which is a band in which the output signal light spectrum is flattened, by shifting the pumping light spectrum as a whole with respect to the wavelength.

In the pumping light source unit LU shown in FIG. 1, the plurality of pumping light sources 11 to 14 included in the pumping light supply system 1 are all tunable pumping light sources. Regarding the number of the above, if at least one of the plurality of pumping light sources is a wavelength tunable pumping light source, the pumping light channel wavelength may be fixed in other pumping light sources. Regarding the number of such variable wavelength pumping light sources or the ratio of the variable wavelength pumping light sources in the pumping light supply system 1, the channel spacing (wavelength spacing) of each pumping light or the Raman to which the pumping light source unit is applied It may be appropriately set according to the controllability of the output signal light spectrum required by the amplifier.

Further, in the pumping light source unit LU shown in FIG. 1, the output structure 3 for outputting pumping light to the optical transmission line L, in addition to the output optical waveguide 31, combines pumping light and signal light. The output multiplexer 32 for wave is provided. The output multiplexer 32 has a structure in which only the output optical waveguide 31 is provided without providing a multiplexer on the pumping light source unit LU side, and the pumping light source unit is provided on the coupler provided on the optical transmission line L side. The configuration may be such that the output optical waveguide 31 of the LU is connected. Alternatively, the output end of the pumping light multiplexer 2 may be included in the output structure as it is.

Further, FIG. 1 shows a configuration in which the pumping light from the output optical waveguide 31 is guided to the optical transmission line L in the direction opposite to the transmission direction of the signal light. The direction may be a forward direction that matches the transmission direction of the signal light, depending on the configuration of the Raman amplifier and the like.

FIG. 4 is a diagram showing the configuration of the second embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the second embodiment is, as a plurality of pumping light sources constituting the pumping light supply system, channel wavelengths λ _{1 to} λ ₄ (λ ₁ <λ ₂₎ as in the first embodiment. <
Four wavelength variable pumping light sources 11 to 14 for outputting pumping light of λ ₃ <λ ₄ ) are provided.

Further, as the pumping light multiplexer 2 which multiplexes the pumping light output from each of the pumping light sources 11 to 14,
A wavelength multiplexer 21 that multiplexes the excitation light according to the wavelength is provided.

The structure of the excitation light sources 11 to 14 will be described by taking the first excitation light source 11 as an example. In the second embodiment, the first wavelength tunable pumping light source 11 is a first semiconductor laser 1 suitable for a pumping laser as its pumping light generation source.
Have 10. This semiconductor laser 110 and wavelength multiplexer 2
An optical waveguide 111 for guiding the excitation light from the excitation light source 11 to the wavelength multiplexer 21 is provided between the optical waveguide 111 and the optical waveguide 1. The semiconductor laser 1 is placed at a predetermined position on the optical waveguide 111.
A resonance grating 112 that reflects the light output from 10 is provided. As the resonance grating, a Bragg grating that reflects light having a Bragg wavelength is preferable. Further, the pumping light source 11 preferably includes a channel wavelength adjusting system for adjusting the reflection wavelength of the resonance grating 112. Accordingly, the semiconductor laser 110 as the pumping light source 11 and the resonance grating 112 provided on the optical waveguide 111 can control the wavelength of the pumping light to be output. A tunable laser is obtained.

In the second embodiment, the four pumping light sources 11 to 14 are all variable wavelength pumping light sources.
The other three excitation light sources 12 to 14 are also the first
It has the same configuration as the wavelength variable pumping light source 11.

That is, the second wavelength variable pumping light source 12
Is a second semiconductor laser 120 suitable for an excitation laser and a resonance grating 12 provided on an optical waveguide 121.
2. An external resonator type wavelength tunable laser provided with a channel wavelength adjusting system for adjusting the reflection wavelength of the resonance grating. In addition, the third wavelength variable pumping light source 13
Also, a third semiconductor laser 130 suitable for an excitation laser and a resonance grating 13 provided on the optical waveguide 131.
2 and a channel wavelength adjustment system for adjusting the reflection wavelength of the resonance grating. Furthermore, the fourth
The variable wavelength pumping light source 14 includes a fourth semiconductor laser 140 suitable for a pumping laser, a resonance grating 142 provided on the optical waveguide 141, and a channel wavelength adjusting system for adjusting the reflection wavelength of the resonance grating. It is an external cavity type wavelength tunable laser provided with.

The pumping lights of the channel wavelengths λ _{1 to} λ ₄ output from the four wavelength tunable pumping light sources 11 to 14 are combined by the wavelength combiner 21 which is the pumping light combiner 2, and all of them are combined. It has a predetermined power spectrum in a wavelength band including channels. Then, the multiplexed excitation light is output to the optical transmission line L through the output structure 3 including the output optical waveguide 31 and the output multiplexer 32.

According to the pumping light source unit LU of the second embodiment, the resonance gratings 112 to 142 are used.
By variably controlling the wavelength of the light reflected by
Wavelength variable pumping light sources 11 to 1 which are external resonator type lasers
It is possible to efficiently control the wavelengths λ _{1 to} λ ₄ of the pumping light output from each of the four.

FIG. 5 is a power spectrum of the pumping light supplied from the pumping light source unit LU according to the second embodiment shown in FIG. In FIG. 5, channel wavelengths λ _{1 to} λ ₄
An example of adjusting each channel wavelength of the pumping light to the wavelengths λ ₁ ', λ ₂ ' and λ ₄ '(broken line) when the pumping light of the channel wavelength λ ₃ of the pumping light (dotted line) is powered down. It is shown. Even in the second embodiment, the remaining three wavelength tunable pump light sources 11, 12 and 14 which are not downed have a power variation of 2 dB or less for each channel of Raman-amplified signal light. The wavelength is preferably controlled.

When the external resonator type laser having the above-mentioned structure is applied as the variable wavelength pumping light source, the Bragg grating is preferable as the resonance grating for the external resonance of the pumping light. Further, with respect to the specific configuration of the Bragg grating, various forms of grating can be applied.

FIG. 6 is a diagram showing an example of a first configuration of a wavelength variable pumping light source applied to the pumping light source unit LU shown in FIG. However, in FIG. 6, among the four pumping light sources 11 to 14, the first wavelength tunable pumping light source 1 is used.
Only one configuration is shown. Other excitation light sources 12-1
No. 4 has the same structure as the first wavelength tunable pumping light source 11 shown in FIG.

The first wavelength tunable pumping light source 11 is provided with a first semiconductor laser 110 and a resonance grating 112 provided on the optical waveguide 111, and is tuned by external resonance between the semiconductor laser 110 and the resonance grating 112. It is an external resonator type wavelength tunable laser that generates pumping light with a channel wavelength λ ₁ .

FIG. 6 shows an optical waveguide 111 that guides the pumping light output from the pumping light source 11 to the wavelength multiplexer 21.
An optical fiber 111a provided between the semiconductor laser 110 and the wavelength multiplexer 21 is shown. Further, the resonance grating 11 is provided at a predetermined portion of the optical fiber 111a.
2, a fiber Bragg grating 112a is built in.

Further, the pumping light source 11 is provided with a channel wavelength adjusting system 112b for adjusting the reflection wavelength of the fiber Bragg grating 112a. The channel wavelength adjustment system 112b is controlled by a control signal from the outside. As a result, the resonance grating 1 having the channel wavelength λ ₁ of the pumping light
The 12 reflected wavelengths are adjusted.

According to such a fiber grating, the pumping light source 11 which is an external resonator type wavelength tunable laser is used.
It is possible to realize both the configuration of the external resonance in and the configuration of the optical waveguide 111 that outputs the excitation light from the excitation light source 11 to the wavelength multiplexer 21 with a simple configuration.

As the channel wavelength adjusting system 112b, for example, a stress applying means can be applied. The stress applying unit causes the optical fiber 111a to expand and contract by applying a predetermined stress to the optical fiber 111a. As a result, the fiber Bragg grating 11
The grating period of 2a is changed, and the reflection wavelength of the resonance grating 112 is adjusted. The channel wavelength λ ₁ of the pumping light supplied from the pumping light source 11 is controlled by the external resonator composed of the resonance grating 112 whose reflection wavelength is adjusted and the semiconductor laser 110.

The channel wavelength adjusting system 11
As 2b, heating means can also be applied. This heating means heats the optical fiber 111a to thereby cause the grating refractive index of the fiber Bragg grating 112a (the refractive index of the core region of the optical fiber 111a having the fiber Bragg grating 112a built therein).
Change. As a result, the resonance grating 11
The channel wavelength of the pumping light supplied from the pumping light source 11 is controlled by changing the reflection wavelength of No. 2.

Here, as shown in FIG. 6, when the channel wavelength of pumping light supplied from the pumping light source is controlled by using the channel wavelength adjusting means such as a resonance grating, the pumping light is multiplexed. The transmission wavelength characteristic of light in the pumping light multiplexer 2 such as the wavelength multiplexer 21 may cause a problem.

FIG. 5 shows the channel wavelength λ ₁ before wavelength adjustment.
~ Λ ₄ pump light, and the channel wavelength λ ₁ 'after wavelength adjustment,
Transmission wavelength characteristics T _{1 to} T ₄ are shown as an example of transmission wavelength characteristics (combining wavelength characteristics) in the wavelength multiplexer 21 with respect to λ ₂ ′ and λ ₄ ′ excitation lights.

These transmission wavelength characteristics T _{1 to} T ₄ are generally optimized so that the pumping lights of the channel wavelengths λ _{1 to} λ ₄ are satisfactorily multiplexed during the normal operation of the pumping light source unit LU. Has been done. On the other hand, the channel wavelengths of other pumping lights are changed to λ ₁ ', λ ₂ ', and λ ₄ 'to adjust the pumping light spectrum in response to the power down of the pumping light of the channel wavelength λ _3. In some cases, the wavelength multiplexer 21 may not be able to obtain sufficient transmission characteristics for pumping light with a large amount of change in channel wavelength.

[0081] For example, as shown in FIG. 5, the channel wavelength lambda ₄ of excitation light near the channel wavelength lambda ₃ of the excitation light power down, channel wavelength from lambda ₄ due to the wavelength tuning to lambda ₄ ' The amount of change is large. When there is a possibility that the channel wavelength of the pumping light is significantly changed in this way, the wavelength multiplexer 21 is required to ensure sufficient transmission characteristics for the pumping light of each channel in the pumping light multiplexer 2. It is preferable to have a structure capable of adjusting the transmission wavelength characteristic.

FIG. 7 is a diagram showing an example of the configuration of a pumping light source unit having a pumping light multiplexer whose transmission wavelength characteristic can be adjusted. In the configuration of FIG. 7, the transmission characteristic adjusting system 22 for adjusting the transmission characteristic of the wavelength multiplexer 21 is used.
Is provided. The pumping light multiplexer 2 whose transmission wavelength characteristic can be adjusted is constituted by the wavelength multiplexer 21 and the transmission characteristic adjusting system 22. Transmission characteristic adjustment system 22
Is controlled by a control signal from the outside. As a result, the pumping light multiplexer 2 is changed in accordance with changes in the channel wavelengths λ _{1 to} λ ₄ of the pumping light output from the pumping light sources 11 to 14.
The transmission characteristics of the excitation light in are optimally controlled.

The wavelength tunable pumping light source applied to the pumping light source unit is not limited to the external resonator type wavelength tunable laser utilizing the fiber Bragg grating shown in FIG. 6, and various pumping light sources can be used. Applicable.

FIG. 8 is a diagram showing a second configuration of a wavelength variable pumping light source applicable to the pumping light source unit shown in FIG. In this case, the wavelength tunable pumping light source 11 includes a first semiconductor laser 110, a resonance grating 112 provided on the optical waveguide 111, and a channel wavelength adjusting system as an electric field applying unit 112d. The pumping light source 11 is an external resonator type wavelength tunable laser that uses the first semiconductor laser 110 and the resonance grating 112 to generate pumping light having a channel wavelength λ ₁ by external resonance.

In FIG. 8, as the optical waveguide 111 for guiding the pumping light output from the pumping light source 11 to the wavelength multiplexer 21, the optical fiber 111b is sequentially provided from the semiconductor laser 110 toward the wavelength multiplexer 21. , An optical waveguide 111c, and an optical fiber 111d are provided.

Of these optical waveguides, the optical waveguide 11
Reference numeral 1c is an optical waveguide formed of a material having an electro-optical effect on a predetermined substrate. In addition, the optical waveguide 111
A Bragg grating 112c is formed as a resonance grating 112 at a predetermined portion of c.

Further, the electric field applying means, which is a channel wavelength adjusting system, is provided with a pair of electrodes 112d arranged on the same substrate with the Bragg grating 112c interposed therebetween so as to apply an electric field of a predetermined intensity to the Bragg grating 112c. . The electrode 112d is controlled by a control signal from the outside. As a result, the reflection wavelength at the resonance grating 112, which is the channel wavelength λ ₁ of the pumping light, is variably controlled. That is, when an electric field of a predetermined intensity is applied to the optical waveguide 111c having an electro-optical effect by the electrode 112d which is an electric field applying means, the reflection wavelength of the Bragg grating 112c changes. As a result, the channel wavelength λ _{1 of the} pumping light supplied from the pumping light source 11 can be variably controlled.

Also with such a grating, the structure of the external resonance in the pumping light source 11 which is the external resonator type wavelength tunable laser, and the wavelength multiplexer 2 from the pumping light source 11 are used.
Both of the configuration of the optical waveguide 111 that outputs the excitation light to the first component can be realized with a simple configuration.

FIG. 9 is a diagram showing a third configuration of a wavelength variable pumping light source applicable to the pumping light source unit shown in FIG. This wavelength tunable pumping light source 11 is a heating means 11 for adjusting the temperature of the first semiconductor laser 110 and the chip of the semiconductor laser 110 as a channel wavelength adjusting system.
3 and 3. The heating means 113 is controlled by a control signal from the outside. As a result, the oscillation wavelength of the semiconductor laser 110, which becomes the channel wavelength λ ₁ of the pumping light, is variably controlled.

FIG. 10 is a diagram showing a fourth structure of a wavelength tunable pumping light source applicable to the pumping light source unit shown in FIG. The wavelength tunable pump light source 11 is a fiber ring wavelength tunable laser that uses the first pump laser 114 and the ring-shaped optical fiber 115 to generate pump light having a channel wavelength λ ₁ .

The ring-shaped optical fiber 115 includes a rare earth element-doped optical fiber having a light amplification function. A wavelength multiplexer 116 is installed at a predetermined position of the ring-shaped optical fiber 115 on the pump laser 114 side. The light output from the pumping laser 114 is supplied to the ring-shaped optical fiber 115 via this wavelength multiplexer 116 and is amplified in the ring-shaped optical fiber 115 which is a rare earth element-doped optical fiber. An optical isolator 118 and a bandpass filter 119 are installed at predetermined positions on the ring-shaped optical fiber 115, and the bandpass filter 11
The channel wavelength λ _{1 of the} pumping light generated in the pumping light source 11 is determined according to the transmission wavelength characteristic of the pump light 9.

A branching device 117 for branching the light at a constant ratio is installed at a predetermined position on the wavelength multiplexer 21 side of the ring-shaped optical fiber 115. Ring-shaped optical fiber 115
The light of the channel wavelength λ ₁ amplified by
It is branched to the optical waveguide 111 by 7 and is output to the wavelength multiplexer 21 as excitation light.

In the wavelength tunable pumping light source 11 of FIG. 10, the bandpass filter 119 that determines the channel wavelength λ ₁ of the pumping light amplified by the ring-shaped optical fiber 115 is a tunable bandpass filter whose transmission wavelength can be changed. (Included in the channel tuning system) is utilized. The bandpass filter 119 is controlled by a control signal from the outside. As a result, the channel wavelength λ ₁ of the pumping light is variably controlled in the ring-shaped optical fiber 115.

As the bandpass filter 119 whose transmission wavelength characteristic is variable, for example, an optical filter made of a dielectric multilayer film can be used. The dielectric multilayer filter can variably and easily control the transmission wavelength characteristic by rotating the angle of the filter with respect to the optical path of the light to be transmitted. Further, a bandpass filter other than the dielectric multilayer film filter can be used.

Regarding the embodiment of the excitation light source unit,
Further description will be made.

FIG. 11 is a diagram showing the configuration of the third embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the third embodiment has a plurality of pumping light sources that form a pumping light supply system and have channel wavelengths λ _{1 to} λ ₄ (λ ₁ <λ ₂ <λ ₃ <λ ₄ ), respectively. It is provided with four wavelength variable pumping light sources 11 to 14 which output pumping light. The configuration of each of the excitation light sources 11 to 14 is shown in FIG.
It is similar to the second embodiment shown in FIG.

Further, the pumping light multiplexer 2 for multiplexing the pumping light output from each of the pumping light sources 11 to 14 has two polarizations for respectively multiplexing pumping lights of two channels having adjacent wavelengths. It is composed of multiplexers 23a and 23b, and a wavelength multiplexer 21 that multiplexes the excitation light by wavelength.

Of the four variable wavelength pumping light sources 11 to 14, the pumping lights of the channel wavelengths λ ₁ and λ _{2 which} are adjacent to each other and are output from the pumping light sources 11 and 12 are polarization multiplexers. The polarized wave is multiplexed by 23a. Also, the excitation light source 1
The pumping lights of the channel wavelengths λ ₃ and λ _{4 having} wavelengths adjacent to each other, which are output from 3 and 14, are polarization-multiplexed by the polarization multiplexer 23b.

Further, the pumping light of the channel wavelengths λ ₁ and λ ₂ output from the polarization multiplexer 23a and the pumping light of the channel wavelengths λ ₃ and λ ₄ output from the polarization multiplexer 23b are After being multiplexed by the multiplexer 21, the pumping light having the predetermined pumping light spectrum as a whole is output from the wavelength multiplexer 21. Then, the multiplexed excitation light is output to the optical transmission line L via the output structure configured by the output optical waveguide 31 and the output multiplexer 32.

As described above, when the polarization multiplexers 23a and 23b are applied to the pump light multiplexer 2 that multiplexes the pump light, the polarization multiplexers 23a and 23b do not combine the pump light into polarizations. ,
It is not necessary to adjust the transmission characteristics even when the channel wavelength of the pumping light supplied from each of the pumping light sources 11 to 14 changes. Therefore, the plurality of polarization multiplexers 23a, 23a
By combining b and the wavelength multiplexer 21 to form the pumping light multiplexer 2, the pumping light can be easily multiplexed.

FIG. 12 is a power spectrum of the pumping light supplied from the pumping light source unit LU shown in FIG. 12, the channel wavelengths λ _{1 to} λ ₄ are the same as in FIG.
An example of adjusting the pump lights of the channel wavelengths λ ₁ ′, λ ₂ ′, and λ ₄ ′ when the pump light of the channel wavelength λ ₃ among the pump lights of 1) is powered down is shown. In addition, in FIG.
The transmission wavelength characteristics T _a and T _b of the wavelength multiplexer 21 with respect to the pumping light output from the polarization multiplexers 23a and 23b are shown.

In the wavelength multiplexer 21, since the pumping light is polarization-multiplexed by the polarization multiplexers 23a and 23b in the preceding stage, as shown in FIG. 12, its transmission wavelength characteristic T _a ,
It is preferable that T _b has transmission wavelength characteristics in a rather wide wavelength range. In this case, even if the channel wavelength of the pumping light changes to some extent, sufficient transmission characteristics can be obtained.

FIG. 13 is a diagram showing the configuration of the fourth embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the fourth embodiment has a plurality of pumping light sources that form a pumping light supply system and have channel wavelengths λ _{1 to} λ ₄ (λ ₁ <λ ₂ <λ ₃ <λ ₄ ), respectively. It is provided with four wavelength variable pumping light sources 11 to 14 which output pumping light. The configuration of each of the excitation light sources 11 to 14 is shown in FIG.
It is similar to the second embodiment shown in FIG.

Further, the pumping light multiplexer 2 which multiplexes the pumping light output from each of the pumping light sources 11 to 14 includes two polarization multiplexing devices which combine two channels of pumping light whose wavelengths are adjacent to each other. The wave filters 23a and 23b and the wavelength multiplexer 21 that multiplexes the excitation light according to the wavelength are provided. Furthermore, the pumping light multiplexer 2 in the fourth embodiment includes the polarization multiplexer 2
Depolarizers 24a and 24b are installed between 3a and 23b and the wavelength multiplexer 21, respectively.

Of the four wavelength variable pumping light sources 11 to 14, the pumping lights of the channel wavelengths λ ₁ and λ ₂ which are the wavelengths output from the pumping light sources 11 and 12 adjacent to each other are the polarization multiplexer 23 a. Are polarized and multiplexed by the depolarizer 24a, and depolarized by the depolarizer 24a. Further, the wavelengths output from the pumping light sources 13 and 14 are channel wavelengths λ ₃ and λ ₄ which are adjacent to each other.
The excitation light of is polarized and multiplexed by the polarization multiplexer 23b,
It is depolarized by the depolarizer 24b.

Further, the pumping light of the channel wavelengths λ ₁ and λ ₂ output from the polarization multiplexer 23a via the depolarizer 24a and the channel wavelength λ output from the polarization multiplexer 23b via the depolarizer 24b. The pump lights of ₃ and λ ₄ are multiplexed by the wavelength multiplexer 21, and the wavelength multiplexer 21 outputs the pump light having a predetermined pump light spectrum as a whole. Then, the multiplexed pumping light is output to the optical transmission line L via the output structure including the output optical waveguide 31 and the output multiplexer 32.

The pumping light multiplexer 2 is connected to the polarization multiplexers 23a and 23a.
In the configuration to which b is applied, the polarization multiplexing is performed on the pumping lights of different two channels, and therefore the pumping light that is polarization-combined by the polarization combiner 23a and the polarization combining is performed by the polarization combiner 23b. The polarization state is different from that of the excitation light. In this case, the Raman amplification gain may change under the influence of the polarization state of the pump light. On the other hand, as in the pumping light source unit according to the fourth embodiment, the polarization multiplexer 23
According to the configuration in which the depolarizers 24a and 24b are installed in the subsequent stages of a and 23b, the influence of the polarization dependence of the Raman amplification gain is effectively reduced.

FIG. 14 is a diagram showing the configuration of the fifth embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the fifth embodiment has a plurality of pumping light sources that form a pumping light supply system and has channel wavelengths λ _{1 to} λ ₄ (λ ₁ <λ ₂ <λ ₃ <λ ₄ ), respectively. It is provided with four wavelength variable pumping light sources 11 to 14 which output pumping light. The configuration of each of the excitation light sources 11 to 14 is shown in FIG.
It is similar to the second embodiment shown in FIG.

In the fifth embodiment, the arrayed waveguide diffraction grating (AW) is used as the pumping light multiplexer 2 that multiplexes the pumping lights output from the pumping light sources 11 to 14, respectively.
G: Arrayed Waveguide Grating) 25 is provided.

The pumping lights of the channel wavelengths λ _{1 to} λ ₄ output from the four wavelength tunable pumping light sources 11 to 14 are multiplexed by the AWG 25, which is the pumping light multiplexer 2, and the pumping light multiplexers are combined. 2 outputs pumping light having a predetermined pumping light spectrum as a whole. Then, the multiplexed pumping light is output to the optical transmission line L via the output structure including the output optical waveguide 31 and the output multiplexer 32.

FIG. 15 is a power spectrum of the pumping light supplied from the pumping light source unit LU shown in FIG. FIG. 15 shows an example in which the channel wavelengths λ _{1 to} λ ₄ of the pumping light are changed to the wavelengths λ ₁ ′ to λ ₄ ′ which are totally shifted. Further, FIG. 15 also shows the transmission wavelength characteristic T of the AWG 25.

The AWG 25, as shown in FIG.
It has a transmission wavelength characteristic T that is periodic with respect to the channel wavelength λ. Therefore, the channel intervals (wavelength intervals) of the channel wavelengths λ _{1 to} λ ₄ of the pumping light supplied from the pumping light sources 11 to 14 or the channel wavelengths are respectively set to the wavelength λ
Channel wavelength change amount AW when changing to ₁ 'to [lambda] _4'
If the wavelength cycle of the transmission wavelength characteristic T in G25 matches, the pumping lights from the pumping light sources 11 to 14 can be suitably combined even when the channel wavelength of the pumping light is changed overall. You can Such a multiplexing characteristic is particularly effective in the case where the channel wavelength of each pumping light is entirely shifted and the amplification wavelength band in the Raman amplifier is shifted, as shown in FIG.

FIG. 16 is a diagram showing the configuration of the sixth embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the sixth embodiment outputs two pumping lights of channel wavelengths λ ₁ and λ ₂ (λ ₁ <λ ₂ ) as a plurality of pumping light sources constituting the pumping light supply system. The wavelength tunable excitation light sources 11 and 12 are included. The configuration of each of the excitation light sources 11 and 12 is the second one shown in FIG.
It is similar to the embodiment.

Further, in the sixth embodiment, an interleaver 26 is provided as the pumping light multiplexer 2 that multiplexes the pumping lights output from the pumping light sources 11 and 12.

The pumping lights of the channel wavelengths λ ₁ and λ ₂ output from the two wavelength tunable pumping light sources 11 and 12 are combined by the interleaver 26 which is the pumping light multiplexer 2, and the interleaver 26 The leaver 26 outputs pumping light having a predetermined pumping light spectrum as a whole. Then, the multiplexed pumping light is output to the optical transmission line L via the output structure including the output optical waveguide 31 and the output multiplexer 32.

FIG. 17 shows the power spectrum of the pumping light supplied from the pumping light source unit LU shown in FIG. In FIG. 17, the channel wavelength λ of the two-channel pump light is shown.
_1, generally the wavelength lambda ₂ is lambda ₁ ', lambda _2' Example shifted in is shown. In addition, in FIG. 17, the excitation light sources 11 and 12 are shown.
The transmission wavelength characteristics T ₁ (solid line) and T ₂ (broken line) of the interleaver 26 with respect to the pumping light output from each of the above are shown.

As shown in FIG. 17, the interleaver 26 has periodic transmission wavelength characteristics T ₁ and T ₂ with respect to the channel wavelength λ. Also, the transmission wavelength characteristics T ₁ , T
₂ has a shorter wavelength cycle than AWG. Therefore, it becomes possible to cope with a smaller channel interval (wavelength interval) of pumping light or a shift amount (change amount) of channel wavelength than when the AWG is applied as the pumping light multiplexer 2.

FIG. 18 is a diagram showing the configuration of the seventh embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the seventh embodiment has channel wavelengths λ _{1 to} λ ₈ (λ ₁ <λ ₂ <λ ₃ <λ ₄ <λ as a plurality of pumping light sources that form a pumping light supply system. ₅ <λ ₆ <
Eight wavelength tunable pumping light sources 11 to 18 that output pumping light of λ ₇ <λ ₈ ) are provided. The structure of each of the excitation light sources 11 to 18 is the same as that of the second embodiment shown in FIG.

Further, in the seventh embodiment, two arrayed waveguide type diffraction gratings (AWG) 25a are used as the pumping light multiplexer 2 which multiplexes the pumping lights outputted from the pumping light sources 11 to 18, respectively. , 25b and an interleaver 26 are provided.

Of the eight variable wavelength pumping light sources 11 to 18, channel wavelengths λ ₁ , λ ₃ , λ ₅ and λ ₇ output from the pumping light sources 11, ₁₃ , ₁₅ , ₁₇ every other channel wavelength.
The excitation light of is combined by the AWG 25a. Also,
The pumping light of the channel wavelengths λ ₂ , λ ₄ , λ ₆ and λ ₈ output from the pumping light sources 12, 14, 16 and 18 is the AWG 25b.
Are combined by.

Furthermore, the pump light of the channel wavelengths λ ₁ , λ ₃ , λ ₅ , and λ ₇ output from the AWG 25 a and the AWG 25 b.
The pump lights of the channel wavelengths λ ₂ , λ ₄ , λ ₆ , and λ ₈ output from the are interleaved by the interleaver 26, and the interleaver 26 outputs the pump light having a predetermined pump light spectrum as a whole. It Then, the multiplexed pumping light is output to the optical transmission line L via the output structure including the output optical waveguide 31 and the output multiplexer 32.

As shown in FIG. 16, the pump optical multiplexer 2
If a single interleaver is applied as, the number of pump lights that can be combined is limited to two. On the other hand,
As shown in FIG. 8, in the configuration in which the AWGs 25a and 25b in the former stage and the interleaver 26 in the latter stage are combined, the multiplexing by the interleaver capable of coping with the pumping light having a smaller channel spacing (wavelength spacing) or wavelength variation amount. It becomes possible to combine the pumping lights of an arbitrary number of channels while utilizing the characteristics.

FIG. 19 is a diagram showing the structure of the eighth embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the eighth embodiment has a plurality of pumping light sources constituting the pumping light supply system and has channel wavelengths λ _{1 to} λ ₄ (λ ₁ <λ ₂ <λ ₃ <λ ₄ ), respectively. Four (N) wavelength variable pumping light sources 11 to 14 that output pumping light
Is equipped with. The configuration of each of the excitation light sources 11 to 14 is the same as that of the second embodiment shown in FIG.

Further, in this eighth embodiment, three (N-1) three-port optical circulators are used as the pumping light multiplexers 2 for multiplexing the pumping lights output from the pumping light sources 11 to 14, respectively. 27a, 27b and 27c are provided. These optical circulators 27a, 27b, 27c
Are connected in three stages (N-1 stages) so as to sequentially combine the pumping lights outputted from the pumping light sources 11 to 14 which are four (N) external resonator type lasers. .

That is, the first-stage optical circulator 27
The optical waveguide 14 from the excitation light source 14 is provided at the first port of c.
1 is connected, an optical waveguide 131 from the excitation light source 13 is connected to the second port, and an optical waveguide 43 is connected to the third port.
0 is connected. The optical waveguide 430 from the optical circulator 27c is connected to the first port of the second-stage optical circulator 27b, the optical waveguide 121 from the excitation light source 12 is connected to the second port, and the third port is connected to the third port. The optical waveguide 420 is connected. The optical waveguide 420 from the optical circulator 27b is connected to the first port of the third-stage optical circulator 27a, the optical waveguide 111 from the excitation light source 11 is connected to the second port, and the third port is connected to the third port. The output optical waveguide 31 is connected.

Resonance grating 1 of excitation light source 11
12 and the optical circulator 27a, a reflection grating 41 that reflects the excitation light of the channel wavelength λ ₂ is provided.
2. A reflection grating 413 that reflects the excitation light of the channel wavelength λ ₃ and a reflection grating 414 that reflects the excitation light of the channel wavelength λ ₄ are installed. Further, between the resonance grating 122 of the excitation light source 12 and the optical circulator 27b, a reflection grating 423 that reflects the excitation light of the channel wavelength λ ₃ and a reflection grating that reflects the excitation light of the channel wavelength λ ₄ are provided. 424 is installed. A reflection grating 434 that reflects the excitation light having the channel wavelength λ ₄ is provided between the resonance grating 132 of the excitation light source 13 and the optical circulator 27c. Each reflection grating has approximately 100% of the light of the corresponding channel wavelength.
It is preferably a reflective Bragg grating.

In the above structure, the pumping light of the channel wavelength λ ₁ supplied from the pumping light source 11 is output to the output optical waveguide 31 via the optical circulator 27a.

The pumping light of the channel wavelength λ ₂ supplied from the pumping light source 12 is output to the optical waveguide 111 via the optical circulator 27b, the optical waveguide 420, and the optical circulator 27a. Then, the pumping light of the channel wavelength λ ₂ is reflected by the reflection grating 412, input again to the optical circulator 27a, and output to the output optical waveguide 31 via the optical circulator 27a.

The pumping light of the channel wavelength λ ₃ supplied from the pumping light source 13 is output to the optical waveguide 121 via the optical circulator 27c, the optical waveguide 430, and the optical circulator 27b. Then, the pumping light of the channel wavelength λ ₃ is reflected by the reflection grating 423 and input again to the optical circulator 27b, and the optical circulator 27b, the optical waveguide 420, and the optical circulator 2 are provided.
It is output to the optical waveguide 111 via 7a. Further, the pumping light of the channel wavelength λ ₃ is reflected by the reflection grating 41.
It is reflected by 3 and is input again to the optical circulator 27a, and is output to the output optical waveguide 31 via the optical circulator 27a.

Further, the cha supplied from the excitation light source 14
Channel wavelength λ_FourExcitation light is transmitted through the optical circulator 27c.
And output to the optical waveguide 131. And the channel wave
Long λ _FourThe excitation light of is reflected by the reflection grating 434.
Is reflected and input again to the optical circulator 27c,
Optical circulator 27c, optical waveguide 430, and optical circulator
Output to the optical waveguide 121 via the curator 27b
It In addition, the channel wavelength λ_FourThe excitation light of the
The optical circulator is reflected again by the lighting 424
Data is input to the optical circulator 27b and the optical
Light is guided through the waveguide 420 and the optical circulator 27a.
It is output to the waveguide 111. Then the channel wavelength λ_Fourof
The excitation light is reflected by the reflection grating 414.
Input to the optical circulator 27a again, and the optical circulator 27a
Output to the output optical waveguide 31 via the modulator 27a
It

As described above, the channel wavelength λ ₁ output from each of the four wavelength tunable pump light sources 11 to 14
The pump lights of λ ₄ are multiplexed by the three 3-port optical circulators 27a, 27b, 27c which are the pump light multiplexers 2 and pumped from the pump light multiplexer 2 as a whole having a predetermined pump light spectrum. Light is output. Then, the multiplexed pumping light is output to the optical transmission line L via the output structure including the output optical waveguide 31 and the output multiplexer 32.

As described above, for N pumping light sources,
Even with the configuration in which (N-1) three-port optical circulators are applied as the pumping light multiplexer 2, the pumping light from each pumping light source can be satisfactorily multiplexed. As the reflection grating, various gratings can be applied as in the resonance grating of the excitation light source.

Here, the wavelength of the light reflected by each reflection grating is variably controlled so as to be synchronized with the reflection wavelength of the resonance grating when the corresponding excitation light source is a variable wavelength excitation light source. Is preferred. In the eighth embodiment, since the pumping light sources 11 to 14 are all variable wavelength pumping light sources, a channel wavelength adjusting system that variably controls all the reflection gratings as described above is installed. This makes it possible to efficiently guide the pumping light supplied from each of the pumping light sources 11 to 14 to the output optical waveguide 31.

Specifically, the reflection grating 412 that reflects the excitation light of the channel wavelength λ ₂ is the excitation light source 1
It is preferably controlled in synchronization with the second resonance grating 122. Moreover, it is preferable that the reflection gratings 413 and 423 that reflect the excitation light of the channel wavelength λ ₃ be controlled in synchronization with the resonance grating 132 of the excitation light source 13. Further, the reflection gratings 414, 424, ₄ that reflect the pumping light of the channel wavelength λ ₄
Reference numeral 34 denotes a resonance grating 142 of the excitation light source 14.
It is preferable to control in synchronization with.

FIG. 20A is a diagram showing the structure of the ninth embodiment of the excitation light source unit according to the present invention. The pumping light source unit LU according to the ninth embodiment has channel wavelengths λ _{1 to} λ ₄ (λ ₁ <λ ₂ <λ ₃ <λ ₄ ) as a plurality of pumping light sources constituting the pumping light supply system. Four (N) wavelength variable pumping light sources 11 that output pumping light
To 14 are provided. The configuration of each of the excitation light sources 11 to 14 is the same as that of the second embodiment shown in FIG.

Further, as the pumping light multiplexer 2 which multiplexes the pumping light output from each of the pumping light sources 11 to 14,
One 5-port (N + 1 port) optical circulator 27
Is provided. The optical circulator 27 includes pump light sources 11 to 11 which are four (N) external resonator type lasers.
They are connected so as to combine the pumping lights output from the respective fourteen.

That is, the optical waveguide 141 from the excitation light source 14 is connected to the first port of the optical circulator 27, and the optical waveguide 13 from the excitation light source 13 is connected to the second port.
1 is connected, the optical waveguide 121 from the excitation light source 12 is connected to the third port, and the excitation light source 1 is connected to the fourth port.
The optical waveguide 111 from 1 is connected, and the output optical waveguide 31 is connected to the fifth port.

Resonance grating 1 of pumping light source 11
12 and the optical circulator 27, a reflection grating 412 that reflects the pumping light of the channel wavelength λ ₂ ,
A reflection grating 413 that reflects the excitation light of the channel wavelength λ ₃ and a reflection grating 414 that reflects the excitation light of the channel wavelength λ ₄ are installed. Also,
Between the resonance grating 122 of the excitation light source 12 and the optical circulator 27, a reflection grating 423 that reflects the excitation light of the channel wavelength λ ₃ and a reflection grating 42 that reflects the excitation light of the channel wavelength λ ₄ are provided.
4 are installed. Further, between the resonance grating 132 of the pumping light source 13 and the optical circulator 27, a reflecting grating 434 that reflects the pumping light of the channel wavelength λ ₄ is installed.

In the above structure, the pumping light of the channel wavelength λ ₁ supplied from the pumping light source 11 is output to the output optical waveguide 31 via the optical circulator 27.

The pumping light of the channel wavelength λ ₂ supplied from the pumping light source 12 is output to the optical waveguide 111 via the optical circulator 27. Then, the pumping light of the channel wavelength λ ₂ is reflected by the reflection grating 412, input again to the optical circulator 27, and output to the output optical waveguide 31 via the optical circulator 27.

The pumping light of the channel wavelength λ ₃ supplied from the pumping light source 13 is output to the optical waveguide 121 via the optical circulator 27. Then, the pumping light of the channel wavelength λ ₃ is reflected by the reflection grating 423, input to the optical circulator 27 again, and output to the optical waveguide 111 via the optical circulator 27. Further, the pumping light of the channel wavelength λ ₃ is reflected by the reflecting grating 413 and is again guided by the optical circulator 27
Is input to the output optical waveguide 31 via the optical circulator 27.

The pumping light of the channel wavelength λ ₄ supplied from the pumping light source 14 is output to the optical waveguide 131 via the optical circulator 27. Then, the pumping light of the channel wavelength λ ₄ is reflected by the reflection grating 434, input again to the optical circulator 27, and output to the optical waveguide 121 via the optical circulator 27. Further, the pumping light having the channel wavelength λ ₄ is reflected by the reflection grating 424 and is again reflected by the optical circulator 27
Input to the optical waveguide 1 via the optical circulator 27.
It is output to 11. After that, the pumping light of the channel wavelength λ ₄ is reflected by the reflection grating 414, is input again to the optical circulator 27, and is output to the output optical waveguide 31 via the optical circulator 27.

As described above, the channel wavelength λ ₁ output from each of the four wavelength tunable pump light sources 11 to 14
The pump lights of λ ₄ are multiplexed by one 5-port optical circulator 27 which is the pump optical multiplexer 2, and the 5-port optical circulator 27 outputs pump light having a predetermined pump light spectrum as a whole. It Then, the multiplexed excitation light is output to the output optical waveguide 31 and the output multiplexer 32.
The light is output to the optical transmission line L via the output structure composed of.

In this way, for N pumping light sources,
Even with the configuration in which one (N + 1) -port optical circulator is applied as the pumping light multiplexer 2, as in the configuration in which (N-1) three-port optical circulators are applied,
The excitation light from each excitation light source can be suitably combined.

The structure of the pumping light multiplexer 2 to which the optical circulator is applied is not limited to the embodiment shown in FIGS. 19 and 20 (a), and various structures are possible.
For example, in FIG. 20B, the (N + 1) -port optical circulator 27 and the output structure (including the output waveguide 31 and the output multiplexer 32) shown in FIG. 20A are replaced (N + 2). A port optical circulator 27a is shown. This (N + 2) port optical circulator 27a
Can realize the pumping light multiplexing function of the (N + 1) -port optical circulator 27 of FIG. 20A, and can also function as the output waveguide 31 and the output multiplexer 32 forming the output structure.

FIG. 21 is a diagram showing the structure of the tenth embodiment of the excitation light source unit according to the present invention. This first
The pumping light source unit LU according to the 0th embodiment has a structure similar to that of the 8th embodiment shown in FIG. 19, but an optical isolator is provided between the resonance grating and the reflection grating. Different.

That is, on the optical waveguide 111 connecting the pumping light source 11 and the optical circulator 27a, the resonance grating 112 and the reflection grating 412,
An optical isolator 415 is installed between 413 and 414. Further, on the optical waveguide 121 connecting the excitation light source 12 and the optical circulator 27b, the resonance grating 122 and the reflection gratings 423 and 42 are provided.
4, and an optical isolator 425 is installed between the optical isolator 425 and the optical isolator 425.
In addition, the resonance grating 1 is provided on the optical waveguide 131 that connects the excitation light source 13 and the optical circulator 27c.
An optical isolator 435 is installed between 32 and the reflection grating 434. In addition, the excitation light source 14
Optical waveguide 141 that connects the optical circulator 27c with the optical circulator 27c.
An optical isolator 445 is installed above the resonance grating 142 and the optical circulator 27c.

FIG. 22 is a diagram showing the configuration of the eleventh embodiment of the excitation light source unit according to the present invention. This first
The excitation light source unit LU according to one embodiment is shown in FIG.
Although it has a structure similar to that of the ninth embodiment shown in (a) and FIG. 20 (b), an optical isolator is provided between the resonance grating and the reflection grating as in the above-described tenth embodiment. It differs in that it is installed.

That is, on the optical waveguide 111 connecting the pumping light source 11 and the optical circulator 27, the resonance grating 112 and the reflection grating 412,
An optical isolator 415 is installed between 413 and 414. Further, on the optical waveguide 121 connecting the pumping light source 12 and the optical circulator 27, the resonance grating 122 and the reflection gratings 423 and 424 are provided.
And the optical isolator 425 is installed between the two. Further, on the optical waveguide 131 connecting the excitation light source 13 and the optical circulator 27, the resonance grating 132 is provided.
An optical isolator 435 is installed between the reflection grating 434 and the reflection grating 434. The resonance grating 142 and the optical circulator 2 are provided on the optical waveguide 141 that connects the excitation light source 14 and the optical circulator 27.
An optical isolator 445 is installed between the optical isolator 445 and the optical disc 7.

As described above, the optical isolators 415 are provided between the resonance gratings of the pumping light sources 11 to 14 which are external resonator type lasers and the reflection gratings provided on the corresponding optical waveguides 111 to 141, respectively. ~ 4
By installing 45, it is possible to prevent light of a plurality of wavelengths from externally resonating in the external resonator type laser due to the influence of the reflection grating.

In the pumping light source unit LU according to the above-mentioned first to eleventh embodiments, the power spectrum of the output signal light (the gain spectrum of the Raman amplifier) even when the output of any of the plurality of pumping light sources is lowered. In order to maintain the flatness of the pumping light source, the pumping light spectrum is adjusted by changing the channel wavelengths of the remaining pumping light sources. This configuration improves the controllability of the pumping light spectrum, and as a result, it becomes possible to adjust the power spectrum (gain spectrum) of the output signal light in the amplification wavelength band of the Raman amplifier. However, with the above-described configuration, some deterioration of the gain spectrum cannot be avoided. Therefore, the pumping light source unit according to the present invention, together with the main pumping light supply system that constantly outputs pumping light of a plurality of channels, reduces the output of any one of the pumping light sources included in the main pumping light supply unit. A preliminary pumping light supply system for preventing the deterioration of the pumping light spectrum due to this may be provided.

FIG. 23 is a diagram showing a structure of a pumping light source unit having a pumping light supply system having a double structure. This pumping light source unit LU is similar to the first embodiment shown in FIG. 1, and includes a main pumping light supply system 1a that outputs pumping light of a plurality of channels in a steady state, and a main pumping light supply system 1a. A pumping light multiplexer 2 that multiplexes pumping lights of a plurality of channels, and an output structure 3 for outputting the multiplexed light output from the pumping light multiplexer 2 to the optical transmission line L are provided. The output structure 3 includes an output optical waveguide 31 and an output multiplexer 32. The excitation light source unit LU is the excitation light sources 11a to 13a included in the main excitation light supply system 1a.
Output channel wavelengths λ _{1 to} λ ₃ of the auxiliary pumping light supply system 1b for outputting pumping light of the same channel wavelength, the output from the main pumping light supply system 1a and the output from the preliminary pumping light supply system 1b Further provided is an optical switch 4 for switching between and for each channel. The preliminary pumping light supply system 1b includes preliminary pumping light sources 11b to 13b that output pumping light of channels corresponding to the pumping light sources 11a to 13a included in the main pumping light supply system 1a. Further, the optical switch 4 includes a plurality of channel switches 41 to 43 prepared to switch the output of the main pumping light supply system 1a and the output of the preliminary pumping light supply system 1b for each channel.

In the excitation light source unit LU, in the steady state, the excitation light sources 11a to 13a included in the main excitation light supply system 1a output the excitation lights of the channel wavelengths λ _{1 to} λ ₃ , respectively. The pumping light from the pumping light sources 11a to 13a is output to the pumping light multiplexer 2 via the optical switch 4, and is multiplexed in the pumping light multiplexer 2. Then, the combined light output from the pumping light multiplexer 2 is guided to the optical transmission line L via the output optical waveguide 31 and the output multiplexer 32 included in the output structure 3.

On the other hand, of the pumping light sources 11a to 13a included in the main pumping light supply system 1a, for example, the pumping light source 1 is used.
When the optical switch 2a fails, the optical switch 4 is operated by the pump optical multiplexer 2
The input of the corresponding channel switch 42 is switched in order to switch the pumping light guided to. In this way, the pumping light source unit LU in an emergency in which the pumping light source 12a has failed
In the optical switch 4, the pump light of the channel wavelength λ ₁ from the pump light source 11a, the pump light of the channel wavelength λ ₂ from the preliminary pump light source 12b, and the pump light of the channel wavelength λ ₃ from the pump light source 13a The channel switches 41 to 43 are controlled so as to guide the light to the pumping light multiplexer 2.

The pumping light source unit LU described above includes a main pumping light supply system 1a including pumping light sources 11a to 13a for outputting pumping lights of channel wavelengths λ _{1 to} λ _{3 in} a steady state,
A preliminary pumping light supply system 1b including preliminary pumping light sources 11b to 13b prepared corresponding to the pumping light sources 11a to 13a, respectively, and for each channel in accordance with the operating state of the main pumping light supply system. It has a structure for switching the output between the main pumping light supply system 1a and the preliminary pumping light supply system 1b. However, if the pumping light supply system including the same number of pumping light sources as described above is prepared, the manufacturing cost is doubled. Therefore,
An embodiment capable of reducing the number of pre-excitation light sources included in the pre-excitation light supply system 1b will be described below.

FIG. 24 is a diagram showing the structure of the twelfth embodiment of the excitation light source unit according to the present invention. This first
The second embodiment has a structure in which pump light of a plurality of channels is supplied to the optical transmission line L in a steady state, and main pump light that outputs pump light of a plurality of main pump channels as in the pump light source unit shown in FIG. The supply system 1a, the pumping light multiplexer 2 that multiplexes the pumping lights of a plurality of channels from the main pumping light supply system 1a, and the combined light output from the pumping light multiplexer 2 are output to the optical transmission line L. Output structure 3 for The main pumping light supply system 1a has channel wavelengths λ ₁ to
Excitation light sources 11 to 13 that emit excitation light of λ ₃ are included.
The output structure 3 also includes an output optical waveguide 31 and an output multiplexer 32.

In particular, the pumping light source unit LU according to the twelfth embodiment pumps the channel wavelengths approximately the same as the output channel wavelengths λ _{1 to} λ _{3 of the} pumping light sources 11 to 13 included in the main pumping light supply system 1a. Preliminary excitation light supply system 1b for outputting light and the main excitation light supply system 1a
Optical switch 4 for switching between the output from the pre-pumping light supply system 1b and the output from the pre-pumping light supply system 1b for each channel, and 1 × M (≧≧) arranged on the optical path between the pre-pumping light supply system 1b and the optical switch 4. 2) A port output branching device 45 is further provided. The preliminary pumping light supply system 1b includes a variable wavelength pumping light source as a preliminary pumping light source in order to output pumping light having a channel wavelength corresponding to each of the pumping light sources 11 to 13 included in the main pumping light supply system 1a. . As shown in FIG. 8, the wavelength tunable pumping light source included in this pumping light supply system 1b has a channel wavelength adjusting system 11 for adjusting the reflection wavelengths of the semiconductor laser 110 and the resonant grating.
2 is provided. The 1 × M (≧ 2) port output brancher 45 is
The pumping light from the preliminary pumping light supply system 1b is input and output from the output port corresponding to the channel wavelength of the input pumping light.

The channel wavelength adjusting system 11 described above is used.
2 may include a stress applying unit that changes the grating period by applying a predetermined stress to the resonance grating. The channel wavelength adjustment system 1
12 may include heating means for changing the refractive index in the core region by heating the resonance grating. When the resonance grating is formed in the optical waveguide made of a material having an electro-optical effect, the channel wavelength adjustment system 112 applies an electric field of a predetermined intensity to the optical waveguide having the resonance grating formed therein. Electric field applying means for changing the refractive index of the optical waveguide may be included.

The pumping light source unit according to the twelfth embodiment
The main pump light supply system in the steady state
Channel waves from the respective excitation light sources 11 to 13 included in 1a
Long λ ₁~ Λ₃The respective excitation lights of are output. Excitation light source
Excitation light from 11 to 13 is excited via the optical switch 4.
It is output to the optical multiplexer 2 and is combined in the pump optical multiplexer 2.
To be done. Then, the combined light output from the pump light multiplexer 2
Is the output optical waveguide 31 and the output included in the output structure 3.
It is guided to the optical transmission line L via the multiplexer 32.

On the other hand, if, for example, the pumping light source 12 out of the pumping light sources 11 to 13 included in the main pumping light supply system 1a fails, the preliminary pumping light supply system 1b should be output from the failed pumping light source 12. The pumping light having a channel wavelength substantially the same as the channel wavelength is output to the 1 × M (≧ 2) port output splitter 45. The pumping light input to the 1 × M (≧ 2) port output splitter 45 is output from the output port corresponding to the channel wavelength and is guided to the corresponding channel switch 42. The channel switch 42 is 1 × M (≧
2) The input is switched so that the pumping light output from the port output splitter 45 is output to the pumping light multiplexer 2. As described above, in the emergency pumping light source unit LU in which the pumping light source 12 has failed, the optical switch 4 uses the pumping light of the channel wavelength λ ₁ from the pumping light source 11, the preliminary pumping light supply system 1b (variable wavelength pumping). Channel wavelength λ ₂ from the light source)
Of the pumping light of the above and the channel wavelength λ ₃ from the pumping light source 13
The channel switches 41 to 43 are controlled so as to guide the pumping light of 1 to the pumping light multiplexer 2. Each of the channel switches 41 to 43 is preferably an optical switch utilizing an optical interference effect in order to avoid a momentary interruption due to switching of pumping light between the main pumping light supply system 1a and the preliminary pumping light supply system 1b. .

FIG. 25 is a diagram showing the structure of the thirteenth embodiment of the pumping light source unit according to the present invention. Figure 25
Also in the thirteenth embodiment of (a), as a structure for supplying pumping light of a plurality of channels to the optical transmission line L in a steady state, the pumping light of the main pumping a plurality of channels is supplied as in the pumping light source unit shown in FIG. An output main pumping light supply system 1a, a pumping light multiplexer 2 that multiplexes pumping lights of a plurality of channels from the main pumping light supply system 1a, and optical transmission of the combined light output from the pumping light multiplexer 2 An output structure 3 for outputting to the path L is provided. The pumping light supply system 1a includes pumping light sources 11 to ₁ that output pumping lights having channel wavelengths λ _{1 to} λ _3.
Including 3. The output structure 3 also includes an output optical waveguide 31 and an output multiplexer 32.

In particular, the pumping light source unit LU according to the thirteenth embodiment is, as shown in FIG. 25A, the pumping light sources 11 to 1 included in the main pumping light supply system 1a.
Preliminary pumping light supply system 1b for outputting pumping light having a channel wavelength substantially the same as the output channel wavelengths λ _{1 to} λ ₃
And an optical switch 4 for switching the output from the main pumping light supply system 1a and the output from the preliminary pumping light supply system 1b for each channel, the preliminary pumping light supply system 1
The optical switch 400 is further provided on the optical path between b and the optical switch. The preliminary pumping light supply system 1b is the main pumping light supply system 1
In order to output the pumping light of the channel wavelength corresponding to each of the pumping light sources 11 to 13 included in a, a tunable pumping light source is included as the preliminary pumping light source. The configuration of the wavelength variable pumping light source included in this preliminary pumping light supply system 1b is as follows.
As shown in FIG. 8, a channel wavelength adjusting system 112 for adjusting the reflection wavelengths of the semiconductor laser 110 and the resonance grating is provided. The optical switch 400 guides the pumping light from the preliminary pumping light supply system 1b to any of the channel switches 41 to 43 corresponding to the channel wavelength.

The optical switch 4 (channel switch 4
1-43) and the optical switch 400 are preferably optical switches that utilize an optical interference effect in order to avoid a momentary interruption due to switching of pumping light between the main pumping light supply system 1a and the preliminary pumping light supply system 1b. For example, MEMS (Micr
o The switching time of mechanical switches using Electro Mechanical Systems) is usually on the order of milliseconds, but the bit rate of recent optical transmission signals is 10 Gb.
It has been improved to about ps, and if a mechanical switch is applied, about 10 million bits will be lost. Therefore, as an optical switch applied to the pumping light source switch LU according to the present invention, for example, as shown in FIG.
A thermo-optical switch in which a heater 420 is arranged on the surface of the laser and an electro-optical Mach-Zehnder type optical switch are preferable.

The pumping light source unit according to the thirteenth embodiment
The main pump light supply system in the steady state
Channel waves from the respective excitation light sources 11 to 13 included in 1a
Long λ ₁~ Λ₃The respective excitation lights of are output. Excitation light source
Excitation light from 11 to 13 is excited via the optical switch 4.
It is output to the optical multiplexer 2 and is combined in the pump optical multiplexer 2.
To be done. Then, the combined light output from the pump light multiplexer 2
Is the output optical waveguide 31 and the output included in the output structure 3.
It is guided to the optical transmission line L via the multiplexer 32.

On the other hand, the main excitation light supply system 1a includes
Of the excitation light sources 11 to 13
When it fails, the preliminary pumping light supply system 1b fails
Substantially the same as the channel wavelength to be output from the pumping light source 12.
The pumping light of the same channel wavelength is output. Optical switch 400
Is the pumping light output from the preliminary pumping light supply system 1b.
To the channel switch 42 corresponding to the channel wavelength of
The output is switched to guide the light and the optical switch 4
Is the excitation guided from the optical switch 400 to the pump optical multiplexer 2.
In order to switch the light emission, the corresponding channel switch 42
Switch the input of. In this way, the excitation light source 12
In the pumping light source unit LU in the case of an emergency
The switch 4 has a channel wavelength λ from the pumping light source 11.₁of
Excitation light, preliminary excitation light supply system 1b (wavelength variable excitation light
Light source) Channel wavelength λ from 1b ₂Excitation light and excitation
Channel wavelength λ from light source 13₃Excitation light of
Control each channel switch 41-43 to lead to wave filter 2.
Control.

FIG. 26 is a diagram showing the structure of the fourteenth embodiment of the pumping light source unit according to the present invention. This first
In the fourth embodiment, in order to secure a wider amplification wavelength band, the main pumping light supply system 1a uses the pumping light sources 11a-1.
While having the five light sources 5a, the preliminary pumping light supply system 1b enables the Raman amplification in the amplification wavelength band covered by the main pumping light supply system 1a, so that the tunable pumping light source units 11b and 12b (standby Excitation light source). In addition, the pumping light source unit LU according to the fourteenth embodiment includes the output of the main pumping light supply system 1a including the pumping light sources 11a to 15a and the preliminary pumping light source 11.
b, 12b, an optical switch 4 arranged on the optical path between the main pumping light supply system 1a and the pumping light multiplexer 2 in order to enable switching with the output of the preliminary pumping light supply system.
And an optical switch 400 arranged on the optical path between the optical switch 4 and the preliminary pumping light supply system 1b, and the channel switches 41 to 45 of the optical switch 4 and the channel switches included in the optical switch 400. 401, 4
On the optical path between each of the output ports 02 and 02, the resonance gratings 451 to 4 having the reflection wavelengths λ _{1 to} λ ₅ , respectively.
55 are arranged.

The optical switch 4 is provided with a plurality of channel switches 41 to 45 in order to switch the input for each channel wavelength of the pumping light. Also, the optical switch 40
0 is provided with channel switches 401 and 402 for switching the output in order to guide the pumping light from the preliminary pumping light supply system 1b to any of the corresponding channel switches 41 to 45. The output structure 3 also includes an output optical waveguide 31 and an output multiplexer 32. In addition, the preliminary excitation light supply system 1b
As shown in FIG. 8, the configuration of the wavelength tunable pumping light source included in (1) includes a channel wavelength adjustment system 112 for adjusting the reflection wavelengths of the semiconductor laser 110 and the resonance grating. The optical switches 4 and 400 are preferably optical switches utilizing an optical interference effect in order to avoid instantaneous interruption due to switching of pumping light between the main pumping light supply system 1a and the preliminary pumping light supply system 1b.

In the pumping light source unit LU according to the fourteenth embodiment, in the steady state, pumping lights of channel wavelengths λ _{1 to} λ ₅ are output from the pumping light sources 11a to 15a included in the main pumping light supply system 1a, respectively. To be done. The pumping light from the pumping light sources 11a to 15a is output to the pumping light multiplexer 2 via the optical switch 4, and is multiplexed in the pumping light multiplexer 2. Then, the multiplexed light output from the pumping light multiplexer 2 is output to the output optical waveguide 31 included in the output structure 3.
And is guided to the optical transmission line L via the output multiplexer 32.

On the other hand, of the pumping light sources 11a to 15a included in the main pumping light supply system 1a, for example, the pumping light source 1 is used.
When 2a fails, the pumping light source 11b of the preliminary pumping light supply system 1b outputs pumping light having a channel wavelength substantially the same as the channel wavelength to be output from the pumping light source 12a that has failed. At this time, the channel switch 401 performs output switching so as to guide the pumping light to the channel switch 42 corresponding to the channel wavelength of the pumping light output from the preliminary pumping light supply system 1b, and the optical switch 4 causes the optical switch 401 to switch. In order to switch the pumping light guided from the to the pumping light multiplexer 2, the input of the corresponding channel switch 42 is switched. As described above, in the emergency pumping light source unit LU in which the pumping light source 12a has failed, the optical switch 4 uses the pumping light of the channel wavelength λ ₁ from the pumping light source 11b and the wavelength included in the preliminary pumping light supply system 1b. Each channel switch 41 to guides the pumping light of the channel wavelength λ ₂ from the variable pumping light source 11b and the pumping light of the channel wavelengths λ _{3 to} λ ₅ from each of the pumping light sources 13a to 15a to the pumping light multiplexer 2. Control 45.

FIG. 27 is a diagram showing the structure of the fifteenth embodiment of the pumping light source unit according to the present invention. This first
In the fifth embodiment, the pumping light multiplexer 2 has a wavelength multiplexer 21 and
A pumping light source 11 included in the main pumping light supply system 1a,
Of the channel wavelength λ ₂ from the pumping light source 13 included in the main pumping light supply system 1a, which polarization-combines the pumping lights of the channel wavelengths λ _{1 having} different polarization states from each other. Depolarizer 2 for depolarizing pumping light
4 is provided. The configuration for switching between the output of the preliminary pumping light supply system 1b and the output of the main pumping light supply system 1a is the same as in the above-described thirteenth embodiment. Further, between the pumping light sources 11 and 12 and the polarization multiplexer 23 included in the main pumping light supply system 1a, the polarization state of the pumping light output from the pumping light sources 11 and 12 is maintained. , Preferably via a polarization maintaining fiber. Similarly, between the preliminary pumping light supply system 1b and the polarization multiplexer 23,
In order to maintain the polarization state of the pumping light output from the preliminary pumping light supply system 1b, it is preferable that the pumping light is connected via a polarization maintaining fiber. A resonance grating is preferably arranged on the optical path between the optical switch 400 and each of the channel switches 41 to 43 of the optical switch 4 in order to improve reliability.

Next, a Raman amplifier (Raman amplifier according to the present invention) to which the above-mentioned pumping light source unit is applied will be described.

FIG. 28 is a diagram showing the configuration of the first embodiment of the Raman amplifier according to the present invention. The Raman amplifier RA according to the first embodiment includes the Raman amplification optical fiber 5
0 and the excitation light source unit LU. Here, the pumping light source unit LU is the pumping light source unit (first embodiment) shown in FIG. 1, and this pumping light source unit includes four wavelength variable pumping light sources 11 to 14 and pumping light sources. The optical multiplexer 2 and the output structure 3 (including the output optical waveguide 31 and the output multiplexer 32) are provided.

The pumping light source unit LU supplies the pumping light to the Raman amplification optical fiber 50. The pumping light source unit LU is connected to the optical transmission line L in the Raman amplifier RA via an output multiplexer 32 installed behind the Raman amplification optical fiber 50 in the signal light propagation direction. .

The output multiplexer 32 is a pump light source unit L.
The pumping light supplied from U is sent out to the front Raman amplification optical fiber 50 in the direction opposite to the signal light propagation direction. Further, the output multiplexer 32 passes the signal light, which has arrived from the Raman amplification optical fiber 50, in the forward direction in the backward direction.
As a result, the Raman amplifier R according to the first embodiment is
A functions as an optical amplifier for backward pumping (reverse pumping).

An optical branching device 51 is installed at a predetermined position on the optical transmission line L behind the pumping light source unit LU. The optical branching device 51 outputs a part of the output signal light that is amplified in the Raman amplification optical fiber 50 and propagates in the forward direction through the optical transmission line L, into an output signal light measuring device 52 (included in the output power measuring system). To a certain ratio. The output signal light measuring device 52 includes an optical spectrum analyzer, an optical performance monitor, and the like, and measures the output signal light state such as the output signal light spectrum of the output signal light from the optical branching device 51.

The measurement result of the output signal light by the output signal light measuring device 52 is sent to the control unit 60. The control unit 60, based on the measurement result of the output signal light measuring device 52, each channel power or channel wavelength λ of the pumping light output from each of the plurality of pumping light sources 11 to 14 included in the pumping light source unit LU. Control _{1 to} λ ₄ .

As described above, by applying the above-mentioned pumping light source unit LU (pumping light source unit according to the present invention) including the wavelength tunable pumping light source to the Raman amplifier RA, output signal light within the amplification wavelength band is obtained. The spectrum can be well tuned. Therefore, the excitation light sources 11 to 14
Raman amplifier RA having excellent controllability of Raman amplification gain so as to be able to sufficiently cope with various changes, including the case where the output signal light spectrum largely changes due to any power down of Is realized.

Further, the pumping light source unit LU is controlled by controlling the pumping light based on the measurement result of the output signal light.
Both the power spectrum of the entire pumping light supplied from the optical fiber and the power spectrum of the signal light output from the Raman amplifier RA are well controlled according to the state of the signal light.

As a concrete method of controlling the pumping light in this case, it is preferable that the control section 60 controls each channel power or channel wavelength of the pumping light so that the output signal light spectrum becomes substantially flat. As a result, the state of the signal light transmitted through the optical transmission line L can be appropriately maintained.

Further, the control unit 60 has a frequency 13THz to 15THz higher than the frequency at which the signal light power is substantially minimum in the output signal light spectrum (in terms of wavelength,
It is preferable to control the channel wavelength of the pumping light so that the wavelength of the excitation light approaches 100 nm to 120 nm (which corresponds to a shorter wavelength).
As a result, the amplification gain in the wavelength band in which the signal light power is low can be increased, and the output signal light spectrum can be efficiently flattened.

FIG. 29 is a diagram showing the configuration of the Raman amplifier according to the second embodiment of the present invention. The Raman amplifier RA according to the second embodiment includes a Raman amplification optical fiber 5
0 and the excitation light source unit LU. The pumping light source unit LU is connected to the optical transmission line L in the Raman amplifier RA via an output multiplexer 32 installed behind the Raman amplification optical fiber 50 in the signal light transmission direction.

The output multiplexer 32 is a pump light source unit L.
The pumping light supplied from U is sent out to the front Raman amplification optical fiber 50 in the direction opposite to the signal light propagation direction. Further, the output multiplexer 32 passes the signal light, which has arrived from the Raman amplification optical fiber 50, in the forward direction in the backward direction.
Thereby, the Raman amplifier RA functions as a backward pumping optical amplifier.

An optical branching device 51 is installed at a predetermined position on the optical transmission line L behind the pumping light source unit LU. The optical branching device 51 branches a part of the output signal light, which has been optically amplified in the Raman amplification optical fiber 50 and forwarded through the optical transmission line L, to the signal light demultiplexer 53 at a constant rate. Then, the branched output signal light is demultiplexed by the signal light demultiplexer 53 for each channel wavelength. The output signal light components of each channel demultiplexed by the signal light demultiplexer 53 are output signal light measuring devices 54a to 54d, respectively.
Are input to these output signal light measuring devices 54a to 54d.
Thus, the state of the output signal light such as the output signal light spectrum is measured. In addition, the output power measurement system,
Signal light demultiplexer 53 and output signal light measuring devices 54a to 54d
Is included.

The output signal light measurement results of the output signal light measuring devices 54a to 54d are sent to the control unit 60. The control unit 60, based on the measurement results of the output signal light measuring devices 54a to 54d, the channel power or the channel wavelength of the pumping light output from each of the plurality of pumping light sources 11 to 14 included in the pumping light source unit LU. Controls λ _{1 to} λ ₄ .

With such a configuration as well, similar to the configuration shown in FIG. 28 (first embodiment), the power spectrum of the entire pumping light supplied from the pumping light source unit LU,
Also, both the power spectrum of the signal light output from the Raman amplifier RA is well controlled according to the state of the signal light.

FIG. 30 is a diagram showing the configuration of the third embodiment of the Raman amplifier according to the present invention. The Raman amplifier RA according to the third embodiment includes a Raman amplification optical fiber 5
0 and the excitation light source unit LU. The pumping light source unit LU is connected to the optical transmission line L in the Raman amplifier RA via an output multiplexer 32 installed behind the Raman amplification optical fiber 50 in the signal light transmission direction.

The output multiplexer 32 is a pump light source unit L.
The pumping light supplied from U is sent out to the front Raman amplification optical fiber 50 in the direction opposite to the signal light propagation direction. Further, the output multiplexer 32 passes the signal light, which has arrived from the Raman amplification optical fiber 50, in the forward direction in the backward direction.
Thereby, the Raman amplifier RA functions as a backward pumping optical amplifier.

An optical branching device 55 is installed at a predetermined position on the optical transmission line L in front of the Raman amplification optical fiber 50. The optical branching device 55 allows a part of the input signal light transmitted in the forward direction along the optical transmission line L as the signal light optically amplified in the Raman amplification optical fiber 50 to the input signal light measuring device 56. Branch in proportion. The input signal light measuring device 56 (included in the input power measuring system) is
It is composed of an optical spectrum analyzer and an optical performance monitor, and measures the state of the input signal light such as the input signal light spectrum of the input signal light from the optical branching device 55.

The measurement result of the input signal light measuring device 56 is sent to the control unit 60. The control unit 60 uses the input signal light measuring device 5
Channel power or channel wavelength λ of the pumping light output from each of the plurality of pumping light sources 11 to 14 included in the pumping light source unit LU based on the measurement result of No. 6
Control _{1 to} λ ₄ .

As described above, by controlling the pumping light based on the measurement result of the input signal light, the power spectrum of the entire pumping light supplied from the pumping light source unit LU and the signal output from the Raman amplifier RA are obtained. Both the power spectrum of light is well controlled depending on the state of the signal light.

FIG. 31 is a diagram showing the configuration of the Raman amplifier according to the fourth embodiment of the present invention. The Raman amplifier RA according to the fourth embodiment includes a Raman amplification optical fiber 5
0 and the excitation light source unit LU. The pumping light source unit LU is connected to the optical transmission line L in the Raman amplifier RA via an output multiplexer 32 installed behind the Raman amplification optical fiber 50 in the signal light transmission direction.

The output multiplexer 32 is a pump light source unit L.
The pumping light supplied from U is sent out to the front Raman amplification optical fiber 50 in the direction opposite to the signal light propagation direction. Further, the output multiplexer 32 passes the signal light, which has arrived from the Raman amplification optical fiber 50, in the forward direction in the backward direction.
Thereby, the Raman amplifier RA functions as a backward pumping optical amplifier.

Further, the Raman amplifier RA according to the fourth embodiment is provided with an instruction signal input section 57 (included in the instruction signal input system) for inputting an instruction signal from the outside. The instruction signal input from the instruction signal input unit 57 is sent to the control unit 60. The control unit 60 controls the channel power or the channel wavelengths λ _{1 to} λ ₄ of the pumping light output from each of the plurality of pumping light sources 11 to 14 included in the pumping light source unit LU, based on this instruction signal. .

As described above, by controlling the pumping light based on the instruction signal from the outside, the power spectrum of the entire pumping light supplied from the pumping light source unit LU,
Also, both the power spectrum of the signal light output from the Raman amplifier RA is well controlled according to the state of the signal light.

In each of the Raman amplifiers shown in FIGS. 28 to 31, the pumping light supplied from the pumping light source unit LU is transmitted through the output multiplexer 32 in the direction opposite to the signal light propagation direction. The configuration is backward pumping propagating to the transmission line L. On the other hand, also in the configuration of forward pumping (forward pumping) in which pumping light is forwardly multiplexed into the optical transmission line L via the output multiplexer, the same optical amplifier as in FIGS. The configuration is applicable.

Further, the Raman amplifier is used in a distributed constant type or a lumped constant type as will be described later, but the respective configurations described above can be applied to any of the forms.

Next, an optical transmission system to which the Raman amplifier as described above is applied (optical transmission system according to the present invention)
Will be described.

FIG. 32 is a diagram showing the configuration of the first embodiment of the optical transmission system according to the present invention. The optical transmission system according to the first embodiment is a transmission station (transmitter) T that transmits signal light of a plurality of channels within a predetermined signal light wavelength band, and an optical transmission path through which the signal light from the transmission station T propagates. And the receiving station (receiver) R for receiving the signal light propagated through the optical fiber transmission line L.

A multiplexer 35 is provided at a predetermined position on the optical fiber transmission line L. The pumping light source unit LU (pumping light source unit according to the present invention) described above is optically connected to the optical fiber transmission line L via the multiplexer 35. The multiplexer 35 sends the pumping light supplied from the pumping light source unit LU forward and in the opposite direction. The pumping light source unit LU is a Raman amplifier RA that optically amplifies the signal light transmitted through the optical fiber transmission line L.
Is an excitation light supply means for configuring

When the pumping light source unit LU is provided with the output multiplexer 32, the multiplexer 35 functions as the multiplexer 35. Further, the pumping light source unit LU may be connected to the multiplexer 35 separately provided on the optical fiber transmission line L side.

The optical transmission system according to the first embodiment has a Raman amplifier RA including a pumping light source unit LU.
Is an optical transmission system functioning as a distributed constant type optical amplifier. Such distributed constant type Raman amplifier R
In A, as shown in FIG. 32, the optical fiber forming a part of the optical fiber transmission line L is used as the Raman amplification optical fiber 50.

As described above, the excitation light source unit L described above is used.
By installing the distributed constant type Raman amplifier RA to which U is applied at a predetermined position on the optical fiber transmission line L,
It is possible to realize an optical transmission system in which the deterioration of the transmission quality of the signal light is suppressed and the signal light can be reliably transmitted from the transmission station T to the reception station R.

FIG. 33 is a diagram showing the configuration of the second embodiment of the optical transmission system according to the present invention. The optical transmission system according to the second embodiment is a transmission station (transmitter) T for transmitting signal light of a plurality of channels within a predetermined signal light wavelength band, and an optical transmission for transmitting signal light from the transmission station T. An optical fiber transmission line L, which is a line, and a receiving station (receiver) R that receives the signal light transmitted through the optical fiber transmission line L are provided. Further, at a predetermined position between the transmitting station T and the receiving station R,
A relay station S that relays the signal light propagating through the optical fiber transmission line L is provided.

A multiplexer 35 is provided at a predetermined position on the optical fiber transmission line L in the relay station S. And
The excitation light source unit L described above is passed through the multiplexer 35.
U (pumping light source unit according to the present invention) is connected to the optical fiber transmission line L. The multiplexer 35 sends the pumping light supplied from the pumping light source unit LU forward and sends it in the direction opposite to the signal light propagation direction. The pumping light source unit LU is pumping light supply means for forming a Raman amplifier RA that amplifies the signal light transmitted through the optical fiber transmission line L.

The optical transmission system according to the second embodiment has a Raman amplifier RA including a pump light source unit LU.
Is an optical transmission system installed inside the relay station S as a lumped constant type optical amplifier. In such a lumped constant Raman amplifier RA, as shown in FIG. 33, an independent optical fiber inserted in the optical fiber transmission line L is used as the Raman amplification optical fiber 50.

As described above, the lumped-constant type Raman amplifier RA to which the pumping light source unit LU having the above-mentioned configuration is applied is installed at a predetermined position on the optical fiber transmission line L, so that the transmission quality of the signal light is increased. It is possible to realize an optical transmission system in which the signal light can be reliably transmitted from the transmitting station T to the receiving station R by suppressing the deterioration.

FIG. 34 is a diagram showing the structure of a relay station in the optical transmission system shown in FIG.

In the relay station S, a multiplexer 35 is provided at a predetermined position on the optical fiber transmission line L, and the multiplexer 3
The pumping light source unit LU is optically connected to the optical fiber transmission line L via 5. Further, in the relay station S, a dispersion compensating fiber (DCF) for compensating for the dispersion generated in the signal light while being transmitted through the optical fiber transmission line L.
A dispersion compensating module DM having is provided.

In the configuration of FIG. 34, the multiplexer 35 and the pumping light source unit LU are installed in the subsequent stage of this dispersion compensation module DM. In this configuration, the dispersion compensating fiber included in the dispersion compensating module DM is used as the Raman amplification optical fiber 50.

That is, the pumping light supplied from the pumping light source unit LU is sent to the optical fiber transmission line L via the multiplexer 35 in the direction opposite to the signal light propagation direction.
Then, the pumping light that is sent out is supplied to the optical fiber in the dispersion compensation module DM as the Raman amplification optical fiber 50. Thus, a lumped constant type Raman amplifier RA for amplifying the signal light is formed in the relay station S.

Note that the configuration inside the relay station S is shown in FIG.
4 is merely an example, and various configurations other than this are possible. For example, as the Raman amplification optical fiber, an optical fiber dedicated for Raman amplification may be used separately from an optical fiber such as a dispersion compensation fiber. Also, as shown in FIG. 34, in addition to the Raman amplifier RA, another optical amplifier (for example, EDFA) S
a and Sb may be provided side by side.

FIG. 35 is a diagram showing the configuration of the third embodiment of the optical transmission system according to the present invention. In the optical transmission system according to the third embodiment, a plurality of communication users use signal lights A, B, and C that use different signal light wavelength bands.
It is an optical transmission system for transmitting (WDM signal light of a plurality of channels) via the same optical transmission line L. In such an optical transmission system, the above Raman amplifier RA (Raman amplifier according to the present invention) is provided on the optical transmission line L.
Is installed, the signal lights A, B, and C are favorably amplified.

Here, the signal light wavelength bands of the signal lights A, B and C are in the following wavelength ranges, respectively.

(A) 1530 nm to 1570 nm

(B) 1535 nm to 1575 nm

(C) 1540 nm to 1580 nm

Also, the Raman amplifier RA is arranged so that the output signal light spectrum in the wavelength band of each signal light is flattened.
The amplification gain of is controlled. Further, the pumping light source unit of the Raman amplifier RA has three wavelength tunable pumping light sources as a plurality of pumping light sources.

First, of the three signal lights, the flattening of the output signal light spectrum for the signal light B having the intermediate signal light wavelength band will be considered. FIG. 36 is a power spectrum of the signal light B after Raman amplification. Here, regarding the channel wavelength of the pumping light supplied from the pumping light source unit, the signal light wavelength band of the signal light B is 1535 nm to 1
Corresponding to 575 nm, wavelengths of 1428 nm and 1439n
m, 3 channels of 1460 nm are set. By setting these pumping light channels and optimizing their respective powers, the output signal light spectrum is sufficiently flattened with respect to the wavelength band of the signal light B, as shown in FIG.

Next, flattening of the output signal light spectrum for the signal light A having the signal light wavelength band on the short wavelength side will be considered. 37 (a) and 37 (b) are power spectra of the signal light A after Raman amplification.
FIG. 37A is an output signal light spectrum when the 3-channel pumping light having the pumping light wavelengths 1428 nm, 1439 nm, and 1460 nm set for the signal light B is used as it is. In this case, since the pumping light channel is not optimized, the spectrum is not sufficiently flattened, and the flatness is deteriorated particularly on the short wavelength side.

On the other hand, FIG. 37 (b) shows the signal light A
Corresponding to the signal light wavelength band of 1530 nm to 1570 nm, the pumping light is 1424 nm, 1434 nm, 1455 n.
It is an output signal light spectrum when it is set to 3 channels of m. In this way, the channel wavelengths of the pumping light supplied from the pumping light source unit are optimally adjusted, whereby the output signal light spectrum can be sufficiently flattened even in the wavelength band of the signal light A. it can.

Next, the flattening of the output signal light spectrum for the signal light C having the signal light wavelength band on the long wavelength side will be considered. 38A and 38B are power spectra of the signal light C after Raman amplification.
FIG. 38A shows 1428 set for the signal light B.
9 shows an output signal light spectrum when the pumping light having three wavelengths of nm, 1439 nm, and 1460 nm is used as it is. In this case, the spectrum is not sufficiently flattened because the pumping light wavelength is not optimized, and the flatness is deteriorated particularly on the long wavelength side.

On the other hand, the graph of FIG.
Signal light wavelength band of signal light C 1540 nm to 1580 nm
Corresponding to the excitation light of 1432 nm, 1443 nm, 1
It is an output signal light spectrum when it sets to 3 channels of 464 nm. In this way, the channel wavelengths of the pumping light supplied from the pumping light source unit are optimally adjusted, whereby the output signal light spectrum can be sufficiently flattened even in the wavelength band of the signal light C. it can.

As described above, according to the optical transmission system to which the Raman amplifier having the pumping light source unit including the wavelength tunable pumping light source is applied, the signal lights (WDM signal lights) of different wavelength bands propagate. In case, it is possible to cope. That is, the channel wavelength of the pumping light supplied from the pumping light source unit is variably controlled, and the amplification wavelength band in which the power spectrum of the Raman-amplified output signal light is flattened is set to the signal light to be amplified. It is possible to change according to the wavelength band of.

Further, according to the Raman amplifier described above, when the optical fiber transmission line including the Raman amplifier is installed or when the Raman amplifier is introduced into the existing optical fiber transmission line, the pumping is performed while measuring the output signal optical spectrum. Since the channel wavelength and channel power of light can be adjusted, the controllability of optical amplification in the Raman amplifier is improved. Further, as described above, even if one of the plurality of pumping light sources included in the pumping light source unit goes down, the channel wavelength of the pumping light from the other pumping light source is adjusted, The power spectrum of the output signal light can be kept as flat as possible by compensating the pumping light.

The pumping light source unit, Raman amplifier, and optical transmission system according to the present invention are not limited to the above-mentioned embodiments, but various modifications are possible. For example, the number of the plurality of pumping light sources included in the pumping light source unit is not limited to the configuration to which the four pumping light sources shown in the above embodiment are applied, but is required for the Raman amplifier. It is preferable to set a suitable number and configuration according to the width of the amplification wavelength band, the controllability of the optical amplification gain, and the like.

[0226]

As described above, according to the present invention, a pumping light source unit, in which at least one of a plurality of pumping light sources for outputting pumping light of a plurality of channels having different wavelengths is used as a wavelength tunable pumping light source, According to the Raman amplifier and the optical transmission system to which it is applied, when adjusting the power spectrum of the pumping light supplied from the pumping light source unit and the power spectrum of the corresponding output signal light, each channel of the pumping light is adjusted. Not only the power but also the wavelength of the pumping light output from the wavelength tunable pumping light source can be adjusted as necessary.

As a result, the pumping light source unit, the Raman amplifier, and the pumping light source unit whose controllability has been improved so as to be able to sufficiently cope with various changes, including the case where the pumping light spectrum and the output signal light spectrum change greatly, And an optical transmission system is realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an excitation light source unit according to the present invention.

FIG. 2 is a power spectrum of pumping light supplied from the pumping light source unit shown in FIG.

3 is an example of a power spectrum of output signal light in a Raman amplifier to which the pumping light source unit shown in FIG. 1 is applied.

FIG. 4 is a diagram showing a configuration of a second embodiment of an excitation light source unit according to the present invention.

5 is a spectrum of pumping light supplied from the pumping light source unit shown in FIG.

FIG. 6 is a diagram showing a first configuration of a wavelength tunable pumping light source.

FIG. 7 is a diagram showing a configuration of an application example of the excitation light source unit according to the second embodiment.

FIG. 8 is a diagram showing a second configuration of the variable wavelength pumping light source.

FIG. 9 is a diagram showing a third configuration of the variable wavelength pumping light source.

FIG. 10 is a diagram showing a fourth configuration of a wavelength tunable pumping light source.

FIG. 11 is a diagram showing a configuration of a third embodiment of an excitation light source unit according to the present invention.

12 is a spectrum of pumping light supplied from the pumping light source unit shown in FIG.

FIG. 13 is a diagram showing a configuration of a fourth embodiment of an excitation light source unit.

FIG. 14 is a diagram showing the configuration of a fifth embodiment of an excitation light source unit according to the present invention.

15 is a spectrum of pumping light supplied from the pumping light source unit shown in FIG.

FIG. 16 is a diagram showing a configuration of a sixth embodiment of an excitation light source unit according to the present invention.

17 is a spectrum of the excitation light supplied from the excitation light source unit shown in FIG.

FIG. 18 is a diagram showing a configuration of a seventh embodiment of an excitation light source unit according to the present invention.

FIG. 19 is a diagram showing the configuration of an excitation light source unit according to an eighth embodiment of the invention.

FIG. 20 is a diagram showing the configuration of a ninth embodiment of an excitation light source unit according to the present invention.

FIG. 21 is a tenth embodiment of the excitation light source unit according to the present invention.
It is a figure which shows the structure of embodiment.

FIG. 22 is an eleventh embodiment of the excitation light source unit according to the present invention.
It is a figure which shows the structure of embodiment.

FIG. 23 is a diagram showing a configuration of an excitation light source unit having a dual structure excitation light supply system.

FIG. 24 is a twelfth embodiment of the excitation light source unit according to the present invention.
It is a figure which shows the structure of embodiment.

FIG. 25 is a thirteenth excitation light source unit according to the present invention.
It is a figure which shows the structure of embodiment.

FIG. 26 is a fourteenth embodiment of the excitation light source unit according to the present invention.
It is a figure which shows the structure of embodiment.

FIG. 27 is a fifteenth embodiment of the excitation light source unit according to the present invention.
It is a figure which shows the structure of embodiment.

FIG. 28 is a diagram showing a configuration of a first embodiment of a Raman amplifier according to the present invention.

FIG. 29 is a diagram showing the configuration of a second embodiment of a Raman amplifier according to the present invention.

FIG. 30 is a diagram showing the configuration of a Raman amplifier according to a third embodiment of the present invention.

FIG. 31 is a diagram showing the configuration of a Raman amplifier according to a fourth embodiment of the present invention.

FIG. 32 is a diagram showing a configuration of a first embodiment of an optical transmission system according to the present invention.

FIG. 33 is a diagram showing the configuration of a second embodiment of the optical transmission system according to the present invention.

34 is a block diagram showing a configuration of a relay station in the optical transmission system shown in FIG. 28.

FIG. 35 is a diagram showing the configuration of a third embodiment of the optical transmission system according to the present invention.

FIG. 36 is a power spectrum of the signal light B after Raman amplification.

FIG. 37 is a power spectrum of the signal light A after Raman amplification.

FIG. 38 is a power spectrum of the signal light C after Raman amplification.

[Explanation of symbols]

LU ... Excitation light source unit, L ... Optical transmission line, RA ... Raman amplifier, T ... Transmitting station, S ... Relay station, R ... Receiving station, 1, 1
a ... Excitation light supply system (main excitation light supply system), 1
b ... Auxiliary excitation light supply system, 11, 11a, 11b,
12, 12a, 12b, 13, 13a, 13b ... Wavelength variable pumping light source, 110 ... First semiconductor laser, 111 ... Optical waveguide, 112 ... Resonance grating, 113 ... Heating means, 114 ... First pumping laser, 115 ... Ring Optical fiber, 116 ... Wavelength synthesizer, 117 ... Divider, 118 ...
Optical isolator, 119 ... Band pass filter, 12-
18 ... 2nd-8th wavelength variable excitation light source, 2 ... Excitation light multiplexing part, 21 ... Wavelength synthesizer, 22 ... Transmission characteristic adjusting means, 23
a, 23b ... Polarization combiner, 24a, 24b ... Depolarizer (depolarizing means), 25, 25a, 25b ... Arrayed waveguide diffraction grating (AWG), 26 ... Interleaver, 2
7, 27a, 27b, 27c ... Optical circulator, 3 ...
Output unit, 31 ... Output optical waveguide, 32 ... Output multiplexer, 3
5 ... Multiplexer, 4, 41-45, 400-402 ... Optical switch, 420, 430 ... Optical waveguide, 412, 413, 4
14, 423, 424, 434 ... Reflection grating, 415, 425, 435, 445 ... Optical isolator, 50 ... Raman amplification optical fiber, 51 ... Optical brancher,
52 ... Output signal light measuring device, 53 ... Signal light demultiplexer, 54a
54d ... Output signal light measuring device, 55 ... Optical branching device, 56 ...
Input signal light measuring device, 57 ... Instruction signal input unit, 60 ... Control unit.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01S 5/02 H01S 3/091 S (72) Inventor Masakazu Mobara 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries Yokohama Factory Co., Ltd. F-term (reference) 2K002 AA02 AB30 BA01 CA15 DA10 EB12 EB15 HA24 5F072 AB09 AB13 AK06 HH02 HH05 HH06 JJ02 JJ09 KK07 KK11 PP07 QQ07 RR01 YY17 5F073 AB06 AB28 AB30 BA01 EA04 GA13 FA29 FA05 GA05 FA05 GA13

Claims (48)

[Claims] 1. An N pumping light source for outputting pumping lights of N (≧ 2) channels having different wavelengths from each other,
At least one of the pumping light sources is a pumping light supply system that is a wavelength variable pumping light source capable of changing the channel wavelength of pumping light to be output, and the N channels of the N channels output from each of the N pumping light sources. A pumping light source unit for Raman amplification, comprising a multiplexer for multiplexing pumping light, and an output structure for outputting the pumping light multiplexed by the multiplexer. 2. The wavelength tunable pumping light source comprises an pumping light laser, a resonance grating, and an external resonator including a channel wavelength adjusting system for changing the wavelength of light reflected by the resonance grating. The pumping light source unit according to claim 1, further comprising a variable wavelength laser. 3. The excitation light source unit according to claim 2, wherein the resonance grating includes a Bragg grating that reflects light having a Bragg wavelength. 4. The Bragg grating includes a fiber Bragg grating having a periodic refractive index change formed in at least a core region of the optical fiber along a longitudinal direction of the optical fiber. The excitation light source unit described. 5. The pumping light source unit according to claim 4, wherein the channel wavelength adjusting system includes stress applying means for changing a grating period by applying a predetermined stress to the fiber Bragg grating. . 6. The pumping light source unit according to claim 4, wherein the channel wavelength adjusting system includes a heating unit that changes the refractive index in the core region by heating the fiber Bragg grating. 7. The Bragg grating is formed in an optical waveguide made of a material having an electro-optical effect, and the channel wavelength adjustment system has a predetermined strength with respect to the optical waveguide having the Bragg grating formed therein. The excitation light source unit according to claim 3, further comprising an electric field applying unit that changes the refractive index of the optical waveguide by applying an electric field. 8. The variable wavelength pumping light source includes a semiconductor laser and a heating means for changing an oscillation wavelength of the semiconductor laser by adjusting a chip temperature of the semiconductor laser. Excitation light source unit. 9. The pump according to claim 1, wherein the wavelength tunable pumping light source includes a pumping laser and a wavelength tunable laser having a wavelength tunable bandpass filter capable of changing the wavelength of light to be transmitted. Light source unit. 10. The pumping light source unit according to claim 1, wherein the multiplexer includes a transmission characteristic adjusting unit for adjusting a transmission wavelength characteristic thereof. 11. The multiplexer comprises a plurality of polarization multiplexers for respectively polarization-combining pumping lights of mutually paired channels for each pumping light of two channels having adjacent wavelengths. The pumping light source unit according to claim 1, further comprising a wavelength multiplexer that further multiplexes the wavelengths of the pumping light output from the polarization multiplexer. 12. The pumping light source unit according to claim 11, wherein the multiplexer further comprises a depolarizer provided between the polarization multiplexer and the wavelength multiplexer. 13. The pumping light source unit according to claim 1, wherein the multiplexer includes an arrayed waveguide type diffraction grating. 14. The pumping light source unit according to claim 1, wherein the multiplexer includes an interleaver. 15. The pumping light source unit according to claim 1, wherein the multiplexer has a structure in which an arrayed waveguide type diffraction grating and an interleaver are combined. 16. Each of the N pumping light sources comprises:
A pump laser and an external resonator type laser having a resonance grating are included, and at least one of these external resonator type lasers is a channel wavelength adjustment for changing the wavelength of light reflected by the resonance grating. An external cavity type tunable laser further comprising a system, wherein the multiplexer comprises at least one for multiplexing N-channel pumping light outputted from each of the N external cavity type lasers. An optical circulator device, and the N
Each of the pumping light sources is provided between the resonant grating and the optical circulator device included in each of the pumping light sources, and the pumping light of any channel output from the optical circulator device to the resonant grating is the optical circulator. The excitation light source unit according to claim 1, further comprising a reflection grating having a reflection characteristic of reflecting toward the device. 17. The optical circulator device sequentially multiplexes the N-channel pumping light output from the external cavity laser included in each of the N pumping light sources, (N-1). The pumping light source unit according to claim 16, comprising (N-1) three-port optical circulators connected in stages. 18. The (N + 1) port light for multiplexing the N-channel pump light output from the external cavity laser included in each of the N pump light sources, The excitation light source unit according to claim 16, further comprising a circulator. 19. The optical multiplexer according to claim 16, further comprising an optical isolator provided between the resonance grating and the reflection grating.
The excitation light source unit described. 20. One (N + 2) port light for multiplexing the N-channel pump light output from the external cavity laser included in each of the N pump light sources, The excitation light source unit according to claim 16, further comprising a circulator. 21. The channel wavelength adjustment system, wherein the reflection wavelength of a reflection grating that reflects the pumping light from the corresponding external resonator type wavelength tunable laser of the reflection grating corresponds to the corresponding external resonator type. 17. The pumping light source unit according to claim 16, wherein the pumping light source unit is changed in synchronization with the reflection wavelength of the resonance grating included in the wavelength tunable laser. 22. The excitation light source unit according to claim 16, wherein each of the resonance grating and the reflection grating includes a Bragg grating that reflects light having a Bragg wavelength. 23. The Bragg grating includes a fiber Bragg grating having a periodic refractive index change formed in at least a core region of the optical fiber along a longitudinal direction of the optical fiber.
2. The excitation light source unit according to 2. 24. The pumping light source unit according to claim 23, wherein the channel wavelength adjusting system includes stress applying means for changing a grating period by applying a predetermined stress to the fiber Bragg grating. . 25. The pumping light source unit according to claim 23, wherein the channel wavelength adjusting system includes a heating unit that changes the refractive index in the core region by heating the fiber Bragg grating. 26. The Bragg grating is formed in an optical waveguide made of a material having an electro-optical effect, and the channel wavelength adjusting system applies an electric field of a predetermined intensity to the optical waveguide having the Bragg grating formed therein. 23. The excitation light source unit according to claim 22, further comprising an electric field applying unit that changes the refractive index of the optical waveguide by applying the electric field. 27. The output structure is provided in a transmission line through which signal light propagates, and includes an output section that outputs the pumping light from the optical multiplexer into the transmission line and allows the signal light to pass therethrough. The excitation light source unit according to claim 1, wherein 28. A main pumping light supply system including N pumping light sources that respectively output pumping lights of N (≧ 2) channels having different wavelengths, and the pumping light sources output from each of the N pumping light sources. A multiplexer for multiplexing N-channel pumping light, an output structure for outputting the pumping light multiplexed by the multiplexer, and one or more spare pumping light sources, the spare pumping light source At least one of the optical light sources is a tunable pumping light source that is a variable wavelength pumping light source capable of changing the channel wavelength of the pumping light to be output, and an optical path between the main pumping light supply system and the multiplexer. And is included in the main pumping light supply system.
A pumping light source unit for Raman amplification, comprising an optical switch for switching the output from any one of the pumping light sources and the output from the preliminary pumping light source. 29. The pumping light source unit according to claim 28, wherein the optical switch includes an optical switch utilizing an optical interference effect. 30. The pump according to claim 28, further comprising a 1 × M (≧ 2) port optical switch arranged on an optical path between the optical switch and the preliminary pumping light supply system. Light source unit. 31. Output from a pumping light source of the N pumping light sources that is to be switched via the optical switch, which is arranged on an optical path between the optical switch and the 1 × M port optical switch. 31. The pumping light source unit according to claim 30, further comprising a resonance grating having a center reflection wavelength substantially equal to the wavelength of the pumping light to be generated. 32. An M (≧ 2) port output demultiplexer arranged on an optical path between the optical switch and the preliminary pumping light supply system is further provided.
The excitation light source unit described. 33. The pre-pump light supply system and M (≧
2) A resonance grating arranged on an optical path between the port output demultiplexer and a channel wavelength adjusting system for changing a wavelength of light reflected by the resonance grating. The excitation light source unit according to claim 28. 34. The pumping light source unit according to claim 33, wherein the channel wavelength adjusting system includes a stress applying unit that changes a grating period by applying a predetermined stress to the resonance grating. . 35. The pumping light source unit according to claim 33, wherein the channel wavelength adjusting system includes a heating unit that changes the refractive index in the core region by heating the resonance grating. 36. The resonance grating is formed in an optical waveguide made of a material having an electro-optical effect, and the channel wavelength adjusting system is arranged in a predetermined manner with respect to the optical waveguide having the resonance grating formed therein. 4. An electric field applying means for changing the refractive index of the optical waveguide by applying a strong electric field.
3. The excitation light source unit described in 3. 37. An optical fiber for Raman amplification for Raman-amplifying signal light within a predetermined amplification wavelength band by pumping light; and supplying the pumping light to the Raman amplification optical fiber. Or a pumping light source unit according to claim 1; 38. An input power measuring system for measuring the power of the input signal light, and the pumping light source so that the output signal light spectrum becomes substantially flat based on the measurement result of the input power measuring system. 38. The Raman amplifier according to claim 37, further comprising: a control unit that controls the power or wavelength of the N-channel pumping light output from each of the N pumping light sources included in the unit. 39. An output power measurement system for measuring the power of Raman-amplified output signal light, and the pumping so that the output signal light spectrum is substantially flat based on the measurement result of the output power measurement system. 38. The Raman amplifier according to claim 37, further comprising: a control unit that controls the power or wavelength of the N-channel pumping light output from each of the N pumping light sources included in the light source unit. . 40. An instruction signal input system for receiving an instruction signal from the outside, and the pumping so that an output signal light spectrum is substantially flat based on the instruction signal taken by the instruction signal input system. 38. The Raman amplifier according to claim 37, further comprising: a control unit that controls the power or wavelength of the N-channel pumping light output from each of the N pumping light sources included in the light source unit. . 41. The controller controls at least one channel wavelength of the pumping light so as to approach a frequency 13 THz to 15 THz higher than the frequency at which the signal light power in the output signal light spectrum is minimum. Raman amplifier according to any one of claims 38 to 40, characterized in that the Raman amplifier is controlled. 42. The power of pumping light output from one or more pumping light sources of the N pumping light sources included in the pumping light source unit is lowered to such an extent that it cannot contribute to Raman amplification. At this time, the power variation of each channel of the Raman-amplified signal light is 2 dB or less,
38. The Raman amplifier according to claim 37, further comprising a control unit that controls the power of the pumping light output from the remaining pumping light sources other than the pumping light source whose power has been reduced. 43. The control unit controls, among the N pumping light sources included in the pumping light source unit, a pumping light source whose power of pumping light to be output is lowered to such an extent that it cannot contribute to Raman amplification. Control the remaining pumping light source so that the channel wavelength of the pumping light to be output from the pumping light source whose output power has been lowered is brought closer to the channel wavelength of the pumping light to be output from the remaining pumping light source. 42. The Raman amplifier according to claim 41, wherein: 44. The pumping light source unit according to any one of claims 1 to 36 for supplying pumping light of N (≧ 2) channels having different wavelengths, and signal light of a plurality of channels having different wavelengths. And an optical waveguide that Raman-amplifies the signal light by the pumping light supplied from the pumping light source unit, and one or more of the N pumping light sources included in the pumping light source unit. When the power of the pumping light output from the pumping light source decreases to the extent that it cannot contribute to Raman amplification,
And a control unit for controlling the power of the pumping light output from the remaining pumping light sources excluding the pumping light source whose power has been lowered so that the power variation of each channel of the Raman-amplified signal light is 2 dB or less. Raman amplifier. 45. The control unit controls, among the N pumping light sources included in the pumping light source unit, a pumping light source whose power of pumping light to be output is lowered to such an extent that it cannot contribute to Raman amplification. Control the remaining pumping light source so that the channel wavelength of the pumping light to be output from the pumping light source whose output power has been lowered is brought closer to the channel wavelength of the pumping light to be output from the remaining pumping light source. The Raman amplifier according to claim 44, wherein: 46. The optical transmission line through which signal light within a predetermined signal light wavelength band propagates, and a part of the optical transmission line as an optical fiber for Raman amplification, according to any one of claims 37 to 45. Optical transmission system with Raman amplifier. 47. An optical transmission line through which signal light within a predetermined signal light wavelength band propagates, and an end portion which is installed at a predetermined position on the optical transmission line and which is optically connected to the optical transmission line. 47. An optical fiber for Raman amplification, which comprises:
An optical transmission system comprising the Raman amplifier according to claim 1. 48. An optical transmission system having a plurality of repeating sections and including the Raman amplifier according to any one of claims 37 to 45, wherein the power variation of each channel of the signal light per repeating section. The average value is 2
An optical transmission system characterized by being below dB.