JP2003224521A - Wavelength multiplex optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily realize a reduction in transmission characteristics deterioration due to cross-phase modulation that occurs in a wavelength multiplex optical transmission system. <P>SOLUTION: A lumped constant type optical amplifier arranged at the input side of each relay section is used to optically amplify an optical signal, a first gain control part controls the gain of the lumped constant type optical amplifier, a distributed constant type optical amplifier that uses an optical fiber transmission line arranged on the output side of the each relay section as an amplification medium is used to optically amplify the optical signal, a second gain control part controls the gain of the distributed constant type optical amplifier, and a compensation control part controls the gain ratio of the first gain control part to that of the second gain control part, thereby canceling the amounts of blue chirping and red chirping due to cross-phase modulation that occurs between at least adjacent wavelength signals in one section of the each relay section in the optical fiber transmission line to reduce the amount of residual chirping. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long-distance optical transmission system in which a wavelength which suppresses deterioration of transmission characteristics due to cross-phase modulation by appropriately controlling gains of optical amplifiers inserted before and after a repeater. The present invention relates to a multiplex optical transmission system.

[0002]

2. Description of the Related Art In recent long-distance optical transmission systems,
Erubium Doped Fiber Amplifier (hereinafter referred to as "Erubium Doped Fiber Amplifier" that can directly amplify light in the 5 [μm] band
DFA ”. )) Is the mainstream optical repeater amplification transmission system. Furthermore, EDF that can be amplified in a wide band
A has appeared, and a large-capacity transmission system by a wavelength division multiplexing transmission system using them has been realized.

However, with the recent demand for larger capacity and lower cost, as means for realizing this, increase of transmission rate per channel, effective use of amplification band, extension of relay interval, etc. are demanded. There is.

On the other hand, in order to increase the transmission rate and effectively use the amplification band, it is necessary to narrow the wavelength multiplex interval,
Further, in order to extend the relay interval, it is necessary to increase the input power to the transmission line because it is necessary to secure the optical signal to noise ratio at the receiving end. However, the narrowing of the sense of wavelength multiplexing and the increase of the input power to the transmission line lead to the optical pulse distortion due to the nonlinear effect peculiar to the optical fiber transmission.

As a non-linear effect that causes optical pulse distortion,
The four-wave mixing, the self-phase modulation effect, and the cross-phase modulation effect are included.

Among these listed non-linear effects, the pulse distortion due to four-wave mixing is a method of preventing the optical signal wavelength from overlapping the zero dispersion wavelength of the optical fiber, or a method of arranging the wavelength multiplexing intervals at unequal intervals. It is known that

As for the pulse distortion due to the self-phase modulation effect, a method of increasing the pulse waveform change in the transmission line by performing phase modulation on the optical signal at the transmitting end and suppressing the average power of the pulse to a low level is also known. A method is known in which a Raman amplifier capable of performing distributed constant optical amplification using an optical fiber transmission line itself as an amplification medium is used in combination with an EDFA to reduce the output power of the EDFA immediately following the optical fiber transmission line. For these reasons, it is possible to reduce the influence of four-wave mixing and self-phase modulation.

[0008]

If the effects of four-wave mixing and self-phase modulation can be reduced, pulse distortion due to mutual phase modulation becomes a major factor that governs the performance of optical transmission systems. Therefore, how to reduce the influence of the cross-phase modulation is a key to how to increase the transmission rate per channel of the wavelength division multiplexing optical transmission system and extend the relay interval. Therefore, the influence of the mutual phase modulation will be described below by taking as an example the case of dividing two different wavelengths and performing multiplex transmission.

The self-phase modulation of the optical fiber is due to the optical Kerr effect that slightly changes the refractive index of the optical fiber depending on the intensity of the optical signal, but the cross phase modulation is one of the two wavelength-multiplexed signals. This is because a change in the intensity of the signal light acts together with another change in the intensity of the signal light to slightly change the refractive index of the optical fiber.

FIG. 1 is a conceptual diagram showing a phenomenon of self-phase modulation by an optical pulse. When self-phase modulation occurs, the instantaneous frequency of the light pulse is shifted to the lower frequency (hereinafter referred to as "red chirp") at the rising portion of the light pulse (leading edge of the light pulse), and conversely At the trailing edge (the trailing edge of the light pulse), the instantaneous frequency of the light pulse is shifted to a higher frequency (hereinafter referred to as "blue chirp").

On the other hand, FIG. 2 shows cross-phase modulation by optical pulses.
It is a conceptual diagram which shows the phenomenon of. In FIG. 2A, λ₁
And λ₂Is a light pulse of two different wavelengths, λ₁The light of
Ruth's speed is λ₂It is assumed to be earlier than the light pulse of. Two lights
When a pulse travels in an optical fiber, λ₁Light pulse
Is λ₂Since it progresses faster than the optical pulse of
Sea urchin₁The rising part of the optical pulse of₂Light pulse
Begins to overlap with the falling part of. Then λ₂Light of
The falling part of the pulse is λ₁Rising of the light pulse of
Phase shift due to the red chirp induced in the
receive. Furthermore, λ ₁And λ₂Figure showing the progress of optical pulse transmission
As shown in 2 (c), λ₁Optical pulse of λ₂The light of
Rus will be pulled out, λ₁The fall of the light pulse of
The part is λ₂Overlaps with the rising portion of the light pulse. This
Then λ₂The rising part of the optical pulse of is λ₁The light of
Due to the blue chirp induced by the falling part of the lusu
Will undergo a phase shift.

In the optical fiber transmission line through which these two optical pulses are transmitted, if there is no attenuation of optical power, λ
_Since the _second light pulse is equal to the amount of red chirp and blue chirp experienced by lambda ₁ of the optical pulse, chirp that occurs while the lambda ₂ light pulse is overtaken overtaken the lambda ₁ light pulse is mutually canceled, The optical pulse of λ ₂ does not undergo a phase shift due to the cross phase modulation effect.

However, since the optical power is usually attenuated as the optical signal is transmitted through the optical fiber transmission line, the amount of red chirp generated during the overlapping of the optical pulse of λ _{1 and} the optical pulse of λ ₂ is When the optical pulse of λ ₁ overlaps the optical pulse of λ ₂ , the optical pulse of λ ₁ changes to λ ₂
It becomes larger than the blue chirp amount generated while overtaking the optical pulse of, and the chirp amounts of the two do not cancel each other out, and the red chirp generated at a point where the optical signal power is high remains slightly. Therefore, the residual red chirp causes a phase shift in the optical pulse of λ _{2 and} the group velocity propagating through the optical fiber changes. This effect remains at each relay interval, resulting in jitter (deviation of the center position of the received pulse) at the receiving end, which deteriorates the transmission performance.

As described above, in cross-phase modulation, intensity distortion between adjacent wavelengths causes phase fluctuations and deteriorates transmission characteristics. Therefore, wavelength-division long-distance optical transmission system in which collision of optical pulses between adjacent wavelengths is repeated. Is very problematic in.

As a method of reducing this cross phase modulation, for example, Japanese Patent Laid-Open No. 2001-94511 (Prior Art)
1) and Japanese Patent Laid-Open No. 2001-36468 (Prior Art 2).

Prior Art 1. FIG.
It is explanatory drawing which shows the Example described in 6468 publication. In the figure, 111 is a transmitter, 112-1 to 112-
n is a transmitter, 113 is a multiplexer, 114 and 1
Reference numeral 24 is an optical amplifier, 115, 119 and 121 are dispersion shift fibers (negative dispersion), 116, 120 and 122 are dispersion shift fibers (negative, positive and zero dispersion), 117 and 118 are optical linear repeaters, and 123 is a receiver. , 125 is a duplexer, 12
6-1 to 126-n are dispersion equalizers 127-1 to 127
-N is a receiver, which is a transmitter 111 and a receiver 123.
Between them and optical linear repeaters 117 and 118 installed to compensate for the loss of the transmission optical fiber.

In the configuration of FIG. 11, the optical signal output from the transmitter 111 has a chirp coefficient of zero or positive, and all signals within the range from the input end of each transmission section to the effective interaction length. The light is transmitted through the dispersion shift fibers 115, 119, 121 set such that the local dispersion value of the chromatic dispersion of the transmission optical fiber becomes negative with respect to the optical wavelength. As a result, pulse compression occurs on the negative dispersion side, so that the eye opening degree is improved. Thereafter, the optical signal is set to zero dispersion, which is a dispersion amount that minimizes the influence of cross-phase modulation, and the dispersion shift fibers 116, 120, 122.
To transmit in.

In the transmission system as described above, the chromatic dispersion of each transmission section is set so that the optimum total dispersion amount for self-phase modulation becomes zero dispersion which is the optimum dispersion amount for cross phase modulation. We are trying to reduce the deterioration of transmission characteristics due to modulation.

Prior art 2. FIG. 12 is a schematic diagram of JP-A-2001-9.
It is explanatory drawing which shows the Example described in 4511 publication. In the figure, 130 is an optical transmitting station, 132 is an optical receiving station, 1
Reference numeral 34 denotes an optical transmission line connecting the optical transmitting station 130 and the optical receiving station 132, 131A denotes a plurality of optical transmitters (E / O) that output a plurality of optical signals, and 131B denotes a wavelength multiplexing of the plurality of optical signals. A multiplexer 131C is a post-amplifier that amplifies the wavelength-multiplexed signal light from the multiplexer 131B to a required level and outputs it to the optical transmission line 134, and 132A is a wavelength-multiplexed signal light transmitted through the optical transmission line 134. , 132B is a demultiplexer that branches the output light from the preamplifier 132A into a plurality of optical signals according to the wavelength, 1
Reference numeral 32C is a plurality of optical receivers (O / E) that respectively receive and process a plurality of optical signals.

Here, it is assumed that the optical transmission line 134 is controlled so that the transmission line loss is almost 0 [dB / km]. Optical transmission line 134
As a function of compensating for the loss of the optical transmission line in a distributed manner, for example, an optical amplification technique such as stimulated Raman scattering or an optical amplification technique using an optical fiber doped with a rare earth element ion such as erbium as an optical transmission line. It is equipped with.
Optical transmission line 134 has a first to n repeating sections 134 ₁ ～134 _n that between the optical transmitter 130 and the optical receiving station 132 is divided into n.

Here, the length of each optical transmission line in each of the relay sections 134 _{1 to} 134 _n is 50 [km], the chromatic dispersion near the signal wavelength is -1.25 [ps / km / nm], When the frequency interval is 100 [GHz] and the transmission speed is 10 [bit / s], the delay amount of the optical pulse between adjacent wavelengths is ½ of the bit period due to chromatic dispersion in one relay section. 100 [k
[m] After transmission, the optical pulse between adjacent wavelengths is delayed by 1 bit. At this time, when the optical pulse between adjacent wavelengths is about to collide at 0 [km] time, 100
[km] After the transmission, one collision occurred.

Now, the chromatic dispersion characteristics of the optical transmission line 134 are set so that the number of collisions of optical pulses of adjacent wavelengths in each of the optical transmission lines 134 of the relay sections 134 _{1 to} 134 _n becomes an integral multiple. Specifically, the chromatic dispersion D of the optical transmission line 134 per one relay section is set so as to satisfy the relationship shown by the following equation. Where Br is the transmission rate, λ
Is the wavelength, Δf is the optical frequency interval, and c is the speed of light.

[0023]

[Equation 1]

For example, in (Equation 1), the transmission rate Br
Is 10 [Gbit / s], the signal wavelength is 1550 [nm], and the optical frequency interval is 100 [GHz], the wavelength dispersion of the optical transmission line per repeater section is 125 [ps / nm] times N times. .

In the above optical transmission system, the optical transmission line is configured so that the number of collisions of optical pulses of adjacent wavelengths in one repeater section is an integral multiple, that is, optical pulses between adjacent wavelengths are delayed by N bits. By setting the chromatic dispersion characteristic of 134, the total amount of red chirp and blue chirp generated when passing an optical pulse becomes almost the same, and by canceling the chirping due to cross-phase modulation, it is possible to reduce the waveform distortion. ing.

However, as a practical problem, the optical transmission line loss in each repeater section is set to be almost 0 [dB / km] in all wavelength bands as in the case of the prior art 1, and the adjacent optical path is different as in the case of the prior art 2. It is very difficult to manage the chromatic dispersion of the optical transmission line so that the number of collisions of optical pulses between wavelengths is always delayed by N bits.

The present invention has been made in view of the above, and an object of the present invention is to provide a wavelength division multiplexing optical transmission system which easily realizes reduction of transmission characteristic deterioration due to cross phase modulation occurring in a wavelength division multiplexing optical transmission system. To do.

[0028]

In order to achieve the above object, a wavelength division multiplexing optical transmission system according to the present invention multiplexes two or more optical signals having different wavelengths by using an optical fiber transmission line having a plurality of relay sections. In a wavelength division multiplexing optical transmission system for transmitting, a lumped constant type optical amplifier for lumped constant optical amplification of an optical signal arranged on the input side of each repeater section, and a first lumped constant type optical amplifier for controlling the gain of the lumped constant type optical amplifier A gain control unit, a distributed constant type optical amplifier for optically amplifying the distributed constant type optical amplifier using the optical fiber transmission line arranged on the output side of each relay section as an amplification medium, and controlling the gain of the distributed constant type optical amplifier. A second gain control section, and a blue chirping amount and a red chirp pin due to mutual phase modulation generated between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. Wherein the amount and a compensation control unit for controlling a gain ratio between the first gain control unit and the second gain controller as canceled.

According to the present invention, an optical signal is optically amplified by using a lumped constant type optical amplifier arranged on the input side of each relay section,
A first gain control unit controls the gain of the lumped-constant type optical amplifier, and an optical signal is generated by using a distributed-constant type optical amplifier using the optical fiber transmission line arranged on the output side of each relay section as an amplification medium. Optical amplification is performed, the gain of the distributed constant type optical amplifier is controlled by the second gain controller, and the first gain is controlled by the compensation controller.
By controlling the gain ratio between the gain control section and the second gain control section of the optical fiber transmission line, the cross phase modulation generated at least between adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. The amount of blue chirping and the amount of red chirping can be canceled.

A wavelength division multiplexing optical transmission system according to the next invention is a wavelength division multiplexing optical transmission system that multiplex-transmits two or more optical signals having different wavelengths using an optical fiber transmission line having a plurality of relay sections. A first distributed constant type optical amplifier for performing distributed constant optical amplification using the optical fiber transmission line disposed on the input side of the first distributed constant type optical amplifier as a gain medium, and a first distributed constant type optical amplifier for controlling the gain of the first distributed constant type optical amplifier. A gain control unit, a second distributed constant type optical amplifier that optically amplifies the optical fiber transmission line arranged on the output side of each relay section in a distributed constant manner as an amplification medium, and the second distributed constant type optical amplifier A second gain control unit for controlling the gain of the amplifier, and a blue chirping amount and a delay amount due to the cross phase modulation generated between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. Wherein the Dochapingu amount and a compensation control unit for controlling a gain ratio between the first gain control unit and the second gain controller as canceled.

According to the present invention, the optical signal is optically amplified by using the first distributed constant type optical amplifier having the optical fiber transmission line arranged on the input side of each relay section as an amplification medium, and the first gain is obtained. The control unit controls the gain of the first distributed constant type optical amplifier, and the second distributed constant type optical amplifier using the optical fiber transmission line arranged on the output side of each relay section as an amplification medium The signal is optically amplified, the gain of the second distributed constant optical amplifier is controlled by the second gain control unit, and the gain between the first gain control unit and the second gain control unit is controlled by the compensation control unit. By controlling the ratio, it is possible to cancel the blue chirping amount and the red chirping amount due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line.

A wavelength division multiplexing optical transmission system according to the next invention is a wavelength division multiplexing optical transmission system that multiplex-transmits two or more optical signals having different wavelengths by using an optical fiber transmission line having a plurality of relay sections. A distributed constant type optical amplifier for performing distributed constant optical amplification using the optical fiber transmission line arranged on the output side of the section as an amplification medium, a gain control section for controlling the gain of the distributed constant type optical amplifier, and the optical fiber A compensation control unit for controlling the gain of the gain control so that the blue chirping amount and the red chirping amount due to the mutual phase modulation generated at least between adjacent wavelength signals in one section of each relay section in the transmission line are canceled. It is characterized by having and.

According to the present invention, the optical signal is optically amplified by using the distributed constant type optical amplifier using the optical fiber transmission line arranged on the output side of each of the relay sections as an amplification medium, and the gain control section controls the optical signal. By controlling the gain of the distributed constant type optical amplifier and controlling the gain of the gain control section by the compensation control section, at least between adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. It is possible to cancel the blue chirping amount and the red chirping amount by the mutual phase modulation.

A wavelength division multiplexing optical transmission system according to the next invention is characterized in that, in the above invention, the optical fiber transmission line is composed of a plurality of different effective core sectional areas.

According to this invention, in the above invention,
Since the optical fiber transmission line is composed of a plurality of different effective core cross-sectional areas, a mutual signal generated at least between adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. It is possible to cancel the blue chirping amount and the red chirping amount by the phase modulation.

In the wavelength division multiplexing optical transmission system according to the next invention, in the above invention, the chromatic dispersion value in each relay section in the optical fiber transmission line is composed of a positive dispersion value and a negative dispersion value. Characterize.

According to this invention, in the above invention,
One of the relay sections in the optical fiber transmission line is characterized in that the chromatic dispersion value in each relay section in the optical fiber transmission line is composed of a positive dispersion value and a negative dispersion value. In, at least the blue chirping amount and the red chirping amount due to the mutual phase modulation generated between the adjacent wavelength signals can be canceled.

In the above-mentioned invention, the wavelength division multiplexing optical transmission system according to the next invention is set so that the delay amount of the optical pulse between adjacent wavelengths due to the chromatic dispersion in each relay section in the optical fiber transmission line becomes zero. It is characterized by having done.

According to this invention, in the above invention,
By setting the delay amount of the optical pulse between adjacent wavelengths due to chromatic dispersion in each relay section in the optical fiber transmission line to be zero, each relay section in the optical fiber transmission line It is possible to cancel out the blue chirping amount and the red chirping amount due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section.

The wavelength-division-multiplexed optical transmission system according to the next invention is characterized in that, in the above-mentioned invention, the signs of chromatic dispersion in two continuous relay sections in the optical fiber transmission line are different.

According to this invention, in the above invention,
In the optical fiber transmission path, at least two adjacent wavelength signals are adjacent to each other in at least one of the relay sections in the optical fiber transmission path, since the two chromatic dispersions have different signs of chromatic dispersion. It is possible to cancel the amount of blue chirping and the amount of red chirping due to the generated mutual phase modulation.

In the wavelength division multiplexing optical transmission system according to the next invention, in the above invention, the delay amount of the optical pulse between adjacent wavelengths due to the chromatic dispersion of two continuous relay sections in the optical fiber transmission line becomes zero. It is characterized by setting as follows.

According to this invention, in the above invention,
By setting the delay amount of the optical pulse between adjacent wavelengths due to the wavelength dispersion of two continuous relay sections in the optical fiber transmission line to be zero, each in the optical fiber transmission line It is possible to cancel out the amount of blue chirping and the amount of red chirping due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of the relay section.

[0044]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. FIG. 3 is an explanatory diagram of the first embodiment of the wavelength division multiplexing optical transmission system according to the present invention. In the figure, 1 is an optical fiber transmission line and 2 is
The ₁ to 2 _n are repeating sections obtained by dividing the optical fiber transmission line 1 to n, 3 a transmission unit for transmitting the two or more different wavelength signals wavelength-multiplexed signal light wavelength multiplexed light, 4 ₁ to 4 _n wavelength transmitter for transmitting the different wavelength signal light, 5 a multiplexer for multiplexing the plurality of wavelength signal light transmitted from the transmitter 4 ₁ to 4 _n, where 6 is transmitted through the optical fiber transmission line 1 A demultiplexer for demultiplexing the multiplexed signal light, 7 _{1 to} 7 _n are receivers for receiving signal lights having different wavelengths demultiplexed by the demultiplexer 6, and 8 is a demultiplexer 6 and a receiver. Each of the receiving units composed of 7 _{1 to} 7 _n is shown.

Further, in each of the relay sections 2 ₁ to 2 _{n obtained} by dividing the optical fiber transmission path in the same figure, 1a is an optical fiber transmission path of each of the relay sections 2 ₁ to 2 _n , and 10 is an optical fiber transmission path. An input terminal for inputting the wavelength-multiplexed signal light connected to 1a, 11 is a lumped constant type optical amplifier, 12 is a distributed constant type optical amplifier, and 13 is a pump for distributed constant type amplification in the distributed constant type optical amplifier 12. A light source, 14 is an optical combining means for combining the pumping light sent from the distributed constant type amplification pumping light source 13 and the WDM signal light, 15 is an optical output terminal to which the WDM signal light is sent, and 16a is A gain control unit for controlling the gain of the lumped constant optical amplifier 11, 16b is a gain control unit for controlling the gain of the distributed constant optical amplifier 12, 17 is a gain control unit 16a of the lumped constant optical amplifier, and a distributed constant. Type optical amplifier gain control unit 1 6b is a compensation control unit that appropriately controls 6b and cancels the influence of the blue chirp and the red chirp due to the mutual phase modulation generated in the optical fiber transmission line 1a.

FIG. 4 (1) is an explanatory view of the principle that residual chirp is generated due to the influence of mutual phase modulation occurring in the relay section. Reference numeral 1a denotes an optical fiber transmission line composed of a positive dispersion value obtained by dividing the optical fiber transmission line 1 into a plurality, and 10 denotes an input terminal connected to the optical fiber transmission line 1a to which the wavelength-multiplexed signal light is input. , 11 are lumped constant optical amplifiers, 1
Reference numeral 5 denotes an optical output terminal to which the wavelength multiplexed signal light is transmitted. 4 (1)-(a), Pin is the input signal power,
Pout represents the output signal power, and the solid line represents the signal power curve that attenuates as the optical signal is transmitted.

Now, the relay interval in FIG. 4 (1) is 100 [km].
And the chromatic dispersion near the signal light wavelength is 2.5 [ps / km / n
m], the signal wavelength interval is 0.8 [nm], and the transmission speed is 20 [Gbit /
s]. At this time, the delay amount caused by the wavelength dispersion of the signal light of the adjacent wavelength is D for the wavelength dispersion, L for the transmission distance, and Δ.
It can be expressed by the following equation, where λ is a wavelength interval.

[0048]

[Equation 2]

From this (Equation 2), 25 wavelength-multiplexed signal lights can be obtained.
If it is propagated [km], the amount of delay between adjacent wavelengths is 2.5 [ps
/km/nm]×25[km]×0.8[nm]=50[ps], which means that the bit period of a signal with a transmission rate of 20 [Gbit / s] is 50 [ps].
Therefore, it means that adjacent optical pulses are delayed by 1 bit.

In other words, when optical pulses of adjacent wavelengths are about to collide at 0 [km], 25 [km]
During the transmission of the red chirp and the blue chirp, the red chirp and the blue chirp are generated once. That is, the relay section 100
The amount of delay is 2.5 [ps / km / nm] × 10 while transmitting [km].
0 [km] × 0.8 [nm] = 200 [ps], adjacent optical pulses are delayed by 4 bits, and blue chirp and red chirp are generated four times each.

Here, the influence of the cross phase modulation effect in the relay section configuration example shown in FIG. 4A will be described. Here, considering mutual phase modulation between two adjacent wavelengths,
It is assumed that the signal bit patterns of two different wavelength division multiplexed signals are "1" s in sequence. At this time, the wavelength-multiplexed signal light is amplified to the desired optical level Pin by the lumped constant optical amplifier 11 and then transmitted through the optical fiber transmission line 1a section. While transmitting the section of the optical fiber transmission line 1a, 2
It is affected by mutual phase modulation between two different wavelengths.
As shown in (1)-(a), since the optical signal power is attenuated due to the loss caused by the transmission, the optical fiber transmission line 1a
The state of the chirp generated in the longitudinal direction due to the cross phase modulation in the section is that the red chirp is always stronger than the blue chirp while the adjacent optical pulses are delayed by 1 bit as shown in Fig. 4 (1)-(b). Becomes Therefore, while transmitting the section of the optical fiber transmission line 1a, as shown in FIG.
As shown in, the red chirp always remains due to the influence of the mutual phase modulation, and ΔC remains as a whole.

Next, the principle of reducing the residual chirp when the distributed constant type optical amplifier is used on the output side of the relay section will be described. FIG. 4 (2) is an explanatory diagram in the case where the distributed constant type optical amplifier 12 shown in FIG. 3 is inserted on the output side of FIG. 4 (1). In addition, in FIG. 4 (2)-(a), the wavy line indicates the signal power curve when distributed constant optical amplification is not performed, and the solid line indicates the signal power curve when distributed constant optical amplification is performed. As described above, it is assumed that the wavelength division multiplexed signal light input from the input terminal 10 is composed of two different wavelength components, and the signal bit patterns of the two different wavelength division multiplexed signals are continuous "1". At this time, the wavelength-division-multiplexed signal light is amplified by the lumped constant optical amplifier 11 to a desired optical level Pin, and then transmitted through the optical fiber transmission line 1a section. On the output side of the relay section, the distributed constant type optical amplifier 12 is provided,
The pumping light, which is the pumping light output from the pumping light source 13 for distributed constant type amplification, is input to the relay section via the optical multiplexing means 14 in the opposite direction to the wavelength-multiplexed signal light. Therefore, as the transmission progresses and approaches the output end, the wavelength-multiplexed signal light is amplified in a distributed constant manner in the longitudinal direction, so that the signal power profile becomes as shown in FIG. 4 (2)-(a).

As a result, when compared with the signal power profile when distributed constant type optical amplification is not performed, the signal power profile is the same up to point A, so that up to point A, the adjacent optical pulse is delayed by 1 bit. The red chirp is always larger than the blue chirp, and the red chirp remains before point A. However, after point A, the optical signal power gradually increases by performing distributed constant type optical amplification.
As shown in (b), the amount of chirp generated while the adjacent optical pulses are delayed by 1 bit has a stronger blue chirp than the red chirp. Therefore, the state of residual chirp in the longitudinal direction of the section of the optical fiber transmission line 1a is that red chirp remains before point A as shown in FIG. 4 (2)-(c), but blue chirp remains after point A. Therefore, the residual chirp ΔC1 after transmission through the section of the optical fiber transmission line 1a becomes smaller than ΔC.

Even when the distributed constant type optical amplification is performed, residual chirp is generated. This is due to the amount of red chirp remaining before point A and the blue chirp remaining after point A in the optical fiber transmission line section. This is because the amounts are not equal.
If the amount of red chirp remaining before point A is greater than the amount of blue chirp remaining after point A, either decrease the gain of the lumped constant optical amplifier or increase the gain of the distributed constant optical amplifier. The residual chirp in the entire relay section can be further reduced.

FIG. 5 is an explanatory diagram in the case where the residual chirp is minimized by controlling the gain of the distributed constant type optical amplifier 12. Further, in FIG. 5- (a), when the residual chirp (ΔC2) remains in the solid line, the wavy line represents the residual chirp (ΔC1).
3A and 3B respectively show signal power curves in the case where is reduced. In the case of the solid line in FIG. 5- (a), the optical fiber transmission line 1
The chirp generated by cross phase modulation in section a is shown in Fig. 5-
As shown by the solid line in (b), the amount of chirp remaining at the optical output terminal 15 is as shown by the solid line in FIG.
Only ΔC2 will remain. On the other hand, as in the case of the wavy line in FIG. 5- (a), the gain of the lumped constant optical amplifier 11 is lowered (Pin2 <Pin) compared to the case of the solid line in FIG. By increasing the gain ratio of, the amount of chirp remaining at the optical output terminal 15 is shown in FIG.
As shown by the wavy line of ΔC1, it is possible to satisfy ΔC1 <ΔC2. Therefore, when the gain ratio between the lumped constant type optical amplifier 11 and the distributed constant type optical amplifier 12 is optimally set, the amount of residual chirp generated in the section of the optical fiber transmission line 1a can be minimized.

As described above, according to the first embodiment,
In the wavelength division multiplexing optical transmission system shown in FIG. 3, an optical signal is optically amplified by using a lumped constant type optical amplifier on the input side of each repeater section, and a gain of the lumped constant type optical amplifier is controlled by a first gain control unit. , An optical signal is optically amplified by using a distributed constant type optical amplifier using an optical fiber transmission line as an amplification medium at the output side of each relay section, and a gain of the distributed constant type optical amplifier is controlled by a second gain control unit, By controlling the gain ratio between the first gain control unit and the second gain control unit by the compensation control unit, at least between adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. Since the blue chirping amount and the red chirping amount due to the mutual phase modulation can be canceled out, it is possible to construct an optical transmission system with less deterioration of the transmission characteristics due to the mutual phase modulation effect.

Embodiment 2. In the second embodiment, in the wavelength division multiplexing optical transmission system shown in FIG. 3, the lumped constant type optical amplifier on the input side of each repeater section is replaced with a distributed constant type optical amplifier. FIG. 6 is an explanatory diagram for minimizing the residual chirp amount in the second embodiment. In the figure, 1
Reference numeral 0 denotes an input terminal connected to the optical fiber transmission line 1a to which the wavelength-multiplexed signal light is input, 12a denotes a first distributed constant type optical amplifier, and 13a denotes a first distributed constant type optical amplifier 12a. A distributed-constant-type amplification pumping light source 14a is an optical multiplexer for combining the pumping light sent from the first distributed-constant-type amplification pumping light source 13a with the wavelength-division-multiplexed signal light, and 12 is a second distributed-constant-type Reference numeral 1 denotes an optical amplifier, and 13 denotes a pumping light source for distributed constant type amplification in the second distributed constant type optical amplifier 12.
Reference numeral 4 denotes an optical multiplexing means for multiplexing the pumping light sent from the second distributed constant type amplification pumping light source 13 and the wavelength division multiplexed signal light.
Reference numerals 5 respectively denote optical output terminals to which the wavelength-multiplexed signal light is transmitted.

The conditions of the transmission line delay are the same as those in the first embodiment. That is, in FIG. 6, the relay interval is 10
0 [km], and wavelength dispersion near the signal light wavelength is 2.5 [ps / k
m / nm], the signal wavelength interval is 0.8 [nm], and the transmission speed is 20 "Gbi.
t / s ”. Therefore, as in the first embodiment, 0 [k
It is assumed that adjacent optical pulses in [m] are delayed by 1 bit while transmitting 25 [km]. Further, it is assumed that the wavelength division multiplexed signal light input from the input terminal 10 is composed of two different wavelengths and the signal bit patterns of the two different wavelength division multiplexed signals are continuous "1".

Therefore, as shown in the first embodiment, the adjacent optical pulse is delayed by 4 bits during the transmission of 100 km of the relay section, and the blue chirp and the red chirp are generated four times each.

At this time, the wavelength-division-multiplexed signal light is combined with the pumping light outputted from the first distributed constant type amplification pumping light source 13a of the first distributed constant type optical amplifier 12a and the first optical multiplexing means 14.
The wavelength-multiplexed signal light and the pumping light are multiplexed in a and are transmitted in the same direction in the optical fiber transmission line 1a. At this time, in the optical fiber transmission line 1a, since the light is amplified in a distributed constant by the pump light, the wavelength-multiplexed signal light is an optical amplification effect by the pump light output from the first distributed constant type amplification pump light source 13a. Light is amplified until is lost.

On the output side of the section of the optical fiber transmission line 1a, the second distributed constant type optical amplifier 12 is provided, and the pumping light is the pumping light output from the second distributed constant type amplification pumping light source 13. Is input to the optical fiber transmission path section in the opposite direction to the wavelength division multiplexed signal light via the optical multiplexing means 14. Therefore, as the transmission progresses to the vicinity of the output side of the optical fiber transmission line 1a, the wavelength-division-multiplexed signal light is amplified in a distributed constant with respect to the longitudinal direction, as shown in FIG. 6 (a). Signal power profile. At this time, FIG. 6 (a) shows three different signal profiles obtained by controlling the gain ratio between the first distributed constant optical amplifier 12a and the second distributed constant optical amplifier 12.
In these three types of signal profiles, dotted line K1 and solid line K
2 and the point of being amplified in a distributed constant is located on the signal input side in the order of the broken line K3. That is, the gain of the first distributed constant optical amplifier 12a is K1.
>K2> K3, and the gain of the second distributed constant type optical amplifier 12 is set to K1 <K2 <K3.

At this time, the profiles of the generated chirp and the residual chirp in the longitudinal direction at three types of gain ratios are shown in FIGS. 6 (b) and 6 (c). As can be seen from FIG. 6 (b), depending on the gain ratio between the first distributed constant optical amplifier 12a and the second distributed constant optical amplifier 12, mutual transmission is performed during transmission through the optical fiber transmission line 1a. Blue chirp and red chirp occur multiple times due to the phase modulation effect. In FIG. 6A, the optical amplification is performed in a distributed constant manner, and the optical signal power gradually increases after the point where the gain higher than the loss of the optical fiber is obtained, so that adjacent optical pulses are delayed by 1 bit. The amount of chirp generated during the period is such that blue chirp is stronger than red chirp.

In the dotted line K1, before the point A, the chirp generated by the cross phase modulation has a red chirp amount larger than that of the blue chirp, so that the red chirp remains. After point A, the amount of blue chirp is stronger than that of red chirp, and blue chirp remains. But,
Since the amount of blue chirp remaining after point A is smaller than the amount of red chirp remaining after point A, red chirp remains in the chirp remaining in the transmission between the optical fiber transmission lines 1a. On the other hand, in the broken line K3, the red chirp remains until the point C before the point C because the amount of red chirp is stronger than that of the blue chirp. After the point C, the amount of blue chirp is stronger than that of red chirp, and blue chirp remains.
However, from the amount of red chirp remaining before point C, C
Since the amount of blue chirp remaining after the point is large, blue chirp remains in the chirp remaining in the transmission in the section of the optical fiber transmission line 1a.

Therefore, as shown by the signal profile indicated by the solid line K2 in FIG. 6A, the amount of red chirp remaining due to the cross phase modulation before the point B and the amount of blue chirp occurring after the point B due to the cross phase modulation. Are set to be substantially equal to each other, the gain ratio between the first distributed constant optical amplifier 12a and the second distributed constant optical amplifier 12 is appropriately set so that the generated blue chirp and red chirp cancel each other out. In this case, the amount of residual chirp can be reduced as shown in FIG. 6 (c).

As described above, according to the second embodiment,
In the wavelength division multiplexing optical transmission system shown in FIG. 3, an optical signal is optically amplified by using a first distributed constant type optical amplifier having an optical fiber transmission line as an amplification medium on the input side of each relay section, and a first gain control is performed. The gain of the first distributed constant type optical amplifier is controlled by the section, and the optical signal is optically amplified using the second distributed constant type optical amplifier using the optical fiber transmission line as an amplification medium at the output side of each relay section, The second gain control unit controls the gain of the second distributed constant type optical amplifier, and the compensation control unit controls the gain ratio between the first gain control unit and the second gain control unit. Since it is possible to cancel out the blue chirping amount and the red chirping amount due to the mutual phase modulation generated between at least adjacent wavelength signals in one section of each relay section in the transmission path, it is possible to prevent the transmission characteristic deterioration due to the mutual phase modulation effect. Few You can construct an optical transmission system.

Third Embodiment In the third embodiment, in the wavelength division multiplexing optical transmission system shown in FIG. 3, the distributed constant type optical amplifier is provided only on the output side of each relay section. Figure 7
FIG. 11 is an explanatory diagram for minimizing the amount of residual chirp in the third embodiment. In the figure, 10 is an input terminal to which the wavelength-multiplexed signal light connected to the optical fiber transmission line 1a is input, 12 is a distributed constant type optical amplifier, and 13 is a distributed constant type optical amplifier 12 for distributed constant type amplification. 1 excitation light source
Reference numeral 4 denotes an optical multiplexing means for multiplexing the pumping light sent from the distributed constant type amplification pumping light source 13 and the wavelength multiplexed signal light, and 15 denotes an optical output terminal to which the wavelength multiplexed signal light is sent.

The condition of the transmission line delay is the same as in the first embodiment.
And the same as 2. That is, in FIG. 7, the repeater interval is 100 [km], and the adjacent optical pulses at 0 [km] are delayed by 4 bits while transmitting 100 [km] in the repeater section, and blue chirp and red are repeated four times each. A chirp shall occur. Further, it is assumed that the wavelength division multiplexed signal light input from the input terminal 10 is composed of two different wavelengths and the signal bit patterns of the two different wavelength division multiplexed signals are continuous "1".

At this time, the wavelength-multiplexed signal light has its optical signal level attenuated during transmission due to the attenuation characteristic of the optical fiber transmission line 1a. However, the output side of the section of the optical fiber transmission line 1a is provided with the distributed constant type optical amplifier 12, and the pumping light outputted from the pumping light source 13 for distributed constant type amplification is wavelength-multiplexed via the optical multiplexing means 14. Since the light is input to the optical fiber transmission line section in the direction opposite to the signal light, the wavelength-multiplexed signal light is amplified in a distributed constant manner in the longitudinal direction when transmitted near the output side of the optical fiber transmission line 1a. The signal power profile in the longitudinal direction at this time is shown in FIG.
As shown in (a).

As shown in FIG. 7, since the optical signal power is attenuated up to the point A due to the loss due to the transmission, the state of the chirp in the longitudinal direction generated by the cross phase modulation in the section of the optical fiber transmission line 1a is shown in FIG. As shown in b), the red chirp always remains stronger than the blue chirp while the adjacent optical pulses are delayed by 1 bit, so that the red chirp remains. However, after point A, optical amplification is performed in a distributed constant manner as the signal is transmitted and the optical signal level rises. Therefore, the blue chirp is always stronger than the red chirp while the adjacent optical pulse is delayed by 1 bit. , Blue chirp remains. That is, A
The amount of red chirp remaining before the point is almost canceled by the blue chirp remaining in the transmission after the point A, as shown in FIG.
By setting the gain of the distributed constant type optical amplifier 12 so as to have the signal power profile of (a), the amount of residual chirp can be reduced as shown in FIG. 7 (c).

As described above, according to the third embodiment,
In the wavelength division multiplexing optical transmission system shown in FIG. 3, an optical signal is optically amplified using a distributed constant type optical amplifier using an optical fiber transmission line as an amplification medium on the output side of each relay section, and a distributed constant type optical amplifier is used by a gain controller. By controlling the gain of the amplifier and controlling the gain of the gain control unit by the compensation control unit, blue due to cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. Since it is possible to reduce the amount of chirping and the amount of red chirping, it is possible to construct an optical transmission system with less deterioration of transmission characteristics due to the cross-phase modulation effect.

Fourth Embodiment In the fourth embodiment, in the wavelength division multiplexing optical transmission system shown in FIG. 3, the optical fiber transmission line for transmitting the wavelength division multiplexing light is composed of a plurality of optical fibers having different effective core areas. FIG. 8 is an explanatory diagram for minimizing the residual chirp amount in the fourth embodiment. In the figure, 6a is an optical fiber transmission line having an effective core area of B, 6b is an optical fiber transmission line having an effective core area of C, and 10 is a wavelength-multiplexed signal light connected to the optical fiber transmission line 6a. An input terminal to be input, 11 is a lumped constant type optical amplifier, 12 is a distributed constant type optical amplifier,
3 is a pumping light source for distributed constant type amplification in the distributed constant type optical amplifier 12, 14 is an optical multiplexing means for multiplexing the pumping light sent from the pumping light source 13 for distributed constant type amplification and the wavelength multiplexed signal light, and 15 is Each of the optical output terminals to which the wavelength-multiplexed signal light is transmitted is shown.

The condition of the transmission line delay is the same as in the first embodiment.
Same as ~ 3. That is, in FIG. 8, the repeater interval is 100 [km], and at 0 [km], adjacent optical pulses are delayed by 4 bits while transmitting in the repeater section 100 [km], and blue chirp and red are repeated four times each. A chirp shall occur. Further, it is assumed that the wavelength division multiplexed signal light input from the input terminal 10 is composed of two different wavelengths and the signal bit patterns of the two different wavelength division multiplexed signals are continuous "1".

In general, there is a so-called non-linear coefficient γ as an index showing the influence of the non-linear effect in the optical fiber. This can be expressed by the following equation, where n ₂ is the nonlinear coefficient, ω ₀ is the center frequency, c is the speed of light, and Aeff is the effective core area of the optical fiber.

[0074]

[Equation 3]

As can be seen from this (Equation 3), the strength of nonlinearity in the optical fiber is inversely proportional to the effective core area Aeff of the optical fiber. Therefore, the smaller the effective core area, the larger the nonlinearity. A non-linear effect can be obtained. Therefore, when the same optical signal power is input to the optical fiber transmission line 6a and the optical fiber transmission line 6b as shown in FIG. 8, a larger nonlinear effect occurs in the optical fiber 6b.

FIG. 8A shows a signal power profile in the longitudinal direction. However, since the optical signal power is attenuated up to the point A due to the loss accompanying the transmission, the cross phase modulation in the section of the optical fiber transmission line 1a is performed. As shown in FIG. 8B, the state of the chirp in the longitudinal direction caused by is that the red chirp is always stronger than the blue chirp and the red chirp remains while the adjacent optical pulses are delayed by 1 bit. However, after point A, optical amplification is performed in a distributed constant manner in accordance with transmission and the optical signal level increases, so that the blue chirp is always stronger than the red chirp while the adjacent optical pulse is delayed by 1 bit. Blue chirp remains.

Here, the effective core cross-sectional area B of the optical fiber transmission line 6a and the effective core cross-sectional area C of the optical fiber transmission line 6b are equal, and the signal power profile in the longitudinal direction is indicated by the broken line 2 shown in FIG. Think of a certain time. At this time A
Before the point, the red chirp always becomes larger than the blue chirp as described above, and the residual chirp amount ΔC1 as shown in FIG. 8C remains.

At this time, when the effective core area C of 6b smaller than the optical fiber transmission line 6a is arranged in the optical fiber transmission line after the point A, the signal profile after the point A with respect to the longitudinal direction is shown in FIG. As indicated by the solid line 1, the signal power level becomes higher than the broken line 2 by the effective core area ratio B / C of the optical fiber transmission line 6a and the optical fiber transmission line 6b. Therefore, as shown in FIG. 8B, the amount of blue chirp remaining due to the cross-phase modulation in the transmission after the point A can be increased by the effective core area ratio B / C. ), It is possible to reduce the amount of residual chirp due to blue chirp and red chirp generated by cross-phase modulation.

Further, in FIG. 8, the effective core area of the optical fiber transmission line 6b after the point A is made small, but conversely, the effective core area of the optical fiber transmission line 6a constituting before the point A is made large. As a result, the influence of the non-linear effect before the point A is suppressed to be small, and the residual red chirp generated by the mutual phase modulation up to the point A can be reduced, so that the residual chirp of the entire optical fiber transmission line section can be reduced.

In the fourth embodiment, the configuration in which the optical fiber transmission line is a plurality of optical fiber transmission lines having different effective core areas is combined with the first embodiment, and the lumped constant type optical amplifier is provided on the input side of the relay section. And the case where the distributed constant type optical amplifier is applied to the output side of the repeater section has been described, the configuration in which the optical fiber transmission line is a plurality of optical fiber transmission lines having different effective core cross-sectional areas is the second embodiment or the second embodiment. Three
It is also possible to combine with.

As described above, according to the fourth embodiment,
In the wavelength division multiplexing optical transmission system shown in FIG. 3, an optical fiber transmission line is made up of a plurality of optical fiber transmission lines having different effective core areas, and an optical signal is optically amplified by using a lumped-constant type optical amplifier at the input side of each relay section. Then, the gain of the lumped-constant type optical amplifier is controlled by the first gain control unit, and the optical signal is optically amplified using the distributed-constant type optical amplifier using the optical fiber transmission line as an amplification medium at the output side of each relay section. , The second gain control unit controls the gain of the distributed constant type optical amplifier, and the compensation control unit controls the gain ratio between the first gain control unit and the second gain control unit. Since it is possible to cancel out the blue chirping amount and the red chirping amount due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the above, the mutual position can be more effectively and efficiently. You can construct an optical transmission system with less transmission characteristic deterioration due to modulation effect.

Embodiment 5. In the fifth embodiment,
In the wavelength-division-multiplexed optical transmission system of FIG. 3, the optical fiber transmission line section in which the wavelength-division-multiplexed light is transmitted is composed of an optical fiber transmission line having a positive dispersion value and an optical fiber transmission line having a negative dispersion value. . FIG. 9 is an explanatory diagram for minimizing the residual chirp amount in the fifth embodiment. In the figure, 7a denotes an optical fiber transmission line having a positive dispersion value,
b is an optical fiber transmission line having a negative dispersion value, 10 is an input terminal to which the wavelength-multiplexed signal light connected to the optical fiber transmission line 7a is input, 11 is a lumped constant type optical amplifier, and 12 is a distributed constant. Type optical amplifier, 13 is a distributed constant type optical amplifier 12
In FIG. 3, 14 is an excitation light source for distributed constant type amplification, 14 is an optical combining means for combining the pumping light sent from the distributed constant type amplification pumping light source 13 with the wavelength multiplexed signal light, and 15 is the wavelength multiplexed signal light. The optical output terminals are shown respectively.

The relay interval in FIG. 9 is 100 [km], the length of the optical fiber transmission line 7a is 75 [km], and the chromatic dispersion near the signal light wavelength is 2.5 [ps / km / nm]. The length of the fiber transmission line 7b is 25 [km], and the chromatic dispersion near the signal light wavelength is -1.
25 [ps / km / nm], signal wavelength interval is 0.8 [nm], transmission speed is 20 [Gbit / s], and adjacent optical pulse at 0 [km] is 1 bit during transmission of 25 km. There is only a delay.

While transmitting the length of 75 [km] of the optical fiber transmission line 7a, the delay amount of the adjacent optical pulse is 2.5 [ps / km /
Since [nm] × 75 [km] × 0.8 [nm] = 150 [ps], adjacent optical pulses are delayed by 3 bits, and the optical fiber transmission line 7
The amount of delay of the adjacent optical pulse during the transmission of the length 25 [km] of b is -1.25 [ps / km / nm] x 25 [km] x 0.8 [n
Since m] = − 25 [ps], adjacent optical pulses are −0.
With 5 bit delay, 4 red chirps and 3 blue chirps will occur.

Now, consider a case where a wavelength division multiplexed signal is transmitted through an optical fiber having a positive dispersion and an optical fiber having a negative dispersion. When a collision occurs between adjacent optical pulses in dispersion having a positive chromatic dispersion, chirp occurs in the order of red chirp and blue chirp, but when a negative chromatic dispersion is subsequently transmitted, the adjacent optical pulse is The effect of trying to return to the position of is that an optical pulse that overtakes an optical pulse of a different wavelength when propagating in a transmission line of positive chromatic dispersion is reversed in the time direction during negative chromatic dispersion. Start a collision again. At this time, the light pulse to be overtaken receives the blue chirp of the falling portion of the light pulse to be overtaken, and then receives the red chirp of the rising portion, so the blue chirp and the red chirp are chirped by mutual phase modulation in this order. Will be received.

Therefore, during transmission of the optical fiber transmission line 7a having a length of 75 [km], the delay amount of the adjacent optical pulse is 3 bits, and the optical fiber transmission line having a positive chromatic dispersion is transmitted. , Red chirp, and blue chirp are received in this order. Since the signal profile in the longitudinal direction at this time is as shown in FIG. 9B, the chirp remaining between adjacent optical pulses is the red chirp. When transmitting the remaining 25 [km] long optical fiber transmission line 7b, the optical fiber transmission line having negative chromatic dispersion is transmitted, and the delay amount of adjacent optical pulses is 0.5 bit. , The chirp received by cross phase modulation is only blue chirp.

Therefore, the optical fiber transmission line section is shown in FIG.
In the case of a positive dispersion value and a negative dispersion value as shown in (1), the centralized amplification type optical amplifier 11 is arranged so that most of the red chirp remaining before the point A is canceled by the blue chirp remaining after the point A. By appropriately controlling the gain ratio between the distributed constant type optical amplifier 12 and the distributed constant type optical amplifier 12, it is possible to reduce the residual chirp amount due to the blue chirp and the red chirp caused by the mutual phase modulation at least between the adjacent wavelengths.

When the optical fiber transmission line section is configured with a positive dispersion value and a negative dispersion value, the delay amount of the optical pulse between adjacent wavelengths in the optical fiber transmission line section may be zero. Absent.

In the fifth embodiment, the configuration in which the optical fiber transmission line section has the positive dispersion value and the negative dispersion value is applied to the first embodiment, and the lumped constant type optical amplifier and the relay section are provided on the input side of the relay section. The case where the distributed constant type optical amplifier is applied to the output side of the above has been described. However, the configuration in which this optical fiber transmission line section has a positive dispersion value and a negative dispersion value is combined with the second embodiment or the third embodiment. Is also possible.

Furthermore, as described in the fourth embodiment,
The optical fiber transmission line in each relay section may be formed of a plurality of optical fiber transmission lines having different effective core cross-sectional areas.

As described above, according to the fifth embodiment,
In the wavelength division multiplexing optical transmission system shown in FIG. 3, the optical fiber transmission line is a combination of optical fiber transmission lines having a positive chromatic dispersion value and a negative chromatic dispersion value, and a lumped constant type optical amplifier is provided at the input side of each repeater section. An optical signal is optically amplified using the first gain control unit to control the gain of the lumped constant type optical amplifier, and a distributed constant type optical amplifier using an optical fiber transmission line as an amplification medium at the output side of each relay section is used. The optical signal is optically amplified by the second gain control section, the gain of the distributed constant type optical amplifier is controlled by the second gain control section, and the gain ratio between the first gain control section and the second gain control section is controlled by the compensation control section. As a result, it is possible to cancel out the blue chirping amount and the red chirping amount due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. It can be efficiently construct an optical transmission system with less transmission characteristic deterioration due to cross-phase modulation effect.

Sixth Embodiment In the sixth embodiment, in each repeater section of the wavelength division multiplexing optical transmission system shown in FIG. 3, the wavelength dispersion codes of the optical fiber transmission lines of two consecutive repeater sections are different. FIG. 10 is an explanatory diagram for minimizing the residual chirp amount in the sixth embodiment. In the figure, 8a is one relay section of the optical fiber transmission line 1 divided into a plurality of parts, and the first optical fiber transmission line having a positive dispersion value is 8a, and 8b is one continuous relay line with 8a. An optical fiber transmission line having a negative dispersion value, 10 is an input terminal connected to the optical fiber transmission line 8a for inputting wavelength-multiplexed signal light, and 11a is a first lumped constant optical amplifier. , 11b is a second lumped constant type optical amplifier, 12a is a first distributed constant type optical amplifier, 12b is a second distributed constant type optical amplifier, and 13a is a distributed constant type amplifier in the distributed constant type optical amplifier 12a. Excitation light source for
b is a distributed constant type amplification pumping light source in the distributed constant type optical amplifier 12b, and 14a is a distributed constant type amplification pumping light source 13
Reference numeral 14b denotes an optical multiplexing means for multiplexing the pumping light and the wavelength-multiplexed signal light sent from a, and a distributed constant type pumping light source 13b for amplification.
Reference numeral 15 denotes an optical combining means for combining the pumping light and the wavelength-division-multiplexed signal light sent from the optical output terminal 15 and an optical output terminal to which the wavelength-division-multiplexed signal light is sent.

In FIG. 10, each repeat interval is 100 [km], and the chromatic dispersion in the vicinity of the signal light wavelength of the first optical fiber transmission line 8a in the first repeat section in the continuous repeat section is 2. 5 [ps / km / nm], the chromatic dispersion near the signal light wavelength of the second optical fiber transmission line 8b in the second repeater section is -1.25 [ps / km / nm], and the signal wavelength interval is Is 0.8 [nm],
It is assumed that the transmission rate is 20 [Gbit / s] and that adjacent optical pulses at 0 [km] have a delay of 1 bit.

The first optical fiber transmission line 8 shown in FIG.
The amount of delay is 2. while transmitting 100 km of the relay section of a.
Since 5 [ps / km / nm] × 100 [km] × 0.8 [nm] = 200 [ps], adjacent optical pulses are delayed by 4 bits and blue chirp and red chirp are generated 4 times each. It will be. Also, the delay amount is -1.25 [ps / k] while transmitting the relay section 100 [km] of the second optical fiber transmission line 8b.
Since m / nm] × 100 [km] × 0.8 [nm] = 100 [ps], adjacent optical pulses are delayed by -2 bits and blue chirp and red chirp are generated twice each. .

The wavelength multiplexed signal light is transmitted through the optical fiber transmission line 8a.
And the optical signal level is attenuated by the attenuation characteristic of the optical fiber transmission line 8b. However, the optical fiber transmission line 8a
A first distributed constant type optical amplifier 12a and a second distributed constant type optical amplifier 12b are provided on the respective output sides of the section and the section of the optical fiber transmission line 8b, and the first distributed constant type amplification pump light source 13a is provided. And the pumping light output from the second distributed constant type amplification pumping light source 13b is respectively used as the first light combining means 14a and the second light combining means 14b.
Since it is input to the optical fiber transmission line section in the direction opposite to the wavelength-multiplexed signal light through the optical fiber, as the transmission progresses to the vicinity of the output side of the optical fiber transmission line 8a section and the optical fiber transmission line 8b section, The wavelength-multiplexed signal light is amplified in a distributed constant. The signal power profile in the longitudinal direction at this time is as shown in FIG.

Here, as shown in FIG. 10A, up to the points A and B, the optical signal power is attenuated due to the loss due to the transmission, so that in the optical fiber transmission lines 8a and 8b. As shown in FIG. 10 (b), the state of chirp generated in the longitudinal direction due to the cross-phase modulation is that the red chirp is always stronger than the blue chirp while the adjacent optical pulses are delayed by 1 bit. The chirp remains. However, after point A, optical amplification is performed in a distributed constant manner as the signal is transmitted, and the optical signal level increases. Therefore, the blue chirp is always stronger than the red chirp while the adjacent optical pulse is delayed by 1 bit. Therefore, the blue chirp remains.

On the other hand, after the point B, only blue chirp occurs. That is, between the optical fiber transmission lines 8a,
Between the optical fiber transmission lines 8b, the amount of red chirp remaining before point A is almost canceled out by the amount of red chirp remaining before point A, so that the amount of red chirp remaining before point B is canceled out. The first lumped-constant type optical amplifier 11a and the first distributed-constant type optical amplifier 12a are so set as to cancel each other by the blue chirp remaining in the transmission.
Gain ratio and the second lumped constant optical amplifier 11b and the second
By controlling the gain ratio of the distributed constant type optical amplifier 12b, the amount of residual chirp between the optical fiber transmission lines 8a and between the optical fiber transmission lines 8b can be reduced as shown in FIG. 8 (c).

Regarding the sum of the positive dispersion value and the negative dispersion value of each optical fiber transmission line in the two continuous optical fiber transmission line sections, two continuous relays are taken into consideration when the cost of dispersion compensation is taken into consideration. It is preferable that the total dispersion value of the section is small.

Further, in the sixth embodiment, one relay section is used as an optical fiber transmission line having a positive dispersion value, and the other section is used as an optical fiber transmission line having a negative dispersion value. 1 has been applied to the input side of the repeater section and the distributed constant type optical amplifier is applied to the output side of the repeater section, but one section of the repeater section has a positive dispersion value. The same effect can be obtained when the configuration in which the optical fiber transmission line is used and the other section is the optical fiber transmission line having a negative dispersion value is applied to the second or third embodiment.

Further, as described in the fourth embodiment, if the optical fiber transmission line in each relay section is composed of a plurality of fiber transmission lines having different effective core cross-sectional areas, the transmission characteristic deterioration due to the cross phase modulation will be more effective. Can be reduced.

As described above, according to the sixth embodiment,
In the wavelength division multiplexing optical transmission system shown in FIG. 3, one continuous relay section in each relay section is configured by an optical fiber transmission line having a positive dispersion value, and the other is an optical fiber transmission line having a negative dispersion value. Optical signal is optically amplified by using a lumped constant optical amplifier on the input side of each relay section, and the gain of the lumped constant optical amplifier is controlled by the first gain control unit.
An optical signal is optically amplified using a distributed constant type optical amplifier using an optical fiber transmission line as an amplification medium at the output side of each relay section,
The gain control unit controls the gain of the distributed constant type optical amplifier, and the compensation control unit controls the gain ratio between the first gain control unit and the second gain control unit in each relay section. Since it is possible to cancel the blue chirping amount and the red chirping amount due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the fiber transmission line, it is possible to more effectively and efficiently It is possible to construct an optical transmission system with little deterioration in transmission characteristics due to the phase modulation effect.

[0102]

As described above, according to the wavelength division multiplexing optical transmission system of the present invention, the optical signal is optically amplified by using the lumped constant type optical amplifier on the input side of each repeater section.
The gain control unit controls the gain of the lumped constant optical amplifier, and optically amplifies an optical signal using a distributed constant optical amplifier using the optical fiber transmission line as an amplification medium at the output side of each relay section, The second gain control unit controls the gain of the distributed constant type optical amplifier, and the compensation control unit controls the gain ratio between the first gain control unit and the second gain control unit. Since it is possible to cancel out the blue chirping amount and the red chirping amount due to the cross phase modulation generated between at least adjacent wavelength signals in one section of each relay section in the fiber transmission line, it is possible to prevent the transmission characteristic deterioration due to the cross phase modulation. Can be suppressed.

According to the wavelength division multiplexing optical transmission system of the next invention, an optical signal is optically amplified by using the first distributed constant type optical amplifier using the optical fiber transmission line as an amplification medium at the input side of each repeater section. Then, the gain of the first distributed constant type optical amplifier is controlled by the first gain control unit, and the second distributed constant type optical amplifier using the optical fiber transmission line as an amplification medium at the output side of each relay section. To optically amplify the optical signal, the second gain control unit controls the gain of the second distributed constant type optical amplifier, and the compensation control unit controls the first gain control unit and the second gain control. By controlling the gain ratio with the
Since it is possible to cancel the blue chirping amount and the red chirping amount due to the cross phase modulation generated between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line, the transmission characteristic by the cross phase modulation Deterioration can be suppressed.

In the wavelength division multiplexing optical transmission system according to the next invention, an optical signal is optically amplified by using a distributed constant type optical amplifier using the optical fiber transmission line as an amplification medium at the output side of each relay section, The gain control unit controls the gain of the distributed constant type optical amplifier, and the compensation control unit controls the gain of the gain control unit, so that at least one of the relay sections in the optical fiber transmission line is adjacent to each other. Since it is possible to cancel the blue chirping amount and the red chirping amount due to the mutual phase modulation that occurs between the wavelength signals, it is possible to suppress the deterioration of the transmission characteristics due to the mutual phase modulation.

In the wavelength division multiplexing optical transmission system according to the next invention, the optical fiber transmission line is constituted by the effective core cross-sectional areas of a plurality of optical fibers. Since it is possible to cancel out the amount of blue chirping and the amount of red chirping due to the mutual phase modulation generated between at least adjacent wavelength signals in one section of each of the relay sections, the transmission by the mutual phase modulation is more effective and efficient. The characteristic deterioration can be suppressed.

In the wavelength division multiplexing optical transmission system according to the next invention, the chromatic dispersion value in each relay section in the optical fiber transmission line is composed of a positive dispersion value and a negative dispersion value. As a result, it is possible to cancel out the amount of bull chirping and the amount of red chirping due to the mutual phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line, which is more effective. Moreover, it is possible to efficiently suppress the deterioration of the transmission characteristics due to the mutual phase modulation.

According to the wavelength division multiplexing optical transmission system of the next invention, the delay amount of the optical pulse between adjacent wavelengths due to the chromatic dispersion in each relay section in the optical fiber transmission line is set to zero. By characterizing
Since it is possible to cancel out the blue chirping amount and the red chirping amount due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line, it is more effective and efficient. Moreover, it is possible to suppress the deterioration of the transmission characteristics due to the mutual phase modulation.

In the wavelength division multiplexing optical transmission system according to the next invention, the signs of the chromatic dispersion of two continuous relay sections in the optical fiber transmission line are different from each other. Since it is possible to cancel out the amount of blue chirping and the amount of red chirping due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the above, the cross-phase modulation can be performed more effectively and efficiently. It is possible to suppress deterioration of transmission characteristics.

According to the wavelength-multiplexed optical transmission system of the next invention, the delay amount of the optical pulse between adjacent wavelengths is set to zero due to the chromatic dispersion of two consecutive relay sections in the optical fiber transmission line. With this feature, it is possible to cancel the blue chirping amount and the red chirping amount due to the cross-phase modulation that occurs between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line. Therefore, it is possible to more effectively and efficiently suppress the deterioration of the transmission characteristics due to the mutual phase modulation.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a phenomenon of self-phase modulation by an optical pulse.

FIG. 2 is a conceptual diagram showing a phenomenon of mutual phase modulation due to an optical pulse.

FIG. 3 is an explanatory diagram of the first embodiment of the wavelength division multiplexing optical transmission system.

FIG. 4A is an explanatory diagram in the case where residual chirp occurs due to the influence of cross-phase modulation that occurs in a relay section.
(2) is an explanatory view when the distributed constant type optical amplifier shown in FIG. 3 is inserted on the output side of FIG. 4 (1).

FIG. 5 is an explanatory diagram in the case where the residual chirp amount is minimized by the gain control of the distributed constant type optical amplifier in the configuration of FIG. 4 (2).

FIG. 6 is an explanatory diagram for minimizing the amount of residual chirp in the second embodiment.

FIG. 7 is an explanatory diagram for minimizing the residual chirp amount in the third embodiment.

FIG. 8 is an explanatory diagram for minimizing the residual chirp amount in the fourth embodiment.

FIG. 9 is an explanatory diagram for minimizing the residual chirp amount in the fifth embodiment.

FIG. 10 is an explanatory diagram for minimizing the residual chirp amount in the sixth embodiment.

FIG. 11 is an explanatory diagram showing an example of prior art 1.

FIG. 12 is an explanatory diagram showing an example of prior art 2.

[Explanation of symbols]

1, 1a, 6a, 6b, 7a, 7b, 8a, 8b optical fiber transmission line, 2 ₁ to 2 _n relay section, 3 transmitter, 4 ₁
~ 4 _n transmitter, 5 multiplexer, 6 demultiplexer, 7 ₁ ~ 7 _n
Receiver, 8 receiver, 10 input terminals, 11, 11a, 1
1b Lumped constant type optical amplifier, 12, 12a, 12b Distributed constant type optical amplifier, 13, 13a, 13b Distributed constant type amplification pump light source, 14, 14a, 14b Optical multiplexing means,
15 Optical output terminal.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04B 10/17 H01S 3/094 S 10/18 H04J 14/00 14/02 (72) Inventor Katsuhiro Shimizu Tokyo 2-3, Marunouchi, Chiyoda-ku Sanryo Electric Co., Ltd. (72) Inventor, Kazuyuki Ishida Tokyo 2-3, Marunouchi, Chiyoda-ku Sanryo Electric Co., Ltd. (72) Inventor, Satoshi Kajiya Tokyo 2-3 2-3 Marunouchi, Chiyoda-ku Sanryo Electric Co., Ltd. (72) Inventor Tatsuya Kobayashi 2-3-2 Marunouchi, Chiyoda-ku Sanryo Electric Co., Ltd. F-term (reference) 5F072 AB07 AK06 HH04 HH06 JJ07 MM07 PP07 YY17 5K002 CA01 CA10 CA13 DA02 FA01

Claims (8)

[Claims] 1. In a wavelength division multiplexing optical transmission system that multiplex-transmits two or more optical signals having different wavelengths using an optical fiber transmission line having a plurality of repeating sections, the optical signal is arranged at the input side of each repeating section, A lumped-constant type optical amplifier for performing lumped-constant optical amplification, a first gain control unit for controlling the gain of the lumped-constant type optical amplifier, and an optical fiber transmission line arranged on the output side of each relay section. A distributed constant type optical amplifier that optically amplifies in a distributed constant manner as an amplification medium, a second gain control unit that controls the gain of the distributed constant type optical amplifier, and one section of each relay section in the optical fiber transmission line. In the first gain control unit and the second gain control unit so that the blue chirping amount and the red chirping amount due to the mutual phase modulation generated at least between the adjacent wavelength signals are cancelled. Wavelength multiplexing optical transmission system, characterized in that it and a compensation control unit for controlling. 2. In a wavelength division multiplexing optical transmission system that multiplex-transmits two or more optical signals having different wavelengths using an optical fiber transmission line having a plurality of repeating sections, the optical fiber is arranged at the input side of each repeating section. A first distributed constant type optical amplifier for optically amplifying a distributed constant in a transmission line as an amplification medium; a first gain control section for controlling a gain of the first distributed constant type optical amplifier; A second distributed constant type optical amplifier disposed on the output side and optically amplifying in a distributed constant manner using the optical fiber transmission line as an amplification medium; and a second gain for controlling the gain of the second distributed constant type optical amplifier. The controller and the blue chirping amount and the red chirping amount due to the mutual phase modulation generated between at least adjacent wavelength signals in one section of each relay section in the optical fiber transmission line are cancelled. Wavelength multiplexing optical transmission system comprising: the compensation control unit, the controlling the gain ratio between the first gain control unit and the second gain controller. 3. A wavelength division multiplexing optical transmission system that multiplex-transmits two or more optical signals having different wavelengths by using an optical fiber transmission line having a plurality of relay sections, wherein the optical transmission line is arranged at the output side of each of the relay sections. A distributed constant type optical amplifier for performing a distributed constant optical amplification using a fiber transmission line as an amplification medium, a gain control unit for controlling the gain of the distributed constant type optical amplifier, and one section of each relay section of the optical fiber transmission line In at least the wavelength controller, a compensation control unit that controls the gain of the gain control so that the blue chirping amount and the red chirping amount due to the cross-phase modulation that occur between adjacent wavelength signals are canceled, Multiplex optical transmission system. 4. The optical fiber transmission line comprises a plurality of different effective core cross-sectional areas.
[3] The wavelength division multiplexing optical transmission system according to any one of [3] to [3]. 5. The chromatic dispersion value in each relay section of the optical fiber transmission line is composed of a positive dispersion value and a negative dispersion value, according to any one of claims 1 to 4. WDM optical transmission system. 6. A delay amount of an optical pulse between adjacent wavelengths due to wavelength dispersion in each relay section of the optical fiber transmission line is set to be zero.
The wavelength division multiplexing optical transmission system according to any one of 1. 7. The wavelength division multiplexing optical transmission system according to claim 1, wherein two consecutive sections of the optical fiber transmission line have different chromatic dispersion signs. 8. The delay amount of the optical pulse between adjacent wavelengths due to the chromatic dispersion of two continuous relay sections of the optical fiber transmission line is set to be zero. The wavelength division multiplexing optical transmission system according to any one of 1.