JP2000286489A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical amplifier which amplifies light rays in batch in both C and L bands. SOLUTION: A WDM coupler 28a multiplexes the signal light made incident from an input-side optical fiber 30 with an exciting light which is outputted from an exciting laser diode 20a and transmitted through a fiber 24a and makes the combined light incident to a core layer 12 from the other surface of an optical amplifying fiber 10. The exciting light emitted from another laser diode 20b is propagated through a fiber 24a and made incident to an inner clad layer 14 from the other end face of the optical amplifying fiber 10 by means of another WDM coupler 28b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband optical amplifier, and more particularly, to an optical amplifier capable of optically amplifying a band of 1.5 to 1.6 .mu.m.

[0002]

2. Description of the Related Art The low-loss wavelength range of a quartz fiber is as follows.
The band of 5 to 1.6 μm is the most useful wavelength range for optical wavelength division multiplexing communication, and an optical amplifier corresponding to this wavelength range has been proposed. As a conventional optical amplifier in this wavelength range, 1.53
A C-band optical amplifier for amplifying a wavelength band of 1.56 μm to 1.56 μm;
There is an L-band optical amplifier that amplifies the wavelength range (hereinafter, referred to as L-band). There is no optical amplifier that can amplify both the C band and the L band.

[0003] A C-band optical amplifier is a 0.1-dB pump light source.
A 98 μm or 1.48 μm semiconductor laser is used, and a short Er-doped fiber (hereinafter, referred to as EDF) is used as an optical amplification medium. The L-band optical amplifier uses a 1.48 μm band semiconductor laser as an excitation light source, and has a long ED.
An ultra-large EDF is used as an optical amplification medium for F.

[0004]

As described above, in the 1.5 to 1.6 μm band which is regarded as promising for optical wavelength division multiplexing communication,
A C-band optical amplifier must be prepared for C-band optical amplification, and an L-band optical amplifier must be prepared for L-band optical amplification. Further, in order to amplify both the C band and the L band, the C band optical amplifier and the L band optical amplifier must be used together.

An object of the present invention is to provide a wide-band optical amplifier capable of optically amplifying both the C band and the L band.

[0006]

SUMMARY OF THE INVENTION An optical amplifier according to the present invention has an optical amplifying medium having a core to which an optical amplifying material is added and a plurality of claddings, and has an absorption cross section and a stimulated emission cross section of the optical amplifying material. A first band generating first excitation light for exciting the optical amplifying material for a first band that is both large and for a second band having a small absorption cross section and a stimulated emission cross sectional area of the optical amplifying material; Pumping light generating means, second pumping light generating means for generating second pumping light for exciting the optical amplifying material for the first band, and signal light to be optically amplified by the first pumping means. A first optical coupling means for multiplexing with the light and entering the core at one end of the optical amplifying medium; and a second optical coupling means for entering the second excitation light into the inner cladding at the other end of the optical amplifying medium. And a light coupling means.

The optical amplifier according to the present invention further comprises an optical amplifying medium to which an optical amplifying material is added, and a first pump for generating a first pump light for exciting the optical amplifying material for the C band and the L band. Light generation means, second excitation light generation means for generating second excitation light for exciting the optical amplification material for the C band,
First optical coupling means for multiplexing the signal light to be optically amplified with the first pump light and entering one end of the optical amplification medium;
A second optical coupling means for inputting the second excitation light to the other end of the optical amplification medium, wherein the wavelength of the second excitation light is 0.91 to 0.96 μm, It belongs to any one of the .05 μm band and the 1.40 to 1.45 μm band.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic block diagram of an embodiment of the present invention. Reference numeral 10 denotes an optical amplification fiber doped with Er. Outside the core layer 12 doped with Er, a first cladding layer 14 having a lower refractive index than the core layer 12 and a refractive index lower than the first cladding layer 14. And a double-clad fiber having a second clad layer 16 having a low thickness. E of the core layer 12
The r concentration and the length of the optical amplification fiber are set to such an extent that an L-band gain can be secured when the inside of the core layer 12 is pumped by the 1.48 μm or 0.98 μm band pumping light.

Reference numerals 20a and 20b denote laser diodes for generating excitation light. The wavelengths λp1 and λp2 of the laser diodes 20a and 20b are 1.48 μm and 0.98 μm
Either may be used. Excitation lights output from the laser diodes 20a and 20b are respectively condensed lenses 22a and 22a.
2b, the light enters the core layers 26a, 26b of the pumping light transmitting fibers 24a, 24b,
4a and 24b, and are incident on wavelength division multiplexing (WDM) couplers 28a and 28b. Excitation light transmission fiber 2
The diameter of the core layer 26a of 4a is set so that the output light is easily incident on the core layer 12 of the optical amplification fiber 10 by the WDM coupler 28a. Excitation light transmission fiber 24
The diameter of the core layer 26b of the first cladding layer 14b of the optical amplification fiber 10 is determined by the WDM coupler 28b.
It is set so that it is easy to be incident on. Specifically, the diameter of the core layer 26a of the pumping light transmission fiber 24a is made equal to the diameter of the core layer 12 of the optical amplification fiber 10, and the diameter of the core layer 26b of the pumping light transmission fiber 24b is adjusted to the optical amplification fiber 10a.
The diameter of the first cladding layer 14.

The signal light (wavelength λs) to be amplified enters the WDM coupler 28a from the input side optical fiber 30.

The input-side WDM coupler 28a has the following configuration. That is, the collimator lens 32a
However, the signal light output from the input side optical fiber 30 is converted into a parallel light flux and is incident on the multilayer mirror 34a. The collimator lens 36a converts the pumping light output from the pumping light transmission fiber 24a into a parallel light beam and enters the multilayer mirror 34a. The multilayer mirror 34a transmits the signal light (wavelength λs) from the lens 32a and reflects the pumping light (wavelength λp1) output from the pumping light transmission fiber 24a, and combines and condenses both lights. As shown in FIG. 1, it is arranged obliquely with respect to the parallel light beam from the collimator lens 32a so as to enter the lens 38a. Condensing lens 3
Reference numeral 8a denotes a signal light transmitted through the multilayer mirror 34a and an excitation light reflected by the multilayer mirror 34a.
0 is incident on the core layer 12. An optical isolator 40a for removing unnecessary return light is inserted between the collimator lens 32a and the multilayer mirror 34a.

The WDM coupler 28b on the output side has the following configuration. That is, the collimator lens 32b
Converts the signal light (wavelength λs) output from the core layer 12 of the optical amplifying fiber 10 into a parallel light beam and converts the signal light into a multilayer mirror 34b.
Incident on. The collimator lens 36b converts the pumping light output from the pumping light transmission fiber 24b into a parallel light beam, and enters the multilayer mirror 34b. Multilayer mirror 34b
Transmits the signal light (wavelength λs) from the condenser lens 32b and supplies it to the condenser lens 38b, and reflects the pump light (wavelength λp2) output from the excitation light transmission fiber 24b to collect the condenser light. As shown in FIG. 1, it is arranged obliquely with respect to the luminous flux of the signal light between the collimator lens 32b and the condenser lens 38b so as to supply the signal light to the direction opposite to the signal light. The condenser lens 32b includes a multilayer mirror 34b
The excitation light reflected by the light enters the first cladding layer 14 of the optical amplification fiber 10. An optical isolator 40b for removing unnecessary return light to the optical amplification fiber 10 is inserted between the multilayer mirror 34b and the condenser lens 38b.
The condenser lens 38b makes the signal light transmitted through the multilayer mirror 34b enter the core layer of the output side optical fiber 42.

The operation of this embodiment will be described. The WDM coupler 28a combines the signal light incident from the input side optical fiber 30 with the pump light output from the pumping laser diode 20a and transmitted through the fiber 24a, and forms a core on one other surface of the optical amplification fiber 10. Light is incident on the layer 12. On the other end face of the optical amplification fiber 10, pumping light output from the pumping light laser diode 20b is incident on the inner cladding layer 14 by the WDM coupler 28b.

In the optical amplification fiber 10, the excitation light from the excitation laser diode 20a incident from the front side immediately excites the Er ions of the core layer 12, while the excitation light from the laser diode 20b incident from the rear side is While gradually traveling to the core layer 12 while propagating through the inner cladding layer 14, Er ions in the core layer 12 are excited. Therefore, the pumping light incident from the rear side can propagate through the optical amplification fiber 10 for a longer distance than when directly entering the core layer. As a result, the pump light exists over a longer distance than the conventional one on the rear side of the optical amplification fiber 10 (the output side of the amplified signal light), and the pump light is attenuated and eliminated in the conventional example. C band absorption or light amplification. Thereby, even if the optical amplification fiber 10 is too long for the C band, a sufficient gain for the C band light can be secured. That is, it can be used as a C-band optical amplifier.

Since the optical amplification fiber 10 has a sufficient length for the optical amplification of the L band, the L band is optically amplified without any problem while propagating through the optical amplification fiber 10 and enters the WDM coupler 28b.

The difference between the conventional C-band optical amplifier using the Er-doped fiber and the conventional L-band optical amplifier is essentially only the length of the Er-doped fiber used. C
In the case of the band optical amplifier, when the Er concentration is about 1000 ppm, the length of the Er-doped fiber is about 10 m. In the case of the L-band optical amplifier, the length of the Er-doped fiber is about 100 times, which is almost 10 times the same Er concentration. is there. Er
The reason why the amplification band of the doped fiber changes depending on the length is the wavelength dependence of the absorption cross section and the stimulated emission cross section.

FIG. 2 shows an absorption cross section and a stimulated emission cross section of Er ions added to quartz glass. The horizontal axis indicates the wavelength, and the vertical axis indicates the cross-sectional area. As shown in FIG. 2, in the C band, both the absorption cross section and the stimulated emission cross section are large. This indicates that if the pumping light is strong, a large gain is obtained, but if there is no pumping light, the signal light is attenuated immediately due to strong absorption. The light in the 0.98 μm or 1.48 μm band, which is a normal excitation wavelength, is absorbed and attenuated if it propagates through an Er-doped fiber by about several meters. Long-wavelength light generated by re-emission also has greater attenuation at shorter wavelengths than C-band effective for C-band excitation.
It disappears at about 10m at most. Therefore, in the C-band optical amplifier, the length of the Er-doped fiber must be as short as the length in which the C-band pump light can exist, that is, about 10 m. With a short Er-doped fiber used in a C-band optical amplifier, L-band optical amplification with a small gain cannot be realized. That is, the conventional C-band optical amplifier cannot optically amplify the L-band.

On the other hand, in the L band, both the absorption cross section and the stimulated emission cross section are small. That is, although the gain is small, the attenuation due to absorption is also small. Since the gain is small, it is necessary to lengthen the Er-doped fiber in the L-band optical amplifier. The 0.98 μm or 1.48 μm band light that is incident as the excitation light propagates through the Er-doped fiber while being absorbed and attenuated. In the propagation process, long-wavelength light is generated by re-emission. This long-wavelength light functions as pump light for L-band optical amplification. Therefore, for the L band, the excitation light exists over the entire length of the Er-doped fiber due to the small absorption coefficient. By increasing the length of Er-doped fiber,
An L-band optical amplifier can be realized.

When the C-band light is incident on a long Er-doped fiber for L-band optical amplification, the effective pump light, including the initial pump light and the long-wave light derived therefrom, is effectively attenuated at the short wavelength. Since the light is light, the L-band signal light is optically amplified in the vicinity of the incident end where the pump light exists, but attenuates rapidly and disappears as it propagates through the fiber at the Er point. Therefore, the conventional L-band optical amplifier cannot optically amplify the C-band.

Based on these considerations, the inventor of the present application has first set the length of the Er-doped fiber in order to satisfy the condition for optically amplifying the L band having a small gain in order to realize optical amplification of both bands. It has been concluded that the length must be at least about 100 m for a length normally used in an L-band optical amplifier, that is, a quartz fiber having an Er concentration of about 1000 ppm. The absorption of the C band in such a long Er-doped fiber is prevented by allowing the excitation light of the C band to exist over the entire length of the long Er-doped fiber.

In the embodiment shown in FIG. 1, the pumping light output from the laser diode 20b is for C-band pumping, and is condensed by the condenser lens 32b.
By being incident on the cladding layer 14, it is present over a longer distance in the longitudinal direction of the optical amplification fiber 10 than in the case of being incident on the core layer 12. Moreover, since the light is amplified from the output side of the signal light and enters the optical amplification fiber 10 in a direction opposite to the propagation direction of the signal light, attenuation of the C-band light in the optical amplification fiber 10 can be suppressed. The wavelength λp2 of the pump light output from the laser diode 20b is C
The wavelength may be 0.98 μm, 1.48 μm, or another wavelength as long as the optical amplification fiber 10 can be excited for band light amplification. By adjusting the core diameter, the mode field diameter, the first cladding diameter, the excitation light intensity, and the like of the optical amplification fiber 10, the excitation light incident on the first cladding device 14 is gradually transferred to the core layer 12, and the optical amplification fiber The C-band excitation light can be made to exist over almost the entire length of 10.

In this embodiment, since the C-band excitation light exists over almost the entire length of the optical amplification fiber, the C-band light amplified near the signal input end of the optical amplification fiber 10 is:
The light propagates through the optical amplification fiber 10 without attenuation and is output. Further, since the optical amplification fiber 10 is long enough to amplify the L-band light, the L-band light is amplified by the optical amplification fiber 10 and output. In this way, the optical amplifier of this embodiment can optically amplify both the C band and the L band.

FIG. 3 is a schematic block diagram of a second embodiment of the present invention. The WDM coupler 50 multiplexes the signal light incident from the input fiber 52 and the pump light from the pump light source 54. The wavelength of the excitation light output from the excitation light source 54 is C
0.98 μm or 1.48 μm useful for band and L band amplification. The light multiplexed by the WDM coupler 50 passes through the optical isolator 56 and enters the core of the optical amplification fiber 58. The optical amplification fiber 58 is a normal single mode fiber in which Er ions are added to the core. The signal light that has passed through the optical amplification fiber 58 is WD
The light passes through the M coupler 60 and the optical isolator 62 and enters the output fiber 64. Excitation light is applied to the WDM coupler 60 from an excitation light source 66. The wavelength of the excitation light output from the excitation light source 66 is 0.91 to 0.96 μm, and 1.
It belongs to either the 0 to 1.05 μm band or the 1.40 to 1.45 μm band. The WDM coupler 60 causes the excitation light from the excitation light source 66 to enter the core of the optical amplification fiber 58.

The optical isolators 56 and 62 are provided for removing unnecessary return light as in the embodiment shown in FIG.

The point that the optical amplification fiber 58 does not have to be a double clad fiber, that is, the point at which the WDM coupler 60 enters the excitation light from the excitation light source 66 into the core of the optical amplification fiber 58, and the wavelength of the excitation light source 66 The embodiment shown in FIG. 3 has the same structure as the embodiment shown in FIG.

A feature of the embodiment shown in FIG. 3 lies in that the wavelength of the rear-incident pumping light is set to a special wavelength band. Excitation light source 6
6 possible wavelength band 0.91 to 0.96 μm, 1.0 to
The 1.05 μm band and the 1.40 to 1.45 μm band are Er.
This is a wavelength band where the absorption by ions is small. Since the absorption by the Er ions is small, the excitation light output from the excitation light source 66 has a small attenuation due to the absorption in the optical amplification fiber 58, and therefore reaches far from the incident end. Thereby, C
Band attenuation can be prevented.

For example, 1.4 of a normal Er-doped fiber is used.
The absorption in the 8 μm band is about 3 dB / m, which is 1.4.
The 8 μm band excitation light is attenuated to 1/10 at a little over 3 m from the incident end. However, if the 1.41 μm band light having an absorption of 0.1 dB / m is used as the excitation light, the attenuation to 1/10 is only 100 m.
This pump light is distributed over the entire length of the Er-doped fiber having a length of 100 m necessary for pumping the L band. If the excitation light intensity is set so that the gain of the C band is 0 dB or more, the signal light of the C band propagates without being attenuated by the optical amplification fiber and is output. Thereby, C band and L
Both lights in the band can be amplified. That is, one unit can be used as an optical amplifier for the C band as an optical amplifier for the L band, and further, both the C band and the L band can be optically amplified simultaneously.

In order to facilitate understanding of the embodiment shown in FIG. 2, only one pumping light source 66 for generating C-band pumping light is shown, but when a longer optical amplification fiber 58 is used, or When a larger gain is required for the C-band, in the longitudinal direction of the optical amplification fiber 58,
Needless to say, a plurality of excitation light sources 66 may be arranged.

[0030]

As can be easily understood from the above description, according to the present invention, an optical amplifier capable of optically amplifying both the L band and the C band can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention.

FIG. 2 is a wavelength characteristic diagram of an absorption cross section and a stimulated emission cross section of an Er-doped quartz fiber.

FIG. 3 is a schematic configuration diagram of a second embodiment of the present invention.

[Explanation of symbols]

 10: Optical amplification fiber 12: Core layer 14: First cladding layer 16: Second cladding layer 20a, 20b: Laser diode 22a, 22b: Condensing lens 24a, 24b: Fiber for pumping light transmission 26a, 26b: Core layer 28a , 28b: wavelength division multiplexing (WDM) coupler 30: input side optical fiber 32a: collimator lens 34a: multilayer mirror 36a: collimator lens 38a: condenser lens 40a: optical isolator 28b: WDM coupler 32b: collimator lens 34b: multilayer film Mirror 36b: Collimator lens 38b: Condensing lens 40b: Optical isolator 42: Output side optical fiber 50: WDM coupler 52: Input side fiber 54: Pump light source 56: Optical isolator 58: Optical amplifier fiber 60: WDM coupler 62: Optical isolator Tab 64: Output side fiber 66: Excitation light source

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Nakai 2-1-1-15 Ohara, Kamifukuoka City, Saitama Prefecture Inside Kadeidi Laboratory Co., Ltd. (72) Toshio Tani 2-1-1 Ohara, Kamifukuoka City, Saitama Prefecture No. 5 F072 AB09 AB13 JJ20 KK30 PP07

Claims (13)

[Claims] An optical amplification medium comprising a core and a plurality of claddings to which an optical amplification material is added, a first band having a large absorption cross section and a stimulated emission cross section of the optical amplification material, and First excitation light generating means for generating a first excitation light for exciting the optical amplification material for a second band having a small absorption cross section and a stimulated emission cross section of the amplification material; and for the first band. A second pumping light generating means for generating a second pumping light for pumping the optical amplifying material, and multiplexing the signal light to be optically amplified with the first pumping light to one of the optical amplification media. The first optical coupling means is incident on the core at one end, and the second optical coupling means is incident on the inner cladding at the other end of the optical amplifying medium at the other end. Optical amplifier. 2. The optical amplifier according to claim 1, wherein said optical amplification material is Er ions. 3. The optical amplifier according to claim 1, wherein said optical amplification medium comprises an optical amplification fiber. 4. The wavelength of the first excitation light is 1.48 μm.
The optical amplifier according to claim 1, wherein the optical amplifier is in one of the m and 0.98 μm bands. 5. The wavelength of the second excitation light is 1.48 μm.
The optical amplifier according to claim 1, wherein the optical amplifier is in one of the m and 0.98 μm bands. 6. The first excitation light generating means includes:
And a core having a diameter substantially equal to the diameter of the core of the first optical transmission medium, and outputting the output light of the first excitation light source to the first optical transmission medium. A first optical transmission medium that leads to the optical coupling means, wherein the second excitation light generating means includes a second excitation light source that outputs the second excitation light, and a second excitation light source that outputs the second excitation light. Comprising a core having a diameter substantially equal to the diameter of the inner cladding;
The optical amplifier according to claim 1, further comprising a second optical transmission medium that guides output light of the second pump light source to the second optical coupling unit. 7. The optical amplifier according to claim 1, wherein the first band is a C band, and the second band is an L band. 8. The optical amplifier according to claim 1, wherein the second pumping light prevents at least disappearance of the first band on the other end side of the optical amplifying medium. 9. An optical amplifying medium to which an optical amplifying material is added, first excitation light generating means for generating a first excitation light for exciting the optical amplifying material for the C band and the L band, A second pumping light generating means for generating a second pumping light for pumping the optical amplifying material for the band, and a signal light to be amplified with the first pumping light to multiplex the signal light. A first optical coupling means incident on one end of the optical amplifying medium, and a second optical coupling means incident on the other end of the optical amplification medium, wherein a wavelength of the second excitation light is , 0.91 to 0.96 μm, 1.0 to 1.05 μm band, and 1.40 to 1.45 μm band. 10. The optical amplifier according to claim 9, wherein said optical amplification material is Er ions. 11. The optical amplifier according to claim 9, wherein said optical amplification medium comprises an optical amplification fiber. 12. The wavelength of the first excitation light is 1.48.
The optical amplifier according to claim 9, wherein the optical amplifier is in one of a μm band and a 0.98 μm band. 13. The optical amplifier according to claim 9, wherein the second pumping light prevents at least disappearance of the C band on the other end side of the optical amplifying medium.