JP3976912B2 - Composite module for optical fiber amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite module for an optical fiber amplifier used in optical communication.
[0002]
[Related background]
The optical fiber amplifier is for amplifying the power of the signal light attenuated in the middle of the transmission line and sending it again to the optical transmission line. For example, a plurality of optical components such as an erbium-doped fiber and an optical isolator are fused. It is made by connecting. In recent years, with the rapid development of optical communications, the optical components have been integrated into a single package in response to demands for reducing the cost of optical fiber amplifiers, shortening assembly work time, or reducing the mounting area. Composite modules have come to be used.
[0003]
As an optical component used in such a packaged optical fiber amplifier, for example, there is one described in Japanese Patent Laid-Open No. 10-10353. As apparent from the configuration shown in FIG. 9, the optical fiber amplifier 80 includes a case 81 for blocking external light, and an isolator element 82 and a beam splitter 83 are disposed in the case 81, and the isolator element Before and after 82 and the beam splitter 83 are sandwiched, a pair of diverging and condensing lenses 84 and 85 and optical fibers 86 and 87 for entering and exiting are provided, respectively. A light receiving element 88 such as a photodiode is disposed in the vicinity of the beam splitter. The inner wall of the case 81 is covered with a light absorption film 81a having a characteristic of absorbing light with little reflection. The light absorption film 81a is formed, for example, by applying a black paint or performing a black alumite treatment.
[0004]
Since the light absorption film 81a is formed, when the excitation light traveling backward from the excitation light source via the amplification optical fiber is incident on the optical fiber amplifier 80, the light scattered in the case 81 is received by the light receiving element. 88 is prevented from being received, and the output of the excitation light source can be accurately feedback-controlled by the controller.
However, the work of applying black paint to the entire inner wall of the case is time consuming and may not be completely painted. In addition, a large amount of black paint must be used, which is expensive. Furthermore, the black paint may be peeled off during use of the optical fiber amplifier 80. A similar problem occurs in anodizing.
[0005]
In addition, when the optical component is fixed in the package by laser welding, soldering, or the like, impurities may be mixed into the molten metal, which may adversely affect the fixing strength and reliability of the optical component. For this reason, the method of applying black paint to the entire inner wall of the case cannot provide the optical fiber amplifier 80 with sufficient reliability.
[0006]
[Problems to be solved by the invention]
In order to prevent the above problems, for example, as described in Japanese Examined Patent Publication No. 6-56445, each optical component accommodated in the case is divided by a partition wall so that each optical component is scattered light or the like. A configuration that prevents adverse effects from stray light is conceivable. More specifically, a hybrid optical multiplexer / demultiplexer 90 described in Japanese Patent Publication No. 6-56445 includes a light emitting element collimator 92, a light receiving element collimator 93, and an optical fiber collimator in a case 91 as shown in FIG. 94 are fixedly arranged in the accommodation spaces defined through the partition wall 91a. The partition wall 91a is provided with light passage holes, and interference filters 95, 96, and 97 are disposed in the respective light passage holes. The partition wall 91 a prevents stray light in the package from reaching the light receiving element 93.
[0007]
Therefore, in the optical fiber amplifier, the holding part that holds the optical isolator also serves as a partition wall that defines the area on the incident side of the excitation light and the area on the side of the receiver in the package, It is also conceivable that the scattered stray light is prevented from entering the light receiving element.
However, even in such a case, there may be a slight gap between the partition wall and the package due to the component processing accuracy. This is because, in order to ensure sealing performance, the package is generally formed by joining plate-like alloys by laser welding or silver brazing, so that the package may be distorted by thermal stress. Because there is.
[0008]
If there is a gap between the partition wall and the package, stray light on the light emitting element side is led out to the light receiving element side, and a sufficient light shielding effect cannot be obtained. Further, if two areas are defined in the package by a partition wall having a sufficient thickness to prevent the passage of light, it causes an increase in the size and cost of the package.
On the other hand, a method of completely preventing the passage of stray light, for example, by previously applying a black silicon resin material or the like between the package and the partition wall and closing the gap between the package and the partition wall is also conceivable. However, in order to maintain the product quality of the optical fiber amplifier, the inside of the package is generally filled with nitrogen. When the above-mentioned silicon resin material is applied to the inside of the package, the optical fiber amplifier is used for a long time after that. When a gas other than nitrogen is generated and this gas component is incorporated in a photodiode or the like, for example, an LD element or a PD element, it may adhere to these optical components except for the can type and cause fluctuations in output characteristics. .
[0009]
An object of the present invention is to provide a composite module for an optical fiber amplifier that can prevent stray light of excitation light from reaching a photodiode and maintain operational stability and reliability over a long period of time.
[0010]
[Means for Solving the Problems]
To achieve the above object, an optical fiber composite module according to the present invention includes a light guide attached to a box package, a semiconductor laser, and a Peltier attached to the bottom of the box package to cool the semiconductor laser. A cooler, an optical isolator, a holding unit that holds and fixes the optical isolator in the box-type package, and a light receiver that monitors a part of the signal light. The holding unit has no gap on the outer wall of the box-type package. It is shaped to contact the optical isolator and held fixed to the box-package, as well as defining an interior of said box-package and the semiconductor laser side area and the light receiver arranged side area, the holding parts are grooves formed in the bottom surface, the bottom end edges excluding the grooves of the semiconductor laser side by abutting the package body bottom Rear stray light, characterized in that to not pass through between the box type package and the holding portion.
According to this configuration, stray light is blocked by the holding portion having the grooved bottom structure, and heat transfer to the optical isolator can be minimized.
[0011]
When a package is formed by bonding plate materials made of an alloy by silver brazing or the like, the package may be slightly distorted due to thermal stress. As a result, even if there is a gap between the package and the holding part, stray light in the excitation light incident side area is not received on the receiver arrangement side area without applying silicon resin or the like that may generate undesirable gas to the gap. Intrusion can be reliably prevented.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a back excitation type composite module will be described in detail with reference to FIG. 1 as an embodiment of the composite module for an optical fiber amplifier (hereinafter referred to as “composite module”) of the present invention.
Here, in this specification, backward pumping refers to a case where pumping light is incident on an optical amplification fiber, for example, an erbium-doped fiber, in the direction opposite to the signal light transmission direction, and forward pumping refers to pumping light. Is incident in the same direction as the transmission direction of the signal light.
[0013]
As shown in FIG. 1, the composite module 10 includes a box-type package (hereinafter referred to as “package”) 12, a first fiber component 13, a second fiber component 14, a third fiber component 15, an interference film filter 16, and an optical isolator. 17, a beam splitter 18 and a photodiode 19 are provided.
The package 12 includes a package main body 12b in which a plate material such as Kovar or copper tungsten alloy is formed in a box shape by silver brazing, and a package lid 12c that closes an opening of the package main body 12b. The package body 12b accommodates and arranges the interference film filter 16 and the beam splitter 18, and the first fiber component 13, the second fiber component 14, the third fiber component 15, and the photodiode 19 are attached at predetermined positions. ing. The package main body 12 b is further provided with an optical isolator 17 and a holding portion 11 that holds and fixes the optical isolator 17 in the package 12 between the interference film filter 16 and the beam splitter 18.
[0014]
The holding unit 11 holds the optical isolator 17 and partitions the inside of the package 12 into a first area A1 on the excitation light incident side and a second area A2 on the photodiode 19 placement side. It has a cylindrical hole for holding without a gap, and is shaped like a bowl or a block so as to be in contact with the outer wall of the package 12 without a gap.
[0015]
Further, grooves 11b and 11c are formed on both side edges of the holding portion 11, and a groove 11d is also formed on the upper edge as shown in FIG. Thereby, the side part of the holding part 11 is in contact with the inner wall side surface of the package body 12b at the side edge part excluding the grooves 11b and 11c, and the upper part of the holding part 11 is also the package lid at the side edge part excluding the groove 11d. It is in contact with the body 12c. The grooves 11b, 11c, and 11d prevent the stray light in the first area A1 from entering the second area A2 through the slight gap G when there is a gap G between the holding portion 11 and the package 12. It is formed as a light capturing portion 11s.
[0016]
As the material of the holding unit 11, for example, metal, ceramics, opaque plastic that blocks the signal light having the wavelength λ1 and the excitation light having the wavelength λ2, or glass having a coating film that blocks the signal light and the excitation light on the surface is used. can do.
A light absorbing film (not shown) is applied to the outer edge of the holding portion 11 and the grooves 11b, 11c, 11d, and part of the inner wall surfaces of the package body 12b and the package lid 12c corresponding thereto. This light absorption film is formed, for example, by applying a black paint, performing a black alumite treatment, or depositing a metal film such as gold black or silver black. The light absorption film may be applied to the portions of the package body 12b and the package lid 12c that are in contact with the holding portion 11.
[0017]
A first fiber component 13 shown in FIG. 1 is for making signal light of wavelength λ1 enter the package 2, and is an optical amplification fiber, for example, an erbium-doped fiber or a normal optical fiber 13a connected thereto, and an end thereof. And a holder 13b attached to the. The holder 13b is attached to one side of the package 12, and contains a collimator (not shown) such as a lens that parallels the signal light. As the optical amplification fiber, a rare earth doped fiber, for example, an erbium doped fiber is used.
[0018]
The second fiber component 14 has an optical fiber 14a and a holder 14b attached to the end thereof. The holder 14b is configured similarly to the holder 13b, and is attached to the other side of the package 12 so as to face the holder 13b. As a result, the composite module 10 forms a signal light transmission path to be the first fiber component 13, the interference film filter 16, the optical isolator 17, the beam splitter 18, and the second fiber component 14 in the package 12.
[0019]
The third fiber component 15 is for making the excitation light of wavelength λ2 enter the package 12, and has an optical fiber 15a and a holder 15b attached to the end thereof. The holder 15b is configured similarly to the holder 13b, and is attached to the package 12 so that incident excitation light is reflected by the interference film filter 16 and transmitted to the first fiber component 13 side.
[0020]
The interference film filter 16 is a filter in which an interference film is formed on the surface of glass or the like. As shown in FIG. 1, the reflected excitation light is transmitted to the first fiber component 13 side with respect to the optical path of the excitation light. They are arranged at a predetermined angle.
The optical isolator 17 is an optical component that transmits signal light only in the direction of the arrow, and is held and fixed at the approximate center in the package 12 by the holding unit 11. Here, as described above, the holding unit 11 partitions the package 12 and divides the package 12 into a first area A1 and a second area A2.
[0021]
The beam splitter 18 is an optical component that transmits the signal light that has passed through the optical isolator 17 to the second fiber component 14 side, and reflects a part of the signal light to reflect it to the photodiode 19 side. Between the optical isolator 17 and the optical isolator 17 so as to be inclined at a predetermined angle with respect to the transmission path of the signal light. The reflectivity of the beam splitter 18 is normally selected within a range of about 1 to 10%. However, the lower the reflectivity, the more the loss of signal light is reduced, and a composite module with higher efficiency can be obtained.
[0022]
The photodiode 19 monitors part of the signal light reflected by the beam splitter 18. The photodiode 19 has a function of monitoring a part of the signal light, and is not particularly limited as long as it meets the object of the present invention, and it is needless to say that the photodiode 19 is not limited to the photodiode. .
The composite module 10 of the present embodiment is configured as described above, and is used as follows when the optical fiber amplifier is pumped backward.
[0023]
First, when excitation light having a wavelength λ 2 is incident on the package 12 from the third fiber component 15, it is reflected by the interference film filter 16 and is incident on the first fiber component 13.
Then, in the first fiber component 13, the signal light having the wavelength λ 1 amplified by the stimulated emission in the optical fiber 13 a is emitted into the package 12.
The signal light passes through the interference film filter 16, the optical isolator 17, and the beam splitter 18 and enters the second fiber component 14. A part of the signal light is reflected by the beam splitter 18 and emitted to the photodiode 19. Used for monitoring.
[0024]
However, in actuality, in the first area A1 of the package 12, there is a coupling loss from the third fiber component 15 to the first fiber component 13 due to reflection of the excitation light with the interference film filter 16 and the holder 13b. . If this coupling loss is estimated to be 10%, for example, when signal light and pump light of 100 mW or more are emitted from the first fiber part 13 and the third fiber part 15, respectively, stray light of about 10 mW is generated in the first area A1. Will exist. On the other hand, when the reflectance of the beam splitter 18 is selected to be about 1%, the signal light incident on the photodiode 19 is about 1 mW, and the intensity of the stray light is considerably larger than that of the signal light. It turns out that it is easy to receive.
[0025]
On the other hand, a slight gap G may occur between the package 12 and the holding portion 11 as shown in FIG. In this case, the package body 12b is formed by forming a plate made of an alloy or the like into a box shape by silver brazing as described above, and thermal stress is generated in the package body 12b in the silver brazing process, and the package body 12b is slightly This is because it may be formed while being deformed. When the holding portion 11 and the optical component (not shown) are attached to the package body 12b deformed in this way and further sealed with the package lid 12c, the outer edge shape of the holding portion 11 and the inner peripheral shape of the package 12 do not match. A gap G is generated. The gap G tends to be noticeably generated between the holding portion 11 and the package lid 12c.
[0026]
The stray light in the first area A1 tries to enter the second area A2 via the gap G. This stray light is captured by the grooves 11b, 11c, and 11d formed in the outer edge of the holding portion 11, and FIG. As shown by the dotted lines in FIG. 3, the light gradually attenuates while being scattered in the grooves 11b, 11c, and 11d, so that stray light does not reach the second area A2. Therefore, it is possible to reliably prevent malfunction of the photodiode 9 due to stray light whose light level is about 10 times larger than that of the monitor light.
[0027]
In the above-described embodiment, the outer edge of the holding portion 11 and the grooves 11b, 11c, 11d and the inner wall surfaces of the package body 12b and the package lid 12c corresponding to the outer edge and the grooves 11b, 11c, 11d do not necessarily have to be formed. . That is, it is sufficiently possible to capture stray light from the first area A1 to the second area A2 only by forming the grooves 11b, 11c, and 11d on the outer edge of the holding portion 11. However, it is preferable that the light absorption film is formed at the predetermined position, and stray light can be captured more reliably.
[0028]
Further, the groove does not necessarily have to be formed over the entire side edge and upper edge of the holding portion 11. That is, the groove 11d may be formed only in the portion of the holding portion outer edge where the gap is most likely to occur between the holding portion outer edge and the package 12, for example, the outer edge above the holding portion. Thereby, most of the stray light traveling from the first area A1 to the second area A2 can be captured, and a sufficient effect can be obtained.
[0029]
Further, as shown in FIG. 3, light capturing grooves 21 x and 21 y may be formed on the outer peripheral edge of the holding portion 21 in a double manner. As a result, as indicated by arrows in the figure, stray light can be more reliably scattered in the groove.
Unlike the above-described embodiment, as shown in FIG. 4, instead of forming a stray light capturing groove on the outer edge of the holding portion 31, a position corresponding to the upper edge of the holding portion 31 of the package lid 12 c. When the groove 12s is formed in the package body 12b and the package lid 12c is fixed to the package body 12b, the upper edge of the holding portion 31 may enter the groove 12s. As a result, even if the package 12 is formed to be somewhat distorted by silver brazing, a gap through which stray light passes is not formed between the package lid 12c and the upper edge of the holding portion 11. That is, as indicated by the dotted line in FIG. 4, stray light in the first area A1 is reflected by the holding unit 11 and does not exit the first area A1.
[0030]
Further, as shown in FIGS. 5 and 6, grooves 12t are formed in a plurality of places (three places in the figure) on the bottom of the inner wall of the package body 12b, and grooves 12u are formed in the package lid 12c. , 12u may be used to hold the optical isolator 17 by the holding portion 41 having a protrusion that can be loosely fitted, and the first area A1 and the second area A2 may be partitioned. Thereby, the possibility that the stray light in the first area A1 reaches the second area A2 can be further reduced.
[0031]
Further, as shown in FIG. 7, a wide groove 51s is formed on the bottom surface of the holding portion 51 so that the holding portion 51 is abutted and supported on the bottom surface of the package body only by the bottom end edges 51a and 51b. good. Thus, the wide groove 51s serves to capture stray light, and at the same time has the effect of minimizing heat transfer to the optical isolator 17. More specifically, when the semiconductor laser LR and the Peltier cooler (shown only in FIG. 12) PC are accommodated in the package adjacent to the holding portion, as shown in FIG. When abutting and fixing to the bottom surface of the package main body, as indicated by an arrow in FIG. 12, most of the heat released from the Peltier cooler PC that cools the semiconductor laser LR is passed through the entire bottom surface of the holding portion to provide an optical isolator. To reduce the characteristics of the optical isolator. However, as shown in FIG. 7, when the wide groove 51s is formed on the bottom surface of the holding portion 51 so that the holding portion 51 is abutted and supported on the bottom surface of the package body 52b only by the bottom end edges 51a and 51b, As shown in FIG. 8, a very small amount of heat radiated from the Peltier cooler PC is transmitted to the holding portion 51, and most of the remaining heat spreads over the entire casing of the package 52 and is naturally cooled.
[0032]
Therefore, by forming the wide groove 51s on the bottom surface of the holding portion 51, stray light can be captured by the wide groove 51s even if a gap is generated between the bottom surface of the holding portion 51 and the bottom surface of the package 12. Even if the semiconductor laser LR and the Peltier cooler PC are arranged in the vicinity, the thermal influence due to this can be minimized.
Note that the above-described light absorbing films may be formed on the bottom end edges 51a and 51b of the holding portion 51, the wide groove 51s and the portion of the package body 12 corresponding thereto.
[0033]
In addition, the composite module for an optical fiber amplifier according to the above-described embodiment is a forward pumping composite module. However, it goes without saying that the present invention is not limited to this and can be applied to a backward pumping composite module.
[0034]
【The invention's effect】
As described above, the composite module for an optical fiber amplifier according to the present invention includes the first light guide for introducing the signal light, the second light guide for deriving the signal light, and the third light guide for introducing the excitation light. Is attached to the box-type package, and the box-type package is integrated with a plurality of optical components including an optical isolator and a light receiver for monitoring a part of the signal light, and the optical isolator is held in the box-type package. An interior is defined by an area on the excitation light incident side and an area on the light receiver arrangement side by a holding part to be fixed, and at least one of the holding part and the box type package, the holding part and the box type A light capturing portion that prevents light from passing between the package and the package is formed.
[0035]
When an alloy is bonded by silver brazing or the like to form a package, for example, when an LD element or PD element is built in, the package is slightly distorted due to thermal stress, and a gap is generated between the package and the holding part. However, stray light in the first area A1 can be prevented from entering the second area A2 without applying silicon resin or the like that may generate undesirable gas to the gap.
[0036]
Further, when the semiconductor laser and the Peltier cooler are accommodated in the package adjacent to the holding portion, the semiconductor laser and the Peltier cooler not only prevent stray light from the first area A1 from entering the second area A2, but also the semiconductor laser and the Peltier cooler. The amount of heat generated from the optical fiber is not transmitted to the optical isolator via the holding unit, and as a result, the stability and reliability of the operation of the optical fiber amplifier composite module can be ensured over a long period of time.
[0037]
Furthermore, even when a light absorbing film is applied, it is not necessary to apply the entire inside of the package as in the case of a conventional composite module for an optical fiber amplifier. Since it only needs to apply to the inner peripheral surface, it is advantageous in terms of cost. Furthermore, when optical components are fixed inside the package by laser welding, soldering, etc., there is almost no possibility that impurities contained in the light absorption film will be mixed into the molten metal, which will adversely affect the fixing strength and reliability of the package. Is not necessary.
[Brief description of the drawings]
FIG. 1 is a plan view showing a composite module 10 for an optical fiber amplifier according to an embodiment of the present invention in a state where a package lid 12b is not attached.
2 is a partial cross-sectional view showing a part of the composite module for optical fiber amplifier 10 of FIG. 1 from the side.
3 is a view corresponding to FIG. 2, showing a modification of the composite module for optical fiber amplifier 10 of FIG. 1. FIG.
4 is a view corresponding to FIG. 2, showing another modification of the composite module for optical fiber amplifier 10 of FIG. 1. FIG.
5 is a view corresponding to FIG. 2, showing still another modification of the composite module for optical fiber amplifier 10 of FIG. 1. FIG.
6 is a VI-VI cross-sectional view of the optical fiber amplifier composite module of FIG. 5;
7 is a perspective view partially showing (only a holding part) another modification of the composite module for optical fiber amplifier 10 of FIG. 1. FIG.
8 is a partial cross-sectional view for explaining a heat transfer state of the optical fiber amplifier composite module 50 of FIG. 7; FIG.
9 is a plan view corresponding to FIG. 1, showing a conventional optical fiber amplifier composite module 80. FIG.
10 is a plan view corresponding to FIG. 1, showing a conventional hybrid optical multiplexer / demultiplexer 90. FIG.
FIG. 11 is a perspective view showing a cage whose entire bottom surface is in contact with and fixed to the package surface.
12 is a partial cross-sectional view for explaining a heat transfer state when the retainer shown in FIG. 11 is fixed and a semiconductor laser and a Peltier cooler are disposed adjacent to the retainer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Composite module 11 Holding | maintenance part 11b, 11c, 11d Groove 11s Optical capture part 12 Package 12a Package main body 12b Package cover body 13 1st fiber component 14 2nd fiber component 15 3rd fiber component 16 Interference film filter 17 Optical isolator 18 Beam splitter 19 Photodiode

Claims (1)

An optical guide attached to the box-type package, a semiconductor laser, a Peltier cooler attached to the bottom of the box-type package to cool the semiconductor laser, an optical isolator, and an optical isolator that holds and fixes the optical isolator in the box-type package And a light receiver that monitors a part of the signal light, and the holding part is formed so as to contact the outer wall of the box-type package without any gap , and the optical isolator is held and fixed in the box-type package. , together defining an interior of said box-package with the semiconductor laser side area and the area of the light receiver disposed side, the holding portion has a groove is formed in the bottom surface, the is a bottom opposite edges excluding the grooves package be such stray areas of the semiconductor laser side by abutting on the bottom of does not pass between the box type package and the holding portion Composite module for an optical fiber, characterized in that.

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