JP2965013B2 - Light emitting module structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a light emitting element for a light source in an optical communication system or an optical information processing system, and more particularly to a light emitting module structure in which a light emitting element has a coupling mechanism with an optical fiber.

[0002]

2. Description of the Related Art As a laser used as a light source in a wavelength division multiplex communication system, it is necessary to use a laser whose resonance wavelength is accurately controlled or selected. In addition, since the resonance wavelength of the laser fluctuates due to a change in environmental temperature or heat generated by the operating current of the laser itself, in some cases, it is necessary to provide the system with a temperature control mechanism for keeping the laser at a constant temperature.

[0003] As described above, a device provided with a temperature control mechanism is expensive. Therefore,
An external cavity laser has been devised in which a fiber grating whose wavelength can be easily set and whose wavelength variation is small due to a change in environmental temperature is coupled to a normal edge emitting laser (Fabry-Perot LD) (Electronic Letters, 199).
1, VOL 27, pages 1115 to 1116). FIG. 10 shows the structure of this external cavity laser.

In FIG. 10, an external cavity laser is
An edge emitting laser 100 and a fiber grating 101 whose incident end face is disposed close to the emitting end face of the edge emitting laser 100 are arranged such that the center of the emitting end face of the edge emitting laser 100 is located on the axis of the fiber core 102. Has been established. The edge-emitting laser 100 has a configuration in which a current is confined in a stripe shape on an active layer 103 on a semiconductor substrate, and both ends thereof are opened, and then an antireflection coating 104 is applied to only one end. The diffraction grating 105 is formed in a direction perpendicular to the direction of the fiber core 102 in the fiber grating 101, and the end portion of the fiber grating 101 is rounded to obtain good optical coupling with the edge emitting laser 100. (Front ball processing unit 106). In this external resonator type laser, a single resonator is formed between the rear end face of the edge emitting laser 100 and the diffraction grating 105 of the fiber grating 101.

[0005]

However, the above-mentioned prior art has the following problems.

In controlling the resonance wavelength of the laser itself, as described above, a temperature control mechanism for maintaining the laser at a constant temperature is required, and thus there is a problem that the cost is high.

In the external cavity type laser shown in FIG. 10, an edge-emitting laser having a low optical coupling efficiency with a fiber is used. Alternatively, it is necessary to perform special processing called spot size conversion on the laser itself. Since such processing causes a high cost, there is a problem that the cost is also high in this external cavity laser.

An object of the present invention is to provide a light emitting module structure having high optical coupling efficiency without requiring the above-mentioned costly mechanism or processing.

[0009]

In order to achieve the above object, a first light emitting module structure of the present invention comprises an optical resonator having first and second semiconductor multilayer films formed with an active layer interposed therebetween. A surface emitting laser in which laser light is emitted through the first semiconductor multilayer film; and a fiber grating in which a diffraction grating is formed in a direction perpendicular to a direction of a fiber core. The fiber grating is optically coupled to a light emitting laser, and an external resonator is constituted by a second semiconductor multilayer film of the surface emitting laser and a diffraction grating of the fiber grating.

In the above light emitting module structure, the outer surface of the surface of the first semiconductor multilayer film of the surface emitting laser from which the laser light is emitted is formed in a shape corresponding to the fiber core diameter of the fiber grating. The incident end face of the fiber core may be arranged close to the laser light emitting face of the semiconductor multilayer film.

The surface emitting laser and the fiber grating may be integrally formed, and the first semiconductor multilayer film of the surface emitting laser may be formed in a fiber core of the fiber grating. Good.

A plurality of surface emitting lasers are formed on the same substrate surface, and the fiber gratings are provided for a plurality of surface emitting lasers formed on the substrate surface, respectively. The reflection peak wavelengths of the gratings may be different from each other.

According to a second light emitting module structure of the present invention, an active layer is formed in a part of a fiber core, and the first and second light emitting module structures are arranged in a direction perpendicular to the direction of the fiber core with the active layer interposed therebetween. Characterized in that the active layer and the first and second diffraction gratings constitute an optical resonator.

In the above structure, a plurality of the fiber gratings may be provided, and the reflection gratings of the plurality of fiber gratings may have different reflection peak wavelengths.

(Operation) In the first light emitting module structure of the present invention, since a surface emitting laser having a good optical coupling efficiency with a fiber is used, the conventionally required processing of the front end of a fiber grating and the laser side are required. No spot size conversion processing is required.

In the light emitting module structure according to the first aspect of the present invention, when the surface of the surface from which the laser light is emitted has a shape corresponding to the diameter of the fiber core, most of the emitted laser light is emitted from the fiber. Guided into the core. In the case where the surface emitting laser and the fiber grating are integrally optically coupled, all the laser light emitted from the emission surface of the surface emitting laser is directly guided into the fiber core of the fiber grating. The loss caused by the reflection at the exit face and the entrance end face of the fiber core is reduced.

In the second light emitting module structure of the present invention, since an optical resonator is formed in a part of the fiber grating, it is conventionally required similarly to the first light emitting module structure. This eliminates the need for rounded fiber grating processing and spot size conversion processing on the laser side.

In both the first and second aspects, the resonance wavelength is determined by the reflection peak wavelength of the diffraction grating of the fiber grating. Therefore, when a plurality of fiber gratings having different reflection peak wavelengths of the diffraction grating are provided, a plurality of different wavelengths can be extracted.

[0019]

Next, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic configuration diagram of a light emitting module structure according to a first embodiment of the present invention. This light emitting module structure includes a surface emitting laser 1 and a fiber grating 2 having an incident end face arranged close to the light emitting surface of the surface emitting laser 1. It is arranged so that the center is located.

In the surface emitting laser 1, an optical resonator is formed by sequentially forming a semiconductor multilayer film 3, an active layer 4, and a semiconductor multilayer film 5 on a semiconductor substrate, and a laser beam is emitted in a direction perpendicular to the substrate surface. It has become. The outer surface of the surface of the semiconductor multilayer film 5 of the surface emitting laser 1 from which the laser light is emitted has a shape corresponding to the diameter of the fiber core 7 of the fiber grating 2. Most are guided into the fiber core 7. The resonance wavelength of the surface emitting laser 1 is determined by the periodic structure of the semiconductor multilayer films 3 and 5 constituting the reflection surface of the optical resonator. Such a surface emitting laser 1 is, for example, G
On the aAs substrate, 15.5 pairs of G
aAs and AlAs, a semiconductor multilayer film, and an active layer 4 of In _{0 . This} can be realized by sequentially forming 18.5 pairs of semiconductor multilayer films made of GaAs and AlAs as the active layer and the semiconductor multilayer film 5 made of 2Ga _0.8 As. In the present embodiment, the laser light is emitted through the semiconductor multilayer film 5, but the laser light may be emitted from the back surface of the substrate through the semiconductor multilayer film 3.

The fiber grating 2 has a diffraction grating 6 formed in a direction perpendicular to the direction of the fiber core 7 and is optically coupled to the surface emitting laser 1 to form one of the reflection surfaces of the diffraction grating 6 and the optical resonator. An external resonator is constituted by the semiconductor multilayer film 3.

FIG. 2 shows the positional deviation dependence of the optical coupling efficiency of the surface emitting laser 1 and the fiber grating 2 in the light emitting module structure configured as described above. As can be seen from FIG. 2, in this light emitting module structure, an optical coupling efficiency of about 80% or more can be obtained with a displacement of 1 μm or less.

Next, the resonance wavelength in the light emitting module structure will be described. The resonance wavelength in this light emitting module structure is equal to the diffraction grating 6 of the fiber grating 2 which is combined with the surface emitting laser 1 to form an external resonator.
Is determined by the reflection peak wavelength. Hereinafter, the relationship between the reflection peak wavelength of the diffraction grating 6 and the resonance wavelength of the light emitting module structure will be described.

The fiber grating 2 used in this embodiment has a diffraction grating formed by providing a refractive index distribution by, for example, irradiating an optical fiber with ultraviolet rays.
When the refractive index of the fiber core 7 is 1.55 and the refractive index of the low refractive index portion is 1.543, the logarithmic dependence of the reflectance as shown in FIG. 3 is shown. That is, in this fiber grating 2, as shown in FIG. 3, the full width at half maximum is about 100 ° for 100 pairs, and about 50 ° for 200 to 400 pairs.
Thus, a peak of 90% is obtained when the reflectance is 400 pairs.

In the case of a light emitting module structure in which a fiber grating 2 having the above structural parameters and a reflection peak wavelength of 9500 ° is optically coupled to the above-described surface emitting laser 1, the resonance wavelength of the surface emitting laser 1 The threshold gain spectra as shown in FIGS. 4 to 6 were obtained based on the relative difference Δλ from the reflection peak wavelength of the diffraction grating of the fiber grating 2. That is, when the relative difference Δλ is 0 (see FIG. 4), the resonance wavelength of the surface emitting laser 1 and the reflection peak wavelength of the diffraction grating of the fiber grating 2 just resonate, and the relative difference Δλ is −10 nm.
In both cases (see FIG. 5) and when the relative difference Δλ is +10 nm (see FIG. 6), although the minimum threshold gain is increased by about 10%, the resonance wavelength of the surface emitting laser 1 is equal to that of the diffraction grating of the fiber grating 2. ± 4Å for reflection peak wavelength
With the precision of. In any case, the resonance wavelength in the light emitting module structure is 9500 which is the reflection peak wavelength of the diffraction grating of the fiber grating 2.
It became Å.

As can be seen from the above results, the resonance wavelength in the module structure of the present embodiment has a single frequency resonance determined by the reflection peak wavelength of the diffraction grating 6 of the fiber grating 2 irrespective of the resonance wavelength of the surface emitting laser 1. Wavelength. In the present embodiment, since a composite resonator of the optical resonator forming the surface emitting laser 1 and the external resonator obtained by adding the diffraction grating 6 of the fiber grating 2 to the optical resonator is formed, the composite resonator forms a single resonator. One-mode oscillation is obtained, and stable operation is obtained.

(Embodiment 2) FIG. 7 is a schematic configuration diagram of a light emitting module structure according to a second embodiment of the present invention. The basic components of the light emitting module structure are the first component described above.
The structure is the same as that of the light emitting module structure of the first embodiment, except that the surface emitting laser 1 and the fiber grating 2 are integrally optically coupled by a coupling method called a butt joint. In the above-described first embodiment, the emission surface of the surface emitting laser 1 and the incident end face of the fiber grating 2 are configured to be separated from each other. In this case, all the laser light emitted from the emission surface of the surface emitting laser 1 is directly guided into the fiber core 7 of the fiber grating 2. Loss due to reflection occurring on each of the exit surface and the incident end surface is reduced, and an optical coupling efficiency of 80% or more is ideally obtained.

In this embodiment, similarly to the first embodiment, a composite of an optical resonator forming the surface emitting laser 1 and an external resonator obtained by adding the diffraction grating 6 of the fiber grating 2 to the optical resonator is used. Since the resonator is configured, single mode oscillation can be obtained by this composite resonator, and stable operation can be obtained.

(Embodiment 3) The light emitting module structures of the first and second embodiments have a structure in which a fiber grating is optically coupled to a surface emitting laser. However, an optical resonator is provided in the fiber grating itself. It is also possible to adopt a formed configuration. Here, a light emitting module structure in which an optical resonator is formed in the fiber grating itself will be described.

FIG. 8 is a schematic configuration diagram of a light emitting module structure according to a third embodiment of the present invention. In this light emitting module structure, the active layer 4 is embedded in a part of the fiber core 7 of the fiber grating 2, and the diffraction gratings 6, 8 extend in a direction perpendicular to the direction of the fiber core 7 with the active layer 4 interposed therebetween. Is formed. In this light emitting module structure, an optical resonator is formed by the active layer 4 and the diffraction gratings 6 and 8, and a single-frequency resonance wavelength determined by the reflection peak wavelength of the diffraction grating 6 is obtained as in the above-described embodiments. In FIG. 8, only the active layer 4 is shown to explain only the main configuration of the present embodiment. However, actually, other than the active layer 4, a configuration (such as an electrode) for obtaining laser oscillation is provided. Will be provided.

(Embodiment 4) As described in the first embodiment, the resonance wavelength in the light emitting module structure is determined by the reflection peak wavelength of the diffraction grating 6 of the fiber grating 2. From this, it is possible to take out a plurality of different wavelengths by using a plurality of fiber gratings having different reflection peak wavelengths of the diffraction grating. Here, a light emitting module structure configured to extract a plurality of different wavelengths will be described.

FIG. 9 is a schematic structural view of a light emitting module structure according to a fourth embodiment of the present invention. This light emitting module structure is the same as the first or second light emitting module structure described above, except that a plurality of surface emitting lasers 1 are formed on the same substrate surface, and a plurality of surface emitting lasers in which a fiber grating 2 is formed on the substrate surface. , Respectively. Each fiber grating 2
The diffraction gratings 6 are configured so that the reflection peak wavelengths are different from each other, and light having different wavelengths output through the respective fibers is multiplexed by the coupler 9.

The light emitting module structure of the present embodiment is an example of a light emitting module structure for wavelength multiplex communication in which communication is performed using light of different wavelengths. For example, a plurality of surface emitting lasers formed on a substrate surface are used. By controlling according to the signal to be transmitted, optical signals of different wavelengths can be obtained. The optical signals of different wavelengths obtained in this manner are multiplexed by the coupler 9 and guided to the receiving side via one optical fiber.

[0035]

According to the present invention having the above-described structure, it is not necessary to perform the conventional ball grating processing of the fiber grating and the spot size conversion processing on the laser side. There is an effect that a cost-effective light emitting module structure can be realized.

In addition, there is an effect that the manufacturing process of the light emitting module can be shortened by eliminating the need for the spherical processing and the spot size conversion processing.

In the present invention, in the case where the light emitting module is constituted by the combination with the surface emitting laser,
Because the surface emitting laser itself is excellent in mass productivity,
Further, there is an effect that an inexpensive product can be provided.

In the conventional edge emitting laser, the oscillation mode in the axial direction is multimode, whereas in the configuration of the present invention, the optical resonator constituting the surface emitting laser and the diffraction A composite resonator with an external resonator formed by adding a grating is formed, and a single mode oscillation is obtained by the composite resonator. Therefore, there is an effect that stable operation which has not been achieved in the past can be expected.

In the present invention, a plurality of fiber gratings having different diffraction peak wavelengths of the diffraction grating can provide a plurality of different wavelengths, so that a light emitting module structure applicable to wavelength multiplex communication is provided. There is an effect that can be.

The above-described effects are obtained between computers.
This is particularly effective in realizing wavelength division multiplex communication performed over a relatively short distance between switches, inside a computer, inside a switch, or the like.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a light emitting module structure according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the positional deviation dependence of the optical coupling efficiency between the surface emitting laser and the fiber grating in the light emitting module structure shown in FIG.

FIG. 3 is a diagram illustrating the logarithmic dependence of the reflectance on the diffraction grating when the refractive index of the fiber core of the fiber grating is 1.55 and the refractive index of the low refractive index portion is 1.543.

FIG. 4 is a diagram showing a threshold gain spectrum when a relative difference Δλ is 0.

FIG. 5 is a diagram showing a threshold gain spectrum when a relative difference Δλ is −10 nm.

FIG. 6 is a diagram showing a threshold gain spectrum when the relative difference Δλ is +10 nm.

FIG. 7 is a schematic configuration diagram of a light emitting module structure according to a second embodiment of the present invention.

FIG. 8 is a schematic configuration diagram of a light emitting module structure according to a third embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of a light emitting module structure according to a fourth embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of a light emitting module structure using a conventional edge emitting laser.

[Explanation of symbols]

 Reference Signs List 1 surface emitting laser 2 fiber grating 3,5 semiconductor multilayer film 4 active layer 6,8 diffraction grating 7 fiber core 9 coupler

Claims (6)

(57) [Claims] A surface emitting laser having an optical resonator having first and second semiconductor multilayer films formed with an active layer interposed therebetween, wherein a laser beam is emitted through the first semiconductor multilayer film; A fiber grating in which a diffraction grating is formed in a direction perpendicular to the direction of the fiber core. The fiber grating is optically coupled to the surface emitting laser, and a second semiconductor multilayer film of the surface emitting laser is provided. And a diffraction grating of the fiber grating to form an external resonator. 2. The light emitting module structure according to claim 1, wherein a surface of the first semiconductor multilayer film of the surface emitting laser from which laser light is emitted has a shape corresponding to a fiber core diameter of the fiber grating. A light emitting module structure, wherein the incident end face of the fiber core is arranged close to the laser light emitting face of the first semiconductor multilayer film. 3. The light emitting module structure according to claim 1, wherein the surface emitting laser and the fiber grating are integrally formed, and wherein the first semiconductor multilayer film of the surface emitting laser is a fiber core of the fiber grating. A light emitting module structure characterized by being formed in the inside. 4. The light emitting module structure according to claim 1, wherein a plurality of said surface emitting lasers are formed on a same substrate surface, and said fiber grating is formed on said substrate surface. A light emitting module structure provided for each of the plurality of surface emitting lasers, wherein the reflection gratings of the plurality of fiber gratings have different reflection peak wavelengths. 5. A fiber grating in which an active layer is formed on a part of a fiber core and first and second diffraction gratings are formed in a direction perpendicular to the direction of the fiber core with the active layer interposed therebetween. And wherein an optical resonator is constituted by the active layer and the first and second diffraction gratings. 6. The light emitting module structure according to claim 5, wherein said plurality of fiber gratings are provided, and said plurality of fiber gratings are configured such that the reflection peak wavelengths of said diffraction gratings are different from each other. Module structure.