JPH09153659A - Light-emitting element module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element module for outputting a light having few distortion. SOLUTION: This light-emitting element module comprises a semiconductor light-emitting element 10 having a light reflecting surface 11 and a light emitting surface 12; and an optical fiber 20a which is arranged so that a light emitted from a light emitting surface of the semiconductor light-emitting element 10 enters, and in which a core 21 is provided with a diffraction grating 30 which changes periodically a refractive index along an optical shaft. The light emitted from the light emitting surface are reflected by the diffraction grating 30 and the light emitting surface, whereby a laser oscillation is made. The diffraction grating 30 is arranged at a location where the lights emitted from the light emitting surface pass through an optical path, of which a length is 20mm or less, from the light emitting surface until the lights reach a top end of the diffraction grating 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device module used as a signal light source for optical communication, a light source for pumping a fiber amplifier, etc. in the field of optical communication.

[0002]

2. Description of the Related Art Light from a semiconductor light emitting device having a light reflecting surface having a high reflectance and a light emitting surface that reflects almost no light is incident on an optical fiber provided with a diffraction grating, and K. Petermann's book “LASER DIODE MODULATION A” describes light emitting device modules that perform laser oscillation by repeatedly reflecting light from the light reflecting surface.
ND NOISE ”(Kluwer Academic Publishers) is known as described on page 266. This light-emitting element module is equipped with a laser resonator using a diffraction grating, so that laser light with high monochromaticity can be obtained. Is output.

A similar light emitting device module is BPVentru.
“Wavelength and Intensity Stabilizatio” by do et al.
n of 980nm Diode Lasers Coupled to Fiber Bragg Gra
tings ”(reference in SEASTAR OPTICS INC. catalog)
It is also described in This light emitting device module is used as a light source for pumping a fiber amplifier.
Then, in this document, it is described that the laser oscillation wavelength of the light emitting element module is stable when the distance between the semiconductor laser and the diffraction grating is 5 cm to 10 cm or more.

[0004]

However, the above-mentioned document does not consider the arrangement condition of the diffraction grating which is suitable for suppressing the distortion of the output light of the light emitting element module.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a light emitting element module that outputs light with little distortion.

[0006]

In order to solve the above problems, a light emitting device module of the present invention comprises: (a) a semiconductor light emitting device having a light emitting surface and a light reflecting surface facing the light emitting surface; (B) A diffraction grating, which is arranged so that the light emitted from the light emitting surface of the semiconductor light emitting element enters from one end surface, has a refractive index periodically changing along the optical axis at a predetermined portion of the core. A light emitting element module comprising: an optical fiber provided, wherein the light emitted from the light emitting surface is oscillated by being reflected by a diffraction grating and a light reflecting surface. It is characterized in that the light emitted from the emission surface is arranged at a position where the length of the optical path that passes from the light emission surface to the tip of the diffraction grating is 20 mm or less.

According to the knowledge of the present inventors, when the optical path length from the light emitting surface to the tip of the diffraction grating is 20 mm or less, the distortion and noise of the laser light output from the light emitting element module are sufficient. Less.

In the light emitting device module of the present invention, the light emitting surface of the semiconductor light emitting device may be coated with a dielectric film that reduces the reflectance of the light emitting surface. In this case, extra reflection between the light reflecting surface and the diffraction grating is reduced, and laser resonance is favorably generated between the light reflecting surface and the diffraction grating, so that a high light output can be obtained. . In addition, by coating such a dielectric film to reduce the reflectance of the light emitting surface, it is possible to easily manufacture the light emitting device module of the present invention using a semiconductor device that has been conventionally used as a semiconductor laser. You can

In the light emitting device module of the present invention, it is preferable that the end face of the optical fiber to which the light emitted from the light emitting face of the semiconductor light emitting device enters is coated with a dielectric film that reduces the reflectance of this end face. In this case, extra reflection between the light reflecting surface and the diffraction grating is reduced, and laser resonance is favorably generated between the light reflecting surface and the diffraction grating, so that a high light output can be obtained. .

In the light emitting device module of the present invention, it is preferable that the end face of the optical fiber on which the light emitted from the light emitting surface of the semiconductor light emitting device is incident is inclined with respect to the incident axis of this light. In this case, extra reflection between the light reflecting surface and the diffraction grating is reduced, and laser resonance is favorably generated between the light reflecting surface and the diffraction grating, so that a high light output can be obtained. .

The light emitting device module of the present invention provides the light emitted from the light emitting surface on the optical path between the light emitting face of the semiconductor light emitting device and the end face of the optical fiber on which the light emitted from the light emitting face enters. An optical coupling lens that focuses the light and makes it enter the optical fiber is preferably arranged. In this case, the optical coupling efficiency between the semiconductor light emitting element and the optical fiber is increased and the optical loss is reduced, so that a high optical output can be obtained.

At this time, it is more preferable that the light entrance surface and the light exit surface of the optical coupling lens are coated with a dielectric film that reduces the reflectance of the light entrance surface and the light exit surface. In this case, extra reflection between the light reflecting surface and the diffraction grating is reduced, and laser resonance is favorably generated between the light reflecting surface and the diffraction grating, so that a high light output can be obtained. .

In the light emitting device module of the present invention, it is preferable that the end face of the optical fiber on which the light emitted from the light emitting face of the semiconductor light emitting device enters is a lens surface. As a result, since the end face of the optical fiber is provided with a lens function, the optical coupling efficiency between the semiconductor light emitting element and the optical fiber is increased, the optical loss is reduced, and a high optical output can be obtained.

At this time, it is more preferable that the end face is coated with a dielectric film that reduces the reflectance of the end face. In this case, extra reflection between the light reflecting surface and the diffraction grating is reduced, and laser resonance is favorably generated between the light reflecting surface and the diffraction grating, so that a high light output can be obtained. .

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

(Embodiment 1) FIG. 1 is a schematic view showing the structure of a light emitting device module of this embodiment. This light emitting device module includes a semiconductor light emitting device 10 that outputs light in a predetermined wavelength band (1.31 μm band) and the semiconductor light emitting device 1.
It is composed of an optical fiber 20a on which light from 0 enters.

The semiconductor light emitting device 10 is made of InGaAsP / I, like a general Fabry-Perot type semiconductor laser.
The hetero structure is made of nP, and the light reflecting surface 11 and the light emitting surface 12 are provided at both ends of the hetero structure so as to face each other in substantially parallel. The light reflecting surface 11 is
Light having a wavelength of 1.31 μm, which is the output wavelength of the semiconductor light emitting device 10, is reflected with a high reflectance of about 80%. On the other hand, the light emitting surface 12 has a low reflectance of about 0.5% or less for light having a wavelength of 1.31 μm.

This semiconductor light emitting device 10 is made of InGaAs.
It can be manufactured by preparing an ordinary Fabry-Perot type semiconductor laser having a P / InP heterostructure and applying a low reflection coating to the light emitting surface thereof. The low reflection coating is completed by covering the light emitting surface of the Fabry-Perot type semiconductor laser with a dielectric film that reduces the reflectance of the light emitting surface.

A drive circuit (not shown) is connected to the semiconductor light emitting element 10, and a predetermined operating current is passed from the drive circuit to the semiconductor light emitting element 10 to excite the heterostructure, and about 1 Spontaneous emission light in the wavelength band centered on 0.31 μm is generated. The spontaneous emission light travels inside the heterostructure while causing stimulated emission, and is emitted from the light emitting surface 12 together with the stimulated emission light.

The optical fiber 20a is used for the semiconductor light emitting device 10.
The light emitted from the light emitting surface 12 is disposed so as to enter the core 21 of the optical fiber 20a from the end face 23 thereof. The optical fiber 20a is a quartz (SiO ₂ ) glass-based single mode optical fiber. Both the core 21 and the clad 22 of the optical fiber 20a are made of quartz glass. The clad 22 is made of substantially pure quartz glass, while the quartz glass forming the core 21 is refracted. GeO ₂ which is a rate increasing material is added. As a result, the core 2 of the optical fiber 20a
1 has a higher refractive index than the clad 22.

The end face 23 of the optical fiber 20a facing the semiconductor light emitting element 10 is processed into a spherical shape. The processing of the tip ball is for imparting a lens function to the end surface of the optical fiber 20a to enhance the optical coupling efficiency between the semiconductor light emitting element 10 and the optical fiber 20a. The end face 23 is covered with a dielectric film that reduces the reflectance of the end face 23.

A diffraction grating 30 is provided on the core 21 of the optical fiber 20a. The diffraction grating 30 is a region in the core where the effective refractive index periodically changes between the minimum refractive index and the maximum refractive index according to the position along the optical axis. In other words, the diffraction grating 30 is a region having an effective refractive index distribution that repeatedly changes along the optical axis between the minimum refractive index and the maximum refractive index. The cycle of the change in the refractive index is called the cycle of the diffraction grating 30, the grating pitch, or the like.

As is well known, the diffraction grating 30 is formed by utilizing the phenomenon that when the quartz glass containing germanium is irradiated with ultraviolet light, the refractive index of the irradiated portion increases by an amount corresponding to the intensity of the ultraviolet light. be able to. That is, by irradiating the interference fringes of ultraviolet light from the surface of the clad of the optical fiber toward the core to which germanium is added, the effective refractive index distribution according to the light intensity distribution of the interference fringes in the interference fringe irradiation region of the core It is formed. The region having such an effective refractive index distribution is the diffraction grating 30. In this case, the diffraction grating 30
Therefore, the minimum refractive index of the core is approximately equal to the initial effective refractive index of the core (effective refractive index before irradiation of ultraviolet light).

The diffraction grating 30 reflects light over a narrow wavelength band centered on a predetermined diffraction wavelength (Bragg wavelength) λ _R. This diffraction wavelength λ _R is expressed as follows: λ _R = 2 · n · Λ (1) n: minimum refractive index of diffraction grating 30 Λ: period of diffraction grating 30

In the light emitting device module according to the present application, the diffraction grating 30 is the most optically arranged from the light emitting surface 12 of the semiconductor laser 10 (actually, the surface of the low reflection film) to the tip of the diffraction grating 30 (the light emitting surface 12 is the most optically reflective surface). Optical path length L up to near part)
Is provided at a position of about 20 mm or less. In addition,
From the light emitting surface 12 of the semiconductor light emitting device 10 to the optical fiber 20
The distance (not the optical path length but the actual distance) to the tip 23 of a is about 10 μm.

Next, the light emitting principle of the light emitting element module of this embodiment will be described. When an operating current is applied to the semiconductor light emitting device 10 from a drive circuit (not shown), spontaneous emission light is generated in the active region of the semiconductor light emitting device 10. This spontaneous emission light travels in the active region while causing stimulated emission and is emitted from the light emission surface 12. Since the light emitting surface 12 has a low reflectance due to the low reflection coating,
Most of the spontaneous emission light and the stimulated emission light generated inside the semiconductor light emitting element 10 are transmitted through the light emission surface 12 and emitted. The light emitted from the light emitting surface 12 enters the fiber 20 a from the end surface 23 that has been processed into a sphere, and reaches the diffraction grating 30.

Of the light from the semiconductor light emitting element 10, the diffraction grating 30 reflects light having a wavelength band narrower than that of the semiconductor light emitting element 10 around the diffraction wavelength of 1.31 μm. The light reflected by the diffraction grating 30 exits the optical fiber 20 a from the end face 23 and enters the semiconductor light emitting element 10 from the light exit face 12. The incident light is emitted from the semiconductor light emitting device 10.
And proceeds to the active region of the device while causing stimulated emission to reach the light reflecting surface 11. After that, the light reflected by the light reflecting surface 11 travels in the active region while causing stimulated emission, and is emitted from the light emitting surface 12 and again the optical fiber 20a.
Incident on. This incident light reaches the diffraction grating 30 and is reflected again. Thus, the diffraction grating 30 and the light reflecting surface 11
The light having a wavelength of 1.31 μm is amplified by being repeatedly reflected between and, and finally laser oscillation occurs. The laser light thus generated passes through the diffraction grating 30,
It advances in the optical fiber 20a. Therefore, by connecting various devices for optical communication to the optical fiber 20a, the light emitting element module of this embodiment can be used as a signal source for optical communication.

In the light emitting element module of the light emitting principle as in the present invention, in order to reduce the noise and distortion of the output light, the feedback time until the light emitted from the semiconductor light emitting element is reflected by the diffraction grating and returns. However, it is better to be sufficiently shorter than the modulation cycle of the output light of the light emitting element module. And in order to shorten the feedback time,
The optical path length from the light emitting surface to the diffraction grating may be shortened. Based on such consideration, the present inventors have determined that the optical path length from the light emitting surface 12 to the tip of the diffraction grating 30 is 20.
It has been found out that the distortion of the output light of the light emitting element module can be sufficiently suppressed by disposing the diffraction grating 30 at a position of not more than mm.

In order to obtain the above findings, the present inventors have
An experiment was conducted to measure the complex second-order distortion of the output light of the light emitting element module while changing the position of the diffraction grating 30. FIG.
FIG. 4 is a diagram showing the relationship between the position of the diffraction grating 30 and the output light distortion of the light emitting element module, which is obtained by this experiment. In this figure, the position of the diffraction grating 30 is represented by L shown in FIG. 1, that is, the optical path length from the light emitting surface 12 to the tip of the diffraction grating 30. The strain is measured by controlling the operating current applied to the semiconductor light emitting device 10,
Signal light having a modulation degree m of 4% was output from the light emitting element module at 77 ch. Moreover, the measurement was performed for each of the modulation frequencies of 300 MHz, 500 MHz, and 1 GHz.

As shown in FIG. 2, at the modulation frequency of 1 GHz or less, when the diffraction grating 30 is arranged within the position of L = 20 mm, the distortion of the output light of the light emitting element module is sufficiently below -25 dB. Less. Therefore, the light emitting element module of this embodiment can be suitably used as a light source for optical communication.

Further, in the light emitting device module of this embodiment, since the light emitting surface 12 of the semiconductor light emitting device 10 and the end face 23 of the optical fiber 20a are coated with a low reflection coating of a dielectric film, the light reflecting surface. 12 and diffraction grating 30
The extra reflection between and is suppressed. This allows
Since suitable laser resonance occurs between the light reflecting surface 12 and the diffraction grating 30, according to the light emitting element module of this embodiment, a high light output can be obtained.

(Embodiment 2) FIG. 3 is a schematic view showing the structure of a light emitting device module of this embodiment. The difference between the present embodiment and the first embodiment is the presence of the minute lens 40 and the shape of the end face of the optical fiber 20, the arrangement of the diffraction grating 30, the low reflection coating of the light emitting surface 12, and the light emission of the light emitting element module. The principle is the same as that of the first embodiment.

As shown in FIG. 3, the minute lens 40 is arranged between the light emitting surface 12 and the end surface 24 of the optical fiber 20b. The minute lens 40 is used for the semiconductor light emitting device 1
The light from 0 is focused and made incident on the optical fiber 20b,
It is a convex lens that couples the optical power from the semiconductor light emitting device 10 to the optical fiber 20b. As the microlens 40, an ordinary optical coupling lens that has been conventionally used in optical communication can be used. The micro lens 4
The shape of 0 is determined so that the optical path length from the light emitting surface 12 to the diffraction grating 30 is 20 mm or less.

As described above, in the present embodiment, by disposing the minute lens 40 between the semiconductor light emitting device 10 and the optical fiber 20b, the semiconductor light emitting device 10 and the optical fiber 20b are arranged.
The optical coupling efficiency with is improved, and high light output is realized.

The lens surface of the minute lens 40, that is, the light incident surface and the light emitting surface of the minute lens 40 are coated with a dielectric film that reduces the reflectance of these surfaces. As a result, extra reflection between the light reflecting surface 12 and the diffraction grating 30 is reduced, and suitable laser resonance occurs, so that a higher light output can be obtained.

The end face 24 of the optical fiber 20b on the semiconductor light emitting device 10 side is provided with the semiconductor light emitting device 10 and the minute lens 40.
Is tilted with respect to the optical axis of the optical system. In other words, the end face of the optical fiber 20b is inclined so that the optical axis direction of the optical system including the semiconductor light emitting element 10 and the minute lens 40 does not coincide with the normal direction of the end face 24. As a result, extra reflection between the light reflection surface 12 and the diffraction grating 30 is reduced, and suitable laser resonance occurs, so that a high light output can be obtained.

Also, as in the first embodiment, the optical fiber 2
Since the end surface 24 of 0b is covered with a dielectric film that reduces the reflectance of the end surface 24, this also reduces extra reflection between the light reflecting surface 12 and the diffraction grating 30, thereby increasing high light. Output can be realized.

(Embodiment 3) FIG. 4 is a schematic view showing the structure of a light emitting device module of this embodiment. The difference between the present embodiment and the second embodiment is the number of minute lenses arranged between the semiconductor light emitting device 10 and the optical fiber 20, the shape of the end face 24 of the optical fiber 20b, the arrangement of the diffraction grating 30, and the light. The low reflection coating on the emitting surface 12 and the light emitting principle of the light emitting element module are the same as those in the second embodiment.

As shown in FIG. 4, in the light emitting device module of this embodiment, two microlenses 41 and 42 are arranged between the semiconductor light emitting device 10 and the optical fiber 20b. The optical system composed of the minute lenses 41 and 42 focuses the light from the semiconductor light emitting element 10 to generate an optical fiber 20.
b from the semiconductor light emitting device 10 to the optical fiber 20.
The optical power is coupled to b. Micro lens 4
As 1, 42, ordinary optical coupling lenses that have been conventionally used in optical communication can be used. The shape and arrangement of the minute lenses 41 and 42 are determined so that the optical path length from the light emitting surface 12 to the diffraction grating 30 is 20 mm or less.

Also in this embodiment, as in the second embodiment, by arranging the minute lenses 41 and 42 between the semiconductor light emitting device 10 and the optical fiber 20b, the semiconductor light emitting device 10 and the optical fiber 20b are optically coupled. High efficiency and high light output are realized.

Further, the light incident surface and the light emitting surface of each of the minute lenses 41 and 42 are covered with a dielectric film which reduces the reflectance of these surfaces. As a result, extra reflection between the light reflecting surface 12 and the diffraction grating 30 is reduced, and suitable laser resonance occurs, so that a higher light output can be obtained.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. For example, in the above embodiment, the output wavelength (wavelength of the gain peak) of the semiconductor light emitting element and the diffraction wavelength of the diffraction grating are set to 1.31 μm, but the output wavelength of the semiconductor light emitting element and the diffraction wavelength of the diffraction grating are the same. May have a deviation within ± 50 nm. Further, the output wavelength of the semiconductor light emitting device and the diffraction wavelength of the diffraction grating are not limited to the 1.31 μm band, but may be 1.4
The band may be 8 μm band or 1.55 μm band.

[0043]

As described above in detail, in the light emitting device module of the present invention, since the optical path length from the light emitting surface of the semiconductor light emitting device to the tip of the diffraction grating is 20 mm or less, there is sufficient distortion. It can output less light.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a light emitting element module according to a first embodiment.

FIG. 2 is a diagram showing a relationship between a position of a diffraction grating 30 and output light distortion of a light emitting element module.

FIG. 3 is a schematic diagram showing a configuration of a light emitting element module according to a second embodiment.

FIG. 4 is a schematic diagram showing a configuration of a light emitting element module according to a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Semiconductor light emitting element, 11 ... Light reflecting surface, 12 ... Light emitting surface, 20a and 20b ... Optical fiber, 21 ... Core, 22
... clad, 23 ... spherical end surface, 24 ... inclined end surface, 30 ... diffraction grating, 40 to 42 ... optical coupling lens.

Claims (8)

[Claims] 1. A semiconductor light-emitting device having a light-emitting surface and a light-reflecting surface facing the light-emitting surface, and light emitted from the light-emitting surface of the semiconductor light-emitting element is arranged so as to enter from one end surface, and a core is provided. An optical fiber provided with a diffraction grating whose refractive index is periodically changed along the optical axis at a predetermined portion of, and the light emitted from the light emitting surface is the diffraction grating and the light reflecting surface. In the light emitting element module that performs laser oscillation by being reflected by, the diffraction grating has a length of an optical path through which the light emitted from the light emitting surface passes from the light emitting surface to the tip of the diffraction grating. A light-emitting element module, which is arranged at a position of 20 mm or less. 2. The light emitting element module according to claim 1, wherein the light emitting surface of the semiconductor light emitting element is coated with a dielectric film that reduces the reflectance of the light emitting surface. 3. The end face of the optical fiber, into which the light emitted from the light emitting face of the semiconductor light emitting element is incident, is coated with a dielectric film that reduces the reflectance of the end face. Item 1. The light emitting device module according to item 1. 4. The optical fiber according to claim 1, wherein the end surface of the optical fiber on which the light emitted from the light emitting surface of the semiconductor light emitting element is incident is inclined with respect to the incident axis of the light. Light emitting device module. 5. The light emitted from the light emitting surface is focused on an optical path between the light emitting surface of the semiconductor light emitting element and the end surface of the optical fiber on which the light emitted from the light emitting surface is incident. The light-emitting element module according to claim 1, further comprising an optical coupling lens disposed to allow the light to enter the optical fiber. 6. The light entrance surface and the light exit surface of the light coupling lens are coated with a dielectric film that reduces the reflectance of the light entrance surface and the light exit surface. The light emitting device module described. 7. The light emitting device module according to claim 1, wherein the end face of the optical fiber on which the light emitted from the light emitting face of the semiconductor light emitting device is incident is a lens surface. 8. The light emitting device module according to claim 7, wherein the end face is coated with a dielectric film that reduces the reflectance of the end face.