JP2744455B2 - Optical amplifier and optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical amplifier having a semiconductor laser structure.

[Prior Art] Generally, an optical amplifier has a semiconductor laser structure and applies a bias current less than a threshold value to amplify optical input light from the outside. Development is being carried out to compensate for the loss that occurs when connecting between them.

Optical amplifiers have different characteristics depending on the reflectivity of the end face, and those with low reflectivity are classified as traveling wave optical amplifiers.

Traveling-wave optical amplifiers typically have non-reflective or low-reflection coatings on the input and output end faces. Generally, a low-reflection coating is applied to the resonance surface of a Fabry-Perot type semiconductor laser so that light is input from one end surface and light is extracted from the other end surface.
ent Application) As disclosed in GB2033648A, a low reflection coating is used on a part of the end face to utilize the reflection of the end face, or a low reflection and high reflection property disclosed in Japanese Patent Publication No. 63-502316. Those composed of a combination of reflective coatings are also considered to be traveling wave types.

Such a traveling-wave amplifier has an excellent characteristic that a gain is obtained with respect to the wavelength. This is achieved by suppressing the end face reflectivity and suppressing the resonance mode occurring in the optical amplifier. Therefore, how to reduce the end face reflectance of the optical amplifier is an important parameter that gives characteristics.

When an optical amplifier is used in an optical communication system,
Coupling with a fiber is essential, but at this time, both the input side and the output side must be accurately aligned. JP-T-63-502316 mentioned above solves the problem of connection between the optical amplifier and the fiber by setting the input and output positions to be the same so that the alignment of the optical amplifier and the fiber is performed once. In this case, a traveling wave type optical amplifier having good characteristics is realized by precisely realizing an extremely low reflectance on the input / output end face side in order to make one surface a reflection surface.

[Problem to be solved by the invention] When one end face is provided with a non-reflective coating,
In order to obtain the same performance as in the case of applying an anti-reflection coating to both end faces, assuming that the reflectance of the latter is 10 ^-3 each, the reflectance of the anti-reflection coating side in the former is 10 ^-5 to 10 ^-6 Is required. Then, if there is a residual reflectance on the low reflection side, the resonance mode appears immediately.

In general, the anti-reflection coating is formed by selecting a material having an appropriate refractive index and strictly controlling the film thickness. However, the obtainable range of the anti-reflection coating is narrow and steep. In order to achieve about 10 ⁻³ to 10 ^−4, it is necessary to control the film thickness with an accuracy of 50 °. Since it is very difficult to perform such film thickness control with good reproducibility, it has caused variations in the characteristics of the optical amplifier which largely depend on the performance of the anti-reflection coating.

The same input / output unit is advantageous for alignment, but when it is necessary to separate input light and output light, optical means such as providing a branch in the fiber is required separately. The problem is that the loss at the branch becomes large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical amplifier having characteristics as a traveling-wave optical amplifier and capable of relatively easily connecting to an optical fiber or the like.

[Means for Solving the Problems] An optical amplifier according to the present invention is an optical amplifier using a semiconductor laser structure, wherein: a light incident portion and a light emitting portion formed at different locations in the same plane; A reflecting portion for reflecting light incident from the light guide portion to guide the light to the light emitting portion; and a light incident from the light incident portion and reflected by the reflecting portion;
A light amplifying region for amplifying light reaching the light emitting portion, and a light amplifying region formed on a surface on which the light incident portion and the light emitting portion are formed;
A film for suppressing light reflection, wherein the reflection portion has a wavelength dependency in its reflectance.

In this case, the reflection section may be constituted by a diffraction grating.

Further, the film for suppressing the reflection of light at the light incident portion or the light emitting portion may be formed at a predetermined angle shifted from a plane perpendicular to the traveling direction of light reaching the film.

An optical device according to the present invention is an optical device in which a light emitting element, a light receiving element, and an optical amplifier are mounted on a same substrate, wherein the optical amplifier has a light incident part and a light emitting part formed at different locations in the same plane. Part, a reflecting part for reflecting light incident from the light incident part and guiding the light to the light emitting part, and entering from the light incident part, being reflected by the reflecting part and reaching the light emitting part. A light amplification region for amplifying light, and a film formed on a surface on which the light incident portion and the light emitting portion are formed, which suppresses reflection of light, and includes a light emitted by the light emitting element. The light is amplified and emitted to the outside, and the incident light is amplified and output to the light receiving element.

[Operation] The coating applied to the light incident portion and the light emitting portion is the same. Further, since the optical amplification region is bent, the resonance mode is suppressed.

FIG. 1 is a view showing a structure of a first embodiment of the present invention, and FIG.
The figure shows an application example.

The optical amplifier 11 has a structure similar to that of a semiconductor laser, and amplifies and emits incident light at an active layer 15 thereof. This optical amplifier
The electrode 14 formed on the upper surface of 11 is formed in a U-shape, and accordingly, the optical amplification region in the active layer 15 also has a U-shape. Therefore, the electrode and the optical amplification region in the present embodiment are composed of the first and second portions which are in a parallel state and the third portion which is in a substantially perpendicular state and is connected to both. become. A reflection portion for making incident light travel along the light amplification region is formed at a joint portion between these light amplification regions. An end surface 13 ₁ inclined at an angle of approximately 45 ° from the traveling direction of the incident light toward the third portion with respect to the junction between the first portion and the third portion.
Is formed by etching, and a junction between the third portion and the second portion is formed at an end face 13 inclined at an angle of approximately 45 ° from the direction of light propagation in the third portion toward the second portion. _Two
Are formed by etching. Light is reflected if the outside of the end faces 13 ₁ and 13 ₂ is set to have a lower refractive index than an optical amplifier region such as air. Therefore, the light incident on the optical amplifier according to the present embodiment is sequentially amplified through the first portion, the third portion, and the second portion, and is emitted to the outside.

Further, a non-reflective coating film 12 is provided on the surface on which the light incident portion and the light emitting portion are arranged.

As an etching method for forming the end faces 13 ₁ and 13 ₂ in the present embodiment, a mask is produced by a photolithography method, and then a chlorine-based reactive ion beam etching is performed. Was completely removed. In addition, anti-reflective coating film 12
Was formed by evaporating ZrO ₂ by an electron beam (EB) evaporation method.

In the optical amplifier shown of this embodiment, it changes the path itself of light by reflection at the end face 13 _1, 13 ₂ formed by etching, the influence of the return directly input the return light can be almost neglected. For this reason, the suppression of the resonance mode which is regarded as important as a traveling wave amplifier is determined by the reflectance of one anti-reflection coating applied to the input / output side end face. In order to secure sufficient characteristics as a traveling wave type, it is required to have a reflectivity of about 10 ^-3, but this antireflection coating needs to be applied twice on the input surface and output surface as in the past. And have the same characteristics.

FIG. 2 is a diagram showing a configuration of a receiver using the optical amplifier 11 of the first embodiment.

Optical amplifier 11 is a semiconductor laser mount 21 which is conventionally used, optical detector 22 an optical amplifier 11 is received through the lens 23 the optical signal from the fiber 24 ₁ is a transmission path. Although the outgoing light of the optical amplifier input 11 is amplified, a part thereof is incident on the detector 22, the other is incident through the lens 23 to the fiber 24 _2.

As described above, in the optical amplifier of the present invention, since the light incident portion and the light emitting portion are provided independently, the coupling with the fiber is easy. As for the coupling with the fiber, the input side and the output side may be separated and coupled to two fibers as in this embodiment, but the input and output sections of the optical amplifier 11 are formed close to each other, and the same It may be coupled to a fiber. In the former case, since the input unit and the output unit can be on the same plane, there is an advantage that the input side, the output side, and the optical system can be handled as one component without distinction. In the latter case, there is an advantage that the optical axis alignment only needs to be performed once.

The photodetector 22 in this embodiment is provided for applying feedback to the optical amplifier 11. For this purpose, optical amplifier 11
It is necessary to extract a part of the spontaneous emission light and the amplified light.
In the present embodiment, the depth of the end faces 13 ₁ and 13 ₂ (see FIG. 1) formed on the optical amplifier 11 by etching is set to a part of the waveguide, and a part of the guided light is extracted.

FIG. 3, FIG. 4 (a), (b) and FIG. 5 are views showing the structure of the second to fourth embodiments of the present invention.

In any of the embodiments, as in the first embodiment shown in FIG. 1, the light incident portion and the light emitting portion are on the same surface, and an anti-reflection coating film is formed thereon.

First, the second embodiment shown in FIG. 3 will be described.

This embodiment is to form an electrode 41 formed on the upper surface M-shape, which the order to advance the corresponding light along the optical amplification region, the conventional end face 42 by using the etching as with _{1-42 3} To form a reflection portion. In other words, the structure of the present invention indicates that the number of reflections and the position thereof can be arbitrarily selected. However, when full firing is used, the angle of incidence is limited. For example, when using a GaAs-based material,
If air is reflected at the boundary, an incident angle of 18 ° or more is required.

Next, a third embodiment shown in FIGS. 4 (a) and 4 (b) will be described.

In this embodiment, a U-shaped electrode is used and a diffraction grating 41 is provided as a reflector, as in the first embodiment shown in FIG.

The diffraction grating 41 is provided in the vicinity of the active layer using corrugation usually used in a DBR-LD or the like. In this case, it is necessary to bend the direction. For this purpose, it is necessary to tilt the diffraction grating 41 from the reflection direction and design the lattice constant. For example, in the case of tilting by 45 ° as in the first embodiment, FIG.
Is expressed by the following equation.

Here, m is the diffraction order, λ is the wavelength, and neff is the effective refractive index. As is apparent from the equation, in this embodiment, the optical amplifier has wavelength dependency, and a traveling-wave optical amplifier having a built-in optical frequency filter can be achieved. However,
Care must be taken in the design of light that returns to the incident light side due to the diffraction grating as reflected light, which leads to generation of a resonance mode.

Next, FIG. 7 is a diagram showing the configuration of the fourth embodiment shown in FIG.

In the present embodiment, the electrode 51 formed on the upper surface has a V-shape, and a high-reflection coating film 52 is formed on the top of the electrode 51 as a reflection portion for reflecting guided light, thereby improving the reflectance. is there. For this purpose, the input / output side optical amplification region is formed so as to be shifted from the input / output end face by a certain angle from the perpendicular.

In this case, it is necessary to perform the anti-reflection coating on the entrance / exit end face in consideration of the inclination angle of the end face. The control of the thickness is also loosened, which is convenient. In the reflection at the high reflection end face, the light returning in the incident direction cannot be ignored, which may lead to the occurrence of a resonance mode. Therefore, it is necessary to carefully design the angle of inclination and the design of the high-reflection and non-reflection coating.

By using a multi-layer coating of SiO ₂ and TiO ₂ as the high reflection coating film 52, the reflectance can be controlled and an effective optical amplifier can be formed.

FIG. 6 is a diagram showing an optical node configured using the optical amplifier of the present invention.

In this embodiment, an optical amplifier 61 having U-shaped electrodes is used as in the first embodiment shown in FIG.

A device in which an optical node unit and a transmitting / receiving unit are integrated on one substrate will be described. Transmitting portion is two different wavelengths from the distributed Bragg reflector laser (DBR-LD) 63 ₁ preliminary 63 ₂ capable of transmitting, optical signals are wavelength-multiplexed by the Y multiplexer 64 is delivered. The lightwave after the Y multiplexing further passes through the isolator 65 and enters the branch coupler 66. Isolator 65
This can be realized by forming an epitaxial film made of CdMnTe on the GaAs epitaxial film by MBE, and configuring a reciprocal portion, a non-reciprocal portion, and a polarizing filter. When a V-shaped branch coupler 66 is used as in this embodiment, the reflection is large, and the isolator 65 is indispensable. The optical amplifier 61 amplifies the light from the transmitting unit and
Together sends out to ₂ amplifies the signal light from the optical fiber 70 ₁ is input to the receiving unit.

Next, the receiving section will be described. Optical signal is black diffracted by the branch waveguide 67 is guided to the diffraction grating 68 _1, 68 ₂ at a branch coupler 66, only an optical signal having a desired light wavelength, is emitted to the slab waveguide of the ridge waveguide side The selected optical signal is detected by independent photodetectors 69 ₁ and 69 ₂ according to the wavelength. Layer structure of the photodetector 69 _1, 69 ₂ can be operated as a photodetector by which are identical to the optical amplifying section 61 to apply a reverse bias.

Since the receiver does not incorporate an isolator,
In order to suppress unnecessary reflection at each stepped portion, it is necessary to take measures such as setting the boundary diagonally or tapering. Of course, if the isolator is installed in both branches, improvement in performance can be expected.

Since the optical amplifier and the branch coupler of the present embodiment have a wide wavelength band, it is considered to be useful as an integrated optical node of a wave-multiplexed optical bus system.

In this apparatus, the antireflection coating film 62 is applied to the end face of the optical amplifier.
The effect of preventing reflection at the end face of 3 ₁ and 63 ₂ is also effective in suppressing Fabry-Perot mode oscillation.
In this configuration, the functions of both the optical amplifier and the optical amplifier are improved.

[Effects of the Invention] The present invention is configured as described above, and has the following effects.

Since the light incident portion and the light emitting portion are provided at different positions on the same surface, the anti-reflection coating process can be performed only once. In addition, since the reflection portion has a wavelength dependency in the reflectance, it is possible to perform wavelength-dependent light amplification, and it can be used as a filter.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a first embodiment of the present invention, FIG. 2 is a diagram showing an application example thereof, FIGS. 3 and 4 (a),
(B), FIG. 5 is a diagram showing the structure of the second to fourth embodiments of the present invention, and FIG. 6 is a diagram showing an optical node configured by using the present invention. 11,61… Optical amplifier, 12,62… Non-reflective coating film, 13 ₁ , 13 ₂ , 42 _{1 to} 42 ₃ … End face, 14,41,51… Electrode, 15… Active layer, 21… … Mount, 22… Detector, 23… Lens, 24 ₁ , 24 ₂ , 70 ₁ , 70 ₂ … Fiber, 41… Diffraction grating, 52… High reflection coating film, 63 ₁ , 63 ₂ …… DBR laser, 64 Y combiner, 65 isolator, 66 branch coupler, 67 branch waveguide, 68 ₁ , 68 _2, diffraction grating, 69 ₁ , 69 _2, photo detector.

Claims (4)

(57) [Claims] 1. An optical amplifier using a semiconductor laser structure, comprising: a light incident portion and a light emitting portion formed at different locations in the same plane; and reflecting the light incident from the light incident portion to emit the light. A light amplifying region for amplifying light that enters from the light incident portion, is reflected by the reflection portion, and reaches the light emitting portion; and a light incident portion and light emitting portion. An optical amplifier, comprising: a film formed on a surface on which a portion is formed, which suppresses light reflection, wherein the reflection portion has a wavelength dependence in reflectance. 2. The optical amplifier according to claim 1, wherein said reflection section is constituted by a diffraction grating. 3. The optical amplifier according to claim 1, wherein the film for suppressing light reflection at the light incident portion or the light emitting portion is shifted by a predetermined angle from a plane perpendicular to a traveling direction of light reaching the film. An optical amplifier characterized by being formed by: 4. An optical device in which a light emitting element, a light receiving element, and an optical amplifier are mounted on the same substrate, wherein the optical amplifier has a light incident part and a light emitting part formed at different places in the same plane. A reflecting portion for reflecting light incident from the light incident portion and guiding the light to the light emitting portion; and a light incident on the light incident portion, reflected by the reflecting portion, and reaching the light emitting portion. A light amplification region for amplifying, and a film formed on a surface on which the light incident portion and the light emitting portion are formed, which suppresses reflection of light, and amplifies light generated by the light emitting element. An optical device which emits light to the outside, amplifies and outputs incident light to the light receiving element.