JP2000081546A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module excellent in stability of laser diode operation and also having a high coupling efficiency. SOLUTION: An optical waveguide 110 is provided with engraved faces 113, and one of the engraved faces 113 is used as a light incident plane 114. Laser light P0 is made incident thereon with an incident angle made to a Brewster angle θB. Reflection of the laser light P0 is suppressed on the incident plane 114 by making the incident angle to a Brewster angle θB, and most of the incident light becomes refracted light P1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module having a light supply means and an optical waveguide.

[0002]

2. Description of the Related Art Hitherto, as this type of optical module, there is known an optical module in which an incident portion of an optical waveguide is formed in a sawtooth shape. Documents that disclose an optical module using an optical waveguide having such a shape include, for example, the following.

[0003] IEEE PHOTONICS TECHNOLOGY LETTERS VO
L.7, NO.1, JANUARY 1995, pp.44-46 ELECTRONICS LETTERS 3rd
August 1995 vol. 31 No16,
pp. 1336-1367

[0004]

FIG. 3 is a cross-sectional view schematically showing a main part of such an optical module.

[0005] As shown in FIG.
It has a serrated surface 311, one of which is an inclined surface 312. The light incident from the incident surface 312 propagates through the core 313.

The angle of inclination of the incident surface 312 is 20 to 35 degrees with respect to the end surface 314 of the optical waveguide. Therefore, the laser light _{P 0} which is output from the active layer 321 of the laser diode 320 is incident surface 3 at an incident angle of 20 to 30 degrees
12 is irradiated. Then, a part of the laser light P ₀ (refracted light P ₁ ) is guided into the core 313, and the other light (reflected light P ₂ ) is reflected on the incident surface 312.

Here, the angle of reflection coincides with the angle of incidence θ _LD according to the law of reflection, so that the angle between the laser light P ₀ and the reflected light P ₂ is 2θ _LD .

Therefore, by appropriately setting the incident angle θ _LD , it is possible to prevent the reflected light P ₂ from irradiating the laser diode 320. Thus, the reflected light P ₂ since it is possible to prevent the adverse effects on the laser diode 320, it is possible to maintain the stability of operation of the laser diode 320.

However, in the optical module shown in FIG. 3, the reflected light P ₂ becomes lossy light. Therefore,
Conventionally, this type of optical module has a disadvantage that the light coupling efficiency is deteriorated because the reflectance of the incident surface 312 is increased.

For this reason, an optical module having high operation stability and high coupling efficiency has been desired.

[0011]

(1) The present invention relates to an optical module including a light supply unit for outputting a light wave and an optical waveguide for transmitting the light wave received from the light supply unit.

Then, the incident angle of the light wave on the incident surface of the optical waveguide is made substantially the same as the Brewster angle.

According to such a configuration, the TM on the incident surface
Since the wave reflectance can be made zero, the coupling rate of the optical module can be improved without impairing the operation stability.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the size, shape, and arrangement of each component are only schematically shown to an extent that the present invention can be understood, and numerical conditions described below are merely examples. Please understand that.

FIGS. 1A and 1B are diagrams schematically showing a main configuration of an optical module according to this embodiment, wherein FIG. 1A is a cross-sectional view and FIG. 1B is a plan view.

In FIG. 1, an optical waveguide 110 includes a clad 111 and a core 112. The core 112 is
The refractive index is formed to be, for example, about 0.4% larger than that of the cladding 111.

The optical waveguide 110 has a serrated surface 113.
Are formed. One inclined surface of the cut surface 113 is used as a light wave incident surface 114. The entrance end of the core 112 is formed on the entrance surface 114. In this embodiment, the inclination angle of the incident surface 114 with respect to the side surface 115 of the optical waveguide 110, substantially identical to the Brewster angle theta _B below.

The laser diode 120 has a cladding layer 1
21 and an active layer 122. Then, the light wave P ₀ is output from the active layer 122. The laser diode 120 is disposed such that the incident angle θ _LD of the light wave P ₀ with respect to the incident surface 114 of the optical waveguide 110 substantially matches the Brewster angle θ _B. That is, the active layer 122
The laser diode 120 is arranged so that the hetero interface of the optical waveguide 110 is parallel to the side surface 115 of the optical waveguide 110.

Here, the refractive index of the _air is n _air , and the core 11
2 is _ng , the incident angle θ _LD of the light wave P ₀ (that is, the Brewster angle θ _B ) and the refraction angle θ of the refracted light P _1
The following equation (1) holds between _G and _G according to Snell's law. That is, the refraction angle θ _G depends on n _air , _ng and θ _B. In this embodiment, the incident surface 114 and the core 1
The angle formed with the refraction angle 12 is matched with the refraction angle θ _G.

N _air × sin θ _B = n _g × sin θ _G (1) Next, the operating principle of the optical module shown in FIG.
This will be described with reference to the graph of FIG.

In the ordinary laser diode 120, when a light wave is output, a mode in which the electric field is deviated in a direction parallel to the active layer 122 (hetero interface), that is, TE (Transverse El
ectric) mode oscillates. For this reason, the polarization direction of the light wave P ₀ emitted from the laser diode 120 is as shown in FIG.
(The direction perpendicular to the plane of FIG. 1B). Then, the light wave P ₀ is incident on the incident surface 114 at an incident angle that matches the Brewster angle.

Here, as shown in FIG. 2, when the light wave P ₀ is incident on the surface where the refractive index changes discontinuously, the angle dependence of the reflectivity depends on the TE wave and the TM (Transverse Magnetic).
Different with the waves. FIG. 2 shows that the refractive index n _air of _air is 1,
The refractive index n _g of the core 112 shows the case of 1.5, the horizontal axis represents light wave P ₀ incident angle, and the vertical axis is the reflectivity.

As can be seen from FIG. 2, the reflectance of the TE wave is
It increases as the angle of incidence increases. On the other hand, the reflectance of the TM wave decreases as the incident angle increases up to a predetermined angle (Brewster angle),
It becomes zero at Brewster's angle. At a Brewster angle or more, the reflectance of the TM wave increases as the incident angle increases.

In the optical module according to this embodiment,
The lightwave P ₀ is in TE mode (ie, polarized light parallel to the plane of incidence 114) for the laser diode 120,
The incident surface 114 is in the TM mode (that is, polarized light perpendicular to the TE mode). Therefore, by making the incident angle of the light wave P ₀ substantially equal to the Brewster angle, the reflectance at the incident surface 114 can be made substantially zero.

As can be seen from FIG. 2, the Brewster angle θ _B in this embodiment (ie, when n _air = 1 and _ng = 1.5) is about 56.5 degrees.

As described above, in the optical module according to this embodiment, since the incident angle of the light wave P _{0 on} the incident surface 114 is set to the Brewster angle θ _B , the optical loss due to reflection can be made substantially zero. it can. Therefore, according to this embodiment, the coupling efficiency of the optical module can be improved.

Further, by eliminating the reflection on the incident surface 114, the reflected light can be prevented from adversely affecting the laser diode 120.
The operation stability of 0 can be maintained.

In this embodiment, the optical waveguide 11
Although a flat type is used as 0, the same effect can be obtained when an optical fiber is used.

In this embodiment, a laser diode is used as the light supply means, but another supply means or the like may be used. For example, the effects of the present invention can be obtained even when an element other than the light emitting element such as an optical amplifier is used as the light supply unit.

[0030]

As described above in detail, according to the present invention, it is possible to provide an optical module having high operation stability and high coupling efficiency.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a configuration of a main part of an optical module according to an embodiment, wherein (A) is a cross-sectional view and (B) is a plan view.

FIG. 2 is a graph showing light reflection characteristics of the optical module according to the embodiment.

FIG. 3 is a cross-sectional view schematically showing a configuration of a main part of a conventional optical module.

[Explanation of symbols]

 Reference Signs List 110 optical waveguide 111 clad 112 core 113 cut surface 114 incident surface 115 side surface 120 laser diode 121 clad layer 122 active layer

Continuation of the front page (72) Inventor Yoshihiko Kobayashi 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. F term (reference) 2H037 BA02 CA10

Claims (4)

[Claims] 1. An optical module comprising: a light supply unit for outputting a light wave; and an optical waveguide for transmitting the light wave received from the light supply unit, wherein an angle of incidence of the light wave on an incident surface of the light waveguide is Brew. An optical module characterized by having substantially the same star angle. 2. The optical module according to claim 1, wherein said light supply means is a semiconductor laser. 3. The optical module according to claim 1, wherein the optical waveguide has a saw-toothed cut surface, and one inclined surface of the cut surface is the incident surface. 4. The optical module according to claim 3, wherein an inclination angle of the inclined surface substantially matches the Brewster angle.