JP2001013379A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify constitution and to attain miniaturization by preparing a 1/4 wavelength plate which is arranged so that an optical axis tilts at a specified angle to polarization outgoing from a semiconductor laser and a means which leads the outgoing light passing through the 1/4 wavelength plate to the outside. SOLUTION: This optical module is composed of a semiconductor laser 11, a 1/4 wavelength plate 1, a lens 4 and a ferrule 5 holding the end of an optical fiber 3. An optical signal exiting from the semiconductor laser 11 passes through the 1/4 wavelength plate 1 and is led to the outside passing through the lens 4 and the optical fiber 3 which are means leading out the optical signal. The outgoing light from the semiconductor laser 11 is linear polarization in an X axial direction (Ex direction), and the 1/4 wavelength plate 1 is arranged so that an optical axis tilts at nearly 45 deg. to the linear polarization. At this time, when the linear polarization passes through the 1/4 wavelength plate 1, output becomes circular polarization because the optical axis of the crystal of the 1/4 wavelength plate 1 is made incident at azimuth 45 deg. to a main cross section. And a polarizing direction of return light is orthogonally crossed with the polarizing direction of oscillation light of the semiconductor laser 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module using a semiconductor laser used in a transmission section of optical communication.

[0002]

2. Description of the Related Art Conventionally, in an optical module, light emitted from a semiconductor laser is reflected by an optical fiber or a lens to become return light, and when this return light enters the semiconductor laser, it adversely affects laser oscillation. An optical isolator is used to remove this return light. The optical isolator includes absorption polarizers 2 before and after a Faraday rotator 6 such as a garnet material as shown in FIG.
A magnet 7 is arranged around the periphery.

As the garnet material, for example, Bi
A substituted garnet material, YIG, or the like is used, and the polarizer 2 provided on one or both sides thereof is in a state where the light source side is rotated by 0 ° with respect to the light source side polarizer by 0 ° as a parallel Nicol condition and the return light incident side is rotated by 45 °. Installed and configured. Usually, the garnet material is provided with a magnet 7 around the garnet material to rotate the polarization direction of the incident light within a saturation magnetic field, and is operated in a state where a magnetic field is applied.

[0004]

However, the optical module using the optical isolator has the following disadvantages.

(1) The garnet material used for the Faraday rotator 6 is expensive, so that the optical isolator itself is expensive and its use is restricted.

(2) There is a need to apply a saturation magnetic field to the garnet, and the magnet 7 must be attached, which increases the size of the optical isolator.

(3) Due to the above-mentioned drawbacks, it is difficult to mount on a small and low-priced optical semiconductor module or the like.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems and solves the above-mentioned drawbacks by forming an optical module without using a Faraday rotator such as a garnet material. It was done.

That is, according to the present invention, a semiconductor laser, a quarter-wave plate arranged so that the optical axis is inclined by approximately 45 ° with respect to polarized light emitted from the semiconductor laser, and a light passing through the quarter-wave plate An optical module is provided with means for leading outgoing light to the outside.

Further, the present invention is characterized in that a polarizer is attached to one side of the quarter wavelength plate.

[0011]

Embodiments of the present invention will be described below.

The optical module shown in FIG. 1 has a semiconductor laser 11, a quarter-wave plate 1, a lens 4, and an optical fiber 3.
The optical signal emitted from the semiconductor laser 11 passes through the quarter-wave plate 1 and passes through the lens 4 and the optical fiber 3 which are means for deriving the optical signal. Derived outside.

The light emitted from the semiconductor laser 11 is linearly polarized light in the X-axis direction (here, Ex direction), and the quarter-wave plate 1 is so tilted that its optical axis is inclined by approximately 45 ° with respect to the linearly polarized light. It is arranged. At this time, when the linearly polarized light passes through the quarter wavelength plate 1 as shown in FIG.
Since the optical axis of the crystal of the wave plate 1 is incident on the main section at an azimuth angle of 45 °, the output is circularly polarized. That is, a phase difference π / 2 is generated between an ordinary ray having a plane of polarization in the X direction after passing through the 波長 wavelength plate 1 and an extraordinary light having a plane of polarization in the Y direction. It becomes polarized light.

When this circularly polarized light returns by reflection from the end face of the fiber, the lens surface, or the like, it becomes circularly polarized light in the opposite direction. When this returned light enters the quarter-wave plate 1, the circularly polarized light returns in the Ey direction orthogonal to the originally emitted light. Semiconductor laser 1
Come back to 1. Since the polarization direction of the return light is orthogonal to the polarization direction of the oscillation light of the semiconductor laser 11, problems such as interference and resonance in the semiconductor laser 11 can be prevented.

As another embodiment of the present invention, FIG.
As shown in (b), an absorption type polarizer 2 can be provided on one side of the quarter wavelength plate 1. In this case, if the polarizer 2 is installed so as to satisfy the parallel Nicol condition with respect to the emitted light (the direction of polarized light Ex), the emitted light passes through as it is. Also in this case, as described above, the polarization direction of the reflected return light is 90 °.
Since the return light component rotates and returns, the return light component is in a perpendicular Nicol condition with respect to the polarizer 2, the return light component is absorbed by the polarizer 2, the return light component to the semiconductor laser 11 is removed, and the reflected return light returns to the semiconductor laser 11. And return light can be removed.

As described above, the optical module of the present invention has the following features.
The inconvenience due to the return light can be prevented only by providing the 波長 wavelength plate 1, and it is not necessary to provide the conventional optical isolator.

In the above embodiment, quartz is usually used as the material of the 1/4 wavelength plate 1, and its thickness t
Is set by the following equation.

T = λ / {4 × (Ne−No)} λ: wavelength of semiconductor laser Ne: refractive index of extraordinary ray at wavelength λ of ４ wavelength plate material No: of １ ／ wavelength plate material Refractive index of ordinary ray at wavelength λ With such a configuration, the polarization direction of the return light is perpendicular to the polarization direction of the output light, and thus the adverse effect on the semiconductor laser 11 can be prevented as described above.

Next, 1 / in the optical module of the present invention.
A specific installation structure of the four-wavelength plate 1 will be described.

For example, as shown in FIG. 3A, the quarter-wave plate 1 may be joined to a circular substrate 12 having a hole, and the circular substrate 12 may be joined to a predetermined position. Alternatively, as shown in FIG. 3B, the 波長 wavelength plate 1 can be mounted upright on the substrate 13 and fixedly mounted, and the substrate 13 can be joined to a predetermined portion. Alternatively, as shown in FIG. 3C, the quarter-wave plate 1 can be mounted by joining the end face of the ferrule 5 on which the optical fiber 3 is mounted.

FIG. 4 shows an embodiment in which the quarter-wave plate 1 is also used as a laser-tight window of the package 14 accommodating the semiconductor laser 11.

FIG. 4A shows a quarter-wave plate 1 fixedly mounted on a hermetic window of a package 14 of a CAN type laser. FIG. 4B shows a butterfly type package 1.
The quarter-wave plate 1 is fixedly mounted on the hermetic window 5. In any case, by using the airtight window and the quarter-wave plate 1 together, the number of components can be reduced and the size can be reduced.

FIG. 5 shows still another embodiment.
(A) shows an optical isolator function by mounting and fixing a quarter-wave plate 1 between a semiconductor laser 11 and a groove 16a on which an optical fiber is mounted on a Si substrate 16 used for a surface mount module. Can be added. FIG.
(B) shows 1/1 on the end face of the cylindrical body 17 holding the lens 4.
The four-wavelength plate 1 is mounted and fixed, and a function including a coupling system is added as an optical isolator with a lens.

In these embodiments, a low-melting glass, an organic adhesive, metal solder, or the like is used as an adhesive for joining the quarter-wave plate 1. In each embodiment, the absorption polarizer 2 may be fixed adjacent to one surface of the quarter-wave plate 1.

In these embodiments, only the quarter-wave plate 1 needs to be provided, and no magnet is required. Therefore, an optical module having a simple structure and an optical isolator function can be obtained.

[0026]

As described above, the optical module of the present invention has the following excellent effects.

(1) Since no Faraday rotator or magnet is used, the optical isolator function can be realized at a low cost with a simple configuration, and a compact configuration can be achieved.

(2) Since it is only necessary to provide a single quarter-wave plate, an optical module having an integrated and miniaturized optical isolator function can be easily obtained.

(3) If the quarter-wave plate is used also as a hermetic window for the semiconductor laser, a semiconductor laser having an optical isolator function with a reduced number of parts and a reduced size can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an optical module of the present invention.

FIGS. 2A and 2B are diagrams illustrating the principle of an optical module according to the present invention.

FIGS. 3A to 3C are views showing a mounting and fixing structure of a 波長 wavelength plate in the optical module of the present invention.

FIGS. 4A and 4B are views showing a mounting and fixing structure of a 波長 wavelength plate in the optical module of the present invention.

FIGS. 5A and 5B are views showing a mounting and fixing structure of a 波長 wavelength plate in the optical module of the present invention.

FIG. 6 is a sectional view showing a conventional optical isolator.

[Explanation of symbols]

 1: 1/4 wavelength plate 2: Polarizer 3: Optical fiber 4: Lens 5: Ferrule 11: Semiconductor laser

Claims (7)

[Claims] 1. A semiconductor laser, comprising: a semiconductor laser; and an optical axis inclined by approximately 45 ° with respect to polarized light emitted from the semiconductor laser.
An optical module comprising: a 波長 wavelength plate; and means for guiding outgoing light passing through the 波長 wavelength plate to the outside. 2. The optical module according to claim 1, wherein a polarizer is mounted on one surface of said quarter-wave plate. 3. The optical module according to claim 1, wherein the quarter-wave plate is fixed by a substrate or a cylindrical body. 4. The semiconductor device according to claim 1, wherein said quarter-wave plate is provided as an airtight window in a semiconductor laser package.
Or the optical module according to 2. 5. The optical module according to claim 1, wherein the quarter-wave plate and the semiconductor laser device are provided on an integrated substrate. 6. The optical module according to claim 1, wherein said quarter-wave plate is mounted integrally with a coupling lens. 7. The optical module according to claim 1, wherein the quarter-wave plate is provided on an end face of the optical fiber.