JPH04235524A - Optical isolator for semiconductor laser module - Google Patents

Abstract

PURPOSE:To set an inclination angle between the optical axis of a module and a optical unit with high precision by sticking and fixing the optical unit and a magnet on the sheet of transparent plate. CONSTITUTION:Rutile crystals 11 and 12 serving as the first and second birefringent optical elements are mutually stuck and fixed, having a YIG crystal 21 in Faraday revolution interposed between them, and the optical unit of an isolator is constituted as a whole. This optical unit is positioned in the center hole of a ring shaped magnet 31, and stuck and fixed on one sheet of glass plate 4, together with a magnet 31. Accordingly, the magnet 31 and the optical unit are not directly attached to each other. With this constitution, positional relation between the magnet 31 and the optical unit is kept through the glass plate 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator that is mounted and used in a semiconductor laser module used for optical communication and optical information processing.

0002

[Prior Art] An optical isolator is an optical component that transmits light in one direction and blocks light in the opposite direction. It is mainly mounted inside a semiconductor laser module, and is an optical isolator that is an optical component that transmits light in one direction and blocks light in the opposite direction. This is used to prevent the reflected light from being re-injected into the semiconductor laser.

As shown in FIG. 2, a conventional optical isolator consists of a Faraday rotator 22, two birefringent materials 51 and 52, and a ring-shaped magnet 32 with a hole in the center. In this case, the unit composed of the Faraday rotator 22 and the birefringent materials 51 and 52 bonded to each other is called an optical unit, and the optical unit is bonded and fixed inside the center hole of the magnet 32. The operating principle of this type of optical isolator is described in detail in other documents (for example, "Introduction to Optical Device Technology", Gijutsu Hyoronsha, published June 25, 1980, pages 128-135). , will be omitted here.

0004

When an optical isolator is used inside a semiconductor laser module, the optical isolator is inserted and fixed within the optical axis of a lens coupling system that optically couples the semiconductor laser and the optical fiber. A conventional method for fixing an optical isolator inside a semiconductor laser module is as shown in Figure 3(A).
holder 9 to which the laser 7, lens 8, and optical fiber 10 are fixed
Alternatively, there is a method of directly fixing the magnet 32 of the optical isolator 6 with adhesive, or a method of fixing the magnet 32 to the holder 9 with screws 100 as shown in FIG. 3(B).

[0005] In semiconductor laser modules for coherent communication and semiconductor laser modules for analog transmission, in which light reflected from the end face of an optical unit is a problem, the light reflected from the optical fiber is reinjected into the semiconductor laser. In order to prevent this, it is necessary to tilt the end face of the optical unit of the optical isolator by about 2 degrees with respect to the optical axis of the semiconductor laser module.

On the other hand, while the dimensional accuracy when forming a hole in the center of the magnet 32 is on the order of 0.1 mm, the length of the optical unit is as short as several millimeters. There may be cases where the magnet is attached inside the magnet at an angle of about 1 to 2 degrees with respect to the magnet.

Therefore, when mounting an optical isolator in a semiconductor laser module, even if the fixed surface of the magnet 32 is set at an angle to the holder 9, the angle of inclination of the optical unit inside the magnet and the magnet set on the holder 9 will be different. There is a possibility that the inclination angles of the fixed surfaces cancel each other out and the optical unit does not incline with respect to the module optical axis. That is, Fig. 3 (A
The fixing methods shown in ) and (B) have the disadvantage that it is difficult to fix the optical isolator at an appropriate inclination angle with respect to the optical axis of the semiconductor laser module.

Furthermore, as mentioned above, since the gap between the magnet 32 and the optical unit is on the order of 0.1 mm, the adhesive layer for fixing the optical unit within the magnet becomes thicker, and the adhesive layer deteriorates over time. Another drawback is that the optical unit tends to tilt with respect to the optical axis of the semiconductor laser module due to the change in shape.

Furthermore, in conventional isolators, the optical unit and the magnet are directly bonded, so if the coefficients of thermal expansion of the two are different, the optical elements of each part of the optical unit may be affected by the magnet due to changes in the environmental temperature. There is a risk that the adhesive surface between the Faraday rotator and the birefringent optical material will peel off due to the tensile force.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical isolator for a semiconductor laser module which can eliminate the above-mentioned drawbacks and which can be fixed at an appropriate inclination angle with respect to the optical axis of the semiconductor laser module.

[0011]

[Means for Solving the Problems] An optical isolator for a semiconductor laser module according to the present invention includes first and second optical elements having birefringence, and a Faraday rotation sandwiched between the first and second optical elements. and a magnet for applying a magnetic field to the Faraday rotator, and the optical unit and the magnet maintain a mutual positional relationship. It is glued and fixed onto a transparent plate.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a longitudinal sectional view of an optical isolator for a semiconductor laser module according to the present invention. Rutile crystals (TiO2) 11 and 12 as first and second birefringent optical elements
is a Faraday rotator YIG crystal (Y3 Fe5
They are adhesively fixed to each other with O12)21 in between, and constitute an optical unit of an optical isolator as a whole.

Further, this optical unit is located in the center hole of the ring-shaped magnet 31, and is adhesively fixed together with the magnet 31 to a transparent plate, here a glass plate 4. As is clear from the figure, the magnet 31 and the optical unit are not directly bonded to each other. With the above configuration, the positional relationship between the magnet and the optical unit is maintained through the glass plate.

Furthermore, in order to mount the present optical isolator inside a semiconductor laser module, the glass plate 4 can be fixed to the holder 9 by adhesive or screws using a structure similar to that shown in FIG. In this case, the angle of inclination between the optical axis of the semiconductor laser module and the end face of the optical unit is
Since it is determined by the fixed angle of the glass plate 4 with respect to the holder 9
The processed shape allows the optical isolator to be accurately fixed to the optical axis of the semiconductor laser module.

Furthermore, since the glass plate 4 and the optical unit are fixed via a thin adhesive layer, there is little change in the shape of the adhesive layer over time. Therefore, the tilt angle of the optical unit with respect to the optical axis of the semiconductor laser module can be stabilized over a long period of time.

[0016]

[Effects of the Invention] Since the present invention is constructed as described above, it is possible to obtain the following effects. (1) When used inside a semiconductor laser module, the transparent plate to which the optical unit is glued can be directly fixed to the structure of the semiconductor laser module, so the optical axis of the module and the optical unit can be directly fixed. The inclination angle can be set with high precision. (2) The adhesive layer that adheres the transparent plate and the optical unit is thin, and the shape of the adhesive layer does not change much over time, so the optical unit can be maintained in a stable state with respect to the optical axis of the semiconductor laser module over a long period of time. Ru. (3) Since the magnet and optical unit are not directly bonded, even if there is a difference in thermal expansion coefficient between the two, there is a risk that the components of the optical unit may separate due to the tensile force of the magnet. do not have.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention.

FIG. 2 is a structural diagram of a conventional optical isolator.

FIG. 3 is a mounting structure diagram when a conventional optical isolator is mounted on a semiconductor laser module.

[Explanation of symbols]

11, 12 Rutile crystal 21 YIG crystal 22 Faraday rotator 31, 32 Magnet 4 Glass plate 51, 52 Birefringent material 6 Optical isolator 7 Semiconductor laser 8 Lens 9 Holder 100 screw

Claims (1)

[Claims] 1. An optical unit comprising first and second optical elements having birefringence, and a Faraday rotator sandwiched between the first and second optical elements, and a Faraday rotator. An optical isolator for a semiconductor laser module having a magnet for applying a magnetic field to a rotor, wherein the optical unit and the magnet are adhesively fixed on one transparent plate.