JPH02135416A - Optical isolator and semiconductor laser device therewith - Google Patents

Abstract

PURPOSE:To reduce the number of parts required for an optical isolator by using a magneto-optical crystal formed with hologram on the surface as a Farady rotator and transforming the form of a light beam passed through the magneto-optical crystal by means of the hologram on the surface of the crystal. CONSTITUTION:Linearly polarized light passed through a polarizer 11 out of the light emitted from a semiconductor laser element 1 receives a Farady effect when the polarized light passes a magneto-optical crystal 4 and its polarizing direction is turned by 45 deg.. At this time, the light emitted from the element 1 is transformed into parallel beam of light by means of a Fresnel lens 12 and emitted through an analyzer 7, the transmitting polarizing direction of which is arranged at 45 deg. to the polarizer 11. On the other hand, in the reflected light to the element 1, the component parallel to the transmitting polarizing direction of the analyzer 7 is passed through the analyzer 7, and receives a Farady effect of 45 deg. when the component is passed through the crystal 4 in the course of the component concentrated to the element 1 by means of the lens 12. The reflected light received the 45 deg. Farady effect cannot pass through the polarizer 11, because the polarizing direction is further turned by 45 deg. due to non- reciprocity of the Farady effect.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical isolator and a semiconductor laser module with an optical isolator used in optical communication, optical control, optical recording, etc.

Conventional technology Optical communication, optical control, and optical control using semiconductor laser elements as light sources
In optical transmission systems such as optical recording, when reflected light from a reflective end in the optical transmission system returns to the active layer of a semiconductor laser element, the reflected return light induces noise, making the operation of the semiconductor laser element unstable. , transmission quality deteriorates. Therefore, in order to prevent the reflected return light from returning to the active layer of the semiconductor laser element and obtain a stable light source, an optical isolator is installed in front of the light source, or a semiconductor laser module with an optical isolator is used. .

As a conventional technology for optical isolators, Applied Optical (AI) I)lied 0p published in 1988
tics) Vol. 27, No. 7, page 1329, the optical isolator itself did not have a beam conversion function.

Semiconductor lasers with optical isolators are cheaper than conventional ones,
Aiming for high reliability and miniaturization, efforts have been made to reduce the number of parts. For example, in Japanese Patent Application Laid-open No. 57-173992, a magneto-optical crystal Y! F esO+a (Y I
G) is described in which it is processed into a spherical shape to have a lens function, and in JP-A-58-185535, a magneto-optic crystal is used as a window material for the hermetic sealing cap of a semiconductor laser, and furthermore, a hermetic sealing method is described. A magneto-optical crystal used as a window material for a stopper cap with a hemispherical lens integrated therein is described. FIG. 9 shows a configuration diagram of a semiconductor laser with an isolator in which a hemispherical lens is integrated with a magneto-optic crystal used as a window material of a hermetic sealing cap disclosed in Japanese Patent Application Laid-Open No. 58-185535. In order to prevent end face deterioration and maintain reliability, a magneto-optic crystal 4 with a hemispherical lens 3 integrated is used as a window material of a hermetically sealed cap 2 of a semiconductor laser device 1 which is hermetically sealed.
A configuration is adopted in which the light emitted from the semiconductor laser element 1 is converted into parallel light and emitted from the airtight sealing cap 2, and is focused onto the optical fiber 6 by the second lens 5. In addition, magneto-optic crystal 4
is the thickness that gives a Faraday rotation angle of 45 degrees,
There is a gap of 45 de between the hermetic sealing cap 2 and the second lens 5.
The analyzer 7 is arranged at an angle through which the emitted light subjected to the Faraday rotation angle of g can be transmitted, and a permanent magnet 8 is arranged around the hermetic sealing cap 2 to provide a saturation magnetic field to the magneto-optic crystal 4.

Optical isolators work as follows.

The emitted light from the semiconductor laser element 1 is linearly polarized light, and the magneto-optic crystal magnetized by the permanent magnet 8 used as the window material before being emitted to the outside of the hermetic sealing cap 2 through the window. At that time, the polarization direction of the linearly polarized light is rotated by 45 degrees, and the polarization direction of the linearly polarized light is rotated by 45 degrees with respect to the polarization direction of the linearly polarized light emitted from the semiconductor laser element 1. Transmits photon 7.

On the other hand, the reflected light from the end of the optical fiber or during optical fiber transmission is emitted from the optical fiber 6 toward the analyzer 7, and the component parallel to the transmitted polarization direction of the analyzer 7 is transmitted and transmitted through the magneto-optic crystal 4. It is sometimes subjected to a Faraday rotation of 45 degrees. The reflected light that has undergone 45 degrees of Faraday rotation has its polarization direction further changed by 45 degrees due to the non-reciprocity of the Faraday effect.
In other words, the polarization direction is perpendicular to the polarization direction of the emitted light from the semiconductor laser device 1, and is coupled to the active layer of the semiconductor laser device 1 by the lens 2. Since the reflected light from the end of the optical fiber or during optical fiber transmission has a polarization direction perpendicular to the polarization direction of the emitted light from the semiconductor laser device 1, even if it is coupled to the active layer of the semiconductor laser device 1, Noise is induced (and the operation of the semiconductor laser device 1 is not disturbed by reflected light from the end of the optical fiber or during optical fiber transmission).

Problems to be Solved by the Invention However, conventional optical isolators do not have a beam conversion function, so when an optical isolator is placed in front of a semiconductor laser to form an optical system, it is difficult to condense the spread beam emitted from the semiconductor laser. lenses are essential for
There was a problem that the number of parts increased. Further, a lens is usually required between the semiconductor laser and the optical isolator, and a device must be devised to prevent the reflected light from the end face of the lens from returning to the semiconductor laser.

Regarding semiconductor laser devices with optical isolators, the number of parts has been reduced by the method explained in the example of the conventional technology, but it is possible to reduce the number of parts by using refraction such as a hemispherical lens in the window of the hermetic sealing cap of the semiconductor laser element. In the method of integrating a refractive lens, the size of the refractive lens is determined by the desired beam shape conversion, so the inside of the hermetic sealing cap becomes wider, and the area of the window of the hermetic sealing cap increases. It was not practical in terms of reliability, ease of manufacture, ease of use, etc. due to its large size.

Means for Solving the Problems The present invention solves the above problems and uses a magneto-optic crystal with a hologram formed on the surface as a Faraday rotator of the optical isolator in order to easily realize an optical isolator that also has a beam conversion function. The present invention provides an optical isolator characterized in that the beam shape of light passing through the magneto-optic crystal is changed by a hologram on the surface of the magneto-optic crystal. In addition, the present invention solves the above problems and realizes a semiconductor laser device with an optical isolator that is easy to manufacture and has a small number of practical parts. The present invention provides a semiconductor laser device with an optical isolator, which is characterized in that it is used as a material.

Function: By using the optical isolator of the present invention, a beam conversion function can be added without changing the shape or size of the optical isolator itself, the number of parts in the optical system can be reduced, and the return light from the lens end face can be reduced. There is no need to prevent the laser from returning to the semiconductor laser, which is practically effective. If the semiconductor laser device with an optical isolator of the present invention is used,
A semiconductor laser device with an optical isolator that is easy to manufacture, small in size, highly reliable, highly practical, and has a small number of parts can be easily obtained.

Embodiment A block diagram of an embodiment of the optical isolator of the present invention is shown in FIG. a polarizer 11, an analyzer 7 whose transmission polarization direction is arranged at an angle of 45 degrees with the transmission polarization direction of the polarizer 11, a permanent magnet 8 for applying an external saturation magnetic field to the magneto-optic crystal 4,
and a hologram function, that is, a Fresnel lens 12 on the surface.
It is composed of a magneto-optic crystal 4 formed with. As the magneto-optic crystal 4, a (B i LuGd
) sFesO+2 replaced with Mg-Zr-Ca GdaGas
Liquid phase epitaxial growth on an O+* substrate was used. The Fresnel lens 12 is made of SiO2 on the magneto-optic crystal 4.
was deposited by RF sputtering, a resist was applied thereon, a Fresnel lens 12 was patterned by photolithography, dry etching was performed using the resist as a mask, and the resist pattern was transferred to SiO2. In this embodiment, the Fresnel lens 12 is formed on the light exit side of the surface of the magneto-optic crystal 4, but in the present invention, the Fresnel lens 12 may be formed on the light incidence side of the surface of the magneto-optic crystal 4. Further, in the present invention, the method for forming the Fresnel lens may be different from that in the embodiments, such as using an electron beam exposure device.

The distance between the semiconductor laser element 1 and the magneto-optic crystal 4 is approximately 3.5
mm, the pitch of the outermost circumference of the Fresnel lens 12 is approximately 3
．． When the diameter was 5 μm, parallel light with a beam diameter of about 2 mm was obtained. 50 is a base substrate, and 60 is a lead.

The optical isolator of the first embodiment operates as follows. Of the light emitted from the semiconductor laser element 1, the polarizer 1
The linearly polarized light transmitted through magneto-optic crystal 4 is subjected to the Faraday effect and its polarization direction is rotated by 45 degrees when it passes through magneto-optic crystal 4 . At this time, the spread light emitted from the semiconductor laser element 1 is converted into parallel light by the Fresnel lens 12. Then, the light passes through the analyzer 7 whose transmission polarization direction is arranged at 45 degrees with respect to the polarizer 11 and is emitted. On the other hand, in the reflected light to the semiconductor laser l, a component parallel to the transmission polarization direction of the analyzer 7 is transmitted, and on the way to being focused on the semiconductor laser element 1 by the Fresnel lens 12, it is transmitted through the magneto-optic crystal 4. It is sometimes subjected to a Faraday rotation of 45 degrees. The reflected light that has undergone 45 degrees of Faraday rotation has its polarization direction further changed by 45 degrees due to the non-reciprocity of the Faraday effect, that is, the polarization direction is orthogonal to the transmitted polarization direction of the polarizer 11. It cannot be penetrated.

FIG. 2 shows a configuration diagram of a semiconductor laser device with an optical isolator as a second embodiment of the present invention.

A magneto-optic crystal 4 having a Fresnel lens 11 formed thereon as an example of a hologram was used as a window material for the window of the hermetic sealing cap 2 of the semiconductor laser device 1.

The magneto-optic crystal 4 is made of (B i
The Fresnel lens 12 is made by depositing S i 02 on the magneto-optic crystal 4 by RF sputtering, and applying a resist on top of it. Fresnel lens 12 using photolithography
A patterning process was performed, dry etching was performed using the resist as a mask, and the resist pattern was transferred onto SiO2. In the second embodiment, the Fresnel lens 12 was formed on the light exit side of the surface of the magneto-optic crystal 4, but in the present invention, as shown in FIG. 3 as a third embodiment, the Fresnel lens 12 is formed on the magneto-optic crystal 4. Alternatively, the hermetic sealing cap 2 may be formed on the light incident side of the surface of the cap 2 as shown in FIG. 4 as a fourth embodiment.
The light exit window may be tilted with respect to the cavity surface of the semiconductor laser device 1. Furthermore, in the present invention, the shape of the hermetic sealing cap and the mounting shape of the semiconductor laser element does not matter;
As shown in the embodiment, a plate-shaped hermetic sealing cap 2 is used to hermetically seal the semiconductor laser device 1 from a fiber fixing location that is difficult to hermetically seal in a flat package.
A magneto-optic crystal 4 having a Fresnel lens 12 formed on its surface may be used as the window material. Furthermore, the function of the hologram used in the optical isolator and semiconductor laser device of the present invention is not limited to the light focusing function as shown in the first to fifth embodiments, but also the function of the hologram as shown in the sixth embodiment shown in FIG. It is also possible to convert the beam shape to parallel light as shown (,
As shown in FIG. 7 as a seventh embodiment, the shape of the emitted beam may be divided into two or more beams 9. Further, the application of the semiconductor laser device with an optical isolator of the present invention is not limited to communications, but may also constitute a light source for optical recording, optical measurement, etc.

FIG. 8 shows an eighth embodiment of the present invention in which a light source for optical recording is constructed using the semiconductor laser device with an optical isolator of the present invention. In the present invention, the method for forming the Fresnel lens may be different from that in the embodiments, such as using an electron beam exposure device.

The operation of the semiconductor laser device with an optical isolator of the present invention will be explained using a second embodiment. The emitted light from the semiconductor laser element 1 is linearly polarized light, and when it passes through the window made of the magneto-optic crystal 4 and is emitted to the outside of the hermetic sealing cap 2, the linearly polarized light emitted from the semiconductor laser element 1 becomes a Faraday light. Due to this effect, the polarization direction is rotated by 45 degrees. Further, at this time, the spread beam shape emitted from the semiconductor laser element 1 is converted by the Fresnel lens 12 formed on the surface of the magneto-optic crystal 4 into a beam shape converging on the end face of the optical fiber 6. The linearly polarized light transmitted through the window made of the magneto-optic crystal 4 is transmitted polarized with respect to the polarization direction of the linearly polarized light emitted from the semiconductor laser element 1 disposed between the hermetic sealing cap 2 and the optical fiber 6. 45deg direction
The light can be transmitted through an analyzer 7 arranged in the same manner as shown in FIG. On the other hand, the reflected light from the end face of the optical fiber 8 or the middle of the optical fiber transmission is transmitted from the optical fiber 6 to the analyzer 7.
A component parallel to the transmitted polarization direction of the analyzer 7 is transmitted toward the Fresnel lens 12 on the surface of the magneto-optic crystal 4.
While the light is being focused on the semiconductor laser device 1, it is subjected to a Faraday rotation of 45 degrees while passing through the magneto-optic crystal 4. The reflected light that has undergone Faraday rotation of 45 degrees has its polarization direction further changed by 45 degrees due to the non-reciprocity of the Faraday effect, that is, the polarization direction is orthogonal to the polarization direction of the emitted light from the semiconductor laser element 1, and the semiconductor laser It is coupled to the active layer of device 1. In addition, the reflected light from the end face of the optical component inside the module behind the window made of magneto-optic crystal 4 maintains the polarization direction immediately after passing through the window made of magneto-optic crystal 4, and passes through magneto-optic crystal 4 again. sometimes 4
It is subjected to 5 degrees of Faraday rotation. The reflected light that has been subjected to 45 degrees of Faraday rotation has its polarization direction further changed by 45 degrees due to the non-reciprocity of the Faraday effect, that is, the polarization direction is perpendicular to the polarization direction of the emitted light from the semiconductor laser element 1, and the Fresnel lens 12 is coupled to the active layer of the semiconductor laser device 1 by. The reflected return light from the end of the optical fiber, the optical fiber transmission midway, and the reflected return light from the end face of the optical component inside the module located after the window made of the magneto-optic crystal 4 are in the polarization direction of the light emitted from the semiconductor laser element 1. Because the polarization direction is perpendicular to the 100% polarization direction, even if it is coupled to the active layer of the semiconductor laser device 1, it will not induce noise, and the end face of the optical component inside the module behind the window made of the magneto-optic crystal 4. The operation of the semiconductor laser device 1 is not disturbed by light or reflected light from the fiber end or during optical fiber transmission. A semiconductor laser device with stable operation can be easily constructed with a small number of parts.

Effects of the Invention By using the optical isolator of the present invention, a beam conversion function can be easily provided, the number of parts of an optical system that requires the optical isolator is reduced, and handling becomes easy. Further, by using the semiconductor laser device with an optical isolator of the present invention, the number of parts of the module is reduced, the manufacturing becomes easy, the cost becomes low, the device can be miniaturized, and it becomes practical. In addition, the semiconductor laser device with an optical isolator of the present invention does not use any adhesive or the like when integrating the lens function, so it is highly reliable and is driven at a constant optical output of 5mW at an ambient temperature of 70"C in a lifetime test. At that time, we were able to guarantee a lifespan of over 400,000 hours.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical isolator according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a semiconductor laser device with an optical isolator according to a second embodiment of the present invention when used as a light source for communication. FIGS. 3 and 4 are enlarged sectional views of the hermetic sealing cap portions of the third and fourth embodiments of the present invention, and FIG. 5 is an illustration of the present invention. FIGS. 6 and 7 are configuration diagrams of a semiconductor laser device with an optical isolator according to a fifth embodiment of the invention when it is mounted in a flat package.
The figures are cross-sectional and perspective views for explaining the beam shape converted by the hologram formed on the surface of the magneto-optic crystal as eighth and seventh embodiments of the present invention.
FIG. 9 is a configuration diagram of a semiconductor laser device with an optical isolator according to the prior art of the present invention, in which a semiconductor laser device with an optical isolator is used as a recording light source. 1... Semiconductor laser element, 4I... Magneto-optic crystal, 7
...Analyzer, 8...Permanent magnet, 11."! Photon, 1
2...Fresnel lens. Name of agent: Patent attorney Shigetaka Kurino and one other person Figure 2 Figure 4 Magneto-optical equipment Figure Figure Figure 4

Claims (2)

[Claims] (1) An optical isolator characterized in that a magneto-optic crystal with a hologram formed on its surface is used as a Faraday rotator, and the beam shape of light passing through the magneto-optic crystal is converted by the hologram on the surface of the magneto-optic crystal. . (2) A semiconductor laser device with an optical isolator, characterized in that a magneto-optical crystal with a hologram formed on its surface is used as a window material of an airtight sealing cap.