JPS6353514A - Optical isolator - Google Patents

Abstract

PURPOSE:To reduce the size, weight, and cost of an optical isolator, by providing an optical waveguide and a grating coupler and 1/4-wave plate installed to the optical waveguide. CONSTITUTION:A luminous flux 20 is guided into an optical waveguide 9 and propagated as TE-mode parallel wave-guided light 10. The light 10 is diffracted by a grating coupler 11 and made incident on a substrate 21 in the direction from the top to the bottom as linearly polarized light 12 having the plane of vibration in the C-C direction. The linearly polarizing light 12 is made incident on an 1/4-wave plate 15 after advancing straight through an optical waveguide 13 without being diffracted by a grating coupler 14 and emitted as circularly polarized light 16. On the other hand, when the same circularly polarized light 17 as the emitted light 16 is made incident on the wave plate 15 from the bottom, the light after passing through the wave plate 15 becomes linearly polarized light having the plane of vibration in the B-B direction and made incident on the optical waveguide 13. The linearly polarized light made incident on the waveguide 13 is diffracted by the grating coupler 14 and emitted as a luminous flux 22 after it is propagated in the C-C direction as TE-mode wave-guided light 19. The other part of the incident light 17 is not diffracted, but emitted to the outside as linearly polarized light 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to optical isolators, and particularly relates to optical isolators using optical waveguides.

[Prior Art and Problems Therewith] A so-called optical isolator is used as an optical element that allows or does not allow light to pass depending on the direction of incidence of the light.

FIG. 4 is a schematic cross-sectional view showing an example of a conventional optical isolator.

In FIG. 4, numerals 1 and 2 are right-angled isosceles triangular prisms, and the pair of prisms are joined to each other at their hypotenuses, and a dielectric multilayer jiff 3 is attached to the joining surface. A polarizing beam splitter 4 is configured. The polarizing beam splitter has a transmittance of 1 for p-polarized light when it is incident at an angle of 45 degrees to the L4it multilayer film.
00%, and the reflectance for S-polarized light is 100%. 5 is a quarter wavelength plate.

In the optical isolator as described below, when linearly polarized light (P-polarized light) 6 is incident on the polarizing beam splitter 4 from below upward, the incident light transmits 100% through the dielectric multilayer film 3 and travels straight. /4 wavelength plate 5. And said 1
The light passes through a /4 wavelength plate and is emitted as circularly polarized light 7. On the other hand, the same circularly polarized light 7a as the output light 7 is made to enter the 11/4 wavelength plate 5 downward from above (for example, a reflecting mirror is placed above the 174 wavelength plate 5 perpendicularly to the optical axis, etc.). ), the light after passing through the quarter-wave plate becomes S-polarized light and enters the polarizing beam splitter 4, and the incident light is 100% reflected by the dielectric multilayer film 3 and becomes linearly polarized light 8. Light is emitted laterally, and no light is emitted downward.

In this manner, light passes in the "-" direction but not in the downward direction, achieving light isolation.

The above-mentioned optical isolator is used, for example, as a component of an optical head in an optical information recording/reproducing device to irradiate a recording medium with light for recording or reproduction and to detect light reflected by the recording medium. .

However, the optical isolator described above uses a polarizing beam splitter obtained by laminating a large number of dielectric layers on the surface of an optically polished prism, which has the disadvantage of high cost. In addition, since the polarizing beam splitter in the optical isolator described above is a so-called bulk component, when the beam diameter of the light used increases, the volume increases as the area of the dielectric multilayer film increases. There are some things that are incompatible with the demands of In particular, when such an optical isolator is used as a component of an optical head of an optical information recording/reproducing device,
If the weight is not sufficiently reduced, it will take a relatively long time to access the information recording medium with the optical head, making it difficult to improve the recording and reproducing speed. A high-output device is also required.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to provide an optical isolator that can be reduced in size and weight, as well as in cost reduction.

[Means for Solving the Problems] According to the present invention, in order to achieve the above objects, the present invention includes an optical waveguide, a grating coupler provided on the optical waveguide, and a quarter wavelength plate. An optical isolator is provided.

[Example] Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1(a) is a schematic perspective view showing a first embodiment of the optical isolator according to the present invention, and FIG. 1(b) and FIG. -C sectional view.

In Figure i1, 21 is a substrate made of a parallel flat plate that is transparent to the light used, and 9.13 is an optical waveguide with a relatively high refractive index formed on its surface. A grating coupler 11 in the C-C direction is formed on the surface of the optical waveguide 9, and a grating coupler 11 in the C-C direction is formed on the surface of the optical waveguide 13 on the substrate 21 side corresponding to the coupler. Grating coupler 1 in B-B direction
4 is formed. Then, on the surface of the optical waveguide 13, 1 is placed on the digit corresponding to the grating coupler 14.
A /4 wavelength plate 15 is provided.

In this embodiment as described above, the light beam 20 from the light source is introduced into the optical waveguide 9 and the parallel waveguide light 10 in the TE mode is generated.
The signal propagates as follows and reaches the grating coupler 11. The grating coupler is configured to diffract the guided light 10 only toward the substrate 21 by using a blazed grating or by attaching an appropriate reflection structure to the upper surface. Therefore, the guided light 10 is diffracted by the grating coupler 11 and enters the substrate 21 from above downward as linearly polarized light 12 having a vibration plane in the C--C direction, and reaches the grating coupler 14 . As mentioned above, since the grating coupler is in the B-B direction,
The linearly polarized light 12 passes straight through the optical waveguide 13 without being diffracted by the grating coupler 14, and is
The light is incident on the four-wavelength plate 15. The light then passes through the quarter-wave plate and is emitted as circularly polarized light 16.

On the other hand, the same circularly polarized light 17 as the output light 16 is made to enter the quarter-wave plate 15 from below upward (for example, l
/4 wavelength plate 15), the light after passing through the 1/4 wavelength plate is B.
- It becomes linearly polarized light with a vibration plane in the B direction and passes through the optical waveguide 1.
3 and reaches the grating coupler 14. As mentioned above, since the grating coupler 14 is in the B-B direction, a part of the incident light 17 is diffracted by the grating coupler 14, leading to a TE mode having an imaging plane in the B-B direction. The light wave 19 propagates in the C-C direction, and is emitted as a light beam 22 from the end face of the optical waveguide 13 in the C-C direction. The other part of the incident light 17 is not diffracted by the grating coupler 14 and passes straight through the grating coupler, enters the optical waveguide 9 via the substrate 21 as linearly polarized light 18, and reaches the grating coupler 11. . As described above, since the grating coupler 2 is in the C-C direction, the incident linearly polarized light 18 is transmitted straight through without being diffracted by the grating coupler, and is emitted to the outside as linearly polarized light 23.

As described above, the incident light of the incident light 20 is emitted from the outgoing position of the outgoing light 16, and the light passes through. The incident light from the incident light 20 is not emitted as the outgoing light from the incident position of the incident light 20, and the light does not pass through, thereby realizing light isolation.

FIG. 2 is a schematic plan view showing a second embodiment of the optical isolator according to the present invention. This embodiment is obtained by adding a light source and a waveguide lens to the optical isolator of the first embodiment. In FIG. 2, the same members as in FIG. 1 are given the same reference numerals. The present embodiment has a structure different from that of the first embodiment only in the portions shown in FIG. 2.

In FIG. 2, 24 is a semiconductor laser as a light source attached to the end face of the optical waveguide 9, and 26 is an optical waveguide 9 between the semiconductor laser 24 and the grating coupler 11.
A waveguide lens is formed on top of the waveguide lens. The waveguide lens is a transmissive Fresnel lens having light focusing properties.

In this embodiment, the light beam from the semiconductor laser 24 is introduced into the optical waveguide 9 and propagates as a divergent waveguided light 25 in the TE mode. The guided light is converted into parallel guided light by the Fresnet lens 25, and then passed through the grating coupler 11.
reach the part.

The guided light hereinafter behaves in the same manner as in the first embodiment.

This embodiment describes the structure of an optical head of an optical information recording/reproducing device.
It can be suitably used as an element.

In this case, an objective lens may be placed at an appropriate distance from the 174-wavelength plate 15, and an appropriate photodetector may be placed on the traveling path of the light beam 22, 23. In particular, the photodetector may be bonded to an optical isolator. It can be fixed or integrated, which makes it possible to make the optical head smaller, lighter, and thinner, and to shorten access time.

FIG. 3 is a schematic partial sectional view showing a third embodiment of the optical isolator according to the present invention.

In FIG. 3, 31 is a substrate made of a parallel flat plate that is transparent to the light used, and 32 and 33 are optical waveguides with a relatively high refractive index formed on its surface.
One end surface of the substrate 31 is formed obliquely, and grating couplers 34.3 are provided on the surfaces of the optical waveguides 32.33 in proximity to the end surface, respectively, in a direction perpendicular to the paper plane of FIG.
5 is formed. The oblique end surface of the substrate 31 has a 1/
A four-wavelength plate 36 is provided.

Of the two grating couplers in this embodiment, one grating coupler 34 selectively diffracts the TE mode waveguide light propagating in the optical waveguide 32 toward the substrate 31, and the grating coupler 35 with external force selectively diffracts the TE mode guided light propagating within the optical waveguide 32. The TM mode guided light propagating within the optical waveguide 33 is selectively diffracted toward the substrate 31 side.

In this embodiment as described above, the light beam 37 from the light source is introduced into the optical waveguide 32, and the parallel waveguide light 3 in the TE mode is generated.
8 and reaches the grating coupler 34 portion. The grating coupler is configured to diffract the guided light 38 only toward the substrate 31 by appropriately setting the grating pitch. Therefore, the guided light 38 is diffracted by the grating coupler 34 and enters the substrate 31 as a linearly polarized light 39 having a vibration plane perpendicular to the paper plane of FIG.
6. Then, it passes through the 174 wavelength plate and is emitted as circularly polarized light 40.

On the other hand, the same circularly polarized light 41 as the output light 40 is made to enter the quarter-wave plate 36 (for example, the quarter-wave plate 36
(by placing a reflecting mirror below perpendicular to the optical axis, etc.), and the light after passing through the quarter-wave plate becomes linearly polarized light with a plane of vibration in the in-plane direction of the paper as shown in Figure 3. 42 and the board 31
The light then enters the optical waveguide 32 and reaches the grating coupler 34 . As mentioned above, since the grating coupler 34 allows the TE momo-selectivity, the incident light 42 is not diffracted by the grating coupler 34, but is totally reflected at the interface between the optical waveguide 32 and air, resulting in a luminous flux. 43, the light enters the optical waveguide 33 through the substrate 31 and reaches the grating coupler 35. As mentioned above, since the grating coupler 35 has TM momo-selectivity, the incident light 43 is diffracted by the grating coupler 35 and the guided light 4
4, and is emitted as linearly polarized light 45.

As described above, the incident light from the incident position of the incident light 37 is output as the output light from the output position of the output light 40 and the light passes, but from the output position of the output light 40, that is, the incident position of the incident light 41. The incident light 37 is not emitted as the outgoing light from the incident position of the incident light 37, and the light does not pass therethrough, achieving light isolation.

[Effects of the Invention] According to the present invention as described above, since an optical waveguide and a grating coupler are used and the polarization characteristics of the grating coupler are utilized, there is no need to use a polarizing beam splitter as a bulk optical component. Therefore, it is possible to make it smaller, lighter, and especially thinner, and since it does not have a multilayer structure like a polarizing beam splitter of a bulk optical component, the manufacturing process is simplified, and simultaneous mass production using Brehner technology is possible. is removable, which makes it possible to reduce costs.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic perspective view of an optical isolator according to the present invention, and FIG. 1(b) and FIG. 1(C) are a BB partial sectional view and a CC sectional view thereof, respectively. FIG. 2 is a schematic plan view of an optical isolator according to the present invention. FIG. 3 is a schematic partial cross-sectional view of an optical isolator according to the present invention. FIG. 4 is a schematic cross-sectional view of a conventional optical isolator. 9.13, 32, 33: Optical waveguide, 11.14, 34, 35 Ni grating coupler, 15.36: l/4 wavelength plate, 21.31: Substrate.

Claims (3)

[Claims] (1) An optical isolator comprising an optical waveguide, a grating coupler provided on the optical waveguide, and a quarter-wave plate. (2) Optical waveguides are formed on opposing surfaces of the same substrate, and each optical waveguide is provided with a grating coupler, and the polarization characteristics of the grating coupler of one optical waveguide and the grating of the other optical waveguide are The optical isolator according to claim 1, wherein the couplers have different polarization characteristics. (3) The optical isolator according to claim 2, wherein an optical path is set from the grating coupler of one optical waveguide to the grating coupler of the other optical waveguide and then to the quarter-wave plate.