JPH0483208A - Grating coupler - Google Patents

Abstract

PURPOSE:To improve the outgoing efficiency and to reduce the size by providing a reflecting means which reflects waveguide light, passed through a grating for light outgoing without outgoing, so that the light is in phase with outgoing light. CONSTITUTION:The grating 12 for light outgoing is formed at a specific place on the optical waveguide 11. Assuming that incident light is entered into the optical waveguide layer 11 from the left side, a reflection type grating 13 is formed on the right side of the grating 12 for light outgoing at a specific distance (d). In this case, the reflection type grating 13 reflects and returns the light, which passes below the grating 12 without outgoing from the grating 12 for light outgoing to travel to the right, to the grating 12, and the light is outgone from the grating 12 in the in-phase relation with the light outgone from the grating 12 for light projection. Consequently, the outgoing light power is increased and the high projection efficiency is obtained. Further, the grating for light outgoing need not be so long, so the side is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a grating coupler that emits light propagating within an optical waveguide layer formed on a substrate to the outside.

Prior Art and Its Problems The output efficiency (coupling efficiency) of a grating coupler is determined by the length of the grating coupler, and the radiation loss coefficient determined by the thickness of the grating and the cross-sectional shape of the grating. Therefore, in order to obtain a highly efficient grating coupler, its length must be increased. This does not necessarily match the demand for miniaturization of optical functional elements.

OBJECTS OF THE INVENTION An object of the present invention is to provide a grating/coupler that can obtain high output efficiency and can be miniaturized.

Arrangement 1 of the Invention Functions and Effects The grating coupler according to the present invention includes a grating that is provided on an optical waveguide layer formed on a substrate and for emitting guided light to the outside, and a grating that does not emit guided light from the light emitting grating. The light emitting device is characterized in that it includes a reflecting means provided on the substrate for projecting the guided light that has passed therethrough so that it is in the same phase as the light emitted from the light emitting grating.

The reflecting means can be realized by a reflection grating formed on the optical waveguide layer, or by a reflection mirror provided on the substrate.

According to this invention, the guided light that has passed through the light emitting grating without being emitted is reflected by the reflecting means, returns to the light emitting grating again, and returns to the light emitting grating in the same phase as the light emitted from the light emitting grating. Emits from.

Since the light reflected by the reflecting means is also emitted, the output light power of the grating/cobra increases accordingly, resulting in high output efficiency. Further, since the length of the light emitting grating does not have to be very long, it is also possible to achieve miniaturization.

Furthermore, the amplitude distribution of the light emitted from the grating coupler is expressed by the addition result of the amplitude distribution of the emitted light of the guided light and the amplitude distribution of the emitted light of the reflected light, so the amplitude is large on both sides and small in the center. becomes. This is similar to the amplitude distribution of super-resolution, and it becomes possible to focus the emitted light into an extremely small beam diameter.

Example FIG. 1 shows a first embodiment of the invention.

An optical waveguide layer 11 is formed on a substrate 10, and this optical waveguide layer 1
A light emitting grating 12 is formed at a predetermined location on the light emitting device 1 . Assuming that incident light is introduced into the optical waveguide layer 11 from the left side in FIG. 1, a reflective grating 13 is formed on the right side of the light output grating 12 at a predetermined distance dM. The reflective grating 13 is not emitted by the light emitting grating 12 and is
The light passing under the grating 12 and traveling to the right is reflected and returned to the grating 12.

This is for emitting light from the grating 12 in the same phase as the light emitted from the light emitting grating 12.

The period ΔR of the reflective grating 13 is the same as the optical waveguide layer ll.
Let λ be the wavelength of the guided light within.

AR-λg/2...(1)
is given by

Light output grating 12 and reflective grating 1
The distance d between 3 and 3 is given by the following equation.

d-mλ/2...(2)m
-1, 2, 3,... In the reflection type grating, by providing a large number of periods, it is possible to obtain something close to perfect reflection.

The intensity (power) of the emitted light from this grating/cobra is determined by the length p of the light emitting grating 12.

The radiation loss coefficient α determined by the thickness h and cross-sectional shape of the grating 12, and the reflective grating 13
The reflection coefficient of the light reflected by the grating 13 (this is specifically determined by the number of stages of the grating 13 and the cross-sectional shape of the grating 13) is determined by three parameters.

In FIG. 1, the dashed line A indicates the power distribution of the guided light emitted from the light output grating 12, and the dashed line B indicates the power distribution of the reflected light. A solid line C shows the combination of both of these output light power distributions. As can be seen from the power distribution represented by the solid line C, the output light power is large at both ends of the grating 12 and small at the center. This is a power distribution that allows super resolution, and allows the light emitted from the grating 12 to be focused to form an extremely small light beam spot.

The grating cover shown in FIG. 1 can be mass-produced using a standber. A standby having an uneven pattern of gratings 12 and 13 is prepared in advance, an ultraviolet (UV) curing resin is filled between the standby and the substrate 10, and the resin is cured by irradiating the standby with ultraviolet light. Finally, by removing the standby, a grating covert in which the optical waveguide layer 11 and the gratings 12 and 13 are integrally formed on the substrate 10 is obtained.

FIG. 2 shows a second embodiment of the invention.

In this embodiment, grooves 14 are formed on the substrate 10 and the optical waveguide layer 11 instead of the reflective grating, and the wall surfaces 14a of the grooves 14 are used as reflective mirrors. wall 1
It is preferable to form a reflective film such as AI on 4a. Distance d between the light emission grating 12 and the wall surface 14a
is expressed by the above equation (2).

FIG. 3 shows a third embodiment of the invention.

In this embodiment, a reflecting mirror 15 is provided on the end face of the substrate IO. The reflecting mirror 15 is formed by depositing AN, for example.

Although a step type grating is illustrated in the above embodiment, a grating of any shape, such as a blazed grating, may be used.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the invention. FIG. 2 is a sectional view showing a second embodiment of the present invention. FIG. 3 is a sectional view showing a third embodiment of the invention. 10...Substrate. 11... Optical waveguide layer. 12... Grating for light emission. 13... Reflective grating. 14...Groove, 14a...Reflection wall surface. 15...Reflection mirror that's all

Claims (3)

[Claims] (1) A grating provided on the optical waveguide layer formed on the substrate for emitting the guided light to the outside, and a grating that passes through the light emitting grating without being emitted from the light emitting grating. A grating coupler equipped with a reflecting means provided on a substrate that reflects light in the same phase as the emitted light. (2) The grating coupler according to claim 1, wherein the reflecting means is a reflective grating formed on the optical waveguide layer. (3) The grating coupler according to claim 1, wherein the reflecting means is a reflecting mirror provided on the substrate.