JP2714097B2 - Optical waveguide device - Google Patents

Description

The present invention relates to an optical waveguide device used for an optical disk memory pickup or the like.

(B) Conventional technology Conventionally, an optical waveguide device is described in, for example, IEICE Technical Report, Vo1.84, No.2
59, pp. 97-104 (1985). FIG. 3 (a) shows a perspective view, FIG. 3 (b) shows a front view, and FIG. 3 (c) shows a side view. In the figure, (1) is a substrate made of Si, (2) is a buffer layer made of SiO ₂ laminated on the substrate (1),
(3) is a waveguide laminated on the buffer layer (2),
For example, Corning # 7059 (trade name) is used as the material. (4) is a semiconductor laser having one light emitting end face coupled to the waveguide by an end face direct coupling method. (5 ') is a condenser grating coupler (hereinafter referred to as FGC) arranged in the traveling direction of light emitted from the semiconductor laser (4) and propagating in the waveguide (3).
It is manufactured by laminating SiN on a desired shape. That is, the guided light enters the FGC (5 ') directly or after being collimated by a waveguide lens (not shown), the traveling direction is changed by the FGC (5'), and is taken out of the waveguide (3). It is collected at a certain point. (6) is an optical disk disposed above the condensing type optical pickup, and light extracted from the waveguide (3) is collected on the disk surface of the optical disk (6). Then, the light reflected by the optical disk (6) is again incident on the FGC (5 '), and is reflected by the waveguide (3).
To join. Such a condensing type optical pickup reads a signal by detecting this light. However, in the figure, elements for signal detection are omitted.

(C) Problems to be Solved by the Invention In the conventional optical waveguide device, the optical axis of the laser light (hereinafter referred to as “emitted light”) emitted from the FGC (5 ′) is set in the direction perpendicular to the waveguide (3) plane. Therefore, it is necessary to incline the laser light (hereinafter referred to as guided light) propagating in the waveguide (3) in the optical axis direction. This is because if the shape of the FGC (5 ') is designed so that the optical axis of the emitted light is perpendicular to the plane of the waveguide (3), the FGC (5') is black for some of the guided light. This is because the condition is satisfied, and part of the guided light is reflected to return to the semiconductor laser (4), and the oscillation characteristics of the semiconductor laser (4) become unstable.

In addition, the optical waveguide device adjusts the optical axis of the laser light emitted from the FGC (5 ') to return the reflected light from the optical disk (6) to the waveguide (3) for signal detection. 6) They must be arranged perpendicular to the plane.

For these reasons, the conventional optical waveguide device is arranged with the optical axis of the guided light inclined with respect to the optical disk (6) surface as shown in FIGS. 3 (b) and 3 (c). Therefore, in the conventional device, as shown in the figure, the occupied length W of the device in the direction perpendicular to the optical disk (6) surface is required.
There is a problem that a pickup using such a conventional device is increased in size.

(D) Means for Solving the Problems The present invention provides a semiconductor laser, a waveguide optically coupled to the semiconductor laser, and propagating laser light emitted from the semiconductor laser, provided on the waveguide, A grating coupler that emits laser light propagating in the waveguide to an external space, and a device perpendicular to the device length of the laser light propagating in the waveguide, rather than the device length in the optical axis direction. An optical waveguide device having a smaller width, wherein an optical axis of laser light emitted from the grating coupler exists in a plane perpendicular to an optical axis propagating in the waveguide, and a plane of the waveguide. The grating coupler is configured to be inclined from a direction perpendicular to the optical disc surface, and the optical axis of the laser beam emitted from the grating coupler is arranged to be perpendicular to the optical disk surface. To.

(E) Function Generally, in the optical waveguide device, the device width B in the direction perpendicular to the device length A in the optical axis direction of the guided light is 1/4.
It can be as follows (see FIG. 3 (a)).

The present invention has been made in view of such structural features of an optical waveguide device, and has an optical axis of outgoing light within a plane perpendicular to the optical axis of guided light, and perpendicular to the plane of the waveguide. Arranged at an angle from the direction. Accordingly, when the device is arranged so that the optical axis of the emitted laser light is perpendicular to the optical disk surface, the device is inclined in the direction perpendicular to the optical axis of the guided light, that is, in the width direction of the device.

(F) Embodiment FIG. 1 shows an embodiment of the apparatus of the present invention. FIG. 1 (a) is a perspective view, FIG. 1 (b) is a front view, and FIG. 1 (c) is a side view. In FIG. 1, the same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. The difference between the present apparatus and the conventional apparatus is that the laser light (emitted light) emitted from the FGC (5)
Is present in a plane perpendicular to the optical axis of the laser light (guided light) propagating in the waveguide (3), and is inclined from a direction perpendicular to the waveguide (3) plane. . This can be achieved by changing the design of FGC (5). For example, as shown in FIG. 2, in spatial coordinates, the xy plane is the plane of the waveguide (3), the point P on the y axis is the light source of the semiconductor laser (4), the y axis is the optical axis of the guided light,
Further, a point Q existing in the zx plane and at a position inclined by θ in a counterclockwise direction from the z axis is set as a focal point of the laser light emitted to the outside of the waveguide (3) by the FGC (5). At this time, if the distance from the light source (P) to the origin (O) is r and the distance from the focal point (Q) to the origin (O) is f, the shape of FGC (5) is expressed by the following equation.

Here, N is the effective refractive index of the waveguide (3), λ is the wavelength of the laser light in a vacuum, and m is an integer of 0, ± 1, ± 2,. Further, c is an arbitrary constant. For example, if x = 0 and m = 0, then C = Nr + f.

When the device of this embodiment is arranged so that the optical axis of the emitted light is perpendicular to the optical disk (6) surface, the device is inclined in the direction perpendicular to the optical axis of the guided light, that is, in the width direction of the device. On the other hand, in such an optical waveguide device, when the device length A in the optical axis direction of the guided light is 15 mm, the device width B is about 3 mm. Therefore, in the device of the present embodiment, the device is tilted in the width direction which is sufficiently shorter than the length direction of the device. be able to.

In the signal detection method in the present embodiment, the amount of reflected light from the optical disk (6) may be different between the left and right sides of the optical axis of the laser light propagating in the waveguide (3). It is necessary to adjust the balance between the amount of light taken in or the intensity of the output signal, but the principle is to use the conventional method as shown in IEICE Technical Report, Vol.84, No.259, P.96-104 (1985), etc. Can be adopted.

As described above, in this embodiment, the case where the light is directly condensed on the optical disk (6) surface by the FGC (5) has been described.
It is also possible to use a configuration in which the outgoing light from is converted into parallel light, which is condensed by an external objective lens. The shape of FGC (5) at this time is expressed by the following equation.

Further, the arbitrary constant c is, as in the above-described equation, x = y = 0,
If m = 0, then C = Nr.

(G) Effects of the Invention According to the device of the present invention, the optical axis of the laser light emitted from the device is present in a plane perpendicular to the optical axis of the laser light propagating in the waveguide, and at the same time, When the device is arranged such that the optical axis of the emitted light is perpendicular to the optical disk surface by tilting from a vertical direction, the device tilts in a width direction that is sufficiently shorter than the length direction. As a result, the occupied length W of the device in the direction perpendicular to the optical disk surface can be reduced, and the thickness of the pickup using the device of the present invention can be reduced. Further, since the optical axis of the emitted light is perpendicular to the optical disk surface, the spot shape of the emitted light on the optical disk is a perfect circle, and the light use efficiency is improved.

[Brief description of the drawings]

1 (a) is a perspective view showing an embodiment of the apparatus of the present invention, FIG. 1 (b) is a front view thereof, FIG. 1 (c) is a side view thereof, and FIG. 2 designs an FGC in the apparatus of the present invention. Explanatory diagram for the third
FIG. 1A is a perspective view showing a conventional apparatus, FIG. 1B is a front view thereof, and FIG. 1C is a side view. (1) substrate, (2) buffer layer, (3) waveguide, (4) semiconductor laser, (5) focusing grating coupler (FGC), (6) optical disk .

Claims (1)

(57) [Claims] 1. A semiconductor laser, a waveguide optically coupled to the semiconductor laser and propagating a laser beam emitted from the semiconductor laser, and a laser beam provided on the waveguide and propagating in the waveguide. A grating coupler that emits light into an external space, wherein the device length and the device width in the vertical direction are smaller than the device length in the optical axis direction of the laser light propagating in the waveguide. The optical axis of the laser beam emitted from the grating coupler is present in a plane perpendicular to the optical axis propagating in the waveguide, and is inclined from a direction perpendicular to the plane of the waveguide. An optical waveguide device, comprising a grating coupler, and arranged so that an optical axis of laser light emitted from the grating coupler is perpendicular to an optical disk surface.