JPH06258534A - Optical device - Google Patents

Abstract

PURPOSE:To provide the optical device which reduces unnecessary propagated light, and performs signal detection with good S/N, and is stable in the oscillation of its light source. CONSTITUTION:This device is constituted by forming reflection type diffracting optical lenses 3a and 3b on the top surface of a transparent substrate 2, providing the light source 1 and a photodetector 5 on the reverse surface of the transparent substrate 2, and forming a light absorbing means 10 on a flank 11 of the transparent substrate, and the projection light 6 emitted by the light source 1 is diffracted by the reflection type diffracting optical lens 3a, the primary diffracted light is collimated at an angle theta to become propagated light 7 and then reflected by the reflecting layer 4c on the reverse surface of the substrate 2 and made incident on another reflection type diffracting optical lens 3b, and the projected primary diffracted light becomes incident light 8 on the photodetector 5. Unnecessary propagated light such as 9 other than the primary diffracted light generated by the diffraction of the reflection type diffracting optical lenses 3a and 3b is absorbed by the light absorbing means 10 on the reverse surface 11 of the substrate and hardly made incident on the photodetector 5 and light source 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat plate type optical integrated circuit in which optical elements including diffractive optical elements are integrated on a flat plate. It concerns a possible optical device.

[0002]

2. Description of the Related Art A flat-plate optical integrated circuit integrates optical elements on a transparent flat plate (substrate) such as glass, and zigzags the optical path by using reflection at the flat plate interface so as to connect each optical element. It processes information. According to this circuit configuration, it is possible to realize a compact, stable and lightweight optical application system, which is drawing attention.

As a conventional flat type optical integrated circuit, there is one shown in FIG. 3 (cross-sectional view) (J. Jahns, YH Lee, C.
A. Burrus Jr., and JL Jewell: "Opticalinterco
nnection using top-surface-emmiting microlasers an
d planar optics ", Applied Optics Vol. 31, No. 5, p
p. 592-597 (1992).).

The optical device shown in FIG. 3 is an example of an optical interconnection for propagating the signal of the light source 1 to the photodetector 5. In the figure, reflective diffractive optical lenses 3 a and 3 b are formed on the front surface of the transparent substrate 2, and the rear surface of the transparent substrate 2 is
This is a structure in which the light source 1, the photodetector 5, and the reflective layer 4c are provided.
The reflective diffractive optical lenses 3a and 3b have a reflective layer 4 on the top.
It is an off-axis type lens provided with a and b, respectively, and having different incident and outgoing optical axes.

The emitted light 6 emitted from the light source 1 is diffracted by the reflection type diffractive optical lens 3a, and the first-order diffracted light has an angle θ.
Is collimated to become propagating light 7. This propagating light 7 is
The light is reflected by the reflective layer 4c on the back surface of the substrate 2, enters the other reflective diffractive optical lens 3b, and the first-order diffracted light becomes incident light 8 on the photodetector 5.

[0006]

In the conventional optical device shown in FIG. 3, reflective diffractive optical lenses 3a and 3b are used.
In the above, only the first-order diffracted light has the collimating / focusing effect as designed, and the other diffracted light becomes unnecessary propagation light. In a diffractive element such as a reflective diffractive optical lens, the ratio of converting incident light into first-order diffracted light, that is, first-order diffraction efficiency is important. This first-order diffraction efficiency depends on the cross-sectional shape of the element, the grating period that constitutes the element, the incident angle, etc., and it is theoretically almost impossible to set this first-order diffraction efficiency to 100%. The actual value is typically about 25% to 85%. Therefore, when integrating a diffractive optical element in an optical device such as a flat optical integrated circuit,
Unwanted propagating light other than the first-order diffracted light is 15
% To about 75%.

For example, regarding the reflection type diffractive optical lens 3b, when the state of the 0th order diffracted light (transmitted light) 9 is shown by a dotted line, this light 9 is partially emitted on the side surface 11c of the substrate (reflected on the side surface) after exiting the lens 3b. When the angle is the total reflection angle, the light is reflected and is incident on the photodetector 5. That is, the diffracted light other than the 1st order (the 0th order diffracted light, the −1st order diffracted light and the high order diffracted light) is
Appearing in various directions satisfying the diffraction condition and being reflected multiple times on the upper and lower side surfaces of the substrate 2 to become unnecessary propagating light, especially when the outgoing light 6 has two-dimensional information or only the incident light 8 is generated. In the case of having information, there is a problem that this unnecessary propagation light is incident on the photodetector 5 to deteriorate the SN ratio. Further, when the light is reflected multiple times in the substrate 2 and enters the light source 1, the oscillation of the light source 1 may become unstable.

The present invention has been made in view of the above problems, and provides an optical device in which oscillation of a light source is stable and a signal with a good SN ratio can be detected by reducing unnecessary propagation light.

[0009]

A transparent substrate and a plurality of optical elements including a diffractive optical element formed on at least one of the front surface and the back surface of the transparent substrate, are arranged in a zigzag pattern in the transparent substrate. In the optical device for propagating light, the light absorbing means is provided on at least one side surface of the transparent substrate.

[0010]

According to the present invention, in a flat optical integrated circuit, by providing a light absorbing means on a side surface of a transparent substrate through which light propagates in a zigzag manner, unnecessary propagating light other than the first-order diffracted light generated by the diffractive optical element is provided. It absorbs and prevents the light source and the photodetector from entering, does not disturb the oscillation of the light source, and improves the SN ratio of the photodetector.

[0011]

1 is a sectional view (a) and a plan view (b) showing the structure of an optical device according to an embodiment of the present invention.

In the figure, as the transparent substrate 1, for example, the thickness (size in the z direction) is 2 mm and the width (size in the x direction) is 5 m.
On the surface of the substrate 2, reflective diffractive optical lenses 3a and 3 are used.
The light source 1 and the photodetector 5 are provided on the back surface of the substrate 2 so as to face each other. On the upper surfaces of the reflective diffractive optical lenses 3a and 3b and the back surface of the substrate 2, reflective layers 4a, 4b, and 4c, which are metal layers of, for example, Ag, Al, Au, or multilayer films of dielectrics, are formed. . The light propagates in a zigzag shape by utilizing the reflection on the front surface and the back surface of the substrate 2. The substrate 2 may be transparent to the wavelength used. In particular, a glass substrate such as quartz is stable in temperature.

As the light source 1, for example, a semiconductor laser array having a 3 × 3 structure and a wavelength of 0.78 μm is used. The emitted light 6 from the light source 1 has, for example, a focal length of 2 mm and a size of 1 m.
The light enters the off-axis diffractive optical lens 3a having an angle of m.
An off-axis lens is a lens in which the angle of the optical axis of the incident light and the angle of the optical axis of the emitted light are different (a lens in which the angle of the optical axis of the incident light and the angle of the optical axis of the emitted light are the same. In-line type). The off-axis type diffractive optical lens 3a is a diffractive lens that collimates a divergent spherical wave and emits it at an angle θ, and its cycle gradually increases in the y direction (center cycle is, for example, 0.74 μm).
m), which is composed of a parabolic grating with a rectangular cross-section that simultaneously reduces curvature. The groove depth of the grating is, for example, 0.17 μm. The incident light has, for example, a first-order diffraction efficiency of 48% and a propagation angle θ = 45, for example.
The light is reflected and diffracted at .degree. To become the collimated propagating light 7.

The propagating light 7 is reflected on the back surface of the substrate 2, propagates in a zigzag shape, enters another off-axis diffractive optical lens 3b, and is condensed with a first-order diffraction efficiency of 48%, for example. It becomes incident light 8 on the photodetector 5. The off-axis type diffractive optical lens 3b has the same specifications as 3a.
The arrangement is rotated by 80 degrees. The photodetector 5 has, for example, a pin structure of a-Si or Si and has a 3 × 3 9-division structure corresponding to the light source 1.
And each element of the photodetector 5 correspond to each other, and the signal of each element of the light source 1 is an optical device as an optical interconnection that propagates to each element of the photodetector 5.

FIG. 2 is a diagram showing the diffraction efficiency in the central region of the off-axis lens 3b. For example, the propagation angle is θ =
In the case of 45 °, as shown in FIG.
When incident on the off-axis lens 3b, the 0th order, the 1st order, the 2nd order
The following three orders of diffracted light were generated, and the respective diffraction efficiencies were, for example, 33%, 48%, and 18%. Since the incident light 8 to the photodetector 5 is the first-order diffracted light, 48% of the propagating light 7 is incident on the photodetector 5. 0th order diffracted light 9
1A, as shown by the dotted line in FIG. 1A, reaches the side surface 11c of the substrate, but is almost absorbed by the light absorbing means 10 provided on the side surface 11 and hardly enters the photodetector 5. Although not shown in the drawing, the second-order diffracted light propagates in a zigzag shape in the −y direction so as to spread, and one part is emitted from the surface of the substrate 2 to the outside, and one part is the substrate side surface 11 a, 1
It reaches 1b and 11d, and is almost absorbed by the light absorbing means 10 provided on the side surface 11 thereof. At this time, the light absorbing means 10
It has been found that the unnecessary propagation light can be considerably reduced even if the side surface 11 of the substrate on which is provided is at least the opposing surface in the light propagating direction, that is, two surfaces 11a and 11c.
Furthermore, the side surface 11 of the substrate on which the light absorbing means 10 is provided is effective even if it is the side surface closest to the diffractive optical element. θ = 3
The measurement results of the diffraction efficiency at 0 ° and 20 ° are also shown in FIGS. 2 (a) and 2 (c), respectively.

In the present embodiment, as the light absorbing means 10, a film having a light absorbing action with respect to the wavelength used, for example, carbon or a phthalocyanine compound was mixed and applied to a polymer such as polyimide or PMMA. On the other hand, an organic film such as a dye having a light absorbing effect may be deposited.

For the diffractive optical elements 3a and 3b, for example, an electron beam resist such as PMMA or CMS is coated on the substrate 2, and an electron beam drawing method is performed to control the irradiation amount according to the film thickness of the element to be manufactured. It was formed by developing and changing the film thickness of the resist. From the optical element (master) thus formed, this mold was produced by, for example, a nickel electroforming method, and the same lenses 3a and 3b as the master were duplicated on the substrate 2 using, for example, a UV curable resin. According to this method, it is possible to easily form a plurality of diffractive optical elements at the same time on the substrate 2 with the same characteristics and with the same characteristics. After the duplication of the reflection type diffractive optical lenses 3a and 3b, metal layers such as Ag, Al and Au were deposited thereon as the reflection layers 4a and 4b.

On the reflective layer 4, metal layers such as Cu and Cr, synthetic resins such as UV curable resins and lacquer paints, dielectric multilayer films, SiO, SiO ₂ , MgF ₂ , SiC, graphite, diamond, etc. Protective layer of, for example, 1000
By depositing from Å to several μm, it was possible to make the surface of the reflective layer less likely to be scratched, at the same time prevent oxidation of the reflective layer, and improve the environmental resistance. In particular, when Ag was used as the reflective layer, it was easily oxidized, and the effect of the protective layer was large.

As the diffractive optical element, the off-axis type has been described in this embodiment. However, in the in-line type diffractive lens, the period of the constituent grating is usually relatively large, the cross-sectional shape control is easy, and the blazing is easy. Since it can be performed, the 1st-order diffracted light can be made, for example, about twice as large as that of the off-axis type lens, so that the unnecessary propagation light can be reduced. Therefore, the effect of the present invention is greater for a flat-plate optical integrated circuit including an off-axis type diffractive lens.

As the optical device of the present invention, the case where the optical element is on the front surface of the substrate 2 has been described above, but it may be on the back surface or on both surfaces. Further, in the present embodiment, the optical interconnection for propagating the information of the light source 1 to the photodetector 5 has been described, but the present invention is of a diffractive type formed on the transparent substrate and at least one of the front surface and the back surface of the transparent substrate. First-order diffracted light generated by a diffractive optical element for an optical device such as a flat-plate optical integrated circuit which is composed of a plurality of optical elements including an optical element and propagates light in a zigzag manner in a transparent substrate. It is possible to reduce unnecessary propagation light other than the above, which is effective.

[0021]

INDUSTRIAL APPLICABILITY The present invention provides an optical device comprising a transparent substrate and a plurality of elements including a diffractive optical element formed on at least one of a front surface and a back surface, and which propagates light in a zigzag manner in the transparent substrate. Since it is an optical device in which the light absorbing means is provided on at least one side surface of the transparent substrate,
It is possible to realize an optical device that reduces unnecessary propagating light, stabilizes oscillation of a light source, and can detect a signal with a good SN ratio.

[Brief description of drawings]

FIG. 1A is a sectional view showing a configuration of an optical device according to an embodiment of the present invention. FIG. 1B is a plan view showing a configuration of an optical device according to an embodiment of the present invention.

FIG. 2 is a diffraction efficiency of a reflective diffractive optical lens of an optical device according to an embodiment of the present invention.

FIG. 3 is a sectional view of a conventional optical device.

[Explanation of symbols]

 1 Light Source 2 Transparent Substrate 3 Reflective Diffractive Optical Lens 4 Reflective Layer 5 Photo Detector 6 Emitted Light 7 Propagated Light 8 Incident Light 9 0th Diffracted Light 10 Light Absorbing Means 11 Side of Transparent Substrate

Claims (6)

[Claims] 1. A light comprising a transparent substrate and a plurality of optical elements including a diffractive optical element formed on at least one of a front surface and a back surface of the transparent substrate, and propagating light in a zigzag shape in the transparent substrate. In the device, a light absorbing means is provided on at least one side surface of the transparent substrate. 2. The optical device according to claim 1, wherein the diffractive optical element is an off-axis lens. 3. The optical device according to claim 1, wherein the side surfaces of the transparent substrate are opposed surfaces in a light propagating direction. 4. The optical device according to claim 1, wherein the light absorbing means is a film having an absorption region at a used wavelength. 5. The optical device according to claim 4, wherein the film having an absorption region is an organic film containing either carbon or a phthalocyanine compound. 6. The optical device according to claim 5, wherein the organic film is a polymer film.