JPH02264906A - High efficiency prism coupling device - Google Patents

Abstract

PURPOSE:To enhance the optical coupling efficiency so as to obtain an optimum optical coupling condition extending over the whole of an incident beam by varying the thickness of a gap adjusting layer along the width direction being orthogonal to the propagating direction of an incident light in accordance with a beam shape of the incident light. CONSTITUTION:On a substrate 6, a waveguide layer 7 is formed, and on the waveguide layer 7, a gap adjusting layer 8 whose refractive index is lower than that of this layer 7 and whose thickness is varied in accordance with a beam shape of an incident light in the width direction (X axis direction) being orthogonal to the propagating direction (Z axis direction) of the incident light is formed, and on the upper part of the gap adjusting layer 8, a dielectric prism 9 having a higher refractive index than that of the waveguide layer 7 is provided. By using the gap adjusting layer 8 as an air layer, and varying a shape of the bottom face of the dielectric prism 9 so that thickness of this air layer becomes thick in the center part 8a and becomes thin in both end parts 8b of a beam in the width direction, the maximum optical coupling efficiency can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a highly efficient prism coupling device used for incident coupling in optical integrated circuits and the like.

2. Description of the Related Art An example of a conventional prism coupling device will be described with reference to FIG. A waveguide layer 2 with a refractive index nf is formed on the substrate 1, and a prism 4 with a refractive index np is provided on the top of the waveguide layer 2 via a gear adjustment layer 3 with a refractive index nc. There is. In the prism coupling device configured in this way, conditions under which optimum coupling efficiency can be obtained will be discussed below. When the incident light 5 is made incident on the bottom surface of the prism 4 with an incident angle of 0 (angle with the vertical direction), the propagation constant β in the direction along the waveguide layer 2 of this optical path is β = np
ksir+&-(1) where k
=2π/λ (λ: wavelength of incident light).

In this case, the propagation constant of a certain waveguide mode in the waveguide layer 2 is β
If the incident angle θ is adjusted so that they are equal, the incident light 5 is coupled to the guided mode, and the guided light is excited. Now, if the isolateral refractive index of the waveguide mode is N, then the propagation constant β of the waveguide mode is
W becomes βw=N k (2).

At this time, in order to efficiently couple the incident light 5 to the waveguide mode, the incident light 5 that has reached the bottom surface of the prism 4 should be made to enter the prism 4 so that it is positioned at the end of the prism 4, and the gap adjustment layer 3 should be positioned at the end of the prism 4. Optimize the thickness. Now, if the length of the incident light 5 at the bottom of the prism 4 is L, and the incident light 5 is a plane wave, αr L= 1.25 ・(3
), the highest coupling efficiency is obtained.

however, shall be.

Teff = T+1 / yc+1 / ysγc=
0...y γs = ni - 〇πy N = nf - sin θf S: Thickness of gap adjustment layer T: Thickness of waveguide layer ns: Refractive index of substrate Therefore, as a specific example, refraction of waveguide layer 2 Rate nf=1.
6. Refractive index n5 of substrate 1 = 1.46, gap adjustment layer 3
is the air layer nc=1, and the thickness T of the waveguide layer 2 is 1.
The length L of the incident light 5 at the bottom of the prism 4 is 5 μm.
FIG. 8 shows the coupling efficiency when the thickness S of the gap adjustment layer 2 is changed when the thickness is 2 mtn. From this, S=0
．． When the thickness is 136 μm, the highest optical coupling efficiency of 81.4% can be obtained under the conditions shown in equation (3).

Problems to be Solved by the Invention However, the conditions for obtaining the highest optical coupling efficiency are satisfied when the length of the incident light 5 is L. Generally, as shown in FIG. 9, the incident light 5 has an elliptical shape (including a circle) on the bottom surface of the prism 4, and the length of the incident light 5 in the propagation direction (Z-axis direction) is the width direction. (X-axis direction).

Therefore, if the width S of the gap adjustment layer 3 is optimally selected with respect to the length near the center of the incident light 5, the optical coupling efficiency of the peripheral portion of the incident light 5 will deteriorate.

Means for Solving the Problems The invention as set forth in claim 1 includes forming a waveguide layer on a substrate, and disposing a layer on the waveguide layer having a lower refractive index and extending in the width direction orthogonal to the propagation direction of incident light. A gap adjustment layer whose thickness varied depending on the beam shape of incident light was formed, and a dielectric prism having a higher refractive index than the waveguide layer was formed on this gap adjustment layer.

In the invention as claimed in claim 2, a waveguide layer is formed on the substrate, and the waveguide layer has a refractive index lower than the waveguide layer and corresponds to the beam shape of the incident light in the width direction perpendicular to the propagation direction of the incident light. A gap adjustment layer having a changed refractive index was formed by doing this, and a dielectric prism having a higher refractive index than the waveguide layer was formed on this gap adjustment layer.

According to the invention as claimed in claim 1, by changing the thickness of the gap adjustment layer in accordance with the beam shape of the incident light along the width direction perpendicular to the propagation direction of the incident light, the thickness of the gap adjusting layer is changed over the entire incident beam. Optimal optical coupling conditions can be obtained.

According to the invention as claimed in claim 2, by changing the refractive index of the gap adjustment layer in accordance with the beam shape of the incident light along the width direction perpendicular to the propagation direction of the incident light, Optimal optical coupling conditions can be obtained.

Embodiment First, a first embodiment of the invention as claimed in claim 1 is shown in FIG.
) (b).

A waveguide layer 7 is formed on the substrate 6. On this waveguide layer 7, there is a layer with a lower refractive index than this, in the propagation direction of the incident light (
A gap adjustment layer 8 is formed in the width direction (X-axis direction) perpendicular to the Z-axis direction, the thickness of which changes in accordance with the beam shape of the incident light. A dielectric prism 9 having a higher refractive index than the waveguide layer 7 is provided above the gap adjustment layer 8 . As this dielectric prism 9,
For example, high refractive index glass can be used.

In this embodiment, the gap adjustment layer 8 is an air layer, and the air layer is thick at the center where the incident light beam reaches, and thinner at both ends along the width direction of the dielectric prism 9. The bottom shape is formed.

A specific example in which the maximum optical coupling efficiency can be obtained in such a configuration will be described. Now, the refractive index nf of the waveguide layer 7=
1.6, its thickness is 1.5 μm, the refractive index nc of the dielectric prism 9 is 1.8, the refractive index n5 of the substrate 6 is 1.46, and the beam shape of the incident light at the bottom of the dielectric prism 9 is Assume that it is a circle with a diameter of 2I [1 m]. In this state, in order to maximize the efficiency with which the incident light is coupled to the waveguide layer 7, the third
As shown by curve A in the figure, the thickness of the gap adjustment layer 8 (here, air layer) with respect to the beam position in the width direction of the incident light is thick at the center part 8a of the beam, and at both ends of the beam in the width direction. The maximum optical coupling efficiency can be obtained by changing the shape of the bottom surface of the dielectric prism 9 so that it becomes thinner toward 8b.

Next, a second embodiment of the invention as claimed in claim 1 is shown in FIG.
) (b).

This embodiment is an example in which a gap adjustment layer 8 and a dielectric prism 9 are bonded together using an adhesive 10 having almost the same refractive index as the dielectric prism 9. Moreover, the thickness of the gap adjustment layer 8 is thick at the center and becomes thinner toward both ends with respect to the width direction (X-axis direction) perpendicular to the incident light. As a specific example, now the gap adjustment layer 8
refractive index ng=1.46, refractive index n of dielectric prism 9
c = 1.8, the refractive index nf of the waveguide layer 7 = 1.6, its thickness 1.5 μm, the refractive index ns of the substrate 6 = 1.46, and the beam of incident light at the bottom surface of the dielectric prism 9. Assume that the shape is a circle with a diameter of 2 mm. Further, a polyimide resin is used for the adhesive 10, and its refractive index is set to 1.75.

In this state, in order to maximize the efficiency with which the incident light is coupled to the waveguide layer 7, the thickness of the gap adjustment layer 8 relative to the beam position in the width direction of the incident light must be adjusted as shown by curve B in FIG. The maximum coupling efficiency can be obtained by changing the thickness so that it is thick at the center 8a of the beam and becomes thinner toward both ends 8b of the beam in the width direction.

In this case, the thickness of the gap adjustment layer 8 can be adjusted by forming a film to a constant thickness by vapor deposition, sputtering, CVD, etc., and then setting the optimal thickness by changing the amount of etching depending on the location when etching. can. In addition, the gap adjustment layer 8 is not formed over the entire surface of the waveguide layer 8, but is formed only at the light coupling portion, and is tapered in the propagation direction of the incident light to prevent loss. A guided mode can be propagated.

Next, the first embodiment of the invention as claimed in claim 2 is shown in FIG.
) (b). Note that the same reference numerals are used for the same parts as in the invention described in claim 1.

Generally, when performing prism coupling, it is necessary to make the incident beam reach the end of the bottom surface of the prism 4, as explained in the prior art in FIG. if,
As shown in FIG. 10, if the beam is incident inside the end of the prism 4, even if the optimal light coupling conditions are met, the beam coupled to the waveguide layer 2 will re-enter the prism. 4 and coupling (this is called decoupling)
and goes out into external space. For this reason, the incident beam needs to coincide with the end of the prism 4. For this reason, in the first embodiment of the invention, the shape of the bottom end of the dielectric prism 9 is matched to the beam shape. In addition, in order to eliminate such a change in the shape of the bottom end of the dielectric prism 9, in the second embodiment of the invention as claimed in claim 1, the surface shape of the gap adjustment layer 8 is curved using the adhesive 10. changed into a shape.

Embodiments of the present invention include such a dielectric prism 9
The purpose is to perform highly efficient light coupling without changing the shape of the bottom end of the gap adjusting layer 8 or changing the surface shape of the gap adjustment layer 8 using the adhesive 1o. This will be explained below.

A waveguide layer 7 is formed on the substrate 6. On this waveguide layer 7, there is a layer with a lower refractive index than this, in the propagation direction of the incident light (
a gap adjustment layer 8 whose refractive index changes in the width direction (X-axis direction) perpendicular to the Z-axis direction in accordance with the beam shape of the incident light;
is formed.

This gap adjustment layer 8 can be formed by using a photosensitive polymer resin and changing the refractive index depending on the amount of exposure by exposure to ultraviolet rays. A dielectric prism 9 having a higher refractive index than the waveguide layer 7 is formed on the gap adjustment layer 8 .

A specific example in which the maximum optical coupling efficiency can be obtained in such a configuration will be described. Now, the thickness of the gap adjustment layer 8 is 0.3 μm, the refractive index nf of the waveguide layer 7 is 1.6, the thickness is 1.5 μrn, and the refractive index nc of the dielectric prism 9 is
1.8, the refractive index n5 of the substrate 6 is assumed to be 1.46, and the beam shape of the incident light at the bottom surface of the dielectric prism 9 is a circle with a diameter of 2 ms.

In this state, in order to maximize the efficiency with which the incident light is coupled to the waveguide layer 7, the refractive index of the gap adjustment layer 8 with respect to the beam position in the width direction of the incident light must be The maximum coupling efficiency can be obtained by changing the value from low at the center 8a of the beam to increasing toward both ends 8b of the beam in the width direction. Furthermore, in the case of this embodiment as well, the gap adjustment layer 8 is limited to only the light coupling portion, and by providing a taper in the propagation direction of the incident light, it is possible to propagate the guided mode without loss. can.

Next, a second embodiment of the invention as claimed in claim 2 is shown in FIG.
) (b).

A waveguide layer 7 is formed on the substrate 6, and a gap adjustment layer 8 having a lower refractive index than the waveguide layer 7 is laminated on the surface of the waveguide layer 7.

A metal layer 11 having a portion removed in the same shape as the beam shape of the incident light is laminated on top of the gap adjustment layer 8. A dielectric prism 9 having a higher refractive index than the waveguide layer 7 is provided above the metal layer 11 .

In this case, the refractive index of the gap adjustment layer 8 changes as shown in FIG. 6 in accordance with the beam shape, as in the first embodiment described above. Further, the metal layer 11 is formed by forming a film by evaporation, sputtering, etc., and then removing it by etching into a predetermined shape having the same diameter as the beam shape using a photolithography technique. The removed portion may be filled with a medium having the same refractive index as the dielectric prism 9.

Effects of the Invention In the invention described in claim 1, by changing the thickness of the gap adjustment layer in accordance with the beam shape of the incident light,
Optimal light coupling conditions can be determined, and thereby high light coupling efficiency can be obtained over the entire incident light beam.

In the invention as claimed in claim 2, by changing the refractive index of the gap adjustment layer in accordance with the beam shape of the incident light, the optimum light coupling condition can be determined, and thereby the thickness of the gap adjustment layer can be determined. It is possible to obtain high light coupling efficiency over the entire incident light beam without the hassle of adjustment.

[Brief explanation of drawings]

FIG. 1(a) is a side view showing the first embodiment of the invention as claimed in claim 1, FIG. 1(b) is a front view thereof, and FIG. 2(a) is the first embodiment of the invention as claimed in claim 1. Side view showing the second embodiment, second
Figure (b) is a front view thereof, Figure 3 is a graph showing the relationship between the beam position in the width direction of incident light and the gap adjustment layer in the invention according to claim 1, and Figure 4 (a) is according to claim 2. FIG. 4(b) is a front view thereof, and FIG. 5(a) is a side view showing a second embodiment of the invention as claimed in claim 2. FIG. 6 is a graph showing the relationship between the beam position in the width direction of the incident light and the gap adjustment layer in the invention according to claim 2, and FIG. 7 is a side view showing the conventional example. Fig. 8 is a graph showing the relationship between the film thickness of the gap adjustment layer and optical coupling efficiency, Fig. 9 is a perspective view showing the shape of the incident beam at the bottom of the prism, and Fig. 10 is the incident position of the light incident on the prism. FIG. 4 is a side view showing the situation when the position is changed to the central part of the bottom surface of the prism. 5... Incident light, 6... Substrate, 7... Waveguide layer, 8
...Gap adjustment layer, 9...Dielectric prism application
People Ricoh Co., Ltd. - A rank member (aTrL) Figure gi \ Tsubu kun! 1MΦTsukihozuki 19 people-) Bini to a 1i (TI mouth 1) Gomo figure 1 'O figure

Claims (1)

[Claims] 1. A waveguide layer formed on a substrate, and a beam of the incident light formed on the waveguide layer and having a lower refractive index than the waveguide layer and extending in the width direction perpendicular to the propagation direction of the incident light. 1. A high-efficiency prism coupling device comprising: a gap adjustment layer whose thickness changes depending on the shape; and a dielectric prism formed on the gap adjustment layer and having a higher refractive index than the waveguide layer. 2. A waveguide layer formed on the substrate, and a waveguide layer formed on the waveguide layer that has a lower refractive index than the waveguide layer and refracts the incident light in the width direction perpendicular to the propagation direction of the incident light in accordance with the beam shape. A high-efficiency prism coupling device comprising a gap adjustment layer with a changed index and a dielectric prism formed on the gap adjustment layer and having a higher refractive index than the waveguide layer.