JPH0269702A - Waveguide and its manufacture, and optical switch - Google Patents

Abstract

PURPOSE:To obtain the waveguide which is small in coupling loss and wave guiding loss and stable in standard frequency by providing a width variation part which is arranged between a wide and a narrow part and varies the widths of the wide and narrow parts continuously. CONSTITUTION:The waveguide is a three-dimensional waveguide. The waveguide 3 is formed by diffusing a material which increases the refractive index in a waveguide substrate 2 and consists of the constant-width wide part 4, the narrow part 5 which has narrower constant width, and the width variation part 6 which is arranged between the wide part 4 and narrow part 5. The narrow part 5 is formed coaxially with the wide part 4 and the width variation part 6 is so formed as to vary the widths of the wide part 4 and narrow part 5 continuously. In the waveguide 1, the specific refractive index difference is smaller at the wide part 4 than at the narrow part 5 and the specific refractive index difference at the width variation part 6 varies continuously from that at the wide part to that at the narrow part. Consequently, the coupling loss and wave guiding loss are small and the standard frequency is stable.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a waveguide with good coupling to an optical fiber, a method for manufacturing the same, and an optical switch using this waveguide.

"Prior Art" Recently, various waveguide type optical devices have been proposed and applied to optical switches and the like.

By the way, the two-dimensional guiding waveguide (hereinafter abbreviated as waveguide), which is the basis of such a waveguide type optical device, has a three-dimensional waveguide layer that has the same width and a uniform relative refractive index in the waveguide. It is common for things to be configured with differences.

"Problem to be Solved by the Invention" However, in the above waveguide, when the cross-sectional area of the waveguide layer in the waveguide is small when connecting to an optical fiber, the cross-sectional area and the core surface of the optical fiber are They do not match, and this causes a problem of increased coupling loss. On the other hand, when applying such a waveguide to an optical switch, for example, if the waveguide layer is fabricated by bending it in the waveguide substrate, the larger the cross-sectional area of the waveguide layer, the larger the bending area. There is a problem that waveguide loss occurs.

Therefore, in order to reduce the above-mentioned loss when applying a waveguide to an optical switch, etc., the cross section of the waveguide layer should be made large at the coupling part with the optical fiber, and the cross section should be made large at the part where the waveguide layer is bent. It may be possible to make the waveguide smaller, but there is currently no method to fabricate a waveguide that satisfies both of the above conditions without changing the normalized frequency. It is impossible to get things.

This invention was made in view of the above circumstances, and its H purpose is to provide a waveguide with low coupling loss and waveguide loss and a stable standard frequency, and a manufacturing method thereof, and to reduce transmission loss. The purpose is to provide fewer light switches.

[Means for solving the problem] In the waveguide of the invention described in claim 1 of the present invention,
A wide part having a constant width, a narrow part having a constant width narrower than the wide part and having the same axis as the wide part, and arranged between the wide part and the narrow part. It has a waveguide layer consisting of a width changing part in which the width of the wide part and the narrow part is continuously changed, and the relative refractive index difference between the wide part and the surrounding waveguide substrate is the narrow part. and its surrounding substrate, and the relative refractive index difference between the variable width portion and its surrounding waveguide substrate is from the relative refractive index difference in the wide portion to the relative refractive index difference in the narrow portion. The solution to the above problem was to change continuously.

In addition, in the method for manufacturing a waveguide according to the second aspect of the present invention, a diffusion path is formed by diffusing a substance that increases the refractive index into the waveguide substrate with a constant width, and then the diffusion path is One width is widened and the other is narrowed, and a substance that lowers the refractive index is deposited on the waveguide substrate so that the width between them changes continuously to form an adhesion layer, and the diffusion path is The part where the substance that lowers the refractive index lσ is not attached is used as a temporary waveguide layer, and then the above-mentioned attached layer is adjusted so that the wider side of the temporary waveguide layer is thinner than the narrower side, and then the above-mentioned attached layer is The solution to the above problem is to diffuse a material constituting the waveguide into a waveguide substrate and form a waveguide layer along the temporary waveguide layer.

Furthermore, in the optical switch according to claim 3 of the present invention, a pair of three-dimensional waveguide layers are formed on the waveguide substrate, and these three-dimensional waveguide layers are arranged between the straight portions serving as both ends and the straight portions. These curved parts are provided with adjacent parts where the curved parts are adjacent to each other through a narrow gap, and an electrode for applying a voltage to the adjacent parts is provided in the adjacent parts. In an optical switch, which is provided in the vicinity or on an adjacent part, and in which the end opposite to the curved part of the straight part forming the three-dimensional waveguide layer serves as an optical fiber coupling part, A means for solving the above problems is to use the waveguides described in claim 1 in each waveguide substrate, and to use the wide part side of the waveguide as an optical fiber coupling part and the narrow width part as a coupling part with the curved part side. And so.

"Example" First, the waveguide described in claim 1 of the present invention will be described.

FIG. 1 shows an example of a waveguide according to the present invention, and reference numeral l in FIG. 1 indicates a waveguide. This waveguide l is a three-dimensional waveguide, and is composed of a waveguide substrate 2 and a waveguide layer 3. The waveguide substrate 2 is made of LiNbO3, LiTao3
, PLZT [PZT (lead titanate/lead zirconate solid solution P
It is made of an electro-optical crystal such as a translucent piezoelectric material in which part of the Pb in bTiO3/PbZr03) is replaced with La), or a material such as glass (Corning 7059) or quartz, and is made of a material such as a conductive material as described below. It is formed by diffusing a substance that lowers the refractive index in the periphery of the wave layer 3. Here, as the substance that lowers the refractive index, elements such as Mg, Na, AI, F, or compounds containing these elements are used.

The waveguide layer 3 is formed by diffusing a substance that increases the refractive index into the waveguide substrate 2, and includes a wide portion 4 having a constant width and a narrow portion having a constant width narrower than the wide portion 4. 5, and a width varying portion 6 disposed between the wide portion 4 and the narrow portion 5.

The narrow width portion 5 is formed along the same axis as the wide width portion 4, and the width changing portion 6 is formed so as to continuously change the width of the wide width portion 4 and the narrow width portion 5. It is. Here, the substances that increase the refractive index include TiJ'e, Ta, Nb,
Elements such as Ag or compounds containing these elements are used.

Also, waveguides! In this case, the relative refractive index difference (Δ) between the waveguide layer 3 and the surrounding waveguide substrate 2 differs depending on each part of the waveguide layer 3, as shown in FIG.

That is, in the waveguide l, the relative refractive index difference in the wide part 4 of the waveguide layer 3 is smaller than the relative refractive index difference in the narrow part 5, and the relative refractive index difference in the width changing part 6 is smaller than the relative refractive index difference in the wide part 5. The refractive index difference changes continuously from the refractive index difference to the relative refractive index difference at the narrow portion.

Next, a method for manufacturing the waveguide 1 will be described based on the manufacturing method according to claim 2.

First, as shown in FIG. 2, a diffusion path 7 is formed in the waveguide substrate 2 by diffusing the above-described substance that increases the refractive index in a constant width. Here, as a method for forming the diffusion path 7, for example, Ti
When producing a diffusion waveguide, a method such as sputtering Ti onto the waveguide substrate 2 to form a waveguide layer pattern and then thermally diffusing it is employed.

Next, as shown in FIGS. 3 and 4, the substance that lowers the refractive index is deposited on the waveguide substrate 2 and the diffusion path 7 by sputtering or the like to form an adhesion layer 8 and The portion along which the substance that lowers the refractive index is not attached is defined as the guiding wave layer 9. Here, in forming the adhesion layer 8, as shown in FIG. 3, one width of the diffusion path 7 is widened and the other width is narrowed, and the width between them is changed continuously. A substance that lowers the refractive index is deposited. That is, on one side of the diffusion path 7, the substance is deposited only on the waveguide substrate 2 outside the diffusion path 7, and on the other side, it is deposited from the top of the waveguide substrate 2 to slightly inside the diffusion path 7, and In between, the edge 8a of the adhesive layer 8
is attached so that it changes continuously from the waveguide substrate 2 side to the inside of the waveguide layer.

Next, as shown in FIG. 5, the adhesive layer 8 is formed so that the wider side of the guiding wave layer 9 is thinner than the narrower side, and the thickness of the adhesive layer 8 between them changes continuously. adjust. In this case, the adhesion layer 8 can be adjusted by attaching a mask to an appropriate location on the adhesion layer 8 and etching it while changing the etching to shave off the wide side of the teaching waveguide 9, or vice versa. A method may be adopted in which a substance that lowers the refractive index is re-attached to appropriate locations on the adhesion layer 8 and the narrower side of the teaching waveguide 9 is made thicker.

Thereafter, the entire waveguide substrate 2 is heated to diffuse the substance constituting the adhesion layer 8 into the waveguide substrate, and as shown in FIG. A waveguide layer 3 is obtained in which the narrow side thereof is a narrow width portion 5 and the space therebetween is a width variation portion 6.

In the waveguide l obtained in this way, the waveguide layer 3
Since one cross section is large and the other is small, if the larger one is used as a coupling part with an optical fiber, the coupling loss will be reduced, and if the smaller one is bent, the waveguide loss will be reduced. Further, the relative refractive index difference in the wide portion 4 is made smaller than the relative refractive index difference in the narrow portion 5, and the relative refractive index difference in the width changing portion 6 is changed from the relative refractive index difference in the wide portion 4 to the narrow portion 5. Since the relative refractive index difference is made to change continuously up to the relative refractive index difference, the normalized frequency becomes approximately constant over the entire length of the waveguide layer 3.

Next, an optical switch according to claim 3 will be explained as an application example of such a waveguide l.

FIG. 6 shows an example of an optical switch according to claim 3 of the present invention, and the reference numeral [0 in FIG. 6 indicates an optical switch.

This optical switch 10 has Y cut L + N bo 3
A pair of three-dimensional waveguide layers 1 are placed on a waveguide substrate ll consisting of
2. I2 is formed, and an electrode 13.13 is provided for applying a voltage between the three-dimensional waveguide layer 12.12.

The three-dimensional waveguide layer I2.12 has straight portions 12a, 12a, . . . which serve as both ends, and these straight portions 12a.

It consists of curved parts +2b and 12b arranged between 12a... The straight parts 12a, 12a, and their surrounding parts have the same configuration as the waveguide I shown in FIG. It is formed so that the relative refractive index difference becomes larger from the wide part to the narrow part. Also,
These straight portions 12a, 12a... are arranged such that their wide portions are placed outward and their narrow portions are placed inward on the waveguide substrate II. It is a coupling part with the optical fiber 14 shown by . The curved portions 12b, 12b have the same width as the narrow portion and are formed to have the same relative refractive index difference, and the adjacent portions 15 that are adjacent to each other with a narrow gap are provided. It is something that was given.

The electrode 13.13 is arranged on the side of the adjacent portion 15, and by applying a voltage between the electrodes 13.13, the refractive index in the adjacent portion 15 is changed by an electro-optical effect. It's Norano.

Based on such a configuration, the optical switch IO has electrodes 13 .
By applying a voltage between the two three-dimensional waveguide layers 13, it becomes possible to transmit an optical signal from one three-dimensional waveguide layer 12 to the other three-dimensional waveguide layer 12.

In such an optical switch 10, the optical fiber I4
Since the cross section of the waveguide layer at the coupling part with the waveguide layer is made large, the coupling loss is reduced, and the curved part 12b is formed with a narrow part having a small cross section of the waveguide layer, so the waveguide loss is reduced.
Furthermore, the normalized frequency is approximately constant over the entire length of the three-dimensional waveguide layer 12.

Specific examples of the present invention will be shown below.

(Specific example 1) A waveguide 1 shown in FIG. 1 was fabricated.

First, as shown in Fig. 2, Y cut L iN bo 3
6 μm of Ti was deposited on the waveguide substrate 2 made by sputtering.
Deposited at shoulder width and further heated at 1060°C in water vapor for 5 minutes.
The mixture was heated for a period of time to cause diffusion, thereby forming a diffusion path 7 having a width of 6 μm and a maximum depth of 3 μm.

Next, as shown in FIGS. 3 and 4, MgO was deposited onto the waveguide substrate 2 and the diffusion path 7 to a thickness of 2 μm by sputtering to form an adhesion layer 8. Here, in forming the adhesion layer 8, the width of the non-adhesion part along the diffusion path 7 indicated by d1 in FIG. It was formed so as to change continuously from the 8μ order to the 5μ order.

Next, a mask layer is formed on the adhesive layer 8 other than on the adhesive layer 8 where the width of the non-adhesive layer is 8μ shoulder, and Ar dry etching is performed to reduce the thickness of the adhesive layer 8 in the area where the mask layer is not provided as shown in FIG. was set to 0.5 μm, and Ar dry etching was performed by appropriately moving the position of the mask layer to continuously change the thickness of the adhesion layer 8 around the part where the width of the non-adhesion layer changed continuously. .

Thereafter, the entire waveguide substrate 2 was heated at 950° C. for 4 hours to diffuse MgO into the waveguide substrate 2, thereby obtaining the waveguide 1 shown in FIG. 1.

When the relative refractive index difference at each part of the obtained waveguide l was investigated, it was found to be 0.1% at the location indicated by A in FIG. 1, 0.12% at the location indicated by B, and 0.0% at the location indicated by C. 14%, and 0.16% at the location indicated by D.

(Specific example 2) An optical switch IO shown in FIG. 6 was manufactured.

The straight portion 12 is made with the same configuration as that produced in the previous specific example 1.
a, 12a..., and the straight portion 12aS
The distance Hd3 between 12a was set to 250 μz.

Further, for the curved portions +2b and 12b, the radius indicated by R1 in FIG. 6 was set to 30R1, and the radius indicated by <R was set to 3OR. Further, the distance d4 between each waveguide layer in the adjacent portion 15 was set to 4 μm.

When we connected an optical fiber to an optical switch with this configuration and examined the transmission loss, we found that the coupling loss was 25 dB and the waveguide loss was 0.5 dB, totaling 3. It was OdB. In addition, as a comparative example, an optical fiber was connected to an optical switch consisting of a conventional waveguide with a uniform width and a uniform relative refractive index difference at each location, and the transmission loss was similarly investigated. The coupling loss was 40 dB and the waveguide loss was 2 dB. From these results, it was confirmed that the optical switch of the present invention has superior transmission performance compared to the conventional one.

"Effects of the Invention" As explained above, in the waveguide according to claim 1 of the present invention, one of the waveguide layers has a large cross section and the other is small, so the larger one is used as the coupling part with the optical fiber. If the smaller one is bent, the waveguide loss will be reduced. Furthermore, the relative refractive index difference in the wide part is made smaller than the relative refractive index difference in the narrow part, and the relative refractive index difference in the beveled width part is increased from the relative refractive index difference in the wide part to the relative refractive index difference in the narrow part. Since it is made to change continuously, the normalized frequency is almost constant over the entire length of the waveguide layer, and it can be used for various optical devices such as optical switches.

Moreover, according to the method for manufacturing a waveguide described in claim 2 of the present invention, the waveguide described in claim 1 can be easily manufactured.

Furthermore, in the optical switch according to claim 3 of the present invention, since the cross section of the waveguide layer at the coupling portion with the optical fiber is increased, the coupling loss is reduced, and the narrow portion with a small cross section of the waveguide layer is Since the curved part is formed in this configuration, the waveguide loss is reduced, and the normalized frequency is almost constant over the entire length of the three-dimensional waveguide layer, so the overall size can be reduced and the optical Application to IC etc. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a waveguide according to claim 1 of the present invention, and FIGS. 2 to 5 are diagrams for explaining the manufacturing method according to claim 2 in order of steps. The figure is a perspective view of the main parts, Figure 3 is a plan view, Figure 4 is a view taken along the ■-IV line in Figure 3, Figure 5 is a view taken along the ■-V line in Figure 2, and Figure 6 is a view taken along the ■-V line in Figure 2. FIG. 3 is a schematic configuration diagram of an optical switch according to claim 3. l... Waveguide, 2... Waveguide substrate, 3
...Waveguide layer, 4...Wide part, 5...
...Narrow width part, 6...Width change part, 7...Diffusion path, 8...Adhesion part, 9...Teaching wave path, IO・
...Optical switch, II...Waveguide substrate,
12... Three-dimensional waveguide layer, 12a... Straight part, +2b... Curved part, 13... Electrode,
14... Optical fiber, 15... Adjacent part.

Claims (3)

[Claims] (1) A wide part with a constant width, a narrow part having a constant width narrower than the wide part and having the same axis as the wide part, and a space between the wide part and the narrow part. It has a waveguide layer consisting of a width changing part that is arranged to continuously change the width of the wide part and the narrow part, and the relative refractive index difference between the wide part and the surrounding waveguide substrate is the same as the width of the narrow part. smaller than the relative refractive index difference between the variable width section and its surrounding substrate, and the relative refractive index difference between the variable width section and its surrounding waveguide substrate is greater than the relative refractive index difference in the wide section to the relative refractive index difference in the narrow section. A waveguide that is characterized by a continuous change in temperature. (2) A diffusion path is formed by diffusing a substance that increases the refractive index in a certain width on the waveguide substrate, and then one of the diffusion paths is widened and the other narrowed, and the width between them is A substance that lowers the refractive index is deposited on the waveguide substrate so that the refractive index changes continuously to form an adhesive layer, and a portion along the diffusion path where the substance that lowers the refractive index is not attached is used as a temporary waveguide layer. ,
Next, the adhesion layer is adjusted so that the wider side of the temporary waveguide layer is thinner than the narrower side of the temporary waveguide layer, and then the substance constituting the adhesion layer is diffused into the waveguide substrate and spread along the temporary waveguide layer. A method for manufacturing a waveguide, the method comprising forming a waveguide layer. (3) A pair of three-dimensional waveguide layers are formed on a waveguide substrate, and each of these three-dimensional waveguide layers is composed of a straight part serving as both ends and a curved part disposed between these straight parts, and The curved portion is provided with adjacent portions where the curved portions are adjacent to each other through a narrow gap, and an electrode for applying a voltage to the adjacent portion is provided near or on the adjacent portion, and the straight portion is provided with an electrode for applying a voltage to the adjacent portion. An optical switch having an end opposite to the curved part as an optical fiber coupling part, wherein the straight part forming the three-dimensional waveguide layer and the waveguide substrate forming the periphery of the straight part forming the three-dimensional waveguide layer are each provided with the waveguide substrate described in claim 1. Using a waveguide,
An optical switch characterized in that the wide side of the waveguide is an optical fiber coupling part, and the narrow side is a coupling part with a curved part.