JPH09105824A - Waveguide type optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress variation in the insertion loss of a reflection type wavelength multiplexer demultiplexer (WDM) and improve the product yield by inserting a curved optical element into a groove which is formed crossing waveguides. SOLUTION: The curved optical element 7 is inserted into the groove 6 which is formed across the single-made optical waveguides 3-5 formed on the plane substrate 1. It is considered that the insertion loss of a dielectric multi- layered film filter reflection type WDM consisting of a dielectric multi-layered film filter a is caused by the tilt angle of the dielectric multi-layered film filter, so when the dielectric multi-layered film is formed, vapor deposition is performed under conditions where the filter curves and the curvature is intentionally utilized to suppress the tiling of the filter. Here, a relation of 0<=Dg->Df<=W×W/(8×R) is valid, where R is the radius of the curvature of the dielectric multi-layered film filter, W is the lateral width of the filter, Df is the film thickness of the filter, and Dg is the groove width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical element for optical communication, and more particularly to a wavelength multiplexer / demultiplexer having a function of multiplexing / demultiplexing lights having different wavelengths.

[0002]

2. Description of the Related Art As shown in FIG. 14, a circuit in which a dielectric multilayer filter 7 is inserted at an intersection 6 of optical waveguides 3, 4, 5 formed on a substrate 1 has a simple and excellent dielectric. Since the wavelength characteristics of the multilayer filter can be effectively used, it is extremely useful as a wavelength division multiplexer (WDM) with small crosstalk. (In FIG. 15, reference numeral 2 is a clad.) The operation principle will be briefly described. When the wavelength-multiplexed light enters from the common port 3 ', the light having the transmission wavelength λ ₁ of the dielectric multilayer filter passes through the dielectric multilayer filter and is output from the port 4'. On the other hand, the light having the blocking wavelength λ ₂ of the dielectric multilayer filter is reflected by the dielectric multilayer filter at the intersection of the waveguides and output from the port 5 '. Generally, it is difficult to realize a wavelength filter having a wavelength resolution of 1 nm or less using a dielectric multilayer filter, but for example, 1.3 μm light transmission / 1.5
It is easy to realize a wavelength filter having a wavelength resolution of 10 nm to several hundreds nm, such as 5 μm light blocking, and its crosstalk is extremely small. In the circuit of FIG. 14 actually manufactured by using a dielectric multilayer filter of 1.3 μm light transmission / 1.55 μm light blocking,
When 1.55 .mu.m light was incident from the common port 3 ', the light leaking into the port 4'was as small as -45 dB as compared with the output light from the port 5', showing extremely good characteristics.
In this way, the reflection type WDM using the dielectric multilayer filter
Has been actively researched and developed as a practical optical component because a simple WDM can be realized by effectively utilizing the excellent wavelength characteristics of the dielectric multilayer filter.

[0003]

Conventionally, when a reflection type WDM using the above-mentioned dielectric multi-layer film filter is manufactured by using a single mode optical waveguide, there is a problem that variation in insertion loss is large. That is, there is a problem in that the insertion loss when the light of wavelength λ ₂ incident from the common port 3'is reflected by the dielectric multilayer filter and output to the port 5'is large. Therefore, suppressing this insertion loss variation was the most important issue in improving the product yield.

Further, when a large number of reflective WDMs are manufactured, the process of inserting the dielectric multilayer filter into the groove is difficult, and the work takes time. In order to realize a low-cost WDM, it was necessary to facilitate the step of inserting the dielectric multilayer filter into the groove.

[0005]

In order to solve the above problems, a waveguide type optical element according to the present invention comprises a single mode optical waveguide formed on a flat substrate and a groove formed across the optical waveguide. , And a warped optical element inserted in the groove.

Here, the optical waveguide is an intersecting single-mode optical waveguide having an intersecting portion, the groove is processed at the intersecting portion, and the warped optical element is composed of a dielectric multilayer film filter. A dielectric multi-layer film filter reflection type wavelength multiplexer / demultiplexer, wherein the radius of curvature R of the warp of the dielectric multi-layer film filter, the lateral width W of the filter, and the film thickness D of the filter.
f, between the groove width Dg,

[0007]

## EQU00002 ## It is preferable that the relational expression 0.ltoreq.Dg-Df.ltoreq.W.times.W / (8.times.R) holds.

Further, it is preferable that the dielectric multilayer filter is composed of a polyimide substrate and a dielectric multilayer, the single mode optical waveguide is a buried waveguide, and the single mode waveguide of the groove is Also, it is preferable that the upper part be provided with a taper so that the groove width widens.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the first problem described above, we first investigated the cause of insertion loss. Most of the insertion loss is caused by reflection in the dielectric multilayer filter. The cause is the tilt angle θ of the dielectric multilayer filter.
it is conceivable that. This state is shown in FIG. Width Dg of groove 6
And the thickness Df of the dielectric multilayer filter 7, the dielectric multilayer filter is inclined. We initially reduced the difference between the filter film thickness Df and the groove width Dg in order to prevent the dielectric multilayer filter from collapsing,
Attempts were made to suppress the collapse of the filter by narrowing the gap between the two and increasing the depth of the groove. However, it has been clarified that when a fine groove is deeply machined by using a saw, the load applied to the teeth during machining becomes large and the groove itself tends to be inclined.

Therefore, in the present invention, in order to prevent the dielectric multilayer filter from collapsing, the warp of the dielectric multilayer filter is used. That is, vapor deposition is performed under the condition that the filter is warped when the dielectric multilayer film is formed,
The warp is intentionally used to prevent the filter from collapsing.
Specifically, if the film thickness Df of the dielectric multilayer filter is the groove width D
less than g and the warp s of the dielectric multilayer filter
If the total thickness of the dielectric film filter and the film thickness Df is set to be larger than the groove width Dg, the central portion of the dielectric multilayer film filter is in close contact with the side surface of the groove. As a result, the problem of the filter falling over in the groove is eliminated. The above condition is expressed by the following formula.

[0011]

## EQU00003 ## 0.ltoreq.Dg-Df.ltoreq.s (1) FIG. 16 shows how the multilayer filter warps. The radius of curvature of the warp is R, the amount of warp is s, and the length corresponding to the chord of the warped filter having a width W is W ′. When R >> W, W '/ 2
= W / 2 can be approximated. The triangles abc and cbd are similar. Therefore, s: W / 2 = W / 2: 2R-s,
Transform this formula

[0012]

(Equation 4)

Therefore, the warp s of the filter is determined by the radius of curvature R
Is sufficiently larger than the lateral width W of the filter, it is expressed by the following relational expression.

[0014]

S = W × W / (8 × R) (2) By selecting the groove width Dg and the film thickness Df of the filter within the range where the following expression is satisfied from the above two expressions, the filter is adhered to the side surface of the groove. It becomes possible.

[0015]

[Equation 6] 0 ≦ Dg−Df ≦ W × W / (8 × R) Since the filter is pressed against the side surface of the groove by its own warp, the dielectric multilayer filter is prevented from falling. Will be done. As a result, it is possible to suppress the variation in the insertion loss of light, which is a problem, and to manufacture a reflective WDM with a low insertion loss and a high product yield.

For the second problem, after the groove whose wall surface is perpendicular to the waveguide surface is processed, the groove entrance is further widened by using V-shaped teeth to form the groove of the dielectric multilayer filter. Facilitates insertion. At this time, by using a waveguide whose core is embedded inside,
Facilitates filter insertion without increasing optical insertion loss,
A low-cost wavelength multiplexer / demultiplexer can be realized.

The reflection type WDM of the present invention has an extremely small crosstalk and an ideal wavelength characteristic, and has a small insertion loss variation, which has been a problem in the past. As a result, the product yield is significantly improved. Further, the insertion work into the groove of the dielectric multilayer filter becomes easier. As a result of the above, a low-cost reflective WDM was realized.

[0018]

【Example】

Example 1 In this example, a silica-based planar lightwave circuit (PLC) manufactured by depositing silica-based glass on a silicon substrate is used. A silica-based PLC is manufactured on a silicon substrate by a flame deposition method and a reactive ion etching method, and an optical waveguide circuit having low loss and good compatibility with a single mode optical fiber is realized. For more details, Masao Kawauchi, "Planar Lightwave Circuit," Denron Theory C, Vol. 113, No. 6, 440-445, 1993,
It is described in.

The circuit configuration of the first embodiment is shown in FIG. The cores 3, 4 and 5 are formed on the silicon substrate 1 so as to be covered with the clad 2 to form the single mode optical waveguides 3, 4 and 5. A groove 6 is formed at a position where the optical waveguides 3 and 5 intersect.
Is formed, and an optical element 7 having a warp in the groove, which is a dielectric multilayer filter in this example, is inserted. Also, in FIG.
An enlarged sectional view of A'is shown in FIG. Further, an enlarged view of the dielectric multilayer filter insertion portion of FIG. 1 is shown in FIG. 3, a view of FIG. 3 seen from directly above is shown in FIG. 4, and an enlarged sectional view of line BB ′ in FIG. 4 is shown in FIG.
Shown in In this example, the optical axes of the optical waveguides 3 and 4 coincide with each other. The waveguide has a relative refractive index difference of 0.45 between the core and the clad.
%, The core size is 7 μm square. The dielectric multilayer filter is designed so that light of 1.3 μm is transmitted and light of 1.55 μm is reflected.

The simple operation principle will be described below. 1.3
When the lights of μm and 1.55 μm are combined and incident from the common port 3 ′, the light propagates through the single mode optical waveguide 3 and then only the light of 1.55 μm is passed through the dielectric multilayer filter 7. The reflected light passes through the optical waveguide 5 and the port 5 '.
Is output to On the other hand, the 1.3 μm light transmits through the dielectric multilayer filter 7, propagates through the optical waveguide 4, and is output from the port 4 ′.

Here, an enlarged view of the dielectric multilayer filter used in this embodiment is shown in FIG. Dielectric multilayer filter is 5
SiO ₂ / TiO ₂ is formed on the surface of the polyimide thin film 8 having a thickness of μm.
The multilayer film 9 was produced by vapor deposition of 9 μm, and the thickness of the entire filter was 14 μm. The conventional dielectric multilayer filter was manufactured under the condition that it hardly warps, but in the present invention, conversely, the internal stress in the dielectric film generated during the deposition of SiO ₂ / TiO ₂ is positively utilized. Then, the warp of the dielectric multilayer filter was generated. Specifically, a filter having a width W of 1 mm and a warp s of 10 μm and a radius of curvature R of 13 mm was manufactured. As a result, the warp amount of the filter is 10
If this filter is inserted into a groove having a width smaller than 24 μm, which is a total of μm and the thickness of the filter of 14 μm, the center portion of the filter is brought into close contact with the side surface of the groove, so that the collapse of the filter in the groove is suppressed. In this embodiment, a groove having a groove width of 20 μm and a groove depth of 150 μm is manufactured by using a dicing saw, and a filter having a radius of curvature of 13 mm, a width of 1 mm and a warp of 10 μm is inserted therein, and a dielectric multilayer filter reflective type. 100 WDM samples were prepared. FIG. 7 shows the distribution of the insertion loss of 1.55 μm light that is incident from the common port 3 ′ and is output from the port 5 ′ at this time. For comparison, FIG. 8 also shows the distribution of insertion loss of a dielectric multilayer filter reflective WDM, which is manufactured by inserting a conventionally used filter having a radius of curvature of 130 mm, a lateral width of 1 mm, and a warp of 1 μm. It can be seen that the average insertion loss and the variation of the insertion loss of the wavelength multiplexer / demultiplexer are reduced by using the dielectric multi-layer film filter having a large warp.

Example 2 By using the warp of the dielectric multilayer filter as described in Example 1, it is possible to manufacture a wavelength multiplexer / demultiplexer having a small insertion loss value and a small variation. However, when the dielectric multi-layered film filter has a warp, the groove insertion of the filter becomes difficult. The groove width is 20 μm as shown in Example 1.
It was quite difficult and time-consuming to insert a 14 μm-thick dielectric multilayer filter having a warp of 10 μm therein.

In order to solve this problem, we have prepared a groove having a constant groove width by using a dicing saw, and then re-machining the groove at the same position by using V-shaped teeth. Widened the entrance. Here, as the order of performing the groove processing, when the V-shaped groove is processed using the V-shaped tooth and then the groove processing is performed using the normal tooth having a constant tooth thickness,
There is a problem that the groove is tilted due to a slight positional deviation between the two groove processes. Therefore, it is effective to first form a groove having a constant groove width with the tooth 10 having a constant tooth thickness, and then perform groove processing using the V-shaped tooth 10 'for the purpose of widening the width of the groove entrance. . Fig. 9 shows the state before and after processing a groove with a constant groove width.
10 (a) and 10 (b), and FIGS. 10 (a) and 10 (b) show the states before and after processing for further widening the entrance of the groove. Here, FIG. 9C and FIG. 10C respectively show cross-sectional shapes of the teeth of the dicing saw.

A radius of curvature of 13 is formed in the groove thus produced.
FIG. 11 shows a state in which a dielectric multilayer filter having a width of 10 mm and a warp of 10 μm is inserted. An enlarged view of the filter portion is shown in FIG. 12, and an enlarged sectional view taken along the line CC ′ in FIG. 12 is shown in FIG.

The specific dimensions are as follows: the core of the waveguide is embedded 23 μm from the surface, and the tooth with the tip of 60 ° has a depth of 2
It was processed at 5 μm. At this time, the width of the entrance of the groove was 29 μm, which made the insertion of the filter much easier than 20 μm when the V-shaped teeth were not processed. As a result, the time required to insert the filter was shortened, and a low-cost wavelength multiplexer / demultiplexer was realized using the dielectric multilayer filter.

Although the embodiment of the present invention has been described with respect to the case where the silica-based waveguide is used, the circuit of the present invention can be applied to any buried waveguide such as a diffusion glass waveguide or a polymer waveguide other than the silica-based waveguide. It can also be applied.

In the present invention, 1.3 μm light is transmitted,
Although the wavelength multiplexer that reflects 1.55 μm light has been described, it is clear that it can be used as a wavelength multiplexer / demultiplexer in other wavelength regions by replacing the dielectric multilayer filters shown in the examples. is there.

Further, in the present invention, a dielectric multilayer filter in which a dielectric multilayer film of SiO ₂ / TiO ₂ is formed on a polyimide thin film substrate is used, but each material is not limited to this, and the filter is not limited to this. It is sufficient if it has the warp shown in the claims.

[0029]

INDUSTRIAL APPLICABILITY The wavelength multiplexer of the present invention has very good characteristics and can be easily manufactured. Therefore, the wavelength multiplexer is applied to a wavelength multiplexer / demultiplexer of a household optical transceiver module, a line monitoring coupler, and the like. It is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a reflective WDM using a dielectric multilayer filter of a first embodiment.

FIG. 2 is an enlarged cross-sectional view taken along the line AA ′ of FIG.

FIG. 3 is an enlarged view of the filter unit in FIG.

FIG. 4 is a view of FIG. 3 seen from above.

5 is an enlarged cross-sectional view taken along the line BB ′ of FIG.

FIG. 6 is a diagram showing the shape of a dielectric multilayer filter used in the first embodiment.

FIG. 7 is a diagram showing an insertion loss distribution of 1.55 μm light that is incident from the common port 3 ′ and is output from the port 5 ′ in the reflective WDM of the first embodiment.

FIG. 8 is a schematic diagram of a reflection type WDM using a conventional dielectric multilayer filter, which is a comparative control of the first embodiment, in which light is incident from a common port 3 ′ and is output from a port 5 ′.
It is a figure which shows the insertion loss distribution of 55-micrometer light.

FIG. 9 is a diagram for explaining groove processing with a constant groove width in the second embodiment.

FIG. 10 is a diagram illustrating a process for widening the entrance of the groove manufactured in FIG.

FIG. 11 is a diagram showing a reflective WDM using the dielectric multilayer filter of the second embodiment.

FIG. 12 is an enlarged view of the filter unit in FIG.

13 is an enlarged cross-sectional view taken along the line CC ′ of FIG.

FIG. 14 is a view showing a reflection type WDM using a dielectric multilayer filter according to a conventional technique.

FIG. 15 is a diagram for explaining the cause of large and varying insertion loss in a conventional reflective WDM filter.

FIG. 16 is a diagram for explaining a warp amount of a filter.

[Explanation of symbols]

1 Silicon Substrate 2 Clad 3 Input Waveguide 3'Common Port 4 First Output Waveguide 4'First Output Port 5 Second Output Waveguide 5'Second Output Port 6 Dielectric Multilayer Filter Insertion Groove 6'Insert groove of the dielectric multilayer filter with widened entrance of the groove 7 Dielectric multilayer filter 8 Polyimide thin film substrate 9 SiO ₂ / TiO ₂ Dielectric multilayer film 10 Dicing saw tooth 10 'Tip shape is V-shaped Of the dicing zo W width of the dielectric multilayer filter s warpage amount of the priority multilayer filter R radius of curvature of the dielectric multilayer filter Df thickness of the dielectric multilayer filter Dg insertion of the dielectric multilayer filter Groove width θ Tilt angle of dielectric multilayer filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Kawachi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. A single mode optical waveguide formed on a flat substrate, a groove formed across the optical waveguide, and a warped optical element inserted in the groove. Waveguide type optical device. 2. A dielectric single-mode optical waveguide in which the optical waveguide has an intersecting portion, the groove is processed in the intersecting portion, and the warped optical element is a dielectric multilayer filter. A multilayer multi-layer film filter reflection-type wavelength multiplexer / demultiplexer, wherein the curvature radius R of the warp of the dielectric multi-layer film filter, the lateral width W of the filter, the film thickness Df of the filter, and the groove width Dg are: The waveguide type optical element according to claim 1, wherein a relational expression of 0 ≦ Dg−Df ≦ W × W / (8 × R) is established. 3. The waveguide type optical device according to claim 2, wherein the dielectric multilayer filter is composed of a polyimide substrate and a dielectric multilayer film. 4. The single-mode optical waveguide is a buried waveguide, and a taper is provided in the groove above the single-mode waveguide so as to widen the groove width. 3. The waveguide type optical element according to any one of 3 above.