JPS63282704A - Manufacture of optical circuit - Google Patents

Abstract

PURPOSE:To execute with high accuracy an optical axis alignment of an optical fiber for constituting an optical element, and an optical fiber for input and output by forming a thin layer consisting of a material for constituting a guide on the whole surface of a substrate, and working the thin layer into a desired pattern. CONSTITUTION:First of all, on the whole surface of a quartz substrate 20, a thin film 21 consisting of quartz is formed. Subsequently, on the whole surface of the thin film 21, a photoresist 22 is formed. Thereafter, on the resist 22, a photomask 23 having an opening in only a part corresponding to a pattern forming area of the thin film 21 is formed and photoirradiation is executed, and the resist 22 being right under the opening of the mask 23 is hardened. After having removed the mask 23, the resist 22 is developed and the resist pattern 22 is formed. In the end, by using the pattern 22 as a mask, etching of the thin film 21 is executed, and the guide 21 is formed. Thereafter, in the guide 21 of the substrate 20, an optical fiber 24 is provided, and an axial alignment and a connection of each optical fiber are executed. In such a way, the optical axis alignment with the optical fiber for input and output can be executed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method of manufacturing an optical circuit incorporating an optical element constructed from an optical fiber.

(Prior art and problems to be solved by the invention) As a low-loss optical branch circuit, a circuit incorporating a quartz waveguide as shown in Fig. 5 has been known. Since the loss is low, there is an advantage that a low-loss circuit can be obtained relatively easily. In FIG. 5, quartz substrate 1
Above, there is a Y-branch waveguide 2 made of quartz, an input optical fiber 3 connected to the input port 2a of the branch waveguide, and an output optical fiber 3 connected to the two output ports 2b and 2c, respectively. Includes fiber 4.5! has been done. These input and output optical fibers 3 to 5 are disposed on the substrate 1 in a guide 6 of a predetermined length formed in parallel with a width approximately equal to the outer diameter of the optical fiber, so that the branch guide Axis alignment with the wave path 20 input/output port is performed. Figure 6 is this guide 6
2 is a cross-sectional view showing a state in which optical fibers are disposed on the substrate 1. Quartz 1i10 is formed on the entire surface of the substrate 1, and on this quartz layer 10, a pair of parallel parallel wires are formed at a spacing slightly larger than the outer diameter of the optical fiber 3. A wall-shaped guide 6 is formed in a direction perpendicular to the plane of the paper, and the optical fiber 3 is disposed within a groove formed by the pair of guides 6.

As shown in the cross section of FIG. 7, the Y-branch waveguide 2 includes a quartz layer 10 formed on a quartz substrate 1, and a high refractive index titania-doped quartz layer formed on the quartz layer 10 with a predetermined width. It consists of a layer IL and quartz N12 formed covering the front surface of this titania-doped quartz layer 11. That is, in the Y-branch waveguide 2, the low refractive index quartz layer 10.12 functions as a talarad, and the high refractive index titania-doped quartz layer 11 functions as a core.

Such a conventional optical branch circuit is manufactured as follows. That is, first, a quartz NIO layer and a titania-doped quartz layer 11 are sequentially formed on the front surface of a quartz substrate 1 by, for example, a flame deposition method. Thereafter, the titania-doped quartz layer 11 is selectively etched using conventional photolithography and reactive ion etching to form a desired pattern. Specifically, through this step, the core portion of the Y-branch waveguide 2 and the aforementioned guide 6 are formed simultaneously.

However, in such an optical branch circuit, connection loss occurs due to optical electromagnetic field profile mismatch between an optical fiber having a circular core and a quartz branch waveguide having a non-circular core as shown in FIG. In addition, there is a problem in that it is difficult to overlook losses such as optical loss due to interface irregularities that inevitably occur in the step of forming the branch waveguide core by etching.

Therefore, in order to solve the above problem, a low-loss optical branching circuit has been proposed that uses a branching waveguide made of optical fiber instead of the quartz branching waveguide.

When forming such an optical circuit having a branch waveguide made of optical fibers, for example, the optical fibers making up the branch waveguide may be connected to each other on the substrate, or the optical fibers making up the branch waveguide may be used for input or output. When joining an optical fiber, it is desired to align the optical axes of the two with high precision and reduce the insertion loss of the optical circuit as much as possible. Conventionally,
It is difficult to align the optical axes with high precision on such a substrate, and there has been a need for a method that can align the optical axes of optical fibers through a simple process.

The present invention has been made in response to the above-mentioned conventional demands, and includes a method for manufacturing an optical circuit incorporating an optical element constituted by an optical fiber such as a branching waveguide. Another object of the present invention is to provide a method for manufacturing an optical circuit, which allows alignment of the optical axis with an output optical fiber in a simple manner and with high precision.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, a guide is formed on the surface of the substrate, and then an optical element made of an optical fiber is connected to the optical element along the guide. The optical fibers forming the optical element are connected to each other, and the optical fibers forming the optical element and the input and output optical fibers are connected to each other. In the method for manufacturing an optical circuit, the step of forming a guide on the surface of the substrate includes a step of forming a thin layer made of a material constituting the guide on the entire surface of the substrate, and a step of processing the "FiiJif" into a desired pattern. It is composed of.

(Function) By selectively etching a thin layer of guide material formed on the entire surface of the substrate using an @phase processing method such as photolithography, a guide with a desired pattern is formed with high precision. Therefore, it is possible to perform axis alignment easily and with high precision without increasing manufacturing costs. Also, when changing the branch waveguide pattern,
After all the guides are removed by etching or the like, a new pattern of guides may be formed on the same substrate, and the substrate can be used repeatedly.

(Example) Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

The method for manufacturing an optical circuit of the present invention is characterized by the step of forming a guide for alignment of optical fibers on a substrate, and this guide forming step will be described in detail below with reference to FIG. 1.

First, a flame deposition method is applied to the entire surface of a quartz substrate 20 to form a thin film 21 made of quartz (FIG. 1(a)).

Next, a photoresist 22 is formed on the entire surface of the quartz thin film 21 (FIG. 1(b)). After that, an opening is formed on the photoresist 22 only in a portion corresponding to the pattern formation area of the quartz thin film 21. For example, by printing the photomask 23 and irradiating it with light, the photomask 2
Harden the photoresist directly under the opening No. 3 (see Figure 1 (
C)) After removing the photomask 23, the resist 2 is removed.
2 is developed to form a resist pattern 22' (FIG. 1(d)).

Finally, using the resist pattern 22° as a mask,
By etching the quartz thin film 21, for example, by reactive ion etching, a desired pattern is formed in the guide 21'.
(Fig. 1(e)). Although this figure shows a case where the photoresist 22 is not etched at all when etching the quartz thin film 21, in reality the photoresist is also etched, albeit in a small amount, so when deep etching is performed, the quartz thin film 21 and the photoresist 22 are etched. A material that is difficult to be etched during substrate etching (
For example, in the above case, after forming a 'gi film of Cr),
An etching pattern is formed on this CrFiJ film using photoresist, and quartz T1 is etched using this thin film as a master.
It is preferable to add a step of etching 1W4 again.

Thereafter, the optical fibers 24 are arranged within the guides 21' of the substrate 20, and the optical circuits are completed by aligning the axes and joining the optical fibers together.

FIG. 2 shows an example of an optical branch circuit manufactured by applying the manufacturing method of the present invention described above. That is, the optical circuit 30
is a 0-branch waveguide 3 composed of a branch waveguide 31, an input optical fiber 35, and an output optical fiber 36, 37.
1 is composed of three optical fibers 32, 33 and 34, and a reflective film 38 is interposed between the optical fibers 32 and 33 to reflect the optical signal at a desired reflection ratio. This reflective film 3
8 can be formed of a dielectric multilayer film, for example.

The optical fiber 34 is a core (not shown) of the optical fiber 32.
The optical fibers 32 and 33 are bonded to the side surfaces of the optical fibers 32 and 33 so that the optical axes of the optical fibers 32 and 33 align with the optical axes of the cores (not shown) of the optical fibers 34 when totally reflected by the reflective film 38. The end of the optical fiber 32 is connected to the input optical fiber 35, and the end of the optical fiber 33.34 is connected to the output optical fiber 36.3.
7, respectively. These input and output optical fibers 35 to 37 and each of the optical fibers 32 to 34 constituting the branch waveguide 31 are formed on the substrate 40 by the above process.
Mutual optical axes are aligned by being disposed within guides 41 to 47 formed above. That is, guide 4
Reference numerals 1 to 47 designate a pair of wall-like bodies that are erected in parallel at intervals substantially equal to the outer diameters of the optical fibers respectively disposed. After each optical fiber is arranged within these guides and the optical axes are aligned, each optical fiber is fixed onto the substrate 40 to complete the optical branch circuit 30. In such an optical branching circuit 30, the input optical fiber 35 is connected to the optical fiber 4 of the branching waveguide 31.
The optical signal incident on the optical fiber 34 is reflected by the reflective film 38 to the optical fiber 34 at a predetermined reflection ratio, and then propagated to the output optical fiber 37.

On the other hand, the optical signal transmitted from the optical fiber 32 through the reflective film 38 and propagated to the optical fiber 33 is propagated to the output optical signal 36, so that the optical signal can be branched at a desired branching ratio. It becomes possible.

However, in the branch waveguide 31 described above, the optical signal reflected by the reflective film 38 is propagated to the core of the optical fiber 34 via the cladding layer of the optical fiber 32, so an optical loss corresponding to the thickness of the cladding is unavoidable. to occur. In order to reduce this optical loss, for example, the optical fibers 32, 33, and 34 constituting the branch waveguide 31 may be constructed of optical fibers with a small diameter (thickness of the cladding is small), or As shown, the distance between the reflective film 38 and the end face of the optical fiber 34 is made extremely small by polishing the side surfaces of the optical fibers 32 and 33 where the optical fiber 34 is joined and reducing the thickness of the cladding layer. Bye. In addition, in FIG. 2, branch optical fibers 32, 33, 34 and another input/output optical fiber 35, 36 are connected.
．． Although the configuration in which 37 is connected is shown, the branch optical fiber 3
One end of 2.33.34 may be extended to serve as an input/output optical fiber.

FIG. 4 shows another example of an optical circuit formed by applying the manufacturing method of the present invention. In the figure, an optical circuit 50 includes an input optical fiber 51, output optical fibers 52 to 56, and It is composed of a branch waveguide 60 interposed between input and output optical fibers 51 to 56. This branching waveguide 60 includes an optical fiber 61 whose one end surface is joined to the end surface of the input optical fiber 51, and an optical fiber 61 whose one end surface is connected to the end surface of the input optical fiber 51.
An optical fiber 62 whose other end face is joined via a reflective film 80 and whose other end face is joined to the output optical fiber 52, and an optical fiber 6 whose one end face is joined to the side surface of the optical fiber 61 and 62.
3. An optical fiber 64 whose one end face is linearly joined to the other end face of the optical fiber 63 via a reflective film 81; one end face is joined to the other end face of the optical fiber 64 through a reflective film 82 and the other end face is completely an optical fiber 65 on which a reflective film 83 is formed; an optical fiber 66 whose one end surface is joined to the side surface of the optical fiber 63;
An optical fiber 67 whose one end surface is joined to the other end surface of the optical fiber 66 via a reflective film 84 and whose other end surface is joined to the output optical fiber 53, whose one end surface is joined to the side surface of the optical fiber 66 and which is totally reflected by the other end surface. an optical fiber 68 on which a film 85 is formed;
An optical fiber 69 whose one end surface is joined to the side surface of the optical fiber 85 and the other end surface is joined to the output optical fiber 54, and an optical fiber whose one end surface is joined to the optical fiber 64 and the other end surface is joined to the output optical fiber 55. 70. It is composed of an optical fiber 71 whose one end surface is joined to the side surface of the optical fiber 65 and the other end surface is joined to the output optical fiber 56. These input and output optical fibers 51 to 56 and the optical fibers 61 to 71 constituting the branching waveguide 60 are formed in the guide 90 formed on the substrate 100 by the above-mentioned method or quartz film photolithography method. By positioning them, they are joined to each other and fixed to the substrate 100. Incidentally, the reflective films 80 to 85 can be formed of a dielectric multilayer film similarly to the above.

In the optical circuit having such a configuration, the input optical fiber 51 and the output optical fiber 52 constitute a main path, and the output optical fibers 53 to 56 constitute a branch path, and the reflection ratio of the reflection film 80 is 10:1, and the reflection ratio is 10:1. The reflection ratio of the film 81.82.84 is 1=
1, since the reflective films 83 and 85 are total reflective films, one-eleventh of the optical signal input from the input optical fiber 51 to the optical fiber 61 of the branching waveguide 60 is reflected by the reflective film 80. The remaining signal is propagated to the output optical fiber 52 via the optical fiber 62.

The optical signal propagated to the optical fiber 63 is reflected by the reflective film 81, 1/2 of it is propagated to the optical fiber 66, 1/2 is further transmitted by the reflective film 84, and the remaining 1 is transmitted to the optical fiber 67.
/2 are reflected and propagated to the optical fibers 68, respectively. Then, the light is totally reflected from the optical fiber 67 to the output optical fiber 53 and from the optical fiber 68 by the total reflection film 85 and propagated to the output optical fiber 54 via the optical fiber 69, respectively. On the other hand, the optical signal transmitted through the reflection M81 and propagated to the optical fiber 64 is reflected by the reflection film 82, attenuated to 1/2, and propagated to the output optical signal 55 through the optical fiber 70. and,
The remaining 1/2 of the optical signal transmitted through the reflective film 82 is transferred to the total reflective film 8.
3, and is propagated to the output optical fiber 56 via the optical fiber 71.

Therefore, the optical signal reflected by the reflective film 80 is output to the output optical fibers 53 to 56, which serve as branch paths, by 1/4 each.

Such an optical branch circuit is useful, for example, as an optical component disposed at each branch point of a system that sequentially distributes optical signals from a center to a plurality of terminals at a plurality of branch points.

In the above-mentioned optical circuit, it is necessary to accurately control the length of each optical fiber 61 to 71 constituting the branch waveguide 60. This is possible by cutting the optical fiber and forming a mirror-like end surface.

It goes without saying that the manufacturing method of the present invention can be applied not only to the optical circuit having the branching waveguide described above, but also to various optical circuits such as a circuit having an optical multiplexer/demultiplexer.

(Effects of the Invention) As explained above, according to the present invention, after forming a guide on the surface of a substrate, an optical element made of an optical fiber is connected along the guide, and an input and an output connected to the optical element. In the manufacturing method of an optical circuit, the optical fibers forming the optical element are placed, and the optical fibers forming the optical element are connected to each other, and the optical fiber forming the optical element and the input and output optical fibers are connected. Since the step of forming the guide on the surface of the substrate consists of a step of forming a thin layer made of the material constituting the guide on the entire surface of the substrate, and a step of processing the thin layer into a desired pattern, there is no branching. A guide can be formed with high precision according to a waveguide pattern, and optical axes of optical fibers can be aligned easily and with extremely high precision by arranging optical fibers within the obtained guide. As a result, insertion loss in the optical circuit is reduced.

[Brief explanation of the drawing]

FIG. 1 is a process explanatory diagram showing the step of forming a guide, which is the main part of the optical circuit manufacturing method of the present invention, and FIG. 2 shows an example of an optical branch circuit obtained by using the manufacturing method of the present invention. A top view, FIG. 3 is a partially enlarged view of the optical branch circuit shown in FIG. 2 when connection loss is reduced, and FIG. 4 is another example of an optical branch circuit obtained by applying the manufacturing method of the present invention. Top view showing 5th
Figure j is a top view of a conventional optical branch circuit with a quartz waveguide.
6 is a cross-sectional view taken along the line Vl--Vl in FIG. 5, and FIG. 7 is a cross-sectional view taken along the line ■--■ in FIG. 20.40.100...Quartz substrate, 21...Quartz thin film, 21°...Guide, 22...Resist, 31.
60... Branch waveguide, 35. 51... Input optical fiber, 361. 37. 52-56... Output optical fiber, 32-34. 61-71... Optical fiber, 41-
47.90...Guide, 38.80-85...Reflection film.

Claims (4)

[Claims] (1) After forming a guide on the substrate surface, an optical element made of an optical fiber and input and output optical fibers connected to the optical element are placed along the guide, and the optical element is In the method for manufacturing an optical circuit that connects optical fibers to be formed and between optical fibers forming the optical element and the input and output optical fibers, the step of forming a guide on the surface of the substrate includes the step of forming a guide on the surface of the substrate. A method for manufacturing an optical circuit, comprising the steps of: forming a thin layer made of a material constituting the guide on the entire surface of the guide; and processing the thin layer into a desired pattern. (2) The step of processing the thin layer into a desired pattern includes forming a mask corresponding to the desired pattern by photolithography, and etching the thin layer using the mask. A method for manufacturing an optical circuit according to claim 1, characterized in that: (3) The method for manufacturing an optical circuit according to claim 1, wherein the optical element is an optical branching coupler. (4) The method for manufacturing an optical circuit according to claim 1, wherein the optical element is an optical multiplexer/demultiplexer.