JPS6172207A - Thick film waveguide - Google Patents

Abstract

PURPOSE:To obtain a mode scrambler in a short length to stabilize a branching ratio for the incidence position of light by providing a waveguide with a high mode eliminating part consisting of a part whose sectional area is made smaller and a mode converting part which converts the light from a lower mode to a higher mode through an optical path intercepting part vertical approximately to the light propagation direction. CONSTITUTION:The part 27 whose sectional area is made smaller is provided between a coupling part 23 and a branching part 24, and an optical path intercepting part 28 vertical approximately to the light propagation direction is provided in the branching part 24, and exit parts 25 and 26 are connected through this optical path intercepting part 28. Rays of light made incident on two entrance parts 21 and 22 cross in the coupling part 23 and have components of the higher mode eliminated by passing the part 27. They are intercepted by the optical path intercepting part 28 and are inputted to two exit parts 25 and 26 connected to both sides of this part 28. In this process, the light of the lower mode is converted to the high of the higher mode and is distributed equally to exit parts 25 and 26. Thus, the mode scrambler is attained in a short length.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a substrate type waveguide, and particularly to a thick film waveguide configured as a branching/coupling element. (b) Prior Art Substrate-type waveguides are expected to be used as branching and coupling elements because their structure allows them to be mass-produced accurately. By the way, as an element for branching or combining optical signals,
There is a problem of instability of the branching ratio due to distribution dependence of mode excitation. That is, if the position of incidence of the optical signal on the waveguide element differs slightly, the branching ratio will change significantly.

In order to prevent this, it is possible to include a mode scrambler in the waveguide element, but since the waveguide element cannot be made long, unlike a normal mode scrambler, this waveguide element has a mode scrambler. The mode scrambler must be achieved over a short distance, which is not easy to achieve.

(C) Objective The object of the present invention is to provide a thick film waveguide with a stabilized branching ratio by including a mode scrambler realized over a short distance.

(D) Structure According to the present invention, in a thick film waveguide in which a waveguide is formed on or in a substrate, a higher-order mode removal portion consisting of a portion with a reduced cross-sectional area is provided in the waveguide; The present invention is characterized in that it includes a mode conversion section that converts from a low-order mode to a high-order mode by passing through an optical path blocking section that is substantially perpendicular to the propagation direction of light.

(E) Embodiment A thick film waveguide according to an embodiment of the present invention includes a substrate 1 and a waveguide (core part) 2 and further this core part 2
The waveguide 2 has two input parts 21, 22, a coupling part 23, one branch part 24, and a cladding part 3 surrounding the waveguide 2.
A unidirectional 2×2 light emitting unit 25 and 26 are provided, and the two incident optical signals are once combined and then branched into two.
It is configured as a coupler. A portion 27 with a reduced cross-sectional area is provided between the coupling portion 23 and the branching portion 24, and the branching portion 24 is further provided with an optical path blocking portion 28 substantially perpendicular to the propagation direction of the light. Emitting parts 25 and 26 are connected via part 28. When viewed from the light propagation direction, the emitting portions 25, 26 and the reduced cross-sectional area portion 27 have approximately half-shaped cross sections as shown in FIG. 2C.

In such a structure, the light incident on the two incident sections 21 and 22 intersects at the coupling section 23, and then passes through the cross-sectional area reduction section 27, whereby higher-order modes are removed. The light from which the higher-order modes have been removed is then blocked by the optical path blocking section 28 and enters the two output sections 25 and 26 connected to both sides of this blocking section 28 . In this process, the low-order mode light is converted into high-order mode light, which is evenly distributed to the output sections 25 and 26. Therefore, a mode scrambler is realized in a short distance.

Figures 1 and 2 A-C are unidirectional 2 x 2 couplers in which input and output can only occur in one direction, but in the case of a bidirectional 2 x 2 coupler in which input and output can occur in both directions, a waveguide is used. In the case of a unidirectional 1×4 coupler, a pattern as shown in FIG. 4 is used.

These thick film waveguides can be manufactured, for example, as follows. First, Si
An Oz film is formed by CVD (chemical vapor deposition).

This Sin film forms the cladding part 3 together with the SiO film that will be formed later.

Next, 12% by weight of G e 02 was added using the same <CVD method.
SiO□-〇em with a relative refractive index difference of about 1%.

Laminate glass layers. This S to2-GeO□ glass layer forms the core part 2 of the waveguide, and is made to have a thickness of about 50 or 80 m to match the core diameter of the optical fiber to be connected. A core portion 2 having a pattern as shown in FIG. 1 etc. is formed using photolithography technology in accordance with the waveguide pattern. After that, CVD
A film of Sin is laminated by a method. This Sin film forms the cladding portion 3 together with the Sioz film formed first.

Finally, connecting portions (not shown) for input/output optical fibers are formed at both ends of the input/output side of the substrate l.

Next, a unidirectional 2×2 coupler with dimensions as shown in FIG. 7A and B was fabricated by CVD. Specifically, the substrate l
Using a 2-inch diameter Sin wafer, this 5i
S i O2-G e O with refractive index 1.474 on n2
z IIQ was laminated to a thickness of 50 m, and then, by reactive ion etching, a film of Sin,
The -Ge02 film was removed, and then a cladding portion 3 of SiO2 was provided to form a waveguide 2. Then, in this unidirectional 2×2 doubler, light was inputted from one input part, and the intensity of the two output lights was measured by changing its position, and data as shown in FIG. 6 was obtained.

As a reference example, a unidirectional 2×2 coupler with a conventional structure was fabricated with the dimensions shown in FIGS. 7A and 7B and measured in the same manner, and data as shown in FIG. 8 was obtained.

Comparing these data, the additional loss of branch loss is
At a wavelength of 1.3 pm, the value in Fig. 5 is 1°1 dB, and the value in Fig. 7 is 0.3 dB. Although Fig. 5 is slightly larger, comparing Fig. 6 and Fig. 8 shows that the incident It was actually verified that the change in output light intensity between each output with respect to position was extremely small.

(f) Effects According to the present invention, a mode scrambler can be realized in a short distance, and a branching/coupling element can be configured including this mode scrambler, so that the branching ratio can be stabilized with respect to the incident position of light.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of an embodiment of the present invention, FIG. 2A,
B and C are cross-sectional views taken along lines AA, BB, and CC in FIG. 1, respectively; FIGS. 3 and 4 are schematic plan views of other embodiments; and FIGS. 5A and B are cross-sectional views of experimental examples. Figure 5A is a plan view, Figure 5B is a side view on the left side of Figure 5A, and Figure 6 is a graph showing the data obtained from Figures 5A and B. Figures 7A and 7B are for showing the dimensions of the conventional reference example; Figure 7A is a plan view, Figure 7B is a side view on the left side of Figure 7A, Figure 8 is Figure 7A, It is a graph showing data obtained by H. 1...Substrate 2...Waveguide (core part)
3...Clad part 21.22...Incidence part 2
3...Joining part 24...Branch part 25.26
...Emission part 27...Cross-sectional area reduction part 28...Optical path blocking part

Claims (1)

[Claims] (1) In a thick film waveguide in which a waveguide is formed on or in a substrate, the waveguide includes a higher-order mode removal portion consisting of a portion with a reduced cross-sectional area, and a portion substantially perpendicular to the propagation direction of light. What is claimed is: 1. A thick film waveguide comprising: a mode conversion section that converts from a low-order mode to a high-order mode by passing through an optical path blocking section.