JPS60173502A - Waveguide type optical branching circuit - Google Patents

Abstract

PURPOSE:To decrease the propagation loss of a main route by eliminating the intersection of waveguides and connecting directly an optical fiber to the side face of the main route for taking out branched light. CONSTITUTION:A photolithographic technique is applied for a quartz optical waveguide film to form an optical circuit; for example, the optical circuit is formed by a reactive ion etching method using amorphous Si as a mask and a gaseous mixture composed of C2F6 and C2H4 as an etching gas. A clad layer is further formed on the side face of the waveguide by a CVD method. A transparent material having a suitable refractive index is put into a reflecting channel 5 in order to function the optical branching circuit. The refractive indices of a main optical waveguide 2'a on the input side and the matching oil in the channel 5 are different in this stage and therefore the propagated light causes a Fresnel reflection at the end face 5a of the waveguide and a part of conducted light I1 is reflected and is made incident I3 on an optical fiber 7c. The remaining light I2 is made incident on a main optical waveguide 2'b on the output side. Only some part of the light propagating in the main optical waveguides 2'a, 2'b is made incident on the fiber 7c and is thus monitored.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optical branch circuit used as a monitor or an accelerator in an optical communication system such as an optical subscriber system or a private optical communication network.

(Prior art) When optical information propagating through the system is transmitted to the end subscriber or monitored in optical subscriber lines, local optical communication networks, etc., it is necessary to minimize the loss of light propagating through the main route of the system. , propagation to the terminal -s (1/ ~ l
) must be taken out.Furthermore, the optical circuits used for these applications are economical and
Must be highly productive.

Hitherto, bulk type, fiber type, waveguide type, etc., have been proposed as optical branch circuits having this function, but the bulk type and fiber type have problems in terms of productivity.

Waveguide types include Y-branch type and reflective type.

The Y-branch type has a problem in that the device characteristics have a large mode dependence, and if there is a change in the mode excitation state of the propagating light, the device characteristics will change greatly. Compared to these component types, the reflective type is superior in terms of mass productivity and stability of device characteristics.

FIG. 1 shows an example of a conventionally proposed reflective waveguide optical branch circuit. 1 Here, 1 is the substrate, ga, 2C is the main leading waveguide, 2b is the branch optical waveguide, and 6 is! ...It is a reflective groove. However, in this structure, since there is one intersection in the waveguide, there is a problem that a loss occurs in the main route propagating light passing through the intersection. Considering the application to the above-mentioned system, the loss of the main route must be made as small as possible. ) (Object of the Invention) The present invention is a reflective groove wave optical branching circuit in which the crossing of waveguides is eliminated and an optical fiber is directly connected to the side surface of the main route in order to take out the branched light. The objective is to reduce the propagation loss 1. of the main route. The present invention will be explained in detail below with reference to the drawings.

(Structure and operation of the invention) FIG. 2 shows a fiber-directly connected reflective waveguide optical circuit according to an embodiment of the present invention, and FIG. 2(a) is a perspective view.
b) is a plan view, in which 1' is a substrate, 2'a is an input side main optical waveguide, and 2'b is an output side main optical waveguide.

5 is a reflective groove. Further, 5a is the end face of the input waveguide,
A reflection occurs here. 5b is an end face of the output waveguide. In this embodiment, 2°'' is the reflection groove 5 and the optical waveguide 2 j a,
2/b at an angle of 145°. In order to directly connect the optical fiber for receiving branched light to the side surface of the waveguide, a fiber guide groove (Japanese Patent Application No. 58-125
69! 'I) was used. The guide groove for this purpose is 6c. In order to facilitate connection with the main optical waveguide, a kite groove 6a is also provided at the input and output ends of the main optical waveguide.
6b was formed. Optical fibers 7a, 7b, and 7c were inserted into these guide grooves and connected.

To form this optical circuit, we applied photolithography technology to a silica-based optical waveguide film. In this example, an optical circuit was formed by a reactive ion etching method using amorphous S, Y, O2F6, and UO, H, 17) mixed gas as the etching gas. Furthermore, a cladding layer was formed on the side surface of the waveguide by the OVD method. The formed optical circuit has a core layer thickness of 502 m and a core layer refractive index of 1,460.
, the relative refractive index difference is greater than 1.

Therefore, the angle ψ between the highest order mode of the propagating light and the side surface of the optical waveguide is 8°. Optical waveguides 2'a, 2 in FIG.
The width of 'b is 50 μm, and the width of the reflective grooves 6 is 8 μm.

In order to make this optical branching circuit function, a material having a suitable refractive index is placed in the reflective groove 5. In this example, matching oil with a refractive index n=L400 was used. At this time, since the refractive index of the input side main optical waveguide 21a and the matching oil in the reflection groove 5 are different, the propagating light causes Fresnel reflection at the waveguide end face 5a, and a part of the guided light (process) It is reflected and ingested by the fiber 70. The remaining light (
8) enters the output side main optical waveguide 2'b. In this manner, only a part of the light propagating through the main optical waveguides 2'a and 2'b enters the branch fiber 7o and can be monitored. The limb ratio at this time is determined by the Fresnel reflection coefficient. The refractive index of the optical waveguide 2'a is i, 460
, the refractive index of the reflection groove 5 is 1.400, which is 9, and the angle of incidence on the reflection surface is in the range of 45°-8° to 45'+8°, so calculate the Fresnel coefficient at the waveguide end face 5a. Then,
The reflectance is approximately 2.5 factors. When the characteristics of the fabricated element were measured (main route output I,/branch route output I, ), it was approximately 46-...

Next, the effect of reducing main route propagation loss according to the present invention will be discussed.

In the case of the conventional type shown in FIG. 1, since there is a waveguide intersection, part of the main route propagating light becomes a radiation mode, causing loss.

In Fig. 8, among the lights propagating at a certain angle ±00,
Light hitting the side surface of the branched optical waveguide 2C is scattered. 0
Of the light propagating at an angle of 0, the component (
θ) is tan(θ) = 50 tanθ (1). Here, the waveguide width is 50 μm. Therefore, among all propagation modes, there is a radiation loss. This shows that 8.6% of the propagating light becomes a loss as a radiation mode.

In contrast, in the case of the embodiment of the present invention, light guide! □Since there are no crossing points of wave paths, there is no radiation loss 1 as mentioned above. Therefore, according to the present invention, the loss of the main route propagating light can be improved by about 8.5 times compared to the conventional type. The excess loss of the main route of the fabricated optical circuit was less than 0.5 dB.

FIG. 4 is a plan view of another embodiment of the present invention, showing a method of configuring an optical circuit when the angle θ of the reflective groove 5' is set to a value other than 45°. Here, 11 is a substrate, 2'A is an input side main optical waveguide, 2'B is an output side main optical waveguide, 5' is a reflection groove, 6'a, 6'b + 6'0 are kite grooves, and 7
'a,'it b,7/.

are each an optical fiber. In this case, the direction of the guide groove 6'0 is determined so that the reflected light is almost parallel to the optical axis of the optical fiber, and the fiber end face is cut diagonally.
It is sufficient to polish it and connect it 15 to the side surface of the waveguide.

Further, in order to impart wavelength selectivity to the optical branching circuit having this structure, an interference film filter may be inserted into the reflection groove 5'.

(7) ? 'a, 7' b, 7' O... Optical fiber.

(Effects of the Invention) As explained above, in the reflective groove wave optical branching circuit of the present invention, there is no intersection between the main root optical waveguide and the branching root optical waveguide, so the loss of the main root propagating light can be suppressed. When using an optical branch circuit in a local area network, etc., such a loss reduction effect is effective because optical circuits are inserted in multiple stages in the main route.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional reflective groove wave optical branch circuit.
The figure shows an embodiment of the waveguide optical branching circuit of the present invention, (a
) is a perspective view, (b) is a plan view, FIG. 8 is a diagram for explaining radiation loss of a conventional reflective groove wave optical branch circuit, and FIG. 4 is a plan view of another embodiment of the present invention. . 1*1'tl"" board, 2 a, 2 b * 20
*2' a, 2' b, 2' A, 2' B,... Optical waveguide, 5.5'...Reflection groove, 5a... Input waveguide end surface, 5b10. Output waveguide end face, 6a, 6b, 6C, 6
'a. 6'b#6'O-...Guide groove, 7a+7b, 7c,
−=(8) Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Scope of Claims] 1. A light beam having a groove formed at a desired angle with respect to the side surface of the optical waveguide in a part of the guide waveguide formed on the substrate, and having an air layer or a transparent material layer in the groove. In a circuit, a floating waveguide is characterized in that it has a guide groove on the side of the optical waveguide for positioning the optical fiber, and the optical fiber is inserted into the guide groove and coupled to the side surface of the optical waveguide. Optical branch circuit. 2. The waveguide optical branch circuit according to claim 1, wherein the optical waveguide is a silica glass optical waveguide.