JPH02197806A - Production of polishing type optical directional coupler - Google Patents

Abstract

PURPOSE:To obtain the optical directional coupler which can greatly improve the fluctuation in a branching ratio with respect to a temp. change by measuring the step between a substrate surface and an optical fiber plane prior to sticking of the substrates embedded and fixed with the optical fibers in grooves and sticking two sheets of the substrates accepted in the test to each other in such a manner that the cores are held in proximity to each other. CONSTITUTION:The groove provided with a curvature is dug in the quartz substrate 1 and the optical fiber from which the covering in the embedding part is removed is embedded into the groove. A resin 3 is then poured into the groove and is cured to fix the optical fiber 2. The optical fiber 2 is polished together with the quartz substrate 1 down to the neighborhood of a core 4 after the resin curing. The step DELTAG between the polished surfaces of the quartz substrate 1 and the optical fiber 2 is measured for all the quartz substrates 1 and the acceptance or rejection of these quartz substrates is screened. Two sheets of the quartz substrates 1 accepted in such screening stage are stuck and tightly adhered to each other in such a manner that the cores 4 of the optical fibers 2 come into proximity to each other. The two quartz substrates 1 are shifted to adjust the coupling in such a manner that the light propagating in the one optical fiber is coupled to the other optical fiber. The optical directional coupler utilizing evanescent wave coupling is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing a polishing type optical directional coupler.

[Prior Art] FIGS. 1(a) and 1(b) show the configuration of a polishing type optical directional coupler. As shown in the figure, the polishing type optical directional coupler has a quartz substrate 1, an optical fiber 2, , and is made of resin 3 to which the optical fiber 2 is fixed. The manufacturing method is as follows.

First, a groove with a curvature, for example, a radius of curvature 2, is formed in a quartz substrate 1.
0 (m, depth of 140 μm in the center) and embed the optical fiber 2 with the coating removed in the hole. Next, in order to fix the optical fiber 2, resin 3 is poured in and hardened. Resin hardening. After that, the optical fiber 2 is polished together with the quartz substrate 1 up to the vicinity of the core 4.
Light is input from one end of the device, and the transmitted light is monitored at the other end until the transmitted light reaches a predetermined value.

Then, the two quartz substrates 1 manufactured in the same manner are brought into close contact with each other, and the two quartz substrates 1 are shifted and adjusted so that the light propagating through one optical fiber is coupled to the other optical fiber.

When the branching ratio characteristics of the directional coupler obtained in this way are measured in a predetermined temperature range, even if the initial adjustment is made to achieve 50% branching, the relative positions of the two optical fibers will fluctuate. Usually it changes from that 50%.

[Problems to be Solved by the Invention] The optical directional coupler described above is applied to optical measurement such as an optical fiber gyro, but generally the branching ratio is 50 from the measurement system.
% stability is required.

However, since optical fibers are generally fixed in a clear manner with resin, the expansion of the resin as the temperature rises causes a change in the relative positional relationship between the optical fibers, which inevitably causes a change in the branching ratio.

Furthermore, in the past, the yield was extremely low because the optical directional coupler had to be measured and then determined whether it was acceptable or not.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing an optical directional coupler that eliminates the drawbacks of the prior art described above and can significantly improve fluctuations in branching ratio due to temperature changes.

[Means for Solving the Problems] The method for manufacturing a polishing type optical directional coupler of the present invention includes embedding and fixing a single mode optical fiber in a groove of a substrate, and polishing the surface of the substrate to the vicinity of the core of the optical fiber. After that, the level difference between the polished substrate surface and the optical fiber surface is measured, and the substrates are judged to pass or fail based on the target value of the level difference set in advance according to the rank of the desired optical transmission characteristics. The optical directional coupler using Evanetset wave coupling is obtained by bonding and adjusting the coupling so that the cores are close to each other.

The target value of the step difference is preferably set so that the sum of the step differences between the two substrates to be laminated together is 0.15 μm or less.

[Operation] For a substrate in which an optical fiber is embedded and fixed in the substrate and polished to the vicinity of the core, the level difference between the substrate surface and the optical fiber surface is measured before the substrates are bonded together. Then, in light of the target value of the step difference set in advance according to the rank of the desired optical transmission characteristics, inappropriate boards are eliminated, and the two boards that pass are pasted together and combined and adjusted to complete the optical directional coupler. be done.

Before an optical directional coupler is completed, the quality of its optical transmission characteristics is predicted from the results of measuring the difference in level between the substrate surface and the optical fiber surface, and the relative positional relationship of the optical fibers is determined by the expansion of the resin as the temperature rises. For substrates whose values vary greatly, they are not subjected to the next bonding process, so that an optical directional coupler with little variation in branching ratio due to temperature changes can be manufactured with an extremely high yield.

[Example] Figure 1 shows a cross-sectional structure of a polished optical directional coupler to be manufactured, in which 1 is a quartz substrate, 2 is a single mode optical fiber, 3 is a resin, 4 is the core of the optical fiber, and 5 is the cladding of the optical fiber.

First, as in the conventional method, a groove with a curvature, for example, a groove with a radius of curvature 20a11 and a depth of 140 μm at the center, is dug in the quartz substrate 1, and the optical fiber 2 with the coating of the embedded portion removed is thoroughly embedded in the resin. 3 is poured and hardened to fix the optical fiber 2. After the resin hardens, the optical fiber 2 is polished together with the quartz substrate 1 to the vicinity of the core 4. This polishing is
Light is input from one end of the optical fiber 2, and the transmitted light is monitored at the other end until the transmitted light reaches a predetermined value.

FIG. 2 shows the state of the polished surface of the quartz substrate tIj, 1. From this figure, it can be seen that a step difference ΔG occurs between the polished surface of the quartz substrate 1 and the polished surface of the optical fiber 2. Therefore, the optical fiber 2 moves due to the expansion of the resin 3 due to temperature changes, and as a result, the branching ratio changes. The optical fiber 2
The maximum positional movement reaches the polished surface of the quartz substrate where the optical fibers come into contact with each other.

Therefore, for each quartz substrate 1 that has undergone the polishing process described above, the step difference ΔG between the polished surfaces of the quartz substrate 1 and the optical fiber 2 is measured, and a target value of the step difference ΔG is set in advance according to the rank of the desired branching ratio. The quartz substrates are judged to be acceptable or not based on the above criteria.

In FIG. 3, quartz substrate 1. From this figure, which shows the relationship between the level difference ΔG between the polished surfaces of both optical fibers 2 and the variation width (%) of the branching ratio, in order to keep the variation width of the branching ratio within ±5%, Δ
It is necessary that G is 0.075 μm or less. Therefore, here, as the target value of the step difference ΔG, the sum of the step differences ΔG of the two quartz substrates bonded together is 0.15 μm.
Set it up as follows.

Two quartz substrates 1 that have passed through this screening process are stuck together so that the cores 4 of the optical fibers 2 are close to each other, so that the light propagating through one optical fiber is coupled to the other optical fiber. By shifting the two quartz substrates 1 and adjusting the coupling, an optical directional coupler using Evanez set wave coupling is obtained.

FIG. 4 shows the relationship between the groove width W of the quartz substrate 1 in which the optical fiber is embedded and the step difference ΔG between the polished surfaces of the quartz substrate and the optical fiber. From this, for example, the step difference ΔG is 0.075μ
As one means for making the width less than m, it is effective to make the groove @W less than 160 μm.

Figure 5 shows ΔG=0.04μm (W=157μm)
Regarding the optical directional coupler with the structure of Δ
G=0.15. The temperature characteristics of the branching ratio are shown for each optical directional coupler with a structure of cz m (W = 197 μm >. From this, ΔG < 010
Regarding the optical directional coupler of FIG. 5, which has a diameter of 75 μm (W<160 μm), the fluctuation of the branching ratio is within 50±5% in the temperature range of -20° to 40°C, but ΔG>0.
075 μm <W> 160 u, m), it is clear that the optical directional coupler of FIG. 5 does not fall within such a variation range.

In any case, during the manufacturing process of the optical directional coupler, the step difference Δ
By providing a process to measure G and select the substrate,
By reducing the step difference ΔG between the polished surfaces of the quartz substrate and the optical fiber after completion of the optical directional coupler, it is possible to obtain an optical directional coupler with small temperature fluctuations in the branching ratio with a high yield.

In the above embodiment, a quartz substrate was used as an example, but the substrate material may be other than quartz, and may also be a metal such as AJ or stainless steel. also includes polarization-maintaining optical fibers.

[Effects of the Invention] According to the present invention, the temperature characteristics of the branching ratio of the polishing type optical directional coupler can be improved compared to the conventional method, and by measuring ΔG in advance, the branching ratio temperature of the optical directional coupler can be improved. Characteristics can be predicted and product yield can be improved. As a result, optical measurements.

The economic efficiency and functionality of optical communications can be improved.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are longitudinal and cross-sectional views of a polished optical directional coupler to be obtained by the method of the present invention, and FIG. 2 is a state diagram of the polished surface of the optical directional coupler. , Fig. 3 is a diagram showing the relationship between the level difference ΔG between the polished surfaces of the quartz substrate and the optical fiber and the variation width of the branching ratio of the optical directional coupler, and Fig. 4 is a diagram showing the relationship between the width W of the groove in which the optical fiber is embedded and ΔG. , FIG. 5, and FIG. 6 are diagrams showing the temperature characteristics of the branching ratio of different optical directional couplers, respectively. In the figure, 1 is the quartz substrate, 2 is the optical fiber, 3 is the resin, 4 is the core of the optical fiber, 5 is the cladding of the optical fiber, ΔG is the step between the polished surface of the quartz substrate and the optical fiber, and W is the embedding of the optical fiber. Indicates the width of the clearing. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani (a) (b) Figure G 4! Core 1IG (XIO, um) Figure 3 Figure 4

Claims (1)

[Claims] 1. A single mode optical fiber is embedded and fixed in a groove of a substrate, the surface of the substrate is polished to the vicinity of the core of the optical fiber, and then the level difference between the polished substrate surface and the optical fiber surface is measured. , the board is judged to pass or fail based on the target value of the level difference set in advance according to the rank of the desired optical transmission characteristics, and the two boards that pass are pasted together so that the cores are close to each other and the bonding is adjusted. A method for manufacturing a polished optical directional coupler, characterized by obtaining an optical directional coupler using wave coupling. 2. The method for manufacturing a polishing type optical directional coupler according to claim 1, characterized in that the target value of the step difference is set so that the sum of the step differences of the two substrates to be bonded together is 0.15 μm or less. .