JPS63501985A - optical coupler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] light cup 2 The present invention relates particularly, but not exclusively, to single mode couplers, and particularly to wavelength division multiplexers. This invention relates to a heavy duty communication (WDM) coupler.

Such couplers can be used to connect two single-mode fiber optic couplers to multiplex and This is highly desirable for easy wavelength division with little loss when canceling multiple communications. be.

In order to use a coupler in WDM, this power and plastic must be able to separate wavelengths to a high degree. ) x odB) and provide possible long-term light polarization.

Therefore, the present invention relates to a coupler useful for wavelength division multiplexing communication, which coupler is compatible with wavelength division multiplexing. Adjacent parts fused to each other and a pair of single-stranded optical fibers, the above fused parts has a substantially circular cross section so that birefringence is essentially zero.

In order to more easily understand the present invention, embodiments of the present invention are carried out according to the accompanying drawings. This will be explained as an example. In these drawings, Figure 1 is a diagram showing the refractive index along the cut of a single mode optical fiber. Figure 2 shows a wavelength coupler using two fused single mode optical fibers. The schematic diagram is sb, and Figure 5 shows several cross-sectional views of fused single mode optical fibers. It shows.

Figure 1 of the accompanying drawings shows the refractive index diagram of a matched single mode optical fiber. . To manufacture a WDM coupler, two optical fibers with a predetermined length are Arrange and hold. Wrap one fiber around the other fiber . In this case, the winding direction is not perpendicular. Next, remove the twisted part, for example. Heated by Shibutane flame. This heating fuses the two fibers together. . After a predetermined period of time, the fused fibers are extruded to form a biconical taper. Up The heating time determines the degree of melting of the two fibers.

While drawing the molten fiber, light with a predetermined wavelength is applied to one fiber. and monitor the power delivered to the fiber. drawing the fiber A biconical taper is formed in the extended portion of Toyoshi, and this taper is a multimode region. Become. In this new multimode domain, local LPo and LP, Due to mode interference, the stain force moves along the taper. The length of the tape is In the fiber configuration, all the power is at the tapered end in one or the other fiber. The length is as shown in the section. Therefore, the power oscillations occurring during taper formation can be By monitoring the actual taber forming process can be controlled and the desired degree of taber formation can be achieved. It can be used as a partner.

In the specific example described here, the extension of the connected 7-eyeper is detected by two power oscillations. stop after being

The resulting pair of fused fibers are designated by reference numbers 10 and 11 in FIG. is shown. The two fibers are integral at the part indicated by reference numeral 12. is fused to. Note that the part indicated by 12 above also includes a double conical taper. As mentioned above, the stretching of this taber requires two electric power sources during the manufacturing process. It is stopped when vibration is detected.

When operated as a WDM coupler, it couples light at two different wavelengths λ1 and λ2. Irradiate the fiber 10 at position 13 and detect the obtained output at positions 14 and 15. put out

The fused portion is surrounded by a suitable botting agent. ideal coupler For example, approximately 90 beams of light λ, appear at the output of fiber 10. , such that the same proportion of light λ2 appears at the output of fiber 11. This wavelength or the degree of channel separation must be maintained over a wide temperature range, and must be independent of the degree of polarization of λ and λ2.

It is difficult to satisfy these requirements, and in fact they are two interconnected It is known that it is highly dependent on the cross-sectional properties of the fused portion of the optical fiber. .

A-C in Fig. 3 shows the fusion cross-sectional shape that can be formed in the fusion cup 2 shown in Fig. 2. It shows the condition.

In the structure shown in Figure 3a, the fused portion of fibers 10 and 11 is completely The outer shapes of the two fibers can be easily distinguished without being completely integral. . This structure has insufficient field shielding effect, and therefore the coupling part (coupling r atio) are very sensitive to the external conditions of the blotting agent. this Moreover, couplers are very sensitive to temperature changes and therefore The degree change changes the refractive index of the blotting agent.

The other two structures 3BK and 3C have a larger degree of fusion between the two fibers. It shows. The amount of fusion is determined by the intensity and duration of heating. In fact, fl The circular shape in the lsc diagram indicates complete melting.

The structure in Figures 3y and 32 shows that the structure is sensitive to changes in the refractive index of the botting agent. does not show great sensitivity.

However, this sensitivity to refractive index changes of the botting agent is sufficient for satisfactory WD This is not the only requirement in the manufacture of M couplers.

All three structures shown in Figure 3 result from birefringence ambush) and It consists of stress birefringence folds S, therefore, the total birefringence fold T is given by the following passage.

BT = Bp -1-(-BB) Stress birefringence is usually the opposite of formation birefringence. The structure in Figure 3a has no total birefringence. Always small. This is because formation birefringence and stress birefringence are very small and almost equal. This is because it is true.

However, the structure of Figure 3a is sensitive to changes in the refractive index, so the temperature It is not suitable to produce stable WDM under changing environment.

The adjacent structure in Figure 5b is sufficiently melted and the field shielding effect is very strong. Because of its superior properties, it is less sensitive to changes in the refractive index. However, its oval shape The birefringence formed by the stress birefringence is also much larger and therefore has a different input polarization. It gives a total birefringence that cannot be maintained at a constant junction with the state. this Therefore, the structure of Figure 3b is also zero, although it is desirable when applied to WDM. reach. In this case, the only remaining birefringence is due to stress.

Just before the cross-sectional shape becomes circular, the formation birefringence has the same value as the stress birefringence, and the Therefore, the total birefringence is zero.

Since the coupler is fused into light, the refraction of the plotting agent surrounding it Less sensitive to rate changes and therefore can be operated over a wide range of degrees can do. Also, the fact that the birefringence of Kagura is zero means that the cup The wavelength of the WDM coupler is The period is also related to the melt cross section, so a structure with zero birefringence will have a maximum period of and if you don't have exactly the desired channel wavelength at the minimum, fine tune it. must match the maximum and minimum values. This fine adjustment will reduce the birefringence. Adjusting the value above zero will result in an equally small sacrifice in polarization sensitivity. Therefore, there are five main requirements: high degree of separation, wide temperature range. maintains a high degree of isolation across the entire range and above despite polarization input conditions It is possible to compromise between satisfying the two requirements.

international search report +lI+--mmh--+hnm, PCT/GB 86100739

Claims (3)

[Claims] 1. Adjacent sections fused together and a biconical taper formed in this fused section used for wavelength division multiplexing communications consisting of a pair of single mode optical fibers with In Katsubura, the fused portion has a substantially circular cross section and is essentially zero. A cutlet characterized by having birefringence of . 2. Heating and melting two single mode optical fibers together, and It consists of applying tension to the bar to form a double conical taper at the melting location, and consists of two different One of the fibers is irradiated with light having a predetermined wavelength, and the two irradiated lights are detected at separate ends of the fiber and the birefringence formed in the molten fiber. The transmitted light is monitored during the melting process until the stress birefringence is equal to the stress birefringence. Optical cutter for wavelength division multiplexing communication characterized by an essentially circular cross section How to manufacture. 3. Stop drawing the fused fiber when two power oscillations are monitored. The method according to claim 2, characterized in that: