JP3102202B2 - Method for manufacturing fusion-type optical fiber coupler and method for manufacturing optical fiber gyro - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a fusion spliced optical fiber coupler and a method for manufacturing an optical fiber gyro using the method.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a fusion-type optical fiber coupler, as shown in FIG.
A loop 53 should be formed, and light from the light source 51 should be incident on one end of the optical fiber 52 on which the loop 53 had been formed, and the optical output emitted from the other end should be monitored by the photodetector 54 to form a fused portion. There has been proposed a configuration in which the portion 56 is melted and stretched by heating using a burner 55, and the loop 53 is cut after fusion (for example, Japanese Patent Application Laid-Open No. 3-160405). In FIG. 15, which shows the relationship between the optical output of the photodetector 54 and the extension amount of the optical fiber fusion splice, the point M1 at which the monitor optical output PO has the minimum value indicates that the coupler branching ratio is 50%. Since this is a point, heating and stretching are stopped with that point as the target.

According to this manufacturing method, only one monitor is required as compared with the case where the optical output is monitored at two places without forming a loop, so that the monitor photodetector 54 is connected. There is an advantage that the optical fiber tip processing operation is only half as much and the characteristic variation due to the variation in the photodetector characteristics is less likely to occur.

[0004]

However, according to the above-mentioned conventional manufacturing method, there is an advantage that the connection work time and the characteristic variation hardly occur because the monitor is required only at one place. Nevertheless, it requires an end treatment of the optical fiber to be connected to the photodetector, and the following problems to be solved remain.

(1) Since optical connection is used, the number of steps is still large and workability is poor.

In order to connect the photodetector to the end of the optical fiber, the coating on the end of the optical fiber is removed, the end face of the optical fiber is cut vertically, and the optical fiber is set on the FC connector. However, since a complicated operation of setting the photodetector on the photodetector is required, the workability is poor.

(2) There are many manual operations and characteristics tend to vary.

[0008] The work (1) of connecting the photodetector involves a lot of manual work, and therefore, it is inevitable that variations in the branching characteristics due to the operator occur.

(3) Consideration on safety is required.

[0010] Since a blade or an organic solvent is used for the operation of removing the coating of the optical fiber, consideration must be given to safety.

(4) When applied to a single coupler type optical fiber gyro, a uniform optical fiber having no variation cannot be obtained.

A single-coupler-type optical fiber gyro having an optical system including one fusion-type optical fiber coupler, a sensing coil, and an optical modulator has attracted attention because of its simple structure and high accuracy. However, when the optical system of the single coupler type optical fiber gyro was manufactured using a conventional manufacturing method, the characteristics were varied due to the reasons described above, and a uniform product could not be obtained between products. In addition, it lacked reliability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a fusion-type optical fiber coupler which can solve the above-mentioned drawbacks of the prior art and can greatly reduce the number of working steps.
Another object of the present invention is to provide a method for manufacturing an optical fiber gyro having an optical fiber coupler having a uniform branching characteristic.

[0014]

According to a first aspect of the present invention, there is provided a method of manufacturing a fusion spliced optical fiber coupler, comprising: holding a loop end of an optical fiber having a loop in parallel and closely; A method of manufacturing a fusion type optical fiber coupler for fusing and extending a portion to be formed, comprising a light source in which at least a semiconductor laser and a photodetector for monitoring the output light thereof are modularized, and the output light from the light source is used as described above. The output light of the light source, which is affected by the intensity of the return light that enters from one end of the optical fiber and returns to the light source, is monitored by the output of the photodetector, and at a predetermined point of the monitor value that changes according to the amount of stretching of the optical fiber. The fusion / stretching is stopped and controlled.

According to a second aspect of the present invention, there is provided a method of manufacturing a fusion type optical fiber coupler according to the above manufacturing method, wherein the light source and the portion to be the fusion portion of the optical fiber into which the output light is incident. An optical coupler with two inputs and two outputs is inserted.
The light emitted from one of the outputs that does not reach the above-mentioned output is monitored, and the light source output is controlled in accordance with the monitor output.

According to a third aspect of the present invention, there is provided a method of manufacturing an optical fiber gyro, wherein a sensing coil and an optical fiber wound around a vibrator at one end thereof to form an optical fiber type phase modulator are continuously connected by the same optical fiber. The formed optical fiber is regarded as the loop, and a fusion type optical fiber coupler is manufactured by the fusion type optical fiber coupler manufacturing method according to claim 1 at a portion to be a fusion portion at the end of the loop. It is characterized by doing. The method for manufacturing an optical fiber gyro according to the fourth invention is characterized in that a light source having a light emitting device having a characteristic of emitting light by current driving and having a characteristic that an emission wavelength is changed by a driving current, and a light source having a light receiving device for detecting return light, and a polarizer are provided. An optical coupler that splits the light from the light source that propagates, a sensing coil that propagates each split light from the optical coupler as left and right bidirectional light, and a periodic between the left and right bidirectional light that propagates through the sensing coil. A phase modulator that adds a phase difference, and a method for manufacturing an optical fiber gyro that takes out interference output by interfering both left-right and right-handed light after propagation, wherein an optical fiber extending from the light source has a base end side that is the light source side. Sequentially, a polarizer, a sensing coil, and a phase modulator are configured, and a base end side of the sensing coil and a front end side of the phase modulator are brought into close contact with each other to form a fused portion. Characterized in that to produce a fused optical fiber coupler by fusing optical fiber coupler manufacturing method according to 1.

The method of manufacturing an optical fiber gyro according to the fifth invention is characterized in that light having a wavelength different from the wavelength of a light source used as a gyro is used as light used in manufacturing a fused optical fiber coupler. And

[0018]

When the output light of the modularized light source is directly monitored by the output of the photodetector when fusing and extending a portion to be a fused portion, the monitor value that increases in accordance with the amount of stretching becomes light. This corresponds to the light output with respect to the amount of stretching when light is input from one end of the fiber and light output from the other end is indirectly monitored. Therefore, an optical coupler having a predetermined branching ratio can be manufactured by directly controlling the stop of the fusion / stretching at a predetermined point of the monitored value. For example, when fusion / stretching is stopped at the point where the monitored value is the maximum, a fusion type optical fiber coupler having a branching ratio of 50% can be manufactured. In order to monitor the output of the light source directly, unlike the case where the optical output emitted from the other end of the optical fiber is optically connected and monitored, a monitor current measuring device is simply added to the photodetector output of the modular light source. It only needs to be electrically connected. Therefore, not only the man-hour during the production of the fused coupler is reduced, but also the variation in the characteristics of the branching ratio is reduced, and the safety is taken into consideration.

An optical coupler is inserted into an optical fiber into which the output of the light source is incident, and the light emitted from the optical fiber is monitored at one output, and the output of the light source is controlled according to the monitor output. Since the influence of the change in the light source output due to the increase of the return light is reduced, the predetermined point at which the fusion / stretching is stopped is stabilized, and the variation in the branching ratio characteristics can be greatly reduced.

Further, an optical fiber in which a sensing coil and an optical fiber type phase modulator are continuously formed is regarded as a loop, and a fusion type optical fiber manufactured by the above-described fusion type optical fiber coupler manufacturing method is formed at the loop end. When the coupler is integrally provided, a single-coupler-type optical fiber gyro having little characteristic variation can be obtained very easily.

Since the polarizer, the sensing coil and the phase modulator are composed of one fiber and the optical fiber coupler is manufactured thereafter, there are no connection points for optical fibers, and the number of assembly steps can be reduced.

Further, when the wavelength of the light source is changed, the monitored value is deviated. By utilizing this, by changing the wavelength, it is possible to accurately specify the monitor value by shifting the hard-to-specify portion in the change in the monitor value.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an overall view of an example of a coupler manufacturing apparatus for carrying out the method for manufacturing a fusion type optical fiber coupler of the present invention. The two optical fibers 12, 13 closely held in parallel by the opposing optical fiber holding stages 14, 17 are:
One continuous optical fiber 10 is folded back, and a loop 20 is formed at the folded portion. A light source 11 is connected to an end of one optical fiber 12 as an input end, and a metal lead wire 21 which is an output of a monitoring PD (photodetector) drawn from the light source 11.
Is connected to a monitor current measuring device 19 for detecting a monitor current, and the other end of the folded optical fiber 13 is an open end.

As shown in FIG. 2, the light source 11 connected to one end of the optical fiber 12 includes a semiconductor laser 22, a monitoring PD 23 for monitoring the output light thereof, an optical fiber coupled to the semiconductor laser 22, and the like. Are integrated and modularized. Therefore, first, the optical fiber 10 taken out from the light source 11 is folded back as it is to form a loop, so that there is no need to reconnect the light source 11 and the optical fiber 10. Next, since the photoelectric conversion output of the built-in monitor PD 23 is extracted from the light source 11 as the metal lead wire 21, the monitor current measuring device 19 described above may be electrically connected, and optical connection is required. There is no.

Now, while using the burner 16 to heat the portion 6 to be a fusion portion of the two optical fibers 12 and 13 held in parallel in close contact, the moving stage on which the holding stages 14 and 17 are fixed. By moving the parts 15 and 18 away from each other (in the directions of the right and left arrows in the figure), the part 6 to be the optical fiber fusion part is fusion-stretched. In the meantime, the light source 1 that receives light from the input end of the optical fiber 12
1 is monitored using the monitor current measuring device 19 connected to the PD 23.

The following three graphs are obtained from the monitoring results. That is, FIG. 3 shows a monitoring PD of the light source 11.
FIG. 4 is a graph showing an example of the relationship between the current value IM and the light intensity PB returning to the light source 11 from the fusion spliced portion; FIG. 4 is a graph showing an example of the relationship between the light intensity PB returning to the light source and the stretching amount of the optical fiber fusion portion;
FIG. 5 is a graph showing an example of the relationship between the monitoring PD current value IM of the light source 11 and the amount of extension of the optical fiber fusion joint.

The light intensity PB which enters the optical fiber 12 from the light source 11 and returns to the light source 11 from the fusion portion through the loop 20
And the sum of the light intensities PA output from the fusion portion through the optical fiber 13 are constant unless there is excessive loss when passing through the fusion coupler.

PB + PA = constant That is, the point M1 of P0min (coupler branch ratio 50%) in FIG. 15 corresponds to the point M2 of PBmax in FIG. Therefore, the point M3 of IMmax in FIG. 5 corresponds to the point of the coupler branching ratio of 50%. This allows
If the monitor current IM value is monitored using the monitor current measuring device 19 and, for example, control is performed so that the extension is stopped at the point M3 of IMmax, a 50% branch ratio coupler can be manufactured.

As described above, the fusion / extension control is performed by using the current detected by the monitor PD incorporated in the light source. Optical fiber tip processing work
It is possible to replace the simple operation of connecting the metal lead wire, which is the output of the PD, to the monitor current measuring device. As a result, the number of man-hours can be significantly reduced, and variations in characteristics among operators can be eliminated. In addition, the frequency of use of the knife and the organic solvent is reduced, and the danger associated with the fiber coating removal operation is reduced.

FIG. 6 shows another embodiment of the method of manufacturing the fusion type optical fiber coupler of the present invention. The difference from the embodiment of FIG. 1 is that a two-input / two-output optical coupler 41 is interposed between the light source 11 and the part 6 to be a fusion part, and one of the two outputs which does not reach the loop 20 is used. The output light exiting through the optical fiber 13 having an open end is output to an automatic output control circuit (APC).
Circuit 42) and controls the output of the light source 11 according to the monitor output. Note that AP
The C circuit 42 is connected to the metal lead 25 (see FIG. 2) of the semiconductor laser drawn from the light source 11, and the output of the semiconductor laser is stably controlled by the output of the APC circuit.
The reason for this is to reduce the influence of the change in the light source output due to the increase in the return light to the light source 11 incident on the optical fiber 12. Thereby, the point M3 which is the target of the fusion / stretching control is stabilized, and the control can be made more accurate.

FIG. 7 shows a loop 2 at the folded portion of the optical fiber.
0 (see FIG. 1), a sensing coil 33 in which a large number of polarization-maintaining optical fibers are wound, and an optical fiber type phase modulator 34 in which an optical fiber is wound around a vibrator at one end thereof are continuously formed. FIG. 2 is a schematic diagram of a single coupler type optical fiber gyro provided with a wearable optical fiber coupler 34. After the sensing coil 33 and the phase modulator 34 are continuously formed in advance by using one polarization-maintaining optical fiber in advance in this way, the fusion-type optical fiber coupler 32 is manufactured by the above-described manufacturing method. The number of man-hours for manufacturing the gyro can be reduced, and desired branch characteristics can be provided.

FIGS. 8, 9 and 10 show a modification of the method for manufacturing an optical fiber gyro.

A polarizer 62, a sensing coil 64, and a phase modulator 65 are sequentially formed on an optical fiber 60 connected to a light source module 61. One end of the sensing coil 64 of the optical fiber 60 (light source module 61 side)
And the sensing coil 6
4, the other end side fiber portion 60B, which is the other end side, is heated, fused and stretched, and the optical coupler 66 is manufactured by the above-described manufacturing method.
To form Note that a polarization-maintaining optical fiber is used as the optical fiber 60. As a light emitting element in the light source module 61, a compact disk LD, a super luminescent diode (SLD), or the like is used.

At this time, the relationship between the amount of stretching and the light output is shown in FIG.
1 is shown in the graph. As can be seen from this graph, the light output that was initially large gradually decreases to 0 as the amount of stretching increases, and increases again. The point where the optical output becomes 0 is where the branching ratio of the optical coupler 66 is 50%.
The fusion stretching is stopped at this point. However, this is an ideal state, and there is a certain width in the production of the actual optical coupler 66. That is, FIG.
As shown in the figure, the point where the branching ratio of the optical coupler 66 becomes 50% does not reach 0, but changes gradually with a certain width. For this reason, it is difficult to specify a point with a branching ratio of 50%.

On the other hand, since the branching ratio of the optical coupler 66 has a wavelength characteristic, when the wavelength of the light source module 61 is changed, the output characteristic changes from the original characteristic curve as shown in the graph of FIG. The changed characteristic curves 70A and 70B are shifted left and right. Therefore, the shifted output characteristic curves 70A, 7A
If the light output value at the point where the branching ratio is 50% is measured in advance at 0B, it is easy to specify the point 70C where the branching ratio is 50%, and it is possible to easily specify the timing of stopping the stretching.

This makes it easy to adjust the amount of fusion stretching.
In addition, it is possible to perform the operation accurately, and the characteristics of the optical coupler and the efficiency of the manufacturing operation are greatly improved.

Further, since it is not necessary to provide an optical fiber connection point in the production of the optical coupler, the number of assembling steps is reduced, and the productivity can be greatly improved. Further, the cost and the size of the device can be reduced.

In the manufacturing method of the optical fiber gyro, the gyro of the phase modulation method has been described.
The same operation and effect as described above can be obtained with a gyro of another system such as the serrodyne system. Instead of the single coupler system, a two coupler system may be used. In addition, if an optical fiber type polarizer is used, one optical fiber connection point can be formed.
If possible, the connection point can be eliminated altogether by omitting the polarizer.

Further, in the above embodiment, the two-branch single coupler system has been described, but the present invention is not limited to this, and can be applied to a coupler having three or more branches.

[0040]

【The invention's effect】

(1) According to the manufacturing method of the fusion type optical coupler according to the first aspect, the fusion / extension is controlled by using the output of the monitoring photodetector incorporated in the modularized light source. As compared with the conventional case where monitoring is performed at the open end of the optical fiber, the process of processing the optical fiber tip and connecting the monitor photodetector are simplified. This eliminates variations in branching characteristics caused by the operator, and reduces the frequency of use of blades and organic solvents in the work of removing the coating on the fiber end, which is advantageous in terms of safety.

(2) According to the method of manufacturing a fusion spliced optical fiber coupler according to the second aspect, the influence of the change in the output of the light source due to the increase in the return light to the light source is reduced, so that the variation in the branching ratio characteristic is achieved. Can be greatly reduced.

(3) According to the method for manufacturing an optical fiber gyro according to the third aspect, a single coupler type optical fiber gyro having no variation in branch characteristics can be easily obtained.

(4) According to the method for manufacturing an optical fiber gyro according to the fourth aspect, there are no connection points for optical fibers, and the number of assembly steps can be reduced.

(5) According to the method of manufacturing an optical fiber gyro according to the fifth aspect, the timing of stopping the drawing can be easily and accurately specified.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for manufacturing a fusion-type optical fiber coupler for implementing a method for manufacturing a fusion-type optical fiber coupler according to the present invention.

FIG. 2 is a schematic configuration diagram of a modularized light source according to the present embodiment.

FIG. 3 is a characteristic diagram showing a relationship between a monitor current flowing through a light detector for monitoring a light source according to the present embodiment and a return light intensity returning to the light source.

FIG. 4 is a characteristic diagram showing the relationship between the intensity of returning light returning to the light source through the optical fiber and the amount of extension of the optical fiber fusion zone according to the embodiment.

FIG. 5 is a characteristic diagram showing a relationship between a current flowing through a light detector for monitoring a light source according to the present embodiment and an extension amount of an optical fiber fusion spliced portion.

FIG. 6 is a schematic view of an apparatus for manufacturing a fusion-type optical fiber coupler for performing a method for manufacturing a fusion-type optical fiber coupler according to another embodiment.

FIG. 7 is a schematic configuration diagram showing an optical system of a single coupler type optical fiber gyro obtained by applying the manufacturing method of FIG. 1;

FIG. 8 is a schematic configuration diagram showing an optical fiber gyro according to a modification of the method for manufacturing an optical fiber gyro.

FIG. 9 is a schematic diagram showing a manufacturing process of the optical fiber gyro of FIG.

FIG. 10 is a schematic diagram showing a manufacturing state of an optical coupler in the optical fiber gyro of FIG. 9;

FIG. 11 is a graph showing a relationship between an amount of stretching and a light output in an ideal state.

FIG. 12 is a graph showing a relationship between a stretching amount and a light output in a real state.

FIG. 13 is a graph showing an original characteristic curve and a characteristic curve shifted to the left and right by changing the wavelength with respect to the original characteristic curve.

FIG. 14 is a schematic view of an apparatus for manufacturing a fusion-type optical fiber coupler for carrying out a method for manufacturing a fusion-type optical fiber coupler according to a conventional example.

FIG. 15 is a characteristic diagram showing a relationship between an optical output and an amount of stretching of an optical fiber according to a conventional example.

[Explanation of symbols]

 Reference Signs List 10 optical fiber 11 light source 12, 13 optical fiber 14, 17 optical fiber holding stage 15, 18 moving stage 16 burner 19 monitor current measuring device 42 automatic output control circuit (APC circuit)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-160405 (JP, A) JP-A-6-129859 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/28-6/293 G01C 9/72

Claims (5)

(57) [Claims] 1. A method of manufacturing a fusion-type optical fiber coupler, comprising: holding a loop end of an optical fiber having a loop in parallel and holding it in parallel; A semiconductor laser and a photodetector that monitors output light thereof include a modularized light source,
The output light from the light source enters from one end of the optical fiber and returns to the light source. The output light of the light source, which is affected by the intensity of the returned light, is monitored by the output of the photodetector, and a portion to be a fusion portion is extended. A method for manufacturing a fusion-type optical fiber coupler, comprising: stopping and controlling fusion / stretching at a predetermined point of a monitor value that changes according to an amount. 2. A two-input two-output optical coupler is interposed between a light source and a portion to be a fusion portion of an optical fiber into which the output light is incident. 2. The fusion type optical fiber coupler according to claim 1, wherein the light emitted from one of the outputs that does not reach the output is monitored, and the output of the light source is controlled in accordance with the monitor output. Manufacturing method. 3. An optical fiber in which a sensing coil and an optical fiber wound around a vibrator at one end thereof to form an optical fiber type phase modulator are continuously formed by the same optical fiber. A method for manufacturing an optical fiber gyro, comprising manufacturing a fusion type optical fiber coupler by a method for manufacturing a fusion type optical fiber coupler according to claim 1 at a portion to be a fusion portion at a loop end. . 4. A light source having a light emitting device which emits light by current driving and has a characteristic that an emission wavelength is changed by a driving current, and a light source having a light receiving device for detecting return light, and splits light from the light source propagating through a polarizer. An optical coupler, a sensing coil that propagates each branch light from the optical coupler as right and left circling light, and a phase modulator that adds a periodic phase difference between the left and right circulating light propagating through the sensing coil. Prepared,
In a method for manufacturing an optical fiber gyro that takes out interference output by interfering both left and right light beams after propagation, an optical fiber extending from the light source is sequentially provided with a polarizer, a sensing coil, a phase modulation Configure the vessel,
A fusion-bonded optical fiber coupler is manufactured by the fusion-bonded optical fiber coupler manufacturing method according to claim 1, wherein a base end side of the sensing coil and a distal end side of the phase modulator are brought into close contact with each other to form a fusion-bonded portion. The manufacturing method of the optical fiber gyro characterized by the above-mentioned. 5. The method for manufacturing an optical fiber gyro according to claim 4, wherein light having a wavelength different from the wavelength of a light source used as a gyro is used as light used when manufacturing a fusion type optical fiber coupler. The manufacturing method of the optical fiber gyro characterized by the above-mentioned.