JPS61103329A - Method and apparatus for giving group delay time difference of optical signal - Google Patents

Abstract

PURPOSE:To attain the provision of a group delay time difference between optical signals in linealy polarized wave directions simply by forming an optical fiber in the form of coil and providing a dual refraction characteristic to the optical fiber. CONSTITUTION:An optical signal propagated to a polarized wave holding optical fiber 1 is connected to one end of an optical fiber 3 by a connector 2. The optical fiber 3 is wound by n-turn in a form of coil on a bobbin 4 having a curvature R. The optical signal irradiated from the other end of the optical fiber 3 is branched into polarized waves in x, y directions by a reflecting plate 7 by direction of polarized wave and they are made incident respectively photodetectors 8, 9. In this case, the polarized direction of the fiber 1 is adjusted by the connector 2 so that the direction of the polarized wave by double refrac tion caused in the optical fiber 3 is made nearly coincident and both the fibers are connected to compensate the group delay time difference produced during propagation through the optical fiber 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is suitable for use in communication devices using optical fibers and optical fiber application measuring devices.

TECHNICAL FIELD The present invention relates to a method and apparatus for imparting birefringent properties to an optical fiber by forming the optical fiber into a coil shape, and utilizing this property.

[Conventional technology]

Polarization-maintaining optical fibers with birefringent properties can propagate optical signals in each orthogonal polarization mode.
A group delay time difference occurs between optical signals having different polarization modes. Depending on the nature of the communication information to be transmitted, it is necessary to compensate this group delay time difference to zero. Conventionally, there is no convenient method of directly compensating for this in the optical signal mode, and a method of compensating for each signal after converting it into an electrical signal has been used.

In addition, it has been pointed out that in optical communication systems using single-mode optical fibers with small birefringence, polarization dispersion is a factor in deteriorating the signal-to-noise ratio of receiving devices (Y, Ya
Mamoto at al: IEEE Journal
ofQuantum Electronics, Q
B-17pp, 9L9-934+ 1980).

This polarization dispersion must be relieved by compensating for group delay time differences for signals in each polarization direction on the receiving side.

On the other hand, it is known that birefringence can be imparted to an ordinary optical fiber by forming it into a coil with a small curvature. Examples of this application include optical gyroscope, polarization controller CH
, C, Lefevre: Filectron"'
Lette...1.16 pp, 778-
780.1980), 5OLC filter (Y, Yen
et al:optical Letter+ vol.
, 6pp, 278-280.4980) and optical isolators (G, W, Dayet al: IEHE, Jou
rnal of Lightwave Tech, LT
-2°pp, 1489-1492.1984).

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple method and apparatus for providing a group delay time difference to mutually orthogonal linearly polarized optical signals.

[Means for solving problems]

According to the present invention, by forming an optical fiber into a coil shape and imparting birefringence characteristics to the optical fiber, it is possible to impart different group delay time differences to optical signals of modes in each polarization direction corresponding to this birefringence. It is something that takes advantage of its nature.

That is, the method of the present invention imparts birefringence characteristics to the optical fiber by forming the optical fiber into a coil shape, and injects an optical signal from one end of the optical fiber in each linear polarization direction corresponding to the birefringence. , by emitting optical signals in each linear polarization direction corresponding to the birefringence from the other end of this optical fiber, a group delay time difference is imparted between the optical signals in each linear polarization direction. shall be.

In addition, the device of the present invention is a device that provides different group delay time differences in each polarization direction for mutually orthogonal linearly polarized optical signals. and a means for inputting the optical signal in each linear polarization direction corresponding to the birefringence into one end of this optical fiber, and an optical signal in each linear polarization direction corresponding to the birefringence from the other end of this optical fiber. The invention is characterized by comprising means for emitting.

〔Example〕

FIG. 1 is a structural diagram of an apparatus according to an embodiment of the present invention. The optical signal propagated to the polarization-maintaining optical fiber 1 is connected to one end of the optical fiber 3 by the connector 2. This optical fiber 3 is wound n times into a coil around a bobbin 4 having a curvature R. The optical signal emitted from the other end of the optical fiber 3 is split into polarized waves in the X direction and polarized waves in the y direction by a polarization-specific reflecting plate 7, and the split waves enter photodetectors 8 and 9, respectively.

The optical fiber 3 itself does not have birefringence characteristics, but when formed into a coil shape with a small curvature, it is given birefringence characteristics, and a group delay time difference occurs in signals in each polarization direction. The smaller the curvature R, the larger the group delay time difference, and the larger the number of turns n, the larger the group delay time difference.

By adjusting the polarization direction of the polarization-maintaining optical fiber 1 with the connector 2 so that the polarization direction due to birefringence generated in the optical fiber 3 almost matches, and connecting both optical fibers, polarization-maintaining light can be produced. The polarized wave of the fiber 1 can be made to enter the optical fiber 3 as it is. Therefore, the group delay time difference that occurs during propagation through the polarization-maintaining optical fiber 1 can be compensated for using this device. That is, the connector 2 connects polarized waves with a small group delay time difference so that the coil 5 gives a large group delay time difference,
By appropriately adjusting the number of turns n, the amount of the group delay time difference can be compensated so that the group delay time difference in each polarization direction becomes zero at the output end of the optical fiber 3.

Next, we will show the results of testing the characteristics of the group delay time difference of this coiled optical fiber. Second
The figure is a configuration diagram of the device under test for this test. The structure shown in FIG. 2 is a structure in which a single optical fiber is wound around a bobbin with a curvature R to create a coil 1), and then wound around a bobbin with a curvature R1 to create a coil 12. Figure 2 (
In structure a), coil 1) gives the optical fiber birefringence characteristics, and coil 12 gives it birefringence characteristics, so that the group delay time differences in two mutually orthogonal polarization directions are added by the two coils. are configured to give birefringence properties in the same direction. On the other hand, in Figure 2), for the polarized wave with the larger group delay time given by coil 1),
Coil 1) and coil 12 are wound in such a way that the winding directions are 99 degrees from each other so that the polarized wave with the smaller group delay time is obtained in coil 12.
0 @ Wrong. As a result, the group delay time difference given by coil 1) and the group delay time difference given by coil 12 become different.

In this exam...): ``I'tzllll.
Curvature R1-2, 8 cranes, number of turns N! -215 coils 1 coil rate R1 = 4.21). The number of turns was N+''417. The group delay time difference between the two polarized waves was measured using a spatial measurement method that utilizes the interference.

This measurement method uses optical heterogain detection to determine the optical path difference between the maximum beat outputs for both orthogonal polarization modes, and divides this by the speed of light to determine the group delay time difference. This method is detailed in Reference N, 5hibata et al:
Applied Optics vol, 19 pp.

1489-1492, 1980 It is described in

FIGS. 3 and 4 are diagrams showing the results of this measurement. Figure 3 (al is coil 1) and Figure 3 (bl is coil 12) are the measurement results of the group delay time difference occurring between two orthogonal polarizations. The horizontal axis is the optical path difference, and the vertical axis is the optical path difference. The axis is the maximum beat amplitude.Since the optical path difference for coil 1) in FIG. 3(a) is 0.324, the group delay time difference is found to be 1.08 pS by dividing by the speed of light. Also, in Figure 3 (bl), the optical path difference for coil 12 is 0.069.
(2) Therefore, the group delay time difference is calculated to be 0.23 pS.

Figure 4 (a) shows the measurement results when these two coils are connected so that the sum of the group delay time differences is the same as in Figure 2 (al).
), and the measurement result when these two coils are connected so that the difference in group delay time difference is obtained as shown in Fig. 2 (mountain) is shown in Fig. 4 (false). In Fig. 4, the horizontal axis is the optical path. The difference, the vertical axis is the maximum beat amplitude.

From the results in Figure 4(a), the sum group delay time difference is 1.31.
pS, and from the results in FIG. 4 (bl), the differential group delay time difference is 0.84 pS.

The sum of the group delay time differences for each coil found in Figure 3 is 1.08 + 0.23 to 1.31 pS, and the difference in group delay time differences for each coil is 1.08 - 0. .23 = 0.85 pS. Therefore, it can be seen that the measurement results in FIG. 4 faithfully represent the sum and difference.

By adjusting the curvature and the number of turns in this way, the magnitude of the group delay time difference due to the given birefringence characteristics can be adjusted, and whether the group delay time difference is added or subtracted can be controlled by the connection direction. , can optionally provide or compensate for group delay time differences.

〔Effect of the invention〕

The method and device of the present invention have a simple configuration, and the group delay time difference provided can be simply set by the curvature of the coil and the number of turns.

The present invention can be applied to a wide range of applications, such as compensation for group delay time differences caused by the birefringence characteristics of optical fibers, optical fiber gyros, and phase detection devices.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a test apparatus according to the method of the present invention. (a) is a form for creating the sum of group delay time differences, and (bl is a form for creating a difference in group delay time differences. Figure 3 is a diagram showing the test results of each coil, (a) is for coil 1). Test results, (bl is the test result of the coil 12. Figure 4 is a diagram showing the result of the test to make the sum and difference. (al is the test result of the form of Figure 2 (a), (b) is the test result of the second coil 12.
Test results in the form of Figure cb>. 1...Polarization maintaining optical fiber, 2...Connector, 3...
...Optical fiber, 4...Bobbin, 5...Coil, 7
...Reflector for each polarization direction, 8.9...Photodetector.

Claims (3)

[Claims] (1) By forming an optical fiber into a coil shape, the optical fiber is given birefringence characteristics, and an optical signal is inputted from one end of this optical fiber in each linear polarization direction corresponding to the above-mentioned birefringence. A method for imparting group delay time differences to optical signals, in which a group delay time difference is imparted between optical signals in each linear polarization direction by emitting optical signals in each linear polarization direction corresponding to the birefringence from the other end. . (2) Claim (1) in which the group delay time difference is adjusted by the curvature of the coiled portion and the number of turns.
The group delay time difference imparting method described in . (3) An optical fiber formed into a coil shape with a small curvature that gives birefringence characteristics, and Means for inputting the optical signal in each linear polarization direction corresponding to the birefringence into one end of the optical fiber, and emitting the optical signal in each linear polarization direction corresponding to the birefringence from the other end of the optical fiber. A group delay time difference imparting device comprising: means.