JPS59210414A - Polarization compensating device - Google Patents

Abstract

PURPOSE:To perform polarization compensation which is stable to the polarization state of single-mode fiber projection light by splitting incident light into two orthogonal linear polarized components, and rotating only one component and then multiplexing both components after passing them through optical paths differing in length. CONSTITUTION:A light wave projected from a single-mode fiber 1 is split into two mutually orthogonal linear polarized components by birefringent crystal 3, and they are coupled with polarization maintaining fibers 4 and 5 respectively. The polarization maintaining fibers 4 and 5 has some difference in fiber length so that two light waves do not interfere with each other when multiplexed by a light guide type Y-shaped multiplexer 6 while only one linear polarized component is rotated by 90 deg.. In this case, axes of polarization are so adjusted that both components propagating in the polarization maintaining fibers 4 and 5 are multiplexed efficiently on the incidence light guide 7 of the light guide type Y- shaped multiplexer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polarization compensator capable of converting incident light of arbitrary polarization into plane linearly polarized light emitted in a desired direction.

In recent years, optical communication systems and optical information processing systems have been put into practical use, and efforts are being made to further increase the amount of information and expand the functions of these systems. Therefore, in order to deal with the increase in the amount of information and the expansion of system functions, progress is being made in the development of small, high-speed waveguide optical devices. A waveguide type optical element is an optical element having an optical waveguide structure, and is an optical element that operates efficiently when the guided light is in a specific single polarization direction, or a type of optical element that operates efficiently when the guided light has a single specific polarization direction.
It refers to an optical element with a single direction of light, and examples include waveguide optical switches, waveguide optical modulators, and laser diodes.

On the other hand, as an optical fiber transmission system that can cope with the increase in the amount of information, there is a single mode fiber transmission system that can transmit high-speed, wideband signals over long distances even though the modal dispersion is in principle zero. It is thought that this transmission system will become dominant.

As mentioned above, in a waveguide type optical element, the magnitude of the effect to fully demonstrate its function usually differs depending on the polarization direction of the guided light. For example, in a waveguide optical switch that utilizes the electro-optic effect or the acousto-optic effect, switching must be performed by allowing only one of the TE mode and TM mode to enter the input section. However, when a single-mode fiber is used for the signal transmission system between these waveguides and the fiber, even if the entire polarization L is incident at the input end of the single-mode fiber, the output end generally does not become linearly polarized. Polarization adjustment is required before entering the waveguide optical element.

Conventionally, when using a single mode fiber to connect waveguide optical elements, a method has been used in which the single mode fiber is subjected to external deformation such as bending or screwing to adjust the r;A polarization. However, when this method is used, the polarization state changes due to changes in the ambient temperature of the single mode fiber or changes in external force, and it is necessary to manually adjust the polarization state each time. There is also a method of inserting a polarizer on the incident side of the four-waveform optical element and making only a certain polarized light component become active and input it to the waveguide optical element, but with this method, all unnecessary 11111 light components are lost. It becomes. Furthermore, since the polarization state of light emitted from a single mode fiber may change moment by moment due to the influence of ambient temperature or external force, there is a possibility that the amount of light incident on the waveguide optical element may change over time.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a polarization compensator d that is stable against changes in the polarization state of light emitted from a cross-mode fiber.

In the present invention, the incident light is separated into two linearly polarized components perpendicular to each other, one of the linearly polarized components is rotated to match the polarization direction of the other, and then both are combined again to obtain polarized light. Eat now.

Next, separate the Mj and J lights and then synthesize them! , snow 2
After combining the optical path lengths of the two linearly polarized lights, we make sure that the first wave (after combining them) does not interfere. Using this configuration, if the loss in both optical paths after separation into two line-side light components is made equal, no matter how the polarization state of the incident light changes, the output light will change along the line. does not occur. There are two ways to rotate only the linearly polarized component on one side: using a polarization-maintaining fiber and using a half-wave plate. The purpose of this oil is to rotate polarized light.

In addition, as an application of the present invention, the above-mentioned M-11 is placed on the incident side.
An optical switch equipped with a polarization compensator equipped with a polarization compensator having a dot can perform stable switching without depending on the polarization state of incident light, and therefore can be applied to a single mode fiber transmission system with EJ performance.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of a polarization compensator according to Kiwata and Akira. In Fig. 1, a light wave emitted from a single mode fiber 1 is divided into two linearly polarized components (
The light is separated into two mutually orthogonal linearly polarized components by the folding crystal 3 and coupled to a polarization maintaining fiber 4 and a polarization maintaining fiber 5, respectively. Two polarization maintaining fibers 4.5
is connected to the waveguide Y-combiner 6, or the two polarization-maintaining fibers have the same polarization direction of the output light at the input waveguide end face of the waveguide Y-combiner 60, and the guided light is efficiently combined. The polarization axis is adjusted so that the polarization direction is the same. A polarization maintaining fiber 8 is connected to the end face of the output waveguide of the waveguide type Y-combiner 6 and is adjusted so that its polarization axis is the same as the polarization axis of the guided light. The above 3 to 6 constitute the polarization compensation device according to the present invention.

In this polarization compensator, no matter what the polarization state of the light emitted from the single mode fiber 1 is, it is separated by the birefringent crystal 3 into two polarization components, E mode and TM mode, which are orthogonal to each other. Ru.

The optical components on both sides are inputted into polarization-maintaining fibers 4 and 5, respectively, in which the directions of the fiber polarization axes are adjusted, and reach the output ends of the polarization-maintaining fibers with the plane polarization maintained. The two polarization-maintaining fibers 4 and 5 are connected to the waveguide Y-combiner 6, but at the end face of the input waveguide 7 of the waveguide Y-combiner 6, both polarization-maintaining fibers are output. The polarization axes of the fibers are adjusted so that the polarization directions of the emitted lights are the same and the guided lights are efficiently combined in the waveguide type Y-combiner 6. As a result, the 92 polarization maintaining fibers 4 and 5 function as means for rotating only one plane-polarized light component by 90 degrees to match the other plane-polarized light component. The output of the waveguide Y-combiner 6 is such that the fiber lengths of the two polarization-maintaining fibers have a difference of about 4 cm to prevent the two light waves from interfering when they are combined by the waveguide Y-combiner 6. A polarization maintaining fiber 8 which is adjusted so that the polarization direction of the synthesized straight optical waveguide and the fiber polarization axis are the same is connected to 1 mK of the four wavepath ends, and this polarization maintaining fiber 8 is connected to the next It is connected to the waveguide optical element in the next stage, but by adjusting the polarization axis by twisting the fiber at the output end of the IR wave storage fiber 8, the waveguide optical element in the next stage can function with full efficiency. In the polarization compensation λ device with this configuration, the light emitted from the masticatory mode fiber is once separated into two mutually old polarization components, and the polarization directions of the two are matched using a polarization-maintaining fiber, and then they are combined again. Therefore, even if the ratio of TE mode to TM mode in the single mode fiber output light is different, the amount of light output from the polarization compensator remains constant.Therefore, even if the ambient temperature or external force changes, Therefore, even if the polarization state of the light emitted from the single mode fiber changes over time, a stable amount of light emitted from the polarization compensator can be obtained.

As described above, in this embodiment, a birefringent crystal that separates the light into two mutually old polarization components, a polarization-maintaining fiber that matches the polarization directions of both light components, and an image whose polarization directions match! With a simple configuration using a waveguide Y-combiner that recombines 1M, linearly polarized light, a stable polarization compensator can be obtained regardless of the polarization state of the light emitted from a single mode fiber.

FIG. 2 is a diagram showing another embodiment of the tliri element supplementary angle device according to the present invention. In FIG. 2, a light wave emitted from an upper mode fiber 11 is separated by a polarization beam splitter 12 into two mutually orthogonal plane polarization components, and coupled to polarization maintaining fibers 14 and 15, respectively. The emitted light from the two polarization-preserving fibers is combined by a 7-fumirror 13 with a 1:1 ratio of transmission and opposite polarization, but at this time, the polarization axes of the emitted light from both polarization-maintaining fibers coincide. It shall be adjusted as follows.Half mirror 13
In order to prevent the two light waves from interfering when they are combined, the fiber lengths of the two polarization maintaining fibers are set to have a difference of about 4σ. . . . The light waves with aligned polarization axes synthesized by the mirror 13 are coupled to the polarization maintaining fiber 16 and transmitted to the next waveguide element while maintaining linear polarization. As many as 12 to 15 polarization correction devices according to the present invention are constructed.

In this polarization compensator, light emitted from a single mode fiber 11 is separated by a polarization beam splitter 12 into two polarization components E mode and TM mode, which are mutually old. Both lA11 light components are phipiA(,; light fl
Direction of at 9 reduction 11! ! polarization maintaining fiber 14
and 15, and are transmitted to the output end of the optical fiber while maintaining linear polarization. The light emitted from the fiber with both sentient waves is a half mirror with a ratio of transmission and reflection of 1:1.
13, but in the gap, both (Ji': h+j light of the emitted light at the output end of the wave fiber is -j'\
In this way, six rounds of fiber light are created, and half-mirror -13 light is combined to form linearly polarized light with aligned polarization axes. The emitted light from the half-mirror Li-ichi 13 is coupled to the (+:i; wave preserving fiber 16) and transmitted to the next waveguide optical element while maintaining the linear polarization. In this configuration, the incident light is orthogonal to each other. A polarization beam splitter is used to separate the two linearly polarized components, and a polarization-maintaining fiber is used to align the polarization axes of the two linearly polarized components, thereby synthesizing the light with the same polarization axes. A half mirror is used as the means. In the polarization compensator with this configuration, the single-mode fiber output light is once divided into mutually orthogonal components, 1i! After entering, a method is used in which the polarization components of both are matched and the two are completely synthesized again, so that no matter what the side light state of the single mode output light is, the amount of light output from the complementary color device is It becomes constant. Therefore, it is possible to obtain a polarization compensator that is stable despite changes in the ambient temperature and external forces of the single mode fiber.

As described above, in this embodiment, a polarization beam sinter that performs polarization separation, a polarization-maintaining fiber that matches the polarization directions of both polarized lights after separation, and a polarization-maintaining fiber that matches the polarization directions of both polarized lights are used again. By using a simple 1.gamma.0 configuration using a half mirror to be synthesized, a stable polarization compensator can be obtained regardless of the polarization state of the light emitted from a single-mode fiber.

FIG. 3 is a diagram showing another embodiment of the monokusodego device according to the present invention. In FIG. 3, a light wave emitted from a single mode fiber 31 is split by a value knob C beam splitter 33 into two mutually orthogonal polarized components.

One of the original beams passes through the half-wave plate 35 and then enters the half mirror 34, and the other beam has its optical path bent by the prism 36 and enters the half mirror 34. The half mirror 34 combines the two beams. After that, it is coupled to a polarization maintaining fiber 32. In order to prevent the two light beams from interfering when they are combined by a half mirror, the optical path lengths of the two original beams are set to have a difference of about 4 cm.

In this polarization compensator, a single mode fiber 31
The emitted light is separated into original beams of two planar polarization component elements, E mode and TM mode, which are orthogonal to each other. When one light beam passes through the half-wave plate 35, its polarization direction is 90
The beam is rotated by .degree., and after matching the polarization direction of the other beam, it enters the half mirror 34. The other beam has its optical path bent by the prism 36 while maintaining its polarization direction, and then enters the half mirror 34, where the two beams are combined. The combined light beam is passed through the 11r'6 wave preserving fiber 32.
and is connected to the next-stage waveguide optical element. In the polarization compensator of this configuration, a polarization beam filter IJ is used for polarization separation, a half-wave plate is used as a means for rotating only one polarization component by 90 degrees, and a half mirror is used as a means for recombining. When this configuration is used, it is possible to downsize the device by using microogistic components, and there is also the advantage that the number of components is small.

In this configuration as well, the single mode fiber output light is polarized once, and only one polarization component is rotated by 90 degrees and matched with the other, and then both are combined. The amount of output light from the polarization compensator is constant regardless of the polarization state of the output light, and it is possible to stably perform polarization compensation even if the polarization state of the output light from a single mode fiber changes over time. As described above, in this example, a single mode fiber output beam is created using a simple and downsized optical circuit configuration using a polarizing beam splitter for polarization separation, a half-wave plate for polarization rotation, and a half mirror for synthesis. A stable polarization compensator can be obtained regardless of the polarization state of the polarization state.

FIG. 4 is a diagram showing an example of a waveguide type optical device using the polarization compensator according to the present invention. In FIG. 4, a single mode fiber 41 is connected to a polarization compensator 50, and the output light from the polarization compensator 50 is connected to a waveguide optical switch 49 through a polarization maintaining fiber 42.

The light emitted from the waveguide optical switch 49 is selectively coupled to one of the single mode fiber arrays 43 and transmitted to the next stage element. In FIG. 4, a waveguide type optical switch is constructed by diffusing T1 into a lithium niobate crystal (LINbOl) substrate 44 to form optical waveguides 45 and 46.

47 and 48 are formed, and these equal optical wave paths are 2 to 5.
It has five parts that are close to each other on the order of μm. A sleep electrode for voltage application is attached to this adjacent part, which functions as a directional coupling type optical switch element using the ``nausea light'' effect, and connects five directional coupling type switch elements. The 4H type original switch operates as a 4x4 matrix switch. In addition, as the polarization compensator section in FIG. 4, any one of the polarization compensators shown in FIGS.
"Optical compensator".As described above, the polarized waveform generator is attached to the polarized waveform generator.

is formed. Note that the number of input/output channels of the waveguide optical switch is not limited to 4×4 (nXn may also be used without any inconvenience).

When a light wave from the single mode fiber 41 is input to this waveguide source switch with polarization compensation 1μ device, the output light from the 1jj 1 component compensation 111 compensation 50 is Linearly polarized light hits. A polarization maintaining fiber 42 is used to connect the polarization unit 50 and the waveguide optical switch 49.
Since the waveguide optical switch input point C is also direct &! It is polarized light. Moreover, with a polarization-maintaining fiber, the direction of linearly polarized light can be changed arbitrarily by twisting the fiber at its output end, so the waveguide optical switch 49
bJ conversion is adjusting the polarization direction of the light emitted from the polarization-maintaining fiber 42 to the direction of plane polarized light that operates most efficiently. In this way, the light 〇M]1 outputted from the single mode fiber 41; whatever the optical state, the incident light to the waveguide optical switch 49 becomes a desired linearly polarized light. By attaching a polarization compensator on the input side as in this configuration, it becomes possible to operate a waveguide optical switch, which is originally polarization dependent, without depending on the incident polarization.

As described above, by attaching the polarization compensator according to the present invention to the input side, the polarization compensation device operates independently of the input polarization state, and can be overused in single mode fiber transmission systems. A waveguide source switch can be configured.

The invention is not limited to the above embodiments. For example, in another embodiment, a polarization beam splitter is used for the polarization splitter 11, a polarization maintaining fiber is used for polarization rotation, and a waveguide Y-combiner or a single mode fiber coupler is used for combining the light beams. The compensation device and polarization beam splitter are configured with a waveguide directional coupler, the J+6 element rotator is configured with a waveguide equipped with comb-shaped electrodes, and the combiner is configured with a waveguide directional coupler or a waveguide Y-shaped combiner. A polarization compensation device in which these are integrated on one lithium niobate (LiNbOs) substrate, and an integrated polarization device in which the above-mentioned integrated polarization compensation device and waveguide optical switch are integrated on one substrate. A waveguide optical switch with a compensator or the like can be constructed.

The application of the present invention is not limited to waveguide optical switches, but also waveguide optical modulators with a polarization compensation device, in which a polarization compensation device is attached to a waveguide optical modulator, and waveguide optical devices with several functions. It is possible to construct a waveguide optical integrated device with a polarization compensator attached to a waveguide optical integrated device, for example, a waveguide optical integrated device for a fiber sensor.

[Brief explanation of the drawing]

1, 2, and 3 are diagrams showing an embodiment of the (Jiii) optical compensation device of the present invention, and FIG. 4 is a diagram showing a waveform source switch to which the polarization compensation device is applied. 1, .11, 31.41 --- one single mode fiber 3
−−−−−−−−−−Birefringent crystal 6-1 −−−−−−−Waveguide type Y-combiner 7−−−−
---------- Waveguide 12.33------
-1λT11 element beam sinter 13.34------
--------Half mirror 35---------One-half wave plate 36----- Prism 43----, Single mode fiber Array 50-, -----, --- is a polarization compensator. ,゛－－〜゛－ 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] Y: comprising means for splitting the incident light into two lkM polarized light components orthogonal to each other, means for rotating only one linearly polarized light component to match the direction of the other iμ-ray light, and means for recombining both, Furthermore, the polarization compensator is characterized in that the optical path lengths of the two linearly polarized lights are different from when the 'Jii light is separated to when it is combined.