JP2005266362A - Polarization independent optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device independent on polarization that has few components and is easy to manufacture. <P>SOLUTION: This device has: an optical element 20 dependent on polarization; a polarization separating means 24 to split the single input light having several polarized components into light waves having different polarized components; and a polarization-combining means 29 to combine light waves having single polarized components, to obtain a light wave having several polarized components. The device introduces the light wave from the polarization-separating means 24 to the optical element 20; and in the optical device constituted so as to introduce the light waves from the means 24 to the means 29, the polarization separating means 24 or the polarization compositing means 29 includes a polarization separating coupler, by using two polarization-keeping fibers, and ends 28 and 30 of one of this polarization-keeping fiber are turned and adjusted to a predetermined angle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical apparatus using a polarization-dependent optical element, and in particular, even when a light wave incident on the optical apparatus has a plurality of polarization components, the polarization-dependent optical element is stable. The present invention relates to a polarization-independent optical device configured to operate.

In recent years, with the advancement of high-speed and large-capacity optical fiber communication systems, as represented by external modulators, high-speed optical modulators using waveguide type optical elements have been put into practical use and are widely used. Yes.
For example, the waveguide type optical element forms a waveguide by thermally diffusing Ti or the like on a substrate having an electrooptic effect such as LiNbO ₃ (lithium niobate). In particular, a Mach-Zehnder type optical waveguide having two branched optical waveguides is often used as the shape of the waveguide. In an optical element having such a configuration, an S-polarization component and a P-polarization component are used. It is known that since the electro-optic constants in the branched optical waveguides are different, it has polarization dependency that the magnitude of the half-wave voltage required for shifting the phase by π is different. It was necessary to use a polarization maintaining fiber as an optical fiber to be transmitted to the incident end.

However, recently, it has been demanded to use a waveguide type optical element in the middle of an optical transmission line composed of a single mode optical fiber. Therefore, even if the optical fiber provided on the incident side of the polarization-dependent optical element is not a polarization-maintaining optical fiber, the optical element operates well even when the polarization state of the incident light changes randomly. There is a need for a configuration to do this.
In the following Patent Document 1, the present applicant has proposed a polarization-independent optical device using a waveguide-type optical element having wavelength dependency.
JP 2003-270591 A

In the invention described in Patent Document 1, as shown in FIG. 1, the incident light 2 from the incident means 1 is separated into the S-polarized component and the P-polarized component by the polarization separating means 3, and the S-polarized component is The light beam converted into the P polarization component by the first polarization rotation means 4 and the light beam having the P polarization component transmitted through the first optical path length correction means 5 pass through the first prism 6 and the first lens. 7 are respectively condensed and made incident on the two optical waveguides 9 and 10 of the waveguide type optical element 8.
In particular, the polarization separation means 3 is provided with a polarization rotation element 3c between two polarization separation elements 3a and 3b made of a birefringent material and having the same length in the traveling direction of incident light.

  With the above-described configuration, even when the polarization state of the propagating light changes at random, it is possible to always enter two light beams having a constant polarization state (only the P polarization component) into the optical waveguide. The optical path difference between the two spectra generated on the incident side can be reduced. Therefore, even if the polarization state of incident light on a waveguide-type optical element having polarization dependence changes randomly, the waveguide-type optical element operates stably and supports high-speed communication systems. A polarization independent optical device that can be obtained can be obtained.

In the polarization-independent optical device described in Patent Document 1, since a spatial optical system is used, a collimator lens, a polarization separation element, and a polarization for making the light emitted from the optical fiber into parallel light at the incident portion. A collimator lens for entering the wave rotating element and the optical element is required, and a similar spatial optical system is also required on the exit side of the optical element.
For this reason, the number of parts is large, the part cost is high, and the manufacturing process is complicated and difficult. In particular, in Patent Document 1, in order to correct an optical path difference between two parallel lights generated in a polarization separation unit when entering an optical element, it is necessary to rotate the polarization and pass the two polarization separation elements. There is a problem that the number of parts is increased and the manufacturing is complicated.

  An object of the present invention is to provide a polarization-independent optical apparatus that solves the above-described problems, has a small number of parts, and is easy to manufacture.

  In order to solve the above-described problem, in the invention according to claim 1, an optical element having polarization dependency and a single incident light having a plurality of polarization components are separated into a plurality of light waves having different polarization components. And a polarization beam combining unit that combines a plurality of light waves having the same polarization component into a single outgoing light having a plurality of polarization components, and the light wave from the polarization beam separation unit In the polarization-independent optical apparatus configured to introduce the light wave from the optical element into the polarization beam combining unit, the polarization separation unit or the polarization beam combining unit includes: It is characterized by comprising a polarization separation coupler using two polarization maintaining fibers.

  According to a second aspect of the present invention, in the polarization independent optical device according to the first aspect, the polarization separation unit and the polarization beam combining unit may be configured by a single polarization separation coupler. Features.

  In the invention according to claim 3, in the polarization independent optical device according to claim 1 or 2, one end of one polarization maintaining fiber of the polarization separation coupler is rotationally adjusted to a predetermined angle. It is characterized by being.

  Further, in the invention according to claim 4, in the polarization independent optical device according to any one of claims 1 to 3, at least one of the light wave incident side and the light exit side of the polarization separating coupler, A support member for fixing and holding the ends of the two polarization maintaining fibers is provided.

  The invention according to claim 5 is the polarization independent optical device according to any one of claims 1 to 4, wherein the optical element is a waveguide type light modulation element. Dependent optical equipment.

  According to the first aspect of the present invention, since the polarization separation coupler using two polarization maintaining fibers is used as the polarization separation means or the polarization synthesis means, the polarization separation means and the polarization synthesis means are not polarized. A single optical component called a wave separation coupler can be used, which contributes to a reduction in the number of components and ease of manufacturing.

  According to the second aspect of the present invention, since the polarization splitting means and the polarization combining means are made common and configured by one polarization splitting coupler, the number of parts can be further reduced. In addition, since the polarization splitting coupler is disposed only on one side of the optical element having polarization dependence, the polarization independent is more compact than the one having the polarization splitting coupler on both sides of the optical element. It is possible to configure a mold optical apparatus.

  According to the third aspect of the present invention, when the polarization component is rotated, it is only necessary to rotate and adjust the end of the polarization maintaining fiber to a predetermined angle without using the conventional polarization rotation means. This contributes to the reduction of the number of parts and the ease of manufacturing.

  According to the invention of claim 4, the polarization separation coupler is provided with the support member for fixing and holding the ends of the two polarization maintaining fibers on at least one of the light wave incident side and the light emission side of the polarization separation coupler. When attaching the polarization maintaining fiber to an optical element or the like, it becomes possible to easily manufacture and assemble.

  According to the invention of claim 5, since the optical element is a waveguide type light modulation element, even if the polarization state of the incident light to the waveguide type light modulation element having polarization dependency changes randomly, the optical element is guided. It is possible to obtain a polarization-independent optical device in which the waveguide optical element operates stably and can cope with a high speed communication system.

Hereinafter, the present invention will be described in detail using preferred examples.
A feature of the present invention is that an optical element having polarization dependency, a polarization separation unit that separates single incident light having a plurality of polarization components into a plurality of light waves having different polarization components, and the same polarization Polarization combining means for combining a plurality of light waves having wave components into a single outgoing light having a plurality of polarization components, and introducing the light waves from the polarization separation means into the optical element, In a polarization-independent optical device configured to introduce a light wave from an optical element into the polarization beam combining unit, the polarization beam separation unit or the polarization beam combining unit uses two polarization maintaining fibers. It is characterized by comprising a polarization separation coupler.

FIG. 2 is a diagram showing an outline of a polarization-independent optical apparatus according to the present invention.
Reference numeral 20 denotes an optical element having polarization dependency. For example, a waveguide type light modulation element in which Mach-Zehnder type waveguides 22 and 23 are formed on a substrate 21 having an electrooptic effect may be used. Is possible.
The optical element according to the present invention is not limited to the above-described waveguide type light modulation element, and two optical elements having polarization dependency are arranged in parallel corresponding to each light wave separated by polarization. If it is, the present invention can be applied.

  On the input side of the optical element 20, a polarization separation coupler 24 composed of two polarization maintaining fibers is disposed. Incident light in a random polarization state having both a P polarization component and an S polarization component is input to the input end 25 of one polarization maintaining fiber. The input end 26 of the other polarization maintaining fiber is not used, and the end is shielded so that no light wave is input from the outside.

  The light wave that has passed through the polarization separation coupler 24 is separated into a P polarization component and an S polarization component. For example, the P polarization component is at the output end 27 of the polarization maintaining fiber, and the S polarization component is at the polarization maintaining fiber. Is output to the output terminal 28.

  When the optical element 20 is an optical element having the highest modulation effect with respect to the P polarization component (hereinafter referred to as “P polarization optical element”), the waveguide 22 of the optical element 20 has a P polarization. The output end 27 of the polarization maintaining fiber is connected so as to maintain the component. On the other hand, the output end 28 of the polarization maintaining fiber is connected to the waveguide 23 so that the S polarization component becomes the P polarization component. ° Connected with rotation adjusted. When the optical element 20 is composed of a combination of a P-polarization optical element and an optical element having the highest modulation effect on the S-polarization component (hereinafter referred to as “S-polarization optical element”). Can be directly connected to the optical element for S polarization without rotating the output end 28 of the polarization maintaining fiber.

  Each light wave introduced into the optical element 20 is a P polarization component, and undergoes phase modulation by a modulation electrode (not shown) formed on the substrate 21 when propagating through the waveguides 22 and 23. The respective modulations in the respective waveguides 22 and 23 are basically the same modulation, and the respective light waves subjected to the same modulation are derived from the optical element 20.

  On the output side of the optical element 20, similarly to the input side, a polarization separation coupler 29 (functioning as a polarization combining unit) composed of two polarization maintaining fibers is disposed. The modulated light of the P polarization component emitted from the waveguide 22 is input to the input end 30 of one polarization maintaining fiber. P-polarized component modulated light emitted from the waveguide 23 is input to the input end 31 of the other polarization maintaining fiber.

  Although it is possible to synthesize two P-polarized components in the state of P-polarized components, in this case, there is a risk of causing a phenomenon in which light waves interfere with each other. By setting the input end of the fiber to be rotated by 90 °, the polarization separating coupler 29 can obtain output light obtained by combining the P polarization component and the S polarization component. FIG. 2 shows an example in which the input end 30 is rotated by 90 °. In the case where the optical element 20 is composed of a combination of a P-polarization optical element and an S-polarization optical element, the optical element for S-polarization can be used without rotating the input end 30 of the polarization-maintaining fiber. It is also possible to connect directly to the element.

As shown in FIG. 2, the light wave that has passed through the polarization splitting coupler 29, which is a polarization beam combining means, has both a P-polarized wave component and an S-polarized wave component from the output end 33 of one of the polarization maintaining fibers. Output as modulated light.
With this configuration, even when a light wave having a random polarization state is incident on the optical element 20 having polarization dependency, the optical element can be effectively functioned, and a polarization-independent optical device can be obtained. Can be obtained.

  In the present invention, since the conversion between the P polarization component and the S polarization component is adjusted by the rotation around the optical axis of the polarization maintaining fiber, a conventional half-wave plate or the like becomes unnecessary. In addition to reducing the number of parts, no special means for adjusting the optical path lengths of the two polarization-separated light waves is required except that the two polarization maintaining fibers have the same length.

  Further, when the light wave is incident on the optical element 20, in order to more appropriately control the polarization component of the light wave, for example, between the output end 27 of the polarization maintaining fiber and the waveguide 22, or the polarization maintaining fiber. It is also possible to install a polarizing plate (not shown) between the output end 28 and the waveguide 23.

Further, in order to facilitate optical connection between the output end or the input end of the two polarization maintaining fibers and the optical element, as shown in FIG. 3, a support for fixing and holding the ends of the two polarization maintaining fibers. The member 40 can also be used.
For example, a method of forming V-grooves 41 and 42 in the support member 40, disposing the end portion of the polarization maintaining fiber in the V-groove, and fixing with an adhesive or the like can be used. The method of joining the polarization maintaining fiber and the support member is not limited to the adhesive, and can be held by mechanical means. However, it should be noted that the polarization maintaining fiber may change its polarization plane when stress is applied.

  By using such a support member, the polarization maintaining fiber is fixed to the support member in an appropriate state (for example, in a state where one polarization maintaining fiber is rotationally adjusted) in advance, so that the polarization to the optical element can be obtained. When the holding fiber is connected, it is possible to easily realize the connection between both by simply fixing the support member to the substrate of the optical element.

FIG. 4 shows an example in which the polarization separating means and the polarization synthesizing means are constituted by one polarization separating coupler.
In the optical element, waveguides 51 and 52 as shown in FIG. 4 are formed on a substrate 50, and a quarter-wave plate 53 and a reflecting plate 54 are connected to the end of the substrate.

The operation of the optical element shown in FIG. 4 is such that, for example, a light wave having a P-polarized component introduced into the input portion of the waveguide 51 is branched into two by the Y branch waveguide, and is not shown in each branch waveguide. The modulation electrode is subjected to phase modulation. The light wave subjected to the phase modulation passes through the quarter-wave plate 53, is reflected by the reflection plate (or reflection film) 54, passes through the quarter-wave plate 53 again, and passes through the same branch waveguide in the reverse direction. Propagate.
Thus, when the light wave passes through the quarter wavelength plate twice, the P polarization component is rotated to the S polarization component, and the light wave propagating in the reverse direction through the waveguide 51 has the S polarization component. Will have.
Such an optical element is also disclosed in Patent Document 2 below. In the present invention, not only the optical element described in FIG. 4 but also various optical elements described in Patent Document 2 can be used. It is.
JP 7-325276 A

In order to construct a polarization-independent optical device using the optical element shown in FIG. 4, a polarization separation coupler 55 is disposed on the input side (also the output side) of the optical element.
Specifically, incident light in a random polarization state having both a P polarization component and an S polarization component is input to the input end 56 of the polarization maintaining fiber. The incident light is separated into a P-polarized component and an S-polarized component by the polarization separation coupler 55. For example, the P-polarized component is at the end 58 of the polarization-maintaining fiber, and the S-polarized component is polarized. Leaded to the end 59 of the fiber.

  When the optical element is a P-polarization optical element, an end 58 of the polarization-maintaining fiber is connected to the waveguide 51 of the optical element so as to maintain the P-polarization component, while the waveguide 52 Are connected in a state in which the end portion 59 of the polarization maintaining fiber is rotated by 90 ° so that the S polarization component becomes the P polarization component.

Each light wave having a P-polarized component introduced into the optical element is subjected to the modulation and rotation of the optical element as described above, becomes an S-polarized component, and is derived from the optical element.
The light wave of the S polarization component emitted from the optical element again enters the end portions 58 and 59 of the polarization maintaining fiber, and the light wave incident from the end portion 58 of the polarization maintaining fiber is polarized as the S polarization component. The light wave returned to the separation coupler 55 and incident from the end portion 59 of the polarization maintaining fiber is rotated from the S polarization component to the P polarization component and returned to the polarization separation coupler 55.

  The polarization separation coupler 55 combines the two return lights and emits modulated light from the output end 57 of the polarization maintaining fiber as a light wave in a random polarization state having a P polarization component and an S polarization component. To do.

  By using the optical element as shown in FIG. 4, not only can the polarization separating means and the polarization synthesizing means be shared by a single polarization separating coupler, but also the entire optical device can be made compact. Is also possible.

FIG. 5 shows another example in which the polarization separating means and the polarization synthesizing means are constituted by one polarization separating coupler.
The operation of the optical element shown in FIG. 5 is basically the same as that shown in FIG. 4 except for the contents described below.
With respect to the waveguide 52, the light wave having the S-polarized component introduced into the input portion of the waveguide 52 is branched into two by the Y-branch waveguide, passes through the quarter wavelength plate 53, and is reflected by the reflection plate (or Reflected by the reflective film 54, passes through the quarter-wave plate 53 again, and propagates in the reverse direction in the same branched waveguide in the state of the P polarization component. When propagating in the opposite direction, the light wave undergoes phase modulation by a modulation electrode (not shown) in each branch waveguide.

However, in order to modulate the waveguide 51 and the waveguide 52 in the same state in an optical element having polarization dependence, for example, as shown in FIG. It is necessary to modulate the light wave propagating in the forward direction (right direction in FIGS. 5 and 6) and to modulate the light wave propagating through the waveguide 52 with a delay of a predetermined period Δt when propagating in the reverse direction. Reference numerals 60, 61 and 62 denote modulation electrodes.
Δt is the same shape of the waveguide 51 and the waveguide 52, and when the light wave A enters the waveguide 51 and the light wave B simultaneously enters the waveguide 52, the light wave A propagating in the positive direction through the waveguide 51 is P point. In this period, the light wave B propagating through the waveguide 52 is reflected by the reflection film 54 and begins to receive the action of the modulation electrode at the point Q.

  In order to apply such a delayed electric signal (RF signal), a structure in which an electric signal applied in the positive direction of the light wave A is continuously introduced in the opposite direction of the light wave B as shown in FIG. Alternatively, as shown in FIG. 6B, separate electrodes may be used for the light wave A and the light wave B, and electrical signals shifted by Δt may be applied individually.

  The present invention is not limited to what has been described above, and it is needless to say that known techniques in the technical field can be applied as necessary.

  As described above, according to the present invention, it is possible to provide a polarization-independent optical device that has a small number of components and is easy to manufacture.

It is a figure which shows an example of the conventional polarization independent optical apparatus. It is a figure which shows the Example of the polarization independent optical apparatus which concerns on this invention. It is a figure which shows the relationship between the polarization maintaining fiber which concerns on this invention, and a supporting member. It is a polarization-independent optical apparatus according to the present invention, and is a diagram showing an embodiment in which a polarization separating unit and a polarization combining unit are shared. It is a polarization independent optical apparatus according to the present invention, and is a diagram showing another embodiment in which the polarization separating means and the polarization combining means are shared. FIGS. 6A and 6B are diagrams illustrating a structure of a modulation electrode in the optical element of FIG. 4 or 5, in which FIG. 4A illustrates a structure using a common modulation electrode, and FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Optical element 24 Polarization separating means 25, 26, 27, 28, 30, 31, 32, 33 Ends of polarization maintaining fiber 29 Polarization combining means 40 Support member 53 1/4 wavelength plate 54 Reflecting plates 60, 61 62 modulation electrode

Claims (5)

An optical element having polarization dependency, polarization separating means for separating a single incident light having a plurality of polarization components into a plurality of light waves having different polarization components, and a plurality of components having the same polarization component Polarization combining means for combining the light wave into a single outgoing light having a plurality of polarization components, and introducing the light wave from the polarization separation means into the optical element, and the light wave from the optical element In a polarization-independent optical instrument configured to be introduced into the polarization combining means,
A polarization-independent optical apparatus, characterized in that the polarization separation means or the polarization multiplexing means is composed of a polarization separation coupler using two polarization maintaining fibers.   2. The polarization independent optical apparatus according to claim 1, wherein the polarization separating means and the polarization synthesizing means are constituted by a single polarization separating coupler. .   3. The polarization independent optical device according to claim 1, wherein one end of one polarization maintaining fiber of the polarization separating coupler is rotationally adjusted to a predetermined angle. Type optical equipment.   The polarization independent optical device according to any one of claims 1 to 3, wherein the ends of the two polarization maintaining fibers are provided on at least one of the light wave incident side and the light exit side of the polarization separating coupler. A polarization-independent optical apparatus, characterized in that a support member for fixing and holding is provided. 5. The polarization-independent optical apparatus according to claim 1, wherein the optical element is a waveguide-type light modulation element.

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