JP6376166B2 - Light modulation device - Google Patents

Description

  The present invention relates to a light modulation device that modulates light incident from one optical fiber by a light modulation element and emits the light from another optical fiber. In particular, the present invention relates to a light modulation device formed on a separate substrate or arranged on a single substrate. The present invention relates to an integrated light modulation device that includes a plurality of formed light modulation elements and outputs two modulated linearly polarized light beams respectively output from the plurality of light modulation elements by polarization combining and wavelength combining.

In high-speed / large-capacity optical fiber communication systems, an optical modulator incorporating a waveguide type optical modulation element is often used. In particular, a light modulation element using LiNbO ₃ (hereinafter also referred to as LN) having an electro-optic effect as a substrate can realize a light modulation characteristic with a small amount of light loss and a wide band, and therefore, a high-speed / large-capacity optical fiber. Widely used in communication systems.

  In this light modulation element using LN, for example, a Mach-Zehnder type optical waveguide is formed on an LN substrate, and a high frequency signal is applied to an electrode formed in the vicinity of the optical waveguide, whereby a modulation signal corresponding to the high frequency signal is obtained. Light (hereinafter referred to as modulated light) is output. When such a light modulation element is used in an optical transmission device, a housing that houses the light modulation element, an incident optical fiber that makes light from the light source incident on the light modulation element, and an output from the light modulation element An optical modulation device composed of an outgoing optical fiber that guides the emitted light to the outside of the housing is used.

  As a modulation method in an optical fiber communication system, in response to a recent increase in transmission capacity, two linearly polarized lights whose polarization directions are orthogonal to each other are phase-shifted or orthogonally amplitude-modulated, respectively. Transmission formats incorporating polarization multiplexing such as DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) and DP-QAM (Dual Polarization-Quadrature Amplitude Modulation) are becoming mainstream.

  In an optical modulation device that performs such DP-QPSK modulation or DP-QAM modulation, linearly polarized light output from one light source is incident on the optical modulation element, and the linearly polarized light that is incident on the optical modulation element is input to the optical modulation element. The light is split into two lights and modulated using two independent high-frequency signals, and the two linearly polarized modulated lights thus modulated are combined by combining into one optical fiber for output.

  On the other hand, in order to further increase the transmission capacity of the optical transmission system, for example, after performing DP-QPSK modulation and DP-QAM modulation on a plurality of lights having different wavelengths, a plurality of light having different modulated wavelengths is obtained. A wavelength multiplexing system is conceivable in which the light beams are combined into a single light beam by a wavelength synthesizer and transmitted through a single optical fiber. In such an optical transmission device that modulates a plurality of lights and transmits the light through a single optical fiber, a plurality of light modulation elements (or a plurality of light beams) are provided in a single housing from the viewpoint of miniaturization of the device. It is desirable to provide an integrated light modulation device that includes an integrated light modulation element in which a modulation element is formed on one LN substrate and modulates a plurality of input lights and outputs a plurality of modulated lights.

  In this case, a polarization beam combiner for combining two light beams (linearly polarized light beams) emitted from each of a plurality of light modulation elements, or a beam emitted from the polarization beam combiner is coupled to an optical fiber. From the need to secure a space for providing an optical component such as a lens, in general, two linearly polarized light beams emitted from one light modulation element, two linearly polarized light beams emitted from another light modulation element, Need to increase the distance between.

  Conventionally, as such an integrated light modulation device, two light modulation elements are provided, and two linearly polarized lights output from one light modulation element and two linear polarization lights output from another light modulation element. After expanding the distance between the wave light by two optical path shifting prisms (prisms for translating the optical path), each two linearly polarized light is polarized by a polarization combining prism or the like, There is known an integrated light modulation device that outputs the light to the outside of the housing with a single optical fiber (Patent Document 1).

  In this light modulation device, the distance from the two light modulation elements to the two light path shifting prisms is made different from each other, thereby preventing damage to the optical component due to the two light path shifting prisms coming into contact with each other. .

  However, when configuring an optical modulation device, the viewpoint of improving the optical coupling efficiency between the optical modulation element and the outgoing optical fiber, the viewpoint of stabilization of temperature fluctuation and secular change of the optical coupling efficiency, and the device size From the viewpoint of miniaturization and reduction in device cost, it is desirable to reduce the number of optical components inserted into the optical path as much as possible.

  In addition, when the conventional optical modulation device is applied to a wavelength division multiplexing transmission system, a plurality of incident lights having different wavelengths are modulated and then wavelength-synthesized. In general, in addition to the optical modulation device, wavelength synthesis is performed. Wavelength synthesis was performed by preparing another optical device for performing the above. In such a conventional configuration, there has been a problem of an increase in optical loss due to an increase in the number of optical fiber connections and an increase in optical loss due to an increase in optical components in an optical device for performing wavelength synthesis. Further, since the number of optical parts increases, it is disadvantageous in terms of stability of optical characteristics (for example, stability against environmental temperature and aging).

  That is, the conventional integrated light modulation device still has room for improvement from the viewpoints of improvement and stabilization of optical characteristics, enhancement of functions, miniaturization, cost reduction, and the like.

JP2015-172630A

  Based on the above background, two modulated linearly polarized light components each having a plurality of light modulation elements formed on a separate substrate or arranged side by side on a single substrate, each output from the plurality of light modulation elements. In an integrated optical modulation device that synthesizes and outputs polarized light, a configuration that can be further improved from the viewpoints of improvement and stabilization of optical characteristics, enhancement of functions, miniaturization, cost reduction, etc. Realization of is desired.

One aspect of the present invention is a light modulation device. The light modulation device includes a first light modulation element and a second light modulation element that respectively modulate light of different wavelengths and emit two output lights, and two light beams from the first light modulation element. A first polarization beam combining element that combines and outputs the output light into one beam, and a second polarization element that combines and outputs the two output lights from the second light modulation element into one beam. A wavelength combining element that combines the beam emitted from the first and second polarization combining elements into a single output light beam, and outputs the first and second light. The modulation elements are arranged so that the respective output lights are emitted side by side, and the first and second polarization beam combining elements are combined and emitted by the first and second polarization beam combining elements, respectively. The distance between the beams is different from the first and second light modulation elements. It is configured to be narrower than in the two mutual spacing of the output light the outermost row of the emitted four of the output light.
According to another aspect of the present invention, the first and second polarization beam combining elements respectively synthesize and emit the beams so that the interval between the beams is emitted from the first and second light modulation elements side by side. Equal to the interval between the two optical axes inside the four rows of output light to be generated.
According to another aspect of the present invention, the first light modulation element and the second light modulation element are arranged at positions symmetrical with respect to a line segment parallel to the direction of the output light emitted side by side. In addition, the first polarization beam combining element and the second polarization beam combining element are arranged in line-symmetric positions with respect to the line segment.
According to another aspect of the invention, the first and second light modulation elements are light modulation elements that perform phase shift keying or quadrature amplitude modulation.
According to another aspect of the present invention, the first and second light modulation elements are formed on different substrates or arranged side by side on the same substrate.
According to another aspect of the present invention, the optical modulator further includes four emission lenses that respectively receive the four output lights emitted from the first and second light modulation elements, an optical fiber, and the optical fiber. A coupling lens that couples an output light beam to the optical fiber, and the four emission lenses are a microlens array formed integrally.

It is a figure which shows the structure of the light modulation device which concerns on one Embodiment of this invention. FIG. 2 is a partial detail view around a microlens array in the light modulation device shown in FIG. 1. It is a figure which shows the modification of the light modulation device shown in FIG.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an optical modulation device according to an embodiment of the present invention. The optical modulation device 100 includes an optical modulator 102, incident optical fibers 104a and 104b, which are optical fibers that allow light from a light source (not shown) to enter the optical modulator 102, an output microlens array 106, a half It includes a wave plate 108, a polarization beam combining prism 110, a wavelength beam combining prism 112, a coupling lens 114, an outgoing optical fiber 116, and a housing 118.

  The incident optical fibers 104 a and 104 b respectively enter linearly polarized light having different wavelengths from two light sources (not shown) into the optical modulator 102.

  The light modulator 102 has two light modulation elements 120a and 120b formed of an optical waveguide formed on a single LN substrate. These light modulation elements 120a and 120b are light modulation elements that perform, for example, DP-QPSK modulation or DP-QAM modulation.

  As shown in FIG. 1, the light modulation elements 120a and 120b are arranged so that output light is emitted side by side. That is, in FIG. 1, in the light modulation elements 120 a and 120 b, all output lights of the light modulation elements 120 a and 120 b are arranged in the left direction in the drawing from the substrate end surface 170 on the left side of the light modulator 102 in the drawing in the vertical direction. It is arranged to be emitted at. Also. In the present embodiment, the light modulation elements 120a and 120b are arranged in line-symmetric positions with respect to the line segment 180 parallel to the direction of the output light emitted side by side.

  In this embodiment, the light modulation elements 120a and 120b are arranged so that all output light emitted from the light modulation elements 120a and 120b is emitted in a straight line in the vertical direction in FIG. However, the present invention is not limited to this, and the light emitted from the light modulation elements 120a and 120b may be arranged so as to have an arbitrary positional relationship as long as they are emitted “in line”. For example, the light modulation elements 120a and 120b are arranged such that the light emission end faces (left end faces in the figure in FIG. 1) of the light modulation elements 120a and 120b are shifted from each other by a predetermined distance in the horizontal direction in FIG. Also good. Further, for example, in the light modulation elements 120a and 120b, the light emission points from the light modulation elements 120a and 120b are in the substrate thickness direction of the light modulation elements 120a and 120b (direction perpendicular to the paper surface of FIG. 1). ) May be configured to be in different positions from each other.

  The light modulation element 120a is a first light modulation element, and the linearly polarized light incident from the incident optical fiber 104a is branched into two lights, modulated by different electrical signals, respectively, and then output waveguides 130a, Output from 132a. The light modulation element 120b is a second light modulation element, and the linearly polarized light incident from the incident optical fiber 104b is branched into two lights, modulated by different signals, respectively, and then output waveguides 130b. , 132b.

  On the substrate end surface 170 on the light output side of the optical modulator 102 (the substrate end surface on the side where the output waveguides 130a, 132a, 130b, and 132b are formed (that is, the substrate end surface on the left side in the drawing)), An emission microlens array 106 including lenses 140a, 142a, 140b, and 142b is disposed.

FIG. 2 is a partial detail view of the periphery of the emission microlens array 106 of the light modulation device 100 shown in FIG.
Light output from the output waveguides 130a and 132a of the light modulation element 120a enters the microlenses 140a and 142a, and light output from the output waveguides 130b and 132b of the light modulation element 120b enters the microlenses 140b and 142b. To do. The light incident on the microlenses 140a, 142a, 140b, and 142b is collimated, for example, and output as parallel light (collimated light).

  Then, the light output from the output waveguide 132a, which is one output light output from the light modulation element 120a, and the light output from the output waveguide 132b, which is one output light output from the light modulation element 120b. Are respectively incident on the half-wave plate 108 after passing through the microlenses 142a and 142b. The half-wave plate 108 is a polarization rotation element. When the output light, which is the two linearly polarized lights incident on the half-wave plate 108, passes through the half-wave plate 108, each of the polarization waves is 90%. Rotated degrees.

  As a result, the light output from the output waveguide 132a, which is one output light output from the light modulation element 120a, and the light output from the output waveguide 130a, which is the other output light, have a polarization direction of each other. It becomes orthogonally polarized light that is orthogonal to the polarization combining prism 110. Similarly, the light output from the output waveguide 132b, which is one output light output from the light modulation element 120b, and the light output from the output waveguide 130b, which is the other output light, have the polarization directions of each other. It becomes orthogonally polarized light that is orthogonal to the polarization combining prism 110.

  Here, the half-wave plate 108 has an optical thickness in a region through which light output from the output waveguide 132a of the light modulation element 120a passes and a region in which light output from the output waveguide 132b of the light modulation device 120b passes through. The optical thickness and the optical thickness can be different from each other according to their wavelengths.

  The half-wave plate 108 is, for example, a region through which light output from the output waveguide 132a of the light modulation element 120a constituting the half-wave plate 108 passes, and light output from the output waveguide 132b of the light modulation element 120b. The passing region is arranged to be line symmetric with respect to the line segment 180.

  The polarization combining prism 110 is configured by integrating two polarization combining prisms, and includes a polarization combining prism unit 110a and a polarization combining prism unit 110b. The polarization beam combining prism unit 110a is a first polarization beam combining element that combines two linearly polarized light beams that are emitted from the light modulation element 120a and whose polarization directions are orthogonal to each other into one beam. Output. The polarization combining prism unit 110b is a second polarization combining element, and combines two linearly polarized lights that are emitted from the light modulation element 120b and whose polarization directions are orthogonal to each other into one beam. And output.

  Here, each of the polarization beam combining prism portions 110a and 110b passes one of the two incident linearly polarized light beams without changing the propagation direction thereof, and is an optical axis parallel to the optical axis of the one linearly polarized light beam. By shifting the optical axis of the other linearly polarized light having the optical axis direction so as to coincide with the optical axis of the one linearly polarized light, one polarization-combined beam is output.

  In the present embodiment, the polarization beam combining prism 110 emits two output lights at the outermost sides of the four output light columns emitted side by side from the light modulation elements 120a and 120b (that is, emitted from the output waveguides 130a and 130b). Output light) is shifted while maintaining the optical axis direction, and two output lights (that is, output waveguides 132a and 132b) inside the four output light columns emitted side by side, respectively. The two polarization-combined beams are output so as to coincide with the optical axis of the output light emitted from (2). Therefore, in this embodiment, the distance between the optical axes of the two polarization-combined beams emitted from the polarization-combining prism 110 is such that the four output lights emitted side by side from the light modulation elements 120a and 120b. It is equal to the distance between the optical axes of the two output lights located inside the column (thus, the distance between the output waveguides 132a and 132b).

  Further, the polarization beam combining prism 110 is arranged so that the polarization beam combining prism portions 110 a and 110 b are line symmetric with respect to the line segment 180, for example.

  The wavelength synthesizing prism 112 is a wavelength synthesizing element, and uses the wavelength difference between the two beams emitted from the polarization synthesizing prism portions 110a and 110b to synthesize these two beams, thereby producing one output light beam. Let it emit.

  The coupling lens 114 causes the output light beam emitted from the wavelength combining prism 112 to enter the outgoing optical fiber 116. Light incident on the outgoing optical fiber 116 is guided to the outside of the housing 118 by the outgoing optical fiber 116.

  The housing 118 is made of, for example, metal (aluminum, stainless steel, etc.), and houses the optical modulator 102, the output microlens array 106, the half-wave plate 108, the polarization combining prism 110, the wavelength combining prism 112, the coupling lens 114, and the like. To do.

  With the above configuration, light having different wavelengths respectively incident from the incident optical fibers 104a and 104b are modulated by the light modulation elements 120a and 120b, and are combined by the polarization combining prism units 110a and 110b, respectively. Thereafter, the wavelength is synthesized by the wavelength synthesizing prism 112 to become one output light beam, which is emitted from the outgoing optical fiber 116.

  In particular, in the present light modulation device 100, two lights having different wavelengths incident from the incident optical fibers 104a and 104b and modulated by the light modulation elements 120a and 120b are combined in the light modulation device 100 for wavelength synthesis. Since it has a function of wavelength synthesis to be emitted as one output light, it is not necessary to perform wavelength synthesis outside the light modulation device as in the prior art.

  Moreover, in the light modulation device 100 according to the present embodiment, as described above, the interval between the two beams that have undergone polarization combining is the row of the four output lights that are emitted side by side from the light modulation elements 120a and 120b. Are configured to be equal to the interval between the two inner output lights (that is, the output lights from the output waveguides 132a and 132b) (that is, the output lights from the output waveguides 132a and 132b are respectively polarized). The light travels straight through the combining prisms 110a and 110b). For this reason, the size of the wavelength synthesizing prism 112 can be made as small as the interval between the output waveguides 132a and 132b.

  That is, in the present optical modulation device 100, since wavelength synthesis is not performed by preparing a wavelength synthesizing element different from the optical modulation device as in the prior art, light loss (emitted from two light sources having different output light wavelengths). Thus, the loss of light until it is coupled to the outgoing optical fiber 116 that outputs the wavelength-combined light is reduced, and the optical characteristics such as the optical loss are stabilized (stabilization of fluctuations with respect to the environmental temperature). In addition, it is possible to reduce the size of the housing 118 and reduce the material cost, the assembly cost, and the like.

  In the present embodiment, the polarization beam combining prism 110 is configured such that the interval between the two beams emitted from the polarization beam combining prism 110 is a row of four output lights emitted side by side from the light modulation elements 120a and 120b. It is assumed that the distance between the two output lights (that is, the output lights emitted from the emission waveguides 132a and 132b) inside is equal to the interval between them. However, the configuration of the polarization beam combining prism 110 is not limited to this, and the intervals between the beams emitted from the polarization beam combining prism units 110a and 110b are emitted side by side from, for example, the light modulation elements 120a and 120b. It is configured to be narrower than the interval (hereinafter referred to as “interval L”) between the two output lights (that is, the output lights emitted from the output waveguides 130a and 130b) located on the outermost side of one output light column. May be.

  In this case, since the polarization combining prism portion does not protrude beyond and occupy the width of the LN substrate as in the prior art, the light modulation device can be reduced in size. Also, the polarization beam combining prism portions 110a and 110b can be arranged smaller than the width of the LN substrate, and in this case, further miniaturization is possible. In addition, since the polarization combining prism 110 is formed by integrating two polarization combining prisms, the polarization combining prism 110 can be arranged in a narrow range compared to the conventional configuration in which the polarization combining prism is discretely arranged in a wide range. Contributing to

  Furthermore, in the light modulation device 100 according to the present embodiment, the light modulation elements 120a and 120b and the polarization beam combining prism portions 110a and 110b, which are the main factors that determine the optical path arrangement in the housing 118, are the light modulation elements 120a and 120b, respectively. It is arranged in a line-symmetrical position with respect to a line segment 180 parallel to the direction of the outgoing light 120b.

  In general, a rectangular housing such as the housing 118 shown in FIG. 1 is substantially symmetrical with respect to the distortion generated when the environmental temperature fluctuates, so that it is incident from the incident optical fibers 104a and 104b as described above. By arranging the optical systems up to the output of the polarization beam combining prism portions 110a and 110b symmetrically with respect to the line segment 180, the positional deviation amounts of the optical elements in the respective optical systems at the time of environmental temperature fluctuations are similar to each other. It can be.

  As a result, the variation of the optical loss for the two lights constituting the two wavelength channels incident from the incident optical fibers 104a and 104b is set to the same level as the variation due to the environmental temperature variation. Generation or increase of loss difference is prevented (thus, generation or increase of transmission light level difference between wavelength channels in the wavelength division multiplexing system is prevented), and transmission quality difference between channels is generated or increased. Can be prevented.

  Further, in the light modulation device 100 according to the present embodiment, one output light combined by the wavelength combining prism 112 is output by one output optical fiber 116, so that the case 118 is guided in order to guide the output light to the outside of the case 118. There may be only one hole provided in.

  For this reason, in the light modulation device 100, compared to the conventional technique in which two holes (or windows) are provided in the housing in order to guide the outgoing light (or the outgoing optical fiber) to the outside of the housing, the processing of the housing accompanying the formation of the holes is performed. Since distortion or the like is reduced, the distortion generated when the environmental temperature of the casing 118 fluctuates can be reduced to reduce the fluctuation of the optical loss. For example, when the cover is pressurized and melted to the casing 118 and hermetically sealed, for example. The distortion of the casing 118 that occurs can be reduced, and the fluctuation of the optical loss before and after hermetic sealing can be reduced.

  In the above-described embodiment, the single light modulator 102 in which the two light modulation elements 120a and 120b are formed on one substrate is used as the light modulator. However, the present invention is not limited to this. Two light modulators composed of one light modulation element formed on the substrate may be used.

  Furthermore, in the above-described embodiment, as shown in FIGS. 1 and 2, the wavelength synthesizing element 112 in which 90-degree reflection occurs is shown as the wavelength synthesizing element. However, the wavelength synthesizing element is not limited to this. A wavelength synthesis element having an arbitrary configuration can be obtained. For example, it is possible to use a wavelength synthesizing element having a configuration using an acute angle reflection of less than 90 degrees or a wavelength synthesizing optical system (consisting of a plurality of optical elements) (hereinafter also referred to as a wavelength synthesizing unit). Such a wavelength combining element using acute angle reflection generally has little polarization dependency of polarization loss (PDL, Polarization Dependent Loss) in the reflection, and is included in the beam emitted from the polarization combining prism 110. It is easy to equalize the optical loss for each of the linearly polarized light components polarized in directions orthogonal to each other, which is advantageous in terms of design and manufacture.

  FIG. 3 is a diagram showing a modification of the light modulation device 100 shown in FIG. The light modulation device 100 ′ illustrated in FIG. 3 has the same configuration as that of the light modulation device 100, and is different from the light modulation device 100 only in that a wavelength combining unit 200 is provided instead of the wavelength combining prism 112.

  The wavelength synthesizing unit 200 is a wavelength synthesizing optical system using acute angle reflection as described above, and includes a mirror 202 and a wavelength synthesizing plate 204. The wavelength synthesis plate 204 reflects light of one wavelength (in this modification, the wavelength of light incident from the incident optical fiber 104b) that is incident at a specific acute incident angle, and other wavelengths (in this modification, A film that transmits the wavelength of light incident from the incident optical fiber 104a is formed. Such a film can be composed of, for example, a dielectric multilayer film.

  The mirror 202 is a total reflection mirror, reflects the beam emitted from the polarization beam combining prism unit 110b, and causes the reflected beam to enter the wavelength combining plate 204 at the specific acute incident angle. As a result, the beam from the polarization beam combining prism unit 110 b incident on the wavelength combining plate 204 reflects the wavelength beam combining plate 204, while the beam emitted from the polarization beam combining prism unit 110 a passes through the wavelength beam combining plate 204. As a result, both beams are combined into one output light beam and output. The single output light beam is coupled to the output optical fiber 116 via the coupling lens 114 and output.

  In this modification, the wavelength synthesizer 200 using acute angle reflection is used, so that the difference in optical loss between mutually orthogonal linearly polarized light components included in the output light beam is reduced to achieve good optical characteristics. Can do.

  DESCRIPTION OF SYMBOLS 100 ... Light modulation device, 102 ... Light modulator, 104a, 104b ... Incident optical fiber, 106 ... Output micro lens array, 108 ... Half-wave plate, 110 ... Polarization Synthetic prism, 112... Wavelength synthesizing prism, 114... Coupling lens, 116... Outgoing optical fiber, 120 a, 120 b... Light modulation element, 130 a, 132 a, 130 b, 132 b. 140a, 142a, 140b, 142b ... microlens, 170 ... substrate end face, 200 ... wavelength synthesis unit, 202 ... mirror, 204 ... wavelength synthesis plate.

Claims (7)

A first light modulation element and a second light modulation element, each of which modulates light of different wavelengths and emits two output lights, and
A first polarization beam combining element that combines the two output lights from the first light modulation element into a single beam;
A second polarization beam combining element that combines the two output lights from the second light modulation element into a single beam and emits it;
A wavelength synthesizing element that synthesizes and emits the beams emitted from the first and second polarization synthesizing elements into one output light beam;
With
The first and second light modulation elements are arranged so that each output light is emitted side by side,
The first polarization combining element and the second polarization combining element are configured to output two output lights inside four rows of the output lights emitted side by side from the first and second light modulation elements. The two output lights that are the outermost of the four rows of output lights that pass through without changing the propagation direction and are emitted side by side from the first and second light modulation elements are the four output lights. Are reflected so as to approach the other two output lights inside the column, and are aligned with the optical axes of the two output lights inside the four output light columns emitted side by side. outputs polarization combined beam, the mutual distance of said beam first and second polarization combining element emits synthesized respectively, along the from the first and second optical modulation element The two output lights at the outermost side of the four rows of output lights emitted from each other It is configured to be narrower than the interval,
Light modulation device.   The light modulation device according to claim 1, wherein the first polarization combining element and the second polarization combining element are configured as a single unit.   3. The polarized wave of two output lights located at the innermost side of the four rows of output lights emitted side by side from the first and second light modulation elements is rotated by a wave plate. Light modulation device.   The light modulation device according to claim 3, wherein the wavelength plate is a single sheet that is shared by the two innermost output lights. The intervals between the beams that are synthesized and emitted by the first and second polarization beam combining elements, respectively, are the four output light columns emitted side by side from the first and second light modulation elements. Equal to the distance between the two optical axes inside
The light modulation device according to claim 1. The first light modulation element and the second light modulation element are arranged in a line-symmetric position with respect to a line segment parallel to the direction of the output light emitted side by side, and
The first polarization combining element and the second polarization combining element are arranged in line-symmetric positions with respect to the line segment.
The light modulation device according to claim 1. Four emission lenses that respectively receive the four output lights emitted from the first and second light modulation elements;
Optical fiber,
A coupling lens that couples the output light beam to the optical fiber;
The four exit lenses are an integrally formed microlens array.
The light modulation device according to claim 1.

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