JP4888313B2 - Light modulator - Google Patents

Description

  The present invention relates to a light modulation device that modulates light.

  Conventionally, a multi-level phase modulation apparatus that performs quadrature phase shift keying (QPSK) that gives 2-bit information to one symbol or four-phase differential phase modulation (DQPSK) (for example, differential QPSK) has been used (for example, , See Patent Document 1 below). QPSK and DQPSK are particularly useful for high-speed, long-distance optical transmission because they have a small spectral spread and high chromatic dispersion tolerance when compared with other modulation systems at the same bit rate.

  FIG. 18 is a diagram illustrating a configuration of a conventional light modulation device. A conventional optical modulation device 1800 shown in FIG. 18 is an optical modulation device that modulates QPSK or DQPSK with respect to input light. The input light is branched by the optical branching unit 1810 and output to the modulator 1820a and the modulator 1820b, respectively. The modulator 1820a and the modulator 1820b perform two-phase (0 and π) phase modulation on the light output from the optical branching unit 1810, respectively.

  The modulator 1820a outputs the modulated light to the phase adjuster 1830. The modulator 1820b outputs the modulated light to the optical coupling unit 1840. The phase adjuster 1830 changes the phase of the light output from the modulator 1820a in accordance with the phase control signal (bias) input from the control unit 1870. Further, the phase shift amount of the phase adjuster 1830 is π / 2 or approximately π / 2 in the initial state.

  The phase adjuster 1830 outputs the light whose phase has been changed to the optical coupling unit 1840. The optical coupler 1840 combines the light output from the phase adjuster 1830 and the light output from the modulator 1820b and outputs the combined light. The optical branching unit 1850 branches a part of the light output from the optical coupling unit 1840 and outputs the branched component to a PD 1860 (Photo Detector).

  The PD 1860 receives the light output from the light branching unit 1850 and outputs an electrical signal corresponding to the intensity of the received light to the control unit 1870. The control unit 1870 adjusts the phase control signal input to the phase adjuster 1830 while monitoring the intensity of the electric signal output from the PD 1860, thereby changing the phase difference of each light combined by the optical coupling unit 1840 to π / Control to approach 2.

  FIG. 19 is a diagram showing a phase arrangement when the phase difference of each light is π / 2. Reference numeral 1910 a indicates the phase arrangement of the light output from the phase adjuster 1830 to the optical coupler 1840. The phase adjuster 1830 changes the phase of the light subjected to the two-phase (0 and π) phase modulation by the modulator 1820a by π / 2, so that the phase of the light output from the phase adjuster 1830 to the optical coupler 1840 is changed. The arrangement is π / 2 and 3π / 2.

  Reference numeral 1910b indicates the phase arrangement of the light output from the modulator 1820b to the optical coupling unit 1840. Since the modulator 1820b performs two-phase (0 and π) phase modulation on the light output from the optical branching unit 1810, the phase arrangement of the light output from the modulator 1820b to the optical coupling unit 1840 is 0 and becomes π.

  Reference numeral 1920 indicates the phase arrangement of the light coupled by the optical coupling unit 1840. As indicated by reference numerals 1910a and 1910b, when the phase difference of each light coupled by the optical coupling unit 1840 is π / 2, the phase arrangement of the light coupled by the optical coupling unit 1840 is π / 4, 3π. / 4, 5π / 4 and 7π / 4.

  FIG. 20 is a diagram illustrating a phase arrangement when the phase difference of each light deviates from π / 2. FIG. 20 shows a phase arrangement when the phase difference of each light coupled by the optical coupling unit 1840 is shifted from π / 2 by Δ. Reference numeral 2010 a indicates the phase arrangement of the light output from the phase adjuster 1830 to the optical coupling unit 1840. Reference numeral 2010 b indicates the phase arrangement of the light output from the modulator 1820 b to the optical coupling unit 1840. Reference numeral 2020 indicates the phase arrangement of the light coupled by the optical coupling unit 1840.

  When the phase difference of each light coupled by the optical coupling unit 1840 is deviated from π / 2 due to changes with time of the electrodes constituting the modulator 1820a and the modulator 1820b, the light coupled by the optical coupling unit 1840 The phase arrangement is not π / 4, 3π / 4, 5π / 4, or 7π / 4, and the modulation characteristic of the optical signal is deteriorated. In contrast, the control unit 1870 described above performs phase control of each light coupled by the optical coupling unit 1840 to compensate for the phase shift of each light.

JP 2007-43638 A

  However, the above-described conventional technique has a problem that it is difficult to control the phase difference of each light coupled by the optical coupling unit 1840 to π / 2. For this reason, it is not possible to compensate for a phase shift due to a change with time of electrodes constituting the modulator 1820a and the modulator 1820b, and the modulation characteristics of the optical signal output from the optical coupling unit 1840 to the outside deteriorate (FIG. 20). (See reference numeral 2020). Hereinafter, this problem will be described in detail.

  FIG. 21 is a graph showing the relationship between the phase difference of each light and the PD output intensity. In FIG. 21, a relationship 2110 indicates the relationship of the intensity of the electrical signal output from the PD 1860 to the control unit 1870 (PD output intensity) with respect to the phase difference of each light coupled by the optical coupling unit 1840. MAX on the vertical axis indicates the maximum value of the PD output intensity. min indicates the minimum value of the PD output intensity. MED indicates the median value of the maximum value MAX and the minimum value min.

  As shown in the relation 2110, the intensity of the electric signal output from the PD 1860 when the phase difference of each light coupled by the optical coupling unit 1840 is π / 2 is the median value MED (reference numeral 2111). The control unit 1870 controls the phase so that the PD output intensity becomes the median MED while monitoring the PD output intensity in order to control the phase difference of each light coupled by the optical coupling unit 1840 to π / 2. Such a phase control is difficult.

  For example, the control unit 1870 changes the phase control current input to the phase adjuster 1830 in order to calculate the median value MED of the PD output intensity, thereby changing the minimum value min and the maximum value MAX of the PD output intensity. The median value MED is calculated based on the acquired information. Further, the maximum value MAX of the PD output intensity changes according to the intensity of the input light. For this reason, the control unit 1870 needs to calculate the median MED for each intensity of input light.

  The disclosed optical modulation device is to solve the above-described problems, and an object thereof is to improve modulation characteristics by simple control.

  A light modulation device for branching input light, and a phase for passing each light branched by the light branching means and changing a phase difference of each light to be passed according to an input phase control signal An adjusting unit; a modulating unit that phase-modulates each of the lights branched by the optical branching unit; an optical coupling unit that combines and outputs the lights that have passed through the phase adjusting unit and the modulating unit; and the phase A part of each component of the light that passes through the adjusting unit and is output to the optical coupling unit is folded, and the folding unit that passes the phase adjusting unit again and the light that has passed through the phase adjusting unit are combined. Second optical coupling means.

  According to the above configuration, the phase difference of each light that is folded by the folding means and passed through the phase adjusting means again is controlled to be close to π, so that the phase difference of each light coupled by the optical coupling means is π / 2. Can be controlled. Thus, the phase difference of each light combined by the optical coupling means can be reduced by simple phase control that adjusts the phase adjustment signal so that the intensity of the combined light of each light passed through the phase adjustment means is minimized. It can be controlled to π / 2.

  According to the disclosed light modulation device, the modulation characteristic can be improved by simple control.

  Exemplary embodiments of a light modulation device according to the present invention will be explained below in detail with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a diagram illustrating a configuration of the light modulation device according to the first embodiment. The optical modulation device 100 according to the first embodiment is a QPSK or DQPSK optical modulation device. As shown in FIG. 1, the optical modulation device 100 includes an optical circulator 110, an optical branching unit 130, parallel waveguides 140a and 140b, a phase adjustment unit 150, a modulation unit 160, a folding unit 170, and an optical coupling. Unit 180, PD 191, and control unit 192.

The optical circulator 110 outputs the input light from the outside of the light modulation device 100 to the optical branching unit 130 and outputs the light output from the optical branching unit 130 to the PD 191 (extraction means). The substrate 120 is a substrate having an electro-optic effect such as LiNbO ₃ . On the substrate 120, an optical branching unit 130, parallel waveguides 140a and 140b, a phase shift unit 150, a modulation unit 160, a folding unit 170, and an optical coupling unit 180 are provided.

  The optical branching unit 130 branches the input light output from the optical circulator 110. The light branching unit 130 outputs each branched light to the parallel waveguide 140a and the parallel waveguide 140b, respectively. In addition, the optical branching unit 130 also has a function as a second optical coupling unit that couples the lights that are folded back and pass through the phase adjusting unit 150 again. The optical branching unit 130 combines the light that has been folded and passed through the phase adjusting unit 150 again, and outputs the combined light to the optical circulator 110.

  The phase adjusting unit 150 is branched by the light branching unit 130, passes each light output to the parallel waveguide 140a and the parallel waveguide 140b, and the phase difference of each passing light according to the input phase control signal Change. Here, the phase adjustment unit 150 includes a phase adjuster 151 and a parallel waveguide 140b provided in the parallel waveguide 140a. The light output from the optical branching unit 130 to the parallel waveguide 140 a passes through the phase adjuster 151. The phase adjuster 151 changes the phase of the light passing therethrough according to the phase control signal input by the control unit 192.

  The phase shift amount of the phase adjuster 151 is π / 2 or approximately π / 2 in the initial state. On the other hand, the phase of light passing through the parallel waveguide 140b does not change. As a result, the phase difference of each light passing through the phase adjusting unit 150 changes by π / 2. Further, the phase difference of each light that has passed through the phase adjusting unit 150 further changes by π / 2. The phase adjuster 151 outputs the light whose phase has been changed to the modulator 160 a of the modulator 160. The light that has passed through the parallel waveguide 140b is output to the modulator 160b of the modulator 160.

  The modulation unit 160 phase modulates each light output from the phase adjustment unit 150. Specifically, the modulation unit 160 includes a modulator 160a and a modulation control unit 166a, and a modulator 160b and a modulation control unit 166b. The modulator 160a and the modulation control unit 166a perform two-phase (0 and π) phase modulation on the light output from the phase adjuster 151 through the parallel waveguide 140a. The modulator 160b and the modulation control unit 166b perform two-phase (0 and π) phase modulation on the light output through the parallel waveguide 140b.

  The modulator 160a is formed on the substrate 120 and includes an optical branching unit 161a, parallel waveguides 162a and 162b, an optical coupling unit 163, signal electrodes 164a and 164b, and a ground electrode 165. The optical branching unit 161a branches the light output from the phase adjuster 151 through the parallel waveguide 140a. The optical branching unit 161a outputs the branched lights to the parallel waveguide 162a and the parallel waveguide 162b, respectively.

  The parallel waveguide 162a and the parallel waveguide 162b pass each light output from the optical branching unit 161a and output the light to the optical coupling unit 163. The optical coupling unit 163 combines the lights output from the parallel waveguide 162a and the parallel waveguide 162b and outputs the combined light to the optical coupling unit 180. The signal electrode 164a is provided along the parallel waveguide 162a. The signal electrode 164b is provided along the parallel waveguide 162b.

  The ground electrode 165 is provided with a predetermined distance from the signal electrode 164a and the signal electrode 164b. In practice, optical waveguides such as the optical branching portion 161a, the parallel waveguides 162a and 162b, and the optical coupling portion 163 are formed near the surface inside the substrate 120, and the signal electrode 164a and the signal electrode 164b are formed thereon. In addition, although not visible because the ground electrode 165 is formed, these optical waveguides are visualized and illustrated for convenience of explanation (the same applies hereinafter).

  The modulation control unit 166a inputs modulation control signals that are inverted with respect to the signal electrode 164a and the signal electrode 164b, respectively. Here, the modulation control signal is a signal indicating information of “0” and “1” based on a data signal, for example. Depending on the modulation control signal information generation method, the modulation by the modulator 160a can be changed to the QPSK method or the DQPSK method. Here, it is assumed that the modulation by the modulator 160a is QPSK.

  As a result, the phase of each light passing through the parallel waveguide 162a and the parallel waveguide 162b changes, and the light output from the optical coupling unit 163 is phase-modulated in two phases. Further, since the phase of the light input to the modulator 160a is changed by π / 2 by the phase adjuster 151, the light output from the optical coupling unit 163 is converted into a modulation control signal input from the modulation control unit 166a. Accordingly, it becomes a phase modulation signal of two phases (π / 2 and 3π / 2).

  The detailed configuration of the modulator 160b is the same as the configuration of the modulator 160a, and a description thereof will be omitted. The modulator 160b phase-modulates the light output from the optical branching unit 130 through the parallel waveguide 140b in two phases according to the modulation control signal input from the modulation control unit 166b. Since the light input to the modulator 160b does not change in phase, the light output from the modulator 160b becomes a two-phase (0 and π) phase modulation signal.

  The modulator 160a and the modulator 160b output the modulated light to the optical coupling unit 180. Note that the signal electrode 164a, the signal electrode 164b, and the ground electrode 165 constituting the modulator 160a, and the signal electrode and the ground electrode (not shown) constituting the modulator 160b change over time due to a temperature change or the like. For this reason, the phase difference of each light that passes through the modulator 160a and the modulator 160b and is coupled by the optical branching unit 130 deviates from π / 2 over time.

  The folding unit 170 is a folding unit that folds some components of each light that passes through the phase adjustment unit 150 and the modulation unit 160 and is output to the optical coupling unit 180, and causes the phase adjustment unit 150 to pass again. The folding | returning part 170 is comprised by the light separation part 171a and the light separation part 171b, and the mirror 172a and the mirror 172b.

  The light separation unit 171a separates some components of the light output from the modulator 160a to the optical coupling unit 180. The light separation unit 171a outputs the separated light to the mirror 172a. The light separation unit 171b separates some components of the light output from the modulator 160b to the optical coupling unit 180. The light separation unit 171b outputs the separated light to the mirror 172b.

  The light separating unit 171a and the light separating unit 171b are each configured by an optical branching waveguide. The branching ratio of the light separation unit 171a and the light separation unit 171b may be set so that the component that passes through and is output to the optical coupling unit 180 is larger than the ratio of the component that is output to the mirror 172a and the mirror 172b. For example, the ratio of the component output to the optical coupling unit 180 and the component output to the mirror 172a and the mirror 172b is set to 9: 1.

  The mirror 172a reflects and returns the light output from the light separation unit 171a. The light reflected by the mirror 172a passes through the light separation unit 171a, the modulator 160a, and the phase adjuster 151 again, and is output to the light branching unit 130. The mirror 172b reflects and returns the light output from the light separation unit 171b. The light reflected by the mirror 172b passes through the light separation unit 171b and the modulator 160b again and is output to the light branching unit 130.

  The optical coupling unit 180 combines the light output from the modulator 160 a and the light output from the modulator 160 b and outputs the combined light to the outside of the light modulation device 100. The light coupled by the optical coupling unit 180 and output to the outside is divided into four phases (π / π) according to the modulation control signals input from the modulation control unit 166a and the modulation control unit 166b to the modulator 160a and the modulator 160b, respectively. 4, 3π / 4, 5π / 4, and 7π / 4).

  The PD 191 and the control unit 192 input the phase control signal to the phase adjustment unit 150 so that the intensity of the light combined by the optical branching unit 130 is minimized, so that the level of each light that has passed through the phase adjustment unit 150 again. Control means for controlling the phase difference to π is configured. The PD 191 receives the light output from the optical circulator 110. The PD 191 outputs an electrical signal having an intensity corresponding to the intensity of the received light to the control unit 192.

  The control unit 192 detects the electrical signal output from the PD 191 and inputs a phase control signal corresponding to the detected electrical signal to the phase adjuster 151. Specifically, the control unit 192 adjusts the strength of the phase control signal input to the phase adjuster 151 so that the strength of the electrical signal output from the PD 191 is minimized. The control unit 192 is configured by, for example, a CPU (Central Processing Unit).

  Here, the case where the phase adjusting unit 150 is configured by the phase adjuster 151 and the parallel waveguide 140b has been described. However, the phase adjusting unit 150 is provided in the phase adjuster 151 and the parallel waveguide 140b. You may comprise by another phase adjuster. In this case, for example, by setting the phase shift amount of the phase adjuster 151 to π / 4 and setting the phase shift amount of the phase adjuster provided in the parallel waveguide 140b to −π / 4, the phase adjuster 150 is changed. The phase difference of each passing light is changed by π / 2.

  In addition, the configuration in which the optical branching unit 130, the parallel waveguides 140a and 140b, the phase shift unit 150, the modulation unit 160, the folding unit 170, and the optical coupling unit 180 are provided on the substrate 120 has been described. The configuration of the light modulation device 100 is not limited to this. For example, the modulation unit 160 may be provided on the substrate 120, and the optical branching unit 130, the parallel waveguides 140a and 140b, the phase shift unit 150, the folding unit 170, and the optical coupling unit 180 may be provided outside the substrate 120.

  In the drawings shown below, reference numerals of the optical branching portion 161a, the parallel waveguide 162a and the parallel waveguide 162b, the optical coupling portion 163, the signal electrode 164a and the signal electrode 164b, and the ground electrode 165 are illustrated. Is omitted. In the drawings shown below, the modulation control unit 166a and the modulation control unit 166b are not shown except for FIG.

FIG. 2 is an enlarged perspective view showing a mirror portion of the light modulation device. As shown in FIG. 2, among the optical waveguides branched by the optical branching waveguide constituting the light separating portion 171a, the optical waveguide 210 to which the separated light is output is led out to the end surface on the mirror 172a side of the substrate 120. Has been. The mirror 172a is formed, for example, by depositing a metal such as Au and a dielectric such as SiO _{2 on} the end face of the substrate 120 from which the optical waveguide 210 is derived.

Similarly, for the mirror 172b, out of the optical waveguides branched by the optical branching waveguide constituting the light separating portion 171b, the optical waveguide from which the separated light is output is led out to the end surface of the substrate 120, and the optical waveguide is led out. It is formed by vapor-depositing a metal such as Au and a dielectric such as SiO _{2 on} the end face of the substrate 120. The configuration method of the mirror 172a and the mirror 172b is not limited to these vapor depositions, and for example, the mirror may be installed on the end surface of the substrate 120.

  FIG. 3 is a flowchart illustrating an example of the operation of the control unit illustrated in FIG. Here, it is assumed that input light is input from the optical circulator 110 to the optical branching unit 130. As shown in FIG. 3, first, input of a phase control signal to the phase adjuster 151 is started (step S301). The intensity of the phase control signal at this time is set as the initial set intensity. Next, the intensity of the electrical signal output from the PD 191 is detected (step S302).

  Next, it is determined whether or not the intensity of the detected electrical signal is equal to or less than a predetermined threshold value (step S303). When the intensity of the electric signal output from the PD 191 is larger than the threshold value (step S303: No), the intensity of the phase control signal input to the phase adjuster 151 is increased from the set intensity at that time (step S303: No). S304). Next, the intensity of the electric signal output from the PD 191 is detected (step S305).

  Next, it is determined whether or not the strength of the electrical signal detected in step S305 has decreased compared to the strength of the electrical signal detected in step S302 (step S306). When the intensity of the electrical signal detected in step S305 decreases (step S306: Yes), the process returns to step S302 to continue the process with the intensity of the phase control signal increased in step S304 as a new set intensity.

  In step S306, when the strength of the electrical signal detected in step S305 has not decreased (step S306: No), the strength of the phase control signal input to the phase adjuster 151 is decreased from the set strength (step S307). ), Using the decreased intensity of the phase control signal as a new set intensity, the process returns to step S302 to continue the process.

  In step S303, when the intensity of the detected electric signal is equal to or lower than the threshold value (step S303: Yes), it is determined whether or not the operation end condition is satisfied (step S308), and the end condition is not satisfied. In the case (step S308: No), the process returns to step S302 to continue the processing. When the termination condition is satisfied (step S308: Yes), the series of operations is terminated.

  FIG. 4 is a graph showing the relationship between the phase difference of each folded light and the PD output intensity. In FIG. 4, the relationship 410 is returned by the mirror 172 a and the mirror 172 b, passes through the phase adjustment unit 150 again, and is coupled by the light branching unit 130, and is output from the PD 191 to the control unit 192. The relationship between the intensity of the electric signal (PD output intensity) is shown. “Min” on the vertical axis indicates the minimum value of the PD output intensity.

  The control unit 192 adjusts the intensity of the phase control signal input to the phase adjuster 151 so that the PD output intensity becomes the minimum value min while monitoring the PD output intensity. As shown in the relationship 410, when the PD output intensity reaches the minimum value min (reference numeral 411), the phase difference of each light that passes through the phase adjustment unit 150 and is coupled by the optical branching unit 130 is π or approximately π. become.

  Since each light that passes through the phase adjustment unit 150 again and is coupled by the optical branching unit 130 passes through the phase adjustment unit 150 twice, the phase difference is doubled with respect to each light that is coupled by the optical coupling unit 180. become. For this reason, when the phase difference of each light couple | bonded by the optical branching part 130 becomes (pi), the phase difference of each light couple | bonded by the optical coupling part 180 will be (pi) / 2. At this time, the modulation characteristic of the optical signal output from the optical coupler 180 is optimal.

  FIG. 5 is a graph showing the relationship between the phase difference of each coupled light and the PD output intensity. In FIG. 5, a relationship 510 indicates a relationship between the phase difference [degree] of each light coupled by the optical coupling unit 180 and the PD output intensity [μW]. A relationship 520 indicates a relationship between the phase difference [degree] of each light coupled by the optical coupling unit 180 and the minimum reception sensitivity difference [dB] of the light coupled by the optical coupling unit 180 and output to the outside. ing.

  As shown in the relationship 510, when the PD output intensity reaches the minimum value (0 [μW]), the phase difference of each light coupled by the optical coupling unit 180 becomes 90 [degrees] (π / 2). Further, as shown in the relationship 520, when the PD output intensity becomes the minimum value (0 [μW]), the minimum reception sensitivity difference of the light output by being coupled by the optical coupling unit 180 to the outside is minimum (0 [0 [μW]). dB]).

  FIG. 6 is a diagram of a modification of the light modulation device according to the first embodiment. In FIG. 6, the same components as those shown in FIG. In FIG. 1, the configuration in which the phase adjustment unit 150 is provided in front of the modulation unit 160 has been described. However, as illustrated in FIG. 6, the optical modulation device 100 according to the first embodiment uses the optical modulation illustrated in FIG. 1. In the configuration of the apparatus 100, the phase adjustment unit 150 may be provided after the modulation unit 160.

  The modulator 160 a modulates the light output from the optical branching unit 130 to the parallel waveguide 140 a and outputs the modulated light to the phase adjuster 151. The phase adjuster 151 changes the phase of the light output from the modulator 160a. The phase adjuster 151 outputs the light whose phase has been changed to the optical coupling unit 180. The light separation unit 171a separates some components of the light output from the phase adjuster 151 to the optical coupling unit 180. The optical coupler 180 couples each light output from the phase adjuster 151 and the modulator 160b.

  As described above, according to the light modulation device 100 according to the first embodiment, some components of each light that passes through the phase adjustment unit 150 and is output to the optical coupling unit 180 are folded back by the folding unit 170, respectively. By controlling the phase difference of each light that has passed through the adjusting unit 150 to approach π, the phase difference of each light coupled by the optical coupling unit 180 can be controlled to substantially π / 2.

  As a result, the light coupling unit 180 is coupled by a simple phase control (see FIG. 3) that adjusts the phase adjustment signal so that the intensity of the combined light of each light that has passed through the phase adjustment unit 150 is minimized. The phase difference of each light can be controlled to substantially π / 2. Therefore, according to the light modulation device 100 according to the first embodiment, the modulation characteristics of the optical signal output from the optical coupling unit 180 to the outside can be improved by simple control of the control unit 192.

  Further, by turning back some components of each light that passes through the modulation unit 160 together with the phase adjustment unit 150 and is output to the optical coupling unit 180, the phase difference of each light coupled by the optical branching unit 130 is It is possible to reflect a shift in phase difference due to a change with time of the modulation unit 160. For this reason, even if the phase difference is shifted due to a change with time of the modulation unit 160 or the like, each phase coupled by the optical coupling unit 180 is controlled by controlling the phase difference of each light coupled by the optical branching unit 130 to be close to π. The phase difference of light can be controlled substantially to π / 2, and the modulation characteristics can be further improved.

  Further, by configuring the second optical coupling unit that couples the lights that have passed again through the phase adjusting unit 150 by the optical branching unit 130, it is possible to configure the second optical coupling unit without providing a new member. . Further, the light circulator 110 provided in the front stage of the light branching unit 130 is configured to extract the light combined by the light branching unit 130, so that the light combined by the light branching unit 130 can be extracted with low loss. it can.

(Embodiment 2)
FIG. 7 is a diagram of a configuration of the light modulation device according to the second embodiment. As illustrated in FIG. 7, the light modulation device 100 according to the second embodiment includes a part of each light that has passed through the phase adjustment unit 150 in the configuration of the light modulation device 100 according to the first embodiment (see FIG. 1). The folding unit 170 that folds each of the components is provided between the phase adjustment unit 150 and the modulation unit 160.

  The light separation unit 171a separates some components of the light output from the phase adjuster 151 to the modulator 160a. The light separation unit 171a outputs the separated light to the mirror 172a. The light separation unit 171b separates some components of the light output from the light branching unit 130 to the modulator 160b. The light separation unit 171b outputs the separated light to the mirror 172b.

  The mirror 172a reflects and returns the light output from the light separation unit 171a. The mirror 172b reflects and returns the light output from the light separation unit 171b. The light reflected by the mirror 172a passes through the light separation unit 171a and the phase adjuster 151 again and is output to the light branching unit 130. The light reflected by the mirror 172b passes through the light separation unit 171b again and is output to the light branching unit 130.

  As described above, according to the light modulation device 100 according to the second embodiment, the effects of the light modulation device 100 according to the first embodiment can be obtained, and each light that has passed through the phase adjustment unit 150 can be transmitted before the modulation unit 160. By turning back, the phase difference of each light coupled by the optical branching unit 130 is not affected by the phase shift of the modulation unit 160. For this reason, by controlling the phase difference of each light coupled by the optical branching unit 130 to substantially π, the phase shift amount of the phase adjusting unit 150 can be accurately controlled to π / 2, and the modulation characteristics Can be further improved.

(Embodiment 3)
FIG. 8 is a diagram illustrating a configuration of the light modulation device according to the third embodiment. In FIG. 8, the same components as those shown in FIG. As shown in FIG. 8, the light modulation device 100 according to the third embodiment includes a half mirror 810a and a half mirror 810b instead of the folding unit 170 of the light modulation device 100 according to the first embodiment (see FIG. 1). I have. The half mirror 810a and the half mirror 810b constitute folding means for folding back a part of each component of each light that has passed through the phase adjustment unit 150.

  The half mirror 810a reflects and folds a part of the light output from the modulator 160a to the optical coupling unit 180. Further, the half mirror 810 a passes the component that does not reflect the light output from the modulator 160 a to the optical coupling unit 180 and outputs it to the optical coupling unit 180. The light reflected by the half mirror 810a passes through the modulator 160a and the phase adjuster 151 again and is output to the optical branching unit 130.

  The half mirror 810b reflects and folds a part of the light output from the modulator 160b to the optical coupling unit 180. Further, the half mirror 810b passes the component that does not reflect the light output from the modulator 160b to the optical coupling unit 180 and outputs it to the optical coupling unit 180. The light reflected by the half mirror 810b passes through the modulator 160b again and is output to the optical branching unit 130. The optical coupler 180 couples the lights output from the modulator 160a and the modulator 160b and passed through the half mirror 810a and the half mirror 810b.

FIG. 9 is an enlarged perspective view showing a half mirror part of the light modulation device by cutting. As shown in FIG. 9, the substrate 120 of the light modulation device 100 according to the third embodiment is provided with a groove 910 that crosses the parallel waveguide 140a by etching or the like. The half mirror 810a is provided in a state of being inserted into the groove 910. The half mirror 810a is formed of, for example, a dielectric multilayer film (Si / SiO ₂ , TiO ₂ / SiO ₂ etc.) or a semiconductor multilayer film (InP / InGaAs, GaAs, GaAs / AlGaAs etc.).

  Further, the reflectance of the half mirror 810a can be arbitrarily designed depending on the film thickness and the number of layers of these multilayer films. Similarly, the half mirror 810b is provided with a groove that crosses the parallel waveguide 140b and is inserted into the provided groove. The mirror 172a shown in FIG. 7 can be configured by providing a total reflection mirror instead of the half mirror 810a shown in FIG. 9, for example. Similarly, the mirror 172b shown in FIG. 7 can also be configured by providing a total reflection mirror instead of the half mirror 810b.

  As described above, according to the light modulation device 100 according to the third embodiment, the effects of the light modulation device 100 according to the first embodiment are obtained, and the half mirror 810a and the half mirror 810b are respectively connected to the parallel waveguide 140a and the parallel waveguide. By providing on the waveguide 140b, it is possible to configure a folding unit that folds back some components of each light that has passed through the phase adjustment unit 150 without providing a light separation unit (see reference numerals 171a and 171b in FIG. 1). .

(Embodiment 4)
FIG. 10 is a diagram illustrating a configuration of the light modulation device according to the fourth embodiment. In FIG. 10, the same components as those shown in FIG. As illustrated in FIG. 10, the light modulation device 100 according to the fourth embodiment includes, in the configuration of the light modulation device 100 according to the first embodiment (see FIG. 1), a circular waveguide 1010 a and A circular waveguide 1010b is provided.

  The circulating waveguide 1010a and the circulating waveguide 1010b constitute folding means that circulates and returns each light that has passed through the phase adjustment unit 150 and passes the light through the phase adjustment unit 150 again. Specifically, the circumferential waveguide 1010a includes a light separating unit 1011a, a light separating unit 1012a, and a folded waveguide 1013a.

  The light separating unit 1011a separates some components of the light output from the modulator 160a to the optical coupling unit 180, and outputs the separated light to the folded waveguide 1013a. The light separation unit 1012a separates a part of the light output from the modulator 160a and passed through the light separation unit 1011a, and outputs the separated light to the folded waveguide 1013a. The light that has passed without being separated by the light separation unit 1011a and the light separation unit 1012a is output to the light coupling unit 180.

  The light separating unit 1011a and the light separating unit 1012a are each configured by an optical branching waveguide. The branching ratio of the light separating unit 1011a and the light separating unit 1012a may be set so that the component output to the optical coupling unit 180 is larger than the ratio of the component output to the folded waveguide 1013a. For example, the ratio of the component output to the optical coupling unit 180 and the component output to the folded waveguide 1013a is set to 9: 1.

  The folded waveguide 1013a is a single optical waveguide having both ends connected to one branch path of the light separating section 1011a and one branch path of the light separating section 1012a. The folded waveguide 1013a returns the light output from the light separating unit 1011a and inputs the light to one branch path of the light separating unit 1012a. The folded waveguide 1013a folds the light output from the light separating unit 1012a and inputs the light to one branch path of the light separating unit 1011a.

  The light input from the folded waveguide 1013a to the light separating unit 1012a is output to the light separating unit 1011a, and is combined with the light input from the folded waveguide 1013a to the light separating unit 1011a by the light separating unit 1011a. The light combined by the light separation unit 1011a passes through the modulator 160a and the phase adjuster 151 again and is output to the light branching unit 130.

  The circular waveguide 1010b includes a light separating unit 1011b, a light separating unit 1012b, and a folded waveguide 1013b. The configuration of each of the circular waveguides 1010b is the same as that of the light separating unit 1011a, the light separating unit 1012a, and the folded waveguide 1013a of the circular waveguide 1010a, and thus description thereof is omitted. The light returned by the circular waveguide 1010b passes through the modulator 160b again and is output to the optical branching unit 130.

  FIG. 11 is a diagram illustrating a modification of the light modulation device according to the fourth embodiment. In FIG. 11, the same components as those shown in FIG. As illustrated in FIG. 11, the light modulation device 100 according to the fourth embodiment includes, in the configuration of the light modulation device 100 according to the first embodiment (see FIG. 1), a circular waveguide 1110 a and A circular waveguide 1110b is provided.

  The circular waveguide 1110 a and the circular waveguide 1110 b constitute a folding unit that circulates and returns each light that has passed through the phase adjusting unit 150 and passes the light through the phase adjusting unit 150 again. Specifically, the circular waveguide 1110a includes an optical separation unit 1111a, an optical branching unit 1112a, and a folded waveguide 1113a.

  The light separation unit 1111a separates some components of the light output from the modulator 160a to the optical coupling unit 180, and outputs the separated light to the light branching unit 1112a. The light branching unit 1112a branches the light output from the light separating unit 1111a, and outputs each branched light to both ends of the folded waveguide 1113a. The branching ratio of the optical branching portion 1112a is, for example, 5: 5.

  The light separation unit 1111a is configured by an optical branching waveguide. The branching ratio of the light separation unit 1111a is set so that the component output to the optical coupling unit 180 is larger than the ratio of the component output to the light branching unit 1112a. For example, the ratio of the component output to the optical coupling unit 180 and the component output to the optical branching unit 1112a is set to 9: 1.

  The folded waveguide 1113a is a single optical waveguide having both ends connected to the two branch paths of the optical branching section 1112a. The folded waveguide 1113a folds the light output from one branch path of the optical branching section 1112a and outputs it to the other branch path of the optical branching section 1112a and is output from the other branch path of the optical branching section 1112a. The light is folded and output to one branch path of the light branching portion 1112a.

  The lights returned by the return waveguide 1113a are input from the two branch paths of the optical branching part 1112a, and are coupled by the optical branching part 1112a. The light combined by the light separation unit 1111a passes through the light separation unit 1111a, the modulator 160a, and the phase adjuster 151 again, and is output to the light branching unit 130.

  The circular waveguide 1110b includes an optical separation unit 1111b, an optical branching unit 1112b, and a folded waveguide 1113b. The configuration of each of the circular waveguides 1110b is the same as that of the light separating unit 1111a, the optical branching unit 1112a, and the folded waveguide 1113a of the circular waveguide 1110a, and thus description thereof is omitted. The light returned by the circular waveguide 1110b passes through the modulator 160b again and is output to the optical branching unit 130.

  As described above, according to the light modulation device 100 according to the fourth embodiment, the effects of the light modulation device 100 according to the first embodiment are achieved, and the circular waveguide 1010a and the circular waveguide 1010b are provided as folding means. The folding means can be configured only by forming the optical waveguide without using a reflecting member such as a mirror. Since the optical waveguide is formed by patterning or the like, the folding means can be configured with high accuracy, and the modulation characteristics can be further improved.

(Embodiment 5)
FIG. 12 is a diagram of a configuration of the light modulation device according to the fifth embodiment. In FIG. 12, the same components as those shown in FIG. As illustrated in FIG. 12, the light modulation device 100 according to the fifth embodiment includes an oscillator 1210 and a low-pass filter 1220 in addition to the configuration of the light modulation device 100 according to the first embodiment (see FIG. 1). I have. The control unit 192 and the oscillator 1210 constitute superimposing means for superimposing the low frequency signal on the phase control signal and inputting it to the phase adjuster 151.

  The oscillator 1210 oscillates a low frequency signal having a frequency f0 lower than the frequency of the phase control signal. The oscillator 1210 outputs the oscillated low frequency signal to the control unit 192. The control unit 192 superimposes the low frequency signal output from the oscillator 1210 on the phase control signal and inputs the signal to the phase adjuster 151. Alternatively, the control unit 192 does not superimpose the phase control signal and the low frequency signal, but superimposes the phase control signal output from the control unit 192 and the low frequency signal oscillated by the oscillator 1210 by the superimposing circuit. It is good also as a structure input into the phase adjuster 151. FIG.

  The low-pass filter 1220 passes a component having a frequency of f0 or less in the electric signal output from the PD 191 to the control unit 192 and outputs the component to the control unit 192. Alternatively, in place of the low-pass filter 1220, a band-pass filter that passes a component near the frequency f0 in the electrical signal output from the PD 191 to the control unit 192 may be provided.

  The control unit 192 performs synchronous detection of the frequency f0 on the electric signal output from the PD 191 and adjusts the strength of the electric signal input to the phase adjuster 151 according to the result of the synchronous detection. Specifically, the control unit 192 adjusts the strength of the electrical signal input to the phase adjuster 151 according to the strength of the electrical signal output from the low pass filter 1220.

  FIG. 13 is a flowchart illustrating an example of the operation of the control unit illustrated in FIG. Here, it is assumed that input light is input from the optical circulator 110 to the optical branching unit 130. As shown in FIG. 13, first, input of a phase control signal to the phase adjuster 151 is started (step S1301). The intensity of the phase control signal at this time is set as the initial setting intensity. Next, a low frequency signal is superimposed on the phase control signal input to the phase adjuster 151 (step S1302).

  Next, the synchronous detection of the frequency f0 is performed with respect to the electric signal output from PD191 (step S1303). Specifically, the intensity of the electrical signal output from the PD 191 via the low-pass filter 1220 is detected. Next, it is determined whether or not the intensity of the electrical signal detected in step S1303 is equal to or less than a threshold value (step S1304).

  In step S1304, when the intensity of the electrical signal output from the PD 191 is greater than the threshold value (step S1304: No), the intensity of the phase control signal input to the phase adjuster 151 is increased above the set intensity (step S1304). S1305). Next, the synchronous detection of the frequency f0 is performed with respect to the electric signal output from PD191 (step S1306).

  Next, it is determined whether or not the strength of the electrical signal detected in step S1306 has decreased compared to the electrical signal detected in step S1303 (step S1307). If the strength of the electrical signal made in step S1306 has decreased (step S1307: Yes), the strength of the phase control signal increased in step S1305 is set as a new set strength, and the process returns to step S1302 to continue the processing.

  In step S1307, when the strength of the electrical signal performed in step S1306 has not decreased (step S1307: No), the strength of the phase control signal input to the phase adjuster 151 is decreased (step S1308) and decreased. The intensity of the phase control signal is set as a new set intensity, and the process returns to step S1302 to continue the process.

  In step S1304, when the intensity of the detected electrical signal is equal to or less than the threshold value (step S1304: Yes), it is determined whether or not the operation end condition is satisfied (step S1309), and the end condition is not satisfied. In the case (step S1309: No), the process returns to step S1302 to continue the processing. If the end condition is satisfied (step S1309: YES), the series of operations is ended.

  FIG. 14 is a diagram illustrating a modification of the light modulation device according to the fifth embodiment. In FIG. 14, the same components as those shown in FIG. 1 or FIG. As shown in FIG. 14, in addition to the configuration of the light modulation device 100 according to the first embodiment (see FIG. 1), the modification of the light modulation device 100 according to the fifth embodiment includes an oscillator 1410 and a low-pass filter 1220. And.

  The low pass filter 1220 may be a band pass filter as described above. The modulation control unit 166a, the modulation control unit 166b, and the oscillator 1410 constitute superimposing means that superimposes the low frequency signal on the modulation control signal and inputs the signal to the modulation unit 160. The oscillator 1410 oscillates a low frequency signal having a frequency f0 lower than the frequency of the phase control signal and the modulation control signal.

  The oscillator 1410 outputs the oscillated low frequency signal to the modulation control unit 166a and the modulation control unit 166b. The modulation control unit 166a superimposes the low frequency signal output from the oscillator 1410 on the modulation control signal and inputs the signal to the modulator 160a. The modulation control unit 166b superimposes the low frequency signal output from the oscillator 1410 on the modulation control signal and inputs the signal to the modulator 160b.

  Alternatively, the modulation control unit 166a and the modulation control unit 166b do not superimpose the modulation control signal and the low frequency signal, but the respective modulation control signals output from the modulation control unit 166a and the modulation control unit 166b and the oscillator 1410 oscillate. The low frequency signal may be superposed by a superposition circuit and input to the modulator 160a and the modulator 160b, respectively.

  FIG. 15 is a flowchart illustrating an example of operations of the control unit and the modulation control unit illustrated in FIG. The control unit 192, the modulation control unit 166a, and the modulation control unit 166b of the modification (see FIG. 14) of the light modulation device 100 according to the fifth embodiment are performed in parallel with the operations of Step S301 to Step S308 illustrated in FIG. The following operations are performed. Here, it is assumed that light is input from the optical circulator 110 to the optical branching unit 130.

  As shown in FIG. 15, first, the modulation control unit 166a and the modulation control unit 166b start inputting a modulation control signal to the modulation unit 160 (step S1501). The intensity of the phase control signal input to the phase adjuster 151 at this time is set as the initial set intensity. Next, the modulation control unit 166a and the modulation control unit 166b superimpose a low frequency signal on the modulation control signal input to the modulation unit 160 (step S1502).

  Next, the control unit 192 performs synchronous detection of the frequency f0 on the electric signal output from the PD 191 (step S1503). Specifically, the intensity of the electrical signal output from the PD 191 via the low-pass filter 1220 is detected. Next, it is determined whether or not the intensity of the electrical signal detected in step S1503 is equal to or less than a threshold value (step S1504).

  In step S1504, when the strength of the electrical signal detected in step S1503 is larger than the threshold value (step S1504: No), the control unit 192 sets the strength of the phase control signal input to the phase adjuster 151 from the set strength. Is also increased (step S1505). Next, the control unit 192 performs synchronous detection of the frequency f0 on the electric signal output from the PD 191 (step S1506).

  Next, it is determined whether or not the strength of the electrical signal detected in step S1506 has decreased compared to the detected electrical signal (step S1507). When the strength of the electrical signal detected in step S1506 decreases (step S1507: Yes), the control unit 192 sets the strength of the phase control signal increased in step S1505 as a new set strength, and returns to step S1502. continue processing.

  In step S1507, if the intensity of the electrical signal detected in step S1506 has not decreased (step S1507: No), the control unit 192 decreases the intensity of the phase control signal input to the phase adjuster 151 (step S1507). In step S1508), the intensity of the reduced phase control signal is set as a new set intensity, and the process returns to step S1502 to continue the process.

  In step S1504, when the intensity of the detected electric signal is equal to or less than the threshold value (step S1504: Yes), it is determined whether or not the operation end condition is satisfied (step S1509), and the end condition is not satisfied. In the case (step S1509: No), the process returns to step S1502 to continue the processing. If the end condition is satisfied (step S1509: Yes), the series of operations is ended.

  For example, the control unit 192, the modulation control unit 166a, and the modulation control unit 166b are configured by one CPU. In this case, the control unit 192, the modulation control unit 166a, and the modulation control unit 166b perform the operations in steps S1501 to S1509 and the operations in steps S301 to S308 shown in FIG. Do.

  As described above, according to the light modulation device 100 according to the fifth embodiment, the effects of the light modulation device 100 according to the first embodiment are achieved, and the low frequency signal is superimposed on the phase modulation signal or the modulation control signal. By performing synchronous detection in this way, it is possible to remove noise that is not related to the phase difference of each light from the electrical signal input to the control unit 192. For this reason, the phase difference of each light couple | bonded by the optical coupling part 180 can be accurately controlled to (pi) / 2, and a modulation characteristic can be improved further.

(Embodiment 6)
FIG. 16 is a diagram illustrating a configuration of the light modulation device according to the sixth embodiment. In FIG. 16, the same components as those shown in FIG. As illustrated in FIG. 16, the light modulation device 100 according to the sixth embodiment has the same configuration as that of the light modulation device 100 according to the first embodiment (see FIG. 1), but instead of the optical circulator 110 and the light branching unit 130. An optical coupler 1610 and an optical isolator 1620 are provided.

  The optical coupler 1610 is a 2 × 2 optical coupler having two input units (1611, 1612) and two output units (1613, 1614). Input light is input to the input unit 1611 from the outside. The optical coupler 1610 branches the input light input from the input unit 1611 and outputs the branched light from the output unit 1613 and the output unit 1614, respectively.

  The light that has been turned back and passed through the phase adjustment unit 150 again is input to the output unit 1613 and the output unit 1614. The optical coupler 1610 combines the lights that have passed through the phase adjustment unit 150 again. The optical coupler 1610 branches the combined light at a ratio corresponding to the phase difference of each light before being combined, and outputs each branched light from the input unit 1611 and the input unit 1612.

  For example, when the phase difference of each light before combining is π, all components of the light combined by the optical coupler 1610 are output from the input unit 1612 to the PD 191. On the other hand, when the phase difference of each light before combining is 0, all components of the light combined by the optical coupler 1610 are output from the input unit 1611. The PD 191 receives light output from the input unit 1612 of the optical coupler 1610 and converts it into an electric signal having an intensity corresponding to the intensity of the received light.

  In this configuration, when the phase difference of each light before being coupled by the optical coupler 1610 is π, the intensity of the light output to the PD 191 becomes maximum. For this reason, the control unit 192 adjusts the phase control signal input to the phase adjuster 151 so that the intensity of the electric signal output from the PD 191 becomes maximum. Thereby, the phase difference of each light coupled by the optical coupler 1610 becomes π, and the phase difference of each light coupled by the optical coupling unit 180 becomes π / 2.

  When the phase difference of each light before being coupled by the optical coupler 1610 is deviated from π, some components of the light coupled by the optical coupler 1610 are output from the input unit 1611. The optical isolator 1620 allows the input light input to the optical coupler 1610 to pass and blocks the light output from the input unit 1611 of the optical coupler 1610. Thereby, it is possible to avoid the light output from the optical coupler 1610 from leaking to the front stage of the light modulation device 100.

  As described above, according to the light modulation device 100 according to the sixth embodiment, the effect of the light modulation device 100 according to the first embodiment is achieved, and the optical branching unit that branches the input light and the phase adjustment unit 150 are provided again. The number of necessary components can be reduced by configuring the second optical coupling unit that couples each light that has passed through and the extraction unit that extracts the light coupled by the second optical coupling unit by the optical coupler 1610. . For example, it is not necessary to provide an optical circulator (see reference numeral 110 in FIG. 1). For this reason, the cost of the light modulation device 100 can be reduced.

(Embodiment 7)
FIG. 17 is a diagram of a configuration of the light modulation device according to the seventh embodiment. In FIG. 17, the same components as those shown in FIG. As illustrated in FIG. 17, the light modulation device 100 according to the seventh embodiment includes, in addition to the configuration of the modification example of the light modulation device 100 according to the first embodiment (see FIG. 6), a light separation unit 1711 a and a light separation device. A portion 1711b and an optical coupling portion 1712 are provided.

  The modulation unit 160 is provided before the phase adjustment unit 150. The light separation unit 1711a, the light separation unit 1711b, and the optical coupling unit 1712 are provided between the modulation unit 160 and the phase adjustment unit 150, and constitute a second optical coupling unit that couples each light that has passed through the phase adjustment unit 150 again. is doing. Further, the light separating unit 1711a, the light separating unit 1711b, and the optical coupling unit 1712 constitute extraction means for extracting light combined by the second optical coupling unit.

  The light separation unit 1711a is separated by the mirror 172a, separates some components of the light that has passed through the phase adjuster 151 again, and outputs the separated light to the optical coupling unit 1712. The light separation unit 1711b is separated by the mirror 172b, separates some components of the light that has passed through the phase adjustment unit 150 again, and outputs the separated light to the optical coupling unit 1712. The optical coupling unit 1712 combines the light output from the light separation unit 1711a and the light output from the light separation unit 1711b and outputs the combined light to the PD 191.

  Here, each light coupled by the optical coupling unit 180 passes through the modulation unit 160 only once. In contrast, each light that is folded by the folding unit 170 and coupled by the optical coupling unit 1712 passes through the modulation unit 160 only once. For this reason, it is possible to accurately reflect the phase difference of each light coupled by the optical coupling unit 1712, which is caused by a change with time of the modulation unit 160 or the like. it can.

  The PD 191 receives the light output from the optical coupling unit 1712 and outputs an electrical signal having an intensity corresponding to the intensity of the received light to the control unit 192. The light separating unit 1711a and the light separating unit 1711b are each configured by an optical branching waveguide. It is preferable to adjust the branching ratio of the light separating unit 1711a and the light separating unit 1711b so that as many components as possible of each light that has passed through the phase adjusting unit 150 again are output to the optical coupling unit 1712.

  As described above, according to the light modulation device 100 according to the seventh embodiment, the effects of the light modulation device 100 according to the first embodiment are obtained, and each light branched by the light branching unit 130 is converted into the modulation unit 160 and the phase. Each light returned by the return unit 170 is combined by the optical coupling unit 1712 after passing through the phase adjustment unit 150 and before passing through the modulation unit 160 again while returning after passing through the adjustment unit 150.

  Thereby, the phase difference of each light coupled by the optical coupling unit 1712 can accurately reflect a shift in the phase difference of each light coupled by the optical coupling unit 180 caused by a change with time of the modulation unit 160 or the like. it can. For this reason, even if the phase difference shifts due to a change with time of the modulation unit 160 or the like, by adjusting the phase control signal according to the light coupled by the optical coupling unit 1712, each light coupled by the optical coupling unit 180 is adjusted. The phase difference can be accurately set to π / 2, and the modulation characteristics can be further improved.

  As described above, according to the light modulation device of the present invention, the modulation characteristics can be improved by simple control.

  In each of the above-described embodiments, the case where the optical modulation device 100 is configured as a Mach-Zehnder QPSK optical modulation device in which the modulator 160a and the modulator 160b are connected in parallel has been described. The present invention can be applied to all light modulation devices that modulate two light beams and combine the modulated light beams with a phase difference of π / 2.

(Appendix 1) Optical branching means for splitting input light;
A phase adjusting means for passing each light branched by the light branching means and changing a phase difference of each passing light according to an input phase control signal;
Modulation means for phase-modulating each light branched by the light branching means;
Optical coupling means for coupling and outputting the lights that have passed through the phase adjusting means and the modulating means;
A folding unit that folds each component of each light that passes through the phase adjusting unit and is output to the optical coupling unit, and passes the phase adjusting unit again;
Second optical coupling means for coupling the lights that have passed again through the phase adjusting means;
An optical modulation device comprising:

(Additional remark 2) It has a control means which controls the phase difference of each light which passed the phase adjustment means again to a desired value,
The optical modulation device according to claim 1, wherein the control unit inputs the phase control signal to the phase adjustment unit in accordance with a PD signal that has received the light combined by the second optical coupling unit. .

(Supplementary note 3) The light modulation device according to supplementary note 1, wherein the light branching unit is the second light coupling unit that branches the input light and combines the light beams that have passed again.

(Additional remark 4) The said modulation | alteration means is provided in the back | latter stage from the said phase adjustment means,
The optical modulation device according to any one of appendices 1 to 3, wherein the folding unit folds a part of each component of the light that has passed through the phase adjusting unit and the modulating unit.

(Additional remark 5) The said modulation | alteration means is provided before the said phase adjustment means,
The optical modulation device according to any one of appendices 1 to 3, wherein the folding unit folds a part of each component of the light that has passed through the phase adjusting unit and the modulating unit.

(Additional remark 6) The said modulation | alteration means is provided in the back | latter stage from the said phase adjustment means,
The folding means is provided between the phase adjustment means and the modulation means, and each of the components of each light that has passed through the phase adjustment means is folded back. The light modulation device according to 1.

(Supplementary note 7) The modulation means is provided in a stage preceding the phase adjustment means,
The folding means folds a part of each component of each light that has passed through the modulating means and the phase adjusting means,
The optical modulation apparatus according to appendix 1, wherein the second optical coupling unit is provided between the modulation unit and the phase adjustment unit, and couples each light that has passed through the phase adjustment unit again.

(Appendix 8) The folding means is
Separating means for separating a part of each component of each light that has passed through the phase adjusting means;
Reflecting means for reflecting and turning back each light separated by the separating means;
The light modulation device according to any one of appendices 1 to 7, characterized in that:

(Additional remark 9) The said folding | returning means is a partial reflection mirror which reflects the partial component of each light which passed the said phase adjustment means, and folds back, and lets the component which does not reflect each said light pass through. The light modulation device according to any one of 1 to 7.

(Supplementary Note 10) The folding means
Separating means for separating a part of each component of each light that has passed through the phase adjusting means;
A circular waveguide that circulates and returns the light separated by the separating means;
The light modulation device according to any one of appendices 1 to 7, characterized in that:

(Supplementary note 11) Superimposing means for superimposing a signal of a predetermined frequency on the phase control signal and inputting it to the phase adjustment means,
The supplementary note 2 is characterized in that the control means inputs the phase control signal to the phase adjustment means according to the intensity of the predetermined frequency component of the light coupled by the second optical coupling means. Light modulation device.

(Additional remark 12) The said modulation | alteration means respectively phase-modulates each light branched by the said optical branching means according to the modulation control signal input,
A superimposing unit that superimposes a signal having a predetermined frequency on the modulation control signal and inputs the signal to the modulation unit;
The supplementary note 2 is characterized in that the control means inputs the phase control signal to the phase adjustment means in accordance with the intensity of the frequency component of the light coupled by the second optical coupling means. Light modulation device.

(Supplementary note 13) A take-out means comprising a one-input two-output coupler that takes out the light coupled by the second optical coupling means,
3. The optical modulation device according to appendix 2, wherein the control unit inputs the phase control signal to the phase adjustment unit in accordance with a PD signal that has received the light extracted by the extraction unit.

(Supplementary note 14) The optical modulation device according to supplementary note 13, wherein the extraction unit is an optical circulator that inputs the input light to the optical branching unit and extracts the light combined by the optical branching unit. .

(Additional remark 15) The said optical branch means has two input parts and two output parts, branches the said input light input from one of the said two input parts, and from said two output parts An optical coupler that outputs each of the light beams that have passed through the phase adjusting means and outputs the light from the other of the two input units;
The supplementary note 2 is characterized in that the control means inputs the phase control signal to the phase adjustment means in accordance with the intensity of light output from the other of the two input sections of the optical coupler. Light modulation device.

(Supplementary Note 16) Light that passes through the input light and is input from one of the two input units of the optical coupler, coupled by the optical coupler, and output from one of the two input units 16. The optical modulation device according to appendix 15, further comprising an optical isolator that blocks light.

(Additional remark 17) The said modulation | alteration means is two phase modulators which respectively perform two-phase phase modulation with respect to each light branched by the said optical branching means, Any one of Additional remarks 1-16 characterized by the above-mentioned. The light modulation device described in 1.

(Additional remark 18) The said control means inputs the said phase control signal to the said phase adjustment means so that the intensity | strength of the light couple | bonded by the said 2nd optical coupling means may become the minimum. The light modulation device according to any one of the above.

1 is a diagram illustrating a configuration of a light modulation device according to a first embodiment. It is an expansion perspective view which cut | disconnects and shows the part of the mirror of a light modulation apparatus. It is a flowchart which shows an example of operation | movement of the control part shown in FIG. It is a graph which shows the relationship between the phase difference of each returned light, and PD output intensity. It is a graph which shows the relationship between the phase difference of each light couple | bonded, and PD output intensity. FIG. 6 is a diagram illustrating a modification of the light modulation device according to the first embodiment. FIG. 3 is a diagram illustrating a configuration of a light modulation device according to a second embodiment. FIG. 4 is a diagram illustrating a configuration of a light modulation device according to a third embodiment. It is an expansion perspective view which cut | disconnects and shows the part of the half mirror of a light modulation apparatus. FIG. 6 is a diagram illustrating a configuration of a light modulation device according to a fourth embodiment. FIG. 10 is a diagram illustrating a modification of the light modulation device according to the fourth embodiment. FIG. 10 is a diagram illustrating a configuration of a light modulation device according to a fifth embodiment. It is a flowchart which shows an example of operation | movement of the control part shown in FIG. FIG. 10 is a diagram illustrating a modification of the light modulation device according to the fifth embodiment. It is a flowchart which shows an example of operation | movement of the control part shown in FIG. 14, and a modulation | alteration control part. FIG. 10 is a diagram illustrating a configuration of a light modulation device according to a sixth embodiment. FIG. 10 is a diagram illustrating a configuration of a light modulation device according to a seventh embodiment. It is a figure which shows the structure of the conventional light modulation apparatus. It is a figure which shows phase arrangement | positioning in case the phase difference of each light is (pi) / 2. It is a figure which shows phase arrangement | positioning when the phase difference of each light has shifted | deviated from (pi) / 2. It is a graph which shows the relationship between the phase difference of each light, and PD output intensity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical modulation apparatus 110 Optical circulator 120 Board | substrate 130 Optical branch part 140a, 140b Parallel waveguide 150 Phase adjustment part 151 Phase adjuster 160 Modulation part 160a, 160b Modulator 161a Optical branch part 162a, 162b Parallel waveguide 163 Optical coupling part 164a , 164b Signal electrode 165 Ground electrode 170 Folded part 171a, 171b Optical separating part 172a, 172b Mirror 180 Optical coupling part 210 Optical waveguide 810a, 810b Half mirror 910 Groove 1010a, 1010b Circulating waveguide 1011a, 1011b, 1012a, 1012b 1013a, 1013b Folded waveguides 1110a, 1110b Circulating waveguides 1111a, 1111b Light separating parts 1112a, 1112b Light branching parts 1113a, 1113b Folded Waveguide 1210, 1410 Oscillator 1220 Low-pass filter 1610 Optical coupler 1611, 1612 Input unit 1613, 1614 Output unit 1620 Optical isolator 1711a, 1711b Optical separation unit 1712 Optical coupling unit

Claims (9)

A light branching means for branching the input light;
A phase adjusting means for passing each light branched by the light branching means and changing a phase difference of each passing light according to an input phase control signal;
Modulation means for phase-modulating each light branched by the light branching means;
Optical coupling means for coupling and outputting the lights that have passed through the phase adjusting means and the modulating means;
A folding unit that folds each component of each light that passes through the phase adjusting unit and is output to the optical coupling unit, and passes the phase adjusting unit again;
Second optical coupling means for coupling the lights that have passed again through the phase adjusting means;
The phase control signal is input to the phase adjustment unit in accordance with the PD signal that has received the light combined by the second optical coupling unit, and the phase difference of each light that has passed through the phase adjustment unit again is a desired value. Control means to control,
An optical modulation device comprising: 2. The optical modulation device according to claim 1, wherein the optical branching unit is the second optical coupling unit that splits the input light and couples the light beams that have passed again. 3. The modulating means is provided at a stage subsequent to the phase adjusting means,
3. The light modulation device according to claim 1, wherein the folding unit folds a part of each component of each light that has passed through the phase adjustment unit and the modulation unit. The modulating means is provided in a stage preceding the phase adjusting means,
3. The light modulation device according to claim 1, wherein the folding unit folds a part of each component of each light that has passed through the phase adjustment unit and the modulation unit. The modulating means is provided at a stage subsequent to the phase adjusting means,
3. The light according to claim 1, wherein the folding unit is provided between the phase adjusting unit and the modulating unit and folds a partial component of each light that has passed through the phase adjusting unit. Modulation device. The modulating means is provided in a stage preceding the phase adjusting means,
The folding means folds a part of each component of each light that has passed through the modulating means and the phase adjusting means,
2. The optical modulation device according to claim 1, wherein the second optical coupling unit is provided between the modulation unit and the phase adjustment unit, and couples each light that has passed through the phase adjustment unit again. 3. . The folding means is
Separating means for separating a part of each component of each light that has passed through the phase adjusting means;
Reflecting means for reflecting and turning back each light separated by the separating means;
The light modulation device according to claim 1, comprising: A superimposing unit that superimposes a signal having a predetermined frequency on the phase control signal and inputs the signal to the phase adjusting unit;
2. The control unit according to claim 1, wherein the control unit inputs the phase control signal to the phase adjustment unit according to the intensity of the predetermined frequency component of the light coupled by the second optical coupling unit. The light modulation device described. A take-out means for taking out the light coupled by the second optical coupling means;
2. The optical modulation device according to claim 1, wherein the control unit inputs the phase control signal to the phase adjustment unit in accordance with a PD signal that has received the light extracted by the extraction unit. 3.

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