JP6106062B2 - Light modulator - Google Patents

Description

  The present invention relates to an optical modulator applicable to an optical communication system.

  In an optical fiber communication system, improving reception sensitivity and extending transmission distance are important issues. In recent years, the rapid development of digital coherent technology that combines digital signal processing (DSP) and coherent transmission technology has greatly expanded the options for modulation formats in optical communications. There are many attempts.

  One modulation method with high reception sensitivity is 3D simplex modulation. In optical transmission, assuming that two orthogonal polarizations are X and Y polarization, X polarization in-phase (XI), X polarization quadrature (XQ), Y polarization in-phase (YI), and Y polarization quadrature (YQ) However, 3D simplex modulation uses 3 of these, and the signal point is located at the apex of the regular tetrahedron (3D simplex) in the 3D space spanned by these axes. Is a modulation scheme. 3D simplex modulation is modulation of 2 bits / symbol, which is theoretically 1.2 dB better than polarization-multiplexed binary phase modulation (dual-polarization binary phase-shift keying, DP-BPSK), which is the same 2 bit / symbol modulation. The reception sensitivity is shown (Non-Patent Documents 1 and 2).

  As a method for generating a 3D simplex signal, as shown in FIG. 1, a polarization multiplexed quaternary phase modulation (dual-polarization phase-shift keying, DP-QPSK) modulator is used with a data signal having a specific correlation. A driving method is known (Non-Patent Document 2).

FIG. 1 is a diagram illustrating a circuit configuration of a conventional 3D simplex modulator 100. Figure 1 3D simplex 100 according to the input port 101 to the input light _{E in} is input, the input light _{E in} a branching ratio of 1: branches and outputs to 1, an optical splitter 130 which are symmetrical light branching means QPSK modulators 191 and 192 serving as quaternary phase modulation means connected to each output port of the optical splitter 130, and polarized light serving as 90-degree polarization rotation means connected to the output port of the QPSK modulator 192 A rotator 151, a polarization optical coupler 152 serving as a polarization optical coupling unit connected to the output port of the QPSK modulator 191 and the output port of the polarization optical rotator 151, and an output port of the polarization optical coupler 152; and an output port 102 for outputting the output light _{E out.}

  The QPSK modulator 191 splits one output light from the optical branching device 130 into a branching ratio of 1: 1 and outputs it to the optical branching device 131 serving as a symmetric optical branching unit, and to each output port of the optical branching device 131. BPSK modulators 111 and 112 serving as connected binary phase modulating means, and a phase adjuster 121 serving as a phase adjusting means connected to the output port of the BPSK modulator 112 to set the phase difference between arms to π / 2. And an optical coupler 132 which is connected to the output port of the BPSK modulator 111 and the output port of the phase adjuster 121 and serves as a symmetric optical coupling means for outputting the coupled light to the polarization optical coupler 152. The QPSK modulator 192 is also connected to an optical branching unit 133 serving as an optical branching unit for branching and outputting the other output light from the optical branching unit 130 at a branching ratio of 1: 1, and to each output port of the optical branching unit 133. BPSK modulators 113 and 114 that serve as the binary phase modulation means, and a phase adjuster 122 that is a phase adjustment means for setting the phase difference between the arms connected to the output port of the BPSK modulator 114 to π / 2, An optical coupler 134 that is connected to the output port of the BPSK modulator 113 and the output port of the phase adjuster 122 and that is a symmetric optical coupling unit that outputs coupled light to the polarization optical coupler 152 is provided.

The BPSK modulators 111 to 113 of the 3D simplex 100 are driven by binary data signals d _{1 to} d ₃ , respectively, and the BPSK modulator 114 is set to be in an off state (a state that does not transmit light). Here, d ₁ and d ₂ are independent transmission data signals, and d ₃ is

To be generated.

For the sake of convenience, let us consider a case where the operating polarization of the BPSK modulators 111 to 114 is X and the polarization orthogonal to X is Y, and X-polarized continuous light having intensity 1 is input to the input port 101. X polarization of the output optical field from the output port 102, respectively Y polarization component _E X, When _{E Y,}

It becomes. Where coefficient

Corresponds to the electric field transmission functions of the optical branching units and optical couplers 130 to 134 and passes through a total of three stages in the optical path of each polarization channel. Further, b _n (n = 1 to 3) are modulation parameters of the BPSK modulators 111 to 113, respectively. At symbol points (symbol center timing on the time axis), b _n when d _n = 0. It is assumed that when _n = −1 (phase π) and d _n = 1, b _n = + 1 (phase 0). _Therefore, (the real part of _{E X)} d 1, the value of _{d 2} and XI, (imaginary part of the _{E X)} XQ, (the real part of _{E Y)} YI, (imaginary part of _{E Y)} YQ values for each component The correspondence is as shown in the table below.

  In the three-dimensional space of XI, XQ, and YI, it can be seen that a regular tetrahedron with one side length of 1 can be obtained by connecting the four signal points. That is, it can be seen that a 3D simplex modulation signal is obtained.

M. Karlsson and E. Agrell, “Which is the most power-efficient modulation format in optical links ?,” Opt. Exp., Vol.17, no.13, pp.108, 191, 0819, 2009. A.Dochhan, H.Griesser, and M. Eiselt, “First Experimental Demonstration of a 3-Dimensional Simplex Modulation Format Showing Improved OSNR Performance Compared to DP-BPSK,” Proc. OFC / NFOEC2013, JTh2A.40, 2013. N. Kikuchi, “Intersymbol Interference (ISI) Suppression Technique for Optical Binary and Multilevel Signal Generation,” J. Lightwave Technol., Vol. 25, No. 8, pp. 2060-2068, 2007.

However, the above prior art has a problem that the fundamental optical loss due to the modulator configuration becomes large. However, the “principal optical loss due to the modulator configuration” (hereinafter referred to as “principle loss”) here is an ideal in which the waveguide loss of the optical waveguide and the loss due to process error are zero. Even under conditions, the optical loss inevitably occurs in the optical signal synthesis process. In the prior art, the output light intensity at the symbol point when the input light intensity is 1 corresponds to | E _X + E _Y | ² in Equation 1, but in any case, | E _X + E _Y | ² = It becomes 3/8, and it turns out that the principle loss 4.26 dB occurs.

Further, in the prior art, an electronic circuit including an XOR gate for generating the binary data signal d ₃ is required, and the binary data signals d ₁ , d ₂ , and d ₃ are converted for 2 bit / symbol modulation. There is a problem that the system uses three binary data driving systems and four BPSK modulators for transmission, and the apparatus is more complicated than necessary (generally, binary data necessary for Nbit / symbol modulation). There are N drive systems and BPSK modulators each). Since each binary data drive system requires a driver amplifier for amplifying a drive signal, the number of data drive systems is preferably small from the viewpoint of reducing power consumption.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a 3D simplex optical modulator having a small optical loss and a simple configuration.

Optical modulator is the implementation form of the invention, input light intensity ratio of 2: a first asymmetric light branching means for branching at 3, wherein the weak branched light ones light intensity of the light after the branch first A first asymmetric light branching means that outputs to a first output port of one asymmetric light branching means and outputs a branched light having a strong light intensity to a second output port of the first asymmetric light branching means; A first binary phase modulation means connected to a second output port of the first asymmetric optical branching means; an output port of the first binary phase modulation means; and the first binary value A second asymmetric light branching means for branching the input light from the phase modulation means at an intensity ratio of 2: 1, wherein the branched light having a high light intensity among the branched lights is the second of the second asymmetric light branching means. 1 to the output port of the first asymmetrical light, and the branched light having a low light intensity is output to the second output port of the second asymmetric light branching means. Output to the first asymmetrical light branching means, a first output port of the first asymmetrical light branching means, and an intermediate optical coupling means connected to the first output port of the second asymmetrical light branching means A second binary phase modulation means connected to the output port of the intermediate optical coupling means, a second output port of the second asymmetric optical branching means, and an output of the second binary phase modulation means And orthogonally polarized light coupling means connected to the port.

  An optical modulator according to another embodiment of the present invention includes an optical phase adjusting unit in at least one of optical paths connecting the first asymmetrical optical branching unit and the intermediate optical coupling unit.

  By using the present invention, it is possible to provide a 3D simplex optical modulator that has a small optical loss and a simple configuration.

It is a figure which shows the circuit structure of the conventional 3D simplex modulator. It is a figure which shows the circuit structure of the 3D simplex modulator which concerns on the 1st Embodiment of this invention. It is a figure which shows the circuit structure of the 3D simplex modulator which concerns on the 2nd Embodiment of this invention.

The present invention relates to a circuit configuration of a modulator, and the effect thereof does not depend on the material forming the modulator. Therefore, in the following embodiments, no material is specified. As a material for forming the modulator, LiNbO ₃ (LN) having a Pockels effect, which is a kind of electro-optic (EO) effect, KTa _1x Nb _x O _3, and K _1-y Li _y Ta _1-x Multi-element oxide crystals such as Nb _x O _3, GaAs-based or InP capable of modulating refractive index or absorption coefficient by electro-absorption (EA) effect or quantum confined stark effect (QCSE) Polymers having an EO effect such as compound semiconductors and chromophores can be used. Furthermore, in order to manufacture a modulator circuit having a complicated configuration with low loss, as shown in Non-Patent Document 1, a substrate using the above material and a quartz-based planar lightwave circuit (PLC). A heterogeneous substrate bonding configuration with the substrate may be used. Furthermore, a bulk type optical element may be used as the polarization rotation means or the polarization coupling means.

  Hereinafter, in each embodiment, it is most common to use an MZI type circuit using a Mach-Zehnder Interferometer (MZI) as a BPSK modulator serving as a binary phase modulation means. As discussed in detail in Non-Patent Document 3, if the MZI type circuit is push-pull driven by the voltage amplitude that gives the phase difference between arms + π to −π, the fluctuation of the optical output due to the drive electric signal noise is minimized. There is an advantage that interference between symbols can be suppressed. However, since the effect of the present invention does not depend on the specific configuration of the BPSK modulator, for example, a linear phase modulator may be used.

  Unless otherwise specified, the optical path lengths of both arms of the MZI circuit are all equal. Actually, a shift in the optical path lengths of both arms occurs due to a process error, a DC drift, or the like, but such a shift in optical path length is generally compensated by adjusting a phase shifter. Here, the compensation amount of the optical path length varies depending on the MZI material, the manufacturing conditions, the usage environment of the modulator, and the like, and thus is not uniquely determined. For this reason, the value of the phase shift amount of the phase shifter in each of the following embodiments does not include the phase shift for compensating the optical path length.

  In the following embodiments, the phase shifter is disposed only on one arm of the MZI type circuit in order to simplify the explanation using mathematical formulas. However, in the MZI type circuit, the phase difference between the arms is an essential parameter. Therefore, it is obvious that the same effect can be obtained regardless of whether the phase shifter is arranged on the other arm or both arms. The other arm, both arms).

  Further, in this specification, in order to simplify the model, an optical splitter, a coupler, a BPSK modulator, a polarization modulator, other circuit elements (including a polarization rotator and a polarization coupler described later), and The optical waveguide connecting them assumes the ideal case with zero excess loss. It is assumed that all circuit elements except for the polarization modulator and the polarization rotator do not cause polarization rotation. However, in reality, there are propagation loss of the waveguide, excess loss associated with optical branching and coupling, and the loss balance between the optical paths may be lost. In such a case, the loss ratio is compensated by shifting the branching ratio of the optical splitter from the ideal model value shown below or installing an intensity adjuster (such as a mechanism that intentionally generates optical loss) in the optical path. It is desirable to do.

[First Embodiment]
FIG. 2 is a diagram illustrating a circuit configuration of the 3D simplex modulator 200 according to the first embodiment of the present invention. 3D simplex modulator 200 according to Figure 2, an input port 201 of input light _{E in} is input, the input light _{E in} 2 different intensities of light (light intensity ratio 4: 1) branches and outputs to the An optical branching unit 230 serving as an asymmetrical optical branching unit, a QPSK modulator 291 serving as a quaternary phase modulation unit connected to one output port (first output port) of the optical branching unit 230, and an optical branching unit 230 BPSK modulator 213 serving as a binary phase modulation means connected to the other output port (second output port) of the QPSK modulator 291 and orthogonal polarization optical coupling connected to each output port of the QPSK modulator 291 and the BPSK modulator 213 A polarization light coupling circuit 281 as a means and an output port 202 connected to the output port of the polarization light coupling circuit 281 and outputting the output light E _out are provided.

  The QPSK modulator 291 includes an optical branching unit 231 serving as a symmetric optical branching unit for branching one output light from the optical branching unit 230 to a branching ratio of 1: 1, and 2 connected to each output port of the optical branching unit 231. BPSK modulators 211 and 212 as value phase modulation means, a phase adjuster 221 connected to the output port of the BPSK modulator 212 as phase adjustment means for setting the phase difference between arms to π / 2, and BPSK modulation An optical coupler 232 connected to the output port of the optical coupler 211 and the output port of the phase adjuster 221 and serving as a symmetric optical coupling means for outputting the coupled light to the polarization optical coupling circuit 281, and the optical splitter 231 and the optical coupler The BPSK modulator 211 is arranged in one arm of the MZI type circuit constituted by H.232, and the BPSK modulator 212 and the phase adjuster 221 are arranged in the other arm.

  The polarization light coupling circuit 281 includes a polarization light rotator 251 serving as a polarization light conversion unit that rotates the polarization output from the BPSK modulator 213 by 90 degrees, an output port of the optical coupler 232, and an output port of the polarization light rotator 251. And a polarization beam coupler 252 connected to the.

The optical E _in is input from the input port 201 and is input to the optical branching unit 230. Hereinafter, for the sake of convenience, the operational polarization of the BPSK modulators 211 to 213 is X, and the polarization orthogonal to X is Y. Consider a case where X-polarized continuous light having an intensity of 1 is input to the port 201. The optical branching device 230 branches the light E _in input from the input port 201 at a light intensity ratio of 4: 1, and _supplies the strong branched light E _in1 to the first output port connected to the QPSK modulator 291. And outputs the branched light E _in2 having low intensity to the second output port connected to the BPSK modulator 213. The optical branching device 231 _outputs branched light E _in3 and E _{in4 obtained} by branching the branched light E _in1 to 1: 1 to the BPSK modulators 211 and 212, respectively. The branched light E _in3 is modulated by the BPSK modulator 211 by the binary data signal d ₁ and output as the output light E _out3 , and the branched light E _in4 is output by the BPSK modulator 212 by the binary data signal d ₂ E _out4 is output. On the other hand, the branched light E _in2 is modulated by the binary data signal d ₃ in the BPSK modulator 213, and is output as the output light E _out2 . The binary data signals d ₁ and d ₂ are independent transmission data signals as in the conventional example, and d ₃ is given by the XOR operation of d ₁ and d ₂ .

Output light _{E out4} is the phase adjuster 221 is adjusted to be given a phase change by [pi / 2 with respect to the output light _{E out3,} coupled to the output light _{E out3} in the optical coupler 232, the output light _{E out1} As output from the optical coupler 232. The output light E _out2 is rotated 90 degrees by the polarization light rotator 251 (rotated from the X polarization to the Y polarization), and is orthogonally combined with the output light E _out1 by the polarization light coupler 252 to be output. The light E _out is output from the output port 202.

In this example, output light from the QPSK modulator 291 is output from the output port 202 as X polarization, and output light from the BPSK modulator 213 is output as Y polarization. Accordingly, X polarized output optical field from the output port 202, respectively Y polarization component _E X, When _{E Y}

It becomes. Where coefficient

and

Corresponds to the electric field transmission function of the asymmetrical light branching means 230,

Corresponds to the electric field transmission functions of the optical splitter 231 and the optical coupler 232. Further, bn (n = 1 to 3) are modulation parameters of the BPSK modulators 211 to 213, respectively. At symbol points (symbol center timing on the time axis), when dn = 0, bn = −1. When (phase π) and dn = 1, a value of bn = + 1 (phase 0) is assumed.

In the present _embodiment, (the real part of _{E X)} d 1, the value of _{d 2} and XI, (imaginary part of the _{E X)} XQ, (the real part of _{E Y)} YI, (imaginary part of _{E Y)} YQ each The correspondence of the component values is as shown in the table below.

In the three-dimensional space of XI, XQ, and YI, the length of one side is obtained by connecting the four signal points.

It can be seen that a regular tetrahedron is obtained. That is, it can be seen that a 3D simplex modulation signal is obtained. Further, in equations 4 and 5, it is found that | E _X + E _Y | ² = 3/5, and the principle loss is 2.22 dB. That is, in this embodiment, a 3D simplex signal can be obtained with a principle loss of about 2 dB less than that of the prior art.

  In this embodiment, in order to match the symbol timing on the X polarization side and the Y polarization side, the optical path length of the optical path from the input port 201 to the output port 202 via the QPSK modulator 291 and the BPSK from the input port 201 It is necessary to design the optical path length of the optical path from the modulator 213 to the output port 202 to be almost equal.

  In addition, a production technique capable of controlling the relative phase of the optical signal in the optical path including the BPSK modulator 211 and the optical path including the BPSK modulator 212 to π / 2 with high accuracy can be used, and a material that does not cause a DC bias drift is used. In this case, the phase adjuster 221 is not necessary.

[Second Embodiment]
FIG. 3 is a diagram showing a circuit configuration of a 3D simplex modulator 300 according to the second embodiment of the present invention. 3D simplex modulator 300 of FIG. 3, an input port 301 of input light _{E in} is input, the input light _{E in} 2 different intensities of light (light intensity ratio 2: 3) branches and outputs to, the The phase difference between arms connected to one output port of the optical branching device 330 (the first output port of the first asymmetric optical branching device) is π / A phase adjuster 321 serving as a phase adjusting unit set to 2 and a binary phase modulating unit connected to the other output port of the optical branching unit 330 (second output port of the first asymmetrical optical branching unit). A BPSK modulator 311. The 3D simplex modulator 300 is connected to the output port of the BPSK modulator 311, and branches the output light from the BPSK modulator 311 into two lights having different intensities (light intensity 2: 1), and outputs them. Optical branching device 331 serving as two asymmetrical light branching means, and intermediate optical coupling connected to one output port (first output port of the second asymmetrical light branching means) of phase adjuster 321 and optical branching device 331 And an optical coupler 341 as means. In other words, the phase adjuster 321 is arranged in one arm of the MZI type circuit constituted by the optical branching device 330 and the optical coupler 341, and the BPSK modulator 311 and the optical branching device 331 are arranged in the other arm. .

Further, the 3D simplex modulator 300 includes a BPSK modulator 312 serving as a binary phase modulation means connected to an output port of the optical coupler 341, an output port of the BPSK modulator 312 and the other output port of the optical branching device 331. a polarization optical coupling circuit 381 as a (second second output port of the asymmetric optical branching means) connected orthogonally polarized optical coupling means, connected to the output port of the polarization beam combining circuit 381, the output light E _out And an output port 302 for outputting.

  The polarization light coupling circuit 381 includes a polarization light rotator 351 serving as a polarization light conversion unit that rotates the polarization output from the other output port of the optical coupler 331, and an output port of the BPSK modulator 312 and polarization light rotation. A polarization optical coupler 352 connected to the output port of the optical device 351.

The optical E _in is input from the input port 301 and is input to the optical branching device 330. Hereinafter, for convenience, the operating polarization of the BPSK modulators 311 and 312 is X, and the polarization orthogonal to X is Y, and the input is input. Consider a case where X-polarized continuous light having an intensity of 1 is input to the port 301. The light E _in is branched into light having different intensities by the light splitter 330. Here, the optical branching device 330, has been a light E _in input from the input port 301, the light intensity ratio of 2: branched by 3, the first of the first asymmetric light branching means connected to the phase adjuster 321 The branch light E _in1 having low intensity is output to the output port, and the branch light E _in2 having high intensity is output to the second output port of the first asymmetrical light branching means connected to the BPSK modulator 311. The branched light E _in2 is modulated by the BPSK modulator 311 with the binary data signal d ₁ and output as the output light E _out2 . The branched light E _in1 is phase-shifted by π / 2 with respect to the output light E _out2 by the phase adjuster 321. Adjusted to give change.

The output light E _out2 is further branched into light having different intensities by the optical splitter 331. Here, the optical branching device 331 branches the output light E _out2 at a light intensity ratio of 2: 1 and has a strong intensity at the first output port of the second asymmetric light branching unit connected to the optical coupler 341. The branched light E _out3 is output, and the weakly branched light E _out4 is output to the second output port of the second asymmetric light branching means connected to the polarization light rotator 351 of the polarization light coupling circuit 381.

The optical coupler 341 combines the output lights E _in1 and E _out3 from the phase adjuster 321 and outputs the combined light E _in5 . The combined light E _in5 is modulated by the binary data signal d ₂ in the BPSK modulator 312 and output as the output light E _out5 . The output light E _out4 is rotated 90 degrees by the polarization light rotator 251 (rotated from the X polarization to the Y polarization), and is orthogonally _combined with the output light E _out5 by the polarization light coupler 352. _It is output from the output port 302 as out.

In this example, the output light from the BPSK modulator 312 is output from the output port 302 as X polarization, and the output light having the smaller light intensity of the asymmetric optical splitter 331 is output as Y polarization. Accordingly, X polarized output optical field from the output port 302, respectively Y polarization component _E X, When _{E Y,}

It becomes. Where coefficient

and

Is a coefficient in the electric field transmission function of the optical splitter 330

and

Is a coefficient in the electric field transmission function of the optical splitter 331

Corresponds to the electric field transmission function of the optical coupler 341. B ₁ and b ₂ are modulation parameters of the BPSK modulators 311 and 312, respectively. At symbol points (symbol center timing on the time axis), b _n = −1 (phase) when d _n = 0. When π) and d _n = 1, the value b _n = + 1 (phase 0) is assumed.

In the present _embodiment, (the real part of _{E X)} d 1, the value of _{d 2} and XI, (imaginary part of the _{E X)} XQ, (the real part of _{E Y)} YI, (imaginary part of _{E Y)} YQ each The correspondence of the component values is as shown in the table below.

  In the three-dimensional space of XI, XQ, and YI, the length of one side is obtained by connecting the four signal points.

It can be seen that a regular tetrahedron is obtained. That is, it can be seen that a 3D simplex modulation signal is obtained. Further, in Equations 6 and 7, it is found that | E _X + E _Y | ² = 3/5, and the principle loss is 2.22 dB. That is, in this embodiment, a 3D simplex signal can be obtained with a principle loss of about 2 dB less than that of the prior art.

  Further, in this embodiment, since only two independent binary data driving systems and two BPSK modulators are used, the conventional example (three binary data driving systems associated by XOR, four BPSKs) The configuration is simple compared to the modulation means).

  In this embodiment, since the symbol timing is matched between the X polarization side and the Y polarization side, the optical path length of the optical path from the asymmetric optical splitter 331 to the output port 302 via the BPSK modulator 312 is asymmetric. It is necessary to design the optical path lengths from the optical branching device 331 to the output port 302 without passing through the BPSK modulator 312 to be substantially equal.

  Further, the relative phase of the optical signal in the optical path from the optical splitter 330 via the BPSK modulator 311 to the optical coupler 341 and the optical path from the optical splitter 330 not through the BPSK modulator 311 to the optical coupler 341. The phase adjuster 321 is not necessary when a material that can be controlled to π / 2 with high accuracy can be used and a material that does not cause DC bias drift is used.

101, 201, 301 Input port 102, 202, 302 Output port 111, 112, 113, 114, 211, 212, 213, 311, 312 BPSK modulator 191, 192, 291 QPSK modulator 121, 122, 221, 321 Phase Coordinators 230, 330, 331 Asymmetrical optical splitters 132, 134, 232, 341 Optical couplers 281, 381 Polarized light coupling circuits 151, 251, 351 Polarized light rotators 152, 252, 352 Polarized light couplers

Claims (2)

A first asymmetrical light branching means for branching the input light at an intensity ratio of 2: 3, wherein the branched light having a low light intensity among the branched light is supplied to the first output port of the first asymmetrical light branching means. First asymmetric light branching means for outputting and outputting branched light having a strong light intensity to the second output port of the first asymmetric light branching means;
First binary phase modulation means connected to a second output port of the first asymmetric light splitting means;
A second asymmetrical light branching means connected to the output port of the first binary phase modulation means and for branching the input light from the first binary phase modulation means at an intensity ratio of 2: 1; The branched light having a high light intensity out of the branched light is output to the first output port of the second asymmetric light branching means, and the branched light having a low light intensity is output to the second of the second asymmetric light branching means. A second asymmetric optical branching means for outputting to the output port;
Intermediate optical coupling means connected to the first output port of the first asymmetric light branching means and the first output port of the second asymmetric light branching means;
Second binary phase modulation means connected to the output port of the intermediate optical coupling means;
Orthogonally polarized light coupling means connected to the second output port of the second asymmetrical light branching means and the output port of the second binary phase modulating means;
An optical modulator comprising: 2. The optical modulator according to claim 1 , further comprising an optical phase adjusting unit in at least one of optical paths connecting the first asymmetrical optical branching unit and the intermediate optical coupling unit.

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