JP5892914B2 - Optical signal generator - Google Patents

Description

  The present invention relates to an optical signal generation device that generates a polarization bit interleaved optical signal sequence in an optical transmission system using an optical fiber as a communication path.

  In a long-distance optical transmission system, an optical repeater amplification transmission system using an erbium-doped fiber amplifier capable of directly amplifying light in the 1.5 μm band is mainstream. Further, in recent years, a large-capacity optical transmission system using a wavelength multiplexing transmission system has been realized by an amplifier capable of amplifying in a wide band. With the rapid increase in communication traffic, a communication system with a larger capacity has been demanded, and the transmission speed per channel can be increased from 10 Gbit / s, which is currently mainstream, to 40 Gbit / s, and further to 100 Gbit / s. Expected.

  In order to increase the transmission speed, a higher optical signal-to-noise ratio is required at the receiving end. Therefore, it is required to transmit with high optical signal power in the optical fiber. However, transmission with a high optical signal power promotes the influence of nonlinear effects in the optical fiber, so that generally increasing the transmission speed limits the transmission distance.

  Therefore, there is a demand for a modulation method with excellent nonlinear tolerance in order to increase the transmission speed, and a polarization bit interleaving (bit alternating polarization) method that makes the polarization state between adjacent pulses orthogonal is attracting attention. In the polarization bit interleaving method, for example, a data signal is transmitted by an optical pulse train that alternately changes in two orthogonal polarization states, such as a TE mode (Transverse Electric mode) and a TM mode (Transverse Magnetic mode). This method is known to be excellent in non-linear strength because it can suppress intersymbol interference between adjacent pulses.

  As an example of a transmitter that performs conventional polarization bit interleaving, a transmitter including a light source, a DPSK generator that performs DPSK (Differential Phase Shift Keying) modulation, and a polarization modulator has been proposed (for example, Patent Document 1). In this example, the optical signal train that has been DPSK-modulated by the DPSK generator is input to the polarization modulator. In the polarization modulator, the polarization can be orthogonalized between adjacent bits (between adjacent signals) by modulating with an alternating signal synchronized with the DPSK-modulated data string.

JP 2005-260696 A

  By using the technique disclosed in Patent Document 1, polarization bit interleaving can be realized. However, since the pulse train is alternated for each bit by the polarization modulator, it is necessary to match the data timing of the DPSK modulation with the modulation timing when the modulation is performed by the polarization modulator. Therefore, it is necessary to adjust the phase of the alternating signal input to the polarization modulator, and furthermore, since this optimum phase changes depending on the temperature, it is difficult to accurately match the modulation timing.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical signal generation device capable of easily generating a polarization bit interleaved optical signal.

A first optical signal generation device according to the present invention is an optical signal generation device that generates a polarization bit interleaved optical signal in which the polarization states of temporally adjacent bits are orthogonal, and an optical modulation unit that modulates light source light And a drive unit for driving the light modulation unit . The light modulation unit includes two four-phase shift optical modulators that modulate light source light according to a drive signal of the drive unit, and two four-phase shift light modulations. A polarization orthogonal multiplexing optical circuit that performs polarization orthogonal multiplexing processing of the modulated light of the optical modulator, and the drive unit has a quadrature phase shift optical modulator with an amplitude that is twice the half-wave voltage of the four phase shift optical modulator Two 1-to-2 switches that distribute two binary signals alternately to 2 outputs per bit, for a total of 4 outputs, 1-to-2 switches in each of 2 sets of 2 outputs When allocating binary signals to one output, the other output is opened and these four The output shall be the drive signal.
The second optical signal generation device of the present invention is an optical signal generation device that generates a polarization bit interleaved optical signal in which the polarization states of temporally adjacent bits are orthogonal to each other. A modulation unit; and a drive unit that drives the light modulation unit. The light modulation unit includes two four-phase shift optical modulators that modulate light source light according to a drive signal of the drive unit, and two four-phase shifts. A polarization orthogonal multiplexing optical circuit that performs polarization orthogonal multiplexing processing on the modulated light of the optical modulator, and each of the four phase-shift optical modulators modulates the first light source light according to the drive signal of the drive unit. And a second Mach-Zehnder modulator that receives the output light of the two first Mach-Zehnder modulators, and the drive unit demultiplexes the input signal and supplies the first Mach-Zehnder modulator to the first Mach-Zehnder modulator. Generates a drive signal from each output duplexer and input signal A drive signal generation unit that drives a phase adjustment unit of the second Mach-Zehnder modulator, and the drive signal generation unit is one of an odd bit and an even bit of the outputs of the two first Mach-Zehnder modulators. The phase adjustment unit of the second Mach-Zehnder modulator is driven so that the phase difference is 90 degrees and the other is the phase difference corresponding to the input signal.

A first optical signal generation device according to the present invention is an optical signal generation device that generates a polarization bit interleaved optical signal in which the polarization states of temporally adjacent bits are orthogonal, and an optical modulation unit that modulates light source light And a drive unit for driving the light modulation unit . The light modulation unit includes two four-phase shift optical modulators that modulate light source light according to a drive signal of the drive unit, and two four-phase shift light modulations. A polarization orthogonal multiplexing optical circuit that performs polarization orthogonal multiplexing processing of the modulated light of the optical device. The driving unit drives the four-phase shift optical modulator with an amplitude twice that of the half-wave voltage of the four-phase shift optical modulator, and outputs two binary signals alternately with two outputs per bit, for a total of four Two one-to-two switches that distribute to the output are provided, and the one-to-two switch opens the other output when distributing the binary signal to one output in each of the two sets of two outputs. Let it be a drive signal. According to the configuration of the present invention, ON / OFF is repeated for each bit, and when one is ON, two modulated lights are generated in which the other is OFF, thereby matching the timing of modulation and polarization orthogonal processing. The polarization bit interleaved optical signal can be easily generated.
The second optical signal generation device of the present invention is an optical signal generation device that generates a polarization bit interleaved optical signal in which the polarization states of temporally adjacent bits are orthogonal to each other. A modulation unit; and a drive unit that drives the light modulation unit. The light modulation unit includes two four-phase shift optical modulators that modulate light source light according to a drive signal of the drive unit, and two four-phase shifts. A polarization orthogonal multiplexing optical circuit that performs polarization orthogonal multiplexing processing on the modulated light of the optical modulator, and each of the four phase-shift optical modulators modulates the first light source light according to the drive signal of the drive unit. And a second Mach-Zehnder modulator that receives the output light of the two first Mach-Zehnder modulators, and the drive unit demultiplexes the input signal and supplies the first Mach-Zehnder modulator to the first Mach-Zehnder modulator. Generates a drive signal from each output duplexer and input signal A drive signal generation unit that drives a phase adjustment unit of the second Mach-Zehnder modulator, and the drive signal generation unit is one of an odd bit and an even bit of the outputs of the two first Mach-Zehnder modulators. The phase adjustment unit of the second Mach-Zehnder modulator is driven so that the phase difference is 90 degrees and the other is the phase difference corresponding to the input signal. According to the configuration of the present invention, ON / OFF is repeated for each bit, and when one is ON, two modulated lights are generated in which the other is OFF, thereby matching the timing of modulation and polarization orthogonal processing. The polarization bit interleaved optical signal can be easily generated.

1 is a configuration diagram of an optical signal generation device according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating an operation of the optical signal generation device according to the first embodiment. FIG. 3 is a diagram illustrating an operation of the optical signal generation device according to the first embodiment. 6 is a configuration diagram of an optical signal generation device according to Embodiment 2. FIG. 6 is a configuration diagram of an optical signal generation device according to Embodiment 3. FIG. FIG. 10 is a diagram illustrating an operation of the optical signal generation device according to the third embodiment. FIG. 6 is a configuration diagram of an optical signal generation device according to a fourth embodiment. FIG. 10 is a diagram illustrating an operation of the optical signal generation device according to the fourth embodiment. FIG. 10 is a configuration diagram of an optical signal generation device according to a fifth embodiment. FIG. 10 is a configuration diagram of an optical signal generation device according to a sixth embodiment. FIG. 10 is a diagram illustrating an operation of the optical signal generation device according to the sixth embodiment.

<A. Embodiment 1>
<A-1. Configuration>
FIG. 1 is a configuration diagram of an optical signal generation device 1 according to the first embodiment. Referring to FIG. 1, the optical signal generation device includes a light source 101 that emits continuous light, a light modulation unit 102 that modulates light source light, and a drive unit 105 that drives the light modulation unit 102.

  The light modulation unit 102 includes Mach-Zehnder modulators 103a and 103b that modulate light source light. The modulated light from the Mach-Zehnder modulator 103b is orthogonally polarized by the polarization circuit 104, multiplexed with the modulated light from the Mach-Zehnder modulator 103a, and output. That is, the optical modulation unit 102 includes a polarization orthogonal multiplexing optical circuit that multiplexes the output lights of the Mach-Zehnder modulators 103 and 103b by orthogonal polarization. The light modulation unit 102 is called a DP-BPSK (Dual Polarization-Binary Shift Shift Keying) modulator, and a modulator using a material such as lithium niobate or indium phosphide has been put into practical use. Used for wave multiplexing transmission.

  Furthermore, the optical signal generation device 1 includes a drive unit 105 that drives the optical modulation unit 102. The drive unit 105 includes a drive signal generation unit 106 that generates a drive signal for the optical modulation unit 102 from a data signal to be transmitted, and amplifiers 107a and 107b that amplify the generated drive signal.

<A-2. Operation>
FIG. 2 is a diagram for explaining an optical output signal of the optical modulation unit 102. FIG. 2A shows a data signal to be transmitted (hereinafter referred to as a transmission data signal) input to the drive unit 105. Here, the data signal 1001100101101001 is transmitted.

  The drive signal generation unit 106 distributes the input signal sequence to two outputs for each bit, and when the signal sequence is allocated to one output, the other output has an intermediate value 0.5 between 0 and 1 Has a function to set. With these two functions, the odd-numbered bits in the data string of 1001100101101001 are distributed to the output on the amplifier 107a side of the drive signal generation unit 106, and between the bits, that is, in the portion where the even-numbered bits existed An intermediate value of 0.5 is output. That is, 1, 0.5, 0, 0.5, 1, 0.5, 0, 0.5, 0, 0.5, 1, 0.5, 1, 0.5, 0, 0.5 (FIG. 2B).

  Similarly, the even-numbered bits of the signal sequence of the transmission data signal are distributed to the output of the drive signal generation unit 106 on the amplifier 107b side, and the intermediate value 0.5 is output to the portion where the odd-numbered bits exist. . That is, 0.5, 0, 0.5, 1, 0.5, 0, 0.5, 1, 0.5, 1, 0.5, 0, 0.5, 0, 0.5, 1 and (FIG. 2 (c)). Thereafter, the respective signals are amplified by the amplifiers 107a and 107b.

  FIG. 3 is a diagram for explaining the operation of the light modulation unit 102. The optical modulation unit 102 performs BPSK modulation with each of the two Mach-Zehnder modulators 103a and 103b. As shown in FIGS. 3A and 3B, BPSK modulation is driven with an amplitude twice that of the half-wave voltage of the Mach-Zehnder modulator, and a center bias is set at the NULL point of the extinction characteristic of the Mach-Zehnder modulator. Realize.

  The Mach-Zehnder modulator 103a is supplied with 1, 0.5, 0, 0.5, 1, 0.5, 0, 0.5, 0, 0.5, 1, 0.5, 1, The signal sequence of 0.5, 0, 0.5 is received, whereby the light from the light source 101 is BPSK modulated. With the odd-numbered bits, BPSK modulated light of π0π00ππ0 is obtained. Further, an even value of 0.5 has an intermediate value 0.5 between 1 and 0. In BPSK modulation, the intermediate value 0.5 is the NULL point of the extinction characteristic of the Mach-Zehnder modulator, so that the extinction state occurs and the output is turned off. Therefore, the Mach-Zehnder modulator 103a repeats ON / OFF for each bit, and π0π00ππ0 BPSK modulated light, that is, π, OFF, 0, OFF, π, OFF, 0, OFF, 0, OFF, π, OFF , Π, OFF, 0, OFF are obtained.

  Similarly, the Mach-Zehnder modulator 103b outputs 0.5, 0, 0.5, 1, 0.5, 0, 0.5, 1, 0.5, 1, 0.5, 0 from the amplifier 107b as a drive signal. , 0.5, 0, 0.5, 1 are received, and thereby, the light from the light source 101 is BPSK-modulated. With even-numbered bits, BPSK modulated light of 0π0ππ00π can be obtained. Further, the intermediate value 0.5 of the odd-numbered bits causes the Mach-Zehnder modulator 103b to be extinguished and the output is turned off. Therefore, the Mach-Zehnder modulator 103b is a 0π0ππ00π BPSK modulated light that is repeatedly turned ON / OFF for each bit, that is, OFF, 0, OFF, π, OFF, 0, OFF, π, OFF, π, OFF, 0, OFF , 0, OFF, π are obtained.

  The modulated light from the Mach-Zehnder modulator 103b is orthogonally polarized by the polarization circuit 104, and then multiplexed with the modulated light from the Mach-Zehnder modulator 103a to be output light from the light modulator 102 shown in FIG. Thereby, it is possible to generate a polarization bit interleave signal in which the polarization states of bits adjacent in time are orthogonal to BPSK modulation.

<A-3. Effect>
The optical signal generation device 1 according to the present embodiment generates a polarization bit interleaved optical signal in which polarization states of temporally adjacent bits are orthogonal, and includes an optical modulation unit 102 that modulates light source light, A drive unit 105 that drives the modulation unit 102. The light modulation unit 102 includes two Mach-Zehnder modulators 103a and 103b (light modulators) that modulate light source light in accordance with a drive signal from the drive unit 105, and a Mach-Zehnder modulator. A polarization orthogonal multiplexing optical circuit that performs polarization orthogonal multiplexing processing on the modulated light of 103a and 103b. According to this configuration, ON / OFF is repeated for each bit, and when one is ON, two modulated lights are generated in which the other is OFF. The polarization bit interleaved optical signal can be easily generated.

  Further, the driving unit 105 alternately distributes the binary signal to two outputs for each bit, sets an intermediate value 0.5 to the other output when the binary signal is allocated to one output, and outputs these two outputs. The drive signals for the Mach-Zehnder modulators 103a and 103b are used. If the Mach-Zehnder modulators 103a and 103b are driven with an amplitude twice that of the half-wave voltage and the center bias is set at the NULL point of the extinction characteristic, the modulated light is extinguished by an intermediate value of 0.5. It is possible to create two modulated lights in which OFF is repeated and one of them is ON when the other is OFF, and a polarization bit interleaved optical signal can be easily generated.

<B. Second Embodiment>
<B-1, Configuration>
FIG. 4 is a configuration diagram of the optical signal generation device 2 according to the second embodiment. The optical signal generation device 2 is different from the optical signal generation device 1 of the first embodiment in the configuration of the drive unit. In the driving unit 105 according to the first embodiment, the driving signal generation unit 106 generates three-stage output signals of 0, 0.5, and 1. However, the drive unit 110 according to the second embodiment includes an amplifier 111 and a one-to-two switch 112.

<B-2. Operation>
The transmission data signal input to the drive unit 110 is amplified by the amplifier 111 and input to the one-to-two switch 112. The one-to-two switch 112 has a function of switching the signal sequence of the transmission data signal to two outputs for each bit. In the case of transmitting a transmission data signal 1001100101101001 similar to that in the first embodiment, since switching occurs for each bit, odd-numbered bits 10100110 of the transmission data signal are allocated to one output and the other output is output. Are assigned even-numbered bits 01011001 of the transmission data signal.

  Further, in the one-to-two switch 112, while one output is selected, the other output is in an open state. Accordingly, odd bits of the transmission data signal with the open state between the bits are input to the Mach-Zehnder modulator 103a, and even bits of the transmission data signal with the open state between the bits are input to the Mach-Zehnder modulator 103b. Is entered.

  The Mach-Zehnder modulators 103a and 103b BPSK-modulate the light from the light source 101 using these signals as drive signals. When one output of the one-to-two switch 112 is in an open state, the input signal of the Mach-Zehnder modulators 103a and 103b corresponding to the output is set to the NULL point of the extinction characteristic of the Mach-Zehnder modulators 103a and 103b. The modulated light is extinguished. Therefore, the Mach-Zehnder modulator 103a performs modulation with odd bits of the transmission data signal, and there is a state in which the light is OFF between the bits. The Mach-Zehnder modulator 103b also performs modulation with an even number of bits of the transmission data signal, and there is a state where the light is OFF between the bits.

  The modulated light from the Mach-Zehnder modulator 103 b is orthogonally polarized by the polarization circuit 104 and then multiplexed with the modulated light from the Mach-Zehnder modulator 103 a to be output light from the light modulator 102. Thereby, it is possible to generate a polarization bit interleave signal in which the polarization states of bits adjacent in time are orthogonal to BPSK modulation.

  4 shows a configuration in which the one-to-two switch 112 is arranged in the next stage of the amplifier 111, but the configuration of the drive unit 110 is not limited to this, and two amplifiers are provided in the next stage of the one-to-two switch 112. It may be configured.

<B-3. Effect>
In the optical signal generation device 2 according to the present embodiment, the drive unit 110 includes a 1-to-2 switch 112 that alternately distributes a binary signal to two outputs for each bit, and the 1-to-2 switch 112 serves as one output. When the binary signal is distributed, the other output is opened, and these two outputs are used as drive signals for the Mach-Zehnder modulators 103a and 103b. Therefore, ON / OFF can be repeated for each bit, and when one is ON, it is possible to create two modulated lights in which the other is OFF, and a polarization bit interleaved optical signal can be easily generated. I can do it.

<C. Embodiment 3>
<C-1. Configuration>
FIG. 5 is a configuration diagram of the optical signal generation device 3 according to the third embodiment. The optical signal generation device 3 is different from the optical signal generation device 1 of the first embodiment in the configuration of the drive unit. The drive unit 120 according to the third embodiment includes a drive signal generation unit 121 that alternately distributes a signal train of transmission data signals into two outputs, and amplifiers 122a and 122b that amplify the output of the drive signal generation unit 121.

  The driving unit 105 according to the first embodiment sets an intermediate value 0.5 between bits, but the driving unit 120 according to the third embodiment sets an OFF level (0) of the transmission data signal between bits. Thereby, it is possible to generate a polarization bit interleaved signal by OOK (On Off Keying) modulation such as RZ (Return to Zero) modulation or NRZ (Non-Return to Zero) modulation.

<C-2. Operation>
FIG. 6 is a diagram for explaining an optical output signal of the optical modulation unit 102. FIG. 6A shows a transmission data signal input to the drive unit 120. Here, the signal sequence of the transmission data signal is assumed to be 1001100101101001 as in the first embodiment.

  The drive signal generation unit 121 has a function of distributing an input signal sequence to two outputs for each bit, and a function of setting 0 to the other output when the signal sequence is allocated to one output. Yes. With these two functions, the odd-numbered bits of the data string of 1001100101101001 are distributed to the output on the amplifier 122a side of the drive signal generation unit 121, and between the bits, that is, in the portion where the even-numbered bits existed 0 is output. That is, 1000100000101000 (FIG. 6B).

  Similarly, the even-numbered bits of the signal sequence of the transmission data signal are distributed to the output of the drive signal generation unit 121 on the amplifier 122b side, and 0 is output to the portion where the odd-numbered bits exist. That is, 0001000101000001 (FIG. 6C). Thereafter, the respective signals are amplified by the amplifiers 122a and 122b.

  The optical modulation unit 102 performs OOK modulation by each of the two Mach-Zehnder modulators 103a and 103b. OOK modulation is realized by driving with the amplitude of the half-wave voltage of the Mach-Zehnder modulator and setting the center bias at the midpoint of the extinction characteristic of the Mach-Zehnder modulator. Signal 0 is extinguished and signal 1 is emitted.

  The Mach-Zehnder modulator 103a receives the signal sequence of the 10100110 from the amplifier 122a as a drive signal, and thereby OOK-modulates the light from the light source 101. Therefore, OOK modulated light (10100110) is obtained. At this time, there is 0 between each bit. For this reason, the Mach-Zehnder modulator 103a can obtain OOK modulated light in which ON / OFF is repeated for each bit. Due to OOK modulation, this signal sequence can also be shown as 1000100000101000.

  Similarly, the Mach-Zehnder modulator 103b receives the signal sequence 01011001 from the amplifier 122b as a drive signal, and thereby OOK-modulates the light from the light source 101. Therefore, OOK modulated light (010101001) is obtained. At this time, there is 0 between each bit. For this reason, the Mach-Zehnder modulator 103b can obtain OOK modulated light in which ON / OFF is repeated for each bit. Due to OOK modulation, this signal sequence can also be shown as 0001000101000001.

  The modulated light from the Mach-Zehnder modulator 103 b is orthogonally polarized by the polarization circuit 104 and then multiplexed with the modulated light from the Mach-Zehnder modulator 103 a to be output light from the light modulator 102. Thereby, it is possible to generate a polarization bit interleave signal in which the polarization states of bits adjacent in time are orthogonal to the OOK modulation.

<C-3. Effect>
In the optical signal generation device 3 of the present embodiment, the driving unit 120 alternately distributes the binary signal to two outputs for each bit, and outputs the other output when the binary signal is divided into one output to the binary signal off. These two outputs are used as drive signals for the Mach-Zehnder modulators 103a and 103b. Thereby, a polarization bit interleave signal can be easily generated even in OOK modulation.

<D. Embodiment 4>
The optical signal generation device 4 according to the fourth embodiment aims to generate a polarization bit interleave signal in QPSK modulation.

<D-1. Configuration>
FIG. 7 is a configuration diagram of the optical signal generation device 4 according to the fourth embodiment. Referring to FIG. 7, the optical signal generation device includes a light source 201 that emits continuous light, a light modulation unit 202 that modulates light source light, and a drive unit 205 that drives the light modulation unit 202.

  The light modulation unit 202 includes two QPSK (Quadrature Phase Shift Keying) modulators 203A and 203B that modulate light source light. The QPSK modulator 203A has a parallel structure of Mach-Zehnder modulators 203a and 203b that modulate light source light. The QPSK modulator 203B has a parallel structure of Mach-Zehnder modulators 203c and 203d that modulate light source light.

  The modulated light from the QPSK modulator 203B is orthogonally polarized by the polarization circuit 204, multiplexed with the modulated light from the QPSK modulator 203A, and output. That is, the optical modulation unit 202 includes a polarization orthogonal multiplexing optical circuit that multiplexes the output lights of the two QPSK modulators 203A and 203B by orthogonal polarization.

  The drive unit 205 includes drive signal generation units 206a and 206b that generate a drive signal for the optical modulation unit 202 from the transmission data signal, and amplifiers 207a, 207b, 207c, and 207d that amplify the generated drive signal.

  The optical modulation unit 202 is called a DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) modulator, and a modulator using a material such as lithium niobate or indium phosphide has been put into practical use. Used for wave multiplexing transmission.

<D-2. Operation>
Since the optical modulator 202 performs QPSK modulation, the transmission data signal is composed of two orthogonal signal components, Ich (in-phase component) and Qch (quadrature component). Ich (in-phase component) and Qch (quadrature component) are input to the drive signal generation units 206a and 206b, respectively. Here, as shown in FIGS. 8A and 8B, as (Ich, Qch), (0, 1) (0, 0) (1, 0) (0, 1) (1, 1) ( 0, 1) (0, 0) (1, 0) (1, 1) (1, 0) (1, 1) (0, 0) (1, 1) (0, 0) (0, 1) ( An example in the case of transmitting data signals 1 and 1) is shown.

  The drive signal generation unit 206a distributes the input Ich signal sequence to two outputs for each bit, and when the signal sequence is allocated to one output, the other output has an intermediate value 0 between 0 and 1 .5 is set. With these two functions, the odd-numbered bits of the data sequence of the Ich signal sequence 0010100111101001 are distributed to the output on the amplifier 207a side of the drive signal generation unit 206a, and there was an even-numbered bit between each bit. The intermediate value 0.5 is output to the portion (FIG. 8C).

  Similarly, the even-numbered bits of the Ich signal sequence are distributed to the output of the drive signal generation unit 206a on the amplifier 207b side, and an intermediate value of 0.5 is output between the bits, that is, the odd-numbered bits. (FIG. 8D). Thereafter, the respective signals are amplified by the amplifiers 207a and 207b.

  The Qch signal sequence is similarly processed by the drive signal generation unit 206b. The odd-numbered bits of the Qch signal string 1001110010101011 are distributed to the output on the amplifier 207c side of the drive signal generation unit 206b, and an intermediate value of 0.5 is set between each bit, that is, the portion where the even-numbered bits exist. Is output (FIG. 8E).

  Similarly, the even-numbered bits of the Qch signal sequence are distributed to the output of the drive signal generation unit 206b on the amplifier 207d side, and an intermediate value 0. 5 is output (FIG. 8F). Thereafter, the respective signals are amplified by the amplifiers 207c and 207d.

  The amplified signals from the amplifiers 207a and 207c are input to the QPSK modulator 203A, and the amplified signals from the amplifiers 207b and 207d are input to the QPSK modulator 203B as drive signals. The Mach-Zehnder modulators 203a, 203b, 203c, and 203d constituting the QPSK modulators 203A and 203B perform BPSK modulation. In other words, the Mach-Zehnder modulators 203a, 203b, 203c, and 203d are driven with an amplitude that is twice the half-wave voltage, and the center bias is set at the null point of the extinction characteristics of the Mach-Zehnder modulators 203a, 203b, 203c, and 203d. For this reason, when an intermediate value 0.5 between 0 and 1 is output to the signal sequence of the drive signal of the optical modulation unit 202, it becomes the NULL point of the extinction characteristic of the Mach-Zehnder modulators 203a, 203b, 203c, 203d. The light is extinguished and the output is turned off.

  That is, the QPSK modulator 203A modulates the light source light in accordance with odd-numbered bits of Ich and Qch, and outputs QPSK modulated light that is repeatedly turned on and off for each bit. Similarly, the QPSK modulator 203B modulates the light source light according to the even-numbered bits of Ich and Qch, and outputs QPSK modulated light that is repeatedly turned on and off for each bit. The ON / OFF timings of these two QPSK modulators 203A and 203B are shifted by 1 bit, and if one is ON, the other is OFF.

  The modulated light from the QPSK modulator 203B is orthogonally polarized by the polarization circuit 204, and then multiplexed with the modulated light from the QPSK modulator 203A to become output light from the optical modulation unit 202. This makes it possible to generate a polarization bit interleave signal in which the polarization states of bits adjacent in time are orthogonal to QPSK modulation.

<D-3. Effect>
In the optical signal generation device 4 of the present embodiment, each of the two optical modulators that modulate the light source light in accordance with the drive signal of the drive unit 205 is a four-phase shift optical modulator QPSK modulator 203A, 203B (four-phase shift). Therefore, it is possible to generate a polarization bit interleave signal in which the polarization states of bits that are temporally adjacent to each other are orthogonal to QPSK modulation.

  In addition, the drive unit 205 distributes two binary signals alternately to two outputs for each bit, for a total of four outputs, when dividing the binary signal into one output in each of the two sets of two outputs. An intermediate value is set for the other output, and these four outputs are used as drive signals. If the Mach-Zehnder modulators 203a, 203b, 203c, 203d constituting the QPSK modulators 203A, 203B are driven with an amplitude twice that of the half-wave voltage, and the center bias is set at the NULL point of the extinction characteristic, the intermediate value 0.5 Thus, the modulated light is extinguished, so that it is possible to create two QPSK modulated lights in which ON / OFF is repeated for each bit, and when one is ON, the other is OFF. Therefore, it is possible to easily generate a polarization bit interleaved optical signal for QPSK modulation.

<E. Embodiment 5>
<E-1. Configuration>
FIG. 9 is a configuration diagram of the optical signal generation device 5 according to the fifth embodiment. The optical signal generation device 5 differs from the optical signal generation device 4 of the fourth embodiment only in the configuration of the drive unit. Therefore, the configuration of the drive unit will be described below, and the description of other configurations will be omitted. The drive unit 210 of the optical signal generation device 5 includes amplifiers 211a and 211b that amplify Ich and Qch transmission data signals, respectively, and one-to-two switches 212a and 212b that distribute the output signals of the amplifiers 211a and 211b to two outputs, respectively. . The output of the one-to-two switch 212a is input to the Mach-Zehnder modulators 203a and 203c, and the output of the one-to-two switch 212b is input to the Mach-Zehnder modulators 203b and 203d.

<E-2. Operation>
The Ich and Qch transmission data signals input to the drive unit 210 are amplified by the amplifiers 211a and 211b. The amplified transmission data signals are input to the one-to-two switches 212a and 212b, respectively.

  The one-to-two switches 212a and 212b have a function of switching the input signal sequence to two outputs for each bit. In the case of transmitting the same Ich transmission data signal 0010100111101001 as in the fourth embodiment, since switching occurs for each bit, odd-numbered bits 01101110 are output to one output and even-numbered output to the other output. Bits 00011001 are allocated.

  In the one-to-two switches 212a and 212b, while the output is selected for one, the other output is opened. Therefore, odd bits of Ich and Qch transmission data signals with an open state between the bits are input to the QPSK modulator 203A, and the light of the light source 201 is QPSK modulated using these signals as drive signals. When one of the outputs of the one-to-two switches 212a and 212b is in an open state, the input signals of the Mach-Zehnder modulators 203a, 203b, 203c, and 203d corresponding to the outputs are quenched by the Mach-Zehnder modulators 203a, 203b, 203c, and 203d. Since the characteristic is set to the NULL point, the modulated light is in the extinction state. Therefore, the QPSK modulator 203A modulates with an odd number of bits of the transmission data signal, and there is a state where the light is OFF between the bits. Similarly, the QPSK modulator 203B performs modulation with the even number bits of the Ich and Qch transmission data signals, and there is a state where the light is OFF between the bits.

  The modulated light from the QPSK modulator 203B is orthogonally polarized by the polarization circuit 204, and then multiplexed with the modulated light from the QPSK modulator 203A to become output light from the optical modulator 202. This makes it possible to generate a polarization bit interleave signal in which the polarization states of bits adjacent in time are orthogonal to QPSK modulation.

  Although FIG. 9 shows a configuration in which the one-to-two switches 212a and 212b are arranged at the next stage of the amplifiers 211a and 211b, the configuration of the drive unit 210 is not limited to this, and the next to the one-to-two switches 212a and 212b. A configuration may be provided in which two amplifiers are provided in each stage, for a total of four amplifiers.

<E-3. Effect>
In the optical signal generation device 5 of the fifth embodiment, the drive unit 210 includes two one-to-two switches 212a and 212b that distribute two binary signals alternately to two outputs for each bit, for a total of four outputs. The pair 2 switches 212a and 212b release the other output when distributing the binary signal to one output in each of the two sets of two outputs, and these four outputs are used as the drive signals for the QPSK modulators 203A and 203B. To do. Since the modulated light of the Mach-Zehnder modulators 203a, 203b, 203c, and 203d constituting the QPSK modulators 203A and 203B is extinguished by an intermediate value of 0.5, ON / OFF is repeated for each bit, and when one is ON, the other is It is possible to create two QPSK modulated lights that are in an OFF relationship. Therefore, it is possible to easily generate a polarization bit interleaved optical signal for QPSK modulation.

<F. Embodiment 6>
<F-1. Configuration>
FIG. 10 is a configuration diagram of the optical signal generation device 6 according to the sixth embodiment. Referring to FIG. 10, the optical signal generation device 6 includes a light source 201 that emits continuous light, a light modulation unit 222 that modulates light source light, and a drive unit 213 that drives the light modulation unit 222.

  The light modulation unit 222 includes two QPSK modulators 223A and 223B that modulate light source light. The QPSK modulator 223A includes a parallel structure of Mach-Zehnder modulators 203a and 203b that modulate light source light, and a Mach-Zehnder modulator 203e at the next stage. The Mach-Zehnder modulator 203e receives the modulated light from the Mach-Zehnder modulators 203a and 203b. Similarly, the QPSK modulator 203B includes a parallel structure of Mach-Zehnder modulators 203c and 203d that modulate light source light, and a Mach-Zehnder modulator 203f at the next stage.

  The modulated light from the QPSK modulator 223B is orthogonally polarized by the polarization circuit 204, multiplexed with the modulated light from the QPSK modulator 223A, and output. That is, the optical modulator 222 includes a polarization orthogonal multiplexing optical circuit that multiplexes the output lights of the two QPSK modulators 223A and 223B by orthogonal polarization.

  The driving unit 213 demultiplexes the Ich transmission data signal into two, the demultiplexer 214a that demultiplexes the Qch transmission data signal into two, and amplifies the output of the demultiplexer 214a. Amplifiers 215a and 215b and amplifiers 215c and 215d for amplifying the output of the duplexer 214b are provided. Further, the drive unit 213 includes a drive signal generation unit 216 that generates drive signals for the Mach-Zehnder modulators 203e and 203f from the transmission data signals of Ich and Qch, and amplifiers 215a. 215f.

<F-2. Operation>
FIG. 11 is a diagram for explaining an optical output signal of the optical modulation unit 222. Transmission data signals Ich and Qch are input to the drive unit 213. Because of QPSK modulation, there are two types of data signals to be transmitted: Ich (in-phase component) and Qch (quadrature component), which are two orthogonal signal components. Here, as (Ich, Qch), (0, 1) (0, 0) (1, 0) (0, 1) (1, 1) (0, 1) (0, 0) (1, 0) The data signals (1, 1) (1, 0) (1, 1) (0, 0) (1, 1) (0, 0) (0, 1) (1, 1) are transmitted.

  The input Ich and Qch are divided into two by the demultiplexers 214a and 214b. The Ich divided into two outputs by the demultiplexer 214a is amplified by the amplifiers 215a and 215b and becomes drive signals for the Mach-Zehnder modulators 203a and 203c (FIGS. 11C and 11G). The Qch divided into two outputs by the demultiplexer 214b is amplified by the amplifiers 215c and 215d and becomes a drive signal for the Mach-Zehnder modulators 203b and 203d (FIGS. 11 (d) and (h)).

  On the other hand, Ich and Qch are also input to the drive signal generation unit 216. One of the outputs of the drive signal generator 216 is amplified by the amplifier 215e and becomes a drive signal for the Mach-Zehnder modulator 203e of the QPSK modulator 223A. The other is amplified by the amplifier 215f and becomes a drive signal for the Mach-Zehnder modulator 203f of the QPSK modulator 223B.

  In the QPSK modulator 223A, in normal QPSK modulation, the phases of the outputs from the two Mach-Zehnder modulators 203a and 203b are changed by +45 degrees and −45 degrees, respectively, and the phase difference of 90 degrees is output from the outputs from the Mach-Zehnder modulators 203a and 203b. Is added. By adding a phase difference of 90 degrees, a quaternary phase change can be added from Ich and Qch.

  The drive signal generation unit 216 has a function of driving the phase adjustment units of the Mach-Zehnder modulators 203e and 203f and adjusting the phase difference of the outputs from the Mach-Zehnder modulators 203a and 203b for each bit. In the Mach-Zehnder modulator 203e of the QPSK modulator 223A, the odd bits are set to a phase difference of 90 degrees, and the even bits are set to a phase difference corresponding to the input Ich and Qch.

  In the example of FIG. 11, the first even-numbered bit is a signal with Ich being 0 and Qch being 0. That is, the light of the same phase is output from the two Mach-Zehnder modulators 203a and 203b. At this time, the phases of these output lights change by +90 degrees and −90 degrees, respectively, according to the drive signal of the amplifier 215e (FIG. 11E), and as a result, a phase difference of 180 degrees is added. As a result, the first output of even bits is interfered and extinguished by the Mach-Zehnder modulator 203e.

  Further, in the second case of even bits, Ich is 0 and Qch is 1. That is, the output lights of the two Mach-Zehnder modulators 203a and 203b have a phase difference of 180 degrees. Due to the drive signal of the amplifier 215e, the phases of these output lights change by +0 degrees and −0 degrees, respectively, and as a result, a phase difference of 0 degrees is added (that is, the phase does not change). As a result, the second output of even bits is interfered and extinguished by the Mach-Zehnder modulator 203e.

  By performing the above operation for all even bits, the Mach-Zehnder modulator 203e to which the amplifier 215e is connected can obtain QPSK modulated light that repeats OFF for even bits and ON for odd bits (FIG. 11 (f)).

  The output signal on the amplifier 215f side of the drive signal generation unit 216 is amplified by the amplifier 215f and drives the Mach-Zehnder modulator 203f of the QPSK modulator 223B. Specifically, the phase adjustment is performed so that the phase difference of the odd bits of the modulation signals of the Mach-Zehnder modulators 203c and 203d is 180 degrees. Thus, in the Mach-Zehnder modulator 203f to which the amplifier 215f is connected, QPSK modulated light that repeats OFF at odd bits and ON at even bits can be obtained.

  The modulated light of the QPSK modulators 223A and 223B has an ON / OFF timing shifted by 1 bit, and if one is ON, the other is OFF. The modulated light from the QPSK modulator 223B is orthogonally polarized by the polarization circuit 204 (FIG. 11 (j)), and then multiplexed with the modulated light from the QPSK modulator 223A to be output light from the optical modulator 222 (FIG. 11). 11 (k)). As a result, it is possible to generate a polarization bit interleave signal in which the polarization states of bits adjacent in time are orthogonal to QPSK modulation.

<F-3. Effect>
In the optical signal generation device 6 of the present embodiment, the QPSK modulators 203A and 203B (four-phase shift optical modulators) are two first Mach-Zehnder modulators 203a that modulate light source light according to the drive signal of the drive unit 213. , 203b, 203c, and 203d, and second Mach-Zehnder modulators 203e and 203f that receive the output lights of the two first Mach-Zehnder modulators 203a, 203b, 203c, and 203d, and the drive unit 213 receives the input signal. Of the first Mach-Zehnder modulators 203a, 203b, 203c, and 203d, and the second Mach-Zehnder modulators 203e and 203f generate drive signals from the input signals. A drive signal generation unit 216 that drives the phase adjustment unit. Phase control of the second Mach-Zehnder modulators 203e, 203f so that one even bit of the output light of the two first Mach-Zehnder modulators 203a, 203b, 203c, 203d is 0 and the other odd-numbered bit is 0. By repeating the above, it is possible to repeat ON / OFF for each bit, and to create two QPSK modulated lights in which one is ON and the other is OFF. Therefore, it is possible to easily generate a polarization bit interleaved optical signal for QPSK modulation.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

  1, 2, 3, 4, 5, 6 Optical signal generation device, 101, 201 light source, 102, 202, 222 optical modulator, 103a, 103b, 203a, 203b, 203c, 203d, 203e, 203f Mach-Zehnder modulator, 104 , 204 Polarization circuit, 105, 110, 120, 205, 210, 213 Drive unit, 106, 121, 206a, 206b, 216 Drive signal generation unit, 107a, 107b, 111, 122a, 122b, 207a, 207b, 207c, 207d , 211a, 211b, 215a, 215b, 215c, 215d, 215e, 215f amplifier, 112, 212a, 212b 1-to-2 switch, 203A, 203B QPSK modulator, 214a, 214b demultiplexer.

Claims (2)

An optical signal generation device that generates a polarization bit interleaved optical signal in which the polarization states of bits adjacent in time are orthogonal,
A light modulation unit that modulates light source light;
A drive unit for driving the light modulation unit,
The light modulator is
Two quadrature phase shift optical modulators that modulate light source light in accordance with the drive signal of the drive unit;
E Bei and a polarization orthogonal multiplexing optical circuit for polarization orthogonal multiplexing processing the modulated light of the two quadrature phase shift modulator,
The driving unit drives the quadrature phase shift optical modulator with an amplitude twice the half-wave voltage of the quadrature phase shift optical modulator, and outputs two binary signals alternately for each bit; It has two 1 to 2 switches that distribute to a total of 4 outputs,
When the one-to-two switch distributes the binary signal to one output in each of the two sets of the two outputs, the other output is opened, and these four outputs are used as the drive signal.
Optical signal generator. An optical signal generation device that generates a polarization bit interleaved optical signal in which the polarization states of bits adjacent in time are orthogonal,
  A light modulation unit that modulates light source light;
  A drive unit for driving the light modulation unit,
  The light modulator is
  Two quadrature phase shift optical modulators that modulate light source light in accordance with the drive signal of the drive unit;
  A polarization orthogonal multiplexing optical circuit that performs polarization orthogonal multiplexing processing of the modulated light of the two quadrature phase shift optical modulators,
  Each of the four phase-shift optical modulators is
  Two first Mach-Zehnder modulators that modulate light source light in accordance with a drive signal of the drive unit;
  A second Mach-Zehnder modulator that receives the output light of the two first Mach-Zehnder modulators,
  The drive unit is
  A demultiplexer that demultiplexes an input signal and outputs the demultiplexed signal to the first Mach-Zehnder modulator;
  A drive signal generation unit that generates a drive signal from the input signal and drives a phase adjustment unit of the second Mach-Zehnder modulator;
  The drive signal generation unit is configured so that one of an odd bit and an even bit of the outputs of the two first Mach-Zehnder modulators has a phase difference of 90 degrees, and the other has a phase difference corresponding to the input signal. Driving the phase adjustment unit of the second Mach-Zehnder modulator;
Optical signal generator.

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