JP2014122964A - Optical modulator, optical transmitter, optical transmission/reception system, and control method of optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of an optical transmitter having a split electrode structure.SOLUTION: An optical modulation part 11 includes a plurality of phase modulation regions formed on an optical waveguides 111 and 112, and outputs an optical signal OUT obtained by binary modulating input light IN. A driver circuit 12 includes drivers 121-127 connected to each of the plurality of phase modulation regions, and outputs a driving signal according to an input digital signal DIN from each of the drivers 121-127 to the corresponding phase modulation region. A determination circuit 13 receives light intensity information INF indicating a desired intensity of an optical signal outputted from the optical modulation part 11 to reach an external optical receiver, and then determines the number of drivers to be activated from among the drivers 121-127. A driver control circuit 14 activates the drivers of the number specified by the determination result of the determination circuit 13, and cuts power supply to the drivers other than the activated drivers.

Description

  The present invention relates to an optical modulator, an optical transmitter, an optical transmission / reception system, and an optical modulator control method.

  Along with the explosive demand for broadband multimedia communication services such as the Internet and video distribution, the introduction of high-distance wavelength-division-multiplexed optical fiber communication systems with longer distances, larger capacities, and higher reliability is increasing in trunk and metro systems. In addition, optical fiber access services are rapidly spreading in subscriber systems. In a communication system using such an optical fiber, it is important to reduce the installation cost of an optical fiber that is an optical transmission line and to increase the transmission band utilization efficiency per optical fiber. For this reason, a wavelength multiplexing technique that multiplexes and transmits optical signals having different wavelengths is widely used.

  Optical transmitters for WDM optical fiber communication systems are capable of high-speed optical modulation, have small optical signal wavelength dependency, and unnecessary optical phase modulation components (modulation) that cause deterioration of the received optical waveform during long-distance signal transmission There is a demand for an optical modulator in which the light intensity modulation component (when the method is a light intensity modulation method) or the light intensity modulation component (when the modulation method is an optical phase modulation method) is suppressed as much as possible. For such applications, an MZ light intensity modulator incorporating an optical waveguide type optical phase modulator similar to an optical waveguide type Mach-Zehnder (hereinafter, MZ) interferometer is practical.

  In addition, when expanding the transmission capacity per wavelength channel, from the viewpoint of spectrum utilization efficiency and resistance to chromatic dispersion and polarization mode dispersion of the optical fiber, the optical modulation spectrum is higher than that of the normal binary light intensity modulation method. A multilevel optical modulation signaling scheme with a narrower bandwidth is advantageous. This multi-level optical modulation signal system is considered to become mainstream particularly in a trunk optical fiber communication system exceeding 40 Gb / s, where future demand is expected to increase. Currently, a monolithic integrated multilevel IQ optical modulator combining the two MZ optical intensity modulators described above and an optical multiplexer / demultiplexer has been developed for such applications.

  When such an optical modulator is used to perform high-speed optical modulation particularly in a high-frequency region where the frequency of the modulated electrical signal exceeds 1 GHz, the length of the electrode provided in the optical phase modulator region of the optical modulator is set. On the other hand, the propagation wavelength of the modulated electric signal is shortened to a level that cannot be ignored. For this reason, the potential distribution of the electrode structure, which is a means for applying an electric field to the optical phase modulator, cannot be regarded as uniform in the optical signal propagation axis direction. Therefore, in order to accurately estimate the light modulation characteristics, it is necessary to treat the electrode itself as a distributed constant line and a modulated electric signal propagating through the optical phase modulator region as a traveling wave. In this case, in order to obtain the effective interaction length between the modulated optical signal and the modulated electrical signal as much as possible, the phase velocity vo of the modulated optical signal and the phase velocity vm of the modulated electrical signal are made as close as possible (phase velocity). A so-called traveling wave type electrode structure is required which is devised.

  An optical modulator module having a split electrode structure for realizing such a traveling wave electrode structure and a multilevel optical modulation signal system has already been proposed (Patent Documents 1 to 4). In addition, there has been proposed an optical modulator module capable of multilevel control of the phase change of the modulated optical signal in each of the divided electrodes. This optical modulator module is a compact, wideband, and capable of generating an arbitrary multilevel optical modulation signal by inputting a digital signal while maintaining phase velocity matching and impedance matching required for traveling wave structure operation. This is an optical modulator module with a low driving voltage.

  In addition, a transmission-side optical communication device for reducing power consumption has been proposed (Patent Document 5). In this transmission-side optical communication device, a plurality of LEDs (Light Emitting Diodes) are driven by a single drive circuit. Then, the drive function of a part of the drive circuit is stopped, and the number of LEDs to be driven is limited by opening the switch. Thereby, power consumption can be reduced.

JP 7-13112 A JP-A-5-289033 JP-A-5-257102 International Publication No. 2011/043079 JP-A-9-130335

  However, the inventor has found that the above-described optical modulator module has the following problems. In the above-described divided electrode structure, usually, a plurality of drivers for driving the divided electrodes are required. During the optical modulation operation, it is necessary to supply power to the plurality of drivers. As a result, power consumption by a plurality of drivers increases. In particular, when the multivalue level of the output signal increases, the number of divided electrodes increases, and the number of drivers increases accordingly. In this case, the increase in power consumption becomes particularly significant.

  The present invention has been made in view of the above problems, and an object of the present invention is to reduce the power consumption of an optical transmitter having a split electrode structure.

  An optical modulator according to one embodiment of the present invention includes: a plurality of phase modulation regions formed on a waveguide; an optical modulation unit that outputs an optical signal obtained by binary modulation of input light; and each of the plurality of phase modulation regions A driver circuit that outputs a drive signal corresponding to an input digital signal to a corresponding phase modulation region from each of the plurality of drivers, and an external output that is output from the light modulator. The first information indicating the desired intensity of the optical signal reaching the receiver is received and specified by a determination circuit that determines the number of drivers to be activated among the plurality of drivers, and a determination result in the determination circuit A driver control circuit that activates a certain number of drivers and shuts off the power of drivers other than the activated drivers.

  An optical transmitter according to an aspect of the present invention includes: a light modulation unit that forms a plurality of phase modulation regions on an optical waveguide, outputs an optical signal obtained by binary-modulating input light; and a light source that outputs the input light. A plurality of drivers that are alternatively connected to each of the plurality of phase modulation regions, and a drive that outputs a drive signal corresponding to an input digital signal from each of the plurality of drivers to a corresponding phase modulation region A circuit and a determination for determining a number of drivers to be activated among the plurality of drivers by receiving first information indicating a desired intensity of an optical signal output from the optical modulation unit and reaching an external receiver; A circuit and a driver control circuit that activates the number of drivers specified by the determination result of the determination circuit and shuts off the power of drivers other than the activated driver.

  An optical transmission / reception system according to an aspect of the present invention includes an optical transmitter that outputs an optical signal and an optical receiver that receives the optical signal, and the optical transmitter includes a plurality of phase modulations on an optical waveguide. A plurality of optical modulation units that output the optical signal obtained by binary modulation of input light, a light source that outputs the input light, and a plurality of phase modulation regions that are alternatively connected to each of the plurality of phase modulation regions. A driver circuit that outputs a drive signal corresponding to an input digital signal to a corresponding phase modulation region from each of the plurality of drivers, and light that is output from the optical modulator and reaches an external receiver Upon receiving first information indicating a desired strength of the signal, a determination circuit for determining the number of drivers to be activated among the plurality of drivers and a number of drivers designated by the determination result in the determination circuit are activated. Activated and activated dry A driver control circuit to shut off the power source other than the driver, those equipped with.

  An optical modulator control method according to one embodiment of the present invention is output from an optical modulation unit that outputs an optical signal obtained by binary-modulating input light using a plurality of phase modulation regions formed on an optical waveguide. A plurality of first information indicating a desired intensity of the optical signal reaching the detector, connected to each of the plurality of phase modulation regions, and outputting a drive signal corresponding to the input digital signal to the corresponding phase modulation region; Among these drivers, the number of drivers to be activated is determined, the number of drivers designated by the determination is activated, and the power of drivers other than the activated drivers is shut off.

  According to the present invention, it is possible to reduce the power consumption of an optical transmitter having a split electrode structure.

It is a block diagram which shows typically the structure of the multivalue optical transmitter 6000 of a general division | segmentation electrode structure. 3 is a plan view schematically showing the configuration of an optical modulator 600. FIG. FIG. 6 is a diagram schematically showing a configuration of an optical multiplexer / demultiplexer 613. FIG. 6 is a diagram schematically showing a configuration of an optical multiplexer / demultiplexer 614. 5 is an operation table showing the operation of the optical modulator 600. FIG. 6 is a diagram schematically showing a light propagation mode in the optical modulator 600. It is a constellation diagram showing light L1 and L2 when phase modulation is not performed by the phase modulation regions PM61_1 to PM61_4 and the phase modulation regions PM62_1 to PM62_4. FIG. 10 is a constellation diagram showing light L1 and light L2 when a binary code of an input digital signal is “0000” in the optical modulator 600. 4 is a constellation diagram showing light L1 and L2 in the optical modulator 600. FIG. 1 is a block diagram schematically showing a configuration of an optical transmitter 1000 according to a first embodiment. 1 is a plan view schematically showing a configuration of an optical modulator 100 according to a first embodiment. 1 is a block diagram schematically showing a configuration of a general optical transmission / reception system 1100. FIG. 1 is a block diagram schematically showing a configuration of a general optical transmission / reception system 1200. FIG. It is a graph which shows the number of activated drivers, and the intensity | strength of an optical signal. 3 is a flowchart illustrating a method for determining the intensity of an optical signal of the optical modulator 100. 4 is a plan view showing an activation driver and a deactivation driver in the optical modulator 100. FIG. 4 is a plan view showing an activation driver and a deactivation driver in the optical modulator 100. FIG. FIG. 6 is a plan view schematically showing a configuration of an optical modulator 200 according to a second embodiment. 5 is a flowchart showing a method for determining the intensity of an optical signal of the optical modulator 200. FIG. 6 is a plan view schematically showing a configuration of an optical modulator 200 according to a third embodiment. 5 is a flowchart illustrating a method for determining the intensity of an optical signal of the optical modulator 300. FIG. 6 is a plan view schematically showing a configuration of an optical modulator 200 according to a fourth embodiment. 5 is a flowchart illustrating a method of determining the intensity of an optical signal of the optical modulator 400. FIG. 10 is a plan view schematically showing a configuration of an optical transmission / reception system 500 according to a fifth exemplary embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

  As a premise for understanding the configuration and operation of an optical transmitter according to the following embodiment, a general multi-value optical transmitter 6000 having a divided electrode structure will be described. The optical transmitter 6000 is a multi-level modulation optical transmitter, but here, for simplicity of explanation, the optical transmitter 6000 will be described as a 3-bit optical transmitter. FIG. 1 is a block diagram schematically showing a configuration of a multi-value optical transmitter 6000 having a general divided electrode structure. The optical transmitter 6000 includes a light source 6001 and an optical modulator 600.

  The light source 6001 is typically a laser diode, and outputs CW (Continuous Wave) light 6002 to the optical modulator 600, for example. The optical modulator 600 is a 3-bit optical modulator. The optical modulator 600 modulates the input CW light 6002 according to the input digital signal D [2: 0], which is a 3-bit digital signal, and outputs a 3-bit optical signal 6003.

  Next, the optical modulator 600 will be described. FIG. 2 is a plan view schematically showing the configuration of the optical modulator 600. The optical modulator 600 includes an optical modulator 61, a decoder 62, and a drive circuit 63.

  The light modulator 61 outputs an optical signal OUT obtained by modulating the input light IN. The input light IN corresponds to the CW light 6002 in FIG. The optical signal OUT corresponds to the optical signal 6003 in FIG. The optical modulation unit 61 includes optical waveguides 611 and 612, optical multiplexers / demultiplexers 613 and 614, phase modulation regions PM61_1 to PM61_7, and PM62_1 to PM62_7. The optical waveguides 611 and 612 are arranged in parallel.

  An optical multiplexer / demultiplexer 613 is inserted on the optical input (input light IN) side of the optical waveguides 611 and 612. On the input side of the optical multiplexer / demultiplexer 613, the input light IN is input to the input port P1, and the input port P2 is not input. On the output side of the optical multiplexer / demultiplexer 613, the optical waveguide 611 is connected to the output port P3, and the optical waveguide 612 is connected to the output port P4.

  FIG. 3A is a diagram schematically illustrating the configuration of the optical multiplexer / demultiplexer 613. In the optical multiplexer / demultiplexer 613, the light incident on the input port P1 propagates to the output ports P3 and P4. However, the phase of light propagating from the input port P1 to the output port P4 is delayed by 90 ° compared to the light propagating from the input port P1 to the output port P3. Further, the light incident on the input port P2 propagates to the output ports P3 and P4. However, the phase of light propagating from the input port P2 to the output port P3 is delayed by 90 ° compared to the light propagating from the input port P2 to the output port P4.

  An optical multiplexer / demultiplexer 614 is inserted on the optical signal output (optical signal OUT) side of the optical waveguides 611 and 612. On the input side of the optical multiplexer / demultiplexer 614, the optical waveguide 611 is connected to the input port P5, and the optical waveguide 612 is connected to the input port P6. On the output side of the optical multiplexer / demultiplexer 614, the optical signal OUT is output from the output port P7.

  FIG. 3B is a diagram schematically illustrating the configuration of the optical multiplexer / demultiplexer 614. The optical multiplexer / demultiplexer 614 has the same configuration as the optical multiplexer / demultiplexer 613. The input ports P5 and P6 correspond to the input ports P1 and P2 of the optical multiplexer / demultiplexer 613, respectively. The output ports P7 and P8 correspond to the output ports P3 and P4 of the optical multiplexer / demultiplexer 613, respectively. The light incident on the input port P5 propagates to the output ports P7 and P8. However, the phase of light propagating from the input port P5 to the output port P8 is delayed by 90 ° compared to the light propagating from the input port P5 to the output port P7. Further, the light incident on the input port P6 propagates to the output ports P7 and P8. However, the phase of light propagating from the input port P6 to the output port P7 is delayed by 90 ° compared to the light propagating from the input port P6 to the output port P8.

  Phase modulation regions PM61_1 to PM61_7 are arranged in the optical waveguide 611 between the optical multiplexer / demultiplexer 613 and the optical multiplexer / demultiplexer 614. Phase modulation regions PM62_1 to PM62_7 are disposed in the optical waveguide 612 between the optical multiplexer / demultiplexer 613 and the optical multiplexer / demultiplexer 614.

  Here, the phase modulation region is a region having electrodes formed on the optical waveguide. When an electric signal, for example, a voltage signal is applied to the electrode, the effective refractive index of the optical waveguide under the electrode changes. As a result, the substantial optical path length of the optical waveguide in the phase modulation region can be changed. Thereby, the phase modulation region can change the phase of the optical signal propagating through the optical waveguide. The optical signal can be modulated by giving a phase difference between the optical signals propagating between the two optical waveguides 611 and 612. That is, the light modulator 61 constitutes a multi-value Mach-Zehnder light modulator having two arms and an electrode division structure.

  The decoder 62 decodes the 3-bit input digital signal D [2: 0] and outputs, for example, multi-bit signals D1 to D7 to the drive circuit 63.

  The drive circuit 63 includes binary drivers DR61 to DR67. Signals D1 to D7 are supplied to the drivers DR61 to DR67, respectively. Drivers DR61 to DR67 output a pair of differential output signals according to signals D1 to D7. At this time, the positive-phase output signals of the differential output signals output from the drivers DR61 to DR67 are output to the phase modulation regions PM61_1 to PM61_7. Respective negative-phase output signals of the differential output signals output from drivers DR61 to DR67 are output to phase modulation regions PM62_1 to PM62_7.

  Here, the differential output signals output from the drivers DR61 to DR67 will be described. The drivers DR61 to DR67 are binary output (0, 1) drivers as described above. That is, the drivers DR61 to DR67 output “0” or “1” as the positive phase output signal according to the values of the signals D1 to D7.

  On the other hand, the drivers DR61 to DR67 output a signal obtained by inverting the normal phase output signal as a negative phase output signal. That is, the drivers DR61 to DR67 output “1” or “0” as a reverse phase output signal according to the values of the signals D1 to D7.

  FIG. 4 is an operation table showing the operation of the optical modulator 600. When the input digital signal D [2: 0] is “000”, the driver DR61 outputs “0” as the normal phase output signal and “1” as the negative phase output signal. When the input digital signal D [2: 0] is “001” or more, the driver DR61 outputs “1” as the normal phase output signal and “0” as the negative phase output signal.

  When the input digital signal D [2: 0] is “001” or less, the driver DR62 outputs “0” as the normal phase output signal and “1” as the negative phase output signal. When the input digital signal D [2: 0] is “010” or more, the driver DR62 outputs “1” as the normal phase output signal and “0” as the negative phase output signal.

  When the input digital signal D [2: 0] is “010” or less, the driver DR63 outputs “0” as the normal phase output signal and “1” as the negative phase output signal. When the input digital signal D [2: 0] is “011” or more, the driver DR63 outputs “1” as the normal phase output signal and “0” as the negative phase output signal.

  When the input digital signal D [2: 0] is “011” or less, the driver DR64 outputs “0” as the normal phase output signal and “1” as the negative phase output signal. When the input digital signal D [2: 0] is “100” or more, the driver DR64 outputs “1” as the normal phase output signal and “0” as the negative phase output signal.

  When the input digital signal D [2: 0] is “100” or less, the driver DR65 outputs “0” as the normal phase output signal and “1” as the negative phase output signal. When the input digital signal D [2: 0] is “101” or more, the driver DR65 outputs “1” as the normal phase output signal and “0” as the negative phase output signal.

  When the input digital signal D [2: 0] is “101” or less, the driver DR66 outputs “0” as the normal phase output signal and “1” as the negative phase output signal. When the input digital signal D [2: 0] is “110” or more, the driver DR66 outputs “1” as the normal phase output signal and “0” as the negative phase output signal.

  When the input digital signal D [2: 0] is “110” or less, the driver DR67 outputs “0” as the normal phase output signal and “1” as the negative phase output signal. When the input digital signal D [2: 0] is “111”, the driver DR67 outputs “1” as the normal phase output signal and “0” as the negative phase output signal.

  Here, the phase modulation operation of the optical modulator 600 will be described. FIG. 5 is a diagram schematically illustrating a light propagation mode in the optical modulator 600. In this example, as shown in FIG. 5, the input light IN is input to the input port P <b> 1 of the optical multiplexer / demultiplexer 613. Therefore, the phase of the light output from the output port P4 is delayed by 90 ° compared to the light output from the output port P3. Thereafter, the light output from the output port P3 passes through the phase modulation regions PM61_1 to PM61_7 and reaches the input port P5 of the optical multiplexer / demultiplexer 614. The light that reaches the input port P5 reaches the output port P7 as it is. On the other hand, the light output from the output port P4 passes through the phase modulation regions PM62_1 to PM62_7 and reaches the input port P6 of the optical multiplexer / demultiplexer 614. The light reaching the input port P6 reaches the output port P7 with a phase delay of 90 °.

  That is, even when the phase modulation regions PM61_1 to PM61_7 and the phase modulation regions PM62_1 to PM62_7 are not subjected to phase modulation, the light L2 reaching the output port P7 from the input port P6 is the light reaching the output port P7 from the input port P5. Compared to L1, the phase is delayed by 180 °.

  FIG. 6A is a constellation diagram showing the lights L1 and L2 when the phase modulation regions PM61_1 to PM61_7 and the phase modulation regions PM62_1 to PM62_7 are not subjected to phase modulation. As described above, the phase of the light L2 reaching the output port P7 from the input port P6 is delayed by 180 ° compared to the light L1 reaching the output port P7 from the input port P5.

  In contrast, in the optical modulator 600, a normal phase output signal is input to the phase modulation regions PM61_1 to PM61_7, and a negative phase output signal is input to the phase modulation regions PM62_1 to PM62_7. Thereby, the phase delay of the light L2 reaching the output port P7 from the input port P6 is compensated.

  FIG. 6B is a constellation diagram illustrating the lights L1 and L2 when the binary code of the input digital signal D [2: 0] is “000” in the optical modulator 600. For example, if the binary code of the input digital signal D [2: 0] is “111”, “1” that is a positive phase output signal is input to the phase modulation regions PM61_1 to PM61_7. On the other hand, “0” that is an antiphase output signal is input to the phase modulation regions PM62_1 to PM62_7. Thereby, the phase of the light passing through the phase modulation regions PM62_1 to PM62_7 is further delayed by 180 °.

  That is, the light L2 reaching the output port P7 from the input port P6 is added with 180 °, which is the phase delay caused by the phase modulation regions PM62_1 to PM62_7, in addition to the original 180 ° phase delay. As a result, a 360 ° phase lag occurs in the light L2 reaching the output port P7 from the input port P6, so that the phase lag with respect to the light L1 reaching the output port P7 from the input port P5 is substantially eliminated.

  6C is a constellation diagram showing the lights L1 and L2 in the optical modulator 600. FIG. As shown in FIG. 6C, by using the differential output signal, the light reaching the output port P4 from the input port P1 and the output port P7 from the input port P6 according to the change of the input digital signal D [2: 0]. While compensating for the phase delay of L2, each of L1 / L2 changes the phase of the light in contrast to the Re axis, and optical D / A conversion in the optical transmitter becomes possible. Accordingly, as shown in the operation table of FIG. 4, the phase modulation amount of the light L1 is 0 to 7Δθ and the phase modulation amount of the light L2 is 0 to −7Δθ according to the value of the input digital signal D [3: 0]. It can be changed in 8 stages.

  In FIGS. 6B and 6C, when the binary code of the input digital signal D [2: 0] is “000” or “111”, the positions of the lights L1 and L2 do not match. It is only for reviewing the drawing. That is, when the binary code of the input digital signal D [2: 0] is “000” or “111”, the positions of the lights L1 and L2 may coincide. Further, here, a case has been described in which the phase change amount modulated in the phase modulation region changes from 0 to 180 degrees according to the input digital signal, but this is not restrictive.

Embodiment 1
First, the optical transmitter 1000 according to the first embodiment of the present invention will be described. The optical transmitter 1000 is an optical transmitter that performs a binary (ie, 1-bit) modulation operation. FIG. 7 is a block diagram schematically illustrating a configuration of the optical transmitter 1000 according to the first embodiment. The optical transmitter 1000 includes a light source 1001 and an optical modulator 100.

  The light source 1001 typically uses a laser diode, and outputs CW (Continuous Wave) light 1002 to the optical modulator 100, for example. The optical modulator 100 is a binary optical modulator. The optical modulator 100 modulates the input CW light 1002 according to the input digital signal DIN that is a binary digital signal, and outputs a binary optical signal 1003.

  Next, the optical modulator 100 will be described. Similar to the optical modulator 600 described above, the optical modulator 100 has a split electrode structure. However, unlike the optical modulator 600, the optical modulator 100 is configured as a binary optical modulator. FIG. 8 is a plan view schematically showing the configuration of the optical modulator 100 according to the first embodiment. The optical modulator 100 includes an optical modulator 11, a drive circuit 12, a determination circuit 13, and a driver control circuit 14.

  The optical modulation unit 11 includes optical waveguides 111 and 112, optical multiplexers / demultiplexers 113 and 114, and phase modulation regions PM1_1 to PM1_7 and PM2_1 to 2_7. The optical waveguides 111 and 112 correspond to the first and second optical waveguides, respectively. The optical multiplexer / demultiplexers 113 and 114 correspond to the first and second optical multiplexer / demultiplexers, respectively. The phase modulation areas PM1_1 to PM1_7 correspond to the first phase modulation area. The phase modulation areas PM2_1 to PM2_7 correspond to the second phase modulation area. The optical modulation unit 11 has a so-called Mach-Zehnder optical resonator structure in which divided electrodes (phase modulation regions PM1_1 to PM1_7, PM2_1 to 2_7) are arranged on two optical waveguides (optical waveguides 111 and 112). .

  The optical waveguides 111 and 112 are arranged in parallel. An optical multiplexer / demultiplexer 113 is inserted on the optical signal input (input light IN) side of the optical waveguides 111 and 112. The optical multiplexer / demultiplexer 113 has the same configuration as the optical multiplexer / demultiplexer 613 described above. On the input side of the optical multiplexer / demultiplexer 113, the input light IN is input to the input port P1, and the input port P2 is not input. On the output side of the optical multiplexer / demultiplexer 113, the optical waveguide 111 is connected to the output port P3, and the optical waveguide 112 is connected to the output port P4. The input light IN corresponds to the CW light 1002 in FIG.

  An optical multiplexer / demultiplexer 114 is inserted on the optical signal output (optical signal OUT) side of the optical waveguides 111 and 112. The optical multiplexer / demultiplexer 114 has the same configuration as the optical multiplexer / demultiplexer 614 described above. On the input side of the optical multiplexer / demultiplexer 114, the optical waveguide 111 is connected to the input port P5, and the optical waveguide 112 is connected to the input port P6. On the output side of the optical multiplexer / demultiplexer 114, the optical signal OUT is output from the output port P7. The optical signal OUT corresponds to the optical signal 1003 in FIG.

  Phase modulation regions PM1_1 to PM1_7 are arranged in the optical waveguide 111 between the optical multiplexer / demultiplexer 113 and the optical multiplexer / demultiplexer 114. Phase modulation regions PM2_1 to PM2_7 are arranged in the optical waveguide 112 between the optical multiplexer / demultiplexer 113 and the optical multiplexer / demultiplexer 114.

  Here, the phase modulation region is a region having one electrode (divided electrode) formed on the optical waveguide. When an electric signal, for example, a voltage signal is applied to the electrode, the effective refractive index of the optical waveguide under the electrode changes. As a result, the substantial optical path length of the optical waveguide in the phase modulation region can be changed. Thereby, the phase modulation region can change the phase of the optical signal propagating through the optical waveguide. The optical signal can be modulated by providing a phase difference between the optical signals propagating between the two optical waveguides 111 and 112. That is, the light modulator 11 constitutes a multi-value Mach-Zehnder light modulator having two arms and an electrode division structure.

  The drive circuit 12 includes drivers 121 to 127. Each of the drivers 121 to 127 outputs a differential signal as a drive signal to the target phase modulation region in accordance with the input digital signal DIN that is a binary digital signal. Specifically, the driver 121 outputs a normal phase drive signal to the phase modulation region PM1_1 and outputs a negative phase drive signal to the phase modulation region PM2_1. The driver 122 outputs a normal phase drive signal to the phase modulation region PM1_2 and outputs a negative phase drive signal to the phase modulation region PM2_2. The driver 123 outputs a normal phase drive signal to the phase modulation region PM1_3 and outputs a negative phase drive signal to the phase modulation region PM2_3. The driver 124 outputs a normal phase drive signal to the phase modulation region PM1_4 and outputs a negative phase drive signal to the phase modulation region PM2_4. The driver 125 outputs a normal phase drive signal to the phase modulation region PM1_5 and outputs a negative phase drive signal to the phase modulation region PM2_5. The driver 126 outputs a normal phase drive signal to the phase modulation region PM1_6 and outputs a negative phase drive signal to the phase modulation region PM2_6. The driver 127 outputs a normal phase drive signal to the phase modulation region PM1_7 and outputs a negative phase drive signal to the phase modulation region PM2_7.

  The determination circuit 13 determines the number of drivers 121 to 127 to be activated from the external light intensity information INF. The light intensity information INF corresponds to the first information. The determination circuit 13 outputs a signal SIG1 designating a driver to be activated to the driver control circuit 14. The driver activation will be described later.

  The driver control circuit 14 activates the driver designated by the signal SIG1. Then, the driver control circuit 14 cuts off the power supply to the driver that is not specified by the signal SIG1.

  Next, the operation of the optical modulator 100 will be described. Here, as a premise for understanding the operation of the optical modulator 100, a general optical transmission / reception system having an optical transmitter and an optical receiver will be described. FIG. 9A is a block diagram schematically showing a configuration of a general optical transmission / reception system 1100. The optical transmission / reception system 1100 includes an optical transmitter 1101, an optical receiver 1102, and an optical transmission path 1103. The optical transmitter 1101 and the optical receiver 1102 are connected by an optical transmission line 1103 having a length L11. The optical transmitter 1101 transmits an optical signal to the optical receiver 1102 via the optical transmission path 1103. The optical transmission line 1103 is, for example, an optical fiber.

  FIG. 9B is a block diagram schematically showing a configuration of a general optical transmission / reception system 1200. The optical transmission / reception system 1200 includes an optical transmitter 1201, an optical receiver 1202, and an optical transmission path 1203. The optical transmitter 1201 and the optical receiver 1202 are connected by an optical transmission line 1203 having a length L12. L12> L11. The optical transmitter 1201 transmits an optical signal to the optical receiver 1202 via the optical transmission path 1203. The optical transmission line 1203 is, for example, an optical fiber.

  Since the optical transmission line 1203 is shorter than the optical transmission line 1103, when an optical signal having the same light intensity is propagated, the attenuation amount of the optical signal propagating through the optical transmission line 1203 is larger than that of the optical transmission line 1103. Become. In FIG. 9A, an optical pulse 1104 is displayed as an optical signal propagating through the optical transmission line 1103. In FIG. 9B, an optical pulse 1204 is displayed as an optical signal propagating through the optical transmission line 1203. As shown in FIGS. 9A and 9B, due to the difference in attenuation of the optical signal, the amplitude A2 of the optical pulse 1204 propagated through the optical transmission line 1203 is smaller than the amplitude A1 of the optical pulse 1104 propagated through the optical transmission line 1103. Become.

  In the optical receiver, normal optical communication can be performed if the optical signal received from the optical transmitter is not less than a predetermined intensity. Therefore, the optical modulator 100 adjusts the intensity of the output optical signal according to the intensity of the optical signal that has reached the optical receiver. Hereinafter, a light intensity adjustment method in the optical modulator 100 will be described. In the present embodiment, the amplitude of the optical signal is used as the intensity of the optical signal that has reached the optical receiver.

  The optical modulator 100 can use drivers 121 to 127 to change the output of the optical signal in eight stages. Specifically, the optical modulator 100 modulates an optical signal with an activated driver, deactivates a driver that is not used for modulation, and stops power supply.

  Hereinafter, driver activation refers to supplying power to the driver, outputting a drive signal from the driver, and modulating the optical signal in the phase modulation region. Inactivation of a driver cuts off the power supply of the driver. Therefore, the phase modulation region connected to the deactivated driver does not contribute to the modulation of the optical signal.

  FIG. 10 is a graph showing the number of activated drivers and the intensity of the optical signal. In FIG. 10, the maximum output of the optical signal from the optical modulator 100 is Pmax. In this case, the output of the optical signal can be changed in the range of 0 to Pmax in steps of 1/8 Pmax according to the number of activated drivers.

FIG. 11 is a flowchart illustrating a method for determining the intensity of the optical signal of the optical modulator 100.
Step S101
First, the light intensity information INF given from the outside is input to the determination circuit 13. The light intensity information INF may be output from an optical receiver or an optical transmission / reception system, or may be given as setting information from a user.

Step S102
The determination circuit 13 determines the number of drivers 121 to 127 to be activated according to the light intensity information INF. Then, a signal SIG1 including information designating the number of drivers to be activated is output to the driver control circuit 14. The signal SIG1 may include information specifying which driver among the drivers 121 to 127 is activated or deactivated.

Step S103
The driver control circuit 14 activates the number of drivers specified by the signal SIG1 and cuts off the power supply to the other drivers.

  Next, selection of the activation driver and the deactivation driver in the optical modulator 100 will be described. FIG. 12 is a plan view showing an activation driver and a deactivation driver in the optical modulator 100. Here, for example, a case where four drivers are activated and three drivers are deactivated will be described. In FIG. 12, “ON” is displayed for an activated driver, and “OFF” is displayed for a deactivated driver. As shown in FIG. 12, in the optical modulator 100, the drivers 121 to 124 are activated and the drivers 125 to 127 are deactivated.

  Another example of selecting the activation driver and the deactivation driver in the optical modulator 100 will be described. FIG. 13 is a plan view showing an activation driver and a deactivation driver in the optical modulator 100. Here, for example, a case where four drivers are activated and three drivers are deactivated will be described. In FIG. 13, “ON” is displayed for the activated driver, and “OFF” is displayed for the deactivated driver. As shown in FIG. 13, in the optical modulator 100, the drivers 121, 122, 124, and 127 are activated, and the drivers 123, 125, and 126 are deactivated.

  That is, for example, when four drivers are activated and three drivers are deactivated, it can be understood that four drivers are appropriately activated from the drivers 121 to 127 and the remaining three drivers are deactivated. Therefore, the activation driver and the deactivation driver can be freely selected from the drivers 121 to 127.

  According to this configuration, it is possible to transmit an optical signal having an appropriate intensity to the optical receiver while driving only a minimum number of drivers. Thereby, the power supply to the driver which is not used can be cut off, and the power consumed by the driver can be reduced.

  The intensity of the optical signal output from the optical modulator 100 can also be adjusted by adjusting the optical output of a light source (for example, a laser diode) of the optical signal. However, the power consumption of a light source such as a laser diode is generally small. On the other hand, the driver has a larger circuit scale than the laser diode, and its power consumption is large. Therefore, by appropriately stopping the power supply to the driver, the power consumption can be greatly reduced as compared with the light source control.

  In a normal optical modulator, an optical attenuator (attenuator) is inserted into the output of the optical signal to adjust the intensity of the optical signal. On the other hand, according to this configuration, the intensity of the optical signal can be easily adjusted without using an optical attenuator (attenuator).

Embodiment 2
Next, an optical modulator 200 according to the second embodiment of the present invention will be described. An optical modulator 200 is a specific example of the optical modulator 100 according to the first embodiment. FIG. 14 is a plan view schematically showing the configuration of the optical modulator 200 according to the second embodiment. In the optical modulator 200, the determination circuit 13 has a look-up table (LUT) 131. The LUT 131 corresponds to the first table.

  The LUT 131 stores information in which the intensity of the optical signal is associated with the distance from the optical modulator 200 to the optical receiver. The LUT 131 is stored in, for example, a storage device provided in the determination circuit 13. The LUT 131 may be stored in the determination circuit 13 in advance, may be input from an optical receiver or an optical transmission / reception system, or may be given as setting information from a user.

FIG. 15 is a flowchart showing a method for determining the intensity of the optical signal of the optical modulator 200.
Step S201
Step S201 is the same as step S101 in FIG.

Step S202
The determination circuit 13 extracts distance information from the light intensity information INF. Then, the distance information is checked against the LUT 131 to determine the number of drivers 121 to 127 to be activated. Then, a signal SIG1 including information designating the number of drivers to be activated is output to the driver control circuit 14.

Step S203
Step S203 is the same as step S103 in FIG.

  According to this configuration, as in the first embodiment, it is possible to transmit an optical signal having an appropriate intensity to the optical receiver while driving only a minimum number of drivers. Thereby, the power supply to the driver which is not used can be cut off, and the power consumed by the driver can be reduced.

Embodiment 3
Next, an optical modulator 300 according to the third embodiment of the present invention will be described. An optical modulator 300 is a specific example of the optical modulator 100 according to the first embodiment. FIG. 16 is a plan view schematically showing the configuration of the optical modulator 300 according to the third embodiment. In the optical modulator 300, the determination circuit 13 has an activation driver number calculation formula 132.

  The activation driver number calculation expression 132 is an expression for calculating the number of drivers to be activated from distance information from the optical modulator 300 to the optical receiver. The activation driver number calculation formula 132 is stored in, for example, a storage device provided in the determination circuit 13. The activation driver number calculation formula 132 may be stored in the determination circuit 13 in advance, may be input from an optical receiver or an optical transmission / reception system, or may be given as setting information from a user.

FIG. 17 is a flowchart illustrating a method for determining the intensity of the optical signal of the optical modulator 300.
Step S301
Step S301 is the same as step S101 in FIG.

Step S302
The determination circuit 13 extracts distance information from the light intensity information INF. Then, the number of drivers 121 to 127 to be activated is determined by substituting the distance information into the activation driver number calculation formula 132. Then, a signal SIG1 including information designating the number of drivers to be activated is output to the driver control circuit 14.

Step S303
Step S303 is the same as step S103 in FIG.

  According to this configuration, as in the first embodiment, it is possible to transmit an optical signal having an appropriate intensity to the optical receiver while driving only a minimum number of drivers. Thereby, the power supply to the driver which is not used can be cut off, and the power consumed by the driver can be reduced.

Embodiment 4
Next, an optical modulator 400 according to the fourth embodiment of the present invention will be described. An optical modulator 400 is a specific example of the optical modulator 100 according to the first embodiment. FIG. 18 is a plan view schematically showing the configuration of the optical modulator 400 according to the fourth embodiment. In the optical modulator 400, the determination circuit 13 has an activation driver number calculation formula 133.

  The activation driver number calculation formula 133 is an expression for calculating the number of drivers to be activated from the distance information from the optical modulator 400 to the optical receiver and the wavelength information of the optical signal. The activation driver number calculation formula 133 is stored in, for example, a storage device provided in the determination circuit 13. The activation driver number calculation formula 133 may be stored in the determination circuit 13 in advance, may be input from an optical receiver or an optical transmission / reception system, or may be given as setting information from a user.

FIG. 19 is a flowchart showing a method for determining the intensity of the optical signal of the optical modulator 400.
Step S401
First, distance information INF_D and wavelength information WL are input to the determination circuit 13 from the outside. The distance information INF_D is an example of the light intensity information INF. Depending on the transmission distance of the optical signal, the light intensity of the optical signal reaching the optical receiver decreases. Therefore, by using the distance information INF_D indicating the transmission distance that is known in advance as a kind of the light intensity information INF, the light intensity of the optical signal reaching the optical receiver can be indirectly specified. The distance information INF_D and the wavelength information WL may be output from the optical receiver or the optical transmission / reception system, or may be given as setting information from the user. The wavelength information WL corresponds to the second information.

Step S402
The determination circuit 13 extracts the transmission distance from the distance information INF_D. Then, the number of drivers 121 to 127 to be activated is determined by substituting the transmission distance and the wavelength information WL into the activation driver number calculation formula 133. Then, a signal SIG1 including information designating the number of drivers to be activated is output to the driver control circuit 14.

  In step S402, since not only the distance information INF_D but also the wavelength information WL is used, the attenuation amount of the optical signal due to the difference in wavelength can be corrected.

Step S403
Step S403 is the same as step S103 in FIG.

  According to this configuration, as in the first embodiment, it is possible to transmit an optical signal having an appropriate intensity to the optical receiver while driving only a minimum number of drivers. Thereby, the power supply to the driver which is not used can be cut off, and the power consumed by the driver can be reduced.

  Further, according to this configuration, the number of drivers to be activated is determined in consideration of the change in the attenuation amount of the optical signal due to the difference in the wavelength of the optical signal. Therefore, according to this configuration, it is possible to realize an optical modulator applicable to an optical transmission / reception system that performs optical communication at various wavelengths.

  The wavelength information WL has been described as being substituted into the activation driver number calculation formula 133. However, for example, the wavelength information WL may be checked against the LUT provided in the determination circuit 13 to determine the number of activation drivers. Good.

Embodiment 5
Next, an optical transmission / reception system 500 according to Embodiment 5 of the present invention will be described. The optical transmission / reception system 500 is an optical transmission / reception system using any of the optical modulators 100, 200, 300, and 400 described above. Here, an example in which the optical transmission / reception system 500 includes the optical modulator 100 will be described. FIG. 20 is a plan view schematically showing the configuration of the optical transmission / reception system 500 according to the fifth embodiment.

  The optical transmission / reception system 500 includes an optical modulator 100, an optical receiver 501, an optical transmission line 502, and a monitor unit 503.

  The optical modulator 100 and the optical receiver 501 are optically connected by an optical transmission line 502, and an optical signal propagates. The optical receiver 501 demodulates the received optical signal into an electric signal 504. The monitor unit 503 monitors the intensity 505 of the optical signal that reaches the optical receiver 501. Then, the monitor result is output as light intensity information INF.

  The optical transmission / reception system 500 can transmit an optical signal using the optical modulator 100 with the above configuration. The intensity information of the optical signal reaching the optical receiver 501 obtained by the monitor unit 503 is fed back to the optical modulator 100. As a result, the intensity of the optical signal reaching the optical receiver 501 can be easily adjusted.

Other Embodiments The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention. For example, the signal SIG1 may include information designating which driver among the drivers 121 to 127 is activated or deactivated.

  In the above-described embodiment, the case where the amplitude of the optical signal reaching the optical receiver is used as the light intensity information INF is described, but this is only an example. For example, even if the amplitude of the optical signal that has reached the optical receiver is sufficiently large, the eye pattern of the optical signal may not provide a sufficient eye opening. In this case, the amplitude of the optical signal must be increased so that a normal eye opening can be obtained. Therefore, in consideration of the communication quality, the pass / fail judgment result of the eye pattern of the optical signal may be used as the light intensity information INF.

  Even if the amplitude of the optical signal reaching the optical receiver is sufficiently large and a sufficient eye opening is obtained for the eye pattern, the error rate is reduced to a desired value or less when actual data communication is performed. There are cases where it cannot be suppressed. In this case, the amplitude of the optical signal must be increased so that the error rate can be suppressed below a desired value. Therefore, an error rate may be used as the light intensity information INF in consideration of communication quality.

  That is, it is possible to use, as the light intensity information INF, one or a plurality of information indicating the amplitude or communication quality of the optical signal reaching the optical receiver that changes according to the length of the optical transmission path.

  In the embodiment described above, the intensity adjustment of the optical signal may be performed as an initial setting at the time of introduction, or may be performed at a predetermined timing and frequency as a fine adjustment during operation of the optical transmission / reception system.

  In the above embodiment, the driver to be deactivated can be rotated as appropriate. By averaging the frequency of deactivation of a plurality of drivers, it is possible to extend the life of the entire drive circuit.

  The method of reducing power consumption by cutting off the power supply to the inactivation driver described in the above embodiment is not limited to a single Mach-Zehnder optical modulator, but also I (In-phase) / Q ( It can also be applied to a quadrature modulator.

  In the above-described embodiment, the example in which the light intensity is changed in eight steps has been described. Needless to say, the light intensity can be changed in steps other than the eight steps by increasing or decreasing the number of phase modulation regions. That is, by providing three or more phase modulation regions on one waveguide of the light modulation unit and providing three or more drivers, the light intensity can be changed in three or more steps.

DESCRIPTION OF SYMBOLS 11, 61 Optical modulation part 12, 63 Drive circuit 13 Determination circuit 14 Driver control circuit 62 Decoder 100, 200, 300, 400 Optical modulator 111, 112, 611, 612 Optical waveguide 113, 114, 613, 614 Optical multiplexer / demultiplexer 121-127, DR61-DR67 Driver 131 Look-up table (LUT)
132, 133
503 Monitor unit 504 Electric signal 505 Optical signal intensity 1000 Optical transmitter 1001, 6001 Light source 1002, 6002 CW light 1003, 6003 Optical signal 500, 1100, 1200 Optical transmission / reception system 1101, 1201 Optical transmitter 501, 1102, 1202 Optical reception Units 502, 1103, 1203 optical transmission lines 1104, 1204 optical pulse DIN input digital signal IN input optical INF optical intensity information OUT optical signals P1, P2, P5, P6 input ports P3, P4, P7, P8 output ports PM1_1 to PM1_7, PM2_1 to PM2_7, PM61_1 to PM61_4, PM62_1 to PM62_4 Phase modulation region

Claims (14)

A plurality of phase modulation regions formed on the optical waveguide, and an optical modulation unit that outputs an optical signal obtained by binary-modulating input light;
A drive circuit having a plurality of drivers connected to each of the plurality of phase modulation regions, and outputting a drive signal corresponding to an input digital signal to a corresponding phase modulation region from each of the plurality of drivers;
A determination circuit that receives first information indicating a desired intensity of an optical signal that is output from the optical modulation unit and reaches an external optical receiver, and determines the number of drivers to be activated among the plurality of drivers; ,
A driver control circuit that activates the number of drivers specified by the determination result in the determination circuit and shuts off the power of drivers other than the activated driver;
Light modulator. The determination circuit includes:
A first table in which a correspondence between a desired intensity of the optical signal and the number of drivers to be activated is defined;
Collating the first information with the first table to determine the number of drivers to be activated;
The optical modulator according to claim 1. The first information represents a desired intensity of the optical signal according to a distance of an optical transmission path between the optical modulator and the optical receiver.
The optical modulator according to claim 2. Second information indicating the wavelength of the optical signal given from the outside is given,
In the first table, the number of drivers to be activated is defined corresponding to the wavelength of the optical signal and the distance of the optical transmission line.
The optical modulator according to claim 3. The determination circuit includes:
Substituting the first information into a predetermined formula to calculate the number of drivers to be activated,
The optical modulator according to claim 1. The first information represents a desired intensity of the optical signal according to a distance of an optical transmission path between the optical modulator and the optical receiver.
The optical modulator according to claim 5. Second information indicating the wavelength of the optical signal given from the outside is given,
The determination circuit calculates the number of drivers to be activated by substituting the wavelength of the optical signal and the distance of the optical transmission path into the formula.
The optical modulator according to claim 6. The first information is generated by monitoring means for monitoring the intensity of the optical signal that has reached the optical receiver.
The optical modulator according to claim 1. The optical modulation unit multiplexes the input light split into two after propagating through the two optical waveguides and phase-modulating both or one of the input light split into the two. And generating the optical signal,
The optical modulator according to claim 1. The light modulator is
A first optical multiplexer / demultiplexer for demultiplexing the optical signal into first input light and second input light;
A first optical waveguide through which the first input light propagates;
A second optical waveguide through which the second input light propagates;
A second optical multiplexer / demultiplexer that combines the light output from the first optical waveguide and the light output from the second optical waveguide and outputs the optical signal;
A plurality of first phase modulation regions formed on the first optical waveguide;
A plurality of second phase modulation regions formed on the second optical waveguide,
The optical modulator according to claim 9. The light modulator is
m (m is an integer of 3 or more) first phase modulation regions;
m second phase modulation regions,
The drive circuit is
comprising m said drivers,
Each of the m drivers is connected to any one of the m first phase modulation regions and any one of the m second phase modulation regions without overlapping with other drivers. The
The optical modulator according to claim 10. A plurality of phase modulation regions formed on the optical waveguide, and an optical modulation unit that outputs an optical signal obtained by binary modulation of input light;
A light source that outputs the input light;
A drive circuit having a plurality of drivers selectively connected to each of the plurality of phase modulation regions, and outputting a drive signal corresponding to an input digital signal from each of the plurality of drivers to a corresponding phase modulation region When,
A determination circuit that receives first information indicating a desired intensity of an optical signal that is output from the optical modulation unit and reaches an external receiver, and determines the number of drivers to be activated among the plurality of drivers;
A driver control circuit that activates the number of drivers specified by the determination result in the determination circuit and shuts off the power of drivers other than the activated driver;
Optical transmitter. An optical transmitter that outputs an optical signal;
An optical receiver for receiving the optical signal,
The optical transmitter is
A plurality of phase modulation regions formed on the optical waveguide, and an optical modulation unit that outputs the optical signal obtained by binary-modulating input light;
A light source that outputs the input light;
A drive circuit having a plurality of drivers selectively connected to each of the plurality of phase modulation regions, and outputting a drive signal corresponding to an input digital signal from each of the plurality of drivers to a corresponding phase modulation region When,
A determination circuit that receives first information indicating a desired intensity of an optical signal that is output from the optical modulation unit and reaches an external receiver, and determines the number of drivers to be activated among the plurality of drivers;
A driver control circuit that activates the number of drivers specified by the determination result in the determination circuit and shuts off the power of drivers other than the activated driver;
Optical transmission / reception system. A first signal indicating a desired intensity of an optical signal output from an optical modulation unit that outputs an optical signal obtained by binary-modulating input light by a plurality of phase modulation regions formed on an optical waveguide and reaching an external receiver. Enter information,
Of each of the plurality of drivers connected to each of the plurality of phase modulation regions and outputting a drive signal corresponding to an input digital signal to the corresponding phase modulation region, the number of drivers to be activated is determined.
Activate the number of drivers specified by the determination, and shut off the power of drivers other than the activated drivers.
Control method of optical modulator.

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