Optical transmitting device and transmitting method

Abstract

This optical transmitter comprises: a first optical phase modulator that phase-modulates output light from a first laser diode, on the basis of a first electrical signal inputted to a first electrical-signal input unit; a second optical phase modulator that phase-modulates output light from a second laser diode, on the basis of a second electrical signal inputted to a second electrical-signal input unit; an optical multiplexer that multiplexes the output light from the first optical phase modulator and the output light from the second optical phase modulator; a photodiode that converts the output light from the optical multiplexer into a heterodyne detection signal; and an optical intensity modulator that modulates the intensity of output light from a third laser diode on the basis of the heterodyne detection signal outputted from the photodiode.

Description

[Technical field]

[0001] The present invention relates to an optical transmitting device and a transmitting method. This application claims priority to PCT / JP2021 / 007862, filed in Japan on March 2, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] As a network system for distributing video to subscribers' homes, for example, an FTTH (Fiber to the Home) CATV (Cable Television) system is known. Fig. 11 shows an example of a network configuration of a conventional FTTH CATV system 1. As shown in Fig. 11, the FTTH CATV system 1 includes, for example, a head end 100 (Head-End), an optical transmitter 200 (Tx), an amplifier 300 (V-OLT), and an optical receiver 400 (V-ONU) installed in each subscriber's home or the like.

[0003] The headend 100 receives radio waves carrying video signals transmitted from broadcast stations via terrestrial transmission towers or artificial satellites, and performs adjustments such as amplification on the received radio waves. The headend 100 then outputs an electrical signal based on the video signal to the optical transmitter 200. The optical transmitter 200 converts the acquired electrical signal into an optical signal, and transmits the optical signal to an optical transmission path constructed of optical fibers. The optical transmission path is divided into a relay network 500 section and an access network 600 section.

[0004] The relay network 500 is a communication network that connects the optical transmitting device 200 and the access network 600. In the relay network 500, when the transmission distance is long, the amplifiers 300 that function as relay amplifiers are configured in multiple stages. Each amplifier 300 (V-OLT) transmits the amplified optical signal to another amplifier 300 in the subsequent stage, transmits the amplified optical signal to a device such as an optical receiving device 400 (V-ONU) in the section of the access network 600, or branches the optical signal by an optical coupler and transmits it to both another amplifier 300 in the subsequent stage and a device in the section of the access network 600.

[0005] On the other hand, the access network 600 is a communication network connecting the relay network 500 and each optical receiving device 400 that terminates an optical signal. In the access network 600, a PON (Passive Optical Network) configuration is generally applied in order to distribute the optical signal output from the relay network 500 to the optical receiving devices 400 installed in a plurality of subscribers' homes. Furthermore, as shown in Fig. 11, an amplifier (access amplifier) ​​(not shown) may also be used in the access network 600 in order to compensate for losses associated with the distribution of optical signals by the PON configuration and losses associated with the branching of optical signals by the amplifier 300.

[0006] In the conventional FTTH CATV system 1 having the above-mentioned network configuration, for example, an FM (Frequency Modulation) batch conversion method is used as an optical transmission method (for example, see Non-Patent Document 1). In this FM batch conversion method, the optical transmitter 200 receives the frequency-multiplexed multi-channel video electrical signal output from the headend 100, and converts the electrical signal into a single-channel wideband frequency modulation (FM) signal in a batch. Furthermore, the optical transmitter 200 converts the converted FM signal into an optical signal by intensity modulation, and sends it to an optical transmission path. On the other hand, when the optical receiver 400 receives an optical signal from the optical transmission path, it converts the optical signal into an electrical FM signal and further demodulates it. In this way, the optical receiver 400 can extract the frequency-multiplexed multi-channel video electrical signal.

[0007] Here, an example of the configuration of a conventional optical transmitter 200 will be described. FIG. 12 shows the configuration of an optical transmitter 200 (Tx) disclosed in Non-Patent Document 2. Frequency-multiplexed multi-channel electric signals are input to the optical transmitter 200 separately for each band. Here, an electric signal A is input to an electric signal input terminal 11, and an electric signal C is input to an electric signal input terminal 13. The electric signal A is input to an optical phase modulator 31 connected to the rear stage of a laser diode 21 (LD), and the optical signal is phase-modulated. On the other hand, the electric signal C is split into two by a splitter 8, and then the laser diode 21 and the laser diode 22 directly modulate the optical signal. The optical signal is directly modulated by the input signal, so that frequency chirping occurs (i.e., frequency modulation is performed). At this time, as shown in FIG. 12, by using a phase shifter 9 on one of the electric signals C split by the splitter 8, electric signals having opposite phases to each other can be input to the laser diode 21 and the laser diode 22, respectively. This suppresses the remaining intensity modulation components.

[0008] The optical signals output from the laser diode 21 and the laser diode 22 are multiplexed by the optical multiplexer 4 and input to the photodiode 5 (PD). The photodiode 5 performs optical heterodyne detection, and outputs an FM signal centered on a frequency equal to the difference in oscillation frequency between the laser diode 21 and the laser diode 22. The FM signal is input to the optical intensity modulator 6, which intensity-modulates the output light from the transmission laser diode 23. The signal light generated by the intensity modulation is transmitted to the optical receiving device 400 through the transmission fiber.

[0009] In this way, when the electrical signals are inputted to the optical transmission device 200 after being separated into bands, there is an advantage that the design of the optical transmission device 200 is simplified. For example, consider a case where the electrical signal A is a low frequency and the electrical signal C is a high frequency. In this case, if the electrical signal A and the electrical signal C are inputted to the optical transmission device 200 without being separated, the processing circuit (e.g., an electrical amplifier, etc.) in the optical transmission device 200 needs to be a processing circuit capable of processing the bands of both the electrical signal A and the electrical signal C. Therefore, the design of the optical transmission device 200 becomes complicated. On the other hand, if the electrical signal A and the electrical signal C are inputted to the optical transmission device 200 after being separated, it is only necessary to separately prepare a processing circuit for processing the band of the electrical signal A and a processing circuit for processing the band of the electrical signal C. Therefore, the design of the optical transmission device 200 becomes simplified.

[0010] Here, the roles of the laser diode 21 and the laser diode 22 when modulating the electrical signal A will be described. Fig. 13 is a block diagram showing an example of the configuration of a conventional optical transmitting device 200. However, components that are not directly related to the modulation of the electrical signal A are omitted.

[0011] At the input end of the photodiode 5, the electric field E1(t) of the output light from the optical phase modulator 31 and the electric field E2(t) of the output light from the laser diode 22 can be expressed by the following equations (1) and (2), respectively.

[0012]

number

[0013]

number

[0014] Here, t is time. E1(t) and E2(t) are the instantaneous values ​​of the electric field at time t. E1 and E2 are the maximum values ​​of the electric field. ω1 and ω2 are the angular frequencies of the electric field when unmodulated. Electric signal φ1(t) is the electric signal input from electric signal input terminal 11 (however, this electric signal is the same as the electric signal input to optical phase modulator 31 because there is no loss or phase shift between electric signal input terminal 11 and optical phase modulator 31). m is a constant representing the modulation efficiency of optical phase modulator 31.

[0015] Based on these optical inputs, heterodyne detection is performed in the photodiode 5. As a result, the current I(t) of the output electrical signal (heterodyne detection signal) is expressed by the following equation (3).

[0016]

number

[0017] Here, "<...>" is an operator that performs averaging processing according to the band of the photodiode 5. In other words, this operator gives an averaged value to components that vary at angular frequencies equal to or greater than ω1 or ω2.

[0018] As is clear from the above formula (1), the role of the laser diode 21 is to output the carrier light for superimposing the electrical signal φ1(t). Also, as is clear from the above formula (2), the role of the laser diode 22 is to output the local light for coherently receiving the electrical signal φ1(t).

[0019] As shown in the above equation (3), the current I(t) output as a result of heterodyne detection is phase modulated with a value proportional to the electrical signal φ1(t) input to the optical phase modulator 31. [Prior art documents] [Non-patent literature]

[0020] [Non-Patent Document 1] "ITU-T J.185: Transmission equipment for transferring multi-channel television signals over optical access networks by frequency modulation conversion," International Telecommunication Union, June 2012. [Non-Patent Document 2] Toshiaki Shimoba et al., "Optical video distribution technology using FM batch conversion method", Institute of Electronics, Information and Communication Engineers, IEICE Technical Report, CS2019-84, IE2019-64, December 2019 Summary of the Invention [Problem to be solved by the invention]

[0021] However, in the above-mentioned optical transmitter 200 (Tx), since the configurations of processing for each of the band-separated electric signals (electric signals A and C) are different, there is a problem that it is difficult to standardize the design, development, and production means of the processing circuits that process the electric signals A and C. That is, different requirements are required, namely, optimizing the phase modulation for the electric signal A, and optimizing the intensity modulation in opposite phases by two laser diodes (laser diode 21 and laser diode 22) for the electric signal C. Therefore, there is a problem that it takes more time and effort to design, develop, and produce the processing circuits that process the band-separated electric signals.

[0022] The present invention has been made in consideration of the above-mentioned technical background, and aims to provide a technology that makes it possible to standardize the design, development, and production means of multiple processing circuits, each of which processes different bands. [Means for solving the problem]

[0023] One aspect of the present invention is an optical transmitting device comprising: a first optical phase modulator that phase-modulates output light from a first laser diode based on a first electrical signal input to a first electrical signal input section; a second optical phase modulator that phase-modulates output light from a second laser diode based on a second electrical signal input to a second electrical signal input section; an optical combiner that combines the output light from the first optical phase modulator and the output light from the second optical phase modulator; a photodiode that converts the output light from the optical combiner into a heterodyne detection signal; and an optical intensity modulator that intensity-modulates output light from a third laser diode based on the heterodyne detection signal output from the photodiode.

[0024] One aspect of the present invention is a transmission method having a first optical phase modulation step of phase-modulating output light from a first laser diode based on a first electrical signal input to a first electrical signal input section, a second optical phase modulation step of phase-modulating output light from a second laser diode based on a second electrical signal input to a second electrical signal input section, an optical combining step of combining the output light phase-modulated by the first optical phase modulation step and the output light phase-modulated by the second optical phase modulation step, a conversion step of converting the output light combined by the optical combining step into a heterodyne detection signal, and an optical intensity modulation step of intensity-modulating output light from a third laser diode based on the heterodyne detection signal. Effect of the Invention

[0025] The present invention makes it possible to standardize the design, development, and production means of a plurality of processing circuits each performing processing for a different band. [Brief description of the drawings]

[0026] [Figure 1] 1 is a block diagram showing a configuration of an optical transmitting device 200a according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating the relationship of bands of electrical signals according to the first embodiment of the present invention. [Diagram 3] 4 is a flowchart showing an operation of the optical transmitting device 200a according to the first embodiment of the present invention. [Figure 4] FIG. 11 is a block diagram showing a configuration of an optical transmitting device 200b according to a second embodiment of the present invention. [Diagram 5] FIG. 11 is a diagram illustrating the relationship between the bands of electrical signals according to the second embodiment of the present invention. [Figure 6] FIG. 11 is a block diagram showing a configuration of an optical transmitting device 200c according to a third embodiment of the present invention. [Figure 7] FIG. 11 is a block diagram showing a configuration of an optical transmitting device 200d according to a fourth embodiment of the present invention. [Figure 8] FIG. 11 is a block diagram showing a configuration of an optical transmitting device 200e according to a fifth embodiment of the present invention. [Figure 9] FIG. 13 is a block diagram showing a configuration of an optical transmitting device 200f according to a sixth embodiment of the present invention. [Figure 10] FIG. 13 is a block diagram showing a configuration of an optical transmitting device 200g according to a seventh embodiment of the present invention. [Figure 11] FIG. 1 is a block diagram showing an example of a network configuration of an FTTH CATV system. [Figure 12] FIG. 1 is a block diagram showing an example of a configuration of a conventional optical transmitting device 200. [Figure 13] FIG. 1 is a block diagram showing an example of a configuration of a conventional optical transmitting device 200. [Figure 14] FIG. 13 is a block diagram showing a configuration of an optical transmitting device 200h according to an eighth embodiment of the present invention. [Figure 15] FIG. 13 is a diagram showing a configuration of a balanced receiver according to an eighth embodiment of the present invention. [Figure 16]FIG. 13 is a block diagram showing a configuration of an optical transmitting device 200i according to a ninth embodiment of the present invention. [Figure 17] FIG. 23 is a block diagram showing a configuration of an optical transmitting device 200j according to a tenth embodiment of the present invention. [Figure 18] FIG. 23 is a block diagram showing a configuration of an optical transmitting device 200k according to an eleventh embodiment of the present invention. [Figure 19] FIG. 26 is a block diagram showing a configuration of an optical transmitting device 200l according to a twelfth embodiment of the present invention. [Figure 20] FIG. 23 is a block diagram showing a configuration of an optical transmitting device 200m according to a thirteenth embodiment of the present invention. [Figure 21] FIG. 26 is a block diagram showing a configuration of an optical transmitting device 200n according to a fourteenth embodiment of the present invention. [Figure 22] 1 is a diagram for explaining the phase relationship between two output lights in a two-input, two-output optical multiplexer 41. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, embodiments of the present invention will be described. Note that the system configuration of the network system in each of the embodiments described below is similar to the network configuration of the conventional FTTH CATV system 1 shown in FIG. 11, and therefore the description will be omitted.

[0028] <First embodiment> Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

[0029] [Configuration of optical transmitter] The configuration of an optical transmission device according to a first embodiment of the present invention will be described below. Fig. 1 is a block diagram showing the configuration of an optical transmission device 200a according to the first embodiment of the present invention.

[0030] As shown in FIG. 1, the optical transmitting device 200a includes two electrical signal input terminals (electrical signal input terminals 11-12), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 4, a photodiode 5 (PD), an optical intensity modulator 6, and an optical signal output terminal 7.

[0031] An electrical signal A is input from an electrical signal input terminal 11 into the optical transmitting device 200a and input to the input terminal of the optical phase modulator 31. In addition, an electrical signal B is input from an electrical signal input terminal 12 into the optical transmitting device 200a and input to the input terminal of the optical phase modulator 32.

[0032] The light output from the laser diode 21 is phase-modulated by an electrical signal A in an optical phase modulator 31. The light output from the laser diode 22 is phase-modulated by an electrical signal B in an optical phase modulator 32. These phase-modulated lights are multiplexed by an optical multiplexer 4 and input to a photodiode 5.

[0033] Heterodyne detection is performed in the photodiode 5. The electrical signal (heterodyne detection signal) output from the photodiode 5 is input to an input terminal of the optical intensity modulator 6. Meanwhile, the light output from the laser diode 23 is intensity-modulated in the optical intensity modulator 6 by the electrical signal output from the photodiode 5. The intensity-modulated signal light is output from the optical signal output terminal 7 to the outside of the optical transmitting device 200a.

[0034] When the optical phase modulator 31 and the optical phase modulator 32, or the optical intensity modulator 6 are driven, the optical transmitting device 200a may adjust the amplitude or bias of the electrical signal input from each electrical signal input terminal to control the modulation amount. For this reason, an amplifier, an attenuator, and a bias T may be used in the optical transmitting device 200a.

[0035] At the input end of the photodiode 5, the electric field E1(t) of the output light from the optical phase modulator 31 and the electric field E2(t) of the output light from the optical phase modulator 32 can be expressed by the following equations (4) and (5), respectively.

[0036]

number

[0037]

number

[0038] Here, t is time. E1(t) and E2(t) are the instantaneous values ​​of the electric field at time t. E1 and E2 are the maximum values ​​of the electric field. ω1 and ω2 are the angular frequencies of the electric field when unmodulated. Electric signals φ1(t) and φ2(t) are electric signals input from electric signal input terminal 11 and electric signal input terminal 12, respectively (however, these electric signals are the same as the electric signal input to optical phase modulator 31, since there is no loss or phase shift between electric signal input terminal 11 and optical phase modulator 31). m is a constant representing the modulation efficiency of optical phase modulator 31 and optical phase modulator 32.

[0039] Based on these optical inputs, heterodyne detection is performed in the photodiode 5. As a result, the current I(t) of the output heterodyne detection signal is expressed by the following equation (6).

[0040]

number

[0041] Here, "<...>" is an operator that performs averaging processing according to the band of the photodiode 5. In other words, this operator gives an averaged value to components that vary at angular frequencies equal to or greater than ω1 or ω2.

[0042] Here, as is clear from the above formulas (4) and (5), the role of the laser diode 21 is to output a carrier light for superimposing the electrical signal φ1(t), and the role of the laser diode 22 is to output a carrier light for superimposing the electrical signal φ2(t). The electrical signal φ1(t) superimposed on the carrier light output from the laser diode 21 is coherently received using the carrier light output from the laser diode 22 on which the electrical signal φ2(t) is superimposed. Similarly, the electrical signal φ2(t) superimposed on the carrier light output from the laser diode 22 is coherently received using the carrier light output from the laser diode 21 on which the electrical signal φ1(t) is superimposed.

[0043] In this way, the configuration of the optical transmission device 200a according to this embodiment is different from the configuration of the conventional optical transmission device 200 shown in Fig. 13 and formulas (1) and (2). Nevertheless, in the current I(t) output as a result of heterodyne detection shown in the above formula (6), the electrical signal φ1(t) input to the optical phase modulator 31 and the electrical signal φ2(t) input to the optical phase modulator 32 are linearly added and then phase-modulated. Therefore, it can be seen that the phase modulation is performed in the same manner as in the configuration of the conventional optical transmission device 200.

[0044] However, here, the electrical signals φ1(t) and φ2(t) must be set so that their frequencies do not overlap. Setting them in this way can eliminate interference between these electrical signals. Setting them in this way also makes it easier to separate the linear sum of these electrical signals (i.e., m(φ1(t)-φ2(t) in the above equation (6)). Figure 2 shows two examples of the placement of the electrical signals φ1(t) and φ2(t) set in this way on the frequency axis.

[0045] [Optical transmitter operation] An example of the operation of the optical transmission device according to the first embodiment of the present invention will be described below. Fig. 3 is a flowchart showing the operation of the optical transmission device 200a according to the first embodiment of the present invention.

[0046] The operation of the optical transmitting device 200a shown in this flowchart starts when an electrical signal A is input to the electrical signal input terminal 11 and an electrical signal B is input to the electrical signal input terminal 12. The electrical signal input terminal 11 inputs the electrical signal A to the optical phase modulator 31. The electrical signal input terminal 12 inputs the electrical signal B to the optical phase modulator 32 (step S01).

[0047] The optical phase modulator 31 phase-modulates the light output from the laser diode 21 with the electrical signal A. The optical phase modulator 32 phase-modulates the light output from the laser diode 22 with the electrical signal B (step S02).

[0048] The optical multiplexer 4 multiplexes the output light from the optical phase modulator 31 and the output light from the optical phase modulator 32 (step S03). The photodiode 5 performs heterodyne detection on the light multiplexed by the optical multiplexer 4 (step S04).

[0049] The optical intensity modulator 6 intensity-modulates the light output by the laser diode 23 with the electrical signal output from the photodiode 5 (step S05). The optical signal output terminal 7 outputs the intensity-modulated signal light to the relay network 500. This completes the operation of the optical transmitting device 200 shown in the flowchart of FIG.

[0050] As described above, the optical transmission device 200a according to the first embodiment includes the laser diode 21 and the optical phase modulator 31 that perform signal processing on the electrical signal φ1(t), and the laser diode 22 and the optical phase modulator 32 that perform signal processing on the electrical signal φ2(t). With such a configuration, the optical transmission device 200a according to the first embodiment can make the signal processing configuration for the electrical signal φ1(t) and the signal processing configuration for the electrical signal φ2(t) the same as the signal processing configuration of the conventional optical transmission device 200. Since the signal processing configuration for each electrical signal is the same, it becomes possible to standardize the design, development, and production means of the processing circuits for each electrical signal in the optical transmission device 200a.

[0051] <Second embodiment> A second embodiment of the present invention will now be described with reference to the drawings.

[0052] [Configuration of optical transmitter] The configuration of the optical transmission device according to the second embodiment of the present invention will be described below. Fig. 4 is a block diagram showing the configuration of an optical transmission device 200b according to the second embodiment of the present invention.

[0053] As shown in FIG. 4, the optical transmitting device 200b includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 4, a photodiode 5 (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, and a phase shifter 9 that shifts the phase of an input signal by 180 degrees.

[0054] An electrical signal A is input from an electrical signal input terminal 11 into the optical transmitting device 200b, and is input to the input terminal of the optical phase modulator 31. In addition, an electrical signal B is input from an electrical signal input terminal 12 into the optical transmitting device 200b, and is input to the input terminal of the optical phase modulator 32.

[0055] Furthermore, an electrical signal C is input from an electrical signal input terminal 13 into the optical transmitting device 200b and is divided into two by a distributor 8. One of the two divided electrical signals C is input to a drive current input terminal of a laser diode 21 and directly modulated. The other of the two divided electrical signals C passes through a phase shifter 9 and is then input to a drive current input terminal of a laser diode 22 and directly modulated.

[0056] The light output from the laser diode 21 is phase-modulated by an electrical signal A in an optical phase modulator 31. The light output from the laser diode 22 is phase-modulated by an electrical signal B in an optical phase modulator 32. These phase-modulated lights are multiplexed by an optical multiplexer 4 and input to a photodiode 5.

[0057] Heterodyne detection is performed in the photodiode 5. The electrical signal output from the photodiode 5 is input to an input terminal of an optical intensity modulator 6. Meanwhile, the light output from the laser diode 23 is intensity-modulated in the optical intensity modulator 6 by the electrical signal output from the photodiode 5. The intensity-modulated signal light is output from an optical signal output terminal 7 to the outside of the optical transmitting device 200b.

[0058] When the optical phase modulator 31 and the optical phase modulator 32, or the optical intensity modulator 6 are driven, the optical transmitting device 200b may adjust the amplitude or bias of the electrical signal input from each electrical signal input terminal to control the modulation amount. For this reason, an amplifier, an attenuator, and a bias T may be used in the optical transmitting device 200b.

[0059] At the input end of the photodiode 5, the electric field E1(t) of the output light from the optical phase modulator 31 and the electric field E2(t) of the output light from the optical phase modulator 32 can be expressed by the following equations (7) and (8), respectively.

[0060]

number

[0061]

number

[0062] Here, t is time. E1(t) and E2(t) are instantaneous values ​​of the electric field at time t. E1 and E2 are maximum values ​​of the electric field. ω1 and ω2 are angular frequencies of the electric field when not modulated. Electric signals φ1(t) and φ2(t) are electric signals input from electric signal input terminal 11 and electric signal input terminal 12, respectively (however, these electric signals are the same as the electric signal input to optical phase modulator 31 because there is no loss or phase shift between electric signal input terminal 11 and optical phase modulator 31). Electric signal φ3(t) is an electric signal input from electric signal input terminal 13. m is a constant representing the modulation efficiency of optical phase modulator 31 and optical phase modulator 32. M / 2 is a value obtained by subtracting the constant representing the modulation efficiency of laser diode 21 and laser diode 22 by the branching loss of distributor 8.

[0063] As described above, the third term expressing the effect of frequency modulation in the operator cos() on the right-hand side of equations (7) and (8) is expressed by integration (Reference: Masahiro Morikura, ed., OHM University Text Communication Method, OHMsha, ISBN978-4-274-21473-8, pp.76-77, November 2013). The sign added before the third term is "+" on the path side that includes phase shifter 9, and "-" on the path side that does not include phase shifter 9.

[0064] Based on these optical inputs, heterodyne detection is performed in the photodiode 5. As a result, the current I(t) of the output heterodyne detection signal is expressed by the following equation (9).

[0065]

number

[0066] Here, "<...>" is an operator that performs averaging processing according to the band of the photodiode 5. In other words, this operator gives an averaged value to components that vary at angular frequencies equal to or greater than ω1 or ω2.

[0067] As shown in the above equation (9), in the current I(t) output as a result of heterodyne detection, the integral value ∫0 t dtφ3(t) is a form in which phase modulation is performed after linear addition. Therefore, by setting the electrical signals φ1(t), φ2(t), and φ3(t) so that their frequencies do not overlap, interference between these electrical signals can be eliminated. Also, by setting them in this way, these electrical signals can be easily separated. Figure 5 shows six examples of the arrangement of the electrical signals φ1(t), φ2(t), and φ3(t) set in this way on the frequency axis.

[0068] As described above, according to the optical transmission device 200b of the second embodiment, the signal processing configuration for the electrical signal φ1(t) and the signal processing configuration for the electrical signal φ2(t) can both be made the same as the signal processing configuration of the conventional optical transmission device 200. By making the signal processing configuration for each electrical signal the same, it becomes possible to standardize the design, development, and production means of the processing circuits for each electrical signal of the optical transmission device 200a. In addition, although the third electrical signal φ3(t) has a different signal processing configuration from the conventional signal processing configuration, it can be multiplexed. That is, according to the optical transmission device 200b of the second embodiment, it becomes possible to increase the number of multiplexed electrical signals compared to the conventional optical transmission device 200.

[0069] <Third embodiment> Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

[0070] [Configuration of optical transmitter] The configuration of the optical transmission device according to the third embodiment of the present invention will be described below. Fig. 6 is a block diagram showing the configuration of an optical transmission device 200c according to the third embodiment of the present invention.

[0071] As shown in FIG. 6, the optical transmitting device 200c includes two electrical signal input terminals (electrical signal input terminals 11-12), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 4, a photodiode 5 (PD), an optical intensity modulator 6, an optical signal output terminal 7, and two integrating circuits (integrating circuits 101-102).

[0072] As shown in FIG. 6, the optical transmission device 200c according to this embodiment has a configuration in which an integrating circuit 101 and an integrating circuit 102 are added to the optical transmission device 200a according to the first embodiment shown in FIG.

[0073] An electrical signal A is taken into the optical transmitting device 200c from the electrical signal input terminal 11 and input to the input terminal of the integrating circuit 101. Also, an electrical signal B is taken into the optical transmitting device 200c from the electrical signal input terminal 12 and input to the input terminal of the integrating circuit 102. The integrating circuit 101 is disposed between the electrical signal input terminal 11 and the optical phase modulator 31. Also, the integrating circuit 102 is disposed between the electrical signal input terminal 12 and the optical phase modulator 32.

[0074] In general, when phase modulation is performed using the value obtained by integrating electrical signal A (φ1(t)) over time, the same FM signal is obtained as when it is frequency modulated with electrical signal φ1(t), and when phase modulation is performed using the value obtained by integrating electrical signal B (φ2(t)) over time, the same FM signal is obtained as when it is frequency modulated with electrical signal φ2(t) (see the references listed above). Therefore, the value ∫0 t The phase modulation is performed with dtφ1(t), and the value ∫0 obtained by integrating the electrical signal φ2(t) with the integrating circuit 102 is t In this configuration in which phase modulation is performed at dtφ2(t), the current I(t) output from the photodiode 5 is expressed by the following equation (10).

[0075]

number

[0076] Here, t is time. E1(t) and E2(t) are the instantaneous values ​​of the electric field at time t. E1 and E2 are the maximum values ​​of the electric field. ω1 and ω2 are the angular frequencies of the electric field when unmodulated. Electric signals φ1(t) and φ2(t) are electric signals input from electric signal input terminal 11 and electric signal input terminal 12, respectively. m is a constant representing the modulation efficiency of optical phase modulator 31 and optical phase modulator 32.

[0077] As described above, according to the optical transmitting device 200c of the third embodiment, it is possible to change the modulation format of the optical signal at the time of output from the optical transmitting device 200c to frequency modulation in response to the input of the electrical signal φ1(t) and the electrical signal φ2(t). As a result, the optical transmitting device 200c of the present embodiment can be applied to a network system using an optical receiving device compatible with the demodulation format of the frequency modulation. Furthermore, by unifying the modulation format, it is only necessary to prepare an optical receiving device compatible with the demodulation format of the frequency modulation, thereby reducing costs such as device costs.

[0078] <Fourth embodiment> Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.

[0079] [Configuration of optical transmitter] The configuration of the optical transmission device according to the fourth embodiment of the present invention will be described below. Fig. 7 is a block diagram showing the configuration of an optical transmission device 200d according to the fourth embodiment of the present invention.

[0080] As shown in FIG. 7, the optical transmitting device 200d includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 4, a photodiode 5 (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and two integrating circuits (integrating circuits 101-102).

[0081] As shown in FIG. 7, the optical transmitting device 200d according to this embodiment has a configuration in which an integrating circuit 101 and an integrating circuit 102 are added to the optical transmitting device 200b according to the second embodiment shown in FIG.

[0082] An electrical signal A is taken into the optical transmitting device 200d from the electrical signal input terminal 11 and input to the input terminal of the integrating circuit 101. An electrical signal B is taken into the optical transmitting device 200c from the electrical signal input terminal 12 and input to the input terminal of the integrating circuit 102. The integrating circuit 101 is disposed between the electrical signal input terminal 11 and the optical phase modulator 31. The integrating circuit 102 is disposed between the electrical signal input terminal 12 and the optical phase modulator 32. An electrical signal C is taken into the optical transmitting device 200d from the electrical signal input terminal 13 and input to the input terminal of the distributor 8.

[0083] In general, when phase modulation is performed using the value obtained by integrating electrical signal A (φ1(t)) over time, the same FM signal is obtained as when it is frequency modulated with electrical signal φ1(t), and when phase modulation is performed using the value obtained by integrating electrical signal B (φ2(t)) over time, the same FM signal is obtained as when it is frequency modulated with electrical signal φ2(t) (see the references listed above). Therefore, the value ∫0 t The phase modulation is performed with dtφ1(t), and the value ∫0 obtained by integrating the electrical signal φ2(t) with the integrating circuit 102 is t In this configuration in which phase modulation is performed with dtφ2(t), the current I(t) of the heterodyne detection signal output from the photodiode 5 is expressed by the following equation (11).

[0084]

number

[0085] Here, t is time. E1(t) and E2(t) are instantaneous values ​​of the electric field at time t. E1 and E2 are maximum values ​​of the electric field. ω1 and ω2 are angular frequencies of the electric field when unmodulated. Electrical signals φ1(t), φ2(t) and φ3(t) are electrical signals input from electrical signal input terminal 11, electrical signal input terminal 12 and electrical signal input terminal 13, respectively. m is a constant representing the modulation efficiency of optical phase modulator 31 and optical phase modulator 32.

[0086] As described above, according to the optical transmitting device 200d of the fourth embodiment, it is possible to change the modulation format of the optical signal at the time of output from the optical transmitting device 200d to frequency modulation for three electrical signals (electrical signal φ1(t), electrical signal φ2(t), and electrical signal φ3(t)). This allows the optical transmitting device 200d of this embodiment to be applied to a network system using an optical receiving device compatible with the demodulation format of frequency modulation. Furthermore, by unifying the modulation format, it is necessary to prepare only an optical receiving device compatible with the demodulation format of frequency modulation, thereby reducing costs such as device costs.

[0087] <Fifth embodiment> Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings.

[0088] [Configuration of optical transmitter] The configuration of an optical transmission device according to the fifth embodiment of the present invention will be described below. Fig. 8 is a block diagram showing the configuration of an optical transmission device 200e according to the fifth embodiment of the present invention.

[0089] As shown in FIG. 8, the optical transmitting device 200e includes three electrical signal input terminals (electrical signal input terminals 11 to 13), three laser diodes (laser diodes 21 to 23) (LD), two optical phase modulators (optical phase modulators 31 to 32), an optical multiplexer 4, a photodiode 5 (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and a differentiation circuit 111.

[0090] As shown in FIG. 8, an optical transmission device 200e according to this embodiment has a configuration in which a differentiation circuit 111 is added to the optical transmission device 200b according to the second embodiment shown in FIG.

[0091] An electrical signal A is taken into the optical transmitting device 200e from the electrical signal input terminal 11 and input to the input terminal of the optical phase modulator 31. An electrical signal B is taken into the optical transmitting device 200e from the electrical signal input terminal 12 and input to the input terminal of the optical phase modulator 32. An electrical signal C is taken into the optical transmitting device 200e from the electrical signal input terminal 13 and input to the input terminal of the differentiation circuit 111. The differentiation circuit 111 is disposed between the electrical signal input terminal 13 and the distributor 8.

[0092] In general, when frequency modulation is performed using a value obtained by differentiating an electrical signal C(φ3(t)) with respect to time, the same phase-modulated (PM) signal as that obtained by phase modulation using the electrical signal φ3(t) is obtained (see the above references). Therefore, in this configuration in which frequency modulation is performed using a value (d / dt)φ3(t) obtained by differentiating the electrical signal φ3(t) using the differentiation circuit 111, the current I(t) of the heterodyne detection signal output from the photodiode 5 is expressed by the following equation (13) (since the process expressed by the following equation (12) is performed).

[0093]

number

[0094]

number

[0095] Here, t is time. E1(t) and E2(t) are instantaneous values ​​of the electric field at time t. E1 and E2 are maximum values ​​of the electric field. ω1 and ω2 are angular frequencies of the electric field when unmodulated. Electrical signals φ1(t), φ2(t) and φ3(t) are electrical signals input from electrical signal input terminal 11, electrical signal input terminal 12 and electrical signal input terminal 13, respectively. m is a constant representing the modulation efficiency of optical phase modulator 31 and optical phase modulator 32.

[0096] As described above, according to the optical transmitting device 200e of the fifth embodiment, it is possible to unify the modulation format of the optical signal at the time of output from the optical transmitting device 200e into phase modulation for three electric signals (electric signal φ1(t), electric signal φ2(t), and electric signal φ3(t)). By unifying the modulation format, it is only necessary to prepare an optical receiving device compatible with the demodulation format of the phase modulation, thereby reducing costs such as device costs.

[0097] Sixth embodiment Hereinafter, a sixth embodiment of the present invention will be described with reference to the drawings.

[0098] [Configuration of optical transmitter] The configuration of an optical transmission device according to the sixth embodiment of the present invention will be described below. Fig. 9 is a block diagram showing the configuration of an optical transmission device 200f according to the sixth embodiment of the present invention.

[0099] As shown in FIG. 9, the optical transmitting device 200f includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 4, a photodiode 5 (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and two differential circuits (differential circuits 111-112).

[0100] As shown in FIG. 9, an optical transmission device 200f according to this embodiment has a configuration in which a differentiation circuit 111 and a differentiation circuit 112 are added to the optical transmission device 200b according to the second embodiment shown in FIG.

[0101] An electrical signal A is taken into the optical transmitting device 200f from the electrical signal input terminal 11, and is input to the input terminal of the optical phase modulator 31. An electrical signal B is taken into the optical transmitting device 200f from the electrical signal input terminal 12, and is input to the input terminal of the optical phase modulator 32. An electrical signal C is taken into the optical transmitting device 200f from the electrical signal input terminal 13, and is input to the input terminal of the distributor 8. The differentiation circuit 111 is disposed between the distributor 8 and the laser diode 21. The differentiation circuit 112 is disposed between the distributor 8 and the phase shifter 9.

[0102] 8, the optical transmitting device 200e according to the fifth embodiment differentiates the electrical signal C before distributing it, whereas the optical transmitting device 200f according to this embodiment differentiates the electrical signal C after distributing it. The difference between the configuration of the optical transmitting device 200e according to the fifth embodiment and the configuration of the optical transmitting device 200f according to this embodiment is only in the above-mentioned respect.

[0103] As described above, according to the optical transmitting device 200f of the sixth embodiment, similarly to the optical transmitting device 200e of the fifth embodiment described above, it is possible to unify the modulation format of the optical signal at the time of output from the optical transmitting device 200f into phase modulation for the three electric signals (electric signal φ1(t), electric signal φ2(t), and electric signal φ3(t)). By unifying the modulation format, it is only necessary to prepare an optical receiving device compatible with the demodulation format of the phase modulation, thereby reducing costs such as device costs.

[0104] Seventh embodiment Hereinafter, a seventh embodiment of the present invention will be described with reference to the drawings.

[0105] [Configuration of optical transmitter] The configuration of an optical transmission device according to the seventh embodiment of the present invention will be described below. Fig. 10 is a block diagram showing the configuration of an optical transmission device 200g according to the seventh embodiment of the present invention.

[0106] As shown in FIG. 10, the optical transmitting device 200g includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 4, a photodiode 5 (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and two differential circuits (differential circuits 111-112).

[0107] As shown in FIG. 10, an optical transmission device 200g according to this embodiment has a configuration in which a differentiation circuit 111 and a differentiation circuit 112 are added to the optical transmission device 200b according to the second embodiment shown in FIG.

[0108] An electrical signal A is taken into the optical transmitting device 200g from the electrical signal input terminal 11 and input to the input terminal of the optical phase modulator 31. An electrical signal B is taken into the optical transmitting device 200g from the electrical signal input terminal 12 and input to the input terminal of the optical phase modulator 32. An electrical signal C is taken into the optical transmitting device 200g from the electrical signal input terminal 13 and input to the input terminal of the distributor 8. The differentiating circuit 111 is disposed between the distributor 8 and the laser diode 21. The differentiating circuit 112 is disposed between the phase shifter 9 and the laser diode 22.

[0109] 8, the optical transmitting device 200e according to the fifth embodiment differentiates the electrical signal C before distributing it, whereas the optical transmitting device 200g according to this embodiment differentiates the electrical signal C after distributing it. The difference between the configuration of the optical transmitting device 200e according to the fifth embodiment and the configuration of the optical transmitting device 200g according to this embodiment is only in the above-mentioned respect.

[0110] As described above, according to the optical transmitting device 200g of the seventh embodiment, like the optical transmitting device 200e of the fifth embodiment and the optical transmitting device 200f of the sixth embodiment, it is possible to unify the modulation format of the optical signals output from the optical transmitting device 200g to phase modulation for the three electric signals (electric signal φ1(t), electric signal φ2(t), and electric signal φ3(t)). By unifying the modulation format, it is only necessary to prepare an optical receiving device compatible with the demodulation format of the phase modulation, thereby reducing costs such as device costs.

[0111] As described above, according to the optical transmitting device (optical transmitting device 200a to 200g) according to each of the above-mentioned embodiments, the signal processing configuration for the electrical signal φ1(t) and the signal processing configuration for the electrical signal φ2(t) can be made the same. By making the signal processing configuration for each electrical signal the same, it becomes possible to standardize the design, development, and production means of the processing circuits for each electrical signal in the optical transmitting device.

[0112] Moreover, according to the optical transmitting devices (optical transmitting devices 200a to 200g) according to the above-mentioned embodiments, it is possible to unify the modulation format of the optical signal at the time of output to either frequency modulation or phase modulation. By unifying the modulation format, it is only necessary to prepare an optical receiving device that supports either one of the demodulation formats of frequency modulation or phase modulation, thereby reducing costs such as device costs.

[0113] <Eighth embodiment> Hereinafter, an eighth embodiment of the present invention will be described with reference to the drawings.

[0114] [Configuration of optical transmitter] The configuration of an optical transmission device according to the eighth embodiment of the present invention will be described below. Fig. 14 is a block diagram showing the configuration of an optical transmission device 200h according to the eighth embodiment of the present invention.

[0115] As shown in FIG. 14, the optical transmitting device 200h includes two electrical signal input terminals (electrical signal input terminals 11-12), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 41, two photodiodes (photodiodes 51-52) (PD), an optical intensity modulator 6, and an optical signal output terminal 7.

[0116] As shown in FIG. 14, the optical transmitting device 200h of this embodiment differs from the optical transmitting device 200a of the first embodiment shown in FIG. 1 in that the 2-input, 1-output optical multiplexer 4 is replaced with a 2-input, 2-output optical multiplexer 41, one photodiode 5 is replaced with two photodiodes 51 and 52, the photodiode 51 and the photodiode 52 are respectively connected to the two output terminals of the optical multiplexer 41, and an electrical signal (heterodyne detection signal) is output from the connection point between the photodiode 51 and the photodiode 52 to the optical intensity modulator 6.

[0117] An electrical signal A is input from an electrical signal input terminal 11 into the optical transmitting device 200h, and is input to the input terminal of the optical phase modulator 31. In addition, an electrical signal B is input from an electrical signal input terminal 12 into the optical transmitting device 200h, and is input to the input terminal of the optical phase modulator 32.

[0118] The light output from the laser diode 21 is phase-modulated by an electrical signal A in an optical phase modulator 31. Moreover, the light output from the laser diode 22 is phase-modulated by an electrical signal B in an optical phase modulator 32. These phase-modulated lights are multiplexed by a two-input, two-output optical multiplexer 41, and then split and input to a photodiode 51 and a photodiode 52, respectively.

[0119] Fig. 15 is a diagram showing the configuration of a balanced receiver according to an eighth embodiment of the present invention. The above-mentioned two photodiodes 51 and 52 constitute a balanced receiver. As a method for forming a balanced receiver, for example, as shown in Fig. 15(a), there is a method in which the anode of the photodiode 51 and the cathode of the photodiode 52 are connected to each other and a current is output from the connection point (note that a constant voltage source or a ground, etc., connected to the cathode of the photodiode 51 and the anode of the photodiode 52 are not shown in Fig. 15(a)).

[0120] As another method for constructing a balanced receiver, for example, as shown in FIG. 15(b), there is a method in which the cathode of photodiode 51 and the anode of photodiode 52 are connected to each other and a current is output from the connection point (note that a constant voltage source or ground, etc., connected to the anode of photodiode 51 and the cathode of photodiode 52 are not shown in FIG. 15(b)).

[0121] Heterodyne detection is performed in the photodiode 51 and the photodiode 52. The electrical signals (heterodyne detection signals) output from the photodiode 51 and the photodiode 52 are combined and then input to an input terminal of the optical intensity modulator 6. Meanwhile, the light output from the laser diode 23 is intensity-modulated in the optical intensity modulator 6 by the electrical signals output from the photodiode 51 and the photodiode 52. The intensity-modulated signal light is output from the optical signal output terminal 7 to the outside of the optical transmitting device 200h.

[0122] When the optical phase modulator 31 and the optical phase modulator 32, or the optical intensity modulator 6 are driven, the optical transmitting device 200h may adjust the amplitude or bias of the electrical signal input from each electrical signal input terminal to control the modulation amount. For this reason, an amplifier, an attenuator, and a bias T may be used in the optical transmitting device 200h.

[0123] The electric field E'1(t) of the output light from the optical phase modulator 31 and the electric field E'2(t) of the output light from the optical phase modulator 32 at the input terminal of the optical multiplexer 41 can be expressed by the following equations (14) and (15), respectively (details will be explained in the appendix below).

[0124]

number

[0125]

number

[0126] Here, t is time. E'1(t) and E'2(t) are the instantaneous values ​​of the electric field at time t. (√2·E1+√2·e1(t)) and (√2·E2+√2·e2(t)) are the amplitudes of the electric field. Among these, √2·E1 and √2·E2 are constants that represent the output electric field amplitudes of laser diode 21 and laser diode 22.

[0127] On the other hand, √2·e1(t) and √2·e2(t) are variables that represent the fluctuations in the output electric field amplitudes at time t of the laser diode 21 and the laser diode 22. Note that these fluctuations also exist in the optical transmission devices according to the first to seventh embodiments described above, but are omitted here for convenience of explanation.

[0128] ω1 and ω2 are angular frequencies of the electric field when unmodulated. Electric signals φ1(t) and φ2(t) are electric signals input from electric signal input terminal 11 and electric signal input terminal 12, respectively. However, since there is no loss or phase shift between electric signal input terminal 11 and optical phase modulator 31, these electric signals are the same as the electric signal input to optical phase modulator 31. m is a constant representing the modulation efficiency of optical phase modulator 31 and optical phase modulator 32.

[0129] In the optical multiplexer 41, generally, when light input from terminal a (or terminal b) is demultiplexed and output from terminals A and B, the output lights have a relative phase difference of 90°.

[0130] For this reason, the electric field at the input end of the photodiode 51 of the light that is transmitted through the optical multiplexer 41 and output from the terminal A is the component E A1 (t) and the component E originating from the optical phase modulator 32 A2 For each (t), it can be expressed by the following equations (16) and (17), respectively (details will be explained in the appendix below).

[0131]

number

[0132]

number

[0133] As a result of the relative phase difference of 90° between the output lights, the phase of the electric field of the light that transmits from terminal a to terminal A does not change (cos in equation (14) ⇒ cos in equation (16)), but the phase of the electric field of the light that transmits from terminal b to terminal A changes by 90° (-sin in equation (15) ⇒ cos in equation (17)).

[0134] Similarly, the electric field at the input end of the photodiode 52 of the light that is transmitted through the optical multiplexer 41 and output from the terminal B is the component E B1 (t) and the component E originating from the optical phase modulator 32 B2 For each (t), it can be expressed by the following equations (18) and (19), respectively.

[0135]

number

[0136]

number

[0137] As a result of the relative phase difference of 90° between the output lights, the phase of the electric field of the light transmitting from terminal a to terminal B changes by 90° (cos in equation (14) ⇒ sin in equation (18)), but the phase of the electric field of the light transmitting from terminal b to terminal B does not change (-sin in equation (15) ⇒ -sin in equation (19)).

[0138] Here, in the photodiode 51, heterodyne detection is performed based on the input of light expressed by equations (16) and (17). As a result, a current I A (t) is expressed by the following equation (20) using equations (16) and (17).

[0139]

number

[0140] Here, "< >" is an operator that performs averaging processing according to the band of the photodiode 51. In other words, this operator gives an average value to components that vary at angular frequencies equal to or greater than ω1 or ω2. Note that, since e1(t) and e2(t) are minute, e1(t) 2 , e2(t) 2 , and the values ​​of e1(t) and e2(t) were set to 0.

[0141] Similarly, in the photodiode 52, heterodyne detection is performed based on the input of light expressed by equations (18) and (19). As a result, a current I B (t) is expressed by the following equation (21) using equations (18) and (19).

[0142]

number

[0143] Here, "< >" is an operator that performs averaging processing according to the band of the photodiode 52. In other words, this operator gives an average value to components that vary at angular frequencies equal to or greater than ω1 or ω2. Note that, since e1(t) and e2(t) are minute, e1(t) 2 , e2(t) 2 , and the values ​​of e1(t) and e2(t) were set to 0.

[0144] The current I output from each of the photodiodes 51 and 52 A (t) and I B As described above, the current I(t) is combined into an electrical signal of current I(t) and then input to the optical intensity modulator 6. This current I(t) (heterodyne detection signal) is expressed by the following equation (22).

[0145]

number

[0146] Here, I A (t) and I B The reason why (t) and (t) are combined with each other with opposite signs is that the photodiode 51 and the photodiode 52 have a balanced receiver configuration.

[0147] As is clear from a comparison of the above equations (20), (21), and (22), the DC component E1 is removed from the output electrical signal by using two photodiodes as a balanced receiver in comparison with the configuration using only one photodiode. 2 , E2 2 In the eighth embodiment, the components E1e1(t) and E2e2(t) caused by the fluctuation are lost. In particular, the components E1e1(t) and E2e2(t) caused by the fluctuation become noise and cause signal degradation. Therefore, according to the optical transmitting device 200h of the eighth embodiment, there is an effect that the signal quality (CNR; Carrier-to-Noise Ratio) is improved by losing the components E1e1(t) and E2e2(t).

[0148] As a prior art using a balanced receiver, a configuration is known in which an optical multiplexer / demultiplexer multiplexes / demultiplexes one signal light and one local oscillator light (unmodulated light), and detects the signal light while removing noise (relative intensity noise) generated from the local oscillator light (reference: Iwashita Masaru, "Advances in Coherent Optical Communication Technology," Journal of the Optical Society of Japan, Vol. 38, No. 5, p. 239, May 2009). However, this reference does not disclose a configuration in which two signal lights are multiplexed / demultiplexed, and detects the signal light while removing noise (E1e1(t) and E2e2(t)) generated from both of the two signal lights, as in the optical transmitting device 200h in the eighth embodiment, and there is no suggestion of the configuration or the effects of the configuration.

[0149] <Ninth embodiment> Hereinafter, a ninth embodiment of the present invention will be described with reference to the drawings.

[0150] [Configuration of optical transmitter] The configuration of an optical transmission device according to the ninth embodiment of the present invention will be described below. Fig. 16 is a block diagram showing the configuration of an optical transmission device 200i according to the ninth embodiment of the present invention.

[0151] As shown in FIG. 16, the optical transmitting device 200i includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 41, two photodiodes (photodiodes 51-52) (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, and a phase shifter 9 that shifts the phase of an input signal by 180 degrees.

[0152] As shown in FIG. 16, the optical transmitting device 200i of this embodiment differs from the optical transmitting device 200b of the second embodiment shown in FIG. 4 in that the 2-input, 1-output optical multiplexer 4 is replaced by a 2-input, 2-output optical multiplexer 41, one photodiode 5 is replaced by two photodiodes 51 and 52, the photodiode 51 and the photodiode 52 are respectively connected to the two output terminals of the optical multiplexer 41, and an electrical signal (heterodyne detection signal) is output from the connection point between the photodiode 51 and the photodiode 52 to the optical intensity modulator 6.

[0153] By combining the mathematical expansion in the second embodiment described above with the mathematical expansion in the eighth embodiment described above, the current I of the heterodyne detection signal output from the photodiode 51 and the photodiode 52 is calculated as follows: A (t) and I B (t) is expressed by the following equations (23) and (24).

[0154]

number

[0155]

number

[0156] The current I output from the photodiode 51 and the photodiode 52 A (t) and I B (t) are combined to become an electrical signal of current I(t), which is then input to the optical intensity modulator 6. This current I(t) (heterodyne detection signal) is expressed by the following equation (25).

[0157]

number

[0158] Here, I A (t) and IB The reason why (t) are combined with mutually opposite signs is that the photodiode 51 and the photodiode 52 have a balanced receiver configuration.

[0159] As is clear from a comparison of the above equations (23), (24), and (25), the DC component E1 is removed from the output electrical signal by using two photodiodes as a balanced receiver in comparison with the configuration using only one photodiode. 2 , E2 2 In particular, the components E1e1(t) and E2e2(t) caused by the fluctuations are lost as noise, which causes signal degradation. Therefore, according to the optical transmission device 200i of the ninth embodiment, there is an effect that the signal quality (CNR) is improved by the loss of the components E1e1(t) and E2e2(t).

[0160] <Tenth embodiment> Hereinafter, a tenth embodiment of the present invention will be described with reference to the drawings.

[0161] [Configuration of optical transmitter] The configuration of an optical transmission device according to the tenth embodiment of the present invention will be described below. Fig. 17 is a block diagram showing the configuration of an optical transmission device 200j according to the tenth embodiment of the present invention.

[0162] As shown in FIG. 17, the optical transmitting device 200j includes two electrical signal input terminals (electrical signal input terminals 11-12), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 41, two photodiodes (photodiodes 51-52) (PD), an optical intensity modulator 6, an optical signal output terminal 7, and two integrating circuits (integrating circuits 101-102).

[0163] As shown in FIG. 17, the optical transmitting device 200j in this embodiment differs from the optical transmitting device 200c according to the third embodiment shown in FIG. 6 in that the 2-input, 1-output optical multiplexer 4 is replaced with a 2-input, 2-output optical multiplexer 41, one photodiode 5 is replaced with two photodiodes 51 and 52, the photodiode 51 and the photodiode 52 are respectively connected to the two output terminals of the optical multiplexer 41, and an electrical signal (heterodyne detection signal) is output from the connection point between the photodiode 51 and the photodiode 52 to the optical intensity modulator 6.

[0164] The current I output from the photodiode 51 and the photodiode 52 A (t) and I B (t) are combined to become an electric signal of current I(t), which is then input to the optical intensity modulator 6. This current I(t) (heterodyne detection signal) is expressed by the following equation (26) by combining the equation expansions of the third embodiment and the eighth embodiment described above.

[0165]

number

[0166] As is clear from the above equation (26), the output electrical signal contains a DC component E1 2 , E2 2 In particular, the components E1e1(t) and E2e2(t) caused by the fluctuations are lost as noise, which causes signal degradation. Therefore, the optical transmitting device 200j according to the tenth embodiment has an effect of improving the signal quality (CNR) by eliminating the components E1e1(t) and E2e2(t).

[0167] <Eleventh embodiment> Hereinafter, an eleventh embodiment of the present invention will be described with reference to the drawings.

[0168] [Configuration of optical transmitter] The configuration of an optical transmission device according to the eleventh embodiment of the present invention will be described below. Fig. 18 is a block diagram showing the configuration of an optical transmission device 200k according to the eleventh embodiment of the present invention.

[0169] As shown in FIG. 18, the optical transmitting device 200k includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 41, two photodiodes (photodiodes 51-52) (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and two integrating circuits (integrating circuits 101-102).

[0170] As shown in FIG. 18, the optical transmitting device 200k of this embodiment differs from the optical transmitting device 200d of the fourth embodiment shown in FIG. 7 in that the 2-input, 1-output optical multiplexer 4 is replaced by a 2-input, 2-output optical multiplexer 41, one photodiode 5 is replaced by two photodiodes 51 and 52, the photodiode 51 and the photodiode 52 are respectively connected to the two output terminals of the optical multiplexer 41, and an electrical signal (heterodyne detection signal) is output from the connection point between the photodiode 51 and the photodiode 52 to the optical intensity modulator 6.

[0171] The current I output from the photodiode 51 and the photodiode 52 A (t) and I B (t) are combined to become an electric signal of current I(t), which is then input to the optical intensity modulator 6. This current I(t) (heterodyne detection signal) is expressed by the following equation (27) by combining the equation developments of the fourth embodiment and the eighth embodiment described above.

[0172]

number

[0173] Here, as is clear from the above equation (27), by using two photodiodes to form a balanced receiver, the DC component E1 2 , E2 2 In the eleventh embodiment, the components E1e1(t) and E2e2(t) caused by the fluctuation are lost. In particular, the components E1e1(t) and E2e2(t) caused by the fluctuation become noise and cause signal degradation. Therefore, according to the optical transmitting device 200k of the eleventh embodiment, there is an effect that the signal quality (CNR) is improved by the loss of the components E1e1(t) and E2e2(t).

[0174] <Twelfth embodiment> Hereinafter, a twelfth embodiment of the present invention will be described with reference to the drawings.

[0175] [Configuration of optical transmitter] The configuration of an optical transmission device according to the twelfth embodiment of the present invention will be described below. Fig. 19 is a block diagram showing the configuration of an optical transmission device 200l according to the twelfth embodiment of the present invention.

[0176] As shown in FIG. 19, the optical transmitting device 200l includes three electrical signal input terminals (electrical signal input terminals 11 to 13), three laser diodes (laser diodes 21 to 23) (LD), two optical phase modulators (optical phase modulators 31 to 32), an optical multiplexer 41, two photodiodes (photodiodes 51 to 52) (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and a differentiation circuit 111.

[0177] As shown in FIG. 19, the optical transmitting device 200l of this embodiment differs from the optical transmitting device 200e of the fifth embodiment shown in FIG. 8 in that the two-input, one-output optical multiplexer 4 is replaced by a two-input, two-output optical multiplexer 41, one photodiode 5 is replaced by two photodiodes 51 and 52, the photodiode 51 and the photodiode 52 are respectively connected to the two output terminals of the optical multiplexer 41, and an electrical signal (heterodyne detection signal) is output from the connection point between the photodiode 51 and the photodiode 52 to the optical intensity modulator 6.

[0178] The current I output from the photodiode 51 and the photodiode 52 A (t) and I B (t) are combined to become an electric signal of current I(t), which is then input to the optical intensity modulator 6. This current I(t) (heterodyne detection signal) is expressed by the following equation (28) by combining the equation expansions of the fifth embodiment and the eighth embodiment described above.

[0179]

number

[0180] Here, as is clear from the above equation (28), by using two photodiodes to form a balanced receiver, the DC component E1 2 , E2 2 In particular, the components E1e1(t) and E2e2(t) caused by the fluctuations are lost as noise, which causes signal degradation. Therefore, the optical transmitting device 200l according to the twelfth embodiment has an effect of improving the signal quality (CNR) by eliminating the components E1e1(t) and E2e2(t).

[0181] <Thirteenth embodiment> Hereinafter, a thirteenth embodiment of the present invention will be described with reference to the drawings.

[0182] [Configuration of optical transmitter] The configuration of an optical transmission device according to the thirteenth embodiment of the present invention will be described below. Fig. 20 is a block diagram showing the configuration of an optical transmission device 200m according to the thirteenth embodiment of the present invention.

[0183] As shown in FIG. 20, the optical transmitting device 200m includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 41, two photodiodes (photodiodes 51-52) (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and two differential circuits (differential circuits 111-112).

[0184] As shown in FIG. 20, the optical transmitting device 200m of this embodiment differs from the optical transmitting device 200f of the sixth embodiment shown in FIG. 9 in that the two-input, one-output optical multiplexer 4 is replaced by a two-input, two-output optical multiplexer 41, one photodiode 5 is replaced by two photodiodes 51 and 52, the photodiode 51 and the photodiode 52 are respectively connected to the two output terminals of the optical multiplexer 41, and an electrical signal (heterodyne detection signal) is output from the connection point between the photodiode 51 and the photodiode 52 to the optical intensity modulator 6.

[0185] 19, the optical transmitting device 200l according to the twelfth embodiment differentiates the electrical signal C before distributing it, whereas the optical transmitting device 200m according to this embodiment differentiates the electrical signal C after distributing it. The difference between the configuration of the optical transmitting device 200l according to the twelfth embodiment and the configuration of the optical transmitting device 200m according to this embodiment is only in the above-mentioned respect.

[0186] Therefore, similarly to the optical transmission device 200l according to the twelfth embodiment, the optical transmission device 200m according to this embodiment also has a configuration in which two photodiodes are used as a balanced receiver, and therefore the DC component E1 is removed from the output electrical signal.2 , E2 2 In addition, components E1e1(t) and E2e2(t) caused by fluctuations are lost. In particular, components E1e1(t) and E2e2(t) caused by fluctuations become noise and cause signal degradation. Therefore, according to the optical transmitting device 200m of the thirteenth embodiment, there is an effect that the signal quality (CNR) is improved by the loss of components E1e1(t) and E2e2(t).

[0187] <Fourteenth embodiment> Hereinafter, a fourteenth embodiment of the present invention will be described with reference to the drawings.

[0188] [Configuration of optical transmitter] The configuration of an optical transmission device according to the fourteenth embodiment of the present invention will be described below. Fig. 21 is a block diagram showing the configuration of an optical transmission device 200n according to the fourteenth embodiment of the present invention.

[0189] As shown in FIG. 21, the optical transmitting device 200n includes three electrical signal input terminals (electrical signal input terminals 11-13), three laser diodes (laser diodes 21-23) (LD), two optical phase modulators (optical phase modulators 31-32), an optical multiplexer 41, two photodiodes (photodiodes 51-52) (PD), an optical intensity modulator 6, an optical signal output terminal 7, a distributor 8, a phase shifter 9, and two differential circuits (differential circuits 111-112).

[0190] As shown in FIG. 21, the optical transmitting device 200n of this embodiment differs from the optical transmitting device 200g of the seventh embodiment shown in FIG. 10 in that the 2-input, 1-output optical multiplexer 4 is replaced by a 2-input, 2-output optical multiplexer 41, one photodiode 5 is replaced by two photodiodes 51 and 52, the photodiode 51 and the photodiode 52 are respectively connected to the two output terminals of the optical multiplexer 41, and an electrical signal (heterodyne detection signal) is output from the connection point between the photodiode 51 and the photodiode 52 to the optical intensity modulator 6.

[0191] 19, the optical transmitting device 200l according to the twelfth embodiment differentiates the electrical signal C before distributing it, whereas the optical transmitting device 200n according to this embodiment differentiates the electrical signal C after distributing it. The difference between the configuration of the optical transmitting device 200l according to the twelfth embodiment and the configuration of the optical transmitting device 200n according to this embodiment is only in the above-mentioned respect.

[0192] Therefore, similarly to the optical transmission device 200l according to the twelfth embodiment, the optical transmission device 200n according to this embodiment also has a configuration in which two photodiodes are used as a balanced receiver, and therefore the DC component E1 is removed from the output electrical signal. 2 , E2 2 In addition, components E1e1(t) and E2e2(t) caused by fluctuations are lost. In particular, components E1e1(t) and E2e2(t) caused by fluctuations become noise and cause signal degradation. Therefore, according to the optical transmitting device 200n of the fourteenth embodiment, there is an effect that the signal quality (CNR) is improved by the loss of components E1e1(t) and E2e2(t).

[0193] <Addendum> Hereinafter, the phase relationship between the two output lights in the two-input two-output optical multiplexer 41 will be described with reference to Fig. 22. Fig. 22 is a diagram for explaining the phase relationship between the two output lights in the two-input two-output optical multiplexer 41.

[0194] Let T be the transfer function that expresses the relationship between the electric field and phase of the two input lights and the two output lights of the optical multiplexer 41. Here, due to symmetry, the change in the electric field and phase when transmitting "from terminal a to terminal A" is the same as the change in the electric field and phase when transmitting "from terminal b to terminal B". Similarly, the change in the electric field and phase when transmitting "from terminal a to terminal B" is the same as the change in the electric field and phase when transmitting "from terminal b to terminal A". Therefore, the transfer function T has symmetry as expressed by the following equation (29).

[0195]

number

[0196] Next, consider transmitting light from left to right in Fig. 22. If the optical electric fields input to terminals a and b of optical multiplexer 41-1 at point 1 are 1 and 0, respectively, the electric field at point 1 is expressed by the following equation (30).

[0197]

number

[0198] Furthermore, the output optical electric fields (point 2) from terminals A and B of the optical multiplexer 41-1, and the output optical electric fields (point 3) from terminals A and B of the optical multiplexer 41-2 are expressed as the following equations (31) and (32) based on the above equations (29) and (30).

[0199]

number

[0200]

number

[0201] If there is no loss in the optical multiplexers 41-1 and 41-2, the powers calculated by the equations (30) to (32) are the same, and the following equations (33) and (34) hold.

[0202]

number

[0203]

number

[0204] By subtracting the square of both sides of the above equation (33) from equation (34), we obtain the following equation (36).

[0205]

number

[0206]

number

[0207] Here, α = |α|exp(iθ α ), β = |β|exp(iθ β ), the above equation (36) can be transformed into the following equation (37).

[0208]

number

[0209] As a result, the phase relationship of the output optical fields from terminals A and B is derived as shown in the following equation (38).

[0210]

number

[0211] The reason why the phase of light depends on the input / output terminals of the optical multiplexer 41 in the optical transmitting devices according to the eighth to fourteenth embodiments has been explained above.

[0212] As described above, the optical transmitting device (optical transmitting devices 200h to 200n) according to each of the above-mentioned embodiments multiplexes two phase-modulated optical signals by the optical multiplexer 41, then splits the signals and converts them into electrical signals by a balanced receiver configuration. By being provided with such a configuration, the optical transmitting device (optical transmitting devices 200h to 200n) can eliminate noise caused by fluctuations in the output electric field amplitude of the laser diode, and can improve the signal quality (CNR).

[0213] Furthermore, according to the optical transmitting device (optical transmitting device 200h to 200n) according to each of the above-mentioned embodiments, the signal processing configuration for the electrical signal φ1(t) and the signal processing configuration for the electrical signal φ2(t) can be made the same. By making the signal processing configuration for each electrical signal the same, it becomes possible to standardize the design, development, and production means of the processing circuits for each electrical signal of the optical transmitting device.

[0214] Moreover, according to the optical transmitting device (optical transmitting device 200h to 200n) according to each of the above-mentioned embodiments, it is possible to unify the modulation format of the optical signal at the time of output to either frequency modulation or phase modulation. By unifying the modulation format, it is only necessary to prepare an optical receiving device that supports either one of the demodulation formats of frequency modulation or phase modulation, thereby reducing costs such as device costs.

[0215] According to the above-mentioned embodiment, the optical transmission device includes a first optical phase modulator, a second optical phase modulator, an optical multiplexer, a photodiode, and an optical intensity modulator. For example, the first optical phase modulator is the optical phase modulator 31 in the embodiment, and the second optical phase modulator is the optical phase modulator 32 in the embodiment. The first optical phase modulator phase-modulates the output light from the first laser diode based on the first electrical signal input to the first electrical signal input section. For example, the first electrical signal input section is the electrical signal input terminal 11 in the embodiment, the first electrical signal is the electrical signal A in the embodiment, and the first laser diode is the laser diode 21 in the embodiment. The second optical phase modulator phase-modulates the output light from the second laser diode based on the second electrical signal input to the second electrical signal input section. For example, the second electrical signal input unit is the electrical signal input terminal 12 in the embodiment, the second electrical signal is the electrical signal B in the embodiment, and the second laser diode is the laser diode 22 in the embodiment. The optical multiplexer multiplexes the output light from the first optical phase modulator and the output light from the second optical phase modulator. The photodiode converts the output light from the optical multiplexer into a heterodyne detection signal. The optical intensity modulator intensity-modulates the output light from the third laser diode based on the heterodyne detection signal output from the photodiode. For example, the third laser diode is the laser diode 23 in the embodiment.

[0216] The optical transmitter may further include a distributor and a phase shifter. In this case, the distributor distributes the third electrical signal inputted to the third electrical signal input section into a fourth electrical signal and a fifth electrical signal. For example, the third electrical signal input section is the electrical signal input terminal 13 in the embodiment, the third electrical signal is the electrical signal C in the embodiment, and the fourth electrical signal and the fifth electrical signal are the electrical signal C distributed by the distributor 8 in the embodiment. The phase shifter shifts the phase of the fifth electrical signal by 180 degrees. The fourth electrical signal outputted from the distributor is inputted to the drive current input terminal of the first laser diode. The fifth electrical signal outputted from the phase shifter is inputted to the drive current input terminal of the second laser diode.

[0217] The optical transmission device may further include a first integrating circuit and a second integrating circuit. For example, the first integrating circuit is the integrating circuit 101 in the embodiment, and the second integrating circuit is the integrating circuit 102 in the embodiment. In this case, the first integrating circuit performs an integration process on the first electrical signal input to the first electrical signal input unit, and outputs the result to the first optical phase modulator. The second integrating circuit performs an integration process on the second electrical signal input to the second electrical signal input unit, and outputs the result to the second optical phase modulator.

[0218] The optical transmission device may further include a differentiation circuit, in which the differentiation circuit differentiates the third electrical signal input to the third electrical signal input unit and outputs the differentiated signal to the distributor.

[0219] The optical transmission device may further include a first differentiation circuit and a second differentiation circuit. For example, the first differentiation circuit is differentiation circuit 111 in the embodiment, and the second differentiation circuit is differentiation circuit 112 in the embodiment. In this case, the first differentiation circuit differentiates the fourth electrical signal output from the distributor and outputs the result to the first laser diode. The second differentiation circuit differentiates the fifth electrical signal output from the distributor and outputs the result to the phase shifter.

[0220] The first electrical signal, the second electrical signal, and the third electrical signal are electrical signals whose frequencies do not overlap with one another.

[0221] The optical multiplexer may have an output terminal connected to the first photodiode and an output terminal connected to the second photodiode, multiplex the output light from the first optical phase modulator and the output light from the second optical phase modulator, demultiplex the multiplexed light, and output the demultiplexed light to the first photodiode and the second photodiode, respectively. For example, the first photodiode is the photodiode 51 (or the photodiode 52) in the embodiment, and the second photodiode is the photodiode 52 (or the photodiode 51) in the embodiment. The photodiode may include the first photodiode and the second photodiode whose cathode is connected to the anode of the first photodiode, and output a heterodyne detection signal to the optical intensity modulator from the connection point between the first photodiode and the second photodiode.

[0222] A part or all of the optical transmitters 200a to 200n in each of the above-mentioned embodiments may be realized by a computer. In that case, a program for realizing the functions may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read into a computer system and executed to realize the functions. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. The term "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, and a storage device such as a hard disk built into a computer system. The term "computer-readable recording medium" may also include a medium that dynamically holds a program for a short period of time, such as a communication line when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in that case. The above-mentioned program may be a program for realizing a part of the above-mentioned functions, or may be a program that can realize the above-mentioned functions in combination with a program already recorded in the computer system, or may be a program that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0223] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Explanation of symbols]

[0224] 1...FTTH CATV system, 4, 41...optical multiplexer, 5, 51, 52...photodiode, 6...optical intensity modulator, 7...optical signal output terminal, 8...distributor, 9...phase shifter, 11, 12, 13...electrical signal input terminal, 21, 22, 23...laser diode, 31, 32...optical phase modulator, 100...head end, 101, 102...integration circuit, 111, 112...differential circuit, 200, 200a to g...optical transmitter, 300...amplifier, 400...optical receiver, 500...relay network, 600...access network

Claims

1. A first optical phase modulator that phase-modulates output light from a first laser diode based on a first electrical signal input to a first electrical signal input section; a second optical phase modulator that phase-modulates output light from a second laser diode based on a second electrical signal input to a second electrical signal input section; a distributor that distributes the third electrical signal input to the third electrical signal input unit into a fourth electrical signal and a fifth electrical signal; a differentiation circuit that performs differentiation on the third electrical signal input to the third electrical signal input unit and outputs the differentiation result to the distributor; a phase shifter that shifts the phase of the fifth electrical signal by 180 degrees; an optical multiplexer that multiplexes an output light from the first optical phase modulator and an output light from the second optical phase modulator; a photodiode for converting the output light from the optical multiplexer into a heterodyne detection signal; an optical intensity modulator that intensity-modulates an output light from a third laser diode based on the heterodyne detection signal output from the photodiode; Equipped with the fourth electrical signal output from the distributor is input to a drive current input terminal of the first laser diode, The fifth electrical signal output from the phase shifter is input to a drive current input terminal of the second laser diode. Optical transmitting device.

2. A first optical phase modulator that phase-modulates output light from a first laser diode based on a first electrical signal input to a first electrical signal input section; a second optical phase modulator that phase-modulates output light from a second laser diode based on a second electrical signal input to a second electrical signal input section; a distributor that distributes the third electrical signal input to the third electrical signal input unit into a fourth electrical signal and a fifth electrical signal; a first differentiation circuit that performs differentiation on the fourth electrical signal output from the distributor and outputs the differentiation result to the first laser diode; a phase shifter that shifts the phase of the fifth electrical signal by 180 degrees; a second differentiation circuit that performs differentiation on the fifth electrical signal output from the distributor and outputs the differentiation result to the phase shifter; an optical multiplexer that multiplexes an output light from the first optical phase modulator and an output light from the second optical phase modulator; a photodiode for converting the output light from the optical multiplexer into a heterodyne detection signal; an optical intensity modulator that intensity-modulates an output light from a third laser diode based on the heterodyne detection signal output from the photodiode; Equipped with the fourth electrical signal output from the first differentiation circuit is input to a drive current input terminal of the first laser diode; The fifth electrical signal output from the phase shifter is input to a drive current input terminal of the second laser diode. Optical transmitting device.

3. a first optical phase modulator that phase-modulates output light from a first laser diode based on a first electrical signal input to a first electrical signal input section; a second optical phase modulator that phase-modulates output light from a second laser diode based on a second electrical signal input to a second electrical signal input section; a distributor that distributes the third electrical signal input to the third electrical signal input unit into a fourth electrical signal and a fifth electrical signal; a first differentiation circuit that performs differentiation on the fourth electrical signal output from the distributor and outputs the result to the first laser diode; a phase shifter that shifts the phase of the fifth electrical signal by 180 degrees; a second differentiation circuit that performs differentiation on the fifth electrical signal output from the phase shifter and outputs the differentiation result to the first laser diode; an optical multiplexer that multiplexes an output light from the first optical phase modulator and an output light from the second optical phase modulator; a photodiode for converting the output light from the optical multiplexer into a heterodyne detection signal; an optical intensity modulator that intensity-modulates an output light from a third laser diode based on the heterodyne detection signal output from the photodiode; Equipped with the fourth electrical signal output from the first differentiation circuit is input to a drive current input terminal of the first laser diode; The fifth electrical signal output from the second differentiation circuit is input to a drive current input terminal of the second laser diode. Optical transmitting device.

4. The first electrical signal, the second electrical signal, and the third electrical signal are electrical signals whose frequencies do not overlap with each other.

4. An optical transmitter according to claim 1.

5. The optical multiplexer comprises: an output terminal connected to the first photodiode; an output terminal connected to the second photodiode; Equipped with after multiplexing the output light from the first optical phase modulator and the output light from the second optical phase modulator, demultiplexing the multiplexed light, and outputting the demultiplexed light to the first photodiode and the second photodiode, respectively; The photodiode is A first photodiode; a second photodiode having a cathode connected to the anode of the first photodiode; Including, The heterodyne detection signal is output from a connection point between the first photodiode and the second photodiode to the optical intensity modulator.

5. An optical transmitter according to claim 1.

6. A first optical phase modulation step of phase-modulating an output light from a first laser diode based on a first electrical signal input to a first electrical signal input section; a second optical phase modulation step of phase-modulating output light from the second laser diode based on the second electrical signal input to the second electrical signal input section; a differentiation step of performing differentiation processing on the third electrical signal input to the third electrical signal input unit; a distribution step of distributing the third electrical signal, which has been subjected to the differentiation process in the differentiation step, into a fourth electrical signal and a fifth electrical signal; a phase shifting step of shifting the fifth electrical signal by 180 degrees; a first input step of inputting the fourth electrical signal distributed by the distribution step to a drive current input terminal of the first laser diode; a second input step of inputting the fifth electrical signal, the phase of which has been shifted by 180 degrees in the phase shift step, to a drive current input terminal of the second laser diode; an optical combining step of combining the output light phase-modulated in the first optical phase modulation step and the output light phase-modulated in the second optical phase modulation step; a conversion step of converting the output light multiplexed by the optical multiplexing step into a heterodyne detection signal; a light intensity modulating step of intensity modulating an output light from a third laser diode based on the heterodyne detection signal; A transmission method comprising:

7. A first optical phase modulation step of phase-modulating an output light from a first laser diode based on a first electrical signal input to a first electrical signal input section; a second optical phase modulation step of phase-modulating output light from the second laser diode based on the second electrical signal input to the second electrical signal input section; a distribution step of distributing the third electrical signal input to the third electrical signal input unit into a fourth electrical signal and a fifth electrical signal; a first differentiation step of performing differentiation processing on the fourth electrical signal distributed by the distribution step and outputting the resultant signal to a drive current input terminal of the first laser diode; a second differentiation step of performing differentiation processing on the fifth electrical signal distributed by the distribution step and outputting the resultant signal; a phase shifting step of shifting the phase of the fifth electrical signal, which has been subjected to the differentiation process in the second differentiation step, by 180 degrees and outputting the fifth electrical signal to a drive current input terminal of the second laser diode; an optical combining step of combining the output light phase-modulated in the first optical phase modulation step and the output light phase-modulated in the second optical phase modulation step; a conversion step of converting the output light multiplexed by the optical multiplexing step into a heterodyne detection signal; a light intensity modulating step of intensity modulating an output light from a third laser diode based on the heterodyne detection signal; A transmission method comprising:

8. a first optical phase modulation step of phase-modulating an output light from a first laser diode based on a first electrical signal input to a first electrical signal input section; a second optical phase modulation step of phase-modulating output light from the second laser diode based on the second electrical signal input to the second electrical signal input section; a distribution step of distributing the third electrical signal input to the third electrical signal input unit into a fourth electrical signal and a fifth electrical signal; a first differentiation step of performing differentiation processing on the fourth electrical signal distributed by the distribution step and outputting the resultant signal to a drive current input terminal of the first laser diode; a phase shifting step of shifting the fifth electrical signal by 180 degrees; a second differentiation step of differentiating the fifth electrical signal, the fifth electrical signal having a phase shift of 180 degrees in the phase shift step, and outputting the result to a drive current input terminal of the second laser diode; an optical combining step of combining the output light phase-modulated in the first optical phase modulation step and the output light phase-modulated in the second optical phase modulation step; a conversion step of converting the output light multiplexed by the optical multiplexing step into a heterodyne detection signal; a light intensity modulating step of intensity modulating an output light from a third laser diode based on the heterodyne detection signal; A transmission method comprising:

9. in the optical multiplexing step, the output light phase-modulated by the first optical phase modulation step and the output light phase-modulated by the second optical phase modulation step are multiplexed, and then the multiplexed light is demultiplexed, and the demultiplexed light is outputted to a first photodiode and a second photodiode having a cathode connected to an anode of the first photodiode, respectively; In the conversion step, the heterodyne detection signal is output from a connection point between the first photodiode and the second photodiode. A transmission method according to any one of claims 6 to 8.

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