Modulator and modulation method

Abstract

Achieving high-frequency modulation with low distortion. [Solution] A modulator comprising: an upper sideband generation unit that generates a signal having an upper sideband component based on a carrier signal and a transmission signal to be transmitted or a transmission signal on which a predetermined calculation has been performed; a lower sideband generation unit that generates a signal having a lower sideband component based on a carrier signal and a transmission signal or a transmission signal on which a predetermined calculation has been performed; and a combined unit that combines the carrier signal, a signal having an upper sideband component, and a signal having a lower sideband component.

Description

Technical Field

[0001] The present invention relates to a modulator and a modulation method.

Background Art

[0002] Conventionally, an Armstrong modulator has been used as a modulator (see, for example, Non-Patent Document 1). The Armstrong modulator gives a displacement to the phase or frequency of a carrier wave with a simple configuration. That is, the Armstrong modulator performs phase modulation or frequency modulation. FIG. 10 is a diagram showing a configuration example of a conventional modulator. The modulator shown in FIG. 10 is an example in which an Armstrong modulator is configured as a phase modulator. When the Armstrong modulator is configured as a frequency modulator, the modulator includes an integrator.

[0003] The modulator shown in FIG. 10 distributes the carrier signal output from the oscillator into two, and outputs it to the amplifier and the balanced modulator. The amplifier amplifies the input carrier signal and then outputs it to the mixer. The balanced modulator obtains a lower sideband wave and an upper sideband wave by multiplying the input carrier signal by the modulation signal. The phase of the lower sideband wave and the upper sideband wave obtained by the balanced modulator is adjusted by an n / 2 phase shifter. For example, the n / 2 phase shifter adjusts so that the phase of the upper sideband wave is 0° and the phase of the lower sideband wave is 180° compared with the carrier signal output from the amplifier, and then outputs it to the mixer. The mixer obtains a modulated wave signal by synthesizing the carrier signal output from the amplifier and the upper sideband wave and the lower sideband wave whose phases are adjusted by the n / 2 phase shifter.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

[0005] The spectrum of the modulated wave signal obtained by frequency modulation or phase modulation in the above-mentioned modulator has a bandwidth of more than twice that of the spectrum of the input modulated signal (for example, from the lower limit of the lower sideband to the upper limit of the upper sideband). Therefore, as the input modulated signal becomes higher frequency, it becomes necessary to adjust the phase of both sidebands in the phase shifter after the output of the balanced modulator (multiplier) so that the phase relationship of the mixer output is satisfied over a very wide bandwidth from the lower sideband to the upper sideband. However, when the modulated signal becomes high frequency, it is difficult to adjust the phase with high precision over a wide bandwidth in the π / 2 phase shifter. As a result, the phase of the sideband components after synthesis in the mixer deviates from the ideal state. In this case, the signal becomes distorted, and the signal quality deteriorates. Thus, conventionally, there has been a problem in that it is difficult to achieve high-frequency modulation with low distortion.

[0006] In view of the above circumstances, the present invention aims to provide a technology that can achieve high-frequency modulation with low distortion. [Means for solving the problem]

[0007] One aspect of the present invention is a modulator comprising: a carrier signal; an upper sideband generation unit that generates a signal having an upper sideband component based on a transmission signal to be transmitted or the transmission signal on which a predetermined calculation has been performed; a lower sideband generation unit that generates a signal having a lower sideband component based on the carrier signal and the transmission signal or the transmission signal on which a predetermined calculation has been performed; and a combined unit that combines the carrier signal, the signal having the upper sideband component, and the signal having the lower sideband component.

[0008] One aspect of the present invention is a modulation method that generates a signal having an upper sideband component based on a carrier signal and a transmission signal to be transmitted or the transmission signal on which a predetermined operation has been performed; generates a signal having a lower sideband component based on the carrier signal and the transmission signal or the transmission signal on which a predetermined operation has been performed; and combines the carrier signal, the signal having the upper sideband component, and the signal having the lower sideband component. [Effects of the Invention]

[0009] This invention makes it possible to achieve high-frequency modulation with low distortion. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example configuration of an optical transmission system equipped with a modulator according to the present invention. [Figure 2] This figure shows an example of the modulator configuration in the first embodiment. [Figure 3] This is a flowchart showing the processing flow of the modulator in the first embodiment. [Figure 4] This figure shows an example of the modulator configuration in the second embodiment. [Figure 5] This is a flowchart showing the processing flow of the modulator in the second embodiment. [Figure 6] This figure shows an example of the modulator configuration in the fourth embodiment. [Figure 7] This is a flowchart showing the processing flow of the modulator in the fourth embodiment. [Figure 8] It is a diagram showing a configuration example of a modulator in the fifth embodiment. [Figure 9] It is a flowchart showing the processing flow of the modulator in the fifth embodiment. [Figure 10] It is a diagram showing a configuration example of a conventional modulator.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] (Overall Configuration) FIG. 1 is a diagram showing a configuration example of an optical transmission system 100 including a modulator according to the present invention. The optical transmission system 100 includes an optical transmitter 10, an optical relay device 20, and an optical receiver 30. In FIG. 1, the case where there is one optical relay device 20 is shown, but a plurality of optical relay devices 20 may be provided between the optical transmitter 10 and the optical receiver 30. Also, the number of optical transmitters 10 and optical receivers 30 included in the optical transmission system 100 may be plural.

[0013] The optical transmitter 10 transmits an optical signal. The optical transmitter 10 includes a modulator 11, a light source 12, and an optical modulation unit 13. The modulator 11 phase-modulates or frequency-modulates the input transmission signal. The light source 12 outputs light of a predetermined wavelength. The optical modulation unit 13 generates an optical signal by modulating the light output from the light source 12 using the transmission signal phase-modulated or frequency-modulated by the modulator 11.

[0014] The optical relay device 20 inputs the optical signal transmitted from the optical transmitter 10, performs processing such as amplification or distribution on the input optical signal, and transfers it to the subsequent optical relay device 20 or optical receiver 30.

[0015] The optical receiver 30 demodulates the modulation signal obtained after converting the optical signal transferred from the optical relay device 20 into an electrical signal.

[0016] The optical relay device 20 and the optical receiver device 30 may be the same devices as the V-OLT and V-ONT described in, for example, Reference 1 below. (Reference 1: “SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS”, ITU-T J.185, June 2012)

[0017] In the present invention, the modulator 11 included in the optical transmitter device 10 has a configuration for realizing high-frequency modulation with low distortion. Hereinafter, the specific configuration of the modulator 11 of the present invention will be described.

[0018] (First Embodiment) In the first embodiment, the configuration when the modulator 11 is used as a phase modulator will be described. FIG. 2 is a diagram showing a configuration example of the modulator 11 in the first embodiment. The modulator 11 includes a carrier signal generation unit 111, a distribution unit 112, a distribution unit 113, a distribution unit 114, an upper sideband generation unit 115, a lower sideband generation unit 116, a multiplexing unit 117, and a multiplexing unit 118.

[0019] The carrier signal generation unit 111 generates and outputs a carrier signal (unmodulated). The distribution unit 112 inputs the carrier signal output by the carrier signal generation unit 111. The distribution unit 112 distributes the input carrier signal. For example, the distribution unit 112 distributes the input carrier signal into two. In this case, the distribution unit 112 distributes the carrier signal to the first path and the second path. The multiplexing unit 118 is connected to the first path distributed by the distribution unit 112, and the distribution unit 113 is connected to the second path distributed by the distribution unit 112. Therefore, the carrier signal distributed by the distribution unit 112 is input to the distribution unit 113 and the multiplexing unit 118.

[0020] The distribution unit 113 receives the carrier signal distributed by the distribution unit 112. The distribution unit 113 distributes the input carrier signal. For example, the distribution unit 113 divides the input carrier signal into two. In this case, the distribution unit 113 distributes the carrier signal to a first path and a second path. The upper sideband generation unit 115 is connected to the first path to which the distribution unit 113 distributes, and the lower sideband generation unit 116 is connected to the second path to which the distribution unit 113 distributes. Therefore, the carrier signal distributed by the distribution unit 113 is input to the upper sideband generation unit 115 and the lower sideband generation unit 116.

[0021] The distribution unit 114 receives a transmission signal from an external source. The transmission signal is the data signal (modulated signal) to be transmitted. The distribution unit 114 distributes the input transmission signal. For example, the distribution unit 114 distributes the input transmission signal into two paths. In this case, the distribution unit 114 distributes the transmission signal to a first path and a second path. The upper sideband generation unit 115 is connected to the first path to which the distribution unit 114 distributes, and the lower sideband generation unit 116 is connected to the second path to which the distribution unit 114 distributes. Therefore, the transmission signal distributed by the distribution unit 114 is input to the upper sideband generation unit 115 and the lower sideband generation unit 116.

[0022] The upper sideband generation unit 115 generates a signal having an upper sideband. For example, the upper sideband generation unit 115 generates a signal having the first upper sideband (hereinafter referred to as the "upper first sideband"). The upper sideband generation unit 115 comprises a multiplier unit 119, a filter 120, and a phase adjustment unit 121. The multiplier unit 119 multiplies the carrier signal distributed by the distribution unit 113 and the transmission signal distributed by the distribution unit 114. The filter 120 extracts (filters) a signal having the upper first sideband component from the signal obtained by the multiplier unit 119. The phase adjustment unit 121 adjusts the phase of the signal having the upper first sideband component extracted by the filter 120.

[0023] The phase adjustment method used by the phase adjustment unit 121 can be any method. For example, the phase adjustment method used by the phase adjustment unit 121 may be a phase shifter, a delay unit, or a method of adjusting the wiring path length. The multiplier unit 119, the filter 120, and the phase adjustment unit 121 are each an embodiment of the first multiplier unit, the first filter, and the first phase adjustment unit, respectively.

[0024] The lower sideband generation unit 116 generates a signal having a lower sideband. For example, the lower sideband generation unit 116 generates a signal having the first lower sideband (hereinafter referred to as the "lower first sideband"). The lower sideband generation unit 116 comprises a multiplier unit 122, a filter 123, and a phase adjustment unit 124. The multiplier unit 122 multiplies the carrier signal distributed by the distribution unit 113 and the transmission signal distributed by the distribution unit 114. The filter 123 extracts (filters) a signal having the lower first sideband component from the signal obtained by the multiplier unit 122. The phase adjustment unit 124 adjusts the phase of the signal having the lower first sideband component extracted by the filter 123.

[0025] The phase adjustment method used by the phase adjustment unit 124 can be any method. For example, the phase adjustment method used by the phase adjustment unit 124 may be a phase shifter, a delay unit, or a method of adjusting the wiring path length. The multiplier unit 122, the filter 123, and the phase adjustment unit 124 are each an embodiment of the second multiplier unit, the second filter, and the second phase adjustment unit, respectively.

[0026] In the phase adjustment unit 121 and the phase adjustment unit 124, the phases of the signals having the upper first sideband component and the lower first sideband component are adjusted so that the phase of the carrier signal output from the distribution unit 112 to the multiplexing unit 118 is in phase with the phase of the signal having the upper first sideband component, and the phases of the signals having the lower first sideband component are out of phase (180° phase difference) with the phase of the carrier signal and the phase of the signal having the upper first sideband component.

[0027] The wave combining unit 117 combines the upper first sideband generated by the upper sideband generation unit 115 with the lower first sideband generated by the lower sideband generation unit 116.

[0028] The combined wave unit 118 combines the carrier signal output from the distribution unit 112 with the combined wave signal combined by the combined wave unit 117.

[0029] (operation) Figure 3 is a flowchart showing the processing flow of the modulator 11 in the first embodiment. Note that the order in which the processes from step S101 to step S103 and the process in step S104 shown in Figure 3 are performed is not particularly limited. The carrier signal generation unit 111 generates a carrier signal (step S101). The carrier signal generation unit 111 outputs the generated carrier signal to the distribution unit 112. The distribution unit 112 distributes the carrier signal output from the carrier signal generation unit 111 to the distribution unit 113 and the multiplexing unit 118 (step S102). The distribution unit 113 distributes the carrier signal distributed by the distribution unit 112 to the upper sideband generation unit 115 and the lower sideband generation unit 116 (step S103). The distribution unit 114 receives a transmission signal from an external source. The distribution unit 114 distributes the input transmission signal to the upper sideband generation unit 115 and the lower sideband generation unit 116 (step S104).

[0030] The upper sideband generation unit 115 generates an upper first sideband based on the carrier signal distributed by the distribution unit 113 and the transmission signal distributed by the distribution unit 114 (step S105). Specifically, the multiplication unit 119 of the upper sideband generation unit 115 multiplies the carrier signal distributed by the distribution unit 113 and the transmission signal distributed by the distribution unit 114. This generates an upper sideband and a lower sideband with respect to the center frequency of the carrier signal. For example, an upper first sideband component and a lower first sideband component are generated with respect to the center frequency of the carrier signal. The filter 120 extracts only the upper first sideband component from the generated upper first sideband component and lower first sideband component. The phase adjustment unit 121 then adjusts the phase of the signal having the extracted upper first sideband component to conform to the above-described relationship. Specifically, the phase adjustment unit 121 adjusts the phase of the signal having the upper first sideband component so that its phase is in the same phase as the carrier signal output from the distribution unit 112 to the multiplexing unit 118. The phase adjustment unit 121 outputs the phase-adjusted upper first sideband component to the multiplexing unit 117.

[0031] The lower sideband generation unit 116 generates a lower first sideband based on the carrier signal distributed by the distribution unit 113 and the transmission signal distributed by the distribution unit 114 (step S106). Specifically, the multiplication unit 122 of the lower sideband generation unit 116 multiplies the carrier signal distributed by the distribution unit 113 and the transmission signal distributed by the distribution unit 114. This generates an upper sideband and a lower sideband with respect to the center frequency of the carrier signal. For example, an upper first sideband component and a lower first sideband component are generated with respect to the center frequency of the carrier signal. The filter 123 extracts only the lower first sideband component from the generated upper first sideband component and lower first sideband component. Then, the phase adjustment unit 124 adjusts the phase of the signal having the extracted lower first sideband component to conform to the above-described relationship. Specifically, the phase adjustment unit 124 adjusts the phase of the signal having the lower first sideband component so that the phase of the signal having the lower first sideband component is in opposite phase (180° phase difference) to the phase of the carrier signal output from the distribution unit 112 to the multiplexing unit 118 and the phase of the signal having the upper first sideband component. The phase adjustment unit 124 outputs the phase-adjusted lower first sideband component to the multiplexing unit 117.

[0032] The combined wave unit 117 combines the phase-adjusted upper first sideband component output from the upper sideband generation unit 115 with the phase-adjusted lower first sideband component output from the lower sideband generation unit 116 (step S106). This generates upper and lower sidebands. The combined wave unit 117 outputs the combined signal (upper and lower sidebands) to the combined wave unit 118. The combined wave unit 118 combines the carrier signal output from the distribution unit 112 with the combined signal (upper and lower sidebands) output from the combined wave unit 117 (step S107).

[0033] According to the modulator 11 configured as described above, the modulator 11 includes an upper sideband generation unit 115 that generates a signal having an upper sideband component based on a carrier signal and a transmission signal to be transmitted, a lower sideband generation unit 116 that generates a signal having a lower sideband component based on a carrier signal and a transmission signal, and a combined unit 118 that combines the carrier signal, the signal having an upper sideband component, and the signal having a lower sideband component.

[0034] Thus, the modulator 11 generates the upper and lower sidebands separately, compared to conventional designs. This allows the corresponding frequency range in each phase adjustment section to be limited to the respective sideband frequencies. Therefore, even when the transmitted signal is high frequency, it becomes possible to precisely match the phases of the signals with each signal component at the output of the combiner 118. As a result, high-frequency modulation can be achieved with low distortion.

[0035] (Second embodiment) In the second embodiment, the configuration when modulator 11 is used as a frequency modulator will be described. Figure 4 shows an example of the configuration of modulator 11a in the second embodiment. Modulator 11a includes a carrier signal generation unit 111, a distribution unit 112, a distribution unit 113, a distribution unit 114, an upper sideband generation unit 115, a lower sideband generation unit 116, a multiplexing unit 117, a multiplexing unit 118, an integrator 125, and an integrator 126. Modulator 11a differs from modulator 11 in that it includes integrators 125 and 126. The following will focus on the differences from modulator 11.

[0036] In modulator 11a, an integrator 125 is provided between the multiplier 119 and the distributor 114, and an integrator 126 is provided between the multiplier 122 and the distributor 114, thereby enabling it to function as a frequency modulator.

[0037] The integrator 125 integrates the transmission signals distributed by the distribution unit 114 and outputs the integrated transmission signal to the multiplication unit 119 of the upper sideband generation unit 115.

[0038] The integrator 126 integrates the transmission signals distributed by the distribution unit 114 and outputs the integrated transmission signal to the multiplication unit 122 of the lower sideband generation unit 116.

[0039] (operation) Figure 5 is a flowchart showing the processing flow of the modulator 11a in the second embodiment. Note that the order in which the processes from step S101 to step S103 and from step S201 to step S202 shown in Figure 5 are performed is not particularly limited. In Figure 5, processes similar to those in Figure 3 are denoted by the same reference numerals as in Figure 3 and their explanation is omitted.

[0040] The distribution unit 114 receives a transmission signal from an external source. The distribution unit 114 distributes the input transmission signal to integrator 125 and integrator 126 (step S201). Integrators 125 and 126 integrate the input transmission signal and output the result to multiplier 119 and multiplier 122 (step S202).

[0041] The upper sideband generation unit 115 generates an upper first sideband based on the carrier signal distributed by the distribution unit 113 and the transmission signal integrated by the integrator 125 (step S203). Specifically, the multiplication unit 119 of the upper sideband generation unit 115 multiplies the carrier signal distributed by the distribution unit 113 and the transmission signal integrated by the integrator 125. This generates an upper sideband and a lower sideband with respect to the center frequency of the carrier signal. For example, an upper first sideband component and a lower first sideband component are generated with respect to the center frequency of the carrier signal. The filter 120 extracts only the upper first sideband component from the generated upper first sideband component and lower first sideband component. The phase adjustment unit 121 then adjusts the phase of the signal having the extracted upper first sideband component to conform to the above-described relationship. Specifically, the phase adjustment unit 121 adjusts the phase of the signal having the upper first sideband component so that the phase of the carrier signal output from the distribution unit 112 to the multiplexing unit 118 is in phase with the phase of the signal having the upper first sideband component. The phase adjustment unit 121 outputs the phase-adjusted upper first sideband component to the multiplexing unit 117.

[0042] The lower sideband generation unit 116 generates a lower first sideband based on the carrier signal distributed by the distribution unit 113 and the transmission signal integrated by the integrator 126 (step S204). Specifically, the multiplication unit 122 of the lower sideband generation unit 116 multiplies the carrier signal distributed by the distribution unit 113 and the transmission signal integrated by the integrator 126. This generates an upper sideband and a lower sideband with respect to the center frequency of the carrier signal. For example, an upper first sideband component and a lower first sideband component are generated with respect to the center frequency of the carrier signal. The filter 123 extracts only the lower first sideband component from the generated upper first sideband component and lower first sideband component. Then, the phase adjustment unit 124 adjusts the phase of the signal having the extracted lower first sideband component to conform to the above-described relationship. Specifically, the phase adjustment unit 124 adjusts the phase of the signal having the lower first sideband component so that the phase of the signal having the lower first sideband component is in opposite phase (a phase difference of 180°) to the phase of the carrier signal output from the distribution unit 112 to the multiplexing unit 118 and the phase of the signal having the upper first sideband component. The phase adjustment unit 124 outputs the phase-adjusted lower first sideband component to the multiplexing unit 117. After that, the processing from step S107 onwards is executed.

[0043] With the modulator 11a configured as described above, it is possible to obtain the same effects as in the first embodiment even in a modulator that functions as a frequency modulator.

[0044] (modified version) In the embodiments described above, the integration process (the integration process performed by integrators 125 and 126) may be replaced with other processes such as addition, if mathematically equivalent results can be obtained instead of integration.

[0045] (Third embodiment) In the first and second embodiments, the case in which the carrier signal generated by the carrier signal generation unit is unmodulated was described. In contrast, the third embodiment describes a configuration in which the carrier signal generated by the carrier signal generation unit is used as a modulated signal.

[0046] The modulator configuration in the third embodiment is the modulator 11 in the first embodiment or the modulator 11a in the second embodiment. The difference from the first and second embodiments is that the carrier signal generated by the carrier signal generation unit 111 is a modulated signal. Other processing is the same as in the first or second embodiment.

[0047] As described above, by not specifically limiting the carrier signal generated by the carrier signal generation unit 111 to unmodulated, it becomes possible to use it as a community channel.

[0048] (Fourth embodiment) In the fourth embodiment, an alternative configuration in which modulator 11 is used as a phase modulator will be described. Figure 6 shows an example of the configuration of modulator 11b in the fourth embodiment. Modulator 11b includes a carrier signal generation unit 111, a distribution unit 112, a distribution unit 113b, an upper sideband generation unit 115b, a lower sideband generation unit 116b, a multiplexing unit 117, a multiplexing unit 118, and a multiplication unit 130b. Modulator 11b differs from modulator 11 in that it includes a distribution unit 113b, an upper sideband generation unit 115b, and a lower sideband generation unit 116b instead of a distribution unit 113, an upper sideband generation unit 115, and a lower sideband generation unit 116, it does not include a distribution unit 114, and it newly includes a multiplication unit 130b. The differences from modulator 11 will be explained below.

[0049] The multiplier 130b multiplies the carrier signal distributed by the distribution unit 112 with the transmission signal input to the modulator 11b. This generates upper and lower sidebands with respect to the center frequency of the carrier signal. For example, an upper first sideband component and a lower first sideband component are generated with respect to the center frequency of the carrier signal. Therefore, the signal obtained by the multiplier 130b (hereinafter referred to as the "multiplied signal") will include an upper first sideband component and a lower first sideband component.

[0050] The distribution unit 113b receives the multiplied signal obtained by the multiplication unit 130b. The distribution unit 113b distributes the input multiplied signal. For example, the distribution unit 113b distributes the input multiplied signal into two paths. In this case, the distribution unit 113b distributes the multiplied signal to a first path and a second path. The upper sideband generation unit 115b is connected to the first path to which the distribution unit 113b distributes, and the lower sideband generation unit 116b is connected to the second path to which the distribution unit 113b distributes. Therefore, the multiplied signal distributed by the distribution unit 113b is input to the upper sideband generation unit 115b and the lower sideband generation unit 116b.

[0051] As described above, the multiplied signal contains components of both the upper first sideband and the lower first sideband. Therefore, the distribution unit 113b needs to distribute a high-frequency signal that includes both the upper first sideband and the lower first sideband. Thus, the distribution unit 113b is required to have high-frequency, wideband characteristics.

[0052] The upper sideband generation unit 115b generates a signal having an upper sideband. For example, the upper sideband generation unit 115b generates a signal having an upper first sideband. The upper sideband generation unit 115b includes a filter 120 and a phase adjustment unit 121. Thus, the upper sideband generation unit 115b does not include a multiplication unit 119. The filter 120 extracts (filters) a signal having an upper first sideband component from the multiplied signal distributed by the distribution unit 113b. The phase adjustment unit 121 adjusts the phase of the signal having an upper first sideband component extracted by the filter 120.

[0053] The lower sideband generation unit 116b generates a signal having a lower sideband. For example, the lower sideband generation unit 116b generates a signal having a lower first sideband. The lower sideband generation unit 116b includes a filter 123 and a phase adjustment unit 124. Thus, the lower sideband generation unit 116b does not include a multiplication unit 122. The filter 123 extracts (filters) a signal having a lower first sideband component from the multiplied signal distributed by the distribution unit 113b. The phase adjustment unit 124 adjusts the phase of the signal having a lower first sideband component extracted by the filter 123.

[0054] (operation) Figure 7 is a flowchart showing the processing flow of modulator 11b in the fourth embodiment. In Figure 7, the same reference numerals as in Figure 3 are used for processing as in Figure 3, and their explanation is omitted. After processing in step S101, the carrier signal generation unit 111 outputs the generated carrier signal to the distribution unit 112. The distribution unit 112 distributes the carrier signal output from the carrier signal generation unit 111 to the multiplier unit 130b and the multiplexer unit 118 (step S301). The multiplier unit 130b multiplies the carrier signal distributed by the distribution unit 112 with the transmission signal input from the outside (step S302). As a result, the multiplier unit 130b generates a multiplied signal that includes the upper first sideband component and the lower first sideband component. The multiplier unit 130b outputs the generated multiplied signal to the distribution unit 113b.

[0055] The distribution unit 113b distributes the multiplied signal output from the multiplier unit 130b to the upper sideband generation unit 115b and the lower sideband generation unit 116b (step S303). The upper sideband generation unit 115b generates an upper first sideband based on the multiplied signal distributed by the distribution unit 113b (step S304). As described above, the multiplied signal includes an upper first sideband component and a lower first sideband component. Therefore, the filter 120 of the upper sideband generation unit 115b extracts only the upper first sideband component from the upper first sideband component and the lower first sideband component included in the multiplied signal. Then, the phase adjustment unit 121 adjusts the phase of the signal having the extracted upper first sideband component. Specifically, the phase adjustment unit 121 adjusts the phase of the signal having the upper first sideband component so that its phase is in the same phase as the carrier signal output from the distribution unit 112 to the multiplexing unit 118. The phase adjustment unit 121 outputs the phase-adjusted upper first sideband component to the multiplexing unit 117.

[0056] The lower sideband generation unit 116b generates a lower first sideband based on the multiplied signal distributed by the distribution unit 113b (step S305). As described above, the multiplied signal includes an upper first sideband component and a lower first sideband component. Therefore, the filter 123 of the lower sideband generation unit 116b extracts only the lower first sideband component from the upper first sideband component and the lower first sideband component included in the multiplied signal. Then, the phase adjustment unit 124 adjusts the phase of the signal having the extracted lower first sideband component. Specifically, the phase adjustment unit 124 adjusts the phase of the signal having the lower first sideband component so that the phase of the signal having the lower first sideband component is in opposite phase (180° phase difference) to the phase of the carrier signal output from the distribution unit 112 to the multiplexing unit 118 and the phase of the signal having the upper first sideband component. The phase adjustment unit 124 outputs the lower first sideband component after phase adjustment to the multiplexing unit 117. Subsequently, steps S107 and S108 are executed.

[0057] The modulator 11b configured as described above includes a multiplier 130b between the distribution unit 112 and the distribution unit 113b. In the modulator 11 of the first embodiment, the carrier signal and the transmission signal were multiplied in the upper sideband generation unit 115 and the lower sideband generation unit 116, respectively, after distribution by the distribution unit 113. In contrast, in the modulator 11b of the fourth embodiment, the carrier signal and the transmission signal are multiplied before distribution by the distribution unit 113b. This reduces the number of multipliers and distribution units compared to the first embodiment. Therefore, it becomes possible to achieve high-frequency modulation with low distortion while keeping the equipment cost lower than that of modulator 11.

[0058] (Fifth embodiment) In the fifth embodiment, an alternative configuration in which modulator 11 is used as a frequency modulator will be described. Figure 8 shows an example of the configuration of modulator 11c in the fifth embodiment. modulator 11c comprises a carrier signal generation unit 111, a distribution unit 112, a distribution unit 113c, an upper sideband generation unit 115c, a lower sideband generation unit 116c, a multiplexing unit 117, a multiplexing unit 118, a multiplication unit 130c, and an integrator 131c. modulator 11c differs in configuration from modulator 11b in that it includes a distribution unit 113c instead of a distribution unit 113b, and newly includes an integrator 131c. The differences from modulator 11b will be explained below.

[0059] Modulator 11c functions as a frequency modulator by incorporating integrator 131c.

[0060] The integrator 131c integrates the input transmission signal and outputs the integrated transmission signal to the multiplier 130c.

[0061] The multiplier 130c multiplies the carrier signal distributed by the distribution unit 112 with the transmission signal integrated by the integrator 131c. This generates upper and lower sidebands with respect to the center frequency of the carrier signal. For example, an upper first sideband component and a lower first sideband component are generated with respect to the center frequency of the carrier signal. Therefore, the multiplied signal obtained by the multiplier 130c will contain an upper first sideband component and a lower first sideband component.

[0062] (operation) Figure 9 is a flowchart showing the processing flow of the modulator 11c in the fifth embodiment. The order in which steps S101 and S301 and step S401 are performed is not particularly limited. In Figure 9, processes similar to those in Figure 7 are denoted by the same reference numerals as in Figure 7, and their explanation is omitted.

[0063] The integrator 131c receives a transmission signal from an external source. The integrator 131c integrates the input transmission signal and outputs it to the multiplier 130c (step S401). In addition to the processing in step S401, the processing in steps S101 and S301 is performed. As a result, the multiplier 130c receives the carrier signal distributed by the distribution unit 112 and the transmission signal integrated by the integrator 131c.

[0064] The multiplier 130c multiplies the input carrier signal and the integrated transmission signal (step S402). As a result, the multiplier 130c generates a multiplied signal that includes the upper first sideband component and the lower first sideband component. The multiplier 130c outputs the generated multiplied signal to the distribution unit 113b. The distribution unit 113b distributes the multiplied signal output from the multiplier 130c to the upper sideband generation unit 115b and the lower sideband generation unit 116b (step S403). Subsequently, steps S304, S305, S107, and S108 are executed.

[0065] With the modulator 11c configured as described above, it is possible to obtain the same effects as in the fourth embodiment even in a modulator that functions as a frequency modulator.

[0066] (modified version) The integral process in the above-described embodiment (the integral process performed by the integrator 131c) may be replaced with other processes such as addition, if an approximately equivalent result can be obtained mathematically.

[0067] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention. [Explanation of Symbols]

[0068] 10…Optical transmitter, 20…Optical relay device, 30…Optical receiver, 11, 11a, 11b, 11c…Modulator, 12…Light source, 13…Optical modulation section, 111…Carrier signal generation section, 112, 113, 113b, 114…Distribution section, 115, 115b…Upper sideband generation section, 116, 116b…Lower sideband generation section, 117, 118…Multiplication section, 119, 122, 130b, 130c…Multiplication section, 120, 123…Filter, 121, 124…Phase adjustment section, 125, 126, 131c…Integrator

Claims

1. An upper sideband generation unit generates a signal having an upper sideband component based on a carrier signal and the transmission signal to be transmitted or the transmission signal on which predetermined calculations have been performed. A lower sideband generation unit generates a signal having a lower sideband component based on the carrier signal and the transmission signal or the transmission signal on which a predetermined calculation has been performed. A combiner unit that combines the carrier signal, the signal having the upper sideband component, and the signal having the lower sideband component, A modulator equipped with the following features.

2. The upper sideband wave generation unit is, A first multiplier unit that multiplies the carrier signal by the transmission signal or the transmission signal on which a predetermined calculation has been performed, A first filter extracts a signal having an upper sideband component from the multiplication result of the first multiplication unit, A first phase adjustment unit adjusts the phase of the signal having the upper sideband component extracted by the first filter, Equipped with, The lower band wave generation unit is, A second multiplier unit that multiplies the carrier signal by the transmission signal or the transmission signal on which a predetermined calculation has been performed, A second filter extracts a signal having a lower sideband component from the multiplication result of the second multiplier, A second phase adjustment unit adjusts the phase of the signal having the lower sideband component extracted by the second filter, Equipped with, The modulator according to claim 1.

3. A multiplication unit that multiplies the carrier signal by the transmission signal or the transmission signal on which a predetermined calculation has been performed, The system further comprises a distribution unit that distributes the multiplied signal obtained by the multiplication of the multiplication unit to the upper sideband generation unit and the lower sideband generation unit, The upper sideband wave generation unit is, A first filter extracts a signal having an upper sideband component from the multiplied signal distributed by the distribution unit, A first phase adjustment unit adjusts the phase of the signal having the upper sideband component extracted by the first filter, Equipped with, The lower band wave generation unit is, A second filter extracts a signal having a lower sideband component from the multiplied signal distributed by the distribution unit, A second phase adjustment unit adjusts the phase of the signal having the lower sideband component extracted by the second filter, Equipped with, The modulator according to claim 1.

4. The first phase adjustment unit is, The phase of the signal having the upper sideband component is adjusted so that the phase of the signal having the upper sideband component is in phase with the phase of the carrier signal. The second phase adjustment unit is, The phase of the signal having the lower sideband component is adjusted so that the phase of the signal having the lower sideband component is in opposite phase to the phase of the carrier signal and the phase of the signal having the upper sideband component. The modulator according to claim 2 or 3.

5. Based on the carrier signal and the transmission signal to be transmitted or the transmission signal on which predetermined calculations have been performed, a signal having an upper sideband component is generated. Based on the carrier signal and the transmission signal or the transmission signal on which a predetermined calculation has been performed, a signal having a lower sideband component is generated. The carrier signal, the signal having the upper sideband component, and the signal having the lower sideband component are combined. Modulation method.

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