Photoelectric conversion device

Abstract

This photoelectric conversion device is provided with: a first light source that outputs a plurality of light beams for generating a first electrical signal; a second light source that outputs a plurality of light beams for generating a second electrical signal; one or more phase adjustment circuits that adjust phases of the plurality of light beams output from at least the second light source such that the phases are different from phases of the plurality of light beams output from the first light source; and one or more photomixers that include at least a first photodiode to which the plurality of light beams output from the first light source and the plurality of light beams output from the second light source are input to generate an AC current, and a second photodiode to which the plurality of light beams output from the first light source and a plurality of light beams having phases adjusted by the one or more phase adjustment circuits are input to generate an AC current, the one or more photomixers generating one or more radio frequency signals on the basis of outputs from the first photodiode and the second photodiode.　

Description

Photoelectric conversion device

[0001] The present invention relates to a photoelectric conversion device.

[0002] The use of high frequency bands, above the millimeter wave band, is progressing as a means of achieving faster and larger capacity wireless communications. The spatial propagation loss of radio waves increases as the frequency increases. For example, free space propagation loss increases in proportion to the square of the frequency. For this reason, antennas with high gain are often used in high frequency bands. High gain antennas always have high directivity, so it is necessary to align the direction of their beam with the other station in the wireless communication. When the direction of the other station changes dynamically, a means of dynamically controlling the beam direction, i.e., the application of beam steering, becomes essential.

[0003] Beam steering in antennas is required not only for wireless communications but also for applications such as radar, imaging, and wireless power transmission. Various beam steering methods have been devised and used, including mechanically controlling the direction of the antenna and controlling the radio waves emitted from the antenna by refracting or reflecting them with a movable lens or reflector. Phased array antennas are widely used because they have high durability and movement tracking capabilities as they do not use mechanical moving parts, and are therefore suitable for miniaturization and weight reduction.

[0004] A phased array antenna performs electronic beam steering by controlling the phase and amplitude of an RF (Radio Frequency) signal fed to each antenna element using means such as a variable delay circuit, a variable attenuator circuit, or digital signal processing connected to multiple antenna elements arranged on a line or a surface. Hereinafter, controlling the phase and amplitude will be referred to as weighting.

[0005] Phased array antennas that use analog circuitry for weighting are widely used in fifth-generation mobile communication systems and millimeter-wave wireless LAN (Local Area Network) systems that use millimeter-wave bands. In many wireless communication systems, the range in which wireless communication partners exist varies not within a two-dimensional plane but within three-dimensional space, requiring beam steering along two axes, such as azimuth and elevation. Therefore, phased array antennas require weighting for two-dimensional beam steering using a two-dimensional array antenna in which multiple antenna elements are arranged in a plane.

[0006] Non-Patent Document 1 discloses a 256-element phased array antenna for use in a fifth-generation mobile communication base station in the 28 GHz band. For example, if the radio frequency increases by approximately 10 times, such as to 300 GHz, the propagation loss in free space increases by 100 times, and tens of thousands of antenna elements would be required. At a radio frequency of 300 GHz, the free-space wavelength is 1 mm, so the spacing between multiple antenna elements is typically half the wavelength, or 0.5 mm. In this case, it is difficult to install phase shifter circuits near the antenna elements at spacings equivalent to the spacing between the multiple antenna elements. Furthermore, to configure a circuit that forms multiple beams (a multi-beam forming circuit), it is necessary to arrange the same number of phase shifters in parallel as the number of beams, which is expected to be even more difficult.

[0007] Instead of implementing phase-shift circuits according to the number of antenna elements, there is a method of using a passive circuit with a fixed phase shift amount and switching the input terminal of the passive circuit. For example, Non-Patent Document 2 discloses a method of performing two-dimensional beam steering using a passive circuit. However, the circuit needs to be assembled three-dimensionally, and implementation in high-frequency bands requires a waveguide configuration, making mass production difficult and making it difficult to accommodate multiple elements.

[0008] Non-Patent Document 3 discloses a method of converting a signal into light and weighting it using an optical circuit. As a method of weighting it using an optical circuit, Patent Document 1 discloses a three-dimensional optical circuit that performs two-dimensional beam steering using a wavelength dispersion line. Non-Patent Document 4 discloses a method that uses a loop configuration in which a phase shifter is repeatedly reused while converting the optical wavelength. Non-Patent Document 5 discloses a means for performing two-dimensional beam steering by combining a planar phase shift circuit with an FBG (Fiber Bragg Grating) reflection line whose delay time varies depending on the optical wavelength, thereby enabling beam steering in a plane perpendicular to the plane performed by the FBG reflection line in addition to one-dimensional (within one plane) beam steering performed by the planar phase shift circuit.

[0009] However, with the above-disclosed devices and methods, as the frequency increases, it becomes difficult to manufacture a three-dimensional structure and the number of components becomes enormous. To realize a high-speed wireless transmission system utilizing high-frequency bands, a large number of antenna elements are required to obtain high antenna gain in order to compensate for the large spatial propagation loss. This results in high directivity and narrow beam widths, so two-dimensional fine beam scanning is required to accurately direct the beam toward the communicating wireless device. For a single base station to accommodate many terminal stations and to achieve higher frequency utilization efficiency in wireless communication, multi-beam communication, which simultaneously uses multiple beams each transmitting a different information stream, is effective. However, when realizing a circuit for controlling the multi-beam, it is also important to simplify and miniaturize the configuration.

[0010] Non-Patent Document 6 discloses a method for configuring a multi-beam control circuit that performs two-dimensional scanning using two phase-shift circuits for one-dimensional scanning, without using a complex and large-scale phase-shift circuit for two-dimensional scanning, in order to easily realize a phase-shift circuit for simultaneous scanning of multiple beams.

[0011] Japanese Patent Application Laid-Open No. 2004-023400

[0012] H. Watanabe, S. Uga, H. Nakamizo, T. Tsutsumi, S. Shinjo, and Y. Kuriyama, “Millimeter-Wave Antenna and RF Front-End Technology for 5th Generation Mobile Communication Base Stations,” IEICE Communications Society Magazine, 2020, Vol. 14, No. 3, pp. 222-231. Dong-Hun KIM, Jiro HIROKAWA, Makoto ANDO, “One-Body 2-D Beam-Switching Butler Matrix with Waveguide Short-Slot 2-Plane Couplers,” IEICE TRANSACTIONS on Electronics, Vol. E100-C, No. 10, pp. 884-892C. Tsokos et al., “Analysis of a Multibeam Optical Beamforming Network Based on Blass Matrix Architecture,” JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 36, NO. 16, AUGUST 15, 2018. Y. Liu and J. Klamkin, “Scalable Integrated Photonics Beamforming Circuits,” Asia Communications and Photonics Conference 2020, pp. 1-3. B. Ortega, J. Mora and R. Chulia, “Optical Beamformer for 2-D Phased Array Antenna With Subarray Partitioning Capability,” in IEEE Photonics Journal, vol. 8, no. 3, pp. 1-9, June 2016. Honoka Ito, Ken Hiraga, and Riichi Kudo, “Study on 2-D Beamforming Using Optical Phase Control,” IEICE Technical Report, vol. 123, pp. 13-17, May 11, 2023.

[0013] In the method described in Non-Patent Document 6, to simultaneously control multiple beams, the RF signals of each beam must be converted into optical signals with different frequencies. In this circuit, photoelectric conversion is performed to generate a radio signal using a "photomixing method," which generates an RF signal using the beat of two waves of light. To generate multiple RF signals, multiple pairs of two-wave light, each arranged in a different optical wavelength band, are input into a single photomixer, and multiple RF signals can be output from the photomixer. However, unnecessary RF components other than the desired frequency are also generated at the same time, which can cause problems such as interference with other wireless communications. The simplest way to prevent the generation of such unwanted RF components when generating RF signals from optical signals is to provide an RF filter circuit that passes only the desired frequency band.

[0014] However, when the wavelength multiplexing interval is small, unwanted RF components occur in frequency bands close to the desired frequency band. Therefore, a filter with a steep cutoff characteristic is required, which makes it difficult to configure such a filter circuit or increases the scale and size of the circuit. When configuring a circuit compatible with multiple RF bands, the passband of the RF filter circuit must be dynamically changed each time the RF band used is changed, which can greatly increase the likelihood of configuring and controlling such a circuit. Other than Non-Patent Document 6, there are few methods disclosed for inputting multiple optical wavelength-multiplexed signals into a photomixer to generate RF signals for multiple radio beams, and there are almost no documents disclosing methods for suppressing unwanted RF components in this process. Thus, conventional techniques have had the problem of being unable to suppress the generation of unwanted RF components with a simple circuit configuration.

[0015] In view of the above circumstances, an object of the present invention is to provide a technique capable of suppressing the generation of unnecessary RF components with a simple circuit configuration.

[0016] One aspect of the present invention is a photoelectric conversion device comprising: a first light source that outputs a plurality of light beams for generating a first electrical signal; a second light source that outputs a plurality of light beams for generating a second electrical signal; one or more phase adjustment circuits that adjust the phases of at least the plurality of light beams output from the second light source so that the phases of the plurality of light beams output from the first light source are different from the phases of the plurality of light beams output from the first light source; a first photodiode that receives the plurality of light beams output from the first light source and the plurality of light beams output from the second light source to generate an AC current; and a second photodiode that receives the plurality of light beams output from the first light source and the plurality of light beams whose phases have been adjusted by the one or more phase adjustment circuits to generate an AC current, and one or more photomixers that generate one or more radio frequency signals based on outputs from the first photodiode and the second photodiode.

[0017] According to the present invention, it is possible to suppress the generation of unnecessary RF components with a simple circuit configuration.

[0018] FIG. 1 is a diagram illustrating an example of the configuration of a conventional photoelectric conversion device; FIG. 2 is a diagram illustrating an example of light generated by an optical signal source; FIG. 3 is a diagram illustrating an example of an RF signal output by a photomixer; FIG. 4 is a diagram illustrating an example of the configuration of a conventional photoelectric conversion device; FIG. 5 is a diagram illustrating an example of the frequency of a pair of optical signal sources; FIG. 6 is a diagram illustrating an example of an RF signal output by a photomixer; FIG. 7 is a diagram illustrating an example of the configuration of a conventional photoelectric conversion device; ｗｄｍ 9 is a diagram showing an example of the frequencies of a pair of optical signal sources when the wavelength multiplexing interval (f ｗｄｍ ) is the RF frequency f ＲＦ24 is a diagram showing an example of the frequency of a pair of optical signal sources when the frequency is smaller than . FIG. 25 is a diagram showing an example of the configuration of a conventional photoelectric conversion device. FIG. 26 is a diagram showing an example of the configuration of a photoelectric conversion device according to the first embodiment. FIG. 27 is a diagram showing an example of an optical signal input to a photodiode. FIG. 28 is a diagram showing the relationship between each frequency component (RF component) and phase of an output AC current generated by a photodiode. FIG. 29 is a diagram for explaining the effect of the photoelectric conversion device according to the first embodiment. FIG. 29 is a diagram showing an example of an optical signal input to a photodiode. FIG. 29 is a diagram for explaining the effect of the photoelectric conversion device according to the second embodiment. FIG. 29 is a diagram showing an example of the configuration of a photoelectric conversion device according to the third embodiment. FIG. 29 is a diagram showing the configuration of a photomixer. FIG. 29 is a diagram showing an example of the configuration of a photoelectric conversion device according to the fourth embodiment. FIG. 29 is a diagram showing an example of the configuration of a photoelectric conversion device according to the fifth embodiment. FIG. 29 is a diagram showing an example of an optical signal and phase input to two photodiodes. FIG. 29 is a diagram showing an example of an output when the optical signal shown in FIG. 23 is input. FIG. 29 is a diagram showing an example of the configuration of a photoelectric conversion device according to the sixth embodiment. FIG. 29 is a diagram showing an example of the configuration of a photoelectric conversion device according to the seventh embodiment.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] (Problems with the Related Art) Before describing the configuration of the present invention, the problems with the related art will be described in detail. As an orthodox method for inputting a plurality of optical wavelength-multiplexed signals into a photomixer to generate RF signals of a plurality of radio beams, there is a technique of suppressing unnecessary RF components using an RF filter.

[0021] Fig. 1 is a diagram showing an example of the configuration of a conventional photoelectric conversion device 1. The photoelectric conversion device 1 includes an information signal source 10, multiple optical signal sources 11, and a photomixer 13. The photoelectric conversion device 1 includes two optical signal sources 11-1 and 11-2 as the multiple optical signal sources 11. The photoelectric conversion device 1 shown in Fig. 1 is the simplest form in which an RF signal is generated by photomixing.

[0022] The information signal source 10 outputs data to be transmitted to the optical signal source 11-2. The optical signal sources 11-1 and 11-2 each have a frequency f ＲＦAn example of the light generated by the optical signal sources 11-1 and 11-2 is shown in FIG. 2. The light from the optical signal source 11-2 is modulated by the information signal source 10, and the amplitude or phase, or both, of the light fluctuate over time in accordance with the information signal. The light output from the optical signal source 11-1 and the light output from the optical signal source 11-2 are multiplexed by a multiplexer (not shown) and input to the photomixer 13. The photomixer 13 outputs an RF signal, which is an electrical signal, based on the multiple input lights. An example of the RF signal output by the photomixer 13 is shown in FIG. 3. As shown in FIG. 3, the frequency of the RF signal output by the photomixer 13 is f ＲＦ In this specification, this f ＲＦ is called the desired RF component. When this photoelectric conversion device 1 is used in a wireless transmitter, the output of the photomixer 13 is radiated into space from a wireless transmission antenna via an RF amplifier or the like.

[0023] Next, a configuration in which a plurality of information signals are input to a single photomixer to generate a plurality of RF signals will be described. Fig. 4 is a diagram showing an example configuration of a conventional photoelectric conversion device 1a. The photoelectric conversion device 1a includes a plurality of information signal sources 10, a plurality of optical signal sources 11, and a photomixer 13. The photoelectric conversion device 1a includes two information signal sources 10-1 and 10-2 as the plurality of information signal sources 10, and four optical signal sources 11-1-1, 11-1-2, 11-2-1, and 11-2-2 as the plurality of optical signal sources 11.

[0024] 4, the light output from the pair of optical signal sources 11-1-1 and 11-1-2 and the light output from the pair of optical signal sources 11-2-1 and 11-2-2 are multiplexed by a multiplexer (not shown) and input to a photomixer 13. The pair of optical signal sources 11-1-1 and 11-1-2 are light sources that output multiple light waves (two or more waves) for generating a first radio beam. In the following description, the pair of optical signal sources 11-1-1 and 11-1-2 are described as light sources that output two waves of light. The pair of optical signal sources 11-2-1 and 11-2-2 are light sources that output multiple light waves for generating a second radio beam. In the following description, the pair of optical signal sources 11-2-1 and 11-2-2 are described as light sources that output two waves of light. The photomixer 13 outputs an RF signal, which is an electrical signal, based on the input light. The frequencies of the pair of optical signal sources 11-1-1 and 11-1-2 are f ＲＦ The frequencies of the pair of optical signal sources 11-2-1 and 11-2-2 are f ＲＦ Far away.

[0025] The frequencies of the optical signal sources 11-1-1 and 11-2-1 are f ｗｄｍ That is, the two optical signal pairs are separated by f ｗｄｍ In this specification, this optical frequency interval is called an optical wavelength multiplexing interval. An example of an RF signal output by the photomixer 13 is shown in FIG. 6. As shown in FIG. 6, in the same way as in FIG. 3, the frequency f ＲＦ In addition to generating an RF signal at frequency f ｗｄｍ -f ＲＦ , f ｗｄｍ , f ｗｄｍ +f ＲＦ ) are also generated. These RF components at other frequencies are undesired RF components and are referred to herein as undesired RF components.

[0026] The generation of unwanted RF components causes radio wave interference with other wireless communications, adversely affecting the speed, capacity, etc. of wireless communications. One example of a configuration for suppressing unwanted RF components is a photoelectric conversion device 1b that includes an RF filter 14 on the output side of a photomixer 13, as shown in FIG. 7. FIG. 7 is a diagram showing an example configuration of a conventional photoelectric conversion device 1b. The photoelectric conversion device 1b includes a plurality of information signal sources 10, a plurality of optical signal sources 11, a photomixer 13, and an RF filter 14. The photoelectric conversion device 1b has the same configuration as the photoelectric conversion device 1a, except for the addition of the RF filter 14.

[0027] The RF filter 14 is provided on the output side of the photomixer 13. The RF filter 14 passes only the frequency band of the desired RF component, or suppresses only the frequency band of the unwanted RF component. By providing the RF filter 14, the photoelectric conversion device 1b can suppress the unwanted RF component (frequency f ｗｄｍ -f ＲＦ , f ｗｄｍ , f ｗｄｍ +f ＲＦ ) output can be suppressed.

[0028] As shown in FIG. 9, the wavelength multiplexing interval f ｗｄｍ In FIG. 9, the wavelength multiplexing interval f ｗｄｍ is the RF frequency f ＲＦ 10 shows the RF signal output in this case. In the example shown in FIG. 10, unwanted RF components are generated in a frequency band closer to the desired RF component than in the case of FIG. 6. In particular, unwanted RF components (frequency f ｗｄｍ -f ＲＦ ) occurs, and it is assumed that it may be difficult to remove it with the RF filter 14.

[0029] Furthermore, as shown in FIG. 11, the wavelength multiplexing interval (f ｗｄｍ ) is the RF frequency f ＲＦIt is also assumed that the wavelength multiplexing interval f is smaller than the desired RF component. In many cases, it can be expected that unwanted RF components with frequencies higher than the desired RF component are unlikely to be generated due to the operating frequency limit of the photomixer 13. On the other hand, unwanted RF components with frequencies lower than the desired RF component cannot be expected to be suppressed due to the operating frequency limit characteristic of the photomixer 13, so an RF filter 14 with high suppression characteristics must be inserted. In this way, when the wavelength multiplexing interval f ｗｄｍ If is small, the frequency bands of the desired RF component and the unwanted RF component are close to each other, so an RF filter with steep frequency characteristics is required, which may make it difficult to configure such a filter circuit or may result in a large circuit scale or size.In addition, it may be possible that unwanted RF components are generated in all or part of the band of the RF signal, making it impossible to remove only the unwanted RF components using the RF filter 14.

[0030] Furthermore, when configuring a circuit compatible with multiple RF frequency bands by utilizing the ultra-wideband nature of RF generation in photomixing, it is necessary to dynamically change the passband of the RF filter circuit every time the RF band being used is changed, and it is highly anticipated that configuring and controlling such a circuit will be difficult.In addition, when configuring an array antenna in which many antenna elements are arranged at a narrow antenna pitch, such as in the millimeter wave band or terahertz band, it is desirable to place a photomixer directly below the antenna elements, but it is highly anticipated that placing an RF filter for each antenna element will be difficult from the perspective of mounting area size.

[0031] Therefore, a method is desired for suppressing unnecessary RF components without using the RF filter 14 or by using only an RF filter with a simple configuration (such an RF filter often does not have a steep frequency characteristic).

[0032] A conventional photoelectric conversion device 1a has the configuration shown in Fig. 12. Fig. 12 is a diagram showing an example of the configuration of the conventional photoelectric conversion device 1a. The photoelectric conversion device 1a includes a plurality of information signal sources 10, a plurality of optical signal sources 11, a multiplexer 15, and a photodiode 16. The photoelectric conversion device 1a includes two information signal sources 10-1 and 10-2 as the plurality of information signal sources 10, and four optical signal sources 11-1-1, 11-1-2, 11-2-1, and 11-2-2 as the plurality of optical signal sources 11.

[0033] The multiplexer 15 multiplexes the light beams output from the optical signal sources 11-1-1, 11-1-2, 11-2-1, and 11-2-2. The photodiode 16 generates RF signals of two radio beams based on the light multiplexed by the multiplexer 15. In the example shown in Fig. 12, the photoelectric conversion device 1a inputs the optical signals of the two radio beams to one photodiode 16 and performs photoelectric conversion using the high-frequency current flowing through the photodiode 16 as an output to generate RF signals of two radio beams. The RF signal of the first radio beam is generated at the difference frequency between the optical signal source 11-1-1 and the optical signal source 11-1-2, and the RF signal of the second radio beam is generated at the difference frequency between the optical signal source 11-2-1 and the optical signal source 11-2-2.

[0034] 13 is a diagram showing an example of the configuration of a photoelectric conversion device 100 according to the first embodiment. The photoelectric conversion device 100 includes a plurality of information signal sources 10, a plurality of optical signal sources 11, a plurality of photodiodes 16, a plurality of distributors 17, a phase inverter circuit 18, and a plurality of multiplexers 19. The photoelectric conversion device 100 includes two information signal sources 10-1 and 10-2 as the plurality of information signal sources 10, four optical signal sources 11-1-1, 11-1-2, 11-2-1, and 11-2-2 as the plurality of optical signal sources 11, two photodiodes 16-1 and 16-2 as the plurality of photodiodes 16, two distributors 17-1 and 17-2 as the plurality of distributors 17, and two multiplexers 19-1 and 19-2 as the plurality of multiplexers 19.

[0035] As shown in FIG. 13 , the photoelectric conversion device 100 generates an RF signal using two photodiodes 16. The photoelectric conversion device 100 photoelectrically converts the optical signals of two radio beams using the two photodiodes 16 to generate an RF signal of one radio beam. The RF signal of the first radio beam is generated at the difference frequency between the optical signal source 11-1-1 and the optical signal source 11-1-2, and the RF signal of the second radio beam is generated at the difference frequency between the optical signal source 11-2-1 and the optical signal source 11-2-2. An information signal to be transmitted in the radio beam may be superimposed on the optical signal. In this case, the light output from the optical signal source 11-1-2 in FIG. 13 may be modulated with the electrical signal output from the information signal source 10-1, and the light output from the optical signal source 11-2-2 may be modulated with the electrical signal output from the information signal source 10-2. The pair of optical signal source 11-1-1 and optical signal source 11-1-2 is one aspect of a first light source, and the pair of optical signal source 11-2-1 and optical signal source 11-2-2 is one aspect of a second light source.

[0036] In this embodiment, the two photodiodes 16-1 and 16-2 are arranged in a push-pull configuration. The photodiodes 16-1 and 16-2 form a photomixer that performs photoelectric conversion on input light and generates RF signals of one or more radio beams. The push-pull configuration in this embodiment refers to an arrangement in which two photodiodes 16-1 and 16-2 with opposite current directions are connected, as shown in FIG. 13, and the AC currents of the two photodiodes 16-1 and 16-2 are combined and extracted. In this manner, the push-pull configuration in this embodiment is such that one photodiode 16 injects (pushes) current into a load, while the other photodiode 16 draws (pulls) current from the load.

[0037] The distributor 17 distributes the input light. For example, distributor 17-1 multiplexes the light output from optical signal sources 11-1-1 and 11-1-2 and then distributes the result to multiplexers 19-1 and 19-2. For example, distributor 17-2 multiplexes the light output from optical signal sources 11-2-1 and 11-2-2 and then distributes the result to multiplexer 19-1 and phase inverter 18.

[0038] The phase inversion circuit 18 is connected to the distributor 17-2 and adjusts the phase of the light distributed by the distributor 17-2. The phase inversion circuit 18, for example, rotates the phase of the input light by 180°. In this way, the phase inversion circuit 18 adjusts the phase of the light by changing the phase of the input light. Note that in the following description, a configuration in which the phase inversion circuit 18 rotates the phase of the light by 180° will be described. However, the phase inversion circuit 18 may simply rotate the phase of the input light so that it is different from the phase of the light output from the optical signal sources 11-1-1 and 11-1-2. In other words, the phase inversion circuit 18 may make the phase of the input light not in phase with the phase of the light output from the optical signal sources 11-1-1 and 11-1-2, thereby suppressing the level of unwanted RF components to some extent. The phase inversion circuit 18 is one aspect of a phase adjustment circuit.

[0039] The multiplexer 19 multiplexes the multiple light beams output from the respective distributors 17. For example, the multiplexer 19-1 multiplexes the light beam output from the distributor 17-1 and the light beam output from the distributor 17-2, and outputs the multiplexed light to the photodiode 16-1. For example, the multiplexer 19-2 multiplexes the light beam output from the distributor 17-1 and the light beam whose phase has been inverted by the phase inversion circuit 18, and outputs the multiplexed light to the photodiode 16-2.

[0040] The photodiode 16 generates an RF signal of a radio beam by performing photoelectric conversion based on the input light, using a high-frequency current flowing through the photodiode 16 as an output. The photoelectric conversion device 100 in this embodiment includes two photodiodes 16. The optical signal of each radio beam is split into two and input to two photodiodes 16-1 and 16-2. Only the optical signal input to the photodiode 16-2 (the light output from the optical signal source 11-2-1 and the light output from the optical signal source 11-2-2) has its phase inverted via the phase inversion circuit 18.

[0041] The optical signal input to photodiode 16-1 is shown in the upper part of Fig. 14, and the optical signal input to photodiode 16-2 is shown in the lower part of Fig. 14. The light output from optical signal source 11-1-1 and optical signal source 11-1-2 is both input to photodiode 16-1 and photodiode 16-2 in phase with each other. The light output from optical signal source 11-2-1 and optical signal source 11-2-2 is both input to photodiode 16-1 and photodiode 16-2 in opposite phases with each other.

[0042] In such a case, the relationship between the phase and each frequency component (RF component) of the output AC current generated by each photodiode 16 is as shown in Fig. 15. Here, the property of photomixing described in Non-Patent Document 6 is utilized. The property of photomixing described in Non-Patent Document 6 is that the phase of the RF signal generated by each photodiode 16 (a relative value with a certain photodiode output RF signal as a reference) is the difference in phase between the two optical signals to be mixed.

[0043] First, the desired RF component will be described. ＲＦ The components are generated in the same phase by the two photodiodes 16. The reason why the phases of the RF signals generated by the two photodiodes 16 are the same even though the light output from optical signal source 11-2-1 and optical signal source 11-2-2 are input in opposite phases to the two photodiodes 16 is that the phase relationship between the optical signal sources 11-2-1 and 11-2-2 mixed in the two photodiodes 16 is the same.

[0044] Next, we will explain the unwanted RF component. For example, let us take a look at the mix of optical signal source 11-1-1 and optical signal source 11-2-1. If we take the phase of this unwanted RF component generated in photodiode 16-1 as a reference, this unwanted RF component generated in photodiode 16-2 will have an opposite phase to the unwanted RF component generated in photodiode 16-1, because it is generated by photomixing an optical signal that is in phase with optical signal source 11-1-1 and input to photodiode 16-1, and an optical signal that is out of phase with optical signal source 11-2-1 and input to photodiode 16-1. The same can be said for the three unwanted RF components generated by combinations of other optical signal components.

[0045] Returning to Fig. 13, the explanation will continue. When a configuration is adopted in which the RF currents generated in photodiodes 16-1 and 16-2 are combined as shown in the figure and input to a load (an antenna if a photoelectric conversion device is used in a wireless transmitter), the desired RF component is input to the load in phase, and the unwanted RF component is input to the load in opposite phase. Therefore, the current of the unwanted RF component is canceled, and the power of the unwanted RF component is not input to the load, as shown in Fig. 16.

[0046] According to the photoelectric conversion device 100 configured as described above, it is possible to suppress the generation of unnecessary RF components with a simple circuit configuration. Specifically, the photoelectric conversion device 100 includes a plurality of optical signal sources 11-1-1 and 11-1-2 that output two waves of light for generating a first radio beam, a plurality of optical signal sources 11-2-1 and 11-2-2 that output two waves of light for generating a second radio beam, a phase inversion circuit 18 that adjusts the phases of the two waves of light output from the plurality of optical signal sources 11-2-1 and 11-2-2 so that they are opposite in phase to the phases of the two waves of light output from the plurality of optical signal sources 11-1-1 and 11-1-2, and and a photomixer including at least a photodiode 16-1 that receives two waves of light output from the optical signal sources 11-1-1 and 11-1-2 and two waves of light output from the plurality of optical signal sources 11-2-1 and 11-2-2 to generate an AC current, and a photodiode 16-2 that receives two waves of light output from the plurality of optical signal sources 11-1-1 and 11-1-2 and two waves of light whose phases have been adjusted by a phase inversion circuit 18 to generate an AC current, and that generates one RF signal based on the outputs of the photodiodes 16-1 and 16-2.

[0047] This makes it possible to eliminate the need for an RF filter circuit on the photomixer output side to suppress the transmission of unwanted RF components in wireless communication devices that use photoelectric conversion to generate RF signals using the "photomixing method," which generates RF signals by beating two waves of light. Furthermore, a simpler circuit can be achieved, and the generation of unwanted RF components can be suppressed. Because the generation of unwanted RF components can be suppressed, interference with other wireless communications can be suppressed, and performance such as the speed and capacity of wireless communications can be improved.

[0048] Second Embodiment In the first embodiment, the difference frequency between the optical signal pair of the first radio beam and the optical signal pair of the second radio beam is the same. In the second embodiment, a difference frequency between the optical signal pair of the first radio beam and the optical signal pair of the second radio beam is different.

[0049] The configuration of the photoelectric conversion device 100 in the second embodiment is the same as that in the first embodiment. The following mainly describes the differences from the first embodiment. When configuring a wireless transmitter using the photoelectric conversion device 100, it is not often expected that multiple signals will be transmitted at the same frequency from a single antenna, but it is quite possible that two wireless signals to be transmitted on adjacent RF channels will be generated by separate pairs of optical signals, as shown in the second embodiment.

[0050] The photoelectric conversion device 100 according to the second embodiment generates RF signals of two radio beams by photoelectrically converting the optical signals of the two radio beams using a photodiode 116. The RF signal of the first radio beam has a difference frequency f between the optical signal source 11-1-1 and the optical signal source 11-1-2. ＲＦ The RF signal of the second radio beam is generated by the difference frequency f between the optical signal source 11-2-1 and the optical signal source 11-2-2. ＲＦ +Δf. This causes the frequency of the pair of optical signal sources 11-1-1 and 11-1-2 to be f ＲＦ The frequencies of the pair of optical signal sources 11-2-1 and 11-2-2 are f ＲＦ +Δf away.

[0051] 17 is input to the photodiode 16. When the frequency of the RF signal of the first radio beam is f ＲＦ The frequency of the RF signal of the second radio beam is generated at the difference frequency between the optical signal source 11-1-1 and the optical signal source 11-1-2. ＲＦ +Δf, which is generated at the difference frequency between the optical signal source 11-2-1 and the optical signal source 11-2-2. In the case where the present invention is not used, two desired RF components (f ＲＦ , f ＲＦ +Δf) and four unnecessary RF components (f ｗｄｍ , f ｗｄｍ -f ＲＦ , f ｗｄｍ +Δf, f ｗｄｍ +f ＲＦ ) (four) are output, but in the case of the present invention, the four unnecessary RF components are suppressed as shown in FIG.

[0052] According to the photoelectric conversion device 100 of the second embodiment configured as described above, the same effect as in the first embodiment can be obtained even when the difference frequency of the pair of optical signal sources 11-1-1 and 11-1-2 is different from the difference frequency of the pair of optical signal sources 11-2-1 and 11-2-2.

[0053] Third Embodiment In a third embodiment, a case where the present invention is used in a wireless transmitter having a multi-beam array antenna will be described.

[0054] 19 is a diagram showing an example configuration of a photoelectric conversion device 100a according to the third embodiment. The photoelectric conversion device 100a includes a plurality of information signal sources 10, a plurality of optical signal sources 11, a multi-beam weighting circuit 20, and a plurality of photomixers 24. The photoelectric conversion device 100a includes two information signal sources 10-1 and 10-2 as the plurality of information signal sources 10, four optical signal sources 11-1-1, 11-1-2, 11-2-1, and 11-2-2 as the plurality of optical signal sources 11, and four photomixers 24-1 to 24-4 as the plurality of photomixers 24. The photoelectric conversion device 100a differs in configuration from the photoelectric conversion device 100 according to the first embodiment in that it newly includes a plurality of photomixers 24 and a multi-beam weighting circuit 20. The following description will focus on the differences from the photoelectric conversion device 100 according to the first embodiment.

[0055] The photoelectric conversion device 100a is provided in a radio transmitter having a multi-beam array antenna connected to each of a plurality of photomixers 24. The radio transmitter forms a plurality of radio beams at the same RF frequency and transmits the beams via different multi-beam array antennas.

[0056] In the photoelectric conversion device 100a, the light sources for the first radio beam (optical signal sources 11-1-1 and 11-1-2) and the light sources for the second radio beam (optical signal sources 11-2-1 and 11-2-2) are each connected to a multi-beam weighting circuit 20. The multi-beam weighting circuit 20 applies a time delay to the input light, thereby weighting each radio beam with a different RF phase.

[0057] The multi-beam weighting circuit 20 is composed of a plurality of dividers 21, a plurality of phase shifters 22, and a plurality of combiners 23. The multi-beam weighting circuit 20 includes four dividers 21-1 to 21-4 as the plurality of dividers 21, sixteen phase shifters 22-1-1 to 22-1-4, 22-2-1 to 22-2-4, 22-3-1 to 22-3-4, and 22-4-1 to 22-4-4 as the plurality of phase shifters 22, and eight combiners 23-1 to 23-8 as the plurality of combiners 23. Hereinafter, when no particular distinction is made between phase shifters 22-1-1 to 22-1-4, they will be referred to as phase shifter 22-1, when no particular distinction is made between phase shifters 22-2-1 to 22-2-4, they will be referred to as phase shifter 22-2, when no particular distinction is made between phase shifters 22-3-1 to 22-3-4, they will be referred to as phase shifter 22-3, and when no particular distinction is made between phase shifters 22-4-1 to 22-4-4, they will be referred to as phase shifter 22-4.

[0058] The distributor 21 distributes the input light. Each distributor 21 distributes light in the same number as the number of antenna elements. For example, distributor 21-1 distributes the light output from optical signal source 11-1-1 to each phase shifter 22-1. For example, distributor 21-2 distributes the light output from optical signal source 11-1-2 to each phase shifter 22-2. For example, distributor 21-3 distributes the light output from optical signal source 11-2-1 to each phase shifter 22-3. For example, distributor 21-4 distributes the light output from optical signal source 11-2-2 to each phase shifter 22-4.

[0059] The phase shifter 22 imparts a time delay, a so-called true-time delay, to the input light that corresponds to the phase shift of the radio signal. For example, the phase shifter 22-1 imparts a time delay corresponding to the phase shift of the radio signal to the light divided by the divider 21-1. For example, the phase shifter 22-2 imparts a time delay corresponding to the phase shift of the radio signal to the light divided by the divider 21-2. For example, the phase shifter 22-3 imparts a time delay corresponding to the phase shift of the radio signal to the light divided by the divider 21-3. For example, the phase shifter 22-4 imparts a time delay corresponding to the phase shift of the radio signal to the light divided by the divider 21-4.

[0060] The multiplexer 23 multiplexes multiple light beams that have been time delayed by the phase shifter 22. The multiplexer 23-1 multiplexes the light beam that has been time delayed by the phase shifter 22-1-1 and the light beam that has been time delayed by the phase shifter 22-2-1, and outputs the result to the photomixer 24-1. The multiplexer 23-2 multiplexes the light beam that has been time delayed by the phase shifter 22-3-1 and the light beam that has been time delayed by the phase shifter 22-4-1, and outputs the result to the photomixer 24-1.

[0061] The multiplexer 23-3 multiplexes the light that has been time delayed by the phase shifter 22-1-2 and the light that has been time delayed by the phase shifter 22-2-2, and outputs the result to the photomixer 24-2. The multiplexer 23-4 multiplexes the light that has been time delayed by the phase shifter 22-3-2 and the light that has been time delayed by the phase shifter 22-4-2, and outputs the result to the photomixer 24-2.

[0062] The multiplexer 23-5 multiplexes the light that has been time delayed by the phase shifter 22-1-3 and the light that has been time delayed by the phase shifter 22-2-3, and outputs the result to the photomixer 24-3. The multiplexer 23-6 multiplexes the light that has been time delayed by the phase shifter 22-3-3 and the light that has been time delayed by the phase shifter 22-4-3, and outputs the result to the photomixer 24-3.

[0063] The multiplexer 23-7 multiplexes the light that has been time delayed by the phase shifter 22-1-4 and the light that has been time delayed by the phase shifter 22-2-4, and outputs the multiplexed signal to the photomixer 24-4. The multiplexer 23-8 multiplexes the light that has been time delayed by the phase shifter 22-3-4 and the light that has been time delayed by the phase shifter 22-4-4, and outputs the multiplexed signal to the photomixer 24-4.

[0064] The photomixers 24 photoelectrically convert the light multiplexed by each multiplexer 23 to generate an RF signal for a radio beam. The photomixer 24-1 generates an RF signal for a radio beam based on the light multiplexed by the multiplexer 23-1 and the light multiplexed by the multiplexer 23-2. The photomixer 24-2 generates an RF signal for a radio beam based on the light multiplexed by the multiplexer 23-3 and the light multiplexed by the multiplexer 23-4. The photomixer 24-3 generates an RF signal for a radio beam based on the light multiplexed by the multiplexer 23-5 and the light multiplexed by the multiplexer 23-6. The photomixer 24-4 generates an RF signal for a radio beam based on the light multiplexed by the multiplexer 23-7 and the light multiplexed by the multiplexer 23-8.

[0065] The specific configuration of the photomixer 24 will be described. FIG. 20 is a diagram showing the configuration of the photomixer 24. The photomixer 24 includes a plurality of photodiodes 16, a plurality of distributors 17, a phase inverter 18, a plurality of multiplexers 19, a plurality of input units 25, and an output unit 26. The plurality of photodiodes 16, a plurality of distributors 17, a phase inverter 18, and a plurality of multiplexers 19 included in the photomixer 24 perform the same processing as the functional units with the same names described in FIG. 13. The multi-beam weighting circuit 20 may be a matrix circuit. The phase shifter 22 may be configured to perform phase weighting in the optical domain. The photomixer 24 includes a plurality of input units 25, 25-1 and 25-2.

[0066] The input units 25-1 and 25-2 are connected to the output side of the multi-beam weighting circuit 20 and receive the light output from the multi-beam weighting circuit 20. The output unit 26 outputs the RF signal generated by the photomixer 24 to the antenna ANT.

[0067] According to the photoelectric conversion device 100a configured as above, it is possible to suppress unnecessary RF components.

[0068] Fourth Embodiment In a fourth embodiment, a configuration in which two photodiodes are connected in series will be described.

[0069] 21 is a diagram showing an example of the configuration of a photoelectric conversion device 100b according to the fourth embodiment. The photoelectric conversion device 100b includes a plurality of information signal sources 10 (not shown), a plurality of optical signal sources 11, a plurality of photodiodes 16, a plurality of distributors 17, a phase inverter 18, a plurality of multiplexers 19, and a plurality of CW light sources 27. The photoelectric conversion device 100b includes two optical signal sources 11-1 and 11-2 as the plurality of optical signal sources 11, two photodiodes 16-1 and 16-2 as the plurality of photodiodes 16, two distributors 17-1 and 17-2 as the plurality of distributors 17, two multiplexers 19-1 and 19-2 as the plurality of multiplexers 19, and two CW light sources 27-1 and 27-2 as the plurality of CW light sources 27.

[0070] 21, a CW light source 27-1 and an optical signal source 11-1 are connected to a splitter 17-1, and a CW light source 27-2 and an optical signal source 11-2 are connected to a splitter 17-2. Furthermore, in the photoelectric conversion device 100b, a photodiode 16-1 and a photodiode 16-2 are connected in series.

[0071] The CW light source 27 outputs continuous wave light. The distributor 17-1, for example, multiplexes the continuous wave light output from the CW light source 27-1 with the light output from the optical signal source 11-1, and then distributes the result to the multiplexers 19-1 and 19-2. The distributor 17-2, for example, multiplexes the continuous wave light output from the CW light source 27-2 with the light output from the optical signal source 11-2, and then distributes the result to the multiplexer 19-1 and the phase inverter 18.

[0072] According to the photoelectric conversion device 100b configured as above, even if the photodiodes 16-1 and 16-2 are connected in series, the same effects as those of the first embodiment can be obtained.

[0073] Fifth Embodiment In the above embodiments, the configuration in which the number of radio beams is two has been described. In contrast, the technique of the present invention can also be applied to cases in which the number of radio beams is three or more. Therefore, in the fifth embodiment, a case in which the number of multiplexed signals is three or more (three or more beams) will be described.

[0074] 22 is a diagram showing an example of the configuration of a photoelectric conversion device 100c according to the fifth embodiment. The photoelectric conversion device 100c includes a plurality of information signal sources 10 (not shown), a plurality of optical signal sources 11, a plurality of photodiodes 16, a plurality of distributors 17, a plurality of phase inverters 18, and a plurality of multiplexers 19. The photoelectric conversion device 100c includes eight optical signal sources 11-1-1, 11-1-2, 11-2-1, 11-2-2, 11-3-1, 11-3-2, 11-4-1, and 11-4-2 as the multiple optical signal sources 11, two photodiodes 16-1 and 16-2 as the multiple photodiodes 16, four dividers 17-1 to 17-4 as the multiple dividers 17, two phase inversion circuits 18-1 and 18-2 as the multiple phase inversion circuits 18, and two multiplexers 19-1 and 19-2 as the multiple multiplexers 19.

[0075] As shown in Fig. 22, when there are three or more beams, the phases of the optical signals input to the photodiode 16-2 are set so that the optical frequencies of adjacent beams are in opposite phases. For example, only the optical signals input to the photodiode 16-2 among the optical signals of the even-numbered radio beams are phase-inverted, and the optical signals and phases input to the two photodiodes 16 are set as shown in Fig. 23. The output in this configuration is as shown in Fig. 24. In Fig. 24, when the frequency is f ｗｄｍ +f ＲＦ The RF components exceeding this are not shown because they are of sufficiently high frequency and can be removed with a simple low-pass filter or due to the limiting characteristics of the operating speed of the photodiode.

[0076] The photoelectric conversion device 100c configured as described above can achieve the same effects as the first embodiment even when generating three or more beams. In particular, the photoelectric conversion device 100c controls the phases of adjacent optical signals to be opposite to each other. This makes it possible to suppress unnecessary RF components in the RF signal generated by the photoelectric conversion device 100c.

[0077] Sixth Embodiment In the sixth embodiment, dynamic control of the amount of phase shift based on the optical signal frequency will be described.

[0078] The optical wavelengths of the optical signal pairs corresponding to each radio beam are not necessarily assigned in a fixed manner, and the optical wavelengths assigned to the optical signal pairs for a certain radio beam may be dynamically changed. For example, the following cases may be assumed.

[0079] (When the optical wavelength is dynamically changed) (1) When the optical wavelength is changed due to the need for optical wavelength management in a radio on fiber (RoF) section outside the wireless transmitter device. (2) When the multi-beam weighting circuit 20 has optical wavelength dependency, and in order to minimize the impact on the quality of the wireless beam formed due to this dependency, the optical wavelength to be assigned is changed depending on the direction and communication distance of the wireless beam.

[0080] Therefore, in the sixth embodiment, this problem is solved by a photoelectric conversion device 100d as shown in Fig. 25. Fig. 25 is a diagram showing an example configuration of the photoelectric conversion device 100d according to the sixth embodiment. The photoelectric conversion device 100d includes a plurality of information signal sources 10 (not shown), a plurality of optical signal sources 11, a plurality of dividers 17, a plurality of phase inversion circuits 18, a phase adjustment control circuit 29, and a photomixer 30. The photoelectric conversion device 100d includes eight optical signal sources 11 as the plurality of optical signal sources 11, four dividers 17-1 to 17-4 as the plurality of dividers 17, and four phase inversion circuits 18-1 to 18-4 as the plurality of phase inversion circuits 18.

[0081] The eight optical signal sources 11 included in the photoelectric conversion device 100d are included in an optical wavelength information collection circuit 28. The optical wavelength information collection circuit 28 collects the frequencies of the optical signals output from each optical signal source 11. The optical wavelength information collection circuit 28 outputs the collected information on the frequencies of the optical signals output from each optical signal source 11 to a phase adjustment control circuit 29 as "optical wavelength information."

[0082] The phase adjustment control circuit 29 controls the phase rotation characteristics of each phase inverter 18 based on the optical wavelength information output from the optical wavelength information collection circuit 28, the number of radio beams (= number of optical signal pairs = number of wavelength multiplexing), the wavelength multiplexing interval, and other information. The phase adjustment control circuit 29 outputs information for controlling the phase rotation characteristics of the phase inverter 18-1 to the phase inverter 18-1 as first phase-shift setting information. Similarly, the phase adjustment control circuit 29 outputs information for controlling the phase rotation characteristics of the phase inverters 18-2 to 18-4 to the phase inverters 18-2 to 18-4 as second to fourth phase-shift setting information.

[0083] Each phase inversion circuit 18 rotates the phase of the input light based on the value indicated by the phase shift setting information output from the phase adjustment control circuit 29 .

[0084] According to the photoelectric conversion device 100d configured as above, even when the optical wavelength is dynamically changed, it is possible to suppress the generation of unnecessary RF components with a simple circuit configuration.

[0085] Seventh Embodiment In the seventh embodiment, dynamic control of the amount of phase shift depending on the generation state of unwanted RF components will be described.

[0086] 26 is a diagram showing an example of the configuration of a photoelectric conversion device 100e according to the seventh embodiment. The photoelectric conversion device 100e includes a plurality of information signal sources 10 (not shown), a plurality of optical signal sources 11, a photomixer 13, a plurality of dividers 17, a plurality of phase inversion circuits 18, a phase adjustment control circuit 29, a photomixer 30, and an unwanted RF component monitoring circuit 31. The photoelectric conversion device 100e includes eight optical signal sources 11 as the plurality of optical signal sources 11, four dividers 17-1 to 17-4 as the plurality of dividers 17, and four phase inversion circuits 18-1 to 18-4 as the plurality of phase inversion circuits 18.

[0087] The unwanted RF component monitoring circuit 31 monitors the level of unwanted RF components in the signal output from the output terminal of the photomixer 30. The unwanted RF component monitoring circuit 31 outputs the monitoring result to the phase adjustment control circuit 29 as "unwanted RF component information." The phase adjustment control circuit 29 controls the phase rotation characteristics of the four phase inverter circuits 18 based on the unwanted RF component information output from the unwanted RF component monitoring circuit 31. At this time, the phase adjustment control circuit 29 may perform control such that unwanted RF components that are difficult to suppress by an RF filter or antenna installed on the output side of the photomixer 30 are preferentially suppressed, for example, to minimize the level of the unwanted RF components. Note that this control may be combined with the control in the fifth embodiment.

[0088] The phase adjustment control circuit 29 outputs information for controlling the phase rotation characteristics of the phase inverter 18-1 based on the unwanted RF component information as first phase-shift setting information to the phase inverter 18-1. Similarly, the phase adjustment control circuit 29 outputs information for controlling the phase rotation characteristics of the phase inverters 18-2 to 18-4 based on the unwanted RF component information to the phase inverters 18-2 to 18-4 as second to fourth phase-shift setting information.

[0089] The photoelectric conversion device 100e configured as described above further includes an unwanted RF component monitoring circuit 31 that monitors the level of unwanted RF components in the signal output from the output terminal of the photomixer 30, and the phase adjustment control circuit 29 controls the phase rotation characteristics of the multiple phase inverter circuits 18 based on the unwanted RF component information output from the unwanted RF component monitoring circuit 31. This makes it possible to control the multiple phase inverter circuits 18 after grasping the level of unwanted RF components based on the actually generated RF signal. Therefore, it is possible to efficiently suppress unwanted RF components.

[0090] (Modifications of the First to Seventh Embodiments) In each of the above-described embodiments, the multiple optical signal sources 11 are used as light sources for forming radio beams, but the multiple optical signal sources 11 may be used for purposes other than forming radio beams. Therefore, the multiple optical signal sources 11 are light sources that output multiple light beams for generating at least electrical signals.

[0091] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0092] The present invention can be applied to a photoelectric conversion device that generates an RF signal by photomixing.

[0093] 10, 10-1 to 10-N... Information signal source, 11, 11-1-1, 11-1-2, 11-2-1, 11-2-2, 11-3-1, 11-3-2, 11-N-1, 11-N-2... Optical signal source, 16, 16-1 to 16-2... Photodiode, 17, 17-1 to 17-2, 21, 21-1 to 21-4... Distributor, 18, 18-1 to 18-4... Phase inversion circuit, 19, 19-1 to 19-2, 23, 23-1 to 23-8... Wave combiner, 20... Multi-beam weighting circuit, 22, 22-1-1 to 22-1-4, 22-2-1 to 22-2-4, 22-3-1 to 22-3-4, 22-4-1 to 22-4-4...phase shifter, 24, 24-1 to 24-4, 30...photomixer, 25, 25-1 to 25-2...input section, 26...output section, 27, 27-1 to 27-2...CW light source, 28...optical wavelength information collection circuit, 29...phase adjustment control circuit, 31...unwanted RF component monitoring circuit, 100, 100a, 100b, 100c, 100d, 100e...photoelectric conversion device

Claims

1. A first light source that outputs a plurality of lights for generating a first electrical signal, a second light source that outputs a plurality of lights for generating a second electrical signal, one or more phase adjustment circuits that adjust at least the phases of the plurality of lights output from the second light source to be different from the phases of the plurality of lights output from the first light source, a first photodiode that inputs the plurality of lights output from the first light source and the plurality of lights output from the second light source to generate an alternating current, and a second photodiode that inputs the plurality of lights output from the first light source and the plurality of lights whose phases are adjusted by the one or more phase adjustment circuits to generate an alternating current, and at least one photomixer that generates one or more radio frequency signals based on the outputs of the first photodiode and the second photodiode. A photoelectric conversion device comprising:

2. The photoelectric conversion device according to claim 1, wherein the first photodiode and the second photodiode are connected in series or in a push-pull manner in which one photodiode can blow current into a load while the other photodiode sucks current out of the load.

3. The first light source outputs a plurality of lights whose frequencies of the plurality of lights are separated by a first frequency, the second light source outputs a plurality of lights whose frequencies of the plurality of lights are separated by a second frequency different from the first frequency, and the photomixer generates one or more radio frequency signals based on the outputs of the first photodiode and the second photodiode. The photoelectric conversion device according to claim 1.

4. Further comprising a weighting circuit that gives a time delay to the plurality of lights output from the first light source and the plurality of lights output from the second light source, the one or more photomixers are a plurality of photomixers, and the plurality of photomixers generate the one or more radio frequency signals based on the plurality of lights given a time delay by the weighting circuit. The photoelectric conversion device according to claim 1 or 2.

5. Further comprising a plurality of Nth light sources (N is an integer of 3 or more) that output a plurality of lights for generating an Nth (N is an integer of 3 or more) electrical signal, wherein the one or more phase adjustment circuits are a plurality of phase adjustment circuits, and the plurality of phase adjustment circuits adjust the phases of lights output from each light source or a plurality of lights output from even-numbered light sources. The photoelectric conversion device according to claim 1 or 2.

6. The photoelectric conversion device according to claim 5, further comprising a phase adjustment control circuit that controls an adjustment amount of the phases of lights input to the plurality of phase adjustment circuits.

7. The phase adjustment control circuit controls the characteristics of the plurality of phase adjustment circuits based on the optical wavelength information collected by an optical wavelength information collection circuit that collects optical wavelength information indicating the frequency of an optical signal output from each optical signal source. The photoelectric conversion device according to claim 6.

8. Further comprising a monitoring circuit that monitors the level of an unnecessary radio frequency component in the radio frequency signal generated by the photomixer, wherein the phase adjustment control circuit controls the characteristics of the plurality of phase adjustment circuits based on the monitoring result of the monitoring circuit. The photoelectric conversion device according to claim 6.

Images