JP2023170362A - Photoelectric conversion device - Google Patents

Abstract

To enable low phase noise and large capacity wireless communication in a terahertz band.SOLUTION: The present invention comprises: a laser emission unit that emits a single frequency laser beam; an optical micro-resonator that is excited by the laser beam and generates an optical frequency comb having a frequency interval of 100 GHz to 3 THz inclusive; an optical modulation unit that modulates the amplitude and/or the phase with a baseband signal composed of a transmit information signal, regarding at least one of mutually adjacent first and second optical frequency modes in the optical frequency comb; a mixing unit that mixes the modulated first and second optical frequency modes; and a photoelectric conversion unit that converts an output signal of the mixing unit into an electrical signal.SELECTED DRAWING: Figure 1

Description

The present invention relates to a photoelectric conversion device that generates terahertz waves using a microscopic optical resonator that generates an optical frequency comb.

Conventionally, in mobile (wireless) communications (2G/3G/4G/5G, etc.), technological innovations accompanying advances in semiconductor technology, such as faster electronic circuits and higher frequencies, have driven generational evolution. However, the frequencies handled by next-generation mobile communications (Beyond 5G/6G) are said to extend to the so-called terahertz band (hereinafter referred to as THz band), which has a carrier frequency of 300 GHz or higher, and there is a possibility that the technical limit (frequency upper limit) of electrical methods will be reached. There is. In other words, it is said that essential problems such as lower power of wireless carrier waves, increased phase noise, increased signal transmission loss, and time delay associated with signal conversion between optical communications and mobile communications will become apparent.

On the other hand, optical communication using optical fiber networks has the fastest information transmission speed, and recently silicon photonics has replaced electronic wiring inside devices with optical wiring to achieve ultra-high speed, large capacity, low delay, and low power consumption. technological development is progressing. Against this background, there have recently been cases in wireless communications where optical devices are used as carrier generation sources or optical communication technology is incorporated into a part of the system. For example, an example has been disclosed in which terahertz waves are generated by modulating and mixing lights of different wavelengths, and used for wireless communication (Non-Patent Document 1).

As another method for generating light of two wavelengths with different frequencies, a method has been disclosed in which an arbitrary optical frequency mode having a desired frequency interval is extracted from an optical frequency comb using a filter. (Patent Document 1). Further, Patent Document 2 discloses a technique in which an optical frequency comb is used as a multicarrier for frequency division multiplex transmission, and a pilot signal is further separated from the optical frequency comb. Furthermore, a technique for generating an optical frequency comb from a microresonator has been disclosed (Non-Patent Document 2). Furthermore, a method has also been proposed in which another laser is locked to an arbitrary optical frequency mode of an optical frequency comb (Non-Patent Document 3).

Japanese Patent Application Publication No. 2009-4858 Special table 2018-526842 publication

Tadao Nagatsuma, “Ultra-high-speed wireless communication developed by terahertz waves”, Journal of the Japan Society of Precision Engineering, Vol. 82, No. 3, 2016 S. ZHANG, J. M. SILVER, X. SHANG, L. D. BINO, N. M. RIDLER, P. DEL'HAYE, "Terahertz wave generation using a soliton microcomb", Optics Express, Vol. 27, No. 24, Nov. 2019 S. Hisatake, G. Carpintero, Y. Yoshimizu, Y. Minamikata, K. Oogimoto, Y. Yasuda, F. Dijk, T. Tekin, and T. Nagatsuma, “W-Band Coherent Wireless Link Using Injection-Locked Laser Diodes”, IEEE Photonics Technology Letters, Vol. 27, No. 14, July, 2015

However, as in Non-Patent Document 1, when independent lasers with wavelengths separated by the frequency of the wireless carrier are used as light sources, frequency fluctuations and phase noise of the carrier waves occur due to fluctuations in frequency or phase between them. Furthermore, even when using an optical frequency comb as a light source, if you try to obtain a high frequency signal from the beat between two optical frequency modes separated as in Patent Document 1, phase noise will increase depending on the number of separated optical frequency modes. Accumulated. This tendency becomes particularly noticeable in the terahertz region and above. Furthermore, although the technology disclosed in Patent Document 2 is aimed at frequency division multiplex transmission, it is necessary to make the frequency interval of the pilot signal wider than the mode interval of the optical frequency comb, and this technology cannot be directly applied to wireless transmission. Similar challenges arise when trying to apply it. Incidentally, in Non-Patent Document 2, a terahertz wave is generated by photoelectric conversion of two-wavelength mode light of an optical frequency comb, but there is no mention of modulation at all.

A photoelectric conversion device according to one aspect of the present invention includes: a laser emitting unit that emits a laser beam of a single frequency; and a minute beam that is excited by the laser beam and generates an optical frequency comb having a frequency interval of 100 GHz or more and 3 THz or less. Modulating at least one of the amplitude and phase of at least one of the first and second optical frequency modes adjacent to each other in the resonator and the optical frequency comb with a baseband signal consisting of a transmission information signal. an optical modulation section that mixes the modulated first and second optical frequency modes, and an opto-electrical conversion section that converts an output signal of the mixing section into an electrical signal.

A first optical modulator and a second optical modulator may be provided for each of the first and second optical frequency modes.

The pair of the first optical frequency mode and the second optical frequency mode may be separated and extracted together, and the optical modulator may perform amplitude modulation on the pair.

The optical modulator may modulate the amplitude of the optical frequency comb and supply the optical frequency comb to the opto-electric converter.

The frequency interval may be 300 GHz or more and 1 THz or less.

The photoelectric converter may be comprised of a single carrier photodiode.

The micro optical resonator is a medium having a nonlinear optical effect, and is made of silicon nitride (Si ₃ N ₄ ), gallium aluminum arsenide (AlGaAs), lithium niobate (LiNbO ₃ ), tantalum pentoxide (Ta ₂ O ₅ ), and gallium nitride (GaN).

The optical modulation section includes an optical subcarrier generation section that generates a plurality of optical subcarrier groups from the first optical frequency mode, and an optical modulation element that independently modulates the optical subcarrier groups according to the baseband signal. It may have a group.

The optical modulation unit includes a first optical subcarrier generation unit that generates first optical subcarrier groups separated by a first difference frequency on both sides from the first optical frequency mode, and each of the optical subcarrier groups. a second optical subcarrier generation unit that generates a second optical subcarrier group separated by a second difference frequency on both sides, and frequency division multiplexing of the second optical subcarrier group according to the baseband signal; It may also include a light modulation element that performs modulation.

The frequency interval of the second optical subcarrier group may be greater than or equal to 10 GHz and less than or equal to 50 GHz.

The optical modulation section includes an optical splitting element that divides the first optical frequency mode into two optical subcarriers, and a group of optical modulation elements that independently modulate the optical subcarriers according to the baseband signal. Further, each of the opto-electric converters has a pair of opto-electric converters whose output waves have orthogonal polarizations, and the two modulated subcarriers each have a pair of opto-electric converters whose polarizations are orthogonal to each other, and each of the two modulated subcarriers It may also be supplied to the converter.

According to one aspect of the present invention, first and second optical frequency modes adjacent to each other are separated and extracted from an optical frequency comb obtained by a micro-optical resonator, and the first optical frequency mode is further transmitted as a carrier. It is possible to generate a modulated signal in the terahertz band by performing optical modulation with a baseband signal consisting of an information signal and beat with a second optical frequency mode that has a small relative phase noise with respect to the first optical frequency mode. Become. Furthermore, by generating optical subcarriers from the first optical frequency mode, multiplexing of baseband signals can be realized, and higher-speed information transmission can be realized.

FIG. 1 is a block diagram including a photoelectric conversion device according to a first embodiment of the present invention. FIG. 2 is a block diagram including a photoelectric conversion device according to a second embodiment of the present invention. FIG. 3 is a block diagram including a photoelectric conversion device according to a third embodiment of the present invention. FIG. 3 is a block diagram including a photoelectric conversion device according to a fourth embodiment of the present invention. FIG. 7 is a block diagram of a light modulation section in a photoelectric conversion device according to a fifth embodiment of the present invention. FIG. 7 is an explanatory diagram of the operation of the fifth embodiment of the present invention. FIG. 7 is a block diagram of a light modulation section in a photoelectric conversion device according to a sixth embodiment of the present invention. FIG. 3 is a diagram showing the flow of processing in the first embodiment of the present invention. FIG. 3 is a block diagram showing an experimental method according to a second embodiment of the present invention. It is a graph showing the experimental results of the second example of the present invention. FIG. 7 is a block diagram showing an experimental method according to a third embodiment of the present invention. It is a graph showing the experimental results of the third example of the present invention. It is a graph showing the experimental results of the third example of the present invention.

(First embodiment)
Hereinafter, the first embodiment will be described in detail with reference to the drawings. The photoelectric conversion device in this embodiment aims to generate terahertz waves with less phase noise by using adjacent frequency modes generated from a microscopic optical resonator in generating carriers used for communication. .

FIG. 1 shows a block diagram of a photoelectric conversion device 1 in this embodiment. In FIG. 1, 100 is a wireless terminal. There may be one or more wireless terminals 100. Further, the terminal may be a mobile terminal or a fixed terminal. 106 is a receiving antenna, which receives the wireless signal S1 from the wireless terminal 100. The receiving antenna 106 may be an antenna array including a plurality of antenna elements to accommodate a plurality of wireless terminals 100. Furthermore, it may be made up of a plurality of antenna groups corresponding to a plurality of wireless communication standards such as frequencies. Information signal demodulation section 107 demodulates the transmission information signal included in radio signal S1. The information signal demodulation unit 107 may be compatible with multiple wireless communication standards such as LTE and 5G.

Furthermore, in FIG. 1, reference numeral 101 is a laser emitting section that emits laser light of a single frequency. A DFB laser that emits light whose emission wavelength is tuned to 1550 nm or around 1550 nm is preferred. 102 is a microscopic optical resonator, which is excited by the laser beam and generates an optical frequency comb. An optical frequency comb has an ultra-discrete multispectral structure in which a large number of optical frequency mode arrays are arranged in a comb-like shape with equal frequency (f _rep ) intervals and uniform optical phases. The micro optical resonator 102 may be formed in a ring shape on a semiconductor substrate. The diameter may be between 40 μm and 400 μm. In addition, it is a medium that has a nonlinear optical effect, and includes silicon nitride (Si ₃ N ₄ ), gallium aluminum arsenide (AlGaAs), lithium niobate (LiNbO ₃ ), tantalum pentoxide (Ta ₂ O ₅ ), and gallium nitride ( It may be composed of one or more types of media selected from the group consisting of GaN).

Since the optical frequency comb generated by the micro optical resonator 102 has a short optical resonator length, the difference frequency (f _rep ) between adjacent optical frequency modes can be increased. The frequency interval (f _rep ) may be, for example, 100 GHz or more and 3 THz or less. More preferably, the frequency may be 300 GHz or more and 1 THz or less. More preferably, it may be 350 GHz or more and 600 GHz or less. On the other hand, in the case of a fiber optical frequency comb using optical fibers, the difference frequency between adjacent optical frequency modes is about 0.1 to 1 GHz. For example, if you try to obtain an optical beat frequency of 300 GHz in the terahertz band from a fiber optical frequency comb, , it is necessary to extract optical frequency modes that are not adjacent but spaced apart by 3000 to 300 modes. However, as the spacing between optical frequency modes increases, the relative phase noise increases cumulatively.

Reference numerals 104 and 105 each indicate a bandpass filter, which constitutes an optical frequency mode separation section. Optical frequency modes (ν ₁ and ν ₀ =ν ₁ −f _rep ) adjacent to each other are separated and extracted from the optical frequency comb. Note that the wavelength division section does not necessarily have to be composed of a pair of bandpass filters as shown in FIG. Alternatively, an AWG (arrayed waveguide diffraction device) may be used. Furthermore, a phase adjustment section configured with a heater or the like may be provided in at least one of the paths of the bandpass filters 104 and 105.

Optical frequency mode m1 (first optical frequency mode) with frequency ν ₁ is sent to optical modulation section 108 and modulated according to baseband signal S2. The baseband signal S2 includes the transmission information signal demodulated by the information signal demodulation section 107. When information signals are being transmitted from a plurality of wireless terminals 100, they may be time-divided into one stream. Alternatively, the channels may be allocated to the frequency division channels shown in the second embodiment. The optical frequency mode m1 that has undergone optical modulation is mixed with the optical frequency mode m0 that has not undergone optical modulation in the mixing section 120, and is supplied to the photoelectric conversion section 110 via the optical amplification element 109. Note that the optical amplifying element 109 may not be inserted depending on the level of the optical signal input to the opto-electrical converter. The photoelectric converter 110 may be composed of a photoelectric converter such as a single traveling carrier photodiode (UTC-PD).

On the other hand, the optical frequency mode m0 (second optical frequency mode) having the frequency _ν 0 is supplied to the opto-electric conversion unit 110 via the mixing unit 120 and the optical amplification element 109. In the mixing unit 120, the optical frequency mode m1 (ν ₁ ) and the optical frequency mode m0 (ν ₀ ) are mixed (S3), and their difference frequency (f _rep ) is output from the opto-electric conversion unit 110 as a terahertz wave. Ru. Note that the configuration may be such that the mixing unit 120 is omitted and the optical frequency modes m0 and m1 are directly input to the opto-electric conversion unit 110. The terahertz wave outputted from the photoelectric converter 110 is input to the antenna 111, and the terahertz wave S4 is radiated into the air from the antenna 111.
Further, in this embodiment, the optical frequency mode m0 is not modulated, but the present invention modulates at least the amplitude, phase, or both of the optical frequency modes m1, m0, or both. Modulation may be performed using a baseband signal, and the present invention is not limited to this embodiment.

(Second embodiment)
The second embodiment will be described below using FIG. 2. In FIG. 2, a wireless terminal 100, a laser emitting unit 101, a microscopic optical resonator 102, an isolator 103, bandpass filters 104 and 105, a receiving antenna 106, an information signal demodulating unit 107, a mixing unit 120, an optical amplification element 109, a photoelectric The conversion unit 110 and the transmitting antenna 111 have the same functions as those shown in FIG.

In this embodiment, the first optical modulator 181 and the second optical modulator 182 are provided in the paths of the optical frequency modes m1 and m0, respectively. Assuming that the optical modulator 181 performs amplitude modulation, when only one of the optical frequency modes is modulated as in the previous embodiment, the beat signal generated by mixing these modes is expressed as follows: Can be written.
E0×E1(t)
Here, E1(t) represents that the optical frequency mode m1 is subjected to amplitude modulation, and E0 represents that the optical frequency mode m0 is a CW signal. Furthermore, if the optical modulation section 182 is also introduced in the optical frequency mode m0 and the same level of amplitude modulation is applied to both modes, the beat signal becomes
E0(t)×E1(t)=E0(t) ² =E1(t) ²
becomes. This means that a deeper modulation signal can be obtained by changing the amplitude in a square manner, and as a result, the SNR and BER of the modulation signal are significantly improved.

(Third embodiment)
When using optical amplitude modulation, the configuration can be further simplified. In FIG. 3, the bandpass filter 1045 transmits an optical frequency mode m1 (frequency ν ₁ ) and an adjacent optical frequency mode m0 (ν ₀ ) at a frequency f _rep interval as a pair. The optical amplitude modulation section 180 simultaneously performs amplitude modulation on the pair of optical mode signals m1 and m0. As a result, the same effects as in the second embodiment described above can be obtained with a simpler configuration.

(Fourth embodiment)
When using optical amplitude modulation, the bandpass filter may be omitted. FIG. 4 shows a block diagram of this embodiment. In FIG. 4, an optical amplitude modulation section 180 modulates the amplitude of the entire optical frequency comb (ultrashort pulse signal on the time axis). After that, the light is amplified and then enters the photoelectric conversion section.

(Fifth embodiment)
The fifth embodiment will be described below. In this embodiment, the optical modulation unit 108 generates four optical subcarrier groups from the optical frequency mode (m1), and modulates these optical subcarriers according to the baseband signal S2 composed of a 4-bit stream. It is characterized by having a configuration in which the group is subjected to frequency division multiplex modulation. The specific configuration is shown in the block diagram of FIG. Components other than the modulation section 108 may be the same as those shown in FIG. 1, and therefore will not be described here. Note that in this embodiment, the number of multiplexing is 4, but the present invention is not limited to this.

In FIG. 5, 1081 represents a local oscillation element, and 1083 represents a light modulation element. Local oscillation element 1081 and optical modulation element 1083 constitute a first optical subcarrier generation section. Further, 1082 indicates a local oscillation element, and 1084 indicates a light modulation element. Local oscillation element 1082 and optical modulation element 1084 constitute a second optical subcarrier generation section.

Local oscillation element 1081 and local oscillation element 1082 may operate electrically. In this embodiment, the oscillation frequency Δf ₁ is 1.5 times the oscillation frequency Δf ₂ of the local oscillation element 1082, which will be described later. The oscillation frequency Δf ₂ is preferably 5 GHz to 50 GHz, and the oscillation frequency Δf ₁ is preferably 7.5 GHz to 75 GHz. The value obtained by doubling the oscillation frequency Δf ₂ (2Δf ₂ ) becomes the frequency band per channel in frequency division multiplex modulation, as will be described later. More preferably, this frequency band 2Δf ₂ is between 10 GHz and 50 GHz. Further, the light modulation element 1083 and the light modulation element 1084 may each be phase modulated by the output of a local oscillation element, preferably DSB modulated.

Furthermore, in FIG. 5, 1085 is an arrayed waveguide diffraction element (AWG) that separates all the optical subcarrier groups (C11, C12, C21, C22) generated by the local oscillation element 1082 and the optical modulation element 1084. be. Note that a wavelength selective switch (WSS) may be used instead of the arrayed waveguide diffraction element 1085 in order to separate the optical subcarrier groups C11, C12, C21, and C22 while blocking light waves of wavelengths other than those. . Optical modulation elements 1086 to 1089 apply optical modulation to each optical subcarrier according to each bit stream (bit ₀ to bit ₃ ) of the information signal S2. The modulation method may be amplitude modulation such as QPSK or QAM, phase modulation, or a method including both of these. The optically modulated optical subcarriers are multiplexed again, outputted from the modulation section 108 as a frequency division multiplexed signal, and inputted to the opto-electrical conversion section 110.

The operation of this embodiment will be described below with reference to FIG. In FIG. 3A, an optical frequency mode m1 is input to the modulation section 108. Optical frequency mode m1 is separated from the optical frequency comb by bandpass filter 104. Note that the optical frequency mode m1 and the adjacent optical frequency mode m0 are separated by a bandpass filter 105 whose pass band is separated from the optical frequency mode m1 by a frequency (f _rep ) equal to the resonant frequency of the microresonator 102, and The signal is input to the photoelectric conversion unit 110 without passing through.

The local oscillation element 1081 and the optical modulation element 1083 generate first optical subcarriers C1 and C2 at frequency positions separated by Δf ₁ on the low frequency side and high frequency side (hereinafter referred to as both sides) of the optical frequency mode m1 ( Figure (b)). Furthermore, the local oscillation element 1082 and the optical modulation element 1083 generate second optical subcarriers C11, C12, C21, and C22 at frequency positions separated by Δf ₂ on both sides of each optical subcarrier C1 and C2, respectively. The frequency interval between optical subcarriers C11 and C12 and the frequency interval between optical subcarriers C21 and C22 are both 2Δf ₂ ((c) in the figure). Here, if there is a relationship of Δf ₁ =1.5×Δf ₂ , the frequency interval between carriers C12 and C21 will also be 2Δf ₂ . For example, when Δf ₁ =37.5 GHz and Δf ₂ =25 GHz, optical subcarriers C11, C12, C21, and C22 are all arranged at 50 GHz intervals.

Optical modulation elements 1086 to 1089 perform optical modulation on optical subcarriers C11, C12, C21, and C22 according to each bit stream (bit ₀ to bit ₃ ) of information signal S2. The bandwidth of each modulation signal may be 2Δf ₂ or less. Generally, when transmitting information by frequency division, increasing the number of divisions allows narrowing the band of each frequency channel, which facilitates the design of signal processing circuits for modulation and demodulation. However, on the other hand, since the transmission speed between the fronthaul of each channel decreases, delays are more likely to occur. In particular, when the technology disclosed in this embodiment is applied to a large capacity line such as between a base station and a switching center, the occurrence of delay should be suppressed as much as possible. Therefore, when transmitting information at a maximum of 100 Gbps, it is preferable that the band of each frequency channel, that is, the frequency interval (2Δf ₂ ) of the second optical subcarriers is 10 GHz or more and 50 GHz or less.

In the above embodiment, the optical frequency mode separated from the optical frequency comb through a bandpass filter or the like is directly modulated and supplied to the opto-electrical converter through the optical amplification element, but as shown in Non-Patent Document 3 Similarly, lasers other than those for excitation may be used, and these lasers may be injection-locked to a desired optical frequency mode, and the output light of these lasers may be modulated.

(Sixth embodiment)
A sixth embodiment of the present invention will be described below. FIG. 7 is a block diagram of this embodiment. In FIG. 7, the modulator 108 includes a light splitting element (beam splitter) 1180 that splits the optical frequency mode m1 and generates two optical subcarriers P1 and P2. Furthermore, it has optical modulation elements 1181 and 1182 that independently modulate optical subcarriers P1 and P2 according to baseband signal S2 composed of a 2-bit stream.

Further, the opto-electric converter 110 is composed of opto-electric converters 1101 and 1102, which convert modulated optical subcarriers P1 and P2, respectively, into terahertz signals having a frequency f _rep . The photoelectric converters 1101 and 1102 are installed so that the polarizations of the terahertz waves emitted from each are orthogonal to each other.

In this example, the transmission gain of the entire system when the carrier frequency is 300 GHz was estimated in consideration of the loss at each step of transmission. The results are shown in FIG. Note that the band of the transmission information signal was 25 GHz.

First, an arbitrary optical frequency mode (m1) is separated from the optical frequency comb by an optical frequency mode separation section, but when an arrayed waveguide grating AWG is used, a loss of about 6 dB may occur. Next, a loss of 10 dB occurs in the optical modulator and 6 dB in the multiplexing process, for a total of 22 dB. Therefore, in this embodiment, an optical amplifier is used to increase the gain by 30 dB. That is, the gain up to this point is 8 dB, so if each mode of the optical frequency comb is 15 mW (11.76 dBm), the optical amplifier outputs 94 mW (19.76 dBm) of light.

However, a 3 dB loss occurs in the next-stage bandpass filter, and a further loss occurs due to conversion efficiency in the photoelectric conversion section. In the case of UTC-PD, the loss varies greatly depending on the frequency of the output (S4), and the loss reaches approximately 30 dB at 300 GHz and approximately 35 dB at 600 GHz. If the carrier frequency is 300 GHz, the gain of the entire system is -25 dB, which is approximately 47 μW (-13.24 dBm).

Next, the measurement results of the mode spacing (f _rep ) relative phase noise of an optical frequency comb (micro optical comb) generated using a micro optical resonator will be explained. FIG. 9 shows the f _rep relative phase noise experimental system. After the micro-optical comb is optically amplified by an Er-doped fiber amplifier (EDFA), it is split into two paths. On the one hand, frequency shifting is performed by an acousto-optic modulation (AOM) element. On the other side, temporal manipulation (delay, etc.) is performed.

After the two paths are combined again, an arbitrary optical frequency mode pair is extracted using a bandpass filter, and FFT (fast Fourier transform) analysis is performed on the mixed signal. The spacing between each mode of an optical frequency comb is in the terahertz frequency band, and direct measurement of relative phase noise requires a high-speed, wideband, and highly accurate spectrum analyzer. However, if the method of this embodiment is used, what the FFT analyzes is a signal in the operating frequency band of the AOM element, and since the relative phase noise is transferred, even a slow spectrum analyzer can accurately analyze the relative phase noise. can be measured.

FIG. 10 shows the measurement results of relative phase noise measured using the experimental system shown in FIG. 9. It was confirmed that the frequency interval of the optical frequency comb is 560 GHz, and the relative phase noise at an offset frequency of 10 kHz is about -60 dB.

(Third example)
In this example, an experimental system (configuration) for evaluating phase noise of terahertz waves and results will be described. Figure 11 shows the experimental system. A terahertz wave generated by inputting a micro optical comb having a comb mode spacing of 560 GHz to a photoelectric converter (single traveling carrier photodiode) is input to a subharmonic mixer (SHM). SHM mixes a terahertz wave and a frequency-multiplied local oscillator (LO) signal to generate an IF signal in the RF band corresponding to the difference frequency between the two. This IF signal is measured with an RF spectrum analyzer. Further, by Fourier transforming the IF signal, a phase noise spectrum can be obtained from the IF signal (corresponding to a terahertz wave).

Experimental results are shown in FIGS. 12 and 13. FIG. 12 shows the frequency spectrum of the IF signal, and a good SN ratio is obtained. Moreover, FIG. 13 shows the phase noise spectrum of the IF signal. For comparison, the f _rep relative phase noise spectrum of FIG. 10 is also shown. A comparison between the two shows that the f _rep relative phase noise characteristics can be transferred to the terahertz wave without loss in the optical terahertz conversion process.

The present invention uses a micro optical resonator that generates an optical frequency comb to generate terahertz waves at wireless base stations that transmit information collected from mobile terminals to a switching center or relay stations that transmit information between wireless base stations. It can be used in photoelectric conversion devices that generate .

1 Optoelectric conversion device 100 Wireless terminal 101 Laser emitting unit 102 Microscopic optical resonator 103 Isolators 104, 105 Bandpass filter 106 Receiving antenna 107 Information signal demodulating unit 108 Optical modulating unit 180 Optical amplitude modulating unit 181 First optical modulating unit 182 Second optical modulation section 109 Optical amplification element 110 Photoelectric conversion section 120 Mixing section 1081, 1082 Local oscillation element 1083, 1084 Optical modulation element 1085 Arrayed waveguide diffraction element (AWG)
1086 to 1089 Light modulation elements 1101, 1102 Photoelectric conversion unit 1180 Light splitting elements 1181, 1182 Light modulation elements

Claims (11)

a laser emitting part that emits laser light of a single frequency;
a microscopic optical resonator that is excited by the laser beam and generates an optical frequency comb having a frequency interval of 100 GHz or more and 3 THz or less;
an optical modulator that modulates at least one of the amplitude and phase of at least one of the first and second optical frequency modes adjacent to each other in the optical frequency comb with a baseband signal consisting of a transmission information signal; and,
a mixing unit that mixes the modulated first and second optical frequency modes;
A photoelectric conversion device comprising a photoelectric conversion section that converts an output signal of the mixing section into an electrical signal. The photoelectric conversion device according to claim 1, wherein a first optical modulation section and a second optical modulation section are provided for each of the first and second optical frequency modes. 2. The photoelectric conversion device according to claim 1, wherein the pair of the first optical frequency mode and the second optical frequency mode are separated and extracted together, and the optical modulator performs amplitude modulation on the pair. The opto-electric conversion device according to claim 1, wherein the optical modulator modulates the amplitude of the optical frequency comb and supplies the optical frequency comb to the opto-electric converter. The photoelectric conversion device according to claim 1, wherein the frequency interval is 300 GHz or more and 1 THz or less. 6. The photoelectric conversion device according to claim 5, wherein the photoelectric conversion section comprises a single carrier photodiode. The micro optical resonator is a medium having a nonlinear optical effect, and is made of silicon nitride (Si ₃ N ₄ ), gallium aluminum arsenide (AlGaAs), lithium niobate (LiNbO ₃ ), tantalum pentoxide (Ta ₂ O ₅ ), and gallium nitride (GaN). The optical modulation section includes an optical subcarrier generation section that generates a plurality of optical subcarrier groups from the first optical frequency mode, and an optical modulation element that independently modulates the optical subcarrier groups according to the baseband signal. The photoelectric conversion device according to claim 5, having a group. The optical modulation unit includes a first optical subcarrier generation unit that generates first optical subcarrier groups separated by a first difference frequency on both sides from the first optical frequency mode, and each of the optical subcarrier groups. a second optical subcarrier generation unit that generates a second optical subcarrier group separated by a second difference frequency on both sides, and frequency division multiplexing of the second optical subcarrier group according to the baseband signal; The photoelectric conversion device according to claim 8, comprising a light modulation element for modulation. The photoelectric conversion device according to claim 8, wherein a frequency interval of the second optical subcarrier group is 10 GHz or more and 50 GHz or less. The optical modulation section includes an optical splitting element that divides the first optical frequency mode into two optical subcarriers, and a group of optical modulation elements that independently modulate the optical subcarriers according to the baseband signal. Further, each of the opto-electric converters has a pair of opto-electric converters whose output waves have orthogonal polarizations, and the two modulated subcarriers each have a pair of opto-electric converters whose polarizations are orthogonal to each other, and each of the two modulated subcarriers The photoelectric conversion device according to claim 8, which is supplied to a conversion section.