Subterahertz wave output device

Abstract

The frequency of electrical signals in the subterahertz band can be precisely varied over a wide range. [Solution] The subterahertz wave output device 1 comprises a master laser 2 that generates an optical comb, a first slave laser 4 that outputs a first laser beam LD1 with a variable optical frequency, a first laser optical frequency control unit 10 that controls the optical frequency f1 of the first laser beam LD1 so that it differs from the optical frequency of the first mode of the optical comb by a first difference frequency fb1, a second slave laser 6 that outputs a second laser beam LD2 with a variable optical frequency, a second laser optical frequency control unit 20 that controls the optical frequency f2 of the second laser beam LD2 so that it differs from the optical frequency of the second mode of the optical comb by a second difference frequency fb2, and a UTC-PD8 that receives the first laser beam LD1 and the second laser beam LD2 and outputs an electrical signal ES with a frequency equal to the difference between the optical frequency f1 of the first laser beam LD1 and the optical frequency f2 of the second laser beam LD2.

Description

Technical Field

[0001] The present invention relates to the control of the frequency of sub-terahertz waves.

Background Art

[0002] Conventionally, for generating an electric signal with a variable frequency, a VCO (Voltage Controlled Oscillator) using a semiconductor IC has been used. However, in order to output an electric signal in the sub-terahertz band (from 100 GHz to less than 1 THz), there are problems such as insufficient output power, difficulty in variable frequency control, and large phase noise in a VCO using a semiconductor IC (see, for example, Non-Patent Document 1).

[0003] Therefore, in order to output an electric signal in the sub-terahertz band, instead of a VCO using a semiconductor IC, photoelectric conversion may be used. A typical method for outputting an electric signal in the sub-terahertz band using photoelectric conversion is a generation method using a uni-traveling carrier photodiode (UTC-PD). The principle of this generation method is that when two laser lights are input to a UTC-PD, an electric signal with the same frequency as the difference Δf in the optical frequencies of the two laser lights is output from the UTC-PD (see, for example, Non-Patent Document 2).

[0004] Here, in order to improve the accuracy of the frequency of an electric signal in the sub-terahertz band, it is necessary to accurately control the optical frequencies of the two laser lights applied to the UTC-PD. When controlling the optical frequencies of these two laser lights, it is known to use an optical comb (optical frequency comb) as a reference for the optical frequency (see, for example, Non-Patent Document 3 and Non-Patent Document 4).

[0005] Regarding an optical comb, a light source using an optical comb (see, for example, Patent Document 1) and a generating device for an optical comb (see, for example, Patent Document 2) are known.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-203550 [Patent Document 2] Japanese Patent Publication No. 2021-092740 [Non-patent literature]

[0007] [Non-Patent Document 1] JS Rieh "Current Status of Semiconductor Technologies and Circuits for THz applications", doc.: IEEE 802.15-08-0437-00-0thz, Project:IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs), July 2008 [Non-Patent Document 2] Ministry of Internal Affairs and Communications, "FY2018 Research Report: Investigation on the Presence or Absence of Non-Thermal Effects of Terahertz Waves, etc.," commissioned by RIKEN, March 2019, pp. 6-7 [Non-Patent Document 3] Tokushima University, et al. (3 others), "Successful Terahertz Communication Using Micro Optical Combs ~Expectations for Next-Generation Mobile Communication Using Light~", Internet, May 25, 2023, < URL: https: / / www.nict.go.jp / press / 2023 / 05 / 25-1.html > [Non-Patent Document 4] Satoshi Kawanishi, et al., "Experiment on 300GHz Generation and Transmission using Microcombs," Proceedings of the Electronics Conference 1, C-14-07, IEICE 2024 General Conference, March 2024, p.181. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, when attempting to obtain subterahertz electrical signals using an optical comb as a reference optical frequency, as in the conventional technology described above, it is difficult to vary the frequency of the electrical signal over a wide range because the optical frequency of the optical comb is determined according to the physical length of the resonator.

[0009] Therefore, the present invention aims to enable the precise and variable frequency of electrical signals in the subterahertz band (100 GHz or more and less than 1 THz) over a wide range. [Means for solving the problem]

[0010] The subterahertz wave output device according to the present invention comprises: an optical comb generation unit that generates an optical comb; a first laser light output unit that outputs a first laser light with a variable optical frequency; a first laser light frequency control unit that controls the optical frequency of the first laser light to differ from the optical frequency of the first mode of the optical comb by a first difference frequency; a second laser light output unit that outputs a second laser light with a variable optical frequency; a second laser light frequency control unit that controls the optical frequency of the second laser light to differ from the optical frequency of the second mode of the optical comb by a second difference frequency; and an electrical signal output unit that receives the first laser light and the second laser light and outputs an electrical signal with a frequency equal to the difference between the optical frequency of the first laser light and the optical frequency of the second laser light, wherein the frequency of the electrical signal is 100 GHz or more and less than 1 THz, and the difference between the first difference frequency and the second difference frequency is 1 / 2 or less of the repetition frequency of the optical comb.

[0011] According to the subterahertz wave output device configured as described above, the optical comb generation unit generates an optical comb. The first laser light output unit outputs a first laser beam with a variable optical frequency. The first laser light frequency control unit controls the optical frequency of the first laser beam so that it differs from the optical frequency of the first mode of the optical comb by only a first difference frequency. The second laser light output unit outputs a second laser beam with a variable optical frequency. The second laser light frequency control unit controls the optical frequency of the second laser beam so that it differs from the optical frequency of the second mode of the optical comb by only a second difference frequency. The electrical signal output unit receives the first laser beam and the second laser beam and outputs an electrical signal with a frequency equal to the difference between the optical frequency of the first laser beam and the optical frequency of the second laser beam. The frequency of the electrical signal is 100 GHz or more and less than 1 THz. The difference between the first difference frequency and the second difference frequency is less than or equal to half the repetition frequency of the optical comb.

[0012] Furthermore, the subterahertz wave output device according to the present invention may be configured such that one or both of the first difference frequency and the second difference frequency are variable.

[0013] Furthermore, in the subterahertz wave output device according to the present invention, the maximum value of the first difference frequency and the maximum value of the second difference frequency may be less than half of the repetition frequency of the optical comb.

[0014] Furthermore, the subterahertz wave output device according to the present invention may be configured such that when one of the first difference frequency and the second difference frequency reaches its maximum value, the other of the first difference frequency and the second difference frequency is reduced.

[0015] Furthermore, the subterahertz wave output device according to the present invention includes a first laser optical frequency control unit which has a first optical signal output unit that outputs an optical signal representing the difference in optical frequency between the first laser light and the first mode of the optical comb, a first difference frequency signal output unit that outputs a signal of the first difference frequency, a first phase difference signal output unit that outputs a first phase difference signal corresponding to the phase difference between the output of the first optical signal output unit and the output of the first difference frequency signal output unit, and a first laser optical control unit that controls the first laser optical output unit to reduce the magnitude of the first phase difference signal. The second laser optical frequency control unit may include a second optical signal outputter that outputs an optical signal representing the difference in optical frequency between the second laser light and the second mode of the optical comb; a second difference frequency signal outputter that outputs a signal of the second difference frequency; a second phase difference signal outputter that outputs a second phase difference signal corresponding to the phase difference between the output of the second optical signal outputter and the output of the second difference frequency signal outputter; and a second laser optical control unit that controls the second laser optical output unit to reduce the magnitude of the second phase difference signal.

[0016] Furthermore, the subterahertz wave output device according to the present invention may be configured such that the first optical signal output device, the first differential frequency signal output device, the first phase difference signal output device, the first laser light control unit, the second optical signal output device, the second differential frequency signal output device, the second phase difference signal output device, and the second laser light control unit are all analog circuits.

[0017] Furthermore, in the subterahertz wave output device according to the present invention, the first optical signal output device, the first laser light control unit, the second optical signal output device, and the second laser light control unit may be configured by analog circuits, while the first differential frequency signal output device, the first phase difference signal output device, the second differential frequency signal output device, and the second phase difference signal output device may be configured by digital circuits.

[0018] Furthermore, the subterahertz wave output device according to the present invention may also be configured such that the electrical signal output section is UTC-PD.

Brief Description of the Drawings

[0019] [Figure 1] It is a functional block diagram showing the configuration of the sub-terahertz wave output device 1 according to an embodiment of the present invention. [Figure 2] It is the frequency spectrum of the optical comb, the first laser beam LD1, and the second laser beam LD2. [Figure 3] It is the frequency spectrum of the optical comb, the first laser beam LD1, and the second laser beam LD2 when the second difference frequency fb2 takes the maximum value (for example, 16 MHz). [Figure 4] It is a functional block diagram showing the configuration of the sub-terahertz wave output device 1 according to a modified example of an embodiment of the present invention.

Modes for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0021] FIG. 1 is a functional block diagram showing the configuration of the sub-terahertz wave output device 1 according to an embodiment of the present invention. The sub-terahertz wave output device 1 according to an embodiment of the present invention includes a master laser 2, a first slave laser 4, a second slave laser 6, a UTC-PD 8, a first laser beam frequency control unit 10, and a second laser beam frequency control unit 20.

[0022] The master laser (optical comb generation unit) 2 generates an optical comb. Let the repetition frequency of the optical comb be frep. The repetition frequency frep is, for example, 40 MHz.

[0023] The first slave laser (first laser beam output unit) 4 outputs a first laser beam LD1 whose optical frequency is variable. The first laser beam frequency control unit 10 controls the optical frequency f1 of the first laser beam LD1 so that it is different from the optical frequency of the first mode of the optical comb by only the first difference frequency fb1.

[0024] The second slave laser (second laser light output unit) 6 outputs a second laser beam LD2 with a variable optical frequency. The second laser light frequency control unit 20 controls the optical frequency f2 of the second laser beam LD2 so that it differs from the optical frequency of the second mode of the optical comb by only the second difference frequency fb2.

[0025] Figure 2 shows the frequency spectra of the optical comb, the first laser beam LD1, and the second laser beam LD2. Figure 2 illustrates optical combs of order -1, 0, 1, N-1, N, and N+1. In Figure 2, the first mode is 0th order, and the first difference frequency fb1 is 10 MHz.

[0026] Furthermore, in Figure 2(a), the second mode is of order N, and the second difference frequency fb2 is 10 MHz. In Figure 2(b), the second mode is of order N, and the second difference frequency fb2 is 16 MHz. In Figure 2(c), the second mode is of order (N+1), and the second difference frequency fb2 is 16 MHz. Here, N is a positive integer.

[0027] Figure 2 illustrates an example where the second difference frequency fb2 is variable. However, the first difference frequency fb1 may also be variable. Furthermore, both the first difference frequency fb1 and the second difference frequency fb2 may be variable.

[0028] The UTC-PD (Uni-Traveling Carrier Photodiode) (electrical signal output unit) 8 receives the first laser beam LD1 and the second laser beam LD2, and outputs an electrical signal ES with a frequency f2-f1, which is the difference between the optical frequency f1 of the first laser beam and the optical frequency f2 of the second laser beam. However, the frequency f2-f1 of this electrical signal ES is set to be between 100 GHz and less than 1 THz.

[0029] In Figure 2(a), the frequency f2-f1 of the electrical signal ES is N×frep. In Figure 2(b), the frequency f2-f1 of the electrical signal ES is N×frep+6MHz. In Figure 2(c), the frequency f2-f1 of the electrical signal ES is (N+1)×frep-26MHz=N×frep+14MHz.

[0030] The maximum values ​​of the first difference frequency fb1 and the second difference frequency fb2 are frep / 2. The minimum values ​​of the first difference frequency fb1 and the second difference frequency fb2 are 0. Therefore, the difference between the first difference frequency fb1 and the second difference frequency fb2 is less than or equal to half the repetition frequency frep of the optical comb.

[0031] However, in Figure 2, the maximum values ​​of the first difference frequency fb1 and the second difference frequency fb2 are less than half the repetition frequency frep of the optical comb (e.g., 16 MHz). For example, the optical frequencies of the first laser beam LD1 and the second laser beam LD2 cannot fall into region A. That is, the optical frequencies of the first laser beam LD1 and the second laser beam LD2 cannot exceed the optical comb of order X + 16 MHz and cannot be less than the optical comb of order X + 24 MHz, where X is any integer.

[0032] The reason for providing such a region A is that if the first difference frequency fb1 becomes approximately the same as frep / 2, the frequency difference between the first laser beam LD1 and the 0th-order optical comb and the frequency difference between the first laser beam LD1 and the 1st-order optical comb will become approximately the same. Therefore, it becomes difficult to extract the signal of the frequency difference between the first laser beam LD1 and the 0th-order optical comb using the first LPF (low-pass filter) 106, which will be described later.

[0033] Furthermore, if the second difference frequency fb2 becomes approximately the same as frep / 2, the frequency difference between the second laser beam LD2 and the Nth-order optical comb and the frequency difference between the second laser beam LD2 and the (N+1)th-order optical comb will become approximately the same. Therefore, it will be difficult to extract the frequency difference signal between the second laser beam LD2 and the Nth-order optical comb using the second LPF (low-pass filter) 206, which will be described later. For this reason, region A is provided.

[0034] Here, because region A is provided, if the first difference frequency fb1 is fixed at 10 MHz, the frequency f2-f1 of the electrical signal ES cannot take a value in the range of N×frep+6 MHz (see Figure 2(b)) and less than N×frep+14 MHz (see Figure 2(c)).

[0035] Therefore, when the second difference frequency fb2 reaches its maximum value (for example, 16MHz), the first difference frequency fb1 is reduced.

[0036] Figure 3 shows the frequency spectra of the optical comb, the first laser beam LD1, and the second laser beam LD2 when the second difference frequency fb2 takes its maximum value (e.g., 16 MHz).

[0037] In Figure 3(a), since the first difference frequency fb1 is 10 MHz, the frequency f2-f1 of the electrical signal ES is N × frep + 6 MHz.

[0038] Here, as shown in Figure 3(b), the first difference frequency fb1 is reduced to 6 MHz. Then, the frequency f2-f1 of the electrical signal ES becomes N × frep + 10 MHz.

[0039] Furthermore, as shown in Figure 3(c), the first difference frequency fb1 is further reduced to 2MHz. Then, the frequency f2-f1 of the electrical signal ES becomes N×frep+14MHz.

[0040] Thus, by decreasing the first difference frequency fb1 by 4MHz each time, the frequency f2-f1 of the electrical signal ES can be increased by 4MHz each time, allowing it to take values ​​in the range of N×frep+6MHz to less than N×frep+14MHz (N×frep+10MHz).

[0041] Furthermore, by decreasing the first difference frequency fb1 by 1MHz each time (10, 9, 8, ..., 3, 2MHz), the frequency f2-f1 of the electrical signal ES can be increased by 1MHz each time (N×frep+6MHz, N×frep+7MHz, N×frep+8MHz, ..., N×frep+13MHz, N×frep+14MHz), and values ​​in the range of N×frep+7MHz, N×frep+8MHz, ..., N×frep+13MHz can be obtained.

[0042] Furthermore, if the first difference frequency fb1 is variable, the second difference frequency fb2 is reduced when the first difference frequency fb1 reaches its maximum value.

[0043] The first laser optical frequency control unit 10 includes a first optical coupler 102, a first PD (photodetector) 104, a first LPF (low-pass filter) 106, a first amplifier 108, a first local oscillator 114, a first comparator 122, a first phase comparator 124, a first loop filter 126, and a first LD driver 128.

[0044] The first optical coupler 102 combines the first laser beam LD1 output by the first slave laser (first laser light output unit) 4 and the optical comb output by the master laser (optical comb generation unit) 2.

[0045] The first PD (photodetector) (first optical signal output device) 104 receives the output of the first optical coupler 102, performs photoelectric conversion, and outputs the result. The first PD 104 outputs an optical signal representing the difference in optical frequency between the first laser beam LD1 and the 0th-order (first-mode) optical comb, due to the beat. However, the output of the first PD 104 is mixed with optical signals with higher optical frequencies than the difference in optical frequency between the first laser beam LD1 and the 0th-order (first-mode) optical comb. For example, the output of the first PD 104 may include an optical signal representing the difference frequency between the first laser beam LD1 and the 1st-order optical comb, and an optical signal representing the repetition frequency frep.

[0046] The first LPF (low-pass filter) 106 allows relatively low-frequency components of the output of the first PD 104 to pass through, thereby allowing the optical signal of the difference in optical frequency between the first laser beam LD1 and the 0th-order (first-mode) optical comb to pass through.

[0047] The first amplifier 108 amplifies the output of the first LPF 106 and feeds it to the first comparator 122.

[0048] Although it was explained that there is one low-pass filter and one amplifier, such as the first LPF 106 and the first amplifier 108, there may be two or more low-pass filters and amplifiers. For example, a low-pass filter, an amplifier, and another low-pass filter (the output of which is connected to the first comparator 122) may be connected after the first amplifier 108 in that order.

[0049] The first local oscillator (first difference frequency signal output device) 114 outputs a signal with a first difference frequency fb1 and supplies it to the first comparator 122. The first local oscillator 114 is composed of, for example, a semiconductor PLL.

[0050] The first comparator 122 shapes the output of the first amplifier 108 and the output of the first local oscillator 114 into a square wave and outputs it.

[0051] The first phase comparator (first phase difference signal output) 124 outputs a first phase difference signal (for example, a square wave signal) corresponding to the phase difference between the output of the first PD (first optical signal output) 104 and the output of the first local oscillator (first difference frequency signal output) 114. When the magnitude of the first phase difference signal becomes 0, the phases of the output of the first PD 104 and the output of the first local oscillator 114 become the same, and the frequencies of both coincide with the first difference frequency fb1. In this way, the first phase comparator 124 compares the frequencies of both by comparing their phases.

[0052] The first loop filter 126 receives the output of the first phase comparator 124, smooths it, and feeds it to the first LD driver 128.

[0053] The first LD driver (first laser light control unit) 128 controls the first laser light output unit (first slave laser 4) by supplying current to reduce the magnitude of the first phase difference signal.

[0054] Furthermore, each component of the first laser optical frequency control unit 10, in particular the first PD (photodetector) 104, the first local oscillator 114, the first phase comparator 124, and the first LD driver 128, are composed of analog circuits.

[0055] The second laser optical frequency control unit 20 includes a second optical coupler 202, a second PD (photodetector) 204, a second LPF (low-pass filter) 206, a second amplifier 208, a second local oscillator 214, a second comparator 222, a second phase comparator 224, a second loop filter 226, and a second LD driver 228.

[0056] The second optical coupler 202 combines the second laser beam LD2 output by the second slave laser (second laser light output unit) 6 and the optical comb output by the master laser (optical comb generation unit) 2.

[0057] The second PD (photodetector) (second optical signal output unit) 204 receives the output of the second optical coupler 202, performs photoelectric conversion, and outputs the result. The second PD 204 outputs an optical signal representing the difference in optical frequency between the second laser beam LD2 and the Nth or (N+1)th order (second mode) optical comb, due to the beat. However, the output of the second PD 204 contains optical signals with higher optical frequencies than the difference in optical frequency between the second laser beam LD2 and the second mode optical comb. For example, the output of the second PD 204 contains optical signals representing the difference frequency between the second laser beam LD2 and the (N+1)th or Nth order optical comb, and optical signals representing the repetition frequency frep.

[0058] The second LPF (low-pass filter) 206 allows relatively low-frequency components of the output of the second PD 204 to pass through, thereby allowing the optical signal of the difference in optical frequency between the second laser beam LD1 and the second-mode optical comb to pass through.

[0059] The second amplifier 208 amplifies the output of the second LPF 206 and supplies it to the second comparator 222.

[0060] Although it was explained that there is one low-pass filter and one amplifier, such as the second LPF 206 and the second amplifier 208, there may be two or more low-pass filters and amplifiers. For example, a low-pass filter, an amplifier, and another low-pass filter (the output of which is connected to the second comparator 222) may be connected after the second amplifier 208 in that order.

[0061] The second local oscillator (second difference frequency signal outputter) 214 outputs a signal with the second difference frequency fb2 and supplies it to the second comparator 222. The second local oscillator 214 is composed of, for example, a semiconductor PLL.

[0062] The second comparator 222 shapes the output of the second amplifier 208 and the output of the second local oscillator 214 into a square wave and outputs it.

[0063] The second phase comparator (second phase difference signal outputter) 224 outputs a second phase difference signal (for example, a square wave signal) corresponding to the phase difference between the output of the second PD (second optical signal outputter) 204 and the output of the second local oscillator (second difference frequency signal outputter) 214. When the magnitude of the second phase difference signal becomes 0, the phases of the output of the second PD 204 and the output of the second local oscillator 214 become the same, and the frequencies of both coincide with the second difference frequency fb2. In this way, the second phase comparator 224 compares the frequencies of both by comparing their phases.

[0064] The second loop filter 226 receives the output of the second phase comparator 224, smooths it, and feeds it to the second LD driver 228.

[0065] The second LD driver (second laser light control unit) 228 controls the second laser light output unit (second slave laser 6) by supplying current to reduce the magnitude of the second phase difference signal.

[0066] Furthermore, each component of the second laser optical frequency control unit 20, in particular the second PD (photodetector) 204, the second local oscillator 214, the second phase comparator 224, and the second LD driver 228, are composed of analog circuits.

[0067] Next, the operation of the embodiment of the present invention will be described.

[0068] First, the output frequency f1 of the first slave laser 4 and the output frequency f2 of the second slave laser 6 are matched so that the frequency f2-f1 roughly matches the desired frequency of the electrical signal ES. The output frequencies of the first slave laser 4 and the second slave laser 6 are variable over a wide range (e.g., on the order of 100 GHz), although the precision is not very high.

[0069] Therefore, the output frequency f1 of the first slave laser 4 and the output frequency f2 of the second slave laser 6 are controlled with fine precision.

[0070] First, the first laser optical frequency control unit 10 controls the optical frequency f1 of the first laser beam LD1 so that it differs from the optical frequency of the first mode (0th order) of the optical comb by only the first difference frequency fb1 (see Figure 2). The first difference frequency fb1 is, for example, 10 MHz, which is smaller than the repetition frequency frep = 40 MHz, allowing for fine and precise control of the optical frequency f1 of the first laser beam LD1.

[0071] The first laser beam LD1 output by the first slave laser 4 and the optical comb output by the master laser 2 are combined by the first optical coupler 102 and supplied to the first PD 104. Then, the first PD 104 outputs an optical signal representing the difference in optical frequency between the first laser beam LD1 and the 0th-order (first-mode) optical comb. The output of the first PD 104 is then filtered by the first LPF 106 and the first amplifier 108 to remove optical signals with a frequency greater than the difference in optical frequency between the first laser beam LD1 and the 0th-order (first-mode) optical comb, and supplied to the first comparator 122.

[0072] Furthermore, a signal with a first difference frequency fb1 is supplied from the first local oscillator 114 to the first comparator 122.

[0073] The output of the first PD104 and the output of the first local oscillator 114 are shaped into a square wave by the first comparator 122 and supplied to the first phase comparator 124. A first phase difference signal corresponding to the phase difference between the output of the first PD104 and the output of the first local oscillator 114 is output from the first phase comparator 124, smoothed by the first loop filter 126, and supplied to the first LD driver 128. The first LD driver 128 controls the first slave laser 4 to reduce the magnitude of the first phase difference signal. This makes the magnitude of the first phase difference signal zero.

[0074] When the magnitude of the first phase difference signal becomes 0, the phases of the output of the first PD104 and the output of the first local oscillator 114 become the same, and the frequencies of both coincide with the first difference frequency fb1.

[0075] Furthermore, the second laser optical frequency control unit 20 controls the optical frequency f2 of the second laser beam LD2 so that it differs from the optical frequency of the second mode (Nth or (N+1)th order) of the optical comb by only the second difference frequency fb2 (see Figure 2). The second difference frequency fb2 is, for example, 10 MHz (see Figure 2(a)) or 16 MHz (see Figures 2(b) and (c)), which is smaller than the repetition frequency frep = 40 MHz, allowing for fine and precise control of the optical frequency f2 of the second laser beam LD2.

[0076] The second laser beam LD2 output by the second slave laser 6 and the optical comb output by the master laser 2 are combined by the second optical coupler 202 and supplied to the second PD204. The second PD204 then outputs an optical signal representing the difference in optical frequency between the second laser beam LD1 and the second-mode optical comb. The output of the second PD204 is then filtered by the second LPF206 and the second amplifier 208 to remove optical signals with a frequency greater than the difference in optical frequency between the second laser beam LD1 and the second-mode optical comb, and supplied to the second comparator 222.

[0077] Furthermore, a signal with a second difference frequency fb2 is supplied from the second local oscillator 214 to the second comparator 222.

[0078] The output of the second PD204 and the output of the second local oscillator 214 are shaped into a square wave by the second comparator 222 and supplied to the second phase comparator 224. A second phase difference signal corresponding to the phase difference between the output of the second PD204 and the output of the second local oscillator 214 is output from the second phase comparator 224, smoothed by the second loop filter 226, and supplied to the second LD driver 228. The second LD driver 228 controls the second slave laser 6 to reduce the magnitude of the second phase difference signal. This makes the magnitude of the second phase difference signal zero.

[0079] When the magnitude of the second phase difference signal becomes 0, the phases of the output of the second PD204 and the output of the second local oscillator 214 become the same, and the frequencies of both coincide with the second difference frequency fb2.

[0080] The first laser beam LD1 and the second laser beam LD2 are supplied to UTC-PD8, and an electrical signal ES with frequencies f2-f1 is output.

[0081] In Figure 2(a), the frequency f2-f1 of the electrical signal ES is N×frep. In Figure 2(b), the frequency f2-f1 of the electrical signal ES is N×frep+6MHz. In Figure 2(c), the frequency f2-f1 of the electrical signal ES is (N+1)×frep-26MHz=N×frep+14MHz. In this way, the frequency of the electrical signal ES can be controlled more precisely and accurately than the repetition frequency frep.

[0082] Since the optical frequencies of the first laser beam LD1 and the second laser beam LD2 cannot be in region A, if the first difference frequency fb1 is kept fixed at 10 MHz, the frequency f2-f1 of the electrical signal ES cannot take a value in the range of N×frep+6 MHz (see Figure 2(b)) or less than N×frep+14 MHz (see Figure 2(c)). Therefore, when the second difference frequency fb2 takes its maximum value (for example, 16 MHz), the first difference frequency fb1 is reduced.

[0083] The first difference frequency fb1 is reduced from 10 MHz to 6 MHz, as shown in Figure 3(b). Then, the frequency f2-f1 of the electrical signal ES becomes N×frep+10 MHz. In this way, the frequency f2-f1 of the electrical signal ES can take values ​​in the range of N×frep+6 MHz and less than N×frep+14 MHz.

[0084] According to embodiments of the present invention, the frequency of electrical signals in the subterahertz band (100 GHz or more and less than 1 THz) can be precisely varied over a wide range.

[0085] First, the output frequencies of the first slave laser 4 and the second slave laser 6 are variable over a wide range.

[0086] Furthermore, the output frequency f1 of the first slave laser 4 can be controlled to differ from the first mode of the optical comb by the first difference frequency fb1. The output frequency f2 of the second slave laser 6 can be controlled to differ from the second mode of the optical comb by the second difference frequency fb2. Since the first difference frequency fb1 and the second difference frequency fb2 are smaller than the repetition frequency frep, the output frequencies of the first slave laser 4 and the second slave laser 6 can be controlled with fine precision.

[0087] In this way, the output frequencies of the first slave laser 4 and the second slave laser 6 can be controlled precisely over a wide range. Furthermore, since the outputs of the first slave laser 4 and the second slave laser 6 are supplied to the UTC-PD8, and an electrical signal ES of the frequency difference f2-f1 is output, the frequency of the electrical signal ES can be precisely varied over a wide range.

[0088] Furthermore, according to embodiments of the present invention, if the optical frequencies of the first laser beam LD1 and the second laser beam LD2 cannot be placed in region A, even if the second difference frequency fb2 takes its maximum value (for example, 16 MHz), the range in which the frequencies f2-f1 of the electrical signal ES can take can be widened by reducing the first difference frequency fb1 (see Figure 3(b)).

[0089] The following modifications are possible embodiments of the present invention.

[0090] In other words, the first local oscillator (first differential frequency signal output) 114, the first phase comparator (first phase difference signal output) 124, the second local oscillator (second differential frequency signal output) 214, and the second phase comparator (second phase difference signal output) 224 are all composed of digital circuits (for example, ASICs or FPGAs).

[0091] Figure 4 is a functional block diagram showing the configuration of a subterahertz wave output device 1 according to a modified embodiment of the present invention. The subterahertz wave output device 1 according to a modified embodiment of the present invention comprises a master laser 2, a first slave laser 4, a second slave laser 6, a UTC-PD8, a first laser optical frequency control unit 10, and a second laser optical frequency control unit 20.

[0092] The master laser 2, the first slave laser 4, the second slave laser 6, and UTC-PD8 are the same as in the embodiments of the present invention and will not be described further.

[0093] Each component of the first laser optical frequency control unit 10 is the same as in the embodiments of the present invention. For example, the first PD (first optical signal output device) 104 and the first LD driver (first laser optical control unit) 128 are configured as analog circuits.

[0094] However, the first local oscillator (first differential frequency signal output) 114, the first phase comparator (first phase difference signal output) 124, and the first loop filter 126 are configured as digital circuits. The output of the first local oscillator 114 is supplied to the first phase comparator 124. The output of the first amplifier 108 is supplied to the first phase comparator 124 via the first ADC (AD converter) 123 (which converts the output of the first amplifier 108 into a digital signal). The first loop filter 126 is supplied to the first LD driver 128 via the first DAC (DA converter) 127 (which converts the output of the first loop filter 126 into an analog signal). The first ADC 123 and the first DAC 127 are configured as digital circuits.

[0095] Each component of the second laser optical frequency control unit 20 is the same as in the embodiments of the present invention. For example, the second PD (second optical signal output unit) 204 and the second LD driver (second laser optical control unit) 228 are configured as analog circuits.

[0096] However, the second local oscillator (second difference frequency signal output) 214, the second phase comparator (second phase difference signal output) 224, and the second loop filter 226 are configured as digital circuits. The output of the second local oscillator 214 is supplied to the second phase comparator 224. The output of the second amplifier 208 is supplied to the second phase comparator 224 via the second ADC (AD converter) 223 (which converts the output of the second amplifier 208 into a digital signal). The second loop filter 226 is supplied to the second LD driver 228 via the second DAC (DA converter) 227 (which converts the output of the second loop filter 226 into an analog signal). The second ADC 223 and the second DAC 227 are configured as digital circuits. [Explanation of Symbols]

[0097] 1. Subterahertz wave output device 2 Master laser (optical comb generation unit) 4. First slave laser (first laser light output unit) 6. Second slave laser (second laser light output unit) 8 UTC-PD (Electrical Signal Output Section) 10 First Laser Optical Frequency Control Unit 102 First Optical Coupler 104 First PD (Photodetector) (First Optical Signal Output Device) 106. First LPF (Low-Pass Filter) 108 First Amplifier 114. First Local Oscillator (First Difference Frequency Signal Output) 122 First Comparator 124 1st phase comparator (1st phase difference signal output device) 126 First Loop Filter 128 First LD driver (first laser light control unit) 20 Second laser optical frequency control unit 202 Second Optical Coupler 204 Second PD (Photodetector) (Second Optical Signal Output Unit) 206. Second LPF (Low-Pass Filter) 208 Second Amplifier 214 Second Local Oscillator (Second Difference Frequency Signal Output Unit) 222 Second Comparator 224 2nd phase comparator (2nd phase difference signal output device) 226 Second Loop Filter 228 Second LD driver (second laser light control unit) frep repetition frequency LD1 First laser beam LD2 Second Laser Light ES Electrical Signal fb1 First difference frequency fb2 Second difference frequency f1 Optical frequency of the first laser beam LD1 f2 Optical frequency of the second laser beam LD2

Claims

1. An optical comb generation unit that generates an optical comb, A first laser beam output unit that outputs a first laser beam with a variable optical frequency, A first laser optical frequency control unit controls the optical frequency of the first laser beam so that it differs from the optical frequency of the first mode of the optical comb by only a first difference frequency, A second laser beam output unit that outputs a second laser beam with a variable optical frequency, A second laser optical frequency control unit controls the optical frequency of the second laser beam so that it differs from the optical frequency of the second mode of the optical comb by only the second difference frequency, An electrical signal output unit that receives the first laser beam and the second laser beam and outputs an electrical signal with a frequency equal to the difference between the optical frequency of the first laser beam and the optical frequency of the second laser beam, Equipped with, The frequency of the aforementioned electrical signal is 100 GHz or more and less than 1 THz. The difference between the first difference frequency and the second difference frequency is less than or equal to half the repetition frequency of the optical comb. Subterahertz wave output device.

2. A subterahertz wave output device according to claim 1, A subterahertz wave output device in which one or both of the first difference frequency and the second difference frequency are variable.

3. A subterahertz wave output device according to claim 2, A subterahertz wave output device in which the maximum value of the first difference frequency and the maximum value of the second difference frequency are less than half the repetition frequency of the optical comb.

4. A subterahertz wave output device according to claim 3, When either the first difference frequency or the second difference frequency takes its maximum value, The other of the first difference frequency and the second difference frequency is reduced. Subterahertz wave output device.

5. A subterahertz wave output device according to claim 1, The first laser optical frequency control unit, A first optical signal output device that outputs an optical signal which is the difference in optical frequency between the first laser beam and the first mode of the optical comb, A first difference frequency signal output device that outputs a signal of the first difference frequency, A first phase difference signal outputter outputs a first phase difference signal corresponding to the phase difference between the output of the first optical signal outputter and the output of the first differential frequency signal outputter, A first laser light control unit controls the first laser light output unit to reduce the magnitude of the first phase difference signal, It has, The second laser optical frequency control unit, A second optical signal output device that outputs an optical signal which is the difference in optical frequency between the second laser beam and the second mode of the optical comb, A second difference frequency signal output device that outputs a signal of the second difference frequency, A second phase difference signal outputter outputs a second phase difference signal corresponding to the phase difference between the output of the second optical signal outputter and the output of the second differential frequency signal outputter, A second laser light control unit controls the second laser light output unit to reduce the magnitude of the second phase difference signal, Having, Subterahertz wave output device.

6. A subterahertz wave output device according to claim 5, The first optical signal output device, the first differential frequency signal output device, the first phase difference signal output device, and the first laser light control unit, The second optical signal output device, the second differential frequency signal output device, the second phase difference signal output device, and the second laser light control unit, However, it is a subterahertz wave output device composed of analog circuits.

7. A subterahertz wave output device according to claim 5, The first optical signal output device and the first laser light control unit, The second optical signal output device and the second laser light control unit, However, it is composed of analog circuits. The first differential frequency signal output device and the first phase difference signal output device, The second differential frequency signal output device and the second phase difference signal output device, However, it is a subterahertz wave output device composed of digital circuits.

8. A subterahertz wave output device according to claim 1, The aforementioned electrical signal output unit is UTC-PD. Subterahertz wave output device.

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