Signal detection device and wireless reception device

Abstract

A signal detection device 1 comprises: an electro / optical conversion element 13 for modulating a first optical signal having a first frequency and a second optical signal having a second frequency using an electric signal; an optical filter for extracting light of a band including the second optical signal and a side band signal of the first optical signal, and also extracting light of a band including the first optical signal and a side band signal of the second optical signal; a first photodiode 16 for generating a first intermediate frequency signal from the second optical signal and the side band signal of the first optical signal; and a second photodiode 17 for generating a second intermediate frequency signal from the first optical signal and the side band signal of the second optical signal. The signal detection device detects an electro-optical signal on the basis of a difference between an output from the first photodiode and an output from the second photodiode.

Description

Signal detection device and radio receiving device

[0001] The present disclosure relates to a signal detection device and a radio receiving device.

[0002] In order to detect signals such as RF waves and terahertz waves, a technique has been proposed in which the electro-optic effect (e.g., the Pockels effect) is used to superimpose information on the detected signal as modulated sideband light onto an optical signal (see, for example, Non-Patent Documents 1 and 2).

[0003] S. Hisatake and T. Nagatsuma "Nonpolarimetric Technique for Homodyne-Type Electrooptic Field Detection" Applied Physics Express 5 (2012).S. Hisatake, HHN Pham, and T. Nagatsuma, "Visualization of the spatial-temporal evolution of continuous electromagnetic waves in the terahertz range based on photonics technology" Optica, Vol. 1, Issue 6, pp. 365-371 (2014).

[0004] The technologies described in Non-Patent Documents 1 and 2 are based on the principle of modulating two optical signals (carrier signals) with different frequencies using a target signal (e.g., a radio signal such as RF) within an electro-optical conversion element (EO element). The sideband light generated by this modulation and nearby strong light are extracted using an optical filter, and then mixed using a photodiode to generate an IF signal (intermediate frequency signal). This IF signal contains amplitude and phase information of the target signal. Therefore, the amplitude and phase of the target signal can be detected by lock-in detection.

[0005] This type of signal detection using the electro-optic effect can instantaneously superimpose the detected signal onto an optical carrier signal and measure it as an optical signal, making it possible to use existing compact, simple, and inexpensive optical communication platforms. As a result, it has the advantages of being highly compatible with optical communications and highly versatile.

[0006] However, the techniques described in Non-Patent Documents 1 and 2 still have room for improvement in terms of sensitivity.

[0007] The present disclosure has been made in light of these circumstances, and its purpose is to achieve highly sensitive signal detection.

[0008] In order to solve the above problem, a signal detection device for detecting an electrical signal according to one embodiment of the present invention includes an electrical / optical conversion element that modulates a first optical signal having a first frequency and a second optical signal having a second frequency with an electrical signal; an optical filter that extracts light in a band including the second optical signal and sideband signals of the first optical signal, and also extracts light in a band including the sideband signals of the first optical signal and the second optical signal; a first photodiode that generates a first intermediate frequency signal from the second optical signal and the sideband signals of the first optical signal; and a second photodiode that generates a second intermediate frequency signal from the sideband signals of the first optical signal and the second optical signal, and performs detection based on the difference between the output from the first photodiode and the output from the second photodiode.

[0009] In an embodiment, the optical filter may include a first bandpass filter that transmits light in a band including the second optical signal and sideband signals of the first optical signal, and a second bandpass filter that transmits light in a band including the sideband signals of the first optical signal and the second optical signal, or may include an FBG filter that reflects light in a band including the sideband signals of the first optical signal and the second optical signal and transmits light in a band including at least the second optical signal and the sideband signals of the first optical signal, and a circulator that receives the first optical signal and the second optical signal modulated by the electrical signal and outputs them to the FBG filter, and outputs the sideband signals of the first optical signal and the second optical signal reflected by the FBG filter to the second photodiode.

[0010] In an embodiment, the first photodiode and the second photodiode may be arranged in a dual configuration or in a balanced configuration.

[0011] In one embodiment, the electrical / optical conversion element is made of lithium niobate (LiNbO ３ ), lithium tantalate (LiTaO3 ３ ), zinc telluride (ZnTe), gallium phosphide (GaP), gallium arsenide (GaAs), OH1 or DAST, or may be composed of an electro-optical polymer.

[0012] Another aspect of the present invention is a wireless receiving device for receiving a wireless signal, the device comprising: a receiving antenna, a multi-tone optical signal source that generates optical signals of multiple frequencies, an electrical-to-optical conversion element that modulates a first optical signal having a first frequency and a second optical signal having a second frequency generated by the multi-tone optical signal source with a wireless signal, an optical filter that extracts light in a band including the second optical signal and sideband signals of the first optical signal and extracts light in a band including the sideband signals of the first optical signal and the second optical signal, a first photodiode that generates a first intermediate frequency signal from the second optical signal and the sideband signals of the first optical signal, and a second photodiode that generates a second intermediate frequency signal from the first optical signal and the sideband signals of the second optical signal, and receives the wireless signal based on a difference between an output from the first photodiode and an output from the second photodiode.

[0013] In an embodiment, the optical filter may include an FBG filter that reflects light in a band including sideband signals of the first optical signal and the second optical signal and transmits light in a band including at least the second optical signal and the sideband signals of the first optical signal, and a circulator that receives the first optical signal and the second optical signal modulated by an electrical signal and inputs them to the FBG filter, and that receives the sideband signals of the first optical signal and the second optical signal reflected by the FBG filter and inputs them to the second photodiode.

[0014] Any combination of the above components, and conversion of the present disclosure into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present disclosure.

[0015] According to the present disclosure, highly sensitive signal detection can be achieved.

[0016] 6(a) and 6(b) are schematic diagrams of an experimental system illustrating the principle of signal detection using electrical-optical conversion.

[0034] FIG. 6(a) is a schematic diagram of an experimental system illustrating the principle of signal detection using electrical-optical conversion.

[0035] FIG. 6(b) is a schematic diagram of a signal detection device according to a first comparative example.

[0036] FIG. 6(c) is a diagram illustrating the spectra of a first optical signal (thick solid line), a second optical signal (thin solid line), a first sideband signal (thin solid line), and a second sideband signal (thin dotted line).

[0037] FIG. 6(d) is a diagram illustrating an example of the arrangement of a first photodiode and a second photodiode.

[0038] FIG. 6(a) shows a dual-type arrangement.

[0039] FIG. 6(b) shows a balanced-type arrangement.

[0039] FIG. 6(c) is a schematic diagram of a signal detection device according to a second comparative example.

[0039] FIG. 6(b) is a schematic diagram of a wireless receiving device according to a third embodiment.

[0039] FIG. 6(a) shows the phase of a detected signal to be detected.

[0039] FIG. 6(b) is the amplitude of a detected signal to be detected.

[0039] FIG. 6(c) is a diagram illustrating the result of signal detection based on the output from the signal detection device of FIG. 3. 11(a) shows the amplitude of the detected signal detected by the output of the first photodiode. FIG. 11(b) shows the phase of the detected signal detected based on the output of the first photodiode. FIG. 11(c) shows the amplitude of the detected signal detected by the output of the second photodiode. FIG. 11(d) shows the phase of the detected signal detected based on the output of the second photodiode. This figure shows the relationship between the signal-to-noise ratio and phase variation of signal detection by the signal detection device 1.

[0017] Before describing specific embodiments, the findings that form the basis of this disclosure will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram of an experimental system 100 that illustrates the principle of signal detection using electrical-optical conversion. Figure 2 is a schematic diagram that illustrates the processing flow of the experimental system 100 of Figure 1.

[0018] The experimental system 100 includes a multi-tone optical signal source 101 , a circulator 102 , an electrical / optical conversion element 103 , an optical filter 104 , and a photodiode 105 .

[0019] A multi-tone optical signal source 101 has a frequency f １ and a first optical signal S1 of frequency f ２ (>f １ The generated first optical signal S1 and second optical signal S2 are input to a first port of the circulator 102.

[0020] The circulator 102 has a three-port configuration, and a first optical signal S1 and a second optical signal S2 input to a first port are input to an electro-optical conversion element 103 from a second port. A signal to be detected (an electrical signal, typically a wireless signal such as an RF signal or a terahertz signal) is also input to the electro-optical conversion element 103. Within the electro-optical conversion element 103, the first optical signal S1 and the second optical signal S2 are modulated by the signal to be detected. At this time, in the optical spectrum output from the electro-optical conversion element 103, in addition to the first optical signal S1 and the second optical signal S2, a sideband signal SB1 of the first optical signal S1 (also referred to as the "first sideband signal SB1") and a sideband signal SB2 of the second optical signal S2 (also referred to as the "second sideband signal SB2") are generated. Here, the frequency f of the first optical signal S1 is １ The difference between the frequency of the first sideband signal SB1 and the frequency of the first sideband signal SB2 is f ＲＦ The difference in frequency between the second optical signal S2 and the sideband signal SB1 of the first optical signal S1 is Δf (f ＲＦ >Δf). The light including the sideband signal output from the electrical / optical conversion element 103 is input to the second port of the circulator 102, output from the third port, and then input to the optical filter 104. Regarding the input / output ports of the circulator 102, it is assumed that an optical signal is sent from the first port to the second port, from the second port to the third port, and from the third port to the first port (the same applies below).

[0021] The optical filter 104 is a filter for a frequency f ２That is, the optical filter 104 extracts the second optical signal S2 and the sideband signal SB1 of the first optical signal S1.

[0022] The light transmitted through the optical filter 104 (i.e., the second optical signal S2 and the sideband signal SB1 of the first optical signal S1) is input to the photodiode 105. These optical signals are mixed by the photodiode to generate an IF signal. The frequency of this IF signal is f ２ -f １ -f ＲＦ is.

[0023] This IF signal contains amplitude and phase information of the signal to be detected, and by performing lock-in detection on this signal, the amplitude and phase of the signal to be detected can be detected.

[0024] The frequency of the IF signal is f １ and frequency f ２ It can be set arbitrarily by adjusting the frequency difference between

[0025] Based on the above findings, an embodiment of the present disclosure will be described.

[0026] 3 is a schematic diagram of a signal detection device 200 according to a first comparative example. The signal detection device 200 includes a multi-tone optical signal source 201, a first circulator 202, an electrical-to-optical conversion element 203, an optical coupler 204, a first optical filter 205, a first photodiode 206, a second optical filter 207, and a second photodiode 208.

[0027] The multi-tone optical signal source 201 emits a first frequency f １ and a first optical signal S1 of a second frequency f ２ The generated first optical signal S1 and second optical signal S2 (hereinafter collectively referred to as "multi-tone optical signals") are input to a first port of a first circulator 202. The multi-tone optical signal source 201 may be realized by any suitable technology, such as a frequency tunable laser, two modes filtered from a multi-frequency light source, or an optical frequency comb.

[0028] The first circulator 202 has a three-port configuration, and outputs the first optical signal S1 and the second optical signal S2 input to the first port from the second port and inputs them to the electrical / optical conversion element 203. The electrical / optical conversion element 203 also includes a frequency f ＲＦ A signal to be detected (an electrical signal, typically a wireless signal such as an RF signal or a terahertz signal) is input. In the electrical / optical conversion element 203, a first optical signal S1 and a second optical signal S2 are modulated by this signal to be detected. At this time, in the optical spectrum output from the electrical / optical conversion element 203, first sideband signals (SB1+, SB1−) and second sideband signals (SB2+, SB2−) of the first optical signal S1 and the second optical signal S2 are generated on both sides of each optical signal. The frequencies of the first sideband signals SB1+ and SB1− are respectively defined as first sideband frequencies f ＳＢ１＋ and f ＳＢ１－ Similarly, the frequencies of the second sideband signals SB2+ and SB2− are set to the second sideband frequency f ＳＢ２＋ and f ＳＢ２－ Then, the first sideband frequency f ＳＢ１＋ and f ＳＢ１－ , the second sideband frequency f ＳＢ２＋ and f ＳＢ２－ are expressed as follows: ＳＢ１＋ = f １ +f ＲＦ f ＳＢ１－ = f １ -f ＲＦ f ＳＢ２＋ = f ２ +f ＲＦ f ＳＢ２－ = f ２ -f ＲＦ Below, the second frequency f ２ and the first sideband frequency f ＳＢ１＋ and the first frequency f １ and the second sideband frequency f ＳＢ２－ Here, it is also possible to omit first circulator 202 and input the multi-tone optical signal supplied from multi-tone optical signal source 201 directly to electrical-to-optical conversion element 203 so that it is modulated by the signal to be detected (hereinafter, such a configuration is referred to as a "transmission type").

[0029] FIG. 4 shows the optical spectra of the first optical signal S1 (thick solid line), the second optical signal S2 (thin solid line), the first sideband signal SB1 (thick dotted line), and the second sideband signal SB2 (thin dotted line).

[0030] The electrical / optical conversion element 203 is made of lithium niobate (LiNbO ３ ), lithium tantalate (LiTaO ３ Electro-optic crystal materials comprising ZnTe, gallium phosphide (GaP), gallium arsenide (GaAs), OH1 or DAST may also be used.

[0031] As the electro-optical polymer (EO polymer), for example, the electro-optical polymer described in International Publication WO2019 / 039530 may be used.

[0032] The multi-tone optical signal output from the electrical / optical conversion element 203 includes sideband signals, is input to the second port of the first circulator 202, output from the third port, and then input to the optical coupler 204. In the case of a transmission type, the multi-tone optical signal output from the electrical / optical conversion element 203 is directly input to the optical coupler 204. The multi-tone optical signal is then branched by the optical coupler 204 and input to the first optical filter 205 and the second optical filter 207.

[0033] The first optical filter 205 is a filter having a frequency f ２ The first optical filter 205 is a bandpass filter that transmits light having a bandwidth of at least Δf with an upper limit of Δf. That is, the first optical filter 205 extracts the second optical signal S2 and the first sideband signal SB1+.

[0034] The second optical filter 207 is a filter having a frequency f １ That is, the second optical filter 207 extracts the first optical signal S1 and the second sideband signal SB2−.

[0035] The light transmitted through the first optical filter 205 (i.e., the extracted second optical signal S2 and first sideband signal SB1) is input to the first photodiode 206. These optical signals are mixed by the first photodiode 206 to generate a first IF signal. The frequency of this first IF signal is f ２ -f １ -f ＲＦ is.

[0036] The light transmitted through the second optical filter 207 (i.e., the extracted first optical signal S1 and second sideband signal SB2) is input to the second photodiode 208. These optical signals are mixed by the second photodiode 208 to generate a second IF signal. The frequency of this second IF signal is f ２ -f ＲＦ -f １ is.

[0037] The signal detection device 200 performs detection based on the difference between the first IF signal output from the first photodiode 206 and the second IF signal output from the second photodiode 208 .

[0038] The first IF signal and the second IF signal contain amplitude and phase information of the signal to be detected, and by performing lock-in detection on this, the amplitude and phase of the signal to be detected can be detected.

[0039] The first photodiode 206 and the second photodiode 208 may be arranged in any suitable manner as long as detection can be performed based on the difference between the first IF signal and the second IF signal. For example, the first photodiode 206 and the second photodiode 208 may be arranged in a dual type (two photodiodes arranged independently) as shown in Fig. 6(a) or a balanced type (two photodiodes connected in series so that their photocurrents cancel each other out) as shown in Fig. 6(b).

[0040] In the experimental system of FIG. 3 , only one set of optical signal and sideband signal (i.e., the combination of the second optical signal and the first sideband signal) is used to detect a signal. This results in a problem of low detection sensitivity. In contrast, in this embodiment, two sets of optical signal and sideband signal (i.e., the combination of the second optical signal and the first sideband signal, and the combination of the first optical signal and the second sideband signal) are extracted, and detection is performed based on the difference between them. In this case, if the system satisfies certain conditions, for example, if the optical path length from the optical coupler 204 to the first optical filter 205 to the first photodiode 206 is approximately equal to the optical path length from the optical coupler 204 to the second optical filter 207 to the second photodiode 208 (more specifically, for example, within half the wavelength of the electrical signal Δf), the in-phase noise component is eliminated. This improves sensitivity.

[0041] 5 is a schematic diagram of a signal detection device 1 according to a first embodiment. The signal detection device 1 includes a multi-tone optical signal source 11, a first circulator 12, an electrical / optical conversion element 13, a second circulator 14, an FBG filter 15, a first photodiode 16, and a second photodiode 17.

[0042] In this signal detection device 1, the multi-tone optical signal source 11, the first circulator 12, and the electrical / optical conversion element 13 have the same configuration as those in the signal detection device 200 of Fig. 3. The second circulator 14 has a three-port configuration, with its first port connected to the third port of the first circulator 12 and its second port connected to an FBG filter 15.

[0043] The FBG filter 15 is an optical filter using a fiber Bragg grating, and has a frequency f １The Bragg wavelength is set to correspond to at least a band of Δf, with f as the lower limit. Here, the Bragg wavelength refers to a wavelength that is selectively reflected by the fiber Bragg grating. Then, the light that has passed through the FBG filter 15 (i.e., the second optical signal S2 and the first sideband signal SB1) is input to the first photodiode 16. These optical signals are mixed in the first photodiode 16 to generate a first IF signal. The frequency of this first IF signal is f ２ -f １ -f ＲＦ is.

[0044] The light reflected by the FBG filter 15 (i.e., the first optical signal S1 and the second sideband signal SB2) is input to the second port of the second circulator 14, output from the third port, and input to the second photodiode 17. These optical signals are mixed in the second photodiode 17 to generate a second IF signal. The frequency of this second IF signal is f ２ -f ＲＦ -f １ is.

[0045] Here, the optical path length from the output on the transmission side of the FBG filter 15 to the first photodiode 16 and the optical path length from the output on the reflection side to the second photodiode 17 via the second circulator 14 are set to be approximately equal (more specifically, within half the wavelength of the electrical signal Δf).

[0046] In this signal detection device 1, as in the signal detection device 200 of Fig. 3, a first IF signal is output from the first photodiode 16 and a second IF signal is output from the second photodiode 17, and detection is performed based on the difference between these signals, thereby making it possible to detect the amplitude and phase of the signal to be detected. The arrangement of these first photodiode 16 and second photodiode 17 may be of a dual type or a balanced type, as in the signal detection device 200 of Fig. 3.

[0047] According to this embodiment, it is possible to realize highly sensitive signal detection and also to detect the second frequency f of the second optical signal S2. ２ Since it is possible to select from a band other than the Bragg wavelength of the FBG filter 15, versatility is increased.

[0048] 7 is a schematic diagram of a signal detection device 2 according to a second embodiment. The signal detection device 2 includes a multi-tone optical signal source 11, an electrical / optical conversion element 13, a third circulator 18, an FBG filter 15, a first photodiode 16, and a second photodiode 17.

[0049] In this signal detection device 2, the multi-tone optical signal source 11, the electrical / optical conversion element 13, the FBG filter 15, the first photodiode 16 and the second photodiode 17 have the same configuration as those in the signal detection device 1 of FIG.

[0050] The third circulator 18 has a four-port configuration, with the multi-tone optical signal source 11 connected to the first port, the electrical / optical conversion element 13 connected to the second port, the FBG filter 15 connected to the third port, and the second photodiode 17 connected to the fourth port. This third circulator 18 has the combined functions of the first circulator 12 and the second circulator 14 of the signal detection device 1 according to the first embodiment.

[0051] In this embodiment, a highly sensitive signal detection can also be realized, and the second frequency f ２ It is possible to select from a band other than the Bragg wavelength of the FBG filter 15, thereby increasing versatility.

[0052] 8 is a schematic diagram of a wireless receiving device 300 according to a second comparative example. The wireless receiving device 300 is configured as a transmission type and includes a receiving antenna 302, a multi-tone optical signal source 301, an electrical-to-optical conversion element 303, an optical coupler 304, a first optical filter 305, a first photodiode 306, a second optical filter 307, and a second photodiode 308.

[0053] The receiving antenna 302 may be any suitable antenna such as a parabolic antenna, a Cassegrain antenna, or a horn antenna. Alternatively, a surface antenna mounted on the surface of the photoelectric conversion element may be used. The receiving antenna 302 receives a radio signal and transmits it at a frequency f ＲＦThe signal to be detected is input to the electrical-optical conversion element 303. The first optical signal S1 and the second optical signal S2 generated by the multi-tone optical signal source 301 are input to the electrical-optical conversion element 303. Within the electrical-optical conversion element 303, the first optical signal S1 and the second optical signal S2 are modulated by the signal to be detected. This modulation by the electrical-optical conversion element 303 is similar to that by the electrical-optical conversion element 203 in FIG. 3. As a result, the light including the sideband signal output from the electrical-optical conversion element 303 is branched by the optical coupler 304 and input to the first optical filter 305 and the second optical filter 307. The configuration and operation of the stages subsequent to the optical coupler 304 are similar to those of the signal detection device 200 in FIG. 3.

[0054] The wireless receiving device 300 may use the first circulator 202, similar to the signal detection device 200 in Fig. 3. In this case, the rest of the configuration and operation of the wireless receiving device 300, excluding the receiving antenna 302, are similar to those of the signal detection device 200 in Fig. 3.

[0055] 9 is a schematic diagram of a wireless receiving device 3 according to a third embodiment. The wireless receiving device 3 is configured as a transmission type and includes a receiving antenna 20, a multi-tone optical signal source 11, an electrical / optical conversion element 21, a second circulator 14, an FBG filter 15, a first photodiode 16, and a second photodiode 17.

[0056] In this wireless receiving device 3, the multi-tone optical signal source 11, the electrical / optical conversion element 21, and the receiving antenna 20 have the same configuration as those in the wireless receiving device 300 of Fig. 8. In addition, the second circulator 14, the FBG filter 15, the first photodiode 16, and the second photodiode 17 have the same configuration as those in the signal detecting device 200 of Fig. 3.

[0057] In this embodiment, the output of the electrical-optical conversion element 21 is connected to a first port of the second circulator 14. As a result, the multi-tone signal (including the sideband signal) modulated by the electrical-optical conversion element 21 is input to the second circulator 14, the first photodiode 16 generates a first IF signal by mixing the second optical signal S2 and the first sideband signal SB1, and the second photodiode 17 generates a second IF signal by mixing the first optical signal S1 and the second sideband signal SB2.

[0058] The wireless receiving device 3 may use the first circulator 12, similar to the signal detection device 1 in Fig. 5. In this case, the rest of the configuration and operation of the wireless receiving device 3, excluding the receiving antenna 20, are the same as those of the signal detection device 1 in Fig. 5. Furthermore, when the first circulator 12 is used, the first circulator 12 and the second circulator 14 can be combined into one using a four-port circulator.

[0059] According to this embodiment, a highly sensitive wireless receiving device can be realized, and the second frequency f ２ Since it is possible to select from a band other than the Bragg wavelength of the FBG filter 15, versatility is increased.

[0060] [Verification experiment]

[0061] The inventors conducted an experiment to verify the effectiveness of the signal detection device of the present disclosure. Figure 10 shows the results of signal detection based on the output of the signal detection device 1 of Figure 5. Figure 10(a) shows the phase of the detected signal to be detected. Figure 10(b) shows the amplitude of the detected signal to be detected. From this, the signal-to-noise ratio obtained is 16.3 dB.

[0062] For comparison, FIG. 11 shows signal detection results based on the outputs from the first photodiode 16 and the second photodiode 17 of the signal detection device 1. FIG. 11(a) shows the amplitude of the detected signal detected using the output of the first photodiode 16. FIG. 11(b) shows the phase of the detected signal detected based on the output of the first photodiode 16. FIG. 11(c) shows the amplitude of the detected signal detected using the output of the second photodiode 17. FIG. 11(b) shows the phase of the detected signal detected based on the output of the second photodiode 17. These results correspond to signal detection using a conventional method (i.e., without detection based on the difference between two signals). The signal-to-noise ratios obtained from signal detection using the outputs from the first photodiode 16 and the second photodiode 17 are 13.2 dB and 13.5 dB, respectively. Comparing this with FIG. 10, it can be seen that the signal-to-noise ratio according to this embodiment is improved by approximately 3 dB compared to the conventional method.

[0063] FIG. 12 shows the relationship between the signal-to-noise ratio and phase variation in signal detection by the signal detection device 1. The horizontal axis represents the signal-to-noise ratio, and the vertical axis represents the standard deviation of the phase. The curve represents the theoretical value, and the dots represent the measurement. As shown in the figure, according to this embodiment, it can be seen that the measured values ​​are almost identical to the theoretical values ​​(they lie on the curve). The above experimental results demonstrate the effectiveness of this embodiment.

[0064] The present disclosure has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and the respective treatment processes, and that such modifications are also within the scope of the present disclosure.

[0065] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present disclosure. A new embodiment resulting from the combination has the combined effects of the respective embodiments and modifications.

[0066] When understanding the abstract technical ideas of the embodiments and modifications, the technical ideas should not be interpreted as being limited to the contents of the embodiments and modifications. The above-described embodiments and modifications are merely illustrative examples, and many design modifications, such as changes, additions, and deletions of components, are possible. In the embodiments, the contents in which such design modifications are possible are emphasized by adding the notation "embodiment." However, design modifications are also permitted even in contents not so notated.

[0067] The present disclosure is particularly useful in the following fields: - Detection of radio signals - Reception of radio signals - Visualization of electric fields - Measurement of material parameters - Measurement of component parameters.

[0068] 1, 2: Signal detection device. 3, 4: Wireless receiving device. 11: Multi-tone optical signal source. 12: First circulator. 13: Electrical / optical conversion element. 14: Second circulator. 15: FBG filter. 16: First photodiode. 17: Second photodiode. 18: Third circulator. 20: Receiving antenna. 21: Electrical / optical conversion element. 100: Experimental system. 101: Multi-tone optical signal source. 102: Circulator. 103: Electrical / optical conversion element. 104: Optical filter. 105: Photodiode. 200: Signal detection device. 20: Multi-tone optical signal source. 202: First circulator. 203: Electrical / optical conversion element. 204: Optical coupler. 205: First optical filter. 206: First photodiode. 207: Second optical filter. 208: Second photodiode. 300: Wireless receiving device. 301: Multi-tone optical signal source. 302: Receiving antenna. 303: Electrical / optical conversion element. 304: Optical coupler. 305: First optical filter. 306: First photodiode. 307: Second optical filter. 308: Second photodiode.

Claims

1. A signal detection device for detecting an electrical signal, comprising: an electro-optical conversion element that modulates a first optical signal having a first frequency and a second optical signal having a second frequency with the electrical signal; an optical filter that extracts light in a band including the sideband signals of the second optical signal and the first optical signal, and extracts light in a band including the sideband signals of the first optical signal and the second optical signal; a first photodiode that generates a first intermediate frequency signal from the sideband signals of the second optical signal and the first optical signal; and a second photodiode that generates a second intermediate frequency signal from the sideband signals of the first optical signal and the second optical signal, wherein the optical filter includes an FBG filter that reflects light in a band including the sideband signals of the first optical signal and the second optical signal, and transmits at least light in a band including the sideband signals of the second optical signal and the first optical signal, and a circulator that receives the first optical signal and the second optical signal modulated by the electrical signal and outputs them to the FBG filter, and outputs the sideband signals of the first optical signal and the second optical signal reflected by the FBG filter to the second photodiode, and the signal detection device is characterized in that detection is performed based on the difference between the output from the first photodiode and the output from the second photodiode.

2. The signal detection device according to claim 1, wherein the difference between the optical path length from the output on the transmission side of the FBG filter to the first photodiode and the optical path length from the output on the reflection side of the FBG filter through the circulator to the second photodiode is within a half wavelength of the electrical signal.

3. The signal detection device according to claim 1, wherein the first photodiode and the second photodiode are arranged in a dual type.

4. The signal detection device according to claim 1, wherein the first photodiode and the second photodiode are arranged in a balanced type.

5. The electro-optical conversion element is made of a lithium niobate (LiNbO ３ ), lithium tantalate (LiTaO ３ ), zinc telluride (ZnTe), gallium phosphide (GaP), gallium arsenide (GaAs), an electro-optic crystal material including OH1 or DAST. The signal detection device according to claim 1, characterized in that it is composed of such materials.

6. The signal detection device according to claim 1, wherein the electro-optical conversion element is constituted by an electro-optical polymer.

7. A wireless receiving device for receiving a wireless signal, comprising: a receiving antenna; a multi-tone optical signal source for generating optical signals of a plurality of frequencies; an electro-optical conversion element for modulating, with the wireless signal, a first optical signal having a first frequency and a second optical signal having a second frequency generated by the multi-tone optical signal source; an optical filter for extracting light in a band including the second optical signal and sideband signals of the first optical signal, and for extracting light in a band including the first optical signal and sideband signals of the second optical signal; a first photodiode for generating a first intermediate frequency signal from the second optical signal and the sideband signals of the first optical signal; and a second photodiode for generating a second intermediate frequency signal from the first optical signal and the sideband signals of the second optical signal. The optical filter includes an FBG filter that reflects light in a band including the sideband signals of the first optical signal and the second optical signal and transmits at least light in a band including the sideband signals of the second optical signal and the first optical signal, and a circulator that receives the first optical signal and the second optical signal modulated with an electrical signal and inputs them to the FBG filter, and receives the sideband signals of the first optical signal and the second optical signal reflected by the FBG filter and inputs them to the second photodiode. The wireless receiving device is characterized in that it receives a wireless signal based on a difference between an output from the first photodiode and an output from the second photodiode.

8. The wireless receiving device according to claim 7, wherein a difference between an optical path length from an output on the transmission side of the FBG filter to the first photodiode and an optical path length from an output on the reflection side of the FBG filter through the circulator to the second photodiode is within a half wavelength of the electrical signal.

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