Coherent photoelectric synthesis device

Abstract

To provide a coherent synthetic radio transmission device of a high output at a low-phase noise, and a phased-array antenna device.SOLUTION: A coherent synthetic light electric conversion device that transmits, from a S4 transmission antenna 5, a radio signal of which a carrier signal is modulated by a base band signal containing an information signal, includes: a fine optical resonator 2 that is excited by a laser beam, and generates an optical frequency comb of a frequency interval frep of 100 GHz or more and 3 THz or less; a modulation part 3 that separates a plurality of pairs of optical frequency modes that are adjacent to each other from the optical frequency comb, and performs optical modulation by using the same base band signal to one of each pair; an optical electric conversion part 4 formed by one or more optical electric conversion parts 41 and 42 that are provided to the transmission antenna, and generate high-frequency radio signals S41 and S42 that are equal to the frequency interval frep by mixing optical frequency modes of the optical frequency mode pair; and phase off-set adjustment parts 301 and 302 that adjust a phase off-set between the phases of high-frequency radio signal groups.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a coherent composite wireless transmission device and a phased array antenna device using the same. [Background technology]

[0002] Traditionally, in mobile (wireless) communications (2G / 3G / 4G / 5G, etc.), technological innovations accompanying advances in semiconductor technology (higher speed and higher frequency electronic circuits) have driven generational evolution. However, the frequencies used in next-generation mobile communications (Beyond 5G / 6G) are expected to extend to the so-called terahertz band (hereinafter referred to as the THz band), which includes carrier frequencies of 300 GHz and above, potentially reaching the technical limits of electrical methods (upper frequency limits). In other words, it is said that fundamental problems such as reduced power output of wireless carrier waves, increased phase noise, increased signal transmission loss, and time delays associated with signal conversion between optical and mobile communications will become apparent.

[0003] On the other hand, optical communication using fiber optic networks offers the fastest information transmission speed, and recently, silicon photonics technology is being developed to replace electronic wiring inside devices with optical wiring, achieving ultra-high speed, large capacity, low latency, and low power consumption. Against this backdrop, examples of using optical devices as carrier sources or incorporating optical communication technology into parts of wireless communication systems have recently been observed. For example, an example has been disclosed in which terahertz waves are generated by modulating and mixing light of different wavelengths and then used in wireless communication (Non-Patent Literature 1).

[0004] Furthermore, there have been reports of a prototype phased array antenna that transmits terahertz-band radio waves obtained by interfering the output light of multiple lasers using silicon photonics technology (Non-Patent Literature 2).

[0005] Another method for generating light of two wavelengths with different frequencies is disclosed, which involves filtering out arbitrary optical frequency modes that have a desired frequency interval from an optical frequency comb (Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-4858 [Non-patent literature]

[0007] [Non-Patent Document 1] Tadao Nagatsuma, "Terahertz Waves Open Up Ultra-High-Speed ​​Wireless Communication," Journal of the Japan Society for Precision Engineering, Vol. 82, No. 3, 2016. [Non-Patent Document 2] Kato, "Outline of Research and Development of High-Security Wireless Communication Technology Utilizing Terahertz Waves," Radio Wave Utilization Webinar 2021, October 28, 2021. http: / / www.kiai.gr.jp / jigyou / R3 / PDF / 1028p4.pdf [Overview of the project] [Problems that the invention aims to solve]

[0008] However, when using multiple lasers as a light source, it was difficult to precisely control the phase noise between lasers, and especially the low-frequency phase noise, known as phase fluctuation. In the method of extracting arbitrary optical frequency modes from an optical frequency comb and obtaining terahertz waves from these beats, even if phase noise could be kept low, the strength of the terahertz waves that could be generated from a single photoelectric conversion element was weak, resulting in a poor signal-to-noise ratio of the received signal and a tendency to lead to communication errors. In addition, because the generated terahertz waves are high-frequency, the beam directivity is strong, and in order to propagate the terahertz waves toward a receiver in a specific direction, a mechanism to mechanically scan the direction of radiation of the terahertz waves is required, which presents the challenge of difficulty in high-speed scanning. [Means for solving the problem]

[0009] A coherent composite photoelectric converter according to one aspect of the present invention is a wireless transmission device that transmits a wireless signal from a transmitting antenna in which a carrier signal is modulated with a baseband signal including an information signal, and is excited by laser light and has a frequency interval f of 100 GHz to 3 THz. rep A miniature optical resonator that generates an optical frequency comb; a modulation signal generation unit that separates multiple pairs of adjacent optical frequency mode pairs from the optical frequency comb and performs optical modulation on one of each pair using the same baseband signal; and a unit provided on the transmitting antenna that mixes the optical frequency modes of each pair and generates the frequency interval f rep The system includes a photoelectric conversion element section consisting of one or more photoelectric conversion elements that generate a group of high-frequency radio wave signals equal to [a certain value], and a phase offset adjustment section that adjusts the phase difference between the high-frequency radio wave signals.

[0010] The aforementioned repetition frequency may be between 300 GHz and 1 THz.

[0011] The phase offset adjustment unit may adjust the phases between adjacent optical frequency modes that are separated from the optical frequency comb.

[0012] The photoelectric conversion element may be composed of a single-travel carrier photodiode.

[0013] The aforementioned micro-optical resonator is a medium having a nonlinear optical effect and may be composed of one or more media selected from the group consisting of silicon nitride (Si3N4), aluminum gallium arsenide (AlGaAs), lithium niobate (LiNbO3), tantalum pentoxide (Ta2O5), and gallium nitride (GaN).

[0014] The transmitting antenna may be composed of a plurality of antenna elements, the photoelectric conversion elements may be provided on each of the antenna elements, and the high-frequency radio wave signal group may be wavefront combined in the transmitting antenna. [Effects of the Invention]

[0015] According to one aspect of the present invention, a plurality of adjacent optical frequency mode pairs are extracted from one optical frequency comb at equal frequency intervals, a photoelectric conversion element is provided for each antenna element constituting a transmission antenna, and terahertz waves radiated from each antenna element can be superposed in the same phase with less phase noise, and as a result, the power of the terahertz waves can be efficiently increased. Further, by appropriately adjusting the phase of the terahertz wavefront radiated from each antenna element, the gain of the transmission antenna can be increased, the radiation pattern of the transmission antenna can be changed, or the beam radiation direction can be scanned.

Brief Description of Drawings

[0016] [Figure 1] It is a block diagram of a wireless transmission device using an optical frequency comb. [Figure 2] It is a block diagram of a coherent combining photoelectric conversion device according to the first embodiment of the present invention. [Figure 3] It is an operation explanatory diagram in the first embodiment of the present invention. Photoelectric [Figure 4] It is a block diagram of a coherent combining photoelectric conversion device according to the second embodiment of the present invention. [Figure 5] It is an operation explanatory diagram of a phased array antenna device having a coherent combining photoelectric conversion device according to the second embodiment of the present invention. [Figure 6] It is a flowchart of an example of the present invention.

Modes for Carrying Out the Invention

[0017] The first embodiment will now be described in detail with reference to the drawings. The wireless transmission device in this embodiment is intended to receive radio waves from wireless terminals within a cell or small cell and transmit them wirelessly between the cell and a network-connected exchange or relay station, the so-called fronthaul. Before describing this embodiment, the basic configuration and operation of a wireless transmission device using an optical frequency comb without coherent synthesis or phased array antenna control will be described as a reference example.

[0018] (Example explanation) Figure 1 shows a block diagram of the wireless transmission device in this embodiment. In Figure 1, 10 is a wireless terminal. There may be one or more wireless terminals 10. It may also be a mobile terminal or a fixed terminal. 11 is a receiving antenna that receives the wireless signal S1 from the wireless terminal 10. The receiving antenna 11 may be an antenna array consisting of multiple antenna elements to accommodate multiple wireless terminals 10. It may also consist of multiple antenna groups that support multiple wireless communication standards such as frequency. The information signal demodulation unit 12 demodulates the information signal contained in the wireless signal S1. The information signal is information such as images, sounds, and data, and is various types of information transmitted from the wireless terminal 10 to this wireless transmission device, and is transmitted in a signal state suitable for wireless transmission. The information signal demodulation unit 12 may support multiple wireless communication standards such as LTE and 5G.

[0019] Furthermore, in Figure 1, 1 is a laser element that emits single-frequency laser light. A DFB laser that emits laser light with an emission wavelength of 1550 nm or a wavelength around that wavelength is preferred. 2 is a micro-optical resonator, which is excited by the laser light to generate an optical frequency comb. An optical frequency comb is a sequence of multiple optical frequency modes with equal frequency f repThis refers to light having a super-discrete multispectral structure in which the light atoms are spaced apart and aligned in phase, arranged in a comb-like pattern. The micro-optical resonator 2 may be formed in a ring shape on a semiconductor substrate. Its diameter may be 40 μm to 400 μm. The medium having a nonlinear optical effect may be composed of one or more media selected from the group consisting of silicon nitride (Si3N4), aluminum gallium arsenide (AlGaAs), lithium niobate (LiNbO3), tantalum pentoxide (Ta2O5), and gallium nitride (GaN).

[0020] The optical frequency comb (micro optical frequency comb) generated by the micro optical resonator 2 has a short optical resonator length, so the frequency interval f between adjacent optical frequency modes is small. rep The frequency interval f can be increased. rep For example, it may be between 100 GHz and 3 THz. More preferably, it may be between 300 GHz and 1 THz. Even more preferably, it may be between 350 GHz and 600 GHz.

[0021] 30 is a coupler, 31 and 32 are bandpass filters, 33 is an optical modulation element, and 34 is an optical amplification element. These elements constitute the optical modulation unit 3. The optical modulation unit 3 separates adjacent optical frequency modes from an optical frequency comb and performs optical modulation on one of them according to a baseband signal S2 containing an information signal. Note that AWG (array waveguide diffractometer) may be used instead of bandpass filters 31 and 32. The optically modulated optical frequency mode m1 (frequency ν1) is supplied to the photoelectric conversion unit 4 via the optical amplification element 34. The photoelectric conversion unit 4 may consist of a single-traveling carrier photodiode (UTC-PD).

[0022] On the other hand, the optical frequency mode m0 of frequency ν0 is supplied directly to the photoelectric conversion unit 4 through the optical amplification element 34. In the photoelectric conversion element 4, the optical frequency modes m1(ν1) and m0(ν0) are mixed (S3), and the difference frequency (f repThe terahertz waves (S4) are output from the photoelectric conversion unit 4 as electromagnetic waves (terahertz waves). The photoelectric conversion unit 4 is directly connected to the antenna 5, and the terahertz waves (S4) are radiated into the air from the antenna 5.

[0023] (First Embodiment) The first embodiment of the present invention will be described below. Figure 2 is a block diagram of this embodiment. In Figure 2, the laser element 1, the micro-optical resonator 2, and the transmitting antenna 5 function in the same way as those shown in Figure 1. The micro-optical resonator 2 is excited by laser light and has a frequency interval f of 100 GHz to 3 THz. rep An optical frequency comb is generated. More preferably, the frequency interval of the optical frequency comb may be 300 GHz or more and 1 THz or less. Even more preferably, it may be 350 GHz or more and 600 GHz or less. Although the wireless terminal, receiving antenna, and information signal demodulation unit are not shown in Figure 2, it is assumed that they have the same functions as the wireless terminal 10, receiving antenna 11, and information signal demodulation unit 12 in Figure 1. In addition, a baseband signal S2 including an information signal is supplied to the optical modulation unit 3.

[0024] In this embodiment, the optical modulation unit 3 is composed of a WDA coupler 300 and two modulation signal generation units. The WDA coupler 300 separates adjacent optical frequency modes m10 and m11 and optical frequency modes m20 and m21 from the optical frequency comb and supplies them to the modulation signal generation units of each system. This is shown in Figure 3.

[0025] Optical frequency modes m10 and m11 are supplied to a modulation signal generation system consisting of optical bandpass filters 311 and 312, optical modulation elements 331, and optical amplification elements 341. These function equivalently to the bandpass filters 31 and 32, optical modulation elements 33, and optical amplification elements 34 shown in Figure 1. Similarly, optical frequency modes m20 and m21 are supplied to optical bandpass filters 321 and 322, optical modulation elements 332, and optical amplification elements 342, which function equivalently to those shown in Figure 1.

[0026] The optical frequency modes that have passed through each system are supplied to the photoelectric conversion unit 4 via optical fibers or optical waveguides. In this embodiment, the photoelectric conversion unit 4 consists of photoelectric conversion elements 41 and 42, both of which are directly attached to the transmitting antenna 5. The photoelectric conversion elements 41 and 42 may each be single-travel carrier photodiodes. Alternatively, they may be formed on the same substrate by a semiconductor process.

[0027] In this embodiment, the same information signal (baseband signal S2) is supplied to the optical modulation elements 331 and 332. Furthermore, after completely phase-synchronizing both systems, optical frequency mode m11 and optical frequency mode 21 modulate the baseband signal S2 in the same manner. The modulation method may be amplitude modulation such as QPSK or QAM, phase modulation, or a method including both.

[0028] The high-frequency radio signals S41 and S42 emitted from the photoelectric conversion elements 41 and 42 are combined at the antenna 5 and radiated into the atmosphere as a radio signal S4. If the phases of the high-frequency radio signals S41 and S42 are not aligned, the transmission power of the radio signal S4 will not be the simple sum of the high-frequency radio signals S41 and S42. To put it extremely, if the phases of the two are 180° apart, they will cancel each other out and the radio signal S4 will not be radiated. Therefore, phase offset adjustment units 301 and 302 are provided to adjust the phase offset between the high-frequency radio signals S41 and S42.

[0029] The phase offset adjusters 301 and 302 adjust the phase between adjacent optical frequency modes separated from the optical frequency comb. The phase offset adjusters 301 and 302 may use the electro-optic effect, or may be composed of micro-sized heaters that locally heat an optical waveguide or fiber. When using heaters, an offset current PO is pre-flowed through the phase offset adjusters 301 and 302, and based on this offset current, the current may be changed complementarily, such as PO + ΔP and PO - ΔP, respectively. As a result, a temperature difference occurs in each heater, the refractive index (optical path length) of the optical waveguide changes relatively, and the phase difference between the two can be changed arbitrarily with high sensitivity. In the generation of radio waves using the photoelectric conversion of two-mode light (optical frequency interval f rep ), there is a characteristic that the transition of the optical phase difference of the two-mode light is directly reflected in the phase transition of the radio wave (frequency f rep ).

[0030] However, from the opposite perspective, if a minute phase fluctuation or phase noise occurs between the paths of m10 (m20) and m11 (m21) in FIG. 2, that is, between the Mach-Zehnder type paths, it is directly transferred as the phase fluctuation or phase noise of the high-frequency radio wave signal. Therefore, the phase error between these paths needs to be minimized. For this reason, it is preferable that the optical bandpass filters 311(321), 312(322), the phase offset adjusters 301(302), and the optical modulation elements 331(332) are integrated and arranged close to each other on a silicon wafer, and the Mach-Zehnder type paths are shortened as much as possible.

[0031] The current flowing through the phase offset adjuster 302 may be controlled by a microprocessor or the like. In this embodiment, an optical phase adjustment element is provided. However, when performing phase modulation using an LN modulation element as the optical modulation element, the bias voltage may be adjusted.

[0032] As described above, according to this embodiment, a coherently synthesized high-frequency radio wave signal can be obtained by extracting multiple optical frequency mode pairs from an optical frequency comb, adjusting the phase offset, and then summing them. Since coherent synthesis is voltage summing rather than power summing, when two waves are coherently synthesized, 2 2 = You can obtain four times the power.

[0033] (Second Embodiment) A second embodiment of the present invention will be described below. Figure 4 shows a block diagram of this embodiment. In Figure 4, the laser element 1 and the micro-optical resonator 2 function in the same way as those shown in Figure 1 or Figure 2. In addition, the optical bandpass filters 311, 312, optical modulation element 331, optical amplification element 341, and optical bandpass filters 321, 322, optical modulation element 332, optical amplification element 342, and phase offset adjustment units 301, 302 also function in the same way as in Figure 2.

[0034] The difference from the configuration in Figure 2 is that in Figure 4, the photoelectric conversion unit 4 is composed of photoelectric conversion elements 41 and 42, and the transmitting antenna 5 is an array configuration consisting of antenna elements 51 and 52. Furthermore, the photoelectric conversion elements 41 and 42 are directly attached to independent antenna elements 51 and 52, respectively. Bowtie antennas are preferably used for the antenna elements 51 and 52. Horn antennas or small parabolic antennas can also be used. The photoelectric conversion elements 41 and 42 are fixed to the reflective surface of each antenna element or near the focal point of the lens. The photoelectric conversion elements 41 and 42 may be connected to the main body of the wireless transmission device by optical fiber. By assigning antenna elements 51 and 52 independently to the photoelectric conversion elements 41 and 42, the antenna can be arrayed, increasing the degree of design freedom. This will be explained in more detail in the following embodiments.

[0035] (Third embodiment) In this embodiment, the transmitting antenna 5 is composed of four antenna elements 501 to 504. Each antenna element may be a bowtie antenna or a horn antenna. A conceptual diagram is shown in Figure 5 as an example. Photoelectric conversion elements 401 to 404 are provided in the waveguides of each antenna element. In addition, a convex lens made of polytetrafluoroethylene or the like is provided at the opening of each antenna element, and spherical waves are radiated from each antenna element.

[0036] As mentioned above, by controlling the phase offset adjustment unit provided in each system of the modulation signal generation unit, the phase of the radio waves at the antenna aperture can be adjusted to be aligned. At this time, the radio waves transmitted from antenna elements 501 to 504 are combined into a single plane wave. In other words, antenna elements 501 to 504 behave as one large antenna. Generally, the gain of an antenna is related to the size of the aperture relative to the wavelength, so this embodiment provides the effect of increasing not only the transmission power but also the antenna gain.

[0037] Furthermore, by applying this embodiment, a phased array antenna can be easily realized. That is, by shifting the phase of the radio waves at the antenna aperture by a predetermined amount for each antenna element, as shown by the dotted line in Figure 5, the radiation angle of the composite wavefront can be changed. In this embodiment, the antenna elements are arranged in a single row, but they may also be arranged in two dimensions.

[0038] The characteristics of a phased array antenna are determined by the overall size of the antenna and the number of antenna elements. First, the larger the overall size of the antenna, the narrower the width of the main beam (main lobe) becomes, and the higher the gain. Also, the more antenna elements that make up the antenna, the closer the combined wavefront can be to a plane wave, and the greater the beam deflection angle can be. However, when the beam is deflected widely, the phase step difference between each antenna element also increases, and the combined wavefront becomes step-like, resulting in the generation of side lobes in the radiation pattern. [Examples]

[0039] (First example) A first embodiment of the present invention will be described below with reference to Figure 6. In this embodiment, the gain of the entire transmission system was estimated after considering the losses in each process of the two-channel coherent composite wireless transmission.

[0040] First, we isolate two pairs of arbitrary adjacent optical frequency modes from the optical frequency comb. Assume the power of each optical frequency mode is 15 mW (11.76 dBm). On the other hand, assuming that 6 dB is lost in the array waveguide diffractometer (AWG), 10 dB in the optical modulator, 6 dB in the multiplexing process, and 3 dB in the optical bandpass filter, and that we aim for a gain increase of 30 dB in the optical amplifier, we obtain a gain of 11.76 - 6 - 10 - 6 + 30 - 3 = 16.76 dBm per single mode up to this point.

[0041] Furthermore, the loss in the optical THz conversion element (photoelectric conversion section) is estimated to reach 30 dB at 300 GHz, resulting in a final output of 47.4 μW (16.76 - 30 = -13.24 dBm) per single mode. When the two modes are coherently combined, 6 dB is added, resulting in an output of 189.6 μW (-7.24 dBm). [Industrial applicability]

[0042] The present invention can be used in base stations that transmit information collected from mobile terminals to a switching station, and in relay stations that transmit information between base stations. [Explanation of symbols]

[0043] 1. Laser element 2 Microscopic optical cavity 3. Optical Modulation Section 4. Photoelectric conversion unit 5 Transmitting antenna 10 Wireless terminals 11 Receiving antenna 12 Information signal demodulation unit 30 Couplers 31, 32 Bandpass filters 33 Optical Modulator 34 Optical Amplifier 41, 42 Photoelectric conversion element 50 Transmitting Antenna 101-104 Laser elements 201~204 Microscopic optical cavity 300 WDA Coupler 301-304 Modulation signal generation section 3011, 3012 Bandpass Filters 33, 3013 Optical Modulation Section 34, 3014 Optical Amplifier 401-404 Photoelectric conversion elements 501-504 Antenna Elements

Claims

1. A wireless transmission device that transmits a wireless signal from a transmitting antenna in which a carrier signal is modulated with a baseband signal containing an information signal, Excited by laser light, with frequency intervals f between 100 GHz and 3 THz. ｒｅｐ A miniature optical resonator that generates an optical frequency comb, Multiple pairs of first and second frequency mode pairs, each consisting of adjacent optical frequency modes, are separated from the aforementioned optical frequency comb. A modulation signal generation unit comprising a first modulation unit that optically modulates one of the optical frequency modes included in the first optical frequency mode pair using the baseband signal, and a second modulation unit that optically modulates one of the optical frequency modes included in the second optical frequency mode pair using the same baseband signal, The above pair of optical frequency modes are mixed to form the frequency interval f ｒｅｐ A photoelectric conversion element section consisting of one or more photoelectric conversion elements that generate a group of high-frequency radio signals equal to, A coherent composite photoelectric converter having a phase offset adjustment unit that adjusts at least one of the phase difference between the first optical frequency mode pair and the phase difference between the second optical frequency mode pair so that the phase difference between the high-frequency radio wave signal groups is eliminated.

2. The coherent synthetic photoelectric converter according to claim 1, wherein the frequency interval f rep is 300 GHz or more and 1 THz or less.

3. The coherent composite photoelectric conversion apparatus according to claim 1, wherein the photoelectric conversion element includes a single-travel carrier photodiode.

4. The aforementioned micro-optical resonator is a medium having a nonlinear optical effect, and is silicon nitride (Si ３ N ４ ), gallium arsenide aluminum (AlGaAs), lithium niobate (LiNbO) ３ ), tantalum pentoxide (Ta ２ O ５ The coherent synthetic photoelectric conversion apparatus according to claim 1, comprising one or more media selected from the group consisting of ), and gallium nitride (GaN).

5. The coherent combined photoelectric conversion apparatus according to claim 1, wherein the transmitting antenna is composed of a plurality of antenna elements, the photoelectric conversion elements are provided on each of the plurality of antenna elements, and the high-frequency radio wave signal group is wavefront combined in the transmitting antenna to become the radio signal.

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