JP2020088598A - Wireless transmission apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust and transmit a terahertz band phase modulation signal received by homodyne reception using an analog electric circuit so as to suppress deterioration of its reception sensitivity. A wireless transmission device according to an embodiment has a first optical coupling branching device that branches reference light from monitor light and combines a modulated optical carrier and an unmodulated optical carrier, and a reference light and a first optical coupling branching device. The second optical coupling branching device that couples the second output light of the above, the first electric signal converted from the first output light of the second optical coupling branching device, and the clock signal synchronized with the digital data signal are multiplied. Unmodulated light from the first filter that extracts components near DC from the signal, the first controller that controls the first phase shifter based on the output signal of the first filter, and the second output light of the second optical coupling brancher. It includes a second filter that extracts an optical carrier component having the same optical frequency as the carrier, and a second controller that controls a second phase shifter based on a second electric signal converted from the output light of the second filter. [Selection diagram] Fig. 1

Description

The present invention relates to wireless transmission technology.

The transmission speed of wireless communication is steadily increasing, and it is expected that the required bandwidth will reach from several 10 Gb/s to 100 Gb/s in the near future. Radio waves with a frequency of more than 100 GHz are called terahertz (THz) waves, and if the specific bandwidth is constant, they have a broadband of 100 times or more compared to the radio waves in the vicinity of 1 GHz used by the current mobile terminals such as smartphones. .. In order to cope with an increase in the required band in the future, high-speed wireless communication using the THz wave band, which is this new frequency band, has recently attracted attention.

Currently, the most intensive research and development in the THz wave band is in the frequency region having a bandwidth of about 200 GHz from 200 GHz to 400 GHz. If this band is used, it is considered that communication of about 100 Gb/s can be sufficiently realized by a simple intensity modulation system (or amplitude modulation system) using a transmission/reception device having a bandwidth of 100 GHz. However, it is difficult at present to realize a transmission/reception device having a bandwidth of 100 GHz. Therefore, it is necessary to reduce the symbol rate of the transmission signal by using a multi-level phase modulation signal such as QPSK (Quadrature Phase Shift Keying) and to reduce the band required for realizing the transmission/reception device.

FIG. 6 is a diagram illustrating a configuration example of a wireless transmission device that generates a THz waveband signal. Since it is difficult to directly generate an electric wave in the THz wave band using an electronic device, for example, the wireless transmitter 9 shown in FIG. 6 indirectly uses an optical carrier in the 1.5 μm band used in optical fiber communication. It has a configuration that is generated dynamically. Specifically, the wireless transmission device 9 includes an optical frequency comb generator 91, a wavelength demultiplexer 92, a data modulator 93, a data generator 94, an optical coupler 95, and a photomixer 96. The optical frequency comb generator 91 includes a laser light source 911, an oscillator 912, and a side mode generator 913.

First, the radio transmitter 9 causes the optical frequency comb generator 91 to generate a multi-wavelength optical carrier having a constant frequency interval. As one method of generating a multi-wavelength optical carrier, continuous light output from a single laser light source 911 of 1.5 μm band is input to a side mode generator 913, and a sine wave signal output from an oscillator 912 is used to generate a side light. There is a method of driving a mode generator 913 to generate a large number of side modes arranged on the frequency axis at the same frequency intervals as the frequency of the sine wave signal. Usually, a LiNbO ₃ modulator is used as the side mode generator, and the side mode is generated by the modulation of the LiNbO ₃ modulator.

The output of the optical frequency comb generator 91 is input to the wavelength demultiplexer 92, and the wavelength demultiplexer 92 cuts out two desired wavelengths from the multi-wavelength optical carrier. Specifically, the wavelength demultiplexer 92 selects the optical carrier to be cut out so that the frequency difference between the cut out two wavelengths becomes the frequency of the THz wave to be generated. One of them is modulated by the digital data signal transmitted from the data generator 94 in the data modulator 93. This modulated optical carrier and the other non-modulated optical carrier are combined by the optical coupler 95 and input to the photomixer 96 to generate a radio signal in the THz wave band. As the photomixer 96, a UTC-PD (Uni-Travelling-Carrier Photodiode) that has a photoelectric conversion band even in the THz wave band is often used. Propagation in the wireless section is performed using an antenna (not shown) in the subsequent stage of the photomixer 96.

On the other hand, it is possible in principle to perform homodyne reception using a multi-level phase modulation signal using an analog electric circuit. However, in order to realize this, the optical phases when the modulated optical carrier and the non-modulated optical carrier are combined in the optical coupler 95 are matched, and the wavelength demultiplexer 92 and the optical coupler 95 are combined. It is necessary to suppress and stabilize the fluctuation of the optical phase caused by the expansion and contraction of the optical path length. As an example of a method of stabilizing the optical phase, a method of dithering the optical phase of an optical carrier passing through the optical path (hereinafter referred to as "first method") has been proposed (for example, see Patent Document 1). ..

An optical phase stabilization method that does not use dithering (hereinafter referred to as “second method”) has also been proposed (see Non-Patent Document 1, for example). In the wireless transmitter according to the second method, the two wavelengths cut out by using the wavelength demultiplexer are combined by the optical coupler, and then the wireless signal is generated in the photomixer by generating a wireless signal corresponding to the difference frequency of the two wavelengths. An optical phase stabilizing circuit that does not use dithering is attached to the basic configuration of the transmitter.

JP, 2016-45443, A

Kakuma Sakuma et al., 100 GHz band 11 Gbit/s error-free transmission using the pseudo Mach-Zehnder type phase stabilization method, 2015 Electronics Society Conference of the Institute of Electronics, Information and Communication Engineers, C-14-2.

In the first method, an error signal (control signal) for the target value is generated based on the dithering signal detected after photoelectric conversion, and the optical phase is stabilized by feedback control using this control signal. The optical phase stabilizing circuit that realizes the first method is attached to each of the optical paths through which the modulated optical carrier and the unmodulated optical carrier pass. According to the first method, the optical phase can be stabilized, but the optical phase is positively fluctuated by dithering. For example, taking a QPSK signal as an example, ideally, a QPSK signal converged at four points on the IQ plane can be obtained as in the constellation of the received signal shown in FIG. On the other hand, in the first method, four QPSK signals are blurred by the influence of dithering as shown in FIG. As a result, the distance between signal points is shortened, and when homodyne reception using an analog electric circuit is performed, the reception sensitivity may be deteriorated.

In addition, the wireless transmission apparatus according to the second method seems to realize optical phase stabilization by a method that does not use dithering for a wireless transmission apparatus similar to the wireless transmission apparatus 9 shown in FIG. Can be seen. However, in the second method, the data modulator cannot be arranged between the wavelength demultiplexer and the optical coupler due to its characteristic, so that the data modulator should be arranged on the output side of the optical coupler. become. Therefore, the cut out two wavelengths are collectively modulated by the same digital data signal by the data modulator arranged on the output side of the optical coupler. If phase modulation is used here, the phase modulation data disappears from the radio wave generated by the photomixer, and the digital data signal cannot be transmitted. Therefore, the modulation method applicable to the second method is limited to intensity modulation (or amplitude modulation), and in principle, there is a possibility that the reception sensitivity may deteriorate as compared with phase modulation such as QPSK.

In view of the above circumstances, the present invention provides a technique capable of adjusting and transmitting a terahertz band phase modulation signal received by homodyne reception using an analog electric circuit so that deterioration of the reception sensitivity thereof is suppressed. It is intended to be provided.

According to an aspect of the present invention, a first optical carrier and a second optical carrier are cut out from a monitor light which is a multi-wavelength optical carrier generated by an optical frequency comb generator, and the first optical carrier is converted into a digital data signal. By inputting the first output light of the first optical coupling/branching device that couples the modulated optical carrier that has been modulated and the unmodulated optical carrier that is the second optical carrier and outputs the branched light to the photomixer, the terahertz A wireless transmission device for generating a wireless signal in a wave band, wherein an optical branching device for branching reference light from the monitor light, the reference light, and a second output light of the first optical coupling/branching device are combined. And a second optical coupling/branching device that outputs two branches, a first opto-electric converter that converts the first output light of the second optical coupling/branching device into a first electrical signal, and the first electrical signal. A mixer that multiplies the clock signal synchronized with the digital data signal, a first filter that extracts a component near DC from the output signal of the mixer, a first phase shifter that changes the phase of the modulated optical carrier, A first controller that controls the first phase shifter based on the output signal of the first filter, and an optical carrier component having the same optical frequency as the unmodulated optical carrier are extracted from the second output light of the second optical coupling and branching device. A second filter, a second opto-electric converter that converts the output light of the second filter into a second electric signal, a second phase shifter that changes the phase of the unmodulated optical carrier, and the second electric signal And a second controller that controls the second phase shifter based on the above.

According to an aspect of the present invention, a first optical carrier and a second optical carrier are cut out from a monitor light which is a multi-wavelength optical carrier generated by an optical frequency comb generator, and the first optical carrier is converted into a digital data signal. By inputting the first output light of the first optical coupling/branching device that couples the modulated optical carrier that has been modulated and the unmodulated optical carrier that is the second optical carrier and outputs in two to the photomixer, the terahertz A wireless transmission device for generating a wireless signal in a waveband, which combines an optical branching device for branching reference light from the monitor light, the reference light, and a second output light of the first optical coupling/branching device. A second optical coupling/branching device, an opto-electric converter for converting the output light of the second optical coupling/branching device into an electric signal, and branching the electric signal into a first electric signal and a second electric signal. A branching device for outputting, a mixer for multiplying the first electric signal and a clock signal synchronized with the digital data signal, a first filter for extracting a component near DC from an output signal of the mixer, and the modulated light A first phase shifter that changes the phase of the carrier, a first controller that controls the first phase shifter based on the output signal of the first filter, and the same optical signal as the unmodulated optical carrier from the second electrical signal. A second filter for extracting an optical carrier component of a frequency, a second phase shifter for changing the phase of an unmodulated optical carrier, and a second controller for controlling the second phase shifter based on an output signal of the second filter And a wireless transmission device including.

According to an aspect of the present invention, a first optical carrier and a second optical carrier are cut out from a monitor light which is a multi-wavelength optical carrier generated by an optical frequency comb generator, and the first optical carrier is converted into a digital data signal. By inputting the first output light of the first optical coupling/branching device that couples the modulated optical carrier that has been modulated and the unmodulated optical carrier that is the second optical carrier and outputs the branched light to the photomixer, the terahertz A wireless transmission device for generating a wireless signal in a wave band, which combines an optical branching device for branching reference light from the monitor light, the reference light, and a second output light of the first optical coupling/branching device. A second optical coupling/branching device that outputs two split optical signals, a balanced receiver that converts the first output light and the second output light of the second optical coupling/branching device into electrical signals, and outputs the electrical signals. A brancher that branches and outputs a first electric signal and a second electric signal, a mixer that multiplies the first electric signal by a clock signal that is synchronized with the digital data signal, and an output of the mixer A first filter for extracting a component near DC from a signal, a first phase shifter for changing the phase of the modulated optical carrier, and a first controller for controlling the first phase shifter based on an output signal of the first filter. A second filter for extracting an optical carrier component having the same optical frequency as the unmodulated optical carrier from the second electric signal, a second phase shifter for changing the phase of the unmodulated optical carrier, and an output signal of the second filter And a second controller that controls the second phase shifter based on the above.

One aspect of the present invention is the above wireless transmission device, wherein the first electric signal is generated by interference between a modulated optical carrier included in the monitor light and an unmodulated optical carrier included in the reference light. The first controller includes, as an error signal, a phase difference related to the first beat signal corresponding to a section in which the output signal of the first filter monotonously changes between a maximum value and a minimum value. By controlling the first phase shifter, the optical phase of the modulated optical carrier is stabilized.

One aspect of the present invention is the wireless transmission device described above, wherein the phase difference related to the first beat signal is a modulated optical carrier that contributes to the generation of the first beat signal and an unmodulated optical carrier included in reference light. Is the optical phase difference.

One embodiment of the present invention is the above wireless transmission device, wherein the second electric signal interferes with an unmodulated optical carrier cut out from a monitor light and an unmodulated optical carrier cut out from a reference light. The second controller includes a second beat signal generated by the second beat signal, and the second controller calculates a phase difference related to the second beat signal corresponding to a section in which the output signal of the second filter monotonously changes between a maximum value and a minimum value. By controlling the second phase shifter as an error signal, the optical phase of the unmodulated optical carrier is stabilized.

One aspect of the present invention is the wireless transmission device described above, wherein the phase difference related to the second beat signal is an unmodulated optical carrier that contributes to the generation of the second beat signal, and is cut out from the monitor light. It is the optical phase difference between the unmodulated optical carrier and the unmodulated optical carrier cut out from the reference light.

According to the present invention, a terahertz band phase modulation signal received by homodyne reception using an analog electric circuit can be adjusted and transmitted so that deterioration of reception sensitivity thereof can be suppressed.

It is a figure which shows the structural example of the wireless transmitter of 1st Embodiment. FIG. 7 is a diagram showing a state in which the optical phases of a modulated optical carrier and an unmodulated optical carrier are stabilized based on the output of a second optical coupling/branching device in the wireless transmission device of the first embodiment. It is a figure which shows the structural example of the wireless transmitter of 2nd Embodiment. FIG. 8 is a diagram showing a state in which the optical phases of a modulated optical carrier and an unmodulated optical carrier are stabilized based on the output of a second optical coupling/branching device in the wireless transmission device of the second embodiment. It is a figure which shows the structural example of the wireless transmitter in 3rd Embodiment. It is a figure which shows the structural example of the conventional radio transmitter. It is a figure which shows the constellation by the conventional radio transmitter.

<First Embodiment>
FIG. 1 is a diagram illustrating a configuration example of the wireless transmission device according to the first embodiment. The wireless transmission device 1 shown in FIG. 1 is an example of the wireless transmission device according to the first embodiment. The wireless transmitter 1 includes an optical frequency comb generator 21, a wavelength demultiplexer 22, a data modulator 23, a data generator 24, a first optical coupling/branching device 25, and a photomixer 26 as a basic configuration of the wireless transmitter. Prepare These configurations are the same as those of the conventional wireless transmission device 9 shown in FIG. Specifically, the optical frequency comb generator 21 is similar to the optical frequency comb generator 91, and the wavelength demultiplexer 22 is similar to the wavelength demultiplexer 92. The data modulator 23 is a phase modulator similar to the data modulator 93, and the data generator 24 is similar to the data generator 94. The first optical coupler/splitter 25 and the photomixer 26 are similar to the optical coupler 95 and the photomixer 96.

In addition to such a basic configuration, the wireless transmission device 1 includes a first phase shifter 311, a first controller 312, a first LPF (Low Pass Filter) 313, a first photoelectric converter 314, a mixer 315, and an oscillator 316. And a second phase shifter 321, a second controller 322, a second opto-electric converter 323 and an optical BPF (Band Pass Filter) 324, an optical branching device 301 and a second optical coupling branching device 302.

The first phase shifter 311, the first controller 312, the first LPF 313, the first opto-electric converter 314, the mixer 315, and the oscillator 316 are used for stabilizing the phase of the modulated optical carrier, and the second phase shifter 321 and the second control. The device 322, the second opto-electric converter 323, and the optical BPF 324 are used to stabilize the phase of the unmodulated optical carrier. Further, the optical branching device 301 and the second optical coupling branching device 302 are commonly used for phase stabilization of both the modulated optical carrier and the non-modulated optical carrier. In the wireless transmission device 1, each of the functional units described above operates as described below, whereby a phase-modulated signal in the terahertz band in which deterioration of reception sensitivity is suppressed can be generated.

First, the multi-wavelength optical carrier generated by the optical frequency comb generator 21 is branched into two by the optical branching device 301. One of the multi-wavelength optical carriers is sent to the wavelength demultiplexer 22 as monitor light and used for generating a radio signal in the THz wave band (terahertz wave band). The other multi-wavelength optical carrier is sent to the second optical coupler/splitter 302 as reference light.

The first optical coupling/branching device 25 and the second optical coupling/branching device 302 are both two-input and two-output directional optical couplers, and the sum and difference of the optical carrier electric fields input from the two input ports are two different. Output from each output port. Here, when one of the two output ports is not used, the first optical coupler/splitter 25 and the second optical coupler/splitter 302 function merely as optical couplers, and the conventional optical coupler 95 shown in FIG. 6 is used. Works the same as. Hereinafter, the two output lights output by each optical coupler/splitter are referred to as “first output light” and “second output light”. For example, when the optical signal E0 is input to the first input port and the optical signal E1 is input to the second input port, the optical signal E0+E1 is output from the first output port and the optical signal E0 is input from the second output port. -E1 is output respectively.

The first output light from the first optical coupler/splitter 25 is sent to the photomixer 26 and used for generating a radio signal in the THz wave band. On the other hand, the second output light of the first optical coupling/branching device 25 is sent to the second optical coupling/branching device 302 as monitor light for stabilizing the optical phase. The second optical coupling/branching device 302 couples the reference light input from the optical branching device 301 and the monitor process input from the first optical coupling/branching device 25, and branches the coupling result into two and outputs it. The first output light and the second output light of the second optical coupler/splitter 302 are used for optical phase stabilization of both the modulated optical carrier and the non-modulated optical carrier.

The clock frequency of the digital data signal transmitted from the data generator 24 is set by an oscillator arranged outside or inside the data generator 24. FIG. 1 shows an example in which an oscillator for setting the clock frequency of a digital data signal is arranged outside the data generator 24 as an oscillator 316. The oscillator 316 outputs a clock signal synchronized with the clock frequency of the digital data signal.

FIG. 2 is a diagram showing how the optical phases of the modulated optical carrier and the non-modulated optical carrier are stabilized based on the output of the second optical coupling/dividing device 302 in the wireless transmission device 1. First, the first output light of the second optical coupler/splitter 302 is converted into an electric signal by the first opto-electric converter 314 and sent to the mixer 315. Hereinafter, the electric signal converted here is referred to as “electric signal #1”. The sine wave signal output from the oscillator 316 is input to the mixer 315 in addition to the electric signal #1.

As shown in FIG. 2, the electrical signal #1 is a beat signal (hereinafter referred to as “beat signal #1”) generated by interference between the modulated optical carrier included in the monitor light and the unmodulated optical carrier included in the reference light. )including. Here, the modulated optical carrier and the non-modulated optical carrier have the same center frequency position, and the beat signal #1 contains the clock component of the digital data signal. Although the electric signal #1 includes other beat signals, none of the other beat signals interferes with the clock component of the beat signal #1 on the frequency axis. Here, when the clock frequency is f _B , this clock component can be expressed by the following equation (1), for example.

In Expression (1), A represents the amplitude of the clock component, and t represents time. Further, θ ₁ represents the optical phase difference between the modulated optical carrier that contributed to the generation of the beat signal #1 and the unmodulated optical carrier included in the reference light. On the other hand, the sine wave signal of frequency f _B output from the oscillator 316 is represented by the following equation (2), where B is the amplitude and φ is the phase.

By multiplying this by the clock component of equation (1) in mixer 315, a signal represented by the following equation (3) is generated.

By passing through the first LPF 313, the component ½ cos(θ ₁ −φ) near the direct current represented by the second term is extracted. In this way, since the component near DC is represented as a cosine function having θ ₁ as a variable, the function value is the value of θ _{1 in} the interval where the function value monotonously changes between the maximum value and the minimum value. Is uniquely determined for. Therefore, if the value of θ ₁ corresponding to this section is used as an error signal (hereinafter referred to as “control signal #1”), the optical phase of the modulated optical carrier is stabilized by PID control (Proportional-Integral-Differential Controller). be able to.

For example, if φ is set to zero, the section of 0≦θ ₁ ≦π can be used. In this case, the optical phase difference between the modulated optical carrier that contributed to the generation of the beat signal and the non-modulated optical carrier included in the reference light is stabilized at the position where the control signal #1 becomes zero, that is, π/2.

On the other hand, the second output light of the second optical coupler/splitter 302 is sent to the optical BPF 324. The transmission center frequency of the optical BPF 324 is the same as the center frequency of the non-modulated optical carrier cut out by the wavelength demultiplexer 22. The optical BPF 324 extracts from the reference light an unmodulated optical carrier having the same frequency position as the unmodulated optical carrier included in the monitor light. Both unmodulated optical carriers extracted from the monitor light and the reference light are converted into electric signals by the second photoelectric converter 323. Hereinafter, the electric signal converted here will be referred to as “electric signal #2”.

Here, the electric signal #2 does not include beat signals other than the beat signal (hereinafter referred to as “beat signal #2”) generated by the interference of both unmodulated optical carriers extracted from the monitor light and the reference light. .. This is because, in the optical BPF 324 in the preceding stage of the second opto-electric converter 323, the optical carrier necessary for generating the beat signal other than the beat signal #2 is extracted from the second output light. The electric signal #2 is represented by the following equation (4), for example.

In Expression (4), C represents a DC offset and D represents an amplitude. Further, θ ₂ represents the optical phase difference between both unmodulated optical carriers extracted from the monitor light and the reference light in the optical BPF 324. Here, the second term of Expression (4) is a cosine function having θ ₂ as a variable, and the value of θ ₂ corresponding to a section in which the function value monotonously changes is an error signal (hereinafter referred to as “control signal #2”). When used as a), the optical phase of the unmodulated optical carrier can be stabilized by PID control (Proportional-Integral-Differential Controller).

For example, a value in the range of 0≦θ ₂ ≦π can be used. In this case, the optical phase difference between both unmodulated optical carriers (unmodulated optical carriers extracted from the monitor light and the reference light) that contributed to the generation of the beat signal is the position where the control signal #2 becomes zero, that is, π/ Stabilized to 2.

However, in this case, in order to generate the control signal #2, a process of subtracting the amount corresponding to the DC offset C from the electric signal #2 is required as a pre-process. This pre-processing may be performed in the second controller 322, for example.

The example has been described above in which the optical phases of the two wavelengths extracted by the wavelength demultiplexer 22 are both stabilized at a phase shifted by π/2 with respect to the optical phase of the reference light. In this case, the optical phases when the cut-out optical carriers of two wavelengths are combined by the first optical coupling/branching device 25 are adjusted, and the optical path length between the wavelength demultiplexer 22 and the first optical coupling/branching device 25 is adjusted. It is possible to stabilize the optical phase of each of the modulated optical carrier and the non-modulated optical carrier without depending on the fluctuation of the optical phase due to the expansion and contraction of.

According to the wireless transmission device 1 of the first embodiment configured as described above, deterioration of the reception sensitivity of a terahertz band phase modulation signal received by homodyne reception using an analog electric circuit is suppressed. It becomes possible to adjust and transmit.

In the above embodiment, the case where the phase difference of the optical carrier between the monitor light and the reference light is stabilized at π/2 is illustrated, but this phase difference is stable at a phase difference other than π/2. It may be embodied.

<Second Embodiment>
FIG. 3 is a diagram illustrating a configuration example of the wireless transmission device according to the second embodiment. The wireless transmission device 1a illustrated in FIG. 2 is an example of the wireless transmission device according to the second embodiment. The wireless transmission device 1a includes an opto-electric converter 303 in place of the first opto-electric converter 314, a mixer 315a in place of the mixer 315, a second opto-electric converter 323 is not provided, and an optical BPF 324. The wireless transmission device 1 according to the first embodiment is different from the wireless transmission device 1 according to the first embodiment in that it is not provided with the second LPF 325 and the branching device 326. Since other configurations are similar to those of the first embodiment, the same configurations will be denoted by the same reference numerals as those in FIG. 1 and description thereof will be omitted.

The opto-electric converter 303 is different from the first opto-electric converter 314 in the first embodiment in that the electric signal #1 is output to the branching device 326 instead of the mixer 315a. In this case, the splitter 326 first splits the electrical signal (hereinafter referred to as “electrical signal #3”) input from the photoelectric converter 303, and outputs one to the second LPF 325 and the other to the mixer 315a.

The mixer 315a extracts, from the electrical signal #3, the beat signal #1 generated by the interference between the modulated optical carrier included in the monitor light and the non-modulated optical carrier included in the reference light. On the other hand, the second LPF 325 extracts, from the electrical signal #3, the beat signal #2 generated by the interference of both unmodulated optical carriers extracted from the monitor light and the reference light.

FIG. 4 is a diagram showing how the optical phases of the modulated optical carrier and the non-modulated optical carrier are stabilized based on the output of the second optical coupler/splitter 302 in the wireless transmission device 1a of the second embodiment. .. In this case, since the modulated light carrier is generated by phase modulation, the modulated light carrier exists at a frequency position different from the center frequency position of the unmodulated carrier before modulation, as shown in FIG. Therefore, the DC component is not generated in the beat signal #1. As a result, the beat signal #1 and the beat signal #2 do not interfere with each other on the frequency axis, so that the beat signal #2 can be extracted from the electric signal #3 by the second LPF 325.

By using the beat signal #1 and the beat signal #2 thus extracted, the optical phases of the modulated optical carrier and the non-modulated optical carrier can be stabilized by the same method as in the first embodiment. According to the wireless transmission device 1a of the second embodiment configured as described above, by using inexpensive electrical components such as a branching device and an LPF instead of expensive optical components such as an opto-electric converter and an optical BPF, it is possible to perform wireless communication. The cost of the transmitter can be reduced.

<Third Embodiment>
FIG. 5 is a diagram illustrating a configuration example of the wireless transmission device according to the third embodiment. The wireless transmission device 1b illustrated in FIG. 5 is an example of the wireless transmission device according to the third embodiment. The wireless transmission device 1b is different from the wireless transmission device 1a in the second embodiment in that a balanced receiver 304 is provided instead of the photoelectric converter 303. Since other configurations are the same as those of the second embodiment, the same configurations will be denoted by the same reference numerals as those in FIG. 3 and description thereof will be omitted.

The balanced receiver 304 individually converts the optical signals input to the two input ports into electric signals, and outputs the difference between the two converted electric signals. Specifically, the balanced receiver 304 inputs the optical signals output by the second optical coupling/dividing device 302 from the two output ports, and individually converts the input two optical signals into electrical signals. As a result, two beat signals whose phases are inverted are generated, so that a control signal can be generated with higher sensitivity by obtaining the beat signal having a large amplitude by taking the difference between these signals.

<Modification>
The wireless transmission device in the above-described embodiment may be realized by a computer. In that case, the program for realizing this function may be recorded in a computer-readable recording medium, and the program recorded in this recording medium may be read by a computer system and executed. The “computer system” mentioned here includes an OS and hardware such as peripheral devices. Further, the “computer-readable recording medium” refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in a computer system. Further, the "computer-readable recording medium" means to hold a program dynamically for a short time like a communication line when transmitting the program through a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system that serves as a server or a client in that case may hold a program for a certain period of time. Further, the program may be for realizing some of the functions described above, or may be one that can realize the functions described above in combination with a program already recorded in the computer system, It may be realized using a programmable logic device such as FPGA (Field Programmable Gate Array).

Of the two optical carriers cut out from the multi-wavelength optical carrier by the wavelength demultiplexer 22 in the above-described embodiment, the optical carrier used as the modulated optical carrier is an example of the first optical carrier in the present invention. The optical carrier used as the modulated optical carrier is an example of the second optical carrier in the present invention. The first LPF 313 is an example of the first filter in the present invention, and the optical BPF 324 and the second LPF 325 are an example of the second filter in the present invention. The electric signal #1 is an example of the first electric signal in the present invention, and the electric signal #2 is an example of the second electric signal in the present invention. The beat signal #1 is an example of the first beat signal in the present invention, and the beat signal #2 is an example of the second beat signal in the present invention.

Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes a design and the like within a range not departing from the gist of the present invention.

INDUSTRIAL APPLICABILITY The present invention is applicable to a wireless transmission device that transmits a terahertz band phase modulation signal received by homodyne reception using an analog electric circuit.

1, 1a, 1b... Wireless transmitter, 21... Optical frequency comb generator, 22... Wavelength demultiplexer, 23... Data modulator, 24... Data generator, 25... First optical coupling/branching device, 26... Photomixer , 301... Optical branching device, 302... Second optical coupling/branching device, 303... Opto-electric converter, 304... Balanced receiver, 311... First phase shifter, 312... First controller, 313... First LPF (Low) Pass filter) 314... First photoelectric converter, 315, 315a... Mixer, 316... Oscillator, 321... Second phase shifter, 322... Second controller, 323... Second photoelectric converter, 324... Optical BPF (Band Pass Filter) 325... Second LPF, 326... Divider, 9... Radio transmitter having conventional configuration, 91... Optical frequency comb generator, 911... Laser light source, 912... Oscillator, 913... Side mode generator, 92 ... Wavelength demultiplexer, 93... Data modulator, 94... Data generator, 95... Optical coupler, 96... Photomixer

Claims (7)

A modulated optical carrier obtained by cutting out a first optical carrier and a second optical carrier from monitor light, which is a multi-wavelength optical carrier generated by an optical frequency comb generator, and modulating the first optical carrier with a digital data signal; A radio signal in the terahertz wave band is generated by inputting to the photomixer the first output light of the first optical coupler/splitter that combines the unmodulated optical carrier that is the second optical carrier and outputs the light in two branches. A wireless transmission device that
An optical branching device that branches reference light from the monitor light,
A second optical coupling/branching device that couples the reference light with the second output light of the first optical coupling/branching device and outputs the light in two branches.
A first opto-electrical converter for converting the first output light of the second optical coupler/splitter into a first electric signal;
A mixer for multiplying the first electrical signal by a clock signal synchronized with the digital data signal;
A first filter for extracting a component near DC from the output signal of the mixer;
A first phase shifter for changing the phase of the modulated light carrier;
A first controller that controls the first phase shifter based on an output signal of the first filter;
A second filter for extracting an optical carrier component having the same optical frequency as that of the unmodulated optical carrier from the second output light of the second optical coupler/splitter;
A second photoelectric converter for converting the output light of the second filter into a second electric signal;
A second phase shifter for changing the phase of the unmodulated optical carrier,
A second controller that controls the second phase shifter based on the second electrical signal;
And a wireless transmission device. A modulated optical carrier obtained by cutting out a first optical carrier and a second optical carrier from monitor light, which is a multi-wavelength optical carrier generated by an optical frequency comb generator, and modulating the first optical carrier with a digital data signal; A radio signal in the terahertz wave band is generated by inputting to the photomixer the first output light of the first optical coupler/splitter that combines the unmodulated optical carrier that is the second optical carrier and outputs the light in two branches. A wireless transmission device that
An optical branching device that branches reference light from the monitor light,
A second optical coupling/branching device that couples the reference light with the second output light of the first optical coupling/branching device;
An optoelectric converter for converting the output light of the second optical coupler/splitter into an electric signal;
A branching device that branches the electric signal into a first electric signal and a second electric signal, and outputs the branched electric signal.
A mixer for multiplying the first electrical signal by a clock signal synchronized with the digital data signal;
A first filter for extracting a component near DC from the output signal of the mixer;
A first phase shifter for changing the phase of the modulated light carrier;
A first controller that controls the first phase shifter based on an output signal of the first filter;
A second filter for extracting an optical carrier component having the same optical frequency as that of the unmodulated optical carrier from the second electric signal;
A second phase shifter for changing the phase of the unmodulated optical carrier,
A second controller for controlling the second phase shifter based on the output signal of the second filter;
And a wireless transmission device. A modulated optical carrier obtained by cutting out a first optical carrier and a second optical carrier from monitor light, which is a multi-wavelength optical carrier generated by an optical frequency comb generator, and modulating the first optical carrier with a digital data signal; A radio signal in the terahertz wave band is generated by inputting to the photomixer the first output light of the first optical coupler/splitter that combines the unmodulated optical carrier that is the second optical carrier and outputs the light in two branches. A wireless transmission device that
An optical branching device that branches reference light from the monitor light,
A second optical coupling/branching device that couples the reference light and the second output light of the first optical coupling/branching device and outputs the light into two branches.
A balanced receiver that converts the first output light and the second output light of the second optical coupler/splitter into electric signals and outputs the electric signals;
A branching device that branches the electric signal into a first electric signal and a second electric signal, and outputs the branched electric signal.
A mixer for multiplying the first electrical signal by a clock signal synchronized with the digital data signal;
A first filter for extracting a component near DC from the output signal of the mixer;
A first phase shifter for changing the phase of the modulated light carrier;
A first controller that controls the first phase shifter based on an output signal of the first filter;
A second filter for extracting an optical carrier component having the same optical frequency as that of the unmodulated optical carrier from the second electric signal;
A second phase shifter for changing the phase of the unmodulated optical carrier,
A second controller for controlling the second phase shifter based on the output signal of the second filter;
And a wireless transmission device. The first electric signal includes a first beat signal generated by interference between a modulated optical carrier included in the monitor light and an unmodulated optical carrier included in the reference light,
The first controller causes the first phase shifter to use a phase difference related to the first beat signal corresponding to a section in which the output signal of the first filter monotonously changes between a maximum value and a minimum value as an error signal. Stabilizing the optical phase of the modulated optical carrier by controlling,
The wireless transmission device according to claim 1. The phase difference regarding the first beat signal is an optical phase difference between the modulated optical carrier that contributed to the generation of the first beat signal and the unmodulated optical carrier included in the reference light.
The wireless transmission device according to claim 4. The second electric signal includes a second beat signal generated by interference between the unmodulated optical carrier cut out from the monitor light and the unmodulated optical carrier cut out from the reference light,
The second controller causes the second phase shifter to use a phase difference related to the second beat signal corresponding to a section in which the output signal of the second filter monotonously changes between a maximum value and a minimum value as an error signal. Controlling to stabilize the optical phase of the unmodulated optical carrier,
The wireless transmission device according to claim 1. The phase difference relating to the second beat signal is an unmodulated optical carrier that contributed to the generation of the second beat signal, the unmodulated optical carrier cut out from the monitor light and the unmodulated optical carrier cut out from the reference light. And the optical phase difference of
The wireless transmission device according to claim 6.

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