JP7590766B2 - Phase Adjuster - Google Patents

Description

The present invention relates to a phase adjuster that can be used in a system that transmits high-frequency signals for wireless transmission using optical signals.

In recent years, the use of mobile phones (especially smartphones) has become increasingly widespread, and in order to cope with the rapid increase in data traffic, a transmission method that increases the transmission capacity of the communication path (also called Mobile Front Haul (MFH)) connecting the backbone station and the radio antenna station is urgently needed. The currently popular transmission method for MFH is the method using optical fiber. This is because it is more rational and economical to transmit the high-frequency radio signal that is the source of radio waves using optical fiber, which is thin, lightweight, and has low transmission loss, than to transmit it directly using a coaxial cable. In the transmission method using optical fiber, a digital transmission method called CPRI (common public radio interface) is often used (for example, Non-Patent Document 1). The transmission capacity of CPRI is a maximum of about 10 Gb/s, which is considerably smaller than the transmission capacity of the currently popular optical fiber communication for the normal backbone transmission network (8000 Gb/s in the case of 100 Gb/s x 80 wavelength multiplexing). This is because MFH is a local network and has an extremely large number of communication paths compared to the backbone network, so low cost is more important than performance (i.e. transmission capacity).

In addition, from the perspective of reducing the size and operating costs of radio antenna stations (including antennas and their power sources, radio equipment, and CPRI equipment, known as RRHs (Remote Radio Heads)) that transmit and receive radio waves to and from user terminals, there is a demand for simplifying RRHs. Furthermore, to improve the transmission and reception efficiency of antennas, antennas are composed of multiple small antennas (synthetic aperture antennas), and a method is adopted in which the transmission and reception of radio waves is concentrated in a specific direction. To obtain the desired characteristics, it is necessary to appropriately control the phase and amplitude (i.e., waveform) of the high-frequency radio signal supplied to each small antenna.

In the current MFH system, this radio signal (for example, if the radio wave is in the 800 MHz band, then a high-frequency signal of 800 MHz) is transmitted digitally over a CPRI line. In this case, the transmission capacity required for the CPRI line is 800 MHz (carrier frequency) x 2 (sampling theorem) x 8 bits (quantization number) = 12.8 Gb/s, which is the limit of CPRI's transmission capability. Of course, there is room for improvement through improvements in the encoding method, etc., but a fundamental improvement in transmission capability is not expected at this point.

On the other hand, in the fifth generation (5G) or later mobile phone services, development is currently proceeding in the direction of increasing the carrier frequency in order to improve the communication speed with user terminals. For example, the use of 28 GHz millimeter waves is being considered, but the CPRI line lacks the transmission capacity required for digitally transmitting millimeter wave wireless signals. In order to address this lack of transmission capacity in the CPRI line, attention has been focused on the RoF (radio over fiber) method, which uses high frequency signals such as millimeter wave signals sent as radio waves to intensity modulate optical signals and transmit them over optical fiber. In the RoF method, the high frequency signal waveform is expressed as it is by the intensity of the optical signal in an analog manner, so there is no increase in the required bandwidth due to sampling in the digital method (CPRI). Therefore, for example, millimeter wave signals of 28 GHz can be easily transmitted over optical fiber, and the RoF method is a promising candidate for the transmission method to be used in the fifth generation or later.

Furthermore, using such high-frequency carrier waves increases the directivity of the antenna. In this case, it is possible to increase the transmission speed per user by intentionally reducing the coverage area of one RRH and reducing the number of users it can accommodate. In this case, beam steering technology is required to vary the directivity of the antenna according to demand (i.e., to control the propagation direction of radio waves).

"Development of LTE base station equipment compatible with W-CDMA system", NTT DOCOMO Technical Journal, April 2011, vol.19, No.1, pp.20-25 H. Takahashi, K. Oda, H. Toba, Y. Inoue, Transmission characteristics of arrayed-waveguide N x N wavelength multiplexer, IEEE Journal of Lightwave Technology, Vol.13, No.3, pp.447-455, March 1995

To achieve beam steering in a radio antenna station such as an RRH, it is necessary to control the phase of the high-frequency signal (millimeter wave signal) supplied to each antenna with high precision. However, in order to reduce the size and power consumption of the RRH, it is not desirable to introduce as many phase controllers for high-frequency signals as there are antennas into the RRH.

The present invention has been made in consideration of the above-mentioned problems, and provides a technique for controlling the phase of a high-frequency signal contained in an RoF optical signal before conversion to a high-frequency signal (millimeter wave signal) for wireless transmission in an MFH system.

In order to solve the above-described problems, a phase adjustment device according to one aspect of the present invention is a phase adjustment device for adjusting the phase of a high-frequency signal for wireless transmission, the phase adjustment device including: an AWG-type first optical frequency filter that receives modulated light obtained by modulating light output from a light source as a carrier wave with the high-frequency signal for wireless transmission, the modulated light including the carrier wave and one of an upper sideband wave and a lower sideband wave, and that separates and outputs the carrier wave and the sideband wave contained in the modulated light; a phase shifter group that imparts a phase difference to the carrier wave and the sideband wave separated by the first optical frequency filter so that the phase of the high-frequency signal is adjusted; and an optical multiplexing section that multiplexes and outputs the carrier wave and the sideband wave output from the group of phase shifters, wherein the first optical frequency filter has a plurality of ports on each of the input side and the output side, and is configured to output light of the carrier wave frequency and light of the sideband wave frequency contained in input light from one port on the input side from separate ports on the output side, and is configured to output the light of the carrier wave frequency and light of the sideband wave frequency contained in the input light from different ports on the output side depending on the port on the input side to which the input light is input .

A phase adjuster according to another aspect of the present invention is a phase adjuster for adjusting the phase of a high frequency signal for wireless transmission, the phase adjuster including: an AWG-type first optical frequency filter that receives modulated light obtained by modulating light output from a light source as a carrier wave with the high frequency signal for wireless transmission, the modulated light including the carrier wave, an upper sideband wave, and a lower sideband wave, and separates and outputs the carrier wave, the upper sideband wave, and the lower sideband wave contained in the modulated light; a phase shifter group that imparts phase differences to the carrier wave, the upper sideband wave, and the lower sideband wave separated by the first optical frequency filter so that the phase of the high frequency signal is adjusted; and and an optical multiplexing section that multiplexes the upper sideband wave and the lower sideband wave and outputs the multiplexed signal, wherein the first optical frequency filter has a plurality of ports on each of the input side and is configured to output the light having the carrier frequency, the light having the upper sideband wave frequency, and the light having the lower sideband wave frequency, which are contained in input light from one port on the input side, from separate ports on the output side, and is configured to output the light having the carrier frequency, the light having the upper sideband wave frequency, and the light having the lower sideband wave frequency, which are contained in the input light, from different ports on the output side depending on the port on the input side to which the input light is input .

According to the present invention, in an MFH system, it becomes possible to control the phase of the high-frequency signal contained in an RoF optical signal before conversion to a high-frequency signal (millimeter wave signal) for wireless transmission.

FIG. 1 is a diagram showing a schematic configuration example of an MFH system; FIG. 1 is a diagram showing a schematic internal configuration example of an optical circuit (first embodiment); A cross-sectional perspective view of an optical waveguide that constitutes an optical circuit. FIG. 1 is a diagram showing a schematic configuration example of an AWG type frequency filter and an example of the relationship between frequencies passing between input and output ports of the frequency filter; 1A and 1B are a perspective view and a cross-sectional view showing a schematic configuration example of a phase shifter; FIG. 13 is a diagram showing a schematic internal configuration example of an optical circuit (second embodiment); FIG. 13 is a diagram showing a schematic internal configuration example of an optical circuit (third embodiment); FIG. 13 is a diagram showing a schematic configuration example of an AWG type frequency filter and an example of the relationship between frequencies passing between input and output ports of the frequency filter (third and fourth embodiments); FIG. 13 is a diagram showing a schematic internal configuration example of an optical circuit (fourth embodiment);

The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any combination. In addition, the same reference numbers are used for the same or similar configurations, and duplicate descriptions are omitted.

In the embodiment described below, transmission in the direction from the core station to the user terminal (i.e., when radio waves are transmitted from the antenna of the RRH to the user terminal) will be described. However, if the flow of the high frequency signal and the optical signal is reversed, transmission in the direction from the user terminal to the core station (i.e., when radio waves from the user terminal are received by the antenna of the RRH and transmitted to the core station) can be similarly explained.

[First embodiment]
FIG. 1 is a diagram showing a schematic configuration example of an MFH system to which the RoF method is applied, which has a beam steering function utilizing a phase adjuster of a high frequency signal according to the first embodiment of the present invention. The configuration example of the MFH system is common to each embodiment from the second embodiment onwards. The MFH system shown in FIG. 1 is composed of a backbone station 1 and an RRH 5 connected via an optical fiber 10. The backbone station 1 includes a millimeter wave transmitter 2, an optical intensity modulator 3, and a light source 4. The RRH 5 includes an optical circuit 6, N photodiodes (PDs) 7 (7-1, 7-2, ..., 7-N), N millimeter wave amplifiers 8 (8-1, 8-2, ..., 8-N), and N antenna elements 9 (9-1, 9-2, ..., 9-N). N is an integer of 2 or more, and each embodiment in this specification will be described taking the case of N=4 as an example.

The millimeter wave transmitter 2 generates a millimeter wave signal (high frequency signal) to be transmitted from the antenna by modulating a millimeter wave carrier with a signal to be sent to the user. The millimeter wave signal generated by the millimeter wave transmitter 2 is input to the optical intensity modulator 3. The optical intensity modulator 3 generates light whose intensity changes according to the waveform of the millimeter wave signal by intensity modulating the light (unmodulated continuous wave) generated by the light source 4 with the millimeter wave signal. This light is a RoF optical signal that propagates through the optical fiber 10 and carries the millimeter wave signal (high frequency signal) to be transmitted from the antenna. (Hereinafter, the light generated by the optical intensity modulator 3 is referred to as "RoF light.") This RoF light corresponds to modulated light obtained by modulating the light output from the light source 4 with a high frequency signal for wireless transmission.

The RoF light is output from the backbone station 1 to the optical fiber 10. The RoF light propagates through the optical fiber 10 and reaches the RRH 5. The RoF light that has reached the RRH 5 is input to the optical circuit 6. Note that the frequency spectrum of the RoF light usually has frequency components f _C of the light source 4, which is a carrier wave, and frequencies f _L and f _U on both sides (high frequency side and low frequency side) of the frequency f _RF of the millimeter wave signal, which is a modulating signal, as shown in the inset in FIG. 1. In this way, the RoF light includes the carrier frequency f _C , light of the lower sideband frequency f _L (lower sideband wave), and light of the upper sideband frequency f _U (upper sideband wave). Alternatively, as shown in the inset in Fig. 1, carrier-suppressed single sideband modulated (SSB) light consisting of a carrier ( _fC ) and one of an upper sideband ( _fU ) and a lower sideband ( _fL ) may be transmitted as the RoF light. In this case, such RoF light is generated by using the optical intensity modulator 3 or by removing the upper sideband or the lower sideband using an optical frequency filter after modulation. Note that Fig. 1 shows RoF light consisting of a carrier ( _fC ) and an upper sideband ( _fU ) as an example, and the following description will be given taking as an example a case where RoF light having such a frequency component is transmitted to the RRH 5.

The optical circuit 6 has the function of controlling the phase of the millimeter wave signal contained in the RoF light and distributing the RoF light to N PDs 7 based on the principle described below. Each PD 7 converts the intensity of the input light into an electrical signal (more specifically, outputs a current proportional to the light intensity) and outputs the resulting electrical signal to its corresponding millimeter wave amplifier 8. The millimeter wave amplifier 8 amplifies the input electrical signal and outputs the amplified electrical signal as a millimeter wave signal. The millimeter wave signal output from each millimeter wave amplifier 8 is transmitted as a millimeter wave radio wave from the corresponding antenna element 9.

The radio waves sent into space from each antenna element 9 are combined to become one radio wave. In this embodiment, the phase of the millimeter waves sent from each antenna element 9 is controlled by the function of the optical circuit 6 so that the phase of the millimeter waves sent from each antenna element 9 is shifted at regular intervals. As a result, the millimeter waves sent from each antenna element 9 and combined are radiated in a direction at an angle θ with respect to the direction perpendicular to the arrangement direction of the N antenna elements 9, as shown in FIG. 1.

Figure 2 is a diagram showing a schematic example of the internal configuration of the optical circuit 6 according to this embodiment. The optical circuit 6 according to this embodiment has a configuration for obtaining multiple phase-adjusted high-frequency signals.

The optical circuit 6 is composed of a linear optical waveguide that guides light. FIG. 3 is a cross-sectional perspective view of the optical waveguide that constitutes the optical circuit 6. As shown in FIG. 3, the optical waveguide is composed of a silicon substrate 32, a cladding layer 33 formed on the silicon substrate 32, and a waveguide core 31 embedded in the cladding layer 33. The cladding (cladding layer 33) and the core (waveguide core 31) are both made of quartz glass, but germanium is added to the core, and the refractive index of the core is slightly higher than that of the cladding. This realizes the function of confining and transmitting light within the core. Note that the material of the optical waveguide is not limited to that used in this embodiment, and various materials such as various dielectrics, semiconductors, or organic materials can be used.

2, the optical circuit 6 includes an input port 20 to which the RoF light (modulated light) is input, and N output ports 25 (25-1, 25-2, ..., 25-N) that output N RoF lights each of which has undergone phase adjustment of a millimeter wave signal for wireless transmission (N=4 in this example). The N output ports 25 correspond to the N antenna elements 9. The optical circuit 6 includes a 1×N type branching circuit 21 (optical branching section), an AWG type optical frequency filter 22, a phase shifter group 23, and an optical multiplexing section 24 between the input port 20 and the N output ports 25. The optical frequency filter 22 includes a plurality of ports (eight in this example) on both the input side and the output side. The phase shifter group 23 is composed of a plurality of optical phase shifters (eight phase shifters 23-1 to 23-8 in this example). In this embodiment, the optical circuit 6 constitutes an example of a phase adjuster that adjusts the phase of a high frequency signal for wireless transmission. In addition, the branch circuit 21, the AWG-type optical frequency filter 22, the phase shifter group 23, and the optical multiplexer 24 are configured as part of the optical circuit 6 formed on a single substrate (silicon substrate 32) and are monolithically integrated on the substrate.

The branching circuit 21 is configured to branch (split) the RoF light (modulated light) input to the input port 20 into N RoF light beams for output. The input port 20 receives RoF light obtained by modulating the light output from the light source 4 with a millimeter wave signal for wireless transmission. The branching circuit 21 may equally divide the power of the input RoF light beam into N beams after splitting, or may distribute the power unequal (for example, in accordance with the power of the N RoF light beams output from the output port 25).

The N RoF light beams output from the branching circuit 21 are input to the optical frequency filter 22. At that time, as shown in FIG. 2, the N RoF light beams are input to ports IN1, IN3, ... on the input side of the optical frequency filter 22. The optical frequency filter 22 is configured to output the input light input from each port on the input side from individual ports OUT1, OUT2, OUT3, ... on the output side for each frequency contained in the input light, according to the characteristics described below.

As described below, the optical frequency filter 22 of this embodiment separates and outputs a carrier wave (f _C ) contained in the RoF light (modulated light) and a sideband wave (one of the upper sideband wave (f _U ) and the lower sideband wave (f _L )) contained in the RoF light. The carrier wave and the sideband wave separated by the optical frequency filter 22 are input to the phase shifter group 23. The phase shifter group 23 imparts a desired phase difference to the input carrier wave and sideband wave. The carrier wave and the sideband wave output from the phase shifter group 23 are multiplexed by the optical multiplexing section 24 and output from the output port 25.

The optical frequency filter 22 is composed of a number of optical waveguides as shown in FIG. 3, and a schematic configuration example thereof is shown in FIG. 4(A) (see Non-Patent Document 2). FIG. 4(B) shows the frequencies of light that reach each output port (OUT1, OUT2, ..., OUT8) from a port on the input side when inputted from the port on the input side in the configuration shown in FIG. 4(A). For example, when light including frequencies f ₇ and f ₈ is inputted from port IN7, light of frequency f ₇ is outputted from port OUT1, and light of f ₈ is outputted from port OUT2. When light including frequencies f ₇ and f ₈ is inputted from port IN5, light of frequency f ₇ is outputted from port OUT3, and light of f ₈ is outputted from port OUT4. In this embodiment, as an example, frequencies f ₇ and f ₈ shown in a thick line frame in FIG. 4(B) are used.

In this embodiment, assuming that the optical circuit 6 shown in Fig. 2 is introduced into an MFH system that transmits SSB modulated light consisting of a carrier wave ( _fC ) and an upper sideband wave ( _fU ) as RoF light, how phase adjustment of a millimeter wave signal is realized will be described in detail below. The optical frequency filter 22 in this embodiment is designed so that the frequency _f7 matches the carrier wave frequency _fC and the frequency _f8 matches the upper sideband wave frequency _fU .

In the optical circuit 6, the RoF light input from the input port 20, which includes light of frequency f _C (hereinafter simply referred to as "f _C ") and light of frequency f _U (hereinafter simply referred to as "f _U "), is split into four by a 1 x 4 type branching circuit 21 and output from four ports, and is input to the four ports IN1, IN3, IN5, and IN7 on the input side of the optical frequency filter 22.

The optical frequency filter 22 separates f _C and f _U contained in the RoF light input to the input port IN1, and outputs them from the output ports OUT7 and OUT8, respectively. That is, the optical frequency filter 22 separates and outputs a carrier wave (f _C ) and an upper sideband wave (f _U ). The carrier wave (f _C ) and upper sideband wave (f _U ) separated by the optical frequency filter 22 are each input to the phase shifter group 23 (phase shifters 23-7 and 23-8).

In this way, the optical frequency filter 22 is configured to output the light of the carrier frequency and the light of the sideband frequency contained in the input light from one port on the input side from separate ports on the output side. Furthermore, as described below, the optical frequency filter 22 is configured to output the light of the carrier frequency and the light of the sideband frequency contained in the input light from different ports on the output side depending on the input port to which the input light is input.

Figures 5 (A) and (B) are perspective and cross-sectional views showing a schematic configuration example of two of the phase shifters constituting the phase shifter group 23. As an example, Figure 5 shows a pair of phase shifters 23-7 and 23-8, but the same is true for the pair of phase shifters 23-1 and 23-2, the pair of phase shifters 23-3 and 23-4, and the pair of phase shifters 23-5 and 23-6. Figure 5 also shows two phase shifters using thin-film heaters as an example. Phase shifter 23-7 (first phase shifter) includes a thin-film heater 34-1 and a waveguide core 31-1 whose temperature is changed by the heater. Phase shifter 23-8 (second phase shifter) includes a thin-film heater 34-2 and a waveguide core 31-2 whose temperature is changed by the heater.

Here, the operation of the phase shifter will be described with reference to FIG. 5. In the first phase shifter, a metal thin-film heater 34-1 and electrodes 42, 43 connected to it are formed on the surface of the cladding layer 33 on the silicon substrate 32. Although not shown in FIG. 5, electrodes connected to the thin-film heater 34-2 are also formed in the second phase shifter. When a current is passed through the thin-film heater 34-1 through the electrodes 42, 43, the thin-film heater 34-1 generates heat and raises the temperature of the waveguide core 31-1 in the overheated area 44-1 directly below it. As a result, the refractive index of the part of the waveguide core 31-1 where the temperature has increased increases due to the thermo-optical effect, and the propagation speed of light passing through that part decreases. Therefore, when light passes through the heated waveguide core 31-1, the phase of the light is changed (delayed) compared to when the waveguide core 31-1 is not heated. The same is true for the second phase shifter, which includes the thin-film heater 34-2 and the waveguide core 31-2. In this way, each phase shifter included in the phase shifter group 23 is configured to impart a phase shift (phase change) to the light passing through its waveguide (waveguide core) by heating the waveguide with a heater (thin-film heater).

By utilizing this type of phase shifter mechanism, it is possible to give a phase difference φ to the carrier wave and the upper sideband wave by changing the heating amount of the waveguide ( _waveguide core) through which the carrier wave (f _C ) and the upper sideband wave (f U ) pass. Specifically, the waveguide in phase shifter 23-7 to which the carrier wave (f _C ) is input and the waveguide in phase shifter 23-8 to which the upper sideband wave (f _U ) is input are heated with different heating amounts. This generates a phase difference between f _C and f _U.

The phase difference thus generated is proportional to the power applied to the thin-film heaters 34-1, 34-2. Although it depends on the thickness of the cladding layer 33, for example, the power required to apply to the thin-film heaters 34-1, 34-2 to generate a phase change of 180 degrees is about 0.3 W. In this way, the phase difference given to the carrier wave (f _C ) and the upper sideband wave (f _U ) by the phase shifters 23-7, 23-8 changes according to the power applied to the thin-film heaters 34-1, 34-2.

In this embodiment, taking into consideration that the material of the optical waveguide is glass, the most practical thermo-optic effect is used as the principle, and a thin film heater is used to generate a phase difference by the phase shifter, but it is also possible to realize the phase shifter of the present invention using other principles. For example, if the material of the optical waveguide is a ferroelectric (lithium niobate, etc.), the phase shifter may be realized using a method of applying an electric field that does not generate heat, based on the electro-optic effect as the principle.

The carrier wave (f _C ) and the upper sideband wave (f _U ) to which a phase difference is given by the phase shifters 23-7 and 23-8 are output to the optical multiplexer 24. The optical multiplexer 24 multiplexes the carrier wave (f _C ) and the upper sideband wave (f _U ) output from the phase shifter group 23, and outputs the obtained RoF light from the corresponding output port 25-4. In this embodiment, the optical multiplexer 24 is configured with a Y-branch type multiplexer that multiplexes the carrier wave and the sideband wave (upper sideband wave in this example) output from the phase shifter group 23. For example, the carrier wave (f _C ) and the upper sideband wave (f _U ) output from the phase shifters 23-7 and 23-8 are multiplexed by being combined in the multiplexer. In this manner, the carrier wave (f _C ) and the upper sideband wave (f _U ) are multiplexed, and the RoF light carried by the RoF light input from port IN1 of the optical frequency filter 22, with the phase of the millimeter wave signal being controlled (adjusted), is output from output port 25-4.

ここで、ω_Cは搬送波の角周波数、ω_Uは上側帯波の角周波数、ω_C＝２πｆ_C、ω_U＝２πｆ_Uであり、右辺第２項の係数１／２は、振幅変調においてよく知られている搬送波と側帯波との振幅比である。 The sum of the electric field E of the carrier wave (f _C ) and the upper sideband wave (f _U ) contained in the RoF light output from the output port 25-4 is given by the following equation, where φ is the phase difference between the carrier wave and the upper sideband wave generated by the phase shifters 23-7 and 23-8.

Here, _ωC is the angular frequency of the carrier wave, _ωU is the angular frequency of the upper sideband wave, _ωC = _2πfC , _ωU = _2πfU , and the coefficient 1/2 of the second term on the right-hand side is the amplitude ratio between the carrier wave and the sideband wave, which is well known in amplitude modulation.

The RoF light output from output port 25-4 is input to PD 7 provided at the rear stage of optical circuit 6, as shown in FIG. 1. The RoF light is input to PD 7-4, one of N PDs 7, which is connected to output port 25-4. PD 7 converts the input RoF light into an electrical signal and outputs it. The current after conversion by PD 7 is proportional to the power of the input RoF light. The power P of this RoF light is calculated as follows:

この光電力振動をＰＤ７で電流に変換した後にミリ波増幅器８で得られる電圧Ｖは、直流成分は遮断されるため、次式で与えられる。

Among the components of the power P of the RoF light, vibration components in the optical frequency region of 100 THz or higher are averaged and are not detected by the PD 7. For this reason, the time average of the power of the RoF light is given by the following equation.

The voltage V obtained by the millimeter wave amplifier 8 after converting this optical power oscillation into a current by the PD 7 is given by the following equation since the DC component is blocked.

In the above equation, (ω _U - ω _C ) is the difference in angular frequency between the carrier wave and the upper sideband wave, and corresponds to each frequency of the millimeter-wave signal carried by the RoF light (ω _U - ω _C = ω _RF ). Therefore, the voltage V obtained by the millimeter-wave amplifier 8 corresponds to high-frequency oscillation of the frequency R _RF of the millimeter-wave signal generated by the millimeter-wave transmitter 2. That is, the millimeter-wave signal generated by the millimeter-wave transmitter 2 is reproduced in the output signal of the millimeter-wave amplifier 8.

In addition, in the above equation, the phase difference φ imparted by the phase shifter group 23 (phase shifters 23-7, 23-8) is included as an argument of a cosine function indicating the oscillation of the millimeter wave signal. This indicates that the phase difference φ between the carrier wave and the upper sideband wave imparted to the RoF light by the phase shifters 23-7, 23-8 appears as a phase change in the millimeter wave signal (high frequency signal) converted from the RoF light. The phase φ of this millimeter wave signal matches the phase of the millimeter wave radiated from the antenna element 9. In other words, the phase change imparted to the RoF light results in matching the phase of the millimeter wave radiated from the antenna element 9.

For this reason, by applying a phase difference φ to the carrier wave (f _C ) and upper sideband wave (f _U ) using the phase shifter group 23 (phase shifters 23-7, 23-8), it becomes possible to control (adjust) the phase of the millimeter wave signal (high frequency signal) carried by the RoF wave. The amount of adjustment of the phase of the millimeter wave signal varies depending on the phase difference φ applied to the carrier wave (f _C ) and upper sideband wave (f _U ) by the phase shifter group 23. In this way, in this embodiment, by controlling the phase of the RoF light using the phase shifter group 23, it is possible to control (adjust) the phase of the millimeter wave radiated from the antenna element 9.

The above explanation is about the RoF light input to port IN1 on the input side of the optical frequency filter 22, but the same applies to the RoF light input to ports IN3, IN5, and IN7. In the optical circuit 6, the RoF light input to port IN1 of the optical frequency filter 22 undergoes phase adjustment of the millimeter wave signal and is output from output port 25-4. Similarly, the RoF light input to ports IN3, IN5, and IN7 of the optical frequency filter 22 undergoes phase adjustment of the millimeter wave signal and is output from output ports 25-3, 25-2, and 25-1, respectively.

Specifically, the following applies:
For the RoF light input to port IN3 of the optical frequency filter 22, the carrier wave (f _C ) and upper sideband wave (f _U ) contained in the RoF light are output from ports OUT5 and OUT6 on the output side. Furthermore, the carrier wave and upper sideband wave are given a phase difference by phase shifters 23-5 and 23-6, then multiplexed by optical multiplexing unit 24 and output from output port 25-3.
For the RoF light input to port IN5 of the optical frequency filter 22, the carrier wave (f _C ) and upper sideband wave (f _U ) contained in the RoF light are output from ports OUT3 and OUT4 on the output side. Furthermore, the carrier wave and upper sideband wave are given a phase difference by phase shifters 23-3 and 23-4, then multiplexed by optical multiplexing unit 24 and output from output port 25-2.
For the RoF light input to port IN7 of the optical frequency filter 22, the carrier wave (f _C ) and upper sideband wave (f _U ) contained in the RoF light are output from ports OUT1 and OUT2 on the output side. Furthermore, the carrier wave and upper sideband wave are given a phase difference by phase shifters 23-1 and 23-2, then multiplexed by the optical multiplexing unit 24 and output from output port 25-1.

In the optical circuit 6, the phase difference φ given by the phase shifter group 23 to the N RoF lights (modulated lights) split by the branching circuit 21 can be controlled independently. Therefore, the phase difference φ given to the N RoF lights is set so that the phase of the millimeter wave signal shifts little by little (for example, the phase difference φ given to the RoF lights output from the output ports 25-1, 25-2, 25-3, and 25-4 is set to φ = 0, 10, 20, and 30 degrees). In this way, it becomes possible to generate a large number of millimeter waves with equally spaced phase differences, which are necessary for beam steering in the RRH 5.

As shown in FIG. 1, millimeter wave signals with slightly different phases are supplied to multiple (N) antenna elements 9 (9-1, 9-2, ..., 9-N), and the resulting combined millimeter wave is radiated in a direction of an angle θ. That is, the radiation direction θ of the radio waves from the N antenna elements 9 is controlled by the supply of millimeter wave signals according to the amount of phase adjustment of the millimeter wave signals corresponding to each of the N RoF lights by the phase adjuster configured as the optical circuit 6.

As described above, the optical circuit 6 configured as a phase adjuster according to this embodiment includes an optical frequency filter 22, a phase shifter group 23, and an optical multiplexer 24. The optical frequency filter 22 receives the RoF light (modulated light) obtained by modulating the light output from the light source with a millimeter wave signal (high frequency signal) for wireless transmission, which includes a carrier wave and one of an upper sideband wave and a lower sideband wave, and separates and outputs the carrier wave and the sideband wave contained in the RoF light. The phase shifter group 23 imparts a phase difference to the carrier wave and the sideband wave separated by the optical frequency filter 22 so that the phase of the millimeter wave signal is adjusted. The optical multiplexer 24 multiplexes and outputs the carrier wave and the sideband wave output from the optical shifter group 23.

In this manner, in this embodiment, the phase difference φ is applied to the carrier wave and sideband wave (upper sideband wave or lower sideband wave) of the RoF light by the phase shifter group 23, thereby adjusting the phase of the millimeter wave signal contained in the RoF light. This makes it possible to control the phase of the millimeter wave signal (high frequency signal) contained in the RoF light, which is an optical signal of the RoF system, before conversion to a millimeter wave signal for wireless transmission. Therefore, the millimeter wave band phase shifter that is normally required is no longer necessary, that is, it is no longer necessary to introduce into the RRH the same number of phase controllers for high frequency signals as the number of antennas, which leads to a smaller RRH and lower power consumption.

In addition, in this embodiment, each phase shifter included in the phase shifter group 23 is configured using a thin-film heater. This allows the operation of the phase shifter to be achieved by controlling the current flowing through the thin-film heater, making it possible to operate the phase shifter with a very simple and low-cost DC power supply (control of the thin-film heater is a general-purpose technology used in thermal paper printers for printing receipts, etc.).

Beam steering requires that the millimeter wave signal to be supplied to the multiple antenna elements must be branched into multiple (N) signals, but according to this embodiment, the branching operation can be achieved with a part of the optical circuit 6 (branching circuit 21). Although a large number of phase shifters are required to make up the phase shifter group 23, each phase shifter is very small (e.g., several tens of μm wide), and so these can also be integrated on a single substrate, resulting in miniaturization and integration.

In this embodiment, an AWG-type optical frequency filter with eight ports on the input and output sides is used to realize four output ports for the optical circuit 6, but the present invention is not limited to this, and a greater number of output ports can be realized. For example, it is known that the number of ports of an AWG-type optical frequency filter is a maximum of about 80, and therefore the number of output ports of the optical circuit 6 can be increased to a maximum of about 40.

[Second embodiment]
In the first embodiment, the optical multiplexing unit 24 of the optical circuit 6 (FIG. 2) is configured with a Y-branch type multiplexer. In contrast, in the second embodiment, an example in which the optical multiplexing unit 24 is configured with an AWG type optical frequency filter will be described. In the following, a description of parts common to the first embodiment will be omitted.

Figure 6 is a diagram showing a schematic example of the internal configuration of the optical circuit 6 according to this embodiment. The configuration of the optical circuit 6 differs from that of the first embodiment (Figure 2) in that the optical multiplexing unit 24 is configured with an AWG-type optical frequency filter 26 rather than a Y-branch type multiplexer. The optical multiplexing unit 24 of this embodiment is configured with an AWG-type optical frequency filter 26 having the same configuration as the optical frequency filter 22. The optical frequency filter 26 (second optical frequency filter) is connected to the phase shifter group 23 so that the input and output are symmetrical with the optical frequency filter 22 (first optical frequency filter) across the phase shifter group 23 (i.e., so that they are in a mirror-symmetric relationship).

Specifically, each port (OUT1, OUT2, ..., OUT8) used as the output side in the optical frequency filter 22 is used as an input side port in the optical frequency filter 26. Also, each port (IN1, IN2, ..., IN8) used as the input side in the optical frequency filter 22 is used as an output side port in the optical frequency filter 26. In this way, in this embodiment, light is propagated in the reverse direction through an optical frequency filter having the same configuration as the optical frequency filter 22, and used as the optical frequency filter 26.

With the above-described configuration of the optical circuit 6, all pairs of f _{C and f U (for the N RoF lights output from the branching circuit 21) separated by the optical frequency filter 22 are multiplexed by the optical frequency filter 26 and output. For example, f C and f U} contained in the RoF light input from the input port IN1 of the optical frequency filter 22 are output from the output ports OUT7 and OUT8. After that, f _C and f _U pass through the phase shifters 23-7 and 23-8, respectively, and are input to the input ports (the two lowest ports in FIG. 6) of the optical frequency filter 26, multiplexed by the optical frequency filter 26, and output from the output port 25-1.

The optical circuit 6 of this embodiment, with the same operating principle as the first embodiment, makes it possible to control the phase of the millimeter wave signal (high frequency signal) contained in the RoF light before conversion to a millimeter wave signal for wireless transmission. As a further practical improvement, this embodiment makes it possible to avoid the 3 dB loss that occurs when the optical multiplexing section 24 is configured as a Y-branch type multiplexer.

[Third embodiment]
In the third embodiment, an example of configuring an optical circuit 6 will be described assuming that modulated light of a normal amplitude modulation method, consisting of a carrier wave ( _fC ), an upper sideband wave ( _fU ), and a lower sideband wave ( _fL ), is used as the RoF light transmitted in the MFH system. In the following, a description of parts common to the first embodiment will be omitted.

Figure 7 is a diagram showing a schematic example of the internal configuration of the optical circuit 6 according to this embodiment. The branching circuit 21, optical frequency filter 27, phase shifter group 23, and optical multiplexing unit 24 used in the optical circuit 6 have the same functions as the branching circuit 21, optical frequency filter 22, phase shifter group 23, and optical multiplexing unit 24 in the first embodiment, respectively. Below, the operation of the optical circuit 6 will be explained according to the order of light propagation.

The RoF light (modulated light) input from the input port 20 is split into N RoF light beams by the splitter circuit 21. Note that FIG. 7 shows an example where N=4, as in the first and second embodiments. The N RoF light beams output from the splitter circuit 21 are input to ports IN1, IN4, IN7, and IN10 on the input side of the optical frequency filter 27, respectively. The optical frequency filter 27 is configured as an AWG-type optical frequency filter, as in the optical frequency filter 22 in the first embodiment, and has 12 ports on each of the input and output sides.

Fig. 8(A) shows a schematic configuration example of the optical frequency filter 27. Fig. 8(B) shows the frequency of light that reaches each port (OUT1, OUT2, ..., OUT12) on the output side from a port on the input side when inputted from the port on the input side in the configuration shown in Fig. 8(A). The optical frequency filter 27 of this embodiment is designed so that the frequencies _f10 , _f11 , and _f12 shown in Fig. 8(B) match the lower sideband frequency _fL , the carrier frequency _fC , and the upper sideband frequency _fU, respectively.

8B, optical frequency filter 27 separates the RoF light input to input port IN1 into _fL , fC, and _fU contained in the RoF light, and outputs them from output ports OUT10, OUT11, and OUT12, respectively. The light of the three frequencies ( _fL , _fC , _fU ) separated by optical frequency filter 27 is input to phase shifter _group 23 (phase shifters 23-10, 23-11, and 23-12), respectively.

Each phase shifter of the phase shifter group 23 gives a phase shift to the input light. Here, the phase shifts that the phase shifters 23-10, 23-11, and 23-12 give to the light of three frequencies (f _L , f _C , f _U ) are assumed to be φ ₁₀ , φ ₁₁ , and φ ₁₂ , respectively. In this embodiment, power is applied to the thin film heaters of the phase shifters 23-10, 23-11, and 23-12 so that φ ₁₀ - φ ₁₁ = -φ and φ ₁₂ - φ ₁₁ = φ. In this way, the phase shifters 23-10, 23-11, 23-12 (first, _second and third phase shifters) impart a phase shift to the carrier wave, the upper sideband wave and the lower sideband wave, respectively, so that the phase difference of the upper sideband wave (f _U ) relative to the carrier wave (f _C ) and the phase difference of the lower sideband wave (f _L ) relative to the carrier wave (f C ) have different polarities and the same magnitude.

The lower sideband wave (f _L ), carrier wave (f _C ), and upper sideband wave (f _U ) to which phase differences have been given by the phase shifters 23-10, 23-11, and 23-12 are output to the optical multiplexer 24. The optical multiplexer 24 multiplexes the lower sideband wave (f _L ), carrier wave (f _C ), and upper sideband wave (f _U ) output from the phase shifter group 23, and outputs the obtained RoF light from the corresponding output port 25-4. The optical multiplexer 24 in this embodiment is composed of a three-branch type multiplexer that multiplexes the lower sideband wave, carrier wave, and upper sideband wave output from the phase shifter group 23.

ここで、右辺の第１項及び第３項の係数１／２は、振幅変調における搬送波と側帯波との振幅比である。 The electric field E of the RoF light output from the output port 25-4 is the sum of the above three lights and is given by the following equation.

Here, the coefficient 1/2 in the first and third terms on the right hand side is the amplitude ratio between the carrier wave and the sideband wave in the amplitude modulation.

The RoF light output from output port 25-4 is input to PD 7 provided at the rear stage of optical circuit 6, as shown in Fig. 1. PD 7 converts the input RoF light into an electrical signal and outputs it. The current after conversion by PD 7 is proportional to the power of the input RoF light. The power P of this RoF light is calculated as follows:

なお、上式の算出過程においてω_C－ω_L＝ω_U－ω_L＝ω_RFの関係を用いている。この光をＰＤ７で電流に変換した後にミリ波増幅器８による増幅が行われる。その際、ミリ波増幅器８では、動作帯域外にある直流成分及び２ω_RFの周波数成分は増幅されない。したがって、ミリ波増幅器８で得られる電圧Ｖは、次式で与えられる。

As in the first embodiment, the time average of the power of the RoF light is calculated based on the above equation and is given by the following equation.

In addition, the relationship _ωC - _ωL = _ωU - _ωL = _ωRF is used in the calculation process of the above equation. This light is converted to current by the PD 7 and then amplified by the millimeter-wave amplifier 8. At that time, the DC component and the _2ωRF frequency component outside the operating band are not amplified by the millimeter-wave amplifier 8. Therefore, the voltage V obtained by the millimeter-wave amplifier 8 is given by the following equation.

In the above equation, as in the first embodiment, the phase difference φ provided by the phase shifter group 23 (phase shifters 23-10, 23-11, 23-12) is included as an argument of a cos function that indicates the oscillation of the millimeter wave signal. Therefore, as in the first embodiment, by controlling the phase of the RoF light with the phase shifter group 23, it is possible to control (adjust) the phase of the millimeter wave radiated from the antenna element 9.

The above explanation is about the RoF light input to port IN1 on the input side of the optical frequency filter 27, but the same applies to the RoF light input to ports IN4, IN7, and IN10.

In the optical circuit 6, the phase difference φ given by the phase shifter group 23 to the N RoF lights (modulated lights) split by the branching circuit 21 can be controlled independently. As in the first embodiment, the phase difference φ given to the RoF lights output from the output ports 25-1, 25-2, 25-3, and 25-4 can be set so that the phase of the millimeter-wave signal shifts slightly. This makes it possible to generate a large number of millimeter waves with equally spaced phase differences, which is necessary for beam steering in the RRH 5.

In this embodiment, an AWG-type optical frequency filter with 12 ports on the input and output sides is used to realize the number of output ports of 4 for the optical circuit 6, but the present invention is not limited to this, and a greater number of output ports can be realized. For example, it is known that the number of ports of an AWG-type optical frequency filter is a maximum of about 80, and therefore the number of output ports of the optical circuit 6 can be increased to a maximum of about 26.

[Fourth embodiment]
In the third embodiment, the optical multiplexing unit 24 of the optical circuit 6 (FIG. 7) is configured with a Y-branch type multiplexer. In contrast, in the fourth embodiment, an example in which the optical multiplexing unit 24 is configured with an AWG type optical frequency filter will be described. In the following, a description of the parts common to the third embodiment will be omitted.

Figure 9 is a diagram showing a schematic example of the internal configuration of the optical circuit 6 according to this embodiment. The configuration of the optical circuit 6 differs from that of the third embodiment (Figure 7) in that the optical multiplexing unit 24 is configured with an AWG-type optical frequency filter 28 rather than a Y-branch type multiplexer. The optical multiplexing unit 24 of this embodiment is configured with an AWG-type optical frequency filter 28 having the same configuration as the optical frequency filter 27. The optical frequency filter 28 (second optical frequency filter) is connected to the phase shifter group 23 so that the input and output are symmetrical with the optical frequency filter 27 (first optical frequency filter) across the phase shifter group 23 (i.e., so that they are in a mirror-symmetric relationship).

Specifically, each port (OUT1, OUT2, ..., OUT12) used as the output side in the optical frequency filter 27 is used as an input side port in the optical frequency filter 28. Also, each port (IN1, IN2, ..., IN12) used as the input side in the optical frequency filter 27 is used as an output side port in the optical frequency filter 28. In this way, in this embodiment, light is propagated in the reverse direction through an optical frequency filter having the same configuration as the optical frequency filter 27, and used as the optical frequency filter 28.

With the above-described configuration of the optical circuit 6, all sets of f _L , f _C and f U (for the N RoF lights output from the branching circuit 21) separated by the optical frequency filter 27 are multiplexed by the optical frequency filter 28 and output. For example, f _L , f _C and f _U contained in the RoF light input from the input port IN1 of the optical frequency filter 27 are output from the output ports OUT10, OUT11 and OUT12. After that, f _L , f _C and f _U pass through the phase shifters 23-10, 23-11 and 23-12, respectively, and are input to the input ports (the three lowest ports _in FIG. 9) of the optical frequency filter 28, multiplexed by the optical frequency filter 28 and output from the output port 25-1.

The optical circuit 6 of this embodiment, with the same operating principle as the third embodiment, makes it possible to control the phase of the millimeter wave signal (high frequency signal) contained in the RoF light before conversion to a millimeter wave signal for wireless transmission. As a further practical improvement, this embodiment makes it possible to avoid the 4.8 dB loss that occurs when the optical multiplexing section 24 is configured as a three-branch multiplexer.

The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the invention.

1: Main station, 2: Millimeter wave transmitter, 3: Optical intensity modulator, 4: Light source, 5: RRH, 6: Optical circuit, 7: PD, 8: Millimeter wave amplifier, 9: Antenna element, 10: Optical fiber, 20: Input port, 21: Branch circuit, 22, 26, 27, 28: AWG type frequency filter, 23: Phase shifter group, 23-n: Phase shifter, 24: Optical multiplexer, 25-n: Output port

Claims (15)

A phase adjuster for adjusting the phase of a high-frequency signal for wireless transmission,
a first optical frequency filter of an AWG type which receives modulated light obtained by modulating light output from a light source as a carrier wave with a high frequency signal for wireless transmission, the modulated light including the carrier wave and one of an upper sideband wave and a lower sideband wave, and which separates and outputs the carrier wave and the sideband wave included in the modulated light;
a phase shifter group that imparts a phase difference to the carrier wave and the sideband wave separated by the first optical frequency filter so that the phase of the high frequency signal is adjusted;
an optical multiplexing unit that multiplexes the carrier wave and the sideband wave output from the phase shifter group and outputs the multiplexed wave,
The first optical frequency filter comprises:
Equipped with a plurality of ports on the input side and the output side,
a light having the carrier frequency and a light having the sideband frequency, both of which are included in an input light from one port on the input side, are output from separate ports on the output side; and
The optical fiber is configured to output the light having the carrier frequency and the light having the sideband frequency contained in the input light from different ports on the output side depending on the port on the input side to which the input light is input.
13. A phase adjuster comprising: the group of phase shifters includes a first phase shifter that imparts a phase shift to the carrier wave and a second phase shifter that imparts a phase shift to the sideband wave,
2. The phase adjuster according to claim 1, wherein each of the phase shifters in the phase shifter group includes a heater and a waveguide whose temperature is changed by the heater, and is configured to give a phase shift to light passing through the waveguide by heating the waveguide by the heater. 3. The phase adjuster according to claim 1, wherein an adjustment amount of the phase of the high frequency signal varies depending on the phase difference provided to the carrier wave and the sideband wave by the group of phase shifters. 4. The phase adjuster according to claim 1, wherein the optical multiplexing unit is configured with a Y-branch multiplexer that multiplexes the carrier wave and the sideband wave output from the group of phase shifters. the optical multiplexing unit is configured with an AWG type second optical frequency filter having the same configuration as the first optical frequency filter,
4. The phase adjuster according to claim 1, wherein the second optical frequency filter is connected to the phase shifter group so that an input and output are symmetrical with respect to the first optical frequency filter across the phase shifter group. an input port to which the modulated light is input;
an optical branching unit that splits the modulated light input from the input port into N modulated lights (N is an integer equal to or greater than 2) and outputs the modulated lights to the first optical frequency filter;
N output ports respectively corresponding to the N modulated lights;
Further comprising:
the first optical frequency filter is configured to separate the carrier wave and the sideband wave contained in each of the N modulated lights and output the separated modulated lights to the phase shifter group;
the group of phase shifters is configured to give a phase difference to the carrier wave and the sideband wave for each of the N modulated lights,
6. The phase adjuster according to claim 1, wherein the optical multiplexing unit is configured to multiplex the carrier wave and the sideband wave output from the phase shifter group for each of the N modulated light beams, and output the modulated light obtained by the multiplexing and subjected to the phase adjustment from a corresponding output port among the N output ports. A phase adjuster for adjusting the phase of a high-frequency signal for wireless transmission,
a first optical frequency filter of an AWG type which receives modulated light obtained by modulating light output from a light source as a carrier wave with a high frequency signal for wireless transmission, the modulated light including the carrier wave and one of an upper sideband wave and a lower sideband wave, and which separates and outputs the carrier wave and the sideband wave included in the modulated light;
a phase shifter group that imparts a phase difference to the carrier wave and the sideband wave separated by the first optical frequency filter so that the phase of the high frequency signal is adjusted;
an optical multiplexing unit that multiplexes the carrier wave and the sideband wave output from the group of phase shifters and outputs the multiplexed wave;
an input port to which the modulated light is input;
an optical branching unit that splits the modulated light input from the input port into N modulated lights (N is an integer equal to or greater than 2) and outputs the modulated lights to the first optical frequency filter;
N output ports respectively corresponding to the N modulated lights;
the first optical frequency filter is configured to separate the carrier wave and the sideband wave contained in each of the N modulated lights and output the separated modulated lights to the phase shifter group;
the group of phase shifters is configured to give a phase difference to the carrier wave and the sideband wave for each of the N modulated lights,
The optical multiplexing unit is configured to multiplex the carrier wave and the sideband wave output from the phase shifter group for each of the N modulated lights, and output the modulated light obtained by the multiplexing and subjected to the phase adjustment from a corresponding one of the N output ports.
13. A phase adjuster comprising: A phase adjuster for adjusting the phase of a high-frequency signal for wireless transmission,
a first optical frequency filter of an AWG type which receives modulated light obtained by modulating light output from a light source as a carrier wave with a high frequency signal for wireless transmission, the modulated light including the carrier wave, an upper sideband wave, and a lower sideband wave, and which separates and outputs the carrier wave, the upper sideband wave, and the lower sideband wave contained in the modulated light;
a group of phase shifters for applying phase differences to the carrier wave, the upper sideband wave, and the lower sideband wave separated by the first optical frequency filter so that a phase of the high frequency signal is adjusted;
an optical multiplexing unit that multiplexes the carrier wave, the upper sideband wave, and the lower sideband wave output from the group of phase shifters and outputs the multiplexed wave,
The first optical frequency filter comprises:
Equipped with a plurality of ports on each of the input side and the output side,
a light having the carrier frequency, a light having the upper sideband frequency, and a light having the lower sideband frequency, which are included in an input light from one port on the input side, are output from separate ports on the output side; and
The light having the carrier frequency, the light having the upper sideband frequency, and the light having the lower sideband frequency, which are included in the input light, are output from different ports on the output side according to the port on the input side to which the input light is input.
13. A phase adjuster comprising: 9. The phase adjuster according to claim 8, wherein the group of phase shifters includes a first phase shifter, a second phase shifter and a third phase shifter that impart phase shifts to the carrier wave, the upper sideband wave and the lower sideband wave, respectively, so that a phase difference of the upper sideband wave relative to the carrier wave and a phase difference of the lower sideband wave relative to the carrier wave have different polarities and the same magnitude. 10. The phase adjuster according to claim 8, wherein the optical multiplexing unit is configured with a three-branch multiplexer that multiplexes the carrier wave, the upper sideband wave, and the lower sideband wave output from the group of phase shifters. the optical multiplexing unit is configured with an AWG type second optical frequency filter having the same configuration as the first optical frequency filter,
10. The phase adjuster according to claim 8, wherein the second optical frequency filter is connected to the phase shifter group so that an input and output are symmetrical with respect to the first optical frequency filter across the phase shifter group. an input port to which the modulated light is input;
an optical branching unit that splits the modulated light input from the input port into N modulated lights (N is an integer equal to or greater than 2) and outputs the modulated lights to the first optical frequency filter;
N output ports respectively corresponding to the N modulated lights;
Further comprising:
the first optical frequency filter is configured to separate, for each of the N modulated lights, the carrier wave, the upper sideband wave, and the lower sideband wave contained in each modulated light, and output the separated waves to the phase shifter group;
the N phase shifters are configured to impart a phase difference to the carrier wave, the upper sideband wave, and the lower sideband wave for each of the N modulated lights;
12. The phase adjuster according to claim 8, wherein the optical multiplexing unit is configured to multiplex the carrier wave, the upper sideband wave, and the lower sideband wave output from the phase shifter group for each of the N modulated lights, and to output the modulated light obtained by the multiplexing and subjected to the phase adjustment from a corresponding output port among the N output ports. A phase adjuster for adjusting the phase of a high-frequency signal for wireless transmission,
a first optical frequency filter of an AWG type which receives modulated light obtained by modulating light output from a light source as a carrier wave with a high frequency signal for wireless transmission, the modulated light including the carrier wave, an upper sideband wave, and a lower sideband wave, and which separates and outputs the carrier wave, the upper sideband wave, and the lower sideband wave contained in the modulated light;
a group of phase shifters for applying phase differences to the carrier wave, the upper sideband wave, and the lower sideband wave separated by the first optical frequency filter so that a phase of the high frequency signal is adjusted;
an optical multiplexing unit that multiplexes the carrier wave, the upper sideband wave, and the lower sideband wave output from the group of phase shifters and outputs the multiplexed wave;
an input port to which the modulated light is input;
an optical branching unit that splits the modulated light input from the input port into N modulated lights (N is an integer equal to or greater than 2) and outputs the modulated lights to the first optical frequency filter;
N output ports respectively corresponding to the N modulated lights;
Further comprising:
the first optical frequency filter is configured to separate, for each of the N modulated lights, the carrier wave, the upper sideband wave, and the lower sideband wave contained in each modulated light, and output the separated waves to the phase shifter group;
the N phase shifters are configured to impart a phase difference to the carrier wave, the upper sideband wave, and the lower sideband wave for each of the N modulated lights;
The optical multiplexing unit is configured to multiplex the carrier wave, the upper sideband wave, and the lower sideband wave output from the phase shifter group for each of the N modulated lights, and to output the modulated light obtained by the multiplexing and subjected to the phase adjustment from a corresponding one of the N output ports.
13. A phase adjuster comprising: 14. The phase adjuster according to claim 6, wherein the optical branching unit, the first optical frequency filter, the group of phase shifters, and the optical multiplexing unit are configured as part of an optical circuit formed on a single substrate, and are monolithically integrated on the substrate. The N output ports are respectively associated with the N antenna elements;
15. The phase adjuster according to claim 6, wherein a radiation direction of radio waves from the N antenna elements is controlled by supplying the high frequency signal in accordance with an adjustment amount of the phase of the high frequency signal for each of the N modulated light beams.

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