JP7297187B2 - Phase adjuster and optical circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a phase adjuster and an optical circuit that can be used in a system that transmits high-frequency signals for wireless transmission by optical signals.

In recent years, mobile phones (especially smartphones) have spread remarkably, and in order to cope with the rapid increase in data communication traffic, a communication path (also known as a mobile front haul (MFH)) that connects the base station and the radio antenna station is used. There is an urgent need for a transmission method that increases the transmission capacity of A currently popular transmission method for MFH is a method using an optical fiber. This is because it is more rational and economical to transmit a high-frequency radio signal, which is the source of radio waves, through an optical fiber that is thin, lightweight, and has low transmission loss, rather than through a coaxial cable. In transmission systems using optical fibers, a digital transmission system called CPRI (common public radio interface) is often used (for example, Non-Patent Document 1). The maximum transmission capacity of CPRI is about 10 Gb/s, which is compared to the transmission capacity of the currently popular optical fiber communication for the backbone transmission network (8000 Gb/s in the case of 100 Gb/s x 80 wavelength multiplexing). and quite few. This is because the 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 (that is, transmission capacity).

In addition, it will be possible to reduce the size and operating costs of radio antenna stations that transmit or receive radio waves to and from user terminals (including antennas and their power sources, radio equipment, and CPRI equipment, and are called RRH (Remote Radio Heads)). From the point of view, simplification of RRH is desired. Furthermore, in order to improve the transmission/reception efficiency of the antenna, the antenna is composed of a plurality of small antennas (synthetic aperture antenna), and a method of concentrating transmission/reception of radio waves in a specific direction is adopted. In order to obtain the desired characteristics, it is necessary to properly control the phase and amplitude (ie waveform) of the high frequency radio signal supplied to each small antenna.

In the current MFH system, this radio signal (for example, a high frequency signal of 800 MHz when radio waves are in the 800 MHz band) is digitally transmitted through 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, reaching the limit of the CPRI transmission capacity. . Of course, there is room for improvement by improving the coding method, etc., but the situation is such that drastic improvement in transmission capability cannot be expected.

On the other hand, in the fifth generation (5G) or later mobile phone services, development is currently progressing in the direction of increasing the carrier wave frequency in order to improve the communication speed with user terminals. For example, the use of millimeter waves of 28 GHz is being studied, but the CPRI line lacks the transmission capacity necessary for digital transmission of millimeter wave radio signals. In order to deal with the lack of transmission capacity of such CPRI lines, the RoF (radio over fiber) method, which modulates the intensity of optical signals with high-frequency signals such as millimeter-wave signals sent as radio waves and transmits them over optical fibers, is attracting attention. It is The above CPRI is also called digital RoF. In the RoF system, since the high-frequency signal waveform is expressed as it is by the intensity of the optical signal in an analog system, there is no limit on the transmission capacity associated with sampling and quantization in the digital system. Therefore, for example, millimeter wave signals of 28 GHz can be easily transmitted through optical fibers, and the RoF system is a strong candidate for the transmission system used in the fifth generation or later.

In addition, the directivity of the antenna is enhanced by using such a high-frequency carrier wave. In this case, it is possible to increase the transmission rate per user by intentionally reducing the coverage area of one RRH to reduce the number of accommodated users. In this case, beam steering technology is required to change the directivity of the antenna according to demand (that is, to control the propagation direction of radio waves).

"Development of Wireless Base Station Equipment for LTE System Compatible with W-CDMA System", NTT DOCOMO Technical Journal, April 2011, vol.19, No.1, pp.20-25

In order to achieve beam steering in a radio antenna station such as an RRH, it is necessary to precisely control the phase of a high frequency signal (millimeter wave signal) supplied to each antenna. 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 into the RRH as the number of antennas.

The present invention has been made in view of the above problems, and in an MFH system, the phase of a high-frequency signal contained in an RoF optical signal is adjusted before conversion into a high-frequency signal (millimeter wave signal) for wireless transmission. Provide technology to control.

In order to solve the above-described problems, a phase adjuster according to one aspect of the present invention is a phase adjuster that adjusts the phase of a high-frequency signal for wireless transmission, wherein light output from a light source is used for wireless transmission. A first optical frequency filter that receives modulated light obtained by modulating with a high-frequency signal, separates and outputs an upper sideband wave and a lower sideband wave included in the modulated light, and adjusts the phase of the high-frequency signal. an optical phase shifter that gives a phase difference to the upper and lower sidebands separated by the first optical frequency filter, and the upper and lower sidebands output from the phase shifter and a second optical frequency filter that multiplexes and outputs the sideband wave.

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

1 is a diagram showing a schematic configuration example of an MFH system; FIG. FIG. 2 is a diagram showing a schematic configuration example of the inside of an optical circuit; 1 is a cross-sectional perspective view of an optical waveguide that constitutes an optical circuit; FIG. 2A and 2B are a perspective view and a cross-sectional view showing a schematic configuration example of a phase shifter; FIG.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined arbitrarily. Also, the same or similar configurations are denoted by the same reference numerals, and redundant explanations are omitted.

In the embodiments described below, transmission in the direction from the base station to the user terminal (that is, 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, the transmission in the direction from the user terminal to the base station (that is, when the radio wave from the user terminal is received by the antenna of the RRH and transmitted to the base station) is the same. I can explain.

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 high-frequency signal phase adjuster, according to an embodiment of the present invention. The MFH system according to this embodiment is composed of a core station 1 and an RRH 5 which are connected via an optical fiber 10 . A core 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 (PD) 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). Note that N is an integer equal to or greater than 2, and the case of N=4 will be described as an example in this embodiment.

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

RoF light is output from the core station 1 to the optical fiber 10 . 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, as shown in the insert diagram in FIG. It has frequency components at frequencies f _L and f _U that are separated by . Thus, the RoF light includes light of frequency f _L in the lower sideband (lower sideband) and light of frequency f _U in the upper sideband (upper sideband).

The optical circuit 6 has a function of controlling the phase of the millimeter wave signal included in the RoF light and distributing the RoF light to the N PDs 7 based on the principle described later. Each PD 7 converts the intensity of the input light into an electric signal (more specifically, outputs a current proportional to the light intensity) and outputs the obtained electric signal to the 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 out into space from each antenna element 9 are synthesized into one radio wave. In this embodiment, the phase of the millimeter wave transmitted from each antenna element 9 is controlled by the function of the optical circuit 6 so that the phase of the millimeter wave transmitted from each antenna element 9 shifts at regular intervals. As a result, as shown in FIG. 1, the millimeter waves that are sent out and synthesized from each antenna element 9 are radiated in the direction of an angle .theta. with respect to the direction perpendicular to the arrangement direction of the N antenna elements 9. be.

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

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

As shown in FIG. 2, the optical circuit 6 includes an input port 20 to which RoF light is input, and N antenna elements 9 corresponding to N antenna elements 9 (9-1, 9-2, . . . , 9-N). output ports 29 (29-1, 29-2, . . . , 29-N). In the optical circuit 6 , an optical splitter 200 , an optical frequency filter 201 , a phase shifter 202 and an optical frequency filter 203 are arranged between the input port 20 and the N output ports 29 . In this embodiment, the optical frequency filter 201, the phase shifter 202, and the optical frequency filter 203 constitute an example of a phase adjuster that adjusts the phase of high-frequency signals for wireless transmission. Further, the optical frequency filter 201, the phase shifter 202, and the optical frequency filter 203 are configured as part of the optical circuit 6 formed on one substrate (silicon substrate 32) and are monolithically integrated on the substrate. there is

The optical branching unit 200 includes a plurality of Y branches 22 arranged in multiple stages, and is configured to branch RoF light (modulated light) input to the input port 20 into N RoF lights and output them. ing. RoF light obtained by modulating the light output from the light source 4 with a millimeter wave signal for wireless transmission is input to the input port 20 . The RoF light input to the input port 20 passes through the optical waveguide 21 and is split into two by the Y branch 22 at the first stage. The two RoF lights branched by the Y branch 22 are again divided into two by the Y branch 22 in the latter stage (second stage). By repeating such branching of the RoF light, N pieces of RoF light divided into N equal parts (4 equal parts in this example) are generated and output from the optical branching unit 200 . The N RoF lights reach the directional coupler 23a of the optical frequency filter 201, respectively.

The optical frequency filter 201 includes a directional coupler 23a, a directional coupler 23b, and short arm waveguides 24 having different lengths provided in parallel between the directional coupler 23a and the directional coupler 23b. and a long arm waveguide 25 . The directional couplers 23a and 23b have a structure in which two waveguides (first and second waveguides) are close to each other, one waveguide is connected to the short arm waveguide 24, and the other A waveguide is connected to the long arm waveguide 25 .

The directional coupler 23a has a function of dividing the input light into two equal parts. The RoF light that has been input to the directional coupler 23a and divided into two halves passes through the directional coupler 23a, propagates through the short-arm waveguide 24 and the long-arm waveguide 25, and passes through the subsequent directional coupler 23b. to reach The two RoF lights are merged and mixed in the directional coupler 23b.

Two directional couplers 23a and 23b and two arm waveguides (a short arm waveguide 24 and a long arm waveguide 25) provided therebetween constitute a Mach-Zehnder interferometer. The output from the directional coupler 23b periodically changes depending on the frequency of the light due to the interference when the light beams are combined in the directional coupler 23b in the subsequent stage. _For example, equally spaced frequencies f _{1 ,} f ₃ , f _{5 ,} . is output from the second waveguide. If Δf is the frequency difference (for example, f ₂ −f ₁ ) between the output light from the first waveguide and the output light from the second waveguide, Δf is expressed by the following equation.
Δf=c/(2·n·ΔL)
Here, ΔL is the difference between the length of the long arm waveguide 25 and the length of the short arm waveguide 24, n is the refractive index of the optical waveguide (more specifically, the group refractive index), and c is the speed of light in vacuum. is.

Note that the optical frequency filter 201 further includes a thin film heater 27 and a half-wave plate 28 . The thin film heater 27 has a structure similar to that shown in FIG. 4, which will be described later, and has a function of changing the phase of light. The thin film heater 27 is used to finely adjust the frequency (including manufacturing error) of the output light of the Mach-Zehnder interferometer to match the designed value.

In addition, the half-wave plate 28 is inserted so as to cross the waveguide with the direction of the optical principal axis inclined at 45 degrees from the substrate surface of the waveguide. (transverse magnetic) mode. A half-wave plate 28 is inserted at the midpoint of the Mach-Zehnder interferometer. This realizes the cancellation of the phase difference between the TE mode and the TM mode occurring in the first half and the second half of the Mach-Zehnder interferometer, respectively (that is, the ideal Mach-Zehnder interferometer that does not depend on the polarization state. to implement the behavior).

Now, consider the spectrum of the RoF light input to this optical circuit 6 . As shown in the inset of FIG. 1, the RoF light modulated by the millimeter-wave signal contains components of the lower sideband frequency f _L and the upper sideband frequency f _U . In this embodiment, the optical frequency filter 201 is designed so that the frequency _f1 of the output light of the Mach-Zehnder interferometer matches _fL and _f2 matches _fU . By designing in this way, the light of frequency f _L in the lower sideband (lower sideband) and the light of frequency _fU in the upper sideband (upper sideband) included in the RoF light are Mach-Zehnder It will be separated by an interferometer (optical frequency filter 201).

Two RoF lights (upper sideband and lower sideband) separated by the optical frequency filter 201 are input to the phase shifter 202 . 4A and 4B are a perspective view and a cross-sectional view showing a schematic configuration example of the phase shifter 202. FIG. As shown in FIG. 4, the phase shifter 202 is an optical phase shifter comprising a thin film heater 26 and two waveguide cores 31a and 31b. The waveguide core 31a is provided with the thin film heater 26 and corresponds to the first waveguide whose temperature is changed by the heater, and the waveguide core 31b corresponds to the second waveguide without the heater. Two RoF lights (upper sideband wave and lower sideband wave) input to the phase shifter 202 pass through the waveguide core 31a (first waveguide) and the waveguide core 31b (second waveguide) of the phase shifter 202, respectively. ) and output to the optical frequency filter 203 .

Here, the operation of phase shifter 202 will be described with reference to FIG. In the phase shifter 202, a thin film heater 26 made of metal and electrodes 42 and 43 connected thereto are formed on the surface of the clad layer 33 on the silicon substrate 32. As shown in FIG. When a current is passed through the thin film heater 26 through the electrodes 42 and 43, the thin film heater 26 generates heat and raises the temperature of the waveguide core 31a in the overheating region 44 immediately below. As a result, the refractive index of the portion of the waveguide core 31a where the temperature has risen increases, and the propagation speed of light when passing through that portion decreases due to the thermo-optic effect. Therefore, compared with the light passing through the waveguide core 31b (second waveguide) provided with no heater, the light passing through the waveguide core 31a (first waveguide) provided with the thin film heater 26 is A phase difference occurs.

Therefore, when the upper sideband of the RoF light passes through one of the first waveguide and the second waveguide of the phase shifter 202 and the lower sideband of the RoF light passes through the other, the upper sideband and the lower sideband A phase difference is generated between the sideband waves. The phase difference generated in this way is proportional to the power applied to the thin film heater 26 . Although it depends on the thickness of the cladding layer 33, the power applied to the thin film heater 26 required to generate a phase difference of 180 degrees, for example, is about 0.3W. Thus, the phase difference given to the upper and lower sidebands of the RoF light by the phase shifter 202 changes according to the power applied to the thin film heater 26 .

In this embodiment, considering that the material of the optical waveguide is glass, the most practical thermo-optical effect is used as a principle, and the thin film heater 26 is used to generate the phase difference by the phase shifter 202. , and other principles can be used to implement the phase shifter of the present invention. For example, when the material of the optical waveguide is a ferroelectric (lithium niobate, etc.), the phase shifter may be realized by applying an electric field that does not generate heat based on the principle of the electro-optic effect.

The upper sideband wave and the lower sideband wave given a phase difference by the phase shifter 202 are output from the phase shifter 202 to the optical frequency filter 203 . The optical frequency filter 203 is composed of a Mach-Zehnder interferometer with the same design as the optical frequency filter 201 and has the same configuration as the optical frequency filter 201 . The upper sideband wave and the lower sideband wave given a phase difference by the phase shifter 202 pass through the first and second waveguides of the optical frequency filter 203, respectively. As a result, the upper sideband wave and the lower sideband wave are combined and output from the output port 29 as RoF light in which the phase of the millimeter wave signal to be carried is controlled (adjusted). Note that if the Mach-Zehnder interferometers used for light separation and multiplexing are of the same design, the loss at the time of multiplexing is theoretically zero. That is, the optical frequency filter 201 and the optical frequency filter 203 are composed of Mach-Zehnder interferometers of the same design (the optical frequency filter 203 has the same configuration as the optical frequency filter 201). It is possible to limit the loss at the time of multiplexing of the lower sideband.

The RoF light in which the phase of the millimeter-wave signal to be carried is controlled (adjusted), which is output from the output port 29, is input to the PD 7 provided after the optical circuit 6, as shown in FIG. As shown in FIG. 2, in the optical circuit 6, the optical frequency filters 201, the phase shifters 202, and the optical frequency filters 203 (that is, the phase adjusters) are N (four in this example) of the optical splitter 200. ) for each of the outputs. The RoF light output from the output of the optical frequency filter 203 is output from one corresponding output port of the N output ports 29, and is connected to the one output port of the N PDs 7 Input to PD. In this way, the N output ports 29 output RoF light (modulated light) phase-adjusted by the corresponding phase adjusters out of the N phase adjusters.

ここで、ω_cは搬送波（すなわちレーザー光）の角周波数、ω_rはミリ波の角周波数である。なお、図１におけるｆ_C、ｆ_L、ｆ_Uとこれらの角周波数との関係は、ω_c＝２πｆ_c、ω_c－ω_r＝２πｆ_L、ω_c＋ω_r＝２πｆ_Uである。なお、上式では、理解を容易にするために周波数ｆ_Cの搬送波成分を省略している。 The electric field E of the sum of the upper and lower sideband waves contained in the RoF light obtained from the output port 29 is the difference between the upper and lower sideband waves generated in the phase shifter 202 by the action of the thin film heater 26. Assuming that the phase difference is φ, it is given by the following equation.

Here, ω _c is the angular frequency of the carrier wave (that is, laser light), and ω _r is the angular frequency of the millimeter wave. The relationships between f _C , f _L , f _U and their angular frequencies in FIG. 1 are ω _c =2πf _c , ω _c −ω _r =2πf _L , ω _c +ω _r =2πf _U . In the above equation, the carrier wave component of frequency f _C is omitted for easy understanding.

The PD 7 converts the input RoF light into a current proportional to the power of the RoF light and outputs the current. Therefore, the power (power) P of this RoF light is calculated as in the following equation.

Ｐ'(ｔ)は、ＰＤ７から出力される電流に比例する。この電流は、その後、ミリ波増幅器８により電圧に変換されて、対応するアンテナ素子９から放射される。このため、Ｐ'(ｔ)はアンテナ素子９から放射されるミリ波の波形と読み替えることが可能である。 Vibration components due to carrier wave frequencies much higher than the millimeter wave frequency are zero when averaged over time. For this reason, the time waveform P'(t) of the power of the RoF light, which takes into consideration the frequency response up to about the millimeter wave frequency, is obtained by the following equation.

P'(t) is proportional to the current output from PD7. This current is then converted into a voltage by the millimeter wave amplifier 8 and radiated from the corresponding antenna element 9 . Therefore, P′(t) can be read as a millimeter wave waveform radiated from the antenna element 9 .

In the above equation, the optical phase term φ is included as an argument of the cos function. This indicates that the phase difference φ between the upper sideband wave and the lower sideband wave given to the RoF light by the phase shifter 202 appears as a phase change in the millimeter wave signal (high frequency signal) converted from the RoF light. ing. 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 given to the RoF light matches the phase of the millimeter wave radiated from the antenna element 9 . Thus, in this embodiment, by driving the thin film heater 26 and giving a phase change to the RoF light with the phase shifter 202 , it is possible to change the phase of the millimeter wave radiated from the antenna element 9 .

The above description is about the millimeter wave signal (high frequency signal) obtained by converting the RoF light output from the output port 29-1 by the PD 7-1. In the optical circuit 6, the RoF light output from the output ports 29-2, . It is possible to vary the phase φ of the included millimeter-wave signal.

In the optical circuit 6 of this embodiment, as shown in FIG. 1, the phases of the plurality of (N) antenna elements 9 (9-1, 9-2, . . . , 9-N) are shifted little by little. The combined millimeter wave signal is radiated in the direction of the angle θ. That is, according to the amount of adjustment of the phase of the millimeter wave signal by each of the N phase adjusters formed as part of the optical circuit 6, radio waves are radiated from the N antenna elements 9 by supplying the millimeter wave signal. Direction θ is controlled.

As described above, the phase adjuster of this embodiment has the optical frequency filter 201 , the optical phase shifter 202 and the optical frequency filter 203 . The optical frequency filter 201 receives RoF (modulated light) obtained by modulating light output from a light source with a millimeter wave signal (high frequency signal) for wireless transmission. Separated from the lower sideband and output. A phase shifter 202 gives a phase difference to the upper and lower sideband waves separated by the optical frequency filter 201 so that the phase of the millimeter wave signal is adjusted. The optical frequency filter 203 multiplexes the upper sideband wave and the lower sideband wave output from the phase shifter 202 and outputs the combined wave.

Thus, in this embodiment, the phase shifter 202 gives a phase difference to the upper sideband wave and the lower sideband wave of the RoF light, thereby adjusting the phase of the millimeter wave signal included in the RoF light. This makes it possible to control the phase of a millimeter wave signal (high frequency signal) included in RoF light, which is an optical signal of the RoF system, before conversion to a millimeter wave signal for wireless transmission. Therefore, a millimeter-wave band phase shifter that is normally required becomes unnecessary, that is, it is possible to eliminate the need to introduce phase controllers for high-frequency signals into the RRH as many times as the number of antennas. leads to

In addition, in this embodiment, by configuring the phase shifter 202 using the thin film heater 26, the operation of the phase shifter 202 can be realized by controlling the current flowing through the thin film heater 26, and a very simple and low-cost DC power supply can be realized. (The control of the thin-film heater 26 is a general-purpose technique used in thermal paper printers for printing receipts, etc.).

Further, in order to perform beam steering, it is necessary to branch a millimeter wave signal to be supplied to a plurality of antenna elements into a plurality of (N) signals. A branching operation can be realized in the section (optical branching section 200). Also, although N phase adjusters having the same configuration are required, these can also be integrated on a single substrate, which has the effect of miniaturization.

The invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the invention.

1: base 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: light Fiber 26: Thin film heater 200: Optical splitter 201: Optical frequency filter 202: Phase shifter 203: Optical frequency filter

Claims (8)

A phase adjuster that adjusts the phase of a high-frequency signal for wireless transmission,
Modulated light obtained by modulating light output from a light source with a high-frequency signal for wireless transmission is input, and first light that separates and outputs an upper sideband wave and a lower sideband wave included in the modulated light a frequency filter;
an optical phase shifter that imparts a phase difference to the upper sideband and the lower sideband separated by the first optical frequency filter so that the phase of the high frequency signal is adjusted;
a second optical frequency filter for combining and outputting the upper sideband wave and the lower sideband wave output from the phase shifter;
A phase adjuster comprising: The phase shifter includes a first waveguide provided with a heater, the temperature of which is changed by the heater, and a second waveguide not provided with the heater. 2. The phase adjuster according to claim 1, wherein said upper sideband wave passes through one of said waveguides, and said lower sideband wave passes through the other of said waveguides. 3. The phase adjuster according to claim 2, wherein the phase difference given to the upper sideband and the lower sideband varies according to the power applied to the heater. The first optical frequency filter includes a first directional coupler, a second directional coupler, and in parallel between the first directional coupler and the second directional coupler. 4. The phase adjuster according to any one of claims 1 to 3, comprising a short arm waveguide and a long arm waveguide having different lengths. 5. The phase adjuster according to claim 4, wherein said second optical frequency filter has the same configuration as said first optical frequency filter. The first optical frequency filter, the phase shifter, and the second optical frequency filter are configured as part of an optical circuit formed on a single substrate and monolithically integrated on the substrate. 6. A phase adjuster according to any one of claims 1 to 5, characterized by: An optical circuit formed on a substrate,
an input port for inputting modulated light obtained by modulating light output from a light source with a high-frequency signal for wireless transmission;
an optical branching unit for branching the input modulated light into N (N is an integer equal to or greater than 2) modulated light and outputting the modulated light;
a phase adjuster according to any one of claims 1 to 6, provided for each of the N outputs of the optical splitter;
N output ports corresponding to N antenna elements, the N outputting the modulated light phase-adjusted by the corresponding phase adjusters out of the N phase adjusters. output ports and
An optical circuit comprising: According to the amount of phase adjustment of the high-frequency signal by each of the N phase adjusters, the direction of radiation of radio waves from the N antenna elements is controlled by supplying the high-frequency signal. Item 8. The optical circuit according to item 7.

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