JP6453593B2 - Microwave sensor and microwave measurement method - Google Patents

Description

  The present invention relates to a parasitic microwave sensor using an optical signal obtained by modulating light with a microwave, and a method for measuring the microwave.

The microwave is a radio wave having a frequency of 300 MHz to 300 GHz, and is a name including a millimeter wave, a centimeter wave, and an ultrashort wave.
In the field of EMC (Electro-Magnetic Compatibility) measurement and radio wave propagation measurement of various microwave / millimeter-wave devices and systems, there is a measurement technique that combines optical fiber and optoelectronic devices, and modulates and transmits light with microwave / millimeter waves. It is attracting attention as a new technology. By replacing coaxial cables and metal waveguides with optical fibers, the disturbance to the radio wave environment can be reduced and more accurate measurements can be made. This is because measurement is possible. Here, transmission / reception of microwave / millimeter wave using an optical fiber as a transmission line requires an opto-electric (OE) conversion device (typically a photodiode) and an electro-optical (EO) conversion device, respectively. However, in order to avoid disturbance to the radio wave environment, it is desirable that these devices have “no power supply operation = zero bias operation” that does not require electric power supply (see, for example, Non-Patent Documents 1 and 2). ).

  Reference 2 reports that good microwave reception can be realized by operating a zero-bias operation of an electro-absorption modulator (EAM) manufactured by a semiconductor as an EO conversion device. The EAM used here has a reflective configuration, and sends a continuous optical signal to the EAM module, returns the optical signal modulated by the microwave as reflected light, and re-converts it into microwave by the photodiode. To do.

When receiving a microwave or a millimeter wave, the power level to be observed is usually relatively low, so that the device normally operates with a low degree of EAM optical modulation. In this state, the return optical signal is almost composed of a direct current component. When the OE conversion from an optical signal to a microwave is performed using a photodiode, there is a problem that the SN ratio is degraded due to current shot noise that depends on the direct current component of the optical power.

As a technique for solving this problem, Patent Document 1 proposes “a technique using an interference signal between a microwave-modulated optical signal and a continuous light having an opposite phase with controlled phase”. As shown in FIG. 7, continuous light emitted from the laser light source (41) is divided by a 3 dB optical coupler (43), and one continuous light is passed through an optical circulator (45) to an electroabsorption optical modulator (EAM) ( 44A-44G), and the optical signal modulated by EO with the microwave is returned to the optical transmission side as reflected light. The optical signal that has passed through the optical circulator is caused to interfere with the original laser beam by the 3 dB optical coupler (48), re-OE converted to a microwave signal by the photodiode (49), and then amplified by the electric amplifier (50). Here, in order to suppress the center frequency (carrier light) component of the reflected light signal, the optical phase and intensity of the continuous light having the opposite phase are adjusted by using the optical phase adjuster ( 46 ) and the optical attenuator (47). Eventually, as a result of the signal interference, the spectral intensity (carrier light component) of the optical center frequency of the optical modulation signal, which is a DC component, is suppressed, and the modulation component becomes the main light reception signal of the photodiode (49). The reception current level of (49) is greatly reduced.

  On the other hand, the signal intensity of the modulation component is not affected by interference and is only a 3 dB decrease at the optical coupler (48), so that the light intensity is relatively higher than the carrier light component. For this reason, the S / N ratio when the modulation component is converted into an electric signal by the photodiode (49) is improved, and microwaves with higher accuracy and a wider dynamic range can be observed.

Japanese Patent Application No. 2013-199090

Toribata N. “Practical application and future prospect of waveguide type electric field sensor”, Laser Research, June 2005, pp. 384-388. S. Kurokawa et al. , “A Novel Evaluation Method for Semi-anechoic Chamber Using Zero-Biased Optical Devices and Time-domain Analysis”, 2010 IEEE Int. Conf. Wireless Information Tech. and Systems (ICWIS) pp. 1-4, 2010.

  However, in the technique disclosed in Patent Document 1, the microwave observation (EO conversion) site (52) and the signal processing (OE conversion) site (53) are connected by an optical fiber transmission line (51). ing. As a result, as the optical fiber transmission line becomes longer, the microwave-modulated optical signal is subject to disturbances due to chromatic dispersion and polarization mode dispersion due to the effects of vibration and temperature fluctuation, and stable interference operation cannot always be performed. There is a problem. Although it is possible in principle to feed back the phase and intensity of continuous light having opposite phases by constantly monitoring the microwave-modulated light, the measurement system must be complicated.

  That is, as described in “Background Art”, by combining an optical fiber and an electro-optical / photoelectric conversion device, a microwave / millimeter-wave sensor that operates in a non-powered state can be configured with higher accuracy. For measurement with a wide dynamic range, “photoelectric reconversion with the spectral intensity of the center frequency of the microwave modulated optical signal suppressed” has a great effect on the improvement of the SN ratio. Such “photoelectric reconversion” can be realized by performing an interference operation between a continuous optical signal and a microwave modulated optical signal divided from the same semiconductor laser. However, according to the conventional measurement system configuration, there is a problem that a stable interference operation cannot always be performed due to the influence of vibration and temperature fluctuation. This is a serious problem particularly when the microwave observation site and the photoelectric conversion site are connected by a long optical fiber transmission line.

  Therefore, in order to solve the above problems, the present invention has an object to provide a microwave sensor and a microwave measurement method that can perform measurement with high accuracy and a wide dynamic range and are not easily affected by vibration, temperature fluctuation, and the like. To do.

  In order to achieve the above object, according to the present invention, when removing a DC component (optical center frequency) of a microwave modulated optical signal, an antenna site is used by using a monolithic EO chip instead of an OE conversion site as shown in FIG. It was decided to improve stability. Furthermore, the present invention enables optimization of DC component removal by adjusting a variable resistor connected in series with the EAM.

Specifically, the microwave sensor according to the present invention is:
Branching means for branching the carrier light from one light source into two parts;
Two light modulating means for modulating at least one of the carrier light branched by the branching means with an electrical signal and outputting output light having different average light intensities;
Interference means for combining and interfering with the output light from the two light modulation means output by the light modulation means, and outputting interference light with reduced carrier light components;
Are provided on the same substrate.

  This microwave sensor does not transmit an optical signal modulated by an observed microwave as it is through an optical fiber, but causes interference on one substrate to remove the DC component of the microwave modulated optical signal. Since the DC component is removed, measurement with high accuracy and a wide dynamic range can be performed, and the microwave-modulated optical signal is not transmitted through the optical fiber, so that it is not easily affected by vibration and temperature fluctuation.

  Therefore, the present invention can provide a microwave sensor that can perform measurement with high accuracy and a wide dynamic range and is not easily affected by vibration, temperature fluctuation, and the like.

The light modulation means of the microwave sensor according to the present invention is a waveguide type electroabsorption optical modulator having a cathode grounded,
The anode of each of the waveguide type electroabsorption optical modulators is grounded through a resistor,
At least one of the resistors is a variable resistor that adjusts an average light intensity of output light output from the modulation unit,
An electrical signal input port to which the electrical signal is input is connected between an anode of at least one waveguide-type electroabsorption optical modulator and the resistor.
By adjusting the average light intensity of the light output from the EAM with the variable resistor, the DC component removal can be optimized.

The light modulation means of the microwave sensor according to the present invention includes a reflector that reflects light from the waveguide-type electroabsorption optical modulator and inputs the light again to the waveguide-type electroabsorption optical modulator. ,
The branching unit and the interference unit are the same optical coupler.
Microwave sensors can be reduced in size and parts can be saved.

A microwave measurement method according to the present invention is a microwave measurement method in the microwave sensor,
A carrier light input step for inputting carrier light from the light source to the branching means;
An electric signal input step of inputting the electric signal to the electric signal input port;
A photoelectric conversion step of receiving the interference light output from the interference means with a light receiver and converting it into an electrical signal;
An adjustment step of adjusting the variable resistor so that the frequency of the electrical signal converted in the photoelectric conversion step is equal to the frequency of the electrical signal input in the electrical signal input step;
Is provided.
The optimization of DC component removal is variable to maximize the main signal intensity and minimize the average current in the range where the second harmonic of the main signal is not included in the electrical signal obtained by OE conversion of the light interfered by the interference means. This can be achieved by adjusting the resistor.

  The present invention can provide a microwave sensor and a microwave measurement method that can perform measurement with high accuracy and a wide dynamic range and are not easily affected by vibration or temperature fluctuation.

It is a figure explaining the microwave sensor which concerns on this invention. It is a figure explaining the microwave sensor which concerns on this invention. It is a figure explaining operation | movement of the microwave sensor which concerns on this invention. It is a figure explaining operation | movement of the microwave sensor which concerns on this invention. It is a figure explaining operation | movement of the microwave sensor which concerns on this invention. It is a figure explaining the microwave sensor which concerns on this invention. It is a figure explaining the microwave sensor relevant to this invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 1 is a schematic diagram illustrating a microwave sensor 301 according to the present embodiment.
The microwave sensor 301
Branching means for branching the carrier light from one light source into two parts;
Two light modulating means for modulating at least one of the carrier light branched by the branching means with an electrical signal and outputting output light having different average light intensities;
Interference means for combining and interfering with the output light from the two light modulation means output by the light modulation means, and outputting interference light with reduced carrier light components;
Are provided on the same substrate.

The light modulation means is a waveguide type electroabsorption optical modulator with a cathode grounded,
The anode of each waveguide-type electroabsorption optical modulator is grounded through a resistor and an inductor,
At least one of the resistors is a variable resistor that adjusts an average light intensity of output light output from the modulation unit,
An electrical signal input port to which the electrical signal is input is connected between the anode of at least one waveguide-type electroabsorption optical modulator and the resistor / inductor circuit.

This will be described in more detail with reference to FIG. The microwave sensor 301 includes an electro-optical conversion chip substrate and an external circuit. The electro-optic conversion chip substrate 12 includes an optical input port 1, an input optical waveguide 2, a 2 × 2 MMI (Multi-Mode Interferometer) optical coupler 3, a branched optical waveguide (4A to 4F), and a waveguide-type electroabsorption modulator (EAM). (5A, 5B), electrical signal input ports (6A, 6B), 2 × 2 MMI optical coupler 7, output optical waveguide 8, and optical signal output port 9 are formed. Then, variable resistors (10A, 10B) and inductors (11A, 11B) are connected in series as external circuits to the electric signal input ports (6A, 6B), respectively.

The 2 × 2 MMI optical coupler 3 corresponds to the branching means, and includes an electric signal input port (6A, 6B), a variable resistor (10A, 10B), an inductor (11A, 11B), and a waveguide type EAM (5A, 5B). The 2 × 2 MMI optical coupler 7 corresponds to the light modulating means and the interference means.

Input optical waveguide 2, 2 × 2 MMI optical coupler (3, 7), branch optical waveguide (4A-4F), waveguide type EAM (5A, 5B), electric signal input port (6A, 6B), output optical waveguide 8 These are monolithically integrated on the electro-optic conversion chip substrate 12, and the variable resistors (10A, 10B) and the inductors (11A, 11B) are connected to the outside of the chip by electrical mounting.

  The manufacturing method of this microwave sensor is not different from the manufacturing method of a 1.5 μm band optical communication transmission device. For example, it can be easily manufactured by using the DFB laser / electroabsorption modulator integrated device technology for 10 Gb / s. Is possible.

  The waveguide type EAM (5A, 5B) typically has a double hetero pin type diode structure, and light absorption increases as the reverse bias voltage is increased. It has been found that it is possible to operate with zero bias by adjusting the structure of the core layer of the waveguide according to the wavelength of light used.

Each waveguide type EAM has a cathode grounded, and inductors (11A, 11B) and variable resistors (10A, 10B) connected in series to function as a “bias circuit”. In a state where no light is introduced, each waveguide type EAM is zero bias (a state where no voltage is applied). On the other hand, when light is introduced, each waveguide type EAM generates a photocurrent associated with light absorption, and this photocurrent flows to cause a voltage drop in the variable resistor. For this reason, the bias voltage of each waveguide type EAM is shifted to the forward bias side by the voltage drop. This forward bias shift lowers the optical absorptance of the waveguide type EAM (increases the transmitted light intensity), so that the transmitted light intensity with respect to a certain light input can be adjusted by changing the resistance value.

Note that a bias circuit including an inductor and a variable resistor has a variable resistance (10A, 10B) value in terms of DC and a high impedance in terms of RF. Therefore, the high frequency impedance viewed from the electric signal input ports (6A, 6B) is equal to the impedance of the waveguide type EAM.

A microwave measurement method using the microwave sensor 301 will be described below.
This microwave measurement method
A carrier light input step for inputting carrier light from a light source to the branching means;
An electric signal input step for inputting an electric signal to the electric signal input port;
A photoelectric conversion step of receiving the interference light output from the interference means with a light receiver and converting it into an electrical signal;
An adjustment step of adjusting the variable resistor so that the frequency of the electrical signal converted in the photoelectric conversion step is equal to the frequency of the electrical signal input in the electrical signal input step;
Is provided.

[Carrier light input step]
Carrier light is introduced into the optical input port 1 from an external laser or the like (not shown). The carrier light introduced from the optical input port 1 passes through the input optical waveguide 2, and its power is divided into two by the 2 × 2 MMI optical coupler 3, passes through the branched optical waveguides (4 </ b> A, 4 </ b> B) and passes through the waveguide type EAM 5A, 5B).

[Electric signal input step]
The received microwave electrical signal is input to the electrical signal input ports (6A, 6B). By the electric signal input to the electric signal input ports (6A, 6B), the carrier light is intensity-modulated by the waveguide type EAM (5A, 5B), and is output to the branched optical waveguides (4C, 4F). Both optical signals interfere with each other at the × 2 MMI optical coupler 7. Here, the optical phase is output in the same phase to the branch optical waveguide 4E, and the optical phase is output in the opposite phase to the branch optical waveguide 4F. This interference state is a characteristic common to 2 × 2 type or directional coupler type optical couplers, and is derived from the fact that the phase of the two optical signals at the coupler output is 90 °.

[Photoelectric conversion step]
When the modulation signals are superimposed in a state where the optical phases are opposite to each other, it is possible to extract a microwave modulation optical signal with a small DC light portion (carrier light component). When the OE conversion is performed again by the photodiode, the photodiode current level becomes much lower, so that the shot noise is reduced and the SN ratio is increased.

[Adjustment step]
When obtaining a microwave modulated optical signal by such interference, it is necessary to adjust the mutual light intensity in addition to the phase of the microwave. In the case of the waveguide type EAM (diode) arrangement of FIG. 1, in order to maximize the amplitude of the modulated optical signal, the microwave electrical signal needs to be input in reverse phase. The mutual light intensity should be superposed within a range in which the optical phase of the optical signal after interference does not invert. Therefore, it is indispensable that the average value of each optical electric field amplitude input to the 2 × 2 MMI optical coupler 7 has a certain difference or more. According to the present invention, by adjusting the value of the variable resistor (10A, 10B), the optical absorption state is changed by changing the bias voltage of the EAM, and each optical electric field amplitude input to the 2 × 2 MMI optical coupler (7). Can be changed. For adjustment of the optical electric field amplitude, one of the values of the variable resistors (10A, 10B) may be adjusted.

  The adjustment method will be described more specifically. As an example, consider a case where the average values of the optical field amplitudes input to the 2 × 2 MMI optical coupler 7 are substantially equal. In this state, the antiphase interference light (branch optical waveguide 4F) output from the 2 × 2 MMI optical coupler 7 is light whose phase is inverted every half cycle because the optical intensity modulation phase and the optical phase are both in reverse phase. Signal. When this optical signal is subjected to OE conversion, its frequency becomes twice that of the electrical signal (as will be described in detail later). On the other hand, when the average value of each optical electric field amplitude input to the 2 × 2 MMI optical coupler 7 is adjusted so that phase inversion of the optical phase does not occur after interference, the interference light output from the 2 × 2 MMI optical coupler 7 The optical electric field amplitude is the frequency of the electric signal input to the electric signal input port (6A, 6B). Therefore, the variable resistor 10A or the variable resistor 10B is set so that the optical electric field amplitude of the interference light output from the 2 × 2 MMI optical coupler 7 becomes the frequency of the electric signal input to the electric signal input ports (6A, 6B). Change the light absorption state.

(Embodiment 2)
FIG. 2 is a diagram illustrating the microwave sensor 302 of the present embodiment. In contrast to the microwave sensor 301 of FIG. 1, in the microwave sensor 302, the light modulation means reflects light from the waveguide-type electroabsorption optical modulator and inputs it again to the waveguide-type electroabsorption optical modulator. The branching unit and the interference unit are the same optical coupler.

  The microwave sensor 302 is an example of the simplest form. The microwave sensor 302 eliminates the 2 × 2 MMI optical coupler 7 of the microwave sensor 301 of FIG. 1, and performs a power splitting of continuous laser light (carrier wave) and interference operation of the microwave modulated optical signal as one 2 × 2 MMI optical coupler. 23. The electric signal input port 26 is disposed in one waveguide EAM, and the other is not input (DC fixed). Of course, it is needless to say that an electric signal may be input to both EAMs as in the first embodiment.

This will be described in more detail with reference to FIG. The microwave sensor 302 includes an electro-optical conversion chip substrate and an external circuit. The electro-optic conversion chip substrate 29 includes an optical input / output port 21, an input / output optical waveguide 22, a 2 × 2 MMI optical coupler 23, a branched optical waveguide (24A to 24D), a waveguide type EAM (25A, 25B), and an electric signal input port. 26 is formed. A variable resistor 27A and an inductor 28 are connected in series as an external circuit to the electric signal input port 26A. On the other hand, a variable resistor 27B is connected to the electric signal input port 26B as an external circuit. In the present embodiment, a case where end faces (40A, 40B) are used as the reflector will be described, but a mirror may be disposed on the end faces (40A, 40B).
Each of these functions is the same as that described in the first embodiment.

FIG. 3 is a diagram for explaining the state of light in each part of the microwave sensor 302.
An electric signal obtained by converting the microwave (frequency f _m ) into electricity is input from the electric signal input port 26. Carrier light (CW light) is input from the optical input / output port 21. One carrier light (π / 2 phase delay) branched by the 2 × 2 MMI optical coupler 23 is modulated by this electric signal (frequency f _m ) by the waveguide type EAM 25A. The modulated optical signal is reflected, for example, in the same optical phase state at the end surface 40A opposite to the optical input / output port 21 of the electro-optic conversion chip substrate 29, and again passes through the waveguide EAM 25A. On the other hand, the other carrier light (no phase delay) branched by the 2 × 2 MMI optical coupler 23 passes through the waveguide EAM 25B. Then, the carrier light is reflected, for example, in the same optical phase state at the end face 40B opposite to the light input / output port 21 of the electro-optic conversion chip substrate 29, and again passes through the waveguide type EAM 25B.

  These lights interfere with each other by the 2 × 2 MMI optical coupler 23. In the 2 × 2 MMI optical coupler 23, the optical signal of π / 2 phase lag from the waveguide type EAM 25A is further combined with the carrier light having no phase lag from the π / 2 phase delay and from the waveguide type EAM 25B. Output to port 21. That is, from the optical input / output port 21, the light is superimposed in reverse phase, and an optical signal with less DC light portion is output. On the other hand, in the 2 × 2 MMI optical coupler 23, the carrier light having no phase delay from the waveguide type EAM 25B is combined with the optical signal having the phase delay of π / 2 and π / 2 phase from the waveguide type EAM 25A. 41 is output. In other words, the optical port 41 outputs an optical signal in which light is superimposed in the same phase.

4 and 5 show the case where the average optical amplitude of the 2 × 2 MMI optical coupler 23 is the same when the light from the waveguide EAM (25A) and the light from the waveguide EAM (25B) are superimposed. It is a figure explaining the case where is different. Since the light from the waveguide type EAM (25A) is a microwave-modulated optical signal, there are both sideband signals in the optical spectrum as shown in FIG. If the light from the waveguide type EAM (25B) (continuous light) and the light from the waveguide type EAM (25A) (microwave modulated optical signal) are in opposite phase and the average optical amplitude is equal, 2 × 2 MMI light the signal after interference coupler 23, rather than the central light wavelength component, the frequency difference of the optical spectrum is 2f _m, the frequency of the electrical signal after re-OE conversion is twice the frequency of the microwave (Figure 4 (A), FIG. 5 (A)).

  Therefore, if the variable resistor (27A or 27B) is adjusted so that the average optical amplitudes of the two are different as shown in FIGS. 4B and 5B, the interference after the 2 × 2 MMI optical coupler 23 is obtained. The center wavelength component remains in the signal, and the frequency of the electric signal after the re-OE conversion becomes equal to the frequency of the microwave (FIGS. 4B and 5B).

  In this example, by setting the resistance value of the variable resistor 27A to be larger than that of the variable resistor 27B, the operating point of the waveguide type EAM 25B is relatively shifted to the forward bias side, and the optical output is increased. It can be set as a state. On the contrary, the resistance value of the variable resistor 27A is set smaller than that of the variable resistor 27B so that the optical amplitude of the phase-inverted continuous light becomes relatively large so that the optical phase is not inverted. It is also possible.

  In the microwave sensor 302, light reciprocates in the waveguide type EAM (25A, 25B). For this reason, the length of the waveguide type EAM (25A, 25B) for obtaining the same light absorption state as that of the waveguide type EAM (5A, 5B) of the microwave sensor 301 of FIG. The length of the waveguide type EAM (5A, 5B) may be ½.

(Embodiment 3)
FIG. 6 is a diagram illustrating the microwave sensor 303 of the present embodiment. The microwave sensor 303 is obtained by performing a push-pull operation on the waveguide type EAM of the microwave sensor 302 of FIG.

The microwave sensor 303 includes an electro-optical conversion chip substrate and an external circuit. The electro-optical conversion chip substrate 39 includes an optical input / output port 31, an input / output optical waveguide 32, a 2 × 2 MMI optical coupler 33, a branched optical waveguide (34A to 34D), a waveguide type EAM (35A, 35B), and an electrical signal input port. (36A, 36B) are formed. Then, variable resistors (37A, 37B) and inductors (38A, 38B) are connected in series as external circuits to the electric signal input ports (36A, 36B), respectively. In the present embodiment, a case where end faces (40A, 40B) are used as the reflector will be described, but a mirror may be disposed on the end faces (40A, 40B).
Each of these functions is the same as that described in the first embodiment.

  The microwave input is introduced between both anode terminals of the waveguide-type EAMs (35A, 35B) connected in series via a balanced transmission line (Balanced Transmission Line). Since the pn junctions of the waveguide-type EAM (35A, 35B) are opposed to each other, a negative polarity voltage is applied to the other EAM while a positive polarity voltage is applied to the other EAM. Further, since the node between the two waveguide type EAMs (35A, 35B) is grounded, it is possible to set the operating point independently by adjusting the variable resistors (37A, 37B). is there.

  As described in the second embodiment, when the interference in the 2 × 2 MMI optical coupler 33 is performed with the same optical signal amplitude, the spectrum of the center optical frequency is reduced, and the frequency after the re-OE conversion is twice the microwave signal frequency. It becomes. In order to maximize the microwave modulation component after interference, the intensity of the valley portion of the amplitude of one microwave modulated optical signal and the intensity of the peak portion of the amplitude of the other microwave modulated optical signal are: The operating point of the waveguide type EAM (35A, 35B) is adjusted by the variable resistors (37A, 37B) so as to be the same.

  The advantage of the microwave sensor 303 is that the amplitude of the microwave modulation component after interference is improved compared to the microwave sensor 302. That is, the drive voltage of each of the waveguide type EAM (35A, 35B) is 1 / √2 times the same microwave input, but the electric field intensity of the microwave modulated optical signal is 2 in the 2 × 2 MMI optical coupler 33. Since the superposition is doubled, the optical electric field amplitude of the microwave modulated component after interference is doubled, the optical signal power is doubled, and the signal current level after OE conversion by the photodiode is doubled. On the other hand, since the average optical signal power of the shot noise current is √2 times, the SN ratio is eventually increased by 3 dB. Each magnification is based on the microwave sensor 302.

[Appendix]
The following describes the microwave sensor of the present invention.
The present invention relates to a “feedless microwave sensor” that uses an optical signal modulated by a microwave, and is a more stable and improved SN ratio without being affected by vibration, temperature fluctuation, or the like. Provide a wave observation technique.

(1): first two-input two-output type 3 dB optical coupler, two pairs of optical waveguides connected to the input port and the output port thereof, and a pair of waveguide-type electric fields connected to one pair of the optical waveguides An absorption light modulator, including a variable resistor connected in series to each of the waveguide-type electroabsorption light modulators as a component;
Both ends of the series connection portion of the waveguide-type electroabsorption optical modulator and the variable resistor are each in a zero-bias state with respect to DC.
The continuous optical input divided by the 3 dB optical coupler is modulated by the waveguide type electroabsorption optical modulator, and the modulated optical signal is again converted into the first 2-input 2-output type 3 dB optical coupler, or the second A microwave sensor that extracts a signal, which is interfered by a 2-input 2-output 3 dB optical coupler, and whose spectrum intensity of an unmodulated optical signal component is suppressed, to an output port.

(2): A microwave sensor in which a microwave signal is input to one of a pair of waveguide-type electroabsorption optical modulators within the range of (1) above.

(3): In the range of (1) above, the anodes or cathodes of a pair of waveguide type electroabsorption optical modulators are electrically connected, and the cathodes of the pair of waveguide type electroabsorption optical modulators A microwave sensor, wherein a microwave signal is input between the electrodes or between the anodes.

  The present invention can expand the dynamic range of a “microwave sensor” using an electroabsorption modulator (EAM) more stably.

1: Optical input port 2: Input optical waveguides 3, 23, 33: 2 × 2 MMI optical couplers 4A-4F, 24A-24D, 34A-34D: Branch optical waveguides 5A, 5B, 25A, 25B, 35A, 35B: Waveguides Electroabsorption modulator (EAM)
6A, 6B, 26, 36A, 36B: Electrical signal input port 7: 2 × 2 MMI optical coupler 8: Output optical waveguide 9: Optical signal output port 10A, 10B, 27A, 27B, 37A, 37B: Variable resistors 11A, 11B 28, 38A, 38B: Inductors 12, 29, 39: Electro-optical conversion chip substrates 21, 31: Optical input / output ports 22, 32: Input / output optical waveguides 40A, 40B: End face 41: Optical ports 301, 302, 303: Microwave sensor

Claims (4)

Branching means for branching the carrier light from one light source into two parts;
Light modulating means of two waveguide-type electroabsorption optical modulators for modulating at least one of the carrier light branched by the branching means with an electrical signal and outputting output light having different average light intensities;
MMI (Multi-Mode Interferometer) interfering means for combining and interfering the two output lights output from the light modulating means to output interference light with reduced carrier light components;
On the same substrate ,
In the waveguide type electroabsorption optical modulator, the transmitted light intensity is adjusted by adjusting the forward bias due to the photocurrent generated by the carrier light branched by the branching means, and the average light intensity of the output light is changed.
Microwave sensor you wherein a. It said waveguide-type field absorption optical modulator of the light modulating means is grounded cathode,
The anode of each of the waveguide type electroabsorption optical modulators is grounded through a resistor,
At least one of the resistors is a variable resistor that adjusts a forward bias due to a photocurrent generated by the carrier light branched by the branching unit by the waveguide-type electroabsorption optical modulator ,
2. The microwave according to claim 1, wherein an electrical signal input port to which the electrical signal is input is connected between an anode of at least one waveguide-type electroabsorption optical modulator and the resistor. Sensor. The light modulation means includes a reflector that reflects light from the waveguide-type electroabsorption optical modulator and re-inputs the light to the waveguide-type electroabsorption optical modulator,
The microwave sensor according to claim 2, wherein the branching unit and the interference unit are the same optical coupler. A microwave measurement method using the microwave sensor according to claim 2 or 3,
A carrier light input step for inputting carrier light from the light source to the branching means;
An electric signal input step of inputting the electric signal to the electric signal input port;
A photoelectric conversion step of receiving the interference light output from the interference means with a light receiver and converting it into an electrical signal;
An adjustment step of adjusting the variable resistor so that the frequency of the electrical signal converted in the photoelectric conversion step is equal to the frequency of the electrical signal input in the electrical signal input step;
A microwave measurement method comprising:

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