Optical sensing circuit and laser Doppler vibrometer

Abstract

This invention provides an optical sensing circuit that can be miniaturized and reduced in cost through mass production technology, and a laser Doppler vibrometer that uses this optical sensing circuit. [Solution] The optical sensing circuit is configured to include a first input / output terminal, a second input / output terminal, a first optical branching and multiplexing section, a second optical branching and multiplexing section, a third optical branching and multiplexing section, a first optical waveguide section, a second optical waveguide section, a third optical waveguide section, a fourth optical waveguide section, a fifth optical waveguide section, a sixth optical waveguide section, an optical detection section, and an optical phase modulator section, all formed on a single circuit support substrate.

Description

[Technical Field]

[0001] This invention relates to an optical sensing circuit that uses light interference to detect minute fluctuations in a measurement target with high precision, and to a laser Doppler vibrometer using this optical sensing circuit. [Background technology]

[0002] As IoT (Internet of Things) technology permeates society, the need for various sensors to support it is increasing. Among these, optical sensing, which utilizes optical technology, is attracting attention because it enables the acquisition of broadband and highly sensitive data. In particular, optical sensing using laser Doppler vibrometers, which measure minute vibrations of objects using the Doppler effect of light, can be used for predictive maintenance and inspection of machinery and equipment installed in factories and plants, as well as various infrastructure and structures, and is important for industrial applications.

[0003] First, we will explain the general overview of conventional laser Doppler vibrometers (see, for example, Patent Document 1). .

[0004] In conventional laser Doppler vibrometers, the laser light generated by the laser light source is split into two, one as the illumination light and the other as the local light (also called the reference light). When the illumination light is shone on the object to be measured, the illumination light is reflected by the object. The reflected light (also called the measurement light or signal light) undergoes a frequency shift due to the Doppler effect depending on the vibration state of the object to be measured, and this frequency shift appears as a phase change. Therefore, if the phase change given by the object to be measured can be measured, the vibration state of the object can be determined.

[0005] Generally, to extract phase information in a laser Doppler vibrometer, heterodyne detection is used, which detects the phase difference between the measurement light and the local light, which have different wavelengths, using an optical interferometer.

[0006] Conventionally, contact-type vibration sensors, widely used for vibration measurement, have had difficulty measuring vibrations of distant objects or objects under high temperature and high magnetic field conditions. In contrast, laser Doppler vibrometers enable non-contact measurement by irradiating light from a distance. Therefore, laser Doppler vibrometers can measure vibrations in situations where contact-type vibration sensors are ineffective.

[0007] For optical sensors, including laser Doppler vibrometers, to become more widely adopted in society, miniaturization and cost reduction are crucial. For example, if laser Doppler vibrometers could be made extremely small and mounted on robots or drones, their applications would expand to a wide range of scenarios, offering numerous advantages.

[0008] Conventional laser Doppler vibrometers have been manufactured by combining individual optical components such as lasers and half-mirrors. This method makes miniaturization difficult, and manufacturing is not easy because it requires the skills, knowledge, and know-how of experienced engineers for the optical connections of each optical component.

[0009] In recent years, photoelectric integration technologies, including silicon photonics, which integrate multiple optical and electronic components on semiconductor substrates such as silicon, have shown remarkable progress. When using photoelectric integration technology, light is confined and propagated within an optical waveguide made of silicon. Therefore, unlike when optical connections between optical components are made using lenses, etc., complex optical axis alignment is not required. Consequently, the manufacturing process is simpler and advantageous in terms of manufacturing costs.

[0010] Applying photoelectric fusion technologies, including silicon photonics, to optical sensors such as laser Doppler vibrometers makes it possible to miniaturize and reduce costs through mass production techniques. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Unexamined Patent Publication No. 2001-159560 Summary of the Invention Problem to be Solved by the Invention

[0012] As described above, heterodyne detection is often used in laser Doppler vibrometers to detect vibration. In this case, an acousto-optic (AO) modulator is required to generate frequency-shifted local light (or signal light).

[0013] However, it is still difficult at present to implement an optical frequency shifter such as an AO modulator using silicon photonics technology.

[0014] Therefore, homodyne detection that does not involve frequency shifting is used in laser Doppler vibrometers using silicon photonics technology. Homodyne detection generally requires integration of four photodetectors and an optical component called a 90° hybrid. For this reason, there are concerns about an increase in element size and a decrease in yield. In addition, skilled techniques are required for operation adjustment, for example, it is necessary to appropriately adjust the light receiving efficiency of the four photodetectors in consideration of variations in insertion loss of a 90° hybrid circuit or the like.

[0015] The present invention has been made in view of the above-described problems. An object of the present invention is to provide an ultra-compact optical sensing circuit using integration technology including silicon photonics technology that can be reduced in cost through miniaturization and mass production technology, and a laser Doppler vibrometer using the optical sensing circuit. Means for Solving the Problem

[0016] To achieve the above object, the optical sensing circuit of the present invention comprises a first input / output terminal, a second input / output terminal, a first optical branching multiplexing unit, a second optical branching multiplexing unit, a third optical branching multiplexing unit, a first optical waveguide unit, a second optical waveguide unit, a third optical waveguide unit, a fourth optical waveguide unit, a fifth optical waveguide unit, a sixth optical waveguide unit, a photodetector unit, and an optical phase modulator unit, all formed on a single circuit support substrate.

[0017] The first branching multiplexing unit has an input port, a first output port, and a second output port, splits light input to the input port into two, and outputs the split light from the first output port and the second output port. The second branching multiplexing unit has an input port, an input / output port, and an output port, outputs light input to the input port from the input / output port, and outputs light input to the input / output port from the output port. The third branching multiplexing unit has a first input port, a second input port, and an output port, multiplexes light input to the first input port and light input to the second input port, and outputs the multiplexed light from the output port.

[0018] The first optical waveguide unit is connected to the first input / output terminal and an input port of the first optical branching multiplexing unit. The second optical waveguide unit is connected to a first output port of the first optical branching multiplexing unit and an input port of the second optical branching multiplexing unit. The third optical waveguide unit is connected to the input / output port of the second optical branching multiplexing unit and the second input / output terminal. The fourth optical waveguide unit is connected to a second output port of the first optical branching multiplexing unit and a first input port of the third optical branching multiplexing unit. The fifth optical waveguide unit is connected to an output port of the second optical branching multiplexing unit and a second input port of the third optical branching multiplexing unit. The sixth optical waveguide unit is connected to an output port of the third optical branching multiplexing unit and the photodetector unit. The optical phase modulator unit is formed on the fourth optical waveguide unit, and phase-modulates light propagating through the fourth optical waveguide unit. The photodetector unit photoelectrically converts light input from the third optical branching multiplexing unit via the sixth optical waveguide unit.

[0019] According to a preferred embodiment of the optical sensing circuit of the present invention, the first input / output terminal, the second input / output terminal, the first optical branching and multiplexing section, the second optical branching and multiplexing section, the third optical branching and multiplexing section, the first optical waveguide section, the second optical waveguide section, the third optical waveguide section, the fourth optical waveguide section, the fifth optical waveguide section, the sixth optical waveguide section, and the optical phase modulator section are all composed of silicon waveguides.

[0020] Furthermore, according to another preferred embodiment of the optical sensing circuit of this invention, the first optical branching and multiplexing section and the second optical branching and multiplexing section are polarized beam splitter type waveguides.

[0021] Furthermore, according to another preferred embodiment of the optical sensing circuit of the present invention, laser light is input to the first input / output terminal, the laser light input to the first input / output terminal is sent to the first optical branching and combining section via the first optical waveguide section, and one of the two branches of the laser light at the first optical branching and combining section is output as illumination light from the second input / output terminal via the second optical waveguide section, the second optical branching and combining section, and the signal light input from the second input / output terminal. The signal light is sent to the third optical waveguide section, the second optical branching and combining section, and the fifth optical waveguide section, where the laser light is branched into two in the first optical branching and combining section, and the other half is phase-modulated in the optical phase modulator section as a reference light. After this, it is sent to the third optical branching and combining section via the fourth optical waveguide section, where the signal light and the local light are combined to generate interference light, and the interference light is sent to the photodetector section via the sixth optical waveguide section.

[0022] Furthermore, in order to achieve the above-mentioned objectives, the laser Doppler vibrometer of this invention is configured to include the above-mentioned optical sensing circuit, laser light source, modulation power supply, and signal processing unit. The laser light source generates laser light and inputs the laser light to the first input / output terminal of the optical sensing circuit. The laser light input to the first input / output terminal is sent to the first optical branching and combining unit via the first optical waveguide section.

[0023] One of the two branches of the laser light obtained by the first optical branching and multiplexing unit is output from the second input / output terminal via the second optical waveguide unit, the second optical branching and multiplexing unit, and the third optical waveguide unit, and irradiates the object to be measured. The signal light generated by the reflection of the irradiated light from the object to be measured is input from the second input / output terminal and sent to the third optical branching and multiplexing unit via the third optical waveguide unit, the second optical branching and multiplexing unit, and the fifth optical waveguide unit. The other two branches of the laser light obtained by the first optical branching and multiplexing unit are phase-modulated in the optical phase modulator unit based on the modulated electrical signal generated by the modulation power supply, and then sent to the third optical branching and multiplexing unit via the fourth optical waveguide unit, as a reference light.

[0024] The optical splitting and multiplexing unit combines the signal light and the local light to generate interference light, and sends the interference light to the photodetector unit via the sixth optical waveguide unit. The received electrical signal generated by the photoelectric conversion of the interference light in the photodetector unit is sent to the signal processing unit. The signal processing unit extracts information about the vibration of the object being measured from the received electrical signal.

[0025] According to a preferred embodiment of the laser Doppler vibrometer of this invention, the modulation power supply has a repetition frequency f m The optical phase modulator unit generates a modulated electrical signal including a sine wave modulated signal, the modulated electrical signal is applied to the optical phase modulator unit to phase modulate the local light, and the signal processing unit processes the frequency f of the received electrical signal. m Nearby signal components and frequency 2f m A frequency discrimination unit that extracts nearby signal components, and frequency f m The amplitude and frequency 2f of the nearby signal components. m An amplitude correction unit that corrects the amplitudes of neighboring signal components to match, and the corrected frequency f m Nearby signal components and frequency 2f m It includes a decoding unit that decodes the vibration waveform of the object being measured from the arctangent of the nearby signal components.

[0026] According to a preferred embodiment of the laser Doppler vibrometer of this invention, the optical sensing circuit, the laser light source, the modulation power supply, and the signal processing unit are mounted on a single support substrate. The laser light source and the first input / output terminal of the optical sensing circuit are connected by a seventh optical waveguide section formed in the optical sensing circuit.

[0027] According to a preferred embodiment of the laser Doppler vibrometer of this invention, the first input / output terminal, the second input / output terminal, the first optical branching and multiplexing section, the second optical branching and multiplexing section, the third optical branching and multiplexing section, the first optical waveguide section, the second optical waveguide section, the third optical waveguide section, the fourth optical waveguide section, the fifth optical waveguide section, the sixth optical waveguide section, and the optical phase modulator section are all composed of silicon waveguides.

[0028] According to another preferred embodiment of the laser Doppler vibrometer of this invention, when a seventh optical waveguide section is provided, the first input / output terminal, the second input / output terminal, the first optical branching and multiplexing section, the second optical branching and multiplexing section, the third optical branching and multiplexing section, the first optical waveguide section, the second optical waveguide section, the third optical waveguide section, the fourth optical waveguide section, the fifth optical waveguide section, the sixth optical waveguide section, the seventh optical waveguide section, and the optical phase modulator section are all composed of silicon waveguides.

[0029] According to a preferred embodiment of the laser Doppler vibrometer of this invention, the first optical branching and multiplexing section and the second optical branching and multiplexing section are polarized beam splitter type waveguides, and either a Faraday rotator or λ / 4 is inserted in the optical path connecting the second input / output terminal and the object to be measured, which rotates the polarization plane by 45° each time light passes through. [Effects of the Invention]

[0030] This optical sensing circuit utilizes integration technologies, including silicon photonics technology, which enables miniaturization and cost reduction through mass production. Furthermore, by using an ultra-compact optical sensing circuit utilizing this integration technology, laser Doppler vibrometers can be made smaller. In addition, since an AO modulator is not required, the configuration is simple. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic diagram illustrating the first vibration meter. [Figure 2] This is a schematic diagram illustrating the signal processing unit. [Figure 3] This is a schematic diagram illustrating the second vibration meter. [Modes for carrying out the invention]

[0032] The embodiments of this invention will be described below with reference to the figures, but the shapes, sizes, and arrangements of each component are only shown in a general manner to the extent that the invention can be understood. Furthermore, preferred configuration examples of this invention will be described below, but these are merely examples. Therefore, this invention is not limited to the following embodiments, and many modifications or alterations can be made to achieve the effects of this invention.

[0033] (Example configuration of the first embodiment) Referring to Figure 1, an example configuration of an optical sensing circuit and a laser Doppler vibrometer according to the first embodiment of this invention will be described. Figure 1 is a schematic diagram illustrating the laser Doppler vibrometer (hereinafter also referred to as the first vibrometer) according to the first embodiment of this invention.

[0034] The first vibration meter is comprised of a laser light source 10, a modulation power supply 20, a signal processing unit 1000, and an optical sensing circuit 101.

[0035] The optical sensing circuit 101 is formed as an optical waveguide circuit on a single semiconductor substrate, which is a circuit support substrate. The optical sensing circuit 101 can be easily manufactured using standard silicon photonics fabrication methods, for example, by using a commercially available SOI (Silicon On Insulator) substrate. In this case, the support substrate layer of the SOI substrate, which is constructed by sequentially stacking a Si support substrate layer, an SiO2 layer, and a Si layer, becomes the circuit support substrate. The SiO2 layer also becomes the lower cladding.

[0036] Dry etching or similar processes are performed on the Si layer in regions other than the optical waveguide core until the lower cladding is reached. As a result, the Si layer is patterned, and the optical waveguide core is formed.

[0037] Subsequently, SiO2 is deposited on the lower cladding using methods such as chemical vapor deposition (CVD) to form the upper cladding. The upper cladding is formed to cover the optical waveguide core.

[0038] As a result, an optical waveguide core is obtained that is embedded within a cladding consisting of a lower cladding and an upper cladding, and extends parallel to the upper surface of the circuit support substrate.

[0039] The cladding is formed from SiO2, which has a lower refractive index than the silicon optical waveguide core. Therefore, due to the difference in refractive index between the optical waveguide core and the cladding, the optical waveguide core functions as a light transmission path, and the input light propagates in a direction corresponding to the planar shape of the optical waveguide core. A waveguide composed of a Si optical waveguide core and a SiO2 cladding surrounding the optical waveguide core is also called a silicon waveguide.

[0040] By constructing the optical sensing circuit 101 using silicon waveguides, unlike cases where optical connections are made using lenses or the like, complex optical axis alignment is not required, enabling the realization of a desired compact, integrated optical sensing circuit. Furthermore, since standard silicon photonics fabrication methods can be used, the manufacturing process is simplified, resulting in cost advantages.

[0041] The optical sensing circuit 101 comprises first and second input / output terminals 111 and 112, first to third optical branching and multiplexing sections 131 to 133, first to sixth optical waveguide sections 121 to 126, an optical detection section 140, and an optical phase modulator section 150. The first and second input / output terminals 111 and 112, the first to third optical branching and multiplexing sections 131 to 133, and the first to sixth optical waveguide sections 121 to 126 are formed in any suitable structure that can be constructed using silicon waveguides formed using an SOI substrate.

[0042] The first optical branching and multiplexing unit 131 has at least one input port and at least two output ports. Here, the first optical branching and multiplexing unit 131 is described as having one input port 131a and first and second output ports 131b and 131c. The light input to the first optical branching and multiplexing unit 131 from input port 131a is branched at an appropriately designed branching ratio and output from the first and second output ports 131b and 131c. One suitable structure for the first optical branching and multiplexing unit 3 is a so-called MMI (Multi-Mode Interference) type waveguide.

[0043] The second optical branching and multiplexing unit 132 has at least one input port, at least one output port, and at least one input / output port. Here, the second optical branching and multiplexing unit 132 is described as having one input port 132a, one output port 132c, and one input / output port 132b. Light input to the second optical branching and multiplexing unit 132 from input port 132a is output from input / output port 132b. Light input to the second optical branching and multiplexing unit 132 from input / output port 132b is output from output port 132c. One suitable structure for the second optical branching and multiplexing unit 132 is an MMI type waveguide.

[0044] The third optical branching and multiplexing unit 133 has at least two input ports and at least one output port. Here, the third optical branching and multiplexing unit 133 is described as having first and second input ports 133a and 133b and one output port 133c. The light input from the first and second input ports 133a and 133b is combined with an appropriately designed branching ratio and output from the output port 133c. One suitable structure for the third optical branching and multiplexing unit 133 is an MMI type waveguide.

[0045] The first and second input / output terminals 111 and 112 perform either one or both functions: inputting light into the optical sensing circuit 101 from outside the optical sensing circuit 101, and outputting light from the optical sensing circuit 101 to the outside of the optical sensing circuit 101.

[0046] The photodetector 140 converts the input light into an electrical signal. One suitable photodetector 140 is one made of germanium (Ge) grown as a crystal on a silicon optical waveguide core when a silicon waveguide is used. The photodetector 140 may also be provided above or below the optical waveguide core so as to be optically evanescently coupled.

[0047] The first optical waveguide section 121 connects the first input / output terminal 111 to the input port 131a of the first optical branching / combining section 131. The second optical waveguide section 122 connects the first output port 131b of the first optical branching / combining section 131 to the input port 132a of the second optical branching / combining section 132. The third optical waveguide section 123 connects the input / output port 132b of the second optical branching / combining section 132 to the second input / output terminal 112. The fourth optical waveguide section 124 connects the second output port 131c of the first optical branching / combining section 131 to the first input port 133a of the third optical branching / combining section 133. The fifth optical waveguide section 125 connects the output port 132c of the second optical branching / combining section 132 to the second input port 133b of the third optical branching / combining section 133. The sixth optical waveguide section 126 connects the output port 133c of the third optical branching and multiplexing section 133 to the photodetector section 140.

[0048] The optical phase modulator section 150 is formed in a part of the fourth optical waveguide section 124. In the optical phase modulator section 150, the refractive index is changed by injecting current or applying voltage to the silicon waveguide that constitutes the fourth optical waveguide section 124. Pad-shaped electrodes or traveling-wave type electrodes for current injection or voltage application are provided near the silicon waveguide that constitutes the fourth optical waveguide section 124.

[0049] The laser light source 10 generates continuous laser light. The laser light generated by the laser light source 10 is sent to the optical sensing circuit 101. The laser light sent to the optical sensing circuit 101 is input to the first input terminal 111 of the optical sensing circuit 101.

[0050] The laser light input to the optical sensing circuit 101 is sent from the first input terminal 111 through the first optical waveguide section 121 to the first optical branching and multiplexing section 131, and is input to the input port 131a of the first optical branching and multiplexing section 131.

[0051] The laser light input to the first optical splitting and multiplexing unit 131 is split into a first laser beam and a second laser beam. One of the split beams, the first laser beam, is output from the first output port 131b. The other split beam, the second laser beam, is output from the second output port 131c.

[0052] The first laser light output from the first output port 131b of the first optical branching and multiplexing unit 131 passes through the second optical waveguide unit 122 and is input to the input port 132a of the second optical branching and multiplexing unit 132.

[0053] The first laser light input to the second optical splitting and multiplexing unit 132 is output from the input / output port 132b.

[0054] The first laser light output from the input / output port 132b of the second optical branching and multiplexing unit 132 is sent to the second input / output terminal 112 via the third optical waveguide unit 123, and output from the second input / output terminal 112 to the outside of the optical sensing circuit 101.

[0055] The first laser light output to the outside from the second input / output terminal 112 of the optical sensing circuit 101 is irradiated onto the object to be measured 900 as illumination light.

[0056] The reflected light (signal light) from the irradiated light reflected by the object 900 is input to the second input / output terminal 112 of the optical sensing circuit 101.

[0057] Furthermore, in order to illuminate the object 900 to be measured with light and to efficiently capture the signal light, optical components such as lenses may be added between the second input / output terminal 112 and the object 900 to be measured.

[0058] The signal light input to the second input / output terminal 112 of the optical sensing circuit 101 passes through the third optical waveguide section 123 and is input to the input / output port 132b of the second optical branching and multiplexing section 132. The signal light input to the input / output port 132b of the second optical branching and multiplexing section 132 is output from the output port 132c and passes through the fifth optical waveguide section 125 and is input to the second input port 133b of the third optical branching and multiplexing section 133.

[0059] The second laser light output from the second output port 131c of the first optical branching and multiplexing unit 131 is sent as local light to the fourth optical waveguide unit 124. A modulating electrical signal is applied from the modulation power supply 20 to the optical phase modulator unit 150 provided in the fourth optical waveguide unit 124, generating local light by phase modulating the second laser light. The local light generated in the optical phase modulator unit 150 is sent through the fourth optical waveguide unit 124 to the third optical branching and multiplexing unit 133, and input to the first input port 133a of the third optical branching and multiplexing unit 133.

[0060] Here, the local light is light that has been phase-modulated by an optical phase modulator section 150 formed in a part of the fourth optical waveguide section 104. In order to generate phase modulation, a modulating electrical signal from a modulation power supply 20 is applied to the silicon waveguide constituting the optical phase modulator section 150. The refractive index of the silicon waveguide is modulated by the modulation of the current or voltage injected into the silicon waveguide section, and as a result, phase modulation occurs. Here, the modulating electrical signal applied to the silicon waveguide has a frequency f m The modulated current or modulated voltage is assumed to be sinusoidal. However, the waveform of the modulated electrical signal is not limited to a sine wave. Depending on the application, waveforms other than sine waves may be used. In addition, a steady-state component (DC bias) may be superimposed in addition to the modulated component for operational optimization.

[0061] The local light input to the first input port 133a of the third optical branching and multiplexing unit 133 and the signal light input to the second input port 133b of the third optical branching and multiplexing unit 133 are combined in the third optical branching and multiplexing unit 133, interfere with each other, and generate interference light. The interference light generated in the third optical branching and multiplexing unit 133 is output from the output port 133c.

[0062] The interfering light output from the output port 133c of the third optical branching and multiplexing unit 133 is input to the photodetector unit 140 via the sixth optical waveguide unit 126. The photodetector unit 140 converts the input interfering light into a received electrical signal. The received electrical signal generated by the photoelectric conversion in the photodetector unit 140 is sent to the signal processing unit 1000.

[0063] Here, the amplitude or phase of the signal light fluctuates in response to vibrations of the object being measured 900. These fluctuations in amplitude or phase are reflected in the waveform changes of the received electrical signal that are ultimately detected. Therefore, the signal processing unit 1000 can detect vibrations of the object being measured 900 by analyzing the waveform changes of the received electrical signal converted by the photodetector 140.

[0064] Furthermore, it is desirable that the wavelength of the laser light generated by the laser light source 10 is such that absorption is sufficiently small by the materials constituting the optical waveguide cores of the first and second input / output terminals 111 and 112, the first to third optical branching and multiplexing sections 131 to 133, and the first to sixth optical waveguide sections 121 to 126. When an SOI substrate is used as the circuit support substrate 101, and the first and second input / output terminals 111 and 112, the first to third optical branching and multiplexing sections 131 to 133, and the first to sixth optical waveguide sections 121 to 126 are constructed using silicon waveguides created on the SOI substrate, it is preferable to set the wavelength of the laser light to the 1.3 μm or 1.5 μm range. In that case, an inexpensive and high-quality semiconductor laser light source commonly used in optical fiber communication can be used as the laser light source 10.

[0065] (Signal processing in the signal processing unit) Refer to Figure 2 to explain the signal processing in the signal processing unit 1000. Figure 2 is a schematic diagram illustrating the flow of signal processing in the signal processing unit.

[0066] Various methods can be considered for the signal processing performed in the signal processing unit 1000, depending on the type of information to be acquired relating to the measurement object 900. Here, an example in which the optical sensing circuit 101 is applied to a laser Doppler vibrometer will be described.

[0067] A modulated electrical signal from the modulation power supply 20 has a repetition frequency f m and includes a sinusoidal modulation signal of

[0068] The received electrical signal sent from the photodetection unit 140 of the optical sensing circuit has a frequency component corresponding to the vibration of the measurement object 900. In the signal processing unit 1000, only this frequency component is extracted, and information relating to the vibration and the like of the measurement object 900 is extracted by analyzing the time waveform and spectrum waveform thereof.

[0069] The signal processing unit 1000 is configured to include a frequency discrimination unit 1100, an amplitude correction unit 1200, and a decoding unit 1300. A frequency discrimination step is performed in the frequency discrimination unit 1100, an amplitude correction step is performed in the amplitude correction unit 1200, and a decoding step is performed in the decoding unit 1300.

[0070] In the frequency discrimination step, among the received electrical signals from the photodetection unit 140, frequency f m neighborhood and frequency 2f m neighborhood signal components are extracted.

[0071] The frequency discrimination step includes a first extraction step, a second extraction step, a second harmonic generation step, a first down-conversion step, and a second down-conversion step.

[0072] When the modulated electrical signal applied to the optical phase modulator unit 150 has frequency f m and is sinusoidal, the time waveform of the received electrical signal after photoelectric conversion of the interference light input to the photodetection unit 140 is given by the following formula (1).

[0073]

Num

[0074] Here, S0 is the DC component of the interference light, and S1 is the amplitude of the modulation component of the interference light. The DC component S0 of the interference light and the amplitude S1 of the modulation component of the interference light are determined by the intensity of the signal light and local light, the sensitivity and frequency characteristics of the photodetector 140, and the insertion loss and propagation loss of each optical element. z is the phase modulation depth of the phase modulator. The phase modulation progress z is determined by the phase modulation characteristics of the optical phase modulator 150, the DC bias provided by the modulation power supply 20, and the amplitude of the modulated electrical signal. θ is the phase difference between the received electrical signal of the interference light and the modulated electrical signal from the modulation power supply 20, and φ(t) is the phase difference caused by the vibration of the object being measured 900.

[0075] Equation (1) above uses the Bessel function to express frequency Nf m It can be expanded using a triangular wave of (N is a natural number). Frequency f m Components around the first frequency component S 11 And the component S around the second frequency component. 12 Extracting and writing out the relevant parts, we obtain the following equations (2-a) and (2-b).

[0076]

number

[0077] Here, J n (z) is the nth-order Bessel coefficient. The actual received electrical signal is of a higher order (frequency 3f). m , 4f m This also includes signals around the frequency components of , ...).

[0078] The first extraction step involves extracting the frequency f from the received electrical signal. m Nearby frequency components are extracted by a first bandpass filter (BPF1) 1111 to obtain a first extracted signal. This first extracted signal is given by equation (2-a) above.

[0079] The second extraction step involves extracting the frequency 2f from the received electrical signal. mNearby frequency components are extracted by a second bandpass filter (BPF2) 1112 to obtain a second extracted signal. This second extracted signal is given by equation (2-b) above.

[0080] Modulated electrical signal V from modulated power supply 20 f (t), and its second harmonic V 2f Let (t) be given by the following equations (3-a) and (3-b), respectively.

[0081]

number

[0082] Here, the modulated electrical signal V f (t) is the repetition frequency f from the modulation power supply 20. m This is a sinusoidal modulated signal. Also, A and B are modulated electrical signals V f (t), and its second harmonic V 2f This is the amplitude of (t).

[0083] In the second harmonic generation step, the second harmonic generation unit 1120 generates the modulated electrical signal V f The second harmonic of (t) is generated to obtain the second harmonic signal given by equation (3-b) above.

[0084] In the first down-conversion step, the first mixer 1131 generates a first product signal by multiplying the first extracted signal and the modulated electrical signal, and then the first LPF (LPF1) 1141 removes the harmonic signals to obtain the first down-converted signal I.

[0085] In the second down-conversion step, the second mixer 1132 generates a second product signal by multiplying the second extracted signal and the second harmonic signal. Then, the second LPF (LPF2) 1142 removes the harmonic signal to obtain the second down-converted signal Q.

[0086] The output P1(t) of the first down-converted signal I and the output P2(t) of the second down-converted signal Q are given by the following equations (4-a) and (4-b), respectively.

[0087]

number

[0088] The transmission bandwidths of the first BPF1111, the second BPF1112, the first LPF1141, and the second LPF1142 can be appropriately selected to correspond to the frequency spectrum of the vibration of the object 900 being measured. For example, if the frequency bandwidth of the vibration of the object 900 being measured is at most Δf, then the transmission bandwidths of the first BPF1111, the second BPF1112, the first LPF1141, and the second LPF1142 can be set to approximately 2Δf.

[0089] For example, if we draw a Lissajous figure with P2(t) on the horizontal axis and P1(t) on the vertical axis, it will generally be an ellipse. If the major axis, minor axis, and inclination of the ellipse can be estimated from the measurement data using the least squares method, in other words, if AJ1(Z)cos(θ) in equation (4-a) and BJ2(Z)cos(2θ) in equation (4-b) can be estimated by appropriate ellipse fitting, then the phase difference φ(t) caused by the vibration of the desired object 900 can be decoded from equation (5) below.

[0090]

number

[0091] Any suitable conventionally known method can be used for elliptic fitting.

[0092] In the first vibration meter, an amplitude correction step is performed in the amplitude correction unit 1200 before the decoding step. In the amplitude correction step, the first amplitude correction unit (amplitude correction 1) 1211 and the second amplitude correction unit (amplitude correction 2) 1212 detect the amplitudes of the first down-converted signal I and the second down-converted signal Q, and perform amplitude correction so that they match, thereby obtaining the corrected electrical signals, the first corrected down-converted signal I' and the second corrected down-converted signal Q', respectively. This amplitude correction step also includes a step of correcting the phase difference (θ) between the first down-converted signal I and the second down-converted signal Q.

[0093] In the decoding step, the decoding unit 1300 decodes the phase difference φ(t) caused by the vibration of the object being measured 900 from the arc-loss tangent of the first corrected down-converted signal I' and the second corrected down-converted signal Q' obtained in the amplitude correction step, thereby obtaining a decoded signal.

[0094] From the phase change φ(t) decoded by the frequency discrimination step, amplitude correction step, and decoding step, the displacements d(t), v(t), and a(t) of the object being measured can be determined by the following equations (6-a) to (6-c).

[0095]

number

[0096] (Other configurations of the first embodiment) Instead of an MMI type waveguide, a polarizing beam splitter type waveguide can also be used for the first optical branching and multiplexing section 131 and the second optical branching and multiplexing section 132. If polarizing beam splitter type waveguides are used for the first optical branching and multiplexing section 131 and the second optical branching and multiplexing section 132, and the polarization direction perpendicular to the upper surface of the silicon waveguide substrate is defined as TM polarization, and the direction parallel to the upper surface of the substrate is defined as TE polarization, then the first optical branching and multiplexing section 131 can be designed such that, of the input light from the input port 111, the TM polarized component of the light is output from the first output port 131b, and the TE polarized component of the light is output from the second output port 131c.

[0097] Furthermore, the second optical branching and multiplexing unit 132 can be designed such that the TM polarization component of the light input to input port 132a is output from input / output port 132b, and the TE polarization component of the light input to input / output port 132b is output from output port 132c.

[0098] In this case, the polarization direction of the laser light input to the first input / output terminal 111 of the optical sensing circuit 101 is tilted from the TE polarization. Preferably, the polarization direction is tilted by 45° from the TE polarization.

[0099] Furthermore, in this case, a Faraday rotator or λ / 4 waveplate, which rotates the polarization plane by 45° each time light passes through, can be inserted in the optical path connecting the second input / output terminal 112 and the object to be measured 900, along with optical components such as lenses. With this configuration, when the laser light irradiated onto the object to be measured 900 as TM polarization is reflected by the object to be measured 900 and returns to the optical sensing circuit 101 as signal light, the polarization rotates by 90° and returns as TE polarization. As a result, the light passes through the second optical branching and multiplexing section 132 without principle loss, and the local light and the signal light interfere with the same polarization in the third optical branching and multiplexing section 133, enabling vibration detection with higher sensitivity.

[0100] Furthermore, the signal processing in the signal processing unit 1000 is not limited to using electrical circuits such as BP, LPF, and integrators. Effective results can also be obtained by performing some or all of the steps in software.

[0101] This first embodiment of the optical sensing circuit allows for miniaturization and cost reduction through mass production by utilizing integration technologies, including silicon photonics technology. Furthermore, by using an ultra-compact optical sensing circuit utilizing this integration technology, the laser Doppler vibrometer can be made smaller. In addition, since an AO modulator is not required, the configuration is simple.

[0102] (Second Embodiment) Referring to Figure 3, an example configuration of an optical sensing circuit and a laser Doppler vibrometer according to a second embodiment of the present invention will be described. Figure 3 is a schematic diagram illustrating a laser Doppler vibrometer (also referred to as a second vibrometer) according to a second embodiment of the present invention.

[0103] The second vibration meter differs from the first embodiment in that the circuit support board including the optical sensing circuit 102, the laser light source 10, the modulation power supply 20, and the signal processing unit 1000 are all mounted on the support board 100, and the circuit support board is provided with a seventh optical waveguide section 127. The seventh optical waveguide section 127 connects the first input / output terminal 111 of the optical sensing circuit 102 to the laser light source 10.

[0104] The rest of the configuration is the same as in the first embodiment, so redundant explanations will be omitted.

[0105] Furthermore, the operation of the optical sensing circuit and the laser Doppler vibrometer is the same as in the first embodiment, so redundant explanations will be omitted.

[0106] In this second embodiment, a seventh optical waveguide section 127 is provided on the circuit support substrate. One end of the seventh optical waveguide section 127 is connected to the first input / output terminal 111, and the other end is connected to the laser light source 10. The laser light is input to the first input / output terminal 111 of the optical sensing circuit 102 via the seventh optical waveguide section 127.

[0107] Here, the other end of the seventh optical waveguide section 127, which is the end that receives the laser light, may be provided with a configuration for efficiently receiving the light. For example, a spot size converter may be provided so that the mode field diameter of the silicon waveguide at the end connected to the laser light source 10 matches the mode field diameter of the laser light source as closely as possible.

[0108] According to the second embodiment of this invention, a circuit support board including an optical sensing circuit 102 is also mounted on the support board 100 on which the laser light source 10, the modulation power supply 20, and the signal processing unit 1000 are mounted. This makes the configuration even smaller than that of the first embodiment.

[0109] Furthermore, since the modulation power supply 20 and the signal processing unit 1000 are also mounted on the support substrate 100, electrical wiring from them to the optical phase modulator unit 150 and the optical detection unit 140 is also facilitated. This contributes to miniaturization and cost reduction.

[0110] If an SOI substrate or the like is used as the support substrate 100, the mounting of the modulation power supply 20 and the signal processing unit 1000 becomes easier. Even if a substrate other than an SOI substrate is used as the support substrate 100, benefits such as miniaturization and cost reduction can still be obtained.

[0111] In this document, the configuration and operation of the present invention were described using a silicon waveguide fabricated on an SOI substrate as an example. However, the effects of the present invention are not limited to this, and can also be realized in cases such as an InGa(As)P waveguide fabricated on an indium phosphide (InP) substrate. In this case as well, the laser light source 10 can be integrated on the same substrate as the optical sensing circuit, enabling further miniaturization. [Explanation of symbols]

[0112] 10 Laser light source 20 Modulated Power Supply 100 Support substrate 101, 102 Optical sensing circuits 111, 112 Input / Output Terminals 121, 122, 123, 124, 125, 126, 127 Optical waveguide section 131, 132, 133 Optical branching and multiplexing section 140 Light detection unit 150 Optical Phase Modulator Section 900 Objects to be measured 1000 Signal Processing Unit 1111, 1112 BPF 1120 2nd harmonic section 1131, 1132 Mixer 1141, 1142 LPF 1100 Frequency discrimination unit 1200 Amplitude Correction Unit 1300 Decoding Unit

Claims

1. The circuit comprises a first input / output terminal, a second input / output terminal, a first optical branching and multiplexing section, a second optical branching and multiplexing section, a third optical branching and multiplexing section, a first optical waveguide section, a second optical waveguide section, a third optical waveguide section, a fourth optical waveguide section, a fifth optical waveguide section, a sixth optical waveguide section, an optical detection section, and an optical phase modulator section, all formed on a single circuit support substrate. The first branching and multiplexing unit has an input port, a first output port, and a second output port, and splits the light input to the input port into two and outputs them from the first output port and the second output port. The second branching and multiplexing unit has an input port, an input / output port, and an output port, and outputs light input to the input port from the input / output port, and outputs light input to the input / output port from the output port, The third branching and multiplexing unit has a first input port, a second input port, and an output port, and combines the light input to the first input port and the light input to the second input port and outputs it from the output port. The first optical waveguide section is connected to the first input / output terminal and the input port of the first optical branching / combining section. The second optical waveguide section is connected to the first output port of the first optical branching and multiplexing section and to the input port of the second optical branching and multiplexing section. The third optical waveguide section is connected to the input / output port of the second optical branching and multiplexing section and to the second input / output terminal. The fourth optical waveguide section is connected to the second output port of the first optical branching and multiplexing section and the first input port of the third optical branching and multiplexing section. The fifth optical waveguide section is connected to the output port of the second optical branching and multiplexing section and the second input port of the third optical branching and multiplexing section. The sixth optical waveguide section is connected to the output port of the third optical branching and multiplexing section and the optical detection section. The optical phase modulator section is formed in the fourth optical waveguide section and phase modulates the light propagating through the fourth optical waveguide section. The light detection unit converts the light input from the third optical branching and multiplexing unit through the sixth optical waveguide unit into photoelectric energy. Optical sensing circuit.

2. The first input / output terminal, the second input / output terminal, the first optical branching and multiplexing section, the second optical branching and multiplexing section, the third optical branching and multiplexing section, the first optical waveguide section, the second optical waveguide section, the third optical waveguide section, the fourth optical waveguide section, the fifth optical waveguide section, the sixth optical waveguide section, and the optical phase modulator section are all composed of silicon waveguides. The optical sensing circuit according to claim 1.

3. The first optical branching and multiplexing section and the second optical branching and multiplexing section are polarized beam splitter type waveguides. The optical sensing circuit according to claim 1.

4. Laser light is input to the first input / output terminal, The laser light input to the first input / output terminal is sent to the first optical waveguide section and then to the first optical branching / combining section. In the first optical splitting and combining section, the laser light is split into two, and one of these two branches is output as the irradiation light from the second input / output terminal after passing through the second optical waveguide section, the second optical splitting and combining section, and the third optical waveguide section. The signal light input from the second input / output terminal is sent to the third optical branching and combining section via the third optical waveguide section, the second optical branching and combining section, and the fifth optical waveguide section. The other of the two laser beams obtained by splitting the laser beam in the first optical splitting and combining section is used as a reference beam, and after being phase-modulated in the optical phase modulator section, it is sent to the third optical splitting and combining section via the fourth optical waveguide section. The optical branching and combining unit combines the signal light and the local light to generate interference light, and sends the interference light to the photodetector unit via the sixth optical waveguide unit. The optical sensing circuit according to any one of claims 1 to 3.

5. The optical sensing circuit, laser light source, modulation power supply, and signal processing unit described in claim 1 are provided, The laser light source generates laser light and inputs the laser light to the first input / output terminal of the optical sensing circuit. The laser light input to the first input / output terminal is sent to the first optical waveguide section and then to the first optical branching / combining section. In the first optical branching and multiplexing unit, the laser light is split into two, and one of these branches is output as irradiation light from the second input / output terminal after passing through the second optical waveguide unit, the second optical branching and multiplexing unit, and the third optical waveguide unit, and irradiating the object to be measured. The signal light generated by the reflection of the irradiated light from the object to be measured is input from the second input / output terminal and sent to the third optical waveguide section, the second optical branching and combining section, and the fifth optical waveguide section, and then to the third optical branching and combining section. The other half of the laser light, which is split into two in the first optical splitting and combining section, is phase-modulated in the optical phase modulator section based on the modulated electrical signal generated by the modulation power supply, and then sent to the third optical splitting and combining section via the fourth optical waveguide section. The optical branching and combining unit combines the signal light and the local light to generate interference light, and sends the interference light to the optical detection unit via the sixth optical waveguide unit. The received electrical signal generated by the photoelectric conversion of the interference light in the light detection unit is sent to the signal processing unit. The signal processing unit extracts information about the vibration of the object being measured from the received electrical signal. Laser Doppler vibrometer.

6. The modulating power supply has a repetition frequency f ｍ A modulated electrical signal is generated that includes a sine wave modulated signal. The optical phase modulator section receives the modulated electrical signal and phase-modulates the local light. The signal processing unit controls the frequency f of the received electrical signal. ｍ Nearby signal components and frequency 2f ｍ A frequency discrimination unit that extracts nearby signal components, frequency f ｍ The amplitude and frequency 2f of the nearby signal components. ｍ An amplitude correction unit that corrects the amplitudes of neighboring signal components to match, Corrected frequency f ｍ Nearby signal components and frequency 2f ｍ A decoding unit that decodes the vibration waveform of the object being measured from the arc-loss tangent of nearby signal components. The laser Doppler vibrometer according to claim 5, comprising:

7. The optical sensing circuit, the laser light source, the modulation power supply, and the signal processing unit are mounted on a single support substrate. The laser light source and the first input / output terminal of the optical sensing circuit are connected by a seventh optical waveguide section formed in the optical sensing circuit. The laser Doppler vibrometer according to claim 5 or 6.

8. The first input / output terminal, the second input / output terminal, the first optical branching and multiplexing section, the second optical branching and multiplexing section, the third optical branching and multiplexing section, the first optical waveguide section, the second optical waveguide section, the third optical waveguide section, the fourth optical waveguide section, the fifth optical waveguide section, the sixth optical waveguide section, and the optical phase modulator section are all composed of silicon waveguides. The laser Doppler vibrometer according to claim 5 or 6.

9. The first input / output terminal, the second input / output terminal, the first optical branching and multiplexing section, the second optical branching and multiplexing section, the third optical branching and multiplexing section, the first optical waveguide section, the second optical waveguide section, the third optical waveguide section, the fourth optical waveguide section, the fifth optical waveguide section, the sixth optical waveguide section, the seventh optical waveguide section, and the optical phase modulator section are all composed of silicon waveguides. The laser Doppler vibrometer according to claim 7.

10. The first optical branching and multiplexing section and the second optical branching and multiplexing section are polarized beam splitter type waveguides. A Faraday rotator or a λ / 4 is inserted in the optical path connecting the second input / output terminal and the object to be measured, causing the polarization plane to rotate by 45° each time light passes through. A laser Doppler vibrometer as described in claim 5 or 6.

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