JPH08201164A - Light signal measuring apparatus - Google Patents

Abstract

PURPOSE: To provide a light signal measuring apparatus which can deeply set a gain modulation by providing output characteristics having large allowance for an incident light and excellent linearity for an incident light intensity. CONSTITUTION: A light emitting unit 500 inputs an electric signal having the component of a frequency = f output by a signal generator 210, and generates an intensity modulation light of a modulation frequency = f. Simultaneously, an electric signal having a frequency = f+Δf generated from a signal generator 220 is supplied to the signal supply terminal of the photoconductive photodetector of a photoreceiver 100 as a modulation electric signal. The intensity modulation light output from the unit 500 is propagated at a predetermined optical propagation medium, received by the photodetector, modulated, only the component of the frequency = Δf is selected sequentially via a current-voltage converter 300 and a frequency selector 400 and output. This signal and a mixed signal of the output signals of the signal generators 210, 220 by a signal mixer 600 are input to a phase detector 700, and the phase or the intensity of the intensity modulation light received by the photoreceiver is analyzed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention receives an intensity-modulated light having a component of a specific intensity-modulated frequency that has been output after propagating in a predetermined optical propagation medium, and receives the intensity-modulated light of the specific intensity-modulated light. The present invention relates to an optical signal measuring device that analyzes a frequency component.

[0002]

2. Description of the Related Art Light is widely used for high-speed phenomenon measurement, high-accuracy measurement, and the like. This is because light is an electromagnetic wave having a very short wavelength and, in principle, a large amount of information on a measurement phenomenon can be carried in a short time. Further, the development of laser technology has made it possible to obtain light with high coherence and high intensity, which is also a driving force for expanding practical use of light. On the other hand, most measuring devices use electrical methods.

In recent years, as the measurement phenomenon has become faster and more accurate, there has been a demand for measurement of the intensity modulation frequency of the light to be measured exceeding the response characteristic of the electric circuit in the subsequent stage. In such a case, it is necessary to reduce the intensity modulation frequency of the input light.

FIG. 11 is a block diagram of a conventional typical optical signal measuring apparatus for performing optical measurement with such frequency reduction. As shown in FIG. 11, the device includes a light emitting unit 910.
The light including the intensity-modulated component of frequency = f output from
The light is received by a photo detector (PD) 920 after passing through a predetermined path. As a result of the light reception, the electric signal generated by the light receiver 920 is
Frequency = f + Δf at signal mixer (mixer: MX) 940
Is mixed with the electric signal of and converted into an electric signal according to the product value of both signals. This converted signal has two frequencies =
It includes a (2f + Δf, Δf) component. The bandpass filter 950 selects and outputs one frequency = Δf component. The signal thus generated is applied to the lock-in amplifier 96.
The phase and the amplitude are analyzed on the basis of a reference signal of frequency = Δf which is input to 0 and is input at the same time. This analysis result reflects the phase and intensity of the optical signal received by the light receiver 920.

Further, a light-receiving device which receives intensity-modulated light by an avalanche photodiode (hereinafter referred to as APD) biased with a signal on which an AC component is superposed, and which performs photoelectric conversion and frequency reduction at the same time is specially proposed. Kaisho 62-279
732 is proposed. FIG. 12 is a circuit configuration diagram of this device. In this device, the intensity-modulated light modulated at the modulation frequency = f is superimposed on the DC signal at the frequency = f + Δ.
The light is received by the APD 970 biased by the signal of f. As a result of the light reception, a current is generated in the APD 970, and a voltage signal including two frequency = (2f + Δf, Δf) components is generated at the position P. The bandpass filter 980 selects and outputs one frequency = Δf component. Instead of the avalanche photodiode, a photomultiplier tube (PMT) can be used as a photodetector whose photoelectric conversion efficiency can be adjusted.

[0006]

Since the conventional optical signal measuring device is constructed as described above, it has the following problems.

In the conventional optical signal measuring device shown in FIG. 11, the saturation of the light receiving element used in the light receiver 920 is saturated in the environment where the background light (DC light or light containing an intensity modulation component unrelated to the measurement) is large. Due to the intermodulation characteristics of the device and circuit elements of the device, sufficient performance cannot be exhibited. In addition, since the light receiver 920 converts the electric signal and then performs the mixing, when the detected optical signal is weak, a signal mixer that exhibits good conversion characteristics and a high frequency response at the weak signal level is required. Become. Moreover, the detection accuracy of the difference frequency may be limited by noise, drift, or offset generated by each circuit element.

A conventional optical frequency mixing device as shown in FIG. 12 which obtains a heterodyne signal directly from a photodetector by superimposing a high frequency voltage on the DC bias voltage of the APD 970 is high without using an electric mixer with large loss. The required heterodyne signal can be easily extracted with conversion efficiency. However, the APD generally has an exponential voltage-current characteristic as shown in FIG. Therefore, applying a high-frequency voltage having a large amplitude value for performing deep modulation is not effective for distortion of the extracted heterodyne signal. Further, in order to secure the avalanche multiplication gain, it is required to apply the bias voltage close to the breakdown voltage value.Therefore, in order to control the breakdown voltage value which has a temperature sensitive characteristic, the bias voltage is controlled. A voltage temperature compensation circuit is essential. Further, in order to increase the photoelectric conversion gain, the bias voltage value (V ₁ )
Is set to a high level and the APD has a large multiplication gain, the operating point fluctuates due to direct current background light or light including an intensity modulation component not related to measurement, and the average current (I ₀ ) The increase makes the APD itself more likely to be saturated.

Further, the APD and the PMT have a drawback that the change of the gain with respect to the applied voltage is non-linear and it is difficult to design an optimum operating condition.

The present invention has been made in view of the above, and has a large tolerance to unnecessary incident light such as background light and measures a predetermined intensity modulation frequency component with good linearity with respect to the incident light intensity. An object is to provide an optical signal measuring device.

[0011]

An optical signal measuring device according to the present invention comprises: (a) a first signal generator for generating a first electric signal having a first frequency component; and (b) a first signal generator. And a light emitting section that generates intensity-modulated light having an intensity-modulated component of a first frequency and (c) a third-frequency component that differs from the first frequency by the second frequency. A second signal generator for generating a second electrical signal;
(D) A voltage signal supply unit that receives the second electric signal, converts the second electric signal into a voltage signal that reflects the time change of the second electric signal, and outputs the voltage signal. (E) A voltage signal output from the voltage signal supply unit Which has a voltage signal application terminal for inputting, and which flows through a photoconductive type photoreceiver that receives the intensity-modulated light output from the light emitting unit and propagated through a predetermined optical propagation medium, and (f) a photoconductive type photoreceiver. A frequency selector for inputting a third electric signal according to the current signal and selecting and outputting a fourth electric signal which is a component having a frequency substantially the same as the second frequency; and (g) the first signal And a second electric signal, the signal mixer having a second frequency and generating a fifth electric signal having information on at least one of a phase and an amplitude of the first signal, and (h) The fourth electrical signal and the fifth electrical signal are input, and the photoconductive type receiver is input. A phase detector for analyzing the intensity and at least one of the phase components of the first frequency of the incident intensity-modulated light to vessel, characterized in that it comprises a.

Here, it may be characterized in that a phase adjuster for changing the phase of the second electric signal is further provided.

Further, the voltage signal applied to the photoconductive type photodetector is periodic, the time average value is approximately 0V, and the time point at the midpoint of adjacent time points when the amplitude is 0V is taken as the origin. The amplitude may be a substantially even function of time.

Further, it may be characterized by further comprising bias adjusting means for adjusting the operating point of the photoconductive type photodetector.

Further, in the photoconductive type photodetector, when the intensity of light to be measured is constant and the applied voltage value is an independent variable, the current flowing through the photoconductive type photodetector in a predetermined domain including the applied voltage value of 0V. The quantity is an almost odd function of the applied voltage, and
When the applied voltage is constant and the measured light intensity value is used as an independent variable, the amount of current flowing through the photoconductive photodetector is a substantially linear function of the irradiation signal intensity when the measured light intensity is in a predetermined domain. May be Here, as the photoconductive type photodetector, a metal-semiconductor-metal photodetector having a structure in which rectifying junctions are connected in opposite directions can be preferably used.

[0016]

In the optical signal measuring device of the present invention, first, the first signal generator generates the first electric signal having the component of the first frequency (= f). The light emitting section receives the first electric signal and generates intensity-modulated light having an intensity-modulated component of frequency = f in synchronization with the first electric signal.

At the same time, a second electric signal generated by the second signal generator and having a third frequency = f + Δf or f−Δf, which differs from the second frequency = f by the second frequency = Δf, is transmitted via the signal supply unit. And is supplied as a modulated electric signal to the signal supply terminal of the photoconductive type photodetector. As a mode of such a modulated electric signal, a voltage signal output in a low output impedance state is preferably used. Hereinafter, for simplification of description, description will be given with the third frequency = f + Δf as a representative. Note that the same operation is performed even when the third frequency = f−Δf.

The intensity-modulated light output from the light emitting section propagates through a predetermined light propagation medium (optical fiber, space, etc.) and then enters a photoconductive type light receiver. On the other hand, the photoconductive photodetector is supplied with the modulated electric signal as described above, and when the optical signal is input to the light receiving section in this state, the modulated electric signal is further modulated. As a result, the modulated current signal flowing through the photoconductive type photodetector has a value of the sum and difference between the intensity modulation frequency of the intensity modulated light and the frequency of the modulated electric signal = (2f + Δf, Δf)
Including a component having. The third electric signal corresponding to the modulated current signal is input to the frequency selective transmission device, only the component of frequency = Δf is selected and output as the fourth electric signal. The fourth electric signal reflects the amplitude and phase of the intensity-modulated light at the time of receiving the light at the light-receiving portion.

That is, in the optical signal measuring device of the present invention,
Substantially reducing the intensity modulation frequency of the received intensity-modulated light is performed by a photoconductive type photodetector, and after being converted into a signal in a frequency region that is electrically easy to handle, electrical amplification and detection are performed.

On the other hand, the first electric signal and the second electric signal are frequency-mixed by a signal mixer to generate a fifth electric signal of frequency = Δf. The fifth electric signal reflects the amplitude and phase of the intensity-modulated light at the time of light emission from the light emitting section.

The fourth electric signal and the fifth electric signal are input to a phase detector such as a lock-in amplifier, and a component of frequency = f of the intensity-modulated light incident on the photoconductive type photodetector by the phase detector At least one of intensity and phase is analyzed.

Further, in the case where the light intensity to be measured is constant and the applied voltage value is an independent variable, such as a metal-semiconductor-metal photodetector having a structure in which the photoconductive type light receivers are connected with the rectifying junctions in opposite directions. , When the applied voltage value is within a predetermined defined range including 0V, the amount of current flowing through the photoconductive type photodetector is a substantially odd function of the applied voltage, the applied voltage is constant, and the measured light intensity value is an independent variable. , If the measured light intensity has a property that the amount of current flowing through the photoconductive type photodetector is a substantially linear function of the irradiation signal intensity in a predetermined defined range, the electricity supplied to the photoconductive type photodetector is An electric signal in which the non-DC component of the signal is periodic, the time average value is substantially 0, and the amplitude is a substantially even function of time with the time at the midpoint of adjacent times when the amplitude becomes 0 as the origin. Select the applied electricity By adjusting the bias of the issue value, together with the removal of the DC component of the background light, measurements are performed by reducing it with respect to the AC background light other than the frequency of the modulation voltage signal.

In the above description, the operation has been described in which the photoconductive photodetector is driven with a low impedance to extract a signal as a current. However, the voltage between both terminals of the photoconductive photoreceiver is driven as a signal by current driving. It may be taken out, or a resistor may be connected in series to the photoconductive type photodetector and the voltage across the resistor may be taken out as a signal.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a basic block diagram of the optical frequency mixing device of the present invention. As shown in FIG. 1, the device is (a)
A signal generator 210 for generating an electric signal of frequency = f,
(B) Frequency output from the signal generator 210 = f (= 5G
(Hz) electric signal is input to generate intensity-modulated light having an intensity-modulated component of frequency = f;
(C) Modulation frequency = f + Δf (= in the light receiving unit 100 including the photoconductive type light receiver that receives the intensity-modulated light passing through a predetermined light propagation medium, and (d) in the photoconductive type light receiver of the light receiving unit 100.
A signal generator 220 for supplying a signal having a frequency of 5 GHz + 1 kHz, and (e) a conversion amplification unit 30 for outputting a voltage signal corresponding to a current signal generated in the light receiving unit 100 as a result of light reception.
0 and (f) a frequency selector 4 for selecting a component of frequency = Δf included in the voltage signal output from the conversion / amplification unit 300.
00 and (g) the electric signal of frequency = f output from the signal generator 210 and the electric signal of frequency = f + Δf output from the signal generator 220 are input, and frequency mixing is performed to obtain a signal of frequency = Δf. A signal mixer 600 for outputting
(H) Output signal of frequency selector 400 and signal mixer 60
The output signal of 0 is input, the output signal of the frequency selector 400 is analyzed using the output signal of the signal mixer 600 as a reference signal, and the information about the intensity or phase of the intensity modulated light received by the light receiving unit 100 is obtained. Phase detector 70 for obtaining and outputting
With 0 and. Here, as the phase detector, the light receiving unit 1
A lock-in amplifier that can obtain information on the intensity and phase of the intensity-modulated light received at 00 can be preferably used.

The signal output from the signal generator 220 may be supplied to the light receiving section 100 via a phase adjuster that changes the phase of the input signal.

Further, in FIG. 1, as the light emitting section 500,
A laser diode (LD) 510 that generates light having an intensity corresponding to a flowing current value, a variable DC power supply VE that supplies a current of a DC component to the LD 510 via a coil L11,
A capacitor C1 that superimposes the AC component of the electric signal input from the signal generator 210 on the DC drive component of the LD 510.
1 illustrates an example of the configuration including 1 and 1.

The light emitting section is not limited to the one for controlling the current of the LD, and the light generated by a lamp, a gas laser, a dye laser, a solid state laser or the like is intensity-modulated using an optical modulator. It is possible. In this case, an EO modulator, an AO modulator, or a mechanical chopper can be preferably used as the optical modulator. A mode-locked laser that oscillates in synchronization with an external signal may be used, or a laser that oscillates at a frequency determined by the configuration of the laser itself may be used to oscillate the frequency of the signal generated by the signal generator 210. May be adjusted to the frequency.

In the optical signal measuring device of the present invention, the light receiving section 10
The intensity-modulated frequency of the intensity-modulated light received at 0 = f and the frequency of the AC signal generated by the signal generator 220 = f + Δf are mixed, that is, the frequency mixture is calculated by multiplying both signals. Run in a container. Then, using the frequency selector 400, the frequency selector 400 selects and extracts the component of frequency = Δf from the component of frequency = 2f + Δf of the sum of frequencies of both signals obtained as a result of the product calculation and the component of frequency = Δf of difference. Thus, the frequency selector 400
The signal output from reflects the intensity and phase of the component of the intensity-modulated frequency = f of the intensity-modulated light at the time of receiving light at the light receiving unit 100.

On the other hand, the electric signal of frequency = f output from the signal generator 210 and the electric signal of frequency = f + Δf output from the signal generator 220 are mixed by the signal mixer 600, and the electric signal of frequency = Δf is mixed. Is generated. The electric signal of frequency = Δf generated in this way is emitted from the light emitting unit 500.
It reflects the intensity and phase of the component of the intensity modulation frequency of the intensity modulated light at the time of being output from.

The signal output from the frequency selector 400 and the signal output from the signal mixer 600 are detected by the phase detector 7
Enter 00. The phase detector 700 analyzes the signal strength output from the frequency selector 400 and the signal strength output from the signal mixer 600, and outputs the signal output from the frequency selector 400 and the signal mixer 600. The phase difference from the processed signal is analyzed and the analysis result is output.

Specific embodiments of the light receiving portion and the signal converting portion of the optical signal measuring device of the present invention will be described below.

FIG. 2 is a block diagram of an embodiment of the light receiving part and the signal converting part of the optical signal measuring device whose basic structure is shown in FIG. As shown in FIG. 2, this apparatus includes (a) a light receiving section 110 including a photoconductive type light receiver for receiving the light to be measured,
(B) Modulation frequency = f in the photoconductive type light receiver of the light receiving unit 110.
A signal generator 220 for providing a signal having + Δf,
(C) As a result of light reception, a current-voltage conversion unit 310 that converts the current signal generated in the light-receiving unit 110 into a voltage signal, and (d) passes a predetermined frequency component included in the voltage signal output from the current-voltage conversion unit 310. Bandpass filter (hereinafter,
(Also referred to as BPF) 400.

Here, the light receiving section 110 includes the signal generator 2
20 has a voltage applying unit 111 for receiving the electric signal output from the circuit 20 and outputting a voltage signal in a low impedance state, and a voltage applying terminal for inputting the voltage signal (V _I ) output by the voltage applying unit 111. The photoconductive type photodetector 112 that receives the measurement light and the photoconductive type photodetector 112 that has an output current value of zero when the direct current such as background light is incident.
Bias adjusting unit 113 for setting the operation of the above, and passive elements (L1, L2, C3) for inductively connecting these elements
And Then, the current generated in the photoconductive type photodetector 112 flows through the choke coils L1 and L2.

FIG. 3 is a circuit configuration diagram of a voltage applying section which can be adopted in this embodiment. In the circuit of FIG. 3A, the capacitors C1 and C2 are inserted in the signal line to convert the voltage signal output from the signal generator 220 into an AC voltage signal in a floating state. FIG.
The circuit of (b) is obtained by inverting the signal polarity of the circuit of FIG. 3 (a). The circuit of FIG. 3C is for inputting the voltage signal output from the signal generator 220 by the transformer T1 and making it an AC voltage signal in a floating state. In the device of this example, the circuit of FIG. 3 (a) was used.

The photoconductive type photodetector 112 is made of GaAs.
It is composed of a metal-semiconductor-metal (MSM) photodetector using as a material. In this photoconductive type photodetector 112, when the irradiation light amount is constant and the applied voltage value is an independent variable, the amount of current flowing through the photoconductive type photodetector is the applied voltage value in a predetermined defined range including the applied voltage value of 0V. It has the property of being an odd function.

General solid-state photodetector (photodiode:
PDs and avalanche photodiodes (APDs) have their operating frequency bands limited by the depletion layer capacitance and the spread of the transit time of carriers traveling in the depletion layer.
Further, in an electron tube such as a PMT, the operating frequency band is limited by the spread of the transit time of electrons in the tube. At present, no operating frequency band exceeding 10 GHz has been obtained. On the other hand, in the case of MSM, the capacitance between the electrodes is dominant, and in general, this capacitance can be set to a value sufficiently smaller than the depletion layer capacitance. Although the inter-electrode capacitance also depends on the terminal spacing between the electrodes, it is possible to easily operate in a wide band as high as 100 GHz by creating it with an optimal terminal spacing. The electrodes are generally comb-shaped.

The bias adjuster 113 comprises a variable resistor VR1 for adjusting the bias voltage value and series connected DC power sources E1 and E2 connected to the terminals of the variable resistor VR1. The DC power source E1 and the DC power source E1 are connected to each other. The connection point with E2 is set to the ground potential.

The current-voltage converter 310 is composed of an operational amplifier 320 having a positive input terminal grounded and a negative input terminal connected to the output terminal via a resistor R1.

FIG. 4 is a circuit configuration diagram of a bandpass filter that can be adopted. FIG. 4A is a circuit configuration example of a passive bandpass filter, and FIG. 4B and FIG.
(C) is a circuit configuration example of an active bandpass filter. In this embodiment, the passive bandpass filter shown in FIG. 4A is adopted. The characteristic value of each element is determined by the target frequency value. If the phase detector 600 can input a current, the signal converter 300
It is also possible to omit the bandpass filter 400 and the bandpass filter 400 and directly input the signal to the phase detector 700 via the coil L2. It is also possible to use a digital filter.

The apparatus of this embodiment executes frequency reduction as follows. It is assumed that the incident light has a constant intensity.

The signal generator 220 generates an AC signal having a component of frequency = f + Δf and supplies it to the light receiving section 110. In the light receiving unit 110, the AC voltage supplied from the signal generator 220 is applied to the voltage application terminal of the photoconductive type photoreceiver 112 via the voltage application unit 111 as a modulation voltage signal. The applied voltage signal to the photoconductive type photodetector 112 is periodic, the time average value is approximately 0 V, and the amplitude is an even number of times with the midpoint of adjacent times when the amplitude is 0 V as the origin. voltage signal which is a function is selected, and in the state of incidence of only background light by adjustment of the bias circuit, the value of the current flowing through the photoconductive light-receiving device 112 (I _B) is set to "0A". FIG. 5 is an explanatory diagram of the modulation characteristic of the photoconductive type photodetector 112 set in this state. As shown in Fig. 5, "0 V" is set to the center voltage value (V _B ) of the bias of the modulation voltage signal in the modulation by the applied voltage, which results in the modulation even if the modulation voltage signal having a large amplitude is used. Output linearity is guaranteed.

In this state, the intensity-modulated light (frequency = f) is input to the light receiving area of the photoconductive type photodetector 112. On the other hand, since the modulation voltage signal is applied to the photoconductive type photodetector 112 as described above, the photodetection signal is modulated by the modulation voltage signal. As a result, the modulated current signal flowing through the photoconductive photodetector 112 contains components having a frequency of the sum (2f + Δf) and the difference (Δf) of the frequency of the beat signal and the frequency of the modulated voltage signal. This modulated current signal is input to the current-voltage converter 310 via the choke coil L2, converted into a voltage signal, and output. Of the two frequency = (2f + Δf, Δf) components output from the current / voltage converter 310, only the difference frequency = Δf component passes through the bandpass filter 400.

In general, the operating frequency band of the lock-in amplifier, which is a typical example of the phase detector, is about 100 kHz. Therefore, in the present embodiment with the frequency Δf = 1 kHz, the lock-in amplifier which is easily available is used as the phase detector 700. Can be adopted as, and accurate measurement is possible. The phase detector is not limited to the lock-in amplifier, but may be any device capable of detecting the amplitude and phase of the AC signal.

In the above embodiment, the frequency f = 5GH
Although z and frequency Δf = 1 kHz, the frequency f may be selected within the operating frequency band of the adopted photoconductive photodetector, and the frequency Δf may be selected within the operating frequency band of the adopted phase detector. .

The apparatus of this embodiment can be modified. FIG. 6 is a configuration diagram of a first modified example of the apparatus of this embodiment. This device differs from the device of the above-described embodiment only in the configuration of the current-voltage converter. As shown in FIG. 6, the current-voltage converter 320 of this device has a resistor R2 that converts a current value into a voltage value by causing a current generated by the photoconductive type photodetector 112 to flow.
And a capacitor C4 for removing the DC component of the voltage signal generated across the resistor R2, and an amplifier circuit 321 for amplifying the AC signal transmitted through the capacitor C4. The current-voltage conversion unit 320 is functionally the same as the current-voltage conversion unit 310 of the embodiment, but is excellent in performance because it can reduce 1 / f noise generated in the amplifier circuit.

FIG. 7 is a block diagram of a second modification of the apparatus of this embodiment. This device is different from the device of the first modified example in the bias adjustment position. As shown in FIG. 7, the bias adjustment point of this device is the position of a terminal different from the connection terminal of the capacitor C4 of the resistor R2. With this device configuration, the same function as that of the device of the embodiment can be realized.

FIG. 8 is a block diagram of a system for measuring internal information of a scattering medium, which is a first application example of the optical signal measuring device of the present invention. As shown in FIG. 8, in this system, instead of the light emitting unit 500 of the optical signal measuring device of the above embodiment,
A plurality of wavelengths (λ ₁ , with the same intensity modulation frequency = f,
, Λ _n ; n is an integer of 2 or more) is used as a light flux, and a light emitting unit 550 is used.
The intensity-modulated light output by 50 is guided to scatter absorber 901.
An optical fiber 860 that emits intensity-modulated light toward
(B) an optical fiber 870 which receives the light propagating through the scattering medium 901 and guides it toward the optical signal measuring device;
(C) According to the instruction from the processing unit 760, the wavelength is λ ₁ , ...,
A wavelength filter 880 that selectively selects and transmits any one of the light of λ _n , and (d) collects the light output from the wavelength filter 880 in the light receiving area of the photoconductive receiver 112 of the light receiver 110. And the signal output from the phase detector 700 (e) is input to the phase detector 700.
And a processing unit 750 that obtains the scattering coefficient μ _s and the absorption coefficient μ _a inside the scattering medium 901 based on the analysis result in (1).

Here, the light emitting section 550 outputs light from a light emitting device 510 _i that emits light of wavelength λ _i (i = 1, ..., N) with an intensity according to the flowing current value, and the light emitting device 510 _i outputs the light. A condenser lens 810 _i for condensing light and a multiplexer 520 _j (j = 1, which inputs and combines two optical signals and outputs them.
, N-1), and a variable DC power supply VE for supplying a current of a DC component to the light emitter 510 _i via the coil L11,
A capacitor C that superimposes the AC component of the electric signal input from the signal generator 210 on the DC drive component of the light emitter 510 _i.
And 11.

Further, the processing section 750 performs phase detection when the light intensity modulation frequency = f and the wavelength (= λ _i ) of the light selectively output by the wavelength filter 880 are used in the theoretical formula obtained by the light diffusion theory. According to the instructions of the arithmetic processing unit 751 and the arithmetic processing unit 751 by substituting the value of the phase change analyzed by the processing unit 700 and obtaining the scattering coefficient μ _s and the absorption coefficient μ _a ,
The scattering coefficient μ _s and the absorption coefficient μ _a obtained by the arithmetic processor 751.
And a display 752 for displaying such as.

In the system of FIG. 8, the following is performed.
The internal information of the scattering medium is measured. The processing unit 750 instructs the wavelength filter 880 to transmit the light of wavelength = λ ₁ .
Further, the signal generator 220 generates a signal of frequency = f + Δf, and the output signal of frequency = f + Δf is converted into a low impedance voltage signal by the voltage applying unit 111, and the voltage applying terminal of the photoconductive type photodetector 112. Is supplied to.

On the other hand, the light emitting section 550 outputs the intensity modulated light having the intensity modulation frequency = f including the component of wavelength = λ _i . The intensity-modulated light output from the light emitting unit 500 is applied to the scattering medium 901 after passing through the optical fiber 860. The intensity-modulated light that has entered the scattering medium 901 propagates in the scattering medium 901, and a part thereof enters the optical fiber 870, and the wavelength filter 880 passes through the optical fiber 870.
To enter. In the wavelength filter 880, the light of wavelength = λ ₁ is selected, transmitted and output, and is incident on the photoconductive type photodetector 112 of the light receiving unit 110 via the condenser lens 820.

As described above, since the voltage signal of frequency = f + Δf is applied to the photoconductive type photodetector 112, the frequency = (2f + Δf, Δf) is applied to the photoconductive type photodetector 112.
A current signal having two frequency components is generated.
The current signal is converted into a voltage signal by the signal converter 310, and then the component of frequency = Δf is selected by the bandpass filter 400. The signal of frequency = Δf thus selected is input to the phase detector 700.

At the same time, the electric signal of frequency = f output from the signal generator 210 and the electric signal of frequency = f + Δf output from the signal generator 220 are mixed in the signal mixer 6
Mixed at 00 to produce an electrical signal with frequency = Δf. The signal of this frequency = Δf is input to the phase detector 700 as a reference signal. The signal of frequency = Δf selected by the signal mixer 600 reflects the intensity and phase of the component of wavelength = λ ₁ of the intensity-modulated light at the time of being output from the light emitting unit 550.

The phase detector 700 inputs two kinds of signals of frequency = Δf, compares these two kinds of signals, and compares the components of the intensity modulation frequency = f ₁ received by the photoconductive type photodetector 112 with respect to the reference signal. The intensity and phase information is analyzed and the intensity information and phase information are output to the processing unit 760. The arithmetic processor 751 of the processing unit 750 inputs the intensity information and the phase information of the component of wavelength = λ ₁ and stores them as data.

Next, the processing section 750 causes the wavelength filter 88.
The transmission output of the light of wavelength = λ _k (k = 2, ..., N) is sequentially instructed to 0. Then, every time the transmission wavelength is designated in the wavelength filter 880, the same operation as above is performed, and the arithmetic processing unit 751 of the processing unit 750 inputs the intensity information and the phase information of the component of wavelength = λ _k , and outputs them as data. Store.

In this way, after collecting the intensity information data and the phase information data for wavelength = λ _i , the arithmetic processing unit 751 substitutes the collected data into the theoretical formula obtained by the light diffusion theory, executes the arithmetic operation, and scatter absorption The scattering coefficient μ _s and the absorption coefficient μ _a of the pair 901 are obtained. The arithmetic processing unit 751
After calculation, the scattering coefficient μ _s and absorption coefficient μ _a are displayed on the display 75.
Notify 2 and display the obtained scattering coefficient μ _s and absorption coefficient μ _a .

By performing the above measurement over time, it is possible to measure the change over time in the scattering coefficient μ _s and the absorption coefficient μ _a inside the scattering medium 901.

The optical signal measuring device used in this application example can be modified in the same manner as in the above-described embodiment of the optical signal measuring device.

Further, when the light is incident on the scattering medium 901 which is the object to be measured, it is possible to dispose an optical element between the emission end of the optical fiber 860 and the scattering medium 901. For example, it is possible to arrange a convex lens or a concave mirror between the emission end of the optical fiber 860 and the scattering medium 901 to condense the light at the incident position of the scattering medium 901 or to collimate the incident light. However, it is also possible to arrange a light scatterer between the emission end of the optical fiber 860 and the scattering medium 901 so that the diffused light is incident on the scattering medium 901, or the emission end of the optical fiber 860. And scattering absorber 9
It is also possible to reduce the reflection on the surface of the scattering medium 901 by disposing an optical member having a refractive index substantially the same as that of the scattering medium 901 between 01 and 01.

When the light is incident on the scattering medium 901 which is the object to be measured, the light emitted from a light source (for example, a laser light source) having a good linearity in the traveling direction of the emitted light is used without using an optical fiber. It is also possible to directly irradiate the scattering medium 901.

Further, in contact with the scattering medium 901, the LED
It is also possible to arrange a minute light source such as an LD or an LD.

Depending on the calculation algorithm associated with the light propagation model inside the scattering medium used for the calculation in the calculation processor, the light incident position on the scattering medium does not have to be a very small point and is appropriate. Light having a different diameter or an appropriate intensity distribution may be incident.

The light diffusion equation is a typical expression used for the operation of the operation processor.
1. The formula obtained based on the physical fact that absorption occurs depending on the effective propagation distance of light that propagates while scattering inside 1 and is detected, and light propagates in the scattering medium 901. An equation expressing the relationship between the average optical path length and the detected phase change, amplitude change, or modulation degree change may be used.

In this application example, only one photoconductive type photodetector, which is a light receiving element, is used. However, the light incident on the light receiving part is wavelength-split, and the photoconductive type photodetector is arranged for each wavelength. Good. However, in such a case, it is necessary to prepare a phase detector for each wavelength or select which photoconductive type light receiver the signal input to the phase detector is derived from.

Note that this application example or a modification of this application example can be applied to a living body, a cloud, or the like as a scattering medium which is an object to be measured.

FIG. 9 is a block diagram of a system for measuring internal information of a scattering medium, which is a second application example of the optical signal measuring device of the present invention. As shown in FIG. 9, in this system,
A signal generator 210 for generating a signal of frequency = f,
A non-linear element 231 which inputs a signal of frequency = f output from the signal generator 210 and outputs a signal including a component of frequency = if (i = 1, ..., N; n is an integer of 2 or more), The oscillating section 230 including the signal supplies an intensity-modulated signal to the light emitting section 500, receives a signal generator 220 that generates a signal of frequency = f + Δf, and a signal of frequency = f + Δf output from the signal generator 220, = I
Non-linear element 2 that outputs a signal including a component of (f + Δf)
The oscillator 240 including the reference numeral 41 supplies the modulated signal to the light receiver 110. Here, the non-linear elements 231 and 241 may be any elements that give distortion to the input signal, and a comb generator that obtains an impulse-shaped electric signal and a pulse generator that is an active circuit can be preferably used.

In this system, the output signal of the oscillator 230 and the output signal of the oscillator 240 are mixed in the signal mixer 600.
Frequency resulting from mixing at = i · Δf (i = 1,
..., provided in accordance with each component of n), the filter 710 _i which transmits any one component frequency = i · Delta] f, and a phase detector 700 _i.

Further, in addition to the above optical signal measuring device, this system has (a) a condenser lens 810 for condensing the intensity-modulated light output from the light emitting section 500, and (b) a condenser lens 8
An optical fiber 860 that guides the light condensed by 10 to emit intensity-modulated light toward the scattering medium 901 and (c) the light that has propagated through the scattering medium 901 are incident to the optical signal measuring device. An optical fiber 870 that guides toward the optical fiber, and (d) a condensing lens 820 that condenses the light output from the optical fiber 870 in the light receiving area of the photoconductive receiver 110 of the light receiving unit 100,
(E) A processing unit 750 that receives the signal output from the phase detector 700 _i and calculates the scattering coefficient μ _s and the absorption coefficient μ _a inside the scattering medium 901 based on the analysis result of the phase detector 700. With. Here, the processing unit 750
When the light intensity modulation frequency = f ₁ , ..., F _n is used in the theoretical formula obtained by the light diffusion theory, the phase detector 7
Substituting the value of the phase change analyzed in 00, the scattering coefficient μ
_s and the absorption coefficient μ _a , and a display 75 for displaying the scattering coefficient μ _s , the absorption coefficient μ _{a, and the} like calculated by the calculation processor 761 according to an instruction from the calculation processor 761.
2 and.

In the system of FIG. 9, the following is performed.
The internal information of the scattering medium is measured.

Frequency output from oscillator 240 = i.multidot.
The signal including the component of (f + Δf) is converted into a low-impedance voltage signal by the voltage application unit 111 and supplied to the voltage application terminal of the photoconductive type photodetector 112.

On the other hand, the signal generator 230 inputs to the light emitting section 500 a light intensity modulation signal having respective components of frequency = f ₁ , ..., F _n , and frequency = f in synchronization with this light intensity modulation signal.
Intensity modulated light having each component of ₁ , ..., F _n is output.
The intensity-modulated light output from the light emitting unit 500 is applied to the scattering medium 901 after sequentially passing through the condenser lens 810 and the optical fiber 860. The intensity-modulated light that has entered the scattering medium 901 propagates in the scattering medium 901, and a part of it propagates to the optical fiber 870. The photoconductive type light reception of the light receiving unit 110 is performed via the optical fiber 870 and the condenser lens 820. Bowl 1
It is incident on 12.

As described above, since a voltage signal of frequency = i. (F + Δf) is applied to the photoconductive type photodetector 112, the photoconductive type photodetector 112 has a frequency = i · Δf as a low frequency component. A current signal having a component of is generated.
This current signal is converted into a voltage signal by the signal converter 310, and then the component of frequency = i · Δf is selected by the bandpass filter 400. Frequency thus selected = i.Δ
The signal having all the components of f is input to all of the phase detectors 700 _i .

At the same time, the electrical signal of the frequency = f ₁ , ..., F _n output from the oscillator 230 and the electrical signal of all components of the frequency = i · (f + Δf) output from the oscillator 240 are signals. Mixing is performed by the mixer 600, and frequency = i ·
An electrical signal having a component of Δf is generated. The signals generated in this way are filtered by the filter 710 _{i at} frequency = i.
The component of Δf is selected, and the signal of this frequency = i · Δf is individually input to the phase detector 700 _i as a reference signal. Note that the frequency selected by the filter 710 _i =
Each component signal of i · Δf reflects the intensity and phase of the component of intensity modulation frequency = i · f of the intensity-modulated light at the time of being output from the light emitting unit 500.

Each phase detector 700 _i has two kinds of frequencies = i
・ Input the signal of Δf, compare these two kinds of signals,
Photoconductive light-receiving device 112 with respect to the reference signal by analyzing the intensity and phase of components of the intensity modulation frequency = f _i of the received light,
The intensity information and the phase information are output to the processing unit 760. Calculation processor 761 of processing unit 760 receives the intensity and phase information of the respective components of the intensity modulation frequency = f _i,
Store as data.

In this way, the intensity modulation frequency = f ₁ , ..., F
After collecting the intensity information data and the phase information data about _n , the arithmetic processing unit 761 substitutes the collected data into a theoretical formula obtained by the light diffusion theory and executes the arithmetic operation to calculate the scattering coefficient μ _s of the scattering medium 901 or Find the absorption coefficient μ _a .
The arithmetic processing unit 761 notifies the scattering coefficient μ _s and the absorption coefficient μ _a to the display device 752 after the calculation is performed, and the obtained scattering coefficient μ _s is notified.
And the absorption coefficient μ _a are displayed.

By performing the above measurement over time, it is possible to measure the change over time in the scattering coefficient μ _s and the absorption coefficient μ _a inside the scattering medium 901.

The optical signal measuring device used in this application example can be modified in the same manner as in the above-described embodiment of the optical signal measuring device.

Further, similarly to the first application example, it is possible to deform the light when it is incident on the scattering medium 901 which is the object to be measured.

Similarly to the first application example, the light diffusion equation is a typical expression used for the calculation of the calculation processor, but light propagates while scattering inside the scattering medium 901. Depending on the effective propagation distance up to detection, the equation obtained based on the physical fact that absorption occurs, the average optical path length when light propagates in the scattering medium 901, and A formula expressing a relationship with a phase change, an amplitude change, or a change in the modulation degree may be used.

Further, as in the first application example, in this application example, the case where the number of the optical signal measuring device of the present invention is one is shown, but a plurality of the optical signal measuring devices of the present invention are provided. The light is incident on the scattering medium from different directions, and the light emitted from multiple directions is measured simultaneously, and each optical signal measuring device measures the scattering coefficient for each direction based on each phase change and intensity change. It is also possible to obtain the absorption coefficient. This makes it possible to obtain a tomographic image of the scattering coefficient and absorption coefficient inside the scattering medium.

FIG. 10 shows a third embodiment of the optical signal measuring device of the present invention.
FIG. 6 is a configuration diagram of a system of a displacement meter that is an application example of, which measures the displacement of the measured object. As shown in FIG. 10, in addition to the optical signal measuring device of the above embodiment, this system is
(A) Collimating lens 830 for collimating the intensity-modulated light output from the light emitting section 500, and (b) DUT 903.
And a condenser lens 840 for condensing the intensity-modulated light reflected by the light receiving area of the photoconductive type light receiver 112 of the light receiving section 110, and replacing the processing section 750 with phase information obtained at intervals. The processing unit 770 that obtains the displacement of the object to be measured is used.

The processing unit 770 collects the values of the phase change analyzed by the phase detector 700 over time and obtains the displacement amount of the DUT 903, and according to the instructions of the operation processor 771. , And a display 752 for displaying the amount of displacement or the like calculated by the arithmetic processing unit 771.

A reflection mirror 905 is attached to the object to be measured 903 of this application example, and efficiently reflects the irradiation light toward the light receiving section 110. Further, in order to reflect the irradiation light efficiently, it is possible to use a corner cube instead of the reflecting mirror. Furthermore, without using a reflector such as a reflector or a corner cube, the object to be measured 903
Scattered light derived from the irradiation light may be detected.

In the system of this application example, the displacement of the object to be measured is measured as follows.

The intensity-modulated light of frequency = f, which is output from the LD 510 of the light emitting section 500, is collimated by the collimator lens 830, and then emitted toward the DUT 903. The intensity of the intensity-modulated light irradiating the DUT 903 causes the reflecting mirror 9
The light incident on 05 is reflected toward the light receiving unit 110. The reflected intensity-modulated light is condensed by the condenser lens 840 in the light receiving region of the photoconductive type photodetector 112.

After that, the optical signal measuring device operates in the same manner as the above-described embodiment of the optical signal measuring device, and the phase information is output from the phase detector 700.

In this state, the arithmetic processor 771 first
Phase information is collected and stored at time t1. Next, the arithmetic processing unit 771 receives the time t2 (= t1 + T) at the time T.
The phase information is collected and stored in. If the position of the DUT 903 at the time t1 and the position of the DUT 903 at the time t2 are different in the optical axis direction, the phase information collected at each time is different, and this difference is from the time t1 to the time t2. This reflects the displacement of the DUT 903 in the optical axis direction. The arithmetic processing unit 771 obtains the phase difference of the intensity-modulated light received at two times based on the collected two pieces of phase information, and computes the displacement amount of the DUT 903 from the phase difference. The displacement amount thus obtained is displayed on the display 752.

In this application example, it is also possible to obtain the displacement velocity of the object 903 to be measured by dividing the displacement amount by the time T in the arithmetic processing unit 771.

Further, the arithmetic processing unit 771 further causes the time t3,
,, by collecting the phase information by
It is possible to measure the time change of the displacement of the object, and further the time change of the displacement speed of the DUT 903.

This application example can be modified to a distance measuring system. In this case, the arithmetic processor previously collects and stores the phase information when the object to be measured is installed at a known distance. After that, distance measurement is performed by comparing with the collected phase information and performing calculation.

In this application example, one kind of frequency = (f) is used as the intensity modulation frequency, but a plurality of intensity modulation frequencies = (f _i ; i = 1, ...) Are used as in the first application example. use, f _i + Δf frequency of the voltage signal supplied to the voltage application terminal to the photoconductive light-receiving device; i = 1, ... can be alternatively be selected from. The detectable distance range differs depending on the intensity modulation frequency of interest, but by changing the intensity modulation frequency of interest, it is possible to perform distance measurement in a wide distance range.

The present invention is not limited to the above embodiments, but can be modified. For example, the photoconductive type photodetector has an electrode structure similar to that of the MSM and is sensitive to wavelengths longer than the wavelength corresponding to the energy-bandgap, or the Schottky contact on the back surface in addition to the MSM electrode structure. It is possible to provide an electrode and use one having sensitivity to a wavelength longer than the wavelength corresponding to the energy-bandgap of the substrate (GaAs). In addition, the above GaAs
Instead of InP, GaP can be preferably used. Also,
A mixed crystal compound semiconductor such as InGaAs can be used for long-wavelength applications of optical communication. Furthermore, although the response frequency is limited, it is also possible to use a photoconductive type photodetector such as PbS, CdS or CdSe.

In the above embodiment, the operation has been described in which the photoconductive type photodetector is driven at a low impedance to extract a signal as a current. You can take out the voltage as a signal,
Alternatively, a resistor may be connected in series to the photoconductive type photodetector to extract the voltage across the resistor as a signal. In addition,
When the voltage between both terminals of the photoconductive type light receiver is taken out as a signal, the current-voltage converter is not necessary.

[0095]

As described above in detail, according to the optical signal measuring device of the present invention, the photoconductive type photodetector is used as the photodetector to reduce the intensity modulation frequency in the case of incidence of the optical signal. Since it was decided to modulate the photodetection signal with this photoconductive type receiver, the intensity modulation frequency reduction operation by frequency mixing was performed over a wide frequency measurement range while reducing the number of parts, and It is possible to supply an electric signal having a frequency component that is easy to handle.

Further, as a photoconductive type photodetector, when the amount of irradiation light of a metal-semiconductor-metal photodetector (MSM) is constant and the applied voltage value is an independent variable, the applied voltage value is 0.
When the amount of current flowing through the photoconductive type photodetector is a substantially odd function of the applied voltage in a predetermined definition range including V, and the applied voltage is constant and the irradiation light amount value is an independent variable, the irradiation light amount is a predetermined definition. In the region, the current amount flowing through the photoconductive type photoreceiver is a substantially linear function of the irradiation light amount, and the voltage signal applied to the photoconductive type photoreceiver is periodic and the time average value is approximately Since the voltage signal whose amplitude is an even function of time is adopted with the origin at the time of the midpoint of adjacent times when the amplitude is 0 and the amplitude is 0, the influence of background light can be reduced, and frequency mixing can be performed accurately. Can be executed.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an optical signal measuring device of the present invention.

FIG. 2 is a configuration diagram of an embodiment of an optical signal measuring device of the present invention.

FIG. 3 is a circuit configuration diagram of a voltage applying unit that can be used in the optical signal measuring device according to the embodiment.

FIG. 4 is a circuit configuration diagram of a bandpass filter that can be used in the optical signal measuring device according to the embodiment.

FIG. 5 is an explanatory diagram of modulation characteristics in the optical signal measuring device according to the embodiment.

FIG. 6 is a configuration diagram of a first modification of the optical signal measuring device according to the embodiment.

FIG. 7 is a configuration diagram of a second modification of the optical signal measuring device according to the embodiment.

FIG. 8 is a configuration diagram of a system of a first application example of the optical signal measurement device of the invention.

FIG. 9 is a configuration diagram of a system of a second application example of the optical signal measurement device of the invention.

FIG. 10 is a configuration diagram of a system of a third application example of the optical signal measurement device of the invention.

FIG. 11 is a configuration diagram of a first conventional example of an optical signal measurement device.

FIG. 12 is a configuration diagram of a second conventional example of the optical signal measuring device.

FIG. 13 is an explanatory diagram of modulation characteristics of Conventional Example 2.

[Explanation of symbols]

100, 110, 120, 130 ... Light receiving part, 111 ... Voltage applying part, 112, 132 ... Photoconductive type light receiving device, 113 ...
Bias adjusting unit, 131 ... Constant current drive circuit, 135 ... Operational amplifier, 136 ... Differential amplifier, 210, 220 ... Signal generator, 230, 240 ... Oscillating unit, 300 ... Conversion amplification unit, 310, 320 ... Current voltage Conversion unit, 330 ... Differential amplifier, 400 ... Frequency selector, 410 ... Band pass filter, 500, 550 ... Light emitting unit, 510 ... Laser diode, 511, 512, 513 ... Light emitting unit, 600 ... Signal mixer, 700 ... Phase detector, 710 ... Filter, 75
0,760,770 ... Processing unit, 751,761,771
... arithmetic processing unit, 752 ... display unit, 810, 820, 83
0,840 ... Lens, 860,870 ... Optical fiber, 8
80 ... Wavelength filter, 910 ... Photo receiver, 930, 950
... band pass filter, 940 ... mixer.

Claims (6)

[Claims] 1. A first signal generator for generating a first electric signal having a first frequency component, and an intensity modulation component of the first frequency, which is synchronized with the first electric signal. A light emitting section for generating intensity-modulated light, a second signal generator for generating a second electric signal having a third frequency component different from the first frequency by a second frequency, and the second Voltage signal supply unit for inputting the electric signal of the second electric signal, converting the voltage signal into a voltage signal reflecting the time change of the second electric signal, and outputting the voltage signal, and a voltage signal for inputting the voltage signal output from the voltage signal supplying unit. According to a photoconductive type photoreceiver that has an application terminal and that receives the intensity-modulated light output from the light emitting unit and propagated through a predetermined light propagation medium, and a current signal that flows through the photoconductive type photoreceiver. Input a third electric signal, A frequency selector for selecting and outputting a fourth electric signal having a frequency component substantially the same as that of the second frequency; and inputting the first signal and the second electric signal, the second frequency And a signal mixer for generating a fifth electric signal having information on at least one of the phase and amplitude of the first signal, and the fourth electric signal and the fifth electric signal are input. ,
An optical signal measuring device, comprising: a phase detector that analyzes at least one of the intensity and the phase of the component of the first frequency of the intensity-modulated light that has entered the photoconductive receiver. 2. The optical signal measuring device according to claim 1, further comprising a phase adjuster for changing the phase of the second electric signal. 3. The voltage signal applied to the photoconductive type photoreceiver is periodic, the time average value is approximately 0 V, and the time point at the midpoint of adjacent time points when the amplitude is 0 V is the origin. 2. The optical signal measuring device according to claim 1, wherein the amplitude is a substantially even function of time. 4. The optical signal measuring device according to claim 1, further comprising bias adjusting means for adjusting an operating point of the photoconductive type photodetector. 5. The photoconductive-type photodetector is characterized in that when the measured light intensity is constant and the applied voltage value is an independent variable, the photoconductive-type photodetector is in a predetermined domain including the applied voltage value of 0V. When the amount of current flowing is an approximately odd function of the applied voltage, and the applied voltage is constant and the measured light intensity value is an independent variable, the measured light intensity flows through the photoconductive type receiver in a predetermined defined range. The optical signal measuring device according to claim 1, wherein the current amount is a substantially linear function of the irradiation signal intensity. 6. The optical signal measuring device according to claim 5, wherein the photoconductive type photodetector is a metal-semiconductor-metal photodetector having a structure in which rectifying junctions are connected in opposite directions.