JP2007024785A - Optical interference type phase sensing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical interference type phase sensing device capable of detecting a phase with high-stability and high-precision, by using two reference light in addition to measurement light and then detecting variation in a phase caused from relative variations in an optical path length between two interferometers to eliminate the variations in the phase. <P>SOLUTION: The sensing device includes a phase detecting means 21 that receives a measurement interference signal from a photoreceiver 8 and a first reference interference signal from a photoreceiver 9 and detects a phase of the measurement interference signal to the first interference signal to output the phase as a measurement phase, a phase detecting means 22 that receives the first reference interference signal from the phtoreceiver 9 and a second reference interference signal from the phtoreceiver 8 and detects a phase generated between the two reference interference signals to output the phase as a reference phase, and a signal processing means 23 that inputs the measurement phase and the reference phase and determines a phase correction value by associating the wavelength of the measurement light in order to correct the phase of the measurement phase based on variations in a phase of the reference phase; and corrects the phase of the measurement phase by the phase correction value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical interference type phase detection apparatus that measures, for example, phase characteristics of an object to be measured from the phase of interference light output from an interferometer, and in particular, using two reference lights separately from measurement light, High stability by detecting phase fluctuation caused by relative optical path length fluctuation between two optical paths (optical path where the device under test is connected and optical path not connected) and removing the phase fluctuation The present invention relates to an optical interference type phase detection device that enables highly accurate phase detection.

  Conventionally, by using the measurement light and one reference light, the relative optical path length variation between the two optical paths of the Mach-Zehnder interferometer (the optical path to which the object to be measured is connected and the optical path that is not connected) is caused. There has been an optical interference type phase detection device in which measurement errors due to phase fluctuations are reduced. (For example, see Non-Patent Document 1)

  A schematic configuration of this type of optical interference type phase detector is shown in FIG. The wavelength variable light source 1 outputs measurement light in a predetermined wavelength range to the optical coupler 3. The light source 2 outputs reference light having a fixed wavelength different from the wavelength of the wavelength tunable light source 1 to the optical coupler 3. The optical coupler 3 combines the measurement light and the reference light, and outputs the wavelength multiplexed light obtained thereby to an acousto-optic frequency shifter (AOFS) 4a.

AOFS4a is driven by the ultrasonic frequency f ₁ input from the ultrasonic generator 4b, and demultiplexes the wavelength-multiplexed light from the optical coupler 3 into two light, the object to be measured 10 is connected to one light And the other light is output to the second optical path to which the delay device 5 is connected. At this time, the light output to the second optical path, i.e. each wavelength of the measurement light and the reference light (frequency) is the frequency f ₁ minute shift of the ultrasonic wave. Then, the optical coupler 6 multiplexes the light in the first optical path that has passed through the device under test 10 and the light in the second optical path that has passed through the delay device 5, and the interference light obtained thereby, that is, The interference light between the measurement lights (referred to as measurement interference light) and the interference light between the reference lights (referred to as reference interference light) that have passed through the two optical paths are output to the wavelength demultiplexer 7. The AOFS 4 a, the ultrasonic generator 4 b, the DUT 10, the delay device 5, and the optical coupler 6 constitute a Mach-Zehnder interferometer 20. The delay unit 5 matches the optical path lengths of the two optical paths of the Mach-Zehnder interferometer 20.

The wavelength demultiplexer 7 receives the interference light (measurement interference light and reference interference light) output from the optical coupler 6, demultiplexes it into each wavelength component of the measurement light and reference light, and receives the light receiver (PD) 8 and Output to a light receiver (PD) 9. The light receiver 8 receives the measurement interference light from the wavelength demultiplexer 7, performs photoelectric conversion (heterodyne detection), and outputs a measurement interference signal having a beat frequency f ₁ . Similarly, the light receiver 9 receives the reference interference light from the wavelength demultiplexer 7 and photoelectrically converts (heterodyne detection), and outputs a reference interference signal having a beat frequency f ₁ . The phase detector 11 detects the phase of the measurement interference signal with respect to the reference interference signal.

51th Japan Federation of Reciprocal Products “Evaluation of Chromatic Dispersion Using a Two-Wavelength Heterodyne Fiber Interferometer” 28p-R-12 (2004.3): Kensuke Ogawa, Titi Ray (DNRI)

  In such a conventional optical interference type phase detector, the measurement light and one reference light are simultaneously input to the Mach-Zehnder interferometer so that each passes through the same two optical paths of the Mach-Zehnder interferometer. Since the phase of the measurement interference light (measurement interference signal) relative to the light (reference interference signal) is detected, the relative distance between the two optical paths of the Mach-Zehnder interferometer (the optical path including the measured object and the optical path not including it) Measurement errors due to phase fluctuations caused by optical path length fluctuations can be reduced. However, there were still the following problems.

That is, when there is a change in the relative optical path length between the two optical paths of the Mach-Zehnder interferometer, the phase change Δθ of the measurement interference signal with respect to the reference interference signal is given by equation (1).
Δθ = ΔL · (ν _s −ν _r1 ) · 2 · π / c (1)
Here, ΔL is a change in the relative optical path length between the two optical paths of the Mach-Zehnder interferometer, ν _s is the frequency of the measurement light, ν _r1 is the frequency of the reference light, and c is the speed of light. The optical path length of ΔL is an optical distance, and is an amount including the refractive index n of the optical path. As can be seen from the above equation (1), the phase change Δθ with respect to the optical path length change ΔL decreases as the frequency (wavelength) of the measurement light approaches the frequency (wavelength) of the reference light, and increases as the distance increases. Therefore, when the wavelength of the measurement light is close to the wavelength of the reference light, measurement is performed based on the phase fluctuation (phase change Δθ) caused by the relative optical path length fluctuation between the two optical paths of the Mach-Zehnder interferometer. Although the error can be almost ignored, there is a problem that the error cannot be ignored when the wavelength of the measurement light is away from the wavelength of the reference light.

  In actual measurement, since the object to be measured is arranged in one of the two optical paths of the Mach-Zehnder interferometer, especially when the interferometer is configured using an optical fiber, the measured object is in one of the optical paths. An optical fiber for connecting an object, and an optical path length adjusting delay optical fiber or the like are connected to the other optical path. Therefore, the optical path length of each optical path easily changes due to external factors such as temperature, and it is generally difficult to keep the relative optical path length between the two optical paths constant, and the influence on the phase change becomes large. . Note that the conventional optical interference type phase detector described above was in the case of the optical heterodyne interference method, but the same problem occurs in the case of the optical homodyne interference method.

  The present invention uses two reference lights separately from the measurement light, and is caused by the relative optical path length fluctuation between the two optical paths of the interferometer (the optical path where the object to be measured is connected and the optical path which is not connected). The objective is to provide an optical interference type phase detection device that solves these problems and detects highly stable and highly accurate phase detection by detecting phase fluctuations that occur as a result, and eliminating the phase fluctuations. Yes.

  In order to solve the above-mentioned problems, in the optical interference type phase detection device according to claim 1 of the present invention, the wavelength variable light source (1) for outputting the measurement light in a predetermined wavelength range and the wavelength different from the wavelength of the measurement light are fixed. A first light source (2) for outputting a first reference light having a wavelength, and a second light source for outputting a second reference light having a fixed wavelength different from the wavelength of the measurement light and the wavelength of the first reference light. A light source (12), optical multiplexing means (13) for receiving and multiplexing the measurement light, the first reference light, and the second reference light, and outputting the wavelength multiplexed light obtained thereby; A first optical path to which the object to be measured is connected and a second optical path to which the object to be measured is not connected; the first light that receives the wavelength-multiplexed light and passes through the first optical path; The first light and the second light which are demultiplexed into the second light passing through the second optical path and passed through the first optical path. Interferometers (30, 40) for combining the second light that has passed through and outputting the interference light obtained thereby, the measurement light, the first reference light, Wavelength demultiplexing means (17) for demultiplexing each wavelength component of the second reference light, and measuring and measuring by receiving measurement interference light related to the wavelength component of the measurement light output from the wavelength demultiplexing means A first light receiver (8) that outputs an interference signal and a first reference interference light related to a wavelength component of the first reference light output from the wavelength demultiplexing means are received and photoelectrically converted to receive a first signal. A second light receiver (9) for outputting a reference interference signal and a second reference interference light related to the wavelength component of the second reference light output from the wavelength demultiplexing means are received and photoelectrically converted to a second one. A third light receiver (18) for outputting the reference interference signal, the measurement interference signal, and the first reference First phase detecting means (21) which receives the interference signal and the reference interference signal of one of the second reference interference signals, detects the phase of the measurement interference signal with respect to the reference interference signal, and outputs it as a measurement phase ) And the first reference interference signal and the second reference interference signal, and detects a phase generated between these two reference interference signals and outputs it as a reference phase (22) And using the phase change of the reference phase, the wavelength-phase characteristics of the object to be measured are obtained based on the measurement phase.

  According to a second aspect of the optical interference type phase detection device of the present invention, in the optical interference type phase detection device of the first aspect described above, the measurement phase and the reference phase are inputted, and a phase change of the reference phase is detected. And a signal processing unit (23) for obtaining a phase correction value for performing phase correction of the measurement phase in association with the wavelength of the measurement light, and performing phase correction of the measurement phase based on the obtained phase correction value. It was.

  According to a third aspect of the present invention, there is provided the optical interference type phase detection apparatus according to the first aspect, wherein the optical interference type phase detection apparatus is provided in one of the two optical paths of the interferometer. The optical path length varying means (15) for changing the relative optical path length between the two optical paths, and the reference phase are inputted, and the optical path length varying means is controlled so that the reference phase becomes constant at a predetermined value. And an optical path length correcting means (24) for generating and outputting a control signal based on the reference phase.

  Further, in the optical interference type phase detection device according to claim 4 of the present invention, in the optical interference type phase detection device according to any one of claims 1 to 3, the interferometer includes the first optical path and the second optical path. The measurement light included in the first light having at least one frequency shifter (14a to 14f, 27a, 27b) in at least one of the optical paths, and passing through the first optical path, Respective frequencies of the first reference light and the second reference light, and the measurement light, the first reference light, and the second included in the second light passing through the second optical path The optical heterodyne interferometer is configured such that the frequency difference between the measurement light, the first reference light, and the second reference light becomes a predetermined beat frequency with respect to each frequency of the reference light. And the first light receiver is the predetermined The measurement interference signal of beat frequency is output, the second light receiver outputs the first reference interference signal of the predetermined beat frequency, and the third light receiver outputs the first interference signal of the predetermined beat frequency. 2 reference interference signals are output.

  In the optical interference type phase detection apparatus according to claim 5 of the present invention, in the optical interference type phase detection apparatus according to any one of claims 1 to 3, the interferometer is an optical homodyne interferometer.

  Further, in the optical interference type phase detection device according to claim 6 of the present invention, in the optical interference type phase detection device according to any one of claims 1 to 5, the interferometer receives the wavelength multiplexed light and receives the wavelength-multiplexed light. An optical demultiplexing means (16, 14a, 14b) for demultiplexing the first light that passes through one optical path and the second light that passes through the second optical path, and the measured object. A Mach-Zehnder including a first optical coupler (6) that combines the first light and the second light input without passing through the device under test to output the interference light. Type interferometer.

  Further, in the optical interference type phase detection device according to claim 7 of the present invention, in the optical interference type phase detection device according to any one of claims 1 to 5, the interferometer receives the wavelength multiplexed light and receives the wavelength-multiplexed light. The first light and the device under test are demultiplexed into the first light passing through the optical path 1 and the second light through the second optical path, and reflected back by the device under test. Michelson type comprising a second optical coupler (25) that combines the second light reflected and returned by the reflecting means (26) without passing through and outputs the interference light It was made to be an interferometer.

In the optical interference type phase detector of the present invention, the phase (reference phase) generated between two reference interference signals is detected, and the wavelength-phase characteristic of the object to be measured is measured by utilizing the phase change of the reference phase. It was determined based on the phase. Therefore, based on the phase change of the reference phase, the phase of the measurement phase is corrected, or the relative optical path length between the two optical paths of the interferometer is controlled so as not to change, so that the wavelength-phase of the device under test is measured. The characteristic may be such that it does not include phase fluctuations caused by relative optical path length fluctuations between the two optical paths of the interferometer. As a result, in the phase measurement, the influence of the optical path length variation of the interferometer accompanying the environmental change or the like can be ignored, and highly stable and highly accurate measurement can be performed in the long term. Further, since the phase can be measured with high accuracy, it is also effective for obtaining the optical length of the object to be measured. The optical length L of the object to be measured can be obtained by the equation (2) by adjusting the optical path lengths of the two optical paths of the interferometer equally in advance.
L = c · θ / {(ν _max −ν _min ) · 2 · π} (2)
Here, c is the speed of light, and θ is the total amount of phase change when the frequency of the measurement light is varied from the minimum frequency ν _min to the maximum frequency ν _max .

  Embodiments of the present invention will be described below.

[First Embodiment]
The configuration of the optical interference type phase detector of the first embodiment of the present invention is shown in FIG. The same elements as those of the conventional optical interference type phase detector are denoted by the same reference numerals, and detailed description thereof is omitted. The wavelength variable light source 1 is, for example, a wavelength variable laser, and outputs measurement light in a predetermined wavelength range (for example, 1530 to 1560 nm) to the optical coupler 13a. The light source 2 is a laser, for example, and outputs a first reference light having a fixed wavelength (for example, 1565 nm) different from the wavelength of the measurement light to the optical coupler 13b. Similarly, the light source 12 outputs the second reference light having a fixed wavelength (for example, 1525 nm) different from the wavelength of the measurement light and the wavelength of the first reference light to the optical coupler 13b. The optical coupler 13b combines the first and second reference lights and outputs them to the optical coupler 13a. The optical coupler 13 a combines the combined light from the optical coupler 13 b and the measurement light, and outputs the wavelength multiplexed light obtained thereby to the optical coupler 16 of the Mach-Zehnder interferometer 30. The optical coupler 13a and the optical coupler 13b constitute an optical multiplexing means 13.

The optical coupler 16 demultiplexes the wavelength multiplexed light from the optical coupler 13a into two lights, one of the lights is connected to the first optical path to which the device under test 10 is connected, and the other light is connected to the AOFS 14e. Output to the second optical path. AOFS14e is driven by the ultrasonic frequency f ₁ input from the ultrasonic generator 14f, the light from the optical coupler 16, i.e. the measurement light, each wavelength of the first reference light and second reference light (Frequency) is output by shifting the ultrasonic frequency f by _one minute. The light passing through the first optical path may be frequency shifted instead of the light passing through the second optical path. Then, the optical coupler 6 multiplexes the light in the first optical path that has passed through the device under test 10 and the light in the second optical path that has passed through the AOFS 14e. Interference light between the measurement lights (referred to as measurement interference light), interference light between the first reference lights (referred to as first reference interference light), and interference light between the second reference lights (referred to as the second reference light) that have passed through the optical path (Referred to as reference interference light) is output to the wavelength demultiplexing means 17. The optical coupler 16, the device under test 10, the AOFS 14e, the ultrasonic generator 14f, and the optical coupler 6 constitute a Mach-Zehnder interferometer 30 of an optical heterodyne interference system.

The wavelength demultiplexing means 17 is, for example, a dielectric multilayer filter, and receives interference light (measurement interference light, first reference interference light, and second reference interference light) output from the optical coupler 6, and receives measurement light. The first reference light and the second reference light are demultiplexed into wavelength components and output to the light receiver (PD) 8, the light receiver (PD) 9, and the light receiver (PD) 18, respectively. The light receiver 8 receives the measurement interference light from the wavelength demultiplexing means 17 and photoelectrically converts it (heterodyne detection), and outputs a measurement interference signal having the beat frequency f ₁ . Similarly, the light receiver 9 and the light receiver 18 receive the first reference interference light and the second reference interference light from the wavelength demultiplexing means 17, respectively, perform photoelectric conversion (heterodyne detection), and beat frequency f _1. The first reference interference signal and the second reference interference signal are respectively output.

  The first phase detection means 21 receives the measurement interference signal output from the light receiver 8 and the first reference interference signal output from the light receiver 9, and determines the phase of the measurement interference signal with respect to the first reference interference signal. Detect and output as measurement phase. Instead of the first reference interference signal, the phase of the measurement interference signal with respect to the second reference interference signal may be detected and output as the measurement phase. The second phase detection means 22 receives the first reference interference signal output from the light receiver 9 and the second reference interference signal output from the light receiver 18, and between these two reference interference signals. The generated phase is detected and output as a reference phase.

  The signal processing unit 23 inputs the measurement phase from the first phase detection unit 21 and the reference phase from the second phase detection unit 22 and performs phase correction of the measurement phase based on the phase change of the reference phase. Therefore, a phase correction value for the measurement phase is obtained in association with the wavelength of the measurement light, and the phase of the measurement phase is corrected by the obtained phase correction value. As a result, the device under test does not include phase fluctuations caused by relative optical path length fluctuations between the two first and second optical paths of the Mach-Zehnder interferometer 30 (hereinafter simply referred to as “between two optical paths”). Ten wavelength-phase characteristics can be obtained.

Here, how to obtain the phase correction value will be described. That is, the phase change Δθ _r between the two first and second reference interference signals caused by the change in the relative optical path length between the two optical paths of the Mach-Zehnder interferometer 30 is given by equation (3). Since the phase change Δθ _r is obtained as a phase change corresponding to the wavelength of the measurement light of the reference phase detected by the second phase detector 22, the two optical paths of the Mach-Zehnder interferometer 30 are obtained from the equation (4). A relative optical path length change ΔL is obtained.
Δθ _r = ΔL · (ν _r2 −ν _r1 ) · 2 · π / c (3)
ΔL = c · Δθ _r / {(ν _r2 −ν _r1 ) · 2 · π} (4)
Here, ν _r1 is the frequency of the first reference light, ν _r2 is the frequency of the second reference light, and c is the speed of light.

When there is a change in the relative optical path length between the two optical paths of the Mach-Zehnder interferometer 30, the phase change Δθ of the measurement interference signal with respect to the first reference interference signal is the frequency of the measurement light ν _s , When the frequency of the reference light 1 is ν _r1 , it is given by equation (5) (same as (1) above). As a result, the phase correction value Δθ _c for performing the phase correction of the measurement phase based on the phase change of the reference phase (above Δθ _r ) is obtained by substituting ΔL of the equation (4) into the equation (5) ( 6) It can obtain | require like Formula.
Δθ = ΔL · (ν _s −ν _r1 ) · 2 · π / c (5)
Δθ _c = {Δθ _r / (ν _r2 −ν _r1 )} · (ν _s −ν _r1 )
(6)
Therefore, calculated in association with the phase correction value [Delta] [theta] _c on the wavelength of the measuring light, by using the phase correction value [Delta] [theta] _c obtained by correcting the measured phase from the first phase detecting means 21, a Mach-Zehnder The wavelength-phase characteristic of the DUT 10 that does not include the phase fluctuation caused by the relative optical path length fluctuation between the two optical paths of the interferometer 30 can be obtained.

[Second Embodiment]
The configuration of the optical interference type phase detector of the second embodiment of the present invention is shown in FIG. In the first embodiment shown in FIG. 1, the optical heterodyne interferometer type Mach-Zehnder interferometer 30 is used as the interferometer. In the second embodiment, the optical homodyne interferometer type Mach-Zehnder interferometer 30 is used. . It differs from FIG. 1 of 1st Embodiment only in following (1) and (2), and others are the same. Therefore, detailed description is omitted. (1) The second optical path of the Mach-Zehnder interferometer 30 is not provided with a frequency shifter (AOFS 14e and ultrasonic generator 14f). (2) The light receiver 8, the light receiver 9, and the light receiver 18 receive the measurement interference light, the first reference interference light, and the second reference interference light from the wavelength demultiplexing means 17, respectively, and perform photoelectric conversion (homodyne detection). The measurement interference signal, the first reference interference signal, and the second reference interference signal are output.

[Third Embodiment]
FIG. 3 shows the configuration of the optical interference type phase detector of the third embodiment of the present invention. In the first embodiment shown in FIG. 1, the wavelength-phase characteristics of the DUT 10 do not include phase fluctuations caused by relative optical path length fluctuations between the two optical paths of the Mach-Zehnder interferometer 30. Therefore, the phase of the measurement phase is corrected based on the reference phase as described above. However, in the third embodiment, between the two optical paths of the Mach-Zehnder interferometer 30 based on the reference phase. Control is performed so that the relative optical path length does not change. It differs from FIG. 1 of 1st Embodiment only in following (1) and (2), and others are the same. (1) The second optical path of the Mach-Zehnder interferometer 30 is provided with an optical path length varying means 15 and an optical path length correcting means 22 for controlling the optical path length varying means 15. The optical path length varying means 15 may be provided in the first optical path. (2) The signal processing means 23 is not provided. Therefore, the description of the same part as FIG. 1 is omitted, and the optical path length varying unit 15 and the optical path length correcting unit 22 will be mainly described.

The optical path length varying means 15 is, for example, an optical delay device, and delays the light from the AOFS 14 e based on the control signal from the optical path length correction means 22 and outputs it to the optical coupler 6. That is, the optical path length varying means 15 equivalently changes the relative optical path length between the two optical paths of the Mach-Zehnder interferometer 30. The optical path length correction unit 24 receives the reference phase from the second phase detection unit 22 and sets the optical path length variable unit 15 so that the reference phase is constant at a predetermined value over a predetermined wavelength range of the measurement light. A control signal for control is generated based on this reference phase and output to the optical path length varying means 15. That is, the phase change Δθ _r in the above equation (3) is controlled so as to approach zero as much as possible, so that the relative optical path length change ΔL between the two optical paths approaches zero as much as possible. As a result, the phase change Δθ in the above equation (5) approaches zero as much as possible. Therefore, the measurement phase detected by the first phase detection means 21 does not include the phase fluctuation caused by the relative optical path length fluctuation between the two optical paths of the Mach-Zehnder interferometer 30. Wavelength-phase characteristics can be obtained.

[Fourth Embodiment]
FIG. 4 shows the configuration of the optical interference type phase detector of the fourth embodiment of the present invention. In the third embodiment shown in FIG. 3, the optical heterodyne interferometer type Mach-Zehnder interferometer 30 is used as the interferometer. In the fourth embodiment, the optical homodyne interferometer type Mach-Zehnder interferometer 30 is used. . It differs from FIG. 3 of 3rd Embodiment only in following (1) and (2), and others are the same. Therefore, detailed description is omitted. (1) The second optical path of the Mach-Zehnder interferometer 30 is not provided with a frequency shifter (AOFS 14e and ultrasonic generator 14f). (2) The light receiver 8, the light receiver 9, and the light receiver 18 receive the measurement interference light, the first reference interference light, and the second reference interference light from the wavelength demultiplexing means 17, respectively, and perform photoelectric conversion (homodyne detection). The measurement interference signal, the first reference interference signal, and the second reference interference signal are output.

[Fifth Embodiment]
FIG. 5 shows the configuration of an optical interference type phase detector according to the fifth embodiment of the present invention. This embodiment differs from the first embodiment shown in FIG. 1 only in that an optical heterodyne interferometer Michelson interferometer 40 is used instead of the optical heterodyne interferometer Mach-Zehnder interferometer 30. Therefore, the description of the same part as FIG. 1 is omitted, and the Michelson interferometer 40 will be mainly described. The Michelson interferometer 40 includes an optical coupler 25, an object to be measured 10, an AOFS 27a, an ultrasonic generator 27b, and reflecting means 26 made of, for example, a mirror.

The optical coupler 25 demultiplexes the wavelength multiplexed light input from the optical coupler 13a into two lights, one of the lights is sent to the first optical path to which the device under test 10 is connected, and the other light is sent to the AOFS 27a. And the second optical path to which the reflecting means 26 is connected. The AOFS 27a is driven by ultrasonic waves having a frequency f _1/2 input from the ultrasonic generator 27b, and each of the light from the optical coupler 25, that is, the measurement light, the first reference light, and the second reference light. The wavelength (frequency) of the laser beam is shifted by the ultrasonic frequency f _1/2 and output to the reflecting means 26, and the light reflected and returned by the reflecting means 26 is shifted again by the frequency f _1/2 (frequency in the round trip). f ₁ shift) and output to the optical coupler 25. The light passing through the first optical path may be frequency shifted instead of the light passing through the second optical path. The optical coupler 25 reflects the light of the first optical path reflected and returned by the DUT 10 and the second optical path of the second optical path reflected by the reflecting means 26 and shifted by the frequency f ₁ by the AOFS 27a. The interference light obtained by combining the light, that is, the interference light between the measurement lights (referred to as measurement interference light) and the interference light between the first reference lights (the first interference light) respectively passing through two optical paths. (Referred to as reference interference light) and interference light between the second reference lights (referred to as second reference interference light) are output to the wavelength demultiplexing means 17.

[Sixth Embodiment]
FIG. 6 shows the configuration of an optical interference type phase detector according to the sixth embodiment of the present invention. In the fifth embodiment shown in FIG. 5, the optical heterodyne interferometer Michelson interferometer 40 is used as the interferometer. In the sixth embodiment, the optical homodyne interferometer Michelson interferometer 40 is used. ing. This embodiment is different from FIG. 5 of the fifth embodiment except for the following (1) and (2). Therefore, detailed description is omitted. (1) A frequency shifter (AOFS 27a and ultrasonic generator 27b) is not provided in the second optical path of the Michelson interferometer 40. (2) The light receiver 8, the light receiver 9, and the light receiver 18 receive the measurement interference light, the first reference interference light, and the second reference interference light from the wavelength demultiplexing means 17, respectively, and perform photoelectric conversion (homodyne detection). The measurement interference signal, the first reference interference signal, and the second reference interference signal are output.

[Seventh Embodiment]
FIG. 7 shows the configuration of the optical interference type phase detector of the seventh embodiment of the present invention. In the fifth embodiment shown in FIG. 5, the wavelength-phase characteristic of the DUT 10 includes phase fluctuations caused by relative optical path length fluctuations between the two optical paths of the Michelson interferometer 40. In order to avoid this, the phase of the measurement phase is corrected based on the reference phase as described above, but in the seventh embodiment, the two optical paths of the Michelson interferometer 40 are based on the reference phase. The relative optical path length is controlled so as not to change. This embodiment is different from FIG. 5 of the fifth embodiment except for the following (1) and (2). (1) The optical path length varying means 15 is provided in the second optical path of the Michelson interferometer 40, and the optical path length correcting means 22 for controlling the optical path length varying means 15 is also provided. The optical path length varying means 15 may be provided in the first optical path. (2) The signal processing means 23 is not provided. Therefore, the description of the same part as FIG. 5 is omitted, and the optical path length varying means 15 and the optical path length correcting means 22 will be mainly described.

The optical path length varying means 15 is, for example, an optical delay device. Based on a control signal from the optical path length correcting means 22, the optical path length varying means 15 is output from the optical coupler 25, reflected by the reflecting means 26, and returned to the optical coupler 25 again. Delay the light. In other words, the optical path length varying means 15 equivalently changes the relative optical path length between the two optical paths of the Michelson interferometer 40. The optical path length correction unit 24 receives the reference phase from the second phase detection unit 22 and sets the optical path length variable unit 15 so that the reference phase is constant at a predetermined value over a predetermined wavelength range of the measurement light. A control signal for control is generated based on this reference phase and output to the optical path length varying means 15. That is, the phase change Δθ _r in the above equation (3) is controlled so as to approach zero as much as possible, so that the relative optical path length change ΔL between the two optical paths approaches zero as much as possible. As a result, the phase change Δθ in the above equation (5) approaches zero as much as possible. Accordingly, the measured object 10 detected by the first phase detection means 21 does not include the phase fluctuation caused by the relative optical path length fluctuation between the two optical paths of the Michelson interferometer 40. The wavelength-phase characteristics can be obtained.

[Eighth Embodiment]
FIG. 8 shows the configuration of an optical interference type phase detector according to the eighth embodiment of the present invention. In the seventh embodiment shown in FIG. 7, an optical heterodyne interferometer Michelson interferometer 40 is used as an interferometer. In the eighth embodiment, an optical homodyne interferometer Michelson interferometer 40 is used. ing. This embodiment is different from FIG. 7 of the seventh embodiment except for the following (1) and (2). Therefore, detailed description is omitted. (1) A frequency shifter (AOFS 27a and ultrasonic generator 27b) is not provided in the second optical path of the Michelson interferometer 40. (2) The light receiver 8, the light receiver 9, and the light receiver 18 receive the measurement interference light, the first reference interference light, and the second reference interference light from the wavelength demultiplexing means 17, respectively, and perform photoelectric conversion (homodyne detection). The measurement interference signal, the first reference interference signal, and the second reference interference signal are output.

  1 to 4 of the first to fourth embodiments described above, the light that is multiplexed by combining the combined light output from the optical coupler 13b and the measurement light output from the wavelength tunable light source 1 is wavelength-multiplexed. The coupler 13a and the optical coupler 16 that demultiplexes the wavelength multiplexed light input from the optical coupler 13a into two lights are functionally distinguished from each other, and each is constituted by another optical coupler. It is obvious that a coupler can also be used.

The optical heterodyne interferometer type Mach-Zehnder interferometer 30 of the first and third embodiments described above may be one shown in FIGS. 9 to 12 in addition to those shown in FIGS. 9 to 12 show a Mach-Zehnder interferometer 30 corresponding to the third embodiment. Therefore, in order to correspond to the first embodiment, the optical path length varying means 15 for the second optical path may be omitted. Further, the frequencies shown in FIGS. 9 to 12 indicate the frequency ν _s of the measurement light included in the wavelength multiplexed light.

In other words, in FIG. 9, the AOFS 14a demultiplexes the input wavelength multiplexed light into two lights, one of the lights into the first optical path to which the DUT 10 is connected, and the other light. The frequency of the ultrasonic wave input from the ultrasonic generator 14b is shifted by ₁ and output to the second optical path to which the optical path length varying means 15 is connected. Then, the optical coupler 6 combines the light of the first optical path that has passed through the DUT 10 and the light of the second optical path that has passed through the optical path length varying unit 15 to output interference light. In this case, the beat frequency is _{f 1.} In this configuration, the AOFS 14a and the ultrasonic generator 14b serve as an optical demultiplexing unit and a frequency shifter.

In FIG. 10, the optical coupler 16 demultiplexes the input wavelength multiplexed light into two lights, and outputs one light to the AOFS 14e and the other light to the AOFS 14c. AOFS14e is output to the first optical path measurement object 10 with the frequency f ₁ minute shift of the ultrasonic wave entered one of the light above the ultrasonic generator 14f is connected, also AOFS14c above other optical Is shifted by the frequency f2 of the ultrasonic wave input from the ultrasonic generator 14d and output to the _second optical path to which the optical path length varying means 15 is connected. Then, the optical coupler 6 combines the light of the first optical path that has passed through the DUT 10 and the light of the second optical path that has passed through the optical path length varying unit 15 to output interference light. In this case, the beat frequency is f ₁ −f ₂ . In this configuration, since the AOFS 14c and the AOFS 14e are arranged in parallel, the phase characteristics (wavelength dispersion) generated by the two AOFSs can be canceled.

In FIG. 11, the AOFS 14a and the AOFS 14c are arranged in series. First, the AOFS 14a demultiplexes the input wavelength multiplexed light into two lights, one of the lights into the first optical path to which the device under test 10 is connected, and the other light into the ultrasonic generator 14b. The frequency of the ultrasonic wave input from _{1 is} shifted by ₁ (giving + _1st order diffraction) and output to the AOFS 14c. Then, AOFS14c is the optical path length changing means 15 light (giving -1 order diffraction) ultrasound frequency _{f 2} min shift inputted from the ultrasonic generator 14d to from AOFS14a is connected 2 to the optical path. Then, the optical coupler 6 combines the light of the first optical path that has passed through the DUT 10 and the light of the second optical path that has passed through the optical path length varying unit 15 to output interference light. In this case, the beat frequency is f ₁ −f ₂ . In this configuration, the AOFS 14a and the ultrasonic generator 14b serve as an optical demultiplexing unit and a frequency shifter.

In FIG. 12, similarly to FIG. 11, the AOFS 14a and the AOFS 14c are arranged in series. First, the AOFS 14a demultiplexes the input wavelength multiplexed light into two lights, and shifts one light to the AOFS 14c and the other light to the frequency f _{1 of the} ultrasonic wave input from the ultrasonic generator 14b. And output to the first optical path to which the DUT 10 is connected. Next, the AOFS 14c shifts the light from the AOFS 14a by the frequency f2 of the ultrasonic wave input from the ultrasonic generator 14d, and outputs it to the _second optical path to which the optical path length varying means 15 is connected. Then, the optical coupler 6 combines the light of the first optical path that has passed through the DUT 10 and the light of the second optical path that has passed through the optical path length varying unit 15 to output interference light. In this case, the beat frequency is f ₁ −f ₂ . In this configuration, the AOFS 14a and the ultrasonic generator 14b serve as an optical demultiplexing unit and a frequency shifter.

[Ninth Embodiment]
FIG. 14 shows the configuration of an optical interference type phase detector according to the ninth embodiment of the present invention. FIG. 1 of the first embodiment described above differs from the two optical paths (first and second) of the Mach-Zehnder interferometer 30 between the AOFS 14 e and the optical coupler 6 in the second optical path of the Mach-Zehnder interferometer 30. The only difference is that a delay device 5 for adjusting the optical path length of the optical path) is provided. Therefore, detailed description is omitted. The delay device 5 may be provided in the first optical path to which the device under test 10 is connected instead of the second optical path.

[Tenth embodiment]
FIG. 15 shows the configuration of the optical interference type phase detector of the tenth embodiment of the present invention. The optical circulator 28 is provided between the optical coupler 16 and the optical coupler 6 in the first optical path of the Mach-Zehnder interferometer 30, and the optical coupler is interposed via the optical circulator 28. The only difference is that light from 16 is input to the object to be measured 10 and light reflected and returned by the object to be measured 10 is output to the optical coupler 6. Therefore, detailed description is omitted.

The figure which shows the structure of 1st Embodiment of this invention. The figure which shows the structure of 2nd Embodiment of this invention. The figure which shows the structure of 3rd Embodiment of this invention. The figure which shows the structure of 4th Embodiment of this invention. The figure which shows the structure of 5th Embodiment of this invention. The figure which shows the structure of 6th Embodiment of this invention. The figure which shows the structure of 7th Embodiment of this invention. The figure which shows the structure of 8th Embodiment of this invention. Diagram showing another configuration of Mach-Zehnder interferometer Diagram showing another configuration of Mach-Zehnder interferometer Diagram showing another configuration of Mach-Zehnder interferometer Diagram showing another configuration of Mach-Zehnder interferometer The figure which shows schematic structure of a prior art example The figure which shows the structure of 9th Embodiment of this invention. The figure which shows the structure of 10th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wavelength variable light source, 2, 12 ... Light source, 3, 6, 13a, 13b, 16, 25 ... Optical coupler, 4a, 14a, 14c, 14e, 27a ... Acousto-optic frequency shifter ( AOFS), 4b, 14b, 14d, 14f, 27b ... ultrasonic wave generator, 5 ... delay device, 7 ... wavelength demultiplexer, 8, 9, 18 ... light receiver (PD), DESCRIPTION OF SYMBOLS 10 ... Measured object, 11 ... Phase detector, 13 ... Optical multiplexing means, 15 ... Optical path length variable means, 17 ... Wavelength demultiplexing means, 20, 30 ... Mach-Zehnder type Interferometer, 21, 22 ... Phase detecting means, 23 ... Signal processing means, 24 ... Optical path length correcting means, 26 ... Reflecting means, 28 ... Optical circulator, 40 ... Michelson Type interferometer.

Claims (7)

A wavelength tunable light source (1) that outputs measurement light in a predetermined wavelength range;
A first light source (2) for outputting a first reference light having a fixed wavelength different from the wavelength of the measurement light;
A second light source (12) for outputting a second reference light having a fixed wavelength different from the wavelength of the measurement light and the wavelength of the first reference light;
Optical multiplexing means (13) for receiving and multiplexing the measurement light, the first reference light, and the second reference light, and outputting the wavelength multiplexed light obtained thereby;
A first optical path to which the object to be measured is connected and a second optical path to which the object to be measured is not connected; the first light that receives the wavelength multiplexed light and passes through the first optical path; Demultiplexing into the second light passing through the second optical path and combining the first light passing through the first optical path and the second light passing through the second optical path; An interferometer (30, 40) for outputting the interference light obtained by
Wavelength demultiplexing means (17) that receives the interference light and demultiplexes the measurement light, the first reference light, and the second reference light into wavelength components;
A first light receiver (8) that receives measurement interference light related to the wavelength component of the measurement light output from the wavelength demultiplexing means, photoelectrically converts the measurement interference light, and outputs a measurement interference signal;
A second light receiver (9) that receives and photoelectrically converts the first reference interference light related to the wavelength component of the first reference light output from the wavelength demultiplexing means, and outputs a first reference interference signal; ,
A third light receiver (18) that receives and photoelectrically converts the second reference interference light related to the wavelength component of the second reference light output from the wavelength demultiplexing means and outputs a second reference interference signal; ,
Receiving the measurement interference signal and the reference interference signal of one of the first reference interference signal and the second reference interference signal, the phase of the measurement interference signal with respect to the reference interference signal is detected and the measurement phase First phase detection means (21) for outputting as
Second phase detection means (22) for receiving the first reference interference signal and the second reference interference signal, detecting a phase generated between the two reference interference signals, and outputting the detected phase as a reference phase; A wavelength-phase characteristic of the object to be measured is obtained based on the measurement phase by using a phase change of the reference phase.   While inputting the measurement phase and the reference phase, a phase correction value for performing phase correction of the measurement phase based on a phase change of the reference phase is obtained in association with the wavelength of the measurement light, and the obtained phase 2. The optical interference type phase detection device according to claim 1, further comprising signal processing means (23) for performing phase correction of the measurement phase based on a correction value. An optical path length varying means (15) that is provided on one of the two optical paths of the interferometer and changes a relative optical path length between the two optical paths;
Optical path length correction means (24) for inputting the reference phase and generating and outputting a control signal for controlling the optical path length variable means based on the reference phase so that the reference phase becomes constant at a predetermined value. The optical interference type phase detection device according to claim 1, comprising: The interferometer includes at least one frequency shifter (14a to 14f, 27a, 27b) in at least one of the first optical path and the second optical path, and passes through the first optical path. Each frequency of the measurement light, the first reference light, and the second reference light included in the first light, and the second light that has passed through the second optical path are included in the second light. With respect to the respective frequencies of the measurement light, the first reference light, and the second reference light, there are respective frequency differences between the measurement light, the first reference light, and the second reference light. An optical heterodyne interferometer configured to have a predetermined beat frequency;
The first receiver outputs the measurement interference signal of the predetermined beat frequency;
The second optical receiver outputs the first reference interference signal having the predetermined beat frequency;
The optical interference type phase detector according to any one of claims 1 to 3, wherein the third light receiver outputs the second reference interference signal having the predetermined beat frequency.   4. The optical interference type phase detector according to claim 1, wherein the interferometer is an optical homodyne interferometer. The interferometer is
Optical demultiplexing means (16, 14a, 14b) for receiving the wavelength-multiplexed light and demultiplexing the first light passing through the first optical path and the second light passing through the second optical path;
A first optical coupler that outputs the interference light by combining the first light input through the device under test and the second light input without passing through the device under test; 6) A Mach-Zehnder interferometer including the optical interference type phase detection device according to any one of claims 1 to 5. The interferometer is
The wavelength multiplexed light is received and demultiplexed into the first light passing through the first optical path and the second light passing through the second optical path, and returned by being reflected by the object to be measured. A second optical coupler (25) that combines the first light and the second light reflected by the reflecting means (26) without passing through the object to be measured and outputs the interference light. The optical interference type phase detection device according to claim 1, wherein the optical interference type phase detection device is a Michelson interferometer configured to include:

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