JP3369538B2 - Optical polarization characteristic measuring device and its measuring method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical polarization characteristic measuring device and a measuring method for measuring the polarization characteristic of light.

[0002]

2. Description of the Related Art Conventionally, for measuring the polarization characteristics of light, an analyzer and a phase shifter are combined to measure the polarization rotation angle and the rotation direction from the rotation angle of the analyzer and the phase between orthogonal polarizations by the phase shifter. There is a method, but the detection of the rotation angle is 10 ^-4 to 10
^-5 (rad) is the limit.

A homodyne detection method as a method for detecting extremely weak light (Japanese Patent Application Laid-Open No. 10-3096 proposed by the present inventors).
5). The homodyne detection method measures an AC signal generated by modulating the optical path difference of an interferometer.

[0004]

However, since the interferometer has a phase change due to the fluctuation of the optical path difference, this fluctuation is converted into the fluctuation of the frequency and the phase of the AC signal to stably measure the phase characteristic. I can't. Therefore, there is a method of generating a modulated signal of the optical path difference of an interferometer by self-sustained pulsation (Japanese Patent Laid-Open No. 11-101694 proposed by the present inventors). However, even with this method, since the interferometer is not stabilized, the AC signal is unstable and cannot be used as a reference signal for phase synchronization detection.

In view of the above situation, the present invention stabilizes a homodyne interferometer by negative feedback control by using a homodyne detection method capable of detecting extremely weak light, and also refers to a phase synchronization detection necessary for phase detection. It is an object of the present invention to provide an optical polarization characteristic measuring device and a measuring method thereof, which can generate a signal by self-excited oscillation of negative feedback control to measure highly sensitive and highly stable polarization characteristic of light.

[0006]

In order to achieve the above object, the present invention provides: [1] means for adjusting the polarization state of output light of a light source (1) in an optical polarization characteristic measuring device; A first optical branching device (3) for branching the output light into orthogonal polarizations, and a sample to be measured (6) arranged in one of the optical paths of the output of the first optical branching device (3). And the first optical branching device (3)
Disposed on the other of the optical path of the output of a linear by adjusting the polarization state
A slight cross polarization component is generated to generate a reference signal for phase synchronization detection.
The resulting Ru means the issue light (5), said first optical splitter (3) either one of means for modulating the optical path difference between the output of the (8),
An optical multiplexer (9) for multiplexing the two output lights of the first optical splitter (3) and a second and a second for splitting the two output lights of the optical multiplexer (9) into orthogonal polarizations, respectively. A third optical branching device (10, 11) and an optical detector (12, 13, 14, 15) for respectively detecting the two output lights of the second and third optical branching devices (10, 11). Of the outputs of the optical detectors (12, 13, 14, 15), the first and second detection signals of the same polarization component of the output light of the second and third optical branching devices (10, 11) are connected. Second differential amplifier (1
6, 17) and means (18) for detecting the amplitude and phase difference between the two output AC signals of the first and second differential amplifiers (16, 17).

[2] In the optical polarization characteristic measuring device according to the above [1] , output signals of the differential amplifiers (16, 17)
Either branches the one issue or receive, filter the output signal to pass (19), the filter and means for amplifying (20) the output signal (19) is arranged, means for amplifying this
The output signal of (20) is supplied to the means (8) for modulating the optical path difference.
It is characterized by connecting .

[3] In the optical polarization characteristic measuring device, means for adjusting the polarization state of the output light of the light source (1), a first optical branching device (3) for branching the output light into orthogonal polarizations,
A sample to be measured (6) arranged in one of the optical paths of the output of the first optical branching device (3) and the other optical path of the output of the first optical branching device (3) , Adjust polarization state
Then, a small amount of orthogonal polarization component is generated to detect the phase synchronization.
The resulting Ru means a reference signal light (5), the first optical splitter and either means for modulating the optical path difference between the output of (3) (8), said first optical splitter (3) Optical multiplexer (9) for multiplexing the two output lights of the above, and second and third optical splitters (10, 11) for splitting the two output lights of the optical multiplexer (9) into orthogonal polarizations. ), An optical detector (12, 13, 14, 15) for respectively detecting the two output lights of the second and third optical branching devices (10, 11), and these detectors (12, 13). , 14, 15), first and second differential amplifiers (16, 17) connecting detection signals of the same polarization component of the output light of the second and third optical branching devices (10, 11). ) And means for detecting the amplitude and phase difference between the two output AC signals of the first and second differential amplifiers (16, 17). 18) and arranged, the light source (1)
Output light is split into orthogonal polarized light by the first optical branching device (3), and either the polarized light rotating component or the polarized light non-rotating component generated in the measured sample (6) arranged in either one of It is characterized in that one optical path difference is modulated, homodyne detection is performed separately for the two orthogonal polarization components, and the amplitude and phase of the polarization rotation component of the AC signal generated by the modulation of the optical path difference are measured.

[4] In the optical polarization characteristic measuring method described in [3] above, a filter (19) for branching one of the connected output signals and passing the output signal.
And an amplifier (20) for amplifying the output signal of the filter (19), and the output signal of the amplifier (20) is connected to the means (8) for modulating the optical path difference for negative feedback control. at the same time, characterized by generating an AC signal modulating the optical path difference in self-oscillation state.

[5] The optical polarization characteristic measuring method described in [4] is characterized in that the frequency of the AC signal generated by self-excited oscillation is the self-resonant frequency of the means for modulating the optical path difference.

[6] In the optical polarization characteristic measuring device, means (2) for adjusting the polarization state of the output light of the light source (1) and a first optical branching device (3) for branching the output light into orthogonal polarizations. ), A sample to be measured (6) placed in one of the optical paths of the output of the first optical branching device (3), and the first sample.
Disposed in the other of the optical path of the output of the optical splitter (3), polarization
Adjust the state to slightly generate orthogonal polarization components and
The optical reference signal for the period detecting the resulting Ru means (5), and means (21, 22) for shifting the frequency of light in the first optical splitter (3) either one of the optical path of the output of the Optical multiplexer (9) for multiplexing the two output lights of the first optical branching device (3)
And second and third optical splitters (10, 10) for splitting the two output lights of the optical multiplexer (9) into orthogonal polarizations.
11) and these second and third optical branching devices (10,
11) An optical detector (1 for detecting each of the two output lights)
2, 13, 14, 15) and these optical detectors (12,
Of the outputs of 13, 14, 15), first and second differential amplifiers (16, 16) for connecting the detection signals of the same polarization component of the output light of the second and third optical branching devices (10, 11) 17)
And these first and second differential amplifiers (16, 1
7) Means (23, 24, 25) for detecting the quadrature phase amplitude of the two output high frequency signals.

[7] In the optical polarization characteristic measuring method, means for adjusting the polarization state of the output light of the light source (1), a first optical branching device (3) for branching the output light into orthogonal polarizations,
A sample to be measured (6) arranged in one of the optical paths of the output of the first optical branching device (3) and the other optical path of the output of the first optical branching device (3) , Adjust polarization state
Then, a small amount of orthogonal polarization component is generated to detect the phase synchronization.
The resulting Ru means a reference signal light (5), and means (21, 22) for shifting the frequency of light in the first optical splitter (3) either one of the optical path of the output of said first light An optical multiplexer (9) for multiplexing the two output lights of the splitter (3), and second and third optical branches for splitting the two output lights of the optical multiplexer (9) into orthogonal polarizations. Bowl (10, 11)
And these second and third optical branching devices (10, 11)
Optical detectors (12, 1) that detect the two output lights of
3, 14, 15) and these optical detectors (12, 13,
First and second differential amplifiers (16, 17) for connecting detection signals of the same polarization component of the output light of the second and third optical branching devices (10, 11) among the outputs of (14, 15) When,
The means (23, 24, 25) for detecting the amplitude and the quadrature phase amplitude of the two output high frequency signals of the first and second differential amplifiers (16, 17) are arranged, and the output of the light source (1) is arranged. After the light is branched into the orthogonal polarized light by the first optical branching device (3), the polarized light rotation component and the polarized light non-rotation component generated in the measured sample (6) arranged in either one of It is characterized in that the frequency of the light in the optical path is shifted, the two orthogonal polarization components are separately subjected to heterodyne detection, and the polarization rotation component of the high frequency signal of the difference frequency generated by shifting the frequency of the light is measured. .

With the above configuration, in measuring the polarization characteristics of light, the optical path difference of the homodyne interferometer is modulated and orthogonal polarization components are homodyne-detected, and the AC signal generated by the modulation of the optical path difference is detected. By performing the phase synchronization detection between the two, it is possible to measure the phase between the orthogonal polarizations of the polarization rotation component and the polarization non-rotation component with high sensitivity.

Further, in order to stabilize the interferometer by using the negative feedback control and forcibly bring it into the self-excited oscillation state to generate the modulated signal of the optical path difference, the frequency and the phase are used as the reference signals for the phase synchronization detection. However, a stable AC signal can be obtained.

When the frequency of the self-excited oscillation is set to the self-resonant frequency of the means for modulating the optical path difference, this self-resonant frequency is determined by the electrical characteristics and the mechanical structure of the means for modulating the optical path difference, and thus it is negative. An AC signal whose frequency and amplitude are more stable than that of self-excited oscillation determined by a filter used for feedback control can be obtained.

Since this interferometer is of the homodyne detection type, the intensity of the signal light on the other optical path can be made extremely small by using a sufficient amount of light as the local oscillation light on one optical path, and it is highly sensitive. It is possible to measure the phase characteristic at the same time as measuring the amplitude characteristic. Further, the photodetector used here has a sufficient bandwidth for detecting an AC signal generated when the optical path difference is modulated, and does not require wideband characteristics.

When the frequency of the light is shifted and the heterodyne detection is performed instead of modulating the optical path difference, the phases of the high-frequency signals of the polarization rotation component and the polarization non-rotation component are subjected to the same fluctuations of the interferometer and are therefore completely synchronized. is doing. This has the advantage that the interferometer does not need to be stabilized by negative feedback control, etc., and has the advantage of simplifying the configuration of the interferometer.Since the heterodyne gain by heterodyne detection can be obtained in the same way as homodyne detection, high sensitivity can be achieved. Can be achieved.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, a first embodiment of the present invention will be described.

FIG. 1 is a block diagram of an optical polarization characteristic measuring apparatus showing a first embodiment of the present invention.

As shown in this figure, the optical polarization measuring device is
Light source 1, wave plate 2, first optical branching device 3, mirror 4, wave plate 5, sample to be measured 6, optical path difference modulation signal generator 7, optical path difference modulation mirror 8, optical multiplexer 9, second Optical splitter 10,
Third optical branching device 11, optical detectors 12, 13, 14, 1
5, differential amplifiers 16 and 17, and a phase detector 18.

Here, the wave plate 2 serves as means for adjusting the polarization state of the output light of the light source 1, the wave plate 5 serves as means for adjusting the polarization state, and the optical path difference modulation signal generator 7 and the optical path difference modulation mirror are provided. Reference numeral 8 is a means for modulating the optical path difference.
3 and the differential amplifier 16, and the photodetectors 14 and 15 and the differential amplifier 17 correspond to the photodetection means, and the phase detector 18 corresponds to the means for measuring the phase difference.

The first optical branching device 3, the second optical branching device 10 and the third optical branching device 11 are for branching into polarized light beams orthogonal to each other, and the polarizing prism, the polarizing beam splitter and the optical multiplexer 9 are It combines two orthogonal polarizations at the same time, and a half mirror, a non-polarization beam splitter, an optical directional coupler, etc. can be used. It is sufficient for the optical path difference modulation mirror 8 to be capable of vibrating about several times the light wavelength, and a piezo element to which an optical mirror is attached can be used.

Further, this action is to continuously change the phase of light, and any action may be used as long as an equivalent phase change can be obtained.

There is also a method of using one photodetector as the photodetector for the outputs of the second optical branching device 10 and the third optical branching device 11, but as shown in this embodiment, two optical detecting devices are used. The optical detectors 12 and 13, the differential amplifier 16, and the optical detectors 14,
In the balanced detection configuration using the combination of 15 and the differential amplifier 17, the amplitude noise of the output light of the light source is suppressed and the noise of the measurement system becomes the shot noise level.
It is clear that the N ratio is improved and the sensitivity becomes higher.

In FIG. 1, the output light from the light source 1 is adjusted in polarization state by the wave plate 2 and is split into two orthogonal polarizations by the first optical splitter 3. For the sake of convenience, the polarized light passing through the first optical branching device 3 will be referred to as P-polarized light (P-wave), and the reflected polarized light will be referred to as S-polarized light (S-wave). Of these, the P wave is reflected by the mirror 4 as local oscillation light of homodyne detection,
And is guided to the optical multiplexer 9.

In the wave plate 5, the polarization state is adjusted to slightly generate the S-polarized component, and the reference signal light for phase synchronization detection is produced. The S wave branched by the first optical branching device 3 is polarized as a probe light by the sample 6 to be measured, and a P wave component is generated. The polarization rotation component of the P wave and the polarization non-rotation component of the S wave (local light emission of the reference signal for phase synchronization detection) are operated by the AC signal generated by the optical path difference modulation signal generator 7, and the optical path difference modulation mirror 8 is operated. Is reflected by and is guided to the optical multiplexer 9.

The P wave component and the S wave component of the local light branched by the first optical branching device 3 and the P wave component and the S wave component of the probe light are simultaneously multiplexed by the optical multiplexer 9. The output light of the optical multiplexer 9 is branched into a P wave component and an S wave component which are orthogonal to each other by the second and third optical branching devices 10 and 11, respectively.

The P-wave component of the local oscillation light branched by the second and third optical branching devices 10 and 11 and the P-wave component generated by the polarization rotation of the sample 6 to be measured are photodetectors as signal light. 1
2 and 13, the AC signal component generated by the modulation of the optical path difference is amplified by the differential amplifier 16, and the phase detector 18
Lead to the measurement signal terminal of.

The polarization non-rotating component of the S wave of the probe light branched by the second and third optical branching devices 10 and 11 and the wave plate 5.
The S wave component generated in 1 is used as a reference light for the photodetectors 14 and 1
The AC signal component detected by 5 and amplified by the optical path difference modulation by the differential amplifier 17 is amplified and guided to the reference signal terminal of the phase detector 18, and the amplitude and phase difference of the signal light component are measured.

Next, a method for measuring the phase characteristics of the sample to be measured will be described using the first embodiment. (1) The polarization state is adjusted by the wave plate 2. (2) The first optical splitter 3 splits the P-polarized light and the S-polarized light orthogonal to each other. (3) The transmitted light or the reflected light from the sample 6 to be measured installed on the S-polarized side has its optical path difference modulated by the optical path difference modulation mirror 8, and is combined with the local light component by the optical multiplexer 9. (4) The respective output lights of the optical multiplexer are supplied to the second optical branching device 1
The 0 and third optical splitters 11 split the light into P-polarized light and S-polarized light. (5) The two AC signals resulting from the modulation of the optical path difference after photodetection are P-waves, which are polarization rotation components generated in the DUT 6, using the S wave component of the polarization non-rotation component in the phase detector 18 as a reference signal. Find the amplitude and phase difference of the components.

Next, a second embodiment of the present invention will be described.

FIG. 2 is a block diagram of an optical polarization characteristic measuring apparatus showing a second embodiment of the present invention. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

The feature of this embodiment is that the DC fluctuation component of the reference signal generated by detecting the S-polarized component is branched, passed through the filter 19, amplified by the amplifier 20, and then the optical path difference modulation mirror 8 is set. It is driven to perform negative feedback control. With such a configuration, since the DC fluctuation component of the reference signal is the fluctuation component of the homodyne interferometer, the homodyne interferometer is stabilized by performing negative feedback control with this signal. Furthermore, by changing the frequency characteristics of the amplitude and phase of the filter 19, it is possible to bring the amplifier 20 into the self-excited oscillation state when the gain of the amplifier 20 is increased.

Here, the filter 19 used in the second embodiment will be described.

The filter used for the negative feedback control is called a lag lead filter, and FIG. 3 shows an example of frequency characteristics. The lag-lead filter used for general negative feedback control is designed to have a phase characteristic of 180 degrees or less so that the self-excited oscillation state does not occur even if the gain of the amplifier is increased (dotted line characteristic in FIG. 3).

This is because if the negative feedback control oscillates by self-excitation, the amplifier is saturated by the oscillation signal, the gain of the amplifier decreases, and control becomes impossible.

However, in this embodiment, the amplitude of the AC voltage of the self-excited oscillation that drives the optical path difference modulation mirror 8 even if the negative feedback control oscillates is a voltage change that changes the optical path difference by a half wavelength. And no more and no less.
If the maximum output amplitude of the amplifier is sufficiently larger than this half-wave voltage, the amplifier will not saturate.

Therefore, the phase characteristic of the lag-lead filter is set to 180 degrees or more as shown by the broken line in FIG. 3 so that self-excited oscillation can be easily performed, and at the same time, stabilization by wide-band negative feedback control in the low frequency region is achieved. It will be possible.

Here, if the phase characteristic of the filter is designed to be 180 degrees or less (dotted line characteristic of FIG. 3) and the gain of the negative feedback is increased, the negative feedback circuit has a self-resonant frequency independent of the characteristic of the filter. Oscillate. This self-resonant frequency is very stable because it is mainly determined by the electrical characteristics and mechanical structure of the means for modulating the optical path difference.

Further, the fact that the gain of the negative feedback can be increased greatly stabilizes the negative feedback, and the bandwidth of the negative feedback can be widened, so that the higher speed fluctuation can be stabilized.

The optimum condition is 1: 1 for the splitting ratio for splitting into the P-polarized light and the S-polarized light which are orthogonal to each other in the first optical branching device 3. Therefore, since the unnecessary S-polarized component remaining after the S-wave probe light has generated the P-wave in the DUT 6 is used as the local light when detecting the reference light, the S-wave generated by the wave plate 5 is used. The wave component is extremely small, which is good. This makes it possible to reduce the loss of the P-wave component of the local light when detecting the P-wave component which is the signal light, and enables highly efficient and highly sensitive measurement of the polarization characteristic.

The detection limit of the optical path difference modulation type homodyne detection is 10 aW (10 ^-17 w) by direct measurement without phase synchronization detection at a wavelength of 800 nm and a local light emission power of 5 mW.
(See Japanese Patent Laid-Open No. 10-30965). Now
If the S-wave probe light is rotated by an angle θ (rad) in the measured sample, the relationship between the power P of the P-wave component generated by this rotation and the probe light power S is

[0044]

[Equation 1]

It becomes Here, the probe optical power S is 1 mW
(10 ^-3 W), the detection limit rotation angle is 10
^It becomes ^-7 (rad), which is 2-3 orders of magnitude more sensitive than the conventional measurement method. Further, if phase synchronization detection is performed, it becomes possible to measure the rotation angle and phase with higher sensitivity.

Next, a third embodiment of the present invention will be described.

FIG. 4 is a block diagram of an optical polarization characteristic measuring apparatus according to the third embodiment of the present invention. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

The feature of this embodiment is that the frequency of the light constituted by the high frequency signal generator 21 and the acousto-optic modulator 22 is shifted instead of the means 7, 8 for modulating one of the optical path differences in FIG. And two detectors 23 and 24 for detecting the high frequency signal after the heterodyne detection in quadrature phase
And a means for detecting the quadrature phase amplitude, which is composed of a branching device 25 for branching the reference signal with a phase difference of 90 degrees.

The frequency of the light passing through the acousto-optic modulator 22 operating with the output signal of the oscillation frequency fs of the high frequency signal generator 21 is shifted by fs. When this frequency-shifted light is combined with the local oscillation light of the source oscillation light and heterodyne detection is performed, the frequency of the measurement signal component and the reference signal component that is the polarization non-rotation component generated by the polarization rotation in the sample 6 to be measured. Is equal to the oscillating frequency fs of the high frequency signal generator 21, but its phase greatly changes due to the influence of the fluctuation of the interferometer.

For this reason, in general, the phase synchronization control PP for detecting the phase fluctuation and negatively feeding it back to the high frequency signal generator 21.
L is used. However, the measurement signal component and the reference signal component are subject to the same fluctuations and their phases are perfectly synchronized, so that PPL control is not required. Therefore, if homodyne detection is performed with two quadrature phase detectors that split the measurement signal into two and the reference signal is split with a phase difference of 90 degrees, the measurement signal with high sensitivity can be obtained without being affected by the fluctuation of the interferometer. Amplitude and phase can be obtained.

Now, the phase of the reference signal input to the detector 23 is 0 degrees, and the phase of the reference signal input to the detector 24 is 90 degrees.
The output signal X of the detector 23 is Si of the measurement signal.
The output signal Y of the detector 24 is the cos
Become an ingredient. Therefore, the amplitude R and phase θ of the measurement signal
Is

[0052]

[Equation 2]

It becomes

As described above, the phases of the measurement signal and the reference signal after the heterodyne detection are completely synchronized because they are subjected to the same fluctuation of the interferometer. This has the advantage that the interferometer does not need to be stabilized by negative feedback control or the like, the structure of the interferometer is simplified and adjustment is easy, and PLL control is not required. Furthermore, since the heterodyne gain obtained by the heterodyne detection is obtained similarly to the homodyne detection, high sensitivity can be achieved.

In the first, second and third embodiments, the configuration of the Mach-Zehnder interferometer is shown, but the similar operation can be performed by the configuration of Michelson interferometer. Furthermore, it is possible to use a component using an optical fiber as the component.

Although a method of using P-polarized light for the signal light and S-polarized light for the reference light has been described here, it is also possible to use a combination of the opposite polarized light or circularly polarized light that rotates to the right or left.

The present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0058]

As described in detail above, according to the present invention, the following effects can be achieved.

(A) The light of the light source is split into orthogonal polarizations by the optical splitter, and the polarization rotation component generated by irradiating one output light on the sample to be measured is locally emitted by the other output light of the optical splitter. Then, the light is multiplexed by an optical multiplexer and homodyne detection is performed to obtain a signal component.
In addition, the polarization non-rotation component of the incident light that irradiates the sample to be measured is used as local light, and the orthogonal polarization component obtained by slightly rotating the polarization direction of the other output light of the optical splitter with the wave plate is homodyne-detected for synchronous detection. Reference signal. At this time, since the output signal of each homodyne interferometer is an AC signal generated by modulating the optical path difference with a mirror that oscillates, the amplitude and phase of the AC signal due to this polarization rotation are synchronously detected, and Since the rotation angle and the direction of the polarized light in the sample are measured, the homodyne detection method is used, so that the sensitivity is very high and the amplitude characteristic and the phase characteristic of the polarized light can be simultaneously measured.

(B) The homodyne interferometer is stabilized by performing negative feedback control using the DC fluctuation component of the reference signal for synchronous detection, and self-oscillation is forcibly performed to generate an AC signal for optical path difference modulation. To generate, a stable phase lock detection reference signal is obtained.

(C) By making the oscillation frequency of self-excited oscillation the self-resonance frequency determined by the electrical characteristics and the mechanical structure of the means for modulating the optical path difference, more stable measurement becomes possible.

(D) In the heterodyne detection using the optical frequency shifter, the high-frequency signals of the polarization rotation component and the polarization non-rotation component are subjected to the same variation of the interferometer, and therefore their phases are completely synchronized. There is. As a result, it is not necessary to stabilize the interferometer by negative feedback control or the like and PLL control, the configuration is simplified and adjustment is facilitated, and high sensitivity can be achieved by the heterodyne gain.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical polarization characteristic measuring apparatus showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical polarization characteristic measuring device showing a second embodiment of the present invention.

FIG. 3 is a diagram showing frequency characteristics of a filter used in the present invention.

FIG. 4 is a configuration diagram of an optical polarization characteristic measuring apparatus showing a third embodiment of the present invention.

[Explanation of symbols]

1 light source 2,5 wavelength plate 3 First optical splitter 4 mirror 6 sample to be measured 7 Optical path difference modulation signal generator 8 Optical path difference modulation mirror 9 Optical multiplexer 10 Second optical splitter 11 Third optical splitter 12, 13, 14, 15 Optical detector 16,17 Differential amplifier 18 Phase detector 19 Filter 20 amplifier 21 High frequency signal generator 22 Acousto-optic modulator (frequency shifter) 23, 24 Detector 25 Splitter with a phase difference of 90 degrees

─────────────────────────────────────────────────── ─── Continued Front Page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01J 3/00-3/453 G01J 4/00-4/04 G01J 9/00-9/04 G01M 11 / 00-11/02 G01N 21/00-21/01 G01N 21/16-21/61 G01B 9/02

Claims (7)

(57) [Claims] 1. (a) means for adjusting the polarization state of output light from a light source; (b) a first optical branching device for branching the output light into orthogonal polarizations; and (c) the first light. A sample to be measured, which is placed in one of the optical paths of the output of the branching device, and (d) which is placed in the other optical path of the output of the first optical branching device, and adjusts the polarization state to reduce the orthogonal polarization component Caused to
And give Ru means optical reference signal for phase synchronization detecting Te, (e) said first means for modulating one of the optical path difference either output of the optical splitter, (f) said first optical branch (G) second and third optical splitters for splitting the two output lights of the optical multiplexer into orthogonal polarizations, respectively, and (h) the An optical detector for respectively detecting the two output lights of the second and third optical branching devices, and (i) the same polarization component of the output light of the second and third optical branching devices among the outputs of the optical detector. And (1) means for detecting the amplitude and phase difference between the two output AC signals of the first and second differential amplifiers. An optical polarization characteristic measuring device characterized by. 2. A filter for branching either one of the output signals of the differential amplifier, a filter through which the output signal passes, and a means for amplifying the output signal of the filter are arranged and amplified. The optical polarization characteristic measuring device according to claim 1, wherein the output signal of the means is connected to the means for modulating the optical path difference. 3. (a) Which of the means for adjusting the polarization state of the output light of the light source, the first optical branching device for branching the output light into orthogonal polarizations, and the output of the first optical branching device. The sample to be measured placed in one of the optical paths and the other optical path of the output of the first optical branching device are arranged in the other optical path, and the polarization state is adjusted to obtain the orthogonal polarization.
Reference signal light for phase synchronization detection by slightly generating optical components
And give Ru means, and means for modulating one of the optical path difference either output of the first optical splitter, an optical multiplexer for multiplexing the two output light of said first optical splitter, the A second and a third optical branching device for splitting the two output lights of the optical multiplexer into orthogonal polarizations, and an optical detector for detecting the two output lights of the second and third optical splitters, respectively. , First and second differential amplifiers connecting detection signals of the same polarization component of the output light of the second and third optical branching devices among the outputs of the optical detector, and the first and second difference A means for detecting the amplitude and phase difference between the two output AC signals of the dynamic amplifier is arranged, and (b) the output light of the light source is split into orthogonal polarizations by the first optical branching device and then arranged in either one. The polarized light rotation component and the polarization non-rotational component generated in the measured sample are modulated by the optical path difference of either one, and A method for measuring optical polarization characteristics, which comprises performing homodyne detection on each of two orthogonal polarization components and measuring the amplitude and phase of the polarization rotation component of an AC signal generated by modulation of the optical path difference. 4. A filter for branching one of the output signals of the differential amplifier, the filter through which the output signal passes, and an amplifier for amplifying the output signal of the filter are arranged. Connecting the output signal to the means for modulating the optical path difference,
The optical polarization characteristic measuring method according to claim 3, wherein an AC signal for modulating the optical path difference is generated in a self-excited oscillation state at the same time as the negative feedback control. 5. The optical polarization characteristic measuring method according to claim 4, wherein the frequency of the alternating-current signal generated by self-excited oscillation is the self-resonant frequency of the means for modulating the optical path difference. 6. (a) means for adjusting the polarization state of the output light of the light source, (b) a first optical branching device for branching the output light into orthogonal polarizations, and (c) the first light. A sample to be measured, which is placed in one of the optical paths of the output of the branching device, and (d) which is placed in the other optical path of the output of the first optical branching device, and adjusts the polarization state to reduce the orthogonal polarization component Caused to
Te and give Ru means optical reference signal for phase synchronization detection, (e) means for shifting the frequency of the first optical branching device of one of the optical path the light output, (f) said first An optical multiplexer that combines the two output lights of the optical splitter, and (g) second and third optical splitters that split the two output lights of the optical splitter into orthogonal polarizations, respectively (h) ) An optical detector for detecting the two output lights of the second and third optical branching devices, respectively, and (i) Of the output lights of the second and third optical branching devices of the outputs of the optical detector. A first and a second differential amplifier for connecting detection signals of the same polarization component; and (j) means for detecting the quadrature phase amplitude of the two output high frequency signals of the first and the second differential amplifier. An optical polarization characteristic measuring device characterized by: 7. (a) Which of the means for adjusting the polarization state of the output light of the light source, the first optical branching device for branching the output light into orthogonal polarizations, and the output of the first optical branching device The sample to be measured placed in one of the optical paths and the other optical path of the output of the first optical branching device are arranged in the other optical path, and the polarization state is adjusted to obtain the orthogonal polarization.
Reference signal light for phase synchronization detection by slightly generating optical components
Means for shifting means Ru obtained, the frequency of the first optical branching device of one of the light path light output, the first
Optical multiplexer for multiplexing the two output lights of the optical splitter, and second and third optical splitters for splitting the two output lights of the optical multiplexer into orthogonal polarizations, respectively, and An optical detector for detecting each of the two output lights of the third optical branching device,
First and second connection of the detection signals of the same polarization component of the output light of the second and third optical branching devices among the outputs of the detector
And a means for detecting the amplitude and the quadrature phase amplitude of the two output high frequency signals of the first and second differential amplifiers, and (b) the output light of the light source is the first light. After branching into polarized light orthogonal to each other by the branching device, the polarized light rotation component and the polarized light non-rotational component generated in the measured sample arranged in either one are shifted in the frequency of the light in one of the optical paths, and the two A method for measuring optical polarization characteristics, which comprises performing heterodyne detection on each of orthogonal polarization components and measuring a polarization rotation component of a high-frequency signal having a difference frequency generated by shifting the frequency of light.