KR20180051694A - Free space Sagnac interferometer using a polarizing beam splitter - Google Patents

Free space Sagnac interferometer using a polarizing beam splitter Download PDF

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KR20180051694A
KR20180051694A KR1020160147522A KR20160147522A KR20180051694A KR 20180051694 A KR20180051694 A KR 20180051694A KR 1020160147522 A KR1020160147522 A KR 1020160147522A KR 20160147522 A KR20160147522 A KR 20160147522A KR 20180051694 A KR20180051694 A KR 20180051694A
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output
light
sensing unit
beam splitter
light source
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KR1020160147522A
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Korean (ko)
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KR101981707B1 (en
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조규만
윤승현
잉싱허
박준규
임효섭
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서강대학교산학협력단
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Priority to PCT/KR2017/012218 priority patent/WO2018084552A1/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
    • G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/14—Beam splitting or combining systems operating by reflection only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/14—Beam splitting or combining systems operating by reflection only
    • G02B27/149—Beam splitting or combining systems operating by reflection only using crossed beamsplitting surfaces, e.g. cross-dichroic cubes or X-cubes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
    • G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
    • G01J2009/0276—Stellar interferometer, e.g. Sagnac

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Gyroscopes (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)

Abstract

The present invention relates to an improved structure of a Sagnac interferometer with improved measurement performance. The Sagnac interferometer comprises: a light source; a sensing unit that divides a light inputted from the light source into first and second beams vertically polarized from each other, moves the first and second beams along a closed path in opposite directions and then combines the first and second beams to output a combined beam; and a demodulation unit for having the first and second beams, outputted from the sensing unit, interfered together and measuring a phase change induced therebetween. The sensing unit includes: a polarizing beam splitter that divides a light inputted from the light source into vertically polarized first and second beams and outputs the beams to different output ports, respectively; a closed path unit that forms a closed path using two or more mirrors and switches the directions of the first and second beams, outputted from the polarizing beam splitter, to be moved along the closed path. The first beam is inputted to the output port for the second beam and the second beam is inputted to the output port for the first beam. The first and second beams outputted from the closed path unit are vertically polarized from each other, combined by the polarizing beam splitter and outputted to the same path to be provided to the demodulation unit. The Sagnac interferometer detects and provides a rotational angular velocity using a phase difference between the first beam and the second beam.

Description

Free space Sagnac interferometer using a polarizing beam splitter.

The present invention relates to a Sagn optical interferometer, and more particularly to a polarizing beam splitter (PBS), which separates input light into polarization components perpendicular to each other, (Hereinafter referred to as 'CW') and counter clockwise (hereinafter referred to as 'CCW'), and then combined in the PBS, each of the polarized light components output from the PBS, The present invention relates to a Sagn optical interferometer capable of measuring a phase difference between different polarized components traveling in a CW direction and a CCW direction by interfering with each other and demodulating using a typical interferometer signal processing method.

The Sagnac interferometer was first developed by G. Sagnac in 1913. 1 is a block diagram illustrating a conventional Sagnac interferometer. As shown in FIG. 1, the sagnac interferometer has a ring structure divided into two halves by a beam splitter (BS), and the two beams are arranged in a CW and CCW directions It is an interferometer designed to measure the phase difference between CW and CCW directions by analyzing the interference signal measured by the photodetector.

Sagnac interferometers are used to measure and observe phenomena that induce optically irreversible changes in the CW and CCW directions. Typical examples are rotation sensors and current sensors. For example, if the interferometer rotates in the CW direction, light traveling in the same direction travels a little longer than when stopped, while light traveling in the opposite direction travels a short distance, so light traveling in the CW direction (Hereinafter referred to as CW light) and a light traveling in the CCW direction (hereinafter referred to as CCW light), thereby changing the interference signal. Therefore, it is possible to measure the rotational angular velocity by demodulating the interference signal output from the photodetector.

As shown in Fig. 1, the existing Sagnac interferometer has a phase difference of 0 between them because the CW and CCW paths are exactly matched. Therefore, when a small phase difference ?? is induced by rotation of the interferometer, the interference signal is cos ? . However, because cosine function is not changed very little phase change △ φ sensitive to the Sagnac interferometer mothada appropriate for measuring very small phase shift between the CW and CCW paths. In order for the interfering signal to be sensitive to small phase differences, the phase difference between the CW and CCW paths must be (2n + 1) π / 2 in the stationary state, where n = 0, ± 1, ... , That is, the interference signal should be proportional to the sine of the phase difference DELTA phi induced by rotation, but there is no way to make this condition because of the symmetry of the existing Sagnac interferometer. Therefore, the existing Sagnac interferometer is not suitable for measuring angular velocity.

Also, a phase difference of 90 degrees occurs between the light reflected from the BS and the transmitted light. In the Sagnac interferometer of FIG. 1, the CW light is reflected by the BS, reflected by the BS twice while being reflected by the optical detector, Since the light is transmitted twice to reach the photodetector, a phase difference of 180 degrees occurs between the CW light and the CCW light reaching the photodetector. That is, in the absence of rotation, extinction interference occurs between CW and CCW light, and the intensity of light directed to the detector is zero. Therefore, when the rotational angular velocity is very small, noise for optical detection is not suitable for measurement of small rotational angular velocity because it is given by the electronic noise given by the electronic elements including the photodetector.

A gyroscope is a device for measuring the rotational kinematics of a rotating object, in particular by measuring the rotational angular velocity. Application areas of gyroscopes are very wide, including navigation devices used in airplanes, missiles, spacecraft and submarines, attitude control of cameras, robots, unmanned automation devices, and gyro compass. Gyroscopes differ in the precision and stability required for their applications. The gyroscope described above has a mechanical gyroscope and an optical gyroscope, and in the ultra precision measurement field, an optical gyroscope is mostly used. The optical gyroscopes described above include ring laser gyroscopes and optical fiber gyroscopes.

A ring laser gyroscope allows a laser beam traveling in opposite directions, for example, clockwise and counterclockwise, to oscillate simultaneously in a resonator composed of three or more mirrors, and the frequency of this laser beam rotates the gyroscope from the outside And the difference in the number of vibrations, that is, the difference between the lengths of the effective resonators in the CW and CCW directions given by the rotation, is detected to measure the rotational angular velocity. Ring laser gyroscopes are mostly applied to navigation systems because of their high bias stability, linearity of conversion factor, wide measuring range and low temperature sensitivity.

However, the output of the ring laser gyroscope appears in the form of a sine wave, and the frequency of the sine wave changes according to the magnitude of the rotational angular velocity. However, when the magnitude of the external rotational angular velocity is small, a frequency locking phenomenon (lock-in effect) which is a phenomenon that the frequencies of two laser beams oscillating in both directions are equal to each other due to back scattering occurring in the reflector occurs, There is a problem that measurement of the gyroscope becomes impossible when the magnitude of the rotational angular velocity is less than a certain limit.

On the other hand, the optical fiber gyroscope basically includes a light source and a sensing unit formed of an optical fiber coil wound around the optical fiber in a circular shape. The operation of the optical fiber gyroscope will be briefly described as follows. First, the light from the light source passes through the directional coupler and is split into two light beams, passing through the optical fiber coil, and the two lights passing through the optical fiber coil in opposite directions interfere with each other in the directional coupler. When the gyroscope is at rest, both light experiences the same phase change as it passes through the fiber optic coil, so it interferes constructively in the directional coupler, and the output of the photodetector is at its maximum. On the other hand, when the gyroscope is rotating, a phase difference proportional to the rotational angular velocity occurs between the two lights due to the Sagnac effect, and the output of the photodetector changes. Therefore, the rotational angular velocity can be detected by measuring the change in the output intensity of the photodetector. These fiber optic gyroscopes have significant advantages over other types of gyroscopes in terms of cost, stability, durability, and fast start-up time. However, the optical fiber gyroscope has temperature-sensitive bias characteristics, and when the length of the optical fiber is extended to increase the measurement sensitivity, there arises a problem that the nonlinearity increases.

As described above, when the gyroscope is constructed using the sagnac interferometer, the problem of the conventional sagnac interferometer limits the measurement performance of the gyroscope.

Korean Patent Registration No. 10-1121879 Korean Patent Registration No. 10-1078387 Korean Patent Publication No. 10-2000-0073036

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and it is an object of the present invention to provide a polarizing beam splitter which is constructed such that two beams vertically polarized from each other proceed in clockwise and counterclockwise directions along the same closed path of free space, And to provide a Sagnac interferometer with an improved structure.

According to an aspect of the present invention, there is provided a sagnac interferometer comprising: a light source for providing linear or circularly polarized light; A sensing unit that divides the light input from the light source into a vertically polarized first beam and a second beam, moves the first beam and the second beam along opposite directions in a closed path, and outputs the combined light again; And a demodulator for interfering with the first beam and the second beam output from the detector and measuring a phase change induced therebetween,

The sensing unit may include a polarizing beam splitter that receives linearly or circularly polarized light at 45 degrees from the light source, divides the input light into vertically polarized first and second beams, and outputs the split light to different output ports. The first beam and the second beam output from the polarizing beam splitter are changed in direction so as to move along the closed path so that the first beam passes through the first beam and the second beam, Wherein the first beam and the second beam output from the menopausing passage are polarized perpendicularly to each other to polarize the beam, And outputted to the demodulation unit.

A sagnac interferometer according to a second aspect of the present invention includes: a light source for providing linearly polarized light; A sensing unit that divides the light input from the light source into a vertically polarized first beam and a second beam, moves the first beam and the second beam along opposite directions in a closed path, and outputs the combined light again; A resonator formed at an input point and an output point of the sensing unit to resonate the first beam and the second beam of the sensing unit; And a demodulator for measuring a phase difference induced between the first beam and the second beam by interfering the first beam and the second beam outputted from the resonator,

The sensing unit receives light linearly polarized at 45 degrees with respect to the polarization beam splitter from the light source, divides the input light into vertically polarized first and second polarized beams, and outputs the first and second beams to different output ports Polarized light; The first beam and the second beam output from the polarizing beam splitter are changed in direction so as to move along the closed path so that the first beam passes through the first beam and the second beam, Wherein the first beam and the second beam output from the menopausal passage unit are combined in a polarizing beam splitter and input to the output port of the first beam through the same path And the first beam and the second beam output from the polarization beam splitter are resonated through a resonator and provided to the demodulator.

In the Sagn optical interferometer according to the second aspect, the resonator may include: first and second mirrors respectively disposed at input and output points of the sensing unit; A first quarter wave plate (QWP) disposed between the first mirror and the sensing unit; And a second s-wave plate disposed between the second mirror and the sensing unit.

A sagnac interferometer according to a third aspect of the present invention includes: a light source for providing polarized light; A sensing unit that divides the light provided from the light source into a first beam and a second beam according to a polarization direction, moves the first beam and the second beam along different directions in a closed path, and outputs the combined light again; A demodulator for measuring a phase change induced between the first beam and the second beam output from the detector; And a beam splitter disposed between the light source and the sensing unit for transmitting a part of the beam provided from the light source and outputting it to the sensing unit and reflecting part of the beam provided from the sensing unit to the demodulating unit,

The sensing unit may include a polarizing beam splitter that splits the light provided from the light source through a beam splitter into a first beam and a second beam that are vertically polarized to each other and outputs the beams to different output ports, respectively. The first beam and the second beam output from the polarizing beam splitter are changed in direction so as to move along the closed path so that the first beam passes through the first beam and the second beam, A menopausal path inputting the first beam to an output port and inputting a second beam to an output port of the first beam; And a half wave plate (HWP) disposed at an arbitrary position on the closed path of the menopausal passage and delaying the light passing through the closed path by a half wavelength. The first beam and the second beam output from the menopausal passage unit are combined and output by the polarization beam splitter, reflected or transmitted by the beam splitter, and then provided to the demodulator.

According to a fourth aspect of the present invention, there is provided a sagnac interferometer comprising: a light source for providing polarized light; A sensing unit that divides the light provided from the light source into a first beam and a second beam according to a polarization direction, moves the first beam and the second beam along different directions in a closed path, and outputs the combined light again; A demodulator for measuring a phase change induced between the first beam and the second beam output from the detector; A light source disposed between the light source and the sensing unit for transmitting a part of the beam provided from the light source and outputting the light to the sensing unit and reflecting a part of the beam provided from the sensing unit to the demodulating unit; And a resonator disposed between the glow plug and the sensing unit,

The sensing unit may include a polarizing beam splitter that splits the light provided from the light source through a beam splitter into a first beam and a second beam that are vertically polarized to each other and outputs the beams to different output ports, respectively. The first beam and the second beam output from the polarizing beam splitter are changed in direction so as to move along the closed path so that the first beam passes through the first beam and the second beam, A menopausal path inputting the first beam to an output port and inputting a second beam to an output port of the first beam; And a half wave plate (HWP) disposed at an arbitrary position on the closed path of the menopausal passage and delaying the light passing through the closed path by a half wavelength. The first beam and the second beam output from the menopausal passage unit are combined and output by the polarization beam splitter, reflected or transmitted by the beam splitter, and then provided to the demodulator.

In sanyak interferometer according to the first feature to the fourth feature receives from the demodulator providing a first phase difference (△ φ) of the phase change of the first beam and a second beam, by using the phase difference angular velocity (Ω) And a control unit for measuring and providing the measured values.

In the Sagn optical interferometer according to the first to fourth aspects, the demodulating unit may include: a phase delay device for applying a bias phase between the first beam and the second beam, which are vertically polarized states provided from the sensing unit; A beam splitter for dividing the beam output from the phase delay device into a third beam and a fourth beam and outputting the beams; An I signal output unit for detecting and outputting an I output signal from a third beam transmitted through the beam splitter; A Q signal output unit for detecting and outputting a Q output signal from a fourth beam reflected by the beam gage; .

In the Sagn optical interferometer according to the first to fourth aspects, the demodulating unit may include: a phase delay device for applying a bias phase between the first beam and the second beam, which are vertically polarized states provided from the sensing unit; A polarizer for aligning the first beam and the second beam phase-delayed by the phase delay device at 45 degrees to output an interference signal between the first beam and the second beam; And a photodetector for outputting a detection signal that detects a beam output from the polarizer.

In the Sagn optical interferometer according to the first to fourth aspects, the demodulating unit may include: a phase delay device for applying a bias phase between the first beam and the second beam, which are vertically polarized states provided from the sensing unit; A polarization beam splitter for interfering the first beam and the second beam output from the phase delay device and outputting the divided beams according to a polarization state; A first photodetector for detecting a third beam reflected from the polarization beam splitter and outputting a first detection signal; A second light detecting element for detecting a fourth beam transmitted through the polarizing beam splitter and outputting a second detection signal; And a differential amplifier for detecting and outputting a difference between the first and second detection signals.

In the sagnac interferometer according to the second and fourth aspects, the resonator mirror fixed to the displacement device such as the piezoelectric transducer may be provided to actively adjust the resonance condition.

The Sagn optical interferometer according to the present invention can be precisely measured even when the angular velocity is small, unlike the conventional Sagnac interferometer, by using the polarizing beam splitter.

In the Sagn optical interferometer according to the second and fourth embodiments of the present invention, the CW light and the CCW light propagate through the resonator a plurality of times and then output. As a result, the rotation can be measured more precisely and the high sensitivity can always be maintained.

1 is a block diagram illustrating a conventional Sagnac interferometer.
FIG. 2 is a block diagram of a Sagn optical interferometer according to a first embodiment of the present invention. Referring to FIG.
FIG. 3 is a block diagram of a Sagn optical interferometer according to a second embodiment of the present invention. Referring to FIG.
FIG. 4 is a block diagram of a Sagn optical interferometer according to a third embodiment of the present invention. Referring to FIG.
FIG. 5 is a block diagram of a Sagn optical interferometer according to a fourth embodiment of the present invention. Referring to FIG.
6 is a schematic diagram illustrating a Sagnac effect used for detecting a rotational angular velocity using a phase difference according to the Sagn optical interferometer according to the present invention.
FIG. 7 is a configuration diagram of an embodiment of a demodulator according to the present invention. FIG.
8 is a configuration diagram showing another embodiment of the demodulator in the Sagn-interferometer according to the present invention.
9 is a configuration diagram showing still another embodiment of the demodulating unit in the Sagn-interferometer according to the present invention.

The Sagnac interferometer according to the present invention is characterized by using a polarizing beam splitter and a resonator.

Hereinafter, a structure and operation of a Sagn optical interferometer having a novel structure according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

≪ Embodiment 1 >

2 is a block diagram of an improved Sagnac interferometer according to a first embodiment of the present invention.

2, the free space gyroscope 1 according to the first embodiment of the present invention includes a light source 10, a sensing unit 20, and a demodulation unit 30, .

The light source 10 provides linearly or circularly polarized light at 45 degrees to the polarization beam splitter 200 of the sensing unit 20. The light source may be configured to output a linear or circularly polarized laser beam at 45 degrees using a single laser beam generator or by combining a laser beam generator and a polarization rotator to form a linear or circularly polarized laser beam at 45 degrees You can also print.

The sensing unit 20 includes a closed path unit 210 including a polarization beam splitter 200 and a plurality of optical path changing elements 211, 212 and 213 to form one closed path. The sensing unit having the structure described above senses the rotation or movement of the sagnac interferometer using the light provided from the light source and outputs a first beam and a second beam having a phase difference according to the rotation angular velocity by rotation or movement to a demodulation unit 30).

The menopausal passage section 210 is composed of two or more optical path changing elements and constitutes one closed path together with the polarizing beam splitter 200. The light path changing elements may use elements that reflect or totally reflect an incident beam such as a reflector or a prism. As shown in FIG. 2, in an embodiment, three mirrors 211, 212, and 213 may be sequentially arranged.

Wherein the first beam and the second beam respectively output from the first output port and the second output port of the polarizing beam splitter are respectively inputted to the menopausal path section and the first beam and the second beam inputted to the menopausal path are transmitted to the closed Are moved along the path in the CCW direction and the CW direction, respectively, so that the first beam is input again to the output port of the second beam and the second beam is input again to the output port of the first beam. The first beam and the second beam output from the menopausal passage are polarized perpendicularly to each other, input to the polarization beam splitter, combined in the polarizing beam splitter, and output to the demodulator.

In particular, the sensing unit 20 divides the light incident from the light source into two beams by being reflected by the polarized light S polarized light S polarized light and transmitted through the P polarized light, They proceed in opposite directions along one closed path, then recombine in polarizing beam splitter and output to demodulation section. The demodulator demodulates the output beam so that it can measure the phase difference between the second beam and the first beam that have traveled in the CW and CCW directions, respectively.

The polarization beam splitter 200 is an optical element that reflects a beam provided from the light source according to a polarization direction and reflects S polarized light and transmits P polarized light. The polarized light beam is reflected or transmitted according to a polarization direction, And the second beam, and outputs it to the menopausal unit 210. The first beam and the second beam outputted to the menopausal conduit rotate in opposite directions to each other and are incident again into the first polarization beam splitter. The re-incident first beam and the second beam are combined and output to the demodulator.

The menopausing path section 210 includes a plurality of light path changing elements sequentially arranged such that the beams output from the polarizing beam splitter are moved in opposite directions along the closed path and are incident on the polarizing beam splitter again , So that the closed path is formed in free space so that the beams can proceed in free space. The first beam reflected from the polarizing beam splitter by the menopausal path portion proceeds in a counterclockwise direction and enters the polarizing beam splitter again, and the second beam transmitted through the polarizing beam splitter is rotated clockwise It proceeds to enter the polarized light beam again. Accordingly, the first beam and the second beam, which are vertically polarized states, move in opposite directions along a closed path of the menopausal passage, enter the polarization beam splitter again, and output to the demodulator.

When the Sagn optical interferometer is rotated while the first beam and the second beam move in the free space of the menopausal passage, the first beam and the second beam have a phase difference according to the rotational angular velocity of the Sagnac interferometer.

The demodulating unit 30 interferes with the first beam and the second beam output from the sensing unit 20 and measures and provides the phase difference induced therebetween.

The control unit 40 calculates a phase difference between the first beam and the second beam from the interference signal of the first beam and the second beam provided from the demodulator and calculates and outputs the rotational angular velocity of the sagnac interferometer using the phase difference. The sagnac interferometer according to the present invention may include the control unit 40 or may be configured without the control unit 40. [ When the Sagnac interferometer is constructed without a control part, the Sagnac interferometer can provide an external control device or a computer with an interference signal of the first beam and the second beam measured by the Sagnac interferometer to an external control device or a computer. The controller or the computer can calculate the phase difference between the first beam and the first beam and the rotational angular velocity of the sagnac interferometer using the interference signals of the first beam and the second beam.

6 is a schematic diagram illustrating a Sagnac effect used to detect a rotational angular velocity using a phase difference between a first beam and a second beam in the Sagnac interferometer according to the present invention. As shown in FIG. 6, when the sagnac interferometer is rotated, the first and second beams traveling in opposite directions to each other due to the menopausal passage portion generate optical path differences ? L according to the rotational angular velocities . Therefore, the optical path difference can be obtained by using the phase difference between the first beam and the second beam measured by the Sagnac interferometer, and the rotational angular velocity can be measured based on the optical path difference.

≪ Embodiment 2 >

3 is a block diagram of an improved Sagnac interferometer according to a second embodiment of the present invention.

3, the gyroscope 2 according to the second embodiment of the present invention includes a light source 12, a sensing unit 22, a demodulating unit 32, and a resonator 52, and the control unit 42 ). Since the structure of the sensing unit 22 of the second embodiment is the same as that of the first embodiment, a duplicate description will be omitted.

The light source 12 may use a linearly polarized laser light source at 45 degrees.

The sensing unit 22 is disposed inside the resonator 52. The sensing unit 22 divides the light input from the light source into a vertically polarized first beam and a second beam, Moves along the closed path in opposite directions, and then outputs the combined signals to the demodulation unit.

The resonator 52 includes a first mirror 520 and a second mirror 522 disposed at input and output points of the sensing unit 22, A quarter wave plate (QWP) 521 and a second quarter wave plate 523 are disposed, respectively. The first and second sine wave plates are phase delay plates for outputting a phase delay of the input beam by? / 4.

It is preferable that the first and second mirrors 520 and 522 are made of mirrors having a large reflection coefficient R. [ For example, assuming that the first and second mirrors are composed of mirrors with a reflection coefficient of 98%, assuming that there is no loss in polarized light, the Finesse of the resonator is 157, and the CW and CCW beams in the resonator are weak Since the phase can be repeated about 100 times, the induced phase value increases by about 100 times. Even when considering the loss in polarizing beam splitter, the performance of the interferometer can be improved by repeating the CW beam and the CCW beam repeatedly several times or more.

The sensing unit 22 has the same structure as that of the sensing unit of the first embodiment. The sensing unit 22 includes a first mirror 520 and a first quarter wave plate (not shown) between the light source and the incident surface of the polarizing beam splitter 200 And a second mirror 522 and a second s-wave plate 523 of a resonator are disposed between the emission surface of the polarization beam splitter and the demodulation unit.

In the Sagn optical interferometer according to the second embodiment of the present invention, the paths of the first beam and the second beam in the sensing unit 22 and the resonator 52 will be described in detail.

First, a part of the linearly polarized light provided from the light source is incident on the first QWP 521 through the mirror. Since the polarization direction of the incident light is parallel to the principal axis of the first QWP, Is maintained in the same state as the incident light. Since the principal axis of the first QWP, that is, the polarization direction of the incident light, forms an angle of 45 degrees with the principal axis of the polarization beam splitter, the P polarization component of the incident beam is transmitted through the polarization beam splitter 200 to form a first beam The S component is reflected to form a second beam. The first beam transmitted through the polarized beam splitter proceeds in the CCW direction through the path formed by the menopausal path portion and the second beam reflected by the polarized beam splitter proceeds in the CW direction formed by the menopausal path portion . The first beam traveling in the CCW direction along the menopause path is again incident on the polarized light beam as P polarized light and transmitted again to pass through the second QWP, the second mirror, and the second QWP, and then enters the polarized light beam again do. At this time, the first beam is transmitted through the second QWP twice, and the polarization direction is rotated by 90 degrees. As a result, the first beam is reflected by the incident polarized light beam, and the menopausal section proceeds again in the CCW direction. By repeating this process, the first beam is repeatedly turned in the CCW direction. Therefore, when the resonator satisfies the standing wave condition, the light incident through the first mirror causes the build-up interference, so that the intensity of light in the resonator gradually increases, and a part of the light is outputted through the second mirror 522. The number of times the first beam travels along the closed path is given by the reflectance of the mirror. On the other hand, the second beam is rotated through the second mirror 522 by the same number of times in the CW direction as the first beam.

For example, if the reflection coefficient (R) of the first and second mirrors constituting the resonator is 98%, the finesse of the resonator becomes 157, and the first beam and the second beam are reflected by other elements If the loss is not taken into account, it is output after about 100 times of operation.

The first beam and the second beam oscillated from the resonator are provided to the demodulator 32. The demodulator 32 demodulates the first beam and the second beam output from the resonator 52 to detect and output a phase difference between the first beam and the second beam.

The Sagnac interferometer according to the second embodiment can improve the sensitivity by the number of times it is returned compared to the Sagnac interferometer according to the first embodiment in which the beam is turned once around the menopausal path portion of the sensing portion by causing the beam to be turned many times by the resonator .

≪ Third Embodiment >

4 is a block diagram of an improved Sagnac interferometer according to a third embodiment of the present invention.

4, the Sagn interferometer 3 according to the third embodiment of the present invention includes a light source 10, a light beam gage 250, a sensing unit 23, and a demodulation unit 30, (40).

The light source 10 provides linearly or circularly polarized light at 45 degrees to the sensing unit 23 through the beam splitter 250. The light source may be configured to output a linear or circularly polarized laser beam at 45 degrees using a single laser beam generator or by combining a laser beam generator and a polarization rotator to form a linear or circularly polarized laser beam at 45 degrees You can also print.

The light beam gage 250 is disposed between the light source 10 and the sensing unit 23 so as to transmit a part of the beam provided from the light source and output it to the sensing unit, .

The sensing unit 23 includes a polarizing beam splitter 200, a menopausal passage unit 210 including a plurality of optical path changing elements 211, 212 and 213, and a half wave plate 240, And detects the rotation or movement of the sagnac interferometer using the provided light and outputs the first beam and the second beam having a phase difference according to the rotational angular velocity due to rotation or movement to the demodulator 30 through the beam splitter 250 do.

The polarization beam splitter 200 divides the light provided from the light source through the beam splitter into vertically polarized first and second beams, and outputs the divided beams to different output ports.

The menopausing path section 210 constitutes one closed path using two or more mirrors and switches the direction of the first beam and the second beam output from the polarization beam splitter to move along the closed path The first beam is input to the output port of the second beam and the second beam is input to the output port of the first beam.

The half wave plate 240 is attached to or directly behind the polarizing beam splitter 200 on the closed path of the menopause path portion to rotate the polarization direction of the beam passing through the closed path by 90 degrees. Therefore, since the polarization state of the light traveling in the CW direction and the CCW direction is the same along the closed path, it is not affected by the birefringent noise that can be applied to the anisotropic flow of air or the like.

The first beam and the second beam outputted from the menopausal passage are polarized perpendicularly to each other and are combined in the polarizing beam splitter and output from the beam splitter 200 along the same path to the demodulator.

In the Sagn optical interferometer according to the third embodiment of the present invention, the path of the first beam and the second beam in the sensing unit 23 will be described in detail.

First, the light incident from the light source is incident on the polarizing beam splitter 200 through the beam splitter 250, and the S polarized beam is reflected according to the polarization direction in the polarizing beam splitter, and the P polarized beam is transmitted, The beam is divided into two beams, which are then propagated in opposite directions along one closed path and then combined again in the polarizing beam splitter.

On the other hand, by arranging the half wave plate 240 by attaching the polarizing beam splitter 200, the beam passing through the closed path of the menopausal passage part is rotated by 90 degrees by the half wave plate. As a result, the first beam, which is P-polarized light transmitted through the polarizing beam splitter, moves along the closed path of the menopausal passage part in the counterclockwise direction and is incident again into the polarizing beam splitter. At this time, As the light is rotated 90 degrees, the light is reflected from the polarized light beam G (200) re-incident and proceeds to the light beam. On the other hand, the second beam, which is the S-polarized light reflected from the polarizing beam splitter, is rotated 90 degrees by the half wave plate to move the closed path of the menopausal beam clockwise, and transmits the re-incident polarized light beam. The Thus, the light traveling in the clockwise and counterclockwise directions has the same polarization state in the closed path, so that a completely reversible Sagnac interferometer can be constructed. In this way, the reflected light beam transmitted through the re- And the second beam are combined in the polarizing beam splitter, and then the beam is progressed to the beam splitter, and then a part of the beam is output to the demodulator 30.

The demodulator demodulates the beam input from the beam splitter so that it can measure the phase difference between the second beam and the first beam, respectively, which proceed in the CW and CCW directions.

When the Sagn optical interferometer is rotated while the first beam and the second beam move in the free space of the menopausal passage, the first beam and the second beam have a phase difference according to the rotational angular velocity of the Sagnac interferometer.

The demodulating unit 30 interferes with the first beam and the second beam output from the sensing unit 20 and measures and provides induced phase shifts between them.

The control unit 40 calculates and outputs a rotational angular velocity of the sagnac interferometer using the phase difference between the first beam and the second beam provided from the demodulator.

<Fourth Embodiment>

FIG. 5 is a block diagram of an improved Sagnac interferometer according to a fourth embodiment of the present invention. Referring to FIG.

5, the Sagn optical interferometer 4 according to the fourth embodiment of the present invention includes a light source 10, a light beam gage 250, a sensing unit 23, a demodulator 30, and a resonator 54, And may further include a control unit 40. The sagnac interferometer 4 according to the present embodiment is characterized in that a resonator 54 is further disposed between the light beam gage 250 of the Sagn interferometer according to the third embodiment and the polarization beam splitter 200 of the sensing part .

The resonator 54 is disposed between the beam splitter 250 and the polarization beam splitter 200 of the sensing unit and includes a mirror 530 and a quarter wave plate (QWP) 531. The sine wave plate is a phase delay plate that outputs the phase difference between the principal polarization components of the input light by lambda / 4. It is preferable that the mirror 530 is made up of mirrors having a large reflection coefficient R. [ For example, assuming that a mirror with a reflection coefficient of 98% has no loss in polarized light, the resonance finesse is 157, and the CW and CCW beams in the resonator can be repeated about 100 times The induced phase value increases by about 100 times. Even when considering the loss in polarizing beam splitter, the performance of the interferometer can be improved by repeating the CW beam and the CCW beam repeatedly several times or more.

The driving method of the resonator 54 is the same as that of the resonator according to the second embodiment.

The configuration and operation of the sensing unit 23 are the same as those of the sensing unit 23 according to the third embodiment.

The Sagn interferometer 4 according to this embodiment having the above-described configuration rotates the free space of the menopausal passage until the first beam and the second beam satisfy the resonance condition by the sensing part and the resonator, and then outputs the rotated free space to the demodulating part The phase difference and the rotational angular velocity induced in the interference signal between the first beam and the second beam are obtained by the demodulator and the control unit.

Hereinafter, various embodiments of the demodulating unit in the Sagn interferometer according to the present invention will be described.

FIG. 7 is a configuration diagram of an embodiment of a demodulator according to the present invention. FIG. Referring to Fig. 7, the demodulator 30 includes a phase delay device 372, a polarizer 375, and a photodetector element PD.

The phase delay device 372 is for applying a bias phase between the first beam and the second beam, which are vertically polarized states mutually provided from the sensing part. For optimum demodulation of the first beam and the second beam, it is desirable to use a phase delay device to make the phase bias between the first beam and the second beam an odd multiple of ninety degrees. For example, a quarter wave plate (QWP) for phase retarding a quarter wavelength between the main polarization components can be used. If the first quarter wave plate (QWP) When the phase of the beam and the second beam are changed by the reflection at the polarizing beam splitter, it is preferable to make the phase difference between the first beam and the second beam to be an odd multiple of 90 degrees by using a phase retarder other than QWP.

The polarizer 375 aligns the first beam and the second beam phase-delayed by the phase delay device 45 degrees to output an interference signal between the first beam and the second beam.

The photodetector PD outputs a detection signal that detects a beam output from the polarizer. When the bias phase between the first beam and the second beam is 90 degrees, the following expression (1) is obtained.

Figure pat00001

Where R is the responsivity of the photodetector, I 0 is the total intensity of the first beam and the second beam, and [Delta] [phi] is the phase difference induced in the first beam and the second beam due to rotation of the interferometer and the like.

8 is a configuration diagram showing another embodiment of the demodulator in the Sagn-interferometer according to the present invention. 8, the demodulating unit 31 includes a phase delay unit 398, a polarizing beam splitter 392, first and second photodetecting devices PD1 and PD2, and a differential amplifier 395. [

The phase delay device 398 is for applying a bias phase corresponding to an odd multiple of 90 degrees or 90 degrees between the first beam and the second beam which are vertically polarized states provided from the sensing unit, (QWP), which phase-quadruple the phase of the main polarized light component, can be used in various ways depending on the phase values of the first beam and the second beam given by reflection in the mirror or the like. have.

The polarization beam splitter 392 aligns the polarization direction of the first beam and the second beam output from the phase delay device by 45 degrees so that the s components of the first beam and the second beam are combined to cause interference, Reflected from the beam, the p components of the first beam and the second beam combine to create interference and transmit the polarized light beam.

The first photodetector element PD1 detects a third beam reflected from the polarizing beam splitter and outputs a first detection signal, and the second photodetector element PD2 detects a third beam that is transmitted through the polarizing beam splitter And detects the fourth beam and outputs the second detection signal. When the phase bias between the first beam and the second beam is 90 degrees, the optical signals output from PD1 and PD2 are given by the following equations (2) and (3), respectively.

Figure pat00002

Figure pat00003

The differential amplifier 395 outputs the difference between the first and second detection signals, and the output signal is given by the following equation (4).

Figure pat00004

Therefore, by demultiplexing the interference signals detected from the third beam and the fourth beam by the differential amplifier, the demodulating unit of the above-described structure eliminates mutually correlated noise carried on each optical signal and doubles the optical signal, The noise ratio can be increased. Such a measurement method is called a balanced detection method.

9 is a configuration diagram showing still another embodiment of the demodulating unit in the Sagn-interferometer according to the present invention. 9, the demodulation unit 32 includes a phase delay unit 300, a light beam gage 310, an I signal output unit 320, and a Q signal output unit 330, Phase signal ( V I ) and a Q output signal (Quadrature-phase signal: V Q ) having a phase difference of 90 ° from each other from the negative and Q signal output sections. The I-phase signal ( V I ) is proportional to cos Δφ and the Q output signal ( V Q ) is proportional to sin Δφ .

The demodulation unit 32 demodulates the first beam and the second beam outputted from the sensing unit to generate an I-phase signal ( V I ) signal and a Q-output signal ( I ) for the first beam and the second beam, (Quadrature-phase signal: V Q ). The phase difference according to the rotational angular velocity can be detected from the I output signal and the Q output signal.

The phase delay device 300 is used to apply a bias phase between the first beam and the second beam, which are vertically polarized from each other, from the detection unit. The phase delay device 300 may be variously selected according to the polarization states of the first beam and the second beam For example, a half-wave plate that rotates the first beam and the second beam by 45 degrees and outputs the beams to the beam splitter 310 may be used.

The beam splitter 310 is provided with a first beam and a second beam rotated by 45 degrees from the phase delay device, and the first beam and the second beam are rotated 50:50 into a third beam and a fourth beam Respectively, and outputs them. A third beam transmitted through the beam splitter is provided to the I signal output, and a fourth beam reflected from the beam splitter is provided to the Q signal output.

The I signal output unit 320 is configured to detect and output an I output signal from a third beam transmitted through the beam splitter. The I signal output unit 320 includes a second polarized beam splitter 322 disposed on the path of the third beam transmitted through the beam splitter, a second polarized beam splitter 322 arranged to detect a beam reflected from the second polarized beam splitter, A second detecting element 324 for detecting a beam transmitted through the second polarized beam splitter and detecting the difference between the beams output from the first detecting element and the second detecting element, And a first differential amplifier 325 for amplifying and outputting the amplified signal. The first and second detecting elements may be constituted by a photodiode.

The Q signal output unit 330 is configured to detect and output a Q output signal from a fourth beam transmitted through the beam splitter. The Q signal output unit 330 is configured to detect and output a Q output signal from the fourth beam reflected from the beam gage. The Q signal output unit 330 includes a QWP (Quarter Wave Plate) 331 for rotating the fourth beam reflected from the beam gage by 45 degrees polarized light, a fourth beam transmitted through the QWP, A third polarizing beam splitter 332 disposed on the traveling path, a third polarizing beam splitter 333 for detecting the beam reflected by the third polarizing beam splitter 333, A fourth detecting element 334 for detecting the beam, and a second differential amplifier 335 for detecting and amplifying the difference between the beams output from the third and fourth detecting elements.

The first differential amplifier of the I signal output unit and the second differential amplifier of the Q signal output unit having the above-described configuration are respectively connected to the I-output signal ( V I ) signal and the Q output signal (Quadrature-phase signal: V Q ).

The control unit 40 receives an I output signal and a Q output signal from the demodulation unit and detects and outputs a rotational angular velocity using the I output signal and the Q output signal. Hereinafter, the process of the control unit 40 detecting the rotational angular velocity OMEGA using the output signal of the demodulation unit according to the present embodiment will be described in detail.

First, the I output signal ( V I ) obtained from the demodulator 32 is proportional to cos Δφ and the Q output signal ( V Q ) is proportional to sin Δφ , so that I The phase difference ?? according to the rotation of the object can be obtained by using Equation 5 using the output signal V I and the Q output signal V Q.

Figure pat00005

The time ( t +) required for the second beam rotating in the clockwise direction to rotate around the optical rotation unit in the sensing unit can be obtained by Equation (6), and the time required for the first beam, which rotates counterclockwise, ( t -) can be obtained by Equation (7).

Figure pat00006

Figure pat00007

The optical path difference ( DELTA L ) between the first beam and the second beam with respect to the rotation of the object can be found from the following equation (8).

Figure pat00008

The optical path difference ? L is generated between the first beam and the second beam traveling in opposite directions to each other due to the rotation of the object. Since the phase change in the interference signal is given as a linear function of the rotational angular velocity, it is possible to measure the phase change and accurately measure the rotational angular velocity .

The phase difference ?? between the first beam and the second beam using the optical path difference ? L between the first beam and the second beam with respect to the rotation of the object can be found by the following equation (9).

Figure pat00009

From Equation (9), the rotational angular velocity (?) According to the rotation of the object can be expressed by Equation (10) and can be expressed as Equation (4) using the I output signal ( V I ) and the Q output signal ( V Q ) The rotational angular velocity (?) According to the rotation of the object can be obtained by using the phase difference ( ? ) Between the beam and the second beam.

Figure pat00010

Where t is the time it takes for the first beam to rotate in the counterclockwise direction to travel around the ring and t + is the time it takes for the second beam to rotate clockwise to travel around the ring Is a rotational angular velocity, C is the speed of light, R is the radius of the ring constituting the optical rotation part, A is the area of the ring, and DELTA L is the distance between the first beam and the second beam Is the optical path difference, and ? Is the phase change value induced by the angular velocity.

The Sagnac interferometer according to the present invention having the above-described configuration uses a polarizing beam splitter to construct a new structure, so that two beams vertically polarized with respect to each other are made to travel in opposite directions along a closed path, It is possible to measure the rotational angular velocity according to the rotation of the object.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. It is to be understood that the present invention may be embodied in many other specific forms without departing from the spirit or essential characteristics thereof.

The sagnac interferometer according to the present invention can be widely used in equipment for measuring rotational dynamics information such as a gyroscope.

1, 2, 3, 4: Sagnac interferometer
10, 12: Light source
20, 22:
30, 31, 32:
40, 42:
52, 54: resonator
200: Let's polarize light
210:
211, 212, 213: reflector

Claims (10)

A light source providing linear or circularly polarized light;
A sensing unit that divides the light input from the light source into a vertically polarized first beam and a second beam, moves the first beam and the second beam along opposite directions in a closed path, and outputs the combined light again;
A demodulator for measuring a phase change induced between the first beam and the second beam output from the detector;
Wherein the sensing unit comprises:
A polarization beam splitter for receiving linearly or circularly polarized light at 45 degrees from the light source, dividing the input light into first and second vertically polarized beams, and outputting the split beams to different output ports;
The first beam and the second beam output from the polarizing beam splitter are changed in direction so as to move along the closed path so that the first beam passes through the first beam and the second beam, And a menopausal path inputting the first beam to an output port and the second beam to an output port of the first beam,
Wherein the first beam and the second beam outputted from the menopausal passage are polarized perpendicularly to each other and are combined in a polarizing beam splitter and outputted through the same path to the demodulator. A light source for providing linearly polarized light;
A sensing unit that divides the light input from the light source into a vertically polarized first beam and a second beam, moves the first beam and the second beam along opposite directions in a closed path, and outputs the combined light again;
A resonator formed at an input point and an output point of the sensing unit to resonate the first beam and the second beam of the sensing unit; And
A demodulator for measuring a phase difference induced between the first beam and the second beam by interfering the first beam and the second beam output from the resonator;
, And the sensing unit
A polarization beam splitter for receiving linearly polarized light at 45 degrees from the light source, dividing the input light into first and second polarized beams, and outputting the divided beams to different output ports;
The first beam and the second beam output from the polarizing beam splitter are changed in direction so as to move along the closed path so that the first beam passes through the first beam and the second beam, And a menopausal path inputting the first beam to an output port and the second beam to an output port of the first beam,
Wherein the first beam and the second beam output from the menopausal path section are combined in a polarization beam splitter and output through the same path, and the first beam and the second beam output from the polarization beam splitter are resonated through a resonator, Wherein the free space Sagn interferometer is provided with a free space Sagn optical interferometer. The resonator according to claim 2, wherein the resonator
First and second mirrors respectively disposed at input and output points of the sensing unit;
A first quarter wave plate (QWP) disposed between the first mirror and the sensing unit; And
A second sine wave plate disposed between the second mirror and the sensing unit;
And a free space Sagn interferometer. A light source for providing polarized light;
A sensing unit that divides the light provided from the light source into a first beam and a second beam according to a polarization direction, moves the first beam and the second beam along different directions in a closed path, and outputs the combined light again;
A demodulator for measuring a phase change induced between the first beam and the second beam output from the detector;
A light source disposed between the light source and the sensing unit for transmitting a part of the beam provided from the light source and outputting the light to the sensing unit and reflecting a part of the beam provided from the sensing unit to the demodulating unit;
, And the sensing unit
A polarizing beam splitter for splitting the light provided from the light source through a beam splitter into a first beam and a second beam, which are vertically polarized and output to different output ports, respectively;
The first beam and the second beam output from the polarizing beam splitter are changed in direction so as to move along the closed path so that the first beam passes through the first beam and the second beam, A menopausal path inputting the first beam to an output port and inputting a second beam to an output port of the first beam; And
A half wave plate (HWP) disposed at an arbitrary position on the closed path of the menopausal passage and rotating the polarization direction of light transmitted through the closed path by 90 degrees;
Wherein the first beam and the second beam output from the menopausing passage are combined and output by a polarizing beam splitter and then reflected or transmitted by the beam splitter and provided to the demodulator. interferometer. The free space interferometer of claim 4, wherein the free space sagnac interferometer further comprises a resonator between the grating grating and the polarization grating grating of the sensing unit. The resonator according to claim 5, wherein the resonator
A mirror disposed between the glare grating and the polarizing grating of the sensing portion; And
A quarter wave plate (QWP) disposed between the mirror and the sensing unit;
And a free space Sagn interferometer. 7. The apparatus of any one of claims 1 to 6, wherein the free space sagnac interferometer comprises:
And a controller for receiving a phase difference ?? according to a phase change of the first beam and the second beam from the demodulator and measuring and providing a rotational angular velocity? Using the phase difference. Sagnac interferometer. 7. The demodulating device according to any one of claims 1 to 6,
A phase delay device for applying a bias phase between the first beam and the second beam, which are vertically polarized states provided from the sensing unit;
A beam splitter for dividing the beam output from the phase delay device into a third beam and a fourth beam and outputting the beams;
An I signal output unit for detecting and outputting an I output signal from a third beam transmitted through the beam splitter;
A Q signal output unit for detecting and outputting a Q output signal from a fourth beam reflected by the beam gage;
And a free space Sagn interferometer. 7. The demodulating device according to any one of claims 1 to 6,
A phase delay device for applying a bias phase between the first beam and the second beam, which are vertically polarized states provided from the sensing unit;
A polarizer for aligning the first beam and the second beam phase-delayed by the phase delay device at 45 degrees to output an interference signal between the first beam and the second beam; And
A photodetector for outputting a detection signal for detecting a beam output from the polarizer;
And a free space Sagn interferometer. 7. The demodulating device according to any one of claims 1 to 6,
A phase delay device for applying a bias phase between a first beam and a second beam that are vertically polarized states provided from the sensing unit;
A polarization beam splitter for interfering the first beam and the second beam output from the phase delay device and outputting the divided beams according to a polarization state;
A first photodetector for detecting a third beam reflected from the polarization beam splitter and outputting a first detection signal;
A second light detecting element for detecting a fourth beam transmitted through the polarizing beam splitter and outputting a second detection signal;
A differential amplifier for detecting and outputting a difference between the first and second detection signals;
And a free space Sagn interferometer.
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