WO2018084552A1

WO2018084552A1 - Free-space sagnac interferometer using polarizing beam splitter

Info

Publication number: WO2018084552A1
Application number: PCT/KR2017/012218
Authority: WO
Inventors: 조규만; 윤승현; 잉싱허; 박준규; 임효섭
Original assignee: 서강대학교 산학협력단
Priority date: 2016-11-07
Filing date: 2017-11-01
Publication date: 2018-05-11
Also published as: KR20180051694A; KR101981707B1

Abstract

The present invention relates to an improved Sagnac interferometer. The Sagnac interferometer comprises: a light source; a sensing section which divides light inputted from the light source into a first beam and a second beam which are perpendicularly polarized with each other, moves the first beam and the second beam in a single closed path along opposite directions, and then rejoins and outputs the first beam and the second beam; a demodulation section which causes the first beam and the second beam outputted from the sensing section to interfere with each other and measures a phase shift induced therebetween. The sensing section comprises: a polarizing beam splitter which divides the light inputted from the light source into a first beam and a second beam which are perpendicularly polarized with each other and outputs the first beam and the second beam respectively to output ports different from each other; and a closed path section which forms the single closed path by using two or more mirrors, changes the direction of the first beam and the second beam outputted from the polarizing beam splitter, moves the first beam and the second beam along the closed path, inputs the first beam to the output port of the second beam, and inputs the second beam to the output port of the first beam. The first beam and the second beam outputted from the closed path section are perpendicularly polarized with each other, are joined in the polarizing beam splitter to be outputted to the same path, and are provided to the demodulation section. The Sagnac interferometer detects a rotating angular speed using the phase difference between the first beam and the second beam, and provides the same.

Description

Free Space Sagnac Interferometer Using Polarized Light

The present invention relates to a Sagnac interferometer, and more particularly, using a polarizing beam splitter (PBS) to separate the input light into polarized components perpendicular to each other to the same path in the opposite direction, that is clockwise (clockwise) , And `` CW '') and counter clockwise (`` CCW '') and then merged together in PBS, each polarized component output from PBS and proceeding together is 90 Since the signals are separated and output, they are interfered and demodulated using a typical interferometer signal processing method. The present invention relates to a sagnac interferometer capable of measuring a phase difference between different polarization components traveling in the CW and CCW directions.

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 two light beams divided in half by a beam splitter (BS) and has a ring structure by two or more mirrors, and proceeds in the CW and CCW directions, respectively. The interferometer is designed to measure the phase difference between two lights traveling in the CW and CCW directions by analyzing the interference signal measured by the photo detector.

Sagnac interferometers are applied to measure / observe phenomena that induce optically irreversible changes in the CW and CCW directions. Typical examples include rotation sensors and current sensors. For example, if the interferometer rotates in the CW direction, the light traveling in the same direction travels a little farther than when it stops, and the light traveling in the opposite direction travels a shorter distance. A phase difference occurs between the CW light) and the light traveling in the CCW direction (hereinafter referred to as CCW light), and thus the interference signal is changed. Therefore, the rotational angular velocity can be measured by demodulating the interference signal output from the photodetector.

In the existing Sagnac interferometer, as shown in FIG. 1, since the CW and CCW paths exactly match, the phase difference between them is 0. Therefore, when a small phase difference Δφ is induced by the rotation of the interferometer, the interference signal is cos Δφ. Will be proportional to 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 respond sensitively to small phase differences, the phase difference must be (2n + 1) π / 2 at rest between the CW and CCW paths, where n = 0, ± 1,... In other words, the interference signal should be made proportional to the sine of the phase difference Δφ induced by rotation, but there is no way to make this condition because of the symmetry of the existing Sagnac interferometer. Therefore, conventional Sagnac interferometers are not suitable for measuring rotations with small angular velocities.

In addition, 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 from the BS and output twice to the photo detector, while reflecting twice from the BS. Since light is transmitted twice to reach the photo detector, a 180 degree phase difference occurs between the CW light and the CCW light reaching the photo detector. That is, in the absence of rotation, an extinction interference occurs between the CW and CCW light, so that the intensity of light directed to the detector is zero. Therefore, when the rotational angular velocity is very small, the noise for the light detection is given by the electronics noise given by the electronic devices including the photodetector, so it is not suitable for the measurement of the small rotational angular velocity.

A gyroscope is a device for measuring the rotational kinematics of a rotating object, and in particular, provides a measurement of the rotational angular velocity. Applications of gyroscopes are very wide, such as navigation systems used in airplanes, missiles, spacecraft, submarines, attitude control of cameras, robots, and unmanned automated devices, and gyro compasses. Gyroscopes require different levels of precision and stability depending on their application. The aforementioned gyroscope includes a mechanical gyroscope and an optical gyroscope, and in the field of ultra-precision measurement, an optical gyroscope is mostly used. The above-mentioned optical gyroscopes include ring laser gyroscopes, optical fiber gyroscopes, and the like.

A ring laser gyroscope allows the laser beams to travel in opposite directions, for example clockwise and counterclockwise, simultaneously in a resonator of three or more reflectors, and the frequency of these laser beams causes the gyroscope to rotate externally. It is a device for measuring the rotational angular velocity by detecting the difference in the frequency, that is, the difference in the effective resonator length in the CW and CCW directions given by the rotation. Ring laser gyroscopes are most commonly used in navigation systems because of their high bias stability, conversion factor linearity, wide measurement 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 lock-in effect occurs, in which frequencies of two laser beams oscillating in both directions are equal to each other by reverse scattering occurring in a reflector. When the magnitude of the rotational angular velocity is below a certain threshold, there is a problem that the measurement of the gyroscope is impossible.

On the other hand, the optical fiber gyroscope basically includes a sensing unit consisting of a light source and a fiber coil wound around the optical fiber in a circular shape. The operation of the optical fiber gyroscope is briefly described as follows. First, the light from the light source passes through the directional coupler and then splits into two lights, passing through the fiber coil, and the two lights passing through the fiber coil in opposite directions meet and interfere in the directional coupler again. When the gyroscope is stationary, both lights experience the same phase shift as they pass through the fiber coil, thus constructively interfering in the directional coupler, and the output of the photodetector is maximized. 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 is changed. Therefore, the rotational angular velocity can be detected by measuring the change in output intensity of the photodetector. Such optical fiber gyroscopes have great advantages over other types of gyroscopes in terms of price, stability, durability, and fast startup time. However, optical fiber gyroscopes have temperature-sensitive bias characteristics, and nonlinearities increase when the optical fiber length is extended to increase measurement sensitivity.

As described above, when a gyroscope is configured using a sagnac interferometer, a problem in that measurement performance of the gyroscope is limited due to problems of the conventional sagnac interferometer.

An object of the present invention for solving the above-mentioned problems is that the two beams polarized perpendicularly to each other by using polarized light beams are configured to proceed clockwise and counterclockwise, respectively, along the same closed path of free space and measure the measurement performance. It is to provide a Sagnac interferometer of the improved structure to improve the.

A sagnac interferometer according to a first aspect of the present invention for achieving the above technical problem is a light source for providing linear or circularly polarized light; A detector for dividing the light input from the light source into vertically polarized first and second beams, and moving the first and second beams in a closed path in opposite directions to each other and then combining and outputting the first and second beams together; And a demodulator for interfering a first beam and a second beam output from the detector to measure a phase change induced therebetween.

The sensing unit may be configured to receive linear or circularly polarized light from the light source at 45 degrees, and divide the input light into vertically polarized first and second beams and output the polarized light to different output ports, respectively; Two or more mirrors are used to form one closed path, and the first beam and the second beam that are output from the polarized light beam are redirected and moved along the closed path, so that the first beam is formed of the second beam. And a closed path unit configured to input the output port and the second beam to the output port of the first beam, wherein the first beam and the second beam output from the closed path unit are vertically polarized with each other to make polarized light thin. Combined and outputted in the same path is provided to the demodulator.

A sagnac interferometer according to a second aspect of the present invention includes a light source for providing linearly polarized light; A detector for dividing the light input from the light source into vertically polarized first and second beams, and moving the first and second beams in a closed path in opposite directions to each other and then combining and outputting the first and second beams together; A resonator formed at an input point and an output point of the detector to resonate the first beam and the second beam of the detector; And a demodulator for interfering a first beam and a second beam output from the resonator to measure a phase difference induced between the first beam and the second beam.

The sensing unit receives light linearly polarized at 45 degrees with respect to the polarized light from the light source, divides the input light into vertically polarized first and second beams, and outputs each of them to different output ports. Polarized light thinner; Two or more mirrors are used to form one closed path, and the first beam and the second beam that are output from the polarized light beam are redirected and moved along the closed path, so that the first beam is formed of the second beam. And a closed path unit configured to input the output port and input the second beam to the output port of the first beam, wherein the first beam and the second beam output from the closed path unit are combined in the polarized light beams in the same path. The first beam and the second beam output from the polarized light beam are resonated through a resonator and provided to the demodulator.

In the sagnac interferometer according to the second aspect described above, the resonator includes: first and second mirrors disposed at input points and output points of the sensing unit, respectively; A first quarter wave plate (QWP) disposed between the first mirror and the sensing unit; And a second quadrant 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 detector which 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 in different directions in one closed path, and then combines and outputs the combined light; A demodulator for interfering a first beam and a second beam output from the detector to measure a phase change induced therebetween; Is disposed between the light source and the sensing unit, and transmits a part of the beam provided from the light source and outputs to the sensing unit, and the light beam to reflect a portion of the beam provided from the sensing unit to output to the demodulator;

The sensing unit may be configured to split light provided from the light source into a first beam and a second beam that are vertically polarized with each other, and to output light to different output ports through the light beam; Two or more mirrors are used to form one closed path, and the first beam and the second beam that are output from the polarized light beam are redirected and moved along the closed path, so that the first beam is formed of the second beam. A closed path unit configured to input an output port and input the 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 closed path portion and retarding the light transmitted through the closed path by half a wavelength. And a first beam and a second beam output from the closed path part are combined and output from the polarized light beam and then reflected or transmitted by the light beam and provided to the demodulator.

According to a fourth aspect of the present invention, a sagnac interferometer includes: a light source for providing polarized light; A detector which 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 in different directions in one closed path, and then combines and outputs the combined light; A demodulator for interfering a first beam and a second beam output from the detector to measure a phase change induced therebetween; A light beam disposed between the light source and the sensing unit to transmit a part of the beam provided from the light source and output to the sensing unit, and reflect a part of the beam provided from the sensing unit to output to the demodulator; And a resonator disposed between the light beam and the sensing unit.

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) It is preferable to further include a control unit for measuring and providing.

In the sagnac interferometer according to the first to fourth features described above, the demodulator comprises: a phase delay device for applying a bias phase between the first beam and the second beam that are perpendicular to each other provided from the sensing unit; Dividing the beam output from the phase delay device into a third beam and a fourth beam, respectively and outputting light; An I signal output unit for detecting and outputting an I output signal from the third beam passing through the light beam; A Q signal output unit for detecting and outputting a Q output signal from the fourth beam reflected by the light beam; It is preferable to have a.

In the sagnac interferometer according to the first to fourth features described above, the demodulator comprises: a phase delay device for applying a bias phase between the first beam and the second beam that are perpendicular to each other provided from the sensing unit; A polarizer for aligning the first beam and the second beam delayed by the phase delay device by 45 degrees to output an interference signal of the first beam and the second beam; And a photodetector for outputting a detection signal detecting the beam output from the polarizer.

In the sagnac interferometer according to the first to fourth features described above, the demodulator comprises: a phase delay device for applying a bias phase between the first beam and the second beam that are perpendicular to each other provided from the sensing unit; A polarized light beam that interferes with the first beam and the second beam output from the phase delay device and outputs the divided light according to the polarization state; A first photodetector for detecting a third beam reflected from the polarized light beam and outputting a first detection signal; A second photodetector for detecting a fourth beam transmitted through the polarized light beam and outputting a second detection signal; And a differential amplifier detecting and outputting a difference between the first and second detection signals.

In the sagnac interferometer according to the second and fourth features described above, it is preferable to include a resonator mirror fixed to a displacement device such as a piezoelectric transducer) to actively adjust the resonance conditions.

The sagnac interferometer according to the present invention can be precisely measured even by a rotation with a small angular velocity unlike the conventional sagnac interferometer by using a polarized light filter.

In addition, the sagnac interferometer according to the second and fourth embodiments of the present invention constitute a resonant structure, so that the CW light and the CCW light are output after a plurality of times in the resonator. As a result, the rotation can be measured more precisely and always maintain high sensitivity.

1 is a block diagram showing a conventional Sagnac interferometer.

Figure 2 is a schematic diagram showing the overall Sagnac interferometer according to a first embodiment of the present invention.

Figure 3 is a schematic diagram showing the overall Sagnac interferometer according to a second embodiment of the present invention.

Figure 4 is a schematic diagram showing the overall Sagnac interferometer according to a third embodiment of the present invention.

5 is a block diagram showing the overall Sagnac interferometer according to a fourth embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating a Sagnac Effect used to detect a rotational angular velocity using a phase difference according to a Sagnac interferometer according to the present invention.

7 is a block diagram showing an embodiment of a demodulation unit in the sagnac interferometer according to the present invention.

8 is a block diagram showing another embodiment of the demodulator in the sagnac interferometer according to the present invention.

9 is a block diagram showing another embodiment of the demodulation unit in the sagnac interferometer according to the present invention.

Sagnac interferometer according to the present invention is characterized in that it is configured using a polarized light filter and a resonator.

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

Figure 2 is a schematic diagram showing the overall improved Sagnac interferometer according to the 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 detector 20, and a demodulator 30, and further includes a controller 40. It can be provided.

The light source 10 provides 45 degrees linear or circularly polarized light to the polarized light beam 200 of the sensing unit 20. The light source may be configured to output a linear or circularly polarized laser beam by 45 degrees using a single laser beam generator, or may be configured by combining the laser beam generator and a polarization rotating device to produce a linear or circularly polarized laser beam by 45 degrees. You could also print

The sensing unit 20 includes a closed path unit 210 formed of a polarized light beam 200 and a plurality of light

path changing elements

211, 212, and 213 to form one closed path. The sensing unit having the above-described structure, detects the rotation or movement of the Sagnac interferometer using the light provided from the light source, and demodulates the first beam and the second beam having a phase difference according to the rotational angular velocity by the rotation or movement ( 30).

The closed path unit 210 is composed of two or more light path changing elements, and together with the polarized light beam 200 constitutes one closed path. The light path changing devices may use devices that reflect or totally reflect an incident beam, such as a reflector or a prism. As illustrated in FIG. 2, in one embodiment, three

reflectors

211, 212, and 213 may be sequentially arranged.

The first and second beams respectively output from the first output port and the second output port of the polarized light beam are input to the closed path part, respectively, and the first and second beams input to the closed path part are closed. Moved along the path in the CCW direction and the CW direction, respectively, so that the first beam is input back to the output port of the second beam and the second beam is input back to the output port of the first beam. The first beam and the second beam output from the closed path part are polarized perpendicularly to each other, input back to the polarized light beam, merged in the polarized light beam, and then output through the same path to the demodulator.

In particular, the sensing unit 20 divides the light incident from the light source into two beams by reflecting the S-polarized light and transmitting the P-polarized light according to the polarization direction in the polarized light beam 200. It proceeds in opposite directions along one closed path and then merges again in the polarized light beam and outputs to the demodulator. The demodulator demodulates the beam thus output, thereby measuring the phase difference between the second beam and the first beam, which have advanced in the CW and CCW directions, respectively.

The polarized light beam 200 is an optical element that reflects S-polarized light and transmits P-polarized light according to the polarization direction according to the polarization direction. The first beam having different polarization directions by reflecting or transmitting it according to the polarization direction It is separated into a second beam and output to the closed path portion 210. The first beam and the second beam output to the closed path portion are rotated in opposite directions, respectively, and re-entered again into the first polarized light beam, and the re-entered first beam and the second beam are combined and output to the demodulator.

The closed path unit 210 includes a plurality of light path changing elements that are sequentially arranged such that beams output from the polarized light beam move in opposite directions along the closed path and then enter the polarized light beam again. By allowing a closed path to be formed in free space, the beams can travel in free space. The first beam reflected from the polarized light beam by the closed path part is output in a counterclockwise direction and re-entered into the polarized light beam, and the second beam transmitted through the polarized light beam is clockwise. Proceed is reincident to the polarized light beam. Accordingly, the first beam and the second beam, which are in the state of perpendicular polarization, move in opposite directions along the closed path of the closed path portion, and are re-entered into the polarized light beam and output to the demodulator.

If the Sagnac interferometer rotates while the first beam and the second beam move through the free space of the closed path portion, the first beam and the second beam have a phase difference according to the rotational angular velocity of the sagnac interferometer.

The demodulator 30 interferes with the first beam and the second beam output from the detector 20, and measures and provides a phase difference induced therebetween.

The controller 40 calculates a phase difference between the first beam and the second beam from the interference signals of the first beam and the second beam provided from the demodulator, and calculates and outputs a rotational angular velocity of the sagnac interferometer. The sagnac interferometer according to the present invention may include the control unit 40 therein or may be configured without the control unit 40. When the sagnac interferometer is configured without a control unit, the sagnac interferometer may 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 using an external control device or a computer. The control device or computer may 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.

FIG. 6 is a schematic diagram illustrating the Sagnac Effect used to detect the rotational angular velocity using the phase difference between the first beam and the second beam in the Sagnac interferometer according to the present invention. As shown in FIG. 6, when the Sagnac interferometer rotates, the optical path difference ΔL occurs between the first beam and the second beam traveling in opposite directions by the closed path part. . Therefore, the optical path difference is obtained 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.

Second Embodiment

Figure 3 is a schematic diagram showing the overall improved Sagnac interferometer according to a second embodiment of the present invention.

Referring to FIG. 3, the gyroscope 2 according to the second embodiment of the present invention includes a light source 12, a detector 22, a demodulator 32, and a resonator 52, and a controller 42. ) May be further provided. Since the structure of the sensing unit 22 of the second embodiment is the same as those of the first embodiment, overlapping description is omitted.

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

The detector 22 is disposed inside the resonator 52, and divides the light input from the light source into a first beam and a second beam polarized perpendicularly to each other, and divides the first beam and the second beam into a single beam. In the closed path, move along the opposite direction and then combine again to output to the demodulator.

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

Preferably, the first and second mirrors 520 and 522 are composed of mirrors having a large reflection coefficient (R). For example, if the first and second mirrors consist of mirrors with a reflection coefficient of 98%, the finesse of the resonator is 157, assuming there is no loss in the polarized light beam, and the CW and CCW beams in the resonator are approximately Since it can go back 100 times, the induced phase value increases by about 100 times. Even considering the loss in the polarized light beam, the performance of the interferometer can be improved accordingly because the CW beam and the CCW beam can be repeatedly returned several dozen times.

The detector 22 has the same structure as that of the detector of the first embodiment, but includes a first mirror 520 and a first quarter wave plate of the resonator between the light source and the incident surface of the polarized light beam 200. 521 is disposed, and a second mirror 522 and a second quarter wave plate 523 of the resonator are disposed between the emission surface of the polarized light beam and the demodulator.

Hereinafter, in the sagnac interferometer according to the second embodiment of the present invention, the paths of the first beam and the second beam in the detector 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, and the polarization state is passed through the first QWP since the polarization direction of the incident light is parallel to the main axis of the first QWP. Is kept in the same state as the incident light. Since the main axis of the first QWP, that is, the polarization direction of the incident light forms an angle of 45 degrees with the main axis of the polarized light beam, the P polarized light component of the incident beam passes through the polarized light beam 200 to form the first beam. The S component is reflected to form a second beam. The first beam transmitted through the polarized light beam goes along the path formed by the closed path part in the CCW direction, and the second beam reflected from the polarized light beam goes along the path formed by the closed path part in the CW direction. . The first beam traveling in the CCW direction along the closed path part is re-entered into the polarized light beam as P-polarized light and transmitted again to transmit the second QWP, the second mirror, and the second QWP, and then enter 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 in the polarized light beam which is incident again, and then proceeds to the closed path part again in the CCW direction. By repeating this process, the first beam is repeatedly returned in the CCW direction. Therefore, when the resonator satisfies the standing wave condition, the light incident through the first mirror causes augmented interference, and the intensity of the light is gradually increased in the resonator, and some of them are output through the second mirror 522. The number of times the first beam returns along the closed path is given by the reflectivity of the mirror. On the other hand, like the first beam, the second beam is output through the second mirror 522 while rotating the same number of times in the CW direction.

For example, when the reflection coefficients (R) of the first and second mirrors constituting the resonator are 98%, the finesse of the resonator is 157, and the first and second beams are separated from other elements such as polarized light. If the loss is not considered, it will be printed after about 100 times.

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, detects and outputs a phase difference between the first beam and the second beam.

The sagnac interferometer according to the second embodiment may improve the sensitivity by the number of times the beam is returned by the resonator as compared with the sagnac interferometer according to the first embodiment in which the beam is rotated once along the closed path part of the sensing unit. .

Third Embodiment

Figure 4 is a schematic diagram showing the overall improved Sagnac interferometer according to a third embodiment of the present invention.

Referring to FIG. 4, a sagnac interferometer 3 according to a third embodiment of the present invention includes a light source 10, a light beam 250, a detector 23, and a demodulator 30. 40 may be further provided.

The light source 10 provides 45 degrees linear or circularly polarized light to the detector 23 through the light beam 250. The light source may be configured to output a linear or circularly polarized laser beam by 45 degrees using a single laser beam generator, or may be configured by combining the laser beam generator and a polarization rotating device to produce a linear or circularly polarized laser beam by 45 degrees. You could also print

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

The sensing unit 23 includes a polarization light path 200, a closed path unit 210 composed of a plurality of light

path changing elements

211, 212, and 213, and a half wave plate 240. 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 by the rotation or movement to the demodulator 30 through the light beam 250. do.

The polarized light beam 200 divides the light provided from the light source through the light beam and divides the first beam and the second beam polarized perpendicularly to each other and outputs them to different output ports.

The closed path unit 210 constitutes one closed path using two or more mirrors, and changes the first and second beams output from the polarized light beam 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 immediately behind, the polarized light beam 200 on the closed path of the closed path part to rotate the polarization direction of the beam transmitted through the closed path by 90 degrees. Therefore, since the polarization state of the light traveling in the CW direction and the CCW direction along the closed path is the same, it is not affected by the birefringence noise that may be applied to an anisotropic flow of air.

The first beam and the second beam output from the closed path part are polarized perpendicularly to each other, merged in the polarized light beam, and output from the light beam 200 along the same path to the demodulator.

Hereinafter, in the sagnac interferometer according to the third embodiment of the present invention, the paths of the first beam and the second beam in the detector 23 will be described in detail.

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

On the other hand, by arranging the half-wave plate 240 in contact with the polarized light beam 200, the beam passing through the closed path of the closed path portion is rotated by 90 degrees by the half-wave plate. As a result, the first beam, which is P-polarized light transmitted through the polarized light beam, moves the closed path of the closed path portion in a counterclockwise direction and reenters the polarized light beam, wherein the polarization direction is caused by the half-wave plate 240. As it is rotated by 90 degrees, it is reflected from the re-incident polarized light beam 200 and proceeds to the light beam. On the other hand, the second beam of S polarized light reflected by the polarized light beam is rotated 90 degrees by the half-wave plate to move the closed path portion clockwise in the clockwise direction to pass through the reentrant polarized light beam You will proceed to crab. Therefore, the light that proceeds clockwise and counterclockwise has the same polarization state in a closed path, thereby constructing a completely reversible sagnac interferometer, and the first beam transmitted or reflected through the reentrant polarized light beam And the second beam is combined in the polarized light beam and proceeds to the light beam, and a part of the beam is output to the demodulator 30.

The demodulator demodulates the beam inputted from the light beam, thereby measuring the phase difference between the second beam and the first beam, which have advanced in the CW and CCW directions, respectively.

The demodulator 30 interferes with the first beam and the second beam output from the detector 20, and measures and provides a phase change induced therebetween.

The controller 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 schematic diagram showing an overall improved sagnac interferometer according to a fourth embodiment of the present invention.

Referring to FIG. 5, the Sagnac interferometer 4 according to the fourth embodiment of the present invention includes a light source 10, a light beam 250, a detector 23, a demodulator 30, and a resonator 54. Is provided, and may further include a control unit 40. In the sagnac interferometer 4 according to the present embodiment, the resonator 54 is further disposed between the light beam 250 of the sagnac interferometer according to the third embodiment and the polarization light beam 200 of the sensing unit. It features.

The resonator 54 is disposed between the light beam 250 and the polarizing light beam 200 of the sensing unit, and comprises a mirror 530 and a quarter-wave plate (QWP) 531. The quarter wave plate is a phase delay plate which delays the phase difference between principal polarization components of the input light by λ / 4 and outputs the delayed phase difference. The mirror 530 is preferably composed of mirrors having a large reflection coefficient (R). For example, in the case of a mirror having a reflection coefficient of 98%, the finesse of the resonator is 157, assuming that there is no loss in the polarized light, and the CW and CCW beams in the resonator can be repeated about 100 times. In this case, the induced phase value increases by about 100 times. Even considering the loss in the polarized light beam, the performance of the interferometer can be improved accordingly because the CW beam and the CCW beam can be repeatedly returned several dozen times.

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

The configuration and operation of the detector 23 are the same as the configuration and operation of the detector 23 according to the third embodiment.

The Sagnac interferometer 4 according to the present embodiment having the above-described configuration rotates the free space of the closed path part until the first beam and the second beam satisfy the resonance condition by the detector and the resonator, and then outputs the demodulator. The phase difference and the rotational angular velocity induced by the interference signals of the first beam and the second beam are calculated by the demodulator and the controller.

Hereinafter, various embodiments of the demodulator in the sagnac interferometer according to the present invention described above will be described.

7 is a block diagram showing an embodiment of a demodulation unit in the sagnac interferometer according to the present invention. Referring to FIG. 7, the demodulator 30 includes a phase delay device 372, a polarizer 375, and a photodetector PD.

The phase delay device 372 is for applying a bias phase between the first beam and the second beam that are perpendicular to each other provided from the sensing unit. For optimal demodulation of the first and second beams, it is desirable to use a phase delay device to make the phase bias between the first and second beams an odd multiple of 90 degrees. Therefore, it can be used in various ways according to the polarization state of the first beam and the second beam, for example, can be used a quarter wave plate (QWP) that phase-delays the quadrant wavelength between the main polarization component, if the first When the phases of the beam and the second beam are changed by reflection in polarized light and the like, it is preferable to use a phase delay device other than QWP to make the phase difference between the first beam and the second beam an odd multiple of 90 degrees.

The polarizer 375 outputs an interference signal between the first beam and the second beam by aligning the first and second beams phase-delayed by the phase delay device at 45 degrees.

The photodetector PD outputs a detection signal that detects a beam output from the polarizer, and is given by Equation 1 below when the bias phase between the first beam and the second beam is 90 degrees.

Where R is the response of the photodetector, I ₀ is the total intensity of the first beam and the second beam, and Δφ is the phase difference induced in the first beam and the second beam by the rotation of the interferometer and the like and has a very small value in ordinary cases.

8 is a block diagram showing another embodiment of the demodulation unit in the sagnac interferometer according to the present invention. Referring to FIG. 8, the demodulator 31 includes a phase delay device 398, polarized light beams 392, first and second photodetectors 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 provided from the sensing unit, in a vertical polarization state. It can be used in various ways according to the phase values of the first and second beams given by the reflection in the mirror. For example, a quarter wave plate (QWP) which phase-delays quadrant wavelengths between the main polarization components can be used. have.

The polarized light beams 392 are aligned at 45 degrees with respect to the polarization directions of the first beam and the second beam output from the phase delay device. Therefore, the s-components of the first and second beams are combined to cause interference and polarization. Reflected at the light beam, the p components of the first and second beams combine to cause interference and to pass through the polarized light beam.

The first photodetector PD1 detects a third beam reflected from the polarized light beam and outputs a first detection signal, and the second photodetector PD2 transmits the polarized light beam. The fourth beam is detected and a second detection signal is output. 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 Equations 2 and 3, respectively.

The differential amplifier 395 outputs a difference between the first and second detection signals, and an output signal is given by Equation 4 below.

Therefore, the demodulator of the above-described structure subtracts the interference signals detected from the third and fourth beams by the differential amplifier, thereby eliminating mutually correlated noise contained in each optical signal and doubling the optical signal. The noise ratio can be increased. Such a measurement method is called a balanced detection method.

9 is a block diagram showing another embodiment of the demodulation unit in the sagnac interferometer according to the present invention. Referring to FIG. 9, the demodulator 32 includes a phase delay device 300, a light beam 310, an I signal output unit 320, and a Q signal output unit 330, and outputs an I signal. An I-output signal (In-phase Signal; V _I ) and a Q-output signal (Quadrature-phase Signal: V _Q ) having a phase difference of 90 ° from each other are generated and output from the negative and Q signal output units, respectively. The I output signal (In-phase Signal; V _I ) is proportional to cos Δφ and the Q output signal (Quadrature-phase Signal: V _Q ) is proportional to sin Δφ .

The demodulator 32 demodulates the first beam and the second beam output from the detector, and outputs an I-output signal ( V _I ) signal and a Q output signal for the first beam and the second beam. (Quadrature-phase Signal: V _Q ) is detected and output. 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 for applying a bias phase between the first beam and the second beam that are perpendicular to each other from the sensing unit, and variously selected according to the polarization states of the first and second beams. For example, a half-wave plate that rotates the first beam and the second beam by 45 degrees and outputs the light beam 310 may be used.

The light beam 310 is provided with a first beam and a second beam rotated by 45 degrees from the phase delay device, and the first and second beams are 50:50 to the third and fourth beams. Divided and transmitted respectively. The third beam transmitted through the light beam is provided to the I signal output unit, and the fourth beam reflected from the light beam is provided to the Q signal output unit.

The I signal output unit 320 is configured to detect and output an I output signal from the third beam transmitted through the light beam. The I signal output unit 320 detects the beam reflected from the second polarized light beam 322 and the second polarized light beam disposed on the traveling path of the third beam passing through the light beam. Detects the difference between the first detection element 323, the second detection element 324 for detecting the beam transmitted through the second polarized light beam, and the beams output from the first detection element and the second detection element And a first differential amplifier 325 for amplifying and outputting the same. The first and second detection elements may be composed of photodiodes.

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

The first differential amplifier of the I-signal output section and the second differential amplifier of the Q-signal output section having the above-described configuration are respectively an in-phase signal ( V _I ) signal and a Q output signal for the first beam and the second beam. Outputs (Quadrature-phase Signal: V _Q ).

The controller 40 receives an I output signal and a Q output signal from a demodulator, and detects and outputs a rotational angular velocity using the I output signal and the Q output signal. Hereinafter, the process of the control part 40 detecting rotation angular velocity (ohm) using the output signal of the demodulation part which concerns on this embodiment is demonstrated concretely.

First, I output signal obtained from the demodulator (32) (In-phase Signal ; V I) is proportional to cos △ φ, and the Q output signal: it (Quadrature-phase Signal V _Q) is proportional to sin △ φ, I Using the output signal V _I and the Q output signal V _Q , the phase difference Δφ according to the rotation of the object can be calculated by Equation 5.

The time ( t +) for the second beam rotating clockwise in the sensing unit to circulate the optical rotating unit can be obtained by Equation 6, and the time taken for the first beam rotating in the counterclockwise direction to circling the optical rotating unit. ( t- ) can be obtained by Equation 7.

The optical path difference ΔL between the first beam and the second beam according to the rotation of the object may be obtained from Equation 8.

By the rotation of the object, an optical path difference ΔL is generated between the first beam and the second beam that travel in opposite directions. The interference signal can be obtained by interfering the first beam and the second beam. Since the phase change in the interference signal is given as a linear function of the rotational angular velocity, the phase angular velocity can be measured and the rotational angular velocity can be accurately measured using this. It becomes possible.

A phase difference (△ φ) of the first beam with a first beam and a second beam using the optical path difference (△ L) of the second beam in accordance with the rotation of the object can be determined in Equation (9).

Rotational angular velocity (Ω) according to the rotation of the object from Equation (9) can be represented by Equation 10, the first obtained by using the I output signal ( V _I ) and Q output signal ( V _Q ) through the equation (4) by using the phase difference (△ φ) of the beam and the second beam it is able to obtain the rotational angular velocity (Ω) according to the rotation of the object.

Where λ is the wavelength of light, t- is the time it takes for the first beam to rotate in the counterclockwise direction, and t + is the time it takes for the second beam to rotate in the clockwise direction, , Ω is the rotational angular velocity, C is the speed of light, R is the radius of the ring constituting the optical rotation, A is the area of the ring, ΔL is the first and second beams traveling in opposite directions Δφ is a phase change value induced by the angular velocity.

The chagnac interferometer according to the present invention having the above-described configuration is constructed in a new structure using polarized light beams, and then, after two beams in a vertical polarization state are advanced in opposite directions along a closed path, the phase difference is obtained. By using the rotation angle of the object can be measured by the rotation.

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

Although the present invention has been described above with reference to preferred embodiments thereof, this is merely an example and is not intended to limit the present invention, and those skilled in the art do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications which are not illustrated above in the scope are possible. And differences relating to such modifications and applications should be construed as being included in the scope of the invention as defined in the appended claims.

Claims

A light source providing linear or circularly polarized light;

A detector for dividing the light input from the light source into vertically polarized first and second beams, and moving the first and second beams in a closed path in opposite directions to each other and then combining and outputting the first and second beams together;

A demodulator for interfering a first beam and a second beam output from the detector to measure a phase change induced therebetween;

Is provided, the detection unit,

Receiving polarized light linearly or circularly polarized by 45 degrees from the light source, dividing the input light into vertically polarized first beams and second beams and outputting the polarized light to different output ports;

Two or more mirrors are used to form one closed path, and the first beam and the second beam that are output from the polarized light beam are redirected and moved along the closed path, so that the first beam is formed of the second beam. And a closed path unit configured to input the output port and the second beam to the output port of the first beam.

And a first beam and a second beam output from the menopausal path part are vertically polarized, merged in a polarized light beam, and output in the same path to be provided to the demodulator.
A light source for providing linearly polarized light;

A detector for dividing the light input from the light source into vertically polarized first and second beams, and moving the first and second beams in a closed path in opposite directions to each other and then combining and outputting the first and second beams together;

A resonator formed at an input point and an output point of the detector to resonate the first beam and the second beam of the detector; And

A demodulator for interfering a first beam and a second beam output from the resonator to measure a phase difference induced between the first beam and the second beam;

Is provided, the detection unit

Receiving polarized light at 45 degrees from the light source, dividing the input light into vertically polarized first beams and second beams and outputting the polarized light to different output ports;

Two or more mirrors are used to form one closed path, and the first beam and the second beam that are output from the polarized light beam are redirected and moved along the closed path, so that the first beam is formed of the second beam. And a closed path unit configured to input the output port and the second beam to the output port of the first beam.

The first beam and the second beam output from the closed path unit are combined in the polarized light beam and output in the same path, and the first beam and the second beam output from the polarized light beam are resonated through a resonator to demodulate the demodulated signal. Free space Sagnac interferometer, characterized in that provided in wealth.
The method of claim 2, wherein the resonator

First and second mirrors disposed at an input point and an output point of the sensing unit, respectively;

A first quarter wave plate (QWP) disposed between the first mirror and the sensing unit; And

A second quarter wave plate disposed between the second mirror and the sensing unit;

Free space Sagnac interferometer comprising the.
A light source for providing polarized light;

A detector which 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 in different directions in one closed path, and then combines and outputs the combined light;

A demodulator for interfering a first beam and a second beam output from the detector to measure a phase change induced therebetween;

A light beam disposed between the light source and the sensing unit to transmit a part of the beam provided from the light source and output to the sensing unit, and reflect a part of the beam provided from the sensing unit to output to the demodulator;

Is provided, the detection unit

Polarizing light beams, which divide the light provided from the light source through the light beams into vertically polarized first and second beams and output the light beams to different output ports;

Two or more mirrors are used to form one closed path, and the first beam and the second beam that are output from the polarized light beam are redirected and moved along the closed path, so that the first beam is formed of the second beam. A closed path unit configured to input an output port and input the second beam to an output port of the first beam; And

A half wave plate (HWP) disposed at an arbitrary position on a closed path of the closed path part to rotate a polarization direction of light transmitted through the closed path by 90 degrees;

And a first beam and a second beam output from the closed path part are combined in the polarized light beam and output and then reflected or transmitted by the light beam and provided to the demodulator. interferometer.
The free space sagnac interferometer of claim 4, wherein the free space sagnac interferometer further comprises a resonator between the light beam and the polarizing light beam of the sensing unit.
The method of claim 5, wherein the resonator

A mirror disposed between the light beam and the polarizing light beam of the sensing unit; And

A quarter wave plate (QWP) disposed between the mirror and the sensing unit;

Free space Sagnac interferometer comprising the.
The free space sagnac interferometer according to any one of claims 1 to 6,

Receiving from the demodulator providing a first phase difference (△ φ) of the phase change of the first beam and the second beam, a free space, characterized in that by using the phase difference further comprising a controller that provides to measure the rotation angular velocity (Ω) Sagnac interferometer.
The demodulation unit according to any one of claims 1 to 6, wherein

A phase delay device for applying a bias phase between the first beam and the second beam which are perpendicular to each other provided from the sensing unit;

Dividing the beam output from the phase delay device into a third beam and a fourth beam, respectively and outputting light;

An I signal output unit for detecting and outputting an I output signal from the third beam passing through the light beam;

A Q signal output unit for detecting and outputting a Q output signal from the fourth beam reflected by the light beam;

A free space Sagnac interferometer comprising: a.
The demodulation unit according to any one of claims 1 to 6, wherein

A phase delay device for applying a bias phase between the first beam and the second beam which are perpendicular to each other provided from the sensing unit;

A polarizer for aligning the first beam and the second beam delayed by the phase delay device by 45 degrees to output an interference signal of the first beam and the second beam; And

A photodetector for outputting a detection signal detecting a beam output from the polarizer;

A free space Sagnac interferometer comprising: a.
The demodulator according to any one of claims 1 to 6, wherein

A phase delay device for applying a bias phase between the first beam and the second beam that are perpendicular to each other provided from the sensing unit;

A polarized light beam that interferes with the first beam and the second beam output from the phase delay device and outputs the divided light according to the polarization state;

A first photodetector for detecting a third beam reflected from the polarized light beam and outputting a first detection signal;

A second photodetector for detecting a fourth beam transmitted through the polarized light beam and outputting a second detection signal;

A differential amplifier detecting and outputting a difference between the first and second detection signals;

A free space Sagnac interferometer comprising: a.