KR101516173B1 - Non-contacting displacement sensor using bi-directional modulation of mach-zehnder electro-optical modulator - Google Patents

Non-contacting displacement sensor using bi-directional modulation of mach-zehnder electro-optical modulator Download PDF

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KR101516173B1
KR101516173B1 KR1020140053586A KR20140053586A KR101516173B1 KR 101516173 B1 KR101516173 B1 KR 101516173B1 KR 1020140053586 A KR1020140053586 A KR 1020140053586A KR 20140053586 A KR20140053586 A KR 20140053586A KR 101516173 B1 KR101516173 B1 KR 101516173B1
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light
optical modulator
optical
modulation
mach
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반재경
김현호
최상진
호일
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전북대학교산학협력단
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/102—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for optical coherence tomography [OCT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/167—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by projecting a pattern on the object
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0128—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on electro-mechanical, magneto-mechanical, elasto-optic effects
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
    • G02F2001/0139—

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  • Nonlinear Science (AREA)
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Abstract

The present invention relates to a non-contact displacement sensor using bi-directional modulation of a Mach-Zehnder electro-optical modulator comprising: a light source for outputting a laser beam; a circulator connected to the light source to change a direction of an incident light beam in a different direction; an optical modulator for RF-modulating an incident light beam and outputting a modulated light beam; a collimator for widening the modulated light beam from the optical modulator and outputting the widened light beam onto a target object, and receiving and supplying a reflected light beam to the optical modulator; an opto/electro conversion unit for receiving the modulated light beam from the optical modulator and converting the optical signal into an electric signal; and an analysis unit for supplying an RF signal to the optical modulator and analyzing a spectrum of the electric signal received from the opto/electro conversion unit. The optical modulator forward RF-modulates the light beam from the circulator and outputs the modulated light beam to the collimator, and reverse RF-modulates the light beam entering from the collimator and measures a displacement of the target object using a time difference between the forward RF-modulated light beam and the reverse RF-modulated light beam.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a non-contact displacement sensor using a bidirectional modulation of a Mach-Zehnder optical modulator,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact displacement sensor using bidirectional modulation of an optical modulator, and more particularly, to a displacement sensor using a Mach-Zehnder Electro-Optical Modulator (MZ-EOM) To a non-contact displacement sensor using bidirectional modulation of a Mach-Zehnder optical modulator.

Displacement sensors are used not only for precise measurement of micro dimensions such as the height, width, or thickness of an object, but also for monitoring and controlling the state of a high speed machining machine. These displacement sensors are of the contact type and non-contact type.

The non-contact displacement sensor includes a magnetoresistance method, an electromagnetic wave method, and an ultrasonic method, and there is a method using a laser.

The non-contact displacement sensor of the conventional magneto-resistive type has a magnetic distortion effect (Korean Patent Registration No. 1010171200000), which generates ultrasonic waves due to magnetic distortion by applying a current pulse and generating a magnetic field, This method has the disadvantage that the error is largely generated in the environment where the electromagnetic field is generated.

In addition, the electromagnetic wave system and the ultrasonic wave system output electromagnetic waves or ultrasonic waves to the object to be measured and measure the reflected signals, which causes an error in an environment where electromagnetic waves are generated.

A non-contact displacement sensor using a bidirectional modulation of a Mach-Zehnder optical modulator that measures a displacement of a measured object in a non-contact manner using a bidirectional modulation of a Mach-Zehnder optical modulator.

A non-contact displacement sensor using bidirectional modulation of a Mach-Zehnder optical modulator according to an embodiment of the present invention includes a light source for outputting laser light; A circulator connected to the light source and outputting light inputted thereto through another path; An optical modulator for RF modulating the input light and outputting the modulated light; a modulator for converting the modulated light input from the light modulator into a large area and outputting the modulated light to a subject; receiving light reflected from the subject; A collimator provided on the part; An optical / electrical conversion section for receiving the modulated light input from the optical modulation section and converting the optical signal into an electrical signal; And an analyzer for applying an RF signal to the optical modulator and analyzing a spectrum of an electrical signal input from the optical / electrical converter, wherein the optical modulator performs forward-RF modulation on light input from the circulator, And the displacement of the measured object can be measured using the time difference between the forward RF modulated light and the backward RF modulated light by reverse-modulating the light input from the collimator.

The displacement (d) of the measured object is

Figure 112014042384639-pat00001
(Where c is the speed of light in free space, and Δτ (d) is the time delay of the change when it occurs by d).

The non-contact displacement sensor using the bidirectional modulation of the Mach-Zehnder optical modulator may include at least one non-contact displacement sensor provided between the circulator and the optical modulator, or between the optical modulator and the collimator or between the circulator and the optical / And may further include a polarization controller.

The non-contact displacement sensor using bidirectional modulation of the Mach-Zehnder optical modulator may further include an amplification unit for amplifying the modulated electrical signal between the optical / electrical conversion unit and the analysis unit.

The analyzer may include a RF oscillator for generating the RF signal and a spectrum analyzer for analyzing the spectrum of the photoelectric signal.

The analyzer may sweep the RF signal to a frequency of several KHz to 500 MHz and supply the RF signal to the optical modulator.

The non-contact displacement sensor using the bidirectional modulation of the Mach-Zehnder optical modulator according to the embodiment of the present invention can accurately measure the dimensions of micro-units such as the height, width, or thickness of an object and can monitor or control the state of the machine moving at high speed Can be used. Further, since the non-contact displacement sensor of the present invention uses light, it is possible to measure the displacement of the measured object without error in an environment where electromagnetic waves are generated due to strong electromagnetic waves and external environment.

The non-contact displacement sensor using the bidirectional modulation of the Mach-Zehnder optical modulator according to the present invention adjusts the length of the optical fiber between the optical modulator and the measured object, the number of samplings of the analyzer, and the power of the light output from the light source, Measuring range or resolution can be adjusted.

1 is a block diagram showing a noncontact optical fiber sensor according to an embodiment of the present invention.
2 is a block diagram showing a bidirectional modulation equivalent model of the optical modulation unit shown in Fig.
FIG. 3 and FIG. 4 are waveform diagrams showing transfer functions calculated according to the displacement of the object to be measured in the optical fiber sensor shown in FIG. 1;
5 is a graph showing FSR and passage time according to displacement of a measured object.

Hereinafter, the description of the present invention with reference to the drawings is not limited to a specific embodiment, and various transformations can be applied and various embodiments can be made. It is to be understood that the following description covers all changes, equivalents, and alternatives falling within the spirit and scope of the present invention.

In the following description, the terms first, second, and the like are used to describe various components and are not limited to their own meaning, and are used only for the purpose of distinguishing one component from another component.

Like reference numerals used throughout the specification denote like elements.

As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It is also to be understood that the terms " comprising, "" comprising, "or" having ", and the like are intended to designate the presence of stated features, integers, And should not be construed to preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 5 attached herewith.

FIG. 1 is a block diagram showing a noncontact optical fiber sensor according to an embodiment of the present invention, and FIG. 2 is a block diagram showing an equivalent model of the optical modulator shown in FIG.

1 and 2, the noncontact optical fiber sensor according to the present invention includes a light source 100, an optical modulator 300, a collimator 400, a circulator 200, an optical / electrical conversion unit 500, (600).

Specifically, the light source 100 is connected to one end of the circulator 200 through an optical fiber. The light source 100 may include a laser diode that oscillates a single wavelength or a wavelength tunable laser that oscillates a plurality of wavelengths. At this time, the light source 100 may use a laser that oscillates a wavelength with less attenuation to match the transmission characteristic of the optical fiber.

The optical modulation unit 300 RF-modulates the input light and outputs the modulated light. For example, the optical modulation unit 300 may include a Mach-Zehnder optical modulator capable of bi-directional modulation. The optical modulator 300 is disposed between the circulator 200 and the collimator 400 and modulates and outputs the light according to the RF signal input from the analyzer 600. The light modulator 300 RF modulates the light input from the light source 100 and outputs the modulated light to the collimator 400. The light modulator 300 modulates the light input from the collimator 400 and outputs the modulated light to the circulator 200 do. Here, RF modulation of light input from the light source 100 is referred to as forward modulation, and RF modulation of light input from the collimator 400 is referred to as reverse modulation.

The optical modulator 300 may use a Mach-Zehnder optical modulator capable of bi-directional modulation. If a Mach-Zehnder optical modulator is used, the light can be modulated according to the frequency of the input RF signal. The Mach-Zehnder optical modulator receives DC and RF signals and performs RF modulation at the DC level.

As shown in FIG. 2, the optical modulator 300 can perform forward modulation and backward modulation on the basis of a reflection point. The transfer function of the forward modulation is H1 (f), and the transfer function of the reverse modulation is H2 (f). At this time, the bias voltage input to the optical modulator 300 is the same. The modulation frequency of the RF signal supplied to the optical modulator 300 in the actual system is the same but the modulation frequency f (t) at the forward modulation in the equivalent model and the modulation frequency f (t-tau ) May be different. At this time, the modulation frequency (f (t-τ)) in the backward modulation in the equivalent model can be reflected in the optical fiber and the free space in comparison with the modulation frequency of the forward modulation.

The collimator 400 is disposed between the light modulator 300 and the object to be measured, outputs the light input from the light modulator 300 to the object to be measured, and transmits the light reflected from the object to the light modulator 300 ). At this time, the collimator 400 can transmit the light input from the light modulation unit 300 to the object to be measured in a large area.

Although not shown in FIG. 1, a horizontal holding means for maintaining the horizontal position of the collimator 400 may be added. The horizontal holding means (not shown) may be formed to be adjustable in angle so as to change the horizontal angle so that light enters perpendicularly to the stop surface of the measured object.

The circulator 200 can transmit the light input to the 3-terminal element by a predetermined path. The circulator 200 is disposed between the light source 100 and the light modulator 300 and supplies the light input from the light source 100 to the light modulator 300. The light modulator 300 And the light can be provided to the light /

The optical / electrical conversion unit 500 may use a photodiode for converting the light input from the circulator 200 into an electric signal. The optical / electrical conversion unit 500 converts the input modulated light into an RF signal converted into an electrical signal, and outputs the RF signal to the analysis unit 600.

The analysis unit 600 may output the RF modulation frequency, provide the RF modulation frequency to the optical modulation unit 300, and analyze the waveform of the electrical signal input from the optical / 3 is a graph showing waveforms measured by the analyzer 600. FIG.

The analyzer 600 may include a RF oscillator and a signal spectrum analyzer. The RF oscillator included in the analyzer 600 may sweep the frequency of the RF signal and output the RF signal.

The spectrum analyzer of the analyzer 600 is swept in frequency and can analyze the spectrum of the input RF signal to display the waveform shown in FIG.

The analyzer 600 can output an RF signal of several KHz to several GHz. The RF signal output from the analyzer 600 of the present invention is input to the optical modulator 300. When the modulation characteristic of the optical modulator is 500 MHz or more, the intensity of the modulated light in the reverse direction is different from the intensity of the modulated light in the forward direction. The size of the spectrum of the signal becomes smaller and it becomes difficult to distinguish the signal from the noise. Therefore, it is desirable to sweep the RF signal of several KHz to 500 MHz.

The non-contact displacement sensor including the above-described components uses the time difference of the forward and backward modulated signals. For example, the time until it is forward-modulated and then back-modulated is shown in equation (1).

Figure 112014042384639-pat00002

Here, τ fiber is the time taken for the optical fiber between the optical modulator 300 and the collimator 400 to reciprocate, and τ free is the time taken for the light incident on the collimator 400 to be reflected (eg, reflected) And then passes through the collimator 400 again. τ fiber is a fixed constant value, but τ free depends on the value of the displacement (d) on which the measured object moves. L fiber is the length of the optical fiber between the optical modulator 300 and the collimator 400, v g is the group velocity of the optical fiber, D 0 is the distance between the end of the optical fiber and the object to be measured, d is the distance The changed displacement, c, represents the velocity of light in free space.

Figure 112014042384639-pat00003

Equation (2) is a formula for calculating the time delay ?? (d) when the measured object is displaced by d at the reference position. From Equation (2), it can be seen that the time delay due to the displacement of the measured object linearly changes from the reference position to the displacement.

Therefore, if the time delay can be measured from Equation (1), the displacement (d) of the measured object can be obtained from Equation (2).

Further, the light modulated in the forward direction by the RF signal f (t) through the bidirectional modulation equivalent model of the optical modulator of Fig. 2 is back-modulated by the RF signal f (t-tau) do. Therefore, the output optical power P out (t) can be calculated as shown in Equation (3).

Figure 112014042384639-pat00004

Where P in is the input optical power input to the optical modulator 300, T D is the loss occurring in the connection and transmission of the optical elements, m 1 and m 2 are the modulation index in the forward and backward modulation, H 1 (f ) And H 2 (f) represent the transfer functions of forward and backward modulation. The total transfer function H (f) of the optical modulator 300 can be expressed by Equation (4) by removing DC and harmonic components from Equation (3) and assuming m 1 = m 2 = m.

Figure 112014042384639-pat00005

Here, A 0 = mRG m P in T D / 4, R is the response of the photodiode (light / redirecting portion), and G m is the gain of the amplifier 900. The FSR (Free Spectral Range) is generated by the dip in the transfer function of Equation (4) and is affected by the time difference? (D) between forward and backward modulation in Equation (4). The FSR according to the change of the displacement (d) is expressed by Equation (5).

Figure 112014042384639-pat00006

Therefore, the FSR is measured using Equation (5), and the time difference between the forward and backward modulation is obtained from the FSR. From the obtained time difference, the measured body displacement d can be obtained using Equations (1) and (2).

3 to 5 are waveform diagrams showing the results of simulating the performance of the noncontact optical fiber displacement sensor according to the embodiment of the present invention. 3 and 4, assuming that L fiber is 1.5 m and D 0 is 84 mm in consideration of the actual measurement environment, d is assumed to be 0, 2.5, 5, 7.5, 10 mm is the waveform of the transfer function H (f).

In FIG. 5, it can be seen that the FSR decreases as the displacement (d) increases. In addition, the smaller the value of L fiber, the larger the change can be measured.

The FSR and the passing time of Equation (1) are obtained from the transfer function according to the five displacements of Fig. 3 and are shown in Fig. 5, the slope between the displacement of the measured object and the time delay is 6.6 ps / mm. If the length of the optical fiber between the optical modulator 300 and the collimator 400 is shortened or the number of samplings of the analyzer is increased or a light source having a large power is used, the slope between the displacement of the measured object and the time delay can be made larger have. According to the embodiment of the present invention, as described above, the optical fiber length, the number of samples, and the optical power of the light source can be appropriately selected according to the purpose of use and the measurement environment, and parameters can be flexibly determined and used.

The noncontact displacement sensor according to the embodiment of the present invention may be applied to a case where a light source 100 and a circulator 200 are disposed between a circulator 200 and an optical modulator 300, between a light modulator 300 and a collimator 400, The circulator 200 and the optical / electrical conversion section 500 may be connected by an optical fiber. The first to third polarization controllers 710 to 730 may be disposed on the optical fiber to control polarization.

The non-contact displacement sensor using bidirectional modulation of the Mach-Zehnder optical modulator described above can measure precise dimensions in micro units such as the height, width, or thickness of an object, and can be used to monitor or control the state of a machine moving at high speed . Further, since the non-contact displacement sensor of the present invention uses light, it is possible to measure the displacement of the measured object without error in an environment where electromagnetic waves are generated due to strong electromagnetic waves and external environment.

The non-contact displacement sensor using the bidirectional modulation of the Mach-Zehnder optical modulator according to the present invention adjusts the length of the optical fiber between the optical modulator and the measured object, the number of samplings of the analyzer, and the power of the light output from the light source, Measuring range or resolution can be adjusted.

100: Light source
200: circulator
300: optical modulation unit
350: Bias
400: collimator
500: light /
600: Analytical Department
710 to 730: First to third polarization controllers
900: amplification unit

Claims (6)

A light source for outputting laser light;
A circulator connected to the light source and outputting light inputted thereto through another path;
An optical modulator for RF-modulating the input light and outputting the modulated light;
A collimator for converting the modulated light input from the light modulator into a large area and outputting the modulated light to a subject, and receiving the light reflected from the subject and providing the light to the light modulator;
An optical / electrical conversion section for receiving the modulated light input from the optical modulation section and converting the optical signal into an electrical signal; And
And an analyzer for applying an RF signal to the optical modulator and analyzing a spectrum of an electrical signal input from the optical /
The optical modulator performs a forward RF modulation on the light input from the circulator and outputs the modulated light to the collimator. The light modulator modulates the light input from the collimator in the reverse direction by using the time difference between the forward-RF modulated light and the reverse- And a displacement of the object to be measured is measured. The non-contact displacement sensor using bidirectional modulation of a Mach-Zehnder optical modulator.
The method according to claim 1,
The displacement (d) of the measured object is
Figure 112014042384639-pat00007

(Where c is the speed of light in free space, and Δτ (d) is the time delay of the change when it occurs by d)
And a non-contact displacement sensor using bidirectional modulation of the Mach-Zehnder optical modulator.
The method according to claim 1,
A bidirectional modulation of a Mach-Zehnder optical modulator further comprising at least one polarization controller provided between the circulator and the optical modulator or between the optical modulator and the collimator or between the circulator and the optical / Non - contact displacement sensor.
The method according to claim 1,
Further comprising an amplifier for amplifying an electric signal photoelectrically converted between the optical / electrical conversion section and the analyzing section, using a bi-directional modulation of the Mach-Zender optical modulator.
The method according to claim 1,
Wherein the analyzing unit includes a RF oscillating unit for oscillating the RF signal and a spectrum analyzer for analyzing a spectrum of an electric signal input from the optical / electrical converting unit, the non-contact displacement sensor using bidirectional modulation of a Mach-Zender optical modulator.
The method according to claim 1,
Wherein the analyzing unit swings the RF signal in the band of 200 MHz to 2 GHz and supplies the swing signal to the optical modulator. The non-contact displacement sensor using the bidirectional modulation of the Mach-Zender optical modulator.






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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20030010881A (en) * 2001-07-27 2003-02-06 전금수 Chromatic dispersion measurement system and the method
KR20110048159A (en) * 2009-11-02 2011-05-11 전북대학교산학협력단 Device for endoscopic functional optical coherent tomography

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20030010881A (en) * 2001-07-27 2003-02-06 전금수 Chromatic dispersion measurement system and the method
KR20110048159A (en) * 2009-11-02 2011-05-11 전북대학교산학협력단 Device for endoscopic functional optical coherent tomography

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