Distance measurement system and method using semiconductor optical amplifier

Abstract

This distance measurement system comprises: a first laser and a second laser; an optical circulator for transmitting, to a measurement unit, a first optical pulse stream that is output from the first laser, and changing the path of the first optical pulse stream reflected from the measurement unit; a semiconductor optical amplifier for receiving the first optical pulse stream transmitted from the optical circulator and a second optical pulse stream that is output from the second laser, causing the first optical pulse stream and the second optical pulse stream to be cross-correlated on the basis of gain dynamics, and outputting the first optical pulse stream including cross-correlation information; an optical detector for converting the first optical pulse stream into an electrical signal; an RF low-pass filter for extracting the envelope of the electrical signal; and a computing device for detecting signal peaks through data processing on a raw signal that passed through the RF low-pass filter, and calculating, through the peak signals, the absolute distance of at least one object to be measured.

Description

Distance measurement system and method using a semiconductor optical amplifier

[0001] The present invention relates to laser-based distance measurement.

[0002] Distance measurement technology has been developed over decades as a fundamental requirement in the fields of science and engineering. Distance measurement methods can be classified into continuous wave laser interferometers and absolute distance measurement.

[0003] Continuous wave laser interferometers offer stable precision down to the nanometer level and are widely used in precision measurement fields such as length and angle measurement and surface profiling; however, due to the limitations of the Non-Ambiguity Range (NAR) determined by the optical wavelength of the laser, they can only be utilized for displacement measurement.

[0004] Absolute distance measurement was introduced with the development of femtosecond lasers, and various optical techniques such as synthetic wavelength interferometry, multi-wavelength interferometry, spectrally resolved interferometry, dual-comb interferometry, and time-of-flight measurement can be used. These measurement systems possess high precision and linearity and can be applied in various fields, including high-precision mechanical engineering and next-generation space missions.

[0005] Dual-comb time-of-flight-based absolute distance measurement can measure absolute distance in real time by measuring the flight times of optical pulses through cross-correlation (XCOR) between two femtosecond lasers. This conventional measurement technique uses non-linear crystals, such as type II barium borate (BBO) and periodically poled potassium titanyl phosphate (PPKTP), for second harmonic generation. Non-linear crystals have the disadvantage of very low optical conversion efficiency during optical cross-correlation and limiting their applicability to measurement targets with high reflectivity.

[0006] Meanwhile, absolute distance measurements for multiple targets are required for machine monitoring, distortion detection in large structures, and wafer alignment in semiconductor manufacturing, and the expansion of measurement channels is essential for the effective application of multi-target measurements. However, measurement techniques using nonlinear crystals with very low optical conversion efficiency for optical cross-correlation have limitations in supporting multi-channel measurements that require high power.

[0007] The present disclosure relates to a multi-channel distance measurement system and method using a semiconductor optical amplifier.

[0008] The present disclosure relates to a multi-channel distance measuring system and method for simultaneously measuring the absolute distances of multiple measurement targets through high-efficiency optical cross-correlation of a semiconductor optical amplifier.

[0009] A distance measuring system according to some embodiments comprises: a first laser and a second laser having a difference in repetition rate; an optical circulator that transmits a first optical pulse train output from the first laser to a measuring unit and changes the path of the first optical pulse train reflected from the measuring unit; a semiconductor optical amplifier that receives the first optical pulse train transmitted from the optical circulator and the second optical pulse train output from the second laser, generates cross-correlation between the first optical pulse train and the second optical pulse train based on gain dynamics, and outputs the first optical pulse train containing cross-correlation information; a photodetector that converts the first optical pulse train output from the semiconductor optical amplifier into an electrical signal; an RF low-pass filter that extracts the envelope of the electrical signal; and a computing device implemented to detect signal peaks through data processing of a raw signal that has passed through the RF low-pass filter and to calculate the absolute distance of at least one measurement target through the peak signals.

[0010] The distance measuring system may further include a first optical bandpass filter and a second optical bandpass filter having different bands for distinguishing optical pulses output from the first laser and the second laser.

[0011] The distance measuring system may further include a third optical bandpass filter for filtering the second optical pulse train at the output of the semiconductor optical amplifier. The third optical bandpass filter may have the same band as the first optical bandpass filter.

[0012] The above measuring unit may include multi-channel optical paths for measuring distances to a plurality of measurement targets.

[0013] The semiconductor optical amplifier described above can be implemented to induce a cross-correlation in which the intensity of the trailing pulse decreases as the gain of the trailing pulse incident adjacent to the leading pulse decreases based on the gain dynamics.

[0014] The first optical pulse train containing the above cross-correlation information may be a first optical pulse train whose intensity has changed due to the above cross-correlation.

[0015] The above raw signal may include a dip-shaped cross-correlation signal and a slow recovery region.

[0016] The computing device may be implemented to convert the raw signal into a signal in the effective time domain through time domain expansion, suppress the signal in the slow recovery region in the signal in the effective time domain, and calculate the absolute distance of the at least one measurement target through the signal peaks that appear when the signal in the slow recovery region is suppressed.

[0017] The computing device may be implemented to perform time domain expansion by multiplying the raw signal by a time scaling factor related to the repetition rate of the first laser and the difference in repetition rates.

[0018] The computing device can be implemented to remove the signal of the slow recovery region through correlation calculation using a correlation function having peaks and valleys.

[0019] The above signal peaks may be peaks of at least one reference signal and at least one target signal reflected from the measurement unit.

[0020] The computing device may be implemented to calculate the absolute distance of the measurement target based on the time difference between the reference signal and the measurement target signal.

[0021] A distance measuring system according to some embodiments comprises: a semiconductor optical amplifier that receives a first optical pulse train reflected from a measuring unit and a second optical pulse train competing for gain with the first optical pulse train, and generates cross-correlation between the first optical pulse train and the second optical pulse train based on gain dynamics, and outputs the first optical pulse train containing cross-correlation information; and a computing device that acquires a raw signal measuring the first optical pulse train containing cross-correlation information, detects a reference signal reflected from a reference path of the measuring unit and at least one measurement target signal reflected from at least one measurement target of the measuring unit through data processing of the raw signal, and calculates the absolute distance of the corresponding measurement target based on the time difference between the reference signal and each measurement target signal.

[0022] Each of the above first optical pulse train and the above second optical pulse train can be output from a first laser and a second laser having a difference in repetition rate.

[0023] The semiconductor optical amplifier described above can be implemented to induce a cross-correlation in which the intensity of the trailing pulse decreases as the gain of the trailing pulse incident adjacent to the leading pulse decreases based on the gain dynamics.

[0024] The first optical pulse train containing the above cross-correlation information may be a first optical pulse train whose intensity has changed due to the above cross-correlation.

[0025] The computing device may be implemented to convert the raw signal into a signal in an effective time domain through time domain expansion, suppress the signal in the slow recovery region in the signal in the effective time domain, and detect the reference signal and the at least one measurement target signal through the signal peaks that appear when the signal in the slow recovery region is suppressed. The raw signal may include a dip-shaped cross-correlation signal and a slow recovery region.

[0026] A method of operation of a computing device according to some embodiments comprises the steps of: acquiring a raw signal obtained by measuring the output of a semiconductor optical amplifier; detecting a reference signal reflected from a reference path of a measurement unit and at least one measurement target signal reflected from at least one measurement target of the measurement unit through data processing of the raw signal; and calculating the absolute distance of the corresponding measurement target based on the time difference between the reference signal and each measurement target signal. The semiconductor optical amplifier receives a first optical pulse train reflected from the measurement unit and a second optical pulse train competing for gain with the first optical pulse train, and generates a cross-correlation between the first optical pulse train and the second optical pulse train based on gain dynamics, and outputs the first optical pulse train containing cross-correlation information.

[0027] The above data processing may include time domain expansion that expands the time domain of the raw signal into an effective time domain using the repetition rate of the first optical pulse train and a temporal scaling factor related to the difference in repetition rates between the first optical pulse train and the second optical pulse train.

[0028] The above data processing may include correlation calculations that suppress signals in the slow recovery region using a correlation function with peaks and valleys.

[0029] According to the present disclosure, by using a semiconductor optical amplifier, distance measurement is possible even with a low amount of light, enabling multi-channel distance measurement, and distance measurement is also possible for objects with low reflectivity.

[0030] According to the present disclosure, the absolute distance between a plurality of measurement targets can be measured in real time, and the distance between one or more measurement targets placed on multiple axes can also be measured.

[0031] The system of the present disclosure is composed solely of optical fiber components without free space elements, so assembly is simple, and it is small and lightweight.

[0032] According to the present disclosure, multi-channel distance measurement required in various fields, such as deformation monitoring, semiconductor wafer measurement, and formation flying of satellites, can be performed.

[0033] According to the present disclosure, light pulses reflected from the upper and lower surfaces of a wafer are received at once, so the distance between wafers and the wafer thickness can be measured simultaneously.

[0034] According to the present disclosure, when an FC / PC ferrule optical fiber is used when a beam is emitted into free space, the absolute distance between a laser probe and a wafer can be simultaneously measured using light pulses reflected from the corresponding surface.

[0035] FIG. 1 is a configuration diagram of a distance measuring system according to one embodiment.

[0036] FIG. 2 is a diagram illustrating the distinction between two lasers according to one embodiment.

[0037] FIGS. 3 and FIGS. 4 are each diagrams illustrating gain dynamics and cross-correlation by a semiconductor optical amplifier according to one embodiment.

[0038] FIG. 5 is an example of a signal including cross-correlation information according to one embodiment.

[0039] FIG. 6 is a diagram illustrating the gain dynamics in a semiconductor optical amplifier according to one embodiment.

[0040] FIG. 7 is a flowchart of a data processing method for distance measurement according to one embodiment.

[0041] FIG. 8 is a diagram showing the results of data processing according to one embodiment.

[0042] Embodiments of the present invention are described below with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification are denoted by similar reference numerals.

[0043] In descriptions, when a part is said to "include" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0044] In the description, drawing symbols and names are provided for convenience of explanation and are not strictly limited to the drawing symbols or names.

[0045] FIG. 1 is a configuration diagram of a distance measuring system according to one embodiment, FIG. 2 is a diagram explaining the distinction between two lasers according to one embodiment, FIG. 3 and FIG. 4 are diagrams explaining gain dynamics and cross-correlation by a semiconductor optical amplifier according to one embodiment, and FIG. 5 is an example of a signal including cross-correlation information according to one embodiment.

[0046] Referring to FIG. 1, the distance measuring system (10) is implemented to measure absolute distance using the cross-correlation of a dual-comb by a semiconductor optical amplifier (150). Specifically, the distance measuring system (10) may include a first laser (100) and a second laser (110) having a repetition rate difference, optical band pass filters (BFP) (120, 121) for distinguishing optical pulses output from the two lasers (100, 110), an optical circulator (130) for transmitting optical pulses to a measuring unit (200) and changing the optical path of optical pulses reflected from the measuring unit (200), an optical combiner (140) for combining optical pulses of the two optical paths, and a semiconductor optical amplifier (SOA) (150) for generating gain dynamics-based cross-correlation (XCOR). And the distance measuring system (10) may include a light bandpass filter (122) that removes a non-interest pulse train (an optical pulse train output from the second laser (110)) from the output of a semiconductor optical amplifier (150), a photo detector (PD) (160) that converts an interest pulse train output from the semiconductor optical amplifier (150) into an electrical signal, an RF low-pass filter (170) that acquires the envelope of the electrical signal, a data acquirer (180) that acquires signal data, and a computing device (190) that processes the signal data to calculate the absolute distance of a target. Meanwhile, the devices constituting the distance measuring system (10) may be replaced with devices having similar functions. The computing device (190) includes at least one processor and memory, and is implemented so that the processor executes instructions stored in memory to perform the operation of the present disclosure.

[0047] The measuring unit (200) provides a measuring environment for measuring the distance of at least one measurement target through the time of flight of a light pulse. In the description, it is assumed that the measuring unit (200) is implemented to include multi-channel optical paths that transmit a light pulse to each of a plurality of measurement targets and a signal reflected from each measurement target. The measuring unit (200) may be implemented to divide the light pulse into wavelengths and transmit it to each path. At this time, the measuring unit (200) may include a reference path through which a light pulse that serves as a reference for the time of flight (TOF) passes, and the light pulse that has passed through the reference path may be used as a reference signal. For example, the measuring unit (200) may be implemented to measure multi-axis absolute distances in engineering applications for monitoring distortion of industrial machinery such as printing systems, but there may be various other targets that the distance measuring system (10) can measure.

[0048] Among the two lasers (100, 110), the first laser (100) is a signal laser that is incident on the measuring unit (200) and outputs a light pulse used for distance measurement, and the second laser (110) outputs a light pulse used for cross-correlation in the semiconductor light amplifier (150), and is called a local oscillator (LO) laser to distinguish it from the signal laser. The light pulse output from the signal laser (100) is called a signal-light pulse, and the light pulse output from the LO laser (110) can be called an LO-light pulse. Meanwhile, among the signal-light pulses, the light pulse that has passed through a reference path that serves as a reference for flight time is called a reference-light pulse, and the light pulse reflected from the measurement target can be called a measurement target-light pulse.

[0049] Each of the two lasers (100, 110) is a pulsed laser and may be a femtosecond laser. For example, each laser may be composed of a semiconductor saturable absorber mirror (SESAM) for mode locking, an erbium-doped fiber (EDF), a laser diode pump connected to a wavelength division multiplex (WDM), a piezoelectric actuator (PZT) for repetition rate stabilization, a dielectric mirror, and an isolator.

[0050] The repetition rates of the two lasers (100, 110) are set to have a slight difference, and in the description, the repetition rate of the signal laser (100) is f r and the repetition rate of the reference laser (110) is f r -Δf r It is assumed that. For example, f r is 203.2 MHz, and Δf r The frequency can be 27 kHz, the output power of the laser can be ~1 mW, and the center wavelength can be 1558 nm. Meanwhile, to create a repetition rate difference between the two lasers (100, 110), at least one laser can adjust the repetition rate through a free-space collimator.

[0051] Referring to FIG. 2, a BFP (120, 121) may be used to distinguish optical pulses output from two lasers (100, 110) by wavelength. The BFP (120, 121) may be a narrowband filter that extracts comb lines from optical frequency combs. For example, the output of a signal laser (100) that passes through a BFP (120) with a center wavelength of 1560 nm may be called a signal-optical pulse train, and the output of an LO laser (110) that passes through a BFP (121) with a center wavelength of 1555 nm may be called an LO-optical pulse train. Since the signal-optic pulse and the LO-optic pulse are distinguished by wavelength in this way, LO-optic pulses of interest can be extracted from the optical pulse train that has passed through the semiconductor optical amplifier (150) through a 1560nm BPF (122) located between the semiconductor optical amplifier (150) and the optical detector (160).

[0052] Referring again to FIG. 1, signal-light pulses output from the signal laser (100) pass through the optical circulator (130) and are incident on the measurement unit (200), and the signal-light pulses reflected from the measurement unit (200) are directed to the semiconductor optical amplifier (150) by the optical circulator (130) so that an optical path can be implemented.

[0053] The signal-light pulses reflected from the measurement unit (200) and the LO-light pulses output from the LO laser (110) can be combined by an optical coupler (140) and then an optical path can be implemented so as to be incident on a semiconductor optical amplifier (150).

[0054] Referring to FIG. 3, a signal-optic pulse train and an LO-optic pulse train are incident on a semiconductor optical amplifier (150). When two adjacent pulses are incident on the semiconductor optical amplifier (150), the gain of the semiconductor optical amplifier (150) decreases rapidly due to gain depletion caused by the preceding pulse, and the intensity of the subsequent pulse may decrease during the period of gain decrease. For example, when an LO-optic pulse is incident on the semiconductor optical amplifier (150), the amplification gain is lowered as the internal electron energy changes, so the intensity of the signal-optic pulse that follows is not amplified or is instead reduced, resulting in cross-correlation in which a difference in relative intensity occurs. That is, the semiconductor optical amplifier (150) can differentiate the relative intensity between adjacent optical pulses based on gain dynamics to induce cross-correlation between adjacent optical pulses and output an optical pulse train containing cross-correlation information (an optical pulse train whose intensity has changed due to cross-correlation). Here, the LO-optic pulse is used to induce gain competition with the signal-optic pulse in the semiconductor optical amplifier (150).

[0055] Referring to FIG. 4, when a signal-optic pulse train and an LO-optic pulse train (300) are incident on a semiconductor optical amplifier (150), a signal-optic pulse train (310) with reduced intensity according to the degree of overlap with the LO-optic pulse can be output by the gain dynamics of the semiconductor optical amplifier (SOA) (150).

[0056] In particular, when examining the cross-correlation results of two adjacent pulses in the microsecond time domain, the cross-correlation signal may appear in the form of a dip (320). In the detected signal, the dip-shaped cross-correlation signal is the repetition rate difference, i.e., 1 / Δf rSince it appears in intervals, the detected signal is converted into the time domain of the original light pulse (i.e., the valid time domain) through temporal scaling, and then the flight time can be measured using the cross-correlation signal detected in the valid time domain. As such, the semiconductor optical amplifier (150) has a very high optical conversion efficiency because it creates a cross-correlation signal based on the intensity difference based on the amount of light of the existing light pulse. Since the cross-correlation signal is sufficient to detect even when the pulse power returned through the cross-correlation of the semiconductor optical amplifier (150) is less than a few milliwatts, the limitations of the existing absolute distance measurement system using amorphous crystals can be overcome, and consequently, distance measurement is possible even with low light intensity, allowing the number of channels to be expanded to more than 10.

[0057] Referring again to FIG. 1, the output of the semiconductor optical amplifier (150) (an optical pulse train whose intensity has changed due to cross-correlation) can pass through a BPF (122) that passes the wavelength (e.g., 1560 nm) of the signal-optical pulse and be incident on the optical detector (160). The LO-optical pulse train is filtered by the BPF (122), and the signal-optical pulse train can be incident on the optical detector (160). The signal-optical pulse train may be an optical pulse train that includes a reference-optical pulse and signal-optical pulses reflected from a measurement target, and includes cross-correlation information with the LO-optical pulse train.

[0058] The photodetector (160) can convert a series of optical pulses containing cross-correlation information into an electrical signal.

[0059] An RF low-pass filter (170) can be used to smooth the electrical signal of an optical pulse train and to extract the envelope of the electrical signal. A data acquirer (180), such as an oscilloscope or a digitizer, can acquire data of the signal that has passed through the RF low-pass filter (170). The signal acquired by the data acquirer (180) may have a shape similar to a fast recovery region and a slow recovery region provided by the gain dynamics of the semiconductor optical amplifier (150).

[0060] The computing device (190) can calculate the absolute distance of the measurement targets by detecting the reference signal and the measurement target signal through data processing of the raw signal acquired from the data acquirer (180). The computing device (190) can detect the reference signal reflected from the reference path of the measurement unit (200) and the measurement target signal reflected from the measurement target through data processing of the raw signal, and can calculate the absolute distance of the measurement target based on the time difference between the reference signal and each measurement target signal.

[0061] The computing device (190) can perform data processing, such as a timing determination algorithm using second-order polynomial fitting or linear fitting of rising edges, to find a reference signal and a signal to be measured. Here, the computing device (190) applies a temporal scaling factor Δf to the raw signal acquired from the data acquirer (180). r / f r By multiplying to perform a temporal domain extension into the effective time domain, and by calculating the correlation in the effective time domain, the signal in the slow recovery region corresponding to noise is removed, and the flight time and absolute distance can be calculated through the signal peaks remaining after the signal in the slow recovery region is removed.

[0062] Referring to FIG. 5, the computing device (190) applies a temporal scaling factor Δf to the raw signal acquired from the data acquirer (180). r / f r It can be multiplied to generate a signal (330) in the valid time domain.

[0063] When examining the signal (330) in the valid time domain, a cross-correlation signal (dip) appears at intervals (e.g., 5ns) corresponding to a repetition rate (e.g., 203.2MHz), and the time duration (e.g., 0.43ns) of the slow recovery region can be observed. Here, since the cross-correlation signal has temporal characteristics of a constant signal duration (e.g., 2.6ps) and a falling edge slope (e.g., 9.5mV / ps), the cross-correlation signal can be detected through these prominent characteristics. The method by which the computing device (190) measures distance through data processing is described in detail in FIG. 7.

[0064] FIG. 6 is a diagram illustrating the gain dynamics in a semiconductor optical amplifier according to one embodiment.

[0065] Referring to FIG. 6, when examining the gain dynamics (340) in a semiconductor optical amplifier, when a laser pulse is incident on the semiconductor optical amplifier (150), the gain decreases rapidly and then increases rapidly to form a dip of about 1 picosecond. This short period is called the fast recovery region. After the fast recovery region, the gain is recharged for several nanoseconds or microseconds until it reaches a steady state, depending on the current injected into the semiconductor optical amplifier (150). This long period is called the slow recovery region.

[0066] The fast recovery region utilizes the gain dip during the cross-correlation process to guide the laser pulse to the main signal of the cross-correlation, but the slow recovery region generates noise and deviates from the baseline. Two pulses that are far apart are amplified by the gain of the semiconductor optical amplifier (150) in the steady state, but when the two pulses are close to each other within the fast recovery region, the trailing pulse loses power due to the lack of gain reduced by the leading pulse.

[0067] This series of processes can be explained through the current injection rate equation, the spectral hole burning equation, and the carrier heating equation derived from the photo-electron rate equations. As the injection current increases, the intensity of the dip due to cross-correlation can increase rapidly, so an appropriate injection current can be selected.

[0068] FIG. 7 is a flowchart of a data processing method for distance measurement according to one embodiment, and FIG. 8 is a diagram showing the results of data processing according to one embodiment.

[0069] Referring to FIGS. 7 and 8, a computing device (190) acquires a raw signal (350) of a signal-optical pulse train containing cross-correlation information with an LO-optical pulse train (S110). The raw signal (350) includes a dip-shaped reference signal (351) and a measurement target signal (352), and a slow recovery region. The repetition period is the difference in repetition rates (1 / Δf) between the two lasers. r It is identical to ) and can be displayed in the time domain of microseconds.

[0070] The computing device (190) expands the raw signal (350) into the time domain of an optical pulse train to generate a signal (360) in the effective time domain (S120). The computing device (190) applies a temporal scaling factor Δf to the raw signal.r / f r By multiplying, the time domain can be extended to the nanosecond level.

[0071] The computing device (190) calculates the correlation between a correlation function (361) with peaks and valleys and a signal (360) in the valid time domain to suppress the signal in the slow recovery region (S130). The duration of the correlation function (361) can be determined to be similar to the duration (~8.5 ps) of the signal (360). Since similar parts between the two signals can be extracted through correlation calculation, the deep-shaped cross-correlation signal becomes clearly defined due to its similarity to the correlation function, while the signal in the slow recovery region can be suppressed. The slow recovery region corresponds to noise and can also reach the signal peak, which interferes with distance measurement, so it needs to be removed.

[0072] The computing device (190) calculates the absolute distance of the measurement target through the signal peaks that appear when the signal of the slow recovery region is suppressed (S140). The graph (370) with the signal of the slow recovery region suppressed shows that all signals can be detected without interference from overshooting caused by the slow recovery region. The computing device (190) can measure the flight times (△τ1, △τ2, △τ3) between the reference signal (371) by the reference-light pulse and the measurement target signals (372, 373, 374) by the signal-light pulses reflected from the measurement targets by applying a timing determination algorithm. For example, a peak detection method using second-order polynomial fitting can be used as the timing determination algorithm. The computing device (190) can calculate the absolute distance D corresponding to each signal peak as in Equation 1.

[0073] [Mathematical Formula 1]

[0074]

[0075] In Equation 1, m is the ambiguity integer, c is the speed of light, N is the refractive index, and f r is the repetition rate of the signal laser (100), and Δf r Δτ is the difference in repetition rates between the signal laser (100) and the LO laser (110). Δτ is the time difference between the reference signal and the signal to be measured, and i is the index of the target to be measured. When the target to be measured is within the NAR, m is 0, and when the distance to the target to be measured is greater than or equal to the NAR, i.e., when m > 0, the value of m can be determined by switching the repetition rate.

[0076] Thus, the computing device (190) can detect the peak positions of multiple measurement target signals, and thus can simultaneously measure the absolute distances of multiple measurement targets. The computing device (190) can determine the absolute distances without interference from slow recovery regions included in the raw data acquired using an oscilloscope or digitizer.

[0077] The embodiments of the present invention described above are not implemented only through devices and methods, but may also be implemented through a program that realizes a function corresponding to the configuration of the embodiments of the present invention or a recording medium on which such program is recorded.

[0078] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

Claims

1. As a distance measuring system, First laser and second laser with a difference in repetition rate, A light circulator that transmits a first light pulse train output from the first laser to a measuring unit and changes the path of the first light pulse train reflected from the measuring unit, A semiconductor optical amplifier that receives the first optical pulse train transmitted from the optical circulator and the second optical pulse train output from the second laser, and generates cross-correlation between the first optical pulse train and the second optical pulse train based on gain dynamics, and outputs the first optical pulse train containing cross-correlation information. A photodetector that converts the first optical pulse train output from the semiconductor optical amplifier into an electrical signal, An RF low-pass filter for extracting the envelope of the above electrical signal, and A computing device implemented to detect signal peaks through data processing of a raw signal passed through the above RF low-pass filter, and to calculate the absolute distance of at least one measurement target through the peak signals. A distance measuring system including 2. In Paragraph 1, A first optical bandpass filter and a second optical bandpass filter having different bands for distinguishing optical pulses output from the first laser and the second laser. A distance measuring system that further includes 3. In Paragraph 2, It further includes a third optical bandpass filter for filtering the second optical pulse train at the output of the semiconductor optical amplifier, and A distance measuring system in which the third wide bandpass filter has the same band as the first wide bandpass filter.

4. In Paragraph 1, The above measuring unit A distance measuring system comprising multi-channel optical paths for measuring distances to multiple measurement targets.

5. In Paragraph 1, The above semiconductor optical amplifier A distance measuring system implemented to induce a cross-correlation in which the strength of the trailing pulse decreases as the gain of the trailing pulse incident adjacent to the leading pulse decreases based on the gain dynamics above.

6. In Paragraph 1, The first optical pulse train including the above cross-correlation information is A distance measuring system, which is a first optical pulse train whose intensity has changed due to the above cross-correlation.

7. In Paragraph 1, The above raw signal is A distance measurement system including a dip-shaped cross-correlation signal and a slow recovery region.

8. In Paragraph 1, The above computing device The above raw signal is converted into a signal in the valid time domain through time domain expansion, and Suppressing the signal in the slow recovery region from the signal in the above effective time domain, and A distance measuring system implemented to calculate the absolute distance of at least one measurement target through signal peaks that appear and where the signal of the slow recovery region is suppressed.

9. In Paragraph 8, The above computing device A distance measuring system implemented to perform time domain expansion by multiplying the original signal by the repetition rate of the first laser and a time scaling coefficient related to the difference in repetition rates.

10. In Paragraph 8, The above computing device A distance measurement system implemented to remove the signal of the slow recovery region through correlation calculation using a correlation function having peaks and valleys.

11. In Paragraph 1, The above signal peaks are A distance measuring system comprising peaks of at least one reference signal and at least one target signal reflected from the above measuring unit.

12. In Paragraph 11, The above computing device A distance measuring system implemented to calculate the absolute distance of a measurement target based on the time difference between the reference signal and the measurement target signal.

13. As a distance measuring system, A semiconductor optical amplifier that receives a first optical pulse train reflected from a measuring unit and a second optical pulse train competing for gain with the first optical pulse train, generates cross-correlation between the first optical pulse train and the second optical pulse train based on gain dynamics, and outputs the first optical pulse train containing cross-correlation information; A computing device implemented to acquire a raw signal obtained by measuring the first optical pulse train including the cross-correlation information, detect a reference signal reflected from a reference path of the measurement unit and at least one measurement target signal reflected from at least one measurement target of the measurement unit through data processing of the raw signal, and calculate the absolute distance of the corresponding measurement target based on the time difference between the reference signal and each measurement target signal. A distance measuring system including 14. In Paragraph 13, A distance measuring system in which each of the first optical pulse train and the second optical pulse train is output from a first laser and a second laser having a difference in repetition rate.

15. In Paragraph 13, The above semiconductor optical amplifier A distance measuring system implemented to induce a cross-correlation in which the strength of the trailing pulse decreases as the gain of the trailing pulse incident adjacent to the leading pulse decreases based on the gain dynamics above.

16. In Paragraph 15, The first optical pulse train including the above cross-correlation information is A distance measuring system, which is a first optical pulse train whose intensity has changed due to the above cross-correlation.

17. In Paragraph 13, The above computing device The above raw signal is converted into a signal in the valid time domain through time domain expansion, and Suppressing the signal in the slow recovery region from the signal in the above effective time domain, and It is implemented to detect the reference signal and the at least one measurement target signal through signal peaks that appear and where the signal of the slow recovery region is suppressed. The above raw signal is A distance measurement system including a dip-shaped cross-correlation signal and a slow recovery region.

18. As a method of operating a computing device, A step of acquiring a raw signal obtained by measuring the output of a semiconductor optical amplifier, A step of detecting a reference signal reflected from a reference path of a measurement unit and at least one measurement target signal reflected from at least one measurement target of the measurement unit through data processing of the raw signal, and It includes a step of calculating the absolute distance of the corresponding measurement target based on the time difference between the above reference signal and each measurement target signal, and The above semiconductor optical amplifier A method of operation that receives a first optical pulse train reflected from the above-mentioned measuring unit and a second optical pulse train competing for gain with the first optical pulse train, and generates a cross-correlation between the first optical pulse train and the second optical pulse train based on gain dynamics, and outputs the first optical pulse train containing cross-correlation information.

19. In Paragraph 18, The above data processing is A method of operation comprising time domain expansion that expands the time domain of the source signal into an effective time domain using the repetition rate of the first optical pulse train and a time scaling factor related to the difference in repetition rates between the first optical pulse train and the second optical pulse train.

20. In Paragraph 18, The above data processing is A method of operation comprising a correlation calculation that suppresses a signal in a slow recovery region using a correlation function having peaks and valleys.

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