CN114486202A - Simple and easily-adjustable ultra-fast dispersion measurement system and method - Google Patents
Simple and easily-adjustable ultra-fast dispersion measurement system and method Download PDFInfo
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- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
- G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
- G01M11/331—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face by using interferometer
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
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- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/45—Interferometric spectrometry
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- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
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- G01M11/333—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face using modulated input signals
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- G01M11/338—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face by measuring dispersion other than PMD, e.g. chromatic dispersion
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- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/45—Interferometric spectrometry
- G01J2003/451—Dispersive interferometric spectrometry
Abstract
The invention provides a simple and easily-adjusted chromatic dispersion ultrafast measurement system and method, the system comprises an interference light signal generating device, a sample to be measured, a waveform collecting device and a spectrometer, wherein the interference signal generating device is used for generating an initial interference light signal which is divided into two paths, one path is stretched by the time domain of the sample to be measured to form a stretched interference light signal, the stretched interference light signal is transmitted to the waveform collecting device, and the other path of the initial interference light signal is directly transmitted to the spectrometer; the waveform acquisition device acquires the waveform of the tensile interference optical signal to obtain a time domain envelope; the spectrometer collects the interference spectrum of the other path of initial interference light signal; and based on the fact that the time domain envelope and the interference spectrum of the initial interference light signal are scaled in equal proportion, iterative fitting is carried out on the time domain envelope and the interference spectrum, and the dispersion amount of the sample to be detected is calculated. The invention improves the dispersion measurement efficiency and simplifies the dispersion measurement data processing method.
Description
Technical Field
The invention belongs to the field of dispersion measurement, and particularly relates to a simple and easily-adjusted ultra-fast dispersion measurement system and method.
Background
In the field of optical equipment application, dispersion is an important parameter describing the propagation characteristics of an optical fiber, and it characterizes the propagation distance of light signals with different wavelengths in the same time during the transmission process of the optical fiber. In order to achieve a good dispersion compensation effect, it is necessary to acquire an accurate fiber dispersion curve or dispersion amount in advance. The method for measuring the chromatic dispersion by utilizing the spectral interference does not need expensive instruments, and has the advantages of simple structure and accurate measurement, thereby being widely applied. The measuring method is that the optical fiber to be measured is placed in a measuring arm, and the optical path difference of two interference arms is adjusted by arranging an adjustable delay line on a reference arm, so that the optical path difference of the two interference arms is kept in a smaller state, and the interference occurrence condition is met. After obtaining the interference fringe intensity information of the optical signals in the two interference arms, the phase of the interference fringe is obtained by means of Fourier transform and the like, and then the dispersion of the optical fiber to be measured is obtained.
The traditional interference spectrum dispersion measurement method needs to adjust the length of the reference arm in the two interference arms once when performing dispersion measurement on the optical fiber to be measured with different lengths, which undoubtedly increases the operation difficulty and complexity. In addition, the measurement speed of this dispersion measurement method is slow due to the limitation of the sampling rate of the spectrometer.
Disclosure of Invention
The invention provides a simple and easily-adjusted ultra-fast dispersion measurement system and method, which are used for solving the problems that the measurement speed is low when the dispersion measurement is carried out by using spectral interference, a reference arm in an interference light path needs to be adjusted once when the dispersion measurement is carried out on samples to be measured with different lengths, and the operation difficulty and complexity are high.
According to a first aspect of the embodiments of the present invention, a simple and easily tunable chromatic dispersion ultrafast measurement system is provided, including an interference optical signal generating device, a sample to be measured, a waveform collecting device and a spectrometer, where the interference signal generating device is configured to generate an initial interference optical signal, which is divided into two paths, one path is stretched in a time domain of the sample to be measured to form a stretched interference optical signal, the stretched interference optical signal is transmitted to the waveform collecting device, and the other path is directly transmitted to the spectrometer;
the waveform acquisition device acquires the waveform of the stretching interference optical signal to obtain a time domain envelope; the spectrometer collects the interference spectrum of the other path of initial interference light signal;
and based on the equal proportional scaling of the time domain envelope and the interference spectrum of the initial interference light signal, performing iterative fitting on the time domain envelope and the interference spectrum, and calculating the dispersion of the sample to be detected.
In an alternative implementation, the interference spectrum of the initial interference light signal is represented as:
where w is the angular frequency, E1(w) represents a first original optical signal, E, for generating said initial interference optical signal2(w) represents a second original optical signal used to generate the initial interference optical signal,
representing the phase difference between the first path of original optical signal and the second path of original optical signal;
based on the time domain envelope and the interference spectrum of the initial interference optical signal, the spectrum expression of the stretched interference optical signal after the time stretching of the sample to be detected is as follows:
wherein
Representing a first original optical signal used to generate the initial interference optical signal,
representing a second original optical signal used to generate the initial interfering optical signal,
representing the phase difference, beta, between the first and second original optical signals2Is the second-order group velocity dispersion parameter of the sample to be measured, and t is time.
In another optional implementation manner, t is obtained from the time domain envelope, and is substituted into the spectral expression (2) of the stretched interference optical signal after the time stretching of the sample to be tested, so as to calculate the second-order group velocity dispersion parameter β of the sample to be tested2；
Or substituting t ═ Dlambda into the spectral expression (2), establishing an equation set comprising at least two spectral expressions (2), and solving to obtain dispersion coefficient D corresponding to each wavelength and second-order group velocity dispersion parameter beta of the sample to be measured2Where λ represents the wavelength, is obtained from the time-domain envelope.
In another optional implementation manner, the interference light signal generating device includes a laser, a first collimator, a first mirror, a first beam splitter, a second mirror, a second collimator, and a second beam splitter, where the laser is connected to the first beam splitter through the first collimator, and the first beam splitter is connected to the first mirror, the second mirror, and the second beam splitter through the second collimator, respectively;
the laser provides a laser signal to the first collimator, the first collimator collimates the laser signal provided by the laser into a spatial light signal and transmits the spatial light signal to the first beam splitter, the first beam splitter divides the spatial light signal into two paths, one path is provided to the first reflector, the other path is provided to the second reflector, the spatial light signals reflected by the first reflector and the second reflector interfere at the first beam splitter to generate an initial interference light signal, the initial interference light signal is coupled to an optical fiber through the second collimator and transmitted to the second beam splitter through the optical fiber, the second beam splitter divides the initial interference light signal into two paths, one path passes through the sample to be measured to form a stretching interference light signal, and the stretching interference light signal is transmitted to the waveform collecting device, the other path of initial interference optical signal is directly transmitted to the spectrometer;
wherein, in expression (1) of the interference spectrum of the initial interference light signal, E1(w) represents the spatial light signal reflected back by the first mirror, E2(w) represents the spatial light signal reflected back by the second mirror,
representing the phase difference of the two reflected spatial light signals;
in the spectral expression (2) of the stretched interference optical signal,
representing the spatial light signal reflected back by the first mirror,
representing the spatial light signal reflected back by the second mirror,
indicating the phase difference of the two spatial light signals reflected back.
In another optional implementation manner, the waveform acquisition device includes a detector and an oscilloscope, where the detector is connected to the sample to be measured, and is configured to receive the path of initial interference optical signal and convert the path of initial interference optical signal into an initial interference electrical signal; and the oscilloscope collects the waveform of the initial interference electric signal, namely the waveform of the initial interference optical signal.
In another alternative implementation, the laser signal is a supercontinuum laser or a broad spectrum laser.
According to a second aspect of the embodiments of the present invention, there is provided a simple and easily tunable dispersion ultrafast measurement method, including the steps of:
s1, generating an initial interference light signal, dividing the initial interference light signal into two paths, wherein one path forms a stretching interference light signal after being stretched by the sample to be measured, acquiring the waveform of the stretching interference light signal to obtain a time domain envelope, and acquiring the interference spectrum of the other path of the initial interference light signal;
s2, based on the fact that the time domain envelope and the interference spectrum of the initial interference light signal are scaled in an equal proportion, iterative fitting is conducted on the time domain envelope and the interference spectrum, and the dispersion amount of the sample to be detected is calculated.
In an alternative implementation manner, in the step S2, the interference spectrum of the initial interference light signal is represented as:
where w is the angular frequency, E1(w) denotes a first original optical signal, E, for generating said interference optical signal2(w) a second original optical signal for generating said interference optical signal,
representing the phase difference between the first path of original optical signal and the second path of original optical signal;
according to the time domain envelope and the interference spectrum of the initial interference optical signal, scaling in equal proportion, wherein the spectrum expression of the interference optical signal after the time stretching of the sample to be detected is as follows:
wherein
Representing a first original optical signal used to generate the interfering optical signal,
representing a second original optical signal used to generate the interfering optical signal,
representing the phase difference, beta, between the first and second original optical signals2Is the second-order group velocity dispersion parameter of the sample to be measured, and t is time.
In another optional implementation manner, in step S2, the iteratively fitting the time-domain envelope and the interference spectrum, and calculating the dispersion amount of the sample to be detected includes:
obtaining t from the time domain envelope, substituting t into the spectral expression (2) of the stretched interference optical signal after the time stretching of the sample to be tested, and calculating to obtain a second-order group velocity dispersion parameter beta of the sample to be tested2；
Or substituting t ═ Dlambda into the spectral expression (2), establishing an equation set comprising at least two spectral expressions (2), and solving to obtain dispersion coefficient D corresponding to each wavelength and second-order group velocity dispersion parameter beta of the sample to be measured2Where λ represents the wavelength, is obtained from the time-domain envelope.
In another optional implementation manner, in step S1, the acquiring the waveform of the stretched interference light signal to obtain a time-domain envelope includes: and averaging multiple groups of waveforms of the collected stretching interference optical signals to obtain the time domain envelope.
The invention has the beneficial effects that:
1. after the optical path difference of the two interference arms in the interference optical signal generating device is adjusted, when dispersion measurement is carried out on samples to be measured with different lengths, the length of the reference arm in the two interference arms does not need to be adjusted repeatedly and adaptively according to the length of the samples to be measured, so that the operation difficulty and complexity are reduced, the dispersion measurement of the samples to be measured with different lengths is facilitated, and the dispersion measurement efficiency of the samples to be measured with different lengths is improved; for a long sample to be measured, the method does not need to adaptively adjust the length of the reference arm, so that the requirement of precisely adjusting the length of the reference arm during dispersion measurement of the long sample to be measured is eliminated, and the volume of a dispersion measurement system is reduced; in addition, when the dispersion measurement is carried out on a plurality of samples to be measured with different lengths, the optical path difference of the interference arm does not need to be adjusted repeatedly according to the length of the samples to be measured, so that the dispersion measurement is more convenient to realize instrumentization; according to the method, the initial interference optical signal is stretched by a sample to be tested to form a stretched interference optical signal, the waveform of the stretched interference optical signal is collected to obtain a time domain envelope, the time domain envelope and the interference spectrum of the initial interference optical signal are scaled in an equal proportion, iterative fitting is carried out on the time domain envelope and the interference spectrum, the dispersion of the sample to be tested can be calculated, and the data processing method is simpler; the data acquisition speed is determined by the sampling rate of the waveform acquisition device and is not limited by the sampling rate of a spectrometer, and the acquisition rate of the waveform acquisition device is higher, so that the data acquisition efficiency required by dispersion measurement is higher, and the dispersion measurement efficiency is higher;
2. in the interference light signal generating device, the space light signals reflected by the first reflecting mirror and the second reflecting mirror interfere at the first beam splitter, and when the positions of the two reflecting mirrors are adjusted, only a small distance difference is needed between the two reflecting mirrors and the first beam splitter, so that the reflecting mirrors are used as a part of an interference arm, and the volume of a dispersion measurement system can be reduced; in addition, compared with the mode that optical fibers with different lengths are used as interference arms and reflectors are used as the interference arms, the distance between the two reflectors and the first beam splitter is easier to adjust, and therefore instrumentization of a dispersion measurement system is facilitated;
3. when the laser signal is the supercontinuum laser, the dispersion measurement range can be wider, and the range of thousands of nanometers (nm) can be measured; when the invention is used for carrying out dispersion measurement on a long sample to be measured, the dispersion measurement requirement can be met even if a wide-spectrum light source is adopted, so that the requirement on laser signals during the dispersion measurement of the long sample to be measured can be reduced;
4. the invention obtains the time domain envelope by averaging a plurality of groups of waveforms of the collected stretching interference optical signals, and can reduce the noise level in the signals, thereby improving the accuracy of chromatic dispersion measurement.
Drawings
FIG. 1 is a block diagram of a simple tunable chromatic dispersion ultrafast measurement system of the present invention;
FIG. 2 is a block diagram of an embodiment of a simple tunable chromatic dispersion ultrafast measurement system of the present invention;
FIG. 3 is a flow chart of the method for measuring ultra-fast dispersion with simple and easy tuning of the present invention.
Detailed Description
In order to make the technical solutions in the embodiments of the present invention better understood and make the above objects, features and advantages of the embodiments of the present invention more comprehensible, the technical solutions in the embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
In the description of the present invention, unless otherwise specified and limited, it is to be noted that the term "connected" is to be interpreted broadly, and may be, for example, a mechanical connection or an electrical connection, or a communication between two elements, or may be a direct connection or an indirect connection through an intermediate medium, and a specific meaning of the term may be understood by those skilled in the art according to specific situations.
Referring to fig. 1, it is a block diagram of the simple and easily tunable chromatic dispersion ultrafast measurement system of the present invention. The simple and easily-adjusted chromatic dispersion ultrafast measurement system can comprise an interference light signal generation device, a sample to be measured, a waveform acquisition device and a spectrometer, wherein the interference signal generation device is used for generating an initial interference light signal, the initial interference light signal is divided into two paths, one path of the initial interference light signal is stretched by the time domain of the sample to be measured to form a stretched interference light signal, the stretched interference light signal is transmitted to the waveform acquisition device, and the other path of the initial interference light signal is directly transmitted to the spectrometer; the waveform acquisition device acquires the waveform of the stretching interference optical signal to obtain a time domain envelope; the spectrometer collects the interference spectrum of the other path of initial interference light signal; and based on the equal proportional scaling of the time domain envelope and the interference spectrum of the initial interference light signal, performing iterative fitting on the time domain envelope and the interference spectrum, and calculating the dispersion of the sample to be detected.
In this embodiment, the first output end of the interference light signal generating device may be connected to the waveform collecting device through the sample to be measured, the second output end may be directly connected to the spectrometer, the output ends of the waveform collecting device and the spectrometer may be connected to the processor, the waveform collecting device sends the time-domain envelope acquired by the waveform collecting device to the processor, the spectrometer sends the acquired interference spectrum to the processor, and the processor may perform iterative fitting on the time-domain envelope and the interference spectrum based on the time-domain envelope scaled in equal proportion to the interference spectrum of the initial interference light signal, and calculate the dispersion of the sample to be measured. The sample to be measured can be an optical fiber to be measured, and the dispersion amount can comprise a dispersion system, a second-order group velocity dispersion parameter and the like.
Wherein the interference spectrum of the initial interference light signal can be represented as:
where w is the angular frequency, E1(w) represents a first original optical signal, E, for generating said initial interference optical signal2(w) represents a second original optical signal used to generate the initial interference optical signal,
representing the phase difference between the first path of original optical signal and the second path of original optical signal;
based on the time domain envelope and the interference spectrum of the initial interference optical signal being scaled in equal proportion, the spectral expression of the interference optical signal after time stretching of the sample to be detected can be as follows:
wherein
Representing a first original optical signal used to generate the initial interference optical signal,
representing a second original optical signal used to generate the initial interfering optical signal,
representing the phase difference, beta, between the first and second original optical signals2Is the second-order group velocity dispersion parameter of the sample to be measured, and t is time.
When the dispersion amount of the sample to be detected is calculated, t can be obtained from the time domain envelope, and is substituted into the spectral expression (2) of the stretched interference optical signal after the time stretching of the sample to be detected, so that the second-order group velocity dispersion parameter beta of the sample to be detected is calculated2(ii) a Or substituting t ═ Dlambda into the spectral expression (2), establishing an equation set comprising at least two spectral expressions (2), and solving to obtain dispersion coefficient D corresponding to each wavelength and second-order group velocity dispersion parameter beta of the sample to be measured2Where λ represents the wavelength, obtainable from the time-domain envelope.
Compared with the traditional interference spectrum dispersion measurement method, the interference light signal is firstly generated, and the two interference arms for generating the interference light signal do not have samples to be measured, namely the samples to be measured do not need to be placed in the measurement arms of the two interference arms, so that the optical path difference of the two interference arms in the interference light signal generation device is adjusted, and the length of the reference arm in the two interference arms does not need to be adjusted repeatedly in an adaptive manner according to the length of the samples to be measured when the samples to be measured with different lengths are subjected to dispersion measurement, thereby reducing the operation difficulty and complexity, facilitating the dispersion measurement of the samples to be measured with different lengths and improving the dispersion measurement efficiency of the samples to be measured with different lengths; in addition, when the optical fiber to be measured has a longer optical path (such as a long optical fiber), the optical path of the two paths of light can be maintained in a smaller state only by finely adjusting the optical path of the reference arm due to lower coherence of a light source, limited resolution of a spectrometer and the like, and the invention does not need to adaptively adjust the length of the reference arm for a long sample to be measured, thereby saving the requirement of precisely adjusting the length of the reference arm during dispersion measurement of the long sample to be measured and reducing the volume of a dispersion measurement system; when the invention is used for carrying out dispersion measurement on a plurality of samples to be measured with different lengths, the optical path difference of the interference arm does not need to be repeatedly adjusted according to the length of the samples to be measured, and the dispersion measurement is more convenient to realize instrumentization.
Secondly, after obtaining the intensity information of the interference fringes of the optical signals in the two interference arms, the traditional interference spectrum dispersion measurement method firstly uses Fourier transform and other methods to obtain the phase of the interference fringes and further obtain the dispersion of the optical fiber to be measured, and the data processing method is complex; according to the invention, the initial interference optical signal is stretched by a sample to be detected to form a stretched interference optical signal, the waveform of the stretched interference optical signal is collected to obtain a time domain envelope, the time domain envelope and the interference spectrum of the initial interference optical signal are scaled in an equal proportion, iterative fitting is carried out on the time domain envelope and the interference spectrum, the dispersion of the sample to be detected can be calculated, and the data processing method is simpler.
Moreover, the acquisition of data required by the traditional interference spectral dispersion measurement method is limited by the sampling rate of the spectrometer, so that the measurement speed of the traditional interference spectral dispersion measurement method is low; the invention only needs to collect the waveform of the stretched interference optical signal formed by stretching the time domain of the sample to be measured under the condition that the spectrum of the initial interference optical signal generated by the optical signal generating device is fixed, the spectrometer is arranged in the invention to ensure that the collected interference spectrum is matched with the time domain envelope in time and is not used for collecting main data required by dispersion measurement, namely the data collection speed of the invention is determined by the sampling rate of the waveform collecting device and is not limited by the sampling rate of the spectrometer, and the collection efficiency of the data required by the dispersion measurement of the invention is higher because the collection rate of the waveform collecting device is higher, thereby ensuring that the dispersion measurement efficiency of the invention is higher.
In one embodiment, as shown in fig. 2, the interference light signal generating device may include a laser, a first collimator, a first mirror, a first beam splitter, a second mirror, a second collimator, and a second beam splitter, wherein the laser is connected to the first beam splitter through the first collimator, and the first beam splitter is connected to the first mirror, the second mirror, and the second beam splitter through the second collimator; the laser provides a laser signal to the first collimator, the first collimator collimates the laser signal provided by the laser into a spatial light signal and transmits the spatial light signal to the first beam splitter, the first beam splitter divides the spatial light signal into two paths, one path is provided to the first reflector, the other path is provided to the second reflector, the spatial light signals reflected by the first reflector and the second reflector interfere at the first beam splitter to generate an initial interference light signal, the initial interference light signal is coupled to an optical fiber through the second collimator and transmitted to the second beam splitter through the optical fiber, the second beam splitter divides the initial interference light signal into two paths, one path passes through the sample to be measured to form a stretching interference light signal, and the stretching interference light signal is transmitted to the waveform collecting device, and the other path of initial interference light signal is directly transmitted to the spectrometer. The two paths of space optical signals divided by the first beam splitter can be perpendicular to the corresponding reflecting mirrors and respectively face and incident to the first reflecting mirror and the second reflecting mirror.
Wherein, in expression (1) of the interference spectrum of the initial interference light signal, E1(w) represents the spatial light signal reflected back by the first mirror, E2(w) represents the spatial light signal reflected back by the second mirror,
representing the phase difference of the two reflected spatial light signals;
in the spectral expression (2) of the stretched interference optical signal,
representing the spatial light signal reflected back by the first mirror,
representing the spatial light signal reflected back by the second mirror,
indicating the phase difference of the two spatial light signals reflected back.
Specifically, in this embodiment, the interference spectrum of the initial interference light signal is represented as:
where w is the angular frequency, E1(w) represents the spatial light signal reflected back by the first mirror, E2(w) represents the spatial light signal reflected back by the second mirror,
representing the phase difference of the two reflected spatial light signals; based on the time domain envelope and the interference spectrum being scaled in equal proportion, the spectrum expression of the stretched interference optical signal after the time stretching of the sample to be detected is as follows:
wherein
Representing the spatial light signal reflected back by the first mirror,
representing the spatial light signal reflected back by the second mirror,
representing the phase difference, beta, of the two spatial light signals reflected back2Is the second-order group velocity dispersion parameter of the sample to be measured, and t is time.
In the interference light signal generating device, the space light signals reflected by the first reflecting mirror and the second reflecting mirror interfere at the first beam splitter, and when the positions of the two reflecting mirrors are adjusted, only a small distance difference is needed between the two reflecting mirrors and the first beam splitter, so that the reflecting mirrors are used as a part of an interference arm, and the volume of a dispersion measurement system can be reduced; in addition, compared with the mode that optical fibers with different lengths are used as interference arms, the reflecting mirrors are used as the interference arms, so that the distance between the two reflecting mirrors and the first beam splitter is easier to adjust, and the dispersion measurement system is convenient to instrument.
In this embodiment, the waveform acquisition device may include a detector and an oscilloscope, where the detector is connected to the sample to be measured, and is configured to receive the path of initial interference optical signal and convert the path of initial interference optical signal into an initial interference electrical signal; and the oscilloscope collects the waveform of the initial interference electric signal, namely collects the waveform of the initial interference optical signal. The first output end of the second beam splitter can be connected with the detection end of the detector through a sample to be detected, the output end of the detector is connected with the oscilloscope, and the second output end of the second beam splitter can be directly connected with the spectrometer. In this embodiment, the oscilloscope and the spectrometer may both be connected to the processor, the oscilloscope sends the time-domain envelope acquired by the oscilloscope to the processor, the spectrometer sends the interference spectrum acquired by the spectrometer to the processor, and the processor may perform iterative fitting on the time-domain envelope and the interference spectrum based on the time-domain envelope scaled in equal proportion to the interference spectrum of the initial interference light signal, and calculate the dispersion amount of the sample to be measured. In addition, the laser signal can be a supercontinuum laser or a broad spectrum laser, wherein the spectrum range of the supercontinuum laser can be thousands of nanometers nm, and the pulse repetition frequency of the laser signal can be more than megahertz; because the coherence requirement of the long sample to be measured on the light source is lower when the long sample to be measured is subjected to dispersion measurement, the invention can meet the dispersion measurement requirement even if a wide-spectrum light source is adopted when the long sample to be measured is subjected to dispersion measurement, thereby reducing the requirement on laser signals when the long sample to be measured is subjected to dispersion measurement. Since the acquisition efficiency of a waveform acquisition device (such as an oscilloscope in this embodiment) is generally high, in order to improve the dispersion measurement accuracy, the time-domain envelope may be obtained by averaging multiple sets of waveforms of the acquired stretched interference optical signal, thereby reducing the noise level in the signal. In the invention, the precision of the dispersion measurement system is mainly determined by the resolution of a spectrometer, the bandwidth and sampling rate of an oscilloscope and a detector and the storage depth of the spectrometer and the oscilloscope; the measurement range is limited by the spectral width of the laser signal and the measurement range of the spectrometer.
In a specific example, a supercontinuum light source with a spectral range of 450nm to 2400nm and a repetition frequency of (78MHz) is utilized, the supercontinuum light source is collimated and output by a first collimator and then is divided into two paths of space optical signals by a first beam splitter, wherein one path of the space optical signals is transmitted to a first reflector, the space optical signals reflected back by the first reflector are returned to the first beam splitter, the other path of the space optical signals reflected back by a second reflector are transmitted to a second reflector, the space optical signals reflected back by the second reflector are interfered at the first beam splitter to form an initial interference optical signal, the initial interference optical signal is coupled to an optical fiber by a second collimator and then is transmitted to a second beam splitter by the optical fiber, the initial interference optical signal is divided into two paths by the second beam splitter, and the path with low power is directly collected by a spectrometer; one path with high power passes through a sample to be detected to form a stretching interference optical signal, and the stretching interference optical signal passes through a detector (with the bandwidth of 20GHz) and then is subjected to waveform acquisition by an oscilloscope (with the sampling rate of 50GHz), so that time domain envelope is obtained. And performing iterative fitting on the acquired time domain envelope and the interference spectrum to obtain the dispersion amount of the measured sample.
It can be seen from the above embodiments that, after the optical path difference between the two interference arms in the interference optical signal generating device is adjusted, when performing dispersion measurement on samples to be measured with different lengths, the length of the reference arm in the two interference arms does not need to be adjusted repeatedly and adaptively according to the length of the sample to be measured, thereby reducing the operation difficulty and complexity, facilitating the dispersion measurement of samples to be measured with different lengths, and improving the dispersion measurement efficiency of samples to be measured with different lengths; for a long sample to be measured, the method does not need to adaptively adjust the length of the reference arm, so that the requirement of precisely adjusting the length of the reference arm during dispersion measurement of the long sample to be measured is eliminated, and the volume of a dispersion measurement system is reduced; in addition, when the dispersion measurement is carried out on a plurality of samples to be measured with different lengths, the optical path difference of the interference arm does not need to be adjusted repeatedly according to the length of the samples to be measured, so that the dispersion measurement is more convenient to realize instrumentization; according to the method, the initial interference optical signal is stretched by a sample to be tested to form a stretched interference optical signal, the waveform of the stretched interference optical signal is collected to obtain a time domain envelope, the time domain envelope and the interference spectrum of the initial interference optical signal are scaled in an equal proportion, iterative fitting is carried out on the time domain envelope and the interference spectrum, the dispersion of the sample to be tested can be calculated, and the data processing method is simpler; the data acquisition speed of the invention is determined by the sampling rate of the waveform acquisition device and is not limited by the sampling rate of a spectrometer, and the acquisition rate of the waveform acquisition device is higher, so that the invention has higher acquisition efficiency of data required by dispersion measurement, and thus has higher dispersion measurement efficiency.
In addition, the present invention also provides a simple and easily tunable dispersion ultrafast measurement method, as shown in fig. 3, which may include the following steps:
s1, generating an initial interference light signal, dividing the initial interference light signal into two paths, wherein one path forms a stretching interference light signal after being stretched by the sample to be measured, acquiring the waveform of the stretching interference light signal to obtain a time domain envelope, and acquiring the interference spectrum of the other path of the initial interference light signal;
s2, based on the fact that the time domain envelope and the interference spectrum of the initial interference light signal are scaled in an equal proportion, iterative fitting is conducted on the time domain envelope and the interference spectrum, and the dispersion amount of the sample to be detected is calculated.
In step S2, the interference spectrum of the initial interference light signal is represented as:
where w is the angular frequency, E1(w) denotes a first original optical signal, E, for generating said interference optical signal2(w) a second original optical signal for generating said interference optical signal,
representing the phase difference between the first path of original optical signal and the second path of original optical signal;
according to the time domain envelope and the interference spectrum of the initial interference optical signal, scaling in equal proportion, wherein the spectrum expression of the interference optical signal after the time stretching of the sample to be detected is as follows:
wherein
Representing a first original optical signal used to generate the interfering optical signal,
representing a second original optical signal used to generate the interfering optical signal,
representing the phase difference, beta, between the first and second original optical signals2Is the second-order group velocity dispersion parameter of the sample to be measured, and t is time.
In step S2, the iteratively fitting the time-domain envelope and the interference spectrum, and calculating the dispersion amount of the sample to be measured includes:
obtaining t from the time domain envelope, substituting t into the spectral expression (2) of the stretched interference optical signal after the time stretching of the sample to be tested, and calculating to obtain a second-order group velocity dispersion parameter beta of the sample to be tested2(ii) a Or substituting t ═ Dlambda into the spectral expression (2), establishing an equation set comprising at least two spectral expressions (2), and solving to obtain dispersion coefficient D corresponding to each wavelength and second-order group velocity dispersion parameter beta of the sample to be measured2Where λ represents the wavelength, is obtained from the time-domain envelope.
In step S1, the acquiring the waveform of the stretched interference optical signal to obtain a time-domain envelope includes: and averaging multiple groups of waveforms of the collected stretching interference optical signals to obtain the time domain envelope. The invention obtains the time domain envelope by averaging a plurality of groups of waveforms of the collected stretching interference optical signals, and can reduce the noise level in the signals, thereby improving the accuracy of chromatic dispersion measurement.
It can be seen from the above embodiments that, after the optical path difference between the two interference arms in the interference optical signal generating device is adjusted, when performing dispersion measurement on samples to be measured with different lengths, the length of the reference arm in the two interference arms does not need to be adjusted repeatedly and adaptively according to the length of the sample to be measured, thereby reducing the operation difficulty and complexity, facilitating the dispersion measurement of samples to be measured with different lengths, and improving the dispersion measurement efficiency of samples to be measured with different lengths; for a long sample to be measured, the method does not need to adaptively adjust the length of the reference arm, so that the requirement of precisely adjusting the length of the reference arm during dispersion measurement of the long sample to be measured is eliminated, and the volume of a dispersion measurement system is reduced; in addition, when the dispersion measurement is carried out on a plurality of samples to be measured with different lengths, the optical path difference of the interference arm does not need to be adjusted repeatedly according to the length of the samples to be measured, so that the dispersion measurement is more convenient to realize instrumentization; according to the method, the initial interference optical signal is stretched by a sample to be tested to form a stretched interference optical signal, the waveform of the stretched interference optical signal is collected to obtain a time domain envelope, the time domain envelope and the interference spectrum of the initial interference optical signal are scaled in an equal proportion, iterative fitting is carried out on the time domain envelope and the interference spectrum, the dispersion of the sample to be tested can be calculated, and the data processing method is simpler; the data acquisition speed of the invention is determined by the sampling rate of the waveform acquisition device and is not limited by the sampling rate of a spectrometer, and the acquisition rate of the waveform acquisition device is higher, so that the invention has higher acquisition efficiency of data required by dispersion measurement, and thus has higher dispersion measurement efficiency.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is to be controlled solely by the appended claims.
Claims (10)
1. A simple and easily-adjusted chromatic dispersion ultrafast measurement system is characterized by comprising an interference light signal generation device, a sample to be measured, a waveform acquisition device and a spectrometer, wherein the interference signal generation device is used for generating an initial interference light signal and dividing the initial interference light signal into two paths, one path of the initial interference light signal is stretched by the time domain of the sample to be measured to form a stretched interference light signal, the stretched interference light signal is transmitted to the waveform acquisition device, and the other path of the initial interference light signal is directly transmitted to the spectrometer;
the waveform acquisition device acquires the waveform of the stretching interference optical signal to obtain a time domain envelope; the spectrometer collects the interference spectrum of the other path of initial interference light signal;
and based on the equal proportional scaling of the time domain envelope and the interference spectrum of the initial interference light signal, performing iterative fitting on the time domain envelope and the interference spectrum, and calculating the dispersion of the sample to be detected.
2. The simple tunable dispersive ultrafast measurement system according to claim 1, wherein the interference spectrum of the initial interference optical signal is represented as:
where w is the angular frequency, E1(w) represents a first original optical signal, E, for generating said initial interference optical signal2(w) represents a second original optical signal used to generate the initial interference optical signal,
representing the phase difference between the first path of original optical signal and the second path of original optical signal;
based on the time domain envelope and the interference spectrum of the initial interference optical signal, the spectrum expression of the stretched interference optical signal after the time stretching of the sample to be detected is as follows:
wherein
Representing a first original optical signal used to generate the initial interference optical signal,
representing a second original optical signal used to generate the initial interfering optical signal,
representing the phase difference, beta, between the first and second original optical signals2Is the second-order group velocity dispersion parameter of the sample to be measured, and t is time.
3. The system of claim 2, wherein t is obtained from the time-domain envelope, and is substituted into the spectral expression (2) of the stretched interference optical signal obtained by time-stretching the sample to be measured, so as to calculate the second-order group velocity dispersion parameter β of the sample to be measured2；
Or substituting t ═ Dlambda into the spectral expression (2), establishing an equation set comprising at least two spectral expressions (2), and solving to obtain dispersion coefficient D corresponding to each wavelength and second-order group velocity dispersion parameter beta of the sample to be measured2Where λ represents the wavelength, is obtained from the time-domain envelope.
4. The simple tunable dispersive ultrafast measurement system according to claim 3, wherein said interference light signal generating means comprises a laser, a first collimator, a first mirror, a first beam splitter, a second mirror, a second collimator and a second beam splitter, wherein said laser is connected to said first beam splitter through said first collimator, and said first beam splitter is connected to said first mirror, said second mirror and said second beam splitter through said second collimator, respectively;
the laser provides a laser signal to the first collimator, the first collimator collimates the laser signal provided by the laser into a spatial light signal and transmits the spatial light signal to the first beam splitter, the first beam splitter divides the spatial light signal into two paths, one path is provided to the first reflector, the other path is provided to the second reflector, the spatial light signals reflected by the first reflector and the second reflector interfere at the first beam splitter to generate an initial interference light signal, the initial interference light signal is coupled to an optical fiber through the second collimator and transmitted to the second beam splitter through the optical fiber, the second beam splitter divides the initial interference light signal into two paths, one path passes through the sample to be measured to form a stretching interference light signal, and the stretching interference light signal is transmitted to the waveform collecting device, the other path of initial interference optical signal is directly transmitted to the spectrometer;
wherein, in expression (1) of the interference spectrum of the initial interference light signal, E1(w) represents the spatial light signal reflected back by the first mirror, E2(w) represents the spatial light signal reflected back by the second mirror,
representing the phase difference of the two reflected spatial light signals;
in the spectral expression (2) of the stretched interference optical signal,
representing the spatial light signal reflected back by the first mirror,
representing the spatial light signal reflected back by the second mirror,
indicating the phase difference of the two spatial light signals reflected back.
5. The simple and easily tunable chromatic dispersion ultrafast measurement system of claim 1, wherein the waveform acquisition device comprises a detector and an oscilloscope, the detector is connected to the sample to be measured, and is configured to receive the one path of initial interference optical signal and convert the one path of initial interference optical signal into an initial interference electrical signal; and the oscilloscope collects the waveform of the initial interference electric signal, namely collects the waveform of the initial interference optical signal.
6. The simple tunable dispersive ultrafast measurement system according to claim 3, wherein said laser signal is a supercontinuum laser or a broad spectrum laser.
7. A simple and easily-adjusted ultra-fast dispersion measurement method is characterized by comprising the following steps:
s1, generating an initial interference light signal, dividing the initial interference light signal into two paths, wherein one path forms a stretching interference light signal after being stretched by the sample to be measured, acquiring the waveform of the stretching interference light signal to obtain a time domain envelope, and acquiring the interference spectrum of the other path of the initial interference light signal;
s2, based on the fact that the time domain envelope and the interference spectrum of the initial interference light signal are scaled in an equal proportion, iterative fitting is conducted on the time domain envelope and the interference spectrum, and the dispersion amount of the sample to be detected is calculated.
8. The method of claim 7, wherein in step S2, the interference spectrum of the initial interference light signal is expressed as:
where w is the angular frequency, E1(w) denotes a first original optical signal, E, for generating said interference optical signal2(w) a second original optical signal for generating said interference optical signal,
representing the phase difference between the first path of original optical signal and the second path of original optical signal;
according to the time domain envelope and the interference spectrum of the initial interference light signal, scaling in equal proportion, and the spectrum expression of the interference light signal after time stretching of the sample to be tested is as follows:
wherein
Representing a first original optical signal used to generate the interfering optical signal,
representing a second original optical signal used to generate the interfering optical signal,
representing the phase difference, beta, between the first and second original optical signals2Is the second-order group velocity dispersion parameter of the sample to be measured, and t is time.
9. The method of claim 8, wherein the step S2 of iteratively fitting the time-domain envelope and the interference spectrum to calculate the dispersion of the sample to be measured includes:
obtaining t from the time domain envelope, substituting t into the spectral expression (2) of the stretched interference optical signal after the time stretching of the sample to be tested, and calculating to obtain a second-order group velocity dispersion parameter beta of the sample to be tested2；
Or substituting t ═ Dlambda into the spectral expression (2), establishing an equation set comprising at least two spectral expressions (2), and solving to obtain dispersion coefficient D corresponding to each wavelength and second-order group velocity dispersion parameter beta of the sample to be measured2Where λ represents the wavelength, is obtained from the time-domain envelope.
10. The method of claim 7, wherein the step S1 of acquiring the waveform of the stretched interference optical signal to obtain the time-domain envelope includes: and averaging multiple groups of waveforms of the collected stretching interference optical signals to obtain the time domain envelope.
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