A method and system for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source

Abstract

The present application provides a method for measuring the instantaneous linewidth of a narrow-linewidth high-speed swept-frequency light source, the steps of which include: prefabricating a frequency scale; coupling the swept-frequency light source to be measured with the prefabricated frequency scale and performing instantaneous parallel sampling to obtain instantaneous sampling information; based on the prefabricated frequency scale, superimposing and accumulating the instantaneous sampling information to obtain the interference spectrum data of the swept-frequency light source to be measured within the cumulative equivalent long-time window; processing and analyzing the interference spectrum data within the cumulative equivalent long-time window to obtain the instantaneous linewidth of the swept-frequency light source to be measured at any time. The present application provides a method for measuring the instantaneous linewidth of a narrow-linewidth high-speed swept-frequency light source, which uses a multi-carrier light source as a frequency scale and performs instantaneous parallel sampling on the swept-frequency light source with a sweep speed not higher than 10 16 The instantaneous linewidth of a swept-frequency light source with a linewidth of 40 kHz or higher is captured and measured. The measurement method has good reproducibility and accurate and stable measurement results. The present application also proposes a system for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source.

Description

Technical Field

[0001] The present application belongs to the technical field of swept-frequency light source linewidth measurement in optoelectronic engineering, and in particular relates to a method and system for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source. Background Art

[0002] A swept-frequency light source is a new type of light source capable of outputting broadband linear swept continuous waves. It has important applications and enormous development potential in systems such as lidar, optical coherence tomography, fiber-optic sensing, and vector network analysis. Instantaneous linewidth is a key parameter of a swept-frequency light source. It is closely related to the source's instantaneous dynamic and phase characteristics, and directly determines its performance in system applications.

[0003] Measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency source essentially requires capturing a wave train (narrow linewidth) of sufficiently long duration within the instantaneous time window. This leads to a conflict between "instantaneous" and "long sampling windows." Because the frequency of a swept-frequency source varies rapidly over time, this conflict becomes increasingly pronounced with higher sweep rates and narrower linewidths. Because the instantaneous linewidth of a swept-frequency source changes dynamically during the sweep, capturing and measuring it presents a challenge. Currently, the following methods are available for measuring the instantaneous linewidth of swept-frequency sources, both domestically and internationally.

[0004] 1. Delayed self-heterodyne method

[0005] The delayed self-heterodyne method uses an interferometer to measure the roll-off of the visibility of the interference fringes of a swept-frequency light source. When the delay fiber length in the interferometer is much longer than the laser coherence time, the average linewidth of the swept-frequency light source over the entire swept spectrum can be roughly estimated. When the delay fiber length is less than the laser coherence length, the Hilbert-Huang transform, local mean decomposition, and other methods are combined to process the weak fluctuations of the interference signal phase noise, and the instantaneous linewidth of the kHz-MHz level can be measured. However, the sweep speed of the swept-frequency light is limited to 10 7 Below the Hz / s level.

[0006] 2. Measurement method based on electro-optical switch

[0007] The electro-optical switch-based measurement method utilizes the switching effect of an electro-optic modulator to directly generate a sampling window. Sweep-frequency light is then collected within this window, and the spectral width within this time window is recorded using a high-resolution spectrometer. This spectral width is defined as the instantaneous linewidth within this time window. However, due to factors such as the multi-cycle averaging measurement of the spectrometer, the spectral broadening caused by the electro-optical modulator, and the nonlinear relationship between the swept-frequency light frequency and the modulator drive signal, this measurement method is only suitable for instantaneous linewidth measurements greater than tens of GHz.

[0008] 3. Measurement method based on electric field reconstruction theory

[0009] The measurement method based on electric field reconstruction theory first experimentally measures the multiple interference light intensities obtained after the swept light passes through a 3×3 coupler. Then, using electric field reconstruction theory, the electric field function of the swept light is reconstructed and the instantaneous linewidth within a specific time window is calculated. The linewidth captured by this method is still the average value within the specified observation window, and its accuracy depends on the selection of the frequency fitting function for the swept light field.

[0010] 4. Measurement method based on tunable filter

[0011] The tunable filter-based measurement method passes the swept-frequency light under test through a tunable narrowband filter. This captures a portion of the spectrum near the filter's center frequency. After photoelectric conversion and oscilloscope sampling, the time-domain signal is deconvolved to obtain the instantaneous linewidth of the swept-frequency light at the filter's center frequency. This method essentially uses the filter's spectral width as the sampling window, resulting in the narrowest measurable linewidth being on the order of hundreds of GHz.

[0012] In summary, for high-speed swept light sources, existing methods can only achieve instantaneous linewidth measurement above the GHz level; while the measurement of instantaneous linewidth at the kHz-MHz level can only be achieved in the measurement of low-speed swept light sources. 16 Hz) and narrow linewidth (<kHz), the methods reported at home and abroad are still unable to solve the contradiction between "instantaneous" and "long time sampling window". Summary of the Invention

[0013] The present application provides a method and system for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source, which is particularly suitable for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source, and solves the technical problem in the prior art that the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source cannot be captured and measured.

[0014] To solve at least one of the above technical problems, the technical solution adopted in this application is:

[0015] A method for measuring the instantaneous linewidth of a narrow-linewidth high-speed swept-frequency light source, comprising:

[0016] Prefabricated frequency scale;

[0017] The frequency sweeping light source to be measured is coupled with a prefabricated frequency scale and instantaneous parallel sampling is performed to obtain instantaneous sampling information;

[0018] Based on the prefabricated frequency scale, the instantaneous sampling information is superimposed and accumulated to obtain the interference spectrum data of the swept-frequency light source to be measured within the accumulation equivalent long time window;

[0019] By processing and analyzing the interference spectrum data within the accumulated equivalent long time window, the instantaneous linewidth of the swept-frequency light source to be measured at any time can be obtained.

[0020] Furthermore, the prefabricated frequency scale includes:

[0021] Acquire a multi-carrier light source;

[0022] Taking the frequency of the light emitted by the multi-carrier light source as a reference, deriving a plurality of frequency scales of different frequency magnitudes;

[0023] Preferably, all the frequency scales are frequencies of light emitted by a continuous wave light source output by the multi-carrier light source, and all the frequency scales are arranged at equal intervals.

[0024] Furthermore, the frequency scale is determined based on the sweep speed and sweep range of the swept-frequency light source to be measured, and the initial value of the frequency scale is an adjustable value.

[0025] Furthermore, coupling the frequency sweeping light source to be measured with a prefabricated frequency scale and performing instantaneous parallel sampling to obtain instantaneous sampling information includes:

[0026] Based on the frequency scale, coupling it with the frequency-sweep light source to be measured to obtain an optical beat signal;

[0027] The optical beat signal obtained by instantaneous sampling is converted into an instantaneous electrical signal through a balanced detector;

[0028] The converted instantaneous electrical signal is then sampled by a high-speed oscilloscope to obtain instantaneous interference spectrum data;

[0029] In each frequency sweep cycle, all optical beat signals are instantaneously and parallelly collected for interference spectrum information;

[0030] A plurality of instantaneous sampling information of the optical beat signal at the same instant in all frequency sweep cycles is obtained.

[0031] Furthermore, the time period of all sweep cycles is the same;

[0032] The instantaneous time position corresponding to the same frequency scale in each frequency sweep cycle is the same.

[0033] Furthermore, the instantaneous sampling information is superimposed and accumulated based on the prefabricated frequency scale to obtain the interference spectrum data of the swept-frequency light source to be measured within the cumulative equivalent long time window, including:

[0034] When sampling spectral data, based on any of the frequency scales, the instantaneous electrical signals are accumulated at the same instant in all frequency sweep cycles and marked as the accumulated equivalent long time window at the same instant;

[0035] The instantaneous spectrum data of the instantaneous electrical signal at the same instantaneous moment in all frequency sweep cycles are accumulated to obtain the accumulated spectrum data in the accumulated equivalent time window based on the frequency scale.

[0036] Furthermore, before sampling the spectral data, the method further includes the steps of amplifying and filtering the instantaneous electrical signal in the electrical domain, and then removing the DC component.

[0037] Furthermore, the processing and analysis of the interference spectrum data within the cumulative equivalent long time window can obtain the instantaneous linewidth of the swept-frequency light source to be measured at any time, including:

[0038] By performing Fourier transform on the accumulated spectral data within the accumulated equivalent time window, the instantaneous line width of the swept-frequency light source to be measured can be obtained.

[0039] A system for measuring the instantaneous linewidth of a swept-frequency light source, comprising:

[0040] Scale prefabrication module: used to prefabricate frequency scale;

[0041] Instantaneous sampling module: couples the frequency sweep light source to be measured with the prefabricated frequency scale and performs instantaneous parallel sampling to obtain instantaneous sampling information;

[0042] Superposition and accumulation module: Based on the pre-made frequency scale, the instantaneous sampling information is superimposed and accumulated to obtain the interference spectrum data of the swept-frequency light source to be measured within the accumulation equivalent long time window;

[0043] Data processing module: Processing and analyzing the interference spectrum data within the accumulated equivalent long time window can obtain the instantaneous linewidth of the swept-frequency light source to be measured at any time.

[0044] Furthermore, the scale prefabrication module includes:

[0045] Acquire a multi-carrier light source;

[0046] Taking the frequency of the light emitted by the multi-carrier light source as a reference, deriving a plurality of frequency scales of different frequency magnitudes;

[0047] Wherein, all the frequency scales are the frequencies of the light emitted by the continuous wave light source output by the multi-carrier light source, and all the frequency scales are arranged at equal intervals;

[0048] Preferably, the instantaneous sampling module includes:

[0049] Based on the frequency scale, coupling it with the frequency-sweep light source to be measured to obtain an optical beat signal;

[0050] The optical beat signal obtained by instantaneous sampling is converted into an instantaneous electrical signal through a balanced detector;

[0051] The converted instantaneous electrical signal is then sampled by a high-speed oscilloscope to obtain instantaneous interference spectrum data;

[0052] In each frequency sweep cycle, all optical beat signals are instantaneously and parallelly collected for interference spectrum information;

[0053] Obtaining a plurality of instantaneous sampling information of the optical beat signal at the same instant in all frequency sweep cycles;

[0054] Preferably, the superposition accumulation module includes:

[0055] When sampling spectral data, based on any of the frequency scales, the instantaneous electrical signals are accumulated at the same instant in all frequency sweep cycles and marked as the accumulated equivalent long time window at the same instant;

[0056] Accumulating instantaneous spectrum data of the instantaneous electrical signal at the same instantaneous moment in all frequency sweep cycles to obtain cumulative spectrum data within the cumulative equivalent time window based on the frequency scale;

[0057] Preferably, the data processing module includes:

[0058] By performing Fourier transform on the accumulated spectral data within the accumulated equivalent time window, the instantaneous line width of the swept-frequency light source to be measured can be obtained.

[0059] The instantaneous linewidth measurement method of a narrow linewidth high-speed swept frequency light source designed in this application is based on a multi-carrier light source as a frequency scale, and the sweep speed is not higher than 10 16 The instantaneous linewidth of a swept-frequency light source with a linewidth of 40 kHz or higher is captured and measured. The measurement method has good reproducibility and accurate and stable measurement results. The present application also proposes a system for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a flow chart of the method for measuring the instantaneous linewidth of a swept-frequency light source in this application;

[0061] Figure 2 This is an exploded diagram of the instantaneous linewidth measurement of the swept-frequency light source during the measurement in this application;

[0062] Figure 3 Schematic diagram of the instantaneous linewidth measurement system of the swept-frequency light source in this application. DETAILED DESCRIPTION

[0063] The present application is described in detail below with reference to the accompanying drawings and specific embodiments.

[0064] This embodiment proposes a method for measuring the instantaneous linewidth of a narrow linewidth high-speed swept frequency light source, such as Figure 1 As shown, the steps include:

[0065] S1. Prefabricated frequency scale.

[0066] A multi-carrier light source can be obtained. Specifically, a multi-carrier light source can be fabricated based on actual conditions. For example, a self-oscillating multi-carrier light source consisting of an ultra-narrow linewidth seed light source (DFB-LD), a cyclic frequency shift loop (RFSL), and a dual-loop OEO feedback loop can be used. This is well known in the art and will not be described in detail here. Of course, other types of multi-carrier light sources are also possible, and they can also serve as the light source for the frequency scale.

[0067] Based on the frequency of the light emitted by the multi-carrier light source, several frequency scales of different frequencies are derived. That is, a light source that can output standard frequency multi-carrier is prefabricated as a scale, which is the local oscillator light. This "scale" is actually a multi-carrier light source, and each carrier frequency it outputs is a continuous wave with an extremely narrow line width (f1, f2, f3...f n ), the frequency intervals between the carriers are equal and adjustable, so as to be applicable to the measurement of the swept light to be measured with different sweep speeds.

[0068] That is, all frequency scales are the frequencies of the light emitted by the continuous wave light source output by the multi-carrier light source, and all frequency scales are set at equal intervals. Figure 2 The vertical axis is the frequency scale f i (i=1,2,3……n), there are n frequency components f, namely f1、f2、f3……f n Since the carrier frequency of each frequency scale output by the multi-carrier light source is a continuous wave with an extremely narrow line width, with f1 as the reference, between f1 and f2, between f2 and f3...f n-1 With f n The intervals between them are the same, which is conducive to calculating in a quantitative manner and accurately obtaining the instantaneous linewidth of the swept frequency source to be measured.

[0069] Furthermore, all frequency scales are based on the sweep speed and sweep range of the swept-frequency light source to be measured, and the initial value of the frequency scale is an adjustable value, that is, the initial frequency f1 of the carrier can also be flexibly selected according to the sweep band of the swept-frequency light to be measured, so as to be applicable to the measurement of the swept-frequency light to be measured with different sweep ranges. In this embodiment, the sweep speed of the swept-frequency light source to be measured is not higher than 10 16 Hz / s, and the narrowest measurable instantaneous linewidth is not less than 40kHz; that is, this method is applicable to the measurement of the instantaneous linewidth of swept-frequency light sources with different sweep speeds and different sweep ranges.

[0070] The frequency ruler can be used as a standard frequency. By coupling it with the swept-frequency light source to be measured through a coupler, an optical beat signal is obtained. The optical beat signal is then converted into an electrical signal through a balanced detector. The electrical signal is then converted into interference spectrum data through a high-speed oscilloscope. After Fourier transformation, the instantaneous linewidth of the swept-frequency light source to be measured can be obtained.

[0071] S2. Couple the frequency sweeping light source to be measured with the prefabricated frequency scale and perform instantaneous parallel sampling to obtain instantaneous sampling information.

[0072] Based on the frequency scale, it is coupled with the swept light source to be measured to obtain the optical beat signal; the optical beat signal obtained by instantaneous sampling is then converted into an instantaneous electrical signal through a balanced detector; the converted instantaneous electrical signal is then sampled for interference spectrum data through a high-speed oscilloscope to obtain instantaneous interference spectrum data; at the same time, the interference spectrum information of all optical beat signals is instantaneously and parallelly collected in each sweep cycle to obtain several instantaneous sampling information of the optical beat signal at the same instant in all sweep cycles.

[0073] Specifically, because the swept-frequency light source to be measured is itself a periodic swept-frequency light source, within each sweep cycle, the frequency scale is instantaneously coupled in parallel with the swept-frequency light source to be measured, and the beat signals of the multi-carrier light source and the swept-frequency light source to be measured are detected by a photoelectric balanced detector to obtain n instantaneous parallel collected optical beat signals.

[0074] Among them, the light beat signal obtained by instantaneous sampling can be converted into an instantaneous electrical signal through a balanced detector; the instantaneous electrical signal is amplified and filtered in the electrical domain in turn, and then the DC component is removed; the converted instantaneous electrical signal is then sampled for interference spectrum data through a high-speed oscilloscope to obtain instantaneous interference spectrum data.

[0075] like Figure 2 As shown, in each sweep cycle, the n frequency components of the multi-carrier are equivalent to sampling the n instantaneous states of the swept light to be measured in the sweep cycle. Among them, the time period t of all sweep cycles is the same, that is, there are m sweep cycles t and each sweep cycle t has n instantaneous moments, which intersect with n frequency scales respectively. The corresponding instantaneous moment is marked as t mn , where m is the number of sweep cycles and n is the instantaneous moment in the sweep cycle. In the first sweep cycle, the interference is obtained at t 11 , t 12 , t 13 ......t 1n The beat frequency information of the multi-carrier frequency scale at the moment and the instantaneous frequency of the swept light to be measured; in the second sweep cycle, t 21 , t 22 , t 23 ......t 2nThe beat frequency information of the multi-carrier frequency and the instantaneous frequency of the scanned light to be measured at the moment. Since the frequency scale of the multi-carrier light source is stable, the instantaneous time position corresponding to the same frequency is the same in each scan cycle, that is, the instantaneous time position corresponding to the same frequency scale is the same in each scan cycle. That is, relative to the frequency scale f1, the instantaneous time at which the beat frequency information with the scanned light to be measured is t in scan cycle 1. 11 , t in sweep cycle 2 21 , t in sweep cycle 3 31 ...t in the sweep period m m1 . Accordingly, t 11 , t 21 , t 31 ......t m1 The time position in each sweep cycle is the same, and parallel sampling of spectral information at different instantaneous moments in each sweep cycle of the swept light source to be measured is completed based on the f1 frequency scale.

[0076] Accordingly, instantaneous parallelism can obtain f n The instantaneous sampling information of the optical beat signal at several instantaneous time points within the m sweep cycles is the instantaneous sampling information of the multi-carrier light source and the swept light source to be measured at each instantaneous time t mn interference pattern information.

[0077] S3. Based on the prefabricated frequency scale, the instantaneous sampling information is superimposed and accumulated to obtain the interference spectrum data of the swept-frequency light source to be measured within the cumulative equivalent long time window.

[0078] When sampling spectral data, based on any frequency scale, the instantaneous electrical signal at the same instantaneous moment within all frequency sweep cycles is first accumulated, marking this as the cumulative equivalent long-term window for that instantaneous moment. In other words, the cumulative equivalent long-term window is the sum of the instantaneous moments within all frequency sweep cycles for the same frequency scale. The instantaneous spectral data for the instantaneous electrical signal at the same instantaneous moment within all frequency sweep cycles is then accumulated to obtain the cumulative spectral data for that frequency scale within the cumulative equivalent time window.

[0079] like Figure 1 As shown, by giving a synchronized trigger signal to the high-speed sampling oscilloscope and the swept-frequency light source to be measured, the accumulation of data points at the same time position in multiple swept-frequency cycles can be obtained, and the accumulation of data points in any cumulative equivalent long-time window can also be obtained.

[0080] like Figure 2 As shown, for t 11 , t 21 , t 31 ......t m1By accumulating these instantaneous moments, we can obtain the cumulative equivalent long time window t1; and so on, we can obtain n cumulative equivalent time windows. 11 , t 21 , t 31 ......t m1 The accumulation of these instantaneous data collected at instantaneous moments is the complete interference spectrum pattern information of the equivalent long time window t1.

[0081] Because in each sweep cycle, there are n frequency scales as the local oscillator frequency components that interfere with the light emitted by the swept source to be measured. Therefore, at different moments in the sweep cycle, n spectral information can be collected in parallel. Accordingly, the time position of these n sampling points needs to be determined by the sweep speed of the swept source to be measured. The higher the sweep speed of the swept source to be measured, the smaller the position interval of the required sampling time should be, that is, the smaller the frequency interval between the multi-carriers described in step S1, that is, f1, f2, f3...f n For each instant, limited by the sampling rate of the oscilloscope, only the local oscillator frequency f can be collected. i (i = 1, 2, 3, ... n) and certain points in the interference spectrum pattern produced by the swept light source under test at that moment. Therefore, it is necessary to accumulate all the data points collected by the oscilloscope over multiple sweep cycles. In other words, it is necessary to provide the oscilloscope with a trigger signal that is synchronized with the sweep cycle of the swept light source under test. This way, in the next sweep cycle, the oscilloscope will sample again at the same time position (i.e., the n sampling time positions in our first cycle).

[0082] Based on the sampling principles and characteristics of a sampling oscilloscope, the oscilloscope can collect another set of data points at the time-sliding position of the interference pattern during the next sweep cycle through time-sliding sampling. By accumulating instantaneous sampling points over multiple cycles, a complete interference pattern can be obtained for each of n fixed moments within the sweep cycle. The duration of the accumulated sampling points can be freely determined based on the magnitude of the measured linewidth. The oscilloscope then uses its own time-sliding sampling function to collect data points in the interference spectrum after the next set of sliding times. After accumulating sampling over multiple sweep cycles, the complete interference spectrum information for this instantaneous, cumulative equivalent long-term window can be obtained.

[0083] For example, taking a sampling oscilloscope with a sampling rate of 20Gsa / s and a time interval of about 50ps as an example, if two data points are sampled at the same instant in each sweep cycle, the time required is 100ps. 16Hz / s, then the frequency range swept by 100ps is 1MHz. Therefore, if the line width of the electrical filter is 1MHz, after accumulating samples for multiple sweep cycles, the oscilloscope can collect enough data required for the corresponding cumulative equivalent long time window. Then the sweep light width of the order of 500kHz can be measured. The sampling rate of the current most advanced real-time oscilloscope in the electrical domain is 256Gsa / s. Using the measurement method of this application, it can be measured at a light source sweep speed of 10 16 Hz / s, measure the instantaneous linewidth at 40kHz.

[0084] S4. The interference spectrum data within the accumulated equivalent long time window is processed and analyzed to obtain the instantaneous line width of the swept-frequency light source to be measured at any time.

[0085] The instantaneous linewidth of the swept-frequency light source to be measured can be obtained by Fourier transforming the accumulated spectral data within the cumulative equivalent time window. In other words, the complete interference spectrum information obtained by sampling any instantaneous cumulative equivalent time window can be Fourier transformed. Given that the linewidth of the multi-carrier light source is much smaller than the width of the swept-frequency light to be measured and that the linewidth data of the multi-carrier light source is known, the instantaneous linewidth of the source to be measured can be calculated.

[0086] For the interference spectrum data collected in step S3, without considering the influence of factors such as filter line width and oscilloscope sampling speed, according to the convolution theorem, the local oscillator light field is set to f Lo (t), the instantaneous frequency sweeping light field to be measured is g(t), then the spectrum information obtained for any instantaneous cumulative sampling point in step S3 is f Lo (t)*g(t), where * is the convolution operation.

[0087] According to the Fourier transform of the convolution function, we can get F[f Lo (t)*g(t)]=F(ω)·G(ω).

[0088] If the selected local oscillator light width is much smaller than the width of the light to be measured, the line width of the swept frequency light to be measured at this moment can be obtained using G(ω).

[0089] A system for measuring the instantaneous linewidth of a swept-frequency light source, such as Figure 3 Shown, including:

[0090] Scale prefabrication module: used to prefabricate frequency scale;

[0091] Instantaneous sampling module: couples the frequency sweep light source to be measured with the prefabricated frequency scale and performs instantaneous parallel sampling to obtain instantaneous sampling information;

[0092] Superposition and accumulation module: Based on the pre-made frequency scale, the instantaneous sampling information is superimposed and accumulated to obtain the interference spectrum data of the swept-frequency light source to be measured within the accumulation equivalent long time window;

[0093] Data processing module: Processing and analyzing the interference spectrum data within the accumulated equivalent long time window can obtain the instantaneous linewidth of the swept-frequency light source to be measured at any time.

[0094] Specifically, the ruler prefabricated module includes:

[0095] Based on the frequency of light emitted by a multi-carrier light source, several frequency scales of different frequency sizes are derived.

[0096] A light source that can output standard frequency multi-carrier is prefabricated as a ruler, which is the local oscillator light. This "ruler" is actually a multi-carrier light source, and each carrier frequency it outputs is a continuous wave with an extremely narrow line width (f1, f2, f3...f n ), the frequency intervals between the carriers are equal and adjustable, so as to be applicable to the measurement of the swept light to be measured with different sweep speeds.

[0097] That is, all frequency scales are the frequencies of the light emitted by the continuous wave light source output by the multi-carrier light source, and all frequency scales are set at equal intervals. Figure 2 The vertical axis is the frequency scale f i (i=1,2,3……n), there are n frequency components f, namely f1、f2、f3……f n Since the carrier frequency of each frequency scale output by the multi-carrier light source is a continuous wave with an extremely narrow line width, with f1 as the reference, between f1 and f2, between f2 and f3...f n-1 With f n The intervals between them are the same, which is conducive to calculating in a quantitative manner and accurately obtaining the instantaneous linewidth of the swept frequency source to be measured.

[0098] Furthermore, all frequency scales are based on the sweep speed and sweep range of the swept-frequency light source to be measured, and the initial value of the frequency scale is an adjustable value, that is, the initial frequency f1 of the carrier can also be flexibly selected according to the sweep band of the swept-frequency light to be measured, so as to be applicable to the measurement of the swept-frequency light to be measured with different sweep ranges. In this embodiment, the sweep speed of the swept-frequency light source to be measured is not higher than 10 16 Hz / s, and the narrowest measurable instantaneous linewidth is not less than 40kHz; that is, this method is applicable to the measurement of the instantaneous linewidth of swept-frequency light sources with different sweep speeds and different sweep ranges.

[0099] Instantaneous sampling module, including:

[0100] Based on the frequency scale, it is coupled with the swept light source to be measured to obtain the optical beat signal; the optical beat signal obtained by instantaneous sampling is then converted into an instantaneous electrical signal through a balanced detector; the converted instantaneous electrical signal is then sampled for interference spectrum data through a high-speed oscilloscope to obtain instantaneous interference spectrum data; at the same time, the interference spectrum information of all optical beat signals is instantaneously and parallelly collected in each sweep cycle to obtain several instantaneous sampling information of the optical beat signal at the same instant in all sweep cycles.

[0101] Specifically, because the swept-frequency light source to be measured is itself a periodic swept-frequency light source, within each sweep cycle, the frequency scale is instantaneously coupled in parallel with the swept-frequency light source to be measured, and the beat signals of the multi-carrier light source and the swept-frequency light source to be measured are detected by a photoelectric balanced detector to obtain n instantaneous parallel collected optical beat signals.

[0102] Among them, the light beat signal obtained by instantaneous sampling can be converted into an instantaneous electrical signal through a balanced detector; the instantaneous electrical signal is amplified and filtered in the electrical domain in turn, and then the DC component is removed; the converted instantaneous electrical signal is then sampled for interference spectrum data through a high-speed oscilloscope to obtain instantaneous interference spectrum data.

[0103] like Figure 2 As shown, in each sweep cycle, the n frequency components of the multi-carrier are equivalent to sampling the n instantaneous states of the swept light to be measured in the sweep cycle. Among them, the time period t of all sweep cycles is the same, that is, there are m sweep cycles t and each sweep cycle t has n instantaneous moments, which intersect with n frequency scales respectively. The corresponding instantaneous moment is marked as t mn , where m is the number of sweep cycles and n is the instantaneous moment in the sweep cycle. In the first sweep cycle, the interference is obtained at t 11 , t 12 , t 13 ......t 1n The beat frequency information of the multi-carrier frequency scale at the moment and the instantaneous frequency of the swept light to be measured; in the second sweep cycle, t 21 , t 22 , t 23 ......t 2n The beat frequency information of the multi-carrier frequency and the instantaneous frequency of the scanned light to be measured at the moment. Since the frequency scale of the multi-carrier light source is stable, the instantaneous time position corresponding to the same frequency is the same in each scan cycle, that is, the instantaneous time position corresponding to the same frequency scale is the same in each scan cycle. That is, relative to the frequency scale f1, the instantaneous time at which the beat frequency information with the scanned light to be measured is t in scan cycle 1. 11 , t in sweep cycle 2 21 , t in sweep cycle 3 31...t in the sweep period m m1 . Accordingly, t 11 , t 21 , t 31 ......t m1 The time position in each sweep cycle is the same, and parallel sampling of spectral information at different instantaneous moments in each sweep cycle of the swept light source to be measured is completed based on the f1 frequency scale.

[0104] Accordingly, instantaneous parallelism can obtain f n The instantaneous sampling information of the optical beat signal at several instantaneous time points within the m sweep cycles is the instantaneous sampling information of the multi-carrier light source and the swept light source to be measured at each instantaneous time t mn interference pattern information.

[0105] Superposition accumulation module, including:

[0106] When sampling spectral data, based on any frequency scale, the instantaneous electrical signal at the same instantaneous moment within all frequency sweep cycles is first accumulated, marking this as the cumulative equivalent long-term window for that instantaneous moment. In other words, the cumulative equivalent long-term window is the sum of the instantaneous moments within all frequency sweep cycles for the same frequency scale. The instantaneous spectral data for the instantaneous electrical signal at the same instantaneous moment within all frequency sweep cycles is then accumulated to obtain the cumulative spectral data for that frequency scale within the cumulative equivalent time window.

[0107] like Figure 1 As shown, by giving a synchronized trigger signal to the high-speed sampling oscilloscope and the swept-frequency light source to be measured, the accumulation of data points at the same time position in multiple swept-frequency cycles can be obtained, and the accumulation of data points in any cumulative equivalent long-time window can also be obtained.

[0108] like Figure 2 As shown, for t 11 , t 21 , t 31 ......t m1 By accumulating these instantaneous moments, we can obtain the cumulative equivalent long time window t1; and so on, we can obtain n cumulative equivalent time windows. 11 , t 21 , t 31 ......t m1 The accumulation of these instantaneous data collected at instantaneous moments is the complete interference spectrum pattern information of the equivalent long time window t1.

[0109] Because in each sweep cycle, there are n frequency scales as local oscillator frequency components that interfere with the light emitted by the swept source to be measured. Therefore, at different moments in the sweep cycle, n spectral information can be collected in parallel. Accordingly, the time position of these n sampling points needs to be determined by the sweep speed of the swept source to be measured. The higher the sweep speed of the swept source to be measured, the smaller the position interval of the required sampling time should be. In other words, the frequency interval between the multi-carriers described in the scale prefabrication module should be smaller, that is, f1, f2, f3...f n For each instant, limited by the sampling rate of the oscilloscope, only the local oscillator frequency f can be collected. i (i = 1, 2, 3, ... n) and certain points in the interference spectrum pattern produced by the swept light source under test at that moment. Therefore, it is necessary to accumulate all the data points collected by the oscilloscope over multiple sweep cycles. In other words, it is necessary to provide the oscilloscope with a trigger signal that is synchronized with the sweep cycle of the swept light source under test. This way, in the next sweep cycle, the oscilloscope will sample again at the same time position (i.e., the n sampling time positions in our first cycle).

[0110] Based on the sampling principles and characteristics of a sampling oscilloscope, the oscilloscope can collect another set of data points at the time-sliding position of the interference pattern during the next sweep cycle through time-sliding sampling. By accumulating instantaneous sampling points over multiple cycles, a complete interference pattern can be obtained for each of n fixed moments within the sweep cycle. The duration of the accumulated sampling points can be freely determined based on the magnitude of the measured linewidth. The oscilloscope then uses its own time-sliding sampling function to collect data points in the interference spectrum after the next set of sliding times. After accumulating sampling over multiple sweep cycles, the complete interference spectrum information for this instantaneous, cumulative equivalent long-term window can be obtained.

[0111] Data processing module, including:

[0112] The instantaneous linewidth of the swept-frequency light source to be measured can be obtained by Fourier transforming the accumulated spectral data within the cumulative equivalent time window. In other words, the complete interference spectrum information obtained by sampling any instantaneous cumulative equivalent time window can be Fourier transformed. Given that the linewidth of the multi-carrier light source is much smaller than the width of the swept-frequency light to be measured and that the linewidth data of the multi-carrier light source is known, the instantaneous linewidth of the source to be measured can be calculated.

[0113] For the interference spectrum data collected in the superposition accumulation module, without considering the influence of factors such as the filter line width and the oscilloscope sampling speed, according to the convolution theorem, the local oscillator light field is assumed to be f Lo(t), the instantaneous frequency sweeping light field to be measured is g(t), then the spectrum information obtained for any instantaneous accumulation point in the superposition accumulation module is f Lo (t)*g(t), where * is the convolution operation.

[0114] According to the Fourier transform of the convolution function, we can get F[f Lo (t)*g(t)]=F(ω)·G(ω).

[0115] If the selected local oscillator light width is much smaller than the width of the light to be measured, the line width of the swept frequency light to be measured at this moment can be obtained using G(ω).

[0116] The instantaneous linewidth measurement method of a narrow linewidth high-speed swept frequency light source designed in this application is based on a multi-carrier light source as a frequency scale, and the sweep speed is not higher than 10 16 The instantaneous linewidth of a swept-frequency light source with a linewidth of 40 kHz or higher is captured and measured. The measurement method has good reproducibility and accurate and stable measurement results. The present application also proposes a system for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source.

[0117] The above embodiments of the present application are described in detail. The contents described are only preferred embodiments of the present application and should not be considered to limit the scope of implementation of the present application. All equivalent changes and improvements made within the scope of the present application should still fall within the scope of the patent application.

Claims

1. A method for measuring the instantaneous linewidth of a narrow linewidth high-speed swept frequency light source, characterized in that the steps include: Prefabricated frequency scale; The frequency sweeping light source to be measured is coupled with a prefabricated frequency scale and instantaneous parallel sampling is performed to obtain instantaneous sampling information; Based on the prefabricated frequency scale, the instantaneous sampling information is superimposed and accumulated to obtain the interference spectrum data of the swept-frequency light source to be measured within the accumulation equivalent long time window; Process and analyze the interference spectrum data accumulated in the equivalent long time window to obtain the instantaneous linewidth of the swept-frequency light source to be measured at any time; The prefabricated frequency scale comprises: Acquire a multi-carrier light source; Taking the frequency of the light emitted by the multi-carrier light source as a reference, deriving a plurality of frequency scales of different frequency magnitudes; All of the frequency scales are the frequencies of light emitted by the continuous wave light source output by the multi-carrier light source, and all of the frequency scales are arranged at equal intervals; The method of coupling the frequency sweeping light source to be measured with the prefabricated frequency scale and performing instantaneous parallel sampling to obtain instantaneous sampling information includes: Based on the frequency scale, coupling it with the frequency sweeping light source to be measured to obtain an optical beat signal; The optical beat signal obtained by instantaneous sampling is converted into an instantaneous electrical signal through a balanced detector; The converted instantaneous electrical signal is then sampled by a high-speed oscilloscope to obtain instantaneous interference spectrum data; In each frequency sweep cycle, all optical beat signals are instantaneously and parallelly collected for interference spectrum information; Obtaining a plurality of instantaneous sampling information of the optical beat signal at the same instant in all frequency sweep cycles; The method of superimposing and accumulating instantaneous sampling information based on a prefabricated frequency scale to obtain interference spectrum data of the frequency-swept light source to be measured within an accumulation equivalent long time window includes: When sampling spectral data, based on any of the frequency scales, the instantaneous electrical signals are accumulated at the same instant in all frequency sweep cycles and marked as the accumulated equivalent long time window at the same instant; The instantaneous spectrum data of the instantaneous electrical signal at the same instantaneous moment in all frequency sweep cycles are accumulated to obtain the accumulated spectrum data in the accumulated equivalent long time window based on the frequency scale.

2. The method for measuring the instantaneous linewidth of a narrow-linewidth, high-speed swept-frequency light source according to claim 1, characterized in that: The frequency scale is determined based on the sweep speed and sweep range of the swept-frequency light source to be measured, and the initial value of the frequency scale is an adjustable value.

3. The method for measuring the instantaneous linewidth of a narrow-linewidth high-speed swept-frequency light source according to claim 1, characterized in that: The time period of all sweep cycles is the same; The instantaneous time position corresponding to the same frequency scale in each frequency sweep cycle is the same.

4. The method for measuring the instantaneous linewidth of a narrow linewidth high-speed swept light source according to claim 1, characterized in that: Before sampling the spectral data, the method also includes the steps of amplifying and filtering the instantaneous electrical signal in the electrical domain and removing the DC component.

5. A method for measuring the instantaneous linewidth of a narrow-linewidth high-speed swept-frequency light source according to any one of claims 1 to 4, characterized in that: The processing and analysis of the interference spectrum data within the accumulated equivalent long time window to obtain the instantaneous linewidth of the swept-frequency light source to be measured at any time includes: By performing Fourier transform on the accumulated spectral data within the accumulated equivalent long time window, the instantaneous line width of the swept-frequency light source to be measured can be obtained.

6. A system for measuring the instantaneous linewidth of a swept-frequency light source, characterized in that: include: Scale prefabrication module: used to prefabricate frequency scale; Instantaneous sampling module: couples the frequency sweep light source to be measured with the prefabricated frequency scale and performs instantaneous parallel sampling to obtain instantaneous sampling information; Superposition and accumulation module: Based on the pre-made frequency scale, the instantaneous sampling information is superimposed and accumulated to obtain the interference spectrum data of the swept-frequency light source to be measured within the accumulation equivalent long time window; Data processing module: processes and analyzes the interference spectrum data accumulated within the equivalent long time window to obtain the instantaneous linewidth of the swept-frequency light source to be measured at any time; The ruler prefabricated module includes: Acquire a multi-carrier light source; Taking the frequency of the light emitted by the multi-carrier light source as a reference, deriving a plurality of frequency scales of different frequency magnitudes; Wherein, all the frequency scales are the frequencies of the light emitted by the continuous wave light source output by the multi-carrier light source, and all the frequency scales are arranged at equal intervals; The instantaneous sampling module includes: Based on the frequency scale, coupling it with the frequency sweeping light source to be measured to obtain an optical beat signal; The optical beat signal obtained by instantaneous sampling is converted into an instantaneous electrical signal through a balanced detector; The converted instantaneous electrical signal is then sampled by a high-speed oscilloscope to obtain instantaneous interference spectrum data; In each frequency sweep cycle, all optical beat signals are instantaneously and parallelly collected for interference spectrum information; Obtaining a plurality of instantaneous sampling information of the optical beat signal at the same instant in all frequency sweep cycles; The superposition accumulation module includes: When sampling spectral data, based on any of the frequency scales, the instantaneous electrical signals are accumulated at the same instant in all frequency sweep cycles and marked as the accumulated equivalent long time window at the same instant; The instantaneous spectrum data of the instantaneous electrical signal at the same instantaneous moment in all frequency sweep cycles are accumulated to obtain the accumulated spectrum data in the accumulated equivalent long time window based on the frequency scale.

7. The system for measuring the instantaneous linewidth of a swept-frequency light source according to claim 6, characterized in that: The data processing module includes: By performing Fourier transform on the accumulated spectral data within the accumulated equivalent long time window, the instantaneous line width of the swept-frequency light source to be measured can be obtained.

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