Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
Referring to fig. 1, fig. 1 is a schematic structural diagram of an ultrafast optical wavelength measurement system according to an embodiment of the present invention, the system includes a narrow-linewidth laser 1, first to fifth optical couplers 13-17, a mode-locked laser 2, first to fifth photodetectors 3-7, a first analog-to-digital conversion module 8, a second analog-to-digital conversion module 9, a digital signal processing module 10, and a dispersion compensation fiber 11, wherein an output optical signal of the mode-locked laser 2 is divided into three paths by the third optical coupler 15 after passing through the dispersion compensation fiber 11, and a reference optical signal and an optical signal 12 to be measured output by the narrow-linewidth laser 1 are divided into two paths by the first optical coupler 13 and the fifth optical coupler 17, respectively. One of the paths of the mode-locked laser 2, the narrow linewidth laser 1 and the measuring optical signal 12 is detected by a third photoelectric detector 5, a first photoelectric detector 3 and a fifth photoelectric detector 7 respectively to output incoherent signals. The remaining two optical signals of the mode-locked laser 2 are coupled to the second photodetector 4 and the fourth photodetector 6 respectively with the reference optical signal and the measurement optical signal. The output signal of the third photodetector 5 is divided into two paths by the electric coupler 18, one path is coupled with the output signals of the first photodetector 3 and the second photodetector 4 to the first analog-to-digital conversion module 8 to output a digital signal; the other path of the output signals of the fourth photoelectric detector 6 and the fifth photoelectric detector 7 are coupled to a second analog-to-digital conversion module 9 to output digital signals. The output digital signals of the first analog-to-digital conversion module 8 and the second analog-to-digital conversion module 9 are coupled to the digital signal processing module 10 to output the final measurement result.
Referring to fig. 1 again, the narrow-linewidth laser 1 outputs a narrow-linewidth single-wavelength laser as a reference light, the narrow-linewidth single-wavelength laser enters the first optical coupler 13 from an input end of the first optical coupler 13, the narrow-linewidth single-wavelength laser is divided into two paths in the first optical coupler 13, wherein the first path of narrow-linewidth single-wavelength laser enters the first photodetector 3 and is converted into a photocurrent, and the photocurrent is output to the first analog-to-digital converter 8, and the second path of narrow-linewidth single-wavelength laser enters the second optical coupler 14.
The mode-locked laser 2 outputs periodic pulse laser, the periodic pulse laser enters the dispersion compensation fiber 11 from the input end of the dispersion compensation fiber 11, is subjected to dispersion stretching in the dispersion compensation fiber 11 to realize wavelength-time mapping, and then enters the third optical coupler 15 from the input end of the third optical coupler 15; in the third optical coupler 15, the dispersion-stretched periodic pulse laser light is divided into three paths, in which:
the first path of pulse laser enters the second optical coupler 14 from the first output port 151 of the third optical coupler 15, the first path of pulse laser and the second path of narrow linewidth single-wavelength laser output by the first optical coupler 13 are coupled and superposed in the second optical coupler 14 to form reference coherent superposed light, and the reference coherent superposed light enters the second photoelectric detector 4, is converted into photocurrent by the second photoelectric detector 4, and is output to the first analog-to-digital conversion module 8.
The second path of pulsed laser enters the third photodetector 5 from the second output port 152 of the third optical coupler 15, and is converted into photocurrent by the third photodetector 5 and output to the electrical coupler 18.
The third path of pulsed laser light enters the fourth optical coupler 16 from the third output port 153 of the third optical coupler 15.
The input end of the fifth optical coupler 17 is a test end, the laser 12 to be tested is coupled into the fifth optical coupler 17 from the input end of the fifth optical coupler 17, and is divided into two paths by the fifth optical coupler 17, wherein the first path of laser to be tested enters the fourth optical coupler 16, and the second path of laser to be tested enters the fifth photoelectric detector 7.
In the fourth optical coupler 16, the third path of pulse laser and the first path of laser to be measured are coupled and superposed to form measurement coherent superposition light, and the measurement coherent superposition light enters the fourth photoelectric detector 6, is converted into photocurrent by the fourth photoelectric detector 6, and is output to the second analog-to-digital conversion module 9.
After entering the fifth photodetector 7, the second path of laser light to be detected is converted into photocurrent by the fifth photodetector 7 and output to the second analog-to-digital conversion module 9.
In the electric coupler 18, the photocurrent output by the third photodetector 5 is divided into two paths, wherein the first path of photocurrent enters the first analog-to-digital conversion module 8 through the third input port 83 of the first analog-to-digital conversion module 8, and the second path of photocurrent enters the second analog-to-digital conversion module 9 through the first input port 91 of the second analog-to-digital conversion module 9.
The first photoelectric detector 3 converts a photoelectric current converted by a first narrow-line-width single-wavelength laser into a first analog-to-digital conversion module 8 through a first input port 81 of the first analog-to-digital conversion module 8, the second photoelectric detector 4 converts a photoelectric current converted by a reference coherent superposition light into a first analog-to-digital conversion module 8 through a second input port 82 of the first analog-to-digital conversion module 8, the electric coupler 18 converts the first photoelectric current into the first analog-to-digital conversion module 8 through a third input port 83 of the first analog-to-digital conversion module 8, and in the first analog-to-digital conversion module 8, three photoelectric currents are sampled and stored as digital signals and output to the digital signal processing module 10.
The electric coupler 18 makes the second path of photoelectric current enter the second analog-to-digital conversion module 9 through the first input port 91 of the second analog-to-digital conversion module 9, the fourth photoelectric detector 6 makes the photoelectric current converted by the measurement coherent superposition light enter the second analog-to-digital conversion module 9 through the second input port 92 of the second analog-to-digital conversion module 9, the fifth photoelectric detector 7 makes the photoelectric current converted by the second path of laser light to be detected enter the second analog-to-digital conversion module 9 through the third input port 93 of the second analog-to-digital conversion module 9, and in the second analog-to-digital conversion module 9, the three paths of photoelectric current are sampled and stored as digital signals and output to the digital signal processing module 10.
In the digital signal processing module 10, the digital signal input from the first analog-to-digital conversion module 8 is subjected to digital signal processing to obtain the coherent information of the reference coherent superimposed light in the second optical coupler 14; the digital signal input from the second analog-to-digital conversion module 9 is subjected to digital signal processing to obtain the coherent information of the coherent superimposed light measured in the fourth optical coupler 16; subsequently, the digital signal processing module 10 further performs digital signal processing on the coherent information of the reference coherent superimposed light and the coherent information of the measurement coherent superimposed light to obtain a final measurement result, so as to further improve the accuracy of the measurement system.
In the embodiment of the present invention, the ultrafast wavelength measurement system needs to be implemented to satisfy the following three conditions: 1) the sampling rate of the analog-to-digital conversion module to the electric signal output by the photoelectric detector should meet the sampling theorem, namely more than twice of the bandwidth of the photoelectric detector; 2) the relative time delay between the reference optical path and the measurement optical path should be as small as possible; 3) the wavelength of the output optical signal of the narrow-linewidth single-wavelength laser 1 is within the output spectral range of the mode-locked laser 2.
When the reference signal is a stable wavelength optical signal, the extracted coherent optical signal is a periodic chirp signal, the bandwidth is the bandwidth of the photodetector, the chirp frequency is the derivative of the dispersion coefficient of the dispersion compensation fiber, and the period is the period of the mode-locked laser. The measuring signal is also a frequency-modulated signal with a bandwidth of the photodetector, and the time position of its coherent signal in each mode-locked laser period varies with the wavelength of the measuring optical signal. And the reference coherent signal and the measurement coherent signal of each mode-locked laser period are compressed into a pulse signal after cross-correlation processing, and the wavelength of the measurement optical signal corresponding to the period moment of the mode-locked laser can be obtained by wavelength-time mapping of the pulse signal at the time position of each mode-locked laser period.
Fig. 2 is a measurement result of 10 single-wavelength optical signals to be measured using a spectrometer as a comparative example. In this comparative example, the spectrometer used was a commercial spectrometer (ADVANTEST Q8384), and the results were compared with those of the inventive example. The light wavelength measurement results of the 10 single-wavelength light signals are 1540.05nm, 1540.995nm, 1542nm, 1542.99nm, 1543.995nm, 1545nm, 1549.99nm, 1546.995nm, 1548nm and 1549.005nm respectively.
Fig. 3 is a measurement result of the 10 single-wavelength optical signals to be measured shown in fig. 2 according to the embodiment of the present invention, and the measurement results of the 10 single-wavelength optical signals to be measured shown in fig. 2 are 1540.007nm, 1540.999nm, 1541.991nm, 1542.985nm, 1543.975nm, 1545nm, 1545.99nm, 1546.994nm, and 1548.016nm, respectively, by using the ultrafast optical wavelength measurement system provided in the embodiment of the present invention.
As can be seen from a comparison between fig. 2 and fig. 3, the average error between the measurement result obtained by using the ultrafast optical wavelength measurement system according to the embodiment of the present invention and the measurement result obtained by using the spectrometer according to the comparative example is 0.013nm, and thus it can be seen that the ultrafast optical wavelength measurement system according to the embodiment of the present invention has a high accuracy in measuring the ultrafast optical wavelength.
FIG. 4 is a time-frequency diagram of a microwave signal. The microwave signal is used as a driving signal of the MZI modulator, and the aim is to generate a single-wavelength laser signal with the wavelength rapidly changing along with time by means of the MZI modulation. The specific method is to perform MZI modulation on a single-wavelength optical signal with a wavelength of 1550nm, and keep a positive first-order sideband through an optical filter, wherein the MZI modulation signal is a microwave signal with a time-frequency relationship shown in FIG. 4. Thus, a continuous laser signal with a theoretical wavelength ranging from 1550.047nm to 1550.091nm and a period of 8 microseconds is generated.
Fig. 5 is a wavelength measurement of an optical signal according to the present invention that remains positive first-order sideband modulated by the microwave signal MZI shown in fig. 4. The measurement result shows that the measurement light changes from 1550.056 nm to 1550.096nm, the change period is 8.06 microns, and the change period accords with a theoretical wavelength value, and the result verifies that the ultrafast optical wavelength measurement system provided by the invention has high-speed characteristics when measuring ultrafast optical wavelength.
FIG. 6 is a measurement of the output optical signal of a fast swept laser with a sweep rate of 0.0866nm/s, in accordance with embodiments of the present invention. Where circles are experimental data and dotted lines are fitted curves. The experimental result shows that the measuring light changes from 1540.87nm to 1548.62nm within 89.5ns time range, the change rate is 0.092nm/ns, and the change rate is consistent with the parameters of the rapid frequency sweeping laser source. The experimental result verifies the high-speed characteristic (about 20ns is measured once) and the large-bandwidth (about 10nm) characteristic of the ultrafast optical wavelength measuring system provided by the invention when the ultrafast optical wavelength is measured.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.