Time-domain optical wave electric field measurement system and method based on vectorial two-pulse supercontinuum

Abstract

The patent relates to a kind of time-domain optical wave electric field measurement techniques based on vector double-pulse supercontinuum, belongs to the field of optoelectronic technology.The technology includes vector double-pulse laser configuration, nonlinear optical medium, optical signal processing unit, photoelectric conversion processing unit and other components.Pulse laser to be measured is first converted into vector double-pulse laser in the system, and is injected into nonlinear optical medium, and then obtains the optical wave electric field information of the laser to be measured after optical signal processing and photoelectric conversion processing.This technology has positive contribution to the characterization of time-domain ultrashort pulse laser.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology. Background Technology

[0002] Current research on ultrashort femtosecond laser pulses mainly focuses on the measurement and characterization of their spectra, lacking technical means for measuring their time-domain characteristics, particularly the inability to directly observe the time-domain electric field of ultrashort pulses. Currently, the primary method for characterizing time-domain characteristics is the pulse's autocorrelation measurement, which can be used to determine the pulse's temporal width and temporal intensity distribution, but cannot generate information on the electric field amplitude. Therefore, there is an urgent need to develop new techniques for measuring the electric field of time-domain optical waves and achieving real-time measurement results. Summary of the Invention

[0003] To address the current lack of technical means for measuring time-domain characteristics and the inability to directly observe the time-domain electric field of ultrashort pulses, a time-domain optical electric field measurement technique based on vector double pulse supercontinuum is proposed.

[0004] The technical solution of the present invention:

[0005] A time-domain optical electric field measurement system based on vector double-pulse supercontinuum includes a pulsed laser source to be measured, a vector double-pulse laser constitutive unit, a nonlinear optical medium, and an optical signal processing unit, wherein the optical signal processing unit is connected to a photoelectric conversion processing unit.

[0006] The pulsed laser source to be measured is split into two beams in a vector double-pulse laser unit: a reference beam and a beam to be measured. The polarization directions of the two beams are independently adjustable, and their relative delay periods are also adjustable. They are combined optically to form a spatially overlapping vector double-pulse laser. The reference beam can undergo power pre-amplification, and the laser pulse length can be controlled in conjunction with dispersion management components. The polarization directions of the two beams are independently adjustable, and their relative delay periods are also adjustable. They are combined optically to form a spatially overlapping vector double-pulse laser.

[0007] Nonlinear optical media exhibit third-order Kerr nonlinearity. The media structure is a bulk material or a waveguide structure. Light propagates in the media in one direction or along the direction of the waveguide extension.

[0008] The optical signal processing unit includes an optical analyzer and an optical filter, which are used to select the output laser in any polarization direction and filter out a specific band of the spectrum for photoelectric signal processing.

[0009] The photoelectric conversion processing unit includes a photodetector, a time-domain waveform acquisition unit, and a digital signal processing unit. It is used to convert optical signals in a selected polarization direction and a selected band into a set of time-domain electrical signals, and then convert them into time-domain optical wave electric field signals through digital signal processing.

[0010] A time-domain optical electric field measurement method based on vector double-pulse supercontinuum includes:

[0011] (1) Adjust the optical polarization state of the two beams in the vector double-pulse laser to a linear polarization state, and make the polarization directions orthogonal to each other; apply a periodic optical delay to the reference beam path.

[0012] (2) Align the propagation axis of the nonlinear optical medium with the spatially coincident, mutually orthogonal polarization directions and periodic relative delay of the vector double pulse laser constructed in step (1), and optimize the coupling process to achieve the best coupling efficiency.

[0013] In step C, the reference light can form a supercontinuum spectrum with a large wavelength span through the silicon nitride photonic waveguide, and the overall flatness of the spectrum is high; the spectral envelope of the light under test remains unchanged after passing through the waveguide; the polarization directions of the reference light and the light under test remain unchanged after passing through the nonlinear medium.

[0014] In step D, an optical analyzer is used to select the polarization direction corresponding to the reference light source, thus filtering out the supercontinuum spectrum caused by the reference light in the polarization direction. Then, an optical filter is used to select a supercontinuum spectrum within a specific band, which is a band where the supercontinuum spectrum and the spectrum of the light to be measured do not coincide. The supercontinuum spectrum within this band is converted into a set of time-correlated electrical signals by a photodetector. Its time axis corresponds to the optical delay of one period between the reference light and the light to be measured. The DC and low-frequency components of this time signal are filtered out by a digital signal processing unit, and the high-frequency components are retained, thus obtaining the time-domain optical electric field signal.

[0015] The beneficial effects of this invention are:

[0016] This invention provides a technique for measuring the electric field of ultrashort pulsed lasers in the time domain. It utilizes optical delay interferometry and the third-order nonlinear Kerr effect to modulate the electric field information of the light wave into a supercontinuum spectrum. Therefore, through appropriate optical signal processing, photoelectric detection, and signal demodulation, the electric field information of the laser under test can be rapidly and in real-time retrieved. In contrast to current autocorrelation pulse measurement methods, which can only obtain the time-domain envelope information of the pulse, this invention can obtain the time-domain electric field amplitude information of the light wave, making a significant contribution to the characterization of the fundamental properties of pulsed lasers. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the implementation principle of a time-domain optical electric field measurement technique based on vector double pulse supercontinuum according to the present invention. 1: Beam splitter; 2: Preamplifier; 3: Dispersion compensation unit; 4: Periodic optical variable delay unit; 5: Beam combiner; 6: Nonlinear optical medium; 7: Optical signal processing unit; 8: Photoelectric conversion processing unit.

[0018] Figure 2 The two mutually orthogonal polarization directions (x, y) of the vector dual-pulse laser shown in this invention are aligned with the birefringence axis of the nonlinear optical waveguide.

[0019] Figure 3 The present invention shows the spectra obtained in two polarization directions after the vector double-pulse laser passes through a nonlinear optical waveguide, and the supercontinuum spectrum of visible light <700nm band filtered by an optical filter.

[0020] Figure 4 The photoelectric signal processing procedure shown in this invention is as follows: (a) the spectrum filtered by the optical analyzer and optical filter is passed through the photodetector to obtain a set of time-related electrical signals, the time axis of which corresponds to the relative delay between the reference light source pulse and the light source pulse under test; (b) the spectrum of the electrical signal in (a) is obtained by Fourier transform, wherein DC / low-frequency components and high-frequency components can be distinguished; (c) the time-domain electric field information of the light source under test is obtained after filtering out the DC / low-frequency components of the electrical signal in (a).

[0021] Figure 5 This invention illustrates the change in electric field of light of different powers after passing through a nonlinear optical waveguide. Detailed Implementation

[0022] Example:

[0023] In this embodiment, the time-domain optical electric field measurement technology based on vector double-pulse supercontinuum includes components such as the pulsed laser source to be measured, a vector double-pulse laser constituting unit, a nonlinear optical medium, an optical signal processing unit, and a photoelectric conversion processing unit. Figure 1 ).

[0024] The pulsed laser source to be measured is a pulsed laser with a center wavelength around 1560 nm, a pulse width of 70 fs, a repetition rate of 100 MHz, and a linear polarization state. In this embodiment, the vector dual-pulse laser constituting unit performs beam splitting, delay, and beam combining operations on the source to be measured. Figure 1 This forms a spatially overlapping vector double-pulse laser.

[0025] The reference optical path can obtain a higher power level after power pre-amplification, while the optical path under test obtains a lower power level. The optical polarization states of both lasers are adjusted to linear polarization states by optical waveplates, and the polarization directions are adjusted to be mutually orthogonal.

[0026] In this embodiment, the nonlinear optical medium exhibiting third-order Kerr nonlinearity uses a silicon nitride photonic waveguide chip. One optical waveguide on the chip has a cross-sectional dimension of 1400 nm wide and 900 nm high. Along the height and width directions of the waveguide, a set of orthogonal birefringence axes are formed on the cross-section. The waveguide length is 5 mm.

[0027] When a vector dual-pulse laser is injected into a silicon nitride photonic waveguide, the reference light can form a supercontinuum spectrum with a large wavelength span after passing through the waveguide. The light under test can maintain its initial spectral envelope after passing through the nonlinear medium, and its spectral span is smaller than that of the supercontinuum spectrum formed by the reference light.

[0028] The optical signal output from the waveguide undergoes optical and electrical processing. The optical signal processing unit includes optical components such as an optical analyzer and an optical filter. The optical analyzer is used to select the output laser in the polarization direction of the reference light, i.e., to select the supercontinuum spectrum, and the optical filter further filters out the spectrum within a specific wavelength band for photoelectric signal processing.

[0029] The photoelectric signal processing unit includes components such as a photodetector, a time-domain waveform acquisition unit, and a digital signal processing unit. It is used to convert the supercontinuum spectral signal in the above-mentioned band into a set of time-domain electrical signals, and then convert it into a time-domain optical electric field signal through digital signal processing.

[0030] The specific working steps of the above-mentioned time-domain optical electric field measurement technique are as follows:

[0031] (1) Input the light source to be tested and construct a vector double-pulse laser. Adjust the power of the reference light to 57mW and the pulse length to approximately 70fs; adjust the power of the light to be tested to 10mW. The reference light undergoes a periodic optical delay with a maximum delay of 50ps and a period of 1s, and the delay varies sinusoidally within the period. Then, it is combined with the light to be tested through an optical polarization combiner. This forms a vector double-pulse laser beam that is spatially coincident, temporally periodically delayed, and orthogonally polarized.

[0032] (2) Vector dual-pulse laser coupling injection into silicon nitride photonic waveguide. The polarization direction of the reference light is aligned with the width direction of the waveguide cross-section, and the polarization direction of the light to be measured is aligned with the height direction of the waveguide cross-section. Figure 2 By optimizing the coupling process, an input-output coupling efficiency of >30% for the reference light and >15% for the light under test can be achieved.

[0033] (3) Observe the supercontinuum dynamics of vector double-pulse laser in a nonlinear medium. Figure 3The reference light, passing through a silicon nitride photonic waveguide, can form a supercontinuum spectrum with a large wavelength span and high overall spectral flatness; the spectral envelope of the light under test remains unchanged after passing through the waveguide. The polarization directions of both the reference light and the light under test remain unchanged after passing through the nonlinear medium.

[0034] (4) Optical and electrical processing is performed on the optical signal output from the nonlinear medium. An optical analyzer is used to select the polarization direction corresponding to the reference light source, thus selecting the supercontinuum spectrum induced by the reference light. Next, an optical filter is used to filter out the supercontinuum spectrum within the visible light <700nm band. This band is the non-overlapping band between the supercontinuum spectrum and the spectrum of the light being measured. Figure 3 The filtered optical signal (approximately 2mW) is converted into a set of time-correlated electrical signals by a photodetector, with its time axis corresponding to the optical delay between the reference light and the light under test. A digital signal processing unit filters out the DC and low-frequency components of this time signal, retaining only the high-frequency components. The time-correlated signal corresponding to the high-frequency components reflects the time-domain electric field information of the light source under test. Figure 4 ).

[0035] (5) Appropriately increase the power of the light under test in the vector double pulse laser, that is, adjust it to 10mW, 30mW, 50mW, 70mW and 90mW respectively. After increasing the power, the light under test will also obtain a certain degree of spectral broadening after passing through the silicon nitride photonic waveguide. However, the spectral span is always smaller than the supercontinuum span caused by the reference light, and the visible light filtering band in (3) is always the non-overlapping band of the supercontinuum spectrum and the spectrum of the light under test. Therefore, there is no need to adjust the optical and electrical processing of the output light signal. The change of the time-domain electric field of the light source under test after spectral broadening can be observed. Figure 5 The power adjustment process described above can be performed in real time, as can the measurement and acquisition of changing electric fields.

[0036] For the purposes of illustration and description, the present invention has provided the above-described specific embodiments. For those skilled in the art, any improvements and modifications made based on the above description without departing from the basic structure of the present invention will be considered within the scope of protection of the present invention. The embodiments were chosen and described to explain the principles of the invention and as potential practical applications of the invention, enabling those skilled in the art to use the invention in various embodiments and make various modifications for specific purposes.

Claims

1. A time-domain optical electric field measurement system based on vector double-pulse supercontinuum, characterized in that: The system comprises a vector dual-pulse laser constitutive unit, a nonlinear optical medium, and an optical signal processing unit. The optical signal processing unit and the photoelectric conversion processing unit input the pulsed laser source to be measured. The photoelectric conversion processing unit outputs the time-domain optical electric field information of the laser. The pulsed laser source to be measured is split into two beams in the vector dual-pulse laser constitutive unit: a reference beam and a beam to be measured. The reference beam, after passing through the nonlinear optical medium, forms a supercontinuum spectrum with a large wavelength span and high overall spectral flatness. The spectral envelope of the beam to be measured remains unchanged after passing through the waveguide. After passing through the nonlinear medium, the reference beam and the beam to be measured exhibit different spectral characteristics. The polarization direction of the light source remains unchanged. An optical analyzer is used to select the polarization direction corresponding to the reference light source, thus filtering out the supercontinuum spectrum caused by the reference light in the polarization direction. Then, an optical filter is used to select the supercontinuum spectrum in a specific band, which is a band where the supercontinuum spectrum and the spectrum of the light to be measured do not coincide. The supercontinuum spectrum in this band is converted into a set of time-correlated electrical signals by a photodetector. Its time axis corresponds to the optical delay of one period between the reference light and the light to be measured. The DC and low-frequency components of this time signal are filtered out by a digital signal processing unit, and the high-frequency components are retained, thus obtaining the time-domain optical electric field signal.

2. The time-domain optical electric field measurement system based on vector double-pulse supercontinuum according to claim 1, characterized in that: The reference light is pre-amplified in power and the laser pulse length is controlled by dispersion management components. The polarization directions of the two beams are independently adjustable, the relative delay period is adjustable, and they are combined by optical beam combining to form a spatially overlapping vector double-pulse laser.

3. The time-domain optical electric field measurement system based on vector double-pulse supercontinuum according to claim 2, characterized in that: Nonlinear optical media exhibit third-order Kerr nonlinearity. The media structure is a bulk material or a waveguide structure. Light propagates in the media in one direction or along the direction of the waveguide extension.

4. The time-domain optical electric field measurement system based on vector double-pulse supercontinuum according to claim 3, characterized in that: The optical signal processing unit includes an optical analyzer and an optical filter, used to select the output laser in any polarization direction and filter out a specific band of the laser spectrum for photoelectric signal processing. The photoelectric conversion processing unit includes a photodetector, a time-domain waveform acquisition unit and a digital signal processing unit, used to convert the optical signal in the selected polarization direction and selected band into a set of time-domain electrical signals, and then convert it into a time-domain optical wave electric field signal through digital signal processing.

5. A method for measuring the time-domain optical electric field based on vector double-pulse supercontinuum, used in the time-domain optical electric field measurement system based on vector double-pulse supercontinuum as described in any one of claims 1-4, characterized in that... The process includes the following steps: A. Connecting the pulsed laser source to be measured into the system to construct a vector dual-pulse laser; B. Injecting the vector dual-pulse laser into a nonlinear optical medium; C. Observe the supercontinuum dynamics of vector double-pulse laser in a nonlinear medium; D. Perform optical and electrical processing on the optical signals output by the nonlinear medium.

6. The time-domain optical electric field measurement method based on vector double-pulse supercontinuum according to claim 5, characterized in that: In step A, the optical polarization states of the two beams in the vector double-pulse laser are adjusted to linear polarization states, and the polarization directions are orthogonal to each other. A periodic optical delay is applied to the reference optical path to form a vector double-pulse laser that is spatially coincident, has orthogonal polarization directions, and has a periodic relative delay.

7. The time-domain optical electric field measurement method based on vector double-pulse supercontinuum according to claim 5, characterized in that: In step B, the vector double-pulse laser constructed in step A is aligned with the propagation axis of the nonlinear optical medium, and the coupling process is optimized to achieve the best coupling efficiency.

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