CN111579072A

CN111579072A - Mid-infrared band ultrashort pulse spectrum detection device

Info

Publication number: CN111579072A
Application number: CN202010473007.0A
Authority: CN
Inventors: 周伟; 曹雪; 王敬如; 鲜安华; 王昊天; 沈德元; 唐定远; 陈祥; 朱强; 邓磊; 李雷; 李仙尼; 李亦非; 丁瑾蓉
Original assignee: Jiangsu Normal University
Current assignee: Chengdu Liyuan Optoelectronic Technology Co ltd
Priority date: 2020-05-29
Filing date: 2020-05-29
Publication date: 2020-08-25
Anticipated expiration: 2040-05-29
Also published as: CN111579072B

Abstract

The invention discloses a mid-infrared band ultrashort pulse spectrum detection device, which is characterized in that an optical signal receiving module, a signal intensity self-adapting module, a dispersion management module and a signal detection module are arranged on the same collimated light path and are sequentially arranged, and a feedback loop is formed by the optical signal receiving module, the signal intensity self-adapting module, the dispersion management module and the signal detection module and a control feedback module; input light generated by an input signal light source passes through an optical signal receiving module, is coupled into a dispersion management module through an input collimator and is coupled into a control feedback module through one path of split output light of a beam splitter I, so that independent control of dispersion intensity and nonlinear intensity can be realized, wherein the dispersion management module realizes linear conversion from an optical signal frequency domain to a time domain by using a dispersion Fourier transform technology guided by large group velocity dispersion and low nonlinear characteristics of micro-nano optical fibers, finally measurement of transient characteristics of ultrashort pulse subpicosecond magnitude can be obtained, and time domain and frequency domain information of the ultrashort pulse subpicosecond magnitude can be accurately obtained.

Description

Mid-infrared band ultrashort pulse spectrum detection device

Technical Field

The invention relates to the technical field of optics, in particular to a mid-infrared band ultrashort pulse spectrum detection device.

Background

The femtosecond pulse laser acts with a medium, and has the unique characteristics of small acting area, small thermal effect, space selectivity and the like different from a long pulse laser due to large energy, high peak power and high beam quality, so that the femtosecond pulse laser is widely applied to the aspects of hyperfine processing, micro-photonic device manufacturing, medical fine surgery, nano-bioengineering and the like. The femtosecond pulse laser is mainly generated by a mode locking technology, and laser pulses can be compressed to picoseconds or even femtosecond magnitude by applying the technologies such as an active mode locking technology, a passive mode locking technology, an additive pulse mode locking technology and the like.

Due to the special waveguide structure of the optical fiber, high laser gain and high beam quality are provided, and simultaneously, inevitable nonlinear effects (self-phase modulation, cross-phase modulation, stimulated raman scattering and the like) are accompanied, and the strong nonlinear effects seriously increase the time domain and frequency domain noise of the ultrafast laser pulse, and also cause nonlinear phase distortion of the pulse to cause pulse splitting. Pulse splitting directly reduces the pulse peak power, and pulse time domain jitter appears, similar to electronic pulse distortion. If the method is applied to a 'magic light' system, the 'miss-target' can be caused, and when the method is applied to the field of speed measurement, false triggering is easy to occur, so that the measurement is inaccurate. In addition, the laser seed source is often required to be amplified in practical application, a linear amplification area is difficult to determine due to the lack of a real-time and accurate ultrafast diagnosis device, and pulses are split after amplification, so that the amplification work is worthless.

In the field of time domain direct detection, the current main mode is a high-speed oscilloscope with several GHz-level real-time bandwidth, but the oscilloscope with high time resolution and high bandwidth is expensive, particularly in the aspect of picosecond pulse detection, the required performance almost reaches the bandwidth limit, and whether the detected pulse is a single pulse or a pulse cluster is difficult to discriminate, so that the high sampling rate and high-precision quantization are difficult to realize simultaneously. The sampling rate and the analog bandwidth of the conventional high-speed real-time oscilloscope are still at the level of hundreds of GS/s and tens of GHz, so that the application requirement of picosecond-order high-speed signals cannot be met. In a high-rate frequency band, the analog bandwidth (sampling rate) and the quantization precision have a constraint relation, so that a spectrum analyzer is also needed to perform frequency domain measurement, the sensitivity and the response speed of the spectrum analyzer are mutually constrained, only an average value of a certain integration time is taken as a measurement result, and the pulse state change cannot be accurately tracked and revealed in real time. For more accurate single pulse judgment, indirect detection is realized mainly through nonlinear processes such as frequency doubling or two-photon absorption and the like by means of an autocorrelation tester through interferometric scanning, although ultrashort pulse detection can be realized, frequency doubling crystals (typically BBO and the like) used are easy to deliquesce, and the autocorrelation tester is complicated in manufacturing, using and maintaining processes and poor in operation repeatability. More importantly, the scanning time of the autocorrelator is in the order of seconds, but the change process of the ultrafast laser is in the order of (sub) picoseconds, and the scanning speed of the ultrafast laser is far as the change time of the ultrafast laser pulse, so that the real-time detection requirement is difficult to meet. Therefore, how to realize the high-resolution real-time measurement of the ultrashort pulse time-frequency domain information and improve the accuracy and reliability of the measurement result so as to meet the requirements of ultrafast process measurement and analysis becomes a hot spot and difficult point problem to be solved urgently in the ultrafast optics and application field.

The Dispersion Fourier Transform (DFT) is an emerging measurement technology, overcomes the limitation of slow test speed of the traditional optical instrument, and realizes the ultrashort pulse real-time measurement in the fields of optical sensing, spectroscopy and imaging. The dispersive fourier transform maps the spectrum of the light pulse to a time-domain waveform of similar intensity to the spectrum, allowing a single-pixel photodetector to capture the spectrum at scan rates far exceeding those of conventional spatial-domain spectrometers. The most common approach to DFT is to use standard single mode fibers, such as commercially available silica-based transmission fibers of kilometer length and dispersion compensating fibers of small core diameter. Other dispersion management elements include chirped fiber bragg gratings that produce large spatial chirps and chromatic dispersion. Normal dispersion is produced based on bulk optical dispersive elements such as grating pairs, prisms, etc., but this approach destroys the system compactness of the fiber laser and is difficult to tune; some researchers use special high numerical aperture optical fibers, but the waveguide dispersion of the special optical fibers is limited and the preparation is complex. DFT techniques have been widely used in the near infrared band and have shown potential for extension to longer wavelengths.

Patent CN 108011282 a discloses a high-speed real-time oscilloscope based on optical time stretching and a sampling quantification method thereof. The dissipation soliton passive mode-locking pulse with flat wide spectrum characteristic and large pulse energy is utilized to perform optical time stretching analog-to-digital conversion, so that the speed and the simulation bandwidth of the electronic real-time oscilloscope are greatly improved, the suppression of signal distortion caused by uneven pulse envelope in the front end of optical pretreatment and the improvement of a time window and an output signal-to-noise ratio are realized by a simple structure. However, this scheme requires time-stretching with several kilometers of fiber, and has low dispersion efficiency and increased nonlinear loss, which reduces the signal-to-noise ratio. And the optical fiber with the magnitude of thousands of meters is large in volume, poor in environmental stability and high in cost. The key problems are that the output laser is sensitive to polarization in the kilometer distance transmission process, the adopted detector is sensitive to polarization, so that the transmission loss (intrinsic absorption) is large, the manufacturing cost is high, and the detector cannot be applied to a mid-infrared band more than 2 microns.

Patent CN 110207837a discloses a high-resolution real-time ultrashort pulse time-frequency domain measuring device and method. The measuring device adopts a time lens and a dispersion Fourier transform technology to realize the real-time measurement of the sub-picosecond transient characteristic of the ultrashort pulse, obtains the time-frequency domain information thereof, breaks through the capacity limitations of the traditional oscilloscope such as bandwidth and spectrometer measuring speed, and is suitable for the femtosecond-magnitude ultrashort pulse. Since the adopted dispersion medium is a dispersion compensation fiber or a chirped bragg grating, etc., the dispersion compensation fiber has a major disadvantage that it is available only in the optical fiber communication frequency band around 1550 nm. A disadvantage of chirped bragg gratings is that the product of the total group dispersion velocity and the optical bandwidth must be less than the repetition period of the laser. Thus, for a given laser repetition frequency and bandwidth, there is an upper limit to the magnitude of the group dispersion speed, and the loss of the grating is relatively large due to the diffraction efficiency limitations. The combined light beam needs to pass through a silicon-based micro-nano waveguide with high nonlinearity and low flat dispersion, the nonlinear loss is increased, and the combined light beam cannot be applied to real-time detection of ultrafast laser in a middle infrared band.

However, the mid-infrared band is a band of great importance for future laser applications. The mid-infrared band covers a plurality of atmospheric windows, is in a stronger water absorption wavelength range, contains characteristic absorption spectral lines of a large amount of gas and biomolecules, and is just positioned in an infrared sensing area, so that mid-infrared laser has important application in the aspects of medical treatment, material processing, environmental monitoring and the like. Currently, optical fibers that generate and transmit visible light to the near infrared band (0.4 to 2.5 μm) are mainly commercial silica-based optical fibers. However, the strong infrared absorption of the quartz fiber in the mid-infrared region limits the extension of the supercontinuum to the mid-infrared band, DFT is always limited to the fiber communication frequency band, the traditional fiber cannot realize high dispersion loss ratio outside the 1550nm band, and the mid-infrared ultrafast laser cannot realize detection.

The soft glass (fluoride glass, tellurate glass and chalcogenide glass) has low loss in the middle infrared wavelength range, and the nonlinear coefficient of the ZBLAN optical fiber is 10-1000 times that of silicon-based glass, so that the ZBLAN optical fiber can be used for generating a middle infrared supercontinuum. The loss of the ZBLAN fiber at 0.5-3.5 μm is less than 50dB/km, the loss of the quartz fiber at 1.55 μm wavelength can be below 0.22dB/km, and the loss at 1.31 μm wavelength is below 0.34 dB/km. There are still several orders of magnitude gaps compared to the loss of silica fiber in the near infrared band and dispersion compensation using a ZBLAN fiber in the kilometer range causes unacceptable loss. Therefore, while ZBLAN fibers have promise for solving this problem, the nonlinear loss increases and the signal-to-noise ratio is greatly reduced for fibers that require time stretching on the order of kilometers. The ZBLAN fiber has poor inherent mechanical strength, is easy to darken, has a low melting point, is difficult to realize full-fiber, is in deep negative dispersion, is difficult to accurately compensate high-order dispersion, and is not easy to obtain pulses with few cycles. And the price is high, the feasibility is not available, and the commercialization and application are difficult to realize.

At present, urgent needs are provided for mid-infrared band laser in the military field and the civil field, however, the existing disclosed technology can not carry out ultrafast real-time detection on the time domain and the frequency domain of the mid-infrared band ultrafast laser, so that the research on the mid-infrared band laser material and the laser technology and the real-time spectrum monitoring on the real-time detection of the band have important application value.

Disclosure of Invention

In order to solve the problems, the invention provides a mid-infrared band ultrashort pulse spectrum detection device.

In order to realize the purpose of the invention, the invention provides a mid-infrared band ultrashort pulse spectrum detection device, which comprises an optical signal receiving module, a signal intensity self-adapting module, a dispersion management module, a signal detection module and a control feedback module;

the optical signal receiving module, the signal intensity self-adapting module, the dispersion management module and the signal detection module are arranged on the same collimated light path and are sequentially arranged, and the optical signal receiving module, the signal intensity self-adapting module, the dispersion management module and the signal detection module form a feedback loop together with the control feedback module; input light generated by an input signal light source passes through an optical signal receiving module, is coupled into a dispersion management module through an input collimator and is coupled into a control feedback module through one path of output light split by a beam splitter I;

the dispersion management module comprises a micro-nano optical fiber device, a single mode optical fiber I and a single mode optical fiber II; one end of the single-mode fiber I is welded with an input signal light source through an optical fiber so as to couple input light into a system, and the input light passes through an optical signal receiving module, a signal intensity self-adaptive module and a dispersion management module in sequence; the other end of the single-mode fiber I is connected with the micro-nano fiber device in a fusion mode; one end of the single mode fiber II is welded with the micro-nano fiber device, and the other end of the single mode fiber II is connected with the signal detection module so as to couple the passing signal light into the signal detection module;

the micro-nano optical fibers adopted by the micro-nano optical fiber device are arranged in series and are positioned in the same collimation light path, and the cross section area of the micro-nano optical fibers is in a sub-wavelength size, so that large group velocity dispersion is ensured;

the sub-wavelength size is any value smaller than the laser transmission wavelength, the micro-nano optical fiber is made of a transparent matrix material in a middle infrared band, the length of the device is centimeter magnitude, and low nonlinearity of the device in the middle infrared band and high signal-to-noise ratio of a near infrared band are guaranteed.

In one embodiment, the optical signal receiving module comprises an input collimator and a beam splitter I;

the input collimator and the beam splitter I are fixed on corresponding collimating light paths to ensure that input light is coupled into a system through the input collimator, the beam splitter I splits signal light output on the light paths to obtain two paths of signal light, and one path of signal light is input into the collimating light path where the oscilloscope II of the control feedback module is located; the other path enters a dispersion management module.

In one embodiment, the signal strength adaptation module comprises an attenuator I;

the attenuator I is arranged in front of the dispersion management module and used for adjusting the intensity of the passing signal light.

In one embodiment, the micro-nano optical fiber device comprises a micro-nano optical fiber formed by tapering a quartz optical fiber, tapered transition regions are reserved at two ends of the micro-nano optical fiber, and the micro-nano optical fiber devices are connected in a welding mode.

Specifically, the micro-nano optical fiber device comprises a ZBLAN fiber.

In one embodiment, the signal detection module comprises an output collimator, a beam splitter II, an attenuator II, a spectrometer, a photoelectric detector and a real-time oscilloscope I;

the output collimator, the beam splitter II, the attenuator II, the photoelectric detector and the real-time oscilloscope I are positioned on the same collimation light path; the output collimator receives output signal light which is coupled into the system by input light through the input collimator and passes through a collimating light path where the beam splitter I, the attenuator I and the dispersion pipeline module are located; transmitting the output signal light to a beam splitter II and splitting the signal light output on the light path to obtain two paths of signal light, wherein the beam splitter II and the spectrometer are positioned in the other collimation light path; one path of signal light output by the beam splitter II sequentially enters the photoelectric detection module and the real-time oscilloscope I through coupling, so that the real-time oscilloscope I records the time-frequency domain information of the signal light to be detected in real time; and the other path of signal light output by the beam splitter II passes through the attenuator II to reduce the power of the other path of signal light to a measurable range, and finally, the spectrometer is used for measuring the spectral width of the other path of signal light.

In one embodiment, the control feedback module comprises a real-time oscilloscope II and a computer;

and the computer receives the signal output by the real-time oscilloscope II and performs data analysis and processing, and sends a control signal to compare the input pulse signal optical signal and the output optical signal measured by the real-time oscilloscope II so as to perform feedback self-adaption to different dispersion management networks.

In one embodiment, the micro-nano optical fiber device adopted by the dispersion management device is a cylindrical waveguide structure with three layers of media: the center part is an air fiber core with the radius of 100 and 800nm, the radius is a quartz medium layer with any value smaller than the transmission wavelength value, and the outermost air medium layer; the micro-nano optical fiber air fiber core can adopt different shapes such as a circle, a square or a D shape; liquid and gas with different refractive indexes can be injected into the hollow part of the micro-nano optical fiber device to fill the fiber core; the filled liquid and gas materials have the characteristics of small absorption coefficient in the optical fiber transmission waveband, affinity with the optical fiber substrate material, easiness in filling, tunable refractive index under the action of an external field and the like; the liquid can be toluene, chloroform, ethanol and other substances with different refractive indexes; the gas is hydrogen.

The infrared band ultrashort pulse spectrum detection device is characterized in that an optical signal receiving module, a signal intensity self-adaptive module, a dispersion management module and a signal detection module are arranged on the same collimated light path and are sequentially arranged, and a feedback loop is formed by the optical signal receiving module, the signal intensity self-adaptive module, the dispersion management module and the signal detection module and the control feedback module; input light generated by an input signal light source passes through an optical signal receiving module, is coupled into a dispersion management module through an input collimator and is coupled into a control feedback module through one path of split output light of a beam splitter I, so that independent control of dispersion intensity and nonlinear intensity can be realized, wherein the dispersion management module realizes linear conversion from an optical signal frequency domain to a time domain by using Dispersion Fourier Transform (DFT) technology guided by large group velocity dispersion and low nonlinear characteristics of micro-nano optical fibers, finally measurement of transient characteristics of ultrashort pulse subpicosecond magnitude can be obtained, and time domain and frequency domain information of the ultrashort pulse subpicosecond magnitude can be accurately obtained.

Compared with the prior art, the mid-infrared band ultrashort pulse spectrum detection device has the following beneficial effects:

1. the ultra-fast signal is subjected to dispersion broadening, frequency domain information measured by a spectrometer is displayed in a time domain based on the similarity of the ultra-short pulse time domain and the frequency domain shape, the integral average effect of the spectrometer is compensated, the bandwidth limit of an oscilloscope and the speed defect of an autocorrelator are compensated, the real-time measurement of the sub-picosecond transient characteristic of the ultra-short pulse is realized, and the time-frequency domain information of the ultra-short pulse is accurately obtained. The invention adopts common quartz fiber, the quartz fiber loss at the wavelength of 1.55 mu m can be below 0.22dB/km, the loss is extremely low, and the invention is very favorable for the transmission of near-infrared wave bands. The air core fused silica micro-nano fiber adopts a device length of centimeter magnitude, is reduced by two magnitude compared with the traditional fiber, and leads to nonlinear great reduction, so that the application of DFT in the middle infrared band becomes possible, and particularly solves the real-time detection problem of an ultrafast laser light source of a band above 2.4 microns transmitted by a non-quartz-based fiber. The dispersion and nonlinear characteristics of the miniaturized and highly integrated micro-nano device waveguide determine the transmission behavior of pulses in the range of submicron and even nano-scale, and the miniaturized and highly integrated micro-nano device waveguide is also very favorable for the application of DFT technology in the fields of middle-infrared waveband nonlinear photoelectric devices, optical communication, optical sensing and the like;

2. the air core quartz micro-nano optical fiber is adopted for dispersion broadening, abnormal waveguide dispersion is achieved, and nonlinear controllability of a transmission process is achieved by injecting liquid or gas with different refractive indexes into a fiber core. Generally, a silica optical fiber is used as a transmission medium in an optical communication system, but when the wavelength of fused silica exceeds 2.5 μm, the absorption is significantly increased and the loss is increased. ZBLAN fiber solves this problem, but requires several km of fiber for time stretching, and the increased nonlinear loss results in a significant decrease in signal-to-noise ratio. And the optical fiber with the number of km is large in volume, poor in environmental stability and high in cost. The adopted sub-wavelength size micro-nano optical fiber has the advantages of anomalous waveguide dispersion, non-linear adjustability and the like, realizes independent control of dispersion and non-linearity for the whole waveband, improves the test precision, and can be detected by adopting a photoelectric detector with GHz bandwidth and an oscilloscope;

3. the adopted microstructure optical fiber can be constructed into an integrated network, and different dispersion units are matched for input optical signals through micro-nano optical fiber integrated devices arranged in an array, so that the purpose of dispersion broadening of ultrafast signals is achieved, and the input signals and broadened detection signals do not have pulse distortion. The control feedback module receives signals of the photoelectric detector and performs data analysis and processing to send control signals to control input pulses of the light source, and the signal light and the output light are compared by the computer to be adaptive to different dispersion management networks, so that the dispersion broadening conditions of different light sources are met more flexibly, and the application range is wide.

4. The optical Fourier transform technology based on dispersion broadening carries out pulse width broadening and time delay on femtosecond laser, and the bandwidth advantage of the photon technology is utilized to improve the bandwidth and speed of ultra-fast signal measurement, thereby revealing more pulse details. In addition, fs pulse signals can be broadened to ps magnitude, enough time delay is obtained, ultrafast pulse signal details can be measured only by using a conventional low-bandwidth probe at a detection module, a high-speed detection device is not required, and the measurement cost is reduced. Furthermore, the intermediate infrared micro-nano optical fiber device is prepared by adopting the quartz material, so that the cost is reduced, and the large-scale commercial popularization is facilitated.

Drawings

FIG. 1 is a schematic diagram of a mid-infrared band ultrashort pulse spectrum detection device according to an embodiment;

FIG. 2 is a schematic diagram of the DFT principle of one embodiment;

FIG. 3 is a structural diagram of a hollow-core quartz micro-nano optical fiber according to an embodiment;

FIG. 4 is a schematic diagram of group velocity dispersion curves of hollow-core micro-nano optical fibers according to wavelength and core diameter according to an embodiment;

FIG. 5 is a schematic diagram of a sub-wavelength dimension quartz micro-nano fiber dispersion management unit cascade network according to an embodiment;

FIG. 6 is an optical time stretched analog-to-digital conversion plot of a soliton light source of one embodiment;

FIG. 7 is a schematic diagram illustrating the pulse width amplification effect of sampled soliton mode-locked optical pulses after time stretching in one embodiment;

FIG. 8 is a graph of optical time stretched analog to digital conversion of a negatively chirped pulsed input signal in one embodiment;

FIG. 9 is a graph of optical time stretched analog to digital conversion of a positively chirped pulsed input signal in one embodiment;

fig. 10 is a schematic diagram illustrating the effect of amplifying mode-locking optical pulses of a positively chirped input signal through time-stretched pulse widths in one embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.

In the optical field, the Dispersion Fourier Transform (DFT) measurement technology overcomes the speed limit of the traditional optical instrument and realizes the ultrashort pulse real-time measurement in the fields of optical sensing, spectroscopy and imaging. The dispersive fourier transform maps the spectrum of the light pulse to a time-domain waveform of similar intensity to the spectrum, allowing a single-pixel photodetector to capture the spectrum at scan rates far exceeding those of conventional spatial-domain spectrometers. The core of DFT is large dispersion, which causes linear broadening of pulses (linear chirp), and low nonlinearity, which causes nonlinear phase shift, resulting in pulse splitting, spectral distortion, and ultimately signal distortion. Under the condition of certain nonlinear effect, the similarity between the frequency domain and the time domain can be obtained according to the ultrashort pulse shape, and the condition of dispersion broadening Fourier transform is as follows:

in equation 1, L is the length of the dispersive medium, τ is the input pulse width, β₂Is the second-order dispersion coefficient of the dispersion medium, and the pulse width expression after broadening:

Δτ＝|D|·L·Δλ (2)

in equation 2: d is the optical fiber dispersion coefficient, delta lambda is the wavelength range of input signals, delta tau is required to be less than T, T is the pulse period of a light source, the optical signals pass through a dispersion medium and then are obtained by a detector and digital-to-analog conversion, and a principle effect diagram is shown in figure 2. The input pulse signal is continuously widened through the dispersion element, more pulse details are revealed, and the ultrafast signal is completely displayed in a time domain by using a GHz low-speed detector.

In actual optical measurements, β is usually replaced by a dispersion parameter D₂The relationship between them is:

in equation 3, D or β₂The wavelength at zero is called the zero dispersion wavelength λ_D(ZDW). For silica fibers, λ_DAround 1.27 μm according to D or β₂Different signs may cause different dispersion characteristics to be exhibited in the optical fiber. If wavelength λ < λ_DD < 0 or β₂> 0, the fiber exhibits normal dispersion. In the normal dispersion region, the refractive index n increases with increasing frequency. Conversely, if the wavelength λ > λ_DD > 0 or β₂< 0, the fiber exhibits anomalous dispersion. In the anomalous dispersion region, the refractive index n decreases with increasing frequency. The right side of the equation represents the nonlinear effect, where:

in formula 4, γ represents a nonlinear coefficient, which is a source of self-phase modulation and cross-phase modulation, and nonlinearity causes nonlinear phase shift, pulse splitting, and spectrum distortion, which finally results in signal distortion. n is₂(ω₀) Is the refractive index at the carrier frequency of the optical wave, A_eff(ω₀) Is the effective mode area at the carrier frequency of the optical wave. By increasing the non-linear refractive index n₂And reducing the effective area of the mode field may increase the nonlinear coefficient lambda. Compared with the common optical fiber, the micro-structure optical fiber can effectively reduce the area of a mode field and can also increase the nonlinear coefficient through reasonable design.

When light waves propagate in an optical fiber, different frequency components, due to chromatic dispersion, will propagate in the optical fiber at different group velocities, resulting in a spectral broadening of the optical field. The variation relationship of the group velocity dispersion phase along with the time is as follows:

in equation 5, z is the transmission distance, L_DFor the length of dispersion, T₀Is the initial pulse width. The frequency variation due to group velocity dispersion is:

equation 6 shows that the frequency variation is linear with time, i.e. the linear frequency is chirped, and the sign of the chirp omega depends on β₂In the anomalous dispersion region (β)₂< 0), leading edge of pulse (T)<0) ω is positive (positive chirp), the frequency is blue shifted (producing short wavelengths), and the trailing edge (T)<0) ω is negative (negative chirp), frequency red-shifted (produces long wavelength.) in the normal dispersion region (β)₂> 0), the opposite is true.

The dispersion of a common single mode fiber is the sum of the material dispersion and the waveguide dispersion, as shown in equation 7.

D(λ)＝D_w(λ)+D_m(λ) (7)

The dispersion of a material is due to the fact that the refractive index of the material varies with wavelength, which results in the conversion of the propagation speed of light as a function of wavelength. The broadening effect of material dispersion on ultrashort pulses. When an optical pulse passes through a certain medium, it obtains a phase shift, expressed by phi (omega), which is frequency dependent, as shown in equation 8.

φ(ω)＝kn(ω)L (8)

GDD describes a non-linear phase shift, i.e. a linear relationship between the frequency content of the pulses and the group velocity delay. If the second derivative of the refractive index of the medium with respect to wavelength

The medium is a positive dispersion medium, normal dispersion can be generated in the transmission process of the pulse passing through the medium, namely, the transmission speed of the high-frequency component of the incident pulse is slower than that of the low-frequency component, the leading edge of the pulse generates red shift in the transmission process of the pulse, and the trailing edge of the pulse generates blue shift, which is called as positive chirp; if the second derivative of the refractive index of the medium with respect to wavelength

It shows that the medium is a negative dispersion medium, and anomalous dispersion is generated in the process of transmitting the pulse through the medium, namely, the transmission speed of the high-frequency component of the incident pulse is faster than that of the low-frequency component, and the phenomenon is called negative chirp.

Waveguide dispersion is an independent effect caused by the wavelength dependence of the mode size with respect to the waveguide size. The waveguide dispersion is generally related to the radius of the optical fiber and the refractive index difference of a fiber core cladding, so that the position of the zero dispersion wavelength in the optical fiber can be adjusted by adjusting the parameters, and the zero dispersion wavelength can be moved to a position of 1.55 mu m, namely, the wavelength with the minimum loss, namely, the dispersion displacement optical fiber, but the displacement is very limited and cannot be expanded to a middle infrared band. The microstructure fiber has abnormal waveguide dispersion, and realizes independent control of dispersion and nonlinearity.

Through the change relation of the group velocity parameter of the micro-nano optical fiber along with the wavelength, the waveguide dispersion of the micro-nano optical fiber can be far larger than the waveguide dispersion and the material dispersion of the weak light guide fiber. As shown in FIG. 4, the waveguide dispersion of the quartz micro-nano fiber with the diameter of about 800nm can reach 2700ps²And/km, the total dispersion value can be flexibly regulated and controlled between zero, anomalous dispersion and larger normal dispersion by changing the diameter of the micro-nano optical fiber, and the wavelength point of the zero dispersion is changed. Near the zero dispersion point, the waveguide dispersion change is positively correlated with wavelength, and at the same wavelength, the waveguide dispersion increases with increasing cladding-core index difference. As the refractive index of the cladding material increases, the core-cladding refractive index difference decreases, the waveguide dispersion gradually decreases at the zero dispersion point and changes from a positive value to a negative value, and the waveguide dispersion curve at the zero dispersion point is flatter. The waveguide dispersion is essentially the differential of phase velocity versus wavelength, according to the relationship of group velocity to waveguide dispersion, as shown in equation 9.

Due to the dielectric waveguide effect, the effective mode index of the fiber is typically slightly lower than the index of the core material, i.e.

Is shown as the dependence of the effective refractive index on the waveguide structure. For the micro-nano optical fiber with sub-wavelength diameter, the total dispersion characteristic of the whole optical fiber is influenced by the waveguide dispersion due to the design particularity of the geometric structure of the micro-nano optical fiber. The calculation result of the waveguide dispersion shows that the waveguide dispersion of the micro-nano optical fiber can reach ns/nm/km magnitude, is 1 to 3 magnitude orders larger than that of a common optical fiber, and the zero dispersion wavelength is reduced along with the reduction of the diameter, so that the micro-nano optical fiber has potential application value in the fields of optical communication, nonlinear optics and the like related to dispersion.

Under the action of strong laser light field, the polarization strength generated by the medium is related to the second and third times of the incident radiation field strength, so that the higher the polarization strength is. The non-linearity in the fiber, which arises from the non-linear refractive index. When the optical field is strong, all media will exhibit some non-linearity to the external field. For the traditional quartz optical fiber and the traditional intermediate infrared optical fiber, the polarization intensity is mainly influenced by the linear polarizability of the field intensity and the third-order polarizability, and the second-order polarizability is weaker. The nonlinear index of refraction produces a dispersion penalty in the negative dispersion region of the fiber and dispersion compensation in the positive dispersion region.

The structure of the micro-nano optical fiber air fiber core can be in different shapes such as a round shape, a square shape or a D shape. Further, liquid and gas with different refractive indexes can be injected to fill the fiber core. Furthermore, the filled liquid and gas materials should have the characteristics of small absorption coefficient in the optical fiber transmission waveband, affinity with the optical fiber substrate material, easy filling, tunable refractive index under the action of an external field, and the like. Specifically, the liquid can be toluene, chloroform, ethanol and other substances with different refractive indexes, and specifically, the temperature sensitivity or tunable characteristic of the micro-nano optical fiber can be effectively improved by adding the temperature sensitive liquid material. The gas can be hydrogen and other substances, and particularly, the range of laser wavelength can be effectively stretched based on a gas filling nonlinear Raman laser frequency conversion technology, and the stretching device is particularly expanded to a middle infrared band. The gas medium filled in the wave bands has good transmission spectrum, and the Raman active gas has the advantages of large frequency shift and high damage threshold. According to the invention, the flexible end face structure design of the micro-nano optical fiber, the selection of the type of the filling material, the diversity of the filling method and the like are combined together, so that the manufactured micro-nano optical fiber device has higher degree of freedom and adaptability, the full optical fiber structure is realized, and the system integration is facilitated.

The ZBLAN fiber has a loss of less than 50dB/km at 0.5-3.5 μm and produces 100ps²For a/km dispersion, it is necessary to use a fiber length of several tens of kilometers, however, dispersion compensation using a fiber of the order of kilometers results in unacceptable losses. The air core micro-nano optical fiber adopted by the invention has enough large group velocity dispersion, and the waveguide dispersion of the quartz micro-nano optical fiber with the diameter of about 800nm can reach 2700ps²And the dispersion amount is the same only by the micro-nano optical fiber with the meter-scale length. Further, the air core micro-nano optical fiber is in centimeter-level device length and sub-wavelength size, and the conversion from the frequency domain to the time domain of the optical signal is realized by using dispersion Fourier transform in a dispersion medium with enough large group velocity dispersion and low nonlinearity. The micro-nano optical fiber network integrated device is an air core structure or low-nonlinearity material filling to realize positive waveguide dispersion, low nonlinearity and mid-infrared band low loss. And matching an input optical signal with a proper dispersion unit through micro-nano optical fiber integrated devices which form a network in different ways, and carrying out dispersion broadening on the ultrafast signal.

To achieve the above functions, in one embodiment, a mid-infrared band ultrashort pulse spectrum detection device is provided, and fig. 1 is a schematic structural diagram of a mid-infrared band ultrashort pulse spectrum detection device of one embodiment, which includes at least one optical signal receiving module 2, at least one signal intensity adaptive module 3, at least one dispersion management module 4, at least one signal detection module 5, and at least one control feedback module 6;

the optical signal receiving module 2, the signal intensity self-adapting module 3, the dispersion management module 4 and the signal detection module 5 are arranged on the same collimated light path and are sequentially arranged, and a feedback loop is formed by the optical signal receiving module, the signal intensity self-adapting module 3, the dispersion management module 4 and the signal detection module 5 and the control feedback module 6; input light generated by the input signal light source 1 passes through the optical signal receiving module, is coupled into the dispersion management module 4 through the input collimator, and is split by the beam splitting mirror I8 of the optical signal receiving module 2, and output light is coupled into the control feedback module 6.

Specifically, the optical signal receiving module 2 comprises an input collimator 7 and a beam splitter i 8;

an input collimator 7 and a beam splitter I8 are fixed on the collimation light path to ensure that input light is coupled into a system (a system where the mid-infrared band ultrashort pulse spectrum detection device is located) through the input collimator, the beam splitter I8 splits signal light output on the light path to obtain two paths of signal light, and one path of signal light is input into the collimation light path where an oscilloscope II 20 of the control feedback module 4 is located; the other path enters a dispersion management module 4;

the dispersion management module comprises a micro-nano optical fiber device 11, a single mode optical fiber I10 and a single mode optical fiber II 12; the micro-nano optical fiber device 11 is a micro-nano optical fiber device with the length of centimeter magnitude; the single-mode optical fiber I10 and the single-mode optical fiber II 12 are single-mode optical fibers with different lengths; one end of the single-mode fiber I10 is in fusion connection with the input signal light source 1 through an optical fiber so as to couple input light into a system, and the input light sequentially passes through the optical signal receiving module 2, the signal intensity self-adaptive module 3 and the dispersion management module 4; the other end of the single-mode fiber I10 is connected with the micro-nano fiber device 11 in a welding mode; one end of the single-mode fiber II 12 is welded with the micro-nano fiber device 11, and the other end of the single-mode fiber II 12 is connected with the signal detection module 5 so as to couple the passing signal light into the signal detection module 5;

the micro-nano optical fibers adopted by the micro-nano optical fiber device 11 are arranged in series and are positioned in the same collimation light path, and the cross section area of the micro-nano optical fibers is in a sub-wavelength size, so that large group velocity dispersion is ensured; the sub-wavelength size is any value smaller than the laser transmission wavelength, the micro-nano optical fiber is made of a transparent matrix material in a middle infrared band, the length of the device is centimeter magnitude, and low nonlinearity of the device in the middle infrared band and high signal-to-noise ratio of a near infrared band are guaranteed.

Specifically, the signal strength adaptive module 3 comprises an attenuator I9;

the attenuator I9 is arranged in front of the dispersion management module 4 and used for adjusting the intensity of the passing signal light; at this time, the attenuator I9, the optical signal receiving module 2, the signal intensity adaptive module 3, the dispersion management module 4 and the signal detection module 5 are located on the same collimated light path.

In one embodiment, the micro-nano optical fiber device 11 comprises a micro-nano optical fiber formed by tapering a quartz optical fiber, tapered transition regions are left at two ends of the micro-nano optical fiber, and the micro-nano optical fiber devices are connected in a welding manner.

Specifically, the micro-nano optical fibers are arranged in series and are positioned in the same collimation light path, and the cross-sectional area of the micro-nano optical fibers is in the sub-wavelength size, so that large group velocity dispersion is ensured;

Specifically, the micro-nano optical fiber device comprises a ZBLAN fiber.

In this embodiment, the dispersion management module 4 includes a micro-nano optical fiber device 11 with a centimeter-level length and single-mode optical fibers with different lengths. The left end of the single-mode optical fiber I10 and the input signal light source 1 are coupled into the system in an optical fiber fusion mode and sequentially pass through the optical signal receiving module 2, the signal intensity self-adaption module 3 and the dispersion management module 4; the right end of the single-mode optical fiber I10 is connected with the micro-nano optical fiber device 11 in a fusion mode; the left end of the single-mode fiber II 12 is welded with the micro-nano fiber device 11, and the right end of the single-mode fiber II is coupled into the signal detection module 5; the micro-nano optical fiber devices 11 are micro-nano optical fibers formed by tapering quartz optical fibers, tapered transition regions are reserved at two ends of the micro-nano optical fibers, and the micro-nano optical fiber devices 11 are connected in a fusion mode; the micro-nano optical fibers are arranged in series and are positioned in the same collimation light path. The micro-nano optical fiber is in sub-wavelength size, and large group velocity dispersion is guaranteed. Furthermore, the micro-nano optical fiber adopts a quartz substrate, the length of the device is centimeter magnitude, and low nonlinearity of the micro-nano optical fiber in a middle infrared band and high signal-to-noise ratio of a near infrared band are ensured. The micro-nano optical fiber is a cylindrical waveguide structure with three layers of media: the diameter of the air fiber core is a sub-wavelength size smaller than the transmission wavelength, the thickness of the quartz medium layer is 200nm, and the outermost air medium layer is arranged. Furthermore, the micro-nano optical fiber air fiber core can adopt different shapes such as a circle, a square or a D shape. Liquid and gas with different refractive indexes can be injected to fill the fiber core, specifically, the liquid can be toluene, chloroform, ethanol and other substances with different refractive indexes, and the temperature sensitivity or tunable characteristic of the micro-nano optical fiber can be effectively improved by adding the temperature sensitive liquid material. The gas can be hydrogen and other substances, and particularly, the range of laser wavelength can be effectively stretched based on a gas filling nonlinear Raman laser frequency conversion technology, and the stretching device is particularly expanded to a middle infrared band. The gas medium filled in the wave bands has good transmission spectrum, and the Raman active gas has the advantages of large frequency shift and high damage threshold. The micro-nano optical fiber device can adopt a space composition mode of array arrangement. A series configuration is employed to achieve a dispersive unit that is matched to the input optical signal. Specifically, the network structure adopts a square array form, and the square array is composed of n rows and n columns of micro-nano optical fiber devices. The micro-nano optical fiber is formed by tapering quartz optical fibers, tapered transition regions are reserved at two ends of the optical fibers, and micro-nano optical fiber devices are connected in a welding mode, so that welding loss is reduced, and better mode field matching is achieved.

Specifically, the signal detection module 5 comprises an output collimator 13, a beam splitter II 14, an attenuator II 15, a spectrometer 16, a photoelectric detector 17 and a real-time oscilloscope I18;

the output collimator 13, the beam splitter II 14, the attenuator II 15, the photoelectric detector 17 and the real-time oscilloscope I18 are positioned on the same collimation light path; the beam splitter II 14 splits the signal light output on the light path to obtain two paths of signal light, and the beam splitter II 14 and the spectrometer 16 are positioned in another collimation light path; the output collimator 13 receives output signal light which is coupled into the system by input light through the input collimator 7 and passes through a collimating light path where the beam splitter I8, the attenuator I and the dispersion pipeline module are located; transmitting the output signal light to a beam splitter II 14 and splitting the signal light output on the light path to obtain two paths of signal light; one path of signal light output by the beam splitter II 14 sequentially enters the photoelectric detection module 17 and the real-time oscilloscope I18 through coupling, so that the real-time oscilloscope I18 records the time-frequency domain information of the signal light to be detected in real time; the beam splitter II 14, the attenuator II 15 and the spectrometer 16 are positioned in the other collimation light path; and the other path of signal light output by the beam splitter II 14 passes through an attenuator II 15 to reduce the power of the other path of signal light to a measurable range, and finally, a spectrometer 16 is used for measuring the spectral width of the other path of signal light.

Specifically, the control feedback module 6 comprises a real-time oscilloscope ii 20 and a computer 19;

and the computer 19 receives the signal output by the real-time oscilloscope II 20 and performs data analysis and processing, and sends a control signal to compare the input pulse signal optical signal and the output optical signal measured by the real-time oscilloscope II 20 so as to perform feedback self-adaption to different dispersion management networks. At this time, the computer 19 may be adopted to receive the signal of the photodetector 17 and perform data analysis processing, and send out a control signal to compare the input pulse signal light and the output light of the light source for adaptive different dispersion management networks.

In this embodiment, the dispersion management apparatus 4 is a core apparatus. The micro-nano optical fiber device 11 adopted by the device is a cylindrical waveguide structure with three layers of media: the center part is an air fiber core with the radius of 100-800nm, the radius is a quartz medium layer with any value smaller than the transmission wavelength value, and the outermost air medium layer. The micro-nano optical fiber air fiber core can be in different shapes such as a circle, a square or a D shape. Liquid and gas with different refractive indexes can be injected into the hollow part of the micro-nano optical fiber device 11 to fill the fiber core. Furthermore, the filled liquid and gas materials should have the characteristics of small absorption coefficient in the optical fiber transmission waveband, affinity with the optical fiber substrate material, easy filling, tunable refractive index under the action of an external field, and the like. Specifically, the liquid can be toluene, chloroform, ethanol and other substances with different refractive indexes, and the addition of the temperature sensitive liquid material can effectively improve the temperature sensitivity or tunable characteristic of the micro-nano optical fiber. The gas may be hydrogen or the like, and in particular, the gaseous medium has a good transmission spectrum in these bands.

In one example, the micro-nano fiber device 11 may adopt a spatial composition manner of array arrangement. A series configuration is employed to achieve a dispersive unit that is matched to the input optical signal. Specifically, the network structure adopts a square array form, and the square array is composed of n rows and n columns of micro-nano optical fiber devices. Furthermore, the micro-nano optical fiber is formed by tapering a quartz optical fiber, tapered transition regions are reserved at two ends of the optical fiber, and micro-nano optical fiber devices are connected in a welding mode, so that welding loss is reduced, and better mode field matching is achieved.

Further, an input collimator 7 and a beam splitter I8 fix a collimation light path. One output of the beam splitter I8 is used for collimating and coupling into the dispersion management module 4, and the other output is used for an oscilloscope measurement II 20.

Preferably, the spectrometer 16 performs the correlation analysis using a DFT (discrete fourier transform) approach, which ameliorates the limited scan rate disadvantage of conventional spectrometers and allows a continuous single measurement of a rapidly evolving or fluctuating spectrum at a scan rate comparable to the repetition rate of the laser pulses. The main requirement of the DFT is that the GVD is large enough and linear to ensure that there is no distortion in the frequency-to-time mapping process. In recent years, various methods for DFT have been proposed and demonstrated, covering different spectral bands centered at 800nm, 1000nm and 1550nm with optical bandwidths within 100 nm. The diameter of the micro-nano optical fiber is smaller than the wavelength of light waves, and the refractive index difference between the optical fiber and the air cladding is large, so that the micro-nano optical fiber has abnormal waveguide dispersion compared with a common optical fiber. The air core micro-nano optical fiber can achieve the purposes of adjustable dispersion and non-linear adjustment by flexibly changing the size of the core diameter, the fiber core filler and the thickness of the cladding. The liquid can be toluene, chloroform, ethanol or other substances with different refractive indexes, and specifically, the temperature sensitivity or tunable characteristic of the micro-nano optical fiber can be effectively improved by adding the temperature sensitive liquid material. The gas can be hydrogen and other substances, and particularly, the range of laser wavelength can be effectively stretched based on a gas filling nonlinear Raman laser frequency conversion technology, and the stretching device is particularly expanded to a middle infrared band. The gas medium filled in the wave bands has good transmission spectrum, and the Raman active gas has the advantages of large frequency shift and high damage threshold. The gas can be hydrogen or other substances with different refractive indexes, so that the purpose of nonlinear control in the transmission process is achieved.

In one embodiment, the above-mentioned mid-infrared band ultrashort pulse spectrum detection device implements time delay and broadening of an ultrafast signal based on a dispersion management module, which substantially corresponds to an optical fourier transform technique based on dispersion broadening, and in one example, the DFT principle adopted by the optical fourier transform technique can be referred to fig. 2, in which 21 denotes a pulse laser in fig. 2; 22 denotes a nonlinear optical fiber; 23 denotes a dispersive element; 24 denotes a single pixel photodiode; and 25, a real-time oscilloscope/spectrometer. The above-mentioned mid-infrared band ultrashort pulse spectrum detection device is further described below by means of several examples.

Example 1

The device for detecting the mid-infrared band ultrashort pulse spectrum comprises an optical signal receiving module, a signal intensity self-adapting module, a dispersion management module, a signal detecting module and a control feedback module. The optical signal receiving device comprises an input collimator and a beam splitter I. The input collimator and the beam splitter I are fixed on a collimation light path, input light can be coupled into a system through the input collimator, the beam splitter I is placed at an angle of 45 degrees, about 10% of light can be measured by the real-time oscilloscope II, and the rest incident light is transmitted to the dispersion management module along the light path. The signal intensity self-adapting module comprises an attenuator I, and the attenuator I is arranged in front of the dispersion management module and used for adjusting the intensity of the signal light.

The dispersion management module comprises a sub-wavelength micro-nano optical fiber device with centimeter-level lengthSingle mode optical fibers of different lengths. The quartz fiber is used as a typical dielectric material for simulation, and is used for the following reasons: (1) silica fibers are the most important photonic and optoelectronic materials in the visible and near infrared range; (2) silica optical fibers with micrometer and nanometer diameters have been successfully manufactured; (3) its optical and physical properties are well studied and it has stable high refractive index typical characteristics. As shown in fig. 3, a denotes an air core radius; b represents the radius of the fused quartz medium layer; n is_cRepresents the air cladding refractive index; n is_fRepresenting the refractive index of the cladding material; n is_sThe core refractive index is shown. The hollow quartz micro-nano optical fiber is a cylindrical waveguide structure with three layers of media: an air fiber core with the radius of 800nm, a fused quartz medium layer with the radius of 1000nm and an outermost air medium layer. The conversion from the frequency domain to the time domain of the optical signal is realized based on the dispersion Fourier transform of the dispersion medium of which the micro-nano optical fiber has enough large group velocity dispersion and low nonlinearity. The structure of the waveguide is changed by changing the radius of the fiber core and the thickness of the cladding, and the dispersion value of the waveguide is adjusted. According to the relationship between the group velocity and the group velocity dispersion, by changing the diameter of the fiber core, the variation relationship of the group velocity dispersion with the wavelength is shown in FIG. 4: the diameter of the micro-nano optical fiber core is 200nm, 400nm, 600nm, 800nm and 1000nm respectively. The core diameter of the micro-nano optical fiber is reduced, especially when the core diameter is less than 1 μm, the effective refractive index of the waveguide is close to the refractive index of the cladding, the group velocity is close to the optical velocity c, and most of the optical energy is transmitted in the air. The change in group velocity and wavelength will determine the group velocity dispersion value. The micro-nano optical fiber network integrated device is an air core structure or low-nonlinearity material filling to realize positive waveguide dispersion, low nonlinearity and mid-infrared band low loss. As shown in fig. 5, the dispersion management unit adopts a network array mode, and can be overlapped and expanded, so that the dispersion management applicability is widened, the nonlinearity is controllable, and different pulse broadening conditions are adapted. The dispersion management module can provide dispersion broadening with different magnitudes by adopting an array network mode, and can broaden picosecond signals to microseconds, nanoseconds or even milliseconds. Microsecond, nanosecond and millisecond signals obtained after broadening are composed ofThe detection module carries out photoelectric conversion and sends the photoelectric conversion to the digital-to-analog conversion and data processing module.

The signal detection module comprises an output collimator, a beam splitter II, an attenuator II, a spectrometer, a photoelectric detector and a real-time oscilloscope I. The output collimator, the beam splitter II, the attenuator II, the photoelectric detector and the real-time oscilloscope I are positioned on the same collimation light path; the output collimator receives output signal light which is coupled into the system by input light through the input collimator and passes through a collimating light path where the beam splitter I, the attenuator I and the dispersion pipeline module are located. The output signal light is transmitted to a beam splitter II and is split into two paths of signal light by the signal light output from the light path; one path of signal light output by the beam splitter II sequentially enters the photoelectric detection module and the real-time oscilloscope I through coupling, so that the real-time oscilloscope I records the time-frequency domain information of the signal light to be detected in real time; the photoelectric detection module is a GHz-bandwidth photoelectric detector and a real-time oscilloscope I; the beam splitter II, the attenuator II and the spectrometer are positioned in the other collimation light path; specifically, the output end of the beam splitter II reduces the signal light power to a measurable range through the attenuator II, and finally the spectrometer measures the spectrum width of the signal light power.

And the control feedback module comprises a real-time oscilloscope II and a computer, the computer is used for receiving the signal of the real-time oscilloscope I and analyzing and processing data, and a control signal is sent out to compare the input pulse signal optical signal and the output optical signal measured by the real-time oscilloscope II so as to feed back the self-adaptive different dispersion management network.

In the example, a soliton mode-locked 1950nm signal light source without a substructure is used as an input signal, time stretching is realized after the input signal passes through a micro-nano optical fiber network, then an output collimator receives an output signal of an optical fiber, the output signal is transmitted to a photoelectric detection module for photoelectric conversion, and finally a real-time oscilloscope I is used for completing sampling and quantification to obtain a digitized stretching signal. As shown in fig. 5, the dispersion management unit is arranged in a network array manner, and can continue to be overlapped and expanded, and is processed by a computer in a signal processing module, so that the self-adaptive dispersion management unit has the advantages of widened applicability, nonlinearity controllability, adaptation to different pulse broadening conditions, improvement of a time window and a signal-to-noise ratio of an optical time stretching system, and simplification of a system structure and a digital domain processing process.

The signal strength adaptive module comprises an attenuator I. The attenuator I is arranged in front of the dispersion management module and used for adjusting the intensity of signal light; the control feedback module comprises a real-time oscilloscope II and a computer, the computer is used for receiving the signal of the real-time oscilloscope I and analyzing and processing data, and a control signal is sent out to compare the input pulse signal optical signal and the output optical signal measured by the real-time oscilloscope II so as to feed back the self-adaptive different dispersion management network.

In the experimental process, the parameters are set to be 5000dB/km loss, the laser wavelength of an input signal light source is 1950nm, and the gamma value is 108W^-1Km^-1The length of one micro-nano optical fiber is 40mm, and the total GVD after 60 micro-nano optical fibers are connected in series is 60ps²And/km, hyperbolic secant fitting is adopted in the simulation process, the sampling rate of the oscilloscope is 10GS/s, the limited pulse width is converted into 1ps, and the dispersion is broadened to 80 ps. Fig. 6 is an optical time stretch analog-to-digital conversion diagram of the soliton light source of the present example, fig. 6(a) and 6(c) are time domain diagrams before and after the soliton light source is subjected to the optical time stretch analog-to-digital conversion, fig. 6(c) is a result diagram after dispersion broadening of the 2400mm micro-nano optical fiber, and a result of 80 times of time stretch broadening can be realized by the micro-nano optical fiber of the meter magnitude, so that high resolution real-time measurement of the ultra-short pulse time-frequency domain can be realized by using an oscilloscope and a photodetector with GHz bandwidth. In addition, the detection module part, a spectrometer YOKOGAWA (AQ6375) measures the wave band range from 1200nm to 2400 nm. Further, the length can be increased through the micro-nano optical fiber network to achieve a larger broadening result. Fig. 6(b) and 6(d) are corresponding spectrograms, and the spectral shape remains unchanged during the simulation process, so that the stability is good. Due to the optical time stretching treatment, the frequency spectrum of the light source is flat enough, the time domain distortion of the stretched signal is small, and no pulse is split. The good feasibility of this approach was demonstrated. As shown in fig. 7, the sampling soliton light source can be widened by 80 times through time stretching pulse width amplification. Analog-digital conversion data within the spectral width range of 20nm near the central wavelength are taken, and simulation results show that the dispersion Fourier transform method adopting micro-nano optical fiber network dispersion compensation can realize large dispersionTime domain amplification and fourier transform at 80 times.

Example 2

This example differs from example 1 in that it uses negatively chirped pulses as the input signal and GDD describes a non-linear phase shift, i.e. a linear relationship between the frequency component of the pulse and the group velocity delay. If the second derivative of the refractive index of the medium with respect to wavelength. The medium is a positive dispersion medium, normal dispersion can be generated in the transmission process of the pulse passing through the medium, namely, the transmission speed of the high-frequency component of the incident pulse is slower than that of the low-frequency component, the leading edge of the pulse generates red shift in the transmission process of the pulse, and the trailing edge of the pulse generates blue shift, which is called as positive chirp; if the second derivative of the refractive index of the medium with respect to the wavelength indicates that the medium is a negative dispersion medium, anomalous dispersion occurs during the transmission of the pulse through the medium, i.e., the high frequency component of the incident pulse is transmitted at a faster rate than the low frequency component, which is called negative chirp. The input signal is subjected to time stretching after passing through a micro-nano optical fiber dispersion management network, then the output signal of the optical fiber is received by an output collimator and transmitted to a photoelectric detection module for photoelectric conversion, and finally sampling and quantification are completed by a real-time oscilloscope I to obtain a digitized stretched signal.

Fig. 8 is an optical time-stretched analog-to-digital conversion graph of the negatively chirped pulsed input signal of the present example. In the simulation process, the spectrum shape is kept unchanged, and the stability is good. Due to the optical time stretching treatment, the frequency spectrum of the light source is flat enough, the time domain distortion of the stretched signal is small, and no pulse is split. The good feasibility of this approach was demonstrated. The negative chirp pulse light source can be expanded by 70 times under the condition of short-time constant through time stretching of the pulse width amplification result. Analog-digital conversion data within a spectral width range of 20nm near the central wavelength are obtained, and simulation results show that the dispersion Fourier transform method adopting micro-nano optical fiber network dispersion compensation can realize time domain amplification and Fourier transform which are more than 70 times.

Example 3

Referring to fig. 9 and 10, in fig. 9, a represents a time domain diagram of the input signal light source, and b represents a spectrum diagram of the input signal light source; c represents the input signal light source is stretched in optical timeA domain map; d represents the input signal light source optical time stretched spectrogram. The air core fused silica micro-nano fiber provided by the example enables the application of DFT in the middle infrared band to be possible, and particularly solves the real-time detection problem of an ultrafast laser light source with the band more than 2.4 microns transmitted by non-silica-based fiber. The difference between the example and the example 1 is that the example adopts 2860nm pulse as input signal, the length of one micro-nano optical fiber used in the experimental process is 40mm, and the total GVD is 50ps after 50 micro-nano optical fibers are connected in series²And/km. The sampling rate of the real-time oscilloscope is 10GS/s, the limited pulse width is converted into 800fs, and the dispersion and the broadening are carried out to 60 ps. In addition, the detection module part, a spectrometer YOKOGAWA (AQ6376) measures the wave band range from 1500nm to 3400 nm. Further, the micro-nano optical fiber device can adopt ZBLAN optical fiber. Fig. 9(a) and 9(c) are time domain diagrams before and after the pulse light source with positive chirp is subjected to optical time stretching analog-to-digital conversion, fig. 9(c) is a result diagram after dispersion broadening of 2000mm micro-nano optical fibers, and a result of 75 times of time stretching broadening can be realized through the micro-nano optical fibers with meter magnitude, so that high-resolution real-time measurement of an ultrashort pulse time-frequency domain can be realized by using a real-time oscilloscope i with a GHz bandwidth and a photoelectric detector. Further, the length can be increased through the micro-nano optical fiber network to achieve a larger broadening result. Fig. 9(b) and 9(d) are corresponding spectrograms, and the spectral shape remains unchanged during the experiment, with good stability. Due to the optical time stretching treatment, the frequency spectrum of the light source is flat enough, the time domain distortion of the stretched signal is small, and no pulse is split. The good feasibility of this approach was demonstrated. As shown in fig. 10, the pulsed light source is amplified by time-stretched pulse width. The analog-digital conversion data within the range of 20nm of the spectrum width near the central wavelength is obtained, and the result shows that the dispersion Fourier transform method adopting the micro-nano optical fiber network dispersion compensation can realize time domain amplification and Fourier transform which are more than 75 times.

According to the specific example, the reasonable prediction result shows that the invention provides the high-precision real-time spectrum detection device for the intermediate infrared band ultra-short pulse based on the sub-wavelength size micro-nano optical fiber. The air core fused silica micro-nano optical fiber provided by the invention adopts a device length of centimeter magnitude, is reduced by two magnitude compared with the traditional optical fiber, and the nonlinearity caused by the air core is greatly reduced, so that the application of DFT in a middle infrared band becomes possible, and particularly the problem of real-time detection of an ultrafast laser light source of a band above 2.4 microns transmitted by a non-quartz-based optical fiber is solved. Independent control of dispersion intensity and nonlinear intensity is achieved through flexible structural design of a micro-nano optical fiber device, linear conversion from an optical signal frequency domain to a time domain is achieved through a Dispersion Fourier Transform (DFT) technology guided by large group velocity dispersion and low nonlinear characteristics of micro-nano optical fibers, measurement of ultrashort pulse subpicosecond magnitude transient characteristics can be finally obtained, and time domain and frequency domain information of the ultrashort pulse subpicosecond magnitude transient characteristics can be accurately obtained. Further, a micro-nano optical fiber integrated network structure is formed through array type spatial arrangement, and on the basis of the quartz matrix micro-nano optical fiber, enhanced positive waveguide dispersion is obtained by adopting an air core structure or a low-nonlinearity material filling method, so that the characteristics of the novel DFT technology in a near infrared band such as high signal-to-noise ratio and the advantages of low nonlinearity and low loss in a middle infrared band are displayed, and meanwhile, the novel DFT technology has important application value in the aspect of middle infrared band light source detection.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

It should be noted that the terms "first \ second \ third" referred to in the embodiments of the present application merely distinguish similar objects, and do not represent a specific ordering for the objects, and it should be understood that "first \ second \ third" may exchange a specific order or sequence when allowed. It should be understood that "first \ second \ third" distinct objects may be interchanged under appropriate circumstances such that the embodiments of the application described herein may be implemented in an order other than those illustrated or described herein.

The terms "comprising" and "having" and any variations thereof in the embodiments of the present application are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product, or device that comprises a list of steps or modules is not limited to the listed steps or modules but may alternatively include other steps or modules not listed or inherent to such process, method, product, or device.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The device is characterized by comprising an optical signal receiving module, a signal intensity self-adaptive module, a dispersion management module, a signal detection module and a control feedback module;

the micro-nano optical fibers adopted by the micro-nano optical fiber device are arranged in series and are positioned in the same collimation light path, and the cross section area of the micro-nano optical fibers is in a sub-wavelength size, so that large group velocity dispersion is ensured; the sub-wavelength size is any value smaller than the laser transmission wavelength, the micro-nano optical fiber is made of a transparent matrix material in a middle infrared band, the length of the device is centimeter magnitude, and low nonlinearity of the device in the middle infrared band and high signal-to-noise ratio of a near infrared band are guaranteed.

2. The apparatus according to claim 1, wherein the optical signal receiving module comprises an input collimator and a beam splitter i;

3. The apparatus according to claim 1, wherein the signal strength adaptation module comprises an attenuator I;

4. The device for detecting the mid-infrared band ultrashort pulse spectrum according to claim 1, wherein the micro-nano optical fiber device comprises a micro-nano optical fiber formed by tapering a quartz optical fiber, tapered transition regions are reserved at two ends of the micro-nano optical fiber, and the micro-nano optical fiber devices are connected in a welding mode.

5. The mid-infrared band ultrashort pulse spectral detection device of claim 1, wherein the micro-nano fiber device comprises a ZBLAN fiber.

6. The mid-infrared band ultrashort pulse spectrum detection device of any one of claims 1 to 5, wherein the signal detection module comprises an output collimator, a beam splitter II, an attenuator II, a spectrometer, a photodetector and a real-time oscilloscope I;

7. The mid-infrared band ultrashort pulse spectroscopy device of any one of claims 1 to 5, wherein the control feedback module comprises a real-time oscilloscope II and a computer;

8. The mid-infrared band ultrashort pulse spectrum detection device of any one of claims 1 to 5, wherein the micro-nano optical fiber device adopted by the dispersion management device is a cylindrical waveguide structure with three layers of media: the center part is an air fiber core with the radius of 100 and 800nm, the radius is a quartz medium layer with any value smaller than the transmission wavelength value, and the outermost air medium layer; the micro-nano optical fiber air fiber core can be circular, square or D-shaped; liquid and gas with different refractive indexes are injected into the hollow part of the micro-nano optical fiber device to fill the fiber core; the filled liquid or gas material has the characteristics of small absorption coefficient in the optical fiber transmission waveband, affinity with the optical fiber substrate material, easiness in filling and tunability of the refractive index under the action of an external field; the liquid is toluene, chloroform or ethanol; the gas is hydrogen.