64 results about "Chirp rate" patented technology

The invention discloses a microwave photon MIMO radar detection method comprising modulating M intermediate-frequency linear frequency-modulated signals with the same bandwidth and chirp rate and non-overlapped frequency on M optical carriers with different wavelengths to generate M optical signals where only the positive and negative second-order sidebands are retained; merging the M optical signals by an optical wavelength division multiplexer and then dividing a combined optical signal into two channels; dividing the optical signal in one channel into N reference light beams; subjecting theoptical signal in the other channel to photoelectric conversion and separating and transmitting M orthogonal linear frequency-modulated signals therein; receiving, by N receiving antennas, the targetreflected signals, performing de-chirp processing and wavelength demultiplexing, and subjecting the obtained M optical signals to photoelectric conversion, low-pass filtering and analog-to-digital conversion to obtain M*N digital signals, processing the digital signals to obtain a target detection result. The invention also discloses a microwave photon MIMO radar system. The method can greatly improve the range resolution and azimuth resolution of the radar system.

Techniques for recovering optical spectral features include receiving a detected time series that represents a temporally varying intensity of an optical signal. The optical signal is formed in response to an interaction between a target optical spectrum and a chirped optical field. The chirped optical field is an optical field that has a monochromatic frequency that varies in time. The target optical spectrum is an optical frequency dependent optical property of a material or device. A phase correction factor is determined based only on one or more properties of the chirped optical field. The detected time series is corrected based on the phase correction factor to produce an output time series that reproduces in time a shape of the target spectrum in frequency. These techniques allow for fast measurement of spectral features and eliminate the need for prior knowledge of the target optical spectrum to adjust the chirp rate.

A system and method for controllably chirping electromagnetic radiation from a radiation source includes an optical cavity arrangement. The optical cavity arrangement enables electromagnetic radiation to be produced with a substantially linear chirp rate and a configurable period. By selectively injecting electromagnetic radiation into the optical cavity, the electromagnetic radiation may be produced with a single resonant mode that is frequency shifted at the substantially linear chirp rate. Producing the electromagnetic radiation with a single resonant mode may increase the coherence length of the electromagnetic radiation, which may be advantageous when the electromagnetic radiation is implemented in various applications. For example, the electromagnetic radiation produced by the optical cavity arrangement may enhance a range, speed, accuracy, and/or other aspects of a laser radar system.

The spurious-free dynamic range of a wideband radar system is increased by apportioning de-ramp processing across analog and digital processing domains. A chirp rate offset is applied between the received waveform and the reference waveform that is used for downconversion to the intermediate frequency (IF) range. The chirp rate offset results in a residual chirp in the IF signal prior to digitization. After digitization, the residual IF chirp is removed with digital signal processing.

Methods and systems for communication systems are disclosed. Chirp signals generated according to a chirp rate and carrier frequency are used for communication. The chirp rate can be determined by solving integrals or by simulation of transmission parameters. A chirp signal is transmitted from a base station and delayed versions of the chirp signals are created. The delayed versions are generated by the chirp signal reflecting off of reflectors. A receiving station receives an incoming signal. The incoming signal includes the LOS signal plus delayed versions, noise and/or interference. Unwanted signals, either LOS or delayed versions, noise and/or interference are removed from the incoming signal to obtain the desired chirp signal. Using the chirp rate, the chirp signal is converted to a corresponding digital signal.

A method apparatus for sensing gases using a semiconductor diode laser spectrometer, the method comprising: introducing a sample gas into a non-resonant optical cell ( 17 ); applying a step function electrical pulse ( 19 ) to a semiconductor diode laser ( 20 ) to cause the laser ( 20 ) to output a continuous wavelength chirp for injecting ( 16 a) into the optical cell ( 17 ); injecting ( 16 a) the wavelength chirp into the optical cell ( 17 ); using the wavelength variation provided by the wavelength chirp as a wavelength scan, and detecting ( 23 ) light emitted from the cell ( 17 ), wherein a chirp rate is selected to substantially prevent light interference occurring in the optical cell ( 17 ).

The invention discloses a fast estimation method for a non-uniform rotating target motion parameter. The method comprises specific steps: an echo signal in a single distance unit is modeled into a QFMsignal; a correlation function is constructed, the QFM signal is converted to a time-chirp distribution plane, and minimum entropy criterion-based weighted least squares Radon transform is adopted toestimate secondary chirp; the estimation accuracy and the robustness of the algorithm in a low signal-to-noise ratio environment are improved effectively at the same time; TFD-based weighted least squares Radon transform is adopted to estimate linear chirp, and through filtering, cross-term interference is eliminated; and according to the geometric information in a distance-Doppler domain, the center frequency is directly estimated. The calculation amount of the target motion parameter estimation process can be significantly reduced, the influences of transmission errors on estimation of eachmotion parameter are effectively avoided, and the final target parameter estimation precision and the ISAR imaging quality are ensured.

An ultra-short pulse time waveform and chirp rate measuring device comprises a first coupling mirror, a second coupling mirror, a spectroscope, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, a cross-correlation crystal, a frequency doubling crystal, a fourth reflecting mirror, a fifth reflecting mirror, a diffraction element, a photoelectric detector and a computer. Front-edge and rear-edge high-resolution ratio measuring of ultra-short pulses is achieved through a cross-correlation method to obtain time waveforms and pulse widths. Ultra-short pulse spectrum measuring is achieved through diffraction elements orthogonal to the time axis to obtain the spectrum width, and accordingly, the chirp rate of measured pulses can be obtained based on the pulse width and the spectrum width, the requirement of physical experiments for the time waveform measuring and the requirement of an Ultra-short pulse laser system for measuring of the chirp rate are met conveniently.

The invention relates to high-order dynamic adjustable dispersion compensation equipment and a dispersion compensation method thereof. In the prior art, the chirp rate of fiber grating can only be linearly changed. In the equipment, the fiber grating and a II port of a fiber circulator are in light connection; a III port of the fiber circulator and a single-port of a fiber coupler are connected; one port of a dual-port of the fiber coupler is in light connection with the input end of a dispersion detector; the input end of the dispersion detector is in signal connection with the input end of a controller; the output end of the controller is in signal connection with the input end of a controllable power supply; and the output end of the controllable power supply is in electrical connection with a semiconductor refrigeration element. The method comprises the following steps: the dispersion compensation equipment is accessed to two ends of the fiber communication network; the controllerperforms analysis feedback according to the measurement parameters of the dispersion detector, and changes the injection current of each semiconductor refrigeration element so as to change the temperature field distribution in a V-shaped groove and realizing the aim of dispersion compensation. The equipment has small module dimension, and can achieve high-order and dynamic adjustment of dispersion.

The invention is applicable to the field of communication, and provides a sound wave communication method based on multi-system chirp-rate keying modulation. The method comprises signal transmission and signal reception, and comprises the steps of generating a modulated signal by performing channel coding and chirp-rate keying modulation on a digital signal needing to be sent, and inserting a synchronization head before the modulated signal to form a transmission signal; and acquiring the original digital signal by performing synchronization processing on the received signal and demodulating the signal subjected to synchronization processing, wherein the synchronization processing comprises frame synchronization processing and/or code element synchronization processing. According to the method provided by the embodiment of the invention, the signal is modulated by using chirp-rate keying modulation, so that an information transmission rate is high; the received signal is subjected to frame synchronization and/or code element synchronization, and thus signal synchronization accuracy is improved to a certain extent, and signal receiving efficiency is further improved.

The invention discloses a high-speed distributed optical fiber sensing system and method based on fractional Fourier transform. A laser module generates an optical signal, a coupler inputs the opticalsignal into an optical signal modulation module and a signal detection module, and the optical signal modulation module modulates the optical signal into x chirped pulse optical signals with different chirp rates and sends the x chirped pulse optical signals to a to-be-detected sensing optical fiber; after passing through the sensing optical fiber to be detected, mixed scattered light signals generated by x chirped pulse light signals with different chirp rates are sent to the signal detection module; the signal detection module obtains a beat frequency signal by using the optical signal sentby the coupler and the mixed scattered light signal, and the signal demodulation module demodulates the beat frequency signal and then outputs a result. According to the invention, different chirp rates can be set under the same sensing bandwidth, the occupied system sensing bandwidth is reduced, the spectrum utilization rate is increased, the measurement speed is increased by x-1 times, measurement can be completed only through a single channel, and the system complexity is reduced.

A light source apparatus emitting two pulse lights of which center wavelengths are different from each other, and an information-obtaining apparatus for use with a light source apparatus, are provided. In at least one embodiment, the light source apparatus may include a light source configured to emit a first pulse light of which a center wavelength is variable, a nonlinear optical medium configured to generate a second pulse light having a center wavelength different from the first pulse light in response to incidence of the first pulse light, and a wavelength dispersion adjustment device configured to give a wavelength dispersion to the second pulse light, wherein a wavelength dispersion amount given by the wavelength dispersion adjustment device to the second pulse light is variable. In one or more embodiments, a light source apparatus may include an adjustment unit to adjust a chirp rate of the second pulse light.

Features that may be computed from a harmonic signal include a fractional chirp rate, a pitch, and amplitudes of the harmonics. A fractional chirp rate may be estimated, for example, by computing scores corresponding to different fractional chirp rates and selecting a highest score. A first pitch may be computed from a frequency representation that is computed using the estimated fractional chirp rate, for example, by using peak-to-peak distances in the frequency distribution. A second pitch may be computed using the first pitch, and a frequency representation of the signal, for example, by using correlations of portions of the frequency representation. Amplitudes of harmonics of the signal may be determined using the estimated fractional chirp rate and second pitch. Any of the estimated fractional chirp rate, second pitch, and harmonic amplitudes may be used for further processing, such as speech recognition, speaker verification, speaker identification, or signal reconstruction.

The invention provides a filter with variable bandwidth or wavelength interval based on chirp rate tuning of fiber bragg grating belongs to optical fiber filter technology field, relates to fiber bragg grating and multiplex optical fiber communication system field. The filter applies strength cantilever girder (2) turning structure of right triangle, the cantilever girder (2) is fixed through splint (1), chirp fiber bragg grating or sampling chirp fiber bragg grating (3) is sticked on side surface of right angle edge in the cantilever girder (2) inclining for 3 to 45 DEG. Applying force or deflection along the vetical direction of free end of the cantilever girder (2), to make the cantilever girder (2) bend for changing chirp rate of the chirp fiber bragg grating (3), and finally reflection peak interval of the sampling chirp fiber bragg grating or reflection spectrum bandwidth of the chirp fiber bragg grating is changed, so as to achieve effect of selecting reflection filter of specific wavelength or wavelength range. The filter has advantages of large bandwidth turning range, high precision, simple structure, low cost, and the filter is siutable for various optical fiber network system especially wavelength division multiplexing system.

Techniques for reconfiguring spectral features stored in a medium based on a two-state atomic system with transition dipole moment μ includes causing a chirp to pass into the medium. The chirp includes a monochromatic frequency that varies in time by a chirp rate κ over a frequency band B_R during a time interval T_R. The amplitude A_R of the chirp is constant over B_R and equal to

A_R=(hbar/μπ)√{square root over ((κ ln [2/ε]))},

The term hbar is reduced Plank's constant, ln is a natural logarithm function, and π is a ratio of a circumference of a circle to a diameter of the circle. For ε<<1, the atomic-state populations in the two states are inverted. For ε=1, prior atomic-state populations are erased, with final populations equal in the two states, regardless of populations before erasure.

The invention belongs to the field of radar signal processing, and discloses an SAR radar moving object imaging method. The SAR radar moving object imaging method comprises the steps of acquiring echo data which are received by an SAR radar, performing distance direction compression on the echo data, making the echo data after distance direction compression pass through a low pass filter, and separating clutter data and detachable data in the echo data after distance direction compression; forming a ground scene picture from the clutter data; performing moving object parameter estimation on the detachable data, obtaining a Doppler central frequency estimated value and a Doppler chirp rate estimated value, and constructing a reference function according to the Doppler central frequency estimated value and the Doppler chirp rate estimated value; performing time domain multiplication or frequency domain convolution on the reference function and the detachable data, thereby obtaining a moving object imaging picture; and adding the ground scene picture with the moving object imaging picture, thereby obtaining an SAR radar moving object imaging result. The SAR radar moving object imaging method can be used for performing fine imaging on the moving object.

The invention discloses a chirp spectral pattern cavity-less optical fiber Fabry-Perot filter. The filter is characterized in that the filter comprises a multi-mode micro-nano optical fiber cladding,a multi-mode micro-nano optical fiber core and a Bragg grating; the multi-mode micro-nano optical fiber cladding is an outermost layer. According to the along-axis cross section of the multi-mode micro-nano optical fiber cladding, transition is realized from a uniform region with a constant radius to a micro-nano region with a gradually-changed radius, and again transition is realized from the micro-nano region with the gradually-changed radius to the other uniform region with a constant radius. The multi-mode micro-nano optical fiber core is an inner layer and is covered by the multi-mode micro-nano optical fiber cladding. According to the along-axis cross section of the multi-mode micro-nano optical fiber core, transition is realized from a uniform region with a constant radius to a micro-nano region with a gradually-changed radius, and again transition is realized from the micro-nano region with the gradually-changed radius to the other uniform region with a constant radius. The Bragg grating is a continuously-inscribed and equal-period Bragg grating which covers all the micro-nano region of the multi-mode micro-nano optical fiber core. With the chirp spectral pattern cavity-less optical fiber Fabry-Perot filter provided by the invention adopted, a chirp spectral pattern which can change in a free spectral range can be realized within a relatively large wavelength range, anda relatively large chirp rate can be realized. The chirp spectral pattern cavity-less optical fiber Fabry-Perot filter has the advantages of compact structure and easiness in manufacture.

The invention discloses a radio frequency time delay rapid measurement device based on chirp signal quadrature demodulation. The device comprises a chirp signal generator, a to-be-measured device, ananalog-to-digital converter, a processor and a memory; the chirp signal generator adopted by the device emits chirp signals with adjustable frequency ranges and adjustable chirp rates, so the rapid measurement of time delay in different frequency ranges is achieved, and the measurement range of the system is large; meanwhile, the time delay of the frequency converter is measured, and extra reference signals are not needed; the system structure is simple, and the anti-jamming capability is high; moreover, the method achieves the extraction of the time delay through the quadrature demodulation technology, avoids the phenomena of phase ambiguity and spectrum leakage in a conventional time delay detection process, and greatly improves the time delay detection precision.