62 results about "Optical heterodyne detection" patented technology

The present invention relates to optical heterodyne detection cavity ringdown spectroscopy. In one aspect the invention relates to an optical system (1) comprising a ring-down cavity cell (3) defining a resonant optical cavity, means for directing coherent light selected from the group consisting of continuous or quasi-continuous light into said optical cavity (8, 9, 10, 11, and 12), means for altering the resonant optical cavity so as to generate a frequency shift of the coherent light in the optical cavity (6, 7), means for coupling said coherent light into the optical cavity and means for decoupling the frequency shifted coherent light out of said optical cavity (5, 6, 7), means for optically combining (10, 11, 12) said decoupled frequency shifted coherent light with another portion of coherent light not in optical communication with the optical cavity and means for optical heterodyne detection (13) of the intensity of said combined light. A method for optical detection is also described as well as methods and apparatus for detecting a parameter of a sample.

A radar apparatus which can simply determine the sign of velocity of an object is provided. Laser light reflected by the object undergoes quadrature optical heterodyne detection performed by mixers, optical detectors, and a π/2 phase shifter, whereby I and Q component signals are output. A frequency analyzer performs FFT on a complex signal composed of the I component signal (real part) and the Q component signal (imaginary part) to thereby obtain its frequency spectrum. Since the frequency spectrum is calculated without being folded back even in a region where the frequency is negative, the sign of the Doppler frequency fd can be determined. When the Doppler frequency fd is positive, the sign of the velocity of the object is a direction toward the radar apparatus. When the Doppler frequency fd is negative, the sign of the velocity of the object is a direction away from the radar apparatus.

A heterodyne communication system uses coherent data modulation that is resistant to phase noise. In particular, a pilot tone and reference clock signal are transmitted along with the modulated data to form the basis of an electrical demodulation local oscillator at the receiver. The pilot tone and/or reference clock signal carry phase noise which is correlated with the phase noise in the data signal. At the receiver, the local oscillator is generated from the pilot tone and reference clock signal in a manner so that the local oscillator also has phase noise which is correlated with the phase noise in the data signal. Thus, the two noise components can be used to cancel each other during demodulation of the data signal using the local oscillator.

A new generation polarimetry apparatus and methodology is disclosed, which involve passing polarized light through a sample including a chiral analyte, where the analyte is under the influence of a periodically varying magnetic field. The apparatus also utilizes optical heterodyne detection and lock-in detection at higher order harmonics of the magnetic field modulation frequency to improve sensitivity and detection limits of optical properties of chiral analytes.

The invention discloses a one-dimensional modulation continuous variable quantum key distribution system based on heterodyne detection, and an implementation method thereof. Pulse laser is divided bya first beam splitter into signal light and local oscillator light at a sending end, an electro-optic phase modulator modulates the signal light, and the modulated signal light is attenuated to a quantum level by an adjustable light attenuator; the signal light at the quantum level is merged with the local oscillator light by a polarization coupler and is transmitted to a receiving end by a quantum channel; signal detection is performed on the receiving end by the heterodyne detection technology, the output information of a first differential amplifier and a second differential amplifier are sent to a data collection card and a computer system for collection and analysis processing, and a group of safe quantum keys is obtained on the sending end and the receiving end separately. Accordingto the one-dimensional modulation continuous variable quantum key distribution system, the modulation process in the continuous variable quantum key distribution system can be achieved just by one electro-optic phase modulator, thereby effectively simplifying the system structure, reducing the volume of the device, reducing the data processing volume and reducing the manufacturing cost.

The invention discloses a coherent anti-stokes raman scattering (CARS) optical comb spectrum detection method for improving the precision. The method comprises the steps of: after two femtosecond optical comb generators as a pumping-detecting light source and a stokes light source of a CARS system pass a CARS spectral measurement system, performing beat frequency and double-optical comb optical heterodyne detection on generated anti-stokes signal light and reference optical combs; eliminating the interference introduced by pumping light by utilizing a polarization dependent balance detection technology at a detecting part so as to realize the quick and real-time CARS optical spectrum detection with high sensitivity and high frequency resolution precision. The method provided by the invention can be used for effectively improving the resolution precision of spectral measurement, realizing the high-precision optical comb imaging within a wide spectral range, effectively inhibiting the environmental noises, eliminating the non-resonant background noise introduced by the pumping light, improving the time and frequency resolution precision and realizing the quick and real-time spectral detection.

A transmitter subsystem generates an optical signal which contains multiple subbands of information. The subbands have different polarizations. For example, in one approach, two or more optical transmitters generate optical signals which have different polarizations. An optical combiner optically combines the optical signals into a composite optical signal for transmission across an optical fiber. In another approach, a single optical transmitter generates an optical signal with multiple subbands. The polarization of the subbands is varied, for example by using a birefringent crystal. In another aspect of the invention, each optical transmitter generates an optical signal containing both a lower optical sideband and an upper optical sideband (i.e., a double sideband optical signal). An optical filter selects the upper optical sideband of one optical signal and the lower optical sideband of another optical signal to produce a composite optical signal.

The invention discloses a high resolution sensing system measuring beat-length and strain of a polarization maintaining optical fiber based on an optical frequency domain reflectometer (OFDR) system. The high resolution sensing system measuring the beat-length and the strain of the polarization maintaining optical fiber based on the OFDR system is characterized by comprising a linear frequency sweeping narrow line width light source, a polarizer, an interference system, a photoelectric detector, an optical heterodyne receiver and a signal processing system, wherein light produced by the linear frequency sweeping narrow line width light source is transformed to linearly polarized light through the polarizer and the linearly polarized light is injected to the interference system, the interference system is connected with the optical heterodyne receiver through the photoelectric detector, and the signal processing system is connected with the optical heterodyne receiver. The system is simple in structure, all-fiber-optical and controllable in linear frequency sweeping of a laser. By means of optical frequency domain detection, the problem that spatial resolution in time domain detection is limited by the optical pulse width and the data sampling rate is solved, high spatial resolution is obtained, and sensibility of the system can be improved and the dynamic range of the system can be enlarged through optical heterodyne detection.

In order to solve a problem that a traditional speed measurement and range finding system is poor in resisting influence, the invention provides a speed measurement and range finding system and method based on laser heterodyne detection. The speed measurement and range finding system comprises a laser, an optical path emission assembly, an optical reception assembly, a processor, a beam splitter, a beam combiner and a focal plane array detector; the input terminal of the beam splitter is connected to the output terminal of the laser; in two paths of optical signals which are split by the beam splitter, one path of optical signals is sent to an optical path emission assembly and is projected to a target object to be measured, and the other path of optical signals is sent into the beam combiner; the optical path reception assembly receives echo signals and converges the echo signals on an input terminal of the beam combiner after filtering; the beam combiner is used for performing coherent mixing on one path of optical signals which is split by the beam splitter and the echo signals to obtain a difference frequency signal; the focal plane array detector performs sampling, processing and analog to digital conversion on the difference frequency signal and then transmits the difference frequency signal to a processor; and the processor obtains speed and distance information of the target object to be measured.

The invention discloses a dynamic strain measurement method based on Brillouin phase shift detection. The dynamic strain measurement method comprises the following steps of dividing laser signals into two paths; after one path of signals are subjected to broadband frequency shift, generating optical heterodyne to detect local oscillator light wave and detection signal light wave, and synchronously injecting the local oscillator light wave and the detection signal light wave into a sensor fiber; after spectrum broadening, causing the other path of laser signals and a pulse generator to generate broadband Brillouin pulse pumping light wave, and injecting the broadband Brillouin pulse pumping light wave into the sensor fiber; setting a modulator to drive a voltage waveform to introduce linear chrip so as to obtain broadband laser, which is approximate to a rectangular spectrum, and extending a linear region with the Brillouin phase shift of the sensor fiber; carrying out coherent detection on the local oscillator light wave and the detection signal light wave through coherent demodulation of a beat frequency signal and a radio frequency signal which are generated by photovoltaic conversion so as to obtain the Brillouin phase shift of the detection signal light wave; demodulating information of a strain signal of the sensor fiber. The dynamic strain measurement method has the advantages that the signal to noise ratio is improved, the dynamic strain measurement range is increased and the detection speed is improved. The invention further discloses a dynamic strain measurement device based on the Brillouin phase shift detection.

The invention discloses a wireless digital communication receiving antenna based on microwave optical wave coherent conversion and a method thereof. wherein the communication receiving antenna comprises a laser,a digital signal modulator, a cesium bubble and beam combiner. a photoelectric detector and a digital signal demodulator, wherein the laser is used for generating local oscillation light required in optical heterodyne detection; wherein the digital signal demodulator modulates a digital signal to microwaves, the cesium bulb modulates and converts the microwaves into modulated light waves, the beam combiner superposes local oscillation light and the modulated light waves to generate an optical heterodyne signal, the photoelectric detector receives the optical heterodyne signal, and the digital signal demodulator is used for recovering the optical heterodyne signal to the digital signal. Coherent conversion of microwaves and light waves in the Rydberg atom six-wave mixing processis utilized, phase modulation of a digital signal on the microwaves is converted into phase modulation on the light waves, coherent demodulation is conducted on the modulated light waves through an optical heterodyne demodulation method to recover the digital signal, and therefore digital communication is achieved.

The invention discloses a light field matching heterodyne detection device and method based on an array detector, and belongs to the field of laser heterodyne detection, especially continuous heterodyne detection capable of utilizing the array detector for carrying out light field matching correction on signal light and local oscillator light. The signal-to-noise ratio of heterodyne detection can be improved. A light signal is received through the array detector, weighted stacking is carried out on receiving signals of all units of the array detector, and finally a total intermediate frequency signal obtained after stacking is output. In the target detection process, firstly, the signal light reflected back by a target is independently received, then the local oscillator light is independently received, weighting coefficients of all the detection units in the array detector are calculated according to detected light field distribution of the signal light and the local oscillator light, then the signal light and the local oscillator light are received at the same time, weighted stacking is carried out on detection signals output by the detection units according to the calculated weighing coefficients, and finally a composite signal obtained after stacking is output. Therefore, the effect of improving the signal-to-noise ratio of heterodyne detection and the effect of easy and convenient operation are achieved.

The invention discloses a Brillouin time-domain analysis system based on a Brillouin laser and automatic heterodyne detection and belongs to the technical field of optical fiber sensors. The Brillouin time-domain analysis system comprises a laser, an isolator, a coupler, a first Er-doped fiber amplifier, the Brillouin laser, a signal generator, a phase modulator, sensing optical fiber, a circulator, a second Er-doped fiber amplifier, a pulse generator, a scrambler, a photovoltaic conversion module, and a digital signal processing module. The Brillouin time-domain analysis system is characterized in that the Brillouin laser is used for realizing broadband frequency shift for incoming laser, the phase modulator is used for modulating laser after frequency downward shift so as to generate double-sideband signals, the signals and pulse pump light generated by the pulse generator generate stimulated Brillouin scattering effect in the sensing optical fiber, and optical signals after action conducts automatic heterodyne detection through the photovoltaic conversion module. The Brillouin time-domain analysis system is weakened in phase noise, improves the signal to noise ratio of detection signal, ensures the temperature/strain measurement accuracy of a whole section of the sensing optical fiber, and is made to be more compact.

The invention relates to a long-distance optical fiber Bragg grating sensing method and device based on self-heterodyne detection. A single frequency light beam sent from a wavelength adjustable narrow line width laser is split into two parts of light beam with the same intensity after passing through a triport optical fiber coupler, one part of the light beam passes through a scrambler and is used as an intrinsic light, and the other part of the light beam passes through a light pulse modulation module and is modulated into a pulse detection light; and the detection pulse light passes through an optical isolator, enters a segment of a long-distance transmission optical fiber, and then enters a sensing optical fiber grating array through a far-end light circulator; and the signal reflected from the optical fiber grating shifts frequency of the returned reflection sensing signal through a frequency shift module and then enters a four-port optical coupler together with the intrinsic light, and the generated coherent light signal enters a balance photoelectric detector through the other two ports of the optical coupler and is converted to an electrical signal. The electrical signal received and converted by a signal collection analysis and control module is collected and analyzed to obtain the time domain track of the sensing signal, and the peak power is the power of the coherent signal.

The invention discloses a heterodyne detection system for wireless laser communication. The system comprises an optical receiving antenna, an optical fiber coupling module, a 3dB coupler, a photoelectric detector, and a digital interface of a digital signal processing module, which are connected sequentially. The system further comprises a local oscillator laser and a modulating circuit. The local oscillator laser is connected with the 3dB coupler, and a decoder module is connected with the digital interface. Heterodyne of a subcarrier at a sending terminal and that at a receiving terminal is realized at the receiving terminal to generate a cross item of intermediate frequency. Base band information is restored by demodulating an intermediate frequency signal. The system and method solve the problem that current optical heterodyne detection structure is complex and hard to realize, and have the characteristics of remoter communication distance, larger capacity, easier implementation and the like.

The invention discloses a phase distance measuring device based on laser heterodyne detection. The phase distance measuring device comprises an infrared optical fiber laser device, a first optical fiber coupler, a first electro-optical intensity modulator, a second electro-optical intensity modulator, a telescope, an optical fiber collimator, a second optical fiber coupler, an A/D acquisition circuit and a computer, and further comprises a signal generation circuit is used for generating an intermediate-frequency sinusoidal signal and an ultrahigh-frequency sinusoidal signal, a first automaticgain control circuit, a second automatic gain control circuit, a photoelectric detector and a photoelectric detection conversion circuit. The phase distance measuring device can effectively solve theproblem of phase fluctuation caused by light intensity change and detector phase nonuniformity in distance measurement by adopting an ultrahigh frequency modulation phase method, and has the advantage of high measurement precision. The invention further discloses a phase ranging method based on laser heterodyne detection.

The embodiment of the invention discloses an optical heterodyne method cavity ring down spectral measurement device and method. The measurement device comprises a laser light source for generating a laser beam, a modulation optical path mechanism, a passive resonant cavity for receiving the laser beam modulated by the modulation optical path mechanism and performing interference superposition on the laser beam, an optical heterodyne detection mechanism for receiving the laser beam subject to the interference superposition and generating an electrical signal, a data processing mechanism for receiving the electrical signal and determining a relationship between the electrical signal and a preset threshold, and if the electrical signal is greater than the preset threshold, the data processingmechanism sends an instruction of turning off the laser light source, collecting and drawing a ring down curve via a data collection circuit, and calculating the concentration of trace substance to be measured. By adoption of the measurement device and method, the measurement accuracy can be improved, the operation is simple, and the cost is low.

A branch portion 101 branches an inputted electrical signal into an in-phase signal and an opposite phase signal which have an opposite relation as to a phase. A first FM laser 104 converts the in-phase signal into an optical frequency-modulated signal (a first optical signal) having a center wavelength λ1 and then outputs the resultant signal. A second FM laser 105 converts the opposite phase signal into an optical frequency-modulated signal (a second signal) having a center wavelength λ2 and then outputs the resultant signal. The two optical signals are combined and then inputted into an optical-electrical converting portion 106. The optical-electrical converting portion 106 subjects the inputted optical signals to optical heterodyne detection by its square-law detection characteristic, and outputs a beat signal between the two optical signals which is a wide-band FM signal at a frequency corresponding to a wavelength difference Δλ(=|λ1−λ2|) between the first optical signal and the second optical signal. It is thus possible to increase frequency deviation of the outputted FM signal and thus greatly improve a CNR.

The invention discloses a device and a method for restraining a de-coherence effect in heterodyne detection based on a CCD camera. The device comprises a laser device, a first beam splitter, a local oscillator light path acousto-optic frequency shifter, a signal light path acousto-optic frequency shifter, a second beam splitter, an optical antenna, a reflector, a third beam splitter, the CCD camera, an image signal processing system and a signal-to-noise ratio feedback system. The frequency of an intermediate-frequency heterodyne signal is reduced to be in a range detectable for the CCD camerathrough the two frequency shifters; a phase difference between the optical heterodyne signals of different pixels is recognized through an image processing technology, and an image signal output sequence is adjusted according to the phase difference, so that all pixel output signals are subjected to in-phase stacking and output; and meanwhile, a heterodyne signal output sequence can be adjusted again according to a signal-to-noise ratio of the heterodyne signal, and the signal-to-noise ratio of the optical heterodyne signal can be calculated again according to the adjusted heterodyne signal output sequence, until the output signal-to-noise ratio of the optical heterodyne signal is larger than or equal to a threshold value, so that the signal-to-noise ratio of the heterodyne detection is obviously improved.

Provided is an SAIT distance imaging speckle effect suppression method. The bandwidth of linear frequency-modulation pulse signals emitted by a laser device is expanded to N (N is larger than or equal to 2) times of the bandwidth needed by resolution ratio design, and optical heterodyne detection is carried out on echo signals and local oscillator signals to obtain light current data needed for imaging. When data processing is carried out, imaging data obtained after bandwidth expanding are divided into N parts in the distance direction, distance dechirping and orientation focusing imaging are carried out on the data, and ultimately N relatively independent data are produced. Incoherent superposition average is conducted on the N relatively independent target images, and finally images are output. Compared with speckle suppression after uniformization, average strength and contrast of the images are improved to some extent. The method plays a certain role in reducing the speckle effect in an SAIT.

In an optical heterodyne surface plasma wave detecting method and apparatus, light that contains correlated P₁ and P₂ wave components (TM waves) is directed to a total reflective component such that two surface plasma waves are generated at an interface of a metal film and a test object. Light reflected from the total reflective component is detected to obtain an optical heterodyne test signal that is compared with an optical heterodyne reference signal to determine changes in at least one of amplitude and phase of the optical heterodyne signal relative to the optical heterodyne reference signal.