178 results about "Heterodyne detection" patented technology

An improved confocal microscope system is provided which images sections of tissue utilizing heterodyne detection. The system has a synthesized light source for producing a single beam of light of multiple, different wavelengths using multiple laser sources. The beam from the synthesized light source is split into an imaging beam and a reference beam. The phase of the reference beam is then modulated, while confocal optics scan and focus the imaging beam below the surface of the tissue and collect from the tissue returned light of the imaging beam. The returned light of the imaging beam and the modulated reference beam are combined into a return beam, such that they spatially overlap and interact to produce heterodyne components. The return beam is detected by a photodetector which converts the amplitude of the return beam into electrical signals in accordance with the heterodyne components. The signals are demodulated and processed to produce an image of the tissue section on a display. The system enables the numerical aperture of the confocal optics to be reduced without degrading the performance of the system.

The invention relates to a method and an apparatus for agile RF spectrum monitoring in a radio system with dynamic frequency access. It provides a spectrum monitor based on non-coherent heterodyne detection that utilizes a DDS signal generator to digitally generate a reference signal at a variable reference frequency for mixing with an input RF signal received from an RF antenna, a pass-band filter and a log amplifier for obtaining energy estimates at a monitored transmission frequency corresponding to the reference frequency. A processor is provided for adaptively selecting sets of monitored transmission frequencies, for controlling the DDS signal generator, and for processing obtained spectral energy estimates to assess spectral usage data.

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.

An optical communications system includes a receiver subsystem with at least two heterodyne receivers. The receiver subsystem receives a composite optical signal having two or more subbands of information and corresponding tones. An optical splitter splits the composite optical signal into optical signals. Each optical signal includes a subband(s) and corresponding tone. Each heterodyne receiver receives an optical signal. The receiver includes a heterodyne detector coupled to a signal extractor. The heterodyne detector mixes the optical signal with an optical local oscillator to produce an electrical signal which includes a frequency down-shifted version of the subband and the tone of the optical signal. The signal extractor mixes the frequency down-shifted subband with the frequency down-shifted tone to produce a frequency component containing the information.

The invention provides a speed measurement and distance measurement system and a speed measurement and distance measurement method based on pseudo-random code phase modulation and heterodyne detection. The basic principle is that laser is divided into two parts via a coupler. The majority part is subjected to phase modulation through an electro-optic phase modulator according to a pseudo-random code signal and is transmitted by a telescope as emergent laser; the other part is subjected to frequency shift through an acousto-optic frequency shifter and is used for coherent detection as a local oscillator signal; a laser echo signal and the local oscillator signal are subjected to a coherent action in the coupler, an electric signal is converted through a photoelectric balance detector, and a digital signal is converted through a dual-channel AD acquisition card; the other channel of the dual-channel AD acquisition card acquires a driving signal of the electro-optic phase modulator; and the acquired two ways of signals are subjected to signal processing in a computer. The invention provides a new method of simultaneously acquiring the target speed and the distance information in a high-precision mode.

The invention discloses a 2 mu m all-fiber coherent laser Doppler wind finding radar system, which consists of a 2 mu m off-axis Cassegrain optical antenna system, a 2 mu m laser beam splitting system, a 2 mu m seed implantation laser amplifier, a 2 mu m monitoring detector system, and a 2 mu m balanced heterodyne detection system. The system overcomes the defect of ambient interference existing in a free space optical path, overcomes the influence of shot noise on heterodyne reception signal-to-noise ratio, and solves the problems of all fiber and miniaturization of the 2 mu m all-fiber coherent laser Doppler wind finding radar system, so that the 2 mu m all-fiber coherent laser Doppler wind finding radar system has a more compact structure. In addition, the system has the characteristics of safe laser for human eye, optical path connection by adopting flexible optical fiber devices, high operability and stability, low cost, good real time, long effectively measured distance, high measurement accuracy (speed measurement and distance measurement) and the like, and has high practical value in the field of coherent laser Doppler wind finding radar.

A heterodyne detection technique for highly localized IR spectroscopy based on an AFM. A pulsed IR source illuminates a sample and causes contact resonance of an AFM probe, which is a function of localized absorption. The probe is operated in intermittent contact mode and is therefore oscillated at a resonance frequency. A secondary oscillation is mixed in to the probe oscillation such that the sum of the secondary oscillation and the IR source pulse frequency is near another harmonic of the probe. A mixing effect causes measurable probe response at the other harmonic allowing data to be taken away from the pulse frequency, resulting in background effect rejection and improved spatial resolution.

The invention discloses a digital-analog hybrid heterodyne detection receiving device applicable to space laser communication and a data method. The digital-analog hybrid heterodyne detection receiving device applicable to space laser communication comprises a primary frequency conversion module, a secondary frequency conversion module and a demodulator module, and is characterized in that the primary frequency modulation module comprises a preposed optical amplifier, an optical mixer, a optical balance detector, an optical local oscillator and a Doppler compensation module, Doppler compensation forms voltage signals used for compensating the Doppler frequency shift, and the voltage signals are outputted to the optical local oscillator; the optical local oscillator forms optical local oscillation signals; the optical mixer receives optical signals and the optical local oscillation signals and acquires low-intermediate frequency IF optical signals through mixing; the optical balance detector is connected with an output end of the optical mixer, converts the low-intermediate frequency IF optical signals into electric intermediate-frequency signals and outputs the electric intermediate-frequency signals to the secondary frequency conversion module; and the secondary frequency conversion module performs amplitude-limiting sampling on the electric intermediate-frequency signals and outputs the sampled signals to the demodulator module, and the demodulator module demodulates the sampled signals and outputs demodulated data.

Systems and methods for precision phase noise measurements of radio frequency (RF) oscillators are provided. An RF signal under test can be modulated on a continuous wave (cw) laser carrier frequency via generation of modulation sidebands using an appropriate modulator. A photonic delay line can be implemented as a self-heterodyne detection system for the phase noise, allowing for photonic down-conversion of the phase noise measurement to direct current (DC). The self-heterodyne detection system allows detection outside of any 1/f noise issues. Ultra-low phase noise detection for RF frequencies in a range from below 1 GHz to beyond 100 GHz is enabled with a low noise floor in the whole frequency range. Higher-order modulation sidebands can further reduce the noise floor of the system. Ultra-low noise RF (microwave) output can be generated. The RF signal under test can be generated by a dielectric resonance oscillator or opto-electronic oscillator.

The invention relates to the field of optical fiber sensing, specifically a phase-light time domain reflection device and method based on heterodyne detection phase demodulation. The device consists of a narrow linewidth laser, an optical fiber coupler with a coupling model of 1*2, a polarization controller, a sound-light modulator, an erbium-doped optical fiber amplifier, a narrow-band optical fiber filter, a first variable optical attenuator, a three-port circulator, a sensing optical fiber, an optical fiber coupler with a coupling model of 2*1, a photoelectric detector, a signal collection and processing module, an arbitrary waveform generator, a power amplifier, and a second variable optical attenuator. The device and method enable the heterodyne detection phase demodulation to be combined together, achieve external vibration sensing through direct phase demodulation, and are higher in sensitivity. In addition, the device and method employ a brand new direct phase modulation method to sense the external vibration, so the positioning method, compared with a conventional method, of each vibrating point is different.

A high frequency power supply device and power supplying method are disclosed, which can rapidly and accurately control power used for generation of plasmas. The device includes a first high frequency power supply, providing power at frequency f1, and a second high frequency power supply providing power at frequency f2 (f1>f2). The first power supply includes: a first high frequency oscillator, which excites the high frequency power at the first frequency and has a variable frequency; a first power amplification block, which amplifies the power of the high frequency oscillator; a heterodyne detection block, which performs heterodyne detection of a reflected wave; and a first control block, which receives a signal after detection of the heterodyne detection block and a traveling wave signal, and controls an oscillating frequency of the first high frequency oscillating block and an output of the first power amplification block.

The invention provides a laser radar system for tracking and identifying a low, small and slow object based on the laser micro-Doppler effect, belongs to the field of laser radar detection, and aims at solving the problem that a present micro-Doppler microwave radar is interfered by ground clutters seriously. A laser source module outputs relatively strong signal light and relatively weak local oscillation light, a frequency shift modulation module carries out frequency shift on the signal light, and the signal light after frequency shift is input to a heterodyne detection module; the heterodyne detection module uses the signal light after frequency shift to scan a target area and obtains a target echo; beam combination is carried out on the target echo and the local oscillation light, the light after beam combination is detected, an intermediate-frequency signal is collected and processed, signal spectral distribution including target motion and micro-motion information is obtained, whether an object is the low, small and slow object is determined, and if YES, the speed and distance of the object are obtained; and the object is tracked according to the obtained speed and distance of the object.

Repeaterless transmission of differential phase-shift keying (DPSK) at 10.7 Gb/s over at least 304 km of standard single-mode fiber is obtained through use of a coherent optical receiver including electronic dispersion compensation. High receiver sensitivity and high tolerance to nonlinearities of DPSK, allow overcoming a total link loss of 58 dB with a 3 dB system margin, through use in the receiver of heterodyne detection to preserve phase distortions resulting from chromatic dispersion, to permit electronic dispersion compensation to be used.

A process for measuring speed or vibration characteristics using a LIDAR device allows the separation of a useful contribution and an interfering contribution in a backscattered signal. To this purpose, a phase characteristic of an optical wave emitted in the direction of a target volume is modulated. The interfering contribution, which originates from a source at a distance from the target volume, appears with variable shifts of said phase characteristic in a heterodyne detection signal. An accumulation then isolates the useful contribution, from which a result is obtained for the speed or vibration measurement. The process can be implemented with a frequency modulation or phase modulation of the optical wave.

The invention provides a wavelength division multiplexing OFDM-PON transmission system based on remote difference frequency detection. The system comprises an optical line terminal, a feed-in type optical fiber network, a far-end node, multiple distribution type optical fiber networks and multiple optical network units which are connected in turn. The optical network units are used for processing a downlink OFDM signal and extracting a specific X-polarized optical carrier used for modulating an uplink OFDM signal. Heterodyne detection of the downlink OFDM signal and a downlink local oscillator optical signal is realized by the optical network units, and the uplink OFDM signal is outputted to the far-end node and the optical line terminal via the distribution type optical fiber networks simultaneously. The optical line terminal receives the uplink OFDM signal and performs self-homodyne detection on the uplink OFDM signal. With adoption of an OFDM and WDM reuse mode, effective transmission channels and data transmission rate are increased so that larger transmission capacity is realized. Meanwhile, receiving sensitivity is enhanced by adopting the difference frequency detection technology so that transmission in longer distance is realized.

The invention relates to a self-heterodyne single-ended vector BOTDA-based dynamic strain measurement method and apparatus. A laser outputs three paths of light; lower frequency-shift continuous light is generated at the first path; the light at the second path is used as pulse substrate light; and double-sideband-structure-based coding pulse light is generated at the third path. The synthesized light from the three paths enters from one end of a sensing fiber. Back Rayleigh scattering light generated by the light from the first path and the second path in the sensing fiber is used as local oscillator light and detection light respectively; the two kinds of light are led into a photoelectric detector to carry out self-heterodyne detection and quadrature and in-phase components in an obtained electric signal are extracted; according to a function relationship between the quotient of the two kinds of components and a stimulated Brillouin scattering phase shift, a stimulated Brillouin scattering phase shift value is obtained. And then a corresponding dynamic strain value is demodulated based on a corresponding relation curve of the stimulated Brillouin scattering phase shift and the dynamic strain. According to the invention, the structure is simple; the application becomes convenient; the reliability and stability are high; non-destructive high-sensitivity and high-signal-to-noise-ratio dynamic strain measurement can be realized.

The invention relates to the field of optical fiber sensing technology, in particular to a Brillouin light time domain analysis device and a method based on dual-wavelength polarization orthogonal light. Two beams of polarization orthogonal light with different wavelengths are used as pump light, so a four-wave mixing phenomenon between the two beams of the pump light is completely restrained and the signal to noise ratio of the tail end of a sensing optical fiber can be truly increased by 3dB. In addition, according to the invention, a direct detection mode is adopted on a detection end, so compared with a Brillouin light time domain analysis device and a method in which a heterodyning detection mode is adopted, quite expensive detection devices and time-consuming demodulation processes are omitted; and development of a Brillouin light time domain analysis system towards a dynamic measuring direction is facilitated.

The invention discloses a laser heterodyne device based on photon counting statistics of MPPC (multi-pixel photon counter), relates to the field of laser active detection research and aims at solving the problem of contradiction between the power of a light source and a coherent phase in the existing laser heterodyne detection. According to the device disclosed by the invention, a light beam emitted by a laser passes through a laser beam splitter mirror and then is reflected and transmitted, a reflected light beam passes through an acousto-optic modulator for acousto-optic diffraction and then is incident to a polarization beam-splitting flat plate, and the light beam after passing through the polarization beam-splitting flat plate is reflected to a laser coupling lens; the transmitted light beam passes through a laser beam expanding lens and then is incident to the surface of a rotating diffused reflection target, echo photons which are collected by a laser echo receiving telescope is subject to filtering processing through an optical narrow-band filter, and the light beam after passing through the polarization beam-splitting flat plate is transmitted to the laser coupling lens; and electric signals are received by a signal receiving device after the light beam is focused to the surface of the MPPC and optical interference occurs. The MPPC is larger in the receiving surface, and a detector can work in a non-high-voltage state so as to facilitate the implementation of signal receiving.

The invention discloses a two-way wired/wireless hybrid optical access method and system based on homodyne/heterodyne detection. The two-way wired/wireless hybrid optical access method includes the steps of modulating a digital signal base band on an optical carrier through an I/Q modulator in a junction center, transmitting the digital signal base band to a mixed ONU through a downlink transmission link, providing coherent light vibration of homodyne reception and heterodyne reception by using a tunable laser in the mixed ONU, using the vibration source as the optical carriers of uplink wired/wireless data signals, carrying the wired access uplink signals and the wireless access uplink signals through a base band I/Q modulation method and a single side band modulation method respectively, using the laser as the vibration source in the junction center to carry out coherent reception, and finishing the full-duplex transmissions of the wired/wireless access signals between the junction center and the mixed ONU and the photovoltaic conversion of the wired/wireless access signals based on the homodyne/heterodyne detection. The two-way wired/wireless optical access method enables the flexible selection of mixed ONU access methods to be increased and achieves high-rate data transmission, sending and receiving, and the spectrum efficiency is high.