389 results about "Frequency standard" patented technology

A communication system adapted to use wavelength (frequency) division multiplexing for quantum-key distribution (QKD). In one embodiment, a communication system of the invention has a transmitter coupled to a receiver via a transmission link. The transmitter has (i) a first optical-frequency comb source (OFCS) adapted to generate a first plurality of uniformly spaced frequency components and (ii) a first multi-channel optical modulator adapted to independently modulate each component of the first plurality to produce a quantum-information (QI) signal applied to the transmission link. The receiver has (i) a second OFCS adapted to generate a second plurality of uniformly spaced frequency components and (ii) a second multi-channel optical modulator adapted to independently modulate each component of the second plurality to produce a local-oscillator (LO) signal. Each of the first and second optical-frequency comb sources is referenced to a frequency standard such that the frequency components generated by these comb sources have substantially the same frequencies. The receiver employs a multi-channel homodyne detector adapted to process interference signals produced by combining the LO signal with the QI signal to ascertain quantum information carried by the QI signal.

A hyper-spectral analysis method for characterizing or distinguishing diverse elements within hyper-spectral images. A plurality of patches of pixels from within the hyper-spectral images are extracted as being patches around pixels of the elements to be characterized or distinguished. The statistics of spectra for each patch of pixels are computed. A first classifier is computed from frequency-wise standard deviation of the spectra in each patch and a set of second classifiers are computed from principal components of the spectral in each patch. A combined classifier is computed based on the output of the first classifier and at least one of the second classifiers. The elements are characterized or distinguished based on the output of at least one of the classifiers, preferably the combined classifier.

The invention provides a measurement and control communication method for a deep space probe and a measurement and control communication system for a deep space probe. The method is used for achieving information interaction between an earth station and a deep space probe and measurement of a probe track. The method comprises following steps. Four microwave radio signal channels are disposed between the deep space probe and the earth station by using an uplink carrier frequency and a downlink carrier frequency and comprise a telecontrol instruction channel, a telemetry data channel, a scientific data channel, and a VLBI track measurement beacon channel. Three channel signals including engineering telemetry data, scientific probing data, and VLBI track measurement beacon are combined into a downlink transmission signal. Finally, a transmitter is used to complete a transmitting function of all downlink transmission signals. A track measurement beacon is generated by using a frequency standard signal of a high-stability frequency source and is transmitted to an earth VLBI measuring network. Using a Doppler frequency speed measurement and signal interference angle measurement manner, the earth VLBI measuring network completes the track measurement tack of the deep space probe.

The invention provides a system and a method for detecting the state of a secondary circuit of a current transformer for metering. The detection system comprises a high frequency voltage signal generation unit, an oscillation and resonance detection unit and a current detection unit which are serially connected between the current transformer for metering and an electric energy meter. The detection method detects the state of the secondary circuit by steps of measuring a practical current value, comparing the practical current value with a measured current value obtained by the electric energy meter, measuring an oscillation frequency value, comparing the oscillation frequency value with an oscillation frequency standard value, inputting high frequency voltage to the secondary circuit and detecting the practical high frequency voltage value of the secondary circuit. The detection system can be independently installed in the secondary circuit, is simple and reliable in structure, and can timely detect required data of the state of the secondary circuit of a detected current transformer. The detection method is more reliable, achieves real-time detection of the state of the secondary circuit of the detected current transformer, and provides a reliable data source for identification of the normal operation state and the open circuit state and analysis of the state of the secondary circuit.

In an optical frequency comb generator the emission frequency of each one of the set of output lasers is repetitively aligned with an associated one of a set of specifically determined frequencies by comparison of that emission frequency with a frequency indicated by an optical frequency meter. The optical frequency meter is repetitively re-calibrated by reference to the emission frequency of each of at least two frequency tuneable calibration lasers emitting at respectively different frequencies. Each of the calibration lasers has its emission frequency continuously or repetitively aligned with the frequency of an associated spectral absorption line frequency standard.

The invention provides a method for identifying digital modulation signals in the presence of complicated noise. The method comprises the following steps that fraction low-order rapid independent composite analysis is conducted on an observation vector x of a received signal, and the received signal is divided into a transmitting signal and Alpha stable distribution noise; ensemble average LMD based on interpolation is conducted on the separated transmitting signal s(n), and the transmitting signal is decomposed into multiple components; the first classification feature, namely the subsection instantaneous frequency standard deviation sigmaf of a component, is extracted, and a corresponding threshold delta 1 is set; a second classification feature, namely subsection instantaneous amplitude standard deviation sigmaa of the components, is extracted and a corresponding threshold delta1 and a corresponding threshold delta2 are set; a signal set {MSK, 2ASK, QPSK and 16QAM} is divided into two types, namely the signal set {MSK} and the signal set {2ASK, QPSK and 16QAM} through the threshold delta1, and signals in the signal set {2ASK, QPSK and 16QAM} are identified through the threshold delta 2 and the threshold delta3. By the adoption of the method for identifying digital modulation signals in the presence of complicated noise, the performance of identifying signals existing in a low-signal-to-noise-ratio environment in the presence of the Alpha stable distribution noise is high, and the stability is high.

The invention discloses a rubidium atom frequency standard digital phase locked frequency multiplier. The input terminal of the digital phase locked loop is connected with the output terminal of the rubidium atom frequency standard 10MHz voltage control crystal oscillatory as the output terminal of the frequency multiplier. The output terminal of the digital phase locked loop is connected with the output terminal of the microwave oven amplifier which is connected with the output terminal of the step matching circuit. The output terminal of the step matching circuit as the output terminal of the frequency multiplier is connected with the input terminal of the rubidium atom frequency standard microwave cavity. The phase detector and the digital frequency synthesizer are integrated by AD 9956. The invention adopts digital synthesizer as the fractional divider in which a digital phase locked loop is inserted, sets and modulate the fractional frequency division ratio of the digital synthesizer through the single chip computer thus enabling the direct fractional frequency multiplying and frequency modulation of the frequency multiplier. The invention with a simple structure, high degree of integration, high purity of the spectrum, low phase noise, small stray and high degree of digitalization is easy to modulate and can be used to produce miniaturized rubidium atom frequency standard.

The invention discloses a locking indication and fault diagnosis method for passive rubidium atom frequency scale, which adding a phase-adjustable square wave sampling time sequence signal on the basis of synchronization phase discrimination modulation signal and reference signal, wherein frequency of the sequence signal is fourfold of a modulation signal, and duty ratio of the sequence is 1:1. The sampling time sequence carries locking signal collection for an alternating current generated after quantum frequency discrimination, light detection amplification and square wave reshaping to estimate atom frequency scale locking condition at this point. The method uses continuous four rising edges of sampling time frequency of fourfold modulation signal as trigger pulse to carry level sampling for signal after quantum frequency discrimination, levels of the four rising edges are recorded as D1, D2, D3 and D4, atom frequency scale is estimated if it is in locking state according to recorded four sampling levels, when D1=D2 and D3=D4, the atom frequency scale is in locking state. The method can detect operation state and fault point of the passive rubidium atom frequency scale system, and can easily and conveniently exchange fault module.

The invention provides a high-precision time-frequency source capable of being tamed to a time-frequency standard in real time. The high-precision time-frequency source can obtain a first time-frequency clock difference sequence generated by a reference side and a global navigation satellite system (GNSS) remotely and in almost real time, and comprises a tamed side; the reference side generates N time-frequency signals of a to-be-calibrated clock; according to the N time-frequency signals and a satellite signal, a second time-frequency clock difference sequence is generated; according to the first time-frequency clock difference sequence and the second time-frequency clock difference sequence, a third time-frequency clock difference sequence between N time-frequency signals of a reference time-frequency source and the N time-frequency signals of the to-be-calibrated clock is obtained; according to the third time-frequency clock difference sequence, a relative frequency difference sequence is computed and acquired; and through the third time-frequency clock difference sequence and the corresponding relative frequency difference sequence, the to-be-calibrated clock is monitored and calibrated. The high-precision time-frequency source capable of being tamed to the time-frequency standard in real time can easily trace time performance and frequency performance of the reference time-frequency source (generally, the time-frequency standard, including a national time-frequency reference) in any laboratory, can trace the time and the frequency back to the International System of Units, and is relatively high in reliability, accuracy and stability.

A time-frequency standard signal fusion transmission system and transmission method are provided. The system compensates the phase noise of optical frequency signal, radio frequency signal and time signal when they are transmitted in the optical fiber link through the compensation module 1, the compensation module 2 and the communication signal transmitter of the local terminal, and sends the calculated link delay to the remote terminal together with the communication data. Through the optical frequency and RF reference signal output module at the remote end, The time signal output module andthe communication signal receiver, the spectrum purification of the optical frequency standard signal, the spectrum purification of the radio frequency standard signal and the time delay calibration of the time signal are realized, so that the user can simultaneously obtain the high-quality optical frequency standard signal, the radio frequency standard signal, the time signal and the communication data signal. The technical scheme of the invention solves the problems of mutual crosstalk and low detection signal-to-noise ratio when a plurality of signals are simultaneously transmitted, and greatly improves the transmission distance and transmission accuracy of the transmission of the plurality of standard signals.

This invention discloses a frequency scale adjusting system based on the GPS frequency standard aiming at the current expensive standard frequency device. Its characters lie in that it consists of the reception system of the GPS frequency standard, frequency scale comparing system, frequency scale measuring system and the computer system. The input signal of the GPS frequency standard receives the GPS frequency via the GPS antenna and carries its output to the frequency scale comparing system which processes the standard frequency from the GPS frequency standard and the detecting frequency from the frequency scale measuring system and carries it to the computer system. After that, the result is displayed on the screen or output by the printer. It has merits as low investment, high accuracy and wide applied range.

A physic package for an atomic clock comprising: a block made of optical glass, a glass ceramic material or another suitable material that includes a plurality of faces on its exterior and a plurality of angled borings that serve as a vacuum chamber cavity, light paths and measurement bores; mirrors fixedly attached using a vacuum tight seal to the exterior of the block at certain locations where two light paths intersect; optically clear windows fixedly attached using a vacuum tight seal to the block's exterior over openings of the measurement bores and at one location where two light paths intersect; and fill tubes fixedly attached using a vacuum tight seal to the exterior of the block over the ends of the vacuum chamber cavity. This physics package design makes possible atomic clocks having reduced size and power consumption and capable of maintaining an ultra-high vacuum without active pumping.

The invention relates to a method for acquiring a high-power broadband green-light optical frequency comb. The method comprises the following steps of: locking a plurality of ytterbium-doped optical frequency combs on a same frequency standard; (2) detecting time delay joggling among optical comb pulses by adopting a balanced optical cross correlation detection method, and always keeping time coincidence of frequency-doubled green-light pulses during a coherent combining process; (3) performing optical frequency doubling on the output pulse of each ytterbium-doped optical frequency comb by using a frequency doubling crystal to generate frequency-doubled green light of which the wavelength is 525-535 nanometers; and (4) performing coherent combining of multiple paths of pulses through a multi-wavelength wavelength division multiplexer to obtain green-light optical comb output having width spectral characteristic. Due to the adoption of the method, the problems of narrow optical spectrum, low pulse power, difficulty in controlling time frequency characteristic and the like existing in the conventional green light generating technology are solved, the average green light power is increased, the green light brightness is enhanced, and the frequency of frequency-doubled light and the average power of green-light pulses are increased.

The invention provides a stable frequency transmission method and a system. The method includes: generating a stable frequency standard signal in a central station; using a tunable laser to generate an optical carrier; modulating the frequency standard signal to the optical carrier to form an initial optical signal; transmitting the initial optical signal to a far end through an optical fiber; returning a part of the far-end optical signal to the same optical fiber to the central station; demodulating the return optical signal to obtain a return RF signal; comparing the phase difference of the return RF signal and the frequency standard signal; controlling the tunable laser according to the phase difference to change the wavelength of the optical carrier, obtaining a compensated optical carrier, and enabling the sum of the chromatic dispersion delay inequality of the compensated optical carrier and the initial optical carrier and the link delay variation caused by environmental factors of temperature change and vibration to be zero; and demodulating the stabilized far-end optical signal to obtain a far-end RF signal and outputting the far-end RF signal. The stable frequency transmission method uses the optical fiber both as a transmission medium and a compensation device, an additional compensation device does not need to be added to realize a delay/phase jitter compensation process, the system structure is simple, and the practicability is strong.

The invention relates to a multi-frequency multi-base high-frequency ground wave radar system and an operating method thereof. The multi-frequency multi-base high-frequency ground wave radar system comprises an analog extension, a digital extension, an ultra-high-stability time frequency standard device, a power amplifier, a transmitting antenna, a receiving antenna and a GPS (global position system) antenna. The analog extension comprises a frequency synthesizer, an analog amplification filtering component, an analog frequency multiplier and a multi-channel analog receiving front end, and the digital extension comprises a multi-channel data acquisition and processing board card, a synchronization control board card and an industrial control computer. The frequency synthesizer adopts a digital up-conversion scheme; the analog receiving front end adopts a multi-stage broadband program-controlled tracking and filtering scheme with no need for frequency mixing; data acquisition adopts a radio-frequency direct sampling and digital down-conversion scheme; and the time frequency standard is provided by a GPS tame low-phase-noise and ultra-high-stability crystal oscillator. The multi-frequency multi-base high-frequency ground wave radar system has the following advantages that the all-digital transmission and reception technology is adopted, and the system has good universality and scalability; and the radar waveform and time sequence are flexible and controllable, and the time-sharing, multi-frequency and single-base or multi-base detection can be realized.

The invention relates to a surface weak high-frequency microwave field strength measurement technology, and in particular relates to a device and a method for measuring high-frequency microwave field strength based on an electromagnetic induction transparent effect. The device and the method are technically characterized in that high-sensitivity and high-accuracy detection for the surface weak microwave field strength can be realized by a specially designed sample absorption cell structure, and atomic line splitting is associated with the microwave field strength by a quantum coherent effect of Rydberg state atoms, so that the measurement of the microwave field strength is traced back to the frequency standard of an atomic transition line, and the self-calibration of the device can be realized by utilizing the linear relation of the microwave field strength and the frequency standard of the atomic transition line; furthermore, due to the high-sensitivity response of high Rydberg state to the weak microwave field, the detection sensitivity of the high-frequency microwave field reaches up to 0.1mV/m and even reaches up to 10mV/m. Furthermore, the whole detection device is high in stability of structure and small in microwave turbulence.

The invention relates generally to optical interference filters and interferometers. Methods, devices and device components for optical signal generation and processing using optical interference filters and interferometers are presented. The invention provides optical interference filters and interferometers having a selected cumulative reflectance phase dispersion capable of providing substantially independent selectable resonance frequency and free spectral range. An exemplary interference filter of the present invention provides a multi-peak transmission spectrum with substantially independent, selectable control over absolute transmission band frequencies and relative transmission band spacing. The methods and devices provided herein are particularly well suited for frequency matching optical signals to a selected frequency standard, such as the International Telecommunication Union frequency standard.

An atomic beam tube for frequency standard which employs either counter propagating optical beams or counter propagating atomic beams and Coherent Population Trapping (CPT) is disclosed. Atoms selected from the group consisting of the alkali metal family (Cesium, Rubidium, Potassium, Sodium and Lithium) are emitted from one or two sources to form a single or double atomic beams. The atoms interact with the optical beams at two crossing points. The optical beams are generated by a laser and are modulated at half the hyperfine frequency. The optical beam is splitted into two counter propagating beams in round paths which interact with the atomic beam at two interaction regions. The interaction with the light causes the atoms to enter a CPT state. A dark line in the fluorescence at the second crossing is used to lock an RF oscillator to the atomic hyperfine transition.

The invention discloses a verifiable and adjustable full synchronous communication network, and an implementation method thereof. The implementation method of the verifiable and adjustable full synchronous communication network comprises the steps: setting a time frequency standard system and a performance monitoring and evaluation system; comparing all the PRCs (Primary Reference Clock), LPRs (Local Primary Reference) and the like of the whole network respectively with the time frequency standard system in a common view satellite mode; according to the obtained clock error through common view comparison between the PRCs and LPRs and the time frequency standard system, calculating, processing and evaluating the technical performance in the performance monitoring and evaluation system; and adjusting the clock of each PRC and each LPR through the clock error so as to realize full synchronization of the communication synchronization network. The implementation method of the verifiable and adjustable full synchronous communication network belongs to a communication synchronization network full synchronizing method based on satellite common view, can establish a high accuracy time frequency measuring system, a synchronization performance evaluation system and a synchronous calibration system, can realize trusted verification and calibration of the synchronization performance quality, and can realize full synchronous operation of the full synchronous communication network based on the above capabilities.