Local Oscillator Requirements Research Articles

Simple laser transmitter pair as polarization-independent coherent homodyne detector.

Coherent optical reception promises performance gains for a wide range of telecom applications and photonic sensing. However, the practical implementation and the particular realization of homodyne detection is by no means straight-forward. Local oscillator requirements and polarization management need to be cost-effectively supported for accurate signal detection at high sensitivity, preferably without relying on digital processing resources. Towards this direction we propose a conceptually simple, laser-based homodyne receiver. We exploit the injection locking of a pair of externally modulated lasers that simultaneously serve as optically synchronized local oscillators and photodetectors in a polarization-diversity analogue coherent receiver arrangement. We demonstrate signal detection at 2.5 Gb/s over an optical budget of 35 dB and a dynamic range of >20 dB. Long-term measurements over field-installed fiber confirm the correct operation independent of the polarization state of light. Stability considerations for the injection locking process are drawn in view of even higher loss budgets.

Reconfigurable All-Band RF CMOS Transceiver for GPS/GLONASS/Galileo/Beidou With Digitally Assisted Calibration

This paper presents a fully integrated reconfigurable all-band RF transceiver for GPS/GLONASS/ Galileo/Beidou in 55-nm CMOS. The transceiver incorporates three low-IF receivers (RXs) and one direct up-conversion BPSK transmitter (TX), which can be configured to receive any two global navigation satellite system (GNSS) signals or switched to process the Chinese Beidou(I) signals. A switching module is integrated to provide the connectivity between different RF front-end and IF channel (IFC), which will effectively simplify the design complexity of the IFC and save power consumption, while the GNSS signals are received. A flexible frequency plan with two frequency synthesizers is utilized to satisfy different local oscillator requirements of the transceiver. An optimized automatic frequency calibration scheme using an error compensation logic enables fast and high-precision calibration process for optimum phase-locked loop operation. Several digitally assisted calibration modules are integrated to ensure that the chip performance only shows a weak process, voltage and temperature (PVT) dependence. While drawing about 21.5–30.2 mA per RX channel from a 1.2-V supply, the RXs achieve an image rejection ratio more than 49 dB after I/Q mismatch calibration, an automatic gain control range of 88 dB, and an input-referred 1 dB compression point of better than −25 dBm with a minimum noise figure of about 2 dB. The output power of the TX is about 5 dBm with about 6% error vector magnitude (EVM) and 30-mA current from a 1.2-V supply. The whole transceiver consumes a die area of $2.8 \times 3~{\rm mm}^{2}$ .

Applications of Superconductivity for Implementation of Phase Conjugation in the Microwave Region

This paper extends a preliminary proposal and description of a superconductivity-based phase conjugating antenna for operation in the microwave range. The complementary properties of high-temperature superconductors and other oxide functional materials are emphasised. The potential applications of such an antenna are very wide. We consider the requirements for the Josephson junction which is at the heart of the phase conjugation operation, especially issues of the use of the internal Josephson oscillation or of an external signal to provide the local oscillator requirement. Other design requirements are also explored and the necessary substrate properties are set out which enable suitable junction properties, as well as phase shifter and interconnection functions.

Article

The accelerated development of laser methods for manipulating the internal state and motion of atoms, and the recent primary evaluation in France of a cesium frequency standard using cold atoms in an atomic fountain configuration, allow the frontiers of time metrology, accuracy, and stability to be pushed near parts in the 1016 level, a factor of 100 over the present primary laboratory clocks. These positive results revived the development of more accurate cesium atomic clocks, and the Institute of National Measurement Standards (INMS), of the National Research Council of Canada (NRC) is undertaking a cesium-fountain project aimed at reaching these new levels of accuracy and stability. This paper reviews its present status. To appreciate the considerable impact of cold atoms in time and frequency metrology, we begin by recalling the background principles of traditional cesium frequency standards, their typical performance and main limitations. After introducing the important theoretical results essential to understanding the techniques of laser cooling and magneto-optical trapping, we focus on describing the characterization and control of our magneto-optical trap (MOT) and report the parameters that allow us to fill the trap with a few million atoms in less than a second and cool them to a temperature lower than 5 muK using optical molasses. We will describe the specifics of our cesium-fountain prototype, which operates with a 2-dimensional moving molasses. This special configuration is applicable for multipulse operation of the fountain, which can greatly relax the local oscillator requirements for time keeping. Finally, progress toward our objective of launching cooled atoms, at a rate of one ensemble per second, at speeds of 7 m/s, for a fountain with an interrogation time of about 1 s, will be analysed.PACS Nos.: 06.20, 06.30, and 32.80P

Cesium-fountain development at the National Research Council of Canada

The accelerated development of laser methods for manipulating the internal state and motion of atoms, and the recent primary evaluation in France of a cesium frequency standard using cold atoms in an atomic fountain configuration, allow the frontiers of time metrology, accuracy, and stability to be pushed near parts in the 10 level, a factor of 100 over the present primary laboratory clocks. These positive results revived the development of more accurate cesium atomic clocks, and the Institute of National Measurement Standards (INMS), of the National Research Council of Canada (NRC) is undertaking a cesium- fountain project aimed at reaching these new levels of accuracy and stability. This paper reviews its present status. To appreciate the considerable impact of cold atoms in time and frequency metrology, we begin by recalling the background principles of traditional cesium frequency standards, their typical performance and main limitations. After introducing the important theoretical results essential to understanding the techniques of laser cooling and magneto-optical trapping, we focus on describing the characterization and control of our magneto-optical trap (MOT) and report the parameters that allow us to fill the trap with a few million atoms in less than a second and cool them to a temperature lower than 5 >K using optical molasses. We will describe the specifics of our cesium-fountain prototype, which operates with a 2-dimensional moving molasses. This special configuration is applicable for multipulse operation of the fountain, which can greatly relax the local oscillator requirements for time keeping. Finally, progress toward our objective of launching cooled atoms, at a rate of one ensemble per second, at speeds of 7 m/s, for a fountain with an interrogation time of about 1 s, will be analysed.

Efficient microwave frequency conversion using photonic link signal mixing

An efficient, high-dynamic range microwave mixer implemented using an analog fiber-optic link with an overdriven optical modulator to produce the local oscillator requirement has been demonstrated and analyzed. This approach is compared with the heterodyned lasers approach to generating the local oscillator requirement and it is shown that increased conversion efficiency and more frequency and phase stable upconverted or downconverted signals are obtainable. Aside from RF link loss, which can be compensated with preamplification, a conversion loss below 5 dB has been demonstrated out to 10 GHz.

The Ka-Band Communication Systems of the Lincoln Experimental Satellites LES-8 and LES-9

Introduction L INCOLN Experimental Satellites LES-8 and LES-9 are a pair of experimental communication satellites designed and built to operate in a synchronous ecliptic orbit and to communicate on a crosslink from satellite to satellite as well as with surface terminals. At synchronous-orbit altitude, each satellite has a groundvisibility area about 8000 miles in diameter. With crosslink communication between two satellites spaced thousands of miles apart, a single pair of satellites could provide communications among terminals anywhere in an area covering more than 3/4 of the surface of the Earth. Communication links are possible at both UHF and Ka-band at approximately 37 GHz. Figure 1 shows a cutaway drawing of LES-9. The side facing the Earth is the forward platform, which is used for mounting and precision alignment of the Ka-band antennas and the Earth sensors. The Ka-band receiver diplexer filters and front ends are mounted as close as possible to the diplexer polarizer mounted on each antenna. The Ka-band transmitter power amplifiers are mounted on sections of the internal decagon adjacent to the forward platform to minimize the length of the waveguide runs to the antennas. LES-8 and LES-9 each utilize two independent Ka-band communication systems (see Fig. 2). The Ka-dish system uses a fixed paraboloidal reflector in conjunction with a steerable flat reflector to provide a narrow beam, tracking antenna for crosslink or uplink/downlink communications. The Ka-horn system includes a fixed horn to provide a wide-beam antenna coverage. Local oscillator requirements for both systems are provided by a single Ka-band local oscillator. Each receiver subsystem features a broadband low-noise mixer utilizing Schottky-barrier diodes to achieve a typical system noise figure of less than 8 dB. Each transmitter includes an array of solid-state amplifiers which utilize IMPATT diodes, and delivers 0.5 W of power to the antenna. The transmitter signal is modulated at a lower frequency and is upconverted to Kaband using a mixer similar to that used in the low-noise receiver. This paper will discuss the Ka-band systems carried on LES8 and LES-9, which were built to demonstrate component and