Automatic Frequency Control System Research Articles

Polarization diversity detection performance of 2.4 Gbit/s CPFSK heterodyne system

AbstractIn the practical implementation of the coherent optical transmission system, it is important to establish the techniques for stabilizing the optical frequency considering the actual environmental condition, as well as a technique for compensating for the variation of the state of polarization in the usual single‐mode optical fiber cable.This paper considers the application of the polarization diversity receiver to the CPFSK heterodyne delay detection in the 2.4‐Gbil/s band and discusses the construction and performance. The regenerative repeater equipment is designed in a compact form to be implemented in a commercial rack (INS cabinet rack). Using the designed equipment and the existing trunk fiber transmission route, an experiment in the actual site is conducted and the results are shown.The first part of this paper presents the construction of both the automatic frequency control (AFC) system and the automatic gain control (AGC) system suited to the polarization diversity system. The design guides are presented for the required frequency response speeds of AFC and AGC, the required frequency stability of AFC, and the response performance to the fluctuation of polarization. A high‐output, high‐sensitivity 2.4‐Gbit/s regenerative repeater equipment (with repeater gain above 48 dB) is realized with the overall performance that the variation of optical received sensitivity against the polarization fluctuation can be suppressed to within 0.5 dB.Finally, the stable operation of the equipment is verified by the experiment at the actual site, and the practical usefulness is indicates.

Sensitivity improvement of a Varian E-109 EPR spectrometer with a low noise microwave amplifier

The installation of a low noise GaAsFET microwave preamplifier into a Varian E-109 homodyne X-band EPR spectrometer is described, and measurements of the resulting improvement in sensitivity as a function of microwave power are presented. Particular attention is paid to modification of the automatic frequency control (AFC) system to compensate for the preamplifier gain, which would otherwise result in instability of the AFC servoloop and decreased spectrometer performance at moderate microwave power levels. Specific details are provided for modification of the Varian E-102 bridge, but the general approach is applicable to other spectrometers.

Long-term stability and reproducibility of the emission frequency of an He–Ne laser with internal mirrors

A study was made of the long-term stability and reproducibility of the emission frequency of a laser with internal mirrors stabilized by the method of thermal control of the resonator length using a fixed ratio of the orthogonally polarized components of the radiation. The spectral characteristics and the thermal regime of the gas-discharge tube were investigated. A theoretical estimate was made of the long-term stability allowing for the drift of the reference point and instability of the parameters of an automatic frequency control system. Experimental values of 2×10−9 for the instability and 2×10−8 for the irreproducibility of the frequency of the investigated laser were obtained.

Use of magnetostriction effect to stabilize laser frequency

The use of magnetostriction to compensate for the thermal changes of the lasercavity length in automatic frequency control systems is considered. Magnetostriction ensures a wide dynamic range of cavity-length compensation, and a transfer coefficient that is 102–103 times larger.

Stabilization of the emission frequency of an internal-mirror laser model ILGN-202

The emission frequency of an ILGN-202 internal-mirror laser was stabilized. An experimental study was made of the dependences of the power of the orthogonal components of laser radiation on the frequency tuning in the free-running regime. The laser was stabilized by maintaining a definite relationship between the intensities of the components by an automatic frequency control (AFC) system utilizing the method of thermal control of the resonator length. A theoretical study was made of the ultimate short-term frequency instability and an expression was derived for the transfer function of the optimal AFC system. The relative frequency instability found experimentally was 5 ? 10?9 in 15 min when the averaging time was 1 sec and the change in the frequency in 8 h was 10 MHz.

Parasitic amplitude modulation of stabilized CO2lasers

An experimental investigation was made of parasitic amplitude modulation in a CO2 laser with intracavity frequency modulation. This effect was due to periodic misalignment of the laser cavity during operation of a piezoelectric ceramic modulator. A method for controlling and minimizing the parasitic modulation was developed. Relationships were derived for the shift of the stabilized frequency due to such parasitic amplitude modulation and estimates were obtained for the case of a stabilized CO2/OsO4 laser. It was found that the parasitic modulation could give rise to a dependence of the stabilized frequency on the phase relationships in the case of phase-sensitive detection in an automatic frequency control system of the laser.

A standing-wave frequency stabiliser

The theory and performance are discussed of an automatic frequency control system based on a low-noise dual detector sampling the standing wave in a reference waveguide. The reference waveguide and detectors are temperature-compensated and constructed from readily available components. The stabiliser can control the frequency of a 9 GHz reflex klystron to 5 parts in 107 per hour. With slight modification the method is applicable to solid state oscillators with narrow-band electrical tuning.

Long-term instability and irreproducibility of a gas laser frequency and requirements to be satisfied by automatic frequency control systems

An analysis is made of monotonic frequency drifts exhibited by gas lasers with automatic frequency control (AFC) systems. The long-term instability and irreproducibility of the emission frequency are found as a function of the long-term instability and irreproducibility of the reference point and errors of the AFC system. Ways of reducing these errors are considered and the experimental results of the error determination are given. Practical recommendations are made for increasing the long-term stability and reproducibility of the laser frequency by a suitable choice of elements of the AFC systems and of their operating conditions.

An Improved Reference Cavity Design for Frequency Tracking of RF Accelerating Structures

A simple automatic frequency control system providing accurate frequency tracking has been built. The system makes use of the temperature difference between inlet and outlet accelerator coolant, establishing this difference between two regions of appropriately shaped reference cavities. Two re-entrant 3 GHz cavities were used to frequency lock a 1.8 MW magnetron to a 1.6 m long standing wave pulsed electron accelerator. Tests show that for a 30°C change in input water temperature and/or a variation of average power between 0.02 and 2.0 kW, the desired frequency tracking is obtained.

Automatic frequency control system for ultrasonic pulse superposition measurements

A system for automatic measurements of changes in ultrasonic velocity in solids is presented, using McSkimin’s pulse superposition method.

Analysis of the influence of fluctuations of the reference frequency and of the resonator length on the frequency instability of a gas laser and requirements to be satisfied by automatic frequency control systems

An analysis is made of technical fluctuations of the emission frequency of a gas laser with an automatic frequency control (AFC) system. The minimum instability of the emission frequency in a time τ is found as a function of τ and of the spectral densities of fluctuations of the reference frequency and of the optical length of the resonator, photodetector and amplifier noise, and parameters of the forced frequency modulation of the output radiation. The transfer function is found for an optimal linear AFC system ensuring minimum instability. The experimental results are given of a determination of the spectral densities of perturbations and of the relative frequency instability. Practical recommendations are given on the design of optical resonators and AFC systems.

Approximate investigation of the dynamics of a pulsed phase-shift automatic frequency control system

Approximate investigation of the dynamics of a pulsed phase-shift automatic frequency control system

Investigation of the dynamics of a pulsed phase-shift automatic frequency control system

Investigation of the dynamics of a pulsed phase-shift automatic frequency control system

Stabilization of the HCN laser

Two methods are described for stabilizing the output of an HCN laser: an automatic power control system suitable for use in a variable temperature environment, and an automatic frequency control system requiring stable laboratory conditions. The former can stabilize the laser output power to within +or-2% of a predetermined level for approximately 200 h. Some of the principles of operation are applicable to other devices.

The synchronization criteria for a phase-shift automatic frequency control system having a nonlinear filter

The synchronization criteria for a phase-shift automatic frequency control system having a nonlinear filter

The effect of the shape of a phase detector characteristic on the operation of a phase-shift automatic frequency control system in the presence of interference

The effect of the shape of a phase detector characteristic on the operation of a phase-shift automatic frequency control system in the presence of interference

A continuous phase-shift automatic frequency control system as a relay automatic control system

A continuous phase-shift automatic frequency control system as a relay automatic control system

On the magnitude of the locking band of a phase-shift automatic frequency control system with a proportionally integrating filter

On the magnitude of the locking band of a phase-shift automatic frequency control system with a proportionally integrating filter

Study of a nonlinear frequency and phase-lock automatic frequency control system with identical integrating filters in the phase and frequency loops

Study of a nonlinear frequency and phase-lock automatic frequency control system with identical integrating filters in the phase and frequency loops

Stabilization of a laser radiation frequency

The computations and experimental investigations thus carried out show that the use of an external resonator as a frequency discriminator of a laser provides it with a low-inertia automatic frequency control system. The design developed for a high-Q optical resonator provides it with a long-term frequency stability. The application of this model in a laser automatic frequency control system serves to obtain under complex conditions a short-term laser frequency stability better than 1·10−8 and a long-term stability not worse than 4·10−8 for 15 min.