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In this paper, we describe the implementation of a microwave cryogenic sapphire oscillator (CSO) at the Laboratoire de Physique et Métrologie des Oscillateurs. In our realization we solved the problem of the spurious modes by operating the sapphire resonator in an open cavity. The CSO compared to a hydrogen maser demonstrates a frequency stability better than 3 &times 10-14 at short term. Its long-term frequency instability of the order of 3 × 10-12/day is limited by a random walk process. A first attempt to use this reference oscillator to characterize other signal sources is presented. [ABSTRACT FROM AUTHOR]

We report new measurements of dielectric properties of Lanthanum gallium silicate (Langasite or LGS) conducted with the whispering-gallery mode technique at microwave frequencies and between 4.2 K and 300 K. The real part of the permittivity tensor of LGS presents two components having temperature coefficients of opposite sign. This unique property enables the design of a temperature compensated resonator that may be useful in building stable microwave oscillators or filters. We report also the first measurements of the two independent components of the imaginary part of the permittivity tensor. It appears LGS is a relatively high-loss dielectric material compared with sapphire or quartz. [ABSTRACT FROM AUTHOR]

In this paper, the electrical and noise performances of a 0.8 µm silicon germanium (SiGe) transistor optimized for the design of low phase-noise circuits are described. A nonlinear model developed for the transistor and its use for the design of a low-phase noise C band sapphire resonator oscillator are also reported. The best measured phase noise (at ambient temperature) is -138 dBc/Hz at 1 kHz offset from a 4.85 GHz carrier frequency, with a loaded QL factor of 75,000. [ABSTRACT FROM AUTHOR]

Evaluates a temperature-compensated sapphire resonator as frequency determining element for high-stability microwave oscillator. Thermal compensation principle; Turnover temperature; Short-term frequency stability; Oscillation circuit; Oscillation frequency characterization.

We report measurements of dielectric permittivity and dielectric losses at microwave frequencies of lanthanum gallium silicate as a function of temperature. The dielectric rod resonator method was used to evaluate the two relative permittivity tensor components ε[sub t] and ε[sub z] of this uniaxial dielectric crystal. Between 10 and 400 K, ε[sub t] varies from 18.92 to 19.65 whereas ε[sub z] ranges from 60.81 to 46.66. Around 300 K, the temperature coefficients of ε[sub t] and ε[sub z] have opposite signs and are equal to 130 and -720 ppm/K, respectively. This characteristic enables one to design a self-compensated microwave resonator presenting a low frequency temperature sensitivity. For the measured dielectric sample the dielectric losses range from 1x10[sup -4] to 5x10[sup -6] between 300 and 20 K and are actually limited by the crystal quality. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The stabilization of lasers on ultra-stable optical cavities by the Pound-Drever-Hall (PDH) technique is a widely used method. The PDH method relies on the phase-modulation of the laser, which is usually performed by an electro-optic modulator (EOM). When approaching the 10 -16 fractional frequency stability level, this technology requires an active control of the residual amplitude modulation (RAM) generated by the EOM in order to bring the frequency stability of the laser down to the thermal noise limit of the ultra-stable cavity. In this article, we report on the development of an active system of RAM reduction based on a free space EOM, which is used to perform PDH-stabilization of a laser on a cryogenic silicon cavity. A minimum RAM instability of 1.4 × 10 -7 is obtained by employing a digital servo that stabilizes the EOM DC electric field, the crystal temperature and the laser power. Considering an ultra-stable cavity with a finesse of 2.5 × 10 5 , this RAM level would contribute to the fractional frequency instability at the level of about 5 × 10 -19 , well below the state of the art thermal noise limit of a few 10 -17 .

We report what we believe to be the lowest phase noise optical-to-microwave frequency division using fiber-based femtosecond optical frequency combs: a residual phase noise of -120 dBc/Hz at 1 Hz offset from an 11.55 GHz carrier frequency. Furthermore, we report a detailed investigation into the fundamental noise sources which affect the division process itself. Two frequency combs with quasi-identical configurations are referenced to a common ultrastable cavity laser source. To identify each of the limiting effects, we implement an ultra-low noise carrier-suppression measurement system, which avoids the detection and amplification noise of more conventional techniques. This technique suppresses these unwanted sources of noise to very low levels. In the Fourier frequency range of ∼200 Hz to 100 kHz, a feed-forward technique based on a voltage-controlled phase shifter delivers a further noise reduction of 10 dB. For lower Fourier frequencies, optical power stabilization is implemented to reduce the relative intensity noise which causes unwanted phase noise through power-to-phase conversion in the detector. We implement and compare two possible control schemes based on an acousto-optical modulator and comb pump current. We also present wideband measurements of the relative intensity noise of the fiber comb.