David Mouneyrac

Use of Whispering-Gallery Modes and Quasi-

The complex permittivity of bulk crystals of semiinsulating gallium arsenide (GaAs) and gallium phosphide (GaP) were measured over the frequency range from 4 to 30 GHz and at temperatures from 30 up to 300 K employing whispering-gallery-mode (WGM) and quasi-TE0 np-mode dielectric-resonator techniques. At temperatures about 40 K, dielectric loss tangent values were below 10 -6 for GaAs and below 10 -5 for GaP. The use of several WGMs, as well as TE0 np modes excited in the same test sample enabled a broad frequency range of measurements (one decade). The real part of the permittivity of GaP and GaAs proved to be frequency independent at microwave frequencies. The dielectric loss tangents of GaAs and GaP increase with temperature and frequency.

{\rm TE}_{0{ np}}

The authors report on observation of Bragg confined mode in a hollow cylindrical dielectric cavity. A resonance was observed at 13.4GHz with an unloaded Q factor of order 2×105, which is more than a factor of 6 above the dielectric loss limit. Previously, such modes have only been realized from pure transverse electric modes with no azimuthal variations and only the Eϕ component. From rigorous numeric simulations, it is shown that the mode is a hybrid mode with nonzero azimuthal variations and with dominant Er and Eϕ electric field components and Hz magnetic field component.

Modes for Broadband Characterization of Bulk Gallium Arsenide and Gallium Phosphide Samples

The complex permittivity of high-purity, semi-insulating, axis-aligned monocrystalline 4H-SiC has been determined over the frequency range 10–40 GHz and at temperatures from 40 up to 295 K using whispering gallery modes and quasi TE0, n, p modes in a dielectric resonator constructed from seven layers of a 375 μm thick wafer. The real part of the permittivity (in the plane of the wafers) was found to be nearly independent of frequency. The dielectric loss tangent of 4H-SiC increases with temperature above 100 K. All results were obtained for the semiconductor in darkness.

Discovery of Bragg confined hybrid modes with high Q factor in a hollow dielectric resonator

We report on the demonstration of a resonator based on electromagnetic field confinement in a hollow-core by implementing an out-of-plane two-dimensional ﲤ2Dﲥ photonic band-gap ﲤPBGﲥ crystal cladding. In contrast with in-plane 2D PBG crystal devices, the PBG crystal studied here is perpendicular to the propagation axis. A resonator was constructed with silica rods to prove the concept at frequencies around 30 GHz. We show that the technique has the potential to reach quality factors ﲤQﲥ of 5 ﲡ 105.

Microwave properties of semi-insulating silicon carbide between 10 and 40 GHz and at cryogenic temperatures

Dielectric resonators are key components for many microwave and millimeter wave applications, including high-Q filters and frequency-determining elements for precision frequency synthesis. These often depend on the quality of the dielectric material. The commonly used material for building the best cryogenic microwave oscillators is sapphire. However, sapphire is becoming a limiting factor for higher frequency designs. It is, then, important to find new candidates that can fulfill the requirements for millimeter wave low noise oscillators at room and cryogenic temperatures. These clocks are used as a reference in many fields, such as modern telecommunication systems, radio astronomy (very-long-baseline interferometry), and precision measurements at the quantum limit. High resolution measurements were taken of the temperature-dependence of the electromagnetic properties of a polycrystalline diamond disk at temperatures between 35 and 330 K at microwave to submillimeter wave frequencies. The cryogenic measu...

Hollow-core resonator based on out-of-plane two-dimensional photonic band-gap crystal cladding at microwave frequencies

Whispering gallery modes in bulk cylindrical gallium arsenide and gallium phosphide samples have been examined both in darkness and under white light at 50K. In both samples we observed change in permittivity under light and dark conditions. This results from a change in the polarization state of the semiconductor, which is consistent with a free electron-hole creation/recombination process. The permittivity of the semiconductor is modified by free photocarriers in the surface layers of the sample which is the region sampled by whispering gallery modes.

Electromagnetic properties of polycrystalline diamond from 35 K to room temperature and microwave to terahertz frequencies

We developed a novel technique for accurate phase synchronization of microwave oscillators based on sapphire dielectric resonators cooled to liquid nitrogen temperature. The achieved quality of phase synchronization (a few milliradians) enables the accurate measurements of extremely weak phase fluctuations expected from the next generation of ultralow phase noise microwave oscillators.

Modified permittivity observed in bulk gallium arsenide and gallium phosphide samples at 50 K using the whispering gallery mode method.

Whispering gallery modes in bulk cylindrical gallium arsenide and gallium phosphide samples have been examined both in darkness and under white light at cryogenics temperatures ≤50 K. In both cases persistent photoconductivity was observed after initially exposing semiconductors to white light from a halogen lamp. Photoconductance decay time constants for GaP and GaAs were determined to be 0.900±0.081 and 1.098±0.063 ns, respectively, using this method.

Precise phase synchronization of a cryogenic microwave oscillator

We report on extremely sensitive measurements of changes in the microwave properties of high purity nonintentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide, and 4H–silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors while they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping re...

Observation of persistent photoconductivity in bulk gallium arsenide and gallium phosphide samples at cryogenic temperatures using the whispering gallery mode method

Dielectric resonators are key components for many microwave and millimetre wave applications, including high-Q filters and frequency-determining elements for precision frequency synthesis. Multilayered, bulk low-loss crystal and polycrystalline dielectric structures have become very important for designing these devices. Proper design requires careful electromagnetic characterisation of low-loss material properties. This includes exact simulation with precision numerical software and precise measurements of resonant modes. Diamond has been recently utilized for an increasing amount of electronic applications. This paper will present the common techniques for characterizing such dielectric samples in the microwave regime, and apply it to the characterization of diamond from 35 to 330K.