Peter G. Huggard

Efficient generation of guided millimeter-wave power by photomixing

A 70-GHz bandwidth commercial photodiode has been coupled to W-band waveguide and used as a photomixing source from 75 to 170 GHz. Maximum power conversion efficiency of 1.8% was obtained at 75 GHz, where an optical input of +10 dBm yielded a nonsaturated millimeter-wave (mm-wave) power of -7.5 dBm. Optimizing the photomixer backshort tuning at individual frequencies showed that the mm-wave power decreased with frequency to a level of -30 dBm at 170 GHz. Fixed tuning allowed the generation of power across the full waveguide band from 75 to 110 GHz, with a variation within 5 dB across the majority of the band.

High-purity millimetre-wave photonic local oscillator generation and delivery

Tunable millimetre wave generation by spectrally slicing a phase modulated lightwave is demonstrated. The low phase noise signal (-95 dBc/Hz at 100 kHz offset) can be delivered through a 9 km fibre link, with no noticeable power penalty.

Submillimeter Wave Frequency Selective Surface With Polarization Independent Spectral Responses

This paper reports the design, construction and electromagnetic performance of a new freestanding frequency selective surface (FSS) structure which generates coincident spectral responses for dual polarization excitation at oblique angles of incidence. The FSS is required to allow transmission of 316.5-325.5 GHz radiation with a loss les 0.6 dB and to achieve ges 30 dB rejection from 349.5-358.5 GHz. It should also exhibit crosspolarization levels below -25 dB, all criteria being satisfied simultaneously for TE and TM polarizations at 45 deg incidence. The filter consists of two identical, 30 mm diameter, 12.5 mum thick, optically flat, perforated metal screens separated by 450 mu m. Each of the ap 5000 unit cells contains two nested, short circuited, rectangular loop slots and a rectangular dipole slot. The nested elements provide a passband spectral response centered at 320 GHz in the TE and TM planes; the dipole slot increases the filter roll-off above resonance. The FSS was fabricated from silicon-on-insulator wafers using precision micromachining and plating processes including the use of deep reactive ion etching (DRIE) to pattern the individual slots and remove the substrate under the periodic arrays. Quasi-optical transmission measurements in the 250-360 GHz range yielded virtually identical copolarized spectral responses, with the performance meeting or exceeding the above specifications. Experimental results are in excellent agreement with numerical predictions.

Manufacturing Tolerance Analysis, Fabrication, and Characterization of 3-D Submillimeter-Wave Electromagnetic-Bandgap Crystals

The sensitivity of the characteristic band edge frequencies of three different 500-GHz electromagnetic-bandgap crystals to systematic variations in unit cell dimensions has been analyzed. The structures studied were square bar woodpiles made with dielectric having epsiv rap12 and epsivr=37.5 and two wide bandgap epsivr=37.5 crystals designs proposed by Fan and Johnson and Joannopoulos. These epsivr values correspond to high-resistivity silicon and a zirconium-tin-titanate ceramic, respectively. For the woodpiles, the fractional frequency bandgap varied very little for dimensional deviations of up to plusmn5% from the optimum. The bandgaps of the Fan and Johnson and Joannopoulos structures were affected to a greater extent by dimensional variations, particular sensitivity being exhibited to the air-hole radius. For all crystals, the effect of increasing the amount of dielectric in the unit cell was to shift the bandgap edges to lower frequencies. Both silicon and ceramic woodpiles, along with a ceramic Fan structure, were fabricated and dimensionally characterized. Mechanical processing with a semiconductor dicing saw was used to form the woodpiles, while the Fan structure required both dicing and UV laser drilling of circular thru-holes. Good agreement with predicted normal incidence transmissions were found on the low-frequency side of the bandgap in all cases, but transmission values above the upper band edge were lower than expected in the ceramic structures

Analysis and Demonstration of a Fast Tunable Fiber-Ring-Based Optical Frequency Comb Generator

Fiber-ring-based optical frequency comb generators are analyzed to understand their behavior and limitations. A numerical frequency-domain model is described for studying dispersion and other phase mismatch causing effects in the fiber ring cavity, as well as for predicting the spectral and temporal evolutions of the comb in time. The results from this analysis are verified with experimental measurements. A flat optical comb, with a terahertz span within a 6-dB power envelope and containing 100 comb lines, with a suppressed central comb line, is demonstrated. The comb shows an excellent coherence dependent on the phase noise from the radio frequency synthesizer that drives the comb generator. Improvement in the error correction loop also enables the comb spacing to be set at precise 12.5-MHz intervals without having to adjust the system. Fast frequency switching of the comb line spacing is demonstrated for the first time. The comb line spacing can be switched to any operation frequency with a resolution of 12.5 MHz between 6 and 12.5 GHz, as limited only by the microwave circuit used. The switching time is less than 1 s, and the spectral profile of the comb is maintained.

Double Corrugated Waveguide for G-Band Traveling Wave Tubes

A novel wide-band traveling wave tube (TWT) based on the double-corrugated waveguide (DCW) is proposed for operating in IEEE G-band (110-300 GHz). The DCW has been conceived for relaxing critical technological issues in terahertz vacuum tube realization, such as assembly, and to support a cylindrical electron beam. The study of the properties of the DCW in the forward wave regime demonstrates wide band performance suitable for TWTs fabrication at millimeter wave-terahertz frequencies. A traveling wave tube with 18-dB gain and up to 3.7 W output power over a bandwidth of about 30 GHz at 225 GHz as central frequency is demonstrated, assuming 13-kV beam voltage and 30-mA beam current.

Sub-Millimeter-Wave Imaging Array at 500 GHz Based on 3-D Electromagnetic-Bandgap Material

The design, fabrication, and characterization of a 500-GHz electromagnetic bandgap (EBG) based heterodyne receiver array is presented. The array contained seven planar dipole antennas that were photolithographically defined on a common 20-mum-thick quartz substrate. Each antenna incorporated a Schottky diode and was connected to coplanar transmission lines that conveyed the down-converted 500-GHz signals to detectors. The quartz substrate was backed by a silicon EBG woodpile structure, which reduced antenna crosstalk and increased directivity. An off-axis parabolic mirror completed the beam-forming network.

A Multichannel THz Detector Using Integrated Bow-Tie Antennas

This paper presents a kind of a multichannel THz detector using lens-based bow-tie array. A hyperhemispherical silicon lens is employed to provide a focal plane; 8 bow-tie elements are arranged on the focal plane with careful design to show a performance of broadband, high gain, well compact, and easy assembling. These characteristics of the detector are preferred for detecting weak THz signal. Measured far field shows that the radiation pattern of each element is shifted angularly, by ≈9°, which can be used for THz imaging. Tested responsivity of the detector shows a good spectral performance from 260 to 400 GHz: respective values were ≥220 V/W, and the best NEP is achieved at about 60 pW/. Besides that, the proposed antenna has advantages of simple structure, easy fabrication, and low cost.

Low-Cost, Continuously Tunable, Millimeter-Wave Photonic LO Generation Using Optical Phase Modulation and DWDM Filters

We report on a low-cost technique for the photonic generation of wideband continuously tunable millimeter-wave local oscillator signals. It is based on sideband filtering using an optical phase modulator and thin-film dense wavelength- division-multiplexing filters. The generated millimeter-wave signal exhibits low phase noise, and its frequency covers the W - and F -bands, from 75 to 140 GHz.

Inter-laboratory comparison of reflection and transmission measurements in WR-06 waveguide (110 GHz to 170 GHz)

This paper describes an exercise that was undertaken recently to compare reflection and transmission measurements in rectangular metallic waveguide from 110 GHz to 170 GHz (i.e. in the WR-06 waveguide size). The comparison involved making measurements on four devices fitted with ‘precision’ MIL-DTL-3922-67D style flanges. These devices were circulated amongst the nine organizations that chose to participate in the exercise. The comparison took place between August 2008 and September 2009. Results from the exercise are presented in graphical form along with a statistical summary showing average variability for the measurements. The authors believe this is the first time that such a comparison of measurements has been made at these frequencies. These results therefore provide a benchmark for the current state-of-the-art for measurements made in waveguide at these frequencies.