Robert A. Minasian

Widely Tunable Single-Passband Microwave Photonic Filter Based on Stimulated Brillouin Scattering

A new ultrawide continuously tunable single-passband microwave photonic filter with very high resolution, is presented. It is based on a stimulated Brillouin scattering technique using a phase modulated optical signal and a dual-sideband suppressed-carrier pump. Results are presented which demonstrate a 1- to 20-GHz measured tuning range, together with continuous tuning, extremely high resolution with a -3-dB bandwidth of only 20 MHz, a single passband, shape-invariant tuning, and a high out-of-band rejection of 31 dB.

A novel high-Q optical microwave processor using hybrid delay-line filters

A new hybrid active-passive photonic signal processor, which achieves high-Q microwave bandpass filtering, is presented. It overcomes the problem of achieving very high-Q values, while still operating the active stage with a large gain margin. This enables a significant increase in Q to be obtained, higher filter frequencies, and robust operation. The general synthesis procedure for the hybrid filter is described. The filter response demonstrates very high-resolution microwave signal filtering with a measured Q of 801.

Photonic signal processing of microwave signals using an active-fiber Bragg-grating-pair structure

A new active photonic signal processor which achieves a high-Q microwave bandpass response is presented. It comprises active fiber within a pair of fiber Bragg gratings, and produces multiple taps with precise delay-time characteristics. The impulse response has demonstrated well in excess of 270 taps. The filter response demonstrates high resolution, having a narrow-band response with a Q of 325. The processor is also tunable, in both passband width and frequency.

Microwave optical filters using in-fiber Bragg grating arrays

A novel multitap optical transversal signal processor based on wavelength multiplexed Bragg grating arrays is presented. This structure enables the realization of a large number of taps for obtaining sharp bandpass filtering with high resolution and also enables arbitrary tap weight profiles to be obtained. Results on a 4-GHz, 29-tap filter demonstrates a sharp bandpass filter response, and windowing techniques on the tap profiles are demonstrated to enhance the sidelobe suppression characteristics.

Tunable microwave fiber-optic bandpass filters

A new photonic filter which can realize both high-resolution bandpass microwave response and which is also widely tunable is presented. This is based on the use of long chirped Bragg gratings and a section of active fiber, and tuning is obtained by changing the carrier wavelength. A fractional tuning range of 20% is demonstrated experimentally, and this can readily be extended. A model is presented to describe the frequency limitations of the filter, and design guidelines are given to overcome the grating dispersion limits. The new structure enables the realization of wide-band continuously tunable filters with fast tuning and high-Q.

Microwave Photonic Downconverter With High Conversion Efficiency

A high conversion efficiency microwave photonic frequency downconverter based on an integrated dual-parallel Mach Zehnder modulator (DPMZM) and optical phase shifter configuration, is presented. This structure features the advantages of high conversion efficiency, robust operation, and ability to function over a very wide frequency range. The introduction of a novel phase shifter that is incorporated within the structure enables a high rejection of over 45 dB of the local oscillator (LO) to be achieved. The integrated DPMZM based photonic mixer also has a lower noise figure and a higher spurious free dynamic range compared to the conventional dual-series modulator based photonic mixer. Experimental results demonstrate a significant improvement of 23.7 dB in the conversion efficiency compared to the conventional dual-series modulator based photonic mixer for the same optical power into the photodetector.

Photonic bandpass filters with high skirt selectivity and stopband attenuation

A new photonic signal processor topology that simultaneously achieves both a high-Q and a high skirt selectivity and stopband attenuation filter response is presented. It is based on a novel dual-cavity bandpass optical structure in which two pairs of active fiber Bragg grating cavities are used with an optical gain offset to control the poles and stopband attenuation characteristics of the filter. This concept enables a large improvement in the filter stopband attenuation, rejection bandwidth, and skirt selectivity to be realized. Measured results demonstrate both a narrow bandpass bandwidth of 0.4% of center frequency and a skirt selectivity factor of 16.6 for 40 dB rejection, which corresponds to a 6.5-fold improvement in comparison to conventional single cavity high-Q structures. To our knowledge, this is the best skirt selectivity reported for a photonic bandpass filter to date. The new photonic filter structure has been experimentally verified and excellent agreement between measured and predicted responses is shown.

Photonic Beamforming Based on Programmable Phase Shifters With Amplitude and Phase Control

A new optically controlled phased array beamforming technique based on phase modulations of wavelength-division-multiplexed (WDM) single sideband modulated light with carrier using a two-dimensional array liquid crystal on silicon (LCoS) pixels device, is presented. It realizes multiple wideband photonic microwave phase shifters, operates over a wide frequency range, and simultaneously integrates the array phase taper and the array amplitude taper within a single unit. The beamforming is software programmable. Experimental results demonstrate multiple independent microwave phase shifters that operate simultaneously over a 10- to 20-GHz frequency range, and results demonstrate beamsteering in a four-element optically controlled beam steering array at 18 GHz.

Tunable and Reconfigurable Photonic Signal Processor With Programmable All-Optical Complex Coefficients

A new all-optical microwave photonic filter structure that can realize arbitrary programmable complex coefficients, multiple taps, and shape-invariant frequency tuning over the full free-spectral range (FSR) range is presented. It is based on a new optical RF phase shifter achieved by using a programmable wavelength processor (PWP) comprising an array of liquid crystal on silicon pixels. It manipulates the amplitude and phase of optical spectral components, which enables both single-sideband modulation and arbitrary complex coefficient function to be obtained simply by versatile programming the PWP only, without changing the rest of the structure. Experimental results demonstrate reconfigurable and tunable shape-invariant multitap RF filters with wideband tuning range over the full FSR by software programming of the complex coefficients.

Dispersion induced RF distortion of spectrum-sliced microwave-photonic filters

A general theoretical model for spectrum-sliced microwave-photonic filter design is presented. It is applicable to arbitrary variable time-delay characteristics, and to both double- and single-sideband modulation formats. Based on this model, dispersion-induced RF characteristics are investigated theoretically and experimentally. The results show that apart from the carrier suppression effect, the performance of spectrum-sliced microwave-photonic filters is limited by a dispersion-induced RF distortion that is related to the sliced spectrum character, and which is modulation format independent. The model provides data for designing the optimum grating optical slicing bandwidth and shape, and for determining the required spectral slice matching tolerance, to overcome nonideal RF characteristics and to enhance the filter frequency response.