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A novel approach to generating background-free microwave pulse based on both bright and dark temporal gate and a single photodetector is proposed and demonstrated. Incoherent wavelength-to-time conversion (WTTC) using only bright or dark gate renders the generation of positive or negative pulse separately. By using both gates simultaneously, background-free pulse is realized with enhanced amplitude compared with that obtained using only bright or dark gate. A dual-output intensity modulator functions as both the bright and dark gate. Narrow drive pulse is provided by the combination of two polarity-opposite electrical pulses with a relative time-delay, which releases the requirement of expensive narrow-pulse generator. Incoherent WTTC using dark gate is demonstrated experimentally. The system resolution remains the same as that using bright gate. Furthermore, UWB pulse with 10-dB bandwidth of 3.8-GHz is generated based on 1-Gb/s gate driven by 1-Gb/s data sequence. Several other background-free pulses are generated to verify the tunability of central frequency, pulse envelope, duty cycle, and repetition rate. In addition, the effect of gate width on WTTC is explored experimentally. With narrower gate width, higher system solution and maximum achievable frequency can be implemented. 10.4-GHz and 14.5-GHz background-free pulses are generated when using 1-Gb/s and 10-Gb/s gate respectively. [ABSTRACT FROM AUTHOR]

The usefulness of a stochastic approach in determining time scales in tunneling processes (mainly, but not only, in the microwave range) is reconsidered and compared with a different approach to these kinds of processes, based on Feynman’s transition elements. This latter method is found to be particularly suitable for interpreting situations in the near field, as results from some experimental cases considered here. [ABSTRACT FROM AUTHOR]

We demonstrated a timing fluctuation suppression in outdoor laser-based atmospheric radio-frequency transfer over a 110 m one-way free-space link using an electronic phase compensation technique. Timing fluctuations and Allan Deviation are both measured to characterize the instability of transferred frequency incurred during the transfer process. With transferring a 1 GHz microwave signal over a timing fluctuation suppressed transmission link, the total root-mean-square (rms) timing fluctuation was measured to be 920 femtoseconds in 5000 s, with fractional frequency instability on the order of 1 × 1 0 − 12 at 1 s, and order of 2 × 1 0 − 16 at 1000 s. This atmospheric frequency transfer scheme with the timing fluctuation suppression technique can be used to fast build an atomic clock-based frequency free-space transmission link since its stability is superior to a commercial Cs and Rb clock. [ABSTRACT FROM AUTHOR]

Abstract: We report the first demonstration of a tunable microwave photonic notch filter based on stimulated Brillouin scattering (SBS) in a photonic chip. Single-sideband with carrier modulation (SSB+C) scheme was used to map the SBS loss spectrum into a frequency notch in the RF domain. The notch frequency can be tuned by modulating the SSB+C signal onto a tunable carrier, which was generated by means of SSB suppressed-carrier (SSB-SC) modulation. The notch filter has a high-resolution with 3-dB and 6-dB bandwidths of 126MHz and 78MHz, respectively. The filter has a notch depth of 20dB, and the notch frequency can be continuously tuned over a range of 2-8GHz, which is limited only by the current measurement setup. [Copyright &y& Elsevier]

Abstract: A novel approach using two cascaded intensity modulators and one single dual-parallel modulator to generate an optical frequency comb (OFC) is proposed and experimentally demonstrated. One broadband OFC with rectangular envelope can be achieved easily by adjusting the power of the microwave signals and the direct current bias applied to the modulators. The scheme is a relatively simple and low-power consumption solution for OFC generation, where specially tailored waveforms and high-power microwave signals are not used. In the experiment, 20 comb lines within 0.6dB spectral power variation are obtained at 10GHz microwave frequency. The experimental results agree well with the theoretical calculation. [Copyright &y& Elsevier]

Abstract: A photonic approach to implementing a microwave channelized receiver based on dense wavelength division multiplexing using an optical comb is proposed. In the approach, a flat optical comb with 11 comb lines is generated using two cascaded Mach-Zehnder modulators. Frequency analysis of a microwave signal with multiple-frequency components is realized by using the optical comb together with an optical etalon with a periodic transfer function, a wavelength division multiplexer (WDM) and a photodetector array. The system is investigated numerically. Frequency measurement of a multi-frequency signal with a measurement range from 0.5-11.5 with an accuracy of ±0.5GHz is achieved. The reconfigurability of the system realized by tuning the comb-line spacing and the peak positions of the etalon is also evaluated. The improvement of the dynamic range of the system using an optimized periodic filter is also discussed. [Copyright &y& Elsevier]

Abstract: A new technique to instantaneously measure microwave frequency and amplitude is presented and experimentally demonstrated. The architecture described is based on a single sideband modulation with suppressed carrier (SSB-SC) and the measurement of the Stokes parameters at the output of a birefringent medium. The results show errors below 50MHz in the 59% of measurements carried out in a range from 1 to 11GHz and an average power error of 0.34dB. The technique shows the potential to increase the resolution and the range by increasing the differential time delay of the birefringent medium. [Copyright &y& Elsevier]

Abstract: I studied experimentally beam self-collimation and splitting in two-dimensional microwave photonic crystals. Using a microwave photonic crystal fabricated from alumina rods, I present an experimental proof of principle for an earlier theoretical proposal [A.F. Matthews, S.K. Morrison, Yu.S. Kivshar, Opt. Commun. 279 (2007) 313] of a photonic crystal beam splitter based on the self-collimation effect. [Copyright &y& Elsevier]

Abstract: According to the magneto-optic (MO) perturbation theory, the coupled-mode equations for guided optical waves (GOWs) with microwave magneto-static waves (MSWs) in MO film waveguides are presented, which cannot only be used to analyze the MO modulation induced by MSW pulses, but also explain the optical pulse compression caused by chirped MSWs. The rectangular pulse modulation of continuous guided optical waves by magnetostatic forward volume waves (MSFVWs) excited under normal bias magnetic field is theoretically studied in detail. It is shown that: (1) the diffracted light pulse approximates to an isosceles trapezoid, which is in agreement with the experimental results, and the duration time and the flat-top response time are equal to the sum and difference between the width and transit time of the rectangular MSFVW pulse, respectively; (2) utilizing a small duty factor of MSFVW pulse helps to improve the modulating data rate, which is in inverse proportion to the transit time, and the relative peak intensity of the diffracted light pulse is less than the corresponding Bragg diffraction efficiency when the MSW duty factor is less than 0.5. [Copyright &y& Elsevier]

Abstract: We experimentally demonstrate a single passband, photonic microwave bandpass filter scheme based on stimulated Brillouin scattering (SBS) in optical fiber. A single side band (SSB)-modulated probe and a single frequency, tunable pump beam that have been produced by the combination of conventional Mach–Zehnder modulators and fiber Bragg grating filters, are used for the generation of SBS phenomenon in a 1-km long highly nonlinear dispersion-shifted optical fiber. Using the proposed scheme a single microwave passband with a ∼26MHz bandwidth is readily achieved over a radio frequency tuning range from 1.3 to 9.3GHz. The maximum Q-factor is measured to be ∼360. [Copyright &y& Elsevier]