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ABSTRACT: A multiple-beam photonic beamforming receiver is proposed and demonstrated. The architecture is based on a large port-count demultiplexer and fast tunable lasers to achieve a passive design, with independent beam steering for multiple beam operation. A single true time delay module with four independent beams is experimentally demonstrated, showing extremely smooth RF response in the -band, fast switching capabilities, and negligible crosstalk.
IEEE Photonics Technology Letters 01/2011; · 2.19 Impact Factor
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ABSTRACT: A scheme for the photonic generation and coherent detection of ultra-wideband radio-frequency (RF) noise is proposed and demonstrated. The technique relies on the amplified spontaneous emission of a broadened stimulated Brillouin scattering process in an optical fiber (SBS-ASE). The SBS-ASE noise is on-off modulated, and down-converted to the RF spectral range via heterodyne beating. The spectrum of the SBS-ASE is broadened beyond 1 GHz by tailored direct modulation of the pump wave. A data transmitter and a coherent receiver are demonstrated experimentally. Coherent detection of the noise waveform is based on the transmission of a delayed, unmodulated replica alongside the data (transmit reference). A performance analysis of the receiver statistics is provided. Q parameter values of 4.6 at data rates of 4 Mb/s are demonstrated.
IEEE Photonics Technology Letters 12/2010; · 2.19 Impact Factor
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ABSTRACT: A photonic beamformer is presented, having smooth behavior. Third-order nonlinearities, resulting from its optoelectronic components, are investigated, with emphasis on their impact on the contrast of imaging radars. This contrast is shown to be severely limited by the induced RF nonlinearities. Limitations on the allowable modulation index are studied for linearly-chirped pulses returned from clutter.
Microwaves, Communications, Antennas and Electronics Systems, 2009. COMCAS 2009. IEEE International Conference on; 12/2009
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ABSTRACT: The contrast of imaging radars is shown to be severely limited by RF nonlinearities, introduced by opto-electronic devices like intensity modulators. Limitations on the allowable modulation index are studied for linearly-chirped pulses returned from clutter.
Microwave Photonics, 2009. MWP '09. International Topical Meeting on; 11/2009
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ABSTRACT: A new approach for multiplexing interferometric fiber optic sensors is described and studied. The approach is based on a lattice of unbalanced Mach-Zehnder interferometers. This configuration is inherently low-loss and can be implemented and deployed in a simple manner. The signals from the cascaded sensors are extracted from the measured data via a layer peeling algorithm. A fifth-order polarimetric implementation of the proposed multiplexing technique has been constructed and characterized. The third sensor was buried in a sandbox while the rest of the sensors were spooled on a bobbin. The system successfully separated and monitored the pressure variations in the different sensors with minor crosstalk.
Journal of Lightwave Technology 11/2009; · 2.78 Impact Factor
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ABSTRACT: With the advent of new forms of true time delay wideband beamformers -both photonic and digital-the effect of noise within the beamformer channels must be taken into account. As an example, in this paper, a multibeam photonic beamformer for a phased array working in receive mode using linear frequency modulated pulses is analyzed. A general expression is obtained showing the effect of the optical noise on the spatial antenna pattern and on the impulse response. The S/N (signal to noise ratio) of the beamformer is examined with regard to both uncorrelated and correlated noise between channels.
Radar Conference, 2008. RADAR '08. IEEE; 06/2008
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ABSTRACT: Flat-top sharp optical filters of gigahertz bandwidth are realized using stimulated Brillouin scattering (SBS). Pump chirp control of the SBS process enables versatile programming of the filter shape and bandwidth. The operating wavelength of the filters is tunable, and their frequency response is inherently aperiodic. Full widths at half maximum of 1.3-2.5 GHz are demonstrated, with a filtering selectivity up to 30 dB and an rms ripple of 0.5-1 dB. The filters are used to convert double sideband to single sideband (SSB) modulations for 1-GHz-wide linear-frequency-modulated (LFM) signals of arbitrary radio-frequency carrier. Such SSB modulation is highly instrumental for photonic implementations of true time delay, for example, in antenna beam-forming. The peak-side-lobe ratio of the processed LFM signal was -32 dB; its main lobe was broadened by only 4%. The integrated side-lobe ratio, which is limited by noise from spontaneous Brillouin scattering, was better than 21 dB, which is a sufficient value for most systems. The technique results in a large modulation index and does not lead to harmonic distortions.
Journal of Lightwave Technology 09/2007; 25(8):2168-2174. · 2.78 Impact Factor
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ABSTRACT: Modern day phased array radar systems are requiring increasingly wider bandwidths. These systems typically use a short pulse or an equivalent waveform. When this pulse travels through the system, it passes through a series of RF components, each with its own impulse response, or equivalently its own transfer function. Calibration of arrays with wide instantaneous bandwidths entails a new methodology. Both the transfer functions of the beamformer and the antenna element must be calibrated in regard to both the temporal and spatial dependences, adding new challenges to the standard phased array analysis.
Antennas and Propagation Society International Symposium, 2007 IEEE; 07/2007
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ABSTRACT: Continuously tunable delay of broadband analog signals for microwave photonics applications is described and demonstrated, based on stimulated Brillouin scattering (SBS) in optical fibers. The optical spectrum of the pump laser is synthesized using chirp control, in order to obtain a broadened SBS "slow light" process, with long delay and low amplitude and phase distortions. The resulting SBS process is applied to delay 1-GHz-wide linear frequency modulated radio-frequency signals of arbitrary carrier frequency. Delays up to 230 ps are observed, with a worst-case sidelobe suppression ratio of -26 dB
IEEE Photonics Technology Letters 05/2007; · 2.19 Impact Factor
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ABSTRACT: A wideband (>10 GHz) beamformer, based on a photonic true-time-delay, with sub-microsecond angle switching is reported. The smooth microwave transmission (ripples <0.5 dB&<3deg) and superb uniformity among the elements (<0.1 dB&<0.5deg) result in excellent RF performance.
Optical Fiber Communication and the National Fiber Optic Engineers Conference, 2007. OFC/NFOEC 2007. Conference on; 04/2007
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ABSTRACT: The general expression for a monochromatic antenna pattern is extended to a two dimensional function with dependence on both space and time. Expressions for the wideband antenna pattern in space and the impulse response in time are developed. The effects of random errors in the spatial domain and errors common to all elements with fluctuations in the frequency domain are analyzed. Examples are given, including RF beamformers and elements in finite arrays, but with an emphasis on a photonic beamformer, which shows improved performance relative to its RF counterparts in both the spatial and time domains
IEEE Transactions on Antennas and Propagation 02/2007; · 2.15 Impact Factor
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ABSTRACT: A generalized conversion matrix (GCM) and numerical analysis are used to study the distortions suffered by a linear frequency-modulated radio frequency (RF) pulse while propagating through photonic links to be used in wideband phased arrays. The analysis shows the effects of dispersion of all orders, coherent crosstalk and nonlinearity of the optical components on the RF pulse, and the high performance needed to achieve acceptable RF performance of the temporal (impulse) response. The effects of the electrical-to-optical (E/O) and optical-to-electrical (O/E) conversions are also considered. Using the GCM, the optical amplitude and phase fluctuations are converted into their RF counterparts, thereby reducing the optical problem into the well-understood RF domain. A photonic wavelength-controlled true delay device is experimentally shown to achieve good RF performance over a 4-GHz bandwidth, with predicted sidelobe levels below 30 dB.
Journal of Lightwave Technology 01/2006; 23(12):4026- 4036. · 2.78 Impact Factor
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ABSTRACT: The discovery of the Rotman lens (Rotman, W. and Turner, R.F., 1963) was an enabling technology that greatly increased the capabilities of multibeam antennas. The original intent of the inventor (WR) was somewhat less ambitious. He wanted to study various interesting configurations of TTD (true time delay) beamforming, and has been somewhat amazed and fascinated to see the evolution of his original idea into its present forms. The paper compares a relatively new TTD technology which, in the near future, for certain usages, may supersede or supplement the Rotman lens - all with the guidance and the blessing of Walt Rotman. Wideband RF phased array beamformers have increasingly stringent requirements as to their performance, given the desire to detect and classify targets with increasing accuracy, and to eliminate false alarms caused by clutter. Instantaneous bandwidths are growing accordingly. Traditional error analyses of phased arrays, which concentrated on spatial patterns, must be supplemented to take into account also pulse distortion created by the transfer function of the beamformer. While these phenomena have been well known for UWB antennas, they have rarely been analyzed for large phased arrays with highly complex feed networks. The paper provides a method to analyze the performance of TTD beamformers and, as an example, shows measured results of a novel photonic beamformer in transmission with a comparison to the traditional Rotman lens.
Antennas and Propagation Society International Symposium, 2005 IEEE; 08/2005
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ABSTRACT: A radio frequency subcarrier modulated wavelength-controlled dense wavelength-division-multiplexing-based photonic true time delay module, with very low phase (±4°) and magnitude (±0.5 dB) ripples over a bandwidth of several gigahertz, is demonstrated to achieve wide-band linear frequency modulation transmission (600 MHz) with -37-dB sidelobe suppression and signal-to-noise exceeding 80 dB/MHz.
IEEE Photonics Technology Letters 06/2005; · 2.19 Impact Factor
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ABSTRACT: A method to implement highly efficient and selective transformation between different fiber modes is presented. It is based on free space wavefront manipulation and enables the construction of high performance high-order mode dispersion compensating modules.
Optical Fiber Communication Conference, 2005. Technical Digest. OFC/NFOEC; 04/2005
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ABSTRACT: We demonstrate for the first time high quality wide bandwidth (600 MHz) LFM transmission through a wavelength-controlled photonic true time delay device with bandwidth-limited resolution and peak sidelobe level below -37 dB at 5 GHz.
Microwave Photonics, 2004. MWP'04. 2004 IEEE International Topical Meeting on; 11/2004
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ABSTRACT: The paper extends the analysis of the CW link for a linear frequency modulated pulse (LFM). It examines the problems of loss, SNR and phase and amplitude ripple, and shows that using COTS elements, a Tx LFM beamformer can be constructed, which satisfies many radar requirements.
Antennas and Propagation Society International Symposium, 2004. IEEE; 07/2004
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ABSTRACT: We demonstrate the advantageous use of highly dispersive (>450 ps/nm·km), high-order-mode (HOM) fiber modules for true time delay applications. Along with their low insertion loss, very low phase ripple (root mean square <0.3° over 0-20 GHz), and high immunity to nonlinear effects, the high dispersion values facilitate the construction of devices with relatively short fibers, resulting in improved tolerance of the radio frequency delay to thermal changes. The implications of multiple path interference effects in HOM modules are also studied and shown to be very small.
IEEE Photonics Technology Letters 06/2004; · 2.19 Impact Factor
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ABSTRACT: A new analytical expression (the conversion matrix) for the effect of an arbitrary optical transfer function on small signal RF modulation is presented with applications to linear-frequency-modulated (LFM) signals. Chromatic dispersion of any order can be investigated, as well as wavelength-dependent insertion loss.
Electronics Letters 05/2004; · 0.96 Impact Factor
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ABSTRACT: Using a novel 4×4 Mueller-like time-dependent matrix to describe the propagation of modulated light in birefringent optical systems, a new method for characterizing the polarization dependence of the RF spectrum in systems having polarization-mode dispersion and polarization-dependent loss is proposed and demonstrated. By measuring the RF spectra for nine different input states of polarization (SOP), the spectrum of any other input SOP is accurately predicted. Another application of the general formulation allows the study of the dependence of the time-resolved characteristics of the SOP of light propagating in a birefringent medium.
Journal of Lightwave Technology 05/2004; · 2.78 Impact Factor
