bahram jalali - Academia.edu (original) (raw)

Papers by bahram jalali

International Topical Meeting on Microwave Photonics. MWP'99. Technical Digest (Cat. No.99EX301)

In this paper we present a 12 Gsample/s continuous-time wavelength division ADC system. The syste... more In this paper we present a 12 Gsample/s continuous-time wavelength division ADC system. The system uses the recirculating photonic filter true-time-delay (TTD) for dispersion-free chirp generation. It can digitize continuous-time analog signals at 12 Gsample/s using three wavelength channels at 4Gsample/s and three real-time electronic digitizers operating at 4Gsample/s

LEOS 2001. 14th Annual Meeting of the IEEE Lasers and Electro-Optics Society (Cat. No.01CH37242)

We provide analytical modeling and the detailed procedure that is used in recently proposed arbit... more We provide analytical modeling and the detailed procedure that is used in recently proposed arbitrary waveform generation technique by using MEMS digital micro-mirror arrays. We estimate the achievable temporal resolution, repetition rate, modulation index and the rise/fall times of the final waveform as figure of merit in the proposed systems. We show that reducing the diffraction limit via increasing the ratio of beam size to lens focal length (>0.075) and the spatial modulation down to single mirror pitch size (10.8μm), waveforms up to 18GHz repetition rates with >90% modulation index and <100ps rise times are achievable. Theoretical calculations are compared with experimental generation of 120MHz square waves and 160MHz sawtooth waves and obtained good agreement.

2nd IET International Conference on Intelligent Signal Processing 2015 (ISP), 2015

In this work a novel approach to edge detection on Synthetic Aperture Radar (SAR) images is intro... more In this work a novel approach to edge detection on Synthetic Aperture Radar (SAR) images is introduced. The proposed method uses an optics inspired transform which emulates the diffraction of an image through a medium with nonlinear dispersive properties. The experimental results show that the output of the introduced Phase Stretch Transform (PST) in conjunction with further morphological operations can be effectively used for image edge detection.

Zeitschrift Fur Pflanzenkrankheiten Pflanzenpathologie Und Pflanzenschutz, 1970

IEEE Photonics Journal, 2015

We experimentally demonstrate, for the first time, a method for arbitrary waveform generation (AW... more We experimentally demonstrate, for the first time, a method for arbitrary waveform generation (AWG) with time-bandwidth product (TBP) expansion beyond the limitations set by a spectral encoder. We show that, by using an anamorphic stretch transform with a specific group delay (GD) profile, one can boost the TBP of the generated electrical waveform in time-stretch AWG. In particular, we show that the TBP expansion can be achieved, depending on the signal sparsity and proper choice of the warped GD dispersion profile. The new waveform generation system is implemented here using a nonlinearly chirped fiber Bragg grating with a warped GD profile. Experimental demonstrations in this paper show a TBP expansion of more than three times above the maximum achievable using conventional methods. Details of the signal dependence and spectral redundancy/sparsity requirement for time-bandwidth compression and expansion are also studied.

(CLEO). Conference on Lasers and Electro-Optics, 2005., 2005

We report the first demonstration of coherent optical MIMO utilizing adaptive equalization for IS... more We report the first demonstration of coherent optical MIMO utilizing adaptive equalization for ISI. Coherent optics implementation is essential to ensure the necessary diversity and hence MIMO benefits, independent of fiber length and data rate.

2014 48th Asilomar Conference on Signals, Systems and Computers, 2014

Application of the recently introduced Discrete Anamorphic Stretch Transform to data clustering i... more Application of the recently introduced Discrete Anamorphic Stretch Transform to data clustering is proposed and demonstrated. We show that the Transform enhances vector quantization in terms of its computation speed and peak SNR by increasing the image coherence. To validate our technique's utility in data compression, we show superior performance compared to JPEG 2000.

UCLA researchers in the Department of Electrical and Computer Engineering have developed an Anamo... more UCLA researchers in the Department of Electrical and Computer Engineering have developed an Anamorphic Spectrum Transformation (AST) scheme for compressing the time-bandwidth product of analog signals, making it easier to digitize wideband signals and to reduce the volume of the digital data generated. BACKGROUND Efficient compression of analog and digital data helps the processing, communication and storage of these forms of data. Compression of temporal signals, such as communication signals or those generated by sensors, involves sampling at a sufficient rate so as to obtain desired signal information and then being able to communicate or store that data efficiently. One existing mechanism for reaching a sufficient sampling rate involves time-stretching to trade off intensity-bandwidth and temporal-duration, thus allowing sampling to be performed at a lower rate while proportionally increasing the temporal duration. Time-stretching performed in the analog domain prior to sampling reduces signal bandwidth, but does not reduce the time-bandwidth product because the signal is temporally stretched in time, whereby storage requirements remain constant. Current data compression techniques operate on digital data only. The analog data from high speed sensors and instruments is often too fast to be digitized in real time. Therefore, a need exists for an enhanced data compression method which reduces modulation intensity bandwidth without a proportional increase in temporal duration.

Optics and Photonics News, 2014

Coping with a deluge of digital information will require more efficient ways to capture, sample a... more Coping with a deluge of digital information will require more efficient ways to capture, sample and store data. One new approach works by selectively “warping” the data to provide better resolution of the fine details - while still reducing total data size.

Optics Letters, 1995

We describe an optically assisted folding-f lash analog-to-digital converter. The periodic transf... more We describe an optically assisted folding-f lash analog-to-digital converter. The periodic transfer function of the Mach-Zehnder interferometer is used to perform analog folding on the electronic signal to be quantized. A novel analog encoding scheme for efficient generation of gray code digital data is proposed. The new encoding scheme eliminates the requirement for interferometers with ultralow V p , which, so far, has hindered the development of such systems. The encoding concept is experimentally demonstrated through the use of LiNbO 3 modulators.

Optics Letters, 1996

A novel wavelength-selective photonic time-delay filter is proposed and demonstrated. The device ... more A novel wavelength-selective photonic time-delay filter is proposed and demonstrated. The device consists of an optical phased-array waveguide grating in a recirculating feedback configuration. It can function as a true-time-delay generator for squint-free beam steering in optically controlled phased-array antennas and as an encoding-decoding filter for wavelength code-division multiple access.

This paper presents an overview of the silicon-on-insulator photonic integrated circuit (SOIPIC) ... more This paper presents an overview of the silicon-on-insulator photonic integrated circuit (SOIPIC) technology. Recent progress in material and device technologies including WDM filters are presented.

Journal of Lightwave Technology, 2006

After dominating the electronics industry for decades, silicon is on the verge of becoming the ma... more After dominating the electronics industry for decades, silicon is on the verge of becoming the material of choice for the photonics industry: the traditional stronghold of III-V semiconductors. Stimulated by a series of recent breakthroughs and propelled by increasing investments by governments and the private sector, silicon photonics is now the most active discipline within the field of integrated optics. This paper provides an overview of the state of the art in silicon photonics and outlines challenges that must be overcome before large-scale commercialization can occur. In particular, for realization of integration with CMOS very large scale integration (VLSI), silicon photonics must be compatible with the economics of silicon manufacturing and must operate within thermal constraints of VLSI chips. The impact of silicon photonics will reach beyond optical communication-its traditionally anticipated application. Silicon has excellent linear and nonlinear optical properties in the midwave infrared (IR) spectrum. These properties, along with silicon's excellent thermal conductivity and optical damage threshold, open up the possibility for a new class of mid-IR photonic devices.

Journal of Lightwave Technology, 2011

Page 1. JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 29, NO. 20, OCTOBER 15, 2011 3099 Photonic Time-Str... more Page 1. JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 29, NO. 20, OCTOBER 15, 2011 3099 Photonic Time-Stretched Analog-to-Digital Converter Amenable to Continuous-Time Operation Based on Polarization Modulation With Balanced Detection Scheme ...

IEEE Transactions on Microwave Theory and Techniques, 1999

We demonstrate a new concept for analog-to-digital (A/D) conversion based on photonic time stretc... more We demonstrate a new concept for analog-to-digital (A/D) conversion based on photonic time stretch. The analog electrical signal is intensity modulated on a chirp optical waveform generated by dispersing an ultrashort pulse. The modulated chirped waveform is dispersed in an optical fiber, leading to the stretching of its envelope. We have derived analytical expressions for the stretch factor and the resolution of the system. An analogto-digital converter (ADC) consisting of the photonic time-stretch preprocessor and a 1-Gsample/s electronic ADC is demonstrated. This technique is promising for A/D conversion of ultrafast signals and, hence, for realization of the digital receiver.

IEEE Transactions on Microwave Theory and Techniques, 1997

We present an all-optical delay-line radio-frequency (RF) notch filter. The filter exploits cross... more We present an all-optical delay-line radio-frequency (RF) notch filter. The filter exploits cross-gain modulation in a homogeneously broadened laser medium to obtain a negative tap in an optically incoherent system. Applications including moving-target indication (MTI) in optically controlled radars are discussed.

IEEE Transactions on Circuits and Systems I: Regular Papers, 2008

Though it promises high bandwidths, the optical medium is not popular in local area networks. Thi... more Though it promises high bandwidths, the optical medium is not popular in local area networks. This is because current optical networks do not offer the ease of use and setup that an uncoordinated multiple access network such as Ethernet offers. In this paper, we propose a novel nonlinear trellis code designed for multiple access among uncoordinated nodes in an optical communications system. This code has been shown to have an efficiency of 30%. We have implemented the codes on Xilinx FPGA's for a 6 user optical system, transmitting data on a single wavelength. The above system was set up using commercial off-the-shelf components and we demonstrated BER of < 10 09 for three users, each running at a channel rate of 2 Gbps. Demonstration of this system required the design of new channel codes, architectural optimizations for the implementation of the channel codes for high speed with limited resources and electrical/optical optimizations to realize the optical channel. Index Terms-High-speed architectures, multiple access network, nonlinear trellis code, optical network, uncoordinated access network. I. INTRODUCTION O PTICAL communications have been becoming more and more important with the ever-increasing demands for bandwidth. Fiber optic technology has been demonstrated for speeds up to hundreds of gigabits per second because of its low loss and low dispersion over extended bandwidths. These properties of optical technology have been well utilized to form the backbone of global networks such as the internet and telephone networks.

IEEE Signal Processing Letters, 2014