Mansour Dastmalchi

Generation of Arbitrary UWB Waveforms by Spectral Pulse Shaping and Thermally-Controlled Apodized FBGs

We propose and experimentally demonstrate an arbitrary UWB pulse generator. The proposed technique is based on spectral pulse shaping and frequency-to-time conversion. The reconfigurability of this technique comes from changing the apodizaton of a chirped fiber Bragg grating (FBG) using a series of heating elements (HE). By setting the appropriate temperature set to the HEs, any predesigned UWB waveforms can be generated with high precision. The effective isotropically radiated power (EIRP)-optimized and U.S. Federal Communications Commission (FCC)-optimized pulses as well as the traditional Gaussian monocycle and doublet UWB waveforms are generated which are in excellent match with the designed target pulse shapes. While other arbitrary pulse generators have used similar strategies (spectral shaping and frequency-to-time conversion), ours uses inexpensive technologies with the potential for practical, compact packaging.

Experimental demonstration of superluminal space-to-time mapping in long period gratings

We experimentally demonstrate a superluminal space-to-time mapping process in grating-assisted (GA) codirectional coupling devices, particularly fiber long period gratings (LPGs). Through this process, the grating complex (amplitude and phase) apodization profile is directly mapped into the devices temporal impulse response. In contrast to GA counterdirectional couplers, e.g., Bragg gratings, this mapping occurs with a space-to-time scaling factor that is much higher than the propagation speed of light in vacuum. This phenomenon has been used for synthesizing customized complex optical pulse data sequences with femtosecond features (3.5 Tbit/s data rate) using readily feasible fiber LPG designs, e.g., with subcentimeter resolutions.

Optical distribution of UWB: Low complexity pulse generation supporting OOK and PSK

Optical transport of UWB signals extends the reach of these power-limited signals. We propose and experimentally demonstrate a simple, low-cost method to generate UWB pulses in optics. Unlike other methods, we use the minimal hardware configuration (source/modulator/photodetector) without requiring RF pulse shaping. A novel combination of data and a sinusoidal signal modulates the intensity of a continuous wave laser to create various UWB pulses. For impulse radio UWB, on-off keying (OOK) or phase-shift-keying is accomplished simply by adjusting the data and the sinusoidal signal amplitudes. Multiband UWB signals with OOK can also be realized by this technique.

FBG-Based Matched Filters for Optical Processing of RF Signals

We demonstrate the detection of RF pulses using complex matched filters implemented in photonics. The optical receiver consists of an intensity Mach-Zehnder modulator (MZM) for electrical-to-optical conversion as well as precisely tailored fiber Bragg grating (FBG) filters performing as matched filters. We examine the performance of the receiver under two bias conditions of the MZM, namely, quadrature and minimum transmission. We design the corresponding matched filters for both cases by optimizing the impulse response of linearly chirped FBGs. We fabricate the FBGs by achieving the required apodization profiles through a multiple-scan writing procedure. We discuss the relative performance of the two solutions.

Pico-second flat-top pulse-shaper based on a linearly-chirped fiber Bragg grating in Transmission

Reshaping of ultrashort (400fs-FWHM) Gaussian-like pulses into 2ps-flat-top pulses is experimentally demonstrated using a specially apodized linearly-chirped fiber Bragg grating (LC-FBG) working in transmission.

Reconfigurable ultra-wideband waveform generation with simple photonic devices

We propose and experimentally demonstrate a low cost, low power consumption technique for ultra-wideband pulse shaping. Our approach is based on thermal apodization of two identical linearly chirped fiber Bragg gratings (LCFBG) placed in both arms of a balanced photodetector. Resistive heating elements with low electrical power consumption are used to tune the LCFBG spectral responses. Using a standard gain switched distributed feedback laser as a pulsed optical source and a simple energy detector receiver, we measured a bit error rate of 1.5×10−4 at a data rate of 1  Gb/s after RF transmission over a 1-m link.

Generation of arbitrary UWB waveforms: A low complexity optical approach

In this paper, we propose a simple and practical technique to generate the arbitrary UWB waveforms with high precision. The re-programmability of this technique comes from changing the effective apodization of a chirped fiber Bragg grating (FBG) using an array of heating elements (HE). By appropriately setting the temperatures of the HEs, many pre-designed UWB waveforms can be generated with high precision. The functionality and the precision of the proposed technique are demonstrated experimentally by generating three different UWB waveforms.