Mohammad Umar Piracha

Range resolved lidar for long distance ranging with sub-millimeter resolution

A lidar technique employing temporally stretched, frequency chirped pulses from a 20 MHz mode locked laser is presented. Sub-millimeter resolution at a target range of 10.1 km (in fiber) is observed. A pulse tagging scheme based on phase modulation is demonstrated for range resolved measurements. A carrier to noise ratio of 30 dB is observed at an unambiguous target distance of 30 meters in fiber.

Optoelectronic loop design with 1000 finesse Fabry-Perot etalon

A 10.287 GHz optoelectronic oscillator is experimentally demonstrated that uses a 1000 finesse Fabry-Perot etalon as the mode selector instead of an rf filter. The results are compared with a standard optoelectronic loop with an rf filter. The substitution of the rf filter with the optical filter results in a higher rf stability and lower phase noise.

Simultaneous ranging and velocimetry of fast moving targets using oppositely chirped pulses from a mode-locked laser

A lidar system based on the coherent detection of oppositely chirped pulses generated using a 20 MHz mode locked laser and chirped fiber Bragg gratings is presented. Sub millimeter resolution ranging is performed with > 25 dB signal to noise ratio. Simultaneous, range and Doppler velocity measurements are experimentally demonstrated using a target moving at > 330 km/h inside the laboratory.

Multicore Fiber Sensors for Simultaneous Measurement of Force and Temperature

We demonstrate a force and temperature sensor consisting of a multicore fiber (MCF) spliced between two single-mode fibers. Increasing of the sensitivity to applied force is achieved through etching of the MCF cladding, with an overall increase of 7× compared with a 125-μm MCF device, and 12× compared with a standard fiber Bragg grating (FBG). Simultaneous decoupling of force and temperature with high accuracy is demonstrated using two MCF sections with different outer diameters. This device has robust operation up to 1000 °C, making it more suitable than FBGs for extreme environments.

Dynamic parabolic pulse generation using temporal shaping of wavelength to time mapped pulses

Self-phase modulation in fiber amplifiers can significantly degrade the quality of compressed pulses in chirped pulse amplification systems. Parabolic pulses with linear frequency chirp are suitable for suppressing nonlinearities, and to achieve high peak power pulses after compression. In this paper, we present an active time domain technique to generate parabolic pulses for chirped pulse amplification applications. Pulses from a mode-locked laser are temporally stretched and launched into an amplitude modulator, where the drive voltage is designed using the spectral shape of the input pulse and the transfer function of the modulator, resulting in the generation of parabolic pulses. Experimental results of pulse shaping with a pulse train from a mode-locked laser are presented, with a residual error of less than 5%. Moreover, an extinction ratio of 27 dB is achieved, which is ideal for chirped pulse amplification applications.

Optical Frequency Stability Measurement Using an Etalon-Based Optoelectronic Oscillator

A novel method of measuring the optical frequency stability of a continuous-wave (CW) laser by using an etalon-based optoelectronic oscillator is demonstrated. A 1000 finesse Fabry-Pérot etalon is used as a reference which eliminates the need of using an independent optical source as a frequency reference. Using this technique, the optical frequency stability of a CW laser is measured with ~3.5-kHz optical frequency resolution at update rates of 90 Hz.

Transform-limited pulses for chirped-pulse amplification systems utilizing an active feedback pulse shaping technique enabling five time increase in peak power

A fiber-based chirped-pulse amplification (CPA) system with an active feedback loop for pulse shaping is experimentally demonstrated. A spectral processor is used in conjunction with a frequency-resolved optical gating measurement to produce high-quality pulses. Spectral phase and intensity shaping are utilized to generate a clean, high-contrast, transform-limited pulse with 15 dB pedestal suppression in the pulse wing tails, resulting in a five time increase in peak power of the CPA system.

A chirped fiber Bragg grating with ripple free group delay and its application in laser ranging

The group delay ripple (<; +/-50ps) of a chirped fiber Bragg grating (dispersion = 1651ps/nm) is removed by spectral phase modulation to achieve twofold improvement in the range resolution (~320μm) of a chirped pulse lidar.

Sub-millimeter resolution laser ranging at 9.3kilometers using temporally stretched, frequency chirped pulses from a mode-locked laser

A sub-millimeter resolution ladar is demonstrated with 9.3km delay using stretched pulses allowing amplification to high powers with negligible nonlinear effects. A coherent heterodyne detection scheme results in 30dB dynamic range.

Sub-millimeter resolution laser ranging at 9.3 kilometers using temporally stretched frequency chirped pulses from a mode-locked laser

A sub-millimeter resolution ladar is demonstrated with 9.3km delay using stretched pulses allowing amplification to high powers with negligible nonlinear effects. A coherent heterodyne detection scheme results in 30dB dynamic range.