Fangxin Li

A simple single-shot frequency chirp characterization technique for telecommunication optical waveforms is introduced. The proposed technique is based on what we believe to be a novel balanced all-optical ultrafast differentiation scheme, and it enables a real-time conversion of the instantaneous frequency variation of an arbitrary complex (amplitude and phase) optical signal into a temporal intensity profile while simultaneously providing an efficient cancellation of the intensity noise. Single-shot real-time frequency chirp measurements of gigahertz-bandwidth phase-only and amplitude and phase temporal modulation waveforms are performed.

We propose and demonstrate a novel technique for group delay (GD) characterization of dispersive devices. The proposed technique involves the measurement of the temporal intensity profiles of a dispersed ultrashort optical pulse (i.e., after the device under test) and its first time derivative, which can be obtained by simple linear propagation through an all-fiber optical filter. The GD can be reconstructed using a direct and noniterative algorithm. We present experimental results for the measurement of the GD (including group-delay ripple) of high-dispersion and low-dispersion chirped fiber Bragg gratings.

We propose and demonstrate a very simple technique for accurately measuring the group delay of dispersive devices. It only requires an optical differentiator (uniform long-period fiber grating), a pulsed laser source and a high-speed oscilloscope.

A simple and general technique for recovering the phase profile of a given optical waveform from temporal intensity measurements is introduced and experimentally demonstrated. The proposed method involves the measurement of the temporal intensity profiles at the input and output of a linear optical time differentiator. The signal phase profile can be unambiguously recovered from these intensity measurements using a direct and noniterative algorithm. Given that ultrafast optical differentiators can be readily implemented in all-fiber or free-space platforms, the proposed technique could be applied over time waveforms with durations ranging from the subpicosecond to the nanosecond regime.

We introduce a simple, linear technique based on all-optical temporal differentiation for recovering the phase profile of optical waveforms from intensity measurements. We demonstrate characterization of low-power complex pulses in the sub-picosecond to nanosecond range.

A simple fiber-based spectral interferometry setup is implemented for characterizing and monitoring the amplitude and phase of ultrafast temporal waveforms generated by optical differentiation with a long-period fiber grating (LPFG). In particular, the system is applied to characterize subpicosecond odd-symmetry Hermite-Gaussian (HG) pulses, consisting of two pi phase-shifted temporal lobes, obtained by temporal differentiation of Gaussian-like pulses. This technique is ideally suited for optimizing the experiment conditions (e.g., wavelength shifting between the input pulse and LPFG transmission characteristic) so as to achieve a nearly ideal odd-symmetry HG temporal waveform (with a sharp discrete pi phase shift at its center), of potential interest as a higher order soliton in dispersion-managed optical communication systems