Derek Chang

Efficiency pedestal in quasi-phase-matching devices with random duty-cycle errors

It is shown that random duty-cycle errors in quasi-phase-matching (QPM) nonlinear optical devices enhance the efficiency of processes far from the QPM peak. An analytical theory is shown to agree well with numerical solutions of second-harmonic generation (SHG) in disordered QPM gratings. The measured efficiency of 1550 nm band SHG in a periodically poled lithium niobate (PPLN) waveguide away from the QPM peak agrees with observations of domain disorder in a PPLN wafer by Zygo interferometry. If suppression of parasitic nonlinear interactions is important in a specific application of QPM devices, control of random duty-cycle errors is critical.

Apodization of chirped quasi-phasematching devices

Chirped quasi-phasematching (QPM) optical devices offer the potential for ultrawide bandwidths, high conversion efficiencies, and high amplification factors across the transparency range of QPM media. In order to properly take advantage of these devices, apodization schemes are required. We study apodization in detail for many regimes of interest, including low-gain difference frequency generation (DFG), high-gain optical parametric amplification (OPA), and high-efficiency adiabatic frequency conversion (AFC). Our analysis is also applicable to second-harmonic generation, sum frequency generation, and optical rectification. In each case, a systematic and optimized approach to grating construction is provided, and different apodization techniques are compared where appropriate. We find that nonlinear chirp apodization, where the poling period is varied smoothly, monotonically, and rapidly at the edges of the device, offers the best performance. We consider the full spatial structure of the QPM gratings in our simulations, but utilize the first order QPM approximation to obtain analytical and semi-analytical results. One application of our results is optical parametric chirped pulse amplification; we show that special care must be taken in this case to obtain high gain factors while maintaining a flat gain spectrum.

104 MHz rate single-shot recording with subpicosecond resolution using temporal imaging.

We demonstrate temporal imaging for the measurement and characterization of optical arbitrary waveforms and events. The system measures single-shot 200 ps frames at a rate of 104 MHz, where each frame is time magnified by a factor of -42.4x. Impulse response tests show that the system enables 783 fs resolution when placed at the front end of a 20 GHz oscilloscope. Modulated pulse trains characterize the systems impulse response, jitter, and frame-to-frame variation.

Characteristics and instabilities of mode-locked quantum-dot diode lasers.

Passively mode-locked quantum-dot diode lasers are very difficult to characterize because they are typically unstable, have low peak powers, and high bandwidth. Measure data indicates these lasers are not typically mode-locked.

Pulse characterization of a passively mode-locked quantum dot semiconductor laser using FROG and autocorrelation

A comparison between the operational map of a QD MLL done by autocorrelation and FROG is made. The results show that the complete mode-locking region is significantly smaller when FROG is used versus autocorrelation.

745 fs Resolution Single-Shot Recording at 2.1 Tsample/s and 104 Mframes/s Using Temporal Imaging

We demonstrate temporal imaging with -42.6x time magnification of 200 ps frames with subpicosecond resolution for waveforms containing 2.5 Gb/s modulated picosecond pulses. 852 GHz signal bandwidth is captured single-shot at 104 MHz frame rates.

Phase-mismatched localized fields in A-PPLN waveguide devices.

Highly phase-mismatched nonlinear interactions can generate spatially localized optical fields that can affect the performance of nonlinear optical devices. We present a theoretical description of the generation of such spatially localized optical fields by ultrafast pulses. The effects of temporal walk-off and pump depletion are discussed, along with methods for suppression of the localized field while maintaining the performance of the nonlinear device. The model is validated by the measurement of the spatial profile of the localized field in a quasi-phase-matched (QPM) aperiodically poled lithium niobate (A-PPLN) waveguide. Finally, we fabricate and characterize A-PPLN devices with a 33% duty cycle to reduce the locally generated field by 90%.

Complex-transfer-function analysis of optical-frequency converters

We measure the complex transfer function (CTF) of aperiodically poled lithium niobate waveguide devices and investigate the sources of CTF distortions, which are related to variations in the spatial distribution of the nonlinear coefficient and phase-mismatch profile.

Characteristics and instabilities of mode-locked quantum-dot diode lasers

Passively mode-locked quantum-dot diode lasers are very difficult to characterize because they are typically unstable, have low peak powers, and high bandwidth. Measure data indicates these lasers are not typically mode-locked.