PACS 63.20.Dj, 77.84.Dy, 78.30.Hv Using confocal Raman spectroscopy at low temperature we investigated the perturbation of the phonon modes across a domain wall region as a function of sample stoichiometry in lithium tantalate and niobate. For all samples, we found that the Raman spectra were changed. The intensity of the A(LO) phonon modes and most of the E(TO) phonon modes were shifted and changed in their relative intensity over a 20 µm length scale. Our measurements suggest that the intensity of the A(LO) phonon modes change due to local charges induced by pyroelectric effect and/or photoionization, while the observed shifts are due to strains that are not relaxed in the domain wall region.

Two-dimensional optical beam steering using an InP photonic integrated circuit has been demonstrated. Lateral beam steering controlled by a 1-D phased array has been made easier through on-chip interferometer monitors. Longitudinal beam steering controlled by the input wavelength has demonstrated an efficiency of 0.14 • /nm. Very fast beam steering (>10 7 • /s) in both dimensions has been demonstrated as well. As the latest development, a widely tunable sampled-grating distributed Bragg reflector laser has been monolithically integrated and 2-D beam steering has been demonstrated with this on-chip tunable laser source.Index Terms-Light detection and ranging (LIDAR), optical beam steering, optical phased array (OPA), photonic integrated circuits (PICs).

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Significant enhancement in the direct amplitude modulation bandwidth of an SG-DBR laser has been demonstrated under strong injectionlocking conditions, where the wavelength detuning between the master and the free-running SG-DBR slave laser is varied from 28.58 to 13.6 nm. It is demonstrated that the relaxation resonance frequency of a strongly injection-locked SG-DBR laser increases from 1.05 GHz for the free-running case to over 20 GHz.Introduction: It is well known that the direct modulation bandwidth of a semiconductor laser is limited by the relaxation oscillations arising from the coupled rate equations that describe the dynamics of the carrier and photon densities inside the laser cavity. It has been shown that the relaxation resonance frequency of a laser can be increased using injectionlocking, resulting in an enhancement of its direct modulation bandwidth. Strong optical injection-locking has attracted attention recently for its potential for providing high-speed laser transmitters, as it improves the dynamic response of directly modulated semiconductor lasers, as well as for enhancing the relaxation oscillation frequencies, suppressing nonlinear distortions and relative intensity noise, and reducing chirp [1 -3].In the strong injection-locking regime, the optical power of the light injected from the master laser into the slave cavity is much larger than the optical power of the free-running slave laser. Recent demonstrations include enhancement of the resonance frequency beyond 100 GHz in a directly modulated strongly injection-locked vertical-cavity surfaceemitting laser (VCSEL) [4].In this Letter, we consider the injection-locking of a widely tunable sampled grating distributed Bragg reflector (SG-DBR) laser that is designed with high-speed gain and phase modulator sections. We study the direct amplitude modulation response of the SG-DBR laser when it acts as a slave laser and is strongly injection-locked to an external master laser. We demonstrate that a strongly injection-locked SG-DBR laser shows significant enhancement in its direct modulation bandwidth, even when the wavelength detuning between the master and the free-running SG-DBR slave laser is varied between 28.58 and 13.6 nm (corresponding to a frequency detuning of 1.072 and 21.68 THz, respectively). To the best of our knowledge, this is the first demonstration of direct modulation bandwidth enhancement of a strong injection-locked SG-DBR laser over a large wavelength detuning range from its free-running state.