Speckle contrast reduction by linear and nonlinear photonic devices
Speckle contrast <; 3.5% was achieved by means of (i) wavelength-diversity using spectrally-broad nonlinear photonic green lasers over the 520-545nm range and (ii) polarization- and phase-diversity using birefringent nano-photonic devices.
Photonic crystal changes coherent laser to incoherent laser with random phase
It is revealed that the phase-shift and polarization properties of laser beam reflected from a photonic crystal (PC) are sensitive to the surface-layer thickness of the PC. A continuous variation of λ/4 in surface-layer thickness produces a continuous change of π in the phase-shift. Besides, in the case of an asymmetric coupled-defect PC, various polarization patterns including linearly polarization in different directions, circular polarization, and different elliptical polarizations, will appear simultaneously within one laser beam. In this paper, a PC with modified surface-layer thickness is designed to induce incoherent laser irradiation with random phase at the focus point of the reflected field. This scheme will satisfy the increasing requirements for incoherent laser irradiation.
Reverse-proton-exchanged waveguide frequency doublers for green light generation
We describe reverse-proton exchanged (RPE) waveguides in MgO-doped lithium niobate capable of stable secondharmonic generation (SHG) of over 100 mW of CW green light with conversion efficiency exceeding 200%/Wcm2. Substantially higher green power would require careful thermal management to limit the phase mismatch due to heating produced by optical absorption. RPE waveguides show ability to support high-power generation of green light superior to anneal-proton exchanged (APE) waveguides containing a higher-index layer. We also demonstrate devices with multipeak spectral response for speckle-reduced green laser by using phase-modulated, quasi-periodic ferroelectric domain structure.