Daisuke Imanishi

Effective speckle reduction in laser projection displays

Two alternative methods for effectively reducing the speckle noise in laser based rear and front projection displays are studied and demonstrated. Firstly, widening of the laser emission spectrum to nearly 4nm by tailoring the structures of 640nm band AlGaInP/GaInP based edge emitting broad-area red laser diode arrays, realized a reduction of speckle contrast from 20% to an acceptable level of 5%. Designing the power/wavelength distribution of the multiple emitters to achieve a flat top profile for the total spectrum plays an important role in maximizing the speckle reduction effect. This approach could easily be adapted to laser diodes arrays of other materials or wavelengths. Secondly, relative oscillation movement within the screen layers can also reduce the speckle contrast to the acceptable level of 5%. The moving layer material and the oscillation period has been studied and optimized to maximize the reduction level for both rear and front projection configurations. The two speckle reduction techniques were evaluated on a front projector utilizing a red laser assisted UHP lamp hybrid light source, and showed significant enhancement in view ability by the suppression of speckle. Combining the two techniques lead to further reduction in speckle and scintillation noise to a supreme level of 2%, enabling a practical solution for wide color gamut and high efficiency laser projection displays.

Highly reliable 7 W operation of 644 nm wavelength laser diode arrays with top-hat near field pattern

AlInP/GaInP 7 W laser arrays with a uniform intensity distribution and a low smile of 1 /spl mu/m have been developed for a display system. The estimated lifetime exceeds 10000 hours under CW operation.

Monolithic-integrated two-wavelength laser diodes for digital-versatile-disk/compact-disk playback

We have developed a monolithic two-wavelength laser diode, which emits 650 and 780 nm wavelengths. This device, which has a separated-confinement-heterostructure multi-quantum-well active region and a gain-guiding tapered-stripe structure, is fabricated using only two steps of metal organic chemical vapor deposition. The operating currents at 5 mW are 57.0 and 61.5 mA for the 650 and 780 nm elements, respectively. The relative intensity noise of the 650 and 780 nm elements was below −130 dB/Hz up to 70 °C without high-frequency superposition circuits.

High temperature operation of 640nm wavelength high power laser diode arrays

A 0.3 W operation for a single emitter broad area red laser at 45degC was achieved, for the first time, and a highly reliable 25 emitter array operation of 6.6 W at 25degC. The laser array is composed of 25 broad stripe lasers with a stripe pitch of 400 mum. The operation current, operation voltage, slope efficiency, emission wavelength and the energy conversion efficiency of the laser diode were obtained. Lifetime test was performed under constant current mode.

Room temperature photo-pumped lasing action of ZnCdSe/ZnSe/ZnMgSSe double heterostructure grown by metal-organic chemical vapor deposition

An internal loss of 4.6 cm-1 is estimated from the cavity length dependence of photo-pumped blue-lasing at room temperature (RT) with ZnSe/ZnMgSSe double- heterostructure (DH) grown by metal-organic chemical vapor deposition (MOCVD). Operation of the first blue-green laser diode grown by MOCVD has been demonstrated at 77 K under pulsed current injection. The laser consists of a ZnCdSe single quantum-well ZnSe optical guiding layers, and ZnMgSSe/ZnSSe dually-stacked cladding layers grown on a (100) n-GaAs substrate. The observed stimulated emission is at a wavelength of 473 nm, with threshold current ranging from 90 to 180 mA (0.9 - 1.8 kA/cm2). The emission also shows a strong transverse electric polarization.