Tomoki Ohno

Self-pulsation in InGaN laser diodes with saturable absorber layers

Self-pulsating InGaN laser diodes with a p-type InGaN saturable absorber (SA) layer are demonstrated. The SA layer consists of a 1-nm-thick p-type InGaN well surrounded by 2-nm-thick p-type In0.02Ga0.98N barriers. The lower barrier of the SA is located on the 18-nm-thick p-type Al0.3Ga0.7N evaporation-prevention layer of the active region. Self-pulsation is demonstrated for output powers in the range 4 to 22 mW with corresponding self-pulsation frequencies in the range 1.6 to 2.9 GHz. Results indicate that the position of the SA layer in the structure has a strong influence on the carrier lifetime and is responsible for the observation of self-pulsation in these devices.

AlGaInN Violet Laser Diodes Grown on GaN Substrates with Low Aspect Ratio

AlGaInN violet laser diodes grown on GaN substrates have been studied. Waveguide simulations have been performed and perpendicular radiation angles have been investigated. A peculiar layer structure has been proposed to reduce the perpendicular radiation angle and compared with a conventional laser. The laser structure has an n-cladding layer consisting of three AlGaN films, the middle film of which has relatively high Al composition. A laser diode with an optimized structure has been fabricated. The threshold current density and slope efficiency have been 2.9 kA/cm2 and 1.4 W/A, respectively. The perpendicular radiation angle has been as small as 16.2°. The AlGaInN violet laser diode with a low aspect ratio of 1.6 and a small threshold current of 29 mA has been realized.

Self-pulsation in an InGaN laser-theory and experiment

Room-temperature operation of self-pulsating InGaN lasers was obtained at a wavelength of 395 nm. The laser structure consists of a multiquantum-well InGaN active layer and a p-type InGaN single-quantum-well saturable absorber. The frequency range of the self-pulsation was from 1.6 to 2.9 GHz. The experimental results were well explained with our theoretical analysis. We found that features of the saturable absorber strongly affect the self-pulsation. Influence of device and material parameters on the laser dynamics was also investigated.

Laser Diode Active Height Control for Near Field Optical Storage

The use of commercial laser diodes as near field, nano-scale position sensors for feedback control systems was experimentally investigated. A static experimental setup was constructed to measure and characterize the laser diode feedback mechanism. Experiments show that the lasers, which act as miniature interferometers, provide a high accuracy, high signal-to-noise ratio (SNR) signal both in the near and far field. The laser diodes were then mounted in commercial digital versatile disc (DVD) actuators and a control system was constructed. The control system can operate both in the near and far field, and a controlled approach from the far to near field is demonstrated using a fringe jump controller. Finally, using the experimentally gathered feedback data, the residual control error of ±1 nm was estimated for this system.

Characterization of blue- and red- very small aperture lasers for hybrid recording

The characterization of a rectangular aperture on a very small aperture laser (VSAL) is described and the parameters of interest to hybrid recording technology is quantified. VSALs based on blue laser diodes (LDs) (/spl lambda/ = 405 nm) and red-LDs (/spl lambda/ = 658 nm) with 100 nm /spl times/ 200 nm rectangular apertures milled into 50 nm thick aluminum by focused ion beam etching (FIBE) are fabricated and their slope efficiencies (SE) captured by a NA 0.65 objective lens in the far field (FF) measured. SE is defined as the-ratio of the measured optical power to the input current. The background SEs (BSE) were measured after coating with Al but prior to forming the aperture for reference. The SEs of these blue and red lasers with apertures were 2.7 mW/A (BSE = 1.3 mW/A) and 3.8 mW/A (BSE = 0.3 mW/A), respectively. Detailed characterization of both lasers before and after aperture fabrication indicate that this greater SE of the red VSAL is primarily due to greater efficiency of coupling between the laser and the aperture, /spl eta//sub coupling/, and greater transmission efficiency of the aperture, /spl eta//sub aperture/, in the red. It is not due to difference in the SBs of the two LDs themselves. Near field simulation of the apertures using the finite difference time domain (FDTD) method supports the above conclusions.