Matsushita develops low-noise visible laser diode for video disks
Matsushita develops low-noise visible laser diode for video disks
A low-noise red-output (650 nm) laser diode that can be used for playing SD-format digital video disks (DVDs) has been developed by Matsushita Electric Industrial Co. Ltd. (Osaka, Japan). The 5-mW device has relative intensity noise of less than -130 dB/H¥with stable self-pulsation at 60°C and beam astigmatism of 3 µm. Noise characteristics are an important aspect of device performance in optical-storage applications, and light reflected back from the disk surface can be a significant source of noise. Conventional noise reduction involves application of high-frequency modulation to the laser drive current, which requires additional circuitry that increases both the package cost and size.
A self-pulsating laser diode functions as its own high-frequency modulator; therefore, such a device has been in strong demand. But, says a Matsushita spokesman, until now, self-pulsation could only be realized using the outside of the active region as the absorbing layer, with the concomitant disadvantages of large astigmatism (>10 µm) and spreading of the current flow, which leads to high operating current and unstability. The new laser diode uses a strained multiple-quantum-well structure that incorporates a saturable absorbing layer onto the active layer. Design and optimization of the structure was done with simulations accounting for the time-transient characteristics of the laser diode.