ROHM has announced the development of self-pulsation dual-wavelength laser diodes for DVD/CD players featuring low noise characteristics and low operating current at high temperatures. Typically, both the light-trapping control structure utilized to apply pulsation and the current-trapping control configuration that affects the temperature characteristics and operating current are controlled simultaneously. In contrast, ROHM’s RLD2WMUR1, RLD2WMFR1, and RLD2WMDR1 utilize a unique configuration that allows separate control, making it possible to maintain self-pulsation characteristics while improving temperature characteristics. This enables stable optical disc reading with low noise, without heat dissipation measures, and without the tendency of conventional self-pulsation laser diodes to revert to single mode operation at high temperatures. A low operating current of 70mA—10mA less than competitor products (at a case temperature of 70ºC for DVD sets)—has been achieved due to improved current-trapping measures.
Until recently most laser diodes used as pickups in CD and DVD players are of the ‘single mode’ variety, which as their name suggests pulsate roughly at a single wavelength. The advantages of this method are low operating current and stable operation at high temperatures (70–90ºC). A significant drawback is the generation of noise caused by irregular reflected light from the disc surface (commonly referred to as ‘return light’), which causes the laser light to pulsate. This often necessitated utilizing a superposition IC that blocks noise by superimposing high frequencies. Additional countermeasures were required in order to shield electromagnetic waves emitted from the IC, increasing costs.
This led to the development of ‘self-pulsation’ laser diodes which are strong against return light noise. Conventional self pulsation are actually single laser diodes that quasi-pulsate at multiple wavelengths by turning on and off at cycles of several hundred megahertz. Although this eliminates the need for superposition ICs and additional countermeasures, operation becomes unstable at high temperatures when the case temperature approaches 70ºC. Also, outside of a particular optical output region pulsation reverts to single mode, necessitating conventional radiation countermeasures (i.e. superposition IC, shielding), leading to an increase in the number of components.
ROHM dual-wavelength self-pulsation laser diodes eliminate these problems, resulting in outstanding temperature characteristics, low current operation, and stable, noise-free operation at 70ºC and 70mA. The novel configuration ensures a recommended minimum output of 1.5mW — 25% less than similar products—for greater ease of use.
Three different packages are offered: a standard 5.6 diameter CAN type (RLD2WMUR1), ideal as a replacement in existing systems, a slim 4-pin flat frame type (RLD2WMFR1), and an easy-to-use covered 4-pin flat frame (RLD2WMDR1).
