RED-EMITTING DIODE LASERS

Researchers at Shar¥Corp. (Osaka, Japan) have developed a window-grown-on-facet technology that yields a record-breaking optical output power of 295 mW from a 680-nm diode laser. This output is a large increase over conventional diodes, which operate at powers between 30 and 50 mW. According to the company, the high-power device will enable faster mass-data-storage systems based on optical disk technology. The development was revealed at the 41st Annual Applied Physics Conference held in Mar

RED-EMITTING DIODE LASERS

Novel visible diode laser produces 295 milliwatts

Paul Mortensen

Researchers at Shar¥Corp. (Osaka, Japan) have developed a window-grown-on-facet technology that yields a record-breaking optical output power of 295 mW from a 680-nm diode laser. This output is a large increase over conventional diodes, which operate at powers between 30 and 50 mW. According to the company, the high-power device will enable faster mass-data-storage systems based on optical disk technology. The development was revealed at the 41st Annual Applied Physics Conference held in March at Meiji University (Tokyo, Japan).

Higher power means that data in an optical disk system can be read and written faster than before, although at

680 nm there are some problems: as the power is raised to increase the recording speed, the facet end of the laser absorbs some of the red output, causing damage. Various methods have been proposed over the years to inhibit the deterioration of red-emitting diode lasers.

In one method, the active layer is made thinner to enable an increase in the maximum power by reducing the optical density of the facet; in another, a window structure is created that inhibits the absorption of light in the vicinity of the laser facet. However, simply working to inhibit facet deterioration does not solve the problem. In previous results, maximum power was limited to around

200 mW, and laser performance was poor.

To control the absorption of light and eliminate crystal deterioration, the Shar¥researchers fabricated a transparent window structure. The newly developed window-grown-on-facet technique uses metal-organic chemical vapor deposition to grow an optically nonabsorptive AlGaIn¥crystal layer onto the cleaved facet of the red-emitting diode laser. The resonator length is 1200 ?m, and the ridge-shaped stripe has a width of

5 ?m (see figure on p. 29).

The active layer is 20 ?m in thickness and has a multiple-quantum-well layer sandwiched between it and the p-clad layer with a compressive strain of 1%. Because the thickness of the grown window layer is less than 1 ?m, it makes no difference to the optical or electrical characteristics of the laser. So far, the maximum optical power has reached 295 mW, which the company claims is a world record for a single-longitudinal-mode laser. The power-current curve is kink-free u¥to the maximum optical power, and the new device can handle twice as much current as a conventional red-emitting diode laser.

Researchers are fabricating the laser wafers using molecular beam epitaxy. Twenty-four application patents are pending on the window-grown-on-facet technology. The company expects to begin production of 500,000 units a month this year.

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