4. Laser Diodes for Laser Printers

Multi-beam Laser Diodes Realize High-speed Printing

The printing speeds of laser printers and digital copiers are increasing with each year, and the printing quality is also attaining higher resolution. In December 1999, Sony successfully released the world's first 4-beam laser products that dramatically increased both printing speed and picture-quality resolution. Since then, Sony has expanded its lineup of multi-beam laser products, and has shipped a cumulative total of 65 million multi-beam lasers thus far.

Multiple Beams Increase Effective Scanning Speed
Laser printers draw images by scanning laser beams using a polygon mirror that rotates at high speed.
The printing speed was formerly determined only by the laser beam scanning speed; that is to say, the rotational speed of the polygon mirror. As printing speeds increased year-by-year, the rotational speed demanded of the motor that rotates the polygon mirror also increased until the motor limit was reached and an alternate technology was required to achieve higher printing speeds.
For this reason, Sony developed multi-beam laser products that can simultaneously draw multiple scanning lines. Multi-beam lasers emit multiple laser beams from a single semiconductor element. By emitting either 2 or 4 beams, the effective scanning speed can theoretically be increased by 2 or 4 times.
An 8-beam laser is currently under development with the aim of mass production in July 2009.

Performance Demanded of Multi-beam Laser Diodes
Multi-beam laser diodes must minimize the relative differences in the laser characteristics of each beam as well as the interference between beams. Sony has successfully reduced the relative difference between beams with its superb wafer process, and care has also been taken in the design to reduce thermal and electrical interference between beams.