Incorporating news from O plus E magazine, Tokyo
TSUKUBA—The AIST Laboratory for Advanced Optical Technology and six collaborating companies—Sharp, TDK, Minolta, Pioneer, Pulsetek, and JVC—have jointly discovered that a recently developed ultrahigh-density optical recording disk termed a super-resolution nearfield structure has photonic transistor properties.
Photonic transistors take input optical signals and amplify or otherwise control them using light. Currently developed models are predominantly amplifiers that use optical nonlinear effects to amplify within optical fibers. However, this method requires extending the fiber length in order to increase the sensitivity of the photonic transistor, thus making it difficult to integrate into electronic devices.
The new method is an application of an ultrahigh-density optical recording technology that uses so-called "super lenses" that are able to read tiny recorded marks using nearfield light. Super lenses pick up surface plasmon light that is produced when recorded marks on optical disks are read. Surface plasmon light has a strong electric-field-enhancing effect, which the new research shows can be used to amplify signals from the optical disk.
The transistor effect can be seen by directing low-power laser light onto tiny marks recorded inside the optical disk and allowing surface plasmon light to accumulate. A readout laser with fluctuating power irradiates the area where the surface plasmon light accumulates; by creating optical scattering on a silver oxide recording film, the accumulated optical signal can be amplified.
In this experiment, a 405-nm-emitting laser and a 635-nm-emitting laser are placed opposite each other with an optical disk in between. The respective laser pickups are movable, and focusing and docking are possible much in the same way as digital versatile disks.
After writing a row of 200-nm marks on a track using the red laser, the blue laser is moved to the same track, where its 1.5-mW beam is modulated at 15 MHz (almost the same frequency as the writing signal). When the power of the red laser reading light increases from 1.5 to 3.5 mW, the strength of the blue laser light transmitted through the disk increases by approximately 60 times. In this experiment, the setup is based on optical disks. In the future, the collaboration hopes to use optical waveguides to miniaturize devices into thin-film form.
Courtesy O plus E magazine, Tokyo