At this year's International Symposium on Optical Memory (ISOM), Sony demonstrated its new "Micro-Reflector recording" system. More affordable than other holographic recording systems, this one splits the beam emitted from a blue violet laser diode so that it can irradiate both sides of a disc. A servo is then used to align the focal points of the two lights.
In the "Micro-Reflector recording" demonstrated by Sony, a laser light emitted from a blue violet semiconductor laser diode is split into two so that one of them irradiates the front side of a medium as a reference light while the other is emitted to the backside as a recording light. By precisely aligning focal points of the two lights with a servo technology, a minute interference fringe corresponding to a 1 bit recording mark is formed. When a laser light (reproduction light) is emitted on the front side of the medium having interference fringes, the recording light is reproduced. This light advances from the fringes to the medium front side as if the fringes reflect the reproduction light. This is why the system is called "Micro-Reflector recording".
The medium comprises a 0.3 mm thick photopolymer sandwiched by 0.6 mm glass substrates. Since the depth of the interference fringes can be controlled by changing the depth of the focal points of the laser lights, multi-layer recording with 10-20 layers can be provided. The recorded interference fringes are small enough to prevent the photopolymer from expanding/contracting due to temperature change. This eliminates the need of adjusting the wavelength of the laser in accordance with the temperature. Therefore, a commercial blue violet semiconductor laser diode is expected to be used as is. Moreover, the setup can easily achieve a reduction in component cost because it requires no spatial light modulators, CMOS sensors or other parts.
While this new recording system sounds promising, Sony still has a lot of work ahead of them. If you'd like to read more, the entire article can be found here.
