http://www.hitachi.co.jp/New/cnews/mont ... /0518.html
I found this part to be the most interesting:
In the multilayer optical disk, in order most to read and write even in record layer of the inner part through the plural record layers to be piled up, layer forward becomes the interference, only the little signal light intensity it is possible to detect. In addition, it was necessary to make the reflectance ratio of layer forward low in order to ease this, you make either the signal light intensity of layer forward small did not obtain. When the signal light intensity decreases, the signal is buried to the electric noise which occurs in the photodetector and the circuit, the possibility error occurring in signal reading becomes high. It is possible to expand the signal which you grasp electrically, but in this case, there was a problem also noise is expanded in the same way.
At Hitachi, in order to solve such problem, the detection signal is expanded developed the technology which applies “homodyne detection method” to the optical disk anew then making use of the interference of light. When homodyne detection method, you divide light from the laser illuminant into 2 systems beforehand due to the half mirror, and the like modulate on the other hand with the signal and (below, signal light), playing back, it is the technology which expands the signal the light which one side has not been modulated anymore (below, reference beam) with by interfering. This time, in order to apply this homodyne detection method to the optical disk, optical system of the current optical disk and the optical system technology whose affinity is high were developed. Merit of this technology is as follows.
I hope we see a press release in English soon. This translation sucks.