Spectral phase codes are used as storage addresses in a frequency-selective optical memory. Data are engraved over a 1.5-THz-wide spectral interval. With the help of a ferroelectric liquid-crystal modulator it takes less than 100 micros to retrieve any spectrally addressed data.
Optical devices have been slower to mature than those based purely on electronics. Yet optical interactions offer a number of unique capabilities expected to support entirely new classes of devices-devices offering unprecedented performance in communications, computing, and data storage applications. In the present work, optical devices based on the interaction of light with frequency-selective recording materials are discussed. A frequency-selective recording material has the capability of supporting multiple independent recording channels. Each channel is addressed by light within a specific narrow band of optical frequencies. In some materials, operative at cryogenic temperatures, millions of distinct spectral channels are available. Through the mechanism of persistent spectral hole-burning, light can be employed to transiently or even permanently modify the absorptive or dispersive properties of the recording material within a selected channel. Such modifications provide a means of recording multiple bits of optical information within single spatial locations. Spectral multiplexing of information has clear potential in information storage systems. Less obviously, the ability to spectrally encode information provides an enabling basis for ultrahigh speed, content-controlled, all-optical switching devices operable at data speeds up to the Terabit/sec level.
In previous investigations of optical data storage in persistent spectral-hole-burning materials, either the spectral or the temporal positions of the data were used as memory addresses. We suggest having the address represented by the spectral shape of the writing field and retrieving information with the aid of pattern recognition of this spectral shape. This procedure is expected to accelerate access to the stored data. To evaluate the validity of the method, we consider various physical effects that may give rise to cross talk among the different addresses. A numerical simulation under realistic conditions is presented.
The persistent spectral hole burning property is known to add a fourth dimension to the optical data storage volume. Full advantage of the large capacity of such memories and of the intrinsic parallelism due to their optical nature can be taken in an application such as image storage. In this frame, the read-out operation has to be effected at video rate at least. This is not achieved by currently developed image-addressing methods. The present paper proposes a new procedure to overcome the so far encountered limitations.
One important possible application of photon echoes is all-optical data storage. Photon echoes have a number of advantageous properties that make diem very good candidates for such applications, such as high areal density (1 Tb/cm2 has been projected [1], which should be compared with approximately 1 Mb/cm2 for commercially available CMOS memories today) and readout speeds >THz have been experimentally demonstrated [2]. We have addressed the problem of how to selectively erase data bits stored using photon echoes. One solution to this problem is to coherently add a new echo, phase shifted 180 degrees relative to the original echo, and thus achieve selective erasure of data [3].