Optical storage technology development direction and key technologies

1. Development direction of optical storage technology

The new generation of optical storage technology based on the principles of optics, integrated optics, photon effects, volume holography, light-induced or magnetic-induced super-resolution will develop in the following directions:

(1) Using the research results of optical non-radiative field and optical super-diffraction limit resolution, the size of recorded information symbols can be further reduced. When a light beam is irradiated onto the surface of an object, it will form a propagation field (propagation wave) and non-radiation (evanescent wave) regardless of transmission or reflection. The propagation wave carries low-frequency information about the structure of the object and is easily detected by the detector. The evanescent wave carries high-frequency information describing the fine structure of the object and propagates along the surface of the object. As long as this part of information is captured, the resolution of the system can be improved.

(2) The super-resolution optical system is designed using the principle of near-field optics, so that the numerical aperture exceeds 1.0, which is equivalent to the radiation field of the detector entering the medium. This makes it possible to obtain ultra-fine structure information, break through the diffraction limit, and obtain higher resolution. The resolution of the classical optical microscope can be increased by two orders of magnitude and the surface density by four orders of magnitude.

(3) Data writing and reading can be realized by replacing the current photothermal effect with the photon effect. In principle, the storage density can be increased to the molecular level or even the atomic level. Moreover, since the quantum effect does not involve thermal processes, its reaction speed can reach the picosecond level (10-12 seconds). In addition, since the reaction of the recording medium is related to the number of photons it absorbs, the recording method can be changed from the current binary storage to multi-value storage, thereby increasing the storage capacity many times.

(4) Three-dimensional multi-volume holographic storage uses the photorefractive effect of certain optical crystals to record holographic images, including binary or grayscale image information. Due to the sensitivity of holographic images to spatial position, this method can achieve extremely high storage capacity. Based on the change of the spatial phase of the grating, the volume holographic storage device can also be selectively erased and rewritten.

(5) Using other achievements of contemporary physics, including the principle of photon echo time-domain coherent photon storage, the principle of photon capture storage, resonant fluorescence, superfluorescence and optical bistability effects, the photochemical effect of photon-induced photochromism, the two-photon three-dimensional bulk photochromism effect, and many new tools and technologies, such as scanning tunneling microscopy (STM), atomic force microscopy (AFM), optical integration technology and micro-fiber array technology, to improve storage density and form a multi-layer, multiple, multi-grayscale, high-speed, parallel read-write mass storage system. Experiments have proved that current technology can achieve an optical storage density of 40-100Gbits/in2.

2. Key technologies for the development of optical storage

(1) High-density, high-efficiency, and high-speed mastering technology

The use of short-wave lasers and large numerical aperture objectives can reduce track spacing and bit length, thereby increasing the recording density of the optical disc; the use of pulse width modulation can significantly improve recording efficiency.

(2) Precision injection molding of single-sided DVD discs and packaging technology for double discs

The qualified templates selected from the DVD master and template production line are injection molded by a precision injection molding machine. The obtained DVD semi-finished products are properly cooled and sent to the sputtering chamber. According to different requirements, gold or lead is sputtered respectively, and then adhesive spin coating, packaging, UV curing, online testing, trademark printing, etc. are carried out to make DVD read-only discs.

(3) Optical disc recording media

Whether DVD-RAM discs are stable and reliable depends on the recording medium. Whether the material design can meet the requirements of high-speed storage depends on whether the recording medium can achieve a fast reversible phase change between two stable states. The design of traditional phase change media materials at home and abroad is based on the thermal effect of lasers. Information writing is achieved by liquid phase rapid quenching; information erasure is completed by nucleation and grain growth. Since the thermal effect is an energy accumulation process, it takes a long time to write a bit, about tens of nanoseconds, and the medium will experience thermal fatigue with a reduced signal-to-noise ratio after hundreds of thousands of write/erase cycles. As the recording laser adopts a short wavelength, the thermal effect of the laser gradually weakens, and the excitation effect of the laser photons becomes prominent; so the new material design is based on the optical effect of the laser. For semiconductor-type media, it only takes tens of picoseconds to write a bit, which increases the recording rate by an order of magnitude. This recording medium based on the nonlinear optical bistable change effect is called an optical bistable recording medium, which can be an inorganic material, an organic material, or an inorganic-organic composite material.