Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE
Fiber optic read-out and write-down head for information storage and processing devices
Sergei N. Andrianov, Ildar R. Bagautdinov, Nadezhda M. Lutfullina, V. S. Maksimyuk, Suren O. Mirumyants, Самарцев Виталий Владимирович, Шегеда Анатолий Михайлович, L. A. Trofanchuk, Nadezhda E. Zalilova, В. А. Зуйков
Fiber-optic head is developed and fabricated for information reading out from and writing-down to hard carriers. Fiber- optic scanner using this head is realized on the basis of existing computer printers and plotters and its characteristics are investigated. Fiber-optic technique is used for excitation of photon echo. Photon echo was observed with multimode fiber when it was coupled with initial pulsed laser radiation in quasi-singlemode regime. Predictions are made for the possibility of creation photon-echo fiber-based echo-processors and their possible schemes are proposed.
Fiber-optic head is developed and fabricated for information reading out from and writing-down to hard carriers. Fiber- optic scanner using this head is realized on the basis of existing computer printers and plotters and its characteristics are investigated. Fiber-optic technique is used for excitation of photon echo. Photon echo was observed with multimode fiber when it was coupled with initial pulsed laser radiation in quasi-singlemode regime. Predictions are made for the possibility of creation photon-echo fiber-based echo-processors and their possible schemes are proposed.
In photon-echo-based optical data storage and data processing the photon echo output intensity generally is about 0.1 - 1% of the input intensity. Many devices, such as processors would require that the photon echo output is used as an input to a new photon echo process. To obtain a sufficient signal-to- noise it would be necessary to first amplify the photon echo output signal. In this paper Pr-doped ZBLAN fibers are used to amplify the photon echo signals generated in Pr-doped Y2SiO5 at 606 nm. The fiber amplifier is pumped by the 476 nm output from an Ar-ion laser. Mirror-less lasing due to reflection at the fiber ends is eliminated by cleaving the fiber ends at an angle. The upper limit of the gain in a fiber is set by the core refractive index and the fiber numerical aperture. By changing from a fiber with numerical aperture of 0.4 to one with 0.15, the gain obtained at 606 nm is increased from 45 to 330.
As it was emphasized several times above, the phenomenon of the photon echo is an optical analog of the spin echo that has been discovered [ 1 ] about a decade earlier. That is why many ideas from the theory of the spin echo has been transferred to the theory of the photon echo and appeared to be fruitful there. One of these ideas put forward by Fernbach and Proctor [ 2 ] is the idea of the possibility of the use of the phenomenon of the spin echo for writing, storage, and processing of the data. The authors [ 2 ] determined the conditions under which the signals of the spin and stimulated spin echo can reproduce (direct or time-reversed) shape of one of the exciting pulses. The theoretical analysis was proved by the corresponding experiments.
Increasing traffic on the Internet demands faster optical transmission networks. Future high-speed communication networks may rely largely on all-optical components that are intrinsically faster than their electronic counterparts. To achieve such networks, however, one needs to overcome a number of obstacles that exist at levels from devices to systems. For example, the lack of all-optical memory for storing optical data remains a bottleneck in modern optical information networks.1 There has been substantial progress in addressing this problem using spatial-spectral holography in systems that operate at cryogenic temperatures2 or stored light based on electromagnetically induced transparency, where optical information is impressed upon internal degrees of freedom of an ensemble of atoms or ions.3 Both of these methods, however, are limited to operating at the resonance wavelength of the ions or atoms used. These limitations have recently been partially overcome using a dynamically controlled resonator in which a single optical pulse was stored for ∼100ps.4 We recently presented a different approach: a simple storedlight approach5 in which optical pulse information is transferred onto a slowly moving hypersonic wave (∼1/40,000 of the light speed) in an optical fiber and converted back at a later time through stimulated Brillouin scattering (SBS) as illustrated in Figure 1. In the storage process, optical data pulses (of carrier frequency ν0) interact with a counterpropagating short intense ‘write’ pulse (of carrier frequency ν0 + νB, where νB is the Brillouin frequency shift of the fiber). The optical data pulses become depleted as energy is shifted to a hypersonic wave in the fiber. In the retrieval process, a short intense ‘read’ pulse at the same frequency as the ‘write’ pulse depletes the acoustic wave and releases the data back to the original optical frequency, thereby generating a replica of the incident data pulses. This stored-light approach has advantages such as room-temperature Figure 1. Stimulated Brillouin scattering allows data storage in an optical fiber. In the storage process, (a) optical data pulses interact with a ‘write’ pulse . (b) The optical data pulses become depleted as the information shifts to an acoustic wave in the fiber. To retrieve the data, (c) a ‘read’ pulse depletes the acoustic wave, (d) generating a replica of the original data pulses.5
Our goal is to quantitatively evaluate the concept of time-domain optical memory (TDOM) based on the stimulated photon echo technique and to prepare for the development of a working prototype. Earlier feasibility studies at SRI International showed that TDOM can store not only digital data in the form a series of on-off laser pulses but also two-dimensional (2-D) images with the same read/write speed. Despite work at SRI and elsewhere, until now the use of TDOM for 2-D images has not been carefully examined and the quality of echo images and their inherent spatial resolution have not been explored. These issues have an important bearing on TDOM as a high-speed, high-density storage device. This year, we focused on using the stimulated echo technique for 2-D image storage and image processing. Specific tasks included incorporating a gated intensified charge-coupled device (CCD) camera system for detecting echo images, digitally recording the echo images, and optimizing the optical system. We have also extended the earlier feasibility study on stimulated-echo-based, 2- D image storage and image processing and demonstrated storage and retrieval of the high-quality, high-resolution echo images. In addition, we demonstrated for the first time that nanosecond pattern recognition can be achieved using the stimulated echo approach. (Author)
Optical data storage has been interested in several decades because of the potential of fast access time and high-density storage. Recently volume holographic data storage technique has drawn much interest as new materials and improved techniques have developed.1 However, the large of hologram storage is restricted by low diffraction efficiency and mainly focused to read only memory because of the material's characteristic difficult to rewrite in short time interval. Another optical memory technique (photon echo optical memory)2 based on time-domain has developed since 1980's and made big progress for the area of real time image processing and dynamic random access memory. In this technique, data pulses interfere with timely separated write pulse (reference), and their interference pattern is written as population gratings. A read pulse (reference) retrieves each data pulse information as a four-wave mixing process. The write and read pulse separations are restricted by phase and population decay times of the material, respectively, and storage density is determined by the ratio of inhomogeneous to homogeneous linewidths. Even though photon echo technique has advantages of fast access time (≥ ns) and high-density (≥ Mbits/laser spot), its operating temperature is kept extremely low around liquid helium temperature. This is because that homogeneous decay time rapidly shortens as temperature increases due to phonon interactions, i.e., the ratio of inhomogeneous to homogeneous decay rates is ~ 1 at liquid nitrogen temperature (77 K) in a rare-earth doped solid, so that restricts its applications.
Photon-echo-based devices have been proposed for many applications in data storage, image processing, and optical communications. Many of these applications would benefit if the output from the photon-echo process could be used as input in a second photon-echo process. We demonstrate the generation of such secondary echoes, using the amplified output from an initial photon-echo process. The amplification is performed with a Pr:ZBLAN fiber amplifier, which gives a gain of more than 300 at 606 nm when pumped with 320 mW of power at 476 nm.