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We propose and demonstrate a silicon-photonics-based laser that outputs multiple independently tunable wavelengths using a single InP gain element. We use it to generate a C-band tunable source for a coherent transceiver and simultaneously a 1480-nm source to pump an Er-doped fiber amplifier on the transmitter output.

A silicon-photonic tunable laser emitting two tunable wavelengths simultaneously is demonstrated. The laser consists of a single semiconductor optical amplifier that provides shared gain and a silicon-photonic chip that provides wavelength selections. A total optical power of 29.3 mW is shown, with 300 mA of gain current at 40°C. Continuous tuning of frequency spacing from 69.5 GHz to 114.1 GHz is demonstrated. The two simultaneous laser channels show highly correlated phase noise, with a phase noise correlation coefficient of 90.7%.

A multiple page fully digital holographic data storage system is demonstrated. This system is used to store and retrieve digital image and compressed video data with a photorefractive crystal. Architecture issues related to spatio-rotational multiplexing and novel error-correcting encoding techniques used to achieve low bit-error rates are discussed.

We propose a technique for data detection in a two-dimensional page-access optical memory. The technique combines sequence detection by the use of the Viterbi algorithm with decision feedback to improve the bit-error-rate performance in a system corrupted by intersymbol interference. It has an advantage in that it can be operated on a row-by-row basis as data are output from the optical detector. Use of the proposed scheme might ease the design tolerances of the optical components or permit the use of large data pages.

A method for coded-wavelength multiplexing according to which a signal waves Si (r) is recorded in a holographic medium in a counter-propagating geometry using corresponding writing reference waves Ri (r). The method involves selecting discrete wavelengths λ and encoding reference wave vectors ρl which make up writing reference waves Ri (r) such that the writing reference waves Ri (r) at each wavelength λ are orthogonal. The stored signal waves Si (r) are reconstructed in the form of reconstruction waves Ac (σ) with reconstruction reference waves Rc (r) selected from among the writing reference waves Ri (r). In the event of angular multiplexing of the reference wave vectors ρl, it is possible to use one reference wave to produce a number of reconstruction waves Ac (σ) and generate a mosaic of desired holographic pages.

We describe a novel method for the recall of linear combinations of stored data pages in a volume holographic memory based on phase-code multiplexing. Recall is demonstrated by use of a compound phase-and-amplitude spatial light modulator in the reference beam path.

A number of spatially nonlinear-optical materials, such as photorefractive media, are suitable for volume holography. High Bragg selectivity of thick media has led to the development of applications of multiplex volume holography ranging from binary and analog data storage, to associative memory, to neural networks, to optical interconnects. An important consideration is the balance between capacity and noise. We examine here crosstalk for angular, phase-encoded, and wavelength multiplexing for holographic data storage and describe the properties of null-matched arrangement of reference waves, presenting new results for adjacent, sparse, and fractal strategies. We emphasize the impact of signal bandwidth on crosstalk and describe how crosstalk limits storage capacity. We consider first crosstalk due to Bragg mismatch (mismatch-limited crosstalk), and then relate it to other noise sources present in a holographic memory system. >

Volume holography is an important candidate for data storage and data processing applications. Its advantages lie in the inherent high capacity of volume memory, fast access due to optical addressing, and fast transfer rates due to the parallel nature of holography [1]. Multiple holograms, or data pages, may be stored using angular multiplexing, wavelength multiplexing, and related techniques. Capacity is determined by the angular bandwidth of the signal, the number of holographic pages, and the acceptable level of noise due to crosstalk and other sources present in the system. Volume holography is also an important candidate for optical interconnects and wavelength division multiplexing in communications and computing systems. Frequently, the same criteria required for data storage coincide with those required for other applications.

The Multi-Anode Microchannel Array (MAMA) detector system is a true photon-counting imager which records the position and arrival time of each detected photon for post facto image reconstruction analysis. Imaging by time-tag photon detection with the MAMA is being used for image stabilization on sounding rockets, and for speckle interferometry and speckle image reconstruction at ground-based telescopes using the Stanford University Speckle Interferometer System (SUSIS). This paper describes the construction and mode-of-operation of the MAMA time-tag photon-detection system, including recent improvements to the data- handling system which permit a data-recording rate in excess of 1 M event s-1. The intrinsic time resolution of the MAMA detector system is < 300 ns and the time resolution of the SUSIS used to date is 3.2 microsecond(s) for each detected photon. A number of examples of both laboratory data and visible-light speckle interferometric deconvolutions and two-dimensional speckle image reconstructions are presented.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We investigate photorefractive media for which quasi-stabilized ionic gratings can be used to prolong readout lifetime. We use coupled-transport-mode theory to describe the coevolution of photorefractive gratings that arise from free-electron transport and ionic transport. We evaluate in detail the differences between low-temperature and high-temperature recording for typical conditions required by multiplex holography. We provide general normalized examples for simple diffusion transport and specific examples for photovoltaic LiNbO3. We introduce a common formalism to compare widely varying results present in the literature and to guide the materials and system development processes.

We present a novel digital holographic data storage system based on wavelength multiplexing in 90 degrees geometry, using an automated tunable diode laser and a lithium niobate crystal. The automatic storage and retrieval of a 60-kbyte data file, as well as the limitations and future implementations of the system, are discussed.

We derive the relationships for coded wave fronts in volume holography for reference and signal waves coded with two-dimensional wave fronts. We develop estimates for cross talk that is due to grating degeneracy, nonorthogonality, and momentum-mismatch reconstruction. We compare a number of multiplexing techniques on the basis of cross talk and other noise sources in a system.

We describe a digital holographic data storage system that uses in situ thermal fixing to achieve nonvolatile readout. The system was used to store and fix 530 holograms representing 1.7 MB of digital data. The system demonstrates that fixing by heating after recording gives adequate performance for multiplex holography in the perpendicular recording geometry. The postrecording heating procedure is preferred over high-temperature recording in the perpendicular geometry to achieve Bragg matching for the entire signal angular bandwidth.

We study detuning effects that modify the Bragg condition in photorefractive crystals and analyze the influence of these effects on the retrieval of information that is stored in such crystals. We examine and integrate several mechanisms that induce Bragg detuning, including the effects of temperature changes, applied electric fields, and polarization changes, taking into account the anisotropic nature of photorefractive crystals. Transfer functions based on these detuning effects are defined and computed to examine and quantify the signal quality that is obtained during the readout of image-bearing holograms. The different recording configurations and geometries that are typically used in photorefractive applications are considered and compared. Finally, we study more specifically the consequences of temperature-induced detuning in the context of a holographic data storage system that uses thermal fixing. We show theoretically and experimentally that distortions (in this case limited field of view) occur on readout, and we propose solutions to improve the quality of the retrieved images.

Various channel codes, including binary, gray-scale, threshold, and differential techniques, are compared for digital holographic data storage. The tradeoffs among bit error rate, storage capacity, and system complexity are discussed.

An encryption method and apparatus for holographic data storage are disclosed. In a system using orthogonal phase-code multiplexing, data is encrypted by modulating the reference beam using an encryption key K represented by a unitary operator. In practice, the encryption key K corresponds to a diffuser or other phase-modulating element placed in the reference beam path, or to shuffling the correspondence between the codes of an orthogonal phase function and the corresponding pixels of a phase spatial light modulator. Because of the lack of Bragg selectivity in the vertical direction, the phase functions used for phase-code multiplexing are preferably one dimensional. Such phase functions can be one-dimensional Walsh functions. The encryption method preserves the orthogonality of reference beams, and thus does not lead to a degradation in crosstalk performance.

The selection of reference beams for cross-talk-limited wavelength- and angular-multiplexed volume-holographic data storage is discussed. It is shown that sparse selection of the reference waves can lead to a significant improvement in the cross-talk-limited signal-to-noise ratio in a wavelength-multiplexed system. In a high-capacity angular-multiplexed system sparse selection offers essentially no advantage.

We report on the first successful speckle imaging studies using the Stanford University speckle interferometry system, an instrument that uses a multianode microchannel array (MAMA) detector as the imaging device. The method of producing high-resolution images is based on the analysis of so-called 'near-axis' bispectral subplanes and follows the work of Lohmann et al. (1983). In order to improve the signal-to-noise ratio in the bispectrum, the frame-oversampling technique of Nakajima et al. (1989) is also employed. We present speckle imaging results of binary stars and other objects from V magnitude 5.5 to 11, and the quality of these images is studied. While the Stanford system is capable of good speckle imaging results, it is limited by the overall quantum efficiency of the current MAMA detector (which is due to the response of the photocathode at visible wavelengths and other detector properties) and by channel saturation of the microchannel plate. Both affect the signal-to-noise ratio of the power spectrum and bispectrum.

We compare the characteristics of cross talk for angular multiplexing and several phase-encoded multiplexing strategies for volume holography. We discuss the implications of these characteristics for holographic data storage and compare noise arising from cross talk with noise arising from scattering that is due to inhomogeneities within a holographic medium.