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For holographic data storage, it is necessary to adjust the wavelength and direction of the reading beam if the reading and recording temperature do not match. An analytical solution for this adjustment is derived using first-order approximations in a two-dimensional model. The optimum wavelength is a linear function of the temperature difference between recording and reading, and is independent of the direction of the reference beam. However, the optimum direction of incidence is not only a linear function of the temperature difference, but also depends on the direction of the reference beam. The retrieved image, which is produced by a diffracted beam, shrinks or expands slightly according to the temperature difference. OCIS codes: 050.1940, 090.7330, 210.2860, 210.4590.

A tunable laser optical source equipped with wavelength and mode-hop monitors was developed to compensate for thermal expansion of the medium in holographic data storage. The laser's tunable range is 402-409 nm, and supplying 90 mA of laser diode current provides an output power greater than 40 mW. The aberration of output light is less than 0.05 [lambda]rms. The temperature range within which the laser can compensate for thermal expansion of the medium is estimated based on the tunable range, which is [+ or -]13.5 [degrees]C for glass substrates and [+ or -]17.5 [degrees]C for amorphous polyolefin substrates. OCIS codes: 090.7330, 140.3600, 210.2860.

An external-cavity laser with a wavelength of 405 nm and an output of 80 mW has been developed for holographic data storage. The laser has three states: the first is a perfect single mode, whose coherent length is 14 m; the second is a three-mode state with a coherent length of 3 mm; and the third is a six-mode state with a coherent length of 0.3 mm. The first and second states are available for angular-multiplexing recording; all states are available for coaxial multiplexing recording. Due to its short wavelength, the recording density is higher than that of a 532 nm laser. OCIS codes: 030.4070, 090.7330, 140.3570, 210.2860.

Holographic recording media with a reflection layer are useful because they make it possible to maintain backward compatibility with CDs and DVDs, and a conventional servo system is easily attachable. The incident beam is fed back to the recording layer by the reflection layer, so there are four beam pairs to record the transmission and reflection holograms. We analyze the basic property of the transmission and reflection holograms and evaluate the problem when the transmission and reflection holograms are recorded at the same time. It is shown that the shrinkage in the photopolymer medium has a different effect on each hologram, so the readout image from the two holograms is misaligned. Those diffraction beams make the interference pattern, and the signal-to-noise ratio (SNR) of the output image decreased. Taking into account the difference in wavelength selectivity between the transmission and the reflection holograms, we propose a way to select one hologram to get the diffraction beam and eliminate the interference pattern using the tuning readout wavelength. By using this method, we can eliminate the diffraction beam from the reflection hologram and keep a high SNR. OCIS codes: 090.7330, 160.5470.

The article reports about the analysis on hologram recording and compensation method's related to the effects of change in temperature. Even without a systematic study, the authors believe that the polymerization rate and monometer-diffusion speed changes are critical for hologram-recording properties. They also suggest a method for compensating temperature changes, and verify its success.