Harald Willy Werlich

Diffraction characteristics of photoresist surface-relief gratings

Theoretical results from rigorous coupled-wave analysis are compared with experimental diffraction characteristics for holographically formed dielectric photoresist surface-relief gratings with deep grooves (greater than a grating period) and high diffraction efficiency (>85%). The angular selectivity (at a fixed wavelength) and the wavelength selectivity (at a fixed angle of incidence) are presented for both TE and TM incident polarizations. Modeling the gratings as a surface-relief modulated half-space and using rigorous coupled-wave analysis are shown to produce good general agreement with the experimentally measured diffraction characteristics.

Spatial Pulse Modulation

Pulse modulation of electronic time signals is a well-proven concept, particularly in the context of data communications and computers. We suggest that pulse modulation of spatial optical signals might be another fruitful concept. The optical components and optical methods for performing the necessary operations for spatial pulse modulation are available. We demonstrate this experimentally by encoding a two-dimensional analog signal (an image) into a one-dimensional pulse signal. This might be of interest in connection with picture transmission over electronic channels, with cinematography, and with holography.

Optical recording in the blue using a frequency-doubled diode laser

We have developed a 428 nm blue laser source based on resonator-enhanced frequency doubling of a GaAlAs diode laser and have used this source to demonstrate writing and reading on an MO disk. The power, beam quality, and noise of the blue laser are sufficient for high-density optical recording.

Holographic light deflection.

An operational holographic laser light deflector is described, which is well suited for applications requiring fast constant-speed scanning, high resolution, and moderately large angles of deflection. A particularly unique application of this device as an opaque document scanner is also described.

Aberration limits for annular Gaussian beams for optical storage.

Annularly apodized beams have been suggested for use in optical storage because of their potential to go beyond the conventional spot size and depth-of-focus limits. One concern for such applications is the effects of small aberrations on beams in which the energy is concentrated in a small annular ring. We present calculations and experimental results that show that annular apodization of a Gaussian beam reduces the sensitivity to defocus as well as balanced spherical and coma aberrations. The sensitivity to astigmatism is increased by a small amount.

Optical systems for high-density storage

Optical super-resolution is one of many techniques being explored to increase the storage density of optical disks. With optical super-resolution, the optical system is modified to reduce the diameter of the central lobe of the spot on the disk. This generally involves increasing the energy in the sidelobes of the spot. We will discuss the trade-offs of this approach.