Effect of various factors on wavelength tolerance in microholographic recording

Abstract

The wavelength tolerance in microholographic recording is reported to be narrow, but the actual value is uncertain. Therefore, the effect of various factors on the wavelength tolerance in microholographic recording was investigated through a numerical simulation. The recording and readout beams were expressed as the superposition of plane waves. The diffraction efficiency of a microhologram was calculated using the coupled wave theory. The wavelength tolerance was defined as the wavelength range where the diffraction efficiency was higher than the half of its maximum value. The center wavelength of the laser was 405 nm, the numerical aperture of the objective lenses was 0.85, and the refractive index, maximum refractive index change, and thickness of the recording medium were 1.5, 1.0 x 10^-3, and 300 μm, respectively. In this case, the wavelength tolerance was as narrow as ±0.18 nm. First, random aberrations were added to the recording and readout beams. Even when the root-mean-square wavefront aberration was increased to 0.14 λ, the maximum diffraction efficiency decreased but the wavelength tolerance did not change. Next, multiple microholograms were recorded in the in-plane and vertical directions and the center microhologram was reproduced. Even when the number of recorded microholograms was increased to 5 x 5 x 5, the maximum diffraction efficiency decreased but the wavelength tolerance only slightly increased to ±0.21 nm. If the actual wavelength tolerance would be much wider, there might be another factor that makes the equivalent thickness of the recording medium much thinner (e.g. nonlinearity of the recording medium).