KEYWORDS: Digital holography, Optical storage, Holography, Holographic materials, Digital recording, Multiplexing, Holograms, Polymerization, Data storage, Digital imaging
Aprilis HMD-050-G-C-400 photopolymerizable holographic recording material for card and disk media, based upon cationic ring-opening polymerization (CROP), has been further optimized for recording in an increased film thickness of 400 µm. A storage density, S2D, of 150 bits/μm2 for digital data recorded holographically as pages and a dynamic range of at least M/# = 22 have been achieved, which are substantially greater than previously reported for photopolymerizable media, while concurrently the inherent low shrinkage, high image fidelity and high sensitivity characteristics of the material have been retained. Dynamic range or cumulative grating strength, Σηi0.5, has been determined from co-locationally recorded peristrophic and planar-angle multiplexed 262 kbit data pages that exhibit low raw bit-error-rates (BER) having an average value of 1E-3 and 5.5E-3 for ~100 and ~150 bits/μm2, respectively. Good Bragg selectivity consistent with the imaged thickness and sinc2 function behavior is observed for the multiplexed digital data page holograms, and both the Bragg selectivity and the diffraction efficiency are stable without the need for post-imaging fixing procedures. Sensitivity during recording of digital data page holograms is in the range of 6.75 cm/mJ diminshing to 0.5 cm/mJ for 87% of the cumulative grating strength that is attained during co-locational recording.
Experimental results demonstrating the coherent scattering properties of a cationic ring-opening photopolymer are presented. The film is exposed continuously with a single beam at a single angle, and the transmission characteristics are measured as a function of exposure. A critical cumulative coherent exposure level is observed. At exposures above this level the presence of noise gratings is observed through a decrease in the transmittance of the photopolymer. The magnitude of the efficiency of these gratings differs depending upon the method used for preconditioning the photopolymer. Noise gratings are also measure in the case of angularly multiplexed exposures, and it is found that if the exposure fluence of each multiplexed recording is reduce to levels consistent with those used for recording data pages in this sensitive recording medium then no measurable noise gratings are formed.
The photopolymer holographic recording materials, ULSH-500, based upon cationic ring-opening polymerization, has been further optimized for recording in an increased film thickness of 200 micrometers . The dynamic range attained, at least M/# equals 16, is substantially greater than previously reported, while concurrently the inherent low transverse shrinkage and high sensitivity characteristics of the material have been retained. Dynamic range or cumulative grating strength, (Sigma) (eta) i0.5, has been determined from co-locationally recorded peristrophic and angle multiplexed plane-wave gratings which exhibit low diffraction efficiencies between about 0.1 and 0.2%. Good Bragg selectivity consistent with the imaged thickness and sinc2 function behavior is observed for the multiplexed holograms, and both the angular response and the diffraction efficiency are stable without the need for post-imaging fixing procedures. Sensitivity is in the range of 1 to 10 cm/mJ, and the refractive index modulation achievable during consumption of the accessible dynamic range is n1 equals 1.3 X 10-2 at the read wavelength of 514.5 nm.
A new photopolymer holographic recording material, ULSH-500, based on cationic ring-opening polymerization, has been further optimized to achieve low transverse shrinkage without sacrificing sensitivity. The extent of transverse (z) and lateral (x) shrinkage was determined explicitly in this study for a range of slant angles, in volume holograms which were recorded to near saturation and in holograms of low diffraction efficiency. (Delta) Kx/Kx and (Delta) Kz/Kz, which represent the physical material shrinkage in the grating vector plane, were ascertained by (1) direct measurement of the differential angle changes in the reference and signal beam angles necessary to achieve Bragg matching and (2) measurement of the average refractive index. The accuracy of this method was primarily limited by the exactness in determining the angle of peak efficiency in the Bragg selectivity curve. It is demonstrated that the peak angle can be established to within a small fraction of a degree. It is shown that the assumption of anchoring and thus uniaxial shrinkage, as embodied in the conventional fringe rotation model, cannot be applied for the photopolymer, ULSH-500, under the recording conditions used herein.
A new photopolymer holographic recording material based on cationic ring-opening polymerization avoids limitations of conventional holographic photopolymers resulting from the free radical chemistry typically employed. The effects of oxygen, moisture, and component characteristics on holographic recording characteristics are described. Sensitivities greater than 0.1 cm2/mJ and refractive index modulations greater than 5 X 10-3 are achievable with negligible changes in the physical dimensions (volume change as low as 0.4%) of the imaged material. Linear recording is observed for exposure fluence up to 20 mJ/cm2. Good Bragg selectivity consistent with the imaged thickness is observed, and both the angular response and the diffraction efficiency are stable in these materials without the need for post-imaging fixing procedures.
Conference Committee Involvement (2)
Organic 3D Photonics Materials and Devices
28 August 2007 | San Diego, California, United States
Organic Holographic Materials and Applications IV
14 August 2006 | San Diego, California, United States
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