Method for controlling the shift invariance of optical correlators

Holographic correlators can implement many correlations in parallel. For most systems shift invariance limits the number of correlation templates that can be stored in one correlator. This is because the output plane must be divided among the individual templates in the system. When the system is completely shift invariant, the correlation peak from one correlator can shift into an area that has been reserved for a different template; in this case a shifted version of one object might be mistaken for a well-centered version of a different object. We describe a technique for controlling the shift invariance of a correlator system by moving the holographic material away from the Fourier plane

Holographic recording of fast phenomena

We report on a holographic method for recording fast events whose speed is limited by the laser pulse duration if the recording material has sufficient sensitivity to reliably record a frame of the fast event with a single pulse. The method we describe uses the angular selectivity of thick holograms to resolve frames that are recorded with adjacent pulses. Two specially designed cavities are used to generate the signal and reference pulse trains. We experimentally demonstrate the system by recording laser induced shock waves with a temporal resolution of 5.9 ns, limited by the pulse width of the Q-switched Nd:yttrium–aluminum–garnet laser used in the experiments

Storage Density of Shift-Multiplexed Holographic Memory

The storage density of shift-multiplexed holographic memory is calculated and compared with experimentally achieved densities by use of photorefractive and write-once materials. We consider holographic selectivity as well as the recording material s dynamic range (M /#) and required diffraction efficiencies in formulating the calculations of storage densities, thereby taking into account all major factors limiting the raw storage density achievable with shift-multiplexed holographic storage systems. We show that the M /# is the key factor in limiting storage densities rather than the recording material s thickness for organic materials in which the scatter is relatively high. A storage density of 100 bits m2 is experimentally demonstrated by use of a 1-mm-thick LiNbO3 crystal as the recording medium

Characterization of phenanthrenequinone-doped poly(methyl methacrylate) for holographic memory

The holographic recording characteristics of phenanthrenequinone- (PQ-) doped poly(methyl methacrylate) are investigated. The exposure sensitivity is characterized for single-hologram recording, and the M/# is measured for samples as thick as 3 mm. Optically induced birefringence is observed in this material

Volume holographic grating-based continuously tunable optical filter

We propose and demonstrate a widely tunable optical filter, realized by angle tuning a volume holographic grating. The volume holographic grating selectively drops a narrow portion of the signal bandwidth into a fiber while passing through the rest of the signals. The demonstrated 1510- to 1590-nm tuning range covers the entire erbium-doped fiber amplifier (EDFA) C band, with small bandwidth variation and low insertion loss (<1 dB). Group delay, polarization-dependent loss, and polarization mode dispersion are measured and investigated for optimizing the filter characteristics

Holographic techniques for recording ultrafast events

In this paper we report on a holographic method used to record fast events in the nanosecond time scale. Several frames of the expansion of shock waves in air and in a polymer sample are recorded holographically in a single shot experiment, using a pulse train generated with a single pulse from a Q-switched Nd:YAG laser. The time resolution is limited by the laser pulse width, which is 5.9 ns. The different frames are recorded on the holographic material using angle multiplexing. Two cavities are used to generate the signal and reference pulses at different angles. We also present a method in which the recording material is replaced by a CCD camera. In this method the holograms are recorded directly on the CCD and digitally reconstructed. The holograms are recorded on a single frame of the CCD camera and then digitally separated and reconstructed

Volume holographic grating-based continuously tunable optical filter

We propose and demonstrate a widely tunable optical filter, realized by angle tuning a volume holographic grating. The volume holographic grating selectively drops a narrow portion of the signal bandwidth into a fiber while passing through the rest of the signals. The demonstrated 1510- to 1590-nm tuning range covers the entire erbium-doped fiber amplifier (EDFA) C band, with small bandwidth variation and low insertion loss (<1 dB). Group delay, polarization-dependent loss, and polarization mode dispersion are measured and investigated for optimizing the filter characteristics

Holographic techniques for recording ultrafast events

In this paper we report on a holographic method used to record fast events in the nanosecond time scale. Several frames of the expansion of shock waves in air and in a polymer sample are recorded holographically in a single shot experiment, using a pulse train generated with a single pulse from a Q-switched Nd:YAG laser. The time resolution is limited by the laser pulse width, which is 5.9 ns. The different frames are recorded on the holographic material using angle multiplexing. Two cavities are used to generate the signal and reference pulses at different angles. We also present a method in which the recording material is replaced by a CCD camera. In this method the holograms are recorded directly on the CCD and digitally reconstructed. The holograms are recorded on a single frame of the CCD camera and then digitally separated and reconstructed

Holographic recording in a photopolymer by optically induced detachment of chromophores

We demonstrate holographic recording in a new photopolymer system. The recording material is created by copolymerization of an optically inert monomer, methyl methacrylate, and a second monomer that is optically sensitive. On exposure of the recording material to light, a portion of the optically sensitive component detaches from the polymer matrix and causes hologram amplification through diffusion of the free molecules. We measured postrecording grating amplifications as high as 170% by this process. The recorded holograms are persistent at room temperature under continuous illumination at the recording wavelength