Scatter noise reduction in holographic storage systems by two-step write

A hologram-write method for increasing detection signal-to-noise ratio by compensating for scatter noise originating from a holographic storage medium, the method comprising the steps of:

• (a) inputting first input data into an input device having M pixels, each input device pixel containing a first data value corresponding to a first expected detection value;
• (b) outputting a first object beam, containing first input data, from the input device;
• (c) interfering a write reference beam with the first object beam to write a first input image into the holographic storage medium;
• (d) illuminating the holographic storage medium with a read reference beam propagating along the centerline of the write reference beam to produce a first output image;
• (e) recording the first output image on a detector array having at least M pixels, each detector array pixel corresponding to an input device pixel and containing a recorded value, the recorded values deviating from the corresponding first expected detection values due to scatter noise originating from the holographic storage medium;
• (f) computing a scatter parameter associated with each detector array pixel, from the recorded value of the associated detector array pixel and the first expected detection value associated with a corresponding input device pixel;
• (g) inputting second input data into the input device, the second input data being formed by modifying amplitude of each input device pixel first data value according to the associated scatter parameter;
• (h) outputting a second object beam, containing the second input data, from the input device;
• (i) interfering the write reference beam with the second object beam to write a second input image into the holographic storage medium, the second input image being superimposed on and in phase with the first input image to produce a combined image, said combined image comprised of a set of M gratings, each of the M gratings having a final expected detection value, and wherein each of the first expected detection values is equal to a fraction of a corresponding final expected detection value;
• (j) illuminating the holographic storage medium with said read reference beam propagating along the centerline of the write reference beam to produce a final output image having substantially reduced scatter noise;
• and
• (k) recording the final output image on the detector array.

A holographic storage system for increasing detection signal-to-noise ratio, the system facilitating a two-step hologram-write operation to reduce detection scatter noise, the system comprising:

• (a) an input device for receiving first and second input data, for outputting a first object beam containing first input data during a first hologram-write operation, and for outputting a second object beam containing second input data during a second hologram-write operation;
• (b) a radiation source for outputting a read reference beam, and a write reference beam during each of the first and second hologram-write operations, the write reference beam interfering with the first and the second object beams to produce a first and a second input image, respectively;
• (c) a holographic storage medium for storing the first input image, the second input image and a combined output image created by superimposing in phase the first and the second input images, and for outputting with the read reference beam the combined output image and a first output image created by the first input image;
• (d) a detector array for recording the first output image and the combined output image;
• and
• (e) a computing circuit for computing a scatter parameter for each pixel of the detector array wherein the scatter parameter is computed according to the following formula:
• ##EQU11## where a is the scatter parameter, V.sub.1 is a recorded value of the associated detector array pixel for the first output image, and fI.sub.d is an expected detection value for the first output image associated with a corresponding input device pixel, and the second input data is then formed by modulating the first input data according to the associated scatter parameter at each input device pixel.