Spatial light modulators with changeable phase masks for use in holographic data storage
View Patent ↗A holographic data storage system that includes a write head that includes a pixellated spatial light modulator and a separate or integral phase mask that varies the phase depending on the location in the phase mask that light passes through. The phase variation can be changed over time in a random, pseudo-random, or predetermined fashion. The spatial light modulator and phase mask can be implemented in a liquid crystal SLM (nematic, ferroelectric, or other), in a DMD SLM, in a magneto-optical SLM, or in any other suitable manner.
1. A write head for a holographic data storage system, the write head comprising:
a spatial light modulator that is arranged into an array of pixels that can each separately modulate light that is directed toward the spatial light modulator; and
a phase mask that is capable of varying the phase of light passing therethrough and directed toward the spatial light modulator, the phase variation being dependent on a particular portion of the phase mask that the light passes through, wherein the phase variation of at least a portion of the phase mask can be changed over time.
2. A write head as defined in claim 1 , wherein the pixels of the spatial light modulator can be switched into one of at least three different optical states.
3. A write head as defined in claim 1 , wherein the spatial light modulator is a liquid crystal spatial light modulator.
4. A write head as defined in claim 3 , wherein the spatial light modulator is a ferroelectric liquid crystal spatial light modulator.
5. A write head as defined in claim 3 , wherein the spatial light modulator includes a layer of liquid crystal material sandwiched between two substantially planar surfaces.
6. A write head as defined in claim 1 , wherein the spatial light modulator includes micromechanical mirrors that can be moved over time.
7. A write head as defined in claim 6 , wherein each of the micromechanical mirrors is tilted to at least one of two different positions to turn the pixel associated with that mirror ON or OFF and each of the micromechanical mirrors is moved in a direction substantially parallel to the incoming light to at least one of two different positions to change the phase of the pixel associated with that mirror.
8. A write head as defined in claim 1 , wherein each pixel in the array of pixels of the spatial light modulator includes a pixel electrode and each pixel electrode includes at least two segments, wherein the two segments can be driven to different voltage levels relative to each other.
9. A write head as defined in claim 8 , wherein the two segments include interleaved portions that can create a diffraction grating.
10. A write head as defined in claim 1 , wherein the phase variation is changed in a random fashion.
11. A write head as defined in claim 1 , wherein the phase variation is changed in a pseudo-random fashion.
12. A write head as defined in claim 1 , wherein the phase variation is changed in a predetermined fashion.
13. A write head as defined in claim 12 , wherein the pixels of the spatial light modulator have an amplitude optical state determined by data supplied thereto, wherein the predetermined fashion is determined in accordance with the supplied data.
14. A write head as defined in claim 13 , wherein the amplitude optical state includes at least two different amplitude optical states, one of which has a very low amplitude and one which has a relatively higher amplitude, wherein for the higher amplitude optical state, the phase variation is of a first amount for a given pixel, and for the next subsequent pixel that is in that same amplitude optical state, the phase variation is of a second amount, with the phase variation continuing to alternate between the first and second amounts for subsequent pixels.
15. A write head as defined in claim 1 , wherein the array of pixels in the spatial light modulator has a pixel pitch of less than 6 μm.
16. A write head as defined in claim 1 , wherein the phase variation is determined by a phase mask generator that is located in a silicon backplane with the spatial light modulator.
17. A write head for a holographic data storage system, the write head comprising a spatial light modulator having an array of pixels, each of the pixels in the array being independently switchable between a high optical throughput state and a low optical throughput state in response to data supplied thereto, each of the pixels in the high optical throughput state further being switchable between a first optical phase state and a second optical phase state in a predetermined fashion in accordance with the supplied data.
18. A write head as defined in claim 17 , wherein each pixel includes a switchable diffractive structure switchable between a first state of greater diffraction and a second state of lesser diffraction.
19. A write head as defined in claim 18 , wherein the high optical throughput state corresponds to the second state of lesser diffraction while the low optical throughput state corresponds to the first state of greater diffraction.
20. A write head for a holographic data storage system, the write head comprising:
a spatial light modulator that is arranged into an array of pixels that can each separately modulate light that is directed toward the spatial light modulator; and
a phase mask that is capable of varying the phase of light passing therethrough and directed toward the spatial light modulator, the phase variation being dependent on which particular portion of the phase mask that the light passes through, wherein the phase variation of at least a portion of the phase mask can be changed over time.
21. A write head as defined in claim 20 , wherein the pixels of the spatial light modulator have an amplitude optical state determined by data supplied thereto, wherein the phase variation is changed in a predetermined fashion that is determined in accordance with the supplied data.