WO2014107696A1

WO2014107696A1 - Systems and methods for multilevel optical storage in tunable photonic crystal cavities

Info

Publication number: WO2014107696A1
Application number: PCT/US2014/010406
Authority: WO
Inventors: Dirk R. ENGLUND
Original assignee: The Trustees Of Columbia University In The City Of New York
Priority date: 2013-01-07
Filing date: 2014-01-07
Publication date: 2014-07-10

Abstract

Systems and methods for multilevel optical storage in tunable photonic crystal cavities are disclosed. An exemplary apparatus for optical storage can include at least one membrane. The membrane can have a plurality of holes defining at least one photonic crystal cavity having a refractive index. At least one film layer can be disposed on the photonic crystal cavity to control the refractive index to store information by optical modes of the photonic crystal cavity.

Description

SYSTEMS AND METHODS FOR MULTILEVEL OPTICAL STORAGE IN TUNABLE PHOTONIC CRYSTAL CAVITIES

PATENT APPLICATION SPECIFICATION

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant No. W91 1NF-10-1-0416 awarded by the Army Research office/DARPA. The government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Patent

Application Serial No. 61/749,655, filed January 7, 2013, which is incorporated by reference herein.

BACKGROUND

The disclosed subject matter relates to systems and methods for multilevel optical storage in tunable photonic crystal cavities.

Conventional data storage techniques can employ binary states of a physical system. For example, magnetic and optical data storage systems, such as hard drives, CDs, DVDs, and magneto optic storage systems can store data in binary states. However, certain data storage techniques involving storage in binary states can limit storage density. Accordingly, there is a need for improved data storage techniques.

SUMMARY

Systems and methods for multilevel optical storage in tunable photonic crystal cavities are disclosed herein.

In one aspect of the disclosed subj ect matter, techniques for optical storage are disclosed. An exemplary apparatus for optical storage can include at least one membrane. The membrane can have a plurality of holes defining at least one photonic crystal cavity having a refractive index. At least one film layer can be disposed on the photonic crystal cavity to control the refractive index to store information by optical modes of the photonic crystal cavity.

In some embodiments, the membrane can include a silicon (Si) membrane. Additionally or alternatively, the photonic crystal cavity can include a cavity defined by a periodic two-dimensional array of holes having at least one defect. Additionally or alternatively, the photonic crystal cavity can have at least one resonance mode at 1.5 μm. In some embodiments, the defect can have a length of at least 1 μm, Additionally or alternatively, the defect can have a linewidth of at least 0.001 nm and/or a plurality of resonance modes, each resonance mode distributed over a respective range of wavelengths. In some embodiments, the film layer can include a photochromic film layer.

In some embodiments, a plurality of membranes and a plurality of film layers can be included. Each film layer can be disposed on a respective one of the plurality of membranes. Additionally or alternatively, a substrate can have a first side and a second side. The plurality of membranes can include a bottom membrane disposed on the first side of the substrate, at least one intermediate membrane disposed on the respective film layer of the bottom membrane, and a top membrane disposed on the respective film layer of the intermediate layer. Additionally or alternatively, the plurality of membranes can further include a second bottom membrane disposed on the second side of the substrate, a second at least one intermediate membrane disposed on the respective film layer of the second bottom membrane, and a second top membrane disposed on the respective film layer of the second intermediate layer.

In some embodiments, a plurality of defects can be included. The plurality of defects can be arranged as a periodic two-dimensional array of defects.

In another aspect of the disclosed subject matter, an exemplary system for optical storage can include at least one membrane having a plurality of holes defining at least one photonic crystal cavity having a refractive index. At least one film layer can be disposed on the photonic crystal cavity to control the refractive index. A first light source can be coupled to the photonic crystal cavity and adapted to illuminate the photonic crystal cavity. At least one spectrum analyzer (e.g., a spectrometer, an optical demultiplexer, a wavelength division demultiplexer, or an arrayed waveguide grating) can be coupled to the photonic crystal cavity to detect the reflectivity of the photonic crystal cavity illuminated by the first light source. In some embodiments, the first light source can include a broad-band light source. For example and not limitation, the wide-spectrum light source can include a superluminescent diode. The spectrum analyzer can be used to detect the frequency state of the cavity. In some embodiments, the first light source and the spectrometer can be coupled to the at least one photonic crystal cavity by a cross- polarized microscope, for example, where a probe field (which can be directed at the cavity) and the component of the reflected field to be analyzed can be orthogonally polarized. This cross-polarization can enable rejection of the probe light not coupled into the cavity, which can improve a signal to noise ratio of the cavity measurements.

In some embodiments, a plurality of photonic crystal cavities can be included. The first light source can illuminate the plurality of photonic crystal cavities simultaneously. Additionally or alternatively, the spectrometer can include a hyperspectral imaging apparatus to detect the reflectivity of the plurality of photonic crystal cavities illuminated simultaneously by the first light source.

In some embodiments, the system can further include a second light source coupled to the film layer to adjust the refractive index of the at least one photonic crystal cavity. Additionally or alternatively, a reversing laser can be coupled to the film layer to reset the refractive index of the photonic crystal cavity. For purpose of illustration and not limitation, the second light source and/or the reversing laser can include a laser, for example, a blue laser or an ultraviolet laser, and the reversing laser can be used to reset the photochromic film. Alternatively, the cavity photocliromic film(s) can be reset by heating the sample, for example, either locally using a heating laser, or globally by heating the entire storage sample.

In another aspect of the disclosed subject matter, methods for optical storage are provided. An exemplary method utilizes, an apparatus including at least one membrane having a plurality of holes defining at least one photonic crystal cavity and at least one film layer disposed on the photonic crystal cavity to control a refractive index of the photonic crystal cavity. The photonic crystal cavity can be illuminated. The reflectivity of the illuminated photonic crystal cavity can be detected to read information stored by optical modes of the photonic crystal cavity.

In some embodiments, the photonic crystal cavity can be illuminated using a wide spectrum of light. Additionally or alternatively, the photonic crystal cavity can be illuminated using light having a first polarization, and the reflectivity of the illuminated photonic crystal cavity can be detected using light having a second polarization.

In some embodiments, a plurality of photonic crystal cavities can be included. The plurality of photonic crystal cavities can be illuminated

simultaneously, and the reflectivity of the simultaneously illuminated plurality of photonic crystal cavities can be detected.

In some embodiments, the refractive index of the film layer can be adjusted to adjust the refractive index of the photonic crystal cavity to store further information by optical modes of the photonic crystal cavity. For example and not limitation, the refractive index of the film layer can be adjusted by one of illuminating or heating the at least one film layer. Additionally or alternatively, the refractive index of the film layer can be reset to reset the refractive index of the at least one photonic crystal cavity. For example and not limitation, the refractive index of the film layer can be reset by one of illuminating or heating the at least one film layer.

The accompanying drawings, which are incorporated and constitute part of this disclosure, illustrate certain embodiments of the disclosed subject matter and serve to explain the principles of the disclosed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an exemplary apparatus and system for optical storage, in accordance with some embodiments of the disclosed subject matter.

FIG. 1B is a diagram illustrating multiple cavity resonance from an exemplary optical cavity, in accordance with some embodiments of the disclosed subject matter.

FIG. 2 is a block diagram of an exemplary cross -polarized microscope for observing the reflectivity of an exemplary optical cavity, in accordance with some embodiments of the disclosed subject matter.

FIG. 3 is a flowchart illustrating an exemplary method for optical storage, in accordance with some embodiments of the disclosed subject matter.

Throughout the drawings, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the present disclosed subject matter will now be described in detail with reference to the FIGS., it is done so in connection with the illustrative embodiments.

DETAILED DESCRIPTION

Techniques for multilevel optical storage in tunable photonic crystal cavities are presented.

The use of larger alphabets can increase the information density in storage systems, such as optical storage systems. For example, techniques such as holographic optical data storage and photochromic optical memory can increase information density. The disclosed subject matter provides techniques for high dimensional optical data storage using the different states of a cavity reflection spectrum to store information. A photochromic film can allow for changing of the cavity properties to change the reflection spectrum.

FIG. 1 A shows a block diagram of an exemplary apparatus and system for optical storage, in accordance with some embodiments of the disclosed subject matter. An apparatus for optical storage can include at least one membrane 101 having a plurality of holes 1 1 1. The holes 11 1 can define at least one photonic crystal cavity 1 12 having a refractive index. At least one film layer 102 can be disposed on the photonic crystal cavity 1 12 to control the refractive index to store information by optical modes of the photonic crystal cavity 112. The film layer 102 can be either on the top side of the photonic crystal cavity 1 12, or it can infiltrate the holes 1 1 1. In the former case, for example, the sample can be fabricated with the film layer 102 deposited before etching to creates the photonic crystal cavity 112 holes 111 , as described herein. In the latter case, for example, the photochromic film can be spin- coated on one or more photonic crystal cavities 112 that have already been fabricated. In some embodiments, when the film layer 102 can infiltrate the holes 1 1 1 , a tenability of the photonic crystal cavity 112 frequency can be wider.

The membrane 101 can be a membrane of any suitable material, including without limitation a membrane of high-index material such as silicon (Si) or other suitable semiconductors. Alternatively, the membrane 101 can be a polymer membrane, such as the polymer photonic crystal devices disclosed in commonly assigned International Patent Application No. PCT/US12/068702, filed December 10, 2012, which is incorporated by reference herein. Alternatively, the membrane 101 can be a layer of (photochromic) film and integral with the film layer 102. For purpose of illustration and not limitation, the membrane 101 can have a thickness on the order of one-half of the wavelength of the cavity resonance inside the material. For example, the thickness can be the wavelength divided by 2n, where n is the refractive index of the material. For certain materials, the membrane thickness can be hundreds of nanometers. For example, a silicon membrane 101 can have a thickness of 100-300 nm.

The photonic crystal cavity 1 12 can be defined by a periodic arrangement of holes 1 1 1. For example and not limitation, the photonic crystal cavity can be defined by a periodic two-dimensional array of holes 11 1 having at least one defect 1 13. Alternatively, the photonic crystal cavities 1 12 can be defined by holes 1 1 1 to form one-dimensional photonic crystal nanobeam cavities. For purpose of illustration and not limitation, the defect 113 can be the size of a certain number of holes 1 11 arranged linearly. For example, an L3 defect can be the size of three holes 1 1 1 arranged linearly, an L5 can be the size of five holes 1 11 arranged linearly, and an LN defect can be the size of N holes 11 1 arranged linearly. Alternatively, the defect 113 can be any suitable defect in the periodic arrangement of holes 1 11.

Alternatively, the defect(s) 1 13 can be any suitable photonic lattice defect(s), including without limitation at least one hole dislocation cavities.

The film layer 102 can be a layer of any suitable material including but not limited to a photochromic film layer. Additionally or alternatively, the film layer 102 can include a thermochromic film layer. For example and not limitation, a photochromic film layer 102 can be a layer of any suitable photochromic material including but not limited to 5 wt % 1,3,3-Trimethylindo linonaphthospirooxazine (which can be commercially available from TCI America).

For purpose of illustration and not limitation, the defect 1 13 can confine multiple optical modes. The photonic crystal cavity 1 12 can be illuminated or probed with an optical field 151. For example and not limitation, the optical field can be any suitable electromagnetic field including light in the infrared, visible, and/or ultraviolet spectrum. Additionally or alternatively, the optical field can include light having one or more wavelengths. For purpose of illustration and not limitation, the optical field 151 can have a first polarization. The reflection 152 can be detected to obtain the reflectivity spectrum showing the resonances of the photonic crystal cavity 1 12. For example and not limitation, the reflection 152 can be detected using a cross- polarized configuration, as discussed below.

FIG. 1B is a diagram illustrating multiple cavity resonance from an exemplary optical cavity, in accordance with some embodiments of the disclosed subject matter. The frequency positions of these resonances can depend on the local refractive index surrounding the photonic crystal cavity 112. Each cavity resonance can have m different states, and each photonic crystal cavity 112 can have n different cavity resonances. The amount of information in the reflectivity spectrum can approach n log₂ m as given by the Shannon entropy. Thus, more than one bit of information can be stored in each photonic crystal cavity 1 12.

Each photonic crystal cavity 1 12 can have any suitable dimensions. For example, each photonic crystal cavity 112 can be as small as 1 μm in lateral dimensions. Additionally or alternatively, the defect 1 13 can have a length of one or more lattice constant(s) of the photonic crystal cavity 1 12, for example, which can be on the order of hundreds of nanometers.

For purpose of illustration and not limitation, the photonic crystal cavity 112 can have at least one resonance, the fundamental resonance mode, and additional higher-order modes.. For example, a planar Si photonic crystal cavity 112 can have a fundamental resonance mode at 1.5 μm. Additionally or alternatively, the periodic two-dimensional array of holes 1 1 1 can be an array of holes 111 having a lattice spacing of 450 nm, for example, and each of the plurality of holes can have a radius 130 nm. The lattice spacing can be chosen so that first photonic crystal cavity 1 12 bandgap can overlap with the desired cavity wavelength range. For certain high- index membranes 101, such as a silicon membrane 101, the lattice spacing a can be about a = 0.3λ, where λ is the average cavity wavelength. The hole radius r can be selected at about r = 0.3a. For a low-index membrane 101, such as a polymer membrane 101, the lattice spacing can be about a = 0.45λ, and the radius related to this lattice spacing can be about r = 0.35a.

In some embodiments, the defect 1 13 can have a linewidth of at least 0.001 nm, for example, a linewidth from 0.001-1 nm, corresponding to cavity quality factors for 10⁶-10³. For example and not limitation, the linewidth of one or more linear defect cavities 113 can be as narrow as 0.001 nm. Additionally, a defect 1 13 can have a plurality of resonances, each resonance distributed over a respective range of wavelengths. By adjusting the refractive index of the film layer 102 and the photonic crystal cavity 1 12 through spatially selective excitation with a light source or laser field, as described herein, these resonances can be individually tuned to encode information on different spectral channels. For example and not limitation, each cavity resonance can be distributed over about 10 nm of spectrum and 10 cavity resonances can be employed. For purpose of illustration and not limitation, each resonance could have up to approximately 8,000 states, corresponding to about 13 bits of information (2¹³ = 8,192). With reduction of spectral overlap, for example by spacing cavity modes further apart, each cavity resonance can encode or store 16- 1024 states with equal probability, which can result in 3-10 bits per cavity resonance. Thus, 10 cavity resonances can yield 30-100 bits of information per defect cavity 113. For example and not limitation, if an exemplary photonic crystal cavity 1 12 has an area of 1 μm , 30-100 bits can be encoded per square micrometer. Additionally or alternatively, a plurality of photonic crystal cavities 1 12 can be employed, each having at least one defect 1 13. Accordingly, 3-10 GB of information can be stored or encoded per square inch per layer of photonic crystal 112.

For purpose of illustration and not limitation, a plurality of defects 113 can be arranged in a two-dimensional array of defects 113; for example, defects may be introduced in a regular lattice with 4-6 lattice periods. The array of defects 113 can have a lattice spacing of at least 1 μm. Each of the defects 1 13 can have a length of several lattice periods, depending on the cavity design.

In the same or a different embodiment, a plurality of membranes 101 can be employed. Additionally, at least one film layer 102 can be disposed on each of the plurality of membranes 101. Each membrane 101 can have at least one photonic crystal cavity 1 12 defined therein, as discussed herein. In such an exemplary embodiment, membranes 101 with photonic crystal cavities 1 12 can be stacked or arranged in multiple layers, and each layer can be configured to store or encode information as described herein, as described herein. Cavities in different layers can be addressed independently, and the multitude of layers can increase the information density per area.

For purpose of illustration and not limitation, a substrate having a first side and a second side can be included. For example and not limitation, the substrate can be a disc made of any suitable material, including but not limited to metal, plastic or polymer. Layers of membranes 101 and film layers 102 can be disposed on the first side, the second side, or both sides of the substrate. For example, the layers can be placed on top of each other, optionally with (low-index) spacer layers between each membrane-film layer. For purpose of illustration and not limitation, the spacer layers can include any suitable material including air or a low-index polymer, such as CYTOP (which can be commercially available from Bellex International

Corporation). For example and not limitation, a bottom membrane 101 can be disposed on the first side of the substrate. At least one intermediate membrane 101 can be disposed on the respective film layer 102 of the bottom membrane. For example, the layers can be rolled on top of each other during the fabrication process. A top membrane 101 can be disposed on the respective film layer 102 of the intermediate membrane 101. Additionally or alternatively, a second bottom membrane 101 can be disposed on the second side of the substrate. A second at least one intermediate membrane 101 can be disposed on the respective film layer 102 of the second bottom membrane 101 , and a second top membrane 101 can be disposed on the respective film layer 102 of the second at least one intermediate membrane 101. As such, for example and not limitation, top and bottom sides of a substrate such as a recording disc can contain multiple layers of photonic crystals 1 12 storing information, such as employed in connection with DVDs. Thus, in such exemplary embodiments, the storage density can be multiplied by the number of layers of membranes 101. For example and not limitation, the storage density can be multiplied by a factor of 2 to 16 or more. Accordingly, embodiments in accordance with the disclosed subject matter can approach 100 GB of data storage per square inch.

Additionally or alternatively, a greater range of the spectrum can be used and/or more cavity resonances can be used. Accordingly, storage density can be increased by additional orders of magnitude. Additionally or alternatively, other degrees of freedom, including without limitation polarization state, reflectivity intensity, and k-states of incident and reflected light (which can be obtained, for example, using back focal plane imaging or other techniques), can also be used for storage of additional information, thereby increasing storage density.

In another aspect of the disclosed subject matter, a system for optical storage can include at least one membrane 101 having a plurality of holes 11 1 defining at least one photonic crystal cavity 1 12 having a refractive index, as described herein. Additionally, at least one film layer 102 can be disposed on the photonic crystal cavity 1 12 to control the refractive index, as described herein. A first light source 121 can be coupled to the at least one photonic crystal cavity 1 12. The first light source 121 can illuminate the photomc crystal cavity 112, as described herein. At least one spectrum analyzer 131, such as a spectrometer or an optical demultiplexer, can be coupled to the photonic crystal cavity 1 12, for example, using any suitable optical device or combination of optical devices, such as a

collection/focusing lens and/or an optical fiber. The spectrum analyzer 131 can detect the reflectivity of the photonic crystal cavity 112 illuminated by the first light source 121, as described herein. For example and not limitation, the system for optical data storage can resemble a conventional DVD player.

For purpose of illustration and not limitation, the first light source 121 can be any suitable light source, including without limitation a laser or a wide- spectrum light source such as a superluminescent diode. Additionally or alternatively, the first light source 121 can be a tunable laser, which can be used to scan the wavelength of the tunable laser across the cavity resonance, in which case the spectrum analyzer 131 can be a simple photodiode as the spectral information can be provided by the laser wavelength. For example, the first light 121 source can be a laser or wide-spectrum light source suitable for reading the information stored in the photonic crystal cavity 1 12. The information in the photonic crystal cavity 112 can be pre-recorded or can be recorded as described below.

The spectrum analyzer 131 can be any suitable spectrum analyzer including without limitation a compact spectrometer, a wavelength division demultiplexer such as an arrayed waveguide grating, and/or a photodiode.

Additionally or alternatively, the first light source 121 and the spectrum analyzer 131 can be coupled to the photonic crystal cavity 1 12 by a cross-polarized microscope, as described below.

In one embodiment, techniques for data storage can include parallel read-out. For purpose of illustration and not limitation, a membrane 101 can include a plurality of photonic crystal cavities 1 12. The first light source 121 can illuminate the plurality of photonic crystal cavities 112 simultaneously. For example and not limitation, the first light source 121 can be a defocused, polarized beam that can illuminate the membrane 101 including the plurality of cavities 1 12. Additionally, each photonic crystal cavity 112 can be read out simultaneously. For example and not limitation, the spectrometer 131 can be a hyperspectral imaging apparatus that can detect the reflectivity of the plurality of photonic crystal cavities 1 12 illuminated simultaneously by the first light source 121.

The system can also include a second light source 122 for recording information. For purpose of illustration and not limitation, the second light source 122 can be coupled to the at least one film layer 102 and can adjust the refractive index of the at least one photonic crystal cavity 1 12. The second light source 122 can be any suitable light source including without limitation a laser. For example, the second light source 122 can be a blue laser or an ultraviolet laser. Additionally or alternatively, a reversing mechanism 123 can be included. For purpose of illustration and not limitation, the reversing mechanism 123, such as a reversing laser 123, can be coupled to the at least one film layer 102 and can reset the refractive index of the at least one photonic crystal cavity 1 12. The reversing mechanism 123 can be any suitable light source, heat source, or other mechanism to reset the refractive index of the film layer 102 and the photonic crystal cavity 112. For example and not limitation, the reversing mechanism 123 can be a laser, such as a green laser or a heating laser.

FIG. 2 is a block diagram of an exemplary cross-polarized microscope for observing the reflectivity of an exemplary optical cavity, in accordance with some embodiments of the disclosed subject matter. As described herein, the photonic crystal cavity 1 12 can be illuminated or probed with an optical field 151 to obtain a reflectivity spectrum that can show the cavity resonances. In some exemplary embodiments, a plurality of photonic crystal cavities 112 can be arranged in an array, as described herein. Each photonic crystal cavity 112 can be illuminated or probed with an optical field 151 such as a focused beam, for example, a beam in the visible and/or infrared spectrums. For purpose of illustration and not limitation, the optical field 151 can be directed to a polarized beam splitter (PBS) 141. The PBS 141 can direct the optical field through a half- wave plate (HWP) 142 and/or an objective 143. The objective 143 can focus the optical field 151 to illuminate the photonic crystal cavity 112 and/or the defect 113. Additionally, the reflection 152 from the photonic crystal cavity 112 and/or defect 113 can pass through the objective 143, the HWP 142, and/or the PBS 141. Additionally or alternatively, a spectrometer 131 can be coupled to the PBS 141 to detect the reflection 152, as described herein.

FIG. 3 is a flowchart illustrating an exemplary method for optical storage, in accordance with some embodiments of the disclosed subject matter. An apparatus including at least one membrane 101 having a plurality of holes 11 1 defining at least one photonic crystal cavity 1 12 and at least one film layer 102 disposed on the photonic crystal cavity 1 12 to control a refractive index of the photonic crystal cavity 1 12 can be used. At 301 , the photonic crystal cavity 112 can be illuminated, as described herein. For example and not limitation, the photonic crystal cavity 112 can be illuminated using a wide spectrum of light, as described herein.

At 302, the reflectivity of the illuminated photonic crystal cavity 112 can be detected to read information stored by optical modes of the photonic crystal cavity 112, as described herein. Additionally or alternatively, the photonic crystal cavity 112 can be illuminated using light having a first polarization, and the reflectivity of the illuminated photonic crystal cavity 112 can be detected using light having a second polarization, as described herein.

In some exemplary embodiments, a plurality of photonic crystal cavities 1 12 can be included. For purpose of illustration and not limitation, the plurality of photonic crystal cavities 1 12 can be illuminated simultaneously, and the reflectivity of the simultaneously illuminated plurality of photonic crystal cavities 112 can be detected.

At 303, the refractive index of the film layer 102 can be adjusted to adjust the refractive index of the photonic crystal cavity 112 to store further information by optical modes of the photonic crystal cavity 112, as described herein. For purpose of illustration and not limitation, the refractive index of the film layer 102 can be adjusted by illuminating or heating the film layer 102. For example and not limitation, the refractive index of the film layer 102 can be adjusted by exposing that film layer 102 to certain light, for example, high frequency light such as blue or ultraviolet laser light.

At 304, the storing of further information by the optical modes of the photonic crystal cavity 1 12 can be reversed or reset. For purpose of illustration and not limitation, the refractive index of the film layer 102 can be reset to reset the refractive index of the photonic crystal cavity 112, as described herein. For example, the refractive index of the film layer 102 can be reset by illuminating or heating the film layer 102. For purpose of illustration and not limitation, resetting or reverse tuning can be implemented using a green laser. Different resonances can have different spatial modes, which can allow different resonances to be tuned

independently.

The foregoing merely illustrates the principles of the disclosed subject matter. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous techniques which, although not explicitly described herein, embody the principles of the disclosed subject matter and are thus within its spirit and scope.

Claims

CLAIMS What is claimed is:

1. An apparatus for optical storage, comprising:

at least one membrane having a plurality of holes defining at least one photonic crystal cavity having a refractive index; and

at least one film layer disposed on the photonic crystal cavity to control the refractive index to store information by optical modes of the photonic crystal cavity.

2. The apparatus of claim 1, wherein the membrane comprises one of a silicon (Si) membrane or a polymer membrane.

3. The apparatus of claim 1, wherein the photonic crystal cavity comprises a cavity defined by a periodic two-dimensional array of holes having at least one defect.

4. The apparatus of claim 1 , wherein the photonic crystal cavity comprises a one-dimensional photonic crystal nanobeam cavity.

5. The apparatus of claim 3, wherein the photonic crystal cavity comprises a cavity having at least one resonance mode at 1.5 μm.

6. The apparatus of claim 3, wherein the at least one defect comprises a defect having a length of one or more periods of the periodic two-dimensional array of holes.

7. The apparatus of claim 3, wherein the at least one defect comprises a defect having a line width of 0.001-1 nm.

8. The apparatus of claim 3, wherein the at least one defect comprises a defect having a plurality of resonance mode, each resonance mode distributed over a respective range of wavelengths.

9. The apparatus of claim 1, wherein the at least one film layer comprises one of a photochromic film layer or a thermochromic film layer.

10. The apparatus of claim 1 , wherein the at least one membrane comprises a plurality of membranes and the at least one film layer comprising a plurality of film layers, each disposed on a respective one of the plurality of membranes.

1 1. The apparatus of claim 10, further comprising a substrate having a first side and a second side,

wherein the plurality of membranes comprises a bottom membrane disposed on the first side of the substrate, at least one intermediate membrane disposed on the respective film layer of the bottom membrane, and a top membrane disposed on the respective film layer of the at least one intermediate layer.

12. The apparatus of claim 1 1, wherein the plurality of membranes further comprises a second bottom membrane disposed on the second side of the substrate, a second at least one intermediate membrane disposed on the respective film layer of the second bottom membrane, and a second top membrane disposed on the respective film layer of the second at least one intermediate layer.

13. The apparatus of claim 3, wherein the at least one defect comprises a plurality of defects.

14. The apparatus of claim 13, wherein the plurality of defects comprises a periodic two-dimensional array of defects.

15. A system for optical storage, comprising:

at least one membrane having a plurality of holes defining at least one photonic crystal cavity having a refractive index;

at least one film layer disposed on the photonic crystal cavity to control the refractive index;

a first light source coupled to the at least one photonic crystal cavity and adapted to illuminate the at least one photonic crystal cavity; and

at least one spectrum analyzer coupled to the at least one photonic crystal cavity and adapted to detect the reflectivity of the at least one photonic crystal cavity illuminated by the first light source.

16. The system of claim 15, wherein the first light source comprises one of a wide-spectrum light source or a laser.

17. The system of claim 16, wherein the wide-spectrum light source comprises a superluminescent diode.

18. The system of claim 15, the spectrum analyzer comprising one of a spectrometer, a grating spectrometer, a wavelength division demultiplexer, or an arrayed waveguide grating.

19. The system of claim 15, wherein the first light source and the spectrometer are coupled to the at least one photonic crystal cavity by a cross- polarized microscope.

20. The system of claim 15, wherein the at least one photonic crystal cavity comprises a plurality of photonic crystal cavities.

21. The system of claim 20, wherein the first light source is further adapted to illuminate the plurality of photonic crystal cavities simultaneously.

22. The system of claim 21, wherein the spectrometer comprises a hyperspectral imaging apparatus adapted to detect the reflectivity of the plurality of photonic crystal cavities illuminated simultaneously by the first light source.

23. The system of claim 15, further comprising:

a second light source coupled to the at least one film layer and adapted to adjust the refractive index of the at least one photonic crystal cavity; and

a reversing laser coupled to the at least one film layer and adapted to reset the refractive index of the at least one photonic crystal cavity.

24. The system of claim 23, wherein the second light source comprises one of a blue laser or an ultraviolet laser.

25. The system of claim 23, wherein the reversing laser comprises one of a green laser or a heating laser.

26. A method for optical storage using an apparatus including at least one membrane having a plurality of holes defining at least one photonic crystal cavity and at least one film layer disposed on the photonic crystal cavity to control a refractive index of the photonic crystal cavity, comprising:

illuminating the at least one photonic crystal cavity; and detecting the reflectivity of the illuminated at least one photonic crystal cavity to read information stored by optical modes of the photonic crystal cavity.

27. The method of claim 26, wherein the illuminating comprises illuminating the at least one photonic crystal cavity using light having a first polarization, and the detecting comprising detecting the reflectivity of the illuminated at least one photonic crystal cavity using light having a second polarization.

28. The method of claim 26, wherein the at least one photonic crystal cavity comprises a plurality of photonic crystal cavities; wherein the illuminating comprises illuminating the plurality of photonic crystal cavities simultaneously; and

wherein the detecting comprises detecting the reflectivity of the simultaneously illuminated plurality of photonic crystal cavities.

29. The method of claim 32, wherein the adjusting comprises adjusting the refractive index of the at least one film layer by one of illuminating or heating the at least one film layer.

30. The method of claim 32, further comprising:

resetting the refractive index of the at least one film layer to reset the refractive index of the at least one photonic crystal cavity.

31. The method of claim 30, wherein the resetting comprises resetting the refractive index of the at least one film layer by one of illuminating or heating the at least one film layer.