CN1255785C - A non-volatile holographic data storage method - Google Patents

Abstract

The invention belongs to the technical fields of optical information storage and volume holographic data storage, and relates to a nonvolatile volume holographic data storage method. Using photochromic material as volume holographic recording medium, fast recording of data information, non-volatile readout and repeated erasure and writing are realized through two-photon recording, single-photon readout and ultraviolet light erasure; the present invention improves The density of volume holographic storage of photochromic materials can be applied in the field of volume holographic data storage based on photochromic materials with high density, fast recording, repeated erasing and writing, and non-volatile readout.

Description

A method of non-volatile volume holographic data storage

technical field

The invention belongs to the technical field of optical information storage and volume holographic data storage, and in particular relates to a method for realizing volume holographic data storage in a photochromic material. It can be applied to volume holographic data storage with high density, fast recording, repeated erasing and writing, and non-volatile readout.

Background technique

Informatization is an inevitable trend of economic development in the world today. With the advent of the information age, people's requirements for information storage, transmission and processing are increasing day by day. Optical information storage technology has become a new storage technology after magnetic storage technology due to its high density and long life, and has become the research object of all countries in the world. Optical volume holographic storage technology has become the most potential optical storage technology due to its advantages of high redundancy, parallel data transmission, high storage density, fast addressing speed and related addressing functions. The volume holographic storage technology with rewritable and non-volatile readout is still a research hotspot in this field.

Under the influence of different wavelengths, the open-loop and closed-loop states of photochromic materials are transformed into each other and accompanied by changes in refractive index and absorption rate. This is used to realize rewritable volume holographic storage. Liu Guodong and others from Tsinghua University in China Volume 20 of Physics Letters, pages 1051-1053, reported volume holographic data storage using diarylene (photochromic material) as a recording medium. Fig. 1 is the structure diagram of the main optical path of the storage system, the system mainly includes a laser light source 11, a pinhole filter 12, a collimating lens 131, a light blocking diaphragm 14 and a first reflector which are sequentially arranged on the outgoing light path of the light source 151, the first half-wave plate 161 and the polarization beam splitter prism 17 are sequentially arranged on the reflected optical path of the first reflector, the second half-wave plate 162, the first group of shutters 181 and the second half-wave plate 162 on the transmitted optical path of the polarization beam splitter prism 17 Two reflecting mirrors 152, the spatial light modulator 19, the Fourier transform lens 132, the recording medium 100, the inverse Fourier transform lens 134, the second group of shutters 182 and the detector CCD200 arranged on the reflection optical path of the second reflecting mirror 152 are arranged on The polarization beam splitter prism 17 reflects the third mirror 153 on the optical path, and the recording medium 100 is also located on the optical path reflected by the third mirror.

The storage method of this storage system is: when recording, the laser light with a wavelength of 514.5nm produced by the laser light source 11 passes through a pinhole filter and a collimator lens to expand and collimate, and then passes through the first reflector 151, the first half-wave plate After 161 adjusts the polarization state, it is vertically incident on the polarization splitter prism 17, and the incident light is divided into transmitted light and reflected light: the transmitted light is adjusted to the S polarization state by the second half-wave plate 162, and modulated by the spatial light modulator 19 , constitutes the object light required for recording, and its optical power is 0.5mW; its reflected light, passing through the third mirror 153, constitutes the reference light required for recording, and its light intensity is 12mW/cm ² . The spatial light modulator 19, the Fourier transform lens 132, the recording medium 100, the Fourier inverse transform lens 134, and the detector CCD 200 constitute a typical 4F structure to realize Fourier spectrum holographic recording and object light readout. The reference light and the object light are incident on the recording medium 100 placed on the spectral surface at an angle of 90 degrees to interfere to form a grating, and record a data page; the optical path of the object light is blocked during the reading process, and the reference light is used as the readout light in the The corresponding data page information is read at the corresponding recording position, and the light intensity of the readout light is adjusted to 110 μW/cm ² when reading out.

After 2 hours of continuous reading using the above method, the quality of the reproduced image did not decrease significantly. But this method has two unfavorable factors because the material has linear absorption to the recording (reading) wavelength: one, because the volume grating in the recording material is an amplitude-phase type hybrid grating, its dynamic range is lower than that of pure phase The dynamic range of the type grating is small, and the storage density will not be as high as the storage density of the latter; second, the linear absorption reaction of the recording material to the readout light wave will erase the existing data information in the material. So after reading continuously for a longer time, the reproduced image will gradually become blurred and finally disappear. It can be seen that single-photon holographic recording using strong light recording and weak light readout cannot truly realize volume holographic data storage with high density, fast recording, rewritable multiple times, and non-volatile readout.

Zhao Jian used copper and cerium-doped lithium niobate crystals as recording media for non-volatile volume holographic data storage in his master's thesis of Tsinghua University in 2003, "Research on Volume Holographic Storage Properties of Double-doped Lithium Niobate Crystals". Fig. 2 is the main optical path structural diagram of this storage system, and its system mainly comprises the first laser light source 211, the first pinhole filter 221, the first collimator lens 231, the first pinhole filter 221, the first collimator lens 231, The first light blocking diaphragm 241, the first reflecting mirror 251, the first half-wave plate 261 and the first polarization beam splitting prism 271 arranged on the reflected light path of the first reflecting mirror 251, the transmitted light of the polarization beam splitting prism 271 The second half-wave plate 262, the first group of shutters 281 and the second mirror 252 are arranged on the road, the spatial light modulator 29, the Fourier transform lens 232 and the volume recording medium 300 are arranged on the reflection optical path of the second mirror 252 , and a Fourier inverse transform lens 234, a second group of shutters 282, a detector CCD200; also include a second laser light source 212, a second pinhole filter 222 and a collimator lens arranged on the outgoing light path of the second laser light source 212 232, the second light blocking diaphragm 241 and the third reflecting mirror 253, the second polarization beam splitting prism 272 is set on the reflection light path of the third reflection mirror 253, and the second polarization beam splitting prism 272 is set on the reflection light path of the second polarization beam splitting prism 272 Three reflection mirrors 253 , the other medium surface of the recording medium 300 is perpendicular to the reflection light path of the third reflection mirror 253 .

The storage method of the system is as follows: when recording, the laser light with a wavelength of 632.8nm generated by the first laser light source 211 is expanded and collimated by the pinhole filter and collimator lens, and then the polarization state is adjusted by the first half-wave plate 261 , is vertically incident on the first polarizing beam splitter prism 271, and the incident light is divided into two paths: the transmitted light is adjusted to the S polarization state by the second half-wave plate 262, passed through the first set of shutters 281 and the second reflector 252 The spatial light modulator 29 modulates to form the object light required for recording, and its light intensity is 50mW/cm ² ; the reflected light passes through the second polarization beam splitter 272 and the third reflector 253 to form the reference light required for recording. Its light intensity was 10 mW/cm ² . At the same time, the laser light with a wavelength of 488 nm generated by the second laser light source 212 is beam-expanded and collimated by the pinhole filter and the collimator lens, and then enters the second polarization beam splitter prism 272, and its reflected light passes through the third reflector 253 to form a Record the required sensitizing light, its light intensity is 5mW/cm ² , and its light path is the same as that of the reference light. The spatial light modulator 29, the Fourier transform lens 232, the recording medium 300, the inverse Fourier transform lens 234, and the detector CCD 200 constitute a typical 4F structure. The reference light and the sensitizing light are respectively incident on the recording medium 300 placed on the spectrum plane at a 90-degree angle with the object light and interfere to form a grating to record a data page. In the reading process, the second laser light source 212 is turned off, and the optical path of the object light is blocked at the same time, and the corresponding data page information is read at the corresponding recording position with the reference light consistent with the recording time. After 5 hours of continuous reading, the image The mass does not change appreciably, enabling optical fixation of the stored information. Although the use of dichroic holographic storage based on double-doped lithium niobate crystals can achieve non-volatile readout of data to a certain extent, it has disadvantages such as small dynamic range, low sensitivity, and inability to achieve fast recording.

Invention content:

The main purpose of the present invention is to overcome the deficiencies of the prior art, to propose a non-volatile volume holographic data storage method and its system, which utilizes photochromic materials that have a strong two-photon absorption effect in solid state And the characteristics of non-linear absorption in the infrared band, using two-photon recording and single-photon readout to achieve fast data recording and non-volatile readout. The present invention improves the density of volume holographic storage of photochromic materials, and can be applied in the field of volume holographic data storage based on photochromic materials with high density, fast recording, repeated erasing and writing, and non-volatile readout .

A non-volatile volume holographic data storage method proposed by the present invention adopts photochromic material as volume holographic recording medium, realizes fast recording of data information through two-photon recording, single-photon readout and ultraviolet light erasing, Nonvolatile read and write multiple times; includes the following steps:

1. Two-photon volume holographic data recording process: First, according to the absorption spectrum characteristics of the photochromic material, select a matching pulse laser as the light source for recording light, and the wavelength of the recording light is in the linear absorption region of the photochromic material Besides; the light emitted by the pulsed laser is divided into two beams of object light and reference light, so that the holographic recording medium is placed in the coherent field of object light and reference light, and secondly, the light intensity of the recording light is adjusted to make the object light and reference light The light intensity of the coherent field is greater than the intensity of the two-photon absorption reaction of the recording medium, and is less than the light intensity damage threshold of the recording medium (to avoid damage to the recording material); finally, adjust the optical path difference between the reference light and the object light, Make the optical path difference of the two beams within the coherence length of the pulsed laser;

2. Single-photon volume holographic data readout process: select a low-power continuous laser with the same wavelength as the recording light as the light source for the readout light, and adjust the optical path of the readout light to be the same as the optical path of the reference light, that is, to realize the non-linearity of data. Volatile readout (because the wavelength of the readout light is the same as the wavelength of the recording light, there will be no distortion of the reproduced image due to Bragg mismatch; and because the material has no linear absorption of this wavelength, there will only be no interference of the readout light The erasure of the stored data information. In this way, the non-volatile readout of the data is truly realized).

The method of the present invention can also include the erasing process of recording information: adopt the ultraviolet light source to emit light, align it with the area to be erased on the recording medium, and then the data information stored in the position can be erased, thereby realizing the erasure of the data information. Rewritable.

The principle of the invention is to use the photochromic material which has a strong two-photon absorption effect in the solid state and the characteristics of non-linear absorption in the infrared band, and adopts two-photon recording and single-photon readout to realize fast recording of data, non-volatile sexual readout.

The method provided by the present invention adopts infrared wavelength two-photon absorption holographic recording, two-photon absorption reaction only occurs in the coherent region of reference light and object light, and the refractive index change of the recording medium material has a linear relationship with the distribution of the recording light field, thus Realize the recording of information. When reading out, a low-power continuous laser with the same wavelength is used to realize the non-volatile readout of information.

Fig. 3 is the one-photon and two-photon absorption spectrum diagram of photochromic material, 31,32 are respectively the single-photon (linear) absorption curve of material in open-loop and closed-loop state, and 33 is that material is transformed into open-loop state by closed-loop state The two-photon (third-order nonlinear) absorption curve of . It can be seen from the figure that in the two-photon absorption wavelength region, the molecules in the open-loop and closed-loop states of the material have no linear absorption, and the two-photon absorption peak wavelength is about twice the absorption peak wavelength in the closed-loop state, that is, the material is both The transition from the closed-loop state to the open-loop state can be realized by absorbing one photon with a wavelength of _λ2 and simultaneously absorbing two photons with a wavelength of _λ3 . The two-photon volume holographic recording process of photochromic materials is actually a process in which a molecule of the material in the closed-ring state absorbs two photons through an intermediate virtual state and transforms into an open-ring state, resulting in a change in the refractive index to form a phase-type Bragg grating. . The erasing process of information is achieved by converting the material into a closed-loop state through light with a wavelength of _λ1 .

Two-photon volume holographic recording needs to meet the following conditions: First, the light intensity of the pulsed laser must be lower than the light intensity damage threshold of the recording medium, but it must be able to cause two-photon absorption in the material; second, the recording light wavelength must be within the range of the material. Outside the linear absorption region, so that only the third-order two-photon absorption reaction occurs in the recording medium, and the readout light does not erase the stored information during single-photon readout. Generally, the photochromic material in the closed-loop state The linear absorption region is 500-650nm, therefore, the two-photon absorption region is generally twice the linear absorption wavelength, that is, 1000-1300nm in the infrared region; finally, the light emitted by the pulsed laser is divided into two beams, namely the reference light and the Object light, the optical path difference when they reach the material must be within the coherence length of the pulsed laser, so that interference can occur and a modulation field is formed. If the single pulse duration of the pulsed laser is 100ps, its coherence length is 30mm. Refer to The optical path difference between light and object light must be within 30mm to form an interference field.

Compared with the previous optical holographic storage system, the advantages of the present invention are:

The two-photon volume holographic recording process is dependent on light intensity. Only when the light intensity reaches a certain threshold can two-photon absorption occur, thereby realizing information recording, which overcomes the problem of using low-power reproduction light of the same wavelength for information reading. erasure effect.

Two-photon volume holographic recording can select a wavelength that does not produce linear absorption for the photochromic material, and the wavelength is far away from the absorption peak of the photochromic material. Therefore, the wavelength in the infrared band is selected to record and read information, because this wavelength has no linear absorption for the open-loop and closed-loop states of the material, and non-volatile readout of data can be realized.

The recording time of two-photon volume holography is very short, which can realize fast recording. Using picosecond or even shorter pulse lasers, the two-photon reaction time is also within the time range of picoseconds or even shorter, and the recording time of information is two-photon time to react. Fast recording is thus possible.

Description of drawings

FIG. 1 is a structural diagram of an existing single-photon volume holographic storage system based on diarylene materials.

FIG. 2 is a structural diagram of an existing two-color body holographic storage system based on a double-doped lithium niobate material.

Figure 3 is the one-photon and two-photon absorption spectra of photochromic materials.

Fig. 4 is a structural diagram of a volume holographic system based on two-photon recording and one-photon readout of a photochromic material according to the present invention.

Detailed ways

The embodiment of a method for storing non-volatile volume holographic data proposed by the present invention is described in detail as follows in conjunction with the accompanying drawings:

The embodiment of the method of the present invention is realized by a holographic storage system with two-photon recording and single-photon readout. The main optical path structure of the system is shown in FIG. The first pinhole filter 421, the first collimating lens 431, the first blocking diaphragm 441 and the first reflector 451, the first half-wave plate 461, and the polarization beam splitter prism 47 are arranged on the polarization beam splitter prism 47 The second half-wave plate 462, the first group of shutters 481 and the second reflector 452, the spatial light modulator 49, and the Fourier transform lens 433 on the transmitted light path constitute the object light path, and are arranged on the polarization beam splitter prism 47 on the reflected light path. The phase compensator 410 and the fourth mirror 454 constitute a reference optical path; the reference light and the object light are incident at an angle of 90 degrees to the volume recording medium 400 placed at the position of the spectral plane; the second laser light source 412 is sequentially arranged on the second The second pinhole filter 422, the second collimating lens 432, the second blocking diaphragm 442, the third group of shutters 483, the semi-reflective and semi-transparent prism 40 (reflection), and the third reflector 453 on the laser light source exit optical path , polarization beam splitter prism 47 (transmission), phase compensator 410, the 4th reflection mirror 454 constitute readout optical path; The spatial light modulator 49, Fourier transform lens 433, recording material 400, Fourier inverse transform lens 434 and The detector CCD200 constitutes a typical 4F structure; it also includes a third light source 413, a third pinhole filter 423, a third collimating lens 433, a third blocking diaphragm 443, The transflective prism 40 (transmission), the third reflection mirror 453, the polarizing beam splitter prism 47 (transmission), the phase compensator 410, and the fourth reflection mirror 454 form an erasing optical path.

The first laser of the above system uses a pulsed laser with a wavelength of 1064nm, its pulse width is 50ps, and the optical power adjustment range is 0.5GW-4GW; the second laser uses a continuous low-power laser with a wavelength of 1064nm, and its output light intensity is 100μW /cm ² , the recording medium adopts a photochromic material with two-photon effect, and the third light source adopts an ultraviolet light source with a wavelength of 384nm.

All other components are conventional products.

The embodiment of the method for storing non-volatile volume holographic data realized by the above system mainly realizes fast recording of data information through two-photon recording, single-photon readout and ultraviolet light erasure, non-volatile readout and multiple times Repeatedly erased. Include the following steps (see Figure 4):

1. Two-photon volume holographic data recording process; laser light with a wavelength of 1064 nm generated by a laser light source 411 with a pulse width of 50 ps is expanded and collimated by a pinhole filter and a collimator lens, and the polarization state is adjusted by a half-wave plate 461 , is vertically incident on the polarizing beam splitter prism 47, and the incident light is divided into two paths: the transmitted light is adjusted to the S polarization state by the half-wave plate 462, and modulated by the spatial light modulator 49 to form the object light required for recording. Its optical power is adjusted to 1.1GW; its reflected light, through the phase compensator 410 and mirror 454, constitutes the reference light required for recording, and its optical power is adjusted to 0.8GW. The spatial light modulator 49, the Fourier transform lens 433, the recording medium 400, the Fourier inverse transform lens 434, and the detector CCD 200 constitute a typical 4F structure to realize Fourier spectrum holographic recording and object light readout. The reference light and the object light are incident at an angle of 90 degrees to the recording medium 400 placed on the spectral surface and interfere with each other to generate a two-photon absorption effect to form a grating, thereby quickly recording a data page.

2. Single photon volume holographic data readout process. Turn off the pulsed laser 411, and the 1064nm laser beam produced by the continuous low-power laser 412 is expanded and collimated through the pinhole filter and the collimator lens, and then transmitted through the reflector 453 and the polarization beam splitter prism 47, and then passed through the phase compensator 410, reflected The mirror 454 constitutes the readout light with a readout light intensity of 100 μW/cm ² , and the optical path of the readout light between the polarizing beam splitter prism 47 and the recording material 400 is the same as that of the reference light at the corresponding position during holographic recording. This enables non-volatile readout of information.

3. The process of erasing the recorded information. Turn off the pulse laser 411 and the continuous low-power laser 412, turn on the ultraviolet light source 413, and after the light from the light source 413 is filtered by the pinhole, beam expanded, and collimated, it is aligned with the area to be erased on the recording material, and then it can be erased. The data information stored in this location is deleted, thereby realizing the rewritable erasing and writing of the data information.

Claims (2)

1. A method for storing non-volatile volume holographic data, characterized in that a photochromic material is used as a volume holographic recording medium, and fast data information is realized through two-photon recording, single-photon readout and ultraviolet light erasing. Recording, non-volatile readout and multi-rewrite; includes the following steps: 1) Two-photon volume holographic data recording process: First, according to the absorption spectrum characteristics of the photochromic material, select a matching pulse laser as the light source for recording light, and the wavelength of the recording light is in the linear absorption region of the photochromic material Besides; the light emitted by the pulsed laser is divided into two beams of object light and reference light, so that the holographic recording medium is placed in the coherent field of object light and reference light; secondly, the light intensity of the recording light is adjusted to make the object light and reference light The light intensity of the coherent field is greater than the intensity of the two-photon absorption reaction of the recording medium, and is less than the light intensity damage threshold of the recording medium; finally, the optical path difference between the reference light and the object light is adjusted so that the optical path difference of the two beams within the coherence length of the pulsed laser; 2) Single-photon volume holographic data readout process: select a low-power continuous laser with the same wavelength as the recording light as the light source for the readout light, and adjust the optical path of the readout light to be the same as the optical path of the reference light, that is, to realize the non-linearity of data. Volatile readout. 2. The method for storing non-volatile volume holographic data as claimed in claim 1, further comprising a process of erasing recorded information: using an ultraviolet light source to emit light so that it is aligned with the area to be erased on the recording medium. area, the data information stored in that location can be erased.

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