KR20060132844A - Magnification Correction Holographic Device - Google Patents

Abstract

The present invention relates to an optical holographic device for reading a data page recorded on the holographic medium 106. The apparatus includes means for accommodating holographic media, means for photographing the data page, and means for detecting the photographed data page 114. In addition, the present invention includes an electro-optical system (200, 300, 400) is provided between the receiving means and the detection means that can change the magnification by applying a voltage between the electrodes.

Description

Magnification Correction Holographic Device {HOLOGRAPHIC DEVICE WITH MAGNIFICATION CORRECTION}

The present invention relates to an optical holographic device for reading a page of data recorded on a holographic medium.

H.J. In Coufal, D. Psaltis, G.T.Sincerbox (Eds), 'Holographic data storage', Springer series in optical sciences, (2000), optical devices capable of recording on and reading from holographic media are known. 1 shows an optical device using phase conjugate readout. Such an optical device includes a radiation source 100, a collimator 101, a first beam splitter 102, a spatial light modulator 103, a second beam splitter 104, a lens 105, and a first deflector 107. And a first telescope 108, a first mirror 109, a half wave plate 110, a second mirror 111, a second deflector 112, a second telescope 113 and a detector 114. . The optical device is configured to record data to and read data from the holographic medium 106.

When writing a data page to the holographic medium, half of the radiation beam generated at the radiation source 100 is directed by the first beam splitter 102 towards the spatial light modulator 103. Some of these radiation beams are called signal beams. Half of the radiation beam generated by the radiation source 100 is deflected towards the telescope 108 by the first deflector 107. Some of these radiation beams are called reference beams. The signal beam is spatially modulated by the spatial light modulator 103. The spatial light modulator consists of a transmission area and an absorption area corresponding to 0 and 1 data bits of a data page to be recorded. After the signal beam passes through the spatial light modulator 103, the light modulator carries a signal recorded on the holographic medium 106, that is, a data page to be recorded. The signal beam is then focused on the holographic medium 106 by the lens 105.

The reference beam is also focused on the holographic medium 106 by the first telescope 108. Thus, the data page is recorded in the form of an interference pattern on the holographic medium 106 as a result of the interference between the signal beam and the reference beam. If a data page is written to the holographic medium 106, another data page is written to the same location of the holographic medium 106. For this purpose, the data corresponding to this data page is sent to the spatial light modulator 103. The first deflector 107 is rotated with respect to the holographic medium 106 to correct the angle of the reference signal. The reference beam is kept in the same position while rotating using the first telescope 108. Thus, the interference pattern is recorded in different patterns at the same position of the holographic medium 106. This is called angular multiplexing. The same position of the holographic medium 106 for recording a plurality of data pages is called a book.

Alternatively, the wavelength of the radiation beam may be adjusted to record different data pages in the same book. This is called wavelength multiplexing. Other types of multiplexing, such as shift multiplexing, may be used to record data pages on the holographic medium 106.

Upon reading the data page from the holographic medium 106, the spatial light modulator 103 is completely absorbed so that a portion of its beam cannot pass through the spatial light modulator 103. By removing the first deflector 107, a part of the beam generated from the radiation source 100 passing through the beam splitter 102 is the first mirror 109, the half wave plate 110 and the second mirror 111. The second deflector 112 is reached via. If angular multiplexing is used to write a data page to the holographic medium 106 and attempt to read a given data page, the second deflector 112 records the holographic given the angle to the holographic medium 106. It is arranged to be equal to the angle used to. Thus, the signal deflected by the second deflector 112 and focused on the holographic medium 106 by the second telescope 113 is the phase conjugate of the reference signal used to record the given holographic. For example, if a data page is written to the holographic medium 106 using wavelength multiplexing and an attempt is made to read a given data page, the same wavelength is used to read the given data page.

The phase conjugate of the reference signal is diffracted by an information pattern, which generates a reconstructed signal beam and reaches the detector 114 via the lens 105 and the second beam splitter 104. . Thus, the captured data page is generated in the detector 114 and detected by the detector 114. The detector 114 includes pixels corresponding to the bits of the photographed data page, respectively. Because of this, the holographic device should be designed to carefully align the imaging data page with the detector 114 such that the bits of the imaging data page hit the corresponding pixel of the detector 114. In other holographic devices, there are more pixels than bits in the image data page. For example, a holographic device is designed such that a bit strikes four pixels.

For this reason, such a holographic device cannot read an undesigned holographic medium. For example, if the holographic device is designed such that one pixel corresponds to one bit, and is designed to read a holographic medium containing a data page of 1500 * 1500 bits, the data page of 1000 * 1000 bits may be read. The containing holographic medium cannot be read because in this case one bit is imaged in more than one pixel. This is a disadvantage because new holographic devices with larger data capacities cannot read holographic media recorded with older holographic devices. However, backward compatibility is an important issue when designing new holographic devices.

(Summary of invention)

An object of the present invention is to provide a holographic device capable of reading a plurality of different holographic media.

To this end, the present invention provides an optical holographic device for reading a data page recorded on a holographic medium, comprising: means for accommodating the holographic medium, means for photographing the data page, And an electro-optical system provided between the accommodating means and the detecting means and capable of changing magnification by applying voltage between the electrodes.

According to the invention, the magnification of the electro-optical system is modified as a function of the type of holographic medium inserted in the holographic device. For example, a holographic medium having a data page of 1000 * 1000 pixels, and a holographic device designed to read a holographic medium having a data page of 1500 * 1500 pixels and designed to hit one pixel with one bit When inserted, the magnification of the electro-optical system is set to image one bit of the data page in one pixel of the detector. In this case, part of the detector is not used to read the holographic medium.

The use of electro-optical systems is particularly advantageous because it reduces the use of expensive, bulky and relatively large power consumption mechanical means.

Further, the present invention is preferably used to correct the magnification of the photographing data page even when the holographic device is designed to read the data page. Indeed, in holographic devices, magnification errors often occur due to mechanical gaps or defects in the manufacture of the holographic medium, since the holographic medium is not always located at the place where the holographic device is designed. For example, a magnification error results in bits that are imaged in more than one pixel where an error occurs in the data page, even if the device is designed to hit one pixel. According to the present invention, these magnification errors can be corrected.

It should be noted that patent US Pat. No. 6,414,296 describes a holographic device with an optical imaging system for adjusting a holographic data page. However, the magnification of the optical imaging system cannot be changed. Moreover, such an optical imaging system uses mechanical means for adjusting the holographic data page.

It should also be noted that patent application US 2003/0223101 discloses a holographic device having a lens which can change the focal length between a holographic medium and a detector by applying a voltage. However, the lens described in this patent application does not have a variable magnification. It is compatible with other optical storage media such as CDs or DVDs.

It is preferable that an electro-optical system is equipped with an electrowetting device. The electrowetting device has two different fluids separated by meniscus that can change their shape by applying an appropriate voltage between the electrodes surrounding the liquid. Changing the shape of the meniscus is fast and does not require a large amount of power.

Preferably, the electrowetting device comprises two different fluids separated into a fluid chamber and a meniscus that binds the edge by the fluid chamber and a first electric disposed to operate along the first side of the edge. And a wet electrode, a second electrowetting electrode arranged to operate separately along the second side of the edge thereof, and voltage control means for supplying different voltages to the first and second electrowetting electrodes. The use of this electrowetting device can translate the imaging data page relative to the detector. This makes it possible to correct the translational error occurring in the holographic device due to the mechanical play. Thus, this improves the detection of data pages.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

The invention will be explained in more detail by way of example with reference to the accompanying drawings in which:

1 shows a holographic device according to the prior art,

2a and 2b show the detection part of the holographic device of FIG. 1 modified according to the invention,

3a and 3b show a holographic device according to a preferred embodiment of the invention,

4a and 4b show a holographic device according to an advantageous embodiment of the invention.

The holographic device according to the invention is shown in Figs. 2a and 2b. The apparatus includes a detector 114 for detecting a photographing data page, and an electro-optical system 200 capable of changing the magnification by applying a voltage between the electrodes. In this example, the electro-optical system 200 consists of a liquid crystal device 201 and a converging lens 202. The holographic device further comprises means for receiving the holographic medium 106 installed at the position of the holographic medium 106. An example of these storage means is a table on which a recording medium can be placed. A table such as that used conventionally in a CD or DVD player can be used as an example.

The liquid crystal device 201 includes a liquid crystal material disposed so as to be separated into a convex surface and two electrodes surrounding the glass. This liquid crystal material has a normal refractive index n _o and an ideal refractive index n _e . The refractive index of the glass is selected to be equal to n _o . 2A and 2B, the liquid crystal material is selected to be oriented parallel to the electrodes when no voltage is applied between the electrodes. This can be done using an appropriate alignment layer in the liquid crystal device 201. 2A and 2B, the polarization of the radiation beam output from the second polarization beam splitter 104 is parallel to the electrode of the liquid crystal device 201.

In FIG. 2A, no voltage is applied between the electrodes of the liquid crystal device 201. For this reason, the liquid crystal molecules are aligned parallel to the polarization of the radiation beam. Thus, the refractive index of the liquid crystal material is n _e . Since n _e is higher than n _o , the liquid crystal device 201 operates as a positive lens. The converging lens 202 is disposed in the path of the radiation beam such that in this configuration, the magnification of the electro-optic system 200 is one.

In FIG. 2B, a voltage is applied between the electrodes of the liquid crystal device 201. For this reason, the liquid crystal molecules rotate in a direction perpendicular to the electrode, and the refractive index of the liquid crystal material is reduced. The result is that the focal length of the liquid crystal device 201 is increased. This is described, for example, in H.R.Stapert, J.Lub, E.J.K. Verstegen, B.M.I. van der Zande, and S. Stalinga, "Photo replicated anisotropic liquid crystalline lenses for aberration control and dual layer read out of optical disks", Adv. Functional Materials vol. 13, pp. 732-738, 2003. For this reason, the magnification of the electro-optical system 200 is reduced. It should be noted that the quality of the beam may be improved by displacing the converging lens 202 so that the focus of the liquid crystal device 201 coincides with the focus of the converging lens 202. In this case, the parallel beam impinges on the detector 114. In this case, mechanical means for displacing the converging lens 202 is used. However, it is necessary to displace only one optical member.

This can be used to compensate for magnification errors in the holographic device. Magnification errors can be detected by alignment marks of holographic media 106, for example as described in US Pat. No. 5,838,650. When a magnification error is detected, the voltage between the electrodes of the liquid crystal device 201 is corrected until the magnification error is removed. Only the reduction in magnification in the holographic device of FIGS. 2A and 2B can be obtained by changing the voltage between the electrodes of the electro-optic system 200, but the electro-optic system 200 can increase and / or decrease magnification. It is possible to design it. For example, when no voltage is applied, when the liquid crystal material is selected to be oriented as in FIG. 2B, the magnification is increased by the application of a positive voltage while the magnification is increased by the application of a negative voltage.

In addition, the electro-optical system 200 may be used for compatibility purposes. When a holographic device is designed such that a data page of 1000 * 1000 bits is imaged in a detector of 1500 * 1500 pixels, and one pixel corresponds to 1 bit, the magnification must be below 1, because the data This is because the area of the bit of the page is larger than the area of the pixel of the detector. The magnification to be applied may be detected by a magnification error detection system such as a system using an alignment mark. Alternatively, the number of bits of the data page may be recorded as data on the holographic medium 106 and detected by the detector 114. Depending on the number of bits and the number of pixels in the detector, the holographic device must determine which magnification to apply and then apply a voltage. These data may be stored in the lookup table.

It should be noted that another liquid crystal device may be used instead of the converging lens 202. The two liquid crystal devices can be separated or can be part of one electro-optical member. For example, two liquid crystal devices have a common electrode. With the use of two liquid crystal devices, since no focal length of the two liquid crystal devices can be changed independently, no mechanical means is used.

3A and 3B show a holographic device according to a preferred embodiment of the present invention. This holographic device replaces the electro-optic system 200 with a member such as the holographic device of FIGS. Equipped. The electrowetting device has two different fluids separated by a fluid chamber and a meniscus whose edge is bound by the fluid chamber. By applying a voltage to the electrode in the fluid chamber, the meniscus becomes more concave or convex depending on the applied voltage. Electrowetting devices are well known to those skilled in the art. For example, such an electrowetting device is described in patent application WO99 / 18456.

In the example of FIG. 3A, no voltage is applied between the electrodes of the electrowetting device 301. The shape of the meniscus is convex and its shape depends on the properties of the two fluids in the fluid chamber. In this example, the refractive index of the two fluids is selected so that the electrowetting device 301 acts as a positive lens when no voltage is applied. In FIG. 3B, a voltage is applied between the electrodes of the electrowetting device 301. Because of this, as the meniscus becomes less convex, the electrowetting device 301 is less converging. Thus, the magnification of the electro-optical system 300 is reduced. As mentioned in the description of FIG. 2A, the converging lens 302 may be displaced to improve the quality of the beam of the detector 114.

It should be noted that the converging lens 302 may be replaced with another electrowetting device. In this case, the two electrowetting devices may be the same and part of one electro-optical member. For example, the zoom lens described in patent application WO2004 / 038480 can be used as the electro-optical system 300. Alternatively, the electro-optical system 300 includes an electrowetting device and a liquid crystal device as described in FIGS. 2A and 2B. The focal length of these devices can be changed independently, so that the magnification of the electro-optical system 300 can be changed without using mechanical means.

A holographic device according to an advantageous embodiment of the invention is shown in Figs. 4a and 4b. This holographic device is similar to the holographic device of FIGS. 3A and 3B except for replacing the electro-optic system 300 with an electro-optical system 400 consisting of a split electrowetting device 401 and a converging lens 402. A member is provided. 4B is a cross-sectional view of the split type electrowetting device 401. This split type electrowetting device 401 includes a plurality of electrodes. Different voltages of V ₁ and V ₂ may be applied between a given electrode and the common electrode, for example, as shown in FIG. 4A. Thus, the split type electrowetting device 401 may include a first electrowetting electrode arranged to act along the first side of the edge and a second electrowetting electrode arranged to operate separately on the second side of the edge. It is provided with a voltage control means for supplying different voltages. Such a split type electrowetting device 401 is known from patent application WO2004 / 051323.

As described in this publication, the application of different voltages to the first and second electrodes results in the angular deflection of the radiation beam passing through the split electrowetting device 401. Thus, it is possible to correct the translational error of the holographic device. When the bits of the captured data page are shifted relative to the pixels of the detector 114, an appropriate voltage is applied to the electrodes of the split electrowetting device 401 until the captured data page is carefully aligned with the detector 114. do. Thus, for example, no mechanical means for translating the detector 114 is used to correct the translational error.

Any reference signs in the following claims should not be construed as limiting the claims. It is to be understood that the use of the verb "comprising" and its utilization does not exclude the presence of any other component other than as described in any claim. The word "a" or "an" before an element does not exclude the presence of a plurality of elements.

Claims (4)

An optical holographic device for reading a data page recorded on a holographic medium 106, the apparatus comprising means for accommodating the holographic medium, means for photographing the data page, and detecting the photographed data page. And an electro-optical system (200, 300, 400) provided between said means (114) and said accommodating means and said detecting means to change the magnification by applying a voltage between the electrodes. The method of claim 1, The electro-optical system (300) is characterized in that it comprises an electrowetting device (301). The method of claim 2, The electrowetting device 401 comprises a fluid chamber, two different fluids separated by a meniscus that binds the edge by the fluid chamber, and a first electric disposed to operate along the first side of the edge. And a wet electrode, a second electrowetting electrode arranged to operate separately along the second side of the edge thereof, and voltage control means for supplying different voltages to the first and second electrowetting electrodes. Optical holographic device. The method of claim 1, The electro-optical system (200) comprises a liquid crystal device (201) characterized in that the optical holographic device.

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