The present invention relates to the field of optical disks, and more specifically to a high-resolution pick-up for an optical disk.
The current storage capacity of optical disks (CD, then DVD, and now BluRay) is linked to the size of the reading spot, and thus submitted to the Rayleigh criterion: p=λ/NA where p is the radius of the light spot, λ the wavelength, and NA the numerical aperture equal to 2 n sin θ where n is the optical index of the material where the optical wave propagates, and θ the maximum angle of aperture of the lens system providing the focusing. To increase the storage capacity of this type of support, several options have been followed.
Options escaping from the Rayleigh criterion:
Options improving the Rayleigh criterion:
This last solution presently is one of the most promising but, as can be seen, it remains limited, with current wavelengths (405 nm), to spot dimensions on the order of 180 nm, that is, it is difficult to analyze patterns smaller than this dimension on an optical disk.
An object of an embodiment of the present invention is to provide an optical pick-up system adapted to the reading of optical disks, enabling to further minimize the spot size.
Thus, an embodiment of the present invention provides a high-resolution pick-up for an optical disk, comprising a monochromatic laser source; a polarizer of radial polarization; an annular diaphragm opaque at the center and at the periphery; an optical beam forming system; and an optical concentration microcomponent comprising a hemispherical lens having a nanowire, orthogonal to the plane of this lens, arranged at its focus, this nanowire being topped with a metal half-ball.
According to an embodiment of the present invention, the hemispherical lens has a diameter approximately ranging from 1 to 5 μm.
According to an embodiment of the present invention, the nanowire is a silicon nanowire having a length from 10 to 100 nm, preferably from 30 to 60 nm, and a diameter from 10 to 60 nm, preferably from 30 to 40 nm.
According to an embodiment of the present invention, the metal half-ball is made of gold.
According to an embodiment of the present invention, the light reflected by the optical concentration microcomponent is sampled by a splitter towards a photodetector.
According to an embodiment of the present invention, the pick-up is capable of reading patterns with a size approximately ranging from 20 to 50 nm from an optical disk.
According to an embodiment of the present invention, the pick-up comprises a device for controlling the distance between the pick-up and the optical disk.
According to an embodiment of the present invention, the pick-up is capable of operating at a wavelength ranging between 400 and 520 nanometers.
The foregoing and other objects, features, and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which:
For clarity, the same elements have been designated with the same reference numerals in the different drawings and, further, as usual in the representation of integrated circuits, the various drawings are not to scale.
The surface of the optical disk is shown to the right of the drawing and is designated with reference numeral 10, it conventionally comprises bumps and holes to be identified.
The assembly comprises an optical concentration microcomponent 11 such as shown in
An annular diaphragm 16 is also arranged on the way of the beam, this diaphragm having an internal radius r1 and an external radius r2. It enables to mask all or part of the beams having an angle of incidence on the pick-up greater than the numerical aperture (which will be chosen to be as high as possible, for example, equal to 0.85). It also enables to mask beams having an angle of incidence smaller than the total internal reflection angle for the interface between the material of the hemispherical lens, for example, silica. The following radiuses are thus selected:
r1=fobj*tan [Arcsin(1/nSIL)],
r2=fobj*tan [Arcsin(NA)],
where:
The diaphragm may be placed after optical system 14, in which case
r1=d*tan [Arcsin(1/nSIL)],
r1=d*tan [Arcsin(NA)],
where d designates the distance between the diaphragm and the planar surface of the hemispherical lens.
A splitter 18 enables to direct the light reflected by microcomponent 11 after having interacted with the optical disk towards a photo-sensor 19 capable of detecting the intensity of the reflected beam.
With such a system, by selecting:
It can further be acknowledged that in such conditions, a very high output efficiency, that is, a contrast between the raised portions and the hollow portions on the optical disk that may be greater than 10%, is obtained. It can also be acknowledged that the amount of reflected light is very large with respect to the injected light. For example, with 1 watt of light sent into the ring delimited by the annular diaphragm, powers on the order of 700 mW are obtained (for example, 730 mW for raised surfaces and 700 mW for hollow surfaces).
It is considered that the system is especially based on evanescent waves, and the metal half-ball of the optical concentration microcomponent used according to the invention will thus be placed at a distance from the optical disk much smaller than the illumination wavelength, for example, at a distance approximately ranging from 5 to 200 nm. A device for controlling the distance between the pick-up and the optical disk will further preferably be provided.
A method for forming the above-mentioned microcomponent is provided by the following steps, typical of the microelectronics industry, and detailed in
In a first step illustrated in
An opening of nanometric dimensions 103 is then formed in this second layer.
The first material may be silicon, the second material may be silicon or silicon oxide, and the third material may be, according to the sub-layers, silicon nitride, silicon oxide, and a metal such as gold or platinum.
In a second step illustrated in
In a third step illustrated in
In a fourth step illustrated in
In a fifth step illustrated in
As an example, the step of forming of the nano-object may be carried out from an etch process in an additional layer or multilayer structure deposited or transferred by layer transfer after structuring of the lens. In the case of a deposited layer, the layer or the multilayer structure is directly structured to form the nano-object. Said nano-object is generally polycrystalline and its form factor is of little importance with this technique. To obtain a single-crystal object, the layer transfer method is better adapted. A method for transferring a layer by molecular bonding on a planar surface formed of several materials is described in patent application US2008/079123. As illustrated in
Number | Date | Country | Kind |
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0951683 | Mar 2009 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR10/50468 | 3/16/2010 | WO | 00 | 12/9/2011 |