CN1254800C - Method of realizing parallel read of multiple wavelength and multilayer optical disc, its optical head and disc - Google Patents
Method of realizing parallel read of multiple wavelength and multilayer optical disc, its optical head and disc Download PDFInfo
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- CN1254800C CN1254800C CNB2004100307849A CN200410030784A CN1254800C CN 1254800 C CN1254800 C CN 1254800C CN B2004100307849 A CNB2004100307849 A CN B2004100307849A CN 200410030784 A CN200410030784 A CN 200410030784A CN 1254800 C CN1254800 C CN 1254800C
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Abstract
The present invention relates to a method of realizing the parallel read of a multiple wavelength and multilayer optical disc, the optical head thereof and the disc thereof, which belongs to the technical field of high density digital optical storage, particularly to the technical field of multiple wavelength and multilayer optical storage. The present invention is characterized in that the method is used for focusing lasers of different wavelengths on different recording layers of the multilayer disc by using the axial chromatic aberration of a chromatic aberration regulating object lens in the optical head so as to realize the parallel read of the lasers of different wavelengths. The method discloses a parameter cooperation relation between the multilayer disc and the chromatic aberration regulating object lens of the optical head; if the relation is satisfied, the lasers of different wavelengths can be focused on different recording layers of the multilayer disc. The present invention also discloses the optical head and the multiple wavelength and multilayer disc which are suitable for the method. The method, the optical head and the disc can be used for realizing the parallel read of the multiple wavelength and multilayer optical disc to greatly weaken read crosstalks among the layers of the multiple wavelength and multilayer optical disc.
Description
Technical field:
Method of realizing parallel read of multiple wavelength and multilayer optical disc, and optical head thereof belong to the high-density digital field of optical storage technology, especially multi-wavelength multilayer field of optical storage technology.
Background technology:
Multi-wavelength multiplayer optical disk and read-write technology thereof
Photochromic multi-wavelength multiplayer optical disk and read-write technology thereof are the parts of Tsing-Hua University's a series of patented technologies in CD national project center, and this technology adopts the multiple photochromic material of different sensitive bands as recording layer; A plurality of wavelength lasers are focused on the CD same point by Multiplexing apparatus, achromatic objective etc., and each recording layer is in together within the depth of focus, thereby realizes each recording layer concurrent reading and concurrent writing of multi-wavelength.
There are being certain research in Shanghai ray machine institute of the Chinese Academy of Sciences, the Industrial Technology Research Institute of Taiwan, Hitachi (Hitachi), Mitsubishi (Mitsubishi), Panasonic (Matsushita) etc. aspect the optical storage of multi-wavelength multilayer, its optical head, storage medium structure and Tsing-Hua University's technology have similar part.But often to adjust focal length, be unfavorable for concurrent reading and concurrent writing in the patent of these research institutions or producer successively to each layer addressing (perhaps the focusing addressing issue is related to very less or do not elaborate).And the existing patent in CD national project center can realize concurrent reading and concurrent writing, helps improving reading speed.
The multi-wavelength optical head
A kind of typical multi-wavelength optical head synoptic diagram is as shown in Figure 1: comprise that laser instrument 1 (contains different wave length one-wavelength laser device 1.1,1.2 ... 1.N), Multiplexing apparatus 2 (comprising N collimation lens and a prism), light-splitting device 3 (comprising polarization splitting prism and quarter wave plate), light-dividing device 4 (being made up of prism and imaging len), detector 5 (contain different wave length detector 5.1,5.2 ... 5.N), achromatic objective 6.7 is multi-wavelength multilayer disc, does not belong to optical head.
The close light, light-dividing device of above multi-wavelength optical head have utilized the closing of prism, light-dividing principle.In addition, also can utilize optical directional coupler, holographic concave diffraction grating etc. to close light, beam split, the optical head synoptic diagram is similar to preceding figure.In the above optical head, light-splitting device utilizes polarization theory with incident, emitting light path separately, can utilize optical fiber etc. to reach same purpose in addition.
In the prior art, focus on the CD same point in order to make a plurality of wavelength lasers, achromatic objective should satisfy condition 1: by color difference eliminating, the N bundle laser focusings that the wavelength that passes Multiplexing apparatus etc. is different are in same point O, that is:
U
1＝U
2＝…＝U
j＝…＝U
N
In the formula, U
1, U
2... U
j, U
NBe respectively the image distance of achromatic objective for the different N bundle laser of wavelength.Image distance is defined as the distance that the N bundle laser focusing that passes the multi-wavelength optical head is put object lens herein.
Multi-wavelength multilayer disc
Multi-wavelength multilayer disc chip architecture synoptic diagram is as shown in Figure 2: wherein, 8 are the dish base; 9 is recording layer, and the N layer respectively comprises a kind of photochromic material, corresponding to the laser of reading of different wave length altogether; 10 is the reflection horizon; 11 is protective seam.Object lens disc spacing, object lens parameter, disc parameter matching relationship
Multi-wavelength multilayer disc is read synoptic diagram such as Fig. 3: wherein, 12 is disc incident laser light beam, that is the laser beam of achromatic objective focusing.Each wavelength laser through achromatic objective, dish base after, focus on same point O on the video disc recording layer, through the reflection horizon, dish base, achromatic objective, light-splitting device, light-dividing device return, read by detector.
Object lens disc spacing, object lens image distance, coil basic thickness, the disc record layer thickness must satisfy matching requirements 2, and the N bundle laser focusing point that passes the multi-wavelength optical head is dropped on the recording layer.That is:
Work as j=1,2 ... N
H+h
0＜U
j＜H+h
0+2∑d
Wherein, H is the distance of disc to object lens, h
0For coiling basic thickness, d
1, d
2..., d
j... d
NBe respectively the thickness of N recording layer, ∑ d=d
1+ d
2+ ... d
jD
NBe the recording layer thickness sum.Consider reflection horizon direct reflection effect, focus point drop on behind the reflection horizon with the symmetrical ∑ d scope of N recording layer in also be fine (but this scope reflects light light intensity decreasing is not recommended to adopt), thereby be limited to H+h on the image distance
0+ 2 ∑ d.
Achromatic objective depth of focus, disc record layer thickness also must satisfy condition 3, and each wavelength depth of focus is greater than the recording layer thickness sum, that is:
Work as j=1,2 ... N
L
j＞∑d
Wherein, L
1, L
2L
jL
NBe respectively each wavelength focus laser beam depth of focus, as shown in Figure 3.
All kinds of data are to the definition and the disunity of depth of focus and concrete numerical value thereof, and in the patent specification, depth of focus is defined as near the interior waist of medium, and the laser axial strength is reduced to the axial spacing that certain value (such as peak strength 80%) is located two positions.Less when this definite value, the depth of focus value is bigger; This definite value is bigger, and the depth of focus value is less.
Crosstalk between multi-wavelength CD wavelength
In the existing patent multi-wavelength sandwich construction of cd centre, recording layer thickness and less than each wavelength depth of focus, each wavelength laser focuses on the CD same point, though being convenient to focusing and multi-wave length parallel reads, but in parallel read-out, inevitably introduced to read between the different wave length signal and crosstalked, influenced the read output signal quality.Above conclusion is by the experimental verification of CD ERC of Tsing-Hua University.
Chinese patent 00124422.1 (Xu Duanyi, Ma Lijun, Li Hexiong etc., multi-layer optical head for 3 D storage) claims to realize concurrent reading and concurrent writing, but by claims and instructions as can be known, by the focusing of ganged focus mechanism zoom, it is serial that each layer read, carry out in turn.
Summary of the invention:
The present invention will utilize the intrinsic axial chromatic aberration of optical system to realize that multilayer focuses on simultaneously, parallel read-out, and weaken multi-wavelength multiplayer optical disk interlayer and read and crosstalk.Compare with the focusing of Chinese patent 00124422.1 ganged focus mechanism realization zoom, the present invention can realize real parallel read-out, and optical system is simpler.
The present invention proposes a kind of axial aberration of optical system that utilizes and realize method and the optical head that a plurality of recording layers of multi-wavelength multiplayer optical disk and line focusing are read.This method can make each wavelength read laser separately, focus point drops on respectively on the multi-wavelength multilayer disc corresponding record layer, each wavelength depth of focus is less than respective record layer thickness and adjacent spaces layer (or basic unit) thickness sum, arbitrary recording layer all is within the corresponding wavelength focus point depth of focus, and any adjacent recording layer is not within the aforementioned depth-of-focus, thereby can realize that multilayer focuses on simultaneously, parallel read-out, reading between recording layer crosstalks obtains weakening.
Method proposed by the invention is characterised in that: it is to utilize the axial chromatic aberration of the toning difference object lens in the optical head that different wavelength of laser is focused on the different recording layer of multilayer disc, thereby realizes the method that the different wave length laser parallel is read; Wherein different wave length laser is the N bundle, and the recording layer number of plies of multilayer disc is the N layer, and the disc wall number of plies is the N layer, and described N layer recording layer and N interlayer interlayer are stacked alternately, and the dish base of described disc is close to the ground floor recording layer; When the toning difference object lens of described multilayer disc and optical head satisfied following condition, the different N bundle laser of wavelength focused on respectively on N recording layer of multilayer disc:
1) toning difference object lens satisfy: U
1＜U
2＜...＜U
j＜...＜U
N
2) the ground floor recording layer of multilayer disc should satisfy:
The first bundle laser focus point drops between dish base and the ground floor wall:
H+H
1-h
0＜U
1＜H+H
1+d
1+h
1
The depth of focus of the first bundle laser is basic to the distance between the ground floor wall less than dish:
L
1＜d
1+h
0+h
1
The depth of focus of the ground floor recording layer and the first bundle laser has the overlapping region:
H+H
1-L
1/2＜U
1＜H+H
1+d
1+L
1/2
Second layer recording layer is not overlapping with the depth of focus of the first bundle laser:
U
1＜H+H
1+d
1+h
1-L
1/2
3) the intermediate record layer of multilayer disc should satisfy:
J bundle laser focus point drops between j-1 and the j interlayer interlayer:
H+H
j-h
j-1＜U
j＜H+H
j+d
j+h
j
The depth of focus of j bundle laser is less than the distance between j-1 and the j interlayer interlayer:
L
j＜d
j+h
j-1+h
j
The depth of focus of j layer recording layer and j bundle laser has the overlapping region:
H+H
j-L
j/2＜U
j＜H+H
j+d
j+L
j/2
J-1 layer or j+1 layer recording layer are not overlapping with the depth of focus of j bundle laser:
H+H
j-h
j-1+L
j/2＜U
j＜H+H
j+d
j+h
j-L
j/2
J=2 in the following formula, 3 ... N-1;
4) effect in consideration reflection horizon, the recording layer adjacent with the reflection horizon should satisfy:
N bundle laser focus point drops between the mirror image of N-1 interlayer interlayer and N-1 interlayer interlayer (comprising this wall and mirror image thereof):
H+H
N-h
N-1＜U
N＜H+H
N+2d
N+2h
N+h
N-1
N restraints the distance of the depth of focus of laser less than (comprising this wall and mirror image thereof) between the mirror image of N-1 interlayer interlayer and N-1 interlayer interlayer:
L
N＜2d
N+2h
N-1+2h
N
The depth of focus of N layer recording layer or its mirror image and N bundle laser has the overlapping region, that is:
H+H
N-L
N/ 2＜U
N＜H+H
N+ d
N+ L
N/ 2, corresponding to recording layer and depth of focus the overlapping region is arranged, or
H+H
N+ d
N+ 2h
N-L
N/ 2＜U
N＜H+H
N+ 2d
N+ 2h
N+ L
N/ 2, corresponding to recording layer mirror image and depth of focus the overlapping region is arranged;
N-1 layer recording layer and mirror image thereof are not overlapping with the depth of focus of N bundle laser:
H+H
N-h
N-1+L
N/2＜U
N＜H+H
N+2d
N+2h
N+h
N-1-L
N/2
In aforementioned each formula:
U
jBe the image distance of poor object lens of mixing colours for j bundle wavelength laser;
H is the distances of object lens to the disc adjacently situated surfaces;
H
jBe the thickness of described disc surface, that is: to j layer recording layer
H
j=h
0+ d
1+ h
1+ d
2+ h
2+ ... + d
J-1+ h
J-1, h wherein
0The thickness of graduated dial base;
L
jIt is the depth of focus of j bundle laser focusing;
h
jBe the thickness of the j interlayer interlayer of disc;
d
jBe the thickness of the j layer recording layer of disc;
When certain wall did not exist, the corresponding interval layer thickness got 0 in aforementioned each formula.
In described condition 1)～4) on the basis, also satisfy: laser focusing is at respective record layer median surface, i.e. U
j=H+H
j+ d
j/ 2; Read better effects if this moment.
Optical head proposed by the invention contains laser instrument (1), Multiplexing apparatus (2), light-splitting device (3), the light-dividing device (4) that can launch different wave length laser, the detector (5) that can survey different wave length laser, it is characterized in that, also contain toning difference object lens (13); Described light-dividing device (4), light-splitting device (3), toning difference object lens (13) are installed with optical axis successively, constitute primary optical axis; Described Multiplexing apparatus (2), light-splitting device (3) are installed with optical axis at an angle of 90 with primary optical axis, constitute secondary optical axis; Light-splitting device (3) is positioned at the position of intersecting point of primary optical axis and secondary optical axis; The different wave length laser of laser instrument emission is synthetic through Multiplexing apparatus (2), after light-splitting device (3) reflection, poor object lens (13) incide on the different layers of multi-wavelength multilayer disc by mixing colours; After the reflection,, impinge upon on the detector (5), finish read operation through the poor object lens (13) of mixing colours, light-splitting device (3), light-dividing device (4).
Another kind of optical head proposed by the invention contains laser instrument (1), Multiplexing apparatus (2), the light-dividing device (4) that can launch different wave length laser, the detector (5) that can survey different wave length laser, it is characterized in that, also contains toning difference object lens (13); Described Multiplexing apparatus (2), toning difference object lens (13) are connected by optical fiber; Described light-dividing device (4), toning difference object lens (13) are connected by optical fiber.After the different wave length laser of laser instrument emission synthesizes through Multiplexing apparatus (2), by inciding respectively on the different layers of multi-wavelength multilayer disc behind optical fiber, the toning difference object lens (13); After the reflection,, impinge upon on the detector (5), finish read operation through the poor object lens (13) of mixing colours, optical fiber, light-dividing device (4).
Experiment showed, that but method proposed by the invention can realize the parallel read-out of multi-wavelength multiplayer optical disk, weaken multi-wavelength multiplayer optical disk interlayer greatly and read and crosstalk that this optical head can with the different wavelength of laser focus point separately reach its intended purposes.
Description of drawings:
Fig. 1 prior art multi-wavelength optical head synoptic diagram;
Fig. 2 prior art multi-wavelength multilayer disc chip architecture synoptic diagram;
Fig. 3 prior art multi-wavelength multilayer disc is read synoptic diagram;
The method synoptic diagram that Fig. 4 is proposed by the invention comprises optical head and disc of the prior art that the present invention proposes;
Fig. 5 multi-wavelength multilayer of the present invention disc synoptic diagram;
Fig. 6 wavelength multilayer of the present invention disc reflection horizon direct reflection synoptic diagram;
Fig. 7 condition 4 synoptic diagram, wherein U
Jmin, U
JmaxFinger is under condition 4 constraints, and j bundle lasing image is apart from minimum, maximal value two limit positions;
Fig. 8 condition 5 synoptic diagram, wherein U
Jmin, U
JmaxFinger is under condition 5 constraints, and j bundle lasing image is apart from minimum, maximal value two limit positions.
Embodiment:
Method proposed by the invention is to utilize the axial chromatic aberration of the toning difference object lens in the optical head that different wavelength of laser is focused on the different recording layer of multilayer disc, thereby realizes the method that the different wave length laser parallel is read; For different wavelength of laser is focused on the different recording layer of multilayer disc, will satisfy following relation between the toning object lens of multilayer disc and optical head: condition 1 ' object lens apart will satisfy for different wave length laser:
U
1＜U
2＜…＜U
j＜…＜U
N
So just can make focus point separately;
Under the more excellent situation, toning difference object lens can meet the following conditions:
U
2-U
1≈U
3-U
2≈…≈U
j-U
j-1≈…≈U
N-U
N-1
Laser focus point is evenly separated, also be convenient to the disc structure design.But this condition might not satisfy.
For the ground floor record layer of different discs, the record layer record layer adjacent with the reflection horizon that mediates, the matching relationship of each parameter is also different, as follows:
Condition 2 ' should satisfy for the ground floor recording layer of multilayer disc:
The first bundle laser focus point drops between dish base and the ground floor wall and (comprises dish base, ground floor wall):
H+H
1-h
0＜U
1＜H+H
1+d
1+h
1
The depth of focus of the first bundle laser is basic to the distance that (comprises dish base, ground floor wall) between the ground floor wall less than dish:
L
1＜d
1+h
0+h
1
The depth of focus of the ground floor recording layer and the first bundle laser has the overlapping region:
H+H
1-L
1/2＜U
1＜H+H
1+d
1+L
1/2
Second layer recording layer is not overlapping with the depth of focus of the first bundle laser:
U
1＜H+H
1+d
1+h
1-L
1/2
Condition 3 ' should satisfy for the intermediate record layer of multilayer disc:
J bundle laser focus point drops between j-1 and the j interlayer interlayer (comprising j-1, j interlayer interlayer):
H+H
j-h
j-1＜U
j＜H+H
j+d
j+h
j
J restraints the distance of the depth of focus of laser less than (comprising j-1, j interlayer interlayer) between j-1 and the j interlayer interlayer:
L
j＜d
j+h
j-1+h
j
The depth of focus of j layer recording layer and j bundle laser has the overlapping region:
H+H
j-L
j/2＜U
j＜H+H
j+d
j+L
j/2
J-1 layer or j+1 layer recording layer are not overlapping with the depth of focus of j bundle laser:
H+H
j-h
j-1+L
j/2＜U
j＜H+H
j+d
j+h
j-L
j/2
J=2 in the following formula, 3 ... N-1;
Condition 4 ' is considered the effect in reflection horizon for the recording layer adjacent with the reflection horizon, sees Fig. 6, should satisfy:
N bundle laser focus point drops between the mirror image of N-1 interlayer interlayer and N-1 interlayer interlayer:
H+H
N-h
N-1＜U
N＜H+H
N+2d
N+2h
N+h
N-1
The depth of focus of N bundle laser is less than the distance between the mirror image of N-1 interlayer interlayer and N-1 interlayer interlayer:
L
N＜2d
N+2h
N-1+2h
N
The depth of focus of N layer recording layer or its mirror image and N bundle laser has the overlapping region, promptly between the tangent A of depth of focus edge and recording layer, B two limit situations, sees Fig. 7:
H+H
N-L
N/ 2＜U
N＜H+H
N+ d
N+ L
N/ 2, corresponding to recording layer and depth of focus the overlapping region is arranged, or
H+H
N+ d
N+ 2h
N-L
N/ 2＜U
N＜H+H
N+ 2d
N+ 2h
N+ L
N/ 2, corresponding to recording layer mirror image and depth of focus the overlapping region is arranged;
N-1 layer recording layer and mirror image thereof are not overlapping with the depth of focus of N bundle laser, and promptly focus point and depth of focus thereof should be between as shown in Figure 8 between C, D two limit situations:
H+H
N-h
N-1+L
N/2＜U
N＜H+H
N+2d
N+2h
N+h
N-1-L
N/2
In aforementioned each formula:
U
jBe the image distance of poor object lens of mixing colours for j bundle wavelength laser;
H is the distances of object lens to the disc adjacently situated surfaces;
H
jBe that aforementioned disc surface is to the j layer recording layer thickness of (not comprising this recording layer), that is:
H
j=h
0+ d
1+ h
1+ d
2+ h
2+ ... + d
J-1+ h
J-1, h wherein
0The thickness of graduated dial base;
L
jIt is the depth of focus of j bundle laser focusing;
h
jBe the thickness of the j interlayer interlayer of disc;
d
jBe the thickness of the j layer recording layer of disc;
When certain wall does not exist, during the recording layer direct neighbor, the corresponding interval layer thickness is got 0 and is got final product in aforementioned each formula.
When laser focusing at respective record layer median surface, i.e. U
j=H+H
j+ d
j/ 2 o'clock, it was better to read effect, is prioritization scheme.Various respective change in the above condition.
As previously mentioned, in the patent specification, depth of focus is defined as near the interior waist of medium, and the laser axial strength is reduced to the axial spacing that certain value (such as peak strength 80%) is located two positions.Less when this axial strength definite value, the depth of focus value is bigger; The intensity definite value is bigger, and the depth of focus value is less.When the depth of focus value was big, aforementioned condition was comparatively strict, crosstalked and subdued obviously; The depth of focus value hour, aforementioned condition is looser, crosstalking, it is poor slightly to subdue effect.Answer factors such as balance material, technology, effect in the practical application, for this definite value is selected optimal value.
The optical head that designs according to method proposed by the invention has two kinds:
Class1: see Fig. 4, remainder is the same with optical head of the prior art shown in Figure 1, only achromatic objective is changed into toning difference object lens, toning difference object lens and unlike achromatic objective by color difference eliminating make wavelength different read laser focusing in same point, but keep suitable aberration, utilize the branch luminous effect of aberration, the N bundle is read laser separately.
Optical head of the present invention comprises that laser instrument 1 (contains different wave length one-wavelength laser device 1.1,1.2 ... 1.N), Multiplexing apparatus 2 (comprising N collimation lens and a prism), light-splitting device 3 (comprising polarization splitting prism and quarter wave plate), light-dividing device 4 (being made up of prism and imaging len), detector 5 (contain different wave length detector 5.1,5.2 ... 5.N), toning difference object lens 13 etc.Described light-dividing device 4, light-splitting device 3, toning difference object lens 13 are installed with optical axis successively, constitute primary optical axis.Described Multiplexing apparatus, light-splitting device are installed with optical axis, and this optical axis and primary optical axis constitute secondary optical axis at an angle of 90.The different wave length laser of laser instrument emission is synthetic through Multiplexing apparatus, after the light-splitting device reflection, incide on the novel multi-wavelength multilayer disc 14 by the poor object lens of mixing colours, after the reflection, through poor object lens 13, light-splitting device 3, the light-dividing device 4 of mixing colours, impinge upon different wave length detector 5.1,5.2 respectively ... 5.N on, finish read operation, as shown in Figure 4.
Type 2: this optical head comprises that laser instrument 1 (contains different wave length Laser Devices 1.1,1.2 ... 1.N), Multiplexing apparatus 2 (comprising N collimation lens and a prism), light-dividing device 4 (being made up of prism and imaging len), detector 5 (contain different wave length detector 5.1,5.2 ... 5.N), toning difference object lens 13 etc.Connect by optical fiber between Multiplexing apparatus, toning difference object lens; Connect by optical fiber between light-dividing device, toning difference object lens.After the different wave length laser of laser instrument emission synthesizes through Multiplexing apparatus,, incide respectively on novel multi-wavelength multilayer disc 14 different layers by separating fully behind optical fiber, the toning difference object lens.After the reflection,, impinge upon different wave length detector 5.1,5.2 through poor object lens 13, optical fiber, the light-dividing device 4 of mixing colours ... 5.N on, finish read operation.
In the relevant patent of existing multi-wavelength optical head, be complete color difference eliminating, should in achromatic objective, introduce apochromatism APO technology, or the whole optical system that comprises object lens is compensated, revises, complex structure, cost is higher.And toning difference object lens do not need complete color difference eliminating, designs simplification, and cost reduces.
Novel multi-wavelength multilayer disc
The multi-wavelength disc that the present invention relates to comprises N information recording layer.Recording layer material is same as the prior art, and under the irradiation of certain wavelength light, structure, energy state or character change, and recorded information.Recording layer material includes but not limited to photochromic material, spectral hole burning material, electron capture material, photographic film material etc.Each recording layer material light corresponding to specific wavelength.By controlling each wavelength incident intensity, can be at each recording layer by the certain format sense data.
Multi-wavelength multilayer disc involved in the present invention relates to following several types:
Class1: basic structure is identical with as shown in Figure 2 multi-wavelength multiplayer optical disk structure of the prior art.
Type 2: on the Class1 basis, add N-1 wall between N recording layer successively, as shown in Figure 5.
Type 3: on the Class1 basis, add M wall between N recording layer, M promptly is not that wall is arranged between all recording layers less than N-1.
Type 4: on the basis of first three types, between the recording layer of near reflection layer and reflection horizon, add wall.
In addition, on preceding four types of bases, in disc structure, add how non-recording layer.Interlayer can be considered the part of dish base between dish base and recording layer, and the interlayer between recording layer, between the recording layer reflection horizon can be considered the part of corresponding wall, thereby is converted into Class1,2,3 or 4, handles.
Add wall and can save recording layer material between recording layer, wall is a transparent material, as transparent plastic film.
Specific embodiment
With three-wavelength optical storage system optical head and disc as embodiment.
If the optical head laser wavelength of incidence is respectively: λ
1=550nm, λ
2=630nm, λ
3=780nm.
Optical material all has chromatic dispersion.With barium flint glass (BaF
8) be example, its Cauchy's chromatic dispersion experimental formula is:
n＝1.6028+0.007/λ
2+0.001/λ
4。
Therefore, same lens have difference for the different color light focal length.
Utilize the optical material combination of different refractivity, different aberration, can eliminate the part aberration, but the focal length variations that the remaining second order spectrum of achromatism causes generally is not less than 2/1000ths of focal length.If for λ
2, objective focal length (converting in the disk media) is f
2=1.5mm, then total focal length variations (converting in the disk media) of causing of second order spectrum is not less than 3000nm.For λ
1=550nm, λ
3=780nm, objective focal length (converting in the disk media) is respectively f
1, f
3
If toning difference back f
2-f
1=1200nm, f
3-f
2=2200nm, then f
3-f
1=4400nm＞3000nm conforms to aforementioned condition, rationally.
If injecting the laser of object lens is the three beams directional light, then image distance, focal length equate U
1=f
1, U
2=f
2, U
3=f
3
But optical disc storage system CD media inner focusing hot spot depth of focus L approximate representation be the function of laser focusing wavelength X and numerical aperture of objective NA: L (λ, NA)=λ/NA
2
If dual wavelength optical storage system numerical aperture of objective is NA=0.6.
Then, for λ
1=550nm:L
1=L (λ
1, NA)=1528nm;
For λ
2=630nm:L
2=L (λ
2, NA)=1750nm;
For λ
3=780nm:L
3=L (λ
3, NA)=2167nm.
The three-wavelength disc meets type 2.The disc substrate is a clear polycarbonate, and refractive index 1.55 is identical with CD, DVD, thickness h
0=1mm; Wall is the transparent polymer film of spin coating, refractive index 1.55, and thickness is respectively h
1=1100nm, h
2=2100nm; Total reflection layer is the aluminium film, and reflectivity is more than 70%; Protective seam is the protection glue of spin coating, through ultraviolet light polymerization.
The disc record layer is selected three kinds of spiro-pyrans for use, and refractive index 1.55 corresponds respectively to three kinds of wavelength laser: λ
1=550nm, λ
2=630nm, λ
3=780nm.These three kinds of photochromic materials, the width of absorption band is all narrower, and when photochromic reactions did not take place, reflectivity was 20%, and after all photochromic reactions taking place, reflectivity is about 60%.The photochromic reactions product of spiro-pyrans is transparent to the laser of above-mentioned three kinds of wavelength.Recording layer thickness is d
1=d
2=d
3=100nm.
In the case, d
1/ 2+h
1+ d
2/ 2=U
2-U
1, d
2/ 2+h
2+ d
3/ 2=U
3-U
2Thereby three-wavelength recording layer median surface spacing conforms to three-wavelength image distance (converting in the disk media) difference.It is rational that each wavelength reads that laser focuses on respectively on the three recording layer median surfaces.H＝U
1-d
1/2-h
0。
With each known quantity substitution condition 1)～4) in, all satisfy, then each wavelength is read laser and is separated fully, focus point drops on respectively on the corresponding record layer, each wavelength depth of focus is less than respective record layer thickness and adjacent spaces layer (or basic unit) thickness sum, and arbitrary recording layer all has the overlapping region with the depth of focus of corresponding wavelength laser, and the adjacent recording layer of arbitrary recording layer is all not overlapping with the depth of focus of corresponding wavelength laser, thereby can realize that multilayer focuses on simultaneously, parallel read-out, reading between recording layer crosstalks obtains weakening.
Utilize optics softwares such as GLAD that system light path is simulated, the present invention is verified.
Existing multi-wavelength CD correlation technique often focuses on the CD same point or to adjust focal length successively to each layer addressing (or relate to very less focus issues), for chromatic dispersion enough attention is not all given in the influence of focusing through achromatic objective with each wavelength laser.In fact, for complete color difference eliminating focuses on same point with each wavelength laser, must eliminate the influence of second order spectrum to the camera lens quality, in achromatic objective, introduce apochromatism (APO) technology, or the whole optical system that comprises object lens compensated, revises, complex structure, cost is higher, is unfavorable for practical application.And, being difficult to realize parallel read-out by adjusting focal length successively to each layer addressing, reading speed is lower; If, will make optical system structure more complicated by multi-focus lens or the first-class solution parallel read-out of many optics problem.This patent structure is simple relatively, and cost is lower, can effectively weaken between multi-wavelength light storage wavelength to crosstalk in parallel read-out.
Claims (4)
1, a kind of method of realizing parallel read of multiple wavelength and multilayer optical disc,, it is characterized in that, it is to utilize the axial chromatic aberration of the toning difference object lens in the optical head that different wavelength of laser is focused on the different recording layer of multilayer disc, thereby realizes the method that the different wave length laser parallel is read; Wherein different wave length laser is the N bundle, and the recording layer number of plies of multilayer disc is the N layer, and the disc wall number of plies is the N layer, and described N layer recording layer and N interlayer interlayer are stacked alternately, and the dish base of described disc is close to the ground floor recording layer; When the toning difference object lens of described multilayer disc and optical head satisfied following condition, the different N bundle laser of wavelength focused on respectively on N recording layer of multilayer disc:
1) toning difference object lens satisfy: U
1＜U
2＜...＜U
j＜...＜U
N
2) the ground floor recording layer of multilayer disc should satisfy:
The first bundle laser focus point drops between dish base and the ground floor wall:
H+H
1-h
0＜U
1＜H+H
1+d
1+h
1
The depth of focus of the first bundle laser is basic to the distance between the ground floor wall less than dish:
L
1＜d
1+h
0+h
1
The depth of focus of the ground floor recording layer and the first bundle laser has the overlapping region:
H+H
1-L
1/2＜U
1＜H+H
1+d
1+L
1/2
Second layer recording layer is not overlapping with the depth of focus of the first bundle laser:
U
1＜H+H
1+d
1+h
1-L
1/2
3) the intermediate record layer of multilayer disc should satisfy:
J bundle laser focus point drops between j-1 and the j interlayer interlayer:
H+H
j-h
j-1＜U
j＜H+H
j+d
j+h
j
The depth of focus of j bundle laser is less than the distance between j-1 and the j interlayer interlayer:
L
j＜d
j+h
j-1+h
j
The depth of focus of j layer recording layer and j bundle laser has the overlapping region:
H+H
j-L
j/2＜U
j＜H+H
j+d
j+L
j/2
J-1 layer or j+1 layer recording layer are not overlapping with the depth of focus of j bundle laser:
H+H
j-h
j-1+L
j/2＜U
j＜H+H
j+d
j+h
j-L
j/2
J=2 in the following formula, 3......N-1;
4) effect in consideration reflection horizon, the recording layer adjacent with the reflection horizon should satisfy:
N bundle laser focus point drops between the mirror image of N-1 interlayer interlayer and N-1 interlayer interlayer:
H+H
N-h
N-1＜U
N＜H+H
N+2d
N+2h
N+h
N-1
The depth of focus of N bundle laser is less than the distance between the mirror image of N-1 interlayer interlayer and N-1 interlayer interlayer:
L
N＜2d
N+2h
N-1+2h
N
The depth of focus of N layer recording layer or its mirror image and N bundle laser has the overlapping region, that is:
H+H
N-L
N/ 2＜U
N＜H+H
N+ d
N+ L
N/ 2, corresponding to recording layer and depth of focus the overlapping region is arranged, or
H+H
N+ d
N+ 2h
N-L
N/ 2＜U
N＜H+H
N+ 2d
N+ 2h
N+ L
N/ 2, corresponding to recording layer mirror image and depth of focus the overlapping region is arranged;
N-1 layer recording layer and mirror image thereof are not overlapping with the depth of focus of N bundle laser:
H+H
N-h
N-1+L
N/2＜U
N＜H+H
N+2d
N+2h
N+h
N-1-L
N/2
In aforementioned each formula:
U
jBe the image distance of poor object lens of mixing colours for j bundle wavelength laser;
H is the distances of object lens to the disc adjacently situated surfaces;
H
jBe described disc surface to j layer recording layer and do not comprise the thickness of this recording layer, that is:
H
j=h
0+ d
1+ h
1+ d
2+ h
2+ ... + d
J-1+ h
J-1, h wherein
0The thickness of graduated dial base;
L
jIt is the depth of focus of j bundle laser focusing;
h
jBe the thickness of the j interlayer interlayer of disc;
d
jBe the thickness of the j layer recording layer of disc;
When certain wall did not exist, the corresponding interval layer thickness got 0 in aforementioned each formula.
2, a kind of method of realizing parallel read of multiple wavelength and multilayer optical disc, as claimed in claim 1 is characterized in that, in described condition 1)～4) on the basis, also satisfy: laser focusing is at respective record layer median surface, i.e. U
j=H+H
j+ d
j/ 2; Read better effects if this moment.
3, method of realizing parallel read of multiple wavelength and multilayer optical disc, according to claim 1 and the optical head that designs, contain laser instrument (1), Multiplexing apparatus (2), light-splitting device (3), the light-dividing device (4) that to launch different wave length laser, the detector (5) that can survey different wave length laser, it is characterized in that, also contain toning difference object lens (13); Described light-dividing device (4), light-splitting device (3), toning difference object lens (13) are installed with optical axis successively, constitute primary optical axis; Described Multiplexing apparatus (2), light-splitting device (3) are installed with optical axis at an angle of 90 with primary optical axis, constitute secondary optical axis; Described light-splitting device (3) is positioned at the position of intersecting point of described primary optical axis and described secondary optical axis; The different wave length laser of laser instrument emission is synthetic through Multiplexing apparatus (2), after light-splitting device (3) reflection, poor object lens (13) incide on the different layers of multi-wavelength multilayer disc by mixing colours; After the reflection,, impinge upon on the detector (5), finish read operation through the poor object lens (13) of mixing colours, light-splitting device (3), light-dividing device (4).
4, method of realizing parallel read of multiple wavelength and multilayer optical disc, according to claim 1 and the optical head that designs, contain laser instrument (1), Multiplexing apparatus (2), the light-dividing device (4) that to launch different wave length laser, the detector (5) that can survey different wave length laser, it is characterized in that, also contain toning difference object lens (13); Described Multiplexing apparatus (2), toning difference object lens (13) are connected by optical fiber; Described light-dividing device (4), toning difference object lens (13) are connected by optical fiber; After the different wave length laser of laser instrument emission synthesizes through Multiplexing apparatus (2), by inciding respectively on the different layers of multi-wavelength multilayer disc behind optical fiber, the toning difference object lens (13); After the reflection,, impinge upon on the detector (5), finish read operation through the poor object lens (13) of mixing colours, optical fiber, light-dividing device (4).
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB2004100307849A CN1254800C (en) | 2004-04-09 | 2004-04-09 | Method of realizing parallel read of multiple wavelength and multilayer optical disc, its optical head and disc |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB2004100307849A CN1254800C (en) | 2004-04-09 | 2004-04-09 | Method of realizing parallel read of multiple wavelength and multilayer optical disc, its optical head and disc |
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| Publication Number | Publication Date |
|---|---|
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| CN1254800C true CN1254800C (en) | 2006-05-03 |
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