CN1302476C - Scanning device including plastic high-numerical aperture objective - Google Patents

Abstract

An optical scanning device for scanning an information layer (104) of an optical record carrier (102) includes a radiation source (110) for generating a radiation beam (108) and a high-NA objective system (118) for converging the radiation beam on the information layer. The objective system includes a first lens (116) and a second lens (117). The first lens and the second lens are made of plastic. The signs of the temperature-dependence of the spherical aberration of the first and second lens are different and the magnitudes of the temperature-dependence of the spherical aberration of the two lenses is substantially equal such that the temperature-dependence of the spherical aberration of the objective system as a whole is reduced to less than 30 mlambda OPDrms for a temperature change of 30 K.

Description

Scanner with plastic objective lens of high-NA

Technical field

The present invention relates to be used for the optical scanner of the Information Level of scanning optical record carrier, this scanner comprises and is used for the objective system of luminous beam convergence on Information Level that described objective system comprises first lens and second lens that all are made of plastics that a light emitting source that is used to produce the luminous bundle with wavelength X and one have a numerical aperture (NA) greater than 0.65.The invention still further relates to the method that is used in the objective system in such scanner and makes this objective system.

Background technology

Highly dense optical information memory storage such as digital video recorder (DVR) higher numerical aperture as 0.85 and shorter wavelength work under as 405 nanometers.Comprise single lens if be used for the objective system of such device, then these lens will have very little tolerance, and it is relatively more expensive that this makes it make.If objective system comprises two lens, then margin tolerance is looser, and this helps the batch process of lens.At present, these object lens all adopt glass molds platen press or so-called glass 2P method usually and are made by glass, so that remain in the still little margin tolerance.Use glazy production cost to be in higher level.In order to reduce production costs, the lens of objective system preferably are made of plastic material.

United States Patent (USP) 5880893 has been described a kind of lens doublet system of high-NA, and two lens are wherein all made by polymethylmethacrylate.A shortcoming of this objective system is that its performance is too responsive to temperature variation.

Summary of the invention

The purpose of this invention is to provide a kind of scanner that comprises plastics lens doublet system, it has higher temperature stability.

According to the present invention, if be equipped with such objective system according to scanner as described in the preamble, then realized purpose of the present invention, first lens and second lens that are it have the spherical aberration of luminous bundle respectively to dependence on temperature, the dependence sign of first lens and second lens is different and the degree of dependence of first lens and second lens is the same basically, thereby the spherical aberration of objective system is reduced to less than the 30m λ OPDrms under the 30K temperature variation on the whole to dependence on temperature.

The objective system of United States Patent (USP) 5880893 described prior aries be the analysis showed that the temperature variation of 30K causes the wavefront deviation of 47m λ OPDrms.The acceptable wavefront deviation of DVR system is 30m λ OPDrms under 30K objective system temperature variation to temperature dependent tolerance level.Because the quality of scanner optical system and wavefront deviation rms square are inversely proportional to, so the objective system of prior art will not be suitable for many highly dense optical recording instruments.The design of objective system seems to concentrate on the eccentric tolerance of two lens in the objective system.

The present invention partly is based on the recognition, and promptly the deviation of lens temperature and design temperature has caused the spherical aberration as main aberration, has perhaps changed the existing spherical aberration of lens.In order to control spherical aberration, we recognize that further the lens spherical aberration can be adjusted to plus or minus to dependence on temperature (being the derivative of spherical aberration about temperature).Objective system is designed to, and the spherical aberration of first lens and second lens is different to temperature dependent sign.In other words, when the temperature variation of objective system, the increase of the spherical aberration of one of them lens of objective system is accompanied by the reducing of spherical aberration of another lens.By suitable design, the spherical aberration of each lens should be adjusted to the degree that equals such to the degree of dependence of temperature, i.e. the counteracting of the spherical aberration of two lens variation is reduced to the spherical aberration of objective system less than the 30m λ OPDrms under the 30K temperature variation to dependence on temperature on the whole.

Increase the eccentric tolerance of these two lens the design proposal of a wisdom of these two lens should not only resemble in the objective system of prior art, and should determine suitably that the spherical aberration of each lens is to temperature dependent sign and degree of dependence thereof.The integrated temperature stability of object lens is applicable to many harsh application scenarios that require.Another advantage of the present invention is, temperature compensation does not require doses optical element in scanner, but can be integrated in two lens of objective system, and these two lens are because of making former thereby existing already.And, compare with compensating with other optical element such as collimating mirror, be preferably in the objective system and compensate.Because the temperature section of objective system is by the intensification decision near the actuator of objective system, so the temperature of collimating mirror and objective system needs not be the same, this has caused passing through the inaccurately temperature of indemnity mirror system of collimating mirror.When the lens of objective system itself compensate mutually to temperature variation, do not produce this problem.

We recognize that the spherical aberration that caused by lens is the function of lens enlargement ratio and can regulates the lens enlargement ratio thus temperature dependent sign and degree, so as to give the lens spherical aberration to dependence on temperature with required sign.In a preferred embodiment, the enlargement ratio of first lens less than the enlargement ratio of 0.2, the second lens greater than 0.2.

In a preferred embodiment, second lens have the enlargement ratio β of 0.3＜β＜0.6.The upper limit of β is by the eccentric tolerance decision of two lens, and this generation is the wavefront deviation of 30m λ OPDrms to the maximum, and lower limit is by the decision of temperature tolerance, because of the 30K temperature variation is limited to 30m λ OPDrms wavefront deviation to spherical aberration.

In a preferred embodiment of objective system, the microscope base integrator of second lens and first lens, thus second lens and microscope base can be made in disposable injection moulding process.The processing of second lens has been simplified in the second less lens and the combination of microscope base.If it is cylindrical that microscope base becomes, then can be according to first lens being packed in this cylindrical microscope base with the described identical mode of WO EP01/-2348 (PHNL000269).When the thickness of the mirror body of first lens during greater than this mirror body radius (also referring to WO EP01/-2348 (PHNL000269)), this method is feasible.As a result, obviously reduced cost, this is because second lens can more easily be made and have only two parts that will assemble up now by injection molding technology, and will assemble three parts not resembling when two lens and microscope base are individual components.

Another aspect of the present invention relates to one and has greater than 0.65 numerical aperture, being used to focus on one has the luminous bundle of wavelength X and comprises first lens that all are made of plastics and the objective system of second lens, wherein according to the present invention, first lens and second lens have respectively put on luminous bundle spherical aberration to dependence on temperature, the dependence sign of first lens and second lens be different and the degree of dependence of first lens and second lens substantially the same, thereby the spherical aberration of objective system is lowered to less than the 30m λ OPDrms under the 30K temperature variation on the whole to dependence on temperature.

Another aspect of the present invention relates to the method for making an objective system, this objective system has greater than 0.65 numerical aperture and focuses on one and has the luminous bundle of wavelength X and comprise first lens and second lens that all are made of plastics, this method comprises: design first lens and second lens, the spherical aberration that makes first lens and second lens is different and make the spherical aberration of first lens and second lens substantially the same to the degree that temperature relies on to temperature dependent sign, thereby guarantee that objective system has less than the spherical aberration of the 30m λ OPDrms under the 30K temperature variation first step to dependence on temperature, and make second step of first lens and second lens and the third step of first lens and second lens combination being dressed up an objective system according to design.

Description of drawings

Now, specifically describe the present invention for example referring to accompanying drawing, wherein:

Fig. 1 represents an objective system that is made of two parts;

Fig. 2 represents the wave front aberration OPDrms by the objective system of 30K intensification functional form that cause and that become the second lens enlargement ratio β;

Fig. 3,4,5 expressions when first lens and second lens respectively by the wave front aberration of the objective system of PMMA, COC, when PC makes and functional form that become the second lens enlargement ratio β;

Fig. 6 represents to work as by PMMA, the wave front aberration of the objective system when COC or PC make, wherein two lens can be that different materials is made, numeral on the transverse axis corresponding to: 1-first lens are made by PC and second lens are made by COC, 2-first lens are made by PC and second lens are made by PMMA, 3-first lens are made by COC and second lens are made by PMMA, 4-first lens are made by PC and second lens are made by PC, 5-first lens and second lens are made by COC, 6-first lens and second lens are made by PMMA, 7-first lens are made by COC and second lens are made by PC, 8-first lens are made by PMMA and second lens are made by PC, and 9-first lens are made by PMMA and second lens are made by COC;

First lens that Fig. 7 is illustrated in objective system are made by COC and second lens are when being made by PMMA and the wave front aberration of the objective system of functional form that become the second lens enlargement ratio β;

Fig. 8 represents to comprise an instrument objective system and that be used for scanning optical record carrier.

Concrete form of implementation

Fig. 1 shows an embodiment according to objective system of the present invention, and it allows not influence eccentric situation ground tilt calibration of lens and simple assembling lens.This objective system comprises first lens 1 that are made of plastics, first lens comprise a roughly lens mirror body of globulate, and objective system also comprises second lens 2 that are made of plastics and the columniform plastics microscope base 3 of one-tenth around more than half this lens mirror body ground.The optics effective diameter of first lens is greater than the optics effective diameter of second lens.Second lens and cylindrical microscope base 3 are made of same plastic and form the single structure unit.The thickness d of the spherical glass mirror body of first lens 1 and radius r are abideed by d＞r.Element 4 is into the objective system of first lens, second lens and microscope base assembled state.In the drawings, luminous bundle is from end face incident objective system, and outgoing beam accumulates in one on the position below the objective system.The Information Level of an optical record carrier can be positioned on this position, so that scan this Information Level by the hot spot that is formed by outgoing beam.

The embodiment of the objective system of Fig. 1 has 3.0 millimeters entrance pupil diameter, the record carrier side numerical aperture of NA=0.85, the design wavelength of 405 nanometers, 0.15 millimeter the free working clearance (FWD) between second lens and CD and 0.1 millimeters thick PC hyaline layer of record carrier.

Fig. 2 represents the optical property behavior of second lens when its temperature variation.The figure shows the variation of the wave front aberration of the whole objective system when having only the temperature rising 30K of second lens.Aberration is the function of the second lens enlargement ratio β as shown in figure.When the enlargement ratio of second lens changes, performance by correspondingly changing first lens and the distance between first lens and second lens and keep the imaging performance of objective system on the whole.The root-mean-square value of well-known path difference (OPDrms) during wave front aberration shows as.The negative value of OPDrms in the drawings means the Zernike coefficient A of spherical aberration ₄₀For negative.Aberration behavior when three lines among the figure are represented second lens by polymethylmethacrylate (PMMA), cyclenes copolymer (COC) and polycarbonate (PC) formation.Table I has been listed the thermal behavior of PMMA, COC and PC.Just being changed to and being big of spherical wave front aberration to lens with infinite conjugate (β=0).For greater than 0.2 enlargement ratio β, being changed to of wave front aberration is negative.Note, when the refractive index of plastic material increases, reduce in this β value that zero crossing takes place.

The thermal behavior of Table I PMMA, COC and PC

	PMMA	COC	PC
				n@405nm	1.5022	1.5499	1.6223
dn/dT[10 -5/k]	-12.5	-10.0	-10.8
				Linear expansion coefficient [10 -5/k]	70	70	70

Can utilize above understanding to weaken the plastic objective lens system of high-NA to dependence on temperature.Consider a double base plastics DVR objective system of working under the infinite conjugate condition, first lens face is to the light emitting source of scanner, and second lens face is to record carrier.When the enlargement ratio of these two lens be selected to can give first lens and second lens spherical aberration to dependence on temperature during with different sign, the spherical aberration of one of them lens compensates dependence on temperature dependence on temperature to the spherical aberration of small part by another lens.So, obviously weakened the spherical aberration of plastic objective lens system of high-NA to dependence on temperature.In the example of Fig. 1, the enlargement ratio of second lens 2 is greater than 0.2.

The present invention allows to make the temperature tolerance of plastic objective lens of high-NA enough wide concerning optical recording, and this will become perfectly clear from following object lesson.

The PC hyaline layer that an embodiment of objective system is designed to make a parallel beam with 405 nano wave lengths to penetrate one 0.1 millimeters thick focuses on one on the focus on the Information Level of an optical record carrier (n=1.6223), and wherein this hyaline layer is arranged on this Information Level.The entrance pupil diameter is 3.0 millimeters, is NA=0.85 in the numerical aperture of the objective system of object lens side.The free working clearance is the FWD=0.15 millimeter.This objective system comprises two aplanasia first lens, and the back is flat aplanasia second lens.Utilization is based on optimizing the objective system design about the aspheric eccentric tolerance of field tolerance, the eccentric tolerance of two lens, two aplanates and the performance function of temperature tolerance.In following examples, the thickness of first lens is fixed on 2.5 millimeters, and the thickness of second lens is fixed on 0.85 millimeter.

Have first lens made by COC and second lens and embodiment that its second lens have the objective system of 0.5 enlargement ratio β and have following design parameter.

First lens have one in the face of convex surface light emitting source and that have rotational symmetric aspherical shape, and described aspherical shape is set by following formula:

$z\left(r\right)=\underset{i=1}{\overset{8}{\mathrm{\Σ}}}{b}_{2i}{r}^{2i}$

Wherein, z be this convex surface on optical axis direction and in the position of millimeter, r is the distance (millimeter) with optical axis, b _2iIt is the coefficient of the 2i power of r.b ₂-b ₁₆Coefficient be respectively 0.27152628,0.0094409894,0.0044407999 ,-0.0079739895,0.0078782292 ,-0.0043791379,0.0012874114 and-0.00015939048.Convex surface at the first lens opposite side also is an aspheric surface, and it has and equals 0.027369439,0.022047913 ,-0.045429955,0.061344633 ,-0.071559255,0.085540565 ,-0.076476945,0.026949936 b respectively ₂-b ₁₆Coefficient value.The enlargement ratio of first lens is zero, because one of its thing conjugation is positioned at infinity.0.310 millimeter at interval on second lens of objective system and first lens.The second lens convex surface that points to first lens has aspherical shape, b ₂-b ₁₆Coefficient be respectively 0.59812098,0.25015439 ,-0.72194864,7.6081286 ,-37.847569,105.36375 ,-153.4902,90.242243.Has unlimited radius-of-curvature at the interface of the second lens opposite side.

When the analysis temperature dependence, the microscope base of two lens is considered to make with the material the same with second lens.Fig. 3,4,5 shows the variation of the objective system wave front aberration of when it is made with PC by PMMA, COC respectively and functional form that become the second lens enlargement ratio β.Under these three kinds of situations, the temperature tolerance increases with β at all.On the other hand, the eccentric tolerance of these two lens reduces with the β increase.With 30m λ OPDrms is the aberration upper limit, the enlargement ratio β of second lens because of eccentric tolerance preferably less than 0.6.The lower limit of enlargement ratio is decided dependence on temperature by spherical aberration, and at β hour, this spherical aberration is main aberration and it along with enlargement ratio reducing and increase in relevant β value scope.So, with 30m λ OPDrms be spherical aberration to the temperature dependent upper limit, under situation about being made of PMMA, the temperature tolerance is limited in β＞0.45 to enlargement ratio, and under situation about being made of COC, this tolerance means β＞0.3.Under the situation of PC, not further restriction.At last, for the ease of making, the enlargement ratio β of second lens should be not too little, because for the little situation of β, the major part of the refractive power of objective system will be arranged in first lens, and second lens have only very little refractive power.Therefore, enlargement ratio β is more preferably greater than 0.3.

When these two lens of objective system all when constituting with a kind of plastic material, system tolerance has improved along with the raising of material refractive index.

Fig. 6 represents the wave front aberration of objective system, and in this objective system, two lens are made by PMMA, COC or PC.These two lens can be made with commaterial or different materials.As shown in the drawing, the best of breed scheme is that first lens are made by COC, and the back is second lens that are made of PMMA.Inferior good scheme is, first lens are made by PC, and the back is second lens that are made of PMMA.Generally speaking, be higher than the array configuration of second lens for the refractive index of first lens wherein, the performance of objective system is better.

Fig. 7 shows that first lens are wherein made by COC and the wave front aberration of the functional form of enlargement ratio β objective system, that become second lens that second lens are made of PMMA changes.As shown in the drawing, when enlargement ratio β satisfies the condition of 0.4＜β＜0.5, obtained optimum performance.

Although above embodiment show lens in the objective system with less enlargement ratio than lens with big enlargement ratio more near light emitting source, the lens with big enlargement ratio also can be arranged to than the lens with less enlargement ratio more near light emitting source.

Objective system can be used in the scanner of optical recording system such as so-called DVR optical system.

Fig. 8 shows the DVR type instrument 101 of an optical record carrier 102 of scanning.Record carrier comprises a hyaline layer 103, is provided with an Information Level 104 on a side of hyaline layer.Make back to the Information Level side of hyaline layer not affected by environment by a protective seam 105.The hyaline layer side of facing instrument is called as the plane of incidence 106.Hyaline layer 103 has played the effect of record carrier bottom by mechanical support is provided to Information Level.Perhaps, hyaline layer may have unique function of protection Information Level, and mechanical support is finished by one deck on the Information Level opposite side such as protective seam 105, perhaps by another Information Level and a hyaline layer that links to each other with this Information Level 104.But information can be stored in the Information Level 104 of record carrier with the form of the mark of optical detection, these marks according to almost parallel with one heart or the track of spiral arrange, this is not shown in the drawings.But the form that described mark can become any light to read for example becomes the concave point form, perhaps has the form in the zone of the direction of magnetization that is different from its surrounding environment or reflectivity, or the array mode of these forms.

Scanner 101 comprises a light emitting source 110 that can send luminous bundle 108.Light emitting source as shown in the figure comprises a semiconductor laser 110.An optical splitter 113 reflects to a collimating mirror 114 dispersing luminous bundle 108 on light path, and this collimating mirror converts divergent beams 108 to parallel beam 115.Parallel beam 115 incides in one first lens 116 of an objective system 118 and incides subsequently in its second lens 117.This objective system may comprise two or more lens and/or a grating.Objective system 118 has an optical axis 119.Objective system 118 is transformed into convergent beam 120 to light beam 115 and makes in its plane of incidence that incides record carrier 102 106.This objective system has and is suitable for making luminous beam to penetrate the spherical aberration correction of hyaline layer 103 thickness.Convergent beam 120 forms a luminous point 121 on Information Level 104.Form divergent beams by Information Level 104 every rays, these divergent beams are transformed into substantially parallel light beam 123 and are transformed into a convergent beam 124 by collimating mirror 114 subsequently by objective system 118.Optical splitter 113 is isolated forward folded light beam by making to 124 transmissions of small part convergent beam to a reflecting system 125.Detection system captures ray and converts thereof into electrical output signal 126.A signal processor 127 converts these output signals to various other signals.One of them signal is exactly an information signal 128, the information that its value representative is read from Information Level 104.This information signal is through a processing that is used for the information process unit 129 of round-off error.Other signal from signal processor 127 is focus error signal and radial error signal 130.Focus error signal is represented the height axial difference between luminous point 121 and the Information Level 104.Distance between the center of the track that the luminous point in luminous point 121 and Information Level of radial error signal representative in Information Level 104 planes will be followed the tracks of.Focus error signal and radial error signal are sent as a servo circuit 131, and it becomes to be used for controlling respectively the servo-control signal 132 of a focus actuator and a radial actuator with these conversion of signals.These actuators are not shown in the drawings.Focus actuator is being controlled the position of objective system 118 on focus direction 133, so controls the physical location of luminous point 121 thus, promptly this physical location basically with the planes overlapping of Information Level 104.Radial actuator is being controlled objective system 118 in the position on 134 radially, so controls the radial position of luminous point 121 thus, promptly it basically with Information Level 104 in the central lines of the track that will follow the tracks of.This track among the figure extends on the direction perpendicular to drawing.

Claims (9)

1, a kind of optical scanner that is used to scan the Information Level of an optical record carrier, it comprises that one is used to produce one and has the light emitting source of luminous bundle of wavelength X and one and have greater than 0.65 numerical aperture and be used for the objective system of described luminous beam convergence on Information Level, this objective system comprises one first lens and one second lens that all are made of plastics, it is characterized in that, described first lens and second lens have the spherical aberration that puts on this luminous bundle respectively to dependence on temperature, the dependent sign of described first lens and second lens is that the degree of dependence of different and described first lens and second lens is substantially the same, thereby the spherical aberration of this objective system is lowered to less than the 30m λ OPDrms under the 30K temperature variation dependence on temperature.

2, optical scanner as claimed in claim 1, it comprises that one is used for pick-up unit and a message handler that is used for the error correction of described information signal of converting information signal from the light of this Information Level to.

3, a kind of objective system, it has greater than 0.65 numerical aperture and focuses on one and has the luminous bundle of wavelength X and comprise one first lens and one second lens that all are made of plastics, it is characterized in that, described first lens and second lens have the spherical aberration that puts on this luminous bundle respectively to dependence on temperature, the dependent sign of described first lens and second lens is that the degree of dependence of different and described first lens and second lens is substantially the same, thereby the spherical aberration of this objective system is lowered to less than the 30m λ OPDrms under the 30K temperature variation dependence on temperature.

4, objective system as claimed in claim 3 is characterized in that, described first lens have less than 0.2 enlargement ratio β and described second lens and have enlargement ratio β greater than 0.2.

5, objective system as claimed in claim 4 is characterized in that, the enlargement ratio β that described second lens have is 0.3＜β＜0.6.

6, objective system as claimed in claim 4 is characterized in that, first lens are made greater than the material of the manufactured materials of described second lens by a kind of its refractive index.

7, objective system as claimed in claim 4 is characterized in that, described first lens are made by COC, and described second lens are made by PMMA, and the enlargement ratio of described second lens is 0.4＜β＜0.5.

8, a kind of manufacturing have greater than 0.65 numerical aperture and focus on one and have the luminous bundle of wavelength X and comprise one first lens all being made of plastics and the method for the objective system of one second lens, it may further comprise the steps:

-design first lens and second lens, the spherical aberration that makes first lens and second lens is different and make the spherical aberration of first lens and second lens substantially the same to the degree that temperature relies on to temperature dependent sign, thereby guarantees that objective system has spherical aberration less than the 30m λ OPDrms under the 30K temperature variation to dependence on temperature;

-make described first lens and second lens according to above-mentioned design;

-described first lens and second lens combination are dressed up an objective system.

9, method as claimed in claim 8, it is characterized in that the spherical aberration of described first lens and second lens is by giving these first lens one less than 0.2 enlargement ratio β and give these second lens one and set greater than 0.2 enlargement ratio to temperature dependent sign.

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