JPS6243842A - Light collecting optical system for recording and reproducing optical system of optical information medium - Google Patents

Abstract

PURPOSE:To obtain a recording and reproducing light collecting optical system having a sufficient performance regardless of a short distance between a light source and an optical information recording face by arranging the light source toward the coupling lens side from the light source side focus of the coupling lens being a spherical single lens and moving an objective lens along at least the optical axis. CONSTITUTION:The system consists of the 1st spherical single lens 3 being a coupling lens and the 2nd lens 2 being an objective lens from the optical source side 4 and the light source is arranged to the 1st lens side from the light source side focus of the 1st lens, the 2nd lens is movable along at least the optical axis so as to attain focusing. Further, the 2nd lens is a single lens is a single lens whose one face is a non-spherical face, movable in a direction vertical to the optical axis and the tracking is applied. In the light collection optical system, the performance of diffraction limit is facilitated both the coupling lens and the objective lens and no deterioration of aberration is less even if the objective lens is moved in a direction vertical to the optical axis.

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) This invention relates to a condensing optical system used in an optical system for recording and reproducing optical information, and in particular to a condensing optical system having a short total optical path length and consisting of a coupling lens and an objective lens. Related to condensing optical system.

(Prior art) Of the condensing optical systems used in recording/reproducing devices for information recording media such as optical disks, those that have been commonly used in recent years are The collimator lens 6 converts the light into parallel light, and the objective lens 2 focuses the light onto the information recording surface 1. In this optical system, focusing is performed by moving the objective lens 2 in the optical axis direction in response to surface wobbling of an optical disk or the like.

For example, a typical objective lens in a compact disc playback optical system has a focal length of 4.5 tm, N
A lens with A of 045 and three elements in two groups is used, and a typical example is Japanese Patent Application Laid-Open No. 1983-4068. On the other hand, the collimator lens has a focal length of 17m%N
Typical examples are those with A of O14, and many have two elements in one group. The light source of the optical system consisting of the collimator and objective lens and the information recording surface of the optical information recording medium have a degree of twist of 25 to 30 m.

(Problems to be Solved by the Invention) In recent years, objective lenses have been made into fist lenses by making use of aspherical surfaces, which has resulted in significant cost reductions and has begun to be widely used. In order to further reduce costs, collimator lens 1
1 Luns (7) Cost reduction is required.

However, in two cases, the total refractive index of the collimator of Kiyosaki Kami was 1.8.
Figure 3 shows various aberration diagrams of a collimator designed with a 6888 glass material and a 7-axis design.
ms (λ=780nm) and Marechal tolerance 1 straight N
1, which is insufficient in terms of performance.

Although it is possible to use an aspherical surface to form a single lens,
In fact, since the cost of the V lens is the same as that of the objective lens, there is little advantage in making it a threat lens, and depending on the cover, there is a risk that the cost -F will increase.

There is a known optical system for playing back original discs in which the collimator lens is made into a collimator lens by increasing the focal length (1) and decreasing the NA, but in this case, a large amount of work is required to completely compensate for the decrease in the utilization efficiency of the light source light. A light source with output power is required.'
Also, the distance between the light source and the information recording surface of the optical information recording medium is 5
(As the ridges become longer as ln, the optical system tube is made more compact. Sixth, it is necessary to bend the optical path (+-υ) due to reflection etc. [11 in Noh is Oshima.

This invention #t% spherical lens 1 piece, 11 sphere lens 1 piece, Dutch acceptance inspection, the light source and the optical information 0 (i distance from the lead surface is 1, but it emits enough +') All Nj
123 in order to obtain a condensing optical system for recording and reproduction.

Configuration of the Invention (Means for Solving the Problem) The optical system of the present invention includes, from the light source side, a first spherical single lens that is a coupling lens, a ? The light source is placed N4 on the second lens 1 from the focal point of the light source 111Il of the second lens, and the second lens 1 is a second lens.
It is movable along the optical axis at least a little, and focusing is possible.

Furthermore, this second lens is a threat lens having at least one aspherical surface, and is movable in a direction perpendicular to the original axis,
Tracking may also be enabled.

(Production Ill) Optical Information 6 [] A condensing optical system for recording and reproducing a recording medium must have diffraction-limited performance. In a conventional condensing optical system, each of the collimator and the objective lens has a one-fold limit performance. This is to prevent aberrations from changing even when focusing or tracking is performed by moving the objective lens. Therefore, the condensing optical system of the present invention also needs to have diffraction-limited performance.

According to third-order aberration theory, the spherical aberration coefficient Ski of a thin lens is expressed by the following equation.

C, -1-C2 B= ・・・・・・・・・(2) C1
'2 tc, h: height of paraxial peripheral ray: refractive power of olfactory lens n: refractive index of lens glass material C3: curvature of first surface of lens C2: curvature of second surface of lens m: condensation Magnification and wavefront aberration coefficient for third-order spherical aberration At this time,
The minimum wavefront aberration due to spherical aberration is expressed by the linear equation fifWsAt.

WSA=OW40(]-ml'NA'!' -=-
...(5) However, NA is the numerical aperture of the emitted light, and f is the focal length of the exposure lens! = 1/.

Equation (]) <41 From (5), when n 0 n % m is given, there exists a twist in which the value in [ ] is the minimum. On the other hand, the value in [ ] is a constant, and when NA f is constant, it is proportional to WsAFi -m)'f.

As mentioned above, a typical conventional collimator with f=17in and NA=0.14 (in this case m=0)
As a result of f-beading, the wavefront aberration is 0.077λrms even if a high refractive index material 'fr is selected such as n = 1.86888 and Bf is optimized.

Now, if f and NA are constant, and m is set to 1/2, for example, the amount of wavefront aberration is predicted to be '/16[ from the above equation. That is, the amount of wavefront aberration is oo.

5λrma or less, and it can be expected that the performance will be equivalent to or higher than that of the conventional collimator lens with two lenses in one group. In this way, the wavefront aberration of the light emitted from the coupling lens is m
A significant improvement is achieved by making f if larger. Specifically, this is achieved by positioning the optical St-coupling lens closer to the coupling lens than the light source side focal point. The design of such an objective lens, which differs from conventional ones in that it is necessary to convert diverging light into convergent light with diffraction-limited performance, is described in Japanese Patent Application No. 59-17, for example.
It has been shown that this can be realized by the inventions of No. 7589 and No. 18932 of 1983. The former is for a double-sided aspherical objective lens, and the latter is for a single-sided aspherical objective lens.

When a coupling lens is conveniently used, since the convergence ratio of the objective lens is relatively close to X, it is often sufficient to make only one surface aspherical. However, the refractive index of the glass material of the objective lens and the effect of the entire optical system are 11! Depending on the magnification, focal length, tracking method, etc., a double-sided aspherical lens may be preferable.

Further, it can also be used in a vitrification lens 1 provided with a transparent plastic layer f having an aspherical outer profile as described in JP-A-60-126616.

As described above, in the condensing optical system of the present invention, it is easy to achieve diffraction-limited performance for both the coupling lens and the objective lens, and even when the objective lens is moved in the direction perpendicular to the optical axis, aberrations do not deteriorate much. For this reason, the objective lens is
It can be used in a recording Φ reproducing optical system that performs tracking by driving in F rows.

When the focusing optical system of the present invention is used in place of the conventional focusing optical system using a collimator with a focal length of 17 to 23 mm and a NAO of 4 to 13.11, the coupling lens is
/4~1/1. The imaging magnification is variable, that is, the distance m't between the light source side focal point of the coupling lens and the light source, and the focal length f fc of the coupling lens is 1/4 fc-'/
It is desirable to set it to 1.5 fc.

When the convergence ratio becomes less than 1/4, Ws
Since the angle is proportional to (1-m)'j', even if a glass material with a high refractive index is used, a large diameter coupling lens with a NA of 0.11 to 0°14 will have a large residual wavefront aberration. Become. On the other hand, if the acid supply incubation rate exceeds 14 degrees, the coupling lens will come close to the concentric lens, making centering difficult.

Furthermore, if the distance between the light source and the recording surface of the optical information medium is reduced, the resulting magnification of the objective lens will be small, and aberrations will deteriorate significantly when the objective lens is driven along the optical axis.

(Example) Examples of the present invention will be shown below. The symbols in the table are ri: radius of apex curvature of the first lens surface from the light source side di: spacing between the first lens surfaces from the light source side n1: refractive index of the first lens glass material from the light source side; It is the Atsube number for the first steel material with respect to d-depression, and the aspherical shape has its apex as the origin and the optical axis direction f
In the orthogonal coordinate system with the
>2.0), then φ=G 丙−,'l,
C=-(](represented by η.

11f. The focal length of the coupling lens objective lens, mc, mo, and nl'p are the imaging magnification of the coupling lens, objective lens, and entire system, respectively.
The imaging magnification of the coupling lens is the imaging magnification seen from the side opposite to the light source. This m. , frost, II) between “c”
When the objective lens is at a steady position at zero, the relationship below 1ttl holds true.

m1□=nl□/mc+++...+ (7) U is the distance between the light source and the recording surface of the optical information medium.

In addition, the values regarding Kli disk GK in the table are also shown.

Example 1 fc=24.0Of,=3.750 g=(F5 +no=-01:(:(3uq-knee 0
26671J=25.72 Example 2 fc=22.0o f□=4. OOO deaf = (+37
5 rl'%, =-0,1mT=-(1,2667U
:;27.66 (1st Example 3 io=24.0Ofo=4.000 "c=05"lo= (11mT=-0, 2U=3
8.53 ri di ni vll -
133748225 (10015H1726412-6
800002L164 (19 32, 616183, 11) r) 0 1.48595
55.11 Examples 1 and 2 are the results of the entire system fI! Magnification is -02
667, and the distance between the light source and the information recording surface is short.

Example 11d m, , = 0.5, a relatively large acid @
a coupling lens having a ratio of m. =-01333
This is a combination of an objective lens with a relatively small imaging magnification of . It is a combination of objective lenses with magnification.

Example 3 Vi'J 1 Example 10 With the combination of the coupling lens and the objective lens of Example 2, the total system's coupling ratio is -()
2, and the light source and TVT information recording surface are also slightly larger than those in Example 1.2.

The amounts of Ayu aberrations of the coupling lenses of Examples 1 and 2 are shown in Figures 4 and 5, and the amounts of various aberrations of the entire system of Examples 1 to 3 are shown in Figure 6.
This is shown in Figure 8. In the figure, W F E rms indicates the root mean square of the wavefront aberration, and is expressed in terms of wavelength, assuming that the light source wavelength is λ=780.

As is clear from these aberration diagrams, the various aberrations of the coupling lens and the entire system are good, and the diffraction limit performance is fully satisfied.

9 to 11 show changes in wavefront aberration when the objective lenses of Examples 1 to 3 are moved in a direction perpendicular to the optical axis, and t represents the movement 117 of the objective lens. Even when tracking +05 fins, the wavefront aberration is 007λrma
It can be seen that the performance within the diffraction limit is maintained as shown below.

This shows that even when used in an optical system that performs tracking by driving the objective lens in a sub-digital direction to the disk, the deterioration of the light focusing performance due to this is extremely small.

Effects of the Invention As seen from the various aberrations of the total focusing system of each example, the focusing optical system 1.1 of the invention has well corrected on-axis and off-axis performance, and both are Vcl lenses. Therefore, it is possible to use a coupling lens and an objective lens (li) as a condensing optical system by inserting one unit into a Km body and moving it in the direction of the optical axis for focusing, or moving it in a direction perpendicular to the optical axis for tracking. I can do it.

In this case, it is desirable that the distance between the coupling lens and the objective lens be small, but it can be made even shorter than in the example by slightly changing the design of the coupling lens. As long as the objective lens has the spherical aberration and sinusoidal conditions well corrected for diverging light and has a diffraction limit performance f, the above effects can be expected, so the objective lens is not only an aspherical lens. Inhomogeneous lenses and hololens can also be used.

[Brief explanation of drawings]

FIG. 1 is a sectional view of one embodiment of the condensing optical system of the present invention, FIGS. 2 and 3 are layout diagrams of a conventional condensing optical system and aberration diagrams of its single-beam collimator, and FIGS. Figures 5 and 6 are aberration diagrams of the coupling lenses of Example 1 and Example 20, respectively.
Figures 7 and 8 show the amount of aberration of the total focusing optical system of Example 1.2.3, and Figures 9, 10, and 11 show Example 1.2.3.
FIG. 2 is a diagram showing changes in wavefront aberration when the objective lens of FIG. 1: Optical information recording mechanism 2: Objective lens 3: Coupling lens 4: Light source 5: Aperture 6: Collimator lens Patent applicant: Dai Konishi Photography Co., Ltd. Patent attorney: Fumiaki Sato (# 1 or 2 people) (] Rare Figure 4 Sphere [Mouth 1 Aberration Sine condition Astigmatism Figure 5 Spherical aberration Sine condition Astigmatism Figure 6 Spherical aberration Sine condition Astigmatism Figure 7 Spherical aberration Sine condition Astigmatism Aberration No. 8 t[ kaido l[1111”I' 7.

Claims (1)

[Claims] From the light source side, it consists of a coupling lens that is a single spherical lens and an objective lens, the light source is placed closer to the coupling lens than the light source side focal point of the coupling lens, and the objective lens is movable at least along the optical axis. Concentrating optical system for recording and reproducing optical systems for optical information media