JPS6161245A - Optical head - Google Patents

Abstract

PURPOSE:To set the number of composition of a lens to one piece, to polish a lens, to decrease the man-day of vapor deposition processing of a reflection preventing film and to improve productivity by using a refractive index distribution type rod lens of a large diameter low aberration large opening number as an object lens. CONSTITUTION:A straight line polarized light 8 from a light source 7a of a semiconductor laser, etc., penetrates a collimator lens 9 and a polarized prism 11 and received through a 1/4 wavelength plate 12 and a whole reflecting prism 13 by using a refractive index distribution type rod lens 14. The light spot 15 is reflected by a track 17 on rotating recording media 16, a reflecting light 18 with recording information is reflected in the polarized prism 11, divided with a half mirror 19 and irradiated to a track detecting device 20 and a focus detecting device 21. Since the lens 14 must be stopped down up to a diffraction limit to form the light spot 15, a large diameter is set to 3.1mm. Since the number of opening is kept to a scope from 0.4-0.6 and the plane aberration and frame aberration are corrected, the plane processing is executed for a light incident edge surface 34.

Description

[Detailed description of the invention] The present invention relates to optics that detect recorded information using light.

Regarding de.

In this type of optics, in order to correctly reproduce information on a recording medium, it is necessary to sufficiently focus the beam from a semiconductor laser to form minute grooves and holes.

Conventionally, the objective lens that forms this tiny spot is composed of a combination of about three lenses designed using the ray tracing method.
It is common that For example, as shown in FIG. 1, a single lens 1,2 DEG 3T-M with a diameter of about 5 mm is assembled into a lens holder 4 to form a combination lens with three lenses in two groups. A small pitch screw is formed on the circumference of the lens holder 40, and a spacer 5 that fits with this screw and a fixture 6 are used to insert the single lens 1, 2.3'i into the lens holder 4, and to adjust the optical axis and focal point. A single lens is fixed with a spacer 5 and an ml fixture 6 while adjusting the distance and the like. The reason why a plurality of lenses of different shapes are combined with the objective lens in this E-C optical system is to eliminate aberrations that occur when the beam is converged.

However, optical systems using such objective lenses may be expensive. The reasons for this are, firstly, the number of processing steps such as lens polishing and vapor deposition for applying an anti-reflection film is large, and secondly, it is common practice to position multiple lenses with high precision and arrange the lens metal discretely. Because of this, it requires additional parts such as the L5 lens holder and spacer shown in Figure 1, and the groove bottom is complicated and the number of parts is large. shaft,
This is because the assembly requires a large number of man-hours since it is assembled while adjusting the focal length and the like. Since there are many groove bottom points like O, there is a drawback that cost reduction cannot be expected through mass production.9.

An object of the present invention is to provide an optical head having an objective lens that can form optical holes and toes equivalent to those of the conventional ones, has excellent productivity, and is inexpensive.

The present invention includes a light source, a light source, and a light source on a recording medium.

an optical system including an objective lens 7 for condensing light from the light source, and a detection means for detecting all recorded information on the track by reflecting light from the track 7 to which the light is irradiated; In de, the objective lens is formed from a focusing rod lens by M, the force, the refraction T=kno at the central axis of the rod lens, the distance from the central axis r, and the parameter t! which indicates the degree of refractive index gradient. When i, refractive index distribution +
1 (rl is n”(r), n@2(1-gr2+h4(
9r2)"IllsCgr) )", and the lens medium has a large ion concentration gradient, and the end face on which the light from the light source enters has a spherical tip.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a plan view showing an optical system according to an embodiment of the present invention that detects recorded information from the reflected light of a light spot that follows and irradiates a track on a recording medium.

As shown in the figure, a wide-angle beam 8 emitted from a light emitting surface 7a of a semiconductor laser 7 is converted into collimated light 10 by a collimating lens 9. The collimated light 10 is polarized by a polarizing prism 1li.
After passing through A, the collimated light enters the quarter-wave plate 12, where the polarization plane of the collimated light is rotated by 45 degrees. The emitted light 33 from the 1/4e long plate 12 is reflected by the total reflection prism 13 and then converged by the converging rod lens 14. Focusing rod lens 14
The light spot 15 converged at is reflected by a track 177 on the rotating recording medium 16, and the reflected light 18 with the recording trt information is again reflected by the objective lens (focusing rod lens)! 4.
After passing through the 1/4 wavelength plate 12, the zero reflected light 18 that enters the polarizing prism 11 is linearly polarized light having a plane of polarization that intersects the incident light 1°, so it is reflected within the polarizing prism 11.
Half mirror - Proceed in the direction of 19. The reflected light 18 divided by the half mirror 19 is irradiated to the track detector 2o and the seven orcus detectors 211C. Well-known track detector 2
In this case, the track signal is used as a signal indicating the position of the light spot 15 on the track 17.The focus detector 21 uses the focusing rod lens 14Vc to detect the deviation of the spot position of the focused light from the focus position. As a signal to indicate,
Outputs focus signal.

Also, a track detector 20 or seven orcus detectors 21
A recorded signal is detected by extracting the difference in relaxation of the recorded information.

FIG. 3 is an enlarged sectional view of the focusing rod lens portion shown in FIG. 2. Collimated light 33 from the quarter wavelength plate 12
passes through a total reflection prism 13 and then a focusing rod lens 14
The light is focused on the recording medium 16 to a light spot 15 with a diameter of exactly 2 μm or less. Convergent mouth.

The input laser beam incident side (prism side) of the drain lens 14 has a spherical tip, and the reflected laser beam incident side (recording medium side) has a flat end surface, and both end surfaces are coated with an engineered anti-reflection film 3 by vapor deposition or the like.
0 is applied. Further, this focusing rod lens 14 is fixed to a cylindrical lens holder 31 1c.

Focusing rod lens 14ii, a glass rod is immersed in molten salt for a long time, and the electronic polarizability contained in the glass is large and the sound movement in the glass is blocked at high temperature, and some of the ions are exchanged with alkali ions in the molten salt. However, the parabolic approximation of the resulting ion diffusion distribution is fully utilized to release the entire refractive index distribution required for the lenticular medium. The refractive index distribution obtained by ion diffusion forms a parabolic distribution that is ideal for a lenticular medium! Since additivity is established between the ion concentration and the refractive index at , the refractive index distribution can be known from the solution of the ion diffusion equation, and the following equation is known.

However, K: ion conversion degree parameter, ro: radius of the glass rod, D: ion diffusion coefficient, t: diffusion time.

When the parameter K is 0.04 or more, the refractive index distribution becomes parabolic, and the converging rod lens 14 of this embodiment has a larger value of K.

Further, the refractive index distribution n, which is an element indicating the characteristics of the converging lens 14, is expressed by .

However, the refraction on the central axis of the n 6 ns rod “J5
．． r is the distance from the central axis, 9 is the square distribution constant, h4゜h
6 is a fourth-order aberration coefficient and a sixth-order aberration coefficient. The converging rod lens 14 has a low aberration and a large diameter converging rod lens by bringing the aberration coefficients h4 and h8 close to the high-order apex ideal values, that is, h4 '' + h'``''''' 4 lenses. I have to. One of the effects of this is that the beam convergence 't-element can be increased.

Further, the converging rod lens 14 has a prism-side end surface having a spherical tip, thereby correcting spherical aberration of Seidel's five aberrations. Therefore, combined with the correction of aberrations by the ion exchange method Vc, the F aberrations are low.

According to one aspect of the present invention, instead of the conventional combination of multiple lenses, it is possible to use a low-aberration, large-diameter focusing wood with a spherical tip on the end surface on which the input laser beam enters among the two light input/output end surfaces. Since the number of groove bottoms on the lens is one, it is clear that the Lohe number required for polishing the lens and for vapor deposition of the anti-reflection film can be greatly reduced. In addition, since the focusing rod lens is cylindrical, a lens holder of O is used, for example, a lens holder that has a hollow part with an inner diameter slightly larger than the outer diameter of the focusing rod lens, and the entire rod lens is press-fitted into this. It can be assembled using a slave layer, etc., and it is possible to eliminate the conventional spacer or threaded portion with a minute pitch in the lens holder, and also eliminates the need for adjustments such as optical axis alignment during assembly.

In this way, with the simplification of the configuration, the number of configuration points is reduced.

With the reduction in the number of man-hours for machining and component parts, and further reduction in the number of assembly man-hours, productivity is improved, and cost reductions can be expected due to the F mass production effect.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the structure of a conventional combination lens, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a partial side sectional view of FIG. 2. 1.2.3... Lens, 4... Lens holder 15... Spacer, 6... Fixture, 7... Semiconductor laser, 8...Wide-angle beam, 9...Collimating lens, 10...
...Collimated light, 11...Polarizing prism,
12...1/4 wavelength plate, 13...Total reflection prism, 14...Focusing rod lens, 1
5... Koko Subo, G, 16... Recording medium, 1
7.Yu...Truck, 18...Reflected light, 19.
... Half mirror, 20 ... Track detector, 21 ... Focus detector, 30 ...
...Anti-reflection film, 31... Lens holder,
33...Collimated light. Agent: Susumu Uchihara, patent attorney −＼;. Procedural amendment (spontaneous) 60.3.17 Showa year, month, day l, case description 1988 Patent Application No. 1839
No. 46 No. 2, Title of the invention: Optical head 3, Relationship to the person making the correction case: Applicant: 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation (Contact information: NEC rN Co., Ltd.' Patent Part) 5. Amendments (1) Full text of the specification■ Figures 2 and 3 of the drawings attached to the specification The figures are corrected to Figures 2 and 3 of the drawings attached to this procedural amendment. Amended specification! 6 Title of the invention Optical head 2, Claims Light source, and a light spot that condenses light from the light source. An optical head comprising: an optical system having an objective lens for detecting the light spot; irradiation means for controlling irradiation of the light spot onto a track on a recording medium; and detection means for reading recorded information from light reflected from the track. The objective lens has a diameter of 3.1 mm or more.Detailed Description of the Invention [Technical Field] The present invention relates to an optical head for detecting recorded information by light.[Prior Art] In order to correctly reproduce information on a recording medium, the light emitted from a light source such as a semiconductor laser is sufficiently narrowed down to a diameter of 1 to 2 micrometers (φ
It is necessary to form a minute spot (1 to 2 μm). Conventionally, an objective lens that forms this fine sporatra requires a large numerical aperture NA of about 0.4 to 0.6, and it is also spherical! It is necessary to reduce aberrations such as aberrations and coma as much as possible. Therefore, it is common to use a combination of about three lenses designed using the % element line tracking method. For example, in the area shown in the first factor, a single lens 1 with a diameter of about 6 millimeters (φ6wl1) and three lenses in a 2.3t-2 group are installed in the lens assembly frame 4 as a base. A screw with a small pitch is formed on the inner periphery of the lens assembly frame 4, and the single lens 1. 2. 3t-The lens assembly frame 41C is inserted and fixed to the bow cans 1 and 23 with the spacer 5 and fixture 6 while adjusting the optical axis, sunspot distance, etc. An optical head using an objective lens based on this unconventional combination is expensive. Reason ζ 11th Ctl
j! (Because it is composed of individual lenses, the number of processing steps such as polishing the lenses and vapor deposition for applying an anti-reflection film increases.) Because it is necessary to
The construction shown in Figure 1 requires additional parts such as the lens assembly frame 4 and spacer 5, making the configuration complex and requiring a large number of parts. Thirdly, a large number of parts are required to fully adjust the original axis, focal length, etc. The number of man-hours required for assembly increases as the parts are assembled at the same time. In addition to the above-mentioned method, there is a disadvantage that conventionally, the bottom of the groove is 0.05 cm, so even if mass production is promoted, a reduction in price cannot be expected. [Object of the Invention] It is an object of the present invention to provide an optical head having an objective lens which can completely bottom out a minute original spot, has excellent productivity, and is inexpensive. [Aspects of the Invention] According to the present invention, there is provided an optical system having an L-shaped binary source, an objective lens that collects most of the light from the light source into an original spot, and irradiates the original spot onto a track on a recording medium. means and
In the optical head, the objective lens has a diameter t.
A large diameter of 3.1 mm (3.1 m) or more,
There is obtained an optical head characterized in that it is comprised of a gradient index rod lens with low aberrations and a large numerical aperture, the end surface of which the light from the light source enters has a spherical tip. [Embodiment] Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a perspective view showing an embodiment of the present invention. In FIG. VC, linearly polarized light 8 from a light source 7a such as an n9 semiconductor laser fixed in a package 7 becomes parallel to the collimating lens 91C. When the parallel light 10 passes through the polarizing prism 11 and enters the quarter-wave plate 12, it becomes circularly polarized light. After the parallel light 10 from the 1/4 wavelength plate 12 is reflected by the total reflection prism 13, the parallel light 10 has a large diameter of 3.1 μm or more in diameter and is incident from the light source 7. The light is focused by a low aberration, large numerical aperture (NA, ) 7) gradient index rod lens 14 having a spherical tip on the yJa plane 347. The condensed original spot 15 is reflected by a track 17 on a rotating recording medium 16, and the reflected light 18 containing recorded information is refracted again by a distributed rod lens 14,1/
4 After passing through the wave plate 12, it returns to the polarizing prism IIVc. 174 The reflected light 18 that has passed through the wavelength plate 12 becomes I-line side light having a polarization plane perpendicular to the parallel light 10 from the hidden source 7, so it is reflected within the polarizing prism 11 and reflected by the half mirror 1.
Proceed through 9rc rotations. A track detector 20 and a focus detector 2 are applied to the reflected light 18 with a divided field of half-mi Y-19.
The detection means 5QK consisting of 1 is irradiated. From the track detector 2o, the amount of positional deviation of the original track 15 from the track 17 is output as a track error signal 22. The focus detector 21 is a refractive index gradient type lens, and the amount of positional deviation between the focal plane of the original spot 15 condensed at 14 and the track 17 on which information is recorded is expressed as a focus error signal 23. Also, the track detector 20 or the focus detector 2
1, the strength of the reflected light 18 is output as recording information. The drift error signal 22 and the focus error signal 23 are each input to the irradiation means 511C. In response to the irradiation means 51 store number 22 and focus error signal 23, the rod lens 14 is moved all the way for accurate positioning. sg3 Figure μ 2nd prisoner shows the gradient index rod lens L
This is an enlarged cross-section of the area near the area. 174 wavelength plate 12 parallel light 10i is reflected by one surface of the total reflection prism 13 and is reflected by the refractive index distribution type Wood lens 14 onto the recording medium 16 at Vcl
The light is focused on an original spot 15 with a diameter of micrometers (φ1 to 2 μm) or less. The gradient index lens 14 is provided with a total reflection prism 13 on the light incident end surface 34 side of the light source 7.
The end surface on the opposite side (on the recording medium 16 side) is entirely flat, and both end surfaces VC are coated with an IC edge antireflection film 30 such as vapor deposition. Further, this gradient index rod lens 14 is fixed within a cylindrical lens holding frame 31. The gradient index rod lens 14μ has a large aperture because the original spot 15 must be stopped by a diffraction-limited housing to achieve t''LFi in order to form the original spot 15.The focused beam diameter S at the position of the original spot 15 is λ S= /, ・・・・・・・・・・・・α).Here, fc focal length (3 to 4 for the original head)
Must be millimeter (3 to 4 m). d is the diameter of the beam incident on the lens 14 (31 to 4 millimeters (m)), and λ is the wavelength (typical Vcl-!780 nanometers (7801 m)). a) Equation F calculation shows that the beam diameter S is approximately 1 micrometer (
φ1μ duck) VC will be narrowed down, but in reality, the beam diameter S becomes small and the intensity distribution at the focal plane is blurred, side ropes occur, and the beam diameter 1 of the original spot 15 (below the floor) Therefore, the large diameter 31 mm (3
, l m). Further, in order to keep the numerical aperture N A t within the range of 0.4 to 0.06 and to correct spherical aberration and coma aberration, the entrance end surface 34 is processed into a spherical surface. Good results were obtained by setting the length in the optical axis direction from the tip of the tip of the tip to the end surface on the recording medium side to be 1.6 mm ((R1 to R3). In the method for manufacturing the gradient index rod lens 14, glass rod'l
tImmerse in molten salt for a long time to pre-contain "1" in glass.
Some of the ions that move through the glass at high temperatures due to their high electron dispersion are combined with alkali ions in the molten salt. In other words, the parabolic approximation of the resulting ion diffusion distribution is utilized to obtain the refractive index distribution shape required for the lens-like medium. In the process in which the refractive index distribution obtained by ion diffusion forms a parabolic distribution that is optimal for a lens-like medium, the bottom-up property balances between the ion concentration and the refractive index, which can be known from the solution of the refractive index distribution gold ion diffusion equation. However, K:
Ion exchange degree parameter, r (radius of Niglass rod, D°
Ion diffusion coefficient, t: diffusion time. When the parameter K becomes 0.04 or more, the refractive index distribution becomes parabolic, but as in this example, when the diameter becomes large, ion diffusion takes a long time tg! Therefore, I set the KO value as high as possible and timed it in a short time. In addition, the refractive index distribution n, which is an element indicating the characteristics of the refractive index distribution type rod lens 14, is n'(r)=no''(1-(gr)'+h4 (gr)
It is expressed as '+ha (gr)'10......). However, not'z is the refractive index on the central axis of the rod, ra is the distance from the central axis, g is the square distribution constant, h
4th and h6 are divided by fourth-order and sixth-order aberration coefficients. The gradient index rod lens 14 is a gradient index rod lens with a large aperture of 3.1 mm (3.1 m') or more in diameter and with low aberrations. I set it to 14. [Effects of the Invention] As described above, the present invention +C: Instead of the conventional combination of multiple lens-like media, a large-diameter gradient index rod lens with a low aberration and a spherical tip on the end face where the light source enters is provided. It is clear that since only one Ic lens is used for each lens, the number of man-hours required for polishing the lens and depositing the anti-reflection film can be greatly reduced. In addition, since the gradient index rod lens has a cylindrical shape, this lens stain-retaining frame T-9
'lJ is refraction! The outer diameter of the distributed rod lens is small - it is a cylindrical lens holding frame with a large inner diameter hollow part, and it refracts! It is now possible to incorporate a distributed rod lens by press-fitting or gluing, eliminating the need for spacers and micro-pitch threads in the lens assembly frame, which were previously used, and making adjustments such as optical axis alignment during IC% assembly possible. No longer needed. As a result of this simplification of the Vc configuration, the number of required parts is reduced, the man-hours for processing groove bottom parts are reduced, the man-hours for assembling the IC are reduced, and the productivity is the same as above, and the price is expected to be reduced due to the effect of fk production. can. 4. Brief Description of the Drawings Fig. 1 is a cross-sectional view showing a conventional objective lens used in a μ-element head, Fig. 2 is a perspective view showing an embodiment of the present invention, a! 3
The figure is a partially enlarged sectional view of an actual example of the present invention. 1.2.3...Single lens, 4...Lens assembly frame, 5...Spacer, 6...Fixing tool, 7...・Light source, 8...Linearly polarized light,
9...Collimating lens, 10...Plate, 13...Total reflection prism, 14...
Gradient index lens, 15...Original spot, 16...Recording medium, 17...Track, 18...Reflected light. 19...Half mirror, 20...Track detector. 21...Focus detector, 22...
Track error signal, 23... Focus error signal, 25... Track drive side a section, 26...
... Focus drive control section, 30 ... Antireflection film, 31 ... Lens holding frame, 34 ...
・Incidence end face, 50------detection arm, 5112 figure t

Claims (1)

[Scope of Claims] An optical system including a light source, an objective lens that focuses light from the light source onto a track on a recording medium, and recording information on the track using reflected light from the track irradiated with light. In the optical head, the objective lens includes a focusing rod lens, and the rod lens has a refractive index n_0 at the central axis, a distance from the central axis r, and a parameter indicating the degree of the refractive index gradient. g, the refractive index distribution n(r) is n^2(r)≒n_0^2{1-gr^2+h_4(g
r^2)^4+h_6(gr^2)^6} An optical head characterized in that the lens medium has a large ion concentration gradient, and the end surface onto which light from the light source enters has a spherical tip.