JP2006099902A - Optical apparatus for optical recording/reproducing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical apparatus for optical recording/reproducing in which optical performance and use efficiency of light are good, a head part is miniaturized, and near-field light is used. <P>SOLUTION: This apparatus is the optical apparatus for optical recording/reproducing provided with a laser diode 2 as a light source, a collimator optical system 3, a beam diameter conversion optical system 4 consisting of a first lens 41 and a second lens 42 converting a beam diameter of parallel light emitted from the collimator optical system 3, and a converging element 6 converging almost parallel light emitted from the beam diameter conversion optical system 4, generating near-field light being smaller than a converging spot near a converging point, and consisting of a single optical element. In the beam diameter conversion optical system 4, its magnification β is set to 0.2<¾β¾<0.8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical recording / reproducing optical apparatus, and more particularly to an optical recording / reproducing optical apparatus used for recording and / or reproducing information by near-field light.

  In recent years, various proposals have been made to use a near-field light generating structure in an optical recording / reproducing technique in order to obtain a minute light spot. In order to realize recording / reproduction using near-field light, a solid immersion lens or a solid immersion mirror is used as a condensing element, a minute spot and a recording medium are brought close to each other, and an evanescent wave is used. Interact with the recording medium. As a result, high density recording or reproduction of information is achieved.

  Patent Documents 1, 2, and 3 disclose an optical apparatus for optical recording / reproducing using a solid immersion lens as a condensing element. By the way, the conventional solid immersion lens requires an objective lens, and it is difficult to adjust both of them. Even after the adjustment, there is a problem that an adjustment shift occurs due to an environmental change such as temperature. In addition, since this type of objective lens is larger than the solid immersion lens, it has a problem that the head portion becomes larger. And, in order to improve the light collecting performance and the light utilization efficiency, how to configure an optical system that guides substantially parallel light to the light collecting element is a major issue.

  That is, in Patent Document 1, the size of the light shielding plate (aperture) for annular illumination is defined using the focal length ratio between the condenser lens and the collimator lens, but no specific focal length ratio is disclosed. .

  In Patent Document 2, a beam diameter conversion optical system including two conversion lenses is disclosed. As a specific numerical example of the focal length, f1 = f2 = 6 mm is shown. Since this is not done, the optical system becomes large.

In Patent Document 3, it is disclosed that the beam diameter is reduced by a combination of a relay lens and an imaging lens, but there is no description of specific numerical examples regarding the lens, and the combination of an objective lens and a solid immersion lens is disclosed. However, it does not solve the problems such as adjustment difficulty and enlargement described above.
JP-A-11-203708 JP 2000-242963 A JP 2000-132858 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical recording / reproducing optical apparatus using near-field light, which has good optical performance and light utilization efficiency, and has a small head portion.

  In order to achieve the above object, the present invention provides an optical recording / reproducing optical apparatus using near-field light, which converts a light source, a collimator optical system, and a beam diameter of parallel light emitted from the collimator optical system. A beam diameter converting optical system composed of at least two lenses, and a single unit that collects substantially parallel light emitted from the beam diameter converting optical system and generates near-field light smaller than the focused spot near the focusing point. A light-condensing element composed of the above optical elements, and the magnification β of the beam diameter converting optical system is 0.2 <| β | <0.8.

  In the optical recording / reproducing optical apparatus according to the present invention, first, a condensing element that generates near-field light is composed of a single optical element (including one that is joined or combined). Upsizing, difficulty in adjustment, deviation after adjustment, and the like due to a combination of an objective lens and a solid immersion lens that have been conventionally known are eliminated, and good optical performance can be achieved.

  The beam diameter conversion optical system has a magnification β of 0.2 <| β | <0.8, that is, is configured as a reduction optical system. With respect to the relationship with the beam diameter emitted from the collimator optical system, it is possible to use light efficiently by interposing an optical system for reducing the beam diameter, which contributes to miniaturization of the head portion. If the magnification β is 0.2 or less, the sensitivity of the light collecting element becomes too high, which is not preferable. If the magnification β is 0.8 or more, it is not effective for downsizing the head portion. A more preferable range of magnification β is 0.3 <| β | <0.6.

  In the optical recording / reproducing optical apparatus according to the present invention, it is preferable that a microscopic structure that generates near-field light smaller than the condensing spot is formed in the condensing portion of the condensing element. By providing a micro structure in the light condensing portion, optical recording / reproduction can be performed with a beam diameter smaller than that of the light condensing spot. Specifically, by devising the shape of the pattern formed on the metal thin film, electric field amplification by surface-excited plasmon polariton occurs, and very high-efficiency optical recording / reproduction is possible while generating minute near-field light. It becomes.

  It is preferable that a plurality of such microstructures are arranged in a matrix at the light condensing portion of the light condensing element. It is difficult to accurately match the focused spot by the focusing element with the microstructure. However, if the microstructures are arranged in a matrix, the focusing spot can be adjusted to one of them, and the adjustment becomes easy. Note that a plurality of micro structures can be simultaneously formed with high accuracy and easily by a conventionally known micro process.

  The optical recording / reproducing optical apparatus according to the present invention may further include a moving means for moving the lens of the beam diameter converting optical system in a direction perpendicular to the optical axis and / or a moving means for moving in the optical axis direction. . By providing such moving means, it is possible to easily adjust the position of the light condensing element and the light condensing spot. That is, by moving the lens of the beam diameter conversion optical system in the direction perpendicular to the optical axis, the angle of the beam incident on the condensing element is changed, and thereby the position of the condensing spot can be adjusted. Further, by moving the lens of the beam diameter conversion optical system in the optical axis direction, the radius of curvature (incident object distance) of the wavefront of the beam incident on the condensing element changes, and the focus position can be adjusted.

  Further, when the beam diameter converting optical system is composed of two lenses, it is preferable that both lenses are aspherical on one side and the curvature of parallel light is stronger. An aspherical surface is advantageous for correcting the aberration, and it is necessary to use a lens having a strong power convex in the parallel direction.

  Embodiments and examples of an optical recording / reproducing optical apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Refer to the first embodiment, FIG. 1 and FIG. 2)
As shown in FIG. 1, an optical recording optical apparatus 1A according to the first embodiment includes a laser diode 2, which is a light source, a collimator optical system 3, a beam diameter converting optical system 4, a plane mirror 5, and a light collecting element. It is comprised with the element 6. FIG.

  The laser diode 2 emits divergent light having a predetermined wavelength in the optical axis direction Z. The collimator optical system 3 converts diffused light emitted from the laser diode 2 into substantially parallel light, and a specific configuration example thereof will be described below with reference to FIGS.

  The beam diameter conversion optical system 4 includes a first lens 41 that is a convex lens, a second lens 42 that is a convex lens, and a diaphragm 43, and converts the beam diameter of parallel light emitted from the collimator optical system 3. Specific construction will be described later as Examples 1 to 5.

  The plane mirror 5 folds the beam emitted from the beam diameter converting optical system 4 and guides it to the condensing element 6. The condensing element 6 condenses the parallel beam reflected by the mirror 5 and generates near-field light smaller than the condensing spot in the vicinity of the condensing point, and a specific configuration example thereof is shown in FIGS. Will be described below.

  Further, as shown in FIG. 2, the position of the first lens 41 of the beam diameter converting optical system 4 can be adjusted in the optical axis direction Z by a piezoelectric actuator 45. The position of the second lens 42 can be adjusted in the directions X and Y perpendicular to the optical axis direction Z by the moving coil 46.

(Refer to the second embodiment, FIGS. 3 and 4)
As shown in FIG. 3, an optical recording optical device 1B according to the second embodiment includes a laser diode 2, a collimator optical system 3, a beam diameter conversion optical system 4, a plane mirror 5, as in the first embodiment. It is comprised with the condensing element 6. FIG. The difference is that the beam diameter converting optical system 4 is composed of a first lens 41 that is a convex lens and a second lens 42 that is a concave lens. Other configurations are the same as those of the first embodiment, and the same members are denoted by the same reference numerals, and redundant description is omitted. Further, specific construction of the beam diameter converting optical system 4 will be described later as Examples 6 to 10.

(Refer to FIG. 5 and FIG. 6 for a configuration example of a collimator optical system)
The collimator optical system 3 can employ various configurations. For example, as shown in FIG. 5, a combination of an optical element 31 that shapes and diffuses a beam and a collimator lens 32 may be used. Or as shown in FIG. 6, the structure which combined the prism 33 may be sufficient. Further, although not shown in the figure, it may be constituted by only a single aspheric lens, may be constituted by an anamorphic optical element, or a pair of anamorphic prisms may be added.

  In general, since the emission angle from the laser diode varies depending on the direction, a spherical or aspherical collimator lens does not become circular when converted to parallel light. In order to approximate a circular shape, it is necessary to incorporate a beam shaping element into the collimator optical system 3, and the anamorphic prism 33, a prism pair, an anamorphic lens, a cylindrical lens, or the like is used.

(Example of beam diameter conversion optical system)
The beam diameter conversion optical system 4 is a combination of first and second lenses 41 and 42 having positive power in the first embodiment, and the first lens 41 having positive power and negative power in the second embodiment. The second lens 42 has a combination.

  Assuming that the incident beam diameter is φ1, the outgoing beam diameter is φ2, the focal length of the first lens 41 is f1, and the focal length of the second lens 42 is f2 (the unit is mm), various values shown in Tables 1 and 2 below. Can be exemplified. Examples 1 to 5 shown in Table 1 are examples of the first embodiment, and Examples 6 to 10 shown in Table 2 are examples of the second embodiment.

  In such a beam diameter converting optical system 4, the distance between the first and second lenses 41 and 42 is such that the principal point interval is the sum of the focal lengths of the lenses 41 and 42. The absolute value of the magnification β is determined by the focal length ratio. The magnification β is set in a range of 0.2 <| β | <0.8, and the reduction optical system is configured.

  In relation to the beam diameter φ1 emitted from the collimator optical system 3, the optical system can be used efficiently by interposing an optical system that reduces the beam diameter to φ2, which contributes to miniaturization of the head portion. If the magnification β is 0.2 or less, the sensitivity of the light collecting element 6 becomes too high, which is not preferable. If the magnification β is 0.8 or more, it is not effective for downsizing the head portion. A more preferable range of magnification β is 0.3 <| β | <0.6.

(Focus adjustment)
By the way, the radius of curvature of the wavefront of the emitted light can be controlled by changing the distance between the first and second lenses 41 and 42. The necessity of this kind of control is due to the fact that the light collecting element 6 itself does not have a focus function because the single light collecting element 6 (including a junction or a composite structure) is used in the present invention. That is, when the focus position slightly changes due to a manufacturing error of the light condensing element 6 and the light condensing spot deviates from the designed light condensing position, the focus position cannot be changed with the light condensing element 6 having a single structure.

  Therefore, it is necessary to control the incident light of the condensing element 6 by the beam diameter converting optical system 4. The distance between the lenses 41 and 42 is preferably adjusted by driving the first lens 41 in the optical axis direction Z by a piezoelectric actuator 45 (see FIGS. 2 and 4), and the reason will be described later. However, driving the second lens 42 in the optical axis direction Z is not excluded.

  The lenses 41 and 42 are preferably aspherical lenses. If the lens is spherical, residual aberrations will occur when condensing. Optimum design of the aspherical surface will satisfy on-axis aberrations, and by satisfying the sine condition, off-axis aberrations will be corrected to some extent. Can do. It is preferable that both surfaces are aspherical in terms of design freedom. In addition, in order to satisfy the performance of on-axis aberration and off-axis aberration, it has been conventionally known that the curvature on the large conjugate side is larger than the curvature on the small conjugate side, and the curvature on the parallel light side is strong. It is also necessary.

  Since the condensing spot of the condensing element 6 is a single element, it is determined by the incident angle of the beam. In the first and second embodiments, if there is an error in the angle of the mirror 5 or the holding of the light condensing element 6, the position of the light condensing spot is shifted from a predetermined position (the optical axis of the light condensing element 6).

  In order to cope with the deviation of the focused spot from the optical axis, the incident angle of the beam with respect to the focused element 6 may be adjusted. Specifically, the first or second lens 41 or 42 may be moved in the X and Y directions orthogonal to the optical axis. That is, the incident angle to the light condensing element 6 can be adjusted by moving the first lens 41 (or the second lens 42) in the direction perpendicular to the optical axis.

  When this moving amount (eccentric amount) is y, the angle θ is determined by the equation y = f · tan θ (f is the focal length of the lens to be moved). In each of Examples 1 to 10 of the first and second embodiments, since the focal length of the second lens 42 is set smaller than that of the first lens 41, the second lens 42 is used to change the same angle. The movement distance can be made shorter by moving in the direction perpendicular to the optical axis. Therefore, the distance between the lenses 41 and 42 is adjusted by moving the first lens 41. Note that adjustment of the focus position and adjustment of the incident angle may be performed using only the first or second lens 41 or 42.

  Regarding the lenses 41 and 42, positive power lenses are used in the first embodiment, and positive power lenses and negative power lenses are used in the second embodiment. Although the beam diameter conversion is the same, it is more advantageous to use two positive power lenses in terms of aberration correction.

(Configuration of condensing element, see FIGS. 7 and 8)
As the condensing element 6, a solid immersion mirror or a junction element of a solid immersion lens and a translucent plate is used. 7A to 7D show specific configuration examples of the mirror type light condensing element 6 and FIGS. 8A and 8B show specific configuration examples of the lens type light condensing element 6. Show. In each drawing of FIG. 7, reference numeral 100 denotes a recording medium.

  The condensing element 6 shown in FIG. 7A is a solid immersion mirror 6a, which reflects incident light from the planar first surface ring zone portion on the second surface which is an aspheric surface, and further, the first surface. The near-field light is generated by being reflected by the reflecting surface of the light and condensing on the condensing spot 61.

  The condensing element 6 shown in FIG. 7B is obtained by joining the solid immersion mirror 6b and the translucent flat plate 65, and the incident light transmitted through the first surface having the positive power is the second having the positive power. The near-field light is generated by being reflected on the surface and condensed on the condensing spot 61 in the vicinity of the second surface of the translucent flat plate 65 joined to the central plane portion of the second surface.

  The condensing element 6 shown in FIG. 7C is formed by joining a solid immersion mirror 6c and a translucent flat plate 65, and refracts incident light from a recess (aspheric surface) on the first surface in the recess. The light is reflected on the second surface, which is a flat surface, reflected on the first surface (aspherical surface), and condensed on the condensing spot 61 near the second surface of the translucent flat plate 65 bonded to the center of the second surface. To generate near-field light.

  A condensing element 6 shown in FIG. 7D is a solid immersion mirror 6d, and reflects incident light transmitted through a first surface, which is a vertical plane, by a reflecting surface formed as a paraboloid, for example. The near-field light is generated by condensing the light at the condensing spot 61 on the second surface. If such a solid immersion mirror 6d is used, the mirror 5 is unnecessary.

  A condensing element 6 shown in FIG. 8A has a solid immersion lens (aspheric lens) 6e having a convex aspherical entrance surface and a flat exit surface, and a plane of the solid immersion lens 6e. It is comprised with the translucent flat plate 65 joined. The beam incident on the solid immersion lens 6e is refracted by the incident surface (aspherical surface), passes through the plane that is the cemented surface, condenses on the condensing spot 61 near the exit surface of the translucent flat plate 65, and near-field light. Is generated.

A condensing element 6 shown in FIG. 8B is obtained by joining a solid immersion lens 6 f and a translucent flat plate 65. The solid immersion lens 6f includes a first lens 6f1 made of a _first material having a refractive index N1, and a second lens 6f2 made of a _second material having a refractive index N2, and the lenses 6f ₁ and 6f. _{The two} opposing surfaces are joined in the same shape. The beam incident on the first lens 6f ₁ is refracted by the incident surface (aspherical surface), passes through the second lens 6f ₂ , and condenses on the condensing spot 61 in the vicinity of the exit surface of the translucent flat plate 65. Generate light.

In the solid immersion lens 6f, it is preferable that the following expression is satisfied when the power of the incident surface of the first lens 6f ₁ is P1 and the power of the cemented surface with the second lens 6f ₂ is P2. Incidentally, CR1 curvature of the entrance surface of the first lens 6f ₁ radius, CR2 is the radius of curvature of the bonding surface of the first lens 6f _1.

0.1 <P1 / P2 <5
P1 = (N1-1) / CR1
P2 = (N2-N1) / CR2

In the condensing element 6 shown in FIG. 8B, the first lens 6f ₁ and the second lens 6f ₂ are joined or combined to form one aspheric lens, so that aberration is caused by two optical surfaces. Can be corrected more freely, and not only on-axis aberrations but also off-axis aberrations can be effectively corrected. The above-mentioned equation defining the power ratio between the lenses 6f ₁ and 6f ₂ is for ensuring good aberration correction.

  When P1 / P2 exceeds 5, the power distribution at the power P1 becomes too large, and the effect of configuring with a cemented lens or a compound lens (mold-integrated type) cannot be exhibited. If P1 / P2 is less than 0.1, the power of the joint surface becomes too large, making it difficult to manufacture the lens. A more preferable range is 0.3 <P1 / P2 <3.

  If the condensing element 6 is a joining type of a lens or mirror and a translucent flat plate 65, it has the advantage of being resistant to disturbances because it is joined. In addition, if the condensing element 6 is designed for an object at infinity, there is an advantage that the focus position is less likely to fluctuate with respect to the relative positional deviation from the incident light.

  The purpose of joining the lens or mirror and the flat plate 65 is that mass production of a microstructure is possible. That is, a micro structure for generating near-field light is formed on the exit surface of the flat plate 65 as will be described below, and this type of micro structure is generally processed by a fine process on a wafer. In addition, by forming a microstructure by process processing and cutting it into a flat plate 65 of a predetermined size, mass production is possible at a low cost.

(Near-field light generating structure, see FIGS. 9 and 10)
By the way, the condensing spot 61 of the condensing element 6 is formed with a microstructure for generating near-field light having a dimension equal to or smaller than the incident wavelength. Such a microstructure is preferably a microstructure that generates surface-excited plasmons, and is particularly preferably made of a metal that generates plasmon resonance.

  Even with a microstructure having a dimension of a wavelength or less, it is necessary to efficiently collect energy in a minute spot, and good light collection efficiency can be obtained by using the electric field amplification effect by surface excitation plasmon resonance. For example, it is known that gold and silver have a large electric field amplification effect at a wavelength of 780 nm, and aluminum and magnesium have a large electric field amplification effect at a wavelength of 405 nm. Therefore, plasmon resonance can be used effectively by selecting a metal material, a fine structure pattern, and a thickness corresponding to the incident wavelength, and a fine spot can be obtained efficiently.

  9 and 10 show specific examples of the microstructure. In the first example shown in FIG. 9, a plurality of butterfly-shaped openings 71 are formed in a matrix on a metal thin film 70 having a thickness of about 50 nm formed on the condensing surface of the element 6. The facing distance between the minute protrusions 72 and 72 is, for example, 20 to 50 nm. When the light is condensed on the facing part of the minute protrusions 72 and 72, a strong electric field is generated only in the vicinity of the facing part, and near-field light is generated.

  In the second example shown in FIG. 10, a plurality of triangular metal thin films 75 having a thickness of about 50 nm are formed in a matrix on the light condensing surface of the element 6. When the light is condensed on the metal thin film 75, a strong electric field is generated only in the vicinity of the top, and near-field light is generated. The periphery of the metal thin film 75 is air or a dielectric.

  In both the first and second examples, by optimizing the thickness and pattern of the thin films 70 and 75, the electric field can be efficiently concentrated in a minute region, and light in the minute region using near-field light can be obtained. Recording / playback can be performed. Although only one micro structure may be formed, by arranging a plurality of micro structures in a matrix, it is only necessary to adjust the focused spot position in any of the micro structures, and the adjustment becomes easy.

(Definition formula of aspherical surface)
Here, the definition formulas of the various aspheric surfaces described above are shown below.

(Other examples)
The optical apparatus for optical recording / reproducing according to the present invention is not limited to the above-described embodiments and examples, and can be variously modified within the scope of the gist.

  In particular, the detailed configurations of the collimator optical system and the beam diameter conversion optical system are arbitrary, and single elements (including junction and composite types) having various configurations can be used as the condensing element. Further, FIGS. 9 and 10 showing a microstructure that generates near-field light are merely examples, and the details of the structure and pattern are arbitrary.

  In FIGS. 1 and 3, information can also be reproduced by providing a half mirror in the optical path and allowing the return light from the recording medium to enter the light detection element from the half mirror.

1 is a schematic configuration diagram showing an optical apparatus for optical recording / reproducing that is a first embodiment of the present invention. It is explanatory drawing which shows the beam diameter conversion optical system in the said 1st Embodiment. It is a schematic block diagram which shows the optical apparatus for optical recording / reproducing which is 2nd Embodiment of this invention. It is explanatory drawing which shows the beam diameter conversion optical system in the said 2nd Embodiment. It is explanatory drawing which shows the 1st example of a collimator optical system. It is explanatory drawing which shows the 2nd example of a collimator optical system. It is explanatory drawing which shows the 1st example-4th example of a condensing element. It is explanatory drawing which shows the 5th example and 6th example of a condensing element. It is explanatory drawing which shows the 1st example of a microstructure. It is explanatory drawing which shows the 2nd example of a microstructure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A, 1B ... Optical element for optical recording 2 ... Laser diode 3 ... Collimator optical system 4 ... Beam diameter conversion optical system 6 ... Condensing element 41 ... 1st lens 42 ... 2nd lens 45 ... Piezoelectric actuator 46 ... Moving coil 61 ... Focusing spot 70 ... Metal thin film 71 ... Opening 75 ... Metal thin film

Claims (7)

In an optical recording / reproducing optical apparatus using near-field light,
A light source;
Collimator optics,
A beam diameter converting optical system comprising at least two lenses for converting the beam diameter of the parallel light emitted from the collimator optical system;
A condensing element consisting of a single optical element that condenses substantially parallel light emitted from the beam diameter conversion optical system and generates near-field light smaller than the condensing spot near the condensing point, and
The magnification β of the beam diameter converting optical system is 0.2 <| β | <0.8;
An optical apparatus for optical recording / reproducing characterized by the above.   2. The optical recording / reproducing optical apparatus according to claim 1, wherein a magnification β of the beam diameter converting optical system is 0.3 <| β | <0.6.   3. The optical recording / reproducing optical device according to claim 1, wherein a micro structure that generates near-field light smaller than a condensing spot is formed in a condensing portion of the condensing element. apparatus.   4. The optical apparatus for optical recording / reproducing according to claim 3, wherein a plurality of the micro structures are arranged in a matrix at a condensing portion of the condensing element.   5. The optical apparatus for optical recording / reproducing according to claim 1, further comprising moving means for moving a lens of the beam diameter converting optical system in a direction perpendicular to the optical axis.   6. The optical apparatus for optical recording / reproducing according to claim 1, further comprising moving means for moving a lens of the beam diameter converting optical system in an optical axis direction. 7. The optical recording / reproducing apparatus according to claim 1, wherein the beam diameter converting optical system has two lenses, each of which has an aspherical surface on one side and a stronger curvature of parallel light. Optical device.

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