JP4593659B2 - Near-field optical head - Google Patents

Description

  The present invention uses near-field light to detect the interaction with a minute area on the surface of the recording medium, thereby observing structural information or optical information in the minute area below the wavelength of the input light, thereby providing high-density information. The present invention relates to a near-field optical head used for recording and reproduction.

  High-resolution probes that use near-field light are used in near-field light microscopes and near-field light heads. By generating near-field light from the tip of the probe and detecting propagating light generated as a result of the interaction between the microscope sample or the recording medium and the near-field light, a spatial resolution exceeding the light diffraction limit can be obtained. There is also a method in which near-field light generated as a result of interaction between incident propagation light and a sample or a recording medium is detected by a probe. The near-field microscope achieves a resolution exceeding the diffraction limit of the conventional optical microscope by this principle. Further, when such a near-field optical probe is used for a near-field optical head, a data recording density exceeding that of a conventional optical disk is possible.

  As a method of using near-field light in a near-field microscope, the distance between the probe micro-aperture and the sample surface is brought close to the diameter of the probe micro-aperture and propagates through the probe toward the probe micro-aperture. There is a method (illumination mode) in which near-field light is generated in the minute aperture by introducing light. In this case, the scattered light generated by the interaction between the generated near-field light and the sample surface is detected by the scattered light detection system with the intensity and phase reflecting the fine structure of the sample surface. It enables observation with high resolution that could not be realized.

  In addition, an information recording / reproducing apparatus has been studied as an apparatus using near-field light described above. Many of the current information reproducing apparatuses perform information reproduction for a magnetic disk or an optical disk as an information recording medium. In particular, a CD, which is one of the optical disks, has high-density information recording and low-cost mass production. Therefore, it is widely used as a medium for recording a large amount of information. The CD has a pit having a size of about the wavelength of the laser beam used for reproduction and a depth of about a quarter of the wavelength on the surface of the CD, and utilizes the light interference phenomenon. Reading is possible.

  In order to read recorded information from an optical disk represented by this CD, a lens optical system generally used in an optical microscope is used. Therefore, when the information recording density is increased by reducing the pit size or the track pitch, the spot size of the laser beam cannot be reduced to a half wavelength or less due to the problem of light diffraction limit. Will hit a wall that cannot be made smaller than the wavelength of the laser beam.

  Further, not only optical disks but also magneto-optical disks that record information by the magneto-optical recording method realize high-density information recording / reproduction with a small spot of laser light. It is limited to the spot diameter obtained by condensing light.

  Therefore, in order to overcome these limitations due to the diffraction limit, an optical head provided with a minute aperture having a diameter equal to or smaller than the wavelength of the laser beam used for reproduction, for example, about 1/10 of the wavelength, is generated at the minute aperture. An information reproducing apparatus using near-field light has been proposed.

  The near-field microscope technology is used not only as a microscope but also by introducing relatively high-intensity light toward the sample through the optical fiber probe, so that near-field light with a high energy density is introduced into the microscopic aperture of the optical fiber probe. It can also be applied to high-density information recording / reproducing technology that generates and locally changes the structure or physical properties of the sample surface by the near-field light.

  Here, as the optical fiber probe described above, for example, as disclosed in US Pat. No. 5,294,790, an opening is formed through the silicon substrate by a semiconductor manufacturing technique such as photolithography, and one of the silicon substrates is formed. A cantilever type optical probe has been proposed in which an insulating film is formed on the surface, and a conical optical waveguide layer is formed on the insulating film on the side opposite to the opening. In this cantilever type optical probe, light can be transmitted through a minute opening formed by inserting an optical fiber into the opening and coating the portion other than the tip of the optical waveguide layer with a metal film.

  Conventionally, the use of a flat probe having no sharpened tip, such as the above-described optical fiber probe, has been proposed. This planar probe is a silicon substrate in which a minute opening having an inverted pyramid structure is formed by anisotropic etching, and its apex is penetrated with a diameter of several tens of nanometers. In addition, in the planar probe, a lens is provided in the inverted pyramid structure portion, and the intensity of near-field light generated in the minute aperture is increased by condensing the laser light to the minute aperture by the lens. ing. This planar probe is used as a near-field optical memory head suitable for reproduction and recording of an optical information recording medium (optical memory) using near-field light.

On the other hand, in recent years, a photonic band gap in which the propagation of light in a certain wavelength region is prohibited by forming two or more types of dielectrics having different dielectric constants in a periodic structure so as to have a lattice constant about the wavelength of light. (E. Yablonovitch, Physical Review Letters, vol.58, no.20, pp2059, 1987). A crystal having a photonic band gap is called a photonic crystal. An optical waveguide formed by providing a light path in a photonic crystal can also bend light at an acute angle (for example, A.Mekis, JCChen, I.Kurland, S.Fan, PRVilleneuve, and JDJoannopolous , Physical Review Letters, vol.77, no.18, pp3787, 1996). Since no light can enter the crystal, optical waveguide with an efficiency close to 100% becomes possible.
E. Yablonovitch, Physical Review Letters, vol.58, no.20, pp2059, 1987 A. Mekis, JCChen, I. Kurland, S. Fan, PRVilleneuve, and JD Joannopolous, Physical Review Letters, vol. 77, no. 18, pp3787, 1996

In the near-field optical head described above as the prior art, for example, in a head in which a minute aperture having an aperture diameter of about 100 [nm] is formed at the tip of a sharpened optical fiber, the output light intensity with respect to the incident light intensity is 10 ^−6. It is very small, about ~ ^10-7 . This means that most of the incident light energy is reflected or absorbed by the inner wall of the head before reaching the minute aperture. Light is diffusely reflected inside the head by a light-shielding film formed by vapor deposition or the like on the tip of the head, and a considerable proportion is absorbed.

  In order to obtain an output signal having a high S / N ratio, it is desired to increase the near-field light intensity generated from the minute aperture. However, when the incident light intensity is increased, the shape of the light-shielding film changes due to the temperature rise, resulting in the minute aperture. There was a problem that the optical characteristics changed. In addition, there is a problem in that stable operation is not possible due to the influence of heat conduction from the head tip to the sample or recording medium. There is also a problem that it is difficult to control the distance between the head and the recording medium due to thermal expansion of the head. Further, the head itself may be damaged because the thermal expansion coefficients of the light shielding film and portions other than the light shielding film are greatly different.

  The present invention has been made in view of the above problems, and an object of the present invention is to improve the efficiency of optical waveguide to a minute aperture of a near-field optical head.

  In order to achieve the above object, a near-field optical head according to the present invention is supported by a suspension arm that applies a load load and obtains a levitating force by relative movement with a recording medium, and the load load and the levitating force are obtained. A slider that creates a gap with the recording medium due to the balance of the recording medium, a hole that penetrates the slider and forms a minute opening in the bottom surface of the slider, and the near-field light when the slider scans the surface of the recording medium. In a near-field optical head that records and reproduces information by the interaction of the recording medium and the minute aperture via the slider, the slider is formed of a crystal having a photonic band gap. To do.

  According to the present invention, the light incident on the slider cannot enter any part other than the hole penetrating the slider, and almost all the light propagates toward the minute aperture. Can be generated, and an output signal with a high S / N ratio can be provided. Further, since light is hardly absorbed during propagation, the slider is prevented from being heated, the head can be stably operated, and the operating life is extended.

  Further, the near-field optical head according to the present invention is the above-described near-field optical head, wherein the hole has an inverted conical shape in the slider, and the apex thereof is the minute opening in the slider bottom surface portion. It is characterized by things.

  According to the present invention, in addition to the above-described effect, the light from the minute aperture has the near-field light component as the main component, so that an output signal with a high S / N ratio can be obtained.

  The near-field optical head according to the present invention is characterized in that, in the above-mentioned near-field optical head, a metal film is formed on the inner wall near the apex of the inverted conical hole.

  According to this invention, in addition to the above effects, light leakage and absorption near the top of the hole can be prevented, and more localized near-intensity light with higher intensity can be generated, which is suitable for high-density recording. A near-field optical head can be obtained.

  The near-field optical head according to the present invention is the near-field optical head according to any one of the above, wherein the minute opening is formed by covering a part of the exit of the hole on the slider bottom surface side with a metal film. It is characterized by having.

  According to the present invention, in addition to any of the above effects, it is possible to prevent leakage of light near the minute aperture, generate more localized near-field light, and suitable for high-density recording. A head is obtained.

  According to the present invention, a slider that is supported by a suspension arm that applies a load load, obtains a floating force by relative movement with the recording medium, and creates a gap between the load medium and the recording medium by balancing the load force and the floating force. A hole that penetrates the slider and forms a microscopic aperture on the bottom surface of the slider, and the recording medium interacts with the microscopic aperture via the near-field light when the slider scans the surface of the recording medium. In the near-field optical head that records and reproduces information, the slider is formed of a crystal having a photonic band gap, so that light incident on the slider penetrates the slider. It is impossible to enter any part other than the hole, and almost all light propagates toward the minute aperture. Because an effect that it is possible to provide an output signal of greater capable of generating near-field light intensity and becomes a high S / N ratio. In addition, as described in [Problems to be Solved by the Invention], changes in the light aperture physical properties due to changes in the shape of the light shielding film, unstable operation due to heat conduction to the recording medium, and between the head and the recording medium due to thermal expansion of the head Problems such as difficulty in distance control and damage to the head itself were solved at the same time.

  According to the present invention, in the near-field optical head described above, the hole has an inverted conical shape in the slider, and a vertex thereof is the minute opening in the bottom surface of the slider. Therefore, in addition to the above-described effect, the light from the minute aperture has a near-field light component as a main component, so that an output signal having a high S / N ratio can be obtained.

  According to the present invention, in the above near-field optical head, a metal film is formed on the inner wall in the vicinity of the apex of the inverted conical hole. In addition to the above effect, the apex of the hole Leakage and absorption of light in the vicinity are prevented, and more localized near-field light with higher intensity can be generated, and a near-field optical head suitable for high-density recording can be obtained.

  According to the present invention, in any one of the above near-field optical heads, the minute opening is formed by covering a part of the outlet of the hole on the slider bottom surface side with a metal film. Therefore, in addition to the above effects, it is possible to prevent light leakage near the minute aperture, generate more localized near-field light, and obtain a near-field optical head suitable for high-density recording. There is an effect.

(Embodiment 1)
FIG. 1 shows a schematic structure of a near-field optical head according to Embodiment 1 of the present invention. The near-field optical head 1 comprises a photonic crystal 2 and a light path 3 opened there. Here, a structure such as a protective film is not shown. The photonic crystal 2 has a thickness of about 10 microns, and the light path 3 opened here has a diameter of about 2 microns at the light entrance (wavelength 515 nanometers), and narrows as the light travels through the head. Finally, the minute opening 6 on the bottom surface of the head has a diameter of 100 nanometers. Incident light 4 is guided to the minute aperture 6 through the light passage 3. At this time, since the periphery of the light path is surrounded by the photonic crystal 2, light cannot escape from the path. As a result, extremely high intensity light is generated in the minute aperture 6. Since this minute aperture is smaller than the light wavelength, a light field 7 whose main component is near-field light is formed. This is scattered by the recording medium 5 to become propagating light 8 and is received by a light receiving unit (not shown), thereby reproducing information. Although information reproduction is described here, information recording can be performed by the same mechanism.

  FIG. 2 is a schematic diagram of an information apparatus using the near-field optical head according to the present embodiment. This information device 20 includes a laser oscillator 21, wave plates 22 and 23 for controlling the polarization direction of laser light, an optical waveguide 24 for transmitting the laser light, an optical head 1 having a minute aperture, an optical head driving actuator 30, Controls the position of the lens 29 that collects the scattered light generated by the interaction between the near-field light 7 and the recording medium 33, the light receiving element 25 that receives the scattered light, the output signal processing circuit 26, the control circuit 27, and the recording medium 33. A recording medium drive actuator 34 is provided. The light generated from the laser oscillator 21 is controlled in polarization direction by the wave plates 22 and 23 and guided to the optical head 1 through the optical waveguide 24. As described in FIG. 1, the near-field light 7 generated on the bottom surface of the optical head generates scattered light as a result of interaction with the recording medium 33. Although FIG. 2 shows a structure for detecting scattered light reflected from the recording medium on the upper surface, a structure that transmits the recording medium can be easily made. The scattered light is collected by the condenser lens 29 and converted into an electrical signal by the light receiving element 25. This signal is sent to the output signal processing circuit 26, and after processing such as extraction of signal components, it is sent to the control circuit 27. The control circuit 27 generates a data output 28 based on the received signal, and sends a control signal to the optical head drive actuator 30 and the recording medium drive actuator 34.

  FIG. 3 shows one method for producing a three-dimensional photonic crystal. This is explained in (Susumu Noda, Optics 27, 1, p6, (1998)). In the figure, (A) is a side view and (B) is a top view. In step 1, a thin film GaAs layer 43 to be a photonic crystal is formed on a semiconductor substrate (GaAs) 41. Below the GaAs layer 43 is a stop layer 42 for subsequent etching. In step 2, a stripe structure is formed by electron beam exposure and dry etching. Two wafers thus prepared are overlapped by 90 degrees and heated in a hydrogen atmosphere to perform wafer fusion (step 3). One unnecessary substrate and the etching stop layer are removed by selective etching (step 4). By repeating this process, a three-dimensional photonic crystal is created (step 5).

  FIG. 4 shows a method for producing a near-field optical head according to the present embodiment using the photonic crystal production method described in FIG. Since the creation of the three-dimensional photonic crystal is the same as that shown in FIG. The difference from FIG. 3 is that, in the process of creating the photonic crystal, a minute aperture having a size of about 100 nanometers is created on the bottom surface of the crystal, and a minute passage 51 of light connected therewith is provided. Although it has been described that the stripe structure is created by electron beam exposure in Step 2 of FIG. 3, it is easy to form a cut of about 100 nanometers at this time. By forming a cut of a predetermined size at a predetermined position for each layer of the GaAs layer, when a multilayer structure is formed, the cuts in adjacent layers are adjacent in the vertical direction, thereby forming a light path 51. The On the bottom surface of the slider, the light path can be tapered by making the minute opening smaller than the light wavelength larger as the cut proceeds toward the upper layer. FIG. 5 shows an example of a mask pattern for forming each layer of the photonic crystal. (A) is a mask pattern for forming the bottom surface of the photonic crystal, (B) is a mask pattern for forming a layer above it, and the same applies to the fifth layer (E). Each mask pattern has a pattern 61 corresponding to a place where the GaAs layer 43 is formed and a pattern 62 corresponding to a place where the GaAs layer is removed by etching.

  Basically, it has a periodic structure, which creates a photonic band gap. The pattern 63 corresponding to the light path in the photonic crystal is removed by etching the GaAs layer. As a result, a photonic crystal having a minute light path inside as shown in FIG. 1 is formed.

  By using the photonic crystal thus created as the near-field optical head of the information device described with reference to FIG. 2, light is guided by the mechanism shown in FIG. 1, resulting in high S / N, high sensitivity, A high-density information device was realized.

(Embodiment 2)
FIG. 6 shows a schematic structure of a near-field optical head according to Embodiment 2 of the present invention. The difference from FIG. 1 is that an Al thin film 71 is formed on the inner wall of the light passage 3 near the minute opening 6. Such a structure was prepared by forming Al by vapor deposition, sputtering, CVD, or the like after forming a GaAs stripe pattern in Step 2 of FIG. 4, and removing Al after resist formation. The other structure is the same as that shown in FIG. The incident light 4 that has propagated through the light path 3 becomes thin when the photonic crystal 2 approaches the minute opening 6, so that the band gap is disturbed and light enters the crystal. Since the thin film 71 reflects light, the thin film 71 is efficiently directed to the minute opening 6.

  Thereby, compared with the near-field optical head shown in Embodiment 1, the light efficiency is improved and a highly sensitive information device is realized. In addition, leakage of light from the periphery of the minute aperture 6 can be prevented, and the near-field light 7 is more localized. As a result, the resolution was improved, and a near-field optical head suitable for higher density recording was realized.

(Embodiment 3)
FIG. 7 shows a schematic structure of a near-field optical head according to Embodiment 3 of the present invention. The difference from FIG. 6 is that an Al film is formed on the bottom surface of the slider. In such a structure, an Al film is formed on the bottom surface of the slider created by the method described in FIG. 4 by a method such as vapor deposition, sputtering, or CVD, and then a minute opening is formed by FIB (Focused Ion Beam). Created with. The effect is the same as in the second embodiment, but the creation method is easier.

  Thereby, compared with the near-field optical head shown in Embodiment 1, the light efficiency is improved and a highly sensitive information device is realized. In addition, leakage of light from the periphery of the minute aperture 6 can be prevented, and the near-field light 7 is more localized. As a result, the resolution was improved, and a near-field optical head suitable for higher density recording was realized.

It is a figure which shows schematic structure of the near-field optical head which concerns on Embodiment 1 of this invention. It is the schematic which shows the structure of the information reproducing apparatus using the near-field optical head which concerns on Embodiment 1 of this invention. It is a figure which shows one of the manufacturing methods of a three-dimensional photonic crystal, (A) is a side view, (B) is a top view. It is a figure which shows the method of producing the near-field optical head based on this Embodiment using the production method of the photonic crystal demonstrated in FIG. 3, (A) is a side view, (B) is a top view. . It is a figure which shows the example of the mask pattern for forming each layer of a photonic crystal. It is a figure which shows schematic structure of the near-field optical head which concerns on Embodiment 2 of this invention. It is a figure which shows schematic structure of the near-field optical head which concerns on Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Near-field optical head 2 Photonic crystal 3 Light path 4 Incident light 5 Recording medium 6 Micro aperture 7 Light field 8 Propagating light 20 Information device 21 Laser oscillator 22, 23 Wave plate 24 Optical waveguide 25 Light receiving element 26 Output signal processing Circuit 27 Control circuit 28 Data output 29 Lens 30 Optical head driving actuator 33 Recording medium 34 Recording medium driving actuator 41 GaAs substrate 42 Etching stop layer 43 GaAs layer 51 Light path 61 Corresponding to the place where the GaAs layer 43 is formed Pattern 62 Pattern corresponding to the location where the GaAs layer is removed by etching 63 Pattern corresponding to the light path in the photonic crystal 70 Near-field optical head 71 Al film 80 Near-field optical head 81 Al film

Claims (2)

A slider that is supported by a suspension arm that applies load load and obtains a floating force by relative movement with the recording medium, and creates a gap between the recording medium and the balance between the load load and the floating force;
A hole that penetrates the slider and forms a micro-opening at the bottom of the slider,
When the slider scans the surface of the recording medium in the near-field optical head for recording and reproduction of information by said microscopic aperture and the recording medium via the near-field light interacting,
A near-field optical head characterized in that the slider is formed of a crystal having a photonic band gap. 2. The near-field optical head according to claim 1, wherein a part of the hole has an inverted conical shape in the slider, and the apex thereof is the minute opening in the bottom surface of the slider.

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