JP4395610B2 - Optical head with semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical head on which a semiconductor laser is mounted and information is recorded on an optical disk using near-field light .
[0002]
The present invention also relates to an optical head on which a semiconductor laser and a magnetoresistive element are mounted and information is recorded and reproduced using near-field light .
[0003]
[Prior art]
As an external storage device of a personal computer, there are magnetic recording such as HDD and FDD, and optical recording such as MO, CD-R, DVD-RAM and the like. The reason is that (1) the program size is enlarged due to the high functionality of applications and OS, and (2) the virtual storage area to be secured 1.5 to 2 times the normal main storage capacity as the main storage capacity increases. Several hundreds of megabytes are required for the increase and caching of CD-RAM, etc. (3) Accumulated data increases without the user's awareness due to the spread of the Internet, (4) Due to the spread of digital video There are increasing demands for recording images on a disc, and (5) there is a demand for installing a server for each home.
[0004]
In response to such demands for large capacity, the adoption of MIG (Metal in Gap) heads, thin film heads to MR (Magneto Resister) heads, and the adoption of giant magnetoresistive elements, that is, GMR (Giant Magneto Resister) heads. The surface recording density of HDD, which is magnetic recording, is increasing.
[0005]
Recently, Seagate in the United States has achieved a recording density of 23.8 Gb / in ² in response to this increase in capacity.
[0006]
On the other hand, optical disc recording has been developed since the introduction of a consumer-use He-Ne laser-equipped video disc by Philippe in 1972, and at present, a recording capacity of 18 Gbytes has been achieved with a double-sided four-layer DVD.
[0007]
In recent years, nanoprobe technology based on near-field optics has attracted attention as high-density recording. However, as the tip of the nanoprobe becomes sharper, the light intensity ratio of the emitted evanescent wave to the incident light is attenuated by 7 to 9 digits.
[0008]
[Problems to be solved by the invention]
In the conventional magnetic recording, when the surface recording density is extremely increased, there is a problem that the data written in the magnetic recording layer loses data with the lapse of time due to the thermomagnetic relaxation phenomenon. Is said to have a limit of a recording density of 50 Gb / in ^{2 to} 100 Gb / in ² .
[0009]
Also, in conventional optical disk recording, when the laser beam is narrowed down using a lens or the like, the beam diameter can be narrowed only to about the wavelength of the laser that is the light source due to the diffraction phenomenon of the light wave, so a 410 nm ultraviolet laser is used. Even so, the surface recording density is said to be about 20-30 Gb / in ^{2 as} the limit of optical recording. Furthermore, the high-precision optical components used are expensive and costly. In other words, both magnetic recording and optical recording will soon reach the limit of recording density.
[0010]
In addition, nanoprobe technology based on near-field optics has not achieved results of application of near-field optics having a high surface recording density higher than the recording density of current optical discs.
[0011]
In order to solve this problem, an object of the present invention is to provide an optical head capable of performing high-density recording on an optical disk using near-field optics without attenuating the amount of laser light.
[0012]
[Means for Solving the Problems]
As a currently obtained short wavelength semiconductor laser light, a wavelength of 635 nm is used, and a pyramid-shaped special optical prism whose tip is sharpened to 90 nm using a semiconductor material which is transparent at this wavelength and has a high refractive index, for example, GaP crystal. When a 635 nm laser beam is made incident from the bottom surface, the half wavelength in the prism becomes 88 nm. Therefore, if the prism tip is a flat surface with a diameter of 90 nm, the laser beam is emitted without any attenuation. By keeping this tip at a distance of about 50 nm or less on the magneto-optical disk medium by using the principle of a contact head or a flying head, an extremely small beam spot can be formed without using a lens.
[0013]
In the present invention, a high refractive index prism material is provided on the output end face of a semiconductor laser, the tip is formed on a plane having a diameter of 90 nm or 90 nm, and the distance between the tip and the optical recording medium is maintained at a distance where near-field optics acts. An optical head for recording on a magneto-optical recording medium is provided.
[0014]
Further, the present invention comprises a semiconductor laser element and a high refractive index trapezoidal prism material provided on an output end face of the semiconductor laser element, and a light wave incident on the front end portion of the high refractive index trapezoidal prism substance. When the wavelength is λ and the refractive index of the trapezoidal prism material is n, the tip opening size is formed to be approximately λ / 2n, and the gap between the tip and the optical recording medium is a λ / 4 wavelength or less. Provided is an optical head for recording on a magneto-optical recording medium by near-field optics, which propagates ordinary light waves within the prism material with almost no attenuation.
[0015]
Further, the present invention provides a semiconductor laser element for generating a laser in a material of a high refractive index prism by providing a high refractive index prism (Tongari pyramid) having a tip formed on a plane having a diameter of 90 nm or 90 nm square on the output end face. And a magnetoresistive element integrated with the semiconductor laser element, and optically performing high-density recording / reproduction with respect to the optical recording medium by near-field optics only for a small distance between the prismatic substance and the optical recording medium. Provide the head.
[0016]
Further, according to the present invention, when λ = 650 nm and n = 3.3, a semiconductor laser element provided with a Tongari pyramid having a tip portion formed on a plane having a diameter of 90 nm or 90 nm square on the output end face, and the semiconductor Provided is an optical head that includes a magnetoresistive element integrated with a laser element and performs high-density recording / reproducing with respect to an optical recording medium by near-field optics.
[0017]
The present invention also provides a laser obtained by returning the intensity of reflected light from a recorded bit of an optical recording medium to a semiconductor laser in a semiconductor laser in which a high refractive index trapezoidal prism-shaped substance for recording is provided on the laser emission surface. An optical head including means for detecting return light induced noise is provided.
[0018]
According to the present invention, optical recording can be performed with a size of about 1/10 of the wavelength. Moreover, almost 100% of the laser output can be used for recording. As the optical recording medium, a TbFeCo perpendicular magnetic medium or a phase change recording medium such as GeSbTe is used. There are two methods for detecting the recording bit at this time, that is, reproducing the recorded information. The first method is a method of detecting a change in magnetization using a giant magnetoresistive element (GMR). In the second method, a thin quarter-wave plate is installed at the output part of the semiconductor laser, and the linearly polarized wave from the semiconductor laser is converted into a clockwise circularly polarized wave. The magneto-optical disk shifts the reflection phase by π rad and returns to the quarter wave plate again. Passing through this wave plate, the counterclockwise circularly polarized wave becomes a linearly polarized wave that is different from the linearly polarized wave by π / 2 rad in the laser (that is, they are orthogonal to each other). The Kerr rotation angle is superimposed on both by the magneto-optical signal. In other words, a phase difference due to Kerr rotation occurs between the two. This phase difference appears as a frequency difference of light. By detecting this beat signal with a high-speed photodiode, the signal can be reproduced.
[0019]
In the present invention, the recording / reproducing head is constituted by a semiconductor laser chip + GMR chip in the first method. In the second method, a semiconductor laser chip + special semiconductor laser chip is used. All the sizes are about 1 mm ³ . Attach this to the flying head slider of the hard disk. It is almost the same size as a magnetic disk drive and realizes a surface recording density three times that of a magnetic disk drive. A large capacity of 30 GB can be realized with a 3.5 inch disk.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an optical head according to an embodiment of the present invention. According to this, the optical head 11 is disposed opposite to the magneto-optical disk 12 rotated by a disk drive motor (not shown), and attached to the tip of the suspension 13 driven by the head position moving motor. Recording can be performed by near-field optics by setting the distance between the optical head 11 and the magneto-optical disk 12 to 50 nm or less.
[0021]
As shown in FIGS. 2A and 2B, the optical head 11 is constituted by an edge-emitting semiconductor laser or a Bixel laser 20. This semiconductor laser 20 is composed of an edge emitting InGaAIP III-V group compound semiconductor laser element 21 oscillating at about 635 nm. A probe 22 made of a Tongari prism ( high refractive index trapezoidal prism) made of, for example, a GaP crystal is provided on the output end face of the semiconductor laser element 21. The high refractive index trapezoidal prism 22 has a tip portion size of (λ / 2n) which is the wavelength in the tube (that is, the wavelength of the light wave propagating in the prismatic material) in the prismatic material of the semiconductor laser element. It is finely processed. High performance antireflection films 23 and 24 are formed on the end face of the semiconductor laser element 21 and the bottom face of the Tongari prism 22, respectively. Further, a leakage preventing / reflecting film 25 is formed on the side surface of the Tongari prism 22 except for both bottom surfaces so that light does not leak. Further, a photodiode 26 is provided on the other end face of the semiconductor laser 21.
[0022]
The bixel laser 20 having the above configuration is attached to a heat sink 27 having three legs as shown in FIG. The heat sink 27 is attached to and held on the suspension 13 via a gimbal 28. At this time, the gap between the tip of the Tongari prism 22 and the optical disk 12 is ≦ λ / 4.
[0023]
The tip of the Tongari pyramid of the probe 22 is polished to a plane having a diameter of about 90 nm or 90 nm . The half-wavelength (λ / 2n) size of a 635 nm laser beam, such as a GaP crystal, is about 80 nm because the refractive index n is very large (about 3.5). The plane having a diameter of about 90 nm or 90 nm is also formed by the high-performance antireflection film.
[0024]
As described above, according to the present embodiment, the trapezoidal prism material having a high refractive index is disposed on the output end face of the semiconductor laser, and the size of the opening at the tip of the trapezoidal prism is approximately the in-tube wavelength ( Ultra-fine processing is performed so as to satisfy (λ / 2n), and a leakage prevention film / reflection film is formed so that light does not leak except for the opening at the tip.
[0025]
With the above configuration, 100% of the semiconductor laser light incident on the Tongari pyramid 22 can reach the tip of 90 nm. This is quite different from the nanoprobe technology for generating evanescent waves with very low efficiency.
[0026]
One of the previous research results is contact head technology using tripart and thin lubricant. By applying this contact head technology, the above-mentioned Tongari cone or Tongari pyramid can be made to correspond to an optical disk medium with a constant accuracy of a gap of 10 nm to 30 nm.
[0027]
As described above, the 635 nm laser beam reaching the tip of the Tongari pyramid 22 reaches the optical disk medium surface with the same size, that is, with a diameter of 80 nm to 90 nm without being attenuated at all. The leather power required for optical recording with a pit size of 80 nm to 90 nm diameter is only 100 μW or less. Therefore, the laser oscillation output required for the optical head of the present invention is sufficient to be only 1 mW or less.
[0028]
On the other hand, the output of a 635 nm semiconductor laser used for DVD-RAM is 30 to 50 mW. The fact that only a small amount of power is required in the optical head of the present invention means that an extremely high bit rate is possible. The phenomenon in which the terminal voltage of the semiconductor laser changes by about 0.5% due to the light returning to the semiconductor laser has already been clarified by studies of lensless floppy disks so far.
[0029]
When a phase change medium (PCR) such as GeSbTe is used as the optical recording medium, it exhibits an amorphous (a) or crystal (c) state depending on the light irradiation time and power. Since the reflectance differs between the amorphous state (a) and the crystal state (c), for example, 10% and 30%, respectively, it is possible to detect a change in the terminal voltage of the semiconductor laser with a high SN if the optical disk medium is used as an external mirror. .
[0030]
When a magneto-optical medium typified by TbFeCo is used as the optical recording medium, signals can be detected or reproduced by the following two methods. (1) Method of detecting change in magnetization with a high-sensitivity giant magnetoresistive element and (2) Semiconductor laser chip by the method of SPIE document “Orthogonal Linear Polarized Laser Waves Oscillation in a Thin Fi1m Integrated Laser Chip for MO Disk Signal Detection” The MO signal can be detected simply by coating a thin film on the substrate.
[0031]
Both of the above two methods can form a very small and light head (1 mm ³ or less).
[0032]
Next, the recording / reproducing optical head will be described. This recording / reproducing optical head is configured as shown in FIG. In other words, the optical head 31 is integrally combined with the Bixel laser 20 and a magnetoresistive element, for example, a GMR (Giant Magnet resistance) element 32. In this case, the bixel laser 20 and the GMR element 32 are arranged side by side in the rotation direction. The bixel laser 20 and the GMR element 32 are attached to a heat sink 33, and the heat sink 33 is attached to the tip of a suspension 34 (corresponding to the suspension 13 in FIG. 1) via a gimbal 35. The tips of the three legs of the heat sink 33 are provided with diamond-like coating (DLC) 33a. Accordingly, the optical head 31 slides on the optical disk 12 via the coating 33a and the lubricant (for example, PFPE) 36 applied to the optical disk 12.
[0033]
The optical disk 12 has a laminated structure of a glass substrate 12a, an optical recording medium (for example, TbFeCo perpendicular magnetization magneto-optical medium) 12b, and a disk protective film (for example, α-carbon) 12c.
[0034]
The bixel laser 20 of the optical head 31 shown in FIG. 3A has the same structure as that shown in FIG. In other words, an antireflection film is formed on the laser output end surface and the upper and lower bottom surfaces of the laser output end surface and the prism trapezoidal high-refractive index material at the semiconductor laser wavelength by being in close contact with the output end surface of the semiconductor laser. The portions other than both bottom surfaces are covered with a light reflectivity material such as a gold film. Such a recording optical head is opposed to the magneto-optical or thermomagnetic recording medium surface with a separation of λ / 4.
[0035]
On the other hand, a magnetoresistive element (reading a change in resistance with an element such as GMR or TMR) 32 is provided for detecting a change in magnetic flux density or magnetization direction in accordance with a change in magnetization of a recorded fine bit.
[0036]
According to the optical head shown in FIG. 3B, a phase change medium (for example, GeSbTe) is coated with a protective film (for example, an amorphous carbon film having a thickness of 2 nm to 5 nm) and a lubricant 36 is coated on the optical disk 12. A contact head or slider head (flying head) is installed, and the flying head or contact head 31 is kept substantially parallel to the optical disk surface by the gimbal 34. The optical head 31 is held by the suspension 34 so that the distance between the optical disk 12 and the head 31 is maintained at ¼ or less of the laser wavelength.
[0037]
The optical head 31 is composed of a semiconductor laser chip and a material having a high refractive index prism shape. The upper and lower bottom surfaces of this material are coated with an antireflection film having a laser wavelength. A light reflectance film is coated except for the bottom surfaces.
[0038]
The recorded bit has different reflectivity depending on whether it is amorphous or crystal. The reflected light returns to the semiconductor laser and the oscillation of the semiconductor laser changes. The signal is read by directly observing the change in the terminal voltage of the semiconductor laser or the change in the laser output.
[0039]
As shown in FIG. 4, the GMR element 32 is attached between a pair of elements 43 formed by bonding a permanent magnet 41 and an electrode plate 42 together.
[0040]
An operation of recording data on the magneto-optical disk 12 by the optical head 31 that is configured as described above and in which the Bixel laser 20 and the GMR element 32 are integrally combined will be described.
[0041]
As shown in FIG. 1, when the magneto-optical disk 12 is rotated by a magneto-optical disk drive (not shown), the optical head 11 is about 10 to 30 nm from the magneto-optical disk 12 with a lubricant 36 (FIG. 3) interposed. Spaced apart. At this time, when the bixel laser 20 of the optical head 11 is driven according to the recording data, a micro beam laser is emitted from the tip of the probe (tongali pyramid or tongaric cone) 22 of the bixel laser 20. The direction of magnetization of the magneto-optical disk is reversed with a diameter of about 50 nm to 80 nm by the heat of the laser and the external magnetic field. That is, the direction of magnetization is different between the portion irradiated with the laser and the portion not irradiated with the laser. As a result, “0” and “1” signals are recorded. That is, data is recorded on the magneto-optical disk 12 by near-field optics.
[0042]
Although not shown, a magnet that gives the direction of the magnetic field is also provided. This is the same structure as a normal MD disk head.
[0043]
As described above, in the present invention, since the semiconductor laser beam is recorded by near-field optics without being squeezed by the lens as in the present magneto-optical recording (MO), the laser wavelength is not affected by the lens diffraction. The spot diameter can be reduced below.
[0044]
When data recorded on the magneto-optical disk 12 is reproduced, a constant current is passed through the GMR element 22 with the optical head 31 separated from the magneto-optical disk 12 by 10 nm to 30 nm. The resistance of the GMR element 32 changes according to the magnetization direction of the magneto-optical disk 12, and the current flowing through the GMR element 32 changes accordingly. This change in current is taken out as a reproduction signal. As a result, the data recorded on the magneto-optical disk 12 is reproduced.
[0045]
In the above-described embodiment, an optical head of 1 Vxel element and 1 G MR element is provided. However, as shown in FIGS. 5 (a) and 5 (b), the present invention provides a 100 × 100 Vic cell array and 200 × 200 It can also be applied to an optical head using a sensitive G MR array for signal detection. In this case, a silicon pyramid array made of a high refractive index material is formed by a microelectromechanical etching technique. As a result, as shown in FIG. 5, the tips of the pyramids can be made uniform. Therefore, the tips of the pyramid array are aligned and close to the optical disc.
[0046]
【The invention's effect】
According to the present invention described above, it is possible to laser light is emitted without attenuation by the prism tips of probe comprising a high refractive index material of the semiconductor laser on the flat surface of the 90nm diameter, light the tip By keeping the distance of about 50 nm or less on the magnetic disk medium using the principle of a contact head or a flying head, an extremely small beam spot can be formed without using an objective lens. Thereby, high-density recording can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram showing an optical head and a magneto-optical disk according to an embodiment of the present invention. FIG. 2 is a diagram showing a structure of a bixel element used in an optical head according to an embodiment of the present invention. FIG. 4 is a diagram showing the structure of an optical head composed of a Bixel laser and a magnetoresistive element according to another embodiment of the invention; FIG. 5 is a diagram showing a configuration of an optical head using a big cell array.
DESCRIPTION OF SYMBOLS 11 ... Optical head 12 ... Magneto-optical disk 13 ... Suspension 20 ... Biccell laser 21 ... Biccell laser element 22 ... High refractive index trapezoid prism 22 23, 24 ... Antireflection film 25 ... Leakage prevention film / reflection film 26 ... Photodiode 27 ... Heat sink 28 ... Gimbal 31 ... Recording / reproducing optical head 32 ... GMR element 33 ... Heat sink 34 ... Suspension

Claims (7)

A semiconductor laser element and an opening tip provided on the output end face of the semiconductor laser element, and the light wave incident on the opening tip is approximately one half of the wavelength at which the inside of the opening tip propagates. formed to have a size, and the opening tip and 1 or less of a gap substantially quarter of a wavelength of the light wave is incident between propagates the inside of the opening tip portion of the optical recording medium, the opening tip An optical head for recording on an optical recording medium with near-field light that propagates a normal light wave with almost no attenuation inside the unit.   The optical head according to claim 1, wherein the semiconductor laser element is a surface emitting laser element.   The optical head according to claim 1, further comprising a heat sink attached integrally to the semiconductor laser. 4. The optical head according to claim 1, wherein the semiconductor laser element includes an edge-emitting InGaAIP III-V group compound semiconductor laser that oscillates at approximately 635 nm. A semiconductor laser and an opening tip provided on the output end face of the semiconductor laser, and the size of the opening tip is approximately one half of the wavelength at which the incident light wave propagates inside the opening tip. An optical head that is ultrafinely processed so that a leakage prevention film and a reflection film are formed so that light does not leak except at the tip of the opening.   Detects return light-induced noise of the laser obtained when the reflected light intensity from the recorded bit of the optical recording medium returns to the semiconductor laser in the semiconductor laser with a prismatic high refractive index substance for recording on the laser emission surface. An optical head including means for performing. An optical head installed on an optical disk in which a phase change medium is coated with a protective film and a lubricant is applied thereon, and is held at a distance of 1/4 or less of the laser wavelength with respect to the optical disk. is composed of a high refractive material of the tip and the prism trapezoidal, said the bottom surface and bottom surface on the high refractive index material of the prism trapezoidal antireflection film of the laser wavelength is formed, the light reflectance film except both bottom An optical head on which is formed.

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