JPH07192280A - Near-field optical scan recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the accuracy of tracking control and to make a disk- shaped recording medium usable in the case of a high-density recording/ reproducing utilizing evanescent light. CONSTITUTION:Laser beams radiated from a semiconductor laser 1 are converged by a lens 6 and applied through an opening 8 to an optical fiber. A scanning head 9 formed at the head part of the tip of the optical fiber 7 is provided with an opening 10, of which diameter is equal or smaller than the wavelength of the laser beam, on a projecting end face and a recording plane 11 is moved relatively to the opening 10. The reflected light extracted from the recording plane 11 through a scanning head 9 is detected by a photodetector 13. A scanning control head 20 integrally juxtaposed at the scanning head 9 is provided with a semiconductor laser 15 as its own original light source, lens system and optic/electric converting element 19 and generates a tracking error detect signal for matching the position of the scanning head 9 with the track of the recording plane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a near-field optical scanning recording / reproducing apparatus for recording or reproducing an information signal using evanescent light.

[0002]

2. Description of the Related Art Information signal light emitted from a light source such as a semiconductor laser is focused by a lens and applied to a recording medium, and an information signal is recorded by partially changing the reflectance or polarization characteristics of the recording medium. Is commonly done. The use of light with a short wavelength and the increase of the numerical aperture of the lens to increase the resolution can increase the density of recording or reproducing the information signal, but there is a limit. Since the focusing of light using a lens is accompanied by a diffraction phenomenon, the lower limit of the diameter of an imaging spot that can be generated by imaging visible light or near infrared light on the recording surface of a recording medium is around 1 μm.

However, even with a traveling wave that causes such a diffraction phenomenon, if a localized wave (evanescent light) localized in a minute region smaller than the wavelength is used, a spot with a smaller diameter can be obtained. Obtainable.

The evanescent light has a characteristic that it is localized in a minute region smaller than the wavelength and does not propagate light energy to the outside. However, while the normal traveling wave does not propagate to the outside through the aperture smaller than the wavelength, the evanescent light can propagate to the outside through the aperture if it is about the wavelength or less.

Therefore, when an aperture that is approximately equal to or smaller than the wavelength of the laser light used is brought close to the recording surface at a distance of about the wavelength or less, the light energy can be concentrated in the minimum area of the recording surface. It is possible to write or read signal pits. In other words, when the laser light is incident on the high refractive index medium (base) so as to be capable of total reflection and the evanescent light is generated on the surface of the base that is a low refractive index medium (air), it is recorded in a minute area. Signal pits can be detected. Further, the signal pit can be written by the evanescent light given through the minute opening.

Such a technique is known by the name of a photon scanning tunneling microscope (photon STM), and its transmission type will be described below with reference to FIG.

Laser light of a predetermined wavelength emitted from the semiconductor laser 1 passes through the collimator lens 2 and becomes parallel rays. When this is made to enter the prismatic dielectric base 3 from the inclined lower surface as reference light for reproducing operation, the incident light reaches the upper surface of the base 3, but the light incident angle on the upper surface is the refraction of the base 3. Since the angle is larger than the critical angle for total reflection determined by the index, total reflection occurs. The totally reflected light is not used as it is and is discarded, but the evanescent light becomes localized in the air layer from the upper surface of the base 3 up to about the wavelength.

The probe 4 for taking in the evanescent light is made of an optical fiber and has an opening with a core diameter of several tens nm on the tip end surface of the tapered tip. And
Since this opening scans the plane separated by about 10 nm from the upper surface of the base 3 in one dimension or in two dimensions, the evanescent light is captured by the probe 4 through the aperture, and the captured light is detected by the photodetector 5. It is photoelectrically converted. That is, the information signal recorded on the upper surface of the base 3 in the form of unevenness or light and shade can be read. Since evanescent light is converted into a normal traveling wave in the optical fiber,
The probe 4 transmits light energy as a normal optical path.

When recording an information signal, a light wave is made incident from the probe 4 side. By concentrating the evanescent light generated in the vicinity of the opening at the tip of the probe 4 in a minute area on the upper surface of the base 3, signal pits can be recorded in the form of unevenness or light and shade.

Of course, magneto-optical recording in which the polarization characteristic of the upper surface of the base 3 is partially changed by the information signal light is also possible. Since the distribution of the reflection intensity of the evanescent light can be made into a map by scanning the probe 4 two-dimensionally, there is also a method of use as a high-resolution microscope capable of directly observing the surface shape. There is also known a reflection resonance type photon STM or the like in which the optical fiber itself has Fabry-Perot resonance characteristics and the shift of the resonance frequency which changes according to the surface shape of the recording medium is detected by the optical phase synchronization technique.

[0011]

[Problems to be Solved by the Invention]
When the information signal is reproduced using the TM, tracking control is required to track the opening of the probe on the target recording line or recording pit of the recording medium, but the probe is used for fine recording lines or recording pits. It was not easy to accurately track the aperture of.

Therefore, it is an object of the present invention to perform high-density recording and reproduction using evanescent light with high accuracy and good trackability, and to use a disc-shaped recording medium in a near-field. An object is to provide an optical scanning recording / reproducing device.

[0013]

In order to achieve the above-mentioned object, the present invention introduces a semiconductor laser that emits a laser beam of a predetermined wavelength, a lens that focuses the laser beam, and a laser beam that is focused by the lens. An optical fiber that has an opening for forming a scanning head with a tapered tip and has an opening on the tip end surface of the scanning head that has a diameter approximately equal to or smaller than the wavelength of the laser beam; A photodetector that detects the reflected light extracted from the recording surface of the medium through the opening of the scanning head, an actuator that moves the scanning head to align the opening of the scanning head with the track on the recording surface, and an integral part of the scanning head Scanning that has a light source, a lens system, and a photoelectric conversion element that are arranged side by side, and optically scans the recording surface to generate a tracking error detection signal necessary for driving the actuator. Near-field optical scanning recording reproducing apparatus characterized by comprising a control head is provided.

[0014]

According to the present invention, the optical fiber for introducing the focused laser beam has the scanning head at the tapered tip end, and the projection end face of the scanning head has an opening having a diameter substantially equal to or smaller than the wavelength of the laser beam. Therefore, the information signal can be recorded / reproduced with high resolution by the evanescent light. Further, since the scanning control head that is integrally arranged in parallel with the scanning head moves together with the scanning head and generates the tracking error detection signal necessary for scanning the scanning head,
The scanning head can be always positioned on a predetermined recording track with good trackability, and fine recording tracks can be arranged at high density. In addition, since the evanescent light is applied from the recording surface side in both recording and reproduction, a disc-shaped recording medium can be used.

[0015]

EXAMPLE An example of the present invention will be described below with reference to FIGS.

In the configuration shown in FIG. 1, the semiconductor laser 1
The information signal light emitted from the optical system is focused by the coupling lens 6 and enters the optical fiber 7 through the opening 8. The optical fiber 7 has a scanning head 9 at its tip, and the optical fiber portion of the scanning head 9 is narrowed down in a tapered manner. Then, the diameter (core diameter) of the opening 10 at the projecting end face is set to several tens nm. The opening 10 faces the recording surface 11 of the recording medium with a minute gap of about 10 nm.

Since the wavelength of the laser light used is around 700 nm, the diameter of the opening 10 is very small compared to this. Therefore, the traveling wave that is normally observed cannot pass through the opening 10, but only the evanescent light localized near the opening 10 reaches the recording surface 11 through the opening 10 and its optical energy is transmitted to the recording surface 11. The information signal can be transmitted and recorded.

When reproducing the information signal, the focused laser light is applied to the optical fiber 7 through the opening 8. The evanescent light that irradiates the recording surface 11 through the opening 10 of the scanning head 9 is diffracted or absorbed by the recording surface 11 and returns to the opening 10 to be converted into a traveling wave in the optical fiber 7. Then, it is guided to the photodetector 13 via the splitter 12 provided in the middle of the optical fiber 7. Photodetector 13
The electric signal photoelectrically converted by is input to the monitor / output device 14 or other signal processing device.

A scanning control head 20 including a semiconductor laser 15, first and second reflecting surfaces 16 and 17, an objective lens 18 and a photoelectric conversion element 19 is integrally arranged in parallel with the scanning head 9. The scanning control head 20 has a compact structure and moves together with the scanning head 9 to generate a tracking error detection signal or the like necessary for scanning.

The light emitted from the semiconductor laser 15 is reflected by the first reflecting surface (hyperbolic surface) 16 and then converted into parallel rays by the second reflecting surface (parabolic surface) 17. Then, the light is focused by the objective lens 18 formed of a micro Fresnel lens to form an image on the recording surface 11.

The imaging spot generated by this imaging produces ± first-order diffracted light as described later by a tracking pregroup (not shown). The 0th-order diffracted light and the ± 1st-order diffracted light of regular reflection return to the first reflecting surface 16 via the objective lens 18 and the second reflecting surface 17. Since a grating or a hologram that gives a deflecting action to the incident light is formed on the whole or a part of the first reflecting surface 16, a part of the returning light is incident on the photoelectric conversion element 19.

As shown in FIG. 2, the photoelectric conversion element 19 has four elements.
It has divided sensor areas S1, S2, S3, S4, and the output of the photodiode forming each sensor area can be taken out separately. Then, each output is calculated to analyze the pattern of the imaging spot, and an error detection signal necessary for each control of focus and tracking of the scanning head 9 is obtained. Four sensor areas S1,
When the outputs of S2, S3, S4 are P1, P2, P3, P4, the focus error detection signal FE is the sum (P1) of the outputs P1, P4 of the sensor areas S1, S4 on both sides.
+ P4) and the outputs P of the remaining sensor areas S2 and S3
2. Take the difference from the sum of P3 and (P2 + P3). That is,
The focus error detection signal FE is obtained by applying the beam size method in which the size of the imaging spot is detected on the sensor to detect the magnitude of defocus.

Regarding the tracking error detection signal TE, the difference between the sum (P1 + P2) of the outputs of the two sensor areas S1 and S2 in the left half and the sum (P3 + P4) of the outputs of the two sensor areas S3 and S4 in the right half is calculated. To take. That is, the tracking error detection signal TE is obtained by applying the push-pull method for comparing the balance of the interference intensities of the ± 1st-order diffracted light and the 0th-order diffracted light generated in the pregroup of the recording surface 11.

When the actuator 21 is drive-controlled using the signal obtained by such photoelectric processing, both the scanning head 9 and the scanning control head 20 are moved in the horizontal direction (track direction) along the pregroup of the recording surface 11. It can be moved stably in the vertical direction (focus direction).

The signal pit has a diameter of about 50 nm on the recording surface 11.
However, a buffer 23 is provided to increase the accuracy. This buffer 23 is used for the scanning head 9
Plays a role of absorbing an undesired movement (vertical vibration) in the focus direction that occurs when the scanning control head 20 is driven.

Next, the tracking drive and buffer 2
The operation of No. 3 will be described with reference to FIG. The light emitted from the semiconductor laser 15 which is the light source of the scanning control head 20 is focused by the lens system to reach the recording surface 11, and is reflected or diffracted by the recording surface 11 to be the + 1st order light A and the −1st order light B.
And 0th order light C. Then, it returns to the scan control head 20 and undergoes the photoelectric processing as described above, and the focus error detection signal FE and the tracking error detection signal TE are received.
To occur.

The scanning head 9 is fixed to the air slider 22, and the recording surface 11 moves slightly at a high speed so that the recording surface 11 slightly floats and its height is kept constant. Further, a shock absorber 23 is provided between the scanning head 9 and the main body portion connected to the scanning head 9 for absorbing undesired shaking. That is, since the dynamic range of fluctuation of the main body portion in the vertical direction is greatly different from that of the scanning head 9, the distortion due to the difference is absorbed by the buffer 23.

The shock absorber 23 can be constituted by a coiled spring as shown in the figure, a leaf spring used in a hard disk or the like, but it must provide a cushioning action only in the vertical direction, and it must be in the track direction. It is important not to cause shaking. According to this structure, even if the main body portion shakes in the vertical direction, the distance between the opening 10 of the scanning head 9 and the recording surface 11 can be constantly maintained at a predetermined value.

Since the plurality of signal pits 24 are lined up in one land portion (on the track) of the recording surface 11, the tracking error detection signal (TE signal) and the deviation amount of the scanning head 9 are represented by the characteristic curve shown in FIG. If set so as to follow, the scanning head 9 scans the target portion (level) on the track with good tracking performance while the trajectory is corrected by the TE signal in the direction perpendicular to the track.

As described above, since the scanning head 9 can be displaced by a slight amount in the direction perpendicular to the track by the offset action by the tracking error detection signal, the scanning head 9 having the minute aperture 10 is used in the conventional optical system. It is possible to achieve a high-density recording / reproducing operation that could not be obtained.

[0031]

As described above, according to the present invention, a high-resolution recording / reproducing operation utilizing an evanescent light is obtained by using a scanning head having a minute aperture. Since the actuator is driven by the tracking error detection signal generated by arranging the scanning control head in parallel with the scanning head, the scanning head can be accurately positioned on a predetermined track. Further, it becomes possible to use a disc-shaped recording medium.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a near-field optical scanning recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a signal generation circuit diagram of a photoelectric conversion element according to an embodiment of the present invention.

FIG. 3 is a perspective view of a main part of a near-field optical scanning recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 4 is a TE signal-deviation amount characteristic diagram of a near-field optical scanning recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of a transmissive photon STM.

[Explanation of symbols]

 1 Semiconductor Laser 7 Optical Fiber 9 Scanning Head 10 Opening 11 Recording Surface 20 Scanning Control Head 21 Actuator

Claims (2)

[Claims] 1. A semiconductor laser that emits a laser beam of a predetermined wavelength, a lens that focuses the laser beam, an opening that introduces the laser beam focused by the lens, and a scanning head is formed by a tapered tip portion. And the reflected light extracted from the recording surface of the recording medium through the opening of the scanning head, and the optical fiber that has an opening with a diameter that is approximately equal to or smaller than the wavelength of the laser light on the projecting end surface of the scanning head. It has a photodetector for detection, an actuator that moves the scanning head to align the aperture of the scanning head with the track on the recording surface, and a light source, a lens system, and a photoelectric conversion element that are installed in parallel with the scanning head. And a scanning control head that optically scans the recording surface to generate a tracking error detection signal necessary for driving the actuator. Recording and reproducing apparatus. 2. A near-field optical scanning recording / reproducing apparatus according to claim 1, wherein the scanning head is mounted on a buffer which absorbs deviation in a direction perpendicular to the recording surface.