Optical device and information recording and reproducing device

Details Optical device and information recording and reproducing device Optical device and information recording and reproducing device

1998-08-27

2001-10-23

Hudspeth, David (Department: 2651)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S112120, C369S112270

Reexamination Certificate

active

06307827

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a device capable of recording or reproducing high density information, or to an optical device that irradiates subjects with microscopic spots of light.
BACKGROUND OF THE INVENTION
A conventional information recording and reproducing device, for example, an SNOM (Scanning Near-Field Optical Microscope), which is described in J. Vac. Sci. technol. B13 (1995) 2813 by S. Hosaka et al., will be explained.
FIG. 9
is a cross sectional view showing a structure of a conventional information recording and reproducing device. In
FIG. 9
, an optical fiber comprises a core
25
having a high refractive index and a clad
26
having a low refractive index surrounding the core. The tip of the cone
25
is sharpened in a conical shape. The clad
26
and a reflective film
27
are formed in a manner in which they surround the sharpened cone. The tip of this cone part faces to a recording film
14
provided on a disc substrate
13
with a small gap &dgr;.
The gap &dgr; is 50 nm or less. The diameter of the tip of the cone part is about 0.1 &mgr;m. When light from aradiation source enters the optical fiber, an evanescent light
29
leaks out from the tip of the cone part. Since the tip is adjacent to the recording film
14
, if the recording film
14
is a phase changeable film, a signal mark
19
having a reflectance that is different from that of surroundings can be formed on the recording film by the thermal energy of the evanescent
29
. Moreover, the signal marks
19
can be confirmed by detecting a reflected scattered light
30
from the recording film
14
by a photo detector
31
.
Such an information recording and reproducing device enables to record and reproduce signals corresponding to the core's diameter of the tip. Thus, if the diameter of the signal mark
19
is 0.1 &mgr;m, an information recording and reproducing device having at least 9 times higher density than a digital video disc (DVD) (the diameter of the signal mark is about 0.3 to 0.4 &mgr;m) can be provided.
The conventional information recording and reproducing device has problems, for example, those shown in FIG.
10
A and FIG.
10
B.
FIG. 10A
shows a main part of the conventional information recording and reproducing device.
FIG. 10B
is a graph showing a distribution of light energy along the direction of light propagation (−z axis) of the device.
In
FIG. 10A
, a guided light
28
propagates in the optical fiber without substantial loss until it reaches the cone part (z>a). In the cone part (a>z>0), however, an incident light
28
a
is divided into a refracted light
28
b
and a reflected light
28
c,
and further the reflected light
28
c
is divided into a refracted light and a reflected light. The reflected light divided repeatedly along the length, that is a, of the cone part. Consequently, the evanescent light
29
radiated from the tip of the cone part is extremely weakened.
In general, if the light energy of the guide light before the cone part is 1, the light energy &eegr; of the evanescent light
29
released from the tip of the cone part is said to be about 10
−7
to 10
−6
. As shown in
FIG. 10B
, the coefficiency of light utilization is extremely bad. Therefore, it takes a long time for recording on the recording film
14
. Thus, the conventional device has a great shortcoming in terms of information transmitting rate, though the high density recording can be achieved.
Moreover, the tip (head) of the cone part is like a dot floating in space. Therefore, heat is liable to converge on the head and deterioration due to a thermal damage can readily occur. Furthermore, in order to stably scan the head while bringing it closer to the recording face
14
, a complex mechanism is required. Furthermore, since the track on the recording film cannot be recognized, it is difficult to realize high density in the track direction.
In addition, in the reproducing principle using the reflected scattered light
30
, only a small part of the reflected scattered light extending broadly in space is detected. Therefore, reproducing sensitivity is extremely poor.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical device and an information recording and reproducing device in which the coefficiency of light utilization is greatly improved, the deterioration due to thermal damage is inhibited, the device head can stably be scanned while being brought closer to the signal surface, the track on the signal surface can be recognized and controlled, and the signal reproduction sensitivity can be greatly enhanced.
In order to achieve the above mentioned object, according to the first aspect of the present invention, an optical device and an information recording and reproducing device comprise a radiation source, a transparent substrate, a waveguide layer provided on the surface of the transparent substrate opposite to the radiation source and an optical coupling means that is provided on the surface of the waveguide layer or on the interface between the transparent substrate and the waveguide layer and that has a concentric circular periodic structure with an optical axis of the radiation source in the center. In the device, the waveguide layer has a cutoff part at the center of the periodic structure, the light from the radiation source excites guided light propagating from the periphery to the center of the periodic structure in the waveguide layer by the optical coupling means, and a part of the guided light leaks out at the cutoff part to a signal surface of a flat substrate provided adjacent to the waveguide layer.
Thus, the transparent substrate is fixed in the same structure as the radiation source and the structure can move relative to the signal surface while being pressed against the signal surface by using a pressing means.
According to the second aspect of the present invention, an optical device and an information recording and reproducing device comprise a radiation source, a light collecting means that converts light radiated from the radiation source to parallel light, a transparent cone part having an optical axis of the parallel light as a central axis, a transparent buffer layer formed on the lower surface of the cone part, a waveguide layer formed on the buffer layer. In the device, the waveguide layer has a cutoff part at the central axis of the cone part; the refractive index of the cone part is larger than the refractive index of the waveguide layer, which is larger than the refractive index of the buffer layer; the parallel light is refracted at the surface of the cone part, passes through the buffer layer and enters the waveguide layer to excite the guided light propagating from the periphery to the center in the waveguide layer; and a part of the guided light leaks out ran at the cutoff part to the signal surface of the flat substrate provided a,adjacent to the waveguide layer.
Thus, the transparent substrate is fixed in the same structure as the radiation source and the structure can move relative to the signal surface while being pressed against the signal surface by using a pressing means.
It is preferable in the above mentioned first optical device and information recording and reproducing device of the present invention that the transparent substrate is fixed in the same structure as the radiation source, the structure moves relative to the signal surface while being pressed thereon by a pressing means, and the structure floats while facing to the signal surface having an air layer between the surface of the waveguide layer and the signal surface.
It is preferable in the above mentioned second optical device and information recording and reproducing device of the present invention that the cone part is fixed in the same structure as the radiation source, the structure moves relative to the signal surface while being pressed thereon by a pressing means, and the structure floats while facing to the signal surface having an air layer between the surface of the waveguide

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