JPS63113947A - Multi-wavelength write type optical element - Google Patents

Abstract

PURPOSE:To easily attain simultaneous or time division write by receiving the rays of light having plural wavelengths simultaneously or in time division from a light source and focusing the light of each wavelength onto the optical recording layer of a recording medium corresponding to the light of each wavelength independently. CONSTITUTION:A collimated pulse light having different wavelength emitted from laser light sources 35-36 via a collimate lens is reflected in half mirrors 32-34 and focused 44, 43, 42 onto optical recording layers 38-40 corresponding to the light of each wavelength of the optical recording medium 41 through the optical element (e.g., Fresnel plate) 31. Thus, simultaneous recording or quick time division recording is applied to the multi-layer recording medium by using a wavelength multiplex light.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multi-wavelength writing type optical element, and in particular, it has a multi-layer structure, and each layer has a maximum energy absorption efficiency in a different wavelength range. When performing optical recording on a wavelength multiplexed multilayer optical recording medium, which can perform optical recording by changing the reflectance and transmittance of each layer by light irradiation, each recording layer can be recorded simultaneously or over time. The present invention relates to an optical element that can distribute optical energy by dividing it.

[Prior Art] In recent years, many optical recording media have been developed and researched in which laser light is focused on a minute spot and optical recording is performed on an optical recording material. Te thin films, Te-dispersed CS2 plasma polymerized films, 5e-Te alloy films, squarylium dye films, naphthoquinone dye films, and the like have already been reported as write-once optical recording media. Also, Te-TeO2゜5e-Ge-Te, 5
Developed a phase change type optical disk that changes the phase between amorphous and crystalline using an e-5n-5e alloy film, and a magneto-optical type rewritable optical disk that utilizes the Kerr effect of a Te-Fe-co amorphous film. It is being done.

All of these optical disk media used a single wavelength of light for optical recording and reproduction, but considering the expansion of the optical wavelength space, multiple wavelengths were used and paralleled on a stacked optical recording medium. A system for performing recording processing has been proposed. That is, attempts have been made to use as an optical recording medium a stack of a thermosensitive coloring medium, a magneto-optical medium, and a photochromic medium, and perform wavelength multiplexing recording on such an optical recording medium.

FIG. 3 shows a recording example of a conventional wavelength multiplexed multilayer optical recording medium of this type. In FIG. 3, reference numerals 11, 12 and 13 indicate a first recording layer, a second recording layer and a third recording layer, respectively, which are stacked to constitute a multilayer optical recording medium. Solid lines 14 and 15 indicate the lens position and recording light during recording with respect to the first recording layer 11. Broken lines 16 and 17 indicate the lens position and recording light during recording with respect to the second recording layer 12. - Dotted and dashed lines 18 and 19 indicate the lens position of the third recording layer 13 and the recording light. Note that the number of multilayers (here, three layers) can be expanded to any desired number of layers n.

By using such a wavelength multiplexing layered medium, the recording density per unit area of the optical disk and the transfer speed due to parallel reading can be improved, if this can be achieved as described for the layered wavelength multiplexing recording medium mentioned above. , we can expect an amazing improvement in this type of record.

[Problems to be Solved by the Invention] However, as an optical element and an optical system used for recording on such a wavelength multiplexing layered optical recording medium, -1QQ
In addition, since the optical disk optical system was used or repurposed, a new focus setting had to be performed each time a different wavelength was used, using a focus servo. The original characteristics of the laminated optical recording medium could not be fully utilized.

For example, as shown in Figure 3, in order to record independently on each [11, 12, and 13], it is necessary to set the lens position for each layer, and to do this, it is necessary to mechanically move the lens. It becomes necessary. However, the problems of time loss due to such lens movement and a complicated lens movement mechanism have hindered the development of this type of wavelength multiplexed multilayer optical recording medium.

For example, if there is no need to set the focus for each laser wavelength, the recording speed can be improved by time-divisionally driving each laser wavelength, and if each laser wavelength can be recorded simultaneously, this would be the most ideal recording system. It is thought that the speed will improve.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the conventional multi-wavelength writing optical element and to provide a multi-wavelength writing optical element that allows simultaneous writing or easy time-division writing. .

[Means for Solving the Problems] In order to achieve such an object, the present invention provides an optical element that performs recording by focusing on different optical recording layers of a wavelength multiplexed multilayer optical recording medium. It is made of a material that has wavelength dispersion according to the wavelength of light, and can receive light of multiple wavelengths from a multi-wavelength light source simultaneously or in a time-divided manner, and has an optical recording layer corresponding to each wavelength of light. It is characterized in that the wavelengths of light are individually focused.

In general, materials and diffraction gratings constituting optical elements exhibit different refractive indexes and diffraction efficiencies for light of different wavelengths. This phenomenon is usually called wavelength dispersion of a substance with respect to wavelength light.

Such materials with low wavelength dispersion have been used as conventional optical elements that process light from a white light source. For example, in optical glass FK-1, the refractive index ratio between wavelengths of 365 nm and 768 nm is 1.0146 (Rika Chronology, published by Tokyo Astronomical Observatory).

In contrast, in the present invention, various wavelength dispersion characteristics such as this refractive index dispersion are used inversely to optimize the optical element.

[Function] By making light from light sources with different wavelengths enter the optical element of the present invention simultaneously or in a time-sharing manner, the light can be focused on the recording layer at a focal position that corresponds to the wavelength of each layer, Thereby, recording can be performed on each recording layer simultaneously or at very short time intervals. Conventionally used optical elements such as lenses required the spatial position control of the main body itself, whereas the present invention does not involve mechanical movement of such spatial position, or only requires a very small amount of movement. nothing.

[Example] The present invention will be described in detail below with reference to the drawings.

The structural concept of the present invention is shown in FIG.

In FIG. 1, 21 is the optical element of the present invention, 22 is the width of the light beam to be focused, and 23 and 24 are focal positions for light of different wavelengths. If the aperture ratio of the optical element 21 is kept constant and wavelength dispersion is considered, different focal positions 23 and 24 will always be obtained, as shown in FIG.

An embodiment of the present invention in which the optical element 21 is constituted by a Fresnel zone plate will be described below.

In this example, differences in diffraction efficiency are used as wavelength dispersion.

Here, rn-J-λ・f −fn・ro (1
) A Fresnel zone plate composed of a plurality of annular plates of (rn) - (rn-1) has a property that the focal length f differs depending on the wavelength used.

(1) In the formula, n is a natural number, λ is the wavelength, f is the focal length, and r
o indicates the radius of the center circle.

When light from a light source with a narrow spectral width such as a laser beam is incident on the optical element 21 using a Fresnel zone plate, the focused spot of the laser beam is limited by the division accuracy of the outer periphery of the zone plate. can obtain a spot diameter at its focal plane equal to that of a glass lenticular optical element of the same numerical aperture.

In the above-described embodiment of the multi-wavelength writing optical element according to the present invention, the output light is Since the light is focused on each layer of the stacked recording medium, the absorption efficiency of the layer structure can be optimized. Therefore, in the present invention, by guiding wavelength-multiplexed light to such an optical element of the present invention, simultaneous recording on a multilayer recording medium or rapid time-division recording,
Furthermore, playback can be performed.

Here, a specific example of the optical element of the present invention will be described.

An optical element 21 of n, A, -0,50 was fabricated by spherical polishing of optical glass SF2, which has a property of wavelength dispersion in which the refractive index differs depending on the wavelength, and was made into a multi-wavelength writing type optical element.

Next, a laminated multiple optical recording medium having the following structure laminated on a substrate was prepared, and multiple optical recording was performed on this recording medium.

Substrate: PMMA 1.5mm thick Color developer: Phenolphthalein vapor-deposited film 2μm thick First light absorber layer Nistilbene vapor-deposited film 300mm thick (λmax =
354 nm) Color former: Crystal violet lactone 7μmf5 Color former: Tl(-107 (Hodogaya Chemical product name: black leuco dye) 7μm thick second light absorbing layer: C, 1, Disperse Red
15,500 people thickness 1λmax = 524 nm) Color developer: phenolphthalein vapor deposited film 14 μm thickness 3rd
Light absorber layer - N-dimethylamino squarylium dye (λmax = 780 nm) Vapor deposited film 700 people thick Color former: RED-[ICF (Product name: Hodogaya Chemical Co., Ltd.)
red leuco dye) 2.0 μm thick First, by slightly moving the fabricated optical element, the spot diameter was 400 μm.
Tunable dye laser light with a wavelength of 354 r+m in μm is adjusted so that its focus is on the first light absorber layer of the recording medium, and then a laser beam with a pulse width of 1 μsec and an optical power of 6 mW is irradiated. The beam diameter was 1.6 μm on the surface of the first light absorbent layer, and crystal violet lactone and phenolphthalein reacted to record blue recording pits on the recording medium.

Next, without moving this optical element, the wavelength 510
When irradiated with nm tunable dye pulse light, the focus was focused on the second light absorber layer, and T)I-107 and phenolphthalein reacted, allowing black bits to be recorded. Furthermore, when the wavelength of the tunable dye laser is set to 780 r+m and pulsed light is irradiated without moving the optical element, the focus is focused on the third light absorbing layer, and the RED-[
ICF and phenolphthalein reacted and a red bit could be recorded.

As another specific example of the present invention, a multi-wavelength writing type optical element is constructed by a zone plate of 7.07 μm in the Fresnel zone plate expressed by formula (1), and this is combined with Although this is a multilayer optical recording medium with a similar structure, the spacing between the first light absorbent layer and the second light absorbent layer, and the spacing between the second light absorbent layer and the third light absorbent layer is 25 μm, respectively. Using optical recording media,
On this medium, using the same wavelength lasers as above, it was possible to perform the same recording and simultaneous recording as in the above embodiment.

In this way, if the surface of the optical recording medium that has been written on is irradiated with white transmitted light on the side opposite to the recording side to read and reproduce the recording, it is possible to read out the recorded pit signal corresponding to each colored pit. Ta.

Next, FIG. 2 shows an embodiment of the present invention in which writing is performed simultaneously on multiple layers.

In FIG. 2, numeral 31 is an optical element as shown in FIG. 1, and along the optical axis of this optical element 31, dichroic mirrors or half mirrors 32, 33 and 34 are arranged. On the other hand, the wavelength is 354 nm, 510
The light source lasers 35.36 and 37 with wavelengths of 780 nm and 780 nm are respectively arranged independently, and these lasers 35.3
Each pulse oscillation light from B and 37 is sent to the half mirror 3.
2) The mixed light is mixed along the optical axis of one tree through 33 and 34, and is made incident on the optical element 31. Below the optical element 31 is a first lens. A multilayer optical recording medium 41 having the above-described structure having second and third light absorbing layers 38, 39 and 40.
Place it. Here, the optical recording medium 41 and the optical element 3
By appropriately adjusting the relative positional relationship with 1,
The laser beams from each of the light sources 35, 36 and 37 could be focused on focal positions 42, 43 and 44, respectively, and thereby bits corresponding to the pulse trains of each light source could be recorded simultaneously.

In this way, if the surface of the optical recording medium that has been written on is irradiated with white transmitted light on the side opposite to the recording side to read and reproduce the recording, it is possible to read out the recorded pit signal corresponding to each colored pit. Ta.

[Effects of the Invention] As described above, by using the multi-wavelength writing optical element according to the present invention, different recording layers on a wavelength multiplexed multilayer optical recording medium can be easily written simultaneously or at very short time intervals. Recording can be done.

Therefore, as in the past, it was not possible to achieve this by focusing the optical element on each layer individually.
According to the present invention, a completely new optical element has been developed which is capable of increasing recording and reproducing rates and parallel writing and reading to each individual layer, and which can fully bring out the advantages of wavelength multiplexed multilayer optical recording media. It is possible to make it happen.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the structural concept of a multi-wavelength writing type optical element according to the present invention, Fig. 2 is a diagram showing an embodiment of a simultaneous writing form of a multi-wavelength writing type optical element according to the present invention, and Fig. 3 is a diagram showing a conventional example. FIG. 2 is an explanatory diagram of a recording example of a wavelength multiplexed multilayer optical recording medium. 11, 12.13... 1st. Second. third recording layer, 14
, 15... Lens position and recording light when recording on the first recording layer, 18, 17... Lens position and recording light when recording on the second recording layer, 18, 19... When recording on the third recording layer Lens position and recording light, 21... Optical element, 22... Width of condensed light beam, 23, 24... Focus position for each different wavelength,
31... Optical element, 32) 33.34... Each wavelength half mirror (dichroic mirror), 35, 36.37... Each wavelength laser light source, 3B, 3
9.40...1st. Second. Third light absorber layer, 41...
- Optical recording medium, 42) 43.44... Focus position.

Claims (1)

[Claims] 1) An optical element that performs recording by focusing on different optical recording layers of a wavelength multiplexing multilayer optical recording medium, which is made of a material that has wavelength dispersion according to the wavelength of light, It is possible to receive light of a plurality of light wavelengths from a light source simultaneously or in a time-divided manner, and the focus of each wavelength light is independently focused on the optical recording layer of the recording medium corresponding to each wavelength light. A multi-wavelength writing type optical element characterized by the following. 2) A multi-wavelength writing optical element according to claim 1, wherein the material has a different refractive index or diffraction efficiency depending on the wavelength. 3) The optical element according to claim 1 or 2, wherein the material is a lens material, and the multi-wavelength writing type is characterized by using a lens whose refractive index wavelength dispersion is optimized. optical element. 4) The optical element according to claim 1 or 2, wherein the material is a Fresnel zone plate, and the multi-wavelength writing type optical element is used by optimizing the wavelength dispersion of the diffraction efficiency. element.