JPH03125348A - Optical memory element - Google Patents

Abstract

PURPOSE:To obtain sufficient reflected light and to improve the position control of an objective lens by providing a reflecting layer which increases its reflectivity at least at >=1 kinds of waveforms in the optical memory element. CONSTITUTION:The reflecting layer 2 consisting of Al, etc., is provided on a substrate 1 consisting of glass, etc., and further, recording layers R1 to R3 are superposed. The recording layers consist of photochromic materials which are changed in coloring state by a photoreaction and are subjected to recording with light of respective waveforms lambda1 to lambda3 by varying the materials. The photochromic materials are, for example, the hetero type fulgide (Me is a methyl group) expressed by the formula and are disposed with the group of an oxazole type in the position of X in the case of the layer R1, a thiophene type in the case of the layer R2 and a pyrrole type in the case of the layer R3, respectively. The reflectivity increases at the intrinsic waveforms. The large reflected light is obtd. when the irradiation light to the optical memory coincides with lambda1 to lambda3. The position control of the objective lens by focus servo is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical memory device that records, reproduces, and erases information signals using light.

[Conventional technology]

In recent years, the need for optical memory devices that record, reproduce, and erase information signals using light has been increasing year by year as high-density, large-capacity memory devices. Therefore, for example, JP-A-62-
Publication No. 165751 discloses an optical memory element in which recording layers Q1 to Q7 capable of recording at mutually different wavelengths λ1 to λ7 are laminated on a substrate 31, as shown in FIG.

Thereby, when recording an information signal, the optical memory element uses a wavelength λ corresponding to each recording layer Q1 to Q.

Multiplex recording of n layers can be performed by irradiating light of ~λ7.

[Problem to be solved by the invention]

However, in the conventional optical memory element described above, it is difficult to control the position of the objective lens that forms a light spot on each recording layer Q, to Q7.

That is, when recording an information signal on an optical memory element, it is generally necessary to apply focus servo to the objective lens in order to maintain a constant distance between the objective lens and the recording layer Q, -Q. At this time, the above-mentioned focus servo is performed by using reflected light from the recording layers Q to Q7 as a servo error signal. However, in the recording layers Q1 to Q7, most of the incident light is transmitted, and almost no reflected light can be obtained. Therefore, in the conventional optical memory element, it is difficult to maintain a constant distance between the objective lens and the recording layers Q, .about.Qfi because the servo error signal is insufficient.

In this way, the optical memory element has a plurality of recording layers Q.

~ Multiple recording is possible by having Q7, but
Since the reflected light from each recording NQ1 to Qn is insufficient, it is difficult to control the position of the objective lens using focus servo. Therefore, it is an object of the present invention to provide an optical memory element that can improve the position control of the objective lens by focus servo by obtaining sufficient reflected light.

[Means to solve the problem]

In order to solve the above problems, the optical memory element according to the present invention multiplexes a plurality of information signals by irradiating a plurality of lights with different wavelengths through an objective lens whose position is controlled by a focus servo. The optical memory element for recording is characterized in that the optical memory element is provided with a reflective layer that exhibits a large reflectance at at least one similar wavelength.

[For production]

According to the above configuration, the information signal is recorded by being irradiated with light through the objective lens. The position of the objective lens described above is controlled by a focus servo, and the focus servo is performed by using the reflected light of the light irradiated on the optical memory element as a servo error signal.

The above reflected light can be efficiently obtained by the reflective layer when the wavelength of the light irradiated to the optical memory element exceeds the wavelength that makes the reflective layer have a high reflectance. Therefore, the servo error signal becomes sufficiently stable due to the above reflected light.

As a result, the optical memory element uses the above-mentioned reflected light for focus servo of the objective lens, thereby making it possible to satisfactorily control the position of the objective lens.

[Example 1] An example of the present invention will be described below based on FIGS. 1 and 2.

As shown in FIG. 1, the optical memory device according to this example has the following features:
a substrate 1; a reflective layer 2 formed on the surface of the substrate 1;
Recordings NR1~ formed in layers on the surface of this reflective layer 2
It consists of R1. Note that a protective layer may be formed on the surface of the recording layer R1.

The substrate 1 is made of, for example, glass, plastic, aluminum, or the like, and supports the reflective layer 2 and the recording layers R1 to R3. Further, the reflective layer 2 formed on the surface of the substrate l is made of aluminum, gold, silver, tantalum, etc., for example, so as to have a high reflectance, and it directs the light incident from the incident direction to the B direction. It is reflective. Further, the recording layer RI-R3 formed on the surface of the reflective layer 2 is a photosensitive recording film made of a photochromic material whose colored state changes due to a photoreaction, and each of the recording layers R1 to R3 is By using different materials, each wavelength λ1~λ
It is designed to be recorded using light that has .

Examples of the above-mentioned photochromic materials include hetero-fulgide represented by the following formula. Note that Me is a methyl group.

For recording NR1, a photochromic material in which an oxazole type represented by the following formula is arranged at the X position of a hetero-fulgide is used. As a result, the recording layer R1 has a wavelength λ of 462rv.

Recording can be performed when the

In addition, Ph is a phenyl group.

Further, the recording layer R2 uses a photochromic material in which a thiophene type represented by the following formula is arranged at the X position of a hetero-fulgide. Thereby, recording can be performed on the recording layer R2 when light has a wavelength λ2 of 523 nm.

Further, the recording layer R3 uses a photochromic material in which a virol type shown by 2 below is arranged at the X position of a hetero-fulgide. Thereby, recording can be performed on the recording layer R1 when light has a wavelength λ3 of 614 nm.

Note that the above optical memory element has three recording layers R1, R2,
Although it has R3, it is not limited thereto. That is, as shown in FIG. 2, the optical memory element may have recording layers RI to R7 stacked in three or more layers by using different photochromic materials. Further, the photochromic material is not limited to the above-mentioned heterofulgide, and may be other types of photochromic materials. Furthermore, the recording layer Rl-R may be formed of at least two types of photochromic materials mixed with dye materials that absorb light of different wavelengths.

In the above configuration, when recording an information signal on the optical memory element, as shown in FIG.
irradiated in the direction. When the light has a wavelength of 462 nm, the colored state of the photochromic material of the recording layer R3 changes due to a photochemical reaction. Further, when the above-mentioned light has a wavelength λ2 of 523 nm, the colored state of the photochromic material of the recording layer R2 changes due to a photochemical reaction, and when the wavelength of the above light has a wavelength λ3 of 614 nm, the colored state of the photochromic material of the recording layer R3 changes. It will change due to photochemical reaction. As a result, the above recording layer R
Separate information signals are recorded in 1, R2, and R3 by light having wavelengths λ, .lambda.2, and .lambda., respectively.

At this time, most of the light having each of the wavelengths C, λ2 and λ passes through the recording layer R+'Rz and R3, but is reflected in the direction B by the reflective layer 2 having a large reflectance. Since the reflected light reflected in the B direction is efficiently reflected by the reflective layer 2, it can be used as a sufficiently stable error signal for servo. Therefore, the objective lens can be subjected to stable focus servo by the reflective layer 2, and position control becomes easy.

[Embodiment 2] Another embodiment of the present invention will be described below with reference to FIG.

The optical memory device according to this example, as shown in FIG.
It has a substrate 7 made of, for example, glass, acrylic, or plastic such as polycarbonate, and this substrate 7 is designed to sufficiently transmit recording light. Further, on the surface of the substrate 7, reflective layers 8 and 9 and recording layers S, -S,
are formed in this order.

The above reflective layers 8 and 9 are composed of high refractive index layers 3 and 5 and low refractive index layers 4 and 6, and the high refractive index layers 3 and 5 are made of ZnS.
is formed with a film thickness of approximately 160 nm. Also,
The low refractive index layers 4 and 6 are made of MgF.

is formed with a film thickness of approximately 280 nm. The reflective layers 8 and 9 are configured to efficiently reflect light having a wavelength around 520 nm by combining the high refractive index layers 3 and 5 and the low refractive index layers 4 and 6 described above.

Further, a recording layer Sl formed on the surface of the reflective layer 9 described above
'S= has a compound represented by the following formula.

The recording layer S is CHZ OCOCt+ H42 and N
O□ is placed at the X position and Y position of the above compound, respectively, and the film thickness is about 10 nm. Thereby, the recording layer S is recorded with light having a wavelength λ4 of 618 nm. In addition, the recording layer S2 is one in which 0CI (and NO□ are arranged at the X and Y positions of the above compound, respectively, and about 10
It is formed to have a film thickness of nm. As a result, the recording layer St
is recorded with light having a wavelength λ of 600 nm.

In the above configuration, when recording an information signal on the optical memory element, first, light having a certain wavelength is irradiated onto the optical memory element from, for example, a semiconductor laser light source. At this time, since the substrate 7 is sufficiently transparent, the above light is transmitted to the recording layer S+.
'The light may be irradiated from either the Sg side or the substrate 7 side. However, when the light is irradiated from the direction C, which is the side of the substrate 7, it is desirable that the thickness of the substrate 7 is about 0.5 to 2.0 nm.

Then, when the above light has a wavelength λ4 of 618 nm, an information signal is recorded in the recording layer Sl, and the wavelength λ4 is 600 nm.
In the case of a wavelength λ of m, an information signal is recorded on the recording layer S2. Each of the wavelengths λ4 and λ above.

Most of the light with 52
When irradiated with light having a wavelength λ6 of 0 nm, about 60% is reflected by the reflective layers 8 and 9.

Therefore, the light having the wavelength λ6 becomes reflected light that can be fully used as a servo error signal.

In this way, the optical memory element according to this embodiment makes it possible to stably apply focus servo to the objective lens by irradiating light for servo error signals in addition to recording, and it is possible to stably apply focus servo to the objective lens. position control becomes easier.

Although the optical memory element described above has a reflection of 2N N8 and 9, it is not limited to this and may have a single layer. This is because even if the reflectance of the layer is -, the reflected light can be sufficiently used as a servo error signal. In addition, the high refractive index layers 3 and 5 and the low refractive index layer 4 of the reflective layers 8 and 9
-6 is not limited to ZnS and M g F z. That is, the reflective layers 8 and 9 may have a high reflectance for light of a specific wavelength by combining a material with a high refractive index and a material with a low refractive index.

Furthermore, if the reflective layers 8 and 9 are formed of a good thermal conductor such as aluminum nitride or silicon nitride, it becomes possible to prevent the temperature of the recording layer S+ -3z from rising during recording, and as a result, the recording layer It becomes possible to prevent destruction of S1 and S2 due to overheating. In addition, the recording layer S,
- S2 does not need to be formed in a layered form, and may be formed by mixing materials sensitive to light of different wavelengths [Effects of the Invention] The optical memory element according to the present invention has the above-mentioned properties. In an optical memory element in which a plurality of information signals are recorded multiplexed by irradiating a plurality of lights with different wavelengths through an objective lens whose position is controlled by a focus servo, the optical memory element has the following features: This is a configuration in which a reflective layer having a large reflectance at least at wavelengths of the l[r class or higher is formed.

As a result, reflected light can be efficiently obtained by the reflective layer having a large reflectance, thereby achieving the effect that the position control of the objective lens by the focus servo can be improved.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention. The first @ is a vertical cross-sectional view of an optical memory element having three recording layers. FIG. 2 is a longitudinal cross-sectional view of an optical memory element having multiple recording layers. FIG. 3 and FIG. 4 show a conventional example, and are longitudinal sectional views of an optical memory element. (2) 7 is a substrate, 2, 8 and 9 are reflective layers, 3 and 5 are high refractive index layers, and 4 and 6 are low refractive index layers.

Claims (1)

[Claims] 1. In an optical memory element in which a plurality of information signals are recorded in multiplex by irradiating a plurality of lights with different wavelengths through an objective lens whose position is controlled by a focus servo, the above-mentioned An optical memory element characterized in that the optical memory element is formed with a reflective layer that exhibits a large reflectance at at least one similar wavelength.