JPH11337756A - Multilayered waveguide type reproducing-only memory card - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayered waveguide type memory card to be used only for reproducing which can constitute a large-capacity storage system without requiring a high-precision film thickness control. SOLUTION: A multilayered waveguide is produced by laminating plane optical waveguides 1 and 2 in many layers and has a structure where a face to couple light to the waveguide is inclined at 45 deg. to the normal of the waveguide plane. A refractive index fluctuation or a scattering factor due to raggedness is formed in each waveguide layer 1 to generate scattered light which leaks from the waveguide plane to the outside of the waveguide, and the position where this scattered light is generated is taken out as two-dimensional pattern information by using a lens 6 and a two-dimensional light reception element 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer waveguide type read-only memory card. For example, CD, CD-R
Applications such as distribution of music or video software or computer software, such as OM or DVD-ROM, are conceivable.

[0002]

2. Description of the Related Art A read-only multiplexed hologram card has been proposed as a memory system having a three-dimensional recording area exceeding the storage capacity of a conventional optical memory and capable of mass production. This method has the advantage that a lens system for forming an image on a two-dimensional light receiving element at the time of reproduction is unnecessary, and the reproduction apparatus can be made small and inexpensive. When the length was shortened, a high-precision film forming technique was required, and there was a limit to the improvement of the storage capacity by shortening the wavelength.

That is, when the refractive index of the cladding is 1.47 and the refractive index of the core is 1.48, the wavelength used is 830 nm.
At the time of the above, the thickness of the core was 2.41 μm or less, but when the wavelength used was 450 nm, 1.3.
The condition is 1 μm or less, which makes production difficult. In addition, since the mode is a single mode, the coupling efficiency of light to the waveguide by the lens is not 100%, and it is necessary to devise a method of not irradiating uncoupled light to the two-dimensional light receiving element.

In order to form a hologram image on a two-dimensional light receiving element, it is necessary to previously calculate the arrangement of scattering factors to be produced in each waveguide by a computer, but this calculation amount is large and forgery is prevented. On the other hand, there is a disadvantage that the manufacturing cost is high.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-layer waveguide type read-only memory card which solves the above-mentioned problems of the prior art.

[0006]

A multi-layer waveguide type read-only memory card according to the present invention, which solves the above-mentioned problems, is formed by stacking planar optical waveguides in multiple layers, and has a surface for coupling light to the waveguides. In a multilayer waveguide having a structure inclined at 45 ° with respect to the normal line of the waveguide plane, the refractive index fluctuates in each waveguide layer, or a scattering factor due to unevenness is formed to move the waveguide from the waveguide plane to the outside of the waveguide. It is characterized in that leaked scattered light is created, and the position where the scattered light is generated is extracted as two-dimensional pattern information using a lens and a two-dimensional light receiving element.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Instead of using diffracted light due to a periodic scattering factor used in a reproduction-only multiplex hologram card, scattered light from independent scattering factors is condensed on a two-dimensional light receiving element by a lens. Method. The scattering element is formed, for example, at the interface between the core 1 and the clad 2, as shown in FIG. Any of fluctuations in refractive index and those due to unevenness may be used.

The surface for coupling light to the waveguide is inclined at 45 ° to the normal to the waveguide plane, and the incident light 7 is incident on the surface by the condenser lens 6. The reproducing lens group 3 is
Each waveguide surface is arranged such that a real image is formed on the two-dimensional light receiving element 4. Therefore, a mechanism is provided to refocus each time the waveguide of interest is changed. For example, as shown in FIG. 1, a focusing mechanism 5 is provided.

Here, since the scattering factors are independent of each other, there is no need to adjust the phase of the scattered light, and therefore the waveguide does not need to be single mode. That is, a multi-mode waveguide having a large core thickness can be used, and the difficulty in manufacturing can be reduced. Further, since the core thickness is large, the coupling efficiency of light by the lens can be made almost 100%. Therefore, the lens arrangement of the imaging system can be designed without concern for stray light due to non-coupled light.

In addition, there is no procedure for producing a computer generated hologram, which facilitates production of a memory card. V is the volume of each scattering factor, Δ is the relative refractive index difference of the waveguide, n is the refractive index of the core,
Assuming that the wavelength is λ and B% of the scattered light can be imaged on the two-dimensional light receiving element by the imaging lens system, when the scattering factor is smaller than the wavelength, the light intensity of the guided light is I _I (W / m ² ) the amount of light J ₂ at the point where scattered light from the scattering factor at the point is imaged
(W) is represented by the following equation.

[0011]

(Equation 1)

For example, λ = 830 nm, B = 20%, n
= 1.48, Δ = 0.01, V = 2.5 × 10 ⁻²⁰ m
³ (0.5μm × 0.5μm × 0.1μm)
J ₂ = 8 × 10 ¹⁹ I _I Assuming that the input power is 20 mW, at the point where the beam spread of the core layer having a thickness of 5 μm is 1 mm, I _{I is} 4 × 10 ⁶ W / m ² , so J ₂ = 3.2 pW.

This value indicates that the number of photons exceeds 13000 even when the reproduction is performed at a frame speed of 1 ms, and that a sufficient S / N is provided. If such scattering factors are arranged in an isosceles triangle having a height of 10 mm and a base of 2.5 mm every 1 μm, 12.5 Mbit of information is packed by the determination of the presence or absence of the scattering factors.

If this is reproduced at a frame rate of 1 ms, a high transfer rate of 12.5 Gbps can be obtained. The storage capacity can be increased by the number of layers by stacking waveguides in multiple layers. By stacking on multiple layers, there is also an effect that scattered light is scattered by scattering factors of other layers, but the effect is, if the depth of scattering factor × relative refractive index difference × number of layers is sufficiently smaller than the wavelength The value can be ignored.

For example, under the above-mentioned conditions, depth = 0.1 μm,
When Δ = 0.01 and the number of layers = 100, their product is 0.1 μm, and this value can be said to be sufficiently small unless the wavelength used is ultraviolet light. As can be seen from equation (1), if the wavelength is halved, equivalent scattered light can be obtained with a volume of 散乱 of the scattering factor. Therefore, assuming that the depth of the scattering factor is fixed at 0.1 μm, the area can be reduced to ４, and the storage capacity is proportional to ４.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. The multi-layer waveguide type read-only memory card according to the present embodiment uses a semiconductor laser having a wavelength of 532 nm as a light source, a UV curable resin having a refractive index of 1.48 and a thickness of 9 μm, a cladding layer, a refractive index of 1.49 and a thickness of 3.0.
μm PMMA is the core layer. The multilayer waveguide type read-only memory card according to this embodiment is manufactured by the method shown in FIG.

First, as shown in FIGS.
Copper 12 is vapor-deposited to a thickness of 0.5 μm on an inch silicon wafer 11, and further, as shown in FIG. 2C, an ultraviolet curable resin 13 is spin-coated thereon to a thickness of 9 μm. As shown in FIG. 2 (d), the composition was cured by ultraviolet irradiation. Next, as shown in FIGS. 2E and 2F, PMMA14 was spin-coated so as to have a thickness of 3 μm, and a roller having a concavo-convex pattern was run thereon.

Further, the steps shown in FIGS.
That is, the operation of UV curable resin coating → UV light exposure → PMMA coat → Roller transfer was repeated for 10 cycles, and further, as shown in FIG. Subsequently, as shown in FIG. 3, the silicon wafer 11 is cut into strips at intervals of 10 mm using a dicing saw (not shown) having an angle of 45 degrees, and finally, immersed in a 5% diluted hydrochloric acid solution as shown in FIG. Then, the copper layer was melted out to obtain a plurality of strip-shaped multilayer waveguide memories having a width of 10 mm.

The long side of the strip-shaped multilayer waveguide memory has an inclination of 45 degrees with respect to the waveguide, and it was confirmed that scattered light forms an image as shown in FIG. In FIG. 5, a strip-shaped multilayer waveguide memory 15 is placed on a slide glass 17 on a stage 16 and the SHG of a YAG laser is used.
When light was introduced from below with an optical system (optical fiber with microlenses) 18 with NA = 0.15 and observed from above with a microscope 19, only scattered light leaking from the unevenness of the layer to which the light was coupled was observed. Was done.

[0020]

As described above in detail with reference to the embodiments, in the multilayer waveguide type read-only memory card according to the present invention, the refractive index fluctuates in the waveguide layer or a scattering factor due to unevenness is formed. As a result, scattered light leaking out of the waveguide from the waveguide plane is created, and the position where the scattered light is generated is extracted as two-dimensional pattern information using a lens and a two-dimensional light receiving element. Instead, a large-capacity storage system can be constructed.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the operation principle of a multilayer waveguide type read-only memory card according to the present invention.

FIG. 2 is a process chart showing a method for manufacturing a multilayer waveguide type read-only memory card according to one embodiment of the present invention.

FIG. 3 is an explanatory view showing cutting out by a dicing saw.

FIG. 4 is an explanatory diagram showing separation of a silicon wafer and a multilayer waveguide.

FIG. 5 is an explanatory diagram showing a method for confirming how scattered light forms an image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core 2 Clad 3 Reproduction lens group 4 Two-dimensional light receiving element 5 Focusing mechanism 11 Silicon wafer 12 Copper 13 Ultraviolet curing resin 14 PMMA 15 Multilayer waveguide memory 16 Stage 17 Slide glass 18 Optical system 19 Microscope

Continued on the front page. (72) Akiyuki Kan, Nippon Telegraph and Telephone Corporation, 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan (72) Makoto Hikita 3-2-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Within Telegraph and Telephone Co., Ltd.

Claims (1)

[Claims] 1. It is made by stacking planar optical waveguides in multiple layers,
In addition, in a multilayer waveguide having a structure in which a surface for coupling light to the waveguide is inclined at an angle of 45 ° with respect to the normal to the waveguide plane, a scattering factor due to a fluctuation in refractive index or unevenness is formed in each waveguide layer. A scattered light leaking out of the waveguide from the waveguide plane, and extracting the position of the scattered light as two-dimensional pattern information using a lens and a two-dimensional light receiving element. Dedicated memory card.