RU2399936C2 - Planar waveguide - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: waveguide has a bottom part with a conical cut of height h<H, where H is thickness of the waveguide. Input radiation propagates from the conical cut to edges of the waveguide. The disclosed waveguide also has a second conical cut on which a mirror coating is applied, coaxial to the conical cut in the bottom part.

EFFECT: device enables uniform radial propagation of light entering the planar waveguide with maximum efficiency.

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Description

The invention relates to the introduction of radiation into a planar waveguide, calculated in the approximation of geometric optics, and can be used to enter light into a planar waveguide from one of its sides to create light panels, lighting devices, flat headlights, backlights of instrument panels and LCD screens.

Also, diffraction gratings are used to introduce light into a planar waveguide (US Patent US 7181108 B2 dated 02.20.2007, G02B 6/34, analogue). The light from the source falls at a given angle onto the diffraction grating deposited on a wide face of the waveguide (lower side) and then propagates in the waveguide.

The disadvantage of this method is the limited efficiency of light input, the difficulty of introducing white light into the waveguide, and a small spread in the angles of incidence of light from the source.

To enter light into the waveguide through a wide face, holographic structures are used (US Patent No. 5,745,266 of 04/28/1998, G03H 1/00, prototype). For a perpendicular incidence of light from an incandescent lamp or other light source onto a diffractive optical element, a parabolic reflector is used.

However, using such a device, it is possible to introduce light into the waveguide, which will propagate linearly. This scheme is not intended for radial propagation of light and has restrictions on the range of angles of incidence of light from the source.

This invention is free from the above disadvantages.

The basis of the invention is the task of obtaining a uniform radial propagation of light introduced into a planar waveguide with maximum efficiency.

This was achieved due to the fact that the radiation is introduced into a planar waveguide containing in the lower part a conical notch of height h <H, where H is the thickness of the waveguide, the radiation being introduced radially symmetrically and propagating from the conical notch to the edges of the waveguide, and coaxially to the conical notch into at the bottom of the waveguide, an additional conical cut is made in the upper part of the waveguide, while the sum of the heights of the conical cuts at the top and bottom of the waveguide is less than the thickness of the waveguide, and a mirror coating is applied to the upper conical cut.

Figure 1 shows a diagram of a waveguide device for introducing radiation into it, the thickness of which is larger than the size of a light source (luminous body LED).

Figure 2 shows a diagram of a waveguide device with two conical cutouts for greater efficiency of light input for low refractive indices of the waveguide.

Figure 3 presents the appearance of the waveguide in the context when performing in it two coaxial cones.

In the device diagram of FIG. 1, a conical hole is drilled in a waveguide of thickness H with a solid angle θ of depth h and an initial diameter D. The refractive index in the fiber is n. The diameter of the hole D depends on the size of the luminous LED body.

The radiation is introduced radially symmetrically and propagates from the conical cut to the edges of the waveguide. The device allows you to enter into the waveguide white light from the LED, having a Lambert radiation pattern.

The table shows the parameters of a single-cone scheme for various refractive indices of the waveguide. The value of η is the efficiency of radiation input as a percentage of the total LED energy. With the calculated refractive index, all the radiation emanating from the LED is introduced into the waveguide or reflected back toward the LED, no radiation passes upward from the waveguide (Figure 1). n _c is the calculated refractive index for which the input circuit operates optimally, n is the refractive index for which the value of η is calculated. Hereinafter, the grayed-out cells in the η column indicate the radiation output in the input region at the top of the waveguide. Unfilled cells η indicate that no radiation comes out from above the waveguide in the input region.

Table Dependence of the parameters of the hole in the waveguide on the refractive index. n _c n h mm θ, ° η,% 1.5 1.5 4.82D 12 99.5 1.4 86.5 1.29 63.9 1.6 1.6 2.47D 23 99.55 1.5 94.3 1.4 79.2 1.29 59.5 1.68 1.68 1.69D 33 99.0 1.6 96.8 1.5 86.12 1.4 71.5 1.29 52.7

The data given in the table are valid for any waveguide thickness H> h.

The results of the operation of the device of FIG. 1 can be improved by changing the upper surface of the waveguide at the light input site. Figure 2 and Figure 3 shows a device for a two-cone circuit for introducing light into a waveguide.

The planar waveguide in FIG. 2 has a light input efficiency of more than 98% with a waveguide refractive index of more than 1.5. In this case, the introduced radiation does not exit the waveguide and propagates exclusively at angles of total internal reflection inside the waveguide, starting from the refractive index n = 1.6.

Coating the top cone further improves the result for refractive indices of less than 1.5.

With a thicker waveguide, it is easier to get a better result. For example, it is possible to obtain an efficiency of light input into the waveguide of more than 98% without undesirable light exit from the waveguide in the input region for the refractive index of the waveguide from 1.29 and higher.

When calculating the one-cone scheme in the table, a small margin of the angle θ (1 °) was taken, and as a result, the hole depth h is minimal. Therefore, if the cone is created by drilling the waveguide, it is necessary to pay attention to the smoothness of the surface of the cone - roughness along the Y axis (ring strips after a poor-quality drill) can lead to radiation coming out from above the waveguide when operating the circuit at the calculated refractive indices and heights h. If the angle at roughness tubercles is 0.5 ° or more, it is recommended to reduce the angle θ and, as a result, increase the depth of the cone h. A slight roughness on the surface of the cone in the XZ plane (grooves along the axis of the cone) is not critical.

In both schemes, the luminous surface of the LED was taken in the lower plane of the waveguide.

When taking a square LED, the radiation is introduced into the waveguide equally uniformly in all directions in the XZ plane.

Claims (1)

A planar waveguide containing in the lower part a conical cutout of height h <H, where H is the thickness of the waveguide, and the radiation is introduced radially symmetrically and propagates from the conical cutout to the edges of the waveguide, and an additional conical cutout is made coaxially with the conical cutout in the lower part of the waveguide in the upper part waveguide, while the sum of the heights of the conical cuts above and below the waveguide is less than the thickness of the waveguide, and a mirror coating is applied to the upper conical cut.

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