KR100843289B1 - Light guide plate provided with diffraction grating and surface lighting device using the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide and a surface light source device for guiding light introduced from an external light source and emitting the light into a plane illumination light. The light guide is a structure for guiding light incident from one or more light sources and converting the light into surface light, and a transmissive diffraction grating corresponding to each light source is formed on an incident surface of the light guide opposite to the light source. According to such a light guide, luminance unevenness does not occur even if disposed close to the light source for the purpose of miniaturization of high brightness, and the luminance can be improved and the size and size of the component can be reduced.

Surface light source device, light guide, diffraction grating

Description

LIGHT GUIDE PLATE PROVIDED WITH DIFFRACTION GRATING AND SURFACE LIGHTING DEVICE USING THE SAME}

Figure 1a is a cross-sectional structure diagram of a direct type surface light source device according to the prior art.

Figure 1b is a plan view of a side-illuminated surface light source device according to the prior art.

2 is a block diagram of a direct type surface light source device according to an embodiment of the present invention.

3 is a cross-sectional view of a blazed diffraction grating showing the path of the diffracted light in accordance with an embodiment of the present invention.

Figure 4 is a graph of the light transmission function of the blaze diffraction grating according to an embodiment of the present invention.

5 is a graph showing a diffraction distribution by a blaze diffraction grating according to an embodiment of the present invention.

6 (a) to 6 (c) are cross-sectional views of the diffraction grating region provided in the light guide according to the embodiment of the present invention.

FIG. 7 is a bottom view of a light guide showing an arrangement of diffraction gratings formed corresponding to a plurality of RGB point light source pairs according to an embodiment of the present invention; FIG.

8 is a perspective view of a side-illuminated surface light source device according to an embodiment of the present invention.

** Explanation of symbols for main parts of drawings **

100: Direct type surface light source device ... 100 ': Side irradiation type surface light source device ... 110: Light source ... 120: Reflector ... 130, 130': Light guide body ... 131,131 ': Incident surface ... 132,132 ': exit surface ... 133: fine particles ... 134': end surface ... 135 ': reflection surface ... 136: fine round ... 137': left and right side cross section ... 140: functional optics Film layer ... 141: Diffusion sheet ... 142: Prism sheet ... 143: Protective sheet ... D, D _R , D _G , D _B : Diffraction grating (area) ... S _D : Diffraction grating plane

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide and a surface light source device for guiding light introduced from an external light source and emitting the light into a plane illumination light.

BACKGROUND ART In a surface light source device used in a transmissive display device such as a liquid crystal panel, a light guide member made of a transparent resin is used to uniformly guide light introduced from an external light source to the display device using planar illumination light. The illumination light introduced from the surface light source device displays an image such as a character or an image by adjusting the transmittance by the transmissive display element.

Referring to FIG. 1A, in the type of the surface light source device, incident light from the light source 110 is introduced through the planar incident surface 131 of the light guide (diffusion plate) 130 to be finely dispersed inside the light guide. There is a direct type surface light source device 100 which is scattered by the fine particles 133 and is emitted as surface light through the emission surface 132 on the opposite side.

In a typical direct type surface light source device 100, a reflector 120 is installed to return the illumination light leaking under the light source 110 toward the light guide 130 to increase the efficiency of the light source 100, and the light guide is provided. Diffusion sheet 141 for scattering outgoing light to remove luminance unevenness on top of exit surface 132 of 130, prism sheet 142 and prism sheet for correcting frontal viewing angle by refracting and condensing outgoing light A functional optical film layer 140 made of a protective sheet 143 or the like is provided to prevent scratches of the 142 and to prevent moire from occurring when the vertical / horizontal prism sheet is used.

In general, a line light source such as a rod-shaped cold cathode fluorescent lamp (CCFL) and an external electrode fluorescent lamp (EEFL) has been used as the light source 110. However, in the display device of a portable device requiring low power consumption, light emission has recently been achieved. Point-like or local light-emitting sources such as diodes (LEDs, OLEDs) are widely used.

On the other hand, in the direct type surface light source device 100, since the plurality of light sources 110 are provided below the light guide body at predetermined intervals, the density of incident light along the incident surface 131 of the light guide body 130. There is a problem that the luminance unevenness is necessarily caused to be different. In order to compensate for the luminance unevenness, if the light source 110 and the light guide 130 are kept at a considerable distance T ₁ or the functional optical film layer 140 is added to the upper surface of the light guide, the brightness is deteriorated. There is a problem that the entire thickness of the surface light source device 100 becomes too large. The problem of such decrease in luminance is further exacerbated by scattering loss caused by the fine particles 133 inside the light guide 130.

In another type of surface light source device, incident light from the light source 110 is introduced through the side cross-section of the light guide and exits the total internal reflection process to the exit surface 132 'provided by the upper plane of the light guide 130'. There is a side-illuminated surface light source device (100 ') of the structure. In the drawing, a plurality of light sources 110 are provided at predetermined intervals along the incident surface 131 'provided on the side end surface of the light guide body 130'. In addition, as in the direct type surface light source device 100 described above, a reflector 120 for returning the leaked light toward the light guide body 130 'is provided, and on the exit surface 132' of the light guide body 130 '. A functional optical film layer (not shown) is stacked and a reflective sheet (not shown) is provided below the opposite side of the exit surface 132 ′.

Also in this side-illumination type surface light source device 100 ', when the light source 110 arrange | positioned at the incident surface 131' of the side cross section of the light guide body 130 'has the form of a point light source 130, There is a problem that the luminance uniformity of the surface light source device 100 'decreases in the x direction on the xy plane due to the presence of a local dark area near the incident surface 131' of the ''). If a predetermined distance is provided between the 131 'and the light guide 130', the luminance decreases and the size of the surface light source device 100 'becomes large, which makes it difficult to downsize.

SUMMARY OF THE INVENTION An object of the present invention devised to solve the problems of the conventional surface light source device is a light guide member having a new structure that does not generate luminance unevenness even if disposed close to a light source for the purpose of miniaturization of high brightness, and a surface light source device using the same. To provide.

The gist of the present invention for achieving the above object is as follows.

(1) A light guide for guiding light incident from one or more light sources and converting the light into surface light, wherein a light-transmitting diffraction grating corresponding to each light source is formed on an incident surface of the light guide opposite to the light source. sieve.

(2) The light guide according to item (1), wherein the diffraction grating is formed on an opposite surface of the light exit surface of the light guide.

(3) The light guide according to item (2), wherein the pitch of the diffraction grating is determined such that the angle of the first diffracted light forms an angle equal to or more than a critical angle for total internal reflection.

(4) The light guide according to item (2), wherein the depth of the diffraction grating is controlled so that the maximum phase shift of incident light by the diffraction grating becomes 2π.

(5) The light guide according to the above (2), wherein the light exit surface of the light guide is formed with fine irregularities for emitting diffracted light.

(6) The light source exists as a pair of point light sources of one or more RGB wavelengths arranged symmetrically under the light guide, and the pitch and depth of the diffraction gratings are respectively determined according to RGB wavelengths. The light guide according to the above (2).

(7) The light guide according to the above (1), wherein the diffraction grating is formed on the side surface of the light guide.

(8) The light guide according to (2) or (7), wherein the diffraction grating is a blaze diffraction grating in cross section.

(9) The light guide according to the above (2) or (7), wherein the diffraction grating has a sine wave or step shape in cross section.

(10) The light guide according to item (2), wherein the area of the diffraction grating corresponds to a region to which incident light from the light source is irradiated.

(11) A light source in the form of a point light source or a linear light source, and a light guide according to any one of (1) to (7) as an element for converting incident light from the light source into surface light. Surface light source device.

(12) The surface light source device as described in the item (11), wherein the light source exists as one or more pairs of RGB point light sources arranged in geometric symmetry below the light guide.

(13) The surface light source device according to item (11), wherein the diffraction grating is a blaze diffraction grating in cross section.

(14) The surface light source device according to item (11), wherein the diffraction grating has a sine wave or step shape in cross section.

(15) The surface light source device according to item (11), wherein the area of the diffraction grating coincides with a region to which incident light from the light source is irradiated.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. In the following embodiments, the same or similar parts will be represented by the same or similar reference numerals. In the accompanying drawings, the parts or parts of the light guide or the surface light source device are schematically illustrated or exaggerated for the purpose of explanation.

2 is a schematic structural diagram of a direct type surface light source device according to an embodiment of the present invention. The direct type surface light source device 100 according to the present exemplary embodiment emits light to the emission surface 132 by guiding the plurality of light sources 110 to generate light and the light incident from the light sources 110 through diffraction and total reflection processes. It includes a light guide 130 to make. In the direct type surface light source device 100, the incident surface 131 faces the exit surface 132.

The light guide 130 is made of a transparent resin material, for example, polymethylmethacrylate (PMMA), and a critical angle for total reflection of incident light by a diffraction grating D formed on the incident surface 131, as will be described later. Since diffracted above results in uniform surface light by the fine irregularities 136 formed on the emission surface 132, unlike the conventional method, it is unnecessary to form scattering fine particles for diffusing incident light inside the light guide body 130. Therefore, the problem that the luminance is lowered due to the light loss due to scattering is improved.

A reflector 120 is provided below the light source 110 to return the leaked light toward the light guide 130. In addition, as in FIG. 1A, a functional optical film layer (not shown), such as a diffusion sheet, a prism sheet, and / or a protective sheet, may be selectively stacked on the light guide 130.

The light source 110 may be formed in the form of a line light source of a cathode fluorescent light source (CCFL), an external electrode fluorescent light source (EEFL), or in the form of a point light source such as a light emitting diode (LED). When a plurality of light sources are installed, the plurality of light sources 110 are installed in a geometrically symmetrical structure so that the distribution density of incident light may have a minimum difference along the incident surface 131 of the light guide 130. In addition, it is preferable that the plurality of light sources 110 have the same shape and size in order to reduce the light distribution density difference with respect to the incident surface 131 due to the difference in shape.

In the present invention, the transmission diffraction grating region (D) is formed on the lower incident surface 131 of the light guide body 130 corresponding to each light source 110, and the transmission diffraction grating (D) forms the light source 110. Since the incident light introduced from the diffraction pattern is diffracted at an angle greater than or equal to the critical angle and propagated through the total reflection process, the light is uniformly distributed throughout the light guide body 130.

In addition, in the direct type surface light source device 100 according to the present invention, the light guided inside the light guide body 130 in the total reflection process as described above is a fine groove 136 formed on the exit surface 132 side of the light guide body 130. The light path is corrected by the light beams and is emitted above the light guide body 130. In this case, unlike the related art, it is not necessary to form scattering fine particles for scattering and diffusing incident light in the light guide body 130.

3 is a schematic diagram showing a diffraction process of light by a blaze diffraction grating having a sawtooth cross section according to an embodiment of the present invention. In FIG. 3, with respect to the direction of incident light, by placing the light source 110 in close proximity to the diffraction grating region D, all incident light introduced from the light source 110 to the diffraction grating region D is transferred to the diffraction grating plane ( It is possible to assume that it is perpendicular to S _D ), in which case the angle of the diffracted light by the transmission diffraction grating can be expressed by the following equation (1).

Where Λ is the pitch of the diffraction grating, n is the refractive index of the medium, m (0, ± 1, ± 2 ...) is the diffraction order, φ _m is the diffraction angle of the mth diffracted light, and λ is the wavelength of the incident light, respectively. Indicates. In this case, since the refractive index (n) of the medium and the wavelength (λ) of the incident light are respectively determined according to the material of the light guide 130 and the light source 110, the diffraction angle φ _{m of the} m-th diffracted light is It depends on the pitch Λ of. On the other hand, the critical angle θ _c for the total reflection is determined from Equation (2) below according to Snell's law of reflection.

For example, when the medium of the light guide 130 is made of a PMMA material having a refractive index n of 1.49, the critical angle θ _c for the total reflection is approximately 42 °.

Therefore, from the above equations (1) and (2), the pitch (Λ _c ) of the diffraction grating where the angle (φ _m ) of the m-th order diffracted light and the total reflection critical angle (θ _c ) are equal can be expressed by the following equation (3). have.

That is, as can be seen from equation (3), the pitch of the diffraction grating in which the angle φ _{m of the} m-th order diffracted light and the total reflection critical angle θ _c are equal is the incident light wavelength λ incident from the light source 110. Is an integer multiple of.

In the present invention, preferably, in determining the lattice pitch Λ in the diffraction grating region D, the angle of the first-order diffracted light diffracted while passing through the incident surface 131 of the light guide 130 is the light guide. By determining to be equal to or greater than the critical angle θ _c for total reflection inside 130, all of the incident light is diffracted to determine total reflection inside the light guide 130. However, when the diffraction angle of the first diffracted light becomes too large, since the amount of light emitted immediately above the light guide body 130 on which the diffraction grating is formed is reduced in other areas, it may cause luminance unevenness. It is necessary to design the second total diffraction light or higher order diffraction light to satisfy the total reflection conditions.

Accordingly, unlike the conventional diffuser plate in the direct type surface light source device, the light guide body 130 for the direct type surface light source device according to the present invention is diffracted by the diffraction grating area (D) so that the total internal reflection process is performed. After the light is uniformly distributed in the light guide body 130 through the uneven surface 136 formed on the light emitting surface 132 of the light guide body 130 by the uniform surface light to prevent luminance unevenness.

That is, by controlling the diffraction grating pitch Λ, the angle and the diffraction order of the appropriate diffracted light required for the light guide body 130 are determined so that the incident light is totally reflected immediately behind the incident surface 131 of the light guide body 130. The uniformity of the luminance emitted from the exit surface 132 of the light guide 130 is ensured despite the presence of light and dark portions generated due to the relative position of the light source 110 with respect to the light guide 130. In this respect, the light guide body 130 in the direct type surface light source device 100 according to the present invention is similar to the light guide plate in the conventional general side-illuminated surface light source in the control method of incident light.

In addition, unlike in the conventional surface light source device, it is not necessary to design a separate mechanism for diffusing into the light guide body 130 (for example, a bead formed in the conventional diffuser), and to secure luminance uniformity. Since there is no restriction to maintain the light source 110 and the light guide 130 at a predetermined distance, it is possible to shorten the distance T ₂ between the light source 110 and the light guide 130 and place them in close proximity. As a result, the surface light source device can be miniaturized / thinned and high brightness can be realized.

On the other hand, in the present invention, the depth of the diffraction grating D is controlled in relation to the diffraction efficiency (ratio of diffracted light amount to incident light amount). For convenience of analysis, assuming that the light irradiated from the light source 110 is incident perpendicularly to the blazed diffraction grating, the incident light undergoes phase modulation by the diffraction grating D, in which case the light transmission by the diffraction grating The function T (x) can be expressed by the following equation (4). This is shown in FIG. 4.

Here, x represents the longitudinal parameter of the light guide 130, Φ ₀ represents the maximum phase shift of the diffraction grating (D), respectively. The symbol? Represents a convolution, comb represents a comb function, and rect represents a rectangular function. For reference, in relation to assuming that the direction of light irradiated from the light source 110 to the diffraction grating is perpendicular, it is true that the light irradiated from the actual light source 110 has a certain divergence angle, but the light source 110 When the distance between the light guide 130 and the light guide 130 is very close, the incident light may be assumed to be vertically incident.

Transmitted light according to Equation (4) can be expressed by Equation (5) below when Fourier transforms into an angular spectrum.

In equation (5), the diffraction orders are represented by the spatial frequency p = N / Λ (N = 0, ± 1, ± 2, ± 3, ...), and the intensity or amplitude of the diffracted light is a sinusoidal function ) Depends on the position p = Φ ₀ / 2πΛ. This is shown in FIG. 5.

Referring to FIG. 5, there is no zero-order diffracted light and the first diffracted light satisfies the internal reflection condition to obtain the maximum diffraction efficiency when the maximum phase shift value of the diffraction grating D is 2π (FIG. 5 (b)). In this case, when there is no zero-order diffracted light, no illumination light directly contributes to the display element in the form of transmitted light among incident light, and all incident light is diffracted, which is advantageous for luminance control. Therefore, by controlling the phase of the diffraction grating appropriately, it is possible to control to become a surface light source by using light according to each diffraction order.

The depth of the diffraction grating such that the phase difference of the diffracted light becomes 2π with respect to the RGB tricolor light required for color implementation is shown in Table 1 below. For example, if the refractive index n of the light guide is 1.49, the depth of the diffraction grating is d = 2 * pi * wavelength / (n-1). However, the wavelength of RGB in the table may vary depending on the light source 110.

As described above, the uniformity of the luminance emitted from the exit surface 132 of the light guide 130 is determined by determining the angle and the diffraction order of the appropriate diffraction light required for the light guide 130 by controlling the above-described diffraction grating pitch. While being secured, it is possible to maintain the emitted light at high luminance by controlling the phase (or depth) of the diffraction grating related to the diffraction efficiency.

The size of the diffraction grating region D is preferably formed to substantially match the area range of the light guide 130 irradiated from a point light source such as an LED or a line light source such as a fluorescent lamp. When the area where the diffraction grating region D is formed is smaller than the irradiation area of the light source 110, some of the incident light does not diffraction and thus is not sufficient to secure luminance uniformity, and vice versa. This is because the light reflected from the back surface of the exit surface 132 abnormally emits light by the remaining portion of the diffraction grating region D, which may leak out of the incident surface 131 of the light guide body 130, resulting in a loss of the amount of emitted light.

In the present invention, the cross-sectional shape of the diffraction length region D is a diffraction grating having a sinusoidal cross section shown in FIG. 6 (b) instead of a blaze diffraction grating having a sawtooth-shaped cross section according to FIG. The cross-section shown in (c) can also be constituted by a diffraction grating having a cross-section in the form of a multi-tier step. Also in the sinusoidal diffraction grating or the multi-layered diffraction grating, only the diffraction efficiency is different compared with the above-described blaze diffraction grating, and the control of the pitch of the diffraction grating in relation to the angle change of the diffracted light is the same.

On the other hand, in the implementation of the color using light, RGB three-color light is required, and as described above, the three-color light supply by the light source 110 is arranged by mixing a pair of RGB point light source in the form of monochromatic light or mixing mixed light of RGB. A fluorescent light source in the form of a linear light source to generate may be used.

7 (a) to 7 (d) are light guides 130 for the direct type surface light source device 100 showing the arrangement of the diffraction gratings formed corresponding to the plurality of RGB point light source pairs according to the embodiment of the present invention. Bottom view of the.

In the embodiment of FIG. 7A, the RGB point light sources form one column for each color, and the rows are alternately arranged sequentially over the entire area of the light guide 130. Diffraction grating regions D _R and D in which the pitch of the diffraction grating is controlled on the incident surface 131 of the light guide 130 corresponding to each RGB light source arranged in units of columns so that each RGB color light satisfies the internal total reflection condition. _G , D _B ) are arranged. In this case, the pitch and depth of each diffraction grating region D _R , D _G , D _B are determined according to the RGB wavelength irradiated from the light source.

Such RGB diffraction grating regions (D _R , D _G , D _B ) or RGB point light sources are arranged in units of columns as shown in FIG. 7 (a), but three diffraction grating regions as shown in FIG. 7 (b). It is also possible that D _R , D _G , and D _B form a triangular cluster C, for example, and the gray lattice region in the unit of the cluster may be repeatedly formed on the bottom surface of the light guide 130. In this case, the geometry of the unit cluster C does not have a limiting meaning.

In each of the diffraction grating regions D _R , D _G , and D _B , the direction of the grating ridges is not aligned in any one direction as shown in FIG. 7 (a), but instead adjacent to the diffraction grating as shown in FIG. 7 (c). It is also possible to form so as to perpendicularly intersect the direction of the lattice ridges of the region, whereby the luminance uniformity is further improved. Furthermore, as shown in FIG. 7D, it is also possible to randomly form the ridge direction of the diffraction grating regions D _R , D _G , and D _B.

7 (a) to 7 (d), the planar shape of each of the diffraction grating regions D _R , D _G , and D _B is shown as a circle, but according to the planar shape of the corresponding point light source, Other shapes are possible.

The diffraction grating as described above may be used to remove a local dark area near the incident surface in the side-illumination type surface light source device using a point light source.

8 is a perspective view of a side-illuminated surface light source device according to an embodiment of the present invention. The light guide 130 ′ provides an incident surface 131 ′ in which at least one of the side cross sections introduces light from the light source 110, and the lower plane has a reflective surface for reflecting the light guided upwards ( 135 ', the upper plane provides an exit surface 132' for emitting illumination light to the outside. The cross-section of the light guide 130 'may be a wedge shaped in which the reflective surface 135' is inclined from the incident surface 131 'to the opposite end surface 134', or the reflective surface 135 'as shown in the drawing. ) And the exit surface 132 ′ may have a parallel flat plate shape. At least one light source 110 in the form of a point light source such as an LED is disposed at a predetermined interval near the entrance surface 131 '. Such a light source may be formed in the end surface 134 'opposite to the incident surface 131' despite being shown in the figure. A reflective sheet (not shown) is disposed on the reflective surface 134 'to cover the entire surface, and an additional diffusion film and at least one optical film layer selected from a prism sheet are further formed on the exit surface 132'. The illumination light emitted from the surface light source device improves the quality.

In the side-illumination type surface light source device 100 'according to the present invention, a diffraction grating region D having a size substantially corresponding to the area of the light source 110 corresponding to the light source 110 has the incident surface 131'. ) Is characterized by. The ridge line of the diffraction grating region D is formed perpendicular to the exit surface 132 'or the reflective surface 135'. Accordingly, incident light incident from the light source 110 is immediately diffracted from the rear surface of the incident surface 131 'toward the left and right side cross-sections 137' of the light guide body 130 ', thereby preventing the point light source 110 from being discontinuous. The local dark area near the incident surface 131 'due to the arrangement can be effectively removed to improve the brightness. In addition, since the light source 110 can be disposed very close to the incident surface 131 'of the light guide plate 130', the overall size of the surface light source device can be reduced and brightness can be improved.

Also in the side-illumination type surface light source device 100 'according to the present embodiment, the portions related to the pitch, depth area, and cross-sectional shape of the diffraction grating area D of the direct type surface light source device 100 are described. It can be controlled in the same manner as in the case.

Although the preferred embodiments of the present invention have been described above, the scope of the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit and characteristic constitution of the present invention. Therefore, the above-described embodiments in the present invention are illustrative only and do not have a limiting meaning, and the technical scope of the present invention should be understood to include the matters described in the claims of the present invention and all modifications that can be understood therefrom. do.

As described above, according to the present invention, a light guide that can prevent luminance unevenness and obtain high luminance can be realized even if the light distribution density of the incident surface is arranged in close proximity to the light source, and the surface light source using the light guide can be realized. The device can be manufactured in small and thin sizes.

Claims (15)

delete A light guide for guiding light incident from one or more light sources and converting the light into surface light, wherein a light diffraction grating corresponding to each light source is formed on an incident surface of the light guide opposite to the light source, and the diffraction grating is the light guide. A light guide, characterized in that formed on the opposite side of the exit surface of the sieve. The light guide according to claim 2, wherein the pitch of the diffraction gratings is determined such that the angle of the first diffracted light forms an angle equal to or greater than a critical angle for total internal reflection. The light guide according to claim 2, wherein the depth of the diffraction grating is controlled such that the maximum phase displacement of incident light by the diffraction grating is 2 [pi]. The light guide according to claim 2, wherein fine projections for emitting diffracted light are formed on an exit surface of the light guide. The method according to claim 2, wherein the light source is present in the point light source pair of one or more RGB wavelengths arranged in a symmetrical structure under the light guide, wherein the pitch and depth of the diffraction grating are each determined to be a separate value according to the RGB wavelength A light guide characterized by the above. delete The light guide according to claim 2, wherein the diffraction grating has a cross-sectional shape of a blaze diffraction grating. The light guide according to claim 2, wherein the diffraction grating has a sine wave or step shape in cross section. The light guide according to claim 2, wherein the area of the diffraction grating corresponds to a region to which incident light from the light source is irradiated. A light source comprising a light source in the form of a point or linear light source and a light guide according to any one of claims 2 to 6 or 8 to 10 as an element for converting incident light from the light source into surface light. Light source device. 12. The surface light source device according to claim 11, wherein the light source exists as one or more pairs of RGB point light sources arranged geometrically symmetrically under the light guide. The surface light source device according to claim 11, wherein the diffraction grating has a cross-sectional shape of a blaze diffraction grating. The surface light source device according to claim 11, wherein the diffraction grating has a sine wave or step shape in cross section. The surface light source device according to claim 11, wherein an area of the diffraction grating corresponds to a region to which incident light from the light source is irradiated.

Images