WO2025181288A1 - Lighting device for a vehicle comprising a light guide - Google Patents

Abstract

The invention relates to a lighting device (1) for a vehicle (2) comprising a light source (10) and a light guide (11), characterised in that the light guide (1) comprises: - a light entry grating (111) comprising first patterns (1110) having a first angle (α) and being repeated periodically, wherein the light source (10) is arranged facing the light entry grating (111); - a light exit grating (112) comprising second patterns (1120) having a second angle (α') and being repeated in the same periodic manner as the first patterns (1110), wherein the first angle (α) and the second angle (α') are equal in terms of absolute value and in the same direction or in opposite directions, and in that the first patterns (1110) and the second patterns (1120) have a cross section in the shape of a right triangle.

Description

Vehicle lighting device comprising a light guide

The present invention relates to a lighting device for a vehicle. It also relates to a lighting assembly comprising such a lighting device. It finds a particular but non-limiting application in motor vehicles.

In the field of motor vehicles, a light device known to those skilled in the art comprises:
- a light source configured to emit light rays,
- a surface light guide comprising a body in the form of a light guide sheet configured to propagate said light rays emitted by the light source.

A disadvantage of this prior art is that the light guide sheet has a very thin thickness and the size of the light source is too large compared to the thickness of the light guide sheet. As a result, a large portion of the light rays emitted by the light source do not enter the light guide; only about 15% of the light generated by the light source is coupled into the surface light guide. The luminous efficiency of the surface light guide is thus low.

In this context, the present invention aims to provide a light device which makes it possible to solve the mentioned drawback.

To this end, the invention provides a vehicle lighting device comprising a vehicle lighting device, said lighting device comprising:
- a light source configured to emit light rays,
- a light guide comprising a body configured to propagate said light rays emitted by said light source,
characterized in that said light guide further comprises:
- a diffraction light input grating comprising a plurality of first optical patterns having a first angle and periodically repeated according to a first period, - a diffraction light output grating comprising a plurality of second optical patterns having a second angle and periodically repeated according to a second period equal to the first period, said first angle and said second angle being equal in absolute value and of the same direction or of the opposite direction,
and in that said light source is arranged opposite said light input array such that light rays enter said light input array.

According to non-limiting embodiments, said light device may further comprise one or more additional characteristics taken alone or in all technically possible combinations, among the following.

According to a non-limiting embodiment, said first patterns and said second patterns have a cross-section in the shape of a right triangle

According to a non-limiting embodiment, said first patterns and said second patterns respectively have a top having a flat surface.

According to a non-limiting embodiment, said light input network and said light output network are arranged on the same surface of the light guide. This makes it possible to simplify the manufacturing process of the light device and to reduce the process time.

According to a non-limiting embodiment, said light input network and said light output network are arranged on different surfaces of the light guide. This allows different integration of the light input network and the light output network in the light device.

According to a non-limiting embodiment, said first optical patterns and said second optics protrude from a surface of the light guide. This allows for a simple manufacturing process.

According to a non-limiting embodiment, said first optical patterns and said second optics are hollow relative to a surface of the light guide. This makes it possible to have a more compact light device.

According to a non-limiting embodiment, said first optical patterns and said second optics are of the same size. This makes it possible to simplify the manufacturing process of the light device. In fact, only a single manufacturing mask is used by reversing the orientation of the mask when necessary.

According to a non-limiting embodiment, said light device further comprises a light collimator arranged between said light source and said light guide so as to form a collimated light beam which arrives with normal incidence on said light input network. This makes it possible to increase the luminous efficiency of the light device.

According to a non-limiting embodiment, said light device comprises a single light output network.

According to a non-limiting embodiment, said light source is monochromatic.

According to a non-limiting embodiment, said light guide is a surface light guide and said body is in the form of a light guide sheet. This makes it possible to extend over all or part of a flat or curved surface.

According to a non-limiting embodiment, the first optical patterns and the second optical patterns are of the same material as said body of said light guide or of a different material.

According to a non-limiting embodiment, the first optical patterns and the second optical patterns have the same refractive index of light as the body of said light guide for a given wavelength.

According to a non-limiting embodiment, the first optical patterns and the second optical patterns are formed in the mass of said body of said light guide.

According to a non-limiting embodiment, the light device has a first direction and a second direction opposite to the first direction and parallel to the first direction, said first direction being transverse to the body of said light guide.

According to a non-limiting embodiment, the first optical patterns have a cross-section in the shape of a right triangle in a plane parallel to the first direction and to the second direction.

According to a non-limiting embodiment, the second optical patterns have a cross-section in the shape of a right triangle in a plane parallel to the first direction and to the second direction.

According to a non-limiting embodiment, said light input network and said light output network are arranged on the same surface of the light guide and each have an arrangement of surface slots extending obliquely relative to the surface of the light guide respectively at said first angle and said second angle.

According to a non-limiting embodiment, the light guide is surrounded by a layer comprising a second transparent material having a second refractive index which is lower than the first refractive index of the material of the light guide, said light input network and/or said light output network are arranged between the light guide and the layer.

According to a non-limiting embodiment, the light guide comprises an element comprising phosphor, said phosphor being intended to receive a light beam from the second diffraction grating, said phosphor being configured to produce a polychromatic light beam.

Further provided is a vehicle lighting assembly, characterized in that said lighting assembly comprises said light device according to one of the preceding characteristics.

According to a non-limiting embodiment, said light assembly is a front face or a rear face of a vehicle or a projector or a rear light of a vehicle. This makes it possible to create illuminated patterns.

According to a non-limiting embodiment, said light assembly is part of an element of the passenger compartment of said vehicle. According to non-limiting variant embodiments, the light assembly is part of the dashboard or a door of the vehicle. This makes it possible to illuminate certain parts of the dashboard or a door inside the passenger compartment of the vehicle.

The invention and its various applications will be better understood by reading the following description and examining the accompanying figures:

is a schematic illustration of a light device according to a first alternative embodiment of a first non-limiting embodiment of the invention, the light device comprising a light source, a light guide with a body, a diffraction light input grating with first patterns, and a diffraction light output grating with second patterns,

is a zoom on the light input network of the light guide of the light device of the ,

is a zoom on a light output network of the light guide of the light device of the ,

is a schematic illustration of a light device according to a second alternative embodiment of a first non-limiting embodiment of the invention, the light device comprising a light source, a light guide with a body, a diffraction light input grating with first patterns, and a diffraction light output grating with second patterns,

is a zoom on the light input network of the light guide of the light device of the ,

is a zoom on the light output network of the light guide of the light device of the ,

is a schematic illustration of a light device according to a first alternative embodiment of a second non-limiting embodiment of the invention, the light device comprising a light source, a light guide with a body, a diffraction light input grating with first optical patterns, and a diffraction light output grating with second optical patterns,

is a schematic illustration of a light device according to a second alternative embodiment of a second non-limiting embodiment of the invention, the light device comprising a light source, a light guide with a body, a diffraction light input grating with first patterns, and a diffraction light output grating with second patterns,

is a schematic illustration of a top view of the body of the light device of the ,

is a schematic illustration of a top view of the light device of the , said light device further comprising a light collimator disposed between said light source and said light guide according to a non-limiting embodiment,

is a schematic illustration of a non-limiting embodiment of a lighting assembly of a vehicle, said lighting assembly comprising a light device according to the ,

is an enlarged view of a first optical pattern of the light input grating of the , when said first pattern is manufactured,

is an enlarged view of a second optical pattern of the light output grating of the , when said second pattern is manufactured,

is an enlarged view of a first optical pattern of the light input grating of the , when said first pattern is manufactured,

is an enlarged view of a second optical pattern of the light output grating of the , when said second pattern is manufactured,

is a 3D view of the light input network of the , And

is a 3D view of the light output network of the .

Identical elements, by structure or function, appearing in different figures retain, unless otherwise specified, the same references.

The light device 1 according to the invention is described with reference to Figures 1 to 17. In a non-limiting embodiment, the light device 1 is a light device of a vehicle 2 (illustrated in the ). In a non-limiting embodiment, the vehicle 2 is a motor vehicle. By motor vehicle is meant any type of motorized vehicle. This embodiment is taken as a non-limiting example in the remainder of the description. In the remainder of the description, the vehicle 2 is thus otherwise called motor vehicle 2. In a non-limiting variant embodiment, the vehicle 2 is a thermal vehicle or an electric vehicle or a hybrid vehicle.

The light device 1 is part of a light assembly 3. In non-limiting embodiments, the light assembly 3 is a front face or a rear face of the motor vehicle 2 or a headlight or a rear light of the motor vehicle 2. In the non-limiting example of the , the light assembly 3 is the front face of the motor vehicle 2. In another non-limiting embodiment, the light assembly 3 is part of an element of the passenger compartment of the motor vehicle 2. In non-limiting variant embodiments, the light assembly 3 is part of the dashboard or a door of the motor vehicle 2. The non-limiting embodiment of the front face is taken as a non-limiting example in the remainder of the description.

As illustrated in Figures 1, 4, 7 and 8, the light device 1 comprises:
- a light source 10, and
- a light guide 11 comprising a body 110, a light input grating 111 by diffraction and a light output grating 112 by diffraction. The light input grating 111 by diffraction is otherwise called light input grating 111 or input diffraction grating 111 in the remainder of the description. Said light output grating 112 by diffraction is otherwise called light output grating 112 or output diffraction grating 112 in the remainder of the description. The light input grating 111 and the light output grating 112 are 1D gratings.

As illustrated in Figures 1, 4, 7 and 8, the light device 1 has a first direction D (otherwise called the observation direction) and a second direction D' opposite the first direction D and parallel to the first direction D. The first direction D is transverse (otherwise called perpendicular) to the body 110 of the light guide 11. The first direction D corresponds to the direction in which an external observer can observe the light assembly 3 of the motor vehicle 2 comprising said light device 1. The light device 1 has a light emission direction which corresponds to the first direction D.

We will speak of forward direction or backward direction respectively for the first direction D and the second direction D'. In the non-limiting example illustrated in the figures, the directions D and D' are substantially parallel to the vehicle axis Ox (illustrated in the ).

The light source 10 is configured to emit light rays R. It is arranged opposite said light input network 111 so that its light rays R which form a first light beam Fx enter the light input network 111.

In a non-limiting embodiment, the light source 10 is a semiconductor light source. In a non-limiting embodiment, the semiconductor light source is part of a light-emitting diode or a laser diode. By light-emitting diode, we mean any type of light-emitting diode, whether in non-limiting examples LEDs (“Light Emitting Diodes” in English), OLEDs (“Organic LEDs” in English), AMOLEDs (“Active-Matrix-Organic LEDs” in English), or FOLEDs (“Flexible OLEDs” in English).

In a non-limiting embodiment, the light source 10 is a monochromatic source. In non-limiting alternative embodiments, it is a monochromatic R (red), G (green) or B (blue) source. As a reminder, for a monochromatic source:
- B: the wavelength of light λ is 455 nanometers (nm),
- G: the wavelength of light λ is 535 nanometers,
- A: The wavelength of light λ is 621 nanometers.

Due to the monochromatic source, the first light beam Fx is monochromatic.

In a first non-limiting embodiment, the light guide 11 is a light guide in the form of a rod. In non-limiting embodiments, it is of round or square section.

In a second non-limiting embodiment, the light guide 11 is surface-based. A surface-based light guide is understood to mean an optical guide element of which one of the dimensions is much smaller than the other two dimensions in space, for example smaller by one or more orders of magnitude. Here, the thickness of the light guide 11 is much smaller than its length and its width. In a non-limiting embodiment, the light guide 11 has a thickness of between 125 and 2000 micrometers. The light guide 11 is thus very thin. When the light guide 11 is surface-based, its body 110 is in the form of a light guide sheet. In a manner known to those skilled in the art, the light guide sheet comprises one or more regions with one or more light emission zones. In a non-limiting embodiment, the light emission zone(s) form all or part of a decoupling pattern (not shown). The decoupling pattern is thus illuminated by the light generated by the light source 10 which emerges from the light guide 11.

The light guide 11 is a flexible light guide. Flexible means that it can bend without being damaged or breaking. Because it is flexible, it can fit on flat or curved surfaces.

The light guide 11 is transparent. The term transparent indicates that the material of which it is composed allows visible light to pass through, at least partially, and in particular the light emitted by the light source 10.

In a non-limiting embodiment, the light guide 11 is made of polycarbonate (PC), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), or polyethylene terephthalate (PET). Such materials make it possible to produce a flexible and transparent light guide 11.

The material of the light guide 11 comprises a refractive index of light n’ less than 1.8. This makes it possible to correctly reflect and propagate the light generated by the light source 10 in the body 110 of the light guide 11.

The light guide 11 comprises a first surface 1.1 and a second surface 1.2 opposite the first surface 11.1.

The body 110 of the light guide 11 is configured to propagate the light rays R emitted by the light source 10. The body 110 has the refractive index of light n'.

In a non-limiting embodiment, the body 110 has a thickness e determined so as to avoid total reflection of the light in said body 110 to prevent the light from exiting through the light entry network 111. In a non-limiting embodiment, the light guide 11 has a thickness e greater than or equal to 125 μm. In a non-limiting embodiment variant, the thickness e is equal to 500 μm. In this way, the light is diffracted in the body with a diffraction angle θ of 45°.

The light input grating 111 and the light output grating 112 are surrounded by air of refractive index n = 1.

As illustrated in Figures 2 and 5, the light input grating 111 comprises a plurality of first optical patterns 1110 which are diffractive optical patterns (otherwise called first patterns 1110) periodically repeated according to a first period T. The light input grating 111 makes it possible to diffract the light generated by the light source 10 and to control the direction in which the light will propagate in the body 110 of the light guide 11. In a non-limiting embodiment, the first period T is between 400 nanometers and 600 nanometers.

The light (namely the first light beam Fx) from the light source 10 is coupled to the light input grating 111. It is diffracted in the material of the light guide 11 by means of the light input grating 111, then when it encounters a wall of the light guide beyond the light input grating 111, it is reflected by reflection in the body 110 of the light guide 11 which achieves the guiding effect in said body 110. Thanks to the first patterns 1110, the light input grating 111 makes it possible to send the light into the body 110 of the light guide with a diffraction angle θ of 45°. This prevents the light from exiting through the light input grating 111.

As illustrated in Figures 2 and 5, the first optical patterns 1110 have a cross-section in the shape of a right triangle in a plane parallel to the first direction D and to the second direction D' opposite to the first direction D. In other words, the first patterns 1110 have in a section through a plane parallel to the first direction D and to the second direction D' a right triangle shape. In particular, the section is in the shape of an open right triangle. For this purpose, the first optical patterns 1110 comprise a first vertex 1110.1, a first wall 1110.2, a second wall 1110.3 and a first open base 1110.4. The first open base 1110.4 is planar. The first wall 1110.2 is vertical, namely it extends along the first direction D. The second wall 1110.3 is inclined.

Since the light input array 111 is a 1D array, its shape can be seen in a 3D view illustrated in the in the context of a non-limiting variant embodiment illustrated in the .

Each first optical pattern 1110 has a first angle α which is the angle between the first open base 1110.4 and the second wall 1110.3. In a non-limiting embodiment, the first angle α is equal to 45° plus or minus 10%. It will be noted that in a certain configuration we can have |α| = |θ|.

As illustrated in Figures 3 and 6, the light output grating 112 comprises a plurality of second optical patterns 1120 which are diffractive optical patterns (otherwise called second patterns 1120) periodically repeated according to a second period T'. The light which has propagated by reflection in the body 110 of the light guide 11 is output coupled with the light output grating 112 and emerges in a second light beam Fx' by said light output grating 112 in the first direction D. This makes it possible to illuminate the light assembly 3 of which the light device 1 is part. The first light beam Fx being monochromatic, the second light beam Fx' is also monochromatic.

As illustrated in Figures 3 and 6, the second optical patterns 1120 have a cross-section in the shape of a right triangle in a plane parallel to the first direction D and to the second direction D' opposite to the first direction D. In other words, the second patterns 1110 have in a section through a plane parallel to the first direction D and to the second direction D' a right triangle shape. In particular, the section is in the shape of an open right triangle. For this purpose, the second optical patterns 1120 comprise a second vertex 1120.1, a third wall 1120.2, a fourth wall 1120.3 and a second open base 1120.4. The second open base 1120.4 is planar. The third wall 1120.2 is vertical, namely it extends along the first direction D. The fourth wall 1120.3 is inclined.

Since the light output array 112 is a 1D array, its shape can be seen in a 3D view illustrated in the in the context of a non-limiting variant embodiment illustrated in the .

Each second optical pattern 1120 has a second angle α’ which is the angle between the second open base 1120.4 and the fourth wall 1120.3. In a non-limiting embodiment, the second angle α’ is equal to 45° plus or minus 10%. The second angle α’ is equal to the first angle α in absolute value. It will be noted that in a certain configuration we can have |α’| = |θ|.

The first period T and the second period T’ are functions of the wavelength λ of the light generated by the light source 10. We recall that the first period T = λ/(n’*sinα).

It is recalled that the wavelength λ = c.t = c/f with t the time period, f the frequency and c the speed. The light which has a given wavelength λ arrives on a light input grating 110 which has a first period T which is close to its time period t. Thus, it can enter into resonance with it and thus allows a coupling of the light with the light input grating 110. The first period T is very close to the time period t. In a non-limiting embodiment, the first period T is different from the time period t by 5% to 10%.

The second period T' is equal to the first period T. Thus, the light output grating 112 has the same periodicity as the light input grating 111. This facilitates the manufacturing process. The diffraction of the light at the output of the light guide 11 will thus also be very efficient since the second period T' is thus also very close to the time period t corresponding to the wavelength λ of the light generated by the light source 10. The first period T and the second period T' are of fixed values.

In a non-limiting embodiment illustrated in Figures 2 and 3, and 5 and 6, the first optical patterns 1110 and the second optical patterns 1120 are of the same size. Thus, they are of the same height h, and distributed respectively according to the same period T, T'. They also have the same width w for their base 1110.4 and 1120.4. This allows for a simpler manufacturing process than if they were of different sizes.

The width w is equal to the fill factor Ff divided by the period T or T’. The fill factor Ff is also called “Fill Factor” in English. We thus have Ff=w/T=w/T’.

In a non-limiting embodiment, for λ=631nm, h=565nm, |α|=|α’|= 45°, T = T’= 565nm, n’=1.58, with w=T.

Thus, the first optical patterns 1110 are defined by the first angle α, and the height h, and the fill factor Ff. Thus, in the same way, the second optical patterns 1110 are defined by the second angle α’, the height h, and the fill factor Ff.

In a first embodiment illustrated in Figures 1 and 4, the light input network 111 and the light output network 112 are arranged on the same surface of the light guide 11, namely on the same surface of the body 110. In the non-limiting example illustrated, they are arranged on the first surface 11.1 which is turned towards the first direction D. Thus, the coupling of the light entering the light guide 11 with the light input network 111 takes place on the same side as the coupling of the light leaving the light guide 11 with the light output network 112.

In this first non-limiting embodiment illustrated in Figures 1 and 4, the second angle α’ and the first angle α are in opposite directions. They are oriented in opposite directions.

In a first non-limiting variant embodiment illustrated in the , the first optical patterns 1110 and the second optical patterns 1120 protrude relative to a surface, here the first surface 1.1, of the light guide 11. They thus form protrusions relative to the body 110 and originate from one of its faces, here the first surface 1.1. The first optical patterns 1110 and the second optical patterns 1120 have the same light refractive index. The first optical patterns 1110 and the second optical patterns 1120 are of the same material as the body 110 or of a different material but with the same refractive index for the given wavelength λ, here 631nm. Thus, in a non-limiting example, if the body 110 is made of PC, the first optical patterns 1110 and the second patterns 1120 are also made of PC. In this projecting case, the first base 1110.4 and the second base 1120.4 respectively of the first optical patterns 1110 and the second optical patterns 1120 are open on the body 110 of the light guide 11. The light device 1 comprises only one light output network 112 arranged on the first surface 1.1 of the light guide 11.

In this first non-limiting variant embodiment, as illustrated in the , the first angle α is the angle between the first open base 1110.4 and the second inclined wall 1110.3, said first angle α being defined in the counterclockwise direction. And, as illustrated in the , the second angle α' is the angle between the second open base 1120.4 and the fourth inclined wall 1120.3, said second angle α' being defined in the clockwise direction.

It will be noted that to produce these first optical patterns 1110 and second optical patterns 1120 in projection, in non-limiting embodiments, it is possible to use:
- the UV (“Ultra-Violet”) illumination process, otherwise known in English as “Grayscale Lithography”,
- the electron beam lithographic process, also known as “E-beam Lithography”, which uses a non-flexible photomask that can be transferred onto a large roller to obtain flexible replica parts of the photomask.

The UV illumination process includes in particular:
- depositing a photoresist layer on a substrate and exposing the assembly to UV rays which arrive in a direction normal to the substrate-photoresist layer assembly to print the first optical patterns 1110 and the second optical patterns 1120 on a flexible surface so as to obtain a flexible photomask called in English "master" with a transmission gradient of the UV lamp at 405 nanometers,
- the transfer of the flexible photomask onto a large roll by nano-lithographic printing, otherwise known in English as “Nanoimprinting Lithography”,
- the production of photomask replica parts industrially with this large roll.

It will be noted that the photoresist layer comprises the same refractive index n' as the body 110 of the light guide 11. This allows the light to be diffracted and then guided into the light guide 11.

The electron beam lithographic process includes in particular:
- depositing a non-photoresist layer on a substrate and etching each first optical pattern 1110 and each second optical pattern 1120 one by one on this non-photoresist layer with an electron beam so as to obtain a non-flexible photomask,
- the production of flexible replica parts by nano-lithographic printing, otherwise known in English as “Nanoimprinting Lithography”,
- the transfer of these flexible replica parts onto a large roller for industrial production.

It will be noted that the non-photoresistive layer comprises the same refractive index n' as the body 110 of the light guide 11. This allows the light to be diffracted and then guided into the light guide 11.

Since these two methods are known to those skilled in the art, they are not described in further detail.

Unlike manufacturing processes such as electron beam lithography or laser etching, which only allow each first optical pattern 1110 and each second optical pattern 1120 to be etched one by one for the photomask, with the UV illumination process, all of the first optical patterns 1110 and the second optical patterns 1120 are directly produced at a nanometric scale. This is compatible with the so-called roll-to-plate process for modeling large light guides 11. It is thus possible to expose a very large surface area and thus etch over a very large surface area in a single pass by removing parts of the photoresist layer to create the first optical patterns 1110 and the second optical patterns 1120.

In this first non-limiting variant embodiment, in a non-limiting embodiment illustrated in the , the first optical patterns 1110 have a top 1110.1 having a flat. This makes it easier to manufacture them. In the same way, in a non-limiting embodiment illustrated in the , the second optical patterns 1120 have a vertex 1120.1 having a flat. This makes it easier to manufacture them. In a non-limiting embodiment, the flat is approximately 25 nanometers. A lower value is difficult to achieve in the manufacturing process.

In a second non-limiting variant embodiment illustrated in the , the first optical patterns 1110 and the second optical patterns 1120 are hollow relative to a surface, here the first surface 1.1, of the light guide 11. They thus form ribs in the body 110. They are hollowed out in the body 110. They are formed in the mass of the body 110 of the light guide 11. The first optical patterns 1110 and the second optical patterns 1120 are here less exposed to the environment which prevents them from being damaged. In this hollow case, the first base 1110.4 and the second base 1120.4 respectively of the first optical patterns 1110 and of the second optical patterns 1120 are open to the outside.

In this second non-limiting variant embodiment, as illustrated in the , the first angle α is the angle between the first open base 1110.4 and the second inclined wall 1110.3, said first angle α being defined in the clockwise direction. And, as illustrated in the , the second angle α' is the angle between the second open base 1120.4 and the fourth inclined wall 1120.3, said second angle α' being defined in the counterclockwise direction.

It will be noted that to produce these first optical patterns 1110 and second optical patterns 1120 in hollow form, in non-limiting embodiments, it is possible to use:
- the UV illumination process described above, or
- the electron beam lithographic process described previously.

Unlike manufacturing processes such as electron beam lithography or laser etching, which only allow each first optical pattern 1110 and each second optical pattern 1120 to be hollowed out one by one for the photomask, with the UV illumination process, all of the first optical patterns 1110 and the second optical patterns 1120 are hollowed out directly by UV at the nanometric scale. This is compatible with a so-called roll-to-plate process for shaping large light guides 11. It is thus possible to expose a very large surface area and thus hollow out a very large surface area in a single pass by removing parts of the photoresist layer to create the first optical patterns 1110 and the second optical patterns 1120.

In this second non-limiting variant embodiment, in a non-limiting embodiment illustrated in the , the first optical patterns 1110 have a top 1110.1 having a flat. This makes it easier to manufacture them. In the same way, in a non-limiting embodiment illustrated in the , the second optical patterns 1120 have a vertex 1120.1 having a flat. This makes it easier to manufacture them. In a non-limiting embodiment, the flat is approximately 25 nanometers. A lower value is difficult to achieve in the manufacturing process.

In a second embodiment illustrated in Figures 7 and 8, the light input network 111 and said light output network 112 are arranged on different surfaces 11.1, 11.2 of the light guide 11. Thus, in the non-limiting example illustrated in Figures 7 and 8, the light input network 111 is arranged on the second surface 11.2 facing the second direction D' and said light output network 112 is arranged on the first surface 11.1 facing the first direction D. Thus, the coupling of the light entering the light guide 11 with the light input network 111 takes place on the opposite side to the coupling of the light leaving the light guide 11 with the light output network 112.

In this second non-limiting embodiment illustrated in Figures 7 and 8, the second angle α’ and the first angle α are in the same direction. They are oriented in the same direction.

In a first non-limiting variant embodiment illustrated in the , the first optical patterns 1110 and the second optical patterns 1120 protrude relative to a surface of the light guide 11. They thus form protrusions relative to the body 110 and originate from one of its faces. The first optical patterns 1110 and the second optical patterns 1120 are of the same material as the body 110 or of a different material but with the same refractive index for the given wavelength λ, here 631nm. In this protruding case, the first base 1110.4 and the second base 1120.4 respectively of the first optical patterns 1110 and of the second optical patterns 1120 are open on the body 110 of the light guide 11. The light device 1 comprises only a single light output network 112 arranged on the first surface 1.1 of the light guide 11.

In this first non-limiting variant embodiment, the first optical patterns 1110 protrude relative to the second surface 1.2 of the light guide 11, and the second optical patterns 1120 protrude relative to the first surface 1.1 of the light guide 11.

In this first non-limiting variant embodiment, as illustrated in the , the first angle α is the angle between the first open base 1110.4 and the second inclined wall 1110.3, said first angle α being defined in the counterclockwise direction. And, as illustrated in the , the second angle α' is the angle between the second open base 1120.4 and the fourth inclined wall 1120.3, said second angle α' being defined in the counterclockwise direction. Note that it is necessary to look at the upside down for this first variant of the production of the , namely by turning it vertically.

It will be noted that to produce these first optical patterns 1110 and second optical patterns 1120 in projection, in non-limiting embodiments, it is possible to use:
- the UV illumination process described above, or
- the electron beam lithographic process described above.

In this first non-limiting variant embodiment, in a non-limiting embodiment illustrated in the , the first optical patterns 1110 have a top 1110.1 having a flat. This makes it easier to manufacture them. In the same way, in a non-limiting embodiment illustrated in the , the second optical patterns 1120 have a vertex 1120.1 having a flat. This makes it easier to manufacture them. In a non-limiting embodiment, the flat is approximately 25 nanometers. A lower value is difficult to achieve in the manufacturing process.

In a second non-limiting variant embodiment illustrated in the , the first optical patterns 1110 and the second optical patterns 1120 are hollow relative to a surface of the light guide 11. They thus form ribs or slots in the body 110. They are hollowed out in the body 110. They are formed in the mass of the body 110 of the light guide 11. The first optical patterns 1110 and the second optical patterns 1120 are here less exposed to the environment which prevents them from being damaged. In this hollow case, the first base 1110.4 and the second base 1120.4 respectively of the first optical patterns 1110 and of the second optical patterns 1120 are open to the outside.

In this second non-limiting variant embodiment, the first optical patterns 1110 are hollow relative to the second surface 1.2 of the light guide 11, and the second optical patterns 1120 are hollow relative to the first surface 1.1 of the light guide 11. The light device 1 comprises only a single light output network 112 arranged along the first surface 1.1 of the light guide 11.

In this second non-limiting variant embodiment, as illustrated in the , the first angle α is the angle between the first open base 1110.4 and the second wall 1110.3, said first angle α being defined in the clockwise direction. And, as illustrated in the , the second angle α' is the angle between the second open base 1120.4 and the fourth wall 1120.3, said second angle α' being defined in the clockwise direction. Note that it is necessary to look at the upside down for this second variant of the production of the , namely by turning it vertically.

It will be noted that to produce these first optical patterns 1110 and second optical patterns 1120 in hollow form, in non-limiting embodiments, it is possible to use:
- the UV illumination manufacturing process described above, or
- the electron beam lithographic process described previously.

In this second non-limiting variant embodiment, in a non-limiting embodiment illustrated in the , the first optical patterns 1110 have a top 1110.1 having a flat. This makes it easier to manufacture them. In the same way, in a non-limiting embodiment illustrated in the , the second optical patterns 1120 have a vertex 1120.1 having a flat. This makes it easier to manufacture them. In a non-limiting embodiment, the flat is approximately 25 nanometers. A lower value is difficult to achieve in the manufacturing process.

There is a top view of a light device 1 comprising a surface light guide 11 applied to the cases of figures 1, 4, 7 or 8. The light output network 112 can be seen next to the light input network 111 which is located in the center of the body 110 which is in the form of a light guide sheet in the case of a surface light guide 11.

In a non-limiting embodiment illustrated in the , the light device 1 further comprises a light collimator 12 arranged between the light source 10 and the light guide 11 so as to form a first collimated light beam Fx'' which arrives with a normal incidence on said light input network 111. The light collimator 12 makes it possible to straighten the light rays R from the light source 10 so that they arrive at normal incidence on the light input network 110 of the light guide 11. Consequently, this makes it possible to recover a plane light wave at the input of the light guide 11 which increases the luminous efficiency of the light guide 11. In non-limiting embodiments, the light collimator is an MLA collimator which is the acronym for "Matrix Lens Array" in English or a light collimator composed of vertical cavity laser diodes referenced VCSEL.

Of course, the description of the invention is not limited to the embodiments described above and to the field described above.

Thus, the invention described has in particular the following advantages:
- it makes it possible to increase the efficiency of light collection at the input of the light guide 11 and the efficiency of the light at the output of the light guide 11. Thus, according to the experiments, an input efficiency of up to substantially 56% is obtained, namely the light emitted by the light source 10 enters the light guide 11 at 56%; and an output efficiency of up to substantially 56% is obtained, namely the light emerges at substantially 56% from the light guide 11 compared to the light propagated in the light guide 11, and an output efficiency between 50% and 56% if a light collimator 12 is added,
- it makes it possible to reduce light losses and is thus more efficient than a light device which would comprise a surface light guide with a light guide sheet and folded light injection elements, known to those skilled in the art, to form a stack through which the light rays from the light source enter. Indeed, in the case of folded light injection elements and thus comprising a fold, the light rays from the light source which reach this fold are not reflected towards the light guide sheet, resulting in a loss in luminous efficiency,
- it makes it possible to have first optical patterns 1110 and second optical patterns 1120 compatible with a large-scale manufacturing method; it reduces the manufacturing process time of the photomask compared to a solution that uses electron beam lithography or laser etching, because the first optical patterns 1110 and second optical patterns 1120 do not have shadow areas, shadow areas that are not reachable by the UV beam for example as in the case of first optical patterns 1110 and second optical patterns 1120 inclined with a parallelogram-shaped cross-section; a shadow area being defined by the projection of an inclined wall of an optical pattern onto the body 110 of the light guide 11 and being hidden when an observer observes from the outside the light assembly 3 comprising the light device 1 with the light guide 11,
- it thus allows for a more efficient lighting device.

According to all the embodiments described below but not illustrated, the aim is to provide a solution to the drawbacks of the prior art by proposing an improved light guide. The light guide is configured to be integrated into a light device which is itself intended to equip a motor vehicle. Throughout the description, the motor vehicle is a motor vehicle of any type, in particular a passenger vehicle, a utility vehicle, a truck or even a bus.

The light device comprises at least one light guide and at least one light source configured to produce a monochromatic light beam. The light from such a light source comprises only rays of a single wavelength, that is, it comprises only light rays having a specific color.

Thus, according to one embodiment of the light device, the light source of said light device emits a monochromatic light of blue color having a wavelength between 450 nm and 460 nm, or even equal to 455 nm.

Generally, the light guide comprises a waveguide comprising a transparent material having a first refractive index. This transparent material may in particular be polycarbonate. The first refractive index is for example between 1.4 and 1.8. According to a preferred embodiment, this first refractive index is more particularly equal to 1.6065.

Optionally, the waveguide may be surrounded by a protective layer comprising a second transparent material having a second refractive index which is lower than the first refractive index of the waveguide material. The waveguide has, for example, a thickness of between 50 µm and 125 µm. According to a preferred embodiment, the thickness of the waveguide is equal to 75 µm.

The light guide further comprises a first diffraction grating at the input of the waveguide and configured to allow the monochromatic light beam from the light source included by the light device within which the light guide is intended to be arranged to pass, so that said light beam enters inside said waveguide to propagate therein. To do this, at least one light source is juxtaposed with the first diffraction grating so that the light beam passes through said first diffraction grating and then enters the waveguide inside which it propagates. In an embodiment not shown, the light beam is reflected by the interface between the waveguide and the protective layer with an angle of 45°.

The light guide also comprises at least one second diffraction grating at the output of the waveguide and distinct from the first diffraction grating, the second diffraction grating being configured to allow the monochromatic light beam to exit the waveguide and towards an environment outside the light guide. A portion of the light beam which propagates inside the waveguide therefore passes through the second diffraction grating to exit the waveguide.

The term "diffraction grating" herein refers to an optical device composed of a series of parallel slits that are regularly spaced. The spacing between two neighboring slits is called the "pitch" of the grating. The term "series of slits" refers to any surface provided with reliefs configured to form a diffraction grating.

Several configurations can be imagined for the distribution of the first diffraction grating and the second diffraction grating(s) within the light guide. Indeed, the light guide can comprise several second diffraction gratings.

The first diffraction grating and the second diffraction grating are arranged on the surface of the waveguide or at the interface between the waveguide and the protective layer surrounding this waveguide.

The first diffraction grating and the second diffraction grating each comprise an arrangement of surface slits. In a non-limiting embodiment, an electron beam lithography process is used to make a photomask for producing the slits, in particular using a silicon mask in a non-limiting example. In a non-limiting embodiment, to make a replica part of the photomask, the slits are manufactured by nanostructuring, for example by nanoimprinting so as to pattern large substrates with microtextures and nanotextures (roll-to-plate process in English). The nanometric sized slits thus manufactured may comprise dielectric materials with a high refractive index, for example a refractive index greater than two.

According to one embodiment, the slots are for example placed on the waveguide. The material of the waveguide is flexible and is chosen to provide suitable structural support and to allow a majority of the light passing through it to pass through.

According to another embodiment, the slots can be hollowed out in the material of the waveguide 6. In this way, the slots are less exposed to the environment, which can prevent their damage. In this embodiment, the slots are for example hollowed out in the substrate using an ion beam directed towards the surface of the material of the waveguide 6.

Generally speaking, the optical properties of a diffraction grating are defined by several parameters, including the wavelength of the light source used to illuminate the light guide that includes these diffraction gratings; the material used for the slits and the shape and dimensions of said slits. In other words, the material density of the diffraction grating considered largely defines the effect that this diffraction grating has on the light beam that passes through it.

The geometry of the slits of diffraction gratings can be specifically defined to optimize the efficiency of the diffraction grating. More specifically, the grating pitch, the angle of inclination of the slits, as well as their height and width can be defined as a function of a given wavelength in order to maximize the efficiency of the first diffraction grating and the second diffraction grating. A density coefficient (fill factor) can also be defined as the width of a slit in a grating divided by the pitch of the diffraction grating in question.

Thus, for the same light guide, the first diffraction grating has a first pitch and the second diffraction grating has a second pitch identical to the first pitch. In other words, the slits of the first diffraction grating have the same spacing as the slits of the second diffraction grating.

In this light guide, at least a portion of the slits of the first and/or second diffraction grating extend obliquely relative to the surface of the waveguide so as to define an angle of inclination between said slits and the surface of the waveguide. More specifically, the slits of the first diffraction grating extend obliquely relative to the surface of the waveguide so as to define a first angle of inclination while the slits of the second diffraction grating extend obliquely relative to the surface of the waveguide so as to define a second angle of inclination.

Furthermore, the slits of the first diffraction grating and the slits of the second diffraction grating also have identical heights. More precisely, the slits of the first diffraction grating have a first height and the slits of the second diffraction grating have a second height identical to the first height. Note that the slits of the same diffraction grating all have the same height.

Similarly, the slits of the first diffraction grating and the slits of the second diffraction grating may have identical widths. More precisely, the slits of the first diffraction grating have a first width and the slits of the second diffraction grating have a second width identical to the first width. Note that the slits of the same diffraction grating all have the same width.

By using identical parameters for the slits of the first diffraction grating and the slits of the second diffraction grating, it is possible to reuse the same dimensions for the electron beam lithography mask when manufacturing said diffraction gratings for the light guide.

According to one embodiment of the light device, the light source emits a blue monochromatic light having a wavelength of between 450 nm and 460 nm, or even equal to 455 nm. The light beam from the light source propagates perpendicular to the surface of the light guide on which the first diffraction grating is arranged, through which the light beam is intended to penetrate into said light guide. In other words, the angle of incidence of the light beam F from the light source 4 relative to the surface of the light guide on which the first diffraction grating is arranged is a right angle; this is a normal incidence.

In this particular embodiment, the first diffraction grating has, for example, a density coefficient equal to 0.5456. According to a specific non-limiting example, the first diffraction grating has a first pitch of 402 nm with slits which have a first width equal to 183 nm. These slits also have a first height of 459 nm and extend obliquely relative to the surface of the light guide so as to form a first inclination angle of 30°. In this specific example, the values of these different parameters contribute to an efficiency of 96% for this first diffraction grating.

In this same light guide, the second diffraction grating has, for example, a density coefficient equal to 0.5456. According to a specific non-limiting example, the second diffraction grating has a second pitch of 402 nm with slits which have a second width equal to 183 nm. These slits also have a second height of 459 nm and extend obliquely relative to the surface of the light guide so as to form a second inclination angle of 30°. In this specific example, the values of the different parameters contribute to an efficiency of 96% for this second diffraction grating.

By adapting the parameters of the first diffraction grating and the second diffraction grating of the light guide as a function of the wavelength of the beam produced by the light source of the light device, the efficiency of the optical result, which corresponds to the light transmission rate of the beam through the light guide comprising such first and second diffraction gratings, is for example greater than 75% and in particular greater than 80%, in particular greater than 90%. Thanks to this high transmission rate, it is thus possible to use a less powerful and more energy-efficient light source for a result that is just as satisfactory as that observed for the prior art. The use of such a light source can also make it possible to avoid heating of said light source and its environment.

In one embodiment, the light guide comprises a phosphor-containing element which is arranged directly on the surface of the waveguide or on the layer surrounding the waveguide. This element is arranged in proximity to the second diffraction grating such that a light beam from said second diffraction grating also passes through said phosphor-containing element. Furthermore, this element is arranged directly on the surface of the waveguide or on the layer surrounding the waveguide.

According to a particular embodiment, the element comprising phosphorus has a third refractive index greater than the first refractive index of the waveguide material and, in this case, also greater than the second refractive index of the material of the layer surrounding the waveguide. According to a particular example, the third refractive index of the element comprising phosphorus is equal to 4.

The light beam from the second diffraction grating is therefore intended to pass through an element comprising phosphorus. This element comprising phosphorus is intended to receive a light beam from a second diffraction grating and is configured to produce a polychromatic light beam at the exit of the light guide.

For example, in the case where the light source is a monochromatic light source which emits blue light, the element comprising phosphorus can make it possible to color part of the blue light into white light, optionally with a yellow tint or a more or less pronounced blue tint.

Such a light guide according to the invention therefore makes it possible to convey a light beam from one place to another efficiently, i.e. with little loss. Thanks to the parameters of the diffraction gratings which are specifically configured for a given wavelength, a majority of the monochromatic light of the light beam produced by the light source is thus transmitted via the light guide.

Such a light guide according to the invention is not susceptible to, or only slightly to, possible shocks and/or vibrations generated by the use of the motor vehicle in which said light guide is integrated and therefore offers a more robust, more reliable and more efficient alternative than the light guides known from the state of the art.

Claims (18)

Light device (1) for vehicle (2), said light device (1) comprising:
- a light source (10) configured to emit light rays (R),
- a light guide (11) comprising a body (110) configured to propagate said light rays (R) emitted by said light source (10),
characterized in that said light guide (1) further comprises:
- a light input grating (111) by diffraction comprising a plurality of first optical patterns (1110) having a first angle (α) and repeated periodically according to a first period (T),
- a light output grating (112) by diffraction comprising a plurality of second optical patterns (1120) having a second angle (α') and repeated periodically according to a second period (T') equal to the first period (T), said first angle (α) and said second angle (α') being equal in absolute value and of the same direction or of the opposite direction,
and in that said light source (10) is arranged opposite said light input array (111) so that light rays (R) enter said light input array (111). A light device (1) according to claim 1, wherein said first patterns (1110) and said second patterns (1120) have a right triangle-shaped cross-section. Light device (1) according to claim 1, wherein said first patterns (1110) and said second patterns (1120) respectively have a top (1110.1) and (1120.1) having a flat. A light device (1) according to claim 1, wherein said light input array (111) and said light output array (112) are arranged on a same surface (11.1) of the light guide (11). A light device (1) according to claim 1, wherein said light input array (111) and said light output array (112) are arranged on different surfaces (11.1, 11.2) of the light guide (11). Light device (1) according to any one of claims 1 to 3, wherein said first optical patterns (1110) and said second optics (1120) protrude from a surface (11.1, 11.2) of said light guide (11). Light device (1) according to any one of claims 1 to 3, wherein said first optical patterns (1110) and said second optics (1120) are recessed relative to a surface (11.1, 11.2) of said light guide (11). A light device (1) according to any preceding claim, wherein said first optical patterns (1110) and said second optics (1120) are of the same size. A light device (1) according to any preceding claim, wherein said light device (1) further comprises a light collimator (12) disposed between said light source (10) and said light guide (11) so as to form a first collimated light beam (Fx'') which arrives with normal incidence on said light input array (111). A light device (1) according to any preceding claim, wherein said light device (1) comprises a single light output array (112). A light device (1) according to any preceding claim, wherein said light source (10) is monochromatic. A light device (1) according to any preceding claim, wherein said light guide (11) is a surface light guide and said body (110) is in the form of a light guide sheet. Light device (1) according to claim 1, wherein said light input network (111) and said light output network (112) are arranged on the same surface (11.1) of the light guide (11) each have an arrangement of surface slots extending obliquely relative to the surface of the light guide (11) respectively at said first angle (α) and said second angle (α'). A light device (1) according to any preceding claim, wherein the light guide (11) is surrounded by a layer comprising a second transparent material having a second refractive index (n2) which is lower than the first refractive index (n1) of the material of the light guide (11), and wherein said light input grating (111) and/or said light output grating (112) are arranged between the light guide (11) and the layer. Light device (1) according to any one of the preceding claims, wherein it comprises an element comprising phosphor, said element being intended to receive a light beam (F) from the second diffraction grating (15), said element (19) being configured to produce a polychromatic light beam. Light assembly (3) for a vehicle (2), characterized in that said light assembly (3) comprises said light device (1) according to any one of the preceding claims. Light assembly (3) according to claim 11, wherein said light assembly (3) is a front face or a rear face of a vehicle (2) or a headlight or a rear light of a vehicle (2). Lighting assembly (3) according to claim 11, wherein said lighting assembly (3) forms part of an element of the passenger compartment of said vehicle (2).