Patent Description:
Source lights are used in a variety of applications, such as providing general illumination and providing light for electronic displays (e.g., LCDs). Historically, incandescent source lights have been widely used for general illumination purposes. Incandescent source lights produce light by heating a filament wire to a high temperature until it glows. The hot filament is protected from oxidation in the air with a glass enclosure that is filled with inert gas or evacuated. Incandescent source lights are gradually being replaced in many applications by other types of electric lights, such as fluorescent lamps, compact fluorescent lamps (CFL), cold cathode fluorescent lamps (CCFL), high-intensity discharge lamps, and solid state source lights, such as light-emitting diodes (LEDs).

<CIT> discloses an optical waveguide with a light entry surface. The optical waveguide has a deflecting surface configured to deflect light from a light source which is coupled via the light entry surface and is incident on the deflecting surface from a point of origin into a main propagation direction, with which the light propagates in the optical waveguide after deflection.

<CIT> provides a compact light source module including a compact light source and a collimator that includes a parabolic first reflective surface to reduce a radiation angle at which a light beam radiates from the compact light source, so as to emit the light beam through a side aperture and a plane second reflective surface which is located under the first reflective surface and comprises an incident portion through which the light beam radiates from the compact light source. The compact light source is located in the vicinity of a focal point of the first reflective surface.

The present disclosure relates to illumination devices, e.g., light guide luminaire modules, in which source light injection is non-parallel to the device's optical axis. According to a first aspect of the present invention, there is provided an optical coupler as set out in independent claim <NUM>. According to a second aspect of the present invention, there is provided an illumination device with the optical coupler as set out in dependent claim <NUM>. Other embodiments are described in the dependent claims.

The details of one or more implementations of the technologies described herein are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the disclosed technologies will become apparent from the description, the drawings, and the claims.

Reference numbers and designations in the various drawings indicate exemplary aspects, implementations of particular features of the present disclosure.

The present disclosure relates to optical couplers wherein input and exit apertures can have oblique orientations as well as illumination devices for providing direct and/or indirect illumination employing such optical couplers. The optical couplers are configured to receive light from an input aperture and direct the light to an exit aperture. The illumination devices can efficiently guide and distribute light from source lights such as solid-state source lights or pumped phosphors received at an input aperture towards work surfaces and/or background regions. The source lights can be oriented in oblique directions relative to an optical axis of the illumination device. In some implementations, the optical couplers can receive light emitted within solid angles of 2π steradian from a flat input aperture. In some implementations, the optical couplers are configured to direct light from the input aperture to the exit aperture via total internal reflection (TIR).

Depending on the implementation, one or more optical couplers can be used in an illumination device. The optical couplers can be used, for example, to direct light to an optical extractor of the illumination device. In some cases, light provided by an optical coupler at their exit apertures is guided to the optical extractor through a light guide. Light extracted by the optical extractor to an ambient environment can be directed to the work surfaces and/or towards background regions to provide illumination or other lighting functions.

<FIG> illustrates a block diagram of an illumination device <NUM> in which source light injection is non-parallel with the optical axis <NUM>. The illumination device <NUM>, also referred to as luminaire module <NUM>, includes a substrate <NUM> having a normal inclined relative to the device's optical axis <NUM> by a finite angle δ, where <NUM> < δ ≤ <NUM>°, one or more light emitting elements (LEEs) <NUM> arranged on the substrate, a corresponding one or more optical couplers <NUM>, and an optical extractor <NUM>. Here, the device's optical axis <NUM> is parallel to the z-axis and passes through an exit aperture <NUM> of the optical couplers <NUM> and through an input aperture of the optical extractor <NUM>. The LEEs <NUM> emit light along an emission direction <NUM> parallel to the normal to the substrate <NUM>, such that the emission direction <NUM> includes an angle δ relative to the device's optical axis <NUM>. In this manner, the emitted light is injected into the optical couplers <NUM> through an input aperture <NUM> along the emission direction <NUM>. In some implementations, the illumination device <NUM> further includes a light guide <NUM>. In some implementations, the LEEs <NUM> are immersion coupled with the input apertures of the couplers <NUM>. Depending on the implementation, such immersion coupling may be between the dies or phosphor layers, if any, or other components or interfaces of the LEEs <NUM>. In some implementations, the couplers <NUM> may be immersion coupled with a phosphor layer (not illustrated in <FIG>) that is remote from the LEEs <NUM>. Depending on the implementation, recovery cavities may be formed between LEEs and remote phosphors to provide a desired optical coupling.

In general, a LEE, also referred to as a light emitter, is a device that emits radiation in one or more regions of the electromagnetic spectrum from among the visible region, the infrared region and/or the ultraviolet region, when activated. Activation of a LEE can be achieved by applying a potential difference across components of the LEE or passing a current through components of the LEE, for example. A LEE can have monochromatic, quasi-monochromatic, polychromatic or broadband spectral emission characteristics. Examples of LEEs include semiconductor, organic, polymer/polymeric light-emitting diodes, other monochromatic, quasi-monochromatic or other light-emitting elements. In some implementations, a LEE is a specific device that emits the radiation, for example a LED die. In other implementations, the LEE includes a combination of the specific device that emits the radiation (e.g., a LED die) together with a housing or package within which the specific device or devices are placed. Examples of LEEs include also lasers and more specifically semiconductor lasers, such as vertical cavity surface emitting lasers (VCSELs) and edge emitting lasers. Further examples of LEEs include superluminescent diodes and other superluminescent devices.

During operation, the LEEs <NUM> provide light within a first angular range <NUM>. Such light can have, for example, a Lambertian distribution relative to the optical axes of the one or more LEEs <NUM>. Here, the optical axes of the LEEs <NUM> are parallel to the normal <NUM> to the substrate <NUM> which makes a non-zero angle δ with the device's optical axis <NUM> (e.g., the z-axis.

The one or more couplers <NUM> receive the light from the LEEs <NUM> within the first angular range <NUM> at the input aperture <NUM> and provide light within a second angular range <NUM> at an exit aperture <NUM>. As used herein, providing light in an "angular range" refers to providing light that propagates in one or more prevalent directions in which each has a divergence with respect to the corresponding prevalent direction. In this context, the term "prevalent direction of propagation" refers to a direction along which a portion of an intensity distribution of the propagating light has a maximum. For example, the prevalent direction of propagation associated with the angular range can be an orientation of a lobe of the intensity distribution. (See, e.g., <FIG>. ) Also in this context, the term "divergence" refers to a solid angle outside of which the intensity distribution of the propagating light drops below a predefined fraction of a maximum of the intensity distribution. For example, the divergence associated with the angular range can be the width of the lobe of the intensity distribution. The predefined fraction can be <NUM>%, <NUM>%, <NUM>%, or other values, depending on the lighting application.

The one or more couplers <NUM> are shaped to transform the first angular range <NUM> into the second angular range <NUM> via total internal reflection, specular reflection or both. As such, the one or more couplers <NUM> can include a solid transparent material for propagating light from the input aperture <NUM> to the exit aperture <NUM> of each of the one or more couplers <NUM>. In this manner, a prevalent direction of propagation of the second angular range <NUM> is along the z-axis, and hence, it is different from a prevalent direction of propagation of the first angular range <NUM>, which is inclined by the angle δ relative the z-axis. Additionally, the divergence of the second angular range <NUM> is smaller than the divergence of the first angular range <NUM>, to ensure that all light provided by the couplers <NUM> in the angular range <NUM> can be injected into the input aperture of the optical extractor <NUM>. Here, a distance D between the exit aperture <NUM> of the optical couplers <NUM> and the input aperture of the optical extractor <NUM> can be <NUM>, <NUM> or <NUM>, for instance. A combination of (i) a third angular range <NUM> in which the light is received by the optical extractor <NUM> and (ii) a numerical aperture of the optical extractor <NUM> is configured such that all the received light is injected into the input aperture of the optical extractor <NUM>.

In some implementations, the illumination device includes the light guide <NUM>. The light guide <NUM> can be made from a solid, transparent material. Here, the light guide <NUM> is arranged to receive the light provided by the optical couplers <NUM> in the second angular range <NUM> at one end of the light guide <NUM> and to guide the received light in a forward direction, e.g., along the device's optical axis <NUM> (in this case the z-axis), from the receiving end to an opposing end of the light guide <NUM>. Here, a distance D between the receiving end of the light guide <NUM> and its opposing end can be <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, for instance. A combination of (i) the second angular range <NUM> in which the light is received by the light guide <NUM> at the receiving end and (ii) a numerical aperture of the light guide <NUM> is configured such that all the received light is guided from the receiving end to the opposing end through total internal reflection (TIR).

One or more of the light guide side surfaces can be planar, curved or otherwise shaped. The light guide side surfaces can be parallel or non-parallel. In embodiments with non-parallel light guide side surfaces, a third angular range <NUM> of the guided light at the opposing end of the light guide <NUM> is different than the angular range <NUM> of the light received at the receiving end. In embodiments with parallel light guide side surfaces, the third angular range <NUM> of the guided light at the opposing end of the light guide <NUM> has at least substantially the same divergence as the angular range <NUM> of the light received at the receiving end. In either of these embodiments, the light guide side surfaces are optically smooth to allow for the guided light to propagate forward (e.g., in the positive direction of the z-axis) inside the light guide <NUM> through TIR.

Additionally, the distance D (along the z-axis) between the optical couplers <NUM> and the optical extractor <NUM> - for embodiments of the illumination device <NUM> without a light guide <NUM> - or a combination of the length D of the light guide <NUM> and its thickness T (along the x-axis) - for embodiments of the illumination device <NUM> with a light guide <NUM> - is chosen to homogenize the light emitted by the discrete LEEs <NUM> - which are distributed along the y-axis - as it propagates from the couplers <NUM> (for embodiments of the illumination device <NUM> without a light guide <NUM>) or is guided from the receiving end to the opposing end of the light guide <NUM> (for embodiments of the illumination device <NUM> with a light guide <NUM>. ) In this manner, the homogenizing of the emitted light - as it propagates from the optical couplers <NUM> to the optical extractor <NUM> or is guided through the light guide <NUM> - causes a change of a discrete profile along the y-axis of the second angular range <NUM> to a continuous profile along the y-axis of the third angular range <NUM> in which the discrete profile is partially or fully blurred.

The optical extractor <NUM> outputs into the ambient environment the light received from the optical couplers <NUM> (for embodiments of the illumination device <NUM> without a light guide <NUM>) or from the light guide <NUM> (for embodiments of the illumination device <NUM> with a light guide <NUM>) in one or more output illumination distributions. As such, the light output by the extractor <NUM> has a first output angular range <NUM>' that can be substantially continuous along the y-axis and has a first output propagation direction with a component opposite to the forward direction (e.g., antiparallel to the z-axis. ) In some implementations, the light output by the extractor <NUM> has, in addition to the first output angular range <NUM>', a second output angular range <NUM>" that is substantially continuous along the y-axis and has a second output propagation direction with a component opposite to the forward direction (e.g., antiparallel to the z-axis. ) In this case, the first output propagation direction and the second output propagation direction have respective component orthogonal to the forward direction that are opposite (antiparallel) to each other (antiparallel and parallel to the x-axis. ) In some implementations, the light output by the extractor <NUM> has, in addition to the first output angular range <NUM>' and the second output angular range <NUM>", a third output angular range <NUM>‴ that can be substantially continuous along the y-axis and has a third output propagation direction along the forward direction (e.g., along the z-axis.

As described above, the light guide <NUM> and the optical extractor <NUM> of illumination device <NUM> are arranged and configured to translate and redirect light emitted by LEEs <NUM> away from the LEEs before the light is output into the ambient environment. The spatial separation of the place of generation of the light, also referred to as the physical (light) source, from the place of extraction of the light, also referred to as a virtual source light or a virtual filament, can facilitate design of the illumination device <NUM>. In this manner, a virtual filament can be configured to provide substantially non-isotropic light emission with respect to planes parallel to an optical axis of the illumination device (for example the z-axis. ) In contrast, a typical incandescent filament generally emits substantially isotropically distributed amounts of light. The virtual filament(s) may be viewed as one or more portions of space from which substantial amounts of light appear to emanate. Furthermore, separating the LEEs <NUM>, with their predetermined optical, thermal, electrical and mechanical constraints, from the place of light extraction, may facilitate a greater degree of design freedom of the illumination device <NUM> and allows for an extended optical path, which can permit a predetermined level of light mixing before light is output from the illumination device <NUM>.

<FIG> shows an x-z cross-section of far-field light intensity profile <NUM> of an example illumination device <NUM> that is elongated along the y-axis (perpendicular to the sectional plane of <FIG>). In some implementations, the far-field light intensity profile <NUM> includes a first output lobe 145a representing light output by the illumination device <NUM> in the first output angular range <NUM>'. In this case, a propagation direction of the first output angular range <NUM>' is along the about -<NUM>° bisector of the first output lobe 145a.

In some implementations, in addition to the first output lobe 145a, the far-field light intensity profile <NUM> includes one or more of a second output lobe 145b representing light output by the illumination device <NUM> in the second output angular range <NUM>" or a third output lobe 145c representing light output by the illumination device <NUM> in the third output angular range <NUM>"'. In this example, a propagation direction of the second output angular range <NUM>" is along the about +<NUM>° bisector of the second output lobe 145b and a propagation direction of the third output angular range <NUM>‴ is along the about <NUM>° bisector of the third output lobe 145c. In other example illumination devices, first and second output lobes 145a and 145b can be asymmetrical. Further in this case, a divergence of each of the first output angular range <NUM>' (represented by a width of the first output lobe 145a) or the second output angular range <NUM>" (represented by a width of the second output lobe 145b) is smaller than a divergence of the third output angular range <NUM>‴ (represented by a width of the third output lobe 145c).

Orientation of the LEEs <NUM> relative the device's optical axis <NUM> (e.g., the z-axis) along with composition and geometry of the couplers <NUM>, the light guide <NUM> and the extractor <NUM> of the illumination device <NUM> can affect the far-field light intensity profile <NUM>, e.g., the propagation direction and divergence associated with the first output lobe 145a, and, optionally, of the one or more of the second and third output lobes 145b and 145c.

Prior to describing details of various embodiments of the illumination device <NUM> in which source light injection is non-parallel with the device's optical axis <NUM>, a light guide illumination device is described in which source light injection is parallel with a device's optical axis.

Referring to <FIG>, in which a Cartesian coordinate system is shown for reference, a luminaire module <NUM> includes a mount <NUM> having a plurality of LEEs <NUM> distributed along a first surface of the mount <NUM>. The mount with the LEEs <NUM> is disposed at a first (e.g., upper) edge <NUM> of a light guide <NUM>. Once again, the positive z-direction is referred to as the "forward" direction and the negative z-direction is the "backward" direction. Sections through the luminaire module <NUM> parallel to the x-z plane are referred to as the "cross-section" or "cross-sectional plane" of the luminaire module. Also, luminaire module <NUM> extends along the y-direction, so this direction is referred to as the "longitudinal" direction of the luminaire module. Implementations of luminaire modules can have a plane of symmetry parallel to the y-z plane, be curved or otherwise shaped. This is referred to as the "symmetry plane" of the luminaire module.

Multiple LEEs <NUM> are disposed on the first surface of the mount <NUM>, although only one of the multiple LEEs <NUM> is shown in <FIG>. For example, the plurality of LEEs <NUM> can include multiple white LEDs. The LEEs <NUM> are optically coupled with one or more optical couplers <NUM> (only one of which is shown in <FIG>). An optical extractor <NUM> is disposed at second (e.g., lower) edge <NUM> of light guide <NUM>.

Mount <NUM>, light guide <NUM>, and optical extractor <NUM> extend a length L along the y-direction, so that the luminaire module is an elongated luminaire module with an elongation of L that may be about parallel to a wall of a room (e.g., a ceiling of the room). Generally, L can vary as desired. Typically, L is in a range from about <NUM> to about <NUM> (e.g., <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, or, <NUM> or more).

The number of LEEs <NUM> on the mount <NUM> will generally depend, inter alia, on the length L, where more LEEs are used for longer luminaire modules. In some implementations, the plurality of LEEs <NUM> can include between <NUM> and <NUM>,<NUM> LEEs (e.g., about <NUM> LEEs, about <NUM> LEEs, about <NUM> LEEs, about <NUM> LEEs). Generally, the density of LEEs (e.g., number of LEEs per unit length) will also depend on the nominal power of the LEEs and illuminance desired from the luminaire module. For example, a relatively high density of LEEs can be used in applications where high illuminance is desired or where low power LEEs are used. In some implementations, the luminaire module <NUM> has LEE density along its length of <NUM> LEE per centimeter or more (e.g., <NUM> per centimeter or more, <NUM> per centimeter or more, <NUM> per centimeter or more, <NUM> per centimeter or more). The density of LEEs may also be based on a desired amount of mixing of light emitted by the multiple LEEs. In implementations, LEEs can be evenly spaced along the length, L, of the luminaire module. In some implementations, a heat-sink <NUM> can be attached to the mount <NUM> to extract heat emitted by the plurality of LEEs <NUM>. The heat-sink <NUM> can be disposed on a surface of the mount <NUM> opposing the side of the mount <NUM> on which the LEEs <NUM> are disposed. The luminaire module <NUM> can include one or multiple types of LEEs, for example one or more subsets of LEEs in which each subset can have different color or color temperature.

Optical coupler <NUM> includes one or more solid pieces of transparent optical material (e.g., a glass material or a transparent organic plastic, such as polycarbonate or acrylic) having surfaces <NUM> and <NUM> positioned to reflect light from the LEEs <NUM> towards the light guide <NUM>. In general, surfaces <NUM> and <NUM> are shaped to collect and at least partially collimate light emitted from the LEEs. In the x-z cross-sectional plane, surfaces <NUM> and <NUM> can be straight or curved. Examples of curved surfaces include surfaces having a constant radius of curvature, parabolic or hyperbolic shapes. In some implementations, surfaces <NUM> and <NUM> are coated with a highly reflective material (e.g., a reflective metal, such as aluminum or silver), to provide a highly reflective optical interface. The cross-sectional profile of optical coupler <NUM> can be uniform along the length L of luminaire module <NUM>. Alternatively, the cross-sectional profile can vary. For example, surfaces <NUM> and/or <NUM> can be curved out of the x-z plane.

The exit aperture of the optical coupler <NUM> adjacent upper edge of light guide <NUM> is optically coupled to edge <NUM> to facilitate efficient coupling of light from the optical coupler <NUM> into light guide <NUM>. For example, the surfaces of a solid optical coupler <NUM> and a solid light guide <NUM> can be attached using a material that substantially matches the refractive index of the material forming the optical coupler <NUM> or light guide <NUM> or both (e.g., refractive indices across the interface are different by <NUM>% or less. ) The optical coupler <NUM> can be affixed to light guide <NUM> using an index matching fluid, grease, or adhesive. In some implementations, optical coupler <NUM> is fused to light guide <NUM> or they are integrally formed from a single piece of material (e.g., coupler and light guide may be monolithic and may be made of a solid transparent optical material).

Light guide <NUM> is formed from a piece of transparent material (e.g., glass material such as BK7, fused silica or quartz glass, or a transparent organic plastic, such as polycarbonate or acrylic) that can be the same or different from the material forming optical couplers <NUM>. Light guide <NUM> extends length L in the y-direction, has a uniform thickness T in the x-direction, and a uniform depth D in the z-direction. The dimensions D and T are generally selected based on the desired optical properties of the light guide (e.g., which spatial modes are supported) and/or the direct/indirect intensity distribution. During operation, light coupled into the light guide <NUM> from optical coupler <NUM> (with an angular range <NUM>) reflects off the planar surfaces of the light guide by TIR and spatially mixes within the light guide. The mixing can help achieve illuminance and/or color uniformity, along the y-axis, at the distal portion of the light guide <NUM> at optical extractor <NUM>. The depth, D, of light guide <NUM> can be selected to achieve adequate uniformity at the exit aperture (i.e., at end <NUM>) of the light guide. In some implementations, D is in a range from about <NUM> to about <NUM> (e.g., <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more, <NUM> or more).

In general, optical couplers <NUM> are designed to restrict the angular range of light entering the light guide <NUM> (e.g., to within +/-<NUM> degrees) so that at least a substantial amount of the light (e.g., <NUM>% or more of the light) is optically coupled into spatial modes in the light guide <NUM> that undergoes TIR at the planar surfaces. Light guide <NUM> can have a uniform thickness T, which is the distance separating two planar opposing surfaces of the light guide. Generally, T is sufficiently large so the light guide has an aperture at first (e.g., upper) surface <NUM> sufficiently large to approximately match (or exceed) the exit aperture of optical coupler <NUM>. In some implementations, T is in a range from about <NUM> to about <NUM> (e.g., about <NUM> or more, about <NUM> or more, about <NUM> or more, about <NUM> or more, about <NUM> or more, about <NUM> or more). Depending on the implementation, the narrower the light guide the better it may spatially mix light. A narrow light guide also provides a narrow exit aperture. As such light emitted from the light guide can be considered to resemble the light emitted from a one-dimensional linear source light, also referred to as an elongate virtual filament.

While optical coupler <NUM> and light guide <NUM> are formed from solid pieces of transparent optical material, hollow structures are also possible. For example, the optical coupler <NUM> or the light guide <NUM> or both may be hollow with reflective inner surfaces rather than being solid. As such material cost can be reduced and absorption in the light guide avoided. A number of specular reflective materials may be suitable for this purpose including materials such as <NUM> Vikuiti™ or Miro IV™ sheet from Alanod Corporation where greater than <NUM>% of the incident light would be efficiently guided to the optical extractor.

Optical extractor <NUM> is also composed of a solid piece of transparent optical material (e.g., a glass material or a transparent organic plastic, such as polycarbonate or acrylic) that can be the same as or different from the material forming light guide <NUM>. In the example implementation shown in <FIG>, the optical extractor <NUM> includes redirecting (e.g., flat) surfaces <NUM> and <NUM> and curved surfaces <NUM> and <NUM>. The flat surfaces <NUM> and <NUM> represent first and second portions of a redirecting surface <NUM>, while the curved surfaces <NUM> and <NUM> represent first and second output surfaces of the luminaire module <NUM>.

Surfaces <NUM> and <NUM> are coated with a reflective material (e.g., a highly reflective metal, such as aluminum or silver) over which a protective coating may be disposed. For example, the material forming such a coating may reflect about <NUM>% or more of light incident thereon at appropriate (e.g., visible) wavelengths. Here, surfaces <NUM> and <NUM> provide a highly reflective optical interface for light having the angular range <NUM> entering an input end of the optical extractor <NUM>' from light guide <NUM>. As another example, the surfaces <NUM> and <NUM> include portions that are transparent to the light entering at the input end <NUM>' of the optical extractor <NUM>. Here, these portions can be uncoated regions (e.g., partially silvered regions) or discontinuities (e.g., slots, slits, apertures) of the surfaces <NUM> and <NUM>. As such, some light is transmitted in the forward direction (along the z-axis) through surfaces <NUM> and <NUM> of the optical extractor <NUM> in an output angular range <NUM>'. In some cases, the light transmitted in the output angular range <NUM>' is refracted. In this way, the redirecting surface <NUM> acts as a beam splitter rather than a mirror, and transmits in the output angular range <NUM>' a desired portion of incident light, while reflecting the remaining light in angular ranges <NUM> and <NUM>'.

In the x-z cross-sectional plane, the lines corresponding to surfaces <NUM> and <NUM> have the same length and form an apex or vertex <NUM>, e.g. a v-shape that meets at the apex <NUM>. In general, an included angle (e.g., the smallest included angle between the surfaces <NUM> and <NUM>) of the redirecting surfaces <NUM>, <NUM> can vary as desired. For example, in some implementations, the included angle can be relatively small (e.g., from <NUM>° to <NUM>°). In certain implementations, the included angle is in a range from <NUM>° to <NUM>° (e.g., about <NUM>°). The included angle can also be relatively large (e.g., in a range from <NUM>° to <NUM>° or more). In the example implementation shown in <FIG>, the output surfaces <NUM>, <NUM> of the optical extractor <NUM> are curved with a constant radius of curvature that is the same for both. In an aspect, the output surfaces <NUM>, <NUM> may have optical power (e.g., may focus or defocus light. ) Accordingly, luminaire module <NUM> has a plane of symmetry intersecting apex <NUM> parallel to the y-z plane.

The surface of optical extractor <NUM> adjacent to the lower edge <NUM> of light guide <NUM> is optically coupled to edge <NUM>. For example, optical extractor <NUM> can be affixed to light guide <NUM> using an index matching fluid, grease, or adhesive. In some implementations, optical extractor <NUM> is fused to light guide <NUM> or they are integrally formed from a single piece of material.

The emission spectrum of the luminaire module <NUM> corresponds to the emission spectrum of the LEEs <NUM>. However, in some implementations, a wavelength-conversion material may be positioned in the luminaire module, for example remote from the LEEs, so that the wavelength spectrum of the luminaire module is dependent both on the emission spectrum of the LEEs and the composition of the wavelength-conversion material. In general, a wavelength-conversion material can be placed in a variety of different locations in luminaire module <NUM>. For example, a wavelength-conversion material may be disposed proximate the LEEs <NUM>, adjacent surfaces <NUM> and <NUM> of optical extractor <NUM>, on the exit surfaces <NUM> and <NUM> of optical extractor <NUM>, and/or at other locations.

The layer of wavelength-conversion material (e.g., phosphor) may be attached to light guide <NUM> held in place via a suitable support structure (not illustrated), disposed within the extractor (also not illustrated) or otherwise arranged, for example. Wavelength-conversion material that is disposed within the extractor may be configured as a shell or other object and disposed within a notional area that is circumscribed between R/n and R*(<NUM>+n<NUM>)(-<NUM>/<NUM>), where R is the radius of curvature of the light-exit surfaces (<NUM> and <NUM> in <FIG>) of the extractor <NUM> and n is the index of refraction of the portion of the extractor that is opposite of the wavelength-conversion material as viewed from the reflective surfaces (<NUM> and <NUM> in <FIG>). The support structure may be a transparent self-supporting structure. The wavelength-conversion material diffuses light as it converts the wavelengths, provides mixing of the light and can help uniformly illuminate a surface of the ambient environment.

During operation, light exiting light guide <NUM> through end <NUM> impinges on the reflective interfaces at portions of the redirecting surface <NUM> and <NUM> and is reflected outwardly towards output surfaces <NUM> and <NUM>, respectively, away from the symmetry plane of the luminaire module. The first portion of the redirecting surface <NUM> provides light having an angular distribution <NUM> towards the output surface <NUM>, the second portion of the redirecting surface <NUM> provides light having an angular distribution <NUM>' towards the output surface <NUM>. The redirected light exits optical extractor through output surfaces <NUM> and <NUM>. In general, the output surfaces <NUM> and <NUM> have optical power, to redirect the light exiting the optical extractor <NUM> in angular ranges <NUM> and <NUM>', respectively. For example, optical extractor <NUM> may be configured to emit light upwards (i.e., towards the plane intersecting the LEEs and parallel to the x-y plane), downwards (i.e., away from that plane) or both upwards and downwards. In general, the direction of light exiting the luminaire module through surfaces <NUM> and <NUM> depends on the divergence of the light exiting light guide <NUM> and the orientation of surfaces <NUM> and <NUM>.

Surfaces <NUM> and <NUM> may be oriented so that little or no light from light guide <NUM> is output by optical extractor <NUM> in certain directions. In implementations where the luminaire module <NUM> is attached to a ceiling of a room (e.g., the forward direction is towards the floor) such configurations can help avoid glare and an appearance of non-uniform illuminance.

In general, the light intensity distribution provided by luminaire module <NUM> reflects the symmetry of the luminaire module's structure about the y-z plane. For example, referring to <FIG>, light output in angular range <NUM>' corresponds to the first output lobe 145a of the far-field light intensity distribution <NUM>, light output in angular range <NUM> corresponds to the second output lobe 145b of the far-field light intensity distribution <NUM> and light output (leaked) in angular range <NUM>' corresponds to the third output lobe 145c of the far-field light intensity distribution <NUM>. In general, an intensity profile of luminaire module <NUM> will depend on the configuration of the optical coupler <NUM>, the light guide <NUM> and the optical extractor <NUM>. For instance, the interplay between the shape of the optical coupler <NUM>, the shape of the redirecting surface <NUM> of the optical extractor <NUM> and the shapes of the output surfaces <NUM>, <NUM> of the optical extractor <NUM> can be used to control the angular width and prevalent direction (orientation) of the first 145a and second 145b output lobes in the far-field light intensity profile <NUM>. Additionally, a ratio of an amount of light in the combination of first 145a and second 145b output lobes and light in the third output lobe 145c is controlled by reflectivity and transmissivity of the redirecting surfaces <NUM> and <NUM>. For example, for a reflectivity of <NUM>% and transmissivity of <NUM>% of the redirecting surfaces <NUM>, <NUM>, <NUM>% of light can be output in the output angular range <NUM>' corresponding to the first output lobe 145a, <NUM>% light can be output in the output angular range <NUM> corresponding to the second output lobe 145b, and <NUM>% of light can be output in the output angular range <NUM>' corresponding to the third output lobe 145c.

In some implementations, the orientation of the output lobes 145a, 145b can be adjusted based on the included angle of the v-shaped groove <NUM> formed by the portions of the redirecting surface <NUM> and <NUM>. For example, a first included angle results in a far-field light intensity distribution <NUM> with output lobes 145a, 145b located at relatively smaller angles compared to output lobes 145a, 145b of the far-field light intensity distribution <NUM> that results for a second included angle larger than the first angle. In this manner, light can be extracted from the luminaire module <NUM> in a more forward direction for the smaller of two included angles formed by the portions <NUM>, <NUM> of the redirecting surface <NUM>.

Furthermore, while surfaces <NUM> and <NUM> are depicted as planar surfaces, other shapes are also possible. For example, these surfaces can be curved or composite. Curved redirecting surfaces <NUM> and <NUM> can be used to narrow or widen the output lobes 145a, 145b. Depending of the divergence of the angular range <NUM> of the light that is received at the input end of the optical extractor <NUM>', concave reflective surfaces <NUM>, <NUM> can narrow the lobes 145a, 145b output by the optical extractor <NUM> (and illustrated in <FIG>), while convex reflective surfaces <NUM>, <NUM> can widen the lobes 145a, 145b output by the optical extractor <NUM>. As such, suitably configured redirecting surfaces <NUM>, <NUM> may introduce convergence or divergence into the light. Such surfaces can have a constant radius of curvature, can be parabolic, hyperbolic, or have some other curvature.

In general, the geometry of the elements can be established using a variety of methods. For example, the geometry can be established empirically. Alternatively, or additionally, the geometry can be established using optical simulation software, such as Lighttools™, Tracepro™, FRED™ or Zemax™, for example.

In general, luminaire module <NUM> can be designed to output light into different output angular ranges <NUM>, <NUM>' from those shown in <FIG>. In some implementations, illumination devices can output light into lobes 142a, 142b that have a different divergence or propagation direction than those shown in <FIG>. For example, in general, the output lobes 145a, 145b can have a width of up to about <NUM>° (e.g., <NUM>° or less, <NUM>° or less, <NUM>° or less, <NUM>° or less, <NUM>° or less, <NUM>° or less, <NUM>° or less). In general, the direction in which the output lobes 145a, 145b are oriented can also differ from the directions shown in <FIG>. The "direction" refers to the direction at which a lobe is brightest. In <FIG>, for example, the output lobes 145a, 145b are oriented at approx. -<NUM>° and approximately +<NUM>°. In general, output lobes 145a, 145b can be directed more towards the horizontal (e.g., at an angle in the ranges from -<NUM>° to -<NUM>°, such as at approx. -<NUM>°, approx. -<NUM>°, approx. -<NUM>°, approx. -<NUM>°, approx. -<NUM>°, and from +<NUM>° to +<NUM>°, such as at approx. +<NUM>°, approx. +<NUM>°, approx. +<NUM>°, approx. +<NUM>°, approx.

The luminaire modules can include other features useful for tailoring the intensity profile. For example, in some implementations, luminaire modules can include an optically diffuse material that can diffuse light in a controlled manner to aid homogenizing the luminaire module's intensity profile. For example, surfaces <NUM> and <NUM> can be roughened or a diffusely reflecting material, rather than a specular reflective material, can be coated on these surfaces. Accordingly, the optical interfaces at surfaces <NUM> and <NUM> can diffusely reflect light, scattering light into broader lobes than would be provided by similar structures utilizing specular reflection at these interfaces. In some implementations these surfaces can include structure that facilitates various intensity distributions. For example, surfaces <NUM> and <NUM> can each have multiple planar facets at differing orientations. Accordingly, each facet will reflect light into different directions. In some implementations, surfaces <NUM> and <NUM> can have structure thereon (e.g., structural features that scatter or diffract light).

Surfaces <NUM> and <NUM> need not be surfaces having a constant radius of curvature. For example, surfaces <NUM> and <NUM> can include portions having differing curvature and/or can have structure thereon (e.g., structural features that scatter or diffract light). In certain implementations, a light scattering material can be disposed on surfaces <NUM> and <NUM> of optical extractor <NUM>.

In some implementations, optical extractor <NUM> is structured so that a negligible amount (e.g., less than <NUM>%) of the light propagating within at least one plane (e.g., the x-z cross-sectional plane) that is reflected by surface <NUM> or <NUM> experiences TIR at light-exit surface <NUM> or <NUM>. For certain spherical or cylindrical structures, a so-called Weierstrass condition can avoid TIR. A Weierstrass condition is illustrated for a circular structure (i.e., a cross section through a cylinder or sphere) having a surface of radius R and a concentric notional circle having a radius R/n, where n is the refractive index of the structure. Any light ray that passes through the notional circle within the cross-sectional plane is incident on surface of the circular structure and has an angle of incidence less than the critical angle and will exit circular structure without experiencing TIR. Light rays propagating within spherical structure in the plane but not emanating from within notional surface can impinge on the surface of radius R at the critical angle or greater angles of incidence. Accordingly, such light may be subject to TIR and won't exit the circular structure. Furthermore, rays of p-polarized light that pass through a notional space circumscribed by an area with a radius of curvature that is smaller than R/(<NUM>+n<NUM>)(-<NUM>/<NUM>), which is smaller than R/n, will be subject to small Fresnel reflection at the surface of radius R when exiting the circular structure. This condition may be referred to as Brewster geometry. Implementations may be configured accordingly.

In some implementations, all or part of surfaces <NUM> and <NUM> may be located within a notional Weierstrass surface defined by surfaces <NUM> and <NUM>. For example, the portions of surfaces <NUM> and <NUM> that receive light exiting light guide <NUM> through end <NUM> can reside within this surface so that light within the x-z plane reflected from surfaces <NUM> and <NUM> exits through surfaces <NUM> and <NUM>, respectively, without experiencing TIR.

In the example implementations described above in connection with <FIG>, the luminaire module <NUM> is configured to output light into output angular ranges <NUM>, <NUM>' and optionally <NUM>'. In other implementations, the light guide-based luminaire module <NUM> is modified to output light into a single output angular range <NUM>'. <FIG> illustrates an example of such light guide-based luminaire module <NUM>* configured to output light on a single side of the light guide <NUM>. The luminaire module <NUM>* is referred to as a single-sided luminaire module. The single-sided luminaire module <NUM>* is elongated along the y-axis like the luminaire module <NUM> shown in <FIG>. Also like the luminaire module <NUM>, the single-sided luminaire module <NUM>* includes a mount <NUM> and LEEs <NUM> disposed on a surface of the mount <NUM> along the y-axis to emit light in a first angular range. The single-sided luminaire module <NUM>* further includes an optical coupler <NUM> arranged and configured to redirect the light emitted by the LEEs <NUM> in the first angular range into a second angular range <NUM> that has a divergence smaller than the divergence of the first angular range at least in the x-z cross-section. Also, the single-sided luminaire module <NUM>* includes a light guide <NUM> to guide the light redirected by the optical coupler <NUM> in the second angular range <NUM> from a first end <NUM> of the light guide to a second end <NUM> of the light guide. Additionally, the single-sided luminaire module <NUM>* includes a single-sided extractor (denoted <NUM>') to receive the light guided by the light guide <NUM>. The single-sided extractor <NUM>' includes a redirecting surface <NUM> to redirect the light received from the light guide <NUM> into a third angular range <NUM>' - like described for luminaire module <NUM> with reference to <FIG> - and an output surface <NUM> to output the light redirected by the redirecting surface <NUM> in the third angular range <NUM>' into a fourth angular range <NUM>'.

A light intensity profile of the single-sided luminaire module <NUM>* is represented in <FIG> as a single output lobe 145a. The single output lobe 145a corresponds to light output by the single-sided luminaire module <NUM>* in the fourth angular range <NUM>'.

<FIG> shows an embodiment <NUM>' of the luminaire module <NUM> that also is elongated along an axis (e.g., y-axis) perpendicular to the forward direction (e.g., along the z-axis. ) In this case, a length L of the light guide <NUM> along the elongated dimension of the luminaire module <NUM>' can be <NUM>', <NUM>' or <NUM>', for instance. A thickness T of the light guide <NUM> orthogonal to the elongated dimension L (e.g., along the x-axis) is chosen to be a fraction of the distance D traveled by the guided light from the receiving end to the opposing end of the light guide <NUM>. For T = <NUM>. 05D, <NUM>. 1D or <NUM>. 2D, for instance, light from multiple, point-like LEEs <NUM> - distributed along the elongated dimension L - that is edge-coupled into the light guide <NUM> at the receiving end can efficiently mix and become uniform (quasi-continuous) along the y-axis by the time it propagates to the opposing end.

<FIG> shows a luminaire module <NUM>" that has (e.g., continuous or discrete) rotational symmetry about the forward direction (e.g., z-axis. ) Here, a diameter T of the light guide <NUM> is a fraction of the distance D traveled by the guided light from the receiving end to the opposing end of the light guide <NUM>. For example, the diameter of the light guide <NUM> can be T = <NUM>. 05D, <NUM>. 1D or <NUM>. 2D, for instance.

Other open and closed shapes of the luminaire module <NUM> are possible. <FIG> show a perspective view and a bottom view, respectively, of a luminaire module <NUM>‴ for which the light guide <NUM> has two opposing side surfaces 232a, 232b that form a closed cylinder shell of thickness T. In the example illustrated in <FIG>, the x-y cross-section of the cylinder shell formed by the opposing side surfaces 232a, 232b is oval. In other cases, the x-y cross-section of the cylinder shell can be circular or can have other shapes. Some implementations of the example luminaire module <NUM>'" may include a specular reflective coating on the side surface 232a of the light guide <NUM>. For T = <NUM>. 05D, <NUM>. 1D or <NUM>. 2D, for instance, light from multiple, point-like LEEs <NUM> - distributed around the z-axis along an elliptical path of length L - that is edge-coupled into the light guide <NUM> at the receiving end can efficiently mix and become uniform (quasi-continuous) along such an elliptical path by the time it propagates to the opposing end.

In the example implementations described above in connection with <FIG>, the luminaire module <NUM> includes a light guide <NUM> to guide (translate) light from the exit aperture of the optical couplers <NUM> to the input end <NUM>' of the optical extractor <NUM>. <FIG> illustrates an example of such "hollow" luminaire module <NUM>-h that includes LEEs <NUM>, one or more corresponding optical couplers <NUM> (like the luminaire module <NUM>) and an optical extractor (simplified relative to the optical extractor <NUM> of the luminaire module <NUM>) that uses only a redirecting surface <NUM> to extract - to the ambient environment - the light provided by the optical couplers <NUM>. The hollow luminaire module <NUM>-h is elongated along the y-axis like the luminaire module <NUM> shown in <FIG>. Also like the luminaire module <NUM>, the hollow luminaire module <NUM>-h includes a mount <NUM> (having a normal along the z-axis) such that the LEEs <NUM> are disposed on a surface of the mount <NUM> along the y-axis to emit light in a first angular range along the z-axis. The optical couplers <NUM> are arranged and configured to redirect the light emitted by the LEEs <NUM> in the first angular range into a second angular range <NUM> that has a divergence smaller than the divergence of the first angular range at least in the x-z cross-section.

Here, the redirecting surface <NUM> is spaced apart from an exit aperture of the optical couplers <NUM> by a distance D and includes two reflecting surfaces arranged to form a v-groove with an apex pointing toward the optical couplers <NUM>. The distance D is selected based on a divergence of the second angular range <NUM> and of a transverse dimension (along the x-axis) of the redirecting surface <NUM>, such that all light provided by the optical couplers in the second angular range <NUM> impinges on the redirecting surface <NUM>. In this manner, a portion of the redirecting surface <NUM> redirects some of the light received from the optical couplers <NUM> into a third angular range <NUM>' and another portion of the redirecting surface <NUM> redirects the remaining light received from the optical couplers <NUM> into a fourth angular range <NUM>. In some cases, the redirecting surface <NUM> is semitransparent. In this manner, a fraction of the light received from the optical couplers <NUM> in angular range <NUM> is transmitted (leaks) through the redirecting surface <NUM> in a fifth angular range <NUM>'. A prevalent propagation direction for the fifth angular range <NUM>' is in the forward direction (along the z-axis. ) A light intensity profile of the hollow luminaire module <NUM>-h can be represented similar to the one shown in <FIG> as first 145a and second 145b output lobes, and optionally as an additional third output lobe 145c. By comparison, the first output lobe 145a corresponds to light output by the hollow luminaire module <NUM>-h in the third angular range <NUM>', the second output lobe 145b corresponds to light output by the hollow luminaire module <NUM>-h in the fourth angular range <NUM>, and the third output lobe 145c corresponds to light output by the hollow luminaire module <NUM>-h in the fifth angular range <NUM>'.

<FIG> is a cross-section of an optical coupler <NUM>-a that can be used in the luminaire modules <NUM>, <NUM>*, <NUM>', <NUM>", <NUM>‴ or <NUM>-h, for example, to receive light emitted by a light source <NUM>-a. The optical coupler <NUM>-a is configured to redirect the received light along an optical axis <NUM>-a of the optical coupler <NUM>-a. It can be configured to do so using only TIR. The shape of the side surfaces of a compact sized optical coupler that can rely only on TIR is described in detail below. Here, an emission direction <NUM>-a of the light source <NUM>-a - representing a prevalent propagation direction of the light emitted by the light source <NUM>-a - is parallel to the z-axis; equivalently, an angle δ between the emission direction <NUM>-a and the z-axis is zero. Further in this example, the optical axis <NUM>-a of the optical coupler <NUM>-a is centered on an exit aperture <NUM>-a of the optical coupler <NUM>-a and also is parallel to the z-axis. The optical axis <NUM>-a coincides with the optical axis of the luminaire module.

A width of the light source <NUM>-a along a direction orthogonal to the optical coupler' optical axis <NUM>-a (e.g., along the x-axis) is <NUM>-unit length. Here, the light source <NUM>-a can be an extended light source (e.g., emitting light uniformly from each surface element of the light source <NUM>-a) or one or more LEEs <NUM> that are part of an LED die, for example. The LEEs <NUM> can include multiple (e.g., LED) emitters, such as an array of emitters in a single package, or an array of emitters disposed on a substrate having a normal <NUM>-a. In the sectional profile illustrated in <FIG>, the light source <NUM>-a is represented by segment OM, where the point O is the origin of a Cartesian coordinate system.

As noted above in connection with <FIG>, the optical coupler <NUM>-a includes one or more solid pieces of transparent material (e.g., glass or a transparent organic plastic, such as polycarbonate or acrylic). An input aperture of the optical coupler <NUM>-a is optically coupled with the light source <NUM>-a. In this example, a width of the input aperture matches the width of the light source <NUM>-a along the x-axis normalized to <NUM>-unit length like the value of the width of the light source <NUM>-a.

In some implementations, the exit aperture <NUM>-a of the optical coupler <NUM>-a is optically coupled to the input end of a light guide <NUM>-a. The optical coupler <NUM>-a and light guide <NUM>-a can be coupled by using a material that substantially matches the refractive index of the material forming the optical coupler <NUM>-a or the light guide <NUM>-a, or both. For example, the optical coupler <NUM>-a can be affixed to the light guide <NUM>-a using an index matching fluid, grease, or adhesive. As another example, the optical coupler <NUM>-a is fused to the light guide <NUM>-a or they are integrally formed from a single piece of material. In this manner, redirected light output by the optical coupler <NUM>-a through the exit aperture <NUM>-a is guided by the light guide <NUM>-a to an optical extractor coupled at an opposing end of the light guide <NUM>-a. In other implementations, when the optical coupler <NUM>-a is part of a luminaire module without light guide, similar to the luminaire module <NUM>-h, redirected light output by the optical coupler <NUM>-a through the exit aperture <NUM>-a is provided to an optical extractor spaced apart from the optical coupler <NUM>-a by a distance D (not shown in <FIG>). In the sectional profile illustrated in <FIG>, the exit aperture <NUM>-a is represented by segment NP.

Additionally, the optical coupler <NUM>-a includes curved side surfaces <NUM>-a, <NUM>'-a that are shaped such the light emitted from any point of the light source <NUM>-a is incident on the curved side surfaces <NUM>-a, <NUM>'-a at angles that exceed a critical angle θC. The critical angle θC is equal to ArcCos(nambient/noptical-coupler). When the ambient is air, nambient ≈ <NUM>, and noptical-coupler = n, the critical angle θC = ArcCos(<NUM>/n). <FIG> shows cross-sections of multiple TIR optical couplers <NUM>-a for refractive indices n = <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

For the examples illustrated in <FIG>, all light emitted by the light source <NUM>-a is redirected by the optical coupler <NUM>-a via TIR towards the exit aperture <NUM>-a. In the sectional profile illustrated in <FIG>, the curved side surface <NUM>-a is represented by curve MM and the curved side surface <NUM>'-a is represented by curve OP, where the point O is the origin of the Cartesian coordinate system.

Any point R<NUM> of the curved side surface <NUM>-a - for which a segment OR<NUM> is inclined by an angle α relative to the segment OM - is separated from the point O of the light source <NUM>-a by a distance OR<NUM>(α) given by <MAT> Here, the angle α satisfies <NUM> ≤ α ≤ θC. Point N on the output aperture <NUM>-a is part of the curved side surface <NUM>-a and separated from the point O of the light source <NUM>-a by a distance ON = OR<NUM>(α = θC). Similarly, any point R<NUM> of the curved side surface <NUM>'-a - for which a segment MR<NUM> is inclined by an angle β relative to the segment MO - is separated from the point M of the light source <NUM>-a by a distance MR<NUM>(β) given by <MAT> Here, the angle β satisfies <NUM> ≤ β ≤ θC. Point P on the output aperture <NUM>-a is separated from the point M of the light source <NUM>-a by a distance MP = MR<NUM>(β = θC). Generally, each of equations (<NUM>) and (<NUM>) describes a curve known as an equiangular spiral (also called a logarithmic spiral), which is a compact shape that can effectuate the TIR condition. In this case, the sectional profile of the curved side surface <NUM>'-a given by equation (<NUM>) - and represented by curve OP - is the mirror inverse of the sectional profile of the curved side surface <NUM>-a given by equation (<NUM>) - and represented by curve MN.

To accommodate tolerances in manufacturing and material properties, the side surfaces can be shaped based on a notional critical angle that is slightly enlarged from the nominal critical angle associated with the nominal properties of the materials employed in the fabrication of the optical coupler.

The curved side surfaces <NUM>-a, <NUM>'-a may be continuously rotationally symmetric about the optical axis <NUM>-a of the optical coupler <NUM>-a (like in the luminaire module <NUM>" illustrated in <FIG>) or have translational symmetry along an axis perpendicular to the sectional plane of <FIG>, e.g., along the y-axis, (like in the luminaire modules <NUM>, <NUM>* or <NUM>' illustrated in <FIG>.

Equations (<NUM>) and (<NUM>) can be used to determine a length (along the optical axis <NUM>-a, e.g., the z-axis) of the optical coupler <NUM>-a and a width (along the x-axis) of the exit aperture <NUM>-a. The length of the optical coupler <NUM>-a is given by a distance between the optical source <NUM>-a (segment OM) and the exit aperture <NUM>-a (segment NP). Additionally, the width of the exit aperture <NUM>-a is equivalent to a length of segment NP. Note that in the example illustrated in <FIG>, the length of the optical coupler <NUM>-a and the width of the exit aperture <NUM>-a (and, hence, a volume and mass of the optical coupler <NUM>-a) increase with decreasing refractive index. For example, for n = <NUM>, the length of the optical coupler <NUM>-a is about <NUM> unit-lengths, and the width of the exit aperture <NUM>-a is about <NUM> unit-lengths.

Luminaire modules like the ones described in this section - in which source light injection is parallel to the device's optical axis - can be modified to obtain luminaire modules in which source light injection is non-parallel to the devices' optical axis, as described in the following section.

<FIG> shows examples of illumination devices <NUM>-b, <NUM>-c, <NUM>-d and 200e in which source light injection is non-parallel to an optical axis of the devices. <FIG> also illustrates - for comparison - an example of illumination device <NUM>-a, similar to the luminaire module <NUM> or <NUM>' described above in connection with respective <FIG> or <FIG>, in which source light injection is parallel to an optical axis of the device. Here, the optical axis of each of the devices <NUM>-a, <NUM>-b, <NUM>-c, <NUM>-d and 200e is the z-axis.

Each illumination device <NUM>-j, where j is in the set {a, b, c, d, e}, includes a light source <NUM>-j and one or more optical couplers <NUM>-j. The light source <NUM>-j is oriented relative the optical axis of the illumination device <NUM>-j such that an emission direction <NUM>-j of the light source <NUM>-j is different for each illumination device <NUM>-j. As described above, the emission direction <NUM>-j represents a prevalent propagation direction of the light emitted by the light source <NUM>-j. In some implementations, the light source <NUM>-j is elongated orthogonally relative the optical axis of the illumination device <NUM>-j, e.g., with a longitudinal dimension L along the y-axis, as illustrated in <FIG> or <FIG>. In this case, L can be <NUM>', <NUM>' or <NUM>', for instance. In other implementations, the illumination device can have another elongated configuration, as illustrated in <FIG>. In these implementations, a single optical coupler <NUM>-j also is elongated in the same manner as the light source <NUM>-j, e.g., along the y-axis, or multiple optical couplers <NUM>-j are distributed along the longitudinal dimension L of the light source <NUM>-j. In some other implementations, the light source <NUM>-j can have a non-elongated configuration, e.g., with rotational symmetry around the z-axis, as illustrated in <FIG>.

Moreover, the optical couplers <NUM>-j redirect, using TIR only, the light received from the light source <NUM>-j under the emission direction <NUM>-j and provides the redirected light along the optical axis (e.g., the z-axis) of the illumination device <NUM>-j. As such, the optical couplers <NUM>-j are referred to as TIR optical couplers <NUM>-j.

In the examples illustrated in <FIG>, the illumination device <NUM>-j also includes a light guide <NUM>-j and an optical extractor <NUM>-j, where j is in the set {a, b, c, d, e}. When needed to accommodate the single TIR optical coupler <NUM>-j that is elongated along the optical axis of the illumination device <NUM>-j, e.g., along the y-axis, or the multiple TIR optical couplers <NUM>-j that are distributed along the y-axis, the light guide <NUM>-j and the extractor <NUM>-j also are elongated along the y-axis with the longitudinal dimension L, as illustrated in <FIG> or <FIG>.

The light guide <NUM>-j guides the light - provided by the TIR optical couplers <NUM>-j at an input end of the light guide <NUM>-j - from the input end to an opposing end along the optical axis of the illumination device <NUM>-j, e.g., the z-axis. The optical extractor <NUM>-j is coupled with the light guide <NUM>-j at the opposing end to receive the guided light. As described above in connection with <FIG>, the optical extractor <NUM>-j outputs most of the light received from the light guide <NUM>-j to an ambient environment along a first backward direction that has a component orthogonal to the optical axis of the illumination device <NUM>-j and as second backward direction that has a component (i) orthogonal to the optical axis of the illumination device <NUM>-j and (ii) opposing the orthogonal component of the first backward direction. The light output by the optical extractor <NUM>-j along the first backward direction corresponds to the first output lobe 145a of the far field intensity profile shown in <FIG>, and the light output by the optical extractor <NUM>-j along the second backward direction corresponds to the second output lobe 145b. In some implementations, the optical extractor <NUM>-j transmits a fraction of the light received from the light guide <NUM>-j to the ambient environment along the forward direction. The light output by the optical extractor <NUM>-j in the forward direction corresponds to the third output lobe 145c.

In the case of illumination device <NUM>-a, the emission direction <NUM>-a is parallel to the optical axis of the illumination device <NUM>-a. Such parallel source light injection associated with a combination of light source <NUM>-a and TIR optical coupler <NUM>-a of the illumination device <NUM>-a is described above in connection with <FIG>.

In the case of illumination device <NUM>-j, where j is in the set {b, c, d}, the emission direction <NUM>-a is oblique to the optical axis of the illumination device <NUM>-j. In the case of illumination device <NUM>-e, the emission direction <NUM>-e is orthogonal to the optical axis of the illumination device <NUM>-e. These cases of non-parallel source light injection associated with each of the combinations of light source <NUM>-j and optical coupler <NUM>-j of respective illumination devices <NUM>-j, where j is in the set {b, c, d, e}, is discussed below.

<FIG> is a cross-section of a TIR optical coupler <NUM>-b used in the illumination device <NUM>-b to receive light emitted by a light source <NUM>-b and to redirect the received light along an optical axis <NUM>-b of the optical coupler <NUM>-b using only TIR. Here, an emission direction <NUM>-b of the light source <NUM>-b - representing a prevalent propagation direction of the light emitted by the light source <NUM>-b - forms a tilt angle δ with the optical axis <NUM>-b. Further in this example, the optical axis <NUM>-b of the optical coupler <NUM>-b (which coincides with an optical axis of the illumination device <NUM>-b) is centered on an exit aperture <NUM>-b of the optical coupler <NUM>-b and is parallel to the z-axis. Here, the tilt angle δ between the emission direction <NUM>-b and the optical axis <NUM>-b is <NUM> < δ = θC/<NUM> < θC, where θC = ArcCos(<NUM>/n) is a critical angle associated with a refraction index n of a transparent, solid material (e.g., glass or a transparent organic plastic, such as polycarbonate or acrylic) from which the optical coupler <NUM>-b is fabricated. Note that <FIG> shows cross-sections of multiple TIR optical couplers <NUM>-b for refractive indices n = <NUM>, <NUM> and <NUM>.

The light source <NUM>-b can be implemented by tilting the light source <NUM>-a - described above in connection with <FIG> - by the tilt angle δ = θC/<NUM> around an axis orthogonal on both the optical axis <NUM>-b and the emission direction <NUM>-b, e.g., around the y-axis. Hence, in a sectional profile illustrated in <FIG>, the light source <NUM>-b is represented by segment OM that has a length of <NUM>-unit length, where the point O is the origin of a Cartesian coordinate system. An input aperture of the optical coupler <NUM>-b is optically coupled with the light source <NUM>-b. In this example, a width and orientation of the input aperture matches respective width and orientation of the light source <NUM>-b.

When used as part of the illumination device <NUM>-b, the exit aperture <NUM>-b of the optical coupler <NUM>-b is optically coupled to the input end of a light guide <NUM>-b as described above in connection with <FIG>. In other implementations, when the optical coupler <NUM>-b can be part of a luminaire module without light guide, similar to the luminaire module <NUM>-h, redirected light output by the optical coupler <NUM>-b through the exit aperture <NUM>-b is provided to an optical extractor spaced apart from the optical coupler <NUM>-b by a distance D (not shown in <FIG>). In the sectional profile illustrated in <FIG>, the exit aperture <NUM>-b is represented by segment NP.

Additionally, for tilt angles δ < θC, the optical coupler <NUM>-b includes a curved side surface <NUM>-b and a composite side surface <NUM>-b that are shaped such the light emitted from any point of the light source <NUM>-b is incident on the curved side surface <NUM>-a and the composite side surface <NUM>-b at angles that are at or exceed the critical angle θC. For the examples illustrated in <FIG>, all light emitted by the light source <NUM>-b is redirected by the optical coupler <NUM>-b via TIR towards the exit aperture <NUM>-b. The composite side surface <NUM>-b includes a curved portion <NUM>'-b and a flat portion <NUM>-b. Here, the flat portion <NUM>-b is aligned with the optical axis <NUM>-b. In the sectional profile of the optical coupler <NUM>-b illustrated in <FIG>, the curved side surface <NUM>-b is represented by curve MM, the curved portion <NUM>'-b of the composite side surface <NUM>-b is represented by curve OQ, where the point O is the origin of the Cartesian coordinate system, and the flat portion <NUM>-b of the composite side surface <NUM>-b is represented by segment QP parallel with the z-axis. Here, the point Q of the composite side surface <NUM>-b separates the curved portion <NUM>'-b from the flat portion <NUM>-b.

Any point R<NUM> of the curved side surface <NUM>-b - for which a segment OR<NUM> is inclined by an angle α relative to the segment OM (which in turn is tilted from the x-axis by the tilt angle δ = θC/<NUM>) - is separated from the point O of the light source <NUM>-b by a distance OR<NUM>(α) given by Equation (<NUM>). In this case, the angle α satisfies <NUM> ≤ α ≤ θC + δ = 3θC/<NUM>. Point N on the output aperture <NUM>-b is part of the curved side surface <NUM>-b and separated from the point O of the light source <NUM>-b by a distance ON = OR<NUM>(α = θC + δ) = OR<NUM>(3θC/<NUM>). Similarly, any point R<NUM> of the curved portion <NUM>'-b of the composite side surface <NUM>-b - for which a segment MR<NUM> is inclined by an angle β relative to the segment MO (which in turn is tilted from the x-axis by the tilt angle δ = θC/<NUM>) - is separated from the point M of the light source <NUM>-b by a distance MR<NUM>(β) given by Equation (<NUM>). In this case, the angle β satisfies <NUM> ≤ β ≤ θC - δ = θC/<NUM>. Point Q on the curved portion <NUM>'-b of the composite side surface <NUM>-b is separated from the point M of the light source <NUM>-b by a distance MQ = MR<NUM>(β = θC - δ) = MR<NUM>(θC/<NUM>).

Moreover, the point Q - with Cartesian coordinates (xQ, zQ) - also is part of the flat portion <NUM>-b of the composite side surface <NUM>-b. Additionally, any point R<NUM> of the flat portion <NUM>-b of the composite side surface <NUM>-b has an x-coordinate equal to xQ - the x-coordinate of the point Q. Hence, the point P on the output aperture <NUM>-b has coordinates (xP, zP), where xP = xQ and zP = zN. In this case, the sectional profile of the composite side surface <NUM>-b including the curved portion <NUM>'-b given by equation (<NUM>) - and represented by curve OQ - and the flat portion <NUM>-b - and represented by segment QP - is not the mirror inverse of the sectional profile of the curved side surface <NUM>-b given by equation (<NUM>) - and represented by curve MN. The curved portion OQ <NUM>'-b is a mirror inverse of only a portion of the curved portion <NUM>-b with respect to <NUM>-b.

The curved side surface <NUM>-b and the composite side surface <NUM>-b may have translational symmetry along an axis perpendicular to the sectional plane of <FIG>, e.g., along the y-axis, (like in the luminaire modules <NUM>, <NUM>* or <NUM>' illustrated in <FIG>.

The above calculations can be used to determine a length (along the optical axis <NUM>-b, e.g., the z-axis) of the optical coupler <NUM>-b and a width (along the x-axis) of the exit aperture <NUM>-b. The length of the optical coupler <NUM>-b is given by a maximum distance between a point of the curved side surface <NUM>-b (curve MN) and the exit aperture <NUM>-b (segment NP). Additionally, the width of the exit aperture <NUM>-b is equivalent to a length of segment NP. Note that in the example illustrated in <FIG>, the length of the optical coupler <NUM>-b and the width of the exit aperture <NUM>-b (and, hence, a volume and mass of the optical coupler <NUM>-b) increase with decreasing refractive index. For example, for n = <NUM>, the length of the optical coupler <NUM>-b is about <NUM> unit-lengths, and the width of the exit aperture <NUM>-b is about <NUM> unit-lengths.

<FIG> are respective cross-sections of TIR optical couplers <NUM>-j used in the illumination devices <NUM>-j, where j is in the set {c, d, e}, to receive light emitted by a light source <NUM>-j and to redirect the received light along an optical axis <NUM>-j of the optical coupler <NUM>-j using only TIR. Here, an emission direction <NUM>-j of the light source <NUM>-j - representing a prevalent propagation direction of the light emitted by the light source <NUM>-j - forms a tilt angle δj with the optical axis <NUM>-j. Further in these examples, the optical axis <NUM>-j of the optical coupler <NUM>-j (which coincides with an optical axis of the illumination device <NUM>-j) is centered on an exit aperture <NUM>-j of the optical coupler <NUM>-j and is parallel to the z-axis.

For the example illustrated in <FIG>, the tilt angle δc between the emission direction <NUM>-c and the optical axis <NUM>-c is <NUM> < δc = θC, where θC = ArcCos(<NUM>/n) is a critical angle associated with a refraction index n of a transparent, solid material (e.g., glass or a transparent organic plastic, such as polycarbonate or acrylic) from which the optical coupler <NUM>-c is fabricated. Note that <FIG> shows cross-sections of multiple TIR optical couplers <NUM>-c for refractive indices n = <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

For the example illustrated in <FIG>, the tilt angle δd between the emission direction <NUM>-d and the optical axis <NUM>-d is θC < δd = 2θC, where θC = ArcCos(l/n) is a critical angle associated with a refraction index n of a transparent, solid material (e.g., glass or a transparent organic plastic, such as polycarbonate or acrylic) from which the optical coupler <NUM>-d is fabricated. Note that <FIG> shows cross-sections of multiple TIR optical couplers <NUM>-d for refractive indices n = <NUM>, <NUM>, <NUM> and <NUM>.

For the example illustrated in <FIG>, the tilt angle δe between the emission direction <NUM>-e and the optical axis <NUM>-e is θC < δe = <NUM>°, where θC = ArcCos(<NUM>/n) is a critical angle associated with a refraction index n of a transparent, solid material (e.g., glass or a transparent organic plastic, such as polycarbonate or acrylic) from which the optical coupler <NUM>-e is fabricated. Note that <FIG> shows cross-sections of multiple TIR optical couplers <NUM>-e for refractive indices n = <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

The light source <NUM>-j, where j is in the set {c, d, e}, can be implemented by tilting the light source <NUM>-a - described above in connection with <FIG> - by the tilt angle δj ≥ θC around an axis orthogonal on both the optical axis <NUM>-j and the emission direction <NUM>-j, e.g., around the y-axis. For example, δc = θC in the example illustrated in <FIG>; δd = 2θC in the example illustrated in <FIG>; and δe = <NUM>° in the example illustrated in <FIG>. Hence, in the sectional profiles illustrated in <FIG>, the light source <NUM>-j is represented by segment OM that has a length of <NUM>-unit length, where the point O is the origin of a Cartesian coordinate system. An input aperture of the optical coupler <NUM>-j is optically coupled with the light source <NUM>-j. In this example, a width and orientation of the input aperture matches respective width and orientation of the light source <NUM>-j.

When used as part of the illumination device <NUM>-j, where j is in the set {c, d, e}, the exit aperture <NUM>-j of the optical coupler <NUM>-j is optically coupled to the input end of a light guide <NUM>-j as described above in connection with <FIG>. In other implementations, when the optical coupler <NUM>-j is part of a luminaire module without light guide, similar to the luminaire module <NUM>-h, redirected light output by the optical coupler <NUM>-j through the exit aperture <NUM>-j is provided to an optical extractor spaced apart from the optical coupler <NUM>-j by a distance D (not shown in <FIG>). In the sectional profiles illustrated in <FIG>, the exit apertures <NUM>-j are represented by corresponding segments NP.

Additionally, for tilt angles δj ≥ θC, where j is in the set {c, d, e}, the optical coupler <NUM>-j includes a curved side surface <NUM>-j and a flat side surface <NUM>-j that are shaped such the light emitted from any point of the light source <NUM>-j is incident on the curved side surface <NUM>-j and the flat side surface <NUM>-j at angles that exceed the critical angle θC. Here, the flat side surface <NUM>-j is aligned with the optical axis <NUM>-j. For the examples illustrated in <FIG>, all light emitted by the light source <NUM>-j is redirected by the optical coupler <NUM>-j via TIR towards the exit aperture <NUM>-j. In the sectional profiles of the optical couplers <NUM>-j illustrated in <FIG>, the curved side surface <NUM>-j is represented by curve MN and the flat side surface <NUM>-j is represented by segment OP parallel with the z-axis, where the point O is the origin of the Cartesian coordinate system.

Any point R<NUM> of the curved side surface <NUM>-j, where j is in the set {c, d, e}, - for which a segment OR<NUM> is inclined by an angle α relative to the segment OM (which in turn is tilted from the x-axis by the tilt angle δj) - is separated from the point O of the light source <NUM>-j by a distance OR<NUM>(α) given by Equation (<NUM>). In this case, the angle α satisfies <NUM> ≤ α ≤ θC + δj. Point N on the output aperture <NUM>-j is part of the curved side surface <NUM>-j and separated from the point O of the light source <NUM>-j by a distance ON = OR<NUM>(α = θC + δ). For the example illustrated in <FIG>, the tilt angle δc = θC, the angle α satisfies <NUM> ≤ α ≤ 2θC, and point N on the output aperture <NUM>-c is separated from the point O of the light source <NUM>-c by a distance ON = OR<NUM>(α = 2θC). Further, for the example illustrated in <FIG>, the tilt angle δd = 2θC, the angle α satisfies <NUM> ≤ α ≤ 3θC, and point N on the output aperture <NUM>-d is separated from the point O of the light source <NUM>-d by a distance ON = OR<NUM>(α = 3θC). Furthermore, for the example illustrated in <FIG>, the tilt angle δe = <NUM>°, the angle α satisfies <NUM> ≤ α ≤ θC + <NUM>° and point N on the output aperture <NUM>-e is separated from the point O of the light source <NUM>-e by a distance ON = OR<NUM>(α = θC + <NUM>°).

Additionally, any point R<NUM> of the flat side surface <NUM>-j, where j is in the set {c, d, e}, has an x-coordinate equal to xo = <NUM> - the x-coordinate of the origin point O. Hence, point P on the output aperture <NUM>-j is part of the flat side surface <NUM>-j and has coordinates (xP, zP), where xP = <NUM> and zP = zN. In this case, the sectional profile of the flat side surface <NUM>-j - and represented by segment OP - is not the mirror inverse of the sectional profile of the curved side surface <NUM>-j given by equation (<NUM>) - and represented by curve MN.

The curved side surface <NUM>-b and the composite side surface <NUM>-b may have translational symmetry along an axis perpendicular to the sectional planes shown in <FIG>, e.g., along the y-axis, (like in the luminaire modules <NUM>, <NUM>* or <NUM>' illustrated in <FIG>.

The above calculations can be used to determine a length (along the optical axis <NUM>-j, e.g., the z-axis) of the optical coupler <NUM>-j and a width (along the x-axis) of the exit aperture <NUM>-j, where j is in the set {c, d, e}. The length of the optical coupler <NUM>-j is given by a maximum distance between a point of the curved side surface <NUM>-j (curve MN) and the exit aperture <NUM>-j (segment NP). Additionally, the width of the exit aperture <NUM>-j is equivalent to a length of segment NP. Note that in the examples illustrated in <FIG>, the length of the optical coupler <NUM>-j and the width of the exit aperture <NUM>-j (and, hence, a volume and mass of the optical coupler <NUM>-j) increase with decreasing refractive index. For n = <NUM> and a tilt angle δc = θC as illustrated in <FIG>, the length of the optical coupler <NUM>-c is about <NUM> unit-lengths, and the width of the exit aperture <NUM>-c is about <NUM> unit-lengths. Further, for n = <NUM> and a tilt angle δd = 2θC as illustrated in <FIG>, the length of the optical coupler <NUM>-d is about <NUM> unit-lengths, and the width of the exit aperture <NUM>-d is about <NUM> unit-lengths. Furthermore, for n = <NUM> and a tilt angle δe = <NUM>° as illustrated in <FIG>, the length of the optical coupler <NUM>-e is about <NUM> unit-lengths, and the width of the exit aperture <NUM>-e is about <NUM> unit-lengths.

<FIG> shows a graph <NUM> that summarizes results of calculations described above in connection with <FIG>, <FIG>, <FIG>, <FIG> and <FIG>. The graph <NUM> represents the determined widths (along the x-axis) of the exit apertures <NUM>-j, where j is in the set {c, d, e}, of optical couplers <NUM>-j used, for example, in the illumination devices <NUM>-j illustrated in <FIG>. The width of the exit apertures are expressed in terms of units of source width (swu). When the width of the light source <NUM>-j is <NUM> unit-length, then <NUM> swu = <NUM> unit-length.

The illumination device <NUM>-a (shown in <FIG>) is configured with parallel source light injection (δa = <NUM>) and uses an optical coupler <NUM>-a (shown in <FIG>) that has the smallest width of the exit aperture <NUM>-a from among the optical couplers <NUM>-j, where j is in the set {a, b, c, d, e}.

The illumination device <NUM>-b (shown in <FIG>) is configured with oblique source light injection (with a shallow tilt angle δb = θC/<NUM> < θC) and uses an optical coupler <NUM>-b (shown in <FIG>) that has a width of the exit aperture <NUM>-b larger than the width of the exit aperture <NUM>-a used in parallel source light injection.

The illumination device <NUM>-c (shown in <FIG>) also is configured with oblique source light injection (with a critical tilt angle δc = θC) and uses an optical coupler <NUM>-c (shown in <FIG>) that has a width of the exit aperture <NUM>-c larger than the width of the exit aperture <NUM>-b used in oblique source light injection with shallow tilt angle.

The illumination device <NUM>-d (shown in <FIG>) also is configured with oblique source light injection (with a steep tilt angle δd = 2θC) and uses an optical coupler <NUM>-d (shown in <FIG>) that has a width of the exit aperture <NUM>-d larger than the width of the exit aperture <NUM>-c used in oblique source light injection with critical tilt angle.

The illumination device <NUM>-e (shown in <FIG>) is configured with orthogonal source light injection (with a tilt angle δe = <NUM>°) and uses an optical coupler <NUM>-e (shown in <FIG>) that has the largest width of the exit aperture <NUM>-e from among the optical couplers <NUM>-j, where j is in the set {a, b, c, d, e}.

In summary, <FIG> illustrates embodiments of illumination devices <NUM>-j, where j is in the set {a, b, c, d, e}, with a coupler <NUM>-j and light source <NUM>-j arrangements that can provide different locations and orientations for the LEEs of the light source. Such different arrangements may be exploited for thermal purposes, direct contact coupling, resilience to placement tolerances between LEEs and coupler <NUM>-j/light guide <NUM>-j and/or other aspects, for example. Depending on the embodiment, the LEEs of the light source <NUM>-j may be placed on a substrate or directly on the coupler <NUM>-j, or the light guide <NUM>-j, for example. The coupler <NUM>-j and the light guide <NUM>-j can be integrally formed and as such considered one component which is referred to herein as coupler or light guide as the case may be. An emission direction <NUM>-j of the light source <NUM>-j can be oriented parallel (like in <FIG> and <FIG>), perpendicular (like in <FIG> and <FIG>) to the optical axis <NUM>-j of the optical coupler <NUM>-j or at an oblique angle (like in <FIG>. ) To achieve an oblique angle, a corner of the optical coupler <NUM>-j, where j is in the set {b, c, d, e}, or the light guide <NUM>-j may have a beveled flat edge for abutting flat LEEs or an edge with suitable indentations for receiving packaged LEEs with dome lenses, for example. An immersion substance such as silicone or other curable or non-curable immersion substance may be applied to reduce air gaps between LEEs and the coupler <NUM>-j/light guide <NUM>-j.

The substrate on which the LEEs are disposed to form a light source <NUM>-j can be oriented substantially orthogonal (like in <FIG> and <FIG>, where j = e), oblique (like in <FIG>, where j is in the set {b, c, d}) or substantially co-planar (like in <FIG> and <FIG>, where j = a) with side surfaces of the light guide <NUM>-j, as a normal to the substrate determines the LEE's dominant direction of emission. A coupler <NUM>-j can be created with either a solid cross section or a hollow metallic reflector cross section that can intercept the rays of light from the LEEs of the light source <NUM>-j and introduce them into the elongated light guide <NUM>-j such that their angular range at the junction between the coupler <NUM>-j and the light guide <NUM>-j is such that substantially all of the light will propagate through the light guide <NUM>-j via total internal reflection until it reaches the extractor <NUM>-j. A hollow coupler may have a shape different from a solid coupler <NUM>-j. The efficiency of the disclosed technologies relies on the relative size of the light source <NUM>-j and the dimensions of the coupler <NUM>-j. As LEDs and other solid state LEEs, such as VCSELs (Vertical Cavity Surface Emitting Lasers) continue to decrease in size and increase in surface luminance, these types of coupling methodologies become increasingly practical since the relative sizes of the coupler <NUM>-j and the light guide <NUM>-j and extractor <NUM>-j combinations can continue to shrink in size and use of materials for increased economic advantage.

Claim 1:
An optical coupler (<NUM>; <NUM>-c; <NUM>-d) comprising:
an input aperture (<NUM>) disposed within a first plane;
an exit aperture (<NUM>; <NUM>-c; 225d) disposed within a second plane, the second plane intersecting the first plane at an acute angle, the acute angle being equal to or larger than a critical TIR angle;
and a first side surface and a second side surface extending between the input aperture (<NUM>) and the exit aperture (<NUM>; <NUM>-c; <NUM>-d), the first and second side surfaces configured to direct incident light from the input aperture (<NUM>) to the exit aperture (<NUM>; <NUM>-c; 225d) via total internal reflection (TIR),
wherein the second side surface is a flat side surface (<NUM>-c; <NUM>-d) being oriented orthogonal to the second plane and being adjacent the exit aperture (<NUM>; <NUM>-c; 225d),
wherein the first side surface is a logarithmic spiral which depends on the acute angle and the critical TIR angle, and
wherein a point (N) of the exit aperture (<NUM>-c; <NUM>-d) that is on the first side surface has the same coordinate along an axis orthogonal to the exit aperture (<NUM>-c; <NUM>-d) as another point (P) of the exit aperture that is on the flat side surface (<NUM>-c; <NUM>-d.