FI117492B - Light emitting device and method for directing light - Google Patents

Description

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117492

LIGHT EMISSIONS AND METHOD OF DIRECTING THE LIGHT

The present invention relates to a light emitting device comprising 5 light emitting diodes and a reflecting surface, said light emitting diode being adapted to emit a diverging light beam, and said reflecting surface being adapted to direct light emitted from said light emitting diode in substantially said direction. The present invention also relates to a method for directing light by said reflecting surface 10. Furthermore, the present invention relates to a combination of an optical waveguide and said light emitting device. The present invention still relates to a display unit comprising said light emitting device.

BACKGROUND OF THE INVENTION

The light diodes emit a beam with great divergence. This is a disadvantage in applications where high optical power should be concentrated in a predetermined direction. On the other hand, light emitted in undesired directions can cause, for example, blinding (blinding) of human viewers or over-switching between different signal channels. Beam divergence: ***: can be reduced by using optical elements such as lenses, hi: *** sensors or combinations thereof.

** ·: · »·:. · *. Japanese Patent Publication JP 10221574 discloses a method for switching * * * V V light from a light source to a fiber by means of a conical reflection * ". * Surface. According to the teaching, the half cone angle ***** of the reflecting surface is preferably selected according to the fiber aperture. is quite large: 30 and some of the incident light may be reflected several times by the conical • * reflective surface before it hits the fiber.

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SUMMARY OF THE INVENTION

It is an object of the present invention to reduce the divergence of a light beam emitting from a light emitting diode • ·:. ** i. It is also an object of the present invention 2 117492 to simplify the implementation of the necessary divergence reduction means.

To achieve these objects, the devices and method of the present invention are essentially characterized by what is set forth in the characterizing part of the independent claims. Further details relating to the invention are set forth in the dependent claims.

To achieve these objects, the devices and method of the present invention are essentially characterized in that the height of the reflecting surface from the active surface of the photodiode is less than or equal to the diameter of said active surface multiplied by 1.5, wherein said photodiode comprises resonance cavity.

Preferably, said reflecting surface is in the shape of a truncated cone, wherein the half-cone angle of said cone is selected to minimize the divergence of the incident light.

It has been found that when a resonance cavity light diode is used as a light source, even a lower reflector effectively reduces the divergence of the outgoing light beam.

*: ***: The device of the present invention can use ··· resonance cavity light emitting diodes with a large active surface and a high:. 25 light beam divergence. therefore, the power of the light emitted from the device according to the present invention having low divergence may be substantially higher than the light emitted from the device of the prior art - ***** when said devices have the same, predetermined height .

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Alternatively, the device of the present invention may be substantially smaller than the device of the prior art, wherein said devices have the same optical power. Therefore, the device of the present invention is well suited for use in very small-scale systems.

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When the reflection surface is low in height, it can easily be accomplished by various stamping, molding or machining techniques. In certain embodiments, the device is implemented by coating a hollow conical reflector with a metal layer and / or an insulating layer. The low height 5 facilitates the coating of said hollow reflector, e.g., by vacuum coating techniques.

Most of the light rays are reflected only once in the reflecting surface. Thus, the reflection losses can be significantly reduced compared to prior art devices.

Embodiments of the invention and their advantages will become more apparent to those skilled in the art from the following description and examples, and from the appended claims.

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BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described in more detail in the following examples, with reference to the accompanying drawings, in which Figure 1 schematically illustrates a resonant cavity light emitting diode, «t * • • ***. Fig. 2 is a schematic representation of a high-divergence optical beam of resonance cavity light emitting diode: * T 25 • · · · · · ***. ' Fig. 3 illustrates an example of an angular distribution of intensity output from two resonant cavity light diodes, * 4 • Fig. 4 schematically illustrates an embodiment of the present invention based on a conical reflection surface, t »1 • · · * · *: Figure 5 schematically shows the dimensions of the reflection surface and the resonance cavity light diode, 994 35 Fig. 6a shows an example of a resonance cavity light source * * '; * ·; angular distribution of low optical power density,;: 5 4.

117492 Figure 6b shows the normalized optical power of a beam of light emitted from a resonant cavity light emitting diode of Figure 6a to a conical space angle as a hemispherical angle, wherein said hemispherical angle defines said space angle Fig. 8 is a schematic view of a light emitting device comprising a reflective layer, a projection of a cone, comprising an asymmetric conical reflector, 1 · 10 • Figure 10 schematically illustrates a light emitting device comprising: a slab with a conical opening, whereby said:. The inner part of the 25 conical aperture is covered with a reflection layer, * 1 · 1 * · · · ** · · · ** ··· Figure 11 schematically illustrates a light emitting device comprising a transparent conical body 30 • · · Figure 12 shows schematically optical waveguide and a combination of the light emitting device of the present invention · <1 ···. · ♦ * • 1 · * · * 4 * · · * 1 1 * 1 5 117492 Figure 13 schematically illustrates an optical waveguide and light Fig. 14 schematically illustrates a light emitting device comprising a reflector having two different cone angles, Fig. 15 schematically illustrating a light emitting device comprising a biaxially curved reflector, and 10 Fig. 16 schematically shows a display unit comprising a plurality of light emitting devices according to the present invention devices.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, a resonance cavity light emitting diode 10, also called an RCLED (resonance cavity light emitting diode), is a device comprising a semiconductor medium 4 formed between at least two mirrors 5, 6. The semiconductor medium emits light based on radiating electron-gap recombination on at least one surface of the p-n-junction. The mirrors 5, 6 are at least partially reflective and define a resonance cavity 7 between them. The light emitted from the semiconductor medium 4 ··· is reflected back and forth between said mirrors 5, 6, amplifying the light radiation. The light exits through the output mirror 5 and forms a non-coherent beam of light BB1 from the resonant cavity photodiode. One or more layers of the semiconductor medium 4 may also act as a cover 5, 6. The resonance cavity LED 10 can also emit light to a human. . at invisible wavelengths.

: 30 ··· The transmitted light beams LL form an outgoing beam bundle BB1 which propagates on average in the SZ direction and has great divergence. Direction * · SZ is the average direction LL of all light beams forming the outgoing beam BB1. The direction SZ is typically perpendicular to the mirrors * ··· * 35 to 5, 6.

117492 Beam BB1 passes through exit mirror 5. The near field NFD1 of the beam BB1 defines the circular portion of the output mirror 5, referred to herein as the active surface 11. The near field diameter NFD1 of the beam BB1 is defined as the diameter of the circle 5 within 95% of the optical power of the beam BB1.

Referring to Figure 2, the optical axis N1 is parallel to the propagation direction SZ of the beam bundle BB1 and passes through the mid-10 points of the active surface 11, α being the angle between the light beam LL and the direction SZ.

Figure 3 illustrates as an example the angular distributions of the intensities INT from the two resonance cavity light emitting diodes 10. The distributions SL, 15 DL are related to different cavity lengths but to the same control current connected to the light emitting diodes 10, which is about 5 milliamps. The distributions SL, DL are shown as polar coordinate curves. 0 ° is defined as SZ. The distributions SL and DL are far-field distributions. The distribution marked SL has a maximum associated with 0 °, i.e. 20 SZ. The distribution marked DL has a maximum associated with approximately 41.5 ° and a local intensity minimum in the 0 ° direction. Thus, the angular distribution of the intensity of the output beam BB1 may also have a local minimum in the direction SZ.

In this example, the optical power associated with the DL distribution is more than two times the optical power associated with the SL distribution. Generally, the maximum optical power emitted by the reso-: * V nano-cavity diode 10 • · · · ;;; is related to the angular intensity distribution having a local minimum: ··· in SZ, as exemplified by DL.

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Referring to Figure 4, the light emitting device 100 of the present invention comprises at least a resonance cavity diode 10 and a reflector. of the surface 20. The reflection surface 20 is arranged to direct the light emitted from the photodiode 10 M substantially in the direction SZ. The light beam LL from the light emitting diode 10 and the beams reflected from the surface 20 form the light beam BB2 emitted from the desired device 100.

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Referring to Figure 5, the circular active surface 11 of the resonance cavity diode 10 has a diameter DIA1. The diameter DIA1 is equal to the diameter NFD1 of the near field of beam BB1 (Figure 1).

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The reflecting surface 20 has a height H1 from the reference plane, i.e. the active surface 11, of the mirror 5 of the resonance cavity diode 10, the angle β between the reflecting surface and the direction SZ being substantially greater than 0 °, i.e. the reflecting surface 20 is oblique to the optical axis N1.

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Figure 6a shows an example of the angular distribution (dP / da) of the optical power density output from the resonance cavity photodiode 10 (Figure 2). Optical. the power density dimension in this case is watt per degree (W / °). The value of the abscissa associated with the maximum power density is denoted by 15 ocMAx · In this case, the highest power density is directed in the directions where a = 45 °. Said directions form a conical surface around the direction SZ.

The angular distribution of the optical power density shown in Fig. 6a is calculated from the angular distribution DL of the intensity of Fig. 3, assuming axial symmetry. The angle αΜΑχ related to the maximum power density is typically somewhat larger than the angle related to the maximum intensity.

• · ·:. ·. Figure 6b shows the normalized optical power P / Pmax transmitted by a reso- "V cavity light emitting diode 10 (Figure 2) to a conical space angle having a half-conic angle α relative to SZ. The values are ** · * 'normalized by dividing the power values P by beam BB1. at the total optical power, the PMax LED 10 is the same as in Figure 6a.

The curve shown in Figure 6a is a derivative of the curve shown in Figure 6b.

* 50% of the optical power exits into a conical space angle with a half cone angle a = 47 °.

Figure 7a shows, by way of example, the angular distribution of the optical power density (dP / da) transmitted by the light emitting device 100, wherein said light emitting device 100 comprises a conical reflecting surface (Figures 4 and 5). The half-cone angle β is 22.5 ° and the height H1 of the reflecting surface 20 is 0.8 times the diameter DIA1 of the active surface 11. The LED 10 is the same as in Figure 6a.

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The half-cone angle β of the reflecting surface is preferably selected according to the following equation:

In other words, the optimum angle β between the reflecting surface 20 and the direction SZ is substantially equal to the angle ocmax divided by two, wherein said angle ocMax is related to the maximum optical angular power density transmitted by the photodiode. In practical implementation, the manufacturing tolerances should be taken into account, and the optimum angle β between the reflecting surface 20 and the direction SZ is preferably αMAX / 2 + 3 °.

The maximum power density transmitted by the resonance cavity diode 10; the associated angle aMAx is typically 30-50 °. In this case, the cone angle β of the reflection surface half-20 is preferably 15-25 °.

** * * * · * ·. * ···. The angular distribution of the power density depends on the light-transmitting material, e.g.

* · "J. The reflection coefficient of the glass. Then the angles cxMax and β in equation (1) represent the situation in the light-transmitting material.

··· · 25:; T Figure 7b shows the normalized optical power P / PMAx transmitted by the light emitting device 100 to a conical space angle having a half-conical angle α relative to SZ (Figures 4 and 5). The values are normalized by dividing the power values P by the total optical power 30 of the beacon BB1 · The light emitting diode 10 and the reflecting surface 20 are the same as in Figure 7a.

* · ·. The curve shown in Fig. 7a is a derivative of the curve of Fig. 7b.

* »« • »* 50% of the optical power exits to a conical space angle with a half-cone angle a = 18 °. 38% of the optical power goes to a space-35 angle with a half-cone angle α = 12 °.

* * 9 117492 To determine the divergence of beams BB1, BB2 (Figures 2 and 4), the boundaries of beams BB1, BB2 must be defined. In the case of Fig. 6b, the divergence of the beam BB1 is 94 ° when the limit of the beam BB2 is set to 50% of the total optical power. In the case of Fig. 7b, the divergence of the 5 beams BB2 is 36 ° when the boundary of the bundle BB2 is set to 50% of the total optical power. In this case, the use of the reflecting surface 20 centers the transmitted light beam BB2 substantially relative to the original beam beam BB1.

10 While the angle αΜΑχ associated with the maximum power density is typically about 45 degrees, the reflective surface has a half-cone angle β of about 22.5 degrees (Figure 5). When the height H1 of the reflecting surface 20 is selected to be less than or equal to 1.5 times the diameter DIA1 of the active surface 11, substantially no light beam LL from the active surface 11 is reflected more than once on the reflecting surface 20, only light beams LL passing through the plane with optical axis N1. Thus, in the case of the metal reflecting surface 20, the reflection losses are minimized.

The height H1 of the reflecting surface 20 is preferably greater than or equal to 0.5 times the diameter DIA1 of the active surface 11. Otherwise: 1 ♦ In 1 light beams LL that start at a 45 degree angle of the active • ·. ** ·. of the surface 11, not reflected.

Referring to FIG. 8, the light emitting device 100 may comprise a conical “Y shell 21. The inside of the shell 21 may be coated with a reflective surface • 1 · γ; with a note 20a. Alternatively, the casing 21 may be transparent and the outside may be coated with a reflective coating 20b.

* »· 30 The casing 21 may be formed by molding or stamping plastic, glass, collector or metal. The casing 21 may also be machined by drilling, lathing and / or grinding. The casing 21 may be coated with a reflective layer by a vacuum coating. The reflective surface can be achieved using aluminum coatings, oxide-coated aluminum coatings, • · ♦ 35 rhodium coatings or dielectric multilayer coatings.

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When the reflective surface 20 contains conductive material, electrical contact with the active surface 11 of the photodiode 10 may be prevented by a suitable spacer between the reflective surface 20 and the active surface 11.

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Referring to Figure 9, the light emitting device 100 may comprise an asymmetric reflecting surface 20, e.g., a portion of a conical reflecting surface. This embodiment may be advantageous if the available space is very limited but maximum power is not required.

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Referring to Figure 10, the reflection surface 20 may be implemented by forming a conical opening in the plate 22 and coating the inside of the conical opening with a reflecting surface 20.

Referring to Figure 11, the reflection surface 20 may be based on total reflection in the transparent conical body 24. The reflection surface 20 may be coated with a protective coating. If the refractive indices of the reflecting surface 20 and / or the orientation with respect to the transmitted light rays do not meet the criterion of total reflection, the surface 20 may be coated with an additional 20 reflection layers.

: * · *: The reflection surfaces 20 based on total reflection are more advantageous than the reflectors based on metal surfaces because the reflection losses in the total reflection are insignificant.

* ··· Λ 25 • * · ** V Physical contact between the body 24 and the active surface 11 can be] detrimental because it can interfere with the proper operation of the cavity mirror 5 of the photodiode 10 (Figure 1). Suitable projections or spacers may be provided in the space between the body 24 and the photodiode 10.

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Referring to Figure 12, the light emitting device 100 may be used to connect light to the core 201 of the optical waveguide 200. It is advantageous to provide bevel and guide surfaces for easy insertion and positioning of the waveguide 200 into a device 100. The light emitting device 100 and the optical waveguide 200 together form a combination 400.

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Referring to Figure 13, a portion of the optical waveguide 200 may be tapered. The heeling surface 20 can be implemented by means of a tapered portion. The operation of the combination 400 may be based on total reflection without additional coatings, however, the tapered portion may be coated with additional reflection layers and / or protective layers. Further, the tapered portion may comprise a sheath layer (not shown) having a lower refractive index than the core 201 of the waveguide 200.

The tapered portion may be accomplished, for example, by molding, grinding, turning, heating, and drawing, or by attaching an additional conical member to the end of the waveguide 200. It is preferred that the tapered portion is short as it is stronger than the long narrow tapered fiber.

The direct portion of the waveguide 200 comprises a cylindrical reflecting surface, i.e. the interface between the core and the sheath. However, since the interface between the core and the sheath is substantially parallel to the direction SZ, the angle α between the light rays and the direction SZ is not reduced in the reflections of the cylindrical portion. The cylindrical portion does not affect the height H1 of the reflecting surface 20 of the light emitting device 100.

Referring to Fig. 14, the device 100 may comprise a plurality of overlapping conical cone surfaces with different cone angles, i.e. different half cone angles β. Height ”·. H1 is the sum of the height of the overlapping reflection surfaces 20 from the active surface 11.

* · * * · * · ·· «· ;; Referring to Figure 15, the reflecting surface 20 may also have a two-dimensionally: ···: curved shape. The shape may be, for example, a paraboloid shape, an ellipsoid shape or a spherical shape.

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Referring to Figure 16, the display unit 500 may be implemented using an X: series of light emitting devices 100. For a single disk, * · · * | arrange multiple light emitting devices 100.

* * • O 35 When a resonance cavity light emitting diode 10 is used, the low reflection surface 20 provides a good efficiency for focusing the light emitted from the resonance cavity light emitting diode 10 12 117492. Compared to prior art devices with high reflectors or collector lenses, the device 100 may be reduced in size and / or the optical power may be increased.

The use of the device 100 of the present invention is advantageous when a low-cost, low-cost device is required to form a centralized powerful beam.

The use of a reflecting surface 20 reduces the light intensity in the undesirable 10 directions, i.e., directions that deviate significantly from the direction SZ.

This helps reduce overconnection between optical signal channels, blinding (glare) to detectors or human viewers, or heating components to radiation.

15 Devices 100, 400, 500 may be used to implement fiber-optic transmitters, e.g. projectors.

·· · • 1 2 t • · .3. It will be apparent to one skilled in the art that modifications and variations of the devices and method of the present invention are possible. The specific embodiments described above with reference to the accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention as defined in the appended claims. | Lii 30 • · «• 1 ♦ · «·· '•« • 1 ♦ • 1 · • · »····' • · • · 'j» 1 · • «• · · · · · 1 ·….

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Claims (11)

117492 A light emitting device (100) comprising at least a light emitting diode (10) and a reflecting surface (20), wherein said light emitting diode (10) is arranged to transmit a diverging light beam (BB1) in the direction (SZ), and said reflecting surface is adapted light emitting from said photodiode (10) in substantially said direction (SZ), wherein the angle (β) between said reflecting surface (20) and said direction (SZ) is greater than zero degrees, characterized in that said photodiode 10 comprises a resonant cavity (7), wherein said near-field diameter (NFD1) of said light beam (BB1) defines said resonant cavity (7) with an output mirror (5) of a circular active surface (11), and wherein said reflection surface height (H1) of said active surface (11) is less than (10) the diameter (DIA1) of said 15 active surfaces (11) multiplied by a factor of 1.5. Device (100) according to claim 1, characterized in that said angle (β) between said reflecting surface (20) and said direction (SZ) is between 15 and 25 degrees. 20 Device (100) according to Claim 1 or 2, characterized in that said reflecting surface (20) is part of a conical surface. A device (100) according to any one of the preceding claims 1-3, characterized in that said device (100) comprises a transparent material '*!:! to be a truncated cone. ♦ ···· - • · «•« Device (100) according to one of the preceding claims 1 to 4, characterized in that said reflecting surface (20) is based on total reflection. * · · ♦ · • I Device (100) according to one of the preceding claims 1 to 4, characterized in that said reflecting surface (20) comprises metal. • · · • · • * ·· * • · · · · 117492 .: 14 Device (100) according to one of the preceding claims 1 to 4, characterized in that said reflecting surface (20) comprises a dielectric coating. A method for directing light, said method comprising at least directing light from the photodiode (10) by a reflecting surface (20), said photodiode (10) transmitting a diverging light beam (BB1) in the direction (SZ), and said reflecting surface (20). aligns light emitted from said photodiode (10) in substantially said direction (SZ), wherein the angle (p) between said reflecting surface (20) and said direction (SZ) is greater than zero degrees, characterized in that said photodiode comprises a resonant cavity ( 7), wherein: the near field diameter (NFD1) of said light beam (BB1) defines said resonant cavity (7) with an output mirror (5) of a circular active surface (11), and said reflecting surface height (H1) of said active surface (11) large than the diameter (DIA1) of said active surface (11) of said LED (10) multiplied by a factor of 1.5. A combination (400) of a light emitting device (100) and an optical waveguide (200), said light emitting device (100) comprising at least a light emitting diode (10) and a reflecting surface (20), wherein said light emitting diode (10) is ·. adapted to emit a diverging light beam (BB1) in the direction "j (SZ), and said reflecting surface is adapted to direct light emitted from said: * ·; 25 light-emitting diode (10) substantially in said direction (SZ), whereby said reflecting surface (20) and said direction (SZ) ··· *: 'angle (β) is greater than zero degrees, characterized in that said I * · light-emitting diode comprises a resonance cavity (7), whereby a near field of said light beam (BB1) diameter (NFD1) defines said resonance cavity (7) on the output mirror (5) as a circular active surface (11), and; ***: wherein said reflection surface height (H1) of said active surface (11) is less than or equal to the diameter (DIA1) of said active surface (11) of said light-emitting diode (10) multiplied by a coefficient i · * · · · · · · · · · · · · · · · · · · · · · · · · · · 117492 A combination (400) according to claim 9, characterized in that the end of said optical waveguide (200) is in the form of a truncated cone, wherein said reflecting surface (20) is formed by said end of said optical waveguide (200). 5 A display unit (500) comprising at least one light emitting device (100) comprising at least a light emitting diode (10) and a reflecting surface (20), said light emitting diode (10) being arranged to emit a diverging light beam (BB1) in direction (SZ), and said reflecting surface 10 being adapted to direct light from said photodiode (10) in substantially said direction (SZ), wherein the angle (β) between said reflecting surface (20) and said direction (SZ) is greater than zero degrees, characterized in that said photodiode comprising a resonance cavity (7), wherein the diameter (NFD1) of the near field 15 of said light beam (BB1) defines a circular active surface (11) of said resonance cavity (7) at an output mirror (5), and wherein said reflection surface height (H1) the active surface (11) being less than or equal to the diameter (DIA1) of said active surface (11) of said photodiode (10) multiplied by Sat 1.5. 20 •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• are are available. · »• · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · English · • 1 · * · 117492