HK1071935A - Laser image projector - Google Patents

Description

Laser image projector

Technical Field

The present invention relates to the field of image projectors.

Background

Image projection apparatus are well known and have been in use for many years. Such systems typically rely on an image modulator and an optical projection device to project an image onto a diffuser screen for viewing by a viewer. Image modulators were originally based on hard copy media, such as films like transparencies and motion picture films. Recently, there have been soft copy projectors based on, for example, micro-electromechanical systems or liquid crystal display devices, and laser projection systems, see, for example, U.S. patent application 2003/0039036A 1 to Kryschwitz et al, published 2, 27/2003. In any case, the image modulator creates an image plane that is projected through an optical system onto a screen, such as is commonly seen in movie theaters or digital computer monitor projectors. Image projection devices are also used in head mounted displays.

Optical systems for image projectors typically include a lens combination with focus control and often zoom control. These controls allow the projector to project focused images onto the screen from various distances and at various display image sizes. These systems suffer from the weight and size of the projection optics and are limited to imaging onto a single screen.

Us patent 6,170,953B1 issued to Lee et al on 1, 9 of 2001, describes a laser video projector for projecting images onto multiple screens. Such systems rely on a large number of beam combining optics to collect the optical paths and project the images on multiple screens.

There is a need for another image projection system that avoids these limitations.

Disclosure of Invention

This need is met by the present invention, which provides a laser image projector comprising: a substrate; and a two-dimensional array of individually addressable laser pixels formed on the substrate for emitting an imaged laser beam perpendicular to the substrate, each laser pixel comprising an addressable Organic Light Emitting Diode (OLED) and an organic vertical cavity laser pumped by the OLED.

It is an advantage of the present invention to provide a projection display that does not require a projection optical system.

Drawings

Fig. 1 is a schematic side view of a laser image projector according to the present invention;

FIG. 2 is a schematic top view of a laser image projector according to the present invention;

FIG. 3 is a schematic diagram of a prior art beam expander that can be used with the present invention;

FIG. 4 is a schematic diagram of a beam splitter and mirror that can be used in the present invention;

FIG. 5 is a schematic cross-sectional view of an OLED pumped organic laser that can be used in the present invention;

FIG. 6 is a schematic cross-sectional view of another OLED pumped organic laser that can be used in the present invention;

FIG. 7 is a schematic cross-sectional view of an organic laser cavity with periodic gain regions that can be used in the present invention;

FIG. 8 is a perspective view of a laser pixel formed by an array of phase-locked laser elements;

FIG. 9 is a perspective view of a laser pixel formed by separate sets of phase-locked laser elements;

FIG. 10 is a schematic view of a laser projector with a speaker;

FIG. 11 is a schematic side view of a laser projector including a lenslet array aligned with a laser in accordance with the present invention.

Detailed Description

Referring to fig. 1, individually addressable laser pixels 11 include an organic laser 12, the laser 12 being optically pumped by light from an OLED 14 formed on a substrate and electrically controlled by a circuit 16. In a passive matrix projector, the circuit 16 comprises only electrical conductors. In an active matrix projector, the circuit 16 contains active electronic elements such as transistors and capacitors.

The OLED 14 emits incoherent light 15 to optically pump the organic laser 12, the laser 12 emits laser light 13 perpendicular to the substrate and the laser light 13 propagates to expose an element, such as a light scattering projection screen 18, where the emitted light is scattered into visible light for a viewer (not shown). The light-diffusing projection screen 18 may be either transmissive or reflective so as to be viewable either from the back or the front.

Referring to fig. 2, the laser projector 8 includes an array of individually addressable laser pixels 11 controlled by a control zone 19. The individually addressable laser pixels 11 can emit light of different colors to form a color laser image projector. The frequency of the light emitted by the light emitting pixels 11 depends on the frequency of the light emitted by the OLEDs 14 and the material and construction of the organic lasers 12, as described below.

In further embodiments of the invention, the element exposed by the laser projector may be a light absorbing element, such as biological tissue. This is useful in medical applications where light of a particular frequency is to be directed in an imaged pattern to biological tissue. Such a laser projection system may be supplemented with an image sensor, so that the feedback system illuminates a specific element within the image area in real time. Alternatively, the element may be a light sensitive material, such as a photoconductor or photographic paper or film. In another alternative, a laser projector may be used to illuminate the heat transfer material for the printing or manufacturing process.

Referring to fig. 3, the image beam of laser light 13 may be expanded or reduced, such as expanding laser light 13 into a wider beam 17, using a beam expander, such as a Galilean beam expander having a plano-concave lens element 30 and a plano-convex lens element 32. Such an expander may also be used to control the angular divergence of the laser beam 17. The magnification of the beam expander is the ratio of the focal lengths of the two lens elements 30 and 32. The distance between elements 30 and 32 is the sum of the focal lengths.

Referring to fig. 4, optical elements such as beam splitters and mirrors may also be used to split or redirect the laser imaging beam so that the laser image projector can direct the light around corners or through complex paths to desired locations. Because the laser image projector of the present invention can project images onto a surface at any distance without the need for optics, folded optics, such as mirrors, can be placed in the projection path to project the image around corners. The image may also be moved either by moving the laser image projector itself or by moving an optical element, for example by moving a reflective surface of a mirror.

The laser image projector of the present invention can also be used to project images onto multiple surfaces at multiple locations by employing a beam splitter. Furthermore, due to the different projection distances, the projection positions are also at different distances from the laser image projector and can be positioned with appropriately positioned mirrors as described above. Suitable beam splitters and mirrors are well known in the optical arts. Referring to fig. 4, laser image projector 8 emits a laser beam 13 that is split by beam splitter 34 and reflected by mirror 36 to produce images on reflected light diffuser screen 18 at various distances from laser image projector 8.

Referring to fig. 5, an electrically pumped organic solid state laser emitter 20 useful in the present invention comprises an OLED 14 and an organic laser 12 and a transparent layer 110 between the OLED 14 and the organic laser 12. The organic laser 12 is a vertical cavity laser that includes a pair of mirrors 112 and 116 (e.g., Distributed Bragg Reflector (DBR) mirrors) and an active layer 114, the active layer 114 being formed of a material system employing a host dopantThe organic material of the system is as follows. The transparent layer 110 is a light-transmissive insulating planar layer compatible with the OLED 14 (e.g., silicon dioxide), but it can be any optical planar layer compatible with the OLED 14 and on which a DBR mirror can be grown. The DBR mirror 112 is deposited on the transparent layer 110. Conventional sputtering or electron beam (e-beam) deposition methods are preferred for growing the DBR mirror 112 because it is important for the dielectric layers to be of precise thickness. The bottom DBR mirror 112 includes alternating layers of dielectric with high and low refractive indices such that its reflectivity is greater than 99.9% at the wavelength of the laser light 13 and it transmits more than 90% of the OLED light 120. The DBR mirror 112 includes a lambda/4 thick layer of alternating high and low refractive index dielectric to provide a wavelength lambda at the laser wavelength₁A high reflectance is obtained under the conditions of (1); additional alternating high and low index dielectric layers are also deposited to provide a wide maximum transmission of incoherent light 15 emitted by the OLED. The organic active layer 114 is deposited on the DBR mirror 112 using a conventional high vacuum (10)^-7Torr) thermal vapor deposition method or using a solution spin casting method. To achieve a low threshold, it is preferable that the thickness of the active layer 114 is an integer multiple of λ/2, λ being the laser wavelength. The lowest threshold may be obtained when the integer multiple is 1 or 2.

The active layer 114 includes host and dopant molecules, preferably organic molecules of small molecular weight, because they can now be deposited more uniformly. The host material used in the present invention is selected from any material that is sufficiently absorptive of the incoherent light 15 and capable of transmitting a substantial portion of its excitation energy to the dopant material by Forster energy conversion. One skilled in the art will be familiar with the concept of Forster energy conversion, which involves the radiationless conversion of energy between a host and a dopant molecule.

One useful host dopant combination for red emitting lasers is tris (8-hydroxyquinoline) aluminum as the host and 4- (dicyanomethylene) -2-tert-butyl-6- (1, 1, 7, 7-tetramethyljulolidin-9-enyl) -4H-pyran (DCJTB) as the red emitting dopant. A DBR mirror 116 is deposited on the active layer 114. Again using conventional electron beam deposition, but this time it is preferred that the temperature of the organic material be maintained below 75 c during the deposition process. The top DBR mirror 116 includes alternating layers of dielectric with high and low refractive indices such that it has a reflectivity of greater than 98% at the wavelength of the laser light 13 and reflects more than 90% of the incoherent light 15. Thus, in addition to depositing a λ/4 thick layer of alternating high and low refractive index dielectric (λ is chosen close to the desired laser wavelength), additional layers of alternating high and low refractive index dielectric are deposited to have a wide maximum reflection of incoherent light 15. Specifically, only the portion of incoherent light 15 that is absorbed by the host material of active layer 114 needs to be reflected.

The OLEDs of the organic solid state laser emitter 20 are one or more electrically driven organic light emitting diodes that produce incoherent light within a predetermined portion of the spectrum. For an example of an OLED device, see U.S. Pat. No.6,172,459 to Hung et al, 1, 9, 2001, and references cited therein, the contents of which are incorporated herein by reference.

The OLED 14 is formed adjacent to the substrate 10, preferably on the substrate 10, and an electrode 100, such as a hole injection anode, is formed on the substrate 10, as shown in fig. 5. The substrate 10 may be any material suitable for fabricating an OLED device as described in the art, such as glass or quartz, and the electrode 100 may be a thin layer of Indium Tin Oxide (ITO) or a thin layer of a conductive metal formed on the substrate 10. The electrodes may be deposited by evaporation, sputtering, chemical vapor deposition, and the like.

Alternatively, the electrodes may be formed on the transparent layer 110, as shown in fig. 6. An organic hole transport layer 102 is formed on the electrode 100, an organic light emitting layer 104 is formed on the hole transport layer 102, and an organic electron transport layer 106 is formed on the light emitting layer 104. As an example of these three layers, one useful structure includes a diamine layer, such as 4, 4' -bis [ N- (1-naphthyl) -N-phenylamino ] biphenyl (NPB) as the hole transport layer 102, undoped 9, 10-bis (2-naphthyl) Anthracene (AND) as the light-emitting layer 104, AND Alq as the electron transport layer 106. These organic layers are typically prepared by high vacuum thermal evaporation. Their preferred thickness: NPB is 40-250nm, AND is 10-50nm, AND Alq is 10-200 nm.

A second transparent electrode layer 108 (e.g., a cathode) is formed on the electron transport layer 106 and is composed of a material selected to have a work function lower than 4.0 eV. One suitable transparent electrode layer 108 is indium tin oxide or MgAg, where the volume ratio of Mg-Ag is 10: 1. May be formed by conventional thermal evaporation deposition methods. An optically transparent insulating planarization layer 110 is formed on the cathode, and an organic laser 12 is formed on the transparent layer 110. Additional layers known in the art may be included in the OLED structure, such as hole injection and electron injection layers. As is known in the art, the application of a voltage V to the electrodes provides the necessary electric field for the light-emitting layer to generate a pump beam and then transport the light out of the organic light-emitting diode device. The voltage V may be continuous or in the form of pulses.

Under typical bias conditions, electrons (negative charge carriers) are injected from electrode layer 108 into organic electron transport layer 106, and holes (positive charge carriers) are injected from electrode 100 into organic hole transport layer 102. The electrons and holes are transported through the respective organic layers 106 and 102 into the light-emitting layer 104. In the organic light-emitting layer 104, electrons and holes are mainly recombined in the vicinity of the junction between the hole transport layer 102 and the light-emitting layer 104. The recombination results in the organic light emitting layer 104 emitting light. Of the light generated by the light-emitting layer, about 50% is emitted directly in the direction of the substrate 10, and the other 50% is emitted directly in the direction of the electrode layer 108. The electrode layer 108 is transparent, allowing light to pass through the transparent layer 110 in order to optically pump the vertical laser.

The electrode 100 and/or underlying substrate may be made reflective so that portion of the light emitted toward the electrode 100 may be reflected outside the device and pass through the transparent insulating planarization layer 110. It is known in the art that the positions of the anode and cathode, and the hole and electron injection and/or transport layers, may be reversed such that, for example, electrode 100 is the cathode and electrode 108 is the anode. At this point, a reflective cathode may be deposited on the substrate, while the anode is transparent.

Incoherent light 15 exits OLED 14 and enters organic laser 12 through bottom BR mirror 112. As a result of the structure of bottom BR mirror 112, most of the light enters active layer 114. By construction, the active layer matrix absorbs a portion of the incoherent light 15. In the portion of the light that is not absorbed (in the case where the absorption length of the active layer is too small), the remaining portion of the light enters the top DBR mirror layer 116, which in turn reflects most of the light back into the active layer, passing through it a second time. In the second pass, another portion of the incoherent light 15 is absorbed by the active layer matrix.

The light energy absorbed by the host is converted radiationless to dopant molecules by the Foster energy conversion mechanism. It is preferred that the dopant molecules have a high quantum efficiency of emission, since this allows the re-emission of a substantial portion of the non-radiatively converted energy as longer wavelength light. For example, using AND as the OLED emissive material, Alq as the active layer host, AND DCJTB as the active layer dopant, the emitted OLED light is blue, Alq absorbs mainly blue light, AND DCJTB emits red light.

The organic laser 12 is designed to have a high Q cavity for red light, specifically the wavelength with the highest reflectivity for the top and bottom DBR mirrors. The skilled person is aware of the concept that: lasing occurs at a specific wavelength with the highest net gain. At that wavelength, the laser light 13 reflects many times between the top and bottom DBR mirrors before being emitted primarily through the top DBR mirror 16 (because the bottom DBR mirror has much lower mirror loss than the top DBR mirror, as designed).

In this embodiment, the organic laser 12 and the electrically driven OLED 14 are combined in an integrated device formed on a substrate 11, with the electrically driven OLED 14 located on a substrate 10, and the organic laser 12 on the OLED 14 and separated therefrom by an optically transparent planarization layer 110. Thus, the bottom DBR mirror includes alternating layers of high and low refractive index dielectric layers that reflect greater than 99.9% and transmit more than 90% of the incoherent light 15 at the wavelength of the laser light 13. Accordingly, the top DBR mirror includes alternating layers of dielectric with high and low refractive indices such that at the wavelength of the laser light 13, the reflectivity is greater than 98% and reflects more than 90% of the incoherent light 15.

Referring to fig. 6, in another embodiment of the present invention, the substrate 10 is transparent and positioned adjacent to the organic laser 12, and preferably the organic laser 12 is formed on the substrate 10 so that the emitted light can penetrate the substrate 10.

For vertical cavity organic laser structures, the efficiency of the laser can be improved by using active region design. Referring to FIG. 7, the periodic gain layer 305 is aligned with an anti-node of the device standing wave electromagnetic field, schematically illustrating the standing wave electromagnetic field pattern 320 of the laser in the laser device 200. Since the excitation emission is highest at the antinodes and negligible at the nodes of the electromagnetic field, it is advantageous to form periodic gain layers 305 separated by organic spacer layers 310 as shown in fig. 7. The organic spacer layer 310 does not experience excitation light or spontaneous emission and does not substantially absorb the wavelength of the laser light 13 or the pumped incoherent light 15. An example of a material suitable for forming the organic spacer layer 310 is the organic material 1, 1-bis- (4-methylphenyl) -aminophenyl) -cyclohexane (TAPC).

TAPC performs well as a spacer material because it does not substantially absorb the energy of the laser output or pump beam and its refractive index is slightly lower than most organic matrix materials. This difference in refractive index is useful because it helps to maximize the overlap between the antinodes of the electromagnetic field and the periodic gain layer 305. As described below in connection with the present invention, the use of periodic gain regions rather than global gain regions results in higher power conversion efficiency and significantly reduces unwanted spontaneous emission. The arrangement of the Gain region can be determined by an optical standard matrix method, see Corzine et al, "Design of Fabry-Perot Surface-Emitting laser a Periodic Gain Structure", IEEE Journal of Quantum electronics, Vol.25, No.6, June 1989. For good results, the thickness of the periodic gain layer 305 needs to be 50nm or less to avoid unwanted spontaneous emission.

With the phase-locked organic laser array 220 as shown in fig. 8, the area of the laser emitting pixels 11 can be increased, and a certain degree of spatial coherence can be maintained. To form a two-dimensional phase-locked laser array 220, laser elements 200 separated by spaces 210 between the elements are defined on the surface of the organic laser 12. To obtain phase lock, intensity and phase information must be exchanged between the laser elements 200. This can be done by slightly confining the laser emission to the lasing region, either with a small value of built-in index or with gain control (e.g. modulating the reflectivity of the mirrors).

In the embodiment shown in fig. 8, the modulation of the reflectivity is achieved by: a two-dimensional array of cylindrical laser elements 200 is formed on the surface of the bottom dielectric stack by patterning and forming etched regions in the bottom dielectric stack using standard photolithographic or etching techniques. The remainder of the organic laser region microcavity structure is deposited over the patterned bottom dielectric stack. The shape of the laser element 200 is circular in the described embodiment, but other shapes are possible, such as rectangular. The inter-element spacing 210 is in the range of 0.25 to 4 μm.

Phased-lock array operation also occurs for larger inter-area spacings, but larger spacings result in inefficient use of the optical pumping energy. The etch depth is preferably from 200 to 1000 nm. With the etch just beyond the even layers in the bottom dielectric stack, the wavelength of the longitudinal mode in the etched region can be shifted significantly away from the peak of the gain medium. In this way, lasing in the region between the laser elements 200 is avoided and spontaneous emission is significantly reduced. The net result of forming the etched regions is to slightly confine the laser emission to the laser element 200, while the areas between the regions are free of lasing, with coherent phase-locked lasing by the laser array 220.

With multiple coherent phase-locked laser emitters, a larger addressable light emitting region emitting a single wavelength may be formed. Different addressable light-emitting regions may be formed to emit different colors of light to provide a full color image display system. It is also possible to manufacture a single individually addressable light-emitting region that emits light of multiple colors, e.g., white. Different groups can be made to emit different colors of light using the following method: the spacing 210 between the elements is varied so that the elements are arranged in groups to form a laser array 220, wherein the spacing 210 between elements within the same group is the same, while the spacing between different groups is large enough to avoid lasing between groups.

Different OLED materials may be used in each group as desired to assist in emitting different colors of light from each group in a single individually addressed light emitting laser pixel. In this way, the individually addressed light-emitting laser pixels can emit light of various combinations of frequencies. The individually addressed light-emitting laser pixels may for example be made to emit white light. The white point of the addressable light-emitting laser pixels can be controlled by adjusting the ratio of the number of groups emitting different colors of light within the elements, for example, making one laser array larger than the other in the addressable light-emitting laser pixels.

Referring to fig. 9, individually addressable emissive laser pixels 11 include three laser arrays 220 of light emitting elements 200 for emitting different colors of light. Each laser array 220 comprises one or more laser elements 200, wherein all laser elements 200 in one laser array 220 emit light of the same color. As described above, the laser array 220 may have a different number of elements to provide a particular luminous intensity for each group. The overall color of the light emitted by the laser pixels 11 can be adjusted by adjusting the intensity of the light emitted by each group, for example by adjusting the white point of the laser pixels 11 emitting white light. Alternatively, the white light emitting pixel 11 may comprise a mixed set of differently colored laser elements 200, the modes of the differently colored laser elements 200 not being locked but being arranged to promote color mixing of the laser elements 200.

Referring to fig. 10, a laser image projector 8 may be combined with a directional sound system 40 that provides a complementary directional sound beam 42, such as described in U.S. patent application 2003/0035552 a1 to Kolano et al, published 2/20/2003. By providing diffuse sound reflector 44, a directional audiovisual system is provided that is portable, operable at various distances and in various environments, and is easy to manufacture. The acoustic beam 42 may be directed near and parallel to the image beam of laser light 13 to impinge on a diffuse acoustic reflecting surface beside the light diffusing projection screen 18 for receiving the image beam of laser light 13 or on a diffuse acoustic reflector 44 behind the light diffusing projection screen 18. Projection screens that are acoustically transparent are well known in the film world.

Referring to fig. 11, in some cases, the laser element 200 may emit light that is not strictly parallel but rather has some degree of divergence. This diverging light 70 may be collimated into parallel light 72 using lenslets 74 located on the substrate and aligned with the laser elements 200. In this case, the addition of the lenslets 74 can reduce the performance requirements for the laser element 200, while making a flat panel projector possible.

Claims (1)

1. A laser image projector comprising:

a) substrate

b) A two-dimensional array of individually addressable laser pixels formed on said substrate for emitting an imaging laser beam perpendicular to said substrate, each said laser pixel comprising an addressable organic light emitting diode and an organic vertical cavity laser pumped by said organic light emitting diode.