Quantum photonic imagers and methods of fabrication thereof

Emissive quantum photonic imagers comprised of a spatial array of digitally addressable multicolor pixels. Each pixel is a vertical stack of multiple semiconductor laser diodes, each of which can generate laser light of a different color. Within each multicolor pixel, the light generated from the stack of diodes is emitted perpendicular to the plane of the imager device via a plurality of vertical waveguides that are coupled to the optical confinement regions of each of the multiple laser diodes comprising the imager device. Each of the laser diodes comprising a single pixel is individually addressable, enabling each pixel to simultaneously emit any combination of the colors associated with the laser diodes at any required on/off duty cycle for each color. Each individual multicolor pixel can simultaneously emit the required colors and brightness values by controlling the on/off duty cycles of their respective laser diodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to emissive imager devices comprising a monolithic semiconductor arrays of multicolor laser emitters that can be used as an image sources in digital projection systems.

2. Prior Art

The advent of digital display technology is causing a phenomenal demand for digital displays. Several display technologies are poised to address this demand; including Plasma Display Panel (PDP), Liquid Crystal Display (LCD), and imager based projection displays that use micro-mirrors, a liquid crystal on silicon (LCOS) device or a high temperature poly-silicon (HTPS) device (Ref. [33]). Of particular interest to the field of this invention are projection based displays that use imager devices, such as those mentioned, as an image forming device. These types of displays are facing strong competition from PDP and LCD displays and as such are in critical need for effective means to improve their performance while significantly reducing their cost. The primary performance and cost driver in these types of displays are the imagers used, such as micro-mirrors, LCOS and HTPS devices. Being passive imagers, such devices require complex illumination optics and end up wasting a significant part of the generated light, which degrades the performance and increases the cost of the display system. The objective of this invention is to overcome the drawbacks of such imager devices by introducing an emissive imager device which comprises an array of multicolor laser emitters that can be used as an image source in digital projection systems.

FIGS. 1A and 1Bare block diagram illustrations of typical projector architectures100used in projection display systems that use a passive imagers, such as those that use reflective imagers including micro-mirrors or LCOS imager devices (FIG. 1A) and those that use a transmissive imager, such as HTPS imager devices (FIG. 1B); respectively. In general, the projector100of a typical projection display system ofFIG. 1Ais comprised of an imager110, illuminated by the illumination optics120which couples the light generated by the light source130onto the surface of the imager120. The light source130can either be a lamp that generates white light or a semiconductor light source, such as light emitting diodes (LED) or laser diodes, that can generate Red (R), Green (G) or Blue (B) light.

In the case of the projector100that uses a reflective imager illustrated inFIG. 1A, when a lamp is used as a light source, a color wheel incorporating R, G and B filters is added between the illumination optics and the imager to modulate the required color. When a semiconductor light source is used in conjunction with a reflective imager, the color is modulated by turning on the semiconductor light source device having the required color, being either R, G or B.

In the case of a projector100that uses the transmissive imager illustrated inFIG. 1B, when a lamp is used as a light source, the illumination optics120includes optical means for splitting the white-light generated by the lamp into R, G and B light patches that illuminate the backsides of three HTPS imager devices and a dichroic prisms assembly is added to combine the modulated R, G and B light and couple it on the projection optics140.

The projection optics140is optically coupled to the surface of the imager110and the drive electronics150is electrically coupled to the imager110. The optical engine generates the image to be projected by modulating the intensity of the light generated by the light source130, using imager110, with the pixel grayscale input provided as image data to the drive electronics150. When a reflective imager (FIG. 1A) such as micro-mirror or LCOS imager device is used, the drive electronics provides the pixel grayscale data to the imager110and synchronizes its operation either with the sequential order of the R, G and B segments of the color wheel, when a white light lamp is used as a light source, or with the sequential order in which the R, G or B semiconductor light source is turned on. When a transmissive imager such as the HTPS imager device is used, the drive electronics provides the pixel grayscale data to the imager110and synchronizes the operation of each of the R, G and B HTPS imager devices in order to modulate the desired color intensity for each pixel.

Typically the losses associated with the coupling of light onto the surface of imager110are significant because they include the intrinsic losses associated with the imager110itself, such as the device reflectivity or the transmissivity values, plus the losses associated with collecting the light from the light source130, collimating, filtering and relaying it to the surface of the imager110. Collectively these losses can add up to nearly 90%; meaning that almost 90% of the light generated by the light source130would be lost.

In addition, in the case of a reflective imager110such as micro-mirror or LCOS imager devices, the imager110being comprised of a spatial array of reflective pixels, sequentially modulates the respective colors of the light coupled onto its pixelated reflective surface by changing the reflective on/off state of each individual pixel during the time period when a specific color is illuminated. In effect, a typical prior art reflective imager can only modulate the intensity of the light coupled onto its pixelated reflective surface, a limitation which causes a great deal of inefficiency in utilizing the luminous flux generated by the light source130, introduces artifacts on the generated image, adds complexities and cost to the overall display system and introduces yet another source of inefficiency in utilizing the light generated by the light source130. Furthermore, both the reflective as well as the transmissive type imagers suffer from an effect known as “photonic leakage” which causes light to leak onto the off-state pixels, which significantly limits the contrast and black levels that can be achieved by these types of imagers.

As stated earlier, the objective of this invention is to overcome the drawbacks of prior art imagers by introducing an emissive imager device comprising an array of multicolor laser emitters that can be used as an image source in digital projection systems. Although semiconductor laser diodes have recently become an alternative light source130(Ref. [1]-[4]) for use in projectors100ofFIG. 1Ato illuminate reflective imagers110such as the micro-mirror imager device, the use of semiconductor laser diodes as a light source does not help in overcoming any of the drawbacks of prior art imagers discussed above. In addition numerous prior art exists that describes projection displays that uses a scanned laser light beam to generate a projection pixel (Ref. [5]-[6]).

Prior art Ref. [7] describes a laser image projector comprising a two dimensional array of individually addressable laser pixels, each being an organic vertical cavity laser pumped by an organic light emitting diode (OLED). The pixel brightness of the laser image projector described in prior art Ref. [7] would be a small fraction of that provided by the pumping light source, which, being an OLED based light source, would not likely to offer an ample amount of light, rendering the brightness generated by the laser projector of prior art Ref. [7] hardly sufficient to be of practical use in most projection display applications.

Although there exist numerous prior art references that describe laser arrays (Ref. [8]-[30]), no prior art was found that teaches the use of multicolor laser emitters as pixels in an imager device. As it will become apparent in the following detailed description, this invention relates a separately addressable array of multicolor laser pixels formed by optically and electrically separating a monolithic layered stack of laser emitting semiconductor structures. With regard to creating an optically and electrically separated (isolated) semiconductor laser emitter array, Ref. [10] teaches methods for forming a single wavelength laser semiconductor structure with isolation regions (i.e. physical barriers) between the light emitting regions formed by either removing material between the light emitting regions or by passivating the regions between the light emitters of the semiconductor structure. However, the methods described in Ref. [10] could only be used to create a one-dimensional linear array of separately addressable single wavelength laser emitters within the range of wavelength from 700 to 800 nm.

With regard to creating an array of separately addressable multicolor laser emitters, Ref [21] describes an edge emitting array of red and blue laser structures. Although Ref. [21] deals with multicolor laser structure, it is only related to a two-color one-dimensional linear array of edge emitting laser structures.

Although Ref. [22] describes a display system that uses an array of vertical cavity surface emitting laser (VCSEL) diodes, because of the inherent size of the VCSEL diodes described in Ref. [22], the approach described would tend to produce substantially large pixels size because of the inherent size of the multiple color of VCSEL diodes it uses which are arranged side-by-side in the same plane to form a pixel array, rendering it not usable as an imager device.

Given the aforementioned drawbacks of currently available imager devices, an imager that overcomes such weaknesses is certain to have a significant commercial value. It is therefore the objective of this invention to provide an emissive imager device comprising a monolithic semiconductor 2-dimensional array of multicolor laser emitters that can be used as an image source in digital projection systems. Additional objectives and advantages of this invention will become apparent from the following detailed description of a preferred embodiments thereof that proceeds with reference to the accompanying drawings.

REFERENCES

U.S. Patent Documents

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

References in the following detailed description of the present invention to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristics described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in this detailed description are not necessarily all referring to the same embodiment.

An emissive imager is described herein. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced with different specific details. In other instance, structures and devices are shown in block diagram form in order to avoid obscuring the invention.

The emissive multicolor digital image forming device described herein, referred to as “Quantum Photonic imager” (QPI), is a semiconductor device comprising a monolithic array of multicolor laser emitters. The Quantum Photonic imager of this invention is comprised of a plurality of emissive multicolor pixels whereby in one embodiment, each pixel comprises a stack of red (R), green (G) and blue (B) light emitting laser diodes. The multicolor laser light of each said pixel is emitted perpendicular to the surface of the Quantum Photonic imager device via a plurality of vertical waveguides that are optically coupled to the optical confinement region of each the R, G and B laser diodes comprising each pixel. The plurality of pixels that comprise the Quantum Photonic imager devices are optically and electrically separated by sidewalls of insulating semiconductor material embedded in which are the electrical interconnects (vias) that are used to route electrical current to the constituent laser diodes of each pixel. Each of the plurality of pixels that comprise the Quantum Photonic imager devices is electrically coupled to a control logic circuit that routes (enable) the electric current signal to each of its constituent red (R), green (G) and blue (B) laser diodes. The drive logic circuits associated with the plurality of pixels form a drive logic array that is bonded together with the stack of red (R), green (G) and blue (B) laser diodes to form a monolithic array of multicolor laser pixels and drive circuitry.

FIGS. 2A,2B and2C illustrate a preferred embodiment of the Quantum Photonic Imager device200of this invention.FIG. 2Aillustrates an isometric view of the Quantum Photonic imager device200, whileFIG. 2Billustrates and isometric view of one of its constituent pixels230andFIG. 2Cis a top view illustration that shows the array of pixels230comprising the Quantum Photonic imager device200and the digital control logic229positioned at the periphery of the pixel array.

As illustrated inFIG. 2A, the Quantum Photonic imager device200would be comprised of two semiconductor structures; namely the photonic semiconductor structure210and the digital semiconductor structure220. The semiconductor structures210and220are bonded together either through die-level bonding or wafer-level bonding to form the Quantum Photonic imager device200illustrated inFIG. 2A. Each of the two semiconductor structures comprising the Quantum Photonic imager device200is further comprised of multiple semiconductor layers. As illustrated inFIG. 2A, the digital semiconductor structure220of the Quantum Photonic imager device200would typically be larger in surface area than the photonic semiconductor structure210to allow for the placement of the digital control logic229and the bonding pads221, through which the power and image data signals are provided to the device, to be accessible at the topside of the device. The photonic semiconductor structure210is comprised of a plurality of emissive multicolor pixels and digital semiconductor structure220is comprised of the digital drive logic circuits that provide power and control signals to the photonic semiconductor structure210.

FIG. 2Bis a cutaway isometric illustration of the semiconductor structure of one of the pixels230comprising the Quantum Photonic imager device200of one embodiment of this invention. As illustrated inFIG. 2B, each of the pixels230would have a sidewall235that provides optical and electrical separation between adjacent pixels. As will be explained in more detail in subsequent paragraphs, the electrical interconnects required to supply power signals to the photonic semiconductor structure210portion of the pixels230would be embedded within the pixel sidewalls235.

As illustrated in the pixel isometric cutaway view ofFIG. 2B, the portion of the photonic semiconductor structure210within the interior of the pixels230would be comprised of the semiconductor substrate240, a red (R) laser diode multilayer231, a green (G) laser diode multilayer232and a blue (B) laser diode multilayer233stacked vertically. The laser light of each of the pixels230comprising the Quantum Photonic imager device200would be emitted in a direction that is perpendicular to the plane of the device top surface, hereinafter referred to as the vertical direction, through the plurality of vertical waveguides290, each of which is optically coupled to the optical resonator (or the optical confinement region) of each of the laser diodes231,232and233. The plurality of vertical waveguides290would form a laser emitter array that would define the laser light emission cross section (or optical characteristics) of each of the pixels230comprising the Quantum Photonic imager device200of this invention. The novel approach of this invention of vertically stacking the laser diodes231,232and233and optically coupling the vertical waveguides290to the optical resonator (or the optical confinement region) of each of the stacked laser diodes231,232and233would enable multicolor laser light generated by these laser diodes to be emitted through the array of vertical waveguides290, thus making the pixels230comprising the Quantum Photonic imager device200of this invention become emissive multicolor laser pixels.

FIG. 2Cis a top view illustration of the Quantum Photonic imager device200showing the top of the photonic semiconductor structure210comprising the 2-dimensional array of multicolor pixels230that forms the emissive surface of the device and the top of the digital semiconductor structure220extending beyond that of the photonic semiconductor structure210to allow for the area required for the device bonding pads221and the layout area for the device control logic229. The typical size of the pixels230of the preferred embodiment of the Quantum Photonic Imager200of this invention would be in the range of 10×10 micron, making the emissive surface of a Quantum Photonic imager device200that provides a VGA resolution (640×480 pixels) be 6.4×4.8 mm. The actual size of the photonic semiconductor structure210would extend beyond emissive surface area by few additional pixels on each side, making the typical size of the photonic semiconductor structure210be in the range of 6.6×5 mm and the digital semiconductor structure220would extend beyond that area to allow for the layout area of the control logic229and the device bonding pads221, making the typical dimensions of a Quantum Photonic imager device200that provides a VGA resolution be in the range 7.6×6 mm.

Having described the underlying architecture of the Quantum Photonic Imager devices200of this invention, the following paragraphs provide detailed description of its constituent parts and manufacturing methods thereof.

FIG. 3is a cross-sectional view illustration of the semiconductor multi structures that form the Quantum Photonic Imager Device200of this Invention. The same reference numbers are used for the same items, however the red, green and blue laser diodes semiconductor structures prior to the formation of the pixels230would be referred to as the multilayer laser diode structures250,260and270; respectively.

In accordance with the preferred embodiment of the fabrication method of the Quantum Photonic Imager device200of this invention, the multilayer laser diode structures250,260and270would be fabricated separately as semiconductor wafers using the appropriate semiconductor processes, then post-processed to create the wafer-size multilayer stack photonic semiconductor structure210that incorporates the metal and insulation layers as illustrated inFIG. 3. The wafer-size multilayer stack photonic semiconductor structure210would then be further post-processed to create the pixels' sidewalls235, which form the laser diodes231,232and233, and the pixels' vertical waveguide290as illustrated inFIG. 2B. Furthermore, the digital semiconductor structure220would also be fabricated separately as a semiconductor wafer using the appropriate semiconductor processes, then wafer-level or die-level bonded with the multilayer stack photonic semiconductor structure210to create the Quantum Photonic Imager device200illustrated inFIG. 2A. The following paragraphs describe the detailed design specifications of the multilayer laser diode structures250,260and270and the digital semiconductor structure220as well as the detailed design specifications of the wafers post-processing and fabrication flow required to create the Quantum Photonic Imager device200of this invention.

The illustration ofFIG. 3shows the Quantum Photonic Imager device200being comprised of the semiconductor structures210and220with each of these two semiconductor structures being further comprised of multiple semiconductor layers. As illustrated inFIG. 3, the photonic semiconductor structure210is comprised of a silicon (Si) substrate240and a stack of three multilayer laser diode structures250,260and270separated by layers241,251,261and271of dielectric insulator, such as silicon dioxide (SiO2), each preferably 150 to 200 nm-thick, which provide top and bottom electrical insulation of each between the three multilayer laser diode structures250,260and270.

Also incorporated within the photonic semiconductor structure210are the metal layers252and253, which constitute the p-contact and n-contact metal layers; respectively, of the red multilayer laser diode250, the metal layers262and263which constitute the p-contact and n-contact metal layers; respectively, of the green multilayer laser diode260and the metal layers272and273which constitute the p-contact and n-contact metal layers; respectively, of the blue multilayer laser diode270. Each of the metal layers252,253,262,263,272and273is preferably 150 to 200 nm-thick of semiconductor interconnect metallization layer having low electromigration and stress-migration characteristics such as gold-tin (Au—Sn) or gold-titanium (Au—Ti) multilayer metallization. The metallization layers252,253,262,263,272and273would also include a diffusion barrier that would prevent excessive diffusion of the metallization layers into the insulation layers241,252,261and271.

As illustrated inFIG. 3, the interfaces between the semiconductor structures210and220are the metal layer282, at the photonic semiconductor structure210side, and the metal layer222at the digital control structure220side. Both of the metal layers282and222would be etched to incorporate the electrical interconnect bonding pads between the two semiconductor structures210and220. The metal layer222would also incorporate the device bonding pads221.

The insulation layers241,251,261and271and metallization layers252,253,262,263,272and273would be deposited using typical semiconductor vapor deposition process such as chemical vapor deposition (CVD). The two layers241and252would be deposited directly on the Si substrate layer240, and the resultant multilayer stack240-241-252is then wafer-level bonded to the p-layer of the red laser diode structure250using either direct wafer bonding, diffusion bonding or anodic bonding techniques or the like.

The resultant semiconductor multilayer structure is then used as a substrate upon which the layers253,251, and262would be deposited using vapor deposition techniques such as CVD or the like and the resultant multilayer stack240-241-252-250-253-251-262is then wafer-level bonded to the p-layer of the green laser diode structures260using either direct wafer bonding, diffusion bonding or anodic bonding techniques or the like, and the substrate on which the green laser diode was formed is removed.

The resultant semiconductor multilayer structure is then used as a substrate upon which the layers263,261, and272would be deposited using vapor deposition techniques such as CVD or the like and the resultant multilayer stack240-241-252-250-253-251-262-260-263-261-272is then wafer-level bonded to the p-layer of the blue laser diode structures270using either direct wafer bonding, diffusion bonding anodic bonding techniques or the like, and the substrate on which the blue laser diode was formed is removed.

The resultant semiconductor multilayer structure is then used as a substrate upon which the layers273,271, and282would be deposited using vapor deposition techniques such as CVD or the like. The metal layer282is then etched to create the bonding pad pattern using semiconductor lithography process and the etched areas are refilled with insulator material, preferably SiO2, and the surface is then polished and cleaned. The resultant photonic semiconductor structure210is then wafer-level bonded to the corresponding bonding pad surface of the digital semiconductor structure220using flip-chip bonding techniques.

Each of the multilayer semiconductor structures250,260and270would be a multiple quantum well (MQW) double heterostructure semiconductor laser diode grown as separate wafers each on its own substrate using well-known epitaxial deposition process commonly referred to as metal-organic chemical vapor deposition (MOCVD). Other deposition processes such as liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), metal organic vapor phase epitaxy (MOVPE), hydride vapor phase epitaxy (HVPE), hydride metal organic vapor phase epitaxy (H-MOVPE) or other known crystal growth processes can also be used.

FIG. 4Aillustrates an exemplary embodiment of the multilayer cross section of the red laser diode structure250of the Quantum Photonic imager device200of this invention. The multilayer semiconductor structure ofFIG. 4Ais phosphide based with its parameters selected such that the laser light generated by the red laser diode structure250would have a dominant wavelength of 615-nm. As shown inFIG. 4A, a substrate removal etch-stop layer412of n-doped GaAs of thickness 100-nm is grown on a thick (approximately 2000 nm) GaAs substrate410which will be etched off after the red laser diode structure250is wafer-level bonded to the multilayer stack240-241-252as explained earlier. The n-doped GaAs etch-stop layer412would have either silicon (Si) or selenium (Se) doping of approximately 8×1018cm−3. A thick GaAs substrate is used to assure the growth of a high quality epi layer thereon.

Upon the substrate removal etch-stop layer412is deposited the cladding layer414of n-type of either Al0.5In0.5P or (Al0.7Ga0.3)0.5In0.5superlattice (SL) which would typically be 120-nm thick and have either Si or Se doping of 1×1018cm−3. Upon the cladding layer414is deposited a 100-nm thick n-type (Al0.55Ga0.45)0.5In0.5P waveguide layer416which would typically be either silicon (Si) or selenium (Se) doped to at least 1×1018cm−3. Upon the waveguide layer416is deposited the active region421of the red laser diode250comprised of multiple Ga0.6In0.4P quantum well layers420which are enclosed within the Al0.5In0.5P barrier layers418, typically either silicon (Si) or selenium (Se) doped at levels of least 0.01×1018cm−3and 0.1×1018cm−3, respectively. As shown inFIG. 4A, the thickness of the quantum well layers420and barrier layers418are selected to be 4.8-nm and 4-nm; respectively, however the thickness of these layers could be increased or decreased in order to fine tune the emission characteristics of the red laser diode250.

AlthoughFIG. 4Ashows the active region421of the red laser diode250being comprised of three quantum wells, the number of quantum wells used could be increased or decreased in order to fine tune the emission characteristics of the red laser diode250. Furthermore, the active region421of the red laser diode250could also be comprised of multiplicity of quantum wires or quantum dots instead of quantum wells.

Above the active region421is deposited a 140-nm thick p-type (Al0.55Ga0.45)0.5In0.5P waveguide layer422which would typically be magnesium (Mg) doped at a level of at least 1×1018cm−3. Upon waveguide layer422is deposited a 23-nm thick Al0.5In0.5P anti-tunneling layer424having a magnesium doping level of at least 1×1018cm−3. Upon anti-tunneling layer424is deposited an electron blocker layer426of thickness 25-nm which is comprised alternating layers of Ga0.5In0.5P quantum wells and Al0.5In0.5P barriers each being magnesium doped at a level of at least 1×1018cm−3. The electron blocker layer426is incorporated in order to reduce the electron leakage current, which would reduce the threshold current and the operating temperature of the red laser diode structure250.

Above the electron blocker layer426is deposited a 120-nm thick p-type of either Al0.5In0.5P or (Al0.7Ga0.3)0.5In0.5SL cladding layer428which would magnesium doped at a level of 0.5×1018cm−3. Upon the cladding layer428is deposited a 100-nm thick p-type GaAs contact layer429which would heavily magnesium doped at a level of at least 1×1018cm−3. As explained earlier, the contact layer429would be the interface layer for the wafer-level bonding of the red laser diode structure250and the multilayer stack240-241-252.

The multilayer416-421-422is known to a person skilled in the art as the optical resonator or optical confinement region of the red laser diode250within which the red laser light generated by the MQW active region421would be confined. As will be explained in the subsequent paragraphs, the light generated by the red laser diode250will be emitted vertically from the surface of the Quantum Photonic imager device200through vertical waveguides290that are optically coupled to the optical confinement multilayer416-421-422of the red laser diode250.

FIG. 4Billustrates an exemplary embodiment of the multilayer cross section of the green laser diode structure260of the Quantum Photonic imager device200of this invention. The multilayer semiconductor structure ofFIG. 4Bis nitride based with its parameters are selected such that the laser light generated by the green laser diode structure260would have a dominant wavelength of 520-nm. As shown inFIG. 4B, a substrate removal etch-stop layer432of n-doped In0.05Ga0.95N of thickness 100-nm and Si-doped at a level 6×1018cm−3is grown on a thick GaN substrate430which will be etched off after the green laser diode structure260is wafer-level bonded to the multilayer stack240-241-252-250-53-251-262as explained earlier. The n-doped In0.05Ga0.95N etch-stop layer432would have silicon (Si) doping of 6×1018cm−3. AlthoughFIG. 4Bshows the substrate430being GaN, InGaN material alloy could also be used for the substrate430.

Upon the substrate removal etch-stop layer432is deposited the cladding layer434of n-type of Al0.18Ga0.82N/GaN SL which would typically be 451-nm thick and have Si doping of 2×1018cm−3. Upon the cladding layer434is deposited a 98.5-nm thick n-type GaN waveguide layer436which would typically be Si-doped at a level of 6.5×1018cm−3. Upon the waveguide layer436is deposited the active region of the green laser diode260which is comprised of multiple In0.535Ga0.465N quantum well layers450each being Si-doped at a level of 0.05×1018cm−3and enclosed within the In0.04Ga0.96N barrier layers438each being Si-doped at a level of 6.5×1018cm−3. As shown inFIG. 4B, the thickness of the quantum well layers450and barrier layers438are selected to be 5.5-nm and 8.5-nm; respectively, however the thickness of these layers could be increased o decreased in order to fine tune the emission characteristics of the green laser diode260.

AlthoughFIG. 4Bshows the active region431of the green laser diode260being comprised of three quantum wells, the number of quantum wells used could be increased or decreased to in order to fine tune the emission characteristics of the green laser diode260. Furthermore, the active region431of the green laser diode260could also be comprised of multiplicity of quantum wires or quantum dots instead of quantum wells.

Above the active region431is deposited a 8.5-nm thick p-type GaN waveguide layer452which would typically be magnesium (Mg) doped at a level of 50×1018cm−3. Upon waveguide layer452is deposited a 20-nm thick Al0.2Ga0.8N electron blocker layer454having a magnesium (Mg) doping level of approximately 100×1018cm−3. The electron blocker layer454is incorporated in order to reduce the electron leakage current, which would reduce the threshold current and the operating temperature of the green laser diode structure260.

Above the electron blocker layer454is deposited a 90-nm thick p-type GaN waveguide layer456which would typically be magnesium (Mg) doped at a level of 75×1018cm−3. Upon the waveguide layer456is deposited a 451-nm thick p-type Al0.18Ga0.82N/GaN SL cladding layer458which would typically be magnesium doped at a level of 75×1018cm−3. Upon the cladding layer458is deposited a 100-nm thick p-type GaN contact layer459which is magnesium (Mg) doped at a level of 75×1018cm−3. As explained earlier, the contact layer459would be the interface layer for the wafer-level bonding of the green laser diode structure260and the multilayer stack240-241-252-253-251-262.

The multilayer436-431-452is known to a person skilled in the art as the optical resonator or optical confinement region of the green laser diode260within which the green laser light generated by the MQW active region431would be confined. As will be explained in the subsequent paragraphs, the light generated by the green laser diode260will be emitted vertically from the surface of the Quantum Photonic imager device200through vertical waveguides290that are optically coupled to the optical confinement multilayer436-431-452of the green laser diode260.

FIG. 4Cillustrates an exemplary embodiment of the multilayer cross section of the blue laser diode structure260of the Quantum Photonic imager device200of this invention. The multilayer semiconductor structure ofFIG. 4Cis nitride based with its parameters selected such that the laser light generated by the blue laser diode structure260would have a dominant wavelength of 460-nm. As shown inFIG. 4C, a substrate removal etch-stop layer462of n-doped In0.05Ga0.95N of thickness 100-nm Si doped at a level 6×1018cm−3is grown on a thick GaN substrate460which will be etched off after the blue laser diode structure270is wafer-level bonded to the multilayer stack240-241-252-250-53-251-262-260-263-261-272as explained earlier. The n-doped In0.05Ga0.95N etch-stop layer462would have silicon (Si) doping of 6×1018cm−3. AlthoughFIG. 4Cshows the substrate460being GaN, InGaN material alloy could also be used for the substrate460.

Upon the substrate removal etch-stop layer462is deposited the cladding layer464of n-type of Al0.18Ga0.82N/GaN SL which would typically be 451-nm thick and have Si doping of 2×1018cm−3. Upon the cladding layer464is deposited a 98.5-nm thick n-type GaN waveguide layer466which would typically be Si doped at a level of 6.5×1018cm−3. Upon the waveguide layer466is deposited the active region of the blue laser diode270which is comprised of multiple In0.41Ga0.59N quantum well layers470each being Si-doped at a level of 0.05×1018cm−3and enclosed within the In0.04Ga0.96N barrier layers468each being Si-doped at a level of 6.5×1018cm−3. As shown inFIG. 4C, the thickness of the quantum well layers470and barrier layers468are selected to be 5.5-nm and 8.5-nm; respectively, however the thickness of these layers could be increased or decreased in order to fine tune the emission characteristics of the blue laser diode270.

AlthoughFIG. 4Cshows the active region431of the green laser diode260being comprised of three quantum wells, the number of quantum wells used could be increased or decreased in order to fine tune the emission characteristics of the green laser diode260. Furthermore, the active region431of the blue laser diode260could also be comprised of multiplicity of quantum wires or quantum dots instead of quantum wells.

Above the active region431is deposited a 8.5-nm thick p-type GaN waveguide layer472which would typically be magnesium (Mg) doped at a level of 50×1018cm−3. Upon waveguide layer472is deposited a 20-nm thick Al0.2Ga0.8N electron blocker layer474having a magnesium (Mg) doping level of approximately 100×1018cm−3. The electron blocker layer474is incorporated in order to reduce the electron leakage current, which would reduce the threshold current and the operating temperature of the blue laser diode structure270.

Above the electron blocker layer474is deposited a 90-nm thick p-type GaN waveguide layer476which would typically be magnesium (Mg) doped at a level of 75×1018cm−3. Upon the waveguide layer476is deposited a 451-nm thick p-type Al0.18Ga0.82N/GaN SL cladding layer478which would typically be magnesium (Mg) doped at a level of 75×1018cm−3.

Upon the cladding layer478is deposited a 100-nm thick p-type GaN contact layer479which is magnesium doped at a level of 75×1018cm−3. As explained earlier, the contact layer479would be the layer for the wafer-level bonding of the blue laser diode structure270and the multilayer stack240-241-252-253-251-262-260-263-261-272.

The multilayer466-461-472is known to a person skilled in the art as the optical resonator or optical confinement region of the blue laser diode270within which the blue laser light generated by the MQW active region461would be confined. As will be explained in the subsequent paragraphs, the light generated by the blue laser diode270will be emitted vertically from the surface of the Quantum Photonic imager device200through vertical waveguides290that are optically coupled to the optical confinement multilayer466-461-472of the blue laser diode270.

An alternative exemplary embodiment of the multilayer red laser diode structure250of the Quantum Photonic imager device200that is nitride-based is illustrated inFIG. 4D. Being nitride-based, the alternative exemplary embodiment of the multilayer red laser diode structure250ofFIG. 4Dwould have comparable design prescription as the nitride-based green laser diode structure260ofFIG. 4Band the blue laser diode structure270ofFIG. 4C, with the exception that its layer parameters would be selected such that the generated laser light would have a dominant wavelength of 615-nm. The alternative nitride-based multilayer red laser diode structure250ofFIG. 4Dwould be enabled by the increase in the indium content of the multiple quantum wells419to 0.68. AlthoughFIG. 4Dshows its active region being comprised of three quantum wells, the number of quantum wells used could be increased or decreased in order to fine tune the emission characteristics of the red laser diode250. Furthermore, the active region of the alternative exemplary embodiment of the red laser diode structure250illustrated inFIG. 4Dcould also be comprised of multiplicity of quantum wires or quantum dots instead of quantum wells. AlthoughFIG. 4Dshows the substrate480being GaN, InGaN material alloy could also be used for the substrate480.

As will be subsequently explained, the color gamut defined by the three colors specified for the laser diodes250,260and270in the aforementioned exemplary embodiment of the Quantum Photonic Imager device200would achieve an extended gamut (Wide Gamut) relative to the defined standards of color image displays such HDTV and NTSC. Specifically, the three colors specified for the laser diodes250,260and270in the aforementioned exemplary embodiment of the Quantum Photonic Imager device200would achieve a color gamut that is nearly 200% of the color gamut defined by the NTSC standard.

The color gamut achieved by the Quantum Photonic Imager device200of this invention can be further extended to include more than 90% of the visible color gamut to achieve an Ultra-Wide Gamut capability by increasing the number of laser diodes incorporated within the photonic semiconductor structure210beyond the three colors specified for the laser diodes250,260and270in the aforementioned exemplary embodiment. Specifically the color gamut of the light emitted by the Quantum Photonic Imager device200could be extended further to achieve an Ultra-Wide Gamut when the number of stacked laser diodes comprising the Quantum Photonic Imager device200is increased to include yellow (572-nm) laser diode semiconductor structure positioned in between the red and the green laser diodes structure250and260and a cyan (488-nm) laser diode semiconductor structure positioned in between the green laser diode structure260and the blue laser diode structure270, thus making the Quantum Photonic Imager device200be comprised of a stack of five laser diode structures covering the wavelengths of red (615-nm), yellow (572-nm), green (520-nm), cyan (488-nm) and blue (460-nm). With this stack of five laser diode semiconductor structures210of the Quantum Photonic Imager device200of this invention would be able to generate an Ultra-Wide color gamut that covers more than 90% of the visible color gamut.

Although in the aforementioned exemplary embodiments of the photonic semiconductor structure210of the Quantum Photonic Imager device200, the wavelengths of the laser diode structures250,260, and270were selected to be 615-nm, 520-nm and 460-nm; respectively, a person skilled in the art would know how to follow the teachings of this invention using other values of wavelengths than those selected for the laser diode structures250,260, and270of the aforementioned exemplary embodiments. Furthermore, although in the aforementioned exemplary embodiments of the Quantum Photonic Imager device200, the photonic semiconductor structure210is comprised of the three laser diode structures250,260, and270, a person skilled in the art would know how to follow the teachings of this invention using more than three laser diode structures. Furthermore, although in the aforementioned exemplary embodiments of the Quantum Photonic Imager device200, the photonic semiconductor structure210is comprised of the three laser diode structures250,260, and270stacked in the order illustrated inFIG. 3, a person skilled in the art would know how to follow the teachings of this invention with the laser diode structures stacked in a different order.

—Laser Diodes Energy Bands

FIG. 5A,FIG. 5BandFIG. 5Cillustrate the energy bands of the aforementioned exemplary embodiments of the phosphide based red laser diode structure250and the nitride based green laser diode260and blue laser diode270; respectively. The energy bands shown inFIG. 5A,FIG. 5BandFIG. 5Cillustrate the thickness of each layer from left to right and the energy from bottom to top. The thickness and energy levels are meant to show qualitative values rather than a quantitative measure of the exact thicknesses and energy levels. Nevertheless, the reference numbers inFIG. 5A,FIG. 5BandFIG. 5Ccorrespond with the reference numbers of the layers inFIG. 4A,FIG. 4BandFIG. 4C; respectively. As these figures illustrate, the energy levels of the p-type and n-type cladding layers energetically confine the p-type and n-type waveguide layers as well as the multiple quantum well levels. Because the energy levels of the multiple quantum wells represent a local low energy level, as illustrated in figuresFIG. 5A,FIG. 5BandFIG. 5C, electrons will be confined within the quantum wells to be efficiently recombined with the corresponding holes to generate light.

In reference toFIG. 5A, the thickness of the anti-tunneling layer424is selected such that it is large enough to prevent electrons tunneling yet small enough to retain electron coherence within the superlattice structure of the electron blocker layer426. In order to lower the lasing threshold, the electron blocker layers426,454and474are used in the exemplary embodiments of the laser diode structure250,260, and270; respectively. As illustrated inFIG. 5A, the electron blocker426used in the red laser structure250is comprised of multiple quantum barriers (MQB) implemented in the p-doped region and having energy level alternating between that of the waveguide layer422and the cladding layer428. The inclusion of the MQB electron blocker426substantially improves the electron confinement due to the quantum interference of the electrons in the MQB, creating a large increase of the barrier height at the waveguide-cladding layers interface, which substantially suppresses the electron leakage current. As illustrated inFIG. 5BandFIG. 5C, the electron blocker used in the green laser structure260and the blue laser structure270is placed in between two segments of the p-type waveguide layers and has energy level that is substantially higher than both the waveguide layers as well as the cladding layers in order to substantially improve the electron confinement and subsequently suppresses the electron leakage current.

The plurality of pixels230that comprises the Quantum Photonic imager device200are optically and electrically separated by the pixel sidewalls235comprised of insulating semiconductor material and embedded within which are the vertical electrical interconnects (contact vias) that are used to route electrical current to the constituent laser diodes of each pixel.FIG. 6Ais a horizontal cross sectional view of one of the plurality multicolor pixels230comprising the Quantum Photonic Imager device200that illustrates the inner structure of the pixel sidewall235. As illustrated inFIG. 6A, the pixel sidewall235defines the boundaries of the multicolor pixel230and is comprised of the metal contact vias236embedded within a sidewall interior237of dielectric material such as SiO2.

FIG. 6Bis a vertical cross-sectional view of one of the pixel sidewalls235that illustrates the interface between the multilayer photonic structure210and the sidewall235. The pixel sidewalls235illustrated inFIG. 6AandFIG. 6Bwould be formed by etching an orthogonal square grid of 1-micron wide trenches into the multilayer photonic structure210. The trenches would be etched at a pitch that equals the pixel width, which in this exemplary embodiment of the Quantum Photonic Imager device200is selected to be 10-micron, and at a depth starting from the bonding pad layer282and ending at the SiO2insulation layer241. The etched trenches are then refilled with low dielectric constant (low-k) insulating material such as SiO2or silicon carbon-doped silicon oxide (SiOC) then re-etched to form 150-nm wide trenches for the contact vias236. The re-etched trenches for the contact vias236are then refilled using vapor deposition techniques, such as CVD or the like, with metal such as gold-tin (Au—Sn) or gold-titanium (Au—Ti) to achieve contact with the metallization layers252,253,262,263,272and273.

The trenches etched for the pixel sidewalls235may have parallel sides as illustrated inFIG. 6Bor the may be slightly sloped as dictated by the etching process used. Although any appropriate semiconductor etching technique may be used for etching the trenches for the sidewalls235and the contact via236, one exemplary etching technique is a dry etching technique, such as chlorine-based, chemically-assisted ion beam etching (Cl-based CAIBE). However, other etching techniques, such as reactive ion etching (RIE) or the like may be used.

The formation of the pixel sidewalls235as described above is performed in multiple intermediate stages during the formation of the multilayer photonic structure210.FIG. 6Cis a vertical cross-sectional view of the contact vias236embedded within the pixel sidewalls235. As illustrated inFIG. 6C, each of the contact vias236would be comprised of the six segments254and256for the red laser diode structure250p-contact and n-contact; respectively,264and266for the green laser diode structure260p-contact and n-contact; respectively, and274and276for the blue laser diode laser270p-contact and n-contact; respectively.

After the multilayer structure240-241-252-250is formed as explained earlier, the trench for the pixel sidewall235is double-etched into the multilayer structure from the side of the red laser diode multilayer250with the first and second stop-etch being below and above the metal layer252. The etched trench is then refilled with insulating material such as SiO2then retched with the stop-etch being the metal layer252and refilled with contact metal material to form the base segment of the contact via254as illustrated inFIG. 6C.

After the contact layer253and the insulation layer251are deposited, the trench for the pixel sidewall235is double-etched into the deposited layers with the first and second stop etch being below and above the metal layer253, refilled with insulating material, re-etched with the stop-etch being the metal layer253and refilled with contact metal material to form the base of the contact via256and to extend the contact via254as illustrated inFIG. 6C.

After the contact layer262is deposited and the green laser diode structure260is bonded with the multilayer structure, the trench for the pixel sidewall235is double-etched into the formed multilayer structure from the side of the green laser diode multilayer250with the first and second stop-etch being below and above the metal layer262. The etched trench is then refilled with insulating material such as SiO2then retched with the stop-etch being the metal layer262and refilled with contact metal material to form the base segment of the contact via264and extend the contact vias254and256as illustrated inFIG. 6C.

After the contact layer263and the insulation layer261are deposited, the trench for the pixel sidewall235is double-etched into the deposited layers with the first and second stop-etch being below and above the metal layer263, refilled with insulating material, re-etched with the stop-etch being the metal layer263and refilled with contact metal material to form the base segment of the contact via266and to extend the contact vias254,256and264as illustrated inFIG. 6C.

After the contact layer272is deposited and the blue laser diode structure270is bonded with the multilayer structure, the trench for the pixel sidewall235is double-etched into the formed multilayer structure from the side of the green laser diode multilayer250with the first and second stop-etch being below and above the metal layer272. The etched trench is then refilled with insulating material such as SiO2then retched with the stop-etch being the metal layer272and refilled with contact metal material to form the base segment of the contact via274and extend the contact vias254,256,264, and266as illustrated inFIG. 6C.

After the contact layer273and the insulation layer271are deposited, the trench for the pixel sidewall235is double-etched into the deposited layers with the first and second stop-etch being below and above the metal layer273, refilled with insulating material, re-etched with the stop-etch being the metal layer263and refilled with contact metal material to form the base segment of the contact via276and to extend the contact vias254,256,264,266and274as illustrated inFIG. 6C.

After the pixel sidewalls235are formed, the metal layer282would be deposited then etched to create separation trenches between metal contacts established with contact vias254,256,264,266,274and276and the etched trenches are then refilled with insulating material such as SiO2then polished to create the pixel contact pad700which is illustrated inFIG. 7. The pixel contact pad700would form the contact interface between the photonic semiconductor structure210and the digital semiconductor structure220.

After the formation of the pixel sidewalls235as explained above, the photonic semiconductor structure210would be partitioned by the formed sidewalls235into electrically and optically separated square regions that define the individual pixels230of the photonic semiconductor structure. The formed photonic semiconductor structure of each of the pixels230would then be comprised of a portion of the laser diode semiconductor structures250,260and270and will be designated231,232and233; respectively.

In addition to electrically and optically separating the multicolor pixels230of the Quantum Photonic Imager device200, the pixel sidewalls235, being comprised of a dielectric material such as SiO2with the metal vias236illustrated inFIG. 6Cembedded within its interior, would also form optical barriers which would optically seal the vertical edges of each of the portions of the optical confinement regions of the laser diode structure250,260and270comprising each multicolor pixel230. In other words, the insulation and metal contact layers in between the laser diode structures250,260and270together with the insulation and contact vias within the pixels sidewalls235would form an array of vertically stacked multicolor laser diode resonators that are optically and electrically separated in the horizontal as well as the vertical planes. Such an electrical and optical separation would minimize any possible electrical or optical crosstalk between the pixels230and allows each pixel within the array as well as each laser diode within each pixel to be separately addressable. The laser light output from each of the pixels230would be emitted vertically through the array of the vertical waveguides290which are optically coupled to the optical confinement regions of each of the vertically stacked laser diodes231,232, and233that form each of the pixels230.

FIG. 8AandFIG. 8Billustrate vertical and horizontal cross-sectional views; respectively, of one of the vertical waveguides290comprising the array of vertical waveguides of one of the pixels230of the Quantum Photonic Imager device200of this invention. As illustrated inFIG. 8AandFIG. 8B, each of the vertical waveguides290would be optically coupled along its vertical height with optical confinement regions of the three vertically stacked laser diodes231,232, and233comprising the pixel230. As illustrated inFIG. 8AandFIG. 8B, each of the vertical waveguides290would be comprised of a waveguide core291which would be enclosed within a multilayer cladding292. The array of pixel's waveguides290would typically be etched through the Si-substrate240side of the photonic multilayer structure210, their interior would then be coated with the multilayer cladding292and the waveguides would then be refilled with the dielectric material to form the vertical waveguide core291. Although any appropriate semiconductor etching technique may be used for etching the vertical waveguides290, one exemplary etching technique is a dry etching technique, such as chlorine-based, chemically-assisted ion beam etching (Cl-based CAIBE). However, other etching techniques, such as reactive ion etching (RIE) or the like may be used. Although any appropriate semiconductor coating technique may be used for forming the core291and the multilayer cladding292of the vertical waveguides290, one exemplary layer deposition technique is plasma-assisted chemical vapor deposition (PE-CVD). The trenches etched for the vertical waveguides290preferably will have slightly sloped sides as illustrated inFIG. 8Ain accordance with the increasing wavelength of the respective laser diodes in the laser diode stack.

As illustrated inFIG. 8AandFIG. 8B, each of the vertical waveguides290would typically have a circular cross-section and its vertical height would extend the thickness of the Si-substrate240plus the combined thicknesses of the three vertically stacked laser diodes231,232, and233comprising the pixel230. Preferably the diameter (index guiding diameter) of the pixel's vertical waveguides290at the center of the coupling region with each of the laser diodes231,232, and233would equal to the wavelength of the respective laser diode.

First Embodiment of the Vertical Waveguides

In one embodiment of the Quantum Photonic Imager device200of this invention the cores291of the pixel's vertical waveguides290would be “evanescence field coupled” to the optical confinement regions of stacked laser diodes231,232, and233that form a single pixel230. In this embodiment the vertical waveguide cladding292would be comprised of an outer layer293of 50-nm to 100-nm thick of insulating material, such as SiO2, and an inner layer294of highly reflective metal such as aluminum (Al), silver (Ag) or gold (Au). The core291of the vertical waveguides290could either be air-filled or filled with a dielectric material such as SiO2, silicon nitride (Si3N4) or tantalum pentoxide (TaO5). Through the evanescence field coupling of this embodiment, a fraction of the laser light confined within the optical confinement region of each of the laser diodes231,232, and233would be coupled into the dielectric core291of the vertical waveguides290where it would be guided vertically through reflections on the highly reflective metallic inner cladding layer294of the waveguide cladding292.

In this embodiment of the Quantum Photonic Imager device200of this invention the coupling between the optical confinement regions of stacked laser diodes231,232, and233comprising each of the pixels230and its constituent vertical waveguide290would occur due to photon tunneling across the metallic inner cladding layer294. Such photon tunneling would occur when the thickness of the reflective metallic inner cladding layer294of the waveguide cladding292is selected to be sufficiently smaller than the penetration depth of evanescence field into the reflective metallic inner cladding layer294of the waveguide cladding292. In other words, the energy associated with the light confined within the optical confinement regions of stacked laser diodes231,232, and233would be transmitted into metallic inner cladding layer294a short distance before it returned into the optical confinement regions of stacked laser diodes231,232, and233and when the thickness of the reflective metallic layer294is sufficiently small, a portion of this energy would be coupled into the vertical waveguide core291and would be guided vertically through reflections on the highly reflective metallic inner cladding layer294of the waveguide cladding292and emitted perpendicular to the surface of the Quantum Photonic Imager device200.

The evanescence field transmitted from the optical confinement regions of stacked laser diodes231,232, and233into the reflective metallic layer294would decay exponentially and would have mean penetration depth “d” that is given by;
d=λ/2π√{square root over (n02sin2θi−n12)}  (1)
Where λ is the wavelength of the coupled light, n0and n1are the refractive index of the outer cladding layer293and the inner cladding layer294; respectively, and θiis the light angle of incidence from optical confinement regions of the laser diodes231,232and233onto the inner cladding layer294.

As indicated by equation (1), for a given n0, n1and θithe evanescence field penetration depth decreases with the decrease in the light wavelength λ. In order to use one thickness value for the inner cladding layer294that would effectively couple the three different wavelengths generated by the laser diodes231,232, and233, the thickness of the inner cladding layer294would be selected using Equation (1) with the value of λ being the wavelength associated with shortest wavelength generated by stacked laser diodes231,232, and233, being in the case of the aforementioned embodiment the wavelength associated with the blue laser diode233. When the thickness of the inner cladding layer294is selected based on this criterion, the light generated by the stacked laser diodes231,232, and233would be coupled into the vertical waveguide290would be 0.492, 0.416 and 0.368; respectively, of the intensity of the light reflected by the interface between optical confinement region of stacked laser diodes231,232, and233and the vertical waveguide290. When the thickness of inner cladding layer294is increased, the amount of light coupled into the vertical waveguide290will decrease proportionally. The reflectivity of the inner cladding layer294toward the optical confinement regions of the laser diodes231,232, and233and toward the vertical waveguide core291would be given; respectively, by:
R01=└(n1−n0)2+k12┘/└(n1−n0)2+k12┘  (2.a)
R12=└(n2−n1)2+k12┘/└(n2−n1)2+k12┘  (2.b)
Where n2is the refractive index of the vertical waveguide core291and k1is the absorption coefficient of the inner cladding layer294.

In the above exemplary embodiment of the evanescence field coupled vertical waveguides290of this invention in which SiO2is used as an outer cladding layer293and Si3N4is used as the waveguide core291material, a 50-nm thick silver (Ag) inner cladding294would couple approximately 36% of the laser light incident on the interface between the optical confinement regions of the laser diodes231,232, and233and the vertical waveguide290while achieving approximately 62% reflectivity within the interior of the vertical waveguides290. It should be noted that the part of the light which is not coupled into the vertical waveguides290would either be absorbed by inner cladding294(approximately 0.025) or would be recycled back into the optical confinement regions of the laser diodes231,232, and233where it would be amplified by the active regions of laser diodes231,232, and233and then re-coupled into the vertical waveguides290.

Second Embodiment of the Vertical Waveguides

In another embodiment of the Quantum Photonic Imager device200of this invention the cores291of the pixel's vertical waveguides290would be coupled to the optical confinement regions of stacked laser diodes231,232, and233that form a single pixel230through the use of anisotropic multilayer thin cladding. What is meant by “anisotropic” in this context is that the reflectance/transmittance characteristics would be asymmetric at either side of the interface between the vertical waveguide290and the optical confinement regions of the stacked laser diodes231,232, and233. The simplest realization of this embodiment would be to use a single thin cladding layer293having a refractive index value between that of the waveguide core291and the optical confinement regions of laser diodes231,232, and233and having the waveguide core291preferably filled with a dielectric material preferably having a refractive index that is at least equal to that of the optical confinement regions of the stacked laser diodes231,232, and233.

The reflectance and transmittance characteristics of thin dielectric multilayer coatings are described in detail in Ref. [39]. At a normal angle of incidence, the reflectivity at the interface between the optical confinement regions of laser diodes231,232, and233and the cladding layer293would be given by:
R=[(n12−n0n1)/(n12+n0n1)]2(3)
Where n0, n1and n2are the refractive index of the optical confinement regions of stacked laser diodes231,232, and233, of the cladding layer293and the waveguide core291; respectively. As the angle of incidence at the interface between the optical confinement regions of laser diodes231,232, and233and the cladding layer293increases, the reflectivity increases until all the light is totally reflected when the critical angle is reached. Since, the critical angle depends on the ratio of the refractive index across the interface, when this ratio is selected such that the critical angle of the interface between the optical confinement regions of laser diodes231,232, and233and the cladding layer293is larger than the critical angle between the waveguide core291and the cladding layer293, a portion of the light would be coupled into the waveguide core291and would be index guided through total internal reflection (TIR) by the pixel's vertical waveguides290to be emitted perpendicular to the surface of the Quantum Photonic Imager device200.

In the above exemplary embodiment of coupling of the vertical waveguides290through the use of multilayer thin cladding in which an approximately 100-nm thick of SiO2is used as a cladding layer293and titanium dioxide (TiO2) is used as the waveguide core291material, approximately 8.26% of the laser light incident on the interface between the optical confinement regions of the laser diodes231,232, and233and the vertical waveguide290would be coupled into the waveguide core291and index guided through total internal reflection by the pixel's vertical waveguides290to be emitted perpendicular to the surface of the Quantum Photonic Imager device200.

In comparison to the evanescence field coupling of the preceding embodiment, coupling of vertical waveguides290through the use of multilayer thin cladding would couple a lesser amount of the light from the optical confinement regions of stacked laser diodes231,232, and233into the waveguide core291, but the coupled light would not experience any losses as it traverses the length of the vertical waveguide290because the light is TIR-guided, hence approximately the same amount of the light would be outputted through the vertical waveguide290perpendicular to the surface of the Quantum Photonic Imager device200. It should be noted that the part of the light which is not coupled into the vertical waveguides290by inner cladding293(which in the case of this example would be 91.74%) would be recycled back into the optical confinement regions of the laser diodes231,232, and233where it would be amplified by the active regions of laser diodes231,232, and233and then re-coupled into the vertical waveguides290.

Although in the above exemplary embodiment of coupling of the vertical waveguides290through the use of multilayer thin cladding only a single layer was exemplified, multiple thin cladding layers could be used to alter the ratio of the light intensity coupled into the vertical waveguide290to that recycled back in the optical confinement regions of the laser diodes231,232, and233. For example when two thin cladding layers are used with the outer cladding being 150-nm thick Si3N4and the inner cladding being 100-nm thick SiO2in conjunction a TiO2waveguide core291, approximately 7.9% of the laser light incident on the interface between the optical confinement regions of the laser diodes231,232, and233and the vertical waveguide290would be coupled into the waveguide core291and TIR-guided by the pixel's vertical waveguides290to be emitted perpendicular to the surface of the Quantum Photonic Imager device200. The selection of the number of thin cladding layers used, their refractive index and thickness are design parameters that could be utilized to fine tune the coupling characteristics of the pixel's vertical waveguides290, and subsequently the overall performance characteristics the Quantum Photonic Imager device200.

Third Embodiment of the Vertical Waveguides290

In another embodiment of the Quantum Photonic Imager device200of this invention the core291of the pixel's vertical waveguides290would be coupled to the optical confinement regions of stacked laser diodes231,232, and233that form a single pixel230through the use of nonlinear optical (NLO) cladding. The primary advantage of this embodiment is that it would enable the Quantum Photonic Imager device200of this invention to operate as a mode-locked laser emissive device (mode-locking enables laser devices to emit ultra-short pluses of light). As a consequence of the mode-locked operation the Quantum Photonic Imager device200enabled by this embodiment, the Quantum Photonic Imager device200would achieve improved power consumption efficiency and a higher peak-to-average emitted light intensity. The mode-locked operation of this embodiment would be incorporated within the cladding292of the pixel's vertical waveguides290in conjunction with the vertical waveguide coupling method of the preceding embodiment.

This embodiment would be realized by adding a thin outer cladding layer295, herein after will be referred to as the gate cladding layer, between the optical confinement regions of stacked laser diodes231,232, and233and the outer cladding layer293as illustrated inFIG. 8B. The gate cladding layer295would be a thin layer of an NLO material such as single crystal poly PTS polydiacetylene (PTS-PDA) or polydithieno thiophene (PDTT) or the like. The refractive index n of such NLO materials is not a constant, independent of the incident light, but rather its refractive index changes with increasing the intensity I of the incident light. For such NLO materials, the refractive index n obeys the following relationship to the incident light intensity:
n=n0+χ(3)I(4)

In Equation (4) χ(3)is the third order nonlinear susceptibility of the NLO material and n0is the linear refractive index value that the NLO material exhibits for low values of the incident light intensity I. In this embodiment the linear refractive index n0and thickness of the NLO material comprising the gate cladding layer295are selected such that at low incident light intensity I, substantially all of the light incident on the multilayer cladding292from the optical confinement regions of stacked laser diodes231,232, and233would be reflected back and recycled into the optical confinement regions of the laser diodes231,232, and233where it would be amplified by the active regions of laser diodes231,232, and233.

As the light intensity within the optical confinement regions of the laser diodes231,232, and233increases due to the integration light flux, the refractive index n of the gate cladding layer295would change in accordance with Equation (4), causing the ratio of the light intensity that is recycled back into the optical confinement regions of the laser diodes231,232, and233to that coupled into the vertical waveguide290to decrease, thus causing a portion of the light flux integrated within the optical confinement regions of the laser diodes231,232, and233to be coupled into the vertical waveguide290and emitted perpendicular to the surface of the Quantum Photonic Imager device200.

As the light is coupled into the waveguide290, the integrated light flux within the optical confinement regions of the laser diodes231,232, and233would decrease, causing the intensity I of the light incident on the gate cladding layer295to decrease, which in turn would cause the refractive index n to change in accordance with Equation (4) causing the ratio of the light intensity that is recycled back into the optical confinement regions of the laser diodes231,232, and233to that that is coupled into the vertical waveguide290to increase, thus causing the cycle of light flux integration within the optical confinement regions of the laser diodes231,232, and233to be repeated.

In effect the use of the multilayer cladding that incorporates an NLO of this embodiment would cause the optical confinement regions of the pixel's laser diodes231,232, and233to operate as photonic capacitors which would periodically integrate the light flux generated by the pixel's laser diodes231,232, and233between periods during which the integrated light flux is coupled into the vertical waveguide290and emitted at the surface of the pixel230of the Quantum Photonic imager device200.

When NLO gate cladding layer295is used in conjunction with the multilayer thin cladding of the vertical waveguide290coupling examples of the preceding embodiment, the coupling performance would be comparable except that the light coupled into the vertical waveguide290and emitted at the surface of the pixel230would occur as a train of pluses. When an NLO gate cladding layer295of PTS-PDA having a thickness of approximately 100-nm is used in conjunction with an approximately 100-nm thick of SiO2inner cladding293and titanium dioxide (TiO2) is used as the waveguide core291material, the light pulses emitted from the surface of the pixel230would typically have a duration in the range of approximately 20-ps to 30-ps with an inter-pulse period in the range of approximately 50-ps to 100-ps. The selection of the number of thin cladding layers used in conjunction with NLO gate cladding layer295, their refractive index and thicknesses are design parameters that could be utilized to fine tune the coupling characteristics of the pixel's vertical waveguides290as well as the pulsing characteristics of the multicolor laser light emitted from the pixel230and subsequently the overall performance characteristics the Quantum Photonic Imager device200.

Fourth Embodiment of the Vertical Waveguides290

A fourth embodiment of vertical waveguides290may be seen inFIG. 2D. In this embodiment, waveguides terminate at the end of the optical confinement region of each laser diode, so that the waveguides terminating at the laser diode positioned at the top of the stack would couple light only from that laser diode and the waveguides terminating at the second from the top laser diode in the stack would couple light from first and second laser diodes and the waveguides terminating at the third laser diode from the top of the stack would couple light from the first, second and third laser diodes in the stack. Preferably these waveguides would be straight, not tapered. These waveguides may also be air filled or filled with a suitable dielectric, such as SiO2. Using these differing height waveguides the amount of light coupled from the first laser diode in the stack would be higher than that coupled from the second laser diode in the stack and the amount of light coupled from the second laser diode in the stack would be higher than that coupled from the third laser diode in the stack. Since a satisfactory color gamut would include more green than red, and more red than blue, one might place the green diode on top, the red in the middle and the blue on the bottom of the stack.

As explained in the preceding discussion, each of the pixels230comprising the Quantum Photonic Imager device200would comprise a plurality of vertical waveguides290through which the laser light generated by the pixel's laser diodes231,232, and233would be emitted in a direction that is perpendicular to the surface of the Quantum Photonic Imager device200. The plurality of pixel's vertical waveguides290would form an array of emitters through which the light generated the pixel's laser diodes231,232, and233would be emitted. Given the vertical waveguides290light coupling methods of the preceding first three embodiments, the light emitted from each of the pixel's vertical waveguides290would have a Gaussian cross-section having an angular width of approximately ±20 degrees at half its maximum intensity. In the preferred embodiment of the Quantum Photonic Imager device200, the plurality of the pixel's vertical waveguides290would be arranged in a number and a pattern that is selected to reduce the maximum divergence angle (collimation angle) of the light emitted from surface of the pixel230, to provide a uniform brightness across the area of the pixel, and to maximize pixel brightness.

In using well known theories of phased emitter arrays Ref. [41], the angular intensity of the light emitted by the pixels230within the meridian plane comprising N of the pixel's vertical waveguides290would be given by;
I(θ)=E(θ){J1[aX(θ)]/aX(θ)}2{ Sin [NdX(θ)]/Sin [dX(θ)]}2(5.a)
Where;
X(θ)=(π Sin θ)/λ  (5.b)

J1(.) the Bessel function, λ is the wavelength of the light emitted by the pixel's vertical waveguides290, a is the diameter of the vertical waveguides290, d is the center-to-center distance between the pixel's vertical waveguides290and E(θ) is the intensity profile of the light emitted from each the pixel's vertical waveguides290, which as stated earlier would typically be a Gaussian profile having an angular width of approximately ±20 degrees at half its maximum intensity. Preferably the parameter a, the diameter (index guiding diameter) of the pixel's vertical waveguides290at the center of the coupling region with each of the laser diodes231,232, and233would equal to the wavelength of the respective laser diode. The typical value of the parameter d, the center-to-center distance between the pixel's vertical waveguides290, would be at least 1.2a and its specific value would be selected to fine tune emission characteristics of the pixel230.

FIG. 9Aillustrates the angular intensity of the light emitted by 10×10 micron pixels230comprising an array of 9×9 uniformly spaced vertical waveguides290, having a diameter a as specified above and center-to-center d=2a, within the meridian plane containing the diagonal of the pixel at the multiple values of wavelength emitted by the pixels230. Specifically, inFIG. 9Athe profiles910,920and930illustrate the angular intensity of the light emitted by the pixels230at the red wavelength (615-nm), the green wavelength (520-nm), and the blue wavelength (460-nm). As illustrated inFIG. 9A, the multicolor laser light emitted by the pixel230, and subsequently the Quantum Photonic image200, would have a tightly collimated emission pattern with collimation angle well within ±5°, thus making the Quantum Photonic Imager device200to have an optical f/# of approximately 4.8.

The pattern of the vertical waveguides290within the pixel230surface could be tailored to achieve the required emission characteristics in terms of the optical f/# for the Quantum Photonic Imager device200. The important design criterion in creating the pattern of the vertical waveguides290is to generate a uniform emission at the required optical f/# while retaining sufficient area for the pixel's light generating laser diodes231,232, and233after the array of vertical waveguides290are etched.FIG. 9Billustrates several possible patterns of the vertical waveguides290within the pixel230surface that could be used in conjunction with the Quantum Photonic Imager device200of this invention. Based on the teachings of this invention, a person skilled in the art would know how to select the pattern of the vertical waveguides290within the pixel230surface that would generate the light emission optical f/# that is best suited for the intended application of the Quantum Photonic Imager device200of this invention.

FIG. 10Aillustrates a vertical cross-section of the digital semiconductor structure220of the Quantum Photonic Imager device200. The digital semiconductor structure220would be fabricated with conventional CMOS digital semiconductor techniques, and as illustrated inFIG. 10A, would be comprised of the multiple metal layers222,223,224and225, separated by thin layers of insulating semiconductor material such as SiO2, and digital control logic226deposited using conventional CMOS digital semiconductor techniques on the Si-substrate227.

As illustrated inFIG. 10B, the metal layer222would incorporate a plurality of pixel's contact pad patterns whereby each contact pad pattern would be substantially identical to that of the pixel contact pad pattern of the photonic semiconductor structure210illustrated inFIG. 7. The plurality of pixel contact pad patterns of the metal layer222would constitute the bonding interface between the photonic semiconductor structure210and the digital semiconductor structure220as explained earlier. The metal layer222would also incorporate at its periphery the device contact bonding pads221of the entire Quantum Photonic Imager device200as illustrated inFIG. 2C.

FIG. 10Cillustrates the layout of the metal layer223which incorporate separate power and ground metal rails310,315and320designated for distributing power and ground to the pixel's red, green and blue laser diodes231,232, and233; respectively, and the metal rails325which are designated for routing power and ground to the digital logic portion of the digital semiconductor structure220.FIG. 10Dillustrates the layout of the metal layer224which incorporates separate metal traces designated for distributing data410, update415and clear420signals to the digital control logic semiconductor structure226section designated for controlling the on-off states of the pixels' red, green and blue laser diodes231,232, and233, respectively.FIG. 10Eillustrates the layout of the metal layer225which incorporates separate metal traces designated for distributing the load510and enable520signals to the digital control logic semiconductor structure226section designated for controlling the on-off states of the pixel's red, green and blue laser diodes231,232, and233, respectively.

The digital control logic semiconductor structure226would be comprised of the pixels' digital logic section228, which is positioned directly under the photonic semiconductor structure210(FIG. 2B), and the control logic region229which is positioned at the periphery of the digital logic region228as illustrated inFIG. 2C.FIG. 11Aillustrates an exemplary embodiment of the control logic section229of the digital control logic semiconductor structure226, which is designed to accept red, green and blue PWM serial bit stream input data and clock signals425,426, and427, respectively, which are generated external to the Quantum Photonic Imager device200, plus the control clock signals428and429, and covert the accepted data and clock signals into the control and data signals410,415,420,510and520which are routed to the digital logic section228via the interconnect metal layers224and225.

The digital logic section228of the digital control logic semiconductor structure226would be comprised of two dimensional arrays of pixels logic cells300whereby each such logic cell would be positioned directly under one of the pixels230comprising the Quantum Photonic Imager device200.FIG. 11Billustrates an exemplary embodiment of the digital logic cell300comprising the digital logic section228of the digital control logic semiconductor structure226. As illustrated inFIG. 11B, the pixel logic cell300associated with each of the pixels comprising the Quantum Photonic Imager device200would be comprised of the digital logic circuits810,815and820corresponding with the red, green and blue pixel's laser diodes231,232, and233, respectively. As illustrated inFIG. 11B, the digital logic circuits810,815and820would accept the control and data signals410,415,420,510and520and based on the accepted data and control signals would enable connectivity of the power and ground signals310,315and320to the red, green and blue pixel's laser diodes231,232, and233, respectively.

The digital semiconductor structure220would be fabricated as a monolithic CMOS wafer that would incorporate a multiplicity of digital semiconductor structures220(FIG. 2A). As explained earlier, the digital semiconductor structure220would be bonded with the photonic semiconductor structure220using wafer-level direct bonding techniques or the like to form an integrated multi wafer structure which would then be etched at the periphery of each single Quantum Photonic Imager device200die area in order to expose the device contact bonding pads221, then would be cut into individual Quantum Photonic Imager device200dies illustrated inFIG. 2AandFIG. 2C. Alternatively, the digital semiconductor210wafer would be cut into dies and separately the photonic semiconductor structure210wafer would also be cut into dies, each having an area that contains the required number of pixel's laser diodes231,232, and233, and then each the photonic semiconductor structure210die would be die-level bonded using flip-chip techniques or the like to the digital semiconductor210die to form a single Quantum Photonic Imager device200illustrated inFIG. 2AandFIG. 2C.

FIG. 12is a flow chart that illustrates the semiconductor process flow that would be used to fabricate the Quantum Photonic Imager device200in accordance with the exemplary embodiment described in the preceding paragraphs. As illustrated inFIG. 12, the process starts with step S02and continues to step S30, during which various wafers are bonded, and insulation and metal layers are deposited, interconnect vias, sidewalls and vertical waveguides are formed. It should be noted that the semiconductor fabrication flow of the laser diode multilayer semiconductor structures250,260and270as well as the digital semiconductor structure220would be performed separately and external to the fabrication process flow illustrated inFIG. 12, which is meant to illustrate an exemplary embodiment of the semiconductor process flow of bonding these wafers and forming the pixel structures230and interconnects.

In step S02the SiO2insulation layer241would be deposited on the base Si-substrate240wafer. In step S04the p-contact metal layer would be deposited and in step S06the formed stack would be bonded with laser diode multilayer semiconductor wafer and the laser diode wafer is etched down to the stop-etch layer. In step S08the pixel sidewalls trenches are double etched first down to the insulation layer preceding the metal layers deposited in step S04then down to the metal layer deposited in step S04and the etched trenches are then refilled with SiO2. In step S10the trenches for the pixels vertical contact vias are etched down to the metal layer deposited in step S04then a thin insulation layer is deposited and etched to expose the deposited vias. In step S12the n-contact metal layer would be deposited then etched to extend the height of the pixels' sidewall trenches. In step S14an insulation layer of SiO2is deposited then the process flow of steps S04through S14is repeated for each of the laser diode multilayer semiconductor wafers that would be incorporated into the Quantum Photonic Imager device200.

In step S16the metal layer required for forming the bonding contact pad700is deposited then etched to form the contact pad pattern illustrated inFIG. 7. In step S20the vertical waveguides290are etched through the Si-substrate side of the formed multilayer structure to form the pixels'230waveguide pattern such as those illustrated inFIG. 9B. In step S22the waveguide cladding layers292are deposited and then the waveguide cavities are refilled with the waveguide core291material in step S24. In step S26the Si-substrate side of the formed multi-layer laser diode structure is polished to optical quality and coated as required to form the emissive surface of the Quantum Photonic Imager device200. Steps S02through S28would result in a wafer-size photonic semiconductor structure210which would be wafer-level pad-side bonded with the digital semiconductor structure220wafer in step S28.

In step S30the resultant multi-wafer stack is etched to expose the contact pads221of the individual dies Quantum Photonic Imager device200and the multi-wafer stack is cut into individual dies of the Quantum Photonic Imager device200.

An alternative approach to the process of step S30would be to cut the photonic semiconductor structure210formed by the process steps S02through S26into the die size required for the Quantum Photonic imager device200and separately cut the digital semiconductor structure220wafer into dies then pad-side bond the two dies using flip-chip technique to form the individual dies of the Quantum Photonic Imager device200.

The Quantum Photonic Imager device200would typically be used as a digital image source in digital image projectors used in front or rear projection display systems.FIG. 13illustrates an exemplary embodiment of a typical digital image projector800that incorporates the Quantum Photonic Imager device200of this invention as a digital image source. The Quantum Photonic Imager device200would be integrated on a printed circuit board together with a companion digital device850(which will be referred to as the image data processor and will be functionally described in subsequent paragraphs) that would be used convert the digital image input into the PWM formatted input to the Quantum Photonic Imager device200. As illustrated inFIG. 13, the emissive optical aperture of the Quantum Photonic Imager device200would be coupled with a projection optics lens group810which would magnify the image generated by the Quantum Photonic Imager device200to the required projection image size.

As explained earlier, the light emitted from Quantum Photonic Imager device200would typically be contained within an optical f/# of approximately 4.8, which makes it possible to use few lenses (typically 2 or 3 lenses) of moderate complexity to achieve source image magnification in the range between 20 to 50. Typical digital projectors that use existing digital imagers such as micro-mirror, LCOS or HTPS imager devices having an optical f/# of approximately 2.4, would typically requires as many as 8 lenses to achieve a comparable level of source image magnification. Furthermore, typical digital projectors that use passive (meaning reflective or transmissive type) digital imagers such as micro-mirror, LCOS or HTPS imager devices would require a complex optical assembly to illuminate the imager. In comparison, since the Quantum Photonic Imager device200is an emissive imager, the digital image projector800which uses the Quantum Photonic Imager device200would not require any complex optical illumination assembly. The reduced number of lenses required for magnification plus the elimination of the illumination optics would make the digital image projector800which uses the Quantum Photonic Imager device200substantially less complex and subsequently more compact and less costly than digital projectors that use existing digital imagers such as micro-mirror, LCOS or HTPS imager devices.

An important aspect of the Quantum Photonic Imager device200of this invention is its luminance (brightness) performance and its corresponding power consumption. A single 10×10 micron pixel230having the laser diode structures231,232, and233of the preceding exemplary embodiment as specified inFIG. 4A,FIG. 4BandFIG. 4C, respectively, would consume approximately 4.5 μW, 7.4 μW and 11.2 μW to generate a radiant flux of approximately 0.68 μW, 1.1 μW and 1.68 μW of red (615-nm), green (520-nm) and blue (460-nm); respectively, which equates to 1 milli lumen of luminous flux at color temperature of 8,000 K°. In other words, the single 10×10 micron pixel230of the Quantum Photonic Imager device200would consume approximately 23 μW to generate approximately 1 milli lumen of luminous flux at color temperature of 8,000 K°, which would be sufficient to provide a brightness of more than 1,200 candela/meter2when the pixel is magnified to 0.5×0.5 millimeter. At the brightness provided by most existing commercial displays, which typically ranges between 350 candela/meter2to 500 candela/meter2, the single 10×10 micron pixel230of the Quantum Photonic Imager device200when magnified in size to 0.5×0.5 millimeter would consume less than 10 μW, which is nearly one and a half orders of magnitude less than the power consumption required by existing commercial displays such as PDP, LCD or projection displays that use a micro-mirrors, LCOS or HTPS devices.

As a direct result of the elimination of the inefficiencies associated with illumination optics and the imager optical coupling required in all projectors that use existing digital imagers such as micro-mirror, LCOS or HTPS imager devices, the Quantum Photonic Imager device200of this invention would achieve substantially higher efficiency when compared to existing digital imagers. Specifically, the losses associated with the digital projector800illustrated inFIG. 13that uses the Quantum Photonic Imager200of this invention would be limited to the losses due to projection optics lens group810, which would approximately be about 4%. Meaning that the efficiency of the digital projector800illustrated inFIG. 13that uses the Quantum Photonic Imager200in terms of the ratio of projected luminous flux to the generated luminous flux would be approximately 96%, which is substantially higher than the efficiency of less than 10% achieved by projectors that use existing digital imagers such as micro-mirror, LCOS or HTPS imager devices.

For example, the digital projector800illustrated inFIG. 13that uses the Quantum Photonic Imager200of this invention having one million pixels would consume approximately 25.4 watts to generate approximately 1,081 lumens of luminous flux at color temperature of 8,000 K°, which would be sufficient to project an image having 60″ diagonal at a brightness of approximately 1,000 candela/meter2on a front projection screen. When the efficiency of a typical projection screen is taking into account, the cited example of the digital projector800would project an image with brightness of approximately 560 candela/meter2on a rear projection screen. For comparison purposes the power consumption of a typical existing rear projection displays that achieve brightness in the range of 350 candela/meter2would be in excess of 250 watts, which indicates that the digital projector800that uses the Quantum Photonic Imager200as an image source would achieve a much higher projected image brightness than existing front and rear projection displays, yet at a substantially lower power consumption.

The compactness and low cost characteristics of the digital image projector800which uses the Quantum Photonic Imager device200when combined with the low power consumption of the Quantum Photonic Imager device200would make it possible to design and fabricate digital image projectors that can be effectively embedded in mobile platforms such as cell phones, laptop PC or comparable mobile devices. In particular, the digital projector800that uses the Quantum Photonic Imager200of this invention such as that illustrated inFIG. 13having 640×480 pixels and designed to achieve ±25 degrees projection field of view would achieve approximately 15×15 mm volume and would consume less than 1.75 watts to project 18″ projected image diagonal with brightness of approximately 200 candela/meter2(for reference purposes, the typical brightness of a laptop PC is approximately 200 candela/meter2).

Because of its compactness and low power consumption, the Quantum Photonic Imager200of the invention would also be suitable for near-eye applications such as helmet-mounted displays and visor displays. Furthermore, because of its ultra-wide gamut capabilities, the Quantum Photonic Imager200of the invention would also suitable for applications requiring realistic image color rendition such as simulator displays and gamming displays.

With its pixel-based laser light generating capabilities described in the preceding paragraphs, the Quantum Photonic Imager device200will be able to convert the digital source image data received from an external input into an optical image which would be coupled into the projection optics of the projector800as illustrated inFIG. 13. In using the Quantum Photonic Imager device200of this invention to synthesize the source image, the luma (brightness) and chroma (color) components of each of the image pixels would be simultaneously synthesized through apportioned setting of the on/off duty cycle of the corresponding pixel's red, green and blue laser diodes231,232, and233. Specifically, for each of the source image pixels, the chroma component of the pixel would be synthesized by setting the corresponding pixel's red, green and blue laser diodes231,232, and233on/off duty cycle relative ratios that reflect the required color coordinates for the pixel. Similarly, for each of the source image pixels, the luma component of the pixel would be synthesized by setting the on/off duty cycle of the corresponding pixel's light generating red, green and blue laser diodes231,232, and233collective on/off duty cycle values that reflect the required brightness for the pixel. In other words, the pixel's luma and chroma components of each of the source image pixels would be synthesized by controlling the on/off duty cycle and the simultaneity of the corresponding pixel's light generating red, green and blue laser diodes231,232, and233of the Quantum Photonic Imager device200.

By controlling the on/off duty cycle and simultaneity of the pixel's laser diodes231,232, and233having the selected wavelengths of the exemplary embodiment of the Quantum Photonic Imager device200described in the preceding paragraphs of 615-nm for the pixel's red laser diodes231, 520-nm for the pixel's green laser diode232, and 460-nm for the pixel's blue laser diode233, the Quantum Photonic Imager device200of this invention would be able to synthesize any pixel's color coordinate within its native color gamut905illustrated inFIG. 14Ain reference to the CIE XYZ color space. Specifically, the aforementioned operational wavelengths of the exemplary embodiment of the Quantum Photonic Imager device200pixel's laser diodes231,232, and233would define the vertices902,903and904; respectively, of its native color gamut905as illustrated inFIG. 14Ain reference to the CIE XYZ color space.

The specific color gamut of the source image would typically be based on image color standards such as NTSC and HDTV standards. For comparison purposes, the display color gamut standards of NTSC308and HDTV309are also shown onFIG. 14Aas a reference to illustrate that the native color gamut305of the exemplary embodiment the Quantum Photonic Imager device200defined by the color primaries wavelengths for red at 615-nm, green at 520-nm and blue at 460-nm would include the NTSC308and HDTV309color gamut standards and would extend beyond these color gamut standards by a significant amount.

Given the extended native color gamut305of the Quantum Photonic Imager device200illustrated inFIG. 14A, the source image data would have to be mapped (converted) from its reference color gamut (such as that illustrated inFIG. 14Afor the NTSC308and the HDTV309color gamut) to the native color gamut305of the Quantum Photonic Imager device200. Such a color gamut conversion would be accomplished by applying the following matrix transformation on the [R, G, and B] components of each of the source image pixels:

[RQPIGQPIBQPI]=M·[RGB](6)
Where the 3×3 transformation matrix M would be computed from the chromaticity values of the coordinates of the white point and color primaries of the source image color gamut and the coordinates of the white point and color primaries902,903and904(FIG. 14B) of the Quantum Photonic Imager device200within a given the reference color space, such as CIE XYZ color space for example. The result of the matrix transformation defined by Equation (6) would define the components of the source image pixel [RQPI, GQPI, BQPI] with respect to the native color gamut305of the Quantum Photonic Imager device200.

FIG. 14Billustrates the result of the matrix transformation defined by Equation (6) to define the components of the source image pixel [RQPI, GQPI, BQPI] of two exemplary pixels906and907with respect to the Quantum Photonic Imager device200native color gamut305defined by the vertices902,903and904. As illustrated inFIG. 14B, the values [RQPI, GQPI, BQPI] could span the entire color gamut305, enabling the Quantum Photonic Imager device200to synthesize the pixels [R, G, B] values of a source image that have a much wider color gamut than that offered by the NTSC308and the HDTV309color gamut (FIG. 14A). As wider color gamut standards and wide-gamut digital image and video input content becomes available, digital projectors800that use the Quantum Photonic Imager200of this invention would be poised to project source images and video content in such wide-gamut format. In the interim, the wide-gamut capabilities of the Quantum Photonic Imager200would allow it to synthesize digital image and video inputs with the existing color gamut (such as NTSC308and the HDTV309color gamut) at an even lower power consumption than the exemplary values cited in an earlier paragraph.

The [R, G, B] values of every pixel in the source image would be mapped (converted) to the native color gamut305(color space) of the Quantum Photonic Imager device200using the transformation defined by Equation (6). Without loss of generality, in assuming that the white point of the source image has an [R, G, B]=[1, 1, 1], a condition which can always be met by dividing [R, G, B] values of every pixel in the source image by the white point's [R, G, B] value, the result of the transformation defined by Equation (6) for each of the source image pixels would be a vector [RQPI, GQPI, BQPI] with values ranging between [0, 0, 0] for black and [1, 1, 1] for white. The above representation has the benefit that the distances within the reference color space, such as CIE XYZ color space for example, between the pixel's and the color primaries902,903and904of the native gamut305of the Quantum Photonic Imager device200defined by the values [RQPI, GQPI, BQPI] would also define the on/off duty cycles values for its respective red, green, and blue laser diodes231,232, and233:
λR=RQPI
λG=GQPI
λB=BQPI(7)
Where λR, λGand λBdenote the on/off duty cycles of the respective pixel230of the Quantum Photonic Imager device200red, green, and blue laser diodes231,232, and233; respectively, required to synthesize [R, G, B] values of each of the pixels comprising the source image.

Typical source image data input, whether static images or dynamic video images, would be comprised of image frames which are inputted at a fame rate, for example either 60 Hz or 120 Hz. For a given source image frame rate, the on-time of the respective pixel230of the Quantum Photonic Imager device200red, green, and blue laser diodes231,232, and233; respectively, required to synthesize the [R, G, B] values of source image pixel would be the fraction of the frame duration defined by the values λR, λG, and λB.

In order to account for possible pixel-to-pixel brightness variations that could result from possible variations in the semiconductor material characteristics comprising the photonic semiconductor structure210, during testing of the Quantum Photonic Imager device200which would typically occur at the completion of the device fabrication steps described earlier, the device luminance profile would be measured and a brightness uniformity weighting factor would be calculated for each pixel. The brightness uniformity weighting factors would be stored as a look-up-table (LUT) and applied by the Quantum Photonic Imager device200companion image data processor850. When these brightness uniformity weighting factors are taken into account, the on-time for each of the pixel230of the Quantum Photonic Imager device200would be given by:
ΛR=KRλR
ΛG=KGλG
ΛB=KBλB(8)
Where KR, KGand KBare the brightness uniformity weighting factors for each of the Quantum Photonic Imager device200pixel's red, green, and blue laser diodes231,232, and233; respectively.

The on-time values of the red, green, and blue laser diodes231,232, and233of each of the pixels230comprising the Quantum Photonic Imager device200expressed by Equation (8) would be converted into serial bit streams using conventional pulse width modulation (PWM) techniques and inputted to the Quantum Photonic Imager device200at the frame rate of the source image together with the pixel address (row and column address of the respective pixel within the array of pixels comprising the Quantum Photonic Imager device200) and the appropriate synchronization clock signals.

The conversion of the image source data into the input signals required by the Quantum Photonic Imager device200would be performed by the companion image data processor850in accordance with Equations (6) through (8).FIG. 15AandFIG. 15Billustrate a block diagram of the Quantum Photonic image data processor850and the timing diagram associated with its interface with the Quantum Photonic Imager device200; respectively. Referring toFIG. 15AandFIG. 15B, the SYNC & Control block851would accept the frame synchronization input signal856associated with the source image or video input and generate the frame processing clock signal857and the PWM clock858. The PWM clock858rate would be dictated by the frame rate and word length of the source image or video input. The PWM clock858rate illustrated inFIG. 15Breflects an exemplary embodiment of the Quantum Photonic Imager200and companion Image Data Processor850operating at a frame rate of 120 Hz and word length of 16-bit. A person skilled in the art would know how to use the teachings of this invention to make the Quantum Photonic Imager200and its companion Image data Processor850support source image or video inputs having frame rates and word lengths that differ from those reflected inFIG. 15B.

In synchronism with the frame clock signal857, the Color-Space Conversion block852would receive each frame of the source image or video data, and using the source input gamut coordinates, would perform the digital processing defined by Equations (6) to map each of the source input pixel [R, G, B] values to the pixel coordinate values [RQPI, GQPI, BQPI]. Using the white-point coordinates of the source image or video data input, the Color-Space Conversion block852would then convert each of the pixel values [RQPI, GQPI, BQPI] using Equation (7) to the on/off duty cycle values λR, λG, and λBof the red, green, and blue laser diodes231,232, and233, respectively, of the corresponding pixel230of Quantum Photonic Imager200.

The values λR, λG, and λBwould then be used by the Uniformity Correction block853in conjunction with the pixel brightness weighting factor KR, KGand KBstored in the Uniformity Profile LUT854to generate the uniformity corrected on-time values [ΛR, ΛG, ΛB] for each of the pixels230of the Quantum Photonic Imager200using equation (8).

The values [ΛR, ΛG, ΛB] generated by the Uniformity Correction block853, which would typically be expressed in three 16-bit words for each pixel, are then converted by the PWM Conversion block855into a three serial bit streams that would be provided to the Quantum Photonic Imager200in synchronism with the PWM clock. The three PWM serial bit streams generated by the PWM Conversion block855for each of the pixels230would provide the Quantum Photonic Imager device200with 3-bit words, each of which define the on-off state of the pixel's light generating red, green and blue laser diodes231,232, and233within the duration of the PWM clock signal858. The 3-bit word generated by the PWM Conversion block855would be loaded into the appropriate pixel address of the digital semiconductor structure220of the Quantum Photonic Imager device200and would be used, as explained earlier, to turn on or off the respective pixel's red, green and blue laser diodes231,232, and233within the duration defined by the PWM clock signal858.

In the preceding exemplary embodiment of the operation of the Quantum Photonic Imager device200of this invention, the source image pixels color and brightness specified by the pixel [R, G, B] values would be directly synthesized for each individual pixel in the source image using the color primaries902,903and904of the native gamut305of the Quantum Photonic Imager device200. Because the individual pixel brightness and color are directly synthesized, this operational mode of the Quantum Photonic Imager device200is referred to as Direct-Color Synthesize Mode. In an alternative exemplary embodiment of the operation of the Quantum Photonic Imager device200the color primaries of the source image color gamut are first synthesized using the color primaries902,903and904of the native gamut305of the Quantum Photonic Imager device200and the pixel color and brightness are then synthesized using the synthesized color primaries of the source image color gamut. In this operational mode of the Quantum Photonic Imager device200, the pixel's red, green and blue laser diodes231,232, and233collectively would sequentially synthesize the RGB color primaries of the source image. This would be accomplished by dividing the frame duration into three segments whereby each segment would be dedicated for generating one of the color primaries of the source image and having the default values (white-point) of each of the pixel's red, green and blue laser diodes231,232, and233reflect the coordinates of one of the source image color primaries in each of the frame segments sequentially. The duration of the frame dedicated to each color primary segment and the relative on-time values of the pixel's red, green and blue laser diodes231,232, and233during that segment would be selected based on the required white-point color temperature. Because the individual pixel brightness and color are sequentially synthesized, this operational mode of the Quantum Photonic Imager device200is referred to as Sequential-Color Synthesize Mode.

In the Sequential-Color Synthesize Mode of the Quantum Photonic Imager device200, the total number of PWM clock cycles within the frame would be apportioned into three color primaries sub-frames, with one sub-frame dedicated to the R-primary, the second dedicated for the G-primary and the third dedicated for the B-primary of the source image gamut. The on-time of each the Quantum Photonic Imager device200pixel's red, green and blue laser diodes231,232, and233during the R-primary sub-frame, G-primary sub-frame and the B-primary sub-frame would be determined based on the distances within the reference color space between the source image color primaries and the color primaries of the Quantum Photonic Imager device200native color gamut. These on-time values would then be modulated sequentially with [R, G, and B] values of the respective pixel of the source image.

The difference between Direct-Color Synthesize mode and Sequential-Color Synthesize mode of the Quantum Photonic Imager device200is illustrated inFIG. 15Bwhich shows the enable signal that would be provided to the pixel's red, green and blue laser diodes231,232, and233in each case. The sequence of enable signals860illustrate the operation of the pixel's red, green and blue laser diodes231,232, and233in the Direct-Color Synthesize mode where the pixel's luma and chroma components of the source image pixels would be directly synthesized by controlling the on/off duty cycle and simultaneity of the corresponding pixel's red, green and blue laser diodes231,232, and233. The sequence of enable signals870illustrate the operation of the pixel's red, green and blue laser diodes231,232, and233in the Sequential-Color Synthesize mode where the primaries of the source image gamut would be synthesized using the color primaries902,903and904of the native gamut305and luma and chroma components of the source image pixels would be synthesized sequentially using the synthesized primaries of the source image gamut.

The Direct-Color Synthesize mode and Sequential-Color Synthesize mode of the Quantum Photonic Imager device200would differ in terms of the achieved operating efficiency of the device as they would tend to require different peak-to-average power driving conditions to achieve comparable level image brightness. However in both operational modes the Quantum Photonic Imager device200of this invention would be able to support comparable source image frame rate and [R, G, B] word length.

QPI Dynamic Range, Response Time, Contrast and Black Level—

The dynamic range capability of the Quantum Photonic Imager device200(defined as the total number of grayscale levels that can be generated in the synthesize for each of the source image pixels) would be determined by the smallest value of PWM clock duration that can be supported, which in turn would be determined by the on-off switching time of the pixel's red, green and blue laser diodes231,232, and233. The exemplary embodiment of the photonic semiconductor structure210(FIG. 2A) described in the preceding paragraphs would achieve on-off switching time that is a fraction of a nanosecond in duration, making the Quantum Photonic Imager device200able to readily achieve a dynamic range of 16-bit. For comparison, most currently available display systems operate at 8-bit dynamic. Furthermore, the on-off switching time of a fraction of a nanosecond in duration that can be achieved by the photonic semiconductor structure210would also enable of the Quantum Photonic Imager device200to achieve a response time that is a fraction of a nanosecond in duration. For comparison, the response time that can be achieved by LCOS and HTPS type imagers is typically in the order of 4 to 6 milliseconds and that of the micro mirror type imager is typically in the order of one microsecond. The imager response time plays a critical role in the quality of the image that can be generated by the display system, in particular for generating video images. The relatively slow response time of the LCOS and HTPS type imagers would tend to create undesirable artifacts in the generated video image.

The quality of a digital display is also measured by the contrast and black level it can generate, with the contrast being a measure of the relative levels of white and black regions within the image and black level being the maximum black that can be achieved in response to a black filed input. Both the contrast and the black level of a display are significantly degraded in existing projection displays that use imagers such as micro mirror, LCoS or HTPS imager because of the significant levels of photonic leakage associated with such imagers. The high photonic leakage typical to these types of imager is caused by light leaking from the on-state of the imager pixel onto its off-state, thus causing the contrast and black levels to degrade. This effect is more pronounced when such imagers are operated in a color sequential mode. In comparison the Quantum Photonic Imager device200would have no photonic leakage since its pixel's red, green and blue laser diodes231,232, and233on-state and off-states are substantially mutually exclusive making, the contrast and black levels that can be achieved by the Quantum Photonic Imager device200orders of magnitude superior to what can be achieved by micro mirror, LCoS or HTPS imagers.

In summary, the Quantum Photonic Imager device200of the present invention overcomes the weaknesses of other imagers plus exhibits the following several advantages:1. It requires low power consumption because of its high efficiency;2. It reduces the overall size and substantially reduces the cost of the projection system because it requires simpler projection optics and does not require complex illumination optics;3. It offers extended color gamut making it is able to support the wide-gamut requirements of the next generation display systems; and4. It offers fast response time, extended dynamic range, plus high contrast and black levels, which collectively would substantially improve the quality of the displayed image.

In the forgoing detailed description, the present invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention. The design details and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Skilled persons will recognize that portions of this invention may be implemented differently than the implementation described above for the preferred embodiment. For example, skilled persons will appreciate that the Quantum Photonic Imager device200of this invention can be implemented with numerous variations to the number of multilayer laser diodes comprising the photonic semiconductor structure210, the specific design details of the multilayer laser diodes250,260and270, the specific design details of the vertical waveguides290, specific design details associated with the selection of the specific pattern of the pixel's vertical waveguides290, the specific details of the semiconductor fabrication procedure, the specific design details of the projector800, the specific design details of the companion Image Data Processor device850, the specific design details of the digital control and processing required for coupling the image data input to the Quantum Photonic device200, and the specific design details associated with the selected operational mode of the chip-set comprising the Quantum Photonic Imager200and its companion Image Data Processor850. Skilled persons will further recognize that many changes may be made to the details of the aforementioned embodiments of this invention without departing from the underlying principles and teachings thereof. The scope of the present invention should, therefore, be determined only by the following claims.