EP3665753A1 - Structure de grille laser haute puissance - Google Patents

Structure de grille laser haute puissance

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Publication number
EP3665753A1
EP3665753A1 EP18843018.5A EP18843018A EP3665753A1 EP 3665753 A1 EP3665753 A1 EP 3665753A1 EP 18843018 A EP18843018 A EP 18843018A EP 3665753 A1 EP3665753 A1 EP 3665753A1
Authority
EP
European Patent Office
Prior art keywords
laser
micro
emitting
epitaxial structure
lens
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP18843018.5A
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German (de)
English (en)
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EP3665753A4 (fr
Inventor
John Richard JOSEPH
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Optipulse Inc
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Optipulse Inc
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Publication date
Application filed by Optipulse Inc filed Critical Optipulse Inc
Publication of EP3665753A1 publication Critical patent/EP3665753A1/fr
Publication of EP3665753A4 publication Critical patent/EP3665753A4/fr
Pending legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/42—Arrays of surface emitting lasers
    • H01S5/423—Arrays of surface emitting lasers having a vertical cavity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0425—Electrodes, e.g. characterised by the structure
    • H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
    • H01S5/04257—Electrodes, e.g. characterised by the structure characterised by the configuration having positive and negative electrodes on the same side of the substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18305—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] with emission through the substrate, i.e. bottom emission
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
    • G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
    • G02B19/0047—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source
    • G02B19/0052—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a laser diode
    • G02B19/0057—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a light source the light source comprising a laser diode in the form of a laser diode array, e.g. laser diode bar
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0425—Electrodes, e.g. characterised by the structure
    • H01S5/04254—Electrodes, e.g. characterised by the structure characterised by the shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1021—Coupled cavities
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1025—Extended cavities
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18308—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a special structure for lateral current or light confinement
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18341—Intra-cavity contacts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18386—Details of the emission surface for influencing the near- or far-field, e.g. a grating on the surface
    • H01S5/18388—Lenses
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2054—Methods of obtaining the confinement
    • H01S5/2059—Methods of obtaining the confinement by means of particular conductivity zones, e.g. obtained by particle bombardment or diffusion
    • H01S5/2063—Methods of obtaining the confinement by means of particular conductivity zones, e.g. obtained by particle bombardment or diffusion obtained by particle bombardment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4012—Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms

Definitions

  • Low-cost, highly efficient, and high-power semiconductor lasers are needed in the art for directed-energy applications—for example, for illumination lasers, beacon lasers, or for pumping other lasers.
  • Surface emitting laser devices are especially adaptable to scaling power. Such devices are typically top-emitting or back-emitting emitting where the entire cavity is grown in a sequence of mirrors and active regions. Other designs move one side of the mirrors' completion out at a relatively long distance of mms.
  • External cavity designs for such laser devices have proven difficult to produce in an array configuration due to nonplanar bowing of the chip after bonding, which adversely affects the intra-cavity mirrors and only optimizes a few of the array at a time, thereby reducing consistent results.
  • a semiconductor laser structure that offers multiple advantages in overcoming bowing.
  • An example of such a structure can be a back-emitting epitaxial structure that includes a plurality of laser regions within a single mesa structure, each laser region having an aperture through which laser beams are controllably emitted.
  • Each aperture can be part of a laser cavity.
  • each cavity is not adversely affected because the completion of the mirror stage which is a series of layers with a contrast in the materials refractive index is completed with the mirror or reflective layers on the wafer layer.
  • This consistent distance can be used in conjunction with beam forming optics to optimize output in a larger device aperture (but with more apertures so as to maintain overall output power of the array of Extended Cavity devices).
  • beam forming optics to optimize output in a larger device aperture (but with more apertures so as to maintain overall output power of the array of Extended Cavity devices).
  • the bowing problems experienced by conventional solutions in the art can be overcome by using the back of the laser substrate as the mounting surface for a micro-lens array; this surface is always planar and perpendicular to all the laser optical axes for the laser regions. While this architecture results in an aperture size that is smaller than conventional designs, this smaller aperture size can be offset by the large number of laser regions and corresponding apertures that can included in the semiconductor laser structure.
  • a non-coherent beam combiner can then be positioned to non- coherently combine the laser beams emitted by these apertures to produce a low coherence length for the overall beam, which is a benefit for illuminator and beacon lasers.
  • the example embodiments described herein result in a unique design architecture that allows for increased power, while reducing pulse width, size, weight and cost.
  • the technology described herein is thus expected to improve performance by achieving a high-power, short-coherent-length beam with high beam quality suitable for use as an illuminator or beacon laser that can be used for drone defense directed-energy weapons.
  • Figures 1-5 show various views of an example top-emitting implant embodiment.
  • Figure 6 shows a view of an example bottom-emitting implant embodiment.
  • Figures 7 and 7A-7C show views of an example top-emitting oxidation embodiment.
  • Figures 8-14c show various views of an example bottom-emitting oxidation embodiment.
  • Figure 15 shows a view of an example microstrip embodiment.
  • Figure 16 shows a view of an example phase coherent embodiment.
  • Figure 17 shows a view of an example embodiment that employs diffractive optical elements.
  • Figure 18 shows a view of an example embodiment that employs pattern diffractive grating.
  • Figure 19 shows a view of an example microlens embodiment.
  • Figure 20 shows a view of an example tenth embodiment.
  • Figure 21 shows a view of an example eleventh embodiment.
  • Figure 22 shows a view of an example twelfth embodiment.
  • Figure 23 shows an example of an additional pattern for a lasing grid with respect to various embodiments.
  • Figure 24 comparatively shows current flow as between an example embodiment designed as described herein and that taught by US Pat App. Pub. 2011/0176567.
  • Figure 25 shows a cross-sectional view of a laser apparatus in accordance with an example embodiment.
  • Figure 26 shows a cross-sectional view of an example extended cavity showing a lens that is positioned on the backside of the laser wafer, where the lens includes a dielectric coating which acts as a mirror.
  • Figure 27 shows simulation results for an example embodiment.
  • Figure 28 shows an example flexible beam-combining technique that can be used with example embodiments of the laser apparatus.
  • Figure 29 shows a perspective view of the flexible beam-combining technique of Figure 28.
  • Figure 30 shows a cross-sectional view of an example laser apparatus that includes a laser structure in combination with a graphene lens structure.
  • Figure 31 discloses an example process that can be used to form the graphene lens structure.
  • Figure 32 shows an example where the graphene lens structure can be designed to vary in terms of width and spacing.
  • Figure 33 shows an example graphene lens design that can replace the formed lens in extended cavity designs for the laser structure.
  • Figure 34 shows an example graphene lens design that can replace a diffractive optical element (DOE) in the laser structure.
  • DOE diffractive optical element
  • Figure 25 shows a cross-sectional view of an example laser apparatus 2500 that includes a laser structure 2502 in combination with a micro-lens array 2504 and a non-coherent beam combiner 2510.
  • the laser structure 2502 can be a laser-emitting epitaxial structure having a front (or top) 2504 and a back 2506, wherein the laser-emitting epitaxial structure is back- emitting.
  • the laser structure comprises a plurality of laser regions within a single mesa structure, each laser region having an aperture through which laser beams are controllably emitted.
  • the micro-lens array 2502 is located on the back 2506 of the laser structure 2502.
  • Each micro-lens of the micro-lens array 2504 is aligned with a laser region of the laser-emitting epitaxial structure 2502.
  • the non-coherent beam combiner 2510 is positioned to non-coherently combine a plurality of laser beams emitted from the apertures.
  • Examples of devices that can be used as laser structure 2502 are disclosed and described in US Pat. App. Pub. 2017/0033535, the entire disclosure of which is incorporated herein by reference and a copy of which is included herewith as Appendix A.
  • Appendix A describes multi -conductive grid-forming laser structures, which in an example embodiment, can be embodied by a single unit of semiconductor lasers in a mesa structure, and their connections to a high speed electrical waveguide for high frequency operation.
  • the laser structure 2502 can be arranged as an array of multiple laser-emitting epitaxial structures, each laser-emitting epitaxial structure having a single mesa structure, where the single mesa structure includes multiple isolated laser regions.
  • the laser structure 2502 may have multiple mesa structures, where each mesa structure includes multiple isolated laser regions.
  • Such a laser grid structure can exhibit high numbers of laser emitters on a small chip.
  • the laser apparatus 2500 can be used in beacon illuminator lasers.
  • the laser cavity can be extended to the back of the wafer to eliminate external alignment of optical components, as shown by Figure 26.
  • This design approach can drastically improve beam quality (M 2 of ⁇ 1.5).
  • the beam coherence length can be reduced to below 1 mm by using multiple low coherence beams with high quality beam characteristics in a non-coherent beam-forming architecture, defined by the individual beams' characteristic.
  • the method of making the combination of laser structure 2502 with micro-lens array 2504 involves 2D photolithography techniques, which enable the deployment of tens of thousands of chips on a single 4" wafer (see substrate 2600 in Figure 26) while also eliminating chip- scale complexities. Examples of extended cavity devices have produced M 2 values ⁇ 1.5. In effect, this wafer-level process will eliminate thousands of hours of adjustments in alignment in a single wafer with a single process, while improving output power and reliability.
  • the micro-lens array can comprise multiple curved lenses 2610, each with a smooth radius of curvature.
  • the lens array can be etched into the surface of the back of the laser substrate opposite the back-emitting epitaxial growth side. Etching an array of lenses occurs when one first patterns with a thin photoresist and heat it above the glass transition state when the photoresist melts and forms a lens type structure due to surface tension.
  • the lens type structure can then be a mask to etch that structure into the GaAs laser wafer surface.
  • the Radius of Curvature (ROC) of the lens can be controlled by adjusting the selectivity between the BC13 or CI containing removal of GaAs as compared to the resist removal rate.
  • a graphene lens could be substituted for the etched lens in making arrays of lens on the back of the chip as discussed below, or if it is used as the beam forming array they could be formed on an external clear or transparent substrtae as a microlens array.
  • Each lens 2610 can be aligned with a laser cavity 2602 in the substrate 2600 that terminates in an aperture at the back 2506 of the substrate 2600. While only one such cavity 2602 is shown by Figure 26 for ease of illustration, it should be understood that each of the lenses 2610 can be aligned with a different laser cavity 2602. Each cavity 2602 exhibits an optical axis that corresponds to a direction of beam emissions through the aperture (e.g., a vertical axis with reference to the arrangement of Figure 26).
  • the lenses 2610 can be covered with a reflective coating such as a reflective dielectric so that they serve as mirrors for some of the light emitted out of the laser cavities 2602.
  • the lenses 2610 can be curved in a manner to provide a feedback mechanism that concentrates light to the center of the cavity 2602 to increase beam quality and beam output.
  • this reflected light in turn gets channeled within the cavity 2602 to create a greater concentration of light energy in beam emitting along the central optical axis of the cavity 2602.
  • stabilization and a better quality of beam output can be achieved.
  • Degradations in beam quality produced as a result of laser feedback into the cavity 2602 can be mitigated by matching the cavity 2602 with the correctly-modeled micro-lens radius of curvature. If the feedback spot is optimized to match the area into the current confinement region of the laser it can optimize power out by not overfilling or underfilling the active region of the laser where the current produce the photons. Furthermore, epitaxial design may also require more growth runs to optimize reflectance in the epitaxial output mirror. Output power is a function of reflectivity of the output mirror. The more reflective the mirror, the lower the number of photons will exit and the higher number of photons will reflect back into the cavity. Adjusting the reflectivities of the output cavity helps to optimize power out. Reflectivity can be adjusted by modification in the epitaxial layers or by adjusting the completion layers of the mirror which are deposited on the surface of the microlens etched array.
  • wafer-scale photolithography techniques that can be used for creating these lenses 2610 is described below with reference to Figures 30-34. With such wafer-scale photolithography, hundreds of thousands of lenses can be aligned and formed at the same time.
  • Figures 25 and 26 Compared to beams from coherent arrays, beams from incoherent arrays such as that shown by Figures 25 and 26 have short coherence length and produce less speckle on target. It is believed that the coherence length for the array of Figures 25 and 26 can be less than 1 mm. All low-coherence arrays tested have shown a linear relationship with power out as lasers are added. 100 lasers, each with an output of 1 mW will produce 100 mW of power, or 1 million lasers of 0.1 W each will produce 100,000 Watts of optical power. A coherent structure has more scintillation in the far field.
  • Figure 27 shows the results of a simulation using a wave-optics beam propagator with respect to an example embodiment in accordance with Figure 26.
  • a hexagonal array of top-hat beams is propagated through one instantiation of turbulence with and without mutual coherence.
  • the white circle in each target irradiance frame indicates the target spot.
  • the incoherent array is simulated as producing less speckle on the target spot.
  • the arrangement of Figures 25-26 also enables new types of beam combining.
  • the non-coherent beam combiner 2510 can take the form of additional lens element such as a microlens that is external to the laser structure 2502 and micro-lens array 2504.
  • Beams will be exiting the micro-lens array 2504 pointed straight ahead, and the beam combiner 2510 operates to bend in the edges of the beams such that all beams converge because of an offset different of the laser pitch to the lens pitch. Accordingly, the beam combiner 2510 directs the beams to a single spot in front of the 2D array.
  • the non-coherent beam combiner 2510 can employ 2D-beam-combining with an overlapping convergence point. However, it should be understood that beam combiner 2510 can also employ 3D- beam-combining with overlapping multiple convergence points.
  • Figure 28 shows an example flexible beam-combining technique that can be used with example embodiments of the laser apparatus 2500.
  • a bottom layer in the array stack can be a full laser grid array, while upper layers in the stack can include an opening in the laser grid array (e.g., a central hole as shown by Figure 28).
  • the micro-lens array 2504 in the upper stacks can employ torus-shaped lenses.
  • a series of these torus-shaped lenses on a series of laser grid arrays in accordance with Figure 26 are arranged in the Z-axis which have the same vertex for both cones of light generated by the torus-shaped lens. The cones go through the torus lens in front of it without interference by the lens.
  • Each system of torus lenses and light grids can be assembled to have multiple cones that generate immense power on the same spot or vertex of all cones.
  • Figure 29 shows a perspective view of the beam combining shown by Figure 28.
  • Figures 25-29 describe an example embodiment for a light grid structure which can exhibit high-speed (in excess of 1 GHz on/off rates) and high-power outputs from VCSEL semiconductor laser arrays,
  • the light grid structure is easy to produce at higher yields due to the architectural array designs discussed herein.
  • This device uses a simplified manufacturing design and process to achieve improved performance for speed and power from an all-semiconductor laser chip which uses wafer-scale processes to eliminate complex assembly tasks.
  • the results achieve miniaturization, reduction in cost, and increase in the flexibility of beam characteristics using the manufacturing process instead of expensive and complex alignment with external micro lens/ mirror arrays.
  • the present technology will advance automated fabrication of high-beam-quality, high-power, short-coherence- length semiconductor laser arrays that could be used for applications such as drone defense - directed-energy weapons.
  • Figure 30 shows a cross-sectional view of an example laser apparatus 2500 where the micro- lens array takes the form of a graphene lens structure 3000.
  • the graphene lens structure 3000 can be a single graphene lens structure or an array of graphene lens structures.
  • Figure 31 discloses an example process that can be used to form the graphene lens structure 3000.
  • graphene is deposited on the back 2506 of the laser structure 2502 (e.g., a back-emitting multi-conductive grid-forming laser structure such as examples described below in Appendix A).
  • photolithography is used to mask areas of the deposited graphene. These masked areas will not be plasma etched.
  • Figures 32-34 show examples of mask patterns that can be used as this step.
  • the graphene lens structure 3000 is formed by plasma etching the deposited graphene so that the masked areas are not plasma etched. As an example, 02 plasma etching can be performed.
  • This innovative process uses the unique high contrast index of refraction difference between the two materials graphene and a semiconductor such as GaAs to index guide or direct the light formed by the laser structure 2500.
  • Figure 32 shows an example where the graphene lens structure 3200 can be designed to vary in terms of width and spacing.
  • the graphene lens structure 3200 comprises a plurality of concentric graphene rings 3202.
  • the width of the graphene rings 3202 and the spacing between the graphene rings 3202 can be controlled and defined during the masking process to achieve a desired optical effect for the graphene lens structure 3200.
  • the example of Figure 32 shows an example 4x4 matrix mask for a unique array of 16 lenses - where 2 masks can be employed for a light field and a dark field.
  • Figure 33 shows an example graphene lens design that can replace the formed lens in extended cavity designs for the laser structure 2500.
  • the upper part of Figure 33 shows different examples of width and spacing properties that can be used for the graphene lens structure, and the lower part of Figure 33 shows the example VCSEL laser structure corresponding to Figure 21 of Appendix A.
  • the graphene lens structure can replace the formed lens described in Appendix A in connection with Figure 21 to improve the design.
  • a reflective coating can be deposited over a surface of the graphene lens structure(s).
  • Figure 34 shows an example graphene lens design that can replace a diffractive optical element (DOE) in the laser structure 2500.
  • the upper part of Figure 34 shows different examples of width and spacing properties that can be used for the graphene lens structure, and the lower part of Figure 34 shows an example laser structure corresponding to Figure 18 of Appendix A (see also the above-referenced and incorporated 62/456,476, 62/456,489, 62/456,501, 62/456,518, and 62/459,061 patent applications).
  • the graphene lens structure can replace the DOE described in various embodiments of Appendix A to improve the design.
  • the graphene lens structure can be used with the laser structure to direct the laser light in a manner that makes the laser light appear as if originating from a single source.
  • Laser arrays are becoming important in the field of communications, light detection and ranging (LiDaR), and materials processing because of their higher operational optical power and high frequency operation as compared to single lasers, fiber lasers, diode pumped solid state (DPSS) lasers, and light emitting diodes (LEDs).
  • LiDaR light detection and ranging
  • DPSS diode pumped solid state
  • LEDs light emitting diodes
  • Laser arrays are commonly used in printing and communications, but in configurations which have a single separate connection to each laser device in the array for parallel communication where each laser could have a separate signal because it had a separate contact from the other devices in the array.
  • mesa structures as described in US Pat App. Pub. 2011/0176567 are typically brittle. This is a problem if there is any mechanical procedure to bond to or touch the laser after the mesa is formed.
  • the mesas structures can be as small as 5 to 10 microns in diameter and consist of an extremely fragile material such as GaAs or AlGas, or other similar crystalline materials. These mesas must be bonded after processing and pressure is applied under heat so that the submount and the tops of the laser mesas are bonded electrically with solder. When bonding an array of back emitting devices a typical failure mechanism at bonding is a cracked mesa which renders the laser useless and can cause a rejection of the entire device.
  • the multi-mesa structure yields relatively low lasing power as a function of chip real estate because of spacing requirements for the multiple mesas that are present on the laser chip.
  • Another problem with the multiple mesa arrays produced by mesa isolation is that the lasers are separated by a distance which limits the overall size of the array due to frequency response-dependent design parameters that prefer shorter distance for a signal to travel across a contact pad.
  • arrays were used with elements which add in power such as the multi Vertical Cavity Surface Emitting Laser (VCSEL) arrays which were used for infrared (IR) illumination.
  • VCSEL Vertical Cavity Surface Emitting Laser
  • IR infrared
  • embodiments of the invention described below incorporate a high frequency electrical waveguide to connect lasers of the array together while reducing capacitance by forming the signal pad on the substrate which employs the electrical waveguide.
  • Embodiments of the invention also comprise the use of multi -conductive current confinement techniques in a single structure to produce multiple areas that are conducting compared to non-conducting part of the structures.
  • the conducting parts form lasing areas or grids of lasing forming lasers without etching around the entire structure of the lasing point.
  • embodiments of the invention disclosed herein are designed and processed so that the laser array is integrated with a high speed electrical waveguide to enable high frequency operation.
  • Embodiments of the present invention support new and unique opportunities in the design of a high power high speed light sources by exhibiting both high frequency operation and a rigid structure, thus enhancing performance and reliability over other designs known in the art.
  • a unique structure processed from a Vertical Cavity Surface Emitting Laser (VCSEL) epitaxial material forms a grid of laser points from a single rigid structure which is conducive to high speed operation by reducing capacitance, increasing structural integrity, and decreasing the fill factor as compared to the typical mesa structures formed in VCSEL arrays such as those mentioned in US Pat App. Pub.
  • VCSEL Vertical Cavity Surface Emitting Laser
  • VCSEL embodiment is only an example, and such a design can work with other laser types, such as Resonant Cavity Light Emitting Diodes (RCLEDs), LEDs, or Vertical Extended (or External) Cavity Surface Emitting Lasers (VECSELs).
  • RCLEDs Resonant Cavity Light Emitting Diodes
  • VECSELs Vertical Extended (or External) Cavity Surface Emitting Lasers
  • the single contiguous structure described herein forms areas of electrical isolation of apertures using implanting of ions or areas of nonconductive oxidation through microstructures or holes while keeping the structural integrity of the material that is typically etched away.
  • the formation of the new structure also allows a high speed signal to be distributed between the different isolated laser conduction points or grid.
  • All of the P-contact areas of the laser grid can be connected in parallel to the signal portion of a ground- si gnal- ground (GSG) integrated electrical waveguide.
  • GSG ground- si gnal- ground
  • the signal or current being switched on and off in the waveguide is distributed between all of the conductive paths which form lasers. It should be understood that other types of electrical waveguides could be used such as a micro- strip waveguide.
  • the single contiguous structure has other benefits such as a larger base for heat distribution within a larger plating structure.
  • the lasing grid is closer together than the array structures to each other. The farther the lasers are apart the slower the frequency response or the speed which limits the ultimate bandwidth of the device due to the distance the signal must travel to every single point in an array.
  • examples of advantages that arise from embodiments of the invention include: 1. Rigid structure has a higher reliability in the chip bonding process
  • Rigid structure has shorter distance between contacts enabling higher frequency high power beams
  • Rigid structure is a better surface topology for a single lens or lens array to be attached
  • Rigid mesa structure produces another area for leads and contacts which offer separation from potentials lowering capacitance.
  • a laser grid is formed by more than one lasing area enabled by confining the current to isolated regions in the structure where conductivity exists as compared to the nonconductive ion implanted areas.
  • the conductive and nonconductive areas form a grid of light which has a single metal contact on the single solid structure for the active Positive contact and a single N Contact on the surrounding ground structure which is shorted to the N contact area at the bottom of the trench isolating the two areas.
  • Figure 7C shows how an opening in the frame would help increase the speed.
  • Figure 1 shows an example of a first embodiment of the invention.
  • a single solid structure is isolated from a surrounding ground with an etch, and where the single solid structure has within it ion implants.
  • the ion implants create areas of the semiconductor material that are non-conductive, and these areas of non-conductivity force current flow through the lasing areas 2.
  • the ion implants form a laser grid of multiple lasing areas 2 where current is confined to isolated regions in the structure where conductivity exists as compared to the nonconductive ion-implanted areas.
  • the conductive and nonconductive areas form a grid of light which has a single metal contact on the single solid structure for the active positive (P) contact and a single negative (N) contact on the surrounding ground structure which is shorted to the N contact area at the bottom of the trench isolating the two areas or to negative metal on the surrounding ground structure which is shorted to the N contact area at the bottom of the trench isolating the two areas (as in, for example, Figure 7C (see reference numbers 781 and 782).
  • P and N contacts are then bonded to a high speed electrical contact, thereby enabling the lasing grid to achieve high frequency operation. While Figure 1 shows the lasing areas 2 arranged in a grid pattern, it should be understood that many shapes and patterns of lasing areas 2 could be formed.
  • Figure 1 shows a top view of the epitaxial side of a laser chip.
  • a single laser-emitting epitaxial structure 1 has an ion-implanted area, all except the lasing areas 2 (which are shown as disks in Figure 1) where the ion implant was masked.
  • Figure 1 thus represents the chip after implant, and etch.
  • the design of Figure 1 shows a single contiguous structure 1 that does not have multiple mesas and can instead be characterized as a single mesa, where this single mesa includes multiple lasing regions 2.
  • the illustration of Figure 1 is meant to show the single mesa structure and not the electrical contacts. This structure 1 could be either bottom emitting or top emitting depending on the design and reflectance on the N mirror as compared to the P mirror.
  • Figure 1 shows:
  • Figure 2 is a cutaway view of the laser chip shown by Figure 1, where the single active mesa structure 1 shown by Figure 1 is numbered as 11 in Figure 2 and where the masked implant areas 2 shown by Figure 1 are numbered as 12 in Figure 2.
  • Figure 2 represents the chip after implant, and etch but no top metal.
  • Etched region 13 isolates the single mesa structure 12 from the "frame" or N mesa 14 (where the single ground structure 4 from Figure 1 is shown as the frame/N mesa 14 in Figure 2).
  • Figure 2 shows:
  • Figure 3 is a perspective view of the chip shown by Figures 1 and 2.
  • the implanted region is invisible.
  • the metal contacts are not shown.
  • This illustration is to show the topology of the single mesa etch, which can be used for either top-emitting or bottom-emitting implanted devices.
  • the process of implant can take place before or after top metal or etch.
  • Figure 4 shows a top view of the epitaxial side of an example top emitting VCSEL grid structure. The view is through a square hole in the top electrical waveguide which is bonded by a solder process to the laser chip. The isolation etched region is hidden in this view by the electrical waveguide. The round disks on this illustration are the holes in the top metal contact or plated metal contact region over the single solid mesa structure.
  • Figure 4 shows:
  • Figure 5 illustrates a cutaway view of the bonded electrical waveguide and laser chip shown by Figure 4.
  • the signal contact for the electrical waveguide is opened to allow the beams to propagate through the opening.
  • Another option of this embodiment would be to have a transparent or transmitting substrate material for the waveguide instead of a hole for the lasers to propagate through.
  • a transparent material such as CVD (Chemical Vapor Deposited) diamond or sapphire or glass could be an example of that material.
  • This figure shows the embodiment with a substrate such as AlNi which is opaque and thus needs a hole or opening. Notice the isolation region is separating the single mesa structure from the single mesa ground or structure or "frame" structure which is shorted to ground.
  • the surface connects to the electrical contact at the bottom of epi design, which is accomplished through the isolation trench (see, for example, Figure 7A reference number 702) surrounding the single structure (see, for example, Figure 7A (reference number 717)).
  • This structure is not based on mesa topology but is simply shorted to the electrical region of the N contact metal (see Figure 7A (reference number 703)) through the metal plating (such as in Figure 7C reference number 782).
  • This is not a built up structure or raised structure as described in US Pat App. Pub. 2011/0176567 but rather uses the chip surface and the epi material to be a surface for bonding, which also makes the device much more stable and robust at bonding.
  • the GSG Signal Pad 51 has Solder 52 electrical connecting the P Contact Metal on the top of the Active Single Mesa Structure. This allows the signal or current to be injected into the metal contact structure with holes in it for laser propagation and then the current flows through the non-implanted regions of the epitaxial structures forcing current to be confined to just those defined regions.
  • the top P mirror region has a slightly lower reflectance than the bottom N mirror allowing the light to emit from the top of the epitaxial structure.
  • the current flows on through the quantum wells which produce the light and heat in there junction, and into the n mirror where it proceeds to the N contact region in or near the n mirror. The current would then proceed up the shorted frame structure which is bonded and in electrical contact to the ground portion of the GSG electrical waveguide.
  • This structure which utilizes top emitting design can be used for lower wavelength output designs which are lower than the transmission cutoff of the GaAs or laser substrate material.
  • Back emitting structures can typically only be designed for wavelengths above ⁇ 905nm.
  • This top emitting structure could be used with ⁇ 850nm or lower to the limits of the epitaxial material set.
  • Small mesas are formed with photoresist positioned by a photolithographic process which protects the epitaxial material from damage then is washed off after the implant takes place.
  • the implant happens in an ion implant machine which accelerates ions down a tube and you put the wafer in front of the stream of ions.
  • Implanted ions can create areas of the semiconductor material that are non-conductive. These areas of non- conductive material will force the current flow through the lase areas. These non-conductive areas can also be created by etching a pattern similar to Figure 1 and oxidizing the single structure as described below in connection with Embodiment 2.
  • Figure 5 shows:
  • Figure 24 shows a comparative view of different current flows as between an embodiment such as Embodiment 1 and the design taught by US Pat App. Pub. 2011/0176567.
  • each mesa is surrounded by an N metal contact area.
  • this old method's N contact had to be large because of the structural limitations from the old method has been removed with the new single structure.
  • a single structure has several lasers on it and only one contact around that single structure.
  • the new structure reduces that N metal area to the outside of the structure making the area per light element much smaller. This involves a large N contact layer calculated to carry the current load of the single structure. The higher current flow from the single contact can be realized through thicker metal and or thicker N contact region.
  • Figure 6 illustrates a cutaway view of an example of a second embodiment, where the second embodiment is a bottom-emitting device with implanted regions for current confinement.
  • the GSG electrical waveguide can be seen solder bonded to the frame -ground structure and the active single laser mesa structure.
  • Figure 6 shows:
  • An example embodiment of the process steps to create the single structure for embodiments 1 and 2 with implant current confinement can be as follows.
  • Step 1 Use photolithography to mask areas which will not have P Metal deposited.
  • Step 2. Deposit P Metal (typically TiPtAu -2000A) Step 3. Photolithography lift off and wafer cleaning. 02 descum or ash all organics off wafer.
  • P Metal typically TiPtAu -2000A
  • Step 4 Dielectric deposit (typically SiNx ⁇ 1000A ) used as an etch mask
  • Step 5 Photolithographic masking using either photoresist or metal deposited in areas to protect the epi material from being damaged from the implant which makes the unprotected regions non-conductive through ion bombardment. This step can be performed later in the process but may be more difficult due to more varied topology.
  • Step 6 Implant- Those skilled in the art of calculating the implant doses will determine the dose and species of implant needed to disrupt the materials structures to the depth which will isolate the p regions and the quantum wells from each other- Step 7 Cleaning this photolithography is difficult due to the implant and a deposition of metal over the photolithography such as plating could help to make it easier to clean off the resist.
  • Step 8 Use photolithography to mask areas of dielectric which will not be etched . This is the unique part which is the design of the mask which creates a large isolated structure
  • Step 9 Use plasma etch to etch through dielectric (typically Fl based etchant) can use wet etch such as BOE (buffered oxide etch).
  • wet etch such as BOE (buffered oxide etch).
  • Step 10 Etch pattern into Laser or Light Emitting Diode Epitaxial material. Stop on Substrate or doped electrical contact layer. This isolates a single large structure from the N shorted regions around the chip
  • Step 11 Clean off mask. 02 descum or ash all organics off wafer.
  • Step 12 Use photolithography to mask areas which will not have N Metal deposited.
  • Step 13 Deposit N Metal (Typically GeAu/Ni/Au eutectic composition of
  • Step 14 Clean off mask (typically called lift off). 02 descum or ash all organics off wafer.
  • Step 15 Dielectric deposit (typically SiNx -2000 A ) used as a non-conductive isolation barrier
  • Step 16 Use photolithography to mask areas of dielectric which will not be etched.
  • Step 17 Use plasma etch to etch through dielectric (typically Fl based etchant) can use wet etch such as BOE (buffered oxide etch).
  • wet etch such as BOE (buffered oxide etch).
  • Step 18 Clean off mask. 02 descum or ash all organics off wafer.
  • Step 19 Use photolithography to mask areas which will not have Plated Metal deposited.
  • Step 20 Plate areas with ⁇ 4-5um of Metal (typically Au) or Cu if diffusion barrier can be deposited first.
  • Metal typically Au
  • Cu diffusion barrier
  • Step 21 Use photolithography to mask areas which will not have Solder deposited.
  • Step 22 Deposit Solder Metal (Typically AuSn/Au eutectic composition of
  • oxidation rather than ion implantation is used to create the grid of top- emitting lasing regions within the single structure.
  • a patterned etch can isolate conductive paths in a single structure, creating a grid of light sources.
  • This structure exhibits multiple laser emission points from the single structure.
  • the lasing structure is isolated with an etched region from the ground contact that forms the outside perimeter of the chip.
  • This structure for Embodiment 3 is top emitting.
  • the conductive areas of the grid are where light will be emitted.
  • the positive electrical contact can be a grid with openings where the light is emitted.
  • the epitaxial material of the laser wafer can be a VCSEL design, and most VCSELs are top emitting.
  • the distribution of the signal using a p type waveguide pad is typically on the laser wafer, but it should be understood that in an oxidated single structure embodiment that has a back emitting design, the waveguide can be on a separate substrate that is separated from the laser n material or layer.
  • Figure 7 which shows an example of Embodiment 3, illustrates an example pattern etched into a wafer to create a single structure which allows multiple point lasing.
  • the single structure of an embodiment such as that shown by Figure 7 is much more rigid than the thin columns made of fragile crystal material as taught by US Pat App. Pub. 2011/0176567. Also, as explained with respect to an embodiment discussed above, it should be understood that pattern of lasing areas other than that shown by Figure 7 may be employed if desired by a practitioner.
  • the diagonally striped areas are preferably etched down to create the patterned single mesa structure in the middle of the isolation trench. All diagonally striped areas are preferably etched down to the bottom N electrically conductive layer 705 in Figure 7A or typically the larger isolation trench will be etched to the electrical contact buried in the epitaxial design, while the smaller patterned etch areas must go deeper than the active region which isolates the lasing points.
  • the patterned structure in the middle of the isolation trench is a single structure with "shaped" holes etched into it. The holes in the large single mesa are large in this case. These holes allow the oxidation process environment to oxidize the layers in the epitaxial region.
  • the oxide layer or layers has high aluminum content and forms A10 2 that grows laterally through the layer until taken out of the oxidation process.
  • White areas are the surface of the chip, dotted lines are where oxidation limits current flow to unoxidized areas only.
  • the holes in the large single mesa are large in this case. These holes allow the oxidation process environment to oxidize the layers in the epitaxial region.
  • the oxidation layer can be formed by using a high Al content layer in the epi design structure which is buried below the surface. The etched areas expose that layer which is then placed in an oxidation chamber allowing the exposed layer to oxidize inward, where AIO2 grows laterally through the layer until taken out of the oxidation process.
  • the oxidation As the length of the oxidation grows in that thin layer, it isolates or closes off the current paths with a dielectric material of AIO2 that is formed during the oxidation process. If the areas 7005 are etched, then the oxidation will continue to grow until only areas 7008 are conductive and the area or part of the epitaxial layers which conduct the current through that section. Electrically conductive areas allow current flow through the quantum wells (see Figure 7A reference number 707) and produce lasing as the light is trapped in the cavity between the p mirror 709 and N mirror 706.
  • Figure 7 shows the large single mesa ground structure. Three views of cross sections are illustrated to identify where Figures 7A, 7B, and 7C are located. Note 7B which clearly shows through this cross section that the mesa in the center is a single structure. Figure 7 shows:
  • Figures 7A, 7A2 and 7B are side views of the example Figure 7 embodiment.
  • Figure 7A2 shows the etched holes 727 that allow the oxidation 731 to form, which confines the current into region 761 of Figure 7B, for formation of laser beams 763.
  • Reference number 706 in Figure 7A is a p mirror diffractive Bragg reflector (DBR) which has one or more layers in it with very high aluminum content 708 which when exposed to hot damp conditions oxidizes 708 confining the current to the areas 761 shown by Figure 7B, which are where the laser beams come out.
  • the N mirror DBR 709 has a conductive layer 705 to take the current flow out through the N metal ohmic contact 703 to the plating 782
  • Embodiments 1 and 2 are examples of the implant to render all other areas nonconductive (e.g., see Embodiments 1 and 2).
  • Figure 7 A shows:
  • Figure 7A2 is a continuation of Figure 7A above, and it further shows:
  • Figure 7B is a Figure 7 cutaway view that also shows the electrical connections and electrical waveguide that are not shown in Figure 7.
  • Figure 7B illustrates the cross section through the apertures created by the oxidized layer. The oxidized layer is exposed to the oxidation process through the holes in the single structure illustrated in Figure 7 A. This view also shows that the Active Mesa Structure is truly a Single Mesa Structure.
  • Figure 7B depicts:
  • Figure 7C is a cross sectional view of the area where the P Contact or Signal of the GSG waveguide is positioned below the Laser Chip where the N Contact Frame or single structure mesa grounded to the N contact of the laser is above the GSG Electrical Waveguide.
  • the large gap between the Laser Ground and the P Signal Pad reduces the capacitance of the circuit enabling higher frequency operation.
  • Figure 7C depicts:
  • An example embodiment of the process steps to create the single structure for embodiment 3 with oxidation current confinement can be as follows.
  • Step 1 Use photolithography to mask areas which will not have P Metal deposited.
  • Step 2 Deposit P Metal (typically TiPtAu -2000A)
  • Step 3 Photolithography lifts off and wafer cleaning. 02 descum or ash all organics off wafer.
  • Step 4 Dielectric deposit (typically SiNx ⁇ 1000A ) used as an etch mask
  • Step 5 Use photolithography to mask areas of dielectric which will not be etched.
  • Step 6 Use plasma etch to etch through dielectric (typically Fl based etchant) can use wet etch such as BOE (buffered oxide etch).
  • wet etch such as BOE (buffered oxide etch).
  • Step 7 Etch pattern into Laser or Light Emitting Diode Epitaxial material. Stop on Substrate or doped electrical contact layer. Typically the etch is CI based with some (high percentage) amount of BC13.
  • Step 8 Clean off mask. 02 descum or ash all organics off wafer.
  • Step 9 Use photolithography to mask areas which will not have N Metal deposited.
  • Step 10 Deposit N Metal (Typically GeAu/Ni/Au eutectic composition of
  • Step 11 Clean off mask (typically called lift off). 02 descum or ash all organics off wafer.
  • Step 12. Dielectric deposit (typically SiNx -2000A) used as a non-conductive isolation barrier
  • Step 13 Use photolithography to mask areas of dielectric which will not be etched.
  • Step 14 Use plasma etch to etch through dielectric (typically Fl based etchant) can use wet etch such as BOE (buffered oxide etch).
  • wet etch such as BOE (buffered oxide etch).
  • Step 15 Clean off mask. 02 descum or ash all organics off wafer.
  • Step 16 Use photolithography to mask areas which will not have Plated Metal deposited.
  • Step 17 Plate areas with ⁇ 4-5um of Metal (typically Au) or Cu if diffusion barrier can be deposited first.
  • Metal typically Au
  • Cu diffusion barrier
  • Step 18 Use photolithography to mask areas which will not have Solder deposited.
  • Step 19 Deposit Solder Metal (Typically AuSn/Au eutectic composition of
  • Step 20 Separate laser chips from wafer with cleaving or dicing.
  • Step 21 Design and Fabricate electrical waveguide to align to laser chip with the design to allow high frequency operation.
  • Step 22 Align and Flip Chip Bond the laser chip to the Submount electrical waveguide Embodiment 4 for US Pat App Pub 2017/0033535 - Bottom-Emitting Oxidation
  • an oxidated single structure with multiple lasing regions is designed as a bottom-emitter rather than a top emitter.
  • Figures 8 through Figure 14C provide details about Embodiment 4 and illustrate the process which can be used to make this embodiment.
  • the lasing grid's light is emitted through the substrate forming a back emitter.
  • Light is transmissive in GaAs from wavelengths around 900nm and greater. If the wavelength of the light engineered in the epitaxial design is in the range ⁇ 900nm and above, the GaAs substrate transmits the light or is transparent to the light. If the epitaxial design includes an N mirror that is less reflective than the P mirror, a laser such as a VCSEL can emit the light from the N mirror through the substrate. The laser beams will propagate through the material, and the substrate can be a platform for optical components to collimate, spread, diverge, converge or direct the light. This enables integrated optical circuits with extremely high bright power to be formed. The single structure and the ground contact can then be integrated to a high speed electrical waveguide substrate enabling high frequency responses from the entire grid. A ground signal ground electrical waveguide is ideal for this high speed electrical waveguide. Another type of electrical waveguide that may be used is a microstrip waveguide (see Figure 15), where the signal pad is separated from the ground pad by a thin dielectric layer on a substrate.
  • Figure 8 is an illustration of a typical epitaxial design. Any high speed design can be used for VCSEL devices. Figure 8 shows:
  • Figure 9 is an illustration of the first process performed, which is P metal deposit. This is typically a Ti/Pt/Au Layer on top of the highly P doped Contact Layer forming an ohmic contact.
  • Figure 9 shows: 91 P Metal forming Ohmic Contact after annealing process
  • Figure 10 is a top view of the etch of the epitaxial layer down to the N contact layer. Figure 10 shows:
  • Figure 1 OA is a cross section view A of Figure 10 formed before oxidation process
  • Figure 10A2 is a cross section view A of Figure 10 formed after oxidation process.
  • Figure 10A2 shows:
  • Figure 10B is a cross sectional view B of Figure 10 illustrating where the current confinement apertures were formed in the areas shown. This view represents a section of the single mesa where no holes are penetrating the cross section, and clearly shows that the mesa structure is a Single Mesa Structure enabling a more robust structure preferred at the bonding process.
  • Figure 10B shows:
  • Figure 11 illustrates the dielectric layer deposited and patterned with opened via "holes" for electrical contact to the epitaxial contact layers and sealing the semiconductor for reliability purposes.
  • Figure 11 shows:
  • Figure 12 shows the N metal contact after it has been deposited.
  • Figure 12 depicts:
  • N Contact Metal is deposited over the N Contact via hole to make an electrical connection to the N Contact Layer.
  • Figure 13 illustrates the next step of plating metal which shorts the N contact region to the top of the single grounded frame region, which will be bonded and electrically conductive to the ground pad of the GSG waveguide.
  • the plating also adds height to the active region reducing capacitance and it removes heat from the active region of the devices to give the devices better performance.
  • the plating over the active single structure is isolated from the N mirror and N contact region by the dielectric layer.
  • Figure 13 shows:
  • Figure 14a illustrates solder deposited on the laser chip. This serves as the electrical conductive bonding adhesion layer between the laser chip and the high speed electrical waveguide.
  • Figure 14a shows: 1401 Solder deposit
  • Figure 14b illustrates the alignment of the GSG electrical waveguide before bonding.
  • Figure 14b shows:
  • Figure 14C illustrates the bonded laser chip to the GSG electrical waveguide.
  • the gap in the single grounded mesa enables high speed operation by reducing capacitance.
  • a microstrip or strip line electrical waveguide is used rather than the GSG waveguide, as shown by Figure 15.
  • This embodiment can also have the gap mentioned in Figure 14c above.
  • This electrical waveguide can also be formed by a ground layer below a thin dielectric with a signal lead on the top of the dielectric forming a strip line or microstrip waveguide. Openings in the dielectric can be used to contact the ground portion of the lasing grid. The width of the lines and thickness of the dielectric can be controlled to produce a specific impedance value for circuit matching characteristics. It should be understood that this technique can also be used for other embodiments, such as Embodiment 2 or any of the embodiments discussed below.
  • the view in Figure 15 shows a cross section across the active single mesa structure:
  • Figure 16 shows a sixth embodiment.
  • the structure is unique in that it leaves paths for a portion of the light of each lase point to be directed to another laser next to it in order to keep the lasing in phase.
  • the laser 161 has some of its outer mode structure reflected 162 down to the laser aperture next to it 163 which produces light in phase with 162.
  • the laser which is in phase is 164 and in turn reflects from an angled reflective surface 165 back to the aperture of the laser next to it 167 which is also in phase with 164 and 161 and so on.
  • An angular and or reflective area 164 just outside of the lens or output area can divert a small portion of the light which is overflowing from the lens or output diameter to the lasing grid adjacent to it, enabling a coherent lasing grid.
  • Some of the light from the neighboring lasing points is injected into the lasing point which sets up the lasing points in a phase relation with each other. This allows a coherent operation of all lasing points when the structure directs some of the light from each laser to its neighbor.
  • the reflectance, distance and angles are very precisely calculated by one skilled in the art of optical modeling.
  • Figure 17 shows a seventh embodiment.
  • the back side of the lasing grid chip has etched patterns to redirect the laser light 172 to particularly beneficial areas. This is accomplished by diffractive optical elements (DOE) 171, which have the surface etched in a way that when light travels through that portion, the angle of the surface and redirects 175 beams or light depending on the angle of the surface of the DOE. This can be used to collimate or diverge, direct or homogenize the light.
  • DOE diffractive optical elements
  • Figure 17 does not illustrate the electrical waveguide.
  • the mode can be controlled by the aperture sizes and characteristics of the reflective surface 173 and 174.
  • Figure 17 shows:
  • Figure 18 shows an eighth embodiment.
  • a patterned diffractive grating 184 (this is the opposite angular pattern than Figure 17's DOE) is placed or etched over the emission points 181 on the backside of the laser wafer in a back emitting VCSEL design which directs the lasing points outward 185 from the grid. From the lens it looks like all the lasers are coming from a single point 186 behind the chip to form a virtual point source where a macro lens 187 can be used to collimate the beam from the virtual converged source behind the chip.
  • Figure 18 shows:
  • DOE Diffractive Optical Element
  • Figure 19 shows a ninth embodiment.
  • Figure 19 illustrates a cross section of the bonded etched and oxidized Embodiment 3, except it has microlens which have been processed on the back of the laser chip and positioned so that one is aligned to the other and one is slightly misaligned on purpose in order to redirect the laser beam emitted from the single mesa structure. While embodiment 3 is referenced for this arrangement, it should be understood that any of the above back emitting embodiments and a microlens array attached to the chip or positioned above the output grid can be used.
  • the microlens array can have values related to the pitch of the light conducting grid points but with a slightly different pitch lens 74 forcing the light emitted by the lasing points to be directed to a single area where the beams come together or seem like they come together in front of the chip or behind the chip as in a virtual point source. If the microlens pitch is smaller than the laser pitch, it will guide the outlying lasers to a point in front of the chip or directed inward. If the microlens arrays pitch is larger than the lasers' grids' pitch, the light will be directed outward as in Figure 19.
  • Figure 19 shows:
  • GSG Waveguide substrate 84 Plating shorting the N metal located on the N contact layer and the single ground mesa which is in electrical contact to the Ground Pad of the GSG electrical waveguide
  • Figure 20 shows a tenth embodiment.
  • Figure 20 illustrates that an extended cavity laser design can be implemented using the single grid structure by reducing the reflectivity of the N epitaxial output mirror 230 to a point where it will not lase, then adding the reflectivity to a reflective surface 231 on the back of the lasing grid which extends the cavity. This structure reduces feedback of the higher mode structure 233 in the cavity, thereby forming a more fundamental mode structure for the output beam 235 from the grid.
  • Figure 20 shows: 230 Arrow pointing to incomplete N output mirror epitaxial region.
  • Reflective region made of dielectrically layers with varying indexes of refraction.
  • Cavity of laser beam now includes laser wafer material extending the cavity for modal rejection.
  • Figure 21 shows an eleventh embodiment.
  • a VCSEL structure can be adapted to the laser grid design like the above embodiment, and the back of the lasing chip where the output reflector (deposited on top of lens shape 241) of the lasing grid emits light can have convex 241 or concave features under the reflector to form better a focused (focus arrows 243) feedback mechanism which rejects high modes and can be designed to have a single mode lasing output 245 from each grid area.
  • the overall lasing structure will then have low M2 values.
  • a lens or microlens can be added to collimate the output.
  • Figure 21 shows:
  • Figure 22 shows a twelfth embodiment.
  • a VCSEL structure can be adapted to the laser grid design like the above embodiment except that the beams which exit straight out of the lens go through an external microlens array which has been designed with different pitch microlens than the laser pitches to allow redirection of the beams either to or from a single location like many of the above embodiments.
  • Other forms of this technique could use a concave lens formed on the bottom of the external lens array which are aligned and have the same pitch as the laser grid, while a convex laser array with a different pitch than the laser grid is at the top.
  • Another technique to direct beams would be to use DOEs as the top optical element instead of the convex microlens which are on the top of the external lens array.
  • 252 is light reflected back into the center of the aperture making a stronger single mode beam while 253 has the reflective coatings which complete the laser output mirror cavity.
  • 254 is the cavity and would have an antireflective coating deposited on the inside of the external lens cavity while also depositing an anti -reflective coating on the top microlens array.
  • Another technique would be to use the flat reflective properties such as in Figure 20 to complete the cavity mirror and have the microlens array offset on the top or a DOE on top to redirect the beams.
  • Figure 22 shows:

Abstract

Divers modes de réalisation de l'invention portent sur des appareils laser. Selon un mode de réalisation donné à titre d'exemple, l'appareil laser comprend (1) une structure épitaxiale émettant un laser présentant une partie avant et une partie arrière, la structure épitaxiale émettant un laser étant à émission par l'arrière et comprenant une pluralité de régions laser dans une structure mesa unique, chaque région laser comportant une ouverture par laquelle des faisceaux laser sont émis de manière commandée, (2) un réseau de microlentilles situé à l'arrière de la structure épitaxiale émettant un laser, chaque microlentille du réseau de microlentilles étant alignée avec une région laser de la structure épitaxiale émettant un laser, et (3) un combineur de faisceaux non cohérent positionné de façon à combiner de manière non cohérente une pluralité de faisceaux laser émis par les ouvertures.
EP18843018.5A 2017-08-11 2018-08-13 Structure de grille laser haute puissance Pending EP3665753A4 (fr)

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US201762543972P 2017-08-11 2017-08-11
PCT/US2018/046556 WO2019033120A1 (fr) 2017-08-11 2018-08-13 Structure de grille laser haute puissance

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