DIRECTLY WRITTEN WAVEGUIDE FOR COUPLING OF LASER TO PHOTONIC INTEGRATED CIRCUIT
Systems, devices, and methods of manufacturing optical engines and laser projectors that are well-suited for use in wearable heads-up displays (WHUDs) are described. Generally, the optical engines of the present disclosure integrate a plurality of laser diodes (e.g., 3 laser diodes, 4 laser diodes) within a single, hermetically or partially hermetically sealed, encapsulated package. Photonic integrated circuits having grating or edge couplers thereon may be used to wavelength multiplex beams of light emitted by the plurality of laser diodes into a coaxially superimposed aggregate beam. A waveguide medium having one or more directly written waveguides may couple light from laser diodes to a photonic integrated circuit, and may optionally hermetically or partially hermetically seal the laser diodes, eliminating the need for a separate seal. Such optical engines may have advantages over existing designs including, for example, smaller volumes, better manufacturability, faster modulation speed, etc. WHUDs that employ such optical engines and laser projectors are also described.
1 . A method of manufacturing an optical engine, the method comprising:
bonding a plurality of lasers directly or indirectly to a base substrate;
coupling at least one laser diode driver circuit to the laser diodes, in operation the at least one laser diode driver circuit selectively drives current to the laser diodes;
bonding a cap comprising at least one wall and at least one optical window to the base substrate, the at least one wall, the at least one optical window, and at least a portion of the base substrate together delimit an interior volume sized and dimensioned to receive at least the plurality of laser diodes, the bonding of the cap to the base substrate providing a hermetic or partially hermetic seal between the interior volume of the cap and a volume exterior to the cap, and the optical window positioned and oriented to allow light emitted from the laser diodes to exit the interior volume;
bonding a photonic integrated circuit proximate the optical window of the cap, the photonic integrated circuit comprising a plurality of input facets and at least one output facet, in operation, the photonic integrated circuit receives a plurality of beams of light at the respective plurality of input facets and wavelength multiplexes the plurality of beams of light to provide an aggregated beam of light at the output facet; and
disposing a waveguide medium between the optical window of the cap and the photonic integrated circuit, the waveguide medium comprising at least one directly written waveguide that couples beams of light emitted by the plurality of laser diodes to the input facets of the photonic integrated circuit.
2 . The method of claim 1 , further comprising:
directly writing the at least one waveguide into the waveguide medium after disposing the waveguide medium between the optical window of the cap and the photonic integrated circuit.
3 . The method of claim 2 wherein directly writing the at least one waveguide into the waveguide medium includes writing a first plurality of waveguides into the waveguide medium, each waveguide of the first plurality of waveguides to receive laser light from a respective laser diode of the plurality of laser diodes and couple the received laser light to an input facet of a respective waveguide in a second plurality of waveguides in the photonic integrated circuit.
4 . The method of claim 1 , further comprising:
forming a surface of the waveguide medium into at least one lens shape which couples beams of light emitted by the plurality of laser diodes to the at least one directly written waveguide.
5 . The method of claim 1 , further comprising:
bonding each of the laser diodes indirectly to the base substrate by bonding each laser diode to a respective chip submount; and
bonding each chip submount to the base substrate.
6 . The method of claim 5 wherein bonding each laser diode to a respective chip submount comprises bonding each laser diode to a respective chip submount using a eutectic gold tin (AuSn) solder process.
7 . The method of claim 5 wherein bonding each chip submount to the base substrate comprises step-soldering each chip submount to the base substrate.
8 . The method of claim 5 wherein bonding each chip submount to the base substrate comprises bonding each chip submount to the base substrate using at least one of a reflow oven process, thermosonic bonding, thermocompression bonding, transient liquid phase (TLP) bonding, or laser soldering.
9 . The method of claim 5 wherein bonding each chip submount to the base substrate comprises bonding a chip submount that has a red laser diode bonded thereto, bonding a chip submount that has a green laser diode bonded thereto, bonding a chip submount that has a blue laser diode bonded thereto, and bonding a chip submount that has an infrared laser diode bonded thereto.
10 . The method of claim 1 wherein coupling at least one laser diode driver circuit to the laser diodes comprises:
bonding a plurality of electrical connections to the base substrate, each electrical connection coupled to a respective laser diode in the plurality of laser diodes;
providing a coupling between each of the plurality of electrical connections and the at least one laser diode driver circuit; and
bonding an electrically insulating cover to the base substrate over the plurality of electrical connections, wherein
bonding the cap to the base substrate comprises bonding the cap to the base substrate and the electrically insulating cover.
11 . The method of claim 10 wherein providing a coupling between each of the plurality of electrical connections and the at least one laser diode driver circuit comprises:
bonding a plurality of electrical contacts to the base substrate, each electrical contact coupled to a respective one of the plurality of electrical connections; and
providing a coupling between each of the electrical contacts and the at least one laser diode driver circuit.
12 . The method of claim 1 wherein bonding the plurality of laser diodes directly or indirectly to a base substrate comprises bonding the laser diodes directly or indirectly to a first surface of the base substrate, and bonding a cap to the base substrate comprises bonding a cap to the first surface of the base substrate, the method further comprising bonding the at least one laser diode driver circuit to a second surface of the base substrate, the second surface of the base substrate opposite the first surface of the base substrate.
13 . The method of claim 1 wherein bonding the plurality of laser diodes directly or indirectly to a base substrate comprises bonding the laser diodes directly or indirectly to a first surface of the base substrate, and bonding a cap to the base substrate comprises bonding a cap to the first surface of the base substrate, the method further comprising bonding the at least one laser diode driver circuit to the first surface of the base substrate.
14 . The method of claim 1 wherein bonding a cap to the base substrate comprises bonding a cap to the base substrate using at least one of a seam welding process, a laser assisted soldering process, or a diffusion bonding process.
15 . The method of claim 1 , further comprising:
positioning and orienting a collimation lens to receive and collimate the aggregate beam of light from the output facet of the photonic integrated circuit.
16 . The method of claim 1 , further comprising laser writing the photonic integrated circuit into writeable glass before bonding the photonic integrated circuit proximate the optical window of the cap.
17 . The method of claim 16 , wherein laser writing the photonic integrated circuit into writeable glass comprises laser writing a plurality of waveguides into the writeable glass, each waveguide of the plurality of waveguides being written for a respective one laser diode of the plurality of laser diodes.
18 . The method of claim 17 , wherein laser writing a plurality of waveguides into the writeable glass comprises writing a waveguide combiner into the writeable glass.
19 . The method of claim 18 , wherein writing a waveguide combiner into the writeable glass comprises writing at least one of: a directional coupler, Y-branch, whispering gallery mode, or multi-mode interface coupler.
20 . The method of claim 17 wherein laser writing a plurality of waveguides into the writeable glass comprises laser writing each waveguide of the plurality of waveguides to have a input facet to receive laser light from a respective laser diode of the plurality of laser diodes and an output facet to output the received laser light, a spacing between the output facets of each waveguide being smaller than a spacing of the input facets of each waveguide.