We are developing midwave infrared (mid-IR) quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) bonded to silicon. The heterogeneous integration of mid-IR photonic devices with silicon promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and electronic technologies. The first Fabry-Perot QCLs on silicon were bonded to pre-patterned silicon-on-nitride-on-insulator (SONOI) substrates. Lateral tapers in the III-V mesas transferred the optical mode from the hybrid III-V/Si active region into the passive silicon waveguides, with feedback provided by reflections from both the III-V tapers and the polished passive silicon facets. Lasing was observed at 4.8 m with threshold current densities as low as 1.6 kA/cm2 when operated in pulsed mode at T = 20 ºC. The first mid-IR DFB lasers integrated on silicon employed gratings patterned into the silicon waveguides before bonding. Over 200 mW of pulsed power was generated at room temperature, and operated to 100 °C with T0 = 199 K. Threshold current densities were measured below 1 kA/cm2.The grating imposed considerable wavelength selectivity and 22 nm of thermal tuning, even though the emission was not spectrally pure. Ongoing research focuses on flip-chip bonding to improve heat sinking for continuous-wave operation, and arrayed waveguide gratings for beam combining. ICLs have also been bonded to silicon and the GaSb substrate has been chemically removed with an InAsSb etch-stop layer. Tapered ICL ridges designed for lasing in a hybrid III-V/Si mode have been processed above passive silicon waveguides patterned on SOI. A goal is to combine the power generated by arrays of QCLs and ICLs residing on the same chip into a single, high-quality output beam.
Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated diode lasers for wavelengths from 1310 to 2010 nm. Recently, Fabry-Perot Quantum Cascade Lasers integrated on silicon provided a 4800 nm light source for MIR silicon photonic applications. Distributed feedback (DFB) lasers are appealing for many high-sensitivity chemical spectroscopic sensing applications that require a single frequency, narrow-linewidth MIR source. While heterogeneously integrated 1550 nm DFB lasers have been demonstrated by introducing a shallow surface grating on a silicon waveguide within the active region, no mid-infrared DFB laser on silicon had previously been reported. Here we demonstrate quantum cascade DFB lasers heterogeneously integrated with silicon-on-nitride-oninsulator (SONOI) waveguides. These lasers emit over 200 mW of pulsed power at room temperature and operate up to 100 °C. Although the output is not single mode, the DFB grating nonetheless imposes wavelength selectivity with 22 nm of thermal tuning.
High-brightness lasers are widely used in fields such as spectroscopy, infrared countermeasures, free-space communication, and industrial manufacturing. Integration of a broad-band, multi-spectral laser is made possible by heterogeneously integrating multiple gain materials on one silicon (Si) substrate chip. A single multi-spectral output with high beam quality can be achieved by wavelength beam combining in multiple stages: within the gain bandwidth of each laser material and then coarsely combining each spectral band to a single output waveguide. To make power scaling feasible with this system, heterogeneously integrated lasers spanning the near- to the mid-infrared with corresponding low-loss wavelength beam combining elements on chip must be demonstrated. In this work, a review of multi-spectral lasers integrated on Si is presented and various waveguide materials are discussed for spanning the visible to the mid-infrared. Recent work integrating 2.0μm diode and 4.8μm quantum cascade lasers on Si extend the previously available 1.3μm and 1.5μm diode lasers on Si to the mid-infrared. Spectral beam combining elements for spanning the visible to the mid-infrared with low loss are discussed.
Recently, there has been a dramatic change in the way space missions are viewed. Large spacecraft with massive propellant-filled launch stages have dominated the space industry since the 1960’s, but low-mass CubeSats and low-cost rockets have enabled a new approach to space exploration. In recent work, we have built upon the idea of extremely low mass (sub 1 kg), propellant-less spacecraft that are accelerated by photon propulsion from dedicated directed-energy facilities. Advanced photonics on a chip with hybridized electronics can be used to implement a laser-based communication system on board a sub 1U spacecraft that we call a WaferSat. WaferSat spacecraft are equipped with reflective sails suitable for propulsion by directed-energy beams. This low-mass spacecraft design does not require onboard propellant, creating significant new opportunities for deep space exploration at a very low cost. In this paper, we describe the design of a prototype WaferSat spacecraft, constructed on a printed circuit board. The prototype is envisioned as a step toward a design that could be launched on an early mission into Low Earth Orbit (LEO), as a key milestone in the roadmap to interstellar flight. In addition to laser communication, the WaferSat prototype includes subsystems for power source, attitude control, digital image acquisition, and inter-system communications.
We review recent breakthroughs in silicon photonics technology and components and describe progress in silicon
photonic integrated circuits. Heterogeneous silicon photonics has recently demonstrated performance that significantly
outperforms native III-V components. The impact active silicon photonic integrated circuits could have on interconnects,
telecommunications, sensors and silicon electronics is reviewed.
Day/Night Band (DNB) earth sensing and meteorological systems like the Defense Meteorological Satellite Program (DMSP) Operational Line Scanner (OLS) provide visible wavelength imagery 24 hours a day that
is used primarily for cloud imaging in support of weather forecasting. This paper describes a compact pushbroom imager that meets low light imaging requirements for DMSP OLS and the NOAA/NASA Joint Polar Satellite System (JPSS) as documented in the Integrated Operational Requirements Document (IORD). The presentation describes the imager design, including system level concepts of operation for data collection, radiometric and spatial calibration, and data transmission to Earth. This small, lightweight imager complies
with the low mass, low power CubeSat standard, and could be built into a variety of different satellites, for example, as a payload on Iridium NEXT, DMSP, or the International Space Station (ISS). Depending on power generation capabilities, the imager could be implemented as a free flyer in formation with other CubeSats or as a free flyer operating on its own. The imager's volume will fill about half of a 3U CubeSat; roughly measuring 170x80x80 mm3 and having mass less than 1.5 kg. Considering an estimated 3U CubeSat average core avionic power usage of 0.8W and total orbit average power of 4W, the available average power for the payload imager is 3.2W.
This paper describes an approach for addressing potential gaps in continuity of critical weather and other Earth
observations begun by SeaWiFS, MODIS and MISR with single band CubeSat imagers that could be used in
combination either onboard a single host satellite or in a constellation of small satellites to provide stable, high SNR
multispectral measurements. These wide field of view, high SNR imagers are enabled by large format (~4000
element long) ultraviolet-near infrared focal plane assemblies and achromatic wide field of view telescopes. This
new class of wide field of view pushbroom imagers offers capability to continue SeaWiFS, MODIS, MISR and, as
discussed in a companion paper, DMSP OLS measurements in support of operational weather observations, Earth
imaging and Earth science studies. In addition, extension of the spectral response to 350 nm enables supplementing
existing and future systems with multispectral observations at near ultraviolet wavelengths of importance to aerosol
and ocean color measurements. The large format size of the array and high optical quality wide field of view
telescope enable an entire ~3000 km wide MODIS or VIIRS swath to be collected simultaneously by a pushbroom
imaging radiometer in polar sun synchronous orbit. The increase in effective integration time made possible by a
pushbroom approach versus the whiskbroom imaging approaches of AVHRR, MODIS and VIIRS enables
measurements with the required SNR using a telescope aperture so small that the entire instrument can fit on a 3U
CubeSat. Small single purpose imager modules like this could be used to supplement much larger systems like
VIIRS by providing measurements of scientifically important bands not in VIIRS like the MODIS chlorophyll
fluorescence and near-infrared water vapor bands and fill possible gaps in measurement continuity not provided by
future systems or resulting from program delays.