PhD Defense: "High-brightness lasers with spectral beam combining on silicon"

Eric Stanton

January 4th (Thursday), 12:30pm
Harold Frank Hall (HFH), Rm 4164

Modern implementations of absorption spectroscopy and infrared-countermeasures demand advanced performance and integration of high-brightness lasers, especially in the molecular fingerprint region. These applications, along with others in communication, remote-sensing, and medicine, benefit from the light source comprising a multitude of frequencies. To realize this technology, a single multi-spectral optical beam of near-diffraction-limited divergence is created by combining the outputs from an array of laser sources. Full integration of such a laser is possible with direct bonding of several epitaxially-grown chips to a single silicon (Si) substrate. In this platform, an array of lasers are defined with each gain material, creating a densely spaced set of wavelengths similar to wavelength division multiplexing used in communications.

Lasers that are both compact and high-brightness are challenging to engineer. As the size of the laser is reduced, either the output power or the beam quality are decreased, primarily due to a combination of thermal effects and high optical intensities. With heterogeneous integration, these limitations are fundamentally avoided. Recent demonstrations of 2.0-µm diode and 4.8-µm quantum cascade lasers on Si have extended this heterogeneous platform beyond the telecom band to the mid-infrared.

In this work, low-loss beam combining elements spanning the visible to the mid-infrared are developed and a high-brightness multi-spectral laser is demonstrated in the range of 4.6–4.7-µm wavelengths. An architecture is presented where light is combined in multiple stages: first within the gain-bandwidth of each laser material and then coarsely between each spectral band to a single output waveguide. All components are demonstrated on a common material platform with a Si substrate, which lends feasibility to the complete system integration. In particular, efforts are to made improve the efficiency of arrayed waveguide gratings (AWGs), used in the dense wavelength combining stage. This requires development of a refined characterization technique involving AWGs in a ring-resonator configuration to reduce measurement uncertainty. New levels of low-loss are achieved for visible, near-infrared, and mid-infrared multiplexing devices. Also, a multi-spectral laser in the mid-infrared is demonstrated by integrating an array of quantum cascade lasers and an AWG with Si waveguides. The output power and spectra are characterized, exhibiting efficient beam combining and power scaling. Thus, a bright light source in the mid-infrared has been demonstrated, along with an architecture and the components for incorporating visible and near-infrared optical bands.

About Eric Stanton:

photo of eric stantonEric J. Stanton received the B.S. degree in electrical engineering in 2012 from California Polytechnic State University San Luis Obispo, San Luis Obispo, CA, USA, and the M.S. degree in electrical and computer engineering in 2014 from the University of California, Santa Barbara, CA, USA, where he is currently working toward the Ph.D. degree with emphasis in photonics, focusing on devices for multi-octave spectral combining of heterogeneously integrated lasers on silicon.

Hosted by: John Bowers