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3 Questions Interview

Photonics Spectra
Nov 2016
Walter Buell, principal director of the Electronics and Photonics Laboratory at The Aerospace Corp. in California, first became interested in lasers and optics more than 30 years ago. When his high school physics teacher allowed him to teach a lab class on interference and diffraction, he “was hooked.”

Walter Buell
Photo courtesy of The Aerospace Corp.

Buell studied physics and optics as an undergrad, and began to engage in the research environment. Since then, his work has been mainly in the application of lasers in atomic physics, such as laser cooling and atomic clocks, and in laser remote sensing — principally in synthetic aperture ladar.

Photonics Spectra spoke with Buell about advances in the lasers field, and what he anticipates for the future.

Q: What are some innovative, exciting advancements you are seeing with lasers, and how are they helping to evolve the field?

A: Two of the major evolutions in laser technology today are: 1) capability for fairly dramatic reductions in size, weight and power (SWaP) requirements, and 2) increased flexibility in wavelength and temporal waveform. New materials and advances in sources like quantum cascade lasers are enabling field and commercial applications that used to be the purview of academic labs. Hybrid architecture lasers (for example, semiconductor laser seeds amplified by fiber and bulk amplifiers) enable long-range communications and remote sensing with advanced waveforms and the potential for electrical efficiency exceeding 30 percent.

At the cutting edge of such low SWaP, high-performance sources are chip-scale integrated photonics where lasers, modulators, frequency converters, and so on, can be integrated onto a single photonic chip via monolithic or heterogeneous integration. Quasi phase-matched materials are realizing their potential for high-efficiency nonlinear wavelength conversion at power levels sufficient to support a wide range of applications in laser sensing. A decade ago I had a tongue-in-cheek line in a journal paper to the effect that “generally, tunable sources are not sufficiently stable and stable sources are not broadly tunable.” Clearly, laser technology has advanced to the point where this is no longer true, and laser sources are available as commercial products with performance only dreamed of a few years ago.

Q: What new applications are laser technologies finding?

A: Laser remote sensing — for example, laser radar — had been an important application area almost since the invention of the laser, but recent advances in laser and detector technology have enabled a proliferation of applications. Examples include lidar altimetry from space, airborne lidar mapping, and even “lidar on a chip.” The advances in high-efficiency, compact and robust fiber lasers [are] beginning to make inroads into laser communications from and in space, with multiwatt high-bandwidth lasers being small enough to fit into CubeSat pico- and nanosatellites.

Advances in complex and high-performance but low-SWaP lasers is taking laser spectroscopy out of the lab, into the field and beyond the bounds of Earth. Already, laser-induced breakdown spectroscopy has been used in an instrument on the surface of Mars, and new missions that require compact and efficient multiwavelength systems are being developed for lunar and interplanetary petrochronology instruments.

In addition to SWaP improvements, integrated photonic technology enables dramatic potential for functional consolidation of photonics-based devices, including atomic time/frequency references and optical signal processing devices. One example is wide-band photonic receivers for RF [radio frequency] compressive sensing, where integrated photonic circuits are being investigated to replace free-space optics, and yield order-of- magnitude reductions in sensor system size and weight with full retention of sensing capability. Another potential outlet for photonic integrated circuitry is high-performance chip-scale atomic clocks, where the generation and stabilization of clock signals require a high degree of control over pump lasers and spectroscopy-based health and status monitors.

Q: What do you foresee for the future of laser technology and potential applications?

A: One exciting area I see is the integration of lasers and other photonic elements into the Internet of Things for sensing, networked communication and high-bandwidth/high-speed signal processing. This involves lasers not as stand-alone elements, but fully integrated elements of complex systems. The capabilities of advanced laser technologies also depend critically on advances in other technology areas. For example, recent advances in lidar mapping depends at least as much on development of high-bandwidth photon-counting detector arrays as on laser development, and on advances in computing capability, algorithm development and data fusion with other sensors.

Other application areas for laser technology, such as medicine and materials processing, are not new but are likely to benefit from accelerating improvements in laser performance capability and reliability. In laser manufacturing, process optimizations are likely to invoke novel laser performance capabilities in the temporal waveforms and instantaneous powers that can be applied toward long-standing objectives such as material deposition and removal, surface treatments and fatigue mitigations, particularly in specialty materials unique to specific markets.


GLOSSARY
lidar
An acronym of light detection and ranging, describing systems that use a light beam in place of conventional microwave beams for atmospheric monitoring, tracking and detection functions. Ladar, an acronym of laser detection and ranging, uses laser light for detection of speed, altitude, direction and range; it is often called laser radar.
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