Publications

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We use broken symmetry III-V semiconductor Fano metasurfaces to substantially improve the efficiency of second-harmonic generation (SHG) in the near infrared, compared to SHG obtained from metasurfaces created using symmetrical Mie resonators.

We report on mode selection and tuning properties of vertical-external-cavity surface-emitting lasers (VECSELs) containing coupled semiconductor and external cavities of total length less than 1 mm. Our goal is to create narrowlinewidth (<1MHz) single-frequency VECSELs that operate near 850 nm on a single longitudinal cavity resonance and tune versus temperature without mode hops. We have designed, fabricated, and measured VECSELs with external-cavity lengths ranging from 25 to 800 μm. We compare simulated and measured coupled-cavity mode frequencies and discuss criteria for single mode selection.

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Nonlinear optical phenomena in nanostructured materials have been challenging our perceptions of nonlinear optical processes that have been explored since the invention of lasers. For example, the ability to control optical field confinement, enhancement, and scattering almost independently allows nonlinear frequency conversion efficiencies to be enhanced by many orders of magnitude compared to bulk materials. Also, the subwavelength length scale renders phase matching issues irrelevant. Compared with plasmonic nanostructures, dielectric resonator metamaterials show great promise for enhanced nonlinear optical processes due to their larger mode volumes. Here, we present, for the first time, resonantly enhanced second-harmonic generation (SHG) using gallium arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical resonators we observe SHG enhancement factors as large as 104 relative to unpatterned GaAs. At the magnetic dipole resonance, we measure an absolute nonlinear conversion efficiency of ∼2 × 10-5 with ∼3.4 GW/cm2 pump intensity. The polarization properties of the SHG reveal that both bulk and surface nonlinearities play important roles in the observed nonlinear process.

Optical diagnostics play a central role in dynamic compression research. Currently, streak cameras are employed to record temporal and spectroscopic information in single-event experiments, yet are limited in several ways; the tradeoff between time resolution and total record duration is one such limitation. This project solves the limitations that streak cameras impose on dynamic compression experiments while reducing both cost and risk (equipment and labor) by utilizing standard high-speed digitizers and commercial telecommunications equipment. The missing link is the capability to convert the set of experimental (visible/x-ray) wavelengths to the infrared wavelengths used in telecommunications. In this report, we describe the problem we are solving, our approach, our results, and describe the system that was delivered to the customer. The system consists of an 8-channel visible-to- infrared converter with > 2 GHz 3-dB bandwidth.

Flip-chip heterogeneously integrated n-p-n InGaP/GaAs heterojunction bipolar transistors (HBTs) with integrated thermal management on wide-bandgap AlN substrates followed by GaAs substrate removal are demonstrated. Without thermal management, substrate removal after integration significantly aggravates self-heating effects, causing poor $I$-$V$ characteristics due to excessive device self-heating. An electrothermal codesign scheme is demonstrated that involves simulation (design), thermal characterization, fabrication, and evaluation. Thermoreflectance thermal imaging, electrical-temperature sensitive parameter-based thermometry, and infrared thermography were utilized to assess the junction temperature rise in HBTs under diverse configurations. In order to reduce the thermal resistance of integrated devices, passive cooling schemes assisted by structural modification, i.e., positioning indium bump heat sinks between the devices and the carrier, were employed. By implementing thermal heat sinks in close proximity to the active region of flip-chip integrated HBTs, the junction-to-baseplate thermal resistance was reduced over a factor of two, as revealed by junction temperature measurements and improvement of electrical performance. The suggested heterogeneous integration method accounts for not only electrical but also thermal requirements providing insight into realization of advanced and robust III-V/Si heterogeneously integrated electronics.

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We report on the development of single-frequency VCSELs (vertical-cavity surface-emitting lasers) for sensing the position of a moving MEMS (micro-electro-mechanical system) object with resolution much less than 1nm. Position measurement is the basis of many different types of MEMS sensors, including accelerometers, gyroscopes, and pressure sensors. Typically, by switching from a traditional capacitive electronic readout to an interferometric optical readout, the resolution can be improved by an order of magnitude with a corresponding improvement in MEMS sensor performance. Because the VCSEL wavelength determines the scale of the position measurement, laser wavelength (frequency) stability is desirable. This paper discusses the impact of VCSEL amplitude and frequency noise on the position measurement.

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This talk will discuss recent work on photonic integration for applications in optical signal processing, digital logic, and fundamental device research with an emphasis on InP-based photonic integrated circuit technology. © 2015 OSA.

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We present a filter consisting of cascaded ring resonators with integrated SOAs. The filter demonstrates an extinction ratio >30 dB, a free spectral range of 56 GHz and a FWHM bandwidth of 3 GHz. © 2010 Optical Society of America.

Vertical-cavity surface-emitting lasers (VCSELs) are well suited for emerging photonic microsystems due to their low power consumption, ease of integration with other optical components, and single frequency operation. However, the typical VCSEL linewidth of 100 MHz is approximately ten times wider than the natural linewidth of atoms used in atomic beam clocks and trapped atom research, which degrades or completely destroys performance in those systems. This report documents our efforts to reduce VCSEL linewidths below 10 MHz to meet the needs of advanced sub-Doppler atomic microsystems, such as cold-atom traps. We have investigated two complementary approaches to reduce VCSEL linewidth: (A) increasing the laser-cavity quality factor, and (B) decreasing the linewidth enhancement factor (alpha) of the optical gain medium. We have developed two new VCSEL devices that achieved increased cavity quality factors: (1) all-semiconductor extended-cavity VCSELs, and (2) micro-external-cavity surface-emitting lasers (MECSELs). These new VCSEL devices have demonstrated linewidths below 10 MHz, and linewidths below 1 MHz seem feasible with further optimization.

We present a photonic integrated circuit (PIC) composed of two strongly coupled distributed Bragg reflector (DBR) lasers. This PIC utilizes the dynamics of mutual injection locking to increase the relaxation resonance frequency from 3 GHz to beyond 30 GHz. Mutual injection-locking and external injection-locking operation are compared. © 2011 IEEE.