Research

Drake Lab research is in the intersection of experimental nonlinear optics and integrated photonics, and we specialize in Kerr-microresonator optical frequency combs. 

Optical frequency combs, whose invention at the turn of the 21st century led to the 2005 Nobel Prize in physics, have revolutionized the fields of precision measurement and spectroscopy. Today, optical frequency combs are used to identify trace amounts of gas (e.g. biomarkers in medical diagnostics and methane leaks over oil fields), in stellar spectroscopy to detect exoplanets, and in conjunction with atomic clocks and other frequency standards to observe and measure the fundamental constants of nature.

Until recently, building and operating an optical frequency comb was a large and expensive endeavor, requiring a specialized optics laboratory, complex equipment, and optics experts to keep the comb operational. However, a new type of comb, the Kerr-microresonator optical frequency comb, is changing that. Kerr-microcombs are formed in microscopic ring-shaped waveguides printed on silicon chips, and these photonic rings can be mass-produced using tools and techniques developed for semiconductors and microelectronics.

Our group studies the physical processes that influence optical frequency combs in nanoscale structures. We investigate nonlinear optical phenomena in novel materials and geometries in order to shape microcomb spectra and to extend microcomb technology to new wavelengths—specifically to the shorter wavelengths associated with atomic qubits (critical for quantum information) and optical clocks. In another project, we investigate the fundamental dynamics of comb formation at the nanoscale, including understanding and mitigating fundamental noise processes that limit comb accuracy. Our group is also proud to be part of several larger collaborations that integrate microresonator combs with other on-chip photonic devices to create compact laboratory-on-a-chip analogs for table-top equipment and experiments.

Fundamental thermal noise in microcombs

For many precision measurement devices, a fundamental limitation comes from thermal energy (temperature and heat). The Fluctuation-Dissipation Theorem is an important underpinning principle in physics that explains how any grouping of matter in equilibrium will continuously be exchanging heat energy with other energies in the system (e.g. motion, electrical, etc.), causing fast fluctuations (i.e. ‘noise’) in the temperature of any system element. This energy exchange results in an uncertainty in any system property that depends on temperature; this can include resistance, size, or refractive index. A famous example of temperature limiting precision measurements comes from the Laser Interferometer Gravitational Wave Observatory (LIGO). In LIGO, laser light is sent along an eight kilometer path. In LIGO’s original design, thermally-driven fluctuations in the thickness and index of refraction in the coatings on LIGO’s mirrors (both of which change the time it takes light to travel through LIGO) were found to limit the system’s ability to detect the small signals coming from gravitational waves. Kerr-microresonators, which send light in a loop of only 140 microns, ten billionths the length of the LIGO light path, are nevertheless also fundamentally limited by thermally-driven fluctuations.

We study the effect of thermodynamics on microcomb light. Surprisingly, although the material that the microresonator is made from follows very exactly the laws of thermodynamics and the Fluctuation-Dissipation Theorem, the effects of thermal fluctuations on the light can be much more variable and complex. Even in the same resonator, two different combs can be made with different amounts of thermal noise. We are interested in exploiting this idea to design resonators with lower thermal noise in the comb.

Related reading on thermal noise in microresonator combs from Drake and colleagues:

B. D. Stone, L. Rukh, G. M. Colación, T. E. Drake, “Reduction of thermal instability of soliton states in coupled Kerr-microresonators,” APL Photonics 10, 051301 (2025).

T. E. Drake, J.R. Stone, T. C. Briles, and S. B. Papp, "Thermal decoherence and laser cooling of a Kerr-microresonator soliton," Nature Photonics 14, 480-485 (2020).

Microcombs design: extending to new wavelengths

Despite numerous successes of microcombs over the last decade, microcomb technology has mostly remained in the telecom wavelengths, where light sources are plentiful and integrated photonics technology is more mature. This is a critical lack in the field, as many comb applications require visible spectrum light. Importantly, the ultra-precise atomic transitions used as the frequency standards for optical atomic clocks are typically at visible and near-visible wavelengths. Optical frequency combs serve as the “clockwork” for atomic clocks, allowing electronic readout of the optical clock frequency, but the comb light must somehow overlap with the clock wavelength.

My group is pursuing several directions to develop microcomb technology at shorter wavelengths. We have a few projects in which we push the limits of dispersion engineering in silicon nitride (SiN) to create combs with spectra that include visible wavelengths. We also are exploring novel materials for visible nonlinear photonics, such as tantalum pentoxide (tantala) and lithium niobate (LN).

For Drake Lab microcombs extending to wavelengths below 800 nm, see:

G. Colación, L. Rukh, T. Melton, A. Aldhafeeri, H.-H. Chin, C. W. Wong, and T. E. Drake, “Design and realization of octave-spanning, low fceo microcombs at sub-telecom wavelengths in silicon nitride,” in CLEO 2024, Technical Digest Series (Optica Publishing Group, 2024), paper SF1P.3.

Microcombs are an example of integrated photonics technology, where optical devices, such as lasers, waveguides, and photodetectors, are miniturized and combined on a quasi-2D chip. These Photonic Integrated Circuits (PICs) move and manipulate light similar to how electronic integrated circuits (ICs) handle electrons. When experts in different integrated photonics technology work together, we can create compact PICs the size of computer chips that have the functionality of an entire optics table in an academic lab. With small footprints, lower power requirements, and the ability to mass-produce using existing foundry processes, integrated photonics has the potential to take specialized optical measurements far from the research lab and into our communities, impacting medical diagnostics, communications technology, manufacturing quality control, and navigation.

Our group is currently collaborating with integrated photonics researchers and developers at Sandia National Labs, Air Force Research Labs, University of Delaware, and UCLA. We are always looking for new partners to exciting discuss comb-enabled projects.

Integrated photonics collaborations that Drake has been involved in include:

Z. L. Newman, V. Maurice, T. E. Drake, J. R. Stone, T. C. Briles, D. T. Spencer, C. Fredrick, Q. Li, D. Westly, B. R. Ilic, B. Shen, M. -G. Suh, K. Y. Yang, C. Johnson, D. M. S. Johnson, L. Hollberg, K. Vahala, K. Srinivasan, S. A. Diddams, J. Kitching, S. B. Papp, M. T. Hummon, "Architecture for the photonic integration of an optical atomic clock," Optica 6, 680-685 (2019).

D. T. Spencer, T. Drake, T. C. Briles, J. Stone, L. C. Sinclair, C. Fredrick, Q. Li, D. Westly, B. R. Ilic, A. Bluestone, N. Volet, T. Komljenovic, L. Chang, S. H. Lee, D. Y. Oh, M.-G. Suh, K. Y. Yang, M. H. P. Pfeiffer, T. J. Kippenberg, E. Norberg , L. Theogarajan, K. Vahala, N. R. Newbury , K. Srinivasan, J. E. Bowers, S. A. Diddams, and S. B. Papp, "An optical-frequency synthesizer using integrated photonics," Nature 557, 81-85 (2018).