Caltech Postdoc Launch Seminar

Lunch will be served at 11:45 AM (RSVP only)

Dr. Shuman Sun

Optical Frequency Division on Photonic Chips for Stable Micro/mm-Wave Generation

Microwave and millimeter waves are extensively used in radar, communications, and radio astronomy. Nowadays, these applications demand higher resolution, faster data transmission, and broader bandwidth, driving microwave technologies to higher carrier frequencies and lower noise. Photonics microwave technologies stand out thanks to their inherent features of low loss at optical frequencies and high fractional frequency stability. Among these photonic micro/mm-wave oscillators, optical frequency division (OFD) technology has set the record for spectral purity. In OFD systems, optical frequencies can be coherently divided down to microwave frequencies, with frequency noise scaling down. This frequency down-conversion is linked by optical frequency combs, a series of optical frequencies with uniform comb line spacing at microwave frequencies. Combined with optical references, optical frequency combs can transfer the reference stability to the comb spacing. OFD systems have been developed over many years, but mostly with table-sized bulk devices. Excitingly, recent advances in integrated photonics have initiated a transformation towards miniaturized OFD systems with chip-scale.

This presentation will discuss integrated OFD systems on CMOS-compatible integrated photonic platforms. Here, a planar-waveguide-based optical reference coil cavity can provide frequency stability due to its low thermal refractive noise. The frequency stability is then transferred to a soliton frequency comb generated on a waveguide-coupled microresonator. As a result, these OFD demonstrations significantly miniaturize the systems and achieve state-of-the-art performance by setting a record for low noise in integrated photonic mmWaveoscillators. Moreover, the waveguide-based devices can be heterogeneously integrated in photonic circuits, facilitating large-volume, low-cost manufacturing for mass-market applications.

Dr. Temple He

Towards Observational Signatures of Quantum Gravity

The unification of gravity and quantum mechanics is currently one of the most important outstanding questions in theoretical physics at the moment. One of the difficulties is the lack of experiments to guide us since traditional methods of calculations using quantum field theory suggest that the size of the quantum fluctuations of gravity is given to be Planck sized. This is unfortunately many orders of magnitudes too small for any feasible experiment to probe in our lifetimes. In this talk, I will outline some recent progress that suggests that there may actually be hope to measure the size of quantum fluctuations due to new theoretical understandings of quantum field theories. I will also highlight an experiment being built at Caltech that will look for such quantum fluctuations of gravity.

For more information, please contact Sejun Kim by email at [email protected] or visit this link to fill up the form and nominate yourself as a speaker.