Research Overview

We are interested in nanophotonic device concepts and circuit design motivated by challenges in system level applications in areas including telecommunications, on-chip interconnects, sensing and imaging, energy conversion and control, and classical and quantum computation and information processing. We are generally interested in first-principles innovation in device design using new physical principles in photonics as well as at the interface of nanophotonics, nanomechanics, solid-state and quantum electronics, and other fields. Our research involves rigorous theory and design of novel devices and concepts, and the experimental study and characterization of fabricated proof-of-concept device chips.

Areas of current research focus

Advanced CMOS photonic integration

Energy-efficient silicon photonic and optoelectronic devices for on-chip interconnects

Nonlinear and quantum photonics

For advanced light sources, quantum communication/computation/metrology/sensing, quantum simulation

Light-force nanophotonics

Nanomechanical photonics and light forces

Nano-optomechanical Photonics using Light Forces

An exciting new field of research is emerging at the interface of nanophotonics and nanomechanics. This field of research concerns light forces, forces due to the electric fields of the guided light itself in a nanophotonic waveguide or resonator. Because nanophotonic structures employ high index contrast or other mechanisms to confine light on a sub-wavelength length scale, it turns out that the optical forces are greatly enhanced compared to radiation pressure in the macroscopic world familiar to us (where radiation pressure due to light is negligible). Moreover, when we use a narrow-linewidth laser as the source of light, we can use high-Q resonators to further greatly enhance light forces. On the nanoscale, at the same time nanomechanical movable parts can be engineered as part of the photonic structure which have very low mass and inertia and can thus greatly be affected by the developed optical forces. One can control whether light forces are attractive or repulsive by design.

We have proposed a unique dual-cavity device geometry that allows enormous enhancement of light forces in a photonic structure, enabling microNewton-level achievable forces that can lead to a gamut of practical nanooptomechanical systems. We have also shown how this concept can be employed to design all-optical self-adaptive photonic devices in which light forces cause motion within the device, motion results in change of resonance frequencies, and this in turn changes the forces themselves. Among designs we have shown are a nanophotonic light-force trapping structure with very strong (10's of eV) trapping potentials, and a unique self-tuning resonator concept -- a resonator that self adjusts to become resonant with incident laser light.

The science and applications of nanooptomechanics and light-force photonics are in infancy, and this technology has the potential to impact a large number of application areas, as well as solve a number of important problems facing conventional nanophotonics, such as enormous sensitivity to dimensional variations and temperature. In particular, we are currently interested in the following areas:

  • Ultra-widely-tunable resonators and devices based on light forces
  • Nonlinear dynamics, all-optical feedback control and self-adaptive photonic devices
  • Nonlinear nanomechanical photonics for laser technology, telecom and on-chip interconnect applications
  • Light-force based photonic nanomotors
  • Optomechanical logic and computation
  • Quantum nanooptomechanical systems, ground state trapping and applications
  • Novel device concepts

We are currently carrying out some of this research in collaboration with Dr. Peter Rakich, Sandia National Labs. This research involves any or all of fundamental theoretical work, rigorous device design, and experimental work. For more information, see papers J12, I18, J15 and contact Milos Popovic.

Active and Passive Nanophotonic Devices for

Ultra-Energy-Efficient Communication and Computation

Nanophotonics may be able to address a number of major challenges in state-of-the-art microelectronics, as well as in next-generation telecom networks and future quantum information technologies including quantum communication and computation. We are interested in device-level innovation that addresses major technological and fundamental challenges in these areas.

Energy efficiency and power constraints are the factors limiting performance in modern electronic circuit design. Nanophotonics may in principle be able to provide energy efficient on-chip communication, but current photonic device technologies are far too power hungry. Revolutionary device concepts and innovation are needed to achieve highly energy efficient devices that can enable future link budgets of a few femtojoules per bit. We are interested in new concepts and implementations of ultra-energy-efficient nanophotonic components for on-chip networks and communication links, including:

  • Energy-efficient modulators and hitless switches for on-chip interconnects, analog signal processing and remote sensing
  • High-fidelity passive components for on-chip communication such as waveguide crossing arrays, crossbars and switches
  • High-efficiency fiber-chip and die-to-die optical waveguide coupling
  • Ultra-sensitive CMOS-compatible detectors

We have previously demonstrated the first high-index-contrast telecom-grade channel add-drop filters, the first polarization transparent nanophotonic circuit and true-hitless switch. In addition, we have designed novel nanophotonic devices that can be fabricated for the first time directly in CMOS technology used to fabricate state-of-the-art electronics like CPUs and DRAM. In previous work, we demonstrated the first nanophotonic devices in a 65nm bulk-Si CMOS process, and designed another chip recently fabricated in a 32nm process, through a collaboration with Profs. V. Stojanovic and R. Ram at MIT.

This research involves any or all of fundamental theoretical work, rigorous device design, and experimental device characterization. For more information, see papers I8, I6, C24 and contact Milos Popovic.

Nanophotonic Engineering and Control of Optical Radiation

Beam forming and phased array concepts are well-known in microwave engineering. In the optical regime, there are new opportunities for leveraging these techniques, as well as new physics concepts to be employed to control far-field radiation. Diffractive nanophotonic elements have already been designed to provide efficient fiber-to-chip coupling through mode matching. However, nanophotonic phased array concepts may have numerous other potential applications, from 3D imaging and sensing, through optical trapping and chip-scale quantum computing, to maskless lithography.

We are interested in the design of novel nanophotonic radiative elements and devices that may address some of these technological opportunities. This research involves fundamental theoretical work, rigorous device design, and experimental work. For more information on these projects, please contact Milos Popovic.

Photonic Circuit Theory

We are always interested in establishing the fundamental limitations on devices that rely on the physics of light. This also leads to insights into new device concepts and technologies (such as time-variant and nonlinear systems like light-force-based nanooptomechanics) which may not share all of the established limitations. For example, we have established a fundamental bound on a geometrical phase of the scattering matrix of a generic lossy photonic circuit. This concept offers guidance in the design of efficient nanophotonic circuits, e.g. filters based on microring resonators. Similar considerations have led to the invention of loop-coupled resonant filters that can circumvent Kramers-Kronig amplitude-dispersion constraints, and of a new class of interferometers called universally balanced interferometers (UBIs).

We are also pursuing new research in a number of other directions that are not large enough to categorize as a separate area above. For more information on these and other projects, please contact Milos Popovic.

Dual-microring nanophotonic light-force system (photo)
Dual-microring resonator nanophotonic system designed to trap nanomechanical movable parts using light forces (paper J12).

Light force trapping potential (photo) Light forces paper (photo)
Design of a trapping potential using light forces in a dual microring cavity; decorating the journal cover (paper J12).

Dispersionless delay line (photo)
Loop-coupled resonator concept also enables dispersionless slow-light structures that circumvent fundamental Kramers-Kronig constraints (papers C18).

Modulator design (photo)
Novel approach and design of an optimal resonant nanophotonic modulator (paper C31).

Nanophotonic grating coupler (photo)
Directional nanophotonic fiber-chip coupler based on phased-array concept (paper C17).

Characteristic phase inequality (photo)
A new, fundamental theoretical phase constraint for electromagnetic devices with loss.

Universally balanced interferometers (photo)
Universally balanced interferometer (UBI), a general new class of interferometer with fixed arm lengths and arbitrary "mirrors" (paper J9).