Publications

2017
Quantum Interference between Transverse Spatial Waveguide Modes
Mohanty, Aseema, Mian Zhang, Avik Dutt, Sven Ramelow, Paulo Nussenzveig, and Michal Lipson. “Quantum Interference between Transverse Spatial Waveguide Modes.” Nature Communications 8 (2017): 14010. Publisher's Version Abstract
Integrated quantum optics has the potential to markedly reduce the footprint and resource requirements of quantum information processing systems, but its practical implementation demands broader utilization of the available degrees of freedom within the optical field. To date, integrated photonic quantum systems have primarily relied on path encoding. However, in the classical regime, the transverse spatial modes of a multi-mode waveguide have been easily manipulated using the waveguide geometry to densely encode information. Here, we demonstrate quantum interference between the transverse spatial modes within a single multi-mode waveguide using quantum circuit-building blocks. This work shows that spatial modes can be controlled to an unprecedented level and have the potential to enable practical and robust quantum information processing.
quantum_interference_between_transverse_spatial_waveguide_modes.pdf
2015
Okawachi, Yoshitomo, Mengjie Yu, Kevin Luke, Daniel O. Carvalho, Sven Ramelow, Alessandro Farsi, Michal Lipson, and Alexander L. Gaeta. “Dual-pumped degenerate Kerr oscillator in a silicon nitride microresonator.” Opt. Lett. 40 (2015): 5267–5270. Publisher's Version Abstract
We demonstrate a degenerate parametric oscillator in a silicon nitride microresonator. We use two frequency-detuned pump waves to perform parametric four-wave mixing and operate in the normal group-velocity dispersion regime to produce signal and idler fields that are frequency degenerate. Our theoretical modeling shows that this regime enables generation of bimodal phase states, analogous to the chi(2)-based degenerate OPO. Our system offers potential for realization of CMOS-chip-based coherent optical computing and an all-optical quantum random number generator.
okawachi_dual_pumped_kerr.pdf
Tunable frequency combs based on dual microring resonators
Miller, Steven A., Yoshitomo Okawachi, Sven Ramelow, Kevin Luke, Avik Dutt, Alessandro Farsi, Alexander L. Gaeta, and Michal Lipson. “Tunable frequency combs based on dual microring resonators.” Optics Express 23 (2015): 21527-21540. Publisher's Version Abstract
In order to achieve efficient parametric frequency comb generation in microresonators, external control of coupling between the cavity and the bus waveguide is necessary. However, for passive monolithically integrated structures, the coupling gap is fixed and cannot be externally controlled, making tuning the coupling inherently challenging. We design a dual-cavity coupled microresonator structure in which tuning one ring resonance frequency induces a change in the overall cavity coupling condition. We demonstrate wide extinction tunability with high efficiency by engineering the ring coupling conditions. Additionally, we note a distinct dispersion tunability resulting from coupling two cavities of slightly different path lengths, and present a new method of modal dispersion engineering. Our fabricated devices consist of two coupled high quality factor silicon nitride microresonators, where the extinction ratio of the resonances can be controlled using integrated microheaters. Using this extinction tunability, we optimize comb generation efficiency as well as provide tunability for avoiding higher-order mode-crossings, known for degrading comb generation. The device is able to provide a 110-fold improvement in the comb generation efficiency. Finally, we demonstrate open eye diagrams using low-noise phase-locked comb lines as a wavelength-division multiplexing channel. (C) 2015 Optical Society of America
miller_tunable_combs_oe_2015.pdf
2014
Ramelow, Sven, Alessandro Farsi, Stephane Clemmen, Jacob S. Levy, Adrea R. Johnson, Yoshitomo Okawachi, Michael R. E. Lamont, Michal Lipson, and Alexander L. Gaeta. “Strong polarization mode coupling in microresonators.” Optics Letters 39 (2014): 5134-5137. Publisher's Version Abstract
We observe strong modal coupling between the TE00 and TM00 modes in Si3N4 ring resonators revealed by avoided crossings of the corresponding resonances. Such couplings result in significant shifts of the resonance frequencies over a wide range around the crossing points. This leads to an effective dispersion that is one order of magnitude larger than the intrinsic dispersion and creates broad windows of anomalous dispersion. We also observe the changes to frequency comb spectra generated in Si3N4 microresonators due to polarization mode and higher-order mode crossings and suggest approaches to avoid these effects. Alternatively, such polarization mode crossings can be used as a tool for dispersion engineering in microresonators. (C) 2014 Optical Society of America
ramelow_pol_mode_coupling_2014.pdf