Griffith, Austin G., Ryan K. W. Lau, Jaime Cardenas, Yoshitomo Okawachi, Aseema Mohanty, Romy Fain, Yoon Ho Daniel Lee, et al.. “Silicon-chip mid-infrared frequency comb generation.” Nature Communications 6 (2015). Abstract
Optical frequency combs are a revolutionary light source for high-precision spectroscopy because of their narrow linewidths and precise frequency spacing. Generation of such combs in the mid-infrared spectral region (2-20 mm) is important for molecular gas detection owing to the presence of a large number of absorption lines in this wavelength regime. Microresonator-based frequency comb sources can provide a compact and robust platform for comb generation that can operate with relatively low optical powers. However, material and dispersion engineering limitations have prevented the realization of an on-chip integrated mid-infrared microresonator comb source. Here we demonstrate a complementary metal-oxide-semiconductor compatible platform for on-chip comb generation using silicon microresonators, and realize a broadband frequency comb spanning from 2.1 to 3.5 mm. This platform is compact and robust and offers the potential to be versatile for use outside the laboratory environment for applications such as real-time monitoring of atmospheric gas conditions.
Zhang, Mian, Shreyas Shah, Jaime Cardenas, and Michal Lipson. “Synchronization and Phase Noise Reduction in Micromechanical Oscillator Arrays Coupled through Light.” Physical Review Letters, 2015. Abstract
Synchronization of many coupled oscillators is widely found in nature and has the potential to revolutionize timing technologies. Here, we demonstrate synchronization in arrays of silicon nitride micromechanical oscillators coupled in an all-to-all configuration purely through an optical radiation field. We show that the phase noise of the synchronized oscillators can be improved by almost 10 dB below the phase noise limit for each individual oscillator. These results open a practical route towards synchronized oscillator networks.
Fridman, Moti, Yoshitomo Okawachi, Stephane Clemmen, Michael Menard, Michal Lipson, and Alexander L. Gaeta. “Waveguide-based single-shot temporal cross-correlator.” Journal of Optics 17 (2015). Abstract
We describe a novel technique for performing a single-shot optical cross-correlation in nanowaveguides. Our scheme is based on four-wave mixing (FWM) between two orthogonally polarized input signals propagating with different velocities due to polarization mode dispersion. The cross-correlation is determined by measuring the spectrum of the idler wave generated by the FWM process.
Guha, Biswajeet, and Michal Lipson. “Controlling thermo-optic response in microresonators using bimaterial cantilevers.” Optics Letters 40 (2015): 103-106. Abstract
We demonstrate a novel platform to control the thermo-optic sensitivity in nanophotonic devices by evanescent coupling of light with bimaterial cantilevers. The cantilever can be designed to provide a negative thermal feedback to passively compensate for the positive thermo-optic effect in the waveguide core. We demonstrate athermal operation over 14 deg in cantilever coupled Silicon ring resonators, limited only by fabrication tolerances. We also show how the same platform can provide positive thermal feedback and overcome the material thermo-optic limit for increasing sensitivity of resonant detectors and thermal imagers.
Graphene electro-optic modulator with 30 GHz bandwidth
Phare, Christopher T., Yoon-Ho Daniel Lee, Jaime Cardenas, and Michal Lipson. “Graphene electro-optic modulator with 30 GHz bandwidth.” Nature Photonics 9 (2015): 511. Abstract
Graphene has generated exceptional interest as an optoelectronic material(1,2) because its high carrier mobility(3,4) and broadband absorption(5) promise to make extremely fast and broadband electro-optic devices possible(6-9). Electro-optic graphene modulators previously reported, however, have been limited in bandwidth to a few gigahertz(10-15) because of the large capacitance required to achieve reasonable voltage swings. Here, we demonstrate a graphene electro-optic modulator based on resonator loss modulation at critical coupling(16) that shows drastically increased speed and efficiency. Our device operates with a 30 GHz bandwidth and with a state-of-the-art modulation efficiency of 15 dB per 10 V. We also show the first high-speed large-signal operation in a graphene modulator, paving the way for fast digital communications using this platform. The modulator uniquely uses silicon nitride waveguides, an otherwise completely passive material platform, with promising applications for ultra-low-loss broadband structures and nonlinear optics.
Shah, Shreyas Y., Mian Zhang, Richard Rand, and Michal Lipson. “Master-Slave Locking of Optomechanical Oscillators over a Long Distance.” Physical Review Letters 114 (2015): 113602. Publisher's Version Abstract
Frequency locking and other phenomena emerging from nonlinear interactions between mechanical oscillators are of scientific and technological importance. However, existing schemes to observe such behavior are not scalable over distance. We demonstrate a scheme to couple two independent mechanical oscillators, separated in frequency by 80 kHz and situated far from each other (3.2 km), via light. Using light as the coupling medium enables this scheme to have low loss and be extended over long distances. This scheme is reversible and can be generalized for arbitrary network configurations.
Stern, Brian, Xiaoliang Zhu, Christine P. Chen, Lawrence D. Tzuang, Jaime Cardenas, Keren Bergman, and Michal Lipson. “On-chip mode-division multiplexing switch.” Optica 2, no. 6 (2015): 530-535. Abstract
Leveraging the spatial modes of multimode waveguides using mode-division multiplexing on an integrated photonic chip allows unprecedented scaling of bandwidth density for on-chip communication. Switching channels between waveguides is critical for future scalable optical networks, but its implementation in multimode waveguides must address how to simultaneously control modes with vastly different optical properties. Here we present a platform for switching signals between multimode waveguides based on individually processing the spatial mode channels using single-mode elements. Using this wavelength-division multiplexing-compatible platform, we demonstrate a 1×2 multimode switch for a silicon chip that routes four data channels with low (<−16.8  dB) crosstalk. We show bit-error rates below 10−9 and power penalties below 1.4 dB on all channels while routing 10 Gb/s data when each channel is input and routed separately. The switch exhibits an additional power penalty of less than 2.4 dB when all four channels are simultaneously routed. These results enable individual processing of multimode signals and high-bandwidth, flexible optical networks.
Dutt, Avik, Kevin Luke, Sasikanth Manipatruni, Alexander L. Gaeta, Paulo Nussenzveig, and Michal Lipson. “On-Chip Optical Squeezing.” Physical Review Applied 3 (2015): 044005. Publisher's Version Abstract
We report the observation of all-optical squeezing in an on-chip monolithically integrated CMOScompatible platform. Our device consists of a low-loss silicon nitride microring optical parametric oscillator (OPO) with a gigahertz cavity linewidth. We measure 1.7 dB (5 dB corrected for losses) of subshot-noise quantum correlations between bright twin beams generated in the microring four-wave-mixing OPO pumped above threshold. This experiment demonstrates a compact, robust, and scalable platform for quantum-optics and quantum-information experiments on chip.
Cardenas, Jaime, Mengjie Yu, Yoshitomo Okawachi, Carl B. Poitras, Ryan K. W. Lau, Avik Dutt, Alexander L. Gaeta, and Michal Lipson. “Optical nonlinearities in high-confinement silicon carbide waveguides.” Optics Letters 40 (2015): 4138-4141. Publisher's Version Abstract
We demonstrate strong nonlinearities of n(2) = 8.6 +/- 1.1 x 10(-15) cm(2) W-1 in single-crystal silicon carbide (SiC) at a wavelength of 2360 nm. We use a high-confinement SiC waveguide fabricated based on a high-temperature smart-cut process. (C) 2015 Optical Society of America
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
Shah, S. Y., M. Zhang, R. Rand, and M. Lipson. “Synchronization of Delay-coupled Micromechanical Oscillators.” ArXiv e-prints (2015). Abstract
Delay-coupled oscillators exhibit unique phenomena that are not present in systems without delayed coupling. In this paper, we experimentally demonstrate mutual synchronisation of two free-running micromechanical oscillators, coupled via light with a total delay 139 ns which is approximately four and a half times the mechanical oscillation time period. This coupling delay, imposed by a finite speed of propagation of light, induces multiple stable states of synchronised oscillations, each with a different oscillation frequency. These states can be accessed by varying the coupling strengths. Our result could enable applications in reconfigurable radio-frequency networks, and novel computing concepts.
Okawachi, Yoshitomo, Michael R. E. Lamont, Kevin Luke, Daniel O. Carvalho, Mengjie Yu, Michal Lipson, and Alexander L. Gaeta. “Bandwidth shaping of microresonator-based frequency combs via dispersion engineering.” Optics Letters 39 (2014): 3535-3538. Publisher's Version Abstract
We investigate experimentally and theoretically the role of group-velocity dispersion and higher-order dispersion on the bandwidth of microresonator-based parametric frequency combs. We show that the comb bandwidth and the power contained in the comb can be tailored for a particular application. Additionally, our results demonstrate that fourth-order dispersion plays a critical role in determining the spectral bandwidth for comb bandwidths on the order of an octave. (C) 2014 Optical Society of America
St-Gelais, Raphael, Biswajeet Guha, Linxiao Zhu, Shanhui Fan, and Michal Lipson. “Demonstration of Strong Near-Field Radiative Heat Transfer between Integrated Nanostructures.” Nano Letters 14 (2014): 6971-6975. Publisher's Version Abstract
Near-field heat transfer recently attracted growing interest but was demonstrated experimentally only in macroscopic systems. However, several projected applications would be relevant mostly in integrated nanostructures. Here we demonstrate a platform for near-field heat transfer on-chip and show that it can be the dominant thermal transport mechanism between integrated nanostructures, overcoming background substrate conduction and the far-field limit (by factors 8 and 7, respectively). Our approach could enable the development of active thermal control devices such as thermal rectifiers and transistors.
Zhang, Mian, Gustavo Luiz, Shreyas Shah, Gustavo Wiederhecker, and Michal Lipson. “Eliminating anchor loss in optomechanical resonators using elastic wave interference.” Applied Physics Letters 105 (2014): 051904. Publisher's Version Abstract
Optomechanical resonators suffer from the dissipation of mechanical energy through the necessary anchors enabling the suspension of the structure. Here, we show that such structural loss in an optomechanical oscillator can be almost completely eliminated through the destructive interference of elastic waves using dual-disk structures. We also present both analytical and numerical models that predict the observed interference of elastic waves. Our experimental data reveal unstressed silicon nitride (Si3N4) devices with mechanical Q-factors up to 10(4) at mechanical frequencies of f = 102 MHz (fQ = 10(12)) at room temperature. (C) 2014 AIP Publishing LLC.
Zhu, Xiaoliang, Kishore Padmaraju, Lian-Wee Luo, Shu Yang, Madeleine Glick, Raj Dutt, Michal Lipson, and Keren Bergman. “Fast Wavelength Locking of a Microring Resonator.” IEEE Photonics Technology Letters 26 (2014): 2365-2368. Publisher's Version Abstract
Microring resonator devices require thermal initialization to match their intended operating wavelengths in a process called wavelength locking. We use the dither technique, where we apply a small periodic signal to the microring's integrated heater, to demonstrate reliable wavelength locking of a microring resonator filter to an operating wavelength at a wavelength shift rate of 0.012 nm/mu s, an order of magnitude faster than previous demonstrations. We also identify and characterize fundamental speed limits of the wavelength locking process, showing that the integrated-heater bandwidth is the limiting factor.
Cardenas, Jaime, Carl B. Poitras, Kevin Luke, Lian-Wee Luo, Paul Adrian Morton, and Michal Lipson. “High Coupling Efficiency Etched Facet Tapers in Silicon Waveguides.” IEEE Photonics Technology Letters 26 (2014): 2380-2382. Publisher's Version Abstract
We demonstrate a platform based on etched facet silicon inverse tapers for waveguide-lensed fiber coupling with a loss as low as 0.7 dB/facet. This platform can be fabricated on a wafer scale enabling mass-production of silicon photonic devices with broadband, high-efficiency couplers.
Tzuang, Lawrence D., Mohammad Soltani, Yoon Ho Daniel Lee, and Michal Lipson. “High RF carrier frequency modulation in silicon resonators by coupling adjacent free-spectral-range modes.” Optics Letters 39 (2014): 1799-1802. Publisher's Version Abstract
demonstrate the modulation of silicon ring resonators at RF carrier frequencies higher than the resonance line-width by coupling adjacent free-spectral-range (FSR) resonance modes. In this modulator scheme, the modulation frequency is matched to the FSR frequency. As an example, we demonstrate a 20 GHz modulation in a silicon ring with a resonance linewidth of only 11.7 GHz. We show theoretically that this modulator scheme has lower power consumption compared to a standard silicon ring modulator at high carrier frequencies. These results could enable future on-chip high-frequency analog communication and photonic signal processing on a silicon photonics platform. (C) 2014 Optical Society of America
Padmaraju, Kishore, Xiaoliang Zhu, Long Chen, Michal Lipson, and Keren Bergman. “Intermodulation Crosstalk Characteristics of WDM Silicon Microring Modulators.” IEEE Photonics Technology Letters 26 (2014): 1478-1481. Publisher's Version Abstract
We elaborate on and experimentally characterize the intermodulation crosstalk properties of a 10-Gb/s silicon microring modulator. Bit-error-rate measurements and eye diagrams are used to discern the degradation in signal quality due to intermodulation crosstalk. Evaluation of the power penalties with varying channel spacing are used to support wavelength-division-multiplexed cascaded microring modulator channel spacings as dense as 100 GHz with negligible expected intermodulation crosstalk.
Johnson, Adrea R., Yoshitomo Okawachi, Michael R. E. Lamont, Jacob S. Levy, Michal Lipson, and Alexander L. Gaeta. “Microresonator-based comb generation without an external laser source.” Optics Express 22 (2014): 1394-1401. Publisher's Version Abstract
We demonstrate a fiber-microresonator dual-cavity architecture with which we generate 880 nm of comb bandwidth without the need for a continuous-wave pump laser. Comb generation with this pumping scheme is greatly simplified as compared to pumping with a single frequency laser, and the generated combs are inherently robust due to the intrinsic feedback mechanism. Temporal and radio frequency (RF) characterization show a regime of steady comb formation that operates with reduced RF amplitude noise. The dual-cavity design is capable of being integrated on-chip and offers the potential of a turn-key broadband multiple wavelength source. (C) 2014 Optical Society of America
Soltani, Mohammad, Jun Lin, Robert A. Forties, James T. Inman, Summer N. Saraf, Robert M. Fulbright, Michal Lipson, and Michelle D. Wang. “Nanophotonic trapping for precise manipulation of biomolecular arrays.” Nature Nanotechnology 9 (2014): 448-452. Publisher's Version Abstract
Optical trapping is a powerful manipulation and measurement technique widely used in the biological and materials sciences(1-8). Miniaturizing optical trap instruments onto optofluidic platforms holds promise for high-throughput lab-on-a-chip applications(9-16). However, a persistent challenge with existing optofluidic devices has been achieving controlled and precise manipulation of trapped particles. Here, we report a new class of on-chip optical trapping devices. Using photonic interference functionalities, an array of stable, three-dimensional on-chip optical traps is formed at the antinodes of a standing-wave evanescent field on a nanophotonic waveguide. By employing the thermo-optic effect via integrated electric microheaters, the traps can be repositioned at high speed (similar to 30 kHz) with nanometre precision. We demonstrate sorting and manipulation of individual DNA molecules. In conjunction with laminar flows and fluorescence, we also show precise control of the chemical environment of a sample with simultaneous monitoring. Such a controllable trapping device has the potential to achieve high-throughput precision measurements on chip.