arXiv subjects

Michal Lipson

Publications and source records attributed to Michal Lipson.

At least 91 records · Page 5Linked to original sources

arXiv2013

Observation of an Effective Magnetic field for Light

Photons are neutral particles that do not interact directly with a magnetic field. However, recent theoretical work has shown that an effective magnetic field for photons can exist if the phase of light would change with its propagating direction. This direction-dependent phase indicates the presence of an effective magnetic field as shown for electrons experimentally in the Aharonov-Bohm experiment. Here we replicate this experiment using photons. In order to create this effective magnetic field, we construct an on-chip silicon-based Ramsey-type interferometer. This interferometer has been traditionally used to probe the phase of atomic states, and here we apply it to probe the phase of photonic states. We experimentally observe a phase change, i.e. an effective magnetic field flux from 0 to 2pi. In an Aharonov-Bohm configuration for electrons, considering the device geometry, this flux corresponds to an effective magnetic field of 0.2 Gauss.

physics.optics↗

arXiv2013

High Q SiC microresonators

We demonstrate photonic devices based on standard 3C SiC epitaxially grown on silicon. We achieve high optical confinement by taking advantage of the high stiffness of SiC and undercutting the underlying silicon substrate. We demonstrate a 20 um radius suspended microring resonator with Q of 18000 fabricated on commercially available SiC-on-silicon substrates.

physics.optics↗

arXiv2013

Overcoming Si3N4 film stress limitations for High Quality factor ring resonators

Silicon nitride (Si3N4) ring resonators are critical for a variety of photonic devices. However the intrinsically high film stress of silicon nitride has limited both the optical confinement and quality factor (Q) of ring resonators. We show that stress in Si3N4 films can be overcome by introducing mechanical trenches for isolating photonic devices from propagating cracks. We demonstrate a Si3N4 ring resonator with an intrinsic quality factor of 7 million, corresponding to a propagation loss of 4.2 dB/m. This is the highest quality factor reported to date for high confinement Si3N4 ring resonators in the 1550 nm wavelength range.

physics.optics↗

arXiv2013

Simultaneous Mode and Wavelength Division Multiplexing On-Chip

Significant effort in optical-fiber research has been put in recent years into realizing mode-division multiplexing (MDM) in conjunction with wavelength-division multiplexing (WDM) to enable further scaling of the communication bandwidth per fiber. In contrast almost all integrated photonics operate exclusively in the single-mode regime. MDM is rarely considered for integrated photonics due to the difficulty in coupling selectively to high-order modes which usually results in high inter-modal crosstalk. Here we show the first demonstration of simultaneous on-chip mode and wavelength division multiplexing with low modal crosstalk and loss. Our approach can potentially increase the aggregate data rate by many times for on-chip ultra-high bandwidth communications.

physics.optics↗

arXiv2013

Deposited low temperature silicon GHz modulator

The majority of silicon photonics is built on silicon-on-insulator (SOI) wafers while the majority of electronics, including CPUs and memory, are built on bulk silicon wafers, limiting broader acceptance of silicon photonics. This discrepancy is a result of silicon photonics's requirement for a single-crystalline silicon (c-Si) layer and a thick undercladding for optical guiding that bulk silicon wafers to not provide. While the undercladding problem can be partially addressed by substrate removal techniques, the complexity of co-integrating photonics with state-of-the-art transistors and real estate competition between electronics and photonics remain problematic. We show here a platform for deposited GHz silicon photonics based on polycrystalline silicon with high optical quality suitable for high performance electro-optic devices. We demonstrate 3 Gbps polysilicon electro-optic modulator fabricated on a deposited polysilicon layer fully compatible with CMOS backend integration. These results open up an array of possibilities for silicon photonics including photonics on DRAM and flexible substrates.

physics.optics↗

arXiv2013

Transformation Inverse Design

We present a new technique for the design of transformation-optics devices based on large-scale optimization to achieve the optimal effective isotropic dielectric materials within prescribed index bounds, which is computationally cheap because transformation optics circumvents the need to solve Maxwell's equations at each step. We apply this technique to the design of multimode waveguide bends (realized experimentally in a previous paper) and mode squeezers, in which all modes are transported equally without scattering. In addition to the optimization, a key point is the identification of the correct boundary conditions to ensure reflectionless coupling to untransformed regions while allowing maximum flexibility in the optimization. Many previous authors in transformation optics used a certain kind of quasiconformal map which overconstrained the problem by requiring that the entire boundary shape be specified a priori while at the same time underconstraining the problem by employing "slipping" boundary conditions that permit unwanted interface reflections.

physics.optics↗

arXiv2013

Microresonator-Based Comb Generation without an External Laser Source

Recent developments demonstrate that parametric four-wave mixing (FWM) in high-Q microresonators is a highly promising and effective approach for optical frequency comb generation, with applications including spectroscopy, optical clocks, arbitrary waveform generation, frequency metrology, and astronomical spectrograph calibration. Each of these microresonator platforms utilizes a scheme in which the system is pumped by a single-frequency laser at a cavity resonance. This scheme requires tuning of the pump wavelength into resonance and the generated comb is susceptible to fluctuations in pump power or frequency which can disrupt the soft thermal lock and comb generation. We demonstrate a novel fiber-microresonator dual-cavity architecture that preferentially oscillates at modes of the microresonator due to its high density of states and generates robust and broadband combs (> 900 nm) without an external pump laser. Such a scheme could greatly simplify the comb generation process and allow for a fully-integrated chip-scale source with an on-chip amplifier.

physics.optics↗

arXiv2012

Device Considerations for Nanophotonic CMOS Global Interconnects

We introduce an analytical framework to understand the path for scaling nanophotonic interconnects to meet the energy and footprint requirements of CMOS global interconnects. We derive the device requirements for sub 100 fJ/cm/bit interconnects including tuning power, serialization-deserialization energy, optical insertion losses, extinction ratio and bit error rates. Using CMOS with integrated nanophotonics as an example platform, we derive the energy/bit, linear and areal bandwidth density of optical interconnects. We also derive the targets for device performance which indicate the need for continued improvements in insertion losses (<8dB), laser efficiency, operational speeds (>40 Gb/s), tuning power (<100 μW/nm), serialization-deserialization (< 10 fJ/bit/Operation) and necessity for spectrally selective devices with wavelength multiplexing (> 6 channels).

physics.optics↗

arXiv2012

Modelocking and Femtosecond Pulse Generation in Chip-Based Frequency Combs

Development of ultrashort pulse sources has had an immense impact on condensed-matter physics, biomedical imaging, high-field physics, frequency metrology, telecommunications, nonlinear optics, and molecular spectroscopy. Although numerous advancements of such sources have been made, it remains a challenge to create a highly compact, robust platform capable of producing femtosecond pulses over a wide range of wavelengths, durations, and repetition rates. Recent observations of frequency comb generation via cascaded parametric oscillation in microresonators11 suggest a path for achieving this goal. Here we investigate the temporal and spectral properties of parametric combs generated in silicon-nitride microresonators and observe a transition to passive modelocking of the comb consistent with soliton-pulse formation, resulting in the generation of 160-fs pulses at a 99-GHz repetition rate. This platform offers the prospect of producing pulses from 10 fs to a few ps at repetition rates from 10 GHz to > 1 THz and over a wavelength range of 0.8 - 6 μm.

physics.optics↗

arXiv2012

Synchronization of Micromechanical Oscillators Using Light

Synchronization, the emergence of spontaneous order in coupled systems, is of fundamental importance in both physical and biological systems. We demonstrate the synchronization of two dissimilar silicon nitride micromechanical oscillators, that are spaced apart by a few hundred nanometers and are coupled through optical radiation field. The tunability of the optical coupling between the oscillators enables one to externally control the dynamics and switch between coupled and individual oscillation states. These results pave a path towards reconfigurable massive synchronized oscillator networks.

physics.optics↗

arXiv2012

Perfect imaging in the optical domain using dielectric materials

The promise of perfect imaging in the optical domain, where light can be imaged without aberrations and with ultra-high resolution, could revolutionize technology and nanofabrication [1, 2, 3, 4, 5, 6]. Recently it has been shown theoretically that perfect imaging can be achieved in a dielectric medium with spatially varying refractive index [7, 8]. The lens geometry is defined using transformation optics [9, 10, 11, 12, 13, 14, 15] for projecting a spherical space onto a real plane space, forming Maxwells fish eye [16, 17, 18, 19]. Most transformation optics demonstrations have been achieved for Euclidean spaces and in the microwave regime, due to ease of fabrication. Here we demonstrate a transformation to a non-Euclidean space [20] in the optical regime using silicon nanophotonic structures.

physics.optics↗

arXiv2011

Electro-optical silicon isolator

We create a non-magnetic CMOS-compatible optical isolator on a silicon chip. The isolator is based on indirect interband photonic transition, induced by electrically-driven dynamic refractive index modulation. We demonstrate an electrically-induced non-reciprocity: the transmission coefficients between two single-mode waveguides become dependent on the propagation directions only in the presence of the electrical drive. The contrast ratio between forward and backward directions exceeds 30dB in simulations. We experimentally observe a strong contrast (up to 3 dB) limited only by our electrical setup, for a continuous-wave (CW) optical signal. Importantly, the device is linear with respect to signal light. The observed contrast ratio is independent of the timing, the format, the amplitude and the phase of the input signal.

physics.optics↗

arXiv2011

Octave-spanning frequency comb generation in a silicon nitride chip

We demonstrate a frequency comb spanning an octave via the parametric process of cascaded four-wave mixing in a monolithic, high-Q silicon nitride microring resonator. The comb is generated from a single-frequency pump laser at 1562 nm and spans 128 THz with a spacing of 226 GHz, which can be tuned slightly with the pump power. In addition, we investigate the RF-noise characteristics of the parametric comb and find that the comb can operate in a low-noise state with a 30-dB reduction in noise as the pump frequency is tuned into the cavity resonance.

physics.optics↗

arXiv2011

High-Performance Silicon-Based Multiple Wavelength Source

We demonstrate a stable CMOS-compatible on-chip multiple-wavelength source by filtering and modulating individual lines from a frequency comb generated by a microring resonator optical parametric oscillator.. We show comb operation in a low-noise state that is stable and usable for many hours. Bit-error rate measurements demonstrate negligible power penalty from six independent frequencies when compared to a tunable diode laser baseline. Open eye diagrams confirm the fidelity of the 10 Gb/s data transmitted at the comb frequencies and the suitability of this device for use as a fully integrated silicon-based WDM source.

physics.optics↗

arXiv2011

A Silicon-Based Monolithic Optical Frequency Comb Source

Recently developed techniques for generating precisely equidistant optical frequencies over broad wavelength ranges are revolutionizing precision physical measurement [1-3]. These frequency "combs" are produced primarily using relatively large, ultrafast laser systems. However, recent research has shown that broad-bandwidth combs can be produced using highly-nonlinear interactions in microresonator optical parametric oscillators [4-11]. Such devices not only offer the potential for developing extremely compact optical atomic clocks but are also promising for astronomical spectroscopy [12-14], ultrashort pulse shaping [15], and ultrahigh-speed communications systems. Here we demonstrate the generation of broad-bandwidth optical frequency combs from a CMOS-compatible integrated microresonator [16,17], which is a fully-monolithic and sealed chip-scale device making it insensitive to the surrounding environment. We characterize the comb quality using a novel self-referencing method and verify that the comb line frequencies are equidistant over a bandwidth that is nearly an order of magnitude larger than previous measurements. In addition, we investigate the ultrafast temporal properties of the comb and demonstrate its potential to serve as a chip-scale source of ultrafast (sub-ps) pulses.

physics.optics↗

arXiv2011

Broadband Tuning of Optomechanical Cavities

We demonstrate broadband tuning of an optomechanical microcavity optical resonance by exploring the large optomechanical coupling of a double-wheel microcavity and its uniquely low mechanical stiffness. Using a pump laser with only 13 mW at telecom wavelengths we show tuning of the silicon nitride microcavity resonances over 32 nm. This corresponds to a tuning power efficiency of only 400 $μ$W/nm. By choosing a relatively low optical Q resonance ($\approx$18,000) we prevent the cavity from reaching the regime of regenerative optomechanical oscillations. The static mechanical displacement induced by optical gradient forces is estimated to be as large as 60 nm.

physics.optics↗

arXiv2010

Second-Harmonic Generation in Silicon Nitride Ring Resonators

The emerging field of silicon photonics seeks to unify the high bandwidth of optical communications with CMOS microelectronic circuits. Many components have been demonstrated for on-chip optical communications, including those that utilize the nonlinear optical properties of silicon[1, 2], silicon dioxide[3, 4] and silicon nitride[5, 6]. Processes such as second harmonic generation, which are enabled by the second-order susceptibility, have not been developed since the bulk $χ^{(2)}$ vanishes in these centrosymmetric CMOS materials. Generating the lowest-order nonlinearity would open the window to a new array of CMOS-compatible optical devices capable of nonlinear functionalities not achievable with the?$χ^{(3)}$ response such as electro-optic modulation, sum frequency up-conversion, and difference frequency generation. Here we demonstrate second harmonic (SH) generation in CMOS compatible integrated silicon nitride (Si3N4) waveguides. The $χ^{(2)}$ response is induced in the centrosymmetric material by using the nanoscale structure to break the bulk symmetry. We use a high quality factor Q ring resonator cavity to enhance the efficiency of the nonlinear optical process and detect SH output with milliwatt input powers.

physics.optics↗

arXiv2010

Direction-dependent Optical Modes in Nanoscale Silicon Waveguides

On-chip photonic networks have the potential to transmit and route information more efficiently than electronic circuits. Recently, a number of silicon-based optical devices including modulators, buffers, and wavelength converts have been reported. However, a number of technical challenges need to be overcome before these devices can be combined into network-level architectures. In particular, due to the high refractive index contrast between the core and cladding of semiconductor waveguides, nanoscale defects along the waveguide often scatter light into the backward-propagating mode. These reflections could result in unwanted feedback to optical sources or crosstalk in bidirectional interconnects such as those employed in fiber-optic networks. It is often assumed that these reflected waves spatially overlap the forward-propagating waves making it difficult to implement optical circulators or isolators which separate or attenuate light based on its propagation direction. Here, we individually identify and map the near-field mode profiles of forward-propagating and reflected light in a single-mode silicon waveguide using Transmission-based near-field scanning optical microscopy (TraNSOM). We show that unlike fiber-optic waveguides, the high-index-contrast and nanoscale dimensions of semiconductor waveguides create counter propagating waves with distinct spatial near-field profiles. These near-field differences are a previously-unobserved consequence of nanoscale light confinement and could provide a basis for novel elements to filter forward-propagating from reflected light.

physics.optics↗