Tymon Barwicz

Fabrication and analysis of add-drop filters based on microring resonators in SiN

Add-drop filters based on microring resonators were fabricated in silicon-rich silicon nitride. Third-order microring filters showed an 80 GHz bandwidth, a 4 dB loss from input to drop, and a 24 nm free spectral-range.

High performance and highly uniform gate-all-around silicon nanowire MOSFETs with wire size dependent scaling

We demonstrate undoped-body, gate-all-around (GAA) Si nanowire (NW) MOSFETs with excellent electrostatic scaling. These NW devices, with a TaN/Hf-based gate stack, have high drive-current performance with NFET/PFET I<inf>DSAT</inf> = 825/950 µA/µm (circumference-normalized) or 2592/2985 µA/µm (diameter-normalized) at supply voltage V<inf>DD</inf> = 1 V and off-current I<inf>OFF</inf> = 15 nA/µm. Superior NW uniformity is obtained through the use of a combined hydrogen annealing and oxidation process. Clear scaling of short-channel effects versus NW size is observed.

Three-dimensional analysis of scattering losses due to sidewall roughness in microphotonic waveguides

We present a three-dimensional (3-D) analysis of scattering losses due to sidewall roughness in rectangular dielectric waveguides valid for any refractive-index contrast and field polarization. The analysis is based on the volume current method and uses array factors to introduce significant mathematical simplifications to better understand the influence of individual waveguide parameters on scattering losses. We show that the typical two-dimensional (2-D) analyses can substantially overestimate scattering losses in small waveguides and that scattering losses exhibit considerable polarization dependence. We produce scattering-loss estimates for a wide variety of waveguides and provide guidelines for design of waveguide cross sections that are less sensitive to sidewall roughness.

Multistage high-order microring-resonator add-drop filters

We propose and demonstrate a multistage design for microphotonic add-drop filters that provides reduced drop-port loss and relaxed tolerances for achieving high in-band extinction. As a result, the first microring-resonator filters with a rectangular notch stopband in the through port (to our knowledge) are shown, with extinctions exceeding 50 dB. Reaching 30 dB beyond previous results, without postfabrication trimming, such extinction levels open the door to microphotonic notch circuits for spectroscopy, wavelength conversion, and quantum cryptography applications. Combined with a low-loss, high-index-contrast electromagnetic design in SiN and frequency-matched microring resonators, this approach led to the first demonstration of flattop microphotonic filters meeting the stringent criteria for high-spectral-efficiency integrated add-drop multiplexers. The 40 GHz wide filters show a 20 nm free spectral range, 2 dB drop loss, and suppression of adjacent channels by over 30 dB.

A 90nm CMOS integrated Nano-Photonics technology for 25Gbps WDM optical communications applications

The first sub-100nm technology that allows the monolithic integration of optical modulators and germanium photodetectors as features into a current 90nm base high-performance logic technology node is demonstrated. The resulting 90nm CMOS-integrated Nano-Photonics technology node is optimized for analog functionality to yield power-efficient single-die multichannel wavelength-mulitplexed 25Gbps transceivers.

Fabrication of add-drop filters based on frequency-matched microring resonators

Frequency mismatches between resonators significantly impact the spectral responses of coupled resonator filters, such as high-order microring filters. In this paper, techniques allowing fabrication of frequency-matched high-index-contrast resonators are proposed, demonstrated, and analyzed. The main approach consists of inducing small dimensional changes in the resonators through alteration of the electron-beam dose used to expose either the actual resonator on a wafer or its image on a lithographic mask to be later used in filter fabrication. Third-order microring filters fabricated in silicon-rich silicon nitride, with optical resonator frequencies matched to better than 1 GHz, are reported. To achieve this, the average ring-waveguide widths of the microrings are matched to within less than 26 pm of a desired relative width offset. Furthermore, optimization and calibration procedures allowing strict dimensional control and smooth sidewalls are presented. A 5-nm dimensional control is demonstrated, and the standard deviation of sidewall roughness is reduced to below 1.6 nm.

Monolithic Silicon Integration of Scaled Photonic Switch Fabrics, CMOS Logic, and Device Driver Circuits

We demonstrate 4 × 4 and 8 × 8 switch fabrics in multistage topologies based on 2 × 2 Mach-Zehnder interferometer switching elements. These fabrics are integrated onto a single chip with digital CMOS logic, device drivers, thermo-optic phase tuners, and electro-optic phase modulators using IBMs 90 nm silicon integrated nanophotonics technology. We show that the various switch-and-driver systems are capable of delivering nanosecond-scale reconfiguration times, low crosstalk, compact footprints, low power dissipations, and broad spectral bandwidths. Moreover, we validate the dynamic reconfigurability of the switch fabric changing the state of the fabric using time slots with sub-100-ns durations. We further verify the integrity of high-speed data transfers under such dynamic operation. This chip-scale switching system technology may provide a compelling solution to replace some routing functionality currently implemented as bandwidth- and power-limited electronic switch chips in high-performance computing systems.

A 25 Gbps silicon microring modulator based on an interleaved junction.

A silicon microring modulator utilizing an interleaved p-n junction phase shifter with a V(π)L of 0.76 V-cm and a minimum off-resonance insertion loss of less than 0.2 dB is demonstrated. The modulator operates at 25 Gbps at a drive voltage of 1.6 V and 2-3 dB excess optical insertion loss, conditions which correspond to a power consumption of 471 fJ/bit. Eye diagrams are characterized at up to 40 Gbps, and transmission is demonstrated across more than 10 km of single-mode fiber with minimal signal degradation.

Maximizing the Thermo-Optic Tuning Range of Silicon Photonic Structures

We demonstrate 20 nm thermo-optic tuning in silicon microring resonators with 16 nm free spectral range (FSR), the largest reported full-FSR thermal tuning, with a tuning efficiency of 28 muW/GHz, enabling telecom microphotonic tunable filters.

Polarization rotator-splitters in standard active silicon photonics platforms

We demonstrate various silicon-on-insulator polarization management structures based on a polarization rotator-splitter that uses a bi-level taper TM0-TE1 mode converter. The designs are fully compatible with standard active silicon photonics platforms with no new levels required and were implemented in the IME baseline and IME-OpSIS silicon photonics processes. We demonstrate a polarization rotator-splitter with polarization crosstalk < -13 dB over a bandwidth of 50 nm. Then, we improve the crosstalk to < -22 dB over a bandwidth of 80 nm by integrating the polarization rotator-splitter with directional coupler polarization filters. Finally, we demonstrate a polarization controller by integrating the polarization rotator-splitters with directional couplers, thermal tuners, and PIN diode phase shifters.