Erman Timurdogan

Large-scale nanophotonic phased array

Electromagnetic phased arrays at radio frequencies are well known and have enabled applications ranging from communications to radar, broadcasting and astronomy. The ability to generate arbitrary radiation patterns with large-scale phased arrays has long been pursued. Although it is extremely expensive and cumbersome to deploy large-scale radiofrequency phased arrays, optical phased arrays have a unique advantage in that the much shorter optical wavelength holds promise for large-scale integration. However, the short optical wavelength also imposes stringent requirements on fabrication. As a consequence, although optical phased arrays have been studied with various platforms and recently with chip-scale nanophotonics, all of the demonstrations so far are restricted to one-dimensional or small-scale two-dimensional arrays. Here we report the demonstration of a large-scale two-dimensional nanophotonic phased array (NPA), in which 64 × 64 (4,096) optical nanoantennas are densely integrated on a silicon chip within a footprint of 576 μm × 576 μm with all of the nanoantennas precisely balanced in power and aligned in phase to generate a designed, sophisticated radiation pattern in the far field. We also show that active phase tunability can be realized in the proposed NPA by demonstrating dynamic beam steering and shaping with an 8 × 8 array. This work demonstrates that a robust design, together with state-of-the-art complementary metal-oxide–semiconductor technology, allows large-scale NPAs to be implemented on compact and inexpensive nanophotonic chips. In turn, this enables arbitrary radiation pattern generation using NPAs and therefore extends the functionalities of phased arrays beyond conventional beam focusing and steering, opening up possibilities for large-scale deployment in applications such as communication, laser detection and ranging, three-dimensional holography and biomedical sciences, to name just a few.

A Monolithically-Integrated Chip-to-Chip Optical Link in Bulk CMOS

Silicon-photonics is an emerging technology that can overcome the tradeoffs faced by traditional electrical I/O. Due to ballooning development costs for advanced CMOS nodes, however, widespread adoption necessitates seamless photonics integration into mainstream processes, with as few process changes as possible. In this work, we demonstrate a silicon-photonic link with optical devices and electronics integrated on the same chip in a 0.18 µm bulk CMOS memory periphery process. To enable waveguides and optics in process-native polysilicon, we introduce deep-trench isolation, placed underneath to prevent optical mode leakage into the bulk silicon substrate, and implant-amorphization to reduce polysilicon loss. A resonant defect-trap photodetector using polysilicon eliminates need for germanium integration and completes the fully polysilicon-based photonics platform. Transceiver circuits take advantage of photonic device integration, achieving 350 fJ/b transmit and 71 µA pp BER = 10 -12 receiver sensitivity at 5 Gb/s. We show high fabrication uniformity and high-Q resonators, enabling dense wavelength-division multiplexing with 9-wavelength 45 Gb/s transmit/receive data-rates per waveguide/fiber. To combat perturbations to variation- and thermally-sensitive resonant devices, we demonstrate an on-chip thermal tuning feedback loop that locks the resonance to the laser wavelength. A 5 m optical chip-to-chip link achieves 5 Gb/s while consuming 3 pJ/b and 12 pJ/bit of circuit and optical energy, respectively.

Automated wavelength recovery for microring resonators

We lock an adiabatic microring resonator to a laser line with a lock-in time of 200μs using a digital control loop, thereby experimentally demonstrating the first automated and scalable wavelength recovery approach for microring resonators.

Large-scale silicon nitride nanophotonic phased arrays at infrared and visible wavelengths

We demonstrate passive large-scale nanophotonic phased arrays in a CMOS-compatible silicon photonic platform. Silicon nitride waveguides are used to allow for higher input power and lower phase variation compared to a silicon-based distribution network. A phased array at an infrared wavelength of 1550 nm is demonstrated with an ultra-large aperture size of 4  mm×4  mm, achieving a record small and near diffraction-limited spot size of 0.021°×0.021° with a side lobe suppression of 10 dB. A main beam power of 400 mW is observed. Using the same silicon nitride platform and phased array architecture, we also demonstrate, to the best of our knowledge, the first large-aperture visible nanophotonic phased array at 635 nm with an aperture size of 0.5  mm×0.5  mm and a spot size of 0.064°×0.074°.

Demonstration of an Optical Chip-to-Chip Link in a 3D Integrated Electronic-Photonic Platform

A full optical chip-to-chip link is demonstrated for the first time in a wafer-scale heterogeneous platform, where the photonics and CMOS chips are 3D integrated using wafer bonding and low-parasitic capacitance thru-oxide vias (TOVs). This development platform yields 1000s of functional photonic components as well as 16M transistors per chip module. The transmitter operates at 6Gb/s with an energy cost of 100fJ/bit and the receiver at 7Gb/s with a sensitivity of 26μA (-14.5dBm) and 340fJ/bit energy consumption. A full 5Gb/s chip-to-chip link, with the on-chip calibration and self-test, is demonstrated over a 100m single mode optical fiber with 560fJ/bit of electrical and 4.2pJ/bit of optical energy.

Four-port integrated polarizing beam splitter.

In this Letter, we report on the first integrated four-port polarizing beam splitter. The device operates on the principle of mode evolution and was implemented in a silicon-on-insulator silicon photonics platform and fabricated on a 300 mm CMOS line using 193 nm optical immersion lithography. The adiabatic transition forming of the structure enabled over a 150 nm bandwidth from λ~1350 to λ~1500  nm, achieving a cross-talk level below -10  dB over the entire band.

Large-Scale Silicon Photonic Circuits for Optical Phased Arrays

We review recent advances in integrated large-scale optical phased arrays. The design and fabrication of large-scale optical phased arrays using silicon photonic circuits are discussed from device designs including the directional couplers, thermo-optic phase shifters, and optical nanoantennas, to system studies including phased array synthesis and noise analysis. By taking advantage of the well-developed silicon complementary metal-oxide-semiconductor (CMOS) fabrication technology, several large-scale integrated silicon photonic phased arrays are demonstrated, including two passive-phased arrays (64 × 64 and 32 × 32) with the ability to generate complex holographic images, an 8 × 8 active phased array for dynamic optical beamforming, and an 8 × 8 active antenna array with amplitude apodization. These optical phased array demonstrations, with up to 12 000 integrated optical elements, represent the largest and densest silicon photonic circuits demonstrated to date.

Vertical emitting aperture nanoantennas

Herein we propose, theoretically investigate, and numerically demonstrate a compact design for a vertical emitter at a wavelength of 1.5 μm based on nanophotonic aperture antennas coupled to a dielectric waveguide. The structure utilizes a plasmonic antenna placed above a Si3N4 waveguide with a ground plane for breaking the up-down symmetry and increasing the emission efficiency. Three-dimensional (3-D) finite-difference time-domain (FDTD) simulations reveal that up to 60% vertical emission efficiency is possible in a structure only four wavelengths long with a 3 dB bandwidth of over 300 nm.

An Interior-Ridge Silicon Microring Modulator

We design and demonstrate a new microring modulator geometry utilizing low-resistance interior ridge contacts and a hard outer waveguide wall to achieve high-speed operation in a device with a large free spectral range (FSR). The depletion-mode silicon microring modulator utilizes a hybrid vertical-horizontal junction to maximize the frequency response for a given voltage within a compact 2.5 μm radius. The 2.5-μm radius microring modulator demonstrates low energy (4.5 fJ/bit) error-free (bit error rate <;10 -12) operation for 30 Gb/s nonreturn-to-zero data transmission without utilizing preemphasis or equalization. The modulator exhibits single mode operation over a wide, uncorrupted FSR of 5.3 THz, the largest reported in a high-speed (>25 Gb/s) modulator. The resulting combination of high-speed, low-energy operation, and a wide FSR offers the potential for very high bandwidth densities in future femtojoule-class communication links.

C-band swept wavelength erbium-doped fiber laser with a high-Q tunable interior-ridge silicon microring cavity

We demonstrate an erbium-doped fiber laser with a tunable silicon microring cavity. We measured a narrow laser linewidth (16 kHz) and single-mode continuous-wave emission over the C-band (1530nm-to-1560nm) at a swept-wavelength rate of 22,600nm/s or 3106THz/s.