Jonathan Klamkin

Integrated Coherent Receivers for High-Linearity Microwave Photonic Links

In this paper, we present a coherent receiver based on an optical phase-locked loop (PLL) for linear phase demodulation. The receiver concept is demonstrated at low frequency. For high-frequency operation, monolithic and hybrid integrated versions of the receiver have been developed and experimentally verified in an analog link. The receiver has a bandwidth of 1.45 GHz. At 300 MHz, a spurious free dynamic range (SFDR) of 125 dB ldr Hz2/3 is measured.

High Output Saturation and High-Linearity Uni-Traveling-Carrier Waveguide Photodiodes

Waveguide uni-traveling-carrier photodiodes (UTC-PDs) have been fabricated and tested. Output saturation currents greater than 40 mA at 1 GHz are demonstrated for a 10 mumtimes150mum photodiode (PD). The third-order intermodulation distortion is also measured and exhibits a third-order output intercept point of 43 dBm at 20 mA and 34 dBm at 40 mA for this same PD. UTC-PDs with geometries of 5 mumtimes100 mum and 10 mumtimes100 mum are also compared and it is shown that a wider waveguide PD has improved saturation characteristics due to the lower optical power density which reduces the saturation at the front end of the device

High-Power, Low-Noise 1.5-μm Slab-Coupled Optical Waveguide (SCOW) Emitters: Physics, Devices, and Applications

We review the development of a new class of high-power, edge-emitting, semiconductor optical gain medium based on the slab-coupled optical waveguide (SCOW) concept. We restrict the scope to InP-based devices incorporating either InGaAsP or InGaAlAs quantum-well active regions and operating in the 1.5-μm-wavelength region. Key properties of the SCOW gain medium include large transverse optical mode dimensions (>;5 × 5 μm), ultralow optical confinement factor (Γ ~ 0.25-1%), and small internal loss coefficient (αi ~ 0.5 cm-1). These properties have enabled the realization of 1) packaged Watt-class semiconductor optical amplifiers (SOAs) having low-noise figure (4-5 dB), 2) monolithic passively mode-locked lasers generating 0.25-W average output power, 3) external-cavity fiber-ring actively mode-locked lasers exhibiting residual timing jitter of <;10 fs (1Hz to Nyquist), and 4) single-frequency external-cavity lasers producing 0.37-W output power with Gaussian (Lorentzian) linewidth of 35 kHz (1.75 kHz) and relative intensity noise (RIN) <; -160 dB/Hz from 200 kHz to 10 GHz. We provide an overview the SCOW design principles, describe simulation results that quantify the performance limitations due to confinement factor, linear optical loss mechanisms, and nonlinear two-photon absorption (TPA) loss, and review the SCOW devices that have been demonstrated and applications that these devices are expected to enable.

SOA Gate Array Recirculating Buffer for Optical Packet Switching

A compact recirculating buffer using an InP-based 2×2 switch with gain and a fiber delay line is demonstrated at 40 Gb/s. Packet throughput of 98% is measured for up to 8 circulations, or 0.18 μs.

A 100-Gb/s noncoherent silicon receiver for PDM-DBPSK/DQPSK signals

An integrated noncoherent silicon receiver for demodulation of 100-Gb/s polarization-division multiplexed differential quadrature phase-shift keying and polarization-division multiplexed differential binary phase-shift keying signals is demonstrated. The receiver consists of a 2D surface grating coupler, four Mach-Zehnder delay interferometers and four germanium balanced photodetectors.

Broadband Electroabsorption Modulators Design Based on Epsilon-Near-Zero Indium Tin Oxide

In this paper, we propose a compact silicon (Si) electroabsorption modulator based on a slot waveguide with epsilon-near-zero indium tin oxide materials. In order to integrate the device with low-loss Si strip waveguides, both butt-coupling and evanescent-coupling schemes are investigated. For both cases, our electroabsorption modulator demonstrates a high extinction ratio and a low insertion loss over a wide optical bandwidth.

RF Engineering Meets Optoelectronics: Progress in Integrated Microwave Photonics

Integrated microwave photonics (IMWP) is concerned with applying integrated photonics technology to microwave photonic systems. It is one of the most active and exciting areas of current research and development in microwave photonics (MWP), building upon the impressive foundations of integrated photonics in various systems involving material platforms such as indium phosphide (InP) and silicon nitride (Si3N4). The aim of this article is to explain to the wider microwave engineering community the significance of the new field of IMWP and to describe how it may potentially be applied to improve the performance and capabilities of microwave and millimeter-wave (mmWave) systems. Just as the microwave monolithic integrated circuit (MMIC) has revolutionized active microwave circuits, IMWP is poised to open up new applications for microwave engineering that take advantage of the unique functionalities offered by photonics, especially with regard to its large bandwidth.

Sharing and placement of on-chip laser sources in silicon-photonic NoCs

Silicon-photonic links are projected to replace the electrical links for global on-chip communications in future manycore systems. The use of off-chip laser sources to drive these silicon-photonic links can lead to higher link losses, thermal mismatch between laser source and on-chip photonic devices, and packaging challenges. Therefore, on-chip laser sources are being evaluated as candidates to drive the on-chip photonic links. In this paper, we first explore the power, efficiency and temperature tradeoffs associated with an on-chip laser source. Using a 3D stacked system that integrates a manycore chip with the optical devices and laser sources, we explore the design space for laser source sharing (among waveguides) and placement to minimize laser power by simultaneously considering the network bandwidth requirements, thermal constraints, and physical layout constraints. As part of this exploration we consider Clos and crossbar logical topologies, U-shaped and W-shaped physical layouts, and various sharing/placement strategies: locally-placed dedicated laser sources for waveguides, locally-placed shared laser sources, and shared laser sources placed remotely along the chip edges. Our analysis shows that logical topology, physical layout, and photonic device losses strongly drive the laser source sharing and placement choices to minimize laser power.

Uni-traveling-carrier variable confinement waveguide photodiodes

Uni-traveling-carrier waveguide photodiodes (PDs) with a variable optical confinement mode size transformer are demonstrated. The optical mode is large at the input for minimal front-end saturation and the mode transforms as the light propagates so that the absorption profile is optimized for both high-power and high-speed performance. Two differently designed PDs are presented. PD A demonstrates a 3-dB bandwidth of 12.6 GHz, and saturation currents of 40 mA at 1 GHz and 34 mA at 10 GHz. PD B demonstrates a 3-dB bandwidth of 2.5 GHz, a saturation current greater than 100 mA at 1 GHz, a peak RF output power of + 19 dBm, and a third-order output intercept point of 29.1 dBm at a photocurrent of 60 mA.

SOA gate array recirculating buffer with fiber delay loop.

We present a compact variable delay buffer for storage of 40 byte packets. The recirculating buffer is based on an InP SOA gate array two-by-two switch which provides greater than 40 dB of extinction, sub-nanosecond switching, and fiber-to-fiber gain. The switch is used with a fiber delay loop 450 centimeters, or 23 ns, in length. The buffer is demonstrated with greater than 98% packet recovery at 40 Gb/s for up to 184 ns of storage.