Hybrid photonic integration combines complementary advantages of different material platforms, offering superior performance and flexibility compared with monolithic approaches. This applies in particular to multi-chip concepts, where components can be individually optimized and tested. The assembly of such systems, however, requires expensive high-precision alignment and adaptation of optical mode profiles. We show that these challenges can be overcome by in situ printing of facet-attached beam-shaping elements. Our approach allows precise adaptation of vastly dissimilar mode profiles and permits alignment tolerances compatible with cost-efficient passive assembly techniques. We demonstrate a selection of beam-shaping elements at chip and fibre facets, achieving coupling efficiencies of up to 88% between edge-emitting lasers and single-mode fibres. We also realize printed free-form mirrors that simultaneously adapt beam shape and propagation direction, and we explore multi-lens systems for beam expansion. The concept paves the way to automated assembly of photonic multi-chip systems with unprecedented performance and versatility. By exploiting two-photon laser lithography for in situ printing of facet-attached beam-shaping elements, hybrid photonic integration can now be realized, opening opportunities for the automated assembly of photonic multi-chip systems with unprecedented performance and versatility.

In situ 3D nanoprinting of free-form coupling elements for hybrid photonic integration

Photonic switches are increasingly considered for insertion in high performance datacenter architectures to meet the growing performance demands of interconnection networks. We provide an overview of photonic switching technologies and develop an evaluation methodology for assessing their potential impact on datacenter performance. We begin with a review of three categories of optical switches, namely, free-space switches, III-V integrated switches and silicon integrated switches. The state-of-the-art of MEMS, LCOS, SOA, MZI and MRR switching technologies are covered, together with insights on their performance limitations and scalability considerations. The performance metrics that are required for optical switches to truly emerge in datacenters are discussed and summarized, with special focus on the switching time, cost, power consumption, scalability and optical power penalty. Furthermore, the Pareto front of the switch metric space is analyzed. Finally, we propose a hybrid integrated switch fabric design using the III-V/Si wafer bonding technique and investigate its potential impact on realizing reduced cost and power penalty.

Photonic switching in high performance datacenters [Invited]

We report a novel type of monolithically integrated tunable semiconductor laser. The tuning is achieved by three intracavity Mach–Zehnder interferometers, realized in passive waveguides and using voltage-controlled electro-optic phase modulators requiring only four control voltages. The potential of the design is demonstrated by a realized laser system that shows an optical linewidth of 363 kHz, output power of 3 mW, and a record tuning range of 74.3 nm. Such a continuous wavelength span is in excess of any monolithic semiconductor laser reported up to date. Precision of the tuning mechanism is demonstrated by a scan over a 0.89-GHz-wide absorption line of acetylene. The laser design is suitable for a number of applications, including gas spectroscopy, telecommunication, and optical coherence tomography. The laser has been fabricated in a multi-project wafer run on an indium phosphide-based generic photonic foundry platform and demonstrates the potential of these technology platforms.

/pdf/novel-widely-tunable-monolithically-integrated-laser-source-2e2sqi2u2r.pdf

Novel Widely Tunable Monolithically Integrated Laser Source

Integrated circuit technologies are enabling intelligent, chip-based, optical packet switch matrices. Rapid real-time re-configurability at the photonic layer using integrated circuit technologies is expected to enable cost-effective, energy-efficient, and transparent data communications. InP integrated photonic circuits offer high-performance amplifiers, switches, modulators, detectors, and de/multiplexers in the same wafer-scale processes. The complexity of these circuits has been transformed as the process technologies have matured, enabling component counts to increase to many hundreds per chip. Active–passive monolithic integration has enabled switching matrices with up to 480 components, connecting 16 inputs to 16 outputs. Integrated switching matrices route data streams of hundreds of gigabits per second. Multi-path and packet time-scale switching have been demonstrated in the laboratory to route between multiple fibre connections. Wavelength-granularity routing and monitoring is realised inside the chip. In this paper, we review the current status in InP integrated photonics for optical switch matrices, paying particular attention to the additional on-chip functions that become feasible with active component integration. We highlight the opportunities for introducing intelligence at the physical layer and explore the requirements and opportunities for cost-effective, scalable switching. Devices that can quickly redirect incoming packets of optically encoded data could substantially increase the speed of the Internet. Kevin Williams and colleagues have reviewed recent developments in large optical switch matrices with a particular focus on the work performed using Indium phosphide integrated photonics at the Eindhoven University of Technology in the Netherlands. Indium phosphide is a semiconducting material that can efficiently produce and amplify light. Optically active switches made from a single material can improve operation speed and reduce the optical and electrical energy consumption of the device. Thus, indium phosphide integrated photonic circuits can combine advanced routing and signal processing functions all on one chip. So far this technology has created switching matrices with up to 480 components, connecting sixteen inputs to sixteen outputs and routed data streams at rates of a few hundred Gigabits per second.

/pdf/integrated-optical-switch-matrices-for-packet-data-networks-54m6egkwq0.pdf

Integrated optical switch matrices for packet data networks

The invention provides a semiconductor optical amplification element which reduces noise light emission and increases saturation output power. The semiconductor optical amplification element has an optical waveguide which includes a core layer formed from an active layer acting as an optical amplification medium and amplifies and outputs an optical signal without electrically converting. The light reflection factor on an inputting side end of the element for the optical signal is lower than the light reflection factor on another outputting side end of the element.

Semiconductor optical amplification element

With the aim of developing a fast wavelength-tunable laser for advanced dynamic network reconfigurations or optical burst switching, a short-cavity (SC) distributed-Bragg-reflector (DBR) laser array with an active-DBR (ADBR) structure (SC-ADBR laser) was fabricated. First, it was experimentally confirmed that the ADBR structure compensates for optical loss and achieves stable single-mode operation during wavelength tuning. An artificial-laser-phase-adjustment technique in the SC-ADBR laser by precise adjustment of a DBR mirror was then proposed. By applying this technique to a six-channel SC-ADBR laser array, perfect wavelength accessibility across a 21-nm range was attained

Wavelength-Tunable Short-Cavity DBR Laser Array With Active Distributed Bragg Reflector

The incorporation of an active single-quantum well in the tuning layer of a DBR laser is proposed as a way of compensating for optical loss and achieving stable single-mode operation during wavelength tuning. Experimental results demonstrate that the structure achieves these goals while maintaining the efficiency of tuning. In application to a short-cavity DBR laser with a gain region 35-µm long, continuous wavelength gtuning over a broad 4.8nm is achieved with stable lasing properties (more than 40dB of side-mode suppression). Fast wavelength switching less than 10ns to cross a wavelength spacing of 2nm is also confirmed.

/pdf/a-wavelength-tunable-short-cavity-dbr-laser-with-active-3xkhq74bfc.pdf

A wavelength-tunable short-cavity DBR laser with active distributed Bragg reflector

A high-speed and compact non-blocking 8×8 InAlGaAs/InAlAs Mach-Zehnder-type optical switch (MZ-OS) fabric consisted of twenty eight 2×2 MZ-OS elements were successfully fabricated. It is expected to operate with switching times of less than 2.5ns.

High-speed and Compact Non-blocking 8×8 InAlGaAs/InAlAs Mach-Zehnder-Type Optical Switch Fabric

High-speed and compact non-blocking 8×8 InAlGaAs/InAlAs Mach-Zehnder-type optical switch fabric

A tunable laser based on a medium wavelength selectivity tunable filter named a lateral-grating-assisted lateral-co-directional-coupler was developed. A wide tuning range of over 65 nm with SMSR of over 35 dB was demonstrated at 50°C.

Aki Takei

Papers

Wavelength-Tunable Short-Cavity DBR Laser Array With Active Distributed Bragg Reflector

A wavelength-tunable short-cavity DBR laser with active distributed Bragg reflector

High-speed and Compact Non-blocking 8×8 InAlGaAs/InAlAs Mach-Zehnder-Type Optical Switch Fabric

High-speed and compact non-blocking 8×8 InAlGaAs/InAlAs Mach-Zehnder-type optical switch fabric

Wide-tuning (65 nm) Semi-cooled (50°C) operation of a tunable laser based on a novel widely tunable filter