Single-mode and low-loss operation of optical waveguides is typically limited to a 200-500 nm wide wavelength range. The lower limit is the boundary between single and multi-mode operation, and the upper limit comes from the decreasing confinement of the fundamental mode inside the core, which eventually leads to too large bending radii, waveguide cross-talk and poor integration density. Many interferometric waveguide components, such as grating couplers and multi-mode interference (MMI) couplers, have even narrower wavelength range. This paper demonstrates photonic integrated circuits (PICs) with ultra-broadband operation from 1.2 to 2.4 μm wavelength based on 3 μm thick silicon-on-insulator (SOI) waveguides. Such thick waveguides maintain ultra-high mode confinement for over 1 μm bandwidth, which supports dense integration with low-loss crossings, Euler bends and total internal reflection (TIR) mirrors. While some parts of the PICs are based on multi-moded strip waveguides, mode filters with rib-waveguides allow to keep the PICs effectively single-moded. The focus of the paper is on passive PICs, although the platform also enables active components. Ultra-broadband test results are provided for long waveguide spirals and waveguide-fiber coupling, as well as for echelle gratings, arrayed waveguide gratings (AWGs) and different types of 2x2 couplers. Low-loss operation is demonstrated with continuous transmission spectra measured from 1.25 μm up to 2.4 μm wavelength, i.e. up to 1.15 μm bandwidth. The measured bandwidths are limited by the available measurement setup, rather than the PIC components themselves. Remaining challenges for ultra-broadband operation, such as anti-reflection coatings, are discussed. Applications for broadband operation in communication, imaging and sensing are also presented.
This paper summarizes the goals and first results of the EU-funded project DYNAMOS, which develops fast (1 ns) and widely tunable (>110 nm) lasers, energy-efficient (~ fJ/bit), broadband (100 GHz) electro-optic modulators, and high-speed (1 ns) broadcast-and-select packet switches as photonic integrated circuits. These components are used to demonstrate novel data centre networks with highly deterministic sub-microsecond latency to enable maximum congestion reduction, full bisection bandwidth and guaranteed quality of service while reducing cost per Gbps. The methods to achieve the goals are first described. Then the first results from optical amplifiers, modulators, and lasers are reported with the main focus on lasers that can be tuned fast over a wide wavelength range.
Optical beamforming for satellite-based phased-array antenna systems can help reduce the payload weight and footprint by replacing the RF hardware with photonic integrated circuits. In this paper, simulation and measurement results are provided for 1×12 optical power splitters that provide a non-uniform Gaussian radio-frequency beam profile, thus eliminating the need for a separate amplitude modulation stage in the beamforming network. This both simplifies the optical beamforming network and reduces the total optical losses. Two splitter designs were studied: a star-coupler with non-uniform output waveguides and a cascade of tapered MMI couplers with unconstrained splitting ratios. These two designs are shown to achieve the target output power profile with insertion losses of 1.7 dB and 0.5 dB, respectively.
We have systematically studied multimode interferometer (MMI) splitters made from multiple tapered sections. The goal is to create a library of robust and low-loss splitters covering all splitting ratios (SR) for our silicon photonics platform based on 3 μm thick waveguides. The starting point is always a non-tapered canonical MMI either with general symmetry (canonical SRs 50:50, 100:0, and reciprocal ratios), with mirror symmetric restricted symmetry (canonical SRs 85:15, 50:50, 100:0, and reciprocal ratios), and with point-symmetric restricted symmetry (canonical SRs 72:28 and 28:72). Splitters of these three types are then divided into one to four subsections of equal length, leading to 12 possible different configurations. In each of these subsections, the width is first linearly tapered either up or down and then tapered back to its starting value ensuring mirror symmetry. For all twelve configurations, we carried out an extensive campaign of numerical simulations. For each given width change, we scanned the splitter length and calculated the power in the fundamental mode at the output as well as its relative phase. We then selected the designs with sufficiently low loss and mapped their SR as a function of either the change in width change or length, therefore creating systematic maps for the design of MMI splitters with any SR. Eventually, we selected and fabricated a subset of designs with SRs ranging from 5:95 to 95:5 in steps of 5% and validated their operation through optical measurements.
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