37 research outputs found
Space Division Multiplexing in Optical Fibres
Optical communications technology has made enormous and steady progress for
several decades, providing the key resource in our increasingly
information-driven society and economy. Much of this progress has been in
finding innovative ways to increase the data carrying capacity of a single
optical fibre. In this search, researchers have explored (and close to
maximally exploited) every available degree of freedom, and even commercial
systems now utilize multiplexing in time, wavelength, polarization, and phase
to speed more information through the fibre infrastructure. Conspicuously, one
potentially enormous source of improvement has however been left untapped in
these systems: fibres can easily support hundreds of spatial modes, but today's
commercial systems (single-mode or multi-mode) make no attempt to use these as
parallel channels for independent signals.Comment: to appear in Nature Photonic
Reconfigurable photonic integrated mode (de)multiplexer for SDM fiber transmission
A photonic integrated circuit for mode multiplexing and demultiplexing in a
few-mode fiber is presented and demonstrated. Two 10 Gbit/s channels at the
same wavelength and polarization are simultaneously transmitted over modes LP01
and LP11a of a few-mode fiber exploiting the integrated mode MUX and DEMUX. The
proposed Indium-Phosphide-based circuits have a good coupling efficiency with
fiber modes with mode-dependant loss smaller than 1 dB. Measured mode
excitation cross-talk is as low as -20 dB and a channel cross-talk after
propagation and demultiplexing of -15 dB is achieved. An operational bandwidth
of the full transmission system of at least 10 nm is demonstrated. Both mode
MUX and DEMUX are fully reconfigurable and allow a dynamic switch of channel
routing in the transmission system
Towards the Design of Robust High-Speed and Power Efficient Short Reach Photonic Links
In 2014, approximately eight trillion transistors were fabricated every second thanks to improvements in integration density and fabrication processes. This increase in integration and functionality has also brought about the possibility of system on chip (SoC) and high-performance computing (HPC). Electrical interconnects presently dominate the very-short reach interconnect landscape (< 5 cm) in these applications. This, however, is expected to change. These interconnects' downfall will be caused by their need for impedance matching, limited pin-density and frequency dependent loss leading to intersymbol interference. In an attempt to solve this, researchers have increasingly explored integrated silicon photonics as it is compatible with current CMOS processes and creates many possibilities for short-reach applications.
Many see optical interconnects as the high-speed link solution for applications ranging from intra-data center (~200 m) down to module or even chip scales (< 2 cm). The attractive properties of optical interconnects, such as low loss and multiplexing abilities, will enable such things as Exascale high-performance computers of the future (equal to 10^18 calculations per second). In fact, forecasts predict that by 2025 photonics at the smallest levels of the interconnect hierarchy will be a reality. This thesis presents three novel research projects, which all work towards increasing robustness and cost-efficiency in short-reach optical links. It discusses three parts of the optical link: the interconnect, the receiver and the photodiode.
The first topic of this thesis is exploratory work on the use of an optical multiplexing technique, mode-division multiplexing (MDM), to carry multiple data lanes along with a forwarded clock for very short-reach applications. The second topic discussed is a novel reconfigurable CMOS receiver proposed as a method to map a clock signal to an interconnect lane in an MDM source-synchronous link with the lowest optical crosstalk. The receiver is designed as a method to make electronic chips that suit the needs of optical ones. By leveraging the more robust electronic integrated circuit, link solutions can be tuned to meet the needs of photonic chips on a die by die basis. The third topic of this thesis proposes a novel photodetector which uses photonic grating couplers to redirect vertical incident light to the horizontal direction. With this technique, the light is applied along the entire length of a p-n junction to improve the responsivity and speed of the device. Experimental results for this photodetector at 35 Gb/s are published, showing it to be the fastest all-silicon based photodetector reported in the literature at the time of publication
Roadmap on multimode photonics
Multimode devices and components have attracted considerable attention in the last years, and different research topics and themes have emerged very recently. The multimodality can be seen as an additional degree of freedom in designing devices, thus allowing for the development of more complex and sophisticated components. The propagation of different modes can be used to increase the fiber optic capacity, but also to introduce novel intermodal interactions, as well as allowing for complex manipulation of optical modes for a variety of applications. In this roadmap we would like to give to the readers a comprehensive overview of the most recent developments in the field, presenting contributions coming from different research topics, including optical fiber technologies, integrated optics, basic physics and telecommunications
Ultra-compact Silicon Multimode Waveguide Bends Based on Special Curves for Dual Polarizations
The multimode waveguide bends (MWBs) with very compact sizes are the key
building blocks in the applications of different mode-division multiplexing
(MDM) systems. To further increase the transmission capacity, the silicon
multimode waveguide bends for dual polarizations are of particular interest
considering the very distinct mode behaviors under different polarizations in
the silicon waveguides. Seldom silicon MWBs suitable for both polarizations
have been studied. In this paper we analyze several dual-polarization-MWBs
based on different bending curve functions. These special curve-based silicon
MWBs have the advantages of easy fabrication and low loss compared with other
structures based on the subwavelength structures such as gratings. A comparison
is made between the free-form curve, Bezier curve, and Euler curve, which are
used in the bending region instead of a conventional arc. The transmission
spectra of the first three TE and TM modes in the silicon multimode waveguide
with a core thickness of 340 nm are investigated. The simulation results
indicate that in the premise of the same effective radius which is only 10 in
this paper, the 6-mode MWB based on the free-form curve has the optimal
performances, including an extremely low loss below 0.052dB and low crosstalk
below -25.97dB for all six modes in the wide band of 1500-1600 nm. The MWBs
based on the Bezier and Euler curve have degraded performances in terms of the
loss and crosstalk. The results of this paper provide an efficient design
method of the polarization insensitive silicon MWBs, which may leverage the
researches for establishing complicated optical transmission systems
incorporating both the MDM and polarization-division multiplexing (PDM)
technology.Comment: 18 page
All-optical mode unscrambling on a silicon photonic chip
Propagation of light beams through scattering or multimode systems may lead
to randomization of the spatial coherence of the light. Although information is
not lost, its recovery requires a coherent interferometric reconstruction of
the original signals, which have been scrambled into the modes of the
scattering system. Here, we show that we can automatically unscramble four
optical beams that have been arbitrarily mixed in a multimode waveguide,
undoing the scattering and mixing between the spatial modes through a mesh of
silicon photonics Mach-Zehnder interferometers. Using embedded transparent
detectors and a progressive tuning algorithm, the mesh self-configures
automatically and reset itself after significantly perturbing the mixing,
without turning off the beams. We demonstrate the recovery of four separate 10
Gbits/s information channels, with residual cross-talk between beams of -20dB.
This principle of self-configuring and self-resetting in optical systems should
be applicable in a wide range of optical applications.Comment: 23 pages, 10 figure