PhD vacancy - Space Division Multiplexed High-capacity Inter-datacenter links (V36.2944)

PhD vacancy - Space Division Multiplexed High-capacity Inter-datacenter links

Department of Electrical Engineering
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Job description

Work environment
Eindhoven University of Technology ( is one of Europe’s top technological universities, situated at the heart of one the most innovative high-tech regions in the world. Thanks to a wealth of collaborations with industry and academic institutes, our research has real-world impact. In 2015, TU/e was ranked 106th in the Times Higher Educational World University ranking and 49th in the Shanghai ARWU ranking (engineering). TU/e has around 3,000 employees and 2,300 PhD students (half of which are international, representing about 70 nationalities).

The Interfaculty institute COBRA (Communication technology: Basic Research and Applications) as of 2017, which is now known as the Institute for Photonic Integration (IPI) performs research in the area of broadband telecommunication techniques, encompassing optical communication as well as radio communication. As a key member of IPI, the Electro-Optical Communication Systems (ECO) group focuses its research on optical communication system techniques, ranging from systems for ultra-high capacity long reach single mode transmission links, multi-mode and multi-core transmission systems, ultra-fast (all-) optical packet switching nodes, to multi-service flexible access and in-building networks.  ECO is has also participated in several national and international projects in the area of access, metro and core optical transmission networks.

More generally, Photonics is a rapidly growing technology: optical communication, LED-lighting, solar cells, displays, optical sensors and imaging are increasingly penetrating our world. Photonics is becoming one of the most important industries for the future. Just as the 20th century was the age of Electronics, the 21st century is set to be the age of Photonics. Key challenges addressed by the COBRA research institute are transport of petabytes of information in communication networks and data centers, delivery of a wealth of services to the users, reduction of energy consumption and the ability for secure information transmission in order to cope with the imminent requirements for increased bandwidth, ubiquitous connectivity of smart products, and the need for a myriad of smart sensors in the forthcoming era of the Internet of Things.

The research within IPI addresses the whole innovation funnel, ranging from fundamental knowledge on nanophotonics and physics, materials science, design technology and device fabrication to system integration. The research is highly multidisciplinary, joining research forces of the departments Applied Physics (Photonics and Semiconductor Nanophysics group) and Electrical Engineering (Photonic Integration and Electro-Optical Communications groups.  More details about the research programme can be found at the IPI website (

IPI is an excellent preparation for an academic or industrial career in the high-tech innovative industry or academia at the interface of Electrical Engineering and Applied Physics.

Research Challenges
As traffic of intra-datacenter networks (DCN) grows, especially with the proliferation of commercial cloud data centers, space-division multiplexing (SDM) has attracted more interest in recently years.  It has been demonstrated by the team at TU/e[1]and others[2] that SDM increases parallel independent data channels in an optical fiber. Compared to multiple single mode fibers (SMFs), few-mode fiber (FMF) could save physical footprint in datacenters. However, due to random inter-mode crosstalk in FMFs, coherent detection and multiple-input-multiple-output (MIMO) digital signal processing (DSP) are usually required for FMF links, which can increase physical complexity and cost of intra DCN. Space division multiplexing (SDM) can potentially do away with coherent detection and MIMO DSP. Therefore, it is foreseen that for short-reach high capacity in a single fiber, multimode fibers will remain the best approach. Up to now, 50um core diameter multimode fibers are optimized for the 850nm wavelength window due to the economies of scale provided by cheap VCSEL transceivers. Recently, the 50um core diameter multimode fiber has been optimized in the 1550nm window. Engineered to have low attenuation, low differential mode group delay (DMGD) and low bending losses even for the higher order modes, these fibers can lower the cost of ownership for service providers whilst allowing the deployment of 1550nm for short-reach intra-datacenter or access network connections. For short reach applications the target is for 100-120km unamplified links.

Crosstalk between mode groups in a fiber can be reduced to minimal levels through the design of novel few-mode fibers[3]. Emerging FMF can support tens of mode groups at 1550nm with index profiles and effective indexes of the mode groups with large index differences thereby allowing for WDM as well as SDM to be exploited in creating Petabit links between hyperscale datacenters.

In SDM, degenerate modes in a mode group can be regarded as one data channel, eliminating the need to suppressing intra-group crosstalk. Another key requirement is low-crosstalk mode (de)multiplexers. In the past, bulky multi-plane (de)multiplexers, have been used, these have been evolving towards fiber based and potentially lossless couplers which are fabricated by tapering carefully arranged SMF fibers placed in a fluorine doped capillary tube. These require long tapering lengths of 5-10cm and although low loss, these mode couplers may not be suitable for integration with a future transceiver or transponder. 

PhD Position in the ECO group –Space Division Multiplexed High-capacity Inter-datacenter links.
With the aim of designing and building up an end-to-end SDM high-capacity inter datacenter link incorporating carefully designed integrated mode multiplexers, novel low-crosstalk FMFs and state-of-the-art modulation formats for Intensity modulated/direct detection links , the PhD candidate will focus on leveraging the in-house COBRA generic process design kits (PDK) for photonic integrated circuits and well demonstrating the operation of this in the lab. Hence the candidate is expected to address to following research challenges:

  • Design and model the best coupling approach from chip to the few-mode and multi-mode fibers in view of minimizing coupling losses and mode-dependent losses
  • Investigate methods for high efficiency and high bandwidth chip-to-fiber interface: to match the waveguide modes to fiber modes ( spot-size converters, modal field/ beam manipulation to match launching to fiber – smooth transitions between active and passive )
  • To exploit electro-optic effects to generate higher-order mode excitation: 1550nm optimized MMF guides higher-order modes which propagate with lowest DMGD. In contrast to SOI device, there is potential for exploiting the active/passive integration to minimize mode-dependent losses typically for the higher-order modes.
  • High density monolithic integration: Investigate the development of denser circuits incorporating spatial multiplexing together with coherent transceiver technology available from the joint experimental platform on Indium Phosphide (JePPIX) e.g. lasers, modulators, coherent receivers,  to develop a compact SDM transceiver
  • Build up an end-to-end (transmitter-to-receiver) intensity modulated direct detection space division multiplexed link.
  • Design from the ground up, novel digital signal processing algorithms to test the operation of the mode multiplexers in terms of crosstalk, mode dependent and coupler insertions loss.
  • Design and test novel equalizers to adapt to the fast changing channel characteristics of the IMDD mode division multiplexed link in a laboratory environment.

[1] R.G.H. van Uden et al., “Ultra-high-density spatial division multiplexing with a few-mode multicore fibre,” Nature Photonics 8, 865 (2014)

[2] D. J. Richardson et al., “Space-division multiplexing in optical fibers,” Nature Photonics, 7, 354 (2013)

[3] H. Liu, et al, "3x10 Gb/s mode group-multiplexed transmission over a 20 km few-mode fiber using photonic lanterns," OFC 2017 paper M2D.5.

Job requirements

Candidates for these challenging positions must have a Master of Science degree in Electrical Engineering or in Applied Physics, with a strong affinity with optical communication, signal processing, EM modelling techniques and/or with photonic devices and circuits. He/she must be familiar with optical and electronic laboratory measurement equipment, optical fiber systems and components, semiconductor devices, and electronic circuits. Knowledge of integration technologies is highly appreciated. He/she must have good communication skills, must be fluent in English, both in speaking and in writing, and must have good team-working capabilities.

Conditions of employment

The appointment is for four years. As an employee of the university you will receive a competitive salary as well as excellent secondary benefits (holiday allowance, etc.). The research must be concluded with the attainment of a PhD degree. A salary is offered starting
at Euro 2222,-  per month (gross) in the first year and increasing up to Euro 2840,- per month (gross) in the last year. Moreover 8% bonus share (holiday supplement) is provided annually. Assistance for finding accommodation can be given.

Information and application

For further information you can contact:

Project Leader:                 Dr. Chigo Okonkwo

ECO group chairman:        Prof. Ton Koonen,

For information concerning employment conditions you can contact Ms. Tanja van Waterschoot, . 


If you are interested in one of these PhD student positions, please use ‘apply now’ button. You must upload the following documents (in pdf):

  • A cover letter explaining your motivation, background and qualifications for the position,
  • A detailed Curriculum Vitae (including a list of publications and awards),
  • Contact information of two persons who can provide reference information about you,
  • Copies of diplomas and a list of your courses taken and grades obtained,
  • Proof of English language skills (if applicable), and
  • All other information that might be relevant.


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