Integrated nonlinear silicon photonics: a route to smaller, faster, greener systems

Lead Research Organisation: University of Southampton
Department Name: Optoelectronics Research Centre (ORC)

Abstract

Silicon photonics is one of the largest and fastest growing areas of research and development of our time. The ability to exploit the semiconductor functionality to process and transmit data in the form of light offers a route to dramatically increase the speeds, capacities, and efficiencies of next generation optoelectronic systems. An important subset of this work is nonlinear silicon photonics, where the aim is to make use of the large, ultrafast, nonlinearity of the material to intricately control and manipulate these light-based signals using light itself. Nonlinear processes in silicon have been widely studied, with significant device demonstrators including Raman lasers, parametric amplifiers, and high-speed modulators. However, most of these devices have been constructed from single crystal material platforms that are notoriously difficult to integrate, either with other elements on-chip or with the optical fibres that are used to link the systems together. Thus, if nonlinear silicon devices are to make the critical transition from a research curiosity to commercially viable products, these integration hurdles must be overcome.

The work in this fellowship application will develop procedures to directly incorporate nonlinear optical components fabricated from cheap and easy to deposit materials within highly functional photonic systems. Compared to their single crystal counterparts, these materials offer a number of key advantages as they are compatible with a wide range of substrates, can be shaped in three dimensions, and can even be post-processed to fine-tune the optical properties and/or the waveguide structure. The components will be fabricated in both fibre and planar form, thus opening an innovative route towards linking these two platforms - one of the most important design challenges in the field of silicon photonics. Following optimization of the integration methods and materials, a range of nonlinear optical systems will be constructed, with the goal to obtaining systems that are smaller, faster, and more efficient. Although the primary focus of this project is the development of integrated platforms for optical communication systems, by extending the device operation into the mid-infrared wavelength region there will be scope to target applications in important areas such as environmental sensing, healthcare, and public security. By looking beyond the traditional single crystal chip-based components to consider more flexible materials and geometries, the work in this programme will help bring the vision of truly integrated nonlinear silicon platforms to fruition.

Planned Impact

The robust and compact integrated nonlinear systems developed within this proposal have the potential to transform modern optoelectronics by offering increased speeds, capacities, and efficiencies. Thus this research is perfectly aligned with the EPSRC theme "Photonics for Future Systems". Although initially I expect the outcomes of this work to have their largest impact in the area of optical communication systems, by extending the device operation into the mid-infrared wavelength region there will also be scope to target applications in imaging, sensing and healthcare.

Communication systems: ICT systems that are both simple to produce and more efficient will not only be of great economic benefit, but also of considerable societal value. For example, the development of all-optical switches, modulators, light sources and amplifiers that can be seamlessly linked with the transport fibres will negate the need to convert between optical and electronic signals, which is slow, costly and energy consumptive. In particular, improving the energy efficiency of ICT systems is of critical importance as the level of global carbon emissions (estimated to be at ~2%) is currently larger than the entire airline industry. In this regard, Intel and HP labs have already recognized the valuable role that deposited materials could play in the development of integrated optical systems, and my partnership with Seagate (one of the largest data storage companies in the world, with a keen interest in silicon photonics for optical interconnects) further demonstrates the relevance of this proposal to the communications sector. I expect that as the material technology matures, other major computer (IBM) and communication companies (Finisar) will find similar merit.

Sensing and healthcare: There is a high demand for sensors and medical components that are robust, versatile and low cost. The UK already has a strong technology base in this area (e.g. OptaSense and Mediwise), and thus continued investment is required to ensure it maintains its competitive edge. Within this programme, there are a number of systems that could be developed that are relevant to this sector. For example, silicon optical fibres coupled to mid-infrared fibre lasers could be used for precise delivery of radiation for in-vivo imaging or keyhole surgeries. Alternatively, integrated systems on-chip consisting of broadband sources, waveguides and multiplexers could form the basis of compact spectrometers for use in environmental monitoring or drug analysis. Thus, the impact of this project will also extend to the EPSRC themes "Healthcare Technologies" and "Global Uncertainties".

The successful outcomes of this proposed work will ultimately help to shift the focus away from single crystal nonlinear components to more flexible and integrable alternatives. As the programme is largely centred on developing the integration procedures, and the subsequent materials optimization, much of the immediate impact will be within the academic community. However, with guidance from the project's industrial partners, it should not take long for the commercial value of these platforms to be widely recognized. By training new staff and students in this technologically important area, the UK will have a solid skill and knowledge base from which to quickly capitalize on future commercial developments.

Publications

10 25 50
 
Description The overall aim of this fellowship is to develop procedures to incorporate nonlinear optical components fabricated from cheap and flexible deposited silicon materials within practical photonic systems. Integration methods have been investigated for both fibre and chip-based components, opening a route towards linking these two platforms. In terms of the fibre platforms, so far we have achieved two key milestones. The first is we have improved the optical quality of our polysilicon (p-Si) fibres fabricated via a tapering method to achieve losses of ~1 dB/cm, which has allowed for the observation of nonlinear supercontinuum generation. Significantly, this result represents the first demonstration of supercontinuum generation in any p-Si waveguide, either fibre or chip-based. By employing a specially designed tapered structure, we have been able to extend the broadening to span ~2 octaves, which is the broadest continuum generation demonstrated in a crystalline silicon waveguide with a silica cladding. The second achievement has been to demonstrate a robust coupling mechanism based on fusion splicing between standard glass fibres and the silicon core fibres (SCF) - thus solving a major integration challenge. This approach makes use of a silicon nano-spike coupler that has been fabricated on to the end of the SCF to reduce the interface losses at the splice joint. These structures have since been employed in all-fibre integrated telecoms systems, most notably to produce a high power frequency comb source suitable for use in signal processing applications. In terms of the chip-base components, most of our attention has been focused on our p-Si waveguides fabricated by laser crystallizing cheap amorphous silicon (a-Si) structures. Using this method, we have produced p-Si waveguides with losses as low as ~4 dB/cm, which have enabled the first demonstration of nonlinear propagation in this material system in a planar form. We are also working on a low temperature a-Si material that has losses as low as ~1 dB/cm and thus could further enhance the nonlinear performance of our integrated circuits. Finally, we have developed a laser processing procedure to write photonic components, such as waveguides, gratings and photodetectors, directly into SiGe alloys, by controlling the high index Ge composition in the films. Thus, our chip-based research has the potential to open new routes to highly functional photonic circuits that could, in future, be directly integrated with electronic layers to realize a complete optoelectronic chip.
Exploitation Route Our methods could be used by both academics and industry to improve the quality and integration of low cost and flexible group IV semiconductor photonic devices.
Sectors Digital/Communication/Information Technologies (including Software),Electronics,Manufacturing, including Industrial Biotechology

 
Description A key achievement in this work has been to develop a robust fibre coupling mechanism based on fusion splicing between standard glass fibres and the silicon core fibres. Our unique all-fibre integrated silicon systems have been employed in advanced telecommunication system by our academic collaborators, most notably to produce a high power frequency comb source suitable for use in signal processing applications.
First Year Of Impact 2021
Sector Digital/Communication/Information Technologies (including Software)
Impact Types Societal

 
Title Dataset for 'Continuous-wave Raman amplification in silicon core fibers pumped in the telecom band' 
Description Data for the journal paper 'Continuous-wave Raman amplification in silicon core fibers pumped in the telecom band' published in APL Photonics, https://doi.org/10.1063/5.0060108 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
Impact Resulted in the journal article: 'Continuous-wave Raman amplification in silicon core fibers pumped in the telecom band' published in APL Photonics, https://doi.org/10.1063/5.0060108 
 
Title Dataset for: Four-wave Mixing-based Wavelength Conversion and Parametric Amplification in Submicron Silicon Core Fibers 
Description Data for the journal paper 'Four-wave Mixing-based Wavelength Conversion and Parametric Amplification in Submicron Silicon Core Fibers' published in IEEE Journal of Selected Topics in Quantum Electronics. DOI: 10.1109/JSTQE.2020.3022100 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Impact Resulted in the journal paper 'Four-wave Mixing-based Wavelength Conversion and Parametric Amplification in Submicron Silicon Core Fibers' published in IEEE Journal of Selected Topics in Quantum Electronics. 
 
Description Collaboration on laser processing of SiGe material platforms 
Organisation IHP Microelectronics GmbH
Country Germany 
Sector Private 
PI Contribution We have been laser processing the SiGe wafers to investigate direct writing of optical components within the wafers.
Collaborator Contribution IHP have provided us with several SiGe wafers for use in our laser materials processing work. They have also done some development work to deposit materials at our desired thickness and characterised the samples.
Impact N/A
Start Year 2019
 
Description Collaboration regarding modelling of laser-materials interactions 
Organisation HiLASE Centre of the Institute of Physics AS CR
Country Czech Republic 
Sector Academic/University 
PI Contribution We have produced a number of samples fabricated via laser crystallization for them to model and compare with our experimental results.
Collaborator Contribution They have modelled our experimental findings, helping us to understand the light-matter interactions in our material.
Impact We have produced one nature materials paper from this collaboration to date, and have had two grant proposals funded, on which they are a partner institute. This collaboration is multi-disciplinary as it combines experimental laser physics with computational physics.
Start Year 2015
 
Description Drawn silicon fibre collaboration 
Organisation Clemson University
Country United States 
Sector Academic/University 
PI Contribution My team has been characterizing the optical properties of fibres made through this partnership, and investigating possible device functionality.
Collaborator Contribution Clemson and NTNU have been collaborating to make silicon fibre samples for my group. The preforms are made in NTNU and then drawn into fibres at Clemson.
Impact We typically publish several journal and conference papers together in each year, making it a highly fruitful collaboration. The collaboration is multi-disciplinary as it draws on expertise in optical physics and materials science.
Start Year 2013
 
Description Drawn silicon fibre collaboration 
Organisation Norwegian University of Science and Technology (NTNU)
Country Norway 
Sector Academic/University 
PI Contribution My team has been characterizing the optical properties of fibres made through this partnership, and investigating possible device functionality.
Collaborator Contribution Clemson and NTNU have been collaborating to make silicon fibre samples for my group. The preforms are made in NTNU and then drawn into fibres at Clemson.
Impact We typically publish several journal and conference papers together in each year, making it a highly fruitful collaboration. The collaboration is multi-disciplinary as it draws on expertise in optical physics and materials science.
Start Year 2013
 
Description OSA Student Chapter visit - University of Bath 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Postgraduate students
Results and Impact Gave a talk to around 60 students (mainly PGR) and staff as part of an event to promote diversity in STEM. Talk covered both career and research aspects.
Year(s) Of Engagement Activity 2020
 
Description OSA travelling lecture - University of Kent 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Around 40 postgraduate students and early career researchers, from a broad range of backgrounds (physics, chemistry and engineering), attended a seminar that I gave hosted by the OSA student chapter at the University of Kent. There were a number of questions before and afterwards as well as a lab tour of their facilities.
Year(s) Of Engagement Activity 2018
 
Description Royal Society Industry Engagement Event: The future of photonics 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact A one-day international conference held by the Royal Society aimed to bring together experts from academia and industry working on photonics technologies.
Year(s) Of Engagement Activity 2019
URL https://royalsociety.org/science-events-and-lectures/2019/10/tof-photonics/
 
Description SPIE Visiting Lecturer - University of Auckland 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact I was a visiting lecturer for the SPIE student chapter at the University of Auckland. I gave a lecture the described my career progression and how this linked to my current research interests, which sparked questions and discussions afterwards.
Year(s) Of Engagement Activity 2017