Surface Nanoscale Axial Photonics (SNAP)

Lead Research Organisation: Aston University


Over the last decade, much interest of scientists and engineers working in optics and photonics has been attracted to the research and development of miniature devices based on the phenomenon of slow light. The idea of slow light consists in reducing its average speed of propagation by forcing light to oscillate and circulate in specially engineered microscopic photonic structures (e.g., photonic crystals and coupled ring resonators). Researchers anticipated that slow light devices will have revolutionary applications in communications, optical and radio signal processing, quantum computing, sensing, and fundamental science. For this reason, the research on slow light has been conducted in many academic laboratories and industrial research centres including telecommunications giants IBM, Intel, and NTT. However, in spite of significant progress, it had been determined that current photonic fabrication technologies are unable to produce practical slow light devices due to the major barriers: the insufficient fabrication precision and substantial attenuation of light.

To overcome these barriers, this project will develop a new photonic technology, Surface Nanoscale Axial Photonics (SNAP) which will allow us to demonstrate miniature photonics devices with unprecedentedly high precision and low loss.

SNAP is a new microphotonics fabrication platform invented by the PI of this project. In contrast to previously considered slow light structures based on circulation of light in coupled ring resonators and oscillations photonic crystals, the SNAP platform employs whispering gallery modes of light in an optical fibre, which circulate near the fibre surface and slowly propagate along its axis. The speed of axial propagation of these modes is so slow that it can be fully controlled by dramatically small nanoscale variations of the fibre radius.

This project will develop the advanced SNAP technology for fabrication of ultraprecise, ultralow loss, tuneable, switchable and fully reconfigurable miniature slow light devices establishing the groundwork for their revolutionary applications in future Information and Communication Technologies. The success of the project will place the UK in the centre of this revolutionary development.

Planned Impact

The growing interest in the development of SNAP, invented by the PI in 2011, was recently triggered by his presentations at international conferences (among them 25 invited talks on SNAP in 2012-2015), invited industrial and academic seminars, and discussions with researchers working in optics and photonics in the UK and worldwide. The anticipated impact of this project in the broad academic communities outlined in the Academic Beneficiaries and its industrial economic and social impact summarized below will place the UK into the centre of this pioneering research.

Industrial and Economic Impact. The ambitious objective of the project is to boost the interest of telecommunication and computer industries in applications of the SNAP technology. It is anticipated that the new technology will attract the industry giants to its potential applications as well as give birth to start-up companies working on the research and applications of SNAP. In particular, one of the objectives of the project consists in creation of a start-up company to assemble SNAP fabrication setups for academic and industrial research centres (see Pathways to Impact). These actions will allow to create new jobs and attract young talented scientists and engineers to the field of modern photonics. In the long term, the market of high tech products, which are fabricated using the developed SNAP technology for the ICT and other applications, is expected to be created and grow significantly.

Societal Impact. The invention of SNAP technology was announced by the OSA press release in 2011, reviewed by the Physics Today editorial article in 2012, and broadcasted and reviewed by numerous other public outlets. In the short-term (1-5 years), the progress achieved in the course of the project will be broadly communicated through press releases and popular articles in the public media. In addition, the project team will deliver popular lectures on the topic of SNAP to the university students and general public. The long-term societal impact (5-50 years) is envisioned in the actual usage of SNAP devices in telecommunication, sensing, and quantum computing. These devices are anticipated to be used in the public sector (e.g., in smartphones and computers) and commercial and defence sectors (e.g., in the radars for aviation and missile defence systems). Since SNAP devices exhibit exceptionally low attenuation of light, their deployment will enable the economy of electric power and, thus, contribute to the cutting down of the world energy consumption. All this will positively impact the life of private individuals, job creation, security, and strength of the UK and world economy.
Description 1. We have demonstrated a thermally tunable SNAP platform. Stable tuning is achieved by heating a SNAP structure fabricated on the surface of a silica capillary with a metal wire positioned inside.Heating a SNAP microresonator with a uniform wire introduces uniform variation of its effective radius which results in constant shift of its resonance wavelengths.The developed approach is beneficial for ultra-precise fabrication of tunable ultralow loss parity-time symmetric, optomechanical, and cavity quantum electrodynamics (QED) devices.
2. We have demonstrated a new method for the creation of SNAP microresonators with harmonic profiles via fiber tapering in a laser-heated microfurnace. This simple procedure makes microresonators that support hundreds of axial modes with good spacing uniformity, yielding a promising prospective method for fabricating miniature frequency comb generators and dispersionless delay lines.
3. We have shown that WGMs in a silica microcapillary can be fully localized (rather than perturbed) by evanescent coupling to a water droplet and, thus, form a high-quality-factor microresonator. The spectra of this resonator, measured with a microfiber translated along the capillary, present a hierarchy of resonances that allow us to determine the size of the droplet and variation of its length due to the evaporation. The resolution of our measurements of this variation equal to 4.5 nm is only limited by the resolution of the optical spectrum analyzer used. The discovered phenomenon of complete localization of light in liquid-filled optical microcapillaries suggests a new type of microfluidic photonic device as well as an ultraprecise method for microfluidic characterization.
4. We have discovered a new phenomenon which potential applications in ultraprecise fabrication of SNAP structures, surface science, and in food industry. We have demonstrated that hot water positioned in a silica microcapillary can introduce nanoscale changes at the silica surface during several hours of heating.
5. We have shown theoretically that specially designed SNAP microresonators coupled to quantum emitters can be used for complete frequency conversion of single photons.
6. We have demonstrated that a SNAP microresonator can be introduced by bending of an optical fibre.
7. We have developed a novel ultraprecise method for fabrication of optical microresonators at the silica microcapillary filled with water by its slow local heating with optical whispering gallery modes. We have investigated processes of nonlinear growing of these microresonators as a function of time and input optical power.
8. We have discovered a new type of microresonator called a bat microresonator which can find important applications for ultraprecise sensing of microparticles, positioning of quantum emitters, and subangstrom precise displacement metrology.
9. We have demonstrated tunnelling of light over the record long distance of ~ 0.5 mm and the phenomenon of transition from the slow light to tunnelling near a cutoff frequency of an optical fibre.
10. We demonstrated theoretically that light can be controllably transported by light at the microscale. We designed a device where an optical soliton loads and unloads optical pulses at designated locations of an optical fibre.
11. We have theoretically predicted and experimentally demonstrated a novel SNAP microresonator, which we called a bat microresonator, which possesses the uniform distribution of the eigenmode fields extended over hundreds of microns. This device may find important applications in ultraprecise sensing and cavity quantum electrodynamics.
12. We discovered the fundamental limit of microresonator field uniformity and theoretically developed the foundation for slow light enabled ultraprecise displacement metrology.
13. We experimentally demonstrated SNAP microresonator devices lithographically introduced at the optical fibre surface.
14. We suggested new approaches to enhance the impedance matched bandwidth of bottle microresonator signal processing devices.
15. We designed microwave photonic tuneable filters with an outstanding performance.
16. We demonstrated the fabrication of SNAP bottle microresonators with angstrom precision using a flame.
17. We developed the semiclassical theory of generation of optical frequency combs created by SNAP microresonators with parameters modulated in time. We determined the optimal spatial modulation profiles required to minimize the consumption power of modulation.
18. We experimentally demonstrated a nonlocal SNAP microfluidic sensor theoretically proposed in 2014.
19. We experimentally demonstrated a new method of fabrication of tuneable SNAP microresonators created by two side-coupled bent optical fibres.
Exploitation Route We believe that our recent results published in 2018-22 in highly rated journals (thirteen Optics Letters papers, one Optica paper, one ACS Photonics paper, and one Physical Review Letters paper) will have significant impact on the worldwide development of the SNAP technology. Our discovery of permanent changes introduced by local heating of silica microcapillaries with water (2019) can potentially be used as a ultraprecise method for diagnostics of containers for food industry, purity of surgical instruments, as well as record-precise method for fabrication of SNAP structures (the results published in ACS Photonics 2021). We have demonstrated that light can be controllably transported by light at the microscale (the results published in Physical Review Letters 2021). The SNAP microresonators fabricated in our lab can find important application as miniature frequency comb generators important for ultraprecise spectroscopic measurements. As the result of our international activity, the SNAP technology is currently being developed in the USA (Army Research Laboratory), Israel (Weizmann Institute), China (Wuhan National Laboratories), Japan (Okinawa Institute of Science and Technology) and other institutions.
Besides the exciting results listed above, which we obtained during the work on this project and reported at the major international conferences (including more than 20 invited presentations), we think we got enough experience and ideas for the future work on the transformation of the SNAP platform into the realistic technology required for both industrial fabrication of ultraprecise and ultralow loss photonic microdevices and academic research. We believe that the work on this project will allow us in the next few years to make a significant step forward and create a robust and scalable SNAP flatform enabling fabrication of photonics microdevices with unprecedented picometre precision. Solution of this challenging problem is required for several critical applications of photonics in optical communications, ultraprecise sensing, and quantum technologies.
Sectors Aerospace, Defence and Marine,Agriculture, Food and Drink,Chemicals,Electronics,Healthcare,Pharmaceuticals and Medical Biotechnology

Description 1. Following our recent and ongoing collaboration, US Army Research Laboratory has created a SNAP laboratory similar to our SNAP lab at Aston University. The main goal of this ARL lab is to apply SNAP microresonators to the development of quantum networks. Recently, several research groups in Germany, Japan, China, and Israel started research on SNAP technology following our work. 2. The work on the project was reported in more than 15 papers published in highly rated peer reviewed journals and, besides other conference presentations, in more than 20 invited talks at the major international conferences on optics and photonics. Our work attracted the interest of public media and was highlighted by the editorial article of the Electro Optics Magazine. 3. Our discovery of the slow cooking phenomenon allows us not only to fabricate new SNAP devices with unprecedented precision approaching a picometer but also paves the way for the creation of new ultra-accurate sensors for applications in food industry for testing the liquid food contamination caused by containers. 4. Our proposal of the way to control the transportation of light by light at the microscale using a SNAP device fills the fundamental gap in the demonstrated so far transportation of matter by matter, light by matter, and matter by light at the microscale. 5. The results of this project pave the way for the creation of a robust and scalable SNAP flatform enabling fabrication of photonics microdevices with unprecedented picometre precision required for several critical industrial applications of photonics in optical communications, ultraprecise sensing, and quantum technologies.
First Year Of Impact 2019
Sector Aerospace, Defence and Marine,Agriculture, Food and Drink,Electronics,Pharmaceuticals and Medical Biotechnology
Impact Types Societal

Description Light microtruck: controlled transportation of light by light at the microscale
Amount £214,347 (GBP)
Funding ID RPG-2022-014 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 08/2022 
End 08/2025
Description MOCCA
Amount € 1,092,000 (EUR)
Funding ID H2020-EU.1.3.1. - Fostering new skills by means of excellent initial training of researchers, grant number 814147 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 02/2019 
End 01/2023
Title microfluidic sensor 
Description We developed the SNAP microfluidic sensor which can detect the spatial and temporary changes at the silica-liquid interface. We discovered permanent nanoscale changes at the liquid-surface interface. This discovery may lead to new method of diagnostics of containers for food industry. 
Type Of Material Technology assay or reagent 
Year Produced 2019 
Provided To Others? No  
Impact We believe that the developed microfluidic sensing device can be used in surface science and also for the investigation of the quality of packaging in food industry. We suggest that our discovery will allow us to fabricate SNAP structures with the record 0.01 angstrom precision in effective radius variation of optical fibre. 
Title SNAP simulation software 
Description We have developed the software for simulation of SNAP structures which can be applied to modeling of SNAP devices and explanation of their characteristics measured experimentally. The software allows us to extract the coupling parameters between the input-output waveguides and SNAP microresonators from the experimental data. 
Type Of Material Computer model/algorithm 
Year Produced 2019 
Provided To Others? No  
Impact This software is routinely used in our laboratory. In 2019, as a part of our collaboration, we have further developed and transferred this software package to US Army Research Laboratory. The software is available to other research groups apon reasonable request. 
Description Flat Endface 
Organisation Arden Photonics
Country United Kingdom 
Sector Private 
PI Contribution Arden Photonics is interested in commercialisation of SNAP technology and transferring the SNAP setup to a commercial product. In addition, Arden Photonics is interested in the application and test of the performance of their device Optical EndFace Interferometer for testing of the cut edges of fibres used for fabrication of SNAP devices in our lab.
Collaborator Contribution Arden Photonics advertises the revolutionary SNAP technology in their contact universities and industry companies. The quality of SNAP microresonators created at the end face of optical fibres significantly depend on the end face flatness. To test it and improve it we use the EndFace Interferometer provided by Arden Photonics which the support of their engineers.
Impact Robust tests of SNAP structures to improve their performance with the equipment of Arden Photonics
Start Year 2018
Description Microcapillaries 
Organisation OFS
Department OFS Labs
Country United States 
Sector Private 
PI Contribution Two papers (in Optics Letters and Optica) were published in 2018 and one paper (ACS Photonics) was published in 2021 as a result of this collaboration. Several conference papers including our report at CLEO in 2022 was published as a result of this collaboration.
Collaborator Contribution OFS Laboratories fabricated thin-wall microcapillary fibers which were used in our laboratory for the creation of SNAP devices. In September 2019 OFS Laboratory fabricated and delivered to my group new set of optical microcapillary fibres for for our future experiments with SNAP devices. Currently OFS is working on fabrication of new set of microcapillaries for our future experiments.
Impact Our ongoing research using the microcapillaries fabricated at OFS Laboratories resulted in discovery of the effect of localization of light by a droplet (Optica 2018) and a new way of sensing the phenomena at the silica-liquid interface at nanoscale. As the result of this collaboration, new phenomenon which we called "slow cooking of SNAP microresonators" was discovered. In 2022 using these microcapillaries we demonstrated the record fabrication precision of SNAP microresonators of 1 picometre in cutoff frequency variation. This result pave the way to robust and reproducible fabrication of SNAP devices with close to picometre precision.
Start Year 2017
Description Optical frequency combs 
Organisation National Physical Laboratory
Country United Kingdom 
Sector Academic/University 
PI Contribution We fabricated SNAP microresonators and submitted them to our collaborators in the NPL for verify their performance as optical frequency comb generators.
Collaborator Contribution The group of Dr Pascal Del'Haye tested our SNAP microresonators to evaluate their applicability for the optical frequency comb generation. During the period of Covid pandemic, our collaboration slowed down. Now we re-establish our collaboration with NPL through the new group leader Dr Jonathan Silver on both the theoretical and experimental aspects of optical frequency comb generation in SNAP microresonators.
Impact While the parabolic profile of fabricated microresonators was satisfactory, it was determined that the Q-factor of our SNAP resonators (typically 10^6) was not enough to generate the optical frequency comb spectrum. We continue our work on the improvement of the Q-factor of our microresonators.
Start Year 2018
Description Quantum SNAP 
Organisation US Army Research Lab
Country United States 
Sector Public 
PI Contribution The postdoc was trained at our group to develop the SNAP technology at the US Army Research Laboratory. Two collaborative papers were published in Optics Letters in 2018.
Collaborator Contribution Two joint papers were published. Consultations on the applications of SNAP technology in quantum networks.
Impact A postdoc working at Aston University and funded by the Army Research Lab was trained to develop the SNAP technology at the Army Research Lab. In summer 2019 I worked at the US Army Research Laboratory (ARL) on the development of SNAP. My research was partly funded by ARL.
Start Year 2017
Description Quantum SNAP 2 
Organisation Penn State University
Country United States 
Sector Academic/University 
PI Contribution Our recent discussion preliminary discussions of Prof Ozdemir, Penn State University (PSU) discovered new emerging applications of the SNAP technology in quantum optical networks and computers. In March 2023 we applied for an Royal Society International Exchanges grant with Prof Ozdemir which we beleive will lead to new applications of SNAP in quantum technologies and to writing a new expanded proposal on this topic.
Collaborator Contribution The group of prof Ozdemir has the critical expertise in quantum devices including optical microresonators operating single photons which is required for the development of quantum SNAP.
Impact Royal Society International Exchanges grant application, March 2023
Start Year 2023
Title Control of resonant optical evanescent coupling between waveguides and resonators 
Description We have developed a method of determining evanescent coupling parameters of a waveguide coupled to a SNAP resonator of an input-output waveguide configured to provide electromagnetic field into the resonator. This method comprises: measurement of a Jones matrix spectrum of the coupled waveguide and resonator at each of multiple contact positions x along the resonator with fixed z; calculating a transmission spectrum of the coupled waveguide and resonator at each of the multiple contact positions x;generating a 2D s pectrogram by combining the calculated transmission spectrum of the coupled waveguide and resonator at each of the multiple contact positions x; estimating resonator parameters by fitting a resonator model to a 1D axial resonance spectrum derived from the 2D spectrogram; fitting a coupled WG/resonator model to a subset of 2D spectrogram data to estimate coupling parameters using estimated resonator parameters. 
IP Reference US20220390677A1 
Protection Patent / Patent application
Year Protection Granted 2021
Licensed No
Impact The developed method is important for succesful design and fabrication of different types of SNAP microresonators and, in particular, microresonators used in this project. It is important for the further development of the SNAP technology.
Title SNAP setup 
Description The SNAP setup for fabrication and characterization of SNAP devices 
Type Of Technology Systems, Materials & Instrumental Engineering 
Year Produced 2019 
Impact We have assembled the SNAP fabrication and characterization setup to be used and further developed on the course of this project. This setup has been upgraded for fabrication of SNAP structures at the surface of optical capillaries. 
Title surface-liquid interface sensor 
Description Based on the SNAP technology, we have demonstrated a new optical capillary device sensing the phenomena in the nanoscale vicinity of the silica-liquid interface. 
Type Of Technology Detection Devices 
Year Produced 2019 
Impact The demonstrated prototype structure can be used for the fabrication of new micro-devices with applications in telecommunications, surface science, and food industry. 
Description lab tours 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact In 2018-2019 and in 2022 we organized three tours to our lab for the school pupils and their parents. In 2018-2023 (with the break caused by Covid pandemic) we had organized numerous tours to our lab for the academic and industrial visitors of Aston University.
Year(s) Of Engagement Activity 2018,2019,2020,2022,2023