3D micro-optics in self-assembled nanostructured transparent materials by femtosecond direct writing

Lead Research Organisation: University of Southampton
Department Name: Optoelectronics Research Ctr (closed)

Abstract

Ultrafast lasers enable the new technique of femtosecond direct optical writing for patterning micro- and nano-optical elements such as photonic crystals, waveguides and gratings in three dimensions, to provide entirely new functionalities.Three-dimensional photonic structures will allow dramatic increases in the scale of integration for of future optical information processing. They also open tantalising possibilities in the fields of micro-optics, micro- and nano-fluidics optical trapping, optical interconnetions and light field synthesis. We aim to provide a new tool and develop the associated technology for directly patterning 3D micro-optical free-space structures such as diffractive optical elements, berifrigent structures and optical waveguides deep within nano-structured transparent glass media. This proposal will explore the ultrafast physics of femtosecond photosensitivity and optimise the direct write of 3D photonic structures in particular exploiting our recent discovery of new regime of ultrashort pulse interaction with matter involving formation of self-assembled nanostructures. The spin-offs of this technology are nano-fluidics and 3D high-dense rewritable optical memory. The effort in this area worldwide is accelerating rapidly, ensuring a window for our research to have high impact. The proven ability of our group to control the intense ultrashort pulses, control the glass composition, and diagnose the multiphoton transformations give us a key edge in realizing this science and technology. International collaborations, in particular with Kyoto University, will continue.
 
Description The common belief in optics that photosensitivity does not change on reversal of light propagation direction was challenged. This effect, reveals the light direction as new degree of freedom for efficient control of interaction of light with matter, with applications ranging from optical data storage to laser machining. The discovery of non-reciprocal femtosecond laser writing excited interest of the leading groups in the field of ultrafast laser machining (74 citations to date) and resulted in numerous invited presentations (CLEO 2009, Photonics West 2010, 22nd `Annual Meeting of the IEEE Photonics Society) and highlights in press (Laser Focus World 04.01.2008, etc.).

A remarkable phenomenon in ultrafast laser processing of transparent materials, in particular silica glass, manifested as a change in material modification by reversing the writing direction is observed. Modifications of materials by light span from photosynthesis to laser writing and there are only few parameters of irradiation which control material transformations: wavelength, intensity, exposure time and pulse duration. This breakthrough result adds one more parameter to this list - a tilt of intensity front of ulrashort pulse. This work has been carried out in collaboration with IMRA America (USA) and Kyoto University (Japan). The result has been highlighted in Photonics Spectra, June 2007.

Elements of singular optics, including vortex, radial and azimuthal polarization converters was demonstrated with femtosecond laser nanostructuring of glass. The unique technology was patented (WO/2012/150566 03.05.2011) and licensed to a leading optical components manufacturing company Altechna Ltd. In first year, 50 units were sold worldwide including such customers as Thorlabs, Bosch and Trumpf. The result also represents a breakthrough in application of ultrafast lasers, as the discovery of "light fingerprint", the smallest embedded structure ever produced by light, after 10 years has been transformed into successful commercial product. The result was highlighted in Nature Photonics (issue 5, p 331 (2011) and The Telegraph (14 August 2011).
Exploitation Route Beams with radial or azimuthal polarization attract significant interest due to unique optical properties associated with their inherent symmetry. In particular, the large longitudinal electric field component of these beams is attractive for various applications, including laser material processing and Raman spectroscopy. Additionally, the high degree of symmetry inherently present in radial/azimuthal polarization leads to an efficient interaction with matter without the undesirable anisotropy produced by linearly polarized light. The main hindrance to the widespread use of such polarization modes is the lack of simple and cost-effective ways to generate them. Current methods are mainly based on liquid crystal technology, segmented waveplates or polarization selection inside laser resonators. However, the low damage threshold restricts the application of liquid crystal based beam converters, which is the most popular method. Alternatively, polarization converters can be produced by spatially variant sub-wavelength gratings, which would generate azimuthally symmetric polarization from conventional linearly or circularly polarized Gaussian modes. Photolithography, which is usually used for fabrication of such elements has a limiting resolution that restricts the wavelength of operation to the infrared. In this respect, the nanogratings induced by femtosecond laser irradiation are the ideal choice for devices working in visible and near-infrared.

The S-waveplate makes the generation of beams with complex polarization as simple as polarization control with standard retardation plates. This allows the integration of the S-waveplate into any optical system with minimum efforts. Depending on induced retardance, two types of converters can be constructed. The first type is a spatially variant quarter wave plate, which converts an incident circularly polarized beam into a radially or azimuthally polarized optical vortex. The second type is a spatially variant half-wave plate, which converts incident linear or circular polarization into radial/azimuthal polarization or optical vortex respectively.

The S-waveplate will help to empower industrial laser users to adopt spatially variant polarizations for developing laser technologies and therefore boost the advanced manufacturing sector. These technologies are essential in enabling world renowned manufacturers to significantly lower cost and bring greater efficiencies in laser materials processing. The S-waveplate is produced using a method with minimal impact on the environment. This is the first optical device fabricated in silica glass, which is one of the most abundant materials on the Earth, solely by using ultra-short pulses of light. A femtosecond laser direct writing is used to print optics without any need of treatment with hazardous chemicals.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics,Healthcare,Manufacturing, including Industrial Biotechology
URL http://www.orc.soton.ac.uk/phyopt.html
 
Description S-waveplate (Southampton Super-Structured waveplate) developed during the project was patented as "Space variant polarization converter" (Pub. No. WO/2012/150566). The patent was licensed to Altechna Ltd. (weblink) and the optical element is also distributed by Edmund Optics. It was used by many researches all over the world. S-waveplate is a super-structured glass waveplate, which converts polarization and/or wavefront of a light beam from uniform to spatially variant, allowing radially/azimuthally polarized and/or vortex beams. Fabrication of S-waveplate exploits unique ultrafast laser nano-structuring of silica glass developed by the University of Southampton and commercialized by Workshop of Photonics (Altechna R&D). The S-waveplate helps to empower industrial laser users to adopt spatially variant polarizations for developing laser technologies and therefore boost the advanced manufacturing sector. These technologies are essential in enabling world renowned manufacturers to significantly lower cost and bring greater efficiencies in laser materials processing.
First Year Of Impact 2012
Sector Digital/Communication/Information Technologies (including Software),Education,Manufacturing, including Industrial Biotechology
Impact Types Economic
 
Description European Commission (EC)
Amount £320,000 (GBP)
Funding ID 260103-FEMTOPRINT 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 05/2010 
End 05/2013
 
Description Collaboration with IMRA America 
Organisation IMRA America
Country United States 
Sector Private 
PI Contribution Performed characterization of laser processed glass samples
Collaborator Contribution Performed laser irradiation on glass samples
Impact "Quill" writing with ultrashort light pulses in transparent materials Appl. Phys. Lett. 90, 151120 (2007); http://dx.doi.org/10.1063/1.2722240
Start Year 2006
 
Description Collaboration with Joensuu University 
Organisation University of Eastern Finland
Country Finland 
Sector Academic/University 
PI Contribution Performed experiments.
Collaborator Contribution Provided theoretical support.
Impact Non-reciprocal ultrafast laser writing. Nature Photonics Vol 2, 99-104, 2008.
 
Description Collaboration with Kyoto University 
Organisation University of Kyoto
Country Japan 
Sector Academic/University 
PI Contribution Our side generated the idea for the experiment to be taken.
Collaborator Contribution The group at Kyoto University provided access to unique experimental facilities.
Impact "Quill" writing with ultrashort light pulses in transparent materials Appl. Phys. Lett. 90, 151120 (2007); http://dx.doi.org/10.1063/1.2722240
 
Title SPACE VARIANT POLARIZATION CONVERTER 
Description This patent describes an optical element, which converts incident linearly or circularly polarized visible light into radially or azimuthally polarized light beam. The polarization converter is a single optical element, produced by direct laser writing technique in an optically transparent substrate. Direct laser writing based on ultra-short pulsed laser radiation forms form birefringence self-assembled nanogratings in optically transparent material, such as fused silica. The period of gratings is smaller than wavelengths of a visible light. 
IP Reference WO2012150566 
Protection Patent granted
Year Protection Granted 2012
Licensed Yes
Impact The S-waveplate significantly simplifies generation and control of radial polarization. Radial polarization enables focusing laser beam into a smaller spot size. Radially polarized beam improves processing quality, reducing the distortions affecting the edge quality of the machined structures. Moreover, radially polarized beam is more efficient at drilling and cutting high-aspect-ratio features. It is also applicable in optical tweezers, laser micromachining, stimulated microscopy, two-photon e