B.D. Snow

Photonic Microcantilevers With Interferometric Bragg Grating Interrogation

Germanosilicate glass microcantilevers are fabricated featuring an integrated Fabry-Pérot interferometer. Direct UV writing of single-mode planar waveguides and Bragg gratings is combined with physical micromachining, using a precision dicing saw, to realize glass microcantilevers on a silicon platform. The device presented here has a wavelength shift force sensitivity of 330 nm/N, which is calibrated using a surface profilometer measurement and is an order of magnitude better than current state-of-the-art Bragg-grating-based sensors. The device also shows an approximately tenfold increase in amplitude modulation compared with a similar device architecture utilizing a single Gaussian-apodized Bragg grating. By forming the Fabry-Pérot cavity around the point of greatest strain, we reduce the unwanted effects of grating chirp as the cantilever is deflected and relate the performance to a mechanical model that relates cavity phase shift to deflection.

Simple planar Bragg grating devices for photonic Hilbert transformer

In this work the theoretical design and experimental realisation of a photonic Hilbert transformer is investigated. Planar Bragg gratings are proposed as a route to realise photonic Hilbert transformers in terms of a finite bandwidth and temporal impulse response. With proper grating apodisation and π-phase shift, the Bragg grating will display the spectral features expected from a Hilbert transformer. The unique features of Direct UV grating writing technology are used to fabricate the proposed device in silica-on-silicon

Line defects and temperature effects in liquid crystal tunable planar Bragg gratings.

Liquid crystal tunable planar Bragg Gratings produced by Direct UV Writing are capable of wavelength tuning of over 100GHz. However, such devices exhibit non-linear tuning curves with threshold points and hysteresis. We show that these effects are due to the formation of disclination structures in the liquid crystal and discuss the role of electrode defects and sample temperature on wavelength tuning.

UV written evanescent devices fabricated in micro-structured substrates for optofluidics

We report our recent developments in micro-structured evanescent devices. Micro-machining prior to direct UV writing of channel waveguides provides additional flexibility to fabricate evanescent interacting devices such as modulators and sensors, which allow adiabatic operation.

All-optical signal processing using planar Bragg gratings

All-optical signal processing offers the prospect of realizing high sampling bandwidth and overcoming many of the limitations of electronics. This work introduces the use of planar Bragg gratings in all-optical signal processing. The key fabrication technique is direct grating writing (DGW). One significant advantage of the DGW system is the small spot size of the focused laser beam used to inscribe the waveguide and grating. Rather than using the wide area exposure such as that from a phase mask, DGW uses a direct UV laser spot such that the dimensions of the UV induced structure are determined by the focal spot size. For complex grating engineering this feature is superior to the conventional phase mask techniques, allowing accurate control of the chirp, phase shifts, apodisation and other parameters to produce intricate optical response.

Liquid crystal based tunable WDM planar Bragg grating devices based on precision sawn groove substrates

Current optical telecommunication systems employ dense Wavelength Division Multiplexing (WDM) techniques to increase the data carrying capacity of fiber networks. Dynamic add/drop and filtering processes are crucial for the precise control of individual channels on these networks. Reconfigurable integrated optical devices, such as planar Bragg gratings, can tune the reflection wavelength over several standard channel spacings, providing the possibility for all-optical dynamic networks. Planar devices have the potential to address and tune several channels simultaneously, and have greater potential for integration than fiber equivalents.

UV written waveguide devices - Bragg gratings and applications in sensors

Ultra‐violet laser direct writing provides a powerful way of creating integrated optical devices. The work reported here describes developments in this field, and particularly the use of two‐beam writing to create Bragg gratings in planar integrated format. The work shows how these structures can be used in a wide range of applications, ranging from creation of wide‐band couplers, through to extremely sensitive sensor devices. UV direct writing removes many of the constraints normally associated with planar integrated optics. It is a mask‐free process that uses direct computer control and it dispenses with the etching steps normally required to make low‐loss waveguide devices. The work reported will show how this flexibility of format may be combined with novel substrate structures to allow new device types.

Direct optical observation of walls and disclination effects in active photonic devices

Liquid crystal tunable Bragg Gratings defined in planar substrates via a laser patterning technique exhibit complex wavelength tuning. This tuning displays threshold points and hysteresis. These tuning features are shown to be a manifestation of physical processes occurring in the confined geometry of our tunable devices. Such physical processes include the formation and removal of line disclinations and an associated wall. We discuss the effect of walls in the liquid crystal with regards to voltage tuning characteristics and whether they may allow faster wavelength tuning.

Controlling disclinations in liquid crystal planar Bragg gratings

Direct-UV-written liquid crystal tunable planar Bragg gratings exhibit complex wavelength tuning with threshold points and hysteresis. We discuss the role of disclinations in the liquid crystal and whether they may allow faster wavelength tuning.

100GHz Electrically Tunable Planar Bragg Gratings via Liquid Crystal Overlay

This study demonstrates Bragg wavelength tuning, with maximum tunability of 114 GHz at 1561.8 nm using patterned ITO glass electrodes with 170 Vpp voltage at 1 kHz. The development of a cascaded architecture of such integrated liquid crystal devices operating at different Bragg wavelengths could pave the way towards true colorless add/drop modules for dynamic dense optical networks.