Lewis G. Carpenter

Low optical-loss facet preparation for silica-on-silicon photonics using the ductile dicing regime

The efficient production of high-quality facets for low-loss coupling is a significant production issue in integrated optics, usually requiring time consuming and manually intensive lapping and polishing steps, which add considerably to device fabrication costs. The development of precision dicing saws with diamond impregnated blades has allowed optical grade surfaces to be machined in crystalline materials such as lithium niobate and garnets. In this report we investigate the optimization of dicing machine parameters to obtain optical quality surfaces in a silica-on-silicon planar device demonstrating high optical quality in a commercially important glassy material. We achieve a surface roughness of 4.9 nm (Sa) using the optimized dicing conditions. By machining a groove across a waveguide, using the optimized dicing parameters, a grating based loss measurement technique is used to measure precisely the average free space interface loss per facet caused by scattering as a consequence of surface roughness. The average interface loss per facet was calculated to be: −0.63 dB and −0.76 dB for the TE and TM polarizations, respectively.

Integrated optic glass microcantilevers with Bragg grating interrogation

A new method for creating microcantilevers in glass allows integration of optical waveguides and Bragg gratings. Devices are fabricated by high precision sawing, followed by direct UV writing of waveguides with Bragg gratings and then chemical etching to release the freestanding glass structures. Optical measurement of the Bragg gratings together with piezo-actuation allows the mechanical resonances to be probed. By measuring the mechanical damping coefficient of the cantilever as a function of the gas pressure in a vacuum system the transition from the viscous to the molecular flow regime can be observed.

Planar waveguide tilted Bragg grating refractometer fabricated through physical micromachining and direct UV writing

A set of rapid prototyping techniques are combined to construct a laterally-tilted Bragg grating refractometer in a novel planar geometry. The tilted Bragg grating is fabricated in a silica-on-silicon planar substrate using a dual beam direct UV writing (DUW) technique. Lateral cladding mode confinement is subsequently achieved by physically micromachining two trenches either side of the direct UV written waveguide. The resulting device is demonstrated as an effective refractometer, displaying a comparable sensitivity to tilted Bragg gratings in a fiber optical geometry, but with the added advantages of planar integration.

Fabrication and characterization of high-contrast mid-infrared GeTe 4 channel waveguides

We report the fabrication and characterization of high index contrast (Δn≈0.9) GeTe4 channel waveguides on ZnSe substrate for evanescent-field-based biosensing applications in the mid-IR spectral region. GeTe4 films were deposited by RF sputtering and characterized for their structure, composition, transparency, and dispersion. The lift-off technique was used to pattern the waveguide channels. Waveguiding from 2.5-3.7 and 6.4-7.5 μm was demonstrated, and mode intensity profile and estimated propagation losses are given for the 3.5 μm wavelength.

Miniaturization of Bragg-multiplexed membrane transducers

This paper reports the miniaturization of Bragg-multiplexed pressure sensing membranes for integrated photonic chips. The analysis compares a novel Fabry-Perot Bragg grating (FPBG) design that integrally spans a thin (54 µm) silica membrane to a recently reported single Bragg grating (BG) design that resides within the membrane. Unlike the single BG, the FPBG maintains spectral integrity as the dimensions of the membrane become sub-millimetre. In addition it is shown that the FPBG structure can also be used for inherent temperature referencing, having a Bragg thermal sensitivtiy of 13.5 pm °C-1, which can be decoupled from pressure effects. For the reported sub-millimetre membrane, pressure resolution was enhanced by a factor of three and spectral bandwidth reduced by over five-fold.

Fabrication of a Multimode Interference Device in a Low-Loss Flat-Fiber Platform Using Physical Micromachining Technique

A physical micromachining technique is demonstrated in a low-loss flat-fiber substrate to fabricate a multimode interference (MMI) device. The flat-fiber substrate is a low-index-contrast material; however, by making use of two physically micromachined trenches, lateral confinement is achieved providing high index contrast for the MMI region. A 1 × 3 MMI device exhibiting 1.89 dB of excess loss has been demonstrated.

Quantifying the optical sensitivity of planar Bragg gratings in glass micro-cantilevers to physical deflection

Here we introduce a novel technique for characterizing the deflection and force sensitivity of a silica micro-cantilever transducer, with inherently defined planar Bragg gratings. The technique uses a 3D scanning surface profiler to deform the micro-cantilever both vertically and horizontally whilst simultaneously monitoring a set of multiplexed Bragg gratings. By using this characterization technique a theoretical model for the cantilevers optical response is tested.

Direct UV-written planar Bragg grating sensors

Integrated photonics is a proven platform for physical and chemical sensing. It offers miniaturised solutions that are suited for use in extreme environments, including strong EM-fields, EM-pulses and contact with flammable materials, often far exceeding electronic sensors in this regard. This review looks into direct UV-written planar Bragg grating technology and its application to integrated photonic sensors. The platform has been demonstrated widely for measurement of physical properties such as temperature, pressure and strain. In addition, by using an evanescent interaction, refractive index can be measured allowing for chemical and biochemical detection. Further to this, the platform has recently been utilised in quantum information processing, where quantum gate operations and single photon detection has been shown.

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.

Nanoscale roughness micromilled silica evanescent refractometer

We demonstrate machining of precision slots in silica with nanoscale roughness for applications in photonics. Using our in-house developed milling system we have achieved machined slots with surface roughness of 3.0 nm (Sa) and 17 µm depth of cut. This result represents eight times improvement in surface roughness and forty times increase in depth of cut than previously reported. We also demonstrate integration of these milled slots with UV-written waveguides and Bragg gratings to create optical refractometers, based on monitoring Fabry-Pérot spectral fringe changes.