Single-mode sapphire fiber Bragg grating

We present here the inscription of single-mode waveguides with Bragg gratings in sapphire. The waveguide Bragg gratings have a novel multi-layer depressed cladding design in the 1550 nm telecommunications waveband. The Bragg gratings have a narrow bandwidth (<0.5 nm) and have survived annealing at 1000{\deg}C. The structures are inscribed with femtosecond laser direct writing, using adaptive beam shaping with a non-immersion objective. A single-mode sapphire fiber Bragg grating is created by writing a waveguide with a Bragg grating within a 425 {\mu}m diameter sapphire optical fiber, providing significant potential for accurate remote sensing in ultra-extreme environments.Comment: Submitted to Optica 12 November 202

On-chip beam rotators, polarizers and adiabatic mode converters through low-loss waveguides with variable cross-sections

Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report on a new optical-fibres-compatible glass waveguide by femtosecond laser writing, namely spherical phase induced multi-core waveguide (SPIM-WG), which addresses this challenging task with three dimensional on-chip light control. Precise deformation of cross-sections is achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions. We observed that these waveguides have high refractive index contrast of 0.017, low propagation loss of 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single mode fibre. SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles, or manipulate polarization state of propagating light for target wavelengths. We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric non-uniform modes; examples include circular, elliptical modes and asymmetric modes from ppKTP waveguides which are generally applied in frequency conversion and quantum light sources. Created inside optical glass, these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths. The compatibility with optical fibre also paves the way toward packaged photonic integrated circuitry, which usually needs input and output fibre connections

High-precision optical fiber sensing beyond 1000{\deg}C

Sapphire fiber can withstand around 2000{\deg}C, but it is multimoded, giving poor precision sensors. We demonstrate a single-mode sapphire fiber Bragg grating temperature sensor operating up to 1200{\deg}C. The repeatability above 1000{\deg}C is within {\pm}0.08%.Comment: 4 Pages, 5 Figure

On-chip beam rotators, polarizers and adiabatic mode converters through low-loss waveguides with variable cross-sections

Photonics integrated circuitry would benefit considerably from the ability to arbitrarily control waveguide cross-sections with high precision and low loss, in order to provide more degrees of freedom in manipulating propagating light. Here, we report on a new optical-fibres-compatible glass waveguide by femtosecond laser writing, namely spherical phase induced multi-core waveguide (SPIM-WG), which addresses this challenging task with three dimensional on-chip light control. Precise deformation of cross-sections is achievable along the waveguide, with shapes and sizes finely controllable of high resolution in both horizontal and vertical transversal directions. We observed that these waveguides have high refractive index contrast of 0.017, low propagation loss of 0.14 dB/cm, and very low coupling loss of 0.19 dB coupled from a single mode fibre. SPIM-WG devices were easily fabricated that were able to perform on-chip beam rotation through varying angles, or manipulate polarization state of propagating light for target wavelengths. We also demonstrated SPIM-WG mode converters that provide arbitrary adiabatic mode conversion with high efficiency between symmetric and asymmetric non-uniform modes; examples include circular, elliptical modes and asymmetric modes from ppKTP waveguides which are generally applied in frequency conversion and quantum light sources. Created inside optical glass, these waveguides and devices have the capability to operate across ultra-broad bands from visible to infrared wavelengths. The compatibility with optical fibre also paves the way toward packaged photonic integrated circuitry, which usually needs input and output fibre connections

The structure and constitution of archaeological ferrous process slags

SIGLELD:D47835/83(2vols) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Reflection-in-action as a collective process: Findings from a study in teaching students of negotiation

Real-time reflection-in-action is a critical capability for effective practitioners, just as the more common reflection-on-action is critical for learning. Reflective practice is typically regarded as an individual activity. However, to be an effective negotiator involves real-time reflection-in-action. Results from a Masters-level Negotiation unit show that reflection in negotiation contexts is emergent rather than sudden, is collective, and typically occurs in a break from the negotiation action. We develop the work of Schön and Yanow and Tsoukas to propose a framework of reflection-in-action that better fits the interactive context of negotiation and explore some implications for the teaching of negotiation and other similar professional situations

Wavelength tuning of the photonic band gap of an achiral nematic liquid crystal filled into a chiral polymer scaffold

In this paper, we demonstrate electric field-induced wavelength tuning of the entire photonic band-gap of an achiral nematic liquid crystal (LC) filled into a chiral polymer scaffold. This chiral polymer scaffold has been formed by creating a template of a chiral nematic LC phase, which remarkably does not compromise the optical finesse of the band-gap when compared to that of a conventional, polymer-stabilized chiral nematic LC. We present results on the spectral shift and temporal evolution of the photonic band-gap in the presence of an external a.c. electric field. It is shown that, initially, there is a rapid (τ ≈ 1 ms) blue-shift of the longwavelength band-edge followed by a considerably slower blue-shift (τ ≈ 6.5 s) of the entire band-gap. We compare the results with those obtained for a polymer-stabilized chiral nematic LC where only a blue-shift of the long-wavelength band-edge is observed. Consequently, we find that, for the templated sample, the tuning range is more than a factor of two greater than that observed for the polymer-stabilized chiral nematic LC for the same range of electric field amplitudes. It is also found that there is little in the way of hysteresis upon increasing and decreasing the applied electric field magnitude. Finally, we present experimental evidence that suggests that the blue-shift of the entire band-gap is due to an additional tuning mechanism present only for the case of the templated samples. This is believed to be caused by a contraction of the pitch that results from a translational motion of the polymer network. The greater tuning range observed in these templated samples are potentially important for the development of tunable 1-dimensional photonic band-gaps and LC lasers. Furthermore, it avoids the use of d.c. electric fields that can lead to long-term issues regarding stability

Speckle contrast reduction of laser light using a chiral nematic liquid crystal diffuser

High coherence in laser light causes spatially distributed interference called speckle. In applications such as holographic projection, this undesirable side effect degrades image clarity. The current methods of speckle reduction, such as a rotating ground-glass diffuser, require additional bulky moving parts. Here, we present an alternative technology based upon a compact, electrohydrodynamic chiral nematic liquid crystal device. A spatially random phase modulation of the incident light is achieved through the electrohydrodynamic instabilities that are induced by an alternating electric field. Using a chiral nematic liquid crystal device that is doped with an ionic compound, we find that the speckle contrast can be reduced by as much as 80%

Speckle contrast reduction of laser light using a chiral nematic liquid crystal diffuser

High coherence in laser light causes spatially distributed interference called speckle. In applications such as holographic projection, this undesirable side effect degrades image clarity. The current methods of speckle reduction, such as a rotating ground-glass diffuser, require additional bulky moving parts. Here, we present an alternative technology based upon a compact, electrohydrodynamic chiral nematic liquid crystal device. A spatially random phase modulation of the incident light is achieved through the electrohydrodynamic instabilities that are induced by an alternating electric field. Using a chiral nematic liquid crystal device that is doped with an ionic compound, we find that the speckle contrast can be reduced by as much as 80%