Air-clad holmium-doped silica fiber laser

Date of Publication : 10 December 2015We report the design, fabrication, and operation of an air-clad holmium-doped fiber laser that was manufactured by directly milling the rare-earth-doped preform. This silica fiber laser operates at 2.1 μm with a slope efficiency of 49.7%, and is in-band pumped with a 1.94-μm thulium fiber laser. To the best of our knowledge, this is the first demonstration of an air-clad holmium-doped fiber laser.Sebastian W. S. Ng, David G. Lancaster, Tanya M. Monro, Peter C. Henry, and David J. Ottawa

Single-frequency mid-infrared waveguide laser

A guided-wave chip laser operating in a single longitudinal mode at 2860 nm is presented. The cavity was set in the Littman-Metcalf configuration to achieve single-frequency operation with a side-mode suppression ratio above 33 dB. The chip laser’s 2 MHz linewidth on a 10 ms scale was found to be limited by mechanical fluctuations, but its Lorentzian contribution was estimated to be lower than 1 Hz using a heterodyne technique. This demonstration incorporates a high coherence source with the simplicity provided by the compactness of chip lasers.Philippe Guay, Jérôme Genest, Vincent Michaud-Belleau, Nicolas Bourbeau Hébert, and David G. Lancaste

Microchip and ultra-fast laser inscribed waveguide lasers in Yb(3+) germanate glass

We report the first Yb³⁺-doped germanate waveguide laser fabricated using femtosecond direct writing. Positive refractive-index channels were inscribed in Yb³⁺ doped high refractive-index (1.85) GPGN glass with molar composition 54.5GeO₂-31PbO-4Ga₂O₃-9Na₂O-1.5Yb₂O₃, resulting in 13 mm long waveguides with a refractive-index change of ∼9×10⁻⁴. The laser performance is investigated in the unguided microchip and in the waveguide configuration. A maximum output power of ∼51 mW at 1.052 µm with a slope efficiency of ∼30% and a lasing threshold of 100 mW was achieved from the Yb³⁺: GPGN microchip laser with a 4.5 mm gain length. A maximum output of ∼15 mW at 1.069 µm with a low lasing-threshold of 83 mW was achieved from the un-optimized 24 µm core-diameter, 13 mm long Yb³⁺: GPGN waveguide laser.M. Khalid, G.Y. Chen, J. Bei, H. Ebendorff-Heidepriem and D.G. Lancaste

On-chip absorption spectroscopy enabled by graded index fiber tips

This paper describes the design and characterization of miniaturized optofluidic devices for sensing based on integrating collimating optical fibers with custom microfluidic chips. The use of collimating graded-index fiber (GIF) tips allows for effective fiber-channel-fiber interfaces to be realized when compared with using highly-divergent standard single-mode fiber (SMF). The reduction in both beam divergence and insertion losses for the GIF configuration compared with SMF was characterized for a 10.0 mm channel. Absorption spectroscopy was demonstrated on chip for the measurement of red color dye (Ponceau 4R), and the detection of thiocyanate in water and artificial human saliva. The proposed optofluidic setup allows for absorption spectroscopy measurements to be performed with only 200 µL of solution which is an order of magnitude smaller than for standard cuvettes but provides a comparable sensitivity. The approach could be integrated into a lab-on-a-chip system that is compact and does not require free-space optics to perform absorption spectroscopy.Kamalpreet K. Gill, Nicolas Riesen, Craig Priest, Nicholas Phillips, Bin Guan, and David G. Lancaste

Very long optical path-length from a compact multi-pass cell

The multiple-pass optical cell is an important tool for laser absorption spectroscopy and its many applications. For most practical applications, such as trace-gas detection, a compact and robust design is essential. Here we report an investigation into a multi-pass cell design based on a pair of cylindrical mirrors, with a particular focus on achieving very long optical paths. We demonstrate a path-length of 50.31 m in a cell with 40 mm diameter mirrors spaced 88.9 mm apart - a 3-fold increase over the previously reported longest path-length obtained with this type of cell configuration. We characterize the mechanical stability of the cell and describe the practical conditions necessary to achieve very long path-lengths

Towards new fiber optic sensors based on the vapor deposited conducting polymer PEDOT:Tos

Conducting polymers are widely researched in terms of both their electrical and optical properties. These optical properties are typically observed on the macroscopic (mm2- cm2) scale using techniques such as UV-Vis-NIR spectroscopy. To broaden their application, fabrication and characterization of conducting polymers on the microscale (μm2) are required. In this paper, microscale poly(3,4-ethylenedioxytiophene)-tosylate (PEDOT:Tos) layers were vapor deposited at the tip of a single mode optical fiber. This was done without the need for intermediate layers such as Indium Tin Oxide commonly used in electropolymerization. The optical properties and behavior of PEDOT:Tos below thicknesses of 500 nm were investigated. Laser-induced damage (LID) behavior of the PEDOT:Tos layer was observed for different intensities of CW or pulsed near infrared light (primarily at 1550 nm). A mathematical model based on energy deposition and the laser-induced damage threshold (LIDT) for low intensity light radiation was developed. It was shown that LID can be avoided by applying irradiance below 31.8 W/mm2 for both CW and pulsed laser. Understanding of LIDT has implications for the use of conducting polymers in new optical fiber sensing applications.Soroush Shahnia, Junaiz Rehmen, David G. Lancaster, Tanya M. Monro, Heike Ebendorff-Heidepriem, Drew Evans and Shahraam Afshar V

Stability of grating-based optical fiber sensors at high temperature

We present a comparison of four different grating-based optical fiber high temperature sensors. Three of the sensors are commercially available and include a heat treated, twisted (chiral) pure-silica microstructured optical fiber, a femtosecond laser written Bragg grating in a depressed cladding single mode fiber and a regenerated fiber Bragg grating. We compare these to an in-house fabricated femtosecond laser ablation grating in a pure-silica microstructured optical fiber. We have tested the sensors in increments of 100°C up to 1100°C for durations of at least 24 hours each. All four sensors were shown to be operational up to 900°C, however the two sensors based on pure-silica microstructured fiber displayed higher stability in the reflected sensor wavelength compared to the other sensors at temperatures of 700°C and higher. We further investigated high temperature stability of silica suspended-core fibers with femtosecond laser inscribed ablation gratings, which show improved stability up to 1050°C following thermal annealing. This investigation can be used as a guide for selecting fiber types, packaging, and grating types for high temperature sensing applications.Stephen C. Warren-Smith, Erik P. Schartner, Linh V. Nguyen, Dale E. Otten, Zheng Yu, David G. Lancaster, and Heike Ebendorff-Heideprie

An ultra-stable 2.9 mu m guided-wave chip laser and application to nano-spectroscopy

We present a configurable guided-wave planar glass-chip laser that produces low-noise and high-quality continuous-wave laser emission tunable from 2.82 to 2.95 µm. The laser has a low threshold and intrinsic power and mode stability attributable to the high overlap of gain volume and pump mode defined by an ultrafast laser inscribed waveguide. The laser emission is single transverse-mode with a Gaussian spatial profile and M²x,y ∼ 1.05, 1.10. The power drift is ∼0.08% rms over ∼2 h. When configured in a spectrally free-running cavity, the guided-wave laser emits up to 170 mW. The benefit of low-noise and stable wavelength emission of this hydroxide resonant laser is demonstrated by acquiring high signal-to-noise images and spectroscopy of a corroded copper surface film with corrosion products containing water and hydroxide ions with a scattering-scanning near-field optical microscope.D.G. Lancaster, D.E. Otten, A. Cernescu, N. Bourbeau Hébert, G.Y. Chen, C.M. Johnson, T.M. Monro, and J. Genes

Single-peak fiber Bragg gratings in suspended-core optical fibers

Femtosecond laser inscribed fiber Bragg gratings in pure-silica suspended-core optical fibers have previously been demonstrated as a promising platform for high temperature sensing. However, the density of gratings that could be written on a single fiber was limited by undesired reflections associated with higher order modes in these high numerical aperture fibers. This resulted in a complex, broadband reflection spectrum with limited multiplexing capability. In this work we utilize modifications to the fine structure of the suspended core optical fibers to fine tune the relative confinement loss of the optical fiber modes, thus reducing the contribution from such higher order modes. The effects of these changes on mode propagation are modeled, giving a range of fibers with different confinement loss properties which can be tailored to the specific length scale of a desired application. We achieve single-peak reflections from individual fiber Bragg gratings, significantly improving performance for multipoint sensing and demonstrate this technique by writing 20 gratings onto a single fiber.Erik P. Schartner, Stephen C. Warren-Smith, Linh V. Nguyen, Dale Otten, Zheng Yu, David G. Lancaster and Heike Ebendorff-Heideprie

Multi-point high temperature optical fiber sensor

ANZCOP, 2019, Melbourne, AustraliaAbstract not availableErik P. Schartner, Linh V. Nguyen, Dale Otten, Zheng Yu, David G. Lancaster, and Heike Ebendorff-Heidepriem, and Stephen C. Warren-Smit