We investigate the measurement of bend losses in few-mode large-mode-area (LMA) fibers. The influence of the light source spectral characteristics, modal power content and cladding light on the measurement accuracy and precision is studied experimentally. Monte-Carlo simulations are performed to understand the distribution of the variations. This study provides practical guidelines for bend loss measurements.
We present an experimental study on mode coupling characteristics of few-mode large-mode-area (LMA) fibers, which are widely used in high power fiber lasers. The modal power allocation is measured by modal decomposition of the nearfield intensity profile of the output beam. Cut-back measurements are carried out with commonly-used fibers with different fiber geometries. The evolution of the modal power content due to mode coupling is presented. The influence of the fiber geometry on mode coupling is discussed.
This paper outlines the most recent work at nLIGHT Oy (formerly Liekki Oy). We give an overview of the current state of the nLIGHT active fiber fabrication technology, discuss the capability of the manufacturing process, and review our results and the results of other groups on the reliability aspects of the manufactured fibers. We also present refractive index tailored and gain tailored Yb doped fibers as examples of recent fiber development.
The ability to integrate micro-channels for fluid transport with optical elements is attractive for the development of
compact and portable chip-based sensors. Femtosecond Laser Direct Writing (FLDW) in transparent materials is a
powerful tool for the fabrication of such integrated devices. We demonstrate the use of FLDW to fabricate coupled
micro-fluidic channels and optical waveguides towards an integrated sensing device for molecular detection.
Waveguides were directly written into the host material and channels were formed by modifying the molecular structure
through FLDW followed by wet chemical etching. Multiple host materials including chalcogenide glasses for IR
detection are discussed.
We demonstrate Si-CMOS-compatible lift-off fabrication of chalcogenide glass waveguides monolithically integrated on
a silicon platform. As a novel route of glass film patterning, lift-off allows several benefits: leverage with Si-CMOS
process compatibility; ability to fabricate single-mode waveguides with core sizes down to submicron range; reduced
sidewall roughness; and wide applicability to other non-silica glass compositions. High-index-contrast (HIC) single-mode strip waveguides have been fabricated with from several glass target compositions including Ge23Sb7S70, As2S3,
As36Ge6S58, As36Sb6S58 and TeO2. We measured Ge-Sb-S waveguides with low loss and excellent wafer-scale uniformity.
We have experimentally demonstrated propagation loss reduction via graded-index (GRIN) cladding layers in HIC glass
waveguides. These efforts have shown that scattering loss arising from sidewall roughness can be significantly reduced
without compromising the high-index-contrast condition by inserting thin GRIN cladding layers with refractive indices
intermediate between the core and topmost cover of a strip waveguide.
Chalcogenide glasses are an ideal material candidate for evanescent biochemical sensing due to their mid and far-infrared
transparency. We have fabricated and tested, to the best of our knowledge, the first microfluidic device
monolithically integrated with planar chalcogenide glass waveguides. High-index-contrast channel waveguides have
been defined using plasma etching in thermally evaporated Ge23Sb7S70 films, followed by microfluidic channel
patterning in photocurable resin (SU8) and channel sealing by a polydimethylsiloxane (PDMS) cover. Using this
device, N-methylaniline can be detected using its well-defined absorption fingerprint of the N-H bond near 1496 nm.
Our measurements indicate linear response of the sensor to varying N-methylaniline concentrations and a sensitivity of
this sensor down to N-methylaniline concentration of 0.7 vol. %. Thermal reflow has been employed as an effective
method to smooth chalcogenide waveguide sidewall roughness from 6.1 nm to 0.56 nm. Given the low-cost fabrication
process and robust device configuration, our integration scheme provides a promising device platform for infrared
chemical sensing applications.
We present the fabrication of waveguides in optical materials using a femtosecond laser. The direct laser writing technique has the unique advantage of allowing volume structures to be fabricated. We investigate several writing schemes in non-oxide glasses and characterize the photo-induced modifications of the optical properties. These changes are linked to structural changes in the glass matrix, as revealed by Raman spectroscopy.
Rapid progress has been made in the last few years in the development direct-write, femtosecond laser micro-structuring and waveguide writing techniques in various materials, particularly semiconductor and other photo-sensitive glasses. There is considerable potential for this becoming a disruptive technology in photonic device fabrication, perhaps even leading to the development of devices that are difficult to fabricate by any other technique. We will review these developments, and with an optimistic eye, offer some perspectives on the future of this technology for opto-electronic systems.
New bismuth zinc tellurite glasses were prepared. The as-quenched glasses were found to contain crystallites confirmed via XRD and TEM studies. The various structural units present in the glasses were probed by Raman and IR spectroscopies. The glasses were poled by conventional thermal poling and also using a new method of two stage poling. The second harmonic generation of the poled glasses were measured using the Maker-fringes technique and it was found that the two stage poling enhanced the SHG efficiency when compared to the conventionally poled samples.
Germanium-based glasses containing heavy metal oxides (Sb2O3) have been investigated. These materials are good candidates for near infrared (IR) applications due to their mid-wave IR cut-off wavelengths (5 ≈ 7 μm). Among inorganic glasses, sulfide materials exhibit the largest third-order optical nonlinear susceptibility and good IR transparency but suffer from low thermal-mechanical stability and photo-induced degradation upon exposure to near-bandgap radiation. The preparation of oxysulfide materials for optical applications offers a unique trade off between the superb chemical stability of the oxide and the attractive optical properties of sulfide. In this presentation we describe a new chemical route for the preparation of oxysulfide glasses for optical applications. The evidence of glass network structural modification is confirmed using infrared and Raman spectroscopy. Film deposition based on sputtering techniques compatible with synthesis of such materials has been performed. The initial characterization of the resulting films has been performed and findings are described.