Tellurite glasses with peak absolute Raman gain coefficients up to 30 times that of fused silica

Low-loss TeO2-coated Si3N4 waveguides for application in photonic integrated circuits

We report on high-quality tellurium oxide waveguides integrated on a low-loss silicon nitride wafer-scale platform. The waveguides consist of silicon nitride strip features, which are fabricated using a standard foundry process and a tellurium oxide coating layer that is deposited in a single post-processing step. We show that by adjusting the Si₃N₄ strip height and width and TeO₂ layer thickness, a small mode area, small bend radius and high optical intensity overlap with the TeO₂ can be obtained. We investigate transmission at 635, 980, 1310, 1550 and 2000 nm wavelengths in paperclip waveguide structures and obtain low propagation losses down to 0.6 dB/cm at 2000 nm. These results illustrate the potential for compact linear, nonlinear and active tellurite glass devices in silicon nitride photonic integrated circuits operating from the visible to mid-infrared.

High-Q tellurium-oxide-coated silicon nitride microring resonators

We report on tellurium-oxide (TeO₂)-coated silicon nitride microring resonators with internal quality factors up to 7.3×10⁵, corresponding to 0.5 dB/cm waveguide loss, at wavelengths around 1550 nm. The microring resonators are fabricated using a silicon nitride foundry process followed by TeO₂ coating deposition in a single post-processing step. The silicon nitride strip height of 0.2 μm enables a small microring bending radius, while the TeO₂ coating thickness of 0.33 μm results in a large modal overlap with the TeO₂ layer. These results are a promising step towards realizing compact and high-performance linear, nonlinear, and rare-earth-doped active integrated photonic devices with this platform.

Numerical investigation on high power mid-infrared supercontinuum fiber lasers pumped at 3 µm

High power mid-infrared (mid-IR) supercontinuum (SC) laser sources in the 3-12 µm region are of great interest for a variety of applications in many fields. Although various mid-IR SC laser sources have been proposed and investigated experimentally and theoretically in the past several years, power scaling of mid-IR SC lasers beyond 3 μm with infrared edges extending beyond 7 μm are still challenges because the wavelengths of most previously used pump sources are below 2 μm. These problems can be solved with the recent development of mode-locked fiber lasers at 3 μm. In this paper, high power mid-IR SC laser sources based on dispersion engineered tellurite and chalcogenide fibers and pumped by ultrafast lasers at 3 µm are proposed and investigated. Our simulation results show that, when a W-type tellurite fiber with a zero dispersion wavelength (ZDW) of 2.7 µm is pumped at 2.78 μm, the power proportion of the SC laser beyond 3 µm can exceed 40% and the attainable SC output power of the proposed solid-cladding tellurite fiber is one order of magnitude higher than that of existing microstructured tellurite fibers. Our calculation also predicts that a very promising super-broadband mid-IR SC fiber laser source covering two atmospheric windows and molecules' "fingerprint" region can be obtained with a microstructured As₂Se₃ chalcogenide fiber pumped at 2.78 μm.

Highly efficient Raman distributed feedback fibre lasers

We demonstrate highly efficient Raman distributed feedback (DFB) fibre lasers for the first time with up to 1.6 W of continuous wave (CW) output power. The DFB Bragg gratings are written directly into two types of commercially available passive germano-silica fibres. Two lasers of 30 cm length are pumped with up to 15 W of CW power at 1068 nm. The threshold power is ~2 W for a Raman-DFB (R-DFB) laser written in standard low-NA fibre, and only ~1 W for a laser written in a high-NA fibre, both of which oscillate in a narrow linewidth of <0.01 nm at ~1117 nm and ~1109 nm, respectively. The slope efficiencies are ~74% and ~93% with respect to absorbed pump power in the low-NA fibre and high-NA fibre respectively. Such high conversion efficiency suggests that very little energy is lost in the form of heat through inefficient energy transfer. Our results are supported by numerical simulations, and furthermore open up for the possibility of having narrow linewidth all-fibre laser sources in wavelength bands not traditionally covered by rare-earth doped silica fibres. Simulations also imply that this technology has the potential to produce even shorter R-DFB laser devices at the centimetre-level and with mW-level thresholds, if Bragg gratings formed in fibre materials with higher intrinsic Raman gain coefficient than silica are used. These materials include for example tellurite or chalcogenide glasses. Using glasses like these would also open up the possibility of having narrow linewidth fibre sources with DFB laser oscillating much further into the IR than what currently is possible with rare-earth doped silica glasses.

A full vectorial model for pulse propagation in emerging waveguides with subwavelength structures part II: Stimulated Raman Scattering

The significance of full vectorial pulse propagation through emerging waveguides has not been investigated. Here we report the development of a generalised vectorial model of nonlinear pulse propagation due to the effects of Stimulated Raman Scattering (SRS) in optical waveguides. Unlike standard models, this model does not use the weak guidance approximation, and thus accurately models the modal Raman gain of optical waveguides in the strong guidance regime. Here we develop a vectorial-based nonlinear Schrödinger Eq. (VNSE) to demonstrate how the standard model fails in certain regimes, with up to factors of 2.5 enhancement in Raman gain between the VNSE and the standard model. Using the VNSE we are able to explore opportunities for tailoring of the modal Raman gain spectrum to achieve effects such as gain flattening through design of the optical fiber.

Estimation of peak Raman gain coefficients for Barium-Bismuth-Tellurite glasses from spontaneous Raman cross-section experiments

In this paper we explore the TeO(2)-Bi(2)O(3)-BaO glass family with varied TeO(2) concentration for Raman gain applications, and we report, for the first time, the peak Raman gain coefficients of glasses within this glass family extrapolated from non-resonant absolute Raman cross-section measurements at 785 nm. Estimated Raman gain coefficients show peak values of up to 40 times higher than silica for the main TeO(2) bands. Other optical properties, including index dispersion from the visible to the long wave Infrared (LWIR) are also summarized in this paper.

Raman scattering and the low-frequency vibrational spectrum of glasses

We present a theory of low-frequency Raman scattering in glasses, based on the concept that light couples to the elastic strains via spatially fluctuating elasto-optic (Pockels) constants. We show that the Raman intensity is not proportional to the vibrational density of states (as was widely believed), but to a convolution of Pockels constant correlation functions with the dynamic strain susceptibilities of the glass. Using the dynamic susceptibilities of a system with fluctuating elastic constants we are able for the first time to describe the Raman intensity and the anomalous vibration spectrum of a glass on the same footing. Good agreement between the theory and experiment for the Raman spectrum, the density of states, and the specific heat is demonstrated at the example of glassy As(2)S(3).

Raman band intensities of tellurite glasses

Raman spectra of TeO2-based glasses doped with WO3, ZnO, GeO2, TiO2, MoO3, and Sb2O3 are measured. The intensity of bands in the Raman spectra of MoO3-TeO2 and MoO3-WO3-TeO2 glasses is shown to be 80-95 times higher than that for silica glass. It is shown that these glasses can be considered as one of the most promising materials for Raman fiber amplifiers.