Widely tunable short-infrared thulium and holmium doped fluorozirconate waveguide chip lasers

Germanate glass for laser applications in ∼ 2.1 μm spectral region: A review

The growing landscape of laser applications in ∼ 2 μm spectral region leads to the development of novel transparent media that provide low attenuation solutions for high power laser applications. This includes investigating glassy media such as heavy metal oxides (e.g. tellurite and germanate), fluoride and chalcogenides as an alternative to the most efficient and widely utilized silica glass. This review article discusses the potential of a heavy metal oxide lead-germanate glass (GeO₂-PbO-Ga₂O₃-Na₂O) for ∼ 2.1 μm laser applications, with a focus on our contribution to the field. Firstly, a comparative study of commercially available silicates and fluorides with germanate glass is presented to reveal germanate to be a favorable material for 2.1 μm laser applications. Secondly, as our contribution to the field, we present the development of the first ∼ 2.1 μm small cavity single frequency laser action in a Ho³⁺ doped GPGN glass that verifies its capability for ∼ 2 μm laser applications and beyond.

Femtosecond laser induced low propagation loss waveguides in a lead-germanate glass for efficient lasing in near to mid-IR

To support the growing landscape of near to mid-IR laser applications we demonstrate a range of low propagation loss femtosecond laser (FSL) written waveguides (WGs) that have achieved guided-mode laser operation in a rare earth (RE) doped lead-germanate glass. The WGs are fabricated in both the athermal and thermal FSL writing regimes using three different pulse repetition frequencies (PRF): 100 kHz (athermal); 1 MHz; and 5 MHz (thermal). The lasing capability of Yb³⁺ doped lead-germanate waveguides is verified in the near-IR. The refractive index contrast (∆n) for 100 kHz WGs is ~ 1 × 10^–4, while for 5 MHz, ∆n increases to ~ 5 × 10^–4. The WGs in the thermal regime are less effected by self-focusing and are larger in dimensions with reduced propagation losses. For the 1 MHz repetition rate thermal writing regime we report a low propagation loss WG (0.2 dB/cm) and demonstrate laser operation with slope efficiencies of up to ~ 28%.

Tm,Ho:LiYF4 planar waveguide laser at 2.05 μm

The first holmium fluoride waveguide laser, to the best of our knowledge, is reported using a 25-μm-thick Gd³⁺-ion-modified 4.5 at. % Tm³⁺, 0.5 at. % Ho³⁺-codoped LiYF₄ active layer grown by liquid phase epitaxy on (001)-oriented LiYF₄ substrate. Pumped by a Ti:sapphire laser at 797.2 nm, the planar waveguide laser generates 81 mW of continuous-wave (CW) output at ∼2051  nm with a slope efficiency of 24%. Power scaling up to 186 mW at 2051 nm and 2065 nm in quasi-CW regime is demonstrated. The parameters of the Tm³⁺↔Ho³⁺ energy transfer are determined. Tm,Ho:LiYF₄/LiYF₄ epitaxies are promising for waveguide lasers and amplifiers at above 2 μm.

Visible laser emission from a praseodymium-doped fluorozirconate guided-wave chip

We report visible continuous-wave laser emission at 636 nm from a praseodymium-doped fluorozirconate glass guided-wave chip laser. This ultra-fast laser inscribed gain chip is demonstrated to be a compact and integrated laser module. The laser module, pumped by 442 nm GaN laser diodes, generates >8  mW lasing output with a beam quality of Mxy2∼1.15×1.1(±0.1). To the best of our knowledge, this is the first visible laser emission from a glass-based waveguide chip laser.

Ultra-compact and low-threshold thulium microcavity laser monolithically integrated on silicon

We demonstrate an ultra-compact and low-threshold thulium microcavity laser that is monolithically integrated on a silicon chip. The integrated microlaser consists of an active thulium-doped aluminum oxide microcavity beside a passive silicon nitride bus waveguide, which enables on-chip pump-input and laser-output coupling. We observe lasing in the wavelength range of 1.8-1.9 μm under 1.6 μm resonant pumping and at varying waveguide-microcavity gap sizes. The microlaser exhibits a threshold as low as 773 μW (226 μW) and a slope efficiency as high as 24% (48%) with respect to the pump power coupled into the silicon nitride bus waveguide (microcavity). Its small footprint, minimal energy consumption, high efficiency, and silicon compatibility demonstrate that on-chip thulium lasers are promising light sources for silicon microphotonic systems.

Holmium-doped 2.1 μm waveguide chip laser with an output power > 1 W

We demonstrate the increasing applicability of compact ultra-fast laser inscribed glass guided-wave lasers and report the highest-power glass waveguide laser with over 1.1 W of output power in monolithic operation in the short-infrared near 2070 nm achieved (51% incident slope efficiency). The holmium doped ZBLAN chip laser is in-band pumped by a 1945 nm thulium fiber laser. When operated in an extended-cavity configuration, over 1 W of output power is realized in a linearly polarized beam. Broad and continuous tunability of the extended-cavity laser is demonstrated from 2004 nm to 2099 nm. Considering its excellent beam quality of M² = 1.08, this laser shows potential as a flexible master oscillator for single frequency and mode-locking applications.