The potential of a Yb3+/Ho3+ co-doped lead-germanate glass as a laser gain medium around 2 µm is investigated by spectroscopic measurements and rate equation modelling. The glass, based on the molar composition of 56GeO2-31PbO-4Ga2O3-9Na2O and co-doped with 1.5 mol% Yb2O3 and 0.4 mol% Ho2O3, possesses a broad Ho3+ emission spectrum covering ∼1.8 µm to 2.2 µm for the Ho3+:5I7→5I8 transition, and a long 5I7 fluorescence lifetime of (7.74 ± 0.03) ms. We estimate a competitive 2 µm quantum efficiency (76%) compared to other germanate glasses. The intensity parameters are calculated to be Ω2 = 3.0×10−20 cm2, Ω4 = 1.2×10−20 cm2 and Ω6 = 2.0×10−20 cm2. The energy transfer analysis from Ho3+ to OH group represents a low Ho3+-OH clustering factor (γ = 0.15) compared to phosphate and other germanate glasses. Applying these parameters to the laser model predicts > 15% laser slope efficiency for cavity losses ≤ 0.5 dB using 976 nm pumping. The results show that this Yb3+/Ho3+ co-doped lead-germanate glass is a promising candidate for efficient lasing around 2 µm.

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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%.

A stable composition (against crystallization) of germanate glass doped with Yb3+ for mid-infrared laser applications is presented. Broad emission spectrum of Yb3+ was obtained for the fabricated glass. Laser operation was demonstrated in 13 mm long waveguide written in the glass using a femtosecond laser operating at 524 nm center wavelength sending 250 fs ultrashort pulses. The resulting CW laser operated at 1.04 µm in the fundamental mode of the waveguide. The propagation loss through the waveguide was 0.6 dB/cm at 1550 nm for 45 µm diameter of the modified structure. The mode analysis of the developed waveguide structure is also presented in COMSOL Multiphysics to study the electric field distribution through different modes of propagation in the waveguide and the confinement loss associated to them.

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