Near-infrared, mode-locked waveguide lasers with multi-GHz repetition rates

Choudhary, A., Lagatsky, A.A., Zhang, Z.Y., Zhou, K.J., Wang, Q., Hogg, R.A., Pradeesh, K., Rafailov, E.U., Sibbett, W., Brown, C.T.A. and Shepherd, D.P. (2014) Near-infrared, mode-locked waveguide lasers with multi-GHz repetition rates. SPIE Photonics West 2014, , San Francisco, United States. 01 - 06 Feb 2014. (doi:10.1117/12.2035639).

Abstract

Ultrafast lasers with multi-GHz repetition rates have a range of important applications in optical frequency metrology, non-linear microscopy, optical sampling and for the calibration of astronomical spectrographs. Solid-state waveguide lasers offer various advantages like a low-threshold operation, high laser efficiency, low mode-locking threshold and the possibility for the realization of compact and integrated systems.

We have fabricated low-loss, ion-exchanged channel waveguides in a phosphate-glass doped with Yb³⁺ and Er³⁺/Yb³⁺ for operation around 1 micron and 1.5 micron, respectively. Using the Yb³⁺:phosphate glass waveguide, mode-locking was achieved at a wavelength of 1052 nm with a repetition rate of 4.9 GHz and a pulse duration of 800 fs at an output power of 80 mW. A commercially available quantum well semiconductor saturable absorber mirror (SESAM) with a modulation depth of 0.4% was employed for passive mode-locking. Using shorter cavity lengths, repetition rates of 10.4 GHz, 12 GHz and 15.2 GHz were achieved with pulse durations in the range of 750-830 fs.

Mode-locking around 1.5 micron was achieved in the Er³⁺,Yb³⁺ co-doped phosphate glass waveguides by using a novel SESAM based on a quantum dot in well (DWELL) structure. Stable, self-starting mode-locked operation was observed at a repetition rate of 4.8 GHz with a pulse width of 2.5 ps and an output power of 9 mW. Using a shorter device length, a repetition rate of 6.8 GHz was achieved, with a pulse-width of 5.4 ps and an output power of 30 mW. The repetition rate was tuned by more than 1 MHz by varying the pump power. This simple technique could offer a way for on-chip stabilization of the repetition frequency from a monolithic waveguide-based laser system.

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Contributors

Author: D.P. Shepherd

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