Ultrafast thulium fiber laser reaches communications-ready 20 GHz

Nov. 1, 2018
Nominal 2 µm thulium fiber lasers have only reached repetition rates up to 1.6 GHz. However, active mode locking extends this rate more than an order of magnitude, making communications and data processing possible.

Since their 2017 demonstration of a passively mode-locked carbon-nanotube (CNT)-based thulium/holmium (Tm/Ho) fiber laser with the broadest tunability across 200 nm from 1860 to 2060 nm, researchers at Nanjing University (Nanjing, China) have now developed an actively mode-locked ultrafast 2 µm fiber laser that reaches communications-capable repetition rates of nearly 20 GHz. This is more than an order of magnitude better than the 1.6 GHz previously possible with this type of laser.

Active mode-locking is a relatively mature technology for pulse generation, but requires stable, finely tuned electro-optical components. To implement this technique, the laser was mode-locked by driving a lithium niobate phase modulator with a radio-frequency (RF) signal equal to integral multiples of the longitudinal mode spacing, enabling tunability from 14.6 MHz to 19 GHz with a 46 dB super-mode suppression ratio for the latter pulse rate. The team also observed rational harmonic mode-locking (RHML) at 2 μm and reached a 21 GHz repetition rate at a 7 GHz RF modulation frequency.

Unlike passive mode-locking, this source can be synchronized to an external clock for better stability and behaves similarly to a frequency comb, with the potential to reach 40 GHz repetition rates and extend further into the mid-infrared region beyond 2 µm. Reference: J. Qin et al., Opt. Express, 26, 20, 25769–25777 (2018).

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.

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