Abstract
A 1.7-
$\mu$
m pulsed laser is of tremendous interest for biomedical imaging applications due to its low scattering loss in bio-tissues, but is relatively difficult to generate in a fiber laser. In this paper, we propose and demonstrate a compact 1.7-
$\mu$
m Tm/Ho-codoped fiber pulsed laser based on a novel intermode-beating modulation (IM) technique. A 1211-nm continuous-wave (CW) Raman fiber laser is especially homemade to pump a
$\sim$
20-cm short-length Tm/Ho fiber for obtaining
$\sim$
1.7-
$\mu$
m optical gain. A pair of fiber end-facet mirrors with 1.7–1.8-
$\mu$
m reflective band is used to form the all-fiber linear cavity. 1.76- or 1.78-
$\mu$
m lasing is successfully achieved, and surprisingly exhibits stable self-gain-switching operation with
$\sim$
1-
$\mu$
s pulse duration. Different from the conventional gain-switching requiring pulsed pumping, herein the gain modulation in the 1.7-
$\mu$
m laser is induced by strong intermode-beating of the CW pump source. The pulse repetition rate with an increasing pump power is fixed at 145 kHz, which exactly coincides with the longitudinal-mode beat frequency of the 1211-nm pump laser. Our results may provide a new type of optical modulation (i.e., intermode-beating modulation technique) for a low-cost, compact pulsed laser.
© 2018 IEEE
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