Double-mode laser sources are attractive for many applications,
such as optical sensing, terahertz (THz) wave generation and
maging, dual-wavelength interferometry, optical switching,
wavelength division multiplexing (WDM) [1–5] . Simultaneous
dualmode emission from a high-power laser source can be useful and
practical to investigate the non-linear optical processes [6] . Fast
kHz) scan rates and wide fine tuning ranges are needed to per-
orm spectroscopic investigations of turbulent media and short-
iving molecules. Furthermore, the lasers emitting within 1550 nm
spectral region are very important for applications in tele-
communication systems [3] .
Biebersdorf et al. demonstrated a quantum-dot laser that can
be operated in a dual-mode modus, where the mode-spacing can
be tuned continuously between 1.1 and 34 nm around 1075 nm
7]. Chi et al. reported a tunable dual-wavelength operation of a
diode laser system based on a tapered diode ampli fi er with dou-
ble-Littrow external-cavity feedback around 80 0 nm. The fre-
quency difference of the two wavelengths was tunable from 0.5 to
5.0 THz [8]. Tsai and Wysocki realized an external cavity diode
aser (ECDL) that can be tuned up to 7 cm 1 with scan rates up to
5 kHz [9].
In the present study, a broadly fast fi ne single-mode (7 cm 1 ,
1.5 nm, 210 GHz) and coarse double-mode (120 nm) wavelength-