Vidia-Discrete
Principles of Operation • 47
Principles of Operation
Overview
Traditional diode-laser technology provides high reliability, high
electrical efficiency, and a wide range of available wavelengths in a
compact package. By using an external cavity built around a diode
laser, the Vidia-Discrete provides enhanced performance compared to
an off-the-shelf diode laser, guaranteeing single-mode operation with
narrow linewidth and precise wavelength tuning.
General Theory
The Vidia Discrete’s laser
cavity is based on the
Littman-Metcalf design
(see refs. on page 49),
which uses a diffraction
grating at grazing
incidence to provide
wavelength selectivity.
Essential to the
performance of tunable
external-cavity diode lasers (ECDLs) is a high-quality anti-reflection
(AR) coating on the front facet of the diode. The AR coating turns the
diode into purely a gain element. A collimating lens directs the output
of the diode across a diffraction grating at grazing incidence. The
retroreflector in the laser cavity reflects the first-order diffraction off
the grating to provide feedback. Dispersion provided by the grating
allows only one cavity mode to lase, resulting in a very narrow
Pivot
Point
Laser Diode
Chip
HR
Coating
AR
Coating
Collimating Lens
Retroreflector
Diffraction
Grating
Laser
Output
Wavelength
Tuning
Littman-Metcalf Laser Cavity
US Patent #5,319,668
64X7 rev E.fm Page 47 Tuesday, April 3, 2001 4:16 PM
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