Page 389 - Tunable Lasers Handbook

Tunable External-Cavity

Semiconductor Lasers

Paul Zorabedian
Photonics Technology Depar-mient
Hevvlett-Puckar-d Labor-utories
Pulo Alto, Culqomiu

1, INTRODUCTION

1 .l What Is an External-Cavity Laser?
A tunable external-cavity laser (ECL) (Fig. 1) comprises an optical gain
medium (a laser diode with antireflection coatings on one or both facets), optics
for coupling the output of the gain-medium waveguide to the free-space mode cf
the externall cavity, one or more wavelength-selective filters, and one or more
mirrors for defining an external feedback path. possibly with a piezoelectric
translator (PZT) for fine tuning. The external cavity may also contain additional
components such as polarization optics. bearnsplitters, prisms. telescopes. etc.

1.2 Why Apply External Feedback to Laser Diodes?
7.2. limitations of Diode lasers
Semiconductor Fabry-Perot diode lasers are compact and easy to use, but
they suffer from a number of performance limitations that are potentially serious
in many applications: Solitary laser diodes are often multimode, and they exhibit
large linewidths due to a short photon cavity lifetime and strong coupling

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