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Monolithic Laser Arrays with Single-Lobed Farfield

IP.com Disclosure Number: IPCOM000115984D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 96K

Publishing Venue

IBM

Related People

Lenth, W: AUTHOR [+2]

Abstract

Coherent arrays of diode lasers have become very attractive as high-power injection lasers. These devices consist of a large number (10-40) of closely-spaced laser elements. The optical coupling between the elements results in phase-locked operation. However, there is no active control of the phase shifts between adjacent laser elements and the array mode - so-called supermode - that results in the lowest laser threshold exhibits a phase shift of 180 degrees between adjacent elements. As a result, the far-field pattern of these linear arrays is dual-lobed which limits the usefulness of these arrays in many important applications.

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Monolithic Laser Arrays with Single-Lobed Farfield

      Coherent arrays of diode lasers have become very attractive as
high-power injection lasers.  These devices consist of a large number
(10-40) of closely-spaced laser elements.  The optical coupling
between the elements results in phase-locked operation.  However,
there is no active control of the phase shifts between adjacent laser
elements and the array mode - so-called supermode - that results in
the lowest laser threshold exhibits a phase shift of 180 degrees
between adjacent elements.  As a result, the far-field pattern of
these linear arrays is dual-lobed which limits the usefulness of
these arrays in many important applications.  Several approaches have
been pursued to obtain single-lobed far-fields including the
construction of external laser cavities containing special optical
elements and the design of Y-shaped laser elements.  All of the
present methods use complicated external optics and/or introduce high
losses for the lasers.

      Disclosed is an approach for obtaining single-lobed farfields
from linear laser arrays.  The approach is based on the use of
etched-mirror technology and lithographic fabrication techniques
which permit in the near-field the introduction of 180 degrees phase
shifts between the output radiation from adjacent laser elements.
This  can be achieved by using appropriate periodic offsets between
adjacent etched laser mirrors or by periodic offsets of 45 degrees
reflectors fabricated in front of each laser element for obtaining
the laser output in the direction perpendicular to the wafer surface.

      The case of surface emitting lasers is illustrated in the
Figure which shows 45 degrees mirrors fabricated a few microns away
from the etched laser facets.  Such reflectors can be fabricated
using gold-plated mirror technology following the
full-wafer-processing approaches described in (1,2).  The facets of a
parallel laser array are etched uniformly along a straight line,
i.e., this phaselocked laser array will exhibit the conventional
180 degrees phase shift between adjacent laser elements at the
location
of the output facets.  The 45 degrees mirrors are positioned in a
staggered arrangement with a displacement of m &lambda./2 where m is
an integer number and &lambda.  the laser wavelength to correct this
180 degrees phase shift in the near-field of the emission from each
element.  As a result, the farfield of the array consisting of the
superposition of th...