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High Power Laser Diode with Self Adjusted Thermal Lateral Mode Control

IP.com Disclosure Number: IPCOM000110122D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 3 page(s) / 115K

Publishing Venue

IBM

Related People

Bona, GL: AUTHOR [+5]

Abstract

This article describes a solution to the lateral mode control problem of high power laser diodes by using a special laser design which automatically corrects refractive index profile changes caused by temperature gradients occurring at high output power levels.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

High Power Laser Diode with Self Adjusted Thermal Lateral Mode Control

       This article describes a solution to the lateral mode
control problem of high power laser diodes by using a special laser
design which automatically corrects refractive index profile changes
caused by temperature gradients occurring at high output power
levels.

      High power laser diodes for, e.g., optical storage
applications, need to operate in the fundamental mode to ensure beam
stability and the possibility of diffraction-limited focussing of the
laser beam.  At the same time the lasers should offer the highest
possible optical output power in that fundamental mode.
Unfortunately, experiments always reveal that for lasers with a weak
lateral guiding, e.g., ridge, rib or stripe geometry lasers, lasing
no longer occurs in the fundamental lateral mode if a certain power
limit is exceeded.  This power limit depends on the laser design.
Our theoretical and experimental analyses of this mode control
problem show that lateral temperature differences in such laser
diodes are the main cause for mode instability.  In more detail, the
lateral mode is determined by the effective refractive index profile
in the lateral direction.  The ohmic heating of the laser diode by
the injected electron current causes an increase of the effective
refractive index of the laser diode in its center region proportional
to the corresponding increase in temperature.  If this increase in
guiding is large enough, it changes a laser with only one allowed
lateral mode (i.e., the fundamental mode) into one with two or even
more allowed lateral modes.  The mode stability or mode control
problem of high power laser diodes is therefore equivalent to the
problem of avoiding large temperature differences in the gain bearing
region of the laser diode cross-section.

      To avoid large temperature differences in or close to the gain
bearing region we introduce additional ohmic heat sources at each
side of the lateral confinement structure, i.e., at the sides of the
ridge for a ridge laser.  Originally, the gain bearing region is also
the dominating heat source in a laser diode since both, gain and
temperature, are caused by the injected electron current.  By adding
the additional heat sources, we increase the temperature in those
regions neighboring the gain bearing region until the temperature
profile is nearly flat in a large region with the gain bearing region
at its lateral center.  In principle, there are two classes of
thermal heating inside a laser.  Firstly, there is the ohmic eating
described by POhm =...