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Actively Controlled Optical Beam Delivery System for Laser Welding

IP.com Disclosure Number: IPCOM000115964D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 114K

Publishing Venue

IBM

Related People

Carden, GR: AUTHOR [+2]

Abstract

An optical delivery system for a Nd:YAG laser is described which is independent of average laser power and allows individual control of the energy in each of the four delivery fibers. The power in each beam can be controlled individually by the variable apertures. The energy is monitored and actively controlled to maintain energy balance between the four welding light beams.

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Actively Controlled Optical Beam Delivery System for Laser Welding

      An optical delivery system for a Nd:YAG laser is described
which is independent of average laser power and allows individual
control of the energy in each of the four delivery fibers.  The power
in each beam can be controlled individually by the variable
apertures.  The energy is monitored and actively controlled to
maintain energy balance between the four welding light beams.

      Laser welding of Optical SubAssemblies (OSAs) has recently
become the preferred attachment technique due to the low residual
stresses and high strengths of laser welds (1,2) (such an OSA is
illustrated in Fig. 2).  A laser welding tool has been developed by
the Dukane Corporation for OSA manufacturing (3).

      The tolerance in lateral misalignment between optical
components in the OSA is on the order of 1 micron.  The present
design incorporates a Lumonics laser, 4 mirrors which split the light
into 4 beams, coupling optics to delivery fibers, and focusing optics
from the fiber onto the part to be welded.  The Lumonics Nd:YAG laser
is set at a constant average power, which determines the spot size
and divergence of the light from the laser.  Changing this average
power affects the amount of coupled power to each of the 4 fibers.
The first three mirrors have mirror mounts which have a height
control.  The height control varies the amount of power clipped from
the beam by that mirror.  Therefore, moving the height of the mirror
to vary the power directed to the fiber in any of the first 3 mirrors
affects the power coupled into the following fibers.  The problems
associated with the present system are the following:
  1.  Alteration of the average power in the Nd:YAG laser will
       significantly alter the power in each of the four beams.
  2.  The energy in each of the beams is coupled, that is, changing
the
       energy in one beam can alter the energy in other beams.
  3.  Then energy and focus of the Nd:YAG laser light is sensitive to
       motion in the delivery fibers.
  4.  There is no monitoring of the energy in each of the guns and no
       feedback method for maintaining constant power in a gun.
  5.  There is no active control of the energy in each fiber to
       maintain an energy balance between the four delivered welding
       beams.

      The following alterations in the beam delivery system are
described (Fig. 1).  Replace the mirrors in the first three mounts
with beam splitters.  It should be noted that the light from the...