Tech Briefs Magazine - May 2022 - PIT-14

TECHNOLOGY LEADERS Topic
Test & Measurement Systems
Ensuring Optical Fiber Alignment
M
ost optical networks
have many fiber
couplings and even
minor losses at
these junctions will produce significant
signal losses that cause
problems in data transmission.
Precise fiber alignment at the
optical couplings in a network
is, therefore, a prerequisite for
accurate and reliable
optical
data transmission since it produces
the least signal loss before
assembly or packaging of an optical
system. Minimal signal loss
also results in the lowest optical
power requirements which, in
turn, means fewer repeaters,
lower capital costs and reduced
incidence of failure.
Alignment Parameters and Procedures
Effective fiber alignment requires the
precise adjustment of a precision motion
control device and a suitable search algorithm
that has been optimized for use
in the alignment application. Figure 1
shows a typical search operation along
with the positional parameters that are
associated with optical fiber alignment.
In the search procedure, the intensity of
a well-characterized optical input beam
(the laser diode in Figure 1) is compared
against the output signal of the optical fiber
being aligned.
Positional/Rotational Parameters
Motion controllers are employed that
use a coordinate system in which an object
is considered to have six degrees of
freedom: three linear position parameters,
along the X, Y, and Z-axes in a Cartesian
co-ordinate system and three rotational
parameters around those axes
(Figure 1). All movements are defined
in terms of translations along and/or
rotations about the Cartesian axes. The
fiber position is moved through a raster
scan to detect first light - when the
laser beam first enters the optical fiber
(Figure 1). Once first light is detected,
the lateral, longitudinal, and angular
coordinates of the fiber are incrementally
adjusted to maximize the intensity
14
Y
Z
X
Figure 1. The operations and positional parameters of optical fiber alignment; (a) scan operations; (b) positional
parameters for the optical fiber alignment.
of the optical signal output from the fiber.
In the simplest case, only lateral (X,
Y) adjustments are necessary, while in
multi-channel cases, adjustments to all
six degrees of freedom (X, Y, Z, θx, θy,
and θz) may be required.
Motion Control Parameters
Linear or rotary motion stages produce
the controlled motions and trajectories
that move objects during optical
fiber alignment. The following
parameters must be considered when
selecting a motion system for optical
fiber alignment:
* Minimum Incremental Motion (MIM)
is the smallest increment of motion
that a device can consistently and reliably
deliver. It is the actual physical
performance of the motion controlPhotonics
& Imaging Technology, May 2022
PIT Tech Leaders MSK 0522_1.indd 14
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4/19/22 9:07 AM
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Tech Briefs Magazine - May 2022

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