FIBRE OPTICAL ICE DETECTOR

DETECTEUR DE GLACE SUR FIBRES OPTIQUES

English Abstract

This invention called "Fiber Optical Ice Detector" (FOID)
remotely detects early formation of ice around dedicated optical
fibers on structure surfaces. The fibers may be glued to the
surface, embedded into it in case of composite materials, or
otherwise attached to it. The invention is based on the light
diffusion by ice and light reflection from ice boundaries, that
optically couple multimode optical fibres in specially built
sensitive zones. Such zones may be multiple in order to achieve
sensing distributed along the fibers (rather than at a single
location). Sensitive zones consist of specially profiled cross
sections that amplify the effects involved by allowing most of
the light to be modulated. Thus, the invention makes it possible
to achieve early detection of small quantities of ice at
multiple locations along the fibers. A most widespread use of
this invention is expected in the aircraft industry for remote
detection of ice formation around critical parts - wings.

French Abstract

Cette invention appelée «Détecteur de glace pour fibres optiques» (DGFI) détecte, à distance, la formation de glace autour de fibres optiques spécialisées sur les structures de surface. Les fibres peuvent être collées à la surface, y être enchâssées dans le cas des matériaux composés, ou y être fixées par un autre moyen quelconque. L'invention est fondée sur la diffusion de la lumière par la glace et la réflexion de la lumière à partir des bordures de la glace, qui couplent optiquement des fibres optiques multimodes dans des zones sensibles spécialement construites. Ces zones peuvent être multiples afin de permettre une détection le long des fibres (au lieu d'un endroit unique). Les zones sensibles consistent en des sections transversales spécialement profilées qui amplifient les effets en cause en permettant de moduler la majeure partie de la lumière. L'invention permet ainsi de détecter des petites quantités de glace à plusieurs endroits le long des fibres. On s'attend à ce que l'usage de cette invention devienne répandu dans l'industrie aéronautique pour fins de détection à distance de la présence de glace sur les parties critiques - ailes.

Claims

CLAIM
Ice monitoring or detection arrangement comprising
paired input and output optical fibres with
corresponding emitter and detector circuits and having
zones of the fibers modified specifically for optical
cross-coupling between them that is modulated by the
onset of the ice formation around such sensitive zones,
whereby the said zones are formed by destroying the
light-guiding properties on one side of both fibers by
removing the cladding and, importantly, the portion of
the fibre core such that what is left of the core
becomes light-diffusive, with the active zones thus
obtained either concatenated to form a single zone or
suitably distributed along the length of the fibre to
correspond to the locations where monitoring for ice
formation is required.

Description

CA 02048991 1998-0~-13 ~
DESCRIPTION
This invention is called "Fiber Optic Ice Detector"
(FOID). It remotely detects formation of ice around
dedicated optical fibers on a structure surface. The
fibres may be glued to the surface, embedded into it in
the case of composite materials, or otherwise attached
to it.
The invention is based on the light diffusion by ice
and light reflection from ice boundaries, which
optically couples multimode optical fibres at
designated locations. Fibres must be laid in groups of
two at least. Groups of two (pairs) are assumed
throughout this text for simplicity. One is designated
as the "IN" fibre. Light from a source is input into
it. Another fibre is the "OUT" fibre. Light is received
by it and passed to the light detector, Figure 1. The
fibers have their active zones treated on one side
anti-symmetrically so as to remove the coating, declad
them and remove a portion of their cores. The remaining
portion of the cores must exhibit light diffusion
properties as indicated in the insert of Figure 1. Such
treatments may be done using hand tools as illustrated
in Figure ~.
The arrangement operates according to the illustration
of Figure 1 where the ''IN'I and "OUT" fi~ers are
normally not coupled and ice couples them optically.
There will normally not be a reading on the light
detector at the end of the "OUT" fibre. Presence of ice
produces a reading on this detector.
Essentially, the arrangement makes use of the fact that
the light refraction index of ice is much larger than
that of either air or water. As ice reaches deep into
the core of the "IN" fibre, much of the light escapes.
With the refraction index of ice larger than that of
the surrounding air or water, ice acts as a core of a
,i ~.

CA 02048991 1998-0~-13 p4
newly formed conduit for light, thus allowing some
light propagating through it to reach the "OUT" fiber
and, in turn, the light detector.
For simplicity, Figure 1 shows only a single sensitive
zone for each fiber. A major feature of the proposed
arrangement is the ability to produce multiple
sensitive zones along the fibers, thus achieving ice
detection/monitoring distributed along the fibres as
desired, reducing the amount of wiring and the number
of signal channels required.
The signal processing used is illustrated in Figure ~.
It is a prior art of differential amplification of two
signals, one from the "IN" fibre's end opposite the
light source and the other from the "OUT" fibre (Figure
1). When one of these increases, the other decreases,
and vice versa. By algebraically subtracting them, this
differential amplification improves the overall
sensitivity [as in (+6)-(-5)=(+11)] while rejecting
much of the common-mode noise such as the light source
intensity fluctuation. The third detector in Figure 3
was used in a PID control loop to regulate the light
source output - representing also a prior art ln the
field.
Zones of the paired fibers as illustrated in Figure 1
are nominally decoupled. Ice couples them. The amount
of light reaching the detector on the "OUT" fibre
increases when there is ice. Another possible
arrangement is when the corresponding zones of the "IN"
and "OUT" fibers are directed towards each other
(relative to Figure 1, both fibers are rotated towards
each other by 90~). They are nominally coupled. Ice
reduces the amount of such coupling by diffusion.
.. ~.

CA 02048991 1998-0~-13
List of Figures:
Figure 1: Schematics of the Principle of Operation
Figure 2: Sample Fiber Profile in the Treated Zone
Figure 3: Making the Zone Using Hand Tools
Figure 4: Signal Processing
~'

Representative Drawing