Note: Descriptions are shown in the official language in which they were submitted.
CA 02293094 1999-12-23
FLOURESCENCE BASED OPTICAL SWITCH
FIELD
The invention relates to a fiber optic switch that
utilizes a flexible fluorescent film assembly to emit
fluorescence excited by incident light from the fiber and
collected back into the fiber.
BACKGROUND OF THE INVENTION
The development of fiber optic switches has been in
response to a need to avoid electrical power in the control
lines of devices used in atmospheres with a risk of
explosion and in the presence of liquid where fatal shock
may result.
U.S. Pat. No. 3,999,074, issued to Callaghan, discloses
the general arrangement of utilizing light transmission to
produce a variable electrical output signal to control an
electronic switch. The electronic switch, in turn, controls
power to a load.
U.S. Pat. No. 4,045,667, issued to Hanson, discloses a
single fiber optical control system utilizing a fiber optic
bundle. The fiber optic bundle functions to carry light
from a transceiver to an optical selector. The light in the
optical receiver is reflected back down the fiber optic
bundle to the transceiver where it impinges on one of
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several photo-detectors depending upon the switch position.
The photo-detectors distinguish the spectrum of colored
light to generate multiple electronic control states.
U.S. Pat. No. 4,315,147, issued to Harmer, discloses a
two-position switch having an active actuator. when the
actuator is depressed, it intercepts light passing from one
segment of an optical fiber to another. Conversely, when
the actuator is on the extended position, it permits the
transmission of light. The actuator must me inserted
between the fiber segments thereby creating a gap between
the fiber segments that light must traverse in going from
one segment to the other.
U.S. Pat. No. 4,904,044, issued to Tamulevich,
discloses a flexible filter oriented between two optical
fibers. The filter serves to filter light passing from one
optical fiber to the other. Again, the filter is spaced
apart from each of the two fibers. Moreover, alignment of
the two fibers is critical.
U.S. Pat. No. 4,704,656 issued to Neiger discloses a
single fiber control system using a mirror to reflect light
received from a fiber back into the fiber, when the mirror
is in a reflecting position. Upon moving the mirror into a
non-reflecting position, light from the fiber is not
reflected back into the fiber. The mirror is attached to an
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actuator that swings it between reflecting and non-
reflecting positions with respect to the fiber tip. The
efficiency of the system is very sensitive to parallelism
errors between the fiber face and mirror surface.
U.S. Pat. No. 5,892,862, issued to Kidder et al.,
describes a fiber optic switching system that includes an
optical switch having a movable actuator and a light fiber
coupled to the actuator. Light directed into the fiber
contacts a flexible reflective film whose reflectivity is
conditioned to provide at least two different reflective
surfaces. The fiber in the actuator abuts or is placed in
close proximity to the film throughout its movement from one
position to another. A detector detects light reflected
from the film. The actuator is movable so as to direct
light from the light fiber from the one reflective surface
of the film to another. The detector detects light
reflected from the film so as to determine which reflective
surface of the film the light has been reflected from.
U.S. Pat. No. 5,046,806, issued to Kidder et al.,
discloses a flexible filter attached to a carrier. The
filters are positionable in front of a fiber by movement of
a switch body. Again, a lens and a retro-reflector are used
after the filter in order to focus and reflect the light
back down the fiber.
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In any mirror actuator, the coupling efficiency of the
reflected light and, therefore, the effectiveness of the
signal detection, are sensitive to alignment problems. The
mirror actuator mechanism must orient the mirror surface
parallel and in very close proximity to the fiber face in
order to maintain good efficiency. In any system in which
there is a gap between an end of the fiber and the mirror,
the surfaces of the fiber and mirror will be prone to
contamination. Both back scattering and contamination in
such systems will cause loss of light and, hence reduced
efficiency. Back scattering at any of the other optical
interfaces can create additional noise in the optical signal
and require additional signal processing or detector
compensation to accurately detect the state of the switch.
One way to eliminate the effect of back-scattered light
on detector performance is to utilize the principle of
atomic or molecular fluorescence to create an optical
switch.
The property of fluorescence is well known in the art.
Fluorescence is the result of activity at the atomic level
and is the result of the interaction of the electrons of an
elemental or molecular target, with incident electromagnetic
energy, typically in the form of light. G,lhen a photon of a
suitable energy level is absorbed by the target, it
transfers its energy to the ground state electron, raising
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it to one of the available energy levels. This higher
energy level is usually an unstable physical state. As the
electron tries to return to a more stable state it loses
some of its energy in non-radiative processes. The electron
then makes a transition to the ground state emitting a
photon with less energy and therefore a longer wavelength of
light than that of the absorbed photon. This shift in
energy levels between illumination, or excitation light, and
emitted light, is a characteristic property of a given
compound and is known as the Stokes shift.
This property of fluorescence can be exploited with
simple and low cost optics, filters and electronics to
differentiate and decouple the higher energy, shorter
wavelength impulse optical signal from the longer wavelength
return optical signal and thus eliminate the problems
associated with optical backscatter affecting reflectance
based optical switches. The present invention provides
these and other related advantages.
SUI~iARY OF THE INVENTION
The present invention provides methods and apparatus that
permit the detection of the state of a switch by optically
guiding excitation light through an optical fiber and
illuminating a fluorescent target, or targets, in the switch
assembly. The fluorescent light emitted from the target is
collected into an optical fiber, and optically guiding into
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a detector assembly capable of measuring the relative
intensity and wavelength of the induced fluorescence
emission of the target. Actuation of the switch causes
movement of the optical fiber relative to the targets, or of
the targets relative to the optical fiber, and introduces
different fluorescent targets with different relative
intensity and wavelength of induced fluorescence emission
into the optical path. By detecting these differences the
apparatus determines the state of the switch and initiates
the action that the switch controls.
The present invention may be used in conjunction with a
variety of devices including, but not limited to, surgical
pencils and controllers.
According to the invention there is provided a fiber
optic switching system that includes an optical switch
having a movable actuator and a light fiber means coupled to
the actuator that terminates at an end surface thereof for
conducting light from a light source to the optical switch
mechanism. A flexible film, whose surface is conditioned to
provide at least two different fluorescent surfaces, is
positioned such that an end surface of the actuator abuts
the film throughout its movement from one position to
another. A detector means detects light emitted from the
film and returned by the fiber means. The actuator is
movable so as to direct light from the light fiber means to
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different fluorescent surfaces of the film. The detector
means detects light emitted from the film so as to determine
from which fluorescent surface of the film light has been
emitted.
The film may have a fluorescent surface and a non-
fluorescent surface.
Alternatively, the film may have multiple fluorescent
surfaces that emit at different wavelength regions. In this
case the detectors would have corresponding filters that
would enable them to detect multiple switch states.
Alternatively, fluorescent targets with graduated
strength of emission may be employed for use as continuously
variable controllers.
A major advantage of the flexible film abutting the end
of the actuator or fiber is the insensitivity of that
arrangement to film misalignment. The flexible film
conforms to the face of the fiber or actuator, thereby
maintaining the parallelism between film and fiber surfaces
that are necessary to achieve high coupling efficiency.
Further, by arranging the end of the fiber to abut the
flexible film throughout its range of movement,
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contamination of the area between the fiber and film with
fluids or air-borne particulate is greatly reduced.
The light fiber means may be a single optical fiber or
a group of fibers providing a single optical path to and
from the switching actuator.
A directional coupler may be coupled to the light fiber
means to direct light returning from the optical switch
mechanism to the detector means. The detector means may
include a photo detector positioned to detect light emitted
from the film.
Other objects and advantages of the invention will become
clear from the following detailed description of the
preferred embodiment, which is presented by way of
illustration only and without limiting the scope of the
invention to the details thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself,
however, as well as other features and advantages thereof,
will be best understood by reference to the description
which follows, read in conjunction with the accompanying
drawings, wherein:
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FIG. 1 is a side elevation view in section of an
electrosurgical pencil with the halves of the casing
slightly separated;
FIG. 2 is a side elevation view of an electrosurgical
pencil with the two halves of the casing separated and the
switching actuator detached;
FIG. 3 is a plan view of electrosurgical pencil with
the switching actuator removed from view;
FIG. 4 is a partial sectional view in side elevation of
the device an electrosurgical pencil showing the switching
actuator and the fluorescent target assembly;
FIG. 5 is a partial sectional view in side elevation of
a flexible filter and an end of a switching actuator,
showing the fiber tip aligned to the central section of a
fluorescent target film;
FIG. 6 is a partial sectional view of a portion of a
flexible film showing the structural detail including three
fluorescent sections, an intermediate transparent section
and a transparent protective coating;
FIG. 7 is a schematic diagram of a single fiber
switching system in which the film has a central fluorescent
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area and two adjacent different fluorescent wavelength
areas;
FIG. 8 is a partial sectional view in side elevation of
the end of a switching actuator, showing the fiber tip
aligned to the upper section of a film, having two different
fluorescent surfaces;
FIG. 9 is a schematic view of system utilizing a send
fiber and a receive fiber;
FIG. 10 is a schematic view of a single fiber system in
which light of a shorter wavelength light emitting diode is
collected into one fiber and two filtered detectors detect
and decode the emitted fluorescent light;
FIG. 11 is a schematic view of the energy transfer
process at the atomic level that occurs during fluorescence;
and
FIG 12 is a graph that represents a typical example of
the Stokes Shift in emission wavelength characteristic of
fluorescence.
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DETAILED DESCRIPTION
Referring to FIG. 1, the casing of the electrosurgical
pencil 9 is made up of two casing portions 10 and 12. The
internal components of the pencil 9 are installed on the
recess in casing portion 12. The components include an
electrode 26 that passes through a sleeve 24 and has
attached at its anterior end a conductive cable 28.
Conductive cable 28 is run along the bottom interior surface
of the casing portion 12 entering a cable sleeve 34 before
exiting through the rear aperture 36 of the pencil 9.
Voltage applied to conductive cable 28 by a remote power
source (not shown) is controlled by means of an optical
fiber switching assembly composed of a light fiber 42 that
runs within cable sleeve 34 adjacent to conductive cable 28
within the cable sleeve 34. The light fiber 42 is captured
by switching actuator 20. The light fiber 42 runs all the
way through the interior of the switching actuator 20.
Referring to FIG. 2, switching actuator 20 is pivotally
attached to a pair of spaced apart mounting brackets 23 by
means of pivotal pins 22 that project from either side of
the switching actuator 20 and fit into receptacles in the
mounting brackets 23. The switching actuator 20 has a pair
of protruding knobs 30 and 32 at opposite ends thereof. The
knobs 30 and 32 pass through apertures 14 and 16,
respectively, in casing portion 10 when the two casing
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portions 10 and 12 are engaged. The optical fiber 42 passes
through the switching actuator 20 and ends at end face 40.
In turn, the switching actuator 20 is pivotally mounted on
mounting brackets 23, and end face 40 abuts or is placed in
close proximity to flexible film 11.
Referring to FIG. 3, a top view of the device of FIGS.
1 and 2 without the switching actuator 20 in place is shown.
On the base of the casing portion 12 between mounting
brackets 23 there are located two spring pads 44. The
spring pads 44 are more clearly shown in FIG. 4 as
consisting of a slightly convex sheet material mounted
within a shallow circular receptacle. Contact projections
54 and 56 of the switching actuator 20 abut the spring pads
44 when in position. At the same time, end face 40 abuts
the flexible film 11 as shown. When knob 30 is depressed,
switching actuator 20 pivots about pins 22. Further, the
depression of knob 30 causes contact projection 54 to
depress spring pad 44 and further causes end face 40 to move
upwardly while maintaining contact with flexible film 11.
Alternatively, depression of knob 32 causes contact
projection 56 to depress spring pad 44 and further causing
end face 40 to move downwardly while maintaining contact
with flexible film 11. The spring pads 44 ensure that
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without pressure on either knob 30 or 32, the switching
actuator 20 will be maintained in an intermediate position.
Referring to FIGS. 5 and 6, the mounting arrangement of
flexible film 11 is shown as consisting of mounting bracket
60 affixed to casing half 12 and fitting between a recess 25
formed by projecting elements 19 and 21 belonging to casing
portion 10. Flexible film 11 is positioned so that it is
locked in position between recess 25 and mounting bracket
60. The flexible film 11 is cemented in a trough 31 at the
base of mounting bracket 60.
In the preferred embodiment, flexible film 11 is Mylar
having a mirror surface 18 formed of an aluminum film on its
surface remote from end face 40. The flexible film 11 has a
fluorescent coating 13 formed adjacent one side of a central
fluorescent portion 15 and another fluorescent coating 17 of
a different emission color formed on the other side thereof.
A protective coating 41 overlays the flexible film 11 to
protect it from scratching.
In the intermediate position, the end face 40 is
positioned against the central fluorescent target 15 in
which flexible film 11 emits a wavelength band that brackets
the wavelengths detected by both optically filtered
detectors. Most of the light that exits optical fiber 42
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excites fluorescence in flexible film 11 and emitted
fluorescent light is returned back along optical fiber 42.
Due to the contact that is maintained between the
flexible film 11, the switching actuator 20 and optical
fiber 42, there is limited back scattering and loss of light
due to contamination. When end face 40 abuts fluorescent
target 13, light emanating from optical fiber 42 passes into
fluorescent target 13, inducing fluorescence which is
emitted directly into optical fiber 42 or reflected from
surface 18 and returned into optical fiber 42. Similarly,
when switching actuator 20 is pivoted so that end face 40
abuts the fluorescent target 17, a similar effect is
produced.
Referring to FIG. 7, a broad band (multi-spectral)
light source 71 emits light onto a parabolic reflector 73
that directs the reflected light into a ferrule 75 coupled
to an optical fiber 77. Light from the optical fiber 77
enters a directional coupler 43, which directs approximately
half of the light into fiber 81. The directional coupler 43
is usually a beam splitter but may also be a butt coupling
of fibers or a graded index rod lens as is known in the art.
The directional coupler 43 is equipped with a wavelength
selection filter to select an appropriate excitation
wavelength. Alternatively the wavelength selection filter
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may be incorporated into the reflector or exit window of
light source 71, 72. Light travels down fiber 81 into
electrosurgical pencil 9. Light emerging from the end of
fiber 81 is incident on one of three areas of flexible film
11. Central broad-band fluorescent portion 15 emits
fluorescence detectable by both detectors and enhanced by
mirror surface 18 on the back while fluorescent surfaces 13
and 17 consist of a compound that emits in a wavelength
detected by only one or the other of the detectors.
The emitted light enters into fiber 81 and travels down
to directional coupler 43 where some of the light is
directed into fiber 79 into beam splitter 70. Part of the
light travels down fiber 83 and part down fiber 85. Filters
72 and 74 are complementary to filters 13 and 17,
respectively, and are used to determine in which of the
three positions the end face 40 of pencil 9 is located, in
order to discriminate the wavelength components contained in
the emitted light. For example, if the light was passed
first to a red emitting fluorescent surface and the emitted
fluorescence then collected back into the fiber, by passing
the filtered light through a complementary corresponding
filter, it can be determined whether or not the end face was
abutting the red fluorescent surface. Similarly, by using a
green emitting fluorescent surface on the other side of the
central portion of the flexible film 11 and passing the
corresponding emitted light through a corresponding filter,
CA 02293094 1999-12-23
it can be determined whether or not the end face 40 was
abutting the green fluorescent surface. Detectors 76 and 78
detect any light that may be transmitted through the
corresponding filters 72 and 74.
By utilizing a fluorescent surface in contact with the
optical fiber, sufficient contrast and efficiency of
excitation and emission takes place to allow the different
switching states to be determined. The absence of any gaps
makes the switching assembly less sensitive to contaminants
from adverse environments including fluids and air-borne
particulate that may coat the optical faces if they are
otherwise separated. The absence of any gap also makes the
switching assembly insensitive to normal optical losses from
separation between any source and receiver of similar
dimensions and numerical aperture.
Referring to FIG. 8 there is shown a flexible film 11
having only two surfaces. Surface 45 is non-fluorescent
while surface 47 is fluorescent. Consequently, a single
photo detector 76 with an excitation blocking long-pass
filter or emission bandpass filter 72 in FIG. 9 will suffice
to detect the two different positions and hence two states
of the actuator or switching actuator 20.
Referring to FIGS. 6 and 9, a blue light emitting diode
88 is focused by lens 87 onto ferrule 48. The light enters
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fiber 90 and conducts to coupler 92 where the send and
return fibers are bundled into fiber assembly 100. The blue
light arrives at switching actuator 20 from which it is
emitted and is incident upon the flexible film 11. The
light passes through the clear protective coating 41 and
excites fluorescence in the fluorescent material. Some
fluorescent light is emitted and directly enters the optical
fiber and some passes through flexible film 11 and is
reflected from the mirror surface 18. The emitted light
enters return fiber 91 and is conducted to dichroic optical
block 87. Optical block 87 collimates the beam emitted from
fiber 90 and spectrally splits the beam into two paths,
which are focused onto a dual detector assembly 89. The gap
that would normally be required in order to couple light
from one fiber to the other is substituted for by protective
clear coating 41 which acts as a spacer and provides a
smooth surface for contact with end face 40 and prevents
abrasion of the flexible film 11, contamination and other
problems that attenuate the light.
It is clear that the electrosurgical pencil 9 is but
one of may different devices in which the invention could be
employed. For example, the invention could be incorporated
into an ordinary dual or multistate switch on a switch
panel. It could be used to detect slight misalignment on
critical machine parts but replacing the single mirrored
surface on the back of the flexible film il with a film with
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one having a graded filter. A slight change in alignment of
the latter would change the amount of reflected light
entering the fiber.
In an alternate embodiment of the invention, the
coupler may consist of an excitation light source, an
optical assembly to direct the excitation light into the
surgical pencil assembly connector and collect the
fluorescent emission from the surgical pencil assembly, a
means to separate the light emitted from the fluorescent
target into particular wavelength regions to be detected and
a plurality of detectors to detect these wavelengths
In a further alternate embodiment of the invention the
coupler optical assembly consists of a lens to collimate
light from the excitation source and direct it through a
dichroic mirror oriented at an angle of 45 degrees to the
optical axis of the collimated beam, and that passes the
shorter wavelength light excitation light of the excitation
source.
In still a further alternate embodiment of the
invention, the coupler may consist of an excitation light
source, an optical assembly to direct the excitation light
into the surgical pencil assembly connector and collect the
fluorescent emission from the surgical pencil assembly, a
means to separate the light emitted from the fluorescent
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target into particular wavelength regions to be detected and
a plurality of detectors to detect these wavelengths.
In still a further alternate embodiment of the
invention, the optical assembly within the coupler may
consist of an arrangement of fibers that conducts light from
the illumination source to the optical switch fiber and
collects light from the optical switch fiber and directs it
to two or more optically filtered photo detectors.
In still a further alternate embodiment of the
invention, it is possible to avoid the need for a
directional coupler between the light source and the
detectors by using a plurality of light fibers in a bundle
with only some coupled to the light source and only the
remainder coupled to the detector(s). However, in order for
a dual fiber path system to work a gap must be provided
between the mirror surface and the fibers, so that some off
axis rays can couple from one fiber to the other.
A dual fiber system can avoid the problems associated
with gap contamination and other problems that attenuate the
light by providing a transparent layer of selected thickness
in front of the fluorescent surface. The flexible film may
be transparent of the selected thickness with a mirror
coating on the back so that the film itself provides the
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requisite spacing without permitting the entry of
contamination.
Accordingly, in certain aspects the present invention
provides controllers and surgical pencil assemblies, the
surgical pencil assembly comprising: a handpiece, hand
actuated switch, cable and connector incorporating an
optical path including a proximal end and a distal end, the
handpiece being configured to position the distal end of the
optical path to the fluorescent target; a light emitter
window proximate to the distal end to direct an illumination
light to the fluorescent target and collect the emitted
light from the target; a controller assembly coupled to the
connector of the surgical pencil assembly at the proximal
end comprising an optical or fiber optic light guide to
receive emanating light conducted to the proximal end of the
surgical pencil assembly from the fluorescent target by the
surgical pencil assembly light guide and an optical system
to conduct the emanating light along at least a portion of a
light path to the detector assembly; a wavelength selection
filter aligned with the collection light guide to be
disposed in the light path, the wavelength selection filter
assembly selectively transmitting one or more desired
wavelength bands of the emanating light.
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In still further preferred embodiments, the controller
further comprises a band pass filter maintained at the
proximal end of the excitation light optical path and
disposed between the excitation light emitter and the
excitation light optical path, wherein the band pass filter
transmits a selected wavelength band of light. The selected
wavelength band can be a suitable wavelength of light able
to induce fluorescence in the surgical pencil assembly
fluorescent target.
In still further preferred embodiments, the
illumination light transmitted to the target consists
essentially of a selected wavelength band and the light
collection system further comprises a long pass filter
disposed in the light path, wherein the long pass filter
blocks light having about the same wavelength as the
selected wavelength band and transmits other light; the long
pass filter can be disposed at the distal end of the light
collection system and can block blue light if desired.
The wavelength selection filter assembly can be maintained
upstream in the light path from the long pass filter or the
long pass filter can be maintained upstream in the light
path from the wavelength selection filter assembly, and the
long pass filter can be maintained upstream from the
collection light guide.
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In still further embodiments of the invention, the
present invention provides for surgical pencil assemblies,
the surgical pencil assembly comprising: a body including a
proximal end and a distal end, the body being configured to
position the distal end of the optical path proximate to the
fluorescent target, means for emitting an illumination light
from a location of the body at least proximate to the distal
end; means for collecting and conducting an emanating light
from the fluorescent target along a light path to a
controller assembly coupled to the connector of the surgical
pencil assembly at the proximal end, the controller
comprising an optical or fiber optic light guide to receive
emanating light conducted to the proximal end of the
surgical pencil assembly from the fluorescent target by the
surgical pencil assembly light guide and an optical system
to conduct the emanating light along at least a portion of a
light path to the detector assembly; a wavelength selection
filter aligned with the collection light guide to be
disposed in the light path, the wavelength selection filter
assembly selectively transmitting one or more desired
wavelength bands of the emanating light.
In certain preferred embodiments, the target is
illuminated by conducting the illumination light from a
light source maintained at the proximal end of the surgical
pencil assembly to a light emitter maintained at the distal
end of the surgical pencil assembly switch via an
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illumination light guide and then emitting the illumination
light to the fluorescent target.
In further preferred embodiments, the illumination
light is transmitted through a band pass filter maintained
at the distal end of the surgical pencil assembly, wherein
the band pass filter transmits a selected wavelength band of
light and blocks other light. The selected wavelength band
can be light able to induce fluorescence in the fluorescent
target.
In other preferred embodiments, the illumination light
emitted from the light emitter consists essentially of a
selected wavelength band and the light collection system
further comprises a long pass filter disposed in the light
path, wherein the long pass filter blocks light having about
the same wavelength as the selected wavelength band and
transmits other light.
In some preferred embodiments, the illumination light
is conducted from a light source maintained at the proximal
end of the surgical pencil assembly and the controller
assembly to the light emitter at the distal end of the
surgical pencil assembly via the illumination light guide,
and wherein a band pass filter that transmits substantially
only a desired wavelength region of excitation light is
disposed at the distal end of the illumination light guide.
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In other preferred embodiments, the controller assembly
comprises a fixed lens that is matched to the numerical
aperture of the light guide of the surgical pencil assembly.
This lens collects collimated light from the illumination
path and focuses and transmits it into the optical light
guide at the proximal end of the surgical pencil assembly.
It also collects and collimates light emitted from the
proximal end of the surgical pencil assembly light guide and
delivers it into the optical path of the controller detector
assembly. The emitted light being transmitted along the
light path passes through optical transmissive and
reflective filters that select and dispose the light toward
the detectors.
In further aspects of the invention light from the
excitation source is coupled into a lens that collects and
collimates the excitation light and delivers it into the
optical filter assembly and then to the lens that couples
the excitation light into the light guide of the surgical
handpiece.
In still more aspects, the present invention provides
filter assemblies for a surgical pencil assembly to transmit
the emission from the fluorescent target to a
controller/detector, comprising: a casing including a distal
end with a first opening to receive a proximal section of
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the surgical pencil assembly, and a transmission passage
extending between the opening and the detector detectors,
the transmission passage being configured to transmit light
along a light path from the distal end to the proximal end
of the casing; a rotatable housing attached to the casing,
the rotatable housing including a knob configured to be
gripped by a user and a filter holder positioned in the
casing, the filter holder having a plurality of windows;
and, at least one filter received in one of the windows, the
housing rotating within the casing to position the at least
one filter in alignment with the light path for selectively
configuring the controller for different devices.
In other preferred embodiments, the filter assembly further
comprises a fixed lens that is matched to the numerical
aperture of the light guide of the surgical pencil assembly.
This lens collects and collects and collimates light from
the proximal end of the surgical pencil.
Accordingly, while this invention has been described
with reference to illustrative embodiments, this description
is not intended to be construed in a limiting sense.
Various modifications of the illustrative embodiments, as
well as other embodiments of the invention, will be apparent
to persons skilled in the art upon reference to this
description. It is, therefore, contemplated that the
CA 02293094 1999-12-23
appended claims will cover any such modifications or
embodiments as fall within the true scope of the invention.
26
