Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MULTIPLE SPECTRAL BAND OPTO-MECHANICAL MODULATOR
Background of the Invention
Prior to the present invention modulation of a large
aperture radiation source was achieved by placing in front
of such source a rotating and stationary wheel of
alternating opaque and transparent radial segments. In
this arrangement all wavelengths are modulated with the
same temporal waveform. For certain applications it is
necessary to modulate a single radiation source to provide
simultaneously distinct outputs in different spectral
regions and at different pulse repetition frequencies.
Summary of the Invention
Accordingly, it is ari object of this invention to
provide a new and novel mechanical modulator.
It is another object of this invention to provide a
mechanical modulator to obtain simultaneously but
independently radiation iri distinct spectral regions at
different pulse repetitiori frequencies.
Briefly, in one embodiment a mechanical modulator
which provides
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simultaneously two distinct signals in two spectral regions at different
pulse repetition frequencies includes three wheels: a first filter wheel
rotating at a first velocity having first and second alternating radial seg-
ments, said first segments being transparent at both spectral regions and
said second segments being transparent at the shorter of the two spectral 5
regions and opaque at the longer; a second filter wheel rotating at a second
velocity having first and second alternating radial segments, said first
segments being transparent at both spectral regions and said second
segments being transparent at the longer of the two spectral regions and
opaque at the shorter; and a third wheel which is stationary, also having 10
first and second alternating radial segments, said first segments being
transparent at both spectral regions and said second segments being opaque
at both spectral regions. This third wheel is arranged intermediate the
first and second filter wheels. When the rotating filter wheels are spun
past the stationary wheel modulation is obtained in that spectral region 15
where the segments are opaque; the first nilter wheel modulates the longer
wavelengths and vice versa.
(U) If desired, additional modulating wheels or other types of modulators
may be used to superimpose modulation on the outputs from the afore-
mentioned modulator. 20
Brief Description of the Drawings
(U) The above-mentioned and other features and objects of this invention
will become more apparent by reference to the following description taken
in conjunction with the accompanying drawings, in which:
(U) FIG. 1 is a sketch of a three wheel rnodulator of utility in the practice
25
of the present invention;
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(U) FIG. 2 is a sketch illustrating the passbands of the.filters employed
in the modulator of FIG. 2; -
(U) FIG. 3 is a sketch showing the output from the modulator of FIG. 1
at two different spectral bands;
(U) FIG. 4 is a sketch of another embodiment of a rnultiband niodulator 5
of utility in the practice of the present invention;
(U) Fig. 5A is a sketch of a modification of the modulator of Fig.l;
Fig. 5B is a sketch illustrating a typical output of the
modulator of Fig. 5A;
(U) FIG. 6 is a pictorial representation illustrating a means for supporting
and driving the modulator of FIG. 1; and
(U) FIGS. 7A-7C are sketches illustrating an alternative modulator re- 10
quiring only two wheels.
Description of Preferred Embodiments
(C) Referring now to FIG. 1, there is illustrated thereby a first embodi-
ment of a mechanical modulator which provides simultaneously but independe t
modulation of a radiation source in two distinct spectral wavelength bands 15
and'1 The modulator comprises three wheels 10, 12 and 14
having substantially identical segments thereon. Wheels 10 and 14 are
rotating filter wheels while wheel 12 is a stationary wheel. For clarity
and purposes of illustration, the means for rotating filter wheels 10 and 14
are for holding the wheels in a fixed relationship to each other are not 20
shown in this FIG. (see FIG. 6). The wheels are normally znaintained
next to a source of radiation (not shown). The wheels are spaced as close
to each other as physically practical in order to minimize waveguiding
effects and direct radiation at large field angles. The radiation 16 impinges
on filter wheel 14 first in this embodiment, however, in alternate e:nbodi- 25
rnents the arrangement could be reversed with wheel 10 positioned adjacent
tize source of radiation.
(C) Filter wheel 14 is made up of alternate radial segments 18 and 20.
5eo:nents 18 are transparent to both spectral wavelength bands of interest.
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13 4 1 - 33
Segments 20 have a transmission characteristic substan-
tially as shown in diagram A of FIG. 2, that is, over the
band shown as AA1 substantial amounts of radiation will
pass through these segments while radiation of longer
wavelengths will be blocked thereby.
Filter wheel 14 is made of a material which will pass
the desired bands. Quartz, glass, sapphire, or silicon,
for example, could be used depending on the bands of
interest. The segments 20 are constructed by a deposition
of filter material on one side of the filter wheel 14.
Such filter material will have the transmission
characteristics as shown in diagram A of FIG. 2. The
filter materials can be evaporated on by a vacuum
deposition process. Dielectric multilayer interference
type filters have been deposited on a substrate with
success.
Filter wheel 12 is made up of alternate radial
segments 22 and 24. Segmerits 22 are transparent to both
spectral wavelength bands of interest and segments 24 are
opaque thereto. Preferably filter wheel 12 is a metal disc
having slots 22 therein. Wheel 12 is preferably plated on
the side facing the energy source to reflect energy so
that the wheel will absorb as little energy as possible.
The other side of wheel 12 is blackened to improve the
emissivity of the material and, thus, minimize blade
heating.
When filter wheel 14 is rotated with respect to
stationary wheel 12, there is provided a modulation of the
incident radiation 16. All energy in the A1,1 band goes
through the filter segments 20 essentially unmodulated as,
of course, does that through the transparent sections 18.
Actually, the energy in the AX1 band exiting the stationary
wheel will have some slight ripple, perhaps 10% or 15%
thereon due to the difference in transmissibility between
the filter segments 20 and the clear segments 18, since
the filter segments 18 are not as transparent as segments
20 in the band DA1.
The energy in the A1~2 band as shown in diagram B of
FIG. 2 is essentially blocked by the filter sections 20 of
wheel 14, while energy in
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1 4153 this band passes through the trardsparent sections 18. Thus, in
conjunction
with stationary wheel 12 there is prav?ded substantially 100% modulation of
the energy in the Z;'',,-, band. T'his modulated signal essentially passes
through wheel 10 undisturbed, as will be described hereinafter, to pruvide
a signal substantially as shown in waveform A of FIG. 3. 5
(C) Filter wheel 10 is made up of alternate radial segments 26 and 28.
Segments 28 are transparent to both spectral wavelength bands of interest.
Segments 26 have a transmission characteristic substantially as shown in
diagram B of FIG. 2, that is, over the band substantial arnounts of
radiation will pass through the segments 26 and shorter wavelengths will 10
be blocked thereby.
(U) Like filter wheel 14, filter wheel 10 is also made of a material which
will pass both the desired bands, and again the segments 26 are constructed
by deposition of filter materials to provide the desired transmission
characteristics. 15
(C) Thel energy, which is essentially unmodulated by filter wheel 14,
as described above, except for a slight ripple thereon, is modulated
by the filter wheel 10 in conjunction with wheel 12. The energy
passes through the clear segments 28 while it is blocked by the filter
segments 26, thus providing a signal substantially as shown in waveform B 20
of FIG. 3.
(C) Although filter wheels have been shown in the embodiment previously
described to obtain sirnultaneous amplitude modulation of a radiation source
in two distinct spectral wavelength bands, this is only the preferred
method of deriving this result. FIG. 4 illustrates an alternative arrange- 25
ment.
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Radiation from a source 30 is directed to a modulator
32 which comprises individual rotating vane type
modulators 34 and 36 driven by motors 35 and 37, respec-
tively. These rotating varle modulators are well known,
however, in this embodiment the individual vanes 38 and 40
are constructed of materials which filter the radiation
from the source 30 in a predetermined manner. For example,
the vanes are constructed of quartz with a filter material
deposited thereon. In the embodiment shown, modulator 34
includes vanes 38 having a transmission characteristic
substantially as shown by diagram A of FIG. 2, and
modulator 36 includes vanes 40 having a transmission
characteristic substantially as shown by diagram B of FIG. 2.
Two distinct signals are provided by this arrangement
in the manner previously described since the rotating
vanes are substantially equivalent to the rotating and
stationary wheel combinations previously described. When
vanes 38 are orientated vertically, only LA1 radiation will
pass through the vanes, and when vanes 38 are rotated
horizontally all radiatiorl will pass through. Therefore,
the modulator 34 provides radiation output of the type
shown in waveform A of FIG. 3, although more rectangular
in shape. Similarly, modulator 36 provides modulation of
the type shown in waveform B of FIG. 3, although, again,
more rectangular in shape.
As mentioned previously, further superimposed
modulation on either or both fundamental signals shown in
FIG. 3 can be achieved by providing additional modulating
members. This is illustrated in FIG. 5A where the output
of radiation source 30 is directed to a modulation system
comprising wheels 10, 12, 14 as previously described, as
well as a further wheel 42. Wheel 42 is constructed in the
same manner as wheels 10 and 14, and is used to further
amplitude modulate one of the signals shown in FIG. 3 and
preferably, that of the wheel which is the closer.
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For exa...e:e, if it is desired to modulate the signal shown in waveform B
of FIG. 3, then wheel 42 would have transmission characteristics similar
to wheel 10.
(C) It is obvious that wheel 42 could be replaced by a vane type modulator
as shown in FIG. 4 and that various combinations of rotating vane and filter 5
wheel modulators can be employed in the manner taught herein.
(C) FIG. 6 illustrates a reduction to practice of the multiple band mechan-
ical modulator of FIG, 1. Stationary wheel 12 is mounted in a housing 50
using screws 52. The rotating -wheels 10 and 14 are mounted on rings 54
and arranged on either side of stationary wheel 12. For clarity purposes, 10
only one side of housing 50 is shown with wheel 10 arranged thereon. Wheel
14 is arranged similarly on the reverse side of the housing.
(C) Wheel 10 is arranged in position on the housing by having the shoulder of
ring 54 arranged in guide rollers 56, 58 and a spring loaded friction drive
wheel 60. Constant pressure is maintained on the wheel 10 by a lever 62. 15
The friction drive wheel 60 receives rotational energy from a motor 64
through a wheel on its shaft which is not shown in the Figure. Wheel 14
on the reverse side of the housing likewise receives power from a motor 66.
(C) A magnetic pickoff 70 is arranged proxiinate the wheel 10 to act as a
chopping frequency mcnitor. The magnetic pickoff operates in conjunction 20
with at least one or rnore of screws 72 which is magnetic.
(C) Arranged on the other side of the shafts of motor 64, 66 are a pair of
corresponding tachometers which in a rate servo arrangement permit
controlled speeds of the wheels 10 and 14 to produce a desired output
frequency. 25
(C) Referring now to FIGS. 7A-7C, there is illustrated thereby another
embodiment of a multiple spectral band opto-mechanical modulator. This
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4 1 5 3 a
embodiment requires two filter wheels and no third wheel. Two identical
filter wheels 80 and 82 are used to provide simultaneously two distinct
amplitude modulators in two distinct wavelength bands. The filter wheels 80
and 82 are positioned so as to receive radiation 84. Wheel 82 is a rotating
wheel while wheel 80 is a stationary wheel. 5
(C) The wheels 80, 82 are shown in detail ir. FIG. 7A and include alter-
nating first and second groupings of radial segments 86 and 88. Only one
each of said groupings are illustrated; however, the wheel is completely
filled with said alternating groupings. Groupings 86 comprise alternate
radial segments 90 and 92. 10
(C) Segments )0 are substantially opaque to both spectral bands of
interest and A' ). Segments 92 have a transmission characteristic
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substantially as shown in diagram A of FIG. 2, that is, over the band
shown as LAI il , substantial amounts of radiation will pass through these
segments while radiation of larger wavelengths will be blocked thereby. 15
(C) Groupings 88 comprise alternate radial segments 93 and 94. Segments
33 have a transmission charact.e:-istic substantially as shown in diagram B
of FIG. 2, that is over the banci shown as substantial amounts of
radiation will pass through these segments while radiation of shorter
wavelengths will be b'ocked thereby. Segments 94 are transparent to both 20
spectral bands of interest ( f1 and ZS .h, ).
(C) In this arrangement no third wheel is required and two outputs are
obtained as shown in FIG. 7C. The only drawback to this arrangement is
that the frequencies of the two signals a and b are not completely in-
dependent of each other as in the earlier described embodiments. As in 25
the manner of FIG. 5A additional means may be employed to further
modulate one of the signals.
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(U) Although the modulators have been described in conjunction with a
radiation source, it is obvious that they could also be used to modulate
a signal into the detector of a receiver. Thus, it is to be understood
that the embodirrients shown are illustrative only and that many variations
and modification.s may be made without departing from the principles of 5
the invention herein disclosed and defined by the appended claims.
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