An optical system for receiving and collimating light and for transporting and processing light received in each of N wavelength ranges, including near-ultraviolet, visible, near-infrared and mid-infrared wavelengths, to determine a fraction of light received, and associated dark current, in each wavelength range in each of a sequence of time intervals

Gore, Warren J.

NASA Technical Reports Server

(12) United States Patent
Gore
(54) MULTIPLE WAVELENGTH LIGHT
COLLIMATOR AND MONITOR
(75) Inventor: Warren J. Gore, Foster City, CA (US)
(73) Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, DC (US)
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 1321 days.
(21) Appl. No.: 11/398,733
(22) Filed:	 Mar. 31, 2006
(51) Int. Cl.
GOIJ3/00	 (2006.01)
(52) U.S.	 Cl .	 ...................................................... 356/300
(58) Field of Classification Search .................. 356/300
See application file for complete search history.
(56) References Cited
U.S. PATENT DOCUMENTS
4,164,373	 A	 *	 8/1979	 Schuss et al .	 ............... 356/316
5,371,358	 A	 *	 12/1994	 Chang et al .	 ................ 250/226
(lo) Patent No.:	 US 7,869,029 B1
(45) Date of Patent:	 Jan. 11, 2011
5,412,200 A *	 5/1995 Rhoads .................... 250/201.9
OTHER PUBLICATIONS
Carbary et al. "Ultraviolet and visible imaging and spectrographic
imaging instrument", Jul. 1, 1994, Applied Optics, vol. 33 No. 19, pp.
4201-4213.*
Tomasko et al. "The Descent Imager/Spectral Radiometer (DISR)
Aboard Huygens", 1997, European Space Agency, 1177, pp. 109-
138.*
Rieser et al. "Luminscence dating: A new high sensitivity TL/OSL
emission spectrometer", 1999, Quarlernary Geochronology, vol. 18,
pp. 311-315.*
* cited by examiner
Primary Examiner Gregory J. Toatley, Jr.
Assistant Examiner Kara E Geisel
(74) Attorney, Agent, or Firm John F. Schipper; Robert M.
Padilla
(57)	 ABSTRACT
An optical system for receiving and collimating light and for
transporting and processing light received in each of N wave-
length ranges, including near-ultraviolet, visible, near-infra-
red and mid-infrared wavelengths, to determine a fraction of
light received, and associated dark current, in each wave-
length range in each of a sequence of time intervals.
6 Claims, 4 Drawing Sheets
^31
Collimator
Shutter
39
	
Heater I SI	 InGaAs	 TEC
Controller ^—
	 Spectrometer	 Spectrometer—^ Controller
	
41	 43
Spectrometer	 Spectrometer
Electronics
	 Electronics
45
Data Acquisition & Control
System
Shortwave Spectroradiometer (SWS) Block Diagram
https://ntrs.nasa.gov/search.jsp?R=20110004222 2019-08-30T14:25:21+00:00Z
/-I1
22
G., -n, 23-n
FE
5
7
19-n (NA-n)
Shutter
13
Light
Source
FIG. 1
U.S. Patent	 Jan. 11, 2011	 Sheet 1 of 4	 US 7,869,029 B1
U.S. Patent	 Jan. 11, 2011	 Sheet 2 of 4	 US 7,869,029 B1
^ x I
31
//—
Collimator
33
35
Shutter
38	 37
	 39	
40
Heater	 SI
	 InGaAs	 TEC
Controller	 Spectrometer
	 Spectrometer	 Controller
41	
-43
Spectrometer
Electronics
Spectrometer
Electronics
Data Acquisition & Control
System
Shortwave Spectroradiometer (SWS) Block Diagram
FIG. 2
45
U.S. Patent	 Jan. 11, 2011
	 Sheet 3 of 4	 US 7,869,029 B1
16	 is	 20	 22	 24	 26
0.05
0.02
0..0l
0.00
0..06
E
.0
0,03
UTC
Fig. 3
0.12
0-10
E
E 0.08
0.06
rylV
O-D4
0.02
U.S. Patent	 Jan. 11,2011	 Sheet 4 of 4	 US 7,869,029 BI
0.00
18.0 UTC
19.0 UTC
21.0 UTC 20.0 UTC
21.0 UTC
2
20.0 UTC	 2.0 UTC
18.0 UTC
ti
ti 22.0 UTC
19.0 UTC
500	 1000	 1500	 2000
Wavelength {n m)
Fig. 4
US 7,869,029 B1
1
MULTIPLE WAVELENGTH LIGHT
COLLIMATOR AND MONITOR
ORIGIN OF THE INVENTION
2
FIGS. 3 and 4 graphically illustrate zenith radiance as a
function of observation time and wavelength on a selected
day, using an embodiment of the invention.
This invention was made, in part, by one or more employ-
ees of the U.S. government. The U.S. government has the
right to make, use and/or sell the invention described herein
without payment of compensation therefor, including but not
limited to payment of royalties.
FIELD OF THE INVENTION
This invention relates to collimation and monitoring of
light intensity in a plurality of wavelength intervals.
BACKGROUND OF THE INVENTION
Determination of useful spectrum of a light source that is
spaced apart from the measuring instrument must take
account of contributions from the ultraviolet, visible, near-
infrared, mid-infrared and (optionally) far-infrared, must take
account of variation of these contributions with time, and
must provide compensation for contributions from dark cur-
rent, which would be sensed when access to the light source
is interrupted. Where possible, the light sensor should use
components that are already known to be reliable and robust.
What is needed is a light collimator and light intensity
monitoring system that simultaneously receives and pro-
cesses light in three or more overlapping or isolated wave-
length intervals and estimates dark current within each inter-
val. Preferably, the system should have a relatively small light
acceptance angle, to discriminate against and prevent pro-
cessing of light from a source outside a small acceptance
region. Preferably, the system should permit comparison of
light received in specified wavelength intervals with a dark
current signal associated with each wavelength interval, for
normalization purposes. Preferably, the system should maxi-
mize use of reliable, off-the-shelf components in order to
maximize interchangeability and data reproducibility.
SUMMARY OF THE INVENTION
These needs are met by the invention, which provides a
light collimation system that processes and monitors light
intensity received in each of two or more overlapping or
isolated wavelength intervals. Light is received at a light
collector and collimator having a relatively small light accep-
tance angle, in an angular range of 1-2°. This light is received
at N subsets (N?2) of non-identical optical fibers, with each
fiber's optical characteristics being chosen for optimal trans-
mission of light in a specified wavelength interval. The sys-
tem includes a shutter having a controllable duty cycle, to
allow comparison of system dark current (system-off) with
system-on current within each wavelength interval, for refer-
ence and correction purposes. An electronics system receives
and analyzes the transmitted light in each wavelength inter-
val, in the system-off and system-on conditions. Dark current
is analyzed over different time intervals, as well as different
wavelength intervals, to identify possible anomalies in the
light source and/or light processing electronics. A plurality of
wavelength intervals is analyzed, for total radiance and for
dark current effects.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 schematically illustrates an embodiment of the sys-
tem.
FIG. 2 is a block diagram of different components of the
system.
5	 DESCRIPTION OF BEST MODES OF THE
INVENTION
FIG. 1 schematically illustrates an embodiment 11 of the
10 system and a possible light source. Light (X) from a source 13
is received at a light collector dome 15 and is passed through
a collimator 17 having a small controllable field of view
(FOV) of 1-2°, with an aperture diameterAD=22 mm and a
focal length FL-50 mm in this embodiment. The collimated
15 light is received at a first end 19FE of each of a plurality of
optical fibers 19-n (n=1, ... , N; N?2), where each fiber has
a relatively small numerical aperture NA-n that serves to
further limit the acceptance angle of the received light. Pref-
erably, but not mandatorily, the numerical aperture NA-n for
20 each of the optical fibers 19-n is approximately the same so
that the light acceptance angle for each of the specified wave-
length intervals is approximately the same.
The collimated and angle-restricted light in each specified
wavelength interval, X,, j ^^ U is passed through a shut-
25 ter 21 having a controllable duty cycle DC. When the shutter
21 is open, light in each of the specified wavelength intervals
is received and the associated light intensity
a,,,U;n;Atl) is collected by a light collector 22 and is pro-
cessed by an accumulated light intensity monitor and elec-
so tronics module 23-n for that wavelength interval (n) for a first
selected time interval of length Atl. When the shutter 21 is
closed, the light monitor and electronics module 23-n senses
a dark current light intensity value I(off;n;At2) for that wave-
length interval, over a second selected time interval of length
35 At2 A normalized, system-off light intensity I(off;n;At2)/At2
is statistically compared with a normalized, system-on light
intensity I(a ^^^ ^^ U;n;Atl)/Atl to determine a corrected,
system-on light intensity I(X,,^^-X^- , U;n;Atl;corr)foreach
40 
of the specified wavelength intervals
A Zeiss monolithic spectrometer, with 8-12 mn resolution,
is preferred for combined near-ultraviolet, visible and near-
infrared wavelength sensing, in a wavelength range of 300
nxn<^I< 12200 nm. Preferably, a data acquisition system and
45 control system 25 using a PC-104 format and USB interfacefor the data collection, using an Ethernet data collection inter-
face.
Two or more corrected, system-on light intensities
I(^ <^ <^ U;n;Atl(m);corr) (m=1, ... , M;M?2) can be
50 compared for different, preferably non-overlapping time
intervals to identify possible anomalies in the light source
and/or drift or other anomalies in the light monitor and elec-
tronics module 23-n for one or more of the specified wave-
length intervals. For example, if only one of the specified
55 wavelength intervals, a i i^^ ^a i U manifests anomalous
behavior over time, this may indicate that the light monitor
and electronics module 23-n1 is experiencing substantial drift
in time, relative to all other light monitor and electronics
modules 23-n (n;-nl). Alternatively, if substantially all of the
60 specified wavelength intervals manifest anomalous behavior,
this may indicate that the light source is primarily responsible
for the observed anomalies.
FIG. 2 is a block diagram illustrating the main components
and their interoperability for the system 31. Light, including
65 a collection of wavelengths 1XI, is received at a light colli-
mator 33, and the collimated light is passed through a shutter
mechanism 35, which has a selected duty cycle and activation
US 7,869,029 B1
3
frequency f_ that can be at most 5 Hz or any other suitable
lower frequency. A first portion of the light admitted by the
shutter 35 is passed to a Si spectrometer 37, with associated
heater-controller 38, to determine the wavelength distribution
of the light in the near-uv, visible and near-infrared portion of
the spectrum (e.g., 300 nm- :^X- :^ 1100 nm). A second portion
of the light admitted by the shutter 35 is passed through an
InGaAs spectrometer 39, with associated TEC controller 40,
to determine the wavelength distribution (overlapping) of the
light in the mid-infrared and (optionally) far-infrared portion
of the spectrum (e.g., 1050 nm:^^X^2200 mu). A signal rep-
resenting the near-uv/visible/near-infrared wavelength distri-
bution sensed by the Si spectrometer 37 is received and pro-
cessed by a first spectrometer module 41, and the processed
signal(s) is received by a data acquisition and control sub-
system 45). A signal representing the mid-infrared/far-infra-
red wavelength distribution sensed by the InGaAs spectrom-
eter 39 is received and processed by a second spectrometer
module 43, and the processed signal(s) is received by the data
acquisition and control sub-system 45.
Among other signals, the data acquisition and control sub-
system 45 can provide a graphical representation of the wave-
length distribution received and sensed, in units of zenith
radiance (Watt-meter 2 /nm/ster) of the sun, by the system on
18 Mar. 2006 for the UTC time interval from 14 hours through
26 hours (daylight), at the selected wavelengths X=382 nm,
505 mu, 762 nm, 941 nm, 1050 nm, 1199 mu, 1602 nm, 1648
mn and 2102 mu, as illustrated in FIG. 3. The uppermost
curve is total radiance received over all wavelengths in the
combined sensitive intervals, including a "dark period" of
five consecutive minutes per hour when the shutter 35 was
closed. The dark current sensed by the system during each
dark period, as a function of the indicated wavelengths, is
subtracted from the current sensed during the "light period"
(shutter open) to provide a dark current-compensated radi-
ance value at each of a selected group of wavelengths. Note
that light received and sensed in several near-infrared wave-
length ranges has a pronounced maximum during a time
interval 18.5 ­4- :^19.5 (UTC hours).
FIG. 4 graphically illustrates the zenith radiance, as a func-
tion of wavelength in a range 300 nm <X<2200 nm, at each of
the UTC times 18.0, 19.0, 20.0, 21.0 and 22.0 hours, indicat-
ing a pronounced maximum associated with the UTC time
21.0 hours. Most of the contribution to zenith radiance from
the sun arise from the visible and near-uv wavelengths.
4
What is claimed is:
1. A system for receiving and processing light from one or
more light sources, the system comprising:
• light collector and collimator that receives light from one
5 or more light sources over a solid angle of substantially
271 steradians in N wavelength ranges (N?3), covering
near-ultraviolet, visible, near-infrared and mid-infrared
wavelengths and numbered n=1, ... , N, and that aligns
the received light within a collimation angle of no more
10	 than about 2°;
• light shutter mechanism that admits light received from
the collector and collimator during a first time interval
and blocks admission of light during a second time inter-
val, to provide an estimate of a dark current within each
15	 of the N wavelength intervals;
• light transporter, having N transporter components, num-
bered n=1, ... , N, where transporter component number
n transports light in the wavelength range number n
substantially optimally for that wavelength range; and
20 a light processor that receives and separately processes
light transported in each of the N wavelength ranges
during the first time interval and during the second time
interval, estimates a fraction of total light intensity
received for each of the N wavelength ranges, and esti-
25 mates a dark current component in each of the N wave-
lengthranges from signals sensed during each of the first
and second time intervals.
2. The system of claim 1, wherein said first and second time
intervals are non-overlapping.
30 3. The system of claim 1, wherein said signal sensed during
said second time interval is subtracted from said signal sensed
during said first time interval, for at least one of said N
wavelength ranges.
4. The system of claim 1, wherein said light processor
35 receives and processes light in said near-ultraviolet, visible
and near-infrared wavelength ranges and receives and sepa-
rately processes light in said near-infrared and mid-infrared
wavelength ranges.
5. The system of claim 1, wherein said light transporter
40 comprises N optical fibers, with each fiber being optimized
for transport of light in one of said N wavelength ranges.
6. The system of claim 1, wherein said light processor
provides an estimate of light received in each of said N wave-
length intervals for a sequence of time intervals that are
45 included in said first time interval.


Multiple wavelength light collimator and monitor

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