U.S. patent number RE44,605 [Application Number 12/613,349] was granted by the patent office on 2013-11-19 for integrated spectroscopy system.
This patent grant is currently assigned to Axsun Technologies, Inc.. The grantee listed for this patent is Walid A. Atia, Dale C. Flanders, Petros Kotidis, Mark E. Kuznetsov. Invention is credited to Walid A. Atia, Dale C. Flanders, Petros Kotidis, Mark E. Kuznetsov.
United States Patent |
RE44,605 |
Atia , et al. |
November 19, 2013 |
Integrated spectroscopy system
Abstract
Integrated spectroscopy systems are disclosed. In some examples,
integrated tunable detectors, using one or multiple Fabry-Perot
tunable filters, are provided. Other examples use integrated
tunable sources. The tunable source combines one or multiple
diodes, such as superluminescent light emitting diodes (SLED), and
a Fabry Perot tunable filter or etalon. The advantages associated
with the use of the tunable etalon are that it can be small,
relatively low power consumption device. For example, newer
microelectrical mechanical system (MEMS) implementations of these
devices make them the size of a chip. This increases their
robustness and also their performance. In some examples, an
isolator, amplifier, and/or reference system is further provided
integrated.
Inventors: |
Atia; Walid A. (Lexington,
MA), Flanders; Dale C. (Lexington, MA), Kotidis;
Petros (Framingham, MA), Kuznetsov; Mark E. (Lexington,
MA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Atia; Walid A.
Flanders; Dale C.
Kotidis; Petros
Kuznetsov; Mark E. |
Lexington
Lexington
Framingham
Lexington |
MA
MA
MA
MA |
US
US
US
US |
|
|
Assignee: |
Axsun Technologies, Inc.
(Billerica, MA)
|
Family
ID: |
34465602 |
Appl.
No.: |
12/613,349 |
Filed: |
November 5, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10688690 |
Oct 17, 2003 |
7061618 |
|
|
Reissue of: |
11380684 |
Apr 28, 2006 |
7292344 |
Nov 6, 2007 |
|
|
Current U.S.
Class: |
356/454;
356/480 |
Current CPC
Class: |
G01N
21/255 (20130101); G01J 3/26 (20130101); G01J
3/10 (20130101); G01J 3/36 (20130101); G01J
3/0256 (20130101) |
Current International
Class: |
G01B
9/02 (20060101); G01J 3/45 (20060101) |
Field of
Search: |
;356/451,454,480,519 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
41 22 925 |
|
Jan 1993 |
|
DE |
|
0 501 559 |
|
Sep 1992 |
|
EP |
|
0524382 |
|
Jan 1993 |
|
EP |
|
0 709 659 |
|
Jan 1996 |
|
EP |
|
0 709 659 |
|
May 1996 |
|
EP |
|
0469259 |
|
Aug 1996 |
|
EP |
|
0911655 |
|
Apr 1999 |
|
EP |
|
1020969 |
|
Mar 2007 |
|
EP |
|
2704651 |
|
Nov 1994 |
|
FR |
|
2118768 |
|
Nov 1983 |
|
GB |
|
2317045 |
|
Mar 1998 |
|
GB |
|
63092917 |
|
Apr 1988 |
|
JP |
|
8148744 |
|
Jun 1996 |
|
JP |
|
2001065734 |
|
Sep 2001 |
|
WO |
|
03/046630 |
|
Jun 2003 |
|
WO |
|
2003096106 |
|
Nov 2003 |
|
WO |
|
Other References
Gmachl et al. "Ultra-broadband semiconductor laser" Nature, Feb.
21, 2002, vol. 415, pp. 883-887. cited by examiner .
Brochure, "Agilent 83437A Broadband Light Source and Agilent 83438A
Erbium ASE Source, Production Overview," Agilent Technologies,
1996, 2002. cited by applicant .
Krawczyk, S. K. et al., "GaN and Related Compunds for MEMS and
MOEMS," Aromagraph DC 2000 System, vol. 51, No. 8, 1999, pp.
623-625. cited by applicant .
Vakhshoori, D. et al., "Raman Amplification Using High-Power
Incoherent Semiconductor Pump Sources," Ahara Corporation, MA,
2003. cited by applicant .
International Search Report, mailed Aug. 16, 2005, from counterpart
International Application No. PCT/US2005/034691, filed on Oct. 13,
2004. cited by applicant .
International Preliminary Report on Patentability, dated Apr. 18,
2006, from counterpart International Application No.
PCT/US2005/034691, filed on Oct. 13, 2004. cited by applicant .
Zhao, M., et al. "Analysis and Optimization of Intensity Noise
Reduction in Spectrum-Sliced WDM Systems Using a Saturated
Semiconductor Optical Amplifier," IEEE Photonics Technology
Letters, vol. 14, No. 3, pp. 390-392, Mar. 2002. cited by applicant
.
Chang, T. et al., "Pulsed Dye-Laser with Grating and Etalon in a
Symmetric Arrangement," Appl. Opt., vol. 19, No. 21, 1980, pp.
3651-3654. cited by applicant .
Coquin, G. et al., "Single- and multiple-wavelength operation of
acoustooptically tuned semiconductor lasers at 1.3 .mu.m," IEEE
Journal of Quantum Electronics, vol. 25, No. 6, Jun. 1989, pp.
1575-1579. cited by applicant .
Klauminzer, GK, "Etalon-Grating Synchronized Scanning of a
Narrowband Pulsed Dye Laser," Optical Engineering, vol. 13, No. 6,
1974; pp. 528-530. cited by applicant .
Kowalski, F.V. et al., "Optical pulse generation with a frequency
shifted feedback laser," Applied Physics Letters, vol. 53, No. 9,
Aug. 1988, pp. 734-736. cited by applicant .
Oshiba, S. et al., "Tunable fiber ring lasers with an
electronically accessible acousto-optic filer," Photonic Switching
II, Proceedings of the International Topical Meeting, Kobe, Japan,
Apr. 1990, pp. 241-244. cited by applicant .
Shimizu, K. et al., "Measurement of Rayleigh Backscattering in
Single-Mode Fibers Based on Coherent OFDR Employing a DFB Laser
Diode," IEEE Photonics Technology Letters, vol. 3, No. 11, 1991,
pp. 1039-1041. cited by applicant .
Takada, K. et al., "Loss distribution measurement of silica-based
waveguides by using a jaggedness-free optical low coherence
reflectometer," Electronics Letters, vol. 30, No. 17, Aug. 18,
1994, pp. 1441-1443. cited by applicant .
Takada, K. et al., "Rapidly-tunable narrowband light source with
symmetrical crossing configuration for low coherence
reflectometry," Electronics Letter, Jan. 5, 1995, vol. 31, No. 1,
pp. 63-65. cited by applicant .
Takada, K. et al., "Tunable Narrow-Band Light Source Using Two
Optical Circulators," IEEE Photonics Technology Letters, vol. 9,
No. 1, 1997, pp. 91-93. cited by applicant .
Telle, J.M. et al., "Very rapid tuning of cw dye laser," Applied
Physics Letters, vol. 26, No. 10, 1975, pp. 572-574. cited by
applicant .
Yun, S.H. et al., "High-speed wavelength-swept semiconductor laser
with a polygon-scanner-based wavelength filter," Optics Letters,
vol. 28, No. 20, 2003, pp. 1981-1983. cited by applicant .
Yun, S.H. et al., "Interrogation of fiber grating sensor arrays
with a wavelength-swept fiber laser," Optics Letters, vol. 23, No.
11, 1998, pp. 843-845. cited by applicant .
Yun, S.H. et al., "Wavelength-Swept Fiber Laser with Frequency
Shifted Feedback and Resonantly Swept Intra-Cavity Acousto-Optic
Tunable Filter," IEEE Journal of Selected Topics in Quantum
Electronics, vol. 3, No. 4, 1997, pp. 1087-1096. cited by applicant
.
Bogatov, A. P. et al., "Anomalous Interaction of Spectral Modes in
a Semiconductor Laser," IEEE Journal of Quantum Electronics, vol.
QE-11, No. 7, Jul. 1975, pp. 510-515. cited by applicant .
Fowles, G., "Introduction to Modern Optics," Dover, Second edition,
1975, pp. 85-91. cited by applicant.
|
Primary Examiner: Lee; Hwa
Attorney, Agent or Firm: Houston & Associates, LLP
Parent Case Text
RELATED APPLICATIONS
This application is a Division of U.S. application Ser. No.
10/688,690 filed on Oct. 17, 2003 now U.S. Pat. No. 7,061,618,
which is incorporated herein by reference in it entirety.
Claims
What is claimed is:
1. A tunable light source spectroscopy system, comprising: a
superluminescent light emitting diode for generating broadband
light; and a tunable Fabry Perot filter for spectrally filtering
the broadband light from the broadband source to generate a tunable
signal; an optical fiber for carrying the tunable signal to
irradiate a sample; a detector for detecting a response of the
sample to the tunable signal to determine a spectroscopic response
of the sample; and an isolator interposed between the
superluminescent light emitting diode and the tunable filter for
preventing back reflections from the tunable filter into the
superluminescent light emitting diode.
2. A tunable light source spectroscopy system as claimed in claim
1, wherein the superluminescent light emitting diode and the Fabry
Perot filter are installed in common on an optical bench.
3. A tunable light source spectroscopy system as claimed in claim
1, wherein the superluminescent light emitting diode, isolator, and
tunable filter are integrated on a common optical bench.
4. A tunable light source spectroscopy system as claimed in claim
1, comprising an amplifier for amplifying the tunable signal.
5. A tunable light source spectroscopy system, comprising: a
superluminescent light emitting diode for generating broadband
light; and a tunable Fabry Perot filter for spectrally filtering
the broadband light from the broadband source to generate a tunable
signal; an optical fiber for carrying the tunable signal to
irradiate a sample; a detector for detecting a response of the
sample to the tunable signal to determine a spectroscopic response
of the sample; and an amplifier for amplifying the tunable signal,
wherein the amplifier is a semiconductor optical amplifier.
6. A tunable light source spectroscopy system as claimed in claim
5, further comprising an isolator interposed between the
superluminescent light emitting diode and the tunable filter for
preventing back reflections from the tunable filter into the
broadband source.
7. A tunable light source spectroscopy system, comprising: a
superluminescent light emitting diode for generating broadband
light; and a tunable Fabry Perot filter for spectrally filtering
the broadband light from the broadband source to generate a tunable
signal; an optical fiber for carrying the tunable signal to
irradiate a sample; a detector for detecting a response of the
sample to the tunable signal to determine a spectroscopic response
of the sample; and an amplifier for amplifying the tunable signal,
wherein the amplifier is a fiber amplifier.
8. A tunable light source spectroscopy system as claimed in claim
7, wherein the fiber amplifier is one of an erbium, ytterbium,
thulium or Raman fiber amplifier.
.Iadd.9. A tandem filtered amplified spontaneous emission (ASE)
scanning optical source, comprising: an ASE source for generating
broadband light in a spectral band; a first tunable Fabry Perot
filter having a first passband that is tuned over a scanband in the
spectral band of the ASE source for filtering the broadband light;
an isolation system between the ASE source and the first tunable
Fabry Perot filter for preventing back reflections from the tunable
first Fabry Perot filter into the ASE source; a second tunable
Fabry Perot filter having a second passband that is tuned over a
scanband in the spectral band of the ASE source for filtering light
from the first tunable Fabry Perot filter; and a second isolation
system between the first tunable Fabry Perot filter and the second
tunable Fabry Perot filter; wherein the first tunable Fabry Perot
filter and the second tunable Fabry Perot filter form a filter
system that has a peak transmissivity to the broadband light where
the first passband and the second passband are
coincident..Iaddend.
.Iadd.10. A source as claimed in claim 9, wherein the first tunable
Fabry Perot filter and the second tunable Fabry Perot have
different free spectral ranges..Iaddend.
.Iadd.11. A source as claimed in claim 9, wherein the isolation
system is an isolator..Iaddend.
.Iadd.12. A source as claimed in claim 9, wherein the isolation
system is a quarterwave plate..Iaddend.
.Iadd.13. A source as claimed in claim 9, wherein the ASE source is
a superluminescent light emitting diode..Iaddend.
.Iadd.14. A source as claimed in claim 9, wherein the first and
second tunable Fabry-Perot filters are MEMS tunable Fabry-Perot
filters..Iaddend.
.Iadd.15. A source as claimed in claim 9, further comprising an
optical bench, the ASE source, first tunable Fabry Perot filter,
and second tunable Fabry Perot filter being integrated together on
the optical bench..Iaddend.
.Iadd.16. A source as claimed in claim 9, further comprising a
reference detector for detecting part of a tunable optical signal
from the filter system and a spectral reference for generating a
fringe pattern on the detector during scanning of the tunable
optical signal..Iaddend.
.Iadd.17. A source as claimed in claim 9, further comprising two or
more broadband sources for generating broadband light that is
converted into a tunable optical signal by the first tunable Fabry
Perot filter and the second tunable Fabry Perot
filter..Iaddend.
.Iadd.18. A source as claimed in claim 9, further comprising lenses
for collecting the broadband light emitted from the ASE source and
coupling the broadband light into the first tunable Fabry Perot
filter and for collecting a tunable optical signal from the first
tunable Fabry Perot filter and coupling the tunable optical signal
into the second tunable Fabry Perot filter..Iaddend.
Description
BACKGROUND OF THE INVENTION
Minimally, optical spectroscopy systems typically comprise a source
for illuminating a target, such as a material sample, and a
detector for detecting the light from the target. Further, some
mechanism is required that enables the resolution of the spectrum
of the light from target. This functionality is typically provided
by a spectrally dispersive element.
One strategy uses a combination of a broadband source, detector
array, and grating dispersive element. The broadband source
illuminates the target in the spectral scan band, and the signal
from the target is spatially dispersed using the grating, and then
detected by an array of detectors.
The use of the grating, however, requires that the spectroscopy
system designer make tradeoffs. In order to increase the spectral
resolution of these systems, aperturing has to be applied to the
light provided to the grating. As more spectral resolution is
required, more light is required to be rejected by the narrowing
spatial filter. This problem makes this strategy inappropriate for
applications requiring a high degree of spectral precision combined
with sensitivity.
Another approach is to use a tunable narrowband source and a simple
detector. A typical approach relies on a tunable laser, which is
scanned over the scan band. By monitoring the magnitude of the
tunable laser's signal at the detector, the spectrum of the sample
is resolved. These systems have typically been complex and often
had limited wavelength scanning ranges, however.
Still another approach uses light emitting diodes (LEDs) and an
acousto-optic modulator (AOM) tunable filter. One specific example
combines multiple light emitting diodes (LEDs) in an array, each
LED operating at a different wavelength. This yields a relatively
uniform spectrum over a relatively large scan band. The light from
the diodes is then sent through the AOM tunable filter, in order to
create the tunable optical signal.
The advantage of this system is the use of the robust LED array.
This provides advantages over previous systems that used other
broadband sources, such as incandescent lamps, which had limited
operating lifetimes and high power consumption.
While representing an advance over the previous technology, the
disadvantages associated with this prior art system were related to
the use of the AOMs, which are relatively large devices with
concomitantly large power consumptions. Moreover, AOMs can also be
highly temperature sensitive and prone to resonances that distort
or alter the spectral behavior, since they combine a crystal with a
radio frequency source, which establishes the standing wave in the
crystal material to effect the spectral filtering.
Grating-based spectrometers also tend to be large devices. The
device packages must accommodate the spatially dispersed signal
from the sample. Further, the interface between the grating and the
detector array must also be highly mechanically stable. Moreover,
these grating based systems can be expensive because of costs
associated with the detector arrays or slow if mechanical scanning
of the detector or grating is used.
SUMMARY OF THE INVENTION
The drawbacks associated with the prior art spectrometers arise
from the large size of the devices combined with the high cost to
manufacture these devices combined with poor mechanical stability.
These factors limit the deployment of spectrometers to applications
that can justify the investment required to purchase these devices
and further accommodate their physical size.
Accordingly, the present invention is directed to an integrated
spectrometer system. Specifically, it is directed to the
integration of a tunable Fabry-Perot system with a source system
and/or detector system. The use of the Fabry-Perot filter system
allows for a high performance, low cost device. The integration of
the filter system with the source system and/or detector system
results in a device with a small footprint. Further, in the
preferred embodiment, the filter system is based on
microelectromechancial systems (MEMS), which yield a highly
mechanically robust system.
In general, according to one aspect, the invention features a
spectroscopy system. The system comprises a source system for
generating light to illuminate a target, such as a fiber grating or
a material sample. A tunable Fabry-Perot filter system is provided
for filtering light generated by the source. A detector system is
provided for detecting light filtered by the tunable filter from
the target. According to the invention, at least two of the source
system, tunable Fabry-Perot filter system, and the detector system
are integrated together.
Specifically, in one embodiment, the source system and tunable
Fabry-Perot system are integrated together on a common substrate,
such as an optical bench, also sometimes called a submount. In
another embodiment, the tunable Fabry-Perot filter system and the
detector system are integrated together on a common substrate, such
as an optical bench. Finally, in still another implementation, all
three of the source system, tunable Fabry-Perot filter system, and
the detector system are integrated together on a common bench, and
possibly even in a common hermetic package.
Temperature control is preferably provided for the system.
Currently this is provided by a heater, which holds the temperature
of the system above an ambient temperature, or a thermoelectric
cooler. For example, the thermoelectric cooler is located between
the bench and the package to control the temperature of the source
system, tunable Fabry-Perot filter system, and/or the detector
system. As a result, a single cooler is used to control the
temperature of the filter and SLED chip, lowering power
consumption, decreasing size, while increasing stability.
In the preferred embodiment, the source system comprises a
broadband source. This can be implemented using multiple,
spectrally multiplexed diode chips. Preferably, superluminescent
light-emitting diodes (SLEDs) are used. These devices have a number
of advantages relative to other sources, such incandescent sources.
Specifically, they have better spectral brightness, longer
operating lifetimes, and a smaller form factor.
In order to increase the spectral accuracy of the system, a tap can
also be used to direct a part of the tunable signal to a detector.
A spectral reference, such as a fixed etalon with multiple spectral
transmission peaks is placed between the detector and the tap, in
order to create a fringe pattern on the detector during the scan,
thereby enabling monitoring of the wavelength of the tunable
signal. An optical power tap can also be included to monitor the
real time emitted optical power during the scan.
The tunable Fabry-Perot filter system comprises single or multiple
filters. In one example, multiple serial filters are used. In
another embodiment, multiple parallel filters are used.
In still further embodiments, multiple detectors can be used. These
detectors can be responsive to different wavelengths or a
calibration signal.
In the preferred embodiment, in order to make the system small,
compact and highly robust, a micro-electro-mechanical system (MEMS)
Fabry-Perot tunable filter is used. These devices can achieve high
spectral resolutions in a very small footprint.
Finally, in the preferred embodiment, isolation is provided between
the source system and the tunable Fabry-Perot filter system. This
prevents back reflections from the filter into the source system
that can disturb the operation of the source system. In one
example, an isolator is installed on the optical bench between the
SLED and the tunable filter. A quarter wave plate can also be used.
This rotates the polarization of the returning light so that it is
not amplified by the highly polarization anisotropic SLED gain
medium. In another embodiment, the isolation is provided on the
bench, with the tunable Fabry-Perot filter system and the detector
system.
The present invention is also directed to an integrated tunable
source that combines a broadband source and a tunable filter, such
as a tunable Fabry-Perot filter, although other tunable filters
could be used in this configuration. Applications for this device
extend beyond spectroscopy.
Between the tunable filter and the light source, isolation is
preferably provided. This stops back reflections from the tunable
filter into the diode, which could impact its performance.
Isolation can be achieved using a number of techniques. In one
embodiment, a discrete isolator is used. In another embodiment,
when a SLED is used as the source, a quarterwave plate is used
between the SLED chip and the filter. Finally, a flat-flat cavity
Fabry-Perot tunable filter is used in still another embodiment,
with isolation being accomplished by tilting the filter relative to
the SLED.
A variety of other light sources can be used, including LEDs, doped
fiber or waveguide amplified spontaneous emission sources, and
thermal sources.
According to still another aspect, the invention features a high
power tunable source. This addresses one of the primary drawbacks
associated with the use of a broadband source and tunable filter
configuration, namely their usually low output power. Specifically,
an optical amplifier is further added in order to increase the
power of the tunable signal. As a result, power levels comparable
to those attainable with tunable lasers can be achieved in this
configuration.
In a typical implementation, the amplifier is a semiconductor
optical amplifier (SOA). In other examples, various types of fiber
amplifiers are used, however.
The above and other features of the invention including various
novel details of construction and combinations of parts, and other
advantages, will now be more particularly described with reference
to the accompanying drawings and pointed out in the claims. It will
be understood that the particular method and device embodying the
invention are shown by way of illustration and not as a limitation
of the invention. The principles and features of this invention may
be employed in various and numerous embodiments without departing
from the scope of the invention.
The above and other features of the invention including various
novel details of construction and combinations of parts, and other
advantages, will now be more particularly described with reference
to the accompanying drawings and pointed out in the claims. It will
be understood that the particular method and device embodying the
invention are shown by way of illustration and not as a limitation
of the invention. The principles and features of this invention may
be employed in various and numerous embodiments without departing
from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, reference characters refer to the
same parts throughout the different views. The drawings are not
necessarily to scale; emphasis has instead been placed upon
illustrating the principles of the invention. Of the drawings:
FIGS. 1A and 1B illustrate embodiments of the integrated
spectroscopy system according to the present invention;
FIG. 2 is a perspective view showing a tunable source, according to
the present invention, and including a detector system for
detecting the tunable signal from the sample;
FIG. 3A is a perspective view of the MEMS Fabry Perot tunable
filter, used in embodiments of the present invention, which is
compatible with tombstone mounting on the optical bench;
FIG. 3B is an exploded view of the inventive Fabry Perot tunable
filter;
FIG. 4 is a perspective view showing an amplified tunable source,
according to the present invention, in a hermetic package;
FIG. 5 is a perspective view showing a reference detector
embodiment of a tunable source, according to the present invention,
in a hermetic package;
FIG. 6 is a block diagram of an embodiment of the tunable source
with both a wavelength and power reference detector;
FIG. 7 is a perspective view showing still another embodiment of a
tunable source, according to the present invention, using two SLED
chips;
FIG. 8 is a perspective view showing a further embodiment of a
tunable source, according to the present invention using multiple
SLED chips and tunable filters;
FIG. 9 is a perspective view showing another embodiment of a
tunable source, according to the present invention, using parallel
filters and multiple SLED sources;
FIG. 10 is a perspective view showing a further embodiment of a
tunable source, according to the present invention, using serial
filters;
FIG. 11 is a plot of wavelength as a function of transmission
showing the relationship between the free spectral ranges of the
serial filters, in one embodiment;
FIG. 12A is a perspective view of a tunable detector spectroscopy
system, according to the present invention;
FIG. 12B is a perspective view of another embodiment of a tunable
detector spectroscopy system, according to the present
invention;
FIG. 13 is a perspective view of still another embodiment of a
tunable detector spectroscopy system, according to the present
invention, using multiple parallel filters; and
FIGS. 14 and 15 show two fully integrated spectroscopy systems in
which a tunable source and a detector system are integrated on the
same bench.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1A and 1B illustrate an integrated spectroscopy system 1,
which has been constructed according to the principles of the
present invention.
Specifically, FIG. 1A shows two alternative integration
configurations.
According to configuration 1, a source system 100 is provided. This
is a broadband source, which generates light 40 for illuminating a
target, such as sample S-1 or a fiber grating, for example. This
target selectively absorbs and/or scatters the light from the
source system 100. The transmitted light is then received by a
tunable Fabry-Perot filter system 200. This functions as a narrow
band tunable spectral filter. It tunes its passband over the scan
band within the spectral band of the source system 100. As a
result, it resolves the spectrum of the target S-1 into a time
response. This time-resolved signal is then detected by detector
system 300.
According to the integration provided by this configuration 1, the
tunable Fabry-Perot filter system 200 and the detector system 300
are integrated together. Specifically, in the preferred embodiment,
the tunable Fabry-Perot filter system 200 and the detector system
300 are installed on a common bench B-1. Moreover, in the current
embodiment, the tunable Fabry-Perot filter system 200 and the
detector system 300 are integrated together on the common bench B-1
in a common hermetic package.
The integration of the Fabry-Perot filter system 200, with the
detector system 300 on the common bench B-1, yields the tunable
detector 20 which is characteristic of the configuration 1
integration.
FIG. 1A also illustrates a second configuration, configuration 2
integration. In this second configuration, the source system 100
and the tunable Fabry-Perot system 200 are integrated together. In
the preferred embodiment, they are installed together on a common
bench B-2. Further, in the current implementation, the source
system 100 and the tunable Fabry-Perot filter system are integrated
together on the common bench B-2 and installed in a common hermetic
package to yield a tunable source 10. This tunable source 10
generates a tunable signal 30, which is used to illuminate a
target, located in this second configuration at position S-2. The
target either scatters or absorbs spectral components of the
tunable signal as it is scanned across the scan band. This allows
the detector system 300 to resolve the time varying signal as the
spectral response of the target S-2.
FIG. 1B illustrates a fully integrated system according to still
another embodiment. Here, the source system 100, the tunable
Fabry-Perot filter system 200, and the detector system 300 are
integrated together. Specifically, in the preferred embodiment,
they are integrated together and installed on a common bench B.
This bench B is preferably located in a hermetic package.
Depending on whether the tunable source system 100, the Fabry-Perot
filter system 200, and detector system 300, are combined as a
tunable source 10 or tunable detector 20, the target is located
either in position S-1 or S-2. Specifically, in the implementation
of a tunable source 10 with the source system 100 and the tunable
Fabry-Perot filter system 200 functioning to create a tunable
signal, the tunable signal 30 is coupled outside of the hermetic
package and off of the bench B to the target S-2, in the case of
configuration 2. Alternatively, if the tunable Fabry-Perot filter
system 200 and the detector system 300 function to yield the
tunable detector 20, then the broadband signal 40 from the source
system 100 is coupled off of the bench and the outside of the
hermetic package to the target S-1 in the case of the first
configuration.
FIG. 2 illustrates a first embodiment of the tunable source 10.
Specifically, in this embodiment, the bench B-2 holds the tunable
Fabry-Perot filter system 200 and the source system 100 on a common
planar surface. The generated tunable signal 30 is coupled off of
the bench B-2 by an optical fiber 102. In the preferred embodiment,
this optical fiber 102 is a single transverse mode fiber. This has
advantages in that it renders the tunable signal 30 very stable,
even in the event of mechanical shock to the single mode fiber
102.
The source system 100 is implemented using, in this embodiment, a
superluminescent light emitting diode (SLED) 110. The diode 110 is
installed on a submount 112. The submount 112 is, in turn,
installed on the bench B-2. In the preferred embodiment, the SLED
chip 110 is solder bonded to the submount 112, which further
includes metallizations 114 to facilitate wire bonding to provide
electrical power to the SLED chip 110. Further, the submount 112 is
solder bonded to the bench B-2, which in turn, has metallizations
115 to enable formation of the solder bonds.
These SLEDs are relatively new, commercially-available devices and
are sold by Covega Corporation, for example, (product numbers SLED
1003, 1005, 1006). These devices are currently available in
wavelength ranges from 1,200 nanometers (nm) to 1,700 nm from a
variety of vendors. They are waveguide chip devices with long gain
mediums similar to semiconductor optical amplifiers. An important
characteristic is their high spectral brightness.
The broadband signal 40 that is generated by the SLED chip is
collimated by a first lens component 114. This lens component 114
comprises a lens substrate 117, which is mounted onto a deformable
mounting structure 118. The deformable mounting structure is
preferably as those structures described in U.S. Pat. No. 6,559,464
B1 to Flanders, et al., which is incorporated herein in its
entirety by this reference. The alignment structure system allows
for post installation alignment by mechanical deformation of the
mounting structure 118 of the lens substrate 117.
The collimated light from the first lens component 114 in the
preferred embodiment is coupled through an isolation system, such
as an isolator 120 or quarterwave plate. The beam from the isolator
is then collimated by a second lens element 122 and coupled into
the Fabry-Perot tunable filter system 200. The isolator system
prevents all back reflections or back reflections that have a
polarization that is aligned with the gain polarization of the SLED
chip 110. These reflections arise from the Fabry-Perot filter
system 200. This isolation promotes the stability in the operation
of the SLED chip 110.
In the preferred embodiment, the tunable filter system 200 is
implemented as a MEMS tunable Fabry-Perot filter 116. This allows
for single transverse mode spectral filtering of the broadband
light 40 from the SLED chip 110, yielding the tunable signal 30.
Tunable signal 30 is coupled into the endface 104 of the single
mode optical fiber 102. In the current embodiment, the endface 104
of the optical fiber 102 is held in alignment with the MEMS tunable
filter 116, via a fiber mounting structure 106. Again, this allows
for post installation alignment of the fiber endface 104 to
maximize coupling of the tunable signal 30, into the single mode
fiber 102. The fiber 102 transmits the tunable signal 30 to target
S-2 and then, the response is detected by detector system 300.
Depending on the embodiment, the Fabry-Perot filter 116 has either
a curved-flat cavity or a flat-flat cavity. The curved flat cavity
increases angular tolerance between the two mirrors of the
Fabry-Perot filter. The flat-flat cavity provides better single
mode operation. Moreover, there is the option to avoid the
necessity for discrete isolators or waveplates by angle isolating
the filter for the source system 100.
FIG. 3A is a close up view of the tunable filter 116. The tunable
filter 116 comprises a MEMS die 410. This has a number of wire bond
locations 412 for making electrical connection to the MEMS die 410.
A MEMS die 410 provides the moveable mirror portion or component of
the tunable filter. A fixed mirror portion or component 414 is
bonded to the MEMS die 410 in order to define the Fabry Perot
cavity. In one embodiment, the fixed mirror component provides the
flat mirror and the MEMS die 410 provides the curved mirror.
In the preferred embodiment, the tunable filter 116 is "tombstone"
mounted onto the bench B, B-1, B-2. Specifically, the fixed mirror
substrate 414 extends down below the bottom of the MEMS die 416 by
a distance L. Specifically, the fixed mirror substrate has a bottom
surface 418 that serves as a foot that is bonded to the bench.
Preferably, a layer of solder 420 is used to attach the fixed
mirror substrate 414 to the bench B. In the preferred embodiment,
the distance L is approximately 1-10 micrometers.
FIG. 3B is an exploded view of the tunable filter 116. This shows
the fixed mirror substrate 414 disconnected from the MEMS die 410.
Flexures 421 define a MEMS membrane 423. The deflectable membrane
423 holds the mirror layer 424 of the tunable mirror and covers a
depression 425 formed in the membrane 423 that forms the curved
mirror of one embodiment. Metallization pads 426 are provided on
the MEMS die 410 in order to solder attach the fixed mirror
substrate 414 to the MEMS die 410.
The general construction of this tunable filter is described in,
for example, U.S. patent application Ser. No. 09/734,420, filed on
Dec. 11, 2000 (now Publication No. U.S. 2002-0018385). This
application is incorporated herein, in its entirety by this
reference.
FIG. 4 illustrates another embodiment of the tunable source 10. In
this embodiment, the broadband signal generated by the SLED chip
110 is again coupled through a first lens component 114 to an
isolator 120. A second lens component 122 is further provided for
coupling the broadband signal into the filter 116 of the
Fabry-Perot filter system 200.
Then, a third lens component 126 is provided to couple the tunable
optical signal 30 into a semiconductor optical amplifier 128. In
the preferred embodiment, this semiconductor optical amplifier chip
128 is installed on an amplifier sub-mount 130, which is installed
on the bench B-2. The amplified tunable optical signal generated by
the semiconductor optical amplifier chip 128 is then coupled into
the endface 104 of the optical fiber 102 to be coupled out of the
hermetic package 132. This allows the tunable signal 30 to be
coupled, in an amplified state, to the target S-2 followed by
detection by the detector system 300.
In some other embodiments additional isolators are located between
the fiber endface 104 and the amplifier chip 128 and between the
amplifier chip 128 and the third lens component 126.
In the preferred embodiment, the hermetic package 132 is a standard
telecommunications hermetic package. Specifically, it comprises a
standard butterfly package. The lid 136 is shown cut away to
illustrate the internal components. Further, the optical bench B-2
is preferably installed on a thermoelectric cooler 134, which
enables a controlled environmental temperature to stabilize the
operation of the SLED chip 110 and the tunable Fabry-Perot filter
system 200.
Electrical leads 138 are further provided to transmit electrical
signals to the pads 146 on the inside of the hermetic package 132.
Wire bond are made between pads 146 and the active components such
as the SLED chip 110, MEMS tunable filter 116, and SOA 128.
The FIG. 4 embodiment has the advantage that the tunable signal 30
received from the tunable Fabry-Perot filter system 200 is
amplified to further increase the dynamic range and the
signal-to-noise ratio of the spectroscopy system.
In the embodiment of FIG. 5, the tunable source 10 also combines a
SLED chip 110, a first lens component 114, isolator 120, and a
second lens component 122. This launches the broadband signal 40
from the SLED chip into the tunable filter system 200. A third lens
component 126 is further provided. This collimates the beam. A
splitter, however, comprising a partially reflective substrate 149,
provides a portion of the tunable signal 30 to a detector 140. This
detector 140 can be used to monitor the magnitude or power in the
tunable signal 30. In another embodiment, a reference substrate 148
is installed between the detector 140 and the tap 149. This
reference substrate 148 provides stable spectral features. In one
embodiment, this is provided by a fixed etalon substrate. A
controller monitoring the output of the detector 140 compares the
tunable signal to the spectral features of the reference substrate
148 to thereby resolve the instantaneous wavelength of the tunable
signal 30.
In still other embodiments, instead of a reference substrate, a gas
cell is used as the spectral reference for calibrating the scan of
the tunable filter 116. Also two splitters can be included to
provide simultaneous spectral and power references.
The tunable signal, which is not coupled to the detector 140 by the
tap 149 is launched by a fourth lens component 147 into the fiber
endface 104 of the optical fiber 102.
FIG. 6 illustrates the general operation provided by a controller
150 of the tunable source 10. Specifically, the controller 150 is
used to control the power or current supplied to the SLED chip 110.
Its broadband signal 40 is coupled to the isolator 120. The
controller also controls the tunable pass band of the tunable
filter system 200 to generate the tunable signal 30.
In the case of monitoring the frequency of the tunable signal, a
first tap 149 couples a portion of the tunable signal to a spectral
reference 148, which in the illustrated embodiment, is a fixed
etalon. This allows the detector 140 to detect the wavelength of
the tunable signal 30 during the scan.
In the preferred embodiment, a power detector 154 is also provided.
This is added to the optical train using second tap 152, which
again couples the portion of the tunable signal 30 to a power
detector 154. The controller 150 controls and monitors the
wavelength detector 140 and the power detector 154 to determine
both the wavelength and the power in the tunable signal 30.
FIG. 7 illustrates another embodiment of the tunable source 10.
This embodiment is used either to increase the power or the
spectral width of the scan band of the tunable source 10.
Specifically, multiple SLED chips, and specifically two SLED chips
110A and 110B, are installed together on the optical bench B-2. In
the illustrated embodiment, the SLED chips 110A and 110B are
installed on a common sub-mount 112, which is in turn, bonded to
the bench B-2.
Two first lens components 118A, 118B are provided to couple the
broadband signals from their respective SLED chips 110A, 110B and
collimate those beams. A combination of a fold mirror 156 and a
combiner 158 are provided to combine the broadband signals from
each of these SLED chips 110A, 110B into a single broadband signal,
which is coupled through the isolator 120.
The beam from the isolator 120 is then focused by a second lens
component 122 into the tunable filter 200. A third lens component
126 then couples the tunable signal into the optical fiber 102 via
the endface 104.
In the high power version of the FIG. 7 embodiment, a polarization
rotator, such as a quarterwave plate 160 is provided in the beam
path of one of the SLED chips 110A, 110B. In the illustrated
embodiment, this polarization rotator 160 is provided in the beam
path of the second SLED chip 110. This rotates the polarization of
the light from the second SLED chip 110B by 90.degree.. Then, the
combiner 158 is a polarization combiner that is transmissive to the
polarization of the light from the first SLED chip 110A, but
reflective to the polarization of light from the second SLED chip
110B. As a result, the beams from each of the SLED chips 110A, 110B
are merged into a common broadband signal with increased power.
In a second implementation of the FIG. 7 embodiment, the SLED chips
110A, 110B operate at different spectral bands. Specifically, SLED
chip 110A generates light in a scan band A and SLED chip 110B
generates light in an adjacent but different scan band B. The
combiner 158 is a wavelength division multiplex combiner that is
configured to be transmissive to the band of light generated by the
SLED chip 110A, but reflective to light in the band generated by
SLED chip 110B. As a result, the combined signal generated together
by the SLED chip 110A, 110B has a broader scanband then could be
generated by each of the SLED chips individually. This allows for
increased bandwidth in the tunable signal 30 that is generated by
the tunable source 10.
FIG. 8 illustrates another embodiment of the tunable source 10.
This embodiment uses a tunable filter system 200, which includes an
array of tunable filters 116 and broadband light sources in order
to increase the spectral width of the scanband. Typically, and in
the illustrated embodiment, an array of five SLED chips 110 are
mounted in common on the bench B-2. The light from each of these
SLED chips 110 is collimated by respective first lens components
118. Specifically, there is a separate lens component 118 for each
of these SLED chips 110. Separate isolators 120 are then provided
for the broadband signals from each of the SLED chips 110.
An array of second lens components 122 is further provided to
couple the broadband signal into an array of tunable filters 200.
Specifically, separate Fabry-Perot tunable filters 116 are used to
filter the signal from each of the respective SLED chips 110.
Finally, an array of third lens components 126 is used to
re-collimate the beam from the tunable Fabry-Perot filters 116 of
the tunable filter system 200.
For channel 1, C-1, a fold mirror 156 is used to redirect the beam
from the SLED chip 110. The WDM filter 160 is used to combine the
broadband signal from the SLED chip 110 of channel C-2 with the
signal from channel C-1. Specifically, the filter 160 is reflective
to the wavelength range generated by the SLED chip 110 of channel
C-2, but transmissive to the wavelength range of light generated by
the SLED chip 110 of channel C-1.
In a similar vein, WDM filter 162 is reflective to the signal band
generated by the SLED chip 110 of channel C-3, but transmissive to
the bands generated by SLED chips 110 of channels C-1 and C-2. WDM
filter 164 is reflective to the light generated by SLED chip 110 of
channel C-4, but transmissive to the bands generated by the SLED
chips 110 of channels C-1, C-2, and C-3. Finally, WDM filter 158 is
reflective to all of the SLED chips, but the SLED chip 110 of
channel C-5. As a result, the light from the array of SLED chips is
combined into a single broad band tunable signal 30.
A first tap 149 is provided to reflect a portion of the light
through the etalon 148 to be detected by the wavelength detector
140. Then, another portion is reflected by tap 152 to the power
detector 154. The remaining tunable signal is coupled by the fourth
lens component 106 into the optical fiber 102 via the endface
104.
The FIG. 8 embodiment can operate according to a number of
different modes via a controller 150. Specifically, in one example,
only one of the SLED chips in channels C-1 to C-5 is operating at
any given moment in time. As a result, the tunable signal 30 has
only a single spectral peak. The full scan band is achieved by
sequentially energizing the SLED chip of each channel C-1 to C-5.
This tunable signal is scanned over the entire scan band covered by
the SLED chips of channels C-1 to C-5 turning on the SLED chips in
series, or sequentially.
In another mode, each of the SLED chips is operated simultaneously.
As a result, the tunable signal has spectral peaks in each of the
scan bands, covered by each of the SLED chips 110 simultaneously.
This system results in a more complex detector system 300, which
must demultiplex the separate scan bands from each of the SLED
chips 110 from each of the channels at the detector. Specifically,
in one embodiment, five (5) detectors are used with a front-end
wavelength demultiplexor.
FIG. 9 shows an embodiment of the tunable source 10 that has both
increased power and increased scanning range over a single SLED. It
comprises two subcomponents, which are configured as illustrated in
FIG. 7 embodiment. Specifically, each channel C-1, C-2 has two SLED
chips 110A, 110B that are polarization combined. The output is
isolated by an isolator 120 and then filtered by a tunable filter
116 for each channel C-1, C-2. The signals from the two channels
are then wavelength multiplexed using a combination of a fold
mirror 170 and a dichroic or WDM filter 172. Specifically, the
dichroic mirror 172 is transmissive to the scan band of the SLED
chips 110A, 110B of channel C-1, but reflective to the SLED chips
110A, 110B of channel C-2.
In order to improve the manufacturing yield of the FIG. 9
embodiment, in one implementation, each of the channels C-1 and C-2
are fabricated on separate sub-benches SB-1 and SB-2. The
sub-benches SB-1, SB-2 are then bonded to each other or to a common
bench in order to yield the FIG. 9 embodiment.
FIG. 10 illustrates still another embodiment, which covers a wide
spectral band. Specifically, it includes five SLED chips 110A to
110E. A series of first lens optical components 118 are used to
collimate the beams from each of the SLED chips 110A-110E. In the
present embodiment, the SLED chips 110A to 110E, each operate over
different spectral bands. They are then wavelength combined using a
combination of fold mirrors and filters 156, 160, 162, 164 and 158,
as discussed with reference to the FIG. 8 embodiment.
The FIG. 10 embodiment further includes, preferably, two isolators
120A, 120B. These isolate respective tunable filters 116A, 116B.
Lens components 180, 182, 184, and 186 are used to couple the
optical signal generated by the SLEDS 110A-110E, through the first
tunable filter 116A and the second tunable filter 116B of the
tunable filter system 200, and then, through the wavelength tap 149
and the power tap 152 to the endface 104 of the optical fiber
102.
The use of the five SLED chips 110 increases the effective scan
band of the tunable source 10. In the preferred embodiment, the
tandem tunable filters have free spectral ranges FSR as illustrated
in FIG. 11.
Specifically, filter 1 116A, and filter 2 116B have different free
spectral ranges. As a result, they function in a vernier
configuration. This addresses limitations in the free spectral
range of the tunable filters individually.
Typically, if a single tunable filter was used, its free spectral
range would have to be at least as wide as the total scan band of
the broad band signals generated by the sources. In the illustrated
embodiment, the tunable filters are combined to increase the free
spectral range of the tunable filter system, since the peak
transmissivity, through both tunable filters 116A-116B, only arises
at wavelengths where the passbands of the two filters 116A-166B are
coincident.
FIGS. 12A and 12B show tunable detector systems 20, to which the
principles of the present invention are also applicable.
Specifically, with reference to FIG. 12A, the tunable detector
system generally comprises a package 132 and an optical bench B-1,
which is sometimes referred to as a submount. The bench B-1 is
installed in the package 132, and specifically on a thermoelectric
(TE) cooler 134, which is located between the bench B-1 and the
package 132, in the specific illustrated embodiment.
The package 132, in this illustrated example, is a butterfly
package. The package's lid 136 is shown cut-away in the
illustration.
The tunable detector optical system, which is installed on the top
surface of the bench B-1, generally comprises the detector system
300, the tunable filter system 200, and an optional reference
source system 24.
In more detail, the optical signal from the target S-1 to be
monitored is transmitted to the system via a fiber pigtail 310, in
the illustrated example. This pigtail 310 terminates at an endface
312 that is secured above the bench B-1 using a fiber mounting
structure 314 in the illustrated implementation. The optical signal
passes through a first lens optical component 316, which collimates
the beam to pass through an isolator 320. A second lens optical
component 318 launches the optical signal into the tunable filter
system 200. A MEMS implementation of the tunable filter is shown.
The filtered signal passes through a third lens optical component
322 and is then detected by an optical signal detector 324.
In the illustrated implementation, each of the lens and tunable
filter optical components comprises the optical element and a
mounting structure that is used to secure the optical element to
the bench, while enabling most installation alignment.
Turning to the path of the optical reference, the emission from a
reference light source 42, such as a broadband source, e.g., a
SLED, passes through reference lens optical component 44 to a fixed
filter 46, which, in the present implementation, is a fixed etalon.
It converts the broadband spectrum of the SLED 42 into a series of
spectral peaks, corresponding to the various orders of the etalon
transmission, thereby producing the stable spectral features of the
optical reference.
The optical reference is then reflected by fold mirror 48 to a
dichroic or WDM filter 50, which is tuned to be reflective at the
wavelength of the optical reference, but transmissive within the
band of the optical signal. Thus, the optical reference is
similarly directed to the optical filter system 200.
At the detector system 20, a dichroic filter 52 reflects the
optical reference to a reference detector 54.
FIG. 12B shows an operationally similar tunable optical filter
system 20, for the purposes of the present invention. Reference
numerals have been used for functionally equivalent parts. The
differential between the two designs lies in the design of the
detector system 300. This second embodiment utilizes only a single
detector 324, 54 that detects both the optical reference and the
optical signal. In this illustration, the package is not shown for
clarity.
FIG. 13 shows another embodiment of the tunable detector 20. The
signal from the target is transmitted to the detector 20 via fiber
310. A first lens component 316 collimates the light from the
fiber. Second lens components 318 couple the light into the tunable
filters 116A, 116B of the filter system 200. Third lens components
322 focus the light to the detector system 300.
This version uses two tunable filters 116A, 116B, each filtering a
portion of the scan band. Corresponding detectors 334A, 334B detect
the transmitted signal from each filter.
The spectrum is divided into two subbands by WDM filter 360, which
reflects half of the spectral scan band to the second filter 116B
via fold mirror 362. The other half of the spectrum is transmitted
through the WDM filter 360 to tunable filter 116A.
FIG. 14 shows a single bench fully integrated system according to
still another embodiment. It generally operates as described
relative to the FIG. 8 embodiment. Specifically, it uses a series
of SLEDs in five channels, yielding a tunable source 10, to
generate a wide band tunable signal 30. The detector system 300 is
integrated on the same bench B and the tunable source.
Specifically, light returning from the target in fiber 310 is
coupled to detector 334 using lens component 322.
FIG. 15 shows another single bench fully integrated system
according to still another embodiment. Here, the light to and from
the target is carried in the same fiber 102, 310. The tap substrate
152 is used to direct outgoing light 30 to the power detector 154
and light returning from the target to the detector 334.
While this invention has been particularly shown and described with
references to preferred embodiments thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the scope of the
invention encompassed by the appended claims.
* * * * *