An external cavity laser (and method of generating laser light) comprising: a laser light source; means for collimating light output by the laser light source; a diffraction grating receiving collimated light; a cavity feedback mirror reflecting light received from the diffraction grating back to the diffraction grating; and means for reliably tuning the external cavity laser to discrete wavelengths

Pilgrim, Jeffrey S.

Silver, Joel A.

A prototype improved external cavity laser (ECL) was demonstrated in the second phase of a continuing effort to develop wavelength-agile lasers for fiber-optic communications and trace-gas-sensing applications. This laser is designed to offer next-generation performance for incorporation into fiber-optic networks. By eliminating several optical components and simplifying others used in prior designs, the design of this laser reduces costs, making lasers of this type very competitive in a price-sensitive market. Diode lasers have become enabling devices for fiber optic networks because of their cost, compactness, and spectral properties. ECLs built around diode laser gain elements further enhance capabilities by virtue of their excellent spectral properties with significantly increased (relative to prior lasers) wavelength tuning ranges. It is essential to exploit the increased spectral coverage of ECLs while simultaneously insuring that they operate only at precisely defined communication channels (wavelengths). Heretofore, this requirement has typically been satisfied through incorporation of add-in optical components that lock the ECL output wavelengths to these specific channels. Such add-in components contribute substantially to the costs of ECL lasers to be used as sources for optical communication networks. Furthermore, the optical alignment of these components, needed to attain the required wavelength precision, is a non-trivial task and can contribute substantially to production costs. The design of the present improved ECL differs significantly from the designs of prior ECLs. The present design relies on inherent features of components already included within an ECL, with slight modifications so that these components perform their normal functions while simultaneously effecting locking to the required discrete wavelengths. Hence, add-in optical components and the associated cost of alignment can be eliminated. The figure shows the locking feedback signal, and the frequency locking achieved by use of this signal, as a mirror is tilted through a range of angles to tune the ECL through 48 channels. The data for the frequency plot were obtained, simultaneously with the data for the locking-signal plot, by using a scanning Michelson interferometer to precisely determine the ECL wavelength (and, hence, frequency). Given the ability of the Michelson interferometer to obtain highly precise readings, the frequency plot can be taken to be a reliable indication of single-mode operation. The discontinuities in the frequency plot signify the switching of the ECL between channels; in other words, they indicate tuning with locking to discrete frequencies. The peaks of the feedbacklocking signal correspond to the centers, or near centers, of the mirror angle scan through the corresponding channels. Thus, it is clear that when the feedback-locking signal is at a local maximum, the ECL is operating at single frequency at or near the middle frequency of the selected channel. This is all that is required for precisely locking the ECL output wavelength. The locking is achieved without additional external optical components

NASA Technical Reports Server

28 NASA Tech Briefs, September 2004
A prototype improved external cavity
laser (ECL) was demonstrated in the sec-
ond phase of a continuing effort to de-
velop wavelength-agile lasers for fiber-optic
communications and trace-gas-sensing ap-
plications. This laser is designed to offer
next-generation performance for incorpo-
ration into fiber-optic networks. By elimi-
nating several optical components and
simplifying others used in prior designs,
the design of this laser reduces costs, mak-
ing lasers of this type very competitive in a
price-sensitive market.
Diode lasers have become enabling de-
vices for fiber optic networks because of
their cost, compactness, and spectral
properties. ECLs built around diode
laser gain elements further enhance ca-
pabilities by virtue of their excellent
spectral properties with significantly in-
creased (relative to prior lasers) wave-
length tuning ranges. It is essential to ex-
ploit the increased spectral coverage of
ECLs while simultaneously insuring that
they operate only at precisely defined
communication channels (wavelengths).
Heretofore, this requirement has typi-
cally been satisfied through incorpora-
tion of add-in optical components that
“lock” the ECL output wavelengths to
these specific channels. Such add-in
components contribute substantially to
the costs of ECL lasers to be used as
sources for optical communication net-
works. Furthermore, the optical align-
ment of these components, needed to at-
tain the required wavelength precision,
is a non-trivial task and can contribute
substantially to production costs.
The design of the present improved
ECL differs significantly from the de-
signs of prior ECLs. The present design
relies on inherent features of compo-
nents already included within an ECL,
with slight modifications so that these
components perform their normal func-
tions while simultaneously effecting
locking to the required discrete wave-
lengths. Hence, add-in optical compo-
nents and the associated cost of align-
ment can be eliminated.
The figure shows the locking feed-
back signal, and the frequency locking
mates the ideal angular response (pro-
portional to the cosine of the angle of
incidence). The filter is chosen to pass
the ultraviolet wavelength of interest
in a specific experiment.
The photodiode is electrically con-
nected to the coulometer. The factor of
proportionality between the charge
stored in the coulometer and ultravio-
let dosage (in units of ESH) is estab-
lished, prior to use, in calibration ex-
periments that involve the use of lamps
and current sources traceable to the
National Institute of Standards and
Technology.
This work was done by Jason A. Vaughn
of Marshall Space Flight Center and
Perry Gray of Micro Craft, Inc.
This invention is owned by NASA, and a
patent application has been filed. For further
information, contact Sammy Nabors, MSFC
Commercialization Assistance Lead, at (256)
544-5226 or sammy.a.nabors@nasa.gov.
Refer to MFS-31316-1.
The Frequency Varies in Steps as a function of the mirror angle. Each step represents locking to the
indicated frequency.
0.0
194
195
196
197
198
199
0.2 0.6 1.0
Fr
eq
u
en
cy
, T
H
z
Mirror Angle, Degrees
Lo
ckin
g
 Feed
b
ack Sig
n
al, A
rb
itrary U
n
its
0.4 0.8 1.2 1.4
200
0.4
0.5
0.6
0.7
0.8
This Simple, Passive Instrument measures the dosage of ultraviolet light in the pass wavelength band
of its filter.
Aluminum Outer Shell
Electrical
Connector
Poly(tetrafluoroethylene)
for Electrical insulation
O-Ring Seal Interface Plate
Electrical Connector
Aluminum Housing
Narrow-Band
Optical Filter
Cosine
Receptor
Photodiode
Coulometer
Hole for 
Connector
Outer Shell Cover
Discrete Wavelength-Locked External Cavity Laser
The laser is locked internally to frequencies of communication channels.
John H. Glenn Research Center, Cleveland, Ohio
https://ntrs.nasa.gov/search.jsp?R=20110020543 2019-08-30T17:59:14+00:00Z
NASA Tech Briefs, September 2004 29
achieved by use of this signal, as a mir-
ror is tilted through a range of angles to
tune the ECL through 48 channels. The
data for the frequency plot were ob-
tained, simultaneously with the data for
the locking-signal plot, by using a scan-
ning Michelson interferometer to pre-
cisely determine the ECL wavelength
(and, hence, frequency). Given the abil-
ity of the Michelson interferometer to
obtain highly precise readings, the fre-
quency plot can be taken to be a reliable
indication of single-mode operation.
The discontinuities in the frequency
plot signify the switching of the ECL be-
tween channels; in other words, they in-
dicate tuning with locking to discrete
frequencies. The peaks of the feedback-
locking signal correspond to the cen-
ters, or near centers, of the mirror angle
scan through the corresponding chan-
nels. Thus, it is clear that when the feed-
back-locking signal is at a local maxi-
mum, the ECL is operating at single
frequency at or near the middle fre-
quency of the selected channel. This is
all that is required for precisely locking
the ECL output wavelength. The lock-
ing is achieved without additional exter-
nal optical components.
Another aspect of the design of this
ECL is a provision for the incorpora-
tion of a particularly simple micro-
electromechanical system (MEMS)
mirror for wavelength tuning. The sim-
plified motion of the mirror enables
facile alignment and rapid tuning,
both important in a network source
laser. This ECL is capable of switching
wavelengths across the entire fre-
quency band indicated in the figure in
a time of less than one millisecond.
Other performance characteristics,
like the side-mode-suppression ratio
and relative-intensity noise, are equal
to or better than those of other lasers
now available.
This work was done by Jeffrey S. Pilgrim and
Joel A. Silver of Southwest Sciences, Inc.
for Glenn Research Center.
Inquiries concerning rights for the commer-
cial use of this invention should be addressed
to NASA Glenn Research Center, Commercial
Technology Office, Attn: Steve Fedor, Mail
Stop 4-8, 21000 Brookpark Road, Cleveland,
Ohio 44135. Refer to LEW-17313-1.


Discrete wavelength-locked external cavity laser

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server

NASA Technical Reports Server