U.S. patent application number 11/057867 was filed with the patent office on 2005-09-29 for method of generating an ultra-short pulse using a high-frequency ring oscillator.
Invention is credited to Delfyett, Peter, Mielke, Michael.
Application Number | 20050215985 11/057867 |
Document ID | / |
Family ID | 34812055 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050215985 |
Kind Code |
A1 |
Mielke, Michael ; et
al. |
September 29, 2005 |
Method of generating an ultra-short pulse using a high-frequency
ring oscillator
Abstract
The present invention provides a method of generating an
ultra-short pulse in a ring oscillator by amplifying a series of
wavelength-swept-with time pulses using one or more amplifiers,
compressing the amplified wavelength-swept-with time pulses,
reducing the compressed pulses to sub-picosecond pulses, stretching
the sub-picosecond pulses into wavelength-swept-with time pulses
and returning the stretched pulses to the one or more
amplifiers.
Inventors: |
Mielke, Michael; (Orlando,
FL) ; Delfyett, Peter; (Oviedo, FL) |
Correspondence
Address: |
CARR & FERRELL LLP
2200 GENG ROAD
PALO ALTO
CA
94303
US
|
Family ID: |
34812055 |
Appl. No.: |
11/057867 |
Filed: |
February 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11057867 |
Feb 13, 2005 |
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10916367 |
Aug 11, 2004 |
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60494275 |
Aug 11, 2003 |
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60503578 |
Sep 17, 2003 |
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Current U.S.
Class: |
606/2 ;
606/9 |
Current CPC
Class: |
A61B 18/20 20130101 |
Class at
Publication: |
606/002 ;
606/009 |
International
Class: |
A61B 018/20 |
Claims
What is claimed is:
1. A method of generating an ultra-short pulse in a ring
oscillator, comprising the steps of: amplifying a series of
wavelength-swept-with time pulses using one or more amplifiers;
compressing the amplified wavelength-swept-with time pulses;
reducing the compressed pulses to sub-picosecond pulses; stretching
the sub-picosecond pulses into wavelength-swept-with time pulses;
and returning the stretched pulses to the one or more
amplifiers.
2. The method of claim 1, wherein the one or more of the one or
more amplifiers comprise one or more semiconductor optical
amplifiers.
3. The method of claim 1, wherein the compressing is preformed by
one or more gratings.
4. The method of claim 3, wherein the one or more gratings comprise
a chirped fiber Bragg grating.
5. The method of claim 1, wherein the reducing is preformed by one
or more nonlinear optical elements.
6. The method of claim 5, wherein the one or more nonlinear optical
elements comprise a carbon nanotube saturable absorber.
7. The method of claim 1, wherein the stretching is preformed by
one or more gratings.
8. The method of claim 7, wherein the one or more gratings comprise
a chirped fiber Bragg grating.
9. The method of claim 1, wherein the ring oscillator is coupled
through an output coupler.
10. The method of claim 9, wherein a portion of each of the
amplified pulses are coupled out through the output coupler.
11. The method of claim 9, wherein a portion of each of the
compressed pulses are coupled out through the output coupler.
12. The method of claim 1, wherein the oscillator runs at a
repetition rate of at least 25 MHz.
13. The method of claim 12, wherein the oscillator further
comprises a pulse selector to give a pulse-selector output with a
repetition rate of less than one-tenth the oscillator repetition
rate.
14. The method of claim 13, further comprising the step of
synchronizing the oscillator and the pulse selector, wherein an
electrical impulse generator is used to activate a device in the
oscillator.
15. The method of claim 14, wherein the electrical impulse
generator is used to activate one or more semiconductor optical
amplifiers.
16. The method of claim 14, wherein the electrical impulse
generator is used to activate an electro-optic modulator to produce
a temporal window of net positive pulse amplification within the
oscillator.
17. The method of claim 1, wherein the oscillator contains one or
more polarization controllers.
18. The method of claim 1, wherein the step of stretching and the
step of compressing are preformed by one or more chirped fiber
Bragg gratings.
19. The method of claim 1, wherein one or more optical connections
between components are made through optical fiber.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation patent application of
U.S. patent application Ser. No. 10/916,367 filed on Aug. 11, 2004,
which claims the benefit of U.S. Provisional Patent Application
Nos. 60/494,275 filed on Aug. 11, 2003 (now abandoned) and
60/503,578 filed on Sep. 17, 2003 (now abandoned). U.S. patent
application Ser. No. 10/916,367 incorporated the contents of U.S.
Provisional Patent Application No. 60/539,024 filed on Jan. 13,
2004 (now abandoned) by reference. The entire content of U.S.
patent application Ser. No. 10/916,367 filed on Aug. 11, 2004 is
hereby incorporated by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates in general to the field of
light amplification and, more particularly to generating an
ultra-short pulse in an oscillator.
BACKGROUND OF THE INVENTION
[0003] Without limiting the scope of the invention, its background
is described in connection with ultra-short pulse in an oscillator,
as an example. Ablative material removal is especially useful for
medical purposes, either in-vivo or on the outside surface (e.g.,
skin or tooth), as it is essentially non-thermal and generally
painless. Ablative removal of material is generally done with a
short optical pulse that is stretched amplified and then
compressed. A number of types of laser amplifiers have been used
for the amplification.
[0004] Machining using laser ablation removes material by
disassociating the surface atoms and melting the material. Laser
ablation is efficiently done with a beam of short pulses (generally
a pulse-duration of three picoseconds or less). Techniques for
generating these ultra-short pulses (USP) are described, e.g., in a
book entitled "Femtosecond Laser Pulses" (C. Rulliere, editor),
published 1998, Springer-Verlag Berlin Heidelberg New York.
Generally large systems, such as Ti:Sapphire, are used for
generating ultra-short pulses.
[0005] The USP phenomenon was first observed in the 1970's, when it
was discovered that mode-locking a broad-spectrum laser could
produce ultra-short pulses. The minimum pulse duration attainable
is limited by the bandwidth of the gain medium, which is inversely
proportional to this minimal or Fourier-transform-limited pulse
duration. Mode-locked pulses are typically very short and will
spread (i.e., undergo temporal dispersion) as they traverse any
medium. Subsequent pulse-compression techniques are often used to
obtain USP's. A diffraction grating compressor is shown, e.g., in
Patent 5,822,097 by Tournois. Pulse dispersion can occur within the
laser cavity so that compression (dispersion-compensating)
techniques are sometimes added intra-cavity. When high-power pulses
are desired, the pulses are intentionally lengthened (e.g., to a
nanosecond) before amplification to avoid internal component
optical damage. This is referred to as "Chirped Pulse
Amplification" (CPA). The pulse is subsequently compressed to
obtain a high peak power (pulse-energy amplification and
pulse-duration compression).
[0006] As a result, there is a need for generating ultra-short
pulses at very-high frequency repetition rates, which allows pulse
selection to be used to accurately vary such very high ablation
pulse repetition rates.
SUMMARY OF THE INVENTION
[0007] Ultra-short optical ablation systems can be operated more
efficiently when pulse-energy is controlled by varying the ablation
pulse repetition rate. The present invention provides a method of
generating an ultra-short pulse in a ring oscillator,
(sub-picosecond) pulses at very-high frequency repetition rates,
which allows pulse selection to be used to accurately vary such
very high ablation pulse repetition rates. The oscillator may
include an amplifier (e.g., a Semiconductor Optical Amplifier
(SOA)), an output coupler, a compressor (e.g., a chirped fiber
Bragg grating with an associated circulator), a nonlinear optical
element (e.g., a saturable absorber, such as a carbon nanotube
saturable absorber), a stretcher (e.g., a chirped fiber Bragg
grating with an associated circulator) arranged in a ring
configuration to provide ultra-short (sub-picosecond) pulses of
repetition rates of 25 MHz to 1 GHz or more. Note that the
components can be connected together using optical fiber. Other
embodiments of the present invention may have an ablation pulse
repetition rate of between about 1 MHz and 25 MHz. The oscillator
of the present invention has relatively few components, is
relatively inexpensive, can be easily miniaturized, and is also
useful for other systems.
[0008] More specifically, the present invention provides a method
of generating an ultra-short pulse in a ring oscillator by
amplifying a series of wavelength-swept-with time pulses using one
or more amplifiers, compressing the amplified wavelength-swept-with
time pulses, reducing the compressed pulses to sub-picosecond
pulses, stretching the sub-picosecond pulses into
wavelength-swept-with time pulses and returning the stretched
pulses to the one or more amplifiers. The one or more amplifiers
may include one or more semiconductor optical amplifiers
(SOAs).
[0009] The oscillator may also include an electrical impulse
generator (EIG) to drive the amplifier (or drive an electro-optic
modulator) and/or a polarization controller to provide cleaner
pulses. The electrical impulse generator can be used to activate a
device in the ring to synchronize the oscillator and the pulse
selector (e.g., the electrical impulse generator may be used to
activate the SOA), or the electrical impulse generator may be used
to activate an electro-optic modulator to produce a temporal window
of net positive pulse amplification within the ring.
[0010] The compressing may be preformed by one or more gratings,
the stretching may be preformed by one or more gratings, or both
the compressing and the stretching may be preformed by one grating
or more than one grating. For example, the compressor and stretcher
can be a single grating having a circulator connected to each end
of the grating. The grating can be a chirped fiber Bragg
grating.
[0011] Generally, the output pulses from the ring oscillator are
coupled out through an output coupler (e.g., a portion of each of
the amplified pulses is coupled out through the output coupler;
either stretched or compressed pulses may be coupled out through
the output coupler). A pulse selector may be used to give a
pulse-selector output with a repetition rate of less than one-tenth
the oscillator repetition rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a more complete understanding of the features and
advantages of the present invention, reference is now made to the
detailed description of the invention along with the accompanying
figures and in which:
[0013] FIG. 1 illustrates a schematic of the ring oscillator in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] While the making and using of various embodiments of the
present invention are discussed in detail below, it should be
appreciated that the present invention provides many applicable
inventive concepts that can be embodied in a wide variety of
specific contexts. The specific embodiments discussed herein are
merely illustrative of specific ways to make and use the invention
and do not delimit the scope of the invention.
[0015] To facilitate the understanding of this invention, a number
of terms are defined below. Terms defined herein have meanings as
commonly understood by a person of ordinary skill in the areas
relevant to the present invention. Terms such as "a", "an" and
"the" are not intended to refer to only a singular entity, but
include the general class of which a specific example may be used
for illustration. The terminology herein is used to describe
specific embodiments of the invention, but their usage does not
delimit the invention, except as outlined in the claims.
[0016] In many applications, an ablation pulse repetition rate of
about 1 MHz or more is desirable. The ring oscillator of the
present invention provides ultra-short (sub-picosecond) pulses at
very-high frequency repetition rates. Ultra-short optical ablation
systems can be operated more efficiently when pulse-energy is
controlled by varying the ablation pulse repetition rate, which
allows pulse selection to be used to accurately vary such high
ablation pulse repetition rates.
[0017] The present invention provides a method of generating an
ultra-short pulse in a ring oscillator, (sub-picosecond) pulses at
very-high frequency repetition rates, which allows pulse selection
to be used to accurately vary such very high ablation pulse
repetition rates. The oscillator may include an amplifier (e.g., a
Semiconductor Optical Amplifier (SOA)), an output coupler, a
compressor (e.g., a chirped fiber Bragg grating with an associated
circulator), a nonlinear optical element (e.g., a saturable
absorber, such as a carbon nanotube saturable absorber), a
stretcher (e.g., a chirped fiber Bragg grating with an associated
circulator) arranged in a ring configuration to provide ultra-short
(sub-picosecond) pulses of repetition rates of 25 MHz to 1 GHz or
more. Note that the components can be connected together using
optical fiber. Other embodiments of the present invention may have
an ablation pulse repetition rate of between about 1 MHz and 25
MHz. The oscillator of the present invention has relatively few
components, is relatively inexpensive, can be easily miniaturized,
and is also useful for other systems.
[0018] More specifically, the present invention provides a method
of generating an ultra-short pulse in a ring oscillator by
amplifying a series of wavelength-swept-with time pulses using one
or more amplifiers, compressing the amplified wavelength-swept-with
time pulses, reducing the compressed pulses to sub-picosecond
pulses, stretching the sub-picosecond pulses into
wavelength-swept-with time pulses and returning the stretched
pulses to the one or more amplifiers. The method may also include
synchronizing the oscillator and the pulse selector.
[0019] Now referring to FIG. 1, a schematic of a ring oscillator
100 in accordance with one embodiment of the present invention is
shown. The oscillator 100 includes one or more amplifiers
(Semiconductor Optical Amplifier (SOA) 102) driven by an electrical
impulse generator (EIG 104), a Faraday Isolator (FI 106), an output
coupler (Output 108), a temporal compressor (first chirped fiber
Bragg grating (CFBG-110) connected to the ring with circulator
112), a nonlinear optical element (saturable absorber (NL 114)), a
polarization controller (PC 116) and a temporal stretcher (second
chirped fiber Bragg grating (CFBG+118) connected to the ring with
circulator 120). All of the connections between these components
can made through an optical fiber as opposed to previous
oscillators that used free-space optical components. In other
embodiments, the electrical impulse generator (EIG 104) may drive
an electro-optic modulator. The output coupler (Output 108)
provides ultra-short (sub-picosecond) pulses having repetition
rates of 25 MHz to 1 GHz or more. The present invention can produce
pulses having a duration of 100 to 200 fs, which may set a new
benchmark for the shortest pulse generated by a diode laser. Other
pulse durations may be produced.
[0020] Some of the mode-locked diode laser cavity 100 components
are generally commercially available, including the semiconductor
optical amplifier 102 (e.g., InPhenix, Covega, Kamelian, or
Exalos). The electrical impulse generator 104 can be originated
from an integrated electronics module (IEM) based on a digital
signal processor (DSP) platform. DSP circuits are currently
available as evaluation boards from several manufacturers (e.g.,
Texas Instruments, Motorola, Analog Devices). The IEM can generate
short current pulses for the modelocked laser cavity 100
coordinated with similar current pulses for biasing subsequent
amplifiers 102. Chirped fiber Bragg gratings 110 and 118 have been
developed by 3M Company. The large group velocity delays (GVD)
imposed by the one or more chirped fiber Bragg gratings 110 and 118
(e.g., >1000 ps/nm) are much greater than the current
intracavity stretcher configuration, which will further linearize
the amplification inside the laser. Nonlinear loss modulation in
the modelocked cavity 100 is established using compound cavity
geometries (e.g., additive pulse modelocking, colliding pulse
modelocking, nonlinear optical loop mirror) using standard fiber
optic components and a novel design.
[0021] Features of femtosecond pulse creation of the present
invention includes the electrical impulse bias of the semiconductor
optical amplifier device 102, the ultrafast nonlinear loss
mechanism of the carbon nanotubes 114, and the dispersion
management using one or more first chirped fiber Bragg gratings 110
and one or more second chirped fiber Bragg gratings 118. Actively
modelocked diode lasers have been injected with very high frequency
sinewaves (>1 GHz) to synchronize longitudinal mode phase and to
provide a brief window of net positive gain in the cavity.
Electrical impulse (delta function) bias enables lower repetition
rates (.ltoreq.10 MHz), while maintaining a limited positive gain
window in the cavity. Nonlinear loss mechanisms, such as saturable
absorption or Kerr lensing, provide additional pulse shortening in
the cavity by shearing off the low intensity edges of the
modelocked pulses. Chirped fiber Bragg gratings 110 and 118 have
low insertion loss at 1550 nm and can provide sufficient group
delay to establish extreme chirped pulse amplification inside the
fiber ring cavity. Laboratory demonstrations thus far have been
limited by use of traditional Treacy grating stretchers and
compressors (not shown), which are limited in their magnitude of
chirp.
[0022] The amplifier 102 may be a semiconductor optical amplifier
that provides optical gains. The Faraday isolator 106 insures
unidirectional beam propagation and prevents feedback from the
output coupler 108. The first chirped fiber Bragg gratings
(CFBG-110) unchirp and compress the optical pulse subsequent to
amplification in the amplifier 102.
[0023] Alternately, an electro-optic modulator (not shown) can
provide cavity loss modulation. The short electrical pulse from the
electrical impulse generator 104 makes the EOM temporarily
transparent which creates a narrow (200 ps) temporal window of net
positive gain inside the laser cavity. The short electrical pulse
prevents build up of amplified spontaneous emission inside the
cavity and synchronizes the modelocked pulse train to an external
timing signal.
[0024] The nonlinear optical element 114 is a passive optical loss
mechanism, such as a carbon nanotube based saturable absorber, that
shears off the long leading edge of the optical pulse thereby
dramatically shortening the pulse temporal width. The second
chirped fiber Bragg gratings 118 chirp and stretch the optical
pulse, which facilitates nearly linear amplification inside the
semiconductor optical amplifier 102. The polarization controller
116 maintains linear polarization along the preferred cavity axis
for stable laser operation. The output coupler 108 can couple a
portion of the pulse energy out (typically for further
amplification) and retains the remainder (e.g., 5%) in the ring as
feedback. Being an oscillator, the ring is self-starting and the
second chirped fiber Bragg gratings 118 stretcher provide
wavelength-swept-with time pulses for amplification by the
amplifier 102.
[0025] Note that the circulators 112 and 120 may be connected to
opposite ends of a single chirped fiber Bragg grating (not shown),
such that a single circulator acts as both a stretcher and a
compressor. Moreover, a Treacy grating (not shown) can be used for
the compressor or stretcher as opposed to one or more chirped fiber
Bragg gratings 110 and 118. The carbon nanotube saturable absorber
114 implementation is novel, as is the use of an impulse-driven
semiconductor optical amplifier 102.
[0026] The present invention may be used in systems along with the
co-owned and previously filed provisional applications noted below
by docket number, title and (generally) provisional number, and are
hereby incorporated by reference herein:
1 Docket US Serial Number Title Number Filing Date ABI-1 Laser
Machining 60/471,922 May 20, 2003 ABI-2 Laser Contact With
W/Dopant/Copper Alloy 60/472,070 May 20, 2003 ABI-3 SOAs
Electrically And Optically In Series 60/471,913 May 20, 2003 ABI-4
Camera Containing Medical Tool 60/472,071 May 20, 2003 ABI-5
In-vivo Tool with Sonic Locator 60/471,921 May 20, 2003 ABI-6
Scanned Small Spot Ablation With A High-Rep- 60/471,972 May 20,
2003 Rate ABI-7 Stretched Optical Pulse Amplification and
60/471,971 May 20, 2003 Compression ABI-8 Controlling Repetition
Rate Of Fiber Amplifier 60/494,102 Aug. 11, 2003 ABI-9 Controlling
Pulse Energy Of A Fiber Amplifier By 60/494,275 Aug. 11, 2003
Controlling Pump Diode Current ABI-10 Pulse Energy Adjustment For
Changes In Ablation 60/494,274 Aug. 11, 2003 Spot Size ABI-11
Ablative Material Removal With A Preset 60/494,273 Aug. 11, 2003
Removal Rate or Volume or Depth ABI-12 Fiber Amplifier With A Time
Between Pulses Of 60/494,272 Aug. 11, 2003 A Fraction Of The
Storage Lifetime ABI-13 Man-Portable Optical Ablation System
60/494,321 Aug. 11, 2003 ABI-14 Controlling Temperature Of A Fiber
Amplifier By 60/494,322 Aug. 11, 2003 Controlling Pump Diode
Current ABI-15 Altering The Emission Of An Ablation Beam for
60/494,267 Aug. 11, 2003 Safety or Control ABI-16 Enabling Or
Blocking The Emission Of An 60/494,172 Aug. 11, 2003 Ablation Beam
Based On Color Of Target Area ABI-17 Remotely-Controlled Ablation
of Surfaces 60/494,276 Aug. 11, 2003 ABI-18 Ablation Of A Custom
Shaped Area 60/494,180 Aug. 11, 2003 ABI-19
High-Power-Optical-Amplifier Using A Number 60/497,404 Aug. 22,
2003 Of Spaced, Thin Slabs ABI-20 Spiral-Laser On-A-Disc 60/502,879
Sep. 12, 2003 ABI-21 Laser Beam Propagation in Air 60/502.886 Sep.
12, 2003 ABI-22 Active Optical Compressor 60/503,659 Sep. 17, 2003
ABI-23 Controlling Optically-Pumped Optical Pulse 60/503,578 Sep.
17, 2003 Amplifiers ABI-24 High Power SuperMode Laser Amplifier
60/505,968 Sep. 25, 2003 ABI-25 Semiconductor Manufacturing Using
Optical 60/508,136 Oct. 02, 2003 Ablation ABI-26 Composite Cutting
With Optical Ablation 60/510,855 Oct. 14, 2003 Technique ABI-27
Material Composition Analysis Using Optical 60/512,807 Oct. 20,
2003 Ablation ABI-28 Quasi-Continuous Current in Optical Pulse
60/529,425 Dec. 12, 2003 Amplifier Systems ABI-29 Optical Pulse
Stretching and Compression 60/529,443 Dec. 11, 2003 ABI-30 Start-Up
Timing for Optical Ablation System 60/539,926 Jan. 23, 2004 ABI-31
High-Frequency Ring Oscillator 60/539,924 Jan. 23, 2004 ABI-32
Amplifying of High Energy Laser Pulses 60/539,925 Jan. 23, 2004
ABI-33 Semiconductor-Type Processing for Solid State 60/543,086
Feb. 09, 2004 Lasers ABI-34 Pulse Streaming of Optically-Pumped
Amplifiers 60/546,065 Feb. 18, 2004 ABI-35 Pumping of
Optically-Pumped Amplifiers 60/548,216 Feb. 27, 2004
[0027] Although the present invention and its advantages have been
described above, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods and steps described in the specification, but only by the
claims.
* * * * *