scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Wideband-tuneable, nanotube mode-locked, fibre laser

02 Nov 2008-Nature Nanotechnology (Nature Publishing Group)-Vol. 3, Iss: 12, pp 738-742
TL;DR: In principle, different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tuneable over a much broader range of wavelengths than other systems.
Abstract: Ultrashort-pulse lasers with spectral tuning capability have widespread applications in fields such as spectroscopy, biomedical research and telecommunications1–3. Mode-locked fibre lasers are convenient and powerful sources of ultrashort pulses4, and the inclusion of a broadband saturable absorber as a passive optical switch inside the laser cavity may offer tuneability over a range of wavelengths5. Semiconductor saturable absorber mirrors are widely used in fibre lasers4–6, but their operating range is typically limited to a few tens of nanometres7,8, and their fabrication can be challenging in the 1.3–1.5 mm wavelength region used for optical communications9,10. Single-walled carbon nanotubes are excellent saturable absorbers because of their subpicosecond recovery time, low saturation intensity, polarization insensitivity, and mechanical and environmental robustness11–16. Here, we engineer a nanotube–polycarbonate film with a wide bandwidth (>300 nm) around 1.55 mm, and then use it to demonstrate a 2.4 ps Er31-doped fibre laser that is tuneable from 1,518 to 1,558 nm. In principle, different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tuneable over a much broader range of wavelengths than other systems.

Summary (1 min read)

F. WANG1, A. G. ROZHIN1, V. SCARDACI1, Z. SUN1, F. HENNRICH2, I. H. WHITE1, W. I. MILNE1 AND A. C. FERRARI1*

  • Even for a wavelength detuning of up to 200 nm from the peak resonance, appreciable saturable absorption can still be observed25.
  • Thus, the authors study the mode-locking of the current laser over the extended wavelength range 1,518–1,565 nm in order to achieve the maximum possible tuning range.
  • An average pulse duration of 2.39 ps is obtained for different wavelengths (Fig. 4a).

SWNTs COMPOSITE

  • The SWNT–polycarbonate composite was prepared first by dispersing SWNT powders in dichlorobenzene (DCB) in the presence of poly(3-hexylthiophene- (Dashed line, optical spectrum without bandpass filter; dotted line; Er3þ fluorescence spectrum).
  • The use of the bandpass filter means that the output spectra have a high signal-to-noise ratio of 50 dB ( 105 contrast).
  • Nature nanotechnology | VOL 3 | DECEMBER 2008 | www.nature.com/naturenanotechnology740 © 2008 Macmillan Publishers Limited. 2,5-diyl) (P3HT) by ultrasonication (Diagenode SA).
  • No SWNT bundles could be detected under the scrutiny of an optical microscope, thus ensuring minimized scattering losses.

POWER-DEPENDENT ABSORPTION MEASUREMENTS

  • Power-dependent absorption measurements were carried out as follows.
  • This was achieved by filtering a commercial femtosecond fibre laser (200 fs, 76.9 MHz, TOPTICA) using a 3-nm band-pass filter.
  • The laser beam was amplified by an erbium-doped fibre amplifier and a 10% tap was used to monitor the input power to the mode-locker assembly, containing their composite, and two appropriately calibrated powerheads were programmed to read the input/output power simultaneously.

TUNEABLE LASER EXPERIMENTAL SETUP

  • The mode-locker was assembled by sandwiching the free-standing SWNT composite between two fibre ferrules inside a physical contact ferrule connector.
  • The estimated input mode diameter on the composite was 10 mm.
  • Two isolators were placed at both ends of the amplifier section to maintain unidirectional laser operation.
  • When the pump power was increased to 45 mW, stable mode-locking could be initiated by introducing a disturbance to the polarization controller.

Author information

  • Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/.
  • Correspondence and requests for materials should be addressed to A.C.F. nature nanotechnology | VOL 3 | DECEMBER 2008 | www.nature.com/naturenanotechnology742 © 2008 Macmillan Publishers Limited.

Did you find this useful? Give us your feedback

Content maybe subject to copyright    Report

W ideband-tuneable, nanotube
mode-locked, fibr e laser
F. W ANG
1
,A.G.ROZHIN
1
,V.SCARDACI
1
,Z.SUN
1
,F.HENNRICH
2
,I.H.WHITE
1
,W.I.MILNE
1
ANDA.C.FERRARI
1
*
1
Department of Engineering, University of Cambridge, 9 JJ Thomson Avenue, Cambridge, CB3 0FA, UK
2
Institut fu
¨
r Nanotechnologie Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany
*
e-mail: acf26@eng.cam.ac.uk
Publishe d online: 2 Novem ber 2008; doi:10.1038/nnano. 2008. 312
Ultrashort-pulse lasers with spectral tuning capability have
widespread applications in fields such as spectroscopy,
biomedical research and telecommunications
1–3
. Mode-locked
fibre lasers are convenient and powerful sources of ultrashort
pulses
4
, and the inclusion of a broadband saturable absorber
as a passive optical switch inside the laser cavity may offer
tuneability over a range of wavelengths
5
. Semiconductor
saturable absorber mirrors are widely used in fibre lasers
4–6
,
but their operating range is typically limited to a few tens of
nanometres
7,8
, and their fabrication can be challenging in the
1.31.5 mm wavelength region used for optical
communications
9,10
. Single-walled carbon nanotubes are
excellent saturable absorbers because of their subpicosecond
recovery time, low saturation intensity, polarization
insensitivity, and mechanical and environmental robustness
11–16
.
Here, we engineer a nanotubepolycarbonate film with a wide
bandwidth (>300 nm) around 1.55 mm, and then use it to
demonstrate a 2.4 ps Er
31
-doped fibre laser that is tuneable
from 1,518 to 1,558 nm. In principle, different diameters and
chiralities of nanotubes could be combined to enable compact,
mode-locked fibre lasers that are tuneable over a much
broader range of wavelengths than other systems.
The development of compact, diode-pumped, ultrafast fibre
lasers as alternatives for bulk solid-state lasers is fast progressing.
To date, short pulse generation has been particularly effective
using passive mode-locking techniques
4
. At present, the
dominant technology in passively mode-locked fibre lasers is
based on semiconductor saturable absorber mirrors (SESAMs)
6
.
Conventional SESAMs use
III V semiconductor multiple
quantum wells grown on distributed Bragg reflectors (DBRs)
3
.
Their fabrication involves molecular beam epitaxy (MBE)
6
.To
reduce the relaxation time to sub-picosecond levels, either post-
growth ion-implantation or low-temperature growth is normally
required
6,17
. Furthermore, SESAMs are based on a resonant
nonlinearity, which tends to limit wavelength tuneability
18,19
for the shortest pulse lasers
20
. Their operating bandwidth is
further limited by the bottom DBR section, which has a finite
bandwidth for high reflectivity
19
. For example, the bandwidth of
conventional Al
x
Ga
12x
As/AlAs SESAMs is limited to about
60 nm by the bottom Bragg mirrors
21
. Wider bandwidth,
&200 nm, was achieved using novel material pairs with larger
refractive index difference (for example, AlGaAs/CaF
2
)
21
,orby
replacing the DBRs with metallic mirrors
22
. However, so far, no
widely tuneable mode-locked laser has been reported using these
novel structures. Trade-offs between design parameters have to
be made in order to obtain targeted device characteristics
10
.
A tuning range over 100 nm was achieved by SESAMs in solid-
state and fibre lasers
18,23
. The widest was 125 nm, for a Yb-doped
fibre laser operating at 1 mm. However, two SESAMs with
complementary spectral properties had to be used
23
. Thus, much
simplified and cost-effective saturable absorbers with wideband
tuneability are needed.
Single-walled carbon nanotubes (SWNTs) are direct-bandgap
materials, with a gap that depends on diameter and chirality
24
.
Many of the applications that might make use of the novel
electronic properties of these materials require individual
nanotubes with a given chirality for optimum performance, but
it is still not possible to grow nanotubes with well-defined
chiralities. However, in optoelectronic applications, this
disadvantage can be turned into an advantage. SWNTs show
large optical nonlinearity
25
, ultrafast carrier relaxation time
26
and
high damage threshold
27
. They are compatible with optical fibres,
and mode-locked laser operation at 1.5 mm has been
demonstrated
15,16,27–32
. The variation of nonlinear absorption is
determined by the number of tubes in resonance with the
incident light. However, even for a wavelength detuning of up to
200 nm from the peak resonance, appreciable saturable
absorption can still be observed
25
. This implies great potential for
wideband tuneable lasers. Previous mode-lockers relied on
SWNT solutions
13
, layers grown or spray-coated over optical
parts
29
, or polymer composites
15,28
. The last of these, polymer
composites, allow homogeneous dispersion and easy integration.
To allow low-cost mounting and ease of use, we fabricated
a 40-mm-thick SWNTpolycarbonate composite with a broad
(300 nm) absorption band in the 1.5 mm spectral region
(described in the Methods and shown in Fig. 1a). This was
achieved by using SWNTs with diameters ranging from 1 to
1.3 nm. Note that pure polycarbonate has a low absorption
around 1,550 nm (Fig. 1a).
We first investigated the wavelength-dependent saturable
absorption within the Er
3þ
-doped fibre gain bandwidth (see
Methods). Figure 1b plots the measured loss as a function of
average pump power at different pump wavelengths. All loss
curves show a saturation depth of about 0.3 dB, against a linear
loss of 2.6 dB (or, equivalently, a 4% increase in transmittance
from a small-signal transmission of 55%). A slight decrease of
modulation depth is detected towards shorter wavelengths,
possibly caused by the mismatch between the pump wavelengths
LETTERS
nature nanotechnology | VOL 3 | DECEMBER 2008 | www.nature.com/naturenanotechnology738
© 2008 Macmillan Publishers Limited. All rights reserved.

and the peak absorption of our SWNTs (1,550 nm). Further
wavelength detuning would lead to a more pronounced decrease
in modulation depth. The data for normalized absorption
are then fitted according to a simple two-level saturable
absorber model
33
:
a
ðIÞ¼
a
0
1 þ I=I
sat
þ
a
ns
ð1Þ
where a(I) is the intensity-dependent absorption coefficient, and
a
0
, a
ns
and I
sat
are the linear limit of saturable absorption, non-
saturable absorption and saturation intensity, respectively. This
gives an average saturable absorption (modulation depth) of
12% and an average saturation intensity of 5.8 MW cm
22
in
the spectral range investigated. As an example, a typical nonlinear
absorption curve for 1,550 nm excitation is shown in Fig. 1c. At
this specific wavelength, a
0
and I
sat
are 12.3% and 5.1 MW cm
22
,
respectively. The modulation depth and saturation intensity for
our devices are comparable with those of SESAMs
6
, but the non-
saturable loss is larger. This is tolerable for fibre lasers with a
relatively large single round-trip gain coefficient
27
. Yet, it degrades
the mode-locking performance, resulting in less output power or
longer pulses. In our case, the contributions to the non-saturable
losses may include residual absorption due to amorphous carbon,
metal catalysts and tubes not in resonance with the incident light,
scattering from residual bundles, absorption and refraction from
the polymer matrix
16
, and linear coupling loss between fibre
ends
34
. By further engineering film thickness and nanotube
loadings and alignment, devices with minimized non-saturable
loss could be obtained.
Figure 2 shows the setup of the tuneable laser and the schematic
of the mode-locker device. Wavelength tuning is provided by the
intracavity filter. By changing the tilt angle it is possible to tune
the filter pass-band from 1,535 to 1,565 nm. Moreover, we find
that the filter can also work from 1,515 to 1,535 nm, but at the
expense of increased insertion losses. The Er
3þ
-doped fibre is
ty pically used to amplify light in the 1,5301,560 nm wavelength
range. However, we can extend the continuous-wave lasing
wavelength down to 1,518 nm by feeding more pump power to
Polarization
controller
ISO
ISO
3
nm filter
Output
WDM
980 nm
diode laser
SWNT–polycarbonate
mode-locker
Highly doped Er
3+
fibre
Coupler
SWNT–polycarbonate
composite film
Fibre ferrule with
index-matching gel
FC/PC
fibre connector
Figure 2 Laser setup and mode-locker assembly. This schematic shows the
standard fibre-opt ic components such as an optical isolator (ISO), a wavelength
division multip lexer (WDM), a power splitter and a polarization controller that are
found in the ring cavity. The total length of the cavity is a bout 13.3 m. The basic
operation of the laser is dis cussed in the Methods.
0.6
0.4
0.2
0.0
800
2.65
2.60
2.55
2.50
2.45
2.40
2.35
2.30
1.00
I
sat
= 5.1 MW cm
–2
0
= 12.3%
ns
= 87.5%
0.98
0.96
0.94
0.92
0.90
0.88
0.86
0.84
–25
0102030
Pump peak intensity (MW cm
–2
)
40 50 60
–20
1,535 nm
1,540 nm
1,545 nm
1,550 nm
1,555 nm
1,560 nm
1,565 nm
–15 –10
Average pump power (dBm)
–5 0 5
1,000
1,200
Wavelength (nm)
Er
3+
ion
gain bandwidth
1,400
1,600
1,800
2,000
Absorbance (a.u.)
SWNT–polycarbonate
Pure polycarbonate
Device loss (dB)Normalized absorption
Figure 1 Optical characterization of the composite films. a,Absorption
spectrum of the SWNT polycarbonate composite and pure polycarbonate. The
red stripe shows the spectral gain region of the Er
3þ
-doped fibre. b, Nonlinear
absorption measurements of our SWNT saturable absorber at seven different
wavelengths. The pump power ranges from 3
m
Wto3mW.c, Typical
normalized absorpti on of the SWNT saturable absorber as a function of pump
pulse peak intensity. Data correspond to the pump at 1,550 nm (red line: tted
curve according to equation (1)).
LETTERS
nature nanotechnology | VOL 3 | DECEMBER 2008 | www.nature.com/naturenanotechnology 739
© 2008 Macmillan Publishers Limited. All rights reserved.

the Er
3þ
-doped fibre. Thus, we study the mode-locking of the
current laser over the extended wavelength range 1,5181,565 nm
in order to achieve the maximum possible tuning range. We find
that a tuning range of 40 nm, from 1,518 to 1,558 nm, is possible
with the current setup. Figure 3a,b illustrates the output spectra
and autocorrelation traces at several wavelengths within the
tuning range. Our cavity uses an anomalous dispersion fibre,
with an overall negative group velocity dispersion, in order to
facilitate soliton-like pulse shaping through the interplay of
group velocity dispersion and self-phase modulation
5
. In this
case, the output pulses are expected to have a sech squared
lineshape
5
. Indeed, the data in Fig . 3b are well fitted by a sech
squared relation, giving an average pulse duration of 2.39 ps. As
can be inferred from Fig. 3a, the laser output power stays
relatively flat from 1,518 to 1,558 nm. An average value of
0.36 mW, with a standard deviation of 0.055 mW (+15%) is
obtained for the wavelengths within the tuning range. As we use
a50/50 coupler, the incident power onto the mode-locker is the
same as the output power. From the average output power and
repetition rate, the energy per pulse is 24 pJ. Considering an
average pulse duration of 2.39 ps and a mode diameter of 10 mm,
we obtain a pulse intensity of 11.2 MW cm
22
, about twice the
saturation intensity of our absorber. By comparison, the laser
output when no filter is present (at a pump level of 35 mW) is
also shown in Fig. 3a,b as a dashed line. In this case, the laser
mode-locks at 1,545 nm (the effective gain maximum of the
cavity) with sidebands arising from periodic cavity
perturbations
5
. The pulse width is 706 fs, shortened due to the
elimination of intracavity spectral limiting effects.
The current laser does not mode-lock at wavelengths beyond
1,558 nm, but it does at shorter wavelengths outside the filter
nominal operating spectral range (such as 1,518 and 1,525 nm).
To verify this, we use the amplified spontaneous emission (ASE)
from an Er
3þ
-doped fibre amplifier as a wideband optical source
to measure the filter pass-band characteristics. We find, as
expected, that the longer wavelength pass-band exhibits much
worse ripple effects than the shorter wavelength one, resulting in
strong narrowband limiting effects. We believe this prevents mode-
locking at longer wavelengths in the current setup. Combined with
the data in Fig. 1a,b, we conclude that the nonlinear absorption
of our mode-locker is not the limiting factor. In principle our
SWNT saturable absorber could also be used to mode-lock and
enable tuning for other telecommunication bands such as the
S (1,4601,530 nm) and L (1,5651,624 nm) bands, if gain fibres
and tuneable filters at these wavelength ranges are available.
Figure 4 summarizes some of the laser output trends and
characteristics within the tuning range. An average pulse duration
of 2.39 ps is obtained for different wavelengths (Fig. 4a). Figure 4a
also plots the product of the pulse temporal and spectral widths.
Different applications demand the shortest pulse duration at a
given spectral width. Figure 4a shows that our typical time
bandwidth products range from 0.32 to 0.36, reasonably close to
0.315, which corresponds to the shortest pulse duration for a given
spectral width, for transform-limited sech squared pulses
5
.
Figure 4b is the measured output pulse train, with a fundamental
repetition rate of 15 MHz (period
t
¼ 66.7 ns). Figure 4c shows
the radio frequency (RF) power spectrum of the laser output after
optical-to-electrical conversion using a fast photodiode.
A 70 dB peak-to-background ratio (10
7
contrast) is observed
for the fundamental peak at a measurement span of 1 kHz
and resolution bandwidth of 10 Hz. This indicates good stability
of the mode-locking regime. In Figure 4d the wideband RF
spectrum up to 1 GHz is shown. The absence of spectral
modulation indicates that the tuneable laser is operating in the
pure continuous-wave mode-locking regime, where the output
pulse train is not subject to low-repetition-rate modulation arising
from relaxation oscillations
6
.
In conclusion, our work makes use of SWNTs with a range of
diameters and chiralities, harnessing the resulting wideband
absorption to produce a wideband-tuneable fibre laser, and
turning a major disadvantage of SWNTs for applications in
nanoelectronics into an advantage. SWNTpolymer composites
are a cost-effective and v iable alternative to saturable absorbers
based on quantum wells and could form the basis of functional
building blocks in future nanoscale photonic integrated circuits.
METHODS
SWNTs COMPOSITE
The SWNTpolycarbonate composite was prepared first by dispersing SWNT
powders in dichlorobenzene (DCB) in the presence of poly(3-hexylthiophene-
–30
–40
1,518 1,525
–50
Without
filter
Er
3+
fluorescence
spectrum
Optical power (dBm)Normalized intensity
–60
–70
–80
1.0
0.8
0.6
0.4
0.2
0.0
Delay time (ps)
–15 –10 –5 0 5 10 15 20
Without filter
1,558 nm
1,552 nm
1,546 nm
1,539 nm
1,532 nm
1,525 nm
1,518 nm
1,520 1,540 1,560
Wavelength (nm)
1,580
1,532 1,539 1,546 1,552 1,558
Figure 3 Wavelength tuning. a, Output spectra at seven different wavelengths.
(Dashed line, optical spectrum without bandpass lter; dotted line;
Er
3þ
fluorescence spectrum). The use of the bandpass filter means that the
output spectra have a high signal-to-noise ratio of 50 dB (10
5
contrast).
No sideband structure is observed due to the spectral limiting effect of the
filter
35
. On the other hand, the filter also limits the mode-locking spectral width
to an average value of 1.2 nm, which keeps the pulse duration above 1 ps.
b, Autocorrelation traces of laser output at different central wavel engths.
(Dashed line, laser output without band pass lter.) All traces do not show
pedestals (low-intensity back grounds), indicative of single pulse operation and
reflection-free design
5
.
LETTERS
nature nanotechnology | VOL 3 | DECEMBER 2008 | www.nature.com/naturenanotechnology740
© 2008 Macmillan Publishers Limited. All rights reserved.

2,5-diyl) (P3HT) by ultrasonication (Diagenode SA). The solution was then
filtered through a 1-mm retention filter (Whatman) and centrifuged (Beckman
Coulter Optima MaxE Ultracentrifuge, MLA130 fixed-angle rotor) to remove
bundles and impurities. Pellets of polycarbonate were dissolved in the solution
by ultrasonication. The final mixture was dried at room temperature to form a
film with a typical thickness of 40 mm. No SWNT bundles could be detected
under the scrutiny of an optical microscope, thus ensuring minimized
scattering losses.
POWER-DEPENDENT ABSORPTION MEASUREMENTS
Power-dependent absorption measurements were carried out as follows. The
SWNT mode-locker assembly was coupled to a 650 fs optical pulse source,
tuneable from 1,535 to 1,565 nm. This was achieved by filtering a commercial
femtosecond fibre laser (200 fs, 76.9 MHz, TOPTICA) using a 3-nm band-pass
filter. The laser beam was amplified by an erbium-doped fibre amplifier and a
10% tap was used to monitor the input power to the mode-locker assembly,
containing our composite, and two appropriately calibrated powerheads were
programmed to read the input/output power simultaneously.
TUNEABLE LASER EXPERIMENTAL SETUP
The mode-locker was assembled by sandwiching the free-standing SWNT
composite between two fibre ferrules inside a physical contact ferrule connector.
The estimated input mode diameter on the composite was 10 mm. The laser
setup is schematically shown in Fig. 2. A 1-m highly doped Er
3þ
fibre was used as
the gain medium. It was pumped by a 980 nm diode laser using a wavelength
division multiplexer. Two isolators were placed at both ends of the amplifier
section to maintain unidirectional laser operation. A tuneable filter with a 3 nm
passband was placed after the isolator at the output of the amplification section.
Light was then extracted from the cavity using a 50/50 coupler. A polarization
controller was used to optimize the mode-locking conditions and the SWNT
film placed between this and the isolator, at the input of the amplification
section. The total length L of the cavity was 13.3 m. We could thus estimate the
expected repetition rate to be 15 MHz, from f
r
¼ c/(nL), where f
r
is the
repetition rate, c the velocity of light in vacuum, and n the average refractive
index of the cavity (n 1.5).
With the filter in the cavity, the threshold pump power for continuous
wave lasing was 15 mW at 1,550 nm. When the pump power was increased
to 45 mW, stable mode-locking could be initiated by introducing a disturbance
to the polarization controller. Once a stable output was achieved, no further
polarization controller adjustment was needed and we could decrease the pump
power to 35 mW while maintaining mode-locking. For optimal polarization
controller settings, the laser self-started with excellent repeatability. The measured
repetition rate was 15.01 MHz, in agreement with the design parameters.
Received 19 May 2008; accepted 24 September 2008;
published 2 November 2008.
References
1. Letokhov, V. S. Laser biology and medicine. Nature 316, 325330 (1985).
2. Shah, J. Ultrafast Spectroscopy of Semiconductors and Semiconductor Nanostructures 2nd edn
(Springer-Verlag, 1999).
3. Keller, U. Recent developements in compact ultrafast lasers. Nature 424, 831838 (2003).
4. Digonnet, M. J. F. Rare-Earth-Doped Fiber Lasers and Amplifiers (CRC Press, 2001).
5. Agrawal, G. P. Applications of Nonlinear Fiber Optics (Academic Press, San Diego, 2001).
6. Keller, U. et al. Semiconductor saturable absorber mirrors (SESAMs) for femtosecond to nanosecond
pulse generation in solid-state lasers. IEEE J. Sel. Top. Quant. Electron. 2, 435 453 (1996).
7. Grange, R. et al. Nonlinear absorption edge properties of 1.3-mm GaInNAs saturable absorbers.
Appl. Phys. Lett. 87, 132103 (2005).
8. Rutz, A. et al. Parameter tunable GaInNAs saturable absorbers for mode locking of solid-state lasers.
J. Cr ys. Grow. 301 302, 570574 (2007).
9. Calvez, S. et al. GaInNAs/GaAs Bragg-mirror-based structures for novel 1.3 mm device applications.
J. Cr ys. Grow. 268, 457 465 (2004).
0.5
–40
–40
–60
–80
–60
–80
–100
–120
Intensity (dBm)
–140
15.0048 15.0051
Frequency (MHz) Frequency (MHz)
15.0054 15.0057 200 400 600 800 1,000
Intensity (dBm)
0.4
0.3
1,510 1,520 1,530 1,540 1,550
~70
dB
1,560
–150 –100 –50 0 50
Time (ns)
100 150
3
0.5
τ
= 66.7 ns
0.4
0.3
0.2
0.1
0.0
2
1
Wavelength (nm)
TBP
Intensity (a.u.)
Pulse durations (ps)
Figure 4 Mode-locking characteristics. a, Output pulse duration and time bandwidth product (TBP ) at different central wavelengths. b, Oscilloscope trace of the
typical laser output. c, Fundamental of a typical radio-frequency (RF) spectru m of the laser output after opti cal-to-electrical conversion. The blue trace depicts the
background when the laser is switched off. d, Wideband RF sp ectrum up to 1 GHz.
LETTERS
nature nanotechnology | VOL 3 | DECEMBER 2008 | www.nature.com/naturenanotechnology 741
© 2008 Macmillan Publishers Limited. All rights reserved.

10. Rutz, A. et al. 1.5 mm GaInNAs semiconductor saturable absorber for passively modelocked
solid-state lasers. Electron. Lett. 41, 321 323 (2005).
11. Set, S. Y., Yaguchi, H., Tanaka, Y. & Jablonski, M. Ultrafast fiber pulsed lasers incorporating carbon
nanotubes. IEEE J. Sel. Top. Quant. Electron. 10, 137146 (2004).
12. Nicholson, J. W., Windeler, R. S. & DiGiovanni, D. J. Optically driven deposition of single-walled
carbon-nanotube saturable absorbers on optical fiber end-faces. Opt. Express 15, 9176 9183 (2007).
13. Il’ichev, N. N., Obraztsova, E. D., Pashinin, P. P., Konov, V. I. & Garnov, S. V. Self-mode locking in a
F
2
2
:LiF laser by means of a passive switch based on single-wall carbon nanotubes. Quant. Electron.
34, 785 786 (2004).
14. Song, Y. W., Set, S. Y., Yamashita, S., Chee, S. G. & Kotake, T. 1300-nm pulsed fiber lasers mode-
locked by purified carbon nanotubes. IEEE Photon. Tech. Lett. 17, 1623 1625 (2005).
15. Dalle Valle, G. et al. Passive mode locking by carbon nanotubes in a femtosecond laser written
waveguide laser. Appl. Phys. Lett. 89, 231115 (2006).
16. Rozhin, A. G. et al. Generation of ultra-fast laser pulses using nanotube mode-lockers.
Phys. Stat. Sol. (b) 243, 3551 3555 (2006).
17. Haiml, M. et al. Optical nonlinearity in low-temperature-grown GaAs: Microscopic limitations and
optimization strategies. Appl. Phys. Lett. 74, 3134 3136 (1999).
18. Jacobovitz-Veselka, G. R., Keller, U. & Asom, M. T. Broadband fast semiconductor saturable
absorber. Opt. Lett. 17, 1791 1793 (1992).
19. Kopf, D., Prasad, A., Zhang, G., Moser, M. & Keller, U. Broadly tunable femtosecond Cr:LiSAF laser.
Opt. Lett. 22, 621 623 (1997).
20. Ka
¨
rtner, F. X., Jung, I. D. & Keller, U. Soliton mode-locking with saturable absorbers. IEEE J. Sel. Top.
Quant. Electron. 2, 540 556 (1996).
21. Scho
¨
n, S., Haiml, M. & Keller, U. Ultrabroadband AIGaAs/CaF
2
semiconductor saturable absorber
mirrors. Appl. Phys. Lett. 77, 782784 (2000).
22. Fluck, R. et al. Broadband saturable absorber for 10-fs pulse generation. Opt. Lett. 21,
743 745 (1996).
23. Gomes, L. A., Orsila, L., Jouhti, T. & Okhotnikov, O. G. Picosecond SESAM-based ytterbium mode-
locked fiber lasers. IEEE J. Sel. Top. Quant. Electron. 10, 129 136 (2004).
24. Kataura, H. et al. Optical properties of single-wall carbon nanotubes. Synth. Met. 103,
2555 2558 (1999).
25. Sakakibara, Y., Tatsuura, S., Kataura, H., Tokumoto, M. & Achiba, Y. Near-infrared saturable
absorption of single-wall carbon nanotubes prepared by laser ablation. Jpn J. Appl. Phys. 42,
L494 L496 (2003).
26. Lauret, J. S. et al. Ultrafast carrier dynamics in single-wall carbon nanotubes. Phys. Rev. Lett. 90,
057404 (2003).
27. Fong, K. H. et al. Solid-state Er:Yb:glass laser mode-locked by using single-wall carbon nanotube
thin film. Opt. Lett. 32, 38 40 (2007).
28. Rozhin, A. G. et al. Sub-200-fs pulsed erbium-doped fiber laser using a carbon nanotube-
polyvinylalcohol mode locker. Appl. Phys. Lett. 88, 051118 (2006).
29. Song, Y. W., Yamashita, S., Goh, C. S. & Set, S. Y. Passively mode-locked lasers with 17.2-GHz
fundamental-mode repetition rate pulsed by carbon nanotubes. Opt. Lett. 32, 430 432 (2007).
30. Schibli, T. et al. Ultrashort pulse-generation by saturable absorber mirrors based on polymer-
embedded carbon nanotubes. Opt. Express 13, 8025 8031 (2005).
31. Song, Y. W., Yamashita, S. & Maruyama, S. Single-walled carbon nanotubes for high-energy optical
pulse formation. Appl. Phys. Lett. 92, 021115 (2008).
32. Kieu, K. & Mansuripur, M. Femtosecond laser pulse generation with a fiber taper embedded in
carbon nanotube/polymer composite. Opt. Lett. 32, 22422244 (2007).
33. Garmire, E. Resonant optical nonlinearities in semiconductors. IEEE J. Sel. Top. Quant. Electron. 6,
1094 1110 (2000).
34. Snyder, A. W. & Love, J. D. Optical Waveguide Theory (Springer, 1983).
35. Tamura, K., Doerr, C. R., Haus, H. A. & Ippen, E. P. Soliton fiber ring laser stabilization and tuning
with a broad intracavity filter. IEEE Photon. Technol. Lett. 6, 697 699 (1994).
Acknowledgements
We acknowledge funding from the Isaac Newton trust, The Royal Society-Brian Mercer Award for
Innovation and the European Research Council Grant NANOPOTS.
Author information
Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/.
Correspondence and requests for materials should be addressed to A.C.F.
LETTERS
nature nanotechnology | VOL 3 | DECEMBER 2008 | www.nature.com/naturenanotechnology742
© 2008 Macmillan Publishers Limited. All rights reserved.
Citations
More filters
Journal ArticleDOI
TL;DR: Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability as discussed by the authors, and its true potential lies in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultrawideband tunability.
Abstract: The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential lies in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultrawideband tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light-emitting devices to touch screens, photodetectors and ultrafast lasers. Here we review the state-of-the-art in this emerging field.

6,863 citations


Cites methods from "Wideband-tuneable, nanotube mode-lo..."

  • ...A simple, cost-effective alternative is to use SWNT...

    [...]

Journal ArticleDOI
TL;DR: An overview of the key aspects of graphene and related materials, ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries are provided.
Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

2,560 citations

Journal ArticleDOI
TL;DR: In this paper, the use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated.
Abstract: The optical conductance of monolayer graphene is defined solely by the fine structure constant, α = (where e is the electron charge, is Dirac's constant and c is the speed of light). The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero-gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band is demonstrated. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the graphene thickness. These results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth, and wideband tunability.

2,217 citations

Posted Content
TL;DR: In this paper, the authors demonstrate the use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band.
Abstract: The optical conductance of monolayer graphene is defined solely by the fine structure constant. The absorbance has been predicted to be independent of frequency. In principle, the interband optical absorption in zero-gap graphene could be saturated readily under strong excitation due to Pauli blocking. Here, we demonstrate the use of atomic layer graphene as saturable absorber in a mode-locked fiber laser for the generation of ultrashort soliton pulses (756 fs) at the telecommunication band. The modulation depth can be tuned in a wide range from 66.5% to 6.2% by varying the thickness of graphene. Our results suggest that ultrathin graphene films are potentially useful as optical elements in fiber lasers. Graphene as a laser mode locker can have many merits such as lower saturation intensity, ultrafast recovery time, tunable modulation depth and wideband tuneability.

2,039 citations

Journal ArticleDOI
25 Jan 2010-ACS Nano
TL;DR: The optoelectronic properties of graphene are exploited to realize an ultrafast laser and pave the way to graphene-based photonics.
Abstract: Graphene is at the center of a significant research effort Near-ballistic transport at room temperature and high mobility make it a potential material for nanoelectronics Its electronic and mechanical properties are also ideal for micro- and nanomechanical systems, thin-film transistors, and transparent and conductive composites and electrodes Here we exploit the optoelectronic properties of graphene to realize an ultrafast laser A graphene-polymer composite is fabricated using wet-chemistry techniques Pauli blocking following intense illumination results in saturable absorption, independent of wavelength This is used to passively mode-lock an erbium-doped fiber laser working at 1559 nm, with a 524 nm spectral bandwidth and approximately 460 fs pulse duration, paving the way to graphene-based photonics

1,878 citations


Cites background from "Wideband-tuneable, nanotube mode-lo..."

  • ...Tunability is possible by using a wide diameter distribution.(8) However, when operating at a particular wavelength, the SWNTs not in resonance are not used and give insertion losses, compromising device performance....

    [...]

  • ...3%) is larger than that of SESAMs(2) but comparable to SWNTs.(8) Note that, for fiber lasers with a relatively large single round-trip gain coefficient, such nonsaturable losses are tolerable....

    [...]

  • ...Note that, for fiber lasers with a relatively large single round-trip gain coefficient, such nonsaturable losses are tolerable.(8) Further decrease in the nonsaturable insertion loss is expected when the device is completely saturated....

    [...]

  • ...However, wideband operation can be achieved with the as-prepared material, with no need of special procedures, such as the chirality or diameter selection needed for SWNTs.(8) Furthermore, all of the...

    [...]

References
More filters
Journal ArticleDOI
TL;DR: In this article, four kinds of single-wall carbon nanotubes (SWNTs) with different diameter distribution have been synthesized and optical absorption spectra have been measured.

2,299 citations

Journal ArticleDOI
14 Aug 2003-Nature
TL;DR: Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution, extremely high peak optical intensities and extremely fast pulse repetition rates.
Abstract: Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

1,914 citations

Book Chapter
01 Jan 2005
TL;DR: In this article, the authors outline the key principles and parameters which describe and define the operation of optical waveguides and fibres, including dispersion and non linear effects, and provide the foundation for understanding the detailed operation of a wide variety of optical components.
Abstract: In this chapter, after presenting a brief review of the various types of optical waveguides, we outline the key principles and parameters which describe and define the operation of optical waveguides and fibres The ways in which propagation through optical fibres affects the properties of the guided waves are discussed, including dispersion and non linear effects Power transfer between propagating waves is essential to the operation of a number of components and the fundamentals of coupling theory are reviewed In summary, the theory given provides the foundation for understanding the detailed operation of a wide variety of optical components and systems based on optical fibre technology

1,867 citations

Journal ArticleDOI
TL;DR: In this paper, the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime were reviewed, and the combination of device structure and material parameters provided sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence.
Abstract: Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-/spl mu/m neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO/sub 4/.

1,866 citations

Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "Wideband-tuneable, nanotube mode-locked, fibre laser" ?

Here, the authors engineer a nanotube –polycarbonate film with a wide bandwidth ( > 300 nm ) around 1. 55 mm, and then use it to demonstrate a 2. The authors first investigated the wavelength-dependent saturable absorption within the Er3þ-doped fibre gain bandwidth ( see Methods ). Furthermore, SESAMs are based on a resonant nonlinearity, which tends to limit wavelength tuneability for the shortest pulse lasers20. Their operating bandwidth is further limited by the bottom DBR section, which has a finite bandwidth for high reflectivity. This implies great potential for wideband tuneable lasers.