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-11, 0.1, 0.8RpF for the PCS switch [4], PIN switch [I] and FET
switch [Z], respectively. The RC product for the LAMPS switch is
superior to those of the PCS and FET switches, and comparable to that
of the PFN switch. The LAMPS switch also has the advantages of nn
low frequency limit of operation, simple switch configuration, and ease
of independently biasing individual switch nodes in a multi-node switch
matrix (compared to FET switches).
Acknon,ledgments: The authors would like to thank N. Yamada,
D. D'Avanzo, D. Hornbuckle, S . Corrine, M. Tan, K. Carey and
K. Yagi.
0 IEE 2003
Electmnics Le1lsr.s Online No: 20030607
DOT: !0. !04Y/ei:2OO30607
8 April 2003
Y. Kaneko, T. Takenaka, Y. Kondoh and M. Saito (Agilenr Labomlories, Agileni Technulogie.~,9-1, Takakura-Cho, Hmhioji-shi, Tokyo
0
IY2-8510, Japan)
T. Low and D. Cook (Microwove Technology Center, Agilenr
Technologies. 1400 Fountaingmve Purkway, MS ILS-C Santa Rosa.
Cdfhmia 95403, USA)
D.E. Mars (Agilenr Labomtories, Agilenl Techno1ogie.s. 3500 Deer
Creek Road, MS26M !O35U Palo Alto, Culijoornio 943030.0867. USA)
Reference
I
2
3
4
5
KOBAYASHI. K.W., TRAN. L., OKI, A . K , and STREIT, C.: 'A 50 MHr-30 GHz
broadband co-planar waveguide SPDT PIN diode switch with 45-dB
isolation', IEEE Micmw: Guid. Wove Len, 1995, 5, pp. 56-58
SCHINDLER, M.J.,and MORRIS, A.: 'DC-40 GHz and 2 M 0 CHa MMlC
SPDT switcher', IEEE 7rms. Micmw. 7?teoty Tech., 1987, 35,
pp. 1486-1493
Ll. s.: 'Semiconductor physics electronics' (Plenum Press, 1993), p. 304
ASDERSSON, I.I., and SVERRRET. ENC: 'Phase and amplirude
characteristics of InPFe modified interdigitated gap photoconductive
microwave switches', IEEE 7 k v s . Micmw Theory Tech., 1989, 37,
pp. 729-733
MORGAN, R.A., er al.: '1 W (pulsed) venical cavity surface emitting laser',
EIecrmn. Lei[., 1993, 29, pp. 206-207
40Gbit/s transmission over photonic
crystal fibre using mid-span spectral
inversion in highly nonlinear photonic
crystal fibre
C. Peucheret, B. Zsigri, P.A. Andersen, K.S. Berg,
A. Tersigni, P. Jeppesen, K.P. Hansen and M.D. Nielsen
,"put pOver dBm
Fig. 5 Fundantentd second harmonic and third harmonics output powers
ugainst inprr1 p o r r r f o r I5 "1 w loser pux,er-
Transmission st 40 Gbit/s over large mode area photonic crystal fibre
(PCF) together with dispersion compensation by optical phase conjugation in a highly nonlinear PCF are dcmonshvtcd for thc first time.
Linearity is another imponant figure of merit for RF switch perfarmance. We characterised the second- and third-order harmonics at a
single-tone signal input with a frequency of 960 MHz, with power up to
30 dBm and kdsa light powcr of 15 mW. Fig. 5 shows the fundamental
output, and the second-order and third-order harmonics against input
power. Suppression ratios from fundamental output power to secondand third-order harmonics at an input power of 30 dBm were 84 and
70 dBc, respectively. Intercept points of secondarder (SOI) and thirdorder (TOI) were I15 and 65 dBm, respectively. We believe this is the
first repoll of linearity charactenstics in photoconductive switch
dcviccs, and the linearity expressed as SO1 and TO1 are better than
FETand PIN switches [I,21. In addition, the off-state (not illuminated)
charactcristics of the HPCS were excellent with an off-state resistance
of 14 MR and breakdown voltage of I 1 V Finally, we measured the
switch responses against time under pulsed illumination with optical
pulses as shon as I ps. Rise and fall times far thc switched currents
were less than the pulse width (i.e. no undesirable switching transients
were observed).
lnrroduction: Photonic crystal fibres (PCFs) are strong candidates for
the realisation of a wide range of optical system functionalities due to
the degrees of freedom offered in the design of their optical properties
such as dispersion, nonlinearity and polarisation. Until now, demonstrations o f their use for system applications have focused on the
exploitation of their nonlinearity for, e.g.,switching [ I , 21, high-speed
signal time demultiplexing [3] or wavelength conversion [4].
However, the recent reduction in the loss of PCFs [5, 61 combined
with improvement in fabrication technology allowing far the drawing
of longer fibres with uniform properties make them worth considering
for transmission purposcs [ 6 , 71. One of the expected benefits is the
possibility t o design pure silica core fibres with large effective area
that will still remain singlemode [SI, resulting in reduced nonlinear
limitations.
In this Letter, we report the first transmission of 40 Gbit/s signals
over 5 . 6 h large mode area PCFs. As the transmission length is
beyond the dispersion limit far 40Gbit/s signals, some form of
dispersion compensation is required. We exploit four-wave mixing in
a highly nonlinear PCF (HNL-PCF) to realise dispersion compensation
by mid-span spectral inversion, hence demonstrating, for the fint time,
an all-crystal fibre dispersion compensated transmission link.
Conclusions: We have demonstrated a new microwave switch
concept called LAMPS, consisting of an HPCS photoconductor
with flip-chip bonded VCSEL light source. The RF switch perfarmance and size compare favourably with conventional semiconductor
switches (PINS and FETs). By combining multiple HPCS devices and
a two-dimensional VCSEL array into a switch circuit, it should be
possible to fabricate either a SPDT (single pole double throw) switch
or SPnT switch with millimetre size.
ELECTRONlCS LEmERS
12th June 2003
Vol. 39
Experimental setup: The experimental setup is shown in Fig., 1. A
Mach-Zehnder modulator is used to modulate continuous-wave (CW)
light at 40 Gbit/s in the non-retum-to-zero (NRZ) format with 13 dB
extinction ratio. The pseudorandom sequence length is 23' I . The
transmission link consists of two spools of PCF with 1.7 d B j k m loss
~
No. 12
919
and 32 ps/(nm.km) dispersion at 1550 nm [9], separated by an optical
phase conjugator (OPC). The first and second PCF spools arc 2.6 and
3 km long, respectively. The nonlinear coefficient and the polarisation
made dispersion of the PCF are measured to be 7 = 1.2 W-' km-' and
0.1 ps/km"2, respectively. Optical phase conjugation is achieved by
four-wave mixing in 50 m highly nonlinear PCF with zero dispersion
at 1552 nm and nonlinear coefficient I = 18 W-' km-' [ l o ] . The
pump originates from a C W laser tuned to the HNL-PCF zero
dispersion wavelength followed by a high power erbium-doped fibre
amplifier (EDFA) and an optical bandpass filter (OBF) for noise
reduction. The signal and the pump are coupled to the HNL-PCF via a
3 dB coupler, resulting in a pump power level of 25 dBm at the fibre
input. The states of polarisation of the signal and pump are adjusted
via two polarisation controllers (PC) in order to maximise the
conversion efficiency. The converted signal is selected at the output
of the HNL-PCF using a combination of OBFs having a full-width
half-maximum bandwidth of I nm. After transmission, the signal is
detected using a preamplified receiver consisting of an EDFA with
4 dB noise figure followed by an OBF and a photodiode with 50 GHr
bandwidth. Both the transmission PCF and HNL-PCF are spliced to
standard singlemode fibre pigtails.
transmission. This is amibuted to the bandpass filtering necessary to
select the converted signal at the output of the OPC. The spectlum at
the output of the OPC is shown as an inset in Fig. 4.
- a , ,
,
. . . . . . . . . . . . . .
...........
,
.
-......
0
Fig. 3 Eye diogramr (50 GHz bandwidth)
At modulator output
h Afler 2.6 km PCF
c Afler 2.6 h PCF, OPC and 3 h PCF
Ho"ronta1 scale is 10 ps/division
U
.....................HNL-PCF
.............
The bit error rate curves measured at the transmincr output and after
transmission are shown in Fig. 4. The back-to-back sensitivity is
-26.6 dBm and a total penalty of 0.7 dB is measured after transmission
BF
+=1552.04nm
1
.................~~~
~, the OPC process). The penalty is attnbutcd to the different
(including
amount of dispersion accumulated before and after the OPC (equal to
&=1555.24 nm
14 ps/nm), mostly due to the length difference between the two PCFs.
The reduced dispersion slope of the PCF, of the order of
0.067 ps/(nm'km), does not contribute much to the difference in
dispersion accumulated by the signal and the converted signal which
Fig. 1 Experimental setup
are spaced 6.4 nm apart. It is therefore expected that tailoring the fibre
CW continuouS-wave laser; P C polarisation contmller; MZM: Mach-Zehnder
lengths before and after the OPC should result in even lower penalty.
modulator; EDFA: erbium-doped fibre amplifier; PCF photonic crystal fibre:
OBF: optical bandpass filter; O P C optical phase conjugator; PD photodiode:
The excess noise induced by the amplification ofthe converted signal at
Rx: receiver
the OPC output is also believed to contribute to the penalty.
Re.sults and discussion: The conversion bandwidth of the HNL-PCF
was first characterised with a CW probe signal and a pump tuned to
1552 nm. Fig. 2 shows the conversion efficiency (defined as the ratio
of the power of the converted signal at the HNL-PCF output to the
power of the signal at the input) against wavelength separation
between the probe and pump. The maximum conversion efficiency
for 25 dBm pump power is -20 dB and the conversion 3 dB bandwidth is 15 nm, primarily limited by the dispersion slope of the HNLPCF. Consequently, a wavelength of 1548.86 nm is chosen for the
signal in the transmission experiment.
5 0
1546 1548 1550 2.1552
nm 1554 1556 1558
4- back-to-back
*
10-9
--A--.
altertransmission + OPC
...............................
,
-30
-28
.
-26
-24
average received power, dBm
,
-22
-20
Fig. 4 BER c u r ~ ~ e s / uhack-to-backnnd
r
./?e. iransniirrion thmugh 5.6 km
link
Inset: Specnum at output of HNL-PCF (0.1 nm resolution bandwidth)
Ppump=25dBm
Ps,gnaI=il 5dBm
- 5 5 1 ,
-20
,
,
-15
,
, . , . ,
-10
-5
0
,
,
,
5
,
,
10
,
15
,
, I
20
pump-signal detuning, nm
Fig. 2 Converrion eflcrency against pump-signal deruning
The eye diagrams of the Signdl along the transmission link are shown
in Fig. 3. Note that the vertical scale is different for the three eyes due to
different average power in the photodetector. AS expected the eye
diagram is strongly deteriorated by the accumulated dispersion after
propagation in the first 2.6 km PCF. A clear and open eye is recovered
after optical phase conjugation and propagation through the remaining
3 km o f t h e link. Some reshaping of the eye diagram is observed after
920
Conclusion: We have demonstrated the tirst transmission at 40 Gbit/s
through 5.6 km of large mode area photonic crystal fibre. Dispersion
compensation was achieved using optical phase conjugation realised
by faur-wave mixing in 50 m of a highly nonlinear photonic crystal
fibre with zero dispersion at 1552 nm. A total penalty of 0.7 dB was
measured for propagation through the entire link, including the OPC.
It is believed that the penalty can be reduced further by aptimisation
of the spool lengths. This experiment constihltes the first demanstration of an optical link (including both transmission and dispersion
compensation) based entifely on photonic crystal fibres.
0 IEE 2003
Electronics Let1er.s Online No; 200305X5
9 April 2003
D o l : IO. 1049/e1:20030585
ELECTRONICS LETTERS
12th June 2003
Vol. 39 No. 12
C. Peucheret, B. Zsigri, P A . Andersen, K.S. Berg, A . Tersigni and
P Jeppesen (COM, Technical University grDenmurk, Building 345Y
DK-2800 Kgs Lyngby, Denmark)
E-mail: cp@com.dtu.dk
K.P. Hansen and M.D. Nidsen (Crystal Fibre A I S , Blokkrn 84,
OK-3460 Eirkerad, Denmark)
pulse, E ( t ) . In FTSI, € ( I ) is delayed by a time, r, with respect to Eo([);
when this pulse pair is spectrally resolved the resulting fringe pattern
contains the spectral phase difference information. In dual-quadrature
spectral interferometry (DQSI) (Fig. l), interferograms are recorded
along both polarisation axes where one axis has a phase delay with
respect to the'other [5].
References
1
2
3
PETROPOULOS. P, MONRO, T.M , BELARDI. W., FURUSAWA, K., LEE. I H., and
RICHARIXON. D.J.: '2R-regenerative all-optical switch based on a highly
nonlinear holey fiber', Opt. Lea., 2001,26, (16), pp. 1233-1235
SHARPING. J.E, FIORENTINO, M., LUMAR, P., and WINDELFR. R.S.: 'Alloptical switching based on cross-phase modulation in microStmCNre
fiber', IEEE Photonicr Techno/. Lett. 2002, 14, ( I ) , pp. 77-79
OXENLob'E. L.K., SIAHLO. A.I., BERG. K.S., TERSICNI, A., CLAUSEN. A.T.,
PEUCHERET, C., IEPPESEN, P., HANSEN. K.E, and JBNSEN, I.R.: 'A photonic
crystal fibre used as a 160 to I O Gb/s demultiplexcr'. Proc. OptoElectronics and Communication Conf., OECC'02, Yokohama, Japan,
post-deadline paper PDI-4
4
LEE. J H . . HELARDI, W., FURUSAWA. K., PETROPOULOS. P., YUSOFF, L.,
MONRO. T U , and RICHARDSON.D.J.: 'Foour~wavemining based IO-Gb/s
tunable wavelength conversion using a holey fiber with a high SBS
threshold', IEEE Photonici Techno/. Len, 2003, 15, (3), pp. 4 4 0 4 4 2
5 FARR.L., KNIGHT.J.C., MASGAN.R.J., and ROBERTS, P.J.: 'Low loss photonic
crystal fibre'. Proc. European Conf. on Optical Communication,
ECOCO2, Copenhagen, Denmark, September 2002, post-deadline
paper PD1.3
6 TAJIMA, K., LHOU. J., NAKAJlMA. K., and SATO, K.: 'Ultra IOW IDSS and long
lcngth photonic crystal fiber'. Tech. Dig. Optical Fiber Communicalion
Conf., OFC'03, Atlanta, GA, USA, March 2003, post-deadline paper
PDI
7 SUZUKI. K., KUBOTA. 11.. KAWANISHI, s., TANAKA, M., and FUJITA, M.:
'Highspeed hi-directional polansation division multiplexed optical
transmission in ultra IOW-loss (1.3 dB/km) polarisation maintaining
photonic crystal fibrc', Electron. Len, 2001, 37, (23), pp. 1399-1401
8 BrnKs. T.A., KNIGHT. J.c., and RUSSELL. EST.J : 'Endlessly single-mode
photonic crystal fibcr', Vpt. Len., 1997, 22, (13), pp. 961-963
9 NIELSEN,M.O., PETERSS0N.A.. JACOBSEN. C.. SIMONSEN, H.K., VIENXE. G.,
and BJARKLEV A.: 'All-silica photonic cry~talfiber with large mode area'.
Proc. European Conf. on Optical Communication, ECOC'02,
Copenhagcn, Denmark, September 2002, Paper 3.4.2
10 HANSEN, K.P., JESSEN, J.R., JACOBSEN. C., SIMONSEN, H.R., BROENC. J.,
SKOVGAARD. P M z, PETERSSON, A., and BJARKLLV A.: 'Highly nonlinear
photonic crystal fiber with zero-dispersion at 1.55 pm'. Tech. Dig.
Optical Fiber Communicaliun Conf., OFC'O2, Anaheim, CA, USA,
March 2002, post-deadline paper FA9
Characterisation of telecommunications
pulse trains by Fourier-transform and dualquadrature spectral interferometry
F.K. Fatemi, T.F. Carmthers and J.W. Lou
The first use o f w o sensitive spechal interferometrictechniques for the
complete intensity and phase churzmctination of high-data rare optical
pulse m i n s with low avenge power is demonstrated. The pulses are
reconstructed either by Fouticr-Ransfam or dualquadrature specbdl
interferometry aRer characterisation of an amplificd rcfcrcncc pulse by
frequency-resolved optical gating.
Iniroduction: The characterisation of ultrashort pulses has been of
great interest in recent years. In particular, the characterisation of
ultraweak, high-repetition rate pulse trains has garnered attention
because of the payoffs in understanding propagation effects in telecommunications equipment and fibres [ I , 21. Pulse characterisation
techniques have been extended to the ultraweak rcgime through a
combination of linear and nonlinear measurements. Trebino et al. [3]
have demonstrated the characterisation of weak free-space laser
pulses by a combination o f frequency-resolved optical gating
(FROG) [4] and Fourier-transform spectral interferometry (FTSI),
which measures the spectral phase difference between two pulses
[5]. Given the profile of a strong reference pulse, E,(t), characterised
by FROG or other nonlinear techniques [6], one can determine the
complete amplitude and phase profile of a much weaker, unknown
ELECTRONlCS LETTERS
ref. arm
OSA 2
to FROG
Fig. 1 Experimentol setup
Inset: Top to booom: reference spectrum, test OveaV) spechum, and interferograms along two polatisation axes.
In this Letter, we demonstrate these techniques for the first time for
telecommunications pulse trains, where the higher power pulses
required by FROG are not always readily available. We have extracted
the full intensity and phase profile of 10 GHz repetition-rate pulse trains
at 1550 nm with an average power of -40 dBm. We show that the
amplitude and phase information can be retrieved in DQSI when the
interfering beam paths have unknown degrees of ellipticity.
One difficulty in these self-referencing techniques is that one must
eliminate timing and phase jitter between pulses. Therefore, E([) must
be interfered with an amplified fully characterised version of itself,
requiring the two m s of the interferometer to be equal and stable over
long lengths (-20 m). Also, FTSI only works when the.delay i is at
least a few pulse lengths. This sets an upper bound on the useful
repetition rate far FTSI, since the high-repetition rate pulses are closely
spaced and may have appreciable energy in the wings. DQSI does not
have this limitation.
FTSI and DQSI have certain advantages over other sensitive characterisation schemes. The technique of Lacourt et d.[I] can characterise
milliwatt-peak power pulses, but is limited to long ( - I O ps) pulses with
narrow bandwidth. Dorrer et al. [2] developed a sensitive technique for
characterising high-repetition-rate pulse trains, but it has a limiting
resolution of -1 ps and is limited to periodic pulse trains. The
techniques demonstrated here have none of these limitations. They
can be used an random bit streams with resolutions limited only by the
FROG characterisation device.
Experiment and discussion: The pulse to be characterised enters a
Mach-Zehnder interferometer (Fig. I ) in which one arm is amplified
to a level that can he characterised by FROG. The waveplates and
linear polarisers (LP) imparl different degrees of ellipticity to the
pulses. The x- and y-polarisation components of the interferometer
output are recorded simultaneously by two optical spectrum analysers
(OSA). Lepetit et 01. [5] discussed the case with one arm linearly
polarised at 45" and the other circularly polarised. However, the final
beam combiner can influence the polarisation states of the two paths,
and hence the relative phase delay, 6, since the reflections do not
occur with pure s- or p-polarised light. Blind application of the
routine can give inaccurate results ifthe polarisations are not checked.
For arsitrary ellipticities, the interference terms SJw) of the
combined spectra on the OSAs become:
S,(u) = Rek(w) exp(iwr)l,
SJw) = IABIRek(w)exp(iwi +is)]
(1)
where g(w) = EZ(o)E(w).A and B depend on the coupling efficiencies
into the OSAs. The inverse Fourier Transform o f these terms gives:
F - ' ( & ) = / ( I - T) +f'(-t
- i)
F-'(S,) = [ f ( t - r)cxp(i6) + f ' ( - 1
- r)exp(-i6)1lABl
(21
where Xt)=F-'(g(w)). S is constant for all delays, i, and can be
calibrated at lengths where the f ( t - T ) and f*(-t - T) terms do not
12th June 2003 Vol. 39 No. 12
921
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