Flexible-Bandwidth and Format-Agile Networking Based on Optical Arbitrary Waveform Generation and Wavelength Selective Switches

Conference Paper (PDF Available) · December 2010with37 Reads
DOI: 10.1109/PHOTONICS.2010.5698775 · Source: IEEE Xplore
Conference: IEEE Photonics Society, 2010 23rd Annual Meeting of the
Abstract
This paper experimentally demonstrates flexible-bandwidth networking by splitting a 500-GHz waveform generated by optical arbitrary waveform generation into its two tributary spectral slices using a liquid-crystal spatial light phase modulator as a wavelength selective switch.

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Flexible-Bandwidth and Format-Agile Networking Based on Optical
Arbitrary Waveform Generation and Wavelength Selective Switches
Tingting He
1
, N. K. Fontaine
1
, R. P. Scott
1
, D. J. Geisler
1
, L. Paraschis
2
, O. Gerstel
2
, J. P. Heritage
1
, and S. J. B. Yoo
1
1
Department of Electrical and Computer Engineering, University of California, Davis, CA 95616, USA
2
Cisco Systems, 170 West Tasman Drive, San Jose, CA 95134, USA
E-mail: yoo@ece.ucdavis.edu
Abstract: This paper experimentally demonstrates flexible-bandwidth networking by splitting a 500-GHz waveform
generated by optical arbitrary waveform generation into its two tributary spectral slices using a liquid-crystal spatial light
phase modulator as a wavelength selective switch.
Rapid increases in Internet traffic coupled with dynamic traffic demands require efficient and scalable transport links
to support future optical networks. Wavelength-division-multiplexing (WDM) technology [1] has had success in
meeting the exponentially growing capacity requirements, but lacks the optimization for dynamically changing traffic
demands. Flexible bandwidth networks, in which a broad spectrum is composed of arbitrarily assigned spectral slices,
can replace fixed wavelength grids to support elastic traffic demands [2] ranging from extremely low capaci-
ty (sub-wavelength) to very high capacity (hyper-wavelength). Optical arbitrary waveform generation (OAWG) has
proven its capability of creating arbitrary waveforms through line-by-line intensity and phase modulations of
broad-bandwidth, coherent optical frequency combs (OFC). With an arbitrary wavelength selective switch (WSS), the
transmitted spectrum can be divided into spectral slices of arbitrary sizes. In this summary, a terahertz OAWG-based
transmitter [3] is used to generate a 500-GHz waveform that is split into its two tributary signals using a liquid-crystal
spatial light phase modulator (LC-SLPM) based WSS.
(b)
10 GHz
OAWG Device
10 GHz
OFC
Waveform Control
(DSP)
WSS
Multiheterodyne
Detection
Optical
Feedback
Flexible-Bandwidth Transmitter
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t
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IM PM
Intensity
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Slice 1
Slice 2 Slice n-1 Slice n
(a)
Flexible Spectrum Assignment
f
Slice 1
Slice 2 Slice n-1 Slice n
Fig. 1. (a) Principle of an OAWG-based transmitter and its application in flexible spectrum networks. (b) Experimental arrangement for the
generation and detection of high speed data packets using a flexible-bandwidth transmitter. OFC: optical frequency comb; OAWG: optical arbitrary
waveform generation; WSS: wavelength selective switch; DSP: digital signal processing.
Fig. 1(a) illustrates the concept of flexible spectrum generation of an OAWG-based terahertz transmitter [3].
Through line-by-line static manipulations of an OFC, repetitive arbitrary waveforms are generated which are com-
posed of multiple spectral slices where each slice forms a unique signal. Fig. 1(b) shows the experimental arrangement.
A dual-electrode Mach-Zehnder modulator and a phase modulator modulate a single-frequency 1550-nm laser to
generate an optical frequency comb (OFC) of 50 comb lines spaced at 10-GHz (not shown). An integrated silica planar
lightwave circuit containing the spectral demultiplexer, thermo-optic intensity/phase modulators and spectral mul-
tiplexer [4] (as illustrated in Fig. 1(a)) operates as the OAWG transmitter producing repetitive bit patterns. The
modulators in the OAWG device achieve more than 30 dB intensity extinction and radians of phase shift. The WSS
splits the shaped 50 comb lines into two different slices. One slice (20 comb lines) contains a 40-bit 400-Gb/s QPSK
signal which occupies a 200-GHz bandwidth, and the other slice (30 comb lines) is a 60-bit 600-Gb/s QPSK signal
which occupies a 300-GHz bandwidth. An optical multiheterodyne method [5] is used to detect those signals. The
waveform control, or digital signal processing (DSP), compares the measured intensity and phase against target values,
and adjusts intensity and phase modulator settings in an iterative fashion in order to approach the target waveform [4].
The WSS used in this experiment is based on a reflection-mode 2D LC-SLPM with 768×768 pixels. The broadband
signal from the fiber undergoes vertical beam expansion by the collimating lens and lateral spectral diffraction by the
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grating. Each spectral column can achieve extinction by setting half of this column to maintain π radians phase dif-
ference compared to the other half [6]. In this experiment, the OAWG signal is equally power-split into two colli-
mators, and spread onto different vertical positions of the LC-SLPM. By applying appropriate phase modulations to
the particular parts of the spread signals, the total 500-GHz-bandwidth OAWG signal is split into two slices: a
200-GHz slice containing the 40-bit 400-Gb/s QPSK signal and a 300-GHz slice containing the 60-bit 600-Gb/s
QPSK signal. Both signal slices reflect back into the corresponding collimators and come out of the third port of the
circulators before detection.
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7-ps window
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(d) (e) (f)
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(a) (b) (c)
Fig. 2. Results for 400-Gb/s (a, b, c) and 600-Gb/s (d, e, f) QPSK signals (target intensity: cyan “x” or cyan dashed line, measured intensity: blue
circle or blue solid line; target phase: magenta “x” or magenta dashed line; measured phase: red circle or red solid line): (a,d) spectrum, (b,e)
waveform, and (c,f) eye-diagrams for real and imaginary parts of the measured signal.
Figs. 2 shows experimental results measured for the 40-bit 400-Gb/s QPSK signal (subfigures a,b,c) and the 60-bit
600-Gb/s QPSK signal (subfigures d,e,f). Figs. 2(a,d) compare the spectra of the target signal with the measured signal.
Figs. 2(b, e) show the corresponding time domain target and measured waveforms. The target and measured signals
nearly overlap, with some small intensity deviations that are mostly due to shaping errors. Figs. 2(c,f) are the com-
puted eye diagrams of both the real and imaginary parts for the measured signals. The eye diagrams are open, which
indicates possibly error-free bit-error-rate performance at high data rates of 400-Gb/s and 600-Gb/s.
We have proposed and realized a flexible-bandwidth transmitter with a spectral-slicing communication. Experi-
mental results show successful splitting of broad bandwidth signals (500-GHz) into two arbitrary slices containing
different signals of 200-GHz and 300-GHz, respectively. Future experiments can extend this to multi-band splits (>2
slices) to demonstrate meshed networking of flexible capacity allocations for dynamically changing traffic demands.
References
[1] R. E. Wagner, et al., “MONET: Multiwavelength optical networking,” J. of Lightw. Technol., 14, 1349-1355 (1996).
[2] M. Jinno, et al., “Spectrum-Efficient and Scalable Elastic Optical Path Network: Architecture, Benefits, and Enabling Technologies,” IEEE
Commun. Mag., 47, 66-73 (2009).
[3] D. J. Geisler, et al., “Modulation-Format Agile, Reconfigurable Tb/s Transmitter Based on Optical Arbitrary Waveform Generation,” Opt.
Express, 17, 15911-15925 (2009).
[4] T. He, et al., “Optical Arbitrary Waveform Generation-Based Packet Generation and All-Optical Separation for Optical-Label Switching,”
IEEE Photon. Technol. Lett., 22, 715-717 (2010).
[5] N. R. Newbury, et al., “Sensitivity of coherent dual-comb spectroscopy,” Opt. Express, 18, 7929-7945 (2010).
[6] N. K. Fontaine, et al., “In situ compensation of 2D SLM phase nonuniformity within pulse shapers,” Conference on Lasers & Elec-
tro-Optics/Quantum Electronics and Laser Science Conference (CLEO/QELS), (2006).
This work was supported in part by the DARPA and SPAWAR under OAWG contract HR0011-05-C-0155.
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