August 10, 2009 / Vol. 7, No. 8 / CHINESE OPTICS LETTERS 679
A PMD-supported 100-Gb/s optical frequency-domain
IM-DD transmission system
Wei Li (
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1∗
, Yaojun Qiao (
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2
, Qingsheng Han (
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1
, and Huan Zhang (
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1
1
Wuhan National Lab for Optoelectronic, Huazhong University of Science and Technology,
Wuhan 430074, China
2
Key Laboratory of Information Photonics and Optical Communications, Ministry of Education,
Beijing University of Posts and Telecommunications, Beijing 100876, China
∗
E-mail: weilee@hust.edu.cn
Received December 4, 2008
A novel method for d istortion-free optical pulse t ransmission is th eoretically prop osed and simulated, in
which two time lenses formed by dispersion fibers and quadratic phase modulations are utilized. One is
used as an optical inverse Fourier transformation (OIFT) device to transform the initial time-domain data
to frequency-domain one at the transmitter and the other as an opt ical Fourier transformation (OFT)
device to recover the data at the receiver. By using the unchanged spectral envelope in linear optical
fiber communication, the initial data can be recovered. Through simulations, a 10×100 Gb/s intensity-
modulated direct-detection (IM-DD) dense wavelength division multiplexing (DWDM) system over 2000-
km transmission without the compensation for polarization mo de dispersion (PMD) and dispersion slope
is achieved, which can be used to upgrade the current 10-Gb/s IM-D D system to a 100-Gb/s one directly.
OCIS codes: 060.0060, 070.0070.
doi: 10.3788/COL20090708.0679.
Recently, with the bit rate increasing to 100 Gb/s and
beyond, the current intensity-modulated direct-detection
(IM-DD) formats are not applicable any more because of
their low tolerance for optical distortions including chro-
matic dispersion, dispersion slope, polarization mode
dispersion (PMD), time jitter, etc. In order to real-
ize ultra high-speed optical transmission over 100 Gb/s,
various advanced modulation formats and transmission
schemes have been developed
[1]
. However, these new
technologies are complex and costly. The temporal opti-
cal Fourier transformation (OFT) based on time lenses is
a promising technique for the ultra short pulse distortion-
free transmission
[2−5]
. The principle is that the spectral
envelope of an optical pulse is kept unchanged during
transmission in optical fiber by using OFT to swap the
spectral and temporal envelope, and the unchanged spec-
tral envelope can be used to recover the original undis-
torted input pulse waveform. Wang et al. used a single
time lens at the receiver to convert the distorted time
domain signals into frequency domain to reconstruct the
input pulses
[2,3]
. Because the ultra short optical pulse pe-
riod leads to the very limited regeneration time for OFT,
this technique can only be used in an optical time divi-
sion multiplexing (OTDM) system. By using cross-phase
modulation with parabolic pulses as a time lens, Hirooka
et al. formed a wider regeneration window
[4]
. But a more
complex system is needed to form such parabolic pulses.
In this letter, we propose a simple OFT-based system,
which is much different from above schemes. In our
scheme, two time lenses are added into a conventional
10-Gb/s IM-DD system to achieve a 100-Gb/s one. One
time lens is put at the transmitter as an optical inverse
Fourier transformation (OIFT) device. At the receiver
after transmission, the other time lens is used as an OFT
device to convert the transmitted signals back into time-
domain for direct detection. A sequence of N pulses
is launched into the OIFT to form one signal. So the
transmission speed is reduced to 1/N of its initial speed.
Moreover, the regeneration time window is N times
longer than the initial data period, much longer than
those in Refs. [2−4]. Potentially, it has a much better
tolerance for linear perturbations. The simulations show
a 10×100 Gb/s IM-DD DWDM system over 2000-km
transmission without using PMD compensation.
The system configuration of our OFT-based IM-DD
system is shown in Fig. 1, where N T is the time win-
dow corresponding to the regeneration time
[5]
, N is the
number of the initial optical pulses in one time window,
T is the initial data period, which is 10 ps in a 100-Gb/s
system. In our system, the initial intensity-modulated
pulses are divided into different continuous sequences
by a new time clock, which is N times longer than the
initial data clock. N initial pulses in each sequence are
converted into one special frequency-domain signal by
the OIFT device. It is a continuous real-time process.
So the OFT and OIFT should be continuous with a pe-
riod of N T . Each OFT and OIFT device has two phase
modulators and a dispersion medium.
After the OIFT, the new signals are lunched into fiber.
During transmission on link, we still use dispersion com-
pensation modules (DCMs) to compensate the chromatic
dispersion as those had been used in a conventional 10-
Gb/s system. DCMs can also ensure the spectral signals
to be confined in the time window during very long dis-
tance transmission.
At the receiver, the transmitted signals constricted in
the time window can be converted back into initial pulse
sequences by an OFT device. The whole system does not
need the compensation for PMD and dispersion slope. If
the time window is wide enough, the whole system may
not need DCMs anymore. Unfortunately, for a 100-Gb/s
1671-7694/2009/080679-04
c
2009 Chinese Optics Letters