ZTE Communications

S pecial Topic
Greater than 200 Gb/s Transmission Using Direct-Detection Optical OFDM Superchannel
Wei-Ren Peng, Itsuro Morita, Hidenori Takahashi, and Takehiro Tsuritani
Greater than 200 Gb/s Transmission
Using Direct-Detection Optical
OFDM Superchannel
Wei-Ren Wei-Ren Peng, Peng, Itsuro Itsuro Morita, Morita, Hidenori Hidenori Takahashi, Takahashi, and and Takehiro Takehiro Tsuritani Tsuritani
(KDDI R&D Laboratories Inc., Fujimino-shi, Saitama 356-8502, Japan)
Abstract
In this paper, we propose direct-detection optical orthogonal frequency division multiplexing superchannel (DDO-OFDM-S) and optical
multiband receiving method (OMBR) to support a greater than 200 Gb/s data rate and longer distance for direct-detection systems. For the
new OMBR, we discuss the optimum carrier-to-sideband power ratio (CSPR) in the cases of back-to-back and post transmission. We
derive the analytical form for CSPR and theoretically verify it. A low overhead training method for estimating I/Q imbalance is also introduced
in order to improve performance and maintain high system throughput. The experiment results show that these proposals enable an
unprecedented data rate of 214 Gb/s (190 Gb/s without overhead) per wavelength over an unprecedented distance of 720 km SSMF in
greater than 100 Gb/s DDO-OFDM systems.
Keywords
orthogonal frequency division multiplexing (OFDM); direct detection; multiband transmission
F1 Introduction
or years, papers have been written on
direct-detection transmission because it uses a
very simple receiver that usually only requires
photodiodes for detection [1], [2]. Most research on
direct-detection has been focused only on the
dispersion-managed links, and not until recently has
electronic equalization has been introduced into optical
communications to compensate for chromatic dispersion (CD)
[3]. Electronic equalization has ushered in a new era of
dispersion-unmanaged links that do not require dispersion
map design and offer a lower-nonlinear transmission medium
[4]. Joint direct-detection receiving and
dispersion-unmanaged links is an interesting topic related to
implementation cost.
To incorporate direct-detection in a
dispersion-unmanaged link, single-carrier transmission with
pre-equalization [3] and multicarrier transmission with
post-equalization [5] have been proposed. The
pre-equalization in [3] could work very well to counter CD;
however, when used in dynamic routing networks, it requires
the link information (the exact information of the accumulated
CD) beforehand via complex signaling methods [6], [7]. The
proposal in [5], commonly referred to as direct-detection
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ZTE COMMUNICATIONS
March 2012 Vol.10 No.1
optical orthogonal frequency division multiplexing
(DDO-OFDM), automatically estimates and compensates for
CD at the receiver, without any link information. Therefore,
DDO-OFDM could easily support both point-to-point and
dynamic routing networks. DDO-OFDM should be
repositioned because of its transparency to different kinds of
network architectures.
Even with these advantages, conventional DDO-OFDM has
limited transmission performance that might restrict its
application only to short-reach networks [8], [9]. Among the
many reported DDO-OFDM systems, a self-coherent OFDM
[10] system extends both the capacity and reach of
conventional DDO-OFDM and significantly increases the
receiver’s complexity, which diminishes the inherent benefits
of using direct detection. Therefore, a laudable goal for a
DDO-OFDM system is to improve transmission with simple
solutions while keeping the cost of direct detection low.
In this paper, we propose DDO-OFDM superchannel
(DDO-OFDM-S) with a simple optical multiband receiving
(OMBR) [11], [12] method. DDO-OFDM-S has dual carriers
at both sides to reduce receiver bandwidth, and OMBR
detects the signal band-by-band to relax the sampling rate
of the receiver and to reduce the frequency gap between
carriers and superchannel for high spectral usage. In this
paper, an optimum carrier-to-sideband power ratio (CSPR)