Liu Xiang, Chandrasekhar S, Wood T H, Tkach R W, Winzer P J, Burrows E C, Chraplyvy A R
Bell Labs, Alcatel-Lucent, 791 Holmdel-Keyport Road, Holmdel, NJ 07733, USA.
Opt Express. 2011 Dec 12;19(26):B868-81. doi: 10.1364/OE.19.00B868.
We present a new class of optical modulation formats based on the combination of m-ary pulse-position modulation (m-PPM) or m-ary frequency-shift keying (FSK) with additional polarization and/or phase modulation, which is applied on the information carrying pulses in the case of m-PPM or on the information carrying frequency carriers in the case of m-FSK. We describe the principle and implementation of this class of optical modulation formats, and formulate their theoretical receiver sensitivities in optically pre-amplified receivers. Pilot-assisted frequency-domain equalization, similar to that used in coherent optical orthogonal frequency-division multiplexing (CO-OFDM), is used for reliable channel estimation and compensation. CO-OFDM also allows m-FSK to be implemented with high spectral efficiency. As a particular format in this class, m-PPM in combination with polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK), termed as PQ-mPPM, offers superior receiver sensitivity in optically pre-amplified receivers at bit error ratios (BERs) around the thresholds of common forward-error correction codes. Record receiver sensitivities of 3.5 photons per bit (ppb) at BER = 10(-3) and 2.7 ppb at BER = 1.5 × 10(-2) are experimentally demonstrated at 2.5 Gb/s and 6.23 Gb/s using PQ-16PPM and PQ-4PPM, respectively. We further demonstrate the transmission of a 6.23-Gb/s PQ-4PPM signal over a 370-km unrepeatered ultra-large-area-fiber span with 71.7-dB total loss budget.
我们提出了一类新型光调制格式，它基于多进制脉冲位置调制（m-PPM）或多进制频移键控（FSK）与额外的偏振和/或相位调制相结合，在m-PPM情况下应用于携带信息的脉冲，在m-FSK情况下应用于携带信息的频率载波。我们描述了这类光调制格式的原理和实现方式，并推导了它们在光预放大接收机中的理论接收灵敏度。类似于相干光正交频分复用（CO-OFDM）中使用的导频辅助频域均衡，用于可靠的信道估计和补偿。CO-OFDM还允许以高光谱效率实现m-FSK。作为这类中的一种特定格式，m-PPM与偏振分复用正交相移键控（PDM-QPSK）相结合，称为PQ-mPPM，在光预放大接收机中，在误码率（BER）接近常见前向纠错码阈值时，具有卓越的接收灵敏度。使用PQ-16PPM和PQ-4PPM分别在2.5 Gb/s和6.23 Gb/s下，实验证明了在BER = 10^(-3)时记录的接收灵敏度为每比特3.5个光子（ppb），在BER = 1.5×10^(-2)时为2.7 ppb。我们还进一步证明了一个6.23-Gb/s的PQ-4PPM信号在总损耗预算为71.7 dB的370公里无中继超大面积光纤跨度上的传输。
