高速全光正交调制新方案：频移键控与强度调制标记结合

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"基于频移键控和强度调制标记的新型高速全光正交调制方案的研究" 这篇研究论文提出了一种创新的高速全光正交调制技术，结合了40-Gbit/s的光学频移键控(OFSK)载波和2.5-Gbit/s的强度调制(IM)标记。这种新型方案旨在提高光通信系统的数据传输速率和效率，同时降低系统复杂性。在传统的光通信系统中，通常需要多个光源来生成不同频率或调制模式的信号，而此方案通过载波抑制调制和差分相移键控(DPSK)到IM的转换，仅需一个光源即可产生OFSK信号，显著降低了系统成本和复杂度。正交调制是光通信中常用的一种技术，它利用正交的频率或相位来编码数据，以实现多路复用和高数据传输速率。在该研究中，40-Gbit/s的OFSK载波作为主数据流，负责承载大部分信息。而2.5-Gbit/s的IM标记则作为一个辅助通道，用于附加控制或同步信息，这在光网络中的资源管理和错误校验中尤为重要。论文通过数值模拟对系统性能进行了详尽的分析，包括IM调制深度的影响、误码率(BER)以及色散限制。IM调制深度是指调制信号相对于未调制光强的比例，它直接影响到信号的可解码性和传输距离。结果显示，当IM调制深度为0.4时，40-Gbit/s的OFSK载波与2.5-Gb/s的IM标记能够成功地通过50公里的标准单模光纤(SMF)传输，且引入的衰减惩罚仅为0.87和0.92dB，显示出对输入功率范围的较高容忍度，最大可达11和1。此外，该方案还展示出了对输入功率波动的鲁棒性，这意味着即使在光功率变化较大的情况下，系统仍能保持良好的性能。这一特性对于实际部署中的光通信系统来说至关重要，因为网络环境中的光功率波动是常见的问题。这项研究提出了一种高效的全光正交调制技术，通过结合OFSK和IM，实现了高速数据传输并简化了系统设计。其优异的性能指标，如低损耗、宽功率容限以及对输入功率波动的适应性，都为未来光通信系统的设计提供了新的思路和可能。

Study of a novel high-speed all-optical

orthogonal modulation scheme based on

frequency-shift keying and intensity-modulated

labeling

Minghao Li

Nan Chi

Wei Hong

Wei Li

Hong Liu

Dexiu Huang

Huazhong University of Science and Technology

School of Optoelectronic Science and

Engineering

Wuhan National Laboratory for Optoelectronics

Wuhan 430074, China

E-mail: hustlmh76@sina.com

Abstract. We propose and demonstrate a novel orthogonal optical la-

beling scheme based on 40-Gbit/s optical frequency-shift keying 共FSK兲

payload and 2.5-Gbit/ s intensity-modulated 共IM兲 labeling. Using the

technology of carrier-suppressed modulation and conversion of differen-

tial phase-shift keying to IM, only one light source is needed to generate

the optical FSK signal. The system performance, including range of IM

modulation depth, bit error ratio, and dispersion limitation, is carefully

investigated by numerical simulation. With IM modulation depth of 0.4,

the 40 Gbit/ s FSK payload and 2.5-Gb/ s IM label are transmitted over a

50-km standard single mode ﬁber 共SMF兲 with 0.87 and 0.92 dB penalty

and show immunity to input power range upto 11 and 15 dB, respec-

tively. Optimal methods to improve the system performance are also

proposed and discussed. After optimization, the IM modulation depth can

be reduced to 0.2.

Engineers. 关DOI: 10.1117/1.2977526兴

Subject terms: frequency-shift keying with intensity modulation 共FSK/IM兲;or-

thogonal modulation; carrier suppression; delay interferometer 共DI兲

Paper 080189R received Mar. 10, 2008; revised manuscript received Jun. 13,

2008; accepted for publication Jul. 3, 2008; published online Sep. 9, 2008.

1 Introduction

All-optical label swapping 共AOLS兲 has become a promis-

ing technique for implementing packet routing and for-

warding functions over wavelength-division multiplexing

共WDM兲 optical networks.

In AOLS networks, optical label

swapping is regarded as an indispensable technology, and

various methods for label coding have been studied,

such

as bit serial labels, optical subcarrier multiplexed labels,

and optical code division multiplexing. A more efﬁcient

scheme of orthogonal frequency-shift keying with intensity

modulation 共FSK/IM兲 was also proposed recently,

3,4

where

the payload is in IM format, while the label is in FSK

format. The main merit of FSK labeling is that the low-

speed FSK label can be superimposed on and extracted

from the optical carrier without affecting its intensity.

However, the FSK label is generated by direct modulation

of electric current in a laser light source, so the FSK bit rate

is limited by the response of the laser. Moreover, a fre-

quency discriminator and a tunable light source must be

used to demodulate the old FSK label and generate a new

one for the next hop at each core router, which may result

in a great increase of the system complexity and cost.

To overcome these problems, a novel scheme using FSK

for the payload with new high-speed external FSK modu-

lation technology is required. An integrated optical FSK

modulator

based on the single sideband 共SSB兲 modulator

technology

8,9

has been reported, employing four optical

phase modulators.

However, the mentioned modulator re-

quires precise phase and amplitude adjustment of four driv-

ing rf signals, which may lead to high cost and discourage

its use. Another scheme, which utilizes the combination of

two demodulated differential phase-shift keying 共DPSK兲

signals to generate an optical FSK payload, has also been

proposed and experimentally demonstrated at 10 Gbit/ s.

However, two light sources are used to generate the FSK

signal in this scheme, which may result in high cost and

performance instability. So far, developement of a

40-Gbit/ s FSK transmitter and its application in payload

coding for AOLS are still a challenge. The performance of

this modulation system has not been investigated either.

In this paper, we propose and numerically demonstrate a

novel high-speed optical FSK/IM orthogonal modulation

scheme using the optical FSK as the modulation format for

the 40-Gbit/ s payload, on which the 2.5-Gbit/ s intensity-

modulated label is superimposed. With the use of the tech-

niques of carrier-suppressed modulation and DPSK-to-IM

conversion, only one light source is needed in the proposed

scheme to generate the high-speed FSK payload.

The paper is organized as follows. In Sec. 2, the opera-

tion principle of the proposed FSK/IM orthogonal modula-

tion scheme is described. In Sec. 3 and its subsections, the

system performance with respect to IM modulation depth,

transmission limitation, and dispersion tolerance is pre-

sented. Some optimization methods that can greatly im-

prove the system performance are also provided and dis-

cussed. In Sec. 4, summarizing conclusions are given.

Optical Engineering 47共9兲, 095002 共September 2008兲

Optical Engineering September 2008/Vol. 47共9兲095002-1

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