混沌波调制激光：高效定位WDM-PON故障

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本文主要探讨了在无源光网络（WDM-PON）的故障定位中应用混沌波调制的多纵模激光技术。作者Hang Xu、Bingjie Wang、Jianguo Zhang等人来自太原理工大学的先进传感器与智能控制系统实验室和光学电子工程学院，他们提出了一种创新且经济高效的方法，旨在解决WDM-PON中的故障定位问题。混沌波调制技术的关键在于利用Colpitts振荡器产生的混沌信号直接对多纵模的Fabry-Perot半导体激光器进行调制。混沌调制使得激光器的每个纵向模式都具有独特的、随机的强度波动特性，这种特性赋予了它们在故障检测中的潜在优势。通过选择合适的可调光滤波器，研究人员能够选取特定模式，并利用混沌相关技术来检测波分复用网络中的匹配分支。这种方法的优势在于其高灵敏度和适应性，即使在复杂的网络环境中，也能有效地识别出故障位置。实验结果显示，这种混沌波调制技术在WDM-PON中的应用展现出优异的性能。它能够精确地定位各种类型的故障，包括末端未连接的光纤、不匹配的连接器以及光纤断裂点。令人印象深刻的是，该技术具有大约75公里的探测范围，这意味着即使在长距离的光纤网络中，也能实现有效的故障定位。同时，它还具有空间分辨率高达14厘米的特性，这对于需要精细定位的场景尤其有用，如密集的城市光纤网络或数据中心内部的连接。这项研究为WDM-PON的维护和优化提供了新的解决方案，减少了故障排查的时间和成本，提高了网络的可靠性和效率。混沌波调制技术作为一种新兴的诊断工具，其在未来通信网络中的应用前景广阔。

FAULT LOCATION FOR WDM-PON

USING A MULTIPLE-LONGITUDINAL-

MODE LASER MODULATED BY

CHAOTIC WAVE

Hang Xu,

1,2

Bingjie Wang,

1,2

Jianguo Zhang,

1,2

Hong Han,

1,2

Li Liu,

1,2

Yuncai Wang,

1,2

and Anbang Wang

1,2

Key Laboratory of Advanced Transducers & Intelligent Control

System (Taiyuan University of Technology), Ministry of Education &

Shanxi Province, Taiyuan 030024, China; Corresponding author:

wanganbang@tyut.edu.cn

Institute of Optoelectronic Engineering, College of Physics &

Optoelectronics, Taiyuan University of Technology, Taiyuan 030024,

China

Received 20 April 2015

ABSTRACT: We experimentally demonstrate a cost-effective method to

locate faults in wavelength-division-multiplexing passive optical network

(WDM-PON) utilizing a multiple-longitudinal-mode Fabry–Perot semi-

conductor laser directly modulated by chaotic wave from a Colpitts

oscillator. Due to chaos modulation, every longitudinal mode of the

laser has chaotic intensity waveform. Using a tunable optical filter

selects a mode to detect the wavelength-matched branch of WDM-PON

using chaos correlation technique. Experimental results show that the

unterminated fiber end, mismatch connector and fiber breakpoint can be

preciously located. A detection range of approximately 75 km and a

range-independent spatial resolution of 14 cm are achieved.

2015

Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2502–2506,

2015; View this article online at wileyonlinelibrary.com. DOI 10.1002/

mop.29375

Key words: wavelength-division-multiplexing; passive optical network;

Colpitts oscillator; chaos; fault location

1. INTRODUCTION

Wavelength-division-multiplexing passive optical network

(WDM-PON) is a promising solution for broadband access net-

work, because of its large capacity, high privacy and low inser-

tion loss [1,2]. It is important and convenient for

troubleshooting to diagnose each channel of WDM-PON at opti-

cal line terminal (OLT) [3,4]. Tunable optical time-domain

reflectometer (OTDR) using wavelength-tunable optical pulse

has been proposed for this purpose [5–7]. Unfortunately, the

pulse OTDR suffers from the tradeoff between spatial resolution

and dynamic range. The spatial resolution is usually limited to

about tens of meters, which is unsuitable for optical accessing

network that may suffer from dense events. The tradeoff can be

overcome using optical pulse sequence to replace single pulse

[8,9]. The dynamic range is increased through increasing

sequence length rather than pulse duration to improve energy.

However, high resolution requires an expensive high-speed

sequence generator and a wideband modulator.

Recently, a wavelength-tunable chaos OTDR has been pro-

posed to diagnose WDM-PON [10], in which a multiple-

longitudinal-mode Fabry–Perot laser diode (FP-LD) with mode-

selective feedback is used to generate wavelength-tunable chaos.

Benefiting from the delta-like autocorrelation function and broad

bandwidth of the chaotic light, a spatial resolution of 2 cm has

been achieved, which is no longer traded off against the dis-

tance. Following this work, other tunable chaotic light sources

have been proposed. In 2013, Xia et al. proposed a semiconduc-

tor optical amplifier (SOA) ring structure to generate optical

wideband chaos, consisting of a SOA and a polarization control-

ler (PC) which needs to be carefully adjusted [11]. In 2014,

Yang et al. proposed an erbium-doped fiber ring laser to gener-

ate the wavelength tunable chaotic laser, which comprises a

980 nm laser diode, an erbium-doped fiber, a 980/1550 nm

wavelength division multiplexer and a PC and so on [12]. How-

ever, from a practical point of view, in the above methods the

generation of wideband chaos is constructed by discrete optical

components, of which the stability and size pose a challenge for

their applications. The reason is the laser nonlinear dynamical

systems are very sensitive to the polarization of feedback light,

which is vulnerable to external disturbance. Moreover, the gen-

erated chaotic light usually has sidelobes in correlation trace

[13,14] induced by the delayed feedback resulting in a “ghost

peak” that causes misjudgment.

In this letter, we experimentally demonstrate a simple

method of fault detection for WDM-PON using a FP-LD which

is directly modulated by a chaotic signal generated from a Col-

pitts oscillator. Colpitts oscillator based on the nonlinearity of a

transistor with a high cutoff frequency can generate a chaotic

signal with a wide spectrum extending to a few GHz [15].

According our previous experiments, this spectral width of GHz

predicts a spatial resolution near ten centimeters, which is suffi-

cient for detection in WDM-PON. More importantly, compared

with the optical generation of chaos, Colpitts oscillator is com-

pact, stable and inexpensive as it is a small electronic integrated

circuit. In addition, the chaotic output of the Colpitts oscillator

possesses autocorrelation traces without obvious sidelobes

caused by feedback delay.

2. EXPERIMENTAL SETUP

Figure 1 shows the experimental setup of the proposed method.

The chaotic wave generated from a Colpitts oscillator is ampli-

fied through an amplifier (AMP) with tunable gain, and then

used to directly modulate a multiple-longitudinal-mode FP-LD

to generate the multimode chaotic laser light. After amplified by

an erbium-doped fiber amplifier (EDFA), a single-mode light is

filtered out from the chaotic laser output by a tunable fiber

Bragg grating (TFBG) with 23-dB linewidth of about 0.2 nm.

The TFBG’s tunable range is about 40 nm, from 1530 nm to

1570 nm. The filtered chaotic laser light is divided by a fiber

coupler into two paths: one (1%) is used as the reference light

and the other (99%) is used as the probe light. The probe light

is launched into the WDM-PON and its back-reflected light is

received through an optical circulator (OC2). The WDM-PON is

constructed with a 20 km feeder line and a 50-GHz-spaced

arrayed waveguide grating (AWG) with 16 channels. Both the

echo light and the reference light are converted into electrical

signals by a pair of identical avalanche photo detectors (APD)

with 1-GHz bandwidth and are recorded by a real-time oscillo-

scope (LeCroy SDA806Zi-A) with 6-GHz bandwidth. The fault

events can be located by calculating the correlation between the

reference and echo signal in a computer. By sweeping the wave-

length of the probe light, different optical branches can be

detected. An optical spectrum analyzer (Agilent 86140B) and a

RF spectrum analyzer (Agilent N9020A) are used to observe the

chaotic laser output.

3. GENERATION OF WAVELENGTH TUNABLE CHAOTIC

LASER LIGHT

In our experiments, the used Colpitts oscillator has an improved

configuration for generating high-frequency chaos, in which the

inductor is moved from the collector circuit of the transistor to

the base circuit [16]. Compared to the standard Colpitts circuit

[17–19], the improved oscillator can generate a chaotic signal

2502 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 57, No. 11, November 2015 DOI 10.1002/mop

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