Xuan Zhang

We propose and experimentally demonstrate an integrated passive optical network monitoring system for fault detection and localization. Fault detection technology is based on the recognition of reflection spectrum generated by each single fiber Bragg grating, which can support large-capacity user fiber fault monitoring. Fault localization method uses two different total received powers measured by an optical power meter to solve the established equation, and it shows a good accuracy compared with the OTDR measurement results. Fault detection and localization are carried out separately but share the same transmitter module. The introduction of the additional module ensures that the troubleshooting does not affect other normal user data communication. We also investigate the dynamic range requirements of the fault detection technology and the measurement error of the fault localization method. The calculation results show the required dynamic range for the recognition device can be maintained within a small range and the use of high-accuracy optical power meter can reduce the measurement error. The proposed monitoring system can simultaneously provide a large-capacity fault detection technology and high-accuracy fault localization method in a cost-sensitive passive optical network market.

We propose and experimentally demonstrate an online PON monitoring scheme that can simultaneously achieve the objectives of fault detection and localization. Fault detection and localization share the same transmitter module and perform in sequence. Based on a simple algorithm, one or several fiber Bragg gratings with different central reflection wavelengths are allocated to each end-user for fault detection. A large number of wavelength combinations are generated by several fiber Bragg gratings with different center wavelengths, and are finally identified in the time domain, which is very suitable for fault detection of large-capacity and high-density PON. An additional module is added before the power splitter/combiner to ensure the online troubleshooting. The model equation is established to locate the fault using two unmodulated broadband light sources. The calculated results of the fault localization method show a good agreement with the OTDR measurement results. The proposed scheme provides an integrated online troubleshooting solution for the detection and localization of PON link faults.

We propose and experimentally demonstrate a centralized PON monitoring scheme using the reflection spectrum of a single fiber Bragg grating. Each fiber Bragg grating used in the scheme adopts different central reflection wavelength or 3-dB reflection bandwidth. The unique reflection spectrum is generated after each fiber Bragg grating used is interrogated by a broadband probe source. These generated reflection spectra are used to identify and distinguish the drop fiber links. The similarity analysis model is established to solve the problem of waveform superposition identification for different 3-dB reflection bandwidths with the same central reflection wavelength, which can further improve the network monitoring capacity. The proposed scheme provides a simple and effective monitoring solution for large-capacity network, especially for high-density network with small end-user distance difference.

We propose and experimentally demonstrate a high capacity optical monitoring scheme using a self-seeding Fabry–Pérot laser diode (FP-LD) with direct modulation in a passive optical network (PON). A simple, stable, and low-cost monitoring source with side mode suppression ratio of 47 dB that consists of a FP-LD, a polarization controller, and a fiber Bragg grating is presented. The detecting signals can be encoded in two-dimension, i.e., pulse widths and wavelengths, which is very suitable for high capacity PON monitoring. The final recognition process is very simple because only the rectangular pulse width needs to be identified, especially compared with the complicated network recognition algorithm.

We propose a time division multiplexing passive optical network (TDM-PON) monitoring scheme based on the optical pulse width modulation (OPWM) by using a simple asymmetric loop (AL) located near the optical network unit (ONU). Various pulse widths can be easily obtained by configuring the appropriate length of the patchcord used to generate the path difference between two branches of a 1 × 2 splitter. Different wavelengths can be assigned to the same pulse width, which can further increase the network size. The optimized parameters of the AL are investigated and analysis models are established. The calculation results show that the proposed scheme has smaller correlation distance (CD) and lower multiple-customers interference probability (MCIP) than the periodic coding (PC) scheme. A simplified PON system with 8 ONUs is set up to experimentally demonstrate the feasibility of the proposed scheme. The network recognition processing used to identify the reflected monitoring signals in the proposed scheme is simple, especially compared with the reduced complexity maximum likelihood sequence estimation (RC-MLSE) used in the typical PC scheme.