Study On Tunable Optical Devices For Next Generation Passive Optical Network System

With the emergence of high-bandwidth services such as IPTV,video on demand and online gaming are emerging,it is no wonder that passive optical network need to provide greater transmission capacity to meet customer access bandwidth growth demand.At present,the passive optical network based on time division multiplexing has reached transmission capacity of 10Gb/s per wavelength.It will face great technical challenges and result in very high upgrade cost when continuing to use current technology to increase the network capacity,which is not applicable for cost-sensitive optical access network.Due to their mature technical solutions and easy system expansion,orthogonal frequency division multiplexing and wavelength division multiplexing technology have been widely studied and discussed in recent years and are considered as two promising cadidates for next generation optical access network.The thesis investigated these two technologies for next-generation optical access network,evaluated transmission performance of OFDM signal in optical access network,and design tunable optical devices which can be used for the next generation optical access network.The work includes:(1)Package of a high-speed directly modulated tunable laserWith adavantage of wide wavelength tuning range and low tuning power consumption,tunable semiconductor laser can satisfy the requirements of next generation optical access network and appears to be research hotspot in recent years.Through the cooperation with Institue of Semiconductors,we package a tunable laser with 3dB bandwidth of more than 10 GHz,whose has wavelength tuning range of more than 9nm and tuning accuracy of less than 0.1nm.Experimental results indicated that it can support 10Gb/s error-free OOK and 16-QAM OFDM signals transmission.(2)Development of micromotor-based tunable optical filterAfter WDM technology is introduced in the optical access network,colorlessness of optical network units is a key problem that should be addressed.The thesis developed tunable optical thin film filters based on micro-motor with 3dB bandwidth of 0.4nm and insertion loss of less than 4dB,whose center wavelength can be tuned from 1551 nm to 1560 nm.Test results showed that it can support error-free transmission of 10Gb/s 16-QAM OFDM signals.The whole system with this tunable filter has a power budget of more than 30 dB,and the power budget penalty introduced by filter is approximately 1dB.This filter provides a practical and feasible solution for the next-generation optical access network.(3)Chirp management of tunable filterCompared with the external modulation,the widely used direct modulation in optical access network is vulnerable to chirp effect.In NRZ digital transmission system with transmission rate of greater than 2.5Gb/s,the chirp will act with fiber dispersion together to degrade the signal's performance and transmission distance greatly.This thesis studied the chirp management of directly modulated signal by steep edge of tunable optical filter,which can improve the quality of received signal while filtering a specific wavelength,and increase receiver's sensitivity and the system's power budget.(4)Proposal and experiment verification of WDM-OFDM-PON based on tunableoptical componentsWith its high spectrum efficiency,OFDM signal is considered as one of candidate modulation format of next generation PON.This thesis studied various nonlinear damage that OFDM signal encountered in transmission chain of the OFDM-PON by qualitative and quantitative methods,discussed the system performance degradation by nonlinear injuries of the different optical/electrical components in the OFDM-PON system,and improve transmission distance and power budget of OFDM signal by designing new linear optical receiver and adopting predistortion algorithm.Finally,this chapter proposed two WDM-OFDM-PON architectures based on tunable optical components,experimental results indicated that both optical access network can provide more than 40Gb/s capacity at downstream side,more than 20 Km transmission distance and 1:32 splitter ratio.(5)Proposal and experiment verification of switched optical access networkWith the wavelength tunablility capability of DBR laser,dynamic schedule and migration of the wavelength in next generation optical access network is possible.This thesis proposed two switched optical access network architectures based on characters of cyclic AWG,in which wavelength can be scheduled and migrated as a resource.Experimental results indicated that both switched optical access network can provide more than 32 dB power budget,which meets the requirement of optical access network standard.