In this paper, we will discuss the utilization of optically injection-locked (OIL) 1.55 μm vertical-cavity surface-emitting
lasers (VCSELs) for operation as low-cost, stable, directly modulated, and potentially uncooled transmitters, whereby the
injection-locking master source is furnished by modulated downstream signals. Such a transmitter will find useful
application in wavelength division multiplexed passive optical networks (WDM-PONs) which is actively being
developed to meet the ever-increasing bandwidth demands of end users. Our scheme eliminates the need for external
injection locking optical sources, external modulators, and wavelength stabilization circuitry. We show through
experiments that the injection-locked VCSEL favors low injection powers and responds only strongly to the carrier but
not the modulated data of the downstream signal. Further, we will discuss results from experimental studies performed
on the dependence of OIL-VCSELs in bidirectional networks on the degree of Rayleigh backscattered signal and
extinction ratio. We show that error-free upstream performance can be achieved when the upstream signal to Rayleigh
backscattering ratio is greater than 13.4 dB, and with minimal dependence on the downstream extinction ratio. We will
also review a fault monitoring and localization scheme based on a highly-sensitive yet low-cost monitor comprising a
low output power broadband source and low bandwidth detectors. The proposed scheme benefits from the high
reflectivity top distributed Bragg reflector mirror of the OIL-VCSEL, incurring only a minimal penalty on the upstream
transmissions of the existing infrastructure. Such a scheme provides fault monitoring without having to further invest in the upgrade of customer premises.
We describe two optical layer schemes which simultaneously facilitate local area network emulation and automatic protection switching against distribution fiber breaks in passive optical networks. One scheme employs a narrowband fiber Bragg grating placed close to the star coupler in the feeder fiber of the passive optical network, while the other uses an additional short length distribution fiber from the star coupler to each customer for the redirection of the customer traffic. Both schemes use RF subcarrier multiplexed transmission for intercommunication between customers in conjunction with upstream access to the central office at baseband. Failure detection and automatic protection switching are performed independently by each optical network unit that is located at the customer premises in a distributed manner. The restoration of traffic transported between the central office and an optical network unit in the event of the distribution fiber break is performed by interconnecting adjacent optical network units and carrying out signal transmissions via an independent but interconnected optical network unit. Such a protection mechanism enables multiple adjacent optical network units to be simultaneously protected by a single optical network unit utilizing its maximum available bandwidth. We experimentally verify the feasibility of both schemes with 1.25 Gb/s upstream baseband transmission to the central office and 155 Mb/s local area network data transmission on a RF subcarrier frequency. The experimental results obtained from both schemes are compared, and the power budgets are calculated to analyze the scalability of each scheme.