Single-chip linear optical amplifier

ABSTRACT: Amplification is a key function in optical networks. Traditionally, amplifiers have been used to compensate losses in optical fiber, enabling longer communication links. Today, amplifiers are being used in increasingly diverse functions ranging from power boosting of transmitters to loss compensation in optical add-drop nodes. Common to all these applications is the requirement to meet optical performance parameters within demanding cost, size and power constraints. The single-chip linear optical amplifier (LOA) is a solution that offers advantages as a discrete module, but also enables higher levels of integration. Examples of system performance and integrated solutions, utilizing the LOA, will be shown. 1. INTRODUCTION The optical network is working its way from the backbone through the metropolitan areas on an inexorable march to the customer premise. However, the closer one gets to the end user, the less cost can be sustained at any node in the network. The profoundly differing economics between the long-haul and the metropolitan markets demand at least an order of magnitude price/performance improvement in metropolitan optical components. In order to meet the emerging demanding requirements of system OEMs and service providers the photonics industry must leverage the power of integration to reduce cost size and power consumption of optical components. Amplification is as vital for the metropolitan networks as it is for the long haul. Without amplification, the amount of switching, power balancing, processing and transport that can be utilized will always be limited because signals become weaker. The obvious solution is to achieve optical amplification with chips. “Semiconductor optical amplifiers” or SOAs, were sidelined as a line amplifier almost a decade ago because of their “non-linear” behavior in today’s dense wavelength-division multiplexing (DWDM), switched network applications. One of the missing links for enabling higher levels of integration has been the existence of a single-chip linear optical amplifier – or “LOA” – that amplifies well, without crosstalk, at any data rate, and free from switching power transients or crosstalk, in DWDM applications in the metro and access markets. There have been numerous methods employed to linearize chip-based optical amplifiers. One obvious case is operating the amplifier at low output power levels [1]. Operating at low output power limits the non-linear effects, but also limits the amount of span length, node loss and cascading possible. Another option is attempting to keep the input power constant[2,3,4]. This method can be complex and generally requires extra components, which defeats the purpose of an integratable chip-based amplifier. The linear optical amplifier (LOA) uses optical feedback to linearize the amplifying gain medium. It was developed to overcome the deficiencies of current optical amplifier solutions while maintaining its inherent integratability. The LOA overcomes both the inter-symbol interference (ISI) and WDM crosstalk of the SOAs, as well as the dynamic transient difficulties of both SOAs and EDFAs. In this paper we describe how the LOA works, and show its performance parameters as a function of power and wavelength. We also demonstrate the use of the amplifier in several key applications. Based on these results, the LOA is an amplifier with the performance, size and cost required for integration in optical networks