A wavelength-tunable optical transmitter using semiconductor optical amplifiers and an optical tunable filter for metro/access DWDM applications

This paper proposes and demonstrates a widely tunable and precisely controllable optical transmitter that uses semiconductor optical amplifiers (SOAs) and an optical tunable filter (OTF) for metro/access dense-wavelength-division-multiplexing (DWDM) systems/networks. The transmitter consists of a fiber-ring-laser section based on SOA(s) and an OTF and a modulation section based on an SOA. First, the requirements imposed on the components intended for the fiber-ring laser are clarified through approximate analyses and basic experiments. To obtain low-noise characteristics, the lower limit of effective OTF bandwidth is investigated by considering the SOA carrier lifetime. For obtaining wavelength precision, the upper limit of the effective OTF bandwidth is derived by considering the SOA ripple effect. Next, the proposed transmitter is demonstrated, where all SOAs are integrated into one planar lightwave circuit (PLC) platform using spot-size converting technology. By designing the fiber-ring-laser section according to the clarified requirements, a wavelength control precision of /spl plusmn/1.75GHz is achieved while realizing the required relative intensity noise (RIN) from 1540 to 1560 nm. Finally, it is demonstrated that the transmitter can handle signals at up to 1.25 Gb/s.

I. Introduction

Wavelength-Tunable optical transmitters offer advanced flexibility in dense-wavelength-divisionmultiplexing (DWDM) systems/networks. They can be used as common spare/inventory transmitters for various wavelength channels in DWDM systems, as well as optical transmitters/wavelength converters in reconfigurable DWDM networks [1]. They also offer the possibility of being used in wavelength-independent optical network units (ONUs) in DWDM-based optical access networks [2]. TABLE I Typical Characteristics of Wavelength-Tunable Lasers for DWDM Metro/Access Applications

Items	Characteristics
Relative intensity noise (RIN)	<-130 dB/Hz…values without inducing optical-SNR degradation at BER of 10–12 for 1.25 Gbps
Wavelength preciseness	< 2 G Hz…for DWDM with channel spacing of 25 GHz or over