This paper presents an automatic optical equalizer based on a pair of in-house developed high efficiency, acousto-optic variable optical attenuators (AO-VOAs). The system is polarization insensitive and presents a wide bandwidth compatible with coarse wavelength division multiplexing (CWDM) requirements: 340？nm. The system operation is automatic and bidirectional and equalization is obtained in one single iteration of algorithm loop. 1. Introduction In the context of an increasing demand for wideband transmission services, coarse wavelength division multiplexing is tackling access network capacity maximization. From the network management’s point of view, the number of optical central offices has to be optimized for economic viability; such an optimization is shown to be possible using optical budget extension; with an amplification technique, the link between the subscriber and central office can be extended or the splitting ratio can be increased (i.e., the number of users) [1, 2]. In this context, an intense activity is devoted to the development of enabling optical technologies to meet next generation distribution network challenges. A straightforward solution to increase the optical budget is to bring optical amplification technique into play; erbium doped fiber amplifier (EDFA), semiconductor optical amplifier (SOA), and Raman type amplifiers have been successfully tuned up to boost optical access networks [3–7]. However, the use of optical amplification requires optical equalization [8]. This paper presents a dynamic optical equalization setup that meets (for the first time to the best of our knowledge) the operation requirements across the full CWDM band: 340？nm. This system is faster than fiber-based/MEMS-based equalizers [8–13]; it is more compact than MEMS-based equalizers [10–12] and even than other acousto-optic based systems [10]. The system operation is bidirectional and fully automatic and the equalizer is able to adapt to all situations encountered during usual optical network processes—adding or dropping channels and input signal level variations. The operation principle is based on the cascade of two acousto-optic (AO) cells which are optimized for the modulation of near infrared signals; a complete description of the AO cells design and testing can be found in [14]. AO devices are known for their wide tuning range and their fast response time (down to the microsecond); they are naturally suited to multispectral filtering. We focus our investigations here on an automatic equalization function. This paper is structured as follows. We
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