US Patent 7916385 Apparatus and methods for optical communication

An optical circuit is disclosed, which may include a semiconductor optical amplifier (SOA); an optical filter operable to filter light emerging from the SOA; and a PIN for converting the light output from the optical filter into an electrical signal, wherein the gain profile of the optical filter is configured to maximize throughout of signal energy within a predetermined wavelength range (in-band), and to impose an insertion loss (Loob) of less than 20 dB on signal energy outside the predetermined wavelength range.