FLAT-TOP TUNABLE FILTER

摘要

A tunable PLC optical filter having sequentially connected thermally tunable Mach-Zehnder (MZ) interferometers is described. The cascade of MZ interferometers, each having a free spectral ranges matching ITU frequency grid spacing, are tuned so as to have a common passband centered on the frequency of the signal being selected, while having at least one of the stopbands centered on any other ITU frequency. Any other optical channel that may be present at any other ITU frequency is suppressed as a result. Another MZ interferometer in series with the cascade of interferometers including an asymmetric or variable coupler, is tuned to have low transmission at the center frequency of the selected optical channel.

主权项

1. A tunable optical filter comprising:
an input port for receiving an optical signal, the optical signal including a plurality of optical frequency channels, each optical frequency channel having a central frequency substantially centered at a different frequency of predetermined frequency grid having a predetermined grid spacing; an output port for transmitting an optical frequency channel selected from the plurality of optical frequency channels; a plurality of sequentially coupled tunable Mach-Zehnder (MZ) interferometers optically disposed between the input port and the output port for isolating the selected optical frequency channel from the plurality of optical frequency channels, each tunable MZ interferometer having a plurality of equidistantly spaced conterminous frequency passbands and frequency stopbands and having a free spectral range substantially equal to an integer multiple of the predetermined grid spacing; a first MZ interferometer optically disposed between the input port and the output port, the first MZ interferometer including first and second interferometer arms optically disposed between first and second optical couplers, the first optical coupler for directing more than 75% of the light received at an input of the first MZ interferometer into the first interferometer arm, the first and second interferometer arms having different lengths, and a controller for tuning the plurality of sequentially coupled MZ interferometers to have one passband of each MZ interferometer centered on the central frequency of the selected optical frequency channel, and to have at least one of the stopbands of the MZ interferometers centered on the central frequency of each remaining optical frequency channel of the optical signal, so as to suppress each said remaining optical frequency channel of the optical signal, and for tuning the first MZ interferometer to have low transmission at the center frequency of the selected optical frequency channel.