BRAGG GRATING ASSISTED MMIMI-COUPLER FOR TUNABLE ADD-DROP MULTIPLEXING
An apparatus for add/drop multiplexing of a wavelength channel multiplex comprises an MMI coupler (1) and MI arm section (3). The MMI coupler includes a multiplex input (7), an add channel input (9), a drop channel output (13), a multiplex output (17), and at least four input/output terminals (21, 23, 25, 27). The MI arm section includes four waveguides (29, 31, 33, 35), wherein each waveguide is optically connected to a respective of said input/output terminals of the MMI coupler; and is at least provided with a first phase control element (37), a reflection grating (39), a second phase control element (49), and a wide frequency range reflection means (51). Further, each of the reflection gratings are provided with a heater means for tuning the respective reflection grating to the wavelength channel to be added/dropped and the wide frequency range reflection means reflect all other channels. The first and second phase control elements are adapted to direct the channel to be added/dropped to the multiplex output/drop channel output and to direct remaining channels to the multiplex output.