Proposal of integrated-optic wavelength-selective modulator based on coupling-efficiency control of distributed Bragg reflector in straight waveguide

A new optical wavelength-selective waveguide modulator consisting of a simple distributed Bragg reflector (DBR) integrated in a two-mode straight waveguide with ITO thin film is proposed and theoretically discussed. The waveguide has double guiding core layers and support two TM guided modes. One is used as a transmission mode whereas the other is as a modulation mode. A wave of a specified wavelength among incident WDM waves of the transmission mode is contra-directionally and wavelength-selectively coupled by the DBR to the modulation mode. The coupling efficiency depends on a coupling length of the DBR. The coupling length varies effectively according to a propagation loss of the modulation mode. Absorption of the ITO layer is controlled to vary the propagation loss. As a result, the transmittance of the DBR is modulated wavelength-selectively. The operation principle is illustrated in detail and design examples are theoretically discussed.