Polymeric tunable optical attenuator with an optical monitoring tap for WDM transmission network

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Abstract
A polymeric tunable optical attenuator has been fabricated using asymmetric Y-branch waveguides integrated with an optical monitoring tap. One arm of the branch serves as the main output port, while the other arm helps remove the residual optical power resulting from attenuation. An optical power tap used for the monitoring port is introduced to take a fraction of the main port power. This monitoring port is useful for observing the main output continuously. Furthermore, it can be fed back to the electrical driver to maintain the attenuated output regardless of variations in input light polarization and power. By utilizing the modal evolution effect in asymmetric branches, the attenuator has enhanced fabrication tolerance and reduced wavelength sensitivity. Also, no electrical bias is needed to achieve maximum optical transmission. The attenuator exhibited a dynamic range of more than 20 dB at 1550 nm and a response time of about 1 ms. The polarization dependent loss was about 0.9 dB, and the wavelength uniformity was less than 1.2 dB over the range of 1530-1560 mm.