Aegis Semiconductor is developing a diverse family of tunable thin film filters based on the thermo-optic properties of amorphous semiconductors. As thin film Fabry-Perot or multiple cavity filters, these devices have the fundamental structure of tunable 1D photonic crystals. We describe the evolution of our designs and the motivations for extending certain structures to 3D photonic crystals to reduce the device volume. Two different types of tunable thermo-optic devices apply for differing telecom functions at 1.5 µm. Continuously scanned filters for monitor purposes are deposited on solid substrates. Set-and-hold filters intended to be maintained at specific wavelengths must have greater thermal isolation, and so must be membranes. But simple planar membrane filters with metal trace resistive heaters have been shown experimentally to be subject to thermally induced strains causing birefringence. To address these limitations, membrane filters with laterally confined active regions are proposed using 2D photonic crystal mechanisms for waveguiding in the plane of the filter. Various methods are considered to provide this structuring, such as deep RIE holes through the full thickness of the membrane. Alternatively, patterning and etching of single quarter wave thicknesses at or near the spacer will create islands of antiresonant regions in the transverse plane to yield lateral guided-wave confinement. Confinement will permit much smaller devices with spot sizes on the order of 3 µm instead of the minimum of 62 µm available using Gaussian beam optics, and will also enable optical instead of resistive heating of the membrane by delivering green light to the filter, eliminating the distortions caused by metallic heater circuits and reducing the required power from 100 mW possibly to 5 mW.
The advantages of low cost amplifier solutions in single-channel link extender or loss compensator systems cannot be fully realized unless the ASE noise around the signal peak is removed. Doing so requires a cost-effective solution with high performance, including low insertion loss (<-2.5dB), low PDL (<-0.25dB), low power operation (<200mW), and fast tuning (<1sec). We have successfully fabricated and packaged a tunable ASE filter into a small form-factor 2-port package which meets these requirements. We obtain filter properties at both the chip and package-levels and examine filter performance operating under optically open and closed loop control.