Soft Lithography Reproduces Integrated Optical Devices

Daniel S. Burgess

As more attention is paid to the use of polymeric materials for optical elements, researchers have been investigating soft lithography as a means to reduce fabrication costs by replicating many devices from a single master. Now a team at California Institute of Technology in Pasadena has demonstrated that the technique is suitable for the production of microring optical resonators for bandpass filters in telecommunications applications.

Microring optical resonators that were reproduced by soft lithography in polymer have extinction ratios and resonance line shapes similar to the master device.

In the demonstration, the scientists created a master device by electron-beam lithography of SU-8 epoxy on silica. The microring resonator featured a 200-µm-diameter ring coupled to a 2-µm-wide waveguide. They then coated the device with poly(dimethylsiloxane), which they baked at 80 °C for one hour to produce the master mold. To reproduce the device, they stamped drops of SU-8 on new silica substrates with the mold and cured them under ultraviolet radiation.

To compare the performance of the master and the reproduced devices, they analyzed the transmission spectra of the resonators at wavelengths around 1550 nm. They found that the notch positions had shifted due to slightly different effective indices, but that their resonance line shapes were similar and their extinctions both were in the range of –9 to –10 dB.