Maximizing Fabrication and Thermal Tolerances of All-Silicon FIR Wavelength Filters

Abstract

Abstract-We propose a method to make silicon optical finite impulse response filters tolerant to fabrication (waveguide geometry) and ambient thermal variations. We experimentally demonstrate a Mach-Zehnder interferometer filter with fabrication and thermal tolerance, both separately and together. The fabrication-tolerant device measurements show a 20-fold improved tolerance to systematic waveguide linewidth variations with a wavelength shift of <60 pm/nm linewidth change. The fabrication-and thermal-tolerant device is possible using orthogonal polarizations in the two arms. The fabricated device shows a shift of less than ±65 pm/nm and a thermal drift smaller than ±15 pm/K over a wavelength range of 40 nm. Simulations show that this concept can be extended to multichannel filters.

Silicon Photonics Circuit Design: Methods, Tools and Challenges

“…As with device optimization, a circuit can be optimized better if the parameter space is somewhat extended. For instance, rather than using a single waveguide width for a filter delay line, using combinations of multiple widths can make filters more robust against linewidth variations, temperature gradients and other effects . Even though the response of all building blocks in the circuit is susceptible to fluctuations, the overall circuit is designed to cancel out these variations.…”

“…For instance, rather than using a single waveguide width for a filter delay line, using combinations of multiple widths can make filters more robust against linewidth variations, temperature gradients and other effects. [156][157][158][159] Even though the response of all building blocks in the circuit is susceptible to fluctuations, the overall circuit is designed to cancel out these variations. This relies on the assumption that the variations between circuit components is similar and correlated.…”

Experimental Extraction of Effective Refractive Index and Thermo-Optic Coefficients of Silicon-on-Insulator Waveguides Using Interferometers

“…For extraction of the TO coefficient of a waveguide, the wavelength sensitivity with respect to temperature needs to be measured and it is given by [4] :…”

“…Effective index changes can therefore cause a wavelength shift of a filter: in silicon wire waveguides this shift is approximately 1 nm for 1 nm of waveguide width change and around 1.4 nm for 1 nm change in waveguide thickness. Similar to geometry variations, local and environmental temperature fluctuations can cause a change in effective index: since silicon has a high thermo-optic (TO) coefficient of 1.86 × 10 −4 K −1 , this can result in a filter wavelength shift of 80 pm/K [4].…”

Coarse wavelength division multiplexer on silicon-on-insulator for 100 GbE

“…There are different methods proposed to maximizing the fabrication and thermal tolerances of filters such as passive compensation [2] or flattening the channel pass band responses [3]. Passive compensation is sometimes limited by narrow bandwidth responses due to the use of different waveguide widths or polarization.…”