Design and Performance of Low-Power, High-Speed, Polarization-Independent and Wideband Polymer Buried-Channel Waveguide Thermo-Optic Switches

This paper analytically and experimentally investigates and compares the characteristics of two kinds of polymer buried-channel waveguide thermo-optic switches such as 1) a multimode interference (MMI) switch using a single MMI coupler and 2) a Mach–Zehnder interferometer (MZI) switch. Especially, the MZI switch experimentally exhibited low-power consumption of 3.5 mW, high-speed with a response time of less than 200 μs, polarization independence as well as in a wideband of about 80 nm. These low-power consumption, relatively high-speed, and polarization-independent switching characteristics are almost coincident with the designed ones. Furthermore, an improved MZI structure is proposed for lower switching power consumption, and it is expected below 0.5 mW with an enhanced thermal localization structure.

I. Introduction

PHOTONIC switches today are expected to be applied to various areas such as optical cross-connect switching, network protection switching, and optical delay/buffer switching in reconfigurable optical add-drop multiplexer systems. One of the crucial challenges for the optical communication fields these days, as the number of communication channels increases, is to reduce power consumption and increase cost-effectiveness. Photonic switches are ones of the vital components that have to meet these challenges. Among various kinds of photonic switches depending on applications, those using thermo-optic (TO) effect operating even in ms-order response times seem valuable for optical cross-connect, channel selectable switching, and even protection switching. So far, reported optical cross-connect switches utilizing TO effect operate in a few to tens of milliseconds of response time and with relatively high power consumption. Common materials used for TO switches include Si [1] and silica [2] , but issues such as high power consumption and polarization dependence still need to be solved. Due to the high thermal conductivity of Si, fast TO switching can be realized for silicon-on-insulator materials where a response time of less than 700 ns was reported. Conversely, high conductivity of Si raises a disadvantage since large driving powers are required for localized index modulation. To compensate for this issue, silicon-silica hybrid devices had been introduced to operate with a switching power consumption of less than 50 mW [3] . Introducing etched trenches around a silicon core, a power consumption was reduced further to 20 mW [4] and even down to 0.6 mW [5] using a suspended silicon waveguide. Through this immense complexity of design and fabrication, power consumption in the sub-mW regime was demonstrated for the first time despite the fact that these switches had, on the contrary, longer response time in a few milliseconds due to large device thicknesses. In addition to their large footprint requirements, cost-ineffectiveness is another major disadvantage.