Ultra-compact, mass-producible photonic crystal wavelength divider Realization of ultra-compact, mass-producible wavelength divider

We have fabricated a wavelength demultiplexer for WDM communications using photonic crystals. A wavelength demultiplexer is a device that splits the integrated signal back to its original state in WDM communications. Figure 1(b) shows a scanning electron micrograph of the fabricated device, and Figure 1(c) illustrates the operating principle of the wavelength demultiplexer. Integrated signals are input from the left side of Figure 1(c) through a silicon (Si) thin-wire waveguide, and each signal is divided in the upper right direction. In this process, the signal passes through a structure called a width-changing resonator, which is shown in the enlarged figure at the upper left of Figure 1(c), and is then divided. By using a width-changing resonator, only certain signals can be passed through. We chose the width-changing resonator structure because our previous research has shown that it is compatible with our fabrication method, photolithography. The lower part of Figure 1(d) shows the transmission spectrum of the fabricated wavelength demultiplexer, which is able to demultiplex eight signals. The upper part of Figure 1(d) shows that the wavelength divider can be adjusted to accommodate various signals by applying heat. For example, applying 0~30 mW of heat to a green signal can be adjusted to accommodate signals from 1568~1570 nm. The center of Figure 1(d) shows the eye pattern of a red signal with a 2.5 Gbps signal input. Compared with the reference eye pattern shown in the upper left corner, the 2.5 Gbps signal can be transmitted without any problem at all.

Our wavelength demultiplexer using photonic crystals has the advantage of a device area that is 200,000 times smaller than that of conventional wavelength demultiplexers made from glass. In addition, the fabrication method we used, photolithography, has the advantage of mass production compared to electron beam lithography, which has been used to fabricate photonic crystal structures in the past.