The research group led by Fang Qing at Kunming University of Science and Technology has proposed and studied a highly low-crosstalk arrayed waveguide grating structure on a Silicon-On-Insulator (SOI) platform. In this arrayed waveguide grating, independent micro-ring resonators are integrated on each output channel. By applying a bias voltage to the individual thermo-optic electrodes of each micro-ring, the control of micro-ring resonance peak shift is achieved, ensuring wavelength matching with the focused output of the arrayed waveguide grating. This accomplishes dual filtering of the target wavelength and significantly reduces crosstalk between adjacent output channels of the arrayed waveguide grating. The integration of these low-crosstalk micro-rings offers a new solution for wavelength-division multiplexing in on-chip optical communication.

Figure 1. The schematic diagram of a low-crosstalk silicon photonic arrayed waveguide grating structure based on dual filtering effects.

The Arrayed Waveguide Grating (AWG) is a critical wavelength-division multiplexer in silicon photonics integrated chips. In view of the demand for high-speed data transmission, research on silicon photonics integrated devices has focused on high-speed transmission characteristics, making the Silicon-On-Insulator (SOI) wafer with a thin (220nm) top silicon layer the preferred choice for device design. However, achieving satisfactory channel crosstalk characteristics on thin top silicon SOI chips with conventional silicon-based AWGs is challenging. This is primarily due to significant phase errors caused by deviations between the existing process conditions and the design in nanowire waveguides with high refractive index cores. AWGs are highly sensitive to phase errors, and large phase errors result in poor channel crosstalk. The crosstalk performance of AWGs on thin top silicon layers represents a bottleneck that limits their widespread application.

Currently, the commonly employed approach to reduce channel crosstalk in arrayed waveguide gratings (AWGs) is cascading, where the wavelength output of each channel is filtered again. However, this method results in higher insertion loss and device size. Addressing the aforementioned challenges, Professor Fang Qing and Associate Professor Chen Hua from the School of Science at Kunming University of Science and Technology have proposed and investigated a low-crosstalk arrayed waveguide grating integrated with micro-ring resonators. Their relevant work was published in Chinese Optics Letters, Volume 22, Issue 3, 2024 (Heming Hu, Shipping Liu, Tianwen Li, et al. Ultra low crosstalk arrayed waveguide grating integrated with tunable micro-ring filter array. Chinese Optics Letters. 2024, Vol.22(3), 031303) and was selected as the cover of the current issue.

This cover demonstrated a ultra-low crosstalk AWG, which is composed of traditional AWG cascaded with tunable MRRs on the SOI platform. By overlap the filter responses of the two filters, the crosstalks between adjacent channels are greatly suppressed and only about 0.5 dB additional loss is induced.

Figure 2. Measured spectra of AWG. (a) Reference normal AWG; (b) ultralowcross talk AWG integrated with MRRs.

Figure 2 presents a comparison of the measured spectra of output channels from a conventional arrayed waveguide grating (AWG) and a low-crosstalk arrayed waveguide grating integrated with micro-rings. The designed low-crosstalk arrayed waveguide grating used in the fabrication has a channel spacing of 3.2 nm, a micro-ring resonator free spectral range (FSR) of 12.8 nm, and a center wavelength of 1550 nm. By measuring the eight output channels of the ultra-low crosstalk arrayed waveguide grating (Figure b), the crosstalk range between adjacent channels was measured to be between -36.6 dB and -45.1 dB. Compared to the average crosstalk of approximately -16.7 dB in the conventional AWG (Figure a), the introduction of the micro-ring filter structure resulted in a minimum reduction in crosstalk of 19.9 dB between adjacent channels, with a corresponding reduction in the baseline noise of about 23 dB. The low-crosstalk AWG exhibited an increase in insertion loss of approximately 0.5 dB compared to the conventional AWG, with the additional loss primarily attributed to the micro-ring resonator, consistent with the independent micro-ring characterization results.

Link：https://www.researching.cn/articles/OJ45415308f21eb314