Experimental Demonstration of a Novel Microwave Photonics Ring Modulator With Reduced Driving Power

We propose and experimentally characterise a novel microwave (MW) ring modulator design that resonantly enhances the electro-optic modulation of MW signals with center frequencies matching an integer multiple of the ring's FSR. We show that the best performance is achieved by placing the MW phase modulator in the ring's coupling section that consists of a Mach-Zehnder structure with asymmetric splitters. We fabricate the device in the SMART Photonics InP multiproject wafer run, and experimentally demonstrate that at MW frequencies corresponding to one and two times the ring's FSR, 9.5 GHz and 19 GHz respectively, our modulator enhances the generated MW output power up to 12.6 dB as compared to the equivalent Mach-Zehnder modulator, over a bandwidth of 3.8 GHz. The experiments further show that this bandwidth can be tuned to a larger value at the expense of a lower enhancement factor and this by changing one of the bias voltages. Tuning this voltage also allows to optimise the linearity of the modulator, thus demonstrating the reconfigurability of the device. Finally, we show that the novel design is not foundry-specific and detail how it can be employed to improve the performance of modulators that are fabricated by other foundries than SMART Photonics. Our design thus paves the way for the realization of devices that operate at low driving powers and can be manufactured in relatively mature fabrication processes, which are two of the key requirements for many applications such as the upcoming microwave and millimeter bands of 5G networks.