Three-Port Optical Phase-Shifters and Modulators With Ultra-High Modulation Efficiency, Positive RF-Linking Gain, and Low Residual Amplitude Modulation

Rui Lin Chao,Zohauddin Ahmad,Yinchieh Lai,Jyehong Chen,Jin-Wei Shi

doi:10.1109/access.2020.2990956

Abstract

A three-port optical phase-shifter and Mach-Zehnder modulator (MZM) based on PNP-type bipolar junction transistor (BJT) is demonstrated. Significant plasma (injected carrier) induced changes of the refractive index for the optical waveguide become possible with an extremely small driving-voltage and a compact device size during operation of this BJT between the saturation and forward active modes. Devices with a standard MZM structure and a small foot-print (0.5 mm) exhibit a moderate optical insertion loss (2 dB), extremely small V π (0.18V) and P π (0.21mW), fast rise/fall time (~1ns), and a residue-amplitudemodulation (RAM) as small as 0.18 dB. Furthermore, thanks to the ultra-high modulation efficiency characteristic of our device, a +4.0 dB net RF-linking gain can be obtained under dynamic operation. Compared to 2-port (base-collector) forward bias operation, under three-port operation, the extra bias current from the base-emitter junction provides a lower V π (0.18 vs. 0.22 V), a smaller RAM (0.18 vs. 0.6 dB), and a larger RF-linking gain (+4 vs. -3.2 dB). The superior performances of the three-port to two-port operations can be attributed to the additional forward bias B-E junction being able to provide more injected carriers to induce stronger plasma effects for optical phase-shifting.

Highlights

Silicon photonics (SiPs) play a leading role in the development of technology ranging from radio frequency (RF) microwave photonics to sensing systems
We demonstrate three-port (PNP)-type bipolar junction transistor (BJT) based phase-shifters and Mach-Zehnder modulator (MZM) fabricated on a standard commercial Si-photonic foundry platform
During dynamic and static operation, our device operates in the saturation regions, which indicates that both the VEB and VCB junctions are under forward bias

Summary

Introduction

Silicon photonics (SiPs) play a leading role in the development of technology ranging from radio frequency (RF) microwave photonics to sensing systems. With a short device length (0.5 mm) and an acceptable insertion loss (2 dB), our device exhibits excellent performance in terms of fast rise time (tR ≈ 1ns), small driving-voltage and small power consumption for π phase-shift (Pπ : 0.21 mW; Vπ : 0.18 V), extremely small RAM (0.18 dB) [14], and a +4.0 dB net RF linking gain at an operating frequency of 100 MHz. Compared with our previous work [15], the doping profile is further optimized by greatly reducing the doping level in the p-type collector layer (from 3 × 1019 to 5 × 1017 cm−3).

Results

Conclusion