Transparent In-Line Optical Power Monitoring Using InP/Si Hybrid Waveguide Phototransistor

• Published in: Journal of lightwave technology 2024-06, Vol.42 (12), p.4281-4288
• Main Authors: Akazawa, Tomohiro, Sumita, Kei, Monfray, Stephane, Boeuf, Frederic, Toprasertpong, Kasidit, Takagi, Shinichi, Takenaka, Mitsuru
• Format: Article
• Language: English
• Subjects: Heterogeneous integration; III-V compound semiconductor; Indium phosphides; Insertion loss; Integrated circuits; Integrated optics; Mach-Zehnder interferometers; Metal oxide semiconductors; Monitoring; Monitors; Optical device fabrication; Optical interferometry; optical phase shifter; optical power monitor; Optical switches; Optical waveguides; Phase shifters; Photoelectric effect; photonic integrated circuit; phototransistor; Si photonics; Silicon; trap-mediated photodetector; waveguide photodetector; Waveguides
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2024.3392471

In-line optical power monitors are essential building blocks in a Si programmable photonic integrated circuit (PIC) for calibrating optical phase shifters and correcting phase errors inevitably induced in a PIC. Nevertheless, current state-of-the-art in-line optical power monitors struggle to simultaneously achieve low optical loss and high responsivity. Here, we demonstrate an in-line optical power monitor using a waveguide phototransistor with an ultrathin InP membrane. The trap-mediated photodetection with the photogating effect of a phototransistor enables the detection of a weak light down to −44 dBm with an optical insertion loss of < 0.25 dB at a wavelength of 1550 nm. We measured the switching speed to be approximately 100 μs, which is sufficiently fast for optical power monitoring applications. Furthermore, a Mach-Zehnder interferometer (MZI) with an energy-efficient InP/Si hybrid metal-oxide-semiconductor (MOS) optical phase shifter was monolithically integrated with the proposed InP/Si hybrid phototransistor using the same fabrication process. The photocurrent of the phototransistor increased with the input light power modulated by the InP/Si hybrid MOS phase shifter, demonstrating in-line optical power monitoring using an InP/Si hybrid phototransistor. The proposed InP/Si hybrid phototransistor is promising for transparent optical power monitoring in a Si programmable PIC by III-V/Si hybrid integration.