Ultrahigh-responsivity waveguide-coupled optical power monitor for Si photonic circuits operating at near-infrared wavelengths

Takaya Ochiai, Tomohiro Akazawa, Yuto Miyatake, Kei Sumita, Shuhei Ohno, Stéphane Monfray, Frederic Boeuf, Kasidit Toprasertpong, Shinichi Takagi and Mitsuru Takenaka ()
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Takaya Ochiai: The University of Tokyo
Tomohiro Akazawa: The University of Tokyo
Yuto Miyatake: The University of Tokyo
Kei Sumita: The University of Tokyo
Shuhei Ohno: The University of Tokyo
Stéphane Monfray: STMicroelectronics
Frederic Boeuf: STMicroelectronics
Kasidit Toprasertpong: The University of Tokyo
Shinichi Takagi: The University of Tokyo
Mitsuru Takenaka: The University of Tokyo

Nature Communications, 2022, vol. 13, issue 1, 1-8

Abstract: Abstract A phototransistor is a promising candidate as an optical power monitor in Si photonic circuits since the internal gain of photocurrent enables high responsivity. However, state-of-the-art waveguide-coupled phototransistors suffer from a responsivity of lower than 103 A/W, which is insufficient for detecting very low power light. Here, we present a waveguide-coupled phototransistor operating at a 1.3 μm wavelength, which consists of an InGaAs ultrathin channel on a Si waveguide working as a gate electrode to increase the responsivity. The Si waveguide gate underneath the InGaAs ultrathin channel enables the effective control of transistor current without optical absorption by the gate metal. As a result, our phototransistor achieved the highest responsivity of approximately 106 A/W among the waveguide-coupled phototransistors, allowing us to detect light of 621 fW propagating in the Si waveguide. The high responsivity and the reasonable response time of approximately 100 μs make our phototransistor promising as an effective optical power monitor in Si photonic circuits.

Date: 2022
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DOI: 10.1038/s41467-022-35206-4

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