Pulse-Width-Modulation-Based Silicon Photonics Receiver with Readout Circuitries for On-chip Optical Power Monitoring
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Pulse-Width-Modulation-Based Silicon Photonics Receiver with Readout Circuitries for On-chip Optical Power Monitoring Kangyeob Park, Jinsuk Ban and Won-Seok Oh∗ SoC Research Center, Korea Electronics Technology Institute, Seongnam 13509, Korea (Received 6 December 2019; revised 26 May 2020; accepted 26 May 2020) In this paper, a pulse-width-modulation (PWM)-based silicon photonics receiver for optical power monitoring that was realized using a 90-nm CMOS silicon-on-insulator (SOI) process is reported. By monitoring the DC or the AC power in the optical nodes and converting it into an electrical signal, large-scale photonic integrated circuits can acquire smartness and automation characteristics. The proposed PWM-based silicon photonics receiver can simply readout the optical power of target nodes without complex mixed-mode circuitries, such as analog-to-digital converters. The PWM receiver consists of a I-V amplifier, simple digital circuitries, free-running on-chip oscillators, and bias circuits. The receiver achieves a 10-nA detection limit, under a 1.5% detection error due to the quantization process of the PWM scheme. The receiver can operate as an on-chip optical power monitor for large-scale silicon-based photonic integrated circuits. Keywords: Pulse-width modulation, Silicon photonics, Optical receiver, Readout circuits DOI: 10.3938/jkps.77.916
I. INTRODUCTION Silicon photonics makes large-scale integration of the photonic devices possible. Due to the higher integration level, multi-functional, adaptive, and smart photonic devices recently become available with on-chip CMOS silicon-on-insulator (SOI) circuitries. For that, an on-chip optical-power-monitoring function is needed for monitoring and transferring information from the optical domain to the electrical domain. The optical receiver for monitoring purposes does not need high-speed operation; however, small area, low power, high sensitivity, and accuracy are required. For efficient signal processing on electrical domain, the final output format of the receiver has to be digital codes, so an analog-todigital conversion process is essential in monitoring circuits. For that, an analog-to-digital converter (ADC) is generally adopted; however, that would make the system too heavy for optical power monitoring. We propose pulse-width modulation scheme for converting analog photocurrent to digital electrical signal for compact power monitoring circuitries [1–3].
∗ E-mail:
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pISSN:0374-4884/eISSN:1976-8524
II. DESIGN, FABRICATION, AND MEASUREMENT OF A SILICON PHOTONICS RECEIVER Figure 1 shows a block diagram of the proposed silicon photonics receiver with adaptive frequency control. The receiver is composed of a silicon photodetector, I-V(t) converter, V(t)-to-PWM converter, PWM-to-digital converter, and clock generator with frequency controller. The limit of detection of a PWM-based optical receiver depends on the clock frequency. If lower photocurrents are to be monitored, a sufficient clock period is needed; that is, a lower clock frequency is re
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