We report an optical–electrical (OE) oscillator using two new key components (a high-power integrated photoreceiver module and a low-driving-voltage lithium niobite (LN) Mach–Zehnder modulator (MZM)) to configure key parts of the entire OE oscillator system. A 60-GHz narrowband photoreceiver module integrated with a 60-GHz photodetector chip with a gain emphasis circuit and a 60-GHz high-power amplifier chip was designed and fabricated. By increasing the input photocurrent to 5 mA at 60 GHz, we successfully achieved a 1-dB power compression level of +16 dBm with good output linearity. The LN-based bulk MZM was specially designed to decrease the driving voltage to 1.5 V by optimizing both the waveguide and electrode length at high frequencies. Excellent performance with a -5 dB insertion loss at 60 GHz was achieved. The OE oscillator system was configured via a feedback loop using optical and electrical components, which primarily consisted of the newly developed photoreceiver and MZM through a 100 m–1 km long optical fiber. We successfully demonstrated -106 dBc/Hz at a 10-kHz offset near 60 GHz. The design and fabrication of the OE system are discussed in detail herein.
KEYWORDS: Digital signal processing, Radio optics, Forward error correction, Transmitters, Receivers, Standards development, Pulse signals, Power consumption, Optical transmission, Modulation
Future short-reach optical fiber communication links for datacenter and optical access applications would require not only high data rate but also low power/complexity. In this work, by leveraging a home-designed LiNbO3 intensity modulator with high slope-efficiency, we experimentally investigate a low-complexity/power optical pulse amplitude modulation (PAM) link with 300Gb/s data rate excluding FEC overhead and the following detailed merits: (1) at the transmitter side, no digital signal processing or a high-resolution wideband DAC is required, while only CMOS-class driving voltages less than 1 volt is needed; (2) at the receiver side, no optical or electrical amplifier is needed. It is found that for C-band 600m transmission, a symbol-spaced decision-feedback equalizer (DFE) with 91 feedforward taps and 1 feedback taps is sufficient to achieve a BER lower than the threshold of a low-power practical FEC. With these features, we expect that the overall system has low power consumption. A bitrate-distance product of >180Gb/s*km in C-band is achieved experimentally.
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