Abstract
A bidirectional free-space optical (FSO) communication through a 600-m free-space transmission is built, employing a phase modulation (PM) scheme and a remotely injection-locked distributed feedback laser diode (DFB LD) for presentation. With optimum injection locking, a DFB LD is excellent for duplex transceiver operations. An injection-locked DFB LD not only operates as a PM-to-intensity modulation converter with an optical detector, but also functions as an upstream optical carrier. To be the first one of employing a remotely injection-locked DFB LD to detect a phase-modulated 25-Gb/s/25-GHz four-level pulse amplitude modulation (PAM4) passband signal, the DFB LD with remote injection locking is successfully intensity-modulated with an upstream 25-Gb/s non-return-to-zero (NRZ) signal. Good bit error rate performance and clear PAM4/NRZ eye diagrams show that this FSO communication can use a remotely injection-locked DFB LD to detect the downstream phase-modulated PAM4 signal and concurrently deliver an upstream intensity-modulated NRZ signal. This bidirectional 25-Gb/s/25-GHz (downstream)/25-Gb/s (upstream) FSO communication is prominent due to its enhancement in two-way high-speed optical wireless communications.
Highlights
W IRELESS broadband access (WBA) is attractive for supplying present and emerging technologies such as highspeed Internet, virtual/augmented reality, 4K/8K high-definition video transmission, and 5G/6G mobile telecommunication [1]– [6]
A bidirectional free-space optical (FSO) communication with downstream phasemodulated 25-Gb/s/25-GHz PAM4 passband signal and upstream intensity-modulated 25-Gb/s NRZ baseband signal through a 600-m free-space transmission is established
With optimal injection wavelength and injection power, a remotely injection-locked distributed feedback laser diode (DFB LD) is sufficient for a duplex transceiver
Summary
W IRELESS broadband access (WBA) is attractive for supplying present and emerging technologies such as highspeed Internet, virtual/augmented reality, 4K/8K high-definition video transmission, and 5G/6G mobile telecommunication [1]– [6]. Increasing demands are pushing the requirements of long-range wireless access and high transmission capacity. Compared with RF-based WBA, FSO communication is enhanced with free-space link of hundreds of meters and data rate of tens of gigabits [7]–[12]. Atmospheric turbulence because of thick fog or heavy rain will affect FSO communication’s link availability and bring on poor performance. As for the eye safety problem of FSO communications, people have a natural aversion to laser light and are liable to turn their heads or close their eyes if exposed, meaning that people will not stare at the laser light due to natural reaction. The risk of eye damage can be alleviated since people’s natural reaction makes it difficult to expose the eyes over a long time
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