We present here a performance comparison of quantum-dash (Qdash) semiconductor amplifiers (SOAs) with three, five, eight, and twelve InAs dash layers grown on InP substrates. Other than the number of Qdash layers, the structures were identical. The eight-layer Qdash SOA gave the highest amplified spontaneous emission power (4.3 dBm) and chip gain (26.4 dB) at 1550 nm, with a 300 mA CW bias current and at 25 °C temperature, while SOAs with fewer Qdash layers (for example, three-layer Qdash SOA), had a wider ASE bandwidth (90 nm) and larger 3 dB gain saturated output power (18.2 dBm) in a shorter wavelength range. The noise figure (NF) of the SOAs increased nearly linearly with the number of Qdash layers. The longest gain peak wavelength of 1570 nm was observed for the 12-layer Qdash SOA. The most balanced performance was obtained with a five-layer Qdash SOA, with a 25.4 dB small-signal chip gain, 15.2 dBm 3 dB output saturated power, and 5.7 dB NF at 1532 nm, 300 mA and 25 °C. These results are better than those of quantum well SOAs reported in a recent review paper. The high performance of InAs/InP Qdash SOAs with different Qdash layers shown in this paper could be important for many applications with distinct requirements under uncooled scenarios.

This paper demonstrates a five-layer InAs/InP quantum-dash semiconductor optical amplifier (QDash-SOA), which will be integrated into microwave-photonic on-chip devices for millimeter-wave (mmWave) over fibre wireless networking systems. A thorough investigation of the QDash-SOA is conducted regarding its communication performance at different temperatures, bias currents, and input powers. The investigation shows a fibre-to-fibre (FtF) small-signal gain of 18.79 dB and a noise figure of 6.3 dB. In a common application with a 300 mA bias current and 25 °C temperature, the peak FtF gain is located at 1507.8 nm, which is 17.68 dB, with 3 dB gain bandwidth of 56.6 nm. Furthermore, the QDash-SOA is verified in a mmWave radio-over-fibre link with QAM (32 Gb/s 64-QAM 4-GBaud) and OFDM (250 MHz 64-QAM) signals. The average error vector magnitude of the QAM and OFDM signals after a 2 m wireless link could be as low as 8.29% and 6.78%, respectively. These findings highlight the QDash-SOA’s potential as a key amplifying component in future integrated microwave-photonic on-chip devices.

This study evaluates and compares four millimeter-wave (mmWave) radio-over-fiber (RoF) frequency multiplexing techniques considering InAs/InP quantum dash (QD) mode-locked lasers (MLLs) for optical carriers. The QD-MLL can generate multiple coherent optical carriers simultaneously with consistent frequency differences. Following heterodyne detection, the radio frequency linewidths of the QD-MLL can be minimized to 2.4 kHz. In this paper, four distinct RoF-based mmWave frequency multiplexing architectures are presented and compared experimentally. It is shown that the error vector magnitude of two 2 GBaud/s 16-QAM mmWave signals can reach as low as 7.1% after demultiplexing for all four techniques.

The phase noise of a radio frequency (RF) signal generated by beating two optical comb lines from an InAs/InP quantum-dash mode-locked laser (QD-MLL) in a radio over fiber (RoF) link is studied theoretically and experimentally. At the central office (CO), a QD-MLL with equidistant comb lines is employed. By selecting two comb lines and sending them to a remote radio unit (RRU) via an optical fiber, a RF signal is generated by beating the two comb lines at a photodetector (PD) in the RRU. The phase noise from each of the comb lines and the differential phase noise between the two comb lines are directly translated to the generated RF signal, which will deteriorate the transmission performance of a RoF link. In this study, we perform a thorough theoretical examination of the phase noise in the generated RF signal. Our findings reveal that the time delay mismatch between the two comb lines will create a phase noise to be added to the RF signal, and the differential phase noise between the comb lines will also create a phase noise to the RF signal. We show that the RF phase noise can be significantly reduced by a hybrid approach using analog time delay matching and digital phase noise compensation. As a result, utilizing a QD-MLL and the hybrid phase noise compensation approach, we successfully transmit a 16QAM orthogonal frequency division multiplexing (OFDM) signal at 10 Gb/s at 25 GHz over a 10 km optical fiber and a 2 m wireless span with improved performance. Error free transmission is achieved within the feedforward error correction (FEC) limits. This finding opens up new possibilities for phase noise management in broadband RoF transmission systems.

We demonstrate a compact mid-infrared (MIR) free-space optical transceiver based on packaged, fiber-coupled intracavity difference-frequency generation (DFG) and sum-frequency generation (SFG) modules operating at room temperature. The system achieves stable MIR generation, recovery of modulated signals up to 1.3 Gb/s, and outdoor validation over a 160 m rooftop link. Link stability measurements confirm robust performance and compatibility with silicon/GaAs detectors, overcoming the limitations of conventional infrared photodiodes. Future work includes rooftop high-speed bit error rate testing, drone-based ∼1km demonstrations, and balloon-assisted ∼25km trials, establishing wavelength conversion as a scalable foundation for next-generation, weather-resistant MIR satellite high-throughput communication systems and quantum communications with short-wavelength detectors.