Free space optical (FSO) communication is considered a critical part of future ICT infrastructure, particularly in non-terrestrial communication segments. In this context, the ability to achieve fast and reliable FSO propagation through long-distance atmospheric channels is the most important factor in choosing technological solutions. One property of optics directly related to this factor is the choice of wavelength. It has been identified that the mid-infrared (mid-IR) regime, which includes two atmospheric transmission windows—the mid-wave IR (MWIR, 3-5 μm) and the long-wave IR (LWIR, 8-12 μm)—can potentially offer a promising solution for achieving such performance. Additionally, viable semiconductor sources and detectors that support high-speed and efficient signal transmission are also considered critical to generating sufficient critical mass to advance the application of mid-IR FSO. Unipolar quantum optoelectronics, including quantum cascade lasers (QCL), Stark modulators, quantum cascade detectors (QCD), and quantum-well IR photodetectors (QWIP), among other components, emerge as potential candidates to build such FSO subsystems and systems. We present our recent efforts in conducting subsystem and system-level studies with different variants of these unipolar quantum optoelectronics and demonstrate the potential for feasible transmitter and receiver performance in a laboratory environment. We also discuss the key challenges and considerations of such technologies towards practical development. Finally, we summarize recent research and development efforts worldwide in advancing this highly promising direction.

The recent AI boom requires more focus on energy-efficient and scalable optical interconnects. Silicon Photonics is enabling technology to satisfy growing demand. However, the lack of lasers and high-performance modulators hinders wide-scale adoption. Therefore, we present a heterogeneously integrated Indium Phosphide electro-absorption modulator with Silicon waveguides. We demonstrate up to 256 Gb/s on-off keying, 340 Gb/s 4-level pulse amplitude modulation, 375 Gb/s 6-level pulse amplitude modulation, and 360 Gb/s 8-level pulse amplitude modulation transmission over 500 m and 6 km of single-mode fiber with performance satisfying requirements of 6.25% overhead hard-decision forward error correction threshold of 4.5x10(-3). Additionally, we investigate the modulator at 200 Gb/s per lane scenarios, demonstrating excellent performance with a simple seven-tap feed-forward equalizer.

We demonstrate record unamplified transmissions of 256 Gbaud OOK, 155 Gbaud PAM4 and 128 Gbaud PAM6 using a C-band differential-drive SiP TW-MZM, achieving BER performance below the 6.25% HD-FEC threshold after 100 m SMF transmission.

We show a record optical amplification-free 400 Gbps PAM4/6/8 net bitrate transmission in the O-band over 500-meter SMF with performance below 6.25% OH HD-FEC threshold using 1 Vpp driving voltage on the TFLN MZM.

Terahertz (THz, 0.3–10 THz) radar systems have garnered significant attention due to their superior capabilities in high-precision and robust sensing. However, the susceptibility to jamming, along with the sensing precision loss and ranging ambiguity induced by inflexible implementation of the conventional radar signal source, presents major challenges to the practical deployment of THz radars. Herein, a flexible photonic chaotic radar system is proposed at the THz band and investigate the ranging performance in precision and ambiguity. The photonic heterodyne detection scheme facilitates the generation of optoelectronic feedback loop-based THz chaos at 300 GHz, achieving a seamless connection between THz domains and optical domains. The system is experimentally demonstrated its superior performance of sub-centimeter resolution with 0.9345 cm and ranging unambiguity simultaneously. This work bridges the THz gap in the practical deployment of chaos theory and will pave the way for a new regime of THz radar empowered by chaos.

This paper explores the role of photonic terahertz technologies in integrated sensing and communication systems, focusing on integrated waveform design, optical processing, and algorithms to enhance communication capabilities and sensing performance.

We present a sensing-assisted multipath channel estimation method for photonic terahertz integrated sensing and communication systems, achieving ~8 dB compensation gain in a 20 Gbps over 20 m multipath 124 GHz wireless communication link.

This paper explores photonic-based analog fronthaul solutions for 6G, highlighting their effectiveness in meeting the RF requirements of standards, supporting future distributed-MIMO networks, and providing insights into prospective solutions for radios in potential 6G bands.

We demonstrate record transmission of 256 Gbaud OOK, 175 Gbaud PAM4 and 145 Gbaud PAM6 using a C-band differential-drive silicon photonics traveling-wave Mach-Zehnder modulator, achieving BER performance below the 6.25 % HD-FEC threshold after 100 m SMF transmission.

Development of Data Center based computing technology require energy efficient high-speed transmission links. This leads to optical amplification-free intensity modulation and direct detection (IM/DD) systems with low complexity equalization compliant with IEEE standardized electrical interfaces. Switching from on-off keying to multi-level pulse amplitude modulation would allow to reduce lane count for next generation Ethernet interfaces. We characterize 106.25 Gbaud on-off keying, 4-level and 6-level pulse amplitude modulation links using two integrated transmitters: O-band directly modulated laser and C-band externally modulated laser. Simple feed forward or decision feedback equalizer is used. We demonstrate 106.25 Gbaud on-off keying links operating without forward error correction for both transmitters. We also show 106.25 Gbaud 4-level and 6-level pulse amplitude modulation links with performance below 6.25% overhead hard-decision forward error threshold of 4.5 × 10^-3. Furthermore, for EML-based transmitter we achieve 106.25 Gbaud 4-level pulse amplitude modulation performance below KP-FEC threshold of 2.2 × 10^-4. That shows that we can use optics to support (2x)100 Gbps Ethernet on single lambda at expense of simple forward error correction.