Local oscillators-free chip-enabled W-band wireless IM-DD PAM-4 data transmission with simultaneous dual-laser modulation and envelope detection.

Wireless data traffic is expected to exponentially increase in the future, and meeting this demand will require high data rate photonic-wireless links operating in the W-band (75-110 GHz). For this purpose, pulse-amplitude-modulation with four levels (PAM-4)-based intensity modulation and direct detection (IM-DD) photonic-wireless systems are preferred due to their simplified configuration. In this Letter, we present an experimental demonstration of an IM-DD PAM-4 photonic-wireless link in the W-band, leveraging a monolithic dual-laser photonic chip to enhance integration. Through injection-locking by an optical comb, the chip generates a W-band wireless signal via photo-mixing with a photodiode. This comb injection approach facilitates the phase correlation of the chip's two modes, resulting in a stabilized beat note. Additionally, the on-chip integration of the dual lasers enables the modulation of the two modes with a single modulator, improving the signal-to-noise ratio (SNR) while eliminating the need for extra splitters or combiners. Meanwhile, the envelope detector (ED) plays a crucial role in the simplified configuration, contributing to the overall decrease in size, weight, power, and complexity of the system. The integration of the chip-based phase-locked light source and the utilization of the ED thus signify noteworthy features of our experimental setup, which functions without the necessity of both optical and electrical local oscillators. PAM-4 signal modulation is simultaneously applied to the two coherent optical carriers. Our experiments have effectively transmitted 5 and 10 Gbaud PAM-4 W-band wireless signals in a cost-effective, lightweight, and straightforward configuration, achieving a line data rate of up to 20 Gbit/s economically. These experimental results demonstrate the practical potential of implementing fully integrated photonic-wireless transmitters.

Femtosecond pulse and terahertz two-tone generation from facet-free multi-segment laser diode in InP-based generic foundry platform.

In this paper, a monolithically integrated ∼1.55 µm semiconductor laser in the fourth harmonic colliding pulse mode locking configuration is reported. This device was developed within a multi-project wafer run at an InP-based active-passive generic foundry. The 1.66-mm Fabry-Pérot cavity is formed with two on-chip reflector building blocks rather than cleaved facets. In the cavity, three absorber sections symmetrically divide the cavity in four gain segments. This laser diode is able to emit 100-GHz pulse trains with 500-fs pulse duration as well as two-tone emissions with a frequency separation of 2.7 THz. The dependence of the spectral behavior on the forward bias current for gain sections and the reverse bias voltage for absorber sections are experimentally demonstrated.

InP femtosecond mode-locked laser in a compound feedback cavity with a switchable repetition rate.

A monolithically integrated mode-locked semiconductor laser is proposed. The compound ring cavity is composed of a colliding pulse mode-locking (ML) subcavity and a passive Fabry-Perot feedback subcavity. These two 1.6 mm long subcavities are coupled by using on-chip reflectors at both ends, enabling harmonic mode locking. By changing DC-bias conditions, optical mode spacing from 50 to 450 GHz is experimentally demonstrated. Ultrafast pulses shorter than 0.3 ps emitted from this laser diode are shown in autocorrelation traces.

Mode-locked laser with pulse interleavers in a monolithic photonic integrated circuit for millimeter wave and terahertz carrier generation.

This Letter presents a photonics-based millimeter wave and terahertz frequency synthesizer using a monolithic InP photonic integrated circuit composed of a mode-locked laser (MLL) and two pulse interleaver stages to multiply the repetition rate frequency. The MLL is a multiple colliding pulse MLL producing an 80 GHz repetition rate pulse train. Through two consecutive monolithic pulse interleaver structures, each doubling the repetition rate, we demonstrate the achievement of 160 and 320 GHz. The fabrication was done on a multi-project wafer run of a generic InP photonic technology platform.

1.8-THz-wide optical frequency comb emitted from monolithic passively mode-locked semiconductor quantum-well laser.

We report on an optical frequency comb with 14 nm (∼1.8 THz) spectral bandwidth at a -3 dB level that is generated using a passively mode-locked quantum-well laser in photonic integrated circuits fabricated through an InP generic photonic integration technology platform. This 21.5-GHz colliding-pulse mode-locked laser cavity is defined by on-chip reflectors incorporating intracavity phase modulators followed by an extracavity semiconductor optical amplifier as a booster amplifier. A 1.8-THz-wide optical comb spectrum is presented with an ultrafast pulse that is 0.35 ps wide. The radio frequency beat note has a 3-dB linewidth of 450 kHz and 35-dB SNR.

Integrated dual-laser photonic chip for high-purity carrier generation enabling ultrafast terahertz wireless communications.

Photonic generation of Terahertz (THz) carriers displays high potential for THz communications with a large tunable range and high modulation bandwidth. While many photonics-based THz generations have recently been demonstrated with discrete bulky components, their practical applications are significantly hindered by the large footprint and high energy consumption. Herein, we present an injection-locked heterodyne source based on generic foundry-fabricated photonic integrated circuits (PIC) attached to a uni-traveling carrier photodiode generating high-purity THz carriers. The generated THz carrier is tunable within the range of 0-1.4 THz, determined by the wavelength spacing between the two monolithically integrated distributed feedback (DFB) lasers. This scheme generates and transmits a 131 Gbits-1 net rate signal over a 10.7-m distance with -24 dBm emitted power at 0.4 THz. This monolithic dual-DFB PIC-based THz generation approach is a significant step towards fully integrated, cost-effective, and energy-efficient THz transmitters.