Modulation bandwidth enhancement of directly modulated semiconductor lasers (DMLs) has attracted broad interest to accommodate the tremendously growing demand for network traffic. In this paper, a monolithically integrated mutually coupled (IMC) laser for the O-band is demonstrated both numerically and experimentally. The direct modulation bandwidth was enhanced utilizing a photon–photon resonance (PPR) effect based on the mutual injection-locking technique. The IMC laser consisted of two distributed feedback (DFB) laser sections with a semiconductor optical amplifier (SOA) section in between. The relationship between the PPR frequency and SOA length was analyzed numerically to achieve a flat modulation response by optimizing the SOA length. Then, an enhanced 3-dB bandwidth of 38.7 GHz was realized experimentally, a nearly threefold enhancement over the modulation bandwidth of a solitary DFB laser at the same bias. Moreover, clear open eyes up to 40 Gb/s transmission over a 25-km single-mode fiber were achieved. Although the dynamic extinction ratio of the eye diagram was 1.1 dB, it can be further improved by increasing the mutual injection locking range of the IMC laser.

A microwave frequency comb (MFC) generator based on an integrated mutually coupled (IMC) distributed feedback (DFB) laser is demonstrated. The proposed MFC generator is simple and compact, only consisting of an IMC laser, a microwave signal generator, and a photodetector. By adjusting the bias currents of the three sections of the IMC laser and the modulation parameters, the bandwidth of the MFC can be significantly enhanced compared to the case adopting a solitary DFB laser. The characteristics of the MFC with the tuning current and the modulation parameters were investigated experimentally to determine the optimum operating condition. A broadband MFC with 40 GHz bandwidth within a 15 dB amplitude variation was achieved under a modulation frequency of 2 GHz.

Synchronized dual-wavelength narrow-linewidth lasers and a wideband frequency-tunable optoelectronic oscillator (OEO) are simultaneously realized using mutual-injection-locked distributed feedback (DFB) lasers. The two laser modes serve as the seeding light and a microwave photonic filter for optoelectronic oscillation. Mutual-injection locking between the two DFB lasers through a delay fiber loop results in synchronized narrow-linewidth operation. Microwave tuning from 19 to 41 GHz has been obtained through thermal-tuning of the DFB lasers, with the single-sideband phase noises below -100 dBc/Hz at a 10-kHz frequency offset from the carrier. Laser linewidth has been reduced from several-MHz to kHz with a linewidth reduction factor over 104.

A wavelength-tunable chaotic optical signal generation and on-chip O/E conversion scheme based on an integrated laser-photodiode chip subject to filtered optical feedback is proposed and experimentally demonstrated. The integrated chip consists of a Fabry-Perot (FP) gain section and a photodiode, which was fabricated on an n-InP substrate with the same active material. By applying a filtered feedback signal to the FP gain section, wavelength-tunable chaotic carrier ranging from 1576 to 1587 nm was achieved. On-chip microwave chaotic signal generation with a standard bandwidth over 5.5 GHz was obtained using the integrated photonic chip.

A simple dual-frequency laser Doppler velocimeter using a monolithically integrated dual-mode amplified feedback laser as the dual-frequency light source is proposed and experimentally demonstrated. A preliminary result of a longitudinal velocity 327.9 μm/s was measured.

A photonic approach to generating an optoelectronic oscillator (OEO) based on an integrated mutually coupled (IMC) distributed feedback (DFB) laser is reported. Compared with the traditional construction of an OEO, the IMC-DFB has functions of the laser source, intensity modulator, and microwave photonic filters (MPFs), which could simplify the OEO scheme. An optical feedback loop (O-Loop) and an optoelectronic feedback loop (OE-Loop) are used simultaneously in the proposed scheme. The optical loop was used to reduce the optical linewidth of the IMC-DFB to improve the quality of the laser source in the OE loop. The IMC laser consisted of two distributed feedback (DFB) laser sections with a semiconductor optical amplifier (SOA) section in between. The optical linewidth of the IMC-DFB is reduced from 5.86 MHz to 3.94 kHz due to the feedback of the optical loop. By tuning the current of the SOA and DFB sections, tunable microwaves ranging from 24.9 to 46.5 GHz with single-sideband (SSB) phase noise below -110 dBc/Hz at a 10 kHz offset from the carrier were realized.