Phase shift optimization of III/V-on-bulk-Si DFB LD for single-mode stability.

A III/V-on-Bulk-Si DFB laser with a long phase shift section optimized for single-mode stability is presented. The optimized phase shift allows stable single-mode operations up to 20 times a threshold current. This mode stability is achieved by a gain difference between fundamental and higher modes maximized by sub-wavelength-scale tuning of the phase shift section. In SMSR-based yield analyses, the long-phase-shifted DFB laser showed superior performance compared to the conventional λ/4-phase-shifted ones.

Photonic ADC: overcoming the bottleneck of electronic jitter.

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated.

Compact, stable 1 GHz femtosecond Er-doped fiber lasers.

We demonstrate a high-repetition-rate soliton fiber laser that is based on highly doped anomalously dispersive erbium-doped fiber. By splicing an 11 mm single-mode fiber to the erbium-doped fiber, the thermal damage of the butt-coupled saturable Bragg reflector (SBR) is overcome. The laser generates 187 fs pulses at a repetition rate of 967 MHz with a measured long-term stability of more than 60 h.

High-repetition-rate, 491 MHz, femtosecond fiber laser with low timing jitter.

We demonstrate a soliton fiber laser based on an anomalously dispersive erbium-doped fiber butt-coupled to a saturable absorber mirror for passive mode locking. The laser generates 180 fs pulses at a repetition rate of 491 MHz and exhibits a timing jitter as low as 20 fs over the frequency range 1 kHz-10 MHz.

Scaling of passively mode-locked soliton erbium waveguide lasers based on slow saturable absorbers.

We assess the scaling potential of high repetition rate, passively mode-locked erbium-doped soliton lasers. Our analysis focuses on three recently demonstrated lasers using saturable Bragg reflectors (SBR) as the mode-locking element. We use the soliton Area theorem to establish the limitations to increasing the repetition rate based on insufficient intracavity pulse energy, SBR properties, and dispersion engineering. Finally, we examine possible approaches to alleviate these limitations by changing the laser's structure and composition.