In this work, self-mode-locking of 100 GHz mode-locked pulses from a single-section InP quantum-dash-based laser chip whilst employed in external cavity geometry at 1550nm is investigated. The chip is operated at a forward current marginally above its monolithic operation's lasing threshold. Ultrashort pulses with 1 ps pulse- width were obtained by compensating the chirp by a single mode fiber (SMF).
In this work, a comparison of self-mode-locking of a 100 GHz repetition-rate monolithic diode as a stand-alone laser source and whilst employed in an external cavity arrangement at 1550 nm is reported. We operated our chip at a forward current slightly above the monolithic chip's lasing threshold and compensated the chirp by a single mode fiber. Ultrashort pulses with 1 ps pulse-width were generated. Changes in the dispersion compensation parameters due to the changed cavity dispersion were analyzed.
The integration of optical sources in Si photonic transceivers has relied so far on externally coupled III-V laser dies within the assembly. These hybrid approaches are however complex and expensive, as there are additional cost-increasing factors coming from the redundant testing of the pre- and post-coupled laser photonic chips. Further optimization of Photonic Integrated Circuits (PICs) cost and performance can be obtained only with radical technology advancements, such as the “holy grail” of Silicon Photonics; the monolithic integration of III-V sources on Si substrates. MOICANA project funded by EU Horizon 2020 framework targets to develop the technological background for the epitaxy of InP Quantum Dots directly on Si by Selective Area Growth with the best-in-class, in terms of losses and temperature sensitivity, in a CMOS fab, i.e. the SiN waveguide technology. In addition, MOICANA will develop the necessary interface for the seamless light transition between the III-V active and the SiN passive part of the circuitry featuring advanced multiplexing functionality and a combination of efficient and broadband fiber coupling. Through this unique platform, MOICANA aims to demonstrate low cost, inherent cooler-less and energy efficient transmitters, attributes stemming directly from the low loss SiN waveguide technology and the QD nature of the laser’s active region. MOICANA is targeting to exploit the advantages of the monolithic integrated PICs for the demonstration of large volume single-channel and WDM transmitter modules for data center interconnects, 5G mobile fronthaul and coherent communication applications.
Silicon photonics technology has demonstrated, over the years, Photonic Integrated Circuits (PICs) relying on Si or Si3N4 materials that feature advanced functionalities for a wide area of applications. However, the fabrication of such PICs is usually compatible only with Front-End-of-Line (FEOL) processes that render very difficult post processing of the involved chips towards providing efficient interfaces with optical sources. This is a major problem for the next generation photonic circuits that are expected to co-integrate III-V laser sources on the Si substrate in a monolithic way, as the coupling interface between the active and the passive part of the PIC should be developed after the epitaxy and the fabrication of the lasers. In this work, we report on the development of a novel Silicon Rich Nitride (SRN) material with low stress and high refractive index (n<3.16), close to that of InP and InGaAsP which are commonly utilized for the laser sources. The SRN has been characterized with spectroscopic ellipsometry and Fourier-Transform Infrared Spectroscopy for estimation of complex refractive index and hydrogen content in the film. Based on this material, a trilayer stack has been developed for the formation of waveguides compatible with the Back-End-of-Line (BEOL) processes, while propagation losses have been extracted through cut-back measurements. These experimental results were then inserted as input parameters in 2D- and 3D-FDTD simulations for the design of efficient interfaces between III-V lasers and Si3N4 waveguides providing coupling efficiencies that can reach 83.81% and back-reflections of 0.032%.
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