Monolithically integrated coherent comb de-multiplexer using facetless semiconductor ring lasers

Due to the growing demand for faster Internet connections and the growth of services requiring high bandwidths, the migration of the networks to higher and higher bit rates is inevitable. The surge in data usage due to real time application in the entertainment, business and medical sector has placed tremendous pressure on the current infrastructure and its ability to keep up with the constant traffic increase. Wavelength division multiplexing (WDM) systems, which currently dominate long-haul optical transmission links employ guard bands between channels to avoid interference. This leads to inefficient use of the system bandwidth, which is limited by the erbium doped fibre amplifier (EDFA). A solution to this problem is to use coherent WDM (Co-WDM), or called optical orthogonal frequency division multiplexing (OFDM) to increase the bandwidth efficiency. In Co-WDM or optical OFDM, the interference from adjacent orthogonal channels can be eliminated at the receiver end. Therefore, the spacing between adjacent channels can be reduced without using guard bands. Moreover, the series of individual lasers used in WDM networks can be replaced with a single coherent comb source. However, Co-WDM still requires the use of discrete bulky components, such as narrow band filters to operate as a comb demultiplexer, modulators and multiplexer. To justify the potential move from WDM to Co-WDM a significant reduction in cost, size and production time is necessary. The photonic integrated circuit (PIC) offers an attractive solution to integrate all components on a single chip. The vision of the larger research project was to design and fabricate a fully integrated Co-WDM transceiver. The initial demonstration PIC will comprise an integrated coherent comb generator, a comb filter and an integrated electro-absorption modulator (EAM). However, this work mainly focused on the filter aspect of the PIC to demultiplex the narrowly spaced comb lines (<25 GHz). The filter has two functions: to demultiplex the comb lines, and to selectively amplify the individual comb line through injection locking. The filter is designed to be facet-less so that it can be suitable for integration with other devices. The fabrication process of the PIC employs Standard UV lithography and a regrowth-free process to further reduce the time, cost and complexity making it suitable for mass production. The process of optimizing the facet-less lasers in term of fabrication yield, consistency and filtering performance will be presented

Tunable L-band semiconductor laser based on Mach–Zehnder interferometer

A regrowth-free tunable L-band semiconductor laser based on Mach–Zehnder interferometer is presented in this paper. The laser exhibit a side mode suppression ratio of 38 dB and linewidth of 500 kHz. A tuning range of 30 nm across the L-band is also demonstrated

Regrowth-free single-mode semiconductor laser suitable for monolithic integration based on pits mirror

A regrowth-free single-mode laser that is made using standard UV photolithography is reported. The laser achieves a single-mode side-mode suppression ratio of 37 dB, linewidth of 450 kHz, and tunes across 2.9 nm and is suitable for monolithic integration as a distributed feedback replacement, due to a large free spectral range of 60 nm

On-chip investigation of phase noise in monolithically integrated gain-switched lasers

Phase noise in gain-switched lasers is investigated theoretically using the semiconductor laser rate equations and compared with the experimental results from monolithically integrated devices. The phase noise of a gain-switched laser is modelled both with and without injection-locking using the rate equations for a single-mode laser. Phase noise is found to increase with gain-switching, and decrease when injection-locked to a master laser. This trend is then observed experimentally on-chip with monolithically integrated devices without the use of an isolator

An integration-friendly regrowth-free tunable laser

This paper presents a single-mode tunable laser operating in the L band. The facetless design, along with a regrowth-free fabrication that does not require high-resolution lithography techniques, contribute to make the laser a suitable candidate for monolithic integration with other components. Vernier tuning is demonstrated over a range of 47nm, with sidemode suppression ratio (SMSR) values over 30dB and a linewidth of 800kHz

Integratable optical comb source for coherent communications systems

A coherent optical comb source is monolithically integrated. Optical combs were generated at 4 GHz and 5 GHz, with the combs produced independent of cleaved facets

An MMI-based tunable laser for integrated photonic circuits

A single mode, tunable semiconductor laser is presented for the L band. This facetless, regrowth-free laser shows a tuning range extending from 1564nm to 1611nm, with side-mode suppression ratio values over 30dB

Deeply etched inner-cavity pit reflector

A deeply etched pit reflector is presented in this paper. The pit is not depth sensitive and has a comparable reflection and loss to a slot. Moreover, a two-section 750 μm laser cavity based on the pits is demonstrated. The laser achieved a side-mode suppression ratio of 40 dB, a linewidth of 280 KHz, and tuning across 40 nm