Padraic E. Morrissey

Monolithically integrated low linewidth comb source using gain switched slotted Fabry-Perot lasers

A monolithically integrated low linewidth optical comb is demonstrated by gain switching of a three-section laser device. The device consists of a slave and master section separated by a shared slotted mirror section. Wavelength tunability has been demonstrated by varying the electrical bias of each section. The number of comb lines is shown to almost double with the addition of optical injection from the master section into the slave. The unmodulated device has a full width half max linewidth of ∼ 500 kHz, while the comb line set were measured to be ∼ 600 kHz, with little degradation as a result of gain switching. The FSR (free spectral range) of the demonstrated comb is 4 GHz, which is tunable within the bandwidth of the device, with a central wavelength of 1580.3 nm.

Coupled Cavity Single-Mode Laser Based on Regrowth-Free Integrated MMI Reflectors

A photonic integrated circuit is demonstrated that couples three Fabry-Pérot (FP) lasers together via an integrated star coupler. The FP lasers rely on a common cleaved facet and individual multimode interference reflectors (MIRs) for lasing operation. The MIRs are monolithically integrated with each FP laser using a single growth step, which allows for epitaxial regrowth-free processing. By suitable independent tuning of each Fabry-Pérot, a single mode operation and a mode selection can be attained from the coupled cavity system. The mode selectivity and side-mode suppression ratios of ~40 dB are demonstrated.

10 Gb/s InP-based Mach-Zehnder modulator for operation at 2 μm wavelengths

We report on the first InP-based Mach-Zehnder modulator (MZM) employing quantum-confined Stark effect (QCSE) for operation around 2000 nm. The polarization sensitive device is based on 15 compressively strained quantum wells and achieves an electro-optic (EO) bandwidth of at least 9 GHz, with a DC extinction ratio of ~9 dB, and a V(π)L ~9.6 V.mm. We demonstrate back-to-back communication with a 10 Gb/s pseudo-random bit sequence (PRBS) of length 2(7)-1 at a wavelength around 2000 nm.

On-chip optical phase locking of single growth monolithically integrated slotted fabry perot lasers

This work investigates the optical phase locking performance of Slotted Fabry Perot (SFP) lasers and develops an integrated variable phase locked system on chip for the first time to our knowledge using these lasers. Stable phase locking is demonstrated between two SFP lasers coupled on chip via a variable gain waveguide section. The two lasers are biased differently, one just above the threshold current of the device with the other at three times this value. The coupling between the lasers can be controlled using the variable gain section which can act as a variable optical attenuator or amplifier depending on bias. Using this, the width of the stable phase locking region on chip is shown to be variable.

Monolithic Integration of Single Facet Slotted Laser, SOA, and MMI Coupler

We demonstrate a monolithically photonic integrated circuit (PIC) comprising a single facet slotted laser (SFSL), a semiconductor optical amplifier (SOA), and a 1 × 2 multimode interference (MMI) coupler. The integrated SFSL generates a tunable single longitudinal mode output, and utilizes a simplified fabrication process for the PIC when compared with distributed feedback or distributed Bragg reflector lasers by eliminating the epitaxial regrowth as well as the ebeam or holographically generated gratings. The integration technique is implemented by biasing the MMIs to transparency, which makes the fabrication comparable the standard ridge waveguide laser. The demonstrated PIC can be used as a 1 × 2 splitter or by integrating with other waveguide devices, such as laser, modulators, or SOAs, to realize different functionality.

Multiple coherent outputs from single growth monolithically integrated injection locked tunable lasers

We present a photonic integrated circuit (PIC) designed to create multiple coherent optical signals for the generation of coherent modulation formats, such as DPSK. A Multimode Interference Coupler (MMI) is monolithically integrated with single facet Slotted Fabry Perot (SFP) lasers at its input and output arms. In this work we show that light from a master SFP laser can be used to injection lock both output slave SFPs for use in the generation of coherent optical channels.

Using adiabatic coupling techniques in atom-chip waveguide structures

Adiabatic techniques are well-known tools in multi-level electron systems to transfer population between different states with high fidelity. Recently, it has been realized that these ideas can also be used in ultracold atom systems to achieve coherent manipulation of the atomic centre-of-mass states. Here, we present an investigation into a realistic setup using three atomic waveguides created on top of an atom chip and show that such systems hold great potential for the observation of adiabatic phenomena in experiments.

Three-coherent-output narrow-linewidth and tunable single frequency 1x2 multi-mode-interferometer laser diode

A 1x2 multi-mode-interferometer (MMI) laser diode was successfully designed and fabricated, which demonstrated three coherent outputs of tunable single frequency emission with more than 30dB side mode suppression ratio (SMSR), a tuning range of 25nm in C and L band, as well as 750 kHz linewidth. This 1x2 MMI laser could be expanded to more advanced configurations such as 1xN or MxN (M≥1, N>2) MMI lasers to achieve a multiple coherent output source. In addition, these lasers do not require material regrowth and high resolution gratings which can significantly increase the yield and reduce the cost.

Regrowth-Free Single Mode Laser Based on Dual Port Multimode Interference Reflector

This letter demonstrates an InP-based photonic integrated circuit that utilizes an etched facet and a dual port multimode interference reflector to create a lasing cavity. The laser was fabricated using UV lithography and did not require any epitaxial regrowth. A single deep etched slot produced single mode behavior due to the coupled cavity effect. By varying the bias of the two sub cavities, mode selectivity with a side mode suppression ratio of 30 dB is demonstrated.

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.