Monolithic and Heterogeneous Integration

Praveen K. J. Singaravelu ,Sharon M. Butler ,Robert N. Sheehan ,Alexandros A. Liles ,Stephen P. Hegarty and Liam O’Faolain

We present a design methodology for hybrid lasers to realise mode-hop free operation by controlling the cavity mode spacing. In this study, a compact hybrid photonic crystal laser (H-PhCL) was employed which allowed a reduction of the Fabry–Perot length of the laser cavity and eliminated the need for an active mode stabilisation mechanism in order to realise mode-hop free operation. The H-PhCL was formed by butt-coupling a reflective semiconductor optical amplifier (RSOA) with a two-dimensional silicon (Si) photonic crystal (PhC) cavity. Continuous stable single frequency operation with >40 dB side-mode suppression ratio (SMSR) of the laser was achieved for gain currents of up to 100 mA, i.e., up to four times the threshold current. The shorter length of the laser cavity enabled single frequency operation due to the selection of a single longitudinal mode by the PhC narrowband reflector. Various longitudinal mode spacing regimes were studied to explain the mode-hop free characteristics of the H-PhCL. The proposed hybrid laser design methodologies can be adapted to eliminate mode-hopping in laser wavelength.

Open access paper here.

Enrica E. Mura*, Agnieszka M. Gocalinska, Megan O’Brien, Ruggero Loi, Gediminas Juska, Stefano T. Moroni, James O’Callaghan, Miryam Arredondo, Brian Corbett, and Emanuele Pelucchi
Abstract: We investigated and demonstrated a 1.3 μm band laser grown by metalorganic vapor-phase epitaxy (MOVPE) on a specially engineered metamorphic parabolic-graded InxGa1–xAs buffer and epitaxial structure on a GaAs substrate. Bottom and upper cladding layers were built as a combination of AlInGaAs and InGaP alloys in a superlattice sequence. This was implemented to overcome (previously unreported) detrimental surface epitaxial dynamics and instabilities: when single alloys are utilized to achieve thick layers on metamorphic structures, surface instabilities induce defect generation. This has represented a historically limiting factor for metamorphic lasers by MOVPE. We describe a number of alternative strategies to achieve smooth surface morphology to obtain efficient compressively strained In0.4Ga0.6As quantum wells in the active layer. The resulting lasers exhibited low lasing threshold with a total slope efficiency of 0.34 W/A for a 500 μm long-ridge waveguide device. The emission wavelength is extended as far as 1360 nm.

Full artical here.

Peter J. Parbrook, Brian Corbett, Jung Han, Tae‐Yeon Seong, Hiroshi Amano
Abstract: Typical light‐emitting diodes (LEDs) have a form factor >(300 × 300) µm². Such LEDs are commercially mature in illumination and ultralarge displays. However, recent LED research includes shrinking individual LED sizes from side lengths >300 µm to values <100 µm, leading to devices called micro‐LEDs. Their advent creates a number of exciting new application spaces. Here, a review of the principles and applications of micro‐LED technology is presented. In particular, the implications of reduced LED size in necessitating mitigation strategies for nonradiative device edge damage as well as the potential for higher drive current densities are discussed. The opportunities to integrate micro‐LEDs with electronics, and into large‐scale arrays, allow pixel addressable scalable integrated displays, while the small micro‐LED size is ideal for high‐speed modulation for visible light communication, and for integration into biological systems as part of optogenetic therapies.

Full article here.

S. Iadanza, M. Clementi, C. Hu, S. A. Schulz, D. Gerace, M. Galli, and L. O’Faolain

Phys. Rev. B 102, 245404 – Published 3 December 2020

The wavelength scale confinement of light offered by photonic crystal (PhC) cavities is one of the fundamental features on which many important on-chip photonic components are based, opening silicon photonics to a wide range of applications from telecommunications to sensing. This trapping of light in a small space also greatly enhances optical nonlinearities and many potential applications build on these enhanced light-matter interactions. In order to use PhCs effectively for this purpose it is necessary to fully understand the nonlinear dynamics underlying PhC resonators. In this work, we derive a first principles thermal model outlining the nonlinear dynamics of optically pumped silicon two-dimensional (2D) PhC cavities by calculating the temperature distribution in the system in both time and space. We demonstrate that our model matches experimental results well and use it to describe the behavior of different types of PhC cavity designs. Thus, we demonstrate the model’s capability to predict thermal nonlinearities of arbitrary 2D PhC microcavities in any material, only by substituting the appropriate physical constants. This renders the model critical for the development of nonlinear optical devices prior to fabrication and characterization.

Full article here.

R. Loi, S. Iadanza, B. Roycroft, J. O’Callaghan, L. Liu, K. Thomas, A. Gocalinska, E. Pelucchi, A. Farrell, S. Kelleher, R. F. Gul, A. J. Trindade, D. Gomez, L. O’Faolain & B. Corbett, IEEE Journal of Quantum Electronics 56 (1), 6400108 (2020).

InP lasers operating in the O- and C- optical bands are required to be integrated onto silicon photonics for high bandwidth telecom and data-communication applications. The first O-band Fabry Perot InP laser was edge coupled to a polymer waveguide by integration into a tailored recess on a silicon photonics chip by using micro transfer printing, which provides accurate planar alignment and scalability. Highly accurate vertical alignment of the laser waveguide and thermal sink are achieved by bonding the devices on an intermediate metal layer of calibrated thickness deposited at the bottom of the recess and connected to the Si substrate. The work presents a roadmap for delivering light to polymer interconnects and potentially enable hybrid polymer-SOI based photonic integrated circuits.

Full article here.

Here comes the last session of our workshop, LASER demo competition! Check details on our YouTube Channel and score them!

We held a 9 sessions LASER workshop for the IPIC summer interns in 2021, who were 2nd/3rd undergraduate students from universities across Ireland. We inluded 4 technical talks, 1 simulation, 2 interactive video session and 1 Ph.D. experience sharing session. Due to the restrictions, they were all done online. Many thanks to Brian Corbett, Sandeep Madhusudan Singh,John McCarthy,Niall Boohan,Megan O’Brien,Hemalatha Muthuganesan, Shengtai Shi, Adarsh Ananthachar, Simone Iadanza!
Check some of the videos on our YouTube channel.

Conal Murphy completed my Bsc Physics degree at University College Cork (UCC) in 2020. I completed a number of summer internships during my undergraduate degree, including an IPIC summer studentship in the Photonics Theory Group under the supervision of Prof. Eoin O’Reilly and Dr.Chris Broderick. Later in 2020 I joined the Photonics Theory Group on an IRC funded PhD studentship, again under the supervision of Prof. O’Reilly and Dr. Broderick.

Details of the talk on our theme YouTube channel.

Summary: There exists significant demand for efficient mid-IR LEDs and lasers for applications in environmental monitoring, medical diagnostics and industrial process control. InAs/GaSb superlattices (SLs) possess type-III (“broken gap”) band offsets. Prototype inter-band cascade LEDs (IC-LEDs) based on [001]-oriented InAs/GaSb SLs have demonstrated high output power and wallplug efficiency relative to competing technologies at wavelengths close to 4 μm. To elucidate the origin of the observed high output power of these IC-LEDs we undertake a quantitative theoretical analysis of their optoelectronic properties. We employ an 8-band k.p Hamiltonian in conjunction with a plane wave expansion method to compute SL optoelectronic properties. Using the calculated SL electronic properties we compute spontaneous emission spectra and estimate the radiative recombination coefficient B. Significant delocalisation of the lowest energy bound electron state (e1) in the SL – a result of a combination of narrow layer thicknesses and low InAs electron effective mass – leads to relatively large spatial overlap of bound electron and hole wave functions in hole-confining GaSb layers. The electron-hole spatial overlap in these structures results in increased inter-band optical matrix elements compared to conventional type-II structures, leading to B values which are comparable to those in several proposed type-I mid-IR quantum well systems.

Dr. Emanuele Peluchi gave a talk ‘What is Quantum Science’ to celebrate the Word Quantum Day, check the video here.

Check our recent theme talk, ‘Applications of UV light for biomedical applications‘. This time, we’re honored to have Stefan Andersson-Engels, the director of the Biophotonics theme in IPIC, Professor in Physics Department, UCC to give us this comprehensive talk.You could find how the 4 themes in IPIC are working together.

Summary: Within IPIC we are designing novel biomedical diagnostic equipment needing UV sources. The sources needed are not easily available, and research is ongoing at IPIC to fill this gap. In this context, I am presenting my understanding of the biomedical need for such light sources. The presentation aims at providing inputs to program for developing UV sources that best utilises our unique expertise and resources, and best fills the unmet needs.

For more talks, please find our theme YouTube channel.

John MaCarthy is currently a Ph.D. student in the Integrated Photonics group working on the development of a chip for frequency comb generation. Presentation abstract: Modern optical networks use hundreds of separate lasers which fill up the limited bandwidth. The channels in the spectral bandwidth are separated by empty regions called guard bands where the purpose is to prevent one channel from interfering with another. The problem is that these guard bands are spectrally inefficient and, due to the increased demand, the bandwidth has become more and more limited. Optical frequency comb sources can potentially reduce or eliminate these guard bands. Optical frequency combs are used to generate a number of precisely spaced spectral carriers with a stable frequency. Due to the fixed phase relation between the carriers in the comb, there is no interference between comb lines.

Details could be found here.