Brendan Roycroft - Profile on Academia.edu (original) (raw)
Papers by Brendan Roycroft
IEEE Journal of Quantum Electronics
O-band InP etched facets lasers were heterogeneously integrated by micro-transfer-printing into a... more O-band InP etched facets lasers were heterogeneously integrated by micro-transfer-printing into a 1.54 µm deep recess created in the 3 µm thick oxide layer of a 220 nm SOI wafer. A 7 × 1.5 µm 2 cross-section, 2 mm long multimode polymer waveguide was aligned to the ridge post-integration by e-beam lithography with <0.7 µm lateral misalignment and incorporated a tapered silicon waveguide. A 170 nm thick metal layer positioned at the bottom of the recess adjusts the vertical alignment of the laser and serves as a thermal via to sink the heat to the Si substrate. This strategy shows a roadmap for active polymer waveguide-based photonic integrated circuits.
41 Congreso de la Sociedad Española de Endoscopia Digestiva (SEED)
IET Optoelectronics
This study presents experimental and simulation results for edge-coupled waveguide unitravelling-... more This study presents experimental and simulation results for edge-coupled waveguide unitravelling-carrier (UTC) photodiodes based on an InGaAs/InP heterostructure. Experimental results are used to calibrate the numerical device simulator. The authors study how different aspects of the UTC photodiode epistructure and contacts impact on the overall device bandwidth, calculating the photoresponse for different structural parameters and doping concentration profiles. The effect of these parameters on the 3-dB cutoff frequency is studied, and design guidelines for UTC photodiodes with improved performance are presented. The UTC photodiode simulated using authors' design guidelines has a 3 dB cutoff frequency of 49 GHz, a factor of 2 larger than the 25 GHz cutoff of the fabricated UTC photodiode.
Low-power-consumption optical interconnect on silicon by transfer-printing for used in opto-isolators
Journal of Physics D: Applied Physics
Journal of Lightwave Technology
Characterization of a Low-Cost, Monolithically Integrated, Tunable 10G Transmitter for Wavelength Agile PONs
IEEE Journal of Quantum Electronics
GHz bandwidth semipolar (112¯2) InGaN/GaN light-emitting diodes
Optics Letters
We report on the electrical-to-optical modulation bandwidths of non-mesa-etched semipolar (112¯2)... more We report on the electrical-to-optical modulation bandwidths of non-mesa-etched semipolar (112¯2) InGaN/GaN light-emitting diodes (LEDs) operating at 430-450 nm grown on high-quality (112¯2) GaN templates, which were prepared on patterned (101¯2) r-plane sapphire substrates. The measured frequency response at -3 dB of the LEDs was up to 1 GHz. A high back-to-back data transmission rate of above 2.4 Gbps is demonstrated using a non-return-to-zero on-off keying modulation scheme. This indicates that (112¯2) LEDs are suitable gigabit per second data transmission for use in visible-light communication applications.
Enhanced efficiency of near-UV emitting LEDs for solid state lighting applications
Manufacturing LEDs for Lighting and Displays
ABSTRACT The performance of a series of near-UV (~385 nm) emitting LEDs, consisting of high effic... more ABSTRACT The performance of a series of near-UV (~385 nm) emitting LEDs, consisting of high efficiency InGaN/AlInGaN QWs in the active region, was investigated. Significantly reduced roll-over of efficiency at high current density was found compared to InGaN/GaN LEDs emitting at a similar wavelength. The importance of optical cavity effects in flip-chip geometry devices has also been investigated. The light output was enhanced by more than a factor of 2 when the light-emitting region was located at an anti-node position with respect to a high reflectivity current injection mirror. A power of 0.49 mW into a numerical aperture of 0.5 was obtained for a junction area of 50 micrometers in diameter and a current of 30 mA, corresponding to a radiance of 30 W/cm2/str.
High Bandwidth (11-22) Semipolar LEDs for Visible Light Communications
Light, Energy and the Environment, 2016
2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007
Vernier tuned coupled cavity ld having a ridge with voids for langitudinal mode suppression
40 Gb/s WDM Transmission over 1.15 km HC-PBGF using an InP-based Mach-Zehnder Modulator at 2 µm
Journal of Lightwave Technology, 2015
The 2-��m wavelength range has emerged as a low-loss and low-latency optical transmission window ... more The 2-��m wavelength range has emerged as a low-loss and low-latency optical transmission window when using hollow-core photonic band gap fiber (HC-PBGF) and high-gain thulium-doped fiber amplifiers (TDFA). Various single and multichannel transmission experiments at these wavelengths have been implemented using directly modulated lasers and LiNbO3-based modulators. Here, we report the transmission performance of an externally modulated 4 �� 10 Gb/s NRZ-OOK WDM signal over 1.15 km of low-loss HC-PBGF employing an InP-based Mach-Zehnder modulator (MZM) in the transmitter for the first time. An OSNR of 25 dB on 100-GHz spaced channels is required using a direct detection scheme. Furthermore, we demonstrate the lowest V�� InP-based MZM operating at 2 ��m by increasing the electro-optical overlap in the optical waveguide. The peak-peak modulation voltage is reduced significantly from 4 to 2.7 V with an electro-optic bandwidth of 9 GHz.
Study of electro-optic effect in asymmetrically ramped AlInGaAs multiple quantum well structures
physica status solidi (a), 2015
Efficient Modelling Approach for an InP based Mach-Zehnder modulator
25th IET Irish Signals & Systems Conference 2014 and 2014 China-Ireland International Conference on Information and Communities Technologies (ISSC 2014/CIICT 2014), 2014
ABSTRACT We present an efficient modelling method based on quasi-static TEM analysis to design tr... more ABSTRACT We present an efficient modelling method based on quasi-static TEM analysis to design travelling wave InP Mach-Zehnder modulators. The analysis uses a conformal mapping technique to determine the equivalent circuit elements directly from the physical structure of the modulator waveguide layer stack. These elements are then used to investigate the propagation properties of the phase shifting section of the modulator. The fast computation time allows extraction of various design curves involving multiple design variables in order to optimise the modulation bandwidth. The contact resistance has been incorporated in the model to demonstrate the significance of low contact resistance for high modulation efficiency. The full structure is then simulated in HFSS. A modulator based on all these design optimisations has been fabricated and tested. Small signal measurements agree very well with the simulations. An electrical bandwidth of 21 GHz has been achieved which is suitable for optical modulation of data rates >20 Gbps. The designed modulator is also suitable for photonic integration.
Considerations on the rate equation description of a twin stripe laser array
Theoretical studies of twin stripe laser arrays have shown an enhanced modulation bandwidth over ... more Theoretical studies of twin stripe laser arrays have shown an enhanced modulation bandwidth over that achieved with single stripe devices. However, experimental data from the devices has concentrated mainly on the device spatio-temporal dynamics, by observation of the near- and far- fields. To our knowledge, only few experiments have been conducted to extract modeling parameters to feed the simulation with
A single growth facetless semiconductor laser platform for photonic integration
2008 10th Anniversary International Conference on Transparent Optical Networks, 2008
ABSTRACT InP based optical and electronic devices have been extensively studied for their enablin... more ABSTRACT InP based optical and electronic devices have been extensively studied for their enabling properties in modern telecommunication systems. There is considerable demand to further improve the performance of lasers and in particular to integrate the lasers with additional optical components such as detectors, waveguides, amplifiers, splitters, interferometers, modulators and multiplexers to realize optical chips with advanced functionality. This is hindered by the dominating costs associated with integrating these devices. On-chip integration is an attractive solution but one which requires the use of complex technologies (electron beam lithography and epitaxial overgrowth) that are generally proprietary and not compatible with foundry manufacture. In this talk, we report on a novel alternative approach to integration using a single epitaxial growth stage and conventional optical lithography. A tuneable laser with an integrated optical amplifier is demonstrated but the technology can be extended to integration of modulators and other optical functions. This device is enabled by the realization of a reflective mirror using etched slots thus freeing the laser designer from the absolute requirement of the cleaved facet and the associated crystal orientation of all semiconductor lasers. The integration of multiple components on a single chip will provide a platform for photonics that can be implemented in a foundry and this mimics the approach of the silicon electronics industry.
On-chip optical phase locking of single growth monolithically integrated Slotted Fabry Perot lasers
Optics express, Jan 15, 2013
This work investigates the optical phase locking performance of Slotted Fabry Perot (SFP) lasers ... more 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.
Physical review. B, Condensed matter, Jan 15, 1995
We present experimental data on saturation of the strong-coupling regime in semiconductor microca... more We present experimental data on saturation of the strong-coupling regime in semiconductor microcav- ities based on intensity-dependent photoluminescence measurements. The saturation can be understood in terms of electron-hole pair screening of the quantum. -well exciton. The very low saturation intensity I',", , ' '"'=100 Wcm leads to a saturation density N, '"=4.3X10' cm in good agreement with a theoretical model. These results are important for applications such as lasers in the strong-coupling re- gime and nonlinear devices.
Physics and Simulation of Optoelectronic Devices X, 2002
The effects of inter-ridge coupling on both the static and high frequency properties of twin stri... more The effects of inter-ridge coupling on both the static and high frequency properties of twin stripe laterally coupled lasers emitting at a wavelength of 1.3 micrometers are investigated. It is found that when both ridges are lasing, the emission spectrum is multi longitudinal mode, with ...
A Novel Two-Section Tunable Slotted Fabry-Pérot Laser Exhibiting ns Wavelength Switching
A novel two-section tunable laser diode is demonstrated by etching slots into the laser ridge. A ... more A novel two-section tunable laser diode is demonstrated by etching slots into the laser ridge. A discontinuous tuning-range of 30 nm was achieved with a SMSR of 38 dB. A wavelength switching time of 1.5 ns is demonstrated.
IEEE Journal of Quantum Electronics
O-band InP etched facets lasers were heterogeneously integrated by micro-transfer-printing into a... more O-band InP etched facets lasers were heterogeneously integrated by micro-transfer-printing into a 1.54 µm deep recess created in the 3 µm thick oxide layer of a 220 nm SOI wafer. A 7 × 1.5 µm 2 cross-section, 2 mm long multimode polymer waveguide was aligned to the ridge post-integration by e-beam lithography with <0.7 µm lateral misalignment and incorporated a tapered silicon waveguide. A 170 nm thick metal layer positioned at the bottom of the recess adjusts the vertical alignment of the laser and serves as a thermal via to sink the heat to the Si substrate. This strategy shows a roadmap for active polymer waveguide-based photonic integrated circuits.
41 Congreso de la Sociedad Española de Endoscopia Digestiva (SEED)
IET Optoelectronics
This study presents experimental and simulation results for edge-coupled waveguide unitravelling-... more This study presents experimental and simulation results for edge-coupled waveguide unitravelling-carrier (UTC) photodiodes based on an InGaAs/InP heterostructure. Experimental results are used to calibrate the numerical device simulator. The authors study how different aspects of the UTC photodiode epistructure and contacts impact on the overall device bandwidth, calculating the photoresponse for different structural parameters and doping concentration profiles. The effect of these parameters on the 3-dB cutoff frequency is studied, and design guidelines for UTC photodiodes with improved performance are presented. The UTC photodiode simulated using authors' design guidelines has a 3 dB cutoff frequency of 49 GHz, a factor of 2 larger than the 25 GHz cutoff of the fabricated UTC photodiode.
Low-power-consumption optical interconnect on silicon by transfer-printing for used in opto-isolators
Journal of Physics D: Applied Physics
Journal of Lightwave Technology
Characterization of a Low-Cost, Monolithically Integrated, Tunable 10G Transmitter for Wavelength Agile PONs
IEEE Journal of Quantum Electronics
GHz bandwidth semipolar (112¯2) InGaN/GaN light-emitting diodes
Optics Letters
We report on the electrical-to-optical modulation bandwidths of non-mesa-etched semipolar (112¯2)... more We report on the electrical-to-optical modulation bandwidths of non-mesa-etched semipolar (112¯2) InGaN/GaN light-emitting diodes (LEDs) operating at 430-450 nm grown on high-quality (112¯2) GaN templates, which were prepared on patterned (101¯2) r-plane sapphire substrates. The measured frequency response at -3 dB of the LEDs was up to 1 GHz. A high back-to-back data transmission rate of above 2.4 Gbps is demonstrated using a non-return-to-zero on-off keying modulation scheme. This indicates that (112¯2) LEDs are suitable gigabit per second data transmission for use in visible-light communication applications.
Enhanced efficiency of near-UV emitting LEDs for solid state lighting applications
Manufacturing LEDs for Lighting and Displays
ABSTRACT The performance of a series of near-UV (~385 nm) emitting LEDs, consisting of high effic... more ABSTRACT The performance of a series of near-UV (~385 nm) emitting LEDs, consisting of high efficiency InGaN/AlInGaN QWs in the active region, was investigated. Significantly reduced roll-over of efficiency at high current density was found compared to InGaN/GaN LEDs emitting at a similar wavelength. The importance of optical cavity effects in flip-chip geometry devices has also been investigated. The light output was enhanced by more than a factor of 2 when the light-emitting region was located at an anti-node position with respect to a high reflectivity current injection mirror. A power of 0.49 mW into a numerical aperture of 0.5 was obtained for a junction area of 50 micrometers in diameter and a current of 30 mA, corresponding to a radiance of 30 W/cm2/str.
High Bandwidth (11-22) Semipolar LEDs for Visible Light Communications
Light, Energy and the Environment, 2016
2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007
Vernier tuned coupled cavity ld having a ridge with voids for langitudinal mode suppression
40 Gb/s WDM Transmission over 1.15 km HC-PBGF using an InP-based Mach-Zehnder Modulator at 2 µm
Journal of Lightwave Technology, 2015
The 2-��m wavelength range has emerged as a low-loss and low-latency optical transmission window ... more The 2-��m wavelength range has emerged as a low-loss and low-latency optical transmission window when using hollow-core photonic band gap fiber (HC-PBGF) and high-gain thulium-doped fiber amplifiers (TDFA). Various single and multichannel transmission experiments at these wavelengths have been implemented using directly modulated lasers and LiNbO3-based modulators. Here, we report the transmission performance of an externally modulated 4 �� 10 Gb/s NRZ-OOK WDM signal over 1.15 km of low-loss HC-PBGF employing an InP-based Mach-Zehnder modulator (MZM) in the transmitter for the first time. An OSNR of 25 dB on 100-GHz spaced channels is required using a direct detection scheme. Furthermore, we demonstrate the lowest V�� InP-based MZM operating at 2 ��m by increasing the electro-optical overlap in the optical waveguide. The peak-peak modulation voltage is reduced significantly from 4 to 2.7 V with an electro-optic bandwidth of 9 GHz.
Study of electro-optic effect in asymmetrically ramped AlInGaAs multiple quantum well structures
physica status solidi (a), 2015
Efficient Modelling Approach for an InP based Mach-Zehnder modulator
25th IET Irish Signals & Systems Conference 2014 and 2014 China-Ireland International Conference on Information and Communities Technologies (ISSC 2014/CIICT 2014), 2014
ABSTRACT We present an efficient modelling method based on quasi-static TEM analysis to design tr... more ABSTRACT We present an efficient modelling method based on quasi-static TEM analysis to design travelling wave InP Mach-Zehnder modulators. The analysis uses a conformal mapping technique to determine the equivalent circuit elements directly from the physical structure of the modulator waveguide layer stack. These elements are then used to investigate the propagation properties of the phase shifting section of the modulator. The fast computation time allows extraction of various design curves involving multiple design variables in order to optimise the modulation bandwidth. The contact resistance has been incorporated in the model to demonstrate the significance of low contact resistance for high modulation efficiency. The full structure is then simulated in HFSS. A modulator based on all these design optimisations has been fabricated and tested. Small signal measurements agree very well with the simulations. An electrical bandwidth of 21 GHz has been achieved which is suitable for optical modulation of data rates >20 Gbps. The designed modulator is also suitable for photonic integration.
Considerations on the rate equation description of a twin stripe laser array
Theoretical studies of twin stripe laser arrays have shown an enhanced modulation bandwidth over ... more Theoretical studies of twin stripe laser arrays have shown an enhanced modulation bandwidth over that achieved with single stripe devices. However, experimental data from the devices has concentrated mainly on the device spatio-temporal dynamics, by observation of the near- and far- fields. To our knowledge, only few experiments have been conducted to extract modeling parameters to feed the simulation with
A single growth facetless semiconductor laser platform for photonic integration
2008 10th Anniversary International Conference on Transparent Optical Networks, 2008
ABSTRACT InP based optical and electronic devices have been extensively studied for their enablin... more ABSTRACT InP based optical and electronic devices have been extensively studied for their enabling properties in modern telecommunication systems. There is considerable demand to further improve the performance of lasers and in particular to integrate the lasers with additional optical components such as detectors, waveguides, amplifiers, splitters, interferometers, modulators and multiplexers to realize optical chips with advanced functionality. This is hindered by the dominating costs associated with integrating these devices. On-chip integration is an attractive solution but one which requires the use of complex technologies (electron beam lithography and epitaxial overgrowth) that are generally proprietary and not compatible with foundry manufacture. In this talk, we report on a novel alternative approach to integration using a single epitaxial growth stage and conventional optical lithography. A tuneable laser with an integrated optical amplifier is demonstrated but the technology can be extended to integration of modulators and other optical functions. This device is enabled by the realization of a reflective mirror using etched slots thus freeing the laser designer from the absolute requirement of the cleaved facet and the associated crystal orientation of all semiconductor lasers. The integration of multiple components on a single chip will provide a platform for photonics that can be implemented in a foundry and this mimics the approach of the silicon electronics industry.
On-chip optical phase locking of single growth monolithically integrated Slotted Fabry Perot lasers
Optics express, Jan 15, 2013
This work investigates the optical phase locking performance of Slotted Fabry Perot (SFP) lasers ... more 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.
Physical review. B, Condensed matter, Jan 15, 1995
We present experimental data on saturation of the strong-coupling regime in semiconductor microca... more We present experimental data on saturation of the strong-coupling regime in semiconductor microcav- ities based on intensity-dependent photoluminescence measurements. The saturation can be understood in terms of electron-hole pair screening of the quantum. -well exciton. The very low saturation intensity I',", , ' '"'=100 Wcm leads to a saturation density N, '"=4.3X10' cm in good agreement with a theoretical model. These results are important for applications such as lasers in the strong-coupling re- gime and nonlinear devices.
Physics and Simulation of Optoelectronic Devices X, 2002
The effects of inter-ridge coupling on both the static and high frequency properties of twin stri... more The effects of inter-ridge coupling on both the static and high frequency properties of twin stripe laterally coupled lasers emitting at a wavelength of 1.3 micrometers are investigated. It is found that when both ridges are lasing, the emission spectrum is multi longitudinal mode, with ...
A Novel Two-Section Tunable Slotted Fabry-Pérot Laser Exhibiting ns Wavelength Switching
A novel two-section tunable laser diode is demonstrated by etching slots into the laser ridge. A ... more A novel two-section tunable laser diode is demonstrated by etching slots into the laser ridge. A discontinuous tuning-range of 30 nm was achieved with a SMSR of 38 dB. A wavelength switching time of 1.5 ns is demonstrated.