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John Donegan

Trinity College Dublin, School of Physics, Faculty Member

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Professor of PhysicsResearch area: PhotonicsResearch themes: Semiconductor Laser Devices with High-Order Gratings for Photonic IntegrationHeat Assisted Magnetic RecordingConical Refraction of Light
Address: School of Physics,
Trinity College Dublin,
Dublin 2, Ireland

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Papers by John Donegan

Self-heating allows Athermal Laser Diode Wavelength Control using a Thermally Insulating Sub-mount over a 70 °C range

The wavelength of a single frequency quantum dot distributed feedback (DFB) laser operating in th... more The wavelength of a single frequency quantum dot distributed feedback (DFB) laser operating in the O-band is athermalised over a 74 °C ambient temperature range. Two techniques are presented, one utilising the laser self-heating for tuning control, the other using a resistive heater. Both techniques show greatly improved power efficiency over conventional wavelength control schemes, and both demonstrate wavelength stability of better than 0.1 nm (17.5 GHz) without mode hops over the entire temperature range. The use of a high temperature quantum dot laser together with an innovative submount design to increase the thermal impedance of the device enables the improved use of the laser self-heating for wavelength tuning. The submount design entails the laser being suspended over an air gap with the use of glass supports, preventing heat from escaping from the diode.

matched 1.5 micron InGaAsN/GaAs

enhancement factor and modulation bandwidth of lattice

Octave-spanning Kerr frequency comb generation with stimulated Raman scattering in an AlN microresonator

Optics Letters, 2021

Octave-spanning optical frequency combs (OFCs) are essential for various applications, such as pr... more Octave-spanning optical frequency combs (OFCs) are essential for various applications, such as precision metrology and astrophysical spectrometer calibration. In this Letter, we demonstrate, for the first time to our knowledge, the generation of octave-spanning Kerr frequency combs ranging from 1150 to 2400 nm in aluminum nitride (AlN) microring resonators, by pumping the T M 00 modes at 250 mW on-chip power. By simply adjusting the pump detuning, we observe the transition and coexistence of Kerr OFC and stimulated Raman scattering. For the T E 00 mode in the same device, a broadband Raman-assisted frequency comb is demonstrated by adjusting the pump power and tuning. These results indicate a crucial development for the fundamentals of nonlinear dynamics and comb applications in AlN.

Characterisation of multi-mode propagation in silicon nitride slab waveguides

Journal of Optics, 2016

A simple experimental method for determining the number of modes in planar dielectric multi-mode ... more A simple experimental method for determining the number of modes in planar dielectric multi-mode waveguides, and the effective index difference of these modes, is presented. Applying a thin, dye-doped polymer cladding, the fluorescence excited by multiple modes propagating in a silicon nitride slab waveguide is imaged to extract information. Interference between the modes produces a structured intensity profile along the waveguide which is constant in time. The spatial frequencies of this intensity profile are directly linked to the propagation constants of the underlying modes. Through a discrete Fourier transform, the modes' effective index differences are found and compare well with analytically calculated values. Furthermore, the amplitudes in the Fourier transform are directly related to the power in each mode. Comparing the amplitudes of the Fourier components as a function of propagation distance, an estimate of the propagation losses of the individual modes relative to one another is made. The method discussed could be applied to analysing mode behaviour in integrated photonic devices, most notably in mode-division multiplexing.

Preparation and Investigation of Quantum-Dot-Loaded Hollow Polymer Microspheres

The Journal of Physical Chemistry C, 2013

Exciton Diffusion in GaN Epitaxial Layers

physica status solidi (b), 2001

ABSTRACT

ICONO 2007: Novel Photonics Materials; Optics and Optical Diagnostics of Nanostructures

We present a detailed study of the localized coupled-cavity modes in a photonic molecule formed f... more We present a detailed study of the localized coupled-cavity modes in a photonic molecule formed from two dielectric spherical microcavities with CdTe nanocrystals, which show a multi-peak narrowband modal structure resulting from lifting of the mode degeneracy with respect to the azimuthal quantum number. The feasibility of photonic molecules as the basis for a multi-channel, wavelength-tunable optical delay device is analysed

Erratum: “Dual-mode microresonators as straightforward access to octave-spanning dissipative Kerr solitons” [APL Photonics 7, 066103 (2022)]

APL Photonics

Highly fabrication tolerant InP based polarization beam splitter based on p-i-n structure

Optics express, 2017

In this work, a novel highly fabrication tolerant polarization beam splitter (PBS) is presented o... more In this work, a novel highly fabrication tolerant polarization beam splitter (PBS) is presented on an InP platform. To achieve the splitting, we combine the Pockels effect and the plasma dispersion effect in a symmetric 1x2 Mach-Zehnder interferometer (MZI). One p-i-n phase shifter of the MZI is driven in forward bias to exploit the plasma dispersion effect and modify the phase of both the TE and TM mode. The other arm of the MZI is driven in reverse bias to exploit the Pockels effect which affects only the TE mode. By adjusting the voltages of the two phase shifters, a different interference condition can be set for the TE and the TM modes thereby splitting them at the output of the MZI. By adjusting the voltages, the very tight fabrication tolerances known for fully passive PBS are eased. The experimental results show that an extinction ratio better than 15 dB and an on-chip loss of 3.5 dB over the full C-band (1530-1565nm) are achieved.

A novel approach towards two-photon absorption based detectors

The summary form only given. We have demonstrated that the inherent inefficiency of the TPA proce... more The summary form only given. We have demonstrated that the inherent inefficiency of the TPA process in semiconductors can be overcome by incorporating the semiconductor in a microcavity structure. Proof of concept devices with a 0.27/spl mu/m Ga/sub 0.7/Al0.3As active region and two Bragg reflectors with the cavity resonance of 890 nm were fabricated. We measured the TPA photocurrent of these devices and have demonstrated a factor of 12000 enhancement over a nonmicrocavity device at 890 nm. Our active length of 0.27 nm is as efficient as 5.4 mm without a microcavity, overcoming the very long detector lengths limiting the use of TPA in practical autocorrelators, optical switches and sampling devices for real telecommunication systems. The effect of the cavity is to enhance the intra-cavity optical intensity, which leads to an increase in the nonlinear response of the active region. We studied, theoretically and experimentally, the impact of the cavity on the temporal response and the...

Wide-Waveguide High-Power Low-RIN Single-Mode Distributed Feedback Laser Diodes for Optical Communication

Optics Express

Two-photon absorption in microcavities for optical autocorrelation and sampling

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666)

Dual-mode microresonators as straightforward access to octave-spanning dissipative Kerr solitons

Haizhong Weng, Adnan Ali Afridi, Jing Li, Michael McDermott, Huilan Tu, Liam P. Barry, Qiaoyin Lu... more Haizhong Weng, Adnan Ali Afridi, Jing Li, Michael McDermott, Huilan Tu, Liam P. Barry, Qiaoyin Lu, Weihua Guo,2,∗ and John F. Donegan1,∗ School of Physics, CRANN and AMBER, Trinity College Dublin, Dublin 2, Ireland Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China Radio and Optical Communications Lab., School of Electronic Engineering, Dublin City University, Dublin 9, Ireland (Dated: February 22, 2022)

Near octave-spanning perfect soliton crystals in AlN microresonators

The perfect soliton crystal (PSC) was recently discovered as an extraordinary Kerr soliton state ... more The perfect soliton crystal (PSC) was recently discovered as an extraordinary Kerr soliton state with regularly distributed soliton pulses and enhanced comb line power spaced by multiples of the cavity free spectral ranges (FSRs). The modulation of continuous-wave excitation in optical microresonators and the tunable repetition rate characteristic will significantly enhance and extend the application potential of soliton microcombs for self-referencing comb source, terahertz wave generation, and arbitrary waveform generation. However, the reported PSC spectrum is generally narrow. Here, we demonstrate the deterministic accessing of versatile perfect soliton crystals in the AlN microresonators (FSR ~374 GHz), featuring a broad spectral range up to 0.96 of an octave-span (1170-2300 nm) and terahertz repetition rates (up to ~1.87 THz). The measured 60-fs short pulses and low-noise characteristics confirms the high coherence of the PSCs

Supplementary document for Near octave-spanning breathing perfect soliton crystal in an AlN microresonator - 5267294.pdf

Experiment setup, devices characterization, and the Kerr comb results obtained from a smaller mic... more

Spectroscopic size and thickness metrics for liquid-exfoliated h-BN

For many 2D materials, optical and Raman spectra are richly structured, and convey information on... more For many 2D materials, optical and Raman spectra are richly structured, and convey information on a range of parameters including nanosheet size and defect content. By contrast, the equivalent spectra for h-BN are relatively simple, with both the absorption and Raman spectra consisting of a single feature each, disclosing relatively little information. Here, the ability to size-select liquid-exfoliated h-BN nanosheets has allowed us to comprehensively study the dependence of h-BN optical spectra on nanosheet dimensions. We find the optical extinction coefficient spectrum to vary systematically with nanosheet lateral size due to the presence of light scattering. Conversely, once light scattering has been decoupled to give the optical absorbance spectra, we find the size dependence to be mostly removed save for a weak but well-defined variation in energy of peak absorbance with nanosheet thickness. This finding is corroborated by our ab initio GW and Bethe-Salpeter equation calculatio...

AlN microresonators fabricated with standard photolithography for broadband Kerr frequency comb generation

Conference on Lasers and Electro-Optics, 2020

A near octave comb spectrum ranging from 1100 to 2150 nm is generated at 406 mW pump power for Al... more

Highly-efficient optical sampling of a 100 Gbit/s OTDM data signal via two-photon absorption in a semiconductor microcavity

31st European Conference on Optical Communications (ECOC 2005), 2005

ABSTRACT By incorporating a semiconductor microcavity device, a highly-efficient two-photon absor... more

Expanding the range of chromatic dispersion monitoring with two-photon absorption in semiconductors

2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007

Investigation of widely tuneable laser diodes for spectroscopic based multigas sensing at 1.5 μm

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666)

Widely tuneable laser diodes, with wavelength tuning ranges of 34 nm and 15 nm are used for simul... more

Self-heating allows Athermal Laser Diode Wavelength Control using a Thermally Insulating Sub-mount over a 70 °C range

The wavelength of a single frequency quantum dot distributed feedback (DFB) laser operating in th... more The wavelength of a single frequency quantum dot distributed feedback (DFB) laser operating in the O-band is athermalised over a 74 °C ambient temperature range. Two techniques are presented, one utilising the laser self-heating for tuning control, the other using a resistive heater. Both techniques show greatly improved power efficiency over conventional wavelength control schemes, and both demonstrate wavelength stability of better than 0.1 nm (17.5 GHz) without mode hops over the entire temperature range. The use of a high temperature quantum dot laser together with an innovative submount design to increase the thermal impedance of the device enables the improved use of the laser self-heating for wavelength tuning. The submount design entails the laser being suspended over an air gap with the use of glass supports, preventing heat from escaping from the diode.

matched 1.5 micron InGaAsN/GaAs

enhancement factor and modulation bandwidth of lattice

Octave-spanning Kerr frequency comb generation with stimulated Raman scattering in an AlN microresonator

Optics Letters, 2021

Octave-spanning optical frequency combs (OFCs) are essential for various applications, such as pr... more Octave-spanning optical frequency combs (OFCs) are essential for various applications, such as precision metrology and astrophysical spectrometer calibration. In this Letter, we demonstrate, for the first time to our knowledge, the generation of octave-spanning Kerr frequency combs ranging from 1150 to 2400 nm in aluminum nitride (AlN) microring resonators, by pumping the T M 00 modes at 250 mW on-chip power. By simply adjusting the pump detuning, we observe the transition and coexistence of Kerr OFC and stimulated Raman scattering. For the T E 00 mode in the same device, a broadband Raman-assisted frequency comb is demonstrated by adjusting the pump power and tuning. These results indicate a crucial development for the fundamentals of nonlinear dynamics and comb applications in AlN.

Characterisation of multi-mode propagation in silicon nitride slab waveguides

Journal of Optics, 2016

A simple experimental method for determining the number of modes in planar dielectric multi-mode ... more A simple experimental method for determining the number of modes in planar dielectric multi-mode waveguides, and the effective index difference of these modes, is presented. Applying a thin, dye-doped polymer cladding, the fluorescence excited by multiple modes propagating in a silicon nitride slab waveguide is imaged to extract information. Interference between the modes produces a structured intensity profile along the waveguide which is constant in time. The spatial frequencies of this intensity profile are directly linked to the propagation constants of the underlying modes. Through a discrete Fourier transform, the modes' effective index differences are found and compare well with analytically calculated values. Furthermore, the amplitudes in the Fourier transform are directly related to the power in each mode. Comparing the amplitudes of the Fourier components as a function of propagation distance, an estimate of the propagation losses of the individual modes relative to one another is made. The method discussed could be applied to analysing mode behaviour in integrated photonic devices, most notably in mode-division multiplexing.

Preparation and Investigation of Quantum-Dot-Loaded Hollow Polymer Microspheres

The Journal of Physical Chemistry C, 2013

Exciton Diffusion in GaN Epitaxial Layers

physica status solidi (b), 2001

ABSTRACT

ICONO 2007: Novel Photonics Materials; Optics and Optical Diagnostics of Nanostructures

We present a detailed study of the localized coupled-cavity modes in a photonic molecule formed f... more We present a detailed study of the localized coupled-cavity modes in a photonic molecule formed from two dielectric spherical microcavities with CdTe nanocrystals, which show a multi-peak narrowband modal structure resulting from lifting of the mode degeneracy with respect to the azimuthal quantum number. The feasibility of photonic molecules as the basis for a multi-channel, wavelength-tunable optical delay device is analysed

Erratum: “Dual-mode microresonators as straightforward access to octave-spanning dissipative Kerr solitons” [APL Photonics 7, 066103 (2022)]

APL Photonics

Highly fabrication tolerant InP based polarization beam splitter based on p-i-n structure

Optics express, 2017

In this work, a novel highly fabrication tolerant polarization beam splitter (PBS) is presented o... more In this work, a novel highly fabrication tolerant polarization beam splitter (PBS) is presented on an InP platform. To achieve the splitting, we combine the Pockels effect and the plasma dispersion effect in a symmetric 1x2 Mach-Zehnder interferometer (MZI). One p-i-n phase shifter of the MZI is driven in forward bias to exploit the plasma dispersion effect and modify the phase of both the TE and TM mode. The other arm of the MZI is driven in reverse bias to exploit the Pockels effect which affects only the TE mode. By adjusting the voltages of the two phase shifters, a different interference condition can be set for the TE and the TM modes thereby splitting them at the output of the MZI. By adjusting the voltages, the very tight fabrication tolerances known for fully passive PBS are eased. The experimental results show that an extinction ratio better than 15 dB and an on-chip loss of 3.5 dB over the full C-band (1530-1565nm) are achieved.

A novel approach towards two-photon absorption based detectors

The summary form only given. We have demonstrated that the inherent inefficiency of the TPA proce... more The summary form only given. We have demonstrated that the inherent inefficiency of the TPA process in semiconductors can be overcome by incorporating the semiconductor in a microcavity structure. Proof of concept devices with a 0.27/spl mu/m Ga/sub 0.7/Al0.3As active region and two Bragg reflectors with the cavity resonance of 890 nm were fabricated. We measured the TPA photocurrent of these devices and have demonstrated a factor of 12000 enhancement over a nonmicrocavity device at 890 nm. Our active length of 0.27 nm is as efficient as 5.4 mm without a microcavity, overcoming the very long detector lengths limiting the use of TPA in practical autocorrelators, optical switches and sampling devices for real telecommunication systems. The effect of the cavity is to enhance the intra-cavity optical intensity, which leads to an increase in the nonlinear response of the active region. We studied, theoretically and experimentally, the impact of the cavity on the temporal response and the...

Wide-Waveguide High-Power Low-RIN Single-Mode Distributed Feedback Laser Diodes for Optical Communication

Optics Express

Two-photon absorption in microcavities for optical autocorrelation and sampling

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666)

Dual-mode microresonators as straightforward access to octave-spanning dissipative Kerr solitons

Haizhong Weng, Adnan Ali Afridi, Jing Li, Michael McDermott, Huilan Tu, Liam P. Barry, Qiaoyin Lu... more Haizhong Weng, Adnan Ali Afridi, Jing Li, Michael McDermott, Huilan Tu, Liam P. Barry, Qiaoyin Lu, Weihua Guo,2,∗ and John F. Donegan1,∗ School of Physics, CRANN and AMBER, Trinity College Dublin, Dublin 2, Ireland Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China Radio and Optical Communications Lab., School of Electronic Engineering, Dublin City University, Dublin 9, Ireland (Dated: February 22, 2022)

Near octave-spanning perfect soliton crystals in AlN microresonators

The perfect soliton crystal (PSC) was recently discovered as an extraordinary Kerr soliton state ... more The perfect soliton crystal (PSC) was recently discovered as an extraordinary Kerr soliton state with regularly distributed soliton pulses and enhanced comb line power spaced by multiples of the cavity free spectral ranges (FSRs). The modulation of continuous-wave excitation in optical microresonators and the tunable repetition rate characteristic will significantly enhance and extend the application potential of soliton microcombs for self-referencing comb source, terahertz wave generation, and arbitrary waveform generation. However, the reported PSC spectrum is generally narrow. Here, we demonstrate the deterministic accessing of versatile perfect soliton crystals in the AlN microresonators (FSR ~374 GHz), featuring a broad spectral range up to 0.96 of an octave-span (1170-2300 nm) and terahertz repetition rates (up to ~1.87 THz). The measured 60-fs short pulses and low-noise characteristics confirms the high coherence of the PSCs

Supplementary document for Near octave-spanning breathing perfect soliton crystal in an AlN microresonator - 5267294.pdf

Experiment setup, devices characterization, and the Kerr comb results obtained from a smaller mic... more

Spectroscopic size and thickness metrics for liquid-exfoliated h-BN

For many 2D materials, optical and Raman spectra are richly structured, and convey information on... more For many 2D materials, optical and Raman spectra are richly structured, and convey information on a range of parameters including nanosheet size and defect content. By contrast, the equivalent spectra for h-BN are relatively simple, with both the absorption and Raman spectra consisting of a single feature each, disclosing relatively little information. Here, the ability to size-select liquid-exfoliated h-BN nanosheets has allowed us to comprehensively study the dependence of h-BN optical spectra on nanosheet dimensions. We find the optical extinction coefficient spectrum to vary systematically with nanosheet lateral size due to the presence of light scattering. Conversely, once light scattering has been decoupled to give the optical absorbance spectra, we find the size dependence to be mostly removed save for a weak but well-defined variation in energy of peak absorbance with nanosheet thickness. This finding is corroborated by our ab initio GW and Bethe-Salpeter equation calculatio...

AlN microresonators fabricated with standard photolithography for broadband Kerr frequency comb generation

Conference on Lasers and Electro-Optics, 2020

A near octave comb spectrum ranging from 1100 to 2150 nm is generated at 406 mW pump power for Al... more

Highly-efficient optical sampling of a 100 Gbit/s OTDM data signal via two-photon absorption in a semiconductor microcavity

31st European Conference on Optical Communications (ECOC 2005), 2005

ABSTRACT By incorporating a semiconductor microcavity device, a highly-efficient two-photon absor... more

Expanding the range of chromatic dispersion monitoring with two-photon absorption in semiconductors

2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007

Investigation of widely tuneable laser diodes for spectroscopic based multigas sensing at 1.5 μm

2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666)

Widely tuneable laser diodes, with wavelength tuning ranges of 34 nm and 15 nm are used for simul... more