Periodic Reporting for period 2 - TeLSCombe (Temporal Laser cavity-Solitons for micro-resonator based optical frequency combs)
Periodo di rendicontazione: 2021-08-01 al 2022-06-30
• What is the problem/issue being addressed?
The proposal addresses the development of new technology for optical frequency combs based on microresonators, or 'microcombs.' Optical frequency combs are pulsed lasers that are usually employed for metrological purposes. Their name derives from their spectrum, composed of a set of equally spaced laser frequencies and resemble a 'comb,' where the laser frequencies play the role of the comb teeth. Very remarkably, they can be used as a fundamental part of an optical atomic clock. Optical atomic references provide highly accurate oscillators (the 'pendulum' in a grandfather clock). Such oscillations are in the range of hundreds of terahertz frequencies, hence are very difficult to count. An optical frequency comb (Nobel prize in Physics in 2005 to Hall and Hänsch) can be linked to the oscillator and allows to count the pulses of the lasers instead of the original frequencies, acting as the reduction gear of the clock, practically as its 'lancet.’
Micro-combs – based on miniature optical resonators – have galvanized the world's attention, promising to realise the full potential of frequency combs in a compact form.
However, these devices need to meet the demand of practical atomic clocks, which require reliable optical sources and currently depend on bulky pulsed lasers, which are well-known for their robustness but unfit for portable applications.
Developing energy-efficient micro-combs with the reliability and versatility of control of modern pulsed lasers will require surpassing the intrinsic limitations of the nonlinear physics exploited so far for their generation. Microcomb sources have often been studied starting from two separate entities, the laser that delivers the optical energy and the nonlinear microresonator that produces the broadband comb radiation. Starting from a configuration where the microresonator is inserted inside the laser cavity itself, this project addresses the physics of microcomb in a holistic fashion, considering the whole set of effects that play a role in the system and provide a path towards robustness.
• Why is it important for society?
Precise timing has led to many advances, such as GPS and the Internet, which depend critically on frequency and time standards. The currently limited accuracy, however, hinders progress towards societal-changing technologies such as telecommunications beyond 5G or precise earth mapping. Specifically, telecommunications, where local clocks are needed for efficient data transfer, requires high temporal accuracy for the next generation of 5G systems and beyond. The highly competitive demand in financial sectors, where timing delays in network synchronisation can lead to financial trade losses in the millions of euros, necessitates highly precise timestamps on transactions. State-of-the-art quantum sensors such as gravimeters and accelerometers require precision timing to provide revolutionary satellite-free portable navigation systems.
Optical atomic clocks based on optical frequency combs are the only technology capable of providing accurate timing up to 10-18 seconds, answering such a demand of time precision. Realising such clocks on a portable scale will change the technology landscape. Recent developments in atomic physics have made available optical references in a portable format. Microcomb technology can push this achievement to the next level, providing a path toward miniaturisation and full integration. Very importantly, a frequency comb is the device that bridges an atomic reference to the end users. Hence, a robust and flexible microcomb technology will provide new avenues in applying ultraprecision timing to current optical and electronic technologies.
• What are the overall objectives?
The goals of this proposal are:
• to investigate new principles, methodologies and technologies for optical frequency combs in micro-resonators ('micro-combs')
• to provide a solution to the key constraints limiting the emerging application of micro-combs in fields like metrology and quantum technologies, with direct application to portable atomic clocks
• to develop a world-leading programme in dissipative nonlinear systems and smart optical control.
This project is a high-gain/ high-risk research plan which steers from the state-of-the-art and builds on a different physics for developing micro-combs with control capabilities beyond the current miniature solutions. TeLScombe, namely 'Temporal Laser cavity-Solitons for micro-resonator based optical frequency combs', develops fundamental research in nonlinear optics and ultrafast photonics in miniaturised devices, with important fallouts in micro-combs, dissipative photonics and complexity in nonlinear systems.
On this basis, this project implements laser cavity-solitons for micro-comb generation, a fundamentally new class of nonlinear waves in micro-cavities directly impacting the hot field of optical frequency combs in micro-resonators ('micro-combs', or 'Kerr combs').
The proposal addresses the development of new technology for optical frequency combs based on microresonators, or 'microcombs.' Optical frequency combs are pulsed lasers that are usually employed for metrological purposes. Their name derives from their spectrum, composed of a set of equally spaced laser frequencies and resemble a 'comb,' where the laser frequencies play the role of the comb teeth. Very remarkably, they can be used as a fundamental part of an optical atomic clock. Optical atomic references provide highly accurate oscillators (the 'pendulum' in a grandfather clock). Such oscillations are in the range of hundreds of terahertz frequencies, hence are very difficult to count. An optical frequency comb (Nobel prize in Physics in 2005 to Hall and Hänsch) can be linked to the oscillator and allows to count the pulses of the lasers instead of the original frequencies, acting as the reduction gear of the clock, practically as its 'lancet.’
Micro-combs – based on miniature optical resonators – have galvanized the world's attention, promising to realise the full potential of frequency combs in a compact form.
However, these devices need to meet the demand of practical atomic clocks, which require reliable optical sources and currently depend on bulky pulsed lasers, which are well-known for their robustness but unfit for portable applications.
Developing energy-efficient micro-combs with the reliability and versatility of control of modern pulsed lasers will require surpassing the intrinsic limitations of the nonlinear physics exploited so far for their generation. Microcomb sources have often been studied starting from two separate entities, the laser that delivers the optical energy and the nonlinear microresonator that produces the broadband comb radiation. Starting from a configuration where the microresonator is inserted inside the laser cavity itself, this project addresses the physics of microcomb in a holistic fashion, considering the whole set of effects that play a role in the system and provide a path towards robustness.
• Why is it important for society?
Precise timing has led to many advances, such as GPS and the Internet, which depend critically on frequency and time standards. The currently limited accuracy, however, hinders progress towards societal-changing technologies such as telecommunications beyond 5G or precise earth mapping. Specifically, telecommunications, where local clocks are needed for efficient data transfer, requires high temporal accuracy for the next generation of 5G systems and beyond. The highly competitive demand in financial sectors, where timing delays in network synchronisation can lead to financial trade losses in the millions of euros, necessitates highly precise timestamps on transactions. State-of-the-art quantum sensors such as gravimeters and accelerometers require precision timing to provide revolutionary satellite-free portable navigation systems.
Optical atomic clocks based on optical frequency combs are the only technology capable of providing accurate timing up to 10-18 seconds, answering such a demand of time precision. Realising such clocks on a portable scale will change the technology landscape. Recent developments in atomic physics have made available optical references in a portable format. Microcomb technology can push this achievement to the next level, providing a path toward miniaturisation and full integration. Very importantly, a frequency comb is the device that bridges an atomic reference to the end users. Hence, a robust and flexible microcomb technology will provide new avenues in applying ultraprecision timing to current optical and electronic technologies.
• What are the overall objectives?
The goals of this proposal are:
• to investigate new principles, methodologies and technologies for optical frequency combs in micro-resonators ('micro-combs')
• to provide a solution to the key constraints limiting the emerging application of micro-combs in fields like metrology and quantum technologies, with direct application to portable atomic clocks
• to develop a world-leading programme in dissipative nonlinear systems and smart optical control.
This project is a high-gain/ high-risk research plan which steers from the state-of-the-art and builds on a different physics for developing micro-combs with control capabilities beyond the current miniature solutions. TeLScombe, namely 'Temporal Laser cavity-Solitons for micro-resonator based optical frequency combs', develops fundamental research in nonlinear optics and ultrafast photonics in miniaturised devices, with important fallouts in micro-combs, dissipative photonics and complexity in nonlinear systems.
On this basis, this project implements laser cavity-solitons for micro-comb generation, a fundamentally new class of nonlinear waves in micro-cavities directly impacting the hot field of optical frequency combs in micro-resonators ('micro-combs', or 'Kerr combs').
This project research practical and simple control methods for stable and efficient micro-combs to catalyse the actual impact of these devices. This proposal targets these goals by demonstrating new fundamental physics with fallouts in complexity and smart optical control. The goals that have been achieved in this period are the following
The goals that have been achieved in this mid-term period are the following:
• producing highly-efficient micro-combs, harnessing the properties of nonlinear waves called laser cavity-solitons, which have played a key role in semiconductor lasers.
Starting from the basis of our preliminary investigation, we recently delivered a full study on the efficiency property of our device. Optics Express 30, 39816-39825 (2022)
• allowing a simple and direct control of the micro-comb fundamental properties, similarly to well-established mode-locked lasers and
• achieving turn-on-key, or self-starting operation
Our two recent publications have covered the last two objectives. Opt. Express 29, 6629-6646 (2021). Nature 608, pages303–309 (2022). The first is a theoretical study of the system's reduced set of equations. In our second paper, by introducing a new approach that addresses the fundamental physics of the system, we ultimately achieve both of these objectives. We essentially transform the soliton states into dominant attractors of the system, and in doing so, demonstrate the simple, spontaneous and natural generation of solitons in a microcavity laser. These pulses are intrinsically stable and robust against large perturbations without any external control.
A summary of the system is reported in the figure displaying, (a)Optical setup with picture of the microresonator integrated on-chip. (b) Soliton start-up. Once the Erbium Doped Amplifier (EDFA) pump current is ramped, the system spontaneously finds solitary operation. (c, d) Power spectral density (PSD) and autocorrelation of the stable soliton output at t=60s. (e) The system restores solitary operation after an abrupt power-down.
Moreover, the underlying physics of our approach is fundamental and general - it applies to a wide range of nonlinear dynamic systems beyond cavity-solitons. Similar to the phase diagram for gaseous, liquid and solid states that condensed matter always displays when a set of global parameters (temperature and pressure) are fixed within a range, we obtain a striking diagram of states for our microcomb. We identify the dominant states (which very remarkably include solitons states) that our microcomb always displays when a set of global parameters (in our case optical gain and cavity length) are fixed.
The goals that have been achieved in this mid-term period are the following:
• producing highly-efficient micro-combs, harnessing the properties of nonlinear waves called laser cavity-solitons, which have played a key role in semiconductor lasers.
Starting from the basis of our preliminary investigation, we recently delivered a full study on the efficiency property of our device. Optics Express 30, 39816-39825 (2022)
• allowing a simple and direct control of the micro-comb fundamental properties, similarly to well-established mode-locked lasers and
• achieving turn-on-key, or self-starting operation
Our two recent publications have covered the last two objectives. Opt. Express 29, 6629-6646 (2021). Nature 608, pages303–309 (2022). The first is a theoretical study of the system's reduced set of equations. In our second paper, by introducing a new approach that addresses the fundamental physics of the system, we ultimately achieve both of these objectives. We essentially transform the soliton states into dominant attractors of the system, and in doing so, demonstrate the simple, spontaneous and natural generation of solitons in a microcavity laser. These pulses are intrinsically stable and robust against large perturbations without any external control.
A summary of the system is reported in the figure displaying, (a)Optical setup with picture of the microresonator integrated on-chip. (b) Soliton start-up. Once the Erbium Doped Amplifier (EDFA) pump current is ramped, the system spontaneously finds solitary operation. (c, d) Power spectral density (PSD) and autocorrelation of the stable soliton output at t=60s. (e) The system restores solitary operation after an abrupt power-down.
Moreover, the underlying physics of our approach is fundamental and general - it applies to a wide range of nonlinear dynamic systems beyond cavity-solitons. Similar to the phase diagram for gaseous, liquid and solid states that condensed matter always displays when a set of global parameters (temperature and pressure) are fixed within a range, we obtain a striking diagram of states for our microcomb. We identify the dominant states (which very remarkably include solitons states) that our microcomb always displays when a set of global parameters (in our case optical gain and cavity length) are fixed.
This project exploits the generation of localised waves called temporal laser cavity-solitons in complex resonators exhibiting lasing and parametric nonlinear interactions. Such a setting is mostly unexplored and this proposal demonstrates the unique features of these waves and their general impact in broader physics. Very importantly, this project has already shown a class of robust micro-combs which can be controlled with user-friendly approaches, leveraging the physics of complex system. This progress is sharply beyond state of the art and we plan to further progress on this physics, targeting the use of our device in portable atomic clock systems.