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Coherent Raman Interaction in Gas-Filled Hollow-Core Photonic Crystal Fibers

A. Abdolvand

Published Jan 1, 2011• 0 citations
OpenAlex

Abstract

In this thesis I study coherent light-matter interactions via stimulated Raman scattering (SRS) in a gas-filled hollow-core photonic crystal fiber (HC-PCF).The HC-PCF constitutes the foundation of the experimental results presented in this thesis, as without its unique properties realization of these experiments would not have been possible.These unique properties include tight confinement of laser light and matter in the small core of the fiber, which leads to extremely high conversion efficiencies in the SRS, and spectral filtering of unwanted nonlinear waves.This setup creates a clean system of two optical fields interacting via Raman medium inside the core of the fiber.This thesis consists of three parts.The first part (chapter 2) includes a general overview of the different types of HC-PCF, their fabrication techniques and guidance mechanisms.Two types of HC-PCF are considered: photonic bandgap HC-PCF and kagomé-HC-PCF.Guidance mechanisms of these two types of fibers are considered in detail.Of particular interest to me is the broadband guidance in kagomé-HC-PCF.Up to now, the mechanism responsible for this broadband guidance is not understood.A simplified semi-analytical model is derived which accounts for this broadband guidance in kagomé-HC-PCF and explain many of its guidance properties.In particular, using the model, the fiber loss as a function of wavelength is reproduced fairly well.The model also explains an important feature of kagomé-HC-PCF, namely, the insensitivity of its loss to the number of cladding layers.In the second part of the thesis (chapter 3), I set the basic theoretical formalism of SRS to be used in the rest of the thesis.The aim of the chapter is to derive the coupled wave equations that govern the evolution of the pump, Stokes and coherence fields using classical as well as semi-classical approaches.The third part of the thesis (chapters 4, 5, 6 and 7) discusses the results of experimental and theoretical investigations of my studies on SRS in gas-filled HC-PCF.I start with an overview of the already know results about SRS in HC-PCF and explain the mechanism of phase-locking for efficient generation of anti-Stokes SRS.This work clarifies high conversion efficiencies to anti-Stokes frequencies observed in early experiments.Most of these early experiments are focused on lowering the threshold for SRS generation and are done at relatively high pressures.In chapters 5 and 6, I use some of the unique properties of the HC-PCF to explore the coherent light-matter SRS interaction regimes not previously accessible.This includes the first experimental observation of backward superluminal solitary waves and self-similar solutions of SRS coupled-wave equations.These results represent a significant advance in the study of coherent effects and point to a new generation of highly engineerable gas cells for studying complex nonlinear phenomena.In chapter 7, I briefly overview the results presented in previous chapters and conclude my thesis by explaining possible improvements as well as new interesting directions in studying coherent light-matter interactions in gas-filled HC-PCF.In particular, I introduce a simple scheme for generating (purely rotational) broadband coherent frequency comb at low pump pulse energies using a gas-filled HC-PCF.Generation of such a frequency comb is quite interesting for synthesizing ultrashort pulses as well as a broad coherent tunable light source with high spectral brightness.The classic system of education is mainly based on the ability of deductive reasoning and knowledge of the classics.Quite often, in the course of learning that, we lose the joy and excitement of thinking.Scientific research, on the other hand, is not just about knowing and reasoning, but also thinking, creativity and courage of realizing new ideas.For that, I am hugely indebted to my supervisor, Prof. Philip Russell.Philip, thank you for teaching me the divergent way of thinking, to see many solutions to one problem, for giving me the courage to express my ideas and for providing excellent facilities and environment to realize them.I would also like to thank Prof. Curtis Menyuk for very nice discussions and comments about my thesis and specially the work he has done on self-similarity.Your deep insight and understanding of the physics and the beauty of mathematics behind it, is truly amazing and I really hope that in future I would have the opportunity to learn more from you.Many thanks go to Dr. Johannes Nold for who he is and

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Dominance of backward stimulated Raman scattering in gas-filled hollow-core photonic crystal fibers

Manoj K. Mridha, David Novoa, Philip St.J. Russell

Backward stimulated Raman scattering in gases provides a promising route to compression and amplification of a Stokes seed-pulse by counter-propagating against a pump-pulse, as has been already demonstrated in various platforms, mainly in free-space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable with, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532-nm-pump. The efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength towards the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.

arXiv:1801.08069•Optica•May 7, 2018•10 citations

Dominance of backward stimulated Raman scattering in gas-filled hollow-core photonic crystal fibers

Mridha, M., Novoa, D., Russell, P.

Backward stimulated Raman scattering in gases provides a promising route to the compression and amplification of a Stokes seed pulse by counter-propagating against a pump pulse, as has been demonstrated already in various platforms, mainly in free space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report, to the best of our knowledge, the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable to, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532 nm pump. Efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers, the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength toward the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.

•May 7, 2018•10 citations

Photonic microcells for quantum optics applications

P. S. Light

This thesis presents the development of photonic microcells for use as the host for coherent optics phenomena and related applications. A photonic microcell consists of a length of hollow-core photonic crystal fibre (HC-PCF) with a gas-filled core that is spliced to conventional optical fibre at either end to seal the gas within the fibre. Towards the goal of demonstrating and assessing the coherence properties of quantum optical effects in photonic microcells, the fabrication of two types of HC-PCF is presented. The established photonic bandgap HC-PCF offers extremely low transmission loss of ~10 dB/km over kilometre distances. However, the fibre has a limited transmission bandwidth of ~50 THz and exhibits modal coupling unfavourable for many applications. Work is presented on the tailoring of this fibre by control and shaping of the core-surround in order to improve its modal properties. A second type of HC-PCF is based on a large-pitch lattice, whose guidance relies on a new mechanism. This fibre exhibits a much improved bandwidth (>1000 THz) and has a relatively higher but still practical loss of ~1 dB/m. The development of photonic microcells at microbar pressure level and with low optical insertion loss is shown, an important step in the improvement of the technology for coherent optics applications which will take advantage of the extreme gas-laser interaction efficiency achieved in HC-PCF. Finally, quantum optical effects are demonstrated in HC-PCF and photonic microcells loaded with both the molecular gas acetylene and atomic vapour rubidium. The observation of electromagnetically induced transparency (EIT) in acetylene-filled HC-PCF represents the first such observation in a molecular gas, while the use of a photonic microcell allows a comparison of many experimental configurations to explore the coherence properties of coherent optical systems in the core of a HC-PCF. Furthermore, EIT is observed unambiguously in a rubidium loaded HC-PCF for the first time, and the anti-relaxation effects of a polymer coating demonstrated in this configuration.

•May 1, 2008•4 citations

Intermodal stimulated Raman scattering in hydrogen-filled hollow-core photonic crystal fiber

M. Ziemienczuk, A. M. Walser, A. Abdolvand +1 more

Stimulated Raman scattering is investigated in a slightly multimode gas-filled hollow-core photonic crystal fiber. Although, second-order Stokes light appears in the fundamental mode below a certain threshold energy, it is observed to switch to a two-lobed higher order mode above this threshold. Conversion to the higher order mode is made possible by the creation of a two-lobed moving coherence wave in the gas that provides both phase-matching and a strong intermodal pump-Stokes overlap. A theoretical model is developed, based on this physical interpretation that agrees quantitatively with the experimental results. The results suggest new opportunities for all-fiber gas-based nonlinear processes requiring phase-matching, such as coherent anti-Stokes Raman scattering, as well as providing a means (for example) of efficiently converting light from a higher order pump mode to a fundamental Stokes mode.

Journal of the Optical Society of America B•Jun 7, 2012•27 citations

Coherent intramodal Raman gain suppression at high pump intensities in gas-filled photonic crystal fibres

Pooria Hosseini, Manoj Kumar Mridha, David Novoa +2 more

Stimulated Raman scattering is coherently suppressed if the rate of phonon creation is exactly balanced by the rate of phonon annihilation, a prediction first made by Bloembergen and Shen in 1964 [1]. Viewed classically, this occurs when the fringe patterns created by the interference of pump-Stokes and pump-anti-Stokes signals cancel each other out. It has been recently shown that gas-filled hollow-core photonic crystal fiber (HC-PCF), pumped in the vicinity of the zero-dispersion point (ZDP), is an ideal vehicle for observing gain suppression. The ultralong path-lengths and the well-controlled dispersion permit dramatic suppression of the effective intramodal Raman gain for the fundamental core mode [2, 3], resulting in strong enhancement of intermodal scattering from the pump to a Stokes signal in a higher-order core mode.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2017•0 citations

Control of ultrafast pulses in a hydrogen-filled hollow-core photonic-crystal fiber by Raman coherence

Federico Belli, A. Abdolvand, John C. Travers +1 more

We present the results of an experimental and numerical investigation into temporally nonlocal coherent interactions between ultrashort pulses, mediated by Raman coherence, in a gas-filled kagome-style hollow-core photonic-crystal fiber. A pump pulse first sets up the Raman coherence, creating a refractive index spatiotemporal grating in the gas that travels at the group velocity of the pump pulse. Varying the arrival time of a second, probe, pulse allows a high degree of control over its evolution as it propagates along the fiber through the grating. Of particular interest are soliton-driven effects such as self-compression and dispersive wave (DW) emission. In the experiments reported, a DW is emitted at $\ensuremath{\sim}300\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ and exhibits a wiggling effect, with its central frequency oscillating periodically with pump-probe delay. The results demonstrate that a strong Raman coherence, created in a broadband guiding gas-filled kagome photonic-crystal fiber, can be used to control the nonlinear dynamics of ultrashort probe pulses, even in difficult-to-access spectral regions such as the deep and vacuum ultraviolet.

arXiv:1703.04543•Physical Review A•Jan 12, 2018•25 citations
In this thesis I study coherent light-matter interactions via stimulated Raman scattering (SRS) in a gas-filled hollow-core photonic crystal fiber (HC-PCF).The HC-PCF constitutes the foundation of the experimental results presented in this thesis, as without its unique properties realization of these experiments would not have been possible.These unique properties include tight confinement of laser light and matter in the small core of the fiber, which leads to extremely high conversion efficiencies in the SRS, and spectral filtering of unwanted nonlinear waves.This setup creates a clean system of two optical fields interacting via Raman medium inside the core of the fiber.This thesis consists of three parts.The first part (chapter 2) includes a general overview of the different types of HC-PCF, their fabrication techniques and guidance mechanisms.Two types of HC-PCF are considered: photonic bandgap HC-PCF and kagomé-HC-PCF.Guidance mechanisms of these two types of fibers are considered in detail.Of particular interest to me is the broadband guidance in kagomé-HC-PCF.Up to now, the mechanism responsible for this broadband guidance is not understood.A simplified semi-analytical model is derived which accounts for this broadband guidance in kagomé-HC-PCF and explain many of its guidance properties.In particular, using the model, the fiber loss as a function of wavelength is reproduced fairly well.The model also explains an important feature of kagomé-HC-PCF, namely, the insensitivity of its loss to the number of cladding layers.In the second part of the thesis (chapter 3), I set the basic theoretical formalism of SRS to be used in the rest of the thesis.The aim of the chapter is to derive the coupled wave equations that govern the evolution of the pump, Stokes and coherence fields using classical as well as semi-classical approaches.The third part of the thesis (chapters 4, 5, 6 and 7) discusses the results of experimental and theoretical investigations of my studies on SRS in gas-filled HC-PCF.I start with an overview of the already know results about SRS in HC-PCF and explain the mechanism of phase-locking for efficient generation of anti-Stokes SRS.This work clarifies high conversion efficiencies to anti-Stokes frequencies observed in early experiments.Most of these early experiments are focused on lowering the threshold for SRS generation and are done at relatively high pressures.In chapters 5 and 6, I use some of the unique properties of the HC-PCF to explore the coherent light-matter SRS interaction regimes not previously accessible.This includes the first experimental observation of backward superluminal solitary waves and self-similar solutions of SRS coupled-wave equations.These results represent a significant advance in the study of coherent effects and point to a new generation of highly engineerable gas cells for studying complex nonlinear phenomena.In chapter 7, I briefly overview the results presented in previous chapters and conclude my thesis by explaining possible improvements as well as new interesting directions in studying coherent light-matter interactions in gas-filled HC-PCF.In particular, I introduce a simple scheme for generating (purely rotational) broadband coherent frequency comb at low pump pulse energies using a gas-filled HC-PCF.Generation of such a frequency comb is quite interesting for synthesizing ultrashort pulses as well as a broad coherent tunable light source with high spectral brightness.The classic system of education is mainly based on the ability of deductive reasoning and knowledge of the classics.Quite often, in the course of learning that, we lose the joy and excitement of thinking.Scientific research, on the other hand, is not just about knowing and reasoning, but also thinking, creativity and courage of realizing new ideas.For that, I am hugely indebted to my supervisor, Prof. Philip Russell.Philip, thank you for teaching me the divergent way of thinking, to see many solutions to one problem, for giving me the courage to express my ideas and for providing excellent facilities and environment to realize them.I would also like to thank Prof. Curtis Menyuk for very nice discussions and comments about my thesis and specially the work he has done on self-similarity.Your deep insight and understanding of the physics and the beauty of mathematics behind it, is truly amazing and I really hope that in future I would have the opportunity to learn more from you.Many thanks go to Dr. Johannes Nold for who he is and
Backward stimulated Raman scattering in gases provides a promising route to compression and amplification of a Stokes seed-pulse by counter-propagating against a pump-pulse, as has been already demonstrated in various platforms, mainly in free-space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable with, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532-nm-pump. The efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength towards the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.
Backward stimulated Raman scattering in gases provides a promising route to the compression and amplification of a Stokes seed pulse by counter-propagating against a pump pulse, as has been demonstrated already in various platforms, mainly in free space. However, the dynamics governing this process when seeded by noise has not yet been investigated in a fully controllable collinear environment. Here we report, to the best of our knowledge, the first unambiguous observation of efficient noise-seeded backward stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber. At high gas pressures, when the backward Raman gain is comparable to, but lower than, the forward gain, we report quantum conversion efficiencies exceeding 40% to the backward Stokes at 683 nm from a narrowband 532 nm pump. Efficiency increases to 65% when the backward process is seeded by a small amount of back-reflected forward-generated Stokes light. At high pump powers, the backward Stokes signal, emitted in a clean fundamental mode and spectrally pure, is unexpectedly always stronger than its forward-propagating counterpart. We attribute this striking observation to the unique temporal dynamics of the interacting fields, which cause the Raman coherence (which takes the form of a moving fine-period Bragg grating) to grow in strength toward the input end of the fiber. A good understanding of this process, together with the rapid development of novel anti-resonant-guiding hollow-core fibers, may lead to improved designs of efficient gas-based Raman lasers and amplifiers operating at wavelengths from the ultraviolet to the mid-infrared.
This thesis presents the development of photonic microcells for use as the host for coherent optics phenomena and related applications. A photonic microcell consists of a length of hollow-core photonic crystal fibre (HC-PCF) with a gas-filled core that is spliced to conventional optical fibre at either end to seal the gas within the fibre. Towards the goal of demonstrating and assessing the coherence properties of quantum optical effects in photonic microcells, the fabrication of two types of HC-PCF is presented. The established photonic bandgap HC-PCF offers extremely low transmission loss of ~10 dB/km over kilometre distances. However, the fibre has a limited transmission bandwidth of ~50 THz and exhibits modal coupling unfavourable for many applications. Work is presented on the tailoring of this fibre by control and shaping of the core-surround in order to improve its modal properties. A second type of HC-PCF is based on a large-pitch lattice, whose guidance relies on a new mechanism. This fibre exhibits a much improved bandwidth (>1000 THz) and has a relatively higher but still practical loss of ~1 dB/m. The development of photonic microcells at microbar pressure level and with low optical insertion loss is shown, an important step in the improvement of the technology for coherent optics applications which will take advantage of the extreme gas-laser interaction efficiency achieved in HC-PCF. Finally, quantum optical effects are demonstrated in HC-PCF and photonic microcells loaded with both the molecular gas acetylene and atomic vapour rubidium. The observation of electromagnetically induced transparency (EIT) in acetylene-filled HC-PCF represents the first such observation in a molecular gas, while the use of a photonic microcell allows a comparison of many experimental configurations to explore the coherence properties of coherent optical systems in the core of a HC-PCF. Furthermore, EIT is observed unambiguously in a rubidium loaded HC-PCF for the first time, and the anti-relaxation effects of a polymer coating demonstrated in this configuration.
Stimulated Raman scattering is investigated in a slightly multimode gas-filled hollow-core photonic crystal fiber. Although, second-order Stokes light appears in the fundamental mode below a certain threshold energy, it is observed to switch to a two-lobed higher order mode above this threshold. Conversion to the higher order mode is made possible by the creation of a two-lobed moving coherence wave in the gas that provides both phase-matching and a strong intermodal pump-Stokes overlap. A theoretical model is developed, based on this physical interpretation that agrees quantitatively with the experimental results. The results suggest new opportunities for all-fiber gas-based nonlinear processes requiring phase-matching, such as coherent anti-Stokes Raman scattering, as well as providing a means (for example) of efficiently converting light from a higher order pump mode to a fundamental Stokes mode.
Stimulated Raman scattering is coherently suppressed if the rate of phonon creation is exactly balanced by the rate of phonon annihilation, a prediction first made by Bloembergen and Shen in 1964 [1]. Viewed classically, this occurs when the fringe patterns created by the interference of pump-Stokes and pump-anti-Stokes signals cancel each other out. It has been recently shown that gas-filled hollow-core photonic crystal fiber (HC-PCF), pumped in the vicinity of the zero-dispersion point (ZDP), is an ideal vehicle for observing gain suppression. The ultralong path-lengths and the well-controlled dispersion permit dramatic suppression of the effective intramodal Raman gain for the fundamental core mode [2, 3], resulting in strong enhancement of intermodal scattering from the pump to a Stokes signal in a higher-order core mode.
We present the results of an experimental and numerical investigation into temporally nonlocal coherent interactions between ultrashort pulses, mediated by Raman coherence, in a gas-filled kagome-style hollow-core photonic-crystal fiber. A pump pulse first sets up the Raman coherence, creating a refractive index spatiotemporal grating in the gas that travels at the group velocity of the pump pulse. Varying the arrival time of a second, probe, pulse allows a high degree of control over its evolution as it propagates along the fiber through the grating. Of particular interest are soliton-driven effects such as self-compression and dispersive wave (DW) emission. In the experiments reported, a DW is emitted at $\ensuremath{\sim}300\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ and exhibits a wiggling effect, with its central frequency oscillating periodically with pump-probe delay. The results demonstrate that a strong Raman coherence, created in a broadband guiding gas-filled kagome photonic-crystal fiber, can be used to control the nonlinear dynamics of ultrashort probe pulses, even in difficult-to-access spectral regions such as the deep and vacuum ultraviolet.