{"id":503,"date":"2024-07-22T07:21:35","date_gmt":"2024-07-22T07:21:35","guid":{"rendered":"https:\/\/www.flarelab.in\/copy-of-projects-2"},"modified":"2026-10-11T09:27:04","modified_gmt":"2026-10-11T03:57:04","slug":"research","status":"publish","type":"page","link":"https:\/\/ece.iisc.ac.in\/~balav\/research\/","title":{"rendered":"Research"},"content":{"rendered":"\n
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Research at FLARe Lab<\/strong><\/h2>\n<\/div>\n\n\n\n
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At FLARe Lab, our research focuses on understanding and controlling the spectrum, intensity noise, and coherence of light as it is generated, amplified, and transformed in optical fibers. These properties are often closely coupled, and improving optical power, spectral bandwidth, or wavelength tunability can introduce new noise and nonlinear limitations. Understanding these interactions and developing ways to overcome them are central to our research.<\/p>\n\n\n\n

We combine laser physics, nonlinear fiber optics, numerical modelling, and precision optical and RF characterization to investigate and develop advanced fiber laser systems. Our research spans low-noise fiber lasers and amplifiers, Raman-based wavelength conversion, broadband supercontinuum generation, and their applications in advanced optical imaging and sensing. By integrating fundamental investigations with experimental system development, we aim to develop optical sources with tailored spectral and noise characteristics for demanding photonic applications.<\/p>\n\n\n\n

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Low-Noise Laser Architectures<\/strong><\/p>\n\n\n\n

How does the architecture of a fiber laser influence its intensity noise, and how can we control this noise without compromising optical power? These questions are central to developing high-performance optical sources, particularly when the laser is used to drive nonlinear processes where intensity fluctuations may be transferred or amplified.<\/p>\n\n\n\n

At FLARe Lab, we investigate continuous-wave rare-earth-doped fiber lasers and amplifiers, with particular emphasis on ytterbium-doped systems. Our experimental platforms include fiber Bragg grating (FBG) oscillators, unidirectional ring oscillators, and master-oscillator power-amplifier (MOPA) architectures. By systematically varying cavity configuration, seed characteristics, pumping geometry, and output power, we study how these parameters influence relative intensity noise across a broad range of frequencies.<\/p>\n\n\n\n

Our investigations have demonstrated that ring-seeded MOPA architectures can substantially suppress high-frequency intensity noise compared with conventional FBG-seeded configurations, while maintaining high optical output power. These findings provide insights into the design of low-noise pump lasers for cascaded Raman wavelength conversion and broadband supercontinuum generation. An important ongoing question is how noise originating in the laser evolves through amplification and subsequent nonlinear propagation.<\/p>\n\n\n\n

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Experimental configurations for investigating intensity noise in Yb-doped fiber lasers and MOPA systems, together with optical and RF characterization techniques.<\/figcaption><\/figure>\n\n\n\n
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Comparison of integrated RMS relative intensity noise across three frequency bands, highlighting the reduced mid- and high-frequency noise achieved with ring-seeded MOPA architectures.<\/figcaption><\/figure>\n\n\n\n
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Nonlinear Spectral Engineering<\/strong><\/p>\n\n\n\n

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How can we generate optical wavelengths beyond the gain bandwidth of conventional lasers while maintaining high spectral purity and low intensity noise? Stimulated Raman scattering in optical fibers enables wavelength conversion through successive Stokes shifts, but the spectral and noise characteristics of the generated light are governed by complex nonlinear interactions and pump-laser dynamics.<\/p>\n\n\n\n

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At FLARe Lab, we investigate cascaded random Raman fiber lasers based on half-open cavity configurations, where distributed feedback and successive Raman interactions enable wavelength conversion. We study how pump-laser architecture, operating power, and Raman conversion order influence spectral purity and relative intensity noise (RIN). Using our high-power Yb-doped fiber laser platforms, we have experimentally demonstrated seven Stokes orders spanning approximately 1117\u20131580 nm, achieving spectral purity approaching 98% with appropriate spectral filtering. Our measurements also reveal significant differences in intensity noise between pump architectures and a non-monotonic, U-shaped dependence of RIN on operating power.<\/p>\n\n\n\n

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Building on these findings, we are investigating the physical mechanisms governing noise transfer through successive Raman orders and exploring tunable and polarization-maintaining Raman laser architectures. Our broader objective is to develop wavelength-agile optical sources with deliberately engineered spectral and noise characteristics for nonlinear photonics and advanced optical systems.<\/p>\n\n\n\n

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Experimental configuration for cascaded random Raman generation using in-house-developed rare-earth fiber-laser pump architectures, with optical and RF-noise characterization.<\/figcaption><\/figure>\n\n\n\n
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Measured cascaded Raman spectra for different fiber-laser pump architectures, demonstrating wavelength conversion through successive Stokes orders.<\/figcaption><\/figure>\n\n\n\n
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Evolution of relative intensity noise and spectral purity with Raman laser output power for different pump configurations.<\/figcaption><\/figure>\n\n\n\n
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Engineering Broadband Light<\/strong><\/p>\n\n\n\n

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Generating a broad optical spectrum is only part of the challenge in supercontinuum generation. For demanding optical applications, spectral shape, spectral power density, and intensity noise across the generated bandwidth can be just as important as the bandwidth itself. How can these properties be simultaneously controlled during nonlinear light propagation in optical fibers?<\/p>\n\n\n\n

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At FLARe Lab, we investigate continuous-wave (CW) supercontinuum generation in standard telecommunication fibers, using in-house-developed fiber lasers to drive cascaded Raman conversion and nonlinear spectral broadening. We study how pump-laser architecture, fiber dispersion, nonlinear interactions, and propagation length influence spectral evolution and wavelength-resolved intensity noise. Our experiments have demonstrated broadband supercontinuum generation spanning approximately 1000\u20131700 nm, with output powers reaching 32 W. Through detailed optical and RF-noise characterization, we have also demonstrated significantly lower intensity noise than a commercial photonic-crystal-fiber supercontinuum source under the investigated conditions.<\/p>\n\n\n\n

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Our ongoing research focuses on understanding the physical mechanisms governing noise evolution during supercontinuum generation and developing strategies to simultaneously improve spectral flatness, power density, and noise performance. We are exploring wavelength-tunable pumping near the zero-dispersion wavelength of telecom fibers, pulsed excitation schemes, and numerical modelling of nonlinear propagation to develop broadband sources tailored for advanced optical imaging and sensing.<\/p>\n\n\n\n

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Experimental configuration for continuous-wave supercontinuum generation in standard telecommunication fiber using in-house-developed fiber-laser pump architectures, together with optical and RF-noise characterization.<\/figcaption><\/figure>\n\n\n\n
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Experimental supercontinuum spectra generated in standard telecommunication fiber, illustrating broadband spectral generation and comparison with a commercial photonic-crystal-fiber supercontinuum source.<\/figcaption><\/figure>\n\n\n\n
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Wavelength-resolved relative intensity noise of continuous-wave supercontinuum sources, showing the influence of pump architecture and comparison with a commercial photonic-crystal-fiber source.<\/figcaption><\/figure>\n\n\n\n
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From Engineered Sources to Optical Systems<\/strong><\/p>\n\n\n\n

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How does engineering the spectrum and noise of a light source translate into improved performance in an optical system? For applications such as optical coherence tomography (OCT), a broad optical bandwidth is essential for high axial resolution, but the usable spectral distribution, intensity noise, and detection characteristics can be equally important in determining imaging performance.<\/p>\n\n\n\n

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At FLARe Lab, we investigate the integration of advanced fiber-based optical sources with ultrahigh-resolution spectral-domain OCT systems. Our research connects source development with system-level characterization, examining how spectral bandwidth, spectral shape, and intensity noise influence axial resolution and detection sensitivity. We have developed an experimental OCT platform operating around 1.55 \u00b5m and investigated the performance of our in-house continuous-wave supercontinuum sources in comparison with conventional superluminescent diode sources.<\/p>\n\n\n\n

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Building on these investigations, we aim to develop broadband optical sources specifically engineered for the requirements of high-resolution imaging. Our ongoing research explores approaches to improving spectral flatness, reducing source noise, and optimizing the usable bandwidth of OCT systems, particularly in the near-infrared wavelength region. More broadly, we seek to understand how source-level control of optical properties can enable new capabilities in precision optical measurements and sensing.<\/p>\n\n\n\n

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Experimental spectral-domain optical coherence tomography (SD-OCT) setup operating around 1.55 \u00b5m, used to compare in-house-developed continuous-wave supercontinuum sources with a conventional superluminescent diode (SLD).<\/figcaption><\/figure>\n\n\n\n
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Experimental comparison of axial point-spread functions, axial resolution, sensitivity, and depth-dependent response of the SD-OCT system using ring-MOPA-pumped supercontinuum, FBG-MOPA-pumped supercontinuum, and SLD sources.<\/figcaption><\/figure>\n\n\n\n
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Selected Collaborative Research<\/strong><\/p>\n\n\n\n

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Beyond our primary research programme, we contribute to collaborative investigations of high-power, high-coherence fiber laser systems, including the mitigation of stimulated Brillouin scattering and the engineering of optical spectra for power scaling. This work, undertaken in collaboration with Prof. V. R. Supradeepa at CeNSE, IISc, complements our broader interest in understanding and controlling nonlinear effects and coherence in fiber lasers.<\/p>\n\n\n\n

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How We Do Research<\/strong><\/p>\n\n\n\n

At FLARe Lab, our research combines fundamental physical understanding with numerical modelling, experimental development, and quantitative characterization. A typical investigation begins with a scientific question, progresses through theoretical analysis and numerical simulations, and leads to the design, construction, and testing of an optical system. Experimental observations, particularly those that differ from initial predictions, often motivate deeper investigations and new research directions.<\/p>\n\n\n\n

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Our laboratory provides opportunities to work across multiple aspects of experimental photonics, including fiber laser and amplifier development, nonlinear optical propagation, fiber processing and splicing, optical spectrum characterization, high-speed photodetection, RF-noise measurements, and interferometric imaging. We emphasize understanding the underlying physics, systematically evaluating experimental results, and connecting measurements with theoretical and numerical models.<\/p>\n\n\n\n

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We encourage researchers to take intellectual ownership of their work, from formulating research questions and designing experiments to troubleshooting, interpreting results, and communicating scientific findings. Our research environment emphasizes curiosity, scientific rigor, independence, collaboration, and continuous learning, with the goal of developing researchers capable of identifying and solving challenging problems in photonics.<\/p>\n\n\n\n

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Interested in joining FLARe Lab? Explore research opportunities<\/a><\/p>\n\n\n\n

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Research at FLARe Lab At FLARe Lab, our research focuses on understanding and controlling the spectrum, intensity noise, and coherence of light as it is generated, amplified, and transformed in optical fibers. These properties are often closely coupled, and improving optical power, spectral bandwidth, or wavelength tunability can introduce new noise and nonlinear limitations. Understanding […]<\/p>\n","protected":false},"author":246927411,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"_links":{"self":[{"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/pages\/503"}],"collection":[{"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/users\/246927411"}],"replies":[{"embeddable":true,"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/comments?post=503"}],"version-history":[{"count":52,"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/pages\/503\/revisions"}],"predecessor-version":[{"id":3112,"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/pages\/503\/revisions\/3112"}],"wp:attachment":[{"href":"https:\/\/ece.iisc.ac.in\/~balav\/wp-json\/wp\/v2\/media?parent=503"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}