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Erbium-Doped Fibre Lasers
Published in Shyamal Bhadra, Ajoy Ghatak, Guided Wave Optics and Photonic Devices, 2017
Aditi Ghosh, Deepa Venkitesh, R. Vijaya
Both multiwavelength and broadband emissions have been obtained using EDFLs. These have been achieved primarily by utilizing different kinds of nonlinearities that can be invoked in a fibre, such as stimulated Brillouin scattering (SBS) [42], Raman scattering [43–45], four-wave mixing (FWM) [46–48] and with the use of specialty fibres [49–52]. In the process of supercontinuum generation, an intense pump pulse gets spectrally broadened over a wide range of wavelengths by nonlinear mechanisms on propagation through a medium. However, these schemes that make use of multiple nonlinear effects usually use high powers of the order of watts and result in spectral widths of ~100–200 nm [53]. For broadband generation of spectral widths of 30–40 nm, a single nonlinear mechanism can be adopted, which inherently creates multiple wavelengths. Cascaded FWM is capable of producing equispaced frequencies in a nonlinear medium. This is useful for broadband generation when the frequency spacing is very small. With fibres of significant nonlinear coefficient, CW powers as low as 200 mW are sufficient for this purpose.
Microstructured optical fibers
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Jesper Lægsgaard, Anders Bjarklev, Tanya Monro, Tanya Monro
Supercontinuum sources have seen a wide range of applications, including optical coherence tomography [43] and frequency metrology [44]. However, the most important application is perhaps within the rapidly growing field of biomedical imaging, especially confocal microscopy, where fluorescent markers are introduced in biological samples, and excited by focused laser light [45,46]. Thus, a wavelength-flexible light source with good spatial coherence can give a very large degree of flexibility in the number and range of fluorophores, which can be used for imaging the movement of, for example, different proteins in a biological specimen. Commercial use of supercontinuum sources in this area took off in 2008 with their incorporation in the Leica TCS SP5 X confocal microscope. Coupled with a tunable acousto-optic filter, the supercontinuum replaces a large battery of lasers at different excitation wavelengths, which was previously a necessity in such instruments.
Nonlinear Optics of Fibre Waveguides
Published in Yu. N. Kulchin, Modern Optics and Photonics of Nano and Microsystems, 2018
As was shown above, the nonlinear optical properties of optical fibres depend significantly on the dispersion characteristics of the modes directed to them. Figure 36 shows the calculated dispersion profiles (DGV) for four PC‐fibre lightguides with a hollow core. As can be seen, all optical fibres have two zero‐dispersion wavelengths localized near the values of 0.96 and 1.45 μm $ {{\mu m}} $ . In connection with this, such optical fibres are able to exhibit nonlinear optical properties, and, in particular, can be used to generate a supercontinuum.
Investigation of As2S3-borosilicate chalcogenide glass-based dispersion-engineered photonic crystal fibre for broadband supercontinuum generation in the mid-IR region
Published in Journal of Modern Optics, 2020
Shruti Kalra, Sandeep Vyas, Manish Tiwari, Yaseera Ismail, Preecha Yupapin, Jalil Ali, Ghanshyam Singh
Supercontinuum (SC) generation has, since its inception fascinated researchers, due to its wide range of applications in diverse areas of science and engineering, such as spectroscopy, microscopy, telecommunications, biomedical imaging and sensing, and meteorology [1–3]. Supercontinuum generation (SCG) is the extreme broadening of a short pulse while it traverses through a nonlinear medium, due to a combination of many nonlinear effects such as Raman scattering, soliton dynamics, four-wave mixing (FWM), cross-phase modulation (XPM), self-phase modulation (SPM) along with the high nonlinearity and dispersion profile of the medium [4]. In 1970, Alfano and Shapiro reported this nonlinear phenomenon in bulk BK7 glass where they observed a ten times broader spectrum than was previously reported, extending from 400 to 700 nm in the visible range [5]. The successful generation of SC with photonic crystal fibres (PCF) in the year 2000 by Ranka et al. gave a new dimension to SCG [1].
Tellurium-oxide coated silicon-nitride hybrid waveguide for near-to-mid-IR supercontinuum generation: design and analysis
Published in Journal of Modern Optics, 2021
Than Singh Saini, V. R. Supradeepa
The spectral broadening of the supercontinuum mainly depends on the nonlinearity and the dispersion characteristic of the waveguide structure [38]. The dispersion profile of designed hybrid waveguide at various thickness of the TeO2 layer is illustrated in Figure 3. It indicates that, on increasing the thickness of TeO2 layer, the dispersion profile shifts from deep-normal to flat and nearly-zero all-normal dispersion profile up to 3.5 µm in mid-IR region. For the optimized geometric parameters (listed in Table 1) of the hybrid waveguide, the simulated numerical values of the dispersion are −49.2 and −4.0 ps/nm/km at 1.5 and 2.0 µm, respectively.
Dual-cavity spectrometer for monitoring broadband light extinction by atmospheric aerosols
Published in Aerosol Science and Technology, 2020
Aiswarya Saseendran, Susan Mathai, Shreya Joshi, Anoop Pakkattil, Tyler Capek, Gregory Kinney, Claudio Mazzoleni, Ravi Varma
Cavity enhanced absorption spectroscopy (CEAS), in a broad sense, exploits the property of high finesse optical cavities, which increases the interaction probability of light with matter, and helps to retrieve the spectral information over a wide range of wavelengths, while retaining high sensitivity (Fiedler, Hese, and Ruth 2003). An incoherent broadband light source can be used in this technique (incoherent broadband cavity enhanced absorption spectroscopy or IBBCEAS) enabling the simultaneous extinction measurements of trace gases and aerosols continuously over a broad wavelength region. This simple, cost effective method does not require mode matching, which makes it suitable for field measurements. IBBCEAS has been effectively used to quantify trace gases like NO2 (Ball, Langridge, and Jones 2004), NO3 (Suhail et al. 2019; Ball, Langridge, and Jones 2004; Venables et al. 2006), I2 (Dixneuf et al. 2009; Ball, Langridge, and Jones 2004), HONO (Gherman et al. 2008), glyoxal (Washenfelder et al. 2008), natural gases (Prakash et al. 2018), 1,4-dioxane (Chandran and Varma 2016), etc. in both laboratory and in-situ field measurements. Many recent studies have been performed for aerosol extinction measurements exploiting the high detection sensitivity of IBBCEAS techniques (Washenfelder et al. 2013; Zhao et al. 2013; Thalman and Volkamer 2010; Varma et al. 2009). Combinations of different instruments like CEAS and nephelometer, called albedometer (Zhao et al. 2014; Zhou et al. 2020), CRDS, photoacoustic spectroscopy and nephelometry (Bluvshtein et al. 2016; Sanford et al. 2008), integrated photoacoustic nephelometers (Sharma et al. 2013; Chakrabarty et al. 2010; Lewis et al. 2008) etc. are several further developments in this area for highly sensitive measurement of aerosol optical properties. Among different cavity enhanced setups, significant modifications have been reported in the literature with the implementation of new light sources. The light source used to develop an instrument should be robust with a long life time and it should have a broad emission spectrum with comparatively low noise. Among broadband light sources, usually used in cavity-based experiments, are Xenon arc lamps and LEDs (Zhao et al. 2014; Varma et al. 2009; Fiedler, Hese, and Ruth 2003) but these have low intensity for in-situ detection. High brightness supercontinuum light sources (SC) provide broadband spectra with high power density. A few CEAS instrumentations using SC sources have been reported for trace gas detection (Chandran and Varma 2016; Ruth, Dixneuf, and Orphal 2015; Langridge et al. 2008). One drawback of some SC laser sources for CEAS applications is spectral intensity and shape fluctuations that result in spectral baseline shifts and intermittent spurious peaks. The best method to overcome this drawback is the simultaneous detection of reference as well as sample intensities, which can be attained by a dual cavity system (Chandran, Puthukkudy, and Varma 2017).