Specialty Optical Fibers for Mid-IR Photonics - Springer Link

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Specialty Optical Fibers for Mid-IR. Photonics. Bishnu P. Pal, A. Barh, S. Ghosh, R.K. Varshney, J. Sanghera,. L.B. Shaw and I.D. Aggarwal. Abstract We present ...
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Specialty Optical Fibers for Mid-IR Photonics Bishnu P. Pal, A. Barh, S. Ghosh, R.K. Varshney, J. Sanghera, L.B. Shaw and I.D. Aggarwal

Abstract We present chalcogenide (Ch) glass-based all-fiber application-specific microstructured optical fibers (MOFs)-based devices like all-fiber efficient discrete and broad-band light sources as well as fibers for distortion free high power light guidance in the mid-IR spectral regime. For new source generation, nonlinearities and dispersion of index guided Ch-MOFs were suitably tailored through structural optimization, while for high power guidance, an ultra large mode area fiber design and a second design for distortion free parabolic pulse generation will be described.

3.1 Introduction In recent years eye safe mid-infrared (mid-IR) spectral range (2–10 µm) has assumed great important owing to a host of potential applications ranging from nondestructive medical diagnostics to strategic applications in military/defense. This wavelength (λ) range is also aptly known as molecular fingerprint regime of various organic/inorganic molecules [1, 2]. B.P. Pal (&) School of Natural Science, Mahindra Ecole Centrale, Bahadurpally, Hyderabad 500043, India e-mail: [email protected] A. Barh  R.K. Varshney Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India S. Ghosh INSPIRE Faculty, Institute of Radio Physics and Electronics, University of Calcutta, Kolkata 700009, India J. Sanghera  L.B. Shaw Naval Research Laboratory, Code 5620, Washington, DC 20375, USA I.D. Aggarwal Physics Department, University of North Carolina, Charlotte, NC 28223, USA © Springer India 2015 V. Lakshminarayanan and I. Bhattacharya (eds.), Advances in Optical Science and Engineering, Springer Proceedings in Physics 166, DOI 10.1007/978-81-322-2367-2_3

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Chalcogenide glass (S-Se-Te)-based microstructured optical fibers (MOFs) are potentially a versatile platform for mid-IR applications due to their high optical transparency, extraordinary linear and nonlinear (NL) properties. Studies on MOFs reveal that, their zero dispersion wavelength (λZD) as well as dispersion slope could be tailored over a large wavelength (λ) range. This fascinating dispersion feature along with high Kerr nonlinearity of Ch-glasses (n2 * 100 times higher than silica) make them imminently suitable for generating new wavelengths via NL effects, such as, four wave mixing (FWM), supercontinuum generation etc. In this talk, we would present some of our recent work on FWM-based mid-IR source generation within 3–6.5 μm λ-range [3–5]. At the other extreme, NL effects could be detrimental when guided wave high optical power delivery becomes necessary or propagation of high optical power is essential in high-power fiber lasers. These problems can be overcome either by distributing the powers across a large mode area (LMA) fiber or by reshaping a propagating high power Gaussian pulse to a parabolic pulse (PP), which can overcome NL-induced distortions like pulse breaking in a fiber laser. We theoretically demonstrate applicability of Ch-based MOF platform for designing ultra-LMA MOF for mid-IR [6] and an up-tapered MOF for generating PP at 2 μm [7].

3.2 Modelling and Key Results 3.2.1 Ch-MOF Based Mid-IR Source Generation NL-FWM in a tailored Ch-MOF is exploited for generating an all-fiber mid-IR source [3] through choice of appropriate pump power level to suppress other NL effects. In highly NL single-mode (SM)-fibers, FWM-induced frequency shift depends on both the magnitude and sign of its GVD parameters, e.g. a positive β4 leads to broad-band and flat gain, while a negative β4 reduces the flatness and bandwidth (BW) of the FWM output [4]. For high efficiency, perfect phase matching, large mode overlap, and low fiber loss are essential. Further, a small idler as seed enhances its efficiency [3]. Arsenic sulphide (As2S3)-based MOF with hexagonally arranged air holes is designed and proposed (Fig. 3.1a) to attain a discrete mid-IR source at 4.36 μm by assuming a 2.04 μm Tm3+-doped fiber laser of 5 W power as the pump. Structural optimization led to attainment of signal amplification factor (AFs) *20 dB with a BW of 16 nm (Fig. 3.1b). Further, this design can be tuned to get broad-band source, where thermally compatible borosilicate glass is assumed to fill the air holes in a suitable As2S3-MOF. With a pump (*2.8 μm), broad-band mid-IR 3–4.2 μm source is realizable (Fig. 3.1c). We have also designed arsenic selenide (As2Se3) and PES based-MOF structures which can generate both narrow (*6.46 μm) and broad-band (5–6.3 μm) sources with a CO laser as the pump (Fig. 3.1d, e) [5].

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Fig. 3.1 a Typical cross-section of holey Ch-MOF. b AFs of discrete source around 4.36 μm. c AFs of broad-band source ranging from 3 to 4.2 μm. d AFs of discrete source around 6.46 μm. e AFs of broad-band source ranging from 5 to 6.3 μm. f Variation of effective area (Aeff) of MCOF. g Transformation of a Gaussian pulse to PP in a *20 cm length of up-tapered MOF

3.2.2 High Power Mid-IR Light Guidance Two thermally compatible, low index contrast Ch-glass based novel design of a microstructured core fiber (MCOF) is proposed as LMA fiber design [6], where ultra-LMA ≥ 75,000 μm2 could be realized over 3–5 μm with effective SM operation (Fig. 3.1f). On the other hand, an up-tapered MOF design is proposed to achieve transformation of a high power Gaussian pulse to a PP at a wavelength of 2 μm within *20 cm length of the tapered MOF (Fig. 3.1g) [7].

3.3 Conclusions and Acknowledgments This talk will cover our recent theoretical work on Ch-MOF based new light source generation and high power light guidance at mid-IR spectral range. This work relates to Department of the Navy Grant N62909-10-1-7141 issued by Office of Naval Research Global. The United States Government has royalty-free license throughout the world in all copyrightable material contained herein.

References 1. Jackson SD (2012) Towards high-power mid-infrared emission from a fibre laser. Nat Photon 6 (7):423–431 2. Serebryakov VA, Boĭko EV, Petrishchev NN, Yan AV (2010) Medical applications of mid-IR lasers. Problems and prospects. J Opt Technol 77(1):6–17

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3. Barh A, Ghosh S, Agrawal GP, Varshney RK, Aggarwal ID, Pal BP (2013) Design of an efficient mid-IR light source using chalcogenide holey fibers: a numerical study. J Opt (IOP) 15 (3):035205 4. Barh A, Ghosh S, Varshney RK, Pal BP (2013) An efficient broad-band mid-wave IR fiber optic light source: design and performance simulation. Opt Exp 21(8):9547–9555 5. Barh A, Ghosh S, Varshney RK, Pal BP, Sanghera J, Shaw LB, Aggarwal ID (2014) Mid-IR fiber optic light source around 6 µm through parametric wavelength translation. Laser Phys (IOP) 24(11):115401 6. Barh A, Ghosh S, Varshney RK, Pal BP (2013) Ultra-large mode area microstructured core chalcogenide fiber design for mid-IR beam delivery. Opt Commun 311:129–133 7. Barh A, Ghosh S, Varshney RK, Pal BP (2014) A tapered chalcogenide microstructured optical fiber for mid-IR parabolic pulse generation: design and performance study. IEEE J Sel Top Quantum Electron 20(5):7500507