Complete characterization of ultrashort pulse sources at 1550 nm

This paper reviews the use of frequency-resolved optical gating (FROG) to characterize mode-locked lasers producing ultrashort pulses suitable for high-capacity optical communications systems at wavelengths around 1550 nm, Second harmonic generation (SHG) FROG is used to characterize pulses from a passively mode-locked erbium-doped fiber laser, and both single-mode and dual-mode gain-switched semiconductor lasers. The compression of gain-switched pulses in dispersion compensating fiber is also studied using SHG-FROG, allowing optimal compression conditions to be determined without a priori assumptions about pulse characteristics. We also describe a fiber-based FROG geometry exploiting cross-phase modulation and show that it is ideally suited to pulse characterization at optical communications wavelengths. This technique has been used to characterize picosecond pulses with energy as low as 24 pJ, giving results in excellent agreement with SHG-FROG characterization, and without any temporal ambiguity in the retrieved puls

Resonant Bend Loss in Leakage Channel Fibers

Leakage channel fibers, designed to suppress higher-order modes, demonstrate resonant power loss at certain critical radii of curvature. Outside the resonance, the power recovers to the levels offset by the usual mechanism of bend-induced loss. Using C$^2$-imaging, we experimentally characterize this anomaly and identify the corresponding physical mechanism as the radiative decay of the fundamental mode mediated by the resonant coupling to a cladding mode.Comment: 3 pages, 4 figures, submitted to Optics Letter

Polarization control for slow and fast light in fiber optical, Raman-assisted, parametric amplification

Efficient slow and fast light fiber devices based on narrow band optical parametric amplification require a strict polarization control of the waves involved in the interaction. The use of high birefringence and spun fibers is studied theoretically, possible impairments evaluated, and design parameters determined.Comment: 20 pages, 7 figures, preprint submitted to Comptes Rendue

Intrinsic, multiplexable sensors for electric field strength using structural slow light in phase-shifted fibre Bragg gratings

In this paper we demonstrate through simulation the potential for phase-shifted fibre Bragg gratings incorporating structural slow light to enable intrinsic reflection-mode point sensors for electric field or voltage. It is shown that lo-bi FBGs incorporating multiple phase shifts yield large enhancements in group index (group delay) at resonance, thus amplifying and localizing time-dependent non-reciprocal effects. A relative, multiplexable measurement of electric field by comparison of the phase unbalance between linear modes on and off resonance is proposed, yielding static resolutions of 24 V and 18 mV respectively in unpoled (dc Kerr effect) and poled (Pockels effect) fibres

Ring-core few-mode fiber for tunable true time delay line operation

© 2019 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited.[EN] We propose, for the first time to our knowledge, tunable true time delay line operation for radiofrequency signals on a few-mode fiber link. In particular, the custom design of a 7-LP-mode ring-core few-mode fiber together with a set of 5 broadband long period gratings inscribed at the proper positions along the fiber allows 4-sample true time delay line tunability over a 20-nm optical wavelength range. We study the performance of the designed true time delay line in the context of reconfigurable microwave photonics signal processing by theoretically evaluating microwave signal filtering and optical beamforming networks for phased array antennas.European Research Council (Consolidator Grant 724663); Ministerio de Economia, Industria y Competitividad, Gobierno de Espana (BES-2015-073359 for S. Garcia, RYC-2014-16247 for I. Gasulla, TEC2016-80150-R).García-Cortijo, S.; Guillem-Cogollos, R.; Gasulla Mestre, I. (2019). Ring-core few-mode fiber for tunable true time delay line operation. Optics Express. 27(22):31773-31782. https://doi.org/10.1364/OE.27.03177331773317822722Richardson, D. J., Fini, J. M., & Nelson, L. E. (2013). Space-division multiplexing in optical fibres. Nature Photonics, 7(5), 354-362. doi:10.1038/nphoton.2013.94Barrera, D., Gasulla, I., & Sales, S. (2015). Multipoint Two-Dimensional Curvature Optical Fiber Sensor Based on a Nontwisted Homogeneous Four-Core Fiber. Journal of Lightwave Technology, 33(12), 2445-2450. doi:10.1109/jlt.2014.2366556Gasulla, I., & Capmany, J. (2012). Microwave Photonics Applications of Multicore Fibers. IEEE Photonics Journal, 4(3), 877-888. doi:10.1109/jphot.2012.2199101Capmany, J., Ortega, B., Pastor, D., & Sales, S. (2005). Discrete-time optical Processing of microwave signals. Journal of Lightwave Technology, 23(2), 702-723. doi:10.1109/jlt.2004.838819Ng, W., Walston, A. A., Tangonan, G. L., Lee, J. J., Newberg, I. L., & Bernstein, N. (1991). The first demonstration of an optically steered microwave phased array antenna using true-time-delay. Journal of Lightwave Technology, 9(9), 1124-1131. doi:10.1109/50.85809Wang, C., & Yao, J. (2013). Fiber Bragg gratings for microwave photonics subsystems. Optics Express, 21(19), 22868. doi:10.1364/oe.21.022868Morton, P. A., & Khurgin, J. B. (2009). Microwave Photonic Delay Line With Separate Tuning of the Optical Carrier. IEEE Photonics Technology Letters, 21(22), 1686-1688. doi:10.1109/lpt.2009.2031500Capmany, J., Mora, J., Gasulla, I., Sancho, J., Lloret, J., & Sales, S. (2013). Microwave Photonic Signal Processing. Journal of Lightwave Technology, 31(4), 571-586. doi:10.1109/jlt.2012.2222348Gasulla, I., Barrera, D., Hervás, J., & Sales, S. (2017). Spatial Division Multiplexed Microwave Signal processing by selective grating inscription in homogeneous multicore fibers. Scientific Reports, 7(1). doi:10.1038/srep41727García, S., & Gasulla, I. (2016). Dispersion-engineered multicore fibers for distributed radiofrequency signal processing. Optics Express, 24(18), 20641. doi:10.1364/oe.24.020641Guillem, R., García, S., Madrigal, J., Barrera, D., & Gasulla, I. (2018). Few-mode fiber true time delay lines for distributed radiofrequency signal processing. Optics Express, 26(20), 25761. doi:10.1364/oe.26.025761García, S., Guillem, R., Madrigal, J., Barrera, D., Sales, S., & Gasulla, I. (2019). Sampled true time delay line operation by inscription of long period gratings in few-mode fibers. Optics Express, 27(16), 22787. doi:10.1364/oe.27.022787Zhao, Y., Liu, Y., Zhang, L., Zhang, C., Wen, J., & Wang, T. (2016). Mode converter based on the long-period fiber gratings written in the two-mode fiber. Optics Express, 24(6), 6186. doi:10.1364/oe.24.006186Marcuse, D. (1972). Derivation of Coupled Power Equations. Bell System Technical Journal, 51(1), 229-237. doi:10.1002/j.1538-7305.1972.tb01911.xOgawa, K. (1977). Simplified Theory of the Multimode Fiber Coupler. Bell System Technical Journal, 56(5), 729-745. doi:10.1002/j.1538-7305.1977.tb00536.xErdogan, T. (1997). Cladding-mode resonances in short- and long-period fiber grating filters. Journal of the Optical Society of America A, 14(8), 1760. doi:10.1364/josaa.14.001760Capmany, J., Ortega, B., & Pastor, D. (2006). A tutorial on microwave photonic filters. Journal of Lightwave Technology, 24(1), 201-229. doi:10.1109/jlt.2005.860478Ortega, B., Cruz, J. L., Capmany, J., Andres, M. V., & Pastor, D. (2000). Variable delay line for phased-array antenna based on a chirped fiber grating. IEEE Transactions on Microwave Theory and Techniques, 48(8), 1352-1360. doi:10.1109/22.85948

Equalizer tap length requirement for mode group delay-compensated fiber link with weakly random mode coupling

The equalizer tap length requirement is investigated analytically and numerically for differential modal group delay (DMGD) compensated fiber link with weakly random mode coupling. Each span of the DMGD compensated link comprises multiple pairs of fibers which have opposite signs of DMGD. The result reveals that under weak random mode coupling, the required tap length of the equalizer is proportional to modal group delay of a single DMGD compensated pair, instead of the total modal group delay (MGD) of the entire link. By using small DMGD compensation step sizes, the required tap length (RTL) can be potentially reduced by 2 orders of magnitude