Monitoring the dynamic chemical and thermal state of a cell during operation is crucial to making meaningful advancements in battery technology as safety and reliability cannot be compromised. Here we demonstrate the feasibility of incorporating optical fiber Bragg grating sensors inside commercial 18650 cells. By adjusting fiber morphologies, wavelength changes associated with both temperature and pressure are decoupled with high accuracy, and this allows for tracking of chemical events such as solid electrolyte interphase formation and structural evolution. Additionally, we demonstrate how multiple sensors can function as a microcalorimeter to monitor the heat generated by the cell. Resolving this heat in detail is not possible with conventional isothermal calorimetry and the importance of assessing the cell's heat capacity contribution is presented. Collectively, these findings offer a scalable solution for screening electrolyte additives, rapidly identifying the best formation processes of commercial batteries, and designing thermal battery management systems with enhanced safety.

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A fiber-optic strain sensor is demonstrated by using a short length of polarization-maintaining photonic crystal fiber ͑PM-PCF͒ as the sensing element inserted in a Sagnac loop interferometer. Spectrum shift in response of strain with a sensitivity of 0.23 pm/ is achieved, and the measurement range, by stretching the PM-PCF only, is up to 32 m. Due to the ultralow thermal sensitivity of the PM-PCF, the proposed strain sensor is inherently insensitive to temperature, eliminating the requirement for temperature compensation.

We report on an experimental observation of bound states of solitons in a passively mode-locked fiber soliton ring laser. The observed bound solitons are stable and have discrete, fixed soliton separations that are independent of the experimental conditions. DOI: 10.1103/PhysRevA.64. 033814 PACS number͑s͒: 42.55.Wd, 42.81.Dp, 42.60.Fc, 42.65.Re Bound states of solitons known as high-order soliton solutions of the nonlinear Schrödinger equation ͑NLSE͒ have been extensively studied ͓1-5͔. A bound state of solitons of the NLSE is formed because two or more fundamental solitons coexist, and they have the same velocity and locate at the same position. Recently, another form of bound solitons has also been theoretically predicted ͓6͔ to exist in nonlinear dynamical systems such as the Ginzburg-Landau equation ͓7,8͔, and the coupled nonlinear Schrödinger equations ͓9͔. In contrast, the formation of these bound solitons is due to a direct interaction between the solitons, and the propagation of them is characterized by the fact that the solitons have discrete, fixed separations.It is well known that the dynamics of passively modelocked fiber soliton lasers can be well modeled by the complex Ginzburg-Landau equation ͓10,11͔. The same equation also describes the soliton propagation in the long-distance optical transmission lines ͓12-13͔. It would be expected that the predicted bound states of solitons could be observed in these systems. However, to the best of our knowledge, so far no bound states of solitons of this form have been experimentally confirmed in the systems.Two effects in optical fibers are detrimental to the formation of the predicted bound states of solitons. One is the Raman effect. Theoretical studies have shown that a strong Raman effect destroys the bound solitons ͓6͔. Another one is the random-phase variations of the solitons, which causes random soliton interactions. Although in fiber soliton lasers, the influence of the Raman effect can be significantly reduced by the effect of laser gain dispersion ͓14͔, no efficient way has been found to suppress the random relative phase variations between solitons. In this paper, we report on an experimental observation of bound states of solitons in a passively mode-locked fiber soliton laser. We confirm experimentally the existence of stable bound states of solitons with discrete, fixed soliton separations.Our experiment is conducted on a passively mode-locked fiber soliton ring laser. A schematic of the laser configuration is shown in Fig. 1. The laser cavity is about 10 m long, which comprises of a 4-m long 2000 ppm erbium-doped fiber with a group velocity dispersion of about Ϫ10 ps/nm km and two pieces of 3-m-long single-mode dispersion-shifted fiber, whose group velocity dispersion is Ϫ1 ps/nm km. The nonlinear polarization rotation technique ͓15͔ is used to achieve the self-started mode locking in the laser. To this end, a polarization-dependent isolator together with two polarization controllers is used to adjust the polarization of light in the cavi...

We have experimentally investigated the soliton interaction in a passively mode-locked fiber ring laser and revealed the existence of three types of strong soliton interaction: a global type of soliton interaction caused by the existence of unstable cw components, a local type of soliton interaction mediated through the radiative dispersive waves, and the direct soliton interaction. We found that the appearance of the various soliton operation modes observed in the passively mode-locked fiber soliton lasers are the direct consequences of these three types of soliton interactions. The soliton interaction in the laser is further numerically simulated based on a pulse tracing technique. The numerical simulations confirmed the existence of the dispersive-wave-mediated soliton interaction and the direct soliton interaction. Furthermore, it was shown that the resonant dispersivewave-mediated soliton interaction in the laser always has the consequence of causing random irregular relative soliton movement and the experimentally observed states of bound solitons are caused by the direct soliton interaction. In particular, as the solitons generated in the laser could have a profile with long tails, the direct soliton interaction could extend to a soliton separation that is larger than 5 times the soliton pulse width.