We report on an optical fiber surface plasmon resonance sensor that exhibits multiple resonance peaks. The sensor is based on a uniform-waist single-mode tapered fiber coated on one side with a thin metal layer. Owing to the asymmetry of the sensor structure, the different hybrid surface plasmon modes supported by the semicircular layer can be excited by the fundamental fiber mode. As a result, the sensor transmission spectrum exhibits several dips that depend on the taper waist diameter. The advantages of a plasmon resonance sensor with multiple dips are discussed.

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We report laser oscillation at 481 nm when pumping a Tm 3+ -doped fluorozirconate fiber by two Raman-generated signals at 1117 and 1175 nm. A superior efficiency was achieved when pumping with both lines. For example, the conversion efficiency was 20% when pumping with 83 mW of 1117 nm and reached 33% when copumping with 29 mW of 1175 nm. As higher powers of the copumping signal were applied, a powerful amplified spontaneous emission at ϳ790 nm started to compete with 481 nm. The slope efficiency evolved from 16% to 48% when pumping with a simpler, noncontrolled Raman source that provided a single-to multi wavelength evolving spectrum.

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This paper presents a theoretical and experimental study on the behavior of the Raman gain efficiency for any Stokes and excitation wavelength. Analyzing the Raman threshold for two adjacent Stokes we find a mathematical relationship to the Raman gain efficiency. This equation scales inversely with wavelength and directly with the fiber attenuation, and also provides approximate quantities to numbers already published. From experimental data for a LEAF fiber, we construct two curves, one based on our equation and the other based on the approach normally used, and the comparison of the two curves reveals significant errors. Additionally, we show that the spectrum of the Raman gain efficiency has the same shape as the attenuation spectrum.