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Optical Fiber
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Reference Guide, 2002
David R. Goff, Kimberly Hansen, Michelle K. Stull
Figure 3.35 illustrates self-phase modulation. Like FWM, self-phase modulation (SPM) is due to the power dependency of the refractive index of the fiber core. It interacts with the chromatic dispersion in the fiber to change the rate at which the pulse broadens as it travels down the fiber. Whereas increasing the fiber dispersion will reduce the impact of FWM, it will increase the impact of SPM. As an optical pulse travels down the fiber, the leading edge of the pulse causes the refractive index of the fiber to rise, resulting in a blue shift. The falling edge of the pulse decreases the refractive index of the fiber causing a red shift. These red and blue shifts introduce a frequency chirp on each edge which interacts with the fiber's dispersion to broaden the pulse.
Fiber Limits
Published in David R. Goff, Kimberly Hansen, Michelle K. Stull, Fiber Optic Video Transmission, 2013
David R. Goff, Kimberly Hansen, Michelle K. Stull
Whereas increasing the fiber dispersion will reduce the impact of FWM, it will increase the impact of SPM. As an optical pulse travels down the fiber, the leading edge of the pulse causes the refractive index of the fiber to rise, resulting in a blue shift. The falling edge of the pulse decreases the refractive index of the fiber causing a red shift. These red and blue shifts introduce a frequency chirp on each edge which interacts with the fiber's dispersion to broaden the pulse. This increased SPM, however, can be minimized in dispersion-managed systems by alternating lengths of positive and negative dispersion fiber.
Thin-Film Designs for Oblique Incidence
Published in Andrew Sarangan, Optical Thin Film Design, 2020
For example, consider a structure with several layers with refractive indices of nf 1 = 1.5 and nf 2 = 2.5. When the incidence angle is θ = 30°, the nfz index of the low-index film becomes nf1z=nf12−na2sin2θ=1.414. The original phase thickness will now occur at a larger value of k0, by a factor of 1.51.414=1.06.. The reference wavelength will therefore decrease by a factor of 1.4141.5=0.94. Next consider the high-index film. It’s nfz index will become nf2z=nf22−na2sin2θ=2.45 and k0 has to increase by a factor of 1.02, and the wavelength will decrease by a factor 0.98. Therefore, even though each layer will experience a blue shift of its reference wavelength, the exact shift will be different in each layer. The structure will not be able to reproduce the same phase thickness at any other wavelength. As a result, we see a blue shift combined with a spectral distortion.
Reflex optical fiber probe for simultaneous determination of seawater salinity and temperature by surface plasmon resonance
Published in Instrumentation Science & Technology, 2019
Qi-Lu Wu, Yong Zhao, E. Si-Yu, Ya-nan Zhang
Figure 9 shows the temperature calibration. The shift in sensitivity at SPR-S was smaller than at SPR-T, but these changes were not negligible and could not be ignored. The temperature may indirectly change the refractive index of the water and is a principal reason for the double parameter cross-interference. With an increase in the temperature, the characteristic wavelength of SPR-T varied significant due to the sensitizing of the PDMS coating. The intensity was shown to slightly increase with temperature. The wavelength value displayed a blue shift.