Polarization maintaining fibers

An intensity-modulated version of such a sensor was shown to provide a refractive index resolution better than 2x10 RIU. A wavelength-modulated version of this sensor exhibited even better resolution -5 X 10 RIU [64]. However, these SPR sensors suffered from polarization in-stabihty, even when fight depolarization was introduced. To eliminate this source of instability, SPR sensors using polarization-maintaining fibers were introduced [65]. These sensors were demonstrated to provide a refractive index resolution of about 2x10 RIU. 

J. Noda, K. Okamoto and Y. Sasaki, Polarization-maintaining fibers and their applications, J. Lightwave Technology. Vol. LT-4, No. 8.1071-1089 (1986). 

Fig. 4 (a) The D1 transitions coupled by a fiequency modulated coupling field and two probe fields (one as the signal Qs and another as the control Qc) behaves as the coherently coupled three-level A-type system. The spontaneous decay rate of the excited state 3> is 73 (=271x5.4x10 s for the 5Pi/2 F =3 state), (b) Simplified diagram of the experimental set up. AOM acousto-optic modulator EOM electro-optic modulator, PMF polarization maintaining fiber X/4 quarter-wave plate DL extended-cavity diode laser, M mirror, D photodetector. 

Al-Qaisi, M. K. Akkin, T., Polarization-Sensitive Optical Coherence Tomography Based on Polarization-Maintaining Fibers and Frequency Multiplexing , Optics Express 2008,16, 13032-13041. 

Piliarik, M., Homola, J., Mamkova, Z., Ctyroky, J. (2003) Surface plasmon resonance sensor based on a single-mode polarization-maintaining optical fiber. Sensors and Actuators B 90 236-242. 

For completeness, it should be noted that silica-based photonic crystal fibers have also received attention for lasers and amplifiers (predominantly Yb -doped systems, although Nd + and Er + have been studied), as well as polarization-maintaining structures. ... 

Suzuki, K., Kubota, H., Kawanishi, S. et al., Optical properties of a low-loss polarization-maintaining photonic crystal fiber, Opt. Express, 9, 676, 2001. 

Due to of the mass-production of single-mode fibers, they are cheaper than other t3rpes and therefore often preferred for sensor purposes. For special purposes, such as pressure or current measurements, and sometimes for impact detection, high-birefringent (Hi-Bi) polarization-maintaining (PM) fibers are used because the polarization state of the output signal is definitely affected by external perturbations. 

The primer chosen for this investigation consisted of an equimolar mixture of phenyl- and amino-functional silanes, suggested as a potential superior primer for aluminum/epoxy adhesive joints [7], The amino-functional silane is known to be effective as an adhesion promoter for fiber-reinforced composite materials [1, 2] as well as for epoxy/metal adhesive joints [8, 9] and provides for strong chemical interaction between the adhesive and primer, while the phenyl functional silane should reduce the overall concentration of polar, hydrophilic functional groups in the interphase region and at the same time maintain or improve the ability of the resin and primer to interpenetrate due to its structural similarity to the adhesive resin. 

Membrane Flux Performance for the Hollow Fiber Units. Figures 3a and 3b show the results of a cell separation pilot scale run in which transmembrane pressure was maintained constant at 4.0 psi and linear velocity through the fibers was maintained at 1.0 m/sec (100 1pm). Transmembrane pressure was controlled with a backpressure valve on the combined permeates from the hollow fibers. Note that the flux vs. concentration curve for this run does not conform to theoretical predictions for concentration polarization (see Figure 3b). Flux on this semi-log plot does not decline linearly, but, rather, shows two phases of fouling. The initial phase (approximately 20 minutes in duration) is characterized by a rapid loss in flux, while the second stage (approximately 90 minutes in duration) is more gradual. The initially rapid decline caused an unacceptably low average flux of 10 l/m -hr. 

A concentration difference of 12 percent between the surface and the bulk solution would not have much effect on the salt rejection or the water flux. The estimate of may be conservative, because the mass-transfer coefficient in a bundle of fibers should be greater than for a single fiber. However, if good flow distribution is not maintained, sections receiving little flow might have significant polarization. 

---