This work was to introduce a reference mechanism in fiber based-SPR (surface plasmon resonance)
sensors to increase their sensitivity. We fabricated two tandem SPR sections in a single optical fiber and
coated one of the sections with a reference material to split a regular single resonant peak into two peaks,
one in regular wavelength range for sensing and another one in longer wavelength range for referencing.
By using the referencing peak to specifically detect the SPR changes caused by uncontrolled factors, such
as temperature variation, non-specific bonding, we were able to subtract the contribution of these factors
to the sensing peak using an established relationship, and thus increase the sensitivity of the sensing dip. With the method, we have demonstrated a fiber-based SPR humidity sensor whose sensitivity is immune to the variation of environment temperature.
Optical fiber sensors have shown great potentials for aerospace applications. But two issues need to be addressed before
these applications can be realized. One is how to reliably implement optical sensors in the air vehicles. The other is the
need of compact, low weight sensor interrogation systems. We propose to use planar lightwave circuits (PLC) to address
the second issue. In this article, we report some of our results on the development of both echelle diffractive gratings
based sensor interrogator and arrayed waveguide gratings based sensor interrogators. Both approaches offer miniaturized
solutions for the development of optical fiber sensor interrogation systems.
Using an arrayed waveguide gratings (AWG) based demultiplexer, a simple channel gain equalizer can be designed. The gain equalization and blocking functions are realized by the hybrid waveguide based variable optical attenuators fabricated on the output waveguides of the demultiplexer. This paper discusses the operation principle of the design and presents some simulation results.
By using two orthogonally-polarized pump beams, an ultrabroad tunable wavelength converter is demonstrated with uniform efficiency and equalized signal-to-noise ratio (SNR) through four-wave mixing (FWM) in an 1500-nm semiconductor optical amplifier (SOA). This device allows the conversion of the input data signal to lower or higher frequencies with nearly-constant conversion efficiency and SNR over a 10.66 THz tuning range. This result is a significant improvement of both the conversion efficiency and the SNR as compared with the conventional FWM-based wavelength converters. We have also investigated the effect of parameters of both input power and wavelength of pump P<sub>2</sub> on conversion efficiency and SNR of the wavelength-converted signals.
We present a simple method to generate a stable high-power (> 30 dBm) multi-wavelength ytterbium/erbium co-doped double-cladding fiber ring laser source at room temperature. This method is based a wavelength-dependent filter through spatial mode beating between the LP<sub>01</sub> and LP<sub>11</sub> modes within the multimode fiber section. We also investigate the relationship between the lasing wavelengths and the length of the ytterbium/erbium fibers (YEFs), the number of lasing wavelength lines dependent on the total pumping power level and the polarization states, and the characteristics of both the wavelength switching operation and the total output power. Eight simultaneous lasing wavelengths with 0.78 nm spacing were generated at room temperature.
We have developed a widely tunable, narrow-linewidth, simultaneous triple-wavelength oscillation erbium-doped fiber ring laser (EDFRL), which can produce double-wavelength oscillations with the same polarization output, as well as another widely tunable wavelength oscillation with orthogonal polarization from 1522.2 nm to 1595.9 nm. By using this EDFRL along with a method of measuring polarization-mode dispersion (PMD) in optical fibers based on a broad-band orthogonal-pump four-wave mixing in a semiconductor optical amplifier (SOA), we have measured the PMD values of optical fibers, which are in good agreement with values measured by means of commercial PMD testing equipment. We have also proposed several novel devices for in-field PMD measurement and monitoring on dense wavelength-division multiplexed (DWDM) traffic-carrying links, which will significantly reduce the cost and time of the PMD testing in the running DWMD networking systems.
A novel polarization scrambling optical signal-to-noise ratio (OSNR) monitor has been proposed and demonstrated. The OSNR monitor consists of a polarization scrambler, a polarizer and a photodetector. When the channel signal input to the polarizer is a linear polarization state aligned parallel (orthogonal) to the polarizer the output reaches its maximum (minimum). The OSNR can be obtained from the measured maximum and minimum of the output power if the sampling time is long enough to ensure a good coverage on Poincare sphere. The new OSNR monitor is polarization mode dispersion insensitive. The effect of polarizer extinction ratio and sampling time on the accuracy has been discussed.