Jingming Song

Structure optimization of small-diameter polarization-maintaining photonic crystal fiber for mini coil of spaceborne miniature fiber-optic gyroscope

A small-diameter polarization-maintaining photonic crystal fiber (PM-PCF) for mini coils of spaceborne miniature fiber-optic gyroscopes is proposed in this paper. To ensure the strength of the small-diameter PM-PCF, a four-ring air holes structure is adopted. Using the full vector finite element method, dependence studies of modal field distribution, birefringence, and confinement loss on several key structure parameters are numerically investigated. The optimized parameter region is obtained. An optimized PM-PCF is fabricated, which can achieve similar to or even better optical properties than that of commercial PM-PCFs. The coating and cladding diameters of the optimized PM-PCF are 135 μm and 100 μm, respectively. Meanwhile, the optimized small-diameter PM-PCF shows a proof test level of 0.5%. The attenuation of the PM-PCF at 1550 nm is ∼2  dB/km. Typical volume of a mini coil wound with 300 m optimized PM-PCF is 5.9  cm3, which is decreased by ∼60% compared with a commercial PM-PCF coil of the same length. The bias stability of this coil is comparable with that of a conventional PMF coil of comparable length. Thus, the optimized small-diameter PM-PCF is suitable for mini coils of spaceborne miniature fiber-optic gyroscopes.

Phase sensitivity to temperature of the guiding mode in polarization-maintaining photonic crystal fiber.

The propagating phase changing of a polarization-maintaining photonic crystal fiber (PM-PCF) caused by temperature variation is theoretically studied, as well as compared with conventional PANDA fiber. As to verifying numerical analysis, a platform based on a Michelson interferometer for phase versus temperature measurement was built for both kinds of fiber. Experiments show that PM-PCF has similar temperature sensitivity with conventional polarization-maintaining fiber. With optimized PM-PCF design (thinner coating layer and coating material with smaller thermal expansion coefficient), the sensitivity could be further reduced to about 80% of the present level.

Measurement of modes backreflection at flat termination of hollow-core photonic bandgap fiber based on Mach-Zehnder and Michelson hybrid interferometer

A Mach-Zehnder and Michelson Hybrid (M2) interferometer is promoted to measure backreflection of modes at the hollow-core photonic bandgap fiber (HC-PBF) terminations. The results show that compared to the incident light intensity into the HC-PBF, the modes reflectivity is less than −80 dB at the flat termination, and it is about −90 dB for the fundamental modes.

Gamma-radiation effects in pure-silica-core photonic crystal fiber

We investigated the steady state gamma-ray radiation response of pure-silica-core photonic crystal fibers (PSC-PCFs) under an accumulated dose of 500 Gy and a dose rate of 2.38 Gy/min. The radiation-induced attenuation (RIA) spectra in the near-infrared region from 800 nm to 1700 nm were obtained. We find that the RIA at 1550 nm is related with hydroxyl (OH−) absorption defects in addition to the identified self-trapped hole (STH) defects. Moreover, it is proposed and demonstrated that reduced OH− absorption defects can decrease the RIA at 1550 nm. The RIA at 1550 nm has effectively declined from 27.7 dB/km to 3.0 dB/km through fabrication improvement. Preliminary explanations based on the unique fabrication processes were given to interpret the RIA characteristics of PSC-PCFs. The results show that the PSC-PCFs, which offer great advantages over conventional fibers, are promising and applicable to fiber sensors in harsh environments.

Radiation Induced Attenuation Effect in High Water Peak Polarization Maintaining Photonic Crystal Fiber

RIA spectra of high water peak pure-silica-core polarization maintaining photonic crystal fiber was measured. Hypotheses involving OH- and IR absorption defect were given to interpret the nonideal RIA characteristics of PM-PCF.

Analysis of polarization-maintaining photonic crystal fiber’s phase sensitivity to temperature and its influence to fiber-optic gyroscope

The polarization-maintaining photonic crystal fiber’s phase sensitivity dependence on temperature was analysis. The relationship between temperature and phase of normal polarization-maintaining fiber and polarization-maintaining photonic crystal fiber was numerical analyzed and experimental tested. Furthermore, the Shupe effects in fiber optical gyroscopes with the two fibers were studied. The contrast results showed that the phase sensitivity dependence on temperature of the polarization-maintaining photonic crystal fiber is quantitatively comparable to normal panda fiber. And the Shupe errors of the gyroscopes with the two different fibers were at the same level.

Novel bidirectional path measurement of polarization cross-coupling distribution in PMF

The measurement accuracy of polarization cross-coupling strength based on white-light interferometry obviously decreases in long-distance polarization maintaining fiber (PMF), due to the difference of dispersion between two eigenmodes (birefringence dispersion). In this paper, we demonstrate a bidirectional measurement method with the scheme including a polarization maintaining coupler, a magnetic optical circulator and an Optical Coherence Domain Polarimeter (OCDP). The experiment setup and results are described in detail. The cross-coupling distribution results from each direction measurement were processed to mitigate the influence of dispersion. The compensation is conducted on coupling strength results, instead of raw interference signal in traditional method. The method saves the investigation of birefringence dispersion coefficient and light source parameters compared with compensation in frequency domain. Our experiment with a PMF coil of 200m length demonstrates the effectiveness in improving strength accuracy with absolute deviation less than 0.31dB, and spatial resolution recovered to 8.4cm.

Electrons and Holes Charging Current Peaks in Silicon Nanocrystals within SiO2 Layers Fabricated by Plasma Enhanced Chemical Vapor Deposition

Metal-insulator-semiconductors structures (MIS) with a layer of silicon nanocrystals embedded within two SiO2 layers are fabricated by using plasma enhanced chemical vapor deposition. By using current-voltage (I-V) measurements with different sweep rates, we study the mechanism of electrons and holes charging/discharging characteristic of the MIS structures. Distinct current peaks duo to electrons (holes) charging into the nc-Si dots and discharging out of the nc-Si dots are observed. The current peaks are depended on the sweep rate and the areas of current peaks have been used to calculate the charged charge density. The experimental result demonstrates that each nc-Si dots underlying the electrode is charged by one carrier.

High Density of Si Nanocrystals Fabricated in a VHF-PECVD System for Light-Emitting Devices

High-quality nanocrystalline silicon films were fabricated in plasma enhanced chemical vapor deposition system by using a high excitation frequency (40.68 MHz) at low temperatures. It is found that the nanocrystalline Si films with high crystallinity of 89% can be obtained by using SiH4 highly diluted with H2. Furthermore, the area density of the nanocrystalline Si is as high as 4.41011/cm2. The Fourier transform infrared spectroscopy and transmission spectroscopy manifest that the nanocrystalline Si film possesses small microstructure factor, low hydrogen content and wide optical band gap.