Ningfang Song

Effect of Color Center Absorption on Temperature Dependence of Radiation-Induced Attenuation in Optical Fibers at Near Infrared Wavelengths

In order to explain the contradictory results on the temperature dependence of the radiation-induced attenuation (RIA) in optical fiber, the temperature dependence of color center absorption was proposed as a complementary explanation. The temperature tests were conducted on the four prototype optical fibers after irradiation. During the temperature tests the RIA in the fibers at the near infrared (NIR) wavelengths was measured continuously. The temperature dependence of color center absorption was verified. The competition between the thermally color center annealing and the temperature-dependent absorption of color center was observed. The test results show that the temperature dependent absorption of the color center at NIR wavelengths is an important factor influencing the temperature dependence of RIA besides the thermally driven color center generation, conversion and annealing process.

Investigation of residual core ellipticity induced nonreciprocity in air-core photonic bandgap fiber optical gyroscope

Air-core photonic bandgap fiber (PBF) is an excellent choice for fiber optic gyroscope owing to its incomparable adaptability of environment. Strong and continuous polarization mode coupling is found in PBFs with an average intensity of ~-30 dB, but the coupling arrives at the limit when the maximum optical path difference between the primary waves and the polarization-mode-coupling-induced secondary waves reaches ~10mm, which is corresponding to the PBF length of ~110 m according to the birefringence in the PBF. Incident light with the low extinction ratio (ER) can suppress the birth of the polarization-mode-coupling-induced secondary waves, but the low-ER light obtained by the conventional Lyot depolarizers does not work here. Consequently, a large nonreciprocity and a bias error of ~13°/h are caused in the air-core photonic bandgap fiber optical gyroscope (PBFOG) with a PBF coil of ~268 m.

Analysis and simulation of a fiber optical gyroscope with Shupe error compensated optically

Shupe error, a kind of bias error over temperature-varying environments, still exists even with strict quadrupolar winding pattern, and it affects the environment adaptability of fiber optical gyroscope (FOG) and limits its application. A novel configuration to realize optical compensation for Shupe error in FOG is promoted, employing the opposite polarity of Shupe error in two FOGs working with polarization-maintained (PM) fiber’s fast and slow axis, respectively, in a single PM fiber coil. Analysis is also made for polarization non-reciprocity (PNR) in both FOGs, based on which the optimum coupling angles between integrated optic chip and PM fiber coil are obtained to guarantee that Shupe error arising from both FOGs can be counteracted to zero, and PNR error is suppressed to be minimum at the same time.

Reflection-induced bias error in an air-core photonic bandgap fiber optic gyroscope.

Analysis of the bias error induced by reflections in an air-core photonic bandgap fiber gyroscope is performed by both simulation and experiment. The bias error is sinusoidally periodic under modulation, and its intensity is related to the relative positions of the reflection points. A simple and effective method for the suppression of the error is proposed, and it has been verified experimentally.

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.

Influence of grating fabrication on radiation sensitivity of fiber Bragg gratings

Fiber Bragg Gratings (FBGs) are candidates for a number of applications in space-borne systems not only owing to their optical functionality but also because they have low mass, small dimensions, and because they are immune to electromagnetic interference. In the case of Earth observation and telecommunication satellites the multiplexing in the optical domain, based on the FBGs, allows a significant reduction of the complexity of on-board electronic systems. Another perspective domain is the fiber sensor systems, such as strain sensors integrated into fuel tanks or structural health monitoring of large space structures. In order to be actually used in space-born systems, FBGs must demonstrate a high stability of their properties over the whole mission time. However, radiation may affect its properties. The possible ways of improving the radiation tolerance of FBGs should be researched. The influence of grating fabrication on radiation sensitivity of the FBGs has been investigated experimentally in this paper. The FBGs were fabricated in different process and GeO2 concentrations. Pre-irradiation and H2-loading were applied to change the radiation sensitivity of the FBGs. The FBGs were fabricated in photosensitive fiber and coupling single mode fiber with a GeO2 concentration in a range from 0.33 to 23 mol%. The lowest Bragg wavelength shift (13 pm) was obtained by a grating written in photosensitive fiber PSF-GeB-125, with pre-irradiation and without H2-loading for a total dose of about 50 kGy.

Spectra of fiber Bragg grating in nuclear environment

Dense wavelength division multiplexing (DWDM) technology is a promising way for high transmission-rate demand in the ever complex Earth Observation satellites and space station. However, fiber Bragg grating (FBG) filters used in DWDM systems may fail to check out the correct wavelength affected by cosmic rays. In order to analyze the spectra characteristics of FBGs in gamma radiation environment, we simulate the wavelength shift by controlling gamma-induced effective index change. The effect caused by gamma radiation is taken as a perturbation to the effective refractive index of the guided mode of interest. Coupled-mode theory is involved to establish the model describing the effect of gamma radiation on Bragg wavelength shift. The results show that the gamma-induced effective index change has good linearity with the change of Bragg wavelength. Meanwhile, the bandwidth of the reflection spectra broadens with the increased dose of gamma irradiation.

Test method for FOG loop eigenfrequency and half-wavevoltage based on square wave modulation

A novel approach was presented to solve the problem of fiber optic gyro(FOG) loop eigenfrequency and half-wavevoltage measuring. The method comes from the mechanism of reciprocal shift modulation, insteads of measuring loop eigenfrequency it measures the optics power of ineffective-modulation that having a peak; and insteads of measuring half-wavevoltage it measures the optics power of effective-modulation that having a low plain part. The modulation square wave whose frequence and amplitude could be programmed is made of the technique of direct digital synthesis. The scheme was tested by Matlab simulation, and implemented in circuit. The result of the loop eigenfrequency and half-wavevoltage is much more preciser than handwork test, whats more, it takes much less time.