The accurate and adjustable structural model of hollow-core photonic bandgap fibers (HC-PBFs) is crucial for design and fabrication of high-performance HC-PBFs. The traditional modeling method based on air holes or silica struts has non-negligible structural differences and few adjustable parameters degree of freedom. The 2D structural modeling method of HC-PBFs based on feature points location is proposed. The ideal structure and common distorted structure of HC-PBFs are constructed by this method before fiber fabrication. The scale and scope of irregularities and distortions are continuously tunable. Meanwhile, the realistic HC-PBFs structure and homemade HC-PBFs are reconstructed by this method after fiber fabrication. The universality, robustness, and accuracy of this method are verified successfully according to the result of contrast between model and realistic structure. According to the simulated result from this model, the modification could be conducted precisely before and after fiber fabrication. Thus, the overall manufacturing process of HC-PBFs is considerably accelerated.
Transmission of dark hollow beams is crucial for blue-detuned guiding of cold atoms, and it is fundamental for cold-atom interferometers. We proposed four anti-resonant hollow-core fiber structures for transporting dark hollow beam, and then comparing their confinement loss. We chose the fiber structure with simpler structure and lower confinement loss to get fiber samples. Besides we built a fiber-coupled system to test the fiber properties. The experimental results show that the fiber can better maintain the light intensity of the hollow beam, which are crucial for guiding atoms.
In recent years, the research in the fields of quantum computing, quantum communication and quantum precision measurement has set off the "second quantum revolution" and become an international hotspot. Background cold atomic vapor density is an important parameter in the vacuum systems. At present, the methods of measuring atomic vapor density include absorption line method and fluorescence method. However, for the negative exponential relation between the atomic vapor density and the measurement results of the existing methods, it is impossible to accurately measure the lowdensity atomic vapor. Therefore, based on the principle of magneto-optical Effect and coherence detection, we propose a method to measure the atomic vapor density of rarefied alkali metals. Taking 87Rb atom as an example, under different temperature and pressure conditions, the final measured atomic vapor density range is 1.47 x 1012~5.66 × 1013 m-3. The accuracy of this method is about 3~4 orders of magnitude higher than the existing method. The method effectively solves the measurement problem of low-density atomic vapor.
In designing photonic-bandgap fibers, the most effective and well-known approach utilized to suppress surface modes is the T ∼ S / 2 rule, which translates to using a core surround with only half the thickness of the average cladding strut. We investigate transmission loss in a commercial 7-cell hollow-core photonic-bandgap fiber. To reduce transmission loss at 1550 nm, we apply the T ∼ S / 2 rule to suppress the surface modes. While the strut surface modes are suppressed, the rod surface modes (RSMs) are blueshifted to wavelengths near 1550 nm because the round-core diameters of the cladding-layer corners resting against the fiber core are quite small, which leads to the coupling between the fundamental mode and the RSMs. This induces attenuation at 1550 nm, which indicates that the T ∼ S / 2 rule is applicable only within certain limits. By optimizing the round-core diameters of the corners resting against the fiber core, we obtain a structure that is free of surface modes, with the subsequent transmission loss at 1550 nm being ∼10 dB / km lower than that of the original fiber. Moreover, we propose a simple method to modify the round-core diameters to aid in surface-mode suppression.
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.
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.
We have developed a fiber optic gyroscope with accuracy better than 0.01°/s, size about 30 cm3. To reduce the size and the cost, the design utilizes the cheaper and smaller optical components, such as 850 nm light source without temperature control, a small fiber coil with only about 55 m fiber length and a PIN in place of the traditional PIN-FET. In electronic circuit, the minimum configuration with integration and multiplexing of electronic components is used. To guarantee the performance, the output power stability and degree of polarization of light source, the strong birefringence in small coil and I/V conversion in preamplifier circuit has been taken into consideration in the design. Having a small size, low cost and sufficient performance, this kind of fiber optic gyro is suitable for applications in a wide variety of weapon systems.
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