We couple He-Ne laser into a tapered fiber tip made of single-mode fiber. To explore spatial filtering mechanism, we observe its output-light diffraction pattern variation by displacing the imaging lens or changing the tapering ratio.
In this experiment, we wrap a single-mode optical fiber around various sizes of cylindrical acrylic tubes, forming a series of manually controllable birefringent optical fibers. We launch linearly polarized external-cavity feedback wavelength-tunable visible diode laser light into the stressed birefringent fiber and capture simultaneously the fiber cross-sectional images of two orthogonally polarized modes under various wavelengths by a Wollaston prism polarizer. Through image analysis, we can obtain the two orthogonally polarized light intensities and calculate the phase difference of the two orthogonally polarized modes in the fiber core. By examining the variations of the phase difference with the optical wavelength, we can thus obtain the refractive-index difference of the birefringent fiber. Then by successively changing the size of the acrylic tube, we demonstrate that the refractive-index difference of a coiled fiber varies with its bending radius in a square inverse law. This experiment can reveal precisely the variations in the birefringence of a coiled fiber by a home-made wavelength-tunable diode laser and a mode-image analysis method, providing an advanced teaching kit in the optics laboratory.
In this report we demonstrated a method for measuring the beat length of a birefringent fiber. In this method the beat length is determined from the wavelength dependence of the phase difference between two orthogonally polarized modes at the output end of a sample fiber. In addition to the mode hopping of the laser diode’s optical wavelength due to the temperature variation, we have also observed the phase hopping of the output light polarization at the end face of the birefringent fiber. It is a simple and precise method to determine the birefringence magnitude of anisotropic materials in an optics laboratory course.
A wave plate is a commonly used optical element in optical experiments. In this report, we have achieved measuring the phase retardations of a half-wave plate and a quarter-wave plate using a Mach-Zehnder interferometer. Besides, when we rotate the half-wave plate’s c-axis form the vertical to the horizontal directions, or vice versa, the phase retardations of the two orthogonally polarized beams are observed to be exchanged between 180° and -180°. In addition, we also predict the expected results by the Jones calculus theory in order to check the experimental results. This system can be applied to explore intuitively the birefringence characteristics of anisotropic materials in an optics teaching laboratory.
We explore the temporal coherence characteristics of the output light of a SLD system with different optical feedback ratios by a Michelson interferometer, and we also observe the long-scan-range interference patterns with the one by one wave packets due to the Fabry-Perot modulation of the SLD device. We can obtain the effective cavity length of the SLD active layer and get more information of the temporal coherence length or spectral width from the long-scan-range interference patterns. This tunable light source system can provide more insights into the optical coherence or lasing phenomena often discussed in the optics course.
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