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A tapered hyperbolic-shaped microlens has been improved for efficient the coupling of the output from a laser diode into an optical fiber. A tapered hemispherical-end fiber microlens is also evaluated for comparison purposes. The Fresnel diffraction theory is used to evaluate laser to fiber coupling using microlenses. Experimental results demonstrate that, for an elliptical Gaussian laser diode with an aspect ratio of 1:1.5, the coupling efficiencies for the hyperbolic-shaped microlenses and the hemispherical-end fiber microlenses are 87% and 62%, respectively. Simulation results show excellent agreement with the measurements. The research results illustrate that a hyperbolic-shaped microlens has a much higher coupling efficiency than a hemispherical-end microlens due to efficient mode matching and phase matching.

This study proposes a new scheme of the tapered hyperbolic-end fiber (THEF) by etching the fiber end in a hydrofluoride (HF) solution with a thin layer of oil floating on top of the HF. This study makes it possible to fabricate the hyperbolic microlenses using unique etching and fusion techniques. Compared with previous hemispherical microlenses, the study shows that a THEF with a smaller taper angle and longer taper length fabricated by lower oil density exhibits a smaller radius of curvature, thus resulting in a better coupling efficiency. The THEF microlens results in a more than 2 dB improvement in coupling efficiency when compared with the currently available hemispherical microlenses. The calculation of the effect of oil density in HF etching solution on taper angle and taper length based on an empirical model is in agreement with the measured results. The THEFs have demonstrated up to 86% coupling efficiency for a laser with an aspect ratio of 1:1.5 at a wavelength of 1550 nm.

The measurement of surface roughness of optical thin films based on fast Fourier transform (FFT) associated with a Gaussian filter was presented. The measurement of the surface roughness is performed by a Fizeau-type microscopic interferometer combined with the Matlab program to analyse the captured interferograms. The surface profile can be obtained by the fringe pattern analysis program using FFT method. In order to improve the accuracy, we normalize the fringe pattern to eliminate the background variation before using the FFT. The roughness profile is filtered by the Gaussian filter after the phase change is converted to surface height distribution. The root-mean-square value of surface roughness of optical thin films was determined by our proposed method. The results were verified by atomic force microscopy (AFM).

A new approach for fringe normalization by Zernike polynomial fitting to cancel background illumination in an interferogram is proposed. With this method, background illumination can be suppressed, high frequency noise is immunized and the contrast is improved by normalization. The main idea for this paper is to use the Zernike polynomial fitting interferogram to cancel background illumination; the high frequency noise is then filtered by a Wiener filter. Finally, the paper uses the method of local region contrast modulation to enhance fringe contrast. This method can overcome the problem of the non-uniformity illumination of fringe patterns resulting from the marginal reflection of optical components and a non-uniformity light source

An uncoated tapered hemispherical-end fiber microlens, formed by etching a single-mode fiber in a hydroflouride solution, is spliced with a fiber grating to form an external cavity for a 1.55 µm fiber grating laser (FGL). The fiber microlens provides a coupling efficiency of more than 65% between the semiconductor laser and the fiber grating external cavity. The FGL has spectral characteristics of a single line (λ0=1555.6 nm), a single longitudinal mode (SMSR>30 dB), and a high output power (>1 mW). However, the SMSR shows a current-dependent oscillation, which can be consistently explained by calculating the rate equations of an equivalent external cavity model on the FGL.

Over the past years, the internet core rapidly increases, transparent protocols become more available for DWDM system in the fiber to the home, fiber to the institutions service. In densely spaced wavelength-routed and large-capacity optical network systems, single-mode lasers with narrow linewidth and low temperature sensitivity are of particular importance as the light sources in transmitter modules. The efficient coupling of a laser diode to an optical fiber has been a problem of general concern since the advent of fiber-optic communication systems. This chapter will introduce to fabricate a fiber grating external cavity laser (FGECL) module with a low cost while still maintaining a good single longitudinal mode performance by using a low-cost AR(Anti-reflection)-coated(5×10-3) laser and a tapered hyperbolic-end fiber (THEF) microlens for strong coupling the fiber grating external cavity. Previously, high-performance FGECL modules have only been available by using a complicated AR-coated(1×10-5) laser process that leads to a high packaging cost. The FGECL consisted of a HR/AR-coated diode laser, an uncoated THEF microlens, and a fiber grating. The results showed that the FGECL module exhibits a side-mode suppression ratio (SMSR) higher than 44 dB, a higher output power of more than 2 mW, and a larger operation current range of over 50 mA. In addition, excellent wavelength stability and a low-penalty directly modulated 2.488 Gbit/s were also obtained for FGECL modules. The THEF microlens demonstrated up to 86% coupling efficiency for a laser with an aspect ratio of 1:1.5. A fiber microlens which provides an efficient coupling mechanism to match the spot size of the diode laser to the fiber is commonly used for optical alignment in FGECL modules. Low-cost FGECL modules with good performance were achieved primarily owing to the THEF microlens having a high coupling efficiency (typically 75%) which enhanced the feedback power from the fiber grating external cavity to the HR/AR-coated laser compared with the currently available hemispherical microlens which has low coupling efficiency (typically 50%). Therefore, the packaged FGECL module is suitable for use in low cost 2.5 and 10 Gbit/s lightwave transmission systems, such as gigabit passive optical networks (GPONs), metropolitan area networks (MANs), and fiber-to-the-home (FTTH) applications. This chapter is organized as follows: Part I: A tapered hyperbolic-shaped microlens has been improved for efficient the coupling of the output from a laser diode into an optical fiber. A tapered hemispherical-end

We propose a new design of 25-GHz flat-top multichannel optical filter. The flat-top of optical filters can improve to 2.288×10-11dB which is superior to that of 5 orders of previous study. The superior performance of dispersion and channel spacing isolation improve 73.5% and 94%, respectively, which compared with current available commercial products and previous study.

We propose a new design of 25-GHz flat-top multichannel optical filter. The flat-top of optical filters can improve to 2.288×10−11dB which is superior to that of 5 orders of previous study. The superior performance of dispersion and channel spacing isolation improve 73.5% and 94%, respectively, which compared with previous study.

A flat-top 25GHz optical interleavers based on a ring cavity with spectral characteristics demonstrate in the following. Also, group velocity dispersion and ripple as well as phase of reflector have improved a lot with dispersion compensators.

We propose a QPM waveguide incorporated with power management technology and time delay to achieve a maximum conversion efficiency by 232% compared with a normal QPM waveguide with 0.6 ps pulsewidth and 100 pJ energy.

The hyperbolic-end microlens has higher coupling efficiency than the hemispherical-end microlens. This study propose the theoretic analysis concerning the optical-field variations of intensity and wavefront in the SMF waveguide both the hyperbolic-end microlens and the hemispherical-end microlens.

This study demonstrates that it is possible to fabricate a fiber grating external cavity laser (FGECL) module with a low cost while still maintaining a good performance by using a low-cost AR-coated (5times10 -3) laser and a tapered hyperbolic-end fiber (THEF) microlens

We report on the first fabrication of a Cr-doped fiber using a drawing-tower method with Cr:YAG as the core of the preform. The Cr-doped fibers have potential for use as fiber amplifier to cover the bandwidths in the whole 1.3-1.6 /spl mu/m range.