Wen-Hsuan Hsieh

New Scheme of Hyperboloid Microlens for High-Average and High-Yield Coupling High-Power Lasers to Single-Mode Fibers

A new scheme of hyperboloid microlens (HM) employing automatic grinding and precise fusing techniques to achieve high-average and high-yield coupling efficiency from high-power 980-nm lasers into single mode fibers is proposed and demonstrated. The fiber endface of the HM exhibited a double-variable curvature in the major and minor axes that was characterized as a hyperboloid. By selecting half transverse length of the hyperbola and using fusing process to precise and quantitative controlling the required minor radius of curvature within 2.4-2.8 μ m and offset within 0.8 μ m, the HMs exhibited a high-average coupling efficiency of 83%. For fabricated high-coupling HMs, the result was also found that the tolerance of minor radius of curvature decreased as the offset increased. This study demonstrates that the proposed HMs through both automatic grinding and precise fusing techniques can achieve high-average and high-yield coupling efficiency better than any other grinding techniques to form asymmetric microlenses for utilizing in many low-cost lightwave interconnection applications.

A New Scheme of Oriented Hyperboloid Microlens for Passive Alignment Lasers to Polarization Maintaining Fibers

A new scheme of oriented-hyperboloid microlens (OHM) with passive alignment to achieve high polarized extinction ratio (PER) is proposed and demonstrated high efficiency coupling of high-power 980 nm pump lasers to polarization maintaining fibers (PMFs). Using an automatic grinding machine and a charge-coupled-device to precisely control and attain the required minor radius of curvature 4-4.8 μm, offset within 0.7 μm, and axis orientation accuracy ±1°, the OHM exhibited a high-average PER of 31.7 dB, and a high-average coupling efficiency of 83.4%. For a 30 dB PER, the angular misalignment tolerance of the OHM was measured to be ±2°. The unique advantage of the proposed OHM is passive alignment to achieve high PER by only aligning the OHM endface of the fast axis parallel to the axis of laser polarization. This newly developed OHM with unique passive alignment to achieve high polarization is beneficial for the applications of laser/PMF modules where mode polarization and high coupling efficiency are required for use in high precision fiber optic gyroscopes as well as many low-cost and high-performance lightwave interconnection applications.

Micro-hyperboloid lensed optical fibers for laser chip coupling

This study develops a novel approach for producing hyperboloid microlens structure directly on a single-mode optical fiber for high performance diode laser coupling. The hyperboloid shape lensed tip is for matching with the rectangular output of the semiconductor laser diode. The hyperboloid lensed fiber is produced a three-step process including a precision mechanical grinding, a spin-on-glass (SOG) coating and an electrostatic pulling process. A flat-end single mode fiber with the core diameter of 6.6 μm is aligned, fixed and grinded into trapezoid shape. Trace amount of spin-on-glass is applied on the grinded tip and then an electrostatic pulling is used to tune the radius of curvature of around 4.5 μm for the grinded tip. A high coupling efficiency around 80% is obtained while using the produced hyperboloid fibers, which is about double compared to the coupling efficiency of the flat end fiber. The measured coupling stability for 5 individual hyperboloid fibers is 0.116±0.044%, indicating the good coupling stability for the produced hyperboloid microlensed fibers. The developed hyperboloid microlensed fibers provides a solution for direct light coupling between the single mold fiber and the semiconductor diode laser.

An Oriented-Dependence-Microlens Visual Alignment and Packaging for Lasers Coupling to PMFs

An oriented-dependence-microlens (ODM) visual alignment and packaging for lasers coupling to polarization-maintaining-fibers (PMFs) is proposed and demonstrated. The ODM is fabricated by automatic grinding and accurate positioning techniques. The position accuracy of the grinding machine is ±1°, which is less than the aligned and fabricated angular tolerance of ±2° for the ODM necessary to achieve both high coupling of 80% and high polarized extinction ratio of 30 dB. This indicates that the ODM endface of the fast axis can be visually observed and then surface feature aligned to the axis of the laser polarization direction. A practical package of laser/PMF with compact size and a few components employing the ODM is also demonstrated. The proposed ODM with visually precise surface feature alignment to achieve both high coupling and polarization is beneficial for the application of laser/PMF modules for use in high-precision fiber optic gyroscopes and many high-performance and low-cost lightwave interconnections.

Mode Matching and Coupling of Lensed and Cleaved Fibers Employing Near-Field Technique

An experimental coupling mechanism is presented that demonstrates efficient coupling between a high-power 980-nm laser diode and a lensed fiber by employing mode (spot size and wavefront) matching in the near-field regime. The results show that the beam spot pattern of the lensed fiber of a horizontally elliptical shape is spot-size matched to the laser. The wavefront of the lensed fiber with a minor radius of curvature ranging from -9 to 10 μm exhibits a curve wave that is also phase matched to the laser. This indicates that the similarity in the mode patterns of both the spot size and the wavefront between lensed fiber and laser is responsible for mode-matched beam coupling, leading to a coupling efficiency of more than 80%. In contrast to the lensed fiber, the spot-size of the cleaved fiber is round, and the wavefront is a plane wave. The different mode distributions between the laser and the cleaved fiber lead to a mode mismatch, resulting in a coupling efficiency of lower than 40%. This experimental coupling mechanism investigation in the near-field regime provides useful information for practical micro-optic design with better mode matching to achieve efficient coupling from active to passive components for interconnect applications.

Micro-hyperboloid lensed fibers for efficient coupling from laser chips

A novel technique is presented for producing micro-hyperboloid lensed fibers for efficient coupling to semiconductor laser chips. A three-step process including a precision mechanical grinding, a spin-on-glass (SOG) coating and an electrostatic pulling process is used to form the hyperboloid lens structure on a flat-end single mold fiber (SMF) with the core diameter of 6.6 μm. Micro-hyperboloid lensed fibers with tunable radii of curvature around 4.18 - 4.83 μm can be formed on the SMF end face. A high average coupling efficiency around 80% and low coupling variation of 0.116 ± 0.044% are obtained for the produced fibers. The developed method is efficient to produce micro-hyperboloid lensed fibers for high-performance light coupling between the SMF and the semiconductor diode lasers.

Direct near-field phase measurements of lensed fiber employing a single-mode fiber interferometer

A method of direct measurement of near-field wavefront and intensity distribution of lensed fiber employing a single-mode fiber interferometer is proposed and demonstrated. The wavefront of lensed fiber showed a curved wave with the radius of curvatures from 8 to 32 μm at various locations along the z axis. The wavefront radius of curvatures of laser diode and lensed fiber were in good agreement with each other that the similar curved wavefront distributions between laser and lensed fiber was mode matching, results in high coupling from laser to fiber. Detailed measurements of the near-field phase and intensity distributions of laser and fiber are essential for micro-optic design with better mode matching to achieve efficient coupling.