Zhaobing Tian

Single rolled-up InGaAs/GaAs quantum dot microtubes integrated with silicon-on-insulator waveguides.

We report on single rolled-up microtubes integrated with silicon-on-insulator waveguides. Microtubes with diameters of ~7 μm, wall thicknesses of ~250 nm, and lengths greater than 100 μm are fabricated by selectively releasing a coherently strained InGaAs/GaAs quantum dot layer from the handling GaAs substrate. The microtubes are then transferred from their host substrate to silicon-on-insulator waveguides by an optical fiber abrupt taper. The Q-factor of the waveguide coupled microtube is measured to be 1.5×10(5), the highest recorded for a semiconductor microtube cavity to date. The insertion loss and extinction ratio of the microtube are 1 dB and 34 dB respectively. By pumping the microtube with a 635 nm laser, the resonance wavelength is shifted by 0.7 nm. The integration of InGaAs/GaAs microtubes with silicon-on-insulator waveguides provides a simple, low loss, high extinction passive filter solution in the C+L band communication regime.

Controlled Transfer of Single Rolled-Up InGaAs–GaAs Quantum-Dot Microtube Ring Resonators Using Optical Fiber Abrupt Tapers

We report on the controlled transfer of single rolled-up semiconductor microtube-based optical cavities from their host substrate to a foreign one. Such microtube devices, with diameters of ~5 ¿m, wall thicknesses of ~50 nm, and lengths of >100 ¿m, are fabricated by selectively releasing a coherently strained InGaAs-GaAs quantum-dot layer from the handling GaAs substrate. With the use of fiber abrupt tapers inserted into two ends of the tubes, rolled-up microtubes are lifted off from the substrate and subsequently transferred, with a precisely controlled position, onto the cleaved facet of a single-mode fiber. The resulting devices exhibit strong coherent emission at room temperature and may lead to integrated micro- and nanoscale lasers with greatly simplified packaging.

Double-layer Fano resonance photonic crystal filters.

We report ultra-compact surface-normal high-Q optical filters based on single- and double-layer stacked Fano resonance photonic crystal slabs on both Si and quartz substrates. A single layer photonic crystal filter was designed and a Q factor of 1,737 was obtained with 23 dB extinction ratio. With stacked double-layer photonic crystal configuration, the optical filter Q can increase to over 10,000,000 in design. Double-layer filters with quality factor of 9,734 and extinction ratio of 8 dB were experimentally demonstrated, for a filter design with target Q of 22,000.

850-nm VCSEL Transmission Over Standard Single-Mode Fiber Using Fiber Mode Filter

We report on a novel fiber mode filter consisting of an LP11 spatial mode rotator and an LP11/LP01 mode coupler to mitigate 850-nm modal dispersion over standard single-mode fibers (SMF-28). We demonstrate 10-Gb/s error-free transmission over 1 km of SMF-28 fiber using directly modulated vertical-cavity surface-emitting lasers and we measure a 3.3-dB reduction in the received optical power required to achieve a bit-error-ratio of 10-12 when compared to transmission over 800 m of OM3 multimode fiber.

Selective polarization mode excitation in InGaAs/GaAs microtubes

We report on selective polarization mode excitation in InGaAs/GaAs rolled-up microtubes. The microtubes are fabricated by selectively releasing a coherently strained InGaAs/GaAs quantum dot layer from its host GaAs substrate. An optical fiber abrupt taper is used to pick up the microtube, while an adiabatically tapered optical fiber is used to couple light into the resonant optical modes of the microtube. By varying the polarization of the light in the adiabatically tapered fiber both transverse electric and transverse magnetic modes are observed in the microtube. We also show that the microtube can be used as a red (0.6 μm) to infrared light (1.5 μm) optical-optical modulator taking advantage of the thermal-optical effect.

25-Gb/s Direct Modulation of Implant Confined Holey Vertical-Cavity Surface-Emitting Lasers

A 25-Gb/s direct modulation of an 850-nm implant-confined holey vertical-cavity surface-emitting laser (VCSEL) is demonstrated with a low operation current density of 7.4 KA/cm2 . The high-speed performance arises from cavity designs that are achieved using standard fabrication and epitaxial materials. The etched holey structure is incorporated into the top mirror of the VCSEL to tailor the size of the optical cavity independent from that of the electrical current aperture, enabling us to achieve high-speed modulation and low operation current density simultaneously.

Thermally controlled coupling of a rolled-up microtube integrated with a waveguide on a silicon electronic-photonic integrated circuit

We report on the first experimental demonstration of the thermal control of coupling strength between a rolled-up microtube and a waveguide on a silicon electronic-photonic integrated circuit. The microtubes are fabricated by selectively releasing a coherently strained GaAs/InGaAs heterostructure bilayer. The fabricated microtubes are then integrated with silicon waveguides using an abruptly tapered fiber probe. By tuning the gap between the microtube and the waveguide using localized heaters, the microtube-waveguide evanescent coupling is effectively controlled. With heating, the extinction ratio of a microtube whispering-gallery mode changes over an 18 dB range, while the resonant wavelength remains approximately unchanged. Utilizing this dynamic thermal tuning effect, we realize coupling modulation of the microtube integrated with the silicon waveguide at 2 kHz with a heater voltage swing of 0-6 V.

Characterization of azimuthal and longitudinal modes in rolled-up InGaAs/GaAs microtubes at telecom wavelengths

We report on theoretical and experimental investigation of azimuthal and longitudinal modes in rolled-up microtubes at telecom wavelengths. These microtubes are fabricated by selectively releasing a coherently strained InGaAs/GaAs bilayer. We apply planar waveguide method and a quasi-potential model to analyze the azimuthal and longitudinal modes in the microtubes near 1550 nm. Then we demonstrate these modes in transmission spectrum by evanescent light coupling. The experimental observations agree well with the calculated results. Surface-scattering-induced mode splitting is also observed in both transmission and reflection spectra at ~1600 nm. The mode splitting is in essence the non-degeneracy of clockwise and counter-clockwise whispering-gallery modes of the microtubes. This study is significant for understanding the physics of modes in microtubes and other microcavities with three-dimensional optical confinement, as well as for potential applications such as microtube-based photonic integrated devices and sensing purposes.

Picosecond flat-top pulse generation using dual-mode fiber Mach–Zehnder interferometers

We report on an optical fiber Mach-Zehnder interferometer made by offset splicing a dual-mode fiber with two single-mode fibers. The extinction ratio can be tuned from less than 1 dB to greater than 28 dB by rotating the dual-mode fiber along its axial direction. The interferometer is utilized as a pulse shaper to convert a 2.5 ps Gaussian pulse to a 5.2 ps flat-top pulse.

Single- and Dual-Wavelength Fiber Ring Laser Using Fiber Microdisk Resonator

We demonstrate a fiber ring laser using a fiber-based microdisk resonator as the wavelength filter and a 2-mm-long tapered fiber as the coupling component. The fabrication process of the microdisk and tapered fiber is described. Depending on the optical coupling between the microdisk and the tapered optical fiber, either the fundamental or higher order transverse optical modes in the axial direction of the microdisk can be excited. When only the fundamental transverse mode of the microdisk is excited, the fiber laser operates at single wavelength and is polarization-insensitive. When the higher order transverse modes are excited, the fiber laser exhibits polarization sensitivity, and can operate in either single or dual-wavelength operation. A small spectral separation of 0.62 nm is achieved for dual-wavelength operation.