We propose and demonstrate a compact and portable-size 84-GHz passive mode-locked fiber laser, in which a dual-fiber coupled fused-quartz microresonator is employed as the intracavity optical comb filter as well as the optical nonlinear material for optical frequency comb generation. About eight coherent optical tones can be generated in the proposed fiber laser. The 20-dB bandwidth is larger than 588 GHz. The full-width half-maximum pulse-width of the proposed laser is 2.5 ps. We also demonstrate the feasibility of using the proposed passive mode-locked fiber laser to carry a 5-Gbit/s on-off-keying signal and transmit over 20-km standard single mode fiber. A 7% forward error correction requirement can be achieved, showing the proposed fiber laser can be a potential candidate for fiber-wireless applications.
A compact and portable microresonator-based optical frequency comb generation system was developed to provide an array of multiwavelength laser sources for dense wavelength division multiplexing (DWDM) fiber optic communication. The reported comb generation system was capable of producing comb lines after 7 km of travel without environmental control, indicating the effectiveness of the packaging. The comb spacing is about 98.3 GHz (i.e., ∼0.79 nm around 1553 nm), thus the comb line frequencies coincide nicely with 100-GHz DWDM channel frequencies, assuming the suggested channel bandwidth is 0.3 nm. The quality of selected comb lines was evaluated individually based on error vector magnitude (EVM) measurements along with RF spectrum measurements. An average EVM value observed is as low as 3.8%, close to typical EVM values of less than 3% used for fiber optic communication.
Metallic rod array is successfully demonstrated to be integrated a parallel plate waveguide and used as a slab-waveguide for sensing applications. Both the waveguide properties are characterized from the transmission spectra using different polarization conditions of terahertz electromagnetic fields, which are parallel and perpendicular to the rod axis. When THz field polarization is parallel to the rod axis, there is high-pass filtering feature with structure-period-dependent threshold frequency, corresponding to the plasma frequency of the rod-array composite. For the polarization perpendicular to the rod axis, there is Bragg diffraction frequency as forbidden band with considerably low transmission power. The metal-rod-array integrated parallel-plate waveguide is connected with a microfluidic channel to sense liquids, and the minimum detectable quantity is about 13μmol/mm3. The metal-rod-array slab waveguide is able to sense thinfilm with nanometer level, and the detectable optical path difference is down to λ/2380. The sensor properties of multiple functions for sensing various analyte conformations, microfluidic integration and high sensitivity would be applied in biomedicine and biochemical applications.
A terahertz plasmonic waveguide sensor is experimentally demonstrated to utilize surface waves propagated in a onedimension
metal grating that constructed on a plastic ribbon waveguide. The grating conformation couples evanescent
waves of a subwavelength terahertz waveguide onto the metal surface and highly confines the extended powers within
λ/22-range for the phase-matching condition. The confined terahertz waveguiding waves resemble surface plasmonpolaritons
but transmit with almost zero dispersion when the coupled surface waves interfere along the metal grating.
Based on the dispersion-free guidance, there is Bragg reflection dominated by grating periods and strongly dependent on
the refractive index of surface plasmon-polaritions. We successfully detect different thicknesses of polyethylene layers
covered on the metal grating with thickness resolution of 1μm when the effective waveguide indices are modified in the
vicinity of the metal grating, corresponding to 0.01-index variation. Potentially, terahertz subwavelength ribbon
waveguide based plasmonic sensors could be manipulated to detect molecules with extremely low-density or small
thickness in the metal-dielectric interface for probing pollution particles and any label-free detection.
A dielectric hollow-core tube utilized as a terahertz anti-resonant reflecting hollow-core waveguide (THz-ARRHW)
sensor has been demonstrated to detect the minute variation of both refractive index and thickness in macromolecule
layers, deposited on the tube wall, and to identify liquid vapors from the various core indices. The minimal quantity of
macromolecule layers loaded on the tube wall of a polypropylene tube can be detected at 1.2picomole/mm2 and 0.2%,
corresponding to the variation of 2.9μm-thickness and 0.001-refractive-index. And the sensing performance of a THz-
ARRHW to detect core index variation for identifying volatile liquids is also realized at 0.0001g/cm3- vapor density.
We present the first characterization of a simple subwavelength-diameter plastic wire by using wideband terahertz timedomain
spectroscopy. The propagation characteristics including waveguide dispersion, group velocity, and attenuation
constant of various plastic wires with different diameters and refractive indices are studied. The experimental results
show the subwavelength plastic wire has extremely low waveguide dispersion and low attenuation constant (<0.01cm-1)
at its THz transmission band due to much reduced fractional power delivered inside the lossy core, which is consistent
with the theoretical calculations. With the large evanescent-fields, the subwavelength plastic wire has capability to
integrate with micro-fluid channel for sensitive bio-sensing applications.
Significant difference in temporal and spectral characteristics of THz radiation emitted by large- (1mm) and small- (5micrometers ) aperture dipole antennas fabricated on arsenic-ion-implanted GaAs and undoped semi-insulating GaAs is reported and attributed to the geometry of the antenna.
A DC-voltage controlled optoelectronic phase shifter (OEPS) integrated with a PZT-controlled active stabilizer is proposed for both the reduction in timing jitter and the tuning in delay-time of optical pulses generated from argon- ion-laser-pumped, passively mode-locked femtosecond Ti:sapphire laser with intracavity saturable Bragg reflector (SBR). The rms timing jitter (100 - 500 Hz) of the Ti:sapphire/SBR laser is significantly suppressed down to 290 fs with uncorrelated single-sided-band phase noise of less than -120 dBc/Hz at offset frequency of 5 KHz. The pulsewidth, the repetition rate, and the single-sided-band phase noise of the laser are found to keep invariant during the delay-time tuning process. The maximum phase-tuning range and tuning gain of the OEPS is approximately equals 11.3 ns and 2.3 ns/volt.
Subpicosecond carrier lifetimes of arsenic-rich GaAs grown by molecular beam epitaxy at low substrate temperatures have been determined by time-resolved reflectivity. Effect of growth temperature on change of transient reflectivity and antisite defect concentration were also demonstrated. For the first time carrier lifetime as short as 0.13 ps was observed (resolution limited).
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