[Show abstract][Hide abstract] ABSTRACT: We design a novel long-range hybrid wedge plasmonic (LRHWP) waveguide composed of two identical dielectric nanowires symmetrically placed on two opposed wedges of a diamond shaped metal wire. With strong coupling between the dielectric nanowire mode and long-range surface plasmon polariton (SPP) mode, both deep subwavelength mode confinement and low propagation loss are achieved. On one hand, when compared to the previous long-range hybrid SPP waveguide, LRHWP waveguide can achieve smaller mode size with similar propagation length; on the other hand, when compared to the previous hybrid wedge SPP waveguide, LRHWP waveguide can provide an order of magnitude longer propagation length with similar level of mode confinement. The designed LRHWP waveguide also features an overall advantage of one-order improvement of Figure of Merit. We further evaluate in detail the impacts of possible practical fabrication imperfections on the mode properties. The obtained results of mode properties show that the proposed LRHWP waveguide with an optimized wedge tip angle of 140 degree is fairly tolerant to practical fabrication errors in geometry parameters such as misalignment in the horizontal direction, asymmetry in the vertical direction, variation of wedge tip angle, tilt or rotation of metal wire, and variation of wedge tip curvature radius.
[Show abstract][Hide abstract] ABSTRACT: We present modulation-format-transparent data exchange for m-ary quadrature amplitude modulation (m-QAM) signals using a single silicon-organic hybrid slot waveguide which offers tight light confinement and enhanced nonlinearity. By exploiting the parametric depletion effect of non-degenerate four-wave mixing (ND-FWM) process in the slot waveguide, we simulate low-power (<10 mW) ultrahigh-speed optical data exchange of 640 Gbaud (2.56 Tbit/s) optical time-division multiplexed (OTDM) 16-QAM and 640 Gbaud (3.84 Tbit/s) OTDM 64-QAM signals and characterize the operation performance in terms of error vector magnitude (EVM) and bit-error rate (BER). The calculated signal-to-noise ratio (SNR) penalties of data exchange are negligible for 2.56 Tbit/s 16-QAM signals and less than 2 dB for 3.84 Tbit/s 64-QAM signals at a BER of 2e-3. For a given pump power of 9 mW, the operation performance dependence on the waveguide length is studied, showing an optimized waveguide length of ~17 mm. For a given waveguide length of 17 mm, the SNR penalty of data exchange, at a BER of 2e-3, is kept below 4 dB when varying input pump power from 8.4 to 9.8 mW for 2.56 Tbit/s 16-QAM and from 8.9 to 9.2 mW for 3.84 Tbit/s 64-QAM. In addition, data exchange running at low speed (e.g. 20 Gbaud) and data exchange taking into account waveguide propagation loss are also analyzed with favorable operation performance.
[Show abstract][Hide abstract] ABSTRACT: We report on-chip all-optical wavelength conversion of multicarrier multilevel modulation signals in a silicon waveguide. Using orthogonal frequency-division multiplexing (OFDM) combined with advanced multilevel quadrature amplitude modulation (QAM) signals (i.e., OFDM m-QAM), we experimentally demonstrate all-optical wavelength conversions of 3.2 Gbaud/s OFDM 16/32/64/128-QAM signals based on the degenerate four-wave mixing (FWM) nonlinear effect in a silicon waveguide. The measured optical signal-to-noise ratio (OSNR) penalties of wavelength conversion are ∼3 dB for OFDM 16-QAM and ∼4 dB for OFDM 32-QAM at 7% forward error correction (FEC) threshold and ∼3.5 dB for OFDM 64-QAM and ∼4.5 dB for OFDM 128-QAM at 20% FEC threshold. The observed clear constellations of converted idlers imply favorable performance obtained for silicon-waveguide-based OFDM 16/32/64/128-QAM wavelength conversions.
[Show abstract][Hide abstract] ABSTRACT: A new silica antireflective coating with improved hydrophobicity and optical stability in a vacuum is obtained by a two-step route. Firstly, silica sols are prepared with a sol-gel process, in which tetraethyl orthosilicate is utilized as a precursor. And by introduction of fluorine containing glycol into the sols, the porosity of silica particles and surface polarity of the coatings are decreased. Afterward, coatings are constructed with low surface roughness by modification of PMBA-PMMA. The coatings retain transmission of up to 99.6%, and laser damage threshold of about 50 J/cm2 at a wavelength of 532 nm (1-on-1, 10 ns).
Chinese Optics Letters 07/2014; 12(7). · 1.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tunability is a desirable property of microring resonators to facilitate superior performance. Using light to control light, we present an alternative simple approach to tuning the extinction ratio (ER) and Q-factor of silicon microring resonators based on optical forces. We design an opto-mechanical tunable silicon microring resonator consisting of an add-drop microring resonator and a control-light-carrying waveguide ("controlling" waveguide). One of the two bus waveguides of the microring resonator is a deformable nanostring put in parallel with the "controlling" waveguide. The tuning mechanism relies on the optical force induced deflection of suspended nanostring, leading to the change of coupling coefficient of microring and resultant tuning of ER and Q-factor. Two possible geometries, i.e. double-clamped nanostring and cantilever nanostring, are studied in detail for comparison. The obtained results imply a favorable structure with the microring positioned at the end of the cantilever nanostring. It features a wide tuning range of ER from 5.6 to 39.9 dB and Q-factor from 309 to 639 as changing the control power from 0 to 1.4 mW.
[Show abstract][Hide abstract] ABSTRACT: We fabricate on-chip two/three mode division (de)multiplexing using a tapered asymmetrical directional coupler on SOI platform. System experiments of OFDM 64/128/256-QAM data transmission have been carried out for on-chip two/three mode (de)multiplexing application.
[Show abstract][Hide abstract] ABSTRACT: We experimentally demonstrate power-controllable multicasting of OFDM 64-QAM signal from single Gaussian mode to multiple OAM modes using a single phase-only spatial light modulator assisted by a feedback control. The precision of power control is less than 1 dB.
[Show abstract][Hide abstract] ABSTRACT: We design an optically-controlled mode converter using optical force. A deformable nanostring can be deflected by optical gradient force, changing the coupled mode in a multimode waveguide and enabling a mode converter.
[Show abstract][Hide abstract] ABSTRACT: Vibration-assisted grinding, in which harder abrasives than materials to be machined are employed, has been a viable and effective approach to increasing material removal rate (MRR) and/or reducing surface roughness of ground surfaces. We transfer this ideology to fused silica polishing by incorporating ultrasonic vibration into recently developed fixed-abrasive pellets in an attempt to enhance MRR and/or to improve manufactured surface quality. A prototype ultrasonic vibrator, the heart of the polishing head, was designed and the related experimental work was performed on an in-house built setup in conjunction with the constructed head. The vibrator is devised for the generation of 2-D tool path despite using only one actuator in lieu of two actuators in conventional 2-D ultrasonic machining systems. We then combined the ultrasonic vibration with fixed abrasive polishing pellets to machine fused silica glass. Machining experiments reveal that MRR is considerably increased up to >50% upon the introduction of ultrasonic vibration (UV) whilst surface roughness is not degraded appreciably. It was also noted that a overwhelmingly greater deal of polishing debris was dispelled during ultrasonic vibration assisted polishing than conventional bound-abrasive polishing, which may account for the greater MRR in UV assisted polishing.
International Journal of Precision Engineering and Manufacturing 05/2014; 13(12). · 1.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: By designing and fabricating 3D printed spiral phase plates (SPPs), we demonstrate basic functionalities for terahertz (THz) orbital angular momentum (OAM) communications, including the generation, detection, conversion, multicasting and manipulation of OAM at 0.1 THz.
[Show abstract][Hide abstract] ABSTRACT: We reviewed recent works on optical transmission using OAM modes. Free-space OAM transmissions with 100.8Tbit/s capacity, 230.1bit/s/Hz spectral efficiency and 1.6-Tbit/s fiber OAM transmission were demonstrated. OAM networking functionalities and future challenges were discussed.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate the multiplexing/demultiplexing of pol-muxed 22 orbital angular momentum (OAM) modes. Using 17.9-Gbit/s OFDM/OQAM 64-QAM signals over pol-muxed 22 OAM modes (44 channels in total), we achieve an ultra-high spectral efficiency of 230 bit/s/Hz.
[Show abstract][Hide abstract] ABSTRACT: We present a compact (130 μm cladding diameter) trench-assisted multi-orbital-angular-momentum (OAM) multi-ring fiber with 19 rings each supporting 22 modes with 18 OAM ones. Using the high-contrast-index ring and trench designs, the trench-assisted multi-OAM multi-ring fiber (TA-MOMRF) features both low-level inter-mode crosstalk and inter-ring crosstalk within a wide wavelength range (1520 to 1630 nm), which can potentially enable Pbit/s total transmission capacity and hundreds bit/s/Hz spectral efficiency in a single TA-MOMRF. Moreover, the effective refractive index difference of even and odd fiber eigenmodes induced by the ellipticity of ring and fiber bending and their impacts on the purity of OAM mode and mode coupling/crosstalk are analyzed. It is found that high-order OAM modes show preferable tolerance to the ring ellipticity and fiber bending. The designed fiber offers favorable tolerance to both small ellipticity of ring (<-22 dB crosstalk under an ellipticity of 0.5%) and small bend radius (<-20 dB crosstalk under a bend radius of 2 cm).
[Show abstract][Hide abstract] ABSTRACT: We design an ultra-compact active hybrid plasmonic ring resonator for lasing applications at deep sub-wavelength scale. The combined contributions of hybrid plasmonic mode, circular-shaped cross section of nanowire, and ring resonator structure with round-trip whispering-gallery cavity, benefit reduced metallic absorption loss, tight mode confinement, enhanced cavity feedback, achieving high quality factor (Q), small mode volume (V), high Purcell factor (Fp), low threshold gain (Gth), and ultra-small footprint with sub-micron size. The performance dependence on the geometrical parameters, including gap height (Hg), cross section radius (Rc), and ring radius (Rr), are comprehensively analyzed, showing high Q factor of 1650 (Hg = 30 nm, Rc = 100 nm, Rr = 800 nm), ultra-small mode volume of 0.0022 μm(3) (Hg = 5 nm, Rc = 100 nm, Rr = 800 nm), cut off of all photonic modes for pure plasmonic mode lasing with Rc<70 nm (Hg = 10 nm, Rr = 800 nm), maximum Purcell factor of 813 and minimum threshold gain of 1407 cm(-1) (Hg = 5 nm, Rc = 50 nm, Rr = 400 nm). The general design rules of the presented hybrid plasmonic ring resonator provide the potential to further extend ultra-compact sub-micron lasing applications (i.e. different lasing wavelength band) with proper choice of gain materials and geometric structures.
[Show abstract][Hide abstract] ABSTRACT: A model for interactions of a single large impurity particle with the optic and pad during pad-polishing has been developed to detailedly illustrate the scratch formation process. Equations for calculating the normal load applied on the optic by the impurity particle are provided, and the friction between the optic and impurity particle has also been considered in scratch formation. Initiation and evolution of the scratches under the combined effects of the normal and friction forces are illustrated in the model. The most important factors affecting the normal load and thus scratch formation have been analyzed and verified using published experimental results. Based on the model, the implications in reduction of scratch formed on optics during pad polishing have been analyzed.
Journal of Non-Crystalline Solids 01/2014; 391:96–100. · 1.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Spatial structure of a light beam is an important degree of freedom to be extensively explored. By designing simple configurations with phase-only spatial light modulators (SLMs), we show the ability to arbitrarily manipulate the spatial full field information (i.e. amplitude and phase) of a light beam. Using this approach to facilitating arbitrary and independent control of spatial amplitude and phase, one can flexibly generate different special kinds of light beams for different specific applications. Multiple collinear orbital angular momentum (OAM) beams, Laguerre-Gaussian (LG) beams, and Bessel beams, having both spatial amplitude and phase distributions, are successfully generated in the experiments. Some arbitrary beams with odd-shaped intensity are also generated in the experiments.
[Show abstract][Hide abstract] ABSTRACT: We propose a simple approach for simultaneous optical half-adder and half-subtracter using a single-slot waveguide that offers tight light confinement and enhanced nonlinearity. By exploiting the parametric depletion effect of twin degenerate four-wave mixing processes in the slot waveguide, we simulate 160-Gbit/s half-adder (A + B) and half-subtracter (A - B, B - A) and characterize the operation performance in terms of quality Q factor, extinction ratio ER, and eye opening EO. Two different nonlinear materials are considered as the slot region for comparison. One is silicon-nanocrystal (Si-nc) with Kerr nonlinear index of refraction (n2) of 4.8 ×10-17 m2/W and two-photon absorption (TPA) coefficient (βTPA) of 7 ×10-11 m/W at 1550 nm, and the other is a specific polydiacetylene, poly-[2,4 hexadiyne -1,6 diol-bis-( p -toluene sulfonate)] (PTS) with n2 = 6.25 ×10-17 m2/W and βTPA ≈ 0 at 1550 nm. PTS slot waveguide features superior performance of half-adder and half-subtracter compared with Si-nc slot waveguide under the same waveguide length and input signal power. Moreover, we study the performance dependence on the waveguide length and input power, providing an easy-to-follow theoretical basis for achieving the desired performance of half-adder and half-subtracter.
[Show abstract][Hide abstract] ABSTRACT: A compact low-crosstalk multi-ring fiber transmitting multiple orbital angular momentum (OAM) modes is presented. The multi-OAM-mode multi-ring fiber (MOMRF) consists of 7 rings, each supporting 22 modes with 18 OAM ones (i.e., 154 channels in total), which can be used for high-density space-division multiplexing. The employed high-contrast-index ring structure benefits tight light confinement and large effective refractive index difference of different OAM modes , featuring both low-level inter-ring crosstalk ( 30 dB for a 100-km-long fiber) and intermode crosstalk over a wide wavelength range (1520-1580 nm). The designed MOMRF is also compatible with wavelength-division multiplexing technique (e.g., 75 ITU-grid wavelengths from 1520.25 to 1579.52 nm with 100-GHz spacing) and advanced multilevel amplitude/phase modulation formats (e.g., 16-ary quadrature amplitude modulation), which might be used to achieve petabit-per-second total transmission capacity and hundred bits-per-second-per-hertz aggregate spectral efficiency.
[Show abstract][Hide abstract] ABSTRACT: We propose a simple approach to broadband generation of orbital angular momentum (OAM) carrying vector beams based on compact metamaterials. It consists of two concentric rings in a gold film, where each ring is composed of subwavelength rectangular apertures with gradually varied orientation. The subwavelength rectangular aperture serves as a localized spatial polarizer. We show the generation of different OAM-carrying vector beams with OAM charge number and polarization order varying from -3 to +3 using a 11.2×11.2 μm device. The extinction ratio can exceed 20 dB, and the operation bandwidth (1500 nm) can cover from 1000 to 2500 nm (from near-infrared to mid-infrared). The device provides three degrees of freedom (polarization order l, polarization of input beam σ, and initial orientation angle α<sub>0</sub>) to flexibly generate different OAM-carrying vector beams. We can use a single device to generate two OAM-carrying vector beams with opposite charge sign of OAM by simply controlling the polarization of the input beam. We further study the performance dependence of the designed metamaterials on the offset of the initial orientation angle, length, and width of the rectangular apertures. The obtained results indicate favorable fabrication tolerance.