Kuiru Wang

Optical millimeter wave generated by octupling the frequency of the local oscillator

What we believe to be a new scheme to generate an optical millimeter wave with octupling of the local oscillator via a nested LiNbO3 Mach-Zehnder modulator (MZM) is proposed and implemented by numerical simulation. Since the response frequency of the modulator and the local frequency are largely reduced, the bandwidth requirement of the transmitter to the optical and electrical components is reduced greatly. Then, the parameters of the nested modulator are analyzed theoretically, and we find that both the extinction ratio of the MZM and the phase imbalance between its two arms have influence on the performance of the generated optical millimeter wave.

New sampling-based design of simultaneous compensation of both dispersion and dispersion slope for multichannel fiber Bragg gratings

The design of a multichannel fiber Bragg grating to compensate simultaneously the fiber dispersion and dispersion slope is proposed and analyzed. It is found that constituent gratings with equal length would result in unequal channel bandwidth and large band edge sidelobes in broad bandwidth channels due to large dispersion slope. To overcome these short-comings, we propose a new design procedure in that both the physical length and apodization function of the constituent gratings be allowed to vary. This results in a multichannel grating with equal bandwidth and negligible band edge sidelobes. Of course, this grating compensates both the fiber dispersion and dispersion slope very well.

Aberration analyses for improving the frontal projection three-dimensional display

The crosstalk severely affects the viewing experience for the auto-stereoscopic 3D displays based on frontal projection lenticular sheet. To suppress unclear stereo vision and ghosts are observed in marginal viewing zones(MVZs), aberration of the lenticular sheet combining with the frontal projector is analyzed and designed. Theoretical and experimental results show that increasing radius of curvature (ROC) or decreasing aperture of the lenticular sheet can suppress the aberration and reduce the crosstalk. A projector array with 20 micro-projectors is used to frontally project 20 parallax images one lenticular sheet with the ROC of 10 mm and the size of 1.9 m × 1.2 m. The 3D image with the high quality is experimentally demonstrated in both the mid-viewing zone and MVZs in the optimal viewing plane. The 3D clear depth of 1.2m can be perceived. To provide an excellent 3D image and enlarge the field of view at the same time, a novel structure of lenticular sheet is presented to reduce aberration, and the crosstalk is well suppressed.

Widely Wavelength-Tunable Two-Colored Solitons and Small Spectral Component for Broadband Mid-Infrared Wavelength Generation in a Highly Birefringent Photonic Crystal Fiber

With a highly birefringent photonic crystal fiber (HB-PCF) specially designed and fabricated in our laboratory, the two-colored solitons and small spectral component formed by the balance between the dispersion and birefringence effect are generated above 2000 nm when the polarization direction of pump pulse is aligned along the fast and slow axis of HB-PCF. When the average power of the pump at 870 nm increases from 100 to 300 mW, the broadband solitons at the fast and slow axis and small spectral component can be efficiently generated from 2120 to 2230 nm, 2070 to 2180 nm, and 2260 to 2370 nm, and the tunable wavelength range can be up to 300 nm. To the best of our knowledge, the largest span of soliton wavelength shift over 1300 nm is achieved. The widely tunable soliton pulse and small spectral component can provide the particularly useful short-pulse source for the mid-infrared photonics and spectroscopy.

Enhanced intermodal four-wave mixing for visible and near-infrared wavelength generation in a photonic crystal fiber

We demonstrate experimentally an enhanced intermodal four-wave mixing (FWM) process through coupling positively chirped femtosecond pulses into the deeply normal dispersion region of the fundamental mode of an in-house fabricated photonic crystal fiber (PCF). In the intermodal phase-matching scheme, the energy of the pump waves at 800 nm in the fundamental mode is efficiently converted into the anti-Stokes waves around 553 nm and the Stokes waves within the wavelength range of 1445-1586 nm in the second-order mode. The maximum conversion efficiency of η(as) and η(s) of anti-Stokes and Stokes waves can be up to 21% and 16%, respectively. The Stokes frequency shift Ω is 5580  cm(-1). The fiber bending and intermodal walk-off effect of pulses do not have significant influence on the nonlinear optical process.

Efficient Red-Shifted Dispersive Wave in a Photonic Crystal Fiber for Widely Tunable Mid-Infrared Wavelength Generation

Red-shifted dispersive waves (DWs) at the mid-infrared wavelengths are generated for the first time by pumping a photonic crystal fiber (PCF) with two zero dispersion wavelengths specially designed and fabricated in our laboratory, and the central wavelength of the soliton generated lies on the negative slope of the PCF dispersion profile. The experimental result shows that the conversion efficiency η of red-shifted DWs increases from 5 to 15% as the input power changes from 100 to 300 mW with the pump wavelength of 810 nm. By adjusting both the pump wavelength and power, the tunable range of the wavelength generated by red-shifted DWs can be over 100 nm.

Generation of Multiple Mid-Infrared Wavelengths by Soliton Fission in a Photonic Crystal Fiber

Higher-order solitons are formed by coupling femtosecond pulses into the fundamental mode of a highly nonlinear silica photonic crystal fiber (HNL-SPCF) fabricated in our laboratory. It is experimentally observed that the higher-order solitons break up into a series of stable and broadband discrete fundamental solitons at the mid-infrared wavelength longer than 2000 nm through the process of soliton self-frequency shift due to the perturbations induced by the higher-order dispersive and nonlinear effects. The maximum soliton red-shift and the tunable wavelength range can be up to 1600 nm and over 400 nm, respectively. The nonlinear dynamic processes of femtosecond pulse breakup are consistent with the solution of the generalized nonlinear Schrödinger equation. This multiple stable and broadband mid-infrared wavelengths generated in such an HNL-SPCF can be used as all-fiber multiwavelength ultrashort pulse sources for multiphoton microscopy and ultrafast photonics.

Coherent Anti-Stokes Raman Scattering Microscopy by Dispersive Wave Generations in a Polarization Maintaining Photonic Crystal Fiber

The polarization maintaining photonic crystal flber (PM- PCF) with two zero dispersion wavelengths is designed and fabricated by the improved stack-and-draw technology in our laboratory. The broadband blue-shifted and red-shifted dispersive waves (DWs) are e-ciently generated from soliton self-frequency shift (SSFS) along the slow axis of PM-PCF. By optimizing the pump parameters and the flber length, the polarized DWs centered in the normal dispersion region can be used as the pump and Stokes pulses for the high resolution coherent anti-Stokes Raman scattering (CARS) microscopy. Moreover, it is demonstrated that the widely tunable relevant CARS wavelengths can be obtained by adjusting the pump wavelength. The CARS microscopy based on DWs can flnd important applications in detecting the biological and chemical samples with the C = N, S-H, C-H, and O-H stretch vibration resonances of 2100 to 2400cm i1 , 2500 to 2650cm i1 , 2700 to 3000cm i1 , and 3000 to 3750cm i1 .

High Sensitivity Ammonia Gas Sensor Based on a Silica-Gel-Coated Microfiber Coupler

In this paper, a high-sensitivity ammonia gas sensor is proposed based on a silica-gel-coated microfiber coupler (MFC). The MFC structure is formed by the two tapered fibers with 3 μm waist diameter each, which were fabricated by using a customized microheater brushing technique. Silica gel coating was prepared by a sol-gel technique and applied on the surface of the MFC as a thin layer. The spectral characteristics of the proposed sensor were studied under various ammonia gas concentrations. The experimental results show that the coating thickness strongly affected the sensitivity of the MFC-based sensor to ammonia gas concentration. For the sensor with a 90 nm silica gel coating thickness, the highest measurement sensitivity is 2.23 nm/ppm for ammonia gas concentration, and the resolution is as good as 5 ppb, while the measured response and recovery times are ∼50 and 35 s, respectively. Finally, it is demonstrated that the proposed sensor offers good repeatability and selectivity to ammonia gas.

Highly Coherent Supercontinuum Generation in the Normal Dispersion Liquid-Core Photonic Crystal Fiber

In this paper, a liquid-core photonic crystal fiber (LCPCF) with small hollow-core filled by chalcogenide material CS2 is designed. The supercontinuum (SC) generation in such a LCPCF with nonlinear coefficient of 3327 W−1·km−1 at 1550 nm and wide normal dispersion regime spanning from 1200 to 2500 nm is numerically studied by solving the generalized nonlinear Schrödinger equation. The influences of the pump pulse parameters on the SC spectral width and coherence are demonstrated, and the optimum pump condition for the SC generation is determined. Our study work can provide an alternative way for obtaining highly coherent SC, which is important for the applications in optical coherence tomography, frequency combs, and ultrashort pulse generation.