Tianye Huang

All-fiber multiwavelength thulium-doped laser assisted by four-wave mixing in highly germania-doped fiber

An all-fiber multiwavelength Tm-doped laser assisted by four-wave mixing (FWM) in highly Germania-doped highly nonlinear fiber (HG-HNLF) has been experimentally demonstrated. Benefiting from the high nonlinearity of the HG-HNLF, intensity-dependent gain caused by FWM is introduced into the laser cavity to mitigate the gain competition in Tm-doped fiber. Thanks to a 50-m HG-HNLF, 9, 22, and 36 lasing lines with considering 10-dB, 20-dB, and 30-dB bandwidth, respectively is obtained at room temperature with wavelength spacing of 0.86 nm. More than 30-nm broad-band lasing can be obtained. The stability of the proposed fiber laser has also been studied. Repeat measurements show the power fluctuations and wavelength drifts of the lasing lines are less than 1.6 dB and 0.05 nm, respectively. The laser performances without the assistance of HG-HNLF have fewer center wavelengths lasing, which indicates that FWM in HG-HNLF plays an important role for the multiwavelength laser operation.

Efficient one-third harmonic generation in highly Germania-doped fibers enhanced by pump attenuation

We provide a comprehensive study on one-third harmonic generation (OTHG) in highly Germania-doped fiber (HGDF) by analyzing the phase matching conditions for the step index-profile and optimizing the design parameters. For stimulated OTHG in HGDF, the process can be enhanced by fiber attenuation at the pump wavelength which dynamically compensates the accumulated phase-mismatch along the fiber. With 500 W pump and 35 W seed power, simulation results show that a 31% conversion efficiency, which is 4 times higher than the lossless OTHG process, can be achieved in 34 m of HGDF with 90 mol. % GeO2 doping in the core.

Efficient phase-matched third harmonic generation in an asymmetric plasmonic slot waveguide

An asymmetric plasmonic slot waveguide (APSW) for efficient phase-matched third harmonic generation (THG) is proposed and demonstrated theoretically. Nonlinear organic material DDMEBT polymer is integrated into the bottom of the metallic slot, while silicon is used to fill the top of the slot. We introduce the rigorous coupled-mode equations of THG in the lossy APSW and apply them to optimize the waveguide geometry. Taking advantage of the surface plasmon polaritons (SPPs), the electric fields can be tightly confined in the metallic slot region and the nonlinear effect is greatly enhanced accordingly. Then, we investigate the relationships between THG efficiency and parameters such as slot width and height, phase matching condition (PMC), modal overlap related nonlinear parameter, figure-of-merit, pump power and detuning. With the proposed asymmetric waveguide, we demonstrate a high THG conversion efficiency of 4.88 × 10(-6) with a pump power of 1 W and a detuning constant of -36 m(-1) at a waveguide length of 10.65 ����m.

Temperature- and strain-insensitive curvature sensor based on ring-core modes in dual-concentric-core fiber

We report on a high-performance curvature sensor based on a long-period grating (LPG) in a dual-concentric-core fiber (DCCF). The LPG is inscribed to couple light from the fundamental mode of the central core to the ring-core modes, resulting in the generation of a series of resonant dips. Two adjacent dips shift toward each other when the LPG is bent. By monitoring the variation of the wavelength interval between these two dips, this LPG can be applied in curvature measurement with a sensitivity as high as -9.046  nm/m(-1). More importantly, such a wavelength interval is almost immune to the cross impacts of temperature and axial strain, since the sensitivities to temperature and axial strain are only 2.6 pm/°C and 0.083 pm/με, respectively.

Design and analysis of surface plasmon resonance sensor based on high-birefringent microstructured optical fiber

Optical fiber based surface plasmon resonance (SPR) sensors are favored by their high sensitivity, compactness, remote and in situ sensing capabilities. Microstructured optical fibers (MOFs) possess microfluidic channels extended along the entire length right next to the fiber core, thereby enabling the infiltrated biochemical analyte to access the evanescent field of guided light. Since SPR can only be excited by the polarization vertical to metal surface, external perturbation could induce the polarization crosstalk in fiber core, thus leading to the instability of sensor output. Therefore for the first time we analyze how the large birefringence suppresses the impact of polarization crosstalk. We propose a high-birefringent MOF based SPR sensor with birefringence larger than 4 × 10−4 as well as easy infiltration of microfluidic analyte, while maintaining sensitivity as high as 3100 nm/RIU.

Coupling-length phase matching for efficient third-harmonic generation based on parallel-coupled waveguides.

We study third-harmonic generation (THG) in parallel-coupled waveguides where the spatial modulation of the mode intensity provides quasi-phase matching, called coupling-length phase matching (CLPM), for efficient nonlinear frequency conversion. Different types of CLPM are investigated for THG, and it is found that two sets of CLPM conditions can be practically implemented with traditional waveguides. These two CLPM conditions are further investigated by considering nonlinear phase modulations, which can degrade the CLPM-based THG conversion. However, up to 45% efficiency is still possible in this scheme. The greatest significance of this approach is that the requirement of perfect phase matching in a single waveguide is no longer necessary, leading to an alternative waveguide design for THG.

Supermode Bragg grating combined Mach-Zehnder interferometer for temperature-strain discrimination.

We report on a compact sensor by integrating a Mach-Zehnder interference and a cladding Bragg grating in a same section of all-solid photonic bandgap fiber. Theoretical investigation reveals that the Bragg grating resonance stems from the coupling of counter-propagating cladding LP01-like supermodes and the Mach-Zehnder interference works between a LP01-like supermode and LP01 core mode. Compared with the interference fringe, such supermode grating dip responses to axial strain in a more sensitive and opposite-direction manner. Whereas, the interference fringe shows a higher temperature sensitivity than the supermode grating dip. By means of these different responses, this device finds a useful application in the discrimination of temperature and axial strain.

Photonic Generation of Frequency-Quadrupled Microwave Signal With Tunable Phase Shift

A photonic scheme for frequency-quadrupled microwave signal generation with full 360 ° arbitrarily tunable phase shift is proposed and experimentally demonstrated. Two coherent optical components are generated by biasing a Mach-Zehnder modulator at maximum transmission point to suppress odd-order sidebands. Then, two second order sidebands together with the optical carrier are sent to a programmable filter to reject the optical carrier and introduce a phase shift to one of the second order sidebands. A frequency-quadrupled microwave signal with tunable phase is finally obtained by beating the two sidebands at a photodetector. Tunable phase shift of full 360 ° with a microwave frequency from 30 to 42.4 GHz is experimentally demonstrated. The proposed approach has potential applications in the broadband array signal processing system.

Efficient Third-Harmonic Generation From 2

We propose the asymmetrical plasmonic slot waveguide (APSW) design for third-harmonic generation (THG) from 2.25 μm. In this configuration, the phase-matching condition is fulfilled between the zeroth-order mode at fundamental frequency (FF) and the first-order mode at third-harmonic frequency (THF). Due to the asymmetrical geometry, the mode overlap between the two involved modes is significantly enhanced, leading to an efficient THG process. According to the numerical calculation, the conversion efficiency is predicted up to 1.4% with 1-W pump power. The proposed APSW has the potential to realize an integrated efficient THG device in nanometer scale.

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The conversion efficiency of third harmonic generation (THG) from mid-IR (3600 nm) to near-IR (1200 nm) regions in a silicon-silicon-nanocrystal hybrid plasmonic waveguide (SSHPW) was calculated. The required modal phase-matching condition (PMC) between the 0-th mode at fundamental wave (FW) and the 2-nd mode at third harmonic (TH) is achieved by carefully designing the waveguide geometry. Benefiting from the hybridized surface plasmon polariton (SPP) nature of the two guided modes, the SSHPW is capable of achieving both high THG nonlinear coefficient |I₆| and reasonable linear propagation loss, thereby resulting in large figure-of-merits (FOMs) for both FW and TH. According to our simulation, THG conversion efficiency up to 0.823% is achieved at 62.9 ����m SSHPW with pump power of 1 W.