Jihua Zhang

Highly efficient phase-matched second harmonic generation using an asymmetric plasmonic slot waveguide configuration in hybrid polymer-silicon photonics.

We theoretically investigate the possible increase of the second harmonic generation (SHG) efficiency in silicon compatible waveguides by considering an asymmetrical plasmonic slot waveguide geometry and a χ((2)) nonlinear polymer infiltrating the slot. The needed phase matching condition is satisfied between the fundamental waveguide mode at the fundamental frequency (FF) and second-order waveguide mode at the second harmonic frequency (SHF) by an appropriate design of the waveguide opto-geometrical parameters. The SHG signal generated in our starting waveguide is three orders of magnitude higher than those previously reported for a FF corresponding to λ = 1550 nm. Then, the SHG performance was further improved by increasing the asymmetry of the structure where nonlinear coupling coefficients as large as 292 psm(-1)W(-1/2) are predicted. The device length is shorter than 20 µm and the normalized SHG conversion efficiency comes up to more than 1 × 10(5) W(-1)cm(-2).

Phase regeneration of phase-shift keying signals in highly nonlinear hybrid plasmonic waveguides

Phase regeneration of phase-shift keying signals is theoretically proposed, we believe for the first time, based on the efficient optical parametric amplification (OPA) process in a highly nonlinear symmetric hybrid plasmonic waveguide. This optimized stacked waveguide with nonlinear organic materials has a relatively low loss of about 0.005 dB/μm and an effective nonlinear OPA coupling coefficient up to 60 ps/m/W(1/2). The phase-recovery process was achieved in this waveguide within a length as short as 150 μm.

Wideband and Compact TE-Pass/TM-Stop Polarizer Based on a Hybrid Plasmonic Bragg Grating for Silicon Photonics

Based on a transverse electric (TE)/transverse magnetic (TM) polarization diversity waveguide, we theoretically propose a TE-pass/TM-stop polarizer by etching a polarization dependent Bragg grating into the oxide layer of a silicon/thin SiO2 gap/metal cap hybrid plasmonic waveguide. The simulation results indicate that the device is characterized by high TE-transmission and large TM-reflection levels in a wide waveband from 1.48 to 1.7 μm combined with an excellent compactness (length less than 5 μm). Transmission and reflection extinction ratio are both larger than 17.1 dB in the 1.48-1.64 μm wavelength range, while losses are smaller than 1.36 and 0.69 dB for the TE and TM modes, respectively.

Efficient second harmonic generation from mid-infrared to near-infrared regions in silicon-organic hybrid plasmonic waveguides with small fabrication-error sensitivity and a large bandwidth

We theoretically investigate the quadratic nonlinear property of a silicon-organic hybrid plasmonic waveguide with a thin polymer layer deposited on top of a silicon slab and covered by a metal cap. Due to the hybridization property of the waveguide modes, efficient phase-matched second harmonic generation (SHG) from mid-infrared (IR) (~3.1 μm) to near-IR (~1.55 μm) wavelengths are achieved with a small fabrication-error sensitivity (225 nm ≤ tolerated waveguide width ≤ 378 nm) and a large bandwidth (Δλ=100 nm). The SHG yield is as large as 8.8% for a pumping power of 100 mW.

Designing Appointed and Multiple Focuses With Plasmonic Vortex Lenses

A plasmonic vortex lens (PVL), which enables to focus the spin or orbital angular momentum to a specific spatial position in the form of a plasmonic vortex, has been widely studied. Here, we present a specific PVL structure to focus the surface plasmon polariton wave on an arbitrary spatial position. Both analytical and numerical analyses are presented. The plasmonic field of our PVL is an approximate Bessel beam. In particular, the PVL can focus the input beam into a zeroth-order Bessel beam with a central peak. Based on this principle, multiple focuses by combining multiple different PVLs are designed. We can freely control the focuses just by changing the input modes. Owing to the tuning ability of the focuses, these findings can motivate the applications for optical trapping, optical data, and digital display on chip.

In-line polarization-dependent microfiber interferometers and their applications in UWB signal generation

A novel in-line polarization-dependent microfiber interferometer (PD-MFI) is proposed and experimentally demonstrated, which is tapered from a commercial polarization-maintaining fiber. Different from conventional MFIs, the transmission spectra of such MFIs are highly polarization-dependent, due to the mode-sensitive birefringence. The experimental results agree well with the theoretical predictions. Moreover, exploiting the polarization-dependent property of PD-MFIs, we demonstrate a simple and flexible scheme of generating polarity-switchable ultra-wideband pulses in the optical domain. Doublet pulses with a central frequency of 6.28 GHz and a 10-dB bandwidth of 7.86 GHz are obtained. Hence, with the advantages of being fiberized, simple fabrication and robustness, these PD-MFIs can be attractive elements in optical signal processing, optical sensing, optical fiber communication, and microwave photonics.

Retrieving orbital angular momentum distribution of light with plasmonic vortex lens

We utilize a plasmonic vortex lens (PVL) to retrieve the orbital angular momentum (OAM) distribution of light. The OAM modes are coupled to the surface plasmon polaritons (SPPs) in the form of various Bessel functions respectively. By decomposing the interference pattern of SPPs into these Bessel functions, we can retrieve the relative amplitude and the relative phase of input OAM modes simultaneously. Our scheme shows advantage in integration and can measure hybrid OAM states by one measurement.

All-optical 1st- and 2nd-order differential equation solvers with large tuning ranges using Fabry-Pérot semiconductor optical amplifiers

We experimentally demonstrate an all-optical temporal computation scheme for solving 1st- and 2nd-order linear ordinary differential equations (ODEs) with tunable constant coefficients by using Fabry-Pérot semiconductor optical amplifiers (FP-SOAs). By changing the injection currents of FP-SOAs, the constant coefficients of the differential equations are practically tuned. A quite large constant coefficient tunable range from 0.0026/ps to 0.085/ps is achieved for the 1st-order differential equation. Moreover, the constant coefficient p of the 2nd-order ODE solver can be continuously tuned from 0.0216/ps to 0.158/ps, correspondingly with the constant coefficient q varying from 0.0000494/ps(2) to 0.006205/ps(2). Additionally, a theoretical model that combining the carrier density rate equation of the semiconductor optical amplifier (SOA) with the transfer function of the Fabry-Pérot (FP) cavity is exploited to analyze the solving processes. For both 1st- and 2nd-order solvers, excellent agreements between the numerical simulations and the experimental results are obtained. The FP-SOAs based all-optical differential-equation solvers can be easily integrated with other optical components based on InP/InGaAsP materials, such as laser, modulator, photodetector and waveguide, which can motivate the realization of the complicated optical computing on a single integrated chip.

Electrically controlled second-harmonic generation in silicon-compatible plasmonic slot waveguides: a new modulation scheme

The possible realization of an active electro-optical control of the nonlinear second-harmonic generation (SHG) mechanism in a plasmonic slot waveguide is theoretically investigated. Both the conventional SHG and the electrically induced SHG are taken into account with a moderate pump power of 40 mW at the fundamental wavelength (1550 nm). The generated power of the second-harmonic frequency can be modulated by the applied voltage in a quadratic and almost linear form for centrosymmetric and noncentrosymmetric nonlinear polymers integrated in the slot, respectively. Converted power up to 140 μW within a short distance of only 16 μm is predicted for a voltage of 10 V. This mechanism may open a new route to realize high-speed advanced modulations or inversely to detect ultrafast electrical signals.

Optical nonreciprocity with large bandwidth in asymmetric hybrid slot waveguide coupler

On-chip broadband optical nonreciprocal transmission based on asymmetric hybrid slot waveguide (HSW) coupler is proposed. Filled with flint glass LaSF-010 and organic material DDMEBT in slots, respectively, two branches of an asymmetric HSW coupler have very distinct nonlinear coefficients, yet very close effective indexes. Since asymmetric coupler with low linear mismatch has a large free spectral range, the results show that our device has a 10-dB nonreciprocal transmission bandwidth (NTB) as large as about 66 nm corresponding to 80-mW operating power. The NTB could be even larger when the incident power is raised. This indicates over two orders of magnitude enhancement compared to previous on-chip passive schemes. Owing to the large NTB, the device also functions properly for sub-picosecond pulses. Our scheme paves a path toward practical all-optical nonreciprocal applications.