A new type of photonic crystal electro-optic modulator with wavy PN junction has been designed. The proposed device is mainly composed of photonic crystal line defect waveguide and triangular of lattice circular air holes are applied in Si photonic crystal slab. SiO2 is used as substrate material with a thickness of 2 μm, reverse bias voltage is added to the upper and lower sides of the photonic crystal slab. According to the plasma dispersion effect, when the reverse bias voltage is applied on both sides of the photonic crystal, the refractive index of the doped silicon-based slab will change by introducing wavy PN junction in the center of the waveguide. After that, the transmittance of light is changed, achieving the purpose of modulation. Finite-difference time-domain (FDTD) method is used to calculate the steady-state field intensity distribution and mode field distribution. The results show that when applied voltage is 1.2 V, it has a refractive index difference of 0.0025 compared with the voltage of 0 V, the narrow bandwidth on-off modulation of transverse electric (TE) mode at 1550.68 nm can be realized. The extinction ratio of the device is as high as 30.8 dB, the insertion loss is 0.5 dB, the Q value is 14097. Besides, the modulation rate is as high as 7 GHz.
Based on an integrated silicon platform, we propose a device for generating and multiplexing optical orbital angular momentum modes(OAM), which is consisted of asymmetric directional couplers and trench waveguides. Asymmetric directional coupler is composed of single-mode and multi-mode waveguides . According to the principle of phase matching, the fundamental mode TE00 is coupled to the second-order mode via an asymmetric directional coupler. Single-trench waveguide can support two orthogonal eigenmodes. By adjusting the phase difference of two orthogonal eigenmodes to make them degenerate, they can be converted into orbital angular momentum modes with topological charges of +1, 0, -1, and multiplexed in the second trench. We simulate and analyze the characteristics of the device using three-dimensional finite difference domain method (3D-FDTD). The simulation results show that the device can realize the generation and multiplex of orbital angular momentum modes with topological charges +1, 0, -1. The proposed device is very compact with a footprint of 92 μm×5.3 μm and an insertion loss of 0.359 dB. The structure woks on a wavelength range from 1.48 μm to 1.57 μm. The structure is simple and easy to integrate, having a good application in OAM multiplexing system.
A double-trench silicon waveguide based on SOI chip is proposed to generate high-order OAM modes (OAM±2). The double-trench structure excites two high-order orthogonal modes with π/2 (or 3π/2) phase difference, and can couple into high-order OAM±2 modes at the output terminal. The FDTD simulation results show that the mode conversion efficiency is greater than 95% and the intersection loss is less than 0.22dB during the wavelength range of 1.3 μm to 1.8 μm. The proposed method to generate OAM beams in SOI waveguide would be interesting for on-chip integrated optical communication, optical trapping and quantum information processing.
A D-type fiber optic refractive index sensor based on surface plasmon resonance (SPR) principle is proposed in this paper. The sensor is composed of a double core structure and a grid-coated photonic crystal fiber (PCF) on the polishing surface. The resonant wavelength can be adjusted and the refractive index sensitivity can be improved by introducing a gold grating film. Under the anisotropic perfect matching layer boundary condition, the simulation was preformed through the full-vector finite element method (FEM). The results show that the refractive index measurement range of the sensor is 1.30~1.33, the sensitivity can reach 12000 nm• RIU-1, and the resolution can reach 1.01×10-5 RIU.
In this paper, a 6-channel wavelength-mode division hybrid multiplexer/demultiplexer based on photonic crystals is proposed. The device consists of three combined resonators, three wavelength selective reflection microcavities, single mode waveguides, multimode waveguides and tapered coupled waveguides. The filtering is realized by the structure of combined resonator and wavelength selective reflection microcavity, and the mode conversion is realized by the structure of the asymmetric parallel waveguide. The simulation analysis by time-domain finite difference method shows that the device can realize the multiplexing/demultiplexing of six channels, i. e. , the 1550 nm TE0 mode, 1530 nm TE0 mode, 1550 nm TE1 mode, 1530 nm TE1 mode, 1550 nm TE2 mode and 1530 nm TE2 mode. Its insertion loss is <0.132dB and the channel crosstalk is <-15.01dB. The device has important application value for large-capacity optical communication system.
This paper presents a 1×4 polarization-independent beam splitter based on silicon waveguides. The device is mainly consisted of a coupling structure and a sub-wavelength structure. According to the coupled mode theory, in the traditional directional coupled structure, the coupling strength of TM mode is stronger than that of TE mode, which makes it difficult to realize polarization-independent beam splitting. Adding a sub-wavelength structure in the coupling region can weaken the coupling strength of the TM mode while enhancing the coupling strength of the TE mode, so that the coupling strengths of the TE mode and the TM mode are equal. Therefore, polarization-independent beam splitting can be achieved by adjusting the parameters of the directional coupling structure and the sub-wavelength structure. The time-domain finite difference method (FDTD) is used for simulation analysis. The simulation results show that the device can realize polarization-independent beam splitting at 1550nm, the insertion losses of TE and TM modes are 0.36 dB and 0.55 dB, respectively. The length of the device is 23.421 μm and the bandwidth is about 10 nm. The device has the advantages of small size and simple structure, and it is easily to be integrated.
A simple optical orbital angular momentum (OAM) mode generator based on silicon-on-insulator (SOI) strip waveguides is proposed, which is consisted of a coupled waveguide and a trench waveguide. The fundamental mode TE00 is coupled to the second-order mode via an asymmetric directional coupler. Single-trench waveguide can support two orthogonal LP-like modes whose optical axes are rotated by around 45° with respect to the horizontal and vertical directions. We simulate and analyze the mode properties and propagation effects of OAM modes with charge numbers of 1or -1 by FDTD. When the phase difference between two LP-like eigenmodes is π/2,the second-order mode is further converted to the OAM mode over a wide wavelength range from 1.43μm to 1.58μm.The simulation results indicate that the loss can achieve approximately 0.16 dB. The proposed device is very compact with footprint of <47μm×2μm and the mode conversion efficiency is over 97%. Thus, such structure of OAM mode generator is a promising candidate for applying in OAM multiplexing system and other fields.
We proposed a high-Q in-plane channel drop filter using photonic crystal (PhC) cavities that are defined by an effective Aubry-André-Harper (AAH) bichromatic potential. The channel drop filter consists of AAH cavities and line-defect waveguides. Three-port structure with a wavelength-selective reflection cavity is applied. The parameters of the channel drop filter is analyzed by two-dimensional (2D) finite-difference-time-domain (FDTD) method. The simulation results are namely, the center wavelength of the filter being 1573.0 nm, and the insertion loss being smaller than 0.6 dB. The 3 dB bandwidth is 0.2 nm, and the loaded Q is up to 8×103. So the proposed device can be applied in a dense wavelength division multiplexing (DWDM) system with a 100 GHz channel spacing. Besides, the channel drop filter has a broad free spectral range (FSR) of around 250 nm, covering from 1350 nm to 1600 nm. The footprint of the channel drop filter unit is only 10 μm×20 μm.
A hybrid multiplexer (HMUX) for wavelength/mode-division (WDM/MDM) based on photonic crystals (PCs) is proposed. The device can realize TE0 and TE1 modes multiplexing at wavelengths of 1550nm and 1570nm. According to quasi phase matching, a structure with an asymmetrical parallel waveguide (APW) was used to achieve mode conversion. The transmittance of the TE0 mode at wavelengths of 1550nm and 1570nm are 98.4% and 96.3%, the corresponding insertion loss are 0.07dB and 0.16dB respectively. The crosstalk of the TE0 mode at wavelengths of 1550nm and 1570nm are -27.66dB and -27.32dB respectively. The transmittance of the TE1 mode at wavelengths of 1550nm and 1570nm are 95.8% and 93.9%, the corresponding insertion loss are 0.19dB and 0.27dB respectively. The crosstalk of the TE1 mode at wavelengths of 1550nm and 1570nm are -38.73dB and -38.9dB respectively. The PC-based HMUX has great performance, and it will have great application potential in future ultrahigh-speed and large-capacity communication systems.
A two rings, triangular lattice photonic crystal fiber sensor element using surface plasma resonance phenomenon is proposed. The performance of the sensor is analyzed by finite element (FEM) analysis software Multiphysics COMSOL. The influence of structural parameters on the performance of the sensor is discussed. The results show that the maximum sensitivity is 6000nm/RIU, when refractive index is in the range of 1.31 to 1.38. The sensor can be directly placed in the liquid and platinum layer is placed outer surface of the photonic crystal fiber, which can simplify the manufacturing process and the measurement process , has important practical value.