| Photonic crystal(PhC)sensor has high application value in the fields of biochemical sensing,pressure sensing,temperature sensing due to its advantages including high sensitivity,ultra-compact size,more suitable for monolithic integration.What's more,the multiplexing structure based on PhC beam splitter and microcavity sensor is essential for optical integrated circuit in the future.Thus,this paper have done research on PhC microcavity sensor,PhC beam splitter and the series-parallel multiplexing of them,including the stability of the series-parallel multiplexing structure.The main achievements of this paper are as follows:Firstly,a PhC butt-coupled mini-hexagonal-H1 defect(MHHD)microcavity sensor is proposed and simulated.The MHHD micro-cavity is designed by introducing six mini-holes with diameters are significantly smaller than the lattice constant into the initial H1 defect region.By using Finite-difference time-domain(FDTD)simulations method and adjusting the radius of the mini-holes and the shift distance of the two air holes along the-x and x,the quality factor(Q)of the MHHD micro-cavity has been optimized.As statistics show,the Q of our optimal MHHD microcavity attains higher than 7×104,while the sensitivity(S)reaches up to 233 nm/RIU(RIU = refractive index unit).Then,by observing the function of mass sensitivity and the refractive index sensitivity with the change of the sensing area,the optimal sensing region is given.When the optimal sensing region in our optimal MHHD microcavity sensor is used to detect the analytes,the S is 213.4nm/RIU.Meanwhile,the figure of merit(FOM)>104 of the sensor is obtained,which is enhanced by an order of magnitude compared to the previous butt-coupled microcavity sensors[1-5].Secondly,a PhC 1×3 beam splitter based on PhC waveguide is proposed.The method to form the beam splitter is as follow:first introduce PhC waveguide into the PhC to form 1×3 branch,then triangle columns with proper angle and size are introduced to the branch waveguide junctions to guide the incoming wave effectively.By using Finite-difference time-domain(FDTD)simulations method and altering the refractive index of the two right triangle columns in the beam splitter,the total output power of the beam splitter has been optimized.As statistics show,when the refractive index of the two right triangle columns equals to 1.12,the total output power of the beam splitter attains higher than 99.66%at the operating wavelength of 1550nm.It is found that,by adjusting the vertical distance d between the two right triangle columns and the horizontal center line,the PhC beam splitter can achieve the even power distribution at the specified frequency.Use the wavelength of 1550nm as an example,the optimization beam splitter can splitter the power equally at six wavelengths including the specified wavelength 1550nm.What's more,the total output powers of the PhC beam Splitter at the six operating wavelengths are all greater than 99%.In addition,the transmission spectrum of the optimization PhC 1×3 beam splitter is stable at 1538nm to 1638nm and the difference of the output power between this three output channels is small.Thus,the optimization PhC 1×3 beam splitter is suitable for PhC integrated sensing multiplexing.Then,based on the proposed high performance PhC microcavity sensor and high efficiency PhC beam splitter,by connecting an optimized PhC MHHD sensor to each parallel output channels of the optimization PhC 1×3 beam splitter,a series-parallel multiplexing structure of PhC beam splitter and microcavity sensor is designed.The three optimal MHHD microcavity sensors with different lattice constants(a),so that the three microcavity have different resonant frequency and possess the optimal sensing performance.By using FDTD simulation method,the Q values of the three sensing units are 55724,55066,62039 and the refractive index sensitivities are 231nm/RIU,224nm/RIU and 229nm/RIU,respectively.Thus,the FOMs of the three sensing units are 8179,8000 and 9119,which is enhanced by an order of magnitude compared to the previous multiplexing structure[6-7].Moreover,each sensor unit of this series-parallel multiplexing structure is independent of each other and does not affect each other,so the structure can be used to realize high performance parallel sensing,which improves the detection efficiency and the integration of the sensing system.At last,we have done preliminary stability research on the proposed series-parallel multiplexing structure of PhC beam splitter and microcavity sensor.The simulation results show that when the primary structural parameters(rmini?L?d)of the series-parallel multiplexing structure have a±5nm random manufacturing errors,Q of each MHHD microcavity is about 4×104.Though it is lower than that of standard series-parallel multiplexing structure,it still has a significant improvement compared to the previous butt-coupled microcavity sensors[1-5]and the microcavity of the previous multiplexing structure[6-7].The three MHHD microcavity sensor units can still be synchronous applied to the refractive index sensing and noninterference each other.The refractive index sensitivities of them are 231nm/RIU,224nm/RIU and 229nm/RIU,respectively,which is slightly increased compared with the standard series-parallel multiplexing structure.The FOMs of the three sensing units are differ rarely,which are 5775,5600 and 5725,respectively,which have decreased compared to the FOMs>8000 of the standard series-parallel multiplexing structure,but they have still increased by an order of magnitude compared to the previous multiplexing structure[6-7].When the series-parallel multiplexing structure have a ±5nm random manufacturing errors,the wavelength shifts of the resonant peaks are no more than 2nm compared with the standard series-parallel multiplexing structure.In short,when the primary structural parameters(rmini?L?d)of our proposed series-parallel multiplexing structure of PhC beam splitter and microcavity sensor have a ±5nm random manufacturing errors,the performance of the series-parallel multiplexing structure is relatively stable.Meanwhile,each MHHD microcavity sensor units can still be synchronous applied to the high performance refractive index sensing without interference each other.Thus,the proposed series-parallel multiplexing structure can be applied to further experiment sensing and detection research. |
PDF Full Text Request