Investigation On The Slow Light Property Of Photonic Crystals And Optical Pulse Compression Technology

The nomination of slow and fast light,which can be changed affectedly by the group index of the medium over a specified range of frequencies,is a broad category of science and technology.Promoting the speed and bandwidth of telecommunication systems request all-optical on-chip solutions.Micro-photonic devices have a glamorous solution for realizing slow light property and provide the way to produce slow light at room temperature for realistic and ubiquitous applications,well-matched with on-chip integration and flexibility with dispersion engineering.It has an attractive feature of wider bandwidth and higher group index.This thesis looks at high buffering performance and low-distortion slow light transmission of picosecond pulses in photonic crystal waveguides coupled with cavities.We modeled the realistic structures,which are feasible in practical fabrications.The simulations of slow-light properties,buffering performance and propagating property were carried out by using Plane Wave Expansion?PWE?and Finite Difference Time Domain?FDTD?methods.The successive cavities can be regarded as energy reservoirs of electromagnetic energy and light-speed reducers.As the first part of this research work,cavities were introduced in the first and second rows of rods on the walls of an intrinsic photonic crystal waveguide?PCW?for slow-light transmission in the PCW concerning applications for optical communication,optical computation,and optical signal processing.Group index as exceedingly large as 6123 is obtained with normalized delay bandwidth product?NDBP?as high as 0.48.As the second part of this research work,by separating two photonic crystals with a distance of 2?3(6,where a is the lattice constant,shifting the positions of some discriminatory air holes in the upper and lower edges,and inserting a defect central row,a specific waveguide,W3 photonic crystal waveguide?W3 PCW?,is set up.An equivalent transmission line model is specified,giving the theoretical basis of the proposed waveguide to have a wider transmission bandwidth and thus high NDBP.Ultra-wideband of 65.70 nm with low group-velocity dispersion and at the same time a high NDBP of 0.496 are obtained through optimization.NDBP is a worthy indicator for slow light device performance because wider bandwidth can allow shorter duration of pulse waves,causing higher field intensity and stronger nonlinear effect.As the third part of this research work,a five-line?5L?PCW capable of realizing optical buffering with compact structure and low-distortion data interconnection of picosecond pulse is presented and studied.By appropriately modifying the radii of defects in the 5L PCW,high buffering performance and low-distortion slow light transmission of picosecond pulses are achieved,which are guaranteed by an optimized value of NDBP of 0.6811 for the proposed PCW.The largest buffering storage capacity and bandwidth obtained are about 219.73 bit and 19.55 nm respectively.It is found that the distortion of pulse transmission in a PCW is greatly affected by the waveguide length.With these optimized parameters,a relative pulse distortion per unit length of1.15×10^-4?m^-1 is obtained for a 2.19 ps pulse,meaning that for a signal pulse with a dutyfactor of 0.5,the proposed structure can process optical digital pulse signals at the speed of 0.22831Tb/s.Moreover,the NDBP value of 0.6811 obtained is much higher than that of all other structures based on waveguides reported in literature previously,so that high performance of the proposed PCW can be achieved for buffering of pulse light.The waveguide proposed is suitable for data interconnections among chips or among processing units within a chip in optical signal processing,and optical computations where the size of the transmission line or interconnector is highly limited.As the fourth part of this research work,by introducing cavity analogous to rhombus shape in the PCW center,a PCW-coupled-with-cavity?CC?was formed.Slow light properties are studied for ultra-high-group-index slow light with high optical buffering performance.Numerical results show that both the rhombus cavity radii and some discriminatory rods around rhombus cavity have a plentiful effect on slow light properties and buffering fulfillment.By adjusting the cavity rod radii,we obtained high group index of 5163 with buffering bit length L_bit about 17.968?m and delay time T_s reaching to 51.967 ps through the waveguide-cavity length of 3.02?m.Moreover,low group velocity dispersion can be achieved,with governable positive and negative values.To regulate the optimal parameters to increase the group index and demonstrate the delay time performance,some discriminatory rods around the rhombus cavity are adjusted in the upper and lower edges confronting each other in the waveguide,and an ultra-high group index as exceedingly large as 22350 is obtained that is extremely higher than previous studies.Simultaneously,the corresponding buffer bit length L_bitit and delay time T_s reach respectively to 25.8279?m and 225.7783 ps through the waveguide-cavity length of 3.0306?m.As the fifth part of this research work,high capability micro optical buffer?MOB?based on a hexagonal cavity in PCW is investigated,by breaking the translational symmetry of the periodicity in the proposed MOB three times after introducing different types of cavities.In each time,we attained ultra-high group index and high Q-factor with high delaying time.Ultra-high group index of 21030 is obtained with Q-factor of4309,buffer time of 70.1 ns and buffer capacity of 8.41bit.On the other hand the bit rate and storage density turn into 117.73 Gb/s and 0.06121 bit/?m,corresponding to approximately 16.33?m occupied by 1 bit for optical communication wavelength.Coupling a number of different types of cavities,higher Q-factor and longer buffer time than that of an individual cavity can be obtained.It is shown that by coupling two cavities,the Q-factor is heightened to be 1.748×10⁵.The results show that the proposed structure has significant for promising application in optical signal processors and random access memories.Furthermore,it has long delaying time and high Q-factor,which have important applications in low threshold lasers,high finesse filters and high-speed switching.At present,NDBP is not satisfied,so we explore various structure s or ways to get high NDBP to realize high performance slow light devices,e.g.,buffers,distortionless transmission lines,and light pulse compressors.