Design And Performance Analysis Of Tunable Wavelength Filter Based On Complex Period Photonic Crystal

At present, the human society has already entered the information-basedsociety, which need broadband communication network that can offer variouscommunication service , has enormous communication capacity. Therefor, opticalfiber communication has already been recognized as the best transmission mediumin the broadband network. by its enormous superiority. With the development ofWDM, the realization of the full optic network is not far too, but the requirementfor devices is more and more strict . The tunable wavelength filter is one of thepivotal devices, we demand them to not only have accurate and steady wavelengthcharacteristics, the performance of which can't be infuenced by the change offactors such as temperature , wearing out ,etc., but also be small and easy to beintegrated and low loss. However, the development level of the existing opticaldevice technology has restricted the development of the optical communication,developing optic tunable filter with new performance becomes necessary conditionof realization of intelligence network..Because of its close and controlling light capability, The photonic crystal, as akind of new material, is very suitable for designing the tunable wavelength filterwith wide tunable bandwidth and low loss in WDM system.. By unique newlymethod of conelrad, photonic crystal can obtain photonic gap band.when thecertain defect is introduced into the photonic gap band, photonic crystal appeardefect state , and have filter property.On the other hand, the liquid crystal is a kind of effective electro-opticalmaterial, its electrical control birefringent makes the birefringent of the liquidcrystal change with change of the voltage . Because the molecular axis of liquidcrystal is along with the change of electric field, its effective refractive index hasbeen just changed. These properties of the liquid crystal, such as electrical controlbirefringent, easily modulation and apt tropism, make liquid crystal suitable fordoing small bulk and resl time tunable filter with the liquid crystal.On the basis of above properties, this text proposes a kind of tunablewavelength filter with the complex period photonic crystal infiltrated with nematicliquid crystal. Utilizing the electrical control birefringent of the liquid crystal, thenwe can modulate the refracting index of the liquid crystal by changing the voltageinflicted in the liquid crystal layer, and combine photonic crystal filter principle torealize tunable wavelength filter.This text uses the transfer matrix method to analyse the reason of choosingcomplex period photonic crystal (making up by Si , SiO2 , TiO2) at the first.Compared with one dimensional photonic crystal, it has two obvious advantages intransmission properties: Firstly, we find the photonic gap band of the complexperiod photonic crystal is one point five times than one dimensional photoniccrystal in the central wavelength(1550nm), and offers the wide job windows.Secondly , the photonic gap band of the complex period photonic crystal is lessinfluenced by medium thickness perturbation, and has very good stability, which ishelpful to the craft of making photonic crystal.Then introducing liquid crystal Jones' matrix, we synthetically analyze theproperties of the complex period photonic crystal infiltrated with nematic liquidcrystal and the influence of many factors such as liquid crystal thickness , photoniccrystal periodicity and adjoint medium thickness increment.Get following filterproperties:1. When voltage rises from 0.5v to 5v, the wavelength of the transmissionpeak of tunable filter moves from 1520nm to 1552nm, the tuning range is about32nm. We can find the wavelength of the transmission peak moves to the directionof the long wavelength with the increase of the voltage, and the bandwidth of thetransmission peak is very narrow.2. The wavelength position of Transmission peak is influenced by thethickness of liquid crystal. when we increase the thickness of the liquid crystal, thewavelength of the greatest transmission peak will move toward the shortwave;Thetransmission rate has connection with the thickness and inherent birefringent of theliquid crystal. When the birefringent exceeds 0.14,or when the thickness is thickerthan 600nm, transmission rate will drop fast.3. By increasing the periodicity of complex period photonic crystal, theedge precipitous degree is elevated, the bandwidth of peak become narrow at thesame time, transmission rate will be drop correspondly,but the wavelength of thetransmission peak is hardly changed.4. In the structure of our tunable filter , we introduce the incrementparameter of the thickness of the adjoint medium material behind the liquid crystal.By adjusting this parameter, we can change the position of the tuning range inphotonic gap band. Therefor we can obtain different jobs windows in the widerphotonic gap band. Which only depends on the change of adjoint medium thicknessincrement.So, such a new tunable wavelength fiter that this text puts forward has manyexcellent properties:flexible tuning range , the better voltage sensitivity, lowerconsumption. And because photon crystal have better characteristics of photonicgap band, which restrains light above 30dB, precipitous degree is very apt toapproach 90 degrees;and small bolk, low loss. The filter has extensive range ofapplicationThe main work and content of this text are summarized by five chapters:Chapter one, through the introduction of the development situation of WDMsystem, put forward the concept , classification and filter characteristic of thephotonic crystal.Chapter two, the main introduction is transfer matrix method, and utilize it toanalyse the light propagation characteristics of complex period photonic crystal anddiscuss the influence of various factors of crystal structure. Compared with onedimensional photonic crystal, complex period photonic crystals not only containsimilar transmission characteristic of 1DPC, but also have wider photonic gap bandand less influenced by medium thickness perturbation. To make highertechnological requirement of photon crystal it is very helpful, So there is morepractical value.Chapter three, this chapter mainly starts off from basic characteristis of theliquid crystal, and combines the filter principium of complex period photoniccrystal to analyze the feasibility which the liquid crystal is regard as defect layer inthe complex period photonic crystal to realize tunable wavelength filter. We designtentatively the new tunable filter with photonic crystal.Chapter four, the mian work is to decide the parameters of the complex periodphotonic crystal infiltrated with nematic liquid crystal. And to analyze the filtercharacteristics of the new tunable filter through academic emluative results ofcomputer.Chapter five, summarize full paper, put forward some problems are yet to beresolved synchronously, and then point out the study direction need to be studied inthe next step.