Development of photonic crystal structures for on-board optical communication
Abstract: We present designs for sharp bends in polymer waveguides using colloidal photonic crystal (PhC) structures. Both silica (SiO2) sphere based colloidal PhC and core-shell colloidal PhC structures having a titania (TiO 2) core inside silica (SiO2) shells are simulated. The simulation results show that core-shell Face Centered Cubic (FCC) colloidal crystals have a sufficient refractive index contrast to open up a bandgap in the desired direction when integrated into polymer waveguides and can achieve reflection >70% for the appropriate plane. Different crystal planes of the FCC structure are investigated for their reflection and compared with the calculated bandstructure. Different techniques for fabrication of PhC on rectangular seed layers namely slow sedimentation; spin coating and modified doctor blading are discussed and investigated. FCC and Random FCC silica structures are characterized optically to show realisation of (001) FCC. © 2014 SPIE.
Summary (1 min read)
- Single mode polymer waveguides can be used to guide information-carrying light from one component to another on a backplane.
- The authors have designed the different photonic crystal structures to be integrated with 5 µm wide polymer waveguides.
- The Face Centre Cubic (FCC) structure is formed only if the exact positioning of each individual horizontal layer of spheres repeats itself at every third layer in vertical direction.
- Defects in the sedimentation process can change the repetition from say the third to every second layer resulting in AB, BC or AC stacking.
- FCC structures fabricated using both natural sedimentation and the new proposed technique are simulated to show that pure FCC structures having sufficient index contrast can be used to achieve in-plane bending of light at sharp angles.
2. FCC STRUCTURES FOR IN-PLANE BENDING
- The optical properties of a FCC structure with 1000nm diameter silica spheres is modelled and simulated.
- The larger refractive index contrast = 0.67 between the core-shell particles and the background air is very helpful for the photonic crystal to act as a reflector.
- It can be observed in Fig. 7(b) that the reflection peak for 45° incidence is situated at larger values of frequencies which is as per predictions from the bandstructure.
3. MANUFACTURING AND CHARACTERIZATION OF COLLOIDAL CRYSTALS
- The crystal structure and orientation of the particles in the colloidal crystals determine the reflection and transmission of the light and thus the properties of the photonic crystal.
- The preferred crystal form of mono-dispersed particles is the FCC stacking.
- Fabrication of FCC structures without any external field or force will result in a hexagonal ground plane as shown in Fig. 8(A).
- The template is manufactured by nano-imprint lithography.
- The cracks, due to FCC stacking adband white sample.
- The authors have simulated different FCC structures that can be integrated into polymer waveguides to show that core-shell colloidal photonic crystal structures can be used for achieving sharp bends in polymer waveguides.
- Air-clad silica spheres photonic crystal structures can only provide reflections 15% as compared to more than 50% reflections from core-shell structures.
- Truncated core-shell photonic crystal structures on rectangular seed layer are calculated to reflect more than 70% of the incident light.
- Different fabrication techniques for fabrication of silica spheres FCC structures on top of rectangular seed layer have been investigated and implemented.
- The authors initial characterization results show that FCC structures with (001) FCC ground plane can be fabricated which can be distinguished from (111) FCC or RFCC structures using optical characterization.
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The authors present designs for sharp bends in polymer waveguides using colloidal photonic crystal ( PhC ) structures. Different techniques for fabrication of PhC on rectangular seed layers namely slow sedimentation ; spin coating and modified doctor blading are discussed and investigated.