Photonic stop-band

Films of pure CNLCs have a unique transmission behavior as CP light with the same sense of circular polarization as the CNLC is filtered out by reflection, while CP light of the opposite handedness as the CNLC film is transmitted. This selective optical transmission characteristic is referred to as a one-dimensional photonic stop-band or a selective reflection band. The stop-band is centered at a certain wavelength Ac, which is dependent on the pitch length p and the average refractive index n of the CNLC ... 

VI Kopp, B Fan, HKM Vithana, and AZ Genack, Low-threshold lasing at the edge of a photonic stop band in cholesteric liquid crystals, Opt. Lett., 23 1707-1709, 1998. 

Colloidal crysfals can be viewed as the mesoscopic counterpart of atomic or molecular crystals. They have been used to explore diverse phenomena such as crystal growth [52-54] and glass transition [55,56], and have many interesting applications for sensors [57], in catalysis [58,59], advanced coatings [60], and for optical/electro-optical devices for information processing and storage [61,62]. In particular, their unusual optical properties, namely the diffraction of visible light and the existence of a photonic stop band, make them ideal candidates for the development of photonic materials [61,63-66]. They may lead to the fabrication... 

Over the last several decades photonic band-gap materials attracted considerable interest due to the possibility of inhibition of the spontaneous emission and light propagation [1-3]. Mesoporous structures like three-dimensional artificial opals and two-dimensional PAA are considered as photonic band gap materials, demonstrating the photonic stop-band in transmission and reflection spectra [4,5] and anisotropy of photonic density of states (DOS) on scattering indicatrices [6]. An influence of photonic band-gap materials on photoluminescence and spontaneous emission rate of the embedded inclusions have been reported and discussed [7-9]. 

This simple description does not take into account the so-called photonic stop-band effect, which forbids propagation at wavelength exactly satisfying the Bragg condition. According to the coupled mode theory [66, 67], distributed feedback (DFB) lasers normally oscillate on the edge of this photonic stopband (Figure 15.14). 

Fig. 12.14 Calculated transmission spectra of a planar cholesteric texture in zero field and in field = 5.7 V/)im applied perpendicular to the helical axis. Note appearance of the strong second order photonic stop-band even for nonpolarized light...

Artoni M, La Rocca GC. Optically tunable photonic stop bands in homogeneous absorbing media. Physical Review Letters 2006 Feb 24 96(7) 073905(4). 

Flong, J.C., Park, J.H., Chun, C., Kim, D.Y. Photoinduced tuning of optical stop bands In azopolymer based inverse opal photonic crystals. Adv. Funct. Mater. 17, 2462-2469 (2007)... 

Although many diode lasers work as multimode lasers, the distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers show a mode selection because of their periodic structure. The mode selectivity is generated by the optical properties of the periodic stmctures because (Mily the modes that are associated with a standing wave/stop band are amplified. DFB structures are photonic structures, which are doped throughout the volume with chromophores (in an optimal case at the maxima of the standing waves), whereas DBR lasers have a miniature Fabry-Perot cavity in which the dye is localized, and the mirrors are replaced by periodic gratings [85]. 

Aliev et al. (2010) used acoustic transmission spectroscopy to measure directly the bandgap of an ADBR showing a first-order bandgap at 0.65 GHz with a stop band depth of at least 50 dB and a weaker second-order gap at 1.3 GHz. The sample was also characterized using both its photonic and phononic stop band properties, i.e., consistently using Eqs. 1 and 2, which demonstrates the phoxonic nature (Sadat-Saleh et al. 2009) of porous silicon superlattices. 

Reflectivity is greatly increased in a dielectric stack with a larger number of layers. A typical spectral dependence of a dielectric mirror is shown in Fig. 2.37. The wavelength range of maximum reflectivity is called the stop band (sometimes also called one-dimensional photonic band gap). Increasing the ratio between the low and high-refractive index parts extends the width of the stop band. 

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