InTo produce a one-dimensional photonic crystal, [[thin film]] layers of different dielectric constant may be periodically deposited oron adhereda togethersurface towhich formleads to a band gap in a singleparticular propagation direction (such as normal to the surface). A [[Bragg grating]] is an example of this type of photonic crystal. One-dimensional photonic crystals can beinclude eitherlayers isotropicof or[[non-linear optics|non-linear]] optical materials in which the non-linear behaviour is accentuated due to field enhancement at wavelengths near a so-called degenerate band edge. This field enhancement (in terms of intensity) can reach <math>N^2</math> where ''N'' is the total number of layers. However by using layers which include an optically [[Birefringence|anisotropic]] material, withit has been shown that the latterfield havingenhancement can reach <math>N^4</math>, which, in conjunction with non-linear optics, has potential useapplications such as in the development of an all-[[optical switch]].<ref>{{cite journal |doi=10.1142/S1793528808000033 |title=Third Order Nonlinear Effect Near a Degenerate Band Edge |journal=Optics and Photonics Letters |volume=1 |issue=1 |pages=1–7 |year=2008 |last1=Cao |first1=Y |last2=Schenk |first2=J. O |last3=Fiddy |first3=M. A }}</ref>
One-dimensional photonic crystal can form as an infinite number of parallel alternating layers filled with a [[metamaterial]] and vacuum.<ref>{{cite journal|last1=Pravdin|first1=K. V.|last2=Popov|first2=I. Yu.|title=Photonic crystal with negative index material layers|journal=Nanosystems: Physics, Chemistry, Mathematics|date=2014|volume=5|issue=5|pages=626–643|url=http://nanojournal.ifmo.ru/en/wp-content/uploads/2014/10/NPCM55P626.pdf}}</ref> This produces identical photonic band gap (PBG) structures for [[Distributed Bragg reflector#TE and TM mode reflectivity|TE and TM modes]].
