This paper presents a new lateral confinement mechanism based on the self-collimation effect in planar photonic crystals(PhCs). In this mechanism, planar PhCs with approximately flat equi-frequency contours (EFCs) are utilized for laterally confining the light and total internal reflection (TIR) is used for the vertical confinement. Since this mechanism relies on dispersion engineering, no photonic band gap nor defect modes are required. Using this approach, it is possible to engineer flat EFCs completely below the light cone using relatively low-index-contrast material systems. Therefore, in this work we first engineer a low-index-contrast planar PhC with approximately flat EFCs in the first band, which is always below the light cone. Then, we investigate the lateral divergence of self-guided beams in this structure using the plane wave method (PWM). It is found that light with a narrow band frequency in the first band can be very well self-confined laterally.
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