This paper presents our recent studies on photonic devices based on antisymmetric Bragg gratings (ASBGs). ASBGs can realize backward mode conversion between the fundamental and first order transverse electric mode, i.e., TE0 and TE1. If a π phase shift is inserted in the middle of ASBG, light resonance along with mode conversion can be set up. We call this new resonance as the “Hybrid mode resonance”. Based on this structure, several photonic devices are realized. For example, we experimentally demonstrated an on-chip light filter with dropped reflected light. It can be equivalent to the light circulator in some cases and benefits the application to photonic integrated systems. Besides, other photonic devices such as single wavelength resonator and narrow band reflector are also realized. We think the proposed grating structure may give a new way to design high-performance photonic devices.
We propose an on-chip optical narrowband reflector (NBR) based on two cascaded Bragg gratings (BGs). A π phase shifted anti-symmetric Bragg grating (π-PS-ASBG) and a rear uniform Bragg grating (UBG), are in-line connected. The π-PS-ASBG provides a hybrid mode resonance between the even- and odd TE (TE0 and TE1) modes, while the UBG is used as a rear reflector to reflect the TE0 mode that transmitted from the π-PS-ASBG. The reflection bandwidth decreases when the coupling coefficient increases, which is different from traditional UBG. The performances are theoretically studied via both the rigorous three-dimensional finite-difference time-domain (3D-FDTD) method and multimode transmission matrix method (MTMM). The calculated 3-dB bandwidth is 0.16 nm when the whole grating length is 400 μm (π-PS-ASBG: 200 μm and UBG: 200 μm) and the coupling coefficients of the π-PS-ASBG and rear UBG are 240cm-1 and 110cm-1, respectively. The proposed NBR can be applied in the cases requiring narrow reflection such as narrow linewidth semiconductor lasers.