Unequally Spaced Waveguide Arrays for Silicon Nanomembrane-Based Efficient Large Angle Optical Beam Steering

Three Dimensionally Interconnected Silicon Nanomembranes for Optical Phased Array (OPA) and Optical True Time Delay (TTD) Applications

“…Techniques such as high temperature annealing, special hydrogen plasma passivation steps, and patterning waveguides before the solid-phase crystallization (SPC) of deposited amorphous silicon were shown to reduce the propagation loss [12,13]. Lowest losses ranging from 7dB/cm to 13dB/cm were reported in polycrystalline silicon waveguides with cross sectional dimensions of approximately 450 x 250 nm [12,14,15], and from 1dB/cm to 2dB/cm in crystalline silicon waveguides withsimilar dimensions [16,17]. Additionally, if the temperature process is limited to about 600°C, which is compatible with standard CMOS processes, the Q-factor of the ring resonators fabricated on polysilicon layers drops by an order of magnitude [10,18], indicating even higher losses.…”

“…Another interesting class of such artificial materials is the subwavelength nanostructure (SWN). Using SWN as a low index material was proposed in 2009 15 . A coupling efficiency of 43% (3.7dB) has been reported for TM polarized light around 1550 nm 16 .…”

“…1b. The subwavelength region is regarded as a homogeneous material with an effective index sub n 15 . The uniform material is then replaced with a SWN, as shown in Fig.…”

“…2b, is evaluated by calculating the overlap integral with the Gaussian mode in a single mode fiber. Since the width of the grating is much larger than its height, decoupled 3D modes can be established in the y and z directions 15 . Since the y dependent overlap integral is close to 1 21 , the overlap integral can be simplified to an integration along the z direction.…”

“…Consequently, when approaching the edge of the photonic band gap, the percentage of energy concentration in the low index slot will increase rather than decrease 9 . The increasing optical confinement with slower group velocity is a very advantageous property for compact optical communication devices [9][10][11][12][13][14][15][16][17][18][19] and on-chip sensors 20, 21 . Despite these benefits, optical coupling between a strip waveguide and a slotted PCW is more challenging than conventional PCW due to the exotic mode profile and slow group velocity in the slotted PCW.…”