Design and characterization of a grating-assisted coupler enhanced by a photonic-band-gap structure for effective wavelength-division demultiplexing

Photoerasable and photorewritable spatially-tunable laser based on a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant

This study investigates, for the first time, a photoerasable and photorewritable spatially-tunable laser using a dye-doped cholesteric liquid crystal (DDCLC) with a photoisomerizable chiral dopant (AzoM). UV illumination via a photomask with a transmittance-gradient can create a pitch gradient in the cell such that the lasing wavelength can be spatially tuned over a wide band of 134nm. The pitch gradient is generated by the UV-irradiation-induced gradient of the cis-AzoM concentration and therefore the induced gradient of the cell HTP value, resulting in the spatial tunability of the laser. Furthermore, the laser has advantages of photoerasability and photorewritability. The spatial tunability of the laser can undergo more than 100 cycles of photoerasing and photorewriting processes without decay or damage.

Comparative study of the modeling of three-dimensional photonic bandgap structures

A comparative study of theoretical models of different three-dimensional photonic bandgap (3D-PBG) structures has been performed, taking into account instability and convergence problems. Some rules for solving these problems and for reducing the computational time by finding symmetries in the structures are also explained. Finally, some applications produced by defects in 3D structures are shown by studying the creation of a complete bandgap in one of them and the variation of partial bandgaps in several 3D-PBG structures when several parameters of the defects, such as the number of layers stacked at each side of the defect, its thickness, and the real and imaginary parts of its index of refraction, are changed.

Two compact structures for perpendicular coupling of optical signals between dielectric and photonic crystal waveguides

Two structures are analyzed with numerical modeling as candidates for perpendicular coupling of optical signals from a dielectric waveguide to a photonic bandgap (PBG) waveguide. The first consists of a perfectly electric conducting (PEC) grating and PBG mirror to couple power out of the dielectric waveguide, along with a circular-like lens to couple that power into the PBG waveguide. The second consists of a slanted inline fiber Bragg grating to couple power out of the dielectric waveguide, and a graded-index (GRIN) lens to couple that power into the PBG waveguide. Power transfer efficiencies of 50% and 71%, respectively, are reported. Such structures would be useful in WDM applications, and/or where circuit real estate restrictions demand coupling perpendicular to the dielectric guide over small distances.

Ultrafast pulsed mode effects on the performance of grating-assisted output couplers of finite extent

The performance of grating-assisted output couplers of finite extent excited by finite ultrafast pulsed modes is characterized numerically by the finite-difference time-domain method. The results for pulsed excitations with extremely long pulse envelopes are compared with those that contain only a few optical cycles for gratings that are both long and short compared with the equivalent pulse length. We demonstrate that the shortest length of either the grating or the pulse dictates the far-field performance of the grating-assisted output couplers.