Sidewall Gratings Research Articles

Integrated III–V Bragg Gratings for Arbitrary Control Over Chirp and Coupling Coefficient

In this work, integrated chirped Bragg gratings based on tapered waveguide sidewall gratings are presented, along with the method by which arbitrary variations of Bragg condition and coupling coefficient may be achieved. Fabricated devices with constant Bragg condition, linear, and nonlinear chirp are exhibited with and without apodized coupling coefficient profiles. Finally, an integrated Michelson interferometer setup is used to confirm the grating phase characteristics.

Demultiplexer with blazed waveguide sidewall grating and sub-wavelength grating structure

We propose an original diffraction grating demultiplexer device with a very small footprint, designed for the silicon-on-insulator waveguide platform. The wavelength dispersive properties are provided by a second-order diffraction grating designed to be lithographically defined and etched in the sidewall of a curved Si waveguide. The grating is blazed to maximize the -1st order diffraction efficiency. The diffracted light is coupled into the silicon slab waveguide via an impedance matching subwavelength grating gradient index antireflective interface. The waveguide is curved in order to focus the light onto the Rowland circle, where different wavelengths are intercepted by different receiver waveguides. The phase errors were substantially reduced using an apodized design with a chirped grating, which assures a constant effective index along the grating length. The simulated crosstalk is -30 dB. The device has 15 channels with a spacing of 25 nm, thus a broadband operational bandwidth of 375 nm. Its performance approaches the diffraction limit. The layout size is 90 microm x 140 microm, which is the smallest footprint yet reported for a mux/dmux device of a similar performance.

Reduce the start current of Smith-Purcell backward wave oscillator by sidewall grating

A sidewall grating for the Smith-Purcell device is proposed to enhance the coupling of the optical mode with the electron beam and, consequently, relax the stringent requirements to the electron beam. With the help of three-dimensional particle-in-cell simulations, it has been shown that, comparing with the general grating, the usage of a sidewall grating improves the growth rate and dramatically shortens the time for the device to reach saturation. It is also found that the sidewall grating holds the potential to reduce the start current for the operation of a Smith-Purcell backward wave oscillator.

Optical waveguides with apodized sidewall gratings via spatial-phase-locked electron-beam lithography

We describe a technique to fabricate Bragg gratings in the sides of optical waveguides using a single lithographic step. This technique is particularly suited to the apodized gratings required for add/drop filters in dense-wavelength-division multiplexing. Apodization minimizes cross talk between channels and improves the filter response. Silicon-on-insulator rib waveguides with both uniform and apodized gratings were fabricated using direct-write spatial-phase-locked electron-beam lithography (SPLEBL). This approach combines SPLEBL’s pattern-placement accuracy with the flexibility of direct-write device prototyping. The resulting grating-based devices exhibited substantially reduced side-lobe levels.

Fabrication of high density ultrafine GaAs quantum wire array structures using selective metalorganic chemical vapor deposition

High density GaAs quantum wire array structures have been successfully fabricated on an extremely short-period pattern. The quantum wire arrays were formed on the sidewall gratings of a rectangular AlGaAs/GaAs multilayer structure, selectively grown on a SiO 2 masking (111)B substrate. The quantum wires with the dimension of 25 × 35 nm 2 had a period as small as 95 nm. The fabrication process involved only selective metalorganic chemical vapor deposition and a selective etching technique. No nanolithography patterning techniques were used. The detailed fabrication process is presented.