Graphene Oxide Waveguide and Micro‐Ring Resonator Polarizers

Abstract

Integrated waveguide polarizers and polarization‐selective micro‐ring resonators (MRRs) incorporated with graphene oxide (GO) films are experimentally demonstrated. CMOS‐compatible doped silica waveguides and MRRs with both uniformly coated and patterned GO films are fabricated based on a large‐area, transfer‐free, layer‐by‐layer GO coating method that yields precise control of the film thickness. Photolithography and lift‐off processes are used to achieve photolithographic patterning of GO films with precise control of the placement and coating length. Detailed measurements are performed to characterize the performance of the devices versus GO film thickness and coating length as a function of polarization, wavelength and power. A high polarization dependent loss of ≈53.8 dB is achieved for the waveguide coated with 2‐mm‐long patterned GO films. It is found that intrinsic film material loss anisotropy dominates the performance for less than 20 layers whereas polarization‐dependent mode overlap dominates for thicker layers. For the MRRs, the GO coating length is reduced to 50 µm, yielding a ≈8.3 dB polarization extinction ratio between transverse electric (TE) and transverse magnetic (TM) resonances. These results offer interesting physical insights and trends of the layered GO films and demonstrate the effectiveness of introducing GO films into photonic‐integrated devices to realize high‐performance polarization selective components.

2D Layered Graphene Oxide Films Integrated with Micro‐Ring Resonators for Enhanced Nonlinear Optics

“…Using this GO coating method, we achieved GO patterning on integrated photonic devices via photolithography and lift‐off processes. [ 43 ] Figure 1e shows microscopic images of an integrated MRR patterned with 50 layers of GO (≈50 µm pattern length). Note that only the center ring of the nine concentric rings (see inset) was coupled to through/drop bus waveguides to form an MRR—the rest were to aid in visual identification.…”

“…We achieved GO film patterning with lengths down to ≈150 nm via e‐beam lithography and accurate placement on the MRR (deviation < 20 nm) by using gold alignment markers. [ 43 ] The schematic illustration of the fabrication process flow is provided in Figure 1f. The combination of GO coating with photolithography and lift‐off allows precise control of the film placement, size, and thickness on integrated devices.…”

“…Finally, along with the large‐area uniform coating capability, our fabrication techniques enable large‐scale integrated devices incorporated with GO films. This is not only for nonlinear photonic devices but also for integrated devices based on other extraordinary material properties of GO such as broadband photoluminescence/light absorption, [ 37,39 ] strong material anisotropy, [ 43 ] and flexible bandgap engineering. [ 27,42,49 ]…”

“…We chose the TE polarization for the experiments because it supported the in‐plane interaction between the evanescent field and the thin GO film, which is much stronger than the out‐of‐plane interaction due to the large optical anisotropy of 2D layered materials. [ 43,51 ]…”

“…[ 41,42 ] Recently, we achieved highly precise control of the placement, thickness, and length of the GO films coated on integrated photonic devices by using a large‐area, transfer‐free, layer‐by‐layer GO coating method together with standard photolithography and lift‐off processes. [ 43 ] This overcomes critical fabrication limitations in terms of layer transfer and precise patterning for on‐chip integration of 2D materials and represents a significant advance toward manufacturing integrated photonic devices incorporated with 2D materials.…”