Enhanced linear absorption coefficient of in-plane monolayer graphene on a silicon microring resonator

Abstract

Abstract:We demonstrate that linear absorption coefficient (LAC)of a graphene-silicon hybrid waveguide (GSHW) is determined by the optical transmission spectra of a graphene coated symmetrically coupled add-drop silicon microring resonator (SC-ADSMR), of which the value is around 0.23 dB/µm. In contrast to the traditional cut-back method, the measured results aren't dependent on the coupling efficiency of the fiber tip and the waveguide. Moreover, precision evaluation of graphene coated silicon microring resonator (SMR) is crucial for the optoelectronic devices targeting for compact footprint and low power consumption.Graphene is a two-dimensional material [1][2][3], which exhibits remarkable optoelectronic characteristics, such as ultrahigh carrier mobility at room temperature [4,5], ultra-broadband absorption [6,7], controllable band-gap transition [8], and giant Kerr coefficient [9,10]. Graphene has been integrated on photonic integrated circuits (PICs) in which the hexagonal carbon sheet is evanescently coupled to the waveguide, leading to unprecedented optical performances [11][12][13][14][15][16].Recently, grapheme resting on silicon-on-insulator (SOI) platform offers great potential for optoelectronic devices. Broadband optical modulator [17,18], mode locked laser [19], broadband photodetectors [20,21], and enhanced parametric frequency conversion [22] have all been demonstrated utilizing graphene-silicon hybrid waveguides (GSHWs). Owing to its intrinsic physical properties, the linear absorption coefficients (LACs) of GSHWs range from 0.04dB/µm to 0.33 dB/µm [23,24],which are much larger than those of silicon waveguides [25]. The LACs of GSHWs are dependent on the quality of the transferred graphene and the waveguide configurations [26], thus are required to be optimized for practical applications. For instance, Strong LAC is preferred in electro-absorption modulator (EAM) [27] to obtain a large modulation depth, while in the nonlinear optical application [28], the LAC should be as small as possible to avoid linear absorption. Therefore, it is of great importance to precisely evaluate the optical absorption loss induced by grapheme [29].Previously, the LACs of graphene-comprising waveguides were obtained by a cut-back method [14][15][16] in which the light-graphene interaction lengths were varied. And this method is subject to the following limitations:1. In order to measure the LACs induced by graphene, multiple stripe waveguides should be patterned with different lengths of graphene [14][15][16], of which the processes are burden some, time consuming and even expensive.2. The coupling efficiencies between the fiber tips and the waveguides as well as waveguide end facets maintain non-uniformity. Moreover, such fiber-to-waveguide coupling losses are often comparable to or even much higher than the propagation losses in the waveguides [27], leading to high uncertainties in loss measurements, as stated in [30].3. Because of the imperfect coverage of grapheme with cracks, the measured losses in these stripe...

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

“…The low‐power (W/O in Figure 3e) propagation loss of the uncoated waveguide and the waveguide with a monolayer of GO were ≈0.26 and ≈1.27 dB cm −1 , respectively, corresponding to an excess propagation loss of ≈1 dB cm −1 induced by the GO film. This is over two orders of magnitude lower than that of integrated waveguides coated with graphene, [ 54,55 ] indicating the low material absorption of GO and its strong potential for the realization of high‐performance nonlinear photonic devices. The propagation loss increased with the GO layer number—a combined result of mode overlap and several other possible effects such as increased scattering loss and absorption induced by imperfect contact between the multiple GO layers as well as interaction between the GO layers, as reported previously.…”

Transforming silicon into a high performing in tegrated nonlinear photonics platform by integrati on with 2D graphene oxide films

“…Aside from the Kerr nonlinearity (n2, γ) and the nonlinear FOM (FOMeff), the other remaining key factor affecting nonlinear performance is the linear loss. As mentioned the loss of our hybrid waveguides is about 2 orders of magnitude lower than comparable devices integrated with graphene [48], and this played a key role for achieving high BFs in our SPM experiments.…”

“…We employed lensed fibers to butt couple the CW light into and out of the SOI nanowires with inverse-taper couplers at both ends with a butt coupling loss of ~5 dB per facet. This is about 2 orders of magnitude smaller than SOI nanowires coated with graphene [48], indicating the low material absorption of GO and its strong potential for the implementation of high-performance nonlinear photonic devices. The propagation loss increased with GO layer number − a combined result of increased mode overlap and several other possible effects such as increased scattering loss and absorption induced by imperfect contact between the multiple GO layers as well as interaction between the GO layers, as reported previously [43,47].…”

Silicon Photonic Platform for Passive Waveguide Devices: Materials, Fabrication, and Applications

“…[22][23][24] Among these materials, graphene, a single atom thick carbon sheet with atoms arranged in a hexagonal structure, was first studied for integrated optoelectronic devices due to its excellent optical and electrical properties. [25][26][27][28][29] A mono-graphene layer has a constant absorption of 2.3% over a wide wavelength range, from infrared to visible. Graphene also has a high carrier mobility (200 000 cm 2 V −1 s −1 at room temperature), which is about two orders of magnitude higher than that of silicon.…”