All-optical switching in two cascaded nonlinear directional couplers

All-optical mode switching with a graphene-buried polymer waveguide directional coupler

We demonstrate all-optical mode switching with a graphene-buried polymer waveguide asymmetric directional coupler (DC) by using the photothermal effect of graphene, where TE-polarized pump light and TM-polarized signal light are employed to maximize pump absorption and minimize graphene-induced signal loss. Our experimental device, which uses a graphene length of 6.2 mm, shows a pump absorption of 3.4 dB (at 980 nm) and a graphene-induced signal loss of 0.1 dB. The device can spatially switch between the fundamental mode and the higher-order mode with extinction ratios larger than 10 dB (at 1580 nm) and switching times slightly shorter than 1 ms at a pump power of 36.6 mW. Graphene-buried polymer waveguides offer many new possibilities for the realization of low-power all-optical control devices.

All-optical switching structure based on a photonic crystal directional coupler

A novel all-optical switching structure based on a photonic crystal directional coupler is proposed and analyzed. Efficient optical switching is achieved by modifying the refractive index of the coupling region between the coupled waveguides by means of an optical control signal that is confined in the central region. Small length (around 1.1 mm) and low optical power consumption (over 1.5 W) are the main features estimated for this switching structure.

Variable coupling coefficient nonlinear directional couplers with self-focusing and self-defocusing nonlinearity

Nonlinear directional couplers (NLDCs) with a variable coupling coefficient (VCC) in self-focusing and self-defocusing materials are investigated. Specifically, the Gaussian type VCC NLDCs are studied in detail. The results show that the responses of the VCC NLDCs on self-focusing and self-defocusing materials are different, especially when input power is high. The coupled-mode theory can also be used to predict the characteristics of the VCC NLDC on self-focusing material, even when input power is high.

All-optical logic devices with cascaded nonlinear couplers

The switching behaviors of cascaded nonlinear couplers were investigated. They have nearly ideal digital-switching characteristics, and their output power levels can be adjusted by means of varying the nonlinear coupling coefficient of the final coupler. The two-input excitation nonlinear cascaded couplers can perform not only switching operations but also a series of logic operations. The logic operations depend mainly on the coupling length of the two-input coupler and its initial inputs. The power corresponding to the rising and falling ridge of the logic operating waveforms can be shifted effectively by means of varying the switching power of the reshaper. Allowable ranges of three important parameters--coupling length of the two-input coupler L(1), bias optical power P(bia), and phase difference psi between the signal and bias beams for six fundamental logic operations--were calculated. Curves for design considerations and suggestions for the best choice of parameters for stable and reliable logic operations and, or, xor, nand, nor, and nxor are also presented individually.

Temporal soliton switching in a rectangular nonlinear directional coupler

We address the theory of temporal soliton switching in a planar geometry directional coupler constructed from silica and doped silica glass and operating at the central wavelength of 1.55 microm, significant for erbium-doped amplification. We formulate the field in the coupler in terms of the supermodes of the total structure and take account of the two transverse dimensions of the rectangular channels. In the case of the weak coupling between channels consistent with elimination of pulse breakup, the effect of the fields in the outer corner regions of the channels results in a switching intensity that differs significantly from that derived from coupled-mode theory on the basis of a slab model of the coupler.