MMI Waveguide Research Articles

Compact silicon-based polarization-independent 1.55/2 μm wavelength diplexer based on a multimode interference coupler with multiple shallow grooves

Faced with the rapid growth of internet traffic demand, which has posed a huge challenge to the current fiber-based communications systems, expanding the telecommunications bands from traditional near-infrared (NIR) region to mid-infrared (MIR) region is emerging as an attractive solution. And on-chip wavelength division multiplexing (WDM) application for NIR/MIR wavelengths is an essential element in future optical telecommunication systems. Here, we propose a compact silicon-based polarization-independent wavelength diplexer for the NIR/MIR wavelengths of 1.55/2 μm, where multiple rectangular grooves are shallowly etched on the silicon MMI waveguide for introducing the refractive-index perturbations on the MMI waveguide eigenmodes. And this refractive-index perturbation scheme provides a simple and scalable method to manipulate the four beat lengths of the two wavelengths at TE- or TM-polarization in a single waveguide via self-imaging effect, leading to a compact footprint. By optimizing the structural parameters, both NIR/MIR wavelength demultiplexing and polarization independence, for the first time, are obtained simultaneously in the present single device. From the results, the proposed diplexer is only 21.6 μm in length, and shows a wide bandwidth of ∼ 100/120 nm around the wavelength of 1.55/2 μm for insertion loss (IL) < 1 dB and extinction ratio (ER) > 15 dB. Moreover, we also realize a compact and polarization-independent wavelength diplexer for 1.31/2 μm by flexibly changing the dimensions, showing the flexibility and extensibility of our refractive-index perturbation scheme. Besides, fabrication tolerances are analyzed and mode propagation profiles are also demonstrated.

Proposal and simulated characteristics of high-extinction-ratio electroabsorption modulator based on multimode interference waveguide

We proposed an electroabsorption modulator (EAM) based on a 1 × 1 multimode interference waveguide (MMI-EAM). A partial electroabsorption (EA) region is asymmetrically placed in a MMI. In a multiple quantum well core layer of the region, the electrorefractive index change is also exhibited in addition to the EA effect, which leads to change in the position of a self-image at the output port of the MMI waveguide. Owing to the combination of the EA effect and change in electrorefractive index, the extinction ratio is significantly improved compared with a conventional EAM with almost the same area of the EA region. We discuss the optimization of the MMI-EAM structure and investigate its modulation characteristics theoretically using the beam propagation method. The results show that the extinction ratio can be increased by 25 dB in the MMI-EAM with the length of 152 μm and the width of 6 μm.

Silicon-on-insulator multimode-interference waveguide-based arrayed optical tweezers (SMART) for two-dimensional microparticle trapping and manipulation

We demonstrate two-dimensional optical trapping and manipulation of 1 μm and 2.2 μm polystyrene particles in an 18 μm-thick fluidic cell at a wavelength of 1565 nm using the recently proposed Silicon-on-insulator Multimode-interference (MMI) waveguide-based ARrayed optical Tweezers (SMART) technique. The key component is a 100 μm square-core silicon waveguide with mm length. By tuning the fiber-coupling position at the MMI waveguide input facet, we demonstrate various patterns of arrayed optical tweezers that enable optical trapping and manipulation of particles. We numerically simulate the physical mechanisms involved in the arrayed trap, including the optical force, the heat transfer and the thermal-induced microfluidic flow.

Photopolymer-Based Diffractive and MMI Waveguide Couplers

Diffractive and multimode-interference waveguide couplers constructed from photopolymer materials are presented. Two-material grating-in-the-waveguide optical interconnects are fabricated and tested with respect to waveguide propagation loss and grating out-coupling. Waveguide/grating interconnects have been constructed with both index-defined and air-clad waveguide channel regions, where air-clad channels exhibit measured propagation losses of /spl alpha//sub wg/=0.47-3 dB/cm. Measurements of output coupling coefficients of volume grating couplers terminating various waveguide channels range from /spl alpha//sub g/=1.4-5.3 mm/sup -1/. A 1 /spl times/ 4 photopolymer-based multimode-interference power-splitting coupler fabricated and tested for the provision of in-plane optical coupling is found to demonstrate 0.3-0.6-dB output power uniformity.

Design of optical polarization splitters in a single-section deeply etched MMI waveguide

The design of a single-section polarization splitter in a deeply etched semiconductor MMI waveguide is presented. Numerically simulated results indicate that the semiconductor MMI exhibits considerable polarization dependence and, utilizing this effect, a compact 1.6-mm-long polarization splitter may be fabricated to yield more than 8-dB polarization separation and only 0.11-dB optical loss, using a very simple design-approach.

Simulation study on semiconductor laser mode locking using nonlinear coupling in multimode-interference waveguide amplifiers

The feasibility of a passively mode-locked semiconductor laser with a multimode-interference (MMI) waveguide amplifier is numerically studied using a two-dimensional time-domain beam-propagation method. In an appropriately designed ring cavity, a pulse can be compressed from a few hundred picoseconds to several picoseconds, as a result of the interplay between linear coupling and gain saturation in the MMI waveguide amplifier. The asymptotically stable pulse peak position and pulsewidth imply the feasibility of passively mode-locking semiconductor lasers. The frequency chirping of the compressed pulse and the lateral distribution of the output beam are numerically analyzed in detail. Our simulations show that mode locking can be implemented within a fairly broad range of injection current and cavity alignment.