Multimode Interference Combiner Research Articles

Numerical investigation of an electro-optic majority voting circuit utilizing graphene-silicon nitride waveguides

In this paper, an electro-optic majority voting circuit based on graphene-silicon nitride waveguides is proposed and numerically investigated. The proposed circuit is composed of 2×1 multimode interference combiners and Mach-Zehnder interferometers where graphene-silicon nitride waveguides are designed for phase shifters. By adjusting graphene’s chemical potential electrically, the proposed graphene-silicon nitride waveguide has a large variation in the real part of the effective refractive index so that a relatively compact and low-energy-consumption majority voting circuit can be realized. Simulation results show that as graphene’s chemical potential is increased from 0.50 to 0.60 eV at an operating wavelength of 1550 nm, the designed graphene-silicon nitride waveguide with a 5 nm spacer of TiO2can have 0.34 pJ/bit energy consumption andVπ • Lπ of 43.15 V•μm.The corresponding electro-optic majority voting circuit has an extinction ratio larger than 20.11 dB.

4 × 40 GHz mode-locked laser diode array monolithically integrated with an MMI combiner

We report a distributed-Bragg-reflectors-based 4 × 40 GHz mode-locked laser diode (MLLD) array monolithically integrated with a multimode interference (MMI) combiner. The laser produces 2.98 ps pulses with a time-bandwidth product of 0.39. The peak wavelength of the MLLD array can be tuned by 8.4 nm while maintaining a good mode-locked state. The four mode-locked channels could work simultaneously with the peak wavelength interval around 3 nm.

Electro-optical logic gates based on graphene–silicon waveguides

In this paper, designs of electro-optical AND/NAND, OR/ NOR, XOR/XNOR logic gates based on cascaded silicon graphene switches and regular 2×1 multimode interference combiners are presented. Each switch consists of a Mach–Zehnder interferometer in which silicon slot waveguides embedded with graphene flakes are designed for phase shifters. High-speed switching function is achieved by applying an electrical signal to tune the Fermi levels of graphene flakes causing the variation of modal effective index. Calculation results show the crosstalk in the proposed optical switch is lower than −22.9dB within a bandwidth from 1510nm to 1600nm. The designed six electro-optical logic gates with the operation speed of 10Gbit/s have a minimum extinction ratio of 35.6dB and a maximum insertion loss of 0.21dB for transverse electric modes at 1.55μm.

Simultaneous Wavelength- and Mode-Division (De)multiplexing for High-Capacity On-Chip Data Transmission Link

We present designs of wavelength-division-multiplexing (WDM) and mode-division-multiplexing (MDM) optical links using mode de/multiplexers (DE/MUXs) based on multimode interference (MMI) couplers with a tilt joint as a phase shifter. The properties of WDM-MDM links with three wavelengths and two optical modes are numerically studied by using 3-D beam propagation method. In the first design, the wavelength combiner is also an MMI coupler type. The insertion loss of the design is around 6 dB because of the inherent loss of the MMI combiner. The size of the main passive optical parts (mode DE/MUXs and wavelength combiner) of the design is only 10.4 × 114.2 μm 2 , making the design promising for future compact and high-capacity optical interconnection applications. In another design, arrayed waveguide gratings are used for wavelength multiplexing, leading to a lower insertion loss of the optical connections. For both designs, the mode crosstalk between the two different modes for the same wavelength are below -22 dB.

Four-Channel 1.55-μm DFB Laser Array Monolithically Integrated with a 4×1 Multimode-Interference Combiner Based on Nanoimprint Lithography

A monolithically integrated four-channel λ/4 phase shift distributed feedback (DFB) laser array with a 4 × 1 multimode interference combiner is designed and fabricated using nanoimprint lithography. The threshold currents of the lasers are less than 10 mA, which are as good as a discrete DFB laser. Moreover, the side-mode suppression ratio is also better than 50 dB. The channel space is about 200 GHz for dense wavelength division multiplexing applications in an 1.55 μm system.

High-Speed Optical Label Recognition Technique Using an Optical Digital-to-Analog Conversion and Its Application to Optical Label Switch

Operation performance of a 40 Gbps, 2-bit Optical Digital-to-Analog converter (ODAC) and its application to optical label switching systems have been investigated. The device is composed of a 1 × 2 multi-mode interference (MMI) splitter, one-bit-delay line, and a 2 × 1 MMI combiner. It has a high-mesa structure fabricated on InP-based materials. Dependence of output signal level on input signal wavelength and device temperature was measured. Due to the optical phase variation caused by the refractive index change with wavelength and temperature, output signal level varied, and it agreed well with simulation results. Four-level signals were generated and a quarter dependence of phase on temperature and wavelength compared with that for 10-Gbit/s was verified. Next, operation tolerance of the ODAC as an optical label processor, bit error rate (BER) of the digital-to-analog (DA)-converted signal was simulated. The tolerance against fluctuation of light source power, optical phase in the device, optical chirp, and extinction ratio of input signal was estimated. For all parameters, operation tolerance could be kept, but that for 40 Gbps is smaller than that for 10 Gbps. Then, autonomous label processing and optical label switching performance using a gate pulse generation scheme based on phase-shifted preamble was investigated. Optical DA conversion and three kinds of optical label were recognized at a bit rate of 40 Gbps, and optical packet transfer could be confirmed.

Dynamic switching characteristics of InGaAsP/InP multimode interference optical waveguide switch

Multimode interference (MMI) waveguide switches show promise for switch in optical packet switching (OPS). In this work, we fabricated 1 x 4 InGaAsP/InP MMI waveguide switch device which consists of a 1 x 4 MMI splitter, 4 equally spaced single-mode waveguides with phase shifters, and a 4 x 4 MMI combiner. Good crosstalk and extinction ratio of -14.47 dB and 23.39 dB, respectively, are obtained. In addition, we experimentally demonstrate dynamic switching, and the rise and fall time of 1.4 ns and 1.2 ns, respectively, are obtained.

Straight multimode interference phased array structure using periodic segmented waveguide phase array

A new design of a multimode interference (MMI) phased array structure is proposed. This design is based on replacing the arrayed delay arms between the first MMI power splitter and the second MMI combiner by periodic segmented waveguides. This allows a straight structure without curved waveguides and thus reduces greatly the size of the structure. A design example of an 8 channel multiplexer is presented showing a size reduction by a factor of 23 when compared with conventional design, while keeping nearly the same performance.

Study on Tapered Multimode Interference-Based Coherent Lightwave Combiners

In this paper we analyze the characteristics of tapered multimode interference (MMI)-based coherent lightwave combiners, and theoretically confirm that the stable and clear multimode interference images exist in the tapered MMI combiners. We present the output characteristics of 2 x 1 tapered MMI-based coherent lightwave combiners under various structures, which are useful to optimally design the combiners. In order to extend the combiner to a multi-port (N x 1, N > 2) configuration, a new structure with the border shapes of two tangent arcs is proposed, by which we show an output power imbalance of about 0.5 dB between different input ports of an 8 x 1 tapered coherent lightwave combiner. Due to the advantages of no end-facet reflection, easy extension to a multi-port configuration, high tolerance for fabrication errors and a compact size, the tapered MMI structure is a good candidate as a coherent lightwave combiner used in large-scale nhotonic integrated circuits.

Integrated optical digital-to-analogue converter and its application to pulse pattern recognition

An optical digital-to-analogue converter that enables optical pulse pattern recognition, fabricated on the silica-based planar lightwave circuit, is proposed. The converter features an optical transversal filter with a multimode interference combiner. Various kinds of four-bit pulse patterns at 10 Gbit/s have been successfully recognised with the fabricated converter.

Compact InP-based ring lasers employing multimode interference couplers and combiners

Multimode interference (MMI) 3 dB couplers and MMI power combiners have been integrated with compact InP/InGaAsP ring lasers (R=150 μm). Radiative loss from the curves is small, and MMI 3 dB couplers are shown to be more efficient than conventional Y junctions. In addition, we demonstrate improved efficiency by combining counterpropagating beams in a single output by means of a MMI combiner. Single mode spectral behavior, with 35 dB side mode suppression, has been measured and is explained as resulting from coupled cavities.