MMI Coupler Research Articles

Optical pulse controlled two mode interference coupler based logic gates

In this paper, an optical pulse controlled 1×2 two mode interference (OTMI) coupler having silicon core and GaAsInP cladding has been introduced as NOT and AND gates. The coupling characteristics of OTMI coupler are analyzed by using a simple mathematical model based on sinusoidal modes. It is seen that the length of OTMI based logic gate is eight times lower than that of existing MMI coupler based logic gates and the effect of power imbalance on fabrication tolerances of the device is also less than that of MMI device.

Temperature-independent broadband silicon modulator

We demonstrate a 20Gb/s temperature-independent silicon modulator based on symmetrical Mach–Zehnder Interferometer. The MMI coupler was used as splitter/combiner in symmetrical MZI for balanced propagation. The ±15°C temperature-independent eye diagrams were measured at 10Gb/s with over 15dB extinction ratio. Based on over 30nm flat optical bandwidth, the broadband modulation was demonstrated from 1530nm to 1560nm. The temperature-independent broadband silicon modulator is adaptable to interconnection and communication systems in practice.

Theory Analysis and Simulation of Optical 90° Hybrid without Intersection

An optical 90ohybrid consisting of a general interference based 4×4 MMI coupler, a phase shifter and a 2×2 MMI coupler was proposed. This device can demodulate optical signal without intersections. The output power formula of this device was derived from theory, and the effect on phase shifter was discussed analytically and numerically. It is not necessary to control phase shifter accurately, a deviation 10oform perfect phase shift will introduce 2% AC component loss of Q information only.

The cascaded exponential-tapered multimode interference couplers based triplexer design for FTTH system

A novel compact triplexer, which consists of series cascaded exponential-tapered multimode interference couplers, is introduced in this paper. General self-image properties of the exponential-tapered multimode interference couplers are investigated thoroughly to fulfill the compact integrated triplexer. By combining four exponential-tapered MMI couplers, a novel compact 0.6cm-long triplexer that is with ITU standard wavelength of 1310nm, 1490nm and 1550nm for FTTH is achieved without requiring complicated design. And it can be fabricated by common planar lightwave circuit (PLC) technology. From the simulation results for wavelength of 1310nm, 1490nm and 1550nm, the insertion losses are 0.34dB, 0.9dB and 1.17dB, with isolations for each output waveguide ranging from 12.74dB to 37.15dB. The 3dB passband widths for 1310nm, 1490nm and 1550nm are 112.39nm, 29.44nm and 26.7nm.

Preliminary investigation of an SOI-based arrayed waveguide grating demodulation integration microsystem.

An arrayed waveguide grating (AWG) demodulation integration microsystem is investigated in this study. The system consists of a C-band on-chip LED, a 2 × 2 silicon nanowire-based coupler, a fiber Bragg grating (FBG) array, a 1 × 8 AWG, and a photoelectric detector array. The coupler and AWG are made from silicon-on-insulator wafers using electron beam exposure and response-coupled plasma technology. Experimental results show that the excess loss in the MMI coupler with a footprint of 6 × 100 μm2 is 0.5423 dB. The 1 × 8 AWG with a footprint of 267 × 381 μm2 and a waveguide width of 0.4 μm exhibits a central channel loss of −3.18 dB, insertion loss non-uniformity of −1.34 dB, and crosstalk level of −23.1 dB. The entire system is preliminarily tested. Wavelength measurement precision is observed to reach 0.001 nm. The wavelength sensitivity of each FBG is between 0.04 and 0.06 nm/dB.

A triplexer based on cascaded $$2\times 2$$ 2 × 2 butterfly MMI couplers using silicon waveguides

An ultra-compact triplexer is designed by mean of the construction of \(2\times 2\) generalized interference–multimode interference (GI–MMI) couplers. In order to reduce the device length these couplers are formed into linear butterfly shape. Firstly, a butterfly \(2\times 2\) MMI coupler is designed to separate the wavelength 1,490 nm into one port and wavelengths 1,310 and 1,550 nm into an another port. Then another one is used to drop wavelengths of 1,310 and 1,550 nm to output ports individually. Numerical simulations with three-dimensional beam propagation method and effective index method are utilized to design and optimize the operation of the proposed triplexer.

1.3-μm 1 × 4 MMI coupler based on shallow-etched InP ridge waveguides

A 13-μm 1 × 4 MMI coupler is designed and fabricated on an InP substrate based on a shallow etched waveguide structure. Tapered input/output waveguides and a bending waveguide design are adopted and applied in the device to optimize the performance. The average excess losses of the 1 × 4 MMI coupler per channel are 2.8, 1.7, 2.9, and 2.9 dB, respectively. The smallest excess loss can be lower than 0.5 dB in the 40-nm spectrum bandwidth. The average uniformity between the four channels of the MMI coupler is 1.3 dB, while the smallest uniformity is only 0.4 dB.

Development of Low Loss Ultra-High Δ ZrO<SUB>2</SUB>-SiO<SUB>2</SUB> PLC for Next Generation Compact and High-Density Integrated Devices

For next generation planar lightwave circuit (PLC) devices, high function and high-density integration are required as well as downsizing and cost reduction. To realize these needs, high refractive index difference between a core and a clad (∆) is required. To use PLC for practical applications, silica-based PLC is one of the most attractive candidate. However, degradation of the optical properties and productivity occur when ∆ of the core becomes high. Thus, ∆ of most of the conventional PLC with GeO2-SiO2 core is designed less than 2.5%. In this paper, we report a silica-based ultra-high ∆ PLC with ZrO2-SiO2 core. 5.5%-∆ ZrO2-SiO2 PLC has been realized with low propagation loss and basic characteristics has been confirmed. Potential of chip size reduction of the ZrO2-SiO2 PLC is shown. key words: integrated optics, MMI coupler, optical communication, optical device, planar lightwave circuit

Ultra-compact optical 90° hybrid based on a wedge-shaped 2 × 4 MMI coupler and a 2 × 2 MMI coupler in silicon-on-insulator

We propose an ultra-compact optical 90° hybrid with the smallest length of 107μm, consisting of a wedge-shaped 2 × 4 MMI coupler connected with a 2 × 2 MMI coupler using silicon nanowaveguide technology. Neither cascaded phase shifters nor waveguide crossings are attached to the proposed 90° hybrid in coherent receiving system. The proposed device is demonstrated on silicon-on-insulator (SOI) with 220nm thick top-silicon layer and 2μm thick buried oxide layer. A high performance of the proposed 90° hybrid is exhibited experimentally with a high extinction ratio larger than 20dB, an excess loss mostly less than 0.5dB, a common mode rejection ratio better than -20dB and phase deviation within the range of 5° over C-band spectral range.

A design of triplexer based on a 2×2 butterfly MMI coupler and a directional coupler using silicon waveguides

A novel ultra-compact triplexer is designed by basing it on a combination of a 2×2 generalized interference-multimode interference (GI-MMI) coupler. The MMI is formed into linear butterfly shape and a directional coupler using silicon rib waveguides. Firstly, the 2×2 MMI coupler is designed to separate the wavelength 1490nm into one port and wavelengths of 1310nm and 1550nm into another port. Then a directional coupler is used to drop wavelengths of 1310nm and 1550nm to output ports individually. Numerical simulations with three-dimensional Beam Propagation Method (BPM) are utilized to design and optimize the operation of the proposed triplexer.

A compact thermo-optical multimode-interference silicon-based 1×4 nano-photonic switch

An ultra-compact multimode-interference (MMI)-based 1 × 4 nano-photonic switch is demonstrated by employing silicon thermo-optical effect on SOI platform. The device performance is systematically characterized by comprehensively investigating the constituent building blocks, including 1 × 4 power splitter, 4 × 4 MMI coupler and groove-isolated thermo-optical heaters. An instructive model is established to statistically estimate the required power consumption and investigate the influence of the power imbalance of the 4 × 4 MMI coupler on the switching performance. At the designed wavelength of 1550 nm, the average insertion loss of different switching states is 1.7 dB, and the transmission imbalance is 1.05 dB. The worst extinction ratio and crosstalk of all the output ports reach 11.48 dB and -11.38 dB, respectively.

Normal-Mode Analysis of Switching Dynamics in Nonlinear Directional Couplers

The dynamic properties of a nonlinear directional coupler made of Kerr materials are investigated using a normal-mode theory based on even and odd supermodes. This analysis provides a good platform to study the pulse propagation in nonlinear multimode waveguides, since the device is simple and can be regarded as a bimodal waveguide. Although the nonlinear directional coupler has already been well investigated using the standard coupled-mode theory, this paper presents new knowledge concerning the device operation from the standpoint of supermodes. Under the normal-mode model, power exchange between the two supermodes is performed through non-phase-matched four-wave mixing (FWM) and new frequency components are created on propagation, leading to spectral broadening of optical pulses. It is found that the group-delay mismatch between the two modes induces instability in collaboration to the nonlinearity when the duration of input pulses is of the order of sub-picoseconds. The dynamic properties of the nonlinear directional coupler are quite similar to those of the nonlinear MMI coupler that were more recently investigated by the present authors.

An ultra‐compact multimode interference coupler with a subwavelength grating slot

AbstractMultimode interference couplers (MMIs) are fundamental building blocks in photonic integrated circuits. Here it is experimentally demonstrated, for the first time, a two‐fold length reduction in an MMI coupler without any penalty on device performance. The design is based on a slotted 2 × 2 MMI fabricated on a commercial silicon‐on‐insulator (SOI) substrate. The slot is implemented with a subwavelength grating (SWG) comprising holes fully etched down to the oxide cladding, thereby allowing single etch step fabrication. The device has been designed using an in‐house tool based on the Fourier Eigenmode Expansion Method. It has a footprint of only 3.5 μm x 23 μm and it exhibits a measured extinction ratio better than 15 dB within the full C‐band (1530 nm‒1570 nm). SWG engineered slots thus offer excellent perspectives for the practical realization of MMIs couplers with substantially reduced footprint yet with outstanding performance.

InP based DFB laser array integrated with MMI coupler

The techniques used for the fabrication of photonic integrated circuit (PIC) chip are introduced briefly. Then a four channel DFB laser array integrated with MMI coupler and semiconductor optical amplifier (SOA) fabricated with butt-joint technique, varied ridge width and holographic exposure techniques is reported.

An Ultra Compactmulti Mode Interference Coupler with Parabolic Down Tapered Geometry

A 2x2 multimode interference structure with parabolic down tapering has been proposed and realized by using silica waveguides with silicon oxinitride (SiON) core for the reduction of coupling length. The coupling behavior and dependence of fabrication tolerances on power imbalance of the proposed tapered structure have been compared with those of other tapered MMI structures having both down and up tapering by using a mathematical model based on sinusoidal modes. It has been found both theoretically and experimentally that the beat length (Lπ) of the proposed tapered MMI coupler with Δn=5% is ∼ half that of conventional MMI coupler and the deviation of power imbalance from its minimum value with fabrication tolerances (± ∂w values) for the proposed tapered structure is more than that of other tapered structures.

Analysis of hybrid dielectric-plasmonic slot waveguide structures with 3D Fourier Modal Methods

Recently, plasmonic waveguides have been intensively studied as promising basic building blocks for the construction of extremely compact photonic devices with subwavelength characteristic dimensions. A number of different types of plasmonic waveguide structures have been recently proposed, theoretically analyzed, and their properties experimentally verified. The fundamental trade-off in the design of plasmonic waveguides for potential application in information technologies lies in the contradiction between their mode field confinement and propagation loss: the higher confinement, the higher loss, and vice versa. Various definitions of figures of merit of plasmonic waveguides have been also introduced for the characterization of their properties with a single quantity. In this contribution, we theoretically analyze one specific type of a plasmonic waveguide – the hybrid dielectric-loaded plasmonic waveguide, or – as we call it in this paper – the hybrid dielectric-plasmonic slot waveguide, which exhibits very strong field confinement combined with acceptable losses allowing their application in some integrated plasmonic devices. In contrast to the structures analyzed previously, our structure makes use of a single low-index dielectric only. We first define the effective area of this waveguide type, and using waveguide parameters close to the optimum we analyze several waveguide devices as directional couplers, multimode interference couplers (MMI), and the Mach-Zehnder interferometer based on the MMI couplers. For the full-vector 3D analysis of these structures, we use modelling tools developed in-house on the basis of the Fourier Modal Method (FMM). Our results thus serve to a dual purpose: they confirm that (i) these structures represent promising building blocks of plasmonic devices, and (ii) our FMM codes are capable of efficient 3D vector modelling of plasmonic waveguide devices.

An MMI-based polarization splitter using patterned metal and tilted joint

A novel polarization splitter on an InP substrate utilizing an MMI coupler loaded with a dielectric and gold layer pad is proposed and simulated. A tilted joint is used for adjusting the phases of TE and TM modes. The MMI section is less than 540 μm. Simulations show that the device has a polarization extinction ratio over 23 dB and an insertion loss below 0.7 dB over the entire C-band for both TE and TM polarizations. The device design was optimized to maximize the wavelength range and tolerance for manufacturing variations.

Ultra Linear Modulator with High Output RF Gain Using a 1×2 MMI Coupler

Ultra Linear Modulator with High Output RF Gain Using a 1×2 MMI Coupler

Wide-bandwidth, low-waveguide-width-sensitivity InP-based multimode interference coupler designed by wavefront matching method

A wavefront matching design method is successfully applied to a high-index-contrast InP waveguide for the first time. Fabricated 2×2MMI coupler exhibits a 1.6 times wider operation wavelength range than a conventional MMI coupler. This coupler has less waveguide-width sensitivity and is suitable for InP-based large-scale photonic integrated circuits.

Fabrication and characterization of polymer thermo-optic switch based on mmi coupler

The 2×2 polymer thermo-optic switch based on MMI coupler is realized. This device is fabricated using standard fabrication techniques such as coating, photolithography, and dry etching. A crosstalk level of −36.2dB is achieved at cross and bar states. A power consumption of 1.85mW is applied to change the state of the switch from the cross to the bar state. A switching time of less than 0.7ms is traced to change a state of the realized switch.