Tapered Multimode Interference Coupler Research Articles

A parallel design scheme for ultra-compact silicon waveguide crossing based on the tapered multimode interference coupler

We demonstrate two ultra-compact high efficiency silicon waveguide crossing devices based on the tapered multimode interference coupler in the entire wavelength range of 1520 to 1580 nm. A parallel waveguide crossing structure for transverse-electric (TE) mode with a footprint of only 1.05 × 2.6 μm2 is designed, which can provide single mode crossing with the insertion loss better than 0.12 dB and the crosstalk lower than −23 dB in the broadband. A polarization-insensitive waveguide crossing with a footprint of only 1.1 × 2.3 μm2 is also designed, which can provide insertion loss lower than 0.54 dB and crosstalk lower than −23 dB for both TE and transverse-magnetic modes. The proposed parallel crossing scheme can efficiently save rooms for building up sophisticated waveguide crossing networks by avoiding the waveguide bending before or after crossing. These devices can have great application potential in the dense photonic integrated systems.

Compact Microring Resonator With 2$\,\times\,$2 Tapered Multimode Interference Couplers

Compact microring resonator devices are realized by using a small SU-8 polymer strip waveguide that has an SU-8 polymer core (n ~ 1.573), an SiO2 buffer (n ~ 1.445), and an air cladding. Due to the high index contrast of the optical waveguide, a small bending radius ( ~ 150 mum) is used for the MRR. To enhance the coupling between the access optical waveguides and the microring, 2 times 2 multimode interference couplers are used. The measured spectral response of the through port shows a high extinction ratio of over 15 dB and a 3-dB bandwidth of about 0.38 nm (corresponding to a moderate Q-value of ~ 4500).

Parabolic tapered structure for an ultracompact multimode interference coupler

A parabolic tapered structure based on general interference has been proposed and studied theoretically with silica waveguides of silicon oxinitride (SiON) core by using a mathematical model based on sinusoidal modes for the reduction of coupling length of a 2x2 multimode interference (MMI) coupler. The coupling behaviors of the proposed structure are compared with those of other MMI structures. It is seen that the beat length for the proposed tapered MMI coupler is approximately half of that of a conventional MMI coupler. The effect of power imbalance on the fabrication tolerance of a 3 dB coupler using the proposed tapered structure is also studied and compared with that of other MMI structures.

Compact 2×2 tapered multimode interference couplers based on SU-8 polymer rectangular waveguides

A 2×2 tapered multimode interference (MMI) coupler is designed and fabricated by using air-cladded SU-8 rectangular waveguide, which is effective in reducing the device size and improving the self-imaging quality. The parabolically tapered MMI section is used to reduce further the size of the MMI coupler. A compact 2×2 coupler with a total MMI size of about 5.3×34.2μm2 is demonstrated and characterized. The measurement results show that the fabricated 2×2 MMI coupler has relatively small excess loss and nonuniformity for both polarizations in a broad wavelength range (from 1480to1630nm).

A Tapered Structure for Compact Multimode Interference Coupler

A new tapered structure based on general interference has been proposed and realized by using silica waveguides with a silicon oxinitride (SiON) core for the reduction of coupling length of the 2times2 multimode interference (MMI) coupler. The coupling characteristics of the proposed structure are compared with those of conventional MMI structures using a simple mathematical model based on sinusoidal modes. The beat length for the proposed tapered MMI coupler is reduced by 45% of that of a conventional MMI coupler. The effect of power imbalance on fabrication tolerance of the proposed tapered MMI coupler are also studied and compared with other tapered MMI couplers.

Design of a wavelength demultiplexer based on a parabolically tapered multimode interference coupler

A compact wavelength demultiplexer is designed for the operation at 1.30 and 1.55 μm wavelengths using the three-dimensional semi-vectorial beam propagation method. The parabolically tapered multimode interference (MMI) coupler based on the deep-etched SiO 2/SiON rib waveguide is introduced into the present demultiplexer for reducing the length. The numerical results show that a MMI section of 330.0 μm in length, which is only 76% length of a straight MMI coupler, is achieved with the contrasts of 42.3 and 39.2 dB in quasi-TE mode, and 38.4 and 37.8 dB in quasi-TM mode at wavelengths 1.30 and 1.55 μm, respectively and the insertion losses below 0.2 dB. The modified finite difference scheme is applied to approximate the resulting equations along the transverse directions, in which the discontinuities of the derivatives of magnetic field components H y and H x along the vertical and horizontal interfaces, respectively, are involved.

A 2×2 multimode interference coupler with exponentially tapered waveguide

An exponentially tapered structure is introduced into multimode interference (MMI) devices. Compared with a parabolically tapered structure, which has been successfully used in MMI devices, this structure can further reduce the length of these devices. The performances of the 2×2 MMI coupler with exponentially tapered structure, such as the optical transmission, the splitting ratio, the wavelength response and the fabrication tolerance, are investigated by the 2D finite difference beam propagation method. Results show that the exponentially tapered MMI coupler exhibits a similar property to that with a parabolically tapered structure except for the splitting ratio. The exponentially tapered structure can offer a possible application in MMI couplers with a free choice of the splitting ratio.

Semi-vectorial analysis of a compact wavelength demultiplexer based on the tapered multimode interference coupler

Based on a parabolically tapered multimode interference (MMI) coupler with a deep-etched SiO2/SiON rib waveguide, a compact wavelength demultiplexer operating at 1.30 and 1.55µm wavelengths is proposed and analysed by using three-dimensional semi-vectorial finite-difference beam propagation method (3D-SV-FD-BPM). The results show that a MMI section of 330.0µm in length, which is only 76% length of a straight MMI coupler, is achieved with the contrasts of 42.3 and 39.2dB in quasi-TE mode, and 38.4 and 37.8dB in quasi-TM mode at wavelengths 1.30 and 1.55 µm, respectively, and the insertion losses below 0.2dB at both wavelengths and in both polarization states. The alternating direction implicit algorithm with the Crank–Nicholson scheme is applied to the discretization of the 3D-SV-FD-BPM formulation along the longitudinal direction. Moreover, a modified FD scheme is constructed to approximate the resulting equations along the transverse directions, in which the discontinuities of the derivatives of magnetic field components Hy and Hx along the vertical and horizontal interfaces, respectively, are involved.

Theory and Design of Adiabatically Tapered Multimode Interference Couplers

Tapered-multimode-interference (MMI) splitters and couplers result in more compact designs than conventional MMI devices. In this paper, we analyze the adiabatic limit of the tapered MMI and present new designs that are both compact and result in minimal loss

Size tolerance analysis of a 4×4 tapered multimode interference coupler in a silicon-on-insulator structure

Size tolerance of a 4X4 general interference tapered multimode interference (MMI) coupler in a silicon-on-insulator (SOI) structure is investigated by means of a 2-D finite difference beam propagation method (2D-FDBPM), together with an effective refractive index method (EIM). The results show that the tapered multimode interference coupler exhibits relatively larger size tolerance when light is launched from the edgeport than from midport, though it has much better output power uniformity when light is launched from midport. Besides that, it can reduce the device length greatly. The 4X4 general interference tapered MMI coupler has a slightly larger size tolerance compared with a conventional straight multimode interference coupler. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Compact 3-dB tapered multimode interference coupler in silicon-on-insulator

We have fabricated a compact 3-dB multimode interference coupler with a large silicon-on-insulator cross section. To reduce the length of the usual symmetric interference multimode interference coupler, we propose using a parabolically tapered structure. The length of the device is 398microm . The device has a uniformity of 0.28 dB.

Signal bandwidth of general n×n multimode interference couplers

Analytical expression of signal bandwidth of general straight and tapered N/spl times/N multimode interference (MMI) couplers is presented. The signal bandwidth is characterized as a function of mode relative energy, mode propagation delay time, and mode pulse broadening in the multimode section of MMI coupler. The model is used to evaluate the signal bandwidth of specific couplers. Results indicate that the signal bandwidth decreases seriously with the increase of channel number and channel guide space. Compared with the straight MMI coupler, the tapered MMI coupler has an improved signal bandwidth.