Yang-Tung Huang

Quantitative Analysis of a Flat-Top Planar Waveguide Demultiplexer

A three-focal-point method is used for the design of a flat-top planar waveguide concave grating. With the Gaussian approximation a modified formula is proposed and is compared with the numerical model of the scalar diffraction theory by using a design example. The sources of loss caused by the flat-top design and the grating are taken into consideration. The optimal separation between the two outmost focal points is obtained and the spectral response of the demultiplexer with a ripple below 0.04 dB is achieved.

Double-layer networks with holographic optical switches

The double-layer networks have the advantages of being strictly nonblocking and having a simpler routing algorithm, the lowest system insertion loss, a zero differential loss, fewer drivers, fewer interconnection lines, fewer crossovers, and the best signal-to-noise-ratio characteristic compared with any nondilated network. Using holographic optical switches to construct these networks not only eliminates all interconnection lines and crossovers but also reduces the number of drivers.

A strictly nonblocking network based on nonblocking 4 × 4 optical switches

Abstract Recently, the demand for communication has been growing rapidly. Hence, optical multistage network technologies are more appreciated nowadays. A double-layer network is a strictly nonblocking network, and it has the lowest system insertion loss of non-dilated networks. A Benes network is a rearrangeably nonblocking network, and it has the same system insertion loss as a double-layer network. We have proposed the use of modified polarization selection elements (PSEs). The system insertion loss, number of drivers, and number of required components of a double-layer network could be reduced if it is constructed with modified PSEs. A nonblocking 4×4 optical switch with two stages of polarization selective elements has been presented in our previous study. Based on this nonblocking 4×4 optical switch, we propose a strictly nonblocking network structure which features even lower system insertion loss than those of a double-layer network and a Benes network. The signal-to-noise ratio of the proposed network structure is a constant, and is higher than the constraint, although it is lower than that of the double-layer network. The number of major components of the proposed network is less than that of a double-layer network and larger than that of a Benes network, since a Benes network is rearrangeably nonblocking. We also offer a routing algorithm for the new proposed network; the time complexity of the routing algorithm is O ( 1 ) .

Design of a Photonic Crystal Tapered Coupler with Different Section Lengths Based on Multimode Interference and Mode Matching

Step tapered couplers, which act as mode converters, are usually used between photonic crystal (PC) waveguides and other optical devices for efficient coupling. In this study, the multimode interference (MMI) phenomena in multiple-line-defect PC waveguides are observed. It is found that the optimal length of each section in a PC step tapered coupler is related to the imaging length of MMI. Therefore, a PC step tapered coupler with different section lengths can be designed. Because the modes are matched between two adjacent sections and the scattering losses occurring at the corners of abrupt steps are reduced, it can provide an excellent transmission between PC waveguides and other optical devices. This study also reveals the reason why in some cases, the transmission of PC step tapered couplers decreases counterintuitively when the taper length is increased.

Cyclic crossbar network for photonic switching

Feature Issue on Optical Interconnection Networks (OIN). The rectangular crossbar network is commonly used in switching networks because it has the advantages of easy connection-path rebuilding, wide-sense nonblocking, and no crossover in its interconnection lines. However, this kind of network has two major disadvantages: one is that it has nonzero differential loss, and the other is that its signal-to-noise ratio (SNR) is decreased by both the increase of the network dimension and the insertion loss of switches. Here the cyclic crossbar network structure is presented. The cyclic crossbar network is similar to the rectangular crossbar network. For both types of network, an N×N network is constructed by N columns, and each column consists of N switches. The major difference is that construction with N backslash lines and N slash lines is used for the cyclic crossbar network. For every backslash line to have its crosspoint on the right side, the network structure is designed into a circle shape. In this type of network, the differential loss is eliminated and SNR is independent on insertion loss of switches, but the original advantages are maintained.

Component Reducing and Routing Algorithm of Double-Layer Network with Rearranging the Channel Allocation

Recently, there has been a growing demand for communication systems. The implementation of optical multistage interconnection networks (MINs) is more and more noticed. In our previous study, we have presented a modified version of holographic optical switches (HOSs). The double-layer network constructed by the modified version of HOSs and rearranged the channels allocation, the number of electro-optic halfwave plates (EOHWPs) could be significantly decreased from 2N^2-2N to 2Nlog2N. We propose a routing algorithm for the novel DLN and the time complexity of the routing algorithm is O (1).

Multicast Network with MMI-Based Optical Switches on Active Splitter/Active Combiner Structure

Multicast communications have become more and more important recently, especially in their applications in multimedia communication, quality of service (QoS), video conferencing, and distance education. In a point-to-point (PTP) optical communication system, how to provide multicast services is an essential issue. There are some advantages of active splitter/active combiner (AS/AC) networks, such as strictly nonblocking, simpler routing algorithm, lower system-insertion-loss, zero differential loss, and better signal-to-noise characteristics. The active multimode interference (MMI) coupler can provide splitting/combining operations with low loss and good balancing. It has been demonstrated that the AS/AC network constructed by active MMI switching devices can implement the multicast and PTP communications simultaneously. In this study, we offer two multicast algorithms, parallel multicast, and tunable multicast, on AS/AC network. The parallel multicast algorithm is suitable when there are multi requests arriving at the same time. The tunable multicast algorithm is suitable for balancing the output signals’ power.

High performance rearrangeable nonblocking networks with polarization selective elements

A nonblocking 4 times 4 optical switch with polarization selective elements has been proposed, which control configuration has been changed. Compared with other nonblocking 4 times 4 optical interconnection network with polarization selective elements, this switch has lower insertion loss and requires fewer elements. In this presentation, this nonblocking 4 times 4 optical switch will be dilated to increase the contrast ratio. Finally, a rearrangeable nonblocking network by this high contrast ratio nonblocking 4 times 4 optical switch will be proposed, which has higher signal-to-noise ratio, lowest system insertion loss, and fewest required components.

The Impact of Fabrication Errors on a Flat-Top Grating-Based Planar Waveguide Demultiplexer

The spectral performance of a demultiplexer is significantly affected by the phase and amplitude errors due to fabrication errors. We estimate the impact of fabrication errors on a flat-top grating-based planar waveguide demultiplexer using a design example. Simulation results show that the photomask resolution resulting in a phase error should be lower than 40 nm when a crosstalk criterion of -30 dB is given. The impact of amplitude errors is not distinct until the reduced amount of the facet width is greater than 0.5 µm and the grating side-wall angle offset from the vertical is larger than 1°.