• Journal of the Optical Society of Korea
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• v.20 no.2
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• pp.291-299
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• 2016

We have investigated the ultimate limits of nonuniform grating couplers (NGCs) for optimized fiber coupling to silicon waveguides, compared to uniform grating couplers (UGCs). Simple grating coupler schemes, which can be fabricated in etching steps of the conventional complementary metal-oxide semiconductor (CMOS) process on silicon-on-insulator (SOI) wafers without forming any additional overlay structure, have been simulated numerically and demonstrated experimentally. Optimum values of the grating period, fill factor, and groove number for ultimate coupling efficiency of the NGCs are determined from finite-difference time-domain (FDTD) simulation, and confirmed with experimentally demonstrated devices by comparison to those for the UGCs. Our simulated results indicate that maximum coupling efficiency of NGCs is possible when the minimum pattern size is below 50 nm, but the experimental value for the maximum coupling efficiency is limited by the attainable fabrication tolerance in a practical device process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.114-117
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• 1996

The wavelength selectivity in grating-assisted optical waveguide couplers is studied using a matrix method to analyse optical filter characteristics. The matrix method is extended to both 2-system modes and all guided system modes. The influence of fundamental design parameters on the performances of the optical filters by waveguide couplers is discussed.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.126-130
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• 2003

The optical power transfer of TM modes in grating-assisted directional couplers (GADCs) with three-guiding channels is rigorously evaluated by defining a novel coupling efficiency amenable to the rigorous analytical solutions of modal transmission-line theory (MTLT). The results reveal that the incident power is sensitively partitioned through three output channels in terms of such grating parameters as the period, the duty cycle, and wavelength.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.25-30
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• 2008

In this paper, a novel architecture for device miniaturization of multimode interference-based (MMI) couplers is proposed. The coupling length of $N{\times}N$ MMI couplers scales as the square of the MMI region width so that the use of these structures with large-N ports can require large chip size. To solve the design problem, the butterfly grating-assisted MMI couplers, that have smaller device dimensions than conventional MMI couplers, are discussed and evaluated. Numerical simulations and novel design rules for such structures derived through theoretical analysis are presented.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.7
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• pp.79-87
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• 1997

Untill now, the most well-known cofiguration for waveguide grating router(WGR) is composed of radiative star couplers and arrayed waveguide grating(AWG), which usually suffer form the rdiation loss of around 3dB or more. Therefore, te improved design of WGRs is needed to reduce the loss. In ths paper, we propose a novel WGR composed of multimode interference couplers which have good unifiormity, fabrication tolerance, and very low excess loss, and suggest the efficient algorithm to find the proper path length differences of AWG for given channel spacing and channel assignment to each output prot. The simulated spectral responses of the proposed WGR using the finite difference beam propagation method (BPM) show that the excess loss is less than 0.3dB and the crosstalk less than -25dB in case of 4x4 WGR, and the excess loss less than 0.4dB and the crosstalk less than -25dB in case of 8x8 WGR for all the channel wavelengths.

• Proceedings of the IEEK Conference
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• summer
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• pp.276-280
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• 2004

This paper first takes advantage of a rigorous modal transmission-line theory (MTLT) to analyze the filtering properties of optical waves guiding by grating-assisted fiber couplers (GAFCs). The numerical results reveal that MTLT serves as a suitable and powerful approach to evaluate systematically the dispersion properties and the characteristics of optical power transfer in GAFCs.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.945-948
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• 2000

The coupling properties of supermodes guided by grating-assisted directional couplers (GADCs) can be phrased in rigorous modal theory. Such a modal solution for TE modes expressed by simple electrical transmission-line networks is utilized to analyze the power distribution of GADCS with three guiding channels. In particular, the modal transmission-line theory can serve as a template for computational algorithms that systematically evaluate the coupling efficiency that are not readily obtained by other methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.9
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• pp.2526-2532
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• 1996

In this paper, the efficient algorithm for design of waveguide grating router(WGR) composed of star couplers is proposed. It is well demostrated that a star coupler design can be easily adjusted to the optimumstate using the proposed design method, which analyzes relations between various parameters. This method enables designers to estimate the spectral properties of waveguide grating router at the initial design level of the star coupler. A 5*5 WGR with 2.75nm(343GHz) channel spacing is designed using the proposed scheme. The BPM(Beam Propagation Method) simulation results show that the channel spacing of the WGR agrees very well with the design, the excess loss is smaller than 2.5dB, and the crosstalk is less than -21dB.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.120-126
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• 2006

A grating-assisted fiber coupler(GAFC), which consists of a thin-film waveguide with grating and circular optical fiber, is proposed and the optimized power coupling is evaluated by using a technique amenable to rigorous longitudinal modal transmission-line theory(L-MTLT). In addition, novel criteria to couple an optical signal incident through the grating waveguide to a single-mode optical fiber are proposed. The numerical result reveals that the optimized power coupling occurs at minimum-gap condition between rigorous modes rather than for the conventional phase-matching condition.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.1
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• pp.1-7
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• 1988

A new type broadband channel dropping filter which has a potential use as a millimeter-wave multiplexer has been realized by properly connecting 3-dB directional couplers and bandstop filters. 90\ulcorner3-dB directional couplers have been designed using two nonuniformly coupled dielectric image guides, while bandstop filters with Chebyshev passbands have been designed using dielectric image-guide grating structure. Effective dielectric constant method has been aplied to the image-guide dispersion analysis and to the design of bandstop gratings and 3-dB couplers. Experimental results in excellent agreement with computed responses are demonstrated.