Photonic crystal tapers for ultracompact mode conversion

Happ, T.; Kamp, M.; Forchel, A.

doi:10.1364/ol.26.001102

Cited by 117 publications

(52 citation statements)

References 11 publications

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“…A number of strategies to deal with this coupling problem have been reported. The first is the use of an adiabatic taper [2], but these tend to be long and lack a systematic design procedure. The second is the use of a uniform matching region [3][4][5].…”

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confidence: 99%

Efficient slow-light coupling in a photonic crystal waveguide without transition region

et al. 2008

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We consider the coupling into a slow mode that appears near an inflection point in the band structure of a photonic crystal waveguide. Remarkably, the coupling into this slow mode, which has a group index n g Ͼ 1000, can be essentially perfect without any transition region. We show that this efficient coupling occurs thanks to an evanescent mode in the slow medium, which has appreciable amplitude and helps satisfy the boundary conditions but does not transport any energy. , but these tend to be long and lack a systematic design procedure. The second is the use of a uniform matching region [3][4][5]. Though this works well, it obviously requires the inclusion of an additional, finite region. Here, we discuss a third approach that does not require any matching region. We show that efficient coupling into a slow mode can be mediated by an evanescent mode that does not carry energy but helps match the slow mode's field to that of other modes. Though evanescent modes have been identified to play a role in coupling to slow PC waveguide modes [5], the mechanism was not studied in detail. Our geometry is illustrated in Fig. 1; light is incident through PC1, a silicon PC with a waveguide and with a / d = 0.3, where a is the radius of the air holes and d is its period. The input waveguide's properties have been adjusted by changing the radii of the holes two rows from the waveguide to a 1 = 0.38d. The slowlight waveguide in PC2 is identical, except that its properties have been adjusted by taking a 2 = 0.404d.At frequency d / = 0.2662, where is the wavelength, the waveguides in PC1 and PC2 each support a single propagating mode with group indices n g = 7.6 and n g = 1067, respectively. These calculations, and all those below, model the PC as two dimensional by taking the effective index of the silicon background to be 2.86. Our computational method [6] generates Fresnel interface coefficients very accurately from a complete Bloch-mode basis that includes modes that are propagating and evanescent in the direction of the waveguide. Because of the orthogonality of the Bloch modes [6], we may solve the interface field matching problem in a least-squares sense and, in doing so, identify a minimal set of modes that efficiently solves the problem to given accuracy. Without precautions, the transmittance from PC1 into PC2 is found to exceed T = 99.4%. This is remarkable, since coupling into a slow mode tends to be poor. We now discuss why the transmission might be expected to be low, and then explain why it is almost perfect in the structure considered here.We first consider the relevant part of the band structures of PC1 and PC2 (solid curves in Fig. 2). PC2 has been designed to have an inflection point where the group velocity d /dk becomes very small. High transmission into slow modes close to such an inflection point was earlier noted by Ballato et al. [7] in a one-dimensional geometry. The dashed curves show some of the complex bands, i.e., solutions to Maxwell's equations with complex k at real frequencies. These solutions,...

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Efficient slow-light coupling in a photonic crystal waveguide without transition region

et al. 2008

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“…The optimization was also carried out for a three-defect configuration, but the transmission efficiency was, once again, not substantially improved. However, just as occurs in conventional dielectric tapers, the transmission efficiency depends on the length of the PhC taper [10]. Below, it is shown how higher transmission efficiencies could be achieved by using a PhC taper longer than the previously considered.…”

Section: Defects Configuration Determined By a Ga-mst Toolmentioning

confidence: 87%

High-efficiency defect-based photonic-crystal tapers designed by a genetic algorithm

Håkansson

Sanchís

Sánchez‐Dehesa

et al. 2005

J. Lightwave Technol.

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Abstract-A method based on a genetic algorithm (GA) is used to design the optimum configuration of defects that when put within a photonic-crystal (PhC) taper improve the coupling efficiency between dielectric and PhC waveguides (WGs). This approach optimizes the whole configuration of defects simultaneously and, therefore, takes into account the correlation among the defects. Transmission efficiencies up to 94% have been predicted for a 3-µm-wide dielectric WG into a single-line-defect PhC-WG. This result significantly improves the transmission efficiency of the same PhC taper without defects. The influence on the coupling efficiency of the PhC taper length and geometry are also discussed.

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“…Nevertheless, for the future integrated PC circuits and nanophotonic devices it is very important to obtain single mode emission in order to couple to PC waveguides or fibers, thus requiring additional efforts for mode conversion. 10 In this letter, the effect of the introduction of an H1 cavity 11 located in the six corners of a hexagonal waveguide ringlike resonator is studied. We use R8 to call the structure without cavities, where the number denotes the amount of holes removed per side and R8H1 for the structure with cavities in the corners.…”

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Coupled-cavity two-dimensional photonic crystal waveguide ring laser

Alija

Martínez

Postigo

et al. 2006

Applied Physics Letters

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Coupled-cavity hexagonal ringlike photonic crystal lasers are fabricated as a class of single mode photonic crystal laser light sources. The structures are formed by placing one missing hole nanocavity ͑H1 type͒ between each two segments at 60°that form the hexagonal ringlike photonic crystal laser. The H1 cavities act as a mode filter, clamping the frequency of emission of the laser device. The emission frequency in these rings with cavities varies as the filling factor is changed, allowing the tuning of the laser emission. Stable single mode lasing occurs with side mode suppression greater than 20 dB. This kind of devices may be used as an efficient selective filter of modes and may have important applications in future photonic devices for optical communications and optical sensing.

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Photonic crystal tapers for ultracompact mode conversion

Cited by 117 publications

References 11 publications

Efficient slow-light coupling in a photonic crystal waveguide without transition region

Efficient slow-light coupling in a photonic crystal waveguide without transition region

High-efficiency defect-based photonic-crystal tapers designed by a genetic algorithm

Coupled-cavity two-dimensional photonic crystal waveguide ring laser

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