## Compact filters and demultiplexers based on long-range air-hole assisted subwavelength waveguides |

Optics Express, Vol. 21, Issue 23, pp. 28456-28468 (2013)

http://dx.doi.org/10.1364/OE.21.028456

Acrobat PDF (2434 KB)

### Abstract

Compact filters and demultiplexers based on long-range air-hole assisted subwavelength (LR-AHAS) waveguides have been proposed and numerically demonstrated. The tunable reflective filters possess the characters of high extinction ratio (17.5dB) and narrow bandwidth (10.1nm). The average demultiplexing bandwidth of a 1 × 3 wavelength demultiplexer based on LR-AHAS waveguide is 17.3 nm. The drop efficiencies can be significantly enhanced up to 60% by employing proposed filters in the structure. With distinguished wavelength-filtering/dropping characters and compact footprints, the proposed filters and demultiplexers could become the fundamental signal processing components in the LR-AHAS waveguides for large-scale photonic integrations.

© 2013 Optical Society of America

## 1. Introduction

1. Y. A. Vlasov and S. J. McNab, “Losses in single-mode silicon-on-insulator strip waveguides and bends,” Opt. Express **12**(8), 1622–1631 (2004). [CrossRef] [PubMed]

2. K. Yamada, T. Shoji, T. Tsuchizawa, T. Watanabe, J. Takahashi, and S. Itabashi, “Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges,” Opt. Lett. **28**(18), 1663–1664 (2003). [CrossRef] [PubMed]

3. J. Dionne, L. Sweatlock, H. Atwater, and A. Polman, “Plasmon slot waveguides: Towards chip-scale propagation with subwavelength-scale localization,” Phys. Rev. B **73**(3), 035407 (2006). [CrossRef]

4. R. Oulton, V. Sorger, D. Genov, D. Pile, and X. Zhang, “A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation,” Nat. Photonics **2**(8), 496–500 (2008). [CrossRef]

5. D. Dai, Y. Shi, S. He, L. Wosinski, and L. Thylen, “Gain enhancement in a hybrid plasmonic nano-waveguide with a low-index or high-index gain medium,” Opt. Express **19**(14), 12925–12936 (2011). [CrossRef] [PubMed]

6. Z. Han and S. I. Bozhevolnyi, “Radiation guiding with surface plasmon polaritons,” Rep. Prog. Phys. **76**(1), 016402 (2013). [CrossRef] [PubMed]

7. T. Holmgaard, J. Gosciniak, and S. I. Bozhevolnyi, “Long-range dielectric-loaded surface plasmon-polariton waveguides,” Opt. Express **18**(22), 23009–23015 (2010). [CrossRef] [PubMed]

8. W. Zhou and X. G. Huang, “Long-range air-hole assisted subwavelength waveguides,” Nanotechnology **24**(23), 235203 (2013). [CrossRef] [PubMed]

^{−1}) can be boosted with a smaller value of the center-to-center separation (1.14 μm). In contrast, the separation and integration density are respectively 2.8 μm and 357 mm

^{−1}for silicon waveguides with a typical waveguide width of 500 nm at the same isolation level, based on our simulation results (detail in Appendix B). Here, we should emphasize that LR-AHAS waveguide performs broad optical bandwidth (1.47-1.80 μm) and almost 100% transmittances in the wavelength range from 1.48 to 1.65 μm in the transmission spectrum of the straight LR-AHAS waveguide, which is decided by the propagation loss of the fundamental mode transmitted in the LR-AHAS waveguide without back-refection. Besides that, it will be gradually influenced by the Bragg-reflection in the z-direction or multimode state with larger propagation loss of the higher-order modes for the wavelength larger than 1.65 μm or shorter than 1.48 μm, which give rise to slight drops in the transmission spectrum of the straight LR-AHAS waveguide. The calculated figure of merit (FOM) and corresponding integration density for the LR-AHAS waveguide are 6 × 10

^{8}and 877 mm

^{−1}, which achieved two orders of and a nearly five times improvement compared to the long-rang surface plasmon polariton (LR-SPP) waveguide with the best FOM [6

6. Z. Han and S. I. Bozhevolnyi, “Radiation guiding with surface plasmon polaritons,” Rep. Prog. Phys. **76**(1), 016402 (2013). [CrossRef] [PubMed]

9. S. Zamek, D. T. Tan, M. Khajavikhan, M. Ayache, M. P. Nezhad, and Y. Fainman, “Compact chip-scale filter based on curved waveguide Bragg gratings,” Opt. Lett. **35**(20), 3477–3479 (2010). [CrossRef] [PubMed]

10. A. Boltasseva, S. Bozhevolnyi, T. Nikolajsen, and K. Leosson, “Compact Bragg gratings for long-range surface plasmon polaritons,” J. Lightwave Technol. **24**(2), 912–918 (2006). [CrossRef]

11. Q. Xu and M. Lipson, “Carrier-induced optical bistability in silicon ring resonators,” Opt. Lett. **31**(3), 341–343 (2006). [CrossRef] [PubMed]

12. T. Holmgaard, Z. Chen, S. Bozhevolnyi, L. Markey, A. Dereux, A. Krasavin, and A. Zayats, “Wavelength selection by dielectric-loaded plasmonic components,” Appl. Phys. Lett. **94**(5), 051111 (2009). [CrossRef]

## 2. Characteristics and principles of in-line stub-like (ILSL) filters based on LR-AHAS waveguides

*r*

_{e}≥ 0.35•

*Period*) in the same column can constitute a Bragg mirror with high reflectivity, which means that a pair of Bragg mirrors (four enlarged air-holes in the same column) at left or right side of silicon core can confine the local resonant light in the z direction. To provide strong localization in the z-direction, we tried to enlarge eight air-holes at top and bottom sides of the centre row at the same time, however, the radius of right centered air-hole between a pair of Bragg mirrors should be very close to or larger than that of the enlarged air-holes in the Bragg mirror in case of the splitting (two) resonant dips emerged in the spectrum instead of only a single dip due to the formation of double stubs with different cavity sizes in the same row. To exclude the splitting resonant dips, we enlarged nine air-holes in the ILSL region at the same time, and the standing wave pattern will obviously emerge at the stub junction under the resonant condition, and the incident light will be highly reflected back as shown in the upper contour profile of Fig. 1(d). The directions of the k-vectors of resonant light and incident light are almost orthogonal. As a result, the filtering phenomenon of the ILSL region can be comprehended with the coherent interference between the scattering light denoted by the red arrow, which is partly splitting (or escaping) from the resonant light caused by the T-shaped splitting structure, and the z-direction transmitted light, which is represented by the blue arrows as shown in Fig. 1(b). More interestingly, the reflective peak wavelength can be easily tuned and blue shifted by compressing the duty circle of the silicon core in the ILSL region. Later, we will discuss the above phenomena based on the simple and robust model.

*r*

_{s},

*r*

_{e}and

*r*are respectively the radii of the defective air-hole (the smallest one in ILSL region), the rest nine air-holes in the ILSL region and the assisting air-holes in the LR-AHAS waveguides.

*l*

_{r}denotes the distance between the centers of two adjacent air-holes in the same row.

*l*

_{s}is the distance between the centers of the defective air-hole and its adjacent ones in the same column, while the distance of all the rest adjacent air-holes in the same column is defined as the symbol

*Period*because of the periodic distribution in the z direction.

*w*

_{s}and

*w*

_{m}denote the width of the silicon core and the metallic sidewalls, respectively. The symbols of ε

_{a}, ε

_{s}, and ε

_{m}are the relative permittivity of air, silicon, and metal, respectively.

*l*

_{r}= 745 nm,

*l*

_{s}= 410 nm,

*r*= 130 nm,

*Period*= 430 nm,

*w*

_{s}= 1.04 μm,

*w*

_{m}= 100 nm, ε

_{a}= 1, and ε

_{s}= 12.25. The metal is silver, whose relative permittivity ε

_{m}can be described by the well-known Drude model with (ε

_{∞}, ω

_{p}, γ) = (3.7, 9.1eV, 0.018eV) [13

13. X. S. Lin and X. G. Huang, “Tooth-shaped plasmonic waveguide filters with nanometeric sizes,” Opt. Lett. **33**(23), 2874–2876 (2008). [CrossRef] [PubMed]

_{∞}is the dielectric constant at the infinite frequency, γ and ω

_{p}represent the electron collision frequency and bulk plasma frequency, respectively. The grid size is 5nm for both x and z directions and perfectly matched layers (PML) conditions are applied to all the boundaries. In addition, we should emphasize that the value of

*w*

_{s}should be kept in a proper range, such as 0.86 tο 1.16 μm for the ILSL filter with

*r*

_{e}= 0.38•

*Period*, to observe obvious wavelength filtering phenomena in the spectra. On the other hand, the propagation length will decrease if

*w*

_{s}becomes smaller because more portion of light will contact with lossy metal.

*w*

_{s}was chosen as 1.04 μm to make sure that the LR-AHAS waveguide has both the merits of compact configuration and optimal propagation length.

*φ*(

*λ*) is the total phase shift and equals (

*φ*

_{1}+

*φ*

_{2}+

*φ*

_{s}).

*φ*

_{1}and

*φ*

_{2}are phase shifts caused by the reflections at two different silver-dielectric interfaces, and

*φ*

_{s}is the one caused by the scattering. The left silver-silicon interface is set as the zero point of x axis.

*n*(

_{eff}*x*,

*λ*) is the effective refractive index at position

*x*with a specific wavelength. If the change of the effective index is approximated as one-dimensional problem along the x axis, the effective length

*L*is the integral of

_{eff}*n*(

_{eff}*x*,

*λ*) from zero point to

*w*

_{s}. When the phase delay satisfies (2m + 1)π, the resonant wavelength is given by:Thus, the resonant wavelength can be easily tuned by changing the effective length of the cavity.

*Period*. The length

*L*of the silicon material in the cavity is decreased with the increase in the radius

*r*of the one air-hole, with the expression of Δ

*L*= −Δ

*r*. As a result, the effective length, and thus the resonant wavelength are decreased. From the blue line in Fig. 2(a), the original resonant wavelength is 1.624 μm. When Δ

*L*is −30 nm, the resonant wavelength is shifted to 1.569 μm. The other factor to influence the resonant wavelength is the width of the stub. A pair of Bragg mirrors were moved closer, as shown in the red dotted circles in the inset of Fig. 2(a). When Δ

*W*equals −30 nm, the resonant wavelength is shifted from 1.624 to 1.621 μm (Δ

*λ*= 3 nm). The slope of the red line is much smaller than the blue one. This can be comprehended that the effective refractive index is decreased a little as a pair of Bragg mirrors get closer, which derives small decrease in the integral of

*n*(

_{eff}*x*,

*λ*) and thus small decrease in the effective length. Both the major and the minor variation factors prove that the resonant cavity is between two metal-dielectric interfaces, and it is in accordance with field evolution of the standing wave patterns shown in Fig. 2(b).

*r*

_{e}as 0.38•

*Period*and 0.41•

*Period*, while varying the radius of the defective air-hole. Obviously, by decreasing the size of the defective air-hole, the resonant wavelength can be red-shifted. The minimum transmittances of the red and cyan curves are smaller than the rest ones. Therefore, the defective air-hole acts as the scattering or obstructive object for the resonant light. To obtain a high extinction ratio, the defective air-hole should be removed from the ILSL filter. And under this condition, the spectra of the proposed filters with five different values of

*r*

_{e}were investigated as shown in Fig. 2(d). The resonant wavelength is blue shifted while increasing the value of

*r*

_{e}. It can be comprehended that the effective length of the resonator is decreased. For the above five structures with

*r*

_{e}from 0.38 to 0.42•

*Period*, the Q-factors are 143.2, 147.0, 149.6, 167.5, and 184.3, respectively. The average values of FWHM and minimum transmittance at the spectral dips are 10.1 nm and −17.5 dB. Because the performances of plasmonic single stub filters [13

13. X. S. Lin and X. G. Huang, “Tooth-shaped plasmonic waveguide filters with nanometeric sizes,” Opt. Lett. **33**(23), 2874–2876 (2008). [CrossRef] [PubMed]

15. J. Tao, X. Huang, and S. Liu, “Optical characteristics of surface plasmon nanonotch structure,” J. Opt. Soc. Am. B **27**(7), 1430–1434 (2010). [CrossRef]

^{−1}) can be maintained because of the in-line configuration without the lateral extension or opening the silver sidewalls.

16. X. Piao, S. Yu, S. Koo, K. Lee, and N. Park, “Fano-type spectral asymmetry and its control for plasmonic metal-insulator-metal stub structures,” Opt. Express **19**(11), 10907–10912 (2011). [CrossRef] [PubMed]

*n*(

_{eff}*x*,

*λ*) and

*L*are effective index and length of the stub, respectively.

*A*

_{R}= 2(ω−ω

_{R})/Γ

_{0}is the asymmetry factor, which determines asymmetry strength. ω

_{R}is the resonance frequency of the junction resonator, Γ

_{0}is the FWHM of the junction resonator. Depending on the sign of the phase term sin

*ϕ*around the operation frequency, the transmittance of stub becomes to have spectral asymmetry.

_{f}can be embedded in the centre of the ILSL filter. Through modifying the n

_{f}, one can adjust the resonance frequency (ω

_{R}) or FWHM (Γ

_{0}) of the junction resonator. As a result, the asymmetry factor (

*A*

_{R}) as well as Fano asymmetry of spectrum can be controlled.

_{f}= 2, the lineshape of spectrum is nearly symmetrical (

*A*

_{R}~0) at the wavelength near resonant dip (λ = 1.546 μm), and the corresponding FWHM is 4.8 nm (Q-factor = 322). Increasing n

_{f}to larger value, the Fano-type asymmetry will gradually occur. Especially, the strong Fano-type resonance can be seen in Fig. 3(e), whose resonant wavelength is 1.555 μm and FWHM is 15.9 nm. Strong Fano-asymmetry in the spectrum accompanied by the emergence of local mode in the junction resonator shown as the inset in Fig. 3(e). As a result, the asymmetry factor (

*A*

_{R}) is tunable by employing different refractive index material in the junction resonator, which can increase the sensitivity of the filter, compress FWHM at a symmetrical point and may find potential application in the low-power optical switching devices [17

17. X. Piao, S. Yu, and N. Park, “Control of Fano asymmetry in plasmon induced transparency and its application to plasmonic waveguide modulator,” Opt. Express **20**(17), 18994–18999 (2012). [CrossRef] [PubMed]

## 3. Characteristics and dropping efficiencies enhancement of wavelength demultiplexers based on LR-AHAS waveguides

*w*

_{dc}and

*w*

_{dm}, and are chosen to be

*w*

_{dc}= 0.3 μm and

*w*

_{dm}= 0.25 μm. The relation between the transmission efficiency of the ILSL CDF (

*r*

_{e}= 0.38•

*Period*and

*r*

_{s}= 0) and the thickness of the silver gap is investigated, and is shown as the black curve with triangle dots in Fig. 4(c). When the thickness of the silver gap equals 20 nm, the transmittance is 0.396. It follows exponential decay as increasing the thickness of the silver gap. The transmittance is nearly zero when the thickness equals 50 nm. As a result, the thickness of 20 nm is chosen for ILSL CDFs in the following.

*r*

_{e}= 0.42•

*Period*. The corresponding values of the FWHM are also plotted as the blue circles in Fig. 4(b), all of which are between 10 nm and 20 nm. The average value of the FWHM is calculated as 16.2 nm, which is a little larger than that of the ILSL filter because a portion of light is coupled to the dropping waveguide as well as the additional coupling loss, which reduce the Q-factor of the stub-like resonator.

18. H. Lu, X. Liu, Y. Gong, D. Mao, and L. Wang, “Enhancement of transmission efficiency of nanoplasmonic wavelength demultiplexer based on channel drop filters and reflection nanocavities,” Opt. Express **19**(14), 12885–12890 (2011). [CrossRef] [PubMed]

*S*. Based on the resonant tunneling effect, the dropping efficiency can be maximally enhanced if the phase shift

*φ*( = 2π

*S*•

*n*/

_{eff}*λ*) corresponding to the center-to-center separation satisfies (2m’ + 1)π/2, where m’ is an integer. It gives

*S*= (2m’ + 1)

*λ*/(4

*n*). Here, the radius of each air-hole in the ILSL CDF and the ILSL filter is chosen as 0.38•

_{eff}*Period*, one can adjust the center-to-center separation to reinforce the dropping efficiencies. The effective index of the TE-eigenmode in the LR-AHAS waveguide with

*r*

_{e}of 0.38•

*Period*is 3.24, by utilizing the supercell technique as described in the previous article [8

8. W. Zhou and X. G. Huang, “Long-range air-hole assisted subwavelength waveguides,” Nanotechnology **24**(23), 235203 (2013). [CrossRef] [PubMed]

*λ*= 1.628 μm,

*S*is calculated to be 2.14 μm. According to the simulation results shown as the blue curve with triangular dots in Fig. 4(c), the dropping efficiencies can be significantly enhanced from 0.396 to the maximum value of 0.63, when the center-to-center separation equals 2.16 μm, which is close to the theoretical value.

*r*

_{1},

*r*

_{2}, and

*r*

_{3}, respectively. Here, we choose

*r*

_{1}= 0.35•

*Period*,

*r*

_{2}= 0.39•

*Period*, and

*r*

_{3}= 0.42•

*Period*, while the radius of each assisting air-hole in the LR-AHAS waveguide maintains the same value. The corresponding dropping wavelengths for three channels are 1.675 μm, 1.614 μm and 1.554 μm. When the light with one of the resonant wavelengths incidents from the bottom of the demultiplexer, a standing wave will be formed at the corresponding demultiplexing unit, and the energy is partially coupled to its dropping channel. As shown in Fig. 5(b), the peak transmittances of three dropping channels are 34.8%, 38.5% and 35.5%, respectively. The FWHMs of the first channel to the third one are 18.9 nm, 17.5 nm, and 16.9 nm. While the average value of the FWHM is around 120 nm for the plasmonic wavelength demultiplexers [19

19. J. Tao, X. G. Huang, and J. H. Zhu, “A wavelength demultiplexing structure based on metal-dielectric-metal plasmonic nano-capillary resonators,” Opt. Express **18**(11), 11111–11116 (2010). [CrossRef] [PubMed]

21. G. Wang, H. Lu, X. Liu, D. Mao, and L. Duan, “Tunable multi-channel wavelength demultiplexer based on MIM plasmonic nanodisk resonators at telecommunication regime,” Opt. Express **19**(4), 3513–3518 (2011). [CrossRef] [PubMed]

*r*

_{i}. One can adjust the center-to-center separation

*S*

_{i}to enhance the drop efficiency. When

*S*

_{1}~

*S*

_{3}are chosen as 2.21 μm, 2.11 μm, and 2.31 μm, the drop efficiencies from the first channel to the third one are respectively increased to be 61.4%, 64.3% and 65.0%, as shown in Fig. 5(b). The drop efficiencies are improved by more than 65% compared to the case without ILSL filters. The FWHMs of the drop efficiency enhanced structure are 16.2 nm, 18.87 nm, and 16.8 nm, respectively. Thus, the proposed 1 × 3 wavelength demultiplexer has important potential for the design of narrow bandwidth and highly efficient WDM systems in large-scale photonic integrated circuits.

## 4. Conclusion

## Appendix A

*N*(z)=

*n*(z)/

_{Si}W_{Si}*W*+

_{total}*n*(z)

_{air}W_{air}*/W*. And

_{total}*W*(

_{total}= W_{Si}*z*)

*+ W*(

_{air}*z*), where

*W*(

_{Si}*z*) and

*W*(

_{air}*z*) are respectively local widths of silicon and air-hole in region I or II at the coordinate of z.

*n*(λ). When the wavelength is far away from the Bragg wavelengths or transmission dips of the LR-AHAS waveguide, one can make further approximation to neglect the Bragg-effect in propagation direction. Based on negligible Bragg reflection and the effective index approximation, the right structure in Fig. 6(b) gives the equivalent treatment for the left equivalent waveguide of a period of a LR-AHAS waveguide.

_{eff}*ε*is the effective relative permittivity for regions I and II. Here, we define

_{eff}*n*=

_{eff}*p*·

*n*+(1-

_{air}*p*)·

*n*, where

_{Si}*p*=πR

^{2}/(

*Period*·

*d*

_{2}),

*d*

_{2}=0.295 μm,

*d*

_{1}=0.45 μm,

*R*=0.13 μm and

*Period*=0.43 μm. Thus

*ε*

_{eff}= n_{eff}^{2}= 6.02. The transverse electric-field of TE

_{0}mode in the equivalent waveguide can be generally written a

8. W. Zhou and X. G. Huang, “Long-range air-hole assisted subwavelength waveguides,” Nanotechnology **24**(23), 235203 (2013). [CrossRef] [PubMed]

**24**(23), 235203 (2013). [CrossRef] [PubMed]

## Appendix B

*Width*and the

*Length*of silicon waveguides are respectively chosen as a typical number of 500 nm and 100 μm. For the isolation of 50.3 dB, the separation between two silicon waveguides is 2.8 μm, while the separation between two LR-AHAS waveguides is 1.14 μm. If the integration density is defined to be the number of parallelly-integrated waveguides with the high isolation over 50 dB in one millimeter in the x direction, the integration densities of LR-AHAS waveguides and silicon waveguides are 877 mm

^{−1}and 357 mm

^{−1}, respectively. Inset of Fig. 8 shows a vivid comparison between LR-AHAS waveguide array and silicon waveguide array to highlight the difference in terms of on-chip integration density.

^{−1}) is maintained when the filters are integrated into the LR-AHAS waveguides.

## Acknowledgments

## References and links

1. | Y. A. Vlasov and S. J. McNab, “Losses in single-mode silicon-on-insulator strip waveguides and bends,” Opt. Express |

2. | K. Yamada, T. Shoji, T. Tsuchizawa, T. Watanabe, J. Takahashi, and S. Itabashi, “Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges,” Opt. Lett. |

3. | J. Dionne, L. Sweatlock, H. Atwater, and A. Polman, “Plasmon slot waveguides: Towards chip-scale propagation with subwavelength-scale localization,” Phys. Rev. B |

4. | R. Oulton, V. Sorger, D. Genov, D. Pile, and X. Zhang, “A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation,” Nat. Photonics |

5. | D. Dai, Y. Shi, S. He, L. Wosinski, and L. Thylen, “Gain enhancement in a hybrid plasmonic nano-waveguide with a low-index or high-index gain medium,” Opt. Express |

6. | Z. Han and S. I. Bozhevolnyi, “Radiation guiding with surface plasmon polaritons,” Rep. Prog. Phys. |

7. | T. Holmgaard, J. Gosciniak, and S. I. Bozhevolnyi, “Long-range dielectric-loaded surface plasmon-polariton waveguides,” Opt. Express |

8. | W. Zhou and X. G. Huang, “Long-range air-hole assisted subwavelength waveguides,” Nanotechnology |

9. | S. Zamek, D. T. Tan, M. Khajavikhan, M. Ayache, M. P. Nezhad, and Y. Fainman, “Compact chip-scale filter based on curved waveguide Bragg gratings,” Opt. Lett. |

10. | A. Boltasseva, S. Bozhevolnyi, T. Nikolajsen, and K. Leosson, “Compact Bragg gratings for long-range surface plasmon polaritons,” J. Lightwave Technol. |

11. | Q. Xu and M. Lipson, “Carrier-induced optical bistability in silicon ring resonators,” Opt. Lett. |

12. | T. Holmgaard, Z. Chen, S. Bozhevolnyi, L. Markey, A. Dereux, A. Krasavin, and A. Zayats, “Wavelength selection by dielectric-loaded plasmonic components,” Appl. Phys. Lett. |

13. | X. S. Lin and X. G. Huang, “Tooth-shaped plasmonic waveguide filters with nanometeric sizes,” Opt. Lett. |

14. | X. Lin and X. Huang, “Numerical modeling of a teeth-shaped nanoplasmonic waveguide filter,” J. Opt. Soc. Am. B |

15. | J. Tao, X. Huang, and S. Liu, “Optical characteristics of surface plasmon nanonotch structure,” J. Opt. Soc. Am. B |

16. | X. Piao, S. Yu, S. Koo, K. Lee, and N. Park, “Fano-type spectral asymmetry and its control for plasmonic metal-insulator-metal stub structures,” Opt. Express |

17. | X. Piao, S. Yu, and N. Park, “Control of Fano asymmetry in plasmon induced transparency and its application to plasmonic waveguide modulator,” Opt. Express |

18. | H. Lu, X. Liu, Y. Gong, D. Mao, and L. Wang, “Enhancement of transmission efficiency of nanoplasmonic wavelength demultiplexer based on channel drop filters and reflection nanocavities,” Opt. Express |

19. | J. Tao, X. G. Huang, and J. H. Zhu, “A wavelength demultiplexing structure based on metal-dielectric-metal plasmonic nano-capillary resonators,” Opt. Express |

20. | F. Hu, H. Yi, and Z. Zhou, “Wavelength demultiplexing structure based on arrayed plasmonic slot cavities,” Opt. Lett. |

21. | G. Wang, H. Lu, X. Liu, D. Mao, and L. Duan, “Tunable multi-channel wavelength demultiplexer based on MIM plasmonic nanodisk resonators at telecommunication regime,” Opt. Express |

**OCIS Codes**

(060.4230) Fiber optics and optical communications : Multiplexing

(130.3120) Integrated optics : Integrated optics devices

(140.4780) Lasers and laser optics : Optical resonators

(230.7370) Optical devices : Waveguides

(130.7408) Integrated optics : Wavelength filtering devices

**ToC Category:**

Integrated Optics

**History**

Original Manuscript: August 21, 2013

Revised Manuscript: October 22, 2013

Manuscript Accepted: November 1, 2013

Published: November 12, 2013

**Citation**

Wen Zhou and Xu Guang Huang, "Compact filters and demultiplexers based on long-range air-hole assisted subwavelength waveguides," Opt. Express **21**, 28456-28468 (2013)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-23-28456

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### References

- Y. A. Vlasov and S. J. McNab, “Losses in single-mode silicon-on-insulator strip waveguides and bends,” Opt. Express12(8), 1622–1631 (2004). [CrossRef] [PubMed]
- K. Yamada, T. Shoji, T. Tsuchizawa, T. Watanabe, J. Takahashi, and S. Itabashi, “Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges,” Opt. Lett.28(18), 1663–1664 (2003). [CrossRef] [PubMed]
- J. Dionne, L. Sweatlock, H. Atwater, and A. Polman, “Plasmon slot waveguides: Towards chip-scale propagation with subwavelength-scale localization,” Phys. Rev. B73(3), 035407 (2006). [CrossRef]
- R. Oulton, V. Sorger, D. Genov, D. Pile, and X. Zhang, “A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation,” Nat. Photonics2(8), 496–500 (2008). [CrossRef]
- D. Dai, Y. Shi, S. He, L. Wosinski, and L. Thylen, “Gain enhancement in a hybrid plasmonic nano-waveguide with a low-index or high-index gain medium,” Opt. Express19(14), 12925–12936 (2011). [CrossRef] [PubMed]
- Z. Han and S. I. Bozhevolnyi, “Radiation guiding with surface plasmon polaritons,” Rep. Prog. Phys.76(1), 016402 (2013). [CrossRef] [PubMed]
- T. Holmgaard, J. Gosciniak, and S. I. Bozhevolnyi, “Long-range dielectric-loaded surface plasmon-polariton waveguides,” Opt. Express18(22), 23009–23015 (2010). [CrossRef] [PubMed]
- W. Zhou and X. G. Huang, “Long-range air-hole assisted subwavelength waveguides,” Nanotechnology24(23), 235203 (2013). [CrossRef] [PubMed]
- S. Zamek, D. T. Tan, M. Khajavikhan, M. Ayache, M. P. Nezhad, and Y. Fainman, “Compact chip-scale filter based on curved waveguide Bragg gratings,” Opt. Lett.35(20), 3477–3479 (2010). [CrossRef] [PubMed]
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