Abstract

We demonstrate a robust 3-dB directional coupler which has a narrow silicon wire core and a wide gap. Sensitivity to the gap variation is decreased to one tenth that of a conventional directional coupler. Better spectral stability due to the enhanced robustness to waveguide geometrical fluctuations was experimentally verified.

© 2014 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. K. Yamada, “Silicon photonic wire waveguides: fundamentals and applications,” in Silicon Photonics II. Topics in Applied Physics119, 1−29 (2011), D. J. Lockwood and L. Pavesi, eds. (Springer-Verlag Berlin Heidelberg, 2011).
  2. M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
    [CrossRef]
  3. T. Shoji, K. Kintaka, S. Suda, H. Kawashima, T. Hasama, H. Ishikawa, “Low-crosstalk 2 x 2 thermo-optic switch with silicon wire waveguides,” Opt. Express 18(9), 9071–9075 (2010).
    [CrossRef] [PubMed]
  4. J. Van Campenhout, W. M. Green, Y. A. Vlasov, “Design of a digital, ultra-broadband electro-optic switch for reconfigurable optical networks-on-chip,” Opt. Express 17(26), 23793–23808 (2009).
    [CrossRef] [PubMed]
  5. K. Suzuki, K. Tanizawa, T. Matsukawa, G. W. Cong, S. H. Kim, S. Suda, M. Ohno, T. Chiba, H. Tadokoro, M. Yanagihara, Y. Igarashi, M. Masahara, and H. Kawashima, “Ultra-compact Si-wire 8×8 PILOSS Switch,” PD2.D.2, ECOC2013 (London, 2013).
  6. S. Nakamura, S. Takahashi, M. Sakauchi, T. Hino, M-B. Yu, and G-Q. Lo, “Wavelength selective switching with one chip silicon photonic circuit including 8×8 matrix switch,” OFC/NFOEC 2011, OTuM2.
  7. S. Sekiguchi, T. Kurahashi, L. Zhu, K. Kawaguchi, K. Morito, “Compact and low power operation optical switch using silicon-germanium/silicon hetero-structure waveguide,” Opt. Express 20(8), 8949–8958 (2012).
    [CrossRef] [PubMed]
  8. K. Voigt, L. Zimmermann, G. Winzer, and K. Petermann, “SOI based 2×2 and 4×4 waveguide couplers – evolution from DPSK to DQPSK,” The 5th IEEE International Conference on Group IV photonics, pp. 209–211 (2008).
  9. S. Selvaraja, L. Fernandez, M. Vanslembrouck, J.-L. Everaert, P. Dumon, J. Van Campenhout, W. Bogaerts, and P. Absil, “Si photonic device uniformity improvement using wafer-scale location specific processing,” IEEE Photonics Conference 2012, pp. 725−726 (2012).
    [CrossRef]
  10. J. Van Campenhout, W. M. Green, S. Assefa, Y. A. Vlasov, “Low-power, 2 x 2 silicon electro-optic switch with 110-nm bandwidth for broadband reconfigurable optical networks,” Opt. Express 17(26), 24020–24029 (2009).
    [CrossRef] [PubMed]

2012 (1)

2010 (1)

2009 (2)

2008 (1)

M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
[CrossRef]

Assefa, S.

De La Rue, R. M.

M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
[CrossRef]

Gnan, M.

M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
[CrossRef]

Green, W. M.

Hasama, T.

Ishikawa, H.

Kawaguchi, K.

Kawashima, H.

Kintaka, K.

Kurahashi, T.

Macintyre, D. S.

M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
[CrossRef]

Morito, K.

Sekiguchi, S.

Shoji, T.

Sorel, M.

M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
[CrossRef]

Suda, S.

Thoms, S.

M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
[CrossRef]

Van Campenhout, J.

Vlasov, Y. A.

Zhu, L.

Electron. Lett. (1)

M. Gnan, S. Thoms, D. S. Macintyre, R. M. De La Rue, M. Sorel, “Fabrications of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44(2), 115–116 (2008).
[CrossRef]

Opt. Express (4)

Other (5)

K. Yamada, “Silicon photonic wire waveguides: fundamentals and applications,” in Silicon Photonics II. Topics in Applied Physics119, 1−29 (2011), D. J. Lockwood and L. Pavesi, eds. (Springer-Verlag Berlin Heidelberg, 2011).

K. Voigt, L. Zimmermann, G. Winzer, and K. Petermann, “SOI based 2×2 and 4×4 waveguide couplers – evolution from DPSK to DQPSK,” The 5th IEEE International Conference on Group IV photonics, pp. 209–211 (2008).

S. Selvaraja, L. Fernandez, M. Vanslembrouck, J.-L. Everaert, P. Dumon, J. Van Campenhout, W. Bogaerts, and P. Absil, “Si photonic device uniformity improvement using wafer-scale location specific processing,” IEEE Photonics Conference 2012, pp. 725−726 (2012).
[CrossRef]

K. Suzuki, K. Tanizawa, T. Matsukawa, G. W. Cong, S. H. Kim, S. Suda, M. Ohno, T. Chiba, H. Tadokoro, M. Yanagihara, Y. Igarashi, M. Masahara, and H. Kawashima, “Ultra-compact Si-wire 8×8 PILOSS Switch,” PD2.D.2, ECOC2013 (London, 2013).

S. Nakamura, S. Takahashi, M. Sakauchi, T. Hino, M-B. Yu, and G-Q. Lo, “Wavelength selective switching with one chip silicon photonic circuit including 8×8 matrix switch,” OFC/NFOEC 2011, OTuM2.

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (7)

Fig. 1
Fig. 1

(a) Schematic of conventional and robust directional couplers, denoted as CDC and RDC, respectively. (b) Reciprocal of the index difference (∆n) between the odd and even modes of directional couplers calculated by a mode solver. 1/∆n and the gap (g) follow a relationship of log (1/∆n) = α⋅g + β, where α and β are coefficients.

Fig. 2
Fig. 2

(a) Dependences of ∆L3dB/∆g on the gap. (b) Splitting ratio and deviation in percentage from the ratio of 0.5 for ± 20 nm gap variation at the gap of 230 nm for CDC and of 900 nm for RDC. L3dB and g denotes the 3-dB coupling length and the gap, respectively. Wavelength dependences of (c) ∆L3dB/∆g, (d) ∆L3dB/∆w and (e) ∆L3dB/∆h calculated at the gap of 900 nm for RDC and 230 nm for CDC. w: waveguide width. h: waveguide height. All subfigures were calculated using a mode solver.

Fig. 3
Fig. 3

(a) Optical microscope picture of an asymmetric MZI (AMZI). The bar and cross ports are defined respect to the port for inputting the light in. (b) Schematic of RDC. Upper numbers are waveguide widths in nm and lower numbers are section lengths in μm. The central section length is denoted as the coupling length (L). g: gap in nm. R: radius in μm. (c) and (d) are the scanning electron microscope pictures of RDC and CDC, respectively.

Fig. 4
Fig. 4

(a) Spectra at the bar and cross ports of an AMZI consisting of RDCs with the gap of 895 nm. (b) Spectra derived from the extreme values in (a). Annotated max and min mean the maximum and minimum values, respectively.

Fig. 5
Fig. 5

(a) A group of chips with the same fabricated gaps. In each chip, there is a series of AMZIs in which the coupling length (L) of directional coupler is varied with a step of 1 μm. (b) Schematic spectra of different coupling lengths in different chips. These spectra have 3-dB wavelengths close to a specified wavelength λa. T: transmission. (c) Plot of all coupling lengths from (b) to the gap. (d) Combination of subfigures (c) for different gaps. Linearly fitting the gap dependent coupling length yields the slope that is the sensitivity figure of ∆L3dB/∆g for λa. Experimental spectra of the coupling lengths selected for four gaps of (e) 850 nm,(f) 895 nm, (g) 942 nm, and (h) 995 nm. The specified wavelength λa (1542.3 nm) hits all the spectra with an extinction ratio of 20 dB or higher as indicted by the dashed green line.

Fig. 6
Fig. 6

Dependence of the 3-dB coupling length (L3dB) on the gap for (a) robust directional coupler (RDC) and (b) conventional direction coupler (CDC). (c) Wavelength dependence of ∆L3dB/∆g obtained by a linear fit from (a) and (b).

Fig. 7
Fig. 7

(a) Plot of 3-dB wavelength (λ3dB) versus the gap for constant coupling lengths. The top and bottom axes are set to the same scope. (b) Shift of 3-dB wavelength (∆λ3dB) per 10-nm gap change at several coupling lengths. The waveguide width changes are ± 10 nm for RDC and ± 5nm for CDC. Average lines are indicated. (c) 20-dB bandwidth statistics of the bar port at different gaps. (d) A spectral comparison between RDC and CDC at the gaps of 895 and 230 nm, respectively. The RDC spectra are reproductions of Fig. 4(b).

Tables (1)

Tables Icon

Table 1 Coefficient α in the equation of log(1/∆n) = α⋅g + β of CDC and RDC at transverse-electric (TE) and transverse-magnetic (TM) modes.

Metrics