Abstract

We have previously demonstrated high efficiency small-area 45° single air interface waveguide bends in a perfluorocyclobutyl (PFCB) material system [Opt. Express 12, 5314 (2004)]. In this paper we show how the loss per bend can be decreased through improved bend interface position accuracy and sidewall smoothness. This is achieved with electron-beam lithography (EBL) in a scanning electron microscope (SEM) at the cost of increased fabrication complexity compared to our previous work based on a UV contact mask aligner. Using the EBL-based fabrication process, the measured loss per bend decreases from 0.33 dB/bend to 0.124 dB/bend (97.2% bend efficiency) for TE polarization (electric field in plane) and from 0.30 dB/bend to 0.166 dB/bend (96.2% bend efficiency) for TM polarization (electric field out of plane). Since the alignment accuracy and patterning capability within a single exposure field for our low-end electron-beam lithography approach is comparable to what is achievable in high-end stepper tools, the significance of this work is that very low loss air trench bends in low refractive index and low refractive index contrast waveguide materials should be achievable using a conventional high volume microfabrication toolset.

© 2006 Optical Society of America

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References

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  1. L. Li, G. P. Nordin, J. M. English, and J. Jiang, "Small-area bends and beamsplitters for low-index-contrast waveguides," Opt. Express 11,282-290 (2003).
    [CrossRef] [PubMed]
  2. J. Cardenas, S. Kim, and G. P. Nordin, "Compact low loss single air interface bends in polymer waveguides," Opt. Express 12,5314-5324 (2004).
    [CrossRef] [PubMed]
  3. D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
    [CrossRef]
  4. D. W. Smith, Jr., A. B. Hoeglund, H. V. Shah, M. J. Radler, C. A. Langhoff, "Perfluorocyclobutane Polymers for Optical Fibers and Dielectric Waveguides," in Optical Polymers, J. Harmon, ed., ACS Symp. Ser. 795, Chap. 4, pp. 49-62 (2001).
    [CrossRef]
  5. J. Ballato, D. W. SmithJr, and S. H. Foulger, "Optical Properties of Perfluorocyclobutyl (PFCB) Polymers," J. Opt. Soc. Am. B 20, 1838-1843 (2003).
    [CrossRef]
  6. M. J. Madou, "Lithography," in Fundamentals of Microfabrication: The Science of Miniaturization, 2nd ed. (CRC Press, Fla., 2002) pp. 28-29.

2004

2003

2002

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

Ballato, J.

J. Ballato, D. W. SmithJr, and S. H. Foulger, "Optical Properties of Perfluorocyclobutyl (PFCB) Polymers," J. Opt. Soc. Am. B 20, 1838-1843 (2003).
[CrossRef]

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

Cardenas, J.

Chen, S.

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

English, J. M.

Foulger, S. H.

J. Ballato, D. W. SmithJr, and S. H. Foulger, "Optical Properties of Perfluorocyclobutyl (PFCB) Polymers," J. Opt. Soc. Am. B 20, 1838-1843 (2003).
[CrossRef]

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

Jiang, J.

Kim, S.

Kumar, S.

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

Li, L.

Nordin, G. P.

Shah, H.

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

Smith, D. W.

J. Ballato, D. W. SmithJr, and S. H. Foulger, "Optical Properties of Perfluorocyclobutyl (PFCB) Polymers," J. Opt. Soc. Am. B 20, 1838-1843 (2003).
[CrossRef]

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

Topping, C.

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

J. Opt. Soc. Am. B

Opt. Express

S. Adv. Mater.

D. W. Smith, Jr., S. Chen, S. Kumar, J. Ballato, H. Shah, C. Topping, and S. H. Foulger, "Perfluorocyclobutyl Copolymers for Microphotonics," S. Adv. Mater. 14, pp. 1585-1589 (2002).
[CrossRef]

Other

D. W. Smith, Jr., A. B. Hoeglund, H. V. Shah, M. J. Radler, C. A. Langhoff, "Perfluorocyclobutane Polymers for Optical Fibers and Dielectric Waveguides," in Optical Polymers, J. Harmon, ed., ACS Symp. Ser. 795, Chap. 4, pp. 49-62 (2001).
[CrossRef]

M. J. Madou, "Lithography," in Fundamentals of Microfabrication: The Science of Miniaturization, 2nd ed. (CRC Press, Fla., 2002) pp. 28-29.

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Figures (11)

Fig. 1.
Fig. 1.

PFCB waveguide bend geometry. (a) Cross section of PFCB channel waveguide structure on top of silicon substrate. (b) Top view of air trench and waveguide structure; Z defines the distance from the intersection of the center lines of the input and output waveguides to the air trench interface in a direction normal to the interface. (c) Schematic diagram of bend angle definition.

Fig. 2.
Fig. 2.

The bend efficiency as a function of the parameter Z defined in Fig. 1 (after Ref. 2).

Fig. 3.
Fig. 3.

Microscope images of verniers in (a) 120 µm×120 µm and (b) 1,000 µm×1,000 µm exposure fields. The light colored vernier scales in each pair are 57.5 µm long optically patterned Cr/Au (5 nm/50 nm thick) on a silicon substrate. EBL alignment marks (not shown) are patterned in each corner of each exposure field in the same lithography step. The blue colored vernier scales are exposed and developed regions of 400 nm thick e-beam resist, ZEP 520. They are patterned with e-beam lithography using the NPGS two-level autoalignment feature.

Fig. 4.
Fig. 4.

Mask layout for a set of equal length waveguides, each with a different number of air trench bends. See text for details.

Fig. 5.
Fig. 5.

Schematic illustration of fabrication process. See text for details.

Fig. 6.
Fig. 6.

Optical microscope image of the sample at different steps in the fabrication process: (a) after Cr/Au lift off, (b) after ICP-RIE waveguide etch, (c) after the removal of upper cladding material on top of the Au alignment mark regions, (d) after the deep air trench ICP-RIE etch and before strip of the Al etch mask.

Fig. 7.
Fig. 7.

(a). Au alignment marks after the opening etch is not electrically connected to the Al etch mask which results in charging during alignment. (b) 30 nm sputtered Al eliminates this problem and still permits imaging of the Au alignment mark.

Fig. 8.
Fig. 8.

SEM image of single air trench bend.

Fig. 9.
Fig. 9.

SEM image of a typical sidewall after deep anisotropic ICP-RIE air trench etch.

Fig. 10.
Fig. 10.

Measured loss of the PFCB waveguide air trench bend as a function of number of bends at λ=1.55 µm for TE and TM polarization. Error bars are not included since they are smaller than the markers used to indicate the experimental measurement results.

Fig. 11.
Fig. 11.

Normalized transmission spectrum for the waveguide with 12 bends.

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