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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 11 — May. 26, 2008
  • pp: 7588–7594

Laterally tapered undercut active waveguide fabricated by simple wet etching method for vertical waveguide directional coupler

Fang-Zheng Lin, Yi-Jen Chiu, Shun-An Tsai, and Tsu-Hsiu Wu  »View Author Affiliations

Optics Express, Vol. 16, Issue 11, pp. 7588-7594 (2008)

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A novel structure, namely a laterally tapered undercut active-waveguide (LTUAWG) for an optical spot-size converter (SSC) is proposed and demonstrated in this paper. Using a selectively undercut-etching-active-region (UEAR) on a laterally tapered ridge to define a LTUAWG, a vertical waveguide directional coupler (VWGDC) can be fabricated simply by a wet etching-based technique. The VWGDC comprises a top LTUAWG and a bottom passive waveguide (PWG). An electroabsorption modulator (EAM) is monolithically integrated with a LTUAWG-VWGDC serving as the connecting active waveguide (AWG) and the optical transmission testing device. Through a loss budget analysis on an EAM-integrated VWGDC, an optical mode transfer loss of -1.6 dB is observed between the PWG and the AWG. By comparing the reverse directions of optical excitation, the identical optical transmission relations with bias are observed, further verifying the high efficiency properties in a SSC. Optical misalignment tolerance is employed to test the two transferred optical modes. 1dB misalignment tolerance of ±2.9 µm (horizontal) and ±2.2 µm (vertical) is obtained from the PWG, which is better than the value of ±1.9 µm (horizontal) and ±1.6 µm (vertical) from the AWG. Far-field angle measurement shows 6.0° (horizontal) ×9.3° (vertical) and 11° (horizontal) ×20° (vertical) for the PWG and the AWG, respectively, exhibiting the capability of a mode transformer. All of these measurements are also examined by a 3D beam propagation method (BPM) showing quite consistent results. In this wet etching technique, no regrowth is needed during processing. Furthermore, UEAR processing controlled by in situ monitoring can lead to a simple way for submicron-size processing, showing that a highly reliable processing technique can thus be expected. A low cost of fabrication can also be realized, indicating that this method can be potentially used in optoelectronic integration.

© 2008 Optical Society of America

OCIS Codes
(130.2790) Integrated optics : Guided waves
(130.3120) Integrated optics : Integrated optics devices
(230.4205) Optical devices : Multiple quantum well (MQW) modulators

ToC Category:
Integrated Optics

Original Manuscript: December 3, 2007
Revised Manuscript: January 12, 2008
Manuscript Accepted: January 15, 2008
Published: May 12, 2008

Fang-Zheng Lin, Yi-jen Chiu, Shun-An Tsai, and Tsu-Hsiu Wu, "Laterally tapered undercut active waveguide fabricated by simple wet etching method for vertical waveguide directional coupler," Opt. Express 16, 7588-7594 (2008)

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