A. Li, X. Chen, A. Al Almin, and W. Shieh, “Fused fiber mode couplers for few-mode transmission,” Photon. Technol. Lett., vol. 24, no. 21, pp. 1953–1956, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

B. Huang, C. Xia, G. Matz, N. Bai, and G. Li, “Structured directional coupler pair for multiplexing of degenerate modes,” in Proc. Opt. Fiber Commun. Conf., OSA Tech. Dig., 2013, Paper JW2A.25.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

W.-J. Chen, S. M. Eaton, H. Zhang, and P. R. Herman, “Broadband directional couplers fabricated in bulk glass with high repetition rate femtosecond laser pulses,” Opt. Exp., vol. 16, no. 15, pp. 11470–11480, 2008.

A. Li, X. Chen, A. Al Almin, and W. Shieh, “Fused fiber mode couplers for few-mode transmission,” Photon. Technol. Lett., vol. 24, no. 21, pp. 1953–1956, 2012.

W.-J. Chen, S. M. Eaton, H. Zhang, and P. R. Herman, “Broadband directional couplers fabricated in bulk glass with high repetition rate femtosecond laser pulses,” Opt. Exp., vol. 16, no. 15, pp. 11470–11480, 2008.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 $\times$ 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Exp., vol. 14, no. 6, pp. 2335–2343, 2006.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

N. Hanzawa, “Demonstration of mode-division multiplexing transmission over 10 km two-mode fiber with mode coupler,” presented at the Opt. Fiber Commun. Conf., Los Angeles, CA, USA, 2011, Paper OWA4.

W.-J. Chen, S. M. Eaton, H. Zhang, and P. R. Herman, “Broadband directional couplers fabricated in bulk glass with high repetition rate femtosecond laser pulses,” Opt. Exp., vol. 16, no. 15, pp. 11470–11480, 2008.

C. M. Herzinger, B. Johs, W. A. McGahan, J. A. Woollam, and W. Paulson, “Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation,” J. Appl. Phys., vol. 83, no. 6, pp. 3323–3336, 1998.

B. Huang, C. Xia, G. Matz, N. Bai, and G. Li, “Structured directional coupler pair for multiplexing of degenerate modes,” in Proc. Opt. Fiber Commun. Conf., OSA Tech. Dig., 2013, Paper JW2A.25.

K. Y. Song, I. K. Hwang, S. H. Yun, and B. Y. Kim, “High performance fused-type mode-selective coupler using elliptical core two-mode fiber at 1550 nm,” Photon. Technol. Lett., vol. 14, no. 4, pp. 501–503, 2002.

K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 $\times$ 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Exp., vol. 14, no. 6, pp. 2335–2343, 2006.

C. M. Herzinger, B. Johs, W. A. McGahan, J. A. Woollam, and W. Paulson, “Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation,” J. Appl. Phys., vol. 83, no. 6, pp. 3323–3336, 1998.

N. Jovanovic, “Direct laser written multimode waveguides for astronomical applications,” Proc. SPIE, vol. 7739, pp. 773923-1–773923-8, 2010.

K. Y. Song, I. K. Hwang, S. H. Yun, and B. Y. Kim, “High performance fused-type mode-selective coupler using elliptical core two-mode fiber at 1550 nm,” Photon. Technol. Lett., vol. 14, no. 4, pp. 501–503, 2002.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

A. Li, X. Chen, A. Al Almin, and W. Shieh, “Fused fiber mode couplers for few-mode transmission,” Photon. Technol. Lett., vol. 24, no. 21, pp. 1953–1956, 2012.

B. Huang, C. Xia, G. Matz, N. Bai, and G. Li, “Structured directional coupler pair for multiplexing of degenerate modes,” in Proc. Opt. Fiber Commun. Conf., OSA Tech. Dig., 2013, Paper JW2A.25.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

B. Huang, C. Xia, G. Matz, N. Bai, and G. Li, “Structured directional coupler pair for multiplexing of degenerate modes,” in Proc. Opt. Fiber Commun. Conf., OSA Tech. Dig., 2013, Paper JW2A.25.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

C. M. Herzinger, B. Johs, W. A. McGahan, J. A. Woollam, and W. Paulson, “Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation,” J. Appl. Phys., vol. 83, no. 6, pp. 3323–3336, 1998.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 $\times$ 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Exp., vol. 14, no. 6, pp. 2335–2343, 2006.

K. Okamoto, Fundamentals of Optical Waveguides.New York, NY, USA: Elsevier, 2006.

C. M. Herzinger, B. Johs, W. A. McGahan, J. A. Woollam, and W. Paulson, “Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation,” J. Appl. Phys., vol. 83, no. 6, pp. 3323–3336, 1998.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 $\times$ 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Exp., vol. 14, no. 6, pp. 2335–2343, 2006.

A. Li, X. Chen, A. Al Almin, and W. Shieh, “Fused fiber mode couplers for few-mode transmission,” Photon. Technol. Lett., vol. 24, no. 21, pp. 1953–1956, 2012.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

K. Y. Song, I. K. Hwang, S. H. Yun, and B. Y. Kim, “High performance fused-type mode-selective coupler using elliptical core two-mode fiber at 1550 nm,” Photon. Technol. Lett., vol. 14, no. 4, pp. 501–503, 2002.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 $\times$ 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Exp., vol. 14, no. 6, pp. 2335–2343, 2006.

C. P. Tsekrekos and D. Syvridis, “All-fiber broadband LP$_{02}$ mode converter for future wavelength and mode division multiplexing systems,” Photon. Technol. Lett., vol. 24, no. 18, pp. 1638–1641, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

C. P. Tsekrekos and D. Syvridis, “All-fiber broadband LP$_{02}$ mode converter for future wavelength and mode division multiplexing systems,” Photon. Technol. Lett., vol. 24, no. 18, pp. 1638–1641, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

C. M. Herzinger, B. Johs, W. A. McGahan, J. A. Woollam, and W. Paulson, “Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation,” J. Appl. Phys., vol. 83, no. 6, pp. 3323–3336, 1998.

B. Huang, C. Xia, G. Matz, N. Bai, and G. Li, “Structured directional coupler pair for multiplexing of degenerate modes,” in Proc. Opt. Fiber Commun. Conf., OSA Tech. Dig., 2013, Paper JW2A.25.

K. Y. Song, I. K. Hwang, S. H. Yun, and B. Y. Kim, “High performance fused-type mode-selective coupler using elliptical core two-mode fiber at 1550 nm,” Photon. Technol. Lett., vol. 14, no. 4, pp. 501–503, 2002.

W.-J. Chen, S. M. Eaton, H. Zhang, and P. R. Herman, “Broadband directional couplers fabricated in bulk glass with high repetition rate femtosecond laser pulses,” Opt. Exp., vol. 16, no. 15, pp. 11470–11480, 2008.

C. M. Herzinger, B. Johs, W. A. McGahan, J. A. Woollam, and W. Paulson, “Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation,” J. Appl. Phys., vol. 83, no. 6, pp. 3323–3336, 1998.

R. Ryf, S. Randel, A. H. Gnauck, C Bolle, A. Sierra, S. Mumtaz, M. Esmaeelpour, E. C. Burrows, R. Essiambre, P. J. Winzer, D. W. Peckham, A. H. McCurdy, and R. Lingle, “Mode-division multiplexing over 96 km of few-mode fiber using coherent $6\times 6$ MIMO processing,” J. Lightw. Technol., vol. 30, no. 4, pp. 521–531, 2012.

M. Salsi, C. Koebele, D. Sperti, P. Tran, H. Mardoyan, P. Brindel, S. Bigo, A. Boutin, F. Verluise, P. Sillard, M. Astruc, L. Provost, and G. Charlet, “Mode-division multiplexing of $2\times 100$ Gb/s channels using an LCOS-based spatial modulator,” J. Lightw. Technol., vol. 30, no. 4, pp. 618–623, 2012.

K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 $\times$ 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Exp., vol. 14, no. 6, pp. 2335–2343, 2006.

W.-J. Chen, S. M. Eaton, H. Zhang, and P. R. Herman, “Broadband directional couplers fabricated in bulk glass with high repetition rate femtosecond laser pulses,” Opt. Exp., vol. 16, no. 15, pp. 11470–11480, 2008.

C. P. Tsekrekos and D. Syvridis, “All-fiber broadband LP$_{02}$ mode converter for future wavelength and mode division multiplexing systems,” Photon. Technol. Lett., vol. 24, no. 18, pp. 1638–1641, 2012.

K. Y. Song, I. K. Hwang, S. H. Yun, and B. Y. Kim, “High performance fused-type mode-selective coupler using elliptical core two-mode fiber at 1550 nm,” Photon. Technol. Lett., vol. 14, no. 4, pp. 501–503, 2002.

A. Li, X. Chen, A. Al Almin, and W. Shieh, “Fused fiber mode couplers for few-mode transmission,” Photon. Technol. Lett., vol. 24, no. 21, pp. 1953–1956, 2012.

N. Hanzawa, “Demonstration of mode-division multiplexing transmission over 10 km two-mode fiber with mode coupler,” presented at the Opt. Fiber Commun. Conf., Los Angeles, CA, USA, 2011, Paper OWA4.

B. Huang, C. Xia, G. Matz, N. Bai, and G. Li, “Structured directional coupler pair for multiplexing of degenerate modes,” in Proc. Opt. Fiber Commun. Conf., OSA Tech. Dig., 2013, Paper JW2A.25.

K. Okamoto, Fundamentals of Optical Waveguides.New York, NY, USA: Elsevier, 2006.

N. Jovanovic, “Direct laser written multimode waveguides for astronomical applications,” Proc. SPIE, vol. 7739, pp. 773923-1–773923-8, 2010.