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A wide wavelength tunable quantum dot (QD) external cavity laser operating in the 1.31-μm waveband with a narrow line-width is successfully demonstrated. A high-density, high-quality InAs/InGaAs QD optical gain medium for the 1.31-μm waveband was obtained using a sandwiched sub-nano separator growth technique. A wide wavelength tunability of 1.265–1.321 μm and a narrow line-width of 210 kHz were successfully achieved using a compact and robust external cavity system constructed with multiple optical band-pass and etalon filters for active optical mode selection. The laser also achieved an error-free 10-Gb/s photonic data transmission over an 11.4-km-long holey fiber.
©2011 Optical Society of America
1. Introduction
Recently, photonic transport systems in the C- and L-bands (C-band: 1.530–1.565 μm, and L-band: 1.565–1.625 μm) have been extensively employed in conventional long-haul photonic network systems [1, 2]. The ever-increasing demand for high data transmission capacities necessitates the use of alternative wavebands and the development of methods for increasing the frequency utilization efficiency of existing technologies. Expansion of the wavelength division multiplexing (WDM) channels increases the usable wavelength bands and optical frequency resources. We have therefore focused on the T- and O-band (Thousand-band: 1.000–1.260 μm, and O-band: 1.260–1.360 μm) for the photonic transport system, because optical frequency resources greater than 70 THz can be employed in this waveband [3–5]. These wavelength bands have been greatly sought for short-reach communications, optical interconnects in the data-center, and metro/access network systems [6]. To increase the frequency utilization efficiency for the data transmission, coherent communication technology has also been investigated globally [7]. One of the key components for realizing both coherent and high-density WDM optical communication systems has been the use of a narrow line-width and a wavelength tunable laser. It is well known that a narrow optical spectrum line-width of around a few hundred kilohertz is required to achieve a quadrature amplitude modulation (QAM) format [7]. In the near future, it is projected that coherent and high-density WDM communication technologies will be applied to the T- and O-band photonic transport systems for obtaining ultra-high bit-rates, large data-capacities, and many data-channels for short-reach optical communications.
Self-assembled quantum dot (QD) structures are one of the most promising candidates among optical gain media for lengthening the operating wavelengths of light sources [8, 9]. A T- and O-band QD light source, fabricated on GaAs wafers, has attracted considerable attention as a low cost light source offering low power consumption and high performance [10–17]. In addition, it is expected that the consumption of Indium may be reduced using a novel QD technology, using GaAs substrates, when long-wavelength light sources are produced. It should be noted, however, that it is not easy to achieve a high-quality light source that can operate at a wavelength over 1.30 μm while forming InAs QD structures on the GaAs substrate. Recently, we proposed a sandwiched sub-nano separator (SSNS) growth technique as an easy means for obtaining high-quality and high-density QD structures embedded in the QW structure operating in the T- and O-bands [17].
From these considerations, it is considered that a narrow line-width and a wavelength tunable QD laser operating in the 1.0 to 1.3 μm (and beyond) wavelength range will be an attractive component for future high-density WDM and coherent communication systems operating in the T- and O-bands. We, therefore, have developed a narrow line-width and wavelength tunable InAs/InGaAs QD external cavity laser using the SSNS growth technique for O-band operation. In this paper, we report the successful demonstration of a narrow line-width around 200 kHz and an ultra-broadband wavelength tuning range (1.265–1.320 μm) of the fabricated wavelength tunable QD external cavity laser. Additionally, we have also demonstrated a 10-Gb/s, error-free data transmission over an 11.4-km long holey fiber (HF) transmission line using the developed wavelength tunable QD light source tuned at the 1.31-μm node as a center wavelength of the O-band.
2. Fabrication of QD optical gain with SSNS growth technique
Self-assembled InAs QD structures were grown on (001)-oriented n-type GaAs substrates by solid-source molecular-beam epitaxy (MBE). To lengthen a light-emitting wavelength from the QD structure, a useful structure such as the InAs QD embedded in an InGaAs QW has been proposed [9]. Figure 1(a) shows a cross-sectional image of the conventional structure of the QD embedded in QWs. However, it was found that QD structures are highly susceptible to the surface conditions of the InGaAs QW1, as shown in Fig. 1(a). We also confirmed that many giant dot structures are formed on the InGaAs QW when using the conventional growthtechnique. It has been postulated that the giant dot structure may cause a formation of crystal defects and affect individual device performance. Recently, considering these findings, we have proposed a novel InAs/InGaAs QD structure using the SSNS growth technique, as shown in Fig. 1(b) [17]. The sandwiched thin film acts as a slight separator between the QD and QW layers while also modifying the surface conditions of the QW. In our case, a sub-nm GaAs thin-film was employed as the SSNS structure. This technique is very simple and suitable for conventional growth methods such as MBE and/or a metal-organic chemical vapor deposition (MOCVD). Figure 1(b) also shows an atomic force microscope (AFM) surface image of the QD structure using the SSNS growth technique. A 2.76-ML InAs QDs in an InGaAs QW structure was subsequently fabricated at 490 °C in the GaAs matrix. A 3-ML (0.85-nm) GaAs thin film was used as the SSNS structure. Additionally, the Indium composition of the InGaAs is fixed at 0.15, and the thicknesses of the InGaAs QW1 and QW2 are respectively 10 ML and 28 ML. We confirmed that the SSNS growth technique most often suppresses the formation of the giant dot structures, where an ultra-high QD density of approximately 8.2 × 1010 /cm2 can be achieved. The photoluminescence (PL) of an electrical ground state of the fabricated InAs/InGaAs QD structure with the SSNS growth technique has a peak around the center of the O-band (1.31 μm waveband). We briefly discuss the mechanism of the SSNS technique. It is known that the formation of the InAs QD structure is greatly influenced by the atomic surface conditions. We consider the formation of the giant dot structure and the conjugation/segregation of Indium to be affected by the distribution of indium atoms on the InGaAs surface [18]. Additionally, we also considered it difficult to obtain a uniform distribution of the indium atoms on the InGaAs surface. We believe that a good uniform distribution of the III-V atoms on the surface may be achieved by using the SSNS growth technique for obtaining a high-quality QD structure. However, a more detailed study of the mechanism will be needed for optimizing the QD growth conditions in the future work.
Fig. 1 (a) Cross-sectional schematic image of conventional InAs QD structure embedded in QW layers and AFM image of the InAs QD formed on the InGaAs QW1. (b) Cross-sectional image and AFM image of novel InAs/InGaAs QD structure with SSNS growth technique. The AFM images are scaled to (1 × 1)-μm2 areas on the surface.
3. Fabrication and characterization of wavelength tunable QD external cavity laser
To develop a 1.31-μm waveband QD optical gain chip, a multi-stacked InAs/InGaAs QD as an active-region was formed on the n-type GaAs substrate. Figure 2(a) shows a cross-sectional schematic image of the fabricated optical gain chip consisting of the 7 stacked InAs/InGaAs QD using the SSNS growth technique. In the active region, each InAs/InGaAs QD layer was separated using a 45-nm GaAs spacer layer, and a 3-ML GaAs layer was also used as the SSNS structure. Additionally, carrier-doped 1.5-μm AlGaAs cladding layers were grown at 540 °C. The total thickness of the active region is approximately 445 nm. A ridge-type waveguide structure was fabricated using GaAs semiconductor process sequences with an electrode width of 3.4 μm and a waveguide length of 1950 μm. The structural parameters of the device, such as the ridge width and etching depth, were estimated using a laser device simulator to optimize the optical confinement into the ridge-type waveguide structure. Figure 2(b) shows a photograph of the developed QD optical gain chip using the SSNS growth technique for the 1.31-μm waveband. The QD optical gain chip was mounted on a Cu-W heat-sink stem using a conventional bonding method.
Fig. 2 (a) Cross-sectional schematic image of a ridge-type 1.31-μm waveband InAs/InGaAs QD optical gain chip formed on a GaAs substrate through the SSNS growth technique. (b) Photograph of a developed novel InAs/InGaAs QD optical gain chip using the SSNS growth technique included into the external cavity system.
Figure 3(a) shows an external cavity optical set-up for the narrow line-width and wavelength tunable InAs/InGaAs QD laser. The fabricated QD optical gain chip, as shown in Fig. 2(b), was set into an edge of the optical cavity set-up. The temperature of the QD gain chip was fixed at 300 K using a thermo-electric controller (TEC). One of the cleaved facets of the QD optical gain chip has an anti-reflection (AR) coat for the 1.31-μm waveband. A cleaved facet of the optical gain chip and a half-mirror (reflectance: 60%) form an external cavity structure, where the total length of the cavity is as small as approximately 40 mm. It seems that an optical grating was generally used to tune a lasing wavelength in the external cavity laser. However, it is expected that a more robust light source could be realized by adopting optical filters for controlling the lasing wavelength. We therefore used multiple optical filters, such as a narrow optical band-pass filter (bandwidth: <0.4-nm) and an etalon filter (free spectral range: 100 GHz), to control the lasing wavelength and the active optical mode [19]. A center wavelength of the narrow optical band-pass filter can be simply controlled by modifying the angle of the filter. The free spectral range of the etalon filter is finely adjusted by temperature control. An optical output was coupled to a polarization-maintaining single-mode optical fiber using a collimator lens. As seen in Fig. 3(b), a compact bench-top coherent light source module was successfully developed for the wavelength tunable QD external cavity laser.
Fig. 3 (a) External cavity optical set-up for narrow line-width and wavelength tunable QD laser. To control the active optical mode, multiple optical filters are utilized in this set-up. (b) Photograph image of developed compact bench-top light source module of the wavelength tunable QD external cavity laser.
Figure 4 shows that a dependence exists between the threshold current (DC operation) and lasing wavelength for the developed wavelength tunable QD light source (also shown in Fig. 3). Lasing operations performed on the developed QD light source in a wide wavelength range between 1.265 and 1.321 μm were clearly observed. The threshold current of the wavelength tunable QD external cavity laser was as low as approximately 60 mA at a wavelength of around 1.3 μm. Additionally, it was also observed that the threshold current slightly increased in the wavelength regions of <1.275 μm and >1.315 μm. The QD optical gain in these wavelength regions is considered to be slightly lower than that at a center wavelength in the tuning range. However, from the result shown in Fig. 4, the threshold current was found to be less than 100 mA for the wide wavelength tuning range. In this experiment, the current injection for operating the QD optical gain was fixed at 100 mA. Figure 5(a) shows the wavelength tunable characteristics of the fabricated wavelength tunable QD external cavity laser, as shown in Fig. 3(b). It is clear that the ultra-broadband tuning range, between 1.265 and 1.321 μm (56 nm), was successfully achieved using the InAs/InGaAs QD optical gain with the SSNS growth technique. This wavelength tuning range generally corresponds to an electrical ground state of the QD structure. In Fig. 5(a), an output power from the QD light source was finely controlled to −3.0 dBm with an optical attenuator included in the light source module. Figure 5(b) shows an output power from the single-mode fiber without attenuator controlling. The lasing optical power at each wavelength was determined to be almost observed between 4.8 dBm (3.01 mW) and −2.65 dBm (0.54 mW). We also observed a power fluctuation between each wavelength peak in the wavelength tuning range between 1265 and 1320 nm, as shown in Fig. 5(b). This power fluctuation is considered to be caused by the slight misalignment of the optical modes of the 100-GHz etalon filter and external cavity of the laser system. It is believed that the ultra-wide optical frequency resources of more than 10-THz threshold, which is approximately twice as large as that in the C-band (4.4 THz), could be employed for an O-band WDM optical communication system using this wavelength tunable QD external cavity laser. We also estimated an optical spectrum line-width of the wavelength tunable QD external cavity laser. Figure 6 shows the measurement result of the spectrum line-width of the wavelength tunable QD laser by using a delayed self-heterodyne method. This was done when the lasing wavelength peak was fixed at 1.30 μm. In Fig. 6, the modulation frequency was shifted to the center, which was at 0 Hz. It is known that a measured spectrum bandwidth at −3 dB is twice that of a real line-width obtained using this method [20]. Therefore, a half-value of the frequency was used as the x-axis in Fig. 6. It is clear that a narrow line-width spectrum at 210 kHz can successfully be obtained from the wavelength tunable InAs/InGaAs QD external cavity laser. It is expected that the narrow line-width of the fabricated QD light source will be used for future QAM coherent communication systems in the O-band.
Fig. 4 Dependence of threshold current on lasing wavelength of a wavelength tunable InAs/InGaAs QD external cavity laser.
Fig. 5 (a) Ultra-broad wavelength tuning range of wavelength tunable InAs/InGaAs QD external cavity laser. The output power is adjusted using an optical attenuator included in the light source module. (b) Dependence of optical output power on lasing wavelength from the developed QD light source without the attenuator control.
Fig. 6 Estimation result for narrow line-width and stable operation of a wavelength tunable InAs/InGaAs QD external cavity laser.
4. Demonstration of photonic transmission using 1.31-μm wavelength tunable QD external cavity laser
We have demonstrated that a wide-wavelength tunable QD light source operating in the 1.3-μm waveband can be obtained using two essential techniques. They are the SSNS growth technique for fabricating high-quality QD optical gain materials and an optical mode selection technique employing multiple optical filters in the external cavity set-up of the QD laser. Additionally, it has been previously demonstrated that simultaneous optical data transmissions in the 1.0-μm, C-band and L-band can be achieved over an ultra-broadband photonic transport system using a holey fiber (HF) transmission line [21]. We have focused on the HF as a micro-structured optical fiber for a novel ultra-broadband transmission line for optical communications, since an HF has attractive characteristics such as an endlessly single-mode operation, highly controllable optical properties, and high flexibility. We consider that the wide transmission window will become an attractive characteristic for achieving a photonic data transmission in the ultra-broadband. We believe that the QD optical gain technique will become a great candidate expansion of usable optical frequency in the 1.0-, 1.3, and over 1.55-μm wavebands. Therefore, we expect that the ultra-broadband photonic transport system using the HF may be suitable for QD photonic device technology to expand a usable optical frequency resource for optical communications.
In this section, to evaluate the usability of the developed QD light source as a wavelength tunable laser for future O-band optical data transmission, we constructed a photonic transport sub-system, as shown in Fig. 7 , using two attractive devices. These devices were the developed 1.31-μm wavelength tunable QD external cavity laser and an 11.4-km long HF transmission line. A continuous wave (CW) light source of approximately 0 dBm at 1.31 μm was obtained from the fabricated wavelength tunable QD laser. A 9.953-Gb/s optical data-stream at the 1.31-μm wavelength was formed by an external LiNbO3 intensity modulator, and then, it was amplified to 1.59 dBm using a Pr-doped fiber amplifier (PDFA). The fiber amplifier was used for compensating an optical loss in the external modulator. We consider that the high output power of the QD-based light source may be needed for constructing a useful photonic transport system without amplifiers. In the QD-based light source shown in Fig. 3, a high-reflection (HR) coat is still not used on the backside of the QD optical-gain chip. We expect that a higher output power and low-threshold current will be achieved by using the HR coating in our future work. A pseudorandom binary bit sequence (PRBS) with a pattern length of 231–1 was transmitted for bit error rate (BER) detection. The developed HF was used as the 1.31-μm waveband single single-mode transmission line. The zero-dispersion wavelength and dispersion value at 1.31-μm were measured to be approximately 1.19 μm and + 12.5 ps/nm/km, respectively. The transmission loss was as low as 1.3 dB/km. In the experiment, we used HF of length 11.4 km. The transmitted optical data was directly detected using a high-speed photo-detector. In Fig. 8(a) , clear eye-openings are successfully observed before and after the 11.4-km long transmission. Figure 8(b) shows the measured BERs. An error-free (<10−9) photonic transmission of the 10-Gb/s signal was successfully achieved over the 11.4-km HF using the developed wavelength tunable QD external cavity light source in the 1.31-μm waveband. A power penalty was found to be less than 0.5 dB. We consider that one of the possible influences of this power penalty is a transmission loss in the HF. From these results, it was successfully confirmed that the developed wavelength tunable QD external cavity laser can be applied to high-speed optical communication systems.
Fig. 7 Optical setup for demonstration of 10-Gb/s photonic data transmission using the developed wavelength tunable QD external cavity laser over the 11.4-km-long HF transmission line. (a) Fabricated QD structure with SSNS technique for the optical gain, (b) developed wavelength tunable QD light source, and (c) cross-sectional image of HF transmission line are re-shown as inset photographs.
Fig. 8 (a) Eye diagrams and (b) BER measurement results before and after transmission using the developed wavelength tunable QD external cavity light source operating at the 1.31-μm wavelength. In (a), the x-axis is fixed to 17 ps/div.
5. Conclusion
We proposed a useful growth method of a sandwiched sub-nano separator (SSNS) growth technique for the fabrication of QD optical gain materials for the 1.31-μm waveband (O-band). It was confirmed that a high-density (8.2 × 1010 /cm2) and a high-quality InAs/InGaAs QD structure in its waveband can be obtained on GaAs substrates using the SSNS growth technique while suppressing the formation of condensed giant dot structures. Using this technique, we developed a wavelength tunable InAs/InGaAs QD external cavity laser operating in the 1.31-μm waveband. A wide tuning range between 1.265 and 1.321 μm was achieved using an external cavity system constructed with multiple optical narrow band-pass and etalon filters. The spectrum line-width was 210 kHz at 1.30 μm. Additionally, an error-free 10-Gb/s photonic data transmission was successfully achieved over an 11.4-km long holey fiber using the developed QD light source operating at 1.31 μm. From these results, we expect that the developed wavelength tunable QD external cavity laser with a narrow line-width characteristic will become a great candidate for the light source of future high-density WDM and coherent optical communication systems in the 1.0–1.3-μm waveband.
Acknowledgment
The authors would like to thank the staff of Koshin Kogaku Co., Ltd. and Sevensix, Inc.; the staff of the Photonic Device Laboratory; and Dr. A. Kanno and Dr. I. Hosako of NICT. The authors are very grateful to Dr. K. Mukasa, Dr. K. Imamura, Dr. R. Miyabe, Dr. T. Yagi, and Dr. S. Ozawa of FURUKAWA ELECTRIC CO. for producing the novel optical fibers.
References and links
1. A. H. Gnauck, G. Charlet, P. Tran, P. Winzer, C. Doerr, J. Centanni, E. Burrows, T. Kawanishi, T. Sakamoto, and K. Higuma, “25.6-Tb/s C+L-Band Transmission of Polarization-Multiplexed RZ-DQPSK Signals,” in Optical Fiber Communication Conference, OSA Technical Digest Series (Optical Society of America, 2007), paper PDP19.
2. A. Sano, H. Masuda, T. Kobayashi, M. Fujiwara, K. Horikoshi, E. Yoshida, Y. Miyamoto, M. Matsu, M. Mizoguchi, H. Yamazaki, Y. Sakamaki, and H. Ishii, “69.1-Tb/s (432 x 171-Gb/s) C- and Extended L-Band Transmission over 240 Km Using PDM-16-QAM Modulation and Digital Coherent Detection,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2010), paper PDPB7.
3. N. Yamamoto and H. Sotobayashi, “All-band photonic transport system and its device technologies,” Proc. SPIE 7235, 72350C, 72350C–11 (2009). [CrossRef]
4. N. Yamamoto, H. Sotobayashi, K. Akahane, M. Tsuchiya, K. Takashima, and H. Yokoyama, “10-Gbps, 1-microm waveband photonic transmission with a harmonically mode-locked semiconductor laser,” Opt. Express 16(24), 19836–19843 (2008). [CrossRef] [PubMed]
5. N. Yamamoto, Y. Omigawa, K. Akahane, T. Kawanishi, and H. Sotobayashi, “Simultaneous 3 x 10 Gbps optical data transmission in 1-mum, C-, and L-wavebands over a single holey fiber using an ultra-broadband photonic transport system,” Opt. Express 18(5), 4695–4700 (2010). [CrossRef] [PubMed]
6. H. Liu, C.-F. Lam, and C. Johnson, “Scaling Optical Interconnects in Datacenter Networks - Opportunities and Challenges for WDM,” in Proceedings of 18th IEEE Symposium on High Performance Interconnects (IEEE, 2010), pp. 113–116.
7. A. Sano, T. Kobayashi, E. Yoshida, and Y. Miyamoto, “Ultra-high capacity optical transmission technologies for 100 Tbit/s optical transport networks,” IEICE Trans. Commun, E 94-B, 400–408 (2011).
8. Y. Arakawa and H. Sakaki, “Multidimensional quantum well laser and temperature dependence of its threshold current,” Appl. Phys. Lett. 40(11), 939–941 (1982). [CrossRef]
9. H. Y. Liu, M. Hopkinson, C. N. Harrison, M. J. Steer, R. Frith, I. R. Sellers, D. J. Mowbray, and M. S. Skolnick, “Optimizing the growth of 1.3 μm InAs/InGaAs dots-in-a-well structure,” J. Appl. Phys. 93(5), 2931–2936 (2003). [CrossRef]
10. K. Otsubo, N. Hatori, M. Ishida, S. Okumura, T. Akiyama, Y. Nakata, H. Ebe, M. Sugawara, and Y. Arakawa, “Temperature-Insensitive Eye-Opening under 10-Gb/s Modulation of 1.3-µm P-Doped Quantum-Dot Lasers without Current Adjustments,” Jpn. J. Appl. Phys. 43(No. 8B), L1124–L1126 (2004). [CrossRef]
11. Y. Tanaka, M. Ishida, Y. Maeda, T. Akiyama, T. Yamamoto, H. Song, M. Yamaguchi, Y. Nakata, K. Nishi, M. Sugawara, and Y. Arakawa, “High-Speed and Temperature-Insensitive Operation in 1.3-μm InAs/GaAs High-Density Quantum Dot Lasers,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2009), paper OWJ1.
12. A. Gubenko, I. Krestnikov, D. Livshtis, S. Mikhrin, A. Kovsh, L. West, C. Bornholdt, N. Grote, and A. Zhukov, “Error-free 10 Gbit/s transmission using individual Fabry-Perot modes of low-noise quantum-dot laser,” Electron. Lett. 43(25), 1430–1431 (2007). [CrossRef]
13. E. U. Rafailov, M. A. Cataluna, and W. Sibbett, “Mode-locked quantum-dot lasers,” Nat. Photonics 1(7), 395–401 (2007). [CrossRef]
14. N. Yamamoto, K. Akahane, S. Gozu, and N. Ohtani, “Over 1.3 µm continuous-wave laser emission from InGaSb quantum-dot laser diode fabricated on GaAs substrates,” Appl. Phys. Lett. 86(20), 203118 (2005). [CrossRef]
15. N. Yamamoto, K. Akahane, T. Kawanishi, R. Katouf, and H. Sotobayashi, “Quantum Dot Optical Frequency Comb Laser with Mode-Selection Technique for 1-µm Waveband Photonic Transport System,” Jpn. J. Appl. Phys. 49(4), 04DG03 (2010). [CrossRef]
16. A. Y. Nevsky, U. Bressel, I. Ernsting, C. Eisele, M. Okhapkin, S. Schiller, A. Gubenko, D. Livshits, S. Mikhrin, I. Krestnikov, and A. Kovsh, “A narrow-line-width external cavity quantum dot laser for high-resolution spectroscopy in the near-infrared and yellow spectral ranges,” Appl. Phys. B 92(4), 501–507 (2008). [CrossRef]
17. N. Yamamoto, K. Akahane, T. Kawanishi, H. Sotobayashi, H. Fujioka, and H. Takai, “Broadband light source using modulated quantum dot structures with sandwiched sub-nano separator (SSNS) technique,” Phys. Status Solidi., C Curr. Top. Solid State Phys. 8(2), 328–330 (2011). [CrossRef]
18. M. Pfister, M. B. Johnson, S. F. Alvarado, H. W. M. Sa-lemink, U. Marti, D. Martin, F. Morier-Genoud, and F. K. Reinhart, “Indium distribution in InGaAs quantum wires observed with the scanning tunneling microscope,” Appl. Phys. Lett. 67(10), 1459–1461 (1995). [CrossRef]
19. N. Yamamoto, Y. Yoshioka, K. Akahane, T. Kawanishi, H. Sotobayashi, and H. Takai, “100-GHz channel spacing and O-band quantum dot optical frequency comb generator with interference injection locking technique,” in Proceedings of Conference on Lasers and Electro-Optics (CLEO) 2011, paper CTuV7.
20. T. Okoshi, K. Kikuchi, and A. Nakayama, “Novel method for high resolution measurement of laser output spectrum,” Electron. Lett. 16(16), 630–631 (1980). [CrossRef]
21. K. Mukasa, K. Imamura, R. Sugizaki, and T. Yagi, “Comparisons of merits on wideband transmission systems between using extremely improved solid SMFs with Aeff of 160 mm2 and loss of 0.175 dB/km and using large-Aeff holey fibers enabling transmission over 600 nm bandwidth,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2008), paper OThR1.
