Feng Xian, Loh Wei H, Richardson David J
Optoelectronics Research Centre, University of Southampton, Highfield, Southampton, UK, SO17 1BJ.
Appl Opt. 2008 Oct 1;47(28):5078-80; discussion 5081. doi: 10.1364/ao.47.005078.
We comment on the recent paper by Zhou et al. [Appl. Opt.45, 4433 (2006)APOPAI0003-693510.1364/AO.45.004433], in which transmission losses of 0.2-0.3 dB/m were claimed across the wavelength range 420-900 nm in a high-index (n(d)=1.80518 at 587.6 nm) SF6 glass-based photonic crystal fiber fabricated by novel die-cast technique. If confirmed, these losses are at least 1 order of magnitude lower than previous reported losses of SF6 photonic crystal fibers from other fabrication approaches. Here we present a statistic survey on the relationship between the refractive index and the bulk material attenuation, based on a large number of commercial Schott optical glasses with the n(d) ranging between 1.40 and 2.05. It shows that the loss of a high-index (n(d)=1.80) glass optical fiber should be at the levels of 10-50 dB/m at 420 nm and 1-10 dB/m at 500 nm, respectively. Moreover, the material attenuation of such a high-index glass fiber should intrinsically show a large decay, from 10-50 dB/m at 420 nm to the level of 1 dB/m at 700 nm, which arises from the tail on the UV absorption edge of the high-index glass extending to the visible region. Therefore, we conclude that: (1) the low loss of 0.2-0.3 dB/m reported in the cited paper is abnormally one or two magnitudes lower than the material attenuation that a high-index (n(d)=1.80) glass optical fiber should have in the range between 420 and 500 nm and that (2) the flat loss curve between 420 and 700 nm in the cited paper deviates greatly from the intrinsic behavior of a high-index (n(d)=1.80) glass fiber.
我们对周等人最近的论文[《应用光学》45, 4433 (2006)，APOPAI0003 - 6935，10.1364/AO.45.004433]进行评论。该论文称，采用新型压铸技术制造的高折射率（在587.6 nm处n(d)=1.80518）的基于SF6玻璃的光子晶体光纤，在420 - 900 nm波长范围内的传输损耗为0.2 - 0.3 dB/m。如果得到证实，这些损耗至少比之前其他制造方法报道的SF6光子晶体光纤的损耗低一个数量级。在此，我们基于大量n(d)在1.40至2.05之间的商业肖特光学玻璃，对折射率与块状材料衰减之间的关系进行了统计调查。结果表明，高折射率（n(d)=1.80）的玻璃光纤在420 nm处的损耗应为10 - 50 dB/m，在500 nm处应为1 - 10 dB/m。此外，这种高折射率玻璃光纤的材料衰减本质上应呈现大幅下降，从420 nm处的10 - 50 dB/m降至700 nm处的1 dB/m水平，这是由于高折射率玻璃的紫外吸收边的尾部延伸到了可见光区域。因此，我们得出以下结论：(1) 上述引用论文中报道的0.2 - 0.3 dB/m的低损耗比高折射率（n(d)=1.80）的玻璃光纤在420至500 nm范围内应有的材料衰减异常低一到两个数量级；(2) 上述引用论文中420至700 nm之间的平坦损耗曲线与高折射率（n(d)=1.80）玻璃光纤的固有特性有很大偏差。
