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High-birefringent photonic crystal fiber-Optical Fiber Communication Conference and Exhibit, 2001. OFC 2001
| Content Provider | Semantic Scholar |
|---|---|
| Author | Libori Barkou, Stig Eigil Overgaard, Anders Simonsen |
| Copyright Year | 2004 |
| Abstract | A highly birefringent Photonic Crystal Fiber design is analysed. Birefringence up to is found. Random fluctuations in the cladding design are analysed, and the fiber is found to be a feasible polarization maintaining fiber. @ 2000 Optical Society of America OCIS codes: (260.1440) Birefringence; (060.2400) Fiber properties Introduction: Photonic Crystal Fibers, PCFs, have generated tremendous interest during the last few years [l, 2, 31. The cladding of a PCF consist of a large number of air-holes embedded within a silica background. The fibres are invariant in the longitudinal direction. Usually, as is the case for the PCFs investigated in this paper, the core-region is formed by omitting the central air-hole, thereby creating a silica core-region with a higher index than the effective index of the surrounding air-filled cladding. Such PCFs are especially renowned by their ability to support only a single degenerate mode in the entire wavelength range [l], if the air-filling fraction of the cladding is not to large. In this paper we explore the attractive possibility of employing PCFs as polarisation maintaking fibres. This is specifically relevant as more and more optical processing becomes necessary in optical networks, where enhanced optical functionality is required. We find that a high degree of birefringence is indeed possible in PCFs. To be able to successfully maintain the polarization of light transmitted by the fibre, it is necessary to be able to control the magnitude of birefringence-one can expect in PCFs due to small production deviations away from a perfect crystalline symmetry of the cladding. To our knowledge, this is the first theoretical investigation of the magnitude of intentional birefringence compared to non-intentional birefringence in PCFs. Intentionally introduced birefringence: For single mode PCFs (as are the fibres investigated in this paper), the guided mode consists of two degenerate polarizations. To deliberately introduce birefringence into this guided mode, we have enlarged two of the central air-holes, as shown in Fig.1. Fig.1 also defines the lattice constant A, and the cladding hole diameter D1. The two enlarged cladding holes have diameter D2. To further increase the birefringence, the two enlarged cladding holes are placed at a reduced distance, A2 from the center of the core. As seen in Fig.1 this design breaks the 60 degrees symmetry usually present in PCFs, and instead introduces an elongated core region with 180 degrees symmetry.We expect such a core-region to yield the highest degree of birefringence (this is in complete analogy with standard optical fibres). The particular structure analysed here, has D1 = 0.45A1 and D2 = 0.75Al, while A2 = O.8A1. All calculations, in this paper, were performed with a plane-wave method [4], using a supercell with the area of 48 simple cells. We use 256 x 256 plane waves for each polarization. The geometrical size of the core-region of this PCF design is uniquely determined by A l . By assuming that material dispersion only has limited influence on the birefringence (we have used 1.45 as the refractive index of silica in our calculations), it becomes possible to illustrate the effect of changing the wavelength and or A1 in a single plot. This is illustrated in Fig.2a, where the curve 1 shows the magnitude of the birefringence of this fibre as a function of the normalized frequency, 2, where X is the free space wavelength. Working with this normalized frequency also aids the design process, since one may easily find the necessary A1 for a desired combination of birefringence and wavelength. From Fig.2a we conclude that a birefringence of more than is possible, when the structure-size A1 is smaller than twice the free-space wavelength. It is worth noticing, that % = 3 corresponds to a core-diameter of 5-6 microns! We conclude, that it is possible to design PCFs with high birefringence, while maintaining a realistic core-size. Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on March 09,2010 at 04:44:13 EST from IEEE Xplore. Restrictions apply. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://orbit.dtu.dk/files/4236749/libori.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
