Dispersion manipulating fiber

Details Dispersion manipulating fiber Dispersion manipulating fiber

2001-07-20

2004-09-14

Lee, John D. (Department: 2874)

Optical waveguides

Optical fiber waveguide with cladding

Utilizing nonsolid core or cladding

C385S126000

Reexamination Certificate

active

06792188

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to optical fibres and especially to optical fibres having micro-structures in core and/or cladding region(s). The fibres may be utilized for dispersion compensation and non-linear applications.
BACKGROUND OF THE INVENTION
The dispersion properties of conventional optical fibres are receiving a continuously high research interest in connection with high-capacity optical communication, soliton propagation, and control of non-linear effects. Accordingly, there is a strong interest in realizing new types of optical fibres that may provide new dispersion properties or may counteract some of the undesired dispersion properties of existing fibres.
Recently a new type of optical fibre that is characterized by a so-called micro structure has been proposed. Optical fibres of this type (which are referred to by several names—as e.g. micro-structured fibres, photonic crystal fibre, holey fibre, and photonic bandgap fibres) have been described in a number of references, such as WO 99/64903, WO 99/64904, and Broeng et al (see Pure and Applied Optics, pp. 477-482, 1999) describing such fibres having claddings defining Photonic Band Gap (PBG) structures, and U.S. Pat. No. 5,802,236, Knight et al. (see J. Opt. Soc. Am. A, Vol. 15, No. 3, pp. 748-752, 1998), Monro et al. (see Optics Letters, Vol. 25 (4), p. 206-8, February 2000) defining fibres where the light is transmitted using modified Total Internal Reflection (TIR). This application covers fibres that may guide by both physical principles and we shall use the term micro-structured fibres to generally describe these fibres.
Micro-structured fibres are known to exhibit dispersion properties that are unattainable in conventional optical fibres (see e.g. Ranka et al., Optics Letters, Vol. 25, No. 1, pp.25-27, 2000, Broderick et al. Optics Letters, Vol. 24, No. 20, pp. 1395-1397, 1999, Mogilevtsev et al. Optics Letters, Vol. 23, No. 21, pp. 1662-1664, 1998). These properties include shifting the zero dispersion wavelength below 1.3 &mgr;m. This has e.g. in the above-cited Ranka-reference been utilized for super-continuum generation of light over a very broad frequency range (covering visible to near-infrared wavelengths). The development of such white-light generators using micro-structured fibres was made possible through the design of micro-structured fibres with high anomalous waveguide dispersion at visible wavelength—and it has fuelled a large research interest into non-linear effects in micro-structured fibres (Fedotov et al. JETP Letters, Vol. 71, No. 7, pp. 281-284, 2000, Wadsworth et al. CLEO 2000, Paper PD1.5, 2000). The above-cited references all describe fibres with zero dispersion wavelength shifted below 1.3 &mgr;m. The fibres are characterized by a relatively high cladding air-filling fraction—air hole diameters, d, of more than 0.45 times the centre-to-centre distance between two nearest air holes, &Lgr;, and they all have a solid core. The size of the core is relatively small—about 1.5 &mgr;m in diameter. It is a disadvantage of the prior art fibres with zero-dispersion wavelength shifted below 1.3 &mgr;m that they are not strictly single-mode at visible wavelengths, but support a few (or more) guided modes. In the above-cited reference by Ranka et al., it is demonstrated that for relatively short fibre lengths, the fundamental mode of such fibres may be considered undisturbed by any higher order guided modes (i.e. there is a low coupling coefficient between the fundamental and the higher order modes). However, for guidance over longer fibre lengths (i.e. hundred of meters) it is a disadvantage of the prior art fibres with zero dispersion wavelength shifted below 1.3 &mgr;m that they are not strictly single mode at visible wavelengths. It is a further disadvantage of the prior art fibres with zero dispersion wavelength below 1.3 &mgr;m that they will be highly multimode at visible wavelengths if the core size is increased above 2 &mgr;m. It would be an advantage if fibres with zero dispersion wavelength shifted below 1.3 &mgr;m could be realized so as to have a core that was comparable in size to that of standard transmission optical fibres (i.e. to have a core of around 5 micron in diameter).
Another important aspect of micro-structured fibres is that they may exhibit normal dispersion (or so-called negative dispersion) at near-infrared wavelengths. Fibres with large negative dispersion at 1.55 &mgr;m are attractive for use as insertion-components in existing optical fibre communication links, as they may be used to compensate the positive dispersion around 1.55 &mgr;m of already installed standard transmission fibres (i.e. fibres that are designed to operate in the second telecommunication window and have a zero dispersion wavelength at 1.3 &mgr;m).
Monro et al. have presented micro-structured fibres having dispersion values of about −30 ps
m/km at 1.55 &mgr;m (see Journal of Lightwave Technology, Vol. 17, No. 6, pp. 1093-1102, 1999). The fibres presented by Monro et al. are characterized by a solid core surrounded by micro-structured cladding with a close-packed arrangement of identical air holes. The cladding holes have a size d/&Lgr; around 0.2. It is a disadvantage of the fibres presented by Monro et al. that the dispersion is not more negative than −30 ps
m/km. DiGiovanni et al. (see U.S. Pat. No. 5,802,236) have presented micro-structured fibres that provide significantly larger negative dispersion at near-infrared wavelengths. DiGiovanni et al. disclose micro-structured fibres that are characterized by a core and a micro-structured cladding. The cladding consists of inner and outer cladding features, thereby forming an inner and an outer cladding region. Both the inner and outer cladding of the fibres have an effective index that is lower than the core refractive index at all wavelengths. The features of the inner cladding region (preferably air holes) act to lower the effective refractive index compared to the effective refractive index of the outer cladding region. Hence, the fibres disclosed by DiGiovanni have a so-called “depressed” cladding design. The use of depressed cladding regions is well-known from the development of conventional dispersion compensating fibres (see e.g., M. Monerie, Propagation in doubly clad single-mode fibres, IEEE Journal of Quantum Electronics, vol. QE-18, no. 4, April 1982, pp. 535-542). To those skilled in the art, it will be recognised that in order to increase the negative dispersion of the fibres disclosed by DiGiovanni et al., the size of the cladding features must be increased. Digiovanni et al. disclose fibres that have dispersion of up to −1700 ps
m/km. It is a disadvantage of the fibres disclosed by DiGiovanni that the depressed cladding design does not allow to increase the inner cladding feature size so as to obtain negative dispersion of more than −2500 ps
m/km. This latter limit of maximum obtainable negative dispersion was predicted by Birks et al. (see Photonics Technology Letters, Vol. 11, No. 6, pp. 674-676, 1999). Birks et al. studied the fundamental limits of negative dispersion that can be obtained in solid core micro-structured fibres made of pure silica and air. Birks et al. argue in the above-cited reference that by increasing the void size (air holes), the negative dispersion of micro-structured fibres is generally increased. Hence, an ideal micro-structured fibre (with respect to negative dispersion) consists—according to Birks et al.—merely of a thin silica rod (the fibre core) surrounded by air. Hence, Birks et al. made a prediction of the maximum obtainable negative dispersion based on the study of a solid silica rod surrounded completely by air (this case corresponds to the inner cladding features of the fibres disclosed by DiGiovanni et al. being so large that they overlap each-other). For such an ideal micro-structured fibre, Birks et al. found a dispersion of −2000 ps
m/km. This result has been taken as the maximum obtainable negative dispersion that can be obtained

Affiliated with

Also associated with

Rating

Dispersion manipulating fiber does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dispersion manipulating fiber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dispersion manipulating fiber will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3209786