Patent Description:
The optical fiber communication has been widely used in long distance backbone networks to metropolitan area networks and access networks, due to features such as large capacity, long transfer distance, fast transfer speed, and cost saving. The development of the optical fiber communication technology has always been aimed at faster transfer speed, larger capacity, and longer transfer distance, and continuously promotes and improves the performance indexes of an optical fiber and the communication technology of the optical fiber. Especially, in recent years, with the explosive growth in the volume of IP services, the communication network starts to head towards a next generation of sustainable development, and a constructed optical fiber infrastructure having a huge transfer capacity and long distance is the physical basis of the next generation of networks. To satisfy development requirements of the optical fiber communication system, relevant performance indexes of the optical fiber as a transfer medium of an optical fiber communication network also needs to be further improved.

The attenuation coefficient of an optical fiber of one of important performance indexes of the optical fiber, to which the relay distance of the optical fiber communication majorly depends. A small attenuation coefficient of an optical fiber indicates a long distance for which an optical signal carried in the optical fiber can be transferred, and indicates a small attenuation amplitude of a carried optical signal at the same transfer distance. The Optical Signal to Noise Ratio (OSNR) in the optical fiber communication can be effectively increased by reducing the attenuation coefficient, to further improve the transfer quality and the transfer distance of the system. In long-distance transfer distance, an optical signal is transferred by means of relay stations. If the attenuation coefficient of an optical fiber is small, the transfer distance without relay of the optical signal is long, and therefore the distance between relay stations can be increased, thereby greatly reducing the number of relay stations and reducing the operating costs. Therefore, reducing the attenuation coefficient of the optical fiber has a significant meaning in aspects of both system structure optimization and operating costs reduction. In another aspect, with continuously development of FTTX in recent years, it is difficult for the performance of the existing G. <NUM> fiber to meet users' requirements. In an actual application environment, the optical fiber needs to have a particular bending resistance. Therefore, a new generation of bending-insensitive single-mode fiber, G. <NUM> optical fiber, is developed based on the G. <NUM> fiber. <NUM> optical fiber includes a G. A optical fiber that is compatible with the G. <NUM> standard and a G. B optical fiber that is not compatible with the G. <NUM> standard. A type optical fiber has a good compatibility with the G. D fiber and has a better bending resistance relative to common G. D fibers, and therefore is considered as one of products that are most probably used for replacing the G. <NUM> fiber. Therefore, creation of a new generation of single-mode fiber that is compatible with the G. <NUM> standard, has a low attenuation and a relatively large mode field diameter, and meanwhile also has a bent insensitive property becomes a search focus in the field of communication optical fibers.

Generally, the following several methods may be used to reduce the attenuation of an optical fiber in a manufacturing process of an optical fiber preform. For example, the probability of introduction of external impurities can be reduced by using high-purity raw materials and improving the manufacturing environment and equipment sealing. For example, in <CIT>, the introduction of external impurities is reduced by using the method of improving the sealing in the process of depositing an optical fiber preform. Alternatively, a process of manufacturing a preform with a larger outer diameter is used, and the over whole attenuation of the optical fiber is reduced by means of the dilution effect of a larger scale perform. In addition, the coating processing used for coating the surface of bare fiber in the process of manufacturing the optical fiber is also a significant factor that influences the attenuation performance of the optical fiber. However, no matter in the aspect of theories or the control of costs and processing in the actual preparation of the optical fiber, reducing doping of the optical fiber and optimizing the cross sections of the optical fiber are the simplest and most effective methods for reducing the attenuation of the optical fiber. Generally, a small concentration of doped material indicates a small loss caused by Rayleigh scattering. In a conventional single-mode fiber, to guarantee total reflection in the optical fiber, a sufficient difference between the refractive indexes of the core layer and the inner cladding layer needs to be ensured, so that the relative refractive index of the core layer is far larger than that of the inner cladding layer of the optical fiber. To ensure such the design, a large amount of doping in a Ge or Ge/F co-doped form needs to be performed in the core layer. However, in the design of cross sections of the conventional optical fiber, laser energy forms a Gaussian distribution in the cross sections of the optical fiber, and approximately <NUM>% laser energy transfers in the core layer with relatively larger doping in the optical fiber. That is, laser transfer of high energy density is centralized in the high-concentration doped core layer having a larger Rayleigh coefficient. By means of proper optical cross section design, a cross section in which energy is not distributed in a Gaussian distribution form is designed, to reduce energy loss in the high-concentration doped core layer, thereby significantly reducing the attenuation performance of the optical fiber.

However, in the conventional cross section design and manufacturing methods for G. <NUM> optical fibers, a relatively large amount of Ge/F co-doping is used in the core layer, and to obtain the optimal macrobending performance, the relative refractive index of the core layer generally is larger than <NUM>%. That is, the Ge doping in the core layer is relatively large, thereby causing a relatively large Rayleigh scattering and increasing attenuation of the optical fiber.

<CIT> discloses a design of ultralow attenuation optical fiber, in which the design of an outer cladding layer of pure silica is used. However, a typical step cross section structure is used in the design, instead of using a trench cladding layer design to optimize bending of the optical fiber, and Ge is not used for doping in the core layer thereof, which may therefore cause viscosity mismatch during preparation of the perform. In addition, the attenuation and bending ability thereof are relatively poor. <CIT> discloses a low attenuation single mode optical fibre used in an optical fibre communication system, including a core layer and claddings. <CIT> discloses a single-mode fibre of ultralow attenuation. In addition to that, from <CIT> an optical fiber is known that includes a fiber configured to transmit optical data in a plurality of modes or in a single mode; a core region in the fiber that comprises fluorine-doped silica; and a cladding in the fiber that surrounds the core region and that comprises fluorine-doped silica. Furthermore, <CIT> discloses an optical fibre including a core, an inner cladding and a low index ring of silica-based glass. Another optical fibre is known from <CIT>. <CIT> discloses high-bandwidth multimode optical fibers for high radiation applications. <CIT> relates to a single-mode optical fiber applied to an access network, which has excellent bending resistance and belongs to the field of optical fiber communication.

The following is the definitions and instructions of some terms involved in the the invention being defined by the claims.

From a central axis of an optical fiber, according to changing of a refractive index, a layer closest to the axis is defined as a core layer, i.e., the core layer refers to a central area of a cross section of the fiber, and an outmost layer of the fiber, i.e., a pure-silicon-dioxide layer, is defined as an outer cladding layer of the fiber.

As used herein, a relative refractive index difference Δni of a layer of a fiber is defined according to the following formula: <MAT> where ni is a refractive index of the corresponding layer, and nc is a refractive index of the outer cladding layer, that is, a refractive index of the pure silicon dioxide.

A contribution of doped Ge in the core layer of the optical fiber to the refractive index ΔGe is defined according to the following equation: <MAT> where nGe is a change of the refractive index of the silicon dioxide glass caused by the doped substance Ge doped in the core layer, provided that the doped substance Ge doped in the core layer is doped in the pure silicon dioxide that includes no other doped substance.

Cable cut-off wavelength λcc: As defined in the IEC (International Electrotechnical Commission) standard <NUM>-<NUM>-<NUM>, a cable cutoff wavelength λcc is a wavelength for which an optical signal no longer transmits as a single-mode signal after transmitting about <NUM> meters in an optical fiber. During a test, the optical fiber needs to be bent/wound into a circle (one round/turn) with a radius of about <NUM> and two circles (two rounds/turns) with a radius of <NUM> to obtain data.

One of the objectives of the present invention is to provide a bending-insensitive single-mode fiber with ultralow attenuation having relatively low optical fiber manufacturing costs, relatively low attenuation coefficient, and excellent bending performance.

The bending-insensitive single-mode fiber with ultralow attenuation includes a core layer and cladding layers surrounding the core layer.

The cladding layers comprises an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary cladding layer.

The core layer has a radius r<NUM> in a range of about <NUM> to <NUM>, and a relative refractive index difference Δn<NUM> in a range of about -<NUM>% to <NUM>%.

The core layer is a germanium-fluorine co-doped silica glass layer, wherein a doping contribution of germanium is in a range of about <NUM>% to <NUM>%.

The inner cladding layer has a radius r<NUM> in a range of about <NUM> to <NUM>, and a relative refractive index difference Δn<NUM> in a range of about -<NUM>% to -<NUM>%. The trench cladding layer has a radius r<NUM> in a range of about <NUM> to <NUM>, and a relative refractive index difference Δn<NUM> in a range of about -<NUM>% to -<NUM>%. The auxiliary outer cladding layer has a radius r<NUM> in a range of about <NUM> to <NUM>, and a relative refractive index difference Δn<NUM> in a range of about -<NUM>% to -<NUM>%. The outer cladding layer is a pure silica glass layer, and has a diameter of about <NUM>.

The core layer is a germanium and fluorine co-doped silicon-dioxide glass layer, or a germanium-doped silicon-dioxide glass layer, where a doping contribution of germanium is in a range of about <NUM>% to <NUM>%, preferably, in a range is about <NUM>% to <NUM>%.

In certain embodiments, the bending-insensitive single-mode fiber has a mode field diameter (MFD) at a wavelength of about <NUM> being in a range of about <NUM> to <NUM>, preferably, being in a range of about <NUM> to <NUM>.

In certain embodiments, the bending-insensitive single-mode fiber has a cable cut-off wavelength being less than or equal to about <NUM>.

In certain embodiments, the bending-insensitive single-mode fiber has a zero dispersion point in a wavelength range of about <NUM> to <NUM>, and a zero dispersion slope being less than or equal to about <NUM> ps/(nm<NUM>*km).

In certain embodiments, the bending-insensitive single-mode fiber has a dispersion at a wavelength of about <NUM> being less than or equal to about <NUM> ps/(nm*km); and a dispersion at a wavelength of about <NUM> being less than or equal to about <NUM> ps/(nm*km).

The bending-insensitive single-mode fiber has an attenuation at a wavelength of about <NUM> being less than or equal to about <NUM> dB/km, preferably, being less than or equal to about <NUM> dB/km.

In certain embodiments, the bending-insensitive single-mode fiber has an attenuation at a wavelength of about <NUM> being less than or equal to about <NUM> dB/km, preferably, being less than or equal to about <NUM> dB/km.

In certain embodiments, at a wavelength of about <NUM>, a macrobending loss of the optical fiber that is wound in <NUM> rounds with a bending radius R of about <NUM> is less than or equal to about <NUM> dB, and the macrobending loss of the optical fiber that is wound in one round with the bending radius R of about <NUM> is less than or equal to about <NUM> dB.

In certain embodiments, the bending-insensitive single-mode fiber has an coating thickness with a typical value being about <NUM> or <NUM>.

Among other things, the present invention has the following beneficial effects:
The cross section structure of the core and cladding layers of the optical fiber and the internal viscosity match are properly designed so that defects in the optical fiber preparation process and the attenuation of the optical fiber are reduced.

By properly designing the fluorine-doped trench structure of the optical fiber and the cross section structure of the core and cladding layers of the optical fiber, the optical fiber has an MFD equal to or larger than about <NUM>.

Comprehensive performance parameters, such as the cut-off wavelength, bending loss, and dispersion, are good in applicable bands, to form a cable cut-off wavelength small enough, to ensure single-mode state of an optical signal that is transferred at the C band in such the type of optical fibers. The multi-step trench cladding layer structure is used in the cross section structure of the optical fiber. The optical fiber has a relatively broad trench cladding layer structure for limiting fundamental mode leakage, thereby improving the bending performance of the optical fiber. The optical fiber is compatible with standard G.

The design of pure silica is used for the outer cladding layer structure at the outermost layer, thereby reducing the proportion of the fluorine-doped glass in the optical fiber, and reducing the costs for manufacturing the optical fiber.

<FIG> is a diagram of a refractive-index profile structure distribution according to an embodiment of the present invention.

The core layer is a germanium and fluorine co-doped silicon-dioxide glass layer, or a germanium-doped silicon-dioxide glass layer.

The cladding layers comprises an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary cladding layer. The outer cladding layer is a pure silica glass layer, and has a diameter of about <NUM>.

Table <NUM> lists optical fiber profile parameters of the bending-insensitive single-mode fibers according to embodiments of the present invention, where ΔGe is a contribution of the doped Ge in the core layer to a refractive index. Table <NUM> shown corresponding optical parameter properties of the optical fibers listed in Table <NUM>.

Claim 1:
A bending-insensitive single-mode fiber with ultralow attenuation, comprising:
a core layer and cladding layers, wherein the cladding layers comprises an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary cladding layer;
wherein the inner cladding layer has a radius r<NUM> in a range of <NUM> to <NUM> and a relative refractive index difference Δn<NUM> in a range of -<NUM>% to - <NUM>%;
wherein the trench cladding layer has a radius r<NUM> in a range of <NUM> to <NUM>, and a relative refractive index difference Δn<NUM> in a range of - <NUM>% to -<NUM>%;
wherein the auxiliary outer cladding layer has a radius r<NUM> in a range of <NUM> to <NUM>, and a relative refractive index difference Δn<NUM> in a range of -<NUM>% to -<NUM>%; characterized in that
the outer cladding layer is a pure silica glass layer, and has a diameter of <NUM>;
the core layer has a radius r<NUM> in a range of <NUM> to <NUM>, and a relative refractive index difference Δn<NUM> in a range of -<NUM>% to <NUM>%:
the core layer is a germanium-fluorine co-doped silica glass layer,
wherein a doping contribution of germanium to refractive index difference is in a range of <NUM>% to <NUM>%, and the bending-insensitive single-mode fiber has an attenuation at a wavelength of <NUM> being less than or equal to <NUM> dB/km.