JP2006133314A - Optical fiber and transmission system and wavelength division multiplexing transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber capable of increasing the threshold power of stimulated Brillouin scattering as compared with a conventional optical fiber, a transmission system using the optical fiber, and a wavelength multiplexing transmission system.
A single-mode optical fiber mainly composed of quartz glass, which contains germanium and fluorine as dopants, and a portion A having the highest germanium concentration is located on the line connecting the central axis and the outer periphery of the optical fiber. Each optical fiber is characterized in that each dopant is added so that a portion B having a highest fluorine concentration exists closer to the outer periphery than A.
[Selection] Figure 2

Description

  The present invention relates to an optical fiber that can suppress the occurrence of stimulated Brillouin scattering (hereinafter referred to as SBS) and can transmit a signal with a higher power.

  In recent years, a fiber to the home (hereinafter referred to as FTTH) service has been started in which an optical fiber is extended to each home and various information is exchanged using the optical fiber.

  As one form of FTTH for transmitting various information, there is a system for simultaneously transmitting a broadcast signal and other communication signals using different optical systems using a single optical fiber (ITUT Recommendation G. 983.3). In general, in this system, the broadcast signal is often an analog signal, a baseband signal, or an optical SCM signal.

The characteristics of the system from the viewpoint of an optical fiber as a transmission medium are as follows.
FTTH is usually a double star PON (Passive Optical Network), and has a large distribution loss (usually a maximum of 32 branches is assumed).
-Since analog signals, baseband signals, or optical SCM signals are transmitted, it is necessary to increase the CNR (Carrier Noise Ratio) at the receiver, and the minimum signal light power at the required light receiving unit is used for digital transmission used in communication. Larger than that.

  Therefore, in this system, it is necessary to increase the required signal light power in the signal input unit. In particular, considering attenuation and distribution loss during transmission of signal light, higher power is required for longer-distance lines and more branched lines. As a matter of course, it is advantageous from various viewpoints (construction cost, maintainability, system design, etc.) that signals can be transmitted as far as possible and distributed to many subscribers at the same time.

  However, in optical transmission using an optical fiber, even if light exceeding the power existing in the optical fiber is made incident by SBS, which is a kind of nonlinear phenomenon, only a certain amount of light (hereinafter referred to as SBS threshold power) is used. There is a case in which the incident cannot be made and the rest becomes backscattered light and returns to the incident light side, which may limit the signal light power at the input unit, which has been a problem (for example, non- (See Patent Document 1).

Conventionally, as a method for realizing SBS suppression, a method of changing optical characteristics, dopant concentration, and residual stress in the longitudinal direction has been reported (see, for example, Patent Document 1 and Non-Patent Document 2).
ARCharaplyvy, J. Lightwave Technol., Vol.8, pp.1548-1557 (1990) Japanese Patent No. 2584151 K. Shiraki, et al., J. Lightwave Technol., Vol. 14, pp. 50-57 (1996)

  However, the SBS suppression methods described in Patent Literature 1 and Non-Patent Literature 2 inevitably change the optical characteristics in the longitudinal direction of the optical fiber.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical fiber, a transmission system using the same, and a wavelength multiplexing transmission system that can increase the SBS threshold power as compared with a conventional optical fiber.

  In order to achieve the above object, the present invention provides a single mode optical fiber mainly composed of quartz glass, containing germanium and fluorine as dopants, and the concentration of germanium on a line connecting the central axis and the outer periphery of the optical fiber. Each dopant is added so that the highest part (A) exists near the central axis and the part (B) with the highest fluorine concentration exists closer to the outer periphery than the above (A). An optical fiber is provided.

  In the optical fiber of the present invention, it is preferable that a portion where germanium and fluorine are co-doped exists in a part of the optical fiber.

  In the optical fiber of the present invention, it is preferable that the portion (A) having the highest germanium concentration does not exist in the central axis of the optical fiber.

  The present invention also provides a transmission system configured to perform analog signal transmission, baseband transmission, or optical SCM transmission using the above-described optical fiber according to the present invention.

  Further, the present invention is characterized in that data transmission and / or voice transmission is performed together with analog signal transmission and / or baseband transmission or optical SCM transmission using the optical fiber according to the present invention. A wavelength division multiplexing transmission system is provided.

  According to the present invention, there are provided an optical fiber capable of suppressing the generation of SBS and transmitting with a higher power signal, a transmission system capable of multi-branching and long-distance transmission using the same, and a wavelength division multiplexing transmission system. can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing an embodiment of an optical fiber according to the present invention, and FIG. 2 is a graph showing the addition concentrations of germanium and fluorine in the radial direction of the optical fiber.
The optical fiber 1 of the present embodiment is a single mode optical fiber mainly composed of quartz glass, contains germanium and fluorine as dopants, and has the highest germanium concentration on the line connecting the central axis C and the outer periphery of the optical fiber. Each dopant is added so that a high part (A) exists near the central axis, and a part (B) having the highest fluorine concentration exists nearer the outer periphery than the above (A).

  As known to those skilled in the art, the optical fiber 1 includes a core 2 having a high refractive index through which light passes and a clad 3 having a lower refractive index than the core 2 surrounding the optical fiber 1 as shown in FIG. Are arranged in a cylindrical shape and transmit light as an information transmission medium along the axial direction thereof. In FIG. 1, the boundary between the core 2 and the cladding 3 is clearly shown for easy understanding. However, in actuality, the refractive index of the core 2 and the cladding 3 changes continuously. The boundaries are not always clear.

  In general, in the optical fiber 1 mainly composed of quartz glass, a dopant having a function of increasing the refractive index such as germanium is added in order to increase the refractive index of the core 2. In the present invention, fluorine is intentionally doped in order to form an acoustic core capable of propagating acoustic waves around the core 2. In this case, germanium and fluorine have a concentration distribution in the radial direction by, for example, diffusion of a dopant through the optical fiber manufacturing process. At this time, the concentration distribution of each dopant is such that the portion A having the highest germanium concentration is located near the central axis on the line connecting the central axis C and the outer periphery of the optical fiber 1 and the portion B having the highest fluorine concentration is It exists closer to the outer periphery than A.

  The 1st example of each dopant concentration distribution of the radial direction in the optical fiber 1 of this invention is shown in FIG. In this example, germanium is added so as to have a concentration distribution that spreads around the center axis C, and the concentration distribution of fluorine spreads in the radial direction is closer to the outer periphery than the germanium addition region. It has been added to. The part A having the highest germanium concentration exists at the position of the central axis C or a position near the center axis C, and the part B having the highest fluorine concentration exists on the outer peripheral side of the central axis C.

  This optical fiber 1 uses a conventionally known optical fiber preform manufacturing method such as VAD method or MCVD method, and a portion A having the highest germanium concentration is centered on a line connecting the central axis C and the outer periphery of the optical fiber 1. For example, germanium chloride gas or silicon fluoride gas is included in the silicon chloride gas for generating silica so that the portion B having the highest fluorine concentration exists closer to the outer circumference than A, and is located closer to the axis. An optical fiber preform mainly composed of quartz glass is produced while mixing an appropriate amount, and the obtained optical fiber preform is drawn in the same manner as a normal optical fiber spinning (drawing) process, and the obtained optical fiber is further obtained. Can be obtained by forming one or more appropriate resin coatings on the outer periphery of the substrate.

This optical fiber is a single-mode optical fiber mainly composed of quartz glass, contains germanium and fluorine as dopants, and a portion A having the highest germanium concentration on a line connecting the central axis C and the outer periphery of the optical fiber 1. Is located closer to the central axis, and the portion B having the highest fluorine concentration is located closer to the outer periphery than A, the following effects can be obtained.
(1) An acoustic core capable of propagating acoustic waves by fluorine addition is formed outside the optical core 2, and as a result, the field of the acoustic mode expands more than the optical mode, and SBS generated by the interaction between the signal light and the acoustic phonon. Can be provided, and a transmission system and a wavelength division multiplexing transmission system capable of multi-branching and long-distance transmission using the optical fiber can be provided.
(2) Since the refractive index near the boundary between the optical core 2 and the optical cladding 3 is steep, an optical fiber having excellent optical transmission characteristics and multi-branch / long-distance transmission using the optical fiber Possible transmission systems as well as wavelength division multiplexing transmission systems can be provided.

  FIG. 3 is a graph showing a second example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. In the optical fiber of this example, germanium is added so as to have a concentration distribution having a radial extension centered on the outer periphery from the central axis C, and fluorine is added to a portion closer to the outer periphery than the germanium-added portion. It is added so as to obtain a concentration distribution having a spread in the radial direction. The portion A having the highest germanium concentration exists at a position closer to the outer periphery than the central axis C, and the portion B having the highest fluorine concentration exists on the outer peripheral side from the A.

  The optical fiber of this example can obtain the same effect as the first example. The absence of the portion A having the highest germanium concentration on the central axis C of the optical fiber makes it possible to achieve acoustic characteristics without greatly changing the optical characteristics. Since the shape of the core can be changed, it is more preferable.

  FIG. 4 is a graph showing a third example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. In the optical fiber of this example, germanium is added so as to have a concentration distribution having a radial expansion centered closer to the outer periphery than the central axis C, and fluorine partially overlaps the germanium addition site. Is added so as to obtain a concentration distribution having a radial expansion toward the outer periphery. The portion A having the highest germanium concentration exists at a position closer to the outer periphery than the central axis C, and the portion B having the highest fluorine concentration exists on the outer peripheral side from the A. The optical fiber of this example has a Ge / F co-added portion D in part.

  The optical fiber of this example can obtain the same effects as those of the second example. Further, since the Ge and F co-added portion D is provided in a part of the optical fiber, particularly with respect to (2) above. This is more preferable because the effect becomes large.

  FIG. 5 is a graph showing a fourth example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. The optical fiber of this example is a low peak in which germanium is added so as to have a concentration distribution that spreads around the center axis C, and fluorine is partially overlapped with the germanium addition site, but the center is shifted closer to the outer periphery. It is added so as to obtain a concentration distribution. The part A having the highest germanium concentration exists at the position of the central axis C or a position near the center axis C, and the part B having the highest fluorine concentration exists on the outer peripheral side of the central axis C. The optical fiber of this example has a Ge / F co-added portion D in part. The optical fiber of this example can obtain the same effect as the third example.

  FIG. 6 is a graph showing a fifth example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. In the optical fiber of this example, germanium does not exist in the central axis, and germanium is added so as to have a concentration distribution having a radial extension with the center closer to the outer periphery than the central axis C, and fluorine. In addition, it is added so as to have a concentration distribution that partially overlaps with the germanium-added site but has a radially expanding center. The portion A having the highest germanium concentration exists at a position closer to the outer periphery than the central axis C, and the portion B having the highest fluorine concentration exists on the outer peripheral side from the A. The optical fiber of this example has a Ge / F co-added portion D in part. The optical fiber of this example can obtain the same effect as the third example.

  FIG. 7 is a graph showing a sixth example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. In the optical fiber of this example, germanium is added so as to have a concentration distribution having a radial boundary and a steep boundary around the central axis C, and fluorine is partially overlapped with the germanium addition site. Is added so as to obtain a concentration distribution having a radial expansion with the center shifted toward the outer periphery. The part A having the highest germanium concentration exists at the position of the central axis C or a position near the center axis C, and the part B having the highest fluorine concentration exists on the outer peripheral side of the central axis C. The optical fiber of this example has a Ge / F co-added portion D in part. The optical fiber of this example can obtain the same effect as the third example.

  FIG. 8 is a graph showing a seventh example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. In the optical fiber of this example, germanium does not exist in the central axis, and germanium is added so as to have a concentration distribution having a radial extension with the center closer to the outer periphery than the central axis C, and fluorine. In addition, it is added so as to have a low mountain-shaped concentration distribution in which the center overlaps with the germanium addition site but the center is closer to the outer periphery. The portion A having the highest germanium concentration exists at a position closer to the outer periphery than the central axis C, and the portion B having the highest fluorine concentration exists on the outer peripheral side from the A. The optical fiber of this example has a Ge / F co-added portion D in part. The optical fiber of this example can obtain the same effect as the third example.

  FIG. 9 is a graph showing an eighth example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. In the optical fiber of this example, germanium is added so as to have a concentration distribution having a radially extending center with a center closer to the outer periphery than the central axis C, and fluorine is overlapped with the germanium addition site. It is added so as to obtain a concentration distribution having a radial expansion near the outer periphery. The portion A having the highest germanium concentration exists at a position closer to the outer periphery than the central axis C, and the portion B having the highest fluorine concentration exists on the outer peripheral side from the A. The optical fiber of this example has Ge and F co-added sites D. The optical fiber of this example can obtain the same effect as the third example.

  FIG. 10 is a graph showing a ninth example of each dopant concentration distribution in the radial direction in the optical fiber of the present invention. In the optical fiber of this example, germanium is added so as to have a concentration distribution having a radial expansion centered closer to the outer periphery than the central axis C, and fluorine partially overlaps the germanium addition site. Is added so as to form a low mountain-shaped concentration distribution near the outer periphery. The portion A having the highest germanium concentration exists at a position closer to the outer periphery than the central axis C, and the portion B having the highest fluorine concentration exists on the outer peripheral side from the A. The optical fiber of this example has a Ge / F co-added portion D in part. The optical fiber of this example can obtain the same effect as the third example.

The present invention also provides a transmission system using the above-described optical fiber according to the present invention.
As described above, the advantage of using the optical fiber according to the present invention described above is that higher power signal light can be introduced. Therefore, by performing analog transmission and baseband transmission that require relatively high power using the optical fiber of the present invention, it becomes possible to perform transmission with more multi-branches and longer distances, and can enjoy great benefits. In particular, in the case of a system in which the transmission distance is 15 km or more and / or the number of branches is 32 or more, the greatest benefit can be obtained.

In addition to the above-described analog transmission and baseband transmission, the optical fiber according to the present invention can be used for wavelength division multiplexing transmission in which other transmissions are simultaneously performed. As wavelength multiplexing transmission, ITU-TG As one form of FTTH as shown in 983.3, CWDM or the like is conceivable. In particular, in the case of a system in which the transmission distance is 15 km or more and / or the number of branches is 32 or more, the greatest benefit can be obtained.
Of course, the transmission system need not be limited to these applications. For example, it can be used not only for ordinary public data communication but also for digital long-distance repeaterless transmission systems, ITS, sensor applications, remote laser cutting systems, and the like.

It is a perspective view of the optical fiber which shows one Embodiment of this invention. It is a graph which shows the 1st example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 2nd example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 3rd example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 4th example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 5th example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 6th example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 7th example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 8th example of each dopant concentration distribution of the radial direction in the optical fiber of this invention. It is a graph which shows the 9th example of each dopant concentration distribution of the radial direction in the optical fiber of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... Core, 3 ... Cladding, A ... A site | part with the highest density | concentration of germanium, B ... A site | part with the highest density | concentration of a fluorine, C ... Optical fiber center axis | shaft, D ... Ge, F co-addition site | part.

Claims (5)

  A single-mode optical fiber mainly composed of quartz glass, which contains germanium and fluorine as dopants. On the line connecting the central axis and the outer periphery of the optical fiber, the portion (A) having the highest germanium concentration is closer to the central axis. Each optical fiber is characterized in that each dopant is added so that the portion (B) that exists and has the highest fluorine concentration exists closer to the outer periphery than the above (A).   The optical fiber according to claim 1, wherein a portion where germanium and fluorine are co-doped exists in a part of the optical fiber.   The optical fiber according to claim 1 or 2, wherein a portion (A) having the highest germanium concentration does not exist in the central axis of the optical fiber.   A transmission system configured to perform analog signal transmission, baseband transmission, or optical SCM transmission using the optical fiber according to claim 1. The optical fiber according to claim 1 is configured to perform data transmission and / or voice transmission together with analog signal transmission and / or baseband transmission or optical SCM transmission. Wavelength multiplex transmission system.

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