Optical fiber

Abstract

The present invention relates to an optical fiber having a structure to enable both prevention of resin coating combustion due to leaked light, and low-loss light transmission. The optical fiber comprises a core region, and a cladding region. The cladding region is constituted by an optical cladding which affects the transmission characteristics of light propagating in the core region, and a physical cladding which does not affect the transmission characteristics of light propagating in the core region. Particularly, a leakage reduction portion is provided in the physical cladding so as to surround an outer periphery of the core region through the optical cladding. The leakage reduction portion functions to suppress propagation of the leaked light propagating from the core region toward outside the cladding region.

1 . An optical fiber comprising: a core region extending along an optical axis; and a cladding region provided on an outer periphery of the core region,
 wherein the cladding region comprises: an optical cladding, as a region which affects transmission characteristics of light propagating through the core region, provided on the outer periphery of the core region; and a physical cladding, as a region which does not affect transmission characteristics of light propagating through the core region, provided on an outer periphery of the optical cladding, and   wherein the physical cladding includes a leakage reduction portion for suppressing the propagation, outside the cladding region, of leaked light which has arrived via the optical cladding from the core region.   
   
   
       2 . An optical fiber according to  claim 1 , wherein, in a cross-section of the optical fiber orthogonal to the optical axis, the leakage reduction portion is provided between a position, where a distance from the optical axis is 5/2 times the mode field diameter of the optical fiber at wavelength 1.55 μm, and an outer surface of the cladding region. 
   
   
       3 . An optical fiber according to  claim 1 , wherein, in a cross-section of the optical fiber orthogonal to the optical axis, the leakage reduction portion is provided between a position, where an electric field amplitude of the optical fiber is 10 −4  of a peak value or less, and an outer surface of the cladding region. 
   
   
       4 . An optical fiber according to  claim 1 , wherein, in a state that the optical fiber is bent at a predetermined radius, the leakage reduction portion reduces a ratio of the light quantity of leaked light, passing through the leakage reduction portion, to the light quantity of leaked light arriving from the bent portion of the core region to 1/10 or less. 
   
   
       5 . An optical fiber according to  claim 1 , wherein, by absorbing part of leaked light arriving from the core region, the leakage reduction portion reduces the light quantity of leaked light which propagates outside the cladding region. 
   
   
       6 . An optical fiber according to  claim 1 , wherein, by causing the leaked light arriving from the core region to be deflected, the leakage reduction portion reduces the light quantity of leaked light which propagates outside the cladding region. 
   
   
       7 . An optical fiber according to  claim 6 , wherein the leakage reduction portion has a hole or a trench extending along the core region, whereby the existence of the hole or trench confines the leaked light, which has arrived from the core region, within an inside region positioned on the core region side of the leakage reduction portion. 
   
   
       8 . An optical fiber according to  claim 6 , wherein the leakage reduction portion has a higher refractive index than those of the optical cladding and the physical cladding from which the leakage reduction portion is excluded, whereby the leaked light, which has arrived from the core region, propagates through the leakage reduction portion. 
   
   
       9 . An optical fiber according to  claim 6 , wherein the leakage reduction portion includes a minute anisotropic member, whereby the existence of the minute anisotropic member increases scattering of the leaked light which has arrived from the core region.