Fibre optic termination

Apparatus for optical time domain reflectometry comprising an elongate optical fibre having a core of refractive index n', surrounded by cladding of refractive index n.sub.c, a termination at one extremity thereof, said termination including a surface termination including a surface through which light is, in use injected into the core of the fibre at an angle .phi. relative to a normal to said surface, the surface being arranged such that the longitudinal axis of the core is inclined at an angle .alpha. to said surface, and wherein

• 90.degree.-.phi..sub.c '-.theta..sub.c '.ltoreq..alpha..ltoreq.90.degree.-.phi.'+.theta..sub.c '
• where
• .phi..sub.c '=arc sin (n/n')
• .theta..sub.c '=arc sin (2.DELTA.n.sub.m).sup.1/2
• .phi.'=arc sin (sin .phi./n')
• .DELTA.n.sub.m =(n'-n.sub.c)/n' and
• wherein arc sin [n' sin (.phi..sub.c '-2.theta..sub.c ')].ltoreq..phi..ltoreq.90.degree., a source of light for injecting a beam of light into said surface at said angle .phi. relative to the normal to said surface and a detector located adjacent to said termination and arranged to receive back-scattered light reflected at said surface through the core and cladding of the termination.

Apparatus for transmission of signals comprising

• an elongate optical fibre having a core of refractive index n', surrounded by cladding of refractive index n.sub.c,
• said elongate optical fibre having first and second terminations at first and second ends respectively,
• each said termination including a surface through which light is, in use injected into the core of the fibre at an angle .phi. relative to a normal to said surface, the surface being arranged such that the longitudinal axis of the core is inclined at an angle .alpha. to said surface, and wherein
• 9.degree.-.phi..sub. c '-.theta..sub.c '.ltoreq..alpha..ltoreq.90.degree.-.phi.'+.THETA..sub.c '
• where
• .phi..sub.c '=arc sin (n/n')
• .theta..sub.c '=arc sin (2.DELTA.n.sub.m).sup.178
• .phi.'=arc sin (sin .phi./n')
• .DELTA.n.sub.m =(n'-n.sub.c)/n' and
• wherein arc sin [n' sin (.phi..sub.c '-2.theta..sub.c ')].ltoreq..phi..ltoreq.90.degree.,
• a first source of light arranged to inject a first beam of light into said surface of said first termination at a first angle .phi. relative to the normal to said surface of the first termination, such that said first beam is subjected to refraction at said surface of said first termination and transmission through said core towards said second termination,
• a first detector located adjacent to said second termination and arranged to receive components of said first beam which are reflected at said surface of said second termination through the core and cladding of the second termination,
• a second source of light arranged to inject into said surface of said second termination a second beam of light at a second angle .phi. relative to the normal to said surface of the second termination, such that said second beam is subjected to refraction at said surface of said second termination and transmission through said core towards said first termination, and
• a second detector located adjacent to said first termination and arranged to receive components of said second beam which are reflected at said surface of the first termination through the core and cladding of the first termination.

A method of optical time domain reflectometry testing an elongate optical fibre having a core of refractive index n', surrounded by cladding of refractive index n.sub.c, said method including the steps of providing

• a termination at one end of the fibre, said termination including a surface through which light is, in use injected into the core of the fibre at an angle .phi. relative to a normal to said surface, the surface being arranged such that the longitudinal axis of the core is inclined at an angle .alpha. to said surface, and wherein
• 90.degree.-.phi..sub.c '-.theta..sub.c '.ltoreq..alpha..ltoreq.90.degree.-.phi.'+.theta..sub.c '
• where
• .phi..sub.c '=arc sin (n/n')
• .theta..sub.c '=arc sin (2.DELTA.n.sub.m)hu 1/2
• .theta.'=arc sin (sin .phi./n')
• .DELTA.n.sub.m =(n'-n.sub.c)/n' and
• wherein arc sin [n' sin (.phi..sub.c '-2.theta..sub.c ')].ltoreq..phi..ltoreq.90.degree.,
• injecting a beam of light into said surface, and
• detecting back-scattered light reflected at said surface through the core and cladding of the termination.

A method of optical signal transmission in an elongate optical fibre having a core of refractive index n', surrounded by cladding of refractive index n.sub.c ', said method including the steps of

• providing first and second terminations at first and second ends respectively of the elongate optical fibre, each said termination including a surface through which light is, in use injected into the core of the fibre at an angle .phi. relative to a normal to said surface, the surface being arranged such that the longitudinal axis of the core is inclined at an angle .alpha. to said surface, and wherein
• 90.degree.-.phi..sub.c '-.theta..sub.c '.ltoreq..alpha..ltoreq.90.degree.-.phi.'+.theta..sub.c '
• wherein
• .phi.c'=arc sin (n/n')
• .theta..sub.c '=arc sin (2.DELTA.n.sub.m).sup.1/2
• .phi.'=arc sin (sin .phi./n')
• .DELTA.n.sub.m =(n'-n.sub.c)/n' and
• wherein arc sin [n' sin (.phi..sub.c '-2.theta..sub.c ')].ltoreq..phi..ltoreq.90.degree.,
• injecting a first beam of light into said surface of said first termination,
• detecting components of said first beam which are reflected at said surface of said second termination through the core and cladding of the second termination,
• injecting a second beam of light into said surface of said second termination, and
• detecting components of said second beam which are reflected at said surface of said first termination through the core and cladding of the first termination.

A method of optical signal transmission in an elongate optical fibre having a core of refractive index n', surrounded by cladding of refractive index n.sub.c, said method including the steps of

• providing first and second terminations at first and second ends respectively of the elongate optical fibre, each said termination including a surface through which light is, in use injected into the core of the fibre at an angle .phi. relative to a normal to said surface, the surface being arranged such that the longitudinal axis of the core is inclined at an angle .alpha. to said surface, and wherein
• 90.degree.-.phi..sub.c '-.theta..sub.c '.ltoreq..alpha..ltoreq.90.degree.-.phi.'+.theta..sub.c '
• where
• .phi.c'=arc sin (n/n')
• .theta..sub.c '=arc sin (2.DELTA.n.sub.m).sup.1/2
• .phi.'=arc sin (sin .phi./n')
• .DELTA.n.sub.m =(n'-n.sub.c)/n' and
• wherein arc sin [n' sin (.phi..sub.c '-2.theta..sub.c ')].ltoreq..phi..ltoreq.90.degree.,
• injecting a first beam of light into said surface of said first termination, such that said first beam is subjected to refraction at said surface of said first termination and transmission through said core towards said second termination,
• detecting components of said first beam which are reflected at said surface of said second termination through the core and cladding of the second termination,
• injecting a second beam of light into said surface of said second termination such that said second beam is subjected to refraction at said surface of said second termination and transmission through said core towards said first termination, and
• detecting components of said second beam which are reflected at said surface of said first termination through the core and cladding of the first termination.