Chapter 5 Laser-Fiber Connection

Content Launching optical power into a fiber Fiber-to-Fiber coupling Fiber Splicing and connectors

Coupling Efficiency [5-1] SourceOptical Fiber

Radiance (Brightness) of the source B= Optical power radiated from a unit area of the source into a unit solid angle [watts/(square centimeter per stradian)]

Surface emitting LEDs have a Lambertian pattern: [5-2]

Edge emitting LEDs and laser diodes radiation pattern For edge emitting LEDs, L=1 [5-3]

Power Coupled from source to the fiber [ 5-4]

Power coupled from LED to the Fiber [5-5]

Power coupling from LED to step-index fiber Total optical power from LED: [5-6] [5-7]

Equilibrium Numerical Aperture

Examples of possible lensing schemes used to improve optical source-to-fiber coupling efficiency

Laser diode to Fiber Coupling

Fiber-to-Fiber Joint Fiber-to-Fiber coupling loss: Low loss fiber-fiber joints are either: 1- Splice (permanent bond) 2- Connector (demountable connection) [5-8]

Different modal distribution of the optical beam emerging from a fiber lead to different degrees of coupling loss. a) when all modes are equally excited, the output beam fills the entire output NA. b) for a steady state modal distribution, only the equilibrium NA is filled by the output beam.

Mechanical misalignment losses Lateral (axial) misalignment loss is a dominant Mechanical loss. [5-9]

Longitudinal offset effect Losses due to differences in the geometry and waveguide characteristics of the fibers [5-10] E & R subscripts refer to emitting and receiving fibers.

Experimental comparison of Loss as a function of mechanical misalignment

Fiber end face Fiber end defects

Fiber splicing Fusion Splicing

V-groove optical fiber splicing

Optical Fiber Connectors Some of the principal requirements of a good connector design are as follows: 1- low coupling losses 2- Interchangeability 3- Ease of assembly 4- Low environmental sensitivity 5- Low-cost and reliable construction 6- Ease of connection

Connector Return Loss