INPUT/OUTPUT PHENOMENON

In theory for a straight fiber whose end faces are perpendicular to its axis, a small collimated beam of rays entering the fiber at 25 degrees off axis will exit the fiber at 25 degrees off axis.

In practice, multiple internal reflections, fiber length, micro-bending (external surface features) and manufacturing defects will spread collimated rays out to fill an annulus (or doughnut) of a cone whose total angle is twice that of the input angle. The thickness of the annulus will equal the diameter of the input beam. If the input beam is conical and focused on the face of the fiber, the output beam will still form an annulus of a cone whose nominal angle is twice the input angle, but the thickness of the annulus will now be determined by the angle of the input beam cone.

Temporal imaging system. Input and output dispersions play the role of free-space diffraction while quadratic phase modulation acts as a time lens. Output wave form envelope is a magnified version of the input envelope.

Schematic diagram of up-conversion time microscope. Input wave form I(t) is a 4 bit 100 Gb/s word. Input and output dispersion is obtained by two sets of diffraction grating pairs. The up-conversion time lens is achieved by sum frequency generation of the input wave form and a linearly chirped pump E(t). The output wave form is the magnified and inverted I(t/M).