Methods and apparatus to determine a twist parameter and/or a bend angle associated with a multi-core fiber

An apparatus for making measurements of a multi-core fiber having multiple optical cores, comprising:

• detection circuitry configured to detect, for each different core of a set of different cores of the multiple optical cores, a total change in optical length representing an accumulation of all changes in optical length for multiple segments of that different core up to a point on the multi-core fiber;
• and
• calculation circuitry configured to determine a difference between the total changes in optical length for cores of the set of different cores and a twist parameter associated with the multi-core fiber at the point on the multi-core fiber based on the difference.

An apparatus for making measurements of a multi-core fiber having multiple optical cores, comprising circuitry configured to:

• detect a total change in optical length between different cores of the multiple optical cores, the total change in optical length representing an accumulation of all changes in optical length for multiple segments between the different cores of the multiple optical cores up to a position on the multi-core fiber, and
• calculate a bend angle of the multi-core fiber at the position along the multi-core fiber based on the total change in optical length up to the position along the multi-core fiber.