The spiral includes turns of rectangular section, whose pitch p and/or thickness e can vary from the inside curve towards the outside curve, or whose winding can deviate from the line of a perfect spiral. The inside curve can also be extended by a self-locking washer for fixing the spiral on the balance arbour with no play. The spiral is manufactured by photolithography and galvanic growth, or by micro-machining an amorphous or crystalline material, such as a silicon wafer.

A method to manufacture a hairspring of a timepiece movement, which includes: producing a malleable elongated element in a form of under a fiber or ribbon form, from a first heated material capable of guiding light; conforming the malleable elongated element in order to achieve into a spiral form; and handling processing the spiral form thus created in order to obtain a hairspring for providing both a mechanical oscillating function in a balance wheel and a light guiding guide lighting function arranged for in situ adjusting of a mechanical performance of said hairspring. The conforming includes coiling the malleable elongated element around a rotating mobile conformation tool, and receiving the malleable elongated element in a guiding channel within a guiding mechanism and guiding the received malleable elongated element via mobile equipment turning on an inner periphery of the guiding mechanism.

A balance-spring intended to equip a balance of an horological movement, comprising a core made of NbTi made from an alloy consisting of: niobium: balance to 100% by weight, titanium: between 5 and 95% by weight, traces of elements chosen from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu, Al, each of said elements being present in a quantity between 0 and 1600 ppm by weight, the total quantity formed by all of said elements being between 0% and 0.3% by weight, wherein the core made of NbTi is coated with a layer of niobium, said layer of niobium having a thickness between 20 nm and 10 ?m.

A tool for separating a plate of balance springs after winding in, including substantially parallel lower and upper rolling surfaces which are movable relative to one another, vertically or longitudinally, in order to deform the plate by ovalisation, and to subject it to a rolling movement between the rolling surfaces, and further relates to a method for separating balance springs from a plate using this tool in order to mechanically crush it in the elastic range and initiate sequences of compressing and rolling the plate.