Abstract: An amplification optical fiber includes: a core doped with an active element; an inner cladding; and an outer cladding. The inner cladding is twisted about a center axis of the core, an outer circumference of the inner cladding has a polygon with rounded corners; and an angularity c defined by Expression (1) and Expression (2) is 0.15 or more and 0.8 or less, A=cos(?/n) . . . (1), c={1?(d1/d2)}/(1?A) . . . (2), where a number of vertices of the polygon is defined as n, a diameter of a circumcircle of the outer circumference of the inner cladding is defined as d2, and a diameter of an inscribed circle of the outer circumference of the inner cladding is defined as d1.

Abstract: A magnetic sensor drive circuit that measures a magnetic field by passing a feedback current, which cancels changes in magnetic flux density using measured magnetic field, through a prescribed coil. The drive circuit includes: a first circuit block which controls the feedback current by using an external power source as a power source; a second circuit block which has an output adjustment circuit adjusting a signal according to the strength of the feedback current to be a signal proportional to the voltage of the power source; a first power source line which supplies the external power source to the first circuit block; a second power source line which supplies the external power source to the second circuit block in parallel to the first power source line; a first low pass filter; and a second low pass filter.

Abstract: A magnetic sensor drive circuit that measures a magnetic field by passing a feedback current, which cancels changes in magnetic flux density using measured magnetic field, through a prescribed coil. The drive circuit includes: a first circuit block which controls the feedback current by using an external power source as a power source; a second circuit block which has an output adjustment circuit adjusting a signal according to the strength of the feedback current to be a signal proportional to the voltage of the power source; a first power source line which supplies the external power source to the first circuit block; a second power source line which supplies the external power source to the second circuit block in parallel to the first power source line; a first low pass filter; and a second low pass filter.