The invention concerns transparent materials having good impact resistance, a high modulus and good heat resistance. The circulators utilize various arrangements of birefringent elements, polarization rotators and non-reciprocal polarization rotators to route optical signals from a first inputoutput port to a second IO port, from the second IO port to a third IO port, from the third IO port to a fourth, and from the fourth IO port to the first IO port. Adjustment of thermowell length is achieved by rotation of the thermocouple-thermowell assembly from a position exterior to a mounting flange connected to the machine or process unit. The read signal can be obtained by positioning a transducer over a storage media. According to the present invention, the composite protective component may be mounted in a power input unit of the various power supply equipment, thereby stably shutting off an overcurrent and absorbing external surge.