Automatic power control with electronic amplified spontaneous emission compensation

Semiconductor-based optical amplifiers (SOAs) offer solutions to a variety of amplification needs covering wavelengths ranging from of 0.6 to 1.6 μm. Gain adjustment, through the bias current, enables automatic power control to be implemented. However, this requires knowledge of the signal strength. The amplified spontaneous emission power, particularly in high gain SOAs, can be significant with respect to the signal strength, and therefore additional components may be required to derive an accurate measure of the signal strength. This increases both the complexity and cost of implementing automatic power control (APC). We report on a method for estimating the signal strength based on measurement of the total output power and the SOA drive current. The method is extendable to other methods of optical amplification, e.g., erbium-doped fiber amplifiers

Induced Voltage Measurements on a YBa2Cu3O7−δ Superconducting Thin Film Due to a Pair of Rotating Magnets

[[abstract]]In this study, the induced voltages due to the rotation of a pair of magnets on an YBCO superconducting thin film sample (SS) with and without bias current were measured. It was found that the induced root mean square voltage (Vrms) was a constant (V0) at temperatures higher than the critical temperature (Tc) of the SS, as expected from Faraday’s law. At a temperature in the superconducting transition region, the induced Vrms is a sensitive function of both the motion of the magnet and the bias current applied to the SS. These results can be understood by considering the superposition of the two kinds of induced voltages. One is induced according to Faraday’s law, and the other one is induced by the vortex movements inside the SS which is caused by the bias current. At temperatures below the transition region, the induced Vrms had a value equal to V0 and remained unchanged as the temperature further decreased. An explanation based on the distribution of the magnetic flux inside the SS was given, and it was concluded that the superconductor-normal conductor loop acted like a normal-normal conductor loop to the moving magnetic fields in this low temperature region.[[notice]]補正完