Keysight Technologies 81650A User Manual

Contents

22 Keysight Laser Source Modules User’s Guide3 SpecificationsConditionsUninterrupted line voltage, constant power level setting, CW operation,operating temperature change within specified limits, minimum return lossas specified, all polarization states of back-reflection included.MeasurementThe change of the output power is monitored while the source’ssusceptibility to back-reflection is tested by disturbing the laser oscillationwith power reflected back into the laser, P back. The back-reflectionsensitivity depends on the absolute power level of Pback and on thepolarization state of Pback .At fixed power levels of Pback, back-reflection sensitivity has its maximumwhen the states of polarization (SOP) of P back and P in (the source’s outputpower) are identical. To achieve this condition a polarization controllergenerates all SOPs of Pback. Thus the measured CW stability is a worstcase value with respect to the SOP. The test should be done at variouspower levels of Pback to address the fact that the CW stability is specifiedfor a range of back reflectance.However, the highest back reflection is the most critical by experience.NOTE Power reflected back from the radiating fiber end in general createsinstability in the laser cavity (mode jumps) resulting in output powerinstability. The ratio of the incident optical power Pin to the reflectedoptical power P back of an optical component is called return loss, symbolRL: