Optical power monitor for two‐beam laser diodes using electric operational circuits

This paper presents a method for monitoring individual laser beams from an array-type, two-beam laser diode with two emission points in one laser chip using an electric operational circuit. the characteristics of the two-beam monitoring system are evaluated by experiment. This system analytically monitors optical output powers on the principle that the two laser beams are received at different ratios by a photodiode having two detecting surfaces located near the laser facet. the main feature of the system is the possibility of signal separation using a simple circuit configuration and adjustmentfree arrangement of the photodiode. Evaluation of a trial two-beam monitoring circuit has revealed that a gain deterioration of 3 dB is exhibited at 1 MHz. Crosstalk, which represents the degree of signal separation, depends on frequency and is -54 dB at 10 kHz and -23 dB at 1 MHz, exhibiting excellent separation characteristics. These results can be used without problems in optical disk drives incorporating two-beam laser diodes. Thus, they demonstrate the effectiveness and practicality of the proposed system.