QFPQL010400D is a high performance QSFP+ transceiver module for 40 Gigabit Ethernet data links over two single mode fibr es. The transmi tters (4×) are CWDM DFB (Distributed Feedback) lasers, the receivers (4×) are PIN photodiodes. It provides an expert-curated supplier directory, buyer-focused technical background information, and structured selection criteria to support professional procurement decisions. A & A INTERNATIONAL SERVICES, INC. REILLY. Such lasers are referred to as single-frequency or single-longitudinal-mode lasers and in view of their potential application in optical communication systems were studied extensively during the 1980s. They are used in commercial light wave systems by 1990. A DFB laser's periodic structure acts as a distributed reflector, providing optical feedback and. The acronym DFB laser stands for distributed feedback laser.