Quantum key distribution (QKD) has rapidly developed recently. The repetition frequency of the QKD system increases from tens or hundreds of MHz to GHz. A laser diode (LD) operating in gain-switched mode is widely used as a weak coherent light source in a QKD system. We present an LD driver circuit fabricated in 0.18 μm SiGe heterojunction bipolar transistor bipolar complementary metal oxide semiconductor technology. The circuit can operate at frequencies up to 2.5 GHz, satisfying the requirements of high-speed laser drives in practical QKD systems. The output current of the driver circuit can reach 100 mA when driving an LD whose input equivalent resistance is ∼21 Ω. The extinction ratio of the 1550-nm distributed feedback LD light source driven by our driver circuit reaches 23 dB at the operating frequency of 2.5 GHz, meeting the requirements of QKD systems. This circuit will be used in miniaturized QKD systems.
We present a laser source driver using a 130-nm complementary metal oxide semiconductor technology, named quantum laser source driver 2018 (QLSD2018). QLSD2018 drives the optical source with a current pulse signal, and the output of QLSD2018 has an adjustable pulse-width from 300 ps to 3.8 ns and an adjustable amplitude up to 70 mA. The data rate is up to 625 Mb/s, and the extinction ratio of the optical source (the 1550-nm distributed feedback laser or the 850-nm vertical-cavity surface-emitting laser) driven by QLSD2018 can reach 26 dB. The test results indicate that QLSD2018 can be used in quantum key distribution experiments. Using QLSD2018 on the transmitter side can significantly simplify the peripheral circuit of the optical source.
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