Research On Driver Chip Of Electro-optic Modulator In Quantum Key Distribution System

Quantum Key Distribution(QKD)is a key distribution technology with information-theoretic security that combines quantum mechanics and classical cryptography.Its security advantages and many years of development in theory and practice make QKD technology the most mature technology in the field of quantum secure communication.China’s QKD experiments and applications are also developed rapidly in recent years.Many major achievements such as Micius,BeijingShanghai Trunk Line and the successful construction of the world’s first spaceground integrated QKD network on this basis mark the gradual expansion of the scale of QKD technology.A wide range of network scales and abundant application scenarios require QKD equipment to have a smaller volume,accordingly the miniaturization of key components in the QKD system is an important direction for the subsequent development of QKD equipment.At this stage,the transceiver devices of the QKD system are based on board-level discrete devices,which have large volume and power consumption,and the devices used have low autonomy.At the sender of the system,it mainly includes the main control module,the optical module and the front-end analog electronics module.At present,domestic research on the integration of the main control module and the optical module is gradually carried out.Application specific data processing SOC chip in QKD and silicon photonics integrated chip obtain some achievements on research.This paper focuses on the integration of the front-end electronics modulator driver module in the QKD system,and designs a modulator driver chip based on Application Specific Integrated Circuit(ASIC)technology including the first version of the modulator driver chip based on the CMOS process with an application frequency of 312.5 MHz and an upgraded modulator driver chip based on the SiGe process with an application frequency of 1.25 GHz.The modulator driver chip is design to generate a multi-platform pulse signal to drive the modulator under the trigger of the random code signal at the control end.In practice,most high-speed electro-optic modulators have high driving voltage requirements,consequently they are driven by a combination of modulation driving chips and power amplifiers.The final test results show that the modulator driver chip of CMOS process can realize the adjustable output amplitude of the driving signal at a data rate of 312.5 Mbps,the maximum amplitude can reach 600 mV,the pulse width can be adjusted,and the adjustment range is 400 ps-1.4 ns.In the QKD experimental system with repetition frequency of 312.5 MHz based on the 1550 nm laser,photonics integrated chip and superconducting detector,the extinction ratio between the intensity modulation signal state and the vacuum state is not less than 29 dB,and the average extinction ratio for the four polarization states are about 23 dB.The modulator driver chip based on the SiGe process is an upgrade of the various performance indicators of the CMOS process chip.It can realize that the output amplitude of the driver is adjustable and the maximum amplitude can reach 1.5 V at a data rate of 1.25 GHz.The pulse width of the chip output signal can be fine-tuned and this chip will be gradually applied to the 1.25 GHz QKD system.In conclusion,the modulator driver chip reschs the design expectations,and the test results meet the design requirements.The innovations of this paper are as follows:1.An integrated solution is proposed for the QKD transmitter modulator driver module.This scheme replaces the existing modulation and driving scheme that realizes multi-state output through board-level circuits,and has independent intellectual property rights.2.In the modulator driving chip,in order to realize the electrical pulse output corresponding to the optical signals of four polarization states or three amplitude states independent of each other,a scheme of randomly gating three different amplitude paths is proposed.In this scheme,only the output of one signal corresponding to the electrical signal is gated each time to ensure that each channel has no correlation when reducing the phase jitter of the signal,that is,the independent adjustment of the amplitude of each electrical pulse is realized.