R&D background
Under the general trend of the development of the information society, the total amount of information generated by humans and machines will continue to grow exponentially at a rate of 50-60% per year in the next 15 years. Whether the optical fiber network can provide the communication capacity required for the rapid growth of mass information transmission in the future is a fundamental issue related to the sustainability of information technology development. The key challenge it faces is how to continuously expand the optical channel bandwidth and signal-to-noise ratio to improve the information transmission capacity, at the same time, not only reduce the energy consumption per unit capacity, but also further reduce the total energy consumption of the channel, thus reversing the overall trend that the energy consumption increases with the amount of information. The physical hardware technology represented by optoelectronic chips and devices is the main breakthrough to solve the above key technical challenges and neck problems.
Increasing the symbol rate (baud rate) of optical fiber transmission can greatly reduce the number of chips and devices at the transmitting end of optical fiber communication. It is an important means to increase the speed, reduce energy consumption and control costs of optical fiber communication networks. At present, the commercial coherent optical transmission system adopts the digital signal processing (DSP) chip of 7nm process node, which can support 800Gbit/s data transmission rate with the modulation code type of 96G baud symbol rate and 64QAM. The next generation transmission system adopts 5nm DSP, 130G baud symbol rate, QPSK modulation code type, and can support long-distance transmission with 400Gbit/s data rate of 1500km. Whether the next step can realize coherent optical communication system with symbol rate exceeding 200G baud has become the focus of the industry. The key lies in whether optoelectronic chips and microelectronic chips can break through the current performance bottleneck. The electro-optic modulator with a super large electro-optic bandwidth of more than 100GHz and an ultra-low drive voltage of less than 1V is the core key optoelectronic chip to achieve this goal.
Major innovations
In January 2022, Sun Yat sen University, in cooperation with Huawei, published the world's first polarization multiplexing coherent light modulator chip based on lithium niobate film (M. Xu, et al. There are still many challenges to raise the baud rate above 200Gbaud. All optoelectronic components in the system need to have sufficient bandwidth, and the amplitude of the electric drive signal at high baud rate is only 100 millivolts, which puts forward strict requirements for electro-optic modulator chips and test instruments.
On the basis of the above work, Niobium Austria Optoelectronics, Sun Yat sen University, Bell Laboratory (France), III-V Laboratory (France) and Zede Technology formed a joint research and development team to further optimize and design the optical design and microwave design of lithium niobate film electro-optical modulator, use quartz substrate to achieve ultra-low microwave loss, and use capacitive traveling wave electrode to achieve on-chip synchronous transmission of microwave rate and light wave rate, A high-performance dual polarization coherent light modulator with 3dB electro-optical bandwidth up to 110 GHz and half wave voltage as low as 1 V has been successfully developed, as shown in Figure 1. In order to carry out stable transmission experiments, Niobio Optoelectronics also completed the coupling of low loss optical fiber array and modulator chip, and realized the packaging module that can flexibly arrange RF interfaces.
Lithium Niobate Thin Film IQ Modulator
The joint team further realized the record breaking 260G ultra-high baud rate DP-QPSK modulation (as shown in Figure 2) and demonstrated the 100km single-mode optical fiber transmission by using the highest performance arbitrary waveform generator (AWG), the Deutsch M8199B prototype, with a sampling rate of up to 260Gsa/s and a bandwidth of over 75GHz. Furthermore, the 185G baud PCS-64QAM high-order modulation format is used to achieve 1.84 Tb/s achievable information ratio (AIR) (as shown in Figure 3). The excellent performance of lithium niobate film modulator, such as large bandwidth and low drive voltage, makes it unnecessary to use nonlinear DSP algorithm and MLSE equalizer with complex algorithm in transmission experiment, thus creating a record of coherent optical transmission again with lower DSP complexity and power consumption.
This work demonstrates the current highest optical fiber communication baud rate
