**4. Conclusions**

We propose a two-bit encoding device working at terahertz frequencies. The device assembles the two graphene-based hybrid metamaterials with different shapes deposited on the front and back surfaces of a silicon wafer. Using the external electrodes to change the conductivities of the graphene on each side individually, we realize the active control of dual-band transmission amplitudes. The results demonstrate that our device can function at 0.20 THz and 0.33 THz with good performance, and the modulation depth can reach 79.6%. Comparing with the present THz modulators, our encoder can not only maximally enhance the coding number in a single chip, but also guarantee the modulation efficiency. The functionality of the device may also be expanded by arranging more separately controlled resonators in multilayer structures. Moreover, the device proposed in this paper can also be widely used in other bands. Our encoder may pave a new way to develop multifunctional and integrated devices, such as multiband filter and sensor, frequency division multiplexer and logical circuitry, which will promote the development of THz communications and other applications.
