THz to Optical Conversion in 6G Wireless

This article explains the process of THz to Optical conversion in 6G wireless communication, utilizing a THz to Optical converter. It also briefly touches upon Optical to THz conversion.

THz refers to radio frequencies operating within the Terahertz range.

Introduction

The integration of optical fiber networks with THz (terahertz) frequency-based wireless systems aims to combine the advantages of both technologies: the immense bandwidth offered by optical communication and the high mobility inherent in wireless communication. Emerging cellular technologies like 5G NR (New Radio) and 6G are increasingly utilizing THz over fiber systems.

Figure 1: THz over fiber architecture

Figure 1 illustrates a typical Terahertz (THz) over fiber architecture. As shown, the fiber optic network is interfaced with the terahertz (THz) wireless system using O/T (Optical to THz) and T/O (THz to Optical) converter transceivers. A horn antenna is used for wireless signal transmission and reception at THz frequencies. Baseband processing is performed using a DSP (Digital Signal Processor).

Optical to THz Conversion

Figure 2: Optical to THz Conversion

Figure 2 shows the process of Optical to THz conversion.

• As illustrated, the baseband signal waveform is modulated onto an optical carrier frequency at frequency “fo”.
• This optical signal frequency is then translated to the THz RF carrier frequency using an ultra-fast UTC-PD (Uni-Travelling Carrier Photodiode).
• The UTC-PD mixes a CW LO (Local Oscillator) at frequency f Tx,LO with the optical carrier frequency to generate frequencies within the THz frequency range.
• The converted THz frequency signal is then transmitted into the air using a horn antenna.

THz to Optical Conversion

Figure 3: THz to Optical Conversion

Figure 3 depicts the THz to optical conversion process.

• The THz signal is received using a horn antenna and amplified by a THz amplifier before undergoing T/O conversion.
• The amplified THz signal is provided as one input to a MZM (Mach-Zehnder Modulator) along with another input at a CW optical carrier frequency of f Rx,LO. The MZM generates a modulated optical carrier frequency corresponding to the input THz frequency received by the horn antenna.
• The output of the MZM is amplified using an EDFA (Erbium-Doped Fiber Amplifier).
• The MZM output contains both upper and lower modulation sidebands. A BPF (Band Pass Filter) is used to select the appropriate sideband after eliminating the carrier frequency and any undesired sidebands.