A Cost-effective Sub-terahertz Continuous Wave Generation Scheme Using a Broadband Optical Source and An Optical Feedback Loop

We have proposed a cost-effective sub-terahertz (THz) continuous wave (CW) generation scheme based on a usual double sideband-suppressed carrier (DSB-SC) scheme. The usual DSB-SC scheme, which consists of a discrete optical source, an optical intensity modulator (OIM), a local oscillator (LO), an optical notch filter, and an erbium doped fiber amplifier (EDFA), is one of well-known photonic-based sub-THz CW generation schemes. As the discrete optical source of the usual DSB-SC scheme is eliminated and an optical feedback loop is incorporated with the usual DSB-SC scheme, our proposed scheme is constructed to decrease implementation costs. Without an optical input, the output of the pump laser of the DC-biased EDFA is inserted to the optical notch filter. Reflected lightwaves with fiber bragg grating wavelengths of the optical notch filter is fed back to the input of the OIM through the optical feedback loop, which is composed of a circulator and a 90:10-coupler. DSB-SC lightwaves have been made by modulating feedbacked lightwaves on the OIM with the frequency of the LO. A sub-THz CW is generated by photomixing them. To verify feasibility of our proposed scheme, we generated and characterized a 120 GHz CW. The measurement results were also compared to those of the usual DSB-SC scheme. Based on our measurement results, we found that characteristics of the generated 120 GHz CW using our proposed scheme are comparable to those using the usual DSB-SC scheme. Consequently, our proposed scheme can be helpful to make a cost-effective sub-THz CW generator based on photonics.