A low-loss downconverting analog fiber-optic link

Optoelectronic RF signal mixing using an electroabsorption waveguide as an integrated photodetector/mixer

“…The up-and down-converted signals appear to have different RF power, caused by the bandwidth limitation of the circulator. When the RF signal power was increased to 10 dBm, the converted signal powers increased by 10 dB, closely following the prediction by (1). We found that the device tested became saturated around 10-mW LO optical power.…”

“…The conversion gain is mainly limited by LO optical power and the saturation power of the EA waveguide used. It can be improved by using an EA waveguide with higher saturation, as increasing the LO power can increase the converted RF power, in accordance with (1). Decreasing the coupling loss from the fiber to the EA waveguide is another approach, which also increases .…”

“…Wide-bandwidth, lightweight, high degree of security, long-distance remoting capability, and immunity to electromagnetic interference are some of the advantages to be gained. Recently, sending down-converted RF signals over the fiber has received much attention, as it avoids costly high-speed photodetectors and fiber dispersion at high RF frequency [1], [2]. Many of the conversion schemes take advantages of the optical local oscillator (LO), which is simpler than the electronic LO at high frequency, and has less phase noise [3].…”

“…Unlike previous approaches [1], [2], [4]- [6], frequency converted electrical RF signals from an EA waveguide, operating as an OEM, are generated and made available for subsequent signal processing. The down-converted RF signal can be sent through conventional electrical cable that has low attenuation at low frequency, or processed locally near the antenna using usually inexpensive electronics.…”

Radio-Frequency Transparent Demodulation for Broadband Hybrid Wireless-Optical Links

“…However, the detection of these vector modulated multigigabit signals using conventional electrical methods becomes complicated when the bit rate increases and RF carrier frequency approaches millimeter-wave frequencies. Recently, several photonic techniques for demodulation of -QAM signals have been proposed ( [4], [5] references therein), but they still require relatively complex high-bandwidth analog phase-locked-loop and RF components. Additionally, digital coherent receiver structures have also been proposed for RF-over-fiber links [6], [7].…”