Abstract
The main problem with the radio-over-fiber (RoF) link is the decrease in the recovered radio frequency (RF) power due to the chromatic dispersion of the fiber known as dispersion power fading. One of the methods for dealing with dispersion power fading is to use the optical single sideband (OSSB) modulation scheme. The OSSB modulation scheme can be generated by biasing the dual-drive Mach–Zehnder modulator (DD-MZM) to the quadrature bias point (QBP) and shifting the RF drive signal phase (θ) by 90°, which is called the regular θ. However, the OSSB modulation scheme only overcomes dispersion power fading well at the modulation index (m) < 0.2. This paper proposes an irregular θ method to overcome dispersion power fading at all m. There are two irregular θ for every m used. The irregular θ managed to handle dispersion power fading better than OSSB modulation scheme did at every m. Specifically, the irregular θ could handle the dispersion power fading well at m ≤ 1. In sum, the irregular θ could overcome the dispersion power fading at any RF frequency and optical wavelength without having to re-adjust the transmitter.
Highlights
A radio-over-fiber (RoF) system transmits radio frequency (RF) (XTX (t)) signals through optical fiber used to support wireless communication services
The XTX (t) in the RoF system is converted to an optical signal using an electro-optic (E/O) converter located at the central office (CO)
The optical signal is later transmitted through a fiber link, and the RF signal is recovered using an opto-electric (O/E) converter positioned on the radio access point (RAP)
Summary
A radio-over-fiber (RoF) system transmits radio frequency (RF) (XTX (t)) signals through optical fiber used to support wireless communication services. The Xrec (t) is generated only from the multiplication between the upper and lower sidebands, so no interference resulting in dispersion power fading is possible The disadvantage of this method is that the Xrec (t) frequency is twice the XTX (t) frequency, so the receiver has to do additional works to turn the Xrec (t) frequency to its original frequency. The OSSB generated using DD-MZM manages to effectively overcome dispersion power fading if the XTX (t) spectrum is made up only of optical carriers and sideband fundamentals without harmonics. To produce XTX (t) without harmonics, the DD-MZM must be operated at a modulation index (m) < 0.2 This method cannot overcome dispersion power fading efficiently at m ≥ 0.2. Generating a simple RoF link with standard DD-MZM as an E/O converter that can overcome dispersion power fading at all m. Has Xrec (t) set at the same frequency as that of XTX (t), thereby removing any additional work
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