Proposal of a nonlinear compensation scheme using an optical chirp controller in SCM/OFM RoF link

Abstract

SUMMARYAn SCM optical FM method can obtain an FM gain, so it is effective on employing an RoF link which transfers a broad-band or multicarrier RF signal. However, the RF signal quality is degraded by intermodulation distortions due to the nonlinearity of LDs and optical frequency discriminator. The nonlinear compensation technique in the RoF link has been investigated in order to obtain a higher RF signal quality. This paper proposes an insertion-type distortion nonlinear compensation. In the proposed scheme, a nonlinear device is inserted between transmitter and receiver and we propose an optical chirp controller as the nonlinear device. The proposed scheme suppresses the higher order intermodulation distortion which degrades RF signal quality in the adaptive transmittance control method.In this paper we theoretically analyze the SFDR of the optical FM method using the optical chirp controller and show that improvement in the SFDR at 9 and 5 dB compared to methods without nonlinear compensation and the adaptive transmittance control method, respectively, can be obtained.

A Study of a SCM/OFM Radio-on-Free Space Optics Link Using Chirp Controller

“…Table 1 shows the parameters used in calculation. The parameter b2 and b3 are set to reduce IM3 distortion power [14]. Figure 5 shows CNR versus the received optical signal power when Pi, = -20 dBm.…”

“…(21)-(23) that a chirp frequency in frequency modulating can be controlled to improve the frequency modulation efficiency, a', by using the proposed scheme. Therefore the large FM index and low IM3 distortion can be realized to control the parameter, b1, b2, and b3, of the chirp controller [14]. In the system without chirp controller, the A2 times input RF signal power is required to obtain the same FM index as the proposed method.…”

“…Solving a grating equation, the relationship the position, x, with the optical frequency, f, is expressed as A cos (f fclY (14) where A, H, 9, c, and f are the period of the grating, the focal length, the angle of the first diffraction, the light speed, and the optical frequency, respectively. If ffc A< «c in Eq(14), x is approximately expressed as z = -P (f -fc),…”

“…This paper also proposes SCM/OFM RoFSO link using the chirp controller. In the proposed method, the low intermodulation distortion and large FM index can be achieved because the large frequency modulation efficiency is obtained by using chirp controller such as an Armstrong FM system [14].…”

“…So it is possible to apply the coherent optical communication which realizes high performance to the RoFSO link [7]. As the RF signal transmission method, N--A~Home Gate Way 0 Media Converter (CCS) Figure 1: Configuration of RoF bus link an optical FM method have been studied in order to demand for high quality wireless services in SCM RoF link [8]- [14] and is excepted to overcome the optical link loss and the background noise. This paper proposes the OFM method in SCM RoFSO link (SCM/OFM RoFSO link) for the indoor network such as home or office to obtain the high RF signal quality because of FM detection gain.…”