## 1 Introduction  
Optical code-division multiple-access (OCDMA) schemes allow multiple users in a local area network (LANs) to access the same fiber channel asynchronously without delays or the need for scheduling. Accordingly, OCDMA represents an attractive access technique for radio-over-fiber (RoF) networks [1; 2]. In the RoF system, micro-cells are connected by optical fibers to radio base stations (RBSs), which are connected in turn to central control stations (CSs). Regarding the configuration of RoF networks, a linear bus or passive star optical link is generally preferable since architecture of this type lowers the cost of implementation and enables the straightforward addition of additional access points. In a RoF network with OCDMA access, different RBSs assign different codes. The advantage of the network is easily to add/remove the access points by changing the length of codes. In the past decade, spectral-amplitude-coding OCDMA (SAC-OCDMA) systems have gained increasing attention. When SAC-OCDMA systems are coupled with quasi-orthogonal code, multiple access interferences (MAI) can be eradicated in ideal conditions, rendering SAC-OCDMA systems extremely suitable for RoF systems. The SAC-OCDMA is the most appropriate way for signal transmitting because it is uncomplicated and the information data can be regenerated without any synchronization and can be implemented in analog intensity modulation (IM) radio links. The detailed operational theorem of the decoding scheme has been proposed in [34]. The other OCDMA scheme is coding in polarized domain. In spectral polarization coding architectures, light sources are divided into two mutually orthogonal states of polarization (SOPs), one vertical and one horizontal. The two SOPs are then coded and user data are uploaded to the two coded and polarized optical carriers, improving spectrum utilization and increasing the user volume in the system. Moreover, phase-induced intensity noise (PIIN) can be effectively suppressed by combining SAC-OCDMA with polarization division multiplexing (PDM) technology, thereby increasing overall system efficiency [5; 6]. However, in the multi-wavelength OCDMA (MW-OCDMA) system, the decoder is sensitive to the relative temporal positioning of optical pulses transmitted simultaneously along different wavelength channels. When the optical fiber transmitting distance of the network is more than 500 m, the system performance will be significantly degraded by chromatic dispersion, which results in temporal skewing among wavelength channels [7]. To improve the distortion, the dispersion compensation scheme is needed in the MW-OCDMA system for compensating dispersion distortion. There are some researches regarding dispersion compensation, such as the following: the compensators that are used to construct a dispersion slope equalizer have been demonstrated in the form of sampled chirped fiber Bragg gratings [8], virtually imaged phased arrays [9], all-pass filters [10], waveguide grating routers with thermal lenses [11], and dispersion compensating fibers (DCFs) [12]. The length of DCFs required to compensate for the dispersion from single-mode fiber (SMF) is long and optical amplifiers will be needed because the insertion loss of DCF is high. Integrated dispersion slope equalizer of AWG-based optical CDMA is then proposed [13]. However, series connections of Mach-Zehnder Interferometers (MZIs) have serious group delay ripples and dispersion compensation is not easier to adjust precisely. Discussion of other issues, such as negative group delay (NGD) at microwave wavelengths, are also presented; the NGD is useful for the compensation of radio frequency/microwave signal delays [14; 15]. Orthogonal frequency-division multiplexing (OFDM) is the fastest developing technology in the academic and industrial fields of wireless transmission. OFDM technologies are resistant to frequency-selective interference and demonstrate high transmission rate and high bandwidth usage efficiency.