## 1 Introduction  
Orthogonal frequency-division multiplexing (OFDM) is an emerging technology in optical fiber communications due to its inherent advantages, which include simplified digital signal processing for channel estimation and the compensation of linear fiber-induced impairments, such as chromatic dispersion and polarization-mode dispersion [1]. OFDM is essentially a method of encoding digital data on multiple carrier frequencies, harnessing the (inverse) fast Fourier transform (IFFT) [2], and is widely used in wireless local area networks (802.11 a/g) and wireless metropolitan area networks (802.16 d). In the wireless domain, OFDM's advantages also include the support of several multiple access schema (e.g., time-division multiplexing access (TDMA), frequency-division multiplexing access (FDMA), code-division multiplexing access (CDMA)) and the compensation of multipath propagation [3, 4]. In wireline communications, OFDM has been implemented in asynchronous digital subscriber lines (ADSLs) and digital video broadcasting (DVB). On the other hand, CDMA is a multiplexing scheme based on the user code signature with great potential for providing bandwidth allocation, maximization of network user capacity and security enhancement. Further, CDMA offers simple network management with great capacity to support asynchronous bursty traffic, low latency access, transparency to overlaid protocols and high network flexibility [5]. Hybrid OFDM-CDMA systems have been reported in the literature using one dimensional (1D) codes, such as Walsh-Hadamard (WH), and mutually orthogonal complementary pairs (MOCP) in optical and wireless communication systems, respectively [6, 7]. However, to increase the number of simultaneous users, the length of 1D codes should be increased, which results in higher decoding computational complexity. A practical solution to this issue is the employment of 2D codes by merging the 1D code structure and spatial/frequency hopping schema. Two-dimensional optical CDMA (OCDMA) codes have been implemented in the wavelength-division multiplexing (WDM) passive optical networks (PON) context [8, 9, 10, 11, 12, 13, 14]. The effectiveness of classical optical code-division multiplexing access (OCDMA) can be potentially improved by employing orthogonal frequency-division multiplexing (OFDM) with high-order quadrature amplitude modulation (QAM) in order to increase the spectral efficiency and signal capacity, while overcoming linear fiber impairments by simplified digital signal processing. In the state of the art, various hybrid systems based on 2D codes are proposed for OCDMA-PON, intensity modulation and direct detection OFDM-OCDMA (IM/DD OFDM-CDMA) [15, 16], coherent optical OFDM-CDMA (CO-OFDM-CDMA) [17] and OFDM-SAC-OCDMA systems [18, 19]. The Fast-OFDM technique is a spectral-efficient multicarrier modulation scheme based on reducing the subcarrier spacing. Thanks to the discrete cosine transform (DCT), the Fast-OFDM technique provides twice the bandwidth efficiency of the fast Fourier transform (FFT) used by the classical OFDM technique. Furthermore, Fast-OFDM is an emergent and cost-effective technique used to reduce the system complexity, and it has been widely applied in multimode fiber (MMF) [20, 21] and single mode fiber (SMF) as well [22]. The aim of this research paper is to propose a new solution based on the combination of two technologies, such as OCDMA and Fast-OFDM, in order to increase the reachability distance in the context of access network applications. Then, we make a comparison between the proposed solution and other works proposed in the literature, to show the added value of the proposed solution in the PON configuration as a function of the allowed simultaneous users (cardinality), performance metrics (BER and Q-factor), systems components and reachability distance of the optical fiber link.