Approximate empirical relations for nonlinear photonic crystal fibers (PCFs) are newly proposed. Replacing a PCF with a conventional step-index fiber, closed form expressions for the effective refractive index and the effective core area of nonlinear PCFs are derived. To define the equivalent cladding index, the effective index of the so-called fundamental space-filling mode, which is calculated using empirical relations for the effective normalized frequency, is introduced, and thus, nonlinear guided waves propagating in PCFs can be easily characterized without the need for numerical computations. The validity of the method proposed here is ensured by comparing the calculated results with those obtained by a fullvector finite-element method.

We propose a maximum likelihood detection (MLD) technique that incorporates beat noise estimation (BNE). MLD can minimize a bit error rate theoretically because a bit pattern with the maximum posteriori probability is selected as the detected signals. Also, BNE can extract a specific beat noise from mixed multiple signals using a correlation. By combining these techniques, the influence of beat noise is reduced and the bit error rate becomes lower in an OCDM-based system. This paper describes the MLD algorithm and the BNE design. And numerical simulation results confirm the validity and performance of this technique.

SUMMARYThis paper proposes an analytical approximation theory for evaluation of the transmission characteristics of a nonlinear photonic crystal fiber. A photonic crystal fiber with a complex cross-sectional structure is replaced equivalently with a conventional step-index fiber so that an analytical approximation theory developed for the conventional nonlinear optical fiber can be applied directly to the nonlinear photonic crystal fiber. In order to derive an effective index of refraction of the clad region of the photonic crystal fiber with holes, an empirical formula for the normalized frequency of the photonic crystal fiber proposed recently is introduced. Hence, the fundamental quantities describing the transmission characteristics of the nonlinear photonic crystal fiber, specifically the effective index of refraction and the effective core cross section, can easily be derived without numerical calculations. By using the proposed method, the optical power dependence of the transmission characteristics of the nonlinear photonic crystal fiber is analyzed. Validity of the proposed method is verified by comparison of the results with those by calculations based on the full-vectorial finite element method.

At NTT Network Technology Laboratories, with a view to implementing a smart world that accelerates digital transformations, we are developing technology that improves the precision of positioning measurements made using GPS (Global Positioning System) and other forms of GNSS (global navigation satellite systems) in urban canyon environments with many high-rise buildings. We are also developing technology that can dramatically improve the positioning measurements by doing some of the positioning calculations on cloud edge nodes, resulting in services with new added value.

Ahstract-We propose an enhanced beat noise estimation technique with correlation for maximum likelihood detection in an OCDM-based PON system. By correcting the fluctuation of the data bit pattern, the estimation error can be reduced.