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Using a two-dimensional photonic crystal lattice, a compact and simple structure has been introduced in the present study to construct an all-optical half adder. The designed structure operates under the interference effect. The phase difference has been created in different states by putting the point defects and the difference in the length of the input waveguides. To do analyses, the finite-difference time-domain method and the plane wave expansion have been used. The advantages of this design include the small dimensions, high possibility of construction, compatibility with the silicon-based technology, and equality of the output power in the logic states 0 and 1. The contrast ratio calculated for the port Sum and the port Carry has been equal to 9.3 and 8.22 dB. The response time has been equal to 0.22 ps, generating the data transfer rate of 4.55 Tbps.

In this study, the authors investigate theoretically a periodic non-linearity effect and its compensation in a three-longitudinal-mode heterodyne interferometer (TLMI). An analytical formula of the frequency mixing error in the TLMI is obtained based on the Jones calculus taking into account experimental parameters. We find that the non-ideal polarisation states and imperfect alignment of the optical setup play the major role to produce four- and eight-cycle non-linearities. The operation of non-linearity compensation system on the four- and eight-cycle non-linear errors is also presented.

The effects of periodic nonlinearity, intermodulation distortion, phase detection uncertainty and electrical cross-talk in a three-longitudinal-mode laser heterodyne Doppler interferometer (TLMI) displacement measurement system are presented. A frequency-path model consisting of three frequency components and two paths is also designed. As a result, there will be six frequency-path elements and 21 distinct interference terms. The periodic nonlinearity in the TLMI is mathematically modelled and simulated. Simulation results are compared with the typical two-mode heterodyne interferometer to confirm the designed model performance. The authors demonstrate that the nonlinearity of TLMI can be greatly reduced using the same compensation method as used in a two-frequency interferometer proposed by Hou et al.

In this study, a new photonic crystal fibre (PCF) structure is proposed which is suitable for optical telecommunications. This PCF has some features including low- and ultra-flattened dispersion and low confinement loss as well as a large effective area in a wide range of wavelengths. To analyse this PCF, finite-difference time-domain (FDTD) method with the perfectly matched layers boundary conditions has been used. For the proposed PCF, dispersion has small variations about 0.8 ps/(nm km) in the wavelength range from 1.1 to 1.7 m and dispersion value is less than 2.5 ps/(nm km) in applicable wavelengths. The confinement loss is obtained less than 10 -6 dB/km in this range, whereas the effective area is around 61.2 m 2 at 1.55 m wavelength. The results show that the confinement loss of the designed hexagonal PCF is small, although the effective area is large. The optimal structural parameters are designed to achieve minimum confinement loss, dispersion and dispersion variation which can be properly utilised in broadband optical transmission applications.