In this paper, we present a phase multiplication algorithm (PMA) to obtain scalable fringe precision in laser self-mixing interferometer under a weak feedback regime. Merely by applying the double angle formula on the self-mixing signal multiple times, the continuously improved fringe precision will be obtained. Theoretical analysis shows that the precision of the fringe could be improved to λ/2ⁿ⁺¹. The validity of the proposed method is demonstrated by means of simulated SMI signals and confirmed by experiments under different amplitudes. A fringe precision of λ/128 at a sampling rate of 500 kS/s has been achieved after doing 6th the PMA. Finally, an amplitude of 50 nm has been proved to be measurable and the absolute error is 3.07 nm, which is within the theoretical error range. The proposed method for vibration measurement has the advantage of high accuracy and reliable without adding any additional optical elements in the optical path, thus it will play an important role in nanoscale measurement field.

为了提高光子晶体光纤的非线性系数，降低色散斜率和制作难度，提出了一种硅纳米纤芯光子晶体光纤，其纤芯和包层空气孔都为圆形。利用平面波展开法进行仿真，研究了硅纳米纤芯直径、包层空气孔直径、晶格常数三个参量分别对色散和非线性系数的影响。通过优化，最终得到零色散波长在1550 nm处，具有高非线性、低色散斜率的光子晶体光纤。1550 nm处光纤的色散斜率低至0.251 ps·nm^-2·km^-1，非线性系数高达1.0×10⁵ W^-1·km^-1，限制损耗为0.39 dB/km。此外，该光纤结构简单、制作方便，在较小的工艺误差下仍能保持较好的性能。

提出了利用掺氟同心圆环的光纤结构来提高光子晶体光纤(PCF)的非线性，所需控制的参量仅有两个。设计了三种具有高非线性、低色散斜率和低限制损耗的全固光子晶体光纤。这三种光纤分别具有正常色散、双零色散点和零色散点恰好在1.55 μm波长处的色散曲线特性。所设计的零色散点恰好在1.55 μm波长处的光子晶体光纤色散斜率值为5.12×10-4 ps/(km·nm2)，这比传统的高非线性光纤的色散斜率小了2个数量级。同时，该光纤在1.55 μm波长处的非线性系数为31.5 W-1·km-1，限制损耗为9.62×10-5 dB/km。

A simple design procedure is used to generate photonic crystal fibers (PCFs) with ultra-flattened chromatic dispersion. Only four parameters are required, which not only considerably saves the computing time, but also distinctly reduces the air-hole quantity. The influence of the air-hole diameters of each ring of hexagonal PCFs (H-PCF, including 1-hole-missing and 7-hole-missing H-PCFs), circular PCFs (C-PCF), square PCFs (S-PCF), and octagonal PCFs (O-PCF) is investigated through simulations. Results show that regardless of the cross section structures of the PCFs, the 1st ring air-hole diameter has the greatest influence on the dispersion curve followed by that of the 2nd ring. The 3rd ring diameter only affects the dispersion curve within longer wavelengths, whereas the 4th and 5th rings have almost no influence on the dispersion curve. The hole-to-hole pitch between rings changes the dispersion curve as a whole. Based on the simulation results, a procedure is proposed to design PCFs with ultra-flattened dispersion. Through the adjustment of air-hole diameters of the inner three rings and hole-to-hole pitch, a flattened dispersion of 0+-0.5 ps/(nm.km) within a wavelength range of 1.239–2.083 \mum for 5-ring 1-hole-missing H-PCF, 1.248–1.992 \mum for 5-ring C-PCF, 1.237–2.21 \mum for 5-ring S-PCF, 1.149–1.926 \mum for 5-ring O-PCF, and 1.294–1.663 \mum for 7-hole-missing H-PCF is achieved.

This letter describes a novel optical method for wavelength fine-selection in the optical spectrum analysers (OSAs) for dense wavelength division multiplexing (DWDM) applications. The proposed new method employs a 'refractive optical lever' system consisting of a rotating optical wedge prism. A new OSA system based on Littman-type monochromator is proposed and the wavelength selection accuracy and resolution of OSA that has included such an optical lever system have been improved by a factor of 20 to 100 depending on the wedge angle and offset orientation angle of the optical wedge prism. This proposed 'refractive optical lever' may also simplify the rotation mechanism of the mirror in the commercially available OSAs.