High-precision Gratings Research Articles

High-Precision Grating Projection 3-D Measurement Method Based on Multifrequency Phases for Printed Circuit Board Inspection

High-Precision Grating Projection 3-D Measurement Method Based on Multifrequency Phases for Printed Circuit Board Inspection

Design of Four-Channel Wavelength-Selectable In-Series DFB Laser Array With 100-GHz Spacing

A four-channel wavelength-selectable in-series DFB laser array with good single-longitudinal-mode (SLM) property is proposed and theoretically analyzed. To realize good SLM property, a linearly chirped Bragg grating with multiple π phase shifts are implemented in the laser cavity. In addition, two reflector sections with chirped Bragg grating are specially designed for reflection compensation at both ends. In our simulation, the split-step time-domain model with coupled-wave equations and carrier rate equations are used. Based on the simulation results, all the channels work with low threshold currents and the SLM properties are considerably enhanced compared with the conventional in-series laser array. Notably a high precision control of grating phase is required in the practical fabrication due to the ultra-small variation of grating period. Therefore, the reconstruction-equivalent-chirp technique is discussed to provide the fabrication of high-precision grating. In addition, the complex heterogeneous integration or butt-joint technique is not required during the whole fabrication process, which simplifies the fabrication and reduces the cost. The proposed wavelength-selectable in-series laser array is deemed to be applied in the dense wavelength division multiplexing technology, especially when fast wavelength switching is needed, such as in the application of NG-PON2.

A New Microhardness Testing Method on Grating Films

The manufacturing process of large-area, high-precision gratings is a very complicated and time-consuming process. The hardness testing of grating films is an important step in the entire process. In order to simplify the manufacturing process of gratings, we have proposed a new method for testing microhardness based on tool edge indentation. Also, it unified tool adjustment and microhardness testing steps in the grating manufacturing process. First, a mathematical model of the relationship between tool load and indentation contour length is established. The model parameters were then modified using tool indentation experiments with different loads. When measured with a nanoindenter, the average hardness of the grating film was 447 MPa. The hardness value of the grating film obtained by our proposed method is almost the same as that measured by the nanoindenter, and the maximum deviation is about 2.2% of the average hardness value. The experimental results show that our proposed method can replace the microhardness test method of using a nanoindenter. Therefore, the disadvantages of using a nanoindenter to test the hardness of a grating film are avoided, such as the limited sample size, the sensitivity of the indenter to the roughness of the film and the depth of the indentation, and the accuracy of film testing, and the efficiency of grating ruling can be improved.

Precision fringe period metrology using an LSQ sine fit algorithm.

High-precision grating fabrication is a precondition of grating-based displacement measurement techniques. Likewise, the value of high-precision fringe period is an essential parameter in the grating fabrication process, especially in scanning beam interference lithography. In this paper, a procedure for measuring the fringe periods of interference beams is introduced. The procedure includes signal acquisition and signal processing. The precisions of both the configuration for acquisition and the algorithm for processing are discussed. Experiments for fringe period measurement are also conducted, and an average value of 564.374nm with a standard deviation of 1.5pm is obtained, reaching a repeatability of 2.6ppm. The value of precision period lays a solid foundation for the fabrication of high-precision gratings.

A reflectometer for at-wavelength characterisation of gratings

The design for an UHV-reflectometer for XUV-radiation is presented, which is dedicated to at-wavelength characterisation on high precision gratings. At-Wavelength Metrology is a powerful and necessary characterisation tool for the development and characterisation of optical elements. Since the optical constants of the coating materials involved are dependent on wavelength, information on e.g. reflectivity can only be obtained at-wavelength and cannot be provided by ex-situ methods.In our institute a technology centre for production and characterisation of highly efficient precision gratings is established. Within this project a reflectometer for at-wavelength characterisation of the fabricated blazed gratings is developed and manufactured. This reflectometer complements the SXR-metrology instrumentation at BESSY-II: the existing reflectometer and the polarimeter/ellipsometer chamber for polarisation studies on magneto-optical samples or non-magnetic multilayers.The main feature of the reflectometer is the possibility to incorporate real gratings with a length up to 600mm, adjustable in six degrees of freedom by a custom designed tripod system. The reflectivity is measured between −180° and +180° incidence angle for both s- and p-polarisation geometry. A variety of detectors with a high dynamic range is accessible.The reflectometer is coupled permanently to the new optics beamline on a BESSY-II bending magnet operating in the UV, EUV and soft x-ray range with the polarisation adjustable to either linear or elliptical. The station will be available by the end of 2013.

Efficient semiconductor ring lasers made by a simple self-aligned fabrication process

We present what we believe is the highest efficiency and lowest threshold current density ever reported for semiconductor ring resonator lasers. Ring lasers are interesting components, e.g. for fiber-to-the-home systems, because they can readily be integrated and their very simple fabrication process, which is discussed and compared with other common approaches, does not require overgrowth or the fabrication of high-precision gratings. An asymmetric coupler geometry has been tested that leads to a further increase in efficiency, but is more sensitive to changes in the input field than the symmetric equivalent.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>