Ngoi Kok Ann Bryan

Diffractive optical elements with continuous relief fabricated by focused ion beam for monomode fiber coupling

The design, microfabrication and testing of diffractive optical elements (DOEs) with continuous relief used for fiber coupling are discussed in detail. DOEs with diameters as small as 50 mm are fabricated by means of focused ion beam (FIB) technology. A focused Ga+ ion beam is used to mill a continuous relief microstructure at a 50 kV acceleration voltage. The optical performance of DOEs made in this way was compared with that of DOEs fabricated by other methods. The focusing performance of DOEs fabricated with three and six annulus by FIB milling was investigated. Testing of the system which has a coupling efficiency of -1.25 dB (75%) shows that the design meets the applications requirement for fiber coupling, and that DOEs manufactured by our FIB technology are practicable. Compared with a conventional fiber coupling system that uses a plano - convex lens, our system has the advantages of simplicity, short focal length, low cost for the lens and high coupling efficiency.

Integrated micro-cylindrical lens with laser diode for single-mode fiber coupling

The integration of a laser diode with a microlens on its emitting surface is introduced in this letter. Calculated results are based on integration of micro-cylindrical lens to laser diode. The lens is directly microfabricated on the emitting surface of the laser diode with operating wavelength 635 nm by focused ion beam (FIB) SiO/sub 2/ deposition function. The controlled SiO/sub 2/ deposition process is realized by programming our FIB machine. Using single-mode fiber with core diameter of 10 /spl mu/m as testing prototype, coupling efficiency of the compact and miniaturized system reaches as high as 80.1%. Measured far field angle (full angle) is 2.1 and 31/spl deg/ with and without the lens, respectively.

Influence analysis of dwell time on focused ion beam micromachining in silicon

Influence of dwell time on focused ion beam (FIB) micromachining process by means of single pixel writing mode sputtering silicon is discussed in this paper. It affects line broadening and sputtering depth during the milling process in silicon material. It is proved by the experimental results that long dwell time leads to deep milling depth due to reducing scanning numbers of pixel. The broadening effect by the wing of Gaussian distribution profile is different from the variation of beam limiting aperture size. In the case of the aperture size 150 μm and below, the effect is little with changing of dwell time. It is obviously serious for large aperture size with the short dwell times of less than 3 μs.

Characterization of focused ion beam induced deposition process and parameters calibration

Deposition of metal or insulator by focused ion beam (FIB) technology is very useful for microsensor fabrication, IC chip modification and failure analysis. Characteristics of depositing tungsten is studied, and physical model is put forth in this paper. The deposition quality of the deposited layer was analyzed by varying operating parameters, such as dwell time, beam spot size, beam current and refresh time. By analyzing the experimental results, optimum parameters are derived for deposition process so as to provide experimental basis for actual application in the future. It is verified by the results that the physical model is in accordance with actual operation condition.

Quasi-direct writing of diffractive structures with a focused ion beam.

A new method for fabrication of diffractive structures, which we call quasi-direct writing, is illustrated. The diffractive structures can be generated by changing the pixel spacing along the direction of the cross scan (with zero overlap) and keeping the pixel spacing constant along the other scan direction, with a normal overlap of 50%-60%, while the substrate surface is scanned with a focused ion beam (FIB). Quasi-direct writing is a method for achieving special customer designs when the milling machine has no computer programming function. Diffractive structures with various periods and depths can be derived by controlling the parameters of pixel spacing, beam current, ion incidence angle, and the scan time or ion dose. The method is not restricted to any one material and can be used for metals, insulators, and semiconductors.

Hybrid microdiffractive-microrefractive lens with a continuous relief fabricated by use of focused-ion-beam milling for single-mode fiber coupling.

The design, microfabrication, and testing of a hybrid microdiffractive-microrefractive lens with a continuous relief that is used with a laser diode for monomode fiber coupling is discussed. The hybrid microlens with a diameter as small as 65 mum and a numerical aperture of 0.25 is fabricated directly onto a spherical surface by use of focused-ion-beam milling technology. A focused Ga(+) ion beam is used to mill the continuous relief microstructure at an acceleration voltage of 50 kV. From the test results a coupling efficiency of 71% (-1.49 dB) was achieved at room temperature. A diffraction efficiency of the main diffractive order, -1, was measured to as high as 90.5% at a wavelength of 635 nm. This indicates that the hybrid microlens was suitably designed within the application requirements and satisfactorily manufactured with focused-ion-beam milling.

Investigation of 3D microfabrication characteristics by focused ion beam technology in silicon

Abstract Combining with experimental milling, 3D microfabrication by FIB technology has been studied. The relationship among limiting aperture size, dwell time, retrace time, tail of Gaussian distribution, etc. have been analyzed in terms of experimental results. Some phenomena are explained from the theoretical point of view. In addition, the influence of redeposition for the sidewall root of the microstructure in the process of milling is analyzed, and the avoiding methods for its avoidance are determined. It was established by experiment that beam current (representing ion beam energy), and spot size (FWHM represents the profile of Gaussian distribution) play an important role in the etching process. Nonlinear variation of these parameters led to the broadening of the edge periphery and redeposition at the root of the sidewall.

Design of hybrid micro-diffractive-refractive optical element with wide field of view for free space optical interconnections

A new design is presented to achieve a hybrid micro-diffractiverefractive lens with wide field of view (WFOV) of 80 degrees integrated on backside of InGaAs / InP photodetector for free space optical interconnections. It has an apparent advantage of athermalization of optical system which working in large variation of ambient temperature ranging from -20 degrees C to 70 degrees C. The changing of focal length is only 0.504 m in the ambient temperature range with the hybrid microlens, which opto-thermal expansion coefficient matches with thermal expansion coefficient of AuSn solder bump used in corresponding flip-chip packaging system. The hybrid lens was designed via CODE-VTM professional software. The results show that the lens has good optical performance for the optical interconnection use.

Microfabrication of diffractive optical element with continuous relief by focused ion beam

The diffractive optical element (DOES) with continuous relief and submicron feature size is very useful for optical fibre communication due to its perfect coupling. Microfabrication of the DOES by focused ion beam (FIB) technology is introduced in detail in this paper. Based on analyzing influencing factors such as ion dose, beam spot size, beam current and dwell time etc., controlling the process of continuous relief form is discussed. It is shown by testing results that the form of milled continuous relief is accurate enough for the application of fibre communication with its high diffraction efficiency.

Investigation of microfabrication of diamond-like film via focused ion beam milling

Optical properties (transmission and refractive index) and chemical structure (x-ray photoelectron spectroscopy) of a diamond-like coating (DLC) before and after focused ion beam milling (FIBM) process were investigated in this article. We find no influence of FIBM on optical properties and chemical structure of the DLC in the near-infrared region. The film can be used for optical applications. As an application example, a diffractive optical element (DOE) was directly fabricated on the film by FIBM. The measured diffraction efficiency of the DOE is 73%, which is acceptable for conventional use.