Study Of Angle Tunable Optical Filter Employing MEMS Technology

Tunable optical filter is the key device of modem optical communication and sensor systems. The research and development of tunable optical filters of low cost, small size, quick response, broad tunable range and insensitive to polarization are in great need. In the thesis, a novel structure of tunable optical filters based on MEMS (Micro-electro Mechanical System) technologies has been put out. With the advantage of simple structure, easy to fabricate, quick responding time, low PLD (Polarization Depended Loss) and wide continuous tunable range, the device has certain practical value.In the thesis, dielectric multilayer filter, the technology of which is fully developed, is used to filter and the electromagnetic actuated tunable structure based on MEMS is used to tune the angle. The content of the thesis mainly contains three parts: the principle analysis and design of the whole structure, the design of the torsion structure and the fabrication and test of the device. The details are as follows:(1) The principle analysis and design of the whole structure. First, the polarization effect of the filter is analyzed under the oblique incident condition. A way of reducing the polarization effect has been put forward: Before filtering, the incident beam is split into two and transformed into the same polarization state by means of double refraction crystal, half-wave plate. After filtering, the two beams revert to the primary polarization state and combine. Secondly, to the disadvantage of low angular deviation sensitivity near the vertical incident, a way of making the filter works initially at an inclined angle has been put out. By means of this, the needed range of the tunable angle is reduced. Last, the work-off effect under oblique incident condition is analyzed. The width of the beam spot alone with the incident angle is analyzed by a recursive method in frequency field.(2) The design of the torsion structure. By the law of electromagnetic induction, an electromagnetic actuated tunable structure with damping coils are designed. This structure is able to reduce the responding time of the angle tunable device effectively. Both sides of the torsion plate are galvanized metal coils. The front coils are used as actuating coils while the rear coils are used as damping coils. By means of static as well as dynamic analysis on the mechanical model of the torsion plate, the optimum parameters of the structure were decided.(3) The fabrication and test of the device. The fabrication process of this device was developed and emphatically introduced several key fabrication technologies such as sacrifice layer technology, galvanization and deep iron reaction etcher. The parameters of the fabrication process have been decided and the chip of the torsion plate was achieved. By assembling the torsion plate, dielectric multilayer filter, double refraction crystal, half-wave plate and permanent magnet, the angle tunable optical filter was produced. The dielectric multilayer filter with the central wavelength at 1610nm is used to test the performance of the device. The test results are obtained by setting the initial angel at 25 ° . The results show that within the tunable range of ±5° , the tunable range of wavelength is 40nm(1532nm~1572nm),The test results show that the angle tunable optical filter fabricated in the thesis has a good performance of filtering. Based on the test results, the further measures to improve the performance were also discussed in this thesis.