High-speed Photo Detector Frequency Response Characteristics Test Research

The telecommunications and information technology industries must continually advance their ability to deliver high-speed, reliable, and interoperable communication and information processing systems with greater information-carrying capacity and lower cost. Higher speeds and information capacities correspond to larger bandwidths and higher frequencies. Integrated digital and microwave electronics now used by industry require measurement bandwidths in excess of 110 GHz, larger than can be supported by current coaxial connector based microwave technology. Electro-optic information technology, microwave microelectronics. and digital are driving the need for reliable higher-frequency measurements to enable further advancements. The ultimate need is for the calibration of high-speed sampling oscilloscopes. microwave mismatch-corrected sampling oscilloscopes, digital pattern generators, light-wave component analyzers. vector signal analyzers, vector signal sources, microwave transition analyzers, and nonlinear network analyzers.Detectors that respond to modulation at microwave frequencies are needed for very high speed fiber-optic links, and for optical transmission and processing of microwave signals. As the bandwidth of these detectors reaches beyond 100GHz, it becomes increasingly difficult to measure their frequency response. Therefore, the establishment of a set of test equipment of high speed electro-optic detector's frequency response characteristics has becoming into a new direction for high frequency metrology.The main contents of this paper are as follows:(1) Based on comprehensive reference, the techniques used for ultrafast electrical signal's characterization are reviewed and compared.(2) We analyzed the principle of electro-optic sampling analysis, and got the horizontal and vertical electro-optic modulation manifestations. We researched the method for decreasing the half-wave voltage of the electro-optic modulator of LiTaO3, and the effects on the output characteristics by changing the DC bias operating point. Although the vertical modulation is independent of polarization, this paper is still apply horizontal modulation in designing LiTaO3 electro-optic modulator. According to the electro-optic modulator bandwidth of the lumped electrode structures and the traveling wave electrode structure, we analyzed the influence of light waves and the radio waves bandwidth mismatch degree, which give the theory evidence for the design of coplanar waveguide structure.(3) We established the electro-optic sampling system basic framework, and analyzed the function and role of every important part, including the interaction of transmitted microwave field and light wave in the coplanar waveguide. We established the simulation model of OTT, ETT and optical pulse limits, and calculated the OTT half wave width, ETT half wave width and-3dB bandwidth. The results show that the high refractive index of LiTaO3 and the path through the substrate are important for the optical resolution of time-effect on the system. Some key parameters, such as, the system time resolved force, spatial resolution, speed matching and voltage sensitivity, are calculated, their impacts on the system are analyzed.(4) According to the equivalent time sampling principle, analyzed the effects of light mechanical delay line, calculated the minimum deviation angle,itinerary and sampling period. Then, based on the theory and formulas analysis derive two different structures characteristic parameters of coplanar waveguides. Under the condition of different center electrode width,different ground plane width,different substrate thickness and different line-to-ground gap size. For the first time, we analyzed the characteristic impedance, calculated the different structures of various parameters of coplanar waveguide range which matched impedance was 50Ω. After comparing the theoretical calculations and test results obtained good consistency and accuracy, provided basis for optimal design parameters.(5) We show our home made LiTaO3 electro-optic modulator, and tested the impact of the sampling beam in a static electric field. Sampling beam polarization changed linearly with the static electric field loaded onto the electro-optic modulator. The optical delay line in our system show good mobility and linear distance, which meet the requirements of system. Meanwhile, we developed a user-friendly measurement software. Characterized-3dB frequency response and pulse response of time tested, achieved the relevant parameters. Applied mismatch correction technology for the pulse time response waveform of detectors.