Femtosecond Pulse Measurement Based On Two-photon Absorption In Silicon Photodiode

Ultrashort optical pulses have developed by leaps and bounds in recent years,and their applications have become more and more extensive,especially in high-speed optical communications and quantum control.In order to achieve more precise control,the precision of ultrashort pulses measurement is becoming more and more important.This paper mainly studies the precision measurement of femtosecond laser based on silicon photodiode two-photon absorption.The specific content is as follows:1.A comprehensive survey of the current main ultrashort pulse measurement methods,analysis of the advantages and disadvantages of various methods and the scope of application,in order to more accurately measure each part of the ultrashort pulse directly,this article on the basis of a detailed summary of previous research programs,choose autocorrelation measurement method based on two-photon absorption of silicon photodiodes.2.According to the energy band structure of silicon,the characteristics and realization conditions of its two-photon absorption are analyzed.It is found that silicon can achieve high-efficiency two-photon absorption in the communication band around1550 nm,and it can also occur at a lower average power,so it is suitable for situations where the pulse power of the communication band is small.In addition,using silicon photodiodes as non-linear devices and photoelectric conversion devices at the same time can not only reduce the number of devices,but also make the operation easier.3.Using a mode-locked fiber laser to generate an ultrashort pulse of 76 fs,the photon energy is 0.795 e V(1560nm),and the indirect band gap of silicon P-I-N photodiode photosensitive material silicon is 1.12 e V.Although the photon energy is smaller than the indirect band gap of silicon,the photon energy is less than the indirect band gap of silicon.When incident on a silicon-based photodiode,an obvious pulsed light signal is detected.When the output peak electrical signal and the input peak optical power take the logarithm at the same time,the slope is 2 ± 0.05,indicating that two-photon absorption has indeed occurred,and the relationship formula between the voltage and the incident optical power is fitted.4.The autocorrelation waveform of the ultrashort gaussian light pulse was simulated in detail,and the meaning of each item after the formula was analyzed was analyzed,and the autocorrelation waveform containing interference fringes and conforming to the theoretical prediction of 8:1 contrast was obtained,and promoted To hyperbolic secant pulse and Lorentz pulse.Next,the autocorrelation change of pulse intensity with different delays under the condition that the pulse interference cannot be responded to is studied,and it is proved that the non-collinear autocorrelation method of eliminating the background item of the pulse self-response is more accurate in measuring the pulse width.5 The autocorrelation waveform measurement system of Michelson interferometer based on high-sensitivity silicon photodiode two-photon absorption was built,and the femtosecond pulse waveform of the communication band was measured,and the autocorrelation waveform diagram consistent with the simulation results was obtained.The error of measuring the pulse width of 76 fs pulse with the center wavelength of1560 nm is about 6%,but the autocorrelation waveform is relatively clearer when measuring the pulse of 392 fs,the measurement is more accurate,and the error is less than 1%.Furthermore,the reason for the error of measuring 76 fs pulse and the direction of improvement in the future are analyzed.The method in this paper does not require complex phase matching,is simple to operate,low in cost,and has great application potential.