Tham khảo tài liệu 'photodiodes communications bio sensings measurements and high energy part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Single Photon Detection Using Frequency Up-Conversion with Pulse Pumping 71 where ISFG Ipump and Isignai are the intensities of SFG pump and signal light respectively L is the waveguide length and Ak is the phase-mismatching which determines the bandwidth of the spectral response. According to Eq. 6 for a given SFG intensity the waveguide length and the spectral response bandwidth are inversely proportional the shorter the waveguide the broader the spectral response bandwidth. Fig. 9 a shows the spectral response measured experimentally for the 1-cm PPLN waveguide. Its 3-dB bandwidth is about nm which is about 5 times wider than that of the 5-cm PPLN waveguide nm Ma et al. 2009 . In this experiment the wider bandwidth allows two pumps at wavelengths nm and nm to operate with almost the same conversion efficiency which is about 85 of the maximum conversion efficiency. Detection efficiency is a significant trade off for a short waveguide. From Eq. 3 to compensate for the reduced conversion efficiency in a shorter waveguide the pump power must be scaled quadratically. For example the pump power required to achieve the maximum conversion efficiency in a 1-cm waveguide is 25 times higher than that for a 5-cm waveguide. Fig. 9 b shows the detection efficiency of the up-conversion detector as a function of the average pump power. The pump power on the x-axis is measured at the input fiber of the PPLN waveguide. Although the maximum output power of the EDFA is 1 W the maximum power at the input fiber is approximately 510 mW due to losses in the WDM couplers and connectors between the EDFA and the waveguide. In our system the combined pulse duration of the two pumps covers 67 of each clock period and therefore the peak power of each pulse is only times higher than the average power. Fig. 9 b indicates that the up-conversion efficiency of the detector does not reach its potential maximum value and is limited by the available pump power. Besides the
