Research On Novel Photodiode And Photodiode Array For Optical Communication System

With the rapid development of the information technology in the modern society,the network traffic is "exploding".The demand for long-distance transmission of massive data and broadband mobile access is growing.Ultra-high-speed optical fiber communication technology and broadband wireless technology has received great attention as the main solution to these problems.In the ultra-high-speed long-distance fiber transmission system,coherent detection with different modulation formats is the main receiving method.The applications of local oscillator lasers and preamplifiers in the communication systems requires photodetectors with high-speed,high saturation and high linearity.In the radio over fiber systems,millimeter-wave modulated optical signals with high frequency and high dynamic range also requires a photodetector with higher-speed,larger dynamic range and better linearity.Therefore,by optimizing the structure of photodetectors and designing noval photodiode arrays,this paper improves the frequency response,dynamic range and linearity of photodetectors.The main innovation and research results of this paper are as follows:1.A novel uni-traveling-carrier photodiode with an InAlAs/InGaAs p-type hetero-structure was purposed.Benefiting from its higher valence band and conduction band energies,InAlAs could more effectively block the electrons from diffusing into p-region and reduce the transit barrier of holes comparing to InP.So,the purposed photodiode structure should have better saturation property comparing to UTC-PD with InP/InGaAs p-type hetero-structure.The simulated InAlAs/InGaAs UTC photodiode with a 800nm absorption layer thickness and a 20?m active region diameter achieved a zero-bias 3dB bandwidth of over 20GHz.The DC saturation current and saturation input optical power of the device were 1.64mA and 2.512mW,respectively.2.We proposed,designed and fabricated a novel two-element symmetric-connected p-i-n photodiode array.The fabricated device with a 20?m active region diameter has a 3dB-bandwidth of over 14GHz at 5mA photocurrent.At a high-power working condition,the device maintains a 3dB-bandwidth of 12GHz with a 60mA photocurrent.It also achieved a high saturation current of 66mA and an output RF power of 1.03dBm.In comparison,a two-element traveling-wave photodiode array with the same epitaxial structure and size only has a saturation current of 42mA and an lower output RF power of-2.74dBm.Meanwhile,the saturation current of a single photodiode is only 31mA.Test results show that the purposed two-element symmetric-connected structure improves the saturation property of photodiode array under these circumstances.The proposed device also solved the phase mismatch issue in traveling-wave photodiode array.3.The electrode of the two-element symmetric-connected photodiode array was optimized for the first time.Due to the limitation of the testing devices,we only tested the transmission property of the electrode before and after optimizing in 0-40GHz range.The transmission loss of the optimized electrode at 40GHz was lowered by 1.1 dB.A two-element symmetric-connected p-i-n photodiode array with the optimized electrode has a 6.6GHz increase of its 3 dB-bandwidth.Test results of the device give firm proof of the increased performance induced by the electrode structure.4.The photodiode element arrangement and electrode of photodiode array with more elements was purposed and further studied.The optimized electrode structure of three-element and four-element center-symmetric photodiode array was given.This work layed a firm ground on the research of photodiode arrays with higher saturation current and higher saturation RF power.5.A novel device structure that hybrid integrated the two-element symmetric-connected photodiode array and a subwavelength grating based beam-splitter was purposed.The beam splitter was designed,fabricated and tested.Test results indicate a beam splitting ratio of 1:0.9.Beam-splitter integrated with p-i-n photodiode array and UTC photodiode array were fabricated.The insertion loss of the purposed device structure is below 5dB.The integrated UTC photodiode array achieved a 23GHz bandwidth,a 87.9mA saturation current and a 16dBm output RF power.The purposed device structure fixed the phase mismatch issue and eliminated the need for phase compensation machenism,which simplified the coupling complexity of photodiode arrays.6.An automatic semiconductor opto-electronic device parameter measure program based on GPIB and Python was developed.The measure program use computer as the control unit and connect test devices with GPIB bus,which can be applied on the measurement of figures of merits of photodiodes,lasers and passive optical devices.It was developed with Python with good rubustness,easy usage and extending potential.