Mourad Chtioui

High-Power High-Linearity Uni-Traveling-Carrier Photodiodes for Analog Photonic Links

We have fabricated and characterized two high-power high-linearity uni-traveling-carrier photodiode (UTC-PD) structures. The UTC performances are compared regarding their respective collector design. A -3-dB bandwidth improvement (from 16-25 GHz to 19-32 GHz) is achieved when the collector layer thickness is increased (from 250 to 350 nm, respectively). The bandwidth improvement for large photocurrent is at the origin of a ldquosupra-linearityrdquo effect. Photocurrent saturation effects are investigated and -1-dB compression current measurements at 20 GHz show saturation currents as high as 70 mA at -4 V. We also report third-order intermodulation distortion measurements at 20 GHz. The ldquosupra-linearityrdquo effect enhances the PD linearity with increased photocurrent, leading to a record third-order intercept point of 35 dBm at 40 mA.

High-Performance Uni-Traveling-Carrier Photodiodes With a New Collector Design

We report two uni-traveling-carrier photodiode (PD) structures, for high-power and high-linearity applications. Using a thick collection layer (500 nm), the fabricated 25-m-diameter PDs achieve a 3-dB bandwidth up to 29 GHz, and a maximum dissipated heat power of about 480 mW, simultaneously. A new collector design with a nonuniform doping profile is proposed to better relax the space charge effect. Its performances are compared to a uniformly doped collector layer. Saturation currents and third-order intermodulation distortion measurements at 20 GHz confirm the advantage of the new collector design for high-power and high-linearity performances: 1-dB saturation current as high as 120 mA and a third-order intercept point in excess of 35 dBm at 70 mA are recorded.

Thick Absorption Layer Uni-Traveling-Carrier Photodiodes With High Responsivity, High Speed, and High Saturation Power

High responsivity backside-illuminated uni-traveling-carrier photodiodes (PDs) with a 1.2-mum-thick p-doped absorption layer are demonstrated. The fabricated PDs achieve simultaneously high speed, high responsivity, and good linearity under high-power operation. The measured responsivity at 1.55 mum is larger than 0.83 A/W at low photocurrent and increases up to 1 A/W at 75 mA. The measured bandwidth increases from 9 GHz at 1 mA up to 24 and 29 GHz at 50 mA, for 25- and 20-mum-diameter PDs, respectively. Good linearity is demonstrated with a third-order intercept point of 30 dBm at 10 GHz and 50 mA.

Simulation of microwave optical links and proof of noise figure lower than electrical losses

The operation of a microwave photonic link is thoroughly investigated both theoretically and experimentally. To this aim, we have developed a simulation tool based on an accurate physical model embedded in a radio frequency (RF) chain simulator. The theoretical predictions are tested on an intensity modulation-direct detection (IMDD) link we have specifically developed to this purpose. Our simulation tool takes into account both optical and electrical characteristics of the link components including the laser dynamics and impedance matching networks. It thus enables an accurate understanding of the different physical and electrical phenomena governing the links performances even under unusual operation conditions. Specifically, we were able to isolate an unusual behavior and to confirm it experimentally. It is thereby clear that the noise figure of a microwave optical link can be lower than the electrical losses, such as a mismatched output passive electrical network. This state is reached when the optical losses are high enough and when the links output impedance is mismatched, too.

Comparison of theoretical and measured P1dB of a photonic microwave link: influence of some physical parameters of the DFB laser

This paper studies a microwave photonic link built as an IM/DD or intensity modulation–direct detection semiconductor laser system. The radiofrequency gain and 1xa0dB compression point of the link are both simulated with a modelling approach and compared to measurements. The electrical model of the electro-optic transducer, a distributed feedback laser, is first presented. Taking into account the nonlinearities and noise sources, it is developed on the commercial electrical software Advanced Design System. Owing to this accurate model, the impact of the relaxation oscillation frequency is presented on the system nonlinearity characteristic as for example the input 1xa0dB compression point. The comparison of simulated results to measured ones confirms the accuracy of this model.

Experimental and Theoretical Linearity Investigation of High-Power Unitraveling-Carrier Photodiodes

In this letter, the third-order intermodulation distortion of a high-power InGaAs-InP unitraveling-carrier photodiode is examined. Based on experimental data, we have developed an analytical model using a harmonic balance method. The response-time reduction, under high-current operation, is identified as the main nonlinear mechanism before saturation occurss. In addition, a linearity enhancement with increased photocurrent (up to ~40 mA) is observed and analyzed. This leads to a measured third-order intercept point, at 40-50 mA, as high as 32 and 37 dBm at 20 and 5 GHz, respectively.

InGaAs-InP Uni-Traveling-Carrier photodiodes for high power capability

We compare two uni-traveling-carrier photodiodes for high power applications. Saturation current is increased from 62 mA to 90 mA at 20 GHz due to improved series-resistance and heat power dissipation. The associated 3 -dB bandwidth is shown to increase simultaneously from 30 GHz at 40 mA to 32 GHz at 70 mA.

Optical Summation of RF Signals

We present two concepts dedicated to the optical summation of RF signals for radar applications. The first technique is based on a traveling wave detector array. We experimentally demonstrate the summation of four signals in the whole 25 GHz photodiodes bandwidth. However, a deeper study reveals that amplitude and phase errors increase dramatically at high frequency, limiting the practical application to 10 GHz. The second technique relies on a photodiode simultaneously illuminated on its top and back sides. We experimentally demonstrate the summation of two signals covering the whole 25 GHz photodiode bandwidth, with amplitude and phase errors below plusmn1dB and plusmn4deg, respectively. The heterodyne beating noise which occurs in this type of summation remains below -40 dB