Xiaojun Xie

High-Power and High-Linearity Photodetector Modules for Microwave Photonic Applications

We demonstrate hermetically packaged InGaAs/InP photodetector modules for high performance microwave photonic applications. The devices employ an advanced photodiode epitaxial layer known as the modified uni-traveling carrier photodiode (MUTC-PD) with superior performance in terms of output power and saturation. To further improve the thermal limitations, the MUTC-PDs were flip-chip bonded on high thermal conductivity substrates such as Aluminum Nitride (AlN) and Diamond. Modules using chips with active area diameters of 40, 28, and 20 μm were developed. The modules demonstrated a 3-dB bandwidth ranging from 17 GHz up to 30 GHz. In continuous wave mode of operation, very high RF output power was achieved with 25 dBm at 10 GHz, 22 dBm at 20 GHz, and 17 dBm at 30 GHz. In addition, the linearity of the modules was characterized by using the third order intercept point (OIP3) as a figure of merit. Very high values of OIP3 were obtained with 30 dBm at 10 GHz, 25 dBm at 20 GHz and more than 20 dBm at 30 GHz. Under short pulse illumination conditions and by selectively filtering the 10 GHz frequency component only, a saturated power of >21 dBm was also measured. A very low AM-to-PM conversion coefficient was measured, making the modules highly suitable for integration in photonic systems for ultralow phase noise RF signal generation.

High-power, high-linearity photodiodes

This talk will describe modified uni-traveling carrier photodiodes (MUTCs) that have achieved high RF output power and high saturation current. Discrete photodiodes, 4×1 phase matched arrays, and balanced detectors will be discussed.

High-Power Flip-Chip Bonded Photodiode With 110 GHz Bandwidth

Back-illuminated flip-chip-bonded charge-compensated modified uni-traveling-carrier photodiodes (PDs) with bandwidths in excess of 110 GHz are demonstrated. PDs with 10- and 6-μm-diameters deliver RF output power levels as high as 9.6 dBm at 100 GHz and 7.8 dBm at 110 GHz, respectively. An analytical model based on parameter extraction from S-parameter fitting was used to assess the bandwidth limiting factors.

Photonic Generation of High-Power Pulsed Microwave Signals

Photonic generation of high-power pulsed microwave signals is demonstrated using charge-compensated modified unitraveling-carrier photodiodes. The impulse response without RF modulation achieved unsaturated peak voltage of 33.5 V and full-width at half-maximum of 50 ps. The peak power levels for gated modulation at 1 and 10 GHz were 41.5 dBm (14.2 W) and 40 dBm (10 W), respectively.

High-Power Photodiode Integrated With Coplanar Patch Antenna for 60-GHz Applications

A high-power V-band photodiode integrated with a coplanar patch antenna is demonstrated. Modified unitraveling carrier photodiodes with broad 3-dB bandwidth (60 GHz) and high-output power up to 16.7 dBm at 50 GHz were integrated with antennas. The radiation pattern characteristics of the coplanar patch antenna were investigated at V-band. The experimental results agree well with simulations. The effective radiated power of the photodiode-integrated antenna is ~20 dBm at 60 GHz.

High-Gain, Low-Noise-Figure, and High-Linearity Analog Photonic Link Based on a High-Performance Photodetector

We report a high-gain, low-noise-figure, and high-linearity analog photonic link. The link combines a high-power and low-noise fiber laser, a Mach-Zehnder modulator, a high-gain erbium-doped fiber amplifier (EDFA), and a high-performance charge-compensated modified unitraveling-carrier photodiode. The critical characteristics of the photodiode include 16-GHz bandwidth, 200-mA saturation current, and >35 dBm third-order intercept point. In the link, low biasing is utilized to reduce the noise and maximize the signal-to-noise ratio, and an EDFA is used to provide sufficient optical input to the MUTC photodiode to ensure that the link can achieve high gain and high output RF power. The combination of high-power low-noise fiber laser and high-bandwidth high-power photodiode, we have enabled high gain (27.8 dB at 6 GHz and 24.5 dB at 12 GHz), low noise figure (4.7 dB at 6 GHz and 6.9 dB at 12 GHz), and high spur free dynamic range (>120 dB · Hz2/3) in the frequency range 6-12 GHz.

High-Power and High-Speed Heterogeneously Integrated Waveguide-Coupled Photodiodes on Silicon-on-Insulator

InP-based high-power and high-speed modified unitraveling carrier photodiodes heterogeneously integrated on silicon-on-insulator waveguides are demonstrated. Internal responsivity up to 0.95A/W and bandwidth up to 48 GHz have been achieved. The maximum RF output power of a 20×35 μm2 photodiode was 16.6, 15.8, and 13.5 dBm at 10, 20, and 30 GHz, respectively. The maximum output RF power of a 10×μm2 photodiode was 12 dBm at 40 GHz. Using the same integration technology, we show that balanced waveguide photodiodes reach 0.78-A/W internal responsivity, 14-GHz bandwidth, and >20-dB common-mode rejection ratio. In the differential mode, the unsaturated RF output power was 17.2 dBm at 10 GHz and 15.2 dBm at 20 GHz.

Characterization of Amplitude Noise to Phase Noise Conversion in Charge-Compensated Modified Unitravelling Carrier Photodiodes

The phase noise, i.e., amplitude modulation to phase modulation (AM-PM) in the photodetector. In general, AM-PM of charge-compensated modified uni-travelling carrier (CC-MUTC) photodiodes originates from the combined nonlinearities of the detector impedance and carrier transit times, which depend on the electric field distribution and the velocity-field characteristics of carrier transport. In this work, we report measurements of AM-PM in transit-time-limited CC-MUTC photodiodes. A Crosslight-based simulation of the photodetection process is used to quantitatively estimate the AM-PM of CC-MUTC photodiodes. Simulated AM-PM of a 15-GHz microwave signal shows good agreement with experimental results. The measured and simulated AM-PM versus photocurrent exhibit a null point that originates from the competition between hole deceleration due to the collapsed electric field in the depleted absorption region and electron acceleration in the self-induced electric field in the undepleted absorption region.

Computational Study of Amplitude-to-Phase Conversion in a Modified Unitraveling Carrier Photodetector

We calculate the amplitude-to-phase (AM-to-PM) noise conversion in a modified unitraveling carrier photodetector. We obtained two nulls as measured in the experiments, and we explain their origin. The nulls appear due to the transit time variation when the average photocurrent varies, and the transit time variation is due to the change of electron velocity when the average photocurrent varies. We also show that the AM-to-PM conversion coefficient depends only on the pulse energy and is independent of the pulse duration when the duration is less than 500 fs. When the pulse duration is larger than 500 fs, the nulls of the AM-to-PM conversion coefficient shift to larger average photocurrents. This shift occurs because the increase in that pulse duration leads to a decrease in the peak photocurrent. The AM-to-PM noise conversion coefficient changes as the repetition rate varies. However, the repetition rate does not change the AM-to-PM conversion coefficient as a function of input optical pulse energy. The repetition rate changes the average photocurrent. We propose a design that would in theory improve the performance of the device.

Numerical modeling of amplitude-to-phase conversion in modified uni-traveling carrier (MUTC) photodetector

We calculate the amplitude-to-phase noise conversion in a MUTC photodetector. We obtained two nulls as measured in the experiments, and we explain their origin.