Comparison of photodiode nonlinearity measurement systems.

Photodiode nonlinearity measurements using one-, two- and three-tone measurement systems are compared with each other, to investigate the comparison accuracy between setups. The mathematical relationship between each setup is analyzed, and data on multiple devices are compared to find under which conditions the measurements are comparable. It is shown that the three measurement systems can be used interchangeably only when the distortion adheres to the expected mathematical slopes.

Novel directional coupled waveguide photodiode-concept and preliminary results.

A novel photodiode is presented using a directional coupler incorporated with a UTC style photodiode with 0.88 A/W responsivity and 35 dBm OIP3 at 25 mA. The device responsivity is characterized at various photocurrents up to 10 mA and the OIP3 is measured up to 25 mA and 10 GHz. Additionally, the device capacitance is measured and used to model the capacitance limited OIP3 of the device. The failure of the device was compared to a traditional waveguide photodiode showing burnout no longer occurs at the front of the device and demonstrated the potential of the new design to control the photocurrent density profile for a waveguide style photodiode.

Behaviors of the third order intercept point for p-i-n waveguide photodiodes.

Waveguide PIN photodiodes with different absorber thicknesses and lengths were fabricated and characterized for linearity. Device A has a thicker absorber and shorter length, resulting in a bandwidth of 20 GHz while device B reduces the absorber by half while maintaining the intrinsic layer thickness and almost doubles the length, resulting in a smaller optical overlap factor and a bandwidth of 10 GHz. Device B shows a significant enhancement in OIP3 with a record high maximum value for a PIN waveguide photodiode of 42.4 dBm at 28 mA and -4V bias compared to device A which has a maximum OIP3 of 32.7 dBm at 10 mA and -4V bias. The increased linearity in device B is attributed to the reduction in optical overlap factor and increase in device length resulting in an easing of the front facet photocurrent density and overall device heating. The DC saturation points are about 75 mA and >160 mA for device A and B at -2V bias.

Three laser two-tone setup for measurement of photodiode intercept points.

The third-order intermodulation product intercept (IP3) has become an important figure of interest for photodiodes in high-performance, externally modulated, analog links. With the desire for highly linear photodiodes comes the need to be able to accurately measure the device without additional variables. The purpose of this work is to redesign the current IP3 setup to accurately measure the third order intermodulation distortions of the photodiode and to also be able to measure the second order intercept point (IP2) using the same setup. The new setup will isolate equipment contributed nonlinearities by maintaining a small RF drive voltage amplitude on the modulators and by optically changing the photodiode input modulation depth while maintaining a constant input optical power to the photodiode. The goal is to measure a specific knee point where different slopes will indicate the change to photodiode dominated nonlinearity.