Computational Study of Amplitude-to-Phase Conversion in a Modified Uni-Traveling Carrier (MUTC) Photodetector

TL;DR

This study analyzes the amplitude-to-phase noise conversion in a modified MUTC photodetector, revealing nulls due to transit time variations and how pulse duration and repetition rate influence the conversion, with implications for device design.

Contribution

It provides a detailed explanation of nulls in AM-to-PM conversion and how pulse parameters affect noise conversion, offering insights for improved photodetector design.

Findings

Nulls in AM-to-PM conversion are due to transit time variations.

AM-to-PM conversion depends on pulse energy, not pulse duration below 500 fs.

Repetition rate affects average photocurrent but not the conversion coefficient as a function of pulse energy.

Abstract

We calculate the amplitude-to-phase (AM-to-PM) noise conversion in a modified unitraveling carrier (MUTC) 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.