An approach for tuning optical field distribution in high-speed and high-power MUTC-PDs

To enhance the linearity of MUTC photodiode, an approach optimizing the fiber coupling distance under fixed optical power is proposed. This approach reduces the photocurrent to 80% of its maximum value, thereby mitigating saturation caused by the Gaussian distribution of the optical field. It achieves a uniform radial electron concentration in the absorption layer and suppresses space charge effects. Consequently, the peak RF output power at 30 GHz was enhanced for all device sizes: the values for the 20 μm, 18 μm, and 15 μm devices increased from 15.87 dBm, 14.15 dBm, and 12.2 dBm to 17.07 dBm, 15.6 dBm, and 14.57 dBm, respectively. A packaged 20 μm MUTC photodiode module was evaluated, yielding peak RF output powers of 8.24 dBm and 12.51 dBm at 30 GHz under biases of − 4 V and − 5 V, respectively. This study establishes a practical strategy for optimizing linearity and bandwidth in MUTC-PDs through precise fiber coupling control, demonstrating its effectiveness in suppressing nonlinearities and improving high-frequency operation.