Photonic integrated coherent beam combiner based on MMI and the SPGD algorithm

Area of Science:

• Optical Engineering
• Photonics
• Free-Space Optical Communications

Background:

• Atmospheric turbulence degrades optical wavefronts, reducing free-space optical (FSO) receiver coupling efficiency.
• Multi-channel receivers offer a convenient and economical solution to mitigate turbulence effects.
• Combining multiple single-mode fibers (SMFs) after a multi-channel receiver is essential for signal integration.

Purpose of the Study:

• To propose and demonstrate photonic integrated coherent beam combiners for FSO systems.
• To enhance the coupling efficiency of FSO receivers by mitigating atmospheric turbulence effects.
• To avoid electrical domain signal processing by enabling coherent beam combination in the optical domain.

Main Methods:

• Utilizing multimode interference (MMI) devices for coherent beam combination.
• Implementing the stochastic parallel gradient descent (SPGD) algorithm for optimizing beam combination.
• Developing integrated photonic devices for 4-channel and 16-channel beam combining.

Main Results:

• A 4-channel coherent beam combiner achieved a maximum combined optical power enhancement of 96% with approximately 21 SPGD iterations.
• A 16-beam combination using five 4x1 MMIs reached 89% combined power after 140 SPGD iterations.
• The proposed method effectively enhances combined optical power without electrical domain signal manipulation.

Conclusions:

• Photonic integrated coherent beam combiners based on MMI and SPGD offer a viable solution for improving FSO communication systems.
• The demonstrated approach provides theoretical insights for enhancing the integration and performance of FSO systems.
• This technology contributes to more robust and efficient free-space optical communication.