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Free-space coherent optical dot-product multiplier with lensless fan-in
Optics Express
|August 14, 2026
Summary
Optical processors offer a low-power solution for AI linear computations. This study introduces a novel free-space dot-product multiplier using coherent detection and a common-path architecture for efficient multiply-and-accumulate operations.
Area of Science:
- Optics and Photonics
- Artificial Intelligence Hardware
- Computer Engineering
Background:
- Linear operations in AI processors consume significant power.
- Optical processing offers inherent linearity and parallelism for energy-efficient computation.
- Multiply-and-accumulate (MAC) operations are fundamental to AI linear algebra.
Purpose of the Study:
- To present a novel free-space dot-product multiplier for analogue MAC operations.
- To demonstrate a strictly common-path architecture for enhanced optical processing.
- To enable signed vector representation using coherent detection.
Main Methods:
- Utilized a single spatial light modulator (SLM) for phase modulation and optical fan-in.
- Implemented a common-path architecture with an internally generated reference beam.
- Employed coherent detection for signed vector representation.
Main Results:
- Achieved dot products for 8-bit vectors (N=2025) and 4-bit vectors (N=32400).
- Demonstrated low RMS error (0.06%) and high SNR (42 dB).
- Showcased simultaneous independent dot products via SLM aperture partitioning with minimal precision loss.
Conclusions:
- The proposed design represents a step towards robust coherent optical processors.
- Fan-in embedding enables a compact, phase-drift-tolerant, and parallelizable architecture.
- This technology has the potential to reduce the energy consumption of linear computations in future AI platforms.
