Multi-Emitter Holographic Projection for Laser Speckle Reduction
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Solution Overview
Problem
Holographic projectors using lasers suffer from image degradation due to laser speckle, which results in low efficiency and non-uniformities in image quality, particularly with high spatial coherence leading to blurring at field of view edges.
Innovation Solution
A holographic projector with a single laser diode chip having multiple emitters, where each emitter forms a respective beamlet, and these beamlets are incoherent with each other, overlapping to form a continuous beam that smooths out speckle patterns, thereby reducing noise and increasing resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single laser source is used to illuminate the hologram, then high optical power and coherence are achieved, but laser speckle causes non-uniformities and degrades image quality
Solution Approach 1:
The single laser source is segmented into multiple independent emitters (e.g., 3-10 emitters) arranged in an array on the laser diode chip. Each emitter produces a separate beamlet that illuminates a portion of the hologram. The incoherent superposition of these multiple beamlets reduces laser speckle while maintaining high optical power, as the speckle patterns from different emitters do not correlate and average out to produce a more uniform intensity distribution.
2Object-affected harmful factors
If multiple separate laser sources are used to reduce speckle, then laser speckle is reduced, but device complexity and alignment difficulty increase
Solution Approach 1:
Multiple independent laser emitters are merged into a single integrated laser diode chip. This consolidation maintains the speckle-reduction benefits of multiple incoherent sources while eliminating the complexity of aligning and stabilizing multiple separate laser systems. The emitters are fabricated in close proximity on the same chip, ensuring stable relative positions and simplified optical path management.
Solution Approach 2:
The multi-emitter laser diode chip serves multiple functions simultaneously: it provides high optical power through combined emission from all emitters, reduces laser speckle through incoherent superposition, maintains spatial coherence within each beamlet for high-quality holographic reconstruction, and simplifies the overall system architecture by replacing what would otherwise require multiple separate laser systems with a single integrated component.
3Object-affected harmful factors
If beamlets are overlapped to form a continuous beam, then speckle patterns are smoothed, but maintaining beam uniformity becomes challenging
Solution Approach 1:
The optical system is designed with emitter-specific optics (lenses or mirrors) for each beamlet, allowing independent optimization of each beam's properties. The optics are positioned and configured to ensure that all beamlets converge and overlap in a controlled manner at the hologram plane, creating a continuous beam with uniform intensity distribution. The local quality of each beamlet is tailored to contribute optimally to the overall beam uniformity when combined.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances image quality by reducing non-uniformities caused by laser speckle, achieving higher resolution and maintaining high uniformity of illumination, while simplifying the projector design by using a single collimation optic and minimizing wavelength spread.
Implementation Method 1
the beamlets are incoherent with each other such that they form different speckle patterns. The holographic projector comprises an optic arranged to receive the plurality of beamlets and form a continuous beam in which beamlets of the plurality of beamlets at least partially overlap, thereby to smooth/even out the different speckle patterns
Data Source
AI summary
A holographic projector comprising a display device, a laser diode chip and at least one optic. The display device is arranged to display a hologram of a picture. The laser diode chip comprising a plurality of emitters. Each emitter is arranged to form a respective beamlet. The beamlets are incoherent with each other such that they form different speckle patterns. The at least one optic is arranged to receive the plurality of beamlets and form a continuous beam in which beamlets of the plurality of beamlets at least partially overlap. The holographic projector is arranged to illuminate the hologram with the continuous beam and form a holographic reconstruction of the picture. The speckle patterns of the beamlets reduce noise in the holographic reconstruction through addition of intensity rather than amplitude and phase.