Low-speckle laser projection with a broad-area vertical-cavity surface-emitting laser in the nonmodal emission regime

Abstract

We demonstrate low-speckle laser projection using a broad-area vertical-cavity surface-emitting laser (VCSEL) emitting at 840 nm wavelength as the illumination source. By driving the source in a nonmodal emission regime, we were able to achieve speckle contrast values as low as 3.5% in a realistic projection setup. This was done by driving the VCSEL with specific current pulses without using any additional or mechanically moving components to destroy the coherence of the laser beam. We quantitatively model the speckle contrast reduction based on polarization scrambling and the reduced temporal and spatial coherence of the VCSEL.

Characterization of a low-speckle laser line generator

“…In our case, however, we do not use mechanically moving parts, and in this work we study optical systems that generate an optical line (instead of the laser projection system in [7]). Our results are also comparable to the previous investigation that we performed on speckle contrast reduction in a projection setup [9][10][11]. We expect that the speckle contrast can be further lowered by increasing the size of the BA-VCSEL, as the number of beamlets is proportional to the VCSEL aperture area.…”

“…For our pulsed driving conditions (i.e., a 2 μs pulse with an amplitude of 240 mA), we estimate the chirp to be 1.6 nm. The roughness σ v of the paper screen has been determined to be 380 μm at a wavelength of 800 nm [11]. Assuming this value to be valid at the BA-VCSEL's wavelength of 840 nm, a speckle contrast reduction factor of 0.5 is obtained.…”

“…Previous work [9][10][11] has shown that speckle in a projection setup can be reduced by properly exploiting partial spatially coherent laser emission from a broad-area vertical-cavity surface-emititing laser (BA-VCSEL) [12][13][14]. This type of semiconductor laser can be driven into a regime of spatially incoherent emission [15][16][17][18].…”

The influence of a light pipe on the coherence properties in laser projectors

“…As speckle is a coherence effect, observed as a granular pattern on the projection screen, we will as a future task employ our simulation model to investigate the effect of micro-structured projection screens to reduce the speckle. 4,24 We can conclude that the usage of a light pipe does change the coherence properties of the light. These outcomes have also been experimentally verified making use of a reversing wavefront Michelson interferometer.…”

Speckle reduction using phase plate array and lens array

“…Speckle is a drawback of laser display for it can downgrade the image quality greatly. To solve this problem, numerous methods have been proposed, such as: using a deformable mirror 3 or a scanning mirror 4,5 to realize angle diversity; using a broad-area vertical-cavity surface-emitting laser 6 or random lasers 7 to realize wavelength diversity; using a staircase element 8 or a refractive steppers 9 to realize optical path difference; rotating independent speckle patterns 10 or a magneto-optical disk 11 to realize polarization diversity; using a light pipe 12 or a multimode optical fiber bundle 13 to realize time averaging and so on. J. I. Trisnadi firstly proposed the speckle reduction method using Hadamard phase diffuser 14,15 .…”