Light-emitting optoelectronic modules
Light-emitting optoelectronic modules operable to generate an emission characterized by reduced speckle can include a coherent light source, a diffuser, and a Fresnel element. The coherent light source is operable to generate a coherent emission, characterized by a coherence length, incident on the diffuser. The diffuser is characterized by a divergence angle. The divergence angle is the angle between a first path-length from the diffuser to a Fresnel element and a second path-length from the diffuser to the Fresnel element, wherein their difference defines a path difference. In some instances, the path difference is substantially larger than the coherence length.
1. A light-emitting optoelectronic module comprising:
a coherent light source operable to generate coherent light, the coherent light being characterized by a coherence length, a bandwidth, and a center wavelength;
a diffuser, characterized by a divergence angle, the diffuser being positioned with respect to the coherent light source such that the coherent light is incident on the diffuser and the diffuser is operable to generate a diffuse emission; and
a Fresnel lens element including an array of Fresnel rings;
wherein the Fresnel lens element is positioned with respect to the diffuser such that the diffuse emission is incident on the Fresnel lens element and the Fresnel lens element generates an emission,
wherein the divergence angle is an angle between a first path-length from the diffuser to the Fresnel lens element and a second path-length from the diffuser to the Fresnel lens element, the first and second path-lengths emanating from a same point on the diffuser,
wherein the first path-length is orthogonal to the diffuser and the Fresnel lens element, and wherein a difference in length between the first and second path lengths is a path difference, the path difference being larger than the coherence length.
2. The light-emitting optoelectronic module of claim 1 ,
wherein the path difference is larger than the coherence length by a factor sufficient to generate an emission with reduced speckle.
3. The light-emitting optoelectronic module of claim 2 , wherein the factor is between two and 1000.
4. The light-emitting optoelectronic module of claim 2 , wherein the factor is between 1000 and 10,000.
5. The light-emitting optoelectronic module of claim 1 ,
wherein the array of Fresnel rings includes at least ten discrete Fresnel rings within the array of Fresnel rings.
6. The light-emitting optoelectronic module of claim 5 , wherein the diffuse emission is incident on at least ten of the Fresnel rings within the array of Fresnel rings.
7. The light-emitting optoelectronic module of claim 1 , wherein the coherent light source includes an array of laser diodes.
8. An imaging system, the imaging system comprising:
an imager; and
a light-emitting optoelectronic module comprising:
a coherent light source operable to generate coherent light, the coherent light being characterized by a coherence length, a bandwidth, and a center wavelength;
a diffuser, characterized by a divergence angle, the diffuser being positioned with respect to the coherent light source such that the coherent light is incident on the diffuser and the diffuser is operable to generate a diffuse emission; and
a Fresnel lens element including an array of Fresnel rings;
wherein the Fresnel lens element is positioned with respect to the diffuser such that the diffuse emission is incident on the Fresnel lens element and the Fresnel lens element generates an emission,
wherein the divergence angle is the angle between a first path-length from the diffuser to the Fresnel lens element and a second path-length from the diffuser to the Fresnel lens element, the first and second path-lengths emanating from the same point on the diffuser,
wherein the first path-length is orthogonal to the diffuser and the Fresnel lens element, and wherein the difference in length between the first and second path lengths is a path difference, the path difference being larger than the coherence length.
9. The imaging system of claim 8 , the imager including an array of light-sensitive pixels, an optical assembly, and a spectral filter.
10. The imaging system of claim 8 , wherein the path difference is larger than the coherence length by a factor sufficient to generate an emission with reduced speckle.
11. The imaging system of claim 8 , wherein the array of Fresnel rings includes at least ten discrete Fresnel rings within the array of Fresnel rings.
12. The imaging system of claim 11 , wherein the diffuse emission is incident on at least ten of the Fresnel rings within the array of Fresnel rings.
13. The imaging system of claim 8 , wherein the coherent light source includes an array of laser diodes.