Optical apparatus for wide-angle illumination
Incident optical signals propagate within a diffuser substrate and impinge upon an optical diffuser within the diffuser substrate or on its output surface. The optical diffuser redirects or transforms respective portions of each incident signal into corresponding forward- and backward-directed optical signals. The backward-directed signals are redirected or transformed into additional incident signals, and so on. The forward-directed optical signals collectively form the optical output of an illumination source that exhibits reduced speckle. The illumination source can include multiple laser sources formed on or attached to an input surface of the diffuser substrate.
1. An optical apparatus to provide optical output from optical signals having an operational wavelength range, the optical apparatus comprising:
a substrate having an input surface for input of the optical signals and having an output surface, the substrate being transparent over the operational wavelength range of the optical signals that propagate as incident optical signals therethrough; and
an optical diffuser disposed at an interface with the output surface of the substrate,
the interface being configured to redirect a portion of each of the incident optical signals incident thereto into a backward-directed optical signal that propagates toward the input surface of the substrate,
the input surface of the substrate being configured to redirect a portion of each of the backward-directed optical signals incident thereto into one of the incident optical signals that propagates toward the output surface of the substrate,
the optical diffuser being configured to redirect a portion of each of the incident optical signals incident thereto into a forward-directed optical signal that propagates outside the substrate away from the output surface as the optical output, constituent optical beams arising from each of the forward-directed optical signals differing from the incident optical signal to which the each forward-directed optical signal corresponds.
2. The apparatus of claim 1 , wherein the each forward-directed optical signals differ from the incident optical signal corresponding thereto with respect to one or more of: a number of the constituent optical beams, a propagation direction of one or more of the constituent optical beams, or an angular divergence of one or more of the constituent optical beams.
3. The apparatus of claim 2 , wherein the constituent optical beams comprise multiple non-zero-order diffracted beams arising from a single incident beam, or different spatial portions of the single incident beam independently redirected into corresponding forward-directed beams.
4. The apparatus of claim 2 , wherein the each forward-directed optical signals differ from the incident optical signal corresponding thereto with respect to the propagation direction of one or more of the constituent optical beams by non-zero-order diffracting, refraction, or reflection.
5. The apparatus of claim 2 , wherein the each forward-directed optical signals differ from the incident optical signal corresponding thereto with respect to the angular divergence of one or more of the constituent optical beams by refractive or diffractive focusing elements or by refractive or diffractive elements of small transverse size.
6. The apparatus of claim 2 , wherein the optical diffuser is configured to reduce transmission of forward-transmitted optical signals arising from portions of the incident optical signals input into the substrate without being redirected as a backward-directed optical signal.
7. The apparatus of claim 1 , wherein the substrate propagates the incident optical signals therethrough by one or more of specular transmission, refraction, reflection, diffraction, and scattering.
8. The apparatus of claim 1 , wherein the optical diffuser is attached to the output surface by an adhesive; wherein the optical diffuser is formed on the output surface; or wherein the optical diffuser is formed within the output surface.
9. The apparatus of claim 1 , further comprising one or more optical sources positioned relative to the input surface and being configured to produce the optical signals for input having the operational wavelength range.
10. The apparatus claim 9 , wherein the one or more optical sources include: one or more light-emitting diodes; one or more semiconductor lasers; a two-dimensional array of semiconductor lasers at least partly formed on the substrate, at least partly formed within the substrate, or at least partly positioned on a common source substrate attached to the substrate; or a two-dimensional array of VCSELs.
11. The apparatus of claim 9 ,
wherein the one or more optical sources are attached to the input surface by an adhesive transparent over the operational wavelength range;
wherein at least a corresponding portion of each one of the one or more optical sources is formed on the output surface; or
wherein at least a corresponding portion of each one of the one or more optical sources is formed at least partially within the substrate.
12. The apparatus of claim 9 , wherein an optical propagation distance through the substrate from the optical diffuser to the input surface and back to the optical diffuser is greater than a coherence length within the substrate of one or more of the optical signals produced by the one or more optical sources.
13. The apparatus of claim 9 , wherein the one or more optical sources, the substrate, and the optical diffuser are configured to:
increase a signal-to-noise ratio of the optical output due to optical speckle;
effectively extend the one or more optical sources;
increase an angular field-of-illumination from the one or more optical sources;
exhibit a specified collective spatial profile of illumination intensity; or
suppress a collective contribution to a collective spatial profile of illumination intensity, relative to a collective contribution of the forward-directed optical signals, of portions of the incident optical signals transmitted by the optical diffuser without redirection.
14. The apparatus of claim 9 , further comprising:
a first reflector formed on the input surface of the substrate;
a set of one or more gain layers and one or more confinement layers formed on the first reflector; and
a second reflector formed on the set of gain and confinement layers,
wherein (i) each one of the one or more optical sources comprises a VCSEL defined by the first reflector, the gain and confinement layers, and the second reflector, and (ii) one or more of the backward-directed optical signals are redirected at least partly by a single specular reflection at the input surface by the first reflector.
15. The apparatus claim 1 , further comprising a partially reflective layer formed on the output surface or on the optical diffuser, the partially reflective layer being configured to provide partial reflectivity at the interface of the output surface with the optical diffuser.
16. The apparatus of claim 1 , wherein the optical diffuser or the output surface comprises a diffuse scatterer being configured to redirect portions of one or more of the incident optical signals incident thereto into at least portions of the backward-directed optical signals.
17. The apparatus of claim 1 , wherein the optical diffuser comprises:
an array of refractive or diffractive lenses being configured to redirect the incident optical signals into at least portions of the backward-directed optical signals and into at least portions of the forward-directed optical signals;
an array of refractive or diffractive prisms being configured to redirect portions of the incident optical signals into at least portions of the backward-directed optical signals and into at least portions of the forward-directed optical signals; or
an array of diffraction gratings being configured to redirect, by non-zero-order back diffraction, portions of one or more of the incident optical signals into at least portions of the corresponding backward-directed optical signals and being configured to redirect, by non-zero-order forward diffraction, portions of the one or more incident optical signals into at least portions of the corresponding forward-directed optical signals.
18. The apparatus of claim 1 , wherein one or more lateral surfaces of the substrate are configured to reflect into the substrate at least a portion of each backward-directed optical signal that impinges thereupon.
19. The apparatus of claim 1 , further comprising a partially reflective layer formed on the input surface and being configured to provide partial reflectivity at the input surface.
20. A method comprising:
generating optical signals from one or more optical sources;
propagating the optical signals as incident optical signals through a substrate having an input surface and having an output surface, the substrate being transparent over an operational wavelength range of the incident optical signals propagating therethrough;
redirecting a portion of each of the incident optical signals, incident to an interface of an optical diffuser with the output surface, into a backward-directed optical signal that propagates toward the input surface of the substrate;
redirecting a portion of each of the backward-directed optical signals, incident to the input surface, into one of the incident optical signals that propagates toward the output surface;
redirecting a portion of each of the incident optical signals, incident to the optical diffuser, into a forward-directed optical signal that propagates outside the substrate away from the output surface; and
outputting the forward-directed optical signals as optical output having constituent optical beams arising from each of the forward-directed optical signals that differ from the incident optical signal to which the each forward-directed optical signal corresponds.