Laser illumination system with reduced speckle

Abstract

A despeckling device and method in which an optical path difference staircase element is disposed between a fly's eye lens array and the image plane in a position near the focus position of the fly's eye lens array, and a laser generating unit generates and transmits pulsed laser beams to the optical path difference staircase element, wherein the pulsed laser beams are driven at a very short pulsed rate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is related to and claims the benefit of provisional U.S. application No. 61 / 388,238 filed Sep. 30, 2010.FIELD OF THE INVENTION[0002]This invention relates to a laser annealing device with reduced speckle, especially to a laser annealing machine to create a thin film transistor for a large size organic LED display. This invention also relates to laser display devices and laser display methods, and more particularly, to laser display devices and laser display methods directed to achieving reduced speckle.RELATED ART[0003]In general, a laser is an optical source that emits a coherent light beam (also referred to herein as “coherent light” or “laser light”). The coherent light may be emitted as a relatively narrow beam and may be focused to very small spots. Because lasers emit coherent light, lasers may be prone to speckle. Speckle is a random intensity pattern on reflection from a diffuse surface generally caused by mutual ...

AI Technical Summary

Benefits of technology

[0020]According to another aspect, there is provided a method to despeckle a laser beam, comprising generating a pulsed laser beam having a coherence length; transmitting the pulsed laser beam through a first transparent element comprising a plurality of microlenses so that the pulsed laser beam is output as a beamlet from each of the microlenses; and transmitting each one of the beamlets through a respective step included in a second transparent element comprising a plurality of the steps having a one-to-one correspondence with the plurality of microlenses, to an image plane, wherein a height of each step of at least two of the steps is configured to produce an optical path difference of the beamlets longer than the coherence length, wherein the second transparent element is disposed approximately at the foci of the beamlets output from the first transparent element. The generating of the pulsed laser beam may comprise driving the pulsed laser beam using a pulse of less than 10 nanoseconds. The method may further comprise collimating the generated pulsed laser beam and outputting the collimated generated pulsed laser beam to the first transparent element; and focusing the received beamlets transmitted through the respective steps by the second transparent element on the image plane using a field lens. The at least two of the steps may be configured as a one-dimensional staircase and the microlenses may be configured as a one-dimensional array of microlenses. The method may further comprise polarizing the pulsed laser beam with a linear polarization having a polarization direction; and changing the polarization direction of the pulsed laser beam by passing the pulsed laser beam through an optical wave plate comprising one of the steps of the second transparent element. The method may further comprise polarizing the pulsed laser beam with a linear polarization; and changing the linear polarization of the pulsed laser beam to right and left circular polarization by passing the pulsed laser beam through corresponding first and second optical wave plates each comprising one of the steps of the second transparent element. The method may further comprise transmitting each one of the beamlets output from the second transparent element through a third transparent element comprising another plurality of microlenses, to provide focus control of the beamlets.

[0021]According to another aspect, there is provided a two-dimensional despeckling unit, comprising a first transparent element comprising a surface having a plurality of microlenses to receive collimated light having a coherence length from a pulsed laser beam, each of the microlenses configured to output a beamlet which is shaped in two-dimensions; and a second transparent element comprising a light incident surface forming a two-dimensional area comprising two first boundaries and two second boundaries perpendicular to and connecting the two first boundaries; and a plurality of steps protruding out from the light incident surface and arranged in rows, wherein the steps in each row are configured to increase in height along a first direction parallel to the first boundaries, and the rows increase in height along a second direction parallel to the second boundaries, each of the steps having a different height from each other, and each of the steps being configured to receive a corresponding one of the beamlets; wherein the height of each step is configured to produce an optical path difference longer than the coherence length, and the light incident surface is disposed approximately at a foci of the beamlets output from the first transparent element.

Problems solved by technology

Because lasers emit coherent light, lasers may be prone to speckle.

Speckle patterns may severely degrade the image quality of components illuminated with a laser source, such as laser annealing, laser projection displays and laser microscopes.

However, devices that use dynamic reduction methods tend to be larger than those devices that use static reduction methods, for example, because of the number of additional mechanical components involved to generate the time-varying component.

Devices that use static reduction methods may also be large.

Microlens arrays, however, tend to give rise to speckle because in forming the ultimate image they merge the split beamlets.

First, because the incident beam 3 passes through the staircase element 1 and gets diffracted before entering the first fly's eye lens, the diffracted beamlets 4 may deviate in uniformity before entering the first fly's eye lens, thereby reducing the effectiveness of the despeckling.

Second, each of the beamlets 4 diffracted by the staircase element 1 can enter not only the respective targeted lenslet, but also an adjacent lenslet, thereby further reducing the effectiveness of homogenization by using the fly's eye system.

Images