Apparatus and method for producing light using laser emission

An apparatus is provided that includes a laser that produces light at a first wavelength, an optical element that converts the light at the first wavelength received at an input end thereof into light at a second wavelength, and an optical interface proximate the input end of the optical element that directs light at the second wavelength through the optical element toward an output end of the optical element.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The disclosure herein relates generally to apparatus and method for producing visible light using laser emission.

2. Description of the Related Art

A variety of display systems, such as televisions and projectors, utilize light illumination systems to project images on display media. Image brightness is a useful metric in such display systems. The brightness can limit the size of a projected image and can be a factor in how well the image can be seen in high levels of ambient light. One approach to increasing brightness of a display has been to employ solid-state lasers. Conventional solid-state lasers typically emit light in infrared (IR) wavelengths. A frequency-multiplying optical element converts the IR laser emissions into visible light, such as red, green, or blue light, depending on the initial frequency or wavelength of the IR laser emissions. The resulting visible light may then be used to illuminate optical elements, such as a digital micromirror device (DMD) or a spatial light modulator (SLM) of the projection display system.

Often a filter, such as a Volume Bragg Grating (VBG), at the exit end of the frequency-multiplying element is used to pass a wavelength of narrowband (red, blue or green) light corresponding to the wavelength conversion properties of the frequency-multiplying element. Such a filter is aligned to reflect IR back to the relatively small aperture of the laser. A second filter at the interface between the laser and the frequency-multiplying element polarizes the light and passes the IR light. The second filter also is utilized to reflect the visible light back emission out of the frequency-multiplying element and the optical resonant cavity, which results in the use of additional optical and mechanical components that are relatively precisely aligned. The overall output efficiency of such systems can be relatively low. Accordingly, there is a need to provide an improved laser illumination system.

SUMMARY OF THE DISCLOSURE

The disclosure in one aspect provides an apparatus that includes a laser that produces light corresponding to a first wavelength, an optical element that converts the light corresponding to the first wavelength received at a first surface thereof into light corresponding to a second wavelength, and a first optical interface that directs light corresponding to the second wavelength through the optical element toward a second surface of the optical element.

in another aspect, the apparatus may include a frequency multiplier that converts light at a first wavelength received at a first end thereof into light at a second wavelength and passes the light at the second wavelength toward a second end thereof, and an optical interface associated with the first end that directs light at the second wavelength through the frequency multiplier toward the second end. In one aspect, the frequency multiplier may be configured to double the frequency of an input laser light. In another aspect, the first wavelength may correspond to an infrared light and the second wavelength may correspond to a visible light. A second interface may be utilized to reflect light at the second wavelength proximate the second end of the frequency multiplier back into the frequency multiplier

In another aspect, a method is provided that includes producing a laser light at a first wavelength, converting the light at the first wavelength into a light at a second wavelength in an optical element, and directing at least a portion of the light at the second wavelength present proximate an input end of the optical element through the optical element and toward an output end of the optical element.

Examples of the more important features of the apparatus and method for producing light using laser emission have been summarized herein rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of such apparatus and method that are described hereinafter and which will form the subject of the claims appended hereto.

DETAILED DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present claimed subject matter are described in detail below. In the interest of clarity, not all features of an actual implementation are described in this disclosure. It will of course be appreciated that in the numerous implementation-specific embodiments, features may be added or changes may be made by one of ordinary skill in the art having the benefit of the disclosure, which changes, modifications etc. will vary from one implementation to another but fall within the scope of the disclosure and the claimed subject matter.

FIG. 1shows an illustrative embodiment of a laser illuminator100that converts laser emission at a first frequency to produce a beam of light at a second frequency, according to one embodiment of the disclosure that may be utilized for displaying images on a display medium. In the exemplary embodiments discussed herein, the first frequency is typically an infrared (IR) frequency and the second frequency is typically a frequency of visible light. The laser illuminator100is shown to include a laser110, such as a vertical cavity surface-emitting laser (VCSEL) for producing the IR laser emission. The VCSEL is shown only as an exemplary laser. Any other solid-state laser may be utilized for the purposes of this disclosure. The laser110has a die110aand an extended resonant cavity110band produces an IR laser emission115that exits the cavity110avia an aperture110cand is directed into an optical element120at a first surface or end120aof the optical element. The optical element120in one aspect, may be a frequency-multiplying optical element also referred to herein as a frequency multiplier. The laser110includes a laser resonator having an upper distributed Bragg reflector (DBR) mirror180and a lower DBR mirror184and an active region therebetween including one or more quantum wells (QWs)182for the generation of the laser emission115. Typically, the upper and lower mirrors (180and182) are doped as p-type and n-type materials, forming a diode junction. The planar DBR mirrors typically include layers of alternating high and low refractive indices. High reflectivity mirrors are typically used in the laser110to balance the short axial length of the gain region. The exemplary laser110is based on a gallium arsenide (GaAs) substrate194which focuses the laser emission via thermal focusing into a beam115. In one aspect, the p-DBR layer184is in contact with n-contacts188and p-contacts190for pumping of the laser resonator. The n-contacts and the p-contact may be in contact with a heat spreading sub-mount192for the purposes of dissipating heat. Although a VCSEL is shown and described as the laser emission source, any other suitable laser emission source, including any suitable solid-state laser, may be utilized for the purpose of this disclosure.

The frequency multiplier120has an upstream end portion120aand a downstream end portion120b, wherein “upstream” and “downstream” are defined with respect to the direction of propagation of the light emitted from the laser110. The upstream end portion may also be referred to herein as an input end, and the downstream end portion may also be referred to herein as an output or exit end. Light passes through the input end at a first surface of the frequency multiplier and exits via a second surface at the output end of the frequency multiplier. The frequency multiplier120converts a first portion of an input beam, generally an IR laser emission115, into visible laser light, which results in a visible output light beam140. In one aspect, the frequency multiplier120may include a periodically-poled lithium niobate (PPLN) element or a periodically-poled lithium tantalate (PPLT) element. In one aspect, the output beam140may be a collimated, polarized, and broadband visible laser light. In an exemplary embodiment, the frequency-multiplying optical element120is a frequency doubler and the output beam140therefore has a frequency that is double the frequency of the IR laser emission115. The output beam140typically appears as visible light, such as red, green, or blue light, depending on the initial wavelength of the IR laser emission115. However, the laser110and the optical element120may be configured to generate any other color of light. For example, an IR laser emission at a wavelength of about 1060 nanometers (nm) may be converted into an output beam of visible laser light at a wavelength of about 530 nm, visible as green light. The resulting output beam may be used to illuminate further optical elements such as a spatial light modulator as described inFIG. 5for displaying images via an optical display system such as is described inFIG. 4.

In one aspect, the laser illuminator100includes a first optical interface150between the laser source110and the frequency multiplier120that is arranged to transmit the laser emission beam115from the laser110into the frequency multiplier120and to direct light at certain selected wavelengths present at the approximate input end of the frequency multiplier120through the frequency multiplier toward the output end. The first optical interface150, in one aspect, is a color filter that may be aligned with, attached to or coated on the frequency multiplier. The first optical interface150may include a wire-grid polarizer170and an input filter150a, both oriented substantially perpendicular to an optical propagation axis190of the laser emission115. Due to the reflections at the output end120b(discussed below), light may be forward-propagating or backward-propagating along the propagation axis190within the frequency multiplier120. The input filter150ais selected to generally transmit IR light and reflect visible light and is arranged with respect to the frequency multiplier120so as to transmit the IR laser emission115into the optical element and to direct or reflect the visible wavelengths of light back into the optical element (i.e. toward the downstream end portion120b). An exemplary input filter may include a “cold mirror” for reflecting the desired visible wavelengths and transmitting the IR laser emissions. For the purpose of this disclosure a “cold mirror” may be any interface, including a dielectric mirror and a dichroic reflector that reflects visible light and transmits IR light. The input filter150amay include one or more diffractive elements, one or more holographic elements, one or more dielectric interference filters, and a glass substance or member. The input filter150amay be integrated with, attached to, or coated directly onto a surface or an end of the frequency multiplier. The input filter150amay also be polarized, for example, to provide light into the optical element120having a particular polarization, such a p-polarization (parallel to the plane of incidence) and thereby providing effective laser output.

The frequency multiplier120may include at the output end120ba second optical interface160arranged to reflect the IR laser emission back into the resonant cavity110band to transmit the visible laser light from the frequency multiplier120to provide the output light beam140. The output optical element160may include an output filter160aorientated substantially perpendicular to the optical propagation axis190. The output filter160amay be integrated with, attached to or coated directly onto a surface or an end of the frequency multiplier. The output filter160amay include one or more diffractive elements, one or more holographic elements, one or more dielectric interference filters, or a glass substance or member. The output filter is selected to transmit the desired visible wavelengths to provide the output beam140and to reflect the wavelengths of the laser emission back into the optical element120. An exemplary output filter160amay include a “hot mirror” for reflecting the IR laser emissions and transmitting the desired visible wavelengths. For the purpose of this disclosure, a “hot mirror” may be any interface filter, including dielectric mirror and dichroic reflector that reflects IR light and transmits visible light. If polarization rotation is desired for any downstream optics, a half-wave retarder160bmay be used along with the output filter160a. The half-wave retarder160brotates a polarization of a polarized beam incident from the frequency multiplier120.

The input filters150aand the output filter160amay be designed for proper coupling to the frequency multiplier for efficient energy output of the frequency-multiplied output beam140, while retaining the IR laser emissions within the extended resonant cavity110b. Either the input filter150aor the output filter160aor both may be polarized along a desired plane, including the p-plane, for substantially increased laser output and/or coupling to the frequency multiplier. One or both of the input filter150aand the output filter160amay be made of durable materials, such as dielectrics or glass, that typically do not substantially degrade under exposure to high-energy IR laser emissions and visible laser light.

Due to the reflective aspects of the input filter150aand the output filter160a, the frequency multiplier120typically contains multiple beams of both IR laser emissions and visible light propagating backward and forward along the direction of the propagation axis190. The frequency multiplier120may be dimensioned or adjusted to be of a length so as to reduce or minimize interference patterns between forward-propagating and backward-propagating beams. The distance between the input filter150aand the output filter160amay be selected to reduce interference patterns between the forward-propagating and the backward-propagating beams within the frequency multiplier120. The cut-on and the cut-off wavelengths of the input filter150aand the output filter160amay be relatively loosely specified, due to the relatively wide separation between the wavelengths of the IR spectrum and the visible spectrum.

FIG. 2shows an alternative embodiment200of the present disclosure for multiplying the frequency of a laser emission. The apparatus ofFIG. 2includes a VCSEL110and a frequency multiplier120having a first surface at an input end120aand a second surface at an output end120b. The laser emission215produced by the VCSEL is directed into the input optical element150which may further include a prism250having a reflection surface and a polarizing beam splitter250adisposed along the reflection surface of the prism. The polarizing beam splitter250apolarizes and redirects (folds) the IR laser emission by about 90° toward the frequency multiplier120. The first surface of the frequency multiplier may be covered by a first optical interface, such as an input filter150aarranged to transmit IR laser emissions into the frequency multiplier120and reflect visible wavelengths from within the frequency multiplier back into the frequency multiplier. The second surface of the frequency multiplier120also may be covered by a second optical element, such as an output optical element160arranged to reflect the IR laser emission back into the frequency multiplier and transmit the visible laser light out of the frequency multiplier to provide output beam140. The output optical element160may further include output filter160adesigned to transmit a selected wavelength such as a wavelength of the visible spectrum (i.e., red, green, blue).

FIG. 3shows another illustrative embodiment300suitable for multiplying the frequency of an infrared laser emission. The exemplary embodiment300includes the laser110, such as a VCSEL or another solid-state laser, a frequency multiplier320for multiplying the frequency of the laser emission of the laser110to a wavelength of the visible spectrum of light, and a first optical interface150for receiving laser emission315from the laser and directing the laser emission into the frequency multiplier. The frequency multiplier320has a first surface at an input end320aand a second surface at an output end320b. The output end320bmay have a second optical interface, such as an output optical element160arranged to reflect IR laser emissions back into the frequency multiplier and transmit visible laser light out of the frequency multiplier to produce output beam140.

The first optical interface150may further include a first prism350and a second prism360, wherein a face of the first prism is aligned with a face of the second prism, and the aligned faces have an IR pass filter350bdisposed therebetween. The first prism has a reflection surface and a surface in optical contact with the laser110. The second prism has a reflection surface and a surface in contact with the frequency multiplier and a quarter-wave plate. The first and second prisms may be arranged to have a polarizing beam splitter350adisposed along their reflection faces. In one aspect, the IR laser emission315originating at the laser enters the first prism, reflects off of the beam splitter350aat the reflection surface of the first prism, passes through the IR pass filter350binto the second prism and into the input end of the frequency multiplier320. In another aspect, backward propagating light from the frequency multiplier320exit the input end320a, enters the second prism360, reflects off of the IR pass filter350band the beam splitter350aand passes through a quarter-wave plate370to a reflector380. The reflector reflects the incident light back through the quarter-wave plate370. In another aspect, the reflected light at the reflector380is directed through the quarter-wave plate370into the second prism360, reflects off of the beam splitter360aand the IR pass filter350band into the input end320aof the frequency multiplier. Within the frequency multiplier, the light that traverses the quarter-wave plate has a different polarization than the light originating at the laser110. As a result of the combination of light beams, the output beam340includes visible wavelength laser light having a mixture of polarizations. The output beam340thus may include both s-polarized (perpendicular to the plane of incidence) visible wavelength laser light as well as p-polarized (parallel to the plane of incidence) visible wavelength laser light. An output beam340that includes different polarization states can be suitable for optical elements used in sequential color display systems, for example, to reduce speckle in a final screen image.

FIG. 4shows an exemplary light projection optical system usable to project a spatially modulated light beam as described in the present disclosure. The optical system includes a coherent light source such as a laser illuminator405. The projector400includes one or more light collection, integration, and/or etendue-matching optical elements420arranged to collect and/or to spatially integrate light emitted by the light source. Etendue, as one skilled in the art and having the benefit of the present disclosure would know, is the product of the area of emission and the solid angle into which the emission is emitted. The projector400may also optionally include a relay430(such as a telecentric relay) using one or more aspherical refractive and/or reflective components (not shown), and/or a pupil (not shown) for controlling stray light. The projector400may also optionally include an illumination wedge prism440to direct a light beam such as beam425towards an optical element. The projector400also includes a spatial light modulator (SLM)410, such as the digital micro mirror device (DMD) of Texas Instruments, arranged to modulate spatially substantially the light425projected onto it. The projector may also include a projection total internal reflection (TIR) prism460disposed between the illumination wedge prism440and the digital micro mirror device (DMD)410. In one aspect, the TIR prism460may be separated by an air gap (not shown) from the illumination wedge prism440. The projector may also include a projection lens470for projecting the output beam onto a display screen.

The relay430provides substantially all the light emitted by the laser illuminator405through the illumination wedge prism440and through the projection total internal reflection (TIR) prism460to the digital micromirror device (DMD)410. The DMD reflects and spatially modulates light425back through the projection total internal reflection (TIR) prism460that totally internally reflects the spatially modulated light420through the projection lens470and onto a projection display screen.

FIG. 5shows an illustration of an exemplary spatial light modulator (SLM)500suitable for use with the apparatus described in relation toFIGS. 1-3of the present disclosure.FIG. 5shows, in particular, a top perspective view of an SLM500usable with an integrated circuit, such as the micro-electro-mechanical system (MEMS) spatial light modulator (SLM) integrated circuit. The SLM500has a wafer level package (WLP) DMD chip515bonded thereon. One of ordinary skill in the art having the benefit of the present disclosure would appreciate that the device500could be used with any suitable integrated circuit, including the MEMS SLM integrated circuit described herein. In one aspect, the device500may have the DMD chip515wire-bonded on two sides to bond pad area520. A top surface530may provide a substantially flat area for a system aperture and gasket all around (not shown). The device500may also have one or more primary datum (‘a’) alignment features540, one or more secondary datum (‘B’) alignment features550, and one or more tertiary datum (‘C’) alignment features560disposed on the top surface530. In one embodiment, the SLM may be actuated to orient a light beam at a frequency consistent to provide an image of a single frame at a display screen. Each micro mirror of the SLM is actuated according to a selected program. In one aspect, a micro mirror may be actuated in response to an electric current passing through a piezoelectric material attached to the micro mirror.

FIG. 6describes an exemplary method according to one aspect of the disclosure for producing light using laser emission. The method600includes providing a first beam comprising the infrared laser emission into an input end of a frequency multiplier as indicated at610. The method600also provides for converting within the frequency multiplier at least a portion of IR light into visible laser light having a second frequency, as indicated at620. The method600further provides reflecting the IR light beam back into the frequency multiplier at an output end of the frequency multiplier, as indicated at630.

The method600further may include transmitting the visible light through the output end of the frequency multiplier, as indicated at640. The method600may further include directing visible light present proximate the input end through the frequency multiplier toward the output end of the frequency multiplier as indicated at660. The method may further include rotating a polarization of the visible light. The output may include collimated polarized broadband visible laser light.

Thus, in one aspect, the present disclosure provides an apparatus for producing light that includes: a laser that produces light corresponding to a first wavelength; an optical device that converts the light corresponding to the first wavelength received at an input end thereof into light corresponding to a second wavelength; and a first optical interface proximate the input end of the optical device that directs light corresponding to the second wavelength through the optical device toward an output end of the optical device. The first optical interface may be a color filter that allows transmission of light produced by the laser into the first end of the optical device. The first optical interface typically is arranged in a manner that is one of: (i) aligned substantially perpendicular to the input end of the optical device; (ii) attached to the input end of the optical device; and (iii) sprayed onto a surface of the optical device. The first optical interface may include one of: (i) a diffractive element; (ii) a holographic element; (iii) a dielectric material; and (iv) a glass. In one aspect, the light corresponding to the first wavelength is an infrared light and the light corresponding to the second wavelength is a visible light. The optical device may be a frequency multiplier that is adapted to double the frequency of light corresponding to the first wavelength.

The apparatus also may include a second optical interface proximate the output end of the optical device that reflects light corresponding to the second wavelength back into a cavity associated with the optical device. The second optical interface may be a color filter that is arranged in manner that is one of: (i) aligned substantially perpendicular to the output end of the optical device; (ii) attached to the output end of the optical device; and (iii) sprayed onto a surface of the optical device. A prism may be used to fold the light corresponding to the first wavelength at a suitable angle, including substantially 90 degrees, prior to input of such light to the first optical interface. At least one of the first optical interface and the second optical interface may be polarized in a selected plane to enhance the laser output and coupling to polarization-sensitive PPLN and PPT elements.

In another aspect, a method for producing light is provided that includes producing a laser light at a first wavelength, converting the light at the first wavelength into a light at a second wavelength in an optical element, and directing at least a portion of the light at the second wavelength present proximate an input end of the optical element through the optical element and toward an output end of the optical element. In one aspect, the light at the first wavelength may be IR light and the light at the second wavelength may be a visible light. The method may include doubling the frequency of the IR light to produce the visible light. In another aspect, the method may include reflecting at least a portion of the light at the first wavelength from the output end of the optical element back into the optical element. In another aspect, the method may include folding light produced by the laser by a selected angle prior to receiving such light at the input end of the optical element. Directing at least a portion of the light may include reflecting visible light traveling toward the input end back into the optical element. In another aspect, the method provides for reducing an interference pattern between light beams passing in opposite directions through the optical element. In another aspect, the method provides for reflecting light corresponding to the first wavelength proximate the second end back into the optical element

While the foregoing disclosure is directed to certain specific embodiments that include certain specific elements, such embodiments and elements are shown as examples and various modifications thereto apparent to those skilled in the art may be made without departing from the concepts described and claimed herein. It is intended that all variations within the scope of the appended claims be embraced by the foregoing disclosure.