AMPLIFIED LASER LIGHT WITH MULTIPLE OPTICAL AMPLIFIERS
A seed laser is configured to emit seed laser light. A plurality of optical amplifiers is configured to generate amplified laser light by amplifying the seed laser light. Each of the optical amplifiers is configured to separately direct its respective amplified laser light to a medium without being optically combined within the laser assembly with any of the other amplified laser light emitted by other optical amplifiers in the plurality of optical amplifiers.
This application claims priority to U.S. Non-Provisional Application No. 16/540,514 filed Aug. 14, 2019, which is hereby incorporated by reference.
BACKGROUND INFORMATIONImaging devices are used in contexts such as healthcare, navigation, and security, among others. Imaging systems often measure radio waves or light waves to facilitate imaging. Imaging that measures light scattered by an object is especially challenging and advances to the devices, systems, and methods to improve optical imaging are sought to increase speed, increase resolution, reduce size and/or reduce cost. Some imaging systems require high-intensity light sources and may require laser light sources due to the specific features of laser light (e.g. spatial and/or temporal coherence). Other contexts may also require high-intensity laser light having particular high-power light requirements.
Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.
Embodiments of a laser device and an imaging device are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
This disclosure will generally describe imaging a diffuse medium in the context of human tissue in the medical context, however, the content of this disclosure may be applied to medical imaging, navigation, security, scientific research, or other contexts that image diffuse mediums or objects.
Human tissue is translucent to infrared light, although different parts of the human body (e.g. skin, blood, bone) exhibit different absorption and scattering coefficients. Researchers have attempted to use the properties of infrared light for medical imaging purposes, but size and cost constraints have been prohibitive for wide-scale adoption. Illuminating tissue and other diffuse media with near-infrared light for imaging purposes is sometimes referred to as Diffuse Optical Tomography. In one Diffuse Optical Tomography technique, time-of-flight (TOF) imaging can theoretically be employed by measuring the time it takes for “ballistic” photons (those photons that are not scattered) to pass through tissue. Since the ballistic photons reach the sensor the fastest, they are the least impeded (have the shortest optical path) and thus some conclusion can be drawn to create an image of the tissue that is illuminated by infrared light. However, TOF imaging generally requires specialty hardware (e.g. picosecond pulsed lasers and single photon detectors) to facilitate ultrafast shutters on sensors that are able to image at the speed of light and the systems are overall very expensive and bulky. TOF imaging also requires an input of approximately 10 - 100 fold (or more) light intensity into the body than is used at the detector; thus efficacy and power limitations as well as safety limits on input intensity limit TOF imaging resolution and utility.
In contrast to TOF imaging, some embodiments of this disclosure may illuminate a diffuse medium with an infrared illumination light while an ultrasound emitter is focusing an ultrasonic signal on a particular voxel. The infrared illumination light encountering the particular voxel may be wavelength-shifted by the ultrasonic signal and thus form a wavelength-shifted exit signal that exits the diffuse medium. A light detector (e.g. photodiode, array of photodiodes, or an image pixel array) may capture a signal (e.g. an image) of an interference between the wavelength-shifted exit signal and an infrared reference beam having the same wavelength as the wavelength-shifted exit signal. The signal of the interference between the wavelength-shifted exit signal and an infrared reference beam can be used to measure an absorption value of the particular voxel. In one example, a Fourier transform of an image of the interference pattern between the wavelength-shifted exit signal and an infrared reference beam generates an absorption value for the particular voxel. As the ultrasound emitter raster-scans to different voxels and absorption values for different voxels are generated, the absorption values can be aggregated to generate a two-dimensional or three-dimensional image of the diffuse medium.
The infrared illumination light for illuminating a diffuse medium such as tissue may have particular requirements that are not easily generated. For example, it may be advantageous for the infrared illumination light to have a particular line-width. It may be advantageous for the infrared illumination light to be pulsed laser light (rather than continuous-wave) where a high-intensity pulse is delivered over a short period of time (e.g. 250 ns). Example conventional laser designs for achieving high-intensity laser light includes amplifying laser light via optical amplification where the laser light propagates down a single common optical fiber. This approach can be problematic at certain power-thresholds as high-power laser light propagating along a single optical fiber suffers from stimulated Brillouin scattering that erodes the intensity of the laser light. If parallel optical amplifiers are used to generate high-intensity laser light, the outputs of the parallel optical amplifiers are coupled together to a common laser light output so that the amplified laser beam retains a particular spatial and/or temporal coherence within the same amplified laser beam. However, embodiments of the disclosure may include a laser device that include a plurality of optical amplifiers for amplifying seed laser light where the outputs of the optical amplifiers are not coupled to a common output. Rather, respective amplified laser light emitted by each optical amplifier is directed to a common target (e.g. a diffuse medium). In most any other contexts, separately emitting the amplified laser light from the output of different optical amplifiers to a common target fails to achieve the desired light output characteristics. However, in the context of optical imaging, directing separate, yet synchronized amplified laser light to a common diffuse medium may provide an illumination light of the diffuse medium that meets the requirements (e.g. high-power, short pulse, narrow line-width) of the imaging system. These embodiments and others will be described in more detail with references to
Optical amplifiers 130 may utilize semiconductor or fiber laser amplifiers, for example. Optical amplifiers 130 may be identical in some embodiments so that the characteristics of their respective amplified infrared laser light are the same or very similar. In some embodiments, an electrical drive current that drives each of the plurality of optical amplifiers is synced so that the amplified infrared laser light 135(1), 135(2)... 135(n) are synchronized. This may assist in ensuring that the optical amplifiers are mutually phase-stable when amplified infrared laser light 135 is illuminating the diffuse medium so that the illumination of diffuse medium 180 is by light having identical or almost identical characteristics. For example, if the optical amplifiers are not mutually phase-stable, the different amplified infrared laser lights 135 may have slightly different wavelengths or line-widths. Each optical amplifier 130 may have a power in the range of 1-50 Watts. The output aperture of the optical amplifiers 130 may have a wider taper than conventional optical amplifiers because the beam quality of light 135 that is illuminating the diffuse medium target can have an M2 parameter (beam quality factor) that is very high (e.g. more than 1,000 or even in the millions) while still being suitable as the illumination light for purposes of imaging device 100. In contrast, conventional lasers in a fiber-optic communications context strive for an M2 of close to 1. In embodiments that include reference optical amplifier 140, the reference optical amplifier 140 may have an output aperture taper that supports an M2 that is closer to 1 so that reference light 143 can be coupled into fiber optic 145.
Each of the optical amplifiers is configured to direct its respective amplified infrared laser light 135 into diffuse medium 180 to as infrared illumination light to ultimately generate infrared exit signal 153. In one embodiment, the amplified infrared laser light 135 has a line-width of 1 nm or less and has a wavelength between 680 nm and 1000 nm. In one embodiment, the amplified infrared laser light 135 has a line-width of 1 nm or less and has a wavelength between 1500 nm and 1700 nm.
Directional ultrasonic emitter 115 may be configured to deliver an ultrasonic signal 117 to a given voxel (e.g. voxel 183) of the diffuse medium 180 while the amplified infrared laser light 135 from the plurality of optical amplifiers 130 illuminates the given voxel. Ultrasonic emitter 115 is configured to focus an ultrasonic signal 117 to a point in three-dimensional space. Ultrasonic emitter 115 may utilize a phase-array ultrasound architecture. In the medical context, ultrasonic emitter 115 may be configured to focus an ultrasonic signal 117 to a voxel within the human body. The voxel may be within the brain, abdomen, or uterus, for example. In some embodiments, ultrasonic signal 117 is a plane wave or a linear combination of waves (orthogonal system).
Amplified infrared laser light 135 collectively scatters (scattering not illustrated) within diffuse medium 180 and a portion of the amplified infrared laser light will propagate through voxel 183. In
In
Referring again to
Optical system 325 is configured to generate distributed beams illuminating the inputs of optical amplifiers 130. In
In some embodiments, focusing optical element 427 is positioned at approximately one focal length (of the focusing optical element 427) from the inputs 137 of the optical amplifiers 130. In an embodiment, focusing optical element 427 is positioned less than one focal length from the inputs to the optical amplifiers so the distributed beams are defocused and a beam spot of the distributed beams slightly over-illuminates input apertures of the inputs of the optical amplifiers. Slightly over-illuminating the input apertures to the optical amplifiers may relieve some tolerance constraints since the input aperture will be fully illuminated by the distributed beam as long as the input aperture is positioned so that the beam spot illuminates the entire input aperture. In one embodiment, focusing optical element 427 is positioned more than one focal length from the inputs to the optical amplifiers so the distributed beams slightly over-illuminate input apertures of the inputs of the optical amplifiers.
Referring to
The example optical paths of amplified infrared laser light 835(1) through voxels 883 is illustrated in
Amplified infrared laser light 835(1) outputted by output 831(1) of an optical amplifier 830(1) (not illustrated) scatters in head 805 and a portion encounters voxel 883(1). Light 835(2), 835(3)...through 835(n) may also illuminate voxel 883(1). One or more of ultrasonic emitters 815 may focus their ultrasound signal (not illustrated) to voxel 883(1) which generates a wavelength-shifted infrared exit signal 853(1) of the light 835 that illuminated voxel 883(1). Imaging module(s) 890 may capture an image of an interference pattern generated by exit signal 853(1) interfering with an infrared reference beam as a measurement of the absorption of voxel 883(1) to light 835.
Scientific literature suggests that the penetration depth of infrared light into tissue is around 10 cm so multiple imaging modules 890 may be needed to image the entire brain or other tissue. A wearable hat may include system 800 so that system 800 can be worn as a wearable, in some embodiments. Other wearables may also include all or part of system 800.
The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.
Claims
1. A laser assembly comprising:
- a seed laser configured to emit seed laser light; and
- a plurality of optical amplifiers configured to generate amplified laser light by amplifying the seed laser light, each of the optical amplifiers configured to separately direct its respective amplified laser light to a medium without being optically combined within the laser assembly with any of the other amplified laser light emitted by other optical amplifiers in the plurality of optical amplifiers.
2. The laser assembly of claim 1 further comprising:
- a reference optical amplifier configured to generate reference light by amplifying the seed laser light, wherein plurality of optical amplifiers provide a first beam quality factor, and wherein the reference optical amplifer provides a second beam quality factor that is different from the first beam quality factor.
3. The laser assembly of claim 2, wherein the first beam quality factor is larger than the second beam quality factor.
4. The laser assembly of claim 3, wherein the amplified laser light from each optical amplifier have intensities that are approximately equal.
5. The laser assembly of claim 1 further comprising:
- an optical distribution assembly configured to distribute the seed laser light to inputs of the optical amplifiers.
6. The laser assembly of claim 5 wherein the optical distribution assembly includes:
- a focusing optical element to focus the seed laser light to the inputs of the optical amplifiers; and
- an actuator configured to move the focusing optical element along a translation axis to selectively focus and defocus the seed laser light to the inputs of the optical amplifiers.
7. The laser assembly of claim 1, wherein the seed laser light is seed near-infrared laser light, and wherein the amplified laser light is amplified near-infrared laser light.
8. The laser assembly of claim 1, wherein the plurality of optical amplifiers are arranged as a two-dimensional array of stacked chips, wherein each of the stacked chips includes a one-dimensional array of the optical amplifiers.
9. The laser assembly of claim 1, wherein electrical drive currents that drive the plurality of optical amplifiers are synced.
10. The laser assembly of claim 1, wherein the seed laser is one of a fiber laser or a seed laser.
11. The laser assembly of claim 1, wherein each optical amplifier in the plurality of optical amplifiers includes a frequency converter that down-coverts a first wavelength of the seed laser light to a second wavelength of the amplified laser light.
12. A laser device comprising:
- a seed laser configured to emit seed laser light; and
- a plurality of optical amplifiers configured to generate amplified laser light by amplifying the seed laser light, each of the optical amplifiers configured to direct its respective amplified laser light to a common target, wherein the optical amplifiers in the plurality of optical amplifiers provide a beam quality factor of the amplified laser light that is greater than 1,000.
13. The laser device of claim 12 further comprising:
- a reference optical amplifier configured to generate reference light by amplifying the seed laser light, wherein the reference optical amplifer provides a beam quality factor close to one.
14. A method comprising:
- emitting seed laser light with a seed laser; and
- generating amplified laser light with a plurality of optical amplifiers, each of the optical amplifiers configured to separately direct its respective amplified laser light to a medium without being optically combined with any of the other amplified laser light emitted by other optical amplifiers in the plurality of optical amplifiers.
15. The method of claim 14 further comprising:
- generating reference light by amplifying the seed laser light with a reference optical amplifier, wherein the plurality of optical amplifiers provide a first beam quality factor that is larger than a second beam quality factor of the reference light.
16. The method of claim 14, wherein the amplified laser light from each optical amplifier have intensities that are approximately equal.
17. The method of claim 14 further comprising:
- driving an actuator to move a focusing optical element along a translation axis to selectively focus and defocus the seed laser light to inputs of the optical amplifiers.
18. The method of claim 14, wherein the plurality of optical amplifiers are arranged as a two-dimensional array of stacked chips, wherein each of the stacked chips includes a one-dimensional array of the optical amplifiers.
19. The method of claim 14, wherein electrical drive currents that drive the plurality of optical amplifiers are synced.
20. The method of claim 14, wherein the seed laser is one of a fiber laser or a seed laser.
Type: Application
Filed: Dec 21, 2022
Publication Date: Apr 27, 2023
Inventors: Albert P. Heberle (Santa Clara, CA), Gregory Lee Keaton (San Francisco, CA), Mary Lou Jepsen (Sausalito, CA), Craig Newswanger (Oakland, CA), Hosain Haghany (San Francisco, CA)
Application Number: 18/086,182