Eye-safe divergent beam optical wireless communication system

Abstract

To provide an eye-safe divergent beam optical wireless communication system and a divergent beam optical transmitter.SOLUTION: The divergent beam optical transmitter includes a laser array 312 that emits an optical beam 316, one or more lenses 324 that collimate the optical beam to the overall divergence of the optical beam, a diffuser 314 that is arranged between the laser array and the lens, which increases the intrinsic divergence of the optical beam and spreads out the intrinsic divergence of the optical beam to a specific portion of the lens to be safe for the eyes after the lens. The overall divergence of the optical beam and the intrinsic divergence of the optical beam can be independently controlled. The overall divergence of the optical beam is greater than the intrinsic divergence of the optical beam.SELECTED DRAWING: Figure 3B

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 901,391, entitled “Eye Safe Diverged Beam Optical Wireless Communications System,” filed September 17, 2019, the contents of which are incorporated herein by reference.

[0002] FIELD OF THE DISCLOSURE The present disclosure relates generally to wireless optical communications, and more particularly to eye-safe diverging beam wireless optical communications. [Background technology]

[0003] The concept of free-space optical (FSO) communications using lasers dates back to the invention of the laser. However, the difficulty of generating and modulating high-power lasers has limited the use of FSO to direct-line systems using tightly collimated beams. Very low power and low modulation rates with divergent pulsed light are used for a few niche applications such as remote controls for televisions and other appliances. Even during the telecom boom of the late 1990s and early 2000s, when billions of dollars were invested in components and systems, FSO systems never went beyond a collimated beam in a direct-line configuration. There are several companies selling FSO direct-line systems, but these systems require precise alignment and skilled installation. The cost of these systems starts at about US$10,000 per link, and only a few thousand systems are shipped per year.

[0004] A recently developed FSO communications system that takes into account and overcomes at least some of the above challenges, and possibly others, is described in U.S. Patent No. 9,847,834, which is incorporated herein by reference. Nevertheless, further improvements and enhancements to existing systems and methods are often desirable. Summary of the Invention

[0005] An exemplary implementation is based on the divergent beam free space optical link described in the '834 patent and other related applications including U.S. Patent Application Publication No. 2017 / 0257167 to Adams et al. and U.S. Patent Application Publication No. 2018 / 0196139 to Brown et al., the contents of both of which are incorporated herein by reference. An exemplary implementation of the present disclosure adds a diffuser between the laser and the transmission lens of the divergent beam system. In particular, the exemplary implementation provides a high power laser (or array) with a diffuser and lens configured to increase the illumination area of ​​the output aperture, thus expanding the angular range of the emitted laser beam as perceived by the human eye by maximizing the amount of light that can be delivered while remaining eye safe.

[0006] The diffuser divergence and laser spot size provide at least two advantages: 1. Diffusers increase the divergence of the laser beam so that it spans almost the entirety of the transmission lens. This increases the illuminated area at the exit aperture, allowing for higher total delivery power. 2. The beam intrinsic divergence (called alpha, α) is set by dividing the laser spot size on the diffuser by the distance between the diffuser and the transmitting lens. The larger the value of α, the wider the eye-safe intensity limit.

[0007] The spot illuminated by the laser on the diffuser becomes the effective area of ​​beam divergence, and the diffuser spreads the light out enough or nearly enough for the optical system to increase the allowable intensity by a factor of 50 in certain configurations, and the total output power by a factor of 100 or more.

[0008] The intrinsic and overall divergence can be controlled independently with the requirement that the overall divergence be greater than the intrinsic divergence.

[0009] The exemplary implementation of the present disclosure has several differences from the prior art. For example, Wick (U.S. Pat. No. 4,453,806) teaches and claims a collimated laser beam that passes through a transmissive optical element (or from a reflective optical element), passes through a transmissive diffuser, and finally passes through a collimating optical system. Notable differences include that the exemplary implementation of the present disclosure (1) uses a diverging laser array, (2) eliminates the first optical element, and (3) produces a diverging beam rather than a collimated beam.

[0010] Lopez-Hernandez (U.S. Patent No. 6,867,929) teaches and claims a light focusing system with a laser source, a diffuser, a collimator, and a laser light focused onto the diffuser, all three optics formed from one piece. This differs from the present approach of using laser divergence, where the diffuser sets the divergence and then the lens changes the divergence of the beam.

[0011] Joseph (US Patent Application Publication No. 2013 / 0223846) teaches short-distance (several meters) connections between circuit boards. His teachings include using sections of a vertical-cavity surface-emitting laser (VCSEL) array to achieve multi-level amplitude modulation, as well as selectively using sections of subsets of the array to achieve some degree of beam steering. Finally, he claims to achieve optical switching by selecting subsets of the array. He further teaches the use of MIMO (multiple-input multiple-output) technology, a standard in optical communication systems, by using multiple detectors at the receiving end and subsections of the array at the transmitting end. In this patent, a diffuser is used to make the laser array look like an extended source and to mix the elements so that the beam is incoherent. However, like Wick, the output beam after the lens is still collimated, which is physically impossible with an extended source as he teaches.

[0012] Chan et al. (U.S. Pat. No. 6,504,634) describe using a diffuser with a small amount of intrinsic scattering (approximately 1°) to increase the beam divergence up to 1.5 mrad. For eye safety considerations, this is still a collimated beam. They teach this as an upper limit, but exemplary implementations use intrinsic divergence well above this value for higher power applications. Because the divergence of their beam is limited, these teachings are limited to lower powers, since the beam is still considered nearly collimated for eye safety parameters.

[0013] Chacko and Davies (published paper, INTERNATIONAL JOURNAL FOR TRENDS IN ENGINEERING & TECHNOLOGY, VOLUME 5 ISSUE 2, MAY 2015, ISSN: 2349-9303) describe a visible light system using LEDs with lenses and diffusers. The links described there are very short (a few meters) and therefore can have high divergence or low power levels to reach such a minimum distance. When longer distances are required, it becomes essential to preserve eye safety without sacrificing optical power or narrowing the divergence too much, and it is not obvious how to do this.

[0014] O'Brien and Katz (Website, Wireless World Research Forum (WWRF) ~2004) mention the use of diffusers in FSO links to increase the allowable power. They do not go into the details, but rather give a general overview of FSO for various applications.

[0015] Khoo et al. (IEEE Colloquium Optical Wireless Communications, 1999, p3) use a collimating lens followed by a diffuser. The laser-lens spacing sets the spot size, and then the divergence is set by an engineered diffuser. The paper describes a very short range optical distance of approximately 2 meters in length. This concept can be scaled to larger powers, but has several drawbacks compared to the exemplary implementation of this disclosure. The most significant drawback is that the engineered diffuser described in this paper makes small diverging beams difficult or impossible to achieve. Khoo et al. describe a total divergence of 14 degrees. A particular exemplary implementation of this disclosure uses a total divergence of 2 degrees, but has the ability to diffuse to smaller angles. The diffusers specified in the prior art do not allow for collimated beams with divergence of less than 1-2 degrees.

[0016] A second shortcoming of Khoo is that due to the setup, the overall divergence and the intrinsic divergence (α) of the beam are the same value and are controlled by the diffuser. In an exemplary implementation of the present disclosure, the exemplary implementation of the present disclosure includes a setup in which the divergence and the intrinsic divergence of the beam can be independently and individually controlled. One advantage is that the two divergences can be independently controlled, allowing flexibility in the setup and overall footprint size. This is also advantageous for flexibility in applications where one needs to be optimized at the expense of the other.

[0017] In addition, the overall system size is larger in Khoo's teachings. The distance between the laser and the lens is set by the natural divergence of the laser and therefore must be farther apart to achieve the same spot size on the lens as obtained in the exemplary implementation of the present disclosure. A diffuser is behind the lens, further increasing the size. As an example, a 1 Gbps link of the present invention has an output optical power of 1 W and a divergence of 2 degrees. For eye safety, the area occupied by the spot needs to be 2 inches in diameter. To achieve this with a source-lens-diffuser setup, twice the optical path length is required compared to the source-diffuser-lens setup of the present invention.

[0018] Kare et al. (US Patent Application Publication No. 2018 / 0131450) propose a high power beam configuration based on VCSELs, optics, and photodiodes. In this work, a diffusing device is set up between the VCSEL and the lens, but there is no mention of the inherent divergence from the finite range of the source, which in their view is considered to be zero, which is unphysical. Furthermore, the divergence is considered to be fully controllable, which is also unphysical from the finite range of the source. Their argument may be true for a theoretical textbook point source, but it is not feasible for a physical source with a finite non-zero source range. Furthermore, one of their references violates the second law of thermodynamics. On page 18, line 27, they state that "it will increase the radiance," but radiance cannot be increased in a passive system, like etendue, because it violates the second law of thermodynamics.

[0019] Their references to eye safety and what determines eye safety are also only partially correct. On page 19, line 14, they state that "Such spreading over a determined projection aperture increases the apparent angular size of the high flux power beam 106, thereby reducing the eye hazards associated with the high flux power beam 106 and increasing safety with respect to certain U.S. and international laser safety standards." However, they are incorrect in stating that spreading over a projection aperture reduces eye hazards. It is the increase in the beam's intrinsic divergence that reduces eye hazards. This is stated in this disclosure. They ignore the intrinsic divergence and assume that the intrinsic divergence can be reduced back to zero when in fact it cannot be reduced at all. Furthermore, eye safety is measured in mW / cm 2 Since the optical axis is set at θ = θ , increasing the spread over the projection aperture increases the total allowable power throughput, and therefore increasing the area increases the total power throughput.

[0020] Accordingly, the present disclosure includes, but is not limited to, the following example implementations.

[0021] Certain exemplary implementations provide a divergent beam light transmitter comprising a laser light source configured to emit a light beam, one or more lenses, and a diffuser disposed between the laser light source and the one or more lenses and configured to increase the inherent divergence of the light beam and spread the light beam over a particular portion of the one or more lenses so that it is eye-safe after the one or more lenses.

[0022] In certain exemplary implementations of a diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the optical beam intrinsic divergence has different values ​​in different directions.

[0023] In certain exemplary implementations of the diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the laser light source includes a vertical cavity surface emitting laser array.

[0024] In a particular exemplary implementation of the diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the laser source includes a fiber-coupled laser that is amplified by an erbium-doped fiber amplifier and then connected to the diverging beam optical transmitter by another fiber.

[0025] In certain exemplary implementations of the diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the diffuser is a transmissive diffuser.

[0026] In certain exemplary implementations of the diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the diffuser is configured to translate toward or away from the laser source to change the intrinsic divergence.

[0027] In a particular exemplary implementation of a diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the diffuser is configured to translate closer to the laser source to increase the intrinsic divergence during link acquisition and then translate away from the laser source to decrease the intrinsic divergence and increase the data transmission rate.

[0028] In certain exemplary implementations of the diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the transmissive diffuser is an engineered diffuser.

[0029] In certain exemplary implementations of the diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the diffuser is an active element configured to change the divergence in response to an input.

[0030] In certain exemplary implementations of the diverging beam optical transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the active element is a mechanically movable element.

[0031] In certain exemplary implementations of the diverging beam light transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the mechanically movable element substantially prevents transmission of light in a rest position.

[0032] In a particular exemplary implementation of the diverging beam light transmitter of any preceding exemplary implementation or any combination of any preceding exemplary implementations, the diverging beam light transmitter further comprises an additional passive diffuser between the active diffuser and the one or more lenses.

[0033] In certain example implementations of the diverging beam light transmitter of any preceding example implementation or any combination of any preceding example implementations, the diverging beam light transmitter is Class 1 eye-safe.

[0034] In certain example implementations of the diverging beam light transmitter of any preceding example implementation or any combination of any preceding example implementations, the diverging beam light transmitter is Class 1M eye-safe.

[0035] A particular exemplary implementation provides a diverging beam optical communication system comprising: a laser light source configured to emit a light beam; one or more lenses configured to collimate the light beam to an overall divergence of the light beam; a diffuser configured to increase the intrinsic divergence of the light beam and spread the light beam to a specific portion of the one or more lenses so that it is eye-safe after the one or more lenses; a receive lens; and a detector, the receive lens configured to focus the light beam onto the detector, the detector having an etendue sufficient to receive light from the receive lens with an acceptance angle greater than 1.7 mrad.

[0036] Certain exemplary implementations provide a diverging beam optical communication system comprising: a laser light source configured to emit a light beam; one or more lenses configured to collimate the light beam to an overall divergence of the light beam; a diffuser configured to increase the intrinsic divergence of the light beam and spread the light beam to a specific portion of the one or more lenses so that it is eye-safe after the one or more lenses; a receive lens; and a detector, the receive lens configured to focus the light beam onto the detector, the detector having an etendue sufficient to receive light from the receive lens with an acceptance angle greater than 5 mrad.

[0037] Certain exemplary implementations provide a diverging beam optical communication system comprising: a laser light source configured to emit a light beam; one or more lenses configured to collimate the light beam to an overall divergence of the light beam; a diffuser configured to increase the intrinsic divergence of the light beam and spread the light beam to a specific portion of the one or more lenses so that it is eye-safe after the one or more lenses; a receive lens; and a detector, the receive lens configured to focus the light beam onto the detector, the detector having an etendue sufficient to receive the light beam from the receive lens with an acceptance angle greater than 17 mrad.

[0038] These and other features, aspects, and advantages of the present disclosure will become apparent from a reading of the following detailed description in conjunction with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four, or more features or elements described in the present disclosure, regardless of whether such features or elements are explicitly combined or recited in a particular example implementation described herein. The present disclosure is intended to be read holistically such that any separable features or elements of the disclosure are deemed combinable in any of its aspects and example implementations, unless the context of the disclosure clearly dictates otherwise.

[0039] It is therefore understood that this summary is provided only for the purpose of summarizing certain exemplary implementations in order to provide a basic understanding of certain aspects of the present disclosure. It will therefore be understood that the above exemplary implementations are merely examples and should not be construed to narrow the scope or spirit of the present disclosure in any way. Other exemplary implementations, aspects, and advantages will become apparent from the following detailed description, taken in conjunction with the accompanying figures illustrating the principles of certain described exemplary implementations.

[0040] Having thus described exemplary implementations of the present disclosure in general terms, reference is now made to the accompanying drawings, which are not necessarily drawn to scale. [Brief description of the drawings]

[0041] [Figure 1] 1 illustrates the maximum allowable exposure of a collimated beam at a particular wavelength and exposure duration, according to certain exemplary implementations of the present disclosure. [Diagram 2] 13 illustrates a plot of eye-safe light intensity for a particular range of values ​​of α in accordance with certain example implementations. [Figure 3A] 1 shows a diverging beam optical transmitter without a diffuser. [Figure 3B] 1 illustrates a diverging beam optical transmitter with a diffuser in accordance with certain exemplary implementations. [Figure 4] 1 illustrates a diverging beam optical transmitter with a diffuser in a reflective configuration according to a particular exemplary implementation. [Figure 5A] 1 illustrates a diverging beam optical transmitter with an active diffuser in accordance with a particular exemplary implementation. [Figure 5B] 1 illustrates a diverging beam optical transmitter with a diffuser that can be physically moved relative to the light source and lens to change the overall divergence of the beam, according to certain exemplary implementations. [Figure 5C] 1 illustrates a diverging beam optical transmitter with both active and passive diffusers in accordance with certain exemplary implementations. [Figure 6]1 illustrates an example in which the laser light source includes a fiber-coupled laser, in accordance with a particular exemplary implementation. [Figure 7] 1 illustrates a diverging beam optical communication system in accordance with a particular exemplary implementation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Specific implementations of the present disclosure will now be described more fully below with reference to the accompanying figures, in which some, but not all, implementations of the present disclosure are shown. Indeed, various implementations of the present disclosure may be embodied in many different forms and should not be construed as being limited to the implementations set forth herein, but rather, these exemplary implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements.

[0043] Unless otherwise stated or clear from the context, references to first, second, etc. should not be construed to imply a particular order. A feature described as being above another feature may instead be below, and vice versa (unless otherwise stated or clear from the context), and similarly, a feature described as being to the left of another feature may instead be to the right, and vice versa. Also, while reference may be made herein to quantitative measures, values, geometric relationships, and the like, unless otherwise stated, any one or more, if not all, of these may be absolute or approximate to account for possible acceptable variations, such as variations due to engineering tolerances, and the like.

[0044] Unless otherwise stated or clear from the context, the "or" of a set of operands as used herein is an "inclusive or" and thus true if and only if one or more of the operands are true, as opposed to an "exclusive or" which is false when all of the operands are true. Thus, for example, "[A] or [B]" is true if [A] is true, or if [B] is true, or if both [A] and [B] are true. Additionally, the articles "a" and "one" mean "one or more" unless otherwise stated or clearly directed to the singular form by the context. Additionally, it should be understood that the terms "data," "content," "digital content," "information," and similar terms may at times be used interchangeably, unless otherwise stated.

[0045] Laser eye safety. There are several physical mechanisms by which lasers can damage the human eye. Very short high intensity pulses can cause both protein denaturation and water bumping in the eye. Longer exposure times can lead to photochemical damage, where the light triggers chemical reactions in tissue.

[0046] The wavelength of light determines the effect it has on the human eye. Visible light usually elicits a blink response, and therefore higher light powers are considered safe for the eye. At longer wavelengths, water in the eye absorbs much of the light, preventing it from reaching the retina. As an example, for 1550 nm light, the eye safety limit is approximately 100 mW / cm, the point at which the light causes burns to the cornea. 2 The maximum output power is set by the point with a value of 0.01 W. For a lens with a diameter of 50 mm, the maximum output power is about 2 W. In between there is a range of wavelengths that can still pass through the water in the eye, but the beam appears much dimmer to the eye than it actually is, because the retina has a much lower response. In this range, the eye safety power limit is lower.

[0047] The intrinsic divergence of a light beam (usually called alpha, α, and given in units of milliradians) also determines its effect on the eye. Since the eye's lens can only focus to a minimum spot size of about 20 microns on the retina, beams with α<1.5 milliradians are considered collimated for eye safety. Beams with α>1.5 milliradians can focus to a spot larger than 20 microns and have a higher intensity without causing eye damage. Note that the intrinsic divergence of a beam is different from the overall divergence of the beam. A laser coming out of a single mode fiber may cover a range of tens of degrees (the overall divergence of the beam), but the intrinsic divergence (α) is still less than 1.5 milliradians because the emission area set up by the fiber is very small (5-10 microns).

[0048] Figure 1 shows the MPE (Maximum Permissible Exposure, American National Standard Z136.1-2014, p104) for collimated beams (α<1.5 mrad) at wavelengths ranging from 400 nm to 1400 nm and exposure durations from 0.1 s to approximately 30,000 s (8 h). cm vs. exposure time shown on the x-axis 100. 2 Irradiance, measured in watts per inch, is plotted on the y-axis 102. Generally, the longer the wavelength, the higher the MPE, with the exception of 1400 nm, which is below 1315 nm. The MPE generally plateaus after 10 seconds.

[0049] If the beam comes from an extended source, such as a light bulb, then α is much larger than 1.5 milliradians, and the eye focuses the light to a larger spot rather than a minimum spot. This larger spot can have more total power without damaging the retina. The intensity of the beam entering the eye can then be higher.

[0050] Figure 2 shows the eye-safe light intensity 202 (units: mW / cm2) for a range of α200 values ​​from 1.5 mrad to 100 mrad. 2) is calculated for a wavelength of 850 nm and exposure times of 10 seconds 204 and 60 seconds 206. The upper level of 100 mrad (approximately 6°) is the point where the total power on the retina becomes problematic.

[0051] Eye safety is used herein as defined in laser safety standards, such as the American National Standards Institute (ANSI) Z136.1 standard (ANSI Z136.1 standard), the International Electrotechnical Commission (IEC) 60825-1 standard (IEC-60825-1 standard), etc. Eye safety is set by classes, with different safety rules for each class. Current classes include Class 1, Class 1M, Class 2, Class 2M, Class 3R, Class 3B, and Class 4. Various exemplary implementations are of various classes of eye safety. Many exemplary implementations are of Class 1 or Class 1M. Certain exemplary implementations are of Class 2 or Class 2M. Certain exemplary implementations may be of Class 3R, Class 3B, or Class 4.

[0052] Previous FSO Systems. Most FSO communication systems use either fiber-coupled lasers or single-element laser diodes. These sources have a natural emission angular range, which is collimated into a beam using one or more lenses or mirrors. There is still a residual divergence, set by the diameter of the emitting area relative to the focal length of the collimated lens, or in the extreme case of a very small emitting area, by the ratio of the spot size on the lens to the wavelength of the light. This divergence is very small and can be less than 1 microradian for a single-mode fiber and a 50 millimeter collimation lens. In all of these systems, α is <1.5 milliradians and minimum eye-safety strengths apply.

[0053] For example, at 850 nm, as light passes through the water in the eye, the limit is low, about 2 mW / cm for a collimated beam. 2 The maximum power output of the 50 mm diameter lens is then limited to about 40 mW of total optical power. The total power of this beam limits the link distance in FSO systems.

[0054] To increase this limit, many FSO systems use lasers with a wavelength of 1310 nm, where the light does not pass through the water in the eye and the eye safety threshold is set by the power level that causes a burn to the cornea, which is around 200 mW / cm2. 2 , then a 50 mm diameter lens can deliver nearly 4 W. However, as mentioned in previous applications, 850 nm may be preferred because it can now use silicon-based components which are much cheaper than materials such as InGaAs used for longer wavelength devices.

[0055] Advantages of DBFSO Links: An exemplary implementation of the present disclosure adds a diffuser between the laser and the lens such that the beam spreads nearly across the entire lens and the inherent divergence of the beam is up to but not exceeding the overall divergence of the beam. This increases the maximum launch power and therefore the maximum distance and data rate that the link can achieve.

[0056] In previous disclosures and applications, diverging beam systems have been described where the light source consists of a laser or laser array and one or more lenses to set the divergence of the system. If the lens is set at a certain focal distance from the laser, the overall divergence of the beam is set by the size of the laser area relative to the focal length of the lens, i.e., the minimum divergence is given by (laser array size) / (lens focal length). Figure 3A shows this configuration. The laser array 300 has a finite width and the laser beam 302 diverges at the natural divergence angle of the laser or laser array 300. The beam makes an angle σ 304 with the focusing lens 306 and then has a different divergence angle θ 308 with the normal. The finite extent of the laser on the other side of the lens is given by α 310.

[0057] In general, the divergence of a system's beam can be increased by moving the lens closer to the laser. In that case, even though the overall divergence of the beam increases, the local (or intrinsic) divergence is still set by the laser size divided by the distance to the lens. This continues until the lens is close enough to the laser, i.e., limited by the divergence of the laser beam. At this point, the overall divergence is set by the divergence of the laser itself, i.e., the lens starts to look like a window with little or no focusing power.

[0058] Many lasers and laser arrays have a divergence in the range of 20° to 40°, and in one implementation, the divergence is 24° to 34°. Each of the individual laser elements can also be collimated by a lens, but because the elements are at different lateral positions relative to the lens axis, each beam is collimated in a different angular direction. The laser elements are also very close together, within tens of microns of each other, so building a lens array where there are lenses for one or several laser elements can be difficult.

[0059] Diverging Beam Without Diffuser. Figure 3A provides an example implementation of the higher power allowed in a diverging beam system without a diffuser. In one example, assume that the laser 300 is about 1 mm wide and the lens 306 is about 40 mm away. The divergence for eye safety is then about 25 milliradians, which allows an allowable intensity of 2 mW / cm. 2 to 34mW / cm 2 (for a 10 second exposure). The lens spot size is only 2.1 cm wide, so the maximum output power of the system is 118 mW.

[0060] Diverging beam with diffuser. An exemplary implementation of the present disclosure increases the allowable intensity by adding a diffuser between the laser and the lens. The diffuser scatters the light over a controlled angular range. This angular range is always larger than the divergence of the beam from the laser itself, otherwise the system would violate the conservation of etendue and the second law of thermodynamics. The spot illuminated by the laser on the diffuser becomes the effective area of ​​the laser at the intrinsic beam divergence as it propagates through the rest of the transmitter and then the system.

[0061] The illuminated area on the transmission lens is then set by the output angle of the diffuser and the distance between the diffuser and the transmission lens. The goal is to spread as much as possible across the transmission lens while still maintaining a large enough value of α. A longer distance between the diffuser and the lens means a larger beam size at the lens, but a longer distance means a smaller value of α.

[0062] Figure 3B shows an example implementation. The laser array 312 has a natural divergence with the diffuser 314 at an angle σ 322. The beam 316 from the diffuser is at a different divergence angle, making an angle σ 2 with the lens 324. The lens 324 also changes the divergence of the beam to an angle θ with respect to the normal. The illuminated area on the transmitting lens 324 results in an angle α 2 326 behind the lens 324. This value of α is larger than in Figure 3A due to the diffuser.

[0063] As an exemplary implementation of the present disclosure, a 3 mm spot on a diffuser 40 mm from the lens has a divergence of 75 milliradians and a power output of 100 mW / cm 2 gives an acceptable intensity (for a 10 second exposure) of 1963 mW. Since the beam size at the lens is approximately 5 cm, the maximum power of the system is then 1963 mW, which is about 16 times more than the implementation without a diffuser shown in Figure 3A.

[0064] The laser source can be any of several laser sources including, but not limited to, a vertical cavity surface emitting laser (VCSEL), a VCSEL array, a strip laser, a fiber laser, or a fiber coupled laser with an additional amplification stage. An example of a fiber coupled laser is a C-band telecom laser connected to an EDFA (Erbium Doped Fiber Amplifier), the fiber output of the EDFA is connected to a transmitter. The size of the laser source can range from a small 5 micron for visible wavelength fiber to a large 10 millimeter for a VCSEL array. Other specific examples include a 1 mm VCSEL array, a 9 micron core, a single mode telecom fiber, and a 100 micron multimode fiber. The laser wavelength can be any physically realizable value including UV, visible, near infrared, far infrared, etc. Common wavelengths already available that can be used in these implementations include 800 nm, 850 nm, 905 nm, 1300 nm, telecom C band, and telecom L band.

[0065] In a particular exemplary system, a diffuser from Brightview Technologies can be used. In one implementation, the spot product uses the C-HE40-PE-SM-RA12, which increases the + / - 12° divergence of the VCSEL array to approximately + / - 27°. In this implementation, the diffuser is approximately 7mm from the laser. There is a limit to how close the diffuser can be. If it is too close to the laser, a small amount of absorption can heat up the diffuser and melt it. Additionally, the further away the diffuser is located, the larger α can be, since the spot size on the diffuser increases as the distance between the laser and the diffuser increases. The efficiency of this diffuser is very high, ranging from 89% to 97%. The divergence can be engineered by choosing a particular diffuser. Brightview has standard products ranging from approximately 5° to 127° (FWHM), and custom diffusers can hit any target within that range.

[0066] Other diffusers can range from 1 degree to 2π steradians.

[0067] Note that this scheme may only work for highly divergent beam systems, since the divergence introduced by the diffuser is far beyond the allowable beam divergence in a collimated FSO system. That is, the angular range of the system may be too wide and the laser power may not be sufficient to achieve any distance. This does work with divergent beam disclosures, since the beam is already diverging, and a divergence of 25-200 mrad has a range of 0.1° (1.75 mrad) to 20° (349 mrad) or at most a hemisphere or 2π steradians, which is within the design range of the overall system divergence.

[0068] Note that divergence (including laser emission, intrinsic, and total) can have different values ​​in different directions. This is due to the design of the laser, e.g., strip lasers typically have a larger divergence in the horizontal direction compared to the vertical divergence. This can be designed in intentionally, e.g., for use in a broadcast configuration where one transmitter broadcasts to many receivers near the ground, it may be beneficial to have a transmitter with a larger divergence in the horizontal direction than in the vertical direction.

[0069] The intrinsic divergence and the overall divergence can be controlled independently with the requirement that the overall divergence be greater than the intrinsic divergence. The intrinsic divergence is set by the ratio of the spot size on the diffuser to the distance from the diffuser to the lens. The overall divergence can be changed by moving the lens from the focal point (where the overall divergence is equal to the intrinsic divergence) closer to the diffuser, which increases the overall divergence. This affects the intrinsic divergence, but it is small compared to the change in overall divergence when moving the lens.

[0070] An exemplary implementation can also be used in a reflective configuration where the laser is aimed at the front of a diffuser, where the laser light reflects and scatters, increasing the divergence angle. Figure 4 shows an exemplary implementation of this configuration. The beam from the laser array 400 hits the diffuser 404 and is reflected 406 to hit the lens 402. Again, the final beam divergence can range from 0.1 degrees to 20 degrees, up to 2π steradians.

[0071] An additional benefit of the exemplary implementations of the present disclosure is that shorter focal length lenses can be used, especially for the transmitter. This can reduce the overall size of the system. For example, to spread light diverging at + / -12° from a laser across a 5cm lens, a focal length of about 12cm is required to spread it almost across the entire lens. By increasing that angle to + / -25° with a diffuser, the same spot size on a 5cm lens can be achieved with a focal length of about 6cm, thus reducing the distance between the laser and the lens and reducing the size of the system.

[0072] The diffuser can be a passive or active element. One exemplary implementation uses a passive engineered diffuser from Brightview Technologies. Other passive diffusers can be used, including ground glass and the like. For the purposes of this description, active elements can also be used for the diffuser. These include elements that change certain relevant optical properties through a change in voltage, current, mechanical strain or stress, or some other property. Active elements can be used to adjust the divergence of the beam based on various scenarios or feedback loops. For example, in a cloudy scenario, the inherent divergence of the beam can be reduced to increase the amount of light detected by the receiver.

[0073] 5A shows one implementation, where a laser array 500 emits light that makes an angle σ 504 with an active diffuser 502. The diffuser 502 can scatter the light at any angle ranging from none 506, which makes an angle σ 1 508 with the lens, to a maximum beam 510 that makes an angle σ 2 512. Note that σ 1 508 is equal to σ 504.

[0074] In another scenario, a very wide divergence may be used for link acquisition, and the divergence may be reduced when the transceivers are pointed at each other. The data rate may vary with divergence, for example a very low data rate with a very wide divergence may be used for link acquisition, and then when the transceivers are aligned the divergence may be reduced and the data rate increased. A receiver may exploit a similar effect to allow one detector to have a wide field of view with a very low data rate, then reduce the field of view and increase the data rate.

[0075] In some implementations, the diffuser is physically moved relative to the light source and lens to change the overall divergence of the beam. Figure 5B shows one implementation, where a laser array 516 emits light that hits a diffuser 518 in one of two positions (position 1 520 or position 2 522). The diffracted light rays from the diffuser in position 1 520 are shown by dashed and dotted lines 524. If the diffuser is further away from the light source in position 2 522, the light rays are given by solid lines 526. Each of these positions has an associated α as well. For position 1 520, α is given by α1 530 in the figure, and for position 2 522, α is given by α2 532. Although this figure shows only two positions, there are an infinite number of positions over a given range that the diffuser could take, each diffusing into different ranges of the lens and resulting in different associated α.

[0076] In some implementations, there may be both active and passive diffusers. The active diffuser, if closer to the laser (array) light source, can control the intrinsic divergence by controlling the spot size on a second static diffuser. The static diffuser and lens then control the overall divergence. This is shown in FIG. 5C. A laser array 534 emits light that hits an active diffuser 538. The active diffuser controls the intrinsic divergence of the light by determining how much the beam spreads to a passive diffuser 540. The passive diffuser 540 and lens 536 then control the overall divergence and therefore the power density. As mentioned before, both of these quantities are important for eye safety. Alternatively, the passive diffuser can be closer to the light source and the active diffuser can be placed behind the passive diffuser but still in front of the lens.

[0077] It should be noted that wherever a lens is described, the system may use one or more lenses or mirrors to achieve the desired effect. Lenses may be spherical, parabolic, aspheric, achromatic, or other types.

[0078] Similarly, at the receiving end, there is an acceptance angle at the receiver, which is roughly set by the size of the detector divided by the focal length of the receiving lens. The acceptance angle at the receiver can be anywhere from microradians to 2π steradians. In certain implementations, the acceptance angle may be greater than 1.7 mrad. In some implementations, the acceptance angle is within a few milliradians of the divergence angle of the light source. In other cases, the acceptance angle at the receiver is greater than the divergence angle of the laser, which can help align the two ends of the link with each other. In some cases, the acceptance angle at the receiver may be smaller than the divergence angle at the transmitter, which can increase the overall link distance, or ensure that if the receiver is aligned with the transmitter at the other end of the link, the transmitter at this end is also aligned with the receiver at the other end of the link.

[0079] As previously mentioned, the laser source can be any of a number of laser sources, including but not limited to a VCSEL, a VCSEL array, a strip laser, a fiber laser, or a fiber coupled laser with an additional amplification stage. Figure 6 shows an example where the laser source includes a fiber coupled laser 600 that is amplified by an EDFA 602 and then connected by another fiber 604 to a diverging beam optical transmitter.

[0080] 7 illustrates a diverging beam optical communication system 700 according to a particular exemplary implementation. The system includes a laser light source 702 configured to emit a light beam and one or more lenses 704 configured to collimate the light beam to an overall divergence of the light beam. The system includes a diffuser 706 configured to increase the inherent divergence of the light beam and spread the light beam over a particular portion of the one or more lenses so that it is eye-safe after the one or more lenses.

[0081] As also shown, system 700 includes a receive lens 708 configured to focus the light beam onto a detector 710. In some examples, the detector has an etendue sufficient to receive light from the receive lens with an acceptance angle greater than 1.7 mrad. In other examples, the detector has an etendue sufficient to receive light from the receive lens with an acceptance angle greater than 5 mrad. And in yet other examples, the detector has an etendue sufficient to receive the light beam from the receive lens with an acceptance angle greater than 17 mrad.

[0082] Those skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the above description and the associated drawings will come up with many modifications and other implementations of the disclosure described herein. It is therefore understood that the disclosure is not limited to the particular implementations disclosed, and that modifications and other implementations are intended to be included within the scope of the appended claims. Furthermore, while the above description and the associated drawings describe example implementations in the context of certain example combinations of elements and / or functions, it is understood that different combinations of elements and / or functions may be provided by alternative implementations without departing from the scope of the appended claims. In this regard, for example, it is contemplated that combinations of elements and / or functions different from those explicitly described above may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. 1. A diverging beam optical transmitter comprising: a laser light source configured to emit a light beam; one or more lenses configured to collimate the light beam to a general divergence of the light beam; a diffuser disposed between the laser light source and the one or more lenses, the diffuser configured to increase the inherent divergence of the light beam and spread the light beam to a particular portion of the one or more lenses after the one or more lenses such that the light beam is eye-safe; 1. A divergent beam optical transmitter comprising: A diverging beam optical transmitter, wherein the total divergence of the light beam and the intrinsic divergence of the light beam are independently controllable, and wherein the total divergence of the light beam is greater than the intrinsic divergence of the light beam.

2. 10. The diverging beam optical transmitter of claim 1, wherein the intrinsic divergence of said optical beam has different values ​​in different directions.

3. 10. The diverging beam optical transmitter of claim 1, wherein the laser source comprises a vertical cavity surface emitting laser array.

4. 2. The diverging beam optical transmitter of claim 1, wherein the laser source comprises a fiber-coupled laser amplified by an erbium-doped fiber amplifier and then coupled to the diverging beam optical transmitter by another fiber.

5. 10. The diverging beam optical transmitter of claim 1, wherein the diffuser is a transmissive diffuser.

6. The diverging beam optical transmitter of claim 1 , wherein the diffuser is configured to translate toward or away from the laser source to change the intrinsic divergence.

7. 7. The divergent beam optical transmitter of claim 6, wherein the diffuser is configured to translate toward the laser source to increase the intrinsic divergence during link acquisition and then translate away from the laser source to decrease the intrinsic divergence and increase data transmission rate.

8. 6. The diverging beam optical transmitter of claim 5, wherein said transmissive diffuser is an engineered diffuser.

9. 10. The diverging beam optical transmitter of claim 1, wherein the diffuser is an active element configured to change its diffusivity in response to an input.

10. 10. The diverging beam optical transmitter of claim 9, wherein the active element is a mechanically movable element.

11. 11. The divergent beam optical transmitter of claim 10, wherein the mechanically movable element substantially prevents the transmission of light in a rest position.

12. 10. The diverging beam optical transmitter of claim 9, further comprising an additional passive diffuser between the active element and the one or more lenses.

13. 10. The diverging beam light transmitter of claim 1, wherein said diverging beam light transmitter is Class 1 eye safe.

14. 10. The diverging beam light transmitter of claim 1, wherein said diverging beam light transmitter is Class 1M eye safe.

15. 1. A diverging beam optical communication system, comprising: a laser light source configured to emit a light beam; one or more lenses configured to collimate the light beam to a general divergence of the light beam; a diffuser configured to increase the inherent divergence of the light beam and spread the light beam over a particular portion of the one or more lenses such that the light beam is eye-safe after the one or more lenses; A receiving lens and a detector, the receive lens configured to focus the light beam onto the detector, the detector having an etendue sufficient to receive light from the receive lens with an acceptance angle greater than 1.7 mrad; 1. A divergent beam optical communication system comprising: A diverging beam optical communication system, wherein the total divergence of the light beam and the intrinsic divergence of the light beam are independently controllable, and wherein the total divergence of the light beam is greater than the intrinsic divergence of the light beam.

16. 1. A diverging beam optical communication system, comprising: a laser light source configured to emit a light beam; one or more lenses configured to collimate the light beam to a general divergence of the light beam; a diffuser configured to increase the inherent divergence of the light beam and spread the light beam over a particular portion of the one or more lenses such that the light beam is eye-safe after the one or more lenses; A receiving lens and a detector, the receive lens configured to focus the light beam onto the detector, the detector having an etendue sufficient to receive light from the receive lens with an acceptance angle greater than 5 mrad; 1. A divergent beam optical communication system comprising: A diverging beam optical communication system, wherein the total divergence of the light beam and the intrinsic divergence of the light beam are independently controllable, and wherein the total divergence of the light beam is greater than the intrinsic divergence of the light beam.

17. 1. A diverging beam optical communication system, comprising: a laser light source configured to emit a light beam; one or more lenses configured to collimate the light beam to a general divergence of the light beam; a diffuser configured to increase the inherent divergence of the light beam and spread the light beam over a particular portion of the one or more lenses such that the light beam is eye-safe after the one or more lenses; A receiving lens and a detector, the receive lens configured to focus the light beam onto the detector, the detector having an etendue sufficient to receive the light beam from the receive lens with an acceptance angle greater than 17 mrad; 1. A divergent beam optical communication system comprising: A diverging beam optical communication system, wherein the total divergence of the light beam and the intrinsic divergence of the light beam are independently controllable, and wherein the total divergence of the light beam is greater than the intrinsic divergence of the light beam.

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