Fresnel lens

The following figures illustrate the advantage of using SWIR cameras in earth-to-earth and earth-to-space configurations. Visibility is increased compared to visible range imaging, demonstrating how SWIR signal propagates efficiently.

FSO communications are limited by a series of factors. Fortunately, some can be overcome by using Short Wave InfraRed (SWIR) (900 - 1700 nm) rather than visible (400 - 700 nm) or Near InfraRed (700 - 900 nm) wavelengths.

Jul 8, 2024 — object distance = -image distance/magnification . Knowing the object distance, calculate the focal length with the following formula: f = ( ...

Example of the improvement provided by an AO correction to the detection of a laser spot. λλ is the wavelength, D is the optic's diameter, R0 is the diameter of the atmosphere turbulence nodule.

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For applications requiring lower framerates and longer exposure times, the C-RED 2 camera is the cooled equivalent of C-RED 3. The cooling allows to reach a lower dark current (< 600 e-/pix/s).

A microlens array can be characterized by parameters such as focal length, quality of transmitted wavefront, and size. Many microlens arrays are made of UV fused silica, which has high transmission from the UV into the IR range. The fill factor will depend on the specific geometry of the microlenses and the arrangement chosen, but these arrays  are typically designed to have a high fill factor to avoid zero-order hotspots.  Their optical properties— large field of view angles, low aberration and distortion, infinite depth of field, and high temporal resolution— make them highly desirable for many different applications.

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For example, very high framerate correction is required to perform FSO with Low Earth Orbite (LEO) satellites, where the apparent wind is high due to the satellite speed.

Powerphotonic

In conclusion, Free Space Optics benefits from using SWIR wavelengths (typically 1550 or 1330 nm), rather than shorter infrared ones (typically 785-850 nm).

Other applications of these arrays include use as solar concentrators, focusing sunlight to solar cells; in the optical switches and modulators of fiber optical communication systems; in AR and VR imaging systems, and in optical microscopy and spectroscopy.

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Designed by astronomers for astronomers and benefiting from the expertise gained when designing the OCAM² and CRED One cameras, First Light Imaging's C-RED 3 is the best choice for your SWIR FSO applications.

Microlens

Fabricating a microlens array is a little different from traditional lens manufacturing simply because the lenses we are working with are so very small. Typically, all of the microlenses in a microlens array are produced in just one step, and the manufacturing methods used are often adapted from semi conductor processing technology.

Note: When installed on a lens with a diameter greater than F67-F74mm, the transmission may slip or get stuck. Please make sure the size is correct before ...

Simplified schematic of the Adaptive Optics closed-loop approach. The wavefront from a distant object is distorted by the atmosphere. The deformable mirror compensates the distortions. The control system computes the commands for the deformable mirrors. The wavefront sensor measures the deviation from an undistorted wave

GRIN lens

The availability of low noise fast infrared cameras to build wavefront sensors changes somewhat the paradigm of Free Space Optical communications. With improved penetration of SWIR lasers – compared to visible range lasers - in bad weather conditions, and reduced effects of atmospheric turbulence, there is a real benefit of performing FSO in the SWIR range. Adaptive optics can further optimize the signal detection.

C-RED 3 has been designed specifically for this purpose [4], and completely addresses the challenges of high speed wavefront sensing.

These factors attenuate the transmitted signal, leading to a higher number of errors when detecting the signal. Laser power increase is not the solution as the laser power density is limited to class 1M in order to keep an eye-safe environment.

C-RED 3 is a plug-and-play SWIR camera. Our C-RED range of cameras offers hardware optimization to adjust to your specific use case.

What if you could bring the power of nature’s compound eyes to your optical assembly— in a tiny package 10 mm x 10 mm? It turns out, you can! Whether you need to homogenize light from line-narrowed excimer lasers or high power LEDS, microlens arrays can give you the high efficiency and non-gaussian uniformity you need. These optical assemblies are composed of many tiny micro lenses, arranged in a one or two dimensional array.

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Several mitigation strategies have been developed, but the best way to suppress scintillation is to use Adaptive Optics (AO). The idea of correcting the atmospheric turbulence in real time for astronomy was firstly introduced by Babbock as early as 1953 [1]. With the progress of wavefront sensors, deformable mirrors and real time computers, AO systems have become very popular and relatively straightforward to make. The figure illustrates the working principle of the close loop approach.

Microlens arrays may be produced as separate optical components, and even in mounted form, surrounded by metal or polymer that enables them to fit neatly into an optical mount. They can also be designed to incorporate directly into a larger optical system. Each microlens array may contain thousands or possibly even millions of tiny lenses, arranged to make a square grid, rectangle, or circle.

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One method of fabricating microlens involves photolithography, using a lens pattern defined by a photolithographic mask. Etching techniques are sometimes used, as are hot embossing and printing methods which rely on the surface tension of the liquified substrate.  Another manufacturing method involves using laser materials processing, and here sometimes the microlenses are formed individually using multiple processing beams. Laser materials processing offers more versatility than many other methods, but is also more expensive.

Free Space Optics can be used for high throughput and long-distance communications. Demanding applications, such as space telecommunications, can be addressed.

Visible versus SWIR imaging of a landscape in foggy conditions. Note how the view is much clearer and we can see some 10 km further in SWIR. Raw images acquired with a Nikon D5200 camera (left) and a C-RED 3 camera (right).

Are you intrigued by the world of microlens arrays, and would you like to have more information about just how they could be incorporated into your optical system? At Avantier, we specialize in creating custom optics that meet the exact needs of your application— and microlens arrays are one of our areas of expertise. Contact us today if you’d like more information or to set up an initial consult.

FSO can be used for ground to ground communication: outdoor wireless 2G/3G and 4G networks, to cover the edge of physical networks (“the last mile access”), CCTV surveillance networks, etc. More importantly, it can be used for ground to space (satellite) communications. FSO enables simultaneously establishing a large number of independent links with high throughput; two major advantages compared to the radio bandwidth which is limited by its low directionality and radio frequency throughput (< 40 GHz). For example, Earth-observation satellites only overpass ground stations for a couple of minutes per day, it is critical that the large amount of data they collected can be transmitted in a short amount of time. Even more so for military satellites which very often may only communicate with ground stations within a limited geographical zone. Finally, FSO is the best option for extra-terrestrial communication which may come in use in the next decades… In short, FSO is a fast-growing segment for telecommunications, both in civil and military fields.

ThorlabsMicrolens Array

The use of the camera is, of course, not restricted to Free Space Optics. C-RED 3 is very flexible and can be used for multiple applications, ranging from surveillance to agriculture monitoring. Moreover, the low size, weight, and power consumption (SWaP) opens the possibility to use this technology on airborne material (planes, UAVs).

1-2000. Focal length (FoV ~ 0°). Focal length is out of rangeFocal length is fixed. Illustration. Requirement. px/m. Fulfilled. Detect, 25, close. Observe, 63 ...

Microlens arrays can also be integrated into light field cameras, mounted between the main lens and light sensor. This enables the production of a  light, compact camera that does not require focus before capturing an image; the focus is chosen during  post-processing.

Microlens arrays are often used to homogenize  and shape beams, or to collimate the output of fiber arrays. Square array lenses, for instance, might be used in pairs for applications in welding, drilling, fiber coupling and laser ablation. Fly’s eye condenser arrays, which are formed of dual-surface micro cylindrical lenses, are ideal for flat-top and line generation. These arrays are often used when one has a large illuminated field but a very short working distance; for instance, in fluorescence microscopy, semiconductor instrumentation and in applications involving medical lasers.

Jul 10, 2024 — ... Mount lenses with the FT-1 adapter to take advantage of the 2.7X crop factor. Nikon 1 J5 + 1 Nikon CX 70-300mm f/4.5-5.6 @ 300mm, efov 810mm ...

C-RED 3 is a 640 x 512 SWIR camera running at 600 FPS full frame. It holds the legacy of all the developments of astronomical infrared fast wavefront sensors on top of specific features for industrial applications: smart, low cost and low SWaP. It is particularly well suited to be the detector used in an Adaptive Optics loop for wavefront sensing in a complete Free Space Optical communication system.

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When used with CCD arrays and CMOS sensors, microlens arrays can collect light that would otherwise have fallen on non-sensitive sensor areas, thus improving efficiency. They are used to focus light for digital projectors and photocopiers.

In the C-RED 3 camera, all the cooling system has been removed and the electronics squeezed to give a very compact high-speed SWIR camera. Below is a few insight into its advantages

Cylindrical lensarray

C-RED 3 is a high-performance camera designed for short wave infrared applications. It enables very high-speed high-quality sensing (up to 600 fps in full frame) and gives its best performance at short exposure times. The camera was developed for Free Space Optical communications applications, particularly for adaptive optics.

The major constraint on the camera used as an AO wavefront sensor is that it must provide a real-time snapshot of the wavefront to enable real-time compensation. Hence the camera should have a high framerate, low latency, and high sensitivity

A Shack-Hartmann wavefront sensor is an optical device used to measure the wavefront shape of incident light, often used in adaptive optics. It may be used to determine the wavefront shape of star light, in an optical telescope, or to determine the wavefront in an attenuated laser beam. An important component of the Shack-Hartmann wavefront sensor is a microlens array, which probes the wavefront orientation from many separate points over the cross-section of the beam of light. Essentially what happens is that each of the tiny microlenses focuses the radiation it receives to a spot on the image sensor. Since the position of that spot tells us the orientation of that tiny piece of wavefront, a computer can use the aggregate data from each of the lensless on the microlens array to produce a good estimate of the wavefront distortions.

An FSO system in its simplest form is illustrated below. The data to be transmitted is converted to a binary format (1 and 0), then into light pulses (ON/OFF). A transmitter (laser source and focusing lens) sends the light pulses, aiming the direction of a receiver. The receiver collects the light pulses, which are then processed and converted. Note that the system can be used in the reverse direction. The system is interfaced at both ends with a physical network (cable, fiber). In more complex implementations, the laser beam can be modulated.

Compared the visible range, SWIR allows a deeper penetration through atmospheric perturbations. Using small diodes enables fast FSO communications but requires fast and sensitive cameras to perform wavefront sensing. C-RED 3 has been designed for this purpose.

Light propagating through the atmosphere is known to be disturbed by atmospheric turbulence. The most difficult-todeal-with problem is beam scintillation: as the atmosphere in the beam path fluctuates, the optical power, tilt, etc. of the light beam vary, causing random phase aberrations and often-large variation in detected intensity.

Information can travel from point A to point B through a solid cable, a common example would be corded phones. However, physical connections (cable, wire, fiber) may sometimes be impractical or too expensive. In these cases, being able to transmit data through “free space” (air, outer space, vacuum, etc.) is crucial. Using light to transmit data through Free-Space Optical (FSO) communications overcomes the major drawback of cable-based communications.

VCSELarray

The key parameter of an adaptive optics system is the wavefront sensor and its ability to give an instantaneous picture of the incoming wavefront. A wavefront sensor typically consists of a ShackHartmann combined to a photon sensor. First Light Imaging worked a lot on the improvements of visible cameras for wavefront sensing with the OCAM², which is to date the fastest and lowest noise (visible photon counting) camera, tailored for this application [2].

The use of SWIR band lasers is extremely pertinent because of their ability to go through obstacles such as fog or some types of plastics. The recent rise of eye-safe lasers in the SWIR band has allowed a major improvement. A camera based on an InGaAs detector array must be used at the receiver end, as visible cameras are not sensitive to SWIR wavelengths.

As we have seen previously, there was a real interest to go to SWIR wavelengths. To optimize communication speed, small diodes are used. To reduce power losses and enable the injection of the transmitted optical beam into a single mode fiber [3], AO is mandatory (see the figure on the right).