CN116685896A - Illumination system and method for reducing speckle - Google Patents

Abstract

The present application provides a laser source comprising at least one diode; and a predefined length of optical fiber disposed between the laser source and the location of the target such that the optical fiber transmits a pulse of light from the laser source as source light to the location of the target, wherein the location is illuminated by the source light so as to reduce speckle in the captured image of the target. The present application also provides a method of providing source light for generating an image, the method comprising: generating illumination using one or more laser diodes; the illumination is passed through an optical fiber having a plurality of bends therein such that source light is emitted from the optical fiber to illuminate a target with the source light, the source light reducing speckle in an image of the target.

Description

Illumination system and method for reducing speckle

RELATED APPLICATIONS

The present application claims priority and benefit from U.S. patent application Ser. No. 63/125,259, "Reduced Speckle Illumination Systems and Methods" (filed on day 12, month 14 of 2020), and U.S. patent application Ser. No. 63/287,335, "Reduced Speckle Illumination Systems and Methods" (filed on day 12, month 8 of 2021). The foregoing application is incorporated herein in its entirety for any and all purposes.

Technical Field

The present disclosure relates to the field of laboratory lighting systems.

Background

In the past, the speckle that occurs in conventional imaging has been addressed by averaging many different speckle patterns during camera exposure. However, such schemes are essentially very efficient and also occur in the time domain because they work by generating multiple speckle patterns and averaging the results over time. Some examples of these methods include vibrating an optical fiber, passing light through a rotating glass disk, and passing light through a rotating set of optical fibers.

The diameter of the rotating disk may be, for example, 2 inches, the rotational speed is 50,000rpm, and the displacement speed at the disk edge is 10 microns/100 nanoseconds. However, this arrangement requires a significant amount of hardware, which increases the complexity and footprint of the low speckle device. Vibrations for achieving multimode illumination may be in the range of tens of Hz to tens of kHz, and a 10 nanosecond pulse may require a vibration frequency exceeding 10MHz, since the displacement is proportional to 1/frequency. However, vibration-based approaches may introduce undesirable hardware complexity.

While the above approach may be effective in reducing speckle in some cases, the above approach also occurs within millisecond timescales, which makes the scheme less suitable for the short exposure times required for flow cytometry. Accordingly, there is a long felt need in the art for systems and methods for reducing speckle suitable for flow cytometry applications, particularly in achieving speckle reduction within a time scale suitable for flow cytometry.

Disclosure of Invention

To meet the long-felt need, the present disclosure first provides a light source for capturing an image, the light source comprising: a laser source comprising at least one diode; and an optical fiber arranged to transmit light pulses having a plurality of modes between the laser source and the target location so as to reduce speckle in a captured image of the target at the target location, at least some of the optical fiber being present in one or more layers wrapped around a mandrel, the mandrel optionally comprising a circumferential wall and a layer between which the optical fiber is wrapped, the layer comprising a taut winding of at least one optical fiber.

The invention also provides a method comprising operating a light source according to the present disclosure (e.g. according to any one of aspects 1 to 21) to illuminate a target.

The invention further provides a method comprising placing optical fibers in optical communication with an illumination source such that the optical fibers are placed to transmit light from the illumination source to a target disposed at a target location, at least some of the optical fibers being present in one or more layers wrapped around a mandrel, the mandrel optionally comprising circumferential walls and layers, the optical fibers being wrapped between the circumferential walls, the layers comprising a taut winding of at least one optical fiber.

The present invention also provides a method of providing source light for generating an image, the method comprising: generating illumination using one or more laser diodes; and passing illumination through an optical fiber, the optical fiber being present in one or more layers wrapped around a mandrel, the mandrel optionally comprising a circumferential wall and a layer, the optical fiber being wrapped between the circumferential walls, the layer comprising a taut winding of at least one optical fiber, the passing being performed such that multimode source light is emitted from the optical fiber to illuminate the target with illumination light, the illumination reducing speckle in an image of the target.

The invention further discloses a cytometer, the cytometer comprising: a flow chamber configured to contain one or more particles therein, the flow chamber defining a target area; an illumination train comprising at least (1) a laser source comprising at least one diode and (2) an optical fiber in optical communication with the laser source, at least some of the optical fiber being present in one or more layers wound around a mandrel, the mandrel optionally comprising circumferential walls and layers, the optical fiber being wound between the circumferential walls, the layers comprising a tension winding of the at least one optical fiber.

The present invention further discloses an imaging device comprising: a sample region configured to contain a sample therein; an illumination train comprising at least (1) a laser source comprising at least one diode and (2) an optical fiber in optical communication with the laser source, at least some of the optical fiber being present in one or more layers wound around a mandrel, the mandrel optionally comprising circumferential walls and layers, the optical fiber being wound between the circumferential walls, the layers comprising a tension winding of at least one optical fiber; and an image capturing device configured to capture an image of a sample disposed within the sample region when illuminated by illumination of at least one diode, the at least one diode in communication via an optical fiber, the imaging device further optionally comprising a movement train configured to effect relative movement between the sample within the sample region and the illumination of the at least one diode, the at least one diode in communication via the optical fiber.

The present invention further provides a light source comprising: a laser source comprising at least one diode; and an optical fiber arranged to transmit light between the laser source and the imaging plane so as to reduce light coherence and thereby reduce speckle at the imaging plane, at least some of the optical fiber being bent around the support so as to create mechanical tension within the optical fiber.

The invention also provides a method comprising operating a light source according to the present disclosure (e.g. a light source according to any one of aspects 47 to 74).

Drawings

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example and not by way of limitation, various aspects discussed in the present document. In the drawings:

FIG. 1 provides an exemplary illustration of single-mode illumination and multi-mode illumination transmitted over various optical fibers;

FIG. 2 provides an exemplary image of a 10 micron bead illuminated by a 10 nanosecond illumination pulse transmitted through a 2 meter fiber;

FIG. 3 provides an exemplary depiction of speckle contrast as a function of length of an optical fiber conveying illumination;

FIG. 4 provides a view of an exemplary laser assembly according to the present disclosure, showing a plurality of laser diodes in optical communication with an optical fiber;

FIG. 5 provides a view of (left) a 100 nanosecond illumination pulse transmitted through a 2 meter fiber and (right) a comparable bead by a 100 nanosecond illumination pulse transmitted through a 50 meter fiber; and is also provided with

Fig. 6 provides an illustration of an exemplary system according to the present disclosure.

Fig. 7 provides a view of a tightly wound fiber optic spool (left panel) and a view of a loosely wound fiber optic spool (right panel).

FIG. 8 provides a view of a fiber spool in which an optical fiber is wound on another fiber loop, thereby creating a bulge in the optical fiber wound on the inner fiber loop.

Fig. 9 provides a view of the neatly wrapped optical fiber layers (left panel) and the randomly wrapped optical fiber layers (right panel), showing the resulting fiber crossover.

Fig. 10 provides a view of an exemplary fiber winding arrangement.

FIG. 11 provides a cross-sectional view of the fiber optic layer in a spool that winds the optical fiber.

Fig. 12 provides an image of a loosely wound fiber optic spool (right panel) and an image collected by the loosely wound fiber optic spool (left panel).

Fig. 13 provides an image of a tightly wound fiber spool (right panel) and an image collected by the tightly wound fiber spool (left panel).

Fig. 14 provides images produced by different optical fibers wound by the techniques described in this disclosure, showing the consistency and repeatability of the techniques.

FIG. 15 provides a view of a technique for manufacturing a coiled optical fiber according to the present disclosure, showing the coiling of the optical fiber by a custom spool that is fed with the optical fiber by a supplier spool.

Detailed Description

The present disclosure may be understood more readily by reference to the following detailed description of the desired embodiments and the examples included therein.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing, the preferred methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

As used in the specification and claims, the term "comprising" may include embodiments that "consist of … …" and "consist essentially of … …. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "can," "contains," "containing," and variants thereof are intended to be open-ended transitional phrases, terms, or words that require the presence of a specified element/step and allow the presence of other elements/steps. However, such descriptions should be understood as also describing the composition or method as "consisting of" and "consisting essentially of" the enumerated components/steps, which allows for the presence of only the components/steps, along with any impurities that may result therefrom, and the exclusion of other components/steps.

As used herein, the terms "about" and "equal to or about" mean that the amount or value in question may be a value designated as being approximately or approximately the same as some other value. As used herein, it is generally understood that it varies by ±10% of the nominal value specified unless otherwise indicated or inferred. The terms are intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is to be understood that the amounts, sizes, formulations, parameters, and other amounts and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, reflecting tolerances, conversion factors, rounding off, measurement error and the like as desired, among other factors known to those of skill in the art. Generally, an amount, size, formulation, parameter, or other quantity or property is "about" or "approximately," whether or not explicitly stated. It is to be understood that, unless explicitly stated otherwise, where "about" is used before a quantitative value, the parameter also includes the particular quantitative value itself.

Unless indicated to the contrary, numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the specified values by less than the experimental error of conventional measurement technique described in the present application to determine the type of the value.

All ranges disclosed herein are inclusive of the recited endpoints and independent of the endpoints, 2 grams, and 10 grams, and all intermediate values). The ranges and any value end points of the ranges and any values disclosed herein are not limited to the precise ranges or values. They are not sufficiently accurate and may include values approximating these ranges and/or values.

As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Thus, in some cases, values modified by one or more terms such as "about" and "substantially" may not be limited to the precise value specified. In at least some examples, the approximating language may correspond to the precision of an instrument for measuring the value. The modifier "about" should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression "about 2 to about 4" also discloses a range of "2 to 4". The term "about" may refer to plus or minus 10% of the indicated number. For example, "about 10%" may indicate a range of 9% to 11%, and "about 1" may mean from 0.9-1.1. Other meanings of "about" may be known from the context, such as rounding, so that, for example, "about 1" may also mean from 0.5 to 1.4. In addition, the term "comprising" is to be understood as having an open-ended meaning of "comprising", but the term also includes a closed-ended meaning of the term "consisting of … …". For example, the composition comprising component a and component B may be a composition comprising A, B and other components, but may also be a composition made from only a and B. Any document cited herein is incorporated by reference in its entirety for any and all purposes.

With the continued development of higher speed and higher quantum efficiency CMOS sensors, cameras are becoming increasingly suitable for flow cytometry applications. In addition to the advances made by high power laser diodes and thereby reducing the cost per watt of optical power, combining a high speed camera with a laser source is a very powerful method for flow cytometry imaging. However, the effect of such methods may be somewhat compromised due to the presence of unwanted laser speckle in the image collected by the camera.

In order to reduce such unwanted speckle, the present disclosure provides, among other things, using optical fibers to deliver multimode illumination to a target, which in turn reduces speckle in imaging of the target.

Multimode illumination may be achieved in a variety of ways, for example using multimode optical fibers. Multimode optical fibers may contain thousands or even tens of thousands of propagation modes. Each mode has a different spatial path during propagation as shown in fig. 1 of the drawings herein. This may lead to a temporal spread of light at the output of the fiber. As a rough description for reducing speckle, different modes can be envisaged as many different sources, which in turn form different speckle patterns.

In addition to geometric mode expansion, additional perturbations to the fiber and/or excitation can be created, which can increase coupling with higher order modes. For example, increasing the cone angle of excitation light into the fiber may increase mode coupling. This can couple light into higher order modes propagating at larger angles within the fiber. For this purpose, an optical fiber having a relatively high numerical aperture and a relatively high number of higher order modes may be used. As a non-limiting example, an optical fiber having a numerical aperture value of about 0.2 to about 0.55, for example, may be used. Bending, coiling or otherwise bending the fiber to further mix the modes and achieve higher orders may enable long distances to bend light from lower modes to higher modes.

The source bandwidth may even further mix modes. Different wavelengths have different mode patterns, thereby forming different mode structures for a range of wavelengths. For this purpose, a plurality of modes of sources (e.g., laser diodes) may be used, for example, a first diode emitting a first wavelength and a second diode emitting a second wavelength. Multimode diodes, such as diodes that emit laser light at multiple wavelengths, may also be used.

In existing approaches, relatively short fibers are used, on which the length is short, passive mode mixing is small and efficiency is low in reducing speckle in the image. As described elsewhere herein, some techniques use vibration or movement to deform the fiber optic cable, thereby creating and subsequently obtaining more geometric modes for averaging multiple speckle patterns.

Since most conventional microscopy techniques use exposure times of tens to hundreds of milliseconds, most applications are able to withstand fiber vibration on the millisecond timescale. However, for the high-speed imaging required in flow cytometry, the mode mixing must be achieved within a time window of about 100 nanoseconds, which is several orders of magnitude shorter than the appropriate time window of conventional microscopy. Thus, this relatively short time window precludes the use of most current active speckle reduction techniques in flow cytometry.

In the present disclosure, the characteristics of multimode fibers are used to implement ultra-high speed speckle reduction techniques. This can be achieved by using the slow mode mixing/pulse spreading characteristics of the multimode fiber in combination with the listed additive perturbations to increase the mode mixing. In this embodiment, a different length of fiber and laser wavelength bandwidth may be used than is encountered in standard imaging applications.

High speed speckle reduction can be achieved by adding passive mode mixing using each of the techniques listed above. Independently, mixing is insufficient, but by moving the parameters out of the current specification and combining the techniques, sufficient speckle reduction can be achieved in a very short time scale.

In one embodiment, a relatively long (e.g., 50 meters in length) multimode, high numerical aperture optical fiber is interposed between the light source and the imaging target. The optical fiber may be wound around a mandrel to have a continuous bend that may allow additional modes to be obtained. Furthermore, the source bandwidth can be increased by coupling light of slightly different wavelengths from a plurality of laser diodes into the optical fiber. Each of these effects is a cumulative effect.

Drawings

The drawings are merely illustrative and do not necessarily limit the scope of the disclosure or the appended claims.

FIG. 1 provides an exemplary illustration of single-mode illumination and multi-mode illumination transmitted through various optical fibers, which are single-mode/step-index fibers; multimode/gradient index fibers and multimode/step index fibers.

FIG. 2 provides an exemplary image of a 10 micron bead illuminated by a 10 nanosecond illumination pulse transmitted through a 2 meter fiber;

fig. 3 provides an illustrative depiction of speckle contrast as a function of length of an optical fiber carrying illumination. As shown, the NA of the fiber (0.2-corresponding to line 300; 0.3-corresponding to line 302; and 0.4-corresponding to line 304) can affect the speckle contrast as the fiber length evolves. For example, in the case of an optical fiber length of 50 meters, an optical fiber having an NA of 0.4 exhibits a relatively lower speckle contrast than an optical fiber having an NA of 0.2.

Fig. 4 provides a view of an exemplary laser assembly according to the present disclosure. As shown, the assembly may include a plurality of laser diodes in optical communication with the optical fibers.

FIG. 5 provides (left) a view of a 10 micron bead 504 moving at 4m/s within a background 506 and illuminated by a 100 nanosecond illumination pulse delivered through a 2 meter multimode fiber; and (right) a view of comparable beads 500 (moving within background 502) illuminated by a 100 nanosecond illumination pulse transmitted through a 50 meter multimode fiber wrapped around a mandrel; the NA of both fibers was 0.5. An optical fiber having a high NA of 0.5 and a length of 50 meters was irradiated with a plurality of laser diodes having a wavelength of about 405 nm. The target is strobed with a light pulse of about 100 nanoseconds synchronized between the plurality of diodes and the exposure time is about 6 microseconds. As shown, using the disclosed method produces a significant difference (right panel) compared to the comparative method (left panel).

Fig. 6 provides an illustration of an exemplary system according to the present disclosure. As shown, the system 600 may include a controller 602, which may be in communication with one or more laser diodes 604; the diode may be a single-mode diode or a multi-mode diode. The laser diode 604 may be in communication with an optical fiber 606, which may be a multimode optical fiber. The optical fiber 606 may also be wrapped around a mandrel (or mandrels), and may also be bent or curved in other ways. Illumination delivered from the optical fiber 606 may be delivered to a sample location 610, such as a flow cell, microscope stage, or other location where the sample is illuminated. The image capture system 608 then captures an image of the sample illuminated at the sample location 610, which image exhibits reduced speckle. The controller 602 may be in communication with the image capture system 608, although this is not a requirement as the image capture system may be in communication with an alternative controller.

Fig. 7 provides a view of a tightly wound fiber optic spool (left panel) and a view of a loosely wound fiber optic spool (right panel). As shown, the loosely wound optical fiber is not uniform in radius around its circumference. Without being bound by any particular theory or implementation, tightly wound optical fibers produce a constant bend radius such that only propagation modes of a particular order remain within the fiber core. In contrast, when the fiber is loosely wound around a spool or the fiber is loose, the bend radius of the fiber is not well controlled and the light can be coupled into different order modes rather than the desired mode.

FIG. 8 provides a view of a fiber spool in which the optical fibers are wound around another fiber loop in a "cross" fashion, thereby creating a bulge in the optical fibers wound around the inner fiber loop. Without being bound by any particular theory or implementation, having such intersections may result in non-uniform radii of the optical fibers; winding an optical fiber around another fiber loop may introduce different bending radii, which may result in different order modes being generated. Thus, when the optical fiber is neatly wound around a mandrel or reel, such windings reduce the number of crossings and avoid small bends with different radii, which in some cases may propagate higher order modes and/or reduce optical fiber transmission.

Fig. 9 provides a view of the neatly wrapped optical fiber layers (left panel) and the randomly wrapped optical fiber layers (right panel), showing the resulting fiber crossover. As shown in fig. 8, the presence of such intersections (several intersections in fig. 9) may result in non-uniform or non-uniform fiber radii.

Fig. 10 provides a view of an exemplary fiber winding arrangement. Without being bound by any particular theory or embodiment, the optical fiber may be wound around the mandrel in a reel-to-reel fashion; as shown in fig. 8, a circumferentially rotating mandrel for the fiber source and/or the coiled fiber and a source and/or axially moving coiling mandrel are used to achieve a fiber wrap that is free or substantially free of cross-overs. The fiber windings may be arranged in a side-by-side winding pattern as shown, for example, in fig. 11.

FIG. 11 provides a cross-sectional view of the fiber optic layer in a spool that winds the optical fiber. As shown, the number of windings for a given fiber layer may be the same as the layers below or above the given layer, although this is not a requirement.

In fig. 11, the numbers in the circles refer to the nth loop of the winding process. The two vertical lines refer to the walls on the reel. The winding process starts with the 1 st loop of the bottom layer, then to the 2 nd loop, the 3 rd loop, etc. Once the fiber reaches the other wall, it moves up to the next layer and continues to wrap around layer 2. This process will continue until the full length of fiber (e.g., 50 meters) is wound onto a spool. The fiber can be tightly wound throughout the winding process to ensure consistent bend radii.

Fig. 12 provides an image of a loosely wound fiber optic spool (right panel) and an image collected by the loosely wound fiber optic spool (left panel). As shown, it is difficult to discern specific contrast areas in an image. Without being bound by any particular theory, loosely coiled fibers result in higher order modes around the center of the beam, poor contrast, and pronounced speckle.

Fig. 13 provides an image of a tightly wound fiber spool (right panel) and an image collected by the tightly wound fiber spool (left panel). As shown (and by comparison with fig. 13), the image shows improved contrast relative to fig. 12, which was made using a loosely wound fiber spool.

Fig. 14 provides images produced by different optical fibers wound by the techniques described in this disclosure, showing the consistency and repeatability of the techniques. Without being bound by any particular theory or implementation, the tighter windings produce better "mode filtering" to remove higher order illumination modes transmitted through the optical fibers. Again and without being bound by any particular theory or implementation, the non-uniform bend radius may in some cases result in propagating higher order modes and increasing speckle.

FIG. 15 provides a view of a technique for manufacturing a coiled optical fiber according to the present disclosure, showing the coiling of the optical fiber by a custom spool that is fed with the optical fiber by a supplier spool.

Aspects of the application

The following aspects are merely illustrative and do not limit the scope of the application or the appended claims.

Aspect 1. A light source for capturing an image, the light source comprising: a laser source comprising at least one diode; and an optical fiber arranged to transmit light pulses having a plurality of modes between the laser source and the target location so as to reduce speckle in a captured image of the target at the target location, at least some of the optical fiber being present in one or more layers wrapped around a mandrel, the mandrel optionally comprising a circumferential wall and a layer between which the optical fiber is wrapped, the layer comprising a taut winding of at least one optical fiber.

By "tensioned" is meant that the optical fiber does not relax, e.g., there is substantially no space under the optical fiber. An example is shown in fig. 11, where the windings of the optical fiber (e.g., winding n+3 shown in fig. 11) are not relaxed.

The laser source may comprise one, two, three or more diodes, for example a plurality of diodes. The diode may be a single mode diode, but may also be a multimode diode. The one or more laser sources may provide illumination at one or more wavelengths, for example 405 nanometers, 450 nanometers, 488 nanometers, 532 nanometers, 561 nanometers, and 640 nanometers. The diode may also provide illumination at a particular wavelength range (e.g., 400 nm to 410 nm).

Aspect 2 the light source according to aspect 1, wherein the one layer of optical fibers comprises a tension winding of at least two optical fibers substantially parallel to each other.

As described elsewhere herein, the optical fibers may be disposed about a mandrel, but this is not a requirement as the optical fibers may be disposed within a tray or other feature that accommodates bends or undulations of the optical fibers. Without being bound by any particular theory or embodiment, the optical fiber may be disposed within or even on the housing of the instrument. In this way, the unit may be configured to accommodate relatively long optical fibers while maintaining a relatively small footprint.

The light source may comprise a mandrel around which the optical fibre is arranged so as to create a bend in the optical fibre. The spindle may be circular in cross-section, but it may also be oval or even polygonal in cross-section. The diameter of the mandrel along its height may be constant, but its diameter may also vary, for example, be configured as a cone or a truncated cone. The mandrel may taper in an upward direction, but may also be wider at its top and narrower at its bottom. Such mandrels may comprise, for example, a constant cross-sectional profile. The cross-section of the mandrel may be variable, for example, by being expandable. In such embodiments, adjusting the cross-section of the mandrel (e.g., by expanding the cross-sectional dimension of the mandrel, by changing the profile of the cross-section of the mandrel, by reducing the cross-sectional dimension of the mandrel) may enable adjustment of the illumination delivered to the target.

Aspect 3 the light source according to any one of aspects 1 to 2, wherein the windings of the optical fibers in the outer layer are substantially parallel to the windings of the optical fibers in the inner layer immediately below the outer layer.

A light source according to the present disclosure may also include a processing or control system. Such processing or control systems may be arranged to adjust the settings of the illumination supplied to the target (e.g. by changing the characteristics of the illumination supplied by the one or more laser diodes, by changing the characteristics of the optical fibre) in order to achieve a particular speckle contrast.

Speckle contrast is defined as the standard deviation of the spatial intensity divided by the average intensity measured in the region and is expressed as a dimensionless number. Without being bound by any particular theory, lower speckle-contrast maps are typically required. As just one example, if the first set of settings for the light source yields a desired speckle contrast for the first sample, but does not yield a desired speckle contrast for the second sample, the processing or control system may be configured to adjust the settings of the illumination such that the desired speckle contrast for the second sample is achieved. Although the illumination setting may be automatically adjusted, the illumination setting may also be manually adjusted.

Aspect 4 the light source according to any one of aspects 1 to 3, wherein the windings of the optical fibers in the outer layer do not cross the windings of the optical fibers in the inner layer immediately below the outer layer. Such an arrangement is shown in fig. 10.

Aspect 5 the light source according to any one of aspects 1 to 4, comprising an inner layer of an optical fiber comprising a plurality of tension windings of an optical fiber and an outer layer of an optical fiber comprising a plurality of tension windings of an optical fiber, wherein

(i) The tension windings of the plurality of optical fibers in the outer layer are parallel to each other,

(ii) The tension windings of the plurality of optical fibers in the inner layer are parallel to each other, and

(iii) The taut windings of the plurality of optical fibers in the outer layer are parallel to the windings of the plurality of optical fibers in the inner layer. Such an arrangement is shown in fig. 11.

Aspect 6 the light source according to any one of aspects 1 to 5, wherein a cross-sectional dimension of the mandrel is constant.

Aspect 7. The light source according to any one of aspects 1 to 5, wherein a cross-sectional dimension of the mandrel is variable.

Aspect 8 the light source of any one of aspects 1 to 7, wherein the mandrel has a cross-sectional dimension of about 1 cm to about 10 cm.

Aspect 9 the light source according to any one of aspects 1 to 8, wherein the light pulses from the laser sources are synchronized. For example, if the laser source comprises three diodes, the light pulses from the three diodes may be synchronized with each other. However, synchronization is not a requirement.

Aspect 10 the light source of any one of aspects 1 to 9, wherein the pulse of light from the laser source is about 100 nanoseconds to gate the target. The light pulse may be from about 5 milliseconds to about 1 nanosecond, for example, from about 1 millisecond to about 1 nanosecond, or from about 0.5 milliseconds to about 10 nanoseconds, or even from about 100 nanoseconds to about 10 nanoseconds.

Aspect 11 the light source according to any one of aspects 1 to 10, further comprising an image capturing device configured to capture a captured image of the target, the captured image optionally having an exposure time of about 6 microseconds. . The image capture system may include a camera (CCD, sCMOS, CMOS), PMT array, avalanche photodiode, photodiode array, or other module. The image capture system may include a processor configured to enable processing of images collected by the image capture system.

Aspect 12 the light source according to any one of aspects 1 to 11, wherein the optical fiber is a multimode optical fiber.

Aspect 13 the light source according to any one of aspects 1 to 12, wherein the optical fiber is a high numerical aperture optical fiber. For example, optical fibers having a numerical aperture greater than about 0.22 are considered high numerical aperture optical fibers.

The light source according to any one of aspects 1 to 13, wherein the numerical aperture of the optical fiber is about 0.5. The numerical aperture may be, for example, from about 0.1 to about 0.5, such as from about 0.1 to about 0.5, from about 0.15 to about 0.45, from about 0.2 to about 0.4, from about 0.25 to about 0.35, or even about 0.3.

The light source of any one of aspects 1 to 14, wherein the length of the optical fiber is between about 2 meters and about 75 meters. The optical fibers may be, for example, from about 2 meters to about 75 meters, from about 5 meters to about 70 meters, from about 10 meters to about 65 meters, from about 15 meters to about 60 meters, from about 20 meters to about 55 meters, from about 25 meters to about 50 meters, from about 30 meters to about 45 meters, or even from about 35 meters to about 40 meters.

Aspect 16 the light source of aspect 15, wherein the length of the optical fiber is about 50 meters.

Aspect 17 the light source of any one of aspects 1 to 16, wherein the laser source comprises a plurality of laser diodes, and wherein each of the plurality of laser diodes is positioned spatially separated from other ones of the plurality of laser diodes.

The light source according to any one of aspects 1 to 17, wherein the position of the target is spatially separated from the plurality of laser diodes.

Aspect 19 the light source according to any one of aspects 1 to 18, wherein the laser source comprises a first laser diode generating source light of a predefined wavelength.

Aspect 20 the light source of any one of aspects 1 to 19, wherein the laser source comprises at least one multimode laser diode.

Aspect 21 the light source according to any one of aspects 1 to 20, wherein the laser source comprises a plurality of laser diodes, wherein at least one of the plurality of laser diodes generates light having a wavelength different from light generated by another of the plurality of laser diodes.

Aspect 22. A method comprising operating the light source according to any one of aspects 1 to 21 to illuminate a target. The target may be located within the flow chamber, for example, within a flow cytometer. The target may be moving (e.g., a chamber in a flow cytometer), but may also be stationary. For example, the target may be disposed within a microscope system, e.g., at a location on a microscope stage.

Aspect 23. The method of aspect 22, the method further comprising collecting an image of the target.

Aspect 24. A method includes placing optical fibers in optical communication with an illumination source such that the optical fibers are placed to transmit light from the illumination source to a target disposed at a target location, at least some of the optical fibers being present in one or more layers wrapped around a mandrel, the mandrel optionally including circumferential walls and layers between which the optical fibers are wrapped, the layers including a tension winding of at least one optical fiber.

Aspect 25 the method of aspect 24, wherein the one layer of optical fiber comprises a tension winding of at least two optical fibers that are substantially parallel to each other.

The method of any one of aspects 24 to 25, wherein the windings of the optical fibers in the outer layer are substantially parallel to the windings of the optical fibers in the inner layer immediately below the outer layer.

The method of any one of aspects 24 to 26, wherein the windings of the optical fibers in the outer layer do not cross the windings of the optical fibers in the inner layer immediately below the outer layer.

Aspect 28 the method of any one of aspects 24 to 27, wherein the optical fiber presents an inner fiber layer and an outer fiber layer, the inner fiber layer comprising a plurality of tension windings of the optical fiber and the outer fiber layer comprising a plurality of tension windings of the optical fiber, and wherein

(i) The tension windings of the plurality of optical fibers in the outer layer are parallel to each other,

(ii) The tension windings of the plurality of optical fibers in the inner layer are parallel to each other, and

(iii) The taut windings of the plurality of optical fibers in the outer layer are parallel to the windings of the plurality of optical fibers in the inner layer.

Aspect 29. A method of providing source light for generating an image, the method comprising: generating illumination using one or more laser diodes; and passing illumination through an optical fiber, the optical fiber being present in one or more layers wrapped around a mandrel, the mandrel optionally comprising a circumferential wall and a layer, the optical fiber being wrapped between the circumferential walls, the layer comprising a taut winding of at least one optical fiber, the passing being performed such that multimode source light is emitted from the optical fiber to illuminate the target with illumination light, the illumination reducing speckle in an image of the target.

Aspect 30 the method of aspect 29, wherein the illumination is generated by at least two laser diodes that generate light having wavelengths different from each other, such that the at least two laser diodes produce illumination having multiple modes.

Aspect 31 the method of any one of aspects 29 to 30, wherein generating the source light comprises generating a synchronization light pulse from at least one laser diode.

The method of any of aspects 29-31, wherein generating illumination comprises causing a pulse period of at least one of the one or more laser diodes to be about 100 nanoseconds to gate the target.

Aspect 33 the method of any one of aspects 29 to 32, further comprising capturing an image of the target using an image capture device, the image capture device optionally having an exposure time of about 6 microseconds.

The method of any one of aspects 29 to 32, wherein the optical fiber is a multimode optical fiber.

The method of any one of aspects 29 to 34, wherein the optical fiber is a high numerical aperture optical fiber.

Aspect 36. The method of aspect 35, wherein the optical fiber has a numerical aperture of about 0.5.

The method of any one of aspects 29-36, wherein the length of the optical fiber is between about 2 meters and about 50 meters.

Aspect 38 the method of aspect 37, wherein the length of the optical fiber is about 50 meters.

Aspect 39 the method of any one of aspects 29 to 38, wherein the illumination is generated by a plurality of laser diodes, each laser diode of the plurality of laser diodes being positioned spatially separated from other laser diodes of the plurality of laser diodes.

Aspect 40 the method of any one of aspects 29 to 39, wherein the target is located within the flow chamber.

Aspect 41 the method of any one of aspects 29 to 40, further comprising effecting relative movement between the illumination and the target.

Aspect 42. The method of any one of aspects 29 to 41, wherein the target is stationary during application of the illumination.

Aspect 43. The method of any one of aspects 29 to 42, wherein the target moves during application of the illumination.

Aspect 44. A cytometer includes a flow chamber configured to contain one or more particles therein, the flow chamber defining a target region; an illumination train comprising at least (1) a laser source comprising at least one diode and (2) an optical fiber in optical communication with the laser source, at least some of the optical fiber being present in one or more layers wound around a mandrel, the mandrel optionally comprising circumferential walls and layers, the optical fiber being wound between the circumferential walls, the layers comprising a tension winding of the at least one optical fiber.

The cytometer may include one or more of hydrodynamic focusing or sheath fluid focusing and acoustic radiation pressure focusing. Hydrodynamic focusing is known to those of ordinary skill in the art, and an exemplary discussion of acoustic radiation pressure focusing is found, for example, in U.S. patent No. 2020/0074995 to Kaduchak et al.

Aspect 45. The cytometer of aspect 44, further comprising an image capture device configured to capture an image of a target disposed within the target region when illuminated by illumination of at least one diode, the at least one diode in communication via an optical fiber.

Aspect 46. An imaging device, the imaging device comprising: a sample region configured to contain a sample therein; an illumination train comprising at least (1) a laser source comprising at least one diode and (2) an optical fiber in optical communication with the laser source, at least some of the optical fiber being present in one or more layers wound around a mandrel, the mandrel optionally comprising circumferential walls and layers, the optical fiber being wound between the circumferential walls, the layers comprising a tension winding of at least one optical fiber; and an image capturing device configured to capture an image of a sample disposed within the sample region when illuminated by illumination of at least one diode, the at least one diode in communication via an optical fiber, the imaging device further optionally comprising a movement train configured to effect relative movement between the sample within the sample region and the illumination of the at least one diode, the at least one diode in communication via the optical fiber.

Aspect 47. A light source, the light source comprising: a laser source comprising at least one diode; and an optical fiber arranged to transmit light between the laser source and the imaging plane so as to reduce light coherence and thereby reduce speckle at the imaging plane, at least some of the optical fiber being bent around the support so as to create mechanical tension within the optical fiber.

Aspect 48 the light source of aspect 47, wherein the support is characterized as a mandrel.

Aspect 49 the light source of aspect 47, wherein the support is characterized as a post.

Aspect 50 the light source of any one of aspects 47-49, wherein the support defines a constant cross-sectional dimension.

Aspect 51 the light source of any one of aspects 47-50, wherein the optical fiber comprises at least one winding around the support.

Aspect 52. The light source of aspect 51, wherein the optical fiber comprises a plurality of windings around the support.

Aspect 53 the light source of aspect 52, wherein the optical fiber comprises a plurality of layers surrounding the support, each layer comprising a plurality of windings.

Aspect 54 the light source of any one of aspects 47-53, wherein the light source is configured to produce less than about 2% speckle at the imaging plane.

Aspect 55 the light source of aspect 54, wherein the light source is configured to produce less than about 1% speckle at the imaging plane.

Aspect 56 the light source of aspect 54, wherein the light source is configured to produce about 1% speckle at the imaging plane.

Aspect 57 the light source of any one of aspects 47-56, wherein the optical fiber has a long-term bend radius, and wherein the optical fiber is bent at a radius that is less than the long-term bend radius.

The light source of any one of aspects 47-57, wherein the transmission of light through the optical fiber is about 60% to about 90%.

Aspect 59 the light source of aspect 58, wherein the transmission is about 75% to about 90%.

The light source of any one of aspects 47-59, wherein the imaging plane is disposed within the flow chamber.

Aspect 61. The light source of aspect 60, wherein the flow cell is included in a flow cytometer.

Aspect 62 the light source of any one of aspects 47-61, wherein the mechanical tension maintains the optical fiber in tension.

Aspect 63 the light source of any one of aspects 47-62, wherein the laser source provides light as light pulses, the light pulses optionally being synchronized.

Aspect 64 the light source of aspect 63, wherein the pulses of light from the laser source are about 100 nanoseconds to gate the target.

Aspect 65 the light source of any of aspects 47 to 64, further comprising an image capture device configured to capture a captured image of the target, the captured image optionally having an exposure time of about 6 microseconds.

The light source of any one of aspects 47-65, wherein the optical fiber is a multimode optical fiber.

Aspect 67 the light source of any one of aspects 47 to 66, wherein the optical fiber is a high numerical aperture optical fiber.

The light source of any one of aspects 47-67, wherein the optical fiber has a numerical aperture of about 0.5.

Aspect 69 the light source of any one of aspects 47-68, wherein the optical fiber has a length of between about 2 meters and about 75 meters.

Aspect 70 the light source of aspect 69, wherein the optical fiber has a length of about 50 meters.

Aspect 71 the light source of any one of aspects 47 to 70, wherein the laser source comprises a plurality of laser diodes, and wherein each of the plurality of laser diodes is positioned spatially separated from other ones of the plurality of laser diodes.

Aspect 72 the light source of any one of aspects 47 to 71, wherein the laser source comprises a first laser diode that generates source light of a predefined wavelength.

Aspect 73 the light source of any one of aspects 47-72, wherein the laser source comprises at least one multimode laser diode.

Aspect 74 the light source of any one of aspects 47 to 73, wherein the laser source comprises a plurality of laser diodes, wherein at least one of the plurality of laser diodes generates light having a wavelength different from light generated by another of the plurality of laser diodes.

Aspect 75. A method comprising operating the light source according to any one of aspects 47 to 74.

Aspect 76. The method of aspect 75, wherein the operation comprises illuminating one or more particles or cells at the imaging plane.

Aspect 77. The method of aspect 76, further comprising collecting an image of a target illuminated by a light source and located at an imaging plane.

Claims (77)

1. A light source, the light source comprising:

a laser source comprising at least one diode; and

an optical fiber arranged to transmit pulses of light having a plurality of modes between the laser source and a target location to reduce speckle in a captured image of a target at the target location,

At least some of the optical fibers are present in one or more layers wrapped around the mandrel,

the mandrel optionally includes circumferential walls between which the optical fibers are wound, the layers including at least one tension winding of the optical fibers.

2. The light source of claim 1, wherein a layer of the optical fibers comprises a tension winding of at least two of the optical fibers substantially parallel to each other.

3. A light source according to any one of claims 1 to 2, wherein the windings of the optical fibres in the outer layer are substantially parallel to the windings of the optical fibres in the inner layer immediately below the outer layer.

4. A light source according to any one of claims 1 to 3, wherein the windings of the optical fibres in the outer layer do not cross the windings of the optical fibres in the inner layer immediately below the outer layer.

5. The light source according to any one of claims 1 to 4, comprising an inner fiber layer and an outer fiber layer, the inner fiber layer comprising a plurality of the tension windings of the optical fiber and the outer fiber layer comprising a plurality of the tension windings of the optical fiber, and wherein

(i) The plurality of tension windings of the optical fibers in the outer layer are parallel to each other,

(ii) The tension windings of the plurality of the optical fibers in the inner layer are parallel to each other, and

(iii) The tensioned windings of the plurality of the optical fibers in the outer layer are parallel to the windings of the plurality of optical fibers in the inner layer.

6. A light source as claimed in any one of claims 1 to 5, wherein the cross-sectional dimension of the mandrel is constant.

7. A light source as claimed in any one of claims 1 to 5, wherein the cross-sectional dimension of the mandrel is variable.

8. The light source of any one of claims 1 to 7, wherein the mandrel has a cross-sectional dimension of about 1 cm to about 10 cm.

9. The light source of any one of claims 1 to 8, wherein the light pulses from the laser sources are synchronized.

10. The light source of any one of claims 1 to 9, wherein the pulses of light from the laser source are about 100 nanoseconds to gate the target.

11. The light source according to any one of claims 1 to 10, further comprising an image capturing device configured to capture a captured image of the target, the captured image optionally having an exposure time of about 6 microseconds.

12. The light source according to any one of claims 1 to 11, wherein the optical fiber is a multimode optical fiber.

13. The light source according to any one of claims 1 to 12, wherein the optical fiber is a high numerical aperture optical fiber.

14. The light source of any one of claims 1 to 13, wherein the optical fiber has a numerical aperture of about 0.5.

15. The light source of any one of claims 1 to 14, wherein the length of the optical fiber is between about 2 meters and about 75 meters.

16. The light source of claim 15, wherein the optical fiber has a length of about 50 meters.

17. The light source of any one of claims 1 to 16, wherein the laser source comprises a plurality of laser diodes, and wherein each of the plurality of laser diodes is positioned spatially separated from other ones of the plurality of laser diodes.

18. The light source of any one of claims 1 to 17, wherein the location of the target is spatially separated from the plurality of laser diodes.

19. The light source of any one of claims 1 to 18, wherein the laser source comprises a first laser diode that generates the source light at a predefined wavelength.

20. The light source of any one of claims 1 to 19, wherein the laser source comprises at least one multimode laser diode.

21. The light source of any one of claims 1 to 20, wherein the laser source comprises a plurality of laser diodes, wherein at least one of the plurality of laser diodes lases two

The polar tube generates light having a wavelength different from that of light generated by another laser diode of the plurality of laser diodes.

22. A method comprising operating a light source according to any one of claims 1 to 21 to illuminate a target.

23. The method of claim 22, further comprising collecting an image of the target.

24. A method, the method comprising:

placing an optical fiber in optical communication with an illumination source such that the optical fiber is placed to transmit light from the illumination source to a target disposed at a target location,

at least some of the optical fibers are present in one or more layers wrapped around the mandrel,

the mandrel optionally includes circumferential walls between which the optical fiber is wound, and

a layer comprising at least one tension winding of said optical fiber.

25. The method of claim 24, wherein a layer of the optical fibers comprises a tension winding of at least two of the optical fibers that are substantially parallel to each other.

26. The method of any one of claims 24 to 25, wherein the windings of the optical fibers in an outer layer are substantially parallel to the windings of the optical fibers in an inner layer immediately below the outer layer.

27. The method of any one of claims 24 to 26, wherein windings of the optical fiber in an outer layer do not cross windings of the optical fiber in an inner layer immediately below the outer layer.

28. The method of any of claims 24-27, wherein the optical fiber presents an inner fiber layer and an outer fiber layer, the inner fiber layer comprising a plurality of tension windings of the optical fiber and the outer fiber layer comprising a plurality of tension windings of the optical fiber, and wherein

(i) The plurality of tension windings of the optical fibers in the outer layer are parallel to each other,

(ii) The tension windings of the plurality of the optical fibers in the inner layer are parallel to each other, and

(iii) The tensioned windings of the plurality of the optical fibers in the outer layer are parallel to the windings of the plurality of optical fibers in the inner layer.

29. A method of providing source light for generating an image, the method comprising:

generating illumination using one or more laser diodes; and

the illumination is passed through optical fibers present in one or more layers wound around a mandrel,

the mandrel optionally includes circumferential walls between which the optical fiber is wound, and

a layer comprising at least one tension winding of said optical fiber,

the passing is performed such that multimode source light is emitted from the optical fiber to illuminate a target with the illumination light, the illumination reducing speckle in an image of the target.

30. The method of claim 29, wherein the illumination is generated by at least two laser diodes that generate light of different wavelengths from each other such that the at least two laser diodes produce the illumination having multiple modes.

31. The method of any of claims 29 to 30, wherein generating the source light comprises generating synchronized light pulses from the at least one laser diode.

32. The method of any of claims 29-31, wherein generating the illumination comprises causing a pulse period of at least one of the one or more laser diodes to be about 100 nanoseconds to gate the target.

33. The method of any of claims 29 to 32, further comprising capturing the image of the target using an image capture device, optionally with an exposure time of about 6 microseconds.

34. The method of any one of claims 29 to 32, wherein the optical fiber is a multimode optical fiber.

35. The method of any one of claims 29 to 34, wherein the optical fiber is a high numerical aperture optical fiber.

36. The method of claim 35, wherein the numerical aperture of the optical fiber is about 0.5.

37. The method of any one of claims 29 to 36, wherein the length of the optical fiber is between about 2 meters and about 50 meters.

38. The method of claim 37, wherein the length of the optical fiber is about 50 meters.

39. The method of any of claims 29 to 38, wherein the illumination is generated by a plurality of laser diodes, each laser diode of the plurality of laser diodes being positioned spatially separated from other laser diodes of the plurality of laser diodes.

40. The method of any one of claims 29 to 39, wherein the target is located within a flow chamber.

41. The method of any one of claims 29 to 40, further comprising effecting relative movement between the illumination and the target.

42. The method of any one of claims 29 to 41, wherein the target is stationary during application of the illumination.

43. The method of any one of claims 29 to 42, wherein the target moves during application of the illumination.

44. A cytometer, the cytometer comprising:

a flow chamber configured to contain one or more particles therein, the flow chamber defining a target area;

an illumination system comprising at least (1) a laser source comprising at least one diode and (2) an optical fiber in optical communication with the laser source,

at least some of the optical fibers are present in one or more layers wrapped around the mandrel,

the mandrel optionally includes circumferential walls between which the optical fiber is wound, and

a layer comprising at least one tension winding of said optical fiber.

45. A cytometer according to claim 44 further comprising an image capture device configured to capture an image of a target disposed within the target region upon illumination by illumination of the at least one diode, the at least one diode in communication through the optical fiber.

46. An imaging device, the imaging device comprising:

a sample region configured to contain a sample therein;

an illumination system comprising at least (1) a laser source comprising at least one diode and (2) an optical fiber in optical communication with the laser source,

at least some of the optical fibers are present in one or more layers wrapped around the mandrel,

the mandrel optionally includes circumferential walls between which the optical fiber is wound, and

a layer comprising at least one tension winding of the optical fiber; and

an image capturing device configured to capture an image of a sample disposed within the sample area when illuminated by illumination of the at least one diode, the at least one diode being in communication via the optical fiber,

the imaging device further optionally includes a motion train configured to effect relative motion between the sample within the sample region and illumination of the at least one diode, the at least one diode in communication through the optical fiber.

47. A light source, the light source comprising:

a laser source comprising at least one diode; and

An optical fiber arranged to transmit light between the laser source and an imaging plane so as to reduce coherence of the light, thereby reducing speckle at the imaging plane, at least some of the optical fiber being bent around a support so as to create mechanical tension within the optical fiber.

48. The light source of claim 47, wherein the support is characterized as a mandrel.

49. The light source of claim 47, wherein the support is characterized as a post.

50. The light source of any one of claims 47 to 49, wherein the support defines a constant cross-sectional dimension.

51. The light source of any one of claims 47 to 50, wherein the optical fibre comprises at least one winding around the support.

52. The light source of claim 51, wherein the optical fiber comprises a plurality of windings around the support.

53. The light source of claim 52, wherein the optical fiber comprises a plurality of layers surrounding the support, each layer comprising a plurality of windings.

54. The light source of any one of claims 47-53, wherein the light source is configured to produce less than about 2% speckle at the imaging plane.

55. The light source of claim 54, wherein the light source is configured to produce less than about 1% speckle at the imaging plane.

56. The light source of claim 54, wherein the light source is configured to produce about 1% speckle at the imaging plane.

57. The light source of any one of claims 47 to 56, wherein the optical fiber has a long-term bend radius, and wherein the optical fiber is bent at a radius less than the long-term bend radius.

58. The light source of any one of claims 47-57, wherein the transmission of the light through the optical fiber is about 60% to about 90%.

59. The light source of claim 58, wherein the transmission is about 75% to about 90%.

60. The light source of any one of claims 47-59, wherein the imaging plane is disposed within a flow chamber.

61. The light source of claim 60, wherein the flow cell is included in a flow cytometer.

62. The light source of any one of claims 47 to 61, wherein the mechanical tension holds the optical fiber in tension.

63. The light source of any one of claims 47 to 62, wherein the laser source provides light as light pulses, the light pulses optionally being synchronized.

64. The light source of claim 63, wherein the pulses of light from the laser source are about 100 nanoseconds to gate the target.

65. The light source of any one of claims 47 to 64, further comprising an image capture device configured to capture a captured image of the target, the captured image optionally having an exposure time of about 6 microseconds.

66. The light source of any one of claims 47 to 65, wherein the optical fiber is a multimode optical fiber.

67. The light source of any one of claims 47 to 66, wherein the optical fiber is a high numerical aperture optical fiber.

68. The light source of any one of claims 47 to 67, wherein the optical fiber has a numerical aperture of about 0.5.

69. The light source of any one of claims 47 to 68, wherein the length of the optical fiber is between about 2 meters and about 75 meters.

70. The light source of claim 69, wherein the optical fiber has a length of about 50 meters.

71. The light source of any one of claims 47 to 70, wherein the laser source comprises a plurality of laser diodes, and wherein each of the plurality of laser diodes is positioned spatially separated from other ones of the plurality of laser diodes.

72. The light source of any one of claims 47 to 71, wherein the laser source comprises a first laser diode that generates the source light at a predefined wavelength.

73. The light source of any one of claims 47 to 72, wherein the laser source comprises at least one multimode laser diode.

74. The light source of any one of claims 47 to 73, wherein the laser source comprises a plurality of laser diodes, wherein at least one of the plurality of laser diodes generates light having a wavelength that is different from a wavelength of light generated by another of the plurality of laser diodes.

75. A method comprising operating a light source according to any one of claims 47 to 74.

76. The method of claim 75, wherein the operation comprises illuminating one or more particles or cells at the imaging plane.

77. The method of claim 76, further comprising collecting an image of a target illuminated by the light source and located at the imaging plane.