ES2540921B2 - Opto-electronic device and methods to collimate and determine the degree of collimation of a light beam - Google Patents

Abstract

Opto-electronic device and methods for collimating and determining the degree of collimation of a light beam # The present invention refers to an opto-electronic device for determining the degree of collimation of a light beam that, by incorporating a collimation element 2, can also be used to collimate beams. The device comprises a diffraction grating 3, a mask 5 that includes a multiplicity of windows 4 each with a diffraction grating, the diffraction gratings of the windows 4 being offset from each other, a matrix 7 of photodetectors 6 whose number it can be equal to or greater than the number of windows 4 of the mask 5 or they can be located in a matrix with two-dimensional distribution (CMOS or CCD) and one or more data processing elements 8. The invention also includes methods to determine the degree of collimation of a beam of light or to collimate a beam.

Description

Opto-electronic device and methods to ~ olieve and determine the degree of

collimation of a beam of light

Sector of the technique

The present invention falls within the field of Optical Technology and more specifically in the sector of Opto-electronic Devices.

State of the art

The determination or knowledge of the degree of collimation of a beam of light is of great importance in numerous optical applications, such as metrological devices, systems for lighting, consumer optics, applications of lasers, etc. There are simple and well-known methods for roughly collimating a general light source, through the use of a lens, such as the autocollimation method. Interferometric techniques for measuring the degree of collimation of a beam are among the most precise, having been known for several decades [D. Malacara, ed., Optical Shop Testing (Wiley, New York, 1978)]. However, they can only be used with beams of light that have a high degree of temporal or spatial coherence, such as lasers.

On the other hand, in many situations it is necessary to know the degree of collimation of a beam of light coming from other types of sources such as light emitting diodes (LEOs), laser diodes, vertical emission cavity lasers (VCSELs) and other sources that present a degree of temporal and / or spatial partial coherence.

There are techniques that allow to measure the degree of collimation of light beams by means of double network systems, but they need to make lateral displacements, so that the collimation devices become complicated [L.M. Sanchez-Brea, F.J. TorcalMilla, F. J. Salgado-Remacha, T. Morlanes, 1. Jimenez-Castillo, and E. Bernabeu, "Collimation method using a double grating system"; Appl. Opt. 49, 3363 (2010)].

On the other hand, systems to determine the degree of collimation based on a conjunction of linear and circular networks have appeared, but the processing of the signals is complicated and not intuitive [K. Patorski, K. Pokorski, and M. Trusiak, quot; Circularlinear grating Talbot interferometry with moiré Fresnel imaging for beam collimationquot; Opt. Lett. 39, 291 (2014)].

Likewise, the degree of collimation can be determined by measuring the period of a self-image and comparing it with the period of the diffraction network generated by said self-image [L.M. Sanchez-Brea, F.J. Torcal-Milla, J.M. Herrera-Fernandez, T. Morlanes, and E. Bernabeu quot; Self-imaging technique for beam collimation; Optics Letters 39 (19) 5764-5767 (2014)]. When the period of the self-image is the same as that of the network, then the beam is collimated. The disadvantage of this technique is that it requires a very high precision in the positioning of optical and optoelectronic elements to ensure the measurement of the period with the required precision, of the order of nanometers in many cases.

The advantage of using the self-images of a diffraction grating to determine the degree of collimation of a beam is that the requirements of the illumination source are less restrictive, since the phenomenon is not due to interference, but to diffraction. In this way it is not necessary for the source to be punctual to produce self-images, nor does it need to be monochromatic. For example, it is known that polychromatic sources can generate stable self-images over a long distance [N Guérineau, B. Harchaoui, J. Primot quot; Talbot experiment re-examined: demonstration of an achromatic and continuous self-imaging regime, quot; Optics Communications 180 199203 (2000)].

Among the patents related to the invention include:

Patent CN1080997 (A) showing a device that tests the degree of collimation of a laser light source in a comprehensive computerized manner. It includes a wide range of measurements provided it is a laser light source.

The patent CN 1 01469977 (A) which shows a device that tests the collimation by increasing the accuracy and with a compact structure.

That is why the object of the present patent is a device that determines the degree of collimation of a beam in a robust and simple way, which serves for different types of light sources, and not only for laser beams. Also, using the

device that measures the degree of collimation described in this patent develops a method to obtain a beam with high degree of collimation.

Detailed description of the invention

Opto-electronic device and methods to collimate and determine the degree of

collimation of a beam of light.

An aspect of the present invention relates to an optoelectronic device that allows to measure the degree of collimation of a laser beam or a beam of light with a partial spatial or temporal coherence and that, likewise, serves to collimate a beam of light with accuracy when a collimator element is added.

In this specification, it is meant by "light beam"; or, simply, quot; hazquot; any type of light beam and laser beam.

To measure the degree of collimation of a light beam, a diffraction grating 3 of a period p is used in the present invention. As light propagates due to diffractive effects, auto-images are generated at various distances from the diffraction grating [K. Patorsky, "The self-imaging phenomenon and its applications, quot; Progress in Optics 27 1108 1989). If A is the average wavelength of the light beam, and the diffraction grating modulates the amplitude of the wave, the generated auto-images are located at integer multiples of Talbot's distance z = p2 fA. In reference [L.M. Sanchez-Brea, F.J. Torcal-Milla, F. J. Salgado-Remacha, T. Morlanes, 1. Jimenez-Castillo, and E. Bernabeu, "Collimation method using a double grating system"; Appl. Opt. 49, 3363 (2010)] describes a system that uses a diffraction network of period p and a mask with two windows, each with a diffraction network of period p, displaced from each other p / 4 (90 electrical degrees). By means of the electrical signals, SA and Ss respectively, generated by two photodetectors located behind the diffraction gratings of the two windows, a Lissajous Figure can be obtained by laterally and continuously moving the diffraction grating.

The shape of the Lissajous Figure depends on various aspects. If we use a purely geometric model for the analysis of the device, the Lissajous Figure is quadrangular or rectangular. However, due to diffractive effects, the finite size of the light source, the polychromaticity of the light source, or a poor positioning of the elements that involve the device, the Lissajous Figure presents a more rounded shape. These types of forms can be described mathematically, as we will see later.

The shape of the Lissajous Figure also depends on the degree of beam collimation. When the beam is collimated, the Lissajous Figure is symmetric with respect to the vertical and horizontal axes, whereas when the beam is decoupled the Lissajous Figure becomes ellipsoidal and not symmetric with respect to the same axes. Therefore, the measurement of the ellipticity of the Lissajous Figure obtained allows us to determine the degree of collimation of the light beam. The problem that arises with the solution described in the reference [L.M. Sanchez-Brea, F.J. Torcal-Milla, F. J. SalgadoRemacha, T. Morlanes, 1. Jimenez-Castillo, and E. Bernabeu, "Collimation method using a double grating system"; Appl. Opt. 49, 3363 (2010)] is that, in order to generate the Lissajous Figure, the mechanical lateral displacement of the diffraction network with respect to the mask with two windows and the photodetectors of the device is required. Although this system is viable in laboratory prototypes, the continuous movement of the diffraction network makes a device that uses this technology complicated and expensive.

In the present invention, the method for obtaining the Lissajous Figure is simplified with respect to that described in the preceding paragraphs. A scheme of the device of the invention is shown in Figure 1. Instead of requiring a relative movement between the diffraction grating and the mask formed by two windows, each of which has a photodetector behind, as had the device described in FIG. [LM Sanchez-Brea,

F.J. Torcal-Milla, F. J. Salgado-Remacha, T. Morlanes, 1. Jimenez-Castillo, and E. Bernabeu, "Collimation method using a double grating system"; Appl. Opt. 49, 3363 (2010)], in the present invention said mask is replaced with only two windows by a mask 5 with a multiplicity (N) of windows 4, each with a diffraction network of period p. Figure 2 shows an example of the mask 5 with the multiplicity of windows 4 whose diffraction gratings are displaced with respect to each other. The diffraction gratings of the windows 4 must be displaced from each other a fraction of the period. One option is that, if there

N windows, the relative displacement between them is 2rr / N or 3600 / N, although other options are also viable. Also, instead of locating 2 photodetectors, one behind each of the two windows, N photodetectors 6 or a two-dimensional array, such as a CCO camera, are located in the device of the present invention.

or CMOS. In this way, N signals are obtained which, conveniently arranged in pairs {SA and Ss}, allow obtaining the Lissajous Figure without the need for relative movement of the diffraction grating. Figure 3 shows an example of distribution of intensity that reaches each of the photodetectors 6 for the case of the window distribution of Figure 2. The device of the invention has a great advantage since it greatly simplifies the measurement of the degree of collimation of the beam. With the N photodetectors, which may or may not be duplicated, to improve the quality of the signal, we obtain a series of signal pairs {SA and Ss} that are used to represent the Lissajous Figure. In Figure 4 the Lissajous Figure obtained with the photodetectors 6 of Figure 3 is shown for three different degrees of collimation. When the beam is collimated, Figure 4b, the Lissajous Figure is symmetric with respect to the vertical and horizontal axes while in Figures 4a and 4c the beam is decoupled.

One aspect of the present invention relates to a device for determining the degree of collimation of a light beam comprising:

-

a diffraction grating 3,

-

a mask 5 that includes N windows 4 each with a diffraction grating, where N ~ 4,

-

a matrix 7 of photodetectors 6, located behind each of the windows, its number N being equal to or greater than the number of windows,

-

one or more data processing elements 8.

When the device wants to be used to collimate a beam of light, a collimation element 2 that can be a lens, a lens assembly or a diffractive optical element must be incorporated therein. Therefore, a second aspect of the invention relates to a device for collimating a light beam comprising:

-

a collimation element 2,

-

a diffraction grating 3,

-

a mask 5 that includes N windows 4 each with a diffraction grating, where N ~ 4,

-

a matrix 7 of photodetectors 6, located behind each of the windows, its number N being equal to or greater than the number of windows,

-

one or more data processing elements 8.

the diffraction network 3 can be a Ronchi network that modulates the amplitude although it could also be a network with a sinusoidal modulation or another type of amplitude and / or phase modulation.

The number of windows 4 in the mask 5 is variable, although preferably, it will be an even number and more preferably, the mask 5 includes 16 windows 4. On the other hand, the windows 4 in the mask 5 can be arranged in one or more columns (Figures 9 and 10). It is convenient, although not necessary, that the transverse phase difference between each of the diffraction gratings of each window 4 is equal to 360o / N, where N is the number of windows 4. Another option is to duplicate the windows with the same phase shift, as shown in Figure 2.

One possible configuration is to locate all windows 4 at the same distance d between the optical axis of the beam and the center of the window, as shown in Figure 8. The greater the distance d between the optical axis of the beam and the center of the window, the greater the sensitivity that the measuring device will have. However, since the beam must cover all the windows (or at least most of them), the distance d must be adapted to the estimated size of the beam once it has been collimated.

In relation to the gap between the networks of the different windows, it is also possible that this duplication does not occur. Then, the output data can be conveniently arranged to obtain N data from the lissajous Figure from the N windows used. This example is shown in Figure 11.

Although it simplifies the subsequent signal processing, it is not necessary that all windows 4 are at the same distance from the optical axis of the input light beam. Another possible configuration is to locate the windows 4 and, therefore, the photodetectors 6, in several columns as shown in Figure 9. In this way, the detection area is optimized.

From the electronic point of view, the fastest configuration from the point of view of data processing is to locate N photodetectors 6 one behind each window 4. However, such configuration is simplified if a camera formed by a two-dimensional distribution of photodetectors 6, as is a CCO camera or a CMOS camera. In this case, by means of programming, the photodetectors (also called pixels) suitable for obtaining the data for the Lissajous Figure can be selected.

Among the elements for data processing 8, an electronic board, a microprocessor or a computer can be selected.

If the system is analyzed from a geometric point of view, the Lissajous Figure will be square or rectangular if the networks are Ronchi networks. However, the shape of the Lissajous Figure can change for different reasons. In the first place, diffractive effects are produced which make the auto-image not recover perfectly, especially if the plane of the photodetectors 6 does not coincide with Talbot's distance. In addition, when the light source is not punctual but has a finite size, the diffraction pattern tends to eliminate higher harmonics and the Lissajous Figure becomes increasingly smooth. Also, when the source is polychromatic, harmonics are eliminated in the Lissajous Figure. All this must be taken into account when designing a device that measures the ellipticity of the Lissajous Figure.

Therefore, to determine the degree of ellipticity of the Lissajous Figure in a precise way, the signals {SA and Se} fit a complex figure generated by

[M. Fernandez-Guasti, M. de la Cruz Heredia quot; Oiftraction pattern of a circle I square aperturequot; J. Mod. Opt. 40 (6) 1073-1080 (1993)]

(one)

where x 'e and' are the coordinates of the Figure (signals {SA and Se}), R1 and R2 are the principal axes and s is the parameter that accounts for the shape of the Lissajous Figure. When the parameter s is null, s = 0, the function represents an ellipse I circle. When the parameter s = 1 the function represents a rectangle I squared.

The degree of ellipticity can be measured from the following parameter,

(two)

where Rmin is the lowest value between R1 and R2 and Rmax is the highest value between R1 and R2, although any parameter that compares R1 and R2 is valid.

For physical considerations, when the Lissajous Figure is not circular, the main axes of the ellipse (1) are located at 45 degrees with respect to the x axis. Therefore, considering this change of variables

x = (x'-x) cosO- (y'-y) sinO y = (x'-x) cosO + (y'-y) sinO (3)

where e = 45 °, x is the average value of the signal of the photodetectors 6 that generate SA and y is the average value of the signal of the photodetectors 6 that generate Ss, the equation

(1) becomes the following equation

8 (2 2) 2 1 (1 1) (2 2) (1 1)

4R ~ R ~ x -y -2 R ~ + ~ x + y + R ~ - ~ xy + 1 = 0, (4)

In Figure 5 this equation is shown for various values of s and R1 / R2. In order to obtain the parameters of interest R1, R2, the points of the experimental Lissajous Figure {SA and Ss} have to be adjusted to this equation. To do this, from (4) we will consider the following polynomial

(5)

au + bv + cxy + l = O where u = (x2 -y2) 2, V = (x2 + y2), a = S2 j4RfR ~, b = - (ljRf + ljRDj2 and e = (ljRf -ljRD. a, b, e must be calculated from experimental data {SA and Ss} Then, for each pair of values (Xm, ym) with m = 1, ..., M

of the set {SA and Ss} that generate the Lissajous Figure, we obtain an equation that can be represented in matrix form A * z = B

UI VI XIYI

U2 V2 X2Y2

(6)

0) = (D,

UM VM XMYM

where U1 = (xf -yf) 2, V1 = (xf + yf) and so on. This system of linear equations can be solved by a least squares adjustment

T T

)-one

z = (A · A A · B (7)

and in this way parameters a, b and c are obtained. From these values the best parameters R1 and R2 can be obtained for the adjustment, which by comparison turn out to be

2 -2 Rl = 2b-e

(8)

2 -2 · R2 = 2b + c

Consequently, ellipticity is obtained through

2 2c 2 -2c

e = - or e = - (9)

2b + c 2b-c

depending on the sign of the parameters. For one of the equations (9) e a positive value results and for the other a pure complex number. We will remain as a parameter of ellipticity, e, with the positive value.

Figure 6 shows an example of adjusting the data obtained with the mask 5 of Figure 4 and with the parameters a, b, and c obtained with this procedure for different distances Az between the light source and the focal plane of the lens 2. It is clearly observed that ellipticity is a valid parameter to measure the degree of collimation of the beam and to look for the degree of maximum collimation, which occurs when Az = o.

On the other hand, Figure 7 shows the adjustment of equation (4) for two cases obtained according to the scheme of Figure 1 and the mask of Figure 2. In Figure 7a the distance Zz is the one that corresponds to a self-image and in Figure 7b the distance Zz is different from that corresponding to a self-image. In both Figures the shape of the Lissajous Figure is very different, since the parameter s varies. However, the adjustment obtained with equation (4) is excellent for both cases.

Therefore, another aspect of the invention relates to a method for determining the degree of collimation of a light beam that includes the following steps:

a) passing the light beam through the device of the invention,

b) obtain a Lissajous Figure,

c) determine the degree of ellipticity of the Lissajous Figure.

To determine the degree of ellipticity of the Lissajous Figure thus obtained, one can resort to visual measurement of said Figure or it can be mathematically processed. As for the visual measurement, the light beam will be collimated if the Lissajous Figure is circular / square and will not be collimated if the Lissajous Figure is elliptical / rectangular. For the mathematical measurement the following steps are followed:

d) obtain the data of matrix A (6), e) perform the least-squares adjustment of equation (7), f) obtain the parameters R1 and R2 of equation (8), g) obtain the ellipticity e according to equation (9). The invention also relates to a method for collimating a light beam that includes

Next steps:

a) passing the light beam through the device of the invention that includes a collimator element 2, b) obtain a Lissajous Figure, c) determine the degree of ellipticity of the Lissajous Figure well by measurement

visual well mathematically,

d) displacing the light source 1 with respect to the collimation element 2 along the optical axis, e) monitor the ellipticity parameter e of step c), f) stop the movement of the light source 1 when the parameter e is minimum, taking into account that steps c) and d) are carried out simultaneously or

consecutively and that by minimum the least possible value of the ellipticity is understood

throughout the full measure. To perform the mathematical measurement of the degree of ellipticity of the Lissajous Figure in step c) the following steps are followed:

i) obtain the data from matrix A (6),

ii) perform the least-squares adjustment of equation (7),

iii) obtain the parameters R1 and R2 of equation (8), iv) obtain the ellipticity e according to equation (9) by selecting the ellipticity parameter, e, with positive value.

Brief description of the Figures

Figure 1. Shows, schematically, the basic configuration of the collimating device and the device to determine the degree of collimation of a light beam, and the distribution of the different components: 1 light source, 2 collimation element, 3 diffraction grating, 4 window with diffraction grating, 5 mask containing the multiplicity of windows, 6 photodetector, 7 array of photodetectors and 8 data processing elements. The mask 5, the matrix 7 of photodetectors 6 and the data processing elements 8 are shown separated for a better understanding but in one embodiment they could be glued, at least the mask 5 and the photodetectors

6

Figure 2. Shows, schematically, an example of mask 5 to obtain the Lissajous Figure, for the case of 8 duplicate windows 4 (16 in total) with which eight points are obtained in the Lissajous Figure. In this case, the windows are duplicated for greater robustness, although they may not be. The numbers represent the lateral displacement of each network so that 360 results in a displacement of a period p.

Figure 3. Example of intensity distribution in the photodetectors for a collimated source using mask 5 of Figure 2.

Figure 4. Example of Lissajous figures for the case of convergent and divergent declined faeced beam, Figure 4a and Figure 4c respectively, and for the case of collimated beam, Figure 4b. When the beam is collimated the Lissajous Figure presents symmetry. This example has been obtained with the intensity distribution of Figure 3.

Figure 5. Graph of equation 1 showing an adjustment profile of the Lissajous figure. In Figure 5a the relationship between axes is the same (collimated beam), and the form factor s varies for each curve. In Figure 5b the relationship between axes is different (beam declines) and the form factor s varies for each curve.

s

Figure 6. Variation of ellipticity e (equation 9) as a function of the distance between the light source 1 and the focal point of the collimator element 2, flz, for the mask of Figure 2. Knowing the value of the ellipticity we can know the degree of collimation of the beam, so that the degree of collimation of the beam can be measured from the ellipticity. On the other hand, when you have flz = 0, then the beam is perfectly collimated.

10

Figure 7. Examples of Lissajous figures obtained with the mask of Figure 2 when the beam is perfectly collimated for two different observation planes Z2. In Figure 7a, the distance Z2 between the diffraction grating 3 and the mask 5 with windows 4 is equal to a Talbot plane of the diffraction grating Z2 = p2lA, A = 880 nm, p = 110 f.lm. In Figure 7b, this distance is Z2 = p2 lA + SOO¡.tm. Although the form of

the Lissajous figure changes, and so does the parameter s, with the equation (9) an equal ellipticity value is obtained for the two cases.

lS

Figure 8. Example of mask 5 when windows 4 are located only in 2 separate columns a distance d from the central axis. Each of the windows (black rectangles) contains a diffraction grating with relative phase shifts.

Figure 9. Example of mask 5 when windows 4 are located in 4 columns. Each of the windows (black rectangles) contains a diffraction grating with relative phase shifts.

twenty

Figure 10. Example of mask 5 when windows 4 are arranged in a multiplicity of equally spaced columns. Each of the windows (black rectangles) contains a diffraction grating with relative phase shifts.

2S

Figure 11. Example of mask 5 when the networks of windows 4 are not duplicated. In this way, a greater number of points can be obtained from the Lissajous Figure.

Figure 12. Experimental results of ellipticity as a function of the LED distance obtained with Example 1.

Embodiment of the invention

After defining the geometry of the system and the measurement process, the following are examples of devices to measure the degree of collimation of a beam or collimate a beam.

Example 1.

A collimating device and a device to determine the degree of collimation of a light source 1 LEO of wavelength A = 880 nanometers (Hitachi model HE8807SG) were fabricated, including, as a collimation element 2, a focal lens 25 mm and diameter 20 mm in the case of the device for collimation. The device included a diffraction grating 3 of period p = 110 micrometers, a mask 5 containing 16 windows 4 located in two columns with a distance of d = 2 millimeters between the central axis of the mask 5 and the center of the windows 4 . Every

one of the windows contained a diffraction grating of period p = 110 micrometers with phase lag intervals 360 ° / 8. The diffraction gratings of the windows were duplicated. This mask is shown in Figure 2. For data acquisition, infrared silicon photodetectors 6 from Osram were used - Opto model SFH2400Z 60 °, placing one behind each window 4. Mask 5 is located at a distance from Talbot the diffraction grating 3, Zr = 2 · p2 / A, = 27.5 millimeters. For him

treatment of said data a computer program was used. The dependence of the ellipticity of the Lissajous Figure with the distance between the light source and the focal point of the collimation system is shown in Figure 6. The minimum corresponds to the optimal collimation situation whose Lissajous Figure is shown in the Figure 4b. The experimental result is shown in Figure 12.

Example 2

Devices identical to those described in Example 1 were manufactured but using a number of windows N = 24 arranged in two equally spaced columns on either side of the central axis of the mask. The mask was placed at two distances from Talbot of the diffraction grating. In this case, the difference between the diffraction gratings of the windows was 360 ° / 24 and the windows were duplicated.

Example 3

Devices identical to those described in Example 2 were manufactured by replacing the collimation lens with a lens system, in the case of collimating devices, and the phase differences of the diffraction gratings of the windows 4 of the mask 5 were not duplicated. In this case, the phase shifts were at intervals of 360 ° / 16. An example with 16 windows is shown in Figure 11.

Example 4

Devices identical to those described in Example 2 were manufactured with N = 32 windows, placing them in 4 columns of 8 windows as shown in Figure 9. As a light source a LED of different wavelength was used: A = 650 nanometers.

Example 5

Devices identical to those described in Example 2 were manufactured with N = 72 windows, but placing the windows in 9 columns, as shown in Figure 10. As a collimator element, when it was necessary to include it, a Diffractive Optical Element was used. instead of a lens.

Example 6

Devices identical to those described in Examples 1-5 were manufactured but a two-dimensional array of photodetectors was used for data acquisition. In some cases we used a CMOS camera - model DMK 72BUC02 of Imaging Source - and in others a CCD camera - model DMK 51AU02.AS of Imaging Source-. In these cases, the mask is simulated by software, integrating the light that reaches the corresponding pixels of the camera.

Example 7

Devices identical to those described in Example 2 were manufactured using a laser diode instead of an LED as the light source.

Example 8

The degree of collimation of a beam was determined using the devices for this purpose that are described in Examples 1-7. A beam of light was passed through each of the devices obtaining a Lissajous Figure. Observing in real time the graphic representation of the Lissajous Figure obtained in each case, it was determined visually whether or not the beam of light was properly collimated. If the Lissajous Figure was circular / square the beam was properly collimated.

5 Example 9.

The degree of collimation of a beam was determined using the devices for this purpose that are described in Examples 1-7. For this, the light beam was passed through the device of the invention and a Lissajous Figure was obtained. Next the data of the matrix A of the equation was obtained

(6)

which was solved by the Penrose inverse to obtain the vector z = (a, b, c)

(7)

15 then, from z were obtained the parameters R1 and R2 of the Lissajous Figure

2 -2 Rl = 2b-e '

(8)

2 -2

m = 2b + e '

and the ellipticity of the Lissajous Figure was calculated by the equation

-2 C

20 = - (9)

2b-c

Example 10

A beam of light from a light source 1 was collimated. For this purpose, the devices described in Examples 1-7 were used and included a collimation element 2. A light beam was passed through each of them. the devices

25 obtaining a Lissajous Figure. Observing in real time the graphic representation of the Lissajous Figure, it was determined visually whether or not the beam of light was properly collimated. The light source was moved relative to the collimation element 2, until the Lissajous Figure was circular / square, so that the beam was adequately collimated.

Example 11

A beam of light coming from a light source 1 was collimated using the devices

5 which are described in Examples 1-7 and include a collimation element 2. A light beam was passed through each of the devices obtaining a Lissajous Figure and the ellipticity of the Lissajous. The light source was moved with respect to the collimation element 2, and monitoring the ellipticity thereof following the same method as described in example 9,

10 until finding the minimum, that is, ~ z = 0 that corresponded to the position of optimal collimation. The experimental result obtained using the configuration of Example 1 is shown in Figure 12. The uncertainty in the distance between the light source 1 and the collimator 2 results in oz = 0.087 / -lm. The uncertainty in the

beam divergence calculated as oifgt; = D · oz / 2 · 12 = 1.4 flTad.

Claims (23)

1. Device for determining the degree of collimation of a light beam comprising:

-

a diffraction grating 3,

-

a mask 5 including N windows 4 each with a diffraction grating, the diffraction gratings of the windows 4 being out of phase with each other,

-

an array 7 of photodetectors 6 whose number is at least equal to the number N of windows,

-

one or more data processing elements 8,

where the number of windows N 2 :: 4 AND the displacement between the diffraction gratings of each window 4 is equal to 360o / N.

2.

Device according to claim 1 in which the mask 5 includes 16 windows 4.

3.

Device according to any of the preceding claims in which the windows 4 are duplicated with the same offset.

Four.

Device according to any of the preceding claims, in which the distance d between the optical axis of the light beam and the center of the window 4 is the same for all the windows 4.

5.

Device according to any one of claims 1-3 in which the windows 4 are arranged in 4 or more columns.

6.

Device according to any of the preceding claims, in which the photodetectors 6 are located in a two-dimensional distribution.

7.

Device according to claim 6 in which the two-dimensional distribution is a CMOS camera or a CCD camera.

8.

Device according to any of the preceding claims, in which the elements for data processing 8 are selected from the group consisting of: an electronic board, a microprocessor and a computer.

9.

Device for collimating a beam of light comprising:

-

a collimation element 2,

-

a diffraction grating 3,

-

a mask 5 including N windows 4 each with a diffraction grating, the diffraction gratings of the windows 4 being out of phase with each other,

-

an array 7 of photodetectors 6 whose number is at least equal to the number N of windows,

-

one or more data processing elements 8,

where the number of windows N; ::: 4. 1D. Device according to claim 9, in which the collimating element 2 is a lens, a set of lenses or a Diffractive Optical Element.

eleven.

Device according to any of claims 9-1 D in which the mask 5 includes 16 windows 4.

12.

Device according to any of claims 9-11, in which the displacement between the diffraction gratings of each window 4 is equal to 36Do / N, where N is the number of windows 4.

13.

Device according to any of claims 9-12, in which the windows 4 are duplicated with the same offset.

14.

Device according to any one of claims 9-13 in which the distance d between the optical axis of the light beam and the center of the window 4 is the same for all the windows 4.

fifteen.

Device according to any of claims 9-13, in which the windows 4 are arranged in 4 or more columns.

16.

Device according to any of claims 9-15, in which the photodetectors 6 are located in a two-dimensional distribution.

17.

Device according to claim 16 in which the two-dimensional distribution is a CMOS camera or a CCD camera.

18.

Device according to any of claims 9-17, in which the elements for data processing 8 are selected from the group consisting of: an electronic board, a microprocessor and a computer.

19.

Method to determine the degree of collimation of a light beam that includes the following steps:

a) passing the light beam through a device as defined in claims 1-8, b) get a Lissajous Figure, c) determine the degree of ellipticity of the Lissajous Figure.

twenty.

A method according to claim 19 wherein the degree of ellipticity of the Lissajous Figure is determined by visual measurement.

twenty-one.

Method according to claim 19 in which the degree of ellipticity of the Lissajous Figure is mathematically determined by adding the following steps:

d) obtain experimentally the data of matrix A of the equation 'UI VI: l: IYI 11'2 V2: 1: 2Y2

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O) (; D 'I.t! Vf V! Vf XAiYAl where z = (a, b, e) are obtained from experimental data {SA and Ss} of the signals detected by the photodetectors 6 and where UI = (xi -yi) 2, VI = (xi + yi) and so on successively, by solving the equation e) obtain the parameters R1 and R2 from the equation 2 -2 Rl = 21 ' ) -C 2 -2 R2 = 2b + c1 f) obtain the ellipticity e according to the equation 2e -2e 2 2 e = - or e = - 2b + e 2b -e selecting the ellipticity parameter, e, with a positive value. 22. Method to collimate a beam of light that includes the following steps: a) passing the light beam through a device as defined in claims 9-18, b) obtain a Lissajous Figure, c) determine the degree of ellipticity of the Lissajous Figure, d) moving the light source 1 with respect to the collimating element 2, along the optical axis, e) monitor the ellipticity parameter e from step c) f) stop the movement of light source 1 when the parameter e is minimum, taking into account that steps c) and d) are carried out simultaneously or consecutively and that the minimum value of the ellipticity is understood as the lowest possible value throughout the entire measurement.

2. 3.

Method for collimating a light beam according to claim 22, wherein step c) is performed by visual measurement.

24.

Method for collimating a light beam according to claim 22 in which step c) is carried out mathematically following the following steps:

i) obtain the data of matrix A from the equation Ul VI: r1Ul U2 112: 1: 2U2

-

U) UD, UM VM .1; MUM where z = (a, b, e) are obtained from experimental data {SA and Ss} of the signals detected by the photodetectors 6 and where U1 = (xi -yi) 2, V1 = (xi + yi) and so on successively, by solving the equation T T )-1 z = (A A A B ii) obtain the parameters R1 and R2 from the equation R2 _ -2 1 -2b -e '2 -2 R2 = 2b + e ' iii) Obtain the ellipticity e according to the equation 2 2e 2 -2e e = or e = - 2b + e 2b-e selecting the ellipticity parameter, e, with a positive value.