DE102017104379A1 - OPTOELECTRONIC PARTICLE SENSOR - Google Patents

Abstract

An optoelectronic particle sensor comprises a first emitter, a detector and a dielectric body, wherein a metal layer is arranged above a surface of the dielectric body. The electromagnetic radiation emitted by the first emitter can be introduced into the dielectric body. When an excitation condition is present, surface plasmons can be excited in the metal layer. The electromagnetic radiation emerging from the dielectric body can strike the detector. Particles can accumulate on the metal layer, the excitation condition being dependent on particles deposited on the metal layer. The intensity measured at the detector is dependent on the presence of the excitation condition.

Description

The present invention relates to an optoelectronic particle sensor according to the independent claim.

From the state of the art optoelectronic smoke detection devices are known in which electromagnetic radiation can be scattered and deflected directly to be detected particles.

The object of the present invention is to provide an optoelectronic particle sensor.

This object is achieved by an optoelectronic particle sensor with the features of claim 1. In the dependent claims various developments are given.

An optoelectronic particle sensor according to the invention comprises a first emitter and a detector, wherein the emitter is designed to emit electromagnetic radiation, while the detector is designed to detect electromagnetic radiation. Furthermore, the optoelectronic particle sensor comprises a dielectric body, wherein a metal layer is arranged above a surface of the dielectric body. The electromagnetic radiation emitted by the first emitter can be introduced into the dielectric body. When an excitation condition is present, surface plasmons can be excited in the metal layer. The electromagnetic radiation emerging from the dielectric body can strike the detector. Particles can accumulate on the metal layer, the excitation condition being dependent on particles deposited on the metal layer. The intensity measured at the detector is dependent on the presence of the excitation condition.

Advantageously, an optoelectronic particle sensor, which is based on the excitation of surface plasmons in a metal layer, is particularly sensitive to refractive index changes in the environment of the metal layer and thus to particles attached to the metal layer. Thus, the adsorption of particles can be detected efficiently.

In one embodiment, the excitation of surface plasmons may be by total reflection.

Advantageously, an optoelectronic particle sensor, which is based on the fact that surface plasmons can be excited by total reflection, is particularly simple in design and inexpensive to implement.

In one embodiment of the optoelectronic particle sensor, the dielectric body is a prism with a trapezoidal base surface, over whose oblique side surfaces a metal layer is arranged in each case.

Advantageously, in this embodiment, the first emitter and the detector can be arranged close to each other, so that an optoelectronic particle sensor can be realized in a compact manner and easily integrated into other electrical devices.

In one embodiment, the dielectric body is a waveguide, wherein the excitation of surface plasmons can be done by coupling waveguide modes to surface plasmon modes.

Advantageously, this variant of the optoelectronic particle sensor is particularly space-saving, since the waveguide may be, for example, a thin layer waveguide or a fiber.

In one embodiment, the coupling and / or decoupling of the electromagnetic radiation takes place in the waveguide or from the waveguide by Stirnflächen-, grid or prism coupling.

Advantageously, the electromagnetic radiation can be particularly easily coupled by these methods of coupling in the waveguide and decoupled from the waveguide. In the case of a thin layer waveguide, in particular, the grating coupling offers the possibility of efficiently coupling electromagnetic radiation into the waveguide. On the other hand, the face coupling makes it possible to construct a relatively flat and compact optoelectronic particle sensor, since there is a linear structure of the first emitter, waveguide and detector.

In one embodiment, a further dielectric layer is disposed between the dielectric body and the metal layer.

Advantageously, this results in a particularly favorable coupling situation, since the penetration depth of a surface plasmon is greater for a dielectric layer than for a metal layer. Thus, the overlap of the exponentially decaying, evanescent fields of the surface plasmons and the electromagnetic waves can be increased.

In one embodiment, the interface between the dielectric body and the metal layer forms a periodic lattice. The excitation of surface plasmons can be done by diffracting the electromagnetic radiation at the periodic lattice.

Advantageously, the excitation condition for surface plasmons can be fulfilled particularly easily. For example, with a fixed angle of incidence and a fixed wavelength of the electromagnetic radiation, the presence of the excitation condition can be achieved by adjusting the lattice constant of the periodic grating. Alternatively, the periodic grating may be rotated to find a position for which the excitation condition is met.

In one embodiment, the first emitter is a laser chip, in particular a VCSEL.

A VCSEL (Vertical Cavity Surface-Emitting Laser) is a semiconductor laser chip that emits electromagnetic radiation perpendicular to its surface. Advantageously, a VCSEL emits electromagnetic radiation (eg, visible light) out of a small area and in a directional manner. Unwanted light which is radiated into a larger solid angle can thus be suppressed efficiently. This makes it possible that more power can be deposited in the detection area. Crosstalk with the detector is also avoided by the directed emission. A VCSEL is further characterized by low production costs and low power consumption.

In one embodiment, the optoelectronic particle sensor has a second emitter, wherein the second emitter is designed to emit electromagnetic radiation. The electromagnetic radiation emitted by the second emitter lies in a different spectral range than the electromagnetic radiation emitted by the first emitter.

Advantageously, the use of a second emitter extends the spectral working range of the optoelectronic particle sensor.

In one embodiment, the detector has at least one photodiode.

Advantageously, an optoelectronic particle sensor equipped with photodiodes is compact and inexpensive. In addition, the spectral sensitivity of a photodiode to the wavelength of the first emitter emitted electromagnetic radiation can be adjusted.

In one embodiment, a first filter and a second filter are disposed above the detector. The first filter is designed to transmit only the electromagnetic radiation emitted by the first emitter. The second filter is designed to transmit only the electromagnetic radiation emitted by the second emitter.

Arranging filters over the detector offers the advantage that electromagnetic radiation having a different wavelength than the electromagnetic radiation emitted by the emitters can be efficiently filtered. Thus, the influence of ambient light can be suppressed. This improves the signal-to-noise ratio of the data read out at the detector.

In one embodiment, the optoelectronic particle sensor is a smoke detection device.

Advantageously, a smoke detection device can help to detect a fire, so that measures can be taken to combat the fire or to protect people in the vicinity of the fire.

• 1: eine Seitenansicht eines optoelektronischen Partikelsensors mit einem Prisma als dielektrischer Körper, wobei das Prisma eine dreieckige Grundfläche aufweist;
• 2: eine Seitenansicht einer Ausführungsform, wobei der dielektrische Körper ein Prisma mit trapezförmiger Grundfläche ist;
• 3: eine Seitenansicht einer Ausführungsform mit einem Wellenleiter als dielektrischer Körper;
• 4: eine Oberfläche des dielektrischen Körpers, über der eine weitere dielektrische Schicht und eine Metallschicht angeordnet sind;
• 5: die Grenzfläche zwischen dielektrischem Körper und Metallschicht, die ein periodisches Gitter bildet.

The above-described characteristics, features, and advantages of this invention, as well as the manner in which they are achieved, will be clearer and more clearly understood in connection with the following description of the embodiments, which will be described in connection with the drawings. Shown schematically in each case:

• 1 FIG. 2: a side view of an optoelectronic particle sensor with a prism as a dielectric body, the prism having a triangular base area; FIG.
• 2 FIG. 2 is a side view of an embodiment wherein the dielectric body is a prism with a trapezoidal base; FIG.
• 3 FIG. 2 is a side view of an embodiment having a waveguide as the dielectric body; FIG.
• 4 a surface of the dielectric body over which another dielectric layer and a metal layer are disposed;
• 5 : the interface between the dielectric body and the metal layer forming a periodic lattice.

1 shows a schematic of an optoelectronic particle sensor 100 with a prism 400 as a dielectric body 300. The prism 400 has a triangular base 430 on.

The optoelectronic particle sensor 100 also has a first emitter 200 and a detector 210 on.

The first emitter 200 has a top 201 and a bottom 202 on. The first emitter 200 is trained electromagnetic radiation 220 (for example, visible light). The first emitter 200 For example, a VCSEL (Vertical Cavity Surface-Emitting Laser) may be the electromagnetic radiation 220 at its top 201 sending out.

The first emitter 200 can also be another laser diode. For example, the first emitter 200 be an edge emitter. The first emitter 200 but can also be a light emitting diode. Also conceivable is the use of a polychromatic light source.

The prism 400 has a base surface 420 and two side surfaces 410 on. The base area 420 and the side surfaces 410 are in terms of footprint 430 arranged vertically. The first emitter 200 is opposite one of the side surfaces 410 of the prism 400 arranged. The first emitter 200 emitted electromagnetic radiation 220 can through this side surface 410 in the prism 400 enter and at its base surface 420 be totally reflected. It can also be an optical element between the first emitter 200 and the side surface 410 of the prism 400 be arranged to be from the first emitter 200 emitted electromagnetic radiation 220 to collimate.

Above the base area 420 of the prism 400 is a metal layer 320 arranged. An evanescent field of the electromagnetic radiation 220 present as a result of the total reflection may be present in the metal layer 320 Excite surface plasmons when an excitation condition is met. The excitation of surface plasmons in the metal layer 320 depends on the angle of incidence and the wavelength of the first emitter 200 emitted electromagnetic radiation 220 from. At fixed wavelength so an excitation angle can be adjusted. At a fixed angle of incidence, an excitation wavelength can be selected. In addition, the presence of the excitation condition of the refractive index is the vicinity of the metal layer 320 dependent.

The detector 210 has a top 211 and a bottom 212. The detector 210 is opposite the other side surface 410 of the prism 400 arranged. The detector 210 is trained electromagnetic radiation 220 at its top 211 to detect. The detector 210 may for example have at least one photodiode.

The at the detector 210 measured intensity is dependent on the presence of the excitation condition for surface plasmons. As a result of excitation of surface plasmons becomes a part of the electromagnetic energy of the incident electromagnetic radiation 220 absorbed. This no longer reduces the total incident intensity of the electromagnetic radiation 220 totally reflected. Thus, less intensity gets to the detector 210 ,

The excitation condition for surface plasmons is strongly dependent on the environment of the metal layer 320 , A change in the refractive index near the evanescent field of a surface plasmon through the metal layer 320 Anlagernde particles modified the excitation condition, so that a shift of the excitation angle or the excitation wavelength takes place.

Thus, there are two possibilities, the attachment of particles to the metal layer 320 to detect. First, the angle of incidence and the wavelength of the electromagnetic radiation 220 be chosen such that the excitation condition without on the metal layer 320 Accumulated particles is exactly met. In this case, as a result of the adsorption of particles on the metal layer 320 an increase in intensity at the detector 210 because there is no excitation of surface plasmons, so that the total intensity at the base surface 420 of the prism 400 is totally reflected.

Conversely, the angle of incidence and the wavelength of the electromagnetic radiation 220 be chosen such that initially the excitation condition is just not fulfilled. An addition of particles then leads to the fact that the excitation condition is fulfilled. This will be part of the energy of the incident electromagnetic radiation 220 used for the excitation of surface plasmons, so that a decrease in the intensity at the detector 210 can be observed.

Above the detector 210 is a first filter 700 arranged. The first filter 700 is designed to only those from the first emitter 200 emitted electromagnetic radiation 220 to transmit. The first filter 700 For example, it may be an interference filter. The first filter 700 is meant to be the detector 210 to protect from ambient light. The first filter 700 but can also be omitted. Especially when as the first emitter 200 a laser diode is used, the first filter 700 omitted, since a laser diode monochromatic electromagnetic radiation 220 emits and the spectral sensitivity of the detector 210 to the wavelength of the first emitter 200 emitted electromagnetic radiation 220 can be adjusted.

2 shows a schematic representation of the side view of another embodiment of the optoelectronic particle sensor 100 ,

In this embodiment, the prism 400 a trapezoidal base 430 on. Next to the base area 420 and the side surfaces 410 has the trapezoidal prism 400 another, the base area 420 opposite and parallel to this surface. Another difference to in 1 shown embodiment, in which the metal layer 320 above the base area 420 of the prism 400 is arranged, that in the variant in 2 over both side surfaces 410 of the prism 400 one metal layer each 320 is arranged.

In this embodiment, the first emitter 200 and the detector 210 opposite the base area 420 of the prism 400 arranged side by side. The first emitter 200 emitted electromagnetic radiation 220 can through the base area 420 of the prism 400 in the prism 400 arrive at the first emitter 200 facing side surface 410 of the prism 400 be totally reflected, propagate through the prism, at the detector 210 facing side surface 410 of the prism 400 be totally reflected again and finally through the base area 420 of the prism 400 back from the prism 400 exit and to the detector 210 reach.

Again, the excitation condition for surface plasmons may initially be either satisfied or not, so with the attachment of particles to the metal layers 320 the one from the detector 210 increases or decreases measured intensity.

In this embodiment, the first emitter 200 and the detector 210 be arranged very close to each other, which is the implementation of a compact optoelectronic particle sensor 100 favored. Due to the double total reflection on the side surfaces 410 of the prism 400 and the concomitant excitation of surface plasmons in the presence of an excitation condition, the sensitivity of the optoelectronic particle sensor 100 improved.

3 shows an embodiment of the optoelectronic particle sensor 100 wherein the dielectric body 300 a waveguide 500 is. With a waveguide 500 In this case, a medium is referred to, in which the electromagnetic radiation 200 is guided as a traveling wave. The waveguide 500 has a surface 310 and two opposing faces 520 on. The waveguide 500 may be, for example, a layer waveguide. The waveguide 500 but it can also be a fiber. The metal layer 320 is above the surface 310 of the waveguide 500 arranged.

In this embodiment, the excitation of surface plasmons can be achieved by coupling a waveguide mode 510 done on a surface plasmon mode. The waveguide mode 510 is in 3 schematically indicated by the profile of a single mode.

In the case of excitation of surface plasmons in the metal layer 320 There is an energy dissipation, so that only a part of the first emitter 200 emitted intensity at the detector 210 reached.

Also in this embodiment, the excitation condition for surface plasmons is highly dependent on the environment of the metal layer 320 , A change in the refractive index near the evanescent field of a surface plasmon through the metal layer 320 Anlagernde particles modifies the excitation condition, so that a shift of the excitation wavelength takes place.

Thus, there are two possibilities, the attachment of particles to the metal layer 320 to detect. First, the wavelength of the electromagnetic radiation 220 be chosen such that the excitation condition is met exactly. In this case would be due to the adsorption of particles on the metal layer 320 an increase in intensity at the detector 210 since there is no excitation of surface plasmons, so a guided electromagnetic wave without energy dissipation through the waveguide 500 propagated.

Conversely, the wavelength of the electromagnetic radiation 220 be chosen such that initially the excitation condition is just not fulfilled. An accumulation of particles would lead to the excitation condition being fulfilled. In this case, part of the energy of the electromagnetic wave would be used for the excitation of surface plasmons, so that a decrease in the intensity at the detector 210 would be observed.

In the in 3 Example shown are first emitter 200 and detector 210 each opposite the end faces 520 of the waveguide 500 arranged so that the coupling and decoupling of the electromagnetic radiation 220 in the waveguide 500 or from the waveguide 500 done by face coupling. In this case, additional optical components could be in front of the faces 520 of the waveguide 500 be arranged. For example, an optical element could be that from the first emitter 200 emitted electromagnetic radiation 220 on a face 520 bundle up.

The coupling of the electromagnetic radiation 220 in the waveguide 500 but can also be done by prism or grating coupling. In this case, the electromagnetic radiation 220 is not at the end faces 520 of the waveguide 500 irradiated. The first emitter 200 would be opposite the surface 310 of the waveguide 500 arranged such that from the first emitter 200 emitted electromagnetic radiation 220 slanted on the surface 310 of the waveguide 500 would meet. In this case, a prism or grid would be above the surface 310 of the waveguide 500 and in the beam path of the first emitter 200 arranged.

A coupling of the electromagnetic radiation 220 in the waveguide 500 occurs when the axial component of the wave vector of the incident electromagnetic radiation 220 the wave vector of a guided waveguide mode 510 equivalent. In the case of prism coupling, at a sufficiently small and appropriate distance between waveguides 500 and prism the evanescent field of the incident and at one the waveguide 500 zugwandten surface of the prism totally reflected electromagnetic radiation 220 a waveguide mode 510 in the waveguide 500 stimulate.

The modification and adaptation of the wave vector of the incident electromagnetic radiation 220 can also be done by diffraction on an optical grating, instead of the prism on the surface 310 of the waveguide 500 can be arranged.

The decoupling of the electromagnetic radiation 220 from the waveguide 500 can be done in an analogous manner either by Stirnflächen-, prism or grating coupling. This also requires the detector 210 not necessarily opposite a face 520 of the waveguide 500 be arranged like this in 3 is shown. Like the first emitter 200 can the detector 210 opposite the surface 310 of the waveguide 500 be arranged so that with the aid of a prism or a grid decoupled electromagnetic radiation 220 obliquely in relation to the surface 310 of the waveguide 500 laterally out of the waveguide 500 exit and onto the detector 210 would meet.

It is also possible that surface plasmons share some of their energy in the form of electromagnetic radiation 220 emit again. This electromagnetic radiation 220 can also serve to adsorb particles on the metal layer 320 to detect. For this purpose, the detector 210 be arranged such that the re-emitted by the surface plasmons electromagnetic radiation 220 can be detected.

4 shows an embodiment in which between the surface 310 of the dielectric body 300 and the metal layer 320 another dielectric layer 600 is arranged.

In this variant of the optoelectronic particle sensor 100, the dielectric body 300 both a prism 400 as well as a waveguide 500 be. The prism 400 can be either triangular or trapezoidal 420 have, so that in the 1 and 2 shown configurations of the optoelectronic particle sensor 100 possible are.

This embodiment is referred to as Otto configuration and may have the advantage of more efficient excitation of surface plasmons over the so-called Kretschmann configuration where the metal layer 320 directly on the surface 310 of the dielectric body 300 is arranged to provide. The further dielectric layer 600 but not necessarily above the surface 310 of the dielectric body 300 be arranged. The metal layer 320 may also be at a distance from the surface 310 of the dielectric body 300 be arranged. This would create a gap between the surface 310 and the metal layer 320 exist, so in this case air as the further dielectric layer 600 would act.

5 shows an embodiment in which the interface 330 between dielectric body 300 and the metal layer 320 forms a periodic lattice.

In this embodiment, the excitation of surface plasmons by diffraction of the electromagnetic radiation 220 done on the periodic grid.

In the example shown, the excitation of surface plasmons occurs in reflection. Here are the first emitter 200 and the detector 210 each opposite to the dielectric body 300 arranged. It would also be conceivable that the excitation takes place in transmission. In this case, the first emitter would be 200 the dielectric body 300 arranged opposite. The detector 210 would be opposite the metal layer 320 arranged. To a transmission of electromagnetic radiation 220 ensure the metal layer through the substrate 320 be constructed as a non-continuous layer. For example, the metal layer 320 have periodic stripes on the surface 310 of the dielectric body 300 are arranged.

By a shift of the excitation wavelength for surface plasmons due to the metal layer 320 attached particles, the excitation wavelength is then no longer in the spectral range of the first emitter 200 emitted electromagnetic radiation 220 ,

Around the spectral working range of the opto-electronic Parikelsensors 100 can expand, the optoelectronic particle sensor 100 a second emitter 250 exhibit. The second emitter 250 is also designed to electromagnetic radiation 220 send out. The second emitter 250 emitted electromagnetic radiation 220 lies in a different spectral range than that of the first emitter 200 emitted electromagnetic radiation 220 ,

The second emitter 250 is right next to the first emitter 200 arranged. The second emitter 250 For example, it may be a laser diode, in particular a VCSEL. The second emitter 250 but can also be a light emitting diode. The second emitter 250 but can also be omitted. Especially if the first emitter 200 is a white light source, the second emitter 250 omitted.

Indicates the optoelectronic particle sensor 100 a second emitter 250 on, so can a second filter 750 above the detector 210 be arranged. The second filter 750 is formed, only the second emitter 250 emitted electromagnetic radiation 220 to transmit. The second filter 750 For example, it may be an interference filter. The second filter 750 but can also be omitted. Especially when as the second emitter 250 a laser diode is used, the second filter 750 omitted, since a laser diode monochromatic electromagnetic radiation 220 which can be distinguished from the ambient light.

The optoelectronic particle sensor 100 may be, for example, a smoke detector. This would include smoke or soot particles attached to the metal layer 320 attach, modify the excitation condition for Oberflächenplasmonen. This would be a modification of the detector 210 accompanied by measured intensity.

The optoelectronic particle sensor according to the invention 100 In addition, it can also allow quantitative statements about airborne particles. This could be made possible by the fact that at the detector 210 measured intensity also depends on the layer thickness of deposited particles. For this mode would be the first emitter 220 a white light source can be used to measure the displacement of the excitation wavelength with increasing layer thickness.

Due to its compactness, the optoelectronic particle sensor can 100 also be integrated into electrical devices. For example, the optoelectronic particle sensor 100 could be integrated into a mobile phone. This could be the optoelectronic particle sensor 100 act as a mobile smoke detector.

The present invention has been further illustrated and described with reference to the preferred embodiments. Nevertheless, the invention is not limited to the disclosed examples. Rather, other variations may be deduced therefrom by those skilled in the art without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

100

optoelectronic particle sensor

200

first emitter

201

Top of the first emitter

202

Bottom of the first emitter

210

detector

211

Top of the detector

212

Bottom of the detector

220

electromagnetic radiation

250

second emitter

300

dielectric body

310

Surface of the dielectric body

320

metal layer

330

Interface between dielectric body and metal layer

400

prism

410

Side surfaces of the prism

420

Base surface of the prism

430

Base of the prism

500

waveguides

510

Waveguide mode

520

End faces of the waveguide

600

another dielectric layer

700

first filter

750

second filter

Claims (12)

An optoelectronic particle sensor (100) having a first emitter (200) configured to emit electromagnetic radiation (220), a detector (210) configured to detect electromagnetic radiation (220) and a dielectric body (300), wherein over a surface (310) of the dielectric body (300) a metal layer (320) is arranged, the electrodes of the electromagnetic emitter (220) can be introduced into the dielectric body (300) and excite surface plasmons in the metal layer (320) when an excitation condition exists, with electromagnetic radiation (220) emerging from the dielectric body (300). can encounter the detector (210), whereby particles can deposit on the metal layer (320), the excitation condition being dependent on particles deposited on the metal layer (320), the intensity measured at the detector (210) being dependent on the presence of the Excitation condition is dependent. Optoelectronic particle sensor (100) according to Claim 1 , where the excitation of surface plasmons can be done by total reflection. Optoelectronic particle sensor (100) according to Claim 2 in which the dielectric body (300) is a prism (400) with a trapezoidal base (430), over whose oblique side surfaces (410) a respective metal layer (320) is arranged. Optoelectronic particle sensor (100) according to Claim 1 wherein the dielectric body (300) is a waveguide (500), wherein the excitation of surface plasmons can be done by coupling waveguide modes to surface plasmon modes. Optoelectronic particle sensor (100) according to Claim 4 , Wherein the coupling and / or decoupling of the electromagnetic radiation (220) in the waveguide (500) and from the waveguide (500) by Stirnflächen-, grid or prism coupling takes place. An optoelectronic particle sensor (100) according to one of the preceding claims, wherein a further dielectric layer (600) is arranged between the dielectric body (300) and the metal layer (320). Optoelectronic particle sensor (100) according to Claim 1 wherein the interface (330) between the dielectric body (300) and the metal layer (320) forms a periodic lattice, wherein the excitation of surface plasmons may be by diffraction at the periodic lattice. Optoelectronic particle sensor (100) according to one of the preceding claims, wherein the first emitter (200) is a laser chip, in particular a VCSEL. Optoelectronic particle sensor (100) according to one of the preceding claims, having a second emitter (250), wherein the second emitter (250) is designed to emit electromagnetic radiation (220), wherein the electromagnetic radiation (220) emitted by the second emitter (250) is in a different spectral range than the electromagnetic emitter (220) emitted by the first emitter (200). Optoelectronic particle sensor (100) according to Claim 9 wherein a first filter (700) and a second filter (750) are disposed over the detector (210), wherein the first filter (700) is adapted to transmit only the electromagnetic radiation (220) emitted by the first emitter (200) wherein the second filter (750) is adapted to transmit only the electromagnetic radiation (220) emitted by the second emitter (250). Optoelectronic particle sensor (100) according to one of the preceding claims, wherein the detector (210) comprises at least one photodiode. An optoelectronic particle sensor (100) according to the preceding claims, wherein the optoelectronic particle sensor (100) is a smoke detection device.

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