DE102009035578B3 - Fiber-optic surface plasmon resonance sensor for determining refractive indices of fiber-adjacent media - Google Patents

Abstract

The invention relates to a fiber optic surface plasmon resonance sensor for determining refractive indices of fiber-adjacent media according to patent 10 2008 046 320, comprising at least one optical waveguide used singlemode fiber (3), a light source (4) and a detector (5) are in the radiation and Ausstrahlungsbereich (26) of the single-mode fiber (3), wherein between fiber (3) and light source (4) / detector (5) a fiber coupler (24) or circulator (28) is spliced and wherein the Light at the light source (4) facing the input region (6) enters the fiber (3) and the fiber (3) has a the input portion (6) directed opposite end portion (7), and further functional elements
a long-period Bragg grating (9) - LPG inscribed in the core region (8) of the optical fiber (3) - for coupling the input core mode (10) into a selected cladding mode (11),
a thin cladding metal layer (13) surrounding the surface (25) of the cladding (12) of the fiber (3), at which the selected cladding mode (11) excites a surface plasmon wave (14) and which is arranged to couple the cladding mode (11) , and
wherein the remaining optical power (I _opt ) in the output core mode (15) is supplied to the detector (5) for measurement and evaluation according to a functional dependence I _opt = f (n _A , λ),
wherein the end region (7) both around the fiber cladding (12) with a ...

Description

The invention relates to a fiber optic surface plasmon resonance sensor for determining refractive indices of fiber-limiting media according to patent 10 2008 046 320.

• – ein im Kernbereich 8 der Faser 3 eingeschriebenes langperiodisches Bragg-Gitter 9 – LPG – zur Kopplung einer Eingangs-Kernmode 10 in eine ausgewählte Mantelmode 11,
• – ein kurzperiodisches Faser-Bragg-Gitter 27 – FBG – zur Reflexion der ausgangsseitigen Mantelmode,
• – eine den Mantel 12 der Singlemode-Faser 3 rundum umgebende dünne Metallschicht 13, an der die ausgewählte Mantelmode 11 eine Oberflächenplasmonenwelle 14 anregt und die zwischen dem langperiodischen Bragg-Gitter 9 und dem kurzperiodischen Faser-Bragg-Gitter 27 angeordnet ist, wobei das dem ersten langperiodischen Bragg-Gitter 9 zugeordnete kurzperiodische Faser-Bragg-Gitter 27 die Oberflächenplasmonenwellen 14 anregende Mantelmode 11 in ihrer Strahlrichtung umkehrt und die reflektierte Mantelmode 18 über das langperiodische Gitter 9 in die Ausgangs-Kernmode 15 rückkoppelt, und
• – wobei die verbleibende optische Leistung I_opt in der Ausgangs-Kernmode 15 dem Detektor 5 zur Messung und Auswertung gemäß einer funktionalen Abhängigkeit I_opt = f(n_A, λ) zugeführt wird,

In the 1 are in a reflective arrangement of a surface plasmon resonance sensor 30 a singlemode fiber used as an optical waveguide 3 , a light source 4 and a detector 5 located in the irradiation and radiation area 26 the singlemode fiber 3 being between fiber 3 and light source 4 /Detector 5 a fiber coupler 24 or circulator 28 is spliced and wherein the light is at the light source 4 facing entrance area 6 in the fiber 3 enters and the fiber 3 one in the entrance area 6 oppositely directed end region 7 and further functional elements as follows:

• - one in the core area 8th the fiber 3 inscribed long period Bragg grating 9 - LPG - for coupling an input core mode 10 in a selected coat mode 11 .
• A short-period fiber Bragg grating 27 - FBG - for reflection of the output-side cladding mode,
• - one the coat 12 the singlemode fiber 3 surrounding thin metal layer 13 at which the selected coat mode 11 a surface plasma wave 14 excites and that between the long period Bragg grating 9 and the short period fiber Bragg grating 27 is arranged, wherein the first long-period Bragg grating 9 associated short-period fiber Bragg gratings 27 the surface plasma waves 14 stimulating coat mode 11 reversed in their beam direction and the reflected cladding mode 18 over the long period grid 9 in the output core mode 15 returns, and
• - Where the remaining optical power I _opt in the output core mode 15 the detector 5 for measurement and evaluation according to a functional dependence I _opt = f (n _A , λ) is supplied,

The periods of the short-period fiber Bragg grating 27 are in the range of 100 nm to 1 μm and the periods A of the long-period Bragg grating 9 are specified in the range of 10 .mu.m to 100 .mu.m.

The coat 12 the singlemode fiber 3 surrounding thin metal layer 13 may consist of metals such as gold, silver, palladium, copper or aluminum.

The light source 4 excites the input core mode 10 on, passing through the long-period Bragg grating 9 in the stimulating coat mode 11 where the required period A of the long period Bragg grating 9 is the difference between the effective refractive index n _{LP01 of} the input core _mode 10 and the effective refractive index n _{LP0m of} the exciting cladding _mode 11 and the working wavelength λ.

The surface plasmon resonance sensor 30 according to patent 10 2008 046 320 contains a monochromatic light source 4 having such a limited spectrum that the total optical power between input core mode 10 or output core mode 15 and exciting coat fashion 11 . 18 from the long period Bragg grating 9 is coupled and the short-period fiber Bragg grating 27 the total optical power of the input core mode 10 or the stimulating coat mode 11 reflect.

The light source 4 can be a laser diode and the detector 5 can be a photodiode.

At the interface of the thin metal layer 13 to the adjacent medium 2 become surface plasma waves 14 stimulated, with the amount of power, the stimulating sheath mode 11 is removed from the working wavelength λ of the light source 4 , the effective refractive index n _{LP0m of} the exciting cladding _mode 11 and the refractive index n _{A of} the adjacent medium 2 as well as the complex permittivity ε _{M of} the metal 13 is determined.

On the thin metal layer 13 can be an intermedial layer 19 be upset.

The thin intermediate layer 19 can have a high refractive index to match the low refractive index region n _{A of} the adjacent medium 2 exhibit.

The serving as a reflector short-period fiber Bragg gratings 27 is the surface plasmon wave for the effective refractive index n _LP0m 14 stimulating coat mode 11 designed.

The problem of the reflective arrangement of the Bragg gratings used 9 . 27 within the surface plasmon resonance sensor 30 is that a lot of effort to form the fiber Bragg grating arrangements 9 . 27 within the optical fiber 3 is available.

Modern biosensors not only require high sensitivity and selectivity, but also low costs. Glass fibers used in telecommunications are suitable for such tasks because of their small size, chemical and biological compatibility and their electromagnetic tolerance.

The evaluation of surface plasmone waves represents an already used method for the selective detection of small concentrations of biochemical agents, as in the publication Homola et al .: Surface plasmon resonance sensors: review, Sensors and Actuators, B54, 1999, pp. 3-15 is described.

One problem is that the evanescent field of light guided in the fiber cladding is potentially unable to excite surface plasma waves on a thin metal layer, since the optical power normally propagates within the fiber core. If the fiber cladding is removed before metallization, obviously stability problems arise.

Multimode fibers with a core diameter greater than 1000 μm are used to maintain mechanical stability, as described in the Obando et al.: Manufacture of Robust Surface Plasmon Resonance on Optic Based Dip-Coarse, Sensors and Actuators, B100, 2004, p 439-449. Nevertheless, the required sensitivity of the sensor is only achievable by excitation with a singlemode fiber. While the core diameter of the singlemode fibers used is less than 10 microns and fails to meet the sensor stability requirements for the field, as described in the Chiu et al .: Optimum sensitivity of single-mode D-type optical fiber sensor in the intensity measurement, Sensors and Actuators, B123, 2007, pp. 1120-1124.

On the other hand, the long period Bragg grating is capable of bidirectional coupling with the selected cladding mode, as described in Othonos et al .: Fiber Bragg Gratings, Artech House Inc., 1999, pp. 142-143.

The invention is therefore based on the object of specifying a fiber optic surface plasmon resonance sensor for determining refractive indices n _{A of} fiber-adjacent media, which is designed so that the expense for its production is substantially reduced. In addition, despite the stability problems, a way should be found to bring about an improvement in stability in the region between the fiber and the medium in contact with it.

• – ein im Kernbereich der optischer Faser eingeschriebenes langperiodisches Bragg-Gitter zur Kopplung der Eingangs-Kernmode in eine ausgewählte Mantelmode,
• – eine den Mantel der Faser rundum umgebende dünne Mantelmetallschicht, an der die ausgewählte Mantelmode eine Oberflächenplasmonenwelle anregt und die zur Einkopplung der Mantelmode und zur Auskopplung der den Bereich der Mantelmetallschicht verlassenden Mantelmode angeordnet ist,

wobei die verbleibende optische Leistung I_opt in der Ausgangs-Kernmode dem Detektor zur Messung und Auswertung gemäß einer funktionalen Abhängigkeit I_opt = f(n_A, λ) zugeführt wird,
wobei gemäß dem Kennzeichenteil des Patentanspruchs 1
der Endbereich sowohl rundum um den Fasermantel mit einer Mantelmetallschicht als auch stirnendseitig mit einer Metalldünnschicht belegt ist,
wobei von der Metalldünnschicht aus für die eingekoppelte Mantelmode und im Endbereich verlaufende Mantelmode ein reflektiver Strahlengang mit einer im Endbereich reflektierten Mantelmode und einer den Endbereich verlassenden Mantelmode erzeugt wird und
wobei dasselbe langperiodische Bragg-Gitter im reflektiven Strahlengang zur Kopplung der den Endbereich verlassenden Mantelmode in eine Ausgangs-Kernmode dient, die vom Detektor registriert wird.The object is solved by the features of claims 1 and 11. The fiber optic surface plasmon resonance sensor for determining refractive indices n _{A of} fiber-adjacent media
contains according to patent 10 2008 046 3205
at least one used as an optical waveguide singlemode fiber, a light source and a detector, which are located in the irradiation and Ausstrahlungsbereich the singlemode fiber, wherein between fiber and light source / detector, a fiber coupler or circulator spliced and wherein the light at the Light source facing entrance area enters the fiber and the fiber has a the input area oppositely directed end region,
as well as further following functional units:

• A long-period Bragg grating inscribed in the core region of the optical fiber for coupling the input core mode into a selected cladding mode,
• A thin cladding metal layer surrounding the cladding of the fiber around which the selected cladding mode excites a surface plasmon wave and which is arranged to couple the cladding mode and to decouple the cladding mode leaving the cladding metal layer region,

wherein the remaining optical power I _opt in the output core mode is supplied to the detector for measurement and evaluation according to a functional dependence I _opt = f (n _A , λ),
wherein according to the characterizing part of patent claim 1
the end area is coated all around the fiber cladding with a cladding metal layer as well as at the ends with a metal thin layer,
wherein a reflective beam path with a cladding mode reflected in the end region and a cladding mode leaving the end region is produced from the metal thin layer for the coupled cladding mode and in the end cladding region, and
the same long period Bragg grating serving in the reflective beam path for coupling the cladding mode leaving the end cladding to an output core mode registered by the detector.

The cladding metal layer surrounding the surface of the fiber cladding in the end region and the metal thin layer attached to the end face may constitute a connecting unit metal layer.

An intermediate layer may be applied to the cladding metal layer surrounding the fiber.

The metallization of the end-side end face of the end region and the fiber cladding of the end region can take place in one process step.

The end-face metal thin layer may have a layer thickness of at least 50 nm.

The cladding metal layer surrounding the fiber cladding may have a length parallel to the fiber axis which is at least in the single-digit millimeter range.

The long period Bragg grating has a period A which is mechanically tunable.

The light source may be a laser diode and a photodiode may be provided as the detector.

The thin intermediate layer may have a high refractive index to match the low refractive index region n _{A of} the fiber-adjacent medium.

The intermediate layer may comprise at least one biofunctional layer for examining biotechnological processes, wherein the biofunctional layer selectively binds a surrounding biochemical substance per se and thus brings about a change in the refractive index n _{A of} the fiber-limiting medium for measurement and evaluation.

The advantages of this sensor are:
The invention may represent a novel fiber optic biosensor designed for miniaturized systems.

The sensor incorporates a long-period Fiber Bragg Grating (LPG) in the core region of a singlemode fiber to excite surface plasmon resonance waves that are sensitive to the molecular bonding process on the sensor surface.

• – ein im Kernbereich der optischen Faser eingeschriebenes langperiodisches Bragg-Gitter – LPG – zur Kopplung der Eingangs-Kernmode in eine ausgewählte Mantelmode,
• – eine die Oberfläche des Mantels der Faser rundum umgebende dünne Mantelmetallschicht, an der die ausgewählte Mantelmode eine Oberflächenplasmonenwelle anregt und die zur Einkopplung der Mantelmode angeordnet ist, und

wobei die verbleibende optische Leistung I_opt in der Ausgangs-Kernmode dem Detektor zur Messung und Auswertung gemäß einer funktionalen Abhängigkeit I_opt = f(n_A, λ) zugeführt wird,
wobei gemäß dem Kennzeichenteil des Patentanspruchs 11
die Lichtquelle mehrere Einzellichtquellen zur Einspeisung von Licht unterschiedlicher Arbeitslängenwellen λ₁, λ₂, λ₃ in den Faserkoppler und nachfolgend in die Faser aufweist, wobei am langperiodischen Bragg-Gitter mit der Gitterperiode Λ₁ aus der Eingangs-Kernmode LP₀₁(λ₁, λ₂, λ₃) die Mantelmode LP_0m(λ₁), LP_0m+i(λ₂), LP_0m+k(λ₃) entstehen,
wobei der Endbereich sowohl rundum um den Fasermantel mit einer Mantelmetallschicht als auch stirnendseitig mit einer Metalldünnschicht belegt ist,
wobei die Mantelmetallschicht des Endbereiches einen in Richtung zum langperiodischen Bragg-Gitter verlängerten Endbereich aufweist, zu dem auf dem Fasermantel aufgebrachte Metall-Bragg-Gitter mit jeweils einer zur Gitterperiode Λ₁ des langperiodischen Bragg-Gitters unterschiedlichen Gitterperiode Λ₂, Λ₃ gehören,
wobei aus dem Eingangs-Kernmode LP₀₁(λ₁, λ₂, λ₃) bei Durchlauf des langperiodischen Bragg-Gitters die wellenlängenabhängigen Mantelmode LP_0m(λ₁), LP_0m+i(λ₂), LP_0m+k(λ₃) sowie bei Durchlauf des verlängerten Endbereichs und des Endbereiches unterschiedliche wellenlängenabhängige, reflektierte Oberflächenplasmonenwellenlängen SPR(λ₁), SPR(λ₂), SPR(λ₃) entstehen, die als wellenlängenabhängige modifizierte Mantelmode LP_0m(λ₁), LP0_m+i(λ₂), LP_0m+k(λ₃) das langperiodische Bragg-Gitter reflektiv durchlaufen und nach Auskopplung in die Ausgangs-Kernmode durch eine Referenz-Messung mittels des Detektors einer wellenlängenabhängigen Auswertung zugeführt werden.A second inventive fiber-optic surface plasmon resonance sensor for determining refractive indices n _A of fiber-limiting media according to patent 10 2008 046 320 contains
a singlemode fiber used as an optical waveguide,
a light source and a detector located in the irradiation and radiation area of the singlemode fiber,
wherein a fiber coupler or circulator is spliced between the fiber and the light source / detector and wherein the light enters the fiber at the input region facing the light source and the fiber has an end region oppositely directed to the input region,
and more functional elements

• A long-period Bragg grating - LPG inscribed in the core region of the optical fiber - for coupling the input core mode into a selected cladding mode,
• A thin clad metal layer surrounding the surface of the cladding of the fiber, at which the selected cladding mode excites a surface plasmon wave and which is arranged to couple the cladding mode, and

wherein the remaining optical power I _opt in the output core mode is supplied to the detector for measurement and evaluation according to a functional dependence I _opt = f (n _A , λ),
wherein according to the characterizing part of patent claim 11
the light source has a plurality of individual light sources for feeding light of different working wavelengths λ ₁ , λ ₂ , λ ₃ into the fiber coupler and subsequently into the fiber, the long period Bragg grating having the grating period Λ ₁ from the input core mode LP ₀₁ (λ ₁ , λ ₂ , λ ₃ ), the cladding mode LP _0m (λ ₁ ), LP _{0m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) arise,
wherein the end region is coated all around the fiber cladding with a cladding metal layer as well as at the front end with a metal thin layer,
wherein the cladding metal layer of the end region has an end region which is elongated in the direction of the long-period Bragg grating, to which metal Bragg gratings applied on the fiber cladding each having a grating period Λ ₂ , Λ ₃ different from the grating period Λ _{1 of} the long-period Bragg grating,
wherein from the input core mode LP ₀₁ (λ ₁ , λ ₂ , λ ₃ ) during passage of the long-period Bragg grating, the wavelength-dependent cladding mode LP _0m (λ ₁ ), LP _{0m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) as well as when passing through the extended end region and the end region, different wavelength-dependent, reflected surface plasmone wavelengths SPR (λ ₁ ), SPR (λ ₂ ), SPR (λ ₃ ) arise, which are wavelength-dependent modified cladding modes LP _0m (λ ₁ ), LP0 _{m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) through the long-period Bragg grating and, after decoupling into the output core mode, by a reference measurement by means of the detector to a wavelength-dependent evaluation.

For the purpose of measurement and evaluation, the optical power I _opt = f (n _A , λ) is supplied to the detector according to the functional wavelength-dependent dependence.

For the wavelength-dependent evaluation, an optical spectral analyzer can be provided as the detector and / or filters associated with the wavelengths λ ₁ , λ ₂ , λ ₃ can be connected in front of the photodiode provided as the detector.

Referencing of the SPR signals can thus take place on one and the same fiber.

The fiber-adjacent medium may consist of a single component or of several components of biological or chemical material.

Partial lateral structuring of the layer structure of the cladding metal layer surrounding the cladding including the metal Bragg gratings - MBG - with different periods Λ ₂ , Λ ₃ with a length of about 10 μm-300 μm and its selective coating with biological probe molecules as an intermediate layer are trained.

The operating wavelengths λ ₂ , λ ₃ can trigger a surface plasmon wave SPR (λ ₂ ), SPR (λ ₃ ) only at the corresponding metal Bragg grating.

Further developments and advantageous embodiments of the invention are specified in further subclaims.

The invention will be explained in more detail with reference to drawings, in which:
Show it:

1 a schematic representation of a fiber optic surface plasmon resonance sensor according to patent 10 2008 046 320,

2 a schematic representation of a first optical fiber surface plasmon resonance sensor according to the invention and

3 an effective refractive index (n _eff ) working wavelength (λ) curve for a gold clad metal layer and gold metal thin layer (50 nm each) on an SiO ₂ fiber 2 , in which
3a the effective refractive index n _{eff of} the surface plasmon wave with and without additional Ta ₂ O ₅ coating and LPG parameters at different operating wavelengths λ and
3b the reflectivity of the substrate-metal interface at different operating wavelengths λ as a function of the refractive index n _{A of} a fiber-adjacent medium
show, and

4 a schematic representation of a second optical fiber surface plasmon resonance sensor according to the invention 40 for spatially resolved, simultaneous detection of various fiber-adjacent media 2 - Analytes -.

• – ein im Kernbereich 8 der optischen Faser 3 eingeschriebenes langperiodisches Bragg-Gitter 9 – LPG – zur Kopplung der Eingangs-Kernmode 10 in eine ausgewählte Mantelmode 11,
• – eine die Oberfläche 25 des Mantels 12 der Faser 3 rundum umgebende dünne Mantelmetallschicht 13, an der die ausgewählte Mantelmode 11 eine Oberflächenplasmonenwelle 14 anregt und die zur Einkopplung der Mantelmode 11 angeordnet ist,

wobei die verbleibende optische Leistung logt in der Ausgangs-Kernmode 15 dem Detektor 5 zur Messung und Auswertung gemäß einer funktionalen Abhängigkeit I_ogt = f(n_A, λ) zugeführt wird.In 2 is a first fiber optic surface plasmon resonance sensor 1 for determining refractive indices n _{A of} a surrounding medium 2 according to patent 10 2008 046 320, the
contains
a singlemode fiber used as an optical waveguide 3 .
a light source 4 and a detector 5 located in the irradiation and radiation area 26 the singlemode fiber 3 are located,
being between fiber 3 and light source 4 /Detector 5 a fiber coupler 24 or circulator is spliced and wherein the light is at the light source 4 facing entrance area 6 in the fiber 3 enters and the fiber 3 one in the entrance area 6 oppositely directed end region 7 has, and
Further following functional elements

• - one in the core area 8th the optical fiber 3 inscribed long period Bragg grating 9 - LPG - for coupling the input core mode 10 in a selected coat mode 11 .
• - one the surface 25 of the coat 12 the fiber 3 all around surrounding thin cladding metal layer 13 at which the selected coat mode 11 a surface plasma wave 14 excites and the coupling of the cladding mode 11 is arranged

wherein the remaining optical power is in the output core mode 15 the detector 5 for measurement and evaluation according to a functional dependence I _ogt = f (n _A , λ) is supplied.

According to the invention, the end region 7 both around the fiber coat 12 with a cladding metal layer 13 as well as end face with a metal thin film 17 busy,
being from the metal thin film 17 off for the coupled jacket mode 11 and in the end area 7 running coat mode 14 a reflective beam path with one in the end 7 reflected cladding mode 18 and one the end area 7 leaving coat mode 23 is generated and
the same long-period Bragg grating 9 in the reflective beam path for coupling the end region 7 leaving coat mode 23 in an output core mode 15 serves that from the detector 5 is registered.

The in the end area 7 the surface 25 of the coat 12 the fiber 3 all around surrounding cladding metal layer 13 and at the end-side end face 20 attached metal thin film 17 may be a unitary bonding metal layer 21 represent.

An intermedial layer 19 Can on the the fiber 3 all around surrounding cladding metal layer 13 be upset.

The metallization of the end-side end face 20 and the fiber coat 12 of the end area 7 can be done in one process step.

The front metal thin film 17 can be like the cladding metal layer 13 have a layer thickness of at least 50 nm.

The the fiber coat 12 all around surrounding cladding metal layer 13 can be a length parallel to the fiber axis 16 which lies in the single-digit millimeter range.

It can be a long period Bragg grating 9 be provided, whose period A is mechanically tuned.

The light source 4 can be a laser diode and the detector 5 can be a photodiode.

The thin intermedial layers 19 can have a high refractive index to match the low range of refractive index n _{A of} the fiber-limiting medium 2 exhibit.

The intermedial layer 19 can comprise at least one biofunctional layer for the investigation of biotechnological processes, wherein the biofunctional layer selectively binds to a surrounding biochemical substance and thus a change in the refractive index n _A , the Faserangrenzenden medium 2 for measurement and evaluation brought about.

In 2 is an example of the sensor 1 in one with the liquid medium 2 filled containers 22 introduced to the determined refractive index n _A the liquid medium 2 to determine. But even gaseous media can with the sensor 1 be determined, but then z. B. in a closable container.

To a sensitive sensor 1 with sufficient mechanical stability remains in 2 the sheathing on the fiber sheath 12 , A few millimeters of the fiber jacket 12 of the end area 7 the singlemode fiber 3 and the end face 20 are therefore with the metal layer 13 17 , preferably with gold or silver, occupied.

The indirect encoder is the remaining optical power I _opt that passes through the metallized fiber end 20 reflected and evaluated at a single wavelength λ.

A simple laser diode 4 and a photodiode 5 are therefore through the fiber fusion coupler 24 in the entrance area 6 with the fiber 3 connected.

The optical power I _opt is transmitted through the lossless core mode LP ₀₁ .

The end area 7 of the fiber jacket 12 the cylindrical singlemode glass fiber 3 can thus be provided with a multi-layer system of thin layers (each <100 nm). In this approx. 2 millimeter long end area 7 is excited by a single cladding mode LP _0m a lossy surface plasmon wave. The multilayer system can in the simplest case of a metal layer 13 , preferably of gold or silver, of a dielectric layer for adapting the refractive index to the liquid environment (fiber-adjacent medium 2 ) and an intermedial functional layer 19 biomolecular probes for the selective detection of a biochemical analyte. The remaining after the resonance optical power I _opt , which at the metallized end-side end face 20 is reflected, serves as an indirect measure of the sensor 1 , The evaluation is carried out by a reflection measurement by means of the laser diode 4 and the photodiode 5 passing through a fiber fusion coupler 24 with the entrance area 6 the fiber 3 spliced are connected. The optical power I _opt is lossless in the core mode LP ₀₁ to the illustrated input range 6 transfer. The long-period Bragg grating 9 there allows the bidirectional coupling between the core mode LP ₀₁ and a selected cladding mode LP _0m .

In the 3a illustrated simulations of the effective refractive index n _{eff of} the surface _plasma waves 14 show that the excitation in a wide spectral range is possible. The exemplary working wavelength on the surface plasma wave graph shows the order of excitation of the cladding mode as well as the necessary LPG period A and length L. The reflectivity of the fiber-metal interface in FIG 3b shows highest sensitivity to the fiber-contiguous refractive index n _A (ie, by the molecular bonding process near the metal surface) in the near infrared spectral region.

The simulation results presented concern the working wavelength and its influence on the sensor sensitivity and on the LPG parameters.

• – Durch die Anregung der Oberflächenplasmonen-Resonanz mit einer einzelnen Fasermode kann eine hohe Empfindlichkeit erreicht werden.
• – Durch die zylindrische Faserform arbeitet der Sensor 1 unabhängig von der Polarisation des in der Faser 3 geführten Lichts und gewährleistet so eine hohe Effizienz und Störresistenz.
• – Da die übertragene optische Leistung bei einer diskreten Arbeitswellenlänge ausgewertet werden kann, wird eine teuere und raumgreifende Auswertung durch ein Spektrometer vermieden.
• – Die reflektive Anordnung kann einen einfachen Messaufbau bewerkstelligen. Der Sensor 1 kann so direkt in das zu untersuchende faserangrenzende Medium 2 eingeführt werden, wodurch der Einsatz von mikrofluidischen Komponenten vollständig eliminiert werden kann.
• – Es wird ein Betrieb im infraroten Spektralbereich bei 1550 nm durchgeführt. Dadurch kann nicht nur eine hohe Empfindlichkeit, sondern auch die Kompatibilität zu robusten optischen Komponenten aus der Nachrichtentechnik erreicht werden.

The sensor according to the invention 1 has many advantages over existing sensors:

• By exciting surface plasmon resonance with a single fiber mode, high sensitivity can be achieved.
• - Due to the cylindrical fiber shape of the sensor works 1 regardless of the polarization of the fiber 3 guided light and thus ensures high efficiency and interference resistance.
• - Since the transmitted optical power can be evaluated at a discrete operating wavelength, an expensive and expansive evaluation by a spectrometer is avoided.
• - The reflective arrangement can accomplish a simple measurement setup. The sensor 1 can thus directly into the fiber-adjacent medium to be examined 2 introduced, whereby the use of microfluidic components can be completely eliminated.
• - It is operated in the infrared spectral range at 1550 nm. As a result, not only a high sensitivity, but also the compatibility with robust optical components from telecommunications can be achieved.

berechnet werden. Wird von einer umgebenden Brechzahl n_A, von 1,37 ausgegangen, so ergibt sich der in 3a dargestellte Verlauf der effektiven Brechzahl n_eff über der Wellenlänge λ. Die komplexe Permittivität der Goldschicht 13, 17 kann der Literatur entnommen werden.To the dependence of the sensor according to the invention 1 of the wavelength λ and the refractive index n _{A of} the fiber-limiting medium 2 as well as the necessary parameters of the long-period Bragg grating 9 to be able to estimate, a modeling was done. For simplicity, it was assumed that the surface plasma wave propagates on a flat metal layer, independently of the cladding mode. Under these conditions, the propagation constant of the surface plasmon wave according to equation (I) with

be calculated. Assuming a surrounding refractive index n _A , of 1.37, then the results in 3a illustrated course of the effective refractive index n _eff over the wavelength λ. The complex permittivity of the gold layer 13 . 17 can be taken from the literature.

In 3a the effective refractive index of the surface plasmon wave is shown with additional and without additional Ta ₂ O ₅ coating and LPG parameters at different operating wavelengths λ. The 3b shows the reflectivity of the substrate-metal interface at different operating wavelengths λ as a function of the refractive index n _{A of} the fiber-limiting medium 2 ,

It has been shown that a surface plasmon wave in a broad spectral range can be excited by a cylindrically symmetric cladding mode. At four exemplary operating wavelengths λ are the period A according to equation (II) with Λ _LPG = λ _Bragg / n _LP01 - nLP _0m (II) and the radial order of the cladding mode and the length L of the necessary long-period Bragg grating 9 listed. The calculation of these parameters took place under the greatly simplified assumption of a glass fiber 3 without metal coating. Technical data of commercially available single-mode fibers as well as the programs IFO-GRATINGS and FIBER-CAD were used. For a correct modeling of the sensor system, it becomes expedient to mathematically describe the metallized waveguide structure.

To the sensitivity of the sensor 1 In order to estimate the ratio of incident optical power and total reflected optical power (reflectivity) at the substrate-metal interface was calculated. The dependence on the refractive index n _{A of} the fiber-limiting medium 2 is in 3b represented for different operating wavelengths λ. The calculation is based on a Fresnel method and uses an approach from electrical conduction theory in which the wave impedance of the fiber-limiting medium 2 is transformed by the complex wave impedance of the metal. From the increase in the characteristic curves, the sensitivity of the sensor can be determined 1 derived, which increases with increasing wavelength. It should be noted that, especially in the highly sensitive infrared wavelength range, only high-order cladding modes are suitable for exciting a surface plasma wave. These lead only small field shares in the fiber core 8th so that a very long long period Bragg grating 9 necessary to convert all the optical power. Becomes a thin intermediate layer 19 high refractive index over the gold layer 13 applied, the effective refractive index n _{eff of} the surface plasmon wave can be _shifted to higher values, which can be excited by more favorable cladding mode. In 3a the effect of a 45 nm thin Ta ₂ O ₅ (tantalum pentoxide) is shown. Through such an intermediary layer 19 not just the length of the long-period Bragg grating 9 reduce to practicable values, it is also possible, the sensor of the invention 1 on aqueous fiber-admitting media 2 with low refractive index n _A adapt.

In 4 is a second reflectron-based surface plasmon resonance sensor according to the invention 40 shown working with a Wellenlämgem multiplex from the incident light and the spatially resolved, simultaneous detection of various fiber-adjacent media 2 - of different analytes - serves.

• – ein im Kernbereich 8 der optischen Faser 3 eingeschriebenes langperiodisches Bragg-Gitter 9 – LPG – zur Kopplung der Eingangs-Kernmode 10 in eine ausgewählte Mantelmode 11,
• – eine die Oberfläche 25 des Mantels 12 der Faser 3 rundum umgebende dünne Mantelmetallschicht 13, an der die ausgewählte Mantelmode 11 eine Oberflächenplasmonenwelle 14 anregt und die zur Einkopplung der Mantelmode 11 angeordnet ist,

wobei die verbleibende optische Leistung I_opt in der Ausgangs-Kernmode 15 dem Detektor 5 zur Messung und Auswertung gemäß einer funktionalen Abhängigkeit I_opt = f(n_A, λ) zugeführt wird.The second fiber optic surface plasmon resonance sensor 40 for determining refractive indices n _A of fiber-adjacent media 2 according to patent 10 2008 046 3205
contains
a singlemode fiber used as an optical waveguide 3 .
a light source 4 and a detector 5 located in the irradiation and radiation area 26 the singlemode fiber 3 are located,
being between fiber 3 and light source 4 /Detector 5 a fiber coupler 24 or circulator is spliced and wherein the light is at the light source 4 facing entrance area 6 in the fiber 3 enters and the fiber 3 one in the entrance area 6 oppositely directed end region 7 having,
and further following functional elements

• - one in the core area 8th the optical fiber 3 inscribed long period Bragg grating 9 - LPG - for coupling the input core mode 10 in a selected coat mode 11 .
• - one the surface 25 of the coat 12 the fiber 3 all around surrounding thin cladding metal layer 13 at which the selected coat mode 11 a surface plasma wave 14 excites and the coupling of the cladding mode 11 is arranged

wherein the remaining optical power I _opt in the output core mode 15 the detector 5 for measurement and evaluation according to a functional dependence I _opt = f (n _A , λ) is supplied.

According to the invention, the light source 4 several individual light sources 41 . 42 . 43 for feeding light of different working wavelengths λ ₁ , λ ₂ , λ ₃ into the fiber coupler 24 and subsequently into the fiber 3 on, being on the long-period Bragg grating 9 with the grating period Λ ₁ from the input core mode LP ₀₁ (λ ₁ , λ ₂ , λ ₃ ) 10 the cladding mode LP _0m (λ ₁ ), LP 0 _{m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) 11 arise
the end area 7 both around the fiber coat 12 with a cladding metal layer 13 as well as end face with a metal thin film 17 is occupied,
wherein the cladding metal layer 13 of the end area 7 one towards the long-period Bragg grating 9 extended end area 71 which, on the fiber coat 12 applied metal Bragg gratings 131 . 132 with one to the grating period Λ _{1 of} the long-period Bragg grating 9 different grating period Λ ₂ , Λ _{3 are} assigned,
wherein from the input core mode LP ₀₁ (λ ₁ , λ ₂ , λ ₃ ) during passage of the long-period Bragg grating 9 the wavelength-dependent cladding mode LP _0m (λ ₁ ), LP _{0m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) and when passing the extended end 71 and the end area 7 different wavelength-dependent, reflected surface plasmone wavelengths SPR (λ ₁ ), SPR (λ ₂ ), SPR (λ ₃ ) are obtained, which are wavelength-dependent modified cladding modes LP _0m (λ ₁ ), LP _{0m + i} (λ ₂ ), LP _{0m + k} ( λ ₃ ) the long-period Bragg grating 9 traversing reflective and after extraction into the output core mode 15 by a reference measurement by means of the detector 5 be supplied to a wavelength-dependent evaluation.

The detector 5 For measurement and evaluation, the optical power I _opt = f (n _A , λ) is supplied according to the functional wavelength-dependent dependence.

For wavelength-dependent evaluation can as a detector 5 an optical spectrum analyzer provided and / or wavelength-assigned filters before as a detector 5 be provided provided photodiode.

Thus, the surface plasmon resonance signals are referenced to one and the same fiber 3 ,

This represents a major advantage in terms of the connected measuring electronics and evaluation electronics and the minimum required sample volume of the fiber-limiting medium 2 , Since in this case can be dispensed with a second reference fiber is, wherein the medium 2 can now consist of a single component or of several components biological or chemical material.

The wavelength multiplexing can be several individual light sources 41 . 42 . 43 be used with different working wavelengths λ ₁ , λ ₂ , λ ₃ .

It is necessary for this that a partial lateral structuring of the layer structure of the cladding metal layer surrounding the fiber cladding 12 all around 13 . 131 . 132 including the metal Bragg grating - MBG - 131 . 132 with different periods Λ ₂ , Λ ₃ with a length of about 10 μm-300 μm and its selective coating with biological probe molecules as an intermediate layer 19 . 191 . 192 are formed.

In this case, the operating wavelengths λ ₂ , λ ₃ only at the corresponding metal Bragg grating 131 . 132 each trigger a surface plasmon wave SPR (λ ₁ ), SPR (λ ₂ ), SPR (λ ₃ ).

Thus, various biological probe molecules as multiple components a place, for. B. a liquid mixture in a container 22 , and thus assigned to a wavelength.

The functionality is explained below:
Through the long-period Bragg grating 9 become multiple cladding modes LP _0m (λ ₁ ), LP _{0 (m + i)} (λ ₂ ) i = ± 1, 2, 3 ..., LP _{0 (m + k)} (λ ₃ ) k = ± 1, 2 , 3 ... excited at different wavelengths λ ₁ , λ ₂ , λ ₃ . Since these differing propagation constants n _eff according to the changed equations (II) λ _1,2,3 = Λ ₁ · (n _LP01 - n _LP0m1,2,3 ) (II) and converted n _LP0m1,2,3 = n _LP01 - (λ _1,2,3 / Λ ₁ ) (II) With n _LP0m1 = n _SPW (λ ₁ ), n _LP0m2 ≠ n _SPW (λ ₂ ) and n _LP0m3 ≠ n _SPW (λ ₃ ) only one of the λ operating wavelengths can have an SPR (λ ₁ ) on the restructured cladding metal layer 13 . 131 . 132 be stimulated.

Due to the partial Bragg grating structuring of the cladding metal layer 131 . 132 It is possible to adapt the other cladding mode propagation constants n _eff - with SPR (λ ₂ ) at the MBG 131 with the period Λ ₂ and with SPR (λ ₃ ) at the MBG 132 reach with the period Λ ₃ .

LIST OF REFERENCE NUMBERS

1

first surface plasmon resonance sensor

2

fiber-adjacent medium

3

fiber

4

light source

41

first single light source

42

second single light source

43

third single light source

5

detector

6

entrance area

7

end

71

extended end area

8th

core area

9

long-period Bragg grating - LPG -

10

Input core mode

11

entering first coat mode

12

fiber cladding

13

Coat metal layer

131

first structured cladding metal layer

132

second structured cladding metal layer

14

Surface Plasmon Wave - SPW -

15

Output core mode

16

fiber axis

17

metal thin film

18

reflected surface plasma wave

19

intermedial layer

191

first structured intermediate layer

192

second structured intermediate layer

20

end face

21

Unit metal layer

22

container

23

modified second cladding mode

24

fiber coupler

25

Surface of the jacket

26

Radiation and radiation area

27

Fiber Bragg Grating - FBG -

28

circulator

29

residual core mode

30

Surface plasmon resonance sensor according to patent 10 2008 046 320

40

second surface plasmon resonance sensor

n _A

 Refractive index of the fiber-adjacent medium

n _eff

effective refractive index

 Λ

Grating period of the Bragg gratings

 λ

Working wavelength of the light sources

I _opt

optical performance

SPR (λ)

Surface plasmon wave

LP ₀₁ (λ)

core mode

LP _0m (λ)

Coat Fashion

Claims (18)

Fiber optic surface plasmon resonance sensor ( 1 ) for determining refractive indices (n _A ) of fiber-adjacent media ( 2 ) according to patent 10 2008 046 320, comprising at least one singlemode fiber used as an optical waveguide ( 3 ), a light source ( 4 ) and a detector ( 5 ) located in the irradiation and radiation area ( 26 ) of the singlemode fiber ( 3 ), whereby between fiber ( 3 ) and light source ( 4 ) / Detector ( 5 ) a fiber coupler ( 24 ) or circulator ( 28 ) and wherein the light is at the light source ( 4 ) facing entrance area ( 6 ) in the fiber ( 3 ) and the fiber ( 3 ) one the entrance area ( 6 ) oppositely directed end region ( 7 ), and further following functional elements - one in the core area ( 8th ) of the optical fiber ( 3 ) inscribed long period Bragg grating ( 9 ) - LPG - for coupling the input core mode ( 10 ) in a selected cladding mode ( 11 ), - a surface ( 25 ) of the jacket ( 12 ) of the fiber ( 3 ) all around surrounding thin cladding metal layer ( 13 ) at which the selected jacket mode ( 11 ) a surface plasmon wave ( 14 ) and for coupling the cladding mode ( 11 ), and wherein the remaining optical power (I _opt ) in the output core mode ( 15 ) the detector ( 5 ) is supplied for measurement and evaluation according to a functional dependence I _opt = f (n _A , λ), characterized in that the end region ( 7 ) all around the fiber cladding ( 12 ) with a cladding metal layer ( 13 ) as well as end-face with a metal thin film ( 17 ), wherein of the metal thin layer ( 17 ) for the coupled jacket mode ( 11 ) and in the end area ( 7 ) running jacket mode ( 14 ) a reflective beam path with one in the end region ( 7 ) reflected cladding mode ( 18 ) and one the end area ( 7 ) leaving jacket mode ( 23 ) and wherein the same long period Bragg grating ( 9 ) in the reflective beam path for coupling the end region ( 7 ) leaving jacket mode ( 23 ) into an output core mode ( 15 ) served by the detector ( 5 ) is registered. Surface plasmon resonance sensor according to claim 1, characterized in that in the end region ( 7 ) the surface ( 25 ) of the jacket ( 12 ) of the fiber ( 3 ) surrounding the surrounding metal layer ( 13 ) and at the end face ( 20 ) attached metal thin film ( 17 ) a connecting unit metal layer ( 21 ). Surface plasmon resonance sensor according to claim 1 or 2, characterized in that an intermediate layer ( 19 ) on which the fiber ( 3 ) surrounding cladding metal layer ( 13 ) is applied. Surface plasmon resonance sensor according to claim 2, characterized in that the metallization of the end face ( 20 ) and the fiber jacket ( 12 ) of the end region ( 7 ) takes place in one process step. Surface plasmon resonance sensor according to claim 1, characterized in that the front-end metal thin layer ( 17 ) and the cladding metal layer ( 13 ) has a layer thickness of at least 50 nm. Surface plasmon resonance sensor according to claim 1, characterized in that the fiber cladding ( 12 ) surrounding the surrounding metal layer ( 13 ) a length parallel to the fiber axis ( 16 ), which is at least in the single-digit millimeter range. Surface plasmon resonance sensor according to claim 1, characterized in that a long-period Bragg grating ( 9 ) is provided, whose period (A) is mechanically tunable. Surface plasmon resonance sensor according to claim 1, characterized in that the light source ( 4 ) a laser diode and the detector ( 5 ) are a photodiode. Surface plasmon resonance sensor according to claim 3, characterized in that the thin intermediate layers ( 19 ) has a high refractive index for adaptation to the low refractive index range (n _A ) of the fiber-limiting medium ( 2 ) having. Surface plasmon resonance sensor according to claim 9, characterized in that the intermediate layers ( 19 ) has at least one biofunctional layer for the investigation of biotechnological processes, wherein the biofunctional layer selectively binds a surrounding biochemical substance and thus a change in the refractive index (n _A ) of the fiber-limiting medium ( 2 ) for measurement and evaluation. Fiber optic surface plasmon resonance sensor ( 40 ) for determining refractive indices (n _A ) of fiber-adjacent media ( 2 ) according to patent 10 2008 046 320, containing a singlemode fiber used as an optical waveguide ( 3 ), a light source ( 4 ) and a detector ( 5 ) located in the irradiation and radiation area ( 26 ) of the singlemode fiber ( 3 ), whereby between fiber ( 3 ) and light source ( 4 ) / Detector ( 5 ) a fiber coupler ( 24 ) or circulator is spliced and wherein the light at the light source ( 4 ) facing entrance area ( 6 ) in the fiber ( 3 ) and the fiber ( 3 ) one the entrance area ( 6 ) oppositely directed end region ( 7 ), and further following functional elements - one in the core area ( 8th ) of the optical fiber ( 3 ) inscribed long period Bragg grating ( 9 ) - LPG - for coupling the input core mode ( 10 ) in a selected cladding mode ( 11 ), - a surface ( 25 ) of the jacket ( 12 ) of the fiber ( 3 ) all around surrounding thin cladding metal layer ( 13 ) at which the selected jacket mode ( 11 ) a surface plasmon wave ( 14 ) and for coupling the cladding mode ( 11 ), and wherein the remaining optical power (I _opt ) in the output core mode ( 15 ) the detector ( 5 ) is supplied for measurement and evaluation according to a functional dependence I _opt = f (n _A , λ), characterized in that the light source ( 4 ) several individual light sources ( 41 . 42 . 43 ) for feeding light of different working wavelengths (λ ₁ , λ ₂ , λ ₃ ) into the fiber coupler ( 24 ) and subsequently into the fiber ( 3 ), wherein on the long-period Bragg grating ( 9 ) with the grating period (Λ ₁ ) from the input core mode LP ₀₁ (λ ₁ , λ ₂ , λ ₃ ) ( 10 ) the cladding mode LP _0m (λ ₁ ), LP _{0m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) ( 11 ), the end region ( 7 ) all around the fiber cladding ( 12 ) with a cladding metal layer ( 13 ) as well as end-face with a metal thin film ( 17 ), wherein the cladding metal layer ( 13 ) of the end region ( 7 ) one towards the long-period Bragg grating ( 9 ) extended end region ( 71 ), to which on the fiber cladding ( 12 ) applied metal Bragg gratings ( 131 . 132 ) with one each to the grating period (Λ ₁ ) of the long-period Bragg grating ( 9 ) Of different grating period (Λ ₂ Λ ₃₎ include, wherein (from the input core mode LP ₀₁ (λ _1, λ _2, λ ₃₎ for passage of the long-period Bragg grating 9 ) the wavelength-dependent cladding mode LP _0m (λ ₁ ), LP _{0m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) and when passing the extended end region ( 71 ) and the end area ( 7 ), different wavelength-dependent, reflected surface plasma wavelengths SPR (λ ₁ ), SPR (λ ₂ ), SPR (λ ₃ ) arise, which are wavelength-dependent modified cladding modes LP _0m (λ ₁ ), LP _{0m + i} (λ ₂ ), LP _{0m + k} (λ ₃ ) the long-period Bragg grating ( 9 ) and after coupling into the output core mode ( 15 ) by a reference measurement by means of the detector ( 5 ) are supplied to a wavelength-dependent evaluation. Surface plasmon resonance sensor according to claim 11, characterized in that a referencing of surface plasmon resonance signals on one and the same fiber ( 3 ) he follows. Surface plasmon resonance sensor according to claim 11 or 12, characterized in that the fiber-adjacent medium ( 2 ) consists of a single component or of several components of biological or chemical material. Surface plasmon resonance sensor according to one of claims 11 to 13, characterized in that a partial lateral structuring of the layer structure of the fiber cladding ( 12 ) surrounding cladding metal layer ( 13 . 131 . 132 ) including metal Bragg gratings - MBG - ( 131 . 132 ) with different periods (Λ ₂ , Λ ₃ ) with a length of about 10 μm-300 μm and its selective coating with biological probe molecules as an intermediate layer ( 19 . 191 . 192 ) are formed. Surface plasmon resonance sensor according to one of claims 11 to 14, characterized in that the operating wavelengths (λ ₂ , λ ₃ ) only at the corresponding metal Bragg grating ( 131 . 132 ) each trigger a surface plasmon wave SPR (λ ₂ ), SPR (λ ₃ ). Surface plasmon resonance sensor according to one of the preceding claims, characterized in that, depending on the sensor used ( 1 . 40 ) the end region ( 7 ) and / or the extended one End area ( 71 ) of the fiber jacket ( 12 ) of the cylindrical singlemode fiber ( 3 ) are provided with a multilayer system of thin layers, wherein the multilayer system consists of a metal layer ( 13 ) and / or at least one metal Bragg grating ( 131 . 132 ) and out to the metal layer ( 13 ) and the metal Bragg grating ( 131 . 132 ) corresponding dielectric layer for matching the refractive index to the fiber-adjacent medium ( 2 ) and a correspondingly assigned intermedial, functional layer ( 19 . 191 . 192 ) biomolecular probes for the selective detection of at least one biochemical analyte in the fiber-limiting medium ( 2 ). Surface plasmon resonance sensor according to claim 16, characterized in that the multi-layer system has a layer thickness of less than 500 nm. Surface plasmon resonance sensor according to one of claims 11 to 17, characterized in that for the wavelength-dependent evaluation as a detector ( 5 ) an optical spectrum analyzer is provided and / or wavelength-assigned filters in front of the detector ( 5 ) provided photodiode are connected.

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