Optical detection technique with low SNR value through destructive interference

Abstract

At least one sample parameter of a sample (16) is measured using measuring light. The measuring light is split into sample measuring light and reference measuring light. The sample measuring light interacts with the sample (16), generating modified measuring light with a phase and / or intensity dependent on the sample parameter. The modified measuring light and the reference measuring light overlap to interfere, generating signal light, and the intensity of the signal light is measured. A tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') is determined from the intensity of the signal light and used to control a phase and / or intensity tuner (20, 32, 52, 70', 70'') to make the interference destructive and thus minimize or at least reduce the measured intensity. The sample parameter is determined based on the intensity parameter and / or the tuning parameter. This technique reduces shot noise.It can be used in a variety of applications, but a particularly preferred application is stimulated Raman scattering or NIR reflection / absorption spectroscopy.

Description

Technical area

[0001] The invention relates to a method for the optical measurement of at least one parameter of a sample and to an optoelectronic measuring device for carrying out this method. It also relates to the use of the method or device for measurements using stimulated Raman spectroscopy. background

[0002] Numerous detection methods are based on the interaction of measuring light with a sample, thereby generating modified measuring light that has a phase and / or intensity that depends on a sample parameter to be measured.

[0003] Typically, the modified measuring light is then fed to a photodetector where an intensity parameter is measured, whereby the intensity parameter depends on the sample parameter.

[0004] In one well-known application, for example, an elastic or inelastic scattering parameter is measured by sending the measurement light into the sample and receiving the scattered light as modified measurement light. In another application, the absorption of the sample is measured by sending the measurement light through the sample and measuring the transmitted modified measurement light.

[0005] In another example, the optical length of a sample is measured by passing the measurement light through the sample to generate modified measurement light, which exhibits a phase shift dependent on the optical length. The modified measurement light is caused to interfere with the reference measurement light from the same light source, allowing the measurement of its relative phase.

[0006] In another example, to measure stimulated Raman spectroscopy (SRS) or another third-order nonlinear optical effect in the sample, secondary light is sent into the sample in addition to the measurement light. The secondary light has a different wavelength than the measurement light. Depending on the interaction between the two light fields and the molecules in the sample, the intensity of the modified measurement light can vary depending on the amount of secondary light. Here, too, the modified measurement light must be measured precisely. Description of the invention

[0007] The object to be achieved by the present invention is to provide a method and a measuring device of this type which make it possible to measure the sample parameter with high accuracy.

[0008] This problem is solved by the method and device of the independent claims.

[0009] Accordingly, the method for optically measuring at least one sample parameter of a sample comprises at least the following steps: - Generating “measurement light” using a measurement light source: This is the light that is to be detected after interaction with the sample. - Splitting the measuring light into “sample measuring light” and “reference measuring light”: The sample measuring light is intended to interact with the sample, while the reference measuring light is used for interference in a later step of the procedure. - The sample measuring light is caused to interact with the sample, generating “modified measuring light”: The phase and / or intensity of the modified measuring light depends on the sample parameter to be measured. - Causing the modified measuring light to interfere with the reference measuring light at a beam combiner, thereby generating “signal light”: The signal light is the light resulting from the interference of the modified measuring light and the reference measuring light. - Measuring at least one "intensity parameter" of the signal light using at least one photodetector: The intensity parameter is a parameter that depends on the intensity (i.e. the power) of the signal light. - Determining at least one "tuning parameter" using the intensity parameter and controlling a phase and / or intensity tuner using the tuning parameter. The phase and / or intensity tuner modifies (depending on the tuning parameter) the relative phase and / or intensity of the reference measurement light and the modified measurement light interfering at the beam combiner to cause them to interfere destructively, thereby reducing the intensity parameter or even setting it to zero. In other words, the phase and / or intensity of the reference measurement light and / or the modified measurement light is varied to change the way they interfere with each other. That is, they are intended to interfere destructively, thereby reducing the intensity parameter or even setting it to zero. - Determining the sample parameter using the intensity parameter and / or the tuning parameter: In other words, the sample parameter is determined using the intensity parameter, ie using the signal measured by the photodetector, and / or the tuning parameter, ie using the magnitude of the intensity and / or phase change to achieve destructive interference.

[0010] This technique allows measurements to be performed at a photodetector operating point where the intensity parameter is small, i.e., the amount of light at the photodetector is low. Therefore, the relative proportion of shot noise (which increases with the square root of the photodetector intensity) is low, enabling measurements with a higher signal-to-noise ratio, i.e., more accurate measurements when the background is considered noise.

[0011] In an advantageous embodiment, the method comprises the following steps: - Repeatedly determining the tuning parameter at a plurality of times and minimizing the intensity parameter at this plurality of times: In other words, at this plurality of times, a completely destructive interference is produced at the photodetector by minimizing its signal. - Determine the sample parameter using the tuning parameters at the multiple time points: The tuning parameters correspond to the intensity and / or phase correction that results in completely destructive interference, i.e., the tuning parameters are essentially free of shot noise. This enables a measurement with excellent SNR.

[0012] The sample parameter can also be determined from the tuning parameter, but not from the intensity parameter. This also enables a measurement that is essentially free of shot noise.

[0013] In another embodiment, the method may comprise the following steps: a) Determining the tuning parameter and reducing the intensity parameter: In other words, the determined tuning parameter is used to control the phase and / or intensity tuner and thereby reduce the measured intensity parameter, advantageously by at least a factor of 10, in particular by at least a factor of 100, compared to the situation before the change of the tuning parameter. b) After step a), the tuning parameter is left unchanged and the intensity parameter is measured several times: Since the measurement parameter and / or the sample and thus the relative phase and / or intensity of the modified measurement light and the reference measurement light change, the intensity parameter is measured, which begins to deviate from its original value after tuning. c) Determining the sample parameter using the intensity parameters measured at the time points of step b).

[0014] This embodiment is particularly suitable for systems where the changes in intensity and / or phase over a measurement period are small, i.e., the intensity at the photodetector remains low during step b). Therefore, the shot noise will be low even if the sample parameter is determined at least partially from intensity parameters.

[0015] The measurement light can be split into sample measurement light and reference measurement light using a tunable beam splitter, i.e., a beam splitter where the intensity ratio between the sample measurement light and the reference measurement light can be varied using a control signal. In this case, the tuning parameter can be used to adjust the splitting ratio of the tunable beam splitter. This enables more efficient use of the measurement light compared to methods where part of the reference measurement light and / or part of the sample measurement light or the modified measurement light is absorbed or removed.

[0016] If the relative phase of the reference measurement light and the modified measurement light needs to be changed, a tunable phase shifter can be used. This tunable phase shifter can be placed in the path of the sample measurement light, the path of the modified measurement light, or the path of the reference measurement light. In this case, the tuning parameter can be used to adjust the phase shift of the tunable phase shifter.

[0017] In a particularly advantageous embodiment, the present method can be used to measure third-order nonlinear optical effects, such as stimulated Raman scattering (SRS), in the sample. For this purpose, the method can comprise at least the following steps: - Generating secondary light using a secondary light source: This secondary light advantageously has a different wavelength than the measurement light. It will interact with the measurement light at the sample. - Superposing the secondary light and the sample measurement light on the sample and causing the secondary measurement light and the sample measurement light to interact with the sample, thereby generating the modified measurement light with a phase and / or intensity that depends on the sample parameter as well as on the intensity of the secondary measurement light.

[0018] In this case, the intensity and / or phase of the modified measurement light typically varies slightly depending on the intensity of the secondary light. With conventional detection methods, this slight change is difficult to detect due to the shot noise generated by the DC background of the modified measurement light in the photodetector. However, with the present system, this DC background can be removed or at least greatly reduced through destructive interference between the modified measurement light and the reference measurement light.

[0019] For SRS applications, the wavenumber difference between the measuring light and the secondary light is advantageously less than 3800 cm -1 to couple to vibrational or rotational modes of typical molecules. On the other hand, the wavenumber difference in Raman scattering is advantageously at least 10 cm -1 .

[0020] The technique can also be used for Brillouin scattering measurements, where the wavenumber difference between the measuring light and the secondary light is advantageously in a range between 0.1 and 6 cm -1 .lies

[0021] As far as wavelength is concerned, the wavelengths of both the measuring light and the secondary light are advantageously located in the “biological windows” between 650 nm and 1870 nm, and they differ by at least 1 nm but not more than 200 nm.

[0022] Advantageously, the method comprises at least the following steps: - Changing the wavelength of the measuring light source or the secondary light source. - Determine the sample parameter for several different wavelengths.

[0023] In this case, in a first option, the tuning parameter(s) can be determined from the intensity parameter for each wavelength. The phase and / or intensity tuner can then be controlled using the tuning parameter to change the relative phase and / or intensity of the reference measurement light and the modified measurement light so that they interfere destructively, thereby minimizing the intensity parameter for each wavelength. The material parameter is then determined from the tuning parameter. Since all measurements correspond to a situation with fully destructive interference, the SNR is low.

[0024] Another option is to speed up the process by not performing tuning for each wavelength. In this case, the procedure includes the following steps: a) determining the tuning parameter from the intensity parameter for a first wavelength and controlling the phase and / or intensity tuner using the tuning parameter to change a relative phase and / or intensity of the reference measurement light and the modified measurement light such that they destructively interfere, thereby reducing the intensity parameter. b) After step a), the tuning parameter is left unchanged and the intensity parameter is measured for several second wavelengths. c) Determining the sample parameter at the second wavelengths using the intensity parameters measured at the second wavelengths.

[0025] Advantageously, the coherence length of the measurement light and (if used) the secondary light should be at least 10 mm, especially at least 100 mm, and can even be up to 10 km, for example. This facilitates instrument tuning, as the path lengths of the reference and measurement light do not need to match exactly. Furthermore, better contrast and more complete destructive interference are achieved, even when the components and / or the sample exhibit strong dispersion.

[0026] The invention also relates to an optoelectronic measuring device comprising at least: a measuring light source, a measuring light beam splitter connected to the measuring light source, a sample interface connected to the measuring light beam splitter, a beam combiner connected to the probe light splitter and the sample interface, a photodetector connected to the beam combiner, a phase and / or intensity tuner and a control unit suitable for carrying out the method according to one of the preceding claims.

[0027] In a particularly advantageous application, the present device or method is used for stimulated Raman spectroscopy, where the measurement at low intensities with destructive interference is particularly suitable for improving the SNR of the measurement results. Brief description of the drawings

[0028] The invention will be better understood and objects other than those set forth above will become apparent when the following detailed description of the invention is considered. This description refers to the accompanying drawings, in which: Fig. 1 shows a first embodiment of a measuring device, Fig. 2 shows a second embodiment of a measuring device, Fig. 3 shows a third embodiment of a measuring device, Fig. 4 shows a fourth embodiment of a measuring device, Fig. 5 shows a fifth embodiment of a measuring device, Fig. 6 shows a sixth embodiment of a measuring device, Fig. 7 shows an interferometrically tunable coupler, Fig. Figure 8 shows the sample parameter, the measured intensity parameter I1 and the tuning parameter t1 over a series of measurements xi in a system that attempts to keep the interference completely destructive, and Fig. Figure 9 shows the sample parameter, the measured intensity parameter I1 and the tuning parameter t1 over a series of measurements xi in a system that allows deviations from fully destructive interference. Modes for carrying out the inventionFirst embodiment

[0029] Fig. Figure 1 illustrates some general concepts of the present technique that can be applied to various embodiments. In particular, it shows a measurement device 10 that advantageously includes optoelectronic circuits on a substrate 12.

[0030] A measurement light source 14 generates measurement light to be used to measure at least one sample parameter of a sample 16. The measurement light is guided, for example, via an integrated waveguide 18 to a tunable beam splitter, the "measurement light beam splitter" 20, where it is split into sample measurement light and reference measurement light. The sample measurement light is guided, for example, via a waveguide 22, a device connection 24, and suitable imaging optics (not shown) to a sample 16.

[0031] The sample measurement light is caused to interact with sample 16. This interaction can involve a variety of mechanisms, e.g., elastic or inelastic scattering, reflection, or transmission. The following description contains more specific examples of interactions.

[0032] In the following, we assume that the interaction is elastic scattering.

[0033] The interaction of the measurement light with the sample 16 generates modified measurement light, the phase and / or intensity of which depends on a sample parameter p. In elastic scattering, for example, the absorption and scattering properties of the sample influence the phase and intensity of the modified measurement light.

[0034] The modified measurement light can be collected using suitable collection optics (not shown) and fed to a device port 26 of the device 10. From there, it propagates, for example, through a waveguide 28 to a first input of a beam combiner 30.

[0035] At the same time, the reference measuring light is guided from the measuring light beam splitter 20, e.g. through a tunable phase shifter 32 and a waveguide 34 to a second input of the beam combiner 30.

[0036] In the beam combiner 30, the reference measuring light and the modified measuring light are combined to form “signal light” and emitted, for example, through an output into a waveguide 36, from where the signal light reaches a photodetector D1, for example a photodiode.

[0037] Photodetector D1 is connected to an amplifier 38 and an ADC 40 to generate an intensity parameter I1. The intensity parameter I1 describes the intensity of the signal light, i.e., the intensity of the interfering reference measurement light and the modified measurement light at the location of photodetector D1, and is advantageously linear thereto.

[0038] Under the general assumption that the reference measuring light has the intensity I r , the modified measuring light has the intensity I m and their mutual phase shift at the photodiode D1 is Δφ, the intensity I of the interference light is given by I=Ir+Im+2Ir⋅Im⋅cos(Δφ).

[0039] Therefore, the intensity parameter generally has a DC offset given by I r + I m and oscillates with the phase shift.

[0040] If the intensities I r and I mare not equal and the phase shift is a multiple of 2π, the intensity I is generally not zero.

[0041] As is known to the person skilled in the art, a photodetector, such as a photodiode, when measuring a light intensity generates a signal which is dependent on the light intensity I and which is superimposed by the shot noise, the signal-to-noise ratio being approximately proportional to I is.

[0042] Thus, if the changes in the sample parameter p have only a weak influence on I m and Δφ, they are difficult to detect compared to the shot noise if the DC intensity I at the photodiode D1 is comparatively large.

[0043] Therefore, the device 10 comprises a control unit 42 (e.g., a digital signal processor or other computing device, e.g., a microprocessor or a computer or an analog processing circuit) capable of deriving at least one tuning parameter from the measured intensity parameter I1. This tuning parameter is used to determine the relative phase Δφ and / or the relative intensity I r : I m of the reference measurement light and the modified measurement light so that they destructively interfere at the photodiode D1, thereby minimizing the intensity parameter I1. In other words, the components of the device 10 are tuned so that I r = I m and Δφ = π / 2 + n·π, where n is a natural number.

[0044] In the embodiment of Fig. 1 it is assumed that both the relative intensity I r : I mand the relative phase Δφ are to be tuned, which will be the case in most applications.

[0045] In the embodiment shown, the relative intensity I r : I m tuned using a tunable measuring light beam splitter 20. The control unit 42 generates a first tuning parameter t1, which controls the ratio between the intensities at the two outputs of the measuring light beam splitter 20. Examples of such a tunable beam splitter are described in more detail below.

[0046] Furthermore, in the embodiment shown, the relative phase Δφ is adjusted using a tunable phase shifter 32. The phase shifter 32 may, for example, comprise a waveguide section and an electric heating element for changing the temperature of the waveguide section, thereby changing the effective refractive index of the waveguide. It may also comprise a waveguide section and electrodes for applying an electric field to the waveguide, thus changing its refractive index via the Pockels or Kerr effect. Devices of this type are known to those skilled in the art.

[0047] The control unit 42 generates a second tuning parameter t2 which controls the phase shift generated by the tunable phase shifter 32.

[0048] Advantageously, the control unit 42 implements a control loop that repeatedly measures the intensity parameter I1 and changes the tuning parameter(s) t1, t2 to minimize the value of the intensity parameter I1.

[0049] Ideally, therefore, the intensity I at the photodiode D1 is kept at zero, i.e., a completely destructive interference is maintained between the modified measuring light and the reference measuring light, thereby minimizing the shot noise generated by the photodiode D1.

[0050] The sample parameters p can then be determined from the tuning required for the relative intensity and / or phase shift, ie from the tuning parameters t1, t2

[0051] For this purpose, the device 10 advantageously has one or more output terminals 44, 46 which, for example, emit signals indicating the tuning parameter(s) t1, t2. Second embodiment

[0052] Fig. 2 again illustrates a number of general concepts of the present technique that may be applied to various embodiments.

[0053] On the one hand, the design differs in Fig. 2 of the Fig. 1 by using a single device port 24 to emit the sample measurement light from device 10 and receive the modified measurement light returning from sample 16. A beam splitter 48 is provided to separate the outgoing sample measurement light from the incoming modified measurement light.

[0054] Furthermore, the design differs from Fig. 2 of that of Fig. 1 in that the measurement light beam splitter 20 is not a tunable splitter. Rather, the splitter 20 splits the sample measurement light and the reference measurement light at a fixed intensity ratio. A tunable amplitude modulator 50, which is separate from the measurement light beam splitter 20, is provided to adjust the intensity ratio.

[0055] In the embodiment of Fig. 2, the tunable phase shifter 32 and the tunable amplitude modulator 50 are both arranged along the waveguide 34, ie, in the path of the reference measurement light. Alternatively (or additionally), one or both can also be arranged in the beam path of the sample measurement light and / or the modified measurement light, e.g., at one of the positions 52a, 52b and / or 52c in Fig. 2.

[0056] In another embodiment, a tunable phase shifter 32 and / or a tunable amplitude modulator 50 may be part of the beam combiner 30.

[0057] Furthermore, the design differs from Fig. 2 of that of Fig. 1 in that the beam combiner 30 has two complementary outputs 37a, 37b and is designed to cross-couple the two inputs 35a, 35b, causing them to interfere. Advantageously, the beam combiner 30 is designed such that the ratio between the light powers at its outputs 37a, 37b depends on the phase shift between the reference measurement light and the modified measurement light at its inputs. This ratio is 1:0 (i.e., one of the outputs carries no light, while the other output carries all light) when the ratio of the light powers at its inputs corresponds to a target ratio Rt (e.g., 1:1) and the relative phase shift of the light between its inputs is equal to a target phase shift Δp (e.g., 0°).

[0058] (The above conditions are advantageously fulfilled at least at the middle wavelength of the measuring light).

[0059] A beam combiner 30 with the above-mentioned properties can be realized, for example, by two parallel sections of waveguides of suitable length with evanescent coupling between them, as in Fig. 2 shown.

[0060] In this case, the photodetector D1 is positioned to measure the light at the output 37a, which becomes zero at the target ratio Rt and the target phase shift Δp.

[0061] As in the first embodiment, the control unit 42 is designed to adjust the tuning parameter(s) t1, t2 such that the intensity signal I1 from D1 becomes zero, ie the tuning parameter(s) t1, t2 are selected such that the input power ratio is equal to the target ratio Rt and the relative phase shift between the light at the two inputs 35a, 35b is equal to the target phase shift Δp.

[0062] In the embodiment of Fig. 2, a second photodetector D2 is provided to measure the light at the second output 37b of the combiner 30, whereby the total light output can be measured, e.g. to monitor the proper operation of the device and / or to ensure that reference measuring light is present.

[0063] In a further embodiment, the beam combiner 30 may be a tunable beam combiner, e.g., by placing a heater 54 along the two coupled waveguides, as shown in Fig. 2 with dashed lines. In this case, changing the temperature of the heating element 54 changes the beat length of the coupling between the two coupled waveguide sections of the beam combiner 30, thereby changing the relative intensities of the reference measurement light and the modified measurement light when they interfere at the outputs of the beam combiner 30. In this case, the tunable amplitude modulator 50 can be omitted.

[0064] A beam combiner 30 of this type is described, for example, by D. Perez-Löpez et al. in Optics Express Vol. 27, No. 36, pp. 38071 - 38086, https: / / doi.org / 10.1364 / OE.27.038071 and the references therein. Third embodiment

[0065] Fig. 3 again illustrates a number of general concepts of the present technique that may be applied to various embodiments.

[0066] It is assumed that the interaction with the sample 16 changes the polarization state of the modified measuring light in a way that depends on the parameter(s) of the sample to be measured.

[0067] For example, Raman scattering can change the polarization state of the measured light. Similarly, the sample may contain chiral components that are optically active and can change the polarization state of the measured light depending on their concentration.

[0068] In this case, the amplitudes and / or phases of two polarization states of the modified measuring light must be measured

[0069] In the present embodiment, beam splitters 60', 60" are provided to split the light of both the reference measurement light and the modified measurement light, wherein at least one of these beam splitters, namely the beam splitter 60" used for the modified measurement light, is a polarizing beam splitter.

[0070] In the example of Fig. 3, the 60' and 60" beam splitters both have a fixed splitting ratio.

[0071] The first beam splitter 60' splits the reference measuring light into a first reference branch 64a and a second reference branch 64b.

[0072] The two polarization states of the modified measurement light are guided as two separate modes through a waveguide 28 to the second polarizing beam splitter 60". There, they are split into a first measurement branch 68a and a second measurement branch 68b, i.e., the first measurement branch 68a guides the light of a first polarization state of the modified measurement light, while the second measurement branch guides the light of a second polarization state of the modified measurement light.

[0073] The light in the first reference branch 64a and in the first measuring branch 68a is brought to interference in a first beam combiner 30' and brought to destructive interference by means of a first phase and / or amplitude tuner 70' at a first photodetector D1'. In the embodiment of Fig. 3, the first phase and / or amplitude tuner 70' is arranged in the first reference branch 64a, but it can also be arranged, for example, in the first measuring branch 68a or at least partially integrated into the first beam combiner 30', similar to the embodiment of Fig. 2. The first phase and / or intensity tuner 70' is controlled by tuning parameters t1', t2' generated by the control unit 42.

[0074] The light in the second reference branch 64b and the second measuring branch 68b is caused to interfere in a second beam combiner 30". With the help of a second phase and / or intensity tuner 70", they are destructively interfered at a second photodetector D1". In the embodiment of Fig. 3, the second phase and / or intensity tuner 70'' is arranged in the second reference branch 64b, but it could also be arranged in the second measuring branch 68b or at least partially integrated into the second beam combiner 30'', similar to the embodiment of Fig. 2. The second phase and / or intensity tuner 70'' is controlled by the tuning parameters t1'', ​​t2'' generated by the control unit 42.

[0075] Similar to the above embodiments, the control unit 42 is then able to adjust the first tuning parameter(s) t1', t2' such that the intensity signal I1' of D1' becomes zero. Furthermore, the control unit 42 can adjust the second tuning parameter(s) t1'', ​​t2'' such that the intensity signal I1'' of D1'' becomes zero.

[0076] In this case, the tuning parameters t1', t2', t1'', ​​t2'' describe the phase and / or amplitude of the two polarization states of the modified measuring light returning from the sample 16.

[0077] The beam splitters 60' and 60'' and the beam combiners 30' and 30'' must be constructed so that the light of the two modes propagating through the waveguide 28 interferes with the respective portions of the reference probe light from the first splitter 60'.

[0078] In one embodiment, the first beam splitter 60' may be a simple splitter that couples the light into the TE0 modes of the waveguides 64a, 64b at its outputs when the reference measurement light propagates in only one mode, e.g., TE0, in the waveguide 34. If the two modes of the modified measurement light in the waveguide 28 are TE and TM modes of the waveguide, the second polarizing beam splitter 60'' is advantageously a polarization-rotating beam splitter, e.g., as described by WD Sacher et al. in Optics Express 3777, Vol. 22(4), 3777 - 3786, DOI:10.1364 / OE.22.003777, which, for example, couples the two polarization states of the modified measurement light into the TE0 modes of the waveguides 68a, 68b at its two outputs. In this case, the beam combiners 30', 30'' are designed to cause the TE0 modes to interfere at their two inputs.

[0079] Other methods for combining the different modes, e.g. using TM0 modes instead of TE0 modes, are known to those skilled in the art. Fourth embodiment

[0080] Fig. Figure 4 further illustrates a number of general concepts of the present technique that may be applied to various embodiments.

[0081] Like the third embodiment, the fourth embodiment is also suitable for measuring a change in the polarization state of the modified measurement light. In this embodiment, however, the outputs 68a, 68b of the second polarizing beam splitter 60'', which is advantageously a polarization-rotating beam splitter as described in the previous section, are caused to interfere in the second beam combiner 30'' after their relative phase shift and amplitudes have been tuned in the phase and / or amplitude tuner 70''. The second beam combiner 30'' is again a beam combiner with two complementary outputs 37a'', 37b''. As in the second embodiment, the beam combiner 30'' is constructed such that the ratio between the light powers at its outputs 37a'', 37b'' depends on the phase shift and the relative power between the light at its inputs 35a'', 35b''.For example, if the phase shift is zero and the power ratio of the light at the inputs 35a'', 35b'' is 1:1, all the light is coupled into the first output 37a'' and no light is coupled into the second output 37b''.

[0082] The control unit 42 is capable of adjusting the phase and / or amplitude tuner 70'' using the tuning parameters t1'', ​​t2'' to minimize the signal I'' of the photodetector D'' which detects the light at the second output 37b''.

[0083] This allows the determination of the relative phase and the relative powers of the two modes of the modified measurement light in the waveguide 28 using the respective tuning parameters t1'', ​​t2'', which control the phase and / or amplitude tuner 70''.

[0084] In the embodiment of Fig. 4, a phase and / or amplitude tuner 70" is provided only for one of the two modes of the modified measurement light. It is advantageously arranged to tune the mode that dominates during the measurement.

[0085] If it is impossible to predict which of the two modes will dominate, it is advantageous to have a separate amplitude tuner for each of the two modes, so that the amplitude of the stronger mode can be tuned down to that of the weaker mode. If necessary, a phase tuner can be provided to tune one of the two modes, or phase tuners can be provided for both modes.

[0086] The first output 37a'' of the second beam combiner 30'' is then fed to the first beam combiner 30', where it is caused to interfere with the reference measurement light. A phase and / or amplitude tuner 70' is also provided here to adjust the relative phase and / or amplitude of the reference measurement light and the light from the first output 37a''.

[0087] The control unit 42 is capable of adjusting the phase and / or amplitude tuner 70' using the tuning parameters t1', t2' to minimize the signal I1' of the photodetector D1', which detects the light at the first output 37a' of the first beam combiner 30'. The relative phase and the relative powers of the (interfered) modified measurement light from the output 37a'' and the reference measurement light can then be determined from the tuning parameters t1', t2'.

[0088] In the embodiment of Fig. 4, the first beam combiner 30' again has complementary outputs 37a', 37b', both coupled to the photodetectors D1', D2'. As above, only one of them is required for determining the tuning parameters t1', t2'. The other is not essential but can be used, for example, to monitor system operation. Fifth embodiment

[0089] Fig. Figure 5 shows one possibility of using the present technique to determine third-order nonlinear optical effects in sample 16, in particular to measure stimulated Raman scattering.

[0090] In the example of Fig. 5, the device 10 comprises, in addition to the measuring light source 14, a secondary light source 80. The secondary light source 80 generates light with a different central wavelength than the measuring light.

[0091] The secondary light is guided, e.g., via an integrated waveguide 82, to a beam combiner 84, where it is combined with the measurement light from the beam splitter 20. From there, the combined secondary and measurement light is sent to the sample 16 (e.g., via the beam splitter 48 if the device 10 has a single device port 24 for sending and receiving light to / from the sample 16).

[0092] At sample 16, the secondary light and the sample measurement light overlap. If third-order nonlinear optical effects occur in sample 16, energy can be transferred between the measurement light and the secondary light. Therefore, the light with the wavelength of the measurement light undergoes a change in amplitude and / or phase, at least for one polarization.

[0093] For example, if the wavelength difference between the secondary light and the measuring light corresponds to a vibrational mode of a molecular component of the sample 16, a stimulated Raman gain or loss occurs at the wavelength of the measuring light.

[0094] The modified measurement light is received by the device 10 and then processed, e.g., using the techniques described above. The only difference is that the light returning from the sample 16 typically contains not only the modified measurement light, but also a portion of the secondary light, which must be removed before processing the modified measurement light. In the embodiment of Fig. For this purpose, a bandpass or other filter 86, e.g., a low-pass or high-pass filter, is provided somewhere along the path of the modified measurement light. If a bandpass filter 86 is used, it is advantageously centered on the wavelength of the measurement light and adjusted to block the wavelength of the secondary light.

[0095] In the embodiment of Fig. 5, the techniques of the third embodiment are used to analyze the amplitude, phase, and / or polarization state of the modified measurement light. However, other similar techniques, such as those of the other previous embodiments, may also be used to determine at least some or all of these parameters. Sixth embodiment

[0096] Fig. Figure 6 illustrates some further concepts for using a device with a secondary light source 80 that may be applied to various embodiments of the present technique.

[0097] This embodiment differs from the fifth embodiment by a beam splitter 88 which sends a portion of the secondary light to a photodetector D3 for monitoring the power of the secondary light, e.g., for controlling the operating parameters of the secondary light source 80.

[0098] Furthermore, the bandpass filter 86 of the fifth embodiment is replaced by a wavelength-selective splitter 90 configured to split light at the wavelength of the secondary light onto a photodetector D4, while forwarding light at the wavelength of the measurement light to the phase and amplitude detection hardware. This enables the measurement of the amount of light at the wavelength of the secondary light returning from the sample 16, which in turn provides another means of evaluating the properties of the sample 16. Tunable couplers and beam splitters

[0099] As can be seen from the above examples, the present technology can be advantageously implemented with tunable couplers and beam splitters for tuning the reference measurement light and / or the measurement light to achieve destructive interference at the photodetector. For example, in the embodiment of Fig. 1 the beam splitter 20 is a tunable beam splitter and in the embodiment of Fig. 2, the beam combiner 30 is a tunable beam combiner.

[0100] In the Fig. the beam combiners 30, 30', 30'' have two inputs and two outputs, with the outputs being complementary (i.e. the power goes to one or the other output depending on the beam combiner settings and the relative amplitudes and phase shift of the light at its inputs).

[0101] Such a tunable beam combiner can be used to produce destructive interference at one of its outputs and a monitoring signal or light for further processing at its other output as in the example of Fig. 4. More generally, the invention therefore advantageously comprises the following steps: - Sending the reference measurement light and / or the modified measurement light to a tunable beam combiner with two inputs and two complementary outputs. Depending on the tuning, the light from the inputs is sent to one or the other output, or to both. - Minimize the intensity delivered at one of the two complementary outputs using the tuning parameters.

[0102] As already mentioned, tunable beam splitters and / or combiners can be realized, for example, by coupling two waveguide sections and by changing their coupling by means of a heater (or, for example, by an electric field and electro-optical effects).

[0103] A further advantageous embodiment of such a tunable splitter or beam combiner is described in Fig. 7. Here, two -3 dB directional couplers 92a, 92b are used to form an interferometer 94, in particular a Michelson interferometer, between them. The optical length (ie, the phase shift) of at least one of the interferometer arms 94a, 94b is tunable by means of a first tunable phase shifter 95, e.g., by a heater 96.

[0104] By tuning the first tunable phase shifter 95, the output powers at the first and second outputs 100a, 100b can be controlled, which allows this device to be used as a tunable beam splitter, e.g., as beam splitter 20 in the above embodiments, for controlling the relative powers of the sample measurement light and the reference measurement light. In this application, the measurement light from the measurement light source 14 is fed into one of the inputs 98a, 98b of the device. Fig. 7, while no signal is applied to the other input.

[0105] The device of Fig. 7 can also be used as a tunable beam combiner for analyzing the modified measurement light, e.g., as beam combiner 30, 30', 30'' in the examples above. In this case, both inputs 98a, 98b are used. If the two signals at the inputs 98a, 98b have the same phase, the phase difference between the two arms 94a, 94b alone controls the coupling of each input 98a, 98b to the first and second outputs 100a, 100b. In other words, by controlling the phase difference between the arms 98a, 98b, e.g., using the first phase shifter 95, it is possible to control how the light at the two inputs 98a, 98b is distributed to the two outputs 100a, 100b.

[0106] If there is a non-zero phase shift between the two signals at inputs 98a, 98b, interference will cause additional mixing of the signals at the two outputs. Therefore, a second tunable phase shifter 102, e.g., in the form of an additional heater 104, can advantageously be added to at least one of the inputs 98a, 98b.

[0107] By tuning the first and second phase shifters 95, 102 it is therefore possible to achieve completely destructive interference at a first output, e.g. output 100a, and to direct all the light to the second output, e.g. output 100b.

[0108] This type of tunable beam combiner can, as mentioned, be used, for example, as beam combiner 30, 30' or 30'' in the above embodiments.

[0109] For a more detailed description of the dimensioning of interferometers of this type, see Horst et al., Optics Express Vol. 21, Issue 10, pp. 11652-11658 (2013), https: / / doi.org / 10.1364 / OE.21.011652. calibration

[0110] As already mentioned, the at least one sample parameter can be determined from the tuning parameter(s).

[0111] In some applications, it is sufficient to determine the sample parameter(s) relatively or qualitatively; for example, it may be sufficient to determine a relative change in absorbance or a relative change in phase. In this case, the instrument 10 does not necessarily need to be calibrated.

[0112] For other applications, e.g., when measuring an absolute change in length or an absolute change in the absorption of sample 16, calibration of the device may be advantageous. To calibrate the device 10, a reference sample, such as a calibrated movable mirror or a calibrated adjustable absorber (e.g., a set of filters), may be used instead of sample 16. Using such a reference sample, it is possible, for example, to scale a phase tuning parameter to an absolute phase change or an amplitude tuning parameter to an absolute change in absorption. Applications

[0113] Some applications of the technology are described in more detail below. Transmission or reflection:

[0114] In one embodiment, the present technique may be used to measure linear transmission through and / or reflection from sample 16.

[0115] The sample 16 may, for example, be a gas whose refractive index and / or absorption changes slightly when a sample parameter, e.g. its composition, is changed, and the sample 16 is measured in transmission, ie the modified measuring light is the light that passes through the sample 16.

[0116] In another example, sample 16 is a mirror that specularly reflects the measurement light, and the position of the mirror changes (e.g., by fractions of a wavelength). In this case, the sample parameter to be measured can be the position of the mirror, and the modified measurement light changes its phase depending on the sample parameter.

[0117] In both of the above examples, the sample 16 does not change the polarization state of the modified measurement light depending on the sample parameters. Therefore, although all of the above-described embodiments of the device 10 would be able to successfully analyze the modified measurement light, even a device as simple as that shown in Fig. 1 can be used.

[0118] This class of measurements may also include NIR reflection / absorption spectroscopy and / or Fourier transform infrared spectroscopy (FTIR). Optical rotation:

[0119] In another embodiment, sample 16 can generate an optical rotation in the measurement light that varies with the sample parameter. For example, sample 16 can be a fluid with a chiral, optically active component, and the sample measurement light is passed through the fluid. In this case, the polarization state of the modified measurement light depends on the concentration of the optically active component, which in this case constitutes the sample parameter.

[0120] In this application, the device 10 may be equipped to determine the polarization state of the modified measurement light, e.g., using the techniques of one of the embodiments of Fig. 3 or Fig. 4. Elastic scattering:

[0121] In another embodiment, the sample 16 can elastically scatter the measurement light, and the modified measurement light is then scattered measurement light. In this case, the sample parameter can be, for example, a concentration and / or another parameter (such as particle distribution or composition) of the scattering components in the sample. The sample parameter typically influences the amplitude, phase, and polarization state of the modified measurement light.

[0122] Therefore, in this application, the techniques of, for example, one of the embodiments of Fig. 3 or Fig. 4 can be used. Dependence on wavelength:

[0123] In many applications it is advantageous to carry out measurements at different wavelengths of the measuring light.

[0124] In this case, the measurement light source 14 can be, for example, a wavelength-tunable light source, such as a wavelength-tunable laser. If a secondary light source 80 is used, the secondary light source 80 can also be a wavelength-tunable light source, e.g., a wavelength-tunable laser, in addition to or alternatively to the wavelength-tunable measurement light source 14.

[0125] This system is particularly suitable for performing measurements at different wavelengths because of its self-tuning capability. Thus, if a component, such as a beam splitter or beam combiner, has wavelength-dependent properties to some extent, destructive interference can still be achieved by retuning the system, allowing the system to be used at multiple wavelengths. Closed-loop vs. open-loop control:

[0126] There are various ways to operate the device 10 over a series of measurements.

[0127] Fig. Figure 8 shows a first closed-loop principle in which the control unit 42 adjusts the tuning parameter(s) t1, t2 ... such that the measured intensity parameter(s) is set to zero for each of a series of measurements x1 ... xN.

[0128] For simplicity, the figure shows the parameters for a system that has a single tuning parameter t1 and measures a single intensity parameter I1.

[0129] Initially, the intensity parameter I1 has not yet been optimized for reduced interference. It therefore exhibits a strong DC offset and strong shot noise, as schematically shown. At the time of the first measurement x1, the control unit 42 measures the intensity parameter I1 and then adjusts the tuning parameter t1 such that the intensity parameter I1 is set to zero. The value of the tuning parameter t1(x1) at x1 is the result of the measurement. At the time of the next measurement x2, the sample parameter has changed to some extent, so that the intensity parameter I1 deviates from zero. The control unit 42 then measures the intensity parameter I1 again and adjusts the tuning parameter t1 to bring the intensity parameter I1 to zero. t1(x2) is the result of the measurement at x2. This process is repeated for each measurement xi in a series of N > 1, in particular N > 10, measurements.

[0130] The tuning parameter t1(xi) thus follows the changes in the sample parameter, and the value of the tuning parameter (after tuning) for a particular measurement is an indication of the value of the sample parameter. In other words, the value of the sample parameter (or its change) can be determined from the tuning parameter t1.

[0131] The scheme in Fig. 8 has the advantage that the measurements after tuning do not suffer from shot noise and therefore the sample parameter can be determined with high accuracy from t1, even if it fluctuates only slightly.

[0132] Fig. Figure 9 shows a second "open-loop" principle, in which the control unit 42 does not adjust the tuning parameter(s) for each measurement xi. Rather, it adjusts the tuning parameter(s) only at specific times to generate fully or at least partially destructive interference at the photodetector(s) at specific times, and then keeps the tuning parameter(s) constant across multiple measurements.

[0133] For simplicity, the figure shows the parameters for a system that has a single tuning parameter t1 and measures a single intensity parameter I1.

[0134] Before tuning the device 10, the intensity parameter I1 has a strong DC offset and is subject to shot noise. Then, for example, at the time of the first measurement x1, the control unit 42 changes the tuning parameter t1 to reduce the intensity parameter I1, advantageously by several orders of magnitude compared to the untuned state, thereby reducing the shot noise.

[0135] Then, for several consecutive measurements x2, x3,... xk, the tuning parameter t1 is kept constant. Consequently, the intensity parameter I1 is nonzero and varies with the sample parameter. However, if the sample parameter varies only slightly, the intensity parameter I1 remains low, i.e., the shot noise remains low.

[0136] In this case, the sample parameter for a particular measurement xi can be determined from the values ​​of the tuning parameter t1 and the intensity parameter I1 at xi. If only the relative change of the sample parameter compared to the first measurement x1 is of interest, this relative change can even be determined solely from the intensity parameter I1 at x1, x2, etc.

[0137] The scheme of Fig. 8 has the advantage of requiring fewer recalculations of tuning parameters and tuning steps, which can, for example, allow for an increase in the measurement rate and / or a reduction in the system's power consumption. However, the shot noise is somewhat higher than with the closed-loop control.

[0138] At the times when the tuning parameters are recalculated in the open loop, they can be adjusted so that the intensity parameter(s) become zero. This further reduces shot noise. However, this may have the disadvantage of requiring disambiguation. For example, if the sample parameter affects the phase shift of the modified measurement light at a particular time and the tuning parameter(s) is / are adjusted so that the intensity parameter(s) becomes / becomes zero, a non-zero value of the intensity parameter(s) at the next measurement indicates that the phase shift has changed, but—without changing the tuning parameters again—the sign of the phase shift may be unknown. Likewise, simultaneous changes in phase, amplitude, and / or polarization can lead to ambiguities. Therefore, for example, in the Fig. 9, the tuning parameters are advantageously set to a value at which the intensity signal(s) is / are reduced by several orders of magnitude (to reduce shot noise), but they are not set to zero. Stimulated Raman scattering:

[0139] Stimulated Raman scattering (SRS) measurements are a particularly important application of this technique, since in classical SRS, the scattering parameters produce small relative fluctuations in the intensity of the light returning from the sample. Therefore, the signal of interest is typically masked by strong shot noise.

[0140] For SRS, both pump light and Stokes light are required. Therefore, SRS can be measured, for example, with embodiments of the present application that include a secondary light source 80 in addition to the measurement light source 14, as shown, for example, in the Fig. 5 and Fig. 6 shown.

[0141] In this case, the mean wavelengths of the measuring light and the reference measuring light should be different, as mentioned above, with the frequency difference being chosen such that rotational or vibrational modes of the molecules in the sample 16 are excited.

[0142] In one embodiment, the measurement light from measurement light source 14 corresponds to the pump light, while the secondary light from secondary light source 80 corresponds to the Stokes light. In another embodiment, the measurement light from measurement light source 14 corresponds to the Stokes light, while the secondary light from secondary light source 80 corresponds to the pump light. Because device 10 measures the phase, intensity, and (if desired) polarization of the modified measurement light, the device can measure either the gain or loss in the pump light or the Stokes light.

[0143] In order to be able to carry out spectroscopic SRS measurements, it is advantageous if at least one of the two light sources, ie the measuring light source 14 and the secondary light source 80, is a wavelength-tunable light source.

[0144] Advantageously, the central wavelength of the wavelength-tunable light source is tunable over at least 20 nm. Even more advantageous is the light source being tunable over more than 50 nm. Preferably, the light source is tunable over at least 75 nm.

[0145] The advantage is that the tunable light source can be tuned over the mentioned wavelength range without mode hopping. Some examples: A) The measurement light source 14 may have a fixed wavelength, while the secondary light source 80 may have a tunable wavelength, with the wavelength of the secondary light source 80 being longer than the wavelength of the pump light source 14. For example, the measurement light may have a fixed wavelength of 785 nm, and the secondary light source 80 may be a tunable Stokes laser with a tunable range of at least 800...900 nm. B) The measuring light source 14 may have a tunable wavelength, while the secondary light source 80 may have a fixed wavelength, wherein the wavelength of the measuring light source 14 is longer than the wavelength of the secondary light source 80. For example, the measuring light source 14 may be a tunable Stokes laser with a tunable range of at least 800...900 nm, and the secondary light may have a fixed wavelength of 785 nm.

[0146] When performing a series of measurements at multiple wavelengths, the closed-loop or open-loop control principle described in the previous section can be used.

[0147] During control, the tuning parameters t1', t2', t1'', ​​t2'' are determined from the measured intensity parameters, and the phase and / or intensity tuners 70', 70'' are controlled using the tuning parameters to generate destructive interference and set the measured intensity parameters I1', I1'' to zero.

[0148] In open-loop control, however, the tuning parameters t1', t2', t1'', ​​t2'' are determined, and destructive interference is generated during the measurement at one wavelength to bring the intensity parameter at least close to zero. Subsequently, several measurements are performed at other wavelengths without updating the tuning parameters, and the deviation of the intensity parameters I1', I1'' from zero is monitored.

[0149] As previously mentioned, an optical filter 86 and / or a wavelength-selective splitter 90 can be used to remove the secondary light from the modified measurement light before it is directed to the photodetector(s). If a wavelength-selective splitter 90 is used, a second analyzer can be provided, comprising dedicated beam splitters (corresponding to splitters 60', 60'') and beam combiners (corresponding to beam combiners 30', 30'') for generating interference between the modified secondary light returning from the sample 16 and the reference secondary light derived from the secondary light of the secondary light source 80. These components can, in turn, be tuned for destructive interference, thus enabling the measurement of the gain / loss of both the pump light and the Stokes light with high accuracy. Polarization analysis:

[0150] The embodiments of the Fig. 3 to 6 are designed to detect the change in polarization of the modified measuring light returning from sample 16.

[0151] In general, the polarization of the modified measurement light can be described by the relative amplitude and / or the relative phase of two orthogonal polarization states of the modified measurement light. These states can be, for example, two orthogonally oriented linear polarization components or the two orthogonal circular polarization components (e.g., the L and R polarization states).

[0152] The present method advantageously comprises the step of determining the relative amplitude and / or phase of two orthogonal polarization states of the modified measuring light.

[0153] In one embodiment, e.g. with the device of Fig. 3, the two polarization states of the modified measurement light are each caused to interfere with the reference measurement light, and the phases and / or amplitudes of each polarization state with respect to the reference measurement light are tuned to produce destructive interference of each polarization state with the reference measurement light by determining at least one first and one second tuning parameter t1', t2', t1'', ​​t2'' for at least two phase and / or intensity tuners.

[0154] In another embodiment, e.g. using the device of Fig. 4, the two polarization states of the modified measuring light are caused to interfere with each other, and the relative phases and / or amplitudes of the two polarization states with respect to each other are adjusted to produce a destructive interference of the polarization states with each other by determining at least one first tuning parameter t1'', ​​t2'' for a first phase and / or intensity tuner 70''. Furthermore, "detected light" (e.g., the light at the output 37a'' of Fig. 4) of one or both polarization states are also caused to interfere with the reference measurement light, and the phase and / or amplitude of the detected light with respect to the reference measurement light is / are tuned to produce destructive interference by determining at least one second tuning parameter t1', t2' for a second phase and / or intensity tuner 70'. Notes

[0155] In general, as described above, the relative phase between the reference measurement light and the modified measurement light is changed using the tuning parameter(s) to cause the reference measurement light and the modified measurement light to destructively interfere. Additionally or alternatively, the relative intensity (i.e., power) of the reference measurement light and the modified measurement light is modified using the tuning parameter(s) to cause the reference measurement light and the modified measurement light to destructively interfere.

[0156] As already mentioned, the tunable element(s) controlled by the tuning parameter(s) can be located in the path of the reference measurement light and / or in the path of the sample measurement light. In the latter case, they can be located in the beam path of the sample measurement light (i.e., before the measurement light reaches the sample) and / or in the beam path of the modified measurement light (i.e., after the measurement light has reached the sample).

[0157] The tunable element(s) may also be incorporated, at least partially, into the beam splitter that splits the sample measurement light and the reference measurement light, or into the beam combiner(s) that combine the reference measurement light and the modified measurement light.

[0158] In some of the above-mentioned embodiments, a wavelength-tunable light source is used. Such a light source can be a continuously tunable light source (such as a tunable laser or a broadband light source with a tunable filter) or, for example, an arrangement of several light sources with different central wavelengths, operated sequentially, for example.

[0159] Advantageously, the components of the device 10 are integrated on a single substrate, which enables more robust and stable operation.

[0160] While the presently preferred embodiments of the invention have been shown and described, it is to be clearly understood that the invention is not limited thereto, but may be otherwise embodied and practiced within the scope of the following claims. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] by D. Perez-Löpez et al. in Optics Express Vol. 27, No. 36, pp. 38071 - 38086, https: / / doi.org / 10.1364 / OE.27.038071

[0064] WD Sacher et al. in Optics Express 3777, Vol. 22(4), 3777 - 3786

[0078] Horst et al. referenced, Optics Express Vol. 21, Issue 10, pp. 11652-11658 (2013), https: / / doi.org / 10.1364 / OE.21.011652

[0109]

Claims

[1] A method for the optical measurement of at least one sample parameter of a sample, comprising the following steps: generating measurement light using a measurement light source (14), splitting the measurement light into sample measurement light and reference measurement light, causing the sample measurement light to interact with the sample (16), thereby generating modified measurement light with a phase and / or intensity that depends on the sample parameter, causing the modified measurement light to interfere with the reference measurement light in a beam combiner (30), thereby generating signal light, measuring at least one intensity parameter (I1, I2, I1', I2', I1'', I2'') of the signal light using at least one photodetector (D1, D2, D1', D2', D1'', D2'', D), determining a tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') using the intensity parameter (I1, I2, I1', I2', I1'', I2'') and controlling a phase and / or intensity tuner (20, 32, 52, 70',70'') by means of the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') to change a relative phase and / or intensity of the reference measuring light and the modified measuring light which interfere, in order to cause them to interfere destructively, and determining the sample parameter using the intensity parameter (I1'', I2, I1', I2', I1'', I2'') and / or the tuning parameter (t1, t2, t1', t2', t1'', ​​t2''). [2] Method according to claim 1 comprising the steps of repeatedly determining the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') at a plurality of times (xi) and minimizing the intensity parameter (I1, I2, I1', I2', I1'', I2'') at said plurality of times (xi), and determining the sampling parameter using the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') at said plurality of times. [3] A method according to any one of the preceding claims, comprising the step of determining the sample parameter using the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') but not the intensity parameter (I1, I2, I1', I2', I1'', I2''). [4] Method according to one of the preceding claims comprising the steps a) Determining the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') and reducing the intensity parameter (I1, I2, I1', I2', I1'', I2'') by destructive interference, b) after step a), leaving the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') unchanged and measuring the intensity parameter (I1'', I2, I1', I2', I1'', I2'') at several times (xi), c) Determination of the sample parameter based on the intensity parameters (I1, I2, I1', I2', I1'', I2'') measured at the different time points (xi). [5] Method according to one of the preceding claims, in which the relative phase between the reference measuring light and the modified measuring light is changed so that they interfere destructively. [6] Method according to one of the preceding claims, wherein the relative intensity of the reference measuring light and the modified measuring light is changed so that they interfere destructively. [7] Method according to one of the preceding claims, in which a tunable beam splitter (20) is used to split the measuring light into the sample measuring light and the reference measuring light, and in which the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') is used to set a splitting ratio of the tunable beam splitter (20). [8] Method according to one of the preceding claims, in which at least the measuring light, the modified light and the reference light are passed through a tunable phase shifter (32) and in which the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') is used to adjust a phase shift of the tunable phase shifter (32). [9] Method according to one of the preceding claims, comprising the steps of feeding the reference measuring light and the modified measuring light into at least one Mach-Zehnder interferometer (94) having two arms (94a, 94b) extending between directional couplers (92a, 92b) and a tunable phase shifter (95) in at least one of the arms (94a, 94b), and using the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') to tune a phase shift of the tunable phase shifter (95). [10] Method according to one of the preceding claims, comprising the steps of sending the reference measuring light and / or the modified measuring light to a tunable beam combiner (30, 30', 30'') having two inputs and two complementary outputs and minimizing an intensity value at one of the two complementary outputs using the tuning parameter (t1, t2, t1', t2', t1'', ​​t2''). [11] Method according to one of the preceding claims comprising the step of determining a relative amplitude and / or phase of two orthogonal polarization states of the modified measuring light. [12] The method of claim 11 further comprising the steps of causing each of the two polarization states of the modified measurement light to interfere with the reference measurement light, and tuning the relative phases and / or amplitudes of each polarization state with respect to the reference measurement light to produce destructive interference of each polarization state with the reference measurement light by determining at least one first and one second tuning parameter (t1', t2', t1'', ​​t2'') for at least two phase and / or intensity tuners (20, 32, 52, 70', 70''). [13] The method of claim 11 further comprising the steps of causing the two polarization states of the modified measurement light to interfere with each other, tuning the relative phases and / or amplitudes of each polarization state with respect to each other to produce destructive interference between the polarization states by determining at least one first tuning parameter (t1'', ​​t2'') for a first phase and / or intensity tuner (70''), causing the detected light obtained from at least one of the polarization states to interfere with the reference measurement light, and tuning the phase and / or amplitude of the detected light with respect to the reference measurement light to produce destructive interference by determining at least one second tuning parameter (t1', t2') for a second phase and / or intensity tuner (70'). [14] Method according to one of the preceding claims, further comprising the steps of generating secondary light by means of a secondary light source (80), wherein the secondary light has a different wavelength than the measurement light, overlapping the secondary light and the sample measurement light at the sample (16) and causing the secondary light and the sample measurement light to interact with the sample (16), whereby the modified measurement light is generated with a phase and / or intensity that depends on the sample parameter as well as on an intensity of the secondary light. [15] Method according to claim 14 comprising the steps of changing the wavelength of the measuring light source (14) and / or the secondary light source (80), and determining the sample parameters for a plurality of wavelengths. [16] Method according to claim 15, wherein, for each wavelength, the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') is determined from the intensity parameter (I1, I2, I1', I2', I1'', I2'') and the phase and / or intensity tuner (20, 32, 52, 70', 70'') is controlled by means of the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') in order to modify a relative phase and / or intensity of the reference measuring light and the modified measuring light in such a way that they interfere destructively, whereby the intensity parameter (I1, I2, I1', I2', I1'', I2'') is minimized. [17] Method according to claim 15 comprising, a) for a first wavelength, determining the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') from the intensity parameter (I1'', I2, I1', I2', I1'', I2'') and controlling the phase and / or intensity tuner (20, 32, 52, 70', 70'') with the aid of the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') in order to modify a relative phase and / or intensity of the reference measurement light and the modified measurement light in such a way that they interfere destructively, thereby reducing the intensity parameter (I1, I2, I1', I2', I1'', I2''), b) after step a), leave the tuning parameter (t1, t2, t1', t2', t1'', ​​t2'') unchanged and measure the intensity parameter (I1'', I2, I1', I2', I1'', I2'') for several second wavelengths, c) Determining the sample parameter at the second wavelengths using the intensity parameters (I1, I2, I1', I2', I1'', I2'') measured at the second wavelengths. [18] A method according to any one of claims 14 to 17 comprising the step of changing the wavelength of the secondary light source. [19] Method according to one of the preceding claims comprising the step of changing the wavelength of the measuring light source (14). [20] Method according to one of the preceding claims, wherein the coherence length of the measuring light is at least 1 mm, in particular at least 10 mm. [21] Optoelectronic measuring device comprising a measuring light source (14), a measuring light beam splitter (20) connected to the measuring light source (14), a sample interface (24, 26) connected to the measuring light beam splitter (20), a beam combiner (30, 30', 30'') connected to the measuring light beam splitter (20) and the sample interface (24, 26), a photodetector (D1, D2, D1', D2', D1'', D2'', D) connected to the beam combiner, a phase and / or intensity tuner (20, 32, 52, 70', 70'') and a control unit (42) designed to carry out the method according to one of the preceding claims. [22] Use of the method or device according to any one of the preceding claims for stimulated Raman spectroscopy measurements.

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