Low SNR optical detection technique using destructive interference

Abstract

At least one sample parameter of the sample (16) is measured using a probe light. The probe light is split into a sample probe light and a reference probe light. The sample probe light interacts with the sample (16) to generate a modulated probe light having a phase and / or intensity that corresponds to the sample parameter. The modulated probe light and the reference probe light are superimposed and interfere to generate a signal light, the intensity of which is measured. Tuning parameters (t1, t2, t1', t2', t1", t2") are determined from the intensity of the signal light and used to control the phase and / or intensity tuners (20, 32, 52, 70', 70") to destructively interfere and minimize or at least reduce the measured intensity. The sample parameter is determined using the intensity parameter and / or the tuning parameters. This technique reduces shot noise. While this technique can be used in a variety of applications, a particularly preferred application is stimulated Raman scattering or NIR reflection / absorption spectroscopy.

Description

[Technical Field]

[0001] The present invention relates to a method for optically measuring at least one parameter of a sample, as well as to an optoelectronic measuring device for carrying out the method. The present invention also relates to the use of the method or device for stimulated Raman spectroscopy measurements. [Background technology]

[0002] Many detection methods are based on interacting a sample probe light with a sample, thereby producing a modulated probe light having a phase and / or intensity that depends on the sample parameter being measured.

[0003] Typically, the modulated probe light is then fed to a photodetector, where an intensity parameter is measured, which depends on the sample parameter.

[0004] For example, in one known application, elastic or inelastic scattering parameters are measured by sending a sample probe light into the sample and receiving the scattered light as modulated probe light, while in another application, sample absorption is measured by passing a sample probe light through the sample and measuring the transmitted modulated probe light.

[0005] In another example, to measure the optical length of a sample, a sample probe light is passed through the sample to generate a modulated probe light with a phase shift that depends on the optical length. The modulated probe light is interfered with a reference probe light from the same source, thereby allowing measurement of the relative phase of the modulated probe light.

[0006] In another example, secondary light is sent to a sample in addition to the sample probe light to measure stimulated Raman spectroscopy (SRS) or another third-order nonlinear optical effect in the sample. The secondary light has a different wavelength than the probe light. Depending on the interaction between the two light fields and the molecules in the probe, the intensity of the modulated probe light may vary as a function of the amount of secondary light. Similarly, the modulated probe light needs to be precisely measured. Summary of the Invention

[0007] The problem that the invention aims to solve is to provide a method and a measuring device of this kind, which allows measuring sample parameters with high precision.

[0008] This problem is solved by a method and an apparatus according to the independent claims.

[0009] Thus, a method for optically measuring at least one sample parameter of a sample comprises at least the following steps. - Producing "probe light" by a probe light source, which is detected after interacting with the sample. - Splitting the probe light into a "sample probe light" and a "reference probe light", where the sample probe light interacts with the sample and the reference probe light is used for interference in a later step of the method. - Interacting a sample probe light with the sample, thereby generating a "modulated probe light," the phase and / or intensity of which depend on the sample parameter being measured. - interfering the modulated probe light with the reference probe light in a beam combiner, thereby generating "signal light." The signal light is light that results from the interference between the modulated probe light and the reference probe light. - measuring at least one "intensity parameter" of the signal light by means of at least one photodetector, the intensity parameter being a parameter that depends on the intensity (ie power) of the signal light; - using the intensity parameter to derive at least one "adjustment parameter" and controlling a phase and / or intensity tuner with the adjustment parameter. The phase and / or intensity tuner changes the relative phase and / or relative intensity of the reference probe light and modulated probe light interfering at the beam combiner (as a function of the adjustment parameter) to cause the reference probe light and the modulated probe light to destructively interfere, thereby reducing or zeroing the intensity parameter. In other words, the phase and / or intensity of the reference probe light and / or the modulated probe light is changed to change how the reference probe light and the modulated probe light interfere with each other, i.e., cause the reference probe light and the modulated probe light to destructively interfere, thereby reducing or zeroing the intensity parameter. - Deriving sample parameters using the intensity parameters and / or the adjustment parameters, in other words, the sample parameters are derived by using the intensity parameters (i.e., the signals measured by the photodetectors) and / or by using the adjustment parameters (i.e., the amount of change in intensity and / or phase to achieve destructive interference).

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

[0011] In an advantageous embodiment, the method comprises the following steps: - iteratively deriving the adjustment parameters at multiple times and minimizing an intensity parameter at the multiple times, in other words, minimizing the signal at the multiple times to establish perfect destructive interference at the photodetector. - deriving sample parameters using the adjustment parameters at said multiple times, where the adjustment parameters correspond to intensity and / or phase corrections that result in perfect destructive interference, i.e., the adjustment parameters are substantially shot noise-free, thereby allowing for a measurement with excellent SNR.

[0012] The sample parameters may be derived using the tuning parameters rather than the intensity parameters. As above, this allows measurements to be made that are substantially shot noise free.

[0013] In another embodiment, the method may include the following steps. a) deriving an adjustment parameter and reducing the intensity parameter, in other words using the derived adjustment parameter to control a phase and / or intensity tuner, thereby reducing the measured intensity parameter preferably by a factor of at least 10, in particular by a factor of at least 100, compared to the situation before changing the adjustment parameter. b) after step a), keeping the adjustment parameters unchanged and measuring the intensity parameter at multiple times, the intensity parameter being measured to start to deviate from its original value after adjustment as the measurement parameters and / or probe and thus the relative phase and / or relative intensity of the modulated probe light and the reference probe light change. c) deriving sample parameters using the intensity parameters measured at step b).

[0014] This embodiment is particularly suitable for systems where the intensity and / or phase changes over the measurement period are small, i.e., where the intensity at the photodetector remains small during step b), and therefore the shot noise is similarly small even when the sample parameters are determined at least in part from the intensity parameters.

[0015] Splitting the probe light into the sample probe light and the reference probe light may be performed in a variable beam splitter, i.e., a beam splitter that can change the intensity ratio between the sample probe light and the reference probe light using a control signal. In this case, an adjustment parameter can be used to adjust the splitting ratio of the variable beam splitter. This allows for more efficient use of the probe light compared to methods in which part of the reference probe light and / or part of the sample probe light or modulated probe light is absorbed or removed.

[0016] If the relative phase of the reference and modulated probe lights needs to be changed, a variable phase shifter can be used. The variable phase shifter can be placed in the optical path of the sample probe light, the optical path of the modulated probe light, or the optical path of the reference probe light. In this case, the adjustment parameter can be used to adjust the phase delay of the variable phase shifter.

[0017] In a particularly advantageous embodiment, the method can be used to measure third-order nonlinear optical effects such as stimulated Raman scattering (SRS) in the probe. To measure these optical effects, the method can further comprise at least the following steps: - generating secondary light by means of a secondary light source, which secondary light advantageously has a different wavelength than the probe light, which interacts with the probe light in the sample; - superimposing the secondary light and the sample probe light at the sample and allowing the secondary probe light and the sample probe light to interact with the sample, thereby generating modulated probe light having a phase and / or intensity that depends on the sample parameter and the intensity of the secondary probe light.

[0018] In this case, the intensity and / or phase of the modulated probe light typically changes slightly as a function of the intensity of the secondary light. Conventional detection schemes have difficulty detecting these small fluctuations due to shot noise caused by the DC background of the modulated probe light in the photodetector. However, in our scheme, this DC background can be eliminated or at least significantly reduced by destructive interference between the modulated probe light and the reference probe light.

[0019] For SRS applications, the wavenumber difference between the probe light and the secondary light is advantageously 3800 cm to couple to typical molecular vibrational or rotational modes. -1 On the other hand, the wave number difference is preferably at least 10 cm for Raman scattering. -1 is.

[0020] This technique can also be used for Brillouin scattering measurements, in which the wavenumber difference between the probe light and the secondary light is advantageously less than 0.1 cm -1 ~6cm -1 is within the range.

[0021] In terms of wavelength, the wavelengths of the probe light and secondary light are preferably within the "biological window" between 650 nm and 1870 nm, and the wavelengths of the probe light and secondary light differ by more than 1 nm and less than 200 nm.

[0022] Advantageously, the method comprises at least the following steps: - Changing the wavelength of the probe light source or the secondary light source. - Determining sample parameters for a plurality of different wavelengths.

[0023] In this case, in a first option, tuning parameters can be determined from the intensity parameters at each wavelength. The tuning parameters are then used to control a phase and / or intensity tuner to change the relative phase and / or relative intensity of the reference and modulated probe lights, causing destructive interference between the reference and modulated probe lights, thereby minimizing the intensity parameters at each wavelength. Material parameters are then derived from the tuning parameters. The SNR is low because all measurements correspond to a situation where all measurements are completely destructive interference.

[0024] Another option is to speed up the procedure, since the adjustment is not performed for all wavelengths. In this case, the method comprises the following steps: a) for a first wavelength, deriving an adjustment parameter from the intensity parameter and controlling a phase and / or intensity tuner with the adjustment parameter to change the relative phase and / or relative intensity of the reference probe light and the modulated probe light, thereby causing destructive interference between the reference probe light and the modulated probe light, thereby reducing the intensity parameter; b) after step a), keeping the tuning parameters unchanged and measuring the intensity parameters at a plurality of second wavelengths. c) deriving a sample parameter at the second wavelength using the intensity parameter measured at the second wavelength.

[0025] Advantageously, the coherence length of the probe light, and of the secondary light (if used), should be at least 10 mm, in particular at least 100 mm, and may be, for example, up to 10 km. This facilitates adjustment of the device, since the optical path lengths of the reference and probe light do not need to be perfectly matched. Furthermore, this allows for better contrast and more complete destructive interference, even when the components and / or probes exhibit strong dispersion.

[0026] The present invention also provides a method for manufacturing a semiconductor device comprising: a probe light source; a probe light splitter connected to the probe light source; a sample interface connected to the probe optical splitter; a beam combiner connected to the probe optical splitter and the sample interface; a photodetector connected to the beam combiner; a phase and / or intensity tuner; a control unit configured to carry out the method according to any one of the preceding claims; The present invention relates to an optoelectronic measuring device comprising:

[0027] The device or method of the invention is particularly advantageously used in stimulated Raman spectroscopy, where low intensity measurements under destructive interference are particularly suitable for improving the SNR of the measurement results.

[0028] The invention will be better understood, and further objects thereof will become apparent, from a consideration of the following detailed description, which is made with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0029] [Figure 1] 1 shows a first embodiment of a measuring device. [Figure 2] 2 shows a second embodiment of the measuring device. [Figure 3] 3 shows a third embodiment of the measuring device. [Figure 4] 4 shows a fourth embodiment of the measuring device. [Figure 5] 5 shows a fifth embodiment of the measuring device. [Figure 6] 10 shows a sixth embodiment of the measuring device. [Figure 7] 1 shows an interferometric variable coupler. [Figure 8] Shown are the sample parameters, the measurement intensity parameter I1, and the adjustment parameter t1 over a series of measurements xi in a system that attempts to maintain perfect destructive interference. [Figure 9]1 shows the sample parameters, the measurement intensity parameter I1, and the adjustment parameter t1 over a series of measurements xi in a system that allows deviation from perfect destructive interference. DETAILED DESCRIPTION OF THE INVENTION

[0030] First Embodiment 1 illustrates some general concepts of the present technology that can be applied to various embodiments of the technology. In particular, FIG. 1 illustrates a measurement device 10 that advantageously comprises optoelectronic circuitry on a substrate 12.

[0031] Probe light source 14 generates probe light that is used to measure at least one sample parameter of sample 16. The probe light is transmitted, for example, by integrated waveguide 18, to a tunable splitter, "probe light splitter" 20, where it is split into sample and reference probe light. The sample probe light is transmitted to sample 16, for example, by waveguide 22, device terminal 24, and appropriate imaging optics (not shown).

[0032] The sample probe light is configured to interact with the sample 16. This interaction may involve a variety of mechanisms, such as elastic scattering, inelastic scattering, reflection, or transmission. The following discussion provides more specific examples of interactions.

[0033] In the following, as an example, we will assume that the interaction is elastic scattering. The interaction of the sample probe light with the sample 16 produces a modified probe light whose phase and / or intensity depend on the sample parameter p. For example, in the case of elastic scattering, the absorption and scattering properties of the sample affect the phase and intensity of the modulated probe light.

[0034] The modulated probe light may be collected by suitable collection optics (not shown) and fed to device terminal 26 of device 10. From device terminal 26, the modulated probe light propagates, for example, through a waveguide 28 to a first input port of beam combiner 30.

[0035] At the same time, the reference probe light from the probe light splitter 20 is sent to a second input port of the beam combiner 30 , for example, through a variable phase shifter 32 and a waveguide 34 .

[0036] In the beam combiner 30, the reference probe light and the modulated probe light are combined into a "signal light" that is emitted, for example, through an output port into a waveguide 36. From the waveguide 36, the signal light reaches a photodetector D1, such as a photodiode.

[0037] The photodetector D1 is connected to an amplifier 38 and an ADC 40 to generate an intensity parameter I1, which advantageously linearly describes the intensity of the signal light, i.e., the intensity of the interference of the reference probe light and the modulated probe light, at the position of the photodetector D1.

[0038] Generally, the intensity of the reference probe light is expressed as I r , the intensity of the modulated probe light is I m Assuming that the mutual phase shift between the two in the photodiode D1 is Δφ, the intensity I of the interference light is expressed by the following equation.

[0039]

number

[0040] Therefore, in general, the intensity parameter is I r +I m It has a DC offset represented by

[0041] In general, intensity I r and intensity I mIf θ is equal and the phase shift is not a multiple of 2π, the intensity I will not be zero.

[0042] As known to those skilled in the art, when measuring light intensity, a photodetector such as a photodiode generates a signal corresponding to the light intensity I superimposed with shot noise, and the signal-to-noise ratio is approximately JPEG2025540784000003.jpg1214 is proportional to.

[0043] Therefore, the change in the sample parameter p is I m If the influence on Δφ and Δφ is weak, the relatively large DC intensity I at photodiode D1 makes changes in the sample parameter p difficult to detect relative to shot noise.

[0044] Therefore, the apparatus 10 comprises a control unit 42 (e.g., a digital signal processor or some other computational means such as a microprocessor, computer, analog processing circuitry, etc.) adapted to derive at least one adjustment parameter from the measured intensity parameter I1. This adjustment parameter can be used to adjust the relative phase Δφ and / or the relative intensity I of the reference and modulated probe light. r :I m and cause their probe lights to destructively interfere with photodiode D1 to minimize intensity parameter I1. In other words, the components of device 10 adjust I r =I m and is adjusted to set Δφ=π / 2+n·π (n is a natural number).

[0045] In the embodiment of FIG. 1, the relative intensity I r :I m It is assumed that both the θ and the relative phase Δφ are adjusted, which is the case in most applications.

[0046] In the illustrated embodiment, the relative intensity I r :I mis adjusted by using a variable probe light splitter 20. Control unit 42 generates a first adjustment parameter t1 that controls the intensity ratio at the two outputs of probe light splitter 20. Examples of such adjustable splitters are described in more detail below.

[0047] Furthermore, in the illustrated embodiment, the relative phase Δφ is adjusted by a variable phase shifter 32. The phase shifter 32 may, for example, comprise a section of a waveguide and an electric heater for changing the temperature of the section of the waveguide, thereby changing the effective refractive index of the waveguide. Alternatively, the phase shifter 32 may comprise a section of a waveguide and a section of an electrode for applying an electric field to the waveguide, thereby changing its refractive index via the Pockels effect or the Kerr effect. Such devices are known to those skilled in the art.

[0048] The control unit 42 generates a second adjustment parameter t 2 that controls the phase shift produced by the variable phase shifter 32 .

[0049] Advantageously, the control unit 42 implements a control loop that repeatedly measures the intensity parameter I1 and modifies the adjustment parameters t1, t2 so as to minimize the value of the intensity parameter I1.

[0050] Therefore, ideally, the intensity I at photodiode D1 is kept at 0, i.e., perfect destructive interference between the modulated and reference probe lights is maintained, thereby minimizing the shot noise generated by photodiode D1.

[0051] The sample parameter p can then be determined from the amount of adjustment required for the relative intensity and / or phase shift, ie, from the adjustment parameters t1, t2.

[0052] For this purpose, the device 10 advantageously comprises one or more output terminals 44, 46 for transmitting signals representative of the adjustment parameters t1, t2, for example.

[0053] <Second embodiment> FIG. 2 again illustrates various general concepts of the present technology that may be applied in various embodiments of the technology. 2 differs from the embodiment of FIG. 1 in that a single device terminal 24 is used to emit sample probe light from device 10 and to receive modulated probe light returning from sample 16. A splitter 48 is provided to separate the outgoing sample probe light from the incoming modulated probe light.

[0054] 2 differs from the embodiment of FIG. 1 in that probe beam splitter 20 is not a variable splitter. Rather, splitter 20 splits the sample probe beam and the reference probe beam at a fixed intensity ratio. To adjust the intensity ratio, a tunable amplitude modulator 50 separate from probe beam splitter 20 is provided.

[0055] 2, the variable phase shifter 32 and the variable amplitude modulator 50 are both positioned along the waveguide 34, i.e., in the optical path of the reference probe light. Alternatively (or additionally), one or both of the variable phase shifter 32 and the variable amplitude modulator 50 may be positioned in the optical path of the sample probe light and / or the optical path of the modulated probe light, for example, at one of positions 52a, 52b, and / or 52c in FIG. 2.

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

[0057] 2 differs from the embodiment of FIG. 1 in that the beam combiner 30 has two complementary outputs 37a, 37b and is configured to cross-couple the two inputs 35a, 35b to cause them to interfere. Advantageously, the beam combiner 30 is configured so that the ratio between the light powers at the outputs 37a, 37b depends on the phase shift between the reference and modulated probe lights at the inputs. This ratio is 1:0 (i.e., one output propagates no light and the other propagates all light) when the ratio of the light powers at the inputs corresponds to a target ratio Rt (e.g., 1:1) and the relative phase shift of the light between the inputs is equal to a target phase shift Δp (e.g., 0°).

[0058] (The above condition is advantageously met at least at the central wavelength of the probe light.)

[0059] A coupler 30 having the above properties can be implemented, for example, by providing two parallel waveguide sections of appropriate length with evanescent coupling between the waveguides, as shown in FIG.

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

[0061] As in the first embodiment, the control unit 42 is configured to set the adjustment parameters t1, t2 such that the intensity signal I1 of D1 is 0. That is, the adjustment parameters t1, t2 are selected such that the input power ratio is equal to the target input power ratio Rt and the relative phase shift of the light at the two inputs 35a, 35b is equal to the target phase shift Δp.

[0062] In the embodiment of Figure 2, a second photodetector D2 is provided to measure the light at the second output 37b of the coupler 30. This allows the total optical power to be measured, for example to monitor proper operation of the device and / or to confirm the presence of a reference probe light.

[0063] In yet another embodiment, the beam combiner 30 can be a variable beam combiner, for example, by placing a heater 54 along the two coupled waveguides, as shown by the dotted lines in Figure 2. In this case, changing the temperature of the heater 54 changes the beat length of the coupling between the two coupled waveguide sections of the beam combiner 30, which in turn changes the relative intensities of the reference and modulated probe lights when they interfere at the output of the beam combiner 30. In this case, the variable amplitude modulator 50 may not be necessary.

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

[0065] <Third embodiment> FIG. 3 again illustrates various general concepts of the present technology that may be applied in various embodiments of the technology. It is assumed here that the interaction with the sample 16 changes the polarization state of the modulated probe light depending on the parameters of the sample being measured.

[0066] For example, Raman scattering can change the polarization state of the probe light. Similarly, the probe may contain optically active chiral components, which may change the polarization state of the probe light depending on their concentration.

[0067] In this case, the amplitude and / or phase of the two polarization states of the modulated probe light must be measured.

[0068] In this embodiment, splitters 60′, 60″ are provided to split both the reference probe light and the modulated probe light, and at least one of these splitters, i.e., the splitter 60″ used for the modulated probe light, is a polarization splitter.

[0069] In the example of FIG. 3, both splitters 60', 60'' have a fixed splitting ratio.

[0070] The first splitter 60' splits the reference probe light into a first reference branch 64a and a second reference branch 64b.

[0071] The modulated probe light of the two polarization states is fed as two separate modes via the waveguide 28 to the second polarization splitter 60″, where it is split into a first probe branch 68a and a second probe branch 68b, i.e., the first probe branch 68a propagates light of the first polarization state of the modulated probe light, and the second probe branch 68b propagates light of the second polarization state of the modulated probe light.

[0072] The light from the first reference branch 64a and the light from the first probe branch 68a are interfered in the first beam combiner 30′, and a first phase and / or amplitude tuner 70′ is used to cause the light to destructively interfere at the first photodetector D1′. In the embodiment of FIG. 3, the first phase and / or amplitude tuner 70′ is located in the first reference branch 64a, but it may also be located in the first probe branch 68a, as in the embodiment of FIG. 2, or at least partially incorporated into the first beam combiner 30′. The first phase and / or amplitude tuner 70′ is controlled by adjustment parameters t1′, t2′ generated by the control unit 42.

[0073] The light from the second reference branch 64b and the light from the second probe branch 68b are interfered in the second beam combiner 30''. A second phase and / or amplitude tuner 70'' is used to cause the lights to destructively interfere at the second photodetector D1''. In the embodiment of Figure 3, the second phase and / or amplitude tuner 70'' is located in the second reference branch 64b, but as in the embodiment of Figure 2, it may also be located in the second probe branch 68b or at least partially incorporated in the second beam combiner 30''. The second phase and / or amplitude tuner 70'' is controlled by adjustment parameters t1'', ​​t2'' generated by the control unit 42.

[0074] Similar to the above embodiment, the control unit 42 is then configured to set the first adjustment parameters t1', t2' so that the intensity signal I1' of D1' is 0. The control unit 42 is also configured to set the second adjustment parameters t1", t2" so that the intensity signal I1" of D1" is 0.

[0075] The adjustment parameters t 1 ′, t 2 ′, t 1 ″, t 2 ″ then describe the phase and / or amplitude of the two polarization states of the modulated probe light returning from the sample 16 .

[0076] Beam splitters 60′ and 60″ and beam combiners 30′ and 30″ must be configured so that the two modes of light propagating through waveguide 28 interfere with their respective portions of the reference-probe light from first splitter 60′.

[0077] In one embodiment, if the reference probe light in the waveguide 34 is propagating in one mode (e.g., only TE), the first beam splitter 60′ can be a simple splitter that couples light at its output into the TE mode of the waveguides 64a, 64b. If the two modes of the modulated probe light in the waveguide 28 are the TE and TM modes of that waveguide, the second polarizing beam splitter 60″ is advantageously a polarizing rotor splitter, e.g. as described by W.D. 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 modulated probe light at its two outputs into the TE mode of the waveguides 68 a, 68 b. The beam combiners 30′, 30″ are then configured to interfere with the TE modes at the inputs of the two beam combiners, respectively.

[0078] Other ways to combine different modes are known to those skilled in the art, for example using TM0 mode instead of TE0 mode.

[0079] <Fourth embodiment> FIG. 4 again illustrates various general concepts of the present technology that may be applied in various embodiments of the technology. The fourth embodiment, like the third embodiment, is adapted to measure changes in the polarization state of modulated probe light. However, in this embodiment, the outputs 68a, 68b of the second polarizing beam splitter 60″ (which is advantageously a polarization rotator splitter, as described in the previous section) are directed to interfere with each other in the second beam combiner 30″ after their relative phase shift and amplitude have been adjusted in a phase and / or amplitude tuner 70″. The second beam combiner 30″ is a beam combiner having two complementary outputs 37a″, 37b″, like the previous embodiment. As in the second embodiment, the beam combiner 30″ is configured so that the ratio between the optical powers at the outputs 37a″, 37b″ depends on the phase shift and relative power of the light at the inputs 35a″, 35b″. For example, if the phase shift is 0 and the power ratio of the light at the inputs 35a″, 35b″ is 1:1, all light is coupled into the first output 37a″ and none into the second output 37b″.

[0080] The control unit 42 is configured to adjust the phase and / or amplitude tuner 70″ using adjustment parameters t1″, t2″ to minimize the signal I″ output from a photodetector D″ that detects light at the second output 37b″.

[0081] This allows the relative phase and power of the modulated probe light of the two modes in the waveguide 28 to be determined from the respective adjustment parameters t1'', ​​t2'' controlling the phase and / or amplitude tuner 70''.

[0082] In the embodiment of FIG. 4, there is a phase and / or amplitude tuner 70″ for only one of the two modes of modulated probe light. Advantageously, this tuner is configured to tune to the mode that will dominate during the measurement.

[0083] If it is not possible to predict which mode will dominate, advantageously there are dedicated amplitude tuners for each of both modes, which can adjust the amplitude of the stronger mode to match the amplitude of the weaker mode. If desired, there can also be phase tuners for tuning one of the two modes, or for both modes.

[0084] The first output 37a" of the second beam combiner 30" is then fed to the first beam combiner 30' where it interferes with the reference probe light. As in the previous embodiment, a phase and / or amplitude tuner 70' is provided to adjust the relative phase and / or amplitude of the reference probe light and the light from the first output 37a".

[0085] The control unit 42 is configured to adjust the phase and / or amplitude tuner 70' by adjustment parameters t1', t2' to minimize the signal I1' from the photodetector D1' that detects light at the first output 37a' of the first beam combiner 30'. The relative phase and relative power of the (interfered) modulated probe light and the reference probe light from the output 37a'' can then be determined from the adjustment parameters t1', t2'.

[0086] 4, the first beam combiner 30', like the previous embodiment, has complementary outputs 37a', 37b', both of which are coupled to photodetectors D1', D2'. As before, only one of the outputs is needed to determine the tuning parameters t1', t2'. The other output is not strictly necessary, but can be used, for example, to monitor system operation.

[0087] <Fifth embodiment> FIG. 5 illustrates one way in which the present technique can be used to determine third-order nonlinear optical effects in a sample 16, particularly to measure stimulated Raman scattering.

[0088] 5, the apparatus 10 includes a secondary light source 80 in addition to the probe light source 14. The secondary light source 80 generates light having a different central wavelength than the probe light.

[0089] The secondary light is transmitted, for example, by integrated waveguide 82, to beam combiner 84 where it is combined with the probe light from beam splitter 20. From there, the combined secondary light and sample probe light are transmitted to sample 16. For example, if device 10 has a single device terminal 24 for transmitting light to and receiving light from sample 16, the combined secondary light and sample probe light are transmitted to sample 16 via beam splitter 48.

[0090] The secondary light and the sample probe light overlap at the sample 16. If a third-order nonlinear optical effect occurs at the sample 16, energy can be transferred between the sample probe light and the secondary light. Thus, light at the wavelength of the probe light undergoes an amplitude and / or phase change with respect to at least one polarization.

[0091] For example, if the wavelength difference between the secondary light and the probe light corresponds to a vibrational mode of a molecular component of sample 16, stimulated Raman gain or loss will occur at the wavelength of the probe light.

[0092] The modulated probe light is received by apparatus 10 and then processed, for example, using the techniques described in the above embodiments. The only difference is that the light returning from sample 16 typically contains not only the modulated probe light but also some secondary light, which may need to be removed before processing the modulated probe light. To do so, in the embodiment of FIG. 5, a bandpass or other filter 86, such as a lowpass or highpass filter, is provided somewhere in the optical path of the modulated probe light. When implemented as a bandpass filter, filter 86 is advantageously configured to be centered on the wavelength of the probe light and to block wavelengths of the secondary light.

[0093] In the embodiment of Figure 5, the techniques of the third embodiment are used to analyze the amplitude, phase, and / or polarization state of the modulated probe light, although other similar techniques, such as those of the other previously described embodiments, may also be used to obtain at least some or all of these parameters.

[0094] Sixth Embodiment FIG. 6 illustrates some further concepts using an apparatus with a secondary light source 80 that can be applied in various embodiments of the present technology.

[0095] This embodiment differs from the fifth embodiment in that it includes a beam splitter 88 that sends a portion of the secondary light to a photodetector D3 to monitor the power of the secondary light, e.g., to control the operating parameters of the secondary light source 80.

[0096] Furthermore, the bandpass filter 86 of the fifth embodiment is replaced by a wavelength selective splitter 90 adapted to split the light at the secondary wavelength to photodetector D4, while forwarding the light at the probe wavelength to phase and amplitude detection hardware. This allows the amount of light at the secondary wavelength returning from the sample 16 to be measured, thus providing a further means for characterizing the sample 16.

[0097] <Variable coupler and variable splitter> As can be seen from the above examples, the present technique can be advantageously implemented using a variable coupler and a variable splitter to adjust the reference and / or probe light to obtain destructive interference at the photodetector. For example, in the embodiment of Figure 1, splitter 20 is a variable splitter, and in the embodiment of Figure 2, beam combiner 30 is a variable beam combiner.

[0098] In the embodiments of Figures 2-6, beam combiners 30, 30', 30" have two inputs and two outputs that are complementary (i.e., power is directed to one or the other output depending on the adjustment of the beam combiner and the relative amplitude and phase shift of the light at the inputs to the beam combiner).

[0099] Such a variable beam combiner can be used to produce destructive interference at one output and light at the other output for monitoring or further processing such as in the example of Figure 4. Thus, in more general terms, the invention advantageously comprises the following steps: - transmitting the reference probe light and / or modulated probe light to a variable beam combiner having two inputs and two complementary outputs, where light from an input arrives at one output, the other output, or both outputs depending on the adjustment; - minimizing the intensity at one of the two complementary outputs using an adjustment parameter.

[0100] As mentioned above, variable splitters and / or variable combiners can be implemented, for example, by coupling two waveguide sections and adjusting their coupling using a heater (or, for example, using electric fields and electro-optic effects).

[0101] Another advantageous embodiment for implementing such a variable splitter or variable beam combiner is shown in Figure 7. Here, two -3 dB directional couplers 92a, 92b are used to form an interferometer 94 between them, in particular a Michelson interferometer. The optical path length (i.e., phase shift) of at least one of the interferometer arms 94a, 94b is adjustable by a first variable phase shifter 95 (implemented, for example, by a heater 96).

[0102] Therefore, by adjusting the first variable phase shifter 95, the output power at the first and second outputs 100a, 100b can be controlled, thereby enabling the device to be used as a variable beam splitter (e.g., beam splitter 20 in the above embodiment) to control the relative power of the sample and reference probe light. In the present application, the probe light from the probe light source 14 is fed to one of the inputs 98a, 98b of the device of Figure 7, with no signal fed to the other input.

[0103] The apparatus of FIG. 7 can also be used as a variable beam combiner (e.g., beam combiners 30, 30′, 30″ in the example above) for analyzing modulated probe light. In this case, both inputs 98 a, 98 b are used. If the two signals at inputs 98 a, 98 b have the same phase, only the phase difference between the two arms 94 a, 94 b controls the coupling of each input 98 a, 98 b to the first and second outputs 100 a, 100 b. In other words, by controlling the phase difference between the arms 98 a, 98 b, for example using the first phase shifter 95, it is possible to control how the light at the two inputs 98 a, 98 b is distributed between the two outputs 100 a, 100 b.

[0104] If there is a non-zero phase shift between the two signals at the inputs 98a, 98b, interference will cause additional mixing between the signals at the two outputs. Therefore, a second variable phase shifter 102, implemented for example by another heater 104, can be advantageously added to at least one of the inputs 98a, 98b.

[0105] Therefore, by adjusting the first phase shifter 95 and the second phase shifter 102, it is possible to obtain perfect destructive interference at the first output (e.g., output 100a) while directing all of the light to the second output (e.g., output 100b).

[0106] This type of variable beam combiner may be used, for example, as beam combiner 30, 30', or 30'' in the above embodiments, as previously described.

[0107] For a detailed description of the dimensions of this type of interferometer, see Horst et al., Optics Express Vol. 21, Issue 10, pp. 11652-11658 (2013), https: / / doi.org / 10.1364 / OE.21.011652.

[0108] <Calibration> As previously mentioned, at least one sample parameter can be determined from the adjustment parameter.

[0109] In some applications, it may be sufficient to determine a sample parameter relatively or qualitatively, for example, to determine the relative change in absorption or the relative change in phase, in which case the apparatus 10 does not necessarily need to be calibrated.

[0110] In other applications, such as for measuring absolute changes in length or absolute changes in absorption of sample 16, calibration of the apparatus may be advantageous. To calibrate apparatus 10, for example, a reference sample, such as a calibrated movable mirror or a calibrated tunable absorber (e.g., a set of filters), may be used in place of sample 16. Such a reference sample may be used, for example, to scale a phase adjustment parameter to an absolute change in phase or an amplitude adjustment parameter to an absolute change in absorption.

[0111] <Application example> Below, some applications of this technology are described in more detail.

[0112] [Transmission or Reflection:] In one embodiment, the technique can be used to measure the linear transmission through and / or reflection from the sample 16 .

[0113] For example, sample 16 may be a gas whose refractive index and / or absorption change slightly when modifying sample parameters such as its composition, and sample 16 is measured in transmission, i.e., the modulated probe light is light transmitted through sample 16.

[0114] In another example, sample 16 is a mirror that specularly reflects the sample probe light, and the position of the mirror varies (e.g., by a fraction of a wavelength). In this case, the sample parameter being measured may be the position of the mirror, and the modulated probe light changes phase as a function of the sample parameter.

[0115] In both of the above two examples, the sample 16 does not change the polarization state of the modulated probe light as a function of sample parameters. Thus, while all of the embodiments of the apparatus 10 described above can successfully analyze modulated probe light, simpler apparatus can be used, such as the embodiment of FIG.

[0116] Such measurements may also include NIR reflectance / absorption spectroscopy and / or Fourier transform infrared spectroscopy (FTIR).

[0117] [Optical rotation:] In another embodiment, sample 16 can generate an optical rotation of the sample probe light that varies with a sample parameter. For example, sample 16 can be a fluid having chiral optically active components, and the sample probe light is sent through the fluid. In this case, the polarization state of the modulated probe light depends on the concentration of the optically active components, which in this case form the sample parameter.

[0118] In this application, the apparatus 10 may be configured to determine the polarization state of the modulated probe light, for example using the techniques of either the embodiments of FIG. 3 or FIG.

[0119] [Elastic scattering:] In another embodiment, the sample 16 can elastically scatter the sample probe light, and the modulated probe light becomes the scattered sample probe light. In this case, the sample parameters can be, for example, the concentration and / or other parameters (such as particle distribution or composition) of the scattering components in the sample. The sample parameters typically affect the amplitude, phase, and polarization state of the modulated probe light.

[0120] Thus, in this application, the techniques of either the embodiment of FIG. 3 or FIG. 4 can be used, for example.

[0121] [Wavelength dependence:] In many applications, measurements are advantageously made with probe light of different wavelengths. In this case, for example, the probe light source 14 can be a tunable light source such as a tunable laser. If a secondary light source 80 is used, the secondary light source 80 can also be a tunable light source such as a tunable laser in addition to or instead of the probe light source 14, which is a tunable light source.

[0122] The system is particularly suitable for performing measurements at different wavelengths because the system itself can be tuned, so that even if components such as beam splitters or beam combiners have some wavelength-dependent properties, destructive interference can still be achieved by retuning the system, and the system can be used at multiple wavelengths.

[0123] [Closed-loop and open-loop control:] There are various ways to operate the device 10 in a series of measurements. FIG. 8 shows a first "closed loop" scheme in which the control unit 42 adjusts the adjustment parameters t1, t2... to set the measured intensity parameter to zero for each of the series of measurements x1...xN.

[0124] For simplicity, the diagram shows the parameters of a system having a single tuning parameter t1 and measuring a single intensity parameter I1.

[0125] Initially, the intensity parameter I1 has not yet been optimized for interference reduction. Therefore, as shown schematically in FIG. 8, a strong DC offset and strong shot noise are present. At the first measurement x1, the control unit 42 measures the intensity parameter I1 and then adjusts the adjustment parameter t1 so that the intensity parameter I1 is 0. The value of the adjustment parameter t1(x1) at x1 is the measurement result. At the next measurement x2, the sample parameters have changed to some extent, causing the intensity parameter I1 to deviate from 0. Next, the control unit 42 measures the intensity parameter I1 again and adjusts the adjustment parameter t1 so that the intensity parameter I1 is 0. t1(x2) is the measurement result at x2. This procedure is repeated for each measurement xi in a series of N>1 measurements, particularly in a series of N>10 measurements.

[0126] Therefore, the tuning parameter t1(xi) tracks the change of the sample parameter, and the value of the tuning parameter (after tuning) at a given measurement indicates the value of the sample parameter. In other words, the value (or change of) the sample parameter can be derived from the tuning parameter t1.

[0127] The scheme of FIG. 8 has the advantage that the adjusted measurements are not affected by shot noise, so the sample parameters can be derived very accurately from t1 even if they vary only slightly.

[0128] 9 shows a second "open loop" approach, in which the control unit 42 does not adjust the tuning parameters for each measurement x. Rather, the control unit 42 simply adjusts the tuning parameters at a particular time to produce fully or at least partially destructive interference at the photodetector at a particular time, and then holds the tuning parameters constant across multiple measurements.

[0129] Again, for simplicity, the diagram shows the parameters of a system having a single tuning parameter t1 and measuring a single intensity parameter I1.

[0130] Before tuning the apparatus 10, the intensity parameter I1 has a strong DC offset and contains a lot of shot noise. Then, for example, at the time of the first measurement x1, the control unit 42 adjusts the tuning parameter t1 to make the intensity parameter I1 several orders of magnitude smaller than it would be without tuning, thereby reducing the shot noise.

[0131] Then, for multiple measurements x2, x3...xk, the adjustment parameter t1 is kept constant. Therefore, the intensity parameter I1 is not zero but varies depending on the sample parameters. However, if the sample parameter changes are small, the intensity parameter I1 remains low, i.e., the shot noise also remains low.

[0132] In this case, the sample parameter for a given measurement x can be derived from the values ​​of the adjustment parameter t1 and the intensity parameter I1 for measurement x1. If only the relative change in the sample parameter compared to the first measurement x1 is of interest, this relative change can also be derived from only the intensity parameter I1 of measurements x1, x2, ...

[0133] 8 has the advantage that fewer recalculation and adjustment steps of the tuning parameters are required, which may allow for, for example, increased measurement speed and / or reduced system power consumption, but the shot noise may be slightly higher than in the closed-loop approach.

[0134] In an open-loop approach, the adjustment parameters can be set to values ​​that will cause the intensity parameter to be zero when the adjustment parameters are recalculated. This further reduces shot noise, but can have the drawback of requiring ambiguity removal. For example, if at a given time, the sample parameters affect the phase shift of the modulated probe light and the adjustment parameters are set to zero the intensity parameter, a non-zero value for the intensity parameter in the next measurement indicates that the phase shift has changed. However, if the adjustment parameters are not changed again, the sign of the phase shift may be unknown. Similarly, simultaneous changes in phase, amplitude, and / or polarization state can cause ambiguity. Thus, for example, in the embodiment shown in FIG. 9, the adjustment parameters are advantageously set to values ​​that reduce the intensity signal by several orders of magnitude (to reduce shot noise), but are not adjusted to zero.

[0135] [Stimulated Raman Scattering:] Stimulated Raman scattering (SRS) measurements are a particularly important application of this technique because in conventional SRS the intensity of the light returning from the sample varies relatively little with the scattering parameters, and therefore the signal of interest is usually contaminated with strong shot noise.

[0136] SRS requires not only Stokes light but also pump light, and therefore SRS can be measured using embodiments of the present application that include, in addition to the probe light source 14, a secondary light source 80, such as those shown in Figures 5 and 6.

[0137] In this case, as previously mentioned, the central wavelengths of the probe light and the reference probe light must be different, and the frequency difference is selected to excite rotational or vibrational modes of molecules in the sample 16 .

[0138] In one embodiment, the sample probe light from sample light source 14 corresponds to the pump light, and the secondary light from secondary light source 80 corresponds to the Stokes light. In another embodiment, the sample probe light from sample light source 14 corresponds to the Stokes light, and the secondary light from secondary light source 80 corresponds to the pump light. Because apparatus 10 measures the phase, intensity, and (optionally) polarization state of the modulated probe light, the apparatus can measure gain or loss in the pump light or the Stokes light.

[0139] Advantageously, to perform spectroscopic SRS measurements, at least one of the probe light source 14 and the secondary light source 80 is a tunable light source.

[0140] Advantageously, the central wavelength of the tunable light source is tunable over at least 20 nm. More preferably, the light source is tunable over more than 50 nm. Preferably, the light source is tunable over at least 75 nm.

[0141] Advantageously, the tunable light source can be tuned over said wavelength range without mode hops.

[0142] [Some examples:] A) The probe light source 14 can have a fixed wavelength and the secondary light source 80 can have a tunable wavelength, the wavelength of the secondary light source 80 being longer than the wavelength of the pump light source 14. For example, the probe 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.

[0143] B) The probe light source 14 can have a tunable wavelength and the secondary light source 80 can have a fixed wavelength, the wavelength of the probe light source 14 being longer than the wavelength of the secondary light source 80. For example, the probe light source 14 can be a tunable Stokes laser with a tunable range of at least 800...900 nm, and the secondary light can have a fixed wavelength of 785 nm.

[0144] When performing a series of measurements at multiple wavelengths, either the closed-loop or open-loop control schemes described in the previous section can be used.

[0145] Thus, in a closed-loop control scheme, adjustment parameters t1', t2', t1", t2" are derived from the measured intensity parameters, and the phase and / or intensity tuners 70', 70" are controlled by the adjustment parameters to generate destructive interference and null the detected intensity parameters I1', I1".

[0146] In an open-loop control scheme, tuning parameters t1', t2', t1", and t2" are derived and measurements at one wavelength are made to generate destructive interference to bring the intensity parameters at least close to zero. Then, multiple measurements are made at other wavelengths without updating the tuning parameters and the deviation of the intensity parameters I1', I1" from zero is tracked.

[0147] As previously mentioned, optical filter 86 and / or wavelength-selective splitter 90 can be used to remove secondary light from the modulated probe light before it enters the photodetector. If wavelength-selective splitter 90 is used, a second analyzer can be provided with its own beam splitter (equivalent to splitters 60′, 60″) and beam combiner (equivalent to beam combiners 30′, 30″) to generate interference between the modulated secondary light returning from sample 16 and reference secondary light derived from the secondary light of secondary light source 80. These components may similarly be tuned for destructive interference, allowing the gain / loss of both the pump and Stokes beams to be measured with high precision.

[0148] [Polarization analysis:] The embodiment of FIGS. 3-6 is adapted to detect changes in the polarization state of modulated probe light returning from the sample 16.

[0149] In general, the polarization state of the modulated probe light can be described by the relative amplitude and / or relative phase of two orthogonal polarizations of the modulated probe light, which can be, for example, two orthogonal linearly polarized components or two orthogonal circularly polarized components (e.g., L and R polarization states).

[0150] The method advantageously includes determining the relative amplitude and / or relative phase of two orthogonal polarization states of the modulated probe light.

[0151] In one embodiment, using, for example, the apparatus of FIG. 3 , modulated probe light of two polarization states is respectively interfered with a reference probe light, and the phase and / or amplitude of each polarization state relative to the reference probe light is adjusted to produce destructive interference of each polarization state with the reference probe light by determining at least first and second adjustment parameters t1′, t2′, t1″, t2″ in at least two phase and / or intensity tuners.

[0152] In another embodiment, using, for example, the apparatus of FIG. 4 , modulated probe light of two polarization states is made to interfere with each other, and the relative phase and / or amplitude of the two polarization states with respect to each other is adjusted to produce destructive interference between the two polarization states by determining at least first adjustment parameters t1″, t2″ in a first phase and / or intensity tuner 70″. Furthermore, “derived light” from one or both of the two polarization states (e.g., light at output 37 a″ in FIG. 4 ) is made to interfere with a reference probe light, and the phase and / or amplitude of the derived light with respect to the reference probe light is adjusted to produce destructive interference by determining at least second adjustment parameters t1′, t2′ in a second phase and / or intensity tuner 70′.

[0153] <Notes> Generally, as described above, the relative phase between the reference probe light and the modulated probe light is changed using the adjustment parameter(s) to cause the reference probe light and the modulated probe light to destructively interfere. Additionally or alternatively, the relative intensity (i.e., power) of the reference probe light and the modulated probe light is changed using the adjustment parameter to cause the reference probe light and the modulated probe light to destructively interfere.

[0154] As previously mentioned, the variable components controlled by the adjustment parameter(s) may be located in the optical path of the reference probe light and / or in the optical path of the probe light, in which case they may be located in the optical path of the sample probe light (i.e., before the probe light reaches the sample) and / or in the optical path of the modulated probe light (i.e., after the probe light reaches the sample).

[0155] The variable component(s) may also be at least partially incorporated into a beam splitter that splits the sample probe light and the reference probe light, or into a beam combiner(s) that combines the reference probe light and the modulated probe light.

[0156] In some of the above embodiments, a tunable light source is used, which may include a continuously adjustable light source (such as a tunable laser or a broadband light source with a tunable filter) or an assembly of multiple light sources with different center wavelengths (e.g., operating sequentially).

[0157] Advantageously, the components of device 10 are integrated onto a single substrate, which allows for more robust and stable operation.

[0158] While preferred embodiments of the present invention have been shown and described herein, it is to be clearly understood that the invention is not limited thereto and that the invention may be variously embodied and carried out in other ways within the scope of the following claims.

Claims

1. 1. A method for optically measuring at least one sample parameter of a sample, comprising: generating probe light by a probe light source (14); splitting the probe light into a sample probe light and a reference probe light; interacting the sample probe light with the sample (16) to produce modulated probe light having a phase and / or intensity responsive to the sample parameters; interfering the modulated probe light with the reference probe light in a beam combiner (30) to generate a signal light; measuring at least one intensity parameter (I1, I2, I1', I2', I1", I2") of said signal light by at least one photodetector (D1, D2, D1', D2', D1", D2", D); deriving adjustment parameters (t1, t2, t1', t2', t1", t2") using the intensity parameters (I1, I2, I1', I2', I1", I2"), and controlling a phase and / or intensity tuner (20, 32, 52, 70', 70") by the adjustment parameters (t1, t2, t1', t2', t1", t2") to change the relative phase and / or relative intensity of the interfering reference probe light and the modulated probe light, thereby causing the interfering reference probe light and the modulated probe light to destructively interfere with each other; deriving said sample parameters using at least one of said intensity parameters (I1, I2, I1', I2', I1", I2") and said adjustment parameters (t1, t2, t1', t2', t1", t2"); A method comprising:

2. Iteratively deriving the adjustment parameters (t1, t2, t1', t2', t1", t2") at a plurality of times (xi) and minimizing the intensity parameters (I1, I2, I1', I2', I1", I2") at the plurality of times (xi); deriving the sample parameters using the adjustment parameters (t1, t2, t1', t2', t1", t2") at the multiple times; The method of claim 1 , comprising:

3. 3. The method of claim 1, comprising deriving the sample parameters using the adjustment parameters (t1, t2, t1', t2', t1", t2") rather than the intensity parameters (I1, I2, I1', I2', I1", I2").

4. a) deriving said adjustment parameters (t1, t2, t1', t2', t1", t2") and reducing said intensity parameters (I1, I2, I1', I2', I1", I2") by destructive interference; b) after step a), keeping the adjustment parameters (t1, t2, t1', t2', t1", t2") unchanged, and measuring the intensity parameters (I1, I2, I1', I2', I1", I2") at the plurality of times (xi); c) deriving the sample parameters using the intensity parameters (I1, I2, I1', I2', I1", I2") measured at the plurality of times (xi); 4. The method of claim 1, comprising:

5. 5. The method of claim 1, wherein the relative phase between the reference probe light and the modulated probe light is changed such that the reference probe light and the modulated probe light destructively interfere.

6. 6. The method of claim 1, wherein the relative intensities of the reference probe light and the modulated probe light are varied such that the reference probe light and the modulated probe light destructively interfere.

7. 7. The method according to claim 1, wherein the probe light is split into the sample probe light and the reference probe light using a variable beam splitter (20), and the adjustment parameters (t1, t2, t1', t2', t1", t2") are used to adjust the splitting ratio of the variable beam splitter (20).

8. 8. The method of claim 1, wherein at least one of the sample probe light, the modulated probe light, and the reference probe light is supplied through a variable phase shifter (32), and the adjustment parameters (t1, t2, t1', t2', t1", t2") are used to adjust a phase delay of the variable phase shifter (32).

9. supplying the reference probe light and the modulated probe light to at least one Mach-Zehnder interferometer (94) having two arms (94a, 94b) extending between directional couplers (92a, 92b) and a variable phase shifter (95) provided in at least one of the two arms (94a, 94b); adjusting the phase delay of the variable phase shifter (95) using the adjustment parameters (t1, t2, t1', t2', t1", t2"); 9. The method of any one of claims 1 to 8, comprising:

10. sending the reference probe light and / or the modulated probe light to a variable beam combiner (30, 30', 30") having two inputs and two complementary outputs; minimizing the intensity output at one of the two complementary outputs using the adjustment parameters (t1, t2, t1', t2', t1", t2"); 10. The method of any one of claims 1 to 9, comprising:

11. 11. A method according to any one of claims 1 to 10, comprising determining the relative amplitude and / or relative phase of two orthogonal polarization states of the modulated probe light.

12. interfering each of the modulated probe lights of the two polarization states with the reference probe light; adjusting the relative phase and / or amplitude of each polarization state to the reference probe light by determining at least first and second adjustment parameters (t1', t2', t1", t2") in at least two phase and / or intensity tuners (20, 32, 52, 70', 70") to generate destructive interference between each polarization state and the reference probe light; The method of claim 11 further comprising:

13. causing the modulated probe light of the two polarization states to interfere with each other; adjusting the relative phase and / or amplitude of each polarization state with respect to one another to generate destructive interference of the two polarization states with respect to one another by determining at least first adjustment parameters (t1", t2") in a first phase and / or intensity tuner (70"); interfering derived light from at least one of the two polarization states with the reference probe light; adjusting the phase and / or amplitude of the derived light relative to the reference probe light to generate destructive interference by determining at least second adjustment parameters (t1', t2') in a second phase and / or intensity tuner (70'); The method of claim 11 further comprising:

14. generating secondary light with a secondary light source (80), said secondary light having a different wavelength than said probe light; superimposing the secondary light and the sample probe light at the sample (16) and allowing the secondary probe light and the sample probe light to interact with the sample (16) to produce the modulated probe light having a phase and / or intensity that is responsive to the sample parameter and the intensity of the secondary probe light; 14. The method of any one of claims 1 to 13, further comprising:

15. Varying the wavelength of at least one of the probe light source (14) and the secondary light source (80); determining the sample parameters at a plurality of wavelengths; 15. The method of claim 14, comprising:

16. 16. The method of claim 15, comprising the steps of: deriving, for each wavelength, the adjustment parameters (t1, t2, t1', t2', t1", t2") from the intensity parameters (I1, I2, I1', I2', I1", I2"); and controlling the phase and / or intensity tuner (20, 32, 52, 70', 70") by the adjustment parameters (t1, t2, t1', t2', t1", t2") to change the relative phase and / or relative intensity of the reference probe light and the modulated probe light, thereby causing destructive interference between the reference probe light and the modulated probe light, thereby minimizing the intensity parameters (I1, I2, I1', I2', I1", I2")

17. a) deriving the adjustment parameters (t1, t2, t1', t2', t1", t2") from the intensity parameters (I1, I2, I1', I2', I1", I2") for a first wavelength, and controlling the phase and / or intensity tuner (20, 32, 52, 70', 70") by the adjustment parameters (t1, t2, t1', t2', t1", t2") to change the relative phase and / or intensity of the reference probe light and the modulated probe light, thereby causing destructive interference between the reference probe light and the modulated probe light, thereby reducing the intensity parameters (I1, I2, I1', I2', I1", I2"); b) after step a), keeping the adjustment parameters (t1, t2, t1', t2', t1", t2") unchanged, and measuring the intensity parameters (I1, I2, I1', I2', I1", I2") at a plurality of second wavelengths; c) deriving the sample parameters at the second wavelength using the intensity parameters (I1, I2, I1', I2', I1", I2") measured at the second wavelength; 16. The method of claim 15, comprising:

18. 18. The method of any one of claims 14 to 17, comprising the step of varying the wavelength of the secondary light source.

19. The method of any one of claims 1 to 18, comprising changing the wavelength of the probe light source (14).

20. 20. The method according to any one of claims 1 to 19, wherein the coherence length of the probe light is at least 1 mm, in particular at least 10 mm.

21. a probe light source (14); a probe light splitter (20) connected to the probe light source (14); a sample interface (24, 26) connected to the probe optical splitter (20); a beam combiner (30, 30', 30") connected to the probe light splitter (20) and the sample interface (24, 26); photodetectors (D1, D2, D1', D2', D1", D2", D) connected to the beam combiner; a phase and / or intensity tuner (20, 32, 52, 70', 70"); a control unit (42) configured to carry out the method according to any one of claims 1 to 20; An optoelectronic measurement device comprising:

22. 22. Use of the method or device according to any one of claims 1 to 21 for stimulated Raman spectroscopy.

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