An apparatus for smoothing spectral transmission modulation and a method thereof

Abstract

An apparatus, system, and method for smoothing spectral transmission modulation in an optical fiber includes at least one holder for coupling a portion of the optical fiber, an optical fiber bending member configured to cyclically move a length of the portion from an initial position perpendicular to a longitudinal axis of the portion. The optical fiber bending member is placed adjacent to the at least one holder, and the movement changes a radius of curvature of the portion.

Description

BACKGROUND TECHNICAL FIELD

[0001] The present disclosure relates to devices, systems and methods for smoothing wavelength-dependent transmission modulation of light in an optical fiber. The devices, systems and methods are particularly useful for reducing variations in the baseline when making spectroscopic measurements using a light source with a wavelength that varies over time.

[0002] Description of the Prior Art

[0003] Gas absorption in scattering media (GASMAS) is based on measuring small changes in the optical power transmitted through a medium while varying the wavelength of the light, due to the spectroscopically sharp absorption properties of the free gas. These changes can be in the order of 1%, but can also be as small as 0.02-0.2%. Changes in the source optical power can be filtered in post-processing of the acquired data, provided that the width of these changes is significantly different from the width of the gas absorption features.

[0004] For example, changes in the output power due to linearly scanning the wavelength by increasing and decreasing the laser diode current can be easily handled, for example by fitting the acquired signal to a low order polynomial. However, laser interference originating from weak reflections of the millimeter thick optical elements will provide power change features with a spectral width in the same order of magnitude as the gas absorption features. These changes cannot be filtered out in post-processing, but need to be handled before acquiring the data.

[0005] Similar to the disturbances caused by fixed optical elements, the use of multimode optical fibers will cause small changes in the optical power. These changes are formed when the light entering the fiber is split into different spatial modes, all with slightly different optical path lengths. After leaving the fiber, the light of the different modes will interfere and produce spectral optical power changes and equivalent spatial intensity changes. The periodicity of the spectral changes covers a large interval, most of which can be digitally filtered in post-processing, but changes with a spectral width similar to the gas absorption features will cause problems.

[0006] This is particularly a problem when using TDLAS and the wavelength is swept over an absorption peak. Each step of the sweep can be reduced to a scale below a nanometer. Wavelength-dependent transmission modulation disturbances will cause variations in the baseline over the width of the absorption peak, which will affect the accuracy of the measurement.

[0007] In the art, methods are described to reduce speckle noise, especially when used as a lamp to obtain a spatially uniform light distribution on a surface, for example a surgical lamp in US2018 / 0214237. This will provide a spatially uniform light, but it is not described that the technology provides a homogenous or uniform spectral transmission. The most common techniques include using ultrasonic vibrations of the optical fiber, forming a part of the optical fiber into a ring that remains stationary, twisting or rotating the optical fiber, applying pressure to the optical fiber, etc.

[0008] US 8,786,857 describes an apparatus and method for measuring combustion parameters in a measurement zone of a gas turbine engine using tunable diode laser absorption spectroscopy (“TDLAS”). An apparatus is provided that works in conjunction with a multimode transmission optical fiber for averaging modal and speckle noise caused by signal level variations of light propagating within the multimode transmission optical fiber. The proposed solution is to reduce modal and / or speckle noise, but there is no discussion of the problem of baseline variations, especially when scanning a wavelength of light over an absorption peak.

[0009] The solutions described in the art for reducing spectral or modal noise problems are, in most cases, related to solving the problem of providing a uniform light distribution, and are not related to the problem of baseline variations when making spectral measurements and changing the wavelength (especially not over the width of an absorption peak). Furthermore, some solutions are very complex or cannot be used in certain environments, for example hospitals or other environments that require a high degree of cleanliness, for example a need for disinfection, sterility or cleanliness. Other examples of environments that can require a high degree of cleanliness, for example the food or pharmaceutical industry. Therefore, a simpler and cheaper solution can be an advantage.

[0010] Therefore, a new improved apparatus and method can be advantageous for reducing the problem of interference caused by transmission modulation during light-based measurements, for example spectral-based measurements. Especially a method suitable for use when measuring free gases, for example during medical diagnostic or monitoring purposes. SUMMARY

[0011] Therefore, embodiments of the present disclosure preferably seek to alleviate, mitigate or eliminate one or more of the deficiencies, disadvantages or problems in the art, singly or in any combination, for example as described above, by providing an apparatus, system or method for smoothing spectral transmission modulation in an optical fiber according to the description.

[0012] According to an aspect of the present disclosure, an apparatus for smoothing spectral transmission modulation in an optical fiber is described. The apparatus comprises at least one holder for coupling a portion of the optical fiber to the apparatus, and an optical fiber bending member configured to cyclically move a segment of the portion perpendicularly to a longitudinal axis of the portion from an initial position. The optical fiber bending member can be placed adjacent to the at least one holder, and whereby the movement changes a radius of curvature of the portion.

[0013] In some examples of the present disclosure, the apparatus can comprise two of the at least one holder, and the portion and the optical fiber bending member are arranged between the two holders.

[0014] In some examples of the present disclosure, at least one of the two holders can be configured to slidingly hold the optical fiber. This allows the portion to slide in a longitudinal axial direction in the at least one of the two holders when the segment is moved.

[0015] In some examples of the present disclosure, the optical fiber bending member can be an actuator connected to a first holder of the two holders, and configured to cyclically move the first holder towards a second holder of the two holders and then away from the second holder. This can allow the segment to move perpendicularly to the longitudinal axis of the portion from the initial position and then back to the initial state.

[0016] In some examples of the present disclosure, the bending member can be a force applying member. The force applying member can be configured to apply a force perpendicularly to a longitudinal axis of the portion, thereby moving the segment. The force is a mechanical force pushing perpendicularly at the portion with respect to the longitudinal axis to change the radius of the curvature.

[0017] In some examples of the present disclosure, the radius can be greater than a minimum bending radius of the optical fiber when the segment is moved, e.g. when a force is applied thereon.

[0018] In some examples of the present disclosure, the two holders can be arranged for positioning the portion in the initial position as a straight position before the segment is moved, e.g. when the segment is not moved, e.g. when no force is applied thereon by the optical fiber bending member.

[0019] In some examples of the present disclosure, the at least one holder can be a slit configured to hold the optical fiber.

[0020] In some examples of the present disclosure, the optical fiber bending member can be an electric motor rotating at least one blade configured to move the segment, e.g. by cyclically applying a force.

[0021] In another aspect of the disclosure, a system for smoothing spectral transmission modulation in an optical fiber is described. The system can comprise: an apparatus for smoothing spectral transmission modulation as described herein; an optical fiber having a portion of its length arranged in the apparatus; and a light source connected to the optical fiber.

[0022] In some examples, the light source can emit light having a variable wavelength.

[0023] In another aspect of the disclosure, a method of smoothing spectral transmission modulation in an optical fiber is described. The method can comprise: coupling the optical fiber to at least one holder; using an optical fiber bending member arranged adjacent to the at least one holder to cyclically move a segment of the optical fiber perpendicularly to a longitudinal axis of the optical fiber. Moving the segment changes a radius of curvature of the portion.

[0024] In some examples, the method can comprise coupling the optical fiber to two holders, thereby arranging a portion of the optical fiber between the two holders. The method can then comprise using the optical fiber bending member arranged between the two holders to move the segment as part of the portion.

[0025] In some examples, the method can comprise transmitting light through the optical fiber for spectral measurements.

[0026] In some examples of the method, the light can have a wavelength that varies over time.

[0027] In some examples, the method can comprise changing the radius at a same period time as a measurement time of one wavelength.

[0028] The disclosure also describes use of an apparatus for smoothing spectral transmission modulation in an optical fiber, as described herein, for reducing baseline variations when performing spectral measurements.

[0029] It should be emphasized that the term "comprises / comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0030] BRIEF DESCRIPTION OF DRAWINGS

[0031] These and other aspects, features and advantages of examples of the disclosure will become apparent and be elucidated in the following description of examples of the disclosure with reference to the drawings, in which:

[0032] Figure 1A and 1B A schematic example of a disclosed apparatus for smoothing transmission modulation is shown;

[0033] Figure 2 An illustrative system for smoothing spectral transmission modulation is shown;

[0034] Figure 3 An illustrative example of a flow chart of the described method is shown;

[0035] Figure 4A and 4A Images of a fiber-coupled source probe with a diffuser are shown when the smoothing device is not activated and when the smoothing device is activated; and

[0036] Figure 5A and 5B Absorption signals of light normalized to the maximum peak in each signal are shown when the smoothing device is not activated and when the smoothing device is activated.

[0037] Example description

[0038] Specific examples of the present disclosure will now be described with reference to the accompanying drawings. However, the present disclosure can be embodied in many different forms and should not be construed as being limited to the examples set forth herein; rather, these examples are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0039] Assuming that the spectral gas absorption features remain unchanged over the acquisition time of the measurement, the interference signal generated in the multimode fiber can be observed as a spectral transmission modulation.

[0040] The term "interference" is to be interpreted herein with its general meaning in the field of optics, i.e. the superposition of one or more waves. At each given instant or time, the light transmitted through the fiber can be observed as stationary, and the light waves of different modes can interfere with each other after transmission through the fiber. For some wavelengths, the interference can be weakly coherent, while for some wavelengths, the interference can be weakly destructive. If the wavelength can be scanned at infinite speed, or if white light is transmitted through the fiber, a spectral transmission modulation (relatively weak) can be observed.

[0041] The spectral transmission modulation can be smoothed by varying the way the different modes interfere during the acquisition period, while scanning the wavelength over a wavelength range. The wavelength range can be the width of the absorption peak. Varying the way the different modes interfere can be done by varying the optical path length differently for the different modes of the fiber.

[0042] The inventors have found that one way of smoothing the spectral transmission modulation can be by changing the radius of curvature on a short section of optical fibre, for example by mechanically changing the radius of curvature. At each instant during bending of the section of fibre to obtain a varying radius of curvature, the constructive and destructive interference between light waves of different modes can vary due to the extent to which the section has been bent. By changing the curvature during the acquisition, exposure or integration period, while scanning the wavelength over a range of wavelengths, the spectral transmission modulation can be smoothed. This can reduce variations in the baseline when taking spectral measurements.

[0043] The section of optical fibre to be bent to obtain a change in the radius of curvature can be held in place laterally at two points, the two points being separated by a distance defining the section. The section of fibre can have a length of less than 10 cm, for example less than 5 cm.

[0044] The optical fibre can be allowed to move longitudinally between the two points. Prior to the application of the force, the optical fibre can have an initial shape, for example being in a relaxed position having a straight extension. The change in the radius of curvature, for example the bending of the section, can be obtained by moving a section of the laterally held section of optical fibre orthogonally with respect to the longitudinal axis of the section of optical fibre. The section of optical fibre is thereby bent.

[0045] The section can be a point along the length of the laterally held section of optical fibre.

[0046] In some examples, moving a section of the laterally held section of optical fibre is obtained by applying a force. The change in the radius of curvature of the section is obtained when the force is applied orthogonally with respect to the longitudinal axis of the section of optical fibre. The section can elastically spring back to the initial shape when the force is not applied to the section of optical fibre.

[0047] The optical fibre can be part of a probe for transmitting light to a measurement location. Reflected and / or backscattered light can then be transmitted back in the same optical fibre, or detected by a separate detection system.

[0048] An advantage of the apparatus and method described herein is that in addition to providing a reduction in interference, it provides a simple method of disconnecting and connecting the optical fibre probe to the apparatus. The few components and housing make the apparatus easy to clean and protects the apparatus from contamination. The apparatus is therefore suitable for use in environments requiring a high degree of cleanliness, for example environments requiring sterilisation, sterility or a cleanroom. For example, this can be in a hospital, or in the food and pharmaceutical industries.

[0049] Figure 1A and Figure 1B A schematic example of a disclosed apparatus 10 for smoothing spectral transmission modulation according to the present disclosure is shown. Figure 1A A perspective view of a schematic example of an apparatus 10 for smoothing spectral transmission modulation is shown, and Figure 1BA top view showing a schematic example of an apparatus 10 for smoothing spectral transmission modulation.

[0050] The interference can be wavelength dependent transmission modulation interference. These can cause a change in the spectral baseline when wavelengths are scanned over a wavelength range, for example when using TDLAS. The change in baseline can provide lower accuracy when performing measurements where the wavelength is scanned over a narrow absorption peak, for example an absorption peak of a free gas.

[0051] The optical fibre 12 can be positioned in two holders 13a, 13b to couple the optical fibre 12 to the apparatus 10. The holders 13a, 13b can be arranged on two opposite sides of an optical fibre bending member 19 for moving a section of the optical fibre portion perpendicular to a longitudinal axis of the optical fibre portion. The optical fibre bending member can also be a force member.

[0052] This arrangement can allow a portion 16 of the length of the optical fibre 12 to be positioned in a straight position between the two holders 13a, 13b, for example when the optical fibre bending member 19 does not have a force exerted on it.

[0053] In some examples, the holders 13a, 13b can be slits formed in a protruding or raised edge 15 that can surround the optical fibre bending member 19. Other arrangements for coupling the optical fibre 12 to the apparatus 10 are possible, for example the holders 13a, 13b can be holes through the protruding or raised edge 15 through which the optical fibre 12 passes. In some examples, there is no edge 15 and the holders 13a, 13b are discrete features on either side of the optical fibre bending member 19, i.e. the two holders 13a and 13b are separate features that are not connected by, for example, a protruding or raised edge 15.

[0054] In order to allow the optical fibre 12 to move longitudinally between the two points when the section is moved, for example when a force is exerted on it, at least one of the two holders 13a, 13b can be configured to slidingly hold the optical fibre 12. This can allow the portion 16 to slide along the longitudinal axis 17 in at least one of the holders 13a, 13b when the section is moved by the optical fibre bending member 19 perpendicular to the longitudinal axis of the portion 16, for example when a force is exerted on the portion. Preferably, both holders 13a, 13b are configured to slidingly hold the optical fibre 12.

[0055] The distance between the two holders 13a, 13b can define a portion 16 of the optical fiber 12, for example by moving a segment of this portion 16 to change the radius of curvature of this portion 16 by exerting a force thereon. The optical fiber bending member 19 is configured to cyclically, for example periodically, move a segment of this portion. For example, the segment can be moved by exerting a force on the portion 16. The force can be exerted perpendicular to the longitudinal axis 17 of the portion 16 of the optical fiber 12. The force changes the radius of curvature of the portion 16 when exerted thereon.

[0056] When moving the segment, a minimum radius of curvature of about a few centimeters is obtained. The radius of curvature required to obtain the effect can depend on the type and size of the optical fiber. In one example, for a 400 pm optical fiber, the radius of curvature can be in the range of 60 mm to 100 mm, for example 80 mm, for a 200 pm optical fiber, the radius of curvature can be in the range of 15 mm to 50 mm, for example 30 mm to 40 mm.

[0057] In some examples, the radius can be larger than the minimum bending radius of the optical fiber 12 when the segment of the portion 16 is moved to its maximum position.

[0058] In some examples, the optical fiber bending member 19 is configured to exert a mechanical force by pushing at the portion 16. The force can be exerted perpendicular to the longitudinal axis 17 of the portion 16 to change the radius of curvature. The skilled person will understand that there are many ways to exert a pushing force, for example by a rod moved by a linear motor with a reciprocating motion.

[0059] As an alternative to using two holders, the above described apparatus and method can be configured to use only one holder, for example at least one holder. The optical fiber bending member can then be arranged in the vicinity of the holder instead of between two holders. When the optical fiber bending member moves a segment of the optical fiber, the optical fiber can bend relative to the holder, thereby providing a varying radius of curvature.

[0060] In another example, a portion of an optical fiber can be bent to provide a varying radius of curvature by laterally fixing the optical fiber at two points that are separated by a distance, the distance defining a portion. By changing the distance between the holders, a segment of the portion will move and the optical fiber portion will bend and a varying radius of curvature is obtained on the defined portion.

[0061] The distance between the holders can be changed by connecting one or both holders to an actuator, which can function as the optical fiber bending member.

[0062] The holder for holding the portion of the optical fiber is configured to prevent longitudinal movement of the portion of the optical fiber therein.

[0063] In another example, one of the two retainers is connected to an actuator that can change the direction of the optical fiber, for example, by rotating the retainer, thereby allowing that portion of the optical fiber arranged between the two retainers to bend and its radius of curvature to be changed. The retainer arranged on the actuator can serve as an optical fiber bending member.

[0064] In this example, one or two retainers can be configured to allow the optical fiber to slide within them. The retainer connected to the actuator can be a slit with a length (e.g., between 1 and 3 cm, such as 2 cm). The actuator can be a servo motor. The slit of the retainer connected to the actuator can define the orientation of the optical fiber, and as the retainer rotates, the orientation changes, thereby allowing that portion of the optical fiber arranged between the two retainers to bend.

[0065] exist Figure 1A and Figure 1B In this configuration, the segment is moved by a motor that rotates at least one blade 18a, 18b, 18c. The motor is not shown in the figure because it is housed within the housing 14. The housing 14 can be made of plastic or metal and can be molded as a single unit. A cover 11 can be disposed on top of the housing 14 to protect or seal the area surrounding this portion 16 of the optical fiber 12. The cover may have a recess 20 that adapts to retainers 13a, 13b to restrict movement of the optical fiber 12 in directions other than along the longitudinal axis 17 of this portion 16 of the optical fiber 12.

[0066] As the optical fiber rotates, blades 18a, 18b, and 18c can gradually increase their curvature from the initial shape of portion 16 (e.g., a straight extension) until they reach maximum curvature. The curvature can then gradually decrease until this portion 16 of the optical fiber 13 regains its initial shape. This process can be aided by the elastic properties of the optical fiber 12. The elastic properties of the optical fiber 12 can provide a springback effect, allowing portion 16 to retain its initial shape when it is released.

[0067] exist Figure 1A and Figure 1B In the example shown, a wheel with three blades 18a, 18b, and 18c is connected to a motor. As the wheel rotates, the three blades 18a, 18b, and 18c push that portion 16 of the optical fiber 12 out of its relaxed position every three rotations. This generates a minimum radius of curvature of approximately a few centimeters every three rotations.

[0068] In some examples, the curvature can be varied periodically with a time period equal to the measurement time (e.g., acquisition, exposure, or integration cycle). For example, a measurement can be performed during the time period in which the radius of curvature of the fiber portion changes from its initial shape to its maximum curvature. Another measurement can then be performed from the maximum curvature back to the initial shape of the fiber portion. This can be achieved, for example, by...Figure 1A and Figure 1B half of the blades 18a, 18b, 18c of the wheel as shown in

[0069] In another example, one measurement can be performed during a time period in which the radius of curvature of the optical fiber section changes from the initial shape to the maximum curvature and back to the initial shape more than once, e.g. at least twice, e.g. three times. This can be performed, for example, by a full rotation of the wheel as shown in Figure 1A and Figure 1B half of the blades 18a, 18b, 18c of the wheel as shown in

[0070] In yet another example, one measurement can be performed during a time period in which the radius of curvature of the optical fiber section changes from the initial shape to the maximum curvature and back to the initial shape more than once, e.g. at least twice, e.g. three times. This can be performed, for example, by a full rotation of the wheel as shown in Figure 1A and Figure 1B full rotation of the wheel as shown in

[0071] Figure 2 An illustrative system 30 for smoothing spectral transmission modulation, e.g. interference of light modes in an optical fiber, is shown. The system is configured to perform spectral based measurements using TDLAS. This includes gas in scattering media absorption spectroscopy (GASMAS). The system 30 comprises a device 10 for smoothing spectral transmission modulation as described herein. The system 30 further comprises a light source 31. The light source can emit light with a variable wavelength. The light source 31 can be a laser, e.g. a diode laser or a semiconductor laser, e.g. a distributed feedback laser (DFBL), a vertical cavity surface emitting laser (VCSEL) or other types of available lasers.

[0072] The optical fiber 12 is connected to the light source and a section 16 of the optical fiber 12 is connected to the device 10 for smoothing spectral transmission modulation.

[0073] The optical fiber 12 is arranged to transmit light from the light source 31 to a sample 32. The sample 32 can be a tissue site of a subject to be examined or a cavity having a free gas to be monitored. For example, the cavity can be a part of a pulmonary system, e.g. a part of a lung or a bronchial tree. The cavity can also be a sinus cavity of a subject.

[0074] For a probe to transmit light to an internal site, a member for introducing a light source to inject light into tissue, e.g. a bronchoscope, a nasogastric tube, an endoscope, a tracheal catheter, a colonoscope or similar introducing member can be used.

[0075] A separate detector can be used to detect light transmitted through the sample 32 or backscattered from the sample 32. Alternatively, the optical fiber 12 can be used to transmit light transmitted through the sample 32 or backscattered from the sample 32 to a detector 33.

[0076] Figure 3 A schematic example of a flowchart of a disclosed method 100 for smoothing spectral transmission modulation in an optical fiber is shown. The interference can be wavelength-dependent transmission modulation interference.

[0077] This method 100 is particularly useful when performing spectral measurements in which light has wavelengths that vary over time, such as TDLAS. When performing spectral measurements, this method can reduce baseline variations. The method may include:

[0078] A portion 101 of an optical fiber is arranged between two retainers. This retainer may be part of a device for smoothing spectral transmission modulation as described herein.

[0079] A portion of section 102 is moved, for example, by cyclically (e.g., periodically) applying force to a portion of the optical fiber. For example, by applying a force perpendicular to the longitudinal axis of this portion of the optical fiber, the section can be moved perpendicular to the longitudinal axis of this portion of the optical fiber. Moving the section will change the radius of curvature 103 of that portion.

[0080] The method may include: changing the radius for a wavelength of the light source at a period of the same time as the measurement time (e.g., integration time).

[0081] Example

[0082] To illustrate the performance of the implementation, the TDLAS platform was used to drive a light source with an optical fiber coupled diffuser probe, and to acquire optical signals from a photodiode located a few centimeters above the source probe in the air. Furthermore, an optical imaging system was used to evaluate the spatial intensity distribution from the source probe.

[0083] exist Figure 4A and Figure 4B The image shows the output images of the source diffuser probe with the device for smoothing spectral transmission modulation turned on and off. Figure 4A The speckle pattern observed is a result of optical mode interference in the optical fiber, and it remains unchanged throughout the camera's acquisition time. Figure 4B In this process, speckle is eliminated because the radius of curvature of a section of the optical fiber changes with the image exposure time.

[0084] exist Figure 5A and Figure 5B The image shows samples of absorption signals acquired using the TDLAS platform with the device for smoothing spectral transport modulation turned on and off. This is similar to... Figure 4A and Figure 4B The spatial speckle pattern seen in it Figure 5A In this context, when the device is off, the absorption signal includes a signal that varies considerably around the real gas absorption peak. Figure 5B In this case, by turning on the device, these changes were largely eliminated.

[0085] The obtained light absorption signals were normalized to the maximum peak in each signal, whether in the case of the device closed as shown in Figure 5A or in the case of the device open as shown in Figure 5B Both gas absorption features are clearly seen in both signals. However, when the device is closed, changes in the signal can be seen of about 25% of the true absorption peak in amplitude. These changes are due to interference between the fiber modes. The signal quality improves dramatically when the motor is started. This ultimately demonstrates that the solution presented herein reduces, if not eliminates, the changes in the absorption signal due to interference originating from the optical fiber. The use of the optical fiber improves the sensitivity of the spectroscopic measurement (e.g. TDLAS measurement).

[0086] The application has been described above with reference to specific examples. However, other examples than the above described are equally possible within the scope of the disclosure. Different method steps than those described above can be provided within the scope of the application, and these method steps can be provided in a different order than that described above. The scope of the application is only determined by the appended patent claims.

[0087] The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one." The phrase "and / or," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "either or both".

Claims

1. A system comprising: a device for smoothing spectral transmission modulation in a multimode optical fiber, the device comprising: at least one holder for coupling a portion of the optical fiber to the device; an optical fiber bending member configured to cyclically move a segment of the portion perpendicularly to a longitudinal axis of the portion from an initial position; and wherein the optical fiber bending member is disposed adjacent to the at least one holder and whereby the movement changes a radius of curvature of the portion; a multimode optical fiber having a portion of its length arranged in the device; and a light source connected to the optical fiber, wherein the light source is configured to be scanned over a range of wavelengths to perform spectral measurements using tunable diode laser absorption spectroscopy, thereby reducing baseline variations when performing the spectral measurements.

2. The system of claim 1, wherein, The light source emits light having a variable wavelength.

3. The system of claim 1, wherein, The device comprises two of the at least one holder and the portion and the optical fiber bending member are disposed between the two holders.

4. The system of claim 3, wherein, At least one of the two holders is configured to slidingly hold the optical fiber, whereby the portion slides in the at least one of the two holders in a longitudinal axial direction when the segment is moved.

5. The system of claim 3, wherein, The optical fiber bending member is an actuator connected to a first of the two holders and is configured to cyclically move the first holder towards a second of the two holders and then away from the second holder, whereby the segment moves perpendicularly to the longitudinal axis of the portion from the initial position and then returns to the initial state.

6. The system of any one of claims 1 to 4, wherein, The bending member is a force applying member configured to apply a force perpendicularly to a longitudinal axis of the portion, thereby moving the segment, for example the force is a mechanical force pushing perpendicularly at the portion with respect to the longitudinal axis to change the radius of the curvature.

7. The system of any one of claims 1 to 6, wherein, The radius is greater than a minimum bending radius of the optical fiber when the segment is moved, for example when a force is applied thereon.

8. The system of any one of claims 3 to 7, wherein, The two holders are arranged for positioning the portion in the initial position as a straight position before the segment is moved, for example when no force is applied thereon by the optical fiber bending member.

9. The system of any one of claims 1 to 8, wherein, The at least one holder is a slit configured to hold the optical fiber.

10. The system of any one of claims 1-4 or 6-9, wherein, The optical fiber bending member is an electric motor rotating at least one blade configured to move the segment, for example by cyclically applying a force.

11. A method of smoothing spectral transmission modulation in an optical fiber, comprising: coupling the optical fiber to at least one holder; cyclically moving a segment of the optical fiber perpendicularly to a longitudinal axis of the optical fiber using an optical fiber bending member disposed adjacent to the at least one holder; and wherein moving the segment changes a radius of curvature of the portion; and scanning a light source connected to the optical fiber over a range of wavelengths to perform spectral measurements using tunable diode laser absorption spectroscopy, thereby reducing baseline variations when performing the spectral measurements.

12. The method of claim 11, comprising coupling the optical fiber to two holders, thereby arranging a portion of the optical fiber between the two holders, using the optical fiber bending member arranged between the two holders to move the segment as part of the portion.

13. The method of any one of claims 11 or 12, comprising transmitting light through the optical fiber for a spectral measurement.

14. The method of claim 13, wherein, The light has a wavelength that varies over time.

15. The method of claim 14, comprising varying the radius at a same period time as a measurement time of one wavelength.

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