Supercontinuum system with spectroscopic detection capability

Abstract

A supercontinuum system for providing supercontinuum light to an external device and / or an external sample comprises a supercontinuum module configured to generate supercontinuum light, a spectrometer configured to measure a spectrum of the supercontinuum light or a portion thereof, and a delivery fiber that delivers the supercontinuum light or a portion thereof from its input beginning to its output end.

Description

[Technical field]

[0001] The present disclosure relates generally to supercontinuum systems, more particularly to supercontinuum systems having spectroscopic detection capabilities, and most particularly to supercontinuum systems with control modules based on spectroscopic detection capabilities. [Background technology]

[0002] Supercontinuum systems with spectroscopic detection and / or with control modules that may or may not be based on spectroscopic detection are known in the art.

[0003] Various examples of supercontinuum systems with control systems based or not on spectroscopic monitoring and detection are disclosed in US Pat. No. 5,399,633. In one example of a supercontinuum system, as disclosed in US Pat. No. 6,393,636, measured spectral parameter values ​​are compared to a reference spectrum to generate a control signal for optimizing pump coupling.

[0004] Another example in the '633 patent discloses a supercontinuum system with a control module that controls a tilt actuation system. The supercontinuum system and control module do not perform spectroscopic detection. However, the example discloses a connector disposed between the first and second feed fibers to direct a small portion of the supercontinuum radiation to an intensity detector. In this way, the intensity detector, i.e., an in-line detector, can be used to monitor the amount of radiation coupled into the second feed fiber. This radiation can be used to control the tilt actuation system, and in particular, the radiation beam to the input connector of the first feed fiber.

[0005] US Patent No. 5,399,633 discloses another supercontinuum system based on spectroscopic detection, for example using an in-line spectrometer that is used to calibrate the set points in an acousto-optical tunable filter (AOTF) either before or after the AOTF is used with a calibrated controller.

[0006] A supercontinuum system that has spectroscopic detection to monitor the spectral response of gases in the fiber, but does not perform control based on the detection, is disclosed in Non-Patent Document 1. In the above mentioned prior art related to spectroscopic detection, the supercontinuum system is either concerned with controlling filters, controlling the fiber coupling, or monitoring the spectral composition of the gases in the fiber.

[0007] In other words, the supercontinuum systems disclosed in the prior art cited above are intended to either control a particular module within the supercontinuum system in a particular way, or to measure gases within the supercontinuum system.

[0008] Therefore, the above-mentioned examples of the prior art do not disclose a supercontinuum system that has a spectroscopic detection function, thereby obtaining information about the spectrum of the supercontinuum light from spectroscopic detection, and sending it outside the supercontinuum system, for example to an external device or an external sample.

[0009] That is, in the prior art examples discussed above, the user and / or controller does not obtain information regarding the light that is sent outside the supercontinuum system. For this reason, it is desirable for a supercontinuum system to have spectroscopic detection capabilities that provide information about the generated supercontinuum light, e.g., its spectrum, that can be sent outside the supercontinuum system, such as to an external device and / or an external sample.

[0010] In contrast, as described above, the means disclosed in Patent Document 2 transmits and provides information about the generated supercontinuum light, for example, its spectrum, outside the supercontinuum system, for example, to an external device, in this example, a measurement system.

[0011] The means disclosed in Patent Document 2 achieves this by measuring the spectrum of supercontinuum light generated outside the supercontinuum system, in particular by using a spectrometer at the wafer level of the measurement system.

[0012] However, this is less than ideal as it requires users to place the spectrometer at the wafer level, which means it is at the measurement point and / or sample level, and furthermore, measurements at the sample level can be difficult and influenced by the sample itself.

[0013] It is therefore desirable to improve supercontinuum systems with spectroscopic detection capabilities that provide information about the generated supercontinuum light and transmit the spectrum of the supercontinuum light outside the supercontinuum system, for example to an external device or an external sample. Examples of such systems are disclosed in Patent Document 3 and Non-Patent Document 2. In any case, it is clear that improvements are still desirable. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 2021 / 043593 [Patent Document 2] International Publication No. 2021 / 008929 [Patent Document 3] U.S. Patent No. 9,270,080 [Non-patent literature]

[0015] [Non-Patent Document 1] DFGMina's 2017 PhD thesis: Bi-tapered fiber sensor using a supercontinuum light source for a broad spectral range [Non-Patent Document 2] Developments on using supercontinuum sources for high resolution multi-imaging instruments for biomedical applications” by Nteroli Gianni et al. in Progress in biomedical optics and imaging - SPIE, vol. 11077, 19 July 2019 Summary of the Invention [Problem to be solved by the invention]

[0016] It is an object of the present disclosure to provide a supercontinuum system for supplying supercontinuum light to an external device and / or an external sample, in particular a supercontinuum system with improved spectroscopic detection capabilities for supercontinuum light generated outside the supercontinuum system.

[0017] Furthermore, an object of the present disclosure is to provide a supercontinuum system that allows for easy spectroscopic detection of the generated supercontinuum light outside the supercontinuum system. [Means for solving the problem]

[0018] These and other objects have been achieved by a supercontinuum system as defined in the claims and described hereinafter in this disclosure. In one disclosed aspect of the disclosure, a supercontinuum system for providing supercontinuum light or a portion thereof to an external device and / or an external sample comprises a supercontinuum module configured to generate supercontinuum light, a spectrometer configured to measure a spectrum of the supercontinuum light or a portion thereof, and a delivery fiber that delivers the supercontinuum light or a portion thereof from its input beginning to its output end.

[0019] In one embodiment, the supercontinuum system further comprises an input coupler optically connected to the input origin and optically connected to the supercontinuum module.

[0020] In a preferred embodiment, the supercontinuum system further comprises an output coupler optically connected to the output end of the supply fiber, the output coupler configured to split the supercontinuum light or a portion thereof into two separate signals: an output signal for the external device and / or the external sample, and an input signal for the spectrometer, the input signal being used to mirror the output signal and monitor the spectrum of the supercontinuum light or a portion thereof coupled out by the output coupler.

[0021] The advantage of connecting an output coupler to the output termination, i.e., where an external device and / or external sample receives the output from the supercontinuum system via the feed fiber, is that the input signal mirrors and reflects the signal fed via the feed fiber.

[0022] In this way, the spectrometer can be used to detect and / or analyze the input signal to determine whether the delivery fiber is properly connected to the supercontinuum module and / or whether the delivery capacity of the delivery fiber has not been degraded. Such an advantage is not available, for example, in supercontinuum systems in which the in-line spectrometer or in-line detector is connected to an intermediate output end between the two fibers, rather than to the output end. In the prior art described in the background above, such as Patent Document 2, the output coupler is placed at the intermediate output end before the output end, and the input signal of the detector or spectrometer is for mirroring the input signal and for monitoring the signal of the supercontinuum light coupled into the delivery fiber, rather than the supercontinuum light coupled out of the delivery fiber, as in this disclosure.

[0023] Another advantage of connecting an output coupler to the output termination is that the input signal is not based on a signal from an external device and / or sample, improving the means for spectroscopic detection of supercontinuum light generated outside the supercontinuum system.

[0024] The above and / or additional objects, features, and advantages of the present disclosure will be further described through the following illustrative and non-limiting detailed description of embodiments of the present disclosure, with reference to the accompanying drawings. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 illustrates an example of a supercontinuum system according to the present disclosure. [Diagram 2] FIG. 1 illustrates an example of bandwidth for a supercontinuum system according to the present disclosure. [Diagram 3] FIG. 1 illustrates an example fiber coil for a supercontinuum system according to the present disclosure. [Figure 4] FIG. 1 illustrates an example of speckle noise in a supercontinuum system according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Output Coupler and Input Signal In one embodiment, the output coupler is an output collimator. In another embodiment, the input to the spectrometer is provided by reflection from an output coupler. To provide the reflection from the output coupler, the output coupler can comprise one or more lenses, which can form an output collimator and / or may be configured to reflect the supercontinuum light or a portion thereof. One of the one or more lenses can include a coating configured to reflect the supercontinuum light or a portion thereof. For example, the coating can be configured to reflect wavelengths in the range of 400 nm to 1000 nm.

[0027] In yet another embodiment, an output coupler connected to the output terminus allows the supercontinuum light, or a portion thereof, to propagate externally in free space and couple inside an external device and / or an external sample. For example, an output coupler, such as an output collimator, may be provided in an optical configuration to be directed toward the external sample. In this regard, the output coupler may be configured to illuminate the external sample. An output coupler as described in this embodiment may also be connected to an external device.

[0028] In accordance with the present disclosure, the external devices can form an external system. For example, the output coupler may be connected to a microscope illumination system, which may be formed by at least one optical device or multiple optical devices, such as mirrors and / or lenses.

[0029] In a preferred embodiment, the input signal of the spectrometer is provided through a multimode fiber, the length of the multimode fiber is greater than 10 m, more preferably greater than 40 m, such as 60 m, and most preferably greater than 90 m, such as 100 m, or greater than 150 m, to suppress interference between modes within the resolution of an individual pixel, and to receive a reduced speckle signal at the spectrometer. By noise analysis of a multimode fiber guiding light in the range of 800 to 1000 nm, the inventors of the present disclosure have found that when the multimode fiber is shorter than 10 m, the average speckle noise is about 6%. When the length is increased to more than 10 m, the average speckle noise decreases to about 3%. When the length is increased to more than 40 m, the average speckle noise decreases to about 1.5%. When the length is increased to more than 90 m, such as more than 100 m, the average speckle noise decreases to about 1%. Thus, by increasing the length of the multimode fiber as described above, the average speckle noise is reduced in such a very specific manner, especially when the multimode fiber is connected to an output coupler connected to the output termination. Having an average speckle noise of about 3% or less provides optimal spectroscopic detection. For this reason, a length of 10m or more has been found to be optimal. Furthermore, the inventors of the present disclosure have found by noise analysis of a multimode fiber guiding light in the range of 800 to 1000 nm that when the multimode fiber is less than 10m, the peak-to-peak speckle noise is greater than 6%, such as greater than 10%. When the length is increased to greater than 10m, the peak-to-peak speckle noise is reduced to about 6%. When the length is increased to greater than 40m, the peak-to-peak speckle noise is reduced to about 3%. When the length is increased to greater than 90m, such as greater than 100m, the peak-to-peak speckle noise is reduced to about 2%. Thus, by increasing the length of the multimode fiber as described above, the peak-to-peak speckle noise is reduced in a very specific manner, especially when the multimode fiber is connected to an output coupler connected to the output termination. Optimal spectroscopic detection is obtained by having a peak-to-peak speckle noise of about 3% or less. For this reason, lengths of 10 m or more have been found to be optimal.

[0030] It is well known that in multimode fibers, the spectral correlation width of speckles scales inversely with the length of the multimode fiber, and therefore the inventors have confirmed that their experimental findings are consistent with the theoretical understanding of multimode fibers.

[0031] However, finding a particular length of multimode fiber as described above that can provide optimal spectroscopic detection of a supercontinuum module generating supercontinuum light was not trivial, as will be shown below.

[0032] To suppress modes in a multimode fiber, it is possible to calculate when the transit time in different modes becomes longer than the coherence time of the detected light. Furthermore, the resolution of the spectrometer can be estimated to provide the optimum resolution of the spectrometer. For example, if a resolution of 1 nm is required for the spectrometer, the corresponding coherence time is roughly 0.8 ps at 500 nm and 3.3 ps at 1000 nm.

[0033] A 100 μm step-index fiber has about 2000 modes at 500 nm and about 500 modes at 1000 nm for a numerical aperture (NA) of 0.1 (here arbitrarily chosen between the excitation and receiving NA of the spectrometer).

[0034] The refractive index step in this multimode fiber is on the order of 0.003, and assuming that the effective refractive indices of the modes are equally distributed across this index difference, the effective index difference between the individual modes is 1.5e-6 at 500 nm and 6e-6 at 1000 nm.

[0035] The difference in transit times is dt=L*dn / c, L=dt*c / dn, which means that to ensure that the modes are out of phase within the resolution bandwidth of the spectrometer, the fiber length at 500 nm must be greater than L=0.8ps*3e8 / 1.5e-6=160m, and at 1000nm must be greater than L=3.3e-12*3e8 / 6e-6=165m.

[0036] Therefore, based on various estimates, it can be calculated that a multimode fiber having a length of about 160 m can provide reasonable results with suppressed modes, but it was not clear what the actual speckle noise at such a length would be and whether a shorter length of multimode fiber could be used. The inventors of the present disclosure have found through experiments an optimal multimode fiber length that has the surprising technical effect of producing very small speckle noise, as described above.

[0037] In the field of optical fibers, it is well known that speckle changes with temperature. When a multimode fiber is excited by a spatially coherent light source (such as a supercontinuum module), many of the guided modes are excited. Due to the small difference in propagation speed in the fiber, the phase of the light is preserved throughout the fiber. Therefore, the modes can interfere at the output end of the fiber, giving rise to the well-known speckle pattern.

[0038] The speckle pattern on the output of a multimode fiber is caused by the interference of different modes in the fiber. These modes propagate at different velocities, and since the power and phase of the light in these modes depend strongly on the excitation and perturbation of the fiber, the interference pattern also depends on these parameters. Furthermore, since the actual velocity in the fiber depends on temperature, the speckle pattern also changes with temperature.

[0039] When detected by spectrometers that typically have a spectral resolution of a few nm, this has been found to result in significant pixel-dependent amplitude variations, and the present disclosure provides specific measures to mitigate these variations.

[0040] Furthermore, when the spectrum is measured by a spectrometer, the measured spectrum reacts very sharply to any kind of mechanical or thermal perturbation due to the interference between modes. Therefore, the inventors have also found a solution to provide a fiber coil that is robust to mechanical and thermal perturbations, which will be described in the following embodiments.

[0041] In one embodiment, the multimode fiber is wound onto a fiber coil having a coil diameter of less than 100 mm, preferably less than 90 mm, such as about 80 mm, and the fiber coil, with the fiber wound, is placed into a tray having a tray diameter that matches the coil diameter to mechanically secure the multimode fiber. The tray diameter may differ from the coil diameter by a few millimeters to be consistent, for example, the tray diameter may be 5 to 10 mm larger than the coil diameter.

[0042] In another embodiment, the fiber may be secured in the tray by providing a foam in the tray while wrapped around the fiber coil and placed in the tray. Thus, in some embodiments, the tray includes a foam for securing and holding the fiber. The inventors of the present disclosure have observed that a foam, such as a soft foam, improves the signal in the fiber by about 3%. The foam can improve the signal in the fiber by making the fiber more resistant to shock, vibration, and temperature changes. A soft foam is preferred because it exerts less pressure on the fiber. The soft foam does not induce stress in the fiber and therefore does not interfere with the signal. At the same time, the soft foam can secure and hold the fiber.

[0043] In yet another embodiment, the fiber may be secured in the tray by providing silicone in the tray while wrapped around the fiber coil and placed in the tray. Thus, in some embodiments, the tray includes silicone to secure and hold the fiber. The inventors of the present disclosure have observed that silicone improves the signal in the fiber by about 5%. Silicone can improve the signal in the fiber by making the fiber more resistant to shock, vibration, and temperature changes.

[0044] In another embodiment, the fiber may be wound on itself to form a fiber coil. Supercontinuum light, filter module and control module In one embodiment, the supercontinuum light has a broad spectrum defined by a wavelength range that spans at least 400 nm to 1000 nm, preferably 400 nm to 2000 nm, more preferably 400 nm to 2400 nm. According to the present disclosure, the supercontinuum system comprises a delivery fiber, and the supercontinuum light, or a portion thereof, is delivered through the delivery fiber from an input beginning to an output end. This means that the delivery fiber is configured to deliver light having a wavelength in the range of at least 400 nm to 1000 nm, preferably 400 nm to 2000 nm, more preferably 400 nm to 2400 nm, in the embodiments described below. The ranges specified here are not limitations on the supercontinuum light source, but rather requirements on the delivery fiber. Thus, in one embodiment, the delivery fiber is configured to deliver supercontinuum light, or a portion thereof, having a broad spectrum defined over a wavelength range of at least 400 nm to 1000 nm, preferably 400 nm to 2000 nm, more preferably 400 nm to 2400 nm, through the delivery fiber from an input beginning to an output end.

[0045] In another embodiment, the supercontinuum system further comprises a filter module, the filter module being configured to provide a portion of the supercontinuum light in the form of a bandwidth filtered signal having a narrow bandwidth of about 5 nm to 10 nm, preferably less than 7 nm, such as 5 nm to about 7 nm. This means that if the supercontinuum system generates light having a broad spectrum, as defined above, for example from 400 nm to 1000 nm, the filter module is configured to bandwidth filter this light and generate a wavelength or a range of wavelengths within a defined range of the broad spectrum. Thus, by using the filter module, as defined herein, it is possible to tune the supercontinuum system to output a desired wavelength within the broad spectrum as generated by the supercontinuum module. Furthermore, in the filter module described herein, according to the present disclosure, the supply fiber is configured in one embodiment to supply supercontinuum light, in particular a portion thereof, having a broad spectrum defined in a wavelength range spanning at least 400 nm to 1000 nm, preferably 400 nm to 2000 nm, more preferably 400 nm to 2400 nm, the portion being a bandwidth filtered signal.

[0046] A bandwidth filtered signal, according to embodiments defined herein, may have a narrow bandwidth wavelength of about 5 nm to 10 nm, preferably less than 7 nm, such as 5 nm to about 7 nm.

[0047] According to the present disclosure, a broad spectrum, bandwidth filtered signal as defined above is fed through a feed fiber from an input beginning to an output end. Further, in accordance with the present disclosure, the bandwidth filtered signal is centered around a wavelength.

[0048] A bandwidth filtered signal may be defined by a narrow bandwidth of less than 7 nm and has a minimum transmission of more than 20% in this bandwidth. The transmission may be more than 50%, for example more than 70%, in different definitions. However, in a preferred definition, a bandwidth filtered signal is defined by a narrow bandwidth of less than 7 nm and has a minimum transmission of more than 80% in this bandwidth.

[0049] Thus, a bandwidth filtered signal centered on a wavelength is preferably defined to have a transmission greater than 80%. Because the filter module operates on the generated supercontinuum light having a broad spectrum, a bandwidth filtered signal centered on a wavelength within the broad spectrum is preferably defined to have a transmission greater than 80% for all wavelengths within the broad spectrum, defined to be at least 400 nm to 1000 nm.

[0050] The above mentioned transmission may be defined as the transmission through the filter module and / or as the transmission through the delivery fiber. In a preferred embodiment, the filter module comprises two continuously variable filters that are moved and / or adjusted relative to each other, the two variable filters including a first variable filter in the form of a long wave pass filter and a second filter in the form of a short wave pass filter, the bandwidth of which is controllable. The filter module described herein is advantageous over other filter modules because the two variable filters can be configured to cover a very wide range of wavelengths, such as at least a broad spectrum ranging from 400 nm to 1000 nm, 400 nm to 2000 nm, or even 400 nm to 2400 nm.

[0051] Other filter modules used may be acousto-optical tunable filters (AOTF) and / or volume Bragg gratings. However, such filter modules cannot be used to control the bandwidth. For this reason, it is preferable to use two continuously variable filters that are moved and / or tuned relative to each other.

[0052] Being able to control the bandwidth gives the user of the supercontinuum system full flexibility in tuning characteristics and allows the supercontinuum system to be used in a wide range of applications as well as external samples and / or devices.

[0053] For example, in configurations where the external device is an external spectrometer that receives supercontinuum light from an external sample illuminated by a supercontinuum system as disclosed herein, control of bandwidth is desirable.

[0054] In a most preferred embodiment, the supercontinuum system further comprises a control module connected to one or more motorized stages configured to hold two tunable filters such that the two tunable filters are controlled by the control module In this manner, the spectrum and / or bandwidth of the supercontinuum light may be controlled by the control module.

[0055] In another preferred embodiment, the input signal is used to self-calibrate the first filter module. The self-calibration can be performed, for example, by sequentially defining one or more parameters of the first filter module or a part thereof and measuring and analyzing the spectrum of the transmitted light. An example of a parameter can be, for example, one or more positions of the two variable filters as described above. When defining the position of one or more of the two variable filters, the wavelength obtained at that position is matched to that position. Thus, during the self-calibration, a look-up table of positions and wavelengths can be updated. In general, the relationship between one or more parameters and the spectrum of the transmitted light or a part thereof, for example, the effective filter wavelength, can be verified and calibrated. In an embodiment, the filter module comprises one or more motorized stages, the one or more motorized stages holding, for example, a variable filter, and the input signal can be used to self-calibrate the one or more motorized stages.

[0056] In one embodiment, the input coupler, or a beam splitter positioned in front of the supply fiber, is configured to split the supercontinuum light, or a portion thereof, into two separate signals: (a) a supply signal in the supply fiber, and (b) a spectrometer signal in the spectrometer or another spectrometer, where the spectrometer signal is used to monitor the supply signal and is used to monitor the spectrum of the supercontinuum light, or a portion thereof, internally coupled by the input coupler.

[0057] In another embodiment, the supercontinuum system further comprises a processor configured to compare the spectrometer signal with the input signal. In this way, it is possible to monitor whether there is a significant deviation between the spectrometer signal and the input signal. As part of the calibration, the comparison between the spectrometer signal and the input signal may be used as a reference to calibrate the supercontinuum system, for example by reducing the deviation as much as possible.

[0058] Supply Fiber and Display In one embodiment, the delivery fiber is an endless single mode photonic crystal fiber (PCF) configured to deliver the supercontinuum light, or a portion thereof, through the delivery fiber.

[0059] "Endlessly single mode" is a term widely known in the field of optical fibers. It simply means that it is single mode at all wavelengths. Thus, in the context of the present disclosure, in one embodiment, it can mean that the delivery fiber is single mode for supercontinuum light having a broad spectrum defined by a wavelength range of at least 400 nm to 1000 nm, preferably 400 nm to 2000 nm, more preferably 400 nm to 2400 nm. This is difficult to achieve in practice. Thus, in some embodiments, endlessly single mode is a delivery fiber that is single mode over at least about 50%, such as at least about 80%, of the transmission bandwidth, e.g., over the entire transmission bandwidth of the delivery fiber.

[0060] Further explanation of the term "endlessly single mode" can be found in the article "Endlessly single-mode photonic crystal fiber," by TA Birks, JC Knight, and P. St. J. Russell, Opt. Lett. 22, 961-963 (1997). Endlessly single mode fiber as described in this article is incorporated herein by reference.

[0061] Another example of an endless single mode fiber is disclosed in WO 2016 / 206700, which is also incorporated herein by reference. In another and / or related embodiment, the delivery fiber is a large mode area (LMA) fiber configured to deliver the supercontinuum light or a portion thereof through the delivery fiber. One type of large mode area fiber may be an endless single mode fiber. Another type of large mode area fiber may be a rod. A large mode area fiber with a large cladding can provide a stiff fiber, thus forming a rod in some embodiments. Using a rod is advantageous because bending induced losses can be avoided.

[0062] By using a delivery fiber as described above in connection with the present disclosure, the supercontinuum light or a portion thereof can be delivered to an external sample and / or device with high transmission efficiency for all wavelengths in the spectrum of the supercontinuum light, whether the full spectrum, i.e. full bandwidth, of the supercontinuum light or a bandwidth filtered portion thereof. Furthermore, if the delivery fiber is an endless single mode fiber, light in the range of 400 to 1000 nm can be delivered from the supercontinuum module to the output end of the delivery fiber and thus to the external device and / or sample in a flexible manner and with low, or at least very limited, loss, preferably without loss.

[0063] There may be other delivery fibers that can be used to deliver supercontinuum light to an external sample and / or device, for example in the form of a hollow-core (HC)-PCF as disclosed in US Pat. No. 6,399,433. However, the photonic bandgap delivery fiber, HC-PCF, disclosed in this publication can only guide a limited wavelength range, and not all of the guided wavelengths are single-mode.

[0064] In a preferred embodiment, the supercontinuum system further comprises a display, the display being connected to the spectrometer and configured to display the spectrum in order to inform a user of the supercontinuum system of the spectrum of the supercontinuum light or a part thereof being fed to an external device and / or an external sample at the output end via the output coupler. An advantage of this embodiment is that the spectrum just before being fed to the external sample and / or device can be clearly informed. This can provide the user with information, for example, on whether the feed fiber is properly connected to the supercontinuum module and / or whether the feed fiber is degraded.

[0065] Example 1 - Supercontinuum System FIG. 1 illustrates an example of a supercontinuum system 1 according to the present disclosure. The supercontinuum system 1 according to the present disclosure provides supercontinuum light 2 or a portion thereof 3 to an external device and / or an external sample (not shown). The supercontinuum system 1 comprises a supercontinuum module 4 configured to generate supercontinuum light 2. The supercontinuum system 1 further comprises a spectrometer 5 configured to measure a spectrum of the supercontinuum light 2 or a portion thereof 3. To provide the supercontinuum light 2 or a portion thereof 3 to the external device and / or the external sample, the supercontinuum system 1 further comprises a delivery fiber 6, through which the supercontinuum light 2 or a portion thereof 3 is delivered from an input start 7 to an output end 8. FIG. 1 also illustrates that the supercontinuum system 1 further comprises an input coupler 9, which is optically connected to the input start 7 and optically connected to the supercontinuum module 4. FIG. 1 also shows that the supercontinuum system 1 further comprises an output coupler 10 optically connected to the output end 8 of the supply fiber 6, the output coupler 10 configured to split the supercontinuum light 2 or a portion thereof 3 into two separate signals, namely an output signal 11 for an external device and / or an external sample, and an input signal 12 for a spectrometer 5, the input signal 12 being used to mirror the output signal 11 and monitor the spectrum of the supercontinuum light 2 or a portion thereof 3 coupled out by the output coupler 10.

[0066] In this example, the output coupler 10 is an output collimator configured to output a collimated beam. As can be seen in Fig. 1, the output coupler 10 connected to the output termination 8 allows the supercontinuum light 2 or a portion thereof 3 to propagate externally in free space and couple out inside an external device and / or external sample (not shown).

[0067] Also, the input signal 12 of the spectrometer 5 is provided by reflection from the output coupler 10. The input signal 12 of the spectrometer 5 is fed through a multimode fiber 13. The length of the multimode fiber 13 is more than 10 m, more preferably more than 40 m, such as 60 m, and most preferably more than 90 m, such as 100 m, or more than 150 m. This suppresses interference between modes and a reduced speckle signal is received at the spectrometer 5. The multimode fiber is placed at the output coupler. Also, to avoid a structure with two fibers extending to and from the output coupler, the multimode fiber can be attached to the feed fiber as shown in FIG. 1.

[0068] As shown here, the supercontinuum system further comprises a filter module 14 configured to provide a portion of the supercontinuum light in the form of a bandwidth filtered signal having a narrow bandwidth of less than 7 nm. The filter module 14 comprises two continuously variable filters (15, 16) that are moved relative to each other, the two variable filters (15, 16) including a first variable filter 15 in the form of a long wave pass filter and a second filter 16 in the form of a short wave pass filter, the bandwidth of which is controllable.

[0069] As shown in this example, in addition to the filter module 14, the supercontinuum system comprises one or more blocking filters 17 and an attenuation filter 18, for example in the form of a neutral density filter.

[0070] As shown in this example, the supercontinuum system further comprises a control module 19 connected to one or more motorized stages (not shown) configured to hold the two tunable filters (15, 16) such that the two tunable filters (15, 16) are controlled by the control module 19. The control module 19 receives an input from the spectrometer 5. In this manner, the output from the supercontinuum system is fed back to the control module 19 via the output coupler 10, the multimode fiber 13, and the spectrometer 5. The spectrometer, in one embodiment, may comprise a calibrated photodiode that measures the output power from the supercontinuum system. This ensures an accurate indication of the output power, particularly to ensure, for example, 1 mW output per line.

[0071] The control module 19 shown here is also used to control the attenuating filter 18 and the beam shutter 20. The shutter 20 may be configured to block the supercontinuum light as the wavelength is tuned. This ensures that no light is present between the wavelength tuning steps.

[0072] Example 2 – Bandwidth (BW) of a Supercontinuum System FIG. 2 illustrates an example of a (BW) of a supercontinuum system 1 according to the present disclosure. As illustrated in the previous example, the supercontinuum system in one embodiment further comprises a filter module 14 configured to provide the portion 3 of the supercontinuum light in the form of a bandwidth filtered signal.

[0073] Also, as mentioned above, a bandwidth filtered signal has a narrow bandwidth of wavelengths less than 7 nm. This example explains how this bandwidth should be interpreted. FIG. 2 first shows that the supercontinuum system 1 generates light having a broad spectrum. In this example, the broad spectrum is in the range of 400 nm to 1000 nm, and the filter module 14 is configured to bandwidth filter this light and generate wavelengths within the defined range. In this example, the filter module 14 is configured to tune the supercontinuum system to output desired wavelengths within the broad spectrum as generated by the supercontinuum module 1. As shown in FIG. 2, several wavelengths within the broad spectrum are generated, here the following wavelengths are shown: 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 790 nm.

[0074] Thus, in accordance with the present disclosure, the delivery fiber 6 is configured to deliver supercontinuum light 2 having a broad spectrum defined by a wavelength range spanning at least 400 nm to 1000 nm. The bandwidth filtered signal using the tunable filter or filter module 14 described herein has wavelengths of at least 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, and 790 nm. Thus, the delivery fiber 6 is configured to deliver a broad spectrum bandwidth filtered signal defined by a wavelength range spanning at least 400 nm to 1000 nm.

[0075] As shown in FIG. 2, the bandwidth filtered signals have wavelengths with a narrow bandwidth of less than 7 nm, and the bandwidth filtered signals are centered around wavelengths, here at least centered around wavelengths of 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, and 790 nm.

[0076] As further shown in Figure 2, narrow bandwidths less than 7 nm have a minimum transmission of more than 20%, more than 50%, for example more than 70%. In fact, as shown in Figure 2, a bandwidth filtered signal centered on a certain wavelength has a transmission of more than 80%. Thus, for all wavelengths generated by the supercontinuum system 1 and filtered using the filter module 14, as is evident from Figure 2, the transmission is more than 80% when the bandwidth (BW) is around 7 nm, or even less than 7 nm.

[0077] Therefore, the bandwidth filtered signal 3, centred around a wavelength, is preferably defined to have a transmittance of more than 80%. As shown in this example, the filter module 14 operates on supercontinuum light generated having a broad spectrum, such that the bandwidth filtered signal centered on a wavelength within the broad spectrum is preferably defined to have greater than 80% transmittance for all wavelengths within the broad spectrum, defined to be at least 400 nm to 1000 nm.

[0078] Example 3 – Multimode fiber wound into a fiber coil. FIG. 3 illustrates an example of a multimode fiber wound into a fiber coil for a supercontinuum system according to the present disclosure.

[0079] 3 shows a fiber coil around which multimode fiber is wound. The length of the multimode fiber 13 is greater than 10 m, here greater than 100 m, which suppresses interference between modes and results in a reduced speckle signal being received by the spectrometer 5.

[0080] The multimode fiber is wound into a fiber coil having a coil diameter of less than 100 mm, preferably less than 90 mm, here less than 75 mm, and the fiber coil, with the fiber wound, is placed into a tray having a tray diameter matching the coil diameter to mechanically secure the multimode fiber, which in this example is 85 mm.

[0081] As shown in FIG. 3, the fiber coil is mounted in a tray. This protects the fiber coil from mechanical perturbations. The tray is 3D printed. By 3D printing the tray, the inventors have found that the fiber coil can be placed in a protected manner without being subjected to significant stress. Although the illustrated tray is 3D printed, the tray can be formed from a variety of materials and may be manufactured by other techniques that achieve similar performance.

[0082] To mechanically hold the fiber in the tray, a piece of soft foam is placed over the fiber coil and tray along with tape (covered in plastic to prevent the fiber from sticking.) This configuration has been tested and has shown very good performance.

[0083] When soft foam was used, the transmittance change observed due to small perturbations of the fiber coil was small, about 2%. The inventors found that by changing the coil diameter from 75 mm to 80 mm, thereby reducing the tray clearance by 5 mm, i.e., the distance between the coil diameter and the tray diameter, the fiber became more stable when subjected to mechanical vibration and shock.

[0084] Regarding sensitivity to mechanical perturbations, experiments were performed in which the fiber trays in which the fibers were mounted were shaken, resulting in little or no response to the perturbations. Example 4 (AB) – Speckle noise in a supercontinuum system 4(A) and 4(B) show an example of speckle noise in a supercontinuum system according to the present disclosure.

[0085] In these examples, the spectrometer input signal is provided via a multimode fiber, the length of the multimode fiber being greater than 10 m, more preferably greater than 40 m, such as 60 m, and most preferably greater than 90 m, such as 100 m, or greater than 150 m, such that interference between modes is suppressed and a reduced speckle signal is received at the spectrometer 5.

[0086] These examples demonstrate the technical effect of reducing speckle noise to various low values ​​by using different multimode fiber lengths. As the results in Figure 4(A) show, when the multimode fiber is shorter than 10 m, the average speckle noise is about 6%. When the length is increased beyond 10 m, the average speckle noise decreases to about 3%. When the length is increased beyond 40 m, the average speckle noise decreases to about 1.5%. When the length is increased beyond 90 m, such as beyond 100 m, the average speckle noise decreases to about 1%. Thus, by increasing the length of the multimode fiber as described above, the average speckle noise decreases in this very unusual way, especially when the multimode fiber is connected to an output coupler connected to the output termination.

[0087] Spectroscopic detection is optimized with an average speckle noise of less than about 3%, for which the optimal length was found to be 10 m or more, such as 40 m or more. Additionally, the inventors of the present disclosure have found that for multimode fibers guiding light in the 800 to 1000 nm range, when the multimode fiber is shorter than 10 m, the peak-to-peak speckle noise exceeds 6%, such as exceeds 10%. When the length is increased to greater than 10 m, the peak-to-peak speckle noise decreases to about 6%. When the length is increased to greater than 40 m, the peak-to-peak speckle noise decreases to about 3%. When the length is increased to greater than 90 m, such as to 100 m, the peak-to-peak speckle noise decreases to about 2%.

[0088] Thus, by increasing the length of the multimode fiber as described above, the peak-to-peak speckle noise is reduced in a very specific manner, particularly when the multimode fiber is connected to an output coupler connected to the output termination. Optimal spectroscopic detection is obtained by having a peak-to-peak speckle noise of about 3% or less. For this reason, lengths of 10 m or more, such as 40 m or more, have been found to be optimal.

Claims

1. 1. A supercontinuum system for providing supercontinuum light or a portion of said supercontinuum light to an external device and / or an external sample, said supercontinuum system comprising: a supercontinuum module configured to generate the supercontinuum light; a spectrometer configured to measure a spectrum of the supercontinuum light or a portion of the supercontinuum light; a supply fiber that supplies the supercontinuum light or a portion of the supercontinuum light from an input end to an output end; an input coupler optically connected to the input end and optically connected to the supercontinuum module; an output coupler optically connected to the output end of the delivery fiber; The output coupler couples the supercontinuum light or a portion of the supercontinuum light to: an output signal for the external device and / or the external sample; A supercontinuum system configured to split an input signal for the spectrometer into two separate signals, the input signal being configured to mirror at least a portion of the output signal, and configured to monitor the spectrum of the supercontinuum light or a portion of the supercontinuum light.

2. The supercontinuum system of claim 1 , wherein the output coupler is an output collimator.

3. The supercontinuum system of claim 1 , wherein the input to the spectrometer is provided by reflection from the output coupler.

4. 2. The supercontinuum system of claim 1, wherein the output coupler connected to the output end is configured to propagate the supercontinuum light or a portion of the supercontinuum light in external free space and couple it to the external device and / or the external sample.

5. 2. The supercontinuum system of claim 1, wherein the input signal of the spectrometer is provided via a multimode fiber, the length of the multimode fiber being greater than 10 m, so that interference between modes is suppressed and a reduced speckle signal is received at the spectrometer.

6. 6. The supercontinuum system of claim 5, wherein the multimode fiber is wound into a fiber coil having a coil diameter of less than 100 mm.

7. The supercontinuum system of claim 1 , wherein the supercontinuum light has a broad spectrum defined by a wavelength range extending at least from 400 nm to 1000 nm.

8. A supercontinuum system as described in claim 7, further comprising a filter module configured to provide a portion of the supercontinuum light in the form of a bandwidth filtered signal having a bandwidth.

9. 9. The supercontinuum system of claim 8, wherein the filter module includes two tunable filters configured to be moved and / or tuned relative to each other, such that the bandwidth is controllable.

10. 10. The supercontinuum system of claim 9, further comprising a control module connected to one or more motorized stages configured to hold two tunable filters such that the two tunable filters are controllable by the control module.

11. 2. The supercontinuum system of claim 1, wherein the supply fiber is an endless single-mode photonic crystal fiber configured to supply the supercontinuum light or a portion of the supercontinuum light through the supply fiber.

12. 2. The supercontinuum system of claim 1, wherein the delivery fiber is a large-mode-area fiber configured to deliver the supercontinuum light or a portion of the supercontinuum light through the delivery fiber.

13. 10. The supercontinuum system of claim 1, further comprising a display coupled to the spectrometer and configured to display the spectrum for communicating the spectrum to an end user of the supercontinuum system.

14. The input coupler or a beam splitter disposed before the delivery fiber splits the supercontinuum light or a portion of the supercontinuum light into: (a) a delivery signal on said delivery fiber; 10. The supercontinuum system of claim 1, configured to split a spectrometer signal of the spectrometer or another spectrometer into two separate signals.

15. 15. The supercontinuum system of claim 14, further comprising a processor configured to compare the spectrometer signal with the input signal.

16. A supercontinuum system as described in claim 6, wherein the fiber coil, with the multimode fiber wound around it, is placed in a tray having a tray diameter that matches the coil diameter, and the multimode fiber is mechanically fixed.

17. The supercontinuum system of claim 8, wherein the bandwidth-filtered signal has a bandwidth of 5 nm to 10 nm.

18. The supercontinuum system of claim 9, wherein the two continuously variable filters are continuously variable filters.

19. A supercontinuum system as described in claim 9, wherein the two variable filters include a first variable filter in the form of a long wave pass filter and a second filter in the form of a short wave pass filter.

20. The supercontinuum system of claim 13, wherein the supercontinuum system is configured to notify an end user of the spectrum of the supercontinuum light or a portion of the supercontinuum light as it is supplied to the external device and / or the external sample at the output end.

21. A supercontinuum system as described in claim 14, wherein the spectrometer signal is suitable for monitoring the supply signal and is suitable for monitoring the spectrum of the supercontinuum light or a portion of the supercontinuum light coupled by the input coupler.

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