Optical measurement system and method

Abstract

To provide a low-noise supercontinuum light source.SOLUTION: A supercontinuum light source (1000) comprising an intermediate supercontinuum light source (100) and a single mode coupling unit (300), an optical measurement system comprising such light source, as well as a measurement method are described. The supercontinuum light source comprises a pulse frequency multiplier (103) for increasing a repetition rate, and the single mode coupling unit is configured to dampen and shape a spectrum from the intermediate supercontinuum light source to allow measurements with a reduced noise floor.SELECTED DRAWING: Figure 3a

Description

[Technical Field]

[0001] The present invention relates to a supercontinuum light source including an intermediate supercontinuum (SC) light source and a single-mode coupling unit, wherein the supercontinuum light source is suitable for use in a measurement system, for example, a system in which a sample to be measured or otherwise analyzed is illuminated by light emanating from such a supercontinuum light source, and the measurement system is configured to enable detection of light from the sample. The present invention also relates to a system suitable for measuring at least one parameter relating to an object, wherein the system includes a method for measuring at least one parameter relating to an object in the measurement system, similar to the supercontinuum light source. [Background technology]

[0002] Optical measurement systems exist in many variations. What these systems have in common is that a light beam is guided to a sample, and light from the sample is captured. The captured light may be light reflected from the sample, light transmitted through the sample, and / or light emitted from the sample depending on the incident beam, such as fluorescence.

[0003] Octave-bandwidth supercontinium (SC) sources have been successfully generated by pumping the fiber with a pulsed laser (often in a MOPA configuration) as input, directly through nonlinear fibers such as microstructured fibers, tapered standard fibers, and tapered microstructured fibers. Such spectrally broad continium sources are potentially useful in many measurement systems, such as optical coherence tomography (OCT), optical frequency metrology, fluorescence microscopy, coherent anti-Stokes Raman scattering (CARS) microscopy, and two-photon fluorescence microscopy. Unfortunately, for these experiments, the large amplitude fluctuations of conventional continium sources limit the accuracy and / or sensitivity. Previous studies of SC generation have shown that the SC generation process is highly sensitive to quantum noise, technical noise, and certain parameters such as the input wavelength, duration, and chirp of the input laser pulse. Sources derived from stable continium sources would generally improve the usefulness of SC sources.

[0004] Conventional continium generation in perforated photonic crystals or tapered single-mode long fibers is complex and may involve prominent substructures in the time and frequency domains, leading to undesirable, non-uniformly distributed noise and instability across different wavelength regions. Typically, the continium amplitude exhibits large fluctuations with a significant excess of white noise in the background, which can be revealed using fast detectors and RF spectrum analyzer (RFSA) measurements.

[0005] A common approach to wavelength conversion is to generate supercontinium, then spectrally slice a portion of the continium and use this slice as a light source for a microscopy setup. However, the selected continium likely contains large amplitude fluctuations (noise), which may make it unsuitable for some applications.

[0006] In (Patent Document 1), noise from an SC light source is reduced by tapering a nonlinear fiber and using a femtosecond pulse source that induces so-called soliton splitting. The abstract of this patent states: "A longitudinal change in phase matching state for Cherenkov radiation (CR) and four-wave mixing (FWM) introduced by a DMM enables the generation of a low-noise supercontinium." Tapering requires either post-processing techniques or changes in fiber diameter during manufacturing, which can complicate the manufacturing of the SC light source, and the tapered small cross-section can limit the amount of light that can be safely transmitted. Furthermore, femtosecond pump sources are often relatively complex and expensive.

[0007] (Patent Document 2) describes a light source device having a basic structure capable of generating SC light, and further having a structure that enables shaping of the waveform of the SC light spectrum, adjustment of the power of the SC light, or adjustment of the repetition frequency of a pulse train containing SC light. The light source device of (Patent Document 2) includes an SC fiber pumped at a wavelength of approximately 1550 nm, and the repetition frequency of the SC light pulse train from the light source is located between 1 MHz and 100 MHz. Throughout (Patent Document 2), noise is discussed only with respect to a single pulse, and it is explained that the noise characteristics of the pulsed light P1 are not affected. Regarding the noise characteristics of the SC light pulse train P2, it is mentioned that low-noise detection is possible through synchronization with a photodetector configured outside the light source device. The noise spectra from SC light sources using different pump wavelengths will differ, and therefore the noise suppression may differ. (Patent Document 2) refers to a femtosecond pulse train P1. Such pump sources are often relatively complex and expensive. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 7,403,688 [Patent Document 2] U.S. Patent Application Publication No. 2011 / 0116282 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] In consideration of the foregoing, an object of the present invention is to provide a low-noise supercontinium light source, and, advantageously, a supercontinium light source in which the effects of noise are reduced in the generated supercontinium (SC). Advantageously, the supercontinium light source is suitable for use in optical measurement systems. [Means for solving the problem]

[0010] In embodiments, the present invention relates to a system suitable for measuring at least one parameter relating to an object, which includes a supercontinuum light source, and it is also an object to provide a measurement method using the system.

[0011] These and other objectives have been addressed by the present invention or embodiments thereof, as defined in the claims and described below herein. The present invention and its embodiments have been found to have many additional advantages that will become apparent to those skilled in the art from the following description.

[0012] The supercontinuous light source of the present invention includes a light source output unit, an intermediate supercontinuous light source, and a single-mode coupling unit, wherein the intermediate supercontinuous light source is a. Pulse frequency F seed A seed laser configured to supply a seed pulse comprising, b. Double the seed pulse, and F seed pulse frequency F pump A pulse frequency multiplier (PFM) configured to convert into a pump pulse, wherein F pump is Fseed a larger pulse frequency multiplier (PFM), and c. a non-linear element configured to receive the pump pulse and convert the pump pulse into supercontinuum light having a supercontinuum spectrum ranging from about λ1 to about λ2 and supplied as an output of the non-linear element, wherein λ2 - λ1 > about 500 nm, and

[0013] The output from the non-linear element is coupled to a single-mode coupling unit to supply the output from the single-mode coupling unit, and the light source output includes the output from the single-mode coupling unit. The single-mode coupling unit is configured to attenuate and shape the supercontinuum spectrum from the non-linear element. Preferably, F pump is at least about 100 MHz, for example, at least about 150 MHz, at least about 200 MHz, at least about 300 MHz, at least about 400 MHz, at least about 500 MHz, at least about 600 MHz, at least about 700 MHz, at least about 800 MHz, at least about 1 GHz.

[0014] In a preferred embodiment of the frequency multiplier, the single-mode coupling unit is configured to receive the supercontinuum light and spectrally shape it such that the output spectrum from the single-mode coupling unit ranges from λ3 to λ4, where λ3 - λ4 > 0, λ3 ≧ λ1, and λ4 ≦ λ2, and the spectrally shaped output spectrum output from the single-mode coupling unit is different from the spectrum in the wavelength range of λ3 to λ4 from an intermediate supercontinuum light source.

[0015] The supercontinuum light source of the present invention has been found to have low noise resulting from a highly improved supercontinuum light source particularly useful for applications where low noise is beneficial. The term "low noise" means, for example, significantly lower than would otherwise be possible using prior art white light SC light sources operating at comparable power levels of output power in the spectral region, e.g., significantly lower than would otherwise be possible using prior art supercontinuum light sources operating at comparable power levels of output power, and an average noise beyond the soliton splitting region, as understood when the light source is applied in a measurement system.

[0016] The seed laser of the intermediate supercontinuum light source can be, for example, preferably a mode-locked fiber laser mode-locked via SESAM, and preferably the gain medium of the fiber laser is selected from YtYb-doped fiber, Er-doped fiber, and Er / Yb-doped fiber.

[0017] In an embodiment, the wavelength region "λ3 to λ4" is greater than about 100 nm, for example, greater than about 200 nm, greater than about 300 nm, or greater than about 500 nm. In an embodiment, the wavelength λ3 is less than about 1000 nm, for example, less than about 900 nm, less than about 800 nm, less than about 700 nm, or less than about 600 nm. In an embodiment, λ4 is greater than about 1070 nm, for example, greater than about 1100 nm, greater than about 1200 nm, or greater than about 1300 nm.

[0018] In an embodiment, the single-mode coupling unit includes one or more of the following, namely, one or more of a prism, a low-pass optical filter, a high-pass optical filter, a band-pass optical filter, and a single-mode fiber. Advantageously, the single-mode coupling unit is configured to shape the spectrum from the intermediate supercontinuum light source into a Gaussian spectrum, a double-peak spectrum, or a flat-top spectrum.

[0019] In the embodiment, the attenuation of the supercontinium spectrum in the single-mode coupling unit is given by an optical power attenuation coefficient y, the optical power attenuation coefficient y being a measure of optical power attenuation in the wavelength region λ4 to λ3, and the optical power attenuation coefficient y being greater than about 2, for example, greater than about 3, greater than about 4, greater than about 6, greater than about 8, and greater than about 10.

[0020] In an embodiment, the single-mode coupling unit includes at least one of the following to perform the attenuation: i) an output mismatch or mismatch from a nonlinear element to the single-mode coupling unit; ii) splice loss in the input to and / or output from the single-mode coupling unit; and iii) a broadband attenuation filter such as a neutral density filter or a broadband beam splitter.

[0021] In an embodiment, the single-mode coupling unit includes an input for coupling to a nonlinear element, a dichroic element at the input of the single-mode coupling unit configured to transmit wavelengths less than a threshold wavelength λ5 and having λ5 > λ3, at least one of the following: a prism, a low-pass optical filter, a high-pass optical filter, or a band-pass optical filter, and a single-mode fiber whose output is the output from the single-mode coupling unit. Advantageously, the dichroic element is a single-mode fiber, and the single-mode fiber is a step-index fiber or a microstructure fiber including a microstructure in the form of air or a low-index glass material.

[0022] In the embodiment, the total optical power in the output from the single-mode coupling unit is less than about 100 mW, for example, less than about 50 mW, less than about 30 mW, or less than about 20 mW.

[0023] In one embodiment, the seed laser has a pulse width t seed It is configured to supply a seed pulse having the pulse width tseed is longer than about 0.1 ps, for example, longer than about 0.25 ps, longer than about 0.5 ps, longer than about 0.75 ps, longer than about 1 ps, longer than about 2 ps, longer than about 3 ps, longer than about 5 ps, longer than about 10 ps, longer than about 20 ps, longer than about 50 ps, longer than about 100 ps, longer than about 200 ps, longer than about 300 ps, longer than about 400 ps, longer than about 500 ps, longer than about 1 ns.

[0024] In an embodiment, the seed laser is configured to supply a seed pulse having a pulse width t seed and is configured to output the time-compressed pulse to the nonlinear element. Advantageously, the intermediate supercontinuum light source is a non-interfering light source. seed is shorter than about 1 μs, for example, shorter than about 500 ns, shorter than about 200 ns, shorter than about 100 ns, shorter than about 50 ns, shorter than about 20 ns, shorter than about 10 ns, shorter than about 1 ns, shorter than about 500 ps, shorter than about 100 ps, shorter than about 50 ps, shorter than about 25 ps, shorter than about 20 ps, shorter than about 15 ps, shorter than about 10 ps.

[0025] Advantageously, the nonlinear element is an optical fiber such as a tapered and / or non-tapered microstructure fiber. In an embodiment, the intermediate supercontinuum light source includes a pulse compressor such as a PBG fiber, and the pulse compressor is configured to receive a pulse from the pulse frequency multiplier (PFM)

[0026] The system is suitable for measuring at least one parameter regarding the object, includes the supercontinuum light source of the present invention, and is configured to illuminate the measurement object with at least a part of the output of the single-mode coupling unit, for example, at least about 90% of all of the output of the single-mode coupling unit. The system further includes a detector for detecting light from the object.

[0027] Because of the supercontinium light source of the present invention, which includes a low-noise intermediate supercontinium light source, a highly accurate optical measurement system can be achieved. In the embodiment, the system includes a subject, which is a part of the human or animal body, such as the eye of a mammal or any part thereof. This enables in vivo and / or in vivo measurement of a part of the human or animal body.

[0028] Advantageously, the detector is 50 / F pump Longer, for example, 100 / F pump Longer, 200 / F pump Longer, 500 / F pump Longer, 1000 / F pump Longer, 5000 / F pump It has a longer integration time.

[0029] In embodiments, the measurement system is a reflection mode measurement system configured to measure light reflected from the object, such as a system based on white light interferometry or optical coherence tomography (OCT). Advantageously, the system is based on time-domain, frequency-domain, or sweep light source OCT.

[0030] In one embodiment, the measurement system is used to diagnose age-related macular degeneration (AMD), diabetic retinopathy, or glaucoma.

[0031] In one embodiment, the measurement system is used for diagnosis related to treatments that correct the refractive state of the eye, such as laser ophthalmic surgery (LASIK) to correct the refractive state of the eye. In another embodiment, the measurement system is used to measure the boundary of the Bowman layer inside the human eye.

[0032] A method of the present invention for measuring at least one parameter relating to a sieve includes providing a supercontinuous light source of the present invention, illuminating a sieve with at least a portion of the output of the single-mode coupling unit of the supercontinuous light source of the present invention, such as all of the output of the single-mode coupling unit, and detecting light from the sieve with a detector.

[0033] Advantageously, due to the high precision of the optical measurement system, the target is a part of the human or animal body, such as the eye or a part thereof of a mammal. This makes it possible to measure parts of the human or animal body in vivo and / or in vivo.

[0034] In the following, the present invention will be described in relation to silica-based nonlinear fibers. However, as will be apparent to those skilled in the art, the present invention also includes SC light sources based on other types of nonlinear elements, such as fibers based on other materials (e.g., polymers, chalcogenides, and fluoride glasses), nonlinear plane waveguides, and gas-filled hollow core fibers. Material and / or optical guide-based parameters, such as dispersion and nonlinearity, must be adjusted accordingly to the silica-based fiber parameters.

[0035] Typically, supercontinium (SC) is generated by applying a pulsed pump light source configured to pump a nonlinear fiber, such as the nonlinear fiber described above. The nonlinear process in the nonlinear element converts the pump pulse into supercontinium exiting the fiber. Particularly interesting is the case when substantial pump energy is supplied to wavelengths in a nonlinear fiber exhibiting anomalous dispersion, because this greatly expands the achievable bandwidth. In particular, as described by Dudley et al., Reviews of Modern Physics (Rev. Mod. Phys.), Vol. 78, No. 4, 2006, supercontinium generation is based on so-called modulation instability, in which the pump pulse is split into a series of short pulses (solitons) that enable the efficient generation of a broad supercontinium spectrum. In the normal dispersion region, supercontinium generation is primarily caused by self-phase modulation (SPM), which requires very high peak intensity to induce significant spectral broadening (e.g., >100 nm 10 dB bandwidth).

[0036] Accordingly, in embodiments, the pump pulse and nonlinear fiber (i.e., nonlinear element) are configured such that the supercontinium spectrum is generated primarily through the splitting of the pump pulse induced by modulation instability (MI). That is, most of the input pulse power is initiated at wavelengths located in or very close to the anomalous region, allowing for initial spectral broadening via SPM to shift a substantial portion of the power to the anomalous region. Preferably, more than 50%, e.g., more than 60%, 70%, 80%, 90%, 95%, or 100% of the generated supercontinium spectrum is generated through subsequent processes including MI and solitons generated by MI. Any residual pump light leaving the nonlinear element is not considered part of the generated supercontinium. In embodiments, these percentages are calculated as part of the total supercontinium power. In embodiments, the percentages are calculated as a percentage of the bandwidth scanned by the supercontinium.

[0037] The high nonlinearity of so-called highly nonlinear fibers (HNLFs) generally results from relatively small cross-sections that produce increased peak intensity. More importantly, however, the dispersion of these fibers is typically low and anomalous, at least for some wavelengths, and the fiber guides, for example, at the pump wavelength. The high nonlinearity ensures a long and effective nonlinear interaction length because peak power is maintained, and peak power supports soliton formation and MI splitting. In embodiments, soliton formation and MI-induced splitting are the main mechanisms in ultra-broadband light generation from nonlinear fibers. Other nonlinear processes such as self-phase modulation, cross-phase adjustment, self-steepening, and Raman scattering play a similar role, although they do not require anomalous dispersion.

[0038] The pump pulse and nonlinear element may be configured such that the center wavelength of the pump pulse is preferably in the anomalous dispersion region. Alternatively, the pump wavelength can be in the normal dispersion region (but close enough to the anomalous region) where a moderate spectral broadening (e.g., via SPM or Raman shift) can transfer a substantial portion of the pump energy to the anomalous region, such as ZDW-150nm or higher, ZDW-100nm or higher, ZDW-50nm or higher, ZDW+10nm or higher, ZDW+20nm or higher, ZDW+30nm or higher, ZDW+50nm or higher, ZDW+100nm or higher, and ZDW+150nm or higher. In embodiments, the shape of the resulting supercontinium spectrum can be largely controlled by varying the distance from the pump wavelength to the intersection between normal and anomalous dispersion. This is the so-called zero dispersion wavelength (ZDW).

[0039] The term "substantial pump energy shifted into the abnormal region" is understood to mean that more than 30% of the pulse energy, e.g., more than 50%, 60%, 70%, 80%, 90%, 95%, or 100%, enters the abnormal region before the pulse is split.

[0040] As explained by Dudley et al., "Supercontinuum generation in photonic crystal fiber," Reviews of Modern Physics (Rev. Mod. Phys.), Vol. 78, No. 4, (2006), pp. 1159-1162, supercontinuum is non-coherent when modulation instability is the dominant process in the splitting of pump pulses. Non-coherent supercontinuum can be understood as arising from noise, and therefore the time and spectral stability of the generated light is impaired. According to the authors, pump pulses with soliton order (N) in fibers N < 10 provide interfering supercontinuum, while pump pulses with N > 30 provide non-coherent supercontinuum. Values ​​10 ≤ N ≤ 30 provide a transition between these two states, and the supercontinuum spectrum can be generated interfering or non-coherently, depending on the exact pump and fiber parameters. Here, the soliton order is defined as shown in (Equation 1).

[0041]

number

[0042] Coherence can be dramatically reduced when N > 16 (while noise increases dramatically). Increasing the value of N causes modulation instability (which is pulse splitting induced by quantum noise) to proceed faster than the deterministic soliton splitting process. Therefore, the transition from soliton splitting to MI-induced splitting marks a separation between low-noise / high-interference and high-noise / low-interference. In "Generation of a broadband continuum with high spectral coherence in tapered single-mode optical fibers," Optics Express, January 26, 2004, Vol. 2, No. 2, pp. 347-353 (referenced in U.S. Patent No. 7,403,688, with authors matching the inventors), a short 50 fs pulse provides relatively low N, and the soliton order is further reduced by tapering, providing high spectral coherence and low noise. In "Super continuum generation for real time ultrahigh resolution optical coherence tomography," Proc. of SPIE, Vol. 6102, 61020H (2006), it is concluded that supercontinuum is generated using a 95 fs pump pulse, and only the spectrum generated by pumping in the normal region has sufficiently low noise to be applicable. As mentioned above, such a spectrum is formed by the deterministic process of SPM, thus enabling the generation of low-noise, high-interference SC.

[0043] In embodiments, the nonlinear fiber is not tapered. However, in embodiments, the present invention is combined with a noise reduction effect obtainable through tapering. A new type of tapered fiber suitable for SC generation is described in international patent application PCT / Danish patent application publication 2011 / 050328.

[0044] However, in embodiments, the present invention enables the application of non-interfering or partially non-interfering supercontinium such that the nonlinear fiber and pump pulse are configured such that the soliton order of the pump pulse is substantially 16 or higher, for example, 18 or higher, 20 or higher, 22 or higher, 24 or higher, 26 or higher, 28 or higher, 30 or higher, 40 or higher, 50 or higher, 75 or higher, 100 or higher, 200 or higher, 300 or higher, 400 or higher, or 500 or higher. Thereafter, the supercontinium generation process proceeds primarily through modulation instability.

[0045] In one embodiment, the soliton order is defined when the pulse is split, for example, after shifting into an abnormal region and / or after traversing a tapered section of the fiber. In another embodiment, the soliton order is defined when the pump pulse is input to the fiber.

[0046] Generally, the spectral width of the generated SC depends on the peak power of the pump pulse, and therefore, for longer pulses, the peak power cannot be arbitrarily reduced in order to reduce the soliton order. Longer pulses, such as pulses in the ps or ns region, are often preferred because these pulses often enable simpler pump laser configurations compared to fs lasers. Accordingly, in embodiments, the present invention enables applications with longer pulse widths, such as pulses longer than about 0.1 ps, for example, longer than about 0.25 ps, longer than about 0.5 ps, longer than about 0.75 ps, longer than about 1 ps, longer than about 2 ps, longer than about 3 ps, longer than about 5 ps, longer than about 10 ps, ​​longer than about 20 ps, ​​longer than about 50 ps, ​​longer than about 100 ps, ​​longer than about 200 ps, ​​longer than about 300 ps, ​​longer than about 400 ps, ​​longer than about 500 ps, ​​longer than about 1 ns, and longer than about 10 ns.

[0047] On the other hand, in SCs generated from very long pump pulses and CW, pumping suffers from increased noise. While the present invention can reduce sensitivity to noise, it may also be preferable to reduce noise by reducing the pulse width, and as a result, in embodiments, the seed laser has a pulse width t seed It is configured to supply a seed pulse having the pulse width t seed This refers to durations shorter than approximately 1 μs, for example, shorter than approximately 500 ns, shorter than approximately 200 ns, shorter than approximately 100 ns, shorter than approximately 50 ns, shorter than approximately 20 ns, shorter than approximately 10 ns, shorter than approximately 500 ps, ​​shorter than approximately 100 ps, ​​shorter than approximately 50 ps, ​​shorter than approximately 25 ps, shorter than approximately 20 ps, ​​shorter than approximately 15 ps, and shorter than approximately 10 ps.

[0048] The variable intervals mentioned above may be coupled to form closed intervals with respect to pulse widths, such as pulse widths of 0.1 ps to 1 μs, 0.25 ps to 100 ps, ​​and 1 ps to 50 ps.

[0049] As mentioned above, SC is typically generated by applying a pulsed pump light source. In the supercontinuum light source of the present invention, the pump pulse has a repetition rate F pump Supplied by, with a repetition rate F pump Therefore, the same frequency F pump This generates amplitude modulation of the generated supercontinium, which is provided by the [unclear]. On the other hand, the measurement system of the present invention is 1 / F pump A longer measurement time is typically applied, i.e., a measurement time over which the repetition rate is not determined and the measurements are integrated so that the SC appears as CW radiation. For this reason, pulsed lasers operating in the MHz range are often called "pseudo-CW". However, the pulsed characteristics of supercontinium reduce the effective measurement time over which light is present. Therefore, in embodiments, the SC light source is F pump However, a high repetition rate is applied, such as 100MHz or higher, for example, 150MHz or higher, 200MHz or higher, 300MHz or higher, 400MHz or higher, 500MHz or higher, 600MHz or higher, 700MHz or higher, 800MHz or higher, or 1GHz or higher.

[0050] As will be further described below, a pump laser system typically consists of a main laser oscillator, also called a seed laser, followed by one or more optional optical amplifiers that boost the pulse power level from the seed laser. That is, the pump laser may include a MOPA configuration. Depending on the type of seed laser, providing such a high repetition rate may not be practical or possible. In embodiments, the pump laser (also called a pump laser system) is F pump Lower pulse frequency F seed A seed laser configured to supply a seed pulse with F seed F pump Includes one or more pulse frequency multipliers (PFMs) configured to convert to

[0051] Preferably, the pulse frequency multiplier for a supercontinium light source of the present invention includes a splitter that divides at least one beam of a seed pulse into many sub-beams, and a first coupler configured to recombine at least some of the sub-beams, and preferably the pulse frequency multiplier further includes an adjustable attenuator configured to adjust at least one of the sub-beams.

[0052] In this specification, "beam" means a pulse train. Any type of splitter is acceptable. Such splitters are well known in the art.

[0053] In embodiments, the pulse frequency multiplier includes an adjustable attenuator configured to receive at least one subbeam. Preferably, the adjustable attenuator is configured to receive at least one subbeam having power exceeding the average subbeam power, and the pulse frequency multiplier optionally includes a plurality of adjustable attenuators, preferably each attenuator configured to receive at least one subbeam having pulses within a selected peak power range. Advantageously, to significantly reduce noise, the adjustable attenuator is configured to receive pulses from at least one subbeam and adjust them to a peak power value corresponding to the peak power value of pulses in at least one other subbeam, such that the pulses of the subbeams coupled in the first coupler have substantially identical peak power values.

[0054] In embodiments, the pulse frequency multiplier is configured to time delay at least one of the subbeams. The time delay can be provided, for example, by initially arranging a path from the splitter to the single subbeam coupler that is shorter than a second path from the splitter to the second subbeam coupler. Preferably, the pulse frequency multiplier is configured to time delay at least one subbeam such that the pulses of the subbeams recombined in the first coupler are preferably spaced apart at substantially uniform intervals. [Brief explanation of the drawing]

[0055] [Figure 1a] A schematic intermediate supercontinium light source suitable for the present invention is shown. [Figure 1b] An example of a supercontinium spectrum (10) from λ2 at approximately 460 nm to λ1 at approximately 2400 nm is shown. [Figure 2a] An example of a pulse frequency modulator (PFM) for an intermediate supercontinium light source according to the present invention is shown. [Figure 2b] An example of a pulse frequency modulator (PFM) for an intermediate supercontinium light source according to the present invention is shown. [Figure 3a] Figure 1 shows a suitable measurement setup for measuring intensity noise in the spectrum of an SC light source, such as the SC light source shown. [Figure 3b] Similar to the example of the supercontinium spectral output from the intermediate supercontinium light source 100, examples of spectral output from the single-mode coupling unit 300 are shown. [Figure 3c] An example spectral output from a single-mode coupled unit is shown. [Figure 3d] An example spectral output from a single-mode coupled unit is shown. [Figure 3e] An example spectral output from a single-mode coupled unit is shown. [Figure 4a] This shows the average intensity noise of the intermediate supercontinium light source before and after compensation for spectrometer noise. [Figure 4b] This shows the average intensity noise of the intermediate supercontinium light source before and after compensation for spectrometer noise. [Figure 5] This shows an example of an optical measurement system that uses an SC light source as the light source for OCT. [Figure 6] An example of a single-mode coupling unit is shown, which includes a dichroic element (a dichroic mirror), a dispersive element (a prism), and a single-mode fiber configured to shape the spectrum. [Figure 7]An example of a single-mode coupling unit is shown, which includes a dichroic element that is a single-mode fiber, an attenuating and / or shaping optical element, and a second single-mode fiber. [Figure 8a] Here are three examples of methods for attenuating light power. [Figure 8b] Here are three examples of methods for attenuating light power. [Figure 8c] Here are three examples of methods for attenuating light power. [Modes for carrying out the invention]

[0056] Figure 1a shows a preferred configuration of an intermediate supercontinuum light source 100 included in the supercontinuum light source according to the present invention. A main oscillator (or seed laser) supplies output along the beam path 106. The components are preferably fiber-coupled, but may also be coupled via a free-space optical system. The intermediate supercontinuum light source 100 includes two power amplifiers (PA1 and PA2) 102 and 104. As mentioned above, these amplifiers are optional, but result in an increase in pulse energy and peak power compared to the output from the seed laser 101. The seed laser 101, PA1 102 and PA4 104 are pumped by diode lasers, however, other pumping sources such as power sources can be used as alternatives. An optional regulator 105 is included to show that the intermediate supercontinuum light source may include a feedback system. In this embodiment, the feedback loop is formed by a photodiode 109 that measures a portion of the output 108 and supplies one or more beam-related parameters to a determination point 114 that adjusts the input to the nonlinear element 107. Such a tuner may be formed, for example, by an adjustable attenuator configured to adjust the optical power entering the nonlinear element 107. The concurrently pending U.S. Patent Application 12 / 865,503 (incorporated herein) discusses various embodiments of the feedback loop in an SC light source (see, for example, Figure 1 and the claims), including alternative configurations of the tuner 105 and photodiode 109, various embodiments of the tuner, beam focusing to the photodiode, and the possibility of applying the feedback response to one or more of the pump sources 110-112.

[0057] The PFM 103 may be placed before the first amplifier, between amplifiers, and before the nonlinear fiber. In embodiments, the pulse train saturates the amplifiers (PA1 and / or PA2) such that the peak power of the pulses from the amplifiers is constant regardless of their input power. In Figure 1, the PFM is placed between two power amplifiers (PA1 and PA2 in this case). This may be preferable because, in most cases, the PFA may have significant insertion losses, as it redistributes the optical power from the seed laser into more pulses, and when the output pulses of the seed laser are relatively weak, the PFA may generate a pulse train with an average power too low for the pulse train to be efficiently amplified in the subsequent amplifiers. For this reason, in embodiments, it is preferable to place the PFM after one or more amplifiers, such as between two amplifiers. On the other hand, placing the PFM after one or more amplifiers increases the nominal power loss due to such insertion losses. For this reason, in embodiments, it is preferable to place the PFM before one or more amplifiers, such as between two amplifiers. This may also have the effect of reducing the peak power of pulses passing through one or more power amplifiers (or other components in the system), which in turn may have one or more benefits, such as reducing nonlinearity in the pump laser system. Such nonlinearity often has a pulse-broadening effect, which can result in a reduction in the peak power level to the nonlinear element, which in turn may reduce the spectral width of the generated supercontinium. In embodiments, multiple PFMs are applied, such as multiple PFMs separated by optical components such as optical amplifiers, attenuators, compressors, or filters.

[0058] In embodiments, there is an upper limit to the acceptable average light power for illuminating the object being measured (also called a sample). Examples of such applications include those where the object is sensitive to light power (average power and / or peak power) above a certain threshold (which would be true for most biological samples), and particularly for parts of the mammalian eye, such as the retina. Examples of applications where the object is the ophthalmic mammalian eye include imaging using OCT and multiphoton fluorescence microscopy of the retina or cornea.

[0059] In embodiments, the output of the SC light source or its subsection must conform to one or more of the laser standard classes 1, 1M, 2, 2M, 3R, and 3B. In embodiments, the output power of the SC light source is reduced so that the SC light source itself may have a higher output AEL (Acceptable Emission Level) than the classes cited above, such as 100% or more higher, 200% or more higher, 400% or more higher, or 800% or more higher.

[0060] In embodiments, relatively low noise due to pulse width is desirable, and as a result, pulse widths in the range of 0.5 ps to 30 ps are preferred, such as pulse widths in the range of 1 ps to 20 ps, ​​preferably 2 ps to 20 ps. In embodiments, an increase in average optical power for this system is undesirable because the average optical power from the SC light source is less than 5 watts per ps pulse width, e.g., less than 3 watts per ps pulse width, less than 2 watts per ps pulse width, and less than 1 watt per ps pulse width. In one embodiment, the total average optical power in the visible region (400 nm to 850 nm) is configured to be less than 100 mW, e.g., less than 50 mW, less than 30 mW, and less than 20 mW. As mentioned elsewhere, reducing the average power after output from the SC light source is often improperly complicated or impossible because the optical components required to reduce power modify the spectrum.

[0061] As previously mentioned above, in embodiments, the spectral width of the generated SC depends on the peak power of the pulse up to at least a certain saturation level where further increases in peak power do not increase the spectral width. Also, the conversion efficiency from pump light to SC light depends on the peak power, which means that for a fixed pulse width, the peak power (and corresponding average power) cannot be reduced at all. Below a certain value, the desired spectral width of the generated spectrum is compromised, and consequently, due to poor conversion efficiency, too much unconverted pump light passes through the fiber, which can damage the sample under observation. Therefore, in embodiments, as a result of the minimum peak power, insertion of a PFM causes an increase in average optical output power compared to configurations in which the PFM is omitted. This occurs because the repetition rate of the pump pulse is increased while the peak power and pulse width remain constant. In embodiments, the optical power is reduced by adjusting the pump energy supplied to the last power amplifier before the nonlinear element, however, this can compromise the resulting spectral width, as mentioned above.

[0062] In embodiments, the reduction of average optical power may be achieved by introducing attenuation after a nonlinear element, such as attenuating the beam away from the beam path or splitting a portion of the beam. Applications requiring a tunable portion of the generated spectrum guided to a sample may apply an AOTF to perform such a function. In embodiments, the AOTF may be controlled to reduce the amount of average optical power guided to the sample. For example, in applications requiring broadband illumination, such as in OCT imaging systems, it can be more difficult to apply optical components to the beam without disrupting the spectral shape and / or damaging the optical elements. In embodiments, the pump laser system includes a pulse compressor, such as a PBG fiber (hollow or solid core), configured to compress pump pulses and thus increase peak power. This use of PBG fibers was discussed in the PCT application, International Publication No. 2005041367. In embodiments, by increasing the peak power of individual pulses, the use of a pulse compressor allows for the use of lower average optical power while maintaining the spectral characteristics of the generated spectrum.

[0063] In principle, the PFM of the intermediate supercontinium light source of the present invention is any optical component suitable for receiving a pulse train at a certain repetition rate, and this input may be converted into a pulse train with a higher repetition rate. In embodiments, the input and output pulses have substantially the same pulse width and wavelength. In embodiments, the PFM works by dividing the pulse train at the input into a plurality of sub-pulse trains, each experiencing different delays (optical path lengths) before being recombined. The relative delays cause a temporal shift in the sub-pulse trains when recombined, resulting in the combined pulse train containing more pulses than the input. For example, the input pulse train may be divided into two sub-pulse trains (or sub-beams), one of which is delayed relative to the other. In this case, the repetition rate of the combined train is doubled. Preferably, the relative shift between beams corresponds to half the interval between two pulses in the input pulse train. In embodiments, this principle is extended so that the input beam is initially divided into more than two sub-beams, such as two, three, or four sub-beams, which are delayed relative to each other and recombined. It is well known that optical splitters (or couplers) function in a symmetrical manner. The coupling of several optical beams produces the same amount of output beam. In embodiments, only a single output is used / available, while the optical power allocated for other outputs is lost in the optical system. Therefore, in embodiments, it is advantageous to cascade couplers / splitters, as described below in relation to Figure 2b.

[0064] In embodiments, the present invention relates to a PFM comprising a splitter for splitting a beam into sub-beams, an optional adjustable attenuator configured to receive the sub-beams, and a first coupler configured to couple the sub-beams. Thus, the adjustable attenuator may be tuned to compensate for manufacturing variations in the splitter and / or coupler, as well as coupling variations, and as a result, a pulse train can be generated as a result of pulses with uniform peak power. In embodiments, precise adjustment of peak amplitude is not required, and substantial differences between the peak powers of the recombined sub-beams are acceptable.

[0065] In the embodiment, one or more splitters and couplers have a non-uniform splitting ratio (

[0066]

number

[0067] In embodiments, the PFM includes a plurality of attenuators, each configured to receive a separate sub-beam. In embodiments, a splitter divides the beam into two sub-beams. In embodiments, a splitter divides the beam into more than two sub-beams, e.g., three or more, four or more, five or more, six or more, seven or more, eight or more. In embodiments, a first coupler further acts as a splitter that divides the combined beam into a second sub-beam, followed by a second coupler for the second sub-beam. In embodiments, the PFM includes an adjustable attenuator configured to receive one of the second sub-beams. This attenuator may be applied to adjust for coupling losses and other variations, as well as variations in the first and second couplers. In embodiments, the second coupler is configured to have a non-uniform splitting ratio (and therefore also non-uniform coupling of the input beams), and the output from the adjustable attenuator is configured to supply a larger portion to the output. Again, the second coupler can ensure that a pulse train with uniform power between pulses can be supplied by the PFM.

[0068] In embodiments, the PFM is formed by a free-space optical system such as a bulk beam splitter. In embodiments, the PFM is formed by an optical fiber splitter and / or coupler, which is often preferred in terms of system cost and robustness.

[0069] Figure 1b shows an example of a supercontinium spectrum (10) from λ2 at approximately 460 nm to λ1 at approximately 2400 nm. The spectrum was obtained from the NKT Photonics A / S product SuperK EXW-12.

[0070] Figures 2a and 2b show examples of pulse frequency modulators (PFMs) for intermediate supercontinium light sources according to the present invention. Figure 2a shows an embodiment of PFM 200. The input beam (in free space or via fiber) enters the PFM at input 201. The splitter 214 is exemplified as a 1×2 splitter, but may be any 1×N splitter, or even an M×N splitter. For an M×N splitter, multiple inputs may be coupled, or alternatively, only one of the available inputs of M may be used. The first splitter 214 splits the input beam into two subbeams 202 and 203 with a splitting ratio of x1 / (1-x1). As discussed above, in the embodiment, the larger of x1 and (1-x1) is transmitted to an adjustable attenuator 204. In embodiments, the attenuator is omitted, in which case x1 is preferably about 0.5 (i.e., 50%) so that fluctuations in the peak power of the pulse train in output 207 can be minimized. The sub-beam 202 is supplied to a delay line 205, which is preferably configured to delay the sub-beam 202 by half the period between two pulses in the input beam 201. In embodiments, the delay line is adjustable to absorb fluctuations in the repetition rate of the input beam. In embodiments, small deviations from the uniform spacing of pulses in the output beam (e.g., less than 75%, less than 50%, less than 25%, less than 15%, less than 10%, less than 5%, less than 1%) can be tolerated because the delay line is fixed. The sub-beams 202 and 203 are coupled in a coupler 206 that supplies output 207. The coupler 206 has a splitting ratio of x2 / (1-x2). In embodiments, either the splitter 214 or the coupler is configured to have a non-uniform splitting ratio, i.e., x1 or x2 deviates from 50%, and in this way, the attenuator 204 may be adjusted so that beams 202 and 204 contribute equally, and as a result, the pulses in the input that are split into two pulses are recombined so that they have substantially the same peak power at the output, where "substantially" means including within normal tolerances. The effect of PFM is doubling of the pulse frequency of the input beam.The coupler 206 further has an output 208, which may or may not be a physically available real output. However, the output 208 is included to demonstrate that the coupler introduces insertion loss due to the inherent symmetry of the beam splitter / coupler such that the peak power is reduced to about 25% of the input peak power when other optical losses (such as in the coupling and attenuator) are ignored. In embodiments, the beam of the output 208 is applied to monitor the beam and adjust the attenuator 204.

[0071] Figure 2b shows the PFM of Figure 2a, but with a second coupler 213 to result in a quadrupling of the pulse frequency. In principle, quadrupling can also be achieved by extending the splitter 214 to 1×4 and the coupler 206 to a 4×1 coupler. However, in this case, the coupler would impose an insertion loss of about 75% due to the symmetry of the beam splitter, compared to the approximately 50% loss imposed by the second coupler 213. Preferably, the first delay line is adjusted to half the input period in 201, the first delay line doubles the pulse repetition rate after coupling in coupler 206, and preferably the second delay line 212 is positioned to provide a delay of half of that, i.e., one-quarter of the input period in 201. The division ratio x2 / (1-x2) is set to be equal in the embodiment, and x1 and x3 are configured non-uniformly so that the attenuator 204 can perform the function described in relation to Figure 2a, and the attenuator 211 can perform a similar function to compensate for variations in the division of 206, similar to the coupling in the coupler 213. It is worth noting that further doubling can be obtained by adding couplers and further extending the PFM without increasing the insertion loss due to the symmetric division.

[0072] Figure 3a shows a measurement setup in which the SC light source 1000 of the present invention is configured to illuminate a spectrometer rather than the object being measured. Figure 3a shows that the supercontinuum light source 1000 of the present invention includes an intermediate supercontinuum light source 100 and a single-mode coupling unit 300. The output from the SC light source 1000 is the output from the single-mode coupling unit 300. The output from the intermediate SC light source 100 is the output from a nonlinear element 107 (not shown in Figure 3a). This output from the intermediate SC light source 100 is coupled to the input to the single-mode coupling unit 300. The output from the intermediate SC light source 100 is at least substantially the output from the nonlinear element (107 in Figure 1a, not shown in Figure 3a) of the intermediate supercontinuum light source (100 in Figure 1a). The single-mode coupling unit 300 includes adaptations in which the spectrum is attenuated and / or shaped according to the requirements of the application. In one embodiment, the SM coupling unit 300 includes one of the embodiments in the concurrently pending PCT application PCT / Danish Patent Application Publication No. 2011 / 050475 (incorporated herein). In particular, please refer to any one of the items and / or claims, as well as the embodiments and their variations relating to Figures 5a, 6, 7, 8-10, 13-15 and 17-19.

[0073] Figure 3b shows an example of the supercontinium spectral output from the intermediate supercontinium light source 100 (spectrum 10), as well as an example of the spectral output from the single-mode coupling unit 300 (spectrum 12). In this example, the spectrum after the single-mode coupling unit has a Gaussian distribution and extends from λ4 at approximately 650 nm to λ3 at approximately 950 nm. Therefore, Figure 3b shows that the spectral shape after the single-mode coupling unit is different from the spectral shape in the same wavelength region from the intermediate supercontinium light source.

[0074] Figures 3c, 3d, and 3e show examples of spectral outputs from the single-mode coupling unit 300, i.e., spectral shapes that are Gaussian (Figure 3c), flat-top (Figure 3d), and double-peak distribution (Figure 3e), respectively. A double-peak distribution may be advantageous when the output from the light source is sent through an optical element (such as an optical lens) that has Gaussian properties like a transfer function before illuminating the object, and a flat-top distribution is advantageous for illuminating the object.

[0075] In one embodiment, the spectral shape after the single-mode coupling unit differs from the spectrum in the same wavelength region from the intermediate supercontinium light source, such as a Gaussian, flat-top, or double-peak distribution. Figures 4a and 4b show the measurement results from the setup shown in Figure 3a. The intermediate SC light source was configured according to Figure 1.

[0076] Figure 4a shows the average intensity noise of the intermediate supercontinium light source 100 (see Figure 1), measured at 790–870 nm using a Wasatch Cobra UD spectrometer (310) equipped with a Basler Sprint SPL4096–70 km camera, as a function of power of the 400–850 nm supercontinium light source. Figure 4a shows the average intensity noise after compensation for spectrometer noise, while Figure 4b shows the average intensity noise before compensation for spectrometer noise. Figure 4a shows three different pump pulse frequencies (F) of 80 MHz (curve 401), 160 MHz (curve 402), and 320 MHz (curve 403). pump Includes measurements for ). It can be seen that the noise decreases as the pump pulse frequency increases. Intensity noise is compensated for the noise added by the spectrometer.

[0077] Figure 4b shows the intensity noise data from Figure 4a before noise compensation from the spectrometer. Figure 4b shows three different pump pulse frequencies (F) of 80 MHz (curve 411), 160 MHz (curve 412), and 320 MHz (curve 413). pumpThis includes measurements for ). Again, it can be seen that the noise decreases as the pump pulse frequency increases.

[0078] The MO101 is a mode-locked Yb fiber laser with an output having a center wavelength of approximately 1060 nm and a pulse width of approximately 6 ps. The laser is passively mode-locked via SESAM and supplies pulses with a repetition rate of 80 MHz. This laser type is well-suited for seeding because the all-fiber configuration provides a robust laser that is relatively easy to manufacture for a bulk optical setup. The maximum repetition rate is determined by how short the cavity can be fabricated and the response characteristics of the SESAM. In practice, these limitations often impose a practical upper limit of a repetition rate of approximately 100 MHz. In embodiments, other gain media may be applied to provide other output wavelengths, and the pulse width and repetition rate may also be modified within the limits discussed elsewhere.

[0079] In embodiments, the seed laser is a fiber laser, such as a mode-locked fiber laser, including mode-locked fiber lasers via SESAM. The gain medium may be formed by any suitable laser gain, such as a Yb-doped fiber, an Er-doped fiber, or an Er / Yb-doped fiber. The seed laser may also be, for example, a linear cavity laser or a ring laser.

[0080] The nonlinear medium 107 is a microstructured PCF fiber formed by a silica core surrounded by a hexagonal pattern of holes configured such that the core is formed by missing holes in the pattern. The fiber is configured such that the ZDW of the fiber is relatively close to the pump wavelength so that substantial pump energy is supplied in the anomalous region of the fiber.

[0081] As shown in Figure 1, optical fiber amplifier sets 102 and 104 are arranged around an optional PFM. Without the PFM, the pump system pumps the fiber at approximately 10W, 8-10ps, at 80MHz. By inserting the PFM according to Figure 2a, the repetition rate is increased to 160MHz, and by inserting the PFM according to Figure 2b, the repetition rate is quadrupled to 320MHz. Figures 4a and 4b show experimental results obtained using a Wasatch Cobra UD spectrometer equipped with a Basler Sprint SPL4096-70km camera configured to measure the spectral region of 790-870nm with 4096 pixels, i.e., approximately 0.02nm / pixel. A measurement time of 12.9μs was applied, and the power fluctuation measured at each pixel was recorded. Longer and shorter measurement times, such as 1μs to over 1ms, are possible. Short measurement times are often desirable, such as for Fourier-domain OCT (see Figure 4b), where real-time imaging is frequently required. In Figure 4, the mean relative standard deviation per pixel in the 790-870 nm spectral region is measured as a function of the visible portion of the spectrum. It is observed that the standard deviation and therefore the intensity noise decrease significantly as the pump pulse repetition rate is doubled, and further quadrupled relative to the average power in the visible region. The power in the visible region depends on how effectively the pump energy is converted into visible light, which depends on the peak power of the pump pulse and the total pump power (average power). This is included in Figure 4b, whereas in Figure 4a, the estimated noise contribution from the spectrometer is subtracted.

[0082] Figure 5 shows an example optical measurement system as an OCT system using an SC light source. The system shown in Figure 5 is a Fourier-domain OCT (FD-OCT) system according to the present invention, and therefore, in a Fourier-domain OCT system, the SC light source 1000 is applied as a light source suitable for the optical measurement system according to the present invention. A 2×2 50 / 50 directional splitter / coupler (501) coupled to a light source and spectrometer (310) that acts as a detector on one side, and a lens (502), object to be measured (503), and reference reflector (504) on the other side constitute the interferometer core of the OCT system. Line scanning (depth profile of the sample) is performed by measurement of the spectrometer, in which case the measurement depth is determined by the spectral resolution, and the spatial resolution in the sample is determined by the spectral width of the measurement. The beam is often scanned over the object to provide a 2D or 3D depth profile of the reflectance in the sample. OCT is often a broad field that includes many variations in system configuration, all of which are expected to benefit from aspects of the present invention. The output spectrum is Gaussian, such as in the embodiments discussed in relation to Figures 5a (single-band Gaussian spectrum) and 6 (dual-band Gaussian spectrum) in PCT / Danish Patent Application Publication No. 2011 / 050475, as well as in Figure 16, which is configured to provide a broad and adjustable spectrum, so that in one embodiment the SM coupling unit is configured to shape the spectrum from the SC light source into a Gaussian spectrum. In one embodiment the SM coupling unit includes a filter configured to supply the Gaussian spectrum. The 50 / 50 coupler should be configured to handle a broad spectrum and is typically either a fused fiber coupler or a bulk optical coupler.

[0083] Figure 6 shows an example of a single-mode coupling unit 300, which includes a dichroic element, which is a dichroic mirror, a dispersion element, which is a prism, and a single-mode fiber configured to shape the spectrum. Thus, Figure 6 shows an example of how the single-mode coupling unit 300 is configured. The output of the intermediate supercontinium light source 100 is led to the dichroic element 60 and the dispersion element 61. The mirror and / or angular dispersion element are connected to an electronic control unit 6, which allows rotation between these two elements. The system may also optionally include an adjustable attenuation filter 62 and / or an adjustable spatial filter 63. The light is collimated by a lens system 64 and focused by a fiber 65, which then shapes the spectrum. The system may also optionally include a broadband splitter 66, which sends a portion of the light to an output unit 67 and another portion to a detection system 68. The detection system is connected to an electronic control system 6, which is then connected again to a supercontinuum light source 100 and / or a dichroic element 500 to stabilize the output power. In one embodiment, the dispersion element is a prism. In one embodiment, the fiber 65 is a single-mode fiber such as a step-index fiber or a microstructured fiber. In one embodiment, the collimating lens system 64 includes a plurality of lenses.

[0084] Figure 7 shows an example of a single-mode coupling unit 300, which includes a dichroic element that is a single-mode fiber 60, an attenuating and / or shaping optical element 70, and a second single-mode fiber 65.

[0085] In one embodiment, the first single-mode fiber 60 has high loss above a certain threshold wavelength λ6 and therefore acts as a spectral filter. In one embodiment, the attenuating and / or shaping optical element is selected from the list of a prism, optical low-pass, optical high-pass and optical band-pass filters, and a neutral density filter.

[0086] Figures 8a to 8c show three examples of methods for attenuating the optical power in the supercontinuum light source of the present invention. In Figures 8a to 8c, the supercontinium light source is indicated by reference number 1000, the intermediate supercontinium light source by reference number 100, and the single-mode coupling unit by reference number 300.

[0087] In Figure 8a, the single-mode coupling unit 300 includes an attenuation and shaping unit 81, and the mode field diameter at the output of the attenuation and shaping unit 81 is different from the mode field diameter of the second single-mode fiber 82. Therefore, Figure 8a shows the mismatch in mode field diameter at the output of the attenuation and shaping unit 81 of the single-mode coupling unit 300.

[0088] In Figure 8b, the single-mode coupling unit 300 includes a damping and molding unit in the form of a molding element 60 and a damping element 84. Figure 8c shows an example in which attenuation in the single-mode coupling unit 300 is obtained by having an optical splice with a large loss 86 between the intermediate supercontinium light source 100 and the input of the single-mode coupling unit 300.

[0089] It should be emphasized that the term “including” is to be interpreted as an open term when used herein. That is, it should be understood to identify the presence of particularly declared features such as elements, units, integers, steps, components, and combinations thereof, but not to exclude the presence or addition of one or more other declared features.

[0090] Furthermore, the term "substantially" means including those that fall within normal tolerances. All features of the present invention, including the regions and preferred regions, can be combined in various ways within the scope of the invention unless there is a specific reason not to combine such features.

Claims

1. A supercontinuous light source, Pulse frequency F ｓｅｅｄ A seed laser configured to supply a seed pulse comprising, The pulse frequency F ｓｅｅｄ A seed pulse equipped with a pulse frequency F ｐｕｍｐ A pulse frequency multiplier (PFM) configured to multiply the seed pulse by converting it into a pump pulse equipped with F ｐｕｍｐ is F ｓｅｅｄ A pulse frequency multiplier (PFM) that is larger than the above, receives the pump pulse and converts the pump pulse into a pulse of supercontinuum light having a supercontinuum spectrum spanning at least about λ １ to about λ ２ where the non-linear element is configured to convert the pump pulse into a pulse of supercontinuum light having a supercontinuum spectrum spanning at least about λ １ -λ ２ > about 500 nm, and the non-linear element, The seed laser has a pulse width t ｓｅｅｄ It is configured to supply a seed pulse having the pulse width t ｓｅｅｄ The duration is longer than approximately 1 ps, and the seed laser is a supercontinuous light source including a mode-locked Yb laser.

2. The pulse frequency multiplier is F ｐｕｍｐ The supercontinuous light source according to claim 1, comprising an attenuator configured to attenuate optical pulses having a pulse frequency less than [amount missing].

3. The supercontinuum light source according to claim 1, wherein the nonlinear element includes a microstructured optical fiber.

4. F ｐｕｍｐ The supercontinuous light source according to claim 1, wherein the frequency is 150 MHz or higher.

5. The aforementioned seed laser has a pulse width t longer than approximately 50 ps. ｓｅｅｄ A supercontinuum light source according to claim 1, configured to supply a seed pulse having the same properties.

6. The supercontinuous light source according to claim 1, wherein the supercontinuous light source is configured such that the total average optical power in the range of 400 nm to 850 nm is less than 100 mW.

7. The supercontinuous light source according to claim 1, wherein the supercontinuous light source includes a plurality of amplifiers configured to amplify the seed pulse or the pump pulse.

8. The mode-locked Yb laser includes a fiber laser that is passively mode-locked via a SESAM (Semiconductor Saturable Absorber Mirror) according to claim 1. Supercontinuous light source.

9. The output spectrum from the supercontinuum light source is λ ３ from λ ４ A shaping optical element configured to spectrally shape the supercontinium spectrum so that it extends to λ ３ -λ ４ > 0, λ １ ≥λ ３ , and λ ２ ≤λ ４ The supercontinuum light source according to claim 1, comprising the molded optical element.

10. The supercontinuum light source according to claim 9, wherein the molded optical element includes an element selected from a prism, a low-pass optical filter, a high-pass optical filter, and a band-pass optical filter.

11. The spectral shaping of the supercontinium spectrum is performed by λ ３ -λ ４ <λ ２ -λ １ The supercontinium light source according to claim 9, comprising reducing the spectral width to such a extent.

12. The supercontinuous light source according to claim 9, wherein the shaping optical element is part of a single-mode coupling unit configured to receive the supercontinuous light and shape spectrally.

13. An optical measurement system suitable for measuring at least one parameter of a target, A supercontinuous light source according to claim 1, the supercontinuous light source comprising a single-mode coupling unit configured to supply the output of the supercontinuous light source for illuminating a target for measurement, A detector configured to receive light from a measurement target in response to illumination and to detect the received light, wherein the detection rate is at least about 1 / F ｐｕｍｐ An optical measurement system comprising a detector having an integral time of .

14. The optical measurement system according to claim 13, wherein the optical measurement system is used for the diagnosis of age-related macular degeneration (AMD), diabetic retinopathy or glaucoma, for diagnosis related to treatment of refractive correction of the eye, or for measuring the boundary of the Bowman layer inside the human eye.

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