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JP-7855652-B2 - Optical measurement system and method

JP7855652B2JP 7855652 B2JP7855652 B2JP 7855652B2JP-7855652-B2

Inventors

  • トムセン、カーステン エル．
  • アンデルセン、トマス ベスタガード
  • フォイヒター、トマス

Assignees

  • エヌケイティー フォトニクス アクティーゼルスカブ

Dates

Publication Date
20260508
Application Date
20240829
Priority Date
20120601

Claims (14)

  1. A supercontinuous light source, A seed laser configured to supply a seed pulse with pulse frequency F seed , A pulse frequency multiplier (PFM) configured to multiply a seed pulse having the pulse frequency F seed by converting it into a pump pulse having the pulse frequency F pump , wherein F pump is greater than F seed , and the pulse frequency multiplier (PFM) is configured to multiply the seed pulse, A nonlinear element configured to receive the pump pulse and convert the pump pulse into a pulse of supercontinuous light having a supercontinuous spectrum over at least about λ1 to about λ2 , wherein λ1 - λ2 > about 500 nm, the nonlinear element comprises The seed laser is configured to supply seed pulses having a pulse width t seed , wherein the pulse width t seed is longer than about 1 ps, and the seed laser is a supercontinuous light source including a mode-locked Yb laser.
  2. The supercontinuous light source according to claim 1, wherein the pulse frequency multiplier includes an attenuator configured to attenuate optical pulses having a pulse frequency less than F pump .
  3. The supercontinuous light source according to claim 1, wherein the nonlinear element includes a microstructured optical fiber.
  4. The supercontinuous light source according to claim 1, wherein the F pump is 150 MHz or higher.
  5. The supercontinium light source according to claim 1, wherein the seed laser is configured to supply seed pulses having a pulse width t seed longer than about 50 ps.
  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, comprising a plurality of amplifiers configured to amplify the seed pulse or the pump pulse.
  8. The supercontinuum light source according to claim 1, wherein the mode-locked Yb laser includes a fiber laser that is passively mode-locked via a SESAM (Semiconductor Saturable Absorber Mirror).
  9. A shaping optical element configured to spectrally shape the supercontinuous spectrum such that the output spectrum from the supercontinuous light source extends from λ3 to λ4 , wherein the shaping optical element comprises λ3 - λ4 > 0 , λ1 ≥ λ3, and λ2 ≤ λ4 .
  10. The supercontinuous 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 supercontinium light source according to claim 9, wherein spectral shaping of the supercontinium spectrum includes reducing the width of the spectrum such that λ3 - λ4 < λ2 - λ1.
  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 it 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, An optical measurement system comprising: a detector configured to receive light from a target to be measured in response to illumination and to detect the received light, the detector having an integration time of at least about 1/F pump .
  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 treatments that correct the refractive error of the eye, or for measuring the boundary of the Bowman layer within the human eye.

Description

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, similar to the supercontinuum light source, includes a method for measuring at least one parameter relating to the object of the measurement system. 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. Octave-bandwidth supercontinium (SC) sources have been successfully generated by directly passing nonlinear fibers such as microstructured fibers, tapered standard fibers, and tapered microstructured fibers through the fiber by pumping the fiber with a pulsed laser (often in a MOPA configuration) as input. 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, with respect to 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. Light sources derived from stable continium would generally improve the usefulness of SC light sources. 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 high-speed detectors and RF spectrum analyzer (RFSA) measurements. 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. In (Patent Document 1), noise from an SC light source is reduced by tapering the nonlinear fiber and using a femtosecond pulse source that induces so-called soliton splitting. The abstract of this patent states: "The longitudinal variation of the phase-matched state for Cherenkov radiation (CR) and four-wave mixing (FWM) introduced by a DMM enables the generation of low-noise supercontinium." Tapering requires either post-processing techniques or changes in fiber diameter during manufacturing, which can complicate the manufacturing of SC light sources, 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. (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 in (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. U.S. Patent