Light source

Abstract

1. A light source comprising: a pulse generator for providing an initial sequence of optical pulses, the initial sequence comprising a selected number of optical pulses within a selected time period, the pulse generator having a light source and a modulator; and first and second optical arms for respectively propagating first and second sequences of optical pulses derived from the initial sequence, the first optical arm including a first manipulator for generating the first sequence from the initial sequence, the first sequence having a first number of optical pulses within a selected time period, the first number being greater than the initial number; and the second sequence having a second number of optical pulses within the selected time period, the second number being different from or equal to the initial number; the light source further comprising a nonlinear optical element for receiving either the first sequence or the second sequence; and an optical switch for switching either the first sequence or the second sequence for receipt by the nonlinear optical element.

Description

Technical Field

[0001] The present invention relates to light sources such as, for example, light sources having broadband output and / or light sources operable in different modes.

Background Art

[0002] A broadband light source generally refers to a light source that emits light having a wide wavelength bandwidth of, for example, 50 nm or more. A broadband light source can include, for example, an incandescent lamp or a fluorescent lamp, and typically provides a wide spectrum in the range of 400 to 1700 nm. However, in the case of such light sources, the intensity is limited by the quality of the filament used or the efficiency of gas excitation. Furthermore, since the light is not spatially coherent, it may be difficult to couple the light into a fiber, resulting in a low-power and low-brightness light source with medium quality. One or more of the aforementioned limitations may not be optimal for many applications.

[0003] Supercontinuum generation can often provide improvements that exceed one or more of the above limitations. Supercontinuum generation relates to the formation of a wide, typically continuous spectrum by the propagation of high-power light, typically pulses, through a nonlinear optical element such as a nonlinear fiber. The term supercontinuum does not cover a specific phenomenon, but rather may include at least some of a number of nonlinear effects such as self-phase modulation, Raman scattering, phase matching, and soliton generation that result in a significant broadening of the optical pulse. The spectrum achieved by supercontinuum generation in a nonlinear optical fiber typically covers a wider spectrum, for example, in some cases, a spectrum having wavelengths in the range of 400 to 2400 nm with respect to an incandescent lamp or a fluorescent lamp, and can provide one or more of higher intensity, single-mode beam characteristics, excellent pointing stability, and laser brightness.

[0004] Broadband light sources are applied in fields such as spectroscopy, optical coherence tomography (OCT), metrology, scientific measurement, bioimaging, and semiconductor inspection.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] An object of the present invention is to provide a light source that can operate in different operation modes. Another object of the present invention is to provide a light source that avoids power degradation of a non-linear fiber.

MEANS FOR SOLVING THE PROBLEMS

[0006] This object is achieved by a light source according to the embodiments described below. This object can be achieved by a light source as described in claim 1 of the appended claims, and specific preferred embodiments are disclosed in the dependent claims.

[0007] In some embodiments, the light source includes a pulse generator for providing an initial sequence of optical pulses, the initial sequence of optical pulses having an initial number of optical pulses within a selected period, and the pulse generator includes a light emitting source for generating optical pulses and a modulator in communication with the light emitting source for increasing or decreasing the initial number of pulses provided by the pulse generator within the selected period. The light source further includes first and second optical arms for propagating first and second sequences of optical pulses respectively derived from the initial sequence of optical pulses, the first optical arm including a first manipulator configured to generate the first sequence of optical pulses from the initial sequence of optical pulses, the first sequence of optical pulses having a first number of optical pulses within the selected period, the first number being greater than the initial number. The second sequence of optical pulses has a second number of optical pulses within the selected period, the second number may be different from the initial number, but typically is less than or equal to the initial number. The light source also includes a non-linear optical element arranged to receive the first sequence of optical pulses or the second sequence of optical pulses, and the light source is configured such that the non-linear optical element selectively receives the first sequence of optical pulses or the second sequence of optical pulses.

[0008] The non-linear optical element can in particular be configured to broaden the spectrum of the sequence of optical pulses passing through the non-linear optical element. Thus, the non-linear optical element can generate a broadband or supercontinuum spectrum from the sequence of pulses.

[0009] The light source may include a broadband light source such as a supercontinuum light source. The first sequence of optical pulses, unlike the second sequence of optical pulses, typically provides more pulses per selected period to the non-linear optical element. Thus, when the first sequence of optical pulses is provided to the non-linear optical element, the number of pulses per selected period is higher in the first sequence of optical pulses, so the non-linear optical element generates a broadband spectrum having a higher power than the broadband spectrum generated from the second sequence of optical pulses. The first sequence of optical pulses may be amplified before being incident on the non-linear optical element. Thereby, the total power of the first sequence of optical pulses is increased and the peak power of each pulse is maintained below a predetermined maximum level where material degradation is minimal. This is particularly important with respect to the degradation of the non-linear optical element. In particular, it is possible to maintain the degradation at an acceptable level while providing broadband light or supercontinuum light having high power and / or high spectral energy density.

[0010] Thus, the light source can operate in a high-power mode, for example, when pulses from the first optical arm are received by the non-linear optical element, and in a low-power mode when pulses from the second optical arm are received by the non-linear optical element. Thus, the light source enables the user to select between these two operating modes while, for example, enabling spectroscopic measurements to be performed using the light source.

[0011] The broadband light source may include an optical switch arranged to switch between either the first sequence of optical pulses or the second sequence of optical pulses for reception by the non-linear optical element. The switch can facilitate the operation of the light source in the high-power mode or the low-power mode.

[0012] The high-power mode can be interpreted as the mode in which the supercontinuum light source provides a total output exceeding 5W (e.g., exceeding 6W, e.g., exceeding 10W, and exceeding 20W) measured over the entire supercontinuum spectrum spanning, for example, from 350nm to 850nm, optionally up to at least 1200nm, or up to at least 1300nm. The high-power mode can also be a mode of the supercontinuum light source that provides a total power exceeding 0.5W (e.g., exceeding 1W, e.g., exceeding 2W, e.g., exceeding 5W, e.g., exceeding 10W) measured over the entire visible supercontinuum spectrum from at least 350nm to at least 850nm.

[0013] The high-power mode can also be a mode of the supercontinuum light source that provides a power spectral density exceeding 10mW / nm (e.g., exceeding 20mW / nm, e.g., exceeding 25mW / nm, e.g., exceeding 50mW / nm) measured over a range of at least 10nm within a portion of the supercontinuum spectrum extending from at least 1200nm to at least 1300nm.

[0014] The high-power mode of the supercontinuum light source can provide a power spectral density exceeding 1mW / nm (e.g., exceeding 2mW / nm, e.g., exceeding 5mW / nm, e.g., exceeding 10mW / nm, e.g., exceeding 20mW / nm) measured over a range of at least 10nm within the visible supercontinuum spectrum extending from at least 350nm to at least 850nm.

[0015] In one embodiment, the optical switch has one input and two outputs and is arranged to selectively supply an initial sequence of optical pulses to either the first optical arm or the second optical arm.

[0016] Thus, in this embodiment, it is possible to switch between different operation modes of the light source. In particular, by setting the switch so as to supply the first optical arm with the initial sequence of optical pulses, it is possible to switch to the high-power operation mode, and by setting the switch so as to supply the second optical arm with the second sequence of optical pulses, it is possible to switch to the low-output operation mode.

[0017] In one embodiment, the optical switch has two inputs and one output, and is configured to receive the first sequence of optical pulses and the second sequence of optical pulses and selectively supply either the first sequence of optical pulses or the second sequence of optical pulses to the non-linear optical element. Thus, depending on the setting of the switch, the non-linear optical element is configured to receive the first sequence of optical pulses or the second sequence of optical pulses, and the light source can be selected to operate in the low-power mode or the high-power mode.

[0018] Thus, the switch is arranged after the first and second optical arms and can receive the outputs from both arms. The optical pulses received from the optical arm that are not provided to the non-linear optical element can be directed, for example, to an optical dump.

[0019] The modulator can preferably vary, depending on the switch setting, the light-emitting source to change the number of initial pulses within a selected period provided by the pulse generator, and thus increase the contrast between the high-power mode and the low-power mode. For example, the modulator can be operated such that the initial number of optical pulses within the selected period is higher when the first sequence of pulses is delivered to the non-linear element than when the second sequence of optical pulses is delivered to the non-linear element.

[0020] In some embodiments, the modulator may include an optical modulator, which may be optically communicated with a light source and disposed downstream optically of the light source. Such a modulator may include a pulse picker or may consist of a pulse picker. The pulse picker can generate a second sequence of optical pulses having a repetition rate equal to or lower than the initial repetition rate from an initial sequence of optical pulses having an initial repetition rate. The pulse picker is a device that "picks" or selects some of the pulses in the pulse sequence, thereby reducing the repetition rate of the initial sequence of pulses (or leaving it unchanged if all pulses are selected). An acousto-optic modulator or an electro-optic modulator may be used as the pulse picker.

[0021] In some embodiments, the modulator may include a modulator that electrically modulates the light source, such as when the light source includes a laser diode for generating an initial sequence of optical pulses.

[0022] The light source may include a laser diode for generating optical pulses. The light source may include a mode-locked fiber laser for generating optical pulses. In one embodiment, the pulse generator can supply an initial sequence of optical pulses to a splitter, which may include an optical splitter configured to supply the initial sequence of optical pulses to first and second optical arms. The intensity of the optical pulses in both arms can be reduced to 50%, and the optical splitter becomes a 50 / 50 splitter. However, other splitting modes are also possible.

[0023] The splitter may be used in conjunction with an optical switch disposed after the aforementioned first and second optical arms. In one embodiment, the switch includes a switch having an input and an output, and one of the optical arms includes such a switch in-line. When one of the optical arms includes a component that can also function as a switch, such as when the second optical arm includes a second manipulator that can have a switching function, the other arm, i.e., the first arm, can include the switch in-line. The switching functions of the switch and the second manipulator can operate in opposite manners, i.e., such that when one is "off", the other is "on", and vice versa.

[0024] In one embodiment, each optical arm includes its own switch in-line (i.e., in series with the optical path of the arm), and each switch has an input and an output. These switches can operate in opposite manners such that when one is "off", the other is "on", and vice versa.

[0025] A splitter as described above may be used when one or more in-line switches are used to provide an initial sequence of optical pulses to the first and second optical arms. Accordingly, a switch configured to switch either the first sequence of optical pulses or the second sequence of optical pulses for reception by the non-linear optical element includes, for example, one or more two-port in-line switches each switching only one of the optical arms, and a three-port switch capable of selecting between the optical arms.

[0026] Compared with the generation of a broadband spectrum from an initial optical pulse, the first sequence of optical pulses contains more pulses per period and amplification can be applied to compensate for the splitting of the initial optical pulse into the first sequence of pulses, so the power of the broadband spectrum generated from the first sequence of optical pulses can be higher. By distributing the optical power for generating the broadband spectrum over a larger number of pulses (the first sequence of pulses), a high-power broadband spectrum can be generated without substantially increasing the degradation of the nonlinear optical element.

[0027] Another way to increase the power of the generated spectrum is to increase the peak power of the pulses in the initial sequence of pulses. However, the high peak power of the pulses passing through the nonlinear optical element can accelerate the degradation of the nonlinear optical element or even damage the nonlinear optical element. Therefore, by using the first optical arm and the first manipulator, broadband light can be generated at a higher power while reducing the risk of damaging the nonlinear optical element.

[0028] Depending on the application, it may be desirable to be able to select between different operating modes of the light source, such as a high-power operating mode and a low-power operating mode. In applications of fluorescence spectroscopy, for example, a high-intensity spectrum is required for bleaching experiments, while a low-intensity spectrum is required for lifetime measurements, and it is desirable to be able to switch between these two operating modes. In one aspect, the present invention relates to a method for fluorescence spectroscopy using a light source used in a high-power mode, the method including a bleaching step before the step of irradiating an object to be analyzed to record measurement data. The light source operates in the high-power mode during the bleaching step and in the low-power mode during the irradiation step. This can provide the advantage that, for example, the initial rapid bleaching of fluorophore markers attached to specific molecules in a biological sample does not affect the recording of data.

[0029] The first manipulator may be configured to generate a first sequence of optical pulses having a repetition rate higher than the initial repetition rate from an initial sequence of optical pulses having the initial repetition rate. The first manipulator can be configured, for example, to double the repetition rate.

[0030] In some embodiments, the first manipulator includes a pulse splitter configured to split each pulse of the initial sequence of optical pulses into a given number of pulses, thereby generating a subsequence of a given number of optical pulses, and the subsequence of the given number of optical pulses includes a first subsequence of optical pulses. The pulse splitter can be configured to delay each of the remaining subsequences of optical pulses for a selected period with respect to the first subsequence of optical pulses. The pulse combiner may further be configured to combine the first subsequence of optical pulses with the further delayed subsequences of optical pulses, thereby generating the first sequence of optical pulses.

[0031] The first sequence of optical pulses can be composed of, for example, a sequence of bursts, and each burst includes a plurality of pulses. Thus, the first manipulator can increase the repetition rate of the initial sequence of optical pulses or generate a burst of pulses.

[0032] The pulse burst may have an envelope. The pulse burst may be characterized by a pulse burst repetition rate, a power cycle, an inter-pulse time interval, and a repetition rate of individual pulses within the pulse burst.

[0033] The modulator can vary / fluctuate the initial number of pulses within a selected period, such as by changing the repetition rate of the initial sequence of pulses. As a result, when the first optical arm is selected for receiving the initial sequence of pulses and the non-linear optical element receives the first sequence of optical pulses, the number of pulse bursts or the repetition rate of the pulse bursts is different from when the second arm is selected for reception and transmission to the non-linear element. In order to increase the contrast between the high-power mode and the low-power mode, when the first arm is selected, the number of initial pulses or the repetition rate of the initial pulses can be made higher than when the second arm is selected. Thus, the first manipulator increases the number of pulses in the first sequence of pulses to a larger number of pulses, to a larger number of pulses, or to a higher repetition rate.

[0034] In some embodiments, the light source can operate such that, for example, when the first manipulator is configured to generate an inter-pulse time interval in the second sequence of pulses that is sufficiently smaller than the inter-pulse time interval in the initial sequence of pulses, the second sequence of optical pulses includes pulse bursts.

[0035] The pulse burst may have an envelope. The pulse burst may be characterized by a pulse burst repetition rate, a power cycle, an inter-pulse time interval, and the repetition rate of the individual pulses within the pulse burst. The individual pulses within the pulse burst can be referred to as sub-pulses.

[0036] The splitter of the first manipulator may include optical fibers having different lengths for delaying sub-sequences of optical pulses. Each of the sub-sequences of optical pulses can travel along different optical fibers. Due to their different lengths, the pulses within different sub-sequences are delayed relative to each other.

[0037] In one embodiment, the second optical arm includes at least one optical fiber for propagating a second sequence of optical pulses corresponding to the first sequence of optical pulses, and preferably does not include a manipulator. Thus, the second optical arm can provide a fiber link for providing optical communication between the pulse generator and the nonlinear optical element, and as a result, an initial sequence of optical pulses, referred to as the second sequence of optical pulses, can be provided to the nonlinear optical element, particularly for broadband or supercontinuum generation. Thus, the second optical arm will bypass the first optical arm, and no manipulator is disposed within the second optical arm.

[0038] However, in one embodiment, the light source can include a second manipulator, and the second optical arm can include a second manipulator. The second manipulator can be configured to generate a second sequence of optical pulses such that the second sequence of optical pulses includes a different number of pulses than the initial sequence of optical pulses, typically the same number or less than the initial number, per selected period.

[0039] The nonlinear optical element may be a nonlinear optical fiber, particularly a microstructure optical fiber. The microstructured fiber includes a characteristic array extending in the longitudinal direction, and one or more of the characteristics have a refractive index different from that of the material surrounding the characteristic. The characteristic array functions to guide the light propagated by the fiber. The microstructured optical fiber includes a core region and a cladding region. The cladding region typically includes a characteristic array, and this characteristic typically includes voids. Different types of microstructured fibers can be operated by different physical mechanisms. For example, in some microstructured fibers, the characteristic array extending in the longitudinal direction provides a photonic bandgap such that light cannot exist in the cladding and is thus confined to the core. In other microstructured fibers, the characteristic array extending in the longitudinal direction provides an index guiding mechanism for confining light to the core, similar to total internal reflection in a conventional fiber. Microstructured fibers also rely on other mechanisms. Microstructured fibers can have a hollow or solid core. For example, photonic bandgap type microstructured fibers often have a hollow core.

[0040] The microstructured optical fiber can be, for example, a photonic bandgap fiber. The selected period can be made equal to n*T, where n is a natural number and T is the reciprocal of the pulse repetition rate of the pulses in the initial sequence of the optical pulses.

[0041] The selected period may also be equal to T / n. In particular, in embodiments where the first sequence of pulses includes a burst of pulses, all the pulses within the burst may be included within a predetermined period that is a fraction of T. That is, in this embodiment, the number of pulses within the selected period is increased.

[0042] In order to supply a desired power to the non-linear fiber in particular, at least one amplifier can be arranged upstream of the non-linear element. For example, the pulse generator may include an amplifier such as a fiber amplifier.

[0043] The amplifier can be configured to amplify the first or second pulse sequence according to the setting of the switch such that the peak power of the pulses within each pulse sequence is below the selected maximum level. Thereby, material degradation can be mitigated and damage to the nonlinear optical element can be avoided.

[0044] In some embodiments, the first sequence of optical pulses and the second sequence of optical pulses can be generated such that the peak power of the pulses in both sequences is (at least substantially) the same.

[0045] In some embodiments, the energy or peak power of the selected pulses can be controlled. For example, the peak power or energy of the pulses supplied to the nonlinear optical element can be controlled to a level below a predetermined threshold level, i.e., below a predetermined maximum level. The maximum level may be selected such that damage or degradation of the nonlinear optical element does not occur, or is reduced, or is reduced within an acceptable level. Degradation of the nonlinear optical element is typically a continuous process. High peak power or the energy of the pulses transmitted through the nonlinear optical element causes higher degradation than pulses having low peak power. The degradation rate may be non-linear, and thus, high peak power can cause severe damage or degradation to the nonlinear optical element. In other words, the predetermined maximum level is set such that for peak power and energy below this level, the degradation of the nonlinear optical element is maintained at a sufficiently low level to ensure a long life of the nonlinear optical element and thus the light source. Therefore, having more pulses with peak power below a predetermined maximum value for each selected period in the first sequence of optical pulses helps to increase the life of the nonlinear optical element and avoid damage to the nonlinear optical element, while high power output can be obtained during the selected period. The peak power or energy of the selected pulses can be controlled such that they are "clamped" so as not to exceed a predetermined maximum level. That is, the peak power or pulse energy can vary, for example, as the number of pulses per unit time changes (to some extent such variations are natural when the pulses are amplified and can mean more energy per amplified pulse, and thus peak power, without controlled amplification of fewer amplified pulses per unit time), but are not allowed to vary beyond a predetermined maximum level. Also, the peak power or energy of the pulses can be controlled to remain substantially the same even as the number of pulses per unit time changes. For example, since supercontinuum generation and the profile of the generated spectrum respond to peak power, it can be advantageous to keep the peak power the same and clamp it below a predetermined maximum level selected to reduce damage to the nonlinear optical element, in which case without control or clamping of the peak power or energy it would undesirably increase.

[0046] As described above, in some embodiments, the peak power or energy of the pulses can be controlled such that they remain substantially the same and / or do not exceed a predetermined maximum level. Such control is desirable when, as in the present invention, the number of pulses per unit time can vary. For example, the present invention may include one or more amplifiers. The amplifier is typically optically pumped by a laser diode or the like to provide the energy transmitted to the optical signal to amplify the signal. If the number of pulses amplified per unit time is decreased very frequently, the energy of the optical pump power delivered over a time interval is distributed to fewer amplified pulses, so the energy or peak power per pulse tends to increase.

[0047] Thus, one way to control the optical energy or peak power of the pulses, whether to compensate for variations due to the amplifier itself or in response to other considerations, is to control the amplification process, such as by controlling the pump laser or the laser that pumps the amplifier. For example, the optical pump power can be reduced when fewer pulses are amplified to compensate for a typical increase in the amplified pulse energy or peak power.

[0048] In some embodiments, a variable optical attenuator or modulator, such as an AOM (acousto-optic modulator) or EOM (electro-optic modulator), may be used to control the peak power or energy of the pulses.

[0049] The control of the AOM or EOM can be performed in conjunction with the control of the amplification. The light source can be configured to sample the pulses, for example, using a detector to sample the pulses. The pulses delivered to the non-linear optical element can be sampled prior to their delivery, and the control can respond to the sampled pulse energy or the peak power of the pulse or the burst of pulses (e.g., if the detector does not respond to individual pulses). It is also possible to control the peak power or energy of the pulses in response to a look-up table, or in response to a formula or algorithm, or in response to a selected operation of the light source. Such control may be used in combination with the aforementioned feedback control using a detector, or may be performed independently thereof. For example, if the pulses are directed to an optical arm that increases the number or repetition rate of the pulses, the pulse energy or peak power of the pulses can vary in a at least partially predictable manner. If the pulse manipulator includes a pulse splitter, for example, each of the split pulses has less energy or peak power than the pulse from which it was split. Thus, the pulse energy of the peak power of the pulses can be controlled in response at least partially to the optical arm selected to propagate the pulses. When the pulses are split, the amplification can be adjusted, such as by increasing it. In some embodiments, the peak or energy of the pulses can be controlled according to the switch settings, for example, by adjusting the gain of a downstream optical amplifier to increase the pulse energy or peak power when the pulses are switched such that they are split in the manipulator. Similarly, the pulses can be controlled in response to the operation of the manipulator or modulator. Depending on the application, any pulse of the light source, for example, a pulse from the light emitting source, an initial sequence of pulses, a first or second sequence of pulses, etc. can be sampled and / or controlled. The light source may include a controller (not shown) that appropriately communicates with one or more of the aforementioned elements or components to provide the desired control. The controller may be configured to control the optical switch settings and / or amplification provided by at least one amplifier of the light source.

[0050] A multi-port optical component (also referred to as "MOC") means, as a term used in this specification, an optical component having at least one input and at least two outputs, or having at least one output and at least two inputs. A switch, a coupler, and a splitter may be examples of multi-port optical components.

[0051] In some embodiments, the light source includes at least a first MOC, and the first MOC optically communicates with an optical arm and delivers an arranged optical pulse to the optical arm or receives an optical pulse from the optical arm. The light source can include a second MOC. The first MOC optically communicates with a pulse generator and an optical arm to deliver an optical pulse to the arm, and the second MOC optically communicates with the optical arm and a nonlinear optical element and receives a pulse from the optical arm to deliver it to the nonlinear optical element. A switch can be constituted by one of the MOCs.

[0052] In some embodiments, the light source generates broadband light such as supercontinuum light. All features disclosed in this application can also be used in combination with the aforementioned light source.

[0053] The present invention also relates to an apparatus for irradiating a material sample, particularly for material processing. The apparatus includes a light source according to the present invention and a holder for the material sample. The holder is configured to hold the material. When the light source is used, the material sample is irradiated with broadband light or supercontinuum light emitted from the nonlinear optical element of the light source.

[0054] The present invention also relates to a system for optical analysis of an object and / or a system for optical measurement of at least one parameter of an object. In some embodiments, the system for optical analysis and / or measurement includes a light source according to one of the embodiments, arranged such that the light source irradiates the object, and a detector for detecting light received from the irradiated object. An analyzer configured to analyze the detected light and then derive at least one parameter of the object.

[0055] Broadband light sources, such as supercontinuum light sources, which provide spectrally broad continuous light sources, are useful in many systems for optical analysis and measurement, such as systems configured for optical coherence tomography (OCT), white light interferometry, spectroscopy, optical frequency measurement, fluorescence microscopy, fluorescence lifetime measurement (FLIM), hyperspectral imaging, flow cytometry, coherent anti-Stokes Raman scattering (CARS) microscopy, and two-photon fluorescence microscopy.

[0056] In some embodiments, the system is a reflection mode measurement system arranged to measure light reflected from an object to be analyzed, such as a system based on white light interferometry such as optical coherence tomography (OCT). Advantageously, the system is based on time domain, frequency domain or swept source OCT.

[0057] For applications where light examines the subsurface region of an object to be analyzed, such as OCT analysis of a patient's skin or eye, a higher power would allow deeper parts of the object to be examined within the same duration or analyzed more quickly.

[0058] In one embodiment, the system for optical analysis is configured for in vivo, ex vivo and / or in vitro measurements of parts of the human or animal body. This system can be applied to different ophthalmic analyses and treatments, such as the diagnosis of age-related macular degeneration (AMD), diabetic retinopathy or glaucoma. In some embodiments, the system is used for diagnosis related to treatments for correcting refractive eye conditions, such as laser in situ keratomileusis (LASIK). In some embodiments, the system is used to measure the boundary of the Bowman layer inside the human eye.

[0059] In some embodiments, the system is used for product characteristic evaluation and / or sorting and / or quality inspection. The higher power of the broadband light source enables a larger inspection volume defined by a larger inspection area of the product and / or depth and / or faster optical analysis.

[0060] In one embodiment, the measurement system is used for the analysis and quality inspection of semiconductor materials, such as nitride-containing materials. One advantage of the present light source and the system incorporating the disclosed light source is that it can provide two operating modes (high power mode and low power mode) with only a single light source. Conventional light sources, if they can provide a high power mode or a low power mode, or when the light source operates by simply increasing the peak power of the pulses incident on the nonlinear optical element, will significantly shorten the lifespan. The present invention can provide a long-life general-purpose light source.

[0061] The present invention also relates to a method for optically measuring at least one parameter of an object to be measured. In some embodiments, the measurement method includes providing a measurement system according to one embodiment, irradiating the object to be analyzed with at least a part of the broadband spectrum generated from the light source of the measurement system, detecting the light from the object by a detector, analyzing the detected light to derive at least one parameter of the object, and including.

[0062] In some embodiments, the irradiation step and the detection step are performed simultaneously. This is the case, for example, when the system is configured for OCT measurement or absorption spectroscopy and the optical response of the object to the received light is instantaneous.

[0063] In some embodiments, the detection step is performed after the irradiation step. This is the case, for example, when the system is configured for fluorescence measurement and the fluorescence response of the object to the received light is slightly delayed.

[0064] In some embodiments, the analysis method includes a bleaching step before the irradiation step, and the light source operates in a high-power mode during the bleaching step and in a low-power mode during the irradiation step. This can advantageously provide, for example, an initial rapid bleaching of fluorophore markers attached to specific molecules in a biological sample.

[0065] The present invention also relates to a spectroscopic system and / or apparatus for performing spectroscopy on a sample, including a light source according to the present invention for irradiating the sample with broadband light or supercontinuum light, and at least one detector for detecting light from the sample. The integration time of the detector preferably exceeds the duration of the pulse and / or burst of pulses. Thus, the detector does not "see" the structure of the pulse or burst. However, the burst as a whole is detectable. This is particularly advantageous for the detection of low-power signals. The integration time preferably does not include two or more bursts. In some embodiments, the integration time can include a plurality of bursts, i.e., it can be longer than the time between bursts. The integration time may be longer than the duration of the pulse, but may also be shorter than the duration of the burst of pulses.

[0066] The spectroscopic system may be used, for example, to analyze high-density or thick materials. Hereinafter, the present invention will be described for illustrative purposes only with reference to exemplary embodiments shown in the accompanying drawings. The drawings are shown schematically.

Brief Description of the Drawings

[0067]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0068] FIG. 1 shows a light source 1 operable in at least two different power modes. The pulse generator 2 includes a first component (e.g., a light emitting source 3) and a second component (e.g., a modulator 4), and generates an initial sequence 5 of pulses having a pulse width on the order of femtoseconds, picoseconds, or nanoseconds. The initial sequence 5 of optical pulses includes an initial number of optical pulses within a selected period or an initial period n·T, where n is a natural number such as 1, 2, 3, etc., and T may be the pulse period when the pulses are regular, in which case T is inversely proportional to the pulse repetition rate of the initial sequence of optical pulses.

[0069] One component of the pulse generator 2 includes a light emitting source, and the other component includes a modulator that changes the initial number of optical pulses within the initial period. For example, in one embodiment, the first component 3 includes a modulation circuit that electrically modulates a light emitting source such as a laser diode, such as a gain-switched laser diode constituted by the second optical component 4. In another embodiment, the second component 4 includes an optical modulator located optically downstream of the light emitting source constituted by the first component.

[0070] The optical modulator may include a pulse picker or may consist of a pulse picker. A pulse picker is a device that "picks" or selects some of the pulses within a sequence of pulses, thereby reducing (or not changing if all pulses are selected) the repetition rate of the received pulses. A pulse picker is a standard optical device, and an acousto-optic or electro-optic modulator may be used for this purpose.

[0071] The light source may also generally include a mode-locked laser, such as a mode-locked fiber laser, as a first or second component. Also, the pulse generator 2 can be provided with an optical amplifier (not shown) that functions as a pre-amplifier such as a fiber amplifier.

[0072] Following the pulse generator 2, in the embodiment shown in FIG. 1, the multi-port optical component (MOC) 6 includes an optical switch, and by appropriately setting the switch 6 to switch between the first optical arm 7 or the second optical arm 8, it is possible to switch the initial sequence 5 of optical pulses.

[0073] The first optical arm 7 includes a first manipulator 9, and the first manipulator 9 may include, for example, a delay line device. This device will be described in detail below. The manipulator 9 can increase the repetition rate of the initial sequence 5 of optical pulses by increasing the number of pulses within a selected period n·T for the initial number of pulses. As shown in FIG. 3 and described in detail below, the manipulator can also generate a first sequence 10 of optical pulses that schematically represents the first sequence.

[0074] The second optical arm 8 may include an optical fiber that propagates a second sequence of pulses corresponding to the initial sequence 5 of pulses without changing the number of received pulses or the repetition rate of the received pulses. Thus, the schematic diagram 11 of the second sequence 11 of pulses also schematically shows the initial sequence 5 of pulses when directed by the optical switch 6 to the second arm 8.

[0075] The MOC12 optically arranged "downstream" from the "upstream" MOC6 includes a coupler in the embodiment shown in FIG. 1. The MOC / coupler 12 is in optical communication with both the output of the first optical arm 7 and the output of the second optical arm 8.

[0076] At least one optional amplifier 13 follows the coupler 12 and amplifies the signal to a desired output level. Next, the signal from the amplifier 13 is supplied to the non-linear optical element 14, which broadens the optical pulse and forms an output pulse having a broadband spectrum. The at least one amplifier 13 may be two amplifiers.

[0077] The non-linear optical element 14 is, for example, a non-linear optical fiber, particularly a non-linear microstructure optical fiber. The non-linear optical element can generate a supercontinuum. The output power of the generated supercontinuum can depend on the pulse repetition rate and, more generally, on the number of pulses per period provided to the non-linear optical element 14. The user selects the high power mode of the broadband light source 1 by selecting the first optical arm 7, while selecting the low power mode of the broadband light source 1 by selecting the second optical arm 8.

[0078] The output power of the supercontinuum depends, in particular, on the pulse repetition rate when the peak power of the pulses used for supercontinuum generation is substantially constant or below a certain level. The peak power or energy of the selected pulses can be controlled as described above. For example, the power of the initial sequence 5 of optical pulses can be modified to keep the peak power of the pulses delivered to the non-linear optical element constant. Thus, the first sequence 10 of optical pulses and the second sequence 11 of optical pulses may have different numbers of optical pulses within the selected period, but the peak power of the pulses may be the same. This can be achieved by any of the techniques described above, such as adjusting the pump power used to generate the initial sequence of optical pulses in response to the setting of the optical switch. Alternatively, or in addition, the gain of the amplifier 13 may be controlled by controlling the optical pumping of the amplifier 13 such that the peak power of the pulses is controlled as desired.

[0079] Figure 2 schematically shows an embodiment of the light source of Figure 1, where the first optical component 3 includes a light source such as a laser diode or a mode-locked fiber laser, and the second optical component 4 includes an optical modulator 4 located optically downstream of the light source 3. The modulator 4 can pulse-select the pulse sequence 15 generated by the light source 3 such that the initial sequence 5 of pulses does not include all the pulses generated by the light source 3. The second sequence 11 of optical pulses represents the initial sequence 5 of optical pulses as in the embodiment shown in Figure 2, and the first optical arm 8 does not include components for adding or removing pulses. However, based on the disclosure herein, it will be understood by those skilled in the art that the initial sequence 5 of pulses can also be generated by a modulator that electrically modulates the light source such that the initial sequence of pulses is generated directly by the light source. In this case, the first optical component 3 includes a modulator circuit and the second component 4 includes an electrically modulated light source.

[0080] Fig. 3 shows a configuration example of the first manipulator 9. The initial sequence 5 of optical pulses (only one pulse of this sequence is shown in Fig. 3) enters the first manipulator 9 and is split by the pulse splitter 17 into at least two sub - sequences of optical pulses. Since the pulse splitter in Fig. 3 has one input and four outputs, four sub - sequences of optical pulses are shown in Fig. 3. The input - port:output - port ratio of the pulse splitter is typically 1:2, 1:4, 1:8, 1:16, etc.

[0081] In the apparatus shown in Fig. 3, four optical arms 19, 20, 21, 22 are employed. No delay is inserted in the first arm 19. One delay line 16 is inserted in the second arm 20. Two delay lines 16 are inserted in the third arm 21, and three delay lines are inserted in the fourth arm 22. The synthesizer 18 synthesizes the signals transmitted from different optical arms 19, 20, 21, 22. The resulting signal can be a sequence of pulse bursts 10.

[0082] By changing the number of arms of the first manipulator 9 and the delays of the optical arms 19 - 22, as shown in Fig. 2, it is possible to increase the repetition rate of the initial sequence 5 of optical pulses to generate the pulse 10 and / or generate the pulse bursts described later. When such a signal is amplified and incident on the non - linear optical element 14, a broadband spectrum with a higher output power is generated with respect to the output power generated by selecting the other port of the optical switch, that is, the port connected to the second arm 8. Therefore, when the port of the optical switch leading to the first manipulator 7 is selected, the high - power mode is selected.

[0083] As described above, the four optical arms 19, 20, 21, 22 can be formed by optical fibers of the same length, with one delay line inserted into the second optical arm 20, two delay lines inserted in series into the third optical arm 21, and three delay lines inserted in series into the fourth optical arm 22. Alternatively, the four arms may be formed by four different optical fibers of different lengths.

[0084] In some embodiments of the present invention, the light source can be configured to generate a pulse burst. Referring to FIG. 2, consider that the first optical arm is selected and an initial sequence 5 of pulses is delivered to the first optical arm 7 such that the non-linear optical element 14 receives the first sequence of optical pulses. Referring to FIGS. 4 to 6, an example of the initial sequence 5 of optical pulses output by the pulse generator 2 is schematically shown in FIG. 5 as a plot against time. As can be seen by comparison with FIG. 4, the modulator 4, which can be a pulse picker, is configured such that only 1 out of 5 pulses of the pulses 15 generated by the light source 3 is provided to the first manipulator 9. The remaining pulses may be absorbed by an optical dump disposed within the modulator 4. Thus, in the example described, the first sequence 5 of optical pulses has a repetition rate that is reduced by a factor of 5 with respect to the repetition rate of the pulses 15 provided by the light source. A reduction in the repetition rate by any factor, such as 2, 3, or 4, is also possible. Further, the modulator / pulse picker 4 can be configured to “pick” pulses irregularly from the sequence 15 of optical pulses, thereby generating an initial sequence 5 of optical pulses having no defined repetition rate.

[0085] As can be seen with respect to FIG. 5, an initial sequence 5 of optical pulses includes a first number of optical pulses within a selected period T. For example, it can be assumed that the selected period is n times the reciprocal of the pulse repetition rate R of the pulses of the initial sequence 5 of optical pulses. As shown in FIG. 5, since n = 1, T = 1 / R. This means that in the initial sequence 5 of optical pulses according to the example of FIG. 5, there is one pulse within the period T. The initial sequence 5 can be amplified by an amplifier arranged in front of the first manipulator 9. Such a sequence may have a predetermined maximum level, i.e., a peak power exceeding the damage threshold of the nonlinear optical element, which does not apply in the case after the first manipulator that increases the repetition rate of the initial sequence of optical pulses. Amplification can increase the total optical power provided to the nonlinear optical element. Thereby, a high-power supercontinuum can be provided without using a high peak power that would rapidly degrade the nonlinear optical element.

[0086] The initial sequence 5 of optical pulses is provided to a first manipulator 9 configured to generate a first sequence 10 of optical pulses from the initial sequence 5 of optical pulses. FIG. 6 schematically shows an example of a first sequence 10 of optical pulses generated from an initial sequence 5 of optical pulses in FIG. 5. As seen in FIG. 6, the first manipulator 9 generates a burst 31 of pulses consisting of two or more individual pulses having a relatively short time delay between the pulses from the pulse 29 of the initial sequence 5. Thus, per period (e.g., T), the number of optical pulses in the first sequence 10 of optical pulses is greater than the number of optical pulses in the initial sequence 5 of optical pulses. Such a burst 31 of pulses can be detected by a detector that cannot resolve the individual pulses within the burst 31. If the initial sequence 5 of optical pulses is not amplified, amplification can be performed after the burst occurs. This can be achieved by placing an amplifier after the first manipulator 9. And these pulses may be amplified so as to be below a predetermined maximum level, i.e., the damage threshold of the nonlinear optical element. Thereby, a high-power supercontinuum can be provided without using a high peak power that rapidly degrades the nonlinear optical element.

[0087] And the detector can detect the burst 31 as a relatively long single pulse having high energy, particularly when including a plurality of individually spaced-apart pulses. Thus, the integration time of the detector can be longer than the duration of the burst 31 but shorter than the time T between successive bursts 31.

[0088] The measurement of the duration of the burst may be, for example, the full width at half maximum (FWHM) of the intensity or power signal of the burst 31. In principle, the FWHM of the burst 31 can correspond to, for example, the duration between half of the maximum power or intensity value of the pulse envelope, which corresponds to the midpoint of the front side of the first pulse in the burst and the time of half of the maximum power or intensity value of the rear side of the last pulse. The duration of the burst is denoted as Δt1. Autocorrelation / deconvolution techniques can measure the individual pulse profiles.

[0089] Referring to FIG. 6, the time between individual pulses of the pulse burst 31 is shown as Δt2, which is the time interval between the pulse peaks of the pulses within the burst. When the pulses within the pulse burst are regularly spaced, the reciprocal of Δt2, i.e., 1 / Δt2, corresponds to the repetition rate of the individual pulses within the burst, i.e., the sub-pulses.

[0090] The duration Δt3 between the pulse bursts 31 can correspond to the time interval between the peaks of the pulse burst envelope 31, which is in principle equal to the time difference between the peaks of the first initial pulses of each pulse burst 31. The reciprocal of Δt3, 1 / Δt3, corresponds to the pulse burst repetition rate at which the pulse bursts are regularly spaced.

[0091] FIG. 6 also shows the duration Δt4 between the pulse bursts, which can be referred to as the "inter-burst time interval" and can also be said to be the time difference between the FWHMs points on the opposing sides of the burst. The pulse burst 31 can be considered to have a "power cycle" corresponding to the value of Δt1 divided by Δt3 (Δt1 / Δt3). The power cycle can be expressed as a percentage. The value of the power cycle is related to the number of individual pulses within each pulse burst, which is of course related to the configuration of the first manipulator 9.

[0092] In a particular embodiment of the present invention, the power cycle of the pulse burst is below a selected value, and the selected value may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%.

[0093] In a particular embodiment of the present invention, the power cycle of the pulse burst is greater than or equal to a selected value, and the selected value may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%.

[0094] All of the above reasonable combinations are considered within the scope of the present invention. For example, the power cycle can be 80% or less and 50% or more. In a particular embodiment of the present invention, the ratio of the number of pulses in the first sequence shown in FIG. 6 to the number of pulses in the first initial sequence shown in FIG. 5 may be greater than or equal to a selected value, and the selected value may be 2, 4, 6, 8, 10, 20, 50, 100, or 500.

[0095] In a particular embodiment of the present invention, the ratio Δt3 / Δt2 may be greater than or equal to a selected value such as 5, 10, 25, 50, 100, 1000, etc. When the pulse generator includes a modulation light emitting source in which the light emitting source is directly modulated (pulses are directly generated and not "selected" without being generated), the pulse 15 shown in FIG. 4 is not generated, and the pulse generator 2 directly generates the first sequence 5 of optical pulses. In some embodiments, the interval Δt2 between sub-pulses may be less than 200 ps (for example, less than 100 ps, for example, 10 ps). The interval Δt2 between pulses may be greater than 1.5 times the width of the sub-pulse (for example, 5 times the width of the sub-pulse, for example, 10 times the width of the sub-pulse, for example, 20 to 25 times the width of the sub-pulse).

[0096] Again, all reasonable, that is, physically meaningful combinations of the above-described embodiments that describe selected values and their ranges are within the scope of the present invention. In another non-illustrated example, the first manipulator 9 may be configured to generate the first sequence 10 of optical pulses such that the second first sequence 10 of optical pulses has a first repetition rate that is higher than the repetition rate of the pulses 29 in the initial sequence 5. For example, the repetition rate can be doubled or quadrupled.

[0097] The first manipulator 9 can be configured to insert a pulse burst 31 between the two pulse bursts 31 shown in FIG. 6, thereby increasing the repetition rate of the pulse bursts compared to that shown in FIG. 6.

[0098] Other embodiments In one embodiment of the present invention, the light source may include a second manipulator (not shown), and the second manipulator is similar to the first manipulator 9 and may be a pulse picker type manipulator that increases the number of pulses or decreases the pulse count. The second arm 8 may include the second manipulator, or alternatively, the light source may include a third optical arm that includes the second manipulator. In this case, MOC6, 12 each have three outputs and three inputs.

[0099] Considering the embodiments of the present specification as follows, in both alternative embodiments where the light source includes the second manipulator and where it does not, each can be implemented. As described above, the switches 6 and couplers 12 shown in FIGS. 1 and 2 can more generally be considered as MOCs, respectively.

[0100] In one embodiment, the upstream MOC6 includes a switch and the downstream MOC12 includes another switch. The upstream MOC switch 6 directs the initial pulse sequence to either the first optical arm or the second optical arm, and the downstream MOC switch 12 directs the pulses from the first optical arm or the second optical arm to the nonlinear optical element 14. These switches are typically operated such that both select the same optical arm.

[0101] In one embodiment, the upstream MOC6 includes a splitter and the downstream MOC12 includes a switch. In one embodiment, the upstream MOC6 includes a switch and the downstream MOC includes the coupler 12. This embodiment has already been described in more detail above.

[0102] In one embodiment, the upstream MOC6 includes a splitter and the downstream MOC12 includes a coupler. In the above-described alternative embodiment, the first optical arm 7 includes an in-line optical switch (not shown) having one input port and one output port, and the second optical arm 8 also includes a second manipulator, and the second manipulator can also function as a switch (such as when the second manipulator includes a pulse picker). In connection with FIGS. 1 and 2, such an in-line switch can be arranged, for example, at position 36.

[0103] In another alternative embodiment of the foregoing embodiment, both optical arms each include an in-line optical switch having an input port and an output port, and these switches can operate in opposite manners, that is, when one is on, the other is off, and vice versa. The second manipulator may or may not be present. The in-line switches in the first and second optical arms 8 may be arranged as indicated by reference numeral 38.

[0104] In one embodiment, the foregoing embodiments do not include a non-linear optical element, and the first or second sequence of pulses is output without being spectrally broadened by a non-linear optical element, including the case where the pulse burst is included as described above.

[0105] Unless otherwise explicitly stated, or unless it is obvious to those skilled in the art that such a combination is not intended or not operable, all the features described above in combination with the detailed descriptions of FIGS. 1 to 6 should be considered to be within the scope of the present invention included in the foregoing additional embodiments, either independently or in any arbitrary combination with each other.

[0106] The term "light" in this specification refers to not only visible light but also light in the non-visible wavelength region, including, for example, light in the infrared (IR) or ultraviolet (UV) wavelength regions. The broadband spectrum generated by a non-linear optical element is usually a continuous spectrum, but it may also be a discontinuous spectrum. For example, the spectrum may include bands at very close intervals of wavelengths.

Description of Reference Numerals

[0107] 1: Light source 2: Pulse generator 3: First component of the pulse generator 4: Second component of the pulse generator 5: Initial sequence of optical pulses 6: Multiport optical component such as the optical switch of FIG. 1 7: First optical arm 8: Second optical arm 9: First manipulator 10: First sequence of optical pulses 11: Second sequence of optical pulses 12: Multiport optical component (e.g., the optical coupler of FIG. 1) 13: Amplifier 14: Nonlinear optical element 15: Optical pulse from the light source 16: Delay line 17: Pulse splitter / multiport optical component 18: Pulse combiner / multiport optical component 19: Optical arm 20: Optical arm 21: Optical arm 22: Optical arm 29: Pulse 31: Pulse burst 36: Position where an in-line switch can be inserted 38: Position where an in-line switch can be inserted

Claims

1. a pulse generator (2) for providing an initial sequence of optical pulses (5), the initial sequence of optical pulses (3) comprising an initial number of optical pulses within a selected time period, the pulse generator (2) having an emission source (3) for generating optical pulses (15), and a modulator (4) in communication with the emission source (3) for increasing or decreasing the initial number of pulses provided by the pulse generator within the selected time period; a first optical arm (7) and a second optical arm (8) for propagating, respectively, a first sequence (10) and a second sequence (11) of light pulses derived from said initial sequence (5) of light pulses; A light source (1) comprising: the first optical arm (7) comprises a first manipulator (9) configured to generate the first sequence (10) of light pulses (9) from the initial sequence (5) of light pulses, the first sequence (10) of light pulses having a first number of light pulses within the selected time period, the first number being greater than the initial number; the second optical arm (8) comprises a second manipulator configured to generate a second sequence of light pulses from the initial sequence of light pulses (5), the second sequence of light pulses (11) having a second number of light pulses within the selected period, the second number being different from the initial number; The light source is a nonlinear optical element (14) arranged to receive the first sequence of optical pulses (10) or the second sequence of optical pulses (11); an optical switch (6, 12) configured to switch either the first sequence of optical pulses (10) or the second sequence of optical pulses (11) for reception by the nonlinear optical element (14); The light source further comprises:

2. a pulse generator (2) for providing an initial sequence of optical pulses (5), the initial sequence of optical pulses (3) comprising an initial number of optical pulses within a selected time period, the pulse generator (2) having an emission source (3) for generating optical pulses (15), and a modulator (4) in communication with the emission source (3) for increasing or decreasing the initial number of pulses provided by the pulse generator within the selected time period; a first optical arm (7) and a second optical arm (8) for propagating, respectively, a first sequence (10) and a second sequence (11) of light pulses derived from said initial sequence (5) of light pulses; A light source (1) comprising: the first optical arm (7) comprises a first manipulator (9) configured to generate the first sequence (10) of light pulses (9) from the initial sequence (5) of light pulses, the first sequence (10) of light pulses having a first number of light pulses within the selected time period, the first number being greater than the initial number; the second sequence of light pulses (11) having a second number of light pulses within the selected period, the second number being different from or equal to the initial number; The light source is a nonlinear optical element (14) arranged to receive the first sequence of optical pulses (10) or the second sequence of optical pulses (11); an optical switch (6, 12) configured to switch either the first sequence of optical pulses (10) or the second sequence of optical pulses (11) for reception by the nonlinear optical element (14); Further equipped with The optical switch (12) is in optical communication with the first optical arm and the second optical arm and is configured to receive the first sequence of optical pulses (10) and the second sequence of optical pulses (11) and to selectively provide either the first sequence of optical pulses or the second sequence of optical pulses to the nonlinear optical element (14).

3. the second optical arm (8) comprises a second manipulator configured to generate a second sequence of light pulses from the initial sequence of light pulses (5), the second sequence of light pulses having a second number of light pulses within the selected period, the second number being different from the initial number; 3. The light source of claim 2.

4. the optical switch (12) is in optical communication with the first optical arm and the second optical arm and is configured to receive the first sequence of optical pulses (10) and the second sequence of optical pulses (11) and to selectively provide either the first sequence of optical pulses or the second sequence of optical pulses to the nonlinear optical element (14). The light source of claim 1 .

5. the modulator includes an optical modulator in optical communication with the light emission source and located optically downstream of the light emission source; A light source according to any one of claims 1 to 4.

6. the modulator electrically modulates the light emitting source; A light source according to any one of claims 1 to 5.

7. The light source comprises a laser diode or a mode-locked fiber laser for generating optical pulses. A light source according to any one of claims 1 to 6.

8. the first manipulator is configured to generate two or more pulses from each pulse in the initial sequence of light pulses, the two or more pulses having a time delay between them. A light source according to any one of claims 1 to 7.

9. the first manipulator comprises a pulse splitter (17) configured to split each pulse of the initial sequence of light pulses (5) into a given number of pulses, thereby generating a subsequence of the given number of light pulses, the subsequence of the given number of light pulses comprising a first subsequence of light pulses; the pulse splitter (15) is configured to individually delay each of the remaining subsequences of light pulses relative to the first subsequence of light pulses for a selected period of time; a pulse combiner (18) configured to combine the first subsequence of light pulses and the further delayed subsequence of light pulses, thereby generating the first sequence of light pulses (10). A light source according to any one of claims 1 to 8.

10. the second optical arm includes at least one optical fiber for guiding the second sequence of light pulses, the second sequence corresponding to the initial sequence of light pulses (5). A light source according to any one of claims 1 to 9.

11. the optical switch (6) is in optical communication with the first optical arm and the second optical arm and is configured to selectively provide the initial sequence of light pulses (5) to either the first optical arm (7) or the second optical arm (8); A light source according to any one of the preceding claims.

12. The nonlinear optical element (14) comprises a nonlinear optical fiber or a microstructured optical fiber. A light source according to any one of the preceding claims.

13. At least one amplifier (13) is disposed upstream of the nonlinear fiber for amplifying the optical pulses. A light source according to any one of the preceding claims.

14. the first sequence of optical pulses (10) and the second sequence of optical pulses (11) are generated such that the peak power of the pulses in both sequences is substantially the same value or is fixed below a threshold value, said value or said threshold value being selected to reduce optical damage to the nonlinear optical element. A light source according to any one of the preceding claims.

15. the light source including a controller configured to control the setting of the optical switch and / or the amplification provided by at least one amplifier of the light source; A light source according to any one of the preceding claims.

16. the light source is operable in a high power mode or a low power mode depending on a setting of the optical switch; and providing said high power mode of operation when a setting of said optical switch is such that said nonlinear optical element receives said first sequence of optical pulses; the low power mode of operation is provided when a setting of the optical switch is such that the nonlinear optical element receives the second sequence of optical pulses. A light source according to any one of the preceding claims.

Images