METHOD AND SYSTEM TO SIMULTANEOUSLY GENERATE TUNABLE REDSHIFT AND BLUESHIFT FEMTOSECOND PULSES WITH ADJUSTABLE SPECTRAL BANDWIDTH

Abstract

A method and a system are provided to simultaneously generate blue-shifted and red-shifted femtosecond light sources with tunable spectral peak location and bandwidth, by controlling the input condition (chirp/spectrum) of a fiber-optic nonlinear propagation. The system comprises (A) a seed source, (B) a driving current controller to regulate the spectrum of the seed source, (C) a dispersion controller to control the chirp and pulse width of the seed source, (D) a fiber-optic spectral conversion module to shape and broaden the laser spectrum via fiber-optic nonlinear processes, and (E) a spectral selection module to filter out the required wave packets. With the simultaneous uses of the driving current controller and the dispersion controller, the light sources feature continuously tunable spectral peak with (1) a relatively constant output pulse energy or (2) a tunable spectral bandwidth at a specific peak location.

Claims

1. A laser system to simultaneously generate tunable redshift and blueshift femtosecond pulses with adjustable spectral bandwidth and output power, controlled with fiber-optic nonlinearity for continuous spectral manipulation, and the system includes: a femtosecond seed laser generates femtosecond laser pulses; a driving current controller, connected to the femtosecond seed laser, and the driving current controller controls the output power and spectrum of the femtosecond seed laser; a dispersion controller, connected to the femtosecond seed laser, and the dispersion controller can vary the introduced dispersion to control a temporal pulse width, while maintaining a beam position or/and a light spot size, to achieve the tuning of the peak and bandwidth of the output spectral lobes; a redshift and blueshift of tunable fiber-optic spectral conversion module (spectral conversion module), connected to the dispersion controller; The spectral conversion module comprises a nonlinear medium for spectral broadening, and the spectrum of the femtosecond seed laser can be converted and broadened through this module; The redshift and blueshift can be tuned towards longer wavelength and shorter wavelength respectively; and a spectral selection module, connected to the spectral conversion module, and the spectral selection module can select the outmost lobes of the broadened spectra and can reject the light at the other wavelengths.

2. The laser system to simultaneously generate tunable redshift and blueshift femtosecond pulses with adjustable spectral bandwidth and output power defined in claim 1: the dispersion controller includes a translational stage, and the distance or transmission thickness of a dispersion control component can be regulated electrically or manually to control the introduced dispersion.

3. The laser system to simultaneously generate tunable redshift and blueshift femtosecond pulses with adjustable spectral bandwidth and output power defined in claim 1: the spectral conversion module employs the SPM effect in a fiber to generate broadened spectrum, so that the output spectrum is different from the input pulse spectrum; the module includes one or more than one fiber.

4. The laser system to simultaneously generate tunable redshift and blueshift femtosecond pulses with adjustable spectral bandwidth and output power defined in claim 1: the spectral selection module includes manually or/and automatically switchable optical filter plate, with transverse or/and rotary motion modes or with a resonance tunable material to select and filter out the outmost spectral lobes of the broadened spectra.

5. The laser system to simultaneously generate tunable redshift and blueshift femtosecond pulses with adjustable spectral bandwidth and output power defined in claim 1: the driving current controller can assist the dispersion controller to manipulate the input peak power and temporal pulse shape into the redshift and blueshift tunable fiber-optic spectral conversion module.

6. A method to simultaneously generate tunable redshift and blueshift femtosecond pulses with the optimization of the output spectral bandwidth or the output power, and the steps are given below: S1. a femtosecond seed laser generates femtosecond laser pulses; S2. a driving current controller is used to send control signals to the femtosecond seed laser and to regulate the power, temporal width, or the spectrum of the femtosecond seed laser; S3. a dispersion controller is used to provide dispersion to an optical pulse, and thus to control the temporal width and peak intensity of the pulse, while maintaining a laser beam position or/and a light spot size, so as to tune output spectra; S4. a redshift and blueshift tunable fiber-optic spectral conversion module (spectral conversion module) takes the optical pulse after the dispersion controller as an input, and the spectral conversion module comprises a nonlinear medium for broadening the input spectrum; the redshift and blueshift of the spectral broadening can be simultaneously tuned by the use of the dispersion controller and driving current controller; and S5. a spectral selection module filters out the outmost spectral lobe of the broadened spectra and remove the light at the other wavelengths.

7. The method to simultaneously generate tunable redshift and blueshift femtosecond pulses with the optimization of the output spectral bandwidth or the output power defined in claim 6: wherein the spectral conversion module implements the method to continuously vary the outmost spectral lobes of the broadened spectrum or precisely tune to an optimum spectrum; the output average power after the spectral selection module is not proportional to the amount of blueshift or redshift.

8. The method to simultaneously generate tunable redshift and blueshift femtosecond pulses with the optimization of the output spectral bandwidth or the output power defined in claim 6: wherein the spectral conversion module, assisted with the control of the input average power, implements the method to continuously vary the outmost spectral lobes of the broadened spectrum or to precisely tune to an optimum spectrum without changing the output average power after the spectral selection module.

9. The method to simultaneously generate tunable redshift and blueshift femtosecond pulses with the optimization of the output spectral bandwidth or the output power defined in claim 6: the amount of the redshift/blueshift, from the spectral conversion module using the same fiber, is proportional to the input pulse peak power and is negatively correlated to the input temporal pulse width, and the filtered spectral bandwidth after the spectral selection module is negatively correlated with the input pulse width.

10. The method to simultaneously generate tunable redshift and blueshift femtosecond pulses with the optimization of the output spectral bandwidth or the output power defined in claim 6: the step S3 can be followed by the step A4 to implement a method to fix a peak location of the selected spectral lobes with tunable spectral bandwidths, and the manipulation of the spectral bandwidth follows the steps: A4. an input power stabilizer to control the input peak power into a spectral conversion module, while maintaining the beam path or/and the light spot size, in order to fix the peak location of the output spectral lobes after the spectral selection module; the input pulse width can be thus varied with the cooperation with the dispersion controller and the driving current controller, in order to control the bandwidth of the output spectral lobes; A5. the spectral conversion module receives an input pulse manipulated by the dispersion controller, driving current controller, and input power stabilizer, and then the input spectrum is broadened by this module; by controlling the pulse width and average power of the input pulse, a specific peak power of the input pulse can be found to realize a fixed peak location of the outmost spectral lobes from the broadened spectrum; the bandwidth of the output spectral lobe after the spectral selection module is negatively correlated to the input temporal pulse width: A larger chirp of the input pulse leads to a wider input pulse width in the time domain, which leads to the need of higher input peak power to achieve a fixed peak location of the outmost spectral lobes from the broadened spectrum, and the output spectral bandwidth after the spectral selection module becomes narrower after spectral conversion with a higher output power); and A6. a spectral selection module filters out the required spectral lobes and removes the light at the other wavelengths.

11. The method to simultaneously generate tunable redshift and blueshift femtosecond pulses with the optimization of the output spectral bandwidth or the output power defined in claim 10: the invented laser system can control the input peak power before the spectral conversion module, in order to obtain a specific spectral peak location of the output pulses, and the control of the input temporal pulse width at the same time leads to a tunable output spectral bandwidth at the specific peak location; the output spectral bandwidth is negatively correlated to the input temporal pulse width, the input average power, and the output average power.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 Schematic diagram of femtosecond light source system with simultaneously tunable spectral redshift and blueshift and bandwidth.

[0028] FIG. 2 Schematic diagram of self-phase-modulation-dominated output spectrum from spectral conversion module.

[0029] FIG. 3 Schematic diagram of spectral peak location of leftmost/rightmost lobes under different net group delay dispersion.

[0030] FIG. 4 Schematic diagram of spectral lobes filtered from the spectral broadening.

[0031] FIG. 5 Schematic diagram of wavelength tunable lobes with constant power.

[0032] FIG. 6 Schematic diagram of tunable lobe bandwidth.

[0033] FIG. 7 Schematic diagram of embodiment.

[0034] FIG. 8 Schematic diagram of controllable input temporal width.

[0035] FIG. 9 Output spectra with tunable bandwidth and corresponding output power under a certain peak wavelength.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

[0036] A method and system to simultaneously generate tunable redshift and blueshift femtosecond pulses with adjustable spectral bandwidth and output power. A fiber-optic spectral conversion via self-phase modulation (SPM) is applied, and the invention regulates the spectral peak, the bandwidth, and power of the output, as shown in FIG. 1; the system comprises the below modules and elements:

[0037] A femtosecond seed laser 1, delivering femtosecond optical pulses;

[0038] A driving current controller 2, connected to the femtosecond seed laser 1, and the driving current controller 2 assists a dispersion controller 3, regulating the input peak power and temporal pulse shape (into a redshift and blueshift tunable fiber-optic spectral conversion module 5), so as to control an output spectrum;

[0039] The dispersion controller 3 is connected to the femtosecond seed laser 1.

[0040] The dispersion controller 3 should maintain the position of the light path or/and a light spot size, and a temporal pulse width is controlled by changing the group delay dispersion (GDD) of the optical pulses, so as to control an output spectrum; An input power stabilizer 4, connected to the dispersion controller 3, and the input power stabilizer 4 can control the output spectral wavelength, power, or width in combination with the dispersion controller 3 and the driving current controller 2. The input power stabilizer 4 should also maintain the position of the light path or/and the light spot size;

[0041] The redshift and blueshift tunable fiber-optic spectral conversion module 5 (spectral conversion module) is replaceable, connected to the dispersion controller 3 and the input power stabilizer 4. The spectral conversion module 5 comprises the medium for spectral broadening, and the spectrum of femtosecond optical pulses can be converted through this module. An example output from the spectral conversion module is shown in FIG. 2. The redshift and blueshift can be tuned towards longer wavelength and shorter wavelength respectively, and the spectral peak locations after the control of the input GDD are shown in FIG. 3; and

[0042] A spectral selection module 6, connected to the spectral conversion module 5, and the use of the spectral selection module 6 can isolate the outmost spectral lobes of the broadened spectra, and rejecting the light at the other wavelengths, shown as the example spectrum covered in the dotted frames in FIG. 2. The filtered spectra in FIG. 4 can be achieved with different redshift and blueshift; dark blue light 10, green light 20, yellow light 30, and red light 40.

[0043] Preferably, the femtosecond seed laser 1 comprises a femtosecond laser oscillator and possibly one or more femtosecond laser amplifiers, wherein the material of a laser gain medium includes but not limited to a solid-state crystal, an amorphous material (e.g., optical fiber), and a semiconductor material.

[0044] Preferably, the dispersion controller includes a translational stage, which can be electrically or manually controlled to adjust the distance or penetration thickness of dispersive components to tune the dispersion.

[0045] Preferably, the dispersion controller 3 includes an electric translational stage, as shown in FIG. 7, and an electric control system 7 can be applied to control the distance between dispersion control components (e.g., using reflection or transmission grating pair, prism pair) and vary the introduced dispersion. The use of the electric translational stage enables the precise and continuous control of the introduced dispersion, so as to achieve continuously tunable output spectral lobes.

[0046] Preferably, the dispersive components used for dispersion control in the dispersion controller can be but not limited to grating pairs, prism pairs, chirped mirrors, high dispersion materials, fiber gratings, transparent materials with a variable thickness, active spatial light modulation systems, and active acousto-optic modulation systems.

[0047] Preferably, the spectral conversion module 5 comprises a light focusing optics (e.g., a lens or a concave mirror), a light path regulator, and a nonlinear medium (i.e., a piece of optical fiber), and a collimator. Wave plates and polarizers are possibly employed on the input and/or output ports of the spectral conversion module 5 to regulate the light polarization.

[0048] Preferably, the spectral selection module 6 is the combination of components for filtering out specific spectra. The combination of components includes but not limited to a single or multiple band pass, short pass, and long pass optical filter plates, a resonance tunable material, and a tunable/switchable filter holder; A position tunable slit with a specific width can also be used to select the spectra from the light with angular dispersion, obtained from a prism or/and a grating pair, to allow the transmission of a specific spectral band; a resonance tunable material can also be used.

[0049] Preferably, the spectral selection module comprises manual or/and automatic mechanics, which enables transverse or/and rotary operation to switch the filtered spectral band.

Embodiment 2

[0050] A method and system to simultaneously generate tunable redshift and blueshift femtosecond pulses with adjustable spectral bandwidth and consistent output power. Schematic diagram of the invention is shown in

[0051] FIG. 1, and the steps are given below:

[0052] S1. A femtosecond seed laser 1 generates femtosecond laser pulses;

[0053] S2. A driving current controller 2 regulates the output power of the femtosecond seed laser 1, to control the output spectra of the invented system and to tune the output spectral peak, bandwidth, and the output power;

[0054] S3. The laser beam passing through a dispersion controller 3 remains the path position or/and a light spot size during the dispersion tuning, so that a temporal pulse width can be controlled without changing the other laser parameters, to control the output spectra of the invented system and to tune the spectral peak and bandwidth of the output with a consistent output power;

[0055] S4. A redshift and blueshift tunable fiber-optic spectral conversion module 5 (spectral conversion module) receives the spectrum from the dispersion controller 3. The spectral conversion module 5 comprises a nonlinear medium for spectral broadening, and it leads to the spectral conversion of the input pulse. The redshift and blueshift after the spectral conversion module 5 can be tuned respectively towards longer wavelength and shorter wavelength; and

[0056] S5. The use of a spectral selection module 6 selects the required spectral lobes and reject unnecessary light at the other wavelengths; for example, the choice of long pass and short pass filters depends on the spectra of the outmost spectral lobes: The red-shifted spectral lobes require the long pass filters with a cutoff wavelength less than the peaks of spectral lobes; the blue-shifted spectral lobes require the short pass filters with a cutoff wavelength larger than the peaks of spectral lobes. (e.g., in the case of using 1025-nm input pulse, the outmost blue-shifted spectral lobes with a spectral peak location at the wavelength of 860 nm can be selected by using a 900-nm short pass filter; the red-shift lobe with the spectral peak at the wavelength of 1110 nm can be selected by using a 1100-nm long pass filter).

[0057] In the embodiment, the output power of the selected spectral lobes can be stabilized by using an input power stabilizer before the spectral conversion module.

[0058] The present invention is regarding the method and system for generating femtosecond pulses with simultaneously tunable spectral redshift and blueshift and bandwidth, which employ the fiber-optic nonlinear conversion to implement the method and function of continuously tuning the spectral peak location without changing the output average power. The temporal pulse width and the optical intensity of the input light of the spectral conversion module 3 are manipulated continuously by introducing additional dispersion to the input pulse of the spectral conversion module 5 while maintaining the light power, and the optical intensity is proportional to the strength of SPM. The stronger SPM, leading to more nonlinear phase, results in more spectral redshift and blueshift, so as to achieve the conversion to different wavelengths. When the input temporal pulse width is changed without changing the input average power, the input peak intensity will be negatively correlated with the temporal pulse width, but the average power of the output light is mostly unchanged when the input average power is not changed, so as to implement the function of continuously modifying the wavelength without changing the output average power, as the function proposed in [0009], as shown in FIG. 5.

[0059] A preferred embodiment of the present invention, as shown in FIG. 5, taking a photonic crystal fiber 51 as an example, the power of the filtered lobes remains consistent, and this system shows a similar power consistency with a prior art using non-fiber-based femtosecond laser system (e.g., using Ti:sapphire-based-laser system). Therefore, this system has solved the problem of a prior art, which also employs fiber-optic SPM as the spectral broadening mechanism with a poor output power consistency, leading to insufficient output power from the spectral lobes close to the driving light source wavelength, so as to achieve the function in [0009].

[0060] A preferred embodiment of the present invention, which is a method and system for generating femtosecond pulses with simultaneously tunable spectral redshift and blueshift and bandwidth, employs a fiber-optic nonlinearity (SPM effect) with the control of the introduced dispersion by the dispersion controller 3, to modify the temporal pulse width and peak intensity of the input pulse of the spectral conversion module 5, assisted by input fiber average power fine-tuning from an input power stabilizer, to achieve continuously tunable wavelength and consistent average power during tuning wavelength, as mentioned in [0009].

[0061] As stated above, the fiber-optic SPM effect is the mechanism for continuously spectral tuning, and the output effect is shown in FIG. 2: When the femtosecond optical pulses propagate in the fiber, the output spectrum broadens towards shorter and longer wavelength in comparison to the input spectrum. The spectral broadening is proportional to the peak intensity into the fiber. If the spectral broadening is generated mainly by the SPM effect, most of the spectral energy will fall in the two outmost spectral lobes (the parts in the dotted frames in FIG. 2). Then the two spectral lobes are filtered out, and the wavelength tunable light source can be achieved by modifying the input peak intensity, as shown in FIG. 5.

[0062] Preferably, the input temporal pulse width of the spectral conversion module 5 can be modified by using said two technologies (the management of the nonlinearity and the SPM effect by controlling the introduced dispersion and driving current), and the output spectral bandwidth will change. The output spectral bandwidth is negatively correlated to the input temporal pulse width.

[0063] Preferably, the present invention enables consistent, stable, and continuous tuning of the peak and bandwidth of the output spectra, as shown in FIG. 5, and the tunable light source of this system is used to simultaneously shift the wavelength towards longer wavelength and shorter wavelength from the center wavelength of the femtosecond seed laser 1 (e.g., about 1,025 nm of an ytterbium-doped fiber laser). With the management of dispersion, this technology can deliver stable output pulses with minimum power fluctuation within the adjustable range.

[0064] Preferably, the femtosecond laser source with continuously tunable wavelength of the present invention delivers high intensity short pulses (the unit of pulse duration is femtosecond: 10.sup.−15 sec).

[0065] Preferably, the output power at different tuned wavelengths from the femtosecond tunable laser source is not correlated to the blueshift/redshift amount.

[0066] A preferred embodiment of the present invention: A femtosecond laser system, with simultaneously tunable redshift and blueshift, and with a consistent output power and controllable bandwidth, and the specification is different from the prior art, non-fiber-based solid-state laser systems (e.g., Ti:sapphire lasers with optical parametric oscillators), which requires precise light path alignments with annual maintenance for professional calibration. This system employs fiber-optic technology to manipulate the output wavelength and bandwidth, which saves the costs of expensive laser elements and the needs of annual maintenance.

[0067] Preferably, the device for realizing the tuning of the spectral peak location and the bandwidth in the present invention is the spectral conversion module 5, which only requires focusing the input laser beam into the fiber, featuring a compact and low-cost design. Its integration with a femtosecond fiber laser as the femtosecond seed laser 1 may lead to a compact and low-cost solution as a tunable femtosecond source with a consistent output power.

[0068] Preferably, this system can be easily separated into different modules, and the key unit, the spectral conversion module 5, can be easily replaceable with the ease of maintenance. For example, the spectral conversion module 5 can be switched rapidly within ten minutes. Besides the replacement of a malfunctioning module, the tunable spectral range and tunable spectral bandwidth can be further expanded by using different spectral conversion modules (e.g., with different types and lengths of optical fibers as the nonlinear medium).

[0069] Preferably, this system natively features good heat sinking based on a fiber laser, and this driving light source may be free from additional temperature and humidity control, which enables the smooth operation at least at room temperature from 23 to 30° C. and humidity from 30 to 70%.

[0070] Preferably, this system is relatively tolerable to external vibration, and the influence of vibration on misalignment can be recovered by active-controlled mirrors using a feedback loop.

[0071] Preferably, this system can employ fiber laser system as the driving light source, and the light path can be all fiber-based, which leads to a better isolation to the environment perturbation. Moreover, the volume of driving light source can be reduced within one meter in length, width, and height.

[0072] Preferably, this system uses a small piece of fiber as the key component in the spectral conversion module, and its length, width, and height are about within 20 cm (even possibly smaller than 5 cm), which significantly alleviates the concern in space arrangement.

[0073] Preferably, this system may use different spectral conversion modules 5 to achieve better energy conversion efficiency compared to the prior arts, and the tunable spectral range can be tuned towards longer and shorter wavelengths simultaneously, which enables larger than 30% of total fiber output energy of the continuously tunable filtered lobes in both redshift and blueshift.

[0074] A preferred embodiment of the present invention: An electric translational stage, as shown in FIG. 7, is used in the dispersion controller 3, and a driving current controller 2 controls a pump laser diode 21 in the femtosecond seed laser 1 to manipulate the output spectrum. An optical grating pair is employed in the dispersion controller 3 in this embodiment, but other dispersive components can also be used. An electric control system 7 of the electric translational stage controls the distance between two gratings, so as to manipulate the introduced dispersion and change the input temporal pulse width of the spectral conversion module 5. The spectral broadening is enabled by the coupled input light into a photonic crystal fiber 51, so as to control the range of a tunable wavelength and a tunable bandwidth from the spectral conversion module 5 (the input beam in the figure is indicated as the dash-dotted line), and the output light after the photonic crystal fiber 51 is a tunable broadened spectra. The required spectra of the output pulse are selected by a spectral selection module 6; a polarization beam splitter can be employed before the redshift and blueshift tunable fiber-optic spectral conversion module 5 to control the input power and polarization.

[0075] The dispersion controller 3 mainly provides tunable group delay dispersion (GDD, unit: fs.sup.2) to the input pulse of the spectral conversion module 5.The net GDD of the input pulse includes the dispersion provided by the dispersion controller and the intrinsic chirp from the output of the femtosecond seed laser 1, the smaller absolute value of the net GDD leads to the shorter pulse width (unit: femtosecond (fs)) and stronger SPM during the nonlinear propagation inside the spectral conversion module 5. Stronger SPM results in more spectral broadening and more redshift/blueshift. The embodiment is shown in FIG. 8, which applies a simple prism pair or transmission/reflection grating pair as an example, and the dispersion controller 3 modifies the net GDD amount by controlling the distance between the dispersive elements, so as to manipulate the temporal pulse width into the spectral conversion module. The longer the distance between two prisms leads to the larger negative GDD, and the smaller absolute value of net GDD leads to the shorter temporal pulse width, which leads to stronger SPM during the nonlinear conversion in the spectral conversion module 5 for the larger redshift/blueshift.

[0076] Preferably, this system delivers a light source, featuring continuously tunable blue-shifted and red-shifted spectra with consistent output power, enabled by fiber-optic SPM effect in the spectral conversion module and controlled by the dispersion controller 3 and the driving current controller 2. This method enables simultaneously redshift and blueshift with a wide tuning range. The shifted spectral peak location under different chirp is shown in FIG. 3, and the tuned spectra are indicated in different colors in FIG. 4. The output energy after the spectral selection module 6 is mostly concentrated in the two outmost (red-shifted and blue-shifted) spectral lobes, so as to realize a high energy conversion efficiency. It can be clearly noticed that the output powers of the different tuned spectra (e.g., the colors of spectral lobes shifted to the longer wavelength and shorter wavelength in FIG. 4) are roughly the same, as shown in FIG. 5 with less than 20% of the variation.

[0077] As stated above, the present method uses the dispersion controller 3 and the driving current controller 2 to control the chirp of the pulses and the temporal pulse width, so as to achieve different spectral broadening effects. The less net dispersion leads to shorter temporal pulse width into the spectral conversion module 5, and the stronger nonlinearity during the nonlinear conversion in the spectral conversion module 5 leads to a wider range of spectral broadening.

[0078] As stated above, the spectral selection module 6 includes long-pass and short-pass filter plates or band pass filter plates, and the spectral lobes are filtered out, as the spectra shown in FIG. 4, from the continuously tunable spectrum, as shown in FIG. 2. The tunability of the spectral peak location under different introduced chirp is shown in FIG. 4. The spectral lobes with the same color in FIG. 4 are the blue-shifted and red-shifted lobes from the same broadened spectrum, which can be filtered out simultaneously or individually.

[0079] Preferably, the dispersion controller 3 and the driving current controller 2 can be applied together or individually to generate different red/blueshift spectra with consistent power from the spectral conversion module 5 (definition of “consistent”: difference between the maximum and minimum power is less than 40%) or to generate the tunable spectral bandwidth, with 20% difference between the broadest and narrowest bandwidths.

Embodiment 3

[0080] Another embodiment of the present invention: A method and system to deliver femtosecond pulses with simultaneously tunable spectral redshift and blueshift and bandwidth, which enables tuning the spectral bandwidth at specific spectral peaks, and the bandwidth tuning method can be achieved with the following steps:

[0081] A1. A femtosecond seed laser 1 generates femtosecond laser pulses;

[0082] A2. A driving current controller 2 controls the output power and spectrum of the femtosecond seed laser 1, so as to control the fiber-optic nonlinear effect and to manipulate the output spectrum and pulse shapes;

[0083] A3. The laser beam passing through a dispersion controller 3 fixes the path position or/and a light spot size during the dispersion tuning, so that a temporal pulse width can be controlled without changing the other laser parameters, to control the output spectra of the invented system and to tune the spectral peak location and bandwidth of the output;

[0084] A4. An input power stabilizer 4 regulates the optical power input into a redshift and blueshift tunable fiber-optic spectral conversion module 5 (spectral conversion module), in order to fix the light path or/and the light spot size and to stabilize the power and spectrum of the output pulse, and it can cooperate with the dispersion controller 3 and the driving current controller 2 to control the peak intensity and the duration of the input pulse of the spectral conversion module 5;

[0085] A5. The spectral conversion module 5 receives optical pulses, and the duration and peak power of the input pulse can be controlled by the dispersion controller 3, the driving current controller 2, and the input power stabilizer 4: By controlling the introduced net dispersion and input power to manipulate the pulse width and peak intensity of the input pulse, a certain amount of input peak intensity corresponds a specific tuned spectral peak under a specific dispersion value, and the bandwidth of the spectral lobe is negatively correlated to the input pulse width, realizing the effect of [0010].

[0086] A6. A spectral selection module 6 selects the required spectral lobes and rejects unnecessary light of the residual wavelengths.

[0087] In the embodiment, the temporal pulse width and average power of the input light before the spectral conversion module 5 can be modified under a fixed input peak intensity (i.e., peak power under a unit area) by using the dispersion controller 3, the driving current controller 2, and the input power stabilizer 4, and the spectral peak location of the output can thus remain constant. However, the spectral bandwidth changes when varying input pulse widths, as the characteristics proposed in [0010]. For example, with more dispersion added, the input pulse becomes wider in the time domain, requiring higher input power to maintain the same center wavelength, leading to narrower output spectral and width from the spectral conversion module 5, delivering higher output power, as shown in FIG. 9.

[0088] Preferably, the main factors to control the output peak location of the spectral lobe are the power and temporal pulse width of the input pulse before the spectral conversion module 5. The different combinations of input power and temporal width lead to the spectral lobes with the same peak location but with different bandwidths, as shown in FIG. 6. The dispersion controller 3, the driving current controller 2, and the input power stabilizer 4 can be used simultaneously as the tuning degree of freedom, which enables the simultaneously tunable wavelength and bandwidth of output pulses to achieve the effect mentioned in [0010]. Using the spectral conversion module 5 (e.g., in the same species and length of photonic crystal fiber 51) to achieve a specific peak location of the output spectrum, the shorter input temporal pulse corresponds to a larger output spectral bandwidth with a lower output power, as shown in FIG. 9. To illustrate, a piece of SC-975 photonic crystal fiber is used, and the full width at half maximum of the output spectral lobe at different tuned wavelengths is managed by the input chirp (the solid line) and coupled energy (the dotted line), as shown in FIG. 6. The bandwidth range between the two management methods at a specific spectral peak is the applicable tuning range of the spectral bandwidth at the specific wavelength, and the range is indicated with double arrows. This tunable bandwidth can be customized by users to achieve tunable spectral bandwidth and temporal pulse width at different wavelengths; additionally, the range of tunable wavelength, output power, and tunable spectral bandwidth can be further expanded by using different spectral conversion modules 5 (e.g., changing the species and length of the optical fiber).

[0089] An embodiment of the present invention: The spectral conversion module applies the SPM effect in the fiber to generate broadened spectrum, which differs from the input spectrum. The spectral conversion module 5 may include one or more than one piece of fibers, which can be switched to different species and lengths.

[0090] Preferably, the amount of the tunable spectral redshift/blueshift from the same spectral conversion module 5 is proportional to the input pulse peak power, and it is negatively correlated to the input temporal pulse width; the output bandwidth is negatively correlated to the input pulse width of the spectral conversion module 5.