Optical amplifier for a fiber laser source and fiber laser source

Abstract

The present invention relates to an optical amplifier (1) for a fiber laser source (3) for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0-2.2 μm, comprising a preamplifier, which reacts to an optical input signal (SIN) having an input signal wavelength (λIN) and a first pump beam having a pump wavelength (λp1) and outputs an amplified input signal (SIN2), and a thulium-, thulium:holmium- or holmium-doped power amplifier, which is coupled to an output of the preamplifier and reacts to the amplified input signal (SIN2) and a second pump beam having a pump wavelength (λp2) and outputs an amplified output signal (SOUT), wherein the preamplifier is thulium:holmium-codoped.

Description

[0001] Optical amplifier for a fiber laser source and fiber laser source

[0002] The present invention relates to an optical amplifier for a fiber laser source for generating laser radiation and a fiber laser source for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0 pm to 2.2 pm.

[0003] Particularly for applications involving data transmission over optical fiber networks, such as coherent data communication with lasers, as well as in optronic countermeasures, LiDAR, laser weapons, and material processing with high-power lasers, beam sources with good beam quality are required. The emission range around 2.1 pm has proven advantageous due to its low hazard to the eyes and good atmospheric transmission. Fiber lasers are often used to generate such laser beams.

[0004] An optronic countermeasure is a defense mechanism designed to target sensors or guidance systems based on optical or infrared technology. This defense mechanism aims to reduce or neutralize the effectiveness of optical and infrared sensors used in guided missiles, reconnaissance, and surveillance equipment.

[0005] LiDAR (Light Detection and Ranging) is a remote sensing method that uses laser light to make precise measurements of distances and objects in the environment.

[0006] A known optical amplifier for operation over an eye-friendly bandwidth of 2.0–2.1 pm is described in US 11,276,982 B2. The optical amplifier is based on a holmium-doped fiber preamplifier and a subsequent thulium power amplifier. The fiber preamplifier improves the saturation of the power amplifier, thus enabling more efficient operation.

[0007] Among other disadvantages of the amplifier in US 11,276,982 B2, it has proven necessary to use a special pump laser for the holmium preamplifier, which must achieve a wavelength range of 1940 nm to 2000 nm. Furthermore, the amplifier is quite complex in its construction.

[0008] One object of the present invention is to overcome the disadvantages of the prior art, in particular to create an optical amplifier or fiber laser source that is simplified in construction and / or improved in efficiency.

[0009] This problem is solved by the subject matter of independent claims.

[0010] An optical amplifier for a fiber laser source for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0-2.2 pm, is then provided.

[0011] The amplifier includes a preamplifier that responds to an optical input signal SIN with an input signal wavelength AIN and a first pump beam with a pump wavelength A. pi reacts and outputs an amplified input signal SIN2, and a thulium, thulium:holmium or holmium-doped power amplifier coupled to an output of the preamplifier, which reacts to the amplified input signal SIN2 and a second pump jet with a pump wavelength P 2 reacts and outputs an amplified SOUT signal.

[0012] According to a first aspect of the invention, the preamplifier is thulium:holmium co-doped. This makes the preamplifier's gain band comparable to that of a purely holmium-doped preamplifier, but with the simplification of the pump wavelength of the thulium:holmium preamplifier by 780 nm to 810 nm. Thus, the need for a special, complex pump laser for the preamplifier, designed for the wavelength range of 1940 nm to 2000 nm, is eliminated. This leads to a simplification of the system and an increase in robustness. An advantage of the optical amplifier according to the invention lies in its improved efficiency and its ability to efficiently amplify long wavelengths above 2070 nm. This is particularly useful for applications requiring high beam quality and good atmospheric transmission, such as coherent data communication, optical countermeasures, laser weapons, and high-power laser material processing.Doping refers to the introduction of a dopant, in this case thulium or holmium, into the fiber material to modify its properties. Co-doping refers to the simultaneous introduction of several dopants, in this case thulium or holmium, to achieve synergistic effects and increase efficiency or performance.

[0013] In other words, the development concept can be described as follows: by selecting suitable materials for the preamplifier and the power amplifier, the pump wavelength is simplified, so that the range from 1,940 nm to 2,000 nm can be dispensed with.

[0014] According to a further aspect of the present invention, which can be combined with the preceding aspects and exemplary embodiments, an optical amplifier for a fiber laser source for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0-2.2 pm, is provided.

[0015] The amplifier includes a preamplifier that responds to an optical input signal SIN with an input signal wavelength AIN and a first pump beam with a pump wavelength A. pi reacts and outputs an amplified input signal SIN2, and a thulium, thulium:holmium or holmium-doped power amplifier coupled to an output of the preamplifier, which reacts to the amplified input signal SIN2 and a second pump jet with a pump wavelength P 2 reacts and outputs an amplified SOUT signal.

[0016] According to a further aspect of the invention, the preamplifier is designed such that it is adapted to a pump wavelength A piin the 780-810 nm range. The specific design of the preamplifier, which responds to a pump wavelength in the 780-810 nm range, offers several advantages. First, this pump wavelength allows for more efficient excitation of the thulium:holmium-codoped fiber, resulting in improved gain in the desired wavelength range. Second, choosing this pump wavelength eliminates the need for a dedicated pump laser in the 1940-2000 nm range for the preamplifier, simplifying the system and reducing costs. Third, using a pump wavelength in the 780-810 nm range improves the inversion distribution in the thulium fiber, leading to better efficiency and higher gain or saturation, especially at longer wavelengths above 2070 nm. This is particularly beneficial for applications requiring high beam quality and efficiency, such as...Material processing, optical countermeasures, and data transmission via fiber optic networks. The optimized pump wavelength increases the system's robustness, as fewer sensitive and specialized components are required.

[0017] According to an exemplary embodiment of the present invention, the preamplifier comprises a thulium:holmium-codoped fiber that is pumped in the core and / or the cladding. This specific configuration enables flexible and efficient pumping of the fiber, resulting in improved amplification performance. Core pumping refers to the direct introduction of the pump radiation into the core of the fiber, where the thulium:holmium ions are localized. This leads to efficient excitation of the ions and effective amplification of the optical signal. Cladding pumping, on the other hand, refers to the introduction of the pump radiation into the outer cladding of the fiber, which provides a larger area for the absorption of the pump radiation and thus increases the efficiency of the pumping at high pump power. This dual pumping strategy can be applied either separately or simultaneously to further optimize the amplification performance.One advantage of this configuration is the improved inversion distribution within the fiber, which leads to higher gain in the 2.1 pm range.

[0018] According to an exemplary embodiment of the present invention, a pump sheath is formed by a sheath of the fiber core or a pedestal around the fiber core. The pump sheath is a structural element that can be configured to couple the pump power more efficiently into the amplifier fiber. The fiber core sheath refers to the outer layer of the fiber that retains the light within the core by total internal reflection, while the pedestal is an additional layer around the core that improves the mechanical stability or optical properties of the fiber. This configuration enables an improved distribution of the pump power along the fiber, resulting in a more uniform amplification of the optical signal. An advantage of this arrangement is the increased efficiency of the pump power coupling, since the pump sheath provides a larger surface area for directing the pump light into the amplifier fiber.This leads to better amplifier saturation and thus higher gain of the optical signal. Another advantage is improved heat dissipation through the cladding or pedestal, which increases the amplifier's thermal stability and enables higher output power. Additionally or alternatively, the thulium-holmium codoped fiber can be configured so that the pump radiation is coupled in via a pedestal around the fiber core. The pedestal can serve as an optically active region, supporting the guidance and distribution of the pump radiation and enabling efficient transfer of pump energy into the active fiber core. A further advantage is that the pump radiation coupled in via the pedestal utilizes a larger active area, potentially leading to higher pump power and improved gain efficiency.According to an exemplary embodiment of the present invention, the optical amplifier comprises an optical signal conditioning device arranged in the signal transmission direction between the preamplifier and the power amplifier. This signal conditioning device can include various components such as an isolator, a mode field adapter, a cladding mode stripper, a wavelength selector, a circulator, and / or a modulator. The isolator serves to block reflected radiation and thus prevent feedback that could impair the performance and stability of the amplifier. A mode field adapter enables the matching of the mode field between different fibers, which improves the efficiency of signal transmission. The cladding mode stripper removes unwanted cladding modes that could impair the beam quality.A wavelength-selective element can be used to filter or select specific wavelengths, thus increasing the spectral purity of the output signal. A circulator allows for the targeted steering of light signals in different directions, which can be useful in complex optical networks. A modulator can be used to modulate the optical signal, either to transmit information to the light signal or to influence its waveform. Integrating these components between the preamplifier and the power amplifier offers the advantage of improved beam quality by eliminating unwanted modes and feedback. Furthermore, it increases the amplifier's efficiency by optimizing signal transmission. The flexibility in selecting and combining these components allows the optical amplifier to be tailored to specific requirements and applications.

[0019] According to an exemplary embodiment of the present invention, the pump beam is propagated in the signal transmission direction of the input signal, in particular by means of co-pumping. This means that the pump beam is directed in the same direction as the input signal to be amplified. Co-pumping is a technique in which the pump beam is guided in the same direction as the signal, which can help to improve the efficiency of energy transfer, since the pump energy is continuously transferred to the signal along the fiber. This results in a more uniform amplification of the signal over the entire length of the fiber. Furthermore, co-pumping reduces the back reflections and stray losses that can occur with counter-rotating pumping.

[0020] According to a further aspect of the present invention, which can be combined with the preceding aspects and exemplary embodiments, a fiber laser source is provided for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0-2.2 pm.

[0021] The fiber laser source comprises an optical amplifier, designed in particular according to one of the aspects and / or exemplary embodiments described above, which is directed to an optical input signal SIN with an input signal wavelength AIN and a first pump beam with a pump wavelength A. pi reacts and outputs an amplified input signal SIN2, and has a thulium, thulium:holmium or holmium-doped power amplifier coupled to an output of the preamplifier, which applies a second pump jet with a pump wavelength to the amplified input signal SIN2 P 2 reacts and outputs an amplified SOUT signal.

[0022] Furthermore, the fiber laser source includes a primary pump laser associated with the preamplifier, which generates pump laser radiation with a pump wavelength in the 780–810 nm range. This optimizes the efficiency of the thulium:holmium-codoped preamplifier and eliminates the need for a dedicated pump laser in the 1940–2000 nm range. This simplifies the system and increases its robustness. The primary pump laser is configured to deliver the required pump energy directly to the preamplifier, enabling efficient amplification of the input signal. This configuration offers advantages such as improved inversion distribution in the thulium fiber and more efficient amplification of long wavelengths above 2070 nm.

[0023] According to a further aspect of the present invention, which can be combined with the preceding aspects and exemplary embodiments, a fiber laser source is provided for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0-2.2 pm.

[0024] The fiber laser source comprises a thulium:holmium-codoped fiber and a thulium, thulium:holmium, or holmium-doped power amplifier fiber connected in the signal transmission direction. The thulium:holmium-codoped fiber can act as a preamplifier, amplifying the input signal before it is passed to the power amplifier fiber. The power amplifier fiber, which is either thulium, thulium:holmium, or holmium-doped, further amplifies the already amplified signal to produce an even more amplified output signal. Furthermore, additional optical components such as isolators, mode-field adapters, cladding mode strippers, wavelength-selective elements, circulators, and modulators can be integrated between the amplifier stages to further optimize the system's performance and stability.These additional components help to minimize unwanted effects such as back reflections and mode instabilities, further improving the overall performance and reliability of the fiber laser source.

[0025] According to an exemplary embodiment of the present invention, the thulium:holmium-codoped fiber is configured as a fiber laser and is pumped in the core and / or cladding by means of a pump laser to generate pump laser radiation with a pump wavelength in the range of 780–810 nm. Configuring the thulium:holmium-codoped fiber as a fiber laser means that the fiber not only serves as an amplification medium but also functions as an independent laser source. This can be achieved by various means. The pump wavelength in the range of 780–810 nm is particularly advantageous because it enables efficient excitation of the thulium and holmium ions, leading to improved amplification performance. Pumping in the core and / or cladding offers flexibility in the design of the laser system and allows for optimized energy supply.Pumping in the core ensures direct excitation of the active ions in the fiber core, while pumping in the cladding allows for a more uniform distribution of the pump energy, thus increasing the efficiency of the amplification process. The combination of these pumping methods can further improve the overall power and stability of the laser. Another advantage of this configuration is the ability to efficiently amplify long wavelengths above 2070 nm. When the thulium:holmium-codoped fiber is driven by a multimode emitting pump diode located at the fiber end, the entire fiber end face, encompassing both the core and cladding, can be illuminated and pumped. This pumps the thulium:holmium-codoped fiber with the pump laser radiation in the 780–810 nm range in both the core and the cladding. In this configuration, a portion of the pump laser radiation can be coupled into the core and another portion into the cladding.This allows the fiber laser source to simultaneously serve as an oscillator and as a signal source for downstream amplifier stages. The fiber core can function as the active laser zone, while the cladding can provide additional pumping energy. According to an exemplary embodiment of the present invention, the thulium:holmium-codoped fiber for forming the fiber laser is arranged between two reflective devices, such as fiber Bragg gratings, or at least two reflective devices, such as fiber Bragg gratings, are directly coupled to the thulium:holmium-codoped fiber. These reflective devices serve as optical resonators that reflect the light back and forth within the fiber, thereby further increasing the amplification of the optical signal. Fiber Bragg gratings are special optical filters that reflect certain wavelengths of light and transmit others.Their arrangement within the fiber allows for precise control and stabilization of the amplified light wavelength. Integrating fiber Bragg gratings into the thulium:holmium-codoped fiber enables efficient light feedback, resulting in improved amplification and stability of the output signal. This enhances the beam quality of the laser source. Furthermore, the use of fiber Bragg gratings contributes to increased amplifier system efficiency by filtering out unwanted wavelengths and focusing amplification on the desired wavelengths. This leads to higher output power and better utilization of the supplied pump energy.

[0026] Preferred embodiments are specified in the dependent claims.

[0027] Further properties, features and advantages of the invention will be clarified below by describing preferred embodiments of the invention with reference to the accompanying exemplary drawings, which show:

[0028] Figure 1 shows a schematic view of an exemplary embodiment of an optical amplifier according to the invention; and

[0029] Figure 2 shows a schematic view of an exemplary embodiment of a fiber laser source according to the invention.

[0030] In both embodiments according to Figures 1 and 2, the pump radiation is propagated in the direction of propagation of the signal to be amplified (co-pumping). The arrangements utilize the advantages of thulium:holmium co-doping to achieve higher efficiency and better gain in the range of 2.0–2.2 pm. Figure 1 shows a schematic representation of an exemplary embodiment of an optical amplifier according to the invention, generally designated by reference numeral 1, comprising a thulium:holmium co-doped preamplifier and a downstream power amplifier. An optical input signal SIN with an input signal wavelength AIN is introduced via an input 5, which may, for example, be guided through an insulator 15, and in a signal coupler 19 is coupled with a first pump beam with a pump wavelength A, generated by a pump laser 9. piis combined and finally fed to a thulium:holmium-codoped fiber 23. An amplified input signal SIN2 is output and, for example, passed through an insulator 17 and again in a signal coupler 21 with a second pump beam generated by another pump laser 11 with a pump wavelength P2 combined and finally fed to a thulium:holmium-codoped, holmium-doped, or thulium-doped fiber 25. An amplified output signal SOUT in the desired bandwidth range of 2 pm to 2.2 pm can then be output via an output 7. The pump wavelength of the thulium:holmium preamplifier fiber 23 can be selected in the range of 780 nm to 810 nm. Figure 2 shows an exemplary embodiment of a fiber laser source 3 according to the invention, in which a thulium:holmium-codoped fiber 27, pumped in the core or in a cladding by means of a pump laser, forms a fiber laser in which the fiber 27 is arranged between two fiber Bragg gratings 29, 31. In the direction of signal propagation, at least one thulium-doped, thulium:holmium-co-doped or holmium-doped power amplifier fiber 33 is arranged, the amplified output signal of which is delivered via the output 7.As shown in Figure 32, further optical components, such as insulators, mode field adapters, cladding mode strippers, wavelength-selective elements, circulators, modulators, etc., can also be inserted between the fiber laser 27 and the power amplifier fiber 33.

[0031] The features disclosed in the foregoing description, figures, and claims can be important for the realization of the invention in its various embodiments, both individually and in any combination. List of reference numerals

[0032] 1 Optical amplifier 3 Fiber laser source

[0033] 5 Entrance

[0034] 7 Exit

[0035] 9 first pump laser

[0036] 11 second pump laser

[0037] 13 pump lasers

[0038] 15, 17 Insulator

[0039] 19, 21 Signal coupler

[0040] 23 codominated fiber

[0041] 25 doped fibers

[0042] 29, 31 Fiber Bragg grid

[0043] 33 Power amplifier fiber

Claims

REQUIREMENTS 1. Optical amplifier (1) for a fiber laser source (3) for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0 pm to 2.2 pm, comprising: a preamplifier that responds to an optical input signal SIN with an input signal wavelength AIN and a first pump jet with a pump wavelength A pi reacts and outputs an amplified input signal SIN2; and a thulium, thulium:holmium or holmium-doped power amplifier coupled to an output of the preamplifier, which reacts to the amplified input signal SIN2 and a second pump jet with a pump wavelength P 2 reacts and outputs an amplified output signal SOUT; characterized by the fact that the preamplifier is thulium:holmium co-doped.

2. Optical amplifier (1), in particular according to claim 1, for a fiber laser source (3) for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0 pm to 2.2 pm, comprising: a preamplifier that responds to an optical input signal SIN with an input signal wavelength AIN and a first pump jet with a pump wavelength A pi reacts and outputs an amplified input signal SIN2; and a thulium, thulium:holmium or holmium-doped power amplifier coupled to an output of the preamplifier, which reacts to the amplified input signal SIN2 and a second pump jet with a pump wavelength X P 2 reacts and outputs an amplified output signal SOUT; characterized in that the preamplifier is designed such that it is adapted to a pump wavelength A pi reacts in the range of 780 nm to 810 nm.

3. Optical amplifier (1) according to claim 1 or 2, wherein the preamplifier comprises a thulium:holmium-codoped fiber (23) which is pumped in the core and / or in the cladding.

4. Optical amplifier (1) according to claim 3, wherein a pump sheath is formed by a sheath of the fiber core or a pedestal around the fiber core.

5. Optical amplifier (1) according to one of the preceding claims, further comprising at least one optical signal conditioning device arranged in the signal transmission direction between the preamplifier and the power amplifier, such as an isolator (25, 27), a mode field adapter, a cladding mode stripper, a wavelength-selective element, a circulator and / or a modulator.

6. Optical amplifier (1) according to one of the preceding claims, wherein the pump jet is propagated in the signal transmission direction of the input signal, in particular by means of co-pumping.

7. Fiber laser source (3) for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0 pm to 2.2 pm, comprising: an optical amplifier, in particular designed according to one of the preceding claims, comprising a preamplifier, in particular a thulium:holmium-codoped preamplifier, which is connected to an optical input signal SIN with an input signal wavelength AIN and a first pump jet with a pump wavelength A pi reacts and outputs an amplified input signal SIN2, and has a thulium, thulium:holmium or holmium-doped power amplifier coupled to an output of the preamplifier, which applies a second pump jet with a pump wavelength to the amplified input signal SIN2 P 2 reacts and outputs an amplified SOUT signal; and a first pump laser associated with the preamplifier for generating a pump laser radiation with a pump wavelength A piin the range of 780 nm to 810 nm.

8. Fiber laser source (3), in particular according to claim 7, for generating laser radiation in the infrared range, in particular over a bandwidth of 2.0 pm to 2.2 pm, comprising a thulium:holmium-codoped fiber (23) and a thulium, thulium:holmium or holmium-doped power amplifier fiber (33) adjoining in the signal transmission direction.

9. Fiber laser source (3) according to claim 8, wherein the thulium:holmium-codoped fiber (23) is configured as a fiber laser and is equipped in the core and / or in the cladding by means of a pump laser to generate a pump laser radiation with a pump wavelength A pi is pumped in the range of 780 nm to 810 nm.

10. Fiber laser source (3) according to claim 9, wherein the thulium:holmium-codoped fiber (23) is arranged between two reflective devices, such as fiber Bragg gratings (29, 31), or wherein at least two reflective devices, such as fiber Bragg gratings (29, 31), are directly coupled to the thulium:holmium-codoped fiber (23).

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