EYDFA outputs high-power supercontinuum light source based on XPM effect

Abstract

The invention relates to a supercontinuum light source in the field of laser technology and nonlinear optics, and in particular to an EYDFA output high-power supercontinuum light source based on an XPM effect, which has the advantages of better spectral flatness and wider bandwidth. The invention utilizes an enhanced cross-phase modulation effect to effectively suppress a high-intensity cascade Raman peak in an output supercontinuum spectrum and enhance a low-intensity short-wave component, thereby effectively improving the spectral flatness of a high-power supercontinuum laser within a broadband range. The invention can effectively solve the problem that a high-intensity cascade Raman peak and a low-intensity short-wave component in a supercontinuum output by an optical fiber amplifier affect spectral flatness and width, thereby realizing high-power supercontinuum output.

Description

Technical Field

[0001] The present invention relates to a supercontinuum light source in the field of laser technology and nonlinear optics, and in particular to an Erbium-ytterbium co-doped fiber amplifier (EYDFA) output high-power supercontinuum light source based on a cross-phase modulation (XPM) effect, which has the advantages of better spectral flatness and wider bandwidth. Background Art

[0002] High-power supercontinuum has potential application prospects in hyperspectral lidar, optical coherence tomography, astronomical optical frequency comb, etc. due to its rich spectral components and laser characteristics, and has been booming in recent decades. In some special applications, there are strict requirements on the spectral flatness and spectral bandwidth of the light source. For example, astronomical calibration requires a calibration source with a wide spectral bandwidth and low spectral intensity variation to detect exoplanets.

[0003] The output of high-power supercontinuum spectrum based on fiber amplifier is a common method to obtain high-power supercontinuum spectrum. Common fiber amplifiers based on silica matrix include ytterbium-doped fiber amplifier, erbium-doped fiber amplifier, EYDFA, thulium-doped fiber amplifier, etc. Since the gain fiber of these fiber amplifiers has no additional waveguide design, the zero dispersion wavelength is similar to that of fused silica, which is about 1.3 However, the generation of a flat broadband supercontinuum is usually achieved by pumping a nonlinear fiber with a pump light source whose pump wavelength is located in the anomalous dispersion region near the zero dispersion point of the nonlinear fiber. The output spectrum of the high-power supercontinuum output by the fiber amplifier generally has the problem of high-intensity cascade Raman peak and low-intensity short-wave component affecting the spectral flatness within the broadband range of the output high-power supercontinuum. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes an EYDFA output high-power supercontinuum light source based on the XPM effect. The invention utilizes the enhanced cross-phase modulation effect to effectively suppress the high-intensity cascade Raman peak in the output supercontinuum spectrum and enhance the low-intensity short-wave component, effectively improving the spectral flatness of the high-power supercontinuum laser in a broadband range.

[0005] The technical solution adopted by the present invention is: an EYDFA output high-power supercontinuum light source based on the XPM effect, comprising a first pump laser 11, a second pump laser 12, a wavelength division multiplexer 2, a laser diode 3, a pump signal combiner 4, an erbium-ytterbium co-doped optical fiber 5, a cladding light filter 71, and an optical fiber output end cap 72; wherein the first pump laser 11 and the second pump laser 12 are connected to the signal arm of the pump signal combiner 4 through the wavelength division multiplexer 2, and thus connected to the EYDFA system; the laser diode 3, the pump signal combiner 4, and the erbium-ytterbium co-doped optical fiber 5 together constitute the EYDFA system, and the laser diode 3 is connected to the pump arm of the pump signal combiner 4 through an optical fiber; the cladding light filter 71 and the optical fiber output end cap 72 together constitute a laser output module; the output end of the erbium-ytterbium co-doped optical fiber 5 of the EYDFA system is fused with the input optical fiber of the cladding light filter 71 in the laser output module, and used as the laser output of the system.

[0006] The first pump laser 11 and the second pump laser 12 are used to provide signal light for the EYDFA system. The central wavelength of the first pump laser 11 is located in the ytterbium ion radiation region (900-1200 nm) of the erbium-ytterbium co-doped fiber, and the central wavelength of the second pump laser 12 is located in the erbium ion radiation region (1400-1700 nm) of the erbium-ytterbium co-doped fiber; the first pump laser 11 and the second pump laser 12 can be continuous light lasers or pulsed light lasers at the same time.

[0007] The wavelength division multiplexer 2 is used to inject the signal light emitted by the first pump laser 11 and the second pump laser 12 into the signal input end of the pump signal combiner 4; the wavelength division multiplexer 2 can be a filter type wavelength division multiplexer or a wavelength division multiplexer prepared by the fused taper method.

[0008] The laser diode 3 is used to provide pump light for the Er-Yb co-doped optical fiber 5. The working wavelength can be selected from 915-981 nm, 1018 nm, and 1030 nm; the output pigtail of the laser diode 3 can be 105 / 125 、135 / 155 or 200 / 220 sized multimode optical fiber.

[0009] The pump signal combiner 4 is used to transmit the pump light output by the laser diode 3 and the signal light output by the wavelength division multiplexer 2 to the erbium-ytterbium co-doped optical fiber 5. The pump arm pigtail of the pump signal combiner 4 uses an optical fiber that matches the output pigtail of the laser diode 3; the number of pump arms (i.e., laser diodes 3) of the pump signal combiner 4 can be 1 or 2N, where N is a natural number; the pumping mode can be forward pumping, backward pumping, or bidirectional pumping.

[0010] The erbium-ytterbium co-doped fiber 5 has two functions: 1. It has dual-wavelength radiation characteristics. The erbium-ytterbium co-doped fiber 5 realizes population inversion by absorbing the pump light transmitted by the pump signal combiner 4, and then provides gain for the two signal lights (i.e., the signal lights transmitted by the first pump laser 11 and the second pump laser 12) output by the pump signal combiner 4 at the same time to achieve high power output; 2. It is used for the accumulation of nonlinear effects such as XPM to achieve spectrum broadening. The wavelengths of the two signal lights amplified by the erbium-ytterbium co-doped fiber 5 just meet the group velocity matching condition of the erbium-ytterbium co-doped fiber 5 (i.e., the propagation group velocity is the same in this fiber). When the two signal lights are set to be initially injected into the erbium-ytterbium co-doped fiber 5, they are synchronized in the time domain. Since the propagation group velocity of the signal lights is the same and the time domain is synchronized during the initial injection, the two signal lights overlap in time and space, thereby enhancing the interaction between the two signal lights, and then leading to the generation of enhanced XPM effect. As a nonlinear effect, the XPM effect is positively correlated with the fiber length. The longer the distance that the two signal lights are transmitted along the erbium-ytterbium co-doped fiber 5, the longer the interaction length of the two signal lights, the stronger the XPM effect. In addition, other nonlinear effects (such as four-wave mixing, soliton effect, etc.) will also be successively excited and effectively accumulated due to the longer transmission length of the signal light along the fiber. Ultimately, the XPM effect dominates and combines with other nonlinear effects to lead to spectrum broadening, that is, supercontinuum laser generation. The fiber length of the erbium-ytterbium co-doped fiber 5 is 1-100 m, and the core diameter is 10-50 , cladding diameter is 125-1000 , the numerical aperture is 0.05-0.3.

[0011] The laser output module is used for high-power supercontinuum laser output. The laser output module includes a cladding light filter 71 and an optical fiber output end cap 72, wherein the cladding light filter 71 is used to filter out the light in the cladding to improve the output beam quality, and its core diameter is 10-50 , cladding diameter is 125-1000 The optical fiber output end cap 72 is used to reduce the power density of the laser output interface, thereby reducing the laser damage caused by excessive power density at the output optical fiber interface under high power output conditions. In addition, the optical fiber output end cap 72 is cut at an angle of 8° to reduce the end face feedback of the light and protect the front stage system.

[0012] Furthermore, the present invention also includes a passive optical fiber 6, which is used to further provide the accumulation of nonlinear effects such as the XPM effect to achieve a large broadening of the supercontinuum spectrum. The passive optical fiber 6 is completely matched with the fiber parameters (core cladding size, numerical aperture) of the erbium-ytterbium co-doped optical fiber 5 to ensure low-loss signal transmission of the EYDFA system. The fiber length of the passive optical fiber 6 is 1-500 m to provide sufficient nonlinear accumulation to achieve a large broadening of the supercontinuum spectrum.

[0013] The present invention has the following technical effects:

[0014] 1. The present invention can effectively solve the problem that the high-intensity cascade Raman peak and low-intensity short-wave component in the supercontinuum spectrum output by the optical fiber amplifier affect the spectral flatness and width. The wavelengths of the first pump laser 11 and the second pump laser 12 of the present invention are respectively located in the normal dispersion region and the anomalous dispersion region of the erbium-ytterbium co-doped optical fiber 5 and have the same group velocity, which means that when the output signal light of the first pump laser 11 and the second pump laser 12 are synchronously injected into the erbium-ytterbium co-doped optical fiber EYDFA system, the two signal lights are synchronized in time domain and propagate at the same group velocity, thereby enhancing the interaction between the two signal lights, and further leading to the generation of enhanced XPM effect. On the one hand, the enhanced XPM effect will modify the spectral evolution during normal dispersion region pumping (usually, the spectral evolution in the normal dispersion region is dominated by the stimulated Raman effect), thereby effectively suppressing the stimulated Raman scattering effect; on the other hand, the enhanced XPM will effectively enhance related effects such as soliton capture, thereby leading to the enhancement of the short-wave component generated by the soliton capture effect. Based on these two points, the problem of high-intensity cascade Raman peak and low-intensity short-wave component affecting the spectral flatness in the broadband range is effectively improved, thus achieving the generation of a broadband flat supercontinuum spectrum;

[0015] 2. The present invention can achieve high-power supercontinuum output. The erbium-ytterbium co-doped optical fiber used in the present invention has dual-wavelength radiation characteristics of ytterbium ions and erbium ions. This means that the present invention can simultaneously amplify the signal light of the first pump laser 11 and the second pump laser 12, which can effectively improve the system output power. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structure of the EYDFA outputting a high-power supercontinuum light source based on the XPM effect of the present invention;

[0017] Figure 2 It is a structural schematic diagram of a specific embodiment of the present invention's EYDFA outputting a high-power supercontinuum light source based on the XPM effect;

[0018] Figure 3 is the relationship between the dual-wavelength signal optical power and the supercontinuum power output by the EYDFA system in the embodiment of the present invention;

[0019] Figure 4 is the supercontinuum spectrum output by the embodiment of the present invention when the maximum supercontinuum output power is 104 W;

[0020] Figure 5 is a group velocity matching curve of the erbium-ytterbium co-doped optical fiber 5 in an embodiment of the present invention;

[0021] Figure 6 The comparison diagram of the supercontinuum spectrum output with and without the enhanced XPM effect (by controlling the time domain synchronization state of the two pulse starts). DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] An embodiment of the present invention is an EYDFA output high-power supercontinuum light source based on the XPM effect, such as Figure 2 As shown. It includes a first pump laser 11, a second pump laser 12, a wavelength division multiplexer 2, a first laser diode 31, a second laser diode 32, a third laser diode 33, a fourth laser diode 34, a fifth laser diode 35, a sixth laser diode 36, a pump signal combiner 4, an erbium-ytterbium co-doped optical fiber 5, a passive optical fiber 6, a cladding light filter 71, and an optical fiber output end cap 72; the pigtails of the first pump laser 11 and the second pump laser 12 are connected to the input pigtail of the wavelength division multiplexer 2 by low-loss fusion; the output pigtail of the wavelength division multiplexer 2 is connected to the signal arm of the pump signal combiner 4 by low-loss fusion, and the first and second pump lasers 11 and 12 are connected to the input pigtail of the wavelength division multiplexer 2 by low-loss fusion. The output pigtails of the first laser diode 31, the second laser diode 32, the third laser diode 33, the fourth laser diode 34, the fifth laser diode 35, and the sixth laser diode 36 are connected to the pump arm of the pump signal combiner 4 by low-loss fusion splicing; the output pigtail of the pump signal combiner 4 is connected to the input end of the erbium-ytterbium co-doped optical fiber 5 by low-loss fusion splicing; the output end of the erbium-ytterbium co-doped optical fiber 5 is connected to the input end of the passive optical fiber 6 by low-loss fusion splicing; the output end of the passive optical fiber 6 is connected to the laser output module by low-loss fusion splicing; wherein the cladding light filter 71 and the optical fiber output end cap 72 together constitute the laser output module;

[0024] In this embodiment, the central wavelength of the first pump laser 11 is 1030 nm, and the output pigtail is GDF 10 / 130; the central wavelength of the second pump laser 12 is 1535 nm, and the output pigtail is SM-GDF-1550; the input fiber and the output fiber of the wavelength division multiplexer 2 are both SM-GDF-1550, the working wavelength is 1030 / 1550 nm, the working bandwidth is about 10 nm, and the insertion loss is about 0.3 dB; the laser output wavelengths of the first laser diode 31, the second laser diode 32, the third laser diode 33, the fourth laser diode 34, the fifth laser diode 35, and the sixth laser diode 36 are all 976 nm, and the output pigtails are all 105 / 125 , the output power is about 90 W; the pump arm of the pump signal combiner 4 matches the output pigtails of the first laser diode 31, the second laser diode 32, the third laser diode 33, the fourth laser diode 34, the fifth laser diode 35, and the sixth laser diode 36; the signal arm of the pump signal combiner 4 matches the output pigtail of the wavelength division multiplexer 2; the signal output pigtail of the pump signal combiner 4 matches the input pigtail of the erbium-ytterbium co-doped fiber 5; the core / cladding size of the erbium-ytterbium co-doped fiber 5 is 25 / 300 , the numerical aperture is 0.09, the cladding absorption coefficient at 976 nm is about 7 dB / m, and the fiber length is 1.5 m; the passive fiber 6 matches the erbium-ytterbium co-doped fiber 5, and the fiber length is about 50 m. Since the excitation and accumulation of nonlinear effects are positively correlated with the fiber length, the passive fiber 6 and the erbium-ytterbium co-doped fiber 5 used here are long enough to be used for the effective accumulation of nonlinear effects such as XPM, thereby realizing supercontinuum output.

[0025] In this embodiment, when two signal lights are injected into the EYDFA system, two effects are brought about: on the one hand, the erbium-ytterbium co-doped fiber 5 has the laser radiation characteristics of both ytterbium ions and erbium ions, and can amplify the signal lights of 1030 nm and 1535 nm at the same time, which can effectively improve the system output power. Figure 2 The relationship between the dual-wavelength signal light power and the supercontinuum power output by the EYDFA system under this embodiment is shown. When the amplifier outputs dual-wavelength power of about 192 W, the supercontinuum output power is about 104 W, and the conversion efficiency is about 54%; on the other hand, when the two signal lights are transmitted along the erbium-ytterbium co-doped fiber 5 and the passive fiber 6, since the nonlinear effect is positively correlated with the fiber length, the longer the fiber length along which the two signal lights are transmitted along the erbium-ytterbium co-doped fiber 5 and the passive fiber 6, the better the effect of the accumulation of multiple nonlinear effects. Ultimately, under the dominance of the XPM effect, combined with other multiple nonlinear effects (such as four-wave mixing, soliton effect, etc.), the spectrum is greatly broadened, that is, the generation of supercontinuum laser. Figure 3This is the supercontinuum spectrum output by this embodiment when the maximum supercontinuum output power is 104 W. As can be seen from the figure, the spectral flatness within the 10 dB intensity range covers the visible light to near-infrared region, and the wavelength range is 770-2055 nm (this flatness range does not include the pump peak, which can actually be solved later by replacing a pump laser with a better modulation effect).

[0026] In this embodiment, the generation of the supercontinuum is dominated by the XPM effect. Due to the enhanced XPM effect, the stimulated Raman scattering effect is effectively suppressed and the short-wave component is effectively enhanced, thereby effectively improving the problem of high-intensity cascade Raman peak and low-intensity short-wave component affecting the spectral flatness in a broadband range. Figure 4 The group velocity curve of the Er-Yb co-doped fiber 5 is shown. It is particularly important to note that since the Er-Yb co-doped fiber 5 and the passive fiber 6 have the same waveguide parameters and both use quartz fiber as the matrix material, their waveguide dispersion and material dispersion characteristics are the same, so they have the same group velocity curve. The working wavelengths of the first pump laser 11 and the second pump laser 12 are located in the normal dispersion region and the anomalous dispersion region of the Er-Yb co-doped fiber 5 and have the same group velocity, and the group velocity value is about 2.0456×10 8 m / s. When the output pulses of these two lasers are synchronously injected into the EYDFA system, the two pulses are time-domain synchronized and have the same group velocity, which leads to the time-domain overlap of the two pulses when they are transmitted along the optical fiber. The interaction between them is enhanced, which leads to the generation of an enhanced XPM effect. On the one hand, the enhanced XPM will modify the spectral evolution during normal dispersion region pumping (usually, when the pump laser is located in the normal dispersion region of the optical fiber, the stimulated Raman scattering effect dominates the initial broadening of the spectrum), thereby effectively suppressing the stimulated Raman scattering effect and suppressing the high-intensity cascade Raman peak; on the other hand, the enhanced XPM will effectively enhance related effects such as soliton capture, thereby leading to the enhancement of the short-wave component generated by the soliton capture effect. Based on the above two aspects, the problem of the high-intensity cascade Raman peak and the low-intensity short-wave component in the spectrum affecting the spectral flatness in a broadband range can be effectively solved, resulting in the generation of a flat supercontinuum in a broadband range. Figure 5 The comparison of supercontinuum spectra with and without enhanced XPM effect (by controlling the time domain synchronization state of the two pulse starts) is shown. It can be seen from the figure that when the XPM effect is significantly enhanced, the high-intensity cascade Raman peak can be effectively suppressed, the low-intensity short-wave component can be effectively enhanced, and the spectral flatness in the broadband range can be effectively improved.

Claims

1. Based on the XPM effect, the EYDFA outputs a high-power supercontinuum light source, characterized by: The invention comprises a first pump laser (11), a second pump laser (12), a wavelength division multiplexer (2), a laser diode (3), a pump signal combiner (4), an erbium-ytterbium co-doped optical fiber (5), a cladding light filter (71), and an optical fiber output end cap (72); wherein the first pump laser (11) and the second pump laser (12) are connected to the signal arm of the pump signal combiner (4) through the wavelength division multiplexer (2), thereby being connected to the EYDFA system; the laser diode (3) The diode (3), the pump signal beam combiner (4), and the erbium-ytterbium co-doped optical fiber (5) together constitute an EYDFA system; the laser diode (3) is connected to the pump arm of the pump signal beam combiner (4) through an optical fiber; the cladding light filter (71) and the optical fiber output end cap (72) together constitute a laser output module; the output end of the erbium-ytterbium co-doped optical fiber (5) of the EYDFA system is fused with the input optical fiber of the cladding light filter (71) in the laser output module to serve as the laser output of the system; The first pump laser (11) and the second pump laser (12) are used to provide signal light for the EYDFA system; the central wavelength of the first pump laser (11) is located in the ytterbium ion radiation region of the erbium-ytterbium co-doped optical fiber, and the central wavelength of the second pump laser (12) is located in the erbium ion radiation region of the erbium-ytterbium co-doped optical fiber; The wavelength division multiplexer (2) is used to inject the signal light emitted by the first pump laser (11) and the second pump laser (12) into the signal input end of the pump signal combiner (4); The laser diode (3) is used to provide pump light for the erbium-ytterbium co-doped optical fiber (5); The pump signal combiner (4) is used to transmit the pump light output by the laser diode (3) and the signal light output by the wavelength division multiplexer (2) to the erbium-ytterbium co-doped optical fiber (5); The erbium-ytterbium co-doped optical fiber (5) has two functions:

1. It has dual-wavelength radiation characteristics; the erbium-ytterbium co-doped optical fiber (5) realizes population inversion by absorbing the pump light transmitted by the pump signal combiner (4), thereby simultaneously providing gain for the two signal lights output by the pump signal combiner (4) to achieve high-power output; 2. It is used for the accumulation of XPM nonlinear effects to achieve spectrum broadening; the wavelengths of the two signal lights amplified by the erbium-ytterbium co-doped optical fiber (5) just meet the group velocity matching condition of the erbium-ytterbium co-doped optical fiber (5); when the two signal lights are initially injected into the erbium-ytterbium co-doped optical fiber (5), they are synchronized in the time domain, because the propagation group velocities of the signal lights are the same and the time domain at the time of initial injection is Synchronous, the two signal lights overlap in time and space, resulting in an enhanced interaction between the two signal lights, which in turn leads to the generation of an enhanced XPM effect; and the XPM effect, as a nonlinear effect, is positively correlated with the fiber length. The longer the distance the two signal lights are transmitted along the erbium-ytterbium co-doped fiber (5), the longer the interaction length of the two signal lights is, and the stronger the XPM effect is. In addition, nonlinear effects such as four-wave mixing and soliton effects will also be successively excited and effectively accumulated due to the longer transmission length of the signal lights along the fiber. Ultimately, under the dominance of the XPM effect, combined with a variety of other nonlinear effects, the spectrum is broadened, that is, a supercontinuum laser is generated; The laser output module is used for high-power supercontinuum laser output; the laser output module comprises a cladding light filter (71) and an optical fiber output end cap (72), wherein the cladding light filter (71) is used for filtering light in the cladding so as to improve the output light beam quality, and the core diameter thereof is 10-50 mm, and the cladding diameter is 125-1000 mm; the optical fiber output end cap (72) is used for reducing the power density of the laser output interface so as to reduce laser damage caused by excessive power density at the output optical fiber interface in the case of high power output.

2. The EYDFA output high-power supercontinuum light source based on the XPM effect according to claim 1, characterized in that: The first pump laser (11) and the second pump laser (12) can be continuous light lasers or pulse light lasers at the same time.

3. The EYDFA output high-power supercontinuum light source based on the XPM effect according to claim 1, characterized in that: The wavelength division multiplexer (2) may be a filter-type wavelength division multiplexer or a wavelength division multiplexer prepared by a fused taper method.

4. The EYDFA output high-power supercontinuum light source based on the XPM effect according to claim 1, characterized in that: The working wavelength of the laser diode (3) is selected to be 915-981 nm, 1018 nm, or 1030 nm; the output pigtail is a multimode optical fiber with a size of 105 / 125 mm, 135 / 155 mm, or 200 / 220 mm.

5. The EYDFA output high-power supercontinuum light source based on the XPM effect according to claim 1, characterized in that: The pump arm pigtail of the pump signal combiner (4) uses an optical fiber that matches the output pigtail of the laser diode (3); the number of pump arms of the pump signal combiner 4 is 1 or 2N, where N is a natural number; The pumping mode adopts forward pumping, backward pumping or bidirectional pumping.

6. The EYDFA output high-power supercontinuum light source based on the XPM effect according to claim 1, characterized in that: The erbium-ytterbium co-doped optical fiber (5) has an optical fiber length of 1-100 m, a core diameter of 10-50 mm, a cladding diameter of 125-1000 mm, and a numerical aperture of 0.05-0.

3.

7. The EYDFA output high-power supercontinuum light source based on the XPM effect according to claim 1, characterized in that: The optical fiber output end cap (72) is cut with an angle of 8° to reduce the end face feedback of light and protect the front stage system.

8. The EYDFA output high-power supercontinuum light source based on the XPM effect according to any one of claims 1 to 7, characterized in that: The supercontinuum light source further comprises a passive optical fiber (6), and the passive optical fiber (6) is used to further provide the accumulation of XPM nonlinear effects to achieve a great broadening of the supercontinuum spectrum.

9. The EYDFA output high-power supercontinuum light source based on the XPM effect according to claim 8, characterized in that: The passive optical fiber (6) and the Er-Yb co-doped optical fiber (5) have completely matched optical fiber parameters to ensure low-loss signal transmission of the EYDFA system. The optical fiber length of the passive optical fiber (6) is 1-500 m to provide sufficient nonlinear accumulation to achieve extremely widened supercontinuum spectrum.

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