CN103022869B - Passive mode-locking guide gain-modulated dual-wavelength pulse fiber laser - Google Patents

Abstract

The invention provides a passively mode-locked guided gain-modulated dual-wavelength pulse fiber laser, comprising a pump source for generating continuous pump light, a polarization beam combiner for combining pump light, a dichroic mirror with high transmittance to pump light and high reflection to laser light for guiding resonant laser, a coupling lens, a semiconductor saturable absorption mirror, a Ho ³⁺ -doped or Er ^3+-doped ZBLAN fiber, a Bragg fiber grating and two chirped fiber gratings, and an output end. The pump source adopts an LD pump source or a semiconductor laser pump source; the coupling lens is used to couple the generated pump light into the Ho ³⁺ -doped or Er ^3+-doped ZBLAN fiber; the dichroic mirror forms an angle of 45 degrees with the fiber; the semiconductor saturable absorption mirror is placed horizontally with the Ho ³⁺ -doped or Er ^3+-doped ZBLAN fiber and forms an angle of 45 degrees with the dichroic mirror.

Description

A dual-wavelength pulsed fiber laser with passive mode-locking guided gain modulation

technical field

The invention belongs to the technical field of mid-infrared lasers, in particular to a dual-wavelength pulse fiber laser with passive mode-locking guided gain modulation.

Background technique

Mid-infrared pulsed laser sources with a wavelength of 2-5 μm have important applications in medical treatment (laser minimally invasive surgery), national defense (laser countermeasure guidance), and atmospheric communications. Fiber lasers have significant advantages such as low laser threshold, good output beam quality, high conversion efficiency, good flexibility and flexibility, and easy integration. Therefore, the development of mid-infrared pulsed fiber lasers has important scientific significance and application value. At present, there are three main ways to realize fiber pulse laser: 1. Gain modulation, 2. Q-switching (including active Q-switching and passive Q-switching), 3. Mode locking (including active mode-locking and passive mode-locking). The gain modulation method is to periodically modulate the number of particles in the upper energy level of the laser transition through pulse pumping to realize the pulse output of the laser, but this method requires pulse modulation of the pump laser, which is easy to damage the pump laser and the end face of the fiber . The Q-switching method is mainly used to realize the pulse laser of the ns level, while the mode-locking method is generally used to realize the ultrashort pulse laser of the ps or even fs level. At present, most of the research on mid-infrared pulsed fiber lasers is focused on realizing single-wavelength pulses. In order to meet actual needs, research on dual-wavelength or even multi-wavelength pulsed fiber lasers has attracted people's attention. Recently, it has been reported to realize dual-wavelength mid-infrared pulsed lasers by means of active Q-switching and active Q-switching guided gain modulation. However, the modulation crystal introduced by active Q-switching makes the structure of this method complex and makes fiber lasers lose their inherent flexibility. , compact, small size and other advantages, the cost is also very expensive.

Contents of the invention

The present invention adopts the following technical solutions in order to achieve the above object:

A dual-wavelength pulsed fiber laser with passive mode-locking guided gain modulation, characterized in that it includes a pumping source (1) for generating continuous pumping light, a polarization beam combiner (2) for combining the pumping light ), high transmittance to pump light, high reflection to laser, dichroic mirror (3) for guiding resonant laser, coupling lens (4), semiconductor saturable absorber mirror (5), doped with Ho ³⁺ or Er ^{3 +} the ZBLAN fiber (7), and the fiber Bragg grating (6), the first chirped fiber grating (8), the second chirped fiber grating (9) and the output port (10), the pump source (1) LD pumping source is used; the coupling lens (4) is used to couple the generated pump light into the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ ; the dichroic mirror (3) and The optical fiber is at an angle of 45 degrees; the semiconductor saturable absorbing mirror (5) is placed horizontally with the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ , and at the same time it is at an angle of 45 degrees to the dichroic mirror (3) The fiber Bragg grating (6) and the first chirped fiber grating (8) are written on the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ to form a laser cavity; the Ho ³ doped The second chirped fiber grating (9) on the ZBLAN fiber (7) of ⁺ or Er ³⁺ and the semiconductor saturable absorption mirror (5) constitute another laser resonant cavity.

The dual-wavelength pulsed fiber laser with passive mode-locking guided gain modulation according to claim 1 is characterized in that: when the wavelength of the LD pump source is 975 nm, an Er ^- doped ZBLAN fiber is used; the wavelength of the LD pump source is The Ho ³⁺ -doped ZBLAN fiber was used at 1150 nm.

In the above technical scheme, when using Ho- ^doped fiber:

If the 3.0 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 3.0 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 2.1 μm;

If the 2.1 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 2.1 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 3.0 μm;

When doping Er ³⁺ ZBLAN fiber:

If the 2.7 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 2.7 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 1.6 μm;

If the 1.6 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 1.6 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 2.7 μm.

In the above technical solution, in the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ ,

The energy level transition of Ho ³⁺ ions is the transition radiation of 2.1 μm and 3.0 μm wavelengths, and pulsed laser radiation of two wavelengths is generated at the same time.

The energy level transition of Er ³⁺ ions is the transition radiation of 1.6 μm and 2.7 μm wavelengths, and pulsed laser radiation of two wavelengths is generated at the same time.

In the above technical solution, the semiconductor saturable absorber mirror is used as a saturable absorber to mode-lock the laser with a wavelength of 2.1 μm or 3.0 μm in a laser composed of a Ho ^{3+ -doped} ZBLAN fiber as a gain fiber, and the cascaded laser Perform gain modulation to generate 3.0 μm and 2.1 μm pulsed lasers;

Or the semiconductor saturable absorbing mirror is used as a saturable absorber to mode-lock the laser with a wavelength of 1.6 μm or 2.7 μm in a laser composed of an Er ³⁺ ZBLAN fiber as a gain fiber, and perform gain modulation on its cascaded laser, Generates pulsed laser light at 2.7 μm and 1.6 μm.

The beneficial effects of the present invention are:

1. Avoiding the traditional gain modulation, in the active Q-switching and mode-locking method, the pump light needs to be pulse-modulated, which may cause damage to the pump source and the end face of the fiber, and use an external Q-switching or mode-locking device to Reduce device flexibility and other issues.

2. Using a new pulse generation mechanism, the dual-wavelength pulse output in the 2-3 μm band is realized, which avoids the shortcoming of the traditional saturable absorber with a narrow working wavelength.

3. The device has high portability and integration, which is beneficial to practical application.

Description of drawings

Fig. 1 is a structural diagram of the present invention;

Figure 2 is a schematic diagram of the energy level of Ho ³⁺ doped ZBLAN;

Figure 3 schematic diagram of energy levels of Er ³⁺ doped ZBLAN;

1 is pump source, 2 is polarization beam combiner, 3 is dichroic mirror, 4 is coupling lens, 5 is semiconductor saturable absorber mirror (SESAM1), 6 is fiber Bragg grating, 7 is doped Ho ³⁺ or Er ^{3 +} ZBLAN fiber, 8 is the first chirped fiber grating, 9 is the second chirped fiber grating, and 10 is the output end.

Detailed ways

Mode-locked to 3.0 μm:

The pump source 1 adopts 1150 nm LD, and the dichromatic mirror 3 forms an angle of 45 degrees with the optical fiber, which is highly transparent to the pump light and highly reflective to the resonant laser, and is used to guide the laser. The coupling lens 4 couples the pump light into the optical fiber, and collimates the laser light emitted from the left end face of the optical fiber. The semiconductor saturable absorber mirror (SESAM1) is used to mode-lock the 3 μm laser output from the fiber at the left end, and also serves as an end face of the 3 μm laser resonator to provide feedback for the resonator. The fiber Bragg grating 6 and the first chirped fiber grating 8 constitute the resonant cavity of the 2.1 μm laser, and 8 also performs dispersion compensation for the 2.1 μm laser and serves as the output coupling of the 2.1 μm laser. Both ends of the Ho ^{3+ -doped} ZBLAN fiber are cut at an angle of 8 degrees. The second chirped fiber grating 9 constitutes the other end of the 3 μm laser resonator, and at the same time compensates for the dispersion of the 3 μm laser.

Mode-locked to 2.1 μm:

The pump source 1 uses 1150 nm LD, and the polarization beam combiner 2 is used to combine the pump light. The dichroic mirror 3, which forms an angle of 45 degrees with the optical fiber, is highly transparent to the pump light and highly reflective to the resonant laser, and is used to guide the laser. The coupling lens 4 couples the pump light into the optical fiber, and collimates the laser light emitted from the left end face of the optical fiber. Semiconductor saturable absorber mirror (SESAM2) 5 is used for mode-locking the 2.1 μm laser output from the fiber at the left end, and serves as an end face of the 2.1 μm laser resonator to provide feedback for the resonator. The fiber Bragg grating 6 and the first chirped fiber grating 8 constitute the resonant cavity of the 3 μm laser, and 8 also performs dispersion compensation for the 3 μm laser and serves as the output coupling of the 3 μm laser. Both ends of the Ho ^{3+ -doped} ZBLAN fiber are cut at an angle of 8 degrees. The second chirped fiber grating 9 constitutes the other end of the 2.1 μm laser resonator, and at the same time compensates for the dispersion of the 2.1 μm laser.

Experimental principle:

Schematic diagram of the energy level of Ho ³⁺ doped ZBLAN, as shown in Figure 2,

Mode-locked to 3.0 μm:

When using SESAM1 (saturable absorption for 3 μm laser)

It works like this:

The continuous pump light generated by 1150 nm LD 1 is coupled into Ho ³⁺ doped ZBLAN (fluoride) fiber 7 through polarization beam combiner 2 and lens 4. As the pump power increases, the second chirped fiber grating 9 and a semiconductor saturable absorption mirror (SESAM1) 5 generate a 3 μm continuous laser (corresponding to the transition of ⁵ I ₆ → ⁵ I ₇ energy level), through the semiconductor saturable absorption mirror (SESAM1) 5 Due to saturable absorption, the 3 μm continuous laser is passively modulated to generate a 3 μm mode-locked pulsed laser, the pulse period of which is determined by the length of the resonator. Dispersion compensation so that it is compressed. At this time, the 3 μm mode-locked pulsed light periodically modulates the inversion particle number of ⁵ I ₇ → ⁵ I ₈ , that is, it performs gain modulation on the radiated light corresponding to the energy level transition of ⁵ I ₇ → ⁵ I ₈ , so that in the optical fiber A gain-modulated pulsed laser with a wavelength of 2.1 μm is generated in the resonant cavity formed by the Bragg grating 6 and the first fiber chirped grating 8. At the same time, 8 performs dispersion compensation on the 2.1 μm pulse to compress it, and finally outputs the wavelength through the output terminal 10 at the same time. 3 μm and 2.1 μm pulsed lasers.

Mode-locked to 2.1 μm:

When using SESAM2 (for 2.1 μm laser saturable absorption)

It works like this:

The continuous pump light generated by the 1150 nm LD 1 is coupled into the Ho ³⁺ doped ZBLAN (fluoride) fiber 7 through the polarization beam combiner 2 and the lens 4. As the pump power increases, the second chirped fiber grating 9 and a semiconductor saturable absorption mirror (SESAM2) 5 generate a 2.1 μm continuous laser (corresponding to the transition of ⁵ I ₇ → ⁵ I ₈ energy level), through the semiconductor saturable absorption mirror (SESAM2) 5 Due to saturable absorption, the 2.1 μm continuous laser is passively modulated to generate a 2.1 μm mode-locked pulsed laser, the pulse period of which is determined by the length of the resonator. Dispersion compensation so that it is compressed. At this time, the 2.1 μm mode-locked pulsed light periodically modulates the inversion particle number of ⁵ I ₆ → ⁵ I ₇ , that is, it performs gain modulation on the radiated light corresponding to the energy level transition of ⁵ I ₆ → ⁵ I ₇ , so that in the optical fiber A gain-modulated pulsed laser with a wavelength of 3.0 μm is generated in the resonant cavity formed by the Bragg grating 6 and the first chirped fiber grating 8. At the same time, 8 performs dispersion compensation on the 3.0 μm pulse to compress it, and finally outputs the wavelength through the output port 10 at the same time. 3 μm and 2.1 μm pulsed lasers.

In the same way, replace the Ho ³⁺ doped ZBLAN fiber with Er ³⁺ doped ZBLAN fiber, as described below:

Mode-locked to 2.7 μm:

A 975 nm semiconductor laser is used as the pump source 1. The polarization beam combiner 2 is used to combine the pump light. The dichroic mirror 3 is highly transparent to the pump light and highly reflective to the resonant laser. The coupling lens 4 couples the pump light into the optical fiber and collimates the laser light emitted from the left end face of the optical fiber. The semiconductor saturable absorber mirror (SESAM3) is used to mode-lock the 2.7 μm laser output from the left end fiber, and also serves as an end face of the 2.7 μm laser resonator to provide feedback for the resonator. The fiber Bragg grating 6 and the first chirped fiber grating 8 constitute the resonant cavity of the 1.6 μm laser, and 8 also performs dispersion compensation for the 1.6 μm laser and serves as the output coupling of the 1.6 μm laser. Both ends of the Er ^{3+ -doped} ZBLAN fiber are cut at an angle of 8 degrees. The second chirped fiber grating 9 constitutes the other end of the 2.7 μm laser resonator, and at the same time compensates for the dispersion of the 2.7 μm laser.

Mode-locked to 1.6 μm:

A 975 nm semiconductor laser is used as the pump source 1. The polarization beam combiner 2 is used to combine the pump light. The dichroic mirror 3 is highly transparent to the pump light and highly reflective to the resonant laser. The coupling lens 4 couples the pump light into the optical fiber, and collimates the laser light emitted from the left end face of the optical fiber. The semiconductor saturable absorber mirror (SESAM4) 5 is used to mode-lock the 1.6 μm laser output from the fiber at the left end, and also serves as an end face of the 1.6 μm laser resonator to provide feedback for the resonator. The fiber Bragg grating 6 and the first chirped fiber grating 8 constitute the resonant cavity of the 2.7 μm laser, and 8 also performs dispersion compensation for the 2.7 μm laser and serves as the output coupling of the 2.7 μm laser. Both ends of the Er ^{3+ -doped} ZBLAN fiber are cut at 8 degrees. The second chirped fiber grating 9 constitutes the other end of the 1.6 μm laser resonant cavity, and simultaneously compensates for the dispersion of the 1.6 μm laser.

Experimental principle:

The energy level schematic diagram of Er ³⁺ doped ZBLAN is shown in Fig. 3,

Mode-locked to 2.7 μm:

When using SESAM3 (saturable absorption for 2.7 μm laser),

It works like this:

The continuous pump light generated by the 975 nm semiconductor laser 1 is coupled into the Er ^{3+ -doped} ZBLAN (fluoride) fiber 7 through the polarization beam combiner 2 and the lens 4. With the increase of the pump power, the second chirped fiber The 2.7 μm continuous laser light (corresponding to the transition of ⁴ I _11/2 → ⁴ I _13/2 energy level) is generated in the resonant cavity composed of the grating 9 and the semiconductor saturable absorption mirror (SESAM3), which passes through the semiconductor saturable absorption mirror The saturable absorption effect of (SESAM3)5 passively modulates the 2.7 μm continuous laser to generate a 2.7 μm mode-locked pulsed laser whose pulse period is determined by the length of the resonator. The mode-locked pulsed laser performs dispersion compensation to compress it. At this time, the 2.7 μm mode-locked pulsed light periodically modulates the inversion particle number of ⁴ I _13/2 → ⁴ I _15/2 , that is, the radiation corresponding to the energy level transition of ⁴ I _13/2 → ⁴ I _15/2 The light is gain-modulated, so that a gain-modulated pulse laser with a wavelength of 1.6 μm is generated in the resonant cavity formed by the fiber Bragg grating 6 and the first chirped fiber grating 8, and at the same time, 8 performs dispersion compensation on the 1.6 μm pulse to compress it, Finally, pulse lasers with wavelengths of 1.6 μm and 2.7 μm are simultaneously output through the output terminal 10 .

Mode-locked to 1.6 μm:

When using SESAM4 (saturable absorption for 1.6 μm laser),

It works like this:

The continuous pump light generated by the 975 nm semiconductor laser 1 is coupled into the Er ^{3+ -doped} ZBLAN (fluoride) fiber 7 through the polarization beam combiner 2 and the lens 4. With the increase of the pump power, the second chirped fiber The 1.6 μm continuous laser light (corresponding to the transition of ⁴ I _13/2 → ⁴ I _15/2 energy level) is generated in the resonant cavity composed of the grating 9 and the semiconductor saturable absorption mirror (SESAM4), which passes through the semiconductor saturable absorption mirror The saturable absorption effect of (SESAM4)5 passively modulates the 1.6 μm continuous laser to generate a 1.6 μm mode-locked pulsed laser whose pulse period is determined by the length of the resonator. The mode-locked pulsed laser performs dispersion compensation to compress it. At this time, the 1.6 μm mode-locked pulsed light periodically modulates the inversion particle number of ⁴ I _11/2 → ⁴ I _13/2 , that is, the radiation corresponding to the energy level transition of ⁴ I _11/2 → ⁴ I _13/2 The light is gain-modulated, so that a gain-modulated pulsed laser with a wavelength of 2.7 μm is generated in the resonant cavity formed by the fiber Bragg grating 6 and the first chirped optical fiber 8. At the same time, 8 performs dispersion compensation on the 2.7 μm pulse to compress it, and finally Pulsed lasers with wavelengths of 1.6 μm and 2.7 μm are simultaneously output through the output terminal 10 .

Claims (5)

1. A dual-wavelength pulsed fiber laser with passive mode-locking guided gain modulation, characterized in that: it includes a pumping source (1) for generating continuous pumping light, and a polarization beam combiner for combining the pumping light (2), high transmittance to pump light, high reflection to laser, dichroic mirror (3), coupling lens (4), semiconductor saturable absorber mirror (5), doped with Ho ³⁺ or Er ³⁺ ZBLAN fiber (7), fiber Bragg grating (6), first chirped fiber grating (8), second chirped fiber grating (9) and output end (10), the pump source ( 1) LD pumping source is used; the coupling lens (4) is used to couple the generated pump light into the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ ; the dichroic mirror (3 ) and the optical fiber at an angle of 45 degrees; the semiconductor saturable absorbing mirror (5) is placed horizontally with the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ , and is at 45 degrees to the dichromatic mirror (3) included angle; the fiber Bragg grating (6) and the first chirped fiber grating (8) are written on the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ to form a laser cavity; the doped The second chirped fiber grating (9) on the ZBLAN fiber (7) of Ho ³⁺ or Er ³⁺ and the semiconductor saturable absorption mirror (5) constitute another laser resonant cavity. 2. The dual-wavelength pulsed fiber laser of passive mode-locking guided gain modulation according to claim 1 is characterized in that: when the wavelength of the LD pump source is 975 nm, Er ^-doped ZBLAN fiber is used; the LD pump source When the wavelength is 1150 nm, the Ho ^{3+ -doped} ZBLAN fiber is used. 3. The dual-wavelength pulsed fiber laser of passive mode-locking guided gain modulation according to claim 1, characterized in that: When using Ho ³⁺ doped ZBLAN fiber: If the 3.0 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 3.0 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 2.1 μm; If the 2.1 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 2.1 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 3.0 μm; When using Er ³⁺ doped ZBLAN fiber: If the 2.7 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 2.7 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 1.6 μm; If the 1.6 μm wavelength laser is mode-locked, the second chirped fiber grating (9) and the semiconductor saturable absorber mirror (5) are the 1.6 μm wavelength laser resonator, and the fiber Bragg grating (6) and the first chirped fiber The grating (8) is a laser cavity with a wavelength of 2.7 μm. 4. The dual-wavelength pulsed fiber laser with passive mode-locking guided gain modulation according to claim 1, characterized in that: in the ZBLAN fiber (7) doped with Ho ³⁺ or Er ³⁺ , The energy level transition of Ho ³⁺ ions is the transition radiation of 2.1 μm and 3.0 μm wavelengths, and simultaneously produces pulsed laser radiation of two wavelengths; The energy level transition of Er ³⁺ ions is the transition radiation of 1.6 μm and 2.7 μm wavelengths, and pulsed laser radiation of two wavelengths is generated at the same time. 5. the dual-wavelength pulsed fiber laser of passive mode-locking guided gain modulation according to claim 1, is characterized in that: The semiconductor saturable absorbing mirror is used as a saturable absorber to mode-lock the laser with a wavelength of 2.1 μm or 3.0 μm in a laser composed of a Ho ³⁺ ZBLAN fiber as a gain fiber, and perform gain modulation on the cascaded laser to generate 3.0 μm and 2.1 μm pulsed lasers; Or the semiconductor saturable absorbing mirror is used as a saturable absorber to mode-lock the laser with a wavelength of 1.6 μm or 2.7 μm in a laser composed of an Er ³⁺ ZBLAN fiber as a gain fiber, and perform gain modulation on its cascaded laser, Generates pulsed laser light at 2.7 μm and 1.6 μm.