CN104184042B - A kind of hollow-core photonic crystal fiber and the mum wavelength converter of annular seal space combined type 1.9 - Google Patents

Abstract

The invention relates to a combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter, including a laser, a polarization controller, a hydrogen cylinder, a sealed cavity, a hollow-core photonic crystal fiber, an optical fiber collimator, a lens, and an exhaust port , air inlet, gas circulation pump, flat mirror, optical beam splitter. It is characterized in that the laser and the polarization controller form a light source system, and a sealed cavity is arranged at the rear of the light source system. The sealed cavity is connected with a hydrogen cylinder with a pressure reducing valve, and a hollow-core photonic crystal fiber is placed inside the sealed cavity. The incident end face of the fiber is connected to the The optical fiber collimator is connected, the exhaust port and the air inlet of the sealed cavity are connected with the gas circulation pump, and finally the rear part of the sealed cavity is equipped with a lens, a plane reflector and an optical beam splitter. The invention utilizes the excellent nonlinear characteristics and mode transmission characteristics of the hollow-core photonic crystal fiber, the adjustable hydrogen pressure inside the sealed cavity, the hydrogen fluidity and the like, and has the advantages of low threshold value and high conversion efficiency.

Description

A combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter

technical field

The invention belongs to the technical field of optoelectronics, and in particular relates to a combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter.

Background technique

Pulsed laser sources with a wavelength of 1.9 μm are widely used in laser medical treatment, laser ranging, photoelectric countermeasures, infrared radar, infrared remote sensing, and infrared sensing. In medical treatment, laser lithotripsy uses the strong absorption of water in cells to 1.9 μm laser to vaporize water, transfer energy to stones, and then crush stones into powder. The 1.9μm laser has a very shallow penetration depth to human tissue, and the lithotripsy process causes little damage to surrounding tissues, and can achieve non-invasive or minimally invasive effects. Compared with other lithotripsy methods, laser lithotripsy is extremely safe. The high-power 1.9μm laser has the characteristics of fast vaporization cutting speed, good hemostasis effect and small penetration, and has unique advantages in the treatment of benign prostatic hyperplasia and other diseases. In the military, the 1.9μm laser has strong penetrating power to air and smog, and can be used in fields such as lidar and laser ranging.

At present, there are many ways to obtain a pulsed laser source of 1.9 μm, such as holmium and erbium lasers, critical phase-matched KTP optical parametric oscillators, semiconductor-pumped erbium-doped fiber lasers, LiNbO ₃ crystal difference frequency, and high-pressure hydrogen for 1064nm wavelength. Raman frequency shift, etc. The simplest and most practical way to achieve 1.9μm laser output is to use stimulated Raman scattering (SRS) to achieve Raman frequency shift.

SRS is a typical nonlinear optical effect. For gaseous media, the SRS threshold power is generally above the mW level, and it is very difficult to realize gas SRS by using traditional methods. The traditional method of wavelength converter based on the SRS effect is to use a high-pressure gas Raman cell (raman cell), the system volume is relatively large, the required pump energy is high, the interaction distance between the light wave and the gas is short, and the energy conversion efficiency is low. High, generally only 20%-30%. The invention of the hollow-core photonic crystal fiber (HC-PCF) makes the realization and utilization of the nonlinear effect of light and low-density gas medium simple and efficient. HC-PCF has a unique hollow structure, and the large pores of the fiber core can be filled with gas medium. The light wave is confined in the large-hole fiber core and is transmitted in the fundamental mode with low loss. Its excellent fundamental mode characteristics make the interaction area between the light and the filling medium very small. Moreover, the low-loss transmission characteristics of HC-PCF ensure a long effective interaction distance, thereby further enhancing the nonlinear effect, and can enhance the interaction strength between light and gas medium by several orders of magnitude.

Chinese invention patent application "Fiber-type tunable gas Raman laser light source based on hollow-core photonic crystal fiber (application number: 200910144236.1; publication number: CN101764350A)" provides a tunable gas Raman laser light source filled with high-pressure hydrogen Both ends of the hollow-core photonic crystal are connected with a single-mode optical fiber. Since the two ends of the optical fiber are fused, the internal pressure of the HC-PCF cannot be changed, and the conversion efficiency is limited. This invention has higher requirements on optical fiber fusion splicing technology, so its manufacturing cost is also higher.

"Relation of pump-beam quality and conversion efficiency in the Ramandownward conversion" reported the effect of pressure changes in the Raman cell on the Raman energy conversion efficiency. As the cavity pressure increases, the energy conversion efficiency of the first-order Stokes light increases significantly. The present invention adopts the combination scheme of the hollow-core photonic crystal fiber and the pressure-adjustable sealed cavity, utilizes the excellent nonlinear effect and mode transmission characteristics of HC-PCF, adjusts the internal pressure of the sealed cavity through a hydrogen cylinder with a decompression valve, and the gas circulation pump The heat of the Raman frequency shift process is taken away in time, the pumping threshold power is greatly reduced, and the energy conversion efficiency is improved. The conversion efficiency of 1064nm pulsed laser to 1.9μm pulsed laser can reach 35%-45%.

Contents of the invention

The present invention aims at the disadvantage that the conversion efficiency of the existing Raman conversion to obtain a 1.9 μm laser light source is not high, and proposes a hollow-core photonic crystal fiber combined with a pressure-adjustable sealed cavity to form a hollow-core photonic crystal fiber and a sealed cavity. Cavity combined 1.9μm wavelength converter.

The technical scheme that the present invention takes for solving technical problems is:

A combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter includes: laser, polarization controller, hydrogen cylinder, sealed cavity, hollow-core photonic crystal fiber, fiber collimator, lens, exhaust port, air inlet Port, gas circulation pump, flat mirror, beam splitter.

First, the hydrogen cylinder injects hydrogen into the sealed chamber and controls its internal pressure. The pump light emitted by the laser is adjusted to its polarization state by a polarization controller, and then enters the interior of the HC-PCF through a fiber optic collimator. The hydrogen is under the action of a gas circulation pump. It flows and fully contacts with the incident light to generate stimulated Raman scattering. The converted wavelength is focused and collimated by the lens and output. Under the adjustment of the optical path of the plane mirror, it is finally split by an optical beam splitter to obtain a 1.9 μm laser.

Further, the hydrogen cylinder is equipped with a pressure reducing valve. On the one hand, the hydrogen cylinder fills the sealed cavity with hydrogen to provide a stimulated Raman medium; on the other hand, through the control of the pressure reducing valve, the hydrogen gas in the sealed cavity is adjusted of pressure.

Further, the laser is a 1064nm Nd:YAG nanosecond pulsed laser with its own attenuator, which can quickly change the incident light power.

Further, the polarization controller can conveniently and quickly adjust the polarization state of the incident light to obtain higher Raman gain, and can also be used to measure the influence of the polarization state on the wavelength conversion efficiency.

Further, the fiber collimator uses an aspheric fiber collimator, which can improve the efficiency of laser coupling into the HC-PCF by utilizing its good light-gathering ability, and the light field is in the fundamental mode in the sufficiently long HC-PCF The guided wave mode transmission, and the fundamental mode transmission loss is very low.

Further, the HC-PCF is fixed inside the sealed cavity, and its two ends are open to facilitate hydrogen gas entering into the hollow core part of the photonic crystal fiber.

Further, the exhaust port of the gas circulation pump is next to the optical fiber collimator, and the air inlet and the exhaust port are in symmetrical positions, and its function is to make the hydrogen in the HC-PCF flow, so that the The heat generated during the Mann frequency shift process improves the Raman conversion efficiency.

Further, the HC-PCF, the fiber collimator and the lens are located on a straight line, and there is a short distance between the fiber collimator and the HC-PCF to ensure that the exhaust port and the air inlet of the gas circulation pump are respectively in the Positive and negative pressures are generated at both ends of the photonic crystal fiber, which facilitates the circulation of hydrogen gas inside the hollow-core photonic crystal fiber.

Further, the lens used is an achromatic microscope objective lens.

Further, the hydrogen-filled HC-PCF produces stimulated Raman scattering (SRS), and the frequency formulas of the scattered light are ω _s =ω _L -ω _q and ω _as =ω _L +ω _q (where ω _L is the excitation light frequency of the laser, ω _q is the optical phonon frequency corresponding to the atomic or molecular vibration or rotational energy level change, ω _s and ω _as are the Stokes light and anti-Stokes light frequencies, respectively). With hydrogen as the Raman medium, due to the unique filtering characteristics of HC-PCF, the vibrational Stokes light and high-order Stokes light are located outside the low-loss window, and the last output is mainly driven by pure rotation. First-order Stokes light produced by the Mann scattering effect.

The advantages of the present invention are: the polarization state of the incident light is adjusted by the polarization controller, and the wavelength conversion efficiency is improved; the light collection ability of the aspheric collimator can reduce the loss and improve the coupling efficiency; The heat in the Mann frequency shift process improves the Raman conversion efficiency; the hydrogen cylinder with a pressure reducing valve changes the internal pressure of the sealed chamber, and uses the excellent nonlinear characteristics and mode transmission characteristics of HC-PCF to reduce the pump threshold power and greatly improve Energy conversion efficiency. The low threshold makes the system easier to match with lasers of different powers; the high energy conversion efficiency makes it possible for high-power 1.9μm laser surgery in medicine, and the 1.9μm high-energy laser also promotes military applications such as lidar and laser ranging. field development.

Description of drawings

Fig. 1 is a schematic diagram of the overall structure of a combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter provided by the present invention;

Fig. 2 is a schematic diagram of the position of the exhaust port and the optical fiber collimator of the sealed cavity of the present invention;

Fig. 3 is a comparison diagram of the energy conversion efficiency of the combination scheme of the hollow-core photonic crystal fiber and the sealed cavity (sealed cavity) of the present invention and the conventional Raman cell;

In the accompanying drawings, 1. Laser, 2. Polarization controller, 3. Hydrogen cylinder, 4. Sealed cavity, 5. Hollow-core photonic crystal fiber, 6. Fiber collimator, 7. Lens, 8. Exhaust port, 9 . Air inlet, 10. Gas circulation pump, 11. Plane mirror, 12. Optical beam splitter.

detailed description

The specific implementation manners provided by the present invention will be further described in detail below in conjunction with the accompanying drawings.

A combined 1.9 μm wavelength converter of a hollow-core photonic crystal fiber and a sealed cavity as shown in Figure 1, which includes a laser (1) with a 1064nm pulse width of 5ns and a power-tunable Nd:YAG nanosecond energy lower than 330mJ Pulsed laser; the polarization controller (2) uses a polarization device that can adjust the polarization state arbitrarily; the fiber collimator (6) adopts an aspheric fiber collimator with a focal length of 18mm, and its position is facing the hollow-core photonic crystal fiber (5 ); the hydrogen cylinder (3) has a pressure reducing valve, and hydrogen gas of a certain pressure is filled into the sealed chamber (4); the sealed chamber (4) is made of stainless steel and can withstand 100 atm; the hollow-core photonic crystal fiber (5) fiber The diameter of the core is 10 μm, and the length is 2 m; the lens (7) adopts a 20 times achromatic microscope objective lens.

As shown in Figure 2, at the entrance window of the sealed cavity (4), the exhaust port (8) of the gas circulation pump (10) is next to the fiber collimator (6), and the same air inlet (9) is located between the exit end face and the optical fiber collimator (6). At the symmetrical position of the exhaust port (8), the fiber collimator (6) is facing the incident end face of the hollow-core photonic crystal fiber (5) and separated by a short distance, so that the gas circulation pump (10) is at the exhaust port (8) The positive and negative pressure generated by the air inlet (9) can make the flow of hydrogen gas inside the hollow-core photonic crystal fiber (5).

As shown in Figure 3, the present invention compares the energy conversion efficiency of the combination scheme of the hollow-core photonic crystal fiber and the sealed cavity with the conventional Raman cell. The pump energy required by the conventional Raman cell is very high, and the pressure in the cavity is adjusted to 50atm, the energy conversion efficiency is generally only 20%-30%. The combination of HC-PCF with good nonlinear effect and mode transmission characteristics and a sealed cavity with adjustable internal pressure can increase the energy conversion efficiency to 35%-45% only at 30 atm.

In the following, the specific operation principle and steps in this embodiment will be further described in detail to support the technical problems that can be solved by the combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter provided by the present invention.

Step 1: Adjust the axes of the polarization controller (2), fiber collimator (6), hollow-core photonic crystal fiber (5), and lens (7) on a straight line, so that the laser can enter the hollow core smoothly Photonic crystal fiber (5).

Step 2: Use a vacuum pump to dry up the air in the sealed cavity (4), then use the hydrogen cylinder (3) to inject hydrogen into the sealed cavity (4), wait until the air pressure in the sealed cavity (4) is stabilized at 30atm before proceeding One step operation.

Step 3: 1064nm Nd:YAG laser (1) is preheated and adjusted to output 10mJ pulsed laser with stable energy through a built-in attenuator.

Step 4: Adjust the polarization controller (2) to λ/4 polarization in advance, and the laser light adjusted by the attenuator of the laser (1) is converted into circularly polarized light through the polarization controller (2).

Step 5: The aspheric fiber collimator (6) has the ability to flexibly adjust the light field distribution. After the laser passes through the aspheric fiber collimator (6), it is coupled into the hollow-core photonic crystal fiber (5) with low loss in the fundamental mode. guided wave mode for transmission.

Step 6: During the transmission process, the gas circulation pump (10) circulates the hydrogen gas inside the hollow-core photonic crystal fiber (5), and takes away the heat of the Raman frequency shift process in time, so that the laser and the hollow-core photonic crystal fiber (5) After the internal hydrogen is fully contacted to generate stimulated Raman scattering, the final outgoing light includes first-order Stokes light, second-order Stokes light and pump light, and their wavelengths are 1907nm, 9186nm, and 1064nm, respectively. The Raman scattering wavelength is dominated by the first-order Stokes light at 1907nm.

Step 7: The outgoing light is focused and collimated by the lens (7) and output, and finally passes through the optical beam splitter (12) to obtain pulsed laser light with a wavelength of 1907nm, the output energy is about 4mJ, and its energy conversion efficiency can reach 40%.

Claims (5)

1. A combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter, including a laser (1), a polarization controller (2), a hydrogen cylinder (3), a sealed cavity (4), and a hollow-core photonic crystal fiber (5), fiber collimator (6), lens (7), exhaust port (8), air inlet (9), gas circulation pump (10), plane reflector (11), optical beam splitter ( 12), characterized in that the laser (1) and the polarization controller (2) constitute a light source system, the rear of the light source system is equipped with a sealed cavity (4), and the sealed cavity (4) is connected to the hydrogen cylinder (3) with a pressure reducing valve , a hollow-core photonic crystal fiber (5) is placed inside the sealed cavity (4), the incident end face of the optical fiber is connected with the fiber collimator (6), the exhaust port (8) and the air inlet ( 9) Link to each other with the gas circulation pump (10), and the rear position of the sealed cavity (4) is equipped with a lens (7), a plane reflector (11) and an optical beam splitter (12); the exhaust gas of the gas circulation pump The port (8) is located at the position where the sealed cavity (4) is close to the fiber collimator (6), and the air inlet (9) and the exhaust port (8) are in symmetrical positions. 2. The combined 1.9 μm wavelength converter of hollow-core photonic crystal fiber and sealed cavity according to claim 1, characterized in that: the laser (1) is a 1064nm Nd:YAG nanosecond pulse laser, and automatically with attenuator. 3. A combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter according to claim 1, characterized in that: the sealed cavity (4) is made of stainless steel and can withstand 100 atm. 4. A combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter according to claim 1, characterized in that: the hollow-core photonic crystal fiber (5) is placed in a sealed cavity filled with high-pressure hydrogen (4) Inside, the hollow core part of the photonic crystal fiber is also filled with high-pressure hydrogen. 5. A combined hollow-core photonic crystal fiber and sealed cavity 1.9 μm wavelength converter according to claim 1, characterized in that: the fiber collimator (6) adopts an aspheric lens with high light-collecting ability.