CN102307065B - Pressure-tuned photonic crystal fiber microwave and millimeter wave generator - Google Patents

Abstract

A birefringent photonic crystal fiber microwave millimeter wave generator, the generator includes: a pump source, an optical fiber coupler for coupling the pump light of the pump source into a resonant cavity, and the resonant cavity, characterized in that : the resonant cavity is formed by a fiber grating and a combined optical fiber, the combined optical fiber is formed by connecting an active optical fiber and a birefringent photonic crystal fiber in series, and at least one birefringent photonic crystal fiber is provided with a pressure applying device, using for changing the degree of birefringence of the birefringent photonic crystal fiber.

Description

A pressure-tuned photonic crystal fiber microwave and millimeter wave generator

technical field

The invention relates to a photonic crystal fiber tunable microwave and millimeter wave generator, which belongs to the field of optoelectronic technology.

Background technique

There is a basic material in the photonic industry - photonic crystals. The research on photonic crystals is not only a problem in the field of optical communication, but it will also have a huge impact on other related industries. Since Yablonowitch and John independently proposed the concepts of photonic crystals and photonic band gaps in 1987, photonic crystals have become a hot topic that has received great attention both at home and abroad. In the fields of optical physics, condensed matter physics, electromagnetic waves, and information technology aroused widespread concern. In just two decades, photonic crystals have achieved remarkable results in both theoretical research and experimental research, and have also been applied in certain fields, such as photonic crystal optical integrated circuits, photonic crystal optical waveguides, photonic crystal filter etc.

One of the photonic crystals is made in an optical fiber, which is generally called a photonic crystal fiber. The general structure of a photonic crystal fiber is shown in Figure 1. It is uniformly arranged with pores along the axial direction in the optical fiber. Viewed from the end face of the optical fiber, There is a periodic two-dimensional structure, and the two-dimensional periodic structure is generally a circular air hole, where d represents the diameter of the circular air hole, and Λ represents the period, and one of the air holes is destroyed or missing, so A defect is generated, and light can propagate in the defect. The defect is shown in the central part of Fig. 1. At the central part, the periodic two-dimensional structure is destroyed, thereby producing a A defect capable of guiding light.

There is another kind of photonic crystal fiber, that is, birefringent photonic crystal fiber. Unlike ordinary photonic crystal fiber, birefringence can be generated in birefringent photonic crystal fiber. There are various ways to generate birefringence, including small air holes in the defect area in the central part to break the symmetry, and changing the circular air holes in the cladding to ellipse, of course, there are many other ways to Formation of photonic crystal fibers with high birefringence properties. Wherein, an elliptical hole is set or a small circular hole is set at the central fiber core to destroy the structure of symmetry, as shown in accompanying drawing 2 and accompanying drawing 3 respectively, in accompanying drawing 2 there is an elliptical air hole in the cladding, accompanying drawing 3 There are three small circular holes for breaking the symmetry at the core, all of which are for breaking the symmetry, where Λ represents the period, and a and b represent the diameters in the direction of the short and long axes respectively.

At the same time, in this field, the use of fiber lasers or fiber generators to optically generate microwaves or millimeter waves has attracted people's attention because of its low cost, simple method, and a typical way of generating microwave and millimeter waves is to use The grating made in the polarization-maintaining fiber is used as the reflection or transmission grating of the fiber laser. Due to the birefringence characteristics of the polarization-maintaining fiber, the grating made in the polarization-maintaining fiber has two oscillating lights perpendicular to each other. Because the frequency of light is relatively close, the beat frequency of the two can be used to generate microwaves or millimeter waves on the photodetector. However, in this method, if it is difficult to achieve adjustable microwave and millimeter wave output, it is generally accompanied by The complex structure increases the cost and makes adjustment difficult.

Contents of the invention

The present invention is proposed to solve the above problems, and provides a photonic crystal fiber tunable microwave and millimeter wave generator, which can well solve the problems existing in the prior art.

The idea of the present invention is to use a birefringent photonic crystal fiber instead of a polarization-maintaining fiber, and the cladding of the birefringent photonic crystal fiber used has an elliptical air hole, that is, the birefringent photonic crystal fiber shown in Figure 2 is used , while a pressure applying device is arranged outside the birefringent photonic crystal fiber, when the pressure is applied to the birefringent photonic crystal fiber, due to stress, the volume and ellipse of the elliptical air hole in the photonic crystal fiber The rate will change with the change of the compressive stress, and the change of the volume and ellipticity of the elliptical air hole will lead to the change of the degree of birefringence, and the change of the degree of birefringence will cause the change of the frequency difference between the two polarization modes, thus changing The frequency of the microwave or millimeter wave on the photodetector, thus realizing the tuning of the output microwave or millimeter wave.

The photonic crystal fiber tunable microwave and millimeter wave generator constructed with the above ideas has the advantages of simple adjustment, simple structure, low cost, etc., and well solves the problems in the prior art.

According to an embodiment of the present invention, a birefringent photonic crystal fiber microwave millimeter wave generator is provided, the generator includes: a pump source, a fiber coupler for coupling the pump light of the pump source into the resonant cavity, And the resonant cavity is characterized in that: the resonant cavity is formed by a fiber grating and a combined optical fiber, the combined optical fiber is formed by connecting an active optical fiber and a birefringent photonic crystal fiber in series, and at least one birefringent photonic crystal The optical fiber is provided with a pressure applying device for changing the birefringence degree of the birefringent photonic crystal optical fiber.

According to another embodiment of the present invention, the combined optical fiber includes an active optical fiber and a birefringent photonic crystal optical fiber.

According to another embodiment of the present invention, the combined optical fiber includes multiple active optical fibers and multiple birefringent photonic crystal optical fibers.

According to another embodiment of the present invention, the active fiber is an erbium-doped, ytterbium-doped or erbium-ytterbium co-doped fiber.

According to another embodiment of the present invention, the birefringent photonic crystal fiber is a photonic crystal fiber with elliptical air holes in the cladding.

According to another embodiment of the present invention, the core of the birefringent photonic crystal fiber has a small circular hole for breaking the symmetry structure.

According to another embodiment of the present invention, the core of the birefringent photonic crystal fiber has an elliptical hole for breaking the symmetry structure.

Description of drawings

Accompanying drawing 1 is the structural representation of a common photonic crystal fiber in the prior art;

Accompanying drawing 2 is the structural representation of the birefringent photonic crystal fiber that has ellipse air hole in cladding in the prior art;

Accompanying drawing 3 is the structural schematic view of the birefringent photonic crystal fiber in which the core is provided with a small circular hole for breaking the symmetry structure in the prior art.

Figure 4 is a schematic diagram of a photonic crystal fiber tunable microwave and millimeter wave generator according to an embodiment of the present invention.

In the above-mentioned accompanying drawings, d represents the diameter of the circular air hole in the photonic crystal fiber, Λ represents the period, b and a represent the major and minor axis diameters of the elliptical hole respectively, 1 represents the pump source, 2 represents the fiber coupler, 3 and 4 denotes fiber grating, 5 denotes active optical fiber, 6 denotes a birefringent photonic crystal fiber with elliptical air holes in the cladding, 7 denotes a pressure applying device, and 8 denotes a photodetector.

Detailed ways

The fiber tunable microwave and millimeter wave generator of the present invention will be described in detail below with specific implementation methods.

Accompanying drawing 2 shows the photonic crystal fiber used by the present invention, that is, the birefringent photonic crystal fiber with elliptical air holes in the cladding, as can be seen from the figure, in this photonic crystal fiber, wherein the cladding The air holes in are oval rather than circular.

The microwave and millimeter wave generator proposed by the present invention will be described below on the basis of accompanying drawing 4. The microwave and millimeter wave generator shown in accompanying drawing 4 includes a pumping source 1, which can be a semiconductor laser or other A suitable type of pumping source also includes a fiber coupler 2, which is used to couple the pumping light emitted by the pumping source into the resonant cavity formed by fiber gratings 3 and 4, combined optical fibers, and the combined optical fiber is composed of active The optical fiber 5 and the birefringent photonic crystal fiber 6 are connected in series to form, and the fiber gratings 3 and 4 are respectively located at the two ends of the combined optical fiber, wherein a pressure applying device 7 is arranged on the birefringent photonic crystal fiber 6, and in the resonant cavity The output end is provided with a photodetector 8 . The active fiber 5 is a doped fiber, including erbium-doped, ytterbium-doped, and erbium-ytterbium co-doped active fibers. The birefringent photonic crystal fiber 6 is a photonic crystal fiber with elliptical air holes in the cladding.

The working principle of the above-mentioned microwave and millimeter wave generator is as follows. When the pump source pumps the resonant cavity composed of fiber grating and combined optical fiber through the fiber coupler, laser oscillation will be generated in the resonant cavity. Because the resonant cavity Including a section of birefringent photonic crystal fiber, two polarized lasers perpendicular to each other will be generated, and due to the birefringence effect, there is a certain frequency difference between the two polarized lights, and the beat frequency of the two polarized lights is from After the output end of the resonant cavity is output, it is incident on the photodetector, thereby generating corresponding millimeter waves or microwaves. If the pressure applying device on the birefringent photonic crystal fiber is used to apply pressure to the photonic crystal fiber, due to the effect of compressive stress , will cause the volume or ellipticity of the elliptical air hole in the cladding to change, thereby changing the degree of birefringence, and then changing the frequency difference between the two polarized lasers, thus finally realizing the tuning of microwave or millimeter wave.

It can be understood that the combined optical fiber can not only be a combined optical fiber composed of a section of active optical fiber 5 and a section of birefringent photonic crystal fiber connected in series as shown in Figure 4, but also can be in other forms, such as being located on both sides respectively Two birefringent photonic crystal fibers and an active optical fiber in the middle are connected in series, and the fiber gratings 3 and 4 are respectively fabricated on the birefringent photonic crystal fibers on both sides, and can also be located at two The composite fiber formed by serial connection of two sections of active fiber on the side and the birefringent photonic crystal fiber in the middle can also be a composite fiber formed by interlacing and serial connection of multiple birefringent photonic crystal fibers and multiple active fibers, as long as Wherein at least one section of the birefringent photonic crystal fiber is provided with a pressure applying device.

For another kind of birefringent photonic crystal fiber, that is, several small circular holes or oval small holes are arranged in the fiber core to destroy the symmetry of the structure, and the air holes in the cladding are still circular, as shown in Figure 3 shown. For this kind of birefringent photonic crystal fiber, it can also be applied to the above-mentioned microwave and millimeter wave generator, because the pressure applied by the pressure applying device will also make the small circular hole or the Changes in the volume or ellipticity of the elliptical hole will also affect and change the degree of birefringence of the photonic crystal fiber, but because the small circular hole or elliptical hole is located at the fiber core, the change in the compressive stress applied by the pressure applying device will affect the The impact caused by the core will not be as timely and sensitive as the cladding, so although this birefringent photonic crystal fiber can be used, it is preferred to use the birefringent photonic crystal fiber as shown in Figure 2.

Claims (1)

1. a double refraction photo crystal optical fiber microwave and millimeter wave generator, this generator comprises: pumping source, for the coupling pump light of pumping source being entered the fiber coupler of resonator cavity, and described resonator cavity, it is characterized in that: described resonator cavity is formed by fiber grating and combination of fiber-optic, described combination of fiber-optic to be connected in series with double refraction photo crystal optical fiber by Active Optical Fiber to form, and at least one double refraction photo crystal optical fiber is provided with pressure applying means, for changing the birefringence level of described double refraction photo crystal optical fiber, described combination of fiber-optic comprises an Active Optical Fiber and a double refraction photo crystal optical fiber, or described combination of fiber-optic comprises many Active Optical Fibers and Duo Gen double refraction photo crystal optical fiber, described Active Optical Fiber is er-doped, mix ytterbium or erbium-ytterbium co-doped fiber, described double refraction photo crystal optical fiber is the photonic crystal fiber in covering with oval airport, there is in the fibre core of described double refraction photo crystal optical fiber the small sircle hole for destroying symmetrical structure, or the elliptical aperture had in the fibre core of described double refraction photo crystal optical fiber for destroying symmetrical structure, when applying pressure to described double refraction photo crystal optical fiber, due to effect of stress, the volume of the airport of the ellipse in photonic crystal fiber and ellipticity all can change along with the change of compressive stress, and the change of the volume of oval airport and ellipticity all can cause the change of birefringence level, the change of birefringence level will cause the change of two kinds of polarization mode difference on the frequencies, thus microwave or millimeter wave frequency on change photodetector, thus achieve and export the tuning of microwave or millimeter wave.