阅读说明：本技术 一种基于空间螺旋弯曲的旋光纤波片 (Optical fiber wave plate based on space spiral bending ) 是由 赵斌 於得奋 吴鹏飞 魏成祥 于 2021-08-27 设计创作，主要内容包括：本发明属于光学波片相关技术领域,并公开了一种基于空间螺旋弯曲的旋光纤波片。该波片由一条旋光纤呈空间螺旋盘旋而成,该螺旋盘旋的旋光纤包括三个部分,入射端、中间段和出射端,其中,所述中间段用于形成波片所需的相位延迟。相较于现有的光纤波片,本发明所提出的基于空间螺旋弯曲的旋光纤波片则由于旋光纤其内部呈螺旋结构的高双折射轴而抑制甚至淹没掉外界产生的线性双折射,从而获得确定的输出偏振态。(The invention belongs to the technical field of optical wave plate correlation, and discloses an optical fiber wave plate based on space spiral bending. The wave plate is formed by spirally winding a spiral optical fiber in space, the spirally wound optical fiber comprises three parts, namely an incident end, a middle section and an emergent end, wherein the middle section is used for forming phase delay required by the wave plate. Compared with the existing optical fiber wave plate, the optical fiber wave plate based on the spatial helical bending provided by the invention inhibits or even submerges the linear birefringence generated by the outside because the internal part of the optical fiber is in a helical structure and has a high birefringence axis, so that a determined output polarization state is obtained.)

1. The optical fiber wave plate based on the spatial helical bending is characterized in that the wave plate is formed by spirally winding a spiral optical fiber in a spatial manner, the spirally wound optical fiber comprises three parts, namely an incident end, a middle section and an emergent end, wherein the middle section is used for forming phase delay required by the wave plate.

2. The spatially spiral bend based optically active fiber waveplate of claim 1, wherein the geometric parameters of said spirally wound optical fiber include pitch P, radius R, length L_RBy the phase retardation of the desired wave plate and the period of rotation L of the optical fiber_sAnd the beat length L of the polarization maintaining optical fiber preform_bAnd (4) jointly determining.

3. An optically active fiber plate based on spatial helical bending according to claim 1 or 2, wherein the incident end and the exit end are linear.

4. The fiber optic plate according to claim 3, wherein the length of the incident end and the exit end is a positive integer multiple of the elliptical beat length of the fiber optic.

5. An optically active fiber plate based on spatial helical bending according to claim 4, wherein the elliptical beat length of the optical fiber is calculated as follows:

wherein L is_eIs the elliptical beat length of the optical fiber, L_bIs the beat length, L, of the polarization maintaining optical fiber preform_sIs the spin period of the spinning fiber.

6. The optical fiber waveplate based on the spatial helical bending of claim 1, wherein a carrier is disposed in the middle of the optical fiber, and the optical fiber is coiled on the carrier.

7. An optically active fiber plate based on spatial helical bending according to claim 6, wherein the carrier is cylindrical.

8. The spatially-chirped waveplate according to claim 1, wherein said chirped fiber is obtained by high speed spinning of a polarization-maintaining fiber preform in a molten state.

Technical Field

The invention belongs to the technical field of optical wave plate correlation, and particularly relates to an optical fiber wave plate based on space helical bending.

Background

A wave plate is a commonly used optical device, and is widely used in optical systems to realize polarization state conversion of polarized light. Generally, wave plates are manufactured by cutting optical crystals into parallel thin plates with specific thicknesses, however, the inherent defects of narrow band, heavy weight, difficulty in integrating with fiber optical systems and the like of these bulk optical wave plates greatly restrict the application of the bulk optical wave plates in the fiber optical systems. Compared with the block optical wave plate, the introduction of the all-fiber wave plate can not only reduce the internal loss and the back reflection, but also keep high integration level, thereby improving the comprehensive performance of the fiber optical system. Therefore, the all-fiber wave plate is an important device for meeting the development trend of fiber optical systems.

The commonly used fiber-optic wave plates can be mainly classified into two categories according to the source of the required birefringence, namely stress-induced fiber-optic wave plates and geometric effect fiber-optic wave plates. The geometric effect type optical fiber wave plate uses linear birefringence generated by the geometric effect of the optical fiber to manufacture the wave plate, for example, a quarter-wave plate is manufactured by cutting one quarter beat length of an elliptic core polarization maintaining fiber, or a wave plate is manufactured by rotating the polarization maintaining optical fiber at a variable speed. The former requires extremely accurate cut length, angular alignment and welding operations, and the latter requires a very complicated manufacturing process. The induction type optical fiber wave plate uses mechanical stress such as bending, lateral pressure and axial stress of an optical fiber or linear birefringence generated by thermal stress of a polarization maintaining optical fiber to manufacture the wave plate, and the application is wide, however, single-mode tail fibers at two ends of the wave plate are extremely susceptible to bending and vibration in the using process, so that the linear birefringence with great randomness is generated, and the emergent polarization state is seriously deviated from the preset value. Therefore, a new wave plate is urgently needed to effectively eliminate the defects of random linear birefringence and serious deviation of the emergent polarization state from the preset value.

Disclosure of Invention

In view of the above drawbacks and needs of the prior art, the present invention provides a fiber-optic plate based on spatial helical bending, which solves the problems of random linear birefringence and serious deviation of emergent polarization state from its preset value in the prior art.

To achieve the above object, according to the present invention, there is provided a fiber-optic wave plate based on spatial helical bending, the wave plate being formed by a helical optical fiber spirally wound in space, the spirally wound fiber-optic fiber including three sections, an incident end, an intermediate section and an exit end, wherein the intermediate section is used for forming a phase retardation required for the wave plate.

Further preferably, the geometric parameters of the spirally wound optical fiber include a pitch P, a radius R, and a length L_RBy the phase retardation of the desired wave plate and the period of rotation L of the optical fiber_sAnd the beat length L of the polarization maintaining optical fiber preform_bAnd (4) jointly determining.

Further preferably, the incident end and the exit end are both linear.

Further preferably, the lengths of the incident end and the exit end are positive integer multiples of the elliptical beat length of the optical fiber.

Further preferably, the elliptical beat length of the spiral fiber is calculated as follows:

wherein L is_eIs an elliptical beat length, L_bIs the beat length, L, of the polarization maintaining optical fiber preform_sIs the spin period of the spinning fiber.

Further preferably, a carrier is disposed in the middle of the optical rotary fiber, and the optical rotary fiber is disposed on the carrier.

Further preferably, the carrier is cylindrical.

Further preferably, the spin fiber is obtained by rotating a polarization maintaining optical fiber preform at a high speed in a molten state.

Generally, compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. in the invention, a spirally bent Optical Fiber (round high Birefringent Optical Fiber) is selected as the wave plate, because the inherent linear birefringence of the Optical Fiber is in a spiral structure in space, and when polarized light propagates in the Optical Fiber, the polarization rotation occurs, so that the phase delay generated by the bent birefringence changes unpredictably along with the increase of the length of the Optical Fiber and cannot increase linearly along with the length of the Optical Fiber like the ordinary single-mode Optical Fiber which is bent in a plane; if the rotary optical fiber is rotated in a space spiral bending way, the rotation of the polarization direction and the rotation of the bending stress direction can be kept synchronous, and the linear increase of the phase delay along with the length of the optical fiber is realized, so that the optical fiber can be used as a wave plate;

2. the optical fiber is obtained by high-speed rotation of a polarization-maintaining optical fiber preform in a molten state, after cooling, a high-linear birefringence axis of the optical fiber is spiral in space, and linear birefringence generated by bending, vibration and the like can be inhibited in the using process of the optical fiber, so that the optical fiber has excellent circular polarization maintaining capacity, and therefore, an optical fiber wave plate manufactured by utilizing bending stress birefringence of the optical fiber can obtain an all-fiber wave plate with determined polarization state conversion capacity; compared with the existing optical fiber wave plate, the optical fiber wave plate based on the spatial spiral bending provided by the invention inhibits or even submerges the linear birefringence generated by the outside because the internal part of the optical fiber is in a high birefringence axis of a spiral structure, thereby obtaining a determined output polarization state;

3. the length of the incident end and the exit end in the invention is integral multiple of the ellipse beat length, if the length of the incident end is not integral multiple of the ellipse beat length, the linearly polarized light emitted from the polarizer can be changed into an elliptical polarization state with small ellipticity under the action of the spiral optical fiber of the incident end, namely the linearly polarized light is not emitted from the polarizer when entering the middle section retarder; similarly, when the length of the polarized light after the action of the middle section retarder at the emergent end is not the integral multiple of the ellipse beat length, the polarization state can be changed due to the action of the optical fiber, namely the change of the azimuth angle and the ellipticity, so that the lengths of the incident end and the emergent end are the integral multiple of the ellipse beat length;

4. the optical fiber is adopted as a wave plate, and is different from an ideal common single-mode fiber, the common single-mode fiber is an isotropic dielectric medium, in the actual use process, for example, stress birefringence is easily generated by bending and vibration, so that the emergent polarization state of the polarized light is unpredictably changed after the polarized light is acted by the single-mode fiber with a determined length.

Drawings

FIG. 1 is a schematic diagram of a spatially spiral bend based optically active fiber plate structure constructed in accordance with a preferred embodiment of the present invention;

fig. 2 is a schematic diagram of a fiber optic retarder based on spatial helical bending constructed in accordance with a preferred embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

As shown in FIG. 1, the fiber-spinning plate is composed of three parts, i.e., L in length_iThe length of the incident end-spinning optical fiber pigtail is L_ROptical fiber Retarder (Retarder) of length L_oThe emergent end of the optical fiber is rotated to form the tail optical fiber. The two-end optical fiber tail fiber is used for connecting with other optical devices in the optical fiber optical system, and the middle-part optical fiber retarder is used for generating phase Retardation (Retardation) required by the wave plate. As shown in FIG. 2, the optical fiber retarder is fabricated by bending a length of optical fiber in a spatial helix, the geometric parameters of which helix are such as pitch P, helix radius R, length L_REtc. from the desired amount of phase retardation (depending on the type of wave plate, e.g. quarter-wave plate, half-wave plate, etc.) and the characteristic parameters of the optical fiber, e.g. the period of rotation L_sAnd the beat length L of the polarization maintaining optical fiber preform_bAnd (4) jointly determining. The two ends of the rotary optical fiber pigtail are two straight rotary optical fibers, in order to improve the comprehensive performance of the whole wave plate,the length of the fiber needs to satisfy a certain condition, namely the elliptical beat length L of the optical fiber_ePositive integer multiples of. The ellipse beat length is calculated by

Fig. 2 is a schematic diagram showing the details of the construction of a spatially spirally curved spun retarder, where P is the pitch of the helix, R is the helix radius, and the (n, b, s) coordinate system is a local coordinate system. n, b and s are coordinate axes respectively pointing to the normal, the secondary normal and the tangential direction of the space curve. When linearly polarized light propagates along the spatial spiral path, the polarization direction rotates due to the geometric topological effect, and the rotation speed is omega₂＝2πP/[P²+(2πR)²]The rotating optical fiber is obtained by rotating the polarization-maintaining optical fiber preform at a high speed in a molten state, and the high-linearity double-refraction axis of the rotating optical fiber preform is in a spiral structure in space, so that the inherent polarization rotation of linearly polarized light can occur when the linearly polarized light propagates in the rotating optical fiber preform, and the rotating speed is omega₁＝(Δβ)²(8 xi), (xi is much larger than Δ β, Δ β ═ 2 τ/L_bFor linear birefringence of polarization maintaining optical fiber preform, [ xi ] 2 τ/L_sIs the rotation rate). When the two rotational speeds are the same, i.e. ω₂＝ω₁In the (n, b, s) coordinate system, the polarized light is approximately static, and the phase retardation generated by the bending stress birefringence can be linearly increased along with the length of the spinning optical fiber, so that the optical fiber wave plate with the required phase retardation is manufactured.

The invention is further illustrated by the following specific examples.

Although the method for manufacturing the optical fiber wave plate based on the spatial helical bending can manufacture optical fiber wave plates with various phase retardation amounts, the most commonly used wave plates in the optical system are a quarter wave plate and a half wave plate, and the quarter wave plate and the half wave plate are taken as examples below to give examples of the optical fiber quarter wave plate and the half wave plate based on the spatial helical bending. The optical fiber for manufacturing the optical fiber wave plate is an optical fiber with SH1016-A model of long-flying optical fiber cable GmbH and the characteristic parameter is a rotation period L_sLength of line beat L of 5mm_bThe diameter of the cladding layer is approximately 9.5mm, the diameter of the cladding layer is 125um, the outer diameter of the cladding layer is 900um after the protective sleeve is additionally arranged, and the radius of a cylinder for winding the wave plate is 10 mm. The spiral radius R can be calculated as 10.45mm and the elliptical beat length L of the spiral fiber_e7.34cm, inherent to the optical fiber, and a polarization rotation rate ω₁＝(Δβ)²/(8 ξ) ≈ 43.5 rad/m. From omega₂＝2πP/[P²+(2πR)²]＝ω₁The pitch P is approximately equal to 4.2cm when the radius is 43.5rad/m, and the pitch P is approximately equal to 4.2cm, and the pitch R is 10.45mm when the radius is chi (2 pi)²R/(P²+(2πR)²In (1), the bending curvature χ ≈ 67.8m can be calculated^-1. Then using the expression beta for the bending birefringence_b≈0.215D²χ²The bending birefringence β can be calculated by taking the wavelength of light as 1310nm_b11.3 rad/m. Finally, the phase delay required for the quarter-wave plate is pi/2, and the corresponding optical fiber length is L_Rq＝π/2β_bThe diameter is approximately equal to 14 cm; the phase retardation required for a half-wave plate is pi, which corresponds to an optical fiber length of L_Rh＝π/β_bAbout 28 cm. This yields the geometric parameters R, P, L of the overall helix_R. And winding the optical fiber on a cylinder with a radius of 10mm and marked with scale marks according to the geometric parameters of the obtained spiral line, avoiding extra torsion and stretching of the optical fiber in the winding process, and reasonably fixing the optical fiber on the surface of the cylinder to finish the manufacture of the optical fiber quarter-wave retarder and the half-wave retarder based on space spiral bending.

The tail fibers at two ends of the quarter-wave plate and the half-wave plate are used for connecting other optical devices in the optical fiber optical system, and the elliptic beat length L of the spiral optical fiber is obtained through calculation_e7.34 cm. Since the polarization state of the polarized light is repeated every other elliptical beat length when propagating in the spin fiber, in order to eliminate the polarization state change caused by the tail fiber, the length of the tail fiber should preferably be an integer multiple of the elliptical beat length, i.e., L_i＝n₁L_e、L_o＝n₂L_e，n₁And n₂Is a positive integer. Two ends of optical fiber tail fiber and middle optical fiber quarter waveThe retarder and the half-wave retarder constitute a quarter-wave plate and a half-wave plate of the optical fiber based on the helical bend.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.