CN117706687B - All-fiber nonmagnetic isolator and preparation method thereof - Google Patents
All-fiber nonmagnetic isolator and preparation method thereof Download PDFInfo
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- CN117706687B CN117706687B CN202311791398.0A CN202311791398A CN117706687B CN 117706687 B CN117706687 B CN 117706687B CN 202311791398 A CN202311791398 A CN 202311791398A CN 117706687 B CN117706687 B CN 117706687B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2746—Optical coupling means with polarisation selective and adjusting means comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
- G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
- G02B6/02123—Refractive index modulation gratings, e.g. Bragg gratings characterised by the method of manufacture of the grating
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Abstract
The embodiment of the invention discloses an all-fiber nonmagnetic isolator and a preparation method thereof, wherein the isolator comprises an optical fiber, and a 45-degree inclined fiber grating and a 45-degree incident lambda/4 fiber wave plate are arranged on the optical fiber. The invention utilizes accurate ultraviolet light control to finish the manufacture of the inclined fiber grating and the fiber wave plate on the same fiber on line, and realizes the control of polarization conversion, thereby achieving the aim of low cost and miniaturization of reflected light isolation and solving the problems of high cost, large volume, low reliability and the like of the traditional reflected light isolation which needs to introduce magneto-optical materials.
Description
Technical Field
The invention relates to the technical fields of optical fiber sensing and optical fiber communication, in particular to an all-fiber nonmagnetic isolator and a preparation method thereof.
Background
An optical isolator is an optical device that allows unidirectional transmission of light, and a conventional optical isolator is based on a magneto-optical effect (Faraday effect), specifically, when light passes through a magneto-optical material in a magnetic field, its polarization plane rotates with the propagation direction of the light. By matching with the polarizing element or the polarization separation element with corresponding angles, only one direction of light can be allowed to pass through, and the opposite direction of light is prevented, so that unidirectional light isolation is realized.
The optical isolator is widely applied to the fields of optical fiber amplifiers, optical fiber lasers, optical fiber sensors and the like, plays a role in protecting and stabilizing a system, and is mainly used for protecting a light source from being interfered and damaged by reverse light in the system. For example, in an optical fiber communication system, an optical isolator can prevent reverse light generated by reflection, scattering and the like from entering a light source, thereby protecting a laser from damage and improving the stability of the system.
In the traditional magneto-optical isolator, a new magneto-optical material is introduced outside an optical fiber, and an optical fiber collimator and the like are often required for collimation input and output, so that the complexity of the device is increased, and the reliability of the device is reduced. In addition, such devices are bulky, costly, and particularly the shorter the operating wavelength, the longer the magneto-optical material is required, and the bulky and expensive price limits the widespread use of the isolator.
Disclosure of Invention
The technical problem to be solved by the embodiment of the invention is to provide the all-fiber nonmagnetic isolator and the preparation method thereof, so that the volume is reduced, the cost is lowered, and the reliability is improved.
In order to solve the technical problems, the embodiment of the invention provides an all-fiber nonmagnetic isolator, which comprises an optical fiber, wherein a 45-degree inclined fiber grating and a 45-degree incident lambda/4 fiber wave plate are arranged on the optical fiber.
Further, the grating constant Λ g of the 45 ° inclined fiber grating satisfies:
wherein n is the refractive index of the optical fiber, m is the order of the 45-degree inclined optical fiber grating, and lambda is the working wavelength of the all-fiber nonmagnetic isolator.
Further, the isolation method is applied to isolation of one or more wave band light sources of 850nm, 1310nm and 1550 nm.
Correspondingly, the embodiment of the invention also provides a preparation method of the all-fiber nonmagnetic isolator, which comprises the following steps:
Step 1, inscribing and manufacturing a 45-degree inclined fiber grating on an optical fiber by ultraviolet laser;
And 2, controlling the irradiation intensity of ultraviolet laser, and continuing to inscribe and manufacture a lambda/4 optical fiber wave plate in the side area of the 45-degree inclined optical fiber grating on the same optical fiber, thereby obtaining the all-fiber nonmagnetic isolator.
Further, 193 nm or 248 nm excimer laser or argon ion laser of 244 nm after frequency multiplication is adopted in the step 1 and the step 2 to emit ultraviolet laser.
Further, in step 1, the ultraviolet laser is modulated by a mask plate, the inscribed pattern with alternate brightness is diffracted, the optical fiber absorbs the modulated ultraviolet laser by utilizing the photosensitivity of the optical fiber to form an inclined grating structure with periodically changing refractive index, and the mask plate period lambada p meets the following formula:
;
wherein n is the refractive index of the optical fiber, and lambda is the working wavelength of the all-fiber nonmagnetic isolator.
Further, the linear polarized light of the 45-degree inclined fiber grating of the all-fiber nonmagnetic isolator is 45 degrees with the main axis of the lambda/4 fiber wave plate after filtering.
In step 2, the photosensitivity of the optical fiber is used to control the irradiation intensity of the ultraviolet laser, so that the refractive index of the side facing the ultraviolet laser is higher than the refractive index of the side facing away from the ultraviolet light, thereby generating ultraviolet induced birefringence, controlling the birefringence and the writing length, and delaying the phase generated by the birefringence to pi/2, thus completing the manufacturing of the lambda/4 optical fiber wave plate.
The beneficial effects of the invention are as follows:
1. The invention does not need magneto-optical material, reduces the volume of the optical isolator and reduces the cost of the isolator.
2. The invention uses ultraviolet laser to manufacture on the same optical fiber in an online non-contact way, does not need to break the optical fiber, and greatly improves the reliability of the optical isolator.
3. The invention can be matched with various wavelength systems by changing the period of the grating and the length of the wave plate, and the scheme is flexible.
4. The invention is an all-fiber device, which can be bent and coiled, and greatly reduces the volume of the sensor.
Drawings
FIG. 1 is a light path diagram of an all-fiber nonmagnetic isolator according to an embodiment of the invention.
Fig. 2 is a schematic diagram of a 45 ° tilted fiber grating according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a manufacturing principle of a lambda/4 optical fiber wave plate based on ultraviolet light induction according to an embodiment of the invention.
FIG. 4 is a schematic diagram of induced birefringence as a function of write time according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a writing structure of an inclined fiber grating according to an embodiment of the present invention.
FIG. 6 is a schematic diagram of a write structure of a lambda/4 fiber waveplate in accordance with an embodiment of the present invention.
Description of the reference numerals
The optical fiber grating comprises an optical fiber 1, 45-degree inclined optical fiber grating 2, a lambda/4 optical fiber wave plate 3, a laser 4, a beam expander 5, a cylindrical lens 6 and a mask 7.
Detailed Description
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other, and the present application will be further described in detail with reference to the drawings and the specific embodiments.
In the embodiment of the present invention, if there is a directional indication (such as up, down, left, right, front, and rear, for example), the relative positional relationship between the components, the movement condition, etc. in a specific posture (as shown in the drawings) are merely explained, and if the specific posture is changed, the directional indication is correspondingly changed.
In addition, the description of "first," "second," etc. in this disclosure is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implying an indication of the number of features being indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature.
Referring to fig. 1, an all-fiber nonmagnetic isolator according to an embodiment of the invention includes an optical fiber. The optical fiber is provided with a 45-degree inclined optical fiber grating and a 45-degree incident lambda/4 optical fiber wave plate. The invention reduces the volume of the optical isolator, reduces the cost of the optical isolator and improves the reliability of the optical isolator.
The invention aims to make an optical fiber device by utilizing the photosensitivity of the optical fiber, so that the optical fiber absorbs the ultraviolet laser modulated spatially, a nonmagnetic optical isolator is finished on the same optical fiber, the optical fiber is not required to be broken, a new material is not required to be introduced, and the optical fiber has the characteristics of small volume, low cost and high reliability, and has great significance for the development of a novel optical system.
The preparation method of the all-fiber nonmagnetic isolator comprises the steps 1-2.
And 1, inscribing and manufacturing a 45-degree inclined fiber grating on the fiber by using ultraviolet laser.
And 2, controlling the irradiation intensity of ultraviolet laser, continuing to manufacture a lambda/4 optical fiber wave plate in a side area of the 45-degree inclined optical fiber grating on the same optical fiber, finishing the conversion of the polarization state on the same complete optical fiber, obtaining the all-fiber nonmagnetic isolator, and finishing extinction of reflected light by using a polarizer (45-degree inclined optical fiber grating), thereby realizing isolation of the reflected light under the condition of not introducing magneto-optical materials. The invention is manufactured by connecting an optical fiber, and the devices have no melting point.
The invention uses the photosensitivity of the optical fiber core with weak rising refractive index after absorbing ultraviolet light, uses the space modulation for inscribing ultraviolet light, then makes 45-degree inclined optical fiber grating on the same optical fiber as a polarizer, and makes the wave plate double refraction axis rotate 45 degrees relative to the polarizer pass-through axis to make 45-degree incident lambda/4 optical fiber wave plate to complete the conversion of polarization state, and uses the characteristic of opposite chirality of the reflected light, the polarization state of the reflected light is perpendicular to the optical fiber grating pass-through axis, thereby achieving the goal of isolating the reflected light.
In step 1, the ultraviolet laser is modulated by a mask plate, a inscribed pattern with alternate brightness is diffracted, and the optical fiber absorbs the modulated ultraviolet laser by utilizing the photosensitivity of the optical fiber to form an inclined grating structure with periodically changing refractive index.
In step 2, the photosensitivity of the optical fiber is used to control the irradiation intensity of the ultraviolet laser, so that the refractive index of the side facing the ultraviolet laser is higher than the refractive index of the side facing away from the ultraviolet light, thereby generating ultraviolet induced birefringence, controlling the birefringence and the writing length, and delaying the phase generated by the birefringence to pi/2, thus completing the manufacturing of the lambda/4 optical fiber wave plate.
The working principle of the all-fiber nonmagnetic isolator is shown in fig. 1, elliptical polarized light emitted by a light source passes through a 45-degree inclined fiber bragg grating, an S polarized component is filtered, a P polarized component is kept to pass through in a lossless manner, the linear polarized light is converted into linear polarized light, the linear polarized light is converted into right-handed circularly polarized light through a lambda/4 fiber wave plate with a main shaft of 45 degrees, the right-handed circularly polarized light is transmitted in an optical fiber, and after encountering a reflection point, the light is reflected. The chirality of the reflected light is opposite to that of the incident light, the right-handed circularly polarized light is converted into left-handed circularly polarized light, the left-handed circularly polarized light is converted into S-linear polarized light through a lambda/4 optical fiber wave plate, and the linear polarized light is filtered by a 45-degree inclined optical fiber grating, so that the purpose of isolating the reflected light is realized.
The working principle of the 45-degree inclined fiber grating is shown as 2, and the optical fiber with photosensitivity absorbs periodic ultraviolet light with alternate brightness and darkness to generate periodic photochemical reaction, so that periodic refractive index modulation is generated, and a grating structure is generated. And rotating the periodic ultraviolet light pattern to generate an inclined fiber grating in the optical fiber, and radiating the reflected light out of the optical fiber in the form of S polarized light when the inclination angle of the grating is Brewster angle, so as to keep the P polarized light to be transmitted in the optical fiber without damage. The brewster angle θ is calculated as formula (1):
(1)
Wherein n 1,n0 is the refractive index formed by modulating ultraviolet light on the optical fiber. This results in a refractive index contrast, Δn 1=n1−n0, of about 10 −5~10−3, and such a weak refractive index modulation causes n 1≈n0, hence θ≡45°. The relationship between the grating constant Λ g and the grating period Λ is as shown in formula (2):
(2)
when the grating constant satisfies the wave vector matching condition shown in the formula (3), the radiation mode is amplified by resonance, and the 45-degree inclined fiber grating has the optimal polarization correlation.
(3)
Where n is the refractive index of the fiber, and is reduced to 1.46 without considering dispersion, m is a positive integer, and λ is the operating wavelength. For the most commonly used 1 st order tilted gratings (m=1), for an operating wavelength of 1310nm, the grating constant should be designed to be 634.5nm.
The invention utilizes ultraviolet light to induce the manufacture of the optical fiber wave plate and also utilizes the photosensitivity of the optical fiber to increase the refractive index after absorbing ultraviolet light, the manufacture principle is shown in figure 3, the ultraviolet light irradiates the optical fiber along the lateral direction of the optical fiber, the surface of the optical fiber core facing the light is directly irradiated by the ultraviolet light, and the ultraviolet light absorbed by the surface facing away from the light is attenuated, so that the refractive index n 3 of the surface of the optical fiber core facing the light is slightly higher than the refractive index n 4 of the surface facing away from the light, and differential modulation is generated on the electric field vibration of S light and P light, thereby generating ultraviolet induced birefringence delta n 2. As shown in FIG. 4, the relation of the birefringence with the writing time is that the birefringence becomes larger with the increase of the irradiation time when the irradiation is started, and the refractive index of the side facing the light increases more than the refractive index of the side facing the light after the absorption of the side facing the light approaches saturation, and the birefringence becomes smaller gradually with the increase of the writing time until the absorption approaches 0. And designing a process experiment test according to the optimal irradiation time t and the process conditions such as laser intensity, optical fiber photosensitivity and the like.
When the inscribed birefringence and length l meet the condition shown in the formula (4), the phase difference of the wave plate is pi/2, namely the lambda/4 optical fiber wave plate is manufactured.
(4)
Where k is a non-negative integer.
In view of the fact that ultraviolet light is required to be used for manufacturing the inclined fiber bragg grating and the wave plate to induce refractive index change, two devices can be manufactured on the same optical fiber continuously and online, the optical fiber is rotated for 45 degrees after the 45-degree inclined fiber bragg grating is manufactured, and accordingly the linearly polarized light after filtering and the main axis of the lambda/4 optical fiber wave plate are 45 degrees.
The invention is based on the photosensitivity of the optical fiber to ultraviolet light, which can be derived from the doping of the optical fiber itself or the hydrogen loading sensitization. The ultraviolet laser of the inscribing grating and the wave plate can be 193 nm or 248 nm excimer laser or 244nm argon ion laser after frequency multiplication.
As shown in FIG. 5, the 45-degree inclined fiber grating inscribing method is characterized in that the laser emits ultraviolet laser, and the ultraviolet laser is expanded to the length to be inscribed by the beam expander, wherein the length is generally 30-60 mm. The laser is radially converged on the optical fiber by using the cylindrical lens, and the converging focal point is positioned at the optical fiber, so that the inscribed laser energy is higher. The laser is modulated by the phase mask plate, and the inscribed patterns with alternate brightness and darkness are diffracted. In view of the cylindrical lens effect of the optical fiber, the pattern tilt angle of the reticle is designed to 33.8 °, and the reticle period Λ p can be calculated using equation (5).
(5)
The method of writing the optical fiber wave plate is similar to the method of writing the grating, except that a phase mask is not needed, and as shown in fig. 6, the optimal writing time can be determined by a specific process experiment.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.
Claims (7)
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| CN101369037A (en) * | 2007-08-16 | 2009-02-18 | 湾世伟 | Irradiation type high-precision full-optical fiber optical wave sheet |
| CN105742959A (en) * | 2016-04-06 | 2016-07-06 | 中国科学院上海光学精密机械研究所 | Phase shifting fiber bragg grating based external cavity feedback semiconductor laser |
| CN114185129A (en) * | 2022-02-15 | 2022-03-15 | 深圳奥斯诺导航科技有限公司 | Method for writing inclined grating polarization filter |
Family Cites Families (6)
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| JPH06100732B2 (en) * | 1982-04-12 | 1994-12-12 | 日本電信電話株式会社 | Fiber type isolator |
| JP3011140B2 (en) * | 1997-07-08 | 2000-02-21 | 日本電気株式会社 | Fiber type optical isolator and method of manufacturing the same |
| US6816260B2 (en) * | 2001-05-17 | 2004-11-09 | Thorlabs Gmbh | Fiber polarimeter, the use thereof, as well as polarimetric method |
| CN104180798A (en) * | 2014-09-16 | 2014-12-03 | 中国科学院光电技术研究所 | Multi-optical-fiber-ring-series single-axis optical fiber gyroscope and multi-optical-fiber-ring-series method |
| CN213304578U (en) * | 2020-11-20 | 2021-05-28 | 中国人民解放军国防科技大学 | Integrated all-fiber oscillator |
| CN116338952B (en) * | 2023-05-18 | 2024-10-15 | 希烽光电科技(南京)有限公司 | Construction method of optical isolator based on rotary medium cavity |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101369037A (en) * | 2007-08-16 | 2009-02-18 | 湾世伟 | Irradiation type high-precision full-optical fiber optical wave sheet |
| CN105742959A (en) * | 2016-04-06 | 2016-07-06 | 中国科学院上海光学精密机械研究所 | Phase shifting fiber bragg grating based external cavity feedback semiconductor laser |
| CN114185129A (en) * | 2022-02-15 | 2022-03-15 | 深圳奥斯诺导航科技有限公司 | Method for writing inclined grating polarization filter |
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