CN1179549A - Optical isolator - Google Patents

Abstract

An optical isolator installed between optical fibers that transmits light in the forward direction and blocks reverse light. Among them, the first GRIN lens converts the light from the first optical fiber into parallel rays; the first polarizer doubles it into first (normal) and second (extraordinary) rays; the Faraday rotator makes the first and second (extraordinary) rays The second ray rotates in one direction; the second polarizer, with the crystal axis at a 45° angle to the opposite of the direction of rotation of the Faraday rotator, converts the first ray passing through the Faraday rotator into an extraordinary ray, turning the second The second ray is converted into a normal ray; the second GRIN lens focuses it on the second fiber end.

Description

optical isolator

The present invention relates to an optical device using an optical fiber, in particular to an isolator installed between two optical fibers to allow light to pass forward and prevent light from passing backward.

A general optical isolator uses the polarization state of light to prevent light from passing through in the opposite direction.

Referring now to Fig. 1, the conventional optical isolator utilizing the state of polarization is positioned on the optical path between the first optical fiber 18 and the second optical fiber 19, allowing light to propagate forward from the first optical fiber 18 to the second optical fiber 19 through it, and Blocks backpropagating rays.

The optical isolator comprises first and second glass rings 11 and 17 into which both ends of first and second optical fibers 18 and 19 are inserted and aligned. The light emitted from the first optical fiber 18 becomes a parallel beam when passing through the first GRIN (Graded Refraction) lens 12 . The parallel beam propagates to the second optical fiber 19 and passes through the first polarizer 13 , the Faraday rotator 14 , the second polarizer 15 and the second GRIN lens 16 of the wedge-shaped birefringent crystal.

As shown in Figure 2A, due to the birefringence effect of the first polarizer 13, a forward ray 20, after passing through the first GRIN lens 12, is divided into two beams of light, i.e. normal rays 21, when passing through the first polarizer 13 and very light 22. The ordinary ray 21 is refracted according to the ordinary refractive index n _o of the first polarizer 13 and polarized in a direction parallel to the crystal axis (not shown) of the first polarizer 13 . The extraordinary ray 22 is _refracted according to the extraordinary refractive index ne of the first polarizer 13 and is polarized in a direction perpendicular to the crystal optical axis of the first polarizer 13 .

The respective polarization directions of the ordinary ray 21 and the extraordinary ray 22 passing through the first polarizer 13 are rotated by 45° by the Faraday rotator 14 . Then, the ordinary ray 21 and the extraordinary ray 22 whose polarization directions are rotated are refracted while passing through the second polarizer 15, and become parallel beams. The second polarizer 15 has the same wedge-shaped birefringent crystal as the first polarizer 13 and its crystal axis is at 45° to that of the first polarizer 13 in the direction of light rotation by the Faraday rotator 14 . Thus, the ordinary ray 21 and the extraordinary ray 22 passing through the first polarizer 13 continue in the second polarizer 15 as an ordinary ray 21 ′ and an extraordinary ray 22 ′, respectively.

The output of the ordinary ray 21 ″ and the extraordinary ray 22 ″ from the second polarizer 15 has the same output angle θ with respect to the exit surface of the second polarizer 15 . The ordinary ray 21 ″ and the extraordinary ray 22 ″ are parallel to each other and separated by a predetermined width S. The outputs of light rays 21 ″ and 22 ″ from the second polarizer 15 are combined at the second GRIN lens 16 (see FIG. 1 ) and converged to the end of the second optical fiber 19 .

Referring to FIG. 2B , due to the birefringence of the second polarizer 15 , the reverse ray 23 coming out of the second optical fiber 19 toward the first optical fiber 18 is divided into two rays, ie an ordinary ray 24 and an extraordinary ray 25 . The ordinary rays 24 are refracted according to the ordinary refractive index n _o of the second polarizer 15 , while the extraordinary rays 25 are refracted according to the extraordinary refractive index _ne of the second polarizer 15 .

When the reverse ordinary ray 24 and the extraordinary ray 25 pass through the Faraday rotator 14 , the rotation direction of the forward ray 21 is rotated by 45° in the opposite direction (see FIG. 2A ). Therefore, the ordinary ray 24 passing through the Faraday rotator 14 has a polarization direction perpendicular to the crystal optical axis of the first polarizer 13, and becomes an extraordinary ray 24'. Also, the extraordinary ray 25 passing through the Faraday rotator 14 has a polarization direction parallel to the crystal axis of the first polarizer 13, and becomes an ordinary ray 25'. Due to the change of the two rays, the respective refraction angles of the two rays 24" and 25" when passing through the first polarizer 13 become different from each other, respectively θ-Δθ and θ+Δθ, so that the two rays are not parallel to each other. The light rays 24 ″ and 25 ″ are collected by the first GRIN lens 12 (see FIG. 1 ), and their focal points are not located at the input end of the first optical fiber 18 . Reverse light rays 25 are thus blocked.

With a conventional optical isolator having such a structure, the ordinary ray 21" (see FIG. 2A) and the extraordinary ray 22" are separated when passing through the first and second polarizers 13 and 15, and travel toward the second optical fiber 19 parallel to each other. The optical path difference between the ordinary ray 21 ″ and the extraordinary ray 22 ″ is defined as a “work-off”, therefore, when the two rays 21 ″ and 22 ″ are gathered by the second GRIN lens 16 (see FIG. 1 ) When combined, due to this work-off, a time delay occurs between the two rays 21" and 22", and thus polarization dispersion occurs.

To solve such problems, another conventional optical isolator is disclosed in US Patent 5,557,692 "Optical Isolator with Low Polarization Dispersion" (Dptical Isolator with Low Polarization Mode Dispexsion). In this optical isolator, work-off is reduced by further providing a birefringent plate on the optical path of the optical isolator shown in FIGS. 1, 2A and 2B. But the problem is increasing the number of parts in the optical isolator.

In order to solve the above-mentioned problems, an object of the present invention is to provide an optical isolator that utilizes a polarization state to reduce work-off without additional optical components.

Therefore, in order to achieve the above object, an optical isolator is provided, the optical isolator is arranged on the optical path between the first optical fiber and the second optical fiber, and according to the polarization state of the incident light, transmits light to a second fiber, blocking light emitted by said second fiber, said optical isolator comprising: a first GRIN (Graded Refractive) lens, said lens transforming light emitted by said first fiber into a parallel beam the first polarizer, the first polarizer is arranged along the optical path, and the parallel light beam is double refracted into a first ray of ordinary rays and a second ray of extraordinary rays by virtue of its crystal optical axis, and makes them pass through; a Faraday rotator, the Faraday rotator is arranged on the optical path, so that each of the first and second light rays passing through the first polarizer is rotated in one direction and passes through; the second a polarizer, the second polarizer is arranged on the optical path, and has a crystal optical axis at an angle of 45° to the opposite direction of the polarization rotation direction of the Faraday rotator, passing through the Faraday rotator converting the first ray into an extraordinary ray, converting the second ray into an ordinary ray, and emitting each converted ray; and a second GRIN lens disposed on the second polarizer On the optical path between the second optical fiber and the second optical fiber, the first and second light rays passing through the second polarizer are collected at the end of the second optical fiber.

The above objects and advantages of the present invention will become more apparent by describing the following preferred embodiments in detail with reference to the accompanying drawings.

Figure 1 schematically illustrates a conventional optical isolator;

FIG. 2A shows an optical path of an advancing ray, which sequentially passes through the first polarizer shown in FIG. 1, the Faraday rotator and the second polarizer.

Fig. 2B shows the optical path of a reverse ray, it sequentially passes through the second polarizer shown in Fig. 1, the Faraday rotator and the first polarizer;

Fig. 3 shows the optical structure of the optical isolator of the first embodiment of the present invention;

Fig. 4 is the first polarizer of the first embodiment of the present invention, the perspective view of Faraday rotator and second polarizer;

Fig. 5 shows the optical path of an advancing direction ray, and it sequentially passes through first polarizer shown in Fig. 4, Faraday rotator and second polarizer;

Fig. 6 shows the optical path of a reverse ray, it sequentially passes through the second polarizer shown in Fig. 4, the Faraday rotator and the first polarizer;

Fig. 7 shows the optical structure of the optical isolator of the second embodiment of the present invention;

Fig. 8 shows the optical structure of the optical isolator of the third embodiment of the present invention;

FIG. 9 shows an optical structure of an optical isolator of a fourth embodiment of the present invention.

As shown in FIG. 3, an optical isolator according to the first embodiment of the present invention is arranged on the optical path between the first optical fiber 30 and the second optical fiber 40, including the first optical fiber 30 to the second optical fiber 40 arranged sequentially. A GRIN lens 110 , a first polarizer 120 , a Faraday rotator 130 , a second polarizer 140 and a second GRIN lens 150 . Preferably the respective ends of the first and second optical fibers are secured and aligned by first and second glass collars 35 and 45 . The first GRIN lens 110 converts the divergent light emitted from the first optical fiber 30 into a parallel beam. The first polarizer 120 has a wedge-shaped birefringent crystal, and splits an incident light 50 in a forward direction into first and second light rays 51 and 52 . The first ray 51 is an ordinary ray, which is refracted according to the ordinary refractive index n _o of the first polarizer 120 . The second ray 52 is an extraordinary ray that is _refracted at the extraordinary index ne of the first polarizer 120 .

As shown in FIG. 4, the crystal optical axis 120' of the first polarizer 120 forms an angle of 22.5° with the Y axis of the YZ plane. The first light ray 51 is polarized in a direction denoted D _o parallel to the crystal optical axis 120 ′ of the first polarizer 120 , while the second ray 52 is polarized in a direction denoted D _e perpendicular to the crystal optical axis 120 ′ Up polarized.

The second polarizer 140 has the same wedge-shaped birefringent crystal as the first polarizer 120, and its crystal axis 140' is at -22.5° to the Y-axis of the Y-Z plane. That is, the crystal optical axis 140 ′ of the second polarizer 140 is at an angle of 45° relative to the crystal optical axis 120 ′ of the first polarizer 120 in the direction opposite to the polarization rotation direction of the Faraday rotator 130 .

The Faraday rotator 130 rotates the incident light rays 51 and 52 by 45°. The polarization direction D _o of the first light 51 passing through the first polarizer 120 is rotated by 45° by the Faraday rotator 130 to become a polarization direction denoted by D _o ′. The changed polarization direction D _o ′ of the first ray 51 is perpendicular to the crystal axis 140 ′ of the second polarizer 140 , so that the first ray 51 becomes an extraordinary ray when passing through the second polarizer 140 . In addition, the polarization direction D _e of the second light 52 after passing through the first polarizer 120 is rotated by 45° by the Faraday rotator 130 , thus becoming the polarization direction indicated by D _e ′. The changed polarization direction De _' of the second ray 52 is parallel to the crystal axis 140' of the second polarizer 140, so that the second ray 52 becomes an ordinary ray when passing through the second polarizer 140.

The shapes of the first and second polarizers 120 and 140 are symmetrical with respect to the Faraday rotator 130, and each of the first and second polarizers 120 and 140 is a wedge shape with a wider bottom surface than a top surface.

FIG. 5 shows the optical path of the forward light 50 passing through the first and second polarizers 120 and 140 , and the Faraday rotator 130 . Referring to the figure, when the light 50 traveling parallel to the X axis is incident on the first polarizer 120 , the incident angle θ ₁ of the light 50 is the same as the inclination angle φ ₁ of the first surface 121 of the first polarizer 120 .

Due to the birefringence effect of the first polarizer 120 , the light 50 passing through the first surface 121 is split into a first light 51 and a second light 52 . The first ray 51 is an ordinary ray refracted according to the ordinary refractive index n _o of the first polarizer 120 , and the second ray 52 is an extraordinary ray refracted according to the extraordinary refractive index _ne of the first polarizer 120 .

The outgoing angles θ ₁ and θ ₁ ′ of the first and second light rays 51 and 52 relative to the first surface 121 are, according to Snell’s law of refraction: ${\mathrm{\θ}}_1={\sin }^{-1}\left(\frac{{\mathrm{no}}_{\mathrm{the\; air}}}{{\mathrm{no}}_o}\sin {\mathrm{\θ}}_i\right)\·\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\&Center\; Dot;\left(1\right)$ ${{\mathrm{\θ}}_1}^{\′}={\sin }^{-1}\left(\frac{{\mathrm{no}}_{\mathrm{the\; air}}}{{\mathrm{no}}_e}\sin {\mathrm{\θ}}_i\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\·\&Center\; Dot;\left(2\right)$

Here, n _air is the refractive index of air.

Accordingly, the incident angles of the first and second light rays 51 and 52 with respect to the second surface 122 of the first polarizer 120 are φ ₁ −θ ₁ and φ ₁ −θ ₁ ′, respectively. The exit angles θ ₂ and θ ₂ ′ of the first and second light rays 51 and 52 on the second surface 122 are: ${\mathrm{\θ}}_2={\sin }^{-1}\left[\frac{{\mathrm{no}}_o}{{\mathrm{no}}_{\mathrm{the\; air}}}\sin ({\mathrm{\φ}}_1-{\mathrm{\θ}}_1)\right]\&Center\; Dot;\&Center\; Dot;\·\&Center\; Dot;\·\·\·\·\left(3\right)$ ${{\mathrm{\θ}}_2}^{\′}={\sin }^{-1}\left[\frac{{\mathrm{no}}_e}{{\mathrm{no}}_{\mathrm{the\; air}}}\sin ({\mathrm{\φ}}_1-{{\mathrm{\θ}}_1}^{\′})\right]\&Center\; Dot;\·\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\left(4\right)$

Moreover, the outgoing angles θ ₃ and θ ₃ ′ of the first and second light rays 51 and 52 with respect to the third surface 131 are: ${\mathrm{\θ}}_3={\sin }^{-1}\left(\frac{{\mathrm{no}}_{\mathrm{the\; air}}}{{\mathrm{no}}_f}\sin {\mathrm{\θ}}_2\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(5\right)$ ${{\mathrm{\θ}}_3}^{\′}={\sin }^{-1}\left(\frac{{\mathrm{no}}_{\mathrm{the\; air}}}{{\mathrm{no}}_f}\sin {{\mathrm{\θ}}_2}^{\′}\right)\·\·\·\·\·\·\·\·\left(6\right)$

Here, the refractive index n _f of the Faraday rotator 130 is the same for the rays 51 and 52 .

Moreover, the exit angles θ ₄ and θ ₄ ′ of the first ray 51 and the second ray 52 on the fourth surface 132 are: ${\mathrm{\θ}}_4={\sin }^{-1}\left(\frac{{\mathrm{no}}_f}{{\mathrm{no}}_{\mathrm{the\; air}}}\sin {\mathrm{\θ}}_3\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(7\right)$ ${{\mathrm{\θ}}_4}^{\′}={\sin }^{-1}\left(\frac{{\mathrm{no}}_f}{{\mathrm{no}}_{\mathrm{the\; air}}}\sin {{\mathrm{\θ}}_3}^{\′}\right)\·\·\·\·\·\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(8\right)$

Here, it should be noted that the exit angle θ ₄ in the equation (7) is the same as the exit angle θ ₂ in the equation (5), and the exit angle θ ₄ ′ in the equation (8) is the same as the exit angle in the equation (6). θ ₂ ' is the same.

The exit angles θ ₅ and θ ₅ ′ of the first ray 51 and the second ray 52 on the fifth surface 141 are: ${\mathrm{\θ}}_5={\sin }^{-1}\left(\frac{{\mathrm{no}}_{\mathrm{the\; air}}}{{\mathrm{no}}_2}\sin {\mathrm{\θ}}_4\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\·\&Center\; Dot;\·\·\·\left(9\right)$ ${{\mathrm{\θ}}_5}^{\′}={\sin }^{-1}\left(\frac{{\mathrm{no}}_{\mathrm{the\; air}}}{{\mathrm{no}}_o}\sin {{\mathrm{\θ}}_4}^{\′}\right)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(10\right)$

Here, the first ray 51 is an extraordinary ray, and its refraction angle is according to the directions of the crystal optical axes 120' and 140' of the first and second polarizers 120 and 140, the rotation direction of the Faraday rotator 130 and the second polarizer 140 extraordinary refractive index _ne to determine. Meanwhile, the second ray 52 is an ordinary ray, and its refraction angle is according to the directions of the crystal optical axes 120' and 140' of the first and second polarizers 120 and 140, the rotation direction of the Faraday rotator 130 and the second polarizer 140 normal refractive index n _o to determine.

The incident angles of the first and second light rays 51 and 52 on the sixth surface 142 are θ ₅ +φ ₂ and θ′ ₅ +φ ₂ , respectively. Here, _φ2 is the inclination angle of the sixth surface 142, which is the same as the inclination angle _φ1 of the first surface 121.

The exit angles θ ₆ and θ ₆ ′ of the first and second light rays 51 and 52 on the sixth surface 142 are: ${\mathrm{\θ}}_6={\sin }^{-1}\left[\frac{{\mathrm{no}}_e}{{\mathrm{no}}_{\mathrm{the\; air}}}\sin ({\mathrm{\θ}}_5+{\mathrm{\φ}}_2)\right]\·\·\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\·\&Center\; Dot;\left(11\right)$ ${{\mathrm{\θ}}_6}^{\′}={\sin }^{-1}\left[\frac{{\mathrm{no}}_o}{{\mathrm{no}}_{\mathrm{the\; air}}}\sin ({{\mathrm{\θ}}_5}^{\′}+{\mathrm{\φ}}_2)\right]\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\·\left(12\right)$

Here, n _air = 1, θ _i = φ ₁ , φ ₁ = φ ₂ = 4°, n _o = 2.45 and _ne = 2.709 are substituted into the above equation, the first and second rays 51 on the sixth surface 142 and The outgoing angles θ ₆ and θ ₆ ′ of 52 are equal to -16.848° and -16.842° respectively, and it can be seen that the first and second light rays 51 and 52 passing through the second polarizer 140 are approximately parallel to each other.

Also, the displacements h and h' of the first and second rays 51 and 52 along the Z axis are

h＝t ₁ tan θ ₁ +t ₂ tan θ ₂ +t ₃ tan θ ₃ +t ₄ tan θ ₄ +t ₅ tan θ ₅ (13)

h′=t ₁ tan θ′ ₁ +t ₂ tan θ′ ₂ +t ₃ tan θ′ ₃ +t ₄ tan θ′ ₄ +t ₅ tan θ′ ₅ (14)

Here, _t1 represents the thickness of the first polarizer 120 on the X axis, _t2 is the gap between the first polarizer 120 and the Faraday rotator 130, _t3 is the thickness of the Faraday rotator 130, and _t4 is the Faraday rotator The gap between the polarizer 130 and the second polarizer 140, t ₅ and t ₅ ′ are the thicknesses of the second polarizer 140 where the first and second light rays pass, respectively.

That is, t ₅ ＝T ₅ -(H+t ₁ tan θ ₁ +t ₂ tan θ ₂ +t ₃ tan θ ₃ +t ₄ tan θ ₄ )tanφ ₂

t ₅ ′＝T ₅ -(H+t ₁ tan θ ₁ ′+t ₂ tan θ′ ₂ +t ₃ tan θ′ ₃ +t ₄ tan θ′ ₄ )tanφ ₂

Here, _T5 represents the maximum thickness of the second polarizer 140, H represents the height from the bottom of the first polarizer 140 to the incident point of the light 50, _t1 is represented by _T1 - _Htanφ1 , and _T1 represents the first polarizer 120 the maximum thickness.

The optical path lengths l and l' of the first and first light rays 51 and 52 between the first surface 121 and the second surface 142 can be expressed as follows: $l={\mathrm{no}}_o\frac{t_1}{\cos ({\mathrm{\φ}}_1-{\mathrm{\θ}}_1)}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_2}{\cos {\mathrm{\θ}}_2}+{\mathrm{no}}_f\frac{t_3}{\cos {\mathrm{\θ}}_3}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_4}{\cos {\mathrm{\θ}}_4}+{\mathrm{no}}_e\frac{t_5}{\cos {\mathrm{\θ}}_5}---\left(15\right)$ $l^{\′}={\mathrm{no}}_e\frac{t_1}{\cos ({\mathrm{\φ}}_1-{{\mathrm{\θ}}_1}^{\′})}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_2}{\cos {{\mathrm{\θ}}_2}^{\′}}+{\mathrm{no}}_f\frac{t_3}{\cos {{\mathrm{\θ}}_3}^{\′}}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_4}{\cos {{\mathrm{\θ}}_4}^{\′}}+{\mathrm{no}}_o\frac{{t_5}^{\′}}{\cos {\mathrm{\θ}}_5}---\left(16\right)$

Suppose the values of L and M determined by t ₁ , t ₂ , t ₃ and t ₄ are as follows $L={\mathrm{no}}_o\frac{t_1}{\cos ({\mathrm{\φ}}_1-{\mathrm{\θ}}_1)}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_2}{\cos {\mathrm{\θ}}_2}+{\mathrm{no}}_f\frac{t_3}{\cos {\mathrm{\θ}}_3}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_4}{\cos {\mathrm{\θ}}_4}$ $m={\mathrm{no}}_e\frac{t_1}{\cos ({\mathrm{\φ}}_1-{{\mathrm{\θ}}_1}^{\′})}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_2}{\cos {{\mathrm{\θ}}_2}^{\′}}+{\mathrm{no}}_f\frac{t_3}{\cos {{\mathrm{\θ}}_3}^{\′}}+{\mathrm{no}}_{\mathrm{the\; air}}\frac{t_4}{\cos {{\mathrm{\θ}}_4}^{\′}},$

Equations 15 and 16 can be expressed as follows: $l=L+{\mathrm{no}}_e\frac{t_5}{\cos {\mathrm{\θ}}_5}\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(17\right)$ $l^{\′}=m+{\mathrm{no}}_o\frac{{t_5}^{\′}}{\cos {{\mathrm{\θ}}_5}^{\′}}\&Center\; Dot;\&Center\; Dot;\·\·\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(18\right)$

The optical path difference Δ1=1−1′ between the first ray 51 and the second ray 52 can be expressed by Equations 17 and 18 as follows $\mathrm{\Δl}=(L-m)+{\mathrm{no}}_e\frac{t_5}{\cos {\mathrm{\θ}}_5}-{\mathrm{no}}_o\frac{{t_5}^{\′}}{\cos {{\mathrm{\θ}}_5}^{\′}}\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\left(19\right)$

Here, Δ1 is the value that determines the polarization dispersion, and this value is preferably the minimum value that satisfies the following equation, $L-m\&Greater\; Equal;0,{\mathrm{no}}_e\frac{t_5}{\cos {\mathrm{\&theta;}}_5}{-\mathrm{no}}_o\frac{{t_5}^{\&prime;}}{\cos {{\mathrm{\&theta;}}_5}^{\&prime;}}\&le;0\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&CenterDot;\&CenterDot;\&CenterDot;\left(20\right)$ $L-m<0,{\mathrm{no}}_e\frac{t_5}{\cos {\mathrm{\&theta;}}_5}-{\mathrm{no}}_o\frac{{t_5}^{\&prime;}}{\cos {{\mathrm{\&theta;}}_5}^{\&prime;}}>0\&Center\; Dot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;\&CenterDot;\left(\mathrm{twenty\; one}\right)$

That is, the polarization dispersion of the optical isolator can be compensated by adjusting the optical path length by controlling the thickness of the second polarizer (which is a factor for determining t ₅ and t ₅ ′).

Meanwhile, referring to FIG. 6, when the light 60 emitted by the second optical fiber 40 propagates toward the first optical fiber 30, the first light 61, which is divided into normal light in the second polarizer 140, passes through the Faraday rotator 130 and the first polarization After the polarizer 120, it becomes an ordinary ray, and the second ray 62 that is divided into an extraordinary ray in the second polarizer 140 becomes an extraordinary ray after passing through the Faraday rotator 130 and the first polarizer 120. This is according to the Faraday rotator 130 The direction of polarization rotation is determined by the respective crystal axes of the first and second polarizers 120 and 140 . The exit angles of the first and second light rays 61 and 62 toward the first optical fiber 30 are different from each other, which will be described in detail below.

The light ray 60 incident to the sixth surface 142 is divided into first and second light rays 61 and 62 traveling on different optical paths from each other due to the birefringence characteristic of the second polarizer 140 . The first ray 61 is an ordinary ray refracted according to the ordinary refractive index n _o of the second polarizer 140 , and the second ray 62 is an extraordinary ray refracted according to the extraordinary refractive index _ne of the second polarizer 140 .

When the incident angle of the ray 60 is  _i , the outgoing angle  ₂ of the first ray 61 and the outgoing angle  ₂ ′ of the second ray 62 on the sixth surface 142, according to Snell's law, are as follows:

Accordingly, the incident angles of the first and second light rays 61 and 62 on the fifth surface 141 are φ ₂ − ₁ and φ ₂ − ₁ ′, respectively. The exit angles  ₂ and  ₂ ′ of the first and second rays 61 and 62 on the fifth surface 141 are

The exit angles  ₃ and  ₃ ′ of the first ray and the second ray 61 and 62 on the fourth surface 132 are

Moreover, the exit angles  ₄ and  ₄ ′ of the first and second rays 61 and 62 on the third surface 131 are

Here, it can be seen that the exit angle  ₄ is the same as the exit angle ′ ₂ in Equation 26, and the exit angle  ₄ ′ is the same as  ₂ ′ in Equation 27.

Also, the exit angles _φ5 and _φ5 ′ of the first and second rays 61 and 62 on the second surface 122 are:

The incident angles of the first and second rays 61 and 62 on the first surface 121 are φ ₅ +φ ₁ and φ ₅ ′ +φ ₁ , respectively. Here _1 is the inclination angle of the first surface 121, which is the same as the inclination angle _2 of the sixth surface 142.

The exit angles  ₆ and  ₆ ′ of the first and second light rays 61 and 62 on the first surface 122 are Simplifying Equation 32 with Equations 22, 24 and 30, _6 can be expressed as follows

Simplifying Equation 33 using Equations 23, 25 and 31,  ₆ ′ can be expressed as follows

Here, when  _i =-16.84°, φ ₁ =φ ₂ =4°, n _o =2.45, n _e =2.709, n _air =1, the first and second light rays 61 and 61 on the first surface 121 and The outgoing angles  ₆ and  ₆ ′ of 62 are equal to -2.964° and -5.047°, respectively. Therefore, it can be seen that the first and second light rays 61 and 62 passing through the second polarizer 140 are non-parallel, and thus, reverse light rays are blocked.

Next, an optical isolator according to a second embodiment of the present invention will be described with reference to FIG. 7. FIG. Here, the same numerals represent the same elements having the same functions.

The feature of the second embodiment of the present invention is that the first GRIN lens 110' is installed at the end of the first optical fiber 30, and through the first holder 38, the first GRIN lens 110' is combined with the first glass ring 35' so as to Quasi-first optical fiber 30. Also, the incident surface of the first polarizer 120 , that is, the exit surface 112 of the first GRIN lens 110 ′ facing the first surface 121 forms an angle parallel to the first surface 121 . Based on the above structure, due to the difference between the refractive index of the first GRIN lens 110' and the refractive index of air, the light emitted by the first optical fiber can be refracted to a desired position, so that the first optical fiber can be oriented parallel to the X axis .

Also, a second GRIN lens 150 ′ is installed at the end of the second optical fiber 40 , combined with the second glass ring 45 through the second holder 48 so as to align the second optical fiber 40 . Moreover, the incident surface 151 of the second GRIN lens 150' is at a parallel angle to the exit surface of the second polarizer 140, ie parallel to the sixth surface, so that the second optical fiber 40 can be parallel to the X-axis as described above.

As described above, by improving the structures of the first and second GRIN lenses, the optical arrangement of the first and second optical fibers 30 and 40 can be simplified.

Referring now to FIG. 8, an optical isolator according to a third embodiment of the present invention will be described in detail. Here, the same numerals represent the same elements having the same functions. The optical isolator according to this embodiment further includes a prism 160 disposed along the optical path between the first GRIN lens 110 and the first polarizer 120 , the prism facilitates the arrangement of the first optical fiber 30 .

The incident surface 161 of the prism 160 facing the first GRIN lens 110 is perpendicular to the X axis, that is, perpendicular to the axis of the incident light, and the exit surface 162 is at a parallel angle to the first surface 121, that is, parallel to the incident surface of the first polarizer 120 . Therefore, the advancing direction of the light 50 emitted from the first optical fiber 30 can be changed by refraction, thus making it easy to arrange the first optical fiber 30 . At this time, the incident surface 161 of the first prism 160 is not limited to be perpendicular to the X axis. The incident surface may form an angle within a critical angle of refraction with respect to the incident ray 50 .

Referring to FIG. 9, an optical isolator according to a fourth embodiment of the present invention further includes a prism 170 to facilitate the optical arrangement of the second optical fiber 40, the prism is installed between the second polarizer 140 and the second GRIN lens 150 for light on the way.

Preferably, the incident surface 171 of the prism 170 is at an angle parallel to the sixth surface 142 , that is, parallel to the exit surface of the second polarizer 140 . At this time, since the traveling direction of light passing through the second polarizer 140 can be changed by refraction, the optical arrangement of the second optical fiber 40 is facilitated.

An optical isolator (not shown) according to another embodiment of the present invention may have both the prisms 160 and 170 shown in FIGS. 8 and 9 .

As mentioned above, with respect to the crystal optical axis of the first polarizer 120 in FIG. A polarizer 120 turns ordinary rays into extraordinary rays and vice versa. Therefore, without additional optical elements, the first ray 51 and the second ray 52 are emitted parallel to each other, and by adjusting the optical path difference between the first ray 51 and the second ray 52, the effect of polarization dispersion can be reduced. (work-off) decreases.

Claims (11)

1. optical isolator, described optical isolator is arranged on the light path between first optical fiber and second optical fiber, according to the polarization of incident light state, transmits the light that is transmitted into second optical fiber by described first optical fiber, prevention is by the light of described second optical fiber emission, and described optical isolator comprises:

The one GRIN (graded index) lens, described lens will be transformed into parallel beam by the light of described first optical fiber emission;

First polarizer, described first polarizer be along the light path setting, relies on its optical axis of crystal to make described parallel beam be become to be first light of ordinary ray and to be second light of special ray by birefringence, and they are passed;

Faraday polarization apparatus, described Faraday polarization apparatus is set on the described light path, each described first and second light through described first polarizer is rotated in one direction, and passes through;

Second polarizer, described second polarizer is set on the described light path, and has a optical axis of crystal with the opposite direction angle at 45 of the polarization sense of rotation of described Faraday polarization apparatus, described first light that passes described Faraday polarization apparatus is transformed into special ray, described second light is transformed into ordinary ray, and penetrates the light that each is changed; With

Second grin lens, described second grin lens are set on the light path between described second polarizer and described second optical fiber, will pass the end of described first and second light-ray condensings of described second polarizer at described second optical fiber.

2. optical isolator according to claim 1 wherein, supposes to be decided by the described first polarizer thickness t ₁, clearance t between described first polarizer and the Faraday polarization apparatus ₂, described Faraday polarization apparatus thickness t ₃And clearance t between the described Faraday polarization apparatus and second polarizer ₄L and M value as follows $L=n_o\frac{t_1}{\cos ({\mathrm{\&phi;}}_1-{\mathrm{\&theta;}}_1)}+n_{\mathrm{air}}\frac{t_2}{\cos {\mathrm{\&theta;}}_2}+n_f\frac{t_3}{\cos {\mathrm{\&theta;}}_3}+n_{\mathrm{air}}\frac{t_4}{\cos {\mathrm{\&theta;}}_4}$ $M=n_e\frac{t_1}{\cos \left({\mathrm{\&phi;}}_1{{\mathrm{\&theta;}}_1}^{\&prime;}\right)}+n_{\mathrm{air}}\frac{t_2}{\cos {{\mathrm{\&theta;}}_2}^{\&prime;}}+n_f\frac{t_3}{\cos {{\mathrm{\&theta;}}_3}^{\&prime;}}+n_{\mathrm{air}}\frac{t_4}{\cos {{\mathrm{\&theta;}}_4}^{\&prime;}},$

As the optical path length l of described first and second light between described first and second polarizers and l ' during by following expression $l=L+n_e\frac{t_5}{\cos {\mathrm{\&theta;}}_5}\mathrm{and}{l}^{\&prime;}=M+n_o\frac{{t_5}^{\&prime;}}{\cos {{\mathrm{\&theta;}}_5}^{\&prime;}}$ And as the optical path difference Δ l=l-l ' between described first and first light during by following expression $\mathrm{\&Delta;l}=(L-M)+n_e\frac{t_5}{\cos {\mathrm{\&theta;}}_5}-n_o\frac{{t_5}^{\&prime;}}{\cos {{\mathrm{\&theta;}}_5}^{\&prime;}}$ When $L-M\&GreaterEqual;0,n_e\frac{t_5}{\cos {\mathrm{\&theta;}}_5}-n_o\frac{{t_5}^{\&prime;}}{\cos {{\mathrm{\&theta;}}_5}^{\&prime;}}\&le;0$ When $L-M<0,n_e\frac{t_5}{\cos {\mathrm{\&theta;}}_5}-n_o\frac{{t_5}^{\&prime;}}{\cos {{\mathrm{\&theta;}}_5}^{\&prime;}}>0,$

Wherein, n _eAnd n _oBe respectively the normal refraction rate and the extraordinary refractive index of described first and second polarizers; n _AirIt is air refraction; n _fIt is the refractive index of Faraday polarization apparatus; t ₁Be the thickness of described first polarizer in light incident place; t ₂It is distance between described first polarizer and the Faraday polarization apparatus; t ₃Be described Faraday polarization apparatus thickness; t ₄It is distance between the described Faraday polarization apparatus and second polarizer; t ₅And t ₅' be respectively the described second polarizer thickness at the described first and second beam projecting places; θ ₁And θ ₁' be respectively the emergence angle of described first the above first and second light of polarizer incidence surface; θ ₂And θ ₂' be respectively the emergence angle of described first the above first and second light of polarizer exit surface; θ ₃And θ ₃' be respectively the above first and second beam projecting angle of described Faraday polarization apparatus incidence surface; θ ₄And θ ₄' be respectively the above first and second beam projecting angle of described Faraday polarization apparatus exit surface; θ ₅And θ ₅' be respectively the emergence angle of described second the above first and second light of polarizer incidence surface.

3. optical isolator according to claim 1, wherein, described first and second polarizers all have the birefringece crystal of a wedge shape, and its basal surface is bigger than top surface, with respect to the setting that is mutually symmetrical of described Faraday polarization apparatus.

4. optical isolator according to claim 1, wherein, parallel with the light incidence surface of described first polarizer towards the beam projecting surface of described first grin lens of the described first polarizer light incidence surface.

5. optical isolator according to claim 4 also comprises:

The first glass ring, this first glass ring makes the end alignment of described first optical fiber; With

First retainer, described retainer fits together described first grin lens and the described first glass ring.

6. optical isolator according to claim 1, wherein, parallel with the beam projecting surface of described second polarizer towards the light incidence surface of described second grin lens on the beam projecting surface of described second polarizer.

7. optical isolator according to claim 6 also comprises:

The second glass ring, this second glass ring makes the end alignment of described second optical fiber; With

Second retainer, described retainer fits together described second grin lens and the second glass ring.

8. optical isolator according to claim 1 also comprises:

Prism, described prism are arranged on the light path between described first polarizer and first grin lens, by reflecting the light by it light path of advancing of one light are changed.

9. optical isolator according to claim 8, wherein, parallel with the light incidence surface of described first polarizer towards the beam projecting surface of the described prism of the described first polarizer light incidence surface.

10. optical isolator according to claim 1 also comprises:

Prism, described prism are arranged on the light path between described second polarizer and second grin lens, by reflecting the light by it, the light path of advancing of a light are changed.

11. optical isolator according to claim 10 is wherein, parallel with the beam projecting surface of described second polarizer towards the light incidence surface of the described prism on the described second polarizer beam projecting surface.

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