A magneto-optical variable optical attenuator

Abstract

A magneto-optical adjustable optical attenuator includes, in order along the propagation direction of light: an input collimator, a first birefringent crystal, a first half-wave plate, a first Faraday rotator, a second Faraday rotator, a polarizer, a second half-wave plate, a second birefringent crystal and an output collimator; a variable magnetic field applying mechanism is provided on the periphery of the first Faraday rotator and the second Faraday rotator; the magnetic field direction of the variable magnetic field applying mechanism is parallel to the horizontal axis. The present invention changes the polarization state of light passing through the Faraday rotator by changing the magnetic field intensity passing through the Faraday rotator, thereby changing the polarization state of light passing through the polarizer as a polarizer. The polarizer absorbs light that is not parallel to its polarization direction. The function of adjusting the attenuation of light intensity is realized. The structure is simple, easy to assemble, convenient to control, has high working reliability, low product cost and less stray light.

Description

Technical Field

[0001] The invention belongs to the technical field of optical devices, and in particular relates to a magneto-optical adjustable light attenuator. Background Art

[0002] In optical fiber communication systems, there are many scenarios where the power of optical signals needs to be reduced. For example, optical receivers are very sensitive to optical power overload, and the input power must be controlled within the input range of the optical receiver to prevent saturation. The balance between the input powers of different channels before the optical amplifier can prevent the input power of one or some channels from being too high and the gain saturation of the optical amplifier.

[0003] Optical attenuators can attenuate the power of optical signals as required by users. Optical attenuators include mechanical optical attenuators, magneto-optical adjustable optical attenuators, micro-electromechanical system optical attenuators, thermal optical attenuators, and acousto-optic attenuators.

[0004] The magneto-optical variable optical attenuator has the advantages of fast response speed, insensitivity to ambient temperature, and not prone to classical breakdown.

[0005] Traditional magneto-optical variable optical attenuators generally change the polarization state of the signal light passing through the Faraday rotator in the magnetic field by changing the magnetic field strength, thereby changing the signal light path and reducing the coupling efficiency between the signal light and the receiving collimator. This implementation scheme easily increases the stray light in the optical path, causing unnecessary return loss and crosstalk. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a magneto-optical variable optical attenuator, which uses fewer components, has a smaller size, and reduces the influence of stray light.

[0007] The present invention is achieved in that:

[0008] A magneto-optical adjustable optical attenuator comprises, in order along the propagation direction of light: an input collimator, a first birefringent crystal, a first half-wave plate, a first Faraday rotator, a second Faraday rotator, a polarizer, a second half-wave plate, a second birefringent crystal and an output collimator;

[0009] The first Faraday rotator and the second Faraday rotator are surrounded by a variable magnetic field applying mechanism;

[0010] The magnetic field direction of the variable magnetic field applying mechanism is parallel to the horizontal axis.

[0011] Furthermore, the input collimator and the output collimator both include: a lens, a single-mode optical fiber head, a glass tube or a metal tube; the lens, the single-mode optical fiber head, the glass tube or the metal tube are bonded together by glue.

[0012] Furthermore, the lens is a C-type lens or a self-focusing lens; and the single-mode optical fiber head contains a wedge-angled oblique end surface.

[0013] Furthermore, the optical axis directions of the first birefringent crystal and the second birefringent crystal are parallel to the plane composed of ordinary light and extraordinary light, and have a certain angle with the propagation direction of the light beam incident into the first birefringent crystal and the second birefringent crystal.

[0014] Furthermore, the optical axis directions of the first half-wave plate and the second half-wave plate form an angle of 45 degrees with the polarization direction of the extraordinary light.

[0015] Furthermore, the polarization direction of the polarizer is parallel or perpendicular to the polarization direction of ordinary light.

[0016] Furthermore, the variable magnetic field applying mechanism is an induction coil, and the magnetic field strength is controlled by controlling the amount of current flowing into the induction coil.

[0017] Furthermore, the first Faraday rotator and the second Faraday rotator are Faraday rotators without their own magnetic field.

[0018] The advantages of the present invention are: simple optical path structure, small size, no moving parts, good reliability and repeatability, simple debugging and assembly, low material cost, and less stray light in the optical path. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0020] Figure 1 The diagram is a schematic diagram of the structure and optical path of the magneto-optical variable optical attenuator of the present invention.

[0021] Figure 2 It is a schematic diagram of the optical axis directions of the first birefringent crystal and the second birefringent crystal, the positional relationship between the first birefringent crystal and the first half-wave plate, and the optical axis direction of the first half-wave plate, the positional relationship between the second half-wave plate and the second birefringent crystal, and the optical axis direction of the second half-wave plate in the present invention.

[0022] Marked in the figure: 100, incident light beam, 110, first polarized light beam, 120, second polarized light beam, 130, outgoing light beam.

[0023] 200. Input collimator; 201. First birefringent crystal; 202. First half-wave plate; 203. First Faraday rotator; 204. Second Faraday rotator; 205. Variable magnetic field applying mechanism; 206. Polarizer; 207. Second half-wave plate; 208. Second birefringent crystal; 209. Output collimator; B. Direction of magnetic field applied by variable magnetic field applying mechanism. DETAILED DESCRIPTION

[0024] like Figure 1 As shown, a magneto-optical variable optical attenuator includes, in sequence along the propagation direction of light: an input collimator 200, a first birefringent crystal 201, a first half-wave plate 202, a first Faraday rotator 203, a second Faraday rotator 204, a variable magnetic field applying mechanism 205, a polarizer 206, a second half-wave plate 207, a second birefringent crystal 208, and an output collimator 209.

[0025] The first Faraday rotator 203 and the second Faraday rotator 204 are surrounded by a variable magnetic field applying mechanism 205 .

[0026] like Figure 2 As shown, the optical axis directions of the first birefringent crystal 201 and the second birefringent crystal 208 are parallel to the plane composed of ordinary light and extraordinary light, and have a certain angle with the propagation direction of the light beam incident into the birefringent crystal.

[0027] The direction of the magnetic field B of the variable magnetic field applying mechanism 205 is parallel to the horizontal axis.

[0028] The optical axis directions of the first half-wave plate 202 and the second half-wave plate 207 form an angle of 45 degrees with the polarization direction of the extraordinary light.

[0029] The polarization direction of the polarizer 206 is parallel to the polarization direction of ordinary light.

[0030] The variable magnetic field applying mechanism 205 is an induction coil 205. The intensity of the magnetic field B can be controlled by controlling the amount of current supplied to the induction coil 205.

[0031] The first Faraday rotator 203 and the second Faraday rotator 204 are Faraday rotators without their own magnetic fields.

[0032] Working principle: Figure 1As shown, the light 100 emitted from the input collimator 200 is incident on the first birefringent crystal 201 and is divided into a first polarized light beam 110 and a second polarized light beam 120 whose polarization directions are perpendicular to each other. After the first polarized light beam 110 passes through the first half-wave plate 202, the polarization direction of the light beam rotates 90° and is parallel to the polarization direction of the second polarized light beam 120. The first polarized light beam 110 and the second polarized light beam 120 pass through the first Faraday rotator 203 and the second Faraday rotator 204 in sequence. When the induction coil 205 is not energized, the magnetic field B is equal to 0. When the first polarized light beam 110 and the second polarized light beam 120 pass through the first Faraday rotator 203 and the second Faraday rotator 204, the polarization direction does not deflect. The first polarized light beam 110 and the second polarized light beam 120 then enter the polarizer 206, at which time the polarization directions of the first polarized light beam 110 and the second polarized light beam 120 are parallel to the polarization direction of the polarizer 206. The first polarized light beam 110 and the second polarized light beam 120 are not absorbed by the polarizer 206. The light intensity does not change. After the first polarized light beam 110 passes through the second half-wave plate 207, the polarization of the light beam is rotated by 90°, which is perpendicular to the polarization direction of the second polarized light beam 120. The first polarized light beam 110 and the second polarized light beam 120 enter the second birefringent crystal 208 to synthesize the output light beam 130, which is then received by the input collimator 209. Thus, lossless optical transmission of polarization-independent optical signals from the incident port to the output port is achieved.

[0033] When the induction coil 205 is powered on, the magnetic field intensity B increases. When the first polarized light beam 110 and the second polarized light beam 120 pass through the first Faraday rotator 203 and the second Faraday rotator 204, the polarization direction is deflected by more than 0° and less than or equal to 90°. The first polarized light beam 110 and the second polarized light beam 120 enter the polarizer 206, at which time the polarization directions of the first polarized light beam 110 and the second polarized light beam 120 are not parallel to the polarization direction of the polarizer 206. The first polarized light beam 110 and the second polarized light beam 120 are partially absorbed by the polarizer 206. The light intensity becomes weaker. After the first polarized light beam 110 passes through the second half-wave plate 207, the polarization of the light beam is rotated by 90°, which is perpendicular to the polarization direction of the second polarized light beam 120. The first polarized light beam 110 and the second polarized light beam 120 enter the second birefringent crystal 208, synthesize the output light beam 130, and the output light beam 130 is received by the input collimator 209. In this way, the transmission of the magnetically controlled light attenuation of the polarization-independent optical signal from the incident port to the output port is realized.

[0034] The above description is about the implementation form of the Bright type magneto-optical variable optical attenuator. By replacing the polarizer 206 with a polarizer whose polarization direction is perpendicular to the polarization direction of ordinary light, a Dark type magneto-optical variable optical attenuator can be obtained.

[0035] The present invention adjusts the magnitude of the current of the induction coil and then adjusts the magnitude of the variable magnetic field, thereby achieving adjustment of the attenuation of the optical signal.

[0036] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A magneto-optical variable optical attenuator, characterized in that: The optical system includes: an input collimator, a first birefringent crystal, a first half-wave plate, a first Faraday rotator, a second Faraday rotator, a polarizer, a second half-wave plate, a second birefringent crystal and an output collimator in sequence along the propagation direction of light; The first Faraday rotator and the second Faraday rotator are surrounded by a variable magnetic field applying mechanism; The magnetic field direction of the variable magnetic field applying mechanism is parallel to the horizontal axis; The optical axis directions of the first birefringent crystal and the second birefringent crystal are parallel to the plane composed of ordinary light and extraordinary light, and have a certain angle with the propagation direction of the light beam incident into the first birefringent crystal and the second birefringent crystal; The optical axis directions of the first half-wave plate and the second half-wave plate form an angle of 45 degrees with the polarization direction of the extraordinary light; The polarization direction of the polarizer is parallel or perpendicular to the polarization direction of ordinary light.

2. The magneto-optical variable optical attenuator according to claim 1, characterized in that: The input collimator and the output end collimator both comprise: a lens, a single-mode optical fiber head, a glass tube or a metal tube; the lens, the single-mode optical fiber head, the glass tube or the metal tube are bonded together by glue.

3. The magneto-optical variable optical attenuator according to claim 2, characterized in that: The lens is a C-type lens or a self-focusing lens; the single-mode optical fiber head has a wedge-angled oblique end surface.

4. The magneto-optical variable optical attenuator according to claim 1, characterized in that: The variable magnetic field applying mechanism is an induction coil, and the magnetic field strength is controlled by controlling the amount of current flowing into the induction coil.

5. The magneto-optical variable optical attenuator according to claim 1, characterized in that: The first Faraday rotator and the second Faraday rotator are Faraday rotators without their own magnetic fields.

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