Nondestructive magneto-optical switch and wave plate included angle adjusting method

Abstract

The invention discloses a lossless magneto-optical switch and a wave plate included angle adjusting method, and belongs to the field of optics, an input end is located on one side of a single-fiber collimator, and a first output end and a second output end are located on a third birefringent crystal I. By adopting a plurality of wave plate assemblies, a main sub-beam and a weak sub-beam can be accurately converged to the output ends; when the optical channels are switched, the intensities on the paths of the strong light and the weak light are essentially exchanged, the strong light and the weak light are coupled into different channels, and the sum of the energy at the first output end and the energy at the second output end and the sum of the energy at the first output end and the energy at the second output end after switching are always in a stable state. The change of the rotation angle of the Faraday optical rotation crystal is converted into the phase delay change of polarized light by the 1 / 4 wave plate, the phase delay change of the polarized light is reduced by the full wave plate, the angular dispersion of the Faraday optical rotation crystal is eliminated, and the problem of optical crosstalk generated in an optical transmission system is effectively solved.

Description

Technical Field

[0001] The invention relates to the field of optical elements, in particular to a lossless magneto-optical switch. Background Art

[0002] In the field of fiber-optic communication, optical switches, as an important component of passive devices, are widely used in fiber-optic communication networks to selectively switch optical signals. Magneto-optical switches are optical switches that use the Faraday magneto-optical effect. They mainly change the direction of the Faraday rotation angle in the magneto-optical crystal by changing the direction of the external magnetic field, thereby achieving the purpose of switching the optical path. Compared with traditional optical switches, magneto-optical switches have the advantages of fast switching speed, no moving parts, and high stability, and have received more and more attention and research.

[0003] At present, common magneto-optical switches do not satisfy the energy conservation law during the switching process, that is, the sum of the energy of the connected optical path and the closed optical path cannot maintain a stable value, and the energy loss caused by the switch seriously affects the stability of the optical transmission system. The lossless magneto-optical switch realizes the function of low energy loss during the switch switching process, greatly improving the stability of the optical transmission system, but the existing lossless magneto-optical switch has the problem of poor directionality, which will cause the problem of optical signal crosstalk, which is not conducive to the optical transmission system to selectively switch the optical signal. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, one of the objectives of the present invention is to provide a lossless magneto-optical switch with good directivity.

[0005] In order to overcome the shortcomings of the prior art, a second object of the present invention is to provide a method for adjusting the angle of a wave plate of a lossless magneto-optical switch with good directivity.

[0006] One of the purposes of the present invention is achieved by the following technical solution:

[0007] A lossless magneto-optical switch comprises a single-fiber collimator, a first birefringent crystal, a first wave plate assembly, a quarter wave plate, a full wave plate, a Faraday rotator crystal, a second birefringent crystal, a second wave plate assembly, a third wave plate assembly and a third birefringent crystal, wherein the single-fiber collimator is located on a side of the first birefringent crystal away from the first wave plate assembly, and the lossless magneto-optical switch is provided with an input end, a first output end and a second output end, wherein the input end is located on one side of the single-fiber collimator, and the first output end and the second output end are located on one side of the third birefringent crystal.

[0008] The parallel light beam emitted by the single-fiber collimator is decomposed into two main sub-beams with orthogonal polarization directions through the first birefringent crystal. The polarization directions of the two main sub-beams are changed to be parallel to each other after passing through the first wave plate assembly. The 1 / 4 wave plate can convert the change of the rotation angle of the Faraday rotator crystal into the phase delay change of the polarized light. The full-wave plate can reduce the phase delay change of the polarized light, thereby eliminating the angular dispersion of the Faraday rotator crystal.

[0009] When the optical path from the input end to the first output end is working, the polarization directions of the two main sub-beams with mutually parallel polarization directions rotate counterclockwise after passing through the Faraday rotator crystal and generate two weak sub-beams, the two main sub-beams do not deviate when passing through the second birefringent crystal, the two weak sub-beams deviate when passing through the second birefringent crystal, the two main sub-beams rotate counterclockwise when passing through the upper area of ​​the second wave plate component, the two weak sub-beams rotate counterclockwise when passing through the lower area of ​​the second wave plate component, the polarization directions of the two main sub-beams and the two weak sub-beams are changed to be orthogonal to each other when passing through the third wave plate component, the two main sub-beams combine to enter the first output end when passing through the third birefringent crystal, the two weak sub-beams combine to enter the second output end, and the directionality of the lossless magneto-optical switch is from the input end to the second output end;

[0010] When the optical path channel from the input end to the second output end is working, the polarization directions of the two main sub-beams with mutually parallel polarization directions rotate clockwise after passing through the Faraday rotator crystal and generate two weak sub-beams, the two main sub-beams are offset after passing through the second birefringent crystal, and the two weak sub-beams are not offset after passing through the second birefringent crystal, the two main sub-beams rotate counterclockwise when passing through the lower area of ​​the second wave plate component, and the two weak sub-beams rotate counterclockwise when passing through the upper area of ​​the second wave plate component, and the polarization directions of the two main sub-beams and the two weak sub-beams are changed to be orthogonal to each other when passing through the third wave plate component, and the two main sub-beams and the two weak sub-beams are combined to enter the second output end when passing through the third birefringent crystal, and the two main sub-beams combine to enter the first output end. At this time, the directionality of the lossless magneto-optical switch is from the input end to the first output end.

[0011] Furthermore, the angle between the optical axis direction of the quarter wave plate and the optical axis direction of the first birefringent crystal is 45°.

[0012] Furthermore, the angle between the optical axis of the full-wave plate and the optical axis of the first birefringent crystal is -46°.

[0013] Furthermore, the first wave plate assembly includes two half-wave plates, which are arranged on the left and right, and have different optical axes.

[0014] Furthermore, the second wave plate assembly includes two half-wave plates, which are arranged one above the other and have different optical axes.

[0015] Furthermore, when the optical path channel from the input end to the first output end is working, the two main sub-beams are ordinary light when passing through the Faraday rotator crystal, and the two weak sub-beams generated are extraordinary light; when the optical path channel from the input end to the second output end is working, the two main sub-beams are extraordinary light when passing through the Faraday rotator crystal, and the two weak sub-beams generated are ordinary light.

[0016] Furthermore, the second wave plate assembly rotates the polarization directions of the main sub-beam and the weak sub-beam at different angles.

[0017] Furthermore, when the optical path channel from the input end to the first output end is working, the polarization directions of the two main sub-beams are rotated 45° counterclockwise when viewed along the optical path transmission direction, and the polarization directions of the two weak sub-beams are rotated 135° counterclockwise when viewed along the optical path transmission direction; when the optical path channel from the input end to the second output end is working, the polarization directions of the two main sub-beams are rotated 135° counterclockwise when viewed along the optical path transmission direction, and the polarization directions of the two weak sub-beams are rotated 45° counterclockwise when viewed along the optical path transmission direction.

[0018] Furthermore, the lossless magneto-optical switch also includes a roof prism and a dual-fiber output collimator, the roof prism is located between the second wave plate assembly and the third wave plate assembly, and the dual-fiber output collimator is located between the third birefringent crystal and the first output end and the second output end.

[0019] The second object of the present invention is achieved by adopting the following technical solution:

[0020] A method for adjusting the wave plate angle based on any one of the above lossless magneto-optical switches comprises the following steps:

[0021] The Jones matrix expression of the first wave plate component is:

[0022]

[0023] Wherein, θ1 is the angle between the optical axis direction of the first wave plate assembly and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ1 is the phase delay of the first wave plate assembly, and θ1 and δ1 are known values ​​according to the specific structure of the lossless magneto-optical switch;

[0024] The Jones matrix expression of the 1 / 4 wave plate is:

[0025]

[0026] Wherein, θ2 is the angle between the optical axis direction of the 1 / 4 wave plate and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ2 is the phase delay of the 1 / 4 wave plate, θ2 is the angle to be solved, and δ2 is a known value;

[0027] The Jones matrix expression of the full-wave plate is:

[0028]

[0029] Wherein, θ3 is the angle between the optical axis direction of the full-wave plate and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ3 is the phase delay of the full-wave plate, θ3 is the angle to be solved, and δ3 is a known value;

[0030] The Jones matrix expression of the Faraday optically active crystal is:

[0031]

[0032] Where θ4 is the rotation angle of the polarization direction of the sub-beam after passing through the Faraday rotator crystal,

[0033] θ4=45+k0(λ-λc)+k1(T-Tc) (5)

[0034] Wherein, k0 is the wavelength correlation coefficient of the Faraday rotator crystal, λ is the wavelength of the incident light in a vacuum, λc is the central wavelength of the magneto-optical switch, k1 is the temperature correlation coefficient of the Faraday rotator crystal, T is the temperature at which the magneto-optical switch works, and Tc is the room temperature of 23°C;

[0035] The Jones matrix expression of the second wave plate component is:

[0036]

[0037] Wherein, θ5 is the angle between the optical axis direction of the second wave plate assembly and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ5 is the phase delay of the second wave plate assembly, and θ5 and δ5 are known values;

[0038] The Jones matrix expression of the third wave plate assembly is:

[0039]

[0040] Wherein, θ6 is the angle between the optical axis direction of the third wave plate assembly and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ6 is the phase delay of the third wave plate assembly, and θ6 and δ6 are known values;

[0041] When the optical path from the input end to the first output end is working, the directionality of the lossless magneto-optical switch is from the input end to the second output end.

[0042] The Jones matrix expression of the forward transmission of ordinary light o is:

[0043]

[0044] The Jones matrix expression of the forward transmission of extraordinary light e-light is:

[0045]

[0046] When the optical path from the input end to the second output end is working, the directionality of the lossless magneto-optical switch is from the input end to the first output end.

[0047] The Jones matrix expression of ordinary light o forward transmission is:

[0048]

[0049] The Jones matrix expression of the forward transmission of extraordinary light e-light is:

[0050]

[0051] Since Mo1 and Me1 are positively correlated, and Mo2 and Me2 are positively correlated, when Mo1 is at its maximum value, Me1 is also at its maximum value; when Mo2 is at its maximum value, Me2 is also at its maximum value; therefore, when any one of Mo1 and Me1 is at its maximum value and any one of Mo2 and Me2 is at its maximum value, the corresponding value of θ2 is the angle between the optical axis direction of the 1 / 4 wave plate and the optical axis direction of the first birefringent crystal; the corresponding value of θ3 is the angle between the optical axis direction of the full wave plate and the optical axis direction of the first birefringent crystal.

[0052] Compared with the prior art, the lossless magneto-optical switch of the present invention comprises a first birefringent crystal, a first wave plate assembly, a quarter wave plate, a full wave plate, a Faraday rotator crystal, a second birefringent crystal, a second wave plate assembly, a third wave plate assembly and a third birefringent crystal which are arranged in sequence. The single-fiber collimator is located on the side of the first birefringent crystal away from the first wave plate assembly. The lossless magneto-optical switch is provided with an input end, a first output end and a second output end. The input end is located on one side of the single-fiber collimator, and the first output end and the second output end are located on one side of the third birefringent crystal. By adopting a plurality of wave plate assemblies, it is ensured that all light beams (main sub-beams and weak sub-beams) can be accurately converged to the output end after passing through the third birefringent crystal. When the optical channel is switched, it is essentially the intensities of the strong light and the weak light on the path are interchanged, and both the strong light and the weak light are coupled into different channels. When the switch is switched, there actually needs to be a The switching will be completed only after a certain response time, and during the time when the switching starts but the switching is not completed, when the energy is converted between the strong light and the weak light, the energy of the weak light will increase. However, since the magneto-optical switch in the prior art does not couple the weak light channel, instability occurs in the system, and it will not stabilize until all the switching is completed. In the present application, the sum of the energies at the first output end and the second output end and the sum of the energies at the first output end and the second output end after the switching is completed are always in a stable state, which brings stability to the network transmission; the 1 / 4 wave plate can convert the change of the rotation angle of the Faraday rotator crystal into the phase delay change of the polarized light, and the full-wave plate can reduce the phase delay change of the polarized light, thereby eliminating the angular dispersion of the Faraday rotator crystal. Therefore, the use of 1 / 4 wave plate and full-wave plate compensation can effectively solve the optical crosstalk problem generated by the lossless magneto-optical switch in the optical transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A three-dimensional diagram of the lossless magneto-optical switch of the present invention;

[0054] Figure 2 for Figure 1 Side view of the optical path of the lossless magneto-optical switch;

[0055] Figure 3 for Figure 1 A top view of the optical path of a lossless magneto-optical switch;

[0056] Figure 4 for Figure 1 A light beam polarization direction diagram when the lossless magneto-optical switch is working from the input end to the first output end;

[0057] Figure 5 for Figure 1 A light beam polarization direction diagram when the lossless magneto-optical switch is working from the input end to the second output end;

[0058] Figure 6A graph showing the relationship between the wavelength and directivity of the input end to the second output end before and after compensation at room temperature when the input end to the first output end is working;

[0059] Figure 7 This is a graph showing the relationship between the wavelength and directivity of the input end to the first output end before and after compensation at room temperature when the input end works to the second output end.

[0060] In the figure: 101, single-fiber collimator; 102, first birefringent crystal; 103, first wave plate assembly; 104, 1 / 4 wave plate; 105, full-wave plate; 106, Faraday rotator crystal; 107, second birefringent crystal; 108, second wave plate assembly; 109, roof prism; 110, third wave plate assembly; 111, third birefringent crystal; 112, dual-fiber output collimator. DETAILED DESCRIPTION

[0061] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may be another intermediate component through which it is fixed. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may be another intermediate component at the same time. When a component is considered to be "set on" another component, it may be directly set on the other component or there may be another intermediate component at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0064] See also Figure 1The lossless magneto-optical switch includes a single-fiber collimator 101, a first birefringent crystal 102, a first wave plate assembly 103, a quarter wave plate 104, a full wave plate 105, a Faraday rotator crystal 106, a second birefringent crystal 107, a second wave plate assembly 108, a roof prism 109, a third wave plate assembly 110, a third birefringent crystal 111 and a dual-fiber output collimator 112, which are arranged in sequence.

[0065] The single fiber collimator 101 is used to collimate the incident light at the input end into a parallel light beam.

[0066] The first birefringent crystal 102 is used to decompose the parallel light beam into two sub-beams with orthogonal polarization directions.

[0067] The first wave plate assembly 103 is used to change the polarization directions of the two sub-beams to a state parallel to each other. Specifically, the first wave plate assembly 103 includes two half-wave plates, which are arranged on the left and right, and the optical axes of the two half-wave plates are different. The optical axis angles between the two wave plates are placed at 45° or 135° to each other. Preferably, in this embodiment, the optical axis of the wave plate on the left is +67.5°, and the optical axis of the wave plate on the right is -67.5°.

[0068] The quarter wave plate 104 can convert the change in the rotation angle of the Faraday rotator crystal 106 into a change in the phase delay of the polarized light.

[0069] The full-wave plate 105 can reduce the phase delay change of the polarized light, thereby eliminating the angular dispersion of the Faraday rotator crystal 106 .

[0070] The Faraday rotator crystal 106 controls the operation of different channels of the magneto-optical switch by connecting the positive and negative poles of the voltage to change the direction of the magnetic field. The Faraday rotator crystal 106 rotates the polarization direction of the sub-beam.

[0071] The second birefringent crystal 107 is used to deviate the extraordinary light along the optical axis.

[0072] The second wave plate assembly 108 includes two half-wave plates, which are arranged up and down, and the optical axes of the two half-wave plates are different. The optical axis angles between the two wave plates are placed at 45° or 135° to each other. Preferably, in this embodiment, the optical axis direction of the upper 1 / 2 wave plate is in the +22.5° direction, and the optical axis direction of the lower 1 / 2 wave plate is in the -22.5° direction.

[0073] The roof prism 109 changes the emission angle of the light beam passing through it to match the emission angle of the dual-fiber output collimator 112 .

[0074] The third wave plate assembly 110 changes the polarization directions of the two sub-beams of the main light to be orthogonal to each other, and the polarization directions of the two sub-beams of the weak light are also changed to be orthogonal to each other. The third wave plate assembly 110 includes two half-wave plates, which are arranged on the left and right, and the optical axes of the two half-wave plates are different. The optical axis angles between the two wave plates are placed at 45° or 135° to each other. Preferably, in this embodiment, the optical axis of the wave plate on the left is +67.5°, and the optical axis of the wave plate on the right is -67.5°

[0075] The third birefringent crystal 111 is used to combine two sub-beams of the principal light with orthogonal polarization directions into one output end, and to combine two sub-beams of the weak light with orthogonal polarization directions into the other output end.

[0076] The dual-fiber output collimator 112 is used to focus parallel light to be received in the optical fiber or to collimate the output light in the optical fiber into a parallel light beam.

[0077] An input end P1 is disposed on one side of the single-fiber collimator 101 , and a first output end P2 and a second output end P3 are disposed on the other side of the dual-fiber output collimator 112 .

[0078] Please continue reading Figure 2 , Figure 3 as well as Figure 4 When the magneto-optical switch is in the input end P1->first output end P2 optical path channel: Observed in the light transmission direction, when P1 to P2 is connected, the polarization direction of the light beam after passing through each optical element is as follows Figure 4 shown.

[0079] The divergent light beam outputted by the optical fiber is first collimated into a parallel light beam by a single-fiber collimator 101; after the parallel light beam passes through the first birefringent crystal 102, the parallel light beam is decomposed into two main sub-beams with orthogonal polarization directions; after passing through the first wave plate assembly 103, the polarization directions of the two main sub-beams are changed to be parallel to each other;

[0080] The Jones matrix expression of the first wave plate component 103 is:

[0081]

[0082] Wherein θ1 is the angle between the optical axis direction of the first wave plate assembly 103 and the optical axis direction of the first birefringent crystal 102 , i represents an imaginary number, and δ1 is the phase delay of the first wave plate assembly 103 .

[0083] The quarter wave plate 104 can convert the change of the rotation angle of the Faraday rotator crystal 106 into the phase delay change of the polarized light. The Jones matrix expression of the quarter wave plate 104 is:

[0084]

[0085] Wherein θ2 is the angle between the optical axis direction of the 1 / 4 wave plate 104 and the optical axis direction of the first birefringent crystal 102 , i represents an imaginary number, and δ2 is the phase delay of the 1 / 4 wave plate 104 .

[0086] The full-wave plate 105 can reduce the phase delay change of the polarized light, thereby eliminating the angular dispersion of the Faraday rotator crystal 106. The Jones matrix expression of the full-wave plate 105 is:

[0087]

[0088] Wherein θ3 is the angle between the optical axis direction of the full-wave plate 105 and the optical axis direction of the first birefringent crystal 102 , i represents an imaginary number, and δ3 is the phase delay of the full-wave plate 105 .

[0089] After passing through the Faraday rotator crystal 106, the polarization directions of the two main sub-beams rotate 45°. When the magneto-optical switch is in the P1->P2 optical path channel, the magnetic field direction is along the optical path transmission direction, and the polarization directions of the two main sub-beams rotate 45° counterclockwise along the optical path transmission direction. With respect to the second birefringent crystal 107, the two main sub-beams are both ordinary light at this time. Due to the relationship between the extinction ratio and the wavelength of the Faraday rotator crystal 106, not 100% of the energy is concentrated in the ordinary light (main sub-beam) state, and some very weak light energy is concentrated in the extraordinary light state (i.e., generating two weak sub-beams).

[0090] The Jones matrix expression of Faraday optically active crystal 106 is:

[0091]

[0092] Where θ4 is the rotation angle of the polarization direction of the sub-beam after passing through the Faraday rotator crystal 106,

[0093] θ4=45+k0(λ-λc)+k1(T-Tc)

[0094] Wherein k0 is the wavelength correlation coefficient of the Faraday rotator crystal 106, λ is the wavelength of the incident light in vacuum, λc is the central wavelength of the magneto-optical switch, k1 is the temperature correlation coefficient of the Faraday rotator crystal 106, T is the temperature of the magneto-optical switch when it is working, and Tc is the room temperature of 23°C.

[0095] After passing through the second birefringent crystal 107, the two main sub-beams are both ordinary light, and the light will not be deflected; while the two weak sub-beams are both extraordinary light, and the light will be deflected along the optical axis direction. Figure 4 The red font polarization mark in the figure; after passing through the second wave plate assembly 108, the polarization directions of the two main sub-beams rotate 45° counterclockwise along the optical path transmission direction, while the polarization directions of the two weak sub-beams rotate 135° counterclockwise along the optical path transmission direction;

[0096] The Jones matrix expression of the second wave plate assembly 108 is:

[0097]

[0098] Wherein θ5 is the angle between the optical axis direction of the second wave plate assembly 108 and the optical axis direction of the first birefringent crystal 102 , i represents an imaginary number, and δ5 is the phase delay of the second wave plate assembly 108 .

[0099] After passing through the roof prism 109, the emission angle of the light beam changes to match the emission angle of the dual-fiber collimator 112; after passing through the third wave plate assembly 110, the polarization directions of the main sub-beams change to be orthogonal to each other, and the polarization directions of the weak sub-beams also change to be orthogonal to each other;

[0100] The Jones matrix expression of the third wave plate assembly 110 is:

[0101]

[0102] Wherein θ6 is the angle between the optical axis direction of the third wave plate assembly 110 and the optical axis direction of the first birefringent crystal 102 , i represents an imaginary number, and δ6 is the phase delay of the third wave plate assembly 110 .

[0103] After passing through the third birefringent crystal 111, the sub-beams with orthogonal polarization directions of the two main sub-beams are recombined and enter the first output port P2, and the sub-beams with orthogonal polarization directions of the two weak sub-beams are recombined and enter the second output port P3.

[0104] When the P1->P2 optical path channel is working, the directivity of the lossless magneto-optical switch is P1->P3. When calculating the directivity of the lossless magneto-optical switch, since the light beam deviates downward after passing through the second birefringent crystal 107, the second wave plate assembly 108 through which the light beam passes is the lower half-wave plate, so θ5=-22.5°. The Jones matrix expression of the forward transmission of ordinary light o is:

[0105]

[0106] The Jones matrix expression of the forward transmission of extraordinary light e-light is:

[0107]

[0108] By setting the angle θ2 between the optical axis direction of the 1 / 4 wave plate 104 and the optical axis direction of the first birefringent crystal 102, and the angle θ3 between the optical axis direction of the full wave plate 105 and the optical axis direction of the first birefringent crystal 102, the directional bandwidth of the lossless magneto-optical switch can be increased and the directionality can also be improved.

[0109] Since Mo1 is positively correlated with Me1, when Mo1 is maximum, Me1 is also maximum. Therefore, the values ​​of θ2 and θ3 can be determined inversely by maximizing Mo1 or Me1.

[0110] If the central wavelength of the lossless magneto-optical switch is 1550nm, the angle θ2 between the optical axis direction of the zero-order 1 / 4 wave plate 104 made of quartz material and the optical axis direction of the first birefringent crystal 102 is 45°, and the angle θ3 between the optical axis direction of the full-wave plate 105 and the optical axis direction of the first birefringent crystal 102 is -46°, the lossless magneto-optical switch can obtain the best directional bandwidth and can improve the directionality.

[0111] like Figure 6 As shown, when the working wavelength of the lossless magneto-optical switch is 1520nm-1580nm, the directivity of P1->P3 changes with the wavelength without adding the 1 / 4 wave plate 104 and the full wave plate 105 and with adding the 1 / 4 wave plate 104 and the full wave plate 105. Figure 6 It shows that the directivity of the lossless magneto-optical switch in the prior art is poor at the edge of the band. After compensation by the 1 / 4 wave plate 104 and the full-wave plate 105, the directivity and bandwidth of the lossless magneto-optical switch are significantly improved. Therefore, using the 1 / 4 wave plate 104 and the full-wave plate 105 for compensation can effectively solve the optical crosstalk problem generated by the lossless magneto-optical switch in the optical transmission system.

[0112] Please continue reading Figure 2 , Figure 3 as well as Figure 5 , when the magneto-optical switch is in the P1->P3 optical path (switching by controlling the magnetic field direction in the opposite direction): observed in the light transmission direction, when P1 to P3 is connected, the polarization direction of the light beam after passing through each optical element is as follows Figure 5 As shown:

[0113] The divergent light beam outputted by the optical fiber is first collimated into a parallel light beam by a single-fiber collimator 101; after the parallel light beam passes through the first birefringent crystal 102, the parallel light beam is decomposed into two main sub-beams with orthogonal polarization directions; after passing through the first wave plate assembly 103, the polarization directions of the two main sub-beams are changed to a mutually parallel state; the 1 / 4 wave plate 104 can convert the change of the rotation angle of the Faraday rotator crystal 106 into the phase delay change of the polarized light; the full wave plate 105 can reduce the phase delay change of the polarized light, thereby eliminating the angular dispersion of the Faraday rotator crystal 106; after passing through the Faraday rotator crystal 106, the polarization directions of the two main sub-beams are rotated by 45°, and when the magneto-optical switch is in P1-> When the P3 optical path channel is working, since the direction of the magnetic field is in the opposite direction of the optical path transmission, the polarization directions of the two main sub-beams rotate 45° clockwise along the optical path transmission direction. Relative to the second birefringent crystal 107, the two main sub-beams are both extraordinary light. Similarly, due to the correlation between the extinction ratio and the wavelength of the Faraday rotator crystal 106, not 100% of the energy is concentrated in the extraordinary light state (main sub-beam), and some very weak light energy is concentrated in the ordinary light state (i.e., two weak sub-beams are generated); after passing through the second birefringent crystal 107, the two main sub-beams are both extraordinary light, and the light is offset along the optical axis; while the two weak sub-beams are both ordinary light, and the light is not offset, as shown in FIG. Figure 5 The red font polarization mark in the figure; after passing through the second wave plate component 108, the polarization directions of the two main sub-beams are rotated 135° counterclockwise when viewed along the optical path transmission direction, and the polarization directions of the two weak sub-beams are rotated 45° counterclockwise when viewed along the optical path transmission direction; after passing through the roof prism 109, the emission angle of the light beam changes to match the light emission angle of the dual-fiber collimator 112; after passing through the third wave plate component 110, the polarization directions of the two main sub-beams are changed to be orthogonal to each other, and the polarization directions of the two weak sub-beams are also changed to be orthogonal to each other; after passing through the third birefringent crystal 111, the sub-beams with orthogonal polarization directions of the two main sub-beams are recombined and enter the second output port P3, and the sub-beams with orthogonal polarization directions of the two weak sub-beams are recombined and enter the first output port P2.

[0114] When the P1->P3 optical path channel is working, the directivity of the lossless magneto-optical switch is P1->P2. When calculating the directivity of the lossless magneto-optical switch, since the light beam does not deflect after passing through the second birefringent crystal 107, the second wave plate assembly 108 through which the light beam passes is the upper half-wave plate, so θ5=+22.5°. The Jones matrix expression of the forward transmission of ordinary light o is:

[0115]

[0116] The Jones matrix expression of the forward transmission of extraordinary light e-light is:

[0117]

[0118] Since Mo2 is positively correlated with Me2, when Mo2 is maximum, Me2 is also maximum. Therefore, the values ​​of θ2 and θ3 can be determined inversely by maximizing Mo2 or Me2.

[0119] The angle θ2 between the optical axis of the quarter wave plate 104 and the optical axis of the first birefringent crystal 102 is maintained at 45°, and the angle θ3 between the optical axis of the full wave plate 105 and the optical axis of the first birefringent crystal 102 is maintained at -46°. Figure 7 As shown, when the working wavelength of the lossless magneto-optical switch is 1520nm-1580nm, the directivity of P1->P2 changes with the wavelength without adding the 1 / 4 wave plate 104 and the full wave plate 105 and with adding the 1 / 4 wave plate 104 and the full wave plate 105. Figure 7 It reflects that the directivity of the lossless magneto-optical switch in the prior art is poor at the edge of the band. After compensation by the 1 / 4 wave plate 104 and the full-wave plate 105, the directivity and bandwidth of the lossless magneto-optical switch are significantly improved. Therefore, using the 1 / 4 wave plate 104 and the full-wave plate 105 for compensation can effectively solve the optical crosstalk problem generated by the lossless magneto-optical switch in the optical transmission system.

[0120] The present application also discloses a wave plate angle adjustment method based on the above lossless magneto-optical switch, comprising the following steps:

[0121] The Jones matrix expression of the first wave plate assembly 103 is:

[0122]

[0123] Wherein, θ1 is the angle between the optical axis direction of the first wave plate assembly 103 and the optical axis direction of the first birefringent crystal 102, i represents an imaginary number, δ1 is the phase delay of the first wave plate assembly 103, and θ1 and δ1 are known values ​​according to the specific structure of the lossless magneto-optical switch;

[0124] The Jones matrix expression of the quarter wave plate 104 is:

[0125]

[0126] Wherein, θ2 is the angle between the optical axis direction of the quarter wave plate 104 and the optical axis direction of the first birefringent crystal 102, i represents an imaginary number, δ2 is the phase delay of the quarter wave plate 104, θ2 is the angle to be solved, and δ2 is a known value;

[0127] The Jones matrix expression of the full-wave plate 105 is:

[0128]

[0129] Wherein, θ3 is the angle between the optical axis direction of the full-wave plate 105 and the optical axis direction of the first birefringent crystal 102, i represents an imaginary number, δ3 is the phase delay of the full-wave plate 105, θ3 is the angle to be solved, and δ3 is a known value;

[0130] The Jones matrix expression of Faraday optically active crystal 106 is:

[0131]

[0132] Where θ4 is the rotation angle of the polarization direction of the sub-beam after passing through the Faraday rotator crystal 106,

[0133] θ4=45+k0(λ-λc)+k1(T-Tc) (5)

[0134] Wherein, k0 is the wavelength correlation coefficient of the Faraday rotator crystal 106, λ is the wavelength of the incident light in vacuum, λc is the central wavelength of the magneto-optical switch, k1 is the temperature correlation coefficient of the Faraday rotator crystal 106, T is the temperature of the magneto-optical switch when it is working, and Tc is the room temperature of 23°C;

[0135] The Jones matrix expression of the second wave plate assembly 107 is:

[0136]

[0137] Wherein, θ5 is the angle between the optical axis direction of the second wave plate assembly 107 and the optical axis direction of the first birefringent crystal 102, i represents an imaginary number, δ5 is the phase delay of the second wave plate assembly 107, and θ5 and δ5 are known values;

[0138] The Jones matrix expression of the third wave plate assembly 108 is:

[0139]

[0140] Wherein, θ6 is the angle between the optical axis direction of the third wave plate assembly 108 and the optical axis direction of the first birefringent crystal 102, i represents an imaginary number, δ6 is the phase delay of the third wave plate assembly 108, and θ6 and δ6 are known values;

[0141] When the optical path from the input end to the first output end is working, the directionality of the lossless magneto-optical switch is from the input end to the second output end.

[0142] The Jones matrix expression of the forward transmission of ordinary light o is:

[0143]

[0144] The Jones matrix expression of the forward transmission of extraordinary light e-light is:

[0145]

[0146] When the optical path from the input end to the second output end is working, the directionality of the lossless magneto-optical switch is from the input end to the first output end.

[0147] The Jones matrix expression of ordinary light o forward transmission is:

[0148]

[0149] The Jones matrix expression of the forward transmission of extraordinary light e-light is:

[0150]

[0151] Since Mo1 and Me1 are positively correlated, and Mo2 and Me2 are positively correlated, when Mo1 is at its maximum value, Me1 is also at its maximum value; when Mo2 is at its maximum value, Me2 is also at its maximum value; therefore, when either Mo1 or Me1 is at its maximum value and either Mo2 or Me2 is at its maximum value, the corresponding value of θ2 is the angle between the optical axis direction of the 1 / 4 wave plate 104 and the optical axis direction of the first birefringent crystal 102; the corresponding value of θ3 is the angle between the optical axis direction of the full wave plate 105 and the optical axis direction of the first birefringent crystal 102.

[0152] As can be seen from the above principle, when the optical channel is switched, it is essentially the exchange of the intensity of the strong light and weak light paths. After deducting the material absorption, material reflectivity loss and coupling loss between parts, theoretically the sum of the energy of the two is equal to the input light energy. This solution couples both the strong light and the weak light into different channels (the magneto-optical switches currently on the market only couple the strong light channel, not the weak light channel). When the switch is switched, it actually takes a certain response time to complete the switch. During the time when the switch starts but is not completed, the energy of the weak light increases when the energy is converted between the strong light and the weak light. However, since the conventional magneto-optical switch does not couple the weak light channel, instability occurs in the system, and it will not stabilize until all switches are completed). In this invention, the sum of the energy at the P2+P3 channel and the sum of the energy of the P2+P3 channel after the switch is completed are always in a stable state, which brings stability to the network transmission.

[0153] The present application realizes lossless switching of magneto-optical switches, and changes the polarization direction of light beams by cleverly combining multiple half-wave plate components to ensure that all light beams can be accurately converged to the output end after passing through the third birefringent crystal 111. This design greatly reduces the loss of light energy during the switching process of the optical switch, thereby achieving that the sum of the light energy output from the two ports of the magneto-optical switch remains constant throughout the process, whether at the moment of switching or after the switching is completed. The dispersion of the Faraday rotation crystal 106 is compensated by the 1 / 4 wave plate 104 and the full wave plate 105, which makes up for the defect of poor directivity of the existing lossless magneto-optical switch, and realizes the function of high directivity within the wavelength range of 1520 to 1580 nm. This design can not only greatly reduce the energy loss generated by the magneto-optical switch during the switching process, but also avoid the optical crosstalk problem generated by the lossless magneto-optical switch, providing a high degree of stability and selectivity for the optical transmission system.

[0154] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which are equivalent modifications and improvements made to the above embodiments based on the essential technology of the present invention, and all of them belong to the protection scope of the present invention.

Claims

1. A lossless magneto-optical switch, comprising a single-fiber collimator, characterized in that: The lossless magneto-optical switch also includes a first birefringent crystal, a first wave plate assembly, a quarter wave plate, a full wave plate, a Faraday rotator crystal, a second birefringent crystal, a second wave plate assembly, a third wave plate assembly and a third birefringent crystal which are arranged in sequence. The single-fiber collimator is located on the side of the first birefringent crystal away from the first wave plate assembly. The lossless magneto-optical switch is provided with an input end, a first output end and a second output end. The input end is located on one side of the single-fiber collimator, and the first output end and the second output end are located on one side of the third birefringent crystal. The parallel light beam emitted by the single-fiber collimator is decomposed into two main sub-beams with orthogonal polarization directions through the first birefringent crystal. The polarization directions of the two main sub-beams are changed to be parallel to each other after passing through the first wave plate assembly. The 1 / 4 wave plate can convert the change of the rotation angle of the Faraday rotator crystal into the phase delay change of the polarized light. The full-wave plate can reduce the phase delay change of the polarized light, thereby eliminating the angular dispersion of the Faraday rotator crystal. When the optical path from the input end to the first output end is working, the polarization directions of the two main sub-beams with mutually parallel polarization directions rotate counterclockwise after passing through the Faraday rotator crystal and generate two weak sub-beams, the two main sub-beams do not deviate when passing through the second birefringent crystal, the two weak sub-beams deviate when passing through the second birefringent crystal, the two main sub-beams rotate counterclockwise when passing through the upper area of ​​the second wave plate component, the two weak sub-beams rotate counterclockwise when passing through the lower area of ​​the second wave plate component, the polarization directions of the two main sub-beams and the two weak sub-beams are changed to be orthogonal to each other when passing through the third wave plate component, the two main sub-beams combine to enter the first output end when passing through the third birefringent crystal, the two weak sub-beams combine to enter the second output end, and the directionality of the lossless magneto-optical switch is from the input end to the second output end; When the optical path channel from the input end to the second output end is working, the polarization directions of the two main sub-beams with mutually parallel polarization directions rotate clockwise after passing through the Faraday rotator crystal and generate two weak sub-beams, the two main sub-beams are offset after passing through the second birefringent crystal, and the two weak sub-beams are not offset after passing through the second birefringent crystal, the two main sub-beams rotate counterclockwise when passing through the lower area of ​​the second wave plate component, and the two weak sub-beams rotate counterclockwise when passing through the upper area of ​​the second wave plate component, and the polarization directions of the two main sub-beams and the two weak sub-beams are changed to be orthogonal to each other when passing through the third wave plate component, and the two main sub-beams and the two weak sub-beams are combined to enter the second output end when passing through the third birefringent crystal, and the two main sub-beams combine to enter the first output end. At this time, the directionality of the lossless magneto-optical switch is from the input end to the first output end.

2. The lossless magneto-optical switch according to claim 1, characterized in that: The angle between the optical axis direction of the quarter wave plate and the optical axis direction of the first birefringent crystal is 45°.

3. The lossless magneto-optical switch according to claim 1, characterized in that: The angle between the optical axis direction of the full-wave plate and the optical axis direction of the first birefringent crystal is -46°.

4. The lossless magneto-optical switch according to claim 1, characterized in that: The first wave plate assembly includes two half-wave plates, which are arranged on the left and right, and have different optical axes.

5. The lossless magneto-optical switch according to claim 1, characterized in that: The second wave plate assembly includes two half-wave plates, which are arranged one above the other and have different optical axes.

6. The lossless magneto-optical switch according to claim 1, characterized in that: When the optical path channel from the input end to the first output end is working, the two main sub-beams are ordinary light when passing through the Faraday rotator crystal, and the two weak sub-beams generated are extraordinary light; when the optical path channel from the input end to the second output end is working, the two main sub-beams are extraordinary light when passing through the Faraday rotator crystal, and the two weak sub-beams generated are ordinary light.

7. The lossless magneto-optical switch according to claim 1, characterized in that: The second wave plate assembly rotates the polarization directions of the main sub-beam and the weak sub-beam at different angles.

8. The lossless magneto-optical switch according to claim 7, characterized in that: When the optical path channel from the input end to the first output end is working, the polarization directions of the two main sub-beams are rotated 45° counterclockwise when viewed along the optical path transmission direction, and the polarization directions of the two weak sub-beams are rotated 135° counterclockwise when viewed along the optical path transmission direction; when the optical path channel from the input end to the second output end is working, the polarization directions of the two main sub-beams are rotated 135° counterclockwise when viewed along the optical path transmission direction, and the polarization directions of the two weak sub-beams are rotated 45° counterclockwise when viewed along the optical path transmission direction.

9. The lossless magneto-optical switch according to claim 1, characterized in that: The lossless magneto-optical switch also includes a roof prism and a dual-fiber output collimator. The roof prism is located between the second wave plate component and the third wave plate component. The dual-fiber output collimator is located between the third birefringent crystal and the first output end and the second output end.

10. A method for adjusting the wave plate angle of a lossless magneto-optical switch according to any one of claims 1 to 9, characterized in that: The following steps are involved: The Jones matrix expression of the first wave plate component is: Wherein, θ1 is the angle between the optical axis direction of the first wave plate assembly and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ1 is the phase delay of the first wave plate assembly, and θ1 and δ1 are known values ​​according to the specific structure of the lossless magneto-optical switch; The Jones matrix expression of the 1 / 4 wave plate is: Wherein, θ2 is the angle between the optical axis direction of the 1 / 4 wave plate and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ2 is the phase delay of the 1 / 4 wave plate, θ2 is the angle to be solved, and δ2 is a known value; The Jones matrix expression of the full-wave plate is: Wherein, θ3 is the angle between the optical axis direction of the full-wave plate and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ3 is the phase delay of the full-wave plate, θ3 is the angle to be solved, and δ3 is a known value; The Jones matrix expression of the Faraday optically active crystal is: Where θ4 is the rotation angle of the polarization direction of the sub-beam after passing through the Faraday rotator crystal, θ4=45+k0(λ-λc)+k1(T-Tc) (5) Wherein, k0 is the wavelength correlation coefficient of the Faraday rotator crystal, λ is the wavelength of the incident light in a vacuum, λc is the central wavelength of the magneto-optical switch, k1 is the temperature correlation coefficient of the Faraday rotator crystal, T is the temperature at which the magneto-optical switch works, and Tc is the room temperature of 23°C; The Jones matrix expression of the second wave plate component is: Wherein, θ5 is the angle between the optical axis direction of the second wave plate assembly and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ5 is the phase delay of the second wave plate assembly, and θ5 and δ5 are known values; The Jones matrix expression of the third wave plate assembly is: Wherein, θ6 is the angle between the optical axis direction of the third wave plate assembly and the optical axis direction of the first birefringent crystal, i represents an imaginary number, δ6 is the phase delay of the third wave plate assembly, and θ6 and δ6 are known values; When the optical path from the input end to the first output end is working, the directionality of the lossless magneto-optical switch is from the input end to the second output end. The Jones matrix expression of ordinary light o-light forward transmission is: The Jones matrix expression of the forward transmission of extraordinary light e-light is: When the optical path from the input end to the second output end is working, the directionality of the lossless magneto-optical switch is from the input end to the first output end. The Jones matrix expression of ordinary light o forward transmission is: The Jones matrix expression of the forward transmission of extraordinary light e-light is: Since Mo1 and Me1 are positively correlated, and Mo2 and Me2 are positively correlated, when Mo1 is at its maximum value, Me1 is also at its maximum value; when Mo2 is at its maximum value, Me2 is also at its maximum value; therefore, when any one of Mo1 and Me1 is at its maximum value and any one of Mo2 and Me2 is at its maximum value, the corresponding value of θ2 is the angle between the optical axis direction of the 1 / 4 wave plate and the optical axis direction of the first birefringent crystal; the corresponding value of θ3 is the angle between the optical axis direction of the full wave plate and the optical axis direction of the first birefringent crystal.

Images