Lossless magneto-optical switch and wave plate angle adjustment method

Abstract

The present application discloses a lossless magneto-optical switch and a wave plate angle adjustment method, belonging to the field of optics. The input end is located on one side of a single-fiber collimator, and the first and second output ends are located on a third birefringent crystal. By employing multiple wave plate assemblies, both the main sub-beam and the weak sub-beam can be accurately converged at the output ends. When the optical channel is switched, the intensity of the strong and weak light paths is essentially swapped, coupling both the strong and weak light into different channels. In the present application, the sum of the energies at the first and second output ends and the sum of the energies at the first and second output ends after switching are always in a stable state, thus ensuring stable network transmission. The quarter-wave plate converts changes in the rotation angle of the Faraday rotator crystal into phase delay changes in polarized light. The full-wave plate reduces phase delay changes in polarized light, eliminating the angular dispersion of the Faraday rotator crystal, and effectively resolving the optical crosstalk problem generated in optical transmission systems.

Description

Technical Field

[0001] The present 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 communications, optical switches, as a key passive component, are widely used to selectively switch optical signals within fiber-optic communication networks. Magneto-optical switches utilize the Faraday magneto-optical effect, primarily by altering the direction of an applied magnetic field to change the Faraday rotation angle within a magneto-optical crystal, thereby switching the optical path. Compared to traditional optical switches, magneto-optical switches offer advantages such as fast switching speed, no moving parts, and high stability, and are garnering increasing attention and research.

[0003] Currently, common magneto-optical switches do not adhere to energy conservation during switching. This means the sum of the energies of the connected and closed optical paths cannot maintain a stable value. The energy loss caused by switching severely impacts the stability of optical transmission systems. Lossless magneto-optical switches achieve low energy loss during switching, significantly improving the stability of optical transmission systems. However, existing lossless magneto-optical switches suffer from poor directionality, which can lead to optical signal crosstalk and hinder the selective switching of optical signals in optical transmission systems. 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 deficiencies 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 magneto-optical switch with good directivity and without any loss.

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

[0007] A lossless magneto-optical switch includes 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. The lossless magneto-optical switch includes 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 and second output ends 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 by 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 quarter-wave plate can convert the change in the rotation angle of the Faraday rotator crystal into a 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 channel 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 deflect when passing through the second birefringent crystal, and the two weak sub-beams deflect when passing through the second birefringent crystal. The two main sub-beams both rotate counterclockwise when passing through the upper area of ​​the second wave plate component, and the two weak sub-beams both rotate counterclockwise when passing through the lower area of ​​the second wave plate component. When passing through the third 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 birefringent crystal, the two main sub-beams combine to enter the first output end, and the two weak sub-beams combine to enter the second output end. At this time, 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 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 when passing through the second birefringent crystal, and the two weak sub-beams are not offset when 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. When passing through the third 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 birefringent crystal, the two main sub-beams are combined and enter the second output end, and the two weak sub-beams are combined and 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 from the input end to the first output end is in operation, 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 from the input end to the second output end is in operation, 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 of the above-mentioned 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 of the first wave plate assembly and the optical axis 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 of the quarter wave plate and the optical axis of the first birefringent crystal, i represents an imaginary number, δ2 is the phase delay of the quarter 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 of the full-wave plate and the optical axis 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-rotating 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-dependent 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-dependent coefficient of the Faraday rotator crystal, T is the operating temperature of the magneto-optical switch, 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 of the second wave plate assembly and the optical axis 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 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 light 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 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 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 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 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 multiple 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 weak light paths are interchanged, and the strong light and weak light are coupled into different channels. When the switch is switched, there actually needs to be an The switching will not be completed until a certain response time is required. During the time between the start of switching and the completion of switching, the energy of the weak light will increase during the energy conversion between the strong light and the weak light. However, since the magneto-optical switch in the prior art does not couple the weak light channel, instability occurs in the system and the system will not stabilize until all switching is completed. In the present application, the sum of the energy at the first output end and the second output end and the sum of the energy 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 in 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 caused by the lossless magneto-optical switch in the optical transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a perspective view 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 Top view of the optical path of the lossless magneto-optical switch;

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

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

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

[0059] Figure 7 This is a relationship diagram between the wavelength and directivity from the input end to the first output end before and after compensation at room temperature when working from the input end 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 clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts 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 commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated 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 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 where they are parallel to each other. Specifically, the first wave plate assembly 103 includes two half-wave plates, which are arranged on the left and right sides, and have different optical axes. The optical axes of the two wave plates are arranged at an angle of 45° or 135° to each other. Preferably, in this embodiment, the optical axis of the left wave plate is +67.5°, and the optical axis of the right wave plate 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 polarized light.

[0069] The full-wave plate 105 can reduce the phase delay variation of 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 changing the direction of the magnetic field by connecting the positive and negative polarities of the voltage. The Faraday rotator crystal 106 rotates the polarization direction of the sub-beam.

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

[0072] The second wave plate assembly 108 includes two half-wave plates, which are arranged one above the other and have different optical axes. The optical axes of the two wave plates are arranged at an angle of 45° or 135° to each other. Preferably, in this embodiment, the optical axis direction of the upper half-wave plate is at a +22.5° direction, and the optical axis direction of the lower half-wave plate is at a -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 the two sub-beams of the principal light with orthogonal polarization directions into one output end, and to combine the 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 into the optical fiber for reception or to collimate the output light in the optical fiber into a parallel beam.

[0077] An input end P1 is provided on one side of the single-fiber collimator 101 , and a first output end P2 and a second output end P3 are provided 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 working: Observe 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 output by the optical fiber is first collimated into a parallel beam by the single-fiber collimator 101. After passing through the first birefringent crystal 102, the parallel 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.

[0080] The Jones matrix expression of the first wave plate assembly 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 in the rotation angle of the Faraday rotator crystal 106 into a change in the phase delay 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 quarter 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 quarter wave plate 104 .

[0086] The full-wave plate 105 can reduce the phase delay variation of 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 are rotated 45°. When the magneto-optical switch is operating in the P1->P2 optical path, the magnetic field is aligned with the optical transmission direction, and the polarization directions of the two main sub-beams are rotated 45° counterclockwise along the optical transmission direction. With respect to the second birefringent crystal 107, both main sub-beams are now ordinary light. Due to the wavelength-dependent extinction ratio of the Faraday rotator crystal 106, not 100% of the energy is concentrated in the ordinary light state (the main sub-beam); 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-dependent coefficient of the Faraday rotator crystal 106, 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-dependent coefficient of the Faraday rotator crystal 106, T is the temperature at which the magneto-optical switch operates, and Tc is the room temperature of 23°C.

[0095] After passing through the second birefringent crystal 107, the two main sub-beams are ordinary light and the light will not be deflected; while the two weak sub-beams are extraordinary light and the light will be deflected along the optical axis. Figure 4 The polarization mark in red font in the figure; after passing through the second wave plate assembly 108, the polarization directions of the two main sub-beams are rotated 45° counterclockwise when viewed along the optical path transmission direction, while the polarization directions of the two weak sub-beams are rotated 135° counterclockwise when viewed 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 output angle of the light beam changes to match the output 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 two main sub-beams with orthogonal polarization directions are recombined and enter the first output port P2 , and the two weak sub-beams with orthogonal polarization directions 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 deflects 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 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 selected to be 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 selected to be -46°. The lossless magneto-optical switch can obtain the optimal directional bandwidth and improve the directivity.

[0111] like Figure 6 As shown, when the operating wavelength of the lossless magneto-optical switch is 1520nm-1580nm, the directivity curves of P1->P3 vary with wavelength without adding the quarter wave plate 104 and the full wave plate 105 and with adding the quarter 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 direction of the magnetic field): Observing 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 output by the optical fiber is first collimated into a parallel light beam by a single-fiber collimator 101. After passing through a first birefringent crystal 102, the parallel light beam is decomposed into two main sub-beams with orthogonal polarization directions. After passing through a first wave plate assembly 103, the polarization directions of the two main sub-beams are changed to a mutually parallel state. A quarter-wave plate 104 can convert the change in the rotation angle of a Faraday rotator crystal 106 into a phase delay change of the polarized light. A 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 degrees. When the magneto-optical switch is in P1-> When the P3 optical path channel is operating, the polarization directions of the two main sub-beams rotate 45° clockwise along the optical path propagation direction because the direction of the magnetic field is opposite to the direction of optical transmission. Relative to the second birefringent crystal 107, the two main sub-beams are now both extraordinary light. Similarly, due to the correlation between the extinction ratio and wavelength of the Faraday rotator crystal 106, not 100% of the energy is concentrated in the extraordinary light state (the main sub-beams), and a very weak portion of the light energy is concentrated in the ordinary light state (i.e., generating two weak sub-beams). After passing through the second birefringent crystal 107, the two main sub-beams are both extraordinary light, and the light is deflected along the optical axis. However, the two weak sub-beams are both ordinary light, and the light is not deflected. 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 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. Therefore, θ5 = +22.5°. The Jones matrix expression of the ordinary light in the forward direction 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 operating wavelength of the lossless magneto-optical switch is 1520nm-1580nm, the directivity of P1->P2 varies with wavelength without adding the quarter wave plate 104 and the full wave plate 105 and with adding the quarter wave plate 104 and the full wave plate 105. Figure 7 This 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, the use of 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 method for adjusting the wave plate angle based on the above-mentioned 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 of the quarter wave plate 104 and the optical axis 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-dependent 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-dependent coefficient of the Faraday rotator crystal 106, T is the temperature at which the magneto-optical switch operates, 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 of the third wave plate assembly 108 and the optical axis 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 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 light 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 strong light and weak light into different channels (the magneto-optical switches currently on the market only couple strong light channels, not weak light channels). When the switch is switched, it actually takes a certain response time to complete the switch. During the time from the beginning of the switch to the completion of the switch, the energy of the weak light will increase 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] This application achieves lossless switching of magneto-optical switches by cleverly combining multiple half-wave plate components to change the polarization direction of the light beam, ensuring that all light beams can be accurately converged to the output end after passing through the third birefringent crystal 111. This design significantly reduces the loss of light energy during the switching process of the optical switch, thereby ensuring that the sum of the light energy output from the two ports of the magneto-optical switch remains constant throughout the entire process, both at the moment of switching and 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, making up for the poor directionality of existing lossless magneto-optical switches and achieving high directionality within the wavelength range of 1520-1580nm. This design not only significantly reduces the energy loss generated by the magneto-optical switch during the switching process, but also avoids the optical crosstalk problem generated by lossless magneto-optical switches, providing high stability and selectivity for the optical transmission system.

[0154] The above embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patented invention. It should be noted that those skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention. These variations and improvements are equivalent modifications and improvements to the above embodiments based on the essential technology of the present invention and fall within the scope of protection of the present invention.

Claims

1. A lossless magneto-optical switch, comprising a single-fiber collimator, characterized in that: The lossless magneto-optical switch further 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 by 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 quarter-wave plate can convert the change in the rotation angle of the Faraday rotator crystal into a 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 channel 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 deflect when passing through the second birefringent crystal, and the two weak sub-beams deflect when passing through the second birefringent crystal. The two main sub-beams both rotate counterclockwise when passing through the upper area of ​​the second wave plate component, and the two weak sub-beams both rotate counterclockwise when passing through the lower area of ​​the second wave plate component. When passing through the third 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 birefringent crystal, the two main sub-beams combine to enter the first output end, and the two weak sub-beams combine to enter the second output end. At this time, 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 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 when passing through the second birefringent crystal, and the two weak sub-beams are not offset when 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. When passing through the third 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 birefringent crystal, the two main sub-beams are combined and enter the second output end, and the two weak sub-beams are combined and 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, wherein: The angle between the optical axis of the full-wave plate and the optical axis of the first birefringent crystal is -46°.

4. The lossless magneto-optical switch according to claim 1, wherein: 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, wherein: 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, wherein: When the optical path from the input end to the first output end is in operation, 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 from the input end to the second output end is in operation, 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, wherein: The lossless magneto-optical switch further 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. 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 of the first wave plate assembly and the optical axis 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 of the quarter wave plate and the optical axis of the first birefringent crystal, i represents an imaginary number, δ2 is the phase delay of the quarter 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 of the full-wave plate and the optical axis 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-rotating 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-dependent 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-dependent coefficient of the Faraday rotator crystal, T is the operating temperature of the magneto-optical switch, 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 of the second wave plate assembly and the optical axis 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 the forward transmission of ordinary light 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 light 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 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 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.

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