CN105891956B - Reflective optical circulator array - Google Patents

Reflective optical circulator array Download PDF

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CN105891956B
CN105891956B CN201410680123.4A CN201410680123A CN105891956B CN 105891956 B CN105891956 B CN 105891956B CN 201410680123 A CN201410680123 A CN 201410680123A CN 105891956 B CN105891956 B CN 105891956B
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polarization
degrees
array
displacement
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CN105891956A (en
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陈波
许辉杰
赖泓基
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Jiangsu Xuhai Photoelectric Technology Co ltd
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Jiangsu Xuhai Photoelectric Technology Co ltd
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Abstract

The invention provides a reflective optical circulator array, which introduces a large-angle polarization component device to enable two polarization states of a plurality of paths of optical signals to be completely separated in space and respectively processed. The invention expands the optical circulator to a two-dimensional array, avoids introducing a complex wave plate array or a birefringent crystal array, and eliminates the problem of crosstalk caused by the reduction of polarization extinction ratio. The implementation of the two-dimensional array greatly improves the integration level and greatly reduces the cost of a single optical circulator.

Description

Reflective optical circulator array
Technical Field
The invention belongs to the fields of optical communication, optical sensing and optical information processing, and relates to a small-sized and low-cost integrated optical circulator.
Background
A typical optical circulator has three ports, called a first port, a second port, and a third port, and its basic function is to enable transmission of an optical signal from the first port to the second port, and the signal from the second port cannot return to the first port but can enable transmission of the second port to the third port. Optical circulators are fundamental devices in the fields of optical communication, optical sensing and optical information processing, and have found very important applications in these fields. In the field of optical communication, the use of the optical circulator can also enable a common double-port optical transceiver module to realize single-fiber bidirectional transmission, and is an indispensable device when an old network (double-port double-fiber) is upgraded to single-fiber bidirectional transmission.
However, the optical circulator for the commercial use provided by the prior art has the disadvantages that the volume of the device is large, three ports are respectively connected from two sides of the optical circulator, optical fibers are required to be coiled during actual use, and the whole device is too large, so that the wide application of the optical circulator is hindered. On the other hand, the price of the optical circulator is high, and the application of the optical circulator is limited.
In the prior art, us patent 5909310 provides a more typical optical circulator, and fig. 1 shows the principle of propagation of an optical signal from a first port to a second port in this scheme. After the optical signal inputted from the first port (101) of the optical circulator (100) is collimated by the first collimating lens (104), the optical signal is decomposed into two beams (116 a and 116 b) with mutually perpendicular polarization states by the first birefringent crystal (106), the two beams are polarized by the first half-wave plates (113 a and 113 b) and the first Faraday rotator (108) to be uniform (dot ". Cndot") and are focused by the second collimating lens (105) to the second port (102) by the polarization processing of the second half-wave plates (114 a and 114 b) and the second Faraday rotator (109), the angles of the beams are changed by the direction deflection of the wedge-shaped birefringent crystals (110 and 111) with mutually perpendicular optical axes (115 a and 115 b), and the polarization states of the two beams are mutually perpendicular (dot ". Cndot") and vertical ". Cndot") by the second birefringent crystal (107). A position compensation plate (112) is also included in fig. 1 to reduce the deviation of the beam from the central axis.
During reverse transmission, i.e. the optical signal input from the second port (102) is split by the second collimating lens (105) and then by the second birefringent crystal (107), and the polarization rotation of the second faraday rotator (109) and the second set of half-wave plates (114 a and 114 b) becomes two beams with identical polarization states, and due to the non-reciprocity of the faraday rotator (109), the polarization states of the two light beams transmitted in reverse directions are vertical "|" instead of dot "·", and when the two light beams pass through the wedge-shaped birefringent crystals (110 and 111) in reverse directions, the angle polarization effect of the wedge-shaped birefringent crystals (110 and 111) on the reverse light beams is opposite to that of the polarization state in forward directions, and then the combined light beams cannot return to the first port (101) along the original path due to the polarization combination effect of the first faraday rotator (108) and the first set of half-wave plates (113 a and 113 b).
The prior art described above is a typical representative optical circulator solution, the basic idea being to use wedge-shaped birefringent crystals (110 and 111) to make the polarization angles of the light beams non-uniform in the forward and reverse directions and to convert the beam angles into the exit beam positions (i.e. the port positions) by collimating lenses (104 and 105). The solution uses a large number of optical elements, and is difficult to further reduce the volume and cost. On the other hand, as described above, the three ports of the optical circulator are led out from both sides of the optical circulator, respectively, and it is difficult to further reduce the volume. This solution also cannot realize the array, and it is difficult to use the cost of the array.
In the prior art, U.S. patent 5471340 provides a reflective optical circulator as shown in fig. 2. The three ports (201, 202 and 203) are located on the same side of the optical circulator (200), and an optical signal input from the first port (201) is decomposed into two light beams with vertical polarization states through polarization beam splitting action of the first birefringent crystal (204), and the two light beams respectively pass through the second birefringent crystal (207) in the mode of ordinary rays and extraordinary rays through action of the half-wave plate (205) and the Faraday rotator (206). The 1/4 wave plate (208) and the reflecting mirror (209) rotate the polarization state of the reflected light beam by 90 degrees, and the two light beams respectively pass through the second birefringent crystal (207) in the extraordinary ray and the ordinary ray, so that the positions of the two light beams deviate from the same after passing through the second birefringent crystal (207) in the forward direction and the reverse direction, and then the two light beams are combined into a single light beam to be output from the second port through the polarization rotation effect of the Faraday rotator (206) and the half-wave plate (205) and the polarization beam combining effect of the first birefringent crystal (204). Similarly, an optical signal input from the second port may be pushed out from the third port, it is easy to understand that if more ports (fourth port, fifth port.) are added after the third port, these ports will constitute a new optical circulator.
It should be noted that in the prior art solution shown in fig. 2, one of the half-wave plate (205) and the second birefringent crystal (207) needs to be composed of two parts, the optical axis directions of which are different.
It can be seen that the reflective optical circulator scheme described above allows for one-dimensional array, thus allowing for both device volume and cost sharing. However, when the scheme is extended to a two-dimensional array port, two wave plate arrays with different optical axis directions or two birefringent crystal arrays with different optical axis directions are required, and the two element engineering is difficult to realize. In addition, when the scheme is extended to two-dimensional array ports, serious crosstalk problems exist, because the rotation angle of the Faraday rotator (206) has a certain dependence on wavelength and temperature, and optical axis direction alignment errors exist in the assembly process of the wave plates (205 and 208) and the birefringent crystals (204 and 207), so that the polarization extinction ratio of an optical system is about-24 dB, and residual light beams can enter adjacent ports to form crosstalk between the ports, and the crosstalk level is consistent with the polarization extinction ratio (-24 dB), so that the crosstalk is unacceptable.
The prior art cannot meet the requirements of optical communication on an integrated and low-cost optical circulator in terms of performance, volume and cost, and the integration level of the optical circulator needs to be further improved by adopting a two-dimensional array so as to reduce the volume and the cost.
Disclosure of Invention
In order to meet the demands of integration, miniaturization and low cost of optical communication devices, particularly optical circulators, the invention provides a reflective optical circulator array with low cost and compact structure.
The basic idea is as follows: all ports are accessed from one side by adopting reflection; the method can be expanded to a two-dimensional array to take advantage of the high integration of the two-dimensional array; the large-angle polarization beam splitter-combiner is adopted to completely separate the multipath optical signals of two polarization states in space, so that the crosstalk signal cannot enter the input and output ends.
It is particularly emphasized that the optical signals of multiple paths need to be separated as a whole, and since the optical signals of multiple paths have a large size (several millimeters) as a whole, the displacement type birefringent crystals commonly used in the prior art need to have an overall separation distance of several millimeters, and the length thereof needs several centimeters, which is not acceptable in size and cost. Therefore, the invention adopts a multilayer dielectric film type or sub-wavelength metal grating type polarization beam splitter-combiner to integrally separate two polarization states of a plurality of paths (especially two-dimensional array) of optical signals in a smaller space range.
As shown in fig. 3, the reflective optical circulator array (300) provided by the present invention includes:
1. An input/output port (301) comprising at least three ports for inputting and outputting multiple optical signals;
2. a polarization beam splitter/combiner (303);
3. a first non-reciprocal polarization rotator (304 a);
4. a first displacement birefringent crystal (305 a);
5. a first polarizing reflector (306 a);
6. a second non-reciprocal polarization rotator (304 b);
7. a second displacement birefringent crystal (305 b);
8. a second polarizing reflector (306 b);
the input/output terminal (301) comprises at least one group of ports, each group of ports comprises at least three ports, and a plurality of ports in each group of ports are arranged at equal intervals and have the same port period and port period direction.
An optical signal (307) input from a first port (311) of a first set of ports of the input/output port (301) is split into first and second polarization state optical signals (308 a and 308 b) with orthogonal polarization directions via the polarization beam splitter/combiner (303), propagates along first and second paths which are completely spatially separated, passes through the first and second non-reciprocal polarization rotators (304 a and 304 b), passes through the first and second displacement birefringent crystals (305 a and 305 b) to the first and second polarization reflectors (306 a and 306 b), is reflected via the first and second polarization reflectors (306 a and 306 b), is rotated by 90 degrees before polarization state is relatively reflected, passes back through the first and second displacement birefringent crystals (305 a and 305 b) and the first and second non-reciprocal polarization rotators (304 a and 304 b), becomes third and fourth polarization state optical signals (309 a and 309 b), and further reaches the polarization beam splitter (303). Due to the non-reciprocity of the first and second non-reciprocal polarization rotators (304 a and 304 b), the reflected third and fourth polarization state optical signals (309 a and 309 b) coincide with the polarization states of the first and second polarization state optical signals (308 a and 308 b), respectively, and thus are combined into outgoing light rays of the same direction to the input/output end (301) by the polarization beam combining action of the polarization beam splitter/combiner (303).
The first polarization state optical signal propagation direction and the port period direction form a first reference plane (X-Z plane in fig. 3), and the second polarization state optical signal propagation direction and the port period direction form a second reference plane (X-Z plane in fig. 3, which is still the 90 degree reflection of the polarization beam splitter-combiner).
The first and second displacement birefringent crystals (305 a and 305 b) have the same length in the optical signal propagation direction, and have optical axes (310 a and 310 b) in the first and second reference planes and are at an angle (other than 0 degrees and 90 degrees) to the optical signal propagation direction, so that when the third and fourth polarized optical signals (309 a and 309 b) reach the input/output terminal (301), they have the same direction as the port period (314) of the input/output terminal (301), and are equal in size, so that the third and fourth polarized optical signals (309 a and 309 b) are further combined in position and output from the second port (312) adjacent to the first port (311).
Similarly, the optical signal input from the second port (312) will be output from the third port (313), and it will be readily understood that if more ports (fourth port, fifth port.) are added after the third port, these ports will constitute more optical circulators, forming a one-dimensional array of optical circulators.
Similarly, it can be inferred that more port groups are arranged in a direction (Y axis in the drawing) perpendicular to the plane (X-Z plane in the drawing) in which the first and second polarized light signals (308 a and 308 b) are located, each port group forming a one-dimensional optical circulator array, and all port groups forming a two-dimensional optical circulator array, thereby greatly improving the integration level.
Further, the invention also provides a reflective optical circulator array with a steering reflector, and the steering reflector is arranged on the first path or the second path behind the polarization beam splitting and combining device, so that optical signals with two polarization states have the same propagation direction, the volume is further reduced, and optical elements with the same parameters on the two paths are combined. To compensate for the extra optical path due to the turning mirror, there are two optical path compensation schemes:
optical path compensation scheme one: an optical path compensation element is added to the other path, preferably in front of the mirror comprised by the first or second polarizing reflector.
Optical path compensation scheme II: the first and second polarizing mirrors are replaced with a right angle prism mirror and a 1/2 wave plate, the 1/2 wave plate being on only the first or second path. The effect of the right angle prism mirror is to interchange the optical signal positions on the first and second paths so that the first and second polarization state signals travel through the same path clockwise and counterclockwise, respectively, and thus have the same optical path.
The reflective optical circulator array provided by the invention is further described below.
The input/output end has a one-dimensional or two-dimensional array structure, the arrangement mode is shown in fig. 4a, the same coordinates as those of fig. 3 are adopted, the viewing angle is changed, a plurality of ports are arranged in an X-Y plane and are divided into n port groups L1 and L2. There is no special requirement in the direction perpendicular to the equidistant arrangement of the ports (Y direction), and the equidistant or unequal spacing is possible.
The multipath optical signals input to the polarization beam splitter and combiner by the ports need to have a certain collimation characteristic, so that the multipath optical signals can still obtain higher coupling efficiency when the multipath optical signals return to the input and output ends through the optical system shown in fig. 3. As shown in fig. 4b, the input/output end (400) is composed of an optical fiber array (401) and a lens array (402), and has the same arrangement as that of fig. 4a, so that each lens of the lens array (402) corresponds to each optical fiber of the optical fiber array (401) one by one and has the same relative position, and thus a collimated optical signal array with parallel optical signals can be obtained. Preferably, each optical signal of the array of collimated optical signals is parallel to the normal to the plane of the lens array (402).
The lens array comprises a substrate whose optical thickness (physical thickness d divided by refractive index n of the substrate material) is close to and slightly offset from the focal length of the lens, such that the beam waist of the collimated beam is at the mirrors (306 a and 306 b) shown in fig. 3, with minimal coupling loss of the optical system. The lenses of the lens array may be spherical and aspherical convex lenses or may be self-focusing lenses, and the convex topography of the convex lens surface helps to reduce reflected echoes, and the aspherical surface helps to reduce aberrations, so the preferred mode of the lens array is to have a convex lens array with an aspherical topography.
The optical signal inputted through one of the input and output terminals has two polarization states perpendicular to each other, and for convenience of description, vertical lines "|" and dots "·" are used to indicate the two polarization directions in fig. 3 and 5, respectively. The basic function of the polarization beam splitter/combiner is to completely separate two polarization states of the input multipath optical signals in space so as to facilitate the separate processing of subsequent optical elements, and the polarization beam splitter/combiner can combine the reflected two groups of polarization state optical signals and output the combined signals to an input end and an output end.
Fig. 5a and 5b show two preferred forms of the polarizing beam splitter-combiner. Fig. 5a shows a polarization beam splitter/combiner (501 a) using a multilayer dielectric film, which is formed by bonding two triangular bodies, wherein the bonding surface of each triangular body is plated with a multilayer dielectric film, so that the function of reflecting one polarization and transmitting the perpendicular polarization can be realized. Fig. 5b shows a polarization beam splitter/combiner (501 b) using a sub-wavelength grating, which is formed by micro-machining a sub-wavelength grating on a substrate, and the sub-wavelength grating is preferably a sub-wavelength metal grating, so that the function of reflecting one polarization and transmitting the perpendicular polarization can be realized.
The two polarization states of the incident optical signals (502 a and 502 b) are separated at the polarization beam splitters (501 a and 501 b). The transmitted first polarized optical signals (503 a and 503 b) are reflected by the subsequent optical element and keep the polarization state unchanged, and the reflected optical signals (506 a and 506 b) continue to be transmitted to the input and output ends at the polarization beam splitters and combiners (501 a and 501 b). Similarly, the reflected second polarized optical signals (504 a and 504 b) are reflected and kept unchanged by the processing of the subsequent optical elements as shown in fig. 3, and the reflected optical signals (505 a and 505 b) continue to be reflected to the input/output end at the polarization beam splitters (501 a and 501 b). The outgoing optical signals (507 a and 507 b) combined by the polarization beam splitters (501 a and 501 b) are output from a port adjacent to the input port by a displacement deviation due to the displacement deviation of the subsequent optical element.
The first and second non-reciprocal polarization rotators (304 a and 304 b) are capable of rotating a certain polarization state of the incident light by a certain angle, such as 0 degrees, 45 degrees or 90 degrees, referred to as a rotation angle. After passing through the first and second non-reciprocal polarization rotators in a polarization state orthogonal to the rotated polarization state, the polarization state remains consistent with the polarization state at the time of incidence. Fig. 6a, 6b, 6c correspond to the case where the rotation angle is 0 degrees, 45 degrees or 90 degrees, respectively (viewed along the direction of the first pass of the light rays through the first and second non-reciprocal polarization rotators). To maintain non-reciprocity, the first and second non-reciprocal polarization rotators (304 a and 304 b) comprise a 45 degree Faraday rotator (601 a, 601b, and 601 c), a half-wave plate (602 a in FIG. 6a and 602c in FIG. 6 c), or no half-wave plate (FIG. 6 b). For convenience of explanation, fig. 6a, 6b, and 6c illustrate polarization states of polarization directions of 0 degrees, 90 degrees, -45 degrees, and 45 degrees by horizontal lines "one", vertical lines "|", left-hand lines "/" and right-hand lines "\", respectively, describing changes in polarization states of the first and second nonreciprocal polarization rotators passing through twice.
In fig. 6a, the incident optical signal (603 a) has a polarization direction of 0 degrees, the polarization direction of the optical signal (604 a) passing through the 45-degree faraday rotator (601 a) is rotated 45 degrees clockwise, and the polarization direction of the optical signal (605 a) is rotated to 0 degrees after passing through the half-wave plate (602 a) having an optical axis (609 a) of 67.5 degrees; after the 90-degree polarization direction reverse optical signal (606 a) passes through the half-wave plate (602 a) reversely, the polarization direction of the reverse optical signal (607 a) is rotated to-45 degrees. After passing through the 45-degree Faraday rotator (601 a), the polarization direction of the reverse optical signal (608 a) was 0 degrees, and the polarization direction of the reverse optical signal (603 a) was identical to that of the incident optical signal.
In fig. 6b, the incident optical signal (603 b) has a polarization direction of 0 degrees, the polarization direction of the optical signal (605 b) passing through the 45-degree faraday rotator (601 b) is rotated 45 degrees clockwise, and when the reverse optical signal (606 b) having a polarization direction of-45 degrees passes through the 45-degree faraday rotator (601 b) in the reverse direction, the polarization direction of the reverse optical signal (608 b) is 0 degrees, which coincides with the polarization direction of the incident optical signal (603 b).
In fig. 6c, the incident optical signal (603 c) has a polarization direction of 0 degrees, the polarization direction of the optical signal (604 c) passing through the 45-degree faraday rotator (601 c) is rotated 45 degrees clockwise, and the polarization direction of the optical signal (605 c) is rotated 90 degrees after passing through the half-wave plate (602 c) having an optical axis (609 c) of 22.5 degrees; after the 0-degree polarization direction reverse optical signal (606 c) passes through the half-wave plate (602 c), the polarization direction of the reverse optical signal (607 c) is rotated to-45 degrees. After passing through the 45-degree Faraday rotator (601 c), the polarization direction of the reverse optical signal (608 c) is 0 degrees, and matches the polarization direction of the incident optical signal (603 a).
The 45 degree faraday rotators (601 a, 601b, and 601 c) require a magnetic field (610 a, 610b, and 610 c) to maintain faraday effect, which may be a magnetic field provided by an external magnet or a magnetic field built into the faraday rotator material.
The magnetic field direction of the 45 degree faraday rotators (601 a, 610b, and 601 c) in fig. 6a, 6b, and 6c can also be reversed along the propagation direction of the optical signal, and the effect on the polarization direction can be rotated 45 degrees clockwise and counterclockwise, respectively; the optical axes (609 a and 609 c) of the half-wave plates (602 a and 602 c) may be any one of +/-22.5 degrees and +/-67.5 degrees; the polarization state of the incident optical signals (603 a, 603b, and 603 c) may take any one of 0 degrees and 90 degrees; the positions of the 45 degree faraday rotators (601 a and 601 c) and half wave plates (602 a and 602 c) are also interchangeable.
The first and second displacement birefringent crystals (305 a and 305 b) are parallel-light-passing surfaces, are common optical glass relative to ordinary rays, and are displaced relative to extraordinary rays, the magnitude and direction of the displacement depend on the length of the birefringent crystals (305 a and 305 b) and the direction of the optical axes (310 a and 310 b) thereof, and as mentioned above, the optical axes (310 a and 310 b) are in corresponding reference planes, and are determined according to the polarization directions of the optical signals (605 a, 605b and 605 c) after the first pass through the first and second nonreciprocal polarization rotators in fig. 6a, 6b and 6c, so that the displacement directions (relative to the XY arrangement plane of the input and output ends) generated by the outgoing optical signals after the positive and negative passes through the first and second displacement birefringent crystals are the same; in the present invention, the first and second displacement birefringent crystals (305 a and 305 b) also have the same length so that the displacement directions and magnitudes of the two polarization state components of the outgoing optical signal are the same and coincide with the arrangement period T of the input-output terminals.
As is well known, in order to displace the birefringent crystal (701 a) by a certain amount (703 a), the optical axis (702 a) of the birefringent crystal needs to be at a certain angle to the direction of the incident light (704), which also needs to be extraordinary. The resulting displacement is in a plane formed by the direction of propagation (704) of the optical signal and the optical axis (702 a). The most commonly used birefringent crystals are lithium niobate and yttrium vanadate crystals, and in the case of yttrium vanadate crystals, the optimum angle is about 45 degrees, and the size of the displacement (703) is about one tenth of the length L of the yttrium vanadate crystal, and in combination with the period T of fig. 4, the length L of the yttrium vanadate crystal can be estimated to be about ten times the length L, i.e. l=10t.
It is also possible to see along the light propagation direction, as shown in fig. 7b, when the displacement (703 b) of the extraordinary ray on the birefringent crystal (701 b) is parallel to the projection (702 b) of the optical axis.
It should be noted that, for the configuration shown in FIG. 6b (the non-reciprocal polarization rotator does not contain a half-wave plate), the polarization direction of the optical signal after passing through the first or second non-reciprocal polarization rotator is 45 degrees, as shown in FIG. 7c, where the first and second mobile birefringent crystals are composed of two sub-birefringent crystals (704 and 705), the two sub-birefringent crystals (704 and 705) are superimposed on each other in the figure as viewed against the propagation direction of the optical signal, the optical axes of which are rotated by 45 degrees (706) and-45 degrees (707) about the symmetry axis of the propagation direction of the optical signal, respectively, the lengths of the sub-birefringent crystals being The displacement amounts (708 and 709) areSince the two displacements have an angle of 90 degrees, the resultant displacement (703 c) is T.
As shown in fig. 8a, the first and second polarizing reflectors (800 a) are composed of one mirror (801 a) and a 1/4 wave plate (802 a). The optical axis of the 1/4 wave plate (802 a) forms an angle of 45 degrees with the polarization direction of the optical signal (803 a) incident thereon, the incident optical signal (803 a) is changed into circularly polarized light after passing through the 1/4 wave plate (802 a), the circularly polarized light is reflected by the reflecting mirror (801 a) and then passes through the 1/4 wave plate (802 a) again, the effect of passing through the 1/4 wave plate (802 a) twice is the same as that of passing through one half wave plate, and the polarization direction of the emergent optical signal (804 a) is rotated by 90 degrees.
Instead of the 1/4 wave plate (802 a), a 45-degree faraday rotator may be used, the effect of which is to rotate the outgoing optical signal (804 a) 90 degrees with respect to the polarization direction of the incoming optical signal (803 a) by two passes through the 45-degree faraday rotator.
The reflector can be made of high-reflection multilayer dielectric film, or high-reflection metal film such as gold film or aluminum film.
As shown in fig. 8b, the first and second polarizing reflectors (800 b) may also consist of a retro-reflector (801 b) and half-wave plate (802 b). The half-wave plate (802 b) is located in only one of the two paths with its optical axis at a 45 degree angle to the polarization direction of the optical signal incident thereon (803 b in the figure). The retro-reflector (801 b) inverts the incident light signal, with the angle unchanged. The incident light signal 803b passes through the half-wave plate 802b and then rotates 90 degrees in polarization state, and is reflected twice by the backtracking mirror 801b and then exits. Since the half-wave plate acts only once, the polarization direction of the outgoing optical signal (804 b) is rotated by 90 degrees.
The retrospective mirror (801 b) may be a rectangular prism with total internal reflection as shown in fig. 8b, or may be two plane mirrors with an angle of 90 degrees.
The anti-crosstalk capability of the reflective optical circulator provided by the invention is further analyzed below. The optical circulator provided by the invention and all the prior art needs to use a 45-degree Faraday rotator, but the rotation angle is not always 45 degrees, and for a specific wavelength lambda and a specific use temperature t, the rotation angle has a certain deviation from 45 degrees, and is recorded as delta theta, and the optical circulator has the following relation:
Δθ＝a·(λ-λ 0 )+b·(t-t 0 ) (1)
in the above formula (1), lambda 0 And t 0 For a center wavelength and center temperature at exactly 45 degrees rotation. a is a wavelength correlation coefficient, b is a temperature correlation coefficient, and in the case of wavelength units of nanometers and temperature units of degrees celsius, a is about 0.07 degrees/nanometer and b is about 0.06 degrees/celsius. The delta theta was 3.8 degrees with a 20 nm deviation of the wavelength from the center wavelength, with a 40 degree celsius difference in the use temperature from the center temperature. The polarization extinction ratio (PER-Polarization Extinguish Ratio) resulting from Δθ is given by:
PER＝10·log10(sin 2 (Δθ)) (2)
from this, it can be deduced that the polarization extinction ratio PER generated by the 45-degree faraday rotator is-23.6 dB, and the behavior of this part of the residual optical signal in the optical system provided by the present invention is analyzed in conjunction with fig. 9. The optical signal (907) input from one port (912) of the input/output end (901) is decomposed into two polarized optical signals with polarization states perpendicular to each other on the polarization beam splitter/combiner (903), for simplicity, fig. 9 only analyzes the transmitted first polarized optical signal (vertical line "|") in the drawing, the transmitted first polarized optical signal (908) further passes through the first non-reciprocal polarization rotator (904) and includes a 45-degree faraday rotator, the polarization state is rotated by 90 degrees, the dot "·" in the drawing indicates that after the optical signal passes through the first displacement birefringent crystal (905), the optical signal is reflected from the first polarization reflector (906) and further reversely passes through the first displacement birefringent crystal (905) and the first non-reciprocal polarization rotator (904), and the reflected optical signal (909) is the same as the polarization state of the transmitted first polarized optical signal (908) and further passes through the polarization beam splitter/combiner (903) to reach the adjacent port (913). In addition to the polarized optical signal, the 45-degree faraday rotator also generates a vertical polarized optical signal (vertical line "|") of about-23.6 dB, the polarized optical signal (914) passes through the first shift birefringent crystal (905) with an extraordinary ray, and according to the direction of the optical axis (910), the part of the optical signal is further reflected by the first polarizing reflector (906), the polarized state is rotated by 90 degrees, the ordinary ray passes through the first shift birefringent crystal (905) again, and passes through the first nonreciprocal polarizing rotator (904) again, the optical signal (915) with a dot "·" in polarized state reaches the polarizing beam combiner (903), and the part of the optical signal cannot be transmitted through the polarizing beam combiner (903) to an adjacent port (911) and is reflected out of the optical system.
While only the first polarization state light signal transmitted through the polarization beam splitter and combiner is analyzed, the same is true for the reflected second polarization state light signal. The conclusion is also true of the polarization extinction ratio reduction caused by the optical axis angle alignment errors of the half-wave plate, the displacement birefringent crystal and the 1/4 wave plate.
Furthermore, the reflective optical circulator array provided by the invention introduces a steering reflector on the first or second polarized light signal propagation path after the polarization beam splitter and combiner, so that the propagation directions of the first and second polarized light signals are consistent, the volume is further reduced, parts of elements with the same optical performance are combined, and the number of assembly elements is reduced. Taking fig. 10a and 10b as an example, turning mirrors (1005 a and 1005 b) are introduced on the reflection path of the polarization beam splitter/combiner, fig. 10a is for the case where the turning mirror is a total internal reflection prism, and fig. 10b is for the case where the turning mirror is a plane mirror placed at 45 degrees.
The turning mirrors (1005 a and 1005 b) make the first and second polarization state optical signals separated by the polarization beam splitters (1003 a and 1003 b) of the incident optical signals (1001 a and 1001 b) into two optical signals (1002 a and 1004a,1002b and 1004 b) with identical propagation directions, and the two optical signals are incident on subsequent optical elements (omitted in the figure) and reflected by the first and second polarization reflectors (1006 a and 1007a,1006b and 1007 b) with the same direction.
It should be noted that due to the introduction of turning mirrors (1005 a and 1005 b), the second polarization state optical signals (1004 a and 1004 b) will travel an additional optical path compared to the first polarization state optical signals (1002 a and 1002 b), and if this portion of the optical path is not compensated, a very severe polarization mode dispersion will occur between the first and second polarization state optical signals, which is unacceptable. The present invention also provides an optical path compensation element to eliminate polarization mode dispersion due to steering mirror introduction, as described below.
In general, the optical path compensation element is only required to have the same optical path as the required compensation optical path, and the optical path to be compensated is generated by an optical material with the thickness of d1 and the refractive index of n1, and the optical path to be compensated is n1 d1; setting the thickness of the optical path compensation element as d2, the refractive index as n2, and the generated compensation optical path as n2.d2; the following relationship is naturally true:
n 1 ·d 1 ＝n 2 ·d 2 (3)
the above formula (3) brings a certain degree of freedom to the selection of the material and length of the optical path compensation element, and is not necessarily the same as the refractive index and length of the optical element to be compensated, as long as the product of the refractive index and the length is equal. However, considering that the equivalent optical thickness expression of the optical element in the imaging system is determined by d1/n1, the following relationship must be satisfied for the optical system to have optimal coupling efficiency:
The only solutions that can satisfy both the above equations (3) and (4) are n1=n2 and d1=d2, and the most straightforward solution is to use an optical path compensation element that has the same material and length as the optical element to be compensated.
In the case of a collimated optical signal having a large beam waist (e.g., a beam waist radius greater than 100 microns), satisfying (3) but not (4) will not have a large impact on the optical system coupling efficiency. However, for the array optical circulator provided by the invention, the lens array used by the input end and the output end generally has a shorter focal length, so that the beam waist of each path of optical signal after collimation is smaller (the beam waist radius is smaller than 70 microns), and the integration level is improved. An inability to satisfy the equation (4) will result in a large coupling loss. The optical path compensation elements (1008 a and 1008 b) provided by the present invention have the same refractive index (same optical material) and the same thickness as the turning mirrors (1005 a and 1005 b).
If the steering mirror is a total internal reflection prism (1005 a) composed of BK7, the optical path compensation element (1008 a) is BK7 parallel plate glass of the same thickness; if the turning mirror is a plane mirror (1005 b), the optical path compensation element is an air layer (1008 b) of the same thickness.
In principle the optical path compensation element may be placed anywhere after the polarizing beam splitter and before the first or second polarizing reflector, optimally before the first or second polarizing reflector or before the mirrors comprised in the first or second polarizing reflector, so that part of the optical elements in the two paths before the mirrors may be combined into one whole.
In the case of using turning mirrors, the present invention also provides an optical circulator array with optical path compensation as shown in fig. 10 c. The polarizing reflector shown in fig. 8b is used, consisting of a back mirror (1008 c) and a half wave plate (1007 c). The incident optical signal (1001 c) is decomposed by the polarization beam splitter/combiner (1003 c) and passes through the steering mirror (1005 c), and becomes first and second polarized optical signals (1002 c and 1004 c) having identical (parallel) propagation directions, and the first and second polarized optical signals are reflected by the polarization reflector (1006 c) through the subsequent nonreciprocal polarization rotator and the displacement birefringent crystal (omitted in the figure), and the positions of the first and second polarized optical signals are interchanged while the polarization states are rotated by 90 degrees, and return along the second and first paths, respectively, and pass through equal optical paths without generating additional optical path differences.
From the analysis, the reflective optical circulator array provided by the invention is expanded to a two-dimensional array, and meanwhile, the complex wave plate array or the birefringent crystal array is avoided being introduced, so that the crosstalk problem caused by the reduction of the polarization extinction ratio is eliminated. The implementation of the two-dimensional array greatly improves the integration level and greatly reduces the cost of a single circulator.
Drawings
Figure 1 is a schematic diagram of a three port optical circulator in the prior art
Fig. 2 is a schematic diagram of a conventional reflection type optical circulator
FIG. 3 is a schematic diagram of a reflective optical circulator array according to the invention
FIG. 4a shows an arrangement of input/output terminals according to the present invention
FIG. 4b shows an input/output port of a reflective optical circulator array according to the invention, comprising an optical fiber array and a lens array
FIG. 5a shows a polarization beam splitter/combiner comprising a multilayer dielectric film cube
FIG. 5b shows a polarization beam splitter/combiner comprising a sub-wavelength metal grating
FIG. 6a shows a reflective optical circulator array according to the invention comprising a first or a second non-reciprocal polarization rotator comprising a half-wave plate and a 45 degree Faraday rotator, the rotation angle being 0 degree
FIG. 6b shows a first or second non-reciprocal polarization rotator comprising a 45 degree Faraday rotator with a rotation angle of 45 degrees
FIG. 6c shows a first or second non-reciprocal polarization rotator comprising a half-wave plate and a 45-degree Faraday rotator with a rotation angle of 90 degrees
FIG. 7a is a side view of a first or second displacement birefringent crystal comprised by a reflective optical circulator array provided by the invention
FIG. 7b shows a first or second displacement birefringent crystal included in a reflective optical circulator array according to the invention, looking against the propagation direction of an optical signal
FIG. 7c shows a first or second displacement birefringent crystal comprising two sub-birefringent crystals of the reflective optical circulator array according to the invention
FIG. 8a shows a reflective optical circulator array comprising a first or second polarizing reflector comprising a 1/4 half-wave plate and a reflecting mirror
FIG. 8b shows a reflective optical circulator array comprising a first or second polarizing reflector comprising a half-wave plate and a back-tracking mirror
Fig. 9 shows an anti-crosstalk principle analysis of a reflective optical circulator array according to the present invention
FIG. 10a shows a turning mirror and an optical path compensation element included in a reflective optical circulator array according to the present invention, where the turning mirror is a total internal reflection prism, and the optical path compensation element is parallel plate glass with the same material and thickness
FIG. 10b shows a turning mirror and an optical path compensation element included in a reflective optical circulator array according to the present invention, the turning mirror is a plane mirror, and the optical path compensation element is air with the same thickness
FIG. 10c shows a turning mirror and a polarizing reflector comprising a half-wave plate and a back-tracking mirror, the array of reflective optical circulators according to the present invention
FIG. 11 shows example 1 of a reflective optical circulator array according to the invention
FIG. 12 example 2 of a reflective optical circulator array provided by the invention
FIG. 13 example 3 of a reflective optical circulator array provided by the invention
FIG. 14 example 4 of a reflective optical circulator array provided by the invention
FIG. 15 example 5 of a reflective optical circulator array provided by the invention
FIG. 16 example 6 of a reflective optical circulator array provided by the invention
Detailed Description
Example 1
As shown in fig. 11, an embodiment (1100) of the reflective optical circulator array provided by the invention includes:
1. an input/output port (1101) comprising an optical fiber array (1107) and a lens array (1102);
2. a multilayer dielectric thin film type polarization beam splitter-combiner (1103);
3. a first nonreciprocal polarization rotator (1104 a) consisting of a first half-wave plate (1108 a) and a first 45-degree Faraday rotator (1109 a);
4. a first displacement birefringent crystal (1105 a) having a first optical axis (1110 a);
5. a first polarizing reflector (1106 a) consisting of a first 1/4 wave plate (1111 a) and a first mirror (1112 a);
6. A second nonreciprocal polarization rotator (1104 b) consisting of a second half-wave plate (1108 b) and a second 45-degree Faraday rotator (1109 b);
7. a second displacement birefringent crystal (1105 b) having a second optical axis (1110 b);
8. a second polarizing reflector (1106 b) consisting of a second 1/4 wave plate (1111 b) and a second mirror (1112 b).
Each optical fiber of the optical fiber array (1107) corresponds to each lens of the lens array (1102) one by one, and is arranged at equal intervals along the X direction on the X-Y plane, wherein the arrangement period is T, and T can be within a certain range, and T=0.25 mm is taken in the embodiment. The lens array (1102) collimates a plurality of optical signals input via the fiber array (1107), the collimated optical signals being directed perpendicular to the X-Y plane (i.e., along the Z-direction) to form a collimated plurality of ports.
The first and second non-reciprocal polarization rotators (1104 a and 1104 b) comprising first and second half-wave plates (1108 a and 1108 b) configured with first and second 45 degree faraday rotators (1109 a and 1109 b) are depicted by fig. 6c, rotating the polarization state of the first pass optical signal by 90 degrees;
the first and second displacement birefringent crystals (1105 a and 1105 b) are composed of yttrium vanadate crystals having the same length L in the direction of propagation of the optical signal, the length L being about 10 times the aforementioned period T, and the length being 2.5mm in the case where T is 0.25mm. The optical axes (1110 a and 1110 b) of the first and second displacement birefringent crystals (1105 a and 1105 b) are in the X-Y plane and are at an angle of 45 degrees to the X direction.
The first and second polarizing reflectors (1106 a and 1106 b) comprise first and second 1/4 wave plates (1111 a and 1111 b) and first and second mirrors (1112 a and 1112 b) configured as described in fig. 8 to rotate the polarization state of the reflected optical signal by 90 degrees;
optical signals input from any port of an input/output port (1101) are decomposed into first and second polarized optical signals with perpendicular polarization directions by the multilayer dielectric thin film type polarization beam splitter/combiner (1103), respectively travel along transmission and reflection paths with large separation angles, pass through the first and second nonreciprocal polarization rotators (1104 a and 1104 b), pass through the first and second displacement birefringent crystals (1105 a and 1105 b) to the first and second polarization reflectors (1106 a and 1106 b), are reflected by the first and second polarization reflectors (1106 a and 1106 b), rotate by 90 degrees relative to the pre-reflection polarization state, pass back through the first and second displacement birefringent crystals (1105 a and 1105 b) and the first and second nonreciprocal polarization rotators (1104 a and 1104 b) to become third and fourth polarized signals, and further reach the polarization beam splitter/combiner (1103). Due to the non-reciprocity of the first and second non-reciprocal polarization rotators (1104 a and 1104 b), the reflected third and fourth polarization signals respectively coincide with the polarization states of the first and second polarization state optical signals, and are combined into an outgoing light beam with the same direction and position to the adjacent port output of the input port through the polarization beam combining function of the polarization beam splitting and combining device (1103).
Example 2
As shown in fig. 12, an embodiment (1200) of the reflective optical circulator array provided by the invention includes:
1. an input/output (1201) comprising an optical fiber array and a lens array;
2. a multilayer dielectric thin film type polarization beam splitter/combiner (1203);
3. a non-reciprocal polarization rotator (1204) consisting of a first half-wave plate (1208 a), a second half-wave plate (1208 b), and a 45 degree Faraday rotator (1209);
4. a displacement birefringent crystal (1205) having an optical axis (1210);
5. a polarizing reflector (1206) consisting of a 1/4 wave plate (1211), first mirror (1212 a), second mirror (1212 b) and an optical path compensation element (1214);
6. a total internal reflection prism steering mirror (1213);
this embodiment is similar to embodiment 1, with the addition of a turning mirror (1213) to turn the second polarization state optical signal by 90 degrees, to have the same propagation direction for the first and second polarization state optical signals, and an optical path compensation element (1214) is added in front of the first mirror (1212 a) and has the same thickness and material as the turning mirror (the thickness of the turning mirror can be regarded as the sum of the paths the optical signal has taken inside).
The optical axes of the first half wave plate and the second half wave plate are respectively 22.5 degrees and-22.5 degrees or 67.5 degrees and-67.5 degrees with the port period direction (X axis in the figure) of the input end (1201) so that the polarization states of the first polarized light signal and the second polarized light signal are consistent after passing through. Such that subsequent optical elements will see a uniform polarization state, such that portions of the optical elements are combined into a single element, such as 45 degree Faraday rotator (1209), shift birefringent crystal (1205), and 1/4 wave plate (1211) in the figure, can all be seen as two plates combined in example 1.
The optical path compensation element (1214) is placed in front of the first mirror (1212 a) to ensure that the optical paths of the two paths are identical and the imaging equivalent optical thickness is also identical, and to enable the incorporation of the partial optical elements in front of it. For the same reason, the first and second mirrors (1212 a and 1212 b) are offset in the direction of propagation of the optical signal and cannot be combined.
Example 3
As shown in fig. 13a and 13b, an embodiment (1300) of the reflective optical circulator array provided by the present invention includes:
1. an input/output terminal (1301) composed of an optical fiber array and a lens array;
2. a multilayer dielectric thin film type polarization beam splitter/combiner (1303);
3. A non-reciprocal polarization rotator (1304) consisting of a half-wave plate (1308) and a 45 degree Faraday rotator (1309);
4. a first displacement birefringent crystal (1305 a) having a first optical axis (1310 a);
5. a second shift birefringent crystal (1305 b) having a second optical axis (1310 b);
5. a polarizing reflector (1306) comprising a 1/4 wave plate (1311), a first mirror (1312 a), a second mirror (1312 b) and an optical path compensation element (1314, air segment);
6. a plane mirror type steering mirror (1313);
this embodiment is similar to embodiment 2 in that the total internal reflection type steering mirror is replaced with a plane mirror type steering mirror (1313) in comparison with embodiment 2, and correspondingly, an air section (1314) is used as an optical path compensation element. Further, the port cycle direction of the input-output terminal (1301) is changed to the Y-axis in the figure.
The first and second half-wave plates of example 2 are combined into a single half-wave plate (1308) with an optical axis 22.5 degrees or-22.5 degrees or 67.5 degrees or-67.5 degrees with respect to the port periodic direction (Y-axis in the figure) of the input/output (1301) so that the first and second polarization state optical signals pass through and then are perpendicular to each other and 45 degrees or-45 degrees with respect to the Y-axis, and thus further pass through a 45-degree faraday rotator (1309) and then become 0 degrees or 90 degrees with respect to the Y-axis.
The first and second optical axes (1310 a and 1310 b) of the first and second birefringent crystal (1305 a and 1305 b) are oriented as shown in sub-image (1) and sub-image (2) of fig. 13b, respectively, noting the viewing angle shift, the first and second optical axes being in the Y-Z plane and at 45 degrees or-45 degrees, respectively, to the propagation direction (Z axis), such that the displacement amounts generated after the first and second polarized light signals perpendicular to each other pass through the first and second birefringent crystal (1305 a and 1305 b) twice are the same, and the direction along the Y axis is the same as the port period direction.
Similar to example 2, the 45 degree Faraday rotator (1309) and the 1/4 wave plate (1311) can be seen as two plates combined in example 1.
The optical path compensation element (1314) is an air segment placed in front of the first mirror (1312 a) to ensure that the optical paths of the two paths are identical and the imaging equivalent optical thickness is also identical, and to enable the merging of the partial optical elements in front of it. Similar to embodiment 2, the first and second mirrors (1312 a and 1312 b) are offset in the propagation direction of the optical signal and cannot be combined.
Example 4
As shown in fig. 14a and 14b, an embodiment (1400) of the reflective optical circulator array provided by the present invention includes:
1. An input/output terminal (1401) comprising an optical fiber array and a lens array;
2. a sub-wavelength metal grating type polarization beam-splitting/combining device (1403);
3. a first nonreciprocal polarization rotator (1404 a) consisting of a first 45 degree faraday rotator (1404 a);
3. a second non-reciprocal polarization rotator (1404 b) consisting of a second 45 degree faraday rotator (1404 b);
4. a first displacement birefringent crystal (1405 a) composed of first and second sub-birefringent crystals (1415 a and 1416 a);
5. a second shift birefringent crystal (1405 b) composed of third and fourth sub-birefringent crystals (1415 b and 1416 b);
5. a first polarizing reflector (1406 a) composed of a first 1/4 wave plate (1411 a), a first mirror (1412 a);
6. a second polarizing reflector (1406 b) composed of a second 1/4 wave plate (1411 b), a second mirror (1412 b);
in this embodiment, compared with embodiment 1, the polarization beam splitter/combiner (1403) uses a sub-wavelength metal grating (a multilayer dielectric thin film type is also possible). The two half-wave plates are removed, but the first and second displacement birefringent crystals (1405 a and 1405 b) are split into two pairs of birefringent crystals.
In this embodiment, the port cycle T direction of the input/output terminal is taken as the Y axis, so that the rotation directions of the first and second 45-degree faraday rotators (1404 a and 1404 b) are opposite. When the first and second paths are viewed through the-Z and X axes, the first and second polarization state optical signals will have the same polarization state, causing the first and second displacement birefringent crystals (1405 a and 1405 b), the first and second polarizing reflectors (1406 a and 1406 b) to be optically fully equivalent, so that analysis of the behavior of one of the paths is sufficient.
As in fig. 14b, the same principle of operation as in the case of the sub-birefringent crystal described in fig. 7 above. Note that the viewing angle is changed, and the first and second sub-birefringent crystals (1415 a and 1416 a) are superimposed on each other in the drawing, with their optical axes rotated by 45 degrees (1406) and-45 degrees (1407) with the light propagation direction as the symmetry axis, respectively, as viewed in the direction of propagation of the light signal, and are perpendicular to each other. The length of the sub-birefringent crystal isWhen the first polarization state optical signal passes through the first sub-birefringent crystal (1415 a) for the first time as an extraordinary ray, a first displacement amount (1408) is generated, and then it passes through the second sub-birefringent crystal (1416 a) as an ordinary ray, and no displacement amount is generated; after being reflected by the first polarizing reflector (1406 a), the polarization state is rotated by 90 degrees, and the extraordinary ray passes through the second sub-birefringent crystal (1416 a) reversely, so that a second displacement (1409) is generated, and then the extraordinary ray passes through the first sub-birefringent crystal (1415 a) for the second time, so that no displacement is generated; the first and second displacement amounts (1408 and 1409) are of the size +.>Since the two displacements have a 90 degree angle, the resultant displacement (1403 c) is T and is along the Y-axis, the same size and direction as the port period T.
Example 5
As shown in fig. 15, an embodiment (1500) of a reflective optical circulator array provided by the invention includes:
1. An input/output port (1501) comprising an optical fiber array and a lens array;
2. a multilayer dielectric thin film type polarization beam splitter/combiner (1503);
3. a non-reciprocal polarization rotator (1504) consisting of a first half-wave plate (1508 a), a second half-wave plate (1508 b) and a 45 degree Faraday rotator (1509);
4. a displacement birefringent crystal (1505) having an optical axis (1510);
5. a polarizing reflector (1506) consisting of a half-wave plate (1511) and a retro-reflector (1512);
6. a total internal reflection prism steering mirror (1513);
this embodiment is similar to embodiment 2 in that the polarizing reflector (1206) of embodiment 2 is replaced by a backtracking mirror (1512) and a half-wave plate (1511) that is present only on the first or second path, the other elements being identical, as compared to embodiment 2.
Example 6
As shown in fig. 16a and 16b, an embodiment (1600) of a reflective optical circulator array provided by the present invention includes:
1. an input/output terminal (1601) comprising an optical fiber array and a lens array;
2. a multilayer dielectric thin film type polarization beam splitter/combiner (1603);
3. a nonreciprocal polarization rotator (1604) comprising a half-wave plate (1608) and a 45 degree Faraday rotator (1609);
4. A first displacement birefringent crystal (1605 a) having a first optical axis (1610 a);
5. a second shift birefringent crystal (1605 b) having a second optical axis (1610 b);
5. a polarizing reflector (1606) consisting of a half-wave plate (1611) and a retro-reflector (1612);
6. a plane mirror type steering mirror (1613);
this embodiment is similar to embodiment 3 in that the polarizing reflector (1606) of embodiment 3 is replaced with a backtracking mirror (1612) and a half-wave plate (1611) that is present only on the first or second path, as compared to embodiment 3, the other elements being identical.
As in example 3, the first and second optical axes (1610 a and 1610 b) of the first and second displacement birefringent crystals (1605 a and 1605 b) are oriented as shown in sub-figure (1) and sub-figure (2) in fig. 16b, respectively, and note the viewing angle shift, the first and second optical axes are in the Y-Z plane and are at 45 degrees or-45 degrees, respectively, to the propagation direction (Z axis), so that the displacement amounts generated after the first and second polarization state optical signals perpendicular to each other pass through the first and second displacement birefringent crystals (1605 a and 1605 b) are the same in both directions along the Y axis, and the port period direction is the same.

Claims (40)

1. A reflective optical circulator array comprising:
An input/output terminal for inputting and outputting a plurality of optical signals;
a polarization beam splitter/combiner for spatially separating two polarization states of the multiplexed optical signal; the polarization beam splitting and combining device is one of a multilayer dielectric film type and a sub-wavelength metal grating type; when the multi-layer dielectric film type polarized beam splitting and combining device is adopted, the two triangular bodies of the polarized beam splitting and combining device are bonded, and when the sub-wavelength grating type polarized beam splitting and combining device is adopted, the polarized beam splitting and combining device is manufactured by forming a sub-wavelength grating on a substrate;
a first non-reciprocal polarization rotator;
a first displacement birefringent crystal having a first optical axis;
a first polarizing reflector;
a second non-reciprocal polarization rotator;
a second displacement birefringent crystal having a second optical axis;
a second polarizing reflector;
the input/output end comprises at least one port group, each port group comprises at least three ports, a plurality of ports in each port group are arranged at equal intervals, and each port group has the same port period and port period direction;
the first and second polarizing reflectors may reflect the optical signal and rotate the polarization state of the reflected optical signal by 90 degrees;
The multi-path optical signals input from the input end and the output end are decomposed into first and second polarized optical signals with perpendicular polarization directions by the polarization beam splitter and combiner, and the first and second polarized optical signals respectively propagate along first and second paths which are completely separated in space; the first polarized optical signal propagation direction and the port period direction form a first reference plane, and the second polarized optical signal propagation direction and the port period direction form a second reference plane;
the first polarized light signal sequentially passes through the first non-reciprocal polarization rotator and the first displacement birefringent crystal to the first polarization reflector along a first path, after being reflected by the first non-reciprocal polarization rotator and the first displacement birefringent crystal, the polarized light signal rotates by 90 degrees before being reflected relatively, and then reversely passes through the first displacement birefringent crystal and the first non-reciprocal polarization rotator to become a third polarized light signal, and the third polarized light signal is consistent with the polarized light of the first polarized light signal and reaches the polarization beam splitting and combining device;
the second polarized light signal sequentially passes through the second nonreciprocal polarization rotator and the second displacement birefringent crystal to the second polarization reflector along a second path, after being reflected by the second non-reciprocal polarization rotator and before being reflected by the second displacement birefringent crystal, the polarized light signal rotates by 90 degrees relative to the reflected polarized light, and then reversely passes through the second displacement birefringent crystal and the second nonreciprocal polarization rotator to form a fourth polarized light signal, the fourth polarized light signal is consistent with the polarized light of the second polarized light signal, reaches the polarization beam splitting and combining device, and is combined with the returned third polarized light signal into an optical signal with the same direction, and the optical signal reaches the input and output end for output;
The lengths of the first and second displacement birefringent crystals and the first and second optical axis directions are arranged such that when the third and fourth polarized optical signals reach the input/output end, the third and fourth polarized optical signals have the same displacement as the port period direction of the input/output end and the same displacement as the port period direction of the input/output end, and are combined in position.
2. The reflective optical circulator array of claim 1, wherein said polarization beam splitting and combining means angularly separates two mutually perpendicular polarization states by an angle greater than 20 degrees.
3. A reflective optical circulator array according to claim 2, wherein said polarization beam splitting and combining device has a separation angle of 90 degrees.
4. The reflective optical circulator array of claim 2, wherein said input and output ends are comprised of an array of optical fibers and an array of lenses, each lens in said array of lenses being in one-to-one correspondence with each optical fiber in said array of optical fibers, the input multiple optical signals forming an array of angularly coincident collimated optical signals.
5. The reflective optical circulator array of claim 4, wherein said array of collimated optical signals is oriented parallel to a normal to a plane in which said lens array is located.
6. A reflective optical circulator array according to claim 2, wherein said first or second non-reciprocal polarization rotator comprises a 45 degree faraday rotator.
7. The reflective optical circulator array of claim 6, wherein said first or second non-reciprocal polarization rotator further comprises an external magnet providing a magnetic field required by said 45 degree faraday rotator.
8. A reflective optical circulator array according to claim 6 wherein said 45 degree faraday rotator has a built-in magnetic field.
9. The reflective optical circulator array of claim 6, wherein said first and second shift birefringent crystals are each composed of two sub-birefringent crystals having parallel light passing surfaces and equal lengths, and projections of optical axes of the two sub-birefringent crystals in planes normal to a propagation direction of said first or second polarized optical signals are each at an angle of 45 degrees and-45 degrees to said port period direction.
10. The reflective optical circulator array of claim 9, wherein said sub-birefringent crystal is comprised of yttrium vanadate crystals having a length of said port period Multiple times.
11. The reflective optical circulator array of claim 6, wherein said first or second non-reciprocal polarization rotator further comprises a half-wave plate.
12. The reflective optical circulator array of claim 11, wherein an angle of an optical axis of said half wave plate to a polarization direction of said first or second optical signal is 22.5 degrees or 67.5 degrees.
13. A reflective optical circulator array according to claim 2, wherein said first or second shift birefringent crystal is comprised of birefringent material having parallel light passing surfaces, said first and second optical axes being in said first and second reference planes, respectively.
14. The reflective optical circulator array of claim 13, wherein said first or second displacement birefringent crystal is comprised of a yttrium vanadate crystal having an angle of 45 degrees or-45 degrees with respect to a propagation direction of said first or second polarized optical signal, said yttrium vanadate crystal having a length of 10 times said port period.
15. A reflective optical circulator array according to claim 2, wherein said first or second polarizing reflector is comprised of a 1/4 wave plate and a mirror.
16. A reflective optical circulator array according to claim 15 wherein the optical axis of said 1/4 wave plate is at a 45 degree angle to the direction of polarization of said first or second polarized light signal before it propagates to said first or second polarizing reflector.
17. A reflective optical circulator array according to claim 2, wherein said first or second polarizing reflector is comprised of a 45 degree faraday rotator and a mirror.
18. The array of claim 1-17, further comprising a turning mirror in the first or second path after the polarizing beam splitter/combiner to change the direction of propagation of the first or second polarized light signals such that the directions of propagation of the first and second polarized light signals are coincident, forming a single direction of propagation of the light signals, and remain spatially completely separated; the first reference plane and the second reference plane are overlapped to form a single reference plane; also, an optical path compensation element is included in the second or first path without the turning mirror to provide equal optical paths for optical signals propagating in the first and second paths.
19. The reflective optical circulator array of claim 18 wherein said polarization beam splitting and combining element separates two orthogonal polarization states by 90 degrees and said turning mirror also turns the optical signal by 90 degrees.
20. A reflective optical circulator array according to claim 18 wherein said turning mirror is a planar mirror and said optical path compensation element is a segment of air.
21. A reflective optical circulator array according to claim 18 wherein said turning mirror is a total internal reflection prism and said optical path compensation element is a parallel plate glass of equivalent optical thickness and construction material to said total internal reflection prism.
22. A reflective optical circulator array according to claim 18 wherein an optical path compensation element is located between a 1/4 wave plate contained in said first or second polarizing reflector and the mirror.
23. A reflective optical circulator array according to claim 18, wherein the half-wave plates included in said first and second non-reciprocal polarization rotators have optical axes oriented at 22.5 degrees and-22.5 degrees, or 67.5 degrees and-67.5 degrees, respectively, such that the polarization states of the first and second polarized optical signals are uniform after passing through said first and second non-reciprocal polarization rotators; meanwhile, 45-degree Faraday rotators contained in the first and second nonreciprocal polarization rotators have the same polarization rotation direction and are combined into a whole; the first and second displacement birefringent crystals have the same optical axis direction and are combined into a whole; the 1/4 wave plates in the first and second polarizing reflectors have the same optical axis direction and are combined into a whole.
24. A reflective optical circulator array according to claim 18, wherein said first and second non-reciprocal polarization rotators are substantially identical in optical performance and are combined as a single entity; the first and second optical axes of the first and second displacement birefringent crystals are in the single reference plane and are at 45 degrees and-45 degrees, respectively, to the single optical signal propagation direction; the 1/4 wave plates in the first and second polarizing reflectors have the same optical axis direction and are combined into a whole.
25. The reflective optical circulator array of claim 18, wherein half-wave plates in said first and second non-reciprocal polarization rotators have the same optical axis direction and are combined as a unit, the optical axis direction being 22.5 degrees, -22.5 degrees, 67.5 degrees, or-67.5 degrees; the 45 degree Faraday rotator in the first and second non-reciprocal polarization rotators has opposite polarization rotation directions, such that the polarization states of the first and second polarization state optical signals are identical after passing through the first and second non-reciprocal polarization rotators; the first and second displacement birefringent crystals have the same optical axis direction and are combined into a whole; the 1/4 wave plates in the first and second polarizing reflectors have the same optical axis direction and are combined into a whole.
26. A reflective optical circulator array comprising:
an input/output terminal for inputting and outputting a plurality of optical signals;
a polarization beam splitter/combiner for spatially separating two polarization states of the multiplexed optical signal;
a steering mirror;
a first non-reciprocal polarization rotator;
a first displacement birefringent crystal having a first optical axis;
a second non-reciprocal polarization rotator;
a second displacement birefringent crystal having a second optical axis;
a polarizing reflector;
the input and output end comprises at least one port group, each port group comprises at least three ports, a plurality of ports in each port group are arranged at equal intervals, and each port group has the same port period and port period direction; the polarization beam splitting and combining device is one of a multilayer dielectric film type and a sub-wavelength metal grating type; when the multi-layer dielectric film type polarized beam splitting and combining device is adopted, the two triangular bodies of the polarized beam splitting and combining device are bonded, and when the sub-wavelength grating type polarized beam splitting and combining device is adopted, the polarized beam splitting and combining device is manufactured by forming a sub-wavelength grating on a substrate;
the multi-path optical signals input from the input end and the output end are decomposed into first and second polarized optical signals with perpendicular polarization directions by the polarization beam splitter and combiner, and the first and second polarized optical signals respectively propagate along first and second paths which are completely separated in space;
The steering reflector is arranged on a first path or a second path of the polarization beam splitting and combining device, so that the first polarized optical signal and the second polarized optical signal have the same propagation direction, form a single optical signal propagation direction, and form a reference plane with the port period direction;
the polarizing reflector can reflect the optical signal, rotate the polarization state of the reflected optical signal by 90 degrees and enable the positions of the optical signals on the first path or the second path to be interchanged;
the first polarized light signal sequentially passes through the first non-reciprocal polarization rotator and the first displacement birefringent crystal to the polarization reflector along a first path, after being reflected by the first non-reciprocal polarization rotator and the first displacement birefringent crystal, the polarized light signal rotates by 90 degrees before being reflected relatively, and then reversely passes through the second displacement birefringent crystal and the second non-reciprocal polarization rotator to become a third polarized light signal, and the third polarized light signal is consistent with the polarized light of the second polarized light signal and reaches the polarization beam splitting and combining device;
the second polarized light signal sequentially passes through the second nonreciprocal polarization rotator and the second displacement birefringent crystal to the polarization reflector along a second path, after being reflected by the second non-reciprocal polarization rotator and the second displacement birefringent crystal, the polarization state rotates 90 degrees before being reflected relatively, and then reversely passes through the first displacement birefringent crystal and the first nonreciprocal polarization rotator to form a fourth polarized light signal, the fourth polarized light signal is consistent with the polarization state of the first polarized light signal, reaches the polarization beam splitting and combining device, and is combined with the returned third polarized light signal into an optical signal with the same direction, and the optical signal reaches the input and output end for output.
27. The array of claim 26, wherein the polarization beam splitters and combiners angularly separate two mutually perpendicular polarization states by an angle greater than 20 degrees.
28. The array of claim 27, wherein the polarization beam splitter/combiner has a separation angle of 90 degrees.
29. The reflective optical circulator array of claim 27, wherein said input and output port comprises an array of optical fibers and an array of lenses, each lens in said array of lenses being in one-to-one correspondence with each optical fiber in said array of optical fibers, the input plurality of optical signals forming an array of angularly coincident collimated optical signals.
30. A reflective optical circulator array according to claim 29, wherein said array of collimated optical signals is oriented parallel to a normal to a plane in which said lens array is located.
31. A reflective optical circulator array according to claim 27 wherein said polarizing reflector comprises a 45 degree half-wave plate and a retro-reflector, said 45 degree half-wave plate being located only on said first or second path; the optical axis of the 45 degree half wave plate is at a 45 degree angle to the polarization direction of the first or second polarized light signal before propagating to the polarizing reflector.
32. A reflective optical circulator array according to claim 31 wherein said back mirror is comprised of a total internal reflection rectangular prism or two planar mirrors at right angles to each other.
33. A reflective optical circulator array according to claim 27 wherein said turning mirror is a total internal reflection prism or a planar mirror.
34. A reflective optical circulator array according to claim 27, wherein said first or second non-reciprocal polarization rotator comprises a 45 degree faraday rotator and a half wave plate.
35. A reflective optical circulator array according to claim 34, wherein said first or second non-reciprocal polarization rotator further comprises an external magnet providing a magnetic field required by said 45 degree faraday rotator.
36. A reflective optical circulator array according to claim 34 wherein said 45 degree faraday rotator has a built-in magnetic field.
37. A reflective optical circulator array according to claim 27 wherein said first or second displacement birefringent crystal is comprised of birefringent material having parallel light passing surfaces, said first and second optical axes being in said reference plane.
38. The reflective optical circulator array of claim 37, wherein said first or second displacement birefringent crystal is comprised of a yttrium vanadate crystal having an angle of 45 degrees or-45 degrees with respect to said single optical signal propagation direction, said yttrium vanadate crystal having a length of 10 times said port period.
39. The array of claim 26 to 38, wherein the half-wave plates included in the first and second non-reciprocal polarization rotators have optical axis directions of 22.5 degrees and-22.5 degrees, or 67.5 degrees and-67.5 degrees, respectively, such that the polarization states of the first and second polarization state optical signals are identical after passing through the first and second non-reciprocal polarization rotators; meanwhile, 45-degree Faraday rotators contained in the first and second nonreciprocal polarization rotators have the same polarization rotation direction and are combined into a whole; the first and second displacement birefringent crystals have the same optical axis direction and are combined into a single body.
40. The array of claim 26 to 38, wherein the half-wave plates in the first and second non-reciprocal polarization rotators have the same optical axis direction, combined as a whole, with an optical axis direction of 22.5 degrees, -22.5 degrees, 67.5 degrees, or-67.5 degrees; the 45 degree Faraday rotator in the first and second non-reciprocal polarization rotators has opposite polarization rotation directions, such that the polarization states of the first and second polarization state optical signals are identical after passing through the first and second non-reciprocal polarization rotators; the first and second displacement birefringent crystals have the same optical axis direction and are combined into a single body.
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