CN110933534A

CN110933534A - A wavelength selective directional optical router

Info

Publication number: CN110933534A
Application number: CN201911143745.2A
Authority: CN
Inventors: 何淳; 凌懿谋
Original assignee: XDK COMMUNICATION EQUIPMENT (HUIZHOU) CO Ltd
Current assignee: XDK COMMUNICATION EQUIPMENT (HUIZHOU) CO Ltd
Priority date: 2019-11-20
Filing date: 2019-11-20
Publication date: 2020-03-27

Abstract

The present invention provides a wavelength selective directional optical router, which is characterized by comprising: front-end first and third single-fiber collimators located at the first and third ports, and second and fourth single-fiber collimators located at the rear ends of the second and fourth ports. Four single-fiber collimators, with thin film filters, first to fourth uniaxial birefringent crystals, first and second polarization rotators, irreversible phase rotators, A reversible half-wave plate, the first polarization rotator is located between the first and second uniaxial birefringent crystals, the second polarization rotator is located between the third and fourth uniaxial birefringent crystals, and the irreversible phase rotator is connected to the reversible half-wave plate. A waveplate is located between the second and third uniaxial birefringent crystals. The invention realizes that the optical signal can be selectively guided from one port to the next port, and has the function of wavelength selection at the same time; and also has the advantages of low cost, small footprint and greatly reduced insertion loss.

Description

Wavelength selection directional optical router

Technical Field

The invention relates to the technical field of optical routers, in particular to a wavelength selective directional optical router.

Background

In a wavelength division multiplexing-type passive optical network (WDM-PON), a plurality of different wavelengths operate simultaneously, so the most direct WDM-PON scheme is that a plurality of different light sources are provided in an Optical Line Terminal (OLT), each Optical Network Unit (ONU) also uses a specific wavelength, and if the number of wavelengths is increased, the types of light sources required are increased, which increases the cost and also causes a serious warehousing problem. Therefore, the scheme that a plurality of fixed wavelength lasers are used to form the upstream and downstream light sources is difficult to be applied to the WDM-PON system.

Broadband light source based WDM-PON networks have been proposed, such as a C-band broadband light source that generates an upstream multi-channel transmission signal and an L-band broadband light source that generates a downstream multi-channel transmission signal. All these schemes are based on the same concept but transmit signals in different ways.

It is widely accepted in the industry that WDM-PON is a point-to-point passive optical network using wavelength division multiplexing technology, which is the route to the next generation optical access system. In WDM-PON architectures it is important that the light sources on both the Optical Line Terminal (OLT) and the Optical Network Units (ONUs) be as simple as possible to reduce costs.

The use of reflective semiconductor amplifiers (RSOAs) and arrayed waveguide grating/optical wave multiplexers (AWGs) to provide a reflective optical architecture for multi-wavelength passive optical networks is an attractive solution because it provides low cost upstream and downstream multi-channel optical transmitters.

Fig. 1 shows a more efficient and relatively lower cost WDM-PON system architecture. An important optical device is required in the architecture to direct the light source and signal traffic through a transmission fiber line. The optical device must fulfill the following four functions:

1) routing an L-band Broadband Light Source (BLS) upstream to an RSOA at an OLT end, reflecting back by the RSOA, and modulating by a carrier signal;

2) the optical device then routes the modulated downstream signals to the ONU sites via transmission fiber optic lines, which can be as long as 20 km;

3) meanwhile, the C-band light source is routed to the ONU site downstream and reflected by the RSOA on the ONU site, and modulated by the ONU carrier signal;

4) after transmission over the same transmission fiber line, the optical equipment may route the modulated upstream signal to the OLT site over the transmission fiber line.

At present, no optical router device can fulfill the above four requirements at the same time, and an optical router capable of selectively guiding an optical signal from one port to the next port and having a wavelength selection function needs to be researched.

Disclosure of Invention

The present invention provides a wavelength selective directional optical router to solve the technical problem of selectively guiding optical signals from one port to the next port while having a wavelength selection function.

The invention provides a wavelength selective directional optical router, which comprises a first single fiber collimator and a third single fiber collimator which are positioned at the front ends of a first port and a third port, and a second single fiber collimator and a fourth single fiber collimator which are positioned at the rear ends of a second port and a fourth port, wherein a thin film filter, a first uniaxial birefringent crystal, a second uniaxial birefringent crystal, a first polarization rotator, a second uniaxial birefringent crystal, an irreversible phase rotator and a reversible half-wave plate are arranged between the front end single fiber collimator and the rear end single fiber collimator, the first polarization rotator is positioned between the first uniaxial birefringent crystal and the second uniaxial birefringent crystal, the second polarization rotator is positioned between the third uniaxial birefringent crystal and the fourth uniaxial birefringent crystal, and the irreversible phase rotator and the reversible half-wave plate are positioned between the second uniaxial birefringent crystal and the third uniaxial birefringent crystal.

Further, the thin film filter comprises a long-pass thin film filter and a short-pass thin film filter, and the long-pass thin film filter and the short-pass thin film filter are respectively located at a first port and a third port between the first single optical fiber collimator and the third single optical fiber collimator at the front end and the first uniaxial birefringent crystal.

Or the thin film filter comprises a long-pass thin film filter and a short-pass thin film filter, the long-pass thin film filter is positioned at a first port between the first single fiber collimator and the first uniaxial birefringent crystal at the front end, the third single fiber collimator and the first uniaxial birefringent crystal at the front end, and the short-pass thin film filter is positioned at a second port between the second single fiber collimator and the fourth uniaxial birefringent crystal at the rear end.

Further, the first polarization rotator comprises third and fourth polarization rotation plates at the third and fourth ports and first and second polarization mode dispersion elimination plates at the first and second ports;

the second polarization rotator includes first and second polarization rotation plates at the first and second ports and third and fourth polarization mode dispersion cancellation plates at the third and fourth ports.

Further, the position of the irreversible phase rotator and the reversible half-wave plate can be interchanged.

Furthermore, the long-pass thin film filter is L-band transmission and C-band reflection; the short-pass thin film filter is C-band transmissive and L-band reflective.

Further, the optical axes of the first and fourth uniaxial birefringent crystals are at right angles to the optical axes of the second and third uniaxial birefringent crystals.

Furthermore, the first polarization mode dispersion elimination sheet and the second polarization mode dispersion elimination sheet have the same optical path length with the third polarization rotation sheet and the fourth polarization rotation sheet; the third and fourth polarization mode dispersion elimination sheets have the same optical path length as the first and second polarization rotation sheets.

Further, a long-pass thin film filter at the first port is fixed to the GRIN lens of the first single fiber collimator to form a lens filter assembly, and the lens filter assembly is aligned with the tail fiber of the first single fiber collimator; a short-pass thin film filter at the third port is secured to the GRIN lens of the third single fiber collimator to form a lens filter assembly that is aligned with the pigtail of the third single fiber collimator.

Or the long-pass thin-film filter positioned at the first port is fixed on the GRIN lens of the first single-fiber collimator to form a lens filtering component, and the lens filtering component is aligned with the tail fiber of the first single-fiber collimator; a short-pass thin film filter at the second port is secured to the GRIN lens of the second single fiber collimator to form a lens filter assembly that is aligned with the pigtail of the second single fiber collimator.

The invention has the beneficial effects that: the wavelength selective directional optical router provided by the invention realizes selective transmission of light beams in an L waveband or a C waveband through the long-pass and short-pass thin film filters, splits the transmitted light beams into two beams of rays with orthogonal linear polarization components at the front end through the uniaxial birefringent crystal, and combines the two beams of rays with orthogonal linear polarization components from different paths into one same path at the rear end; the optical signal can be selectively guided from one port to the next port, and the wavelength selection function is realized; the invention also has the advantages of low cost, small occupied area and greatly reduced insertion loss.

Drawings

FIG. 1 is a schematic diagram of a WDM-PON system;

FIG. 2 is a functional schematic diagram of a first embodiment of a wavelength selective directional optical router of the present invention;

FIG. 3 is a block diagram of a first embodiment of a wavelength selective directional optical router of the present invention;

FIG. 4 is a diagram of the operation of a first embodiment of a wavelength selective directional optical router of the present invention;

FIG. 5 is an optical path diagram of a birefringent crystal according to the present invention;

FIG. 6 is a block diagram of a collimator and filter according to the present invention;

FIG. 7 is a functional schematic diagram of a second embodiment of a wavelength selective directional optical router of the present invention;

FIG. 8 is a block diagram of a second embodiment of a wavelength selective directional optical router of the present invention;

fig. 9 is a diagram of the operation of a second embodiment of the wavelength selective directional optical router of the present invention.

Detailed Description

The embodiments of the present invention will be described in detail with reference to the accompanying drawings, which are for reference and illustrative purposes only and are not intended to limit the scope of the invention.

Example 1:

figure 2 shows the combined device of figure 1 implemented by a four-port loop circulator, a long-pass bandpass filter device and a short-pass bandpass filter device. In fig. 2, LC1 and LC2 represent L-band optical paths, and CL1 and CL2 represent C-band optical paths; the remaining arrowless lines indicate the connection of the device body and the optical fiber, and the "LT/CR two-port BPF" indicates an L-band transmission/C-band reflection band-pass filter. The 'CT/LR two-port BPF' refers to a C-band transmission/L-band reflection band-pass filter.

The optical router module of the present invention is a module for placement near the end of a fiber optic cable, which has the optical device functionality described above in connection with fig. 2, and which is capable of selectively splitting a group of optical signals and selectively routing the split optical signals from one of its ports to the next designated port, while providing wavelength selection functionality and support for a variety of fiber types. It can be used with all four ports using common optical fibers. Or in the case where

ports

3 and 4 use normal non-PM single mode fibers and

ports

1 and 2 use polarization maintaining PM fibers, it is also possible to use only port 4 using normal non-PM single mode fibers and

ports

1, 2 and 3 using polarization maintaining PM fibers.

As shown in fig. 3, the present embodiment provides a wavelength selective directional optical router including first and third single fiber collimators C1 and C3 at front ends of first and third ports and second and fourth single fiber collimators C2 and C4 at rear ends of second and fourth ports, a thin film filter F, first to fourth uniaxial birefringent crystals B1-B4, first and second polarization rotators, a non-reversible phase rotator FR, and a reversible half-wave plate are disposed between the front and rear single fiber collimators, the first polarization rotator is disposed between the first and second uniaxial birefringent crystals B1 and B2, the second polarization rotator is disposed between the third and fourth uniaxial birefringent crystals B3 and B4, and the non-reversible phase rotator FR and the reversible half-wave plate WP are disposed between the second and third uniaxial birefringent crystals B2 and B3.

In this embodiment, the collimator is constructed using a single fiber pigtail, a micro-lens (GRIN lens, C lens, or any other type of spherical or aspherical lens that can perform the same function to form a fiber collimator), and a ferrule.

The first to fourth single fiber collimators C1-C4 are standard fiber collimators, typically made with a lens of 1.8mm in diameter and an overall outer diameter of 2.8 to 3.2mm in diameter, or with a lens of 1.0mm in diameter and an overall outer diameter of 1.3 to 1.4mm in diameter.

In this embodiment, the thin film filters include a long-pass thin film filter F1 and a short-pass thin film filter F3, and the long-pass thin film filter F1 and the short-pass thin film filter F3 are respectively located at the first port and the third port between the front-end first and third single-fiber collimators C1, C3 and the first uniaxial birefringent crystal B1.

The long-pass thin film filter is L-band transmissive and C-band reflective; the short-pass thin film filter is C-band transmissive and L-band reflective. The transmission loss of a long-pass filter is typically 0.10 Db; the transmission loss of a short-pass filter is typically 0.15 dB.

In the present embodiment, the first polarization rotator includes third and fourth polarization rotation plates R3, R4 at the third and fourth ports and first and second polarization mode dispersion cancellation plates G1, G2 at the first and second ports;

the second polarization rotator includes first and second polarization rotation plates R1 and R2 at the first and second ports and third and fourth polarization mode dispersion elimination plates G3 and G4 at the third and fourth ports.

R1 and R2 are identical, as are R3 and R4, and are 90-degree polarization rotators, i.e., they are half-wave plates. They are made of uniaxially birefringent crystals, such as calcite (CaCO3), rutile (TiO2), yttrium orthovanadate (YVO4) or lithium niobate (LiNbO3), etc.;

g1 and G2 are the same, as are G3 and G4, and are both polarization independent elements or glasses. In order to ensure phase matching to remove polarization mode dispersion, the first and second polarization mode dispersion removal sheets G1 and G2 have the same optical path length as the third and fourth polarization rotation sheets R3 and R4; the third and fourth polarization mode dispersion eliminating plates have the same optical path length as the first and second polarization rotating plates R1 and R2 of G3 and G4.

The crystallographic axes of B1 and B4 make an angle of 45 ° with the rectangular angle shown in fig. 4. The crystal axes of B2 and B3 point at 45 ° to opposite rectangular angles as shown in fig. 4. The optical axes of the first and fourth uniaxial birefringent crystals B1, B4 are at right angles to the optical axes of the second and third uniaxial birefringent crystals B2, B3. The uniaxial birefringent elements B1 to B4 may be made of any suitable birefringent material, such as calcite (CaCO3), rutile (TiO2), yttrium orthovanadate (YVO4) or lithium niobate (LiNbO3), and the like.

In the present embodiment, the positions of the irreversible phase rotator FR and the reversible half-wave plate WP are interchangeable. The irreversible phase rotator FR is a faraday rotator, an irreversible optical element that rotates incident light clockwise by 45 degrees when viewed from the light propagation direction. WP is a reversible half-wave plate that will rotate the light 45 degrees clockwise, as viewed in the direction of propagation of the light. In fig. 3, light travels from left to right and its polarization direction will be rotated by 90 °. However, when the light travels from right to left in FIG. 3, the Faraday rotator will rotate the light 45 counterclockwise, although the half-wave plate will still rotate 45 clockwise as viewed from the wavelength direction; 45 ° when viewed in the direction of light propagation; whereas in fig. 3 the light travels from right to left, its polarization direction will remain unchanged.

As shown in fig. 4 and 5, the working process of this embodiment is as follows: the L-band light entering from port 1 will pass through the F1 filter. The birefringent crystal B1 will split it into two orthogonal linear polarization components. As shown in FIG. 5, the crystal axis points at-45 of the crystal angle, the o-ray is horizontally polarized (x-direction) and travels straight, while the e-ray is vertically polarized (y-direction) and travels down (y-direction) a distance d, then travels forward and parallel to the o-ray. This displacement causes the electron rays to be incident on the 90 ° polarization rotator R4; while R4 rotates the polarization of the electron ray by 90, the e-ray is also horizontally polarized-the same polarization direction as the o-ray.

The optical axis of B2 is 90 ° perpendicular with respect to B1. That is, the two incident horizontally polarized rays are electron rays of B2. The B2 beam shifter shifts the two light rays by d in the + x direction; the faraday rotator FR rotates both o-rays and e-rays clockwise by 45 °; the half-wave plate WP rotates the two rays clockwise by 45 °. After passing through FR and WP, their polarization directions are rotated by 90 and are in the vertical polarization state.

The optical axis of B3 is the same as B1, or perpendicular to B2. For B3, the two incident vertically polarized rays are o-rays. The B3 beam shifter does not move the two incident beams nor change their polarization states. Now, the lower light is incident on the 90 ° polarization rotator R2; its polarization state is rotated by 90 and then changed to a horizontal polarization state. The upper ray is now incident on the polarization independent element G3; it is still vertically polarized. The purpose of G3 is to delay its progression so that its wavefront does not advance to lower rays until after they leave B3.

B4 is the same as B1, and the lower ray of horizontally polarized light passes without changing its direction of propagation. The vertically polarized upper rays are shifted downward by a distance of-dy and now coincide with the lower rays, which recombine back into the incident beam. The light beam will maintain its original polarization state as it enters the device. The light beam may be unpolarized, linearly polarized, elliptically polarized, circularly polarized, or the like.

Fig. 6 is an exemplary structure of an assembly forming a collimator with a wavelength selective filter. The wavelength selective coating of the bandpass filter faces the GRIN lens. One of the exemplary procedures for aligning filter F1 with collimator C1 is as follows: 1) f1 was fixed and affixed to the GRIN lens; 2) and transmitting the laser with the wavelength of the C waveband to the tail fiber through the tail end of the optical fiber. 3) Aligning the F1+ GRIN lens assembly to the pigtail fiber, reflecting the laser back into the fiber; 4) the relative position of the F1+ GRIN lens assembly was fixed to the pigtail using a sheath tube. The power meter may detect the light propagating backwards along the pigtail through an 50/50 fiber splitter.

The same method is applied to the process of aligning the filter F3 with the collimator C3, and the laser light with the wavelength within the L-band is aligned with the pigtail through the end of the fiber.

By way of comparison, table 1 shows the advantages of the wavelength selective 4-port directional router of the present invention compared to the combination of a long pass bandpass filter device and a short wavelength loop combination by using a four-port circulator. Bandpass filters are considered for use in cost, performance and footprint, manufacturing cost and OEM purchase cost.

TABLE 1

To use a superled as a broadband light source as shown in fig. 1, the light is typically linearly polarized. The use of PM fiber in port 1 and port 2 of a four-port wavelength selective directional router is very convenient because it is located near the OTL site.

Ports

3 and 4 would be standard SM fibers. The invention and its exemplary design shown in fig. 3 and 4 support PM fibers without any additional losses.

Example 2:

the present embodiment is different from embodiment 1 in that:

in this embodiment, as shown in fig. 8, the thin film filters include a long-pass thin film filter and a short-pass thin film filter, the long-pass thin film filter F1 is located at the first port between the front first and third single fiber collimators C1 and C3 and the first uniaxial birefringent crystal B1, and the short-pass thin film filter F2 is located at the second port between the rear second and fourth single fiber collimators C2 and C4 and the fourth uniaxial birefringent crystal B4.

As shown in fig. 7, the WDM-PON structure of the present embodiment is a variation of the structure shown in fig. 1, in that separate optical fibers are routed for upstream C-band signal receivers and downstream L-band signal modulation. This can be achieved by using the four port wavelength selective directional router of the present invention having a three port WDM equipment with C-band transmission, L-band reflective thin film filters to form a five port wavelength selective directional router, port 1, port 2-2, port 3 and port 4. The connection scheme and functional diagram are shown in fig. 6.

Another WDM-PON architecture shown in fig. 7 is to use a comb laser or a WDM laser instead of broadband light as a signal transmission source. This can be achieved by slightly modifying the 4-port wavelength selective directional router of the present invention by using filters at two adjacent ports (e.g., port 1 and port 2) instead of the opposite port (e.g., port 3 and port 4). The detailed design is shown in fig. 7. The polarization state of the input light after passing through it sequentially along its path is shown in fig. 8. The exemplary structure diagram illustrates:

as shown in fig. 9, the router is connected to a 3-port WDM equipment based on C-band transmission, based on L-band reflective thin-film filters, used with a conventional 2-port band-pass filter with C-band transmission, L-band reflective thin-film filters to form a 5-port wavelength selective directional bidirectional router for WDM-PON architecture, which uses separate routing for upstream signal receiver and downstream signal modulation. Variations of the above structure can be used in WDM-PON architectures where comb lasers or WDM lasers are used as signal sources for upstream and downstream transmissions.

It will be appreciated by those skilled in the optical communications industry that, with the present exemplary architecture, appropriate modifications, such as adding prisms to the collimator end faces or spaces therein to increase the separation distance of the optical signals, or exchanging and replacing parts of the components, such as interchanging the positions of FR and WP, etc., without departing from the innovative spirit, should be considered as being within the scope of the claims.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A wavelength selective directional optical router, characterized by: the single-fiber polarization rotation device comprises a first single-fiber collimator and a third single-fiber collimator which are arranged at the front ends of a first port and a third port, and a second single-fiber collimator and a fourth single-fiber collimator which are arranged at the rear ends of a second port and a fourth port, wherein a thin-film filter, first to fourth uniaxial birefringent crystals, a first polarization rotator, a second polarization rotator, an irreversible phase rotator and a reversible half-wave plate are arranged between the front end single-fiber collimator and the rear end single-fiber collimator, the first polarization rotator is arranged between the first uniaxial birefringent crystal and the second uniaxial birefringent crystal, the second polarization rotator is arranged between the third uniaxial birefringent crystal and the fourth uniaxial birefringent crystal, and the irreversible phase rotator and the reversible half-wave plate are arranged between the second uniaxial birefringent crystal and the third birefringent crystal.

2. The wavelength selective directional optical router of claim 1, wherein:

the thin film filter comprises a long-pass thin film filter and a short-pass thin film filter, and the long-pass thin film filter and the short-pass thin film filter are respectively positioned at a first port and a third port between the first single-fiber collimator and the third single-fiber collimator at the front end and the first uniaxial birefringent crystal.

3. The wavelength selective directional optical router of claim 2, wherein:

the thin film filter comprises a long-pass thin film filter and a short-pass thin film filter, the long-pass thin film filter is located at a first port between the first single optical fiber collimator and the first uniaxial birefringent crystal at the front end, the third single optical fiber collimator and the first uniaxial birefringent crystal at the front end, and the short-pass thin film filter is located at a second port between the second single optical fiber collimator and the fourth uniaxial birefringent crystal at the rear end.

4. The wavelength selective directional optical router of claim 1, wherein:

the first polarization rotator comprises third and fourth polarization rotation plates positioned at the third and fourth ports and first and second polarization mode dispersion elimination plates positioned at the first and second ports;

5. The wavelength selective directional optical router of claim 1, wherein:

the positions of the irreversible phase rotator and the reversible half-wave plate can be interchanged.

6. A wavelength selective directional optical router according to any one of preceding claims 1-3, characterized in that: the long-pass thin film filter is L-band transmissive and C-band reflective; the short-pass thin film filter is C-band transmissive and L-band reflective.

7. The wavelength selective directional optical router of claim 1, wherein:

the optical axes of the first and fourth uniaxial birefringent crystals are at right angles to the optical axes of the second and third uniaxial birefringent crystals.

8. The wavelength selective directional optical router of claim 4, wherein:

the first polarization mode dispersion elimination sheet and the second polarization mode dispersion elimination sheet have the same optical path length as the third polarization rotation sheet and the fourth polarization rotation sheet; the third and fourth polarization mode dispersion elimination sheets have the same optical path length as the first and second polarization rotation sheets.

9. The wavelength selective directional optical router of claim 2, wherein:

a long-pass thin film filter at the first port is fixed on the GRIN lens of the first single-fiber collimator to form a lens filtering component, and the lens filtering component is aligned with the tail fiber of the first single-fiber collimator;

a short-pass thin film filter at the third port is secured to the GRIN lens of the third single fiber collimator to form a lens filter assembly that is aligned with the pigtail of the third single fiber collimator.