WO2017007749A1

WO2017007749A1 - Passive optical network and wavelength selective two-port reflectors for use therein

Info

Publication number: WO2017007749A1
Application number: PCT/US2016/040943
Authority: WO
Inventors: Fenfei Liu; Yao Li
Original assignee: Alliance Fiber Optic Products, Inc.
Priority date: 2015-07-06
Filing date: 2016-07-05
Publication date: 2017-01-12

Abstract

A passive optical network and a wavelength selective two-port reflector for use therein are provided. The wavelength selective two-port reflector comprises a common port, a pass-through port, and pair of optical filters that (i) retro-reflect diagnostic and noise wavelength portions of an input signal propagating from the common port of the two-port reflector to a first filter of the two optical filters and (ii) pass a target data wavelength portion of the input signal to the pass-through port of the two-port reflector. The retro-reflection comprises a first reflection from the first optical filter to the second optical filter, a second reflection from the second optical filter to the first optical filter, and a third reflection from the first optical filter to the common port of the two-port reflector.

Description

PASSIVE OPTICAL NETWORK AND WAVELENGTH SELECTIVE TWO-PORT REFLECTORS FOR USE THEREIN

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No.

62/231,375, filed July 6, 2015, the full disclosure of which is incorporated herein by reference.

BACKGROUND

Field

[0002] The present disclosure relates to passive optical networks and, more specifically, to compact integrated optical components for enabling high isolation and high return loss in optical communications.

Technical Background

[0003] A passive optical network (PON) is a form of fiber-optic access network and typically comprises an optical line terminal (OLT) at the service provider's central office (hub) and a number of optical network units (ONUs) or Optical Network Terminals (ONTs), near end users. An optical line termination (OLT), also called an optical line terminal, is a device which serves as the service provider endpoint of a passive optical network (PON). As is well understood in the art of PON design, passive optical components include branching devices such as

Wavelength-Division Multiplexer/Demultiplexers (WDMs), isolators, circulators, and filters. Fiber optic filters are in-line, wavelength selective, components that allow a specific range of wavelengths to pass through (or reflect) with low attenuation. For example, TFF mux/demux modules are typically assembled using multiple three-port devices arranged in sequence (see, e.g., US 2015/0125163 (WDM Mux/DeMux employing filters shaped for maximum use thereof), US 2014/0248057 (WDM Mux/DeMux on cable and methods of making the same), and US 2012/0237222 Micro Free-Space WDM Device).

[0004] Typically, a three -port device will comprise an input port, a transmitted port, and a reflected port. See, for example, the Optical Add-Drop Multiplexer of US 5,712,717 and the Multi-Port High Isolation Filters of US 7,486,891. The building block for each device can be a dielectric component that consists of multiple cavities, each of which is bounded by alternating thin film layers of high and low index materials. The filter can be designed to pass a specific wavelength or band of wavelengths at a certain angle of incidence of light while the remaining input wavelengths are reflected.

BRIEF SUMMARY

[0005] The present inventors have recognized that optical isolation is an important parameter in PON design, particularly for PONs based on wavelength-division-multiplexing (WDM), where data from different sources is encoded to different wavelengths that are multiplexed and transmitted in a single optical fiber. On the receiver side, these wavelengths have to be separated (demultiplexed) for decoding. In general, more than 80 wavelength channels can be used in a high speed long haul optical link, and the channel spacing can be as small as 50 to 100GHz (-0.4 to 0.6nm). Due to the practical limitations of optical filtering technologies, the de-multiplexed signals carry a degree of residual components from adjacent channels that accumulate to the noise floor. With multiple layers of network configurations, it is becoming increasingly important to realize progressively higher isolation and lower return loss to avoid single-to-noise ratio degradation. Furthermore, Next Generation PON (NGPON) will extend into individual homes and migrate to much higher speeds.

[0006] According to the subject matter of the present disclosure, network configurations and components are introduced to improve optical isolation and enhance signal to noise ratio (SNR) in optical network data links. In one respect, the present disclosure introduces an ultra high optical isolation retro-reflector array unit for real-time monitoring, diagnostics, and network maintain applications. The device is based on a free space optics design and robust optical thin film filters (TFF), where multiple channels are integrated in small form factor for significant improved cost and space efficiency. Collimators can be used in the device to allow light to be coupled between fiber and free space. Additionally, it is noted that Optical Time Domain Reflectometer (OTDR) signals can be useful for testing the integrity of fiber optic cables in PONs. For example, an OTDR signal can be used to verify splice loss, measure length, and find faults.

[0007] In accordance with one embodiment of the present disclosure, a passive optical network is provided comprising a service provider terminal, a plurality of customer terminals, an optical splitter, a diagnostic signal terminal, a plurality of wavelength selective two-port reflectors, and network optical fibers. The network optical fibers optically link the service provider terminal, the customer terminals, the optical splitter, the diagnostic signal terminal, and the wavelength selective two-port reflectors. The optical splitter is optically coupled between the service provider terminal and the customer terminals by way of the network optical fibers. The wavelength selective two-port reflectors are optically coupled between the optical splitter and the customer terminals by way of the network optical fibers such that individual ones of the two-port reflectors are dedicated to respective ones of the customer terminals and a data signal originating at the service provider terminal cannot reach a customer terminal without passing through a wavelength selective two-port reflector. The wavelength selective two-port reflectors are optically coupled between the diagnostic signal terminal and the customer terminals by way of the network optical fibers such that a diagnostic signal originating at the diagnostic signal terminal cannot reach a customer terminal without passing through one of the wavelength selective two-port reflectors. Individual ones of the wavelength selective two-port reflectors comprise a common port, a pass-through port, and pair of optical filters. The pair of optical filters of the individual wavelength selective two-port reflectors are structurally configured and optically oriented to (i) retro-reflect diagnostic and noise wavelength portions of an input signal propagating from the common port of the two-port reflector to a first filter of the two optical filters at a certain angle of incidence a and (ii) pass a target data wavelength portion of the input signal to the pass-through port of the two-port reflector. The retro-reflection of the diagnostic and noise wavelength portions of the input signal comprises a first reflection from the first optical filter to the second optical filter, a second reflection from the second optical filter to the first optical filter, and a third reflection from the first optical filter to the common port of the two-port reflector.

[0008] In accordance with another embodiment of the present disclosure, a wavelength selective two-port reflector is provided comprising a common port, a pass-through port, and pair of optical filters. The pair of optical filters of the individual wavelength selective two-port reflectors are structurally configured and optically oriented to (i) retro-reflect diagnostic and noise wavelength portions of an input signal propagating from the common port of the two-port reflector to a first filter of the two optical filters at a certain angle of incidence a and (ii) pass a target data wavelength portion of the input signal to the pass-through port of the two-port reflector. The retro-reflection of the diagnostic and noise wavelength portions of the input signal comprises a first reflection from the first optical filter to the second optical filter, a second reflection from the second optical filter to the first optical filter, and a third reflection from the first optical filter to the common port of the two-port reflector.

[0009] Although the concepts of the present disclosure are described herein with primary reference to PONs, it is contemplated that wavelength selective two-port reflectors disclosed herein will enjoy applicability to a variety of optical networks and optical devices.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0010] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0011] Fig. 1 is a schematic illustration of a PON including wavelength selective two-port reflectors according to the present disclosure;

[0012] Fig. 2 is a schematic illustration of a wavelength selective two-port reflector according to one embodiment of the present disclosure;

[0013] Fig. 3 illustrates the manner in which a plurality of wavelength selective two-port reflectors can be integrated on a common optical platform according to one embodiment of the present disclosure;

[0014] Figs. 4A and 4B illustrate the manner in which different sub-components of a plurality of wavelength selective two-port reflectors can be integrated on opposite sides of common optical platform according to one embodiment of the present disclosure, to facilitate port positioning along a common edge of the optical platform;

[0015] Figs. 5A and 5B are schematic illustrations of a wavelength selective two-port reflector according to one alternative embodiment of the present disclosure; and

[0016] Fig. 6 illustrates the manner in which a plurality of the wavelength selective two-port reflectors illustrated in Figs. 5 A and 5B can be integrated on a common optical platform according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0017] Referring initially to Fig. 1, a passive optical network 100 according to the present disclosure may comprise a service provider terminal 10, a plurality of customer terminals 20, an optical splitter 30, a diagnostic signal terminal 40, a plurality of wavelength selective two-port reflectors 50, and a plurality of network optical fibers 60 that optically link the service provider terminal 10, e.g., and OLT, the customer terminals 20, e.g., an ONU or an ONT, the optical splitter 30, the diagnostic signal terminal 40, and the wavelength selective two-port reflectors 50.

[0018] The optical splitter 30, which is illustrated as a 64 way splitter in Fig. 1, and may be any of a variety of conventional or yet to be developed optical splitters suitable for use in a PON, is optically coupled between the service provider terminal 10 and the customer terminals 20 by way of the network optical fibers 60. The wavelength selective two-port reflectors 50 are optically coupled between the optical splitter 30 and the customer terminals 20 by way of the network optical fibers 60 such that individual ones of the two-port reflectors 50 are dedicated to respective ones of the customer terminals 20. A data signal originating at the service provider terminal 10 cannot reach a customer terminal without passing through a wavelength selective two-port reflector 50.

[0019] The wavelength selective two-port reflectors 50 are also optically coupled between the diagnostic signal terminal 40 and the customer terminals 20 by way of the network optical fibers 60. In this manner, a diagnostic signal, e.g., an OTDR signal, originating at the diagnostic signal terminal 40 also cannot reach a customer terminal 20 without passing through one of the wavelength selective two-port reflectors 50. Although the diagnostic signal terminal 40 is illustrated in Fig. 1 as a dedicated diagnostic signal terminal, it is contemplated that the service provider terminal 10, one of the customer terminals 20, a terminal of an optical component of the PON, or any other suitable terminal may function as a diagnostic signal terminal.

[0020] Referring collectively to Figs. 1 and 2, individual ones of the wavelength selective two-port reflectors 50 may comprise a common port 52, a pass-through port 54, and pair of optical filters 56, 58. The pair of optical filters 56, 58 are structurally configured and optically oriented to (i) retro-reflect diagnostic and noise wavelength portions of an input signal propagating from the common port 52 of the two-port reflector 50 to the first filter 56 at a certain angle of incidence a and (ii) pass a target data wavelength portion of the input signal to the pass-through port 54 of the two-port reflector. More specifically, in the illustrated embodiment, where the input signal λι,...λ_ί,...λ_Ν propagating at angle of incidence a comprises a target data signal λι, residual components λ₁,...λι_-1,...λί_{+ 1} ,...λΝ of a multiplexed data signal using a multiplexer or circulator 65, and a diagnostic OTDR signal, the pair of optical filters 56, 58 are configured to pass the target data signal and reflect the diagnostic OTDR signal and the residual components λ₁,...λι_₁,...λ₁₊₁,...λ_Ν of the multiplexed data signal.

[0021] Referring to the diagnostic OTDR signal and the residual components λι,.,.λ^ ι, ...λπ.ι, ...λ of the multiplexed data signal as diagnostic and noise wavelength portions of the input signal, it is noted that the retro-reflection of the diagnostic and noise wavelength portions of the input signal comprises a first reflection from the first optical filter 56 to the second optical filter 58, a second reflection from the second optical filter 58 to the first optical filter 56, and a third reflection from the first optical filter 56 to the common port 52 of the two-port reflector 50. In the optical configuration illustrated in Fig. 2, the first filter 56 defines a pass band at a non- perpendicular angle of incidence a and the second filter defines an equivalent pass band at a perpendicular angle of incidence.

[0022] The first filter 56, which may comprise a thin film reflector of conventional or yet-to- be developed design, can reflect OTDR and residual wavelengths at a particular incident angle, e.g., 8°, 13.5°, or any angle compliant to the design. The second filter 58 can have the same filter passband as the first filter 56 but is designed to work for a perpendicular incident beam. In this manner, it is contemplated that the signal isolation at the pass through port 54 can reach 40dB and the retro-reflected signal at the common port 52 can have isolation up to 60dB because the retro-reflected signal undergoes reflection at a filter three times prior to returning to the common port 52. Additionally, it is contemplated that return loss can reach lOOdB, partially because of the relatively large incident angle of the pass through target data signal λι, at the first filter 56.

[0023] In operation, it is contemplated that a broadband signal, or a wavelength multiplexed signal, strikes the first optical filter 56. Because the first optical filter 56 has its passband center wavelength at the target data signal λι, the target data signal passes through the filter 56 and all other wavelengths get reflected to the second filter 58. The angle of incidence at the second filter 58 can be finely tuned to ensure proper reflection back to the first filter 56, then to the common port 52 on the same trace of input beam. In this manner, the total reflection isolation of the device is supported by both the first and second filters 56, 58. Although the reflection isolation of each filter is limited by available coating technology, the multiple reflections of the illustrated design boosts the isolation performance through accumulation. The resulting configuration provides high isolation for the pass through target data signal and high return loss of data in the effectively retro-reflected OTDR and residual signals.

[0024] In embodiments where the only concern is return of an OTDR or other diagnostic signal, it is contemplated that the pair of optical filters 56, 58 can be configured to pass a relatively wide band of data signals, e.g., from about 1260 nm to about 1620 nm, and to reflect the diagnostic signal, e.g., at wavelengths from about 1630 nm to about 1670nm.

[0025] Fig. 3 illustrates the manner in which the first and second optical filters 56, 58 and associated optical collimators 55 of a plurality of wavelength selective two-port reflectors 50 can be integrated on a common optical platform 70 according to one embodiment of the present disclosure. More specifically, in Fig. 3, the wavelength selective two-port reflectors 50 are arranged on a common side of the optical platform 70 to define an array of common ports and an array of pass-through ports along opposite edges 72, 74 of the optical platform 70. The optical collimators 55 and the optical filters 56, 58 of the illustrated embodiment, and all of the embodiments described herein, preserve optical collimation and, as such, are well suited for free space optical propagation between the common port 52, the pass-through port 54, and the pair of optical filters 56, 58. It is contemplated that the collimators 55 can be replaced by a fiber array unit (FAU), which is an array of integrated optical fiber with accurate fiber to fiber pitch.

[0026] Figs. 4A and 4B illustrate the manner in which different sub-components of a plurality of wavelength selective two-port reflectors can be integrated on opposite sides 76, 78 of common optical platform 70 to facilitate port positioning along a common edge 72 of the optical platform 70. The first and second optical filters 56, 58 of the wavelength selective two- port reflectors are arranged on a common side 76 of the optical platform 70 to define an array of common ports and the optical platform 70 comprises a reflecting prism 80 that is oriented and structurally configured to direct target data wavelength portions of the input signal from the common side 76 of the optical platform to an array of pass-though ports on an opposite side 78 of the optical platform 70. [0027] Figs. 5A and 5B are schematic illustrations of a wavelength selective two-port reflector 50' according to one alternative embodiment of the present disclosure. In this embodiment, the wavelength selective two-port reflector 50' comprises a target data wavelength reflector 59. Referring specifically to Fig. 5A, the first optical filter 56, the target data wavelength reflector 59, and the second optical filter 58 are structurally configured, positioned, and oriented such that the target data wavelength portion of the input signal is reflected back through the first optical filter 56 and to the second optical filter 58 after it traverses the first optical filter 56 a second time.

[0028] In the embodiment of Figs. 5A and 5B, the data signal goes through a filter coating three times, which can give ultra high isolation, e.g., about 120dB. The OTDR signal is also reflected three times, which can give isolation of at least about 60dB. It is contemplated that the first filter 56 can be replaced by a reflection mirror only, which would lead to 40dB data isolation, 20dB OTDR isolation, and 80dB return loss.

[0029] Fig. 6 illustrates the manner in which a plurality of the wavelength selective two-port reflectors 50' illustrated in Figs. 5 A and 5B can be integrated on a common side and along a common edge of a common optical platform 70, by utilizing a plurality of beam directing prisms 85 that are oriented and structurally configured to direct target data wavelength portions that have passed through corresponding ones of the second optical filters 58 to corresponding ones of the pass through ports 54.

[0030] It is noted that the various embodiments of the present disclosure, particularly those illustrated in Figs. 3, 4A, 4B, and 6, may be hermetically packaged in a compact cassette utilizing the common optical platform 70 to define an array of common ports and an array of pass-though ports. The resulting cassette facilitates easy access connection by either fusion fiber or sophisticated connectivity technologies, such as LC or MPT connectors, to fulfill needs of high density inter connection. The cassette layout also simplifies routing and is readily adaptable for installation in rack modules.

[0031] It is also noted that recitations herein of "at least one" component, element, etc., should not be used to create an inference that the alternative use of the articles "a" or "an" should be limited to a single component, element, etc. [0032] It is noted that recitations herein of a component of the present disclosure being "configured," "oriented," or "positioned" to embody a particular property, or to function in a particular manner, are structural recitations, as opposed to recitations of intended use. More specifically, the references herein to the manner in which a component is "configured,"

"oriented," or "positioned" denotes an existing physical condition of the component and, as such, is to be taken as a definite recitation of the structural characteristics of the component.

[0033] It is noted that terms like "preferably," "commonly," and "typically," when utilized herein, are not utilized to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to identify particular aspects of an embodiment of the present disclosure or to emphasize alternative or additional features that may or may not be utilized in a particular embodiment of the present disclosure.

[0034] Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Further, it will be apparent that modifications and variations are possible without departing from the scope of the present disclosure, including, but not limited to, embodiments defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

[0035] It is noted that one or more of the following claims utilize the term "wherein" as a transitional phrase. For the purposes of defining the present invention, it is noted that this term is introduced in the claims as an open-ended transitional phrase that is used to introduce a recitation of a series of characteristics of the structure and should be interpreted in like manner as the more commonly used open-ended preamble term "comprising."

Claims

1. A passive optical network comprising a service provider terminal, a plurality of customer terminals, an optical splitter, a diagnostic signal terminal, a plurality of wavelength selective two-port reflectors, and network optical fibers, wherein:

the network optical fibers optically link the service provider terminal, the customer terminals, the optical splitter, the diagnostic signal terminal, and the wavelength selective two- port reflectors;

the optical splitter is optically coupled between the service provider terminal and the customer terminals by way of the network optical fibers;

the wavelength selective two-port reflectors are optically coupled between the optical splitter and the customer terminals by way of the network optical fibers such that individual ones of the two-port reflectors are dedicated to respective ones of the customer terminals and a data signal originating at the service provider terminal cannot reach a customer terminal without passing through a wavelength selective two-port reflector;

the wavelength selective two-port reflectors are optically coupled between the diagnostic signal terminal and the customer terminals by way of the network optical fibers such that a diagnostic signal originating at the diagnostic signal terminal cannot reach a customer terminal without passing through one of the wavelength selective two-port reflectors;

individual ones of the wavelength selective two-port reflectors comprise a common port, a pass-through port, and pair of optical filters;

the pair of optical filters of the individual wavelength selective two-port reflectors are structurally configured and optically oriented to (i) retro-reflect diagnostic and noise wavelength portions of an input signal propagating from the common port of the two-port reflector to a first filter of the two optical filters at a certain angle of incidence a and (ii) pass a target data wavelength portion of the input signal to the pass-through port of the two-port reflector; and the retro-reflection of the diagnostic and noise wavelength portions of the input signal comprises a first reflection from the first optical filter to the second optical filter, a second reflection from the second optical filter to the first optical filter, and a third reflection from the first optical filter to the common port of the two-port reflector.

2. The passive optical network as claimed in claim 1 wherein the first filter of the pair of optical filters is structurally configured and optically oriented to pass the target data wavelength portion of the input signal to the pass-through port of the two-port reflector without reflection.

3. The passive optical network as claimed in claim 2 wherein:

the plurality of wavelength selective two-port reflectors are arranged on a common side of an optical platform to define an array of common ports and an array of pass-through ports; and

the respective arrays of common ports and pass-through ports are arranged on the common side of the optical platform, along opposite edges of the optical platform.

4. The passive optical network as claimed in claim 2 wherein:

the first filter defines a first pass band at a non-perpendicular angle of incidence a; and the second filter defines an equivalent pass band at a perpendicular angle of incidence.

5. The passive optical network as claimed in claim 1 wherein:

the plurality of wavelength selective two-port reflectors are arranged on a common side of an optical platform to define an array of common ports; and

the optical platform comprises a reflecting prism that is oriented and structurally configured to direct target data wavelength portions of the input signal of the wavelength selective two-port reflectors from the common side of the optical platform to an array of pass- though ports on an opposite side of the optical platform.

6. The passive optical network as claimed in claim 1 wherein:

individual ones of the wavelength selective two-port reflectors comprise a target data wavelength reflector; and

the first optical filter, target data wavelength reflector, and the second optical filter are structurally configured, positioned, and oriented such that the target data wavelength portion of the input signal is reflected through the first optical filter and the second optical filter after it traverses the first optical filter.

7. The passive optical network as claimed in claim 6 wherein:

the plurality of wavelength selective two-port reflectors are arranged on a common side of an optical platform to define an array of common ports and pass-through ports arranged on the common side of the optical platform, along a common edge of the optical platform; and the optical platform comprises a plurality of beam directing prisms that are oriented and structurally configured to direct target data wavelength portions that have passed through corresponding ones of the second optical filters to corresponding ones of the pass through ports.

8. The passive optical network as claimed in claim 1 wherein the plurality of wavelength selective two-port reflectors are hermetically packaged together on an optical platform to define an array of common ports and an array of pass-though ports.

9. The passive optical network as claimed in claim 1 wherein the wavelength selective two-port optical reflectors are configured for free space optical propagation between the common port, the pass-through port, and the pair of optical filters.

10. The passive optical network as claimed in claim 9 wherein the common port and the pass through port comprise optical collimators and the pair of optical filters are configured to preserve optical collimation.

11. The passive optical network as claimed in claim 1 wherein the first and second filters of the pair of optical filters comprise optical thin film filters that are structurally configured to pass a relatively narrow wavelength band while reflecting wavelengths outside of the relatively narrow wavelength band.

12. The passive optical network as claimed in claim 1 wherein:

the input signal λ₁ ..λι, ...λΝ comprises the target data signal and residual components λ₁,...λι_-1,...λί₊₁ ,...λΝ of a multiplexed data signal;

the pair of optical filters are configured to pass the target data signal and reflect the residual components of the multiplexed data signal.

13. The passive optical network as claimed in claim 1 wherein the pair of optical filters are configured to pass data signals from about 1260 nm to about 1620 nm and to reflect diagnostic signals from about 1630 nm to about 1670nm.

14. The passive optical network as claimed in claim 1 wherein the diagnostic signal terminal comprises the service provider terminal, one of the customer terminals, a terminal of an optical component of the PON, or a dedicated diagnostic signal terminal that is optically coupled to an optical component of the PON.

15. The passive optical network as claimed in claim 1 wherein the service provider terminal comprises an optical line terminal (OLT) and the plurality of customer terminals comprise optical network units (ONUs) or optical network terminals (ONTs).

16. The passive optical network as claimed in claim 1 wherein the diagnostic signal is an OTDR signal comprising wavelength components between about 1630 nm and about 1670nm.

17. A wavelength selective two-port reflector comprising a common port, a pass-through port, and pair of optical filters, wherein:

the pair of optical filters of the individual wavelength selective two-port reflectors are structurally configured and optically oriented to

retro-reflect diagnostic and noise wavelength portions of an input signal propagating from the common port of the two-port reflector to a first filter of the two optical filters at a certain angle of incidence a and

pass a target data wavelength portion of the input signal to the pass- through port of the two-port reflector; and

the retro-reflection of the diagnostic and noise wavelength portions of the input signal comprises a first reflection from the first optical filter to the second optical filter, a second reflection from the second optical filter to the first optical filter, and a third reflection from the first optical filter to the common port of the two-port reflector.

18. The wavelength selective two-port reflector as claimed in claim 17, wherein the first filter of the pair of optical filters is structurally configured and optically oriented to pass the target data wavelength portion of the input signal to the pass-through port of the two-port reflector without reflection.

19. The wavelength selective two-port reflector as claimed in claim 17, wherein:

individual ones of the wavelength selective two-port reflectors comprise a target data wavelength reflector; and the first optical filter, target data wavelength reflector, and the second optical filter are structurally configured, positioned, and oriented such that the target data wavelength portion of the input signal is reflected through the first optical filter and the second optical filter after it traverses the first optical filter.