OPTICAL TRANSCEIVER

Abstract

An optical transceiver of the present invention includes a coexistence element therein. An optical signal according to a first standard and an optical signal according to a second standard are transmitted and received through an optical cable accommodated in a first receptacle of the optical transceiver, and in the coexistence element, the optical signal according to the first standard and the optical signal according to the second standard are divided/combined. Among the divided upstream optical signals, the optical signal according to the first standard is photoelectrically converted in the optical transceiver, and the optical signal according to the second standard is transmitted to the outside through an optical cable accommodated in a second receptacle.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from U.S. Patent Application No. 63/072,177, filed on Aug. 30, 2020, in the United States Patent and Trademark Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field

The following description relates to an optical transceiver.

2. Description of Related Art

Subscriber network technologies using optical cable media are divided into active optical network technologies and passive optical network (PON) technologies. In the is active optical network, an apparatus such as an Ethernet switch or router, which is a device for dividing an optical signal, needs power, and the PON divides an optical signal using a splitter which does not need power.

The PON is classified into a time division multiplexing (TDM)-PON, a wavelength division multiplexing (WDM)-PON, and a time and wavelength division multiplexing (TWDM)-PON according to a multiplexing method of an upstream signal.

G-PON is a technology designed for simultaneously supporting an asynchronous transfer mode (ATM) and Ethernet and complies with the International Telecommunication Union (ITU)-Telecommunication Standardization Sector (T) G.984 standard. G-PON is an abbreviation of Gigabit-capable PON as a technology that supports an upstream/downstream transmission rate of 1.25 Gbps. E-PON is an abbreviation of Ethernet-PON as an Ethernet-specific technology and complies with the Institute of Electrical and Electronics Engineers (IEEE) 802.3ah Ethernet in the first mile (EFM) standard.

XG-PON and XGS-PON are successor technologies of G-PON and are designed for supporting 10 Gbps. The XG-PON supports asymmetric transmission rates of downstream 10 Gbps and upstream 1 Gbps and complies with the ITU-T G.987 standard, and the XGS-PON supports a symmetric transmission rate of upstream/downstream 10 Gbps and complies with the ITU-T G.988 standard.

The PON includes an optical line terminal (OLT), a splitter, an optical network unit (ONU), and an optical network terminal (ONT among which the OLT transmits downstream traffic signals to subscribers in a broadcasting manner, collects upstream traffic signals transmitted from the ONT, and transmits the collected upstream traffic signals to the Internet network at the same time.

Various PON standards are used, and particularly, optical signals of different wavelengths may be transmitted through a single optical cable using WDM. In this case, an optical add-drop multiplexing technique is generally used. A device (for example, coexistence element (CEx) which performs an optical add-drop multiplexing function is installed on an optical transmission path. For example, in a case in which the XGS-PON is introduced to replace the G-PON in a transmission network in which the G-PON is established, there is a problem in that a device which performs the optical add-drop multiplexing function should be additionally installed.

SUMMARY

The proposed invention is directed to providing an optical transceiver which performs an optical add-drop multiplexing function in a case in which optical signals according to two standards are simultaneously transmitted through one optical cable.

In one aspect of the present invention, an optical transceiver includes a first receptacle, a second receptacle, a coexistence element, and a first standard optical signal converter.

The first receptacle may accommodate an optical cable through which an upstream optical signal in which a reception wavelength optical signal according to a first standard and a reception wavelength optical signal according to a second standard coexist and a downstream optical signal, in which a transmission wavelength optical signal according to the first standard and a transmission wavelength optical signal according to the second standard coexist, are transmitted.

The second receptacle may accommodate an optical cable through which the reception wavelength optical signal according to the second standard and the transmission wavelength optical signal according to the second standard are transmitted.

The coexistence element may divide an optical path of the reception wavelength optical signal according to the first standard and the reception wavelength optical signal according to the second standard which are received through the optical cable accommodated in the first receptacle, transmit the reception wavelength optical signal according to the second standard through the optical cable accommodated in the second receptacle, change an optical path of the transmission wavelength optical signal according to the second standard received through the optical cable accommodated in the second receptacle, and transmit the transmission wavelength optical signal according to the second standard through the optical cable accommodated in the first receptacle.

The first standard optical signal converter may photoelectrically convert the reception wavelength optical signal according to the first standard transmitted from the coexistence element and electro-optically convert a signal for data to be transmitted to the transmission wavelength optical signal according to the first standard.

The coexistence element may include a housing, a wavelength division multiplexing (WDM) filter, and an optical path change part including a first mirror and a second mirror.

The WDM filter may allow the reception wavelength optical signal according to the first standard and the transmission wavelength optical signal according to the first standard to pass therethrough and reflect the reception wavelength optical signal according to the second standard and the transmission wavelength optical signal at a preset angle.

The optical path change part including a first mirror and a second mirror may transmit an optical signal received through the first receptacle and reflected by the WDM filter to an outside through the second receptacle and transmit an optical signal received through the second receptacle and reflected by the WDM filter to the outside through the first receptacle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a related art for processing an optical signal in which an XGS-passive optical network (PON) standard and a G-PON transmission standard coexist.

FIG. 2 is a view showing an example of processing optical signals in which an XGS-PON signal and a G-PON signal coexist through an optical line terminal (OLT) in which an optical transceiver of the present invention is installed.

FIG. 3 is a view showing an example of processing optical signals in which a 10G-EthernetPON (EPON) signal and an Ethernet-PON (E-PON) signal coexist through an OLT in which the optical transceiver of the present invention is installed.

FIG. 4 is a block diagram illustrating an optical transceiver according to one aspect of the present invention.

FIG. 5 is a view illustrating an optical path of an optical signal according to a first standard through a coexistence element according to one aspect of the present invention.

FIG. 6 is a view illustrating an optical path of an optical signal according to a second standard through the coexistence element according to one aspect of the present invention.

FIG. 7 is a view illustrating an example of the optical transceiver according to one aspect of the present invention.

DETAILED DESCRIPTION

The above-described and additional aspects of the present invention will be realized from embodiments described with reference to the accompanying drawings. It is understood that components in the embodiments may be variously combined in one embodiment as long as there are no contradictory statements therebetween. Although a block of a block diagram may denote physical components in some cases, the block may denote a partial function of one physical component or may logically denote a function performed by a plurality of components in other cases. In some cases, the substance of a block or a part of the block may be a set of program commands. Some or all of the blocks may be realized by hardware, software, or a combination thereof.

An optical transceiver is a device, which performs a function of transmitting an optical signal and a function of receiving an optical signal at the same time as a single device, converts an electrical signal to an optical signal, transmits the converted optical signal through an optical cable, and converts an optical signal received through the optical cable to an electrical signal in an optical communication device such as an optical line terminal (OLT). An optical transceiver of the present invention may transmit and receive optical signals according to two standards using wavelength division multiplexing (WDM) technology.

FIG. 1 is a view showing an example of a related art for processing an optical signal in which an optical signal according to an XGS-passive optical network (PON) standard and an optical signal according to a G-PON transmission standard coexist. As illustrated in FIG. 1, a transmission network including an XGS-PON optical network terminal (ONT)#1 13-1 and an XGS-PON OLT#1 10-1 uses an XGS-PON transmission standard which supports both downstream/upstream transmission speeds of 10 Gbps, and a transmission network including an XGS-PON ONT#2 13-2, a Gigabit-capable (G)-PON ONT#3 14, an XGS-PON OLT #2 10-2, and a G-PON OLT#3 11 uses both of the XGS-PON transmission standard and the G-PON transmission standard. An XGS-PON upstream signal (optical signal of a wavelength of 1270 nm) of the XGS-PON ONT#2 13-2 and a G-PON upstream signal (optical signal of a wavelength of 1310 nm) of the G-PON ONT#3 14 are combined in a splitter and transmitted, the combined optical signal is divided in a device (for example, coexistence element (CEx) 12) which performs an optical add-drop multiplexing function, the XGS-PON upstream signal is transmitted to the XGS-PON OLT#2 10-2, and the G-PON upstream signal is transmitted to the G-PON OLT#3 11. Conversely, an XGS-PON downstream signal (optical signal of a wavelength of 1577 nm) from the XGS-PON OLT#2 10-2 and a G-PON downstream signal (optical signal of a wavelength of 1490 nm) from the G-PON OLT#3 11 are combined by the CEx 12 and transmitted.

FIG. 2 is a view showing an example of processing an optical signal in which an XGS-PON signal and a G-PON signal coexist through an OLT in which an optical transceiver of the present invention is installed. As illustrated in FIG. 2, a transmission network including an XGS-PON ONT#4 23, a G-PON ONT#5 24, an XGS-PON OLT#4 20, and a G-PON OLT#5 21 uses both of an XGS-PON transmission standard and a G-PON transmission standard. An XGS-PON upstream signal (optical signal of a wavelength of 1270 nm) of the XGS-PON ONT#4 23 and a G-PON upstream signal (optical signal of a wavelength of 1310 nm) of the G-PON ONT#5 24 are combined by a splitter and transmitted, the combined optical signal is divided by the optical transceiver of the present invention installed in the XGS-PON OLT#4, the XGS-PON upstream signal is processed by the corresponding OLT, and the G-PON upstream signal is transmitted to the G-PON OLT#5 21 through an optical cable disposed between and connected to the two OLTs. Conversely, a downstream signal (optical signal of a wavelength of 1490 nm) of the G-PON OLT#5 21 is transmitted to the optical transceiver of the present invention installed in the XGS-PON OLT#4 20, combined with an XGS-PON downstream signal (optical signal of a wavelength of 1577 nm), and transmitted. Although not illustrated in FIG. 2, the optical transceiver of the present invention has an optical add-drop multiplexing function therein to divide optical signals according to two different standards and combine optical signals according to two different standards. Accordingly, a separate CEx does not need to be installed on an optical transmission path.

FIG. 3 is a view showing an example of processing an optical signal in which a 10G-EthernetPON (EPON) signal and an Ethernet-PON (E-PON) signal coexist through an OLT in which the optical transceiver of the present invention is installed. As illustrated in FIG. 3, a transmission network including a 10G-EPON ONT#6 33, an E-PON ONT#7 34, a 10G-EPON OLT#4 30, and an E-PON OLT#7 31 uses both of a 10G-EPON transmission standard and an E-PON transmission standard. A 10G-EPON upstream signal (optical signal of a wavelength of 1270 nm) of 10G-EPON ONT#6 33 and an E-PON upstream signal (optical signal of a wavelength of 1310 nm) of the E-PON ONT#7 34 are combined in a splitter and transmitted, the combined optical signal is divided by the optical transceiver of the present invention installed in the 10G-EPON OLT#6, the 10G-EPON upstream signal is processed in the corresponding OLT, and the E-PON upstream signal is transmitted to the E-PON OLT#7 31 through an optical cable disposed between and connected to two OLTs. Conversely, a downstream signal (optical signal of a wavelength of 1490 nm) of the E-PON OLT#7 31 is transmitted to the optical transceiver of the present invention installed in the 10G-EPON OLT#6 30 and combined with a 10G-EPON downstream signal (optical signal of a wavelength of 1577 nm) and transmitted. Although not illustrated in FIG. 3, the optical transceiver of the present invention has an optical add-drop multiplexing function therein to divide optical signals according to two different standards and combine optical signals according to two different standards. Like an example of FIG. 2, a separate CEx does not need to be installed on an optical transmission path.

FIG. 2 is a view illustrating that the optical transceiver of the present invention processes the optical signals in which the XGS-PON signal and the G-PON signal coexist, FIG. 3 is a view illustrating that the optical transceiver of the present invention processes the optical signals in which the 10G-EPON signal and the E-PON signal coexist, but the optical transceiver of the present invention is not limited to the case of the optical signal in which the XGS-PON signal and the G-PON signal coexist and the case of the optical signal in which the 10G-EPON and the E-PON signal coexist, and can process optical signals according to various combinations of PON standards including the two cases.

FIG. 4 is a block diagram illustrating an optical transceiver according to one aspect of the present invention. An optical transceiver 100 according to one aspect of the present invention include a first receptacle 110, a second receptacle 130, a coexistence element 150, and a first standard optical signal converter 170.

The optical transceiver 100 of the present invention is capable of bidirectional transmission using one optical cable and may be a small form-factor pluggable (SFP) or SFP+type optical transceiver. However, the present invention is not limited thereto, the optical transceiver 100 of the present invention may be one of various types, which satisfy a microservice architecture (MSA), of optical transceivers. The optical transceiver 100 of the present invention includes the first receptacle 110 and the second receptacle 130 which are inductor-capacitor (LC) receptacles. An optical cable is included in each of the two receptacles of the optical transceiver 100 of the present invention, signals, in which an optical signal according to a first standard and an optical signal according to a second standard coexist, are transmitted to and received from OLTs through one optical cable, and an optical signal according to the second standard is transmitted to and received from the optical transceiver accommodated in one port of another OLT (which processes the optical signal according to the second standard) through another optical cable. The first standard and the second standard may be different standards among various PON standards. For example, each of the first standard and the second standard may be any one among various standards including an XGS-PON standard, an XG-PON standard, a G-PON standard, an E-PON standard, a 10G-EPON standard, a next-generation (NG)-PON2 standard, and the like. In the present invention, an example, in which the first standard is the XGS-PON standard and the second standard is the G-PON standard, will be described for the sake of convenience of description.

The first receptacle 110 is an LC receptacle and accommodates an optical cable. The first receptacle 110 accommodates the optical cable through which an upstream optical signal, in which a reception wavelength optical signal according to the first standard and a reception wavelength optical signal according to the second standard coexist, and a downstream optical signal, in which a transmission wavelength optical signal according to the first standard and a transmission wavelength optical signal according to the second standard coexist, are transmitted. As an example, the optical transceiver 100 of the present invention may receive an upstream optical signal of a wavelength of 1270 nm according to the XGS-PON standard and an upstream optical signal of a wavelength of 1310 nm according to the G-PON standard and transmit a downstream optical signal of a wavelength of 1577 nm according to the XGS-PON standard and a downstream optical signal of a wavelength of 1490 nm according to the G-PON standard through the optical cable accommodated in the first receptacle 110.

The second receptacle 130 is an LC receptacle and accommodates an optical cable. The second receptacle 130 accommodates the optical cable through which the reception wavelength optical signal according to the second standard and the transmission wavelength optical signal according to the second standard are transmitted. The other end of the optical cable accommodated in the second receptacle 130 is accommodated in the optical transceiver according to the second standard accommodated in the OLT which is capable of processing the optical signal according to the second standard and processes the optical signal according to the second standard. As another example, in a case in which the OLT, in which the optical transceiver 100 of the present invention is installed, is an OLT capable of processing optical signals according to both of two standards, the other end of the optical cable accommodated in the second receptacle 130 may be accommodated in the optical transceiver according to the second standard accommodated in the other port.

The coexistence element divides upstream optical signals according to two different standards or combines downstream optical signals according to two different standards transmitted through one optical cable and transmits the divided upstream optical signals or the combined downstream optical signal through the optical cable. In the related art, a coexistence element is formed and used as a separate device, but in the present invention, the optical transceiver 100 is used by including a corresponding function therein. The coexistence element 150 may include a coupling part to which the first receptacle 110 and the second receptacle 130 are coupled.

The coexistence element 150 divides an upstream optical signal, in which two different wavelengths coexist, into upstream optical signals having different optical paths according to the wavelengths and combines optical signals having two different wavelengths to generate a downstream optical signal in which two different wavelengths coexist using optical properties. The coexistence element 150 of the present invention separates an optical path of a reception wavelength optical signal according to the first standard and an optical path of a reception wavelength optical signal according to the second standard received through the optical cable accommodated in the first receptacle 110, transmits the reception wavelength optical signal according to the second standard to the optical transceiver according to the second standard through the optical cable accommodated in the second receptacle 130, and transmits the optical signal according to the first standard to the first standard optical signal converter 170.

In addition, the coexistence element 150 changes an optical path of the transmission wavelength optical signal according to the second standard received from the optical transceiver according to the second standard through the optical cable accommodated in the second receptacle 130 and transmits the transmission wavelength optical signal according to the second standard with the transmission wavelength optical signal according to the first standard transmitted from the optical signal converter according to the second standard through the optical cable accommodated in the first receptacle 110.

As an example, in a case in which the optical transceiver 100 of the present invention transmits and receives an XGS-PON optical signal and a G-PON optical signal, the coexistence element receives an upstream optical signal of a wavelength of 1270 nm according to the XGS-PON standard and an upstream optical signal of a wavelength of 1310 nm according to the G-PON standard through the optical cable accommodated in the first receptacle 110, transmits the optical signal of the wavelength of 1270 nm to the first standard optical signal converter 170, changes an optical path of the optical signal of the wavelength of 1310 nm, and transmits the optical signal of the wavelength of 1310 nm to the outside (an optical transceiver according to the second standard) through the optical cable accommodated in the second receptacle 130.

The first standard optical signal converter 170 includes an avalanche photo diode (APD) and photoelectrically converts and outputs a reception wavelength optical signal according to the first standard transmitted from the coexistence element. In addition, the first standard optical signal converter 170 includes an external electro-absorption modulated laser (EML), electro-optically converts an electrical signal for data to be transmitted to a transmission wavelength optical signal according to the first standard, and outputs the converted transmission wavelength optical signal according to the first standard.

The coexistence element 150 may include a housing 151, a WDM filter 153, and an optical path change part including a first mirror 155 and a second mirror 157.

All of the WDM filter 153, the first mirror 155, and the second mirror 157 are accommodated in the housing 151.

The WDM filter 153 is positioned on an optical path through which an optical signal received from the optical cable accommodated in the first receptacle 110 is transmitted to the first standard optical signal converter 170, allows optical signals having some wavelengths to pass therethrough, and reflects optical signals having the other wavelengths. The WDM filter 153 allows a reception wavelength optical signal according to the first standard and a transmission wavelength optical signal according to the first standard to pass therethrough and reflects a reception wavelength optical signal and a transmission wavelength optical signal according to the second standard at a preset angle.

The optical path change part includes the first mirror 155 and the second mirror 157. In the optical path change part, an optical signal, which is received through the first receptacle 110 and reflected by the WDM filter 153, is sequentially reflected by the first mirror 155 and the second mirror 157 to be transmitted to the outside through the second receptacle 130. In addition, in the optical path change part, an optical signal received through the second receptacle 130 is sequentially reflected by the second mirror 157, the first mirror 155, and the WDM filter 153 and transmitted to the outside through the first receptacle 110.

FIG. 5 is a view illustrating an optical path of an optical signal according to the first standard through the coexistence element according to one aspect of the present invention. As illustrated in FIG. 5, a concept is illustrated in which a reception wavelength optical signal according to the first standard received through the optical cable accommodated in the first receptacle 110 passes through the WDM filter 153 and is transmitted to the first standard optical signal converter 170, and a transmission wavelength optical signal according to the first standard output from the first standard optical signal converter 170 passes through the WDM filter 153 and is transmitted to the outside through the optical cable accommodated in the first receptacle 110. As an example, in a case in which the first standard is the XGS-PON standard, an upstream optical signal of a wavelength of 1270 nm passes through the WDM filter 153, and a downstream optical signal of a wavelength of 1577 nm passes through the WDM filter 153.

FIG. 6 is a view illustrating an optical path of an optical signal according to the second standard through the coexistence element according to one aspect of the present invention. As illustrated in FIG. 6, a reception wavelength optical signal according to the second standard received through the optical cable accommodated in the first receptacle 110 is reflected by the WDM filter 153, directed to the first mirror 155, reflected by the first mirror 155 and the second mirror 157, and transmitted to the outside through the optical cable accommodated in the second receptacle 130, and a transmission wavelength optical signal according to the second standard received through the optical cable accommodated in the second receptacle 130 is reflected by the second mirror 157 and the first mirror 155, reflected by the WDM filter 153 again, and transmitted to the outside through the optical cable accommodated in the first receptacle 110. As an example, in a case in which the second standard is the G-PON standard, an upstream optical signal of a wavelength of 1310 nm is sequentially reflected by the WDM filter 153, the first mirror 155, and the second mirror 157 and transmitted to the outside through the optical cable accommodated in the second receptacle 130, and a downstream optical signal of a wavelength of 577 nm is received through the second receptacle 130, sequentially reflected by the second mirror 157, the first mirror 155, and the WDM filter 153, and transmitted to the outside through the optical cable accommodated in the first receptacle 110.

FIG. 7 is a view illustrating an example of the optical transceiver according to one aspect of the present invention. An optical transceiver 100 illustrated in FIG. 7 is an example of an SFP or SFP+type optical transceiver. The optical transceiver 100 may include a first receptacle 110 and a second receptacle 130 which are two LC receptacles and two optical cables. Signals which pass through ONTs and in which an optical signal according to a first standard and an optical signal according to a second standard coexist may be transmitted and received through the optical cable accommodated in the first receptacle 110, and the optical signal according to the second standard may be transmitted and received through the optical cable accommodated in the second receptacle 130.

In an upstream optical signal passing through the first receptacle 110, a reception wavelength optical signal according to the first standard and a reception wavelength optical signal according to the second standard coexist, an optical path is divided through a coexistence element 150, the reception wavelength optical signal according to the first standard is directed to a first standard optical signal converter 170, and the reception wavelength optical signal according to the second standard passes through the second receptacle 130 and is transmitted to the outside.

The coexistence element 150 includes a WDM filter 153, a first mirror 155, and a second mirror 157. The WDM filter 153 allows transmission and reception wavelength optical signals according to the first standard to pass therethrough and reflects the transmission and reception wavelength optical signals according to the second standard. The WDM filter 153, the first mirror 155, the second mirror 157 are installed to have is specific angles so that the reception wavelength optical signal according to the second standard passing through the first receptacle 110 passes through the second receptacle 130 and is transmitted to the outside, and the transmission wavelength optical signal according to the second standard passing through the second receptacle 130 passes through the first receptacle 110 and is transmitted to the outside.

The first standard optical signal converter 170 includes an APD and photoelectrically converts and outputs the reception wavelength optical signal according to the first standard transmitted from the coexistence element 150. In addition, the first standard optical signal converter 170 includes an external EML, electro-optically converts an electrical signal for data to be transmitted to a transmission wavelength optical signal according to the first standard, and outputs the converted transmission wavelength optical signal according to the first standard. The first standard optical signal converter 170 may further include a collimator lens, an optical filter which changes an optical path of a reception wavelength optical signal, and an isolator. Since the collimator lens, the optical filter, and the isolator are the same as those included in an optical transceiver of the related art, detailed descriptions will be omitted.

According to an optical transceiver of the present invention, optical signals according to two transmission standards can be processed by dividing or combining the optical signals according to each standard even when a device which performs an optical add-drop multiplexing function is not installed on an external optical transmission path.

Although the present invention has been described with reference to the accompanying drawings described above, the present invention is not limited thereto and should be construed as encompassing various modifications which may be clearly derived therefrom by those skilled the art. The claims are intended to encompass the various modifications.

Claims

1. An optical transceiver comprising:

a first receptacle which accommodates an optical cable through which an upstream optical signal in which a reception wavelength optical signal according to a first standard and a reception wavelength optical signal according to a second standard coexist, and a downstream optical signal, in which a transmission wavelength optical signal according to the first standard and a transmission wavelength optical signal according to the second standard coexist, are transmitted;

a second receptacle which accommodates an optical cable through which the reception wavelength optical signal according to the second standard and the transmission wavelength optical signal according to the second standard are transmitted;

a coexistence element which divides an optical path of the reception wavelength optical signal according to the first standard and the reception wavelength optical signal according to the second standard which are received through the optical cable accommodated in the first receptacle, transmits the reception wavelength optical signal according to the second standard through the optical cable accommodated in the second receptacle, changes an optical path of the transmission wavelength optical signal according to the second standard received through the optical cable accommodated in the second receptacle, and transmits the transmission wavelength optical signal according to the second standard through the optical cable accommodated in the first receptacle; and

a first standard optical signal converter which photoelectrically converts the reception wavelength optical signal according to the first standard transmitted from the coexistence element and electro-optically converts a signal for data to be transmitted to the transmission wavelength optical signal according to the first standard,

2. The optical transceiver of claim 1, wherein the coexistence element includes:

a housing;

a wavelength division multiplexing (WDM) filter through which the reception wavelength optical signal according to the first standard and the transmission wavelength optical signal according to the first standard pass and which reflects the reception wavelength optical signal according to the second standard and the transmission wavelength optical signal at a preset angle; and

an optical path change part which includes a first mirror and a second mirror, transmits an optical signal received through the first receptacle and reflected by the WDM filter to an outside through the second receptacle, and transmits an optical signal received through the second receptacle and reflected by the WDM filter to the outside through the first receptacle.