Optical fiber filter device and method for manufacturing the same

An optical fiber filter device comprises: a first fiber pigtail assembly (110) having a first optical fiber (111), a second fiber pigtail assembly (120) having a second optical fiber (121), a first optical filtering element (114) and a second optical filtering element (124). The first optical filtering element is arranged between a first port (113) of the first optical fiber and a second port (123) of the second optical fiber and is inclined at an angle to an optical axis of the first optical fiber such that a light component within a first wavelength range emitted from the first port is transmitted through the first optical filtering element and enters the second optical fiber via the second port, and a light component within a second wavelength range emitted from the first port is reflected by the first optical filtering element to form a reflected light. The second optical filtering element is arranged such that the reflected light returns to the first optical fiber via the first port after it has been reflected by the second optical filtering element and again by the first optical filtering element 1.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Chinese Patent Application No. 201010116459.X filed on Feb. 12, 2010 in the State Intellectual Property Office of China (patented—Chinese Patent No. CN102156329), the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the technical field of an optical filter device, in particular, to an optical fiber filter device and a method for manufacturing the same.

2. Description of the Related Art

With rapid development and commercialization of Fiber to the home (FTTH) and Fiber to the X (FTTx), the demand for the real-time monitoring of the optical fiber links at a local end and at a user end has been greatly increased recently. In the current FTTx monitoring system, the links are monitored by an Optical Time Domain Reflector (OTDR). In a dominant TDM-PON configuration, as an Optical Power Splitter is shared by a plurality of users, OTDR can attain results synthesized from the links of the plurality of users instead of the link of a single user. However, in a specific monitoring circumstance, it is necessary to acquire distinct detected images of the links between each user end and the local end.

At present, one solution that has been proposed is to insert a Fiber Brag Grating (FBG) in the user end. The FBG has a very narrow intrinsic band in the reflective spectrum (˜0.5 nm@3 dB). However, the OTDR monitoring system in the FTTx system requires a wider band in the reflective spectrum to be adapted for the deviation or drift (20 nm) of the center wavelength of a laser. Although the technology of chirp can enhance the band width of the FBG, it will be very expensive and the overall optical performance of the monitoring system will be reduced significantly due to the widen band of the FBG.

Conventionally, the FBG may be manufactured by means of a two-beam interferometer or phase masks. The solution employing two-beam interference is generally used in the field of research and development and is not suitable for mass production. In contrast, the phase masks can be used in mass production by virtue of its simplified and controllable process. In consideration of the narrow intrinsic band of the FBG (˜0.5 nm@3 dB) made by single phase mask, a plurality of phase masks or nonperiodic phase masks are necessarily used to form chirp FBG to enhance the band width of reflective spectrum. However, the customized phase mask with the reflective spectrum of 20 nm is extremely expensive. In the meanwhile, in the solution of chirp FBG, the overall optical performance of the system degrades remarkably as the band width of the reflective spectrum of FBG increases.

Therefore, it is desirable to provide an optical filter device with wide reflective spectrum, high reflection isolation and low cost to acquire the required detection signals from the OTDR.

SUMMARY OF THE INVENTION

The object of the present invention is to eliminate or at least alleviate the above problems in the prior art.

Accordingly, an object of the present invention is to provide an optical fiber filter device and a method for manufacturing the same, in which optical filtering elements and the fiber pigtail assemblies separate the incident lights based on the difference in spectra and induce the light with a high band width, a high reflectivity and a high reflection isolation back into the incident optical fiber to provide the detection signals required for the OTDR.

Another object of the present invention is to provide an optical fiber filter device and a method for manufacturing the same, in which the structure and the optical path are configured to implement multiple reflection of the incident light to achieve a high reflection isolation by optical filtering elements with conventional reflection isolation while cost of the device is reduced.

In accordance with an aspect of the present invention, there is provided an optical fiber filter device, comprising: a first fiber pigtail assembly and a second fiber pigtail assembly, the first fiber pigtail assembly comprising a first optical fiber and a first fiber accommodating member which accommodates the first optical fiber, the second fiber pigtail assembly comprising a second optical fiber and a second fiber accommodating member which accommodates the second optical fiber, the first optical fiber having a first port and the second optical fiber having a second port; and a first optical filtering element and a second optical filtering element, which each transmit a light within a first wavelength range and reflect a light within a second wavelength range.

The first optical filtering element is arranged between the first port and the second port and is inclined at an angle to an optical axis of the first optical fiber such that a light component within the first wavelength range emitted from the first port is transmitted through the first optical filtering element and enters the second optical fiber via the second port, and a light component within the second wavelength range emitted from the first port is reflected by the first optical filtering element to form a reflected light. The second optical filtering element is arranged in an optical path of the reflected light such that the reflected light returns to the first optical fiber via the first port after it has been reflected by the first and second optical filtering elements again at least twice.

In an embodiment, a space between the first port and the second port may be filled with a refractivity-matched substance.

In an embodiment, the angle may be more than 0 degree and less than 90 degree.

In an embodiment, the angle may be 45 degree.

In an embodiment, a reflective surface of the second optical filtering element may be perpendicular to a direction in which the reflected light is incident on the second optical filtering element.

In an embodiment, the light component within the first wavelength range emitted from the first port may enter the second optical fiber via the second port along an optical axis of the second optical fiber.

In an embodiment, the first optical filtering element may be arranged on an end face of the first port.

In an embodiment, the second optical filtering element may be arranged on a side surface of the first optical fiber adjacent to the first port.

In an embodiment, the second optical filtering element may be embedded in the first optical fiber adjacent to the first port.

In an embodiment, the end face of the first port may protrude from an end face of the first fiber accommodating member, and an end face of the second port may protrude from an end face of the second fiber accommodating member.

In an embodiment, the end face of the first port may be flush with an end face of the first fiber accommodating member, and an end face of the second port may be flush with an end face of the second fiber accommodating member.

In an embodiment, the first fiber accommodating member may be provided with a slit or a side opening for receiving the second optical filtering element.

In an embodiment, the end face of the first fiber accommodating member may be perpendicular to the optical axis of the first optical fiber, and the end face of the second fiber accommodating member may be perpendicular to the optical axis of the second optical fiber.

In an embodiment, the end face of the first fiber accommodating member may be inclined to the optical axis of the first optical fiber, and the end face of the second fiber accommodating member may be inclined to the optical axis of the second optical fiber.

In an embodiment, the first optical filtering element may be arranged on an end face of the second port.

In an embodiment, the second optical filtering element may be arranged on an end face of the first fiber accommodating member external to the first optical fiber.

In an embodiment, the second optical filtering element may be arranged on an end face of the first port.

In an embodiment, the end face of the second port may be flush with an end face of the second fiber accommodating member.

In an embodiment, the end face of the second port may protrude from an end face of the second fiber accommodating member.

In an embodiment, the first and second optical filtering elements are film filters.

In an embodiment, the optical fiber filter device may further comprise: a tube in which the first and second optical filtering elements and the first and second fiber pigtail assemblies are accommodated separately or in combination; and a housing in which the tube is accommodated.

In accordance with another aspect of the present invention, there is provided a method for manufacturing an optical fiber filter device, comprising the steps of:

(a) providing a first fiber pigtail assembly, a second fiber pigtail assembly, a first optical filtering element and a second optical filtering element, the first fiber pigtail assembly comprising a first optical fiber and a first fiber accommodating member which accommodates the first optical fiber, the second fiber pigtail assembly comprising a second optical fiber and a second fiber accommodating member which accommodates the second optical fiber, the first optical fiber having a first port and the second optical fiber having a second port, the first and second optical filtering elements each transmitting a light within a first wavelength range and reflecting a light within a second wavelength range;

(b) arranging the first optical filtering element in an optical path of a light emitted from the first port, inclining it at an angle to an optical axis of the first optical fiber such that a light component within the first wavelength range emitted from the first port is transmitted through the first optical filtering element, and a light component within the second wavelength range emitted from the first port is reflected by the first optical filtering element to form a reflected light, and arranging the second optical filtering element in an optical path of the reflected light such that the reflected light returns to the first optical fiber via the first port after it has been reflected by the first and second optical filtering elements again at least twice;

(c) accommodating the first and second fiber pigtail assemblies in a tube to allow the light transmitted through the first optical filtering element to enter the second optical fiber via the second port; and

(d) securing the first and second fiber pigtail assemblies in combination with the tube.

In an embodiment, the step (b) may further comprise: filling a space between the first port and the second port with a refractivity-matched substance.

In an embodiment, the step (b) may further comprise: adjusting the optical paths such that the reflected light is reflected by the first and second optical filtering elements to enter the first optical fiber with a maximum power; and the step (c) may further comprise: adjusting the optical paths such that the light transmitted through the first optical filtering element is coupled to the second fiber with a maximum coupling efficiency.

In an embodiment, the method may further comprise: bonding or depositing directly the first optical filtering element onto an end face of the first port.

In an embodiment, the method may further comprise: bonding or depositing directly the second optical filtering element onto a side surface of the first optical fiber adjacent to the first port; or embedding the second optical filtering element in the first optical fiber adjacent to the first port.

In an embodiment, the method may further comprise: bonding or depositing directly the first optical filtering element onto an end face of the second port.

In an embodiment, the method may further comprise: bonding or depositing directly the second optical filtering element onto an end face of the first fiber accommodating member external to the first optical fiber.

In an embodiment, the method may further comprise: bonding or depositing directly the second optical filtering element onto an end face of the first port.

In an embodiment, the method may further comprise: polishing the end face or the side surface and coating the end face or the side surface with antireflection films before the first or the second optical filtering element is bonded or deposited.

With the above configuration, the expensive chirp FBG is replaced with a feedback optical design structure using optical filtering elements to acquire the detection signals required for the OTDR such that the band width of the reflected light is improved to achieve an improved optical performance. The above configurations of the present invention may further have advantages of simplified manufacturing process, low cost and high reliability of the device over the prior art.

The present invention can achieve high reflection isolation, high return loss and good reflectivity by the multiple reflection of light in the optical fiber filter device with the film filters at low cost and low reflection isolation. Furthermore, the optical fiber filter device according to the present invention is easy to be integrated with other optical devices due to its miniature size of the core components.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Specific embodiments of the present invention will be described hereinafter in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like parts. The embodiments are described below in order to explain the general concept of the present invention without limitations on the scope of the invention.

FIG. 1andFIG. 2show an optical fiber filter device. InFIG. 1, the optical fiber filter device100according to an embodiment of the present invention is illustrated. The optical fiber filter device100comprises a first fiber pigtail assembly110and a second fiber pigtail assembly120. The first fiber pigtail assembly110comprises a first optical fiber111and a first fiber accommodating member112which accommodates the first optical fiber111. The second fiber pigtail assembly120comprises a second optical fiber121and a second fiber accommodating member122which accommodates the second optical fiber121. The first optical fiber111has a first port113and the second optical fiber121has a second port123. The first fiber accommodating member112and the second fiber accommodating member122may, for example, be a capillary tube or other members which can accommodate and fix the optical fiber.

The optical fiber filter device100further comprises a first optical filtering element114and a second optical filtering element124. The first optical filtering element114and the second optical filtering element124each transmit a light within a first wavelength range (λ1a, λ1b) and reflect a light within a second wavelength range (λ2a, λ2b). As illustrated in theFIG. 2, the first optical filtering element114may be arranged on an end face115of the first port113such that a light component within the first wavelength range (λ1a, λ1b) emitted from the first port113is transmitted through the first optical filtering element114to form a transmitted light131. The transmitted light131enters the second optical fiber121via the second port123. The first optical filtering element114is inclined at an angle α to an optical axis116of the first optical fiber111such that a light component within the second wavelength range (λ2a, λ2b) emitted from the first port113is reflected by the first optical filtering element114to form a reflected light132. The second optical filtering element124is arranged in an optical path of the reflected light132such that the reflected light132is reflected by the second optical filtering element124to the first optical filtering element114, and returns to the first optical fiber111via the first port113after it is reflected by the first optical filtering element114again. That is, the reflected light132is fed back to the first optical fiber111after it has been reflected by the first and second optical filtering elements114,124again twice in order to provide a detection signal required for the OTDR.

In the above configuration, the light component within the second wavelength range (λ2a, λ2b) emitted from the first port113is reflected by the first optical filtering element114and the second optical filtering element124three times in total. By means of the multiple reflections, the reflection isolation of the optical filtering can be improved significantly. For example, in the circumstance where a light is reflected by a conventional film filter with a reflection isolation of 14 dB, the reflection isolation of the optical filtering can be up to over 40 dB. Further, the return loss also increases as the reflection isolation is enhanced. In the meanwhile, as the selection of the reflected wavelength range (λ2a, λ2b) the first optical filtering element114and the second filtering element124, e.g., the film filters are much wider or more flexible than that of the chirp FBG, the band width of the light fed back to the first optical fiber111can be enhanced prominently instead of being limited to the narrow band width of the FBG. Thus, the negative influence of the wavelength drifts of the OTDR due to the environment variations (e.g., temperature variations) to the reflectivity of the detection signal fed back to the OTDR may be reduced, or substantially eliminated.

In the above embodiment shown inFIG. 1andFIG. 2, the first optical filtering element114is arranged on the end face115of the first port113. However, as appreciated by the skilled person in the art, the present invention is not limited to this. For example, the first optical filtering element114may also be arranged on an end face125of the second port123of the second optical fiber124, or anywhere between the first port113and the second port123by additional mounting means. All of these solutions can achieve the optical filtering of the first optical filtering element114to the light emitted from the first port113such that the light component within the first wavelength range (λ1a, λ1b) is transmitted through the first optical filtering element114and enters the second optical fiber121via the second port123. Other embodiments which can achieve the same function as that of the above embodiments also fall within the scope of the present invention.

In the above embodiment shown inFIG. 1andFIG. 2, the second optical filtering element124is arranged on a side surface of the first optical fiber adjacent to the first port113. In order to grind or polish the side surface on which the second optical filtering element124is arranged, a groove which receives the second optical filtering element124may be formed at the corresponding location on the side surface. The groove may be planar or curve. However, as appreciated by the skilled person in the art, the present invention is not limited to this. For example, the second optical filtering element124may be arranged anywhere in the optical path of the reflected light, e.g., arranged on a certain location internal or external to the first optical fiber111or arranged on a component (e.g. a wedge) protruding from the side surface of the optical fiber. For instance, inFIG. 4, the second optical filtering element124is embedded in the first optical fiber111. In all of these solutions, the reflected light132can return to the first optical fiber111via the first port113after it has been reflected by the first optical filtering element114and the second optical filtering element124at least twice. Other embodiments which can achieve the same function as that of the above embodiments also fall within the scope of the present invention.

As illustrated inFIG. 1, the optical fiber filter device100may further comprise: a tube119in which the first fiber pigtail assembly110is accommodated, a tube129in which the second fiber pigtail assembly120is accommodated, adhesives13and a housing14. The first and second optical filtering elements114,124may also be accommodated in the tubes respectively. The tubes119and129may be housed and fixed in the housing14. The adhesives13, e.g., epoxy glues or ultraviolet glues, additionally adhere and fix the first optical fiber111and the second optical fiber121to the tubes119,129and the housing14. Such arrangement of the tubes and the housing can prevent the optical fiber filter device from being deteriorated by impacts, vibrations and other harmful environment factors. AlthoughFIG. 1shows an arrangement in which the first fiber pigtail assembly110and the first optical filtering element114, the second fiber pigtail assembly120and the second optical filtering element124are accommodated in the two tubes119and129respectively, the embodiments of the present invention are not limited to this. For instance, one or more of the first fiber pigtail assembly110, the first optical filtering element114, the second fiber pigtail assembly120and the second optical filtering element124may be accommodated and fixed in one or more tubes separately or in any combinations.

In an embodiment, a space between the first port113and the second port123may be filled with a refractivity-matched substance in order to reduce the Fresnal reflections and the optical loss. The refractivity-matched substance may have a refractivity which is equal or substantially equal to that of the first optical fiber or the first optical filtering element such that the light component emitted from the first port113or transmitted through the first optical filtering element114is directed substantially in a line at interfaces between different media to enter the second port along an optical axis of the optical fiber121in order to improve the fiber coupling efficiency.

Alternatively, the refractivity-matched substance may also have a different refractivity from that of the first optical fiber or the first optical filtering element such that the light component emitted from the first port113or transmitted through the first optical filtering element114is deflected at the interfaces between different media. The deflection of the direction of the light may be compensated by regulating the position of the second optical fiber with respect to the first optical fiber, e.g., shifting the optical axis126of the second optical fiber121relative to the optical axis116of the first optical fiber111or inclining the optical axis126relative to the optical axis116of the first optical fiber111at a certain angle. With the above regulation, the light transmitted through the first optical filtering element will still enter the second port along the optical axis126of the second optical fiber121to achieve a high fiber coupling efficiency. The refractivity-matched substance may be filled in the space between the first fiber pigtail assembly110and the second fiber pigtail assembly120.

In the circumstance where the refractivity-matched substance is absent, the position of the optical axis126of the second optical fiber121may be regulated relative to the optical axis116of the first optical fiber111, e.g., by shifting the optical axis126of the second optical fiber121relative to the optical axis116of the first optical fiber111or inclining the optical axis126relative to the optical axis116of the first optical fiber111at a certain angle, to improve the fiber coupling efficiency. The shift or angle depends on the refractivity of the optical fibers and the first optical filtering element and the distance between the first end face113and the second end face123.

In the embodiments of the present application, the inclination angle α of the optical filtering element114with respect to the optical axis116of the first optical fiber111is defined as an acute angle between the first optical filtering element114and the optical axis116of the first optical fiber111.

In the embodiment shown inFIG. 1andFIG. 2, the inclination angle α of the optical filtering element114with respect to the optical axis116of the first optical fiber111may be45degree. In this case, the reflected light132is perpendicular to the optical axis116. Thus, the second optical filtering element124may be arranged in parallel to the optical axis116to allow the reflected light132to retrace its optical path. Therefore, the side surface of the optical fiber on which the second optical filtering element is arranged can be processed easily to simplify the procedures and save the costs. However, the inclination angle α may be other values, for example, more than 0 degree and less than 90 degree. The orientation of the second optical filtering element124depends on the inclination angle α. As illustrated inFIG. 3, the inclination angle α is more than 45 degrees, and thus, the reflected light132is inclined outwards the first port113of the first optical fiber111instead of being perpendicular to the optical axis116. In this circumstance, the reflective surface of the second optical filtering element124may be inclined accordingly at another angle with respect to the optical axis116such that the reflected light132retraces its optical path. In contrast,FIG. 4shows the case where the inclination angle α is less than 45 degrees. The reflected light132is inclined inwards the first optical fiber111instead of being perpendicular to the optical axis116. In this circumstance, the orientation and the location of the reflective surface of the second optical filtering element124is also regulated accordingly such that the reflected light132retraces its optical path. For example, inFIG. 4, the second optical filtering element is embedded in the first optical fiber111adjacent to the first port113and inclined relative to the optical axis116.

In an embodiment, the reflective surface of the second optical filtering element124is perpendicular to the reflected light132which is incident on the second optical filtering element124. In such circumstance, the reflected light132is reflected by the second optical filtering element124to retrace the path to the first optical filtering element114, and then is reflected by the first optical filtering element114along the optical axis116of the first optical fiber111back to the first port115. The orientation and location of the second optical filtering element124is matched with the inclination angle α in order to allow the reflective surface of the second optical filtering element124to be perpendicular to the reflected light132which is incident on the second optical filtering element124, as illustrated inFIGS. 2-4.

In the above embodiments, the inclination angle α is selected such that the total reflection is avoided at the interfaces of media to ensure the light within the second wavelength range to transmit through the first optical filtering element.

In the above embodiments, the optical filtering element may be arranged at the corresponding end face or side surface by, e.g., bonding, depositing or coating. In order to improve the transmission efficiency or other optical performance, the corresponding location of the end face or side surface of the optical fiber or the fiber accommodating member may be processed, e.g., grinded, polished, before the optical filtering element is mounted. The polished surface may further be coated with antireflection films.

In the embodiments shown inFIGS. 1-3, the end face117of the first fiber accommodating member112may be perpendicular to the optical axis116of the first optical fiber111, and the end face127of the second fiber accommodating member122may be perpendicular to the optical axis126of the second optical fiber121. However, the present invention is not limited to this. The end face117and the end face127may be inclined relative to the optical axis116and the optical axis117respectively, as illustrated inFIGS. 5-9.

In the embodiments shown inFIGS. 1-6, the end face115of the first port113may protrude from the end face117of the first fiber accommodating member112and the end face125of the second port123may protrude from the end face127of the second fiber accommodating member122. In this case, after the corresponding location of the end face or side surface of the optical fiber or the fiber accommodating member is processed, the end face115of the first port113and the end face125of the second port123are necessarily processed separately to ensure high transmission efficiency before the optical filtering elements are mounted. Thus, the process of the end face115of the first port113and the end face125of the second port123is separated from the process of the end face117of the first fiber accommodating member112and the end face127of the second fiber accommodating member122in order to prevent the quality of the end face115and the end face125from being deteriorated by the process of the end face117and the end face127.

In another embodiment, as shown inFIGS. 7-9, the first port113and the second port123may be buried in the first fiber accommodating member112and the second fiber accommodating member122and the end face115of the first port113is flush with the end face117of the first fiber accommodating member112and the end face127of the second port123is flush with the end face117of the second fiber accommodating member122. As the end face115and end face125are flush with the end face117and the end face127respectively, the end face115and end face117, or the end face125and the end face127may be simultaneously processed, e.g., ground and polished, instead of being processed separately, so as to simplify the processes and save the costs.

In the embodiment in which the end face115and the end face125are flush with the end face117of the first fiber accommodating member112and the end face127of the second fiber accommodating member122, a fiber surface on which the second optical filtering element124is arranged may be exposed such that the second optical filtering element124can be mounted easily. For instance, a slit17may be formed in the first fiber accommodating member112adjacent to the location on which the second optical filtering element is arranged such that the fiber surface can be exposed, as shown inFIG. 7. Alternatively, a side opening18may be formed from a side of the first fiber accommodating member112to expose the location on which the second optical filtering element124is arranged. The side opening18may be a partial side opening, i.e., only a part of the side corresponding to the first fiber accommodating member112and the second optical filtering element124is removed, as shown inFIG. 8; or the side opening18may be a complete side opening, i.e., the side corresponding to the first fiber accommodating member112and the second optical filtering element124is completely removed, as shown inFIG. 9.

FIGS. 10-13show further embodiments according to the present invention. In these embodiments, the first optical filtering element114is arranged on the end face125of the second port123of the second optical fiber121instead of being arranged on the end face of the first port113of the first optical fiber111.

In the embodiment shown in theFIGS. 10-11, the second optical filtering element124is arranged on the end face117of the first fiber accommodating member112external to the first optical fiber111. The first optical filtering element114may be inclined relative to the optical axis116of the first optical fiber111at an angle which is, for example, more than 0 degree and less than 90 degree, such as 18 degree, or 45 degree. As appreciated by the skilled person in the art, the angle α should be selected such that the total reflection is avoided at the interfaces of media to ensure the light within the second wavelength range to transmit through the first optical filtering element. Assuming that the normal of the reflective surface of the first optical filtering element114is inclined to the optical axis116of the first optical fiber111at an angle γ, i.e., γ=90°−α. In accordance with the law of reflection, the angle at which the reflected light132is inclined to the normal of the reflective surface is also γ. In order to simplify the optical path design, the reflective surface of the second optical filtering element124may be perpendicular to the reflected light132which is incident on the second optical filtering element124. In this circumstance, the second optical filtering element124is inclined to the optical axis116of the first optical fiber111at an angle of “90°−2γ”. The reflected light132is reflected by the second optical filtering element124to retrace its optical path to the first optical filtering element114, and then is reflected by the first optical filtering element114directly along the optical axis116of the first optical fiber111back to the first port113. Before the second optical filtering element124is arranged, the location of the end face117(which can located on either side external to the first optical fiber111) corresponding to the second optical filtering element124may be oriented such that the second optical filtering element124can have a suitable inclination angle. For instance, in the circumstance where the reflective surface of the second optical filtering element124is perpendicular to the reflected light132which is incident on the second optical filtering element124, the location of the end face117on which the second optical filtering element124is arranged may be inclined (e.g. by grinding) to the optical axis116of the first optical fiber111at an angle of “90°−2γ”.

As illustrated inFIGS. 10 and 11, the end face125of the second port123is flush with the end face127of the second fiber accommodating member122, i.e., the second optical fiber121is buried in the second fiber accommodating member122. In this circumstance, as the end face125of the second port123is flush with the end face127of the second fiber accommodating member122, the end face125and the end face127may be processed, e.g., ground and polished in a procedure, and the first optical filtering element114may be arranged on the whole end face of the second fiber pigtail assembly comprised of the end face125of the second optical fiber121and the end face127of the second fiber accommodating member122to cover the end face125. Thus, it is not necessary to process the end face125separately and thus to simplify the processes and save the costs.

In the above embodiments, the optical filtering elements may be arranged at the corresponding end face or side surface, for example, by bonding, depositing and coating. The corresponding location of the end face or side surface of the optical fiber or the fiber accommodating member may be processed, e.g., grinded, polished, before the optical filtering element is mounted, in order to improve the transmission efficiency or other optical performance. The polished surface may further be coated with antireflection films.

FIGS. 12-13show another embodiment of the optical fiber filter device according to the present invention. The embodiment has a substantially same construction as that shown inFIGS. 10-11except for the arrangements of the first optical filtering element114, the second optical filtering element124and the second port123of the second optical fiber121.

In the embodiments shown inFIGS. 12 and 13, the second optical filtering element124is arranged on the end face115of the first port113of the first optical fiber111instead of being arranged on the end face117of the first fiber accommodating member112as the previous embodiments. Such arrangement can shorten the optical path and reduce the gap between the end face115of the first port113and the end face125of the second port123. Thus, the optical fiber filter device may be more compact. In this circumstance, the location of the end face115(which can be located on either side external to the first optical fiber111) corresponding to the second optical filtering element124may be oriented such that the second optical filtering element124can have a suitable inclination angle, before the second optical filtering element124is arranged. For instance, in the circumstance where the reflective surface of the second optical filtering element124is perpendicular to the reflected light132which is incident on the second optical filtering element124, the location of the end face115on which the second optical filtering element124is arranged may be inclined (e.g. by grinding) to the optical axis116of the first optical fiber111at an angle of “90°−2γ”.

In the embodiments shown inFIGS. 12-13, the end face125of the second port123may protrude from the end face127of the second fiber accommodating member122, and the first optical filtering element114is arranged on the protruded end face125. In this case, after the corresponding location of the end face of the optical fiber or the fiber accommodating member is processed, the end face125of the second port123is necessarily processed separately to ensure high transmission efficiency before the first optical filtering element114is mounted. Thus, the process of the end face125of the second port123is separated from the process of the end face127of the second fiber accommodating member122in order to prevent the quality of the end face125from being deteriorated by the process of the end face127.

In an embodiment, the end face117of the first fiber accommodating member112and end face127of the second fiber accommodating member122may be inclined to the optical axis116of the first optical fiber111and the optical axis126of the second optical fiber121, as illustrated inFIGS. 10 and 11. Alternatively, the end face117of the first fiber accommodating member112and end face127of the second fiber accommodating member122may be perpendicular to the optical axis116and the optical axis126, as shown inFIGS. 12 and 13.

In the above embodiments, the arrangement in which the end face125of the second port123of the second optical fiber121is flush with the end face127of the second fiber accommodating member122is used in combination with the arrangement in which the second optical filtering element124is arranged on the end face117of the first fiber accommodating member112, while the arrangement in which the end face125of the second port123of the second optical fiber121protrudes from the end face127of the second fiber accommodating member122is used in combination with the arrangement in which the second optical filtering element124is arranged on the end face115of the first port113of the first optical fiber111. However, the present invention is not limited to this. For instance, the arrangement in which the end face125of the second port123of the second optical fiber121is flush with the end face127of the second fiber accommodating member122may also be used in combination with the arrangement in which the second optical filtering element124is arranged on the end face115of the first port113of the first optical fiber111, or the arrangement in which the end face125of the second port123of the second optical fiber121protrudes from the end face127of the second fiber accommodating member122may be used in combination with the arrangement in which the second optical filtering element124is arranged on the end face117of the first fiber accommodating member112.

In the above embodiments shown in Figures, the first optical filtering element114and the second optical filtering element124are arranged such that the reflected light132is reflected by the first optical filtering element114and the second optical filtering element124again twice. However, the present invention is not limited to this. For instance, the other optical paths in which the reflected light132can be reflected by the optical filtering elements may also be designed to improve the reflection isolations, for example, adjusting the optical path by increasing additional reflective elements to redirect the reflected light132, or allowing the reflected light132to be reflected three or more times before it returns to the first optical fiber113.

In an embodiment, the first optical filtering element114and the second optical filtering element124may have same optical filtering performance, or may have a certain offset of the center wavelengths or filtering bands with each other, as long as they can transmit the light within the first wavelength range (λ1a, λ1b) and reflect the light within the second wavelength range (λ2a, λ2b). All of these solutions fall within the concept of the present invention. The optical filtering elements are also not limited to the film filters.

In an embodiment, the second optical fiber121may also receive other working light135(as illustrated inFIGS. 2, 3 and 5-7), for example, the optical signals for transmissions and detections, and allow it to exit the second port123and then enter the first optical fiber111via the first port113. That is, the optical fiber filter device may allow the optical signals for achieving other functions to pass while achieving the above operation of the optical filtering. It further may improve the density of the integration of the optical system.

In the above embodiments, two optical filtering elements are used to reflect the light emitted from the first optical fiber111at least three times in total. However, as appreciated by the skilled person in the art, more optical filtering elements may be used in combination to reflect the light emitted from the first optical fiber111at least three times in order to improve the reflection isolations of the light returning to the first optical fiber111. These solutions also fall within the scope of the present invention.

The skilled person in the art would appreciate that the above embodiments are only illustrative; the present invention may further be implemented in other forms. For instance, the first and second optical fibers or the first and second fiber pigtail assemblies with the above optical filtering arrangements may be provided in other housing components, such as a lock pin or a V-shaped groove, or may be integrated with other optical-electronic devices together to improve interconnection or the integrated level.

The present invention also provides a method for manufacturing an optical fiber filter device. As an example, for the optical fiber filter device100shown inFIG. 1, at first, a first fiber pigtail assembly110, a second fiber pigtail assembly120, a first optical filtering element114and a second optical filtering element124are provided. The first fiber pigtail assembly110may comprise a first optical fiber111and a first fiber accommodating member112which accommodates the first optical fiber111. The second fiber pigtail assembly120may comprise a second optical fiber121and a second fiber accommodating member122which accommodates the second optical fiber121. The first optical fiber111has a first port113and the second optical fiber121has a second port123. The first and second optical filtering elements114,124each may transmit a light within a first wavelength range and reflect a light within a second wavelength range.

Subsequently, the first optical filtering element114is arranged in an optical path of a light emitted from the first port113, and inclined at an angle to an optical axis116of the first optical fiber111such that the light component within the first wavelength range emitted from the first port113is transmitted through the first optical filtering element114, and the light component within the second wavelength range emitted from the first port113is reflected by the first optical filtering element114to form the reflected light132. The second optical filtering element124may be arranged in an optical path of the reflected light such that the reflected light132returns to the first optical fiber111via the first port113after it has been reflected by the first and second optical filtering elements114,124again at least twice.

Then, the first and second fiber pigtail assemblies110,120are accommodated in a tube to allow the light transmitted through the first optical filtering element114to enter the second optical fiber121via the second port123. At last, the first and second fiber pigtail assemblies110,120are fixed in combination with the tube to form the optical fiber filter device100.

In an embodiment, after the first optical filtering element114and the second optical filtering element124are provided, the optical paths may be adjusted such that the reflected light132is reflected by the first and second optical filtering elements114,124to enter the first optical fiber111with a maximum power.

In an embodiment, after the first fiber pigtail assembly110and the second fiber pigtail assembly120are accommodated in the tube respectively, the optical paths may be adjusted such that the light transmitted through the first optical filtering element is coupled to the second fiber with a maximum coupling efficiency. In particular, the optical paths may be adjusted by regulating the position of the optical axis126of the second optical fiber with respect to the optical axis116of the first optical fiber, e.g., by regulating the shift or inclination angle of the optical axis126of the second optical fiber with respect to the optical axis116of the first optical fiber, in order to improve the coupling efficiency of the optical fibers.

In an embodiment, when the first fiber pigtail assembly110and the second fiber pigtail assembly120are loaded into the tube, the space between the first port113and the second port123may be filled with a refractivity-matched substance, in order to decrease the optical loss, reduce the Fresnal reflections and improve the coupling efficiency of the optical fibers.

In an embodiment, the first optical filtering element114may be arranged, e.g., bonded or deposited directly, onto the end face115of the first port113.

In an embodiment, the second optical filtering element124may be arranged, e.g., bonded or deposited directly, onto the side surface of the first optical fiber111adjacent to the first port113; or the second optical filtering element124may be embedded in the first optical fiber111adjacent to the first port113.

In an embodiment, in order to improve the transmission efficiency or other optical performance, the end face or the side surface may be polished and coated with antireflection films before the first or the second optical filtering element is bonded or deposited.

In an embodiment, a groove in which the second optical filtering element124is accommodated may be formed at the location of the side surface corresponding to the second optical filtering element124to make it easier to process, e.g., grind or polish the side surface of the second optical filtering element124.

In another embodiment, the first optical filtering element114may be arranged, e.g., bonded or deposited directly onto the end face125of the second port123. The end face125of the second port123may be flush with the end face127of the second fiber accommodating member122, in order to perform simultaneously the processing of the end face125of the second port123and the processing of the end face127of the second fiber accommodating member122together.

In an embodiment, the second optical filtering element124may be arranged, e.g., bonded or deposited directly onto the end face117of the first fiber accommodating member112external to the first optical fiber111. Furthermore, in order to improve the optical transmission efficiency or other optical performance, the end face125of the second port123and the end face117of the first fiber accommodating member112may be polished and coated with antireflection films before the first or the second optical filtering element is arranged.

In an embodiment, the second optical filtering element124may be arranged, e.g., bonded or deposited directly onto the end face115of the first port113. Furthermore, in order to improve the optical transmission efficiency or other optical performance, the end face125of the second port123and the end face115of the first port113may be polished and coated with antireflection films before the first or the second optical filtering element is arranged.

Although the embodiments of the present invention have been described in conjunction with figures, modifications to the above embodiments can be carried out without departing the spirit of the present invention.

The above technical features or various structures of the present invention can be mutually combined to form new structures. It can be appreciated by those skilled in the art that the combinations fall within the scope of the present invention.