Optical fiber coupled laser source pump with wavelength division multiplexer

Abstract

A pump laser package may include an input optical fiber that transmits signal light on a first optical path. A first lens may be arranged on the first optical path. The pump laser package may include a source that transmits pump light on a second optical path. A second lens and a negative lens may be arranged on the second optical path. The first lens and the negative lens may be arranged to generate a virtual image associated with the pump light. The pump laser package may include an output optical fiber on a third optical path. The first lens may be arranged on the third optical path. The pump laser package may include a combiner that receives the signal light on the first optical path, receives the pump light on the second optical path, and transmits the signal light and the pump light on the third optical path.

Description

[0001] This application is a divisional application of Chinese patent application No. 201710264234.0, whose application date is February 3, 2017 and whose invention name is “Fiber-coupled laser source pumping with wavelength division multiplexer”. Technical Field

[0002] The present disclosure relates to optical amplifier systems for data communications and electrical communications, and more particularly, to a pump laser package that provides a signal and a pump beam as a combined optical signal while performing additional optical functions, saving space, reducing the size of optical components of the optical amplifier system, simplifying the configuration and / or construction of the optical amplifier system, and / or reducing the cost of implementing the optical amplifier system. Background Art

[0003] Optical amplifier systems used for data communications and electrical communications can include discrete components for pump lasers, wavelength division multiplexers (WDMs), and more. These discrete components can be interconnected via optical fibers that are spliced together with signal fibers. Managing the space required for these discrete components, optical fibers, and splices requires routing fibers (which can be sensitive to bend radius issues that introduce loss) and multiple fiber splices (which can introduce additional loss). Summary of the Invention

[0004] According to some possible embodiments, a pump laser package may include: an input optical fiber that sends signal light on a first optical path in free space within the package, wherein a first lens may be arranged on the first optical path, wherein the first lens may have a substantially uniform refractive index within a material of the first lens; a source that sends pump light on a second optical path in free space within the package, wherein a second lens and a third lens may be arranged on the second optical path, wherein the third lens may be a negative lens, wherein the second lens and the third lens may be separated by the free space inside the package, and wherein the first lens and the third lens are arranged to produce a virtual image associated with the pump light at a virtual image plane in the free space inside the package; an output optical fiber on a third optical path in free space within the package, wherein the first lens may be arranged on the third optical path; and a WDM filter in free space within the package that receives signal light on the first optical path and sends the signal light on the third optical path, receives pump light on the second optical path and sends the pump light on the third optical path, and wherein the WDM filter may be arranged between the first lens and the third lens.

[0005] According to some possible embodiments, a fiber-coupled laser source may include an input optical fiber for sending input light on a first optical path in the free space inside the package; a laser diode for sending source light on a second optical path in the free space inside the package; an output optical fiber on a third optical path in the free space inside the package; a first lens arranged on the first optical path and the third optical path, wherein the first lens may include a material having a substantially consistent refractive index; a second lens and a third lens arranged on the second optical path, wherein the third lens may be a negative lens, wherein the second lens and the third lens may be separated by the free space inside the package, and wherein the first lens and the third lens may be arranged to generate a virtual image associated with the source light at a virtual image plane in the free space inside the package; and a combiner arranged between the first lens and the second lens in the free space inside the package, receiving the input light on the first optical path and sending the input light on the third optical path, and receiving the source light on the second optical path and sending the source light on the third optical path.

[0006] According to some possible embodiments, a method may include: sending signal light on a first optical path in free space inside a package through an input optical fiber, wherein a first lens may be arranged on the first optical path, wherein the first lens may have a refractive index that is substantially uniform within a material of the first lens; sending pump light on a second optical path in free space inside the package through a source, wherein a second lens and a third lens may be arranged on the second optical path, wherein the second lens and the third lens may be separated by the free space inside the package, wherein the first lens and the third lens may generate a virtual image associated with the pump light at a virtual image plane in the free space inside the package, and wherein the third lens may be a negative lens; receiving signal light on the first optical path through a WDM filter arranged in the free space inside the package, wherein the WDM filter may be arranged between the first lens and the second lens; receiving pump light on the second optical path through the WDM filter; sending signal light on a third optical path in the free space inside the package to an output optical fiber on the third optical path through the WDM filter, wherein the first lens may be arranged on the third optical path; and sending pump light on the third optical path to the output optical fiber through the WDM filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a diagram of an exemplary pump laser package in which components, devices, and / or systems described herein may be implemented.

[0008] Figures 2A-2His a diagram of an exemplary embodiment of a fiber-coupled laser source pumping including a wavelength division multiplexer (WDM) and three lenses in free space inside a package to achieve wavelength stabilization of a laser diode and combine a pump beam and a signal beam into a combined output beam with reduced alignment sensitivity and / or increased manufacturability, as described herein; and

[0009] Figure 3 There is an existing optical amplifier system comprising a single lens disposed between the WDM and the laser diode. DETAILED DESCRIPTION

[0010] The following detailed description of example embodiments refers to the accompanying drawings, in which the same reference numerals in different figures represent the same or similar elements. The embodiments described below are merely examples and are not intended to limit the embodiments to the precise forms disclosed. Instead, the embodiments selected for description enable one of ordinary skill in the art to practice the embodiments.

[0011] Existing optical amplifier systems include discrete components for pump lasers and wavelength division multiplexers (WDMs). These discrete components can be interconnected via optical fibers that splice together signal fibers associated with the optical signals amplified by the optical amplifier system. However, managing these discrete components, fibers, and splices requires physical space, routing fibers (which are sensitive to loss-inducing bend radius issues), and / or multiple fiber splices (which can introduce additional loss).

[0012] In addition, in existing optical amplifier systems where it is possible to integrate a pump laser and a WDM within a package, alignment sensitivity is important when arranging and / or fixing the components of the optical amplifier system in place within the package, thereby reducing the manufacturability of the optical amplifier system and / or increasing the cost of the optical amplifier system in order to ensure that acceptable alignment is achieved. For example, such existing optical amplifier systems include a pair of collimating lenses, one of which is a GRIN lens, disposed between the optical fiber and the WDM, and another (single) collimating lens disposed between the laser diode and the WDM. However, the alignment of the components of the existing optical amplifier system is sensitive to five degrees of freedom (e.g., x-direction, y-direction, z-direction, polar angle (θ), and azimuthal angle) during manufacturing and / or assembly. ).

[0013] Furthermore, in conventional optical amplifier systems that utilize a single collimating lens disposed between a laser diode and a WDM, a welding head (e.g., a laser welding head) associated with assembly and / or manufacturing of the conventional optical amplifier system is located in a plane corresponding to the laser diode. The location of the welding head in the plane of the laser diode results in significant sensitivity to alignment with respect to the x-, y-, and z-directions during assembly and / or manufacturing of the conventional optical amplifier system. Consequently, manufacturing and / or ensuring reliability of the conventional optical amplifier system is difficult and / or expensive to ensure acceptable alignment with respect to one or more degrees of freedom.

[0014] Embodiments described herein provide a pump laser package including a combiner (e.g., a WDM filter) and three lenses located in free space within the package to provide a signal and pump beam as a combined optical signal. Advantages of the embodiments described herein may include reducing the physical space usage of an optical amplifier system, reducing the number of optical fibers in the optical amplifier system, reducing the number of fiber connectors in the optical amplifier system, reducing the size of optical components in the optical amplifier system, simplifying the configuration and / or construction of the optical amplifier system, increasing the manufacturability of the optical amplifier system, and / or reducing the cost of implementing the optical amplifier system (e.g., compared to existing optical amplifier systems that include discrete components). Further advantages of the embodiments described herein include reducing the alignment sensitivity of the optical amplifier system, such that alignment of the components of the optical amplifier system is only sensitive with respect to three degrees of freedom. Additionally, the optical amplifier system described herein achieves reduced sensitivity with respect to five degrees of freedom. This reduced alignment sensitivity increases the manufacturability of the optical amplifier system, increases reliability, and / or reduces cost (compared to existing optical amplifier systems that include a single collimating lens disposed between the pump laser and the WDM).

[0015] Figure 1is a diagram of an example pump laser package 100 in which the components, devices and / or systems described herein may be implemented. In some embodiments, the pump laser package 100 may enable integration of the functional components of an optical amplifier system in a single coaxial package, as described herein. By doing so, discrete and / or bulky optical components, such as pump lasers and WDMs (e.g., 980 / 1550 WDM filters), may be integrated into a compact package, resulting in significant space savings (e.g., compared to existing optical amplifier systems). Furthermore, labor-intensive fiber splicing among discrete optical components is not required. This allows for the placement of optical amplifiers in small form factor modules, such as ultra-small CFPx transmission modules. In some embodiments, the pump laser package 100 allows integration of a hermetically encapsulated pump laser and four or more other erbium-doped fiber amplifier (EDFA) functional components in the same fiber pigtail package.

[0016] like Figure 1 As shown, in some embodiments, the pump laser package 100 includes a hermetically enclosed portion containing the pump laser (e.g., Figure 1 In some embodiments, the hermetically enclosed portion may also include a light detector and / or one or more other components.

[0017] As further shown, the pump laser package 100 includes a coaxial package (which may be non-hermetic) between a TO-can package and a pair of optical fibers (e.g., input and output fibers). As shown, in some embodiments, the coaxial package may contain free-space optical components (e.g., between the TO-can package and the ends of the optical fibers) associated with performing one or more optical functions, as described in detail below.

[0018] In some embodiments, the coaxial enclosure can have a diameter less than 10 mm. For example, the diameter of the coaxial enclosure can be in a range of about 5.6 millimeters (mm) to about 7.6 mm. In some embodiments, a magnetic ring (not shown) contained in the coaxial enclosure can have an outer diameter of about 2 mm (for example, when the diameter of the coaxial enclosure is about 6.6 mm).

[0019] In some embodiments, the length of the coaxial package including the TO-can package header may be in the range of about 20 mm to about 40 mm (eg, Figure 1 27mm length shown in ).

[0020] In some embodiments, the coaxial package can have a gradually decreasing diameter from the TO-can package to the optical fiber and / or a non-circular cross-section. In some embodiments, the optical path length from the pump chip to the optical fiber face can be approximately 13.5 mm (e.g., when the coaxial package length is approximately 27 mm).

[0021] In some embodiments, a pump laser utilizing the pump laser package 100 may have an output power ranging from about 50 mW to about 150 mW, may be used for C-band single-channel applications, may be used for narrow channel count applications, and / or may be implemented in conjunction with an EDFA.

[0022] In some embodiments, such a pump laser can have a wavelength range of approximately 970 nanometers (nm) to approximately 980 nm, require no active cooling for operation, and can produce a pump beam of up to approximately 150 milliwatts. In some embodiments, the pump laser can produce a pump beam of up to approximately 200 milliwatts. In some embodiments, the pump laser can operate in an environment with a housing temperature in the range of approximately 0 degrees Celsius to approximately 70 degrees Celsius. In some embodiments, the pump laser can have a thermistor resistance of approximately 10,000 ohms at approximately 25 degrees Celsius. In some embodiments, the pump laser can have a fiber pigtail bend radius of less than or equal to approximately 16 mm.

[0023] As an example, Figure 1 The number, arrangement, size, length, diameter, width, etc. of the parts and components of the pump laser package 100 shown in FIG. Figure 1 The pump laser package 100 may include additional parts and / or components, fewer parts and / or components, different parts and / or components, differently arranged parts and / or components, and / or differently sized parts and / or components compared to those shown in .

[0024] Figures 2A-2H is a diagram of an exemplary embodiment of a fiber-coupled laser source pump (referred to herein as a pump laser) 250-285, which includes a combiner (e.g., a wavelength division multiplexer (WDM) filter) and three lenses in free space within a package. The pump lasers 250-285 implement wavelength stabilization of the laser diode and combine the pump beam and the signal beam into a combined output beam with reduced alignment sensitivity and / or increased manufacturability, as described herein. In some embodiments, the pump lasers 250-285 can be housed in the pump laser package 100. Figures 2A-2G In some exemplary embodiments shown, arrows approximately represent edge rays of each light beam.

[0025] Figure 2Ais a diagram of an exemplary pump laser 250 that includes a combiner and three lenses in free space within a package to achieve wavelength stabilization of the laser diode and combine the pump beam and the signal beam with reduced alignment sensitivity and increased manufacturability (e.g., compared to existing optical amplifier systems). Figure 2A As shown, pump laser 250 may include input fiber 205, output fiber 210, distributed feedback (DFB) diode 215, combiner 220, and lenses 225-1, 225-2, and 225-3. Exemplary operation of pump laser 250 is described below in the description of exemplary components of pump laser 250.

[0026] The input fiber 205 is an optical fiber that transmits signal light (ie, signal beam) into free space within the package of the pump laser 250. Figure 2A As shown (by means of a dashed line pointing in a rightward direction), input fiber 205 may be arranged so that input fiber 205 sends signal light on an optical path (herein referred to as a first optical path) from the face of input fiber 205, via lens 225-1, to combiner 220.

[0027] The DFB diode 215 is a DFB diode that transmits pump light (i.e., a beam of pump light, source light) in free space within the package of the pump laser 250. In some embodiments, the DFB diode 215 can transmit pump light of a specific wavelength (e.g., approximately 980 nm) without receiving any reflected pump light (i.e., the DFB diode 215 can achieve internal wavelength stabilization). Figure 2A As shown (with a solid line pointing in a leftward direction to the right of combiner 220), DFB diode 215 can be arranged so that DFB diode 215 sends pump light on an optical path (referred to herein as the second optical path) from the face of DFB diode 215, through lens 225-2 and lens 225-3, to combiner 220. In some embodiments, the use of DFB diode 215 can simplify implementation and / or reduce cost compared to pump lasers using Fabry-Perot diodes or other types of diodes that require a laser cavity external to the laser diode.

[0028] The output fiber 210 is an optical fiber used to receive signal light and pump light (i.e., signal light combined with pump light, referred to herein as signal + pump light) via the free space in the package of the pump laser 250, and output the signal + pump light. Figure 2AAs shown (with a dashed line pointing in a left direction and a solid line pointing in a left direction on the left side of the combiner 220), the output fiber 210 can be arranged so that the output fiber 210 receives the signal + pump light on an optical path (herein referred to as the third optical path) from the combiner 220, via the lens 225-1, to the face of the output fiber 210. As shown, in some embodiments, the input fiber 205 and the output fiber 210 can be arranged in a fiber pigtail at the first end of the package of the pump laser 250.

[0029] The combiner 220 includes components for combining light beams by, for example, transmitting (i.e., passing) a first light beam (e.g., pump light) and reflecting a second light beam (e.g., signal light) based on the wavelength of the light beam, based on the direction of the light beam, based on the source of the light beam, and the like. For example, the combiner 220 may include a WDM filter, a low-pass filter, a beam combiner, and the like. In some embodiments, the combiner 220 may transmit light having a wavelength of approximately 980 nm (e.g., pump light) and reflect light having a wavelength of approximately 1550 nm (e.g., signal light). However, other examples are possible, and the combiner 220 may transmit or reflect light of one or more other wavelengths. In some embodiments, the combiner 220 may be tilted relative to the optical axis of the pump laser 250 (e.g., as shown in FIG. 2 ). Figure 2A ), so that the signal light can be easily aligned with the output optical fiber 210.

[0030] like Figure 2A As shown, in some embodiments, combiner 220 can be arranged to receive signal light transmitted through input fiber 205 on a first optical path and transmit (reflect) the signal light on a third optical path to output fiber 210. As further shown, combiner 220 can be arranged to receive pump light transmitted through DFB diode 215 on a second optical path and transmit (transmit) the pump light on a third optical path to output fiber 210. As further shown, in some embodiments, combiner 220 can be arranged between lens 225-1 and lens 225-3. In some embodiments, combiner 220 can be separated from lens 225-1 and lens 225-3 by free space within the package of pump laser 250.

[0031] The lens 225-1 includes a lens for collimating a light beam or focusing a collimated light beam in the free space of the package of the pump laser 250. For example, the functions of the lens 225-1 may include collimating the signal light on the first optical path, focusing the pump light on the third optical path, focusing the signal light on the third optical path, and so on. Figure 2AAs shown, in some embodiments, lens 225-1 can be arranged in the free space of the package on the first optical path and the third optical path (e.g., between optical fibers 205 / 210 and combiner 220). In some embodiments, lens 225-1 can have a substantially uniform refractive index within the material comprising lens 225-1 (i.e., lens 225-1 is not a gradient refractive index (GRIN) lens).

[0032] The lens 225-2 comprises a lens for causing the light beam to converge in the free space of the package of the pump laser 250. For example, Figure 2A As shown, the function of lens 225-2 may include causing the pump light transmitted by DFB diode 215 to converge onto a portion of the second optical path (eg, a portion of the second optical path from lens 225-2 to lens 225-3). Figure 2A As shown, in some embodiments, the lens 225 - 2 may be arranged on the second optical path in the free space of the package (eg, between the DFB diode 215 and the lens 225 - 3 ).

[0033] Lens 225-3 comprises a negative lens for collimating the light beam focused in the free space of the package of pump laser 250. For example, Figure 2A As shown, the function of lens 225-3 may include collimating the pump light (e.g., after passing through lens 225-2) so that the pump light is collimated on a portion of the second optical path (e.g., a portion of the second optical path from lens 225-3 to combiner 220). Figure 2A As shown, in some embodiments, lens 225 - 3 may be arranged on the second optical path in the free space of the package (eg, between lens 225 - 2 and combiner 220 ).

[0034] In some embodiments, the lens 225-3 and the lens 225-1 may be arranged so that the virtual image associated with the pump light on the second optical path is located on a virtual image plane 227 (eg, a plane perpendicular to the optical axis, such as a plane perpendicular to the optical axis) in the free space of the package. Figure 2A For example, Figure 2A As shown (e.g., by the dashed gray lines converging to a point on the dashed black line), lens 225-3 and lens 225-1 can be arranged so that a virtual image associated with the pump light is located at virtual image plane 227 (e.g., located between lens 225-1 and combiner 220). In some embodiments, lens 225-3 and lens 225-1 can be arranged so that virtual image plane 227 is located at another point within the free space of the package.

[0035] In some embodiments, the alignment sensitivity of the pump laser 250 can be reduced by using separate lenses 225-2 and 225-3 in the second optical path (e.g., compared to existing optical amplifier systems that use a single collimating lens between the laser diode and the combiner). For example, in some embodiments, the use of lenses 225-2 and 225-3 in the free space of the pump laser 250 package reduces the alignment sensitivity of the components of the pump laser 250, making the pump laser 250 sensitive only to alignment changes with respect to three degrees of freedom (e.g., alignment with respect to three orthogonal directions, such as the x-direction, the y-direction, and the z-direction). Here, because the use of separate lenses 225-2 and 225-3 allows a virtual image to be formed on the virtual image plane 227, the weld head plane (e.g., the laser weld head plane) can be positioned at the virtual image plane 227, which reduces and / or eliminates sensitivity to alignment related to angular degrees of freedom (e.g., alignment with respect to polar angles, azimuthal angles, etc.) because all light originating from the virtual image point will be imaged onto the receiving fiber regardless of its angle of incidence. Thus, the use of separate lenses 225-2 and 225-3 may increase the manufacturability of pump laser 250 and / or reduce the cost of the pump laser (e.g., compared to existing optical amplifier systems that include a single lens). In some embodiments, the welds may be located close to virtual image plane 227 to reduce sensitivity, but need not reduce sensitivity to the same degree as in embodiments where the welds are located on virtual image plane 227. In some embodiments, welds associated with manufacturing or assembling pump laser 250 may be located between output fiber 210 and combiner 220.

[0036] Furthermore, the alignment sensitivity of the pump laser 250 (e.g., with respect to the x-, y-, and z-directions) can be reduced based on the generation of a virtual image at the virtual image plane 227. For example, the virtual image generated at the virtual image plane 227 can be larger than the physical size of the pump light source at the DFB diode. Since the alignment sensitivity in the x-, y-, and z-directions depends on the image size, the alignment sensitivity in the x-, y-, and / or z-directions can be reduced (due to the magnification of the virtual image).

[0037] On the contrary, as mentioned above and as Figure 3 As shown, for an existing optical amplifier system using a single lens between a combiner and a diode, a welding point plane (e.g., a laser welding point plane) associated with manufacturing or assembling the existing optical amplifier system is positioned at a plane corresponding to the diode. Figure 3 As shown, the use of a single lens arranged between the diode and the combiner does not generate a virtual image in the free space of the package associated with the pump light. Figure 3 shown, manufactured and / or assembled Figure 3The solder joints associated with existing optical amplifier systems are positioned in a plane corresponding to the face of the laser diode (e.g., rather than in free space within the package). Because the near field is minimized at the face plane of the laser diode, existing optical amplifiers are more sensitive to misalignment at the solder joints.

[0038] However, return Figure 2A , lens 225-3 and lens 225-1 may be arranged to produce a virtual image associated with the pump light at virtual image plane 227. In this case, welds associated with manufacturing and / or assembling pump laser 250 may be positioned at virtual image plane 227. In some embodiments, as described above, compared to Figure 3 In the prior art optical amplifier system shown in , positioning the weld point at the virtual image plane 227 (e.g., between the lens 225-1 and the combiner 220) reduces alignment sensitivity in the x-direction, the y-direction, and the z-direction (e.g., by a factor of two, three, etc.), and / or eliminates alignment sensitivity with respect to the angular degrees of freedom (e.g., thereby eliminating the need for angular alignment), thereby increasing the manufacturability of the pump laser 250 and / or reducing the cost of the pump laser.

[0039] In some embodiments, the face of input fiber 205, the face of output fiber 210, combiner 220, lens 225-1, lens 225-2, and / or lens 225-3 may be included in a non-hermetically enclosed housing. Additionally or alternatively, one or more of the face of input fiber 205, the face of output fiber 210, combiner 220, lens 225-1, lens 225-2, and / or lens 225-3 may be enclosed in a hermetically enclosed housing. In some embodiments, lens 225-2 may serve as a window in a closed enclosure in a TO-can. In cases where flat glass is used as the window in the closed enclosure, lens 225-2 and lens 225-3 may not be hermetically enclosed.

[0040] During operation, input fiber 205 transmits signal light (e.g., 1550 nm light) along a first optical path from the face of input fiber 205 to combiner 220 (e.g., via lens 225-1), and DFB diode 215 transmits pump light (e.g., 980 nm light) along a second optical path from the face of DFB diode 215 to combiner 220 (e.g., via lenses 225-2 and 225-3). Combiner 220 reflects the signal light received on the first optical path to a third optical path (e.g., from combiner 220, via lens 225-1, to the face of output fiber 210), while simultaneously transmitting the pump light received on the second optical path to the third optical path. Here, by transmitting the signal light and pump light along the third optical path, combiner 220 causes the signal light and pump light to combine at the face of output fiber 210 (i.e., to form signal + pump light). Output fiber 210 then outputs this signal + pump light.

[0041] Figure 2B is a diagram of an exemplary pump laser 255 that includes a combiner and three lenses in free space inside a package, achieving wavelength stabilization of the laser diode and combining the pump beam and the signal beam with reduced alignment sensitivity and increased manufacturability. Figure 2B As shown, the pump laser 255 may include an input fiber 205, an output fiber 210, a combiner 220, a lens 225-1, a lens 225-2, a lens 225-3, a Fabry-Perot (FP) diode 230, and a fiber Bragg grating (FBG) 235. The input fiber 205, the output fiber 210, the combiner 220, the lens 225-1, the lens 225-2, and the lens 225-3 may be arranged and / or operated in a manner similar to that described above.

[0042] The FP diode 230 is an FP diode for transmitting pump light (i.e., source light) in free space within the package of the pump laser 255. In some embodiments, the FP diode 230 transmits pump light having a specific wavelength (e.g., approximately 980 nm) based on a portion of the pump light reflected back to the FP diode 230 by the FBG 235. In other words, the wavelength of the pump light transmitted by the FP diode 230 can be stabilized by the FBG 235. Figure 2B As shown (with a solid line pointing to the left to the right of combiner 220), FB diode 230 can be arranged so that FP diode 230 sends pump light on a second optical path (e.g., from the face of FP diode 230, through lens 225-2 and lens 225-3, to combiner 220). Combiner 220 then sends the pump light on a third optical path, as described in more detail below.

[0043] The FBG 235 is a fiber Bragg grating integrated into the output fiber 210 and is used to partially reflect (i.e., reflect a portion of) the pump light transmitted by the FP diode 230, so as to stabilize the wavelength of the pump light transmitted by the FP diode 230 in the free space of the package of the pump laser 255 (e.g., so that the FP diode 230 transmits pump light having a wavelength of approximately 980 nm). For example, the FBG 235 may take the form of a periodic or non-periodic perturbation in the effective refractive index of the core of the output fiber 210 to cause light of a specific wavelength (e.g., 980 nm) to be partially reflected. In some embodiments, the FBG 235 may include another type of grating.

[0044] During operation, input fiber 205 transmits signal light (e.g., 1550 nm light) along a first optical path from the face of input fiber 205 to combiner 220 (e.g., via lens 225-1), and FP diode 230 transmits pump light (e.g., 980 nm light) along a second optical path from the face of FP diode 230 to combiner 220 (e.g., via lenses 225-2 and 225-3). Combiner 220 reflects the signal light received on the first optical path to a third optical path (e.g., from combiner 220, via lens 225-1, to the face of output fiber 210), while simultaneously transmitting the pump light received on the second optical path to the third optical path. Here, by transmitting the signal light and pump light along the third optical path, combiner 220 causes the signal light and pump light to combine at the face of output fiber 210 (i.e., to form signal + pump light). Output fiber 210 then outputs this signal + pump light. In addition, FBG 235 partially reflects the pump light back to FP diode 230 (e.g., in the opposite direction of the third and second optical paths; via lens 225-1, combiner 220, lens 225-3, and lens 225-2) to stabilize the wavelength of the pump light transmitted by FP diode 230.

[0045] Figure 2C is a diagram of an exemplary pump laser 260 that includes a combiner and three lenses in free space inside a package, achieving wavelength stabilization of the laser diode and combining the pump beam and the signal beam with reduced alignment sensitivity and increased manufacturability. Figure 2C As shown, the pump laser 260 may include an input fiber 205, an output fiber 210, a combiner 220, a lens 225-1, a lens 225-2, a lens 225-3, an FP diode 230, and a reflective narrowband device 240. The input fiber 205, the output fiber 210, the combiner 220, the lens 225-1, the lens 225-2, the lens 225-3, and the FP diode 230 may be arranged and / or operated in a manner similar to that described above.

[0046] The reflective narrowband device 240 is a component for partially reflecting the pump light transmitted by the FP diode 230, so as to stabilize the wavelength of the pump light transmitted by the FP diode 230 in the free space of the package of the pump laser 255 (for example, so that the FP diode 230 transmits pump light having a wavelength of approximately 980 nm). In some embodiments, the reflective narrowband device 240 may be in the form of a coating on the surface in the free space of the package of the pump laser 260, on which the pump light is incident. For example, Figure 2CAs shown, the reflective narrowband device 240 can be in the form of a coating on the surface of the output fiber 210 on which the signal + pump light is incident. In some embodiments, such a coating can be applied to additional and / or different surfaces in the package of the pump laser 260 (e.g., the surface of the lens 225-1, the surface of the lens 225-2, the surface of the lens 225-3, the surface of the combiner 220, etc.).

[0047] In some embodiments, the surface on which the coating is applied may transmit light having a wavelength other than a specific wavelength (for example, the coating may transmit light having a wavelength other than approximately 980 nm) and may reflect a narrow band at a specific wavelength (for example, the coating may reflect light having a wavelength of approximately 980 nm). In some embodiments, the surface on which the coating is applied may have a reflectivity of approximately 2-4%. In this way, the coated surface may allow for spectral shaping of FP diode 230.

[0048] During operation, input fiber 205 transmits signal light (e.g., 1550 nm light) along a first optical path from the face of input fiber 205 to combiner 220 (e.g., via lens 225-1), and FP diode 230 transmits pump light (e.g., 980 nm light) along a second optical path from the face of FP diode 230 to combiner 220 (e.g., via lenses 225-2 and 225-3). Combiner 220 reflects the signal light received on the first optical path to a third optical path (e.g., from combiner 220, via lens 225-1, to the face of output fiber 210), while simultaneously transmitting the pump light received on the second optical path to the third optical path. Here, by transmitting the signal light and pump light along the third optical path, combiner 220 causes the signal light and pump light to combine at the face of output fiber 210 (i.e., to form signal + pump light). Output fiber 210 then outputs this signal + pump light. In addition, the reflective narrowband device 240 (e.g., a coating on the surface of the output optical fiber 210) partially reflects the pump light back to the FP diode 230 (e.g., in the opposite direction of the third optical path and the second optical path; via the lens 225-1, the combiner 220, the lens 225-3, and the lens 225-2) so as to stabilize the wavelength of the pump light transmitted by the FP diode 230.

[0049] Figure 2D is a diagram of an exemplary pump laser 265 that includes a combiner and three lenses in free space inside a package, achieving wavelength stabilization of the laser diode and combining pump light and signal light with reduced alignment sensitivity and increased manufacturability. Figure 2DAs shown, the pump laser 265 may include an input fiber 205, an output fiber 210, a combiner 220, a lens 225-1, a lens 225-2, a lens 225-3, an FP diode 230, and a reflective narrowband device 240. The input fiber 205, the output fiber 210, the combiner 220, the lens 225-1, the lens 225-2, the lens 225-3, the FP diode 230, and / or the reflective narrowband device 240 may be arranged and / or operated in a manner similar to that described above.

[0050] As described above, the reflective narrowband device 240 is a component for partially reflecting the pump light transmitted by the FP diode 230 so as to stabilize the wavelength of the pump light transmitted by the FP diode 230 in the free space of the package of the pump laser 255. In some embodiments, as Figure 2D As shown, the reflective narrowband device 240 can take the form of a discrete component in free space within the package of the pump laser 265. For example, the reflective narrowband device 240 can be a volume holographic grating (VHG, also known as a volume Bragg grating), a reflective narrowband filter, a bandpass filter with a partial broadband reflector (e.g., with a reflectivity of a few percent), etc. In some embodiments, broadband feedback is provided by one or more other optical surfaces within the package of the pump laser 265.

[0051] In some embodiments, when a discrete component is used, the reflective narrowband device 240 may be arranged on the second optical path (e.g., Figure 2D (shown between combiner 220 and lens 225-3). Additionally or alternatively, when implemented as a discrete component, reflective narrowband device 240 can be disposed at another location in the free space of the package, such as another location on the second optical path (e.g., between lens 225-3 and lens 225-2, or between lens 225-2 and the face of FP diode 230), another location on the third optical path (e.g., between combiner 220 and lens 225-1, or between lens 225-1 and the face of output fiber 210), and / or another location on the first optical path. In some embodiments, discrete reflective narrowband device 240 can simplify large-scale manufacturing in a wafer format. This can reduce implementation costs and variability between different pump lasers.

[0052] like Figure 2DAs shown, in some embodiments, the combiner 220 and the discrete component reflective narrowband device 240 can be oriented at a specific relative angle (e.g., in the range of about 2 degrees to about 5 degrees). In other embodiments, the combiner 220 and the discrete component reflective narrowband device 240 can be parallel to each other, and one or both of the combiner 220 and the reflective narrowband device 240 can be configured to deflect light from the FP diode 230 at a specific angle (e.g., to reduce coupling of unwanted back reflections or feedback).

[0053] During operation, the pump laser 265 may be Figure 2C The pump laser 260 operates in the manner described above. However, the discrete reflective narrowband device 240 (e.g., arranged between the combiner 220 and the lens 225-3) partially reflects the pump light back to the FP diode 230 (e.g., in the reverse direction on part of the second optical path; via the lens 225-3 and the lens 225-2) to stabilize the wavelength of the pump light transmitted by the FP diode 230.

[0054] Figure 2E is a diagram of an exemplary pump laser 270 that includes a combiner and three lenses in free space inside a package, achieving wavelength stabilization of the laser diode and combining pump light and signal light with reduced alignment sensitivity and increased manufacturability. Figure 2E As shown, the pump laser 270 may include an input fiber 205, an output fiber 210, a combiner 220, a lens 225-1, a lens 225-2, a lens 225-3, an FP diode 230, and a reflective narrowband device 240. The input fiber 205, the output fiber 210, the lens 225-1, the lens 225-2, the lens 225-3, and / or the FP diode 230 may be arranged and / or operated in a manner similar to that described above.

[0055] As described above, the emitting narrowband device 240 is a component for partially reflecting the pump light transmitted by the FP diode 230 so as to stabilize the wavelength of the pump light transmitted by the FP diode 230 in the free space of the package of the pump laser 255. In some embodiments, as Figure 2E As shown, the reflective narrowband device 240 can be integrated with the combiner 220 (e.g., such that the combiner 220 and the reflective narrowband device 240 are included in a single component within the free space of the pump laser 270). For example, the integrated combiner 220 / reflective narrowband device 240 can be a VHG (volume holographic grating) with a WDM coating, a WDM coating with a low-reflective narrowband coating, or the like. In some embodiments, as Figure 2E As shown, the combiner 220 portion of such an integrated component (e.g. Figure 2EThe left part of the middle component 220 / 240) and the reflective narrowband device 240 part of the integrated component (eg Figure 2E The right portion of the middle member 220 / 240) may have a different angle of incidence.

[0056] During operation, the pump laser 270 may be Figure 2D The pump laser 260 operates in the manner described above. However, the integrated combiner 220 / reflective narrowband device 240 partially reflects the pump light back to the FP diode 230 (e.g., in the reverse direction of the second optical path; via lenses 225-3 and 225-2) to stabilize the wavelength of the pump light transmitted by the FP diode 230.

[0057] Figure 2F and 2G Figures are of exemplary pump lasers 275 and 280, respectively, that can improve the efficiency of wavelength stabilization of a pump beam about a desired wavelength by using angled facets. The use of angled facets can reduce broadband feedback reaching a laser diode (e.g., DFB diode 215 or FP diode 230) that would otherwise compete with feedback intended to stabilize the wavelength of the laser diode. For example, in some embodiments, the facet of the laser diode from which the pump light is transmitted can be an angled waveguide (e.g., as in Figure 2F and 2G ), rather than a straight waveguide (e.g., as Figures 2A-2E In particular, although pump lasers 275 and 280 are shown as including DFB diodes 215 (e.g., as with Figure 2A ), similar techniques can also be used for pump lasers including FP diodes 230 (e.g., as described with Figures 2B-2E Related description).

[0058] like Figure 2F As shown, in some embodiments, the DFB diode 215 may include an angled first (e.g., front) face to reflect light away from the diode to improve wavelength stability. Here, since the second (e.g., back) face of the DFB diode 215 generally remains normally incident on the diode waveguide, the diode waveguide is bent at a shallow angle (e.g., 2 degrees, 3 degrees, or a larger or smaller angle greater than 0 degrees) to create the angled front face.

[0059] In some embodiments, the angle at which the pump light is emitted from the DFB diode 215 is different from, for example, Figure 2EAs shown in the exemplary embodiment shown. For example, the rotation of the DFB diode 215, the position of the lens 225-1 and the lens 225-2, and / or the fiber pigtail assembly (FTA) of the pump laser 275 can be selected to modify the angle at which the pump light is emitted and / or reflected. In this way, the pump laser 275 can improve the coupling efficiency of the signal light and the pump light with respect to the output fiber 210, which improves the efficiency of the pump laser 275.

[0060] Similarly, if Figure 2G As shown, in some embodiments, the pump laser 280 can include angled facets at the extreme ends of the input fiber 205 and the output fiber 210. This arrangement can reduce the amount of broadband feedback reaching the DFB diode 215 and / or reduce feedback to the input fiber 205 and / or the output fiber 210.

[0061] In some embodiments, the input fiber 205 and / or the output fiber 210 can be angled to reduce feedback (i.e., reflection) to the input fiber 205 and / or the output fiber 210 and to the DFB diode 215. In some embodiments, the angle of the facets of the input fiber 205 and / or the output fiber 210 can be in the range of about 5 degrees to about 10 degrees (e.g., about 8 degrees). Feedback from the DFB diode 215 and the distal end of the input fiber 205 and / or the output fiber 210 (e.g., the end opposite the angled facet) can be independent. In some embodiments, an anti-reflection coating with low reflectivity can be used instead of angled facets to reduce feedback.

[0062] Figure 2H is a diagram of an exemplary pump laser 285 that includes a combiner and three lenses in free space inside a package to achieve wavelength stabilization of the laser diode, combine a first pump beam and a first signal beam, and combine a second pump beam and a second signal beam with reduced alignment sensitivity and increased manufacturability. Figure 2H As shown, the pump laser 285 may include a first input fiber (e.g., input fiber 205-1), a second input fiber 205 (e.g., input fiber 205-2), a first output fiber 210 (e.g., output fiber 210-1), a second output fiber 210 (e.g., output fiber 210-2), a source (e.g., a chip having two emission points capable of emitting two pump beams, two DFB diodes 215, two FP diodes 230, or the like), a combiner 220, a lens 225-1, a lens 225-2, and a lens 225-3. Figure 2H In the exemplary embodiment shown, arrows represent the center lines of the respective light beams.

[0063] Input fibers 205-1 and 205-2, output fibers 210-1 and 210-2, combiner 220, lens 225-1, lens 225-2, and lens 225-3 may be arranged and / or operate in a similar manner as described above.

[0064] During operation, input fiber 205-1 transmits a first signal light (e.g., a first 1550 nm signal light beam) along a first optical path from the face of input fiber 205-1 to combiner 220 (e.g., via lens 225-1), and DFB diode 215 transmits a first pump light (e.g., a first 980 nm light beam) along a second optical path from the face of DFB diode 215 to combiner 220 (e.g., via lenses 225-2 and 225-3). Combiner 220 reflects the first signal light received on the first optical path to a third optical path (e.g., from combiner 220, via lens 225-1, to the face of output fiber 210-1), while simultaneously transmitting the first pump light received on the second optical path to the third optical path. Here, by transmitting the first signal light and the first pump light to the third optical path, combiner 220 causes the first signal light and the first pump light to combine at the face of output fiber 210-1 (i.e., forming a first signal light + pump light). The output fiber 210 - 1 then outputs the first signal+pump light.

[0065] Similarly, input fiber 205-2 transmits a second signal light (e.g., a second 1550 nm signal light beam) along a fourth optical path from the face of input fiber 205-2 to combiner 220 (e.g., via lens 225-1), and DFB diode 215 transmits a second pump light (e.g., a second 980 nm light beam) along a fifth optical path from the face of DFB diode 215 to combiner 220 (e.g., via lenses 225-2 and 225-3). Combiner 220 reflects the second signal light received on the fourth optical path to a sixth optical path (e.g., from combiner 220, via lens 225-1, to the face of output fiber 210-2), while simultaneously transmitting the second pump light received on the fifth optical path to the sixth optical path. Here, by transmitting the second signal light and the second pump light along the sixth optical path, combiner 220 causes the second signal light and the second pump light to combine at the face of output fiber 210-2 (i.e., forming a second signal light + pump light). The output fiber 210-2 then outputs the second signal + pump light. Figure 2H The pump laser 285 may include a different number of pairs of input fibers 205 and output fibers 210 (eg, three or more pairs of input fibers 205 and output fibers 210) than shown in FIG.

[0066] like Figure 2HAs shown, lenses 225-1, 225-2, 225-3, and / or combiner 220 do not need to be replicated to increase the number of managed fiber pairs (e.g., two fiber pairs are managed in pump laser 285). However, in some embodiments, the size of lenses 225-1, 225-2, 225-3, and / or combiner 220 may need to be increased based, at least in part, on the arrangement and / or number of fiber pairs. Additionally, the source (e.g., a chip with two emission points) should be scaled to provide a sufficient number of source light emission points (one for each fiber pair). In some embodiments, by utilizing a free-space optical system using the same pump laser 285, multiple fiber pairs and optical paths can each share the same virtual image plane 227 and / or weld plane.

[0067] Figures 2A-2H The number and arrangement of the elements shown in FIG are provided as examples. Figures 2A-2H The pump lasers 250-285 may include additional elements, fewer elements, different elements, elements of different form, elements of different design, or elements of different arrangement than those shown. For example, embodiments comprising two or more laser diodes are possible (e.g., where each laser diode emits one or more pump beams in combination with one or more corresponding signal beams, as described above with respect to FIG. Figure 2H Additionally, or alternatively, one set of elements (eg, one or more elements) of the pump lasers 250-285 may perform one or more functions as described for performance by another set of elements of the pump lasers 250-285.

[0068] Embodiments described herein provide a pump laser that includes a combiner and three lenses in free space within a package, providing a signal and pump beam as a combined optical signal. Advantages of the embodiments described herein may include reducing the physical space used by an optical amplifier system, reducing the number of optical fibers in the optical amplifier system, reducing the number of fiber connections required for the optical amplifier system, reducing the size of the optical components of the optical amplifier system, simplifying the configuration and / or construction of the optical amplifier system, and / or reducing the cost of implementing the optical amplifier system (e.g., compared to existing optical amplifier systems that include discrete components).

[0069] Further advantages of the embodiments described herein may include reducing the alignment sensitivity of the optical amplifier system, such that the optical amplifier system has reduced sensitivity associated with only three degrees of freedom (e.g., the x-direction, the y-direction, and the z-direction), thereby increasing the manufacturability of the optical amplifier system and / or reducing the cost of the optical amplifier system (e.g., compared to existing optical amplifier systems that include discrete components between the laser diode and the combiner).

[0070] The foregoing disclosure provides illustration and description and is not intended to exclude or limit the embodiments to the precise form disclosed. Modifications and variations based on the above disclosure or obtained from practice of the embodiments are possible. For example, while the pump lasers 250-285 are described and illustrated as including input fiber 205 and output fiber 210 disposed about a first side of the combiner 220 and a source (e.g., DFB diode 215, FP diode 230, or the like) disposed about a second (opposite) side of the combiner 220, other arrangements are possible. As a specific example, in some embodiments, the input fiber 205 may be disposed about a first side of the combiner 220, and the source and output fiber 210 may be disposed about a second side of the combiner 220. In this case, the combiner 220 may be configured to receive signal light on a first optical path and send (e.g., transmit) the signal light on a third optical path, and to receive pump light on a second optical path and send (e.g., reflect) the pump light on a third optical path.

[0071] Even though particular combinations of features are recited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of possible embodiments. In fact, many of these features can be combined in ways not explicitly recited in the claims and / or disclosed in the specification. Even though each dependent claim listed below is directly dependent on only one claim, the disclosure of possible embodiments includes each dependent claim in combination with every other claim in the claim group.

[0072] The elements, behaviors, or teachings used herein cannot be interpreted as critical or essential unless explicitly described as such. Likewise, as used herein, the article "a" is meant to include one or more items and can be used interchangeably with "one or more". In addition, as used herein, the term "group" is meant to include one or more items (e.g., related items, unrelated items, a combination of related items and unrelated items, etc.), and can be used interchangeably with "one or more". Where only one item is intended, the term "one" or similar language is used. Likewise, as used herein, the term "having" or the like means an open term. In addition, the phrase "based on" is meant to represent "at least in part based on", unless otherwise explicitly stated.

Claims

1. A pump laser package, comprising: an input optical fiber for transmitting signal light on a first optical path in free space within the package, wherein a first lens is disposed on the first optical path, wherein the first lens has a substantially uniform refractive index within a material of the first lens; a source of pump light transmitted on a second optical path in free space within the package, wherein a second lens and a third lens are arranged on the second optical path, wherein the third lens is a negative lens, wherein the second lens and the third lens are separated by the free space within the package, wherein the second lens is arranged to converge the pump light on a first portion of the second optical path from the second lens to the third lens, wherein the third lens is arranged to collimate the pump light such that the pump light is collimated on a second portion of the second optical path from the third lens to a wavelength division multiplexing (WDM) filter, and wherein the first lens and the third lens are arranged to form a virtual image associated with the pump light at a virtual image plane in the free space within the package; an output optical fiber on a third optical path in the free space within the package, wherein the first lens is arranged on the third optical path; as well as The wavelength division multiplexing filter in the free space within the package receives the signal light on the first optical path and sends the signal light on the third optical path, receives the pump light on the second optical path and sends the pump light on the third optical path, and wherein the wavelength division multiplexing filter is arranged between the first lens and the third lens. 2 . The pump laser package of claim 1 , wherein the virtual image plane is located between the output optical fiber and the wavelength division multiplexing filter on the optical axis of the pump laser package. 3 . The pump laser package of claim 1 , wherein welding points associated with manufacturing or assembling the pump laser package are positioned at the virtual image plane.

4. The pump laser package of claim 1, wherein the source comprises a distributed feedback diode.

5. The pump laser package of claim 1, wherein the source comprises a Fabry-Perot (FB) diode, and wherein the output fiber comprises a fiber Bragg grating to stabilize the wavelength of the pump light transmitted by the FB diode.

6. The pump laser package of claim 1 , wherein the source is a Fabry-Perot (FB) diode, and wherein the pump laser package further comprises a reflective narrowband device to reflect a portion of the pump light in free space within the package to the Fabry-Perot diode. 7 . The pump laser package of claim 6 , wherein the reflective narrowband device comprises a coating on a surface of the output optical fiber, the wavelength division multiplexing filter, the first lens, the second lens, or the third lens. 8 . The pump laser package of claim 6 , wherein the reflective narrowband device comprises a volume holographic grating, a volume Bragg grating, a reflective narrowband filter, or a bandpass filter with partial reflection.

9. The pump laser package of claim 6, wherein the reflective narrowband device is a discrete component disposed in free space within the package.

10. The pump laser package of claim 6, wherein the reflective narrowband device and the wavelength division multiplexing filter are integrated into a single component.

11. The pump laser package of claim 1 , wherein at least one of the following is true: The source transmitting the pump light is oriented in a plane to reduce feedback received at the source; The input optical fiber transmitting the signal light is oriented in a manner to reduce feedback received at the input optical fiber or the source; or The output fiber receiving the signal light and the pump light is oriented in a manner to reduce feedback received at the output fiber or the source.

12. The pump laser package of claim 1, wherein the first optical path and the second optical path are substantially separate regions of free space within the package. 13 . The pump laser package of claim 1 , wherein a wavelength of the signal light is approximately equal to 1550 nanometers, and a wavelength of the pump light is approximately equal to 980 nanometers.

14. The pump laser package of claim 1 , wherein the wavelength division multiplexing filter is arranged to receive the signal light at a first side of the wavelength division multiplexing filter and to receive the pump light at a second side of the wavelength division multiplexing filter, wherein the first side and the second side are opposite sides of the wavelength division multiplexing filter, and wherein the wavelength division multiplexing filter reflects the signal light received at the first side or partially reflects the pump light received at the second side.

15. The pump laser package of claim 1, wherein the package forms part of an optical fiber pigtail to the source.

16. A fiber-coupled laser source, comprising: an input optical fiber for transmitting input light on a first optical path in free space within the package; a laser diode for transmitting source light on a second optical path in free space within the package; an output optical fiber on a third optical path in free space within the package; a first lens disposed on the first optical path and the third optical path, the first lens comprising a material having a substantially uniform refractive index; a second lens and a third lens arranged in the second optical path, the third lens being a negative lens, the second lens and the third lens being separated by a free space within the package, the second lens being arranged to converge the source light on a first portion of the second optical path from the second lens to the third lens, the third lens being arranged to collimate the source light so that the source light is collimated on a second portion of the second optical path from the third lens to the combiner, and the first lens and the third lens being arranged to form a virtual image associated with the source light at a virtual image plane in the free space within the package; as well as The combiner, which is arranged between the first lens and the second lens in a free space within the package, receives the input light on the first optical path and sends the input light on a third optical path, and receives the source light on the second optical path and sends the source light on the third optical path. 17 . The fiber-coupled laser source of claim 16 , wherein the virtual image plane is located between the output fiber and the combiner on the optical axis of the fiber-coupled laser source.

18. The fiber-coupled laser source of claim 16, wherein: A weld associated with the fabrication or assembly of the fiber-coupled laser source is located between the output fiber and the combiner.

19. The fiber-coupled laser source of claim 16, wherein the first optical path and the second optical path are substantially separate regions in free space within the package.

20. The fiber-coupled laser source of claim 16, wherein the input fiber is a first input fiber, the input light is a first input light, the source light is a first source light, the output fiber is a first output fiber, and the virtual image is a first virtual image, and The fiber-coupled laser source further comprises: a second input optical fiber that sends second input light on a fourth optical path in the free space within the package, the first lens being arranged on the fourth optical path; a source sending second source light on a fifth optical path in the free space within the package, the second lens and the third lens being arranged on the fifth optical path, and the first lens and the third lens being arranged to form a second virtual image associated with the second source light at the virtual image plane in the free space within the package; a second output optical fiber on a sixth optical path in the free space within the package, wherein the first lens is arranged on the sixth optical path; as well as The combiner receives the second input light on the fourth optical path and sends the second input light on the sixth optical path, and receives the second source light on the fifth optical path and sends the second source light on the sixth optical path.

21. A method comprising: sending signal light on a first optical path in free space within the package through an input optical fiber, a first lens disposed on the first optical path, the first lens having a substantially uniform refractive index within a material of the first lens; sending pump light along a second optical path in the free space within the package through a source, a second lens and a third lens being arranged on the second optical path, the second lens and the third lens being separated by the free space within the package, the second lens being arranged to converge the pump light on a first portion of the second optical path from the second lens to the third lens, the third lens being arranged to collimate the pump light so that the pump light is collimated on a second portion of the second optical path from the third lens to a wavelength division multiplexing (WDM) filter, the first lens and the third lens forming a virtual image associated with the pump light at a virtual image plane in the free space within the package, and the third lens being a negative lens; receiving the signal light on the first optical path through the wavelength division multiplexing filter arranged in the free space within the package, wherein the wavelength division multiplexing filter is arranged between the first lens and the second lens; receiving the pump light on the second optical path through the wavelength division multiplexing filter; The signal light is sent to the output optical fiber on the third optical path in the free space of the package through the wavelength division multiplexing filter, and the first lens is arranged on the third optical path; as well as The pump light is sent to the output optical fiber on the third optical path through the wavelength division multiplexing filter.

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