93 results about "Mode field diameter" patented technology

A hollow core fiber array unit includes hollow core fibers each having a terminal end and an adapter that includes grooves. Each groove receives the terminal end of one of the hollow core fibers. The terminal end of the hollow core fibers is spaced from an end face of the adapter. The hollow core fiber array unit includes a spot size converter coupled to the end face of the adapter. The spot size converter includes a plurality of waveguides that correspond to the hollow core fibers. Each waveguide extends from an input at an input end of the spot size converter that is coupled to the end face of the adapter to an output at an opposite output end of the spot size converter. The input of each waveguide includes a first mode field diameter that corresponds to the hollow core fibers and the output includes a second mode field diameter.

The invention relates to a small-outer-diameter hollow-core optical fiber with a mode field diameter matched with a conventional single-mode optical fiber and application, the small-outer-diameter hollow-core optical fiber comprises an outer cladding and an inner cladding, the inner cladding comprises three groups of anti-resonance structure units, an auxiliary inner cladding is arranged along the circumferential direction of the inner wall of the outer cladding, each anti-resonance structure unit comprises four or more than four layers of anti-resonance tubes with different radiuses, and the anti-resonance tubes are arranged in the outer cladding. Comprising an outer anti-resonance tube and multiple layers of inner anti-resonance tubes, the outer anti-resonance tube and the inner anti-resonance tubes adjacent to the outer anti-resonance tube are arc-shaped, and the rest of the inner anti-resonance tubes comprise arc-shaped anti-resonance tubes and / or circular anti-resonance tubes with different radiuses. When the optical fiber is welded or connected with a conventional single-mode solid-core optical fiber, an intermediate transition optical fiber or a switching device can be omitted, and low-loss and high-quality interconnection is realized. And meanwhile, the small fiber core has the unique macro-bending and micro-bending insensitive characteristic, so that the optical fiber can be allowed to adopt a smaller glass outer diameter and a smaller coating outer diameter, and the fiber accommodating capacity in a single optical cable is improved.

The utility model discloses an optical fiber patch cord comprising at least one transmission optical fiber, and each transmission optical fiber comprises a hollow-core optical fiber used for transmitting optical signals; the single-mode optical fiber is coupled with the hollow-core optical fiber, and the mode field diameter of the hollow-core optical fiber is larger than that of the single-mode optical fiber; the mode field adaptation structure is arranged between the hollow-core optical fiber and the single-mode optical fiber, so that the mode fields of the hollow-core optical fiber and the single-mode optical fiber are matched; and the at least one connector structure is connected with one end, far away from the hollow-core optical fiber, of the single-mode optical fiber of one or more transmission optical fibers in all the transmission optical fibers, and is used for connecting the optical fiber patch cord to external equipment so as to realize optical signal transmission between each transmission optical fiber and the external equipment. According to the scheme, the mode field of the hollow-core optical fiber and the mode field of the single-mode optical fiber of each transmission optical fiber in the optical fiber patch cord can be matched by means of the mode field adaptation structure, so that external equipment can carry out signal transmission which is small in loss, not prone to deformation and higher in transmission speed through the optical fiber patch cord.

Disclosed in the present invention are a conversion core member, a double-lens mode field conversion device and a manufacturing method therefor. The conversion core member comprises a solid-core optical fiber part, a hollow-core optical fiber part and a calibration sleeve, wherein the solid-core optical fiber part comprises a solid-core-end lens and a solid-core single-mode optical fiber having a first mode field diameter, and the solid-core end lens is located at the tail end of the solid-core optical fiber part; the hollow-core optical fiber part comprises a hollow-core-end lens and a hollow-core optical fiber having a second mode field diameter; the calibration sleeve has a hollow cavity I in the axial direction thereof; the solid-core optical fiber part and the hollow-core optical fiber part respectively extend into the cavity I of the calibration sleeve via two open ends of the cavity I; and the solid-core-end lens and the hollow-core-end lens are arranged opposite each other. In the device, the conversion of different mode field diameters between the single-mode optical fiber and the hollow-core optical fiber is implemented by means of two lenses, such that a reliable and stable connection between the single-mode optical fiber and the hollow-core optical fiber is achieved.

A multicore optical fiber may include a common cladding comprising a radius R4 defining a glass portion of the optical fiber and having a cladding relative refractive index Δ4. At least two waveguides may extend through the common cladding. Each waveguide may include a core region, an inner cladding region, and a depressed cladding region. Each core region may include a maximum relative refractive index Δ1max. Each inner cladding region may include a relative refractive index Δ2. Each depressed cladding region may include a minimum relative refractive index Δ3min and a trench volume from 20-45%µm2 such that Δ1max>Δ2>Δ3min, and Δ4>Δ3min. A cable cutoff wavelength of each waveguide is ≤1150 nm. The co-propagating and counter-propagating inter-waveguide cross talk between each waveguide and a nearest waveguide is <-35 dB at 1310 nm and <-20 dB at 1550 nm for application lengths of 20 m. A mode field diameter of each waveguide is 8.2-9.0 µm at 1310 nm.

The application belongs to the technical field of passive optical devices, and discloses a multi-core optical fiber multiplexer / demultiplexer and a preparation method thereof. In the application, a small outer diameter optical fiber is fused at one end of a single-mode optical fiber. The cladding diameter of the small outer diameter optical fiber is smaller than the cladding diameter of the single-mode optical fiber, and the cladding diameter of the small outer diameter optical fiber is equal to the core spacing of the multi-core optical fiber to be matched. The mode field diameter of the small outer diameter optical fiber is consistent with the mode field diameter of each core of the multi-core optical fiber. The small outer diameter optical fiber is used as a transition optical fiber between the single-mode optical fiber and the multi-core optical fiber, high-precision matching between the single-mode optical fiber and the multi-core optical fiber is achieved, the problems existing in the prior art preparation method can be avoided, and the application has the advantages of good scalability, simple preparation, high precision, and industrial mass production.

Architectures and methods for graded index (GRIN) lens expanded beam (EB) coupler for detachable fiber array unit (FAU) for use with a photonic integrated circuit (PIC). A system to optically couple a fiber optic array (FAU) to a PIC die includes a graded index (GRIN) lens to optically couple a single mode fiber (SMF) in the FAU to a waveguide in the PIC die. The GRIN lens has a first mode field diameter (MFD) that is a function of a spot size converter of the waveguide. The SMF is a conduit for optical light with a wavelength and a second MFD. The GRIN lens has a length that is a function of a predetermined whole number of periodic cycles of the wavelength.

A polarization maintaining optical fiber (1) has: a core (11); an inner layer (12) that surrounds the core (11) without a gap; a pair of stress applying portions (13) disposed at positions sandwiching the core (11); and a cladding (14) that encloses the inner layer (12) and the pair of stress applying portions (13), a mode field diameter of light of a wavelength of 1.55 μm is 9.3 μm or less in a case where the light propagates in the core (11), a cutoff wavelength is 1.32 μm or more in a case where the optical fiber length is 0.25 m and the stress applying portions (13) are wound one turn around an axis having a radius of 2 mm in a manner that a slow axis of the stress applying portions (13) is perpendicular to a surface of the axis, and a product of an area of a cross section of the inner layer (12) perpendicular to a length direction and an average of relative refractive index differences of the inner layer (12) as a whole with respect to the cladding (14) is -36% μm 2 or more and 0% μm 2 or less.

The application belongs to the technical field of passive optical devices, and discloses a multiplexer / demultiplexer suitable for a multi-core optical fiber and a preparation method thereof. In the application, a small outer diameter optical fiber is fused at one end of a single-mode optical fiber. The cladding diameter of the small outer diameter optical fiber is smaller than the cladding diameter of the single-mode optical fiber, and the cladding diameter of the small outer diameter optical fiber is equal to the core spacing of the multi-core optical fiber to be matched. The mode field diameter of the small outer diameter optical fiber is consistent with the mode field diameter of each core of the multi-core optical fiber. The small outer diameter optical fiber is used as a transition optical fiber between the single-mode optical fiber and the multi-core optical fiber, high-precision matching between the single-mode optical fiber and the multi-core optical fiber is realized, the problems existing in the prior art preparation method can be avoided, and the application has the advantages of good scalability, simple preparation, high precision, and industrialized mass production.

To provide a mode field diameter measuring device and a mode field diameter measuring method with which it is possible to accurately measure the mode field diameter of a discretionary waveguide mode.SOLUTION: A mode field diameter measuring device 100 pertaining to the present invention measures the mode field diameter of each waveguide mode of a few-mode fiber 10 (optical fiber to be tested) by a VA method using a variable aperture (VA) 14. The mode field diameter measuring device is characterized by having an aligner that adjusts the alignment with the few-mode fiber using a fundamental mode or a waveguide mode where the light intensity at mode field center is maximum, before measuring the mode field diameter of each waveguide mode of the few-mode fiber.SELECTED DRAWING: Figure 2

The invention is suitable for the technical field of optical transmission, and provides an optical fiber connecting device and a manufacturing method and manufacturing equipment thereof, and the manufacturing method of the optical fiber connecting device comprises the steps: obtaining the fiber core diameters of a connecting optical fiber and an input optical fiber, the fiber core diameter of a transmission optical fiber, and propagation constants corresponding to a fundamental mode and a high-order mode of the connecting optical fiber; determining a target mode field diameter according to the fiber core diameter of the input fiber; determining a target fiber core radius according to the target mode field diameter; determining a coupling beat length according to propagation constants corresponding to the fundamental mode and the high-order mode respectively; determining the cone length according to the target fiber core radius, the coupling beat length and the fiber core diameter of the transmission fiber; and tapering and connecting the optical fiber according to the target fiber core radius and the taper length to obtain an optical fiber connecting device. According to the embodiment of the invention, the optical fiber connecting device can be matched with the mode field diameter of the input optical fiber, so that the excitation of a high-order mode is inhibited, the energy of light spots is more concentrated, and the quality of light beams is improved.

A photonic integrated circuit (PIC) includes one or more silicon nitride edge couplers directly formed on exposed portions of the buried oxide layer. Directly forming the SiN edge couplers on the highly-planar buried oxide layer provides structures with significantly reduced minimal dimension possibilities (as compared to SiN edge couplers within the PIC oxide stack), allowing for a beam emitted from the “SiN-on-box” coupler to exhibit a mode field diameter of larger size than associated with conventional SiN edge couplers positioned on dielectric over the silicon waveguide layer.

The invention provides a cladding mode efficient filtering method for microstructure optical fibers, and relates to the technical field of optical fibers, and the method comprises the steps: taking two microstructure optical fibers which are different in structure and have a diameter difference value of a fiber core fundamental mode field within a diameter difference value range, and carrying out the non-oblique-angle cutting of the end faces of the two microstructure optical fibers through a cutting knife; and aligning the axial directions of the two sections of cut micro-structure optical fibers, and splicing at the cutting end surface to obtain a spliced micro-structure optical fiber. The method has the beneficial effects that two sections of microstructure optical fibers with different structures but similar fiber core fundamental mode field diameters are selected, oblique-angle-free cutting is carried out, splicing (welding, butt joint or coupler coupling) is carried out at the cutting end face, and it is ensured that splicing points are axially coaxial but cladding waveguide structures have differences. At a continuous connection point, because the cladding microstructures (such as air hole arrangement, number, shape and the like) of the two sections of optical fibers are discontinuous, the continuity of the cladding waveguide is damaged. Therefore, cladding mode energy is efficiently filtered or scattered, and the strength of the cladding mode energy is greatly weakened.

A multi-core fiber coupler based on single-clad optical fibers (1), and a taper ratio design method therefor. Each single-clad optical fiber (1) comprises a fiber core (13), a cladding (12), and a coating layer (11), arranged in sequence from inside to outside. The multi-core fiber coupler based on single-clad optical fibers (1) comprises single-clad optical fibers (1) and a sleeve (2). Several single-clad optical fibers (1) are nested within the sleeve (2), and the total number of the single-clad optical fibers (1) is equal to the total number of fiber cores in a target multi-core optical fiber (3). One end of the sleeve (2) is tapered, and the other end is not tapered. A mode field diameter of each single-clad optical fiber (1) at the non-tapered end of the sleeve (2) matches a mode field diameter of a single fiber core of the target multi-core optical fiber (3). The single-clad optical fibers (1) and the multi-core fiber coupler have the advantages of low fabrication difficulty, low cost, and the capability of achieving low-loss connection with multi-core optical fibers and standard single-mode optical fibers.

Various exemplary embodiments relate to active optical fibers and devices using active optical fibers. An active optical fiber can include a central portion surrounded by a ring-shaped active core. The optical fiber can have a tapered longitudinal profile such that the optical fiber includes a single-mode portion and a multi-mode portion. The ring-shaped core can have a low birefringence, for example, obtained by rotating (fast-rotating) the optical fiber preform during the optical fiber manufacturing. The refractive index of the ring-shaped core can be higher than the refractive index of the central portion and the cladding(s) surrounding the ring-shaped core. The active optical fiber is capable of selectively generating or amplifying an optical mode field having orbital angular momentum (OAM). Furthermore, the optical fiber has a large mode field diameter (MFD) and is insensitive to internal heating or environmental influences.

A polarization-maintaining optical fiber (1) is provided with: a core (11); a pair of stress applying sections (12a, 12b) disposed at positions so as to sandwich the core (11); and a cladding (13) that encloses the core (11) and the pair of stress-applying sections (12a, 12b), the stress-applying sections (12a, 12b) having a torsion section (1A) in which the stress-applying sections (12a, 12b) are permanently spirally rotated around the core (11), the spiral torsion of the stress-applying sections (12a, 12b) per 47.1 mm in the torsion section (1A) being within one circle, and the polarization-maintaining optical fiber having a mode field diameter of 9.2 [mu] m or less at a wavelength of 1.31 [mu] m and a mode field diameter of 9.2 [mu] m or less at a wavelength of 47.1 [mu] m. When the optical fiber length is 2 m and the bending radius is 140 mm, the cutoff wavelength of the polarization-maintaining optical fiber is 1.15 [mu] m or more and less than 1.31 [mu] m.

The application discloses an optical fiber device, a preparation method of the optical fiber device and a coupling device, and belongs to the technical field of micro-nano photonics. The application sequentially arranges a mode field expansion area and a phase modulation area at an exit end of an optical fiber, uses the mode field expansion area to expand a beam mode field diameter, uses a substrate film matched with the mode field expansion area in refractive index and a micro-nano unit with high refractive index to form the phase modulation area, realizes a target phase distribution based on geometric sizes and / or a rotation angle of the micro-nano unit, and then performs phase modulation and wavefront shaping on the expanded beam, so as to output a target light field such as a focused beam, a collimated beam, a Bessel beam or a Bessel beam array. The optical fiber device can realize high coupling efficiency, high alignment tolerance and multi-functional wavefront regulation at the exit end of the optical fiber, can solve the mode field mismatch problem in optical fiber-chip coupling, can reduce system complexity and realize multi-functional integration.

An object of the present invention is to achieve a low delay core applicable to a Master channel of a Master-Slave CPE (MS-CPE) transmission method with a general-purpose refractive index distribution structure.An optical fiber according to the present invention is a single-mode optical fiber, and has an SI-type refractive index distribution structure, in which a clad region relative refractive index difference Δ (%) with respect to a core region refractive index, a radius a (μm) of the core region, and a group delay time difference Δτ between the Master channel and the Slave channel satisfy “Mathematical Expression 19” and “Mathematical Expression 20”, orhas a W-type refractive index distribution structure, in which a mode field diameter MFD is 9.5 to 10.1 μm, and a relative refractive index difference Δ1 (%) of a low refractive index layer with respect to a core, a relative refractive index difference Δ2 (%) of the clad region with respect to the core, the core radius a1, and the group delay time difference Δτ between the Master channel and the Slave channel satisfy “Mathematical Expression 41”.

A photonic crystal fiber (10) comprises: a core region (11) having a rare earth element added thereto; and a cladding region (12) including a plurality of refractive index reduction parts (13) provided around the core region (11). Each of the refractive index reduction parts (13) is formed of a glass rod having a refractive index lower than that of the cladding region (11) or a hole. The mode field diameter of the basic mode at a wavelength of 1.55 µm is not less than 16.4 µm.

The invention provides an optical receiving device and an optical transmission module, and relates to the technical field of optical fiber communication. The optical receiving device comprises an optical port upper piece and a coaxial packaging receiving piece. The optical port upper piece comprises a shell and an optical fiber bare fiber arranged in the shell. The optical fiber bare fiber comprises a first end and a second end which are oppositely arranged. The mode field diameter of the first end is larger than that of the second end. The second end is connected with an external optical fiber. The coaxial packaging receiving piece comprises a tube base and a photoelectric detector arranged on the tube base. The first end face of the optical fiber bare fiber faces the photoelectric detector and is in optical coupling connection with the photoelectric detector. And the tube seat is fixedly connected with the shell. The optical receiving device is suitable for a photoelectric detector with a small photosensitive surface, the responsivity of the photoelectric detector is not sacrificed while the high bandwidth is met, the coupling efficiency is improved, and the photoelectric performance of a coaxial packaging receiving piece in a high-speed scene is ensured.

An optical fiber (10) comprises a glass fiber (13) including a core (11) and a cladding (12). The cladding (12) includes an inner cladding (121) covering an outer circumference of the core (11), a trench (122) covering an outer circumference of an inner cladding (121), and an outer cladding (123) covering an outer circumference of the trench (122). The absolute value of the inclination of an interface region between the core (11) and the inner cladding (121) is 0.15 % / µm to 2.00 % / µm. The absolute value of the inclination of an interface region between the inner cladding (121) and the trench (122) is 0.15 % / μm to 2.00 % / μm. The mode field diameter with respect to light having a wavelength of 1310 nm is 8.8 μm to 9.6 μm.

The invention discloses a PC type MPO convex lens coupling assembly. According to the coupling assembly, when the two MPO movable connectors are coupled together, light beams in the multiple optical fibers in the two MPO movable connectors are focused through the convex lens in the coupling assembly, so that the mode field diameter in optical fiber transmission is reduced, the multiple optical fibers of the two MPOs are more easily in butt joint, and the coupling loss is reduced to the minimum. Meanwhile, in a link, if the MPO coupler is provided with the assembly, management and operation of the MPO movable connector can be simplified, one connector does not need to be changed to be provided with a pin, and the risk that the MPO movable connector is damaged in the guide pin installation process is avoided.

The invention discloses a hollow-core optical fiber mode field diameter measuring unit and system. The hollow-core optical fiber mode field diameter measuring unit comprises a displacement table, a hollow rotating mechanism, a first swing arm, a rotating motor, a second swing arm and a detection mechanism. The hollow rotating mechanism is fixed on the displacement table; the displacement table is used for changing the spatial position of the hollow rotating mechanism; the hollow rotating mechanism is of a hollow annular structure, an annular rotating part is arranged on the outer side of the hollow rotating mechanism, one end of the first swing arm is connected with the annular rotating part, the other end of the first swing arm is connected with the rotating motor, the rotating end of the rotating motor is connected with the second swing arm, and the end of the second swing arm is connected with the detection mechanism. During measurement, the measured end part of the hollow-core optical fiber is arranged at the center of the hollow rotating mechanism, the hollow rotating mechanism controls the first swing arm to do circular motion around the end part of the hollow-core optical fiber, the rotating motor controls the second swing arm to do circular motion around the rotating end, and the detection mechanism forms a composite scanning track under the common driving of the hollow rotating mechanism and the rotating motor.

Embodiments of current disclosure include a multicore optical fiber including a radius RCC ranging from 126 μm to 180 μm, and core elements disposed within the common cladding. The common cladding may include an inner common cladding region, and an outer common cladding region surrounding the inner common cladding region and doped with TiO2. At least one core element may include a core region, a dedicated inner cladding region surrounding the core region, and a dedicated outer cladding region surrounding the dedicated inner cladding region. A mode field diameter at 1310 nm of the at least one core element may be greater than or equal to 8.6 μm. The at least one core element may be separated from a nearest-neighbor core element by a minimum separation distance DNN greater than or equal to 35 μm and less than or equal to 43 μm.

This invention relates to a single-mode optical fiber supporting fiber-to-chip interconnect applications, comprising a core layer and a cladding layer, wherein the core layer R1 has a radius of 4.2–6.2 μm, and Δ n The cladding thickness ranges from 0.25% to 0.4%, and from the inside out, it consists of an inner cladding, a first planarization layer, a first depressed cladding, a second planarization layer, a second depressed cladding, and an outer cladding. The radius of the inner cladding, R2, is 5.6–9 μm, and Δn2 decreases linearly. The radius of the first planarization layer, R3, is 8.1–9.2 μm, and Δn2 decreases linearly. n 3 is -0.05% to 0.05%, the radius of the first indented blanket R4 is 18.8 to 28.4 μm, Δ n 4 is -0.95% to -0.55%, the radius R5 of the second flattening layer is 24.2 to 29.2 μm, Δ n 5 is -0.05% to 0.05%, the radius of the second indented blanket R6 is 35 to 50 μm, Δ n The 6-value is -0.50% to -0.75%, and the outer cladding layer is a pure silica glass layer. This invention has a low cutoff wavelength, a large mode field diameter, and good bending performance in short-distance applications.

A waveguide structure (400), a silicon optical chip, a detection apparatus (1500), and a terminal device, used for reducing transmission loss caused by a TPA effect in waveguides under high optical power. The waveguide structure (400) comprises an edge coupler (EC) (4111), a first waveguide (4112), and a second waveguide (4113); the first waveguide (4112) is connected to a first output end of the EC (4111); the second waveguide (4113) is connected to a second output end of the EC (4111); an input end of the EC (4111) has a first mode field diameter; the first waveguide (4112) and the second waveguide (4113) each have a second mode field diameter; and the first mode field diameter is greater than the second mode field diameter. An input of the EC (4111) is a large mode field diameter, and outputs of the EC (4111) are two small mode field diameters. The EC (4111) can directly split an input optical signal into two waveguides, so that the optical power in each waveguide is reduced, high optical power density is not prone to occurring in each waveguide, and thus a TPA effect is not prone to occurring, thereby solving the problem of large transmission loss caused by the TPA effect in waveguides under high optical power density.

This multicore optical fiber (1) is provided with a glass fiber (2). The glass fiber (2) comprises a plurality of cores (10) that extends along the central axis of the glass fiber (2), and a first cladding (20) that surrounds the plurality of cores (10). The plurality of cores (10) includes a first core (11) and a second core (12) that are closest to each other. When the effective refractive index of the first core (11) and the effective refractive index of the second core (12) at at least one wavelength in the range of 1260-1625 nm are denoted by n1 and n2, respectively, 250 × 10- 6 ≤ n1 - n2 ≤ 950 × 10- 6 holds, and when the mode field diameter of the first core (11) and the mode field diameter of the second core (12) at the wavelength are denoted by d1 [μm] and d2 [μm], respectively, d1 - d2 ≤ - 0.1 [μm] holds.

An apparatus includes a first photonic crystal fiber. The first photonic crystal fiber includes a first dispersion at a pump wavelength. The first photonic crystal fiber includes a zero dispersion. The pump wavelength is within 100 nm of the zero dispersion. The first dispersion is normal. The first photonic crystal fiber includes a first mode field diameter at the pump wavelength. The apparatus also includes a second photonic crystal fiber coupled to the first photonic crystal fiber and outputs a broadband spectrum. The second photonic crystal fiber includes a second dispersion at the pump wavelength. The second dispersion is anomalous. The second dispersion is negative, and the first dispersion is positive. The second photonic crystal fiber includes a second mode field diameter at the pump wavelength. The second mode field diameter is smaller than the first mode field diameter.

The mode field diameter of each of the plurality of second optical fiber cores (73) at the third end surface (14b) is smaller than the mode field diameter of the first optical fiber core (71) corresponding to the second optical fiber core (73) among the mode field diameters of the plurality of first optical fiber cores (71) at the first end surface (12a). The core pitch of the plurality of third fiber cores (81) at the fourth end surface (22a) is larger than the core pitch of the plurality of second fiber cores (73) at the third end surface (14b). The first lens (42) and the second lens (52) are arranged in this order between the third end surface (14b) and the fourth end surface (22a) from the third end surface (14b) toward the fourth end surface (22a). The arrangement shape of the plurality of second fiber cores (73) on the third end surface (14b) and the arrangement shape of the plurality of third fiber cores (81) on the fourth end surface (22a) are similar to each other.

According to some embodiments disclosed herein, an optical device includes an optical source, a mode field adapter, and an optical output fiber. The optical source is configured to provide source light having a first mode field diameter at a wavelength of the source light. The mode field adapter includes a coreless optical fiber and a graded index optical fiber optically coupled in series with the optical source. The mode field adapter is configured to receive the source light and to provide output light having a second mode field diameter at the wavelength of the source light, and the first and second mode field diameters are different. The optical output fiber has the second mode field diameter at the wavelength. The mode field adapter is optically coupled between the optical source and the optical output fiber. The optical output fiber and the mode field adapter are joined by a splice.