BACKGROUND

1. Technical Field

The present application relates to a method to assemble a transmitter optical sub-assembly (hereafter denoted as TOSA), in particular, the application relates to a TOSA having a function of the wavelength division multiplexing (hereafter denoted as WDM).

2. Prior Arts

Various TOSAs implemented with the WON function have been disclosed. For instance, a United States Patent, U.S. Pat. No. 8,036,533B, has disclosed a TOSA with optical sources, arrayed lenses, and an optical multiplexer where they are enclosed within a package. Optical beams coming from respective optical sources are collimated by arrayed lenses, enter the optical multiplexer by an inclined angle, iterate internal reflection within the optical multiplexer as being multiplexed with other optical beams, and are output as a single multiplexed beam. The inclined angle of the optical multiplexer and the thickness thereof determine the axes of the optical beams.

A Japanese Patent Application laid open No. H01-101511A has disclosed an optical system for multiplexing optical beams each output from a laser diode (hereafter dentoed as LD) and collimated by a collimating lens. The collimated beams enter a concentrating lens but at points different from others. The concentrating lens concetrates thus entered collimated beams on a point.

As a volume of information to be transmitted drastically increases, a new type of an optical transceiver widely called as Centum Form factor Pluggable (hereafter denoted as CFP) has been developed. However, there is no end to request further increase of the transmission capacity by limited power consumption. An optical transceiver with smaller sized and reduced power consumption compared with CFP is eagerly requested in the field. Such an optical transceiver generally needs an enhanced coupling efficiency between an external optical fiber and an optical signal source. The optical systems those disclosed in prior arts described above do not always satisfy the requests.

SUMMARY OF THE INVENTION

One embodiment of the present application relates to a method to assemble a transmitter optical module that includes steps of: preparing an intermediate assembly including a semiconductor laser diode (hereafter denoted as LD), a substrate for mounting the LD, and a housing for installing the substrate with the LD; extracting an optical beam output from the LD to an outside of the housing by using a supplementary jig to offset the optical beam; aligning a first lens, as monitoring the optical beam, in a position where the optical axis of the first lens coincides with that of the LD and the optical beam passing through the first lens becomes a collimated beam; and moving the first lens, as monitoring the optical beam passing through the first lens, in another position where the LD is positioned in a focal point of the first lens.

The supplementary jig may include two prisms each reflecting the optical beam output from the LD to offset the optical axis of the optical beam, the optical bean output from the supplementary jig being substantially in parallel to the optical axis of the optical beam output from the LD.

The step to align the first lens includes a step to monitor the optical beam output from the supplementary jig two-dimensionally. Specifically, the first lens may be aligned such that a position corresponding to the maximum intensity becomes the center of the two-dimensional image, and this two-dimensional image has a predetermined size.

The step to move the first lens includes a step to move the first lens so as to be apart from the LD by a predetermined length as keeping the maximum intensity to be in the center of the two-dimensional image.

The method may include, after moving the first lens, a step to fix the first lens by steps of: lifting the first lens from the substrate slightly, applying an adhesive resin on the substrate beneath the lifted first lens; landing the first lens on the substrate; and curing the adhesive resin by irradiating the resin with ultraviolet rays and/or heating the resin.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other purposes, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:

FIG. 1 is a plan view of a transmitter optical module according to one embodiment;

FIG. 2 is a side view of the transmitter optical module shown in FIG. 1;

FIG. 3 is a flow chart of a process to assembly the transmitter optical module shown in FIG. 1;

FIG. 4 schematically shows a process to assemble the first lens installed in the transmitter optical module;

FIG. 5 is a flow chart of the process to assemble the first lens;

FIG. 6 schematically shows an intensity profile of an optical bema detected in the arrangement shown in FIG. 4;

FIG. 7 schematically shows a process modified from those shown in FIG. 4;

FIG. 8 schematically shows a process subsequent to those shown in FIG. 4 to position the first lens;

FIG. 9 shows a flow chart of a process subsequent to those shown in FIG. 5, where the process assembles the second lens; and

FIG. 10 schematically shows a process to assemble the second lens.

DESCRIPTION OF EMBODIMENTS

Next, some embodiments will be described as referring to drawings. In the description of the drawings, numerals or symbols same or similar to each other will refer to elements same or similar to each other without duplicate explanations. Also, in the figures, symbols, P₁to P₇, denote reference planes each disposed in this order.

A transmitter optical module of an embodiment will be described as referring to FIGS. 1 and 2. The transmitter optical module 2 includes a driver 10, sub-mounts, 11a to 11d, semiconductor laser diodes (LDs), 12a to 12d, first lenses, 13a to 13d, a beam splitter 14, monitor photodiodes (mPDs), 15a to 15d, second lenses, 16a to 16d, and an optical multiplexer 17. The first lenses, 13a to 13d, are a type of concentrating lens; while, the second lenses, 16a to 16d, are a type of collimating lens. The transmitter optical module 2 further includes a substrate 1a, a housing 1b and an output port 18, where the substrate 1a mounts those electrical and optical elements described above; while, the housing 1b provides an output port 18 in one side thereof; and encloses those elements and the substrate 1a therein. The output port 18 provides a bore continuous from an opening provided in one side of the housing 1b. The bore of the output port 18 has a center substantially aligned with the center of the opening of the housing 1b.

The substrate 1a provides a surface 1a₁for mounting the electrical and optical components above described thereon. The LDs, 12a to 12d, which have a structure same with each other in the present embodiment, are disposed along the first reference plane P₁on the primary surface 1a₁of the substrate 1a through respective sub-mounts, 11a to 11d. The LDs, 12a to 12d, each emits an optical beam B₁with a specific wavelength different from others.

The first lenses, 13a to 13d, which have a configuration same with others, are arranged along the second reference place P₂on the primary surface 1a₁of the substrate 1a by adhesive resin J₁. The second reference place P₂is in parallel with the first reference plane P₁. Each of the first lenses, 13a to 13d, concentrates the optical beam B₁coming from respective LDs, 12a to 12d, on the fourth reference plane P₄that is also in parallel to the first and second reference planes, P₁and P₂. The beam splitter 14, which is set between the second and fourth reference planes, 2₂and P₄, divides the optical beams B₂output from the first lenses, 13a to 13d, into two parts, one of which B_2bheads for the second lenses, 16a to 16d, transmitting through the beam splitter 14; while, rest portions advance toward the mPDs, 15a to 15d, each mounted on the beam splitter 14. When the LDs, 12a to 12d, are set on the first reference plane P₁and the first lenses, 13a to 13d, are set on the second reference plane P₂, the optical beams B₂output from the first lenses, 13a to 13d, and partially reflected by the beam splitter 14 focus on the primary surface of respective mPDs, 15a to 15d, as the optical beams B_2a.

The mPDs, 15a to 15d, are disposed along the third reference plane P₃, but the beam splitter 14 in a lateral center thereof is offset from the third reference plane P₃, that is, referring to FIG. 2, the interface between two prisms of the beam splitter 14 has an angle smaller than 45Â° with respect to the primary surface 1a₁of the substrate 1a. Thus, the optical beams B_2aenter respective mPDs, 15a to 15d, by an inclined angle deviating from the normal of the mPDs, 15a to 15d. This optical arrangement of the mPDs, 15a to 15d, and the beam splitter 14 prevents light reflected at the surface of the mPDs, 15a to 15d, from returning to the LDs, 12a to 12d, and entering therein. Re-entered light in an LD causes optical noises in the LD. In the present embodiment, the mPDs, 15a to 15d, each has a structure same with others, and may have the type of, what is called, the top illumination or the back illumination.

The second lenses, 16a to 16d, are the type of the collimating lens. The second lenses, 16a to 16d, are positioned along the fifth reference plane P₅on the primary surface 1a₁of the substrate la also by adhesive resin J₂. The fifth reference plane P₅is in parallel to the first to fourth reference planes, P₁to P₄. The second lenses, 16a to 16d, each converts the optical beam B_2boutput from the beam splitter 14 and focused on the fourth reference plane P₄into collimated beams B₃.

The optical multiplexer 17 multiplexes the optical beams B₃each output from respective second lenses, 16a to 16d, depending on wavelengths thereof and outputs a single optical beam 3₄toward the output port 18. The single optical beam B₄is a collimated optical beam and contains four wavelengths. The third lens 19 put outside of the housing 1b concentrates the optical beam B₄output from the optical multiplexer 17 and passing the output port 17 on an end of an external optical fiber 20.

Next, a process to assemble the transmitter optical module 2 will be described as referring to FIGS. 3 to 10. The description concentrates on a process to assemble one of first lenses 13a and one of second lenses 16a; but a technique substantially same with those described will be applicable to other of the first lenses, 13b to 13d, and other of the second lenses, 16b to 16d.

Referring to FIG. 3, the process first prepares at step S₁an intermediate assembly 1 that includes the substrate 1a, the LDs, 12a to 12d, the beam splitter 14, the mPDs, 15a to 15d, and the optical multiplexer 17, where the latter four components, 12a to 17, are precisely set in respective positions on the substrate 1a, and the substrate 1a thus assembling the components, 12a to 17, is set on the designed position within the housing 1b in advance. The intermediate assembly 1 thus processed is set on a laterally movable stage 26 as illustrated in FIG. 4.

The first lens 13a is assembled with the intermediate assembly 1 in subsequent steps, S₂to S₁₀. Specifically, at step S₂, a supplementary jig 21 is set between the LD 12a and the beam splitter 14, or between the beam splitter 14 and the optical multiplexer 17. The supplementary jig 21 assembles two prisms, 21a and 21b, with a parallelepiped body 21c, where each of the oblique edge of the prisms, 21a and 21b, faces the other as a reflecting mirror. The optical beam B₁output from the LD 12a and passing through the first lens 13a is able to be extracted from the housing lb as the optical beam B₇by the duplicate reflection at respective interfaces, 21a and 21b, of the supplementary jig 21.

Step S₃of the process temporarily adjusts the position of the first lens 13a set between the supplementary jig 21 and the first LD 21a by using the lens holder 25a supported by the positioner 25. The lens holder 25a is a type of, for instance, the vacuum collet generally used in a semiconductor process, and/or the mechanical chuck. The positioner 25, or the lens holder 25a, moves the first lens 13a in up and down directions, and sometimes rotatively moves the first lens 13a around the axis of the lens holder 25a. At step S₄, the LD 12a is practically activated to emit the optical beam B₁.

At step S₅, the first lens 12a is practically aligned on the seventh reference plane P₇as observing an image of the optical beam B₇output from the supplementary jig 21 and detected by the image detector 22. When the relative distance between the first LD 12a, exactly, the front facet thereof, and the first lens 13a becomes the focal length of the first lens 13a, the optical beam B₁output from the LD 12a is converted into a collimated or a parallel beam B₆, which is never focused on a point. The position of the first lens 13a where the optical beam B₆becomes the parallel beam is assumed to be the seventh reference plane P₇.

Step S₅is further specifically described as referring to FIGS. 4 to 6. Step S₅includes two sub-steps, S_5aand S_5b, indicated in FIG. 5. The controller 24, cooperating with the image analyzer 23 and the positioner 25, adjusts the position of the first lens 13a through the positioner 25 such that, as detecting the intensity of the image two-dimensionally by the image detector 23, the maximum K₁becomes the center of the monitor of the image detector 23 as keeping the axial symmetry of the image. The peak position K₁of the intensity of the optical beam B₇is calculated by the image analyzer 23. When the position of the first lens 13a in the optical axis thereof deviates from the axis of the LD 12a, the image is deformed from the axial symmetry.

At step S_5b, the controller 24 further adjusts the position of the first lens 13a through the positioner 25 such that the diameter L₁of the image of the optical beam B₇becomes minimum, which substantially corresponds to a relative intensity of 1/e²with respect to the maximum intensity B. Although the intensity profile of the optical beam B₇strongly depends on the far field pattern of the LD 12a, the minimum diameter or the minimum profile maybe estimated. Thus, the image analyzer 23, based on the image of the optical beam B₇detected two-dimensionally by the image detector 22, may evaluate the maximum intensity of the image and the size thereof. The position of the first lens 13a thus decided is exactly aligned with the LD 12a and just on the seventh reference plane P₇.

The controller 24, co-operating with the image analyzer 25, controls the positioner 25 and the movable stage 26. For instance, the positioner 25 may move the first lens 13a in up and down directions, while, the movable stage 26 may move the LD 12a laterally. The image detector 22 is fixed in a relative position with respect to the positioner 25. That is, the image detector 22 is movable in connection with the positioner 25.

Although step S₅above described uses the image analyzer 23 and the controller 24; the positioning of the first lens 13a on the seventh reference plane P₇may be carried out without these devices. As illustrated in FIG. 7, the output of the image detector 22 is brought to the visual monitor 22a that indicates the profile of the optical beam B₇two-dimensionally by light and shade patterns. Accordingly, the positioner 25, namely the first lens 13a, and the movable stage 26, namely, the LD 12a, may be manually positioned such that the peak K₁and the size L₁of the light and shade pattern become respective designed conditions.

Step S₆further moves the first lens 13a from the position on the seventh reference plane P₇to the designed position on the second reference plane P₂apart by a distance L₂along the optical axis. Specifically, as monitoring the image profile of the optical beam B₇through the supplementary jig 21, the first lens 13a is gradually apart from the LD 12a. As the positioner 25 or the movable stage 26 increases a distance between the first lens 13a and the LD 12a, the image monitored by the image detector 22 becomes clear and sharp. However, the optical axis of the first lens 13a is kept aligned with that of the LD 12a by keeping the center of the image and the shape of the clearer image.

Steps S₇to S₁₀fix the first lens on the designed position on the second reference plane P₂. First, the positioner 25 or the movable stage 26 slightly lifts up the first lens 13a to form a gap against the substrate 1a. Then, an adhesive resin is applied on the surface 1a₁at step S₈. The adhesive resin is a type of ultraviolet curable resin and/or thermo-curable resin. At step S₉, the positioner 25 or the movable stage 26 loads the first lens 13a down to the substrate 1a. Finally, the adhesive resin applied at step S₈is cured by illuminating with ultraviolet rays or heating up to cure the adhesive resin to fix the first lens 13a rigidly and permanently on the second reference plane P₂on the substrate 1a at step S₁₀. Then, the second lens 16a will be positioned. The supplementary jig 21 is removed after the first lens 13a is fixed on the substrate 1a.

Because the first lens 13a is precisely aligned along the second reference plane P₂as described above, the mPD 15a may be also precisely positioned on the third reference plane P₃. When the first lens 13a is positioned on the second reference plane P₂, the focal point of the first lens 13a is set on the light receiving surface 15a₁of the mPD 15a even when the mPD 15a deviates from the designed position on the beam splitter 14. Specifically, even when the beam splitter 14 deviates the position thereof from the designed one, or the mPD 15a set on the beam splitter 14 deviates the position thereof from the designed position on the beam splitter 14, the mPD 15a may effectively detect the optical beam to find the focal point of the optical beam B_2aon the beam splitter 14.

Steps S₁₁to S₁₇align and fix the second lens 16a on the designed position of the intermediate assembly 1. Subsequent to step S₁₀, the lens holder 25a holds the second lens 16a and roughly sets it on the designed position thereof on the substrate 1a at step S₁₁. One of LDs 12a is practically activated at step S₁₂and the positioner 25 moves the second lens 16a on the fifth reference plane P₅as monitoring the optical beam B₈by the image detector 22 such that the two-dimensional image detected by the image detector 22 has the intensity maximum in the center thereof and the preset size, which is substantially same as those for aligning the first lens 13a on the seventh reference plane P₇. The position on the fifth reference plane P₅for the second lens 16a is a position at which the monitored intensity of the optical beam B₈becomes the maximum. The controller 24 manipulates the lens holder 25a through the positioner 25 based on the intensity profile detected by the image detector 22. The image detector 22 in the axis thereof deviates from the axis of the second lens 16a to be aligned by a preset offset because the optical multiplexer 17 shifts the optical axes of the optical beams input therein. Because the second lens 16a is the collimating lens while the lens 27a is the concentrating lens, the deviation of the second lens 16a from the designed position is reflected in the asymmetry of the image profile.

Subsequently, an auxiliary component with an optical fiber 27b assembled with a concentrating lens 27a is replaced from the image detector 22, and the optical output extracted from the optical fiber 27b is detected by the intensity monitor 28, as shown in FIG. 10. The auxiliary component is first aligned with the optical beam B₈output from the output port 18 of the housing lb such that the intensity concentrated by the lens 27a becomes the maximum. Concurrently with the alignment of the auxiliary component, the second lens 16a is further precisely aligned along the optical axis thereof to obtain the maximum intensity by the intensity monitor 28. The positions of the auxiliary component with respect to the optical multiplexer 17, or the output port 18 of the housing 1b, are memorized for the later use.

Then, the second lens 16a is fixed on the fifth reference plane P₅on the substrate la at steps S₁₄to S₁₇. Step S₁₄slightly lifts up the second lens 16a from the aligned position defined through steps S₁₁to S₁₃; then, an adhesive resin is applied on the substrate la; step S₁₆loads the second lens 16a down to the defined position; and step S₁₇cures the adhesive resin. The adhesive resin used for the second lens 16a may be same or similar to that used in the aforementioned steps for the first lens. Specifically, the adhesive resin is the type of the ultraviolet curable resin and/or the thermo-curable resin. Solidifying the former one may be carried out by irradiating with ultraviolet rays, while by heating for the latter one. Thus, the solidified resin J₂for fixing the second lens 16a is formed.

Steps S₁to S₁₀align other first lenses, 13b to 13d, with respective LDs, 12b to 12d, and steps S₁₁to S₁₇align and fix other second lenses, 16b to 16d. However, the steps to position the auxiliary component against the housing 1b are replaceable to the process to position the auxiliary component in the memorized positions. Thus, the first lenses, 13a to 13d, and the second lenses, 16a to 16d, are optically aligned with respective LDs, 12a to 12d.

While there has been illustrated and described what are presently considered to be example embodiments, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from the true scope of the invention. Additionally, many modifications maybe made to adapt a particular situation to the teachings of the present invention without departing from the central inventive concept described herein. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the appended claims.