Light-receiving package for flat-plate mounting, and optical module

A light-receiving package for flat-plate mounting which can make monitor reception sensitivity of an optical signal constant without increasing the size of a module. The light-receiving package for flat-plate mounting is provided with a first subassembly in which a photo diode is fixed to a front surface of a retaining holder, a back surface of the retaining holder is a flat surface capable of moving parallel on a plane parallel to a light-receiving surface of the photo diode and a second subassembly which has a rectangular U-shaped concave holder for retaining the retaining holder, and a flat-plate base disposed on a substrate and in which a surface of the flat-plate base that is mounted on the substrate is a flat surface capable of moving parallel to a substrate surface, the rectangular U-shaped concave holder and the flat-plate base are fixed, at least one of surfaces of the concave holder having a rectangular U-shape being a flat surface is a flat surface capable of moving parallel to the back surface of the retaining holder.

TECHNICAL FIELD

The present invention relates to a light-receiving package for flat-plate mounting, which is mounted with a monitor PD (PhotoDiode), and an optical module.

BACKGROUND ART

A conventional monitor PD102has a coaxial structure with a fiber, and, as shown inFIG. 6, an optical signal is tapped to an optical fiber103of an optical module101to connect the monitor PD102by fusion bonding and, thus, to monitor an output of the optical signal (for example, see Patent Literature 1).

FIG. 7shows a conventional example in which the monitor PD102is integrated in the optical module101(for example, see Patent Literature 2). In the prior art, the monitor PD102is in a form in which a PD bare chip is mounted on a carrier such as ceramic.

CITATION LIST

Patent Literature

Patent Literature 1: JP 1996-122582 A

Patent Literature 2: JP 2002-357743 A

SUMMARY OF INVENTION

Technical Problem

According to the conventional example of Patent Literature 1, since the monitor PD is connected to the middle of the optical fiber of the optical module, the entire module is increased in size, and it is difficult to arrange and store the optical fiber when a board is implemented.

According to the conventional example of Patent Literature 2, since the PD bare chip is exposed inside the optical module, not only a main optical signal but also a stray light component generated in the optical module are received, and thus it is difficult to stably monitor the optical signal. Further, since the monitor PD is implemented without adjustment, there is a problem that reception sensitivity varies depending on a lot and mounting accuracy.

Thus, an object of the present invention is to provide a light-receiving package for flat-plate mounting and an optical module which can make reception sensitivity constant without increasing the size of a module.

Solution to Problem

In order to achieve the above object, a light-receiving package for flat-plate mounting of the present invention is provided with a first subassembly which has a photo diode and a retaining holder and in which the photo diode is fixed to a front surface of the retaining holder, a back surface of the retaining holder is a flat surface capable of moving parallel on a plane parallel to a light-receiving surface of the photo diode and a second subassembly which has the rectangular U-shaped concave holder for retaining the retaining holder and a flat-plate base disposed on a substrate and in which a surface of the flat-plate base that is mounted on the substrate is a flat surface capable of moving parallel to a substrate surface, the rectangular U-shaped concave holder and the flat-plate base are fixed so that a cut-out side of the rectangular U-shaped concave holder faces above the substrate, and at least one of surfaces of the concave holder having a rectangular U-shape is a flat surface capable of moving parallel to the back surface of the retaining holder.

The second subassembly is provided with the flat-plate base, whereby the photo diode can be installed at a desired position on the substrate. The second subassembly is provided with the rectangular U-shaped concave holder, and the first subassembly is provided with the retaining holder, whereby the photo diode can be moved parallel on a surface parallel to the light-receiving surface of the photo diode, and the monitor PD can be fixed at a position where the reception sensitivity of the monitor PD is proper. According to this constitution, the reception sensitivity of the monitor PD can be made constant and stabilized. Accordingly, the light-receiving package for flat-plate mounting of the present invention can make the reception sensitivity constant without increasing the size of a module.

The optical module of the present invention is provided with a waveguide type optical element which is mounted on the substrate and guides light from an optical fiber and the light-receiving package for flat-plate mounting of the present invention which receives monitor light emitted from the waveguide type optical element after separation of a portion of light propagating through the waveguide type optical element.

Since the optical module of the present invention is provided with the light-receiving package for flat-plate mounting of the present invention, even if the monitor PD is disposed in the optical module, the reception sensitivity of the monitor PD can be made constant. Accordingly, the optical module of the present invention can make the reception sensitivity constant without increasing the size of a module.

In the optical module of the present invention, a light emitting window through which the monitor light emits is provided in an end surface of the waveguide type optical element that is connected to the optical fiber, a photo diode of the light-receiving package for flat-plate mounting is provided with a light entering window for the monitor light, and the light emitting window and the light entering window may be arranged to face each other.

In the optical module of the present invention, since the light emitting window is disposed in the end surface of the waveguide type optical element that is connected to the optical fiber, stray light entering the light entering window can be reduced. Consequently, the optical module of the present invention can monitor signal light accurately.

In the optical module of the present invention, the waveguide type optical element is connected to two optical fibers, the light emitting window emits monitor light from which a portion of light from one of the optical fibers is divided, and the light emitting window and the light entering window may pass the monitor light therethrough and shield stray light in the waveguide type optical element.

In the optical module of the present invention, when signal light and local light enter the waveguide type optical element, only the signal light as the monitor light can be extracted from the light emitting window. Since the light emitting window and the light entering window pass the monitor light therethrough and shield the stray light in the waveguide type optical element, only the monitor light from which the signal light is divided can be made enter the monitor PD. According to this constitution, the optical module of the present invention can monitor the signal light accurately.

Advantageous Effects of Invention

The present invention can provide a light-receiving package for flat-plate mounting and an optical module which can make reception sensitivity of a monitor PD constant and stabilize without increasing the size of a module.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described with reference to the accompanying drawings. The embodiment to be described hereinafter is an example of the invention, and the invention is not limited to the following embodiment. Components denoted by the same reference numerals in the present specification and the drawings mutually denote the same components.

An optical module according to the present embodiment is an integrated type receiving FE module corresponding to optical phase modulation accompanying a further increase in communication traffic, that is, a DQPSK transmission method or a DP-QPSK transmission method. A PLC optical demodulator circuit used in those transmission methods is called a delay line interferometer DLI or DPOH (Dual Polarization Optical Hybrid), converts a difference in phase state of an optical signal into a difference in light intensity, and is an optical module which receives and demodulates this by a PD capable of detecting only an intensity difference and integrates a high frequency amplifier which current/voltage converts an electrical signal demodulated by the PD to amplify the converted signal and, thus, to output the amplified signal as a high frequency electrical signal.

FIGS. 1 and 2show an example of the optical module according to the present embodiment.FIG. 1is a top view of the optical module according to the embodiment, andFIG. 2is a side view of the optical module according to the embodiment. The optical module according to the embodiment is provided with a substrate11, an optical semiconductor package12, a PLC optical demodulator circuit13as a waveguide type optical element, an optical lens14, a lens retaining holder17, and a light-receiving package for flat-plate mounting30. The optical semiconductor package12is provided with a receiver for demodulation, and the light-receiving package for flat-plate mounting30is provided with a monitor PD.

An optical signal transmitted from an optical fiber16enters the PLC optical demodulator circuit13. The PLC optical demodulator circuit13is mounted on the substrate11and guides light from the optical fiber16. In the PLC optical demodulator circuit13, a waveguide is divided (tapped), and the optical signal is divided into the optical signal travelling toward the receiver for demodulation and an optical signal travelling toward the monitor PD. The optical signal travelling toward the monitor PD is monitor light and is emitted through a light emitting window34disposed in an end surface connected to the optical fiber16. The light emitting window34as a PLC light-emitting end is obliquely cut for countermeasure against reflection, and an AR plate is mounted. According to this constitution, reflection as a noise component can be suppressed.

The optical signal for monitor PD reception, that is, monitor light is output through the light emitting window34disposed on the side of a fiber input portion33and enters the monitor PD in the light-receiving package for flat-plate mounting30through a light entering window53disposed to face the light emitting window34. The monitor PD in the light-receiving package for flat-plate mounting30receives the monitor light entering through the light entering window53, and optical sensitivity can be obtained. When the monitor PD is mounted on the side of the fiber input portion33, it is possible to suppress that the monitor PD receives scattered light generated in a PLC substrate.

FIGS. 3 and 4show an example of the light-receiving package for flat-plate mounting30.FIG. 3is a side view of the light-receiving package for flat-plate mounting30according to this embodiment, andFIG. 4is a back view of the light-receiving package for flat-plate mounting30according to the embodiment. The light-receiving package for flat-plate mounting30according to the embodiment is provided with a first subassembly31and a second subassembly32. The first subassembly31is provided with a photo diode41and a retaining holder42. The second subassembly32is provided with a rectangular U-shaped concave holder43and a flat-plate base44.

InFIG. 5, an example of a photo diode41is shown. The photo diode41includes a monitor PD51mounted on a small-sized CAN-PKG (package). The monitor PD51is mounted in the small-sized CAN-PKG, constituted of a flat-plate base54, a cap52, and the light entering window53, and sealed airtightly. Thus, even if the monitor PD51is mounted in an unsealed optical module, stabilized operation can be performed. The photo diode41can be aligned in the optical module, and stable reception sensitivity can be always obtained. An indirect component such as a lens can be mounted in the small-sized CAN-PKG. When the effective diameters of the light entering window53and a lens of the small-sized CAN-PKG are controlled, sufficient cross talk to stray light can be secured.

The light entering window53of the small-sized CAN-PKG in which the monitor PD51is mounted may be flat glass or lens. The light entering window53is a predetermined opening. This can suppress entering of stray light and entering of local light inside a module. Consequently, the reception sensitivity with a suppressed noise component can be obtained.

In a mounting structure, first, the photo diode41is fixed to the retaining holder42for alignment, and the first subassembly31is formed. The retaining holder42is preferably a metal material such as Fe—Ni—Co. In a fixing method, an adhesive, laser welding, or the like may be used.

Then, the rectangular U-shaped concave holder43is fixed at a predetermined position of the flat-plate base44, and the second subassembly32is formed. At this time, the rectangular U-shaped concave holder43and the flat-plate base44are fixed so that a cut-out side of the rectangular U-shaped concave holder43faces above the substrate11. The rectangular U-shaped concave holder43is fixed onto the flat-plate base44with an adhesive or the like. The rectangular U-shaped concave holder43is preferably a metal material such as Fe—Ni—Co. The flat-plate base44is preferably formed of alumina.

The second subassembly32is fixed at a predetermined position on the substrate11with an adhesive or the like, for the purpose of retaining the first subassembly31. The surface of the flat-plate base44that is mounted on the substrate11is a flat surface capable of moving parallel to the substrate surface and can be disposed at a predetermined position on the substrate11.

Then, in the optical module a back surface45of the retaining holder42that faces the light entering window53is brought into contact with a PLC-side flat surface46of the rectangular U-shaped concave holder43of the second subassembly32, and optical alignment is performed. Since the PLC-side flat surface46on which the back surface45of the retaining holder42is disposed on the PLC optical demodulator circuit13side of a surface of the rectangular U-shaped concave holder43having a U-shape is a flat surface, optical alignment in an x-y plane parallel to a light-receiving surface of the monitor PD51can be performed by rubbing the back surface45of the retaining holder42with the PLC-side flat surface46of the rectangular U-shaped concave holder43. The alignment is performed in this plane, spot welding using a YAG laser is performed at a position where predetermined reception sensitivity is obtained, and the retaining holder42and the rectangular U-shaped concave holder43are fixed, whereby the first subassembly31is fixed to the second subassembly32, and the light-receiving package for flat-plate mounting30is mounted on the substrate11. According to this constitution, the reception sensitivity of the monitor PD can be made constant.

Electrical connection is performed from a lead55, output from the small-type CAN-PKG mounted with the monitor PD51, to a ceramic terminal19inside the optical module by wire bonding.

The PLC optical demodulator circuit13may be connected to the two optical fibers16. For example, signal light enters the PLC optical demodulator circuit13through one of the optical fibers16, and local light enters the PLC optical demodulator circuit13through the other optical fiber16. In this case, the PLC optical demodulator circuit13divides only a portion of the signal light as monitor light and emits the monitor light through the light emitting window34. At this time, since the local light is dispersed in the PLC optical demodulator circuit13, stray light of the local light may emit through the light emitting window34. Thus, a slit is provided on an optical axis of the monitor light divided in the PLC optical demodulator circuit13and emitted through the light emitting window34. For example, the light emitting window34and the light entering window53are each provided with a slit passing the monitor light therethrough and shielding stray light in the waveguide type optical element. The slits of the light emitting window34and the light entering window53are formed by reducing the opening diameters of the light emitting window34and the light entering window53. According to this constitution, entering of local light can be reduced, and sufficient cross talk can be secured.

As described above, the present invention can provide a receiving FE module with a built-in monitor PD, which can make the reception sensitivity constant and perform stabilized operation.

INDUSTRIAL APPLICABILITY

The present invention is applicable to information and communication industry.

REFERENCE SIGNS LIST