JP2003229626A - Optical module, optical transmitter and wdm optical transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module in which an accuracy of controlling a wavelength is improved by constituting so that a laser beam from a light emitting element is not reflected on an LD sub-mount of a wavelength monitor side and a yield of a product can be improved. <P>SOLUTION: The optical module M1 comprises the light emitting element 1 for outputting the laser beam, an optical filter 3 for transmitting only a laser beam having a predetermined wavelength band input from the element 1, a wavelength monitoring photodetector 4 for photodetecting the laser beam passing through the filter 3, and the LD sub-mount 5 for placing the element 1. A protrusion 5a formed integrally with a heat sink 6 or the sub-mount 5 formed in a substantially equally in a length of the element 1 in the optical axis direction is provided between the sub-mount 5 and the element 1, so that the laser beam output from the element 1 and reflected on the surface of the sub-mount 5 may not be incident to the photodetector 4. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of optical communication, and more particularly to wavelength division multiplexing (WDM).
plexing) The present invention relates to an optical module, an optical transmitter, and a WDM optical transmitter used in the field of communication.

[0002]

2. Description of the Related Art Generally, in the field of high density WDM, it is required to precisely control the wavelength of an optical signal and stabilize it for a long period of time. Therefore, an optical module has been developed in which the emission wavelength of the laser light output from the light emitting element is monitored by a wavelength monitor and is fed back to the control of the emission wavelength of the laser light to perform wavelength control at all times.

FIG. 6A is an explanatory view schematically showing the structure of a conventional optical module having a built-in wavelength monitor. Figure 6
As shown in (A), the conventional optical module M2 is a light emitting element 50 including a semiconductor laser diode or the like that outputs laser light of a predetermined emission wavelength, and the light emitting element 50 is optically coupled to the front side of the light emitting element 50 ( An optical fiber 51 for sending the laser light output from the end surface (right side in FIG. 6) to the outside, and a parallel lens 52 for parallelizing the laser light output from the rear (left side in FIG. 6) end surface of the light emitting element 50, Parallel lens 5
An optical filter 53 made of an etalon or the like, which transmits only the laser light of a predetermined wavelength band that has passed through 2, and the optical filter 53.
And a wavelength monitor light receiving element 54 such as a photodiode for receiving the laser light transmitted through the laser.

The light emitting element 50 is fixed on the LD submount 55, and the wavelength monitor light receiving element 54 is fixed on the PD submount 61.

On the front side (right side in FIG. 6) of the light emitting element 50, there is provided a parallel lens 56 for collimating the laser light outputted from the front end face thereof. Also, the parallel lens 5
An optical isolator 57 that blocks light returning to the light emitting element 50 is provided on the front side of 6. Optical isolator 57
A condenser lens 58 for condensing the laser light on the end surface of the optical fiber 51 is provided on the front side of the. The optical fiber 51 is held by the ferrule 59.

The above-mentioned members are sealed by a package to form an optical module M2. The optical module M2 also includes a control unit 60 that controls the emission wavelength of the light emitting element 50.
Connected to the optical transmitter as a whole.

The laser light output from the front end face of the light emitting element 50 is collimated by the parallel lens 56, is condensed by the condenser lens 58 via the optical isolator 57, is incident on the optical fiber 51, and is sent to the outside. It

On the other hand, the laser light output from the rear end surface of the light emitting element 50 is made parallel by the parallel lens 52,
The light is received by the wavelength monitor light receiving element 54 via the optical filter 53.

The PD current output from the light receiving element 54 for wavelength monitoring is input to the control unit 60, and the control unit 60 emits light based on the value of the input PD current by, for example, a temperature adjusting unit such as a Peltier device. The emission wavelength is controlled by controlling the temperature of the element 50 or the like.

[0010]

As shown in FIG. 6 (B), in the conventional optical module, most of the laser light output from the light emitting element 50 is directly incident on the parallel lens 52, but the LD submount is not used. Some light is reflected by 55 and then enters the parallel lens 52. Therefore, the wavelength discrimination curve that represents the wavelength monitor characteristic may deteriorate. The wavelength discrimination curve depends on the incident angle of the incident beam on the optical filter 53. When there is reflected light on the LD submount 55, the incident angle between the light that is directly incident and the light that is reflected and incident is slightly different. Therefore, for example, as shown in FIG.
The two wavelength discrimination curves are overlapped. With such characteristics, it is difficult to monitor the wavelength sufficiently,
It is also difficult to perform feedback control to lock to a predetermined wavelength. In particular, when the light emitting element 50 is bonded on the LD submount 55 with a junction down, the light emitting point is very close to the surface of the LD submount 55, and the influence of reflection becomes significant. As a result, there has been a problem that the yield of products is deteriorated.

The present invention has been made in order to solve the above-mentioned problems, and the wavelength control accuracy is improved by configuring the laser light from the light emitting element so as not to be reflected on the LD submount on the wavelength monitor side. It is an object of the present invention to provide an optical module, an optical transmitter, and a WDM optical transmitter that can improve the yield of products.

[0012]

A first optical module of the present invention comprises a light emitting element for outputting a laser beam, an optical filter for transmitting only a laser beam of a predetermined wavelength band output from the light emitting element, In an optical module having a wavelength monitor light receiving element for receiving the laser light transmitted through the optical filter, and an LD submount on which the light emitting element is mounted, a laser output from the light emitting element and reflected on the surface of the LD submount In order to prevent light from entering the light receiving element for wavelength monitoring, a heat sink formed between the LD submount and the light emitting element and having a length substantially equal to the optical axis direction of the light emitting element or the LD submount is integrated. It is characterized in that a protruding portion formed in is provided.

The length of the heat sink or the protruding portion protruding from the end surface of the light emitting element on the side of the light receiving element for wavelength monitoring in the optical axis direction is 50 μm or less, and the height thereof is 200 μm.
It is preferably formed to a thickness of at least μm.

A second optical module of the present invention comprises a light emitting element for outputting a laser beam, an optical filter for transmitting only a laser beam in a predetermined wavelength band outputted from the light emitting element,
In an optical module having a wavelength monitor light receiving element for receiving the laser light transmitted through the optical filter, and an LD submount on which the light emitting element is mounted, a laser output from the light emitting element and reflected on the surface of the LD submount A recess is formed in a portion of the LD submount on the side of the wavelength monitoring light receiving element so that light does not enter the wavelength monitoring light receiving element.

An optical transmitter according to the present invention sets an oscillation wavelength of a laser beam output from the light emitting element to a predetermined wavelength based on a signal output from the optical module described above and the wavelength monitoring light receiving element. It has a control part which controls so that it may be fixed.

The WDM optical transmitter according to the present invention is characterized in that it has a plurality of the optical transmitters described above and wavelength-multiplexes and transmits the optical signals output from these optical transmitters.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows the first of the present invention.
FIG. 3 is an explanatory view schematically showing the configuration of the optical module according to the embodiment, and FIG. 3B is a side view for explaining a heat sink provided between the LD submount and the light emitting element.

As shown in FIG. 1A, an optical module M1 according to the first embodiment of the present invention includes a light emitting element 1 including a semiconductor laser diode or the like which outputs laser light having a predetermined emission wavelength, The light emitting device 1 is optically coupled to the light emitting device 1.
A parallel lens for parallelizing the optical fiber 2 for sending the laser light output from the front side (right side in FIG. 1) of the laser light to the outside and the laser light output from the rear (left side in FIG. 1) end surface of the light emitting element 1. 2, an optical filter 3 made of an etalon or the like that transmits only the laser light of a predetermined wavelength band that has passed through the parallel lens 2, and a wavelength monitor light receiving element 4 such as a photodiode that receives the laser light that has passed through the optical filter 3. Have and.

The light emitting element 1 is mounted on the LD submount 5, but in this embodiment, as shown in FIG. 1B, a laser beam emitted from the light emitting element 1 and reflected on the surface of the LD submount 5 is reflected. A heat sink 6 is provided between the LD submount 5 and the light emitting element 1 so as to prevent light from entering the wavelength monitoring light receiving element 4, and the heat sink 6 is formed to have a length substantially equal to the length of the light emitting element 1 in the optical axis direction. There is.

Further, as shown in FIG. 1C, instead of the heat sink 6, a protrusion 5a integrally formed with the LD submount 5 may be provided.

The wavelength monitor light receiving element 4 is fixed on the PD submount 18.

On the front side (right side in FIG. 1) of the light emitting element 1,
A parallel lens 7 for collimating the laser light output from the front end face thereof is provided. Further, on the front side of the parallel lens 7, an optical isolator 8 that blocks the return light to the light emitting element 1 is provided. On the front side of the optical isolator 8, a condenser lens 9 that condenses the laser light on the end surface of the optical fiber 2 is provided. The optical fiber 2 is held by the ferrule 10.

Each of the above members is sealed by a package to form an optical module M1. Further, the optical module M1 is connected to the control unit 11 that controls the emission wavelength of the light emitting element 1 and constitutes an optical transmitter as a whole.

The laser light output from the front end face of the light emitting element 1 is collimated by the parallel lens 7, and the optical isolator 8
Is condensed by the condenser lens 9 through the optical fiber 2
Is transmitted to the outside.

On the other hand, the laser light output from the rear end face of the light emitting element 1 is made parallel by the parallel lens 2 and is received by the wavelength monitoring light receiving element 4 via the optical filter 3.

P output from the wavelength monitor light receiving element 4
The D current is input to the control unit 11, and the control unit 11 controls the emission wavelength by controlling the temperature of the light emitting element by a temperature adjusting unit such as a Peltier element based on the value of the input PD current. To do.

The light emitting element 1 is bonded to the heat sink 6 by soldering. When the laser light is reflected by the solder, the reflected light is incident on the parallel lens 2 and passes through the optical filter 3 to the light receiving element 4 for wavelength monitoring. May be combined.

Therefore, the inventor of the present invention has proposed a length L (see FIG. 1) protruding in the optical axis direction from the end surface of the light emitting element 1 on the side of the wavelength monitoring light receiving element 4 of the heat sink 6 or the protruding portion 5a.
An experiment was conducted to measure the change in the received light power when (see (B)) was changed. FIG. 2 is a graph showing the experimental results. Here, the reflectance of the surface of the heat sink 6 or the protruding portion 5a is 100%. It can be seen from FIG. 2 that if L is formed to 50 μm or less, the reflected light does not couple to the wavelength monitoring light receiving element 4.

Further, the present inventor conducted an experiment for measuring the change in the received light power when the height H (see FIG. 1B) of the heat sink 6 or the protruding portion 5a was changed. FIG. 3 is a graph showing the experimental results. Here, the reflectance of the surface of the heat sink 6 or the protruding portion 5a is 100%. It can be seen from FIG. 3 that when H is formed to 200 μm or more, the reflected light is not coupled to the wavelength monitor light receiving element 4.

From the above, the length of the heat sink 6 or the protruding portion 5a protruding from the end surface of the light emitting element 1 on the side of the wavelength monitoring light receiving element 4 in the optical axis direction is 50 μm or less,
In addition, it is preferable that the height H is 200 μm or more.

FIG. 4A is an explanatory view schematically showing the structure of the optical module according to the second embodiment of the present invention, and FIG.
FIG. 6 is a plan view showing an LD submount.

In the second embodiment, the wavelength monitor light receiving element of the LD submount 5 is arranged so that the laser beam output from the light emitting element 1 and reflected by the surface of the LD submount 5 does not enter the wavelength monitoring light receiving element 4. Recess 5b on side 4
Are formed. According to the second embodiment, the recess 5
Since b is formed, it is not necessary to provide a heat sink or a protrusion between the light emitting element 1 and the LD submount 5.

According to the first and second embodiments, since the laser light from the light emitting element 1 is configured not to be reflected on the LD submount 5 on the wavelength monitor side, deterioration of the wavelength discrimination characteristic is prevented. Therefore, the accuracy of wavelength control can be improved, and the yield of products can be improved.

FIG. 5 is an explanatory view showing a WDM optical transmitter used in the wavelength division multiplexing communication system according to the third embodiment of the present invention.

As shown in FIG. 5, the wavelength division multiplexing communication system includes a plurality of optical transmitters 12 for transmitting an optical signal and a plurality of channels of optical signals transmitted from the optical transmitter 12 for wavelength multiplexing. The multiplexer 13, the plurality of optical amplifiers 14 connected in a plurality of stages for amplifying and relaying the multiplexed optical signal wavelength-multiplexed by the multiplexer 13, and the optical signal amplified by the optical amplifier 14 It has a demultiplexer 15 that demultiplexes the wavelength for each channel, and a plurality of optical receivers 16 that receive the optical signals demultiplexed by the demultiplexer 15.

The WDM optical transmitter 17 according to the third embodiment of the present invention has a plurality of optical transmitters 12 according to the first and second embodiments, and outputs from these optical transmitters 12. An optical signal is wavelength-multiplexed and transmitted. Therefore, the optical transmitter 1
Since the wavelength of the optical signal oscillated from 2 becomes stable, it is possible to construct a highly reliable high density WDM system.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the technical matters described in the claims.

According to the present invention, since the laser light from the light emitting element is configured not to be reflected on the LD submount on the wavelength monitor side, it is possible to suppress the deterioration of the wavelength discrimination characteristic and The control accuracy is improved, and the product yield can be improved.

[Brief description of drawings]

FIG. 1A is an explanatory diagram schematically showing a configuration of an optical module according to a first embodiment of the present invention, and FIG. 1B shows a heat sink provided between an LD submount and a light emitting element. A side view for explaining, (C) is a side view for explaining an example in which a protrusion formed integrally with the LD submount is provided between the LD submount and the light emitting element.

FIG. 2 is a graph showing a change in received light power when the length of the light emitting element on the wavelength monitor light receiving element side of the heat sink or the protruding portion protruding in the optical axis direction is changed.

FIG. 3 is a graph showing changes in received light power when the height of a heat sink or a protrusion is changed.

FIG. 4A is an explanatory view schematically showing a configuration of an optical module according to a second embodiment of the present invention, and FIG. 4B is a plan view showing an LD submount.

FIG. 5 is an explanatory diagram showing a WDM optical transmitter used in a wavelength division multiplexing communication system according to a third embodiment of the present invention.

FIG. 6A is an explanatory view schematically showing the configuration of a conventional optical module with a built-in wavelength monitor, and FIG. 6B shows a part of laser light output from a light emitting element reflected by an LD submount. FIG. 4 is a side view for explaining that light is incident on a parallel lens.

FIG. 7 is a graph showing wavelength discrimination curve characteristics.

[Explanation of symbols]

M1: Optical module 1: Light emitting element 2: Optical fiber 3: Optical filter 4: Photodetector for wavelength monitor 5: LD submount 5a: protrusion 6: Heat sink 7: Parallel lens 8: Optical isolator 9: Condensing lens 10: Ferrule 11: control unit 12: Optical transmitter 13: Combiner 14: Optical amplifier 15: Splitter 16: Optical receiver 17: WDM optical transmitter 18: PD submount

Continued front page    (72) Inventor Mizuki Oike             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F-term (reference) 5F073 AB21 AB25 AB27 AB28 AB30                       BA02 EA03 EA04 FA17                 5K002 BA31 CA12 DA31 FA01

Claims (5)

[Claims] 1. A light emitting element for outputting a laser beam, an optical filter for transmitting only a laser beam of a predetermined wavelength band outputted from the light emitting element, and a wavelength monitor for receiving the laser beam transmitted through the optical filter. In an optical module having a light receiving element and an LD submount on which the light emitting element is mounted, laser light output from the light emitting element and reflected on the surface of the LD submount does not enter the wavelength monitoring light receiving element, Between the LD submount and the light emitting element, there is provided a heat sink having a length substantially equal to the length of the light emitting element in the optical axis direction, or a protrusion integrally formed with the LD submount. Optical module. 2. The heat sink or the protruding portion has a length of 50 μm or less protruding in the optical axis direction from the end surface of the light emitting element on the side of the wavelength monitoring light receiving element, and has a height of 200 μm.
The optical module according to claim 1, wherein the optical module is formed to have a thickness of at least μm. 3. A light emitting element for outputting a laser beam, an optical filter for transmitting only a laser beam of a predetermined wavelength band output from the light emitting element, and a wavelength monitor for receiving the laser beam transmitted through the optical filter. In an optical module having a light receiving element and an LD submount on which the light emitting element is mounted, laser light output from the light emitting element and reflected on the surface of the LD submount does not enter the wavelength monitoring light receiving element, An optical module, wherein a recess is formed in a portion of the LD submount on the side of the wavelength monitor light receiving element. 4. Oscillation of laser light output from the light emitting element based on a signal output from the optical module according to any one of claims 1 to 3 and the wavelength monitoring light receiving element. An optical transmitter comprising: a control unit that controls the wavelength to be fixed to a predetermined wavelength. 5. A WDM optical transmitter, comprising a plurality of optical transmitters according to claim 4, wherein the optical signals output from these optical transmitters are wavelength-multiplexed and transmitted.