JP2008016492A - Light emission module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturized light emission module of low power consumption, and also to provide an optical transceiver with the light emission module mounted thereon. <P>SOLUTION: A light emitter 10 has: a stem 12 for mounting an LD 14, a thermoelectric conversion element 16 for controlling the temperature of the LD 14, and the like; and a cap 11 attached to that stem. A monitor 20 has: a beam splitter 21 for receiving light emitted from the LD 14 and branching it into at least two light beams, a wavelength dependent filter 22 transmitting one of the beams branched by the beam splitter; a PD 23a for receiving one light beam transmitting the wavelength dependent filter; and a PD 23b for receiving the other light beam branched by the beam splitter 21 and not transmitting the wavelength dependent filter 22. The monitor 20 is arranged in a housing 24 independent from the light emitter 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light emitting module having a monitor unit that monitors light emitted from a light emitting unit.

  Currently, in the optical communication field, high-density wavelength division multiplexing (DWDM) communication is performed. In order to perform DWDM communication, it is required to stabilize the oscillation wavelength of an optical signal, that is, the oscillation wavelength of a semiconductor laser (LD: Laser Diode) over a long period of time. Further, since the oscillation wavelength of the LD changes depending on the temperature, it is necessary to monitor the oscillation wavelength of the LD and appropriately adjust the temperature to stabilize the oscillation wavelength of the LD.

  In response to this, for example, a light emitting module including an LD, a wavelength selective transmission filter, a wavelength monitor PD (Photo Diode), a power monitor PD, and a temperature regulator has been proposed. All of these components are built in the same package and mounted on a TEC (Thermo-Electric Cooler: thermoelectric conversion element) to control the overall temperature and stabilize the oscillation wavelength of the LD. (See Patent Document 1).

  On the other hand, in addition to the demand for wavelength stabilization, there is always a demand for low power consumption, miniaturization, and cost reduction. Particularly, in recent years, small form-factor pluggable (SFP) and extended form-factor pluggable (XFP) are required. There is an increasing need to mount a light emitting module in which the oscillation wavelength of an LD is stabilized in an optical transceiver having a housing.

Therefore, in order to realize low power consumption and downsizing, an invention related to an optical transmitter in which a light emitting element (LD) and a monitor PD are separately mounted to reduce power consumption and are packaged in a CAN package has been proposed. (See Patent Document 2).
JP 2003-163408 A JP 2004-2537779 A

  However, in the light emitting module disclosed in Patent Document 1, since the temperature of all elements such as LD and PD is adjusted, there is a problem that the power required for temperature adjustment, that is, the power consumption of TEC increases. there were. Further, since all the elements (LD, PD, etc.) are built in the same package, the number of parts increases, and there is a problem that it is difficult to mount on the CAN package. Furthermore, since there are many lead pins for electrically connecting these LDs and the control circuit board, mounting on the circuit board becomes difficult and the manufacturing process required for mounting increases, resulting in an increase in manufacturing cost. There was a problem to do.

  Further, the CAN package type light emitting module disclosed in Patent Document 2 also has many problems in implementation because of the large number of mounted components and the large number of lead pins. In addition, it is possible to store an LD or the like in a package other than CAN, such as a butterfly package, but in the first place, it is extremely difficult to mount the butterfly package on a small optical transceiver conforming to the SFP or XFP standards. As described above, since there are many lead pins, there is a problem that the manufacturing process and cost required for mounting increase.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a light-emitting module that consumes less power and is miniaturized and an optical transceiver on which the light-emitting module is mounted.

  A light emitting module according to the present invention is a light emitting module having a light emitting part and a monitor part for monitoring light emitted from the light emitting part, and the light emitting part is a stem on which a semiconductor laser and a thermoelectric conversion element for controlling the temperature of the semiconductor laser are mounted. And a cap that forms a package for sealing the semiconductor laser and the thermoelectric conversion element in cooperation with the stem. The monitor unit includes an optical filter that transmits part of the light emitted from the semiconductor laser, a first light receiving element that receives light transmitted through the optical filter, and a second light that receives light that does not pass through the optical filter. The monitor unit and the light emitting unit are disposed in an independent housing. The stem is provided with a lens that transmits light emitted from the semiconductor laser, and the first and second light receiving elements receive the light transmitted through the lens. Furthermore, in the light emitting module according to the present invention, it is preferable that a light branching element is mounted on the monitor unit. The branching element branches the light transmitted through the lens, and the branched light is first filtered through the filter. The other branched light is output to the second light receiving element without passing through the filter. Further, the stem and the cap form a coaxial package.

  An optical transceiver according to the present invention is an optical transceiver having a function of transmitting and receiving an optical signal to and from an optical fiber attached to an optical connector, and includes a receptacle for receiving the optical connector, and light emission and light reception attached to the receptacle. A sub-assembly, a control circuit board on which a circuit electrically connected to the light-emitting and light-receiving sub-assemblies is mounted; and a housing that houses the control circuit board and the light-emitting and light-receiving sub-assemblies. The light emitting subassembly includes a light emitting unit and a monitor unit. The light emitting unit cooperates with the stem on which the semiconductor laser and a thermoelectric conversion element for controlling the temperature of the semiconductor laser are mounted, and the semiconductor laser and the thermoelectric unit. And a cap that forms a package for sealing the conversion element. The monitor unit includes an optical filter that transmits a part of the light emitted from the semiconductor laser, a first light receiving element that receives light transmitted through the optical filter, and a second light that receives light that does not pass through the optical filter. The monitor unit and the light emitting unit are disposed in an independent casing, and the casing is mounted on the control circuit board.

  According to the present invention, the number of parts to be temperature-controlled is reduced, so that power consumption for temperature adjustment can be reduced. In addition, since the number of lead pins arranged on the stem can be reduced, it is easy to secure the arrangement position of the lead pins, and a miniaturized light emitting module in which the light emitting unit is housed in the CAN package can be realized. As a result, it becomes easy to mount on a small-sized optical transceiver compatible with SFP, XFP, and the like.

  An outline of a light emitting module according to the present invention will be described with reference to FIG. The light emitting module 1 according to the present invention includes a light emitting unit 10 and a monitor unit 20 for monitoring light emitted by the LD 14 of the light emitting unit 10. The light emitting unit 10 includes a cap 11 and a metal disc-shaped stem 12, and is formed as a coaxial package including the cap 11 and the stem 12 as illustrated. Further, the openings 11a and 12a formed at the center of the cap 11 and the stem 12 collimate the emitted light from the lenses 13a and LD 14 for converging the emitted light from the LD 14 to an optical fiber (not shown). A lens 13b is provided. Note that the chip of the LD 14 emits coherent light by causing the inside defined by the two end faces to act as a resonator.

  The light emitted from the chip front surface 14a of the LD 14 (the side on which the low reflection film is formed on the two end surfaces) is passed through a lens 13a disposed approximately at the center of the top of the cap 11 and is not shown. Combine with. On the other hand, the light emitted from the chip back surface 14b (the side on which the highly reflective film is formed) of the LD 14 is collimated by the lens 13b and enters the monitor unit 20 through the space, as will be described later.

  The LD 14 and the thermistor 15 are mounted on a carrier 17. The carrier 17 is mounted on a TEC 16 that adjusts the temperature of the LD 14 and is disposed in a space formed by the cap 11 and the stem 12. The TEC 16 is composed of a thermoelectric conversion element such as a Peltier element. Further, the stem 12 is provided with a lead pin 18, and the LD 14, the thermistor 15, and the TEC 16 are electrically connected to a control circuit board (not shown) through the lead pin 18 as will be described later.

  The monitor unit 20 is positioned behind the light emitting unit 10 and has a beam splitter (branching element) 21 for branching light emitted from the chip back surface 14b of the LD 14, and a thin film (thickness 0. 0) having optical flatness and parallelism. A wavelength-dependent filter (parallel plate filter) 22 composed of an etalon filter whose transmission light intensity periodically changes due to interference action, and a light receiving element that receives the light branched by the beam splitter 21 (PD: Photodiode) 23a and 23b, which are housed in a housing 24. The housing 24 is provided with an opening 24a, and light emitted from the chip back surface 14b of the LD 14 is incident on the beam splitter 21 through the opening 24a.

  One of the lights branched by the beam splitter 21 passes through the wavelength-dependent filter (etalon filter) 22 and is received by the PD 23a which is the first light receiving element (PD), and the intensity of the light emitted by the LD 14 is increased. Monitored. On the other hand, the other light branched by the beam splitter 21 is received by the PD 23b which is the second light receiving element (PD), and the intensity of the light emitted by the LD 14 is directly monitored.

  In this way, the oscillation wavelength of the LD 14 is controlled by monitoring the light emitted by the LD 14. That is, since the oscillation wavelength of the LD 14 changes at a rate of about 0.3 nm / ° C. as the operating temperature changes, the TEC is set so that the difference in the received light intensity detected by the two PDs 23a and 23b can be kept constant. The oscillation wavelength of the LD 14 can be made constant by using and adjusting the operating temperature of the LD.

Next, the operation principle of wavelength lock for making the oscillation wavelength constant will be described below.
FIG. 2 is a diagram showing the light reception intensity PDb of the PD 23b of FIG. 1 and the light reception intensity PDa of the PD 23a after passing through the etalon filter. The horizontal axis indicates the wavelength of light transmitted through the etalon filter, and the vertical axis indicates the received light intensity.
An etalon filter is a parallel plate type optical element having two surfaces of optical flatness and parallelism, and its light transmittance has a characteristic that a transmission peak repeatedly appears according to a change in wavelength as shown in FIG. have. When the etalon filter is composed of a mirror with no loss, and light is incident perpendicularly to the etalon filter, if the transmittance is T, the transmittance T, the reflectance R of the mirror, the wavelength λ, the refractive index n of the filter medium, The thickness t of the filter medium is

Satisfy the relationship.

  Therefore, the photocurrent IPDa flowing in the PD 23a placed after the wavelength-dependent filter (etalon filter) 22 has a periodic peak depending on the wavelength, similar to the transmittance of the etalon filter. On the other hand, the light branched by the beam splitter 21 is received by the PD 23b and generates a photocurrent IPDb. However, the light received by the PD 23b does not reflect the transmittance of the etalon filter 22, and therefore has a substantially constant intensity when the wavelength range is limited. Therefore, by controlling the LD temperature so as to keep the difference between the photocurrents IPDa and IPDb (IPDa−IPDb) generated by the light received by the PDs 23a and 23b constant, the oscillation wavelength of the LD is set to a specific wavelength. Can be held.

  However, since the transmittance of the etalon filter 22 has periodicity, the wavelength at which the difference in photocurrent (IPDa-IPDb) becomes the same also appears periodically. In the case of FIG. 2, for example, the wavelengths λ1, λ2, λ3. . . The difference in received light intensity between PD 23a and PD 23b (PDa−PDb) is constant. Therefore, the temperature of the TEC 16 is controlled so that the LD 14 emits light having a wavelength in the vicinity of the wavelength to be locked in advance (for example, λ2), that is, λ2 ± Δλ / 4 (Δλ / 4 is | λ1-λ2 | The TEC 16 is roughly controlled so that the emission wavelength falls within a range of (smaller than). Thereafter, by operating the feedback loop composed of PD and TEC, the emission wavelength of the LD 14 is automatically converged to λ2, and the oscillation wavelength of the LD 14 can be made constant.

FIG. 3 is a view showing the lead pins arranged on the stem.
FIG. 3A is a view showing an example of the arrangement of lead pins arranged on the stem when all elements are built in one package as in the prior art, and FIG. 3B shows the present invention. It is the figure which showed the example of arrangement | positioning of the lead pin arrange | positioned at the stem of the light emission part in.

In FIG. 3A, lead pins 18 ₁ and 18 ₂ are for supplying current to the TEC, lead pins 18 ₃ and 18 ₄ are for outputting signals from the thermistors, and lead pins 18 ₅ and 18. _6, for supplying a driving signal to the LD, the lead pins 18 ₇ provided to collect the signals from the first PD (PD23a), a signal from the lead pin 18 ₈ second PD (PD23b) It is for taking out. Incidentally, PD23a, other lead pin PD23b can be shared by 1 lead pins 18 _9. Furthermore, by sharing the lead pins 18 ₄ low-frequency signal (almost DC signal) flows and the lead pins 18 _9, it is also possible to ground lead pin.

Reference numeral 19 denotes an insulating seal glass. In FIG. 3A, five lead pins (18 ₁ , 18 ₃ , 18 ₅ , 18 ₇ , 18 ₉ ) are combined into one insulating seal glass 19 and the stem 12. The other four lead pins (18 ₂ , 18 ₄ , 18 ₆ , 18 ₈ ) are collectively insulated by one insulating seal glass 19. However, it is difficult to share the lead pins 18 ₁ and 18 ₂ through which a large current flows or the lead pins 18 ₅ and 18 ₆ through which a high-frequency signal flows.

Thus, when all the elements are built in one package as in the prior art, nine lead pins 18 must be arranged on the stem 12 as shown in FIG. Securing and mounting of the package on the control circuit board becomes difficult. However, by separating the light emitting module into the light emitting part and the monitor part as in the present invention, as shown in FIG. 3B, the TEC lead pins 18 ₁ , 18 ₂ disposed on the stem 12 in the present invention, The number of lead pins 18 ₃ , 18 ₄ for the thermistor and the number of lead pins 18 ₅ , 18 ₆ for LD can be reduced to a total of six.

In FIG. 3B, an embodiment is shown in which the upper and lower three lead pins are used as a set, and the insulation of the stem 12 is realized by one insulating seal glass 19. However, according to the present invention, the number of lead pins is reduced. Therefore, it is possible to realize a form in which each lead pin is insulated by the insulating seal glass 19 one by one. In particular, the lead pins ₁₈ 5, 18 ₆ for LD, it is desirable to avoid the common insulation for the seal glass 19 since the high-frequency signal flows further lead pin ₁₈ 1, 18 ₂ a large current (several 10mA for for TEC It may be desirable to seal each individual lead pin as well.

As described above, since the light emitting unit 10 and the monitor unit 20 are separated, the number of components to be subjected to temperature adjustment is reduced, so that power consumption for temperature adjustment can be reduced.
As a result of the reduction in the number of lead pins, the interval between the lead pins is widened, it is easy to secure the arrangement position of the lead pins, the light emitting part can be housed in the CAN package, and it is easy to mount on the control circuit board. Thereby, since the whole light emitting module can be reduced in size, it becomes easy to mount the light emitting module on an optical transceiver that conforms to the SFP or XFP standards.
Further, even if a defect occurs in the light emitting unit 10 or the monitor unit 20, it is only necessary to replace and repair the light emitting unit 10 or the monitor unit 20 in which the defect has occurred, so that the repair cost and time can be reduced.

FIG. 4 is an example of an optical transceiver in which the light emitting module according to the present invention is mounted. 4A is a view of the optical transceiver as viewed from above, and FIG. 4B is a view of the optical transceiver as viewed from the side.
The optical transceiver 2 includes a receptacle 50 for receiving the optical connector 60, a light emitting subassembly including the light emitting unit 10, the monitor unit 20, and the like, a light receiving subassembly including the light receiving module 40 and the like, and a control circuit board 30 on which an electronic circuit is mounted. And a housing 70 for housing these receptacles, optical subassemblies, and control circuit boards.

  The monitor unit 20 of the light emitting module 1 is directly mounted on the control circuit board 30. The control circuit board 30 also includes an LD drive circuit (not shown) for driving the LD, a TEC drive circuit (not shown) for driving the TEC, or an optical signal converted into an electrical signal by the light receiving subassembly. A circuit (not shown) for amplifying and processing the converted received signal is mounted.

  In addition, an electrical connector 31 is formed at the rear end of the control circuit board 30 for electrical connection (signal exchange and power supply) with a host system (not shown) on which the optical transceiver 2 is mounted. Yes. Although the distance between the light emitting unit 10 and the monitor unit 20 slightly changes due to thermal expansion due to temperature change, the emitted light is collimated by the lens 13b disposed in the opening of the stem 12, so that the emitted light is There is no particular problem with monitoring.

On the other hand, since the transmission wavelength of the wavelength-dependent filter (see FIG. 1) depends on the incident angle (the thickness t in (Equation 1) changes equivalently), the wavelength from the LD (see FIG. 1) It is necessary to prevent the incident angle of the emitted light from changing.
Therefore, as shown in FIG. 4A, the stem 12 of the light emitting unit 10 is brought into close contact with the edge with the control circuit board 30. Thereby, the angle of the light emission part 10 is fixed and the change of the incident angle of a wavelength dependence filter can be suppressed to the minimum.

  FIG. 5 is another example of an optical transceiver in which the light emitting module according to the present invention is mounted. Unlike the optical transceiver shown in FIG. 4, the optical transceiver shown in FIG. 5 has a structure in which an LD driver 32 that drives an LD (see FIG. 1) is disposed between the monitor unit 20 and the control circuit board 30. .

When the light emitting module 1 is mounted on the control circuit board 30, the distance between the LD and the LD driver 32 must be minimized in order to maintain the high frequency characteristics of the LD and to maintain a good signal waveform. Even if the emitted light is collimated, if the light emitting unit 10 and the monitor unit 20 are separated too much, it causes various problems. However, since the LD driver 32 is provided, the monitor unit 20 cannot be brought close to the light emitting unit 10.
Therefore, as shown in FIG. 5, this problem can be solved by mounting the monitor unit 20 on the LD driver 32. In this case, the housing (see FIG. 1) of the monitor unit 20 may be made of an insulating material such as plastic.

  The embodiments of the present invention have been described above with reference to the drawings. The present invention is not limited to such an embodiment. For example, in FIG. 1 and the like, the description has been made on the assumption that the optical branching element is mounted on the monitor unit, but this optical branching element is not necessarily an essential part. The optical filter is mounted so as to cover half of the optical path from the semiconductor laser to the light receiving element, and the light that has passed through the filter and the light that has passed through the filter are received by the individual light receiving elements. Is feasible. Further, in the above description, the optical filter is described on the assumption that a parallel plate filter (etalon filter) is used, but the present invention is not limited to this etalon filter. For example, a wedge-type etalon filter can exhibit the same function. What is important is that the light emitted from the semiconductor laser passes through two optical paths having different optical characteristics, is received independently, and the difference in intensity is detected. With this configuration, the oscillation wavelength of the semiconductor laser can be stabilized.

It is a figure explaining the outline of the light emitting module concerning this invention. It is a figure explaining received light intensity of PD. It is the figure which showed an example of the lead pin arrange | positioned at the stem. It is a figure explaining an example of the optical transceiver which mounted the light emitting module concerning this invention. It is a figure explaining the other example of the optical transceiver which mounted the light emitting module concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting module, 2 ... Optical transceiver, 10 ... Light emission part, 11 ... Cap, 11a ... Opening of cap, 12 ... Stem, 12a ... Opening of stem, 13a, 13b ... Lens, 14 ... LD, 14a ... LD the front of the chip (optical connector side), 14b ... LD chip back of the (monitoring), 15 ... thermistor, 16 ... TEC, 17 ... carrier, 18 ... lead pins, ₁₈ 1, 18 2 _... lead pins ± _TEC, 18 3, 18 ₄ ... Lead pins ± Th, 18 ₅ , 18 ₆ ... Lead pins ± LD, 18 ₇ ... Lead pins + PD, 18 ₈ ... Lead pins + PD, 18 ₉ ... Lead pins-PD, 19 ... Insulating sealing glass, 20 ... Monitor section, 21 ... Beam Splitter, 22 ... wavelength dependent filter (etalon filter), 23a ... PD, 23b ... PD, 24 ... monitor housing , The opening of 24a ... housing, 30 ... control circuit board, 31 ... electrical connector, 32 ... LD driver 40 ... light-receiving module, 50 ... receptacle 60 ... optical connector, 70 ... housing of the optical transceiver.

Claims (5)

A light emitting module having a light emitting unit and a monitor unit for monitoring light emitted from the light emitting unit,
The light emitting unit includes a semiconductor laser, a stem on which a thermoelectric conversion element that controls the temperature of the semiconductor laser is mounted, and a cap that forms a package for sealing the semiconductor laser and the thermoelectric conversion element in cooperation with the stem. Have
The monitor unit includes an optical filter that transmits a part of the light emitted by the semiconductor laser, a first light receiving element that receives light transmitted through the optical filter, and a second light that receives light that does not pass through the filter. And a light receiving element
The light emitting module, wherein the monitor unit is disposed in a housing independent of the light emitting unit.   A lens that transmits light emitted from the semiconductor laser is disposed on the stem, and the first light receiving element and the second light receiving element receive light transmitted through the lens. Item 2. The light emitting module according to Item 1.   The light emitting module according to claim 1, wherein the stem and the cap form a coaxial package.   The monitor unit includes an optical branching element that branches at least two light beams emitted from the semiconductor laser, and the optical filter transmits one branched light and outputs the branched light to the first light receiving element. The light emitting module according to claim 1, wherein the other light is output to the second light receiving element. An optical transceiver that transmits and receives an optical signal to and from an optical fiber attached to an optical connector,
A receptacle for receiving the optical connector; a light emitting subassembly and a light receiving subassembly mounted on the receptacle; a control circuit board on which a circuit electrically connected to the light emitting subassembly and the light receiving subassembly is mounted; A control circuit board and a housing for housing the light emitting subassembly and the light receiving subassembly,
The light emitting subassembly includes a light emitting unit and a monitor unit,
The light emitting unit includes a semiconductor laser, a stem on which a thermoelectric conversion element that controls the temperature of the semiconductor laser is mounted, and a cap that forms a package for sealing the semiconductor laser and the thermoelectric conversion element in cooperation with the stem. Have
The monitor unit receives an optical filter that transmits a part of the light emitted from the semiconductor laser, a first light receiving element that receives light transmitted through the optical filter, and a first light receiving element that does not pass through the optical filter. 2. An optical transceiver comprising: two light receiving elements, wherein the monitor unit is disposed in a casing independent of the light emitting unit, and the casing is mounted on the control circuit board.

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