US20050094999A1

US20050094999A1 - Module for bi-directional optical signal transmission

Info

Publication number: US20050094999A1
Application number: US10/966,356
Authority: US
Inventors: Martin Weigert
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies Fiber Optics GmbH; EZconn Corp
Priority date: 2003-10-15
Filing date: 2004-10-15
Publication date: 2005-05-05
Also published as: US20050084268A1; DE10348675B3; US7418208B2; DE502004008013D1

Abstract

A module for bidirectional optical signal transmission having a transmitting component that emits light of a first wavelength, a receiving component that detects light of a second wavelength, a carrier substrate that is transparent to the light of the first wavelength, on which the transmitting component is arranged, and a monitor component that detects a fraction of the light emitted by the transmitting component, wherein the receiving component is integrated in the carrier substrate, the receiving component and the transmitting component are arranged behind one another in relation to the direction of the emitted or received light, the receiving component is optically transparent to the light of the first wavelength, and light emitted by the transmitting component is transmitted through the carrier substrate and the receiving component. A second module complements such a module, in that it detects light of the first wavelength and emits light of the second wavelength.

Description

FIELD OF INVENTION

The invention relates to a module for bidirectional optical signal transmission.

BACKGROUND OF THE INVENTION

Described in EP-A-0 463 214 is a transmitting and receiving module for bidirectional optical signal transmission which is known as a BIDI module. In this module the two active components, namely the light transmitter and the light receiver, are hermetically encapsulated as autonomous components in a common module housing, within which a beam splitter and a lens coupling system are arranged. The module housing furthermore has a fiber connection for a common optical fiber. An optical signal is injected into the connected optical fiber by the transmitter, while at the same time a different optical signal can be received from the same fiber. The two signals are separated by means of a beam splitter, which may also contain a wavelength-selective filter which reflects a specific wavelength and allows another wavelength to pass.
An electro-optical module for transmitting and/or receiving optical signals of at least two optical data channels is known from WO02/095470 A1, in which at least two light waveguide sections each having at least one inclined front face are provided. The light waveguide sections are positioned axially one behind the other at the inclined front faces. A light injection or light decoupling occurs for a particular optical channel on the inclined front face of a light waveguide section at an angle to the optical axis of the light waveguide. The front face is here coated with a wavelength-selective filter to separate the wavelengths.
It is desirable to provide modules for bidirectional data transmission that are characterized by smaller dimensions and fewer components.
A transmission module for optical signal transmission is known from WO02/084358, in which a transmission unit is arranged on a transmission unit substrate and a detection unit is arranged on a detection unit substrate, and the transmission unit substrate and the detection unit substrate are superposed in relation to the direction of the emitted or received light. The transmission unit substrate and/or the detection unit substrate are here transparent to the wavelength emitted by the transmission unit. The known transmitting module provides an advantageous design, but with only one detection unit however.

SUMMARY OF THE INVENTION

The present invention is directed to a module for bidirectional optical signal transmission which is characterized by small dimensions and a small number of components.
The solution according to the invention is characterized in that the transmitting component and receiving component are arranged behind one another in relation to the direction of the emitted or received light so that no beam deflection is required. This considerably facilitates the design of the module. Moreover, a filter for separating the wavelengths is not a mandatory requirement. The arrangement exploits the fact that the materials used for the carrier substrate, the transmitting component and the receiving component are transparent to certain wavelengths, but are not transparent on the other hand to other wavelengths. In particular, the present invention exploits the effect that longer-wave light, having a wavelength of 1310 nm for example, can be transmitted through substrates that emit shorter-wave light of 850 nm for example.
The invention provides a compact design of a bidirectional module with a reduced number of components, and hence low manufacturing costs, in which the module simultaneously permits a monitoring of the light of the transmitting component.
The wavelengths of the transmitting component and of the receiving component are preferably selected in such a way that they correspond to the usual wavelengths used in optical communications technology, and consequently in particular to the optical “windows” of conventional optical fibers. Wavelength combinations of 850 nm/1310 nm, 850 nm/1490 nm or 850 nm/1550 nm are preferably selected for the first and second wavelengths. It is likewise possible to have a combination for the first and second wavelengths of 1310 nm/1550 nm.
The bidirectional modules according to the invention are preferably employed in optoelectronic multimode transceivers, wherein the transmitter and receiver ports of such transceivers may be designed to be bidirectional with the aid of the modules according to the invention. This makes it possible to double the transmission capacity of the transceivers for the same data rate. It is therefore possible to transport exactly as much data on one fiber as on two fibers with previous transceivers. The capacity of existing fiber networks can accordingly be doubled.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail below on the basis of several exemplary embodiments with reference to the figures, in which:
FIG. 1 shows a schematic representation of the design of two mutually complementary modules for bidirectional data transmission;
FIG. 2 shows the design of a first module for bidirectional data transmission that emits light of a first wavelength and receives light of a second wavelength;
FIG. 3 shows the design of a second module for bidirectional data transmission that emits light of the second wavelength and receives light of the first wavelength;
FIG. 4 shows a section through a housing with a module according to FIG. 2 or 3;
FIG. 5 shows a perspective view of the module in FIG. 4, which is connected to a connector receptacle and is contacted by means of a flexible foil;
FIG. 6 shows a perspective view of an optoelectronic transceiver having a housing and two modules in accordance with FIG. 5; and
FIG. 7 shows an alternative design of the module from FIG. 3.

DESCRIPTION OF A PREFERRED EXEMPLARY EMBODIMENT

FIG. 1 shows an arrangement having two modules 1, 2 for bidirectional data transmission. The modules are designed to complement each other, in that the light of a first wavelength emitted by the first module 1 is detected by the second module 2, and the light of a second wavelength emitted by the second module 2 is detected by the first module 1. Located between the modules 1, 2 is a signal transmission section L in which the signals are usually transmitted over optical fibers or other light waveguides. The direct opposition of the modules 1, 2 in FIG. 1 should thus be interpreted only as schematic.
The first module 1 has a carrier substrate 11, a transmission unit 12, a monitor diode 13 and a receiving unit 14. The transmission unit 12 is preferably a VCSEL laser diode with VCSEL structure 121 which is designed in a prefabricated chip. The laser diode 12 is upside-down, that is to say is mounted on the carrier substrate 11 with the light-emitting side facing down so that the light-emitting region 121 is immediately adjacent to the carrier substrate 11.
Arranged on the rear of the laser diode 12 is a monitor diode 13 having a light-sensitive pn-junction 131 which is contacted by means of bond wires. The monitor diode 13 detects a fraction of the light emitted by the laser diode 12. It is connected to an open-loop/closed-loop control device (not illustrated) for controlling the output power of the laser diode 1.
The monitor diode 13 is likewise preferably designed as a prefabricated chip, preferably in an InP substrate. Alternatively, however, the monitor diode can also be monolithically integrated in the laser diode 12. In this case, a pn-junction is integrated in the laser diode 12 on the side facing away from the carrier substrate 11 and is contacted by means of bond wires 9 for instance.
The laser diode 12 emits light of a first wavelength λ1, where λ1 is preferably approximately 1310 nm, alternatively approximately 1490 nm or approximately 1550 nm. A fraction of the light is decoupled in the direction of the monitor diode 13 from the resonator of the laser diode 12 and detected by the monitor diode 13 for monitoring purposes. The substrate of the laser diode 12 is here transparent to the emitted light of the wavelength λ1, as is also the substrate of the monitor diode 13. The substrate of the laser diode 12 consists here, for example, of GaAs which is transparent to light with wavelengths above 950 nm.
The carrier substrate 11 preferably consists of silicon. Silicon is transparent to wavelengths above approximately 1100 nm. It is however also possible for another material which is transparent to the emitted wavelength λ1 to be used as carrier substrate.
The receiving component 14 is integrated in the carrier substrate 11 (i.e., the receiving component 14 is fabricated directly on the downward-facing surface of carrier substrate 11 using well-established integrated circuit fabrication techniques). For this the carrier substrate forms a pn-junction on the downward-facing surface (i.e., the side facing away from the transmitting component 12). The use of silicon for the carrier substrate 11 and as the material for the receiving component 14 is particularly cost-effective.
The receiving component 14 detects light of a second wavelength λ2 which is lower than the first wavelength λ1. The carrier substrate 11 is not transparent to the second wavelength λ2 so that an optical isolation between the transmitting component 12 and the receiving component 14 with respect to the received light of the wavelength λ2 is present. On the other hand, the light of the wavelength λ1 emitted by the laser diode 12 is transmitted through the carrier substrate 11 and also the receiving diode 14 without hindrance.
If the wavelengths 1550 nm and 1310 nm are selected for λ1 and λ2, the carrier substrate must consist of a material other than silicon as silicon is transparent to said wavelengths and consequently an optical isolation between the transmitting component 12 and the receiving component 14 with respect to the received light of the wavelength λ2 is no longer present. For instance, in this case the carrier substrate 11 consists of InP or sapphire with germanium layers.
The complementary module 2 likewise has a carrier substrate 21, a transmitting component 22, a receiving component 24 and a monitor diode 23.
Again the transmission unit is preferably a VCSEL laser diode 22 with a light-emitting region 221 which emits light of the second wavelength λ2. The laser diode 22 is mounted upside-down as chip 22 on the substrate 21. The substrate of the laser diode 12 preferably consists of GaAs which is transparent to light with wavelengths above 950 nm.
In this embodiment, the receiving component 24 is arranged on the side of the laser diode 22 facing away from the carrier substrate 21, said receiving component being preferably designed as a prefabricated photodiode chip (made of InP for example) with an integrated pn-junction 241. The receiving diode 24 is contacted by means of bond wires 9. The receiving diode detects light of the wavelength λ1. In this respect the module 2 complements the other module 1.
In the module 2, the monitor diode 23 is integrated in the carrier substrate 21. According to FIG. 1, the monitor diode 23 is preferably located here on the side of the carrier substrate 21 facing the laser diode 22.
The carrier substrate 21 is transparent to the light of the wavelength λ2 emitted by the laser diode 22, likewise to the light of the wavelength λ1 emitted by the laser diode 12 of the complementary module 1. The substrate of the laser diode 22 itself, however, is only transparent to the light of the wavelength λ1 detected by the receiving diode 204, but not to the emitted light. Light emitted from the resonator of the laser diode 22 in the direction of the receiving diode 24 is therefore absorbed and does not disturb the receiving diode 24. The substrate of the laser diode 22 thus accordingly acts as a blocking filter. A stop-band filter may be optionally arranged on the side of the laser diode 22 facing the receiving diode 24. Additional stop-band filters may also be provided in the module 1.
The light of the wavelength λ2 emitted by the laser diode 22 is first of all transmitted through the monitor diode 23. A small fraction of the emitted light is detected here for monitoring purposes. The non-detected portion is transmitted through the carrier substrate 21 and is decoupled out from the module 2.
FIG. 2 shows the design of the module 1 from FIG. 1 in more detail.
Arranged on one upper side 115 of the silicon carrier substrate 11, which is optically transparent only to light of the emitted wavelength λ1, is the VCSEL laser diode 12 with flip-chip mounting. The p-contact and n-contact of the laser diode are arranged here on the mounting side, that is to say the side facing the carrier substrate 201. Contacting is effected by means of corresponding through-platings on the upper side 115 of the carrier substrate 11 (not illustrated).
Mounted on the rear of the laser diode 12 is the monitor diode 13, detecting a fraction X of the light of the laser diode 12. The electrical connection of the monitor diode 13 is effected by means of two bond wires 9 which are connected to corresponding bond pads on the upper side of the carrier substrate (not illustrated).
Located in the silicon carrier substrate 11 are two vias 111, 112 which contact the receiving diode 14 integrated in the carrier substrate 101. Thus all electrical contacts are on one plane, the mounting plane, which is formed by the one upper side 115 of the carrier substrate 11. In this way it is then possible to perform bonding from the mounting plane 115 onto a leadframe in a simple manner, as is further illustrated in FIG. 4.
The second module 2 in FIG. 1 is illustrated in detail in FIG. 3. The carrier substrate 21 is transparent both to light of the detected wavelength λ1 and to light of the emitted wavelength λ2. It preferably consists of sapphire. Sapphire is transparent to wavelengths between 850 nm and 1550 nm.
The VCSEL laser diode 22 is in turn mounted by means of flip-chip mounting on the one side 215 of the carrier substrate 21 so that both contacts are on the same side. In this respect the design is comparable with that of the laser diode 12 in FIG. 2.
Mounted on the rear of the VCSEL laser diode 22 is the receiving diode 24 with the pn-junction 241 which is sensitive to another wavelength λ2. This is preferably a receiving diode comprising an InP substrate. It serves to detect the light of the wavelength λ1 emitted by the module 1 which was emitted by the complementary module 1.
The monitor diode 23 is integrated in the sapphire. For this purpose a crystalline silicon layer which provides a pn-junction is preferably integrated in the sapphire. The monitor diode 23 is preferably formed on the side of the carrier substrate 21 facing the laser diode 22. This enables simple contacting of the monitor diode by means of contacts on the surface 115 of the carrier substrate.
FIG. 7 shows an alternative design of the module in FIG. 3. With this design, the monitor diode 23′ is not integrated in the carrier substrate 21, but instead is integrated in the laser diode 22′ itself. For this purpose a pn-junction is integrated between the VCSEL structure 221 and the substrate (preferably consisting of GaAs) of the laser diode. In this exemplary embodiment, the laser diode 22′ is slightly larger than the receiving diode 24, so that there is the possibility of contacting a common contact of the laser diode 22′ and the integrated monitor diode 23′ by means of one bond wire 9 which is in contact with the carrier substrate 21, or alternatively directly with a leadframe.
In this embodiment too, the substrate of the laser diode 22′ acts as a blocking filter for light emitted in the direction of the receiving diode 24, once said light has passed through the monitor diode 23′.
FIG. 4 shows the bidirectional module 1, 2 in FIGS. 2, 3, 7 as a housed module 10, 20 in a standard housing. The carrier substrate 11, 21 may have here a lens 6 located on the optical axis which forms the emitted or received light for better coupling with a light waveguide. The carrier substrate 11, 21 is arranged on a leadframe 3 which has a central cutout 5 for optical access to the module and provides the contacting for the module 1, 2. Except for the optical access 5, the arrangement of module 1, 2 and leadframe 3 is sprayed so as to encase it in a non-transparent plastic compound. Such housings are known per se, for instance from DE 102 01 102 A1, so they will not be discussed in greater detail.
FIG. 5 shows a subunit 100 with the housed module 10, 20 of FIG. 4 in conjunction with an optical connector receptacle 8 for accommodating a light waveguide. At the same time a flexible conductor 7 with conductor tracks and contact pads is provided for contacting the connection contacts of the module 10, 20. The end of the flexible conductor 7 not connected to the module 10, 20 is connected to a circuit board (not illustrated).
According to FIG. 6 it is possible to install two subunits 100 in accordance with FIG. 5 into the optical connector region 205 of the housing 201 of an optoelectronic transceiver 200. The connector region 205 has here two coupling regions (ports) 203, 204 for one light waveguide in each case. The subunit 100 is electrically connected in each case via the flexible conductor 7 (cf. FIG. 5) to a circuit board 202 of the transceiver 200. A transceiver 200 which is designed to be bidirectional at each port is provided. In comparison with transceivers known hitherto, this enables the transmission capacity to be doubled for the same data rate.
The invention is not restricted to the exemplary embodiments illustrated. For instance, instead of vertical emitting laser diodes it is also possible to use edge-emitting laser diodes, in which case however a deflection optical system would be additionally required.

Claims

1. A module for bidirectional optical signal transmission, the module comprising:

a transmitting component for emitting light of a first wavelength,

a receiving component for detecting light of a second wavelength,

a carrier substrate that is transparent to the light of the first wavelength, on which the transmitting component is arranged, and

a monitor component for detecting a fraction of the light of the first wavelength emitted by the transmitting component,

wherein the receiving component is integrated in the carrier substrate,

wherein the receiving component and the transmitting component are arranged behind one another in relation to a direction of the emitted or detected light,

wherein the receiving component is optically transparent to the light of the first wavelength, and

wherein the light of the first wavelength emitted by the transmitting component is transmitted through the carrier substrate and the receiving component.

2. The module as claimed in claim 1, wherein the transmitting component is mounted on the carrier substrate with its upper side facing down.

3. The module as claimed in claim 1, wherein the receiving component is integrated in the carrier substrate on the side of said substrate facing away from the transmitting component.

4. The module as claimed in claim 1, wherein the receiving component integrated in the carrier substrate forms a pn-junction integrated in the carrier substrate.

5. The module as claimed in claim 3, wherein the carrier substrate has two vias which start from the side of the carrier substrate facing the transmitting component and contact the receiving component.

6. The module as claimed in claim 1, wherein the carrier substrate is not transparent to light of the second wavelength.

7. The module as claimed in claim 1, wherein the first wavelength is greater than the second wavelength.

8. The module as claimed in claim 5, wherein the first wavelength is around 1310 nm, 1490 nm or 1550 nm, and the second wavelength is around 850 nm or 1310 nm.

9. The module as claimed in claim 1, wherein the carrier substrate consists of silicon.

10. The module as claimed in claim 1, wherein the monitor component is arranged on the side of the transmitting component facing away from the carrier substrate.

11. The module as claimed in claim 1, wherein the transmitting component is designed as a laser chip and the monitor component is designed as a monitor diode chip.

12. The module as claimed in claim 1, wherein the monitor component is integrated in the transmitting component on the side of said component facing away from the carrier substrate.

13. A module for bidirectional optical signal transmission, the module comprising:

a transmitting component for emitting light of a second wavelength,

a receiving component for detecting light of a first wavelength,

a carrier substrate that is transparent to the light of the first wavelength and the light of the second wavelength, on which the transmitting component is arranged, and

a monitor component for detecting a fraction of the light of the second wavelength emitted by the transmitting component,

wherein the transmitting component is optically transparent to the light of the first wavelength,

wherein the light of the second wavelength emitted by the transmitting component is transmitted through the carrier substrate, and

wherein the light detected by the receiving component is transmitted through the carrier substrate and the transmitting component.

14. The module as claimed in claim 13, wherein the monitor component is integrated in the carrier substrate.

15. The module as claimed in claim 14, wherein the monitor component is integrated in the carrier substrate on the side of said substrate facing the transmitting component.

16. The module as claimed in claim 14, wherein the monitor component integrated in the carrier substrate forms a pn-junction integrated in the carrier substrate.

17. The module as claimed in claim 13, wherein the monitor component is integrated in the transmitting component.

18. The module as claimed in claim 13, wherein the transmitting component is arranged on the carrier substrate with its upper side facing down.

19. The module as claimed in claim 13, wherein the photosensitive layer of the receiving component is arranged on the side of the receiving component facing away from the transmitting component.

20. The module as claimed in claim 13, wherein the substrate of the transmitting component is not transparent to the emitted light of the second wavelength.

21. The module as claimed in claim 13, wherein the first wavelength is greater than the second wavelength.

22. The module as claimed in claim 21, wherein the first wavelength is around 1310 nm, 1490 nm or 1550 nm, and the second wavelength is around 850 nm or 1310 nm.

23. The module as claimed in claim 13, wherein the carrier substrate consists of sapphire.

24. The module as claimed in claim 13, wherein the transmitting component is designed as a laser chip and the receiving component is designed as a photodiode chip.

25. The module as claimed in claim 13, wherein a band-stop filter is additionally mounted on the transmitting component and/or the receiving component and/or the monitor component.

26. The module as claimed in claim 13, wherein the transmitting component is a vertical emitting laser.

27. A module for bidirectional optical signal transmission, the module comprising:

a carrier substrate comprising a material that is substantially transparent to light of a first wavelength and substantially opaque to light of a second wavelength, the carrier substrate having opposing first and second sides;

a transmitting component mounted on the first side of the carrier substrate and including means for emitting light of a first wavelength through the carrier substrate to the second side;

a monitor component mounted on the first side of the carrier substrate and including means for detecting light of the first wavelength; and

a receiving component mounted on the second side of the carrier substrate and including means for detecting light of the second wavelength,

wherein the receiving component is optically transparent to light of the first wavelength, and

wherein the receiving component is fabricated directly onto a surface of the carrier substrate.