DE10064577A1 - Control arrangement in optical transmission/reception module, includes circuit board with radio frequency lines which are connected to package terminals in parallel to board plane - Google Patents

Abstract

The circuit board (6) of the module has a set of radio frequency (RF) lines (82). The terminals (41,42) of a transistor outline (TO) package (1), are connected to the lines in parallel to the board plane.

Description

Designation of the invention: Arrangement for operating a optical transmitter or receiver module with high data rates up to at 10 Gbit / s.

The invention relates to an arrangement for operating a optical transmitter or receiver module with high data rates up to at 10 Gbit / s according to the preamble of claim 1.

It is known in optical transmission or reception modules so-called TO (transistor outline) packages at data rates use up to 622 Mbit / s. TO housings are in the state of the Technology known standard housing for optical transmission or Receiving modules, the shape of which is the housing of a (classic) Transistor resembles, however, at the top one Have glass windows for light entry and exit. As a coaxial Laser modules are modules that are a TO laser module included and where a glass fiber to the TO laser module is coupled.

Such a TO housing, known from WO 99/57594, is shown schematically in FIG. 3. The TO housing 1 contains a transmission or reception module 2 . The transmitter module 2 is preferably arranged on a carrier 3 made of silicon. The essential components of the transmitter module 2 , which is also referred to as a laser submount, are a laser chip 21 , deflection prisms 22 , 23 on both sides of the laser chip 21 , a coupling lens 24 and a monitor diode 25 .

The TO housing 1 has a base plate with four electrical feedthroughs, of which only two are shown. The HF signal (data signal) is fed into the interior of the housing via an insulated, for example glassed-in pin 42 and there is electrically connected to the laser chips 21 via bond wires or ribbons. The laser module is supplied with bias current via a further feed-through pin 41 or, if the bias current is provided with the RF signal via pin 41 , connected to ground. The pins, not shown, are used to control the monitor diode 25 .

Via the window of the TO housing 1 there is a coupling to an optical waveguide which couples the light from the laser chip 21 or, if the arrangement is designed as a receiving module in principle with the same structure, couples out light for detection by the receiving chip.

The advantage of using TO packages is low Housing costs and established manufacturing facilities that enable high quantities at low manufacturing costs. When using high data rates, however, the problem arises that TO packages have poor RF characteristics that are caused by comparatively long bond wires in the TO Housing, the carrying capacity of the glazed Enclosures and the generally undefined HF properties of the connection of the TO connection legs with a control board.

Due to the poor RF characteristics when using To date, TO enclosures have been used for high data rates Receiving modules used in so-called butterfly housings. However, such butterfly housings are much more expensive than TO- Casing.

The present invention has for its object a Arrangement for operating an optical transmitter or To provide the receiving module when in use the cost-effective TO structure even with high data rates up to 10 Gbit / s can be used.

This object is achieved by an arrangement with solved the features of claim 1. Preferred and advantageous embodiments of the invention are in the Subclaims specified.  

According to the invention it is provided that the arrangement is a TO housing with an optical transmitter or receiver module and a circuit board for electrical contacting of the electrical connections of the TO housing, wherein the circuit board has RF lines and the electrical connections in an arrangement parallel to Board level are connected directly to the RF lines. The the HF lines are preferably planar lines with defined characteristic impedance, especially as Microstrip lines formed on the electrical Connections in parallel position can be soldered on immediately.

By connecting the connection legs of the TO housing in parallel arrangement directly on the RF lines is a good field adaptation between the HF line and the TO Achievements achieved so that the RF characteristics of the Arrangement are improved.

The use of RF lines with a defined wave impedance enabled the wave impedance of the RF lines optimal to the impedance of the transmitter or receiver module adapt. For this purpose, an adaptation to the frequency-dependent impedance of the transmitting or receiving element of the module and its submount in the TO housing, to which Bond connections to the connector pins of the transmit or Receiving module and the wave impedance of the bushings the electrical connections or pins of the TO housing.

The RF lines of the board are preferred as micro stri pipelines (stripline) or coplanar lines educated. However, there are other planar RF lines used.

If the transmitter module is a directly modulated laser has, the wave resistance of the RF lines preferably 30-50 ohms. If the transmitter module one  Electro absorption modulator (EAM), which is a per se constant laser signal corresponding to a high frequency RF-modulated data signal, the characteristic impedance is RF lines preferably 50-80 ohms.

In a further aspect of the invention it is provided that the RF circuit board a matching circuit for Adaptation of the impedance between the transmitter or receiver module and a driver or arranged on the board Has amplifier circuit. This ensures a particularly effective and trouble-free adjustment of the usually low-resistance semiconductor laser (typically 3 to 5 ohms) to the impedance of a driver circuit (usually 25 or 50 ohms), which makes the high-frequency Properties of the laser module can be significantly improved.

If the receiving module has a photodiode as the receiving chip has, this is usually a preamplifier assigned. In this case, the adaptation circuit ensures an adjustment between the preamplifier and that on the RF PCB located RF line or data line.

It is in the event that the transmitter module one Has semiconductor laser and this with signals one the RF circuit arranged driver circuit is applied is preferably provided that the adaptation circuit for a differential (symmetrical) control of the Transmitter module is designed by the driver circuit. An embodiment of a receiver module is also included differential (symmetrical) outputs of the preamplifier possible.

Alternatively, the matching circuit is for a single-ended Control of the transmitter module designed. The symmetrical Control has, however, compared to single-ended control the advantage that because of the use of both driver outputs  a higher signal swing for modulating the semiconductor laser Available.

The adaptation circuit preferably has at least one Resistance on the impedance of the semiconductor laser Adapts driver circuit.

In a preferred development of the invention, the RF circuit board a bias circuit for generation a bias for the transmitter or receiver module integrated. The bias circuit preferably has a broadband RF choke. This serves an HF Blocking the bias current connection of the semiconductor laser. The choke is, for example, a coil with a ferrite core.

The bias circuit and the matching circuit are preferably integrated in a circuit. In a preferred embodiment, this circuit has:

• - at least a first resistance,
• - An RF choke connected to a voltage source, the the semiconductor laser via the first resistor with a Preloaded and
• - Another resistor, one of which is connected to ground and its other connection with the first resistor connected is.

A second, with the first, is also preferred Resistor in series resistance is provided, whereby the further resistance with its one connection between the Connection point of the two resistors connected in series is laid.

The throttle is preferred over a relatively small capacity additionally switched to ground. This will make the HF Signal better from the bias (bias) supply  blocked. The capacity is on the "cold side" of the Throttle arranged.

In a preferred aspect of the invention, provided that Lines of the adaptation and / or the bias circuit designed as planar RF lines and those in the circuit used components in SMD (Surface Mounted Device) - Technology are carried out, i.e. directly on the PCB can be placed, the planar HF tracks as Solder pads for the SMD components. This avoids the components over otherwise required solder pads on the Fasten the circuit board. By the solder pads or by them trained area would be the wave resistance of the Traces changed. In particular, the solder pads an excessively large additional capacity is formed, which the Realization of the desired bandwidth of 10 Gbit / s would stand in the way.

Microstrip lines are preferred as planar Lines used and serve as the microstrip lines Soldering area for the SMD components.

In a preferred development of the invention, the HF Circuit board a two-layer board, one Connection of the TO housing with HF cables on the top the board and a second connection of the TO housing connected to a ground plane on the underside of the board is. If the TO housing has more than two electrical Has connections, for example with additional Using a monitor diode is the circuit board preferably a multi-layer, in particular four-layer circuit board, preferred the connections of the pins for the monitor diode lie on the underside of the multilayer board and through the Ground level are decoupled from the RF lines.

The TO housing is advantageously located directly on the edge of the board arranged. Accordingly, the electrical  Connections of the TO housing immediately with the HF lines of the Circuit board contacted and there are therefore no significant reflection points for the RF signal.

To improve the RF properties of the TO housing preferably provided that the bonding wires in the TO housing be kept as short as possible to the total inductance to keep low. To realize small inductors, may be parallel bonds or multiple bonds provided.

In the event that the optical transmitter or receiver module with one receiver module is provided, there is another preferred measure to improve the RF properties of the TO module in it, the impedance of the housing bushing of the TO Housing to the value of the impedance of the output of the To adapt the receiver module.

Furthermore, it is preferably provided at the exit of the TO-Ge a short piece of stripline with a high Insert wave resistance. This will increase the Frequency response of the TO housing reached.

The invention is described below with reference to the Figures of the drawing based on several embodiments explained in more detail. Show it:

FIG. 1a an embodiment of a formed on an RF board matching circuit for a laser module TO- with single-ended drive;

FIG. 1b shows a first embodiment of a matching circuit for a laser module with TO-differential driving;

FIG. 1c shows a second embodiment of a matching circuit for a TO-laser module with symmetric control;

Fig. 1d shows a third embodiment of a matching circuit for a TO-laser module with symmetric control;

FIG. 2a shows an inventive arrangement processing board with a scarf, a realized on the circuit board matching circuit for a Lasermo dul with single-ended drive and a TO- laser module;

FIG. 2b shows an inventive arrangement with an RF circuit board, a realized on the circuit board drive circuit for a laser module with symmetric control TO- and a TO-laser module, and

Fig. 3 is a schematic representation of a TO module according to the prior art.

The invention is first explained using the exemplary embodiment in FIG. 2a. As explained at the beginning with reference to FIG. 3, a transmitting or receiving module is arranged in a TO housing 1 in a manner known per se. The TO housing 1 with the transmitting or receiving module is also referred to below as a TO module. Furthermore, the transmission or reception module, if it has a transmission device, is referred to as a transmission module and, if it has a reception device, as a reception module.

The TO housing 1 has two legs or pins 41 , 42 for controlling the transmission or reception module as electrical feed lines. The pin 41 is connected to the bottom of the TO housing (ground pin of the TO housing), while the pin 42 is glazed in the bottom of the TO housing and is therefore isolated from the housing 1 .

Only two feed lines are shown in FIG. 2a. Usually, a transmitter module additionally has a monitor diode for monitoring the transmission power. For such a case, additional feed lines 43 , 44 are provided, as shown schematically in FIG. 2a below.

The RF board 6 has on its upper surface 61, a matching circuit 7 for a single-ended drive to the transmission module. This circuit will be explained in more detail later with reference to FIG. 1a.

The surface 61 of the HF circuit board 6 also has a microstrip line 82 as a contact pad for the pin 42 and a ground area 81 as a contact pad for the pin 41 . The line 81 is electrically connected to a ground surface formed on the underside 62 of the circuit board 2 via plated-through holes 9 (so-called "duks" or "vias").

The connections between the individual components of the matching circuit 5 and the leads for this purpose are likewise designed as planar RF lines, in particular as microstrip lines.

The TO housing 1 is fastened to the edge of the pallet in such a way that the pins 41 , 42 are soldered to the microstrip people 81 , 82 in a parallel, horizontal arrangement and are arranged parallel to them in the fastened state. The gap between the TO housing 1 and the edge of the board is kept as small as possible in order to prevent reflection points for the RF signal from occurring.

The wave impedance of the RF lines on the RF board 2 is optimally adapted to the frequency-dependent impedance of the transmitter element and its submount in the TO housing 1 and the glassed bushings of the pins 11 , 12 through the housing base. The characteristic impedance of the bushings is calculated using the known formula for a coaxial line and optimized by appropriately dimensioning the ratio pin diameter / hole diameter.

For a TO transmitter module 1 with a directly modulated laser, the microstrip line 82 preferably has a value between 30 and 50 ohms. If the TO transmitter module is operated with an electro absorption modulator (EAM), the miniature trip line 82 preferably has a value of 50 ohms to 80 ohms.

When using a laser module, which additionally has a monitor diode for regulating the optical power and corresponding further pins 43 , 44 , a four-layer multilayer board is advantageously used instead of a single-layer circuit board according to FIG Location contains the ground area for the RF cables. The connections of pins 43 , 44 for the monitor diode can then be on the underside of the multi-layer board (bottom layer), so that they are decoupled from the HF lines by the ground plane.

In Fig. 2b in fundamentally the same structure, a matching circuit 7 'for symmetrical control of the TO-module is shown. The circuit will be explained in more detail below with reference to FIGS. 1b to 1d.

Are two legs / pins 42, 45 of the TO package 1 in parallel arrangement on two microstrip lines 82, 83 directly soldered, with the legs 42, 45 substantially over their entire length with the microstrip lines 82, 83 are electrically connected. This significantly improves the high-frequency properties of the coupling.

It is pointed out that the adaptation circuit 7 , 7 'in FIGS. 2a, 2b and also the following FIGS. 1a-1d is only shown schematically. The circuit must be carried out in the usual way for microwave circuits. In particular, the connections of the components are carried out with adapted lines, in particular via microstrip lines. Ground connections are made through vias to the ground surface. The components used are RF-compatible and are used with an appropriately adapted size.

It is provided that the components of the circuits are designed as SMD (Surface Mounted Device) components and are attached to the circuit board surface 62 in such a way that the microstrip lines themselves serve as solder pads. This means that the wave resistance of the conductor tracks on the circuit board is not changed by solder pads that are otherwise required for SMD assembly.

Fig. 1a shows a matching circuit 7 for a TO-can having a laser diode. In the exemplary embodiment shown, the matching circuit has three resistors R1, R2, R3 and an RF choke L. The resistors R1 and R2 are connected in series and connected between a driver circuit (not shown), which generates a high-frequency data signal D for controlling the laser diode, and a light-emitting diode LD. In the exemplary embodiment shown, a blocking capacitor C2 is located between the driver circuit and the resistor R1, which only allows high-frequency signals to pass through.

Resistor R3 is connected across resistors R1, R2 and has one end connected to ground. It is at the same time parallel to an RF choke L, which is connected to a voltage source and outputs a bias current Ibias or a bias voltage via the resistor R2 to the laser diode. The HF choke L is preferably provided with a ferrite core, in particular a tapered ferrite core or a winding with a tapered variable pitch of the winding on the ferrite core. For a better decoupling of the RF signal from the bias supply, the "cold side" of the choke, that is to say the side on which no RF signal is present, is additionally connected to ground with a small capacitance C1, as in FIG. 1a, in an alternative embodiment indicated.

To improve the HF properties, it can also be provided that the HF choke L is additionally connected in series with a resistor corresponding to the resistor R4 in FIG. 1d.

The resistors R1, R2, R3 and the inductor L are preferred executed as SMD components and are immediately on Microstrip tracks placed on the components connect. The conductor tracks are thus themselves used as solder pads used, which means the use of additional solder pads on the PCB becomes superfluous.

If a ceramic board is used as the board, it is provided hen, the resistors R1, R2, R4 as film resistors to in tegrieren.

FIG. 1b shows an adaptation circuit 7 'for a laser module with differential (symmetrical) control with basically the same structure. In the case of a symmetrical control, the laser diode LD is acted upon by a driver with a data signal D, D *. The data signal D * is inverted with respect to the data signal D.

The adaptation circuit 7 'forms two circuit branches for the data signals D and D * with components R1, R2, R3, L and R1 *, R2 *, R3 *, L *. The two circuit branches each correspond to the circuit of FIG. 1a, so that reference is made to the relevant statements. The resistors R1, R1 * etc. and inductors L, L * are each identical.

The symmetrical control used in FIG. 2b has considerable advantages over a single-ended control according to FIG. 2a. Since both driver outputs are used, a higher signal horn is available for modulating the laser. As a result, either the extinction of the modulated laser signal can be increased or the adaptation can be improved by selecting the resistors R1-R3 accordingly.

A driver circuit generally has a strongly frequency-dependent output impedance, so that a good adaptation to the load is difficult. The symmetrical control partially compensates for this mismatch. In addition, the effective inductance of the bond wires is reduced compared to single-ended control. If, for example, the bond inductances from pin 42 to the laser diode and from the laser diode to pin 41 were the same in the two versions of FIGS. 2a, 2b, then the bond inductance effective for the driver output stage would be halved in the symmetrical control compared to the single-ended control.

In Fig. 1c is a variant of the matching circuit is shown at symmetric control of the laser module, in which the resistor R3 connects the two circuit arms for the data signal D and data signal D * and thereby has twice the resistance value.

In Fig. 1d, the resistor R3 is not directly connected to ground, but rather via a small capacitor C3, C3 *, which has a value of 220 pF, for example. This reduces the circuit's direct current requirement.

Preferred values for R1, R2 and R3 in FIGS. 1a to 1d are with a single-ended control of the laser module and with an adaptation to an output resistance of a driver of 50 ohms:
R1 = 0 ohm-47 ohm
R2 = 8 ohms-20 ohms
R3 = 50 ohm-∞.

Preferred values for R1, R2 and R3 (or for R1 *, R2 *, R3 *) with a symmetrical control of the laser module and with an adaptation to an output resistance of a driver of 50 ohms:
R1 = 0 ohms-25 ohms
R2 = 4 ohms-10 ohms
R3 = 50 ohm-∞.

Reduce low values of R1 and R2 or high values of R3 like the signal attenuation of the adaptation circuit. You surrender but generally a worse adjustment.

If a laser with an integrated electro-absorption modulator is used instead of a directly modulated laser chip, then the following preferred values for the matching resistances exist for a single-ended control:
R1 = 10 ohms-30 ohms
R2 = 6 ohms-12 ohms
R3 = 50 ohms-400 ohms.

The following values are preferred for symmetrical control:
R1 = 5 ohms-12 ohms
R2 = 3 ohms-6 ohms
R3 = 25 ohms-200 ohms.

The internal structure of the TO module of FIGS. 2a, 2b is to be carried out with high reproducibility, so that the RF properties of the transmitting or receiving module can be reproduced. In particular, the position and length of the bond wires within the TO module must be precisely defined. The bond connections in the TO housing must be kept as short as possible to improve the HF properties. If necessary, several bonds must be placed in parallel (multiple bonds) or bonded with a ribbon. This keeps the total inductance as low as possible. In the case of a transmitting or receiving module with a receiver chip, the necessary pads for bonding or multiple bonding are to be provided on this.

If the TO housing contains a receiver module, the further the impedance of the TO housing bushing to the value to adapt the output of the corresponding receiver component. Its impedance is usually 50 ohms.

In a variant of the invention, not shown, a short piece of a device with a high characteristic impedance is inserted at the output of the TO housing 1 . As simulation has shown, this leads to an increase in the frequency response of the TO housing at high frequencies.

In particular the combination of the measures described above leads to a flat frequency response of the TO housing up to a frequency of approx. 7 to 10 GHz. So that's one Design can also be used for data rates of 12.5 Gbit / s.

It should be noted that those described above Features to improve the RF properties of the device not with TO housing and HF circuit board must necessarily be trained at the same time. each these features can be done by themselves and without further shown features can be realized. In particular provide the provision of an RF matching circuit which in horizontal connection of the pins of the TO-  Housing on planar RF conductors the RF board as well Fastening components made in SMD construction directly and without additional solder pads on the planar HF lines of the RF board aspects of the invention, which also for taken and not in combination with other measures can be realized.

Claims (22)

1. Arrangement for operating an optical transmission or reception module at high data rates up to 10 Gbit / s, with
a TO housing with electrical connections,
an optical transmitter or receiver module, which is arranged in the TO housing and
a circuit board for electrical contacting of the electrical connections of the TO housing,
characterized by
that the circuit board ( 6 ) has RF lines ( 82 , 83 ) and the electrical connections ( 41-45 ) are connected in an arrangement parallel to the board level with the RF lines. 2. Arrangement according to claim 1, characterized in that the RF lines are designed as planar lines with a defined characteristic impedance, in particular as microstrip lines ( 82 , 83 ), to which the electrical connections ( 41-45 ) are soldered directly in a parallel position. 3. Arrangement according to claim 1 or 2, characterized in that the characteristic impedance of the HF lines ( 82 , 83 ) is adapted to the impedance of the transmitting or receiving module. 4. Arrangement according to at least one of claims 1 to 3, wherein the transmitter module has a directly modulated semiconductor laser, characterized in that the characteristic impedance of the RF lines ( 82 , 83 ) is 30 to 50 ohms. 5. Arrangement according to at least one of claims 1 to 3, in which the transmitter module has an electroabsorption modulator, characterized in that the characteristic impedance of the RF lines ( 82 , 83 ) is 50 to 80 ohms. 6. Arrangement according to at least one of the preceding claims, characterized in that in the RF circuit board, an adaptation circuit ( 7 , 7 ') for adapting the impedance between the transmitter or receiver module (LD) and a driver arranged on the board ( 6 ) - or amplifier circuit is integrated. 7. Arrangement according to claim 6, in which the transmitter module has a semiconductor laser and this is acted upon by signals from a driver circuit arranged on the HF circuit board, characterized in that the adaptation circuit ( 7 ') for a symmetrical control of the transmitter or receiver module (LD ) is designed by the driver circuit. 8. Arrangement according to claim 6, in which the transmitter module has a semiconductor laser and this is acted upon by signals from a driver circuit arranged on the HF circuit board, characterized in that the adaptation circuit ( 7 ) for a single-ended control of the transmitter or receiver module ( LD) is designed by the driver circuit. 9. Arrangement according to at least one of claims 8 to 10, in which the transmitter module has a semiconductor laser and this is acted upon by signals from a driver circuit arranged on the HF circuit board, characterized in that the matching circuit ( 7 , 7 ') has at least one resistor ( R1, R2, R3), which adapts the semiconductor laser (LD) to the impedance of the driver circuit. 10. The arrangement according to at least one of the preceding claims, characterized in that a bias circuit for generating a bias voltage for the transmitter or receiver module (LD) is integrated on the RF circuit board ( 6 ). 11. The arrangement according to claim 10, characterized characterized in that the bias circuit is a broadband RF choke (L) comprises. 12. The arrangement according to claim 6 and 10, characterized in that the bias circuit and the matching circuit are integrated in a circuit ( 7 , 7 '). 13. Arrangement according to claim 12, in which the transmitter module has a semiconductor laser and this is acted upon by signals from a driver circuit arranged on the HF circuit board, characterized in that the circuit comprises:
at least one first resistor (R2),
an RF choke (L) connected to a voltage source, which biases the semiconductor laser (LD) via the first resistor (R2) and
a further resistor (R3), one terminal of which is connected to ground and the other terminal of which is connected to the first resistor (R2). 14. Arrangement according to claim 13, characterized characterized in that the throttle (L) has a relative small capacitance (C1) is also connected to ground. 15. The arrangement according to at least one of claims 6 to 14, characterized in that
the lines of the matching and / or the bias circuit are designed as planar RF lines,
the components used in the circuit (R1, R2, R3, L) are executed in SMD technology and thereby
the planar HF tracks serve as solder pads for the SMD components (R1, R2, R3, L). 16. The arrangement according to claim 15, characterized characterized in that microstrip lines of the circuit serve as solder pads for the SMD components. 17. The arrangement according to at least one of the preceding claims, characterized in that the RF circuit board ( 6 ) has two layers, a first connection ( 42 ) of the TO housing ( 1 ) with RF lines on the top ( 61 ) of the board ( 6 ) and a second connection ( 41 ) of the TO housing ( 1 ) with a ground surface on the underside ( 62 ) of the board ( 6 ) is connected. 18. Arrangement according to at least one of the preceding Claims, characterized in that the HF Circuit board is a multi-layer board. 19. The arrangement according to at least one of the preceding claims, characterized in that the TO housing ( 1 ) is arranged directly on the edge of the board. 20. Arrangement according to at least one of the preceding claims, characterized in that short bonding connections are provided in the TO housing ( 1 ). 21. The arrangement according to at least one of the preceding claims, wherein the receiving module has a receiver module, characterized in that the impedance of the housing bushing of the TO housing ( 1 ) is adapted to the value of the impedance of the output of the receiver module. 22. The arrangement according to at least one of the preceding claims, characterized in that a short piece of a strip line with high impedance is inserted at the output of the TO housing ( 1 ).