EP1751614A2 - Driving circuit for electro absorption modulator - Google Patents

Driving circuit for electro absorption modulator

Info

Publication number
EP1751614A2
EP1751614A2 EP05741247A EP05741247A EP1751614A2 EP 1751614 A2 EP1751614 A2 EP 1751614A2 EP 05741247 A EP05741247 A EP 05741247A EP 05741247 A EP05741247 A EP 05741247A EP 1751614 A2 EP1751614 A2 EP 1751614A2
Authority
EP
European Patent Office
Prior art keywords
driving circuit
absorption modulator
electro absorption
ghz
filter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05741247A
Other languages
German (de)
French (fr)
Inventor
Edgard Goobar
Henrik ÅHLFELDT
Krister FRÖJDH
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Finisar Corp
Original Assignee
Finisar Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Finisar Corp filed Critical Finisar Corp
Publication of EP1751614A2 publication Critical patent/EP1751614A2/en
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0121—Operation of devices; Circuit arrangements, not otherwise provided for in this subclass

Definitions

  • the present invention relates to a driving circuit for driving of an electro absorption modulator as defined in claim 1, and a use of a driving circuit as defined in claim 10.
  • An electro absorption modulator uses electro absorption in a semiconductor to modulate an optical signal.
  • a common application is for generation of an optical signal for fiber optic transmission.
  • a continuous wave (CW) laser is used to generate light and the EA-modulator is used for adding a high speed modulation on the output from the laser.
  • Very common is to integrate both the laser and the modulator on the same substrate.
  • the laser is single frequency laser (DFB or DBR) .
  • the EA modulator commonly used for long distance transmission (>40 km) at high speed over single mode fiber.
  • the purpose of the invention is to provide a better optical output signal from an electro absorption modulator compared to the above mentioned prior art devices.
  • This purpose is achieved by providing a driving signal as defined in the characterizing portion of claim 1.
  • An advantage with the present invention is that better characteristics are obtained.
  • Figure 1 shows an example of waveform degradation with increasing power according to prior art.
  • Figure 2 shows an example of compensating electrical network.
  • Figure 3 shows a combination of compensating network and peaking network.
  • Figure 4 shows an example of improvement from compensating network as measured on real device.
  • Figure 5 shows an example with no compensating network.
  • Figure 6 shows the same device as in figure 5 with compensating network. Notice the reduced noise on the one level and the larger margin to the central mask.
  • Figure 7 shows two oscilloscope pictures of eight consecutive one followed by eight consecutives zeros. To the left is a transmitter without compensating network and to the right the compensating network has been added.
  • Figure 8 is an example of electrical implementation of the invention.
  • Figure 9 is a typical transfer function of the block diagram shown in figure 2.
  • Figure 10 is a transfer function of the block diagram shown in figure 3.
  • Figure 1 shows the optical power output from an EA-modulator as a function of time.
  • the pulse period is 1.8 ns .
  • the input power is increases in the order of curve 1, 2, 3 and 4.
  • the observed behavior of the EA is nonlinear. However it can be well modulated by a linear first order low pass filter. It is thus possible to rather well compensate it by using an electrical filter.
  • the transmitter performance can be further enhanced by also adding a high frequency peaking.
  • a suitable cut-off is around 3 GHz.
  • An example of this is shown in Figure 3.
  • the peaking is prior-art but it is extra advantageous in combination with the compensating network.
  • a comparison for a real device with and without a compensating network is shown in Figure 4.
  • a real device have first been measured without compensating network and the sensitivity have been measured after 0 km of fiber and 90 km of fiber (represented by lines with open squares) . After the compensating network has been added the device was measured again. As one can see the power needed to obtain transmission was reduced by several dB.
  • the mask margin is improved with the compensating network.
  • the improvement on a module where the compensating network was added can be seen when Figure 5 and Figure 6 are compared.
  • the invention is to use a compensating electrical filter in the driving circuit to an electro absorption modulator.
  • the driving circuit could be represented by a high pass filter with a zero in the range of 0.3 - 1.2 GHz, preferably around 0.6 GHz and a pole at a 10 - 50% higher frequency, preferably around 20%, and should be designed to compensate for the pattern dependence seen in the specific EA-modulator.
  • the pole should be 0.72 GHz when the preferred value of 20% higher frequency is selected.
  • the inventive driving circuit is preferably used for applications where the modulation frequency is higher than 8 GHz.
  • the compensating network can also be added before a linear amplifier or integrated in the DFB-EA itself or on its sub carrier .
  • Figure 8 is an example of an electrical implementation of the invention.
  • a standard circuit consists of a driver circuit with 50 ohm output impedance electro absorption modulator (denominated EAM in the figure) works as a reverse bias diode and has a matching resistor in parallel.
  • the invention is implemented as an inductor L2 and a resistor R2.
  • a typical value for R2 is 200 ohms and for L2 is 30 nH.
  • the invention may naturally be implemented in a different way, as is obvious for a skilled person in the arts, for example the filter may be implemented using a capacitor in parallel with a resistor, where the filter is connected in series between the driver and the EA modulator.
  • An optional second high frequency network can be implemented using Rl and LI where LI should be around 7 nH and R is also 200 ohm.
  • the optional second high frequency network could be represented by a high pass filter with a zero in the range of 1.5 - 8 GHz, preferably around 2.4 GHz and a pole at a 10 - 50% higher frequency, preferably around 20%
  • the pole should be 2.88 GHz when the preferred value of 20% higher frequency is selected.
  • Figure 9 shows a typical transfer function of the shown block diagram in figure 2.
  • the transfer function in figure 9 can be written as:
  • Figure 10 shows the transfer function of the shown block diagram in figure 3.

Landscapes

  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Semiconductor Lasers (AREA)

Abstract

The present invention relates to a driving circuit, and the use of a drving circuit, for the driving of an electro absorption modulator. The driving circuit comprises a high frequency emphases electrical circuit to compensate for a low frequency emphasis of the electro absorption modulator. Preferably, the high frequency emphases electrical circuit comprises at least a first filter having a zero in the range of 0.3 - 1.2 Ghz and a pole at a 10 to 50% higher frequency.

Description

DRIVING CIRCUIT FOR ELECTRO ABSORPTION MODULATOR
Technical field
The present invention relates to a driving circuit for driving of an electro absorption modulator as defined in claim 1, and a use of a driving circuit as defined in claim 10.
Background
An electro absorption modulator (EA-modulator) uses electro absorption in a semiconductor to modulate an optical signal. A common application is for generation of an optical signal for fiber optic transmission. A continuous wave (CW) laser is used to generate light and the EA-modulator is used for adding a high speed modulation on the output from the laser. Very common is to integrate both the laser and the modulator on the same substrate. Typically the laser is single frequency laser (DFB or DBR) . The EA modulator commonly used for long distance transmission (>40 km) at high speed over single mode fiber.
For long distance communication, high output optical power is needed. To increase output power, high input optical power to the EA is used and a short modulator is used to minimize losses. However, one can see a degradation of the output signal when the input power is increased. An example of this is shown in Figure 1. Here a square wave pattern with 0.8 ns "1" followed 0.8 ns "0" is applied to a EA-modulator. The initial peak is generated by some HF-peaking of the electrical driver. However, the initial peak is followed by a relative slow rise of the signal. This could be caused by local thermal heating and cooling of the EA-modulator. The absorption will increase with increasing temperature. Tests have shown this property for modulators from different manufactures so a conclusion is that this is a general problem of a EA-modulator although different design may decrease or enlarge problems. For long distance transmission, higher power and higher reverse bias is needed on the modulator which increase the problem.
This slow rise will give a pattern dependence of the output waveform which will give a transmitter penalty and thus reduce the quality of the transmission. The quality of the sent signals as measured with an optical eye will also show degraded the quality of the measured quality mask margin.
Lower laser power or longer modulator will however reduce the problem.
Summary of the invention
The purpose of the invention is to provide a better optical output signal from an electro absorption modulator compared to the above mentioned prior art devices.
This purpose is achieved by providing a driving signal as defined in the characterizing portion of claim 1.
This purpose is also achieved by using the driving circuit as defined in the characterizing portion of claim 10.
An advantage with the present invention is that better characteristics are obtained.
Brief description of the drawings
Figure 1 shows an example of waveform degradation with increasing power according to prior art. Figure 2 shows an example of compensating electrical network.
Figure 3 shows a combination of compensating network and peaking network.
Figure 4 shows an example of improvement from compensating network as measured on real device.
Figure 5 shows an example with no compensating network.
Figure 6 shows the same device as in figure 5 with compensating network. Notice the reduced noise on the one level and the larger margin to the central mask.
Figure 7 shows two oscilloscope pictures of eight consecutive one followed by eight consecutives zeros. To the left is a transmitter without compensating network and to the right the compensating network has been added.
Figure 8 is an example of electrical implementation of the invention.
Figure 9 is a typical transfer function of the block diagram shown in figure 2.
Figure 10 is a transfer function of the block diagram shown in figure 3.
Detailed description of preferred embodiments
Figure 1 shows the optical power output from an EA-modulator as a function of time. The pulse period is 1.8 ns . The input power is increases in the order of curve 1, 2, 3 and 4.
The observed behavior of the EA is nonlinear. However it can be well modulated by a linear first order low pass filter. It is thus possible to rather well compensate it by using an electrical filter.
An example of this is shown in Figure 2. This network was very effective in reducing the filter behavior. Typically the filter should have a high frequency cut off around 1 GHz.
Higher order filter can also be used but a first order filter seems to be sufficient.
The transmitter performance can be further enhanced by also adding a high frequency peaking. For 10 GHz transmission a suitable cut-off is around 3 GHz. An example of this is shown in Figure 3. The peaking is prior-art but it is extra advantageous in combination with the compensating network. A comparison for a real device with and without a compensating network is shown in Figure 4. In the figure, a real device have first been measured without compensating network and the sensitivity have been measured after 0 km of fiber and 90 km of fiber (represented by lines with open squares) . After the compensating network has been added the device was measured again. As one can see the power needed to obtain transmission was reduced by several dB.
Also the mask margin is improved with the compensating network. The improvement on a module where the compensating network was added can be seen when Figure 5 and Figure 6 are compared.
In Figure 7 one can see that the electrical compensating network modifies the pulse shape to a much more ideal square wave shape .
Initial one must first realize that the EA-modulator has this inherent problem with pattern dependence. The invention is to use a compensating electrical filter in the driving circuit to an electro absorption modulator. The driving circuit could be represented by a high pass filter with a zero in the range of 0.3 - 1.2 GHz, preferably around 0.6 GHz and a pole at a 10 - 50% higher frequency, preferably around 20%, and should be designed to compensate for the pattern dependence seen in the specific EA-modulator.
If the zero was selected to be 0.6 GHz, the pole should be 0.72 GHz when the preferred value of 20% higher frequency is selected.
The inventive driving circuit is preferably used for applications where the modulation frequency is higher than 8 GHz.
The compensating network can also be added before a linear amplifier or integrated in the DFB-EA itself or on its sub carrier .
Figure 8 is an example of an electrical implementation of the invention.
A standard circuit consists of a driver circuit with 50 ohm output impedance electro absorption modulator (denominated EAM in the figure) works as a reverse bias diode and has a matching resistor in parallel. The invention is implemented as an inductor L2 and a resistor R2. A typical value for R2 is 200 ohms and for L2 is 30 nH. The invention may naturally be implemented in a different way, as is obvious for a skilled person in the arts, for example the filter may be implemented using a capacitor in parallel with a resistor, where the filter is connected in series between the driver and the EA modulator. An optional second high frequency network can be implemented using Rl and LI where LI should be around 7 nH and R is also 200 ohm. The optional second high frequency network could be represented by a high pass filter with a zero in the range of 1.5 - 8 GHz, preferably around 2.4 GHz and a pole at a 10 - 50% higher frequency, preferably around 20%.
If the zero was selected to be 2.4 GHz, the pole should be 2.88 GHz when the preferred value of 20% higher frequency is selected.
Figure 9 shows a typical transfer function of the shown block diagram in figure 2. The transfer function in figure 9 can be written as:
1 + -
0.82 2 r(λ c 6125 where s = jω and ω = 2πf 1 + - 2π0.15
Figure 10 shows the transfer function of the shown block diagram in figure 3.

Claims

Claims
1. A driving circuit for the driving of an electro absorption modulator, characterized in that the driving circuit comprises a high frequency emphases electrical circuit to compensate for a low frequency emphasis of the electro absorption modulator.
2. The driving circuit according to claim 1, wherein the high frequency emphases electrical circuit comprises at least a first filter having a zero in the range of 0.3 - 1.2 GHz and a pole at a 10 to 50% higher frequency.
3. The driving circuit according to claim 2, wherein the first filter has a zero at approximately 0.6 GHz and a pole at an approximately 20% higher frequency.
4. The driving circuit according to any of claims 2-3, wherein the frequency emphases electrical circuit further comprises a second filter having a zero at 1.5 to 8 GHz and a pole at a 10 to 50% higher frequency.
5. The driving circuit according to claim 4, wherein the second filter has a zero at approximately 2.4 GHz and a pole at an approximately 20% higher frequency.
6. The driving circuit according to any of claims 4-5, wherein the second filter is implemented in a driving circuit in parallel with the electro absorption modulator and comprises a resistor and inductor coupled in series.
7. The driving circuit according to any of claims 2-6, wherein the first filter is implemented in a driving circuit in parallel with the electro absorption modulator and comprises a resistor and inductor coupled in series.
8. The driving circuit according to any of the preceding claims, wherein the modulation frequency of the electro absorption modulator is higher than 8 GHz.
9. The driving circuit according to any of the receding claims, wherein the electro absorption modulator is integrated with a laser.
10. The use of a driving circuit for driving an electro absorption modulator, characterized in that the driving circuit comprises the features according to any of claims 1-9.
EP05741247A 2004-05-13 2005-05-13 Driving circuit for electro absorption modulator Withdrawn EP1751614A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0401235A SE528443C2 (en) 2004-05-13 2004-05-13 Electro absorption modulator drive circuit
PCT/SE2005/000688 WO2005110004A2 (en) 2004-05-13 2005-05-13 Driving circuit for electro absorption modulator

Publications (1)

Publication Number Publication Date
EP1751614A2 true EP1751614A2 (en) 2007-02-14

Family

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Family Applications (1)

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EP05741247A Withdrawn EP1751614A2 (en) 2004-05-13 2005-05-13 Driving circuit for electro absorption modulator

Country Status (4)

Country Link
EP (1) EP1751614A2 (en)
CN (1) CN1981234A (en)
SE (1) SE528443C2 (en)
WO (1) WO2005110004A2 (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101702489B (en) * 2009-11-05 2011-12-28 中兴通讯股份有限公司 Biasing circuit of electro-absorption modulated laser and debugging method thereof
US8896352B2 (en) * 2011-10-21 2014-11-25 Taiwan Semiconductor Manufacturing Company, Ltd. Drivers having T-coil structures
CN102820918B (en) * 2012-08-13 2015-09-02 苏州海光芯创光电科技有限公司 There is integrated optical chip and the high speed optical communication device of high frequency precompensation
CN103399418B (en) * 2013-07-23 2016-01-20 清华大学 Compensate electroabsorption modulator non-linear method and device
CN103457154B (en) * 2013-08-29 2015-10-28 烽火通信科技股份有限公司 With the integrated optical communication laser driver of preemphasis
CN109495185B (en) * 2018-11-14 2020-12-22 青岛海信宽带多媒体技术有限公司 Optical module

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1324102A2 (en) * 2001-12-13 2003-07-02 Nec Corporation Optical modulation system applying a highly stable bias voltage to an optical modulator

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1324102A2 (en) * 2001-12-13 2003-07-02 Nec Corporation Optical modulation system applying a highly stable bias voltage to an optical modulator

Also Published As

Publication number Publication date
CN1981234A (en) 2007-06-13
SE0401235D0 (en) 2004-05-13
WO2005110004A3 (en) 2006-04-27
SE0401235L (en) 2005-12-28
SE528443C2 (en) 2006-11-14
WO2005110004A2 (en) 2005-11-24

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