WO2010139144A1

WO2010139144A1 - Optical module and control method thereof

Info

Publication number: WO2010139144A1
Application number: PCT/CN2009/073891
Authority: WO
Inventors: 曹建光
Original assignee: 中兴通讯股份有限公司
Priority date: 2009-06-05
Filing date: 2009-09-11
Publication date: 2010-12-09
Also published as: CN101592762B; CN101592762A

Abstract

A wavelength tunable optical module comprises an electro-absorption laser, a temperature detecting circuit, a negative feedback temperature control circuit, and a Bragg voltage control circuit. The electro-absorption laser comprises a thermistor, a thermoelectric refrigerator, and Bragg gratings. The thermistor, the temperature detecting circuit and the negative feedback temperature control circuit are connected successively to form an automatic temperature control circuit. The Bragg voltage control circuit is connected to the Bragg gratings and is used for controlling the voltage applied on the Bragg gratings to vary the reflectivity of the Bragg gratings, so as to adjust the wavelength of the electro-absorption laser to a predetermined range. The automatic temperature control circuit is used for controlling the temperature of the electro-absorption laser to a designed working temperature, so as to adjust the wavelength of the electro-absorption laser to a predetermined value. The tune of wavelength is consequently achieved.

Description

Optical module and control method thereof

Technical field

The present invention relates to optical transmission technologies, and in particular to an optical module and a control method thereof.

Background technique

As a key component in optical transmission systems, optical modules largely determine the performance of optical transmission systems. The optical module converts the electrical signal to the optical fiber through electro-optical conversion, and simultaneously receives the optical signal transmitted from the remote end, and converts the optical signal into an electrical signal, thereby implementing optical signal transmission and reception. In the booked DM (Dense Wavelength Division Multiplexing) system, the operating wavelength of the laser is to comply with ITU-T G.692 (G. 692 of the International Telecommunication Union Telecommunication Standardization Group) for G. 652/G. 655 The minimum channel spacing of the fiber is 50 GHz or 100 GHz for specific wavelength requirements. At present, in optical transmission systems, non-wavelength tunable optical modules are commonly used. Since non-wavelength tunable optical modules can only produce a certain wavelength, each specific wavelength is separately prepared during production, which increases the stock of stock preparation. The amount of production has been greatly increased.

The new reconfigurable network architecture requires wavelengths to be adjustable. Some manufacturers (such as Inte l, Bookham, Santur) have introduced full-band tunable lasers for wavelength-tunable functions. Although the technologies of various manufacturers are different, they are generally costly, complex, and consume large amounts of power. Disadvantages such as modulators.

Summary of the invention

In view of the above, the present invention provides an optical module and a control method thereof, which not only realize a wavelength tunable function, but also have low cost.

In order to solve the above technical problems, the present invention uses the following technical solutions:

An optical module comprising an electroabsorption laser, a temperature detecting circuit, a negative feedback temperature control circuit, and a Bragg voltage control circuit, the electroabsorption laser comprising a thermistor, a thermoelectric cooler, a Bragg grating; a grid voltage control circuit coupled to the Bragg grating, the reflection coefficient of the Bragg grating being changed by controlling the Bragg grating voltage;

The thermistor, the temperature detecting circuit and the negative feedback temperature control circuit are sequentially connected to form an automatic temperature control circuit, and the automatic temperature control circuit controls the temperature of the electroabsorption laser to reach a design working temperature, and the electroabsorption laser is detected. When the temperature is higher than the design working temperature, the thermoelectric cooler is started to be cooled; when the temperature of the electroabsorption laser is detected to be lower than the design working temperature, the thermoelectric cooler is started to be heated;

Thereby tuning of the wavelength of the optical module is achieved.

The optical module further includes a backlight detecting diode, a backlight current detecting circuit, and a negative feedback driving current control circuit, wherein the backlight detecting diode is built in the electric absorption laser, and the backlight current detecting circuit and the negative feedback driving current control circuit are sequentially Connected, an automatic optical power control circuit is constructed, and the automatic optical power control circuit performs feedback adjustment on the driving current of the laser according to the detected laser output optical power.

In the above optical module, the negative feedback driving current control circuit includes a transimpedance amplifier and a comparator, and the transimpedance amplifier is configured to perform the photo-generated current after the backlight detecting diode converts the laser output optical power into a photo-generated current. Performing transimpedance amplification and converting into a voltage and inputting to the comparator;

The comparator is arranged to compare the voltage input by the transimpedance amplifier with a set voltage and to adjust the laser drive current by comparing the differences.

In the above optical module, the Bragg voltage control circuit includes a digital-to-analog conversion circuit and an emission-accumulating buffer circuit.

The digital to analog conversion circuit is configured to output a voltage control signal to the shot following amplification buffer circuit; the shot following amplification buffer circuit is configured to buffer the voltage control signal and input the Bragg grating.

In an embodiment of the optical module, the optical module includes an OGBi t/S optical module.

The invention also discloses a control method of an optical module, comprising the following steps:

Setting a control value of an eye intersection and an extinction ratio of the electroabsorption laser; Adjusting the Bragg voltage of the electroabsorption laser by a Bragg voltage control circuit, so that the wavelength of the electroabsorption laser is adjusted to a preset range;

Adjusting the operating temperature of the electroabsorption laser to a design operating temperature by an automatic temperature control circuit, so that the wavelength of the electroabsorption laser is adjusted to a preset value;

The output optical power of the electroabsorption laser is adjusted by an automatic optical power control circuit.

In the optical module of the invention, the Bragg grating voltage is controlled by the Bragg voltage control circuit to change the reflection coefficient of the Bragg grating, so that the grating can be completely transmitted for a specific wavelength, and the other wavelengths are reflected, reaching a wide range of wavelength tuning, through automatic temperature control The circuit control laser reaches the design working temperature, and when the laser temperature is detected to be higher than the design working temperature, the thermoelectric cooler is started for cooling; when the laser temperature is detected to be lower than the design working temperature, the thermoelectric cooler is started to be heated; Range of wavelength tuning and stabilization of the laser output wavelength.

BRIEF abstract

1 is a schematic diagram of a photoelectric conversion implementation of an embodiment of the present invention;

2 is a circuit diagram of a peripheral control circuit of a laser according to an embodiment of the present invention;

3 is a flow chart of debugging an electro-optical conversion part of a module according to an embodiment of the present invention;

4 is a block diagram of a tunable optical module according to an embodiment of the present invention;

FIG. 5 is a circuit diagram of an automatic optical power control implementation according to an embodiment of the present invention; FIG.

6 is a circuit diagram of a laser die temperature control implementation according to an embodiment of the present invention;

Figure 7 is a circuit diagram showing the implementation of a BRAG control in accordance with an embodiment of the present invention.

Preferred embodiment of the invention

The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The optical module of the present invention is mainly a narrowband tunable optical module for use in a 10G DM (Dense Wavelength Division Multiplexing) optical fiber transmission system to provide high-speed electrical/optical, optical/electrical conversion for digital optical fiber communication. It has an in-line wavelength tunable function that meets the specific wavelength requirements of the minimum channel spacing of 50 GHz or 100 GHz as specified by ITU-T G.692. As shown in Fig. 1, in terms of photoelectric conversion, the input optical signal is converted into an electrical signal via a photodiode (APD), and the electrical signal can be transmitted to an external electrical interface.

On the other hand, in order to realize electro-optic conversion, a tunable electro-absorption laser with refrigeration is used. The electrical signal to optical signal conversion function is realized by a built-in electro-absorption (EA) modulator and an external EA laser driver. Through the driver control circuit, the control end of the EA laser driver can be adjusted to achieve the specification of the laser optical interface.

In order to achieve wavelength online tunability, the laser is controlled by a peripheral laser control circuit to achieve online tuning between specific wavelengths as specified by ITU-T G.692.

The peripheral control circuit of the laser and its connection control with the internal structure of the laser are shown in Fig. 1, which includes an automatic optical power control circuit, an automatic temperature control circuit, and a voltage control circuit.

Among them, the automatic optical power control circuit is used to adjust and stabilize the output power of the laser. As shown in FIG. 2, the automatic optical power control circuit includes a backlight detection diode (PD), a backlight current detection circuit, a negative feedback drive current control circuit, a backlight detection diode built-in laser, a backlight current detection circuit, and a negative feedback drive current control circuit. Connected in turn, by detecting the photo-generated current of the backlight detection diode (PD), the output optical power of the laser can be detected, using the output optical power of the laser as the feedback amount, using the PID (proportional adjustment) negative feedback control algorithm, through the PID negative feedback A current control circuit is driven to control the drive current flowing through the illumination cavity (GAIN) of the laser to control the illumination power of the laser.

Stable and wavelength tunable laser output wavelengths can be achieved through automatic temperature control circuitry and voltage control circuitry. The automatic temperature control circuit is composed of a thermistor, a temperature detecting circuit and a negative feedback temperature control circuit. The resistance of the built-in thermistor of the laser can be used to detect the temperature of the laser die, and the PID negative feedback control algorithm is used. The PID negative feedback temperature control circuit can control the current and direction of the flowing superheater (TEC). The basic principle is: When the temperature of the die is detected to be higher than the design working temperature, the TEC is started for cooling; When the core temperature is lower than the design operating temperature, the TEC is activated for heating. By controlling the temperature of the laser's die, it is possible to stabilize the laser output wavelength and achieve a small range of wavelength tuning of the laser. Among them, the design working temperature is related to the wavelength to be tuned, and different wavelengths correspond to different design working temperatures.

The voltage control circuit is connected to the built-in Bragg grating (BRAG) of the laser. By controlling the Bragg grating voltage of the laser, the Bragg grating reflection coefficient can be changed, so that the grating is specific to the grating. The wavelength can be completely transmitted, while the other wavelengths are reflected, thereby achieving a wide range of tuning purposes for the wavelength. In summary, through the use of Bragg voltage control and TEC circuit control, the on-line wavelength tuning function of the laser can be realized, and the stability of the output wavelength of the laser can also be ensured.

The control method of the optical module, the main process of which is shown in Figure 3, mainly includes:

1. Set the control value of the eye intersection and extinction ratio of the laser;

2. Adjusting the working temperature of the laser to the design working temperature through an automatic temperature control circuit; generally, the optical module includes a plurality of optical channels. Therefore, adjusting the operating temperature of the laser actually includes adjusting the temperature of the laser die of each channel;

3. Through the Bragg voltage control circuit, adjust the laser Bragg voltage to a suitable value, suitable for the value, generally so that the laser wavelength is adjusted to a preset range as a standard;

4. Re-adjust the temperature of the laser die through the automatic temperature control circuit until the wavelength is adjusted to the preset value;

5. The output optical power of the laser can be adjusted to the required range by an automatic optical power control circuit;

6. Record the values of all adjustment parameters for each channel.

It should be noted that the above process is only an example. Because wavelength tuning requires higher precision, wavelength tuning is a more complicated process. Wavelength tuning under voltage control and wavelength tuning under temperature control are generally not a one-time completion, but an iterative calibration process. At the same time, there is no strict prioritization of the two wavelengths. In general, wavelength tuning by Bragg voltage adjustment is a coarse tuning process, ie the wavelength will be tuned over a wide range; and the wavelength tuning adjusted by the temperature control circuit is a fine tuning process, ie the wavelength will be tuned over a small range. The temperature control of the temperature control circuit can be subdivided into adjustment and locking from a more precise angle; wherein, the adjustment means that the temperature control circuit adjusts the laser die temperature to the preset wavelength according to the required wavelength preset value. The corresponding design working temperature; locking means that the temperature control circuit always locks the laser die temperature at the required design working temperature during the working process of the laser, so as to maintain the stability of the laser output wavelength.

As shown in FIG. 4, in an optical module according to an embodiment of the present invention, a photodiode (APD) receives an optical signal, generates a photo-generated current proportional to optical power, and the photo-generated current is sent to a transceiver (Trance iver) at the transceiver. The photo-generated current is converted into a positive voltage signal by a transimpedance amplifier, and the positive voltage signal passes through The limiting amplification and CDR decisions are converted to data signals, which are then serial/deserialized by the serial/deserialized devices in the transceiver. Serial/deserial devices can convert serial signals to parallel signals (such as parallel signals that conform to the SFI. 4 protocol). In the optical power detection, the sampling resistor can be connected in series, and the photo-generated current passes through the sampling resistor, and the voltage across the sampling resistor is detected by the operational amplifier, thereby completing the detection of the incoming optical power.

The block diagram of the automatic optical power control circuit is shown in Figure 5. The back-output optical power of the laser is converted into photocurrent by the backlight detection diode built in the laser. The photocurrent is amplified by the transimpedance and sent to the negative feedback controller (with feedback loop). The comparator, the feedback control uses the PID control algorithm, in the feedback loop, the PID control parameter is set by the RC network, and the set value (the voltage value corresponding to the standard optical power) is compared, and the difference is compared. The value signal controls the driving bias current of the laser, so that the laser back-output optical power is constant, thereby achieving the purpose of adjusting and stabilizing the laser optical power. The above set value is realized by the built-in microcontroller unit (Micro Control Unit, MCU) of the optical module through a 12bi t D/A (digital-to-analog converter).

The block diagram of the automatic temperature control circuit (ATC) is shown in Figure 6. It mainly controls the temperature and direction of the thermoelectric cooler (TEC) to keep the temperature of the laser die at the set value, so that the output light of the laser The wavelength (frequency) remains stable. When the laser temperature is higher than the design operating temperature, ATC causes the laser's thermoelectric cooler (TEC) to obtain a positive cooling current, the refrigerator absorbs heat, and the laser die temperature decreases; when the laser temperature is lower than the design operating temperature ATC causes the thermoelectric cooler (TEC) to obtain a reverse heating current, the cooler heats the die, and the laser die temperature rises, thereby stabilizing the operating temperature of the laser die. The ATC function is implemented by a bridge composed of a built-in thermistor of the laser to detect the actual temperature of the laser die and the error of the temperature set by D/A. In Figure 6, the two input terminals of the comparator are connected to a voltage dividing circuit composed of a fixed resistance resistor and a thermistor in the laser. The voltage dividing circuit is used as a temperature detecting circuit, and its output voltage is input to One input of the comparator; the other input of the comparator inputs the voltage value set by the MCU control D/A (corresponding to the voltage value of the design operating temperature); the output voltage of the temperature detection circuit and the MCU control D The difference between the voltage values set by /A is used as the input of the full-bridge controller composed of the operational amplifier. The output of the full-bridge controller is used as the input of the power amplifier, and the output of the power amplifier drives the TEC to change the temperature of the laser.

The block diagram of the voltage control circuit of Prague is shown in Figure 7, where the MCU controls the 12-bit D/A output mode. The quasi-prague voltage is buffered by an amplifier with an operational amplifier and reaches the Bragg grating built into the laser. The debugging process in the actual working of the optical module includes:

1. First, set the value of the control eye intersection and extinction ratio in the control circuit of the EA laser driver. The EA laser driver has an extinction ratio and crosspoint control pin. The MCU controls the analog voltage of the 12-bit D/A output. The analog voltage is buffered by the op amp consisting of an operational amplifier and directly sent to the corresponding control of the EA laser. Pin. By changing the control signal output from the MCU to the D/A, the extinction ratio and intersection of the optical interface can be adjusted accordingly.

1. Calculate the D/A value of the laser temperature control circuit (ATC) for each channel according to the preset requirements (for example, the guide value in the laser index book) and write it into the module.

3. Wavelength measurement can be performed by using a wavelength meter. By observing the wavelength display wavelength, the D/A value of the laser Bragg voltage control circuit is repeatedly adjusted, and the wavelength is adjusted to the wavelength preset range (the wavelength range required in the actual working environment). On the ITU-defined grid.

4. After the wavelength deviation is within the required ± 3 GHz range, the side mode suppression ratio of the laser wavelength is tested, and the D/A value of the laser Bragg voltage control circuit is adjusted again, and the side mode suppression ratio is required to be maximized.

5. Step 4 will cause a slight deviation in wavelength, and then adjust the temperature control circuit (ATC) D/A value to make the wavelength re-adjust to the required range.

6. Adjust the D/A value of the automatic optical power control circuit (APC) to adjust the output optical power of the laser.

7. Complete the above steps, and the parameter adjustment of one channel of the laser is completed. By scaling, all parameters are written to the memory and all values of the channel are recorded.

The optical module of the invention has a wavelength tunable function compared with other optical modules, and can cover 16 wavelengths of C-band 50 GHz or 100 GHz, and has a lower cost while covering a wider wavelength. Dense wavelength division systems have important implications. And the control method is relatively simple.

The above is a further detailed description of the present invention in connection with the specific preferred embodiments, but this is only an example for ease of understanding, and the specific implementation of the present invention should not be construed as being limited to the description. Various possible equivalent changes or substitutions may be made by those skilled in the art to which the present invention pertains, and such changes or substitutions should be The scope of protection of the present invention.

Industrial applicability

The optical module of the invention has a wavelength tunable function compared with other optical modules, and can cover 16 wavelengths of c-band 50 GHz or 100 GHz, and has a lower cost while covering a wider wavelength. The dense wavelength division system has important significance, and the control method is relatively simple.

Claims

Claim

1. An optical module comprising: an electroabsorption laser, a temperature detecting circuit, a negative feedback temperature control circuit, and a Bragg voltage control circuit, wherein

The electroabsorption laser includes a thermistor, a thermoelectric cooler, and a Bragg grating; the Bragg voltage control circuit is disposed to be coupled to the Bragg grating, and the reflection coefficient of the Bragg grating is changed by controlling a voltage of the Bragg grating ;

The thermistor, the temperature detecting circuit, and the negative feedback temperature control circuit are arranged to be sequentially connected to form an automatic temperature control circuit; the automatic temperature control circuit is configured to control the temperature of the electroabsorption laser to be maintained at a design operating temperature, When detecting that the temperature of the electro-absorption laser is higher than the design working temperature, starting the thermoelectric refrigerator to perform cooling; when detecting that the temperature of the electro-absorption laser is lower than the design working temperature, starting the thermoelectric refrigerator Heating

Thereby tuning of the wavelength of the optical module is achieved.

1. The optical module of claim 1, further comprising a backlight detection diode, a backlight current detection circuit, and a negative feedback drive current control circuit, wherein

The backlight detecting diode is built in the electric absorption laser, and the backlight detecting diode, the backlight current detecting circuit, and the negative feedback driving current control circuit are arranged to be sequentially connected to form an automatic optical power control circuit, and the automatic optical power The control circuit is configured to feedback adjust the drive current of the electro-absorption laser based on the detected laser output optical power.

3. The optical module of claim 2, wherein the negative feedback drive current control circuit comprises a transimpedance amplifier and a comparator,

The transimpedance amplifier is configured to, after the backlight detecting diode converts the laser output optical power into a photo-generated current, perform transimpedance amplification on the photo-generated current and convert the voltage into a voltage, and then input the voltage to the comparator;

The optical module according to any one of claims 1 to 3, wherein the Bragg voltage control circuit comprises a digital-to-analog conversion circuit and a follow-up amplification buffer circuit, The digital to analog conversion circuit is configured to output a voltage control signal to the shot following amplification buffer circuit; the shot following amplification buffer circuit is configured to buffer the voltage control signal and input the Bragg grating.

The optical module according to any one of claims 1 to 3, wherein

The optical module includes an OGBi t/S optical module.

6. A method for controlling an optical module, comprising the following steps:

Setting a control value of an eye intersection and an extinction ratio of the electroabsorption laser;

Adjusting the Bragg voltage of the electroabsorption laser by a Bragg voltage control circuit to adjust the wavelength of the electroabsorption laser to a preset range;

Adjusting an operating temperature of the electro-absorption laser to a design operating temperature by an automatic temperature control circuit to adjust a wavelength of the electro-absorption laser to a preset value;