EULAMBIA ADVANCED TECHNOLOGIES LTD User Manual Alexandros Fragkos (alexandros.fragkos@eulambia.com) 11/28/2016
28/11/2016 User Manual
User Manual 28/11/2016 Electro-Optic Modulator Bias Control Unit v2.0 User Manual 3
28/11/2016 User Manual
User Manual 28/11/2016 Contents 1 Bias Control Unit at a Glance... 6 2 Getting Started... 9 3 Bias Control Unit Operation... 10 3.1 POL Calibration... 10 3.2 Response Scan... 11 3.3 PC Connection... 12 3.4 Configuration... 13 3.5 Reset Button... 15 3.6 Firmware upgrade... 15 4 Appendix A: Performance... 17 5
28/11/2016 User Manual 1 Bias Control Unit at a Glance is an electro-optic modulator bias control unit that can be used with any Mach-Zehnder modulator with V π less than 20V. It incorporates a response detection routine in order to automatically detect the response of the target modulator and provides tracking of Quad+, Quad-, Minimum and Maximum bias point as well as tracking of 40 intermediate bias points in the negative and positive slope within the linear region. It features an automatic gain control circuit in order to operate with input optical power in the range of -10 to 10dBm, a second monitoring ADC with adjustable voltage window for high resolution in the region of the Minimum and Maximum bias points, and a Polarization calibration routine in order to align the input signal to the modulation axis of the MZM. In addition, the has all the appropriate ports in order to operate using different monitoring devices. It has a port for connecting MZMs with internal monitoring photodiode, it has an on-board in-line photodiode with a tap ratio of 1% and finally it has an SMA connector to provide the user with the freedom to connect any external photodiode. The also features a 2.4 LCD display with a backlit navigation knob providing an easy to use interface. The display provides all the appropriate information that the user needs to know about the EOM s characteristics as well as real time monitoring of useful parameters such as the bias voltage and the estimated output power. Finally, the board includes a micro-usb connector in order to remotely control the EOM using a computer while enabling the user to update the firmware of the controller to the latest available version. Specifications Parameter Min Value Typical Value Max Value Units Acceptable Optical Power (1) -16 18 dbm Acceptable Electrical Voltage @ External PD SMA Connector 0.01 1 5 V Output DC bias voltage -14-14 V Locking mode Locking slope Quad± / Max / Min / 40 Intermediate points Negative or Positive Dither Frequency 50 Hz Dither peak-to-peak voltage (2) 40.8 95.2 mv Bias point error (3) @Quad± point @MIN/MAX point Modulator full response detection time Electrical Signal Connectors Optical Signal Connectors Power 0.25 0.53 0.32 0.78 0.44 1 5 8 10 sec SMA, pin-header FC/APC 12VDC @ 0.25Amp Operating Temperature 0 +70 Storage Temperature -40 +85 Communication USB degrees 0 C 0 C Note: (1) The operating optical power range can be custom designed. (2) The dithering signal is present only at the tracking of minimum and maximum bias points. (3) The bias point error was measured as the standard deviation of the bias voltage at the operating point.
User Manual 28/11/2016 Power Supply The controller board operates with a direct voltage of +12V and draws a maximum current of 150mA. So, an external regulated +12V power supply with a maximum current rate of 0.25A is adequate to power up and operate the controller. The includes three regulated voltage sources of +3.3V, +5V and a symmetrical ±15V. Signal Ports Port Name PD-C PD-A VBIAS GND SMA-PD SMA-Bias Signal In Signal Out DC port Direction Input Input Output Input Output Input Output Input Description Connects to the photodiode cathode pin of the EOM. Connects to the photodiode anode pin of the EOM. Connects to the bias pin of the EOM. Connects to the ground pin of the EOM. Alternative input for the EOM integrated photodiode. The cathode and anode of the photodiode are connected to the inner and outer contact of an SMA cable, respectively. Alternative bias voltage output port. Optical input for the inline photodiode (Future port). Optical output from the inline photodiode (Future port). Regulated +12V. LEDs Port Name PWR ON TX RX USB Description Power indicator. (BLUE) This LED indicates data transfer from the controller to a connected PC. (GREEN) This LED indicates data transfer from a connected PC to the controller. (YELLOW) This LED indicates an established controller-pc connection. (GREEN) 7
28/11/2016 User Manual
User Manual 28/11/2016 2 Getting Started 1. Plug in a +12V regulated power supply using a Jack connector with inner diameter 1.4mm and outer diameter 3.5mm and turn on the power switch on the board. 2. Connect the bias pin and the ground pin of the modulator to the VBIAS and GND pins on the board, respectively. 3. Choose the monitoring method and connect the appropriate signal ports. If the MZM has an embedded monitoring photodiode connect its cathode and anode to the PD-C and PD-A pins located on the board. Alternatively, the user can either use the optical output of the modulator and connect it to the Signal In optical port on the control unit using a FC/PC optical connector, or use an external photodiode and connect its electrical output to the Ext. PD (1) port with an SMA connector. 4. Using the backlit knob navigate through the main menu and select the Configuration button by pressing the knob. In the new menu that pops up select the Monitoring PD and then select the monitoring source through Internal PD, Tapped PD or External PD. (2) 5. In case that an external polarization controller is inserted between the laser source and the modulator, by selecting the POL Calibration in the main menu, the user can aligned the optical signal to the modulation axis of the MZM and optimize the performance of the system. (3) 6. In case that the bias controller needs to be remotely controlled, connect a mini USB cable to the controller and select the PC <-> Controller tab. 7. If the polarization state of the input signal is optimised, select the Response Scan tab on the main menu to begin the automatic response detection of the target MZM. When the detection routine is completed, the user can then select the desirable bias point. Notes: (1) The Ext. PD SMA port receives voltage signals within the range of 0-5V. (2) The navigation knob flashes in yellow color to indicate that a menu selection is available, lights up in green color to indicate that a selection has been validated, and lights up in red color to indicate that an exit from the current state or a return to a previous state is available. (3) In order to run the polarization calibration routine the input power to the modulator must range between -3dBm to 0dBm. 9
28/11/2016 User Manual 3 Bias Control Unit Operation Below, you will find a detailed description of the individual processes that constitute the complete operation of the. Figure 1: Main menu interface. 3.1 POL Calibration In case that an external polarization controller is inserted between the laser source and the modulator, the POL Calibration routine has to run in order to maximize the performance of the modulator. By selecting the tab, the controller performs an automatic response detection in order to find the point of minimum transmission of the target MZM. When the scanning process is completed, the controller generates a bias voltage that corresponds to that point and prompts the user to adjust the external polarization controller in order to maximize/minimize the monitoring voltage. (1) The voltage of the monitoring photodiode is displayed in real time, so the user can adjust the polarization with absolute accuracy. In addition, a second ADC with adjustable voltage window is engaged in order to increase the resolution and therefore produce high accuracy adjustment on the polarization state. When the adjustment is completed press the button in order to return to the main menu. Figure 2: Polarization calibration interface. Note: (1) Depending on the monitoring source that is selected, the routine will prompt the user either to maximize or minimize the received voltage. This occurs due to the fact that the internal photodiode of a modulator monitors the radiating field hence it has a reverse dependence on the transmitted optical power, while the tapped or external photodiode have proportional dependence on the transmitted optical.
User Manual 28/11/2016 3.2 Response Scan When the polarization of the input optical signal is adjusted, by selecting the Response Scan tab the bias controller starts the automatic response detection routine, in order to scan the response of the target modulator, analyse it and detect all the bias points of interest. The controller performs one fast scan to estimate the power of input signal, then an automatic gain control routine adjusts the received voltage in order to optimize the resolution and avoid any amplitude clipping due to optical power excess at the input of the modulator, and finally a second fast scan and a high resolution scan take place in order to accurately detect all the desirable bias points. In case that the input optical power, after the AGC reconfiguration, is too high, the controller will display a message at the bottom of the screen to inform the user about the power excess. In order to continue the power has to be decreased and the navigation button must be pressed to return to the main menu. The controller is capable of tracking all the main bias points, Quad±, Min, Max as well as 40 intermediate points within the linear region in both negative and positive slope for a input power range of -16dBm to 18dBm. During the scanning sequence, the navigation knob gradually lights up in red color. When the high resolution scanning sequence starts the navigation knob gradually lights up in green color, and when the routine is completed the knob flashes in yellow color to prompt the user to select the desirable bias point. Each point is depicted with its corresponding bias voltage. To select one of the main bias points just press the knob. Alternatively, if an intermediate point is desirable, select the VAR point, navigate through all the possible bias voltages within the linear regions and press the knob to select the point. Figure 3: MZM response acquired by the controller during the detection routine When the bias point is selected, the display will show all the useful parameters that the user needs to know about the locking state of the modulator. These parameters include the bias voltage, the estimated modulator output optical power, the current error of the PID tracker, the peak-to-peak voltage amplitude of the dithering signal in the case of minimum/maximum bias point selection. In addition, the display includes two real time graphs that depict the time evolution of the bias voltage and the photodiode monitoring signal. The refresh rate of the parameters and the graphs is 1 sec when the controller tracks the Minimum/Maximum point and 600msec in any other case. Initially, the controller starts at an intermediate point, enables the PID and tries to track the desirable bias point. When the bias point is successfully locked the EOM Locked tile turns to green and the modulator is ready for use. 11
28/11/2016 User Manual Figure 4: Real time tracking monitor. In case of tracking loss due to sudden change of input polarization, optical power or temperature, the controller will perform an automatic re-calibration in order to locate and track the bias point again. During this process the EOM Locked tile will turn red and the Calibration tile will turn green. Finally, in order to exit from the current operating mode and return to the main menu press the navigation knob. 3.3 PC Connection In this operating mode, the user can control the board by using the PC software that comes with the controller. To establish a connection, plug in a mini USB cable to the board, start the software on the PC and select the PC <-> Controller tile on the main menu. When the connection between the devices is successfully established, the USB LED at the left side of the board will light up in green color and the user can control the board using the software. The operation of the software is straight forward, and offers additional features such as the capability of saving the response of the modulator, saving the time evolution of all the parameters monitored during the locking state and also controlling and monitoring multiple bias controller at the same time. (1) To exit from the remote operation simply press the disconnect button on the software side and press the navigation knob on the controller side. Figure 5: PC to bias controller connection
User Manual 28/11/2016 3.4 Configuration By selecting the Configuration tile, a new menu page pops up which allows the user to configure some additional parameters such as the behavior of the backlit navigation knob, the selection of the monitoring photodiode and the adjustment of the photodiode responsivity. Figure 6: Configuration menu. By pressing the Backlit On/Off tile the user can enable or disable the backlit indications. Figure 7: Backlit navigation button behavior adjustment. By selecting the Monitoring PD tile, a new menu window pops up which allows the user to select one of the monitoring sources available on the controller. Please have in mind that in the case that the tapped photodiode is selected as the monitoring source, its responsivity cannot be changed. In any other case the user has to configure the responsivity according to the datasheet of the product. (2) 13
28/11/2016 User Manual Figure 8: Selection of monitoring photodiode In order to exit from the current configuration menu, the Return to Main Menu tile must be pressed. Before proceeding to the initial menu a prompt will appear to inform the user that the current configurations can be saved. In this case a configuration file will be generated, which will load automatically every time the controller turns on. The file is stored on an external SD card located at the back of the LCD display and it can be modified by the user using a text editor on a PC. Figure 9: Saving of the configuration file Note: (1) The PC software is not available at this moment, but will be soon and will be delivered free of charge. (2) In case that the internal photodiode of the modulator is used, the calculated output optical power is an estimated value of the actual power due to lack of the photodiode s coupling coefficient. As a result, is not significantly accurate and must not be taken under serious consideration.
User Manual 28/11/2016 3.5 Reset Button In case of any kind of improper operation of the controller, press the reset button, located at the back of the board, in order to re-initialize the controller and return to the factory settings. 3.6 Firmware upgrade Every future update of the controller s firmware will be uploaded to EULAMBIA s website in a.hex file format. In order to upgrade the firmware of the controller a PC software for serial programming of the MCU is needed. There are two available free softwares, one for the PC users (http://www.chip45.com/avr_bootloader_atmega_xmega_chip45boot2.php ) and one for the MAC users (http://definefalsetrue.com/index.php/en/softwareprojects/88-bootfeedq ). The update process is described in the seven steps below. Step 1. Connect the controller board to a PC/MAC with a USB cable. Step 2. Start the chip45boot2/bootfeedq software on a PC/MAC. Step 3. Select the appropriate serial channel corresponding to the controller s usb connection, choose the 115200 baud rate and enable the RS485 box. Figure 10: Serial programmer main panel, PC (left) and MAC (right) versions. Step 4. Turn on the power of the controller and simultaneously press the Connect to Bootloader button located on the lower end of the software panel. Step 5. Confirm that the controller is in programming mode. In this case the screen of the controller turns into grey and the log screen on the software side will display the message found chip45boot2 bootloader version v2.9n or successfully connected to bootloader depending on the software version (PC or MAC). In PC version, a green LED will turn on and a Connected! indication will appear at the left side of the LED. If the connection is established proceed to the next step, otherwise repeat the current step. 15
28/11/2016 User Manual PC Version Figure 11: Software connection to the controller established. MAC Version Step 6. Click on the Select Flash Hexfile button, select the updated firmware file and click on the Program Flash button. The TX and RX LEDs on the controller s side will blink continuously during the programming process. Step 7. Wait until the programming process is completed, press Disconnect from Bootloader on the software panel, disconnect the USB cable and restart the controller from the power switch.
User Manual 28/11/2016 4 Appendix A: Performance In order to evaluate the stability performance of the, on every bias point, a custom designed temperature controlled bed was used to adjust the temperature of the target MZM. The temperature drift that the TEC imposed to the modulator was 0.1 0 C/sec. This temperature rate of change is rather fast and it does not correspond to realistic room temperature drifts but it demonstrates the capability of the bias controller to stablize the modulator even under radical temperature variations. In the following graphs the stability of different bias points as a function of the temperature is depicted. (a) (b) (c) Figure 12: Stability of the bias controller as a function of the temperature. The graphs above correspond to the Minimum (a), Quad+ (b) and Maximum (c) bias point. In the figures below, the stability of the bias controller is depicted as measured during a 16h operation with and without modulation on the RF port of the modulator. The temperature of the room was constant during the measurement and equal to 22 0 C ± 0.3. Figure 13: Bias controller stability in 16h operation as a function of time. The controller tracks the minimum bias point of the modulator. (a) 17
28/11/2016 User Manual Figure 14: Stability error as measured by the integrated monitoring photodiode of the EOM. The measurement corresponds to a 16h operation of the bias controller. (a) (a) (b) Figure 15: Locking time as a function of the input optical power for locking on the Quad+ (a) and Minimum bias point (b). (a) (b) Figure 16: Stability error of the bias point as a function of the input optical power for locking at the Quad+ (a) and Minimum (b) point.
User Manual 28/11/2016 (a) (b) Figure 17: Bias point stability during extreme temperature drift introduced at the body of the modulator. The temperature increase slope is about 0.75 0 C/sec for the left graph and 1.5 0 C/sec for the right graph. The left graph corresponds to the Quad+ bias point while the right one corresponds to the Minimum bias point. 19