Select the channel number you want to use for the measurement using the dropdown list labeled âSelect Channelâ (Figure 3.9). âCh nâ denotes channel n where n = 1, 2, ... [[NeoScan]] Optical Bench Manager program opens up with the âCh 1â as the default working channel.
</p>
 <center>[[Image:neoscanfig_3_9.png|thumb|center|600px650px|<i><b>Figure 3.9</b>: Selecting the working channel from NeoScan Optical Bench Manager window.</i>]]</center>
</li>
<li>
If the polarization is maintained, the total return power and the polarization power will lie within the specified optimized range (the default value is ±20%). In this case, âOptimization Indicator LEDâ becomes green. Otherwise, it start blinking and the information panel indicates: âPolarization is not maintained: Optimization is required.â A user can change the threshold from the box labeled âAuto Trigger Marginâ (see Figures 3.7 and 3.8). If the power difference is greater than 20%, the polarization state is found not to be maintained, therefore, the user will be prompted with a dialog window giving an opportunity to initiates the optimization process or skip the optimization by choosing âNo.â
â
<p>The âStopâ button stops the application. To close (kill) the [[NeoScan]] window click on exit button [[Image:icon_Exit.png]] on the top far right in the LabView user interface. To re-start running the program press the start button [[Image:icon_Start.png]] located on the top left in the LabView window as shown in Figure 3.10. During the run, the start button will disappear. Keep [[NeoScan]] Optical Bench Manager program running until the end of the measurement. </p>
<center>
[[Image:neoscanfig_3_10.png|thumb|center|500px600px|<i><b>Figure 3.10</b>: Start and Stop buttons for NeoScan Optical Bench Manager.</i>]]
</center>
<center>
[[Image:neoscanfig_3_10bneoscanfig_3_11.png|thumb|center|600px|<i><b>Figure 3.10</b>: Resetting the power plots and displaying them with the Entire History and Updated options.</i>]]
</center>
</li>
<center>
[[Image:neoscanfig_3_11neoscanfig_3_11b.png|thumb|center|600px|<i><b>Figure 3.11</b>: Optimization Settings page in NeoScan Optical Bench Manager program.</i>]]</center>>
<ol>
<center>
[[Image:neoscanfig_3_12.png|thumb|center|500px|<i><b>Figure 3.12</b>: Lock-in Amplifier Settings in Optimization Settings Page.</i>]]
</center>>
</li>
<li>
Other parameters that should be directly set on SR844 RF Lock-in amplifier â since they are not controlled:
<olul>
<li>
ï¾ Time constant: 24 dB/oct, Figure 3.13(a).
<li>
ï¾ X display: R(dBm), Figure 3.13(d).
</p>
</li>
<li>
</li>
<li>
ï¾ Remote: 50 ï Ω external source, Figure 3.13(f).
</li>
</olul> <center>[[Image:neoscanfig_3_13.png|thumb|center|600px|<i><b>Figure 3.13</b>: Stanford Research Systems SR844 RF Lock-In Amplifier: (a) Time constant: 24 dB/oct, (b) Signal Input: 50 Ω Low noise, (c) Sensitivity: Low noise, (d) X display: R(dBm), e) Y display: θ, (f) Remote: 50 Ω external source.</i>]]</center>
The signal levels at the Signal In port on the Lock-in amplifier are in the range of -100 dBm to -40 dBm or higher, depending on device one measures. It is important to set the sensitivity of the Lock-in amplifier greater than the expected input signal amplitude at the Signal Input port (from the IF Out of the optical mainframe). For example, if you expect a signal less than -67 dBm but greater than -87 dBm, set the sensitivity to -67 dBm and 100 μV (rms) setting. If the input signal is greater than the input signal setting, an OVERLOAD condition will occur and the red LED OVERLOAD indicators on the Lock-in amplifier will flash.
<p>
Optimization parameters are stored in C:\ProgramData\[[NeoScan]]\OptimizationParameters folder.
></p>
</li>
</ol>
<center>
<div class="noprint" style="float:center;margin-right:10px">
{| border="1" class="wikitable"
|+ <i><b>Table 3.1</b>: Default values for the main parameters used in the optimization process.</i>
|-
! <b>Parameter</b>
| <b>Description</b>
| <b>Default Value</b>
|-
! Lock-in Amplifier Visa
| Lock-in Amplifier GPIB address
| GPIB0::8::INSTR
|-
! Sensitivity
| Lock-in Amplifier Sensitivity
| 100 uV / -67 dBm
|-
! Time Constant
| Lock-in Amplifier Time Constant
| 10 ms
|-
! No. Averaging Points
| Number of points used to find the peak value
| 5
|-
! Variation Limit
| Maximum variation from the nominal value
| 1.00 dBm
|-
! PC Voltage
| Maximum voltage applied to the polarization controllers during the optimization process.
| 3.0 V
|-
! Voltage Steps
| Voltage steps applied to the polarization controllers during the optimization process
| 0.01 V
|-
! Wait Time
| Interval delay time
| 1000 ms
|}
</div>
[[Image:neoscanfig_3_14.png|thumb|center|600px|<i><b>Figure 3.14</b>: Optimization parameters settings in Optimization Settings Page.</i>]]
</center>
If the optical signal is low, check to make sure:
<ul>
<li>
<p>
The probe and the crystal on its tip is fine.
</p>
</li>
<li>
<p>
The operating frequency is correct.
</p>
</li>
<li>
<p>
All the components are connected correctly and appropriately.
</p>
</li>
<li>
<p>
All instruments are functioning properly.
</p>
</li>
<li>
<p>
All cables and the PM fiber are fine.
</p>
</li>
<li>
<p>
All connectors are in good conditions â make sure they are not loose.
</p>
</li>
<li>
<p>
CPW is functioning properly.
</p>
</li>
<li>
<p>
Lower the probe down close to the surface of CPW and make sure the probe positions right above the CPW slot and move it around the slot.
</p>
</li>
</ul>
Parameter Description Default Value Lock-in Amplifier Visa Lock-in Amplifier GPIB address GPIB0::8::INSTR Sensitivity Lock-in Amplifier Sensitivity 100 uV / -67 dBm Time Constant Lock-in Amplifier Time Constant 10 ms No. Averaging Points Number of points used to find the peak value 5 Variation Limit Maximum variation from the nominal value 1.00 dBm PC Voltage Maximum voltage applied to the polarization controllers during the optimization process. 3.0 V Voltage Steps Voltage steps applied to the polarization controllers during the optimization process 0.01 V Wait Time Interval delay time 1000 ms Table 3.1: Default values for the main parameters used in the optimization process.=== Probe Optimization ===
â
If the optical signal is low, check to make sure:
⢠The probe and the crystal on its tip is fine.
⢠The operating frequency is correct.
⢠All the components are connected correctly and appropriately.
⢠All instruments are functioning properly.
⢠All cables and the PM fiber are fine.
⢠All connectors are in good conditions â make sure they are not loose.
⢠CPW is functioning properly.
⢠Lower the probe down close to the surface of CPW and make sure the probe positions right above the CPW slot and move it around the slot.
Â
3.3 Probe Optimization
The [[NeoScan]] software monitors and controls the polarization of the optical beam in the system. The optimization status for each probe at each channel needs be maintained for an extended period of time. Not only an initial optimization process for each probe at each channel is needed, but also additional optimization processes are needed if the status is not maintained. In general, you have to perform optimization whenever you detach the fiber connectors from the fiber ports of the [[NeoScan]] system or when the fluctuation in the total return optical power and the polarization power are varied more than 20%. After the optimization procedure, the system is ready for real-time measurement or scan.
3.3.1 ==== Optimization Setup and Procedure ====Â
It is assumed that [[NeoScan]] optical mainframe is already on. The setup for the optimization procedure is similar to Signal Strength Check setup as described in section 3.1.2.
To get the maximum EO signal:
1. <ol><li><p>Move the probe around the CPW slot using the X or Y Miniature Translation Stages. </p></li><li><p>2. Position the probe right above the CPW slot.</p></li><li><p>Using the Z Miniature Translation Stage and lower the probe down close to the surface of CPW as much as possible.</p></li></ol>
3. Using the Z Miniature Translation Stage and lower the probe down close to the surface of CPW as much as possible.==== [[NeoScan]] Optimization Utility Program ====
[[Image:neoscanfig_3_15.png|thumb|right|300px|<i><b>Figure 3.15</b>: Dialog window for initiating the optimization process.</i>]] In order to initiate an optimization, it is assumed:
<ul><li>3.3.2 [[NeoScan]] Optimization Utility Program  In order to initiate an optimization, it is assumed: <p>⢠The channel number and the Probe ID No. of the probe you want to optimize are selected.</p></li><li><p>⢠The steps described in section 3.2.2 in âOptimization Settings Pageâ have been done (GPIB address of the Lock-in Amplifier, Time Constant, and the Sensitivity, have been already chosen).</p></li><li><p>⢠Press âApplyâ button to start new probe optimization (Figure 3.7).</p></li></ul>
A user is presented with a dialog window shown in Figure 3.15, giving an option to initiates the optimization process â which will take about 20 minutes to be completed â or skip the optimization by choosing âNo.â Click on âYesâ for optimization. The system will remind a user to prepare an optimization structure. Align crystal field sensitivity direction to optimization structure field properly and press âContinueâ.
Â
When the optimization process starts, [[NeoScan]] Optimization Utility window will pop up, and the detailed optimization parameters are displayed to a user (Figure 3.16): Table 3.1 lists the main parameters used in optimization process with their default values.
The change of the return power and the EO signal are plotted during the optimization process as shown in Figure 3.17, and their values are displayed in the boxes labeled âPD Powerâ and âEO Signalâ, respectively. a user can monitor âPolarization Controller Parametersâ through the information panel shown in Figure 3.18.
 <center>[[Image:neoscanfig_3_16.png|thumb|center|600px|<i><b>Figure 3.16</b>: NeoScan Optimization Utility program.</i>]]<br>[[Image:neoscanfig_3_17.png|thumb|center|600px|<i><b>Figure 3.17</b>: Change of the return power and the electro-optic signal graphs during the optimization process (left to right direction indicates the start to the end of the process)</i>]]</center> The optimization process takes about 20 minutes. It can be used to diagnose hardware failures. When the phase optimization has completed, the optimization window will prompt a user to perform a probe stability test through a red blinking âStart Stability Testâ button at the bottom of the Window (Figure 3.19). To perform the probe fiber stability test, press the âStart Stability Testâ button shown in Figure 3.19. An information dialog box will pop up and explains the procedure for the test. Press âCloseâ button in dialog box and then lift the middle of the fiber at least 2 m from either the probe head or the optical connector. Move it up and down, and/or left and right several times. The program will record variations in return power on the screen. Be sure not to pull the fiber at the connector or the probe ends. After performing this for approximately 30 seconds, press âEnd Stability Testâ on the window. If signal fluctuations during the motion remains within the variation limit (default value is 1 dBm), the optimization is considered to be valid, otherwise, the program will repeat optimization (see Figure 3.20).
At the completion of the signal optimization process, the optimization window will disappear and the display will return to [[NeoScan]] Optical Bench Manager window. The optimized parameters will be written in files in ProgramData\NeoSca\OptimizationParameters.
You have to perform an optimization:
<ol type="i. "><li><p>When you attach the fiber connectors to the fiber ports of the [[NeoScan]] front panel,</p></li><li><p>Whenever you detach a fiber connector from to the fiber ports of the [[NeoScan]] front panel and re-attach it to the same or the any other port.</p></li><li><p>When the fluctuation in the total return optical power or the polarization power are varied more than the defined threshold value (default value is 20%).</p></li><li><p>When there is an abrupt and sharp change in temperature.</p></li></ol>
ii. Whenever you detach a fiber connector from to the fiber ports of the [[NeoScan]] front panel and re-attach it to the same or the any other port. iii. When the fluctuation in the total return optical power or the polarization power are varied more than the defined threshold value (default value is 20%). iv. When there is an abrupt and sharp change in temperature.<ul><li><p>⢠If the Probe ID No. is not correct, [[NeoScan]] Optical Bench Manager cannot find the files for optimization parameters, therefore, a user will be prompted with a warning dialog window shown in Figure 3.21. </p></li></ul>
When the voltages to the polarization controllers for a channel are set to the correct optimized values, you âmayâ observe a sharp change in the polarization power as shown in Figure 3.22. You can save the power plots by pressing âSave Figuresâ button.
<center>[[Image:neoscanfig_3_18.png|thumb|center|600px|<i><b>Figure 3.18</b>: Information Panel in NeoScan Optimization Utility program.</i>]]<br> [[Image:neoscanfig_3_19. png|thumb|center|600px|<i><b>Figure 3.19</b>: Stability Test in NeoScan Optimization Utility.</i>]]<br>[[Image:neoscanfig_3_20.png|thumb|center|600px|<i><b>Figure 3.20</b>: Comparison of a completed optimization process with a failed one in NeoScan Optimization Utility program.</i>]]â    <br>[[Image:neoscanfig_3_21.png|thumb|center|300px|<i><b>Figure 3.21</b>: Warning dialog window when the files for optimization parameters are not found.</i>]]<br>[[Image:neoscanfig_3_22.png|thumb|center|600px|<i><b>Figure 3.22</b>: The change in the polarization power after applying the optimization voltages to the polarization controllers.</i>]]â</center>