Changes
/* NeoScan Optimization Utility Program */
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[[Image:neoscanfig_3_7.png|thumb|center|600px|<i><b>Figure 3.7</b>: NeoScan Optical Bench Manager Program.</i>]]
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When the program starts, the system detects the total return power and the polarization power in the channel, plots their variations over time and displays their numerical values in mW. Figure 3.8 indicates that channel 1 is selected to deliver the beam to optical probe with Probe ID No. 1505. The Probe ID No. is a four-digit integer number provided by EMAG Technologies Inc. The green “Probe Detected” indicator indicates that the probe is connected to the correct channel.
<center>[[Image:neoscanfig_3_9neoscanfig_3_8.png|thumb|center|600px|<i><b>Figure 3.98</b>: Selecting The total return power and the working polarization power of delivered beam to the optical probe with Probe ID No. 1505 in channel from NeoScan Optical Bench Manager window1.</i>]]</center>
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Select the channel number you want to use for the measurement using the dropdown list labeled “Select Channel” (Figure 3.9). “Ch n” denotes channel n where n = 1, 2, … ... [[NeoScan]] Optical Bench Manager program opens up with the “Ch 1” as the default working channel.
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<center>[[Image:neoscanfig_3_9.png|thumb|center|650px|<i><b>Figure 3.9</b>: Selecting the working channel from NeoScan Optical Bench Manager window.</i>]]</center>
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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, “Optimization Indicator LED” becomes green. Otherwise, it start blinking and the information panel indicates: “Polarization is not maintained: Optimization is required.” A user can change the threshold from the box labeled “Auto Trigger Margin” (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 “No.”
To set the optimization parameters, press “Optimization Settings” tab in [[NeoScan]] Optical Bench Manager program (Figure 3.11): Make sure the GPIB-USB cable from the back panel of Lock-in amplifier is connected to the [[NeoScan]] USB Hub.
<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><p>If you change any value, press “Set Values” button to update.</p></li><li><p>Set Lock-in amplifier parameters:</p><ol type="a. "><li><p>Set Lock-in amplifier sensitivity. The sensitivity of Lock-in amplifier is the rms amplitude of an input sine (at the reference frequency) which results in a full scale DC output (10Vdc).</p></li><li><p>b. Select “Time Constant” from the dropdown lists. The default for time constant of the output low-pass filter that determines the bandwidth of Lock-in amplifier in 10 ms.</p></li></ol></li><li><p>4. Press “Set Values” button to update.</p></li>
Other parameters that should be directly set on SR844 RF Lock-in amplifier – since they are not controlled:
<ul><li> Time constant: 24 dB/oct, Figure 3.13(a). </li><li>
Signal Input: 50 Low noise, Figure 3.13(b).
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Sensitivity: Low noise, Figure 3.13(c).
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X display: R(dBm), Figure 3.13(d).
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Y display: θ, Figure 3.13(e).
</li><li> Remote: 50 Ω external source, Figure 3.13(f).</li></ul> <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.
If the optical signal is low, check to make sure:
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The probe and the crystal on its tip is fine.
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The operating frequency is correct.
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All the components are connected correctly and appropriately.
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All instruments are functioning properly.
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All cables and the PM fiber are fine.
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All connectors are in good conditions – make sure they are not loose.
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CPW is functioning properly.
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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.
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=== 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.
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:
[[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 “Optimization Settings Page” have been done (GPIB address of the Lock-in Amplifier, Time Constant, and the Sensitivity, have been already chosen).</p></li><li><p>• Press “Apply” 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 – which will take about 20 minutes to be completed – or skip the optimization by choosing “No.” Click on “Yes” 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 “Continue”.
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 “PD Power” and “EO Signal”, respectively. a user can monitor “Polarization Controller Parameters” 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 “Start Stability Test” button at the bottom of the Window (Figure 3.19). To perform the probe fiber stability test, press the “Start Stability Test” button shown in Figure 3.19. An information dialog box will pop up and explains the procedure for the test. Press “Close” 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 “End Stability Test” 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>
When the voltages to the polarization controllers for a channel are set to the correct optimized values, you “may” observe a sharp change in the polarization power as shown in Figure 3.22. You can save the power plots by pressing “Save Figures” 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>]] <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>]] </center>
