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Transcript
Visible Light Photon Counter Integrator Group 48: Katie Nguyen, Austin Jin ECE445 Spring 2016 May 1, 2016 Motivation Optical Quantum Information [1] – Quantization of detected photons – Quantum communication: Using properties of photons to securely store and transmit information Introduction Proposed project by Professor Kwiat Current method: threshold method Proposed method: integration method Example of Photon Pulse in MATLAB Pulse height ~-150mV * n for n incident photons Figure 1: One photon per pulse Figure 2: Two photons per pulse Example of Photon Pulse in MATLAB Worst case example Figure 3: Two photons overlapping Figure 4: Three photons overlapping Objectives More precise method of calculating number of photons per pulse – Distinguish between 1 – 5 photons per pulse – Synchronized Integrator with External Trigger Make integral accessible through device for further processing. Add Features for Readability – Graphical User Interface – Logging capabilities Diagram of Design Figure 5: Block diagram Integrator Circuit Figure 6: Integrator circuit diagram Integrator Output Calculations Integrator Simulation Results R (Ω) Calc (mV) Sim (mV) % diff 50 150 144.74 3.507 100 75 73.52 1.973 200 37.5 37.05 1.2 500 15 14.89 0.733 1K 7.5 7.458 0.56 5K 1.5 1.493 0.467 10K 0.75 0.7468 0.427 Figure 7: Integrator simulation Simulated voltage is measured at 10 ns Table 1: Integrator simulation result Integrator Simulation Results Unstable when capacitance is larger than 100 pF Figure 8: Integrator simulation at 1nF Figure 9: Single integrator simulation at 1nF Power Supply Circuit Input: 120V AC wall outlet – Stepped down to 12V AC via center-tapped transformer – Full-wave rectified – Linear regulators on PCB Provide a set of stable voltages – +/- 2.5V to the integrator circuit – 3V to the ADC Power Supply Circuit Transformer Rectifier/Smoothing caps Figure 10: Power supply circuit The constant current load assumed Regulators Power Supply Simulations Voltage level at +/- 2.5V, 3V Negligible ripples Stable level achieved by 1ms Figure 11: Power supply simulation Power Supply Setup Figure 13: Power supply PCB Figure 12: Transformer top-view (top) and front-view (bottom) Power Supply Results Designed Output (V) Actual Output (V) % Difference -2.5 -2.488 0.48 2.5 2.268 9.28 3 2.986 0.56 Table 2: Power supply results Possible explanation for 2.5V – PCB burned during testing, due to narrow traces Should not matter if within the amplifier operational range ADC for Post-Processing Considerations for Design – Fast enough to accurately sample within a narrow window – High Speed ADCs are Expensive • Minimum Speed To Sample • Minimum Resolution ADC for Post-Processing Decision for Design Figure 14 : TI ADC08200 – ADC08200-200Msps will allow us to sample for a 5ns duration • frequency = 1/time = 1/5E-9s = 2E8s = 200Msps – ADC08200 –8 bit ADC IC will accept a voltage range of 0-3.3V • Voltage Resolution = (3.3V - 0V) / 256 bits = 12.94 mV/bit – This tells us that an 8 bit ADC will give us enough resolution to discriminate one photon from another. Proposed Post-Processing Setup Simulate Laser Source for 0-10 Photons Per Pulse in Matlab Integrate Pulses in Matlab Feed Integrated Pulses using a Function Generator into ADC Figure 15 : Flowchart of Experimental Setup Example of Integral in MATLAB Each photon generates a fixed amount of charge. Figure 16 : Integral of One Photon Figure 17: Integral of Two Photons Post-Processing (Software) Use WiringPi to Allow Communication with BCM2835 on Raspberry Pi (8 bit data lines) Enable Serial Peripheral Interface (SPI) bus for SCLK access QT Framework for Graphical User Interface Figure 18 : Flow Chart of Post Processing Post-Processing Results Figure 19 : VLPC GUI Figure 20 : VLPC Log File Post-Processing Results Figure 21 : No photons Figure 22 : One photons Figure 22 : Two photons Challenges Precisely Synchronize Sampling with Trigger – Missing Photon Pulse Account for Large Quantity of Noise – Mindful of Width of PCB Traces – Impedance matching Conclusion Extensive research on a working design Delivered on proposed features – Graphical user interface – Log file Future work : integrator circuit hardware– in progress LTC6409 Figure 23 : DC2266A Schematic (LTC6409 demo board) Special Thanks Ankit (TA) Dr. Sahoo and Dr. Hanumolu Professor Kwiat Fumihiro Keneda (Post-Doc) Questions? References [1] "New nanodevice shifts light's color at single-photon level", Phys.org, 2016. [Online]. Available: http://phys.org/news/201604-nanodevice-shifts-single-photon.html. [Accessed: 30- Apr2016].