Transcript Solid-state Laser Crystal and Device Laboratory Yen

Graduate Institute of Photonics and Optoelectronics
~National Taiwan University
Topic Report
Photo detector/power meter
2012.07.19
Speaker：Yen-Yin Li
Adviser： Sheng-Lung Huang
Solid-state Laser Crystal and Device Laboratory
Yen-Yin Li
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Introduction
NTU
Photosensors or photodetectors are sensors
of light or other electromagnetic energy.
 Photodetector
 Photodiode:
 Thermocouples
photon > electron
photon > heat > electron
 CCD (Charge-coupled device)
 CMOS
Solid-state Laser Crystal and Device Laboratory
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Feature of photodetector
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 Responsibility & Noise
 Bandwidth
 Responsibility and noise determine the signal to noise ratio
(SNR).
 Bandwidth time limits the temporal resolution
 Tradeoff: SNR and temporal resolution
Solid-state Laser Crystal and Device Laboratory
Yen-Yin Li
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Responsibility
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 Responsibility of a photodetector: electrical output per optical input
 A/W: ampere per watt
 Quantum efficiency: # of e- / # of photon
 Material dependent
 Silicon (<1100nm), Ge, InGaAs(<1800nm) … etc.
A/W of IRD x-ray photodetector
A/W of Thorlabs PDA10CS
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Noise of photodiode
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 Thermal noise
 Thermal-generated electrons > dark current
 Electronic noise
 The noise generated in the circuit (i.e. amplifier)
 Higher responsibility reduces the effect of electronic noise to the signal
 Noise-equivalent power (NEP):
 It is defined as the optical signal power that gives a SNR of 1 in a 1Hz output
bandwidth.
 State-of-the-art: ~1fW (10-15W, APD)
Solid-state Laser Crystal and Device Laboratory
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Bandwidth of photodetector NTU
 Limit by RC time constant of circuit and charge collection time
 State-of-the-art: hundreds of GHz
 Gain-bandwidth product
 Bandwidth ↓ as gain ↑
Solid-state Laser Crystal and Device Laboratory
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Power meter
NTU
 A typical optical power meter consists of a
calibrated sensor, measuring amplifier and
display. The sensor primarily consists of a
photodiode selected for the appropriate range
of wavelengths and power levels.
50mW/1nW
Thorlabs.S120C
1W/10μW
Coherent. PS19
30W/1%
300W/1%
Coherent. PM30 Coherent. PM300F-50
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Summary
NTU
 A photodiode is a type of photo detector capable of converting light into
either current or voltage.
 Photodiodes are similar to regular semiconductor diodes except that they
may be either exposed or packaged with a window or optical fiber
connection to allow light to reach the sensitive part of the device. Many
diodes designed for use specifically as a photodiode use a PIN junction
rather than a p-n junction, to increase the speed of response.
 A typical optical power meter consists of a calibrated sensor, measuring
amplifier and display. The sensor primarily consists of a photodiode
selected for the appropriate range of wavelengths and power levels.
Solid-state Laser Crystal and Device Laboratory
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NTU
End
Thank you for your attention
Solid-state Laser Crystal and Device Laboratory
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Noise of CCD
NTU
 Operation of CCD
 Exposure
 Readout by shift register
 charge amplifier
 Saturation: the photo-charge is accumulated in each pixel between
readout
 Well depth: How many e- can be stored in a pixel
 Readout noise: the amplifier noise
 Dynamic range: max. / min. optical power (noise)
 Typical: 30~40dB
 State-of-the-art: ~60dB (Andor EMCCD)
Solid-state Laser Crystal and Device Laboratory
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Speed of CCD
NTU
 The “bandwidth“ of CCD is limited by the readout time
 The time required to read a whole line (with N pixel, N= 256, 512, 1024,
2046, 4096 … etc.)
 The readout time ↑ as number of pixels ↑
 The readout time ↑ as pixel size ↑
 The larger the pixel size, the larger the well depth
 Typical pixel size: >10micron
 Typical: tens of ns/pixel > hundred of MHz
 Compare to hundred of GHz of photodiode
Solid-state Laser Crystal and Device Laboratory
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Outline
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 Introduction
 Mechanism
 Measurement
 Summary
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