1. Topic Report Photodetector and CCD
Tuan-Shu Ho
Add a lambda^2 in the interpolation process
Laser diode = 2:15

2. Introduction Photodetector CCD (Charge-coupled device) CMOS
Photodiode: photon > electron
Thermocouples photon > heat > electron
CCD (Charge-coupled device)
CMOS
CCD camera
Photodetector

3. Basic Principle of Photodiode
Reverse biased PN or PIN diode
Material (i.e. Si) absorbs photon, and generating electron (current) by photoelectric effect
Avalanche photodiode (APD)
with a built-in first stage of gain through avalanche multiplication
photodiode
Avalanche photodiodes

4. Basic Principle of CCD Composed with pixels
Pixel: photoactive element
Exposure: charge generated by photoelectric effect
Photocharge is stored in the pixel before readout
Readout
Charge is moved by shift register
Output to Charge amplifier
EECCD

5. Feature of Photodetector
Responsibility & Noise
Bandwidth
Responsibility and noise determine the signal to noise ratio (SNR).
Bandwidth time limits the temporal resolution
Tradeoff: SNR and temporal resolution

6. Responsibility
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 … etc.
A/W of Thorlabs PDA36A
QE of e2v EM4 CCD

7. Noise of Photodiode Thermal noise Electronic 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/Hz0.5 (10-15W/Hz0.5, APD)
Avalanche Photodiode

8. Bandwidth of Photodetector
Limit by RC time constant of circuit and charge collection time
State-of-the-art: hundreds of GHz
Gain-bandwidth product
Bandwidth ↓ as gain ↑
NEP ↓ as gain ↑

9. Noise of CCD 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)

10. Speed of CCD 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

11. EMCCD Andor iXon3 897 EMCCD Pixel number: 512 x 512
Pixel size: 16 x 16 micron
Frame rate: 4~40fps
Digitization: 16bit
Well depth: 800,000 e-
Noise level:
4fps: 21 e-
20fps: 49 e-
With Electron Multiplication ON: <1 e-

12. e2v EM4 Pixel number: 4096 x 1 Pixel size: 10 x 10 micron
Line rate: <30kHz
Digitization: 12bit
Well depth: 117,500 e-
Noise level: 43 e-

13. Summery The performance of photodiode is better than CCD.
Larger the bandwidth
Higher the saturation power, larger the dynamic range
Noise
CCD offers special features like:
Detector array
Application in imaging and spectroscopy