1. Channel monitoring using MEMS based FT-IR spectrometer
Supervisor:
Eng. Mostafa Medhat
Dr. Ziad El-Sahn

2. Omnia Shehata 1

3. Outline MEMS Technology IR Spectroscopy FTIR Spectroscopy
Channel Monitoring
TDM-PON Monitoring
CWDM PONs
Specs 2

4. What is MEMS ? MEMS stands for Micro-Electro Mechanical Systems.
MEMS can be:
Simple Structure with no moving elements
Complex electromechanical structure with multiple moving elements
Major application of MEMS
Micro-Sensors
Micro-Actuators
So it generally acts like a transducer
MEMS
Mechanical
Electrical
Control Signal 3

5. Advantages of using MEMS
Small Size
Low Cost
Weight little
Energy Efficient
MEMS has more than one name :
In USA it is called MEMS
In other parts in the world it is called “Micro-Machined devices” or “ Micro-Systems technology ”
MEMS Applications
Accelerometers Gyroscopes Silicon Pressure Sensors 4

6. MEMS VS. IC Face Comparison MEMS IC Fabrication Material
Silicon, Gold, Wood, Ceramic, Quartz … etc.
Only Silicon
Size range
Micrometers
Nanometers
Fabrication Processes
Depending on the application.
Has standard fabrication processes, Oxidation, Etching, Deposition….. Etc.
Properties
Mechanical and Electrical
Electrical
No. of Masks
Less Masks
More Masks 5

7. IR Spectroscopy 6

8. Fourier Transform Infrared Spectrometry, PETER R. GRIFFITHS
FTIR Spectroscopy
Infra-red energy that can be monochromatic or polychromatic light source.
Output interferogram will be sampled, apodized if necessary and finally taking its FFT to get the output spectrum which contain a certain characteristic for the sample.
Can be any kind of samples to get its output spectrum like Oil, Blood … etc.
The beam is finally reflected to the detector to measure the output interferogram.
Fourier Transform Infrared Spectrometry, PETER R. GRIFFITHS 7

9. FTIR Spectrometer Channel monitor Sample Detector
White source
Power inside optical fiber
Interferometer
Sample
Detector
Signal and data processing
Power (dBm)
Wavelength(nm)
Amir Shaheen 8

10. Channel monitor
Monitor the optical characteristics of the signal inside an optical fiber ( Power, Wavelength, SNR,…etc)
Power (dBm)
Wavelength(nm) 9

11. TDM-PON Broadband source. FBG.(reflect single wavelength)
Spectrometer.(wavelength against power) 10

12. WDM-PONs CWDM (Coarse wave division multiplexing)
Channel spacing: 20nm (ITU-T G.694.2) 18 channels 11

13. Specs Resolution: 3 nm (Depends on retardation of movable mirror)
Wavelength range: nm
Dynamic range: 50 dB
SNR: 25dB
Insertion loss(IL): 25dB 12

14. Outline Michelson Interferometer. First Model. Simple Case
Second Model.
Effects on optical components.
White source.
Dispersion.
Tilting.
Roughness.
Mirror Size.
Final Design.
Omar Mahmoud 13

15. Michelson Interferometer
Fixed mirror
100µm
1mm
300µm
1mm
Movable mirror
Source
0.5mm
Detector 14

16. Important Equations Losses calculations:
AC Insertion loss.
𝐴𝐶𝐼𝐿=10𝑙𝑜𝑔⁡( 𝑚𝑎𝑥 𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚 −𝑚𝑖𝑛⁡(𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚) 𝑃 𝑖𝑛𝑝𝑢𝑡 )
DC Insertion loss.
𝐷𝐶𝐼𝐿=10 𝑙𝑜𝑔 𝑚𝑎𝑥 𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚 + 𝑚𝑖𝑛 𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚 2 𝑃 𝑖𝑛𝑝𝑢𝑡
Visibility.
𝑉𝑖𝑠𝑖𝑏𝑖𝑙𝑖𝑡𝑦= 𝑚𝑎𝑥 𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚 −𝑚𝑖𝑛⁡(𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚) 𝑚𝑎𝑥 𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚 +𝑚𝑖𝑛⁡(𝑖𝑛𝑡𝑒𝑟𝑓𝑒𝑟𝑜𝑔𝑟𝑎𝑚) 15

17. First Model (General Equation)
Using the general equation of Gaussian Beams and substituting in the equation by z at every optical component.
𝑈 𝑟 = 𝐴 𝑜 𝑊 𝑜 𝑊(𝑧) exp − 𝜌 2 𝑊 2 𝑧 exp −𝑗𝑘𝑧−𝑗𝑘 𝜌 2 2𝑅 𝑧 +𝑗𝜁 𝑧
Intensity X Y 16

18. Simple Case Waist of beam= 100µm Wavelength =1.55µm Infinite mirrors
Reflectivity =100%
Retardation = 100µm.
No tilting at mirrors.
Beam splitter angle = 45 𝑜 with horizontal direction. 17

19. First Model (General Equation)
Resultant interferogram at the detector using MatLab ® :
Pinput = watts.
ACIL = dB.
DCIL = dB.
Visibility = 1. m 18

20. Second Model (Fourier Optics)
Main Idea:
System “ transfer function”
INPUT
OUTPUT 19

21. Second Model (Fourier Optics)
Resultant interferogram at the detector using MatLab ® :
Pinput = watts.
ACIL = 0 dB.
DCIL = dB.
Visibility = 1. m 20

22. Wavelength range = 1.26µm to 1.63µm
White source
Single wavelength = 1.55µm
Wavelength range = 1.26µm to 1.63µm 21

23. White source Effect of white source using MatLab ® :
Mirror size infinity
Wavelength range = 1.26 μm to 1.63 μm.
Reflectivity =100%
Retardation = 100µm
No tilting at mirrors
Beam splitter angle = 45 𝑜 with horizontal direction
Pinput = watts.
ACIL = dB.
DCIL = dB.
Visibility = m
Anas Gasser 22

24. Dispersion Cauchy’s Equation
n(λ) = B + C/ λ For example: crystalline silicon B = C = µm 2 23

25. Laws Fresnel equations (Fresnel loss) Vector form of Snell’s law
normalized light vector l 
normalized plane normal vector n
cos θ 1 = n . (-l)
cos θ 2 = 1− n 1 n (1− (cos θ 1 ) 2 )
V reflect = 1 + (2 cos θ 1 ) n
V refract = n 1 n 2 l + n 1 n 2 cos θ 1 − cos θ 2 n
cos θ 1 must be positive otherwise use
V refract = n 1 n 2 l + n 1 n 2 cos θ 1 + cos θ 2 n
t s = 2 n 1 cos θ i n 1 cos θ i + n 2 cos θ t
r s = n 1 cos θ i − n 2 cos θ t n 1 cos θ i + n 2 cos θ t 24

26. Tilting 25

27. Tilting
Tilting in beam splitter 26

28. ACIL VS Splitter Tilting
For ,
Wo = 50 µm.
Wavelength = 1.55 µm 27

29. Tilting
Tilting in Mirror Y Y X X Z Z 28

30. ACIL VS Mirror Tilting
For ,
Wo = 50 µm.
Wavelength = 1.55 µm 29

31. Roughness
Ideal Mirror
Roughness in mirror
Modeling rough mirrors using a thin layer coated on the mirror.
Reflectivity is modified by the equation:
𝒓= 𝒓 𝟎 𝒆 −𝟐𝑲 𝒏 𝒂𝒊𝒓 𝝈 (𝟏−𝟐 𝑲 𝟐 𝒏 𝒎𝒊𝒓𝒓𝒐𝒓 𝒏 𝒂𝒊𝒓 𝝈 𝟐 )
Where,
ro is reflectivity of mirror.
𝜎 is the RMS of roughness.
Osama Raafat 30

32. Mirror Roughness Effect of mirror roughness using MatLab ® :
Waist of beam= 100µm
Wavelength = 1.55µm
Using mirrors with 400 µm width and 400 µm height.
RMS of roughness is 50 nm.
Reflectivity = 98.8%
Retardation = 100µm
No tilting at mirrors
Beam splitter angle = 45 𝑜 in horizontal direction
Pinput = watts. ACIL = dB. DCIL = dB. Visibility =1. m 31

33. RMS VS ACIL
When using single wavelength =1.55µm 32

34. Mirror Size 33

35. Mirror Size Effect of mirror Size using MatLab ® :
Waist of beam= 100µm
Wavelength = 1.55µm
Using mirrors with 400 µm width and 150 µm height.
Reflectivity =100%
Retardation = 100µm
No tilting at mirrors
Beam splitter angle = 45 𝑜 in horizontal direction
Pinput = watts. ACIL = dB. DCIL = dB. Visibility = 1. m 34

36. Mirror Width VS ACIL
When using single wavelength =1.55µm m 35

37. Mirror Height VS ACIL
When using single wavelength =1.55µm m 36

38. Final Design Fixed mirror Movable mirror Source Detector Y X Z 500µm
1mm
300µm
1mm
Movable mirror
Source
0.5mm
Detector 37

39. Final Design Source Mirrors Beam splitter Detector
Optical fiber 100/125 μm.
From 1.26 μm to 1.63 μm.
Fundamental Gaussian beam with a unity 𝑀 2 .
Beam splitter
Made of crystalline silicon.
Depth is about 150 μm, thickness of 5 μm (at 75 μm depth) and width is 150 μm.
The beam splitter makes 45 𝑜 with the horizontal axis.
Tilt angle is 0.2o.
Mirrors
Made of a silicon substrate coated with Aluminum.
Width should be 400 μm and a height (depth) of 150 μm.
Tilt angle for the mirror is about 0.5o.
Mirror RMS of roughness is 40nm.
The movable mirror travels a distance of 500 µm.
Detector
Optical fiber with a diameter of 150 μm.
Connected to the actual detector. 38

40. Interferogram ACIL = -19.9649 dB. DCIL = -17.4241 dB.
Visibility = m 39

41. Outline MEMS actuators. Comb-drive actuator. Spring design.
Comb Drive Sticking.
Inner fold continuous truss.
Analytical model.
Numerical model.
Parameters effect.
Harmonic analysis.
Layout of comb-drive.
Manal Hafez 40

42. What is an actuator? MEMS actuators
MEMS devices are smaller and smarter.
What is an actuator? 41

43. Comb-drive Actuator Spring Fixed comb
Electrical signal→ Mechanical displacement
Many applications in MOEMS
Spring
Movable comb
Spring restoring force
Electrostatic force 42

44. Comb Drive Sticking
1. Down sticking
Substrate 43

45. Comb Drive Sticking
2. Front sticking 44

46. Comb Drive Sticking
3. side sticking 45

47. Spring design
The spring stiffness in the normal direction 46

48. Spring design Crap beam spring Many spring types Fixed beam spring
Folded beam spring
Crap beam spring 47

49. continuous truss spring
Spring design
We studied two design:
1. Inner fold,
continuous truss spring
2. One sided folded beam,
One sided folded beam
continuous truss spring
Inner fold
continuous truss spring 48

50. Resolution of 3nm A displacement of 500µm
Required Specs
Resolution of 3nm A displacement of 500µm 49

51. Inner Fold Continuous Truss
Analytical model
𝐹 𝑥 = 𝑉 2 𝑛 𝑡  𝑜  𝑟 ( 1 𝑔 + 𝑏 𝑑−𝑥 2 )
Value
Parameter
50 fingers N
10µm Xo
100V V
8μm
Finger gap
1600μm
Beam length
4μm
Beam width
N/m Kx
338000N/m Ky
Kx = 2E h W 3 L 3
Ky= 8Ewh L
Menna Emad 50

52. Inner Fold Continuous Truss Spring
b. Numerical Model 51

53. Inner Fold Continuous Truss
b. Numerical Model
Ky and Kye are intersected at a value of displacement where side sticking occurs Xsi=110.8µm.
W=4μm
L=1600μm
g=8μm
N=50fingers
Electrostatic stiffness and mechanical stiffness in y direction
Displacement in micrometers 52

54. Inner Fold Continuous Truss
1. Effect of gap between fingers over the value of side sticking
W=4μm
L=1600μm
N=50fingers
Side sticking in micrometers
Gap between fingers 53

55. Inner Fold Continuous Truss
2. Effect of length of the beam over the value of side sticking
Side sticking in micrometers
W=4μm
g=8μm
N=50fingers
Length of beam in micrometer 54

56. Inner Fold Continuous Truss
3. Effect of number of fingers over the value of side sticking
W=4μm
L=1600μm
g=8μm
Side sticking in micrometers
Number of fingers 55

57. Inner Fold Continuous Truss
4. Effect of width of the beam over the value of side sticking
g=8μm
L=1600μm
N=50fingers
Side sticking in micrometers
Width of beam in micrometers 56

58. Inner Fold Continuous Truss
Increasing the gap in the original design to be 15 made Xsi=208.9µm.
W=4μm
L=1600μm
g=15μm
N=100fingers
Electrostatic stiffness and mechanical stiffness in y direction
Displacement in micrometers 57

59. Inner Fold Continuous Truss
Dynamic Model
Amplitude of total applied voltage
Displacement in micrometers 58

60. Inner Fold Continuous Truss
Choosing 80 Volt total 59

61. Inner Fold Continuous Truss
Electrostatic stiffness and mechanical stiffness in y direction
W=4μm
L=1600μm
g=15μm
N=100fingers
Vtotal =80 Volt
Displacement in micrometers 60

62. Layout of comb-drive 61

63. IL VS SNR Signal power from source=-60dB
Physical retardation= 500*10-6 m
Frequency of comb drive=280Hz 62

64. Physical Retardation VS SNR
The Interferometer modulates the light at frequency
f= 2VṼ
V: Maximum speed of the comb drive.
Ṽ: Wavenumber.
OBW=2VṼmax - 2VṼmin
NEP is a measure of the sensitivity of a photodetector or detector system. It is defined as the signal power that gives a signal-to-noise ratio of one in a one hertz output bandwidth. [W/Hz1/2]
V∝ Maximum displacement V∝ Frequency of comb drive
InGaAs PIN Photodiode 63

65. Physical Retardation VS SNR
Signal power from source=-60dB
Frequency of comb drive=280Hz
IL=25dB 64

66. Frequency of comb drive VS SNR
Signal power from source= -60dB
Physical retardation=500*10-6
IL=25dB 65

67. Conclusion System Engineer Team MEMS Team Optics Team Resolution 3 nm
IL = 25 dB
MEMS Team
Optics Team 66

68. THANKS Dr. Ziad El-Sahn Eng. Mostafa Medhat Eng. Bassem Mortada
Eng. Youmna El-Tagoury
Dr. Ali El-Rashedy
&
All attendees