Biomedical Engineering Reference
In-Depth Information
4.0
δ
3.0
D
= core
diameter
2.0
1.0
0
0.1 0.2
Radial displacement ratio (δ/
D
)
Effect of lateral displacement
0.3
0.4
0.5
4.0
t
3.0
0.5 NA
D
2.0
1.0
0.15 NA
0
0.1
0.2
Separation ratio (
t
/
D
)
Effect of separation
0.3
0.4
0.5
1.5
0.5 NA
1.0
D
0.5
0.15 NA
0
1΄
2΄
3΄
4΄
5΄
Misalignment
Effect of angular misalignment
FIGURE 4.28
Effects of lateral displacement, separation, and angular misalignment.
4.18.10 Electronic Circuitry
Optical fiber outputs from the second coupler of the Mach Zehnder interfer-
ometer are each coupled to a detector as shown in Figure 4.29—in this case,
UDT PHOTO model UDT-455HS. This is a silicon photodiode combined with
an op amp in a TO-5 housing. It operates from 9 V positive and negative supply
voltages. Gain and bandwidth are adjustable with external feedback compo-
nents. The outputs are applied to an LM258 connected as a difference ampli-
fier. The dynamic interferometer output signal is taken from the output of the
difference amplifier. This output is also low-pass filtered, amplified further
by another LM258 and a high-voltage dc amplifier that supplies the control
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