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Chapter 1 Explanation of Functions
1.1
Block Diagram and Configuration Diagram
Shutter motor
Thermoelectric
cooler
Temperature
sensor
Photodiode
array
(640 cells)
I/V
IM 703753-01E
The block diagram of the optical system is shown below. The optical system employs a
polychromator system consisting of a fixed grating and a photodiode array (PDA sensor).
Because the reflection spectrum of FBG can be detected using an optical system with its fixed
elements (component parts), it is ideal for applications that demand high reliability.
The principles of spectroscopy are described below. The light input from the FC connector is
collimated by the lenses and hits the fixed grating. Here the reflection spectrum of FBG is
dispersed and divided into each wavelength of light. Then, the light is focused on the
photodiode array by the lens. This focal point is detected by scanning the InGaAs photodiode
array (consisting of 640 photodiode elements). The optical system is fixed in place (welded if
necessary) to endure vibration and shock, and to minimize deterioration with age.
Photodiode array
Fixed
grating
Signal processing
and
communication section
The configuration diagram is shown below. The reflection spectrum of FBG that is detected
by the optical system (shown above) is I/V converted, A/D converted, and processed using a
digital signal processor (DSP) to derive the center wavelength and optical power level of
each reflection spectrum of FBG. In addition, in order to determine the optical power level in
a stable manner, the photodiode array is maintained at a constant temperature.
Photodiode array
module
Temperature
control
Photodiode array
module timing
control
A/D
AMP
Up to
Filter
1
16 bits
10
Mirror
Shutter
Input fiber
Depolarizer
(FC/PC connector)
Motor Driver
Serial
interface
DSP
DSP controller
Wavelength computation,
power computation, etc.
1
To Host
RS-422
1-1
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