EXTERNAL CAVITY TUNABLE LD LIGHT SOURCE ECL-210
3-5
NOTE
Output power is controled by controling current to LD. When output power setting
exceeds ATT control range in APC mode or ACC controls current by communication
command in ACC mode, S/N characteristics decrease as the current decreases.
3-5-2. Features and Principle Structure
The feature is the ability to reduce the optical output power loss from installing a variable
attenuator in the optical test set-up. By including an internal ATT, variable attenuation is real-
ized with a minimum of optical power loss when compared with an external attenuator set-up.
An attenuator is made of a mechanically tunable graded ND filter. It can be tuned continuously
with the resolution of 0.1dB within 0 to 20dB attenuation range.
3-5-3. Control Method
ATT option is not designed to frequently control the attenuation level. Both manual control
and automatic control are available and these modes can be set using the external communica-
tion port.
1) Manual Control
Manual control of ATT is initially active when the unit is operated in ACC mode. It directly
controls attenuation by setting parameter from the MLS front panel or via the external commu-
nication.
2) Automatic Control
Automatic control of ATT is initially active when the unit is operated in APC mode. When
APC is in operation and the APC target value changes, if the current reaches its upper limit,
the lower attenuation level is selected. If for some reason the APC target value setting is not
achievable, the previous attenuation setting is used.
3-5-4 Control Method of Use
1) Manual Control Mode (ACC mode)
Manual control is possible using the external communication interface. Switch to manual con-
trol mode when the unit is operated in ACC mode or with external low frequency modulation.
ATT is set to 0dB if APC mode is switched to ACC mode while automatic control mode of
ATT is active. Manual control is effective only in ATT manual mode or in ACC mode.
2) Automatic control (APC mode)
Automatic control is available via key operation from the MLS front panel or via mode switch-
ing through the external communication port. In APC mode, ATT can be automatically set
depending on the change of optical output power. When it is in Automatic Control mode LED
of APC is lit and in the case of control by external communication 1 is added to the 4th digit of
the status display. Details of reading the status display are given in section 10.
3) Confirmation of set value (AT)
Set value of ATT changes by automatic control. And this value can be confirmed (read-out) via
external communication command (AT). Set value is fixed in manual control mode.
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