Santec TSL-210 - 8-3. LD Injection Current, Ambient Temperature Control Function; 8-4. Optical Output Power Control Function

8-2
TSL-210 OPERATION MANUAL
8-3. LD Injection Current, Ambient Temperature Control Function
To keep a stable oscillating condition of the semiconductor laser, the TSL-210 precisely controls
injection current and adjusts for ambient temperature changes. The circuit that supplies the LD
injection current provides a stable, constant current and also has a protection circuit so that the
LD does not become damaged. The injection current is controlled both by CPU and the APC
circuit, which has a built-in photo-detector. The APC circuit by a built-in photo-detector. When
the hardware limit of the current driver is reached, the CURR. LIMIT display is lit. For the
temperature control, when the chamber temperature has stabilized, the TEMP.ERROR display
goes out.
8-4. Optical Output Power Control Function
The TSL-210 has a mechanism to separately monitor part of the optical output power that is split
off of the main output signal by an optical fiber type coupler. It also has a function to
automatically set the injection current by setting optical output power.
The TSL-210 has two modes: Automatic Current Control (ACC) mode, which holds current
constant, and Automatic Power Control (APC) mode, which holds output power constant. In the
APC mode, the TSL-210 uses calibrated feedback from a photo detector (PD) to ensure constant
optical output power. When wavelength tuning is executed in the APC mode, the TSL-210 keeps
almost constant optical output power. It is not possible to have the same optical output across
100% of the tuning range. The gain is tailing off at both ends of the tuning range, especially the
short wave side. In ACC mode, the TSL-210 carries out control by set constant current. If using
the optional LF modulation, use it in the ACC mode.
Adjusting the injection current to the LD controls the optical output power of the system. In APC
mode or when controlling the current using the communication control, please note that if the
current becomes low the SSR will deteriorate. (Please refer to Section 13-4 Built-in Attenuator.)
Relationship between injection current, wavelength and optical output power of TSL-210
Water molecule absorbs light in 1300nm~1500nm and the output power decreases
when measuring with optical spectrum analyzer. It is impossible to avoid it because
it is a physical phenomemon. We recommend to use TSL-210 in the condition with
the extremely low humidity or avoid the water absorption points.
NOTE
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