INTUN Tunable Laser
12372-D02, 12/15/2007
Page 24
www.thorlabs.com
Digital Status: _OPTICAL_POWER_ERROR
When the digital status signal _OPTICAL_POWER_ERROR is TRUE – LOW (0 V), the output optical
power from the unit is lower than that set by the applied voltage to the analog OPTICAL _POWER
control signal (see page 26).
When the digital status signal _OPTICAL_POWER_ERROR is FALSE – HIGH (5 V), the difference
between the actual output power and that set by the applied voltage to the analog OPTICAL _POWER
control signal is within the stated tolerance.
If the +OPTICAL_POWER is increased beyond the voltage corresponding to the maximum
recommended laser diode drive current, the _OPTICAL_POWER_ERROR will change its logical state
to TRUE – LOW (0 V). If the +OPTICAL_POWER is increased even further, some laser units will
increase their optical output power. The increase will vary from model to model. The INTUN TL-T
control electronics will protect the laser diode; however, it is not recommended to operate the laser if the
_OPTICAL_POWER_ERROR is TRUE – LOW (0 V).
Digital Status: _TEMPERATURE_ERROR
When the digital status signal _TEMPERATURE_ERROR is TRUE – LOW (0 V), the laser cavity has
not yet reached the right working temperature. Although the INTUN TL-T unit can still be used, the
optical power and wavelength may not meet specifications.
When the digital status signal _TEMPERATURE_ERROR is FALSE – HIGH (5 V), the unit is at the
correct laser cavity working temperature.
Analog Control Signals
The interface allows the user to set the wavelength, optical power, and internal (cavity) temperature via
analog signals. These inputted values will be realized within the tolerances associated with the INTUN
TL-T unit.
To reach the specified accuracy, one must correct for small nonlinear deviations between the control
signals and their corresponding counterparts (wavelength, optical output power, or cavity temperature).
Therefore, a calibration table is necessary to set the optical output to a specified power and wavelength
(see section
5.3
).
In order to achieve optimal performance, the control signals must be well defined. Ideally, the input
signal accuracy would need to be within a tenth of a millivolt to achieve ultimate wavelength thuning
performance. Resolutions of this order are easily disturbed by stray ground return potentials, which are
typically on the order of tenths of a volt. Therefore, to help the user achieve this level of accuracy, we
have incorporated a differential input amplifier (see Figure 12) that has a very high CMRR (Common
Mode Rejection Ratio).
Note that this is a differential input stage; therefore, both the + and
−
voltage terminals must be
connected.
