AK2571 Datasheet, PDF (25/52 Pages) Asahi Kasei Microsystems – Single-Chip Automatic Power/Temperature Control for WDM Laser Diodes

AKM Confidential
AK2571
5.2.6 Normal operation
After theAK2571 has been properly configured and is in “normal” operating mode, continuous temperature compensation
is performed every 8 milliseconds using the data in EEPROM.
5.3 Register access mode
Register access mode is used to for adjust the characteristics of the Laser Diode Module. Any characteristics can be
adjusted while monitoring by writing to the appropriate register. Please refer to “8. Registers” for details.
5.3.1 ATC and APC Adjustment Example
The following adjustment process example is based on the assumption that polarity of ALM, threshold level of ALM, PID,
Max current of APC feedback, etc. are already fixed and every parameter is written in the EEPROM continuously.
1) Change the operation mode from self-operation to register access by sending the appropriate command through the
Digital interface.
2) Common settings
2-1) Write zero (“0”) to all registers R_CTRL_AKM .to stop the AK2571 working.
2-2) Select I-DACx for APC by using the R_DAC_SET register.
2-3) If the temperature corresponding to wave length is known (either exactly or approximately), set the input
temperature offset by using the R_ATC_OFFSET register. (Please refer to “4.4 Gain & Offset”). In this process, the
target temperature must be set at the midpoint of the ADC (80h).
2-4) Write 80h to the target temperature register (R_TMPRT_TRGT)
2-5) Use register R_TEC_CTRL_SET to select a way to control the TEC.. When using Analog control use register
R_TEC_ANALOG to select Analog-1 or Analog –2.. If using Digital control, use register lR_TEC_PWM_SET to set
the PWM division.
3) ATC adjustment
3-1) Temperature Adjustment
When a “1” is written to the R_CTRL_AKM Atc_main(R_CTRL=08h), the ATC begins control of the TEC to meet
target the temperature. 10 to 30 seconds are required before the LD temperature is fully stabilized. This time depends
on the difference between ambient temperature and target temperature. Stabilization is detected from the ATC Lock
completion signal through the STATUS_MON pin moving from Low to High. To detect this signal, E_LK_CNT_SET
and E_LK_TMPRT_WIN must be set to the appropriate values, STATUS_MON pin must be set to ATC_LK
(R_STATUS_SET=000), and a “1” must be written R_CTRL_AKM.Atc_lk (R_CTRL_AKM=18h) prior to ATC
adjustment.
To complete the ATC adjustment by monitoring the temperature, a preliminary rough adjustment is made using the
offset (R_ATC_OFFSET) and secondary fine adjustment using the target temperature register(R_TMPRT_TRGT)
should be executed to match the temperature required.
3-2) Wavelength Adjustment
It is also possible to adjust the ATC monitoring wavelength. When doing this, the APC be adjusted to work to maintain
consistent light power. Writing “1” in R_CTRL_AKM.Apc_main ( R_CTRL_AKM=28h) starts APC. Follow the APC
adjustment instructions in the next section and roughly set R_DACx_GAIN and R_DACx corresponding to I-DAC for
use.
A preliminary rough adjustment is made using the offset (R_ATC_OFFSET) and secondary fine adjustment using the
target temperature register(R_TMPRT_TRGT) should be executed to match the temperature required.
<Rev. 0.6E Preliminary>
-25-
2001/11