AK2571 Datasheet, PDF (26/52 Pages) Asahi Kasei Microsystems – Single-Chip Automatic Power/Temperature Control for WDM Laser Diodes

AKM Confidential
AK2571
4) APC adjustment
4-1) I-DAC adjustment
a) Adjust R_DACx to set the light power of the LD. Firstly set register R_DACx_GAIN for the full code of I-DAC
being over 80h to get sufficient accuracy. But it is need to take the margin for LD aging compensation for the
APC Feed back DAC. R_DACx_GAIN of APC Feed back must be limited to remain Feed back compensation
current. For example R_DACx must not beyond 80h if aging compensation current is needed by the same
amount of initial current. And not beyond C0h if aging compensation current is needed by the half amount of
initial current.
b) When using the I-DAC1 dithering function, enable R_EA_SW, set the gain using register R_EA_GAIN and set
the frequency using R_EA_FREQ. Monitor the total I-DAC1 current since this dithering current is added to
R_DAC1 R_DAC1 must be adjusted with this in mind.
c) If the wavelength moves after the APC adjustment, adjust R_TMPRT_TRGT to match the wavelength or go
back and readjust the ATC.
4-2) PDMON Gain setting
Set the PD voltage gain monitoring. The range is from 0.4V to 1.1V / 0.1V step. This setting must be executed after
R_PDGAIN is set.
4-3) Initial aging error setting (R_APC_TRGT adjustment)
a) STATUSMON setting: Set R_STATUS_SET = “APC FB”. When the aging compensation current is added to
the I-DAC output, STATUS_MON becomes High.
b) R_CTRL_USER.Apc_fb = 1 executes the APC Feedback function. In this register access mode, actually the APC
Feedback function doesn’t add current to the R_DACx to make sure this adjustment.
c) Moving R_APC_TRGT, identify the point at which STATUS_MON becomes High. This is the initial aging set
point.
5) APC setting
If there are external components affected by ambient temperature changes (current amplifiers, driver IC etc.), training for
cancellation of temperature characteristics is needed. To do this:
5-1) Stabilize the ambient temperature
5-2) Read the R_TV[7:0] (internal T_V converter digital output) through the serial interface.
5-3) Adjust R_DACx to output adequate current at the temperature.
5-4) Store the data 5-2) as address and 5-3) as data in the look-up table.
5-5) Change temperature and repeat this sequence.
6) Set another wavelength
The AK2571 can store the data for four wavelengths in EEPROM. To get the data for another three wavelengths, repeat
the sequence from 2) to 5).
Wavelength selection is via pin control.
7) Writing the EEPROM
7-1) Compose the data to write in the EEPROM based on the adjustment above.
7-2) Change the mode to EEPROM mode.
7-3) Write the data in EEPROM through the serial interface.
8) Test
Change to Self-operation mode, and confirm all functions work. If there are problems, repeat steps1 to7 and readjust.
Caution: All the data in registers is reset when the power is removed or when the operating mode is changed.
<Rev. 0.6E Preliminary>
-26-
2001/11