It turned out that the signal was too small with PDA10A to detect the 22 and 110 MHz RF sidebands.
The DC output coming out from it was about half mV or so (corresponding to few uW in laser power) when the PRCL was locked to the carrier.
This is because PDA10A is a silicon detector which is more sensitive to visible light than IR.
The reason we chose PDA10A was that it has relatively a large diode size of 1 mm in diameter.
However according to the data sheet the responsibility at 1064 nm is about 0.05 A/W which is sad.
I will replace it by PDA10CF, which is made from InGaAs and supposed to have 10 times bigger responsibility.
Though the diode size will be half mm in diameter, which may require another strong lens in front of it.