Truelight VCSELs and PIN Arrays

Packaging

The arrays are assembled onto PCBs containing the MT guide pins. The PCBs are connected to a TX PCB for the VCSEL array and an RX PCB for the PIN array (see PK's talk for more info) . The TX PCB also contains the BPM-12 PCB and multi-DACs. The RX PCB also contains the DRX-12 PCB. These TX and RX PCBs plug into the BOC PCB.

VCSELs

High power versions of the Oxide implant VCSEL arrays have been obtained from Truelight. The first TX plug-in with these high power versions of the VCSELs was made by Minglee. All 12 channels are functional. The power at digital "1" are in the range 1.2 mW to 1.4 mW for a DAC current in the range 11 to 12 mA. The rise and fall times (20%-80%) are about 1 nS. A scope picture of the optical output of one channel of this array being driven by the BPM-12 chip on a TX PCB is available here .

PINs

12 way arrays of silicon PIN diodes are used.

PIN Response Studies

Minglee's scope photos of the response of one channel of a  PIN array to optical signals at different PIN bias voltages are available here. Maurice has compile a summary plot showing the baseline shift as a function of bias voltage see his pdf file here 

Maurice and Tony also studied the response of the PIN array at different bias voltages. The PIN was mounted on an RX plug-in with a DRX-12 chip. The results were similar to Minglee's.

• Optical signal from the VCSEL source with a passive optical probe.
• Optical signal from the VCSEL source with a TTI optical probe.
• PIN response measured with a 50 Ohm at PIN Bias of 1V.
• PIN response measured with a 50 Ohm at PIN Bias of 1.5V.
• PIN response measured with a 50 Ohm at PIN Bias of 2V.
• PIN response measured with a 50 Ohm at PIN Bias of 3V.
• PIN response measured with a 50 Ohm at PIN Bias of 4V.
• PIN response measured with a 50 Ohm at PIN Bias of 5V.
• PIN response measured with a 50 Ohm at PIN Bias of 6V.
• PIN response measured with a 50 Ohm at PIN Bias of 7V.
• PIN response measured with a 50 Ohm at PIN Bias of 8V.
• PIN response measured with a 50 Ohm at PIN Bias of 9V.
• PIN response measured with a 50 Ohm at PIN Bias of 10V.

From this scan the rise and fall times decrease with increasing PIN bias voltage and then reach a plateau at a PIN bias voltage of about 6V. There is also a slow component to the fall time. The amplitude of this component was estimated by measuring the baseline 20 ns after the signal turned off (where the signal was a long burst of "1"s). Further measurements and analysis from Maurice are available here.

PIN Response at higher currents

The PIN response was measured at higher currents by using VCSELs in a pre-series harness. The results are available here.

BER Scans

The performance of the PIN array/DRX-12 system was studies on an RX plug-in PCB mounted on a modified OptIF-B card. This allowed us to vary the  bias voltage on the PIN in the range 0 to 15V. The results of the first set of measurements are available as a note here.

Preliminary Conclusions on PIN arrays

• The RX plug-in with the Truelight PIN array/DRX-12 work well at relatively low PIN bias voltage.
•  More work is needed to reconcile the digital and analogue measurements.
• The conclusions are based on one array so we should repeat the BER scans on the sample of 10 RX plug-ins .