New Results on ATLAS Pixel Opto-Link

We present new results on the optical link for the pixel detector of the ATLAS experiment. An optical package of novel design has been developed for the opto-link. The design is based on a simple connector-type concept and is made of radiation-hard material. The receiver (DORIC) and transmitter (VDC) chips have been designed. The prototype results using the 0.8 and 0.25 μm technologies are presented. The ATLAS pixel detector [1] consists of three barrel layers and three forward and backward disks. The detector covers the pseudo-rapidity region |η| < 2.5 and provides at least three space point measurements. The low voltage differential signal (LVDS) from the pixel detector is converted by the VCSEL Driver Chip (VDC) into a single-ended signal appropriate to drive a Vertical Cavity Surface Emitting Laser (VCSEL). The optical signal is transmitted to the Readout Device (ROD) via a fibre. For the innermost barrel layer, the signal is transmitted using two fibres. The 40-MHz beam crossing clock from the ROD, bi-phase encoded with the command signal to control the pixel detector, is transmitted to a PIN diode via a fibre. The PIN signal is decoded using a Digital Opto-Receiver Integrated Circuit (DORIC). The VSCEL and PIN diodes couple to the fibres inside optical packages. In this paper, we describe the performance of the opto-pack developed by The Ohio State University (OSU) group and status of the VDC and DORIC prototypes. 1. Results on Opto-Packs The main technical challenge in the fabrication of the opto-pack is the alignment tolerance of the VCSEL with respect to the fibre: • 50 μm in z (along the fibre) • 25 μm in r (transverse to the fibre) The requirements can be satisfied either by passive or active alignment. For the former, parts must be fabricated or placed with high precision (≤ 10 μm) so that the overall precision is still within the tolerance. The alignment tolerance of the PIN to the fiber