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StatusOngoing
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Status date2024-07-16
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Activity Code6C.037
This project’s objective is to manufacture a high-sensitivity APD-TIA module for low-noise applications at 1550 nm. The primary target is to achieve a data rate of 2.5 Gb/s with a bit error rate of 10-6, using a low – 43 dBm of average optical power. This work delivers a high-performance APD, as verified through key APD parameters such as the dark current, responsivity, excess noise, and noise equivalent power.
Radiation hardness is also a key consideration given the space applications. The aim is to provide a APD-TIA module that can withstand a total ionising dose (TID) of 50 krad(Si), which is typical during space missions, without optoelectronic degradation. Resistance to non-ionising radiation (TNID) and single event effects (SEE) is also intended with a targeted in-orbit deployment lifetime of at least 7 years.
Given the state of the art -43 dBm target, the main challenge of this project is to minimise the noise from APD and TIA. However, many design parameters that improve the noise also come at the expense of the bandwidth, hence a detailed trade-off analysis is needed to deliver a viable solution. A high responsivity from the module is also needed, requiring minimal coupling and reflection losses. Likewise, a radiation hard and low-noise TIA is needed to be integrated with the APD without significant circuit parasitics.
Current 2.5 Gb/s APD-TIA receivers achieve sensitivities down to -36.6 dBm. Existing APDs, with an InGaAs absorption layer, are limited by the conventional avalanche materials such as InAlAs and InP that have inferior excess noise and gain product bandwidth performance to AlGaAsSb used in this work. Hence, the AlGaAsSb APD is able to operate at higher gains, suppressing the noise of the TIA and improving the sensitivity. Furthermore, AlGaAsSb has a relatively small breakdown temperature coefficient making the APD less sensitive to fluctuations in temperature.
By achieving sensitives down to -43 dBm, much weaker optical signals can be reliably detected allowing for the receiver to be either further away from the transmitter or to operate in poorer atmospheric conditions in free-space applications.
The product consists of a receiver optical sub-assembly (ROSA) fibre coupled for ease of use. Two different APD diameters, one at
50 µm and the other at 200 µm are produced. For 2.5 Gb/s applications, the 50 µm version delivers an optical sensitivity of -43 dBm at a bit error rate of 10-6. Meanwhile, the 200 µm version operates at bandwidths up to 1 GHz.
For each module a TO-can holds an integrated APD-TIA receiver circuit with a low-noise TIA and high performance APD. Both are able to operate from -40 to 60oC and be stored from -55 to 125oC.
Individually, the APDs are to deliver a state-of-the-art performance compared to conventional InGaAs-based APDs. The APDs exhibit a gain of 10, noise equivalent powers below 15 fW/Hz1/2, an excess factor below 2, and a sub 30 nA dark current.
The project work is composed of 6 milestones each individually reported to ESA for approval. Milestone 1 (MS1) is composed of the literature review and initial technical baseline that is updated in MS2 where the design of the receiver is detailed. Later the implementation and verification plan is established in MS3, leading to the measurement stage that is assessed in MS4 and MS5. Finally, MS6 concludes the project with a detailed evaluation and presentation of the results.
Currently, the ANELOQC project has submitted the reports for WP1 and WP2 and has had a telecom for MS1 with a second confirmation telecom planned. A more detailed design of the APD is underway for MS2 through simulations of specific APD structures. More procurement of parts for the BER setup has also taken place such as the VOA and fibres for the setup. Similarly, MACOM has been contacted for further details of the CGY2102UH/C2 TIA and its availability for initial trial bonding.
