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StatusOngoing
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Status date2025-03-12
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Activity Code6C.037
The primary objective of this project is to design, fabricate, and characterize a 2.5 Gbps APD receiver, aiming for a fivefold improvement in sensitivity compared to commercially avaliable InGaAs APDs. Additionally, the project includes the development of APD chips with bandwidths of 200 MHz, 500 MHz, and 1 GHz. These APD chips are designed for operation at a 1550 nm wavelength, featuring low noise, high responsivity, and minimal dark current.
The receiver integrates APD chips developed by Albis, along with commercially available off-the-shelf (COTS) passive components and a radiation-hard transimpedance amplifier (TIA). Furthermore, the project includes the development of an evaluation board to facilitate straightforward testing of the receiver’s functionality in a laboratory setting.
To achieve the targeted 5-fold sensitivity improvement in the AO-LIMA project, the main APD design requirements include:
- High unity gain responsivity to enable high signal amplitude at all multiplication gains.
- Low k-ratio (i.e. low excess noise factor) to reduce APD and receiver NEP, and improves receiver sensitivity.
- Operation at high multiplication gain to achieve the improved sensitivity with low k-material.
- Large gain-bandwidth product to allow for high data rate transmission at high multiplication gain.
- Low APD dark current to reduce APD NEP.
The key challenge is to find an optimum balance between the APD noise and the operational gain.
The APD chips and receivers developed in this project are primarily designed for optical and quantum communications at a 1550 nm wavelength. Their key application is in space optical communication terminal markets, with a particular focus on 2.5 Gbps intersatellite optical links. Due to the similarity in detector requirements, these products can also be utilized in free-space optical (FSO) ground stations, terrestrial FSO communications, quantum communications, LiDAR, LiFi, airborne and drone-based optical communication systems.
In the context of their target users’ systems and services, the developed products play a critical role in enabling high-speed data detection with enhanced sensitivity, thereby alleviating power constraints in the overall link budget. For instance, a fivefold improvement in sensitivity corresponds to an approximate 7 dB enhancement in link margin.
The final products developed in this project are APD chips with bandwidths of 200 MHz, 500 MHz, and 1 GHz, designed to operate at a 1550 nm wavelength. These APD chips offer superior performance compared to existing InGaAs APDs, featuring lower noise, higher responsivity, and reduced dark current.
To demonstrate the performance of the developed APD technology, a 2.5 Gbps APD receiver with a targeted fivefold sensitivity improvement is built in a TO-46 package. This receiver integrates the APD chip with commercially available off-the-shelf (COTS) components, including passive elements (capacitors, resistors, and inductors) and a radiation-hard transimpedance amplifier (TIA). The TO-packaged receiver is equipped with a lensed cap and an LC receptacle for user convenience, enabling straightforward fiber coupling of the APD detector to a 50 µm multimode (MM) fiber.
Additionally, the project includes the development of an evaluation board featuring all necessary input and output connectors, facilitating easy testing of the receiver’s functionalities in a laboratory environment.
The following product tree is a hierarchical breakdown of the product into the hardware and software elements:
The key products or elements are described below:
APD Chip
The avalanche photodiode (APD) chip serves as the optical signal detector, converting incoming optical signals into electrical output. Leveraging a low-noise avalanche multiplication process, the APD chip provides significant internal gain with minimal excess noise, achieving at least a fivefold improvement in detection sensitivity compared to existing InGaAs APDs at 2.5 Gbps. The chip features a large active region with an anti-reflective coating on the front side to enable efficient optical coupling to a 50 µm multimode fiber at a 1550 nm wavelength.
Readout Electronics
The readout circuit amplifies the RF electrical signal generated by the APD and delivers a differential data output pair. Additionally, if required, it can provide a discretized digital signal, enabling a hard decision output (“0” or “1”).
Evaluation Board
The evaluation board is designed to facilitate performance assessment of the receiver. It includes all necessary connections for biasing and signal readout, ensuring ease of use in laboratory testing environments.
The project consists of two development phases: a “Technology-preparation” and a “Technology – development” phase. In the preparation part we conduct literature study to review the state-of-the-art, propose preliminary device design and run simulations. The development phase includes two rounds of APD manufacturing and testing. The first round is to design development test structures to validate the models, verify the compliance with the SoW requirements, and to define the final design. The second round manufactures the final APDs and the receivers, and performs thorough compliance verification testing including radiation testing. Finally, a global analysis of the results is performed.
The project started with a Kick-Off-Meeting in March 2025. The project is currently in the “Technology - preparation” phase.
Albis team concludes an assessment of the current state-of-the-art InGaAs APD and is diving deeply into the simulation models. Albis team is actively engaged in brainstorming sessions to create an innovative and optimal device design that can accommodate the demanding technical requirements of AO-LIMA project.
