Aidan Daly

Bio: Aidan Daly is an academic researcher from Tyndall National Institute. The author has contributed to research in topics: Vertical-cavity surface-emitting laser & Optical modulation amplitude. The author has an hindex of 10, co-authored 19 publications receiving 275 citations.

Directly PAM-4 Modulated 1530-nm VCSEL Enabling 56 Gb/s/ $\lambda $ Data-Center Interconnects

Abstract: We demonstrate a 56 Gb/s four-level pulse-amplitude modulation (PAM-4) transmission using direct detection and a long-wavelength 18-GHz bandwidth vertical-cavity surface-emitting laser as directly modulated light source for short-reach inter- and intra-connects in datacenters and short-reach networks. Error-free transmission over 2 km at 7% hard-decision forward-error correction threshold is achieved by applying powerful equalization schemes at the receiver side. Three equalization schemes, i.e., a maximum likelihood estimation (MLSE), a feed-forward equalizer (FFE), and a combination of the FFE and the MLSE are thoroughly investigated, and the performance comparison between them is carried out.

Flip-chip integration of tilted VCSELs onto a silicon photonic integrated circuit

Abstract: In this article we describe a cost-effective approach for hybrid laser integration, in which vertical cavity surface emitting lasers (VCSELs) are passively-aligned and flip-chip bonded to a Si photonic integrated circuit (PIC), with a tilt-angle optimized for optical-insertion into standard grating-couplers. A tilt-angle of 10° is achieved by controlling the reflow of the solder ball deposition used for the electrical-contacting and mechanical-bonding of the VCSEL to the PIC. After flip-chip integration, the VCSEL-to-PIC insertion loss is -11.8 dB, indicating an excess coupling penalty of -5.9 dB, compared to Fibre-to-PIC coupling. Finite difference time domain simulations indicate that the penalty arises from the relatively poor match between the VCSEL mode and the grating-coupler.

Ge/Si heterojunction photodiodes fabricated by low temperature wafer bonding.

Abstract: We report on the photoresponse of an asymmetrically doped p(-)-Ge/n(+)-Si heterojunction photodiode fabricated by wafer bonding. Responsivities in excess of 1 A/W at 1.55 μm are measured with a 5.4 μm thick Ge layer under surface-normal illumination. Capacitance-voltage measurements show that the interfacial band structure is dependent on both temperature and light level, moving from depletion of holes at -50 °C to accumulation at 20 °C. Interface traps filled by photo-generated and thermally-generated carriers are shown to play a crucial role. Their filling alters the potential barrier height at the interface leading to increased flow of dark current and the above unity responsivity.

Error-free 56 Gb/s NRZ modulation of a 1530 nm VCSEL link

Abstract: We demonstrate a 1530 nm VCSEL that can operate error-free without DSP or FEC to 56 Gb/s. At 50 Gb/s, error-free operation is attained up to 2 km of SMF. A 2-tap FFE driver is used to pre-compensate the VCSEL.

Error-Free 56 Gb/s NRZ Modulation of a 1530-nm VCSEL Link

Abstract: We demonstrate a 1530 nm VCSEL that can operate error-free without DSP or FEC to 56 Gb/s. At 50 Gb/s, error-free operation is attained up to 2 km of SMF. A two-tap FFE driver is used to precompensate the response of the VCSEL. The optical spectrum of the VCSEL under equalization at 50 Gb/s is analyzed and the chirp properties are reported. The low latency of FEC-free NRZ and the distance of 2 km makes these technology suitable for optical links in both high performance computing and large data centers.

Ultrafast and sensitive photodetector based on a PtSe2/silicon nanowire array heterojunction with a multiband spectral response from 200 to 1550 nm

Abstract: The newly discovered Group-10 transition metal dichalcogenides (TMDs) like PtSe2 have promising applications in high-performance microelectronic and optoelectronic devices due to their high carrier mobilities, widely tunable bandages and ultrastabilities. However, the optoelectronic performance of broadband PtSe2 photodetectors integrated with silicon remains undiscovered. Here, we report the successful preparation of large-scale, uniform and vertically grown PtSe2 films by simple selenization method for the design of a PtSe2/Si nanowire array heterostructure, which exhibited a very good photoresponsivity of 12.65 A/W, a high specific detectivity of 2.5 × 1013 Jones at −5 V and fast rise/fall times of 10.1/19.5 μs at 10 kHz without degradation while being capable of responding to high frequencies of up to 120 kHz. Our work has demonstrated the compatibility of PtSe2 with the existing silicon technology and ultrabroad band detection ranging from deep ultraviolet to optical telecommunication wavelengths, which can largely cover the limitations of silicon detectors. Further investigation of the device revealed pronounced photovoltaic behavior at 0 V, making it capable of operating as a self-powered photodetector. Overall, this representative PtSe2/Si nanowire array-based photodetector offers great potential for applications in next-generation optoelectronic and electronic devices. Aligning ultra-thin semiconductors with silicon nanowires enables high-speed sensing of an unusually broad range of ultraviolet, visible, and infrared light frequencies. The shapes of silicon nanowires enable quicker and more effective light detection than conventional thin films, but their spectral response still falls outside the parameters needed for various applications, including optical telecommunication. Researchers led by Di Wu from China’s Zhengzhou University and Yuen Hong Tsang at Hong Kong Polytechnic University turned to the broadband absorption of graphene-like platinum selenide (PtSe2) films to extend the light sensitivity. To parallel the geometry of nanowires, the team used precision deposition techniques to grow 2D PtSe2 films into vertically-oriented layers, some tens of nanometers thick. Direct transfer of the PtSe2 film onto a large-scale nanowire array produced a microsecond-fast device sensitive to multiple optical bands. Platinum diselenide (PtSe2) is a newly discovered Group-10 transition metal dichalcogenide (TMD) which has unique electronic properties, in particular a semimetal-to-semiconductor transition. In this work, we have demonstrated the proposed vertically standing layered structure PtSe2 nanofilms based on hybrid heterojunction with high overall performance was realized for broadband light photodetection ranging from 200 nm to 1550 nm. The high-performance broadband photodetector will open up a new pathway for the development of next-generation two dimensional Group-10 materials based optoelectronic devices.

Photonic Packaging: Transforming Silicon Photonic Integrated Circuits into Photonic Devices

Abstract: Dedicated multi-project wafer (MPW) runs for photonic integrated circuits (PICs) from Si foundries mean that researchers and small-to-medium enterprises (SMEs) can now afford to design and fabricate Si photonic chips. While these bare Si-PICs are adequate for testing new device and circuit designs on a probe-station, they cannot be developed into prototype devices, or tested outside of the laboratory, without first packaging them into a durable module. Photonic packaging of PICs is significantly more challenging, and currently orders of magnitude more expensive, than electronic packaging, because it calls for robust micron-level alignment of optical components, precise real-time temperature control, and often a high degree of vertical and horizontal electrical integration. Photonic packaging is perhaps the most significant bottleneck in the development of commercially relevant integrated photonic devices. This article describes how the key optical, electrical, and thermal requirements of Si-PIC packaging can be met, and what further progress is needed before industrial scale-up can be achieved.

Novel Light Source Integration Approaches for Silicon Photonics

Abstract: Silicon does not emit light efficiently, therefore the integration of other light-emitting materials is highly demanded for silicon photonic integrated circuits. A number of integration approaches have been extensively explored in the past decade. Here, the most recent progress in this field is reviewed, covering the integration approaches of III-V-to-silicon bonding, transfer printing, epitaxial growth and the use of colloidal quantum dots. The basic approaches to create waveguide-coupled on-chip light sources for different application scenarios are discussed, both for silicon and silicon nitride based waveguides. A selection of recent representative device demonstrations is presented, including high speed DFB lasers, ultra-dense comb lasers, short (850nm) and long (2.3 mu m) wavelength lasers, wide-band LEDs, monolithic O-band lasers and micro-disk lasers operating in the visible. The challenges and opportunities of these approaches are discussed.

Vertical-cavity surface-emitting lasers for data communication and sensing

Abstract: Vertical-cavity surface-emitting lasers (VCSELs) are the ideal optical sources for data communication and sensing. In data communication, large data rates combined with excellent energy efficiency and temperature stability have been achieved based on advanced device design and modulation formats. VCSELs are also promising sources for photonic integrated circuits due to their small footprint and low power consumption. Also, VCSELs are commonly used for a wide variety of applications in the consumer electronics market. These applications range from laser mice to three-dimensional (3D) sensing and imaging, including various 3D movement detections, such as gesture recognition or face recognition. Novel VCSEL types will include metastructures, exhibiting additional unique properties, of largest importance for next-generation data communication, sensing, and photonic integrated circuits.

Silicon–Organic and Plasmonic–Organic Hybrid Photonics

Abstract: Chip-scale integration of electronics and photonics is recognized as important to the future of information technology, as is the exploitation of the best properties of electronics, photonics, and plasmonics to achieve this objective. However, significant challenges exist including matching the sizes of electronic and photonic circuits; achieving low-loss transition between electronics, photonics, and plasmonics; and developing and integrating new materials. This review focuses on a hybrid material approach illustrating the importance of both chemical and engineering concepts. Silicon–organic hybrid (SOH) and plasmonic–organic hybrid (POH) technologies have permitted dramatic improvements in electro-optic (EO) performance relevant to both digital and analog signal processing. For example, the voltage–length product of devices has been reduced to less than 40 Vμm, facilitating device footprints of <20 μm2 operating with digital voltage levels to frequencies above 170 GHz. Energy efficiency has been improve...