Optical Data Links Research Articles

A novel high frequency, high bandwidth, three phase Mach-Zehnder optical data link.

In inertial confinement fusion, hydrogen isotopes are fused together under high pressures and temperatures. Typically, the duration of these experiments is incredibly short, on the order of around 60-150ps. Due to the high radiation environment, a detector's signal is typically data linked far distances to a protected location. The diagnostic challenge for fusion reaction history measurements is to measure signals of interest maximizing dynamic range while also maintaining time resolution on the order of 10ps. In this work, we present a new experimental optical data link used to efficiently transport diagnostic signals over great distances to the recording system while not restricting the dynamic range. The concept of a three phase Mach-Zehnder modulator system is introduced as well as a description of the physical prototype. The initial results from testing at the OMEGA facility show that this system is a viable method for signal transportation.

Cryo-VCSELs Operated at 2.8 K and 40 K With Record Bandwidth, Power, and Linearity for Optical Data Links in Quantum Computing

Cryo-VCSELs Operated at 2.8 K and 40 K With Record Bandwidth, Power, and Linearity for Optical Data Links in Quantum Computing

Photonic engineering of InP towards homoepitaxial short-wavelength infrared VCSELs

Many emerging opportunities, such as three-dimensional (3D) sensing, biophotonics, and optical data links, call for vertical cavity surface-emitting lasers (VCSELs) that operate in the short-wavelength infrared (SWIR) range. In this paper, we report the use of InP distributed Bragg reflector (DBR) mirrors to overcome an impasse in wafer-level mass production of SWIR VCSELs. The DBRs were based on homoepitaxial InP structures and selectively converted through electrochemistry into quarter-wavelength stack structures of alternating nanoporous (NP) and nonporous InP layers with a record index contrast (Δn∼1.0) and near-unity reflectivity. We demonstrated VCSEL operation at both 1380 and 1550 nm from two separate structures prepared on InP substrates using NP–InP DBRs as the bottom mirror and dielectric DBRs as the top mirror. Room temperature continuous-wave (CW) operation of SWIR VCSELs was successfully achieved at both wavelengths with a threshold current density below 2kA/cm2, greater than milliwatt optical output, and a peak power conversion efficiency of 17%. Our work provides strong evidence that the decades-old challenge, in preparing an InP-compatible, high-performance DBR to support the SWIR-emitting vertical cavity, has been addressed and is poised to enable new applications.

FPGA-Based Tactile Sensory Platform with Optical Fiber Data Link for Feedback Systems in Prosthetics

In this paper, we propose and validate a tactile sensory feedback system for prosthetic applications based on an optical communication link. The optical link features a low power and wide transmission bandwidth, which makes the feedback system suitable for a large number and variety of tactile sensors. The low-power transmission is derived from the employed UWB-based optical modulation technique. A system prototype, consisting of digital transmitter and receiver boards and acquisition circuits to interface 32 piezoelectric sensors, was implemented and experimentally tested. The system functionality was demonstrated by processing and transmitting data from the piezoelectric sensor at a 100 Mbps data rate through the optical link, measuring a communication energy consumption of 50 pJ/bit. The reported experimental results validate the functionality of the proposed sensory feedback system and demonstrate its real-time operation capabilities.

Extrinsic Parasitics and Design Considerations on Modulation Bandwidth of 850-nm Vertical Cavity Surface Emitting Lasers

The extrinsic parasitics generally limit the modulation bandwidth of vertical cavity surface emitting lasers (VCSELs) for optical data links and interconnects. In this article, the extrinsic parasitics of 850-nm VCSELs are investigated by three different designs: oxide-only (design A), oxide-implant (design B), and oxide-implant with benzocyclobutene (BCB) (design C). The static and dynamic characteristics of all the designs with~7- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> aperture are measured and compared. The maximum modulation bandwidth of design A is only about 12 GHz mainly limited by the large parasitic capacitances. With a proper proton implantation, a thick nonconducting layer is created inside the device with design B, which dramatically reduces the parasitic capacitances, and thus the bandwidth is increased to about 18 GHz. Based on design B, a 4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick BCB layer with low dielectric constant is employed underneath the bond pad of design C to further reduce the pad capacitance, leading to the highest bandwidth about 24 GHz and the highest modulation current efficiency factor (MCEF) of 10.8 GHz/mA <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . The microwave reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{{11}}$ </tex-math></inline-formula> ) parameters of the three designs are measured and compared. Results indicate that design C has the lowest parasitic capacitances and the highest modulation bandwidth, which is preferred for high-speed VCSELs to obtain good static and dynamic performance.

2.9 K VCSEL demonstrates 100 Gbps PAM-4 optical data transmission

A cryogenic packaged vertical-cavity-surface-emitting laser (VCSEL) with microwave input and coupled with OM4 fiber for optical output was developed and demonstrated laser operation from 295 to 2.9 K. Record 2.9 K optical data links of 100 Gbps pulsed amplitude modulation 4-level have been demonstrated with an energy per bit ∼153.4 fJ/bit when TDECQ = 3.79 dB. The energy/bit is limited by the link path bandwidth resulted from the input cable loss to 2.9 K VCSEL and can be further improved. Thus, the VCSEL optical data link is proven to be a viable solution for cryogenic communication and computing.

Superconducting Processor Modulated VCSELs for 4K High-Speed Optical Data Link

Superconducting processor based on single flux quantum (SFQ) technology is a promising solution for cryogenic computing with high-speed operation at extremely low power. However, energy-efficient data link from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 4\text{K}$ </tex-math></inline-formula> operation to room temperature (RT) users has been remained as a key challenger to be resolved. In this work, we report the 5K performance of 51.56 Gb/s PAM-4 optical data link from a VCSEL, coupled by free-space optics inside cryostat to RT receiver through cryostat optical window. Finally, a superconducting bit pattern generator (BPG) is used to modulate a VCSEL at 4 K: 12.5 Gb/s NRZ error-free optical data transmission and 20 Gb/s NRZ open eye-diagrams are demonstrated via an OM4 fiber coupled directly to the VCSEL at 4 K inside cryostat and linked to the outside receiver at RT.

Modulation of Depolarization for Optical Data Links

Modulation of Depolarization for Optical Data Links

High-Speed GaN-Based Superluminescent Diode for 4.57 Gbps Visible Light Communication

Visible light communication (VLC) is a promising technology for next-generation high-speed optical wireless data links. Among various transmitters, GaN-based superluminescent diodes (SLDs) show interesting characteristics, including a large modulation bandwidth, droop free and low speckle noise, which makes them attractive for VLC applications. In this work, we design and fabricate a blue-emitting SLD utilizing tilted facet configuration. Using SLD as the light source, a VLC system is experimentally demonstrated. A record data rate of 4.57 gigabit per second (Gbps) is achieved with adaptive bit-loading discrete multiple tone (DMT) modulation, while the highest modulation format reaches 256 quadrature amplitude modulation (QAM). The corresponding bit error rate (BER) is ~3.5 × 10−3, which is below the forward error correction (FEC) threshold of 3.8 × 10−3.

Multiple-Valued Logic Modelling for Agents Controlled via Optical Networks

The methods of data verification are discussed, which are intended for the distant control of autonomous mobile robotic agents via networks, combining optical data links. The problem of trust servers is considered for position verification and position-based cryptography tasks. In order to obtain flexible quantum and classical verification procedures, one should use the collective interaction of agents and network nodes, including some elements of the blockchain. Multiple-valued logic functions defined within discrete k-valued Allen–Givone algebra are proposed for the logically linked list of entries and the distributed ledger, which can be used for distant data verification and breakdown restoration in mobile agents with the help of partner network nodes. A distributed ledger scheme involves the assigning by distant partners of random hash values, which further can be used as keys for access to a set of distributed data storages, containing verification and restoration data. Multiple-valued logic procedures are simple and clear enough for high-dimensional logic modelling and for the design of combined quantum and classical protocols.

Polarization independent and temperature tolerant AWG based on a silicon nitride platform.

A polarization tolerant optical receiver is a key building block for the development of wavelength division multiplexing based high-speed optical data links. However, the design of a polarization independent demultiplexer is not trivial. In this Letter, we report on the realization of a polarization tolerant arrayed waveguide grating (AWG) on a 300-mm silicon nitride (SiN) photonic platform. By introducing a series of individual polarization rotators in the middle of the waveguide array, the polarization dependence of the AWG has been substantially reduced. Insertion losses below 2.2 dB and a crosstalk level better than -29dB has been obtained for transverse electric and transverse magnetic polarizations on a four-channel coarse AWG. The AWG temperature sensitivity has also been evaluated. Thanks to the low thermo-optical coefficient of SiN, a thermal shift below 12 pm/°C has been demonstrated.

Optical Data Link Module for Data Transmission in Smart Catheters

Abstract We demonstrate a stand-alone optical data link module (ODLM) that fits in the limited space budget of smart imaging catheters. The module is based on an extension of the Flex-to-Rigid (F2R) technology platform for miniaturized system integration. The ODLM is a silicon-based interposer that comprises a commercially available Vertical Cavity Surface Emitting Laser (VCSEL), which has its electrical contacts and laser emitting spot on the same surface. With the flexible interconnects, the ODLM reroutes the flip-chipped VCSEL electrical contacts to the side that is perpendicular to the surface of the VCSEL. This enables the ODLM to be mounted on a flex-PCB and fit into the limited space in the distal tip of the smart catheter. An optical fiber that runs in parallel to the catheter shaft is inserted into the through-silicon hole (TSH) of the ODLM and self-aligned to the VCSEL for optical data transmission. The design of the ODLM and the F2R technology platform are introduced, and an ODLM demonstrator is fabricated and presented.

Implications of four-dimensional weather cubes for improved cloud-free line-of-sight assessments of free-space optical communications link performance

We advance the benefits of previously reported four-dimensional (4-D) weather cubes toward the creation of high-fidelity cloud-free line-of-sight (CFLOS) beam propagation for realistic assessment of autotracked/dynamically routed free-space optical (FSO) communication datalink concepts. The weather cubes accrue parameterization of optical effects and custom atmospheric resolution through implementation of numerical weather prediction data in the Laser Environmental Effects Definition and Reference atmospheric characterization and radiative transfer code. 4-D weather cube analyses have recently been expanded to accurately assess system performance (probabilistic climatologies and performance forecasts) at any wavelength/frequency or spectral band in the absence of field tests and employment data. The 4-D weather cubes initialize an engineering propagation code, which provides the basis for comparative percentile performance binning of FSO communication bit error rates (BERs) as a function of wide-ranging azimuth/elevation, earth-to-space uplinks. The aggregated, comparative BER binning analyzes for different regions, times of day, and seasons applying a full year of 4-D weather cubes data provided numerous occasions of clouds, fogs, and precipitation events. The analysis demonstrated the utility of 4-D weather cubes for adroit management of CFLOS opportunities to enhance performance analyses of point-to-point as well as evolving multilayer wireless network concepts.

Laser Characteristics for VCSELs for 77 K and 4 K Optical Data Applications

Small-sized vertical-cavity surface-emitting laser (VCSEL) offer the possibility of very low power consumption along with high reliability for cryogenic data transfer. Cryogenic data transfer has applications in focal plane array cameras operating at 77 K, and at the lower temperature of 4 K for data extraction from superconducting circuits. A theoretical analysis is presented for 77 K and 4 K operation based on small cavity, oxide-free VCSEL sizes of 2 to $6~\mu \text{m}$ , that have been shown to operate efficiently at room temperature. Temperature dependent operation for optimally-designed VCSELs are studied by calculating the response of the laser at 77 K and 4 K to estimate their bias conditions needed to reach modulation speed for cryogenic optical links. The temperature influence is to decrease threshold for reducing temperature, and to increase differential gain for reducing temperature. The two effects predict very low bias currents for small cavity VCSELs to reach needed data speed for cryogenic optical data links. Changing the number of top-mirror pairs has also been studied to determine how cavity design impacts speed and bit energy. Our design and performance predictions paves the way for realizing highly efficient, ultra-small VCSEL arrays with applications in optical interconnects.

Single Plastic Optical Fiber, Multiple Channel Data Link for Sensing Applications With PCB Implemented Transmitter and Receiver

The limited physical bandwidth of optical data links can be utilised better using pulse amplitude modulation (PAM) schemes. PAM can also be used to implement multiple channels on a single fibre to reduce the fibre count. In this paper, PAM is used with an additional amplitude level transmitting the clock associated with the data. This allows a direct detection of the clock from the signal. Frequent returns to this additional peak level are used to determine the signal strength at the receiver. The paper presents a very compact PCB implemented transmitter achieving a data rate of up to 400 Mbps. Furthermore, three PCB implemented receiver designs that cover different speed (20-400 Mbps) and cost/complexity ranges are presented including measurement results. The proposed solutions are compared to various industry standard solutions in terms of their achievable sampling rate and measurement delay resulting from connected sensors. It is concluded that PAM based data links represent an attractive alternative to the usual time domain multiplexing based 8b/10b encoded no-return-to-zero (NRZ) data links. They lead to an increase of the possible sampling rate (278%) of the sensor and a decrease of the measurement delay (20%), while keeping the same signal bandwidth and number of fibres.

Radiation Effects on High-Speed InGaAs Photodiodes

Photodiodes are important components in optical data links, and their performance degradation under irradiation has to be understood in order to guarantee the long-term functionality of the data links in radiation environments of high-energy physics experiments. Indium gallium arsenide (InGaAs) on indium phosphide (InP) photodiodes are attractive candidates for these applications, thanks to their relatively modest radiation-induced responsivity loss when operated at 850 nm. In this paper, we present the results that confirm earlier observed additional sensitivity penalties in InGaAs-based receivers. This behavior is further investigated by carrying out several proton tests where InGaAs photodiodes are irradiated together with alternative photodiode types. The critical parameters—responsivity, dark current, and capacitance—are measured up to fluences exceeding ${1\times 10^{16}}$ p/cm2. Radiation-induced dark current is shown to be orders of magnitude higher in InGaAs photodiodes than in GaAs and InGaAs on GaAs photodiodes. However, instead of the dark current increase, the additional losses with InGaAs photodiodes are shown to arise from strongly increased capacitance, which is a dominant feature only in InGaAs photodiodes. This is confirmed with simulations where the measured capacitance characteristics are used in the device model. Our results show that without precautions in the receiver design, radiation-induced capacitance can limit the use of InGaAs photodiodes in harsh radiation environments.

Limited-size aperture effects in an orbital-angular-momentum-multiplexed free-space optical data link between a ground station and a retro-reflecting UAV

In this letter, we experimentally explore the limited-size aperture effects in an orbital-angular-momentum (OAM)-multiplexed free-space optical (FSO) data link for aerial platforms. 200-Gbit/s data transmission is demonstrated between a ground transmitter and a ground receiver via a flying, retro-reflecting unmanned-aerial-vehicle (UAV) over 100-m round-trip distance by multiplexing two OAM beams. Our results indicate that when the receiver aperture size is limited, both power loss and channel crosstalk would increase. With a receiver aperture diameter of >5 cm, bit error rate (BER) mostly below 3.8×10−3 has been achieved for both channels

An Analytical Design Method for High-Speed VCSEL Driver With Optimized Energy Efficiency

A universal analytical design approach for laser diode drivers (LDDs) is presented and verified. All design parameters are derived analytically, taking the vertical-cavity surface-emitting laser (VCSEL) characteristics into account. Two optimization strategies are proposed. First, the power consumption is minimized for the highest achievable optical modulation amplitude (OMA) and extinction ratio (ER). Second, the highest achievable data rate (DR) is considered to maximize the energy efficiency. As a result, a simple differential amplifier can be implemented as an LDD to achieve energy efficiencies and DRs comparable or even higher than the one of more complex designs utilizing preemphasis, feedforward equalization, and pulse amplitude modulation. Therefore, drivers designed with this holistic analytical approach accommodate well the demands for high DRs, high energy efficiency, high compactness, high reliability, and low latency in future optical data links. A compact LDD is designed with an active area of only $0.15 \times 0.12$ mm2 in a 130-nm SiGe BiCMOS technology. A DR of 40 Gbit/s with bit error rates $ and an energy efficiency of 2.245 pJ/bit are achieved for an OMA of 1.1 mW and an ER of 10 dB using a 20-GHz 850-nm common-cathode VCSEL. The achieved values deviate less than 10% from the predicted ones, which clearly illustrates the effectiveness of the presented analytical approach. Further improvements are achieved by optimizing the modulation levels and the performance to the link requirements. At 45 and 30 Gbit/s, 1.8 and 1.17 pJ/bit are achieved, respectively.

Isolated sensor networks for high-voltage environments using a single polymer optical fiber and LEDs for remote powering as well as data transmission

Abstract. Many applications in high voltage or explosive environments require sensors which are electrically isolated from other components of a system. These sensors need remote powering as well as wireless or isolated data transmission links. A possible solution can be based on optically powered optical sensor links. These typically employ four different photonic components: for the data communication a fast LED as a transmitter and a photo diode as a receiver, furthermore for sensor powering a high-power light source and a photonic power converter. Additionally, two optical fibers are required for optical remote powering and the optical data link. In this paper we demonstrate an optically powered optical sensor link using only low-cost high-brightness LEDs and a single polymer optical fiber (POF) for all of these tasks. Coupling efficiencies, power transmission and modulation bandwidths are analyzed for LEDs with different colors. Potentials for many mW of electrical remote powering and Mbit s−1 sensor data links are demonstrated over 10 m of POF. This approach can be used for almost any electronic sensor with moderate power requirements.

Analysis of Free-Space Optics Development

AbstractThe article presents state of work in technology of free-space optical communications (Free Space Optics − FSO). Both commercially available optical data links and their further development are described. The main elements and operation limiting factors of FSO systems have been identified. Additionally, analyses of FSO/RF hybrid systems application are included. The main aspects of LasBITer project related to such hybrid technology for security and defence applications are presented.