We demonstrate a C-band gain-switched seed laser intended for a EDFA-based fiber laser meeting the performance, footprint, robustness, and cost targets for volume time-of-flight LiDAR systems. The technology reported here leverages Freedom Photonics high-power DFBs coupled with a Black Forest Engineering control ASIC in a low-inductance package. As a result, the overall package is a compact form factor that can fit within a 16-pin butterfly package. To date, our 1550 nm seed technology delivers more than 2.5 nJ pulse energy for a 480KHz repetition rate on a 4 ns pulse, which is 30 times higher than conventional seed lasers. This technology is the first of its kind to realize a 1550 nm high-pulse energy seed laser for volume deployment of time-of-flight fiber-laser-based LiDAR systems.
Watt-class semiconductor optical amplifiers (SOAs) at 1550nm are an attractive alternative to replace erbium-doped fiber amplifiers (EDFAs) in various applications including free space optical communications (FSO), with the potential to be more efficient, compact, and cost-effective while providing high-power diffraction-limited output. We present a single mode fiber-coupled packaged SOA delivering >30dBm (1.2W) of continuous wave ex-fiber power at 1550nm with 16dB of overall gain, enabled by recent advancements in diffraction-limited output from tapered semiconductor amplifiers. Preliminary data communications measurements are presented, with an open eye diagram achieved with >1W of output power at 10Gbps using the differential phase shift keying (DPSK) communications format. Watt-class collimated and fiber-coupled SOAs are available and being shipped to customers now.
Rare-earth ion defects in solid-state hosts have emerged as a promising candidate for emissive quantum memories owing to their inherent spin–photon interface and long optical and spin coherence times. Erbium (Er3+) in particular has optical transitions in the C-band making it well suited to the use of existing telecom technology infrastructure. In this work, we present a platform to integrate rare-earth ions into standard silicon photonic circuits. Erbium is co-deposited in CMOS-compatible TiO2 host films onto SOI and patterned into high Purcell factor photonic crystal cavities. Purcell factors in excess of 500 are observed and transient spectral hole burning and photoluminescence excitation scans reveal homogeneous linewidths below 15 MHz. Additionally, we show that photonic wirebonding can provide a solution for low-loss and thermally stable fiber-to-chip coupling.
High power, high-speed photodiodes are pivotal in reshaping RF systems, offering potential replacement of conventional RF cabling with more efficient optical fiber. This presentation offers an overview of novel design concepts underlying these high-performance photodiodes, highlighting advancements in high-performance photodiodes for analog photonic links. We will present details of such detectors at Freedom Photonics, as well as an overview of new literature.
A variety of photonic devices is required for the implementation of quantum sensors, computers and communication networks. This presentation will describe the current state-of-the-art and future possibilities for key photonic devices that enable quantum technologies, such as photon sources, photon detectors, optical amplifiers, electro-optic modulators and paths towards the integration of these devices. Specific requirements on these devices that come from quantum technology demands will be explored and technology solution approaches will be described. The presentation will also explore business prospects for photonic devices in the quantum markets, starting from the present and extrapolating to future opportunities.
Digital avionics technology options to consider for fiber optics communication on future generation aerospace platforms encompass transmitters and receivers operating at 25 Gb/sec and higher data rates. A new round of device and packaging innovation and development will likely ensue as a stepping-stone based on prior work in the areas of single wavelength transmitter, receiver / transceiver and multi-wavelength optical subassembly development.
Upgraded particle colliders will require high bandwidth readout capable of withstanding extremely high levels of radiation. Optical links Silicon photonics is a promising solution, but conventional high-speed modulators cannot survive radiation damage. Preliminary results show hardening techniques capable of enduring 1 Grad of total ionizing dose, but without yet demonstrating high speed modulation.
Ring resonator modulators were designed with various radiation hardness by design techniques and irradiated. Most promising is a highly doped ring resonator modulator with an 18 GHz bandwidth that survived 300 MRad of total ionizing dose.
Photonic technologies are being investigated to realize various next-generation devices, including quantum emitters, transducers and detectors, as well as classical devices, such as lasers, modulators, and detectors. A packaging approach that maintains high optical coupling efficiency over a wide temperature and broad wavelength range is needed for these devices and others. Photonic wire bonds (PWBs) may provide greater design flexibility, increased manufacturability, and higher tolerances to thermally driven misalignment at cryogenic temperatures. Freedom Photonics (a Luminar company) is developing high bandwidth optical interconnects for chip-to-chip or chip-to-fiber applications, utilizing PWBs to reduce optical loss at cryogenic temperatures.
Quantum devices have the potential to revolutionize applications in computing, communications, and sensing; however, current state-of-art resources must operate at extremely low temperatures, making the routing of microwave control and readout signals challenging to scale. Interest in microwave photonic solutions to this problem has grown in recent years, in which control signals are delivered to the cold stage via optical fiber, where they are converted to electrical signals through photodetection. Overall link performance depends strongly on the characteristics of the photodiode, yet detailed measurements of many detector properties remain lacking at cold temperatures. In this work, we examine and compare the performance of a modified uni-traveling carrier photodiode (MUTC-PD) at both room (300 K) and liquid nitrogen (80 K) temperatures, focusing in particular on responsivity, bandwidth, and linearity. In line with previous work, we find a sharp reduction in responsivity at 1550 nm as temperature decreases, while RF bandwidth remains steady. Interestingly, our linearity tests reveal that the RF output saturates more quickly at 80 K, suggesting reduced linearity with lower temperature, the cause of which is still under investigation. Our results should help contribute to the understanding and future design of highly linear cryogenic quantum links.
A significant variety of photonic devices is required for the implementation of quantum sensors, computers and communication networks. This presentation will describe the current state-of-the-art and future possibilities for key photonic devices that enable quantum technologies, such as photon sources, photon detectors, optical amplifiers, electro-optic modulators and paths towards the integration of these devices into compact, highly functional components. Specific requirements on these devices that come from quantum technology demands will be explored and technology solution approaches will be described. We will include examples of devices being developed at Freedom Photonics as well as in other leading quantum technology organizations.
Growing demands in high data capacity and low energy consumption have driven the development of high-performance optical interconnects for many commercial applications, such as links for long-haul, intra-/inter-datacenter, and 5G communication. Typically, the photonic devices used in these environments are optimized for operation at or above room temperature, however there is an existing and growing need for optimized photonic devices to operate in cryogenic and/or high-radiation environments. Applications of these optical interconnects range from control and readout from superconducting integrated circuits for quantum computing, to readout of tracking detectors in high-energy physics (HEP) particle accelerators, to readout of next-generation infrared (IR) focal plane array (FPA) detectors. Key to the success of these optical interconnects is the high-performance and ruggedization of the electro-optic modulator (EOM), typically implemented either as a remoted external device or as a directly modulated light source. The underlying semiconductor physics models of the EOM must account for the conditions presented by the harsh environment, leading to optimization challenges at both device and link levels. The current state of the art of optical interconnects for harsh environments will be reviewed, highlighting the current challenges and opportunities, in addition to presenting an outlook on the technology development trends and enabling applications.
High frequency analog RF photonic links are desirable to reduce the size, weight and power of RF systems by offering the replacement of lossy, bulky coaxial RF cabling for lightweight, low loss and broadband optical fiber. This talk presents an overview of high-performance photodiodes for analog photonic links, highlighting recent advances both from the perspective of products and technology in the commercial space, as well as a few notable demonstrations from research institutions over the past year.
The use of photonic integrated circuits and components in many areas across the general area of laser systems is increasing. Example applications of such systems include free space optical communication, remote standoff sensing, solid state and fiber laser pumping, LIDAR for autonomous vehicles, and atomic laser systems for position, navigation, and timing. In this talk we will review the design, performance, and robustness of Freedom Photonics high performance integrated photonic components for these applications and others, focusing in particular on recent advancements in our products at 780 nm, 1060 nm, 1310 nm, and at 1550 nm.
Freedom Photonics and the University of Virginia have developed high power, wide-bandwidth balanced photodetectors based on vertically-illuminated modified uni-traveling carrier (MUTC) photodiode technology. These balanced pairs are based on single photodiodes which achieve 3-dB bandwidths of 25 GHz, coupled with output powers above 23 dBm, as well as 35 GHz photodiodes with output powers greater than 19 dBm. A balanced configuration of these devices offers advantages in common-mode noise reduction, increasing the signal-to-noise ratio. In a photonic link, high-power, balanced photodiodes support high link gain and large bandwidths, while the high linearity of these devices maximizes spurious-free dynamic range (SFDR).
High quantum-efficiency photodiodes support responsivity-critical applications including sensing, metrology, communication and computation. Freedom Photonics has developed high speed, high quantum efficiency PIN photodiodes to fill these needs. In this talk, we report our most recent results on high quantum efficiency devices at wavelengths including 780 nm and 1550 nm. These results include spectral response, bandwidth, and dark current values for devices which are intended for linear-mode operation. These devices are designed to support high responsivity applications while maintaining high bandwidths.
Silicon (Si) photonics is well-positioned to provide high-speed and low-cost optical interconnects. The extraction of data from cryogenically cooled integrated circuits (ICs) has become of great interest for low-power data readout. Utilizing wavelength division multiplexing (WDM), a high capacity optical interconnect can be realized using remoted Si photonic based ring resonator modulators (RRMs). Results include operation up to 20 Gbps and BER < 1E-12 using a 2 Vpp signal, consuming < 100 fJ/bit in the cold environment. Lastly, Si photonic RRM device and interconnect optimizations for operation at temperatures ≤ 77 K will be presented.
Publisher’s Note: This paper, originally published on 6 September 2019, was replaced with a corrected version on 10 October 2019. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
We report on a monolithic indium phosphide photonic integrated transmitter capable of generating high-speed return-tozero differential phase shift keying (RZ-DPSK) data streams for space optical communications as high as 5 Gbps. The integrated transmitter includes a sampled grating distributed Bragg reflector laser continuously tunable over 30 nm in the C-band, a semiconductor optical amplifier for amplification, a Mach-Zehnder modulator for encoding phase-shift-keying data, and electro-absorption modulator for return-to-zero pulse carving. The transmitter is situated in a custom electronics test bed for biasing various PIC sections and driving the modulators. Furthermore, this transmitter can also be utilized for 10 Gbps DPSK or NRZ-OOK.
We present results of an indium phosphide (InP) monolithic photonic integrated circuit (PIC) transmitter suitable for space-optical communications up to 10 Gbps for NRZ-OOK and DPSK modulation and up to 5 Gbps RZ-DPSK modulation. The PIC includes an SG-DBR laser tunable across the entire telecommunications C-Band, a semi-conductor optical amplifier (SOA), a Mach-Zehnder modulator (MZM) for efficient encoding of phase information, and an electroabsorption modulator (EAM) which serves as an RZ pulse carver. The transmitter PIC is integrated in a testbed with a custom board that provides biasing and driving electronics. The commercial-off-the-shelf (COTS) differential driver generates an estimated 4.5-5 Vpp differential modulation voltage for the dual drive MZM. An identical driver was used for the EAM 50% RZ pulse carver but only a single output was used with the other output terminated with a 50Ω load. The SOA and laser gain sections were biased at 90 mA each. Clear eye openings were achieved for all modulation formats.
Links at 1 micron offer key advantages over longer wavelength links. Both ultra-stable, low noise Nd:YAG lasers and high power efficiency, temperature-stable GaAs lasers operate at wavelengths around 1 micron. These components are particularly beneficial for quantum optical systems and links which require stability over a wide range of temperatures, such as are required in avionics. However, a key component missing in these 1 micron photonic links is a high-power photodiode receiver with high linearity and high quantum efficiency. Freedom Photonics and the University of Virginia have collaborated to develop photodiodes which fill this need. The photodetectors are based on an optimized vertically illuminated modified uni-traveling carrier (MUTC) photodiode technology. We report devices with quantum efficiencies in excess of 80% at 1064 nm, with a 3-dB bandwidth of 28 GHz, for a 20µm diameter device. The same device size handles very high power, with a 1-dB compression of >16 dBm RF power at a 64-mA photocurrent. These photodiodes have a major impact on peak performance of a photonic link, supporting high link gain and large bandwidths. Additionally, the high linearity of these devices minimizes noise and signal distortion, maximizing spurious-free dynamic range (SFDR). These are the first photodiodes of this type which have been packaged and made commercially available for this target wavelength.
High frequency analog RF photonic links are desirable to reduce the size, weight and power of RF systems by offering the replacement of lossy, bulky coaxial RF cabling for lightweight, low loss and broadband optical fiber, particularly in applications such as avionics and naval RADAR systems, electronic warfare and distribution of low-jitter clocks or local oscillator signals. Freedom Photonics and the University of Virginia have developed high power, wide-bandwidth optical photodetectors operating in the 1550-nm wavelength range. These photodetectors are based on vertically illuminated modified uni-traveling carrier (MUTC) photodiode technology. The devices have been developed into fully packaged, fiber-pigtailed modules with optimization for high powers or high speeds. This paper will present the architecture and experimental results of our range of photodiodes. One family of devices focuses on high power applications. These include high-power photodiodes with 3-dB bandwidths of 25 GHz coupled with output powers in excess of 23 dBm, as well as 35 GHz photodiodes with output powers greater than 19 dBm. Another family of devices focuses on high speed applications, including photodiodes with 3-dB bandwidths of >65 GHz and >100 GHz. These photodiodes, used in a photonic link, have a major impact on peak performance. The high power-handling capability and high speeds of these devices support high link gain and large bandwidths, while the high linearity of these devices minimizes noise and signal distortion, maximizing spurious-free dynamic range (SFDR).
Deep space exploration will require laser communication systems optimized for cost, size, weight, and power. To improve these parameters, our group has been developing a photonic integrated circuit (PIC) based on indium phosphide for optical pulse position modulation (PPM). A field-programmable gate array (FPGA) was programmed to serve as a dedicated driver for the PIC. The FPGA is capable of generating 2-ary to 4096-ary PPM with a slot clock rate up to 700 MHz.
This work demonstrates the operation of a photonic integrated circuit transmitter for space optical communication utilizing an RZ-DPSK modulation format realized on an indium phosphide monolithic integration platform. It includes a widely tunable sampled grating distributed Bragg reflector laser, a semiconductor optical amplifier for amplification and burst mode operation, a dual drive Mach-Zehnder modulator (MZM) that efficiently encodes phase information, and an electro-absorption modulator RZ pulse carver.
The laser tuning range is approximately 35 nm across the telecommunications C-band. The MZM DC extinction ratio exceeds 15 dB for a differential drive voltage of 6 V peak-to-peak. Clear eye diagrams were demonstrated at 3 Gbps for OOK modulation and 1 Gbps for RZ-DPSK modulation.
Atmospheric methane (CH4) is the second most important anthropogenic greenhouse gas with approximately 25 times the radiative forcing of carbon dioxide (CO2) per molecule. CH4 also contributes to pollution in the lower atmosphere through chemical reactions leading to ozone production. Recent developments of LIDAR measurement technology for CH4 have been previously reported by Goddard Space Flight Center (GSFC). In this paper, we report on a novel, high-performance tunable semiconductor laser technology developed by Freedom Photonics for the 1650nm wavelength range operation, and for LIDAR detection of CH4. Devices described are monolithic, with simple control, and compatible with low-cost fabrication techniques. We present 3 different types of tunable lasers implemented for this application.
High-performance photodetectors (HPPDs), with high output power and bandwidth, are needed for RF photonics links. Applications for these HPPDs range from high-power remote antennas, low-duty-cycle RF pulse generation, linear photonic links, high dynamic range optical systems, and radio-over-fiber (ROF). Freedom Photonics is a manufacturer of high-power photodetectors (HPPD) for the 1480 to 1620nm wavelength range, now being offered commercially. In 2016, Freedom has developed a HPPD for similar applications extending into the V-band. The basic device structure used for these photodetectors can achieve over 100-GHz bandwidths with slight variations. This work shows data for RF power and bandwidth performance for various size photodiodes, between 10 μm and 28 μm in diameter. Measurement data will be presented, which were collected at both assembly level and for fully packaged detectors. For detector devices with bandwidth performance over 50 GHz, the generated RF power achieved is expected to be over 15 dBm. This performance is exceptional considering the photodiode is fully integrated into a hermetic package designed for 65 GHz. Improvements in the coplanar waveguide (CPW) transmission line and flip-chip bonding design were integral in achieving the higher saturation at the higher bandwidth performance. Further development is required to achieve a >100 GHz packaged photodetector module.
RF photonic systems place extremely high demands on optical component performance. To achieve this, a low noise, high power optical source, a high power, linear and low Vπ optical modulator, sharp and uniform optical filters and high saturation power photodetectors are required. While some of these individual components exist, they have not, to date, been integrated in any currently existing monolithic or hybrid photonic integration platform. In this paper, recent advances in discrete component performance is presented, including optical sources, modulators and detectors. In addition, options for the integration of these components onto an integrated photonic platform is reviewed.
High power photodiodes are needed for a range of applications. The high available power conversion efficiency makes these ideal for antenna remoting applications, including high power, low duty-cycle RF pulse generation. The compact footprint and fiber optic input allow densely packed RF aperture arrays with low cross-talk for phased high directionality emitters. Other applications include linear RF photonic links and other high dynamic range optical systems. Freedom Photonics has developed packaged modified uni-traveling carrier (MUTC) photodetectors for high-power applications. Both single and balanced photodetector pairs are mounted on a ceramic carrier, and packaged in a compact module optimized for high power operation. Representative results include greater than 100 mA photocurrent, >100m W generated RF power and >20 GHz bandwidth. In this paper, we evaluate the saturation and bandwidth of these single ended and balanced photodetectors for detector diameter in the 16 μm to 34 μm range. Packaged performance is compared to chip performance. Further new development towards the realization of <100GHz packaged photodetector modules with optimized high power performance is described. Finally, incorporation of these photodetector structures in novel photonic integrated circuits (PICs) for high optical power application areas is outlined.
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