Existing thermal management technologies for diode laser pumps place a significant load on the size, weight and power consumption of High Power Solid State and Fiber Laser systems, thus making current laser systems very large, heavy, and inefficient in many important practical applications. To mitigate this thermal management burden, it is desirable for diode pumps to operate efficiently at high heat sink temperatures. In this work, we have developed a scalable cooling architecture, based on jet-impingement technology with industrial coolant, for efficient cooling of diode laser bars. We have demonstrated 60% electrical-to-optical efficiency from a 9xx nm two-bar laser stack operating with propylene-glycolwater coolant, at 50 °C coolant temperature. To our knowledge, this is the highest efficiency achieved from a diode stack using 50 °C industrial fluid coolant. The output power is greater than 100 W per bar. Stacks with additional laser bars are currently in development, as this cooler architecture is scalable to a 1 kW system. This work will enable compact and robust fiber-coupled diode pump modules for high energy laser applications.
This paper expands on previous work in the field of high power tapered semiconductor amplifiers and integrated master oscillator power amplifier (MOPA) devices. The devices are designed for watt-class power output and single-mode operation for free-space optical communication. This paper reports on improvements to the fabrication of these devices resulting in doubled electrical-to-optical efficiency, improved thermal properties, and improved spectral properties. A newly manufactured device yielded a peak power output of 375 mW continuous-wave (CW) at 3000 mA of current to the power amplifier and 300 mA of current to the master oscillator. This device had a peak power conversion efficiency of 11.6% at 15° C, compared to the previous device, which yielded a peak power conversion efficiency of only 5.0% at 15° C. The new device also exhibited excellent thermal and spectral properties, with minimal redshift up to 3 A CW on the power amplifier. The new device shows great improvement upon the excessive self-heating and resultant redshift of the previous device. Such spectral improvements are desirable for free-space optical communications, as variation in wavelength can degrade signal quality depending on the detectors being used and the medium of propagation.
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.
Single mode tapered semiconductor lasers producing watt-class output powers often suffer from beam quality degradation as drive current increases. The dominant degradation mechanism is believed to be poor gain clamping in the periphery of the optical mode; as the injection current is increased, excess gain in this region eventually leads to parasitic lasing in the amplifier section of the device. However, this effect has not previously been directly observed and other effects such as thermal lensing and gain guiding also likely contribute. Nevertheless, it has been previously shown that by engineering the overlap of the gain profile with the nonuniform optical intensity distribution, performance can be significantly improved. In this work, we report on the direct observation and mapping of the 2D gain profile in a tapered semiconductor laser. InGaAsP-based tapered diode lasers are fabricated with windowed openings on the back (substrate) side of the chip. The devices are soldered junction down for continuous wave operation. An optical microscope is used to observe and map the 2D spontaneous emission profile, and hence gain and carrier density, of the device under operation. The results are compared to a theoretical model to better understand the physical limitations of beam quality degradation in tapered diode lasers.
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.
Proc. SPIE. 9730, Components and Packaging for Laser Systems II
KEYWORDS: Packaging, Cooling systems, High power lasers, Laser applications, Resistance, Solid state lasers, Fiber lasers, Semiconductor lasers, Photonics, Diodes, High power diode lasers, Semiconducting wafers, Laser systems engineering, Liquids, Diode pumped solid state lasers
Existing thermal management technologies for diode laser pumps place a significant load on the size, weight and power consumption of High Power Solid State and Fiber Laser systems, thus making current laser systems very large, heavy, and inefficient in many important practical applications. This problem is being addressed by the team formed by Freedom Photonics and Teledyne Scientific through the development of novel high power laser chip array architectures that can operate with high efficiency when cooled with coolants at temperatures higher than 50 degrees Celsius and also the development of an advanced thermal management system for efficient heat extraction from the laser chip array. This paper will present experimental results for the optical, electrical and thermal characteristics of 980 nm diode laser pump modules operating effectively with liquid coolant at temperatures above 50 degrees Celsius, showing a very small change in performance as the operating temperature increases from 20 to 50 degrees Celsius. These pump modules can achieve output power of many Watts per array lasing element with an operating Wall-Plug-Efficiency (WPE) of >55% at elevated coolant temperatures. The paper will also discuss the technical approach that has enabled this high level of pump module performance and opportunities for further improvement.
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.
In this paper, we report on the latest advances in implementation of the photonic integrated circuits (PICs) required for optical routing. These components include high-speed, high-performance integrated tunable wavelength converters and packet forwarding chips, integrated optical buffers, and integrated mode-locked lasers.
We demonstrate 10Gbit/s operation of two different types of monolithic photocurrent driven wavelength converters (PD-WC). These photonic integrated circuits use a Semiconductor Optical Amplifier (SOA)-PIN photodetector receiver to drive an Electro-absorption (EA), or Mach-Zehnder (MZ) modulator that is integrated with a SGDBR tunable laser. We demonstrate improvements in optical bandwidth, insertion losses, device gain, and modulation efficiency.
Wavelength converters are seen as important to the scalability, flexibility, and cost of future optical networks. These devices have opportunities for deployment in optical switches, routers and add/drop multiplexers. This talk will outline the latest results of monolithic and hybrid photocurrent-driven wavelength converters (PD-WC) based on either the direct modulation of a bipolar cascade SGDBR laser or by external modulation using an Electro-absorption (EA), or Mach-Zehnder (MZ) modulator using integration building blocks such as a semiconductor optical amplifiers (SOA), SGDBR lasers, PIN detectors and EA and MZ modulators. As the input and output waveguides are separate in this configuration of wavelength converter, an optical filter is not required to reject the input signal at the output which is desirable particularly with wavelength tunable applications where the response time of a filter could limit system performance.
We investigate the nonlinear response of an InP-based optoelectronic wavelength converter by three-dimensional device simulation including an advanced many-body model for gain and absorption in the InGaAsP quantum wells. The wavelength converter combines a pre-amplified receiver with a post-amplified sampled-grating distributed Bragg reflector tunable laser diode. Good agreement between simulation and measurements is obtained. The nonlinear signal transmission is mainly attributed to quantum well saturation effects in amplifier and photo-detector. Saturation related microscopic physical processes are analyzed in detail.
In this work, we describe tunable wavelength converters based on a photodiode receiver integrated with a tunable laser transmitter. Devices are fabricated on a robust InP ridge/InGaAsP waveguide platform. The photodiode receiver consists of an integrated SOA pre-amplifier and a PIN diode to improve sensitivity. The laser transmitter consists of a 1550 nm widely tunable SGDBR laser modulated either directly or via an integrated modulator outside the laser cavity. An SOA post-amplifier provides high output power. The integrated device allows signal monitoring, transmits at 2.5 GB/s, and removes the requirements for filtering the input wavelength at the output. Integrating the SGDBR yields a compact wavelength agile source that requires only two fiber connections, and no off-chip high speed electrical connections. Analog and digital performance of directly and externally modulated wavelength converters is also described.
The Sampled-Grating Distributed-Bragg-Reflector laser(SGDBR) provides wide tunability (>40nm), and high output power (>10mW). Driven by the demand for network reconfigurability and ease of implementation, the SGDBR has moved from the research lab to be commercially viable in the marketplace. The SGDBR is most often implemented using an offset-quantum well epitaxial structure in which the quantum wells are etched off in the passive sections. Alternatively, quantum well intermixing has been used recently to achieve the same goal - resulting in improved optical gain and the potential for multiple bandgaps along the device structure. These epitaxial "platforms" provide the basis for more exotic opto-electronic device functionality exhibiting low chirp for digital applications and enhanced linearity for analog applications. This talk will cover state-of-the-art opto-electronic devices based on the SGDBR platform including: integrated Mach-Zehnder modulators, and integrated electro-absorption modulators.