High-Power Narrow-Linewidth C-Band DFB Laser Array With High-Uniform Wavelength Spacing

Summary form only given. Packaging of high-power diode lasers represents a crucial issue regarding device lifetime and reliability. In a series of papers we characterized packaging-induced strains in such devices quantitatively. These measurements were based on photocurrent (PC) data. The spectral positions of the optical transitions of quantum-confined carriers were used to get information about the sign, the absolute value and spatial distributions of packaging-induced strains in high-power laser arrays. Now new systematic studies show that packaging sometimes is accompanied by the creation of additional defects in the laser chip resulting in below-bandgap absorption bands. So far the spatial location of these defects is unknown. In the paper we believe we give the first experimental evidence for packaging-induced defects located in the active region of the high-power lasers. A total of 21 devices InGaAlAs/GaAs 2 W single chip devices (from the same wafer) are investigated.

A suitable structure of narrow linewidth DFB laser is studied experimentally. By thinning the active layer to around 0-07 µm, controlling KL to 1-0, and improving the geometrical uniformity of active region, the linewidth less than 1 MHz is achieved at an output power of around 20 mW in 1.55 μm DFB lasers with 1-2 mm long cavity length.

The coupling technique of high-power semiconductor laser array is an advancing key project. A high power density collimated beam, which facula is much smaller, can be get by coupling high-power laser array with selfoc lens array. At the same time, the coupling efficiency is higher. The factors which affect the coupling efficiency mainly include NA, diameter, length and end surface fabricating of selfoc lens and coupling technique. In this paper, an 1×19 linear laser array which maximum continuous output power is 22W is coupled with a corresponding selfoc lens array. The maximum coupling efficiency is 58.2%.

We propose and experimentally demonstrate a 16-wavelength high-power DFB laser array (HPLA) with phase compensators and 200 GHz spacing for optical I/O technologies. The grating of the proposed HPLA is fabricated using the reconstruction equivalent chirp (REC) technique to simplify the grating fabrication and enhance the precise control of the wavelength. The AR and HR films were coated on the front and rear facets of the laser to increase output power. The Ti-Pt heaters are integrated near the rear facet as the phase compensator to adjust the rear facet phase to improve the single-mode yield and achieve precise control of the lasing wavelength. Besides, the slab-coupled optical waveguide (SCOW) is utilized to improve the output power, reduce the differential resistance, as well as reduce the far-field divergence angle. The experimental results show that the 16-wavelength HPLA achieves precise wavelength control and excellent single-mode characteristics by adjusting the rear facet phase through the phase compensator. The fitted deviations of all the wavelengths are below 0.09 nm. The SMSRs of all wavelengths exceed 50 dB. At a bias current of 600 mA, the kink-free output power is greater than 100 mW, with a maximum differential resistance of 0.46 Ω. The slope efficiencies (SE) of all 16 lasers are above 0.25 W/A, and the power conversion efficiencies (PCE) are above 12% at the 100 mW output power. The measured Lorentzian linewidth and far-field FWHM divergence angle are 273.5 kHz and 11.3°×21.5°, respectively. The super performance of the proposed HPLA enables it to be used as a multi-wavelength source in optical I/O systems.

GaSb based diode laser arrays emitting at wavelengths around 2 µm have a significant potential for a variety of applications including material processing, such as welding of transparent plastic materials, and optical pumping of mid-infrared solid state lasers. Even though high output power broad area single emitters and laser arrays have already been demonstrated, they all suffer from a large fast axis beam divergence of typically 67° FWHM due to the broadened waveguide design employed. Here we will present results on (AlGaIn) (AsSb) quantum-well diode laser single emitters and linear arrays consisting of 19 emitters on a 1 cm long bar emitting at around 1.9 µm. To improve on the poor fast axis beam divergence we abandoned the broadened waveguide concept and changed over to a novel waveguide design which features a rather narrow waveguide core. This results in a remarkable reduction in fast axis beam divergence to 44° FWHM for the new waveguide design. For single emitters a cw output power of more than 1.9 W have been observed. 16.9 W in continuous-wave mode at a heat sink temperature of 20 °C have been achieved for arrays. The maximum wall-plug efficiency amounts to 26% both for the single emitters and the laser arrays. These efficiencies are among the highest values reported so far for GaSb based diode lasers, and allow us to use passively cooled and thus less expensive heat sinking technologies.

Precise gyroscopes and atomic clocks are in high demand for positioning and flight navigation systems or measurement of fundamental constants. The development of techniques such as atom optical pumping (Cs or Rb) requires laser diodes with high power and excellent spectral (narrow linewidth) and beam qualities. For spatial applications a high reliability is required (mission lifetime is around 15 years). We have realized different studies of reliability on our Al-free DFB lasers: Catastrophically Optical Mirror Damage (COMD) evaluation, lifetest, optical and spectral measurements before and after ageing. We obtained high COMD densities (respectively 13MW/cm² in continuous wave CW and 19MW/cm² in pulsed mode. Furthermore, we have realized ageing test on these DFB laser diodes emitting at 852.12nm (D2 line of Cs). We used five different ageing conditions (power and temperature) to determine ageing properties. The extrapolated lifetimes of our DFB laser (for operating current variation equal to 100%) are higher than 140000 hours (about 15 years) for an ageing at T= 25°C and P= 40mW. This confirms the excellent potential of this Al-free technology for long life spatial mission. The Side Mode Suppression Ration (SMSR) of the aged D2 line DFB lasers remains very high with a measured change of -1.4dB ± 8dB. There are no significant drifts of the DFB laser wavelength after aging (average ~0.03 nm). We also measured the linewidth of our aged DFB lasers by the self-heterodyne technique and obtained narrow beating linewidths of around 900kHz.

We have experimentally demonstrated a 16-wavelength high-power DFB laser array with 200 GHz (1.6 nm) channel spacing based on the asymmetric equivalent π phase shift. Good single-longitudinal-mode (SLM) operations are obtained by introducing asymmetric equivalent π phase shifts. The effect of random phase on the high-reflective (HR) coating facet also is weakened by introducing asymmetric equivalent π phase shifts which are implemented at the 1/5 laser cavity close to the facet with HR coating. The average channel spacing is 1.62 nm, which deviated 0.02 nm from our design under the same injection current (300 mA) of each laser. The output power of 16 channels is above 100 mW at the bias current of 400 mA and the average slope efficiency is 0.41 W/A at 25 °C. Good single-longitudinal-mode are obtained for all the 16 channels with side mode suppression ratios of above 50 dB. Besides, the relative intensity noise at an injection current of 200 mA is below -157 dB/Hz.

Spectral line narrowing (by a factor of 8) and stabilization of the emission wavelength (by a factor of 30) of multimode high-power laser diodes and arrays is demonstrated by use of volume Bragg gratings fabricated in high-stability inorganic photorefractive glasses. Applications include stabilization of pump laser diodes and arrays for solid-state lasers and metal-vapor lasers, spin hyperpolarization of noble gases used in medical imaging, and others.

To address the challenge of achieving stable in-phase coherent optical field in high-power laser arrays, we propose a novel dual Talbot diffraction coupling method that combines the on-chip self-injection effect with a mixed-resonant cavity diode laser array (MDLA). The designed MDLA incorporate two types of resonant cavities and an integrated external fractional Talbot cavity to compensate for in-phase mode phase delays. Numerical simulations demonstrate that the near-field optical pattern can be self-imaged via self-organized phase-locking, while the far-field optical pattern of in-phase mode can be coherently enhanced and modulated to exhibit a single-lobe pattern successfully. Furthermore, this method could inherently provide strong optical coupling and overcome the limited scalability of the weakly-coupled laser arrays. Ultimately, by leveraging self-organized phase-locking and Talbot-induced mode discrimination, our approach offers a robust platform for realizing high-power coherent laser sources with scalable integration potential.

NIST has been tasked by DARPA to provide wall plug efficiency and spectral measurements of high-power high-efficiency laser diodes and arrays for DARPA’s Super High Efficiency Diode Sources (SHEDS) program. To meet the needs for this project, the Optoelectronics Division has developed a new laboratory at NIST to measure electrical power, optical power, wavelength and line width, and junction temperature for lasers supplied by project participants. We describe a novel flowing-water optical power meter (FWOPM) that we have developed to meet the unique optical power measurement challenges presented by these lasers. We have also developed a new method for determining the average laser junction temperature through a simple model of laser waste heat as a function of drive current and cooling temperature. In addition, we present a preliminary uncertainty analysis that yields ∼1 % uncertainty (with a confidence interval of 95 %) for the efficiency measurements. We intend to continue offering these measurements as part of the NIST Calibration Services for optical radiation measurements, which are available to anyone for a fee.NIST has been tasked by DARPA to provide wall plug efficiency and spectral measurements of high-power high-efficiency laser diodes and arrays for DARPA’s Super High Efficiency Diode Sources (SHEDS) program. To meet the needs for this project, the Optoelectronics Division has developed a new laboratory at NIST to measure electrical power, optical power, wavelength and line width, and junction temperature for lasers supplied by project participants. We describe a novel flowing-water optical power meter (FWOPM) that we have developed to meet the unique optical power measurement challenges presented by these lasers. We have also developed a new method for determining the average laser junction temperature through a simple model of laser waste heat as a function of drive current and cooling temperature. In addition, we present a preliminary uncertainty analysis that yields ∼1 % uncertainty (with a confidence interval of 95 %) for the efficiency measurements. We intend to continue offering these measurements as...

We present a technology for achieving a significant line narrowing (by approximately an order of magnitude) and stabilization of the emission wavelength of multimode high-power laser diodes and arrays. This volume Bragg grating technology also can achieve a significant reduction in the slow axis divergence of a broad-area laser diode simultaneously with spectral line narrowing.

We present a technology for achieving a significant line narrowing (by approximately an order of magnitude) and stabilization of the emission wavelength of multimode high-power laser diodes and arrays.

Thin-film lithium niobate (TFLN) has emerged as a promising platform for the realization of high-performance chip-scale optical systems, spanning a range of applications from optical communications to microwave photonics. Such applications rely on the integration of multiple components onto a single platform. However, while many of these components have already been demonstrated on the TFLN platform, to date, a major bottleneck of the platform is the existence of a tunable, high-power, and narrow-linewidth on-chip laser. Here, we address this problem using photonic wire bonding to integrate optical amplifiers with a TFLN feedback circuit. We demonstrate an extended cavity diode laser with an excellent side mode suppression ratio exceeding 60 dB and a wide wavelength tunability over 43 nm. At higher currents, the laser produces a high maximum on-chip power of 76.2 mW while maintaining 51 dB side mode suppression. The laser frequency stability over short timescales shows an ultra-narrow intrinsic linewidth of 550 Hz. Long-term recordings indicate a high passive stability of the photonic wire bonded laser with 58 hours of mode-hop-free operation, with a trend in the frequency drift of only 4.4 MHz/h. This work verifies photonic wire bonding as a viable integration solution for high performance on-chip lasers, opening the path to system level upscaling and Watt-level output powers.

We propose and experimentally demonstrate a compact hybrid-integrated multi-port multi-wavelength laser source (MP-MWL) for optical input/output (I/O) technology. A multi-wavelength high-power distributed feedback laser array (DFB LA) with slab-coupled optical waveguide (SCOW) and highly reflective and anti-reflective (HR-AR) coated facet is utilized to achieve simultaneous high-power output of multiple wavelengths. The reconstruction equivalent chirp technique provides highly precise control of the grating phase of the DFB laser and an equivalent π phase shift is introduced to provide single-longitudinal-mode lasing. Employed as a splitter and combiner network, an 8×8 multi-mode interferometer (MMI) on the passive silicon nitride photonic platform contributes to significant bandwidth enhancement. The output from the fiber array (FA) of the proposed MP-MWL has 8 fibers each carrying all 8 wavelengths, for a total of 64 addressable carriers. The photonic wire bonding technique enables the compact and efficient hybrid integration of the LA, MMI and FA. The side mode suppression ratios of all 8 wavelengths are above 42 dB at a 20°C working environment. A wavelength spacing of 100 GHz is achieved, and 87.5% of the wavelengths exhibit a deviation within ± 0.15 nm. Additionally, the relative intensity noise is below -135 dB/Hz, while the Lorentzian linewidth is 379.9 kHz. Furthermore, clear 25 Gb/s non-return-to-zero (NRZ) eye diagrams are obtained for all 64 carriers with the external lithium niobate Mach-Zehnder modulator. The proposed MP-MWL might be applied in optical I/O technology where the dense wavelength division multiplexing (DWDM) technique is required for increasing bandwidth in data centers.

In this paper, the research progress of single-frequency fiber oscillators are introduced in the terms of wavelength expansion, the development of single frequency fiber amplifiers are introduced in the terms of power scaling. Besides, the research achievements of 1 μm-band high-power narrow-linewidth fiber laser are summarized based on the techniques of generating narrow-linewidth seed sources. Then the development trend and main challenges of high-power single-frequency and narrow-linewidth fiber laser are analyzed. The key technologies of high-power narrow-linewidth fiber laser are summarized and discussed. Finally, applications in various fields based on the current development status of high-power narrow-linewidth fiber laser are introduced.