Solid State and Fiber Lasers performance benefits from utilizing highly efficient high brightness wavelength-stabilized pumps. Full wavelength locking in the wide range of operating current and heatsink temperature significantly simplifies overall construction of the Solid State and Fiber Lasers. Thus, stability of lasing wavelength against current and temperature variation has recently become an additional imperative requirement. We report on high power multimode pumps that operate at 878.6nm and 975nm. We discuss on chips’ and packaged pumps’ performance that features high power conversion efficiency (PCE) (up to 60% ex-fiber) and full wavelength locking (40-45 dB) in the wide range of driving current. Laser diode chip and packaged pump devices are produced by high-volume scalable technology which ensures full wavelength stabilization in the wide range of heatsink temperatures (10°C to 50°C range). We present performance of several 878.6nm pump models rated to operate reliably in 30W-120W power range as well as performance of 975nm pumps designed for high efficiency operation at elevated temperature.
We report on new generation high power multimode pumps based on long cavity AlGaInAs/GaAs 9XX-nm chips. These chips are produced in high volume by Solid Source MBE growth on four-inch diameter GaAs wafers. Uniformity of material grown on multi-four-inch wafers is presented. We also demonstrate the uniformity of lasing parameters of ChipOn-Submount (COS) across individual four-inch wafers and across the entire 19”-diameter MBE-platen growth area. We discuss the performance of high power pumps based on simple spatial beam combining. Ultimate ex-fiber (~100 µm core diameter) power launched in CW and QCW modes of operation was recorded in excess of 350 W and 450W, correspondingly. We demonstrate fully wavelength stabilized operation in driving current range in excess of 22A and exfiber power in excess of 135W.
We report on high efficiency multimode pumps that enable ultra-high efficiency high power ECO Fiber Lasers. We discuss chip and packaged pump design and performance. Peak out-of-fiber power efficiency of ECO Fiber Laser pumps was reported to be as high as 68% and was achieved with passive cooling. For applications that do not require Fiber Lasers with ultimate power efficiency, we have developed passively cooled pumps with out-of-fiber power efficiency greater than 50%, maintained at operating current up to 22A. We report on approaches to diode chip and packaged pump design that possess such performance.
V. Gapontsev, N. Moshegov, I. Berezin, P. Trubenko, A. Komissarov, D. Miftakhutdinov, I. Berishev, N. Strougov, V. Chuyanov, O. Raisky, A. Ovtchinnikov
We report on GaAlInAs/GaAs lasers manufactured by the industry’s biggest production MBE tool. This MBE reactor allows for growth on 23 three-inch diameter wafers at a time, at a cost that compares favorably with the MOCVD method. Data on chip-on-submount performance and uniformity across the entire MBE-growth area are presented and compared to the quality of material produced by smaller size production MBE tools. We also present data on performance characteristics of spatially combined fiber coupled passively cooled single emitter-based pumps. The data include performance characteristics of devices operating at ~805nm and ~975nm wavelengths when driven in CW, QCW and pulsed modes; both pumps use ~105μm core diameter fiber to launch power confined within NA<0.15.
The majority of fiber laser volume applications are price sensitive. Therefore, the availability, quality and cost of singleemitter-
based pumps will have decisive impact on the breadth of further fiber lasers' acceptance. Availability and cost
should not come in expense of further improvement in pumps' performance and reliability. Here we report on optimized
high-power and high-brightness wavelength stabilized CW devices. Performance of CW pumps rated for 100W and
50W power is discussed. Pumps launch over 98% output power into a spectral window of 975±0.5nm at driving currents
ranging from 2A to 12A and the heatsink temperature variation from 20°C to 50°C. Such performance qualifies these
wavelength-stabilized pumps for use in many air-cooled and special applications.
Further acceptance and fiber lasers and direct diode systems commercial success greatly depend on diodes' availability
and cost ($/W). These two parameters should not compromise pumps' performance and reliability. We report on two
high-brightness CW devices: high-power module launching over 100W and a pump capable of launching 50W of
wavelength-stabilized emission. Devices are based on a single emitter platform and utilize a 105 μm core diameter fiber;
radiation is confined within NA<0.13 in both designs. These hermetically sealed modules require passive cooling and
are designed to operate with ≤ 30°C diodes' junction overheat. CW peak power efficiency is higher than 55% for both
devices. The 25-30dB isolation option (feedback protection at 10XX-nm) is optional in either package. Modules have
the industry's smallest footprint and are perfectly suited to serve pumping fiber lasers and direct materials processing
markets.
Advanced high volume applications require pumps with high power, high brightness, and high power efficiency. New
generation devices meet all of these challenging requirements, while still maintaining the advantages of distributed
pumping architecture including high reliability inherent to single emitter sources. Based on new-generation long-cavity
diode chips, new pumps are capable of more than 60W CW power ex-fiber output (100 μm core diameter) into NA ~
0.12. Peak power efficiency stays over 60%. All of the above is provided at room heatsink temperature, maintained by
basic air- or water-cooling.
Higher reliability and power efficiency achieved with low-demanding cooling make single emitter diodes a more
effective pump source than monolithic laser diode arrays. Continuously improving performance and increasing
brightness of single emitter pumps are accompanied with a steady reduction of cost of pumping (dollar-per-watt).
Performance advantages do not compromise reliability of the pumps. These features ensure that single emitter diodes are
the most effective solution even for multi-kWatt systems pumping. Here we report on a recent progress in single-mode
and multi-mode edge-emitting diodes.
External cavity lasers (ECL) based on semiconductor diode gain
elements and Fiber Bragg Gratings (FBG) have been developed for
Telecom (OC-48) nd Analog (CATV, QAM) applications. They possess
very narrow linewidth (100 kHz) and exceptional wavelength stability.
These qualities makes them attractive platform for implementation of
heterodyne sources and Optical Phase Locked Loops (OPLL) for
Microwave Photonics applications.
We discuss two types of such heterodyne sources: heterodyne
oscillator based on heterodyning of two ECL, and fixed frequency
heterodyne oscillators based on ECL with FBG written in the polarization maintaining fiber.
All two types of heterodyne sources were built based on industry
standard 14-pin butterfly package. All of them exhibited excellent
wavelength stability (less than 1 pm/mA and 1-2 pm/°C).
Fixed frequency sources provided beat oscillation around 40 GHz.
We present performance characteristics and measurement data on
(linewidth, phase noise, heterodyne mixing, etc.) and discuss the merits of ECL use as heterodyne sources for Microwave Photonics applications.
Directly modulated External Cavity Laser Diode (ECLD) is an attractive alternative for extended reach source lasers for metro area telecommunications. This paper reports ECLD with transmission rate of 2.5Gbit/s and transmission distance of 650 km packaged in industry standard 14pin butterfly package. High stability package was the key in achieving Telcordia qualification. Combination of narrow linewidth and high bandwidth allows OC-48 transmission for distances comparable with the ones typical for EML. This lasers exhibit +/-30 pm wavelength stability over temperature range of -15 to +75C which makes it suitable for 100 and 50 GHz spacing applications without wavelength locker. ECLD can be operated using standard laser driver. Results using Vitesse 7940 and Analog Devises 2841 laser driver are presented. Typical extinction ratio obtained with these drivers was 10dB. Peak to peak jitter was <40ps. Dispersion penalty with these drivers transmission was found to be <1.9dB for the 650km of standard SMF-28 fiber (No dispersion compensation). Dispersion penalty vs transmission distance data will be presented. Results of the study of nonlinear effects in multi channels link will be reported. We observed that there was self phase modulation effect leading to reduction in dispersion power penalty. This effect can be used to transmit single channel over distances longer then 650km. We showed that there was negligible crosstalk penalty and no FWM penalty. Threshold for stimulated Brillouin scattering was also investigated.
We present design and fabrication considerations for a vertically integrated electro-optic polymer modulator. The hybrid design incorporates both passive and active core segments for optimized transmission and modulation of an optical signal. When compared to traditional structures, this vertically integrated modulator potentially reduces fiber coupling and propagation losses by more than 10 dB for a 6 cm structure while maintaining a minimized V(pi ).
The full potential of second order nonlinear polymers can be utilized in electro-optic polymer modulators with a DC biased operation scheme to greatly reduce the V(pi ). This technique makes use of the total achievable electro-optic coefficient, which can be more than three times as high as the residual value after the fast partial relaxation following corona or contact poling. As the result of the DC bias and with high (mu) (beta) chromophores, a low V(pi ) of 1.5 V was achieved with 2 cm long birefringent waveguide modulators at the wavelength of 1.3 micrometer. Results of 200 degrees Celsius stability experiment indicate that this scheme also enables electro-optic polymer devices to meet the stability required for high temperature hermetic sealing because the polymer does not need to be poled before device packaging.
We present design considerations and fabrication results for a vertically integrated waveguide polarization splitter. Fabrication techniques of shadow reactive ion etching (RIE) and variable photolithography exposure produced the required vertical waveguide structures. The fabricated vertical waveguide bends exhibit excess loss of only 0.2dB. By constructing this vertical bend with a birefringent polyimide, simulation results show the possibility of a polarization splitter with an extinction ratio of over 15dB. We demonstrate preliminary waveguide experiments showing the practicality of these structures as three dimensionally integrated optical devices.
We present a novel post-fabrication laser trimming technique to adjust the power splitting ratio of strip waveguide Y-branches made in thermally crosslinked electro-optic polymers. The trimming is based on the irreversible index change due to photobleaching. Our method uses simple equipment and the process takes only a few seconds. Waveguides made by both reactive ion etching and photobleaching are trimmable. An adjustable range of the splitting ratio as wide as is achieved with less than 0.2 dB of excess loss. This in situ trimming technique is effective for both the TE and TM modes of the waveguide and is very suitable for automated device processing.
We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling between channel waveguides and single-m,ode fibers. The taper smoothly converts a highly elliptical waveguide mode into a bigger and more circular mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5-2 mm in length is made in the low index upper cladding to reduce its thickness from several micrometers to zero, followed by the coating of a second upper cladding with index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows bigger a light propagates, whereas the confinement by the lower cladding and lateral confinement are hardly affected. The waveguide mode grows in the vertical direction away from the lossy ground electrode and substrate; therefore no compromise between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and tapered photoresist etching mask, are develop for making this vertical taper. Mode expansion and a 1.8 dB reduction in coupling los, which is not sensitive to waveguide width and polarization, is obtained in our preliminary experiment.
To demonstrate the feasibility of integrating polymer electro-optic devices on Si circuitry, we have vertically integrated a demonstration slab phase modulator on nonplanar VLSI circuitry. Optical loss measurements for waveguides fabricated on planarized circuits demonstrate that more practical devices like channel phase and Mach-Zehnder amplitude modulators can easily be integrated onto the circuits.
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