In recent digital coherent transmission systems, it is necessary to improve the received Optical Signal to Noise Ratio (OSNR) after fiber transmission in order to achieve higher transmission capacity. Fiber Raman Amplifiers (FRAs) are well-known techniques for improving OSNR, especially backward FRAs, which are widely applied in high-capacity digital coherent transmission systems. However, pump lasers having higher output and lower power consumption are required since the Raman gain is small in the FRAs. As a means to realize these characteristics, a laser waveguide structure with a small optical confinement coefficient of the LD chip (low-Γ structure) is very effective. Especially, this makes Inter-Valence Band Absorption (IVBA) could be reduced by distributing an electric field toward the substrate side, and internal loss could be reduced to improve the slope efficiency. We have proposed a novel low-Γ structure consisting of a GaInAsP/InP electric field-controlled layer, which has an advantage of mass production. In this paper, we demonstrate 1W fiber output operation at 35 °C of Fiber-Bragg grating laser modules (FBG-lasers) for Fiber Raman Amplifier using a GaInAsP laser chip with electric field control layer for the first time. In order to realize high power at high temperature operation of 35 °C of laser chip temperature at a case temperature of 70 °C, we optimize the design of a laser chip waveguide keeping a single transverse mode to reduce the series resistance. With an operating current of 2.7 A, FBG-laser exhibits 7.8W of power consumption with 775mW of fiber output.
We have developed a semiconductor optical amplifier (SOA) based incoherent light source for a co-propagating distributed Raman amplifier. By utilizing the incoherent light source as a 1st-order pump of the Raman amplifier, we have experimentally verified the reduction of RIN transfer regardless of the presence of simultaneous amplification by 2nd-order coherent pumps. In addition, improved Q-factor has been demonstrated by 22.5 Gbaud polarization-division multiplexing 16 quadrature amplitude modulation (PDM-16QAM) transmission experiment over 2720 km in a re-circulating fiber loop. From subsequent experimental study, we have redesigned wavelength shifted 1st-order incoherent pump and measured at Raman gains in L-band wavelength.
This paper reviews research and development of 1060nm VCSELs at Furukawa Electric. We pursue the simultaneous
realization of three strong demands for low power consumption, high reliability, and high speed. For this purpose, we
have chosen compressively strained InGaAs/GaAs active layers emitting in a 1060 nm wavelength range because of their
advantages of lower threshold voltage, smaller defect propagation velocity, and larger material differential gain,
compared to those of GaAs/AlGaAs active layers widely used in 850 nm VCSELs. Oxide-confined and double intracavity
structures provide low and stable electrical resistance as well as low optical loss. The developed VCSELs
exhibited low threshold currents of 0.31 mA at 25 °C and 0.56 mA at 90 °C, together with highly uniform slope
efficiency distributions throughout a wafer. We also demonstrated 10 Gbps error free transmission at a very low bias
current of 1.4 mA, yielding low power dissipation operation of 0.14 mW/Gbps. Clear eye openings up to 20 Gbps were
confirmed at a low bias current of 3mA. A series of endurance tests and accelerated aging tests on nearly 5000 VCSELs
have proved Telcordia qualified high reliability and a very low failure rate of 30 FIT/channel at an operating temperature
of 40 °C and a bias current of 6mA, with a 90% confidential level.
The demand for the on board intra-chip optical interconnection as the "Green interconnect" have been growing so
rapidly in order to catch up the speed of the performance development of high performance computing systems. In this
report, our continuous study results expanding to intra-chip application in terms with power consumption and reliability
are shown for the "Green" 1060nm VCSEL arrays developed by Furukawa Electric1.
As the basic performance level, the clear eye opening up to 20Gbps was achieved with low power dissipation level of
160fJ/bit with voltage swing level of 130mVpp. This value would be considered as the same level of the 140fJ/bit in
10Gbps operation with 75mVpp.
In the reliability test, our large scale FIT rate test had been reached up to 7.8E7 device hours and the estimated FIT rate
of 30FIT/ch was obtained from no failure sample and confidence level of 90%. Our wear-out study was performed with
high stress test of 170°C ambient temperature and estimated failure rate for 10years service time was 0.3FIT/ch for this
mode. Our 1060nm VCSEL with low power consumption level of 140fJ/bit and high reliability of 30FIT/ch would be
projected to a light source for intra-chip application.
We report the performance of coarse-WDM (C-WDM) uncooled DFB lasers for upper 8 C-WDM wavelengths (1470~1610nm). Due to well-designed structures and well-controlled detuning, low threshold current, high slope efficiency, and high side-mode suppression ratio were maintained even at 85°C. For 2.5Gbps digital applications, these uncooled DFB lasers have clear eye opening, and can transmit through 100km standard single mode fiber with small dispersion penalty (<1dB). For repeater application of mobile communication system, low Relative Intensity Noise (RIN) level of -165dB/Hz at 2.2GHz and -168dB/Hz at 800MHz were achieved respectively at an optimized bias current of over 55mA, and third order distortion (IMD3) was less than -60dBc even at 85°C. For CATV return-path applications, second order distortion (IMD2) of less than -50dBc and IMD3 of less than -65dBc were achieved at 85°C. We performed accelerated aging test and estimated median lifetime was 105hours at 85°C with output power of 5mW.
This paper reviews the recent progress in 14XXnm-band pump lasers of new design concepts. One is the new packaging scheme with integrating multiple laser stripes and a polarization beam combiner, which brings various benefits in cost-performances of the optical amplifier both in EDF (Erbium doped fiber) and Raman configuration. This "hybrid" designed pump lasers offer stable low-DOP (degree of polarization) of 5% with the standing-alone laser package, and demonstrated the potential optical output beyond one watt with the significant saving factor in board-spaces and electrical power consumption.
The other is the inner-grating multi-mode (iGM) chip design, which integrates the wavelength stabilizer into the laser stripe and maintains stable multi longitudinal-mode oscillation. The "iGM" laser shows very low RIN (relative intensity noise) less than -150dB/Hz together with suppression of SBS (stimulated Brillouin scattering) in the transmission fiber.
We conclude that these new pump lasers, hybrid and iGM lasers, are promising candidates to the 14XXnm-band pump sources for co-propagating Raman-amplifier as well as EDF-amplifiers of next generation.
The requirements for 14XX nm pumps with wavelength range from 1400 to 1520 nm are not only higher output power but also lower degree of polarization (DOP) for preventing the problem due to the polarization-dependent-gain in Raman amplifier.
It is expected that co-propagating Raman pumping could improve system performances in comparison with using only counter pumping. To apply this scheme, the pump lasers should have enough low relative intensity noise (RIN) characteristics. In this paper, we will describe two novel concepts in 14XXnm pumps for Raman amplifiers from above requirements.
One is a low DOP-laser-module with ultra high optical output, achieving just one beam output with two-orthogonal polarization already scrambled from a SMF pigtail on a single package. The scrambled optical outputs is as high as over 1W and has DOP as low as 5% over the range of operating current.
The other is an ultra low noise and wavelength stabilized laser with integrated partial grating in the laser cavity, that is, eliminating an external fiber-Bragg-grating. The laser showed low noise characteristics less than -150dB/Hz of RIN and the stabilized multi-longitudinal-mode oscillation. We also investigated the advantage of this laser in reduction or suppression of the stimulated-Brillouin-scattering induced by pump.
High power pump lasers in wavelength range from 1400 to 1520 nm, namely 14XX nm lasers, are heavily demanded for Raman amplification as well as existing Erbium doped fiber (EDF) amplification in recent Dense Wavelength Division Multiplexing (DWDM) optical communication networks.We achieved the record highest optical power output 14XX nm pump laser of 400 mW at the single mode fiber end as a production level. Rollover fiber coupled power was over 500 mW for this device. The pump laser module with newly designed package operated up to the case temperature of 75 degrees C, and laser chip temperature of 25 degrees C. This is the first demonstration at the operating case temperature as high as 75 degree C with 400 mW optical power output range of 14XX nm pump laser module. The technical challenge for higher optical power output operation is how to minimize the heat-generation from the laser chip. For this purpose, we investigated two different design parameters: the operating power consumption and the operating current of the laser.We found that the former parameter is more effective design goal than the latter one, in order to realize both high optical power output operation and long term reliability performances. We also showed that the reliability performance in 14XX nm lasers is not dependent on the facet optical power output, but dominated by the junction temperature at the active region of the lasers.
Ultra high power 14XX (1400-1520) nm lasers are required for erbium doped fiber amplifiers (EDFAs) and Raman amplifiers in dense wavelength division multiplexing (DWDM) systems. To realize both high-power and high-reliability performances, we introduced a novel concept in laser diode (LD) chip design in terms of energy conversion efficiency. We also investigated the dependency of laser cavity length on LD characteristics to minimize the total power consumption of both the LD-chip and the LD-module with thermal electric cooler. Using this concept, we successfully reduced the total power consumption of the LD-module by 2Watts, comparing with an old-generation chip design. We have developed the next-generation chips for ultra high power LD-modules with over 300mW fiber-coupled-power in the range of 1400nm-1520nm lasing wavelength, which are suitable pumping sources for Raman amplifiers. The stable operation over 4000hrs in the reliability test under 60 degree C was obtained at 90% of maximum rollover power, indicating that the next-generation chip is robust enough to commercial use. In addition, the cavity length dependency on the reliability performances has been studied. We found that activation energy was 0.62eV, which is consistent with any cavity lengths, and that no degradation of reliability is observed as the facet optical power increases.
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