Hiromi Oohashi

Spectral Linewidth Reduction in Widely Wavelength Tunable DFB Laser Array

We have developed an L-band tunable distributed feedback laser array (TLA) with a new design to reduce the spectral linewidth. A wide wavelength tuning range of ~ 40 nm is obtained with a high fiber output power of 20 mW and a high side-mode suppression ratio of >50 dB in the TLA module. A narrow linewidth of less than 580 kHz is achieved over the entire tuning range. Furthermore, we investigated the causes of linewidth variation. We found that a TLA with a longer cavity is more tolerant to external feedback, which reduces the variation in linewidth.

Metalorganic molecular beam epitaxy of strained InAsPInGaAsP multi-quantum-wells for 1.3 μm wavelength laser diodes

This paper describes the growth of both InAsP single layers and InAsPInGaAsP multi-quantum-well (MQW) structures by metalorganic molecular beam epitaxy (MOMBE). The AsP ratio in the InAsyP1−y films is proportional to the ratio of the AsH3PH3 supply sources. The well-number dependence of the MQWs is characterized by X-ray analysis, photoluminescence (PL), and transmission electron microscopy, revealing that the critical thickness of InAs0.5P0.5 is approximately 70 nm at 520°C. The PL spectrum of an MQW with 8 nm thick InAsP well layers has a full width at half maximum (FWHM) of 4.1 meV at 4 K. The MQW lasers have a threshold current density of 0.74 kA/cm2 with a cavity length of 300 μm. The maximum operating temperature is as high as 145°C for a 10-well MQW laser with cleaved facets.

Widely Wavelength-Tunable DFB Laser Array Integrated With Funnel Combiner

A wavelength-tunable distributed feedback (DFB) laser array integrated with a funnel combiner is described. Two types of optical combiner, namely a multimode interferometer (MMI) combiner and a funnel combiner, are compared theoretically and experimentally. It is shown that the funnel combiner is superior in terms of wavelength dependence and fabrication tolerance. The laser module covers the full C-band wavelength range ( ~38 nm), and a high fiber output power of 40 mW (16 dBm) is obtained with stable single-mode operation.

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A 1.3- monolithically integrated light source for metro area 100-Gb/s Ethernet is developed. Four 25-Gb/s electroabsorption modulators integrated with distributed-feedback lasers and their multiplexer are monolithically integrated on one chip. A shallow ridge waveguide is used for lasers and modulators for large modulation bandwidth, and a deep ridge waveguide is used for the multiplexer region due to its low bending and radiation losses. The integration of hetero-waveguide devices enables the very small chip size of 22.6 . With the device, 100-Gb/s (4 25-Gb/s simultaneous) operation is demonstrated with the clear eye-openings, and error-free 40-km single-mode fiber transmission is achieved for the first time.

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We have developed wavelength-selectable arrayed DFB lasers with an integrated MMI coupler and SOA for WDM systems. Arrayed DFB lasers having eight and sixteen channels of DFB lasers are fabricated. The good uniformity of the DFB lasers characteristics provides uniform threshold current with the standard deviation of 0.37 mA in the arrayed 16 DFB lasers. The lasing wavelength difference between each laser is set to 3 nm, which corresponds to wavelength tuning range with a 30-degree temperature change. Wavelength range as wide as 46.9 nm is achieved with the 16 DFB lasers with a temperature control of 30-degree.

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A compact electroabsorption modulators integrated distributed feedback (EADFB) laser array module has been developed for 100-Gb/s Ethernet. Four 25-Gb/s EADFB lasers and an optical multiplexer are monolithically integrated on one chip in an area of only 2 mm × 2.6 mm. As a result, a compact 12 mm × 20 mm EADFB laser array module is achieved. A bridge-type RF circuit board is employed to transmit high-frequency, 4 × 25-Gb/s, electrical signals effectively in a narrow package and improve the electrical/optical response of the module. The module has a 3-dB frequency bandwidth of 20 GHz for the four lanes assigned in 100-Gb/s Ethernet. Furthermore, the possibility of realizing low-driving voltage operation is investigated to reduce the power consumption of the module. An error-free transmission through 10 km of single-mode fiber at 100 Gb/s with a modulation voltage of only 1 V is demonstrated.

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High‐temperature operation of InAsP‐based laser diodes at 1.3 μm has been realized according to guidelines of a large conduction‐band‐offset material (ΔEc) with a large optical confinement factor (Γ). Using photoluminescence excitation spectroscopy measurements, it was found that the conduction‐band offset of InAs0.52P0.48P/InGaAsP is the half of the band‐gap energy difference (0.5 ΔEg), which is larger than that of conventional quaternary material systems. A strain‐compensation growth technique enabled the fabrication of a large number of wells for large Γ. For broad‐area laser diodes, the maximum operating temperature increased as the number of wells increased from 4 to 15. In buried heterostructure lasers with ten wells, with high‐reflectivity coating on both facets, continuous‐wave lasing operation at temperatures up to 150 °C was achieved with a characteristic temperature of 59 K (30

25-Gb/s Monolithically Integrated Light Source for Metro Area 100-Gb/s Ethernet

We demonstrated a 25-Gb/s direct modulation up to 85degC with a 1.3- mum InGaAlAs ridge-waveguide multiple-quantum-well distributed-feedback laser. The dependence of the relaxation oscillation frequency on current was 3.3 GHz/mA1/2, and this is the highest value ever reported for 200-mum-long lasers in the 1.3-mum wavelength region. The alpha parameter was around 2.7 at 25degC, and an error-free operation after a 10-km single-mode fiber transmission was obtained up to 85degC.

46.9-nm wavelength-selectable arrayed DFB lasers with integrated MMI coupler and SOA

The wavelengths of tunable distributed amplification (TDA) distributed feedback (DFB) lasers consisting of multiple units including an active region and a tuning region can be changed without mode hopping. To expand the tuning range of TDA-DFB lasers, an asymmetric periodic structure is proposed where the units in the cavity have different lengths. It is shown theoretically that the asymmetric periodic structure is effective for expanding the mode-hop-free tuning range. In addition, a tunable laser array was fabricated consisting of six TDA-DFB lasers with an asymmetric periodic structure. A total wavelength tuning range of 44 nm was successfully obtained by expanding the tuning range of each laser, which corresponded to 110 channels with a 50-GHz grid. Moreover, the channel switching speed was investigated in relation to thermal drift. A switching time of less than 40 μs with a frequency deviation of less than 1 GHz was achieved with a thermal drift suppression technique that used the tuning regions of non-lasing lasers as heaters for temperature compensation.

A Compact EADFB Laser Array Module for a Future 100-Gb/s Ethernet Transceiver

This paper reports of our study on using dry etching and metalorganic vapor phase epitaxy (MOVPE) to fabricate of buried-heterostructure (BH) InGaAsP-InGaAsP strained layer MQW lasers. With a dry-etched mesa there was anomalously large Zn diffusion into the mesa structure and it seriously degraded the lasing characteristics. Therefore, we inserted a buffer layer between the side wall of the dry-etched mesa and the p-InP current blocking layer. The buffer layer almost entirely eliminates Zn diffusion without changing the mesa geometry unlike the wet-etching treatment of the mesa structure. Fabricated lasers show high performance, high uniformity and good reliability.