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Technologies for high-density integration of optical and electrical components are indispensable for next-generation optical transceivers whose capacity will exceed 400 Gbps. 3-D vertical integration technology with high optical coupling efficiency between a single mode fiber (SMF) array and lens-integrated surface emitting laser (LISEL) array using micro electro mechanical system (MEMS)-based movable micro-mirrors can meet this requirement. Light emitted from the LISEL is reflected at the micro-mirror and coupled to the SMF. Since the micro-mirror can steer the beam emitted from the LISEL to the SMF, the coupling efficiency that depends on the alignment accuracy between the LISEL and SMF is adjustable. After the alignment is completed, the position of the micro-mirror is fixed to keep high coupling efficiency. An optical sub-assembly (OSA) incorporating the LISEL, micro-mirror, and SMF array was fabricated using surface mount technology. All optical components were passively aligned, and the positions of micro-mirrors were adjusted to make a precise optical coupling to the SMFs as a post alignment. To confirm the effectiveness of this post-alignment system, the characteristics of the optical coupling to the SMF array were measured. It was found that the position of the reflected beam could be controlled to sub-micro-meter accuracy.

As a solution to provide a small-size and low-cost 100-Gb/s optical module, direct optical coupling between a lens-integrated surface-emitting DFB laser (LISEL) array and a single-mode fiber (SMF) array is demonstrated. A very-small far-field angle ( $\sim 2$ °) was obtained by monolithic integration of an InP lens with a laser chip. As a result, each channel of the LISEL array can directly couple to an SMF without any additional external optical components. The measured misalignment tolerance between the LISEL array and an SMF array was sufficiently large, namely, $\pm 5.5~\mu \text{m}$ , at excess loss of 1 dB over all four channels with the maximum coupling efficiency of 8.4 dB. These measurement results are in good agreement with a theoretical calculation based on Gaussian optics. These results demonstrate that high coupling efficiency (−3 dB) can be achieved while large misalignment tolerance ( $\pm 4.5~\mu \text{m}$ ) at excess loss of only 1 dB is maintained.

A movable micro-mirror array is proposed for high-density multi-channel single-mode optical sub-assembly. Adjustable optical-coupling loss of over 2dB was confirmed from experiments of 4-ch array optical-coupling between DFB lasers and single-mode fibers using the micro-mirrors.

Technologies for creating cost-effective light-emission optical sub-assemblies (OSAs) are discussed from the point of view of laser diodes. A lens-integrated surface-emitting laser (LISEL), consisting of a DFB laser, integrated mirror, and integrated convex lens, has the potential to achieve light-emission OSAs. An OSA based on the LISEL is proposed, and the capabilities of direct and passively aligned optical coupling, isolator-free operation, non-hermetic packaging, and on-wafer testing are introduced.

Two multichannel 1.3-μ m lens integrated surface-emitting laser arrays for massive data links were fabricated. The basic structure of the lasers consists of a short InGaAlAs multiple-quantum-well distributed-feedback (DFB) active-stripe array monolithically integrated with both a 45° total reflection mirror and an aspheric collimation lens. One of them, a four-channel laser array based on this structure, exhibited clear 25-Gb/s eye openings up to 50°C over all four channels and achieved a total output of 100 Gb/s. The other laser, a multiple-wavelength array for wavelength-division-multiplexing applications, produces multiple-wavelength emission thanks to precisely modified DFB gratings by electron beam lithography. It exhibited nine-wavelength stable single-mode operation (side-mode suppression ratio >; 40 dB) between 1260 and 1290 nm at 3.7-nm intervals, and a clear 25-Gb/s eye opening for each wavelength. These two surface-emitting laser arrays have demonstrated their suitability for next-generation multichannel data links (including 100-Gb Ethernet and optical interconnects).

High-speed 1.3-μm directly modulated lasers (DMLs) have been developed to support sharply rising optical communications traffic. The most crucial requirement for these lasers is the ability to operate over a wide temperature range with no power-consuming electric cooler. Due to poor temperature characteristics resulting from its poor electron confinement in the multiquantum well, DMLs with InGaAsP material systems have been replaced by DMLs with InGaAlAs material systems, which have stronger electron confinement. In this paper, progress in uncooled 25-Gb/s 1.3-μm InGaAlAs DMLs is summarized. A 160-μm-long ridge-waveguide-type laser showed a lower threshold current Ith of 14.9 mA at high temperatures up to 95 °C, and a small signal-frequency-response bandwidth f3dB of 14 GHz was achieved at a bias current of 60 mA at 95 °C. Using this laser, clear 25-Gb/s operation was obtained at 95 °C. In addition, stable operation was achieved for up to 4000 h at 85 °C, indicating the basic applicability of the device to next-generation 25-Gb/s data communication systems. Furthermore, the developed technology was applied to a novel uncooled 25-Gb/s 1.3-μm surface-emitting laser for optical interconnects, in which a 45° mirror and a lens were integrated monolithically.

As a solution to provide small-footprint and low-cost light sources for silicon platforms, light sources using a lens-integrated surface-emitting laser (LISEL), and a grating coupler fabricated on a silicon-on-insulator substrate is proposed. Light emitted from the LISEL (based on an InP distributed feedback laser) has a narrow far-field pattern, so the LISEL can be directly mounted on the silicon platform with no additional external optical components. The alignment tolerance between the LISEL and grating coupler was experimentally measured. This measurement confirmed large alignment tolerance. The excess loss due to misalignment of ±5 μm is only 1.5 dB.

We proposed a perfectly facet-free surface-emitting 1.3-μm DFB laser toward cost-effective light source, and confirmed the same performances as the usual DFB lasers and an on-wafer measurement.

Low-cost optical assemblies for optical interconnections using lens-integrated surface-emitting laser are proposed. High coupling efficiency with single-mode-fibers of over −1.9dB and RIN below −140dB/Hz with large back reflection and 85°C/85% storage test are demonstrated.

A high-speed large-capacity optical printed circuit board (OPCB) for next-generation high-capacity routers and servers was developed. This OPCB is composed of a multilayer polymer optical waveguide, a receiver optical input/output (I/O) module (with a lens-integrated photodiode and a SiGe transimpedance amplifier), and a low-power (7.1 mW/Gb/s) transmitter optical I/O module consisting of a lens-integrated surface-emitting laser and complementary metal-oxide-semiconductor (CMOS) driver IC. A 1-Tb/s (20 Gb/s/ch × 48 ch per transmitter or receiver) large-capacity OPCB prototype was fabricated and demonstrated 20-Gb/s/ch operation.

40-Gb/s (4-ch x 10-Gb/s) operation of a 1.3-µm lens-integrated surface-emitting laser diode array was demonstrated by a CMOS shunt driver. Clearly opened eyes at 10-Gb/s were obtained for 4 channel simultaneous operation at 95°C.

A lens-integrated surface-emitting laser array has been developed for an optical module compliant with Parallel Single-mode 4-lane Multi-Source Agreement (PSM4 MSA) for 100GbE applications. High-efficiency optical coupling to SMF with two-lens configuration and uncooled 25-Gb/s operation over all four-channels were demonstrated.

A 1.3-μm wavelength optical link, which consists of a lens-integrated laser diode and a CMOS optical receiver, was developed. It achieves 25-Gb/s error-free 100-m multi-mode fiber transmission with sensitivity of −6.3-dBm OMA.

We have successfully grown highly strained GaInNAs/GaAs multiple quantum wells (MQWs) ranging from a single-QW (SQW) structure to a five-QW (5QW) structure without strain-compensation layers or Sb surfactant by molecular beam epitaxy (MBE). High-resolution X-ray-diffraction (HRXRD) measurements showed clear multiple reflections of GaInNAs QWs, which suggests their good structural quality. Photoluminescence (PL) measurements revealed that a triple-QW (TQW) structure had a strong PL intensity proportional to the number of QW layers, while the 5QW structure had a PL intensity that was five times less than that of the SQW structure. We fabricated GaInNAs/GaAs TQW edge-emitting lasers and demonstrated a record low-threshold current of 4.3 mA at a long wavelength of 1.29 μm

As a silicon photonics light source, a lens-integrated surface-emitting laser (LISEL) was integrated on a silicon-waveguide platform for the first time. Excess loss due to misalignment of +/-5 Pm between the LISEL and silicon waveguide is only 1.5 dB.

A hybrid integration of a surface emitting DFB lasers and a fully integrated transceiver CMOS chip was proposed for compact 100-Gb/s transceivers of optical backplanes and datacenter optical links.

Multiple-wavelength 25-Gb/s operation of a 1.3-μm-range surface-emitting laser array was demonstrated. The fabricated laser array, which consists of nine distributed-feedback (DFB) active stripes operating between 1260 and 1290 nm at 3.7-nm intervals exhibited clear 25-Gb/s eye openings.

Uncooled 25-Gb/s transmission of a 1.3-µm surface-emitting laser is demonstrated. A fabricated laser, which consists of an InGaAlAs-MQW DFB active stripe and surface-mountable structure, exhibited clear 25-Gb/s eye openings after 2-km SMF transmission up to 85°C.

Four-channel 25-Gb/s direct modulation of a 1.3-µm surface-emitting laser array with a surface mountable device structure was demonstrated. The fabricated laser array, which consists of InGaAlAs-MQW DFB stripes, exhibited a total output of 100 Gb/s with collimated optical outputs.

Recent progress in developing 1.3-um InGaAlAs-MQW directly modulated lasers is reported. Uncooled 25-Gbps operations over a wide temperature range were demonstrated. Clear eye opening up to 100 °C % was successfully obtained.

Recent advances in integrated photonic devices for next-generation Ethernet are described. In particular, 1.3-µm-range uncooled photonic devices (namely, electroabsorption modulator integrated lasers, directly modulated lasers, and lens integrated devices) are focused on. A key technology for uncooled operation is an InGaAlAs multiple quantum well (MQW), which produces a strong electron confinement. The electroabsorption modulator integrated lasers, which incorporated an InGaAlAs-MQW absorption layer, exhibit uncooled 25.8-Gbit/s and 43-Gbit/s single-mode fiber 10-km transmissions. The 1.3-µm directly modulated laser, which consists of an InGaAlAs MQW distributed feedback (DFB) active stripe, exhibits uncooled direct modulation at 25 Gbit/s. To improve the optical coupling of the directly modulated laser, we developed a lens-integrated surface-emitting laser, which incorporates an InGaAlAs DFB active stripe. This lens-integrated laser exhibits 25-Gbit/s direct modulation up to 100°C. Furthermore, the lens-integrated photodiode exhibited high speed (35 GHz), high responsivity (0.8 A/W), and large alignment tolerance (26 µm) for direct coupling to a single-mode fiber. These photonic devices have demonstrated their potential for implementation in cost-effective 100-Gbit/s and 40-Gbit/s Ethernet.

The uncooled 25-Gbit/s direct modulation of a 1.3-µm horizontal-cavity surface-emitting laser was demonstrated. A fabricated laser, which is directly mountable on a high-frequency coplanar line, exhibited 25-Gbit/s eye openings up to 100°C.

Circular, narrow beam emission of a lens-integrated surface-emitting laser operated at 1.3-µm wavelength was demonstrated. The laser consists of a distributed feedback laser cavity monolithically integrated with an etched 45° total reflection mirror and an etched InP lens. The profile of the etched InP lens was estimated to be a highly symmetrical parabolic shape that is ideal for the collimation of a Gaussian beam. A fabricated lens-integrated surface-emitting laser exhibited a circular, narrow far-field pattern with full-width at half-maximums of 3.9° × 3.5°. A highly efficient direct coupling to a single-mode fiber with a coupling efficiency of − 2.7 dB was also confirmed.

A novel 1.3-µm surface-emitting laser integrated with a monolithic InP bulk lens was demonstrated. The laser achieved very narrow far-field angles of around 2° leading to a −2.7 dB direct coupling to a single-mode fiber.

High-performance GalnNAs/GaAs triple quantum well (TQW) edge-emitting lasers were demonstrated. Al-free molecular beam epitaxy (MBE) is effective to prevent any Al impurity or contamination, which had appeared in previous GalnNAs materials, leading to a significant improvement in the photoluminescence intensity. By using this growth method, we have successfully grown highly-strained GalnNAs/GaAs TQW lasers that exhibit a record low threshold current of 4.4 mA at 25degC and a 40-Gbit/s direct modulation at 5degC. These results indicate that GalnNAs lasers are good candidates for future high-frequency operation cost-effective light sources.

We experimentally demonstrated that a record-low threshold current of 4.3 mA is achieved in long-wavelength, 1.29 μm, GaInNAs-TQW RWG lasers. Moreover, 40-Gb/s direct modulation of the laser is confirmedat 5°C.

Monolithically lens-integrated surface-emitting distributed-feedback (DFB) laser arrays and p–i–n photodiode arrays were developed. A combination of dry etching and wet chemical etching was used to fabricate a monolithic InP lens. The lens profile within ±10 µm from the lens center was estimated to be parabolic shape, which is ideal for the collimation of a Gaussian beam. A fabricated lens-integrated surface-emitting DFB laser exhibited a circular, narrow far-field pattern with full-width at half maximums of 3.9×3.5°. An efficient direct coupling of the lens-integrated DFB laser to a single-mode fiber with a coupling efficiency of -3 dB was confirmed. A four-channel lens-integrated surface-emitting laser array and a lens-integrated p–i–n photodiode array were used to fabricate a very compact 100 Gbps (25 Gbps × 4 channel) optical transceiver with 14×9 mm2 footprint.

Low-threshold GaInNAs single-quantum-well (SQW) lasers with emission wavelength over 1.3 mum are demonstrated. Epitaxial layers of the lasers are grown using an aluminium-free gas-source molecular-beam epitaxy (GS-MBE) to prevent any impurity or contamination related to aluminium that might be incorporated into the GaInNAs active layer. The fabricated laser is believed it exhibit the lowest threshold-current density (200 A/cm 2 ) among GaInNAs-SQW lasers grown by MBE. Moreover, record low threshold current (5.2 mA) and long-wavelength (1.31 mum) emission were achieved in a ridge-waveguide laser at 25degC under continuous-wave operation