Masahiro Uemukai

Monolithic integrated-optic position/displacement sensor using waveguide gratings and QW-DFB laser

A monolithic fully-integrated interferometer position/displacement sensor is proposed. The device is implemented with waveguide grating components, a GRIN SCH SQW DFB laser and photodiodes. A prototype device of 6.5/spl times/2.0 mm/sup 2/ chip size and 0.4/spl times/0.4 mm/sup 2/ sensing beam aperture is fabricated, and the sensor operation of submicron resolution is demonstrated.<<ETX>>

Parabolic-confocal unstable-resonator semiconductor lasers-Modeling and experiments

Surface-emitting all-grating-based unstable-resonator lasers, suitable for integration with diffractive beam-forming elements, have been experimentally and theoretically studied. The lasers exhibit single spatial mode operation for a device width of 160 /spl mu/m. The device performance is modeled using a beam propagation method, which accounts for spatial hole burning as well as thermal and carrier diffusion effects. Near- and far-field calculations are incorporated to facilitate the comparison with the experimental results. To achieve high-quality beam forming, it is essential that the wavefront of the guided optical mode is well defined and stable. Using the model, we study the dependence of the wavefront distortion on various parameters and show how these distortions affect the far-field characteristics. The results from the simulations agree well with the experimental work. We find that the laser performance is to a large extent controlled by thermal effects. At low-power operation, these effects can be compensated for, for a range of the injection current, by modifications of the resonator or outcoupler grating geometries.

Grating coupled surface emitters: integrated lasers, amplifiers, and beam shaping outcouplers

Grating coupled surface emitting lasers (GCSELs) are in- plane lasers monolithically integrated with grating outcouplers for beam shaping and image generation. Highly directional and efficient outcouplers can be formed using various grating and waveguide geometries. Beam shaping features are incorporated using a computer generated waveguide hologram that allows the wavefront of the emitted light to be tailored for the required beam shape. Requirements on the integrated in-plane laser include a wide and spatially coherent guided wave with a minimum of wavefront distortion and a stable emission wavelength. Promising lasers for this purpose are master-oscillator power-amplifier configurations as well as various kinds of unstable resonator designs. Here we present results from modeling and experiments on the key elements of GCSELs as well as fully integrated GCSELs of linear and circular geometries.

InGaAs/AlGaAs Quantum Well Laterally-Coupled Distributed Feedback Laser

InGaAs/AlGaAs quantum well laterally-coupled distributed feedback (LC-DFB) laser is designed and fabricated by electron beam lithography and reactive ion etching. The LC-DFB laser eliminates the need of a crystal regrowth in a conventional DFB laser fabrication process. A single mode lasing at a wavelength of 967.8 nm with a side mode suppression ratio of 46 dB was achieved under CW operation at room temperature. The threshold current and maximum peak output power were 15 mA and 19 mW at 90 mA injection, respectively.

Monolithically Integrated Master Oscillator Power Amplifier with Grating Coupler for Collimated Output Beam

A monolithically integrated master oscillator power amplifier with a grating outcoupler for emitting a collimated beam is demonstrated. In order to improve the device performance, theoretical simulation is performed based on the beam propagation method, and both compensation for wavefront distortion produced in the amplifier and optimization of the radiation decay factor are incorporated in a new design of the grating outcoupler. The device was fabricated by a simple process without regrowth. Stable single-mode lasing up to 183 mW output power at a wavelength of 985 nm was obtained under CW operation. As a result of optimization to minimize the divergence angle of the output beam, a well-collimated beam, with a nearly circular profile and divergence angles smaller than 0.28°×0.38°, was maintained in high-power operation.

Integrated AlGaAs Quantum-Well Ridge-Structure Two-Wavelength Distributed Bragg Reflector Laser for Terahertz Wave Generation

An integrated two-wavelength distributed Bragg reflector (DBR) laser consisting of two DBR lasers and a Y-branch waveguide amplifier was designed and fabricated. The optical waves from the two DBR lasers are combined into a single output channel of the Y-branch waveguide amplifier and emitted from the output facet. Laser performances of the same output level of ~10 mW and a wavelength difference of 1.0–3.7 nm (0.47–1.8 THz beat frequency) with a side-mode suppression ratio of 30 dB were obtained. Coherent THz wave generation was also demonstrated by photomixing of the integrated two-wavelength laser output.

Monolithic integration of waveguide gratings and quantum-well distributed-feedback laser for implementation of subminiature optical-disc pickup head

We propose a subminiature optical-disc pickup head implementation by monolithic integration of wave- guide grating components, a graded-index separate-confinement heterostructure single-quantum-well distributed-feedback laser and photodiodes. Fabrication of a prototype device and the results of a preliminary experiment are presented.

Selective Disordering of InGaAs Strained Quantum Well by Rapid Thermal Annealing with SiO2 Caps of Different Thicknesses for Photonic Integration

Area-selective disordering of an InGaAs strained quantum well was performed by rapid thermal annealing with thick and thin SiO2 caps. The lasing wavelength difference as large as 23 nm was obtained between Fabry-Perot lasers in 300 nm and 30 nm capped areas. We present fabrication of lasers integrated with disordered passive waveguides and demonstrate significant reduction of the passive waveguide loss from roughly 40 cm-1 to 3 cm-1.

Broad-area and MOPA lasers with integrated grating components for beam shaping and novel functions

The work of the authors group on monolithic integrated in-plane semiconductor lasers using grating components are reviewed and the recent development is reported. The grating components provide not only feedback for lasing but also novel functions such as output beam shaping and wavelength tuning. The design and fabrication of the grating components in semiconductor waveguide are outlined, and the area-selective quantum-well disordering by impurity-free vacancy diffusion is described as an effective technique to reduce the absorption loss in the passive waveguide. Then, device description, design, fabrication and experimental results of integrated master oscillator power amplifier (MOPA) lasers, high-power tunable extended-cavity lasers, and a broad-area angled-grating distributed Bragg reflector (DBR) lasers using InGaAs/AlGaAs GRIN-SCH-SQW structures are presented. All the lasers have integrated beam forming grating coupler, and allow implementation of compact and stable lensless modules that emit a collimated output beam.

Tunable external-cavity semiconductor laser using monolithically integrated tapered amplifier and grating coupler for collimation

A novel lensless tunable external-cavity laser using monolithically integrated tapered amplifier, grating coupler (GC) and an external half mirror is proposed and demonstrated. It can be fabricated by a simple process and emits a collimated output beam. By making use of wavelength dispersion of the GC, the lasing wavelength can be angle tuned. Wavelength tuning over a wide range of 21.5 nm by 4.5/spl deg/ device rotation and an 84-mW output power were achieved under continuous-wave operation. A well-collimated output beam with a divergence angle as small as 0.3/spl deg/ was maintained over the entire tuning range.