Highly Reliable 1.5-μm DFB Laser With High-Mesa SIBH Structure

The degradation behavior of 1.5-mum uncooled distributed feedback (DFB) lasers with a semi-insulating buried heterostructure during constant-power aging is investigated. Long-term stability is achieved by suppressing the t^0.5 deterioration in the current increase rate (second-stage degradation). The improvement in reliability is attributed to the fact that some defects on the grating interface are simultaneously suppressed by the mutual diffusion that occurs when growing the SI-InP layer. We realized a DFB laser with high reliability (< 1000 failure digits) at 95 degC that is capable of error-free 2.5-Gb/s 80-km transmission at -20degC to 100 degC     

Analysis of interior degradation of a laser waveguide using an OBIC monitor

We propose a novel optical-beam-induced current (OBIC) measurement technique for detecting the degradation in the interior of a waveguide. This technique uses an incident light with a wavelength longer than that of the band edge of the active layer. An OBIC scan image was obtained at a wavelength of 1.6 μm, which was 50 nm longer than the PL peak wavelength in the active layer of the degraded laser, and the OBIC became sensitive to some degradation when a long distance guided light was used. Furthermore, we confirmed that the degradation mechanism of the t^0.5 deterioration property is mainly governed by diffused defects at the waveguide other than those in the vicinity of the AR facet in a DFB laser.     

Optical tap array using distributed-index planar microlens

The letter describes a novel optical tap array by using a two-dimensional array of planar microlenses. The present device is used to monitor a part of light which is transmitted through optical fibres. Planar microlenses to focus the light have been monolithically fabricated by the use of the electromigration technique; the focal length is 3 mm and NA is 0.15. The coupling efficiency of the initial device was 52% for coupling multimode graded-index fibres.     

Low-temperature CW operation of GaInAsP/InP surface-emitting laser with circular buried heterostructure

The first CW operation of a GaInAsP surface-emitting laser has been demonstrated at 77 K. The active region was made to form a 15 ?m-diameter circular mesa shape and was buried with p?n current-confining layers. The minimum CW threshold current was 19 mA at 77 K, and single-longitudinal-mode oscillation has been achieved.     

Vertical cavity surface-emitting laser with an AlGaAs/AlAs Braggreflector

The letter elucidates the room temperature pulsed operation of a vertical cavity surface-emitting laser with an electrically conductive AlGaAs/AlAs distributed Bragg reflector (DBR). The maximum reflectivity of a DBR grown by MOCVD was 96% at 0.88 μm wavelength. The threshold current of 30 μm diameter devices was 200 mA under room temperature pulsed condition, which is the lowest value for such a broad area structure     

GaInAsP/InP surface-emitting lasers with current confining structure

In order to reduce the threshold current of GaInAsP/InP surface-emitting (SE) lasers, we search for an effective current confining structure and examined several types; round-low-mesa, round-high-mesa/polyimide-buried, buried-heterostructure (BH), and planar-buried-heterostructure (PBH). The minimum threshold current was reduced down to 18 mA at 77 K and the threshold current density was estimated to be reduced to 3 kA/cm². The operating temperature has been raised to -10°C (263 K). The longitudinal-mode hopping was first observed for GaInAsP/InP SE lasers. The effective refractive index for GaInAsP/InP SE lasers was 4-5, that was almost the same as conventional edge-emitting lasers.     

Micro-optical bench for alignment-free optical coupling

We propose an optical coupling module, the micro-optical bench, designed for the purpose of completely passive alignment of optical components. The principle is for one to position a planar microlens array, semiconductor device submounts, and optical fibers by using reference planes and V grooves made on a Si substrate. A prototype was fabricated, and we achieved an optical coupling loss of less than 3 dB; small deviations among channels as low as 1 dB were achieved without any precise alignment. For multimode fibers, a coupling loss of approximately 0.5 dB was obtained.     

Monolithic integration of Pb(Zr,Ti)O3 thin film based resonators using a complete dry microfabrication process

Monolithic fabrication of lead zirconate titanate [Pb(Zr,Ti)O₃ or PZT] based thin film resonant devices such as microcantilevers, Lamb wave and bulk acoustic wave resonators are demonstrated. High-performance PZT thin films with a thickness of 2.6 μm are prepared on a silicon on insulator wafer by a sputtering deposition process. A highly selective reactive ion etching process is employed for micro-patterning of PZT, platinum electrodes, and SiO₂ insulation layer. Self-actuation of the PZT microcantilevers is demonstrated and the frequency response is characterized using a laser Doppler vibrometer. The frequency response of the Lamb wave resonator is evaluated by measuring its transmission characteristic using a network analyzer. For a Lamb wave resonator with a length of 240 μm and an interdigital period of 80 μm, the 1st order and 2nd resonance frequencies are 15.3 and 41.8 MHz, respectively.     

Improved distributed-index planar microlens and its application to 2-D lightwave components

A recent improvement of a 2-D array of distributed-index (DI) planar microlenses is presented to demonstrate a 2-D integrated optical component using a planar microlens array. These components are made by stacking planar microlens arrays and other planar optical devices. The improved planar microlens has f = 2.0 mm, a N.A. = 0.23, and its spherical aberration is very small. A fiber coupler is demonstrated. From a preliminary experiment, it is shown that the coupling loss of each channel is <0.5 dB for coupling 50-micron core DI fibers.