Masato Wada

Optical-fiber variable-attenuator arrays using polymer-network liquid crystal

This paper describes compact variable optical attenuator arrays made by using fiber splicers and polymer-network liquid crystal. Fibers are inserted into the splicers and the gaps between the ends of the fibers are filled with the polymer-network liquid crystal. The residual loss for each array element is low (about 0.8 dB), the attenuation of 1.55-/spl mu/m light is about 8 dB and the driving voltage is 20 V/sub rms/. The polarization dependence is <2 dB. The power consumption is also very low (30 nW/ch). They are used for channel power equalizers for WDM systems.

Liquid crystal variable optical attenuators integrated on planar lightwave circuits

Variable optical attenuators using polymer-network liquid crystal have been integrated with the pitch of 250 /spl mu/m on planar lightwave circuits. Trenches are cut in the direction perpendicular to the parallel light waveguides into planar lightwave circuits, a transparent electrode is deposited inside the trenches, and the trenches are filled with polymer-network liquid crystal. The typical attenuation range is 18 dB when the driving voltage is <20 Vrms at 1.55-/spl mu/m wavelength. The power consumption is estimated to be very low (200 nW/ch).

28.3 dB gain 1.3 mu m-band Pr-doped fluoride fiber amplifier module pumped by 1.017 mu m InGaAs-LD's

A praseodymium (Pr)-doped fluoride fiber amplifier (PDFA) module that is pumped by strained quantum-well InGaAs laser diodes (LDs) is described. The amplifier module, consisting of a four LD pump configuration and a high NA Pr-doped fluoride fiber with low scattering loss, exhibits a maximum signal gain of 28.3 dB and a saturation output power of 6 dBm at a signal wavelength of 1.30 mu m. It is shown to be the most promising module for the 1.3- mu m-band optical amplifier.<<ETX>>

Compact optical-fiber variable attenuator arrays with polymer-network liquid crystals

Electrically controlled fiber variable-optical-attenuator arrays with polymer-network liquid crystals are shown to be compact and to have a large attenuation range (30-40 dB) and low residual loss (0.55 dB) at wavelengths from 1.3 to 1.6 mum. Their estimated power consumption is very low (<30 nW/channel), and arrays with more than ten channels can be made. The manufacturing process is simple: Trenches 30-100 mum wide are cut across parallel conductive-layer-coated optical fibers and are filled with a polymer-network liquid crystal. The attenuation properties depend on UV-curing conditions and on trench width.

15.1-dB-gain Pr/sup 3+/-doped fluoride fiber amplifier pumped by high-power laser-diode modules

A Pr/sup 3+/-doped fluoride amplifier pumped by high-power 1.017- mu m laser diode modules is demonstrated. Fiber-pigtail-type devices are used. A net gain of 15.1 dB is achieved for a 1.31- mu m signal at a pump power of 160 mW.<<ETX>>

A narrow beam 1.3-/spl mu/m-super luminescent diode integrated with a spot-size converter and a new type rear absorbing region

The device structure and performance of 1.3-/spl mu/m narrow beam superluminescent diodes (NB-SLDs), which consist of a spot-size converter and a new type rear absorbing region, are reported. A butt-jointed selectively grown spot-size converter (SSC) is employed to realize the narrow beam characteristics. The rear absorbing region is designed as a taper structure with a part of the region is inclined from the active-stripe axes. In order to investigate the effects of both SSC length and active-region length on device performance, two types of NB-SLDs, whose SSC and active-region lengths differ, are fabricated. An electrode to sweep out photoexcited carriers in the absorption region is formed on one device. By comparing the characteristics of these devices, we clarify that a 500-/spl mu/m-active-region device is suitable for high-output power operation, and a 400-/spl mu/m-active-region device is suitable for realizing short coherent length. The light-output power is 13.9 mW at 200-mA-injection current for the former device, and the full-width at half-maximum (FWHM) of the spectrum is 62.6 nm (calculated coherence length is 26.5 /spl mu/m) for the latter device. Very small spectral modulation index (0.015 at 5 mW-output power) is attained by grounding the absorption-region electrode. For the SSC length, a 300-/spl mu/m SSC device shows very narrow far-field patterns (FFPs) and very good fiber-coupling characteristics. The FWHM of horizontal and vertical FFPs are 8.9 and 10.6/spl deg/, respectively. Because of this narrow beam divergence, the coupling efficiency of -1.9 dB to a flat-end 4-/spl mu/m spot-size fiber is obtained without lenses. The alignment tolerance of this device to the fiber for both horizontal and vertical direction is more than 3 /spl mu/m at a loss of when -1 dB from the optimum coupling.

0.98- mu m strained quantum well lasers for coupling high optical power into single-mode fiber

An investigation of epitaxial-layer structures has yielded narrow ridge waveguide structure lasers capable of coupling high optical power into single-mode fiber (SMF). An optical power of well over 60 mW in SMF was obtained for a 2- mu m-wide ridge waveguide laser with a guided separate-confinement-heterostructure (SCH) epitaxial structure. Calculated results indicate that the stringent limit imposed on 0.98- mu m wavelength detuning is relaxed for such high optical power coupled into a SMF. The 0.98- mu m strained-quantum-well lasers thus show considerable promise as a practical low-noise pumping source for Er-doped optical-fiber amplifiers.<<ETX>>

ONE-LD-PUMPED Pr3+-DOPED FLUORIDE FIBER AMPLIFIER MODULE WITH A SIGNAL GAIN OF 23 dB

Pr3+-doped fluoride fiber amplifier (PDFA) is the most promising candidate for the 1.3 µm band optical amplifier1), because it offers the potential of high signal gain2,3), wide amplified bandwidth2) and high saturation output power4).

Laser diodes integrated with butt-jointed spotsize converter fabricated on 2-in wafer

Laser diodes integrated with spotsize converters by butt-joint technology combined with selective area metal organic vapor phase epitaxial (MOVPE) growth have been successfully fabricated. Satisfactory uniformity, reproducibility (>99%) and tolerance for low threshold current, a narrow emitted beam, and low optical coupling loss to fiber (<-2.4 dB) are obtained by using 2-in full wafer fabrication technology in the experimental fabrication. To investigate the tolerance in fabrication, the characteristic dependence on the variation of the wet etching time just before the butt-joint MOVPE growth and also on the mesa stripe width are investigated. A wide tolerance for these fabrication parameters is confirmed. The results indicate that the butt-joint technology is a useful and reliable process for realizing spotsize converters of the present type and also suggest that the technology is widely applicable to various photonic integrated circuits.

3-D semivectorical beam propagation analysis of a spotsize-converter-integrated laser diode in the 1.3-μm-wavelength region

Spotsize converters (SSCs), consisting of a lateral taper, thin-film core, and ridge, have been accurately designed to develop spotsize-converted laser diodes (SS-LDs) in the 1.3-/spl mu/m-wavelength region based on the 3-D semivectorial finite-difference beam propagation method (FD-BPM) with nonequidistant discretization. The effects of the structural parameters on the sum of spot-conversion loss and coupling loss between the laser diode eigenmode and single-mode fiber (SMF) eigenmode are clarified. It is shown that a small loss of around 1.5 dB can be realized by introducing nonlinear tapers to these types of SSCs. The calculated results agree well with the measured results.