Takeshi Kitagawa

Pr 3+ -doped fluoride fiber amplifier operating at 1.31 μm

We propose what is to our knowledge the first use of a Pr(3+)-doped fluoride fiber amplifier as a practical amplifier operating at the 1.3-microm band, based on a demonstration of signal amplification and a spectroscopic investigation. The feasibility of the fluoride fiber amplifier is confirmed.

Pr3+-DOPED FLUORIDE FIBER AMPLIFIER OPERATING AT 1.31 µm

The authors propose a new Pr3+-doped fluoride fiber amplifier operating around 1.3 μm and demonstrate an effective amplification of 5.2 dB at 1.31 μm for the first time.

Erbium-doped silica-based planar-waveguide amplifier integrated with a 980/1530-nm WDM coupler

Erbium-doped glass waveguides are expected to be used as active elements in integrated-optical devices for optical-communication systems.1 Planar-waveguide optical amplifiers have been realized with straight and with curved erbium-doped glass waveguides.2,3 However, there have been no reports to date on sophisticated planar-waveguide amplifiers integrated with a pump/signal-light multiplexing circuit. Here, we describe what we believe to be the first integrated silica-based planar-waveguide amplifier on a silicon substrate with a 980/1530-nm wavelength-division-multiplexing (WDM) directional coupler lor multiplexing the pump and signal lights.

Optical amplification in Er3+‐doped P2O5–SiO2 planar waveguides

The small signal gain of Er3+‐doped P2O5–SiO2 planar waveguides is described with a homogeneous upconversion model. The homogeneous upconversion process accurately describes the absorption saturation at a wavelength of 0.98 μm. Interpretation of the absorption saturation provides homogeneous upconversion coefficients of 4×10−15 cm3 s−1 for a 0.54 wt % Er3+‐doped 14.6 wt % P2O5 codoped silica waveguide and 6×10−18 cm3 s−1 for a 0.46 wt % Er3+‐doped 21.6 wt % P2O5 codoped silica waveguide. The upconversion process occurs in the Er3+ ion rich phase in the P2O5–SiO2 core glass. A calculation that includes the homogeneous upconversion process proves that the gain can be enhanced by codoping the planar waveguide with P2O5. A gain of 20 dB is calculated with an Er3+ ion concentration of 0.4–0.7 wt % and a waveguide length of 40 cm when the pump power is 100 mW and 20 wt % P2O5 codoped Er3+‐doped silica‐based planar waveguides are used.

Gain switching of an erbium‐doped silica‐based planar waveguide laser

The gain switching of an erbium‐doped waveguide laser is investigated both theoretically and experimentally. We analyze the lasing characteristics of gain‐switched laser based on coupled rate equations, taking ground state absorption and the saturation effect into account. The analyzed theory indicates that the repetition rate, pulse width, and peak power vary when the pump conditions are changed. Gain‐switched optical pulses are experimentally generated in the erbium‐doped waveguide laser with intensity modulated optical pumping at 651 nm using a dye laser and an acousto‐optic modulator. The pulses are controlled with widths of 660–2600 ns and peak powers of 1.0–6.5 mW at repetition rates of 18–60 kHz by changing the average pump rate between 2.0 and 7.0. These experimental results agree with theoretical calculations of the pulse width, peak power, and repetition rate against the pump rate.

Optical and structural properties of Er3+-doped P2O5–SiO2 and Al203–SiO2 planar waveguides

Abstract Er3+-doped P2O5–SiO2 planar waveguides, fabricated by flame hydrolysis deposition, are shown to have a higher gain than Er3+-doped Al2O3–SiO2 planar waveguides, fabricated by plasma enhanced chemical vapor deposition. An optical absorption measurement reveals that the high gain of Er3+-doped P2O5–SiO2 waveguides is due to a high population inversion. These optical properties are related to the homogeneity of the waveguide-core glasses which were analyzed with a scanning electron microscope.

A 2.5 Gb/s hybrid integrated multiwavelength light source composed of eight DFB-LDs and an MMI coupler on a silica PLC platform

We report a hybrid integrated multiwavelength light source in which eight DFB-LDs and an MMI coupler are integrated with a silica PLC platform. We also report 2.5 Gb/s operation using LD drivers assembled module. We have demonstrated a hybrid integrated multiwavelength light source (MLS) that operates simultaneously on 8 channels and shows low thermal interference. We also demonstrated 2.5 Gb/s operation after packaging the MLS in LD driver assembled module. We believe that this PLC hybrid integrated MLS is very practical and will be employed in future dense WDM systems.

Recent advances in PLC hybrid integration technology

Opto-electronic hybrid integraiton using a silica-based planar lightwave circuit (PLC) platform is an attractive way to realize the various kinds of opto-electronic components required for future photonic networks. This paper briefly introduces the concept and basic techniques used for PLC hybrid integration, and describes recent advances in this field. We also report on several high-performance optical devices that we recently developed using this technology.

Novel IC-on-PLC technology and its application to compact 1/spl times/128 silica-based PLC switch

We developed new IC-on-PLC technology with which to design IC-chip-integrated PLC switches. This technology reduced the size of a 1/spl times/128 PLC thermo-optic switch module including the driving ICs by 3/4.

64-channel very low crosstalk arrayed-waveguide grating multi/demultiplexer module using a cascade connection technique

We developed a 64-channel 50 GHz-spaced cascaded arrayed waveguide grating (AWG) multi/demultiplexer module, and demonstrated that it effectively reduces crosstalk to -82 dB while achieving a low insertion loss of 3.3 dB and a compact module size of 133/spl times/43 mm/sup 2/, which is suitable for practical use.