Y. Ohmori

Very low insertion loss arrayed-waveguide grating with vertically tapered waveguides

We propose and demonstrate a very low insertion loss silica-based arrayed-waveguide grating (AWG) achieved using a novel structure, which has vertically tapered waveguides between arrayed-waveguides to reduce the slab-to-arrayed-waveguide transition loss. A spot-size converter is also incorporated in the AWG to reduce the fiber-to-waveguide coupling loss. The structure can be formed by a process involving the conventional photolithography and reactive ion etching. The structure provided a loss reduction of 1.5 dB. Moreover, we have successfully obtained a minimum insertion loss of 0.75 dB with a crosstalk of -40 dB and polarization-independent operation.

Polarization mode converter with polyimide half waveplate in silica-based planar lightwave circuits

A TE/TM polarization mode converter, with an excess loss of 0.26 dB, is constructed by inserting a polyimide half waveplate into a groove formed in a silica-based single mode waveguide. The polarization dependence of an arrayed-waveguide grating multiplexer is completely eliminated with this mode converter.<<ETX>>

Low loss and high extinction ratio strictly nonblocking 16/spl times/16 thermooptic matrix switch on 6-in wafer using silica-based planar lightwave circuit technology

We describe a silica-based 16/spl times/16 strictly nonblocking thermooptic matrix switch with a low loss and a high extinction ratio. This matrix switch, which employs a double Mach-Zehnder interferometer (MZI) switching unit and a matrix arrangement to reduce the total waveguide length, is fabricated with 0.75% refractive index difference waveguides on a 6-in silicon wafer using silica-based planar lightwave circuit (PLC) technology. We obtained an average insertion loss of 6.6 dB and an average extinction ratio of 53 dB in the worst polarization case. The operating wavelength bandwidth completely covers the gain band of practical erbium-doped fiber amplifiers (EDFAs). The total power consumption needed for operation is reduced to 17 W by employing a phase-trimming technique which eliminates the phase-error in the interferometer switching unit.

Polarization-insensitive arrayed-waveguide wavelength multiplexer with birefringence compensating film

An integrated-optic polarization-insensitive wavelength multiplexer that is based on an arrayed-waveguide grating is described. Polarization dependence due to thermal stress was eliminated by depositing an a-Si birefringence compensation film on the arrayed-waveguide. The multiplexing operation of 16 wavelength channels with a 0.8 nm spacing was confirmed to be independent of the polarization state.<<ETX>>

Low-loss and high-extinction-ratio silica-based strictly nonblocking 16/spl times/16 thermooptic matrix switch

A low-loss and high-extinction-ratio silica-based 16/spl times/16 thermooptic matrix switch is demonstrated. The switch, which employs a double Mach-Zehnder interferometer switching unit and a matrix arrangement which reduces the total waveguide length, is fabricated with 0.75% refractive index difference waveguides on a 6-in silicon wafer. The average insertion loss and the average extinction ratio are 6.6 and 55 dB, respectively. The total power consumption is 17 W.

Variable group-delay dispersion equalizer using lattice-form programmable optical filter on planar lightwave circuit

The authors report, in detail, an integrated-optic variable group-delay dispersion equalizer based on a lattice-form programmable optical filter. The variable dispersion equalizer consists of an alternating cascade of symmetrical and asymmetrical Mach-Zehnder interferometers. An equalizer with nine symmetrical and eight asymmetrical interferometers is fabricated on a planar lightwave circuit and its dispersion varied step by step from -681 to +786 ps/nm in the operational frequency range of 16.3 GHz. The effectiveness of the equalizer is shown by compensating the dispersion of three different fibers with a single equalizer. The performance of the equalizer is also evaluated and examined by numerical investigations.

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.

Improved 8/spl times/8 integrated optical matrix switch using silica-based planar lightwave circuits

An improved 8/spl times/8 optical matrix switch was fabricated using silica-based planar lightwave circuits (PLCs) on a silicon substrate. Three improvements were made. First, the waveguide material was changed from titanium-doped silica (SiO/sub 22/-TiO/sub 2/) to germanium-doped silica (SiO/sub 22/-GeO/sub 2/) to reduce propagation loss. Second, offset driving powers were supplied to every switch unit to realize high extinction ratios. Third, the dummy switch units were modified to suppress the crosstalk through these units. The average insertion loss of the fabricated device was 3.81 db in the TE mode and 3.82 dB in the TM mode. The average extinction ratio of the switch units was 25.3 dB in the TE mode and 22.3 dB in the TM mode. The accumulated crosstalk was estimated to be less than -14 dB in the TE mode and -11 dB in the TM mode. The average driving power of the phase shifter in the on-state was 0.54 W in the TE mode and 0.52 W in the TM mode. The switching response time was 1.3 ms. The packaged 8/spl times/8 matrix switch with additional fiber-waveguide coupling loss of 2.7 dB was successfully employed in photonic multimedia switching and photonic inter-module connector system experiments. >

Hybrid-integrated 4*4 optical gate matrix switch using silica-based optical waveguides and LD array chips

The fabrication and characteristics of a hybrid-integrated optical gate matrix switch were studied. The switch was composed of a silica-based single-mode guided-wave circuit and two InGaAsP gate array chips, each of which comprised eight laser diode optical gates. The gate array chips were assembled on the guided-wave circuit using a hybrid integration technique. The insertion loss of the fabricated 4*4 matrix switch was scattered among switching paths and ranged from 26 to 33 dB. The switch was applicable to a 400 Mb/s signal system with a bit error rate of 10/sup -9/. The numerical analysis shows that the residual reflectivity at the LD gate and waveguide facets caused the loss scattering among the paths and that reduction of the residual reflectivity is essential for improving the switch characteristics. >

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.