Jang-Uk Shin

Fabrication of 10-Channel Polymer Thermo-Optic Digital Optical Switch Array

We present a 10-channel polymer thermo-optic digital optical switch (DOS) array with very low optical crosstalk. The 10-channel DOS array has a crosstalk-improved structure in which radiation-type attenuators are integrated in a series with a conventional 1 times 2 DOS. It is fabricated using a quartz substrate on which grid patterns for dispersion of stray light are formed to reduce the optical crosstalk. The measured crosstalk values are as low as -45 dB at a low electrical power of 50 mW. Insertion losses of less than 1.35 dB are achieved for all channels.

N × N polymer matrix switches using thermo-optic total-internal-reflection switch.

We have developed fully non-blocking optical matrix switches using a thermo-optic polymer 1 × 2 total-internal-reflection (TIR) switch as a unit switching element. The TIR switch consists of crossed multimode polymer waveguides and an offset heater electrode at the switching node. The fabricated 4 × 4 and 8 × 8 optical matrix switch chips show excellent switching performances. The insertion losses are less than 2.5 and 4.5 dB for the 4 × 4 and 8 × 8 matrix switches, respectively, and their switching isolations during a turned-off state are higher than 38 dB. The switching time is about 3 ms, and the power consumption for each switching element is below 30 mW. Compact integration of the 4 × 4 and 8 × 8 switch chips is achieved at sizes of 25 mm × 4.25 mm, and 42.4 mm × 5 mm, respectively, through an optimization of the waveguide and heater geometries.

Fabrication of a TFF-Attached WDM-Type Triplex Transceiver Module Using Silica PLC Hybrid Integration Technology

An optical triplex transceiver (TRx) module, which consists of thin-film filter (TFF)-attached wavelength-division multiplexer (WDM) and photodiode (PD) carriers, has been fabricated using a silica planar lightwave circuit (PLC) hybrid integration technology. Two types of TFFs were attached to a diced sidewall of a silica-terraced PLC platform to realize the TFF-attached WDM. The PD carriers with a 45deg mirror, on which receiving surface-illuminated PDs were bonded, were assembled with the PLC platform to form receiver (Rx) parts. As the main performances of the packaged TRx module, a very clear transmitter (Tx) eye pattern and minimum Rx sensitivity of -25.7 dBm were obtained under a 1.25-Gb/s Tx-Rx operation for digital applications. For an analog Rx application, a module responsivity of about 0.8 A/W was achieved, and a second-order intermodulation distortion value of less than -70 dBc at an optical modulation index of 40% was obtained under a two-tone test of 400 and 450 MHz

200 GHz-spacing 8-channel multi-wavelength lasers for WDM-PON optical line terminal sources.

We have fabricated modules of 8-channel multi-wavelength lasers (MWLs) with a wavelength separation of 200 GHz for the wavelength division multiplexed-passive optical network (WDM-PON) optical line terminal sources. The variation in the output power is minimized by inserting silicone between the superluminescent diode (SLD) and the silica waveguide. The wavelength shift of each channel is less than 0.21 nm from the ITU grid and can be controlled in the range of 0.36 nm without any reductions of the output power by a tuning heater. MWLs operated successfully in the direct modulation for 1.25 Gbit/s transmissions over 20 km.

1.25-Gb/s bidirectional transceiver module using 1.5%-/spl Delta/ silica directional coupler-type WDM

A 1.5%-/spl Delta/ silica directional coupler-type wavelength-division multiplexer dividing 1310/1550-nm wavelength bands was used to develop a bidirectional optical transceiver module. The active devices such as a spot-size converted Fabry-Pe/spl acute/rot laser diode and waveguide photodetectors were hybridly integrated on a silica-terraced planar lightwave circuit platform. As main performances of the module, the clear eye pattern and the minimum receiver sensitivity of -25.5 dBm were obtained under the full duplex operation at 1.25 Gb/s without a severe power penalty.

2

We present a novel 2 × 2 polymer thermo-optic digital optical switch (DOS) using the total-internal-reflection (TIR) effect. The switch consists of four 1 × 2 TIR-DOSs cascaded with each other. These TIR-DOSs have two branched multimode waveguides and an offset heater electrode in the branched region. Our switch does not have any bent waveguides, and has tapered waveguides and single-mode waveguides only in the input-output fiber coupling region. The fabricated 2 × 2 TIR-DOSs exhibit excellent properties, with very low insertion losses of <; 1.4 dB and switching isolations of >; 50 dB in both turned-off and turned-on states.

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We propose and demonstrate very compact multiwavelength lasers (MWLs) with a novel configuration designed to remove the mode hopping in the modulation region and separate the wavelength-tuning of each channel for cost-effective optical line termination sources in the wavelength-division-multiplexing passive optical network. The mode hopping of MWLs in the modulation region was eliminated by wavelength trimming using a tuning heater. The MWLs operated successfully in direct modulation for 1.25-Gb/s transmission over 20 km.

2 Polymer Thermo-Optic Digital Optical Switch Using Total-Internal-Reflection in Bend-Free Waveguides

Two-step etching, after the full processes of a silica waveguide, was performed to fabricate a silica-terraced planar lightwave circuit platform for the hybrid integration of optoelectronic devices. Spot-size converted distributed feedback laser diodes (SSC DFB LDs) were flip-chip bonded on silica terraces with the height accuracy of less than 1 /spl mu/m, and the resultant coupling loss between the SSC DFB LD and the silica waveguide was about 3.78 dB. The light-current curve of the LD flip-chip bonded on the platform showed the almost linear increase of the output power without any saturation.

Wavelength-Tuning of Hybrid Integrated Multiwavelength Lasers Using a Heater

We present a cost-effective 25-Gb/s electro-absorption modulator integrated laser (EML) transmitter optical sub-assembly (TOSA) using all-in-one flexible printed circuit board (FPCB) wiring and a metal optical bench (MOB). For a low cost and high bandwidth TOSA, internal and external wirings and feed-through of the TOSA to transmit radio-frequency (RF) signal are configured all-in-one using the FPCB. The FPCB is extended from an exterior of the TOSA package up to an EML chip inside the package through the slit formed on a rear sidewall of the package and die-bonded on the MOB. The EML TOSA shows a modulated output power of more than 3.5 dBm and a clear eye pattern with a dynamic extinction ratio of ~8.4 dB at a data rate of 25.78 Gb/s.

A two-step etching technique for silica terraces in the PLC hybrid integration

We describe a hybrid integration module of a 10 × 10-Gb/s distributed feedback laser diode array (DFB-LDA) and a planar light-wave circuit-based arrayed waveguide grating (AWG). For fabrication of the DFB-LDA, we adopted a selective area growth technique to tailor the channel gain properly, and E-beam lithography to accurately control the channel lasing wavelength and grating phase. For implementation of the AWG, we introduced a 2%-Δ structure to reduce the coupling loss between the AWG and DFB-LDA, and designed the tapered and parabolic waveguides at the junctions of the free propagation regions to widen the spectral passband width (i.e., a -1-dB spectral width of 3 nm). The developed module shows a side-mode suppression ratio of >45 dB, a clear eye opening with a dynamic extinction ratio of >4.4 dB at 10 Gb/s, and a power penalty of <;1.5 dB after a 2-km transmission for all channels.