Cost-effective 400-Gbps micro-intradyne coherent receiver using optical butt-coupling and FPCB wirings.

We present a cost-effective and bandwidth-enhanced 64-Gbaud micro-intradyne coherent receiver based on hybrid integration of InP waveguide-photodetector (WG-PD) and silica planar lightwave circuit (PLC). InP waveguide-photodetector (WG-PD) arrays are simply chip-to-chip bonded and optically butt-coupled to a silica-based dual-polarization optical hybrid chip. Multiple flexible printed circuit boards are adapted for electrical RF and DC wirings, which provide low-cost integration and good RF performance of the receiver. A 3-dB bandwidth of the fabricated coherent receiver is extended to ~36 GHz by optimization of bondwire inductance between the WG-PD array and the transimpedance amplifier (TIA), even when commercial TIAs with a typical bandwidth of ~29 GHz are used. Through optimization of the silica hybrid integrated coherent receiver, 64-Gbaud DP-16QAM signal transmission over 1050-km standard single-mode fiber is successfully demonstrated below a bit error rate of 2 × 10-3. This is the threshold for a soft decision-based forward error correction, at the optical signal to noise ratio of 23.8 dB.

High-speed waveguide photodetector for 64 Gbaud coherent receiver.

A high-speed waveguide photodetector has been successfully fabricated for an integrated coherent receiver. Dual laterally tapered structures are introduced for a spot-size converter. We optimize the responsivity and the polarization-dependent loss of the spot-size converter-integrated waveguide photodetector through the beam propagation method simulation. The waveguide photodetector is designed with electrical as well as optical optimizations. The photodetector provides sufficient alignment tolerance, high responsivity of 0.73 A/W, and low polarization-dependent loss of 0.27 dB, which is in good agreement with the simulation results. By increasing the thickness of the matching layer and the n-doped upper taper, the electrical properties of the photodetector are enhanced. The photodetector has a 3 dB bandwidth of 45 GHz, providing high-speed operation. Through the electrical and optical optimizations, we successfully obtain the high-speed waveguide photodetector for a 64 Gbaud integrated coherent receiver.

A 10 × 10 Gb/s DFB laser diode array fabricated using a SAG technique.

We present a ten-channel distributed feedback laser diode array (DFB-LDA) developed for the transmission of 100-Gb/s (10 × 10 Gb/s) signals separated by an 8 nm wavelength grid at a center wavelength of 1.55 µm. For the fabrication of this type of laser array, a selective area growth (SAG) technique, electron-beam lithography, and a reverse-mesa ridge waveguide LD processing technique were adopted to offer a tailored gain spectrum to each channel, providing both accurate lasing-wavelength control and excellent single-mode yield over all channels, and reducing the fabrication cost and electrical and thermal resistances. To evaluate the operational performance of the fabricated chip systematically, we also developed a sub-assembly module containing a ten-channel λ/4-shifted DFB-LDA, ten matching resistors, flexible printed circuit board (FPCB) wiring, and a thermistor on a metal optical bench. The static and dynamic properties of all channels of the fabricated array are examined in this paper. The developed sub-assembly module shows a side-mode suppression ratio (SMSR) of > 50 dB, a modulation bandwidth of > 10 GHz, and a clear eye-opening before and after a 2-km transmission with dynamic extinction ratio of > 5 dB.

A cost-effective 25-Gb/s EML TOSA using all-in-one FPCB wiring and metal optical bench.

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.

Improvement of modulation bandwidth in electroabsorption-modulated laser by utilizing the resonance property in bonding wire.

We present and demonstrate a simple and cost-effective technique for improving the modulation bandwidth of electroabsorption-modulated laser (EML). This technique utilizes the RF resonance caused by the EML chip (i.e., junction capacitance) and bonding wire (i.e, wire inductance). We analyze the effects of the lengths of the bonding wires on the frequency responses of EML by using an equivalent circuit model. To verify this analysis, we package a lumped EML chip on the sub-mount and measure its frequency responses. The results show that, by using the proposed technique, we can increase the modulation bandwidth of EML from ~16 GHz to ~28 GHz.

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.