Joon Ki Lee

Field Trial of 112 Gb/s Dual-Carrier DQPSK Channel Upgrade in Installed 516 km of Fiber Link and ROADM

A field trial of 100GE signal transmission using dual-carrier differential quadrature phase shift keying (DC-DQPSK) based optical transceiver is demonstrated for 100 Gb/s metro area network. Neither high-end ADC/DSP nor fast optical polarization tracking is required in the DC-DQPSK based optical transceiver, which results in low electrical power consumption of ~ 35 W. The measured OSNR sensitivity of DC-DQPSK optical transceiver at the BER of 10- 3 is 18.3 dB. After the transmission through 516 km of installed fiber and ROADM, an error-free transmission of 100GE signal over 106 hours with OTU4 framer and forward error correction (FEC) decoding proves feasibility of DC-DQPSK optical transceiver for 100G metro network applications.

Analysis of dimensional tolerance for an optical demultiplexer of a highly alignment tolerant 4 × 25 Gb/s ROSA module

We have developed a 4 × 25 Gb/s ROSA (receiver optical sub-assembly) module for 100G Ethernet optical transceiver. This ROSA module has very large alignment tolerance of more than ± 250 µm between the optical DMUX (demultiplexer) and four photodiodes, for the reason it has the advantage of being easily assembled. The large alignment tolerance can be attributed to the dimensional tolerant optical DMUX, which is composed of four thin film filters attached to a parallelogram-shaped optic block. Since it is important to define the fabrication specifications for the dimension of the optic block, we analyze dimensional tolerance for the optic block using three-dimensional simulation. This parallelogram-shaped optical DMUX permits length tolerance of ± 300 µm and angular tolerance of ± 0.1°. The fabricated optical DMUX is estimated to have the angular error of less than 0.09°.

A cost-effective and compact 28-Gb/s ROSA module using a novel TO-CAN package

In this paper, we present the implemented a 28-Gb/s a receiver optical sub-assembly (ROSA) module by employing the proposed TO-CAN package and flexible printed circuit board (FPCB). We have proposed that signal path between the TO-CAN package and the FPCB have straight-line path and the FPCB incorporate signal line with open stub in order to alleviate signal distortion due to impedance mismatch. The 3-dB optical-to-electrical (O-E) bandwidth and receiver sensitivity of the ROSA module were measured as over 17 GHz and below -14 dBm at extinction ratio of 12 dB and bit error rate of 10-12.

A compact 4 × 10-Gb/s CWDM ROSA module for 40G Ethernet optical transceiver

For 40GBASE-LR4 application, we designed and fabricated a 4 × 10-Gb/s CWDM receiver optical sub-assembly (ROSA) module integrated with a collimator, an optical demultiplexer (DMUX), and a TO part. The TO part includes focusing lenses, photodiodes (PDs), transimpedance amplifiers (TIAs), and high-speed TO header. The optical DMUX has insertion loss of −1.2 dB and adjacent crosstalk of less than 30 dB. The focusing lenses in the TO part show aspherical lens shape and provide high alignment tolerance of more than ±300µm for single and array lens types. Especially, electrical crosstalk was less than −40 dB and optical crosstalk was negligible in the TO part. The developed 4 × 10-Gb/s ROSA module shows 3-dB OE bandwidth of about 9.1 GHz GHz and an average receiver sensitivity of −17.7 dBm for four channels at extinction ratio of 6 dB and bit error rate of 10−12.

Suppression of thermal wavelength drift in widely tunable DS-DBR laser for fast channel-to-channel switching

We present a simple and effective method for suppressing thermally induced wavelength drift in a widely tunable digital supermode distributed Bragg reflector (DS-DBR) laser monolithically integrated with a semiconductor optical amplifier (SOA). For fast thermal compensation, pre-compensatory currents are injected into the gain medium section of the DS-DBR laser and the SOA. This method can be easily applied to existing commercial tunable lasers, since it is implemented without any modification to manufacturing process. Experimental results exhibit that wavelength stability is noticeably improved to ± 0.01 nm. We also experimentally demonstrate a fast channel-to-channel switching in a wavelength-routed optical switching system employing a 90 × 90 arrayed waveguide grating router (AWGR). The measured switching time is less than 0.81 µs.

All-fiber 6-mode multiplexers based on fiber mode selective couplers

All-fiber 6-mode multiplexer composed of two consecutive LP11-mode selective couplers (MSC), two LP21-MSCs and an LP02-MSC is fully characterized by wavelength-swept interferometer technique. The MSCs are fabricated by polished-type fiber couplers coupling LP01 mode of a single mode fiber into a higher-order mode of a few mode fiber. A pair of the mode multiplexers has minimum mode dependent loss of 4 dB and high mode group selectivity of over 15 dB. Mode division multiplexed transmission enabled by the all-fiber mode multiplexers is demonstrated over fiber spans of 117 km employing an in-line multi-mode optical amplifier. 6 modes of 120 Gb/s dual polarization quadrature phase shift keying signals combined with 30 wavelength channels are successfully transmitted.

Analysis of PAM-N (N=4, 5, 6, 7 and 8) signals operating at 103.125 Gbps for next-generation Ethernet

We compare optical PAM-N (N=4, 5, 6, 7, and 8) signals operating at 103.12-Gbps. From the results, PAM-5 signal is more appropriate than other PAM-N signals by considering the effect of chromatic dispersion for 10-km SMF transmission using wavelength of LAN-WDM.

A compact ROSA module for serial 40-Gb/s optical transceiver

We have implemented and successfully demonstrated a serial 40-Gb/s receiver optical sub-assembly (ROSA) module by employing a popularly used TO-CAN package and a flexible printed circuit board (FPCB). We propose the orthogonally connected scheme between the TO-CAN package and the FPCB for a serial 40-Gb/s data transmission. The proposed scheme has adopted the structure on the FPCB to guarantee a return-current path for signal and optimize a gap between signal and ground pads for signal integrity. For 40 Gb/s, the receiver sensitivity o f t he RO SA module was measured as below -10 dBm at extinction ratio of 7 dB and bit error rate of 10-12.

All-fiber mode selective couplers for mode-division-multiplexed optical transmission

All-fiber mode selective coupler (MSC) is comprised of a few mode fiber (FMF) and a single mode fiber (SMF), coupling the LP01 mode of the SMF to a specific higher-order mode (HOM) of the FMF. In order to achieve high coupling ratio and low insertion loss, phase-matching condition between the LP01 mode of SMF arm and the HOM of FMF arm should be satisfied. A polished-type MSC is made by getting their cores into intimate contact. Prism coupling with a polished coupler block can measure the effective refractive index of the mode accurately. We propose and demonstrate three kinds of allfiber mode multiplexer that is composed of consecutive MSCs. 4-mode multiplexer can multiplex 4 modes of LP01, LP11, LP21, and LP02 by cascading LP11, LP21, and LP02 MSCs. It is used for MDM transmission of three modes with 120 Gb/s DP-QPSK signals. In order to enhance the signal transmission performance by receiving degenerate LP modes simultaneously, a mode multiplexer to utilize two-fold degenerate LP11 modes is proposed. It is composed of two consecutive LP11 MSCs that allows the multiplexing of LP01 mode and two orthogonal LP11 modes. We demonstrates WDM transmission of 30 wavelength channels with 33.3 GHz spacing, each carrying 3 modes, over 560 km of FMF. 6- mode multiplexer can multiplex 6 modes of LP01, LP11a, LP11b, LP21a, LP21b, LP02 modes. We demonstrated WDM-MDM transmission with the all-fiber 6-mode multiplexer. In this paper, the manufacturing method and the recent advancements of the all-fiber mode multiplexer based on the MSCs are reviewed. Long-distance mode division multiplexing (MDM) optical signal transmissions with the all-fiber mode multiplexer are experimentally demonstrated.

Highly alignment tolerant and high-sensitivity 100Gb/s (4 × 25Gb/s) APD-ROSA with a thin-film filter-based de-multiplexer

We investigate and demonstrate a 100-Gb/s (4x25-Gb/s) receiver optical sub-assembly (ROSA) based on avalanche photodiodes and a thin-film filter-based de-multiplexer. The overall alignment tolerances of the ROSA are relaxed to have larger than ± 25 μm by improving optical coupling structure. The receiver sensitivity of each lane is also measured to be less than -22.2 dBm, a record minimum to our knowledge, at the bit error ratio of 10-12 for 25.78-Gb/s NRZ signal.