Chang-Sup Shim

Hybrid WDM/TDM-PON with wavelength-selection-free transmitters

A hybrid wavelength-division-multiplexed/time-division-multiplexed passive optical network serving 128 subscribers with wavelength-selection-free transmitters is presented by cascading 1/spl times/16 arrayed-waveguide gratings (AWGs) and 1/spl times/8 splitters. The wavelength-selection-free transmitter is an uncooled Fabry-Pe/spl acute/rot laser diode (FP-LD) wavelength-locked to an externally injected narrow-band amplified spontaneous emission (ASE). Bit-error rates better than 10/sup -9/ over temperature ranging from 0 to 60/spl deg/C are achieved in all 16 wavelength channels using a single FP-LD with an ASE injection of about -15 and -2 dBm in 622-Mb/s upstream and 1.25-Gb/s downstream transmissions over a 10-km feeder fiber, respectively. It is also reported that the ASE injection does not exert penalty upon burst-mode operations of the FP-LDs in the upstream.

Bit-error-rate analysis of optically preamplified receivers using an eigenfunction expansion method in optical frequency domain

An accurate method of analysis is presented for optically preamplified receivers using an eigenfunction expansion technique in the optical frequency domain. Excluding three conventional simplifying assumptions on optical filters, electrical circuits, and amplified spontaneous emission, our method can give accurate predictions to the bit-error probabilities in real systems where the amplified spontaneous emission is the dominant noise. >

1-fiber WDM self-healing ring with bidirectional optical add/drop multiplexers

We propose a 1-fiber bidirectional WDM self-healing ring that has bidirectional optical add/drop multiplexers. A simple fault detection method is proposed, and no signal degradation due to in-band crosstalk is demonstrated in the failure state. The power penalty of the ring transmission was less than 1 dB at a BER 10/sup -12/ in the normal and failure state.

Reflective SOAs optimized for 1.25 Gbit/s WDM-PONs

We present R-SOAs with improved modulation bandwidth of /spl sim/1.35 GHz as WDM sources in 1.25 Gbit/s WDM-PONs. In back-to-back transmission using the R-SOA seeded by 0.6 nm-wide ASE of -20 dBm, receiver sensitivity at a 10/sup -9 /BER was - 25.3 dBm.

A gain-clamped SOA with distributed Bragg reflectors fabricated under both ends of active waveguide with different lengths

We demonstrate a gain-clamped semiconductor optical amplifier (GC-SOA) which has gratings under both end regions of an active waveguide. Two gratings of the new GC-SOA are fabricated in different lengths. Their lasing modes and gain characteristics are measured and analyzed with different combinations of grating lengths. It shows different gain and noise characteristics according to the measurement direction in asymmetric grating combinations.

Cost-effective optical chirped duobinary transmitter using an electroabsorption modulated laser

We propose and demonstrate a cost-effective way to implement a 10-Gb/s chirped duobinary (CDB) transmitter using an electroabsorption modulated laser (EML) followed by a LiNbO/sub 3/ Mach-Zehnder modulator both driven with binary signals. Successful transmission is achieved over 285 km of dispersion-uncompensated standard single-mode fiber without significantly increasing the complexity and cost of the transmitter, compared to conventional duobinary transmitters. The demonstrated CDB signals exhibit a superior performance to conventional duobinary signals, in terms of back-to-back receiver sensitivity and transmission distance. We achieve consistent transmission performance with three EMLs obtained from two different vendors, each having different chirp and transmission characteristics. Therefore, we believe the use of EMLs greatly reduces the implementation issues of 10-Gb/s CDB transmission systems.

Improvement of dispersion tolerance for electrical-binary-signal-based duobinary transmitters.

We present a way to improve the dispersion tolerance of an electrical-binary-signal-based duobinary transmitter, implemented by using a dual-arm Mach-Zehnder modulator driven with two complementary binary signals. Successful transmission over 200 km of single-mode fiber is achieved by optimizing the relative time delay between the binary signals and the driving voltage.

Cost-effective 10-Gb/s optical duobinary transmission systems using a nonbuffered X-cut LiNbO/sub 3/ Mach-Zehnder modulator

We demonstrate a cost-effective method to implement a 10-Gb/s optical duobinary transmitter using a simple nonbuffered x-cut LiNbO/sub 3/ Mach-Zehnder (MZ) modulator. The bandwidth of the modulator used in our experimental demonstration is 4 GHz. The duobinary signal generated from the nonbuffered MZ modulator exhibits a similar performance to the one using a 9-GHz bandwidth buffered MZ modulator, in terms of dispersion and self-phase modulation tolerance. Thus, the use of cost-effective nonbuffered x-cut MZ modulators will substantially relax the cost issues of duobinary transmitters, by offsetting the cost of the precoder and the encoder which are not needed in conventional on-off keying transmitters.

Characteristics of a spectrum-slicing filter composed of an angle-tuned Fabry-Perot etalon and a Gaussian input beam

We present the first analysis of the spectrum-slicing filter composed of an angle-tuned Fabry-Perot etalon and a slightly divergent Gaussian input beam. The channel bandwidth is strongly dependent on the minimum beam spot size and the refractive index of the etalon substrate but insensitive to other etalon parameters. The channel center and the channel power resemble closely those of the pure plane wave incidence case. Fortunately, the channel shape evolves from the Lorentzian to the more favorable Gaussian as the channel bandwidth increases. >

Polarization-independent, high-power, and angle-flared superluminescent diode for WDM-PON applications

We developed polarization-independent high-power superluminescent diodes (SLDs) for wavelength division multiplexed-passive optical network (WDM-PON) applications. The SLD presents CW output power of 150 mW, spectral bandwidth of 40 nm, polarization-dependent power variation of less than 1 dB, and spectral ripple of 3 dB at current of 1.47 A and temperature of 25 degC