Sheng Z. Zhang

1.54-μm vertical-cavity surface-emitting laser transmission at 2.5 Gb/s

We have demonstrated 2.5-Gb/s single-mode fiber-optic transmission using room temperature vertical-cavity surface-emitting lasers (VCSELs) operating at 1.54 /spl mu/m. The experiments were done over 60-km conventional single-mode fiber and over 75-km dispersion shifted fiber without optical amplification. Transmission over 200 km with one optical amplifier was also observed. Single-mode operation was demonstrated with a side-mode suppression-ratio of 50 dB under pseudo-random modulation. The maximum bandwidth was limited by parasitics to 4.7 GHz.

Fused InP-GaAs vertical coupler filters

A novel vertical coupler filter based on fused InGaAsP-InP and AlGaAs-GaAs waveguide structures is proposed and demonstrated. The large material dispersion difference between InGaAsP and AlGaAs around 1.55 /spl mu/m and similar waveguide geometries are used to realize a less sensitive polarization and narrow-band filter with two separated inputs and outputs and more than -40-dB sidelobe suppression should be possible.

Vertical cavity lasers for telecom applications

The authors review the development of long-wavelength vertical cavity lasers (VCLs) for telecommunications applications. Long-wavelength VCLs provide an attractive choice for inexpensive fiber optic communication. The different designs of such lasers are presented, along with the advantages and disadvantages of each. System requirements and experiments are also presented at 2.5 Gb/s over 200 km of optical fiber.

Integrated tandem traveling-wave electroabsorption modulators for >100 Gbit/s OTDM applications

Integrated tandem traveling-wave electroabsorption modulators are demonstrated as high-speed optical short pulse generators and demultiplexers for >100 Gbit/s optical time-division-multiplexed systems. The tandem significantly increases the extinction ratio and further compresses the optical pulses in comparison to a single modulator. An extinction ratio of /spl sim/50 dB is achieved while optical pulses of 4-6 ps width at 30-40 GHz are generated.

Distributed effects model for cascaded traveling-wave electroabsorption modulator

A distributed model based on the large-signal electrooptic conversion is proposed to analyze cascaded traveling-wave electroabsorption modulators (TWEAMs) for high-speed optical switching applications. The microwave propagation loss, velocity mismatch, as well as frequency chirping are included. The model predicts that a cascaded TWEAM structure has the advantage of a high design tolerance to various distributed effects and an improved extinction ratio and optical loss in comparison to a single device of same total length. The agreement between experimental and calculated results indicates that the cascaded structures can be implemented for efficient TWEAM design.

Simultaneous OTDM demultiplexing and detection using an electroabsorptioa modulator

A traveling-wave electroabsorption modulator is used to simultaneously demultiplex and electrically detect a single 10-Gb/s channel from a 20-Gb/s optical time-division multiplexed data stream while transmitting the other channel in an optically transparent manner. A bit-error-rate penalty of 0.5 dB and an error floor were observed for the dropped channel due to residual absorption of the other channel. Error-free operation was achieved for the transparent channel.

The first hot pluggable 2.5 Gb/s DWDM transceiver in an SFP form factor

For the first time, a hot pluggable 2.5 Gb/s DWDM transceiver with 100 GHz spacing in an SFP form factor has been presented. We demonstrate transmit wavelength drift of plusmn9 pm and optical output power stability of 0.2 dB over an operating case temperature range of -5degC to 70 degC. The minimum receive sensitivity was -33.2 dBm for back-to-back, -32.6 dBm after transmission over 80 km of standard SMF, and -28 dBm for an OSNR level of 16 dB at a BER of 1 times 10-10

Analog modulation of 1.55-μm vertical-cavity lasers

We analyze the performance of InP/GaAs fused 1.55 micrometers vertical-cavity lasers (VCLs) under analog modulation. Our VCLs employ a strain-compensated InGaAsP/InP multi-quantum well (MQW) active region sandwiched between two AlGaAs/GaAs distributed Bragg reflectors. The first AlGaAs layer of the p-doped top mirror is laterally oxidized for optical and electrical confinement. These devices exhibit the lowest threshold current as well as the highest temperature of continuous-wave operation of any electrically pumped long- wavelength VCL. Two different device designs are investigated and compared. Reduction of the MQW barrier strain and enhancement of the optical index guiding by the oxide layer lead to an improvement of VCL performance. However, parasitic effects limit the modulation bandwidth. Higher order harmonic distortion is measured and simulated using a rate equation model. The model includes a non-linear gain function, gain compression, spontaneous emission and Auger recombination as well as carrier density dependent absorption in the quantum wells which reduces the differential gain. The good agreement between measurement and simulation indicates that electron-photon interaction within the quantum wells dominates the non-linear distortion. Multiple higher order response peaks are measured and reproduced by the model.

1.54-/spl mu/m vertical-cavity laser transmission at 2.5 Gbit/s

Vertical cavity surface-emitting lasers (VCSELs) are potentially low-cost sources for optical communications and interconnections because of their advantages in low-cost packaging and testing. The transmission of lasers with wavelengths shorter than 1 /spl mu/m is strongly limited by dispersion and the loss of the fiber. The reported longest single-mode fiber transmission with short wavelength VCSELs was 4.3 km. On the other hand, 1.5 /spl mu/m VCSELs are excellent candidates for fiber-optic communications not only because the wavelength matches the low-loss window of the fiber but also because the use of erbium-doped fiber amplifiers (EDFAs) makes possible long-distance applications and broadcasting systems. We have recently demonstrated 35/spl deg/C CW operation of VCSELs operating at 1.54 /spl mu/m and the single-mode fiber transmission over 200 km at 622 Mbit/s using optical amplifiers. In the paper, the incorporation of lateral oxidation in the laser fabrication increases the output optical power from several microwatts to about 1 mW which allows us to transmit at high bit rates and to investigate systems without optical amplification.

High-speed traveling-wave electro-absorption modulators

Electroabsorption modulators (EAMs) based on the quantum confined Stark effect in multiple quantum wells (MQWs) have advantages for high-speed, low drive voltage, and high extinction ratio applications. In this paper, a traveling- wave electrode structure is proposed to achieve high bandwidths with long devices and lower drive voltages at 1.55 micrometers wavelength. An InGaAsP/InGaAsP MQW traveling-wave electroabsorption modulator (TWEAM) with a bandwidth above 20 GHz is fabricated. A drive voltage of 1.2 V for an extinction ratio of 20-dB is demonstrated. The effects of microwave transmission on the high-speed performance of TWEAMs are discussed. Successful data transmission experiments at 30 Gbit/s show a promising system performance of these devices. By using an integrated tandem TWEAM, pulse data transmission above 100 Gbit/s is achieved.