C. H. Kwok

Link Reliability Improvement for Optical Wireless Communication Systems With Temporal-Domain Diversity Reception

We experimentally demonstrate a simple temporal- domain diversity reception (TD-DR) scheme to enhance the reliability of optical wireless transmission links corrupted by atmospheric turbulence (AT) effects. Both nonreturn-to-zero and Manchester encoded on-off-keying modulation schemes are studied in laboratory environments at a 1.25-Gb/s data rate. AT effects are emulated as a slowly varying log-normal intensity variation for the received signal. System bit-error ratio is tracked for the performance evaluation, and results show that the outage probability due to the AT-induced intensity fluctuation for a 1.25-Gb/s link using Manchester coding is reduced from 3.2%plusmn0.1% to <0.1%, when the TD-DR is employed.

Efficient line launch for bandwidth improvement of 10 Gbit/s multimode fibre links using elliptical Gaussian beam

A novel elliptical Gaussian beam line launch is shown to allow improved system capacity for high speed multimode fibre links. This launch maintains higher bandwidth than dual launch even with misalignment of ±6 µm despite not requiring testing at installation.

Novel passive launch scheme for ultimate bandwidth improvement of graded-index multimode fibers

We propose a new practical multimode fiber optical launch scheme, providing near single mode group excitation for >5 times transmission bandwidth improvement. Equalization-free transmission of a 10-Gb/s signal over 220-m fiber is achieved in experimental demonstrations.

High-brightness tapered lasers with an Al-free active region at 1060 nm

High-brightness diode lasers at 1060 nm are useful in display applications (to provide green light by frequency doubling) and in free-space optical communications. On Al-free active region laser structures, we have obtained low optical losses of 0.9 cm-1, a high internal quantum efficiency of 98% and a low transparency current density of 64 A/cm2. On uncoated broad-area lasers (2 mm x 100 μm) at 20°C CW, we have obtained a high maximum wall-plug efficiency of 66%, and an optical power higher than 3W per facet. Based on these good results, we have realized 3.7 mm long gain-guided tapered lasers, delivering a high power of 3W at 10°C CW, together with a low M2 of 3 at 1/e2 and a high maximum wall-plug efficiency of 57%. We have also realized separate electrode lasers, in which the ridge and tapered sections are biased separately. In this configuration, the current through the ridge section is only a few tens mA while the current on the tapered section is several Amps. This allows to control a large output power with only a small change of the ridge current. By moving the ridge current from 0 to 50 mA, keeping a constant 4A current through the tapered section, we have obtained a large change of the output power from 0.09 W to 2.6 W, which corresponds to a high modulation efficiency of 50 W/A under static operation. In dynamic regime, the separate electrode laser can be operated at 700 Mbps, showing a high modulation efficiency of 19 W/A, optical modulation amplitude of 1.6 W and extinction ratio of 19dB [1]. These modulation efficiencies are, to our knowledge, record values.

Picosecond All-Optical Logic Gates (XOR, OR, NOT, and AND) in a Fiber Optical Parametric Amplifier

We demonstrate all-optical XOR, OR, NOT, and AND gates in a fiber optical parametric amplifier within the same experimental setup. Error-free operation was achieved for 10Gb/s RZ signals with pulsewidth suitable for 100Gb/s operation.

High Modulation Efficiency Gigabit/s Modulation of Twin-Contact High-Brightness Tapered DBR Laser

We report a compact single-chip optical transmitter with 0.4-W output optical modulation amplitude at 1 Gb/s using a twin-contact directly modulated laser with an applied ?100-mA current swing. Bit-error-ratio measurements confirm high signal quality for optical wireless communications.

Versatile parametric wavelength exchange

We review different functionalities that can be achieved by the fiber-based parametric wavelength exchange, such as all-optical demultiplexer in optical time-division multiplexing (OTDM) system and as packet-switch in optical networking.

Receiver Sensitivity Improvement of Optical Wireless Channels with Delayed-Diversified Pulse-Position Modulation

We propose a simple approach to improve the receiver sensitivity in a line-of-sight optical channel using a delayed-diversified pulse-position-modulation scheme. A 5-dB sensitivity improvement is achieved over the conventional RZ-OOK scheme in the presence of atmospheric turbulence.

Two-sections tapered diode lasers for 1 Gbps free-space optical communications with high modulation efficiency

High-power (more than 500 mW) and high-speed (more than 1 Gbps) tapered lasers at 1060 nm are required in freespace optical communications and (at lower frequencies of around 100 MHz) display applications for frequency doubling to the green. On a 4 mm-long tapered laser, we have obtained an open eye diagram at 700 Mbps, together with a high extinction ratio of 19 dB, a high optical modulation amplitude of 1.6 W, and a very high modulation efficiency of 19 W/A. On a 3 mm long tapered laser, we have obtained an open eye diagram at 1 Gbps, together with a high extinction ratio of 11 dB, an optical modulation amplitude of 530 mW, and a high modulation efficiency of 13 W/A.

Progress in ultra-high modulation efficiency tapered lasers for free-space communications

Simultaneous high power (2W), high modulation speed (1Gb/s) and high modulation efficiency (14 W/A) operation of a two-electrode tapered laser is reported.