Mark F. Krol

Self-starting passively mode-locked tunable femtosecond Cr4+:YAG laser using a saturable absorber mirror

Abstract We have demonstrated self-starting, passive mode-locking of a Cr 4+ :YAG laser using a saturable absorber mirror structure. Highly stable femtosecond pulses tunable from 1488 to 1535 nm were generated with average output powers ranging from 40 to 80 mW. Nearly transform limited pulses of 120 fs duration were obtained at 1488 nm.

Five Gb/s operation of a 50-channel optical interconnect

The architecture and experimental demonstration of a novel optical time-division multiple-access (TDMA) interconnect is presented in detail. Optical multiplexing and synchronization is used to overcome the electronic multiple-access bottlenecks associated with gigahertz-bandwidth multiprocessor communication systems. A self-clocking optical TDMA interconnect is described that may be more practical to implement than other shared-medium multiple-access protocols, such as frequency division or code division. An experimental optical TDMA interconnect is reported that uses a 100-MHz repetition rate, mode-locked laser with external modulators to generate the base-band data, and operates at a multiplexed data rate of 5 Gbits/s accommodating up to 50 channels. System measurements reveal bit error rates of less than 10 -9 , low channel crosstalk, and subnanosecond multiaccess capability. A power budget analysis predicts that 100 Gbit/s systems with 1000 nodes are feasible.

Gain variations in optically gain clamped erbium doped fiber amplifiers

We present a study detailing the impact of spectral inhomogeneities on optically gain clamped EDFAs. Our results show that spectral hole burning at the laser wavelength dominates the behaviour of the amplifier gain spectrum on the 1 dB level.

Mode-locked Cr4+:YAG laser: model and experiment

Abstract A mode-locked Cr 4+ :YAG laser was simulated using a complex Landau-Ginzburg equation. The pulse widths and spectrum were determined as a function of laser tuning over a range from 1470 nm to 1550 nm. Simulations exhibit the same trend as the experimental data and the magnitudes are in reasonable agreement, as well. We are able to analytically estimate the pulse width, which is controlled by the cavity dispersion and the pulse energy. We find that the absorber saturation is responsible for determining the pulse energies. The experimentally observed pulse widths widen for long wavelengths; our simulations attribute this to dispersion and to a wavelength-dependent reduction of the saturable absorber modulation combined with the effect of gain saturation.

Time-division optical micro-area networks

Optical micro-area networks (iANs) are proposed as a way of providing flexible communications among VLSI processors and eliminate electrical I/O bottlenecks. Sharedmedium multiple access protocols in jtANs can avoid the access delays associated with statistical multiple access protocols (which are unacceptable in multiprocessor applications) and increase the throughput at the expense of wasting optical bandwidth. Time-division multiple access (TDMA) may be more practical to implement in a pAN than other shared-medium multiple access protocols such as frequency-division or code-division. Since the total throughput of TDMA is given by the inverse of the optical pulsewidth the throughput can be increased by making the pulse width small. Accomplishing this goal requires avoiding the use of low-bandwidth electronics in the portion of the iAN that directly processes these short pulses. Instead optical processing can be used in those protions of the network. The architecture of a TDMA pAN which uses optical multiple access processing and is self-clocking is described in detail. Experimental demonstrations of key subsytems for optically generating modulating synchronizing delaying and correlating short optical pulses are presented. The feasibility of a variable-integer-delay line which provides rapid tuing wide tuning range and high precision is demonstrated. A transmitter consisting of a mode-locked laser with an external modulator is used in the TDMA iAN since arbitrarily short pulses can be controlled with a modulator that need only operate at the bit rate which translates© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electro-optic (Ga,In)As/(Al,In)As coupled quantum well materials and devices

The demonstration of real-space electron transfer in (Ga,In)As/(Al,In)As asymmetric double quantum wells is reported. Real-space electron transfer is then shown to be an efficient mechanism to enhance the electroabsorptive properties of optical fiber compatible opto-electronic semiconductor heterostructures.

Free-space optical TDM switch

A free space optical TDM switch at 1.32 micron is experimentally studied. The architecture of a TDM circuit switching system with a fixed transmitter and tunable receiver assignment is described. Since each user of the TDM switching system is assigned a time slot on the time frame, the corresponding receiver at the output looks only in the preassigned time slot for signal recovery. The electrical data signal from the input source is used to gate the optical pulses from the centralized source for the duration of the signal. It is concluded that large input/output switching systems are feasible.

Na-free glass for elimination of potential induced degradation

Na-free glass was investigated as a means of reducing or eliminating potential-induced degradation (PID) in c-Si PV modules. Multi-cell and single cell modules, manufactured with glass on both the front and back sides (glass/glass), were biased at -1000V while being subjected to PID-accelerating conditions - 85°C and 85%RH, and 85°C while wrapped in Al foil. Under these conditions, all modules having conventional soda lime glass (SLG) on the front side failed. The use of sodium-free (Na-free) glass on both sides of glass/glass modules eliminated both moisture ingress and PID. Modules with Na-free glass on the front and SLG glass on the back exhibited significant PID resistance compared to modules with SLG on the front. Multicell modules with either glass type on the front, but with conventional backsheets, failed due to moisture ingress under 85°C/85% RH conditions. During the course of the testing, it was observed that shunt resistance was a sensitive leading indicator of PID, decreasing by almost two orders of magnitude before a decrease in efficiency became detectable.

Passively mode-locked picosecond erbium-doped fiber lasers using multiple quantum well saturable absorbers

An experimental study of the mode-locking process in erbium- doped fiber lasers (EDFLs) operating at 1.55 micrometer using multiple quantum well saturable absorbers is described. The self-starting passively mode-locked laser was constructed in a Fabry-Perot configuration using the saturable absorber as the back reflector of the cavity. Picosecond pulses that ranged from 3.1 to 38.8 ps were generated using a series of saturable absorbers. The pulse widths were dependent upon the optical properties of the saturable absorber used as the mode- locking element as well as the dispersive elements contained within the cavity. The output power of the EDFL varied from 0.2 to 6.7 mW and was also dependent upon the saturable absorber used in the cavity.

Saturable absorber mode-locked femtosecond Cr4:YAG laser

We have demonstrated self-starting passive mode-locking of a chromium-doped:YAG (Cr4+:YAG) laser using a saturable absorber mirror (SAM) structure. Highly stable femtosecond pulses tunable from 1488 to 1535 nm were generated. Average TEM00 output powers ranged from 40 to 80 mW with a minimum pulse width of 120 fs measured at 1488 nm. The generation of ultrashort pulses in solid-state lasers using the Kerr lens modelocking (KLM) technique has been the center of much attention in recent years. Sub 100 fs pulses have been produced using many different laser systems. However, the KLM process is very sensitive to cavity alignment and is easily perturbed by mechanical vibrations and pump power fluctuations. A more reliable process makes use of a saturable absorber to start and stabilize the soliton formation process. The saturable absorber eliminates the need for critical cavity alignment. The femtosecond pulse train produced by the SAM structure in the Cr4+:YAG laser system is highly stable over very long periods of time. The wide tunability of the Cr4+:YAG laser throughout the 1.5 micrometer transmission window of optical fiber makes it an ideal spectroscopic source for the characterization and development of novel materials and devices for ultrafast optical interconnects.