Walter I. Kaechele

Photonic serial-parallel conversion of high-speed OTDM data

We demonstrate full demultiplexing of a single 100-Gb/s optical time-division multiplexed data stream into eight parallel 12.5-Gb/s streams. This is performed using a photonic serial-to-parallel converter based on lithium niobate intensity modulators, and requires no nonlinear optical elements. Error-free operation is obtained for each of the eight output channels.

Long span repeaterless transmission using adiabatic solitons

We demonstrate transmission of 10 Gb/s data over 296 km without inline amplification using adiabatically propagating optical solitons as the data carrier. Adiabatic soliton propagation suppresses the deleterious effects of self-phase modulation and stimulated Brillouin scattering, allowing higher optical powers at the transmitter. The system power budget is also enhanced by the narrowing of the optical bandwidth under adiabatic propagation, allowing improved receiver sensitivity. We show that the technique may ultimately enable repeaterless spans in excess of 500 km.

Wavelength-division-multiplexed 4 x 10 Gb/s adiabatic soliton transmission over 235 km

We demonstrate four-channel error-free repeaterless transmission using adiabatic propagation of optical solitons. We show that channel-to-channel cross phase modulation does not degrade system performance for as many as eight transmitted WDM channels. No stimulated Brillouin scattering threshold is observed up to launched powers of 29 dBm per channel.

Rational harmonic mode-locking fiber laser

Optical pulse sources with repetition rate approaching terahertz are very important for many photonics applications including ultra-high speed optical communication and generation of sub-mm waves. Both active and passive mode locked fiber lasers are the appropriate choice for this purpose because of the availability of erbium doped fiber amplifier. In general, the mode locking occurs with a repetition rate of nf0, where n is an integer and f0 is the longitudinal mode frequency spacing. This is called harmonic mode locking. In the case of rational harmonic mode locking, the repetition rate is (np plus 1) f0 where p is also another integer. For the case of active mode locking, this is obtained when the modulation frequency to the amplitude or phase modulator used for mode locking is given by (n plus 1/p) f0. For the case of passive mode-locking, the rational harmonic mode-locking occurs when the saturable absorber in a ring laser is offset by a fraction p/L: from the center where L is the length of the cavity. We have developed a theory of the rational mode locked fiber laser. The results of the theory are compared with experimental results obtained from a 1.5 (mu) fiber laser actively mode-locked with a LiNbO3 electro-optic phase modulator.

A mode-locked fiber laser with a chirped grating mirror

A novel fiber laser was built using a multiple-quantum well mode-locking element and a chirped fiber grating to balance dispersion and nonlinearity. Energetic pulses as short as 2 ps were generated in the cavity and propagated in a fiber to determine the pulse characteristics. Laser cavity modeling and pulse propagation simulations are in good agreement with experiments.

Raman-pumped, dense dispersion-managed soliton transmission of 80 Gb/s OTDM data

The effects of radiation from dense dispersion-managed solitons into the normal-dispersion portion of their optical spectrum are observed for the first time in a novel Raman-pumped data transmission system. Filtering allows error-free propagation of 80-Gb/s OTDM data over 963 km.

Photonic 100 Gb/s serial-to-parallel converter

We demonstrate full demultiplexing of a single 100 Gb/s time division multiplexed optical data stream into eight parallel 12.5 Gb/s streams. The device is based on lithium niobate intensity modulators and requires no nonlinear optical elements.

Cross-phase modulation and multiwavelength adiabatic solitons

In an experimental demonstration of four-channel, wavelength-division-multiplexed repeaterless transmission over 235 km, adiabatic soliton propagation allows for precise spectral characterization of cross-phase modulation effects during initial soliton collisions. Theoretical predictions of the spectral shifts that occur are verified for ultrashort solitons. The relationship between the frequency shift and the initial pulse separation is confirmed by measurement of the bit-error ratio as the pulse spacing is varied at the fiber input. Adiabatic expansion of narrow solitons may help to alleviate the channel restrictions that are required for prevention of soliton collisions at the fiber input.

Ultra-high bit rate transmission systems

Describes the development of components and subsystems for dispersion managed soliton transmission of optical time division multiplexed data at rates up to 100 Gb/s.

Characterization and modeling of a dispersive cavity mode-locked erbium-doped fiber laser

A novel, compact, polarization insensitive mode-locked erbium-doped fiber laser producing 2 ps pulses was constructed. The laser was passively mode-locked using a 75 period InGaAs/InAlAs multiple quantum well saturable absorber grown lattice matched on an InP substrate. The laser was constructed in a linear cavity, Fabry-Perot configuration with the saturable absorber at one end of the cavity and a chirped fiber Bragg grating at the other end. The output pulses are chirped and were further characterized by varying their energies and propagating them down different lengths of standard optical fiber. The laser cavity was modeled using the complex Ginzburg-Landau equation derived under the condition that nonlinear changes to the pulse must be small per round-trip. The contribution of the semiconductor saturable absorber was modeled using a two-level rate equation. The free carrier absorption within the semiconductor contributes to the refractive index which was shown numerically to result in an additional frequency shift. The modeling is in close agreement with the pulse propagation experiments.