F. Heismann

Polarization‐independent electro‐optically tunable narrow‐band wavelength filter

We propose and demonstrate the first polarization‐independent electro‐optically tunable wavelengh filter with single‐mode waveguides. The Ti:LiNbO3 filter utilizes narrow‐band electro‐optic TE ↔ TM conversion and employs TE/TM polarization splitters in the input and output waveguides. The filter operates at 1.52 μm with a bandwidth of only 12 A and can be electro‐optically tuned over at least 110 A at a tuning rate of 0.55 A/V.

Electrooptic polarization scramblers for optically amplified long-haul transmission systems

To combat polarization hole burning in erbium-doped fiber amplifiers, we modulate the input polarization state to a 8800-km long 5.33-Gb/s NRZ transmission system at rates between 10 kHz and 10 GHz using integrated-optic polarization scramblers in lithium niobate. At modulation frequencies of 40 kHz and 10.66 GHz, we observe improvements in the signal-to-noise ratio of the received electrical signal of 4 and 5 dB, respectively.<<ETX>>

Fast automatic polarization control system

A fast polarization control system using a lithium niobate electrooptic polarization transformer and a simple electronic feedback circuit is reported. The system produces general elliptical phase retardation at a maximum rate of 6300 rad/s and allows continuous transformations from any general varying input polarization into any desired output state. The automatic stabilization of a rapidly varying polarization state at rates of up to 4900 rad/s was achieved.<<ETX>>

Narrow‐linewidth, electro‐optically tunable InGaAsP‐Ti:LiNbO3 extended cavity laser

We report an electro‐optically tunable, single‐frequency extended cavity laser with a linewidth of less than 60 kHz. The laser consists of a 1.5‐μm InGaAsP gain medium and an electro‐optically tunable, narrow‐band Ti:LiNbO3 wavelength filter (Δλ≊12 A). Electro‐optic tuning over at least 70 A and single‐frequency operation with output power of more than 1 mW have been demonstrated. The laser linewidth was measured by beating the laser against a 1.523‐μm HeNe laser.

Polarization‐independent wavelength filter using a grating‐assisted vertical directional coupler in InP

We demonstrate a polarization‐insensitive optical bandpass filter in indium phosphide (InP) with a 3 dB bandwidth of 1.5 nm at a center wavelength of 1.498 μm. The 5‐mm‐long filter is based on a grating‐assisted vertical directional coupler and features a novel double‐periodic coupling grating.

Polarization-independent photonic switching system using fast automatic polarization controllers

A 16*16 polarization-independent photonic switching system that uses a rapidly reconfigurable, polarization-dependent switch array in combination with fast electrooptic polarization controllers, which automatically transform the arbitrary polarization states of the incoming optical signals into the desired polarization state of the lithium niobate switch array, is reported. In a 1.7-Gb/s fiber-optic transmission experiment, it is demonstrated that the controllers are capable of stabilizing rapid polarization fluctuations of up to 500 rad/s.<<ETX>>

Integrated-optic polarization controller with unlimited transformation range

We demonstrate a novel waveguide polarization controller that allows endless transformations from any varying general input polarization state into any varying general output state. The electro‐optic controller is implemented in lithium niobate and produces adjustable elliptical birefringence of constant total phase retardation via three independent drive voltages. We show that it allows fast and reset‐free automatic polarization control using an entirely analog feedback circuit that derives its error signal from the intensity in the prescribed output polarization.

Field demonstration of 10-Gb/s line-rate transmission on an installed transoceanic submarine lightwave cable

We report the successful field demonstration of 10 Gb/s NRZ line rate transmission on the installed TransPacific Cable (TPC-5) Segment G. Using prototype transmitters, receivers and a bit-synchronous 10-GHz polarization scrambler, we achieved long-term error-free transmission with a bit-error rate below 10 on a 4230-km-long installed fiber cable. We also obtained a bit-error-rate as low as 10/sup -15/ for 8460-km transmission. The measured Q-values for 4230-, 8460-, and 12 690-km transmission are 20, 16.5, and 12.5 dB, respectively.

Integrated-optic, narrow-linewidth laser

We report the demonstration of the single‐frequency and narrow‐linewidth (<100 kHz) operation of an extended cavity laser consisting of a Ti:LiNbO3 single‐mode waveguide circuit and an InGaAsP waveguide gain medium. A parallel coupled cavity, electro‐optic elements for tuning the resonant frequencies of the cavities, and an external phase modulator are integrated on the lithium niobate crystal.

Mirror-folded polarization-independent wavelength filter

A 1.55- mu m polarization-independent optical bandpass filter with a 3-dB bandwidth of 6 AA and a tuning range of at least 100 AA is demonstrated. The photonic circuit of the filter consists of a waveguide TE-TM mode splitter, two parallel electrooptic TE-to-TM, TM-to-TE mode converters as the wavelength selective element, and a reflective mirror at the far end of the crystal. The circuit can be viewed as a mirror-folded version of the polarization-independent filter. It is shown that by passing the light two times through the narrowband mode converters, the filter bandwidth can be reduced by about a factor of two compared to a conventional single-pass filter of the same length. A novel tunable mode converter structure is also demonstrated that allows coherent in-phase mode conversion during the two passes through the mirror-folded filter.<<ETX>>