J.J. Veselka

Proton exchange for high‐index waveguides in LiNbO3

We describe the fabrication and characterization of optical waveguides formed in LiNbO3 by proton exchange in benzoic acid melts at 200–250 °C. Proton exchange, in LiNbO3 the replacement of lithium ions with protons, takes place when the substrate is immersed in the molten acid. We observe a surface increase in the refractive index of 0.12, for the extraordinary polarization only, with a step function index profile. This is the highest index increase obtainable to date for LiNbO3. Measured diffusion rates for x‐cut crystals are 1.37 μm2/h at T = 249 °C and 0.37 μm2/h at T = 217 °C, so that very deep guides can be formed in short times. Diffusion is somewhat slower in the z direction. The process as described is not useful for y‐cut crystals, since it damgaes this surface. Losses, measured on x‐cut samples, were <0.5 dB/cm. All measurements were made at 0.633 μm.

Dispersion penalty reduction using an optical modulator with adjustable chirp

Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value. >

8-Gbit/s transmission experiment over 68 km of optical fiber using a Ti:LiNbO 3 external modulator

We report a single-channel optical fiber data link with the largest bit-rate<tex>x</tex>repeater spacing product achieved to date- ∼ 0.5 Tb . km/s. The multi-gigabit per second system is the first to incorporate a Ti:LiNbO<inf>3</inf>external modulator as the data encoder.

1 Gbit/s PSK homodyne transmission system using phase-locked semiconductor lasers

Homodyne detection of 4-Gb/s pilot-carrier binary-phase-shift-keyed (BPSK) optical signals using external-cavity semiconductor lasers synchronized by a linear phase-locked loop is discussed. A 2/sup 15/-1 pseudorandom binary sequence (PRBS) has been transmitted through a short fiber with a receiver sensitivity of -44.2 dBm or 72 photons/bit. After transmission through 167 km of standard single-mode fiber, the sensitivity is -43.6 dBm or 83 photons/bit. A balanced PIN/HEMT transimpedance receiver which has a 3-dB bandwidth from 100 kHz to 10.1 GHz and an average equivalent input noise current of 10.8 pA/ square root Hz is used. >

A multiwavelength source having precise channel spacing for WDM systems

We report a wavelength-division-multiplexed (WDM) source in which a combination of a periodically driven Mach-Zehnder modulator and a nonlinear fiber are used to generate an optical spectrum that consists of several wavelength components precisely spaced by 64 GHz (>0.5 nm). The 13 strongest spectral components are within a 10-dB optical power range and their performance as channel sources in a WDM transmitter have been evaluated. We also propose and demonstrate a technique to generate an optical spectrum in which the separation between the major components is four times the modulator drive frequency.

A low-voltage 8*8 Ti:LiNbO/sub 3/ switch with a dilated-Benes architecture

An 8*8 switch array with a dilated-Benes architecture that greatly relaxes the crosspoint extinction ratio requirements needed to achieve low overall switch array crosstalk is discussed. This, combined with the low uniform switching voltages (9.2+0.2 V) of the 48 directional coupler crosspoints, facilitates high-speed low-crosstalk operation. The crosspoints can be switched in about 1 ns. The switch array is fully packaged with permanently attached single-mode fiber pigtails. The high data transfer rate inherent in lithium niobate switches in general, combined with the low crosstalk and high switching speed of this switch array, is a good match to the requirements of time-multiplexing switching. >

Fully connectorized high-speed Ti:LiNbO 3 switch/modulator for time-division multiplexing and data encoding

We demonstrate a fully connectorized and packaged, 2×1 high-speed Ti:LiNbO 3 directional coupler switch suitable for both optical time-division multiplexing/demultiplexing and modulation at a 1.3- μm wavelength. The device has an intrinsic switching time of 60 ps and a small-signal 50-percent optical modulation depth bandwidth of 6 GHz. We have actively multiplexed two optical pulse streams with output non-return-to-zero (NRZ) center-to-center bit spacings of less than 100 ps, while incurring an average optical power penalty of only 0.5 dB. In addition, we have used this switch as a modulator to encode a pseudo-random data stream at 2-Gbit/s NRZ without degradation of the eye pattern or the semiconductor laser source spectrum.

4 Gbit/s PSK Homodyne Transmission System Using Phase-Locked Semiconductor Lasers

Homodyne detection of 1 Gb/s pilot-carrier (BPSK) optical signals using phase-locked 1.5 mu m external-cavity semiconductor lasers is discussed. After 209 km fiber transmission of a 2/sup 15/-1 pseudorandom binary sequence (PRBS), the measured receiver sensitivity is 52.2 dBm or 46 photons/bit. Experimental evidence of the data-to-phase-lock crosstalk that potentially limits the usable ratio of linewidth to bit rate in pilot-carrier PSK homodyne systems is presented.<<ETX>>

Greatly reduced losses for small‐radius bends in Ti:LiNbO3 waveguides

We report the demonstration of a new concept that permits the fabrication of low‐loss Ti:LiNbO3 waveguide bends with radii much smaller than previously achieved.

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.