W. Sohler

A transport network layer based on optical network elements

An approach to the realization of a broadband, flexible, multiwavelength transport network employing an optical network layer. The design methodology for a network demonstrator is presented, and the transmission, switching, line, and management/supervisory subsystems and components are described. >

Integrated Optical Devices in Lithium Niobate

Lithium niobate offers incredible versatility as a substrate for integrated optics. Researchers have developed an array of new optical devices based on this material, including waveguide structures, electro-optical wavelength filters and polarization controllers, lasers with remarkable properties, nonlinear frequency converters of exceptional efficiency, ultrafast all-optical signal processing devices and single photon sources.

Advanced Ti:Er:LiNbO/sub 3/ waveguide lasers

This paper reviews the latest developments of diode-pumped Ti,Er:LiNbO/sub 3/ waveguide lasers emitting at wavelengths around 1.5 /spl mu/m. In particular, harmonically mode-locked lasers, Q-switched lasers, distributed Bragg reflector (DBR)-lasers, and self-frequency doubling lasers are discussed in detail. Supermode stabilized mode-locked lasers have been realized using a coupled cavity concept; a side mode suppression ratio of 55 dB has been achieved at 10-GHz pulse repetition rate with almost transform limited pulses. Q-switched lasers with a high extinction ratio (>25 dB) intracavity electrooptic switch emitted pulses with a peak power level up to 2.5 kW and a pulsewidth down to 2.1 ns at 1-kHz repetition frequency. Numerical simulations for both lasers are in a good, almost quantitative agreement with experimental results. A DBR-laser of narrow linewidth (/spl ap/3 GHz) with a permanent (fixed) photorefractive grating and 5 mW output power has been realized. Self frequency doubling lasers have been fabricated with a periodic microdomain structure inside an Er-doped laser cavity; simultaneous emission at the fundamental wavelength, 1531 nm, and at the second harmonic wavelength, 765 nm, has been obtained.

Er‐diffused Ti:LiNbO3 waveguide laser of 1563 and 1576 nm emission wavelengths

The first continuous wave (cw) and pulsed mode operation of an Er‐diffused Ti:LiNbO3 monomode waveguide laser at 1563 nm (E⊥ c) and 1576 nm (E∥ c) wavelengths is reported. A tunable Tl:KCl color center laser was used as a pump source. With π‐polarized (Ep∥ c) pump radiation of 1479 nm wavelength an oscillation threshold of 13 mW coupled pump power was achieved for the 1576 nm emission line. Above 25 mW pump power additional lasing at 1563 nm wavelength was observed. σ‐polarized (Ep⊥ c) pumping led to a single line emission at 1563 nm throughout with the highest cw output power of 3 mW and a slope efficiency of 3%. Time averaged emission linewidths of about 0.6 nm were measured for both wavelengths at about two times the threshold pump power level. With pulsed excitation of about 1 W coupled peak power output pulses of up to 200 mW peak power were measured.

Er-doped integrated optical devices in LiNbO/sub 3/

The state-of-the-art of Er-doped integrated optical devices in LiNbO/sub 3/ is reviewed starting with a brief discussion of the technology of Er-indiffusion. This technique yields high-quality waveguides and allows a selective surface doping necessary to develop optical circuits of higher complexity. Doped waveguides have been used as single- and double-pass optical amplifiers for the wavelength range 1530 nm</spl lambda/<1610 nm. If incorporated in conventional, lossy devices loss-compensating or even amplifying devices can be fabricated. Examples are an electrooptically scanned Ti:Er:LiNbO/sub 3/ waveguide resonator used as an optical spectrum analyzer and an acoustooptically tunable filter used as a tunable narrowband amplifier. Different types of Ti:Er:LiNbO/sub 3/ waveguide lasers are presented. Among them are free running Fabry-Perot lasers for six different wavelengths with a continuous-wave (CW)-output power up to 63 mW. Tunable lasers could be demonstrated by the intracavity integration of an acoustooptical amplifying wavelength filter yielding a tuning range up to 31 nm. With intracavity electrooptic phase modulation modelocked laser operation has been obtained with pulse repetition frequencies up to 10 GHz; pulses of only a few ps width could be generated. With intracavity amplitude modulation Q-switched laser operation has been achieved leading to the emission of pulses of up to 2.4 W peak power (0.18 /spl mu/J) at 2 kHz repetition frequency. Distributed Bragg reflector (DBR) lasers of emission linewidth /spl les/8 kHz have been developed using a dry-etched surface grating as one of the mirrors of the laser resonator. Finally, as an example for a monolithic integration of lasers and extracavity devices on the same substrate, a DBR-laser/modulator combination is presented.

Distributed feedback-distributed Bragg reflector coupled cavity laser with a Ti:(Fe:)Er:LiNbO3 waveguide

A thermally fixed photorefractive Bragg grating is written in a single-mode Ti:Fe:Er:LiNbO3 channel waveguide and used to develop a distributed feedback-distributed Bragg reflector coupled cavity laser with a second broadband dielectric cavity mirror. The optically pumped (lambda(p) = 1480 nm, P = 130 mW) laser emits in single-frequency operation as much as 8 mW at lambda = 1557.2 nm with a slope efficiency of approximately 22%. The laser wavelength can be thermo-optically and electro-optically tuned over 100 pm.

Lithium Niobate Ridge Waveguides Fabricated by Wet Etching

The fabrication of LiNbO3 ridge waveguides etched by a mixture of HF and HNO3 using chromium (Cr) stripes as masks is reported. Smooth etched surfaces are obtained by adding some ethanol into the etchant. Under-etching is nearly avoided by annealing the sample with the Cr masks before the wet etching process. Low-loss monomode ridge guides with a height of up to 8 mum and a width between 4.5 and 7.0 mum are demonstrated. As an example, the propagation losses in a 6.5-mum-wide and 8-mum-high structure are 0.3 dB/cm for transverse-electric and 0.9 dB/cm for transverse-magnetic polarization, respectively, at 1.55-mum wavelength

Nonlinear integrated optical frequency converters with periodically poled Ti:LiNbO3 waveguides

The development of a whole family of near and mid-IR quasi- phase matched parametric frequency converters with periodically poled in Ti:(Er:)LiNbO3 waveguides is reviewed. Due to high quality waveguides with very low losses and excellent homogeneity unprecedented conversion efficiencies have been achieved for second-harmonic generation, difference-frequency generation, optical parametric fluorescence and doubly as well as singly resonant optical parametric oscillation.

Erbium-doped single- and double-pass Ti:LiNbO/sub 3/ waveguide amplifiers

Single-pass and double-pass Er-diffused Z- and X-cut Ti:LiNbO/sub 3/ waveguide amplifiers, optically pumped at /spl lambda//sub p//spl ap/1484 nm, have been investigated. With a 48 mm long Z-cut amplifier device, Er-diffusion doped at 1100/spl deg/C, 6.7 dB (coupled pump power P/sub p,c/=170 mW) and 14.7 dB (P/sub p,c/=90 mW) net small-signal gain have been achieved with a single-pass and a double-pass configuration, respectively, at the signal wavelength /spl lambda//sub s/=1531 nm. A Z-cut sample doped at 1135/spl deg/C showed a considerably improved behavior. 11.3 dB single-pass net small-signal gain has been obtained (P/sub p,c/=170 mW; sample length 5.7 cm). Theoretical calculations predict gain figures up to 20 dB in single-pass and 40 dB in double-pass Er:Ti:LiNbO/sub 3/ amplifiers with increased (realistic) lengths of 10 cm. >

Ti:Er:LiNbO/sub 3/ waveguide laser of optimized efficiency

The development of a Fabry-Perot-type Ti,Er:LiNbO/sub 3/ waveguide laser of optimized CW output power up to 63 mW (/spl lambda//sub s/=1561 nm) at a pump power level of 210 mW (/spl lambda//sub p/=1480 nm) and a slope efficiency of up to 37% is reported. The theoretical model for the waveguide laser is presented and applied to determine the optimum resonator configuration using waveguide parameters obtained from a detailed characterization of the laser sample. With pulsed pumping, waveguide laser pulses of up to 6.2 W peak power were observed. Apart from residual relaxation oscillations, the laser emission proved to be shot-noise limited.