Henri Porte

Continuous radio-frequency tuning of an optoelectronic oscillator with dispersive feedback

We describe and demonstrate a novel technique for continuously tuning the frequency of a dual-loop-configuration optoelectronic rf oscillator. The rf tunability is obtained from a tunable diode laser and dispersive optical fibers. Results are presented for three ranges of frequency, centered at 550 MHz, 3 GHz, and 9 GHz. The frequency can be tuned electrically with constant rf power within a range of 0.1-1.9 MHz, depending on the center oscillation frequency. The tuning range can be increased eightfold through the use of highly dispersive fibers.

Proton exchanged imbalanced Ti:LiNbO3 Mach‐Zehnder modulator

We describe the fabrication process of a LiNbO3 integrated Mach‐Zehnder interferometer featuring a large path‐imbalance between the arms. This path‐imbalance is created by the proton exchange located on one arm. The proton exchange increases the extraordinary refractive index ne of lithium niobate and modifies the effective index of the guided mode. Path‐differences of 80 μm per mm of proton exchange length are obtained with the fabrication process reported here.

A tunable mode-locked erbium-doped fibre laser using a Lyot-type tuner integrated in lithium niobate

In this paper we report the realization of a tunable erbium-doped fibre laser. The intracavity tuner is a filter composed of two cascaded unbalanced Mach-Zehnder interferometers, integrated in a single chip of lithium niobate. Wavelength tuning is achieved electro-optically over a range of 17 nm around 1540 nm. A phase modulator integrated in the same chip allows the tunable laser to operate in a mode-locked regime.

Highly unbalanced GaAlAs–GaAs integrated Mach–Zehnder interferometer for coherence modulation at 1.3 μm

A novel integrated III–V semiconductor waveguide modulator specially designed to generate an optical delay of 100 μm is presented. This is achieved by simultaneous propagation of the TE fundamental mode in both of the arms of a highly unbalanced Mach–Zehnder interferometer with a 29 μm length difference between both arms. In order to minimize the losses in this complex curved structure, trenches were etched on the outsides of curved sections. The modulator has a contrast of 34%, a switching voltage of 6 V with a 10 mm long electrode and is suitable for the transmission and multiplexing of signals by coherence modulation of light in an optical fiber network powered by a short coherence source, such as a 1.3 μm superluminescent diode.

Bistability in wavelength using an electro-optically tuned dye laser

Abstract Bistability in wavelength is demonstrated using a Rh 6 G dye laser tuned electro-optically with an intra-cavity modulator. Laser emission occurs on two wavelengths that can be switched between them by a change in the level of light input. Multistable mode is also possible. The characteristics of the system are discussed. They show that the discrimination between the two wavelengths attached to the stable states can be performed easily. Further prospects deal with bulk systems operating with low driving voltages.

Secrecy improvement in confidential coherence modulation by means of a new keying structure

Abstract In this paper, we present a new keying structure which enhances the secrecy of an already relatively secure coherence modulation method we developed recently. The originality of the method consists in using an encrypting key composed of a large amplitude – low frequency part and a low amplitude – high frequency part. These two components ensure that the spectrum, as well as the signal tapped by an eavesdropper, are efficiently corrupted. When the key is applied simultaneously to both the encoder and the decoder, the signal is correctly restored. Both theoretical aspects and experimental confirmations are presented in this paper.

550-nm emission of erbium-doped Ti:LiNbO3 waveguide pumped at 980 nm

In this paper we demonstrate up-conversion emission at 550 nm into an Er-doped Ti:LiNbO3 waveguide pumped by a 980 nm laser diode. The two main processes of the up-conversion are the sequential two photon absorption (STPA) and the energy transfer (ET). In our case, the fluorescence lifetime of the 4S3/2 energy level of the Er3+ ion is measured as 32 microseconds. The fluorescence spectrum shows two peaks around 550 nm and 558 nm which are strongly polarization dependent. This effect is attributed to the different crystal fields induced by the location of Er3+ ions in the different LiNbO3 crystal lattices. The variations of the fluorescence intensity and the transmitted pump power are studied versus the length of Er-doped waveguide. The fluorescence intensity has a quadratic behavior versus the coupled pump power which demonstrate that the up-conversion mechanism is mainly due to a STPA process.

Evaluation of the effective electro-optic constants of free standing superlattices in the long-wavelength regime

The effective electro-optic constants of an idealized free standing superlattice, composed of thin alternating layers are derived, according to a matrix formulation, as a function of the dielectric and electro-optic constants of each of the constituents. The proposed model is valid only if the energy of light is small compared to the gap of both materials. The results are applied to superlattices with layers of all classes of orthorhombic, hexagonal, tetragonal and cubic symmetries.

Adjustment of the coupling ratio by laser ablation of Ti:LiNbO3 directional couplers

Abstract The coupling ratio of directional couplers in Z-cut Y-propagation and X-cut Z-propagation LiNbO 3 crystals was adjusted by laser ablation. The coupling ratio change is more efficient for the TM-mode of Z-cut couplers. The method can be used to correct the uncertainty of the coupling ratio for directional couplers that occurs during fabrication process.

A tunable filter with electrooptical TE-TM mode conversion in a GaAs/AlAs multiquantum-well waveguide

In this paper, the theoretical study of a new electrooptic tunable filter based on TE–TM mode conversion, and the high form birefringence that occurs in a GaAs/AlAs multiquantum-well waveguide is presented. Then TE–TM conversion can be achieved with a relatively low voltage (30 V). Such a filter shows off a tuning rate voltage ranging around 7 V/channel, and as regards selectivity a 1.3 nm filter bandwidth can be obtained.