Igor Ilichev

Low-power optical bistability and hysteresis in the laser system with absorbing nanosuspension

We demonstrate an optical bistability in a laser system with incoherent optical feedback and a nanosuspension as a nonlinear element. The optical transfer function is shown to exhibit a hysteresis loop for the light power in the range of a few milliwatts. It has been found that the optical bistability relies on the incoherent optical feedback and thermal defocusing nonlinear optical response of the nanosuspension.

Simulation of Ti-indiffused lithium niobate waveguides and analysis of their mode structure

Simulation of Ti-indiffused waveguides on LiNbO3 is described. The influence of diffusion conditions and technological parameters on the waveguide mode structure is considered. Boundaries of multimode, single-mode, and single-mode polarizing regimes of operation are defined.

Fabrication of high extinction ratio lithium niobate integrated optical modulators using photorefractive trimming

A method for increasing the extinction ratio of integrated optical Mach-Zehnder modulators based on LiNbO3 via the photorefractive effect is proposed. The influence of the photorefractive effect on the X- and Y-splitters of intensity modulators is experimentally studied. An increase in the modulator extinction ratio by 17 dB (from 30 to 47 dB) is obtained. It is shown that fabricated modulators with a high extinction ratio are important for quantum key distribution systems.

Fabrication of high-performance lithium niobate photonic integrated circuits using laser microtrimming

Two methods for correction of integrated optical circuits on lithium niobate via laser micro-trimming are proposed. The first method induces changes in the refractive index in waveguides, the second method causes and affects losses in them. The influence of both methods on waveguide elements of integrated intensity modulators is experimentally studied. Increases in the modulators extinction ratio by 17 dB (from 30 to 47 dB) for the first method and by 12 dB (from 28 to 40 dB) for the second method are obtained.

Femtosecond laser micro-inscription and machining for high performance lithium niobate photonic integrated circuits

Lithium niobate (LN) is one of basic materials of integrated optics used, for example, for electro and acousto-optical modulators, switches, diffraction gratings, nonlinear optical wavelength converters, and others [1]. LN-based ion exchange or Ti-indiffused photolithographic techniques are established technologies, however, some modern applications, such as high-purity suppressed carrier synthesis or high extinction ratio pulse generation for precision measurement systems require the use of additional active trimming electrodes [2] and a corresponding servo loop because of finite tolerances of optical elements. Recently developed direct laser writing (DLW) with femtosecond/ultrafast laser pulses [3] can be employed to address the problem, but this method is problematic for mass production and suffer from high insertion loss in optical waveguides (typically ∼ 1 dB/cm compared to <0.1 dB/cm for Ti-indiffused waveguides).

Polarizing properties of Ti-indiffused lithium niobate optical waveguides

Methods for selection, transformation, and control of light polarization in Ti-waveguides on lithium niobate (LiNbO3) substrates are described. The influence of technological parameters and waveguide topology is considered. The polarization extinction ratio higher than 40 dB/cm was experimentally demonstrated.

Generation of high extinction optical pulses by means of LiNbO3 Mach-Zehnder modulators

High extinction optical pulse generation via cw modulation in lithium niobate Mach-Zehnder integrated optical modulators is discussed, and methods for bias point stabilization and pulse shape measurements are presented. Generation of high dynamic extinction (>40 dB) optical pulses by a high static extinction lithium niobate modulator was experimentally demonstrated.

High dynamic extinction ratio and pulse modulation of optical signals

The use of a saturable absorber for increasing the extinction ratio at external modulation of optical signals is considered. An erbium doped fiber was used as the saturable absorber in the experiments. A considerable increase in the static extinction ratio (up to 50 dB) was demonstrated. A rather long erbium doped fiber relaxation time (about 10 ms) was a limiting factor in the case of pulse modulation. Ways of overcoming this drawback are discussed.

Gain optimization of a fiber-optic link with an external electrooptical modulator and erbium doped fiber amplifier

Gain optimization of a radio-frequency fiber-optic link by biasing an external modulator to the transmission minimum was studied. The increase in the gain by up to 5 dB as compared with the conventional quadrature point operation was demonstrated. Dependences of nonlinear distortions on the bias voltage of the electrooptical modulator were investigated.

Optical bistability in colloidal solution of Er-Yb doped LaF 3 nanocrystals

In this paper, we report the investigation of the optical bistability and hysteresis in the device based on phase conjugated mirror in colloidal solution of LaF3: Er,Yb nanocrystals. Oleic acid (OA)-modified LaF3: Er,Yb nanocrystals have been prepared by a phase transfer and separation mechanism occurring at the interfaces of the liquid, solid and solution phases present during the synthesis [1]. We chose 20% (molar ratio) Yb3+ ions as codoping concentration in the preparation of the nanocrystals. The obtained nanocrystals was redistributed in carbon tetrachloride (CCl4) which was used as the solvent based on following three factors: (1) it does not exhibit absorption bands in NIR region because of its low fundamental vibration energy, (2) it eliminates any residual H2O that serves as an effective quencher for NIR emission, and (3) it has a relatively high refractive index compared with other non-polar solvents and therefore minimizes loss of light due to Rayleigh scattering.