Tuning performance and spectral selectivity of widely tunablevertical Mach-Zehnder lasers

The filtering mechanism, spectral selectivity, and tuning performance of the vertical Mach-Zehnder (VMZ) laser diode are studied. Wavelength selection in this device is due to the interference of two modes with different and electronically controllable optical path lengths in analogy to a common Mach-Zehnder interferometer. Different design approaches for the VMZ laser are investigated. The calculations presented show that tuning ranges between 50 nm and 100 nm with side-mode suppression ratios (SSR's) of more than 20 dB are feasible. Designs with tuning ranges of about 35 nm show SSR values of over 30 dB at the 1.55 μm wavelength enabling the realization of widely tunable laser diodes with full wavelength access within the tuning range, suitable for applications in optical communication systems     

High-speed wavelength tunable liquid crystal filter

We describe the first high-speed, continuously tunable liquid crystal optical filter suitable for wavelength division multiaccess (WDMA) optical networks. The filter utilizes chiral smectic A* electroclinic liquid crystal as the active cavity material in a Fabry-Perot etalon to obtain microsecond switching speed. Using the commercially available BDH764E liquid crystal material, we demonstrate a tunable optical filter with a switching speed of less than 10 μs and a tuning range of approximately 30 nm, when the filter passband is centered at 1.55 μm     

Integrated-optic acoustically tunable infra-red optical filter

Demonstrates a narrowband (≈1 nm) LiNbO₃ acoustically tunable optical filter with a tuning range adequate to span the 1.3-1.55 μm wavelength range, exploiting the considerable advantages of an unconventional x-cut design     

Monolithic integration of an all-optical Mach-Zehnder demultiplexerusing an asymmetric twin-waveguide structure

We demonstrate monolithic integration of a twin-waveguide Mach-Zehnder terahertz optical asymmetric demultiplexer (MZ-TOAD). The InGaAsP-InP device operates at 1.55 μm wavelength and has two semiconductor optical amplifiers in the asymmetric MZ interferometer configuration with a single control input and a built-in switching delay. A 28-ps full-width at half-maximum (FWHM) switching window with high contrast ratio for a range of control powers is obtained using a counter-propagating optical signal and control pulses     

Tunable wavelength filter using nano-sized droplets of liquidcrystal

An electrically tunable optical filter has been developed that uses a polymer containing fine droplets of nematic liquid crystal as the active cavity in a Fabry-Perot interferometer (FPI). This FPI filter, whose finesse was 62, had a free spectral range of 37 nm in the 1.55-μm range with a full-width at half maximum of 0.6 nm and a transmission loss of 2.4 dB. The polarization dependent loss was smaller than 0.17 dB. The transmitted peak wavelength decreased with an electric field. This resulted in a tuning range of 10 nm at 300 V. The switching time was about 370 μs     

Vertically integrated Mach-Zehnder interferometer (VMZ) widelytunable laser diode with improved wavelength access

A widely tunable laser diode has been developed in InGaAsP/InP at 1.55 μm wavelength using an integrated vertical Mach-Zehnder (VMZ) interferometer. Regular tuning behaviour is obtained with only one wavelength control current over a tuning range of 30 nm with ~50 accessible wavelengths     

InAlGaAs bulk micromachined tunable Fabry–Pérot filter for dense WDM systems

In this work we report on micromechanically tunable Fabry–Pérot filter concepts for wavelength division multiplexing (WDM) systems. The optical resonator is designed for a cavity length around 30 μm in order to increase the filter selectivity while relaxing the demands on the required mirror reflectance. The introduction of micromechanical actuators, utilizing electrothermal and electrostatic principles, allows wavelength tuning of the filter over a range of more than 40 nm in the 1.55 μm wavelength regime. The movable Bragg mirror, designed as suspended membrane and fabricated with an InP bulk-micromachining technology, consists of a molecular beam epitaxy-grown InAlGaAs quarter-wavelength multilayer stack. The influence of micromechanical actuation and the effect of intrinsic mechanical stress on the mirror deformation has been investigated systematically to optimize the optical filter performance. Filter losses induced by the light absorption within the epitaxial Bragg mirror have been minimized using a highly doped InGaAs/InAlAs composition. Furthermore, low-loss Fabry–Pérot filters have been fabricated using InAlGaAs/InAlAs Bragg mirrors. The measured full-width at half-maximum (FWHM) is 0.24 nm and a filter insertion loss of 2.8 dB has been observed. The FWHM is kept below 0.35 nm over an entire tuning range of 40 nm for an actuation power of 1.3 mW. The bulk-micromachining technology presented here is open for the future development of WDM components, e.g. tunable receivers or laser diodes.     

Widely tunable continuous-wave InGaAsP/InP sampled grating lasers

The 1.55 μm widely tunable sampled grating lasers described here show significant improvements over those previously reported. The authors have obtained, for the first time, continuous wave (CW) operation with 62 nm CW tuning range, 30-50 dB MSR, 10 mW output power, and monotonic tuning     

Tunable stair-guide (TSG) DBR lasers for single current continuouswavelength tuning

The authors have developed a new kind of tunable distributed Bragg reflector (DBR) laser that has a tunable stair guide. This allows continuous wavelength tuning when using single current injection. The laser was fabricated by two-step selective area metal organic vapour phase epitaxy. A continuous wavelength tuning range of 3.8 nm at a wavelength of 1.55 μm was achieved     

Analysis of semiconductor microlasers with an equilateral triangleresonator by rate equations

Semiconductor microlasers with an equilateral triangle resonator (ETR) are analyzed by rate equations with the mode lifetimes calculated by the finite-difference time-domain technique and the Pade approximation. A gain spectrum based on the relation of the gain spectrum and the spontaneous emission spectrum is proposed for considering the mode selection in a wide wavelength span. For an ETR microlaser with a side length of about 5 μm, we find that single fundamental mode operation at about 1.55 μm can be obtained as the side length increases from 4.75 to 5.05 μm. The corresponding wavelength tuning range is 93 nm, and the threshold current is about 0.1 to 0.4 mA     

High-speed continuously tunable liquid crystal filter for WDMnetworks

We describe a high-speed wavelength tunable liquid crystal filter which can be utilized as the tuning element at the receiving end of wavelength division multiaccess (WDMA) optical networks. The filter uses chiral smectic A electroclinic liquid crystals as the active cavity material in a Fabry-Perot etalon in order to obtain a microsecond switching speed. Using the commercially available BDH764E liquid crystal material, we demonstrate a tunable optical filter both in a bulk Fabry-Perot and a fiber Fabry-Perot (FFP) configuration. A bandwidth of about 0.7 mm and effective finesse of 70 were obtained in the FFP configuration. A FFP tuning range of 13 nm with a switching time of less than 10 μs were measured at the operating wavelength of 1.55 μm. A theoretical analysis of the expected filter performance in the FFP configuration is given. Diffraction in the Fabry-Perot cavity is identified as the dominant loss factor, resulting in reduced throughput and finesse broadening. It is calculated theoretically that an effective finesse of 130 and a throughput loss of 2.2 dB are achievable for a mirror finesse of 200 and a liquid crystal cavity thickness of 5 μm. A short waveguide piece is assumed to be included in the cavity. Other expected loss sources for the filter in the FFP configuration have been calculated, showing negligible effect on the filter performance     

Electrically tunable semiconductor Fabry-Perot filter

A key component of Wavelength Division Multiplexed (WDM) networks is a tunable broadband wavelength demultiplexer, with good selectivity and high tuning speed. In this communication we report low waveguide loss InGaAsP Fabry-Perot filters, grown by Metal Organic Vapor Phase Epitaxy, with tuning ranges up to 3.07 nm (380 GHz). These filters have waveguides with bandgap wavelengths between 1.3 and 1.48 μm so that they are transparent at zero bias and at low tuning currents (<2 mA) for 1.55 μm light. Their performance is independent of light level and they should be capable of high speed operation     

Tunable twin-guide (TTG) distributed feedback (DFB) laser with over 10 nm continuous tuning range

By exploiting electronic and thermal tuning by forward and backward biasing the tuning region, a record continuous tuning range of 11nm has been achieved with an improved strained-layer (SL) multiquantum-well (MQW) TTG DFB laser at 1.55 mu m wavelength. Over a wavelength range of 9.2nm an optical power above 1mW and a spectral linewidth below 30MHz can be maintained with 400 mu m long devices.<>     

Electro-optic modulation in a chopped quantum-well electrontransfer structure

The authors demonstrate the first electron-transfer Mach-Zehnder modulators to operate in the 1.55 μm wavelength range. The use of chopped quantum wells provides a wide operating bandwidth compatible with Er-doped fibre amplified systems (>40 nm about 1.54 μm) for electrorefractive waveguide devices. In this wavelength range, obtained voltage-length products are for the 180° optical phase shift V_π×L between 2.7 and 4.0 Vmm     

Guided-wave optical equalizer with α-power chirped grating

A theoretical investigation of a guided-wave optical equalizer with an α-power chirped grating is presented. A group delay dispersion of 3700 ps/nm can be obtained at λ=1.55 μm by a chirped grating with α=0.3. It is shown that the chromatic dispersion of 200 km of a fiber whose zero-dispersion wavelength is located at 1.3 μm can be compensated at 1.55 μm to achieve up to 10 GHz signal bandwidth     

Quasicontinuous wavelength tuning in super-structure-grating (SSG)DBR lasers

The paper describes the design of a super-structure-grating distributed Bragg reflector (SSG-DBR) laser for broad quasicontinuous wavelength tuning with stable single-mode operation. The phase distributions and the effective coupling coefficients of SSG's are optimized to obtain both broad tuning range and high mode selectivity. A computer-aided simulation of wavelength tuning, where the effects of the waveguide loss increase and inhomogeneous gain spectrum are included, provides an optimum cavity structure and indicates the possibility of more than 70 mm quasicontinuous tuning in a 1.55 μm InGaAsP-InP SSG-DBR laser. Experimental results for 34 nm quasicontinuous tuning with a properly designed device are also presented     

Characteristics of Er-doped Al2O3 thin filmsdeposited by reactive co-sputtering

Er-doped Al₂O₃ thin films have been deposited by reactive co-sputtering onto thermally oxidized Si-wafers. The deposition process has been optimized with respect to the requirements originating from the application of these multilayer structures as integrated optical amplifiers for the third telecom window, i.e., the wavelength range 1.52-1.55 μm. The films obtained at a substrate temperature of only 400°C are amorphous and show a homogenous structure, without columns or grains. For slabguides, background losses smaller than 0.25 dB/cm have been obtained, even without any annealing. A relatively broad luminescence band, having an FWHM of ~55 nm around the 1.533-μm wavelength, has been measured. From gain versus pumping power curves, an upconversion coefficient lower then 20·10^-25 m³/s has been derived, being half of the values reported up to now in the literature. Simulations based on experimentally determined material parameters and assuming a channel attenuation of 0.5 dB/cm indicate, for 0.24 at.% Er channel devices with an optimal channel length of 7.7 cm, an amplification of 8 dB at 1.533 μm for a pump wavelength of 1.48 μm, and a pump power of only 8.7 mW     

On the spectral properties of widely tunable lasers usinggrating-assisted codirectional coupling

The analysis of mode-suppression-ratio (MSR) and wavelength tunability of widely tunable semiconductor lasers using grating-assisted codirectional-coupler (GACC) filters is considered. A tradeoff is found between tuning range and spectral purity when using this type of filter as an intracavity mode selector. It is shown that in order to improve the tuning range by a factor of 10 compared to a conventional tunable laser using distributed feedback reflectors (DBRs), one has to tolerate a MSR around 23 dB at 1 mW output optical power/facet for an ideal cavity design. Limitations imposed by the materials are illustrated with design curves based on a vertical-twin-guide structure in both GaAs and InP systems for lasing wavelengths at 0.98 and 1.55 μm, respectively     

Wavelength tuning characteristics of widely tunable distributedforward- and backward-coupling semiconductor laser

A distributed forward- and backward-coupling (DFBC) semiconductor laser for wide wavelength tuning is proposed and analyzed. A 4×4 F-matrix method is established in order to pursue numerical simulation. As a result, over 100: nm tuning around 1.55 μm by simple injection current control, scheme is predicted