External-cavity wavelength tunable laser with an electro-optic deflector

A near-IR tunable external-cavity laser that uses an electro-optic deflector and a reflection grating as a tunable filter is demonstrated. The deflector is an electronically reconfigurable nonpixelated nematic liquid-crystal device. By controlling the voltage applied to the electro-optic deflector, a tuning range of 12 nm and a side-mode suppression higher than 30 dB are obtained.     

Distributed Brillouin sensor system based on offset locking of two distributed feedback lasers

An offset locking technique, which uses an external optical delay line to tune the distributed feedback (DFB) laser frequency and a proportional-integral-derivative (PID) controller to lock the tuned frequency, is proposed for the first time, to the best of our knowledge, in the distributed Brillouin sensor system. This method provides large tuning range (greater than 1 GHz), high tuning speed (less than 100 mus per frequency step), and frequency tuning is independent of the laser frequency and power. The two DFB lasers are phase locked at the Brillouin frequency using a hardware PID controller. Using this offset locking with optical delay line, we demonstrated a high signal-to-noise ratio of 32 dB, which allows 1 m spatial resolution and better than 0.6 MHz frequency measurement accuracy (equivalent to 0.5 degrees C temperature resolution or 8 microepsilon strain resolution) over kilometers sensing length. The bias of the electro-optic modulator is controlled by a lock-in amplifier to provide high temperature or strain measurement accuracy.     

Large-area Fabry-Perot modulator based on electro-optic polymers

We present a large-area electro-optic Fabry-Perot modulator utilizing a photoaddressable bis-azo polymer placed between two dielectric mirrors with an open aperture of 2 cm. A modulation efficiency of 1% at an effective modulation voltage of 20 V for a wavelength of 1.55 microm is demonstrated. By comparing distance tuning of the cavity with wavelength tuning, an effective electro-optic coefficient of -7 pm/V is measured.     

Quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics under both DC and AC bias

The basic quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) transparent ceramics have been studied under both DC and AC electric field bias. The contribution of piezoelectric resonance to electro-optic effect for this quadratic electro-optic ceramics material has been experimentally demonstrated and theoretically analyzed. It is found that, at the piezoelectric resonance frequencies, the piezoelectric induced electro-optic effect dominates and leads to a dramatically high sensitivity for weak electric signal detection. About 20 dB signal-to-noise ratio is attained when detecting AC electric field strength of 1 V/m with optimized DC bias. Besides, the effects of AC frequency and amplitude on halfwave voltage V(π) of PMN-PT are investigated.     

Theory-inspired development of organic electro-optic materials

Real-time, time-dependent density functional theory (RTTDDFT) and pseudo-atomistic Monte Carlo-molecular dynamics (PAMCMD) calculations have been used in a correlated manner to achieve quantitative definition of structure/function relationships necessary for the optimization of electro-optic activity in organic materials. Utilizing theoretical guidance, electro-optic coefficients (at telecommunication wavelengths) have been increased to 500 pm/V while keeping optical loss to less than 2 dB/cm. RTTDDFT affords the advantage of permitting explicit treatment of time-dependent electric fields, both applied fields and internal fields. This modification has permitted the quantitative simulation of the variation of linear and nonlinear optical properties of chromophores and the electro-optic activity of materials with optical frequency and dielectric permittivity. PAMCMD statistical mechanical calculations have proven an effective means of treating the full range of spatially-anisotropic intermolecular electrostatic interactions that play critical roles in defining the degree of noncentrosymmetric order that is achieved by electric field poling of organic electro-optic materials near their glass transition temperatures. New techniques have been developed for the experimental characterization of poling-induced acentric order including a modification of variable angle polarization absorption spectroscopy (VAPAS) permitting a meaningful correlation of theoretical and experimental data related to poling-induced order for a variety of complex organic electro-optic materials.     

Linearized electro-optic modulators based on a two-section Y-fed directional coupler

We experimentally demonstrate a linearized Y-fed directional coupler (DC) modulator based on an electro-optic (EO) polymer waveguide. The spurious free dynamic range of 119 dB/Hz2/3, which is 11 dB higher than that of the conventional Mach-Zehnder modulator, is achieved by introducing the reversed Δβ technique in the two-section Y-fed DC. The in-device EO coefficient (r33) of the fabricated device is as high as 79 pm/V in 1.55 μm wavelength, which is 88% of a single film r33 of LPD-80/APC.     

Bipolar tap photonic microwave notch filter using electroabsorption modulator-integrated distributed feedback laser diodes in a parallel configuration

We propose a bipolar tap photonic microwave notch filter scheme, which can be used to realize a fully integrated, semiconductor-based notch filter. The scheme is based on two electroabsorption modulator (EAM)-integrated distributed feedback laser diodes in a parallel configuration. We show that two filter taps with opposite polarities can be readily obtained by using the negative and positive slopes of the U-shaped electro-optic transfer functions of the EAMs under special design and operating conditions. An experiment was carried out to verify the working principle of the proposed scheme. Notch frequency tuning was also demonstrated by varying the laser wavelength spacing; the spacing was varied by changing the temperature. A frequency tuning range of ~1.8 GHz with a notch depth of ~40 dB was achieved.     

Radio-frequency front-end for 5 GHz wireless local area network transceivers

A transceiver front-end for 5 GHz wireless local area network applications has been designed and implemented in a low-cost 46 GHz f_r pure-silicon bipolar technology. The transceiver front-end adopts a superheterodyne sliding-IF architecture and consists of a down-converter, an up-converter and an LO frequency synthesiser. By exploiting a 1 bit variable-gain low-noise amplifier, the down-converter is able to provide an excellent noise figure of 4 dB while ensuring an input 1 dB compression point of 210 dBm with a current consumption of 25 mA from a 3 V supply voltage. The transmitter front-end is implemented by means of a current-reuse variable-gain up-converter. The circuit provides an output 1 dB compression point of 5.3 dBm although consuming only 45 mA from a 3 V supply voltage. Moreover, a linear-in-dB gain control characteristic is achieved over a 35 dB dynamic range. The LO frequency synthesiser is implemented by means of an integer-N phase-locked loop. It features a phase noise of 2117 dBc/Hz at 1 MHz offset from the centre frequency of 4.1 GHz and exhibits a tuning range of 1.2 GHz, from 3.47 to 4.65 GHz. The LO frequency synthesiser draws 20 mA from a 3 V supply voltage.     

Equivalent-Time Electro-Optic Sampling by use of a Picosecond Laser with a Voltage-Controlled Optoelectronic Pulse-Delay Tuning Circuit

We demonstrate a delay-line-free electro-optic sampling (EOS) system by using a novel ultrafast laser with a voltage-controlled pulse-delay tuning circuit (PDTC). The digital PDTC was designed as a substitute for a conventional optomechanical delay line in the EOS system, which facilitates the theoretical phase-tuning range of 4pi. The maximum delay time, tuning gain, and resolution of the PDTC are 3.6 ns (1.8 periods), 0.54 ns/V, and 0.2 ps, respectively. Arbitrary waveforms generated from microwave synthesizers, electrical pulse generators, and frequency prescalars are successfully sampled by use of this system, with a less than 8% deviation in the results.     

1.5-GHz voltage controlled oscillator with 3% tuning bandwidth using a two-pole DSBAR filter

First results on a novel voltage controlled oscillator (VCO) in the lower gigahertz range, featuring excellent phase noise and high power efficiency are presented. The heart of the VCO is a recently reported novel miniature two-pole decoupled stacked bulk acoustic resonator (DSBAR) filter. With its single 180° phase transition over the 1 dB bandwidth, linear phase, and maximum 1 dB insertion loss, it provides stable single-mode operation over 45 MHz (≈3%) of tuning bandwidth and has negligible heat dissipation when operated at incident power levels of 100 mW or greater. The 1.55-GHz laboratory VCO prototypes operate at 5 V supply voltage, 50 mA supply current, 15 dBm of output power, and >13% efficiency, demonstrating -84 and < -180 dBc/Hz phase noise suppression at 1 kHz carrier offset and in the thermal noise region, respectively. VCOs with cascaded DSBAR filters for further phase noise reduction are also demonstrated.     

Electro-optic multimode interference device using organic materials

We present experimental results verifying the optical robustness of a 1 x 1 multimode interference (MMI) device that is directly butt coupled with optical fibers at 70 degrees C for 1050 h and discuss the gradual increase of polarization dependent loss. Based on this structure, an electro-optic (EO) MMI waveguide device that can control the output optical power by using an electrode structure located directly on top of the multimode is presented. As a proof of principle, we demonstrate the switching operation of the EO-MMI device using commercially available chromophore as the active EO material.     

Tuning of a Ti3+:sapphire laser by an electro-optic beam deflection method

A wavelength-switching method for tuning a self-injection-seeded Ti3+:sapphire laser that uses an electro-optic beam deflection technique is reported. A LiNbO3 prism was employed in a tuning arm of the dual-cavity Ti3+:sapphire laser, and wavelength tuning of approximately 94 pm was attained by altering the deflection angle with the application of an electric field of 10 kV/cm to the prism. The spectral characteristics of the output laser were mainly determined by the diffraction grating in the dual-cavity laser, and the electro-optic prism just behaved as a light-beam deflector for the wavelength tuning purpose. This configuration can allow a simple tuning approach where fast and stable electronic wavelength switching is required in a narrow tuning range, on an order between a few tens of picometers to nanometers, without involving any mechanical movement.     

Optimized half-wave voltage and insertion loss in a strip-loaded waveguide electro-optic polymer modulator

A strip-loaded waveguide, electro-optic modulator was designed and analyzed in terms of single mode conditions, optical loss due to the metal electrodes, modulation efficiency, and mode size. Two designs were compared: Design 1 optimized the half-wave voltage (V(π)=1.1 V) with a nearly symmetric waveguide by maximizing modulation efficiency and minimizing the overall thickness of the waveguide; Design 2 optimized the insertion loss by reducing coupling loss by 4.6 dB via a strongly asymmetric waveguide that maximizes the overall mode size to most efficiently overlap with a single mode fiber. Design 2 also has a favorable half-wave voltage (V(π)=1.75 V). Some general guidelines in the selection of cladding layers in a detailed design of a poled-polymer electro-optic modulator incorporating a strip-loaded waveguide structure are suggested.     

Simulation of cross-talk reduction in multimode waveguide-based micro-optical switching systems by use of single-mode filters

We propose a method to reduce cross talk by using single-mode filters, namely, extracting the fundamental mode from a multimode optical network (EFMON). The EFMON effect is evaluated for a three-step switching system consisting of cascade electro-optic (EO) waveguide prism deflector (WPD) micro-optical switches (MOSs) and a multimode waveguide network. The WPD MOS is optimized for single-mode operation in lead lanthanum zirconate titanate thin films as EO slab waveguides with a driving voltage of 12 V, a length of 310 microm, and a channel distance of 20 microm. Beam propagation method simulation reveals that mode disturbance, higher-order modes, and cross talk are accumulated by switching steps. A single-mode filter for EFMON in the output region of the switching system reduces cross talk to below -20 dB at a propagation length of 2000 microm in the single-mode filter and below -30 dB at 20000 microm.     

Interferometric optical switch enhanced by a multi-resonance ring resonator structure

We propose a novel configuration for optical switches by the use of two coupled ring resonators acting as a phase-shifting element in a Mach–Zehnder interferometer. Because the ring structure is multi-resonant within one period of its phase response, light at any frequency within the period can be addressed by tuning the device across a small frequency interval. This enables the use of low voltages for electro-optic control of the switch, allowing for a tunable photonic switching device that operates at 1?V voltage levels.     

Electric field sensing with a hybrid polymer/glass fiber

We demonstrate the operation of an in-fiber electric field sensor. The sensor is fabricated with selective chemical etching of the core of a D-shaped optical fiber followed by the deposition of an electro-optic polymer (PMMA/DR1), which forms a hybrid core. The device demonstrates electromagnetic field sensitivity less than 100 V/m at a frequency of 2.9 GHz. Epi is estimated to be 60 MV/m with an insertion loss of 14.4 dB.     

Electro-optic polymer waveguide grating with fast tuning capability

A novel fast tunable electro-optic (EO) polymer waveguide grating is proposed and designed. Its resonant wavelength can be linearly tuned via the first-order EO effect with a high sensitivity of 6.1 pm/V. We find that the spectrum characteristics of EO polymer waveguide gratings depend strongly on many grating parameters, such as refractive-index modulation, modulation function, grating period, and period number. Material selection, fabrication technology, EO tuning ability, and polarization dependence of EO polymer waveguide gratings are also discussed. Such a waveguide grating not only overcomes the disadvantages of fiber-optic gratings, such as slow wavelength tuning ability and large-scale integration inconvenience, but also has many advantages, such as high resonant-wavelength tuning sensitivity, the same fabrication technology used for semiconductors, and polarization independence.     

Electro-optic modulator capable of generating simultaneous amplitude and phase modulations

We report on the analysis and prototype characterization of a dual-electrode electro-optic modulator that can generate both amplitude and phase modulations with a selectable relative phase, termed a quadrature variable modulator (QVM). All modulation states can be reached by tuning only the electrical inputs, facilitating real-time tuning, and the device has shown good suppression and stability properties. A mathematical analysis is presented, including the development of a geometric-phase representation for modulation. The experimental characterization of the device shows that relative suppressions of 38, 39, and 30 dB for phase, single sideband, and carrier-suppressed modulations, respectively, can be obtained as well as that the device is well behaved when scanning continuously through the parameter space of modulations. The QVM is compared with existing optical configurations that can produce amplitude and phase-modulation combinations in the context of applications such as the tuning of lock points in optical-locking schemes, single-sideband applications, modulation fast-switching applications, and applications requiring combined modulations.     

Optical, thermo-optic, electro-optic, and photoelastic properties of bismuth germanate (Bi(4)Ge(3)O(12))

To assess the suitability of bismuth germanate as an electro-optic material for high precision applications, we have confirmed and extended previous data on its refractive index, electro-optic tensor element r(41), and thermal expansion coefficient. In addition, we have measured the thermo-optic coefficient dn/dT, the temperature dependence of the electro-optic coefficient, and the stress-optic tensor elements. From the stress-optic tensor elements and previously published data, we have computed the strain-optic tensor elements. The index of refraction is given, to a good approximation, by the single-term Sellmeier equation, n(2) - 1 = S(0)λ(0)(2)/[1 - (λ(0)/λ)(2)], with S(0) = 95.608 μm(-2) and λ(0) = 0.1807 μm. The thermo-optic coefficient is 3.9 × 10(-5)/°C at 632.8 nm and 3.5 × 10(-5)/°C at 1152.3 nm. The electro-optic tensor element varies between approximately 1.05 and 1.11 pm/V over the spectral range of 550-1000 nm; its normalized effective change with temperature is approximately 1.54 × 10(-4)/°C. The thermal expansion coefficient is 6.3 × 10(-6)/°C over the range 15-125 °C. Values of the stress-optic tensor elements are q(11) - q(12) = -2.995 × 10(-13) m(2)/N and q(44) = -0.1365 × 10(-12) m(2)/N. The strain-optic tensor elements are p(11) - p(12) = -0.0266 and p(44) = -0.0595.     

Enhancing the tuning range of a single resonant band long period grating while maintaining the resonant peak depth by using an optimized high index indium tin oxide overlay

We report laboratory test results of a long period grating (LPG) that can maintain a constant resonant peak depth over an enhanced tuning range when it is coated with an indium tin oxide (ITO) electrode that has optimized thickness and refractive index. The authors have experimentally demonstrated a LPG coated with ITO that can be tuned in excess of 200 nm with an ambient refractive index change of less than 0.01. To the best of the authors' knowledge, this is the highest sensitivity reported for a LPG to date. In addition to the tuning performance, the resonant peak remains within 1 dB of its maximum depth for at least 100 nm of the tuning range.