Electro-optic Intensity Modulator Research Articles

Time magnification of electrical signals using chirped optical pulses

The authors report a method for stretching electrical signals in time. A high chirp rate is imposed on the electrical signal by mixing it with a dispersed ultra-short optical pulse in an electro-optic intensity modulator. This is followed by a passive optical dispersion element to produce a time-magnified copy of the input electrical signal.

Time stability of asymmetric Fabry-Perot modulator-based analog lightwave links

Lightwave links for analog signal transfer are being developed and evaluated for application in high-density interconnects. The reflective links are based on compact electrooptic intensity modulators connected by ribbons of single-mode fibers to remotely located transceivers (lasers and photoreceivers) and read-out electronics. For long term characterization, four asymmetric Fabry-Perot modulator (AFPM) prototypes have been continuously operated and monitored during a period of eight months. The collected data allow evaluation of the system time stability and simulation of the possible recalibration procedures. The recalibration requirements to achieve the desirable accuracy and reliability are inferred statistically.

Electrooptic narrow linewidth wavelength tuning and intensity modulation of an erbium fiber ring laser

We report an electrically tunable fiber laser featuring a 50-channel wavelength switching capability with a 0.2 nm linewidth and -20 dB crosstalk. The laser consists of an Er-doped fiber resonator and an electro-optic TE-TM convertor used as a wavelength tunable filter. It allows wavelength tuning over a spectral range of 10 nm with a tuning rate of 0.05 nm/V and a linewidth of 0.06 nm.

GHz-bandwidth optical intensity modulation in self-poled waveguides in strontium barium niobate (SBN)

Wide-band electrooptic intensity modulation at a wavelength of 1.3 /spl mu/m has been demonstrated in single mode channel waveguides in SBN:60 without repoling the substrates after processing at elevated temperatures. Waveguide losses were /spl les/0.7 dB/cm for both polarizations.

Dual-modulation compensation for optical intensity modulator nonlinearities

A dual-modulation technique for the compensation of electrooptic intensity modulator nonlinearities is presented. Analysis, computer simulation, and experimental measurements demonstrate the feasibility of the technique, with an improvement of over 20 dB in the carrier to third-order intermodulation product being achieved. The technique is straightforward to implement and is much less sensitive to signal-level variations than other techniques that have been presented.

Analog lightwave links for detector front-ends at the LHC

Lightwave links are being developed for volume application in the transfer of analog signals from the tracking detector front-ends to the readout electronics. The links are based on electro-optic intensity modulators which are mounted on detectors and connected by optical fibers to remotely located transceivers (lasers and photoreceivers). The modulators are III-V semiconductor reflective devices based on multi-quantum well structures. The transceivers will be integrated devices of a novel design. Modulator prototypes have been fabricated and tested. Neutron and /spl gamma/-ray irradiation studies have been performed on modulators and fibers. The main results achieved so far are reported and key system issues are reviewed. This work is part of the CERN DRDC project RD23.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analogue optical links for detector front ends at the LHC

Analogue lightwave links are being developed for the readout of tracking detectors at the CERN Large Hadron Collider (LHC). The links are based on arrays of reflective electro-optic intensity modulators, mounted on detectors and connected by optical fibres to remotely located transceivers (CW lasers and photoreceivers). The modulators are essentially passive devices with negligible power requirements. The transceivers are integrated optics devices of a novel design. Modulator prototypes have been fabricated and tested. The results achieved so far and the key system issues are reviewed.

Optical and electrical assessment of an electro-optical intensity modulator from the conjugated polymer poly(2,5-dimethoxy- p-phenylenevinylene)

An optical waveguide-based absorption modulator is described having a multilayer structure of the conjugated polymer poly(2,5-dimethoxy- p-phenylenevinylene) (PDMeOPV) and polyimide (Dupont PI2566), sufficiently thick to support several modes at the laser wavelengths of 633 and 780 nm. These structures operate as field-effect devices, and the origin of the electro-optical effect is through optical absorption in the red and infrared caused by charge injection into the conjugated polymer layer. The active length of the devices was 1 mm and modulations of up to 5% were measured when 70 V r.m.s. was applied to the electrodes, with the modulation dropping to zero above about 1 kHz, attributed to the long RC time constant of the device. Waveguides were assessed by prism coupling and end-fire coupling. Insertion losses were 24 to 44 dB and optical propagation losses ranged from 8 to 30 dB cm −1, depending on the mode and polarization.

Lightwave analogue links for LHC detector front-ends

The requirements on optical links for transferring analog and digital signals from the detector front-ends to the readout electronics at future high-luminosity colliders are reviewed. The advantages of external modulation techniques are discussed. An outline is given of the the R&D programme recently started at CERN by a collaboration involving high-energy physics institutes, optoelectronics research laboratories and industry, in order to develop electro-optic intensity modulator arrays, particularly for analogue applications, and to investigate the feasibility of volume production. The design of multichannel demonstrators in lithium niobate and III–V semiconductor technology is described. Preliminary results of the performance measurements are presented.

Fabrication of a novel electro-optical intensity modulator from the conjugated polymer, poly(2,5-dimethoxy-p-phenylene vinylene)

We report an electro-optic absorption modulator based around a metal-insulator-semiconductor field-effect transistor structure in which the active semiconductor is the polymer poly(2,5-dimethoxy-p-phenylene vinylene). It incorporates a single optical waveguide formed by the polymer, insulator, and a polyimide top layer which is ribbed to define the guide laterally. Charge injection creates polaron and bipolaron states which change the subgap absorption between 2 and 1.4 μm and between 800 nm and the band edge at 600 nm.

Electro-optic mode-displacement silicon light modulator

A new type of guided-wave electro-optical intensity modulator is proposed and analyzed. The waveguide consists of an N-type Si core layer on a P-type Si substrate. Foward bias on the N+-N-P-P+ diode decreases the refractive index of the core and displaces the fundamental guided mode downward into the substrate. However, the mode is not extinguished because the substrate is bounded by a P+ contact. A spatial filter at the output converts the mode displacement into optical intensity modulation. A Poisson and continuity equation solver and multilayer waveguide simulation were used to obtain numerical estimates of mode displacement in a realistic structure.

An electrooptic intensity modulator with improved linearity

A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical waveguide intensity modulators based on a tunable electron density multiple quantum well structure

With a recently developed semiconductor heterostructure it has become possible to tune continuously the electron density in multiple quantum wells. Here we demonstrate the first electro-optic waveguide intensity modulators based on this concept. We achieve a 22 dB on/off ratio for 9 V applied at 1.54 μm wavelength in a rib waveguide electroabsorption modulator. Electrorefractive devices include a waveguide Mach–Zehnder interferometer with an active length 650 μm operating at 1.58 μm wavelength with 5.4 V half-wave voltage. We show that the operating voltage can be further reduced by operating the Mach–Zehnder modulators in push-pull configuration.

Second-harmonic light intensity modulation and its possible application in subcarrier-multiplexed optical communication

The paper envisages theoretically the characteristics of second-harmonic subcarrier modulation in a branched-waveguide electro-optic light intensity modulator with a view to exploit a wider bandwidth of the optical carrier in the proposed subcarrier-multiplexed optical communication. It is found that under appropriate operating conditions of the modulator, substantial second-harmonic subcarrier modulation can be obtained, without distorting the useful baseband modulation carried by the microwave subcarrier.

Quaternary quantum wells for electro-optic intensity and phase modulation at 1.3 and 1.55 μm

We demonstrate for the first time that large quantum-confined Stark effect can be obtained in high quality InGaAsP/InP quantum well p-i-n heterostructures. The compositional flexibility of this material system is particularly suited for quantum well device applications in optical communications systems operating between 1.55 and 1.3 μm. We measure the magnitude of the shift of the ground-state exciton transition with applied electric field and find that it is significantly enhanced over ternary wells. We have also determined the electro-optic intensity and phase modulation response in these structures.

Comparison of the limits in performance of multiple quantum well and Franz-Keldysh InGaAs/InP electroabsorption modulators

The use of InGaAs/InP for electro-optical intensity modulation is discussed. In mutiple quantum well (MQW) materials the peak excitonic absorption αp, imposes a limit on the maximum change in intensity due to electroabsorption. For InGaAs (100 Å)/InP(100 Å), αp is only 25% of that for GaAs/AlGaAs. This accounts for the observed modulation limit of 1.4 dB/μm, which is significantly lower than the 3.9 dB/μm for GaAs based MQWs. For comparison, we calculated the maximum contrast possible in bulk InGaAs and found it to be 0.7 dB/μm. We conclude that the major benefit of using InGaAs/InP MQWs is associated with their insertion loss and not their contrast ratio.

Polarisation switching in a single-frequency external-cavity semiconductor laser

Polarisation switching between the TE and TM modes is demonstrated in an external-cavity semiconductor laser. A novel polarisation-selective external cavity with an intra-cavity electro-optic intensity modulator is used to switch the polarisation between two stable single-frequency oscillations

Behaviour of a novel cylindrical glass fibre optical coupler buried in KDP

Electro-optic intensity modulation is reported for the first time in a device consisting of a glass fibre directional coupler with an active KDP cladding. Tests suggest that, within about 0.5μm of the fibre surface, the KDP crystal has its bulk index, but a reduced electro-optic coefficient

Wide-bandwidth guided-wave electro-optic intensity modulator at λ=3.39 μm

A Ti-indiffused guided-wave interferometric modulator has been demonstrated at λ=3.39 μm with a linear small-signal 3-dB bandwidth of 1.8 GHz. This is the first interferometric modulator operating at λ&amp;gt;1.6 μm. An extinction ratio of 18.9 dB was obtained with Vπ=31 V for TE-polarized radiation. This value of Vπ is consistent with predictions based upon λ=0.85 μm modulator data and simple λ2 scaling rules, indicating little dispersion in the electro-optical coefficients of LiNbO3 over the 0.85–3.39-μm region. Such modulators are important components for the long-distance repeaterless data links which is the goal of the large effort in the development of ultra-low-loss fibers at the longer wavelengths.

Optical diffraction study of muscle fibers. I. A theoretical basis.

Abstract We present a simple theoretical model of optical diffraction by striated muscle fibers. The model accounts for (1) changes in diffraction intensity during isometric contraction, (2) spectra of quasielastically scattered light from isometrically contracting muscle, and (3) an electro-optical effect or intensity modulation of diffraction lines by applied electric field. Items (1) and (2) are concerned with the fluctuations of the sarcomere structure during isometric contraction, and item (3) is concerned with the lateral motions of, or the flexibility of, thin filaments in striated muscle at rest.