Electro-optic Amplitude Modulator Research Articles

High-efficiency electro-optic amplitude modulation with delayed coherent addition

Amplitude modulation of laser light is required for resonant sideband extraction employed in gravitational-wave detectors. Amplitude modulation with electro-optic phase modulators is realized by interferometric phase-to-amplitude conversion. Although two outputs modulated at opposite phases to each other are obtained, usually only one of them is utilized and the other is abandoned. The reuse of this abandoned light improves the power efficiency of the modulation. This can be realized by inverting the modulation phase of one output with a delay line and adding it to the other coherently. Moreover, this system selects a high-efficiency operating point and modulates the light in a linear range. We demonstrate that the modulation system can be operated with a power loss that is due only to the losses of the optical components.

Quantum model for electro-optical amplitude modulation

We present a quantum model for electro-optic amplitude modulation, which is built upon quantum models of the main photonic components that constitute the modulator, that is, the guided-wave beamsplitter and the electro-optic phase modulator and accounts for all the different available modulator structures. General models are developed both for single and dual drive configurations and specific results are obtained for the most common configurations currently employed. Finally, the operation with two-photon input for the control of phase-modulated photons and the important topic of multicarrier modulation are also addressed.

Shot-noise-limited laser power stabilization with a high-power photodiode array

The output power of a cw Nd:YAG laser was stabilized in a dc-coupled feedback loop with a low-noise multiphotodiode detector and an electro-optic amplitude modulator in the frequency band from 1 Hz to 1 kHz. For the first time, to our knowledge, an independently measured relative power noise of 2.4 x 10(-9) Hz(-1/2) at 10 Hz was achieved, fulfilling the power stability requirements of the Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) gravitational wave detector.

Generation of frequency-chirped laser pulses by an electro-optic amplitude modulator

We propose a single electro-optic amplitude modulator to modulate both the intensity and the phase of the light of a diode laser to produce frequency-chirped light pulses in the nanosecond time range. The two-in-one property of the Mach–Zehnder type electro-optic amplitude modulator is used to create a specific device available for experiments with cooled atoms. The phase induced in each optical path of the Mach–Zehnder interferometer and the phase-to-intensity modulation ratio, the intrinsic chirp parameter of the device is determined by generating high order optical harmonics.

Measurement of the spatiotemporal surface charge distribution in an ac plasma display cell using Pockels effect

We measured the surface charge distribution in a coplanar type alternating current plasma display panel cell by the longitudinal electro-optic amplitude modulation method with BSO (Bi12SiO20) single crystal. The effects of the initialization condition were investigated to take care of the errors coming from the charge relaxation phenomena of the BSO crystal. Using BSO single crystal as the dielectric layer, the two-dimensional spatiotemporal surface charge distribution was successfully measured in a discharge cell with a discharge gas of neon and xenon 4% at the pressure of 100torr driven by square-type sustaining pulses. The temporal behavior of the surface charge is compared with the simulated result and the measurement of the infrared light emission from the discharge. The positive and negative surface charges show somewhat different spatiotemporal characteristics.

Replica-molded electro-optic polymer Mach–Zehnder modulator

A Mach–Zehnder electro-optic polymer amplitude modulator is fabricated by a simple and high-throughput soft-stamp replica-molding technique. The modulator structure incorporates the highly nonlinear and stable chromophore, AJL8, doped in amorphous polycarbonate. Single-arm phase-retardation results in a halfwave voltage (Vπ) of 8.4V at 1600nm. The on/off extinction ratio is better than 19 dB, resulting from precise Y-branch power splitters and good waveguide uniformity. These results indicate that the simple fabrication process allows for good optical performance from high-fidelity replicas of the original master devices.

An electro-optic modulation technique for direct and accurate measurement of birefringence

We report a convenient and accurate technique for measuring the optical path difference induced by a birefringent crystal. The method is based on the transmission of a low-frequency signal by the electro-optic amplitude modulation of a monochromatic light source. The linear superposition principle of the induced birefringence and the electro-optic effect are employed in the analysis of the optical parameters. Birefringence measurements at the wavelength 0.6328 μm for some common nematic liquid crystal cells are presented. The measurement accuracy is close to 10 −3. In addition, the phase shift of a twisted-nematic liquid crystal spatial light modulator, which is now widely used in optical processing systems, is determined as a function of the gray-scale level.

5.2: Invited Paper: Observation of the Spatiotemporal Variation of Wall Charge Distribution in an ac PDP Cell

AbstractWe measured the spatiotemporal wall charge distributions on sustain and address electrodes in an ac PDP cell using the longitudinal electro‐optic amplitude modulation method. The measured wall charge distributions are used together with the discharge images obtained using high speed, image intensified CCD camera to have a better understanding on the sustain as well as the address discharge occurring in a three electrodes, coplanar sustain discharge type ac PDP cell.

Electro-absorption and fast electro-optics in highly polar molecular crystals

Polar organic crystals show great promise for use in photonic devices such as electro-optic amplitude or phase modulators for telecommunication. We discuss the structural requirements for large electro-optic effects and demonstrate through high frequency electro-optic experiments that acoustic phonon contributions to the linear electro-optic effect can be neglected in the crystals presented here. The small effect of acoustic modes was found to result from a compensation between the effects of piezoelectric length change and elasto-optic contributions. Moreover, we show that the effects of electro-absorption and linear electro-optics can be well understood in the terms of the linear Stark effect.

Polymer based polarization insensitive amplitude modulator: conception, technology and demonstration

Electrooptic (EO) waveguiding polymer devices are very attractive for optical communication systems by virtue of their simple and potentially low-cost fabrication procedures. Several functions such as high speed modulation or switching, have been already demonstrated. However, their so-far polarization dependant response precludes any actual use in optical telecommunication systems. The traditional uniform poling procedure, a prerequisite processing step for electrooptic polymer based devices whereby an electric field is applied at the vicinity of the glass transition temperature, results in uniform statistical polar orientation of the chromophores, and is, therefore, responsible for polarization sensitivity. By means of different coplanar or sandwich electrode configurations, any desired prerequisite modulation axis can, however, be imprinted onto the material, thus resulting in the possibility of balanced TE/TM polarization efficiencies. Monolithic integration of both electrode configurations within a Mach–Zehnder (MZ) modulator is shown to result in an original polarization insensitive electrooptic polymer amplitude modulator for integrated optics. Design procedures including modeling, fabrication as well as performance testing of the integrated sandwich and transverse electrode configurations device are discussed. Cladding is selected in view of ensuring both efficient poling conditions and maximal overlap of the modulation field with the active layer cross-section. Corresponding optimizations are presented for both electrode configurations.

Polarization insensitive electro-optic polymer modulator

Electro-optic waveguiding polymer devices are very attractive for optical communication systems as a result of simple and potentially low-cost fabrication procedures. Several functions, such as high speed modulation or switching, have been already demonstrated. However, their polarization sensitive response precludes any actual use in optical telecommunication systems. The traditional uniform poling procedure, a prerequisite processing step for electro-optic polymer based devices whereby an electric field is applied at the vicinity of the glass transition temperature resulting in statistical polar orientation of the chromophores, is responsible for polarization sensitivity. By way of different coplanar or sandwich electrode configurations, any desired prerequisite modulation axis can, however, be imprinted onto the material resulting in the possibility of balanced TE/TM polarization efficiencies. Monolithic integration of both electrode configurations within a Mach–Zehnder modulator is shown to result in an original polarization insensitive electro-optic polymer amplitude modulator for integrated optics. Design procedures including modeling, fabrication, as well as performance testing of the integrated sandwich and transverse electrode configurations device are discussed. The electrode configuration is optimized in view of ensuring both efficient poling conditions and maximal overlap of the modulation field with the active layer cross section.

Experimental linewidth-insensitive coherent analog optical link

We constructed an experimental linewidth-insensitive coherent analog optical link. The transmitter utilizes an external electro-optic amplitude modulator and a semiconductor laser. The receiver consists of a heterodyne front-end, a wideband filter, square law detector and narrowband lowpass filter. We performed experimental measurements and theoretical analyses of the spurious-free dynamic range (SFDR), link gain and noise figure for both the coherent AM and the direct detection links; we investigated the dependencies of the foregoing parameters on the received optical signal power, laser linewidth, IF bandwidth, and the laser relative intensity noise (RIN). By selecting a wide enough bandpass filter, we made the coherent AM link insensitive to laser linewidth. The coherent AM link exhibits a higher SFDR than the corresponding direct detection link when the received optical signal power is less than 85 /spl mu/W. The noise figure for the coherent link is greater than that for the direct detection link under all conditions investigated. For received optical signal powers greater than 4 /spl mu/W, the link gain for the direct detection link is greater than that for the coherent AM link. The following are the link parameters that have been achieved for the coherent AM link investigated: SFDR=88 dB/spl middot/Hz/sup 2/3/, link gain=-25 dB and noise figure=78 dB; this performance has been obtained with a received optical signal power of 85 /spl mu/W, and a local oscillator power at the photodetector of 228 /spl mu/W. The link performance can be further improved by auxiliary subsystems such as a balanced receiver and impedance matched transmitter and receiver ends; and/or by using better optical and electrical devices like higher power lasers, linearized optical modulators, low-noise and high gain RF amplifiers, and optical amplifiers,. >

Investigation of KTiOPO4 as an electro-optic amplitude modulator

We report on an experimental study of a hydrothermally grown KTiOPO4 (KTP) Pockels cell, utilizing the effective electro-optic coefficient, rc1=28 pm/V. Compensation of the static birefringence of KTP, when it is used as amplitude modulator, has been achieved by temperature tuning. Our study revealed that a KTP Pockels cell does not suffer from piezoelectric-induced parasitics (acoustic ringing). Stable high-repetition rate pulse slicing has been obtained at 30 kHz. Intracavity use of a KTP Pockels cell also has been successfully demonstrated in a Q-switched Nd:YLF laser system.

Optical effects in electrooptic amplitude modulation

Optical effects in electrooptic amplitude modulation

Hybrid bistable devices at 10.6 µm

We present a new hybrid bistable device which depends on the frequency of a modulation carried by the output optical beam. Experiments have been carried out with a CW CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser at 10.6 μm wavelength and an electrooptic CdTe amplitude modulator. The necessary nonlinearity for switching was provided by the tuning characteristics of a resonant circuit. This resonant driver circuit allows application of reduced voltages on the CdTe crystal to obtain bistability. Two feedback loops have been considered using either synchronous (at 0.117 MHz) or envelope detection (at 0.853 MHz).

Determination of electric dipole moment for the ν2 vibrational state of 15NH 3 by infrared-infrared double resonances

An infrared-infrared double-resonance technique, employing the sidebands produced by electro-optic amplitude modulation of a single-frequency CO 2 laser, is used to observe the second-order Stark effect of the ν 2 as R(2, 0) transition of 15NH 3. The technique enables the Stark shifts in ground and vibrationally excited states to be observed separately and yields the electric dipole moments: μ( v 2 = 1) = 1.253 ± 0.003 D, μ( v = 0) = 1.469 ± 0.004 D. The relative intensity distribution, linewidths, and line shapes of features in the double-resonance Stark spectra are also examined.

Switched directional couplers with alternating ΔΒ

Coupled waveguide structures with sections of alternating phase mismatch are proposed as switched directional coupler configurations in which complete conversion of light from one guide to the other can be achieved by an electrical adjustment. These structures can be used to make electrooptic switches and amplitude modulators in integrated optics form with improved conversion and on-off ratios. Couplers with 2, 3, 4, and N sections of alternating phase mismatch are analyzed, and diagrams describing their switching characteristics are given.

Electro-optic amplitude modulation using three-dimensional LiNbO3 waveguide fabricated by TiO2 diffusion

An almost single-mode waveguiding layer has been fabricated by thermal diffusion of TiO2 into LiNbO3. The refractive-index change in the layer is 2–3×10−3 for both ne and no, and the propagation loss is 0.7–0.8 dB/cm. The electro-optic coefficients are found to be nearly equal to those of the bulk crystal. An amplitude modulation has been made with a stripe waveguide 10 μm wide and planar electrodes. The half-wave voltage is 17 V and the maximum extinction ratio is 12 dB.

Experiments on a multistage electrooptic amplitude modulator

A procedure for synthesizing electrooptic amplitude modulators of light has recently been given by the authors. In this correspondence, the results of experiments performed on a three-stage modulator whose configuration was derived using this synthesis procedure are reported.

Synthesis of electrooptic modulators for amplitude modulation of light

A technique is described for synthesizing electrooptic amplitude modulators having arbitrary modulation characteristics. The technique is an adaptation of the procedure of Ammann and Yarborough for synthesizing naturally birefringent networks. The desired amplitude-transmission versus applied-voltage function <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K(\upsilon)</tex> of the modulator is written as an exponential series containing a finite number of terms. The resulting modulator consists of a series of stages between an input and output polarizer, with each stage consisting of an electrooptic element and optical compensator. The induced birefringence of the electrooptic medium is assumed to be directly proportional to the applied modulating voltage υ. The question of how <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K(\upsilon)</tex> should be chosen is also investigated. Two cases are considered: 1) an amplitude modulator to be used with an envelope detector, and 2) an amplitude modulator to be used with a square-law detector. For each case, the ideal <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K(\upsilon)</tex> and several methods of approximating it are given. It is found that the manner in which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K(\upsilon)</tex> is chosen is of great importance. Best results were obtained when the term coefficients (the C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</inf> ) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K(\upsilon)</tex> were chosen to directly optimize the modulator property (or properties) deemed most important. Modulator designs corresponding to several useful <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K(\upsilon)</tex> are given in tabular form.