Fiber-based probe for electrooptic sampling

A fiber-based electrooptic probe that can be incorporated into existing electrooptic sampling systems is presented. The probe is made by attaching an electrooptic crystal to the end of a standard optical fiber and thinned to a thickness of 1.6 /spl mu/m using selective wet etching. Measurements of the electric field over a coplanar waveguide structure verify the probe's ability to sense electric fields. The probe can be accurately placed a few micrometers over a test point by monitoring the power reflected back into the probe off of a conductor on a circuit under test.     

1/spl times/2 and 1/spl times/4 electrooptic switches

We describe the design, fabrication, and testing of two packaged electrooptic switches built from poled LiTaO/sub 3/ crystals. The 1/spl times/2 switch requires a driving voltage of 1200 V and exhibits insertion loss of 2.4 dB and crosstalk of -39.2 dB; the 1/spl times/4 switch exhibits insertion loss and crosstalk of 2.8 dB and -40.6 dB, respectively, and operates using a 1100-V voltage source. The maximum deflection time between the channels is 86 ns.     

Low-loss electrooptic BaTiO/sub 3/ thin film waveguide modulator

A strip-loaded electrooptic waveguide modulator based on an epitaxial BaTiO/sub 3/ thin film was fabricated and characterized for the first time. The strip-loaded waveguide structure greatly improves waveguide propagation and polarization-dependent loss performance. A propagation loss of 1.1 dB/cm and polarization dependent loss of 0.1 dB/cm were measured. The electrooptic waveguide modulator exhibited a half-wave voltage-interaction length product of 4.5 V /spl middot/ cm at a wavelength of 1542 nm. The measured effective electrooptic coefficient of the as-grown BaTiO/sub 3/ waveguide modulator was 38 pm/V. The experimental results indicate that a strip-loaded thin film waveguide modulator is suitable for photonic applications.     

Electrooptic wafer beam deflector in LiTaO/sub 3/

A novel electrooptic beam deflector is reported based on ferroelectric domain inversion extending through the thickness of a Z-cut LiTaO/sub 3/ wafer. The selective domain inversion is achieved by electric-field poling assisted by proton exchange, rather than proton exchange followed by rapid thermal annealing. The deflection sensitivity of the device was measured to be 5.0 mrad/KV. This is 93% of the theoretical value for this geometry, and a significant improvement over the value of 80% of theoretical previously reported for a waveguide deflector. This improvement is attributed to the new domain inversion process. No degradation of deflection sensitivity is observed up to the frequency of 300 KHz, which is then limited by the response time of detectors.     

Bandpass traveling-wave Mach-Zehnder modulator in LiNbO/sub 3/ with domain reversal

A bandpass traveling-wave Mach-Zehnder modulator is demonstrated in a Z-cut LiNbO/sub 3/ substrate where quasi-phase-matching is achieved by using a crystal domain reversal and a simple uniform coplanar waveguide electrode structure. The domain reversal was created, by using electric-field poling, to implement the three-section alternating electrooptic interaction. At the operating wavelength /spl lambda/=1.32 /spl mu/m, the modulator has a 15 GHz-broad bandpass response centered at 25-GHz 3.6-dB fiber-to-fiber insertion loss, 12 V on-off voltage at the center frequency, and -33-dB extinction ratio.     

High-O coplanar transmission line resonator of YBa/sub 2/Cu/sub 3/O/sub 7-x/ on LaAlO/sub 3/

Reports on quality factor measurements of a coplanar waveguide transmission line resonator patterned from a YBa/sub 2/Cu/sub 3/O/sub 7-x/ film on a LaAlO/sub 3/ substrate, resonating at 6.5 GHz. At 77 K the unloaded quality factor is 3850+or-180, that is about 43 times higher than that of an identical copper resonator at the same temperature and frequency. This result demonstrates the usefulness of LaAlO/sub 3/ as a substrate for high-temperature superconducting microwave applications.<>     

Electro-optic sampling using an external GaAs probe tip

The first laser-diode-based external electro-optic (EO) sampling using a GaAs probe tip is described. This tip is a longitudinal electric field sensor, being therefore immune from optical crosstalk. The minimum detectable voltage is 16 mV/ square root (Hz). The EO sampling is compared with that of a conventional electrical sampling oscilloscope, and the two are shown to be in excellent agreement.<>     

High speed III-V electrooptic waveguide modulators at λ-1.3μm

Traveling wave GaAs electrooptic waveguide modulators at a wavelength of 1.3 μm with bandwidth in excess of 20 GHz have been developed and characterized. The design and characteristics of both p-i-n modulators in microstrip configuration and Schottky barrier on n ^--GaAs/semi-insulating (SI) GaAs in the coplanar strip configuration modulators are discussed. It is shown that microwave loss and slowing on n⁺ GaAs substrates will limit the bandwidth of the microstrip modulator to less than 10 GHz for a device 8 mm in length. Modulators with bandwidths in excess of 10 GHz are fabricated on SI GaAs substrates     

砷化镓共面波导内部微波信号的电光取样检测

本文报道了共轴反射式电光取样系统。该系统时间分辨率不低于20ps,空间分辨率不低于3m。用它检测了砷化镓共面波导内部的微波信号。这套系统将被应用于砷化镓高速集成电路内部特性的在片检测。     

Vertically compact 15 GHz GaAs/AlGaAs multiple quantum well laser grown by molecular beam epitaxy

A GaAs/Al/sub x/Ga/sub 1-x/As multiple quantum well laser with an electrical modulation bandwidth exceeding 15 GHz has been fabricated. Optimised design of the waveguide, including development of high Al mole fraction (x=0.8) cladding layers, together with a coplanar electrode geometry, has resulted in a vertically compact laser structure suitable for integration.<>     

Millimetre-wave active probe frequency-multiplier for on-wafer characterisation of GaAs devices and ICs

A millimetre-wave active probe quintupler with an output frequency range of 60 to 100 GHz has been developed. The frequency multiplier circuit was implemented in a coplanar waveguide. Using this probe along with the electro-optic sampling technique, on-wafer millimetre-wave vector measurement up to 100 GHz and time-waveform measurement at 77 GHz of test structures on a GaAs substrate have been demonstrated.<>     

Electrooptic ferroelectric Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films

We report on waveguiding and electrooptic properties of epitaxial Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films grown by radio-frequency magnetron sputtering on Al/sub 2/O/sub 3/(11_02) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.     

Electrooptically wavelength-tunable polarization converter utilizing strain-optic effect on X-cut LiNbO/sub 3/

A new electrooptically wavelength-tunable polarization converter by strain-optic effect on LiNbO/sub 3/ is presented. The polarization conversion is achieved by the tilt of waveguide principal axis caused by the stress induced by the proton-exchanged region on the single side of the waveguide. Simply increasing the proton-exchange time can enlarge the stress-distributed region and its interaction with the input light, thus, the conversion efficiency can be enhanced. By electrooptic effect, the wavelength of maximum conversion can be tuned at a rate of 0.081 nm/V with a maximum conversion efficiency of 92.4%.     

A spatial sampler using integrated optic techniques

A spatial sampler for detecting transient RF and microwave signals is proposed. The sampler consists of a series of electrooptic directional couplers spatially located along an integrated-optic waveguide beneath a coplanar RF stripline. It is theoretically shown that the sampler has the potential of sampling with a temporal resolution of a few picoseconds and a sampling rate in excess of 40 billion samples per second. An electrooptic coupler with a coupling characteristic that is asymmetric with voltage is analyzed and experimentally evaluated for consideration in the sampler.     

Electrooptic Bragg-diffraction modulators in GaAs/AlGaAsheterostructure waveguides

Reports theoretical and experimental results on electrooptic Bragg-diffraction modulators in GaAs/GaAlAs heterostructure waveguides. The devices utilize the linear electrooptic effect in periodic structures to facilitate spatial modulation of the refractive index in the waveguide. A numerical method was established to solve the waveguide equation and quantify the induced changes in the effective index of the waveguide as a result of reverse bias. The numerical calculation has established the guidelines for an optimum design of the modulator that operates in the Bragg regime. The measured diffraction efficiency of the single-grating Bragg modulator was as high as 90 percent at a driving voltage of 15 V. A device consisting of four such basic diffraction gratings was also fabricated and used to demonstrate the function of scalar addition. The highest bandwidth of the devices that have been measured exceeds 1 GHz. The planar waveguide Bragg modulators offer advantages including lower optical propagation loss, greater fabrication tolerance, and spatial separation between the diffracted and the undiffracted light beams     

Integrated optical device with second-harmonic generator,electrooptic lens, and electrooptic scanner in LiTaO3

This paper reports the first demonstration of an integrated optical device in z-cut LiTaO₃ that contains the following three functional parts: a quasiphase-matched second-harmonic generation (SHG) grating, an electrooptic (EO) lens, and an electrooptic scanner. The SHG device consists of channel waveguides passing through periodic domain-inverted gratings. The frequency of the input infrared (IR) light at 864 nm was doubled into blue light at 432 nm. A stack of EO lenses was used to collimate the light from the channel waveguide. The measured beam size at the output facet for various applied voltages to the lenses agreed with simulation. After collimation, light passes through an EO scanner that controls the angle of the output beam. A scanning sensitivity of 17 mrad/kV was measured for the scanner, compared to the calculated value of 15 mrad/kV     

Terahertz attenuation and dispersion characteristics of coplanartransmission lines

Experimental verification of analytic formulas for the dispersion and the attenuation of electrical transient signals propagating on coplanar transmission lines is presented. The verification is done in the frequency domain over a terahertz range although the experiments are in the time domain. The analytic formulas are obtained from fits to the full-wave analysis results. It is quantitatively verified that the full-wave steady-state solutions can be directly applied to the transient time-domain propagation experiments. Subpicosecond electrical pulses and an external electrooptic sampling technique are used to obtain the time-domain propagation data. From the Fourier transforms of the time-domain data both the attenuation and the phase information as a function of frequency are extracted. The dispersion and the attenuation characteristics are investigated for both coplanar waveguide and coplanar strip transmission lines. The investigation is carried out on both semiinsulating semiconductor and dielectric substrate materials. No observable losses caused by the semiconductor material are indicated     

Temperature dependence of permittivity and loss tangent of lithium tantalate at microwave frequencies

Lithium tantalate (LiTaO/sub 3/) exhibits excellent electro-optical, piezoelectric, and pyroelectric properties and a very low thermal expansion. In this paper, we report measurements of loss tangent and the real part of the relative permittivity /spl epsiv//sub r/spl perp// measured in c-axis LiTaO/sub 3/ crystals in the temperature range from 14 K to 295 K at a frequency of 11.4 and 10 GHz. Microwave properties of LiTaO/sub 3/ were determined by measurements of the resonance frequency and the unloaded Q/sub o/ factor of a TE/sub 011/ mode cylindrical cavity containing the sample under test and accounting for uncalibrated cables and adaptors inside the cryocooler. The permittivity of LiTaO/sub 3/ was found to increase from 38.9 to 41.1 and the loss tangent to change from 1.1/spl times/10/sup -4/ to 6.5/spl times/10/sup -4/ over the full temperature range. Due to its low loss and relatively high permittivity, LiTaO/sub 3/ is suitable for microwave applications.     

The transverse electrooptic modulator (TEOM): fabrication,properties, and applications in the assessment of waveguide electroopticcharacteristics

The fabrication of a novel electrooptic modulator with a transverse electrode geometry, formed by parallel electrodes on opposite faces of a thinned lithium niobate substrate straddling a strip waveguide, is reported. The device, referred to as a transverse electrooptic modulator (TEOM), has several advantages over standard electrooptic waveguide modulators using a coplanar electrode geometry. It is shown that it is possible to achieve a 30% reduction in the operating voltage for a given electrode spacing and a substantial reduction in the figure of merit, the power required per unit bandwidth, for electrooptic modulators with either lumped or traveling wave electrode structures. Moreover, a more accurate estimate of the electrooptic coefficients is possible than with modulators using strip waveguides and coplanar electrodes     

Free-space electrooptic sampling of terahertz radiation from optically excited superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films

The characteristics of photogenerated terahertz radiation from a current-biased superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) bow-tie antenna were investigated using a free-space electrooptic sampling technique. Picosecond electromagnetic pulses about 450 fs wide were obtained. The frequency spectrum derived by Fourier transforming the picosecond pulses spans over 0.1-4 THz. The dynamics of the quasi-particles optically induced by the ultrafast laser pulse primarily determines the performances of the transient terahertz radiation generated under different operating parameters. The results indicate a characteristic quasi-particle relaxation time of about 2.5 ps close to the critical temperature T/sub c/, and a faster time at lower temperatures.