A polarization independent GaAs-AlGaAs electrooptic modulator

Two designs for polarization independent GaAs-AlGaAs interferometric electrooptic modulators are described. One design uses the linear electrooptic effect to couple degenerate TE/TM eigenmodes of a single-mode waveguide. In the other design the eigenmodes need only be near degenerate. The design using the coupling between near degenerate TE/TM modes utilizes a novel biasing scheme. A novel polarization independent GaAs-AlGaAs interferometric optical modulator based on this design has been fabricated and characterized at 1.3 μm. This modulator is fabricated as a traveling wave modulator incorporating 50 Ω, phase velocity matched, low microwave loss electrodes for maximum electrical bandwidth     

Ferroelectric liquid crystal optical waveguide switches using thedouble-refraction effect

We propose an optical waveguide device with a bistable ferroelectric liquid crystal as the core. The liquid crystal electrooptic effect device induces a double-refraction phenomenon and the associated optical beamsteering provides a very simple 1×N optical switch. Beamsteering has been experimentally demonstrated and characterized. It exhibits very large angles (φ=40-60 for respective wavelengths λ=0.850-0.632 μm). In the same way, we propose a design that includes polymer integrated lenses for a compact device with a large number of outputs     

Integration of an electrooptic polymer in an integrated opticscircuit on silicon

This paper presents the joining of active nonlinear polymer waveguides with passive silicon nitride waveguides (SiO₂-Si ₃N₄-SiO₂) to form an integrated Mach-Zehnder modulator with a lateral electrode configuration on a silicon substrate. Passive and active waveguides are based on a silicon-nitride-strip guiding structure. In the active waveguide a nonlinear polymer layer is used to obtain an index modulation via the electrooptic effect. Despite the silicon nitride strip based guiding structure, 63% of the energy of the fundamental mode is guided in the nonlinear polymer (provided by Flamel Technology, Venissieux, France). Poling with field strengths up to 75 V/μm applied to the lateral electrodes has been employed to orient the chromophores. A half wave voltage of 35 V has been measured for an electrooptic coefficient of 5.8 pm/V at a wavelength of 1.3 μm. Optical loss measurements have been done on polymer and passive waveguides. The best results have been 1.8 dB/cm for the active and 0.78 dB/cm for the passive waveguides leading to a total loss of 6 dB for a modulator with an interaction length of 2.5 cm. The coupling loss between a laser diode and the passive waveguide structure was measured to be at least 4.6 dB using a microscope objective and piezo-electric displacement elements. Stability tests under atmospheric conditions have shown a decrease of the electrooptic coefficient which might be due to the hygroscopic behavior of the active polymer. The bandwidth of the modulator has been determined to be 4 MHz     

Miniature Mach-Zehnder InGaAsP quantum well waveguideinterferometers for 1.3 μm

Electrooptic Mach-Zehnder interferometers with active lengths as small as 350 μm are discussed. These strip-loaded waveguide devices utilize the electrooptic effect in InGaAsP/InP quantum wells to achieve pi phase shift with single arm drive voltages of 12 V and 6 V drive in push-pull operation     

Electroptic diffraction modulation in ZnO film on sapphire

An electrooptic Bragg diffraction modulator with high diffraction efficiency which utilizes a low-loss epitaxial ZnO optical waveguide on a sapphire substrate is discussed. An interdigital electrode with a spatial period of 20 μm and an aperture of 3 mm was fabricated directly on the film surface using a photolithographic technique. For the TE₀ mode at 6328 Å, a maximum diffraction efficiency of 98% has been obtained from DC to 100 kHz with an applied voltage of about 31 V. The unclamped electrooptic coefficient r ₃₃ is estimated to be 5.8×10^-12 m/V which is much larger than the clamped value of 2.6×10^-12 m/V in the literature     

10 GHz bandwidth traveling-wave LiNbO3optical waveguide modulator

A broad-band traveling-wave electrooptic modulator of Ti-diffused LiNbO3optical waveguide was designed, constructed, and tested at 0.63 μm over a bandwidth of 10.5 GHz. Using a novel asymmetric electrode configuration as a microwave waveguide, practically smooth frequency response of the modulator was obtained. For 300 mW drive power, the phase modulation index was 1 rad at 2 GHz and 0.53 rad at 10 GHz, while the intensity modulation index was 64 and 34 percent, respectively.     

Efficient electrooptic modulator in InGaAlAs/InP optical waveguides

A single heterostructure InGaAlAs/InP phase modulator utilizing the quadratic electrooptic effect (QEO) is reported for the first time. The calculated value of the QEO coefficient from the measurements is 3.7×10^-19 m²/V² at 80 meV below the band edge. In addition, the linear electrooptic effect (LEO) coefficient is estimated to be 1.2×10^-12 m/V, which is comparable to that of GaAs. The propagation loss of a single mode ridge waveguide is in the range of 1.5-1.7 dB/cm, which is better than the previously reported value in this material system. The measured single mode phase shifts are 5.5 and 2.8°/V mm for TE and TM polarizations, respectively. These values are the largest reported so far in an InGaAlAs system     

0-1 GHz waveguide 10.6 μm GaAs electrooptic modulator

A GaAs electrooptic modulator for use in 10.6-μm laser frequency shifting applications is described. High-beam-quality output signals with a frequency tunability of 0.1-1.0 GHz were demonstrated. Thick epitaxial GaAs-AlGaAs waveguide structures were successfully fabricated into single-mode channel waveguides with excellent optical and electrooptic properties. A lumped-element modulator, with electrical and electrooptic characteristics in good agreement with theory, was operated at RF drive power levels up to the reverse breakdown voltage limit. The insertion loss of the modulator was quite high, due to absorption losses in the epitaxial material     

GaAs/AlGaAs多量子阱FET-SEED灵巧象元

将GaAs／AlGaAs多量子阱光探测器、光调制器与GaAs场效应晶体管（FET）混合集成,构成FET-SEED灵巧象元。光探测器和光调制器均为反射型自电光效应器件（SEED）,光源为骨子阱半导体激光器。测出的光输出Pout／光输入Pin特性表明,光输入信号对光输出信号有明显的调制作用,光输入信号较小的变化可以导致光输出信号较大的变化。     

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.     

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     

Quantum interference, Stark, and carrier density infraredelectrooptical modulation based on intersubband transitions inasymmetrical quantum wells

A new approach toward studying electrooptic modulation utilizing intersubband transitions in quantum wells is presented. Using first-order perturbation theory for analyzing the effect of a dc electric field on the linear susceptibility, an understanding of the mechanisms which give rise to intersubband electrooptic susceptibility is presented. This includes modulation due to the dc Stark effect, modulation due to coherent interference of the envelope states, and modulation of the carrier densities in populated subbands. We study several structures that maximize the electrooptic susceptibility of a particular origin and discuss the suitability of the various schemes for practical realizations. Finally, we derive a figure of merit for each type of modulator, taking into account the linear intersubband absorption, and show that highly efficient near-infrared modulators that operate at a wavelength of 1.5 μm can be realized     

Infrared phase modulators with multiple quantum wells

The intraband transition of a graded Ga_1-xAl_xAs/AlAs quantum well is analyzed for its suitability as a phase modulator at infrared wavelengths. Using the effective mass model and numerically solving Schrodinger's equation for a graded energy well with an external electric field, it is found that significant phase changes are possible for comparatively small voltages even for operation far from the absorption resonance. In an example, the calculated value for V_π at 10.6 μm is 150 V, an improvement by over two orders of magnitude over conventional bulk electrooptic material for that wavelength regime     

Efficient, low parasitics 1.3 μm InGaAsP electroabsorptionwaveguide modulators on semi-insulating substrate

The high-speed operation of waveguide modulators is limited by the RC time constant, where the capacitance is primarily due to the parasitics. As part of an effort to reduce the parasitic capacitance, the authors have demonstrated a 1.3 μm InGaAsP electroabsorption waveguide modulator on semi-insulating InP substrate. A parasitic capacitance smaller than 10 fF was achieved by fabricating the bonding pad on an isolated mesa and by making use of an air bridge. For a 400 μm long waveguide modulator, an operating voltage as small as 2 V at an on-off ratio of 10 dB was obtained by optimizing InGaAsP bandgap for the operating laser wavelength. The device consists of a five-layer structure on semi-insulating substrate grown by liquid-phase epitaxy. These layers are undoped-InP buffer layer, undoped-InGaAsP waveguide layer, undoped-InP spacer layer, p-InP cladding layer, and p-InGaAsP contact layer     

Traveling-Wave Coherent Light-Phase Modulator

The use of a rectangular waveguide partially loaded with electrooptic material as a laser beam phase modulator is analyzed theoretically. The characteristic equation, fields, power, and attenuation are obtained in terms of normalized parameters. Design procedure of the modulator is given with particular reference to KDP.     

Theory of refractive index variation in quantum well structure andrelated intersectional optical switch

Attention is focused on the deformation of electron wave functions due to an applied field in a quantum well (QW) neglecting the exciton effect. Compared to the electrooptic effect of bulk semiconductor, the theoretical refractive index variation in a QW structure due to this phenomenon is considerably larger at the wavelength corresponding to the energy gap between the first quantized energy levels in the conduction and valence bands. Since the absorption loss changes by the same mechanism, the appropriate wavelength region is estimated for larger index variation where the absorption loss is relatively smaller. The design of a related intersectional optical switch of a small size is discussed. A switch with a length of about 10 μm is achievable with an intersectional angle of more than 10° at a waveguide width of 1 μm. This optical switch is expected to be of high speed and is integrable monolithically with lasers     

Optical regenerative oscillation and monostable pulse generation in electrooptic bistable devices

Optical regenerative oscillation is discussed theoretically and experimentally in three types of mirrorless bistable optical devices based on the electrooptic light modulator. The devices have two feedback signals proportional to the optical output power, and the oscillation condition and oscillation frequency depend on the time constants and conversion factors for two feedback voltages and biasing phase retardation in the light modulator. Analysis is done by treating the coupled differential equations for the time dependent feedback signals. The experimental results agree with the theoretical prediction. We show also that optical monostable pulses can be generated in the three types of bistable optical devices.     

LiNbO3waveguide modulator with 1.2 µm thick electrodes fabricated by lift-off technique

In order to make efficient high-frequency electrooptic modulators, the microwave loss in the electrodes has to be minimized. A lift-off technique using chlorobenzene to harden the top of AZ1350-J photoresist was adopted to fabricate 1.2 μm thick metal electrodes. A 1 cm long, 15 μm wide strip electrode has a dc resistance of 11 Ω, which is substantially less than that of the 2000 Å thick electrodes routinely fabricated. A 1 cm long traveling-wave phase modulator consisting of a single waveguide was tested. The measured -3 dB bandwidth is 3.8 GHz.     

A waveguide-type optical-frequency comb generator

A waveguide type optical frequency comb (WG-OFC) generator was developed at 1.56 μm wavelength region by utilizing a waveguide type phase modulator. It was confirmed that the envelope of sideband spectra had a width of 2.7 THz and the slope of the envelope profile was 28 dB/THz. The maximum measurable frequency difference, limited by the shot noise, was estimated to be 3.2 THz     

Low-switching-voltage InGaAsP/InP waveguide interferometricmodulator for integrated optics

An InGaAsP/InP electrooptic Mach-Zehnder modulator consisting of two 3-dB Y-branch couplers and phase modulation arms is fabricated by the metal-organic vapor-phase epitaxy growth method. A schematic illustration and cross section of the interferometric modulator as well as the current-voltage characteristics of the arms are shown. The modulator is formed by a waveguide having almost the same cross-sectional configuration as a double-heterostructure laser diode. The switching voltage of 4.5 V applied to one arm of the modulator results in an excitation of about 7 dB