Low-loss fibre-coupled waveguide directional coupler modulator

We report a fibre-coupled Ti: LiNbO3 directional coupler modulator with total fibre-device-fibre insertion loss as low as 1.5 dB for ?=1.32 ?m. Low loss has been achieved by using diffusion parameters to give good mode match to the fibre and low propagation loss, an effective SiO2 buffer layer to eliminate electrode loading loss and a directional coupler geometry which minimises the effect of bend loss.     

Modified 1×2 directional coupler waveguide modulator

A novel 1×2 Ti:LiNbO3 modified directional coupler modulator is demonstrated. The 3 dB operating point requires no bias voltage. The device has a lower switching voltage requirement than a conventional directional coupler.     

A Y-fed directional coupler modulator with a highly linear transfer curve

We demonstrated a linearized Y-fed directional coupler modulator in Z-cut LiNbO/sub 3/. The proof-of-concept device employed two electrode sections of opposite polarity whose lengths were chosen based on the results of our previous theoretical modeling. A highly linear modulation characteristic and improved tolerance to fabrication errors were achieved with a simple design, in excellent agreement with the theory. The linearity exceeded 90% over a wavelength range of 45 nm, centered around 1530 nm, with a maximum linearity of 97% at 1510 nm and a maximum modulation depth of 98%. By comparison, the linearity of conventional modulators is typically around 70%. Thus the device was proven to have a high linearity with a wide usable spectral range and relaxed fabrication tolerances.     

Microstrip directional coupler with flat coupling and high isolation

Based on the open-circuited slotline to realise capacitive compensation, a microstrip directional coupler with high isolation is investigated. Meanwhile, by adding external matching networks at the input/output ports, bandwidth is enhanced and a flat coupling is obtained. Centred at 2.4 GHz, a 3 dB directional coupler is designed, fabricated and examined. Both simulated results and measured data are presented, and good agreement between them is observed     

Microstrip directional coupler with nearly ideal TEM coupler performance

A meandered parallel coupled-line structure is proposed to achieve high directivity within a wide bandwidth. By properly increasing the meandered parallel coupled-line sections, the high-directivity bandwidth becomes much wider. An example coupler is fabricated to verify the theory. More than 50 dB of isolation is achieved over a bandwidth of zero to twice centre frequency.     

Traveling wave optical modulator using a directional coupler LiNbO3waveguide

Fabrication methods for low drive voltage and broad-band LiNbO3waveguide directional coupler optical modulator are described. Optical waveguides were prepared by conventionaly Ti in-diffusion into LiNbO3c-cut plate. To obtain wide-band frequency response, traveling wave electrodes were used. Electrode characteristic impedance measured by time domain reflectometry method coincided well with the calculated value by conformal mapping. Measured electrode conductor losses followed square root of frequency. To reduce electrode conductor losses, asymmetric and 3-μm thick Al electrodes were used. Directional coupler optical modulator frequency response was analyzed, using the phase difference average value along the propagation directions. Calculated value by this method coincided well with measured value obtained by a swept frequency technique. The characteristics of this modulator at the 1.317-μm wavelength are as follows: 100 percent modulation voltage is 4 V, extinction ratio is 17 dB, optical insertion loss is 5.4 dB, 3-dB bandwidth is 3.6 GHz, and rise time is about 400ps.     

一种利用定向耦合调制器的循环干涉型光学陀螺改进方案

循环干涉型光学陀螺的损耗随着循环次数的增加而增大,并且耦合器对于光强的分配起着至关重要的作用,文中提出了一种利用定向耦合调制器代替普通耦合器的改进方案,利用定向耦合器可以通过调整工作电压获得交叉态与直通态的特性,改变光脉冲信号进入光路时及光循环经过耦合器时的耦合态,以此来增大信号光耦合进光路的光强,并减少因循环所导致的额外损耗。仿真表明,文中提出的方法可以明显增大检测到的光强,提高光信号的信噪比,从而提高检测精度。     

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.<>     

Broadband microstrip directional coupler

A nonuniform microstrip directional coupler with sinusoidally modulated coupling function is presented. The ripple and the amplitude response are controlled by the index of modulation m and the periodicity P of the function. For demonstration, a 20 dB ± 6% coupler is constructed on two different substrates and the experiment shows much flatter coupling response than the uniform or exponential line directional couplers.     

Non-evanescent adiabatic directional coupler

A directional coupling mechanism based on an adiabatic coupling between three optical modes is suggested. The optical power transfer between two waveguides which are far apart is mediated by adiabatic coupling between zero-order optical modes of the individual waveguides and a high-order intermediate mode. The analytical model for an adiabatic three-mode coupling based on a scalar wave equation is presented. The directional coupling via the adiabatic mode coupling between copropagating modes is described and compared with a nonadiabatic directional coupling assisted by periodic perturbation. It is shown that adiabatic directional coupling has much less sensitivity to the mode parameters and to the wavelength     

Active surface-wave directional coupler

We report experimental results which show that noncollinear surface-wave mixing on [111]-cut bismuth?germanium oxide can be used to realise an active, switchable directional coupler. For low-level inputs, the coupling is enhanced by as much as 20 dB by a semiconductor placed over the interaction region. The directivity is found to be greater than 40 dB.     

Dual adjacent directional coupler

The design of a compact dual directional coupler, which can be readily broadbanded using existing published data, is presented. The two coupled output transmission lines are laterally aligned on opposite sides of the main transmission line. Experimental results of a 0.3?2.0GHz 23dB coupler are presented.     

Single-mode fiber-film directional coupler

Directional coupling has been observed both from a single-mode fiber to a single mode planar polymer waveguide and vice versa. The fiber coupler was prepared by polishing. The matching of propagation constants was achieved by using a polymer film only a few hundred nanometers thick.     

Novel acoustic-surface-wave directional coupler with diverse applications

An acoustic-surface-wave directional coupler is proposed that may be used on materials having a large electromechanical coupling constant to couple two acoustic beams which are many wavelengths wide. The normal modes of the coupler are identified and used with an equivalent-circuit representation of the device to predict the length of the structure needed for complete energy transfer. The theory indicates that the device can have an intrinsic bandwidth near to 100%.     

Three-Line microstrip directional coupler with dielectric overlay

The letter illustrates that the frequency characteristics of a three-line microstrip directional coupler can be greatly improved by using the dielectric overlay. We show the method of analysis in detail. The examples of design data are shown with the graphs of frequency characteristics of the coupler     

Low-voltage vertical directional coupler switch with suppressedelectroabsorption

We have studied the performance of a vertical directional coupler in which a multiple quantum well and a bulk semiconductor material act as the cores of the two guides in two arms. The power output of the device is expected to be unaffected by the electroabsorption effect in a directional coupler based on quantum confined Stark effect even when operated very close to the excitonic absorption edge. The above principle is utilized in realizing low-voltage switching and almost equal power in bar and cross states in a multiple-quantum-well (MQW) vertical directional coupler. Our calculation for a vertical coupler composed of InGaAsP bulk and InGaAsP-InP MQWs show switching voltages comparable to that of a similar coupler composed of a more complex barrier reservoir and quantum well electron transfer (BRAQWET) structure, with a slightly lower value of power output     

High-speed pulse generation using a sinusoidally driven Ti:LiNbO3 directional coupler travelling-wave optical modulator

We report the generation of 47 ps (FWHM) optical pulses at a 5 Gbit/s repetition rate using a sinusoidally driven Ti-LiNbO3 directional coupler modulator with travelling-wave electrodes By selective DC bias of the switch, these pulses are obtained without overdriving and without velocity matching of the electrical and optical waves.     

CPW multilayer slot-coupled directional coupler

A new 3 dB CPW multilayer slot-coupled directional coupler between two CPW lines coupled through a rectangular slot etched on a common ground plane located between these lines is presented. The proposed directional coupler showed promising results, especially in terms of bandwidth (/spl sim/80%). The simulated results are compared with the measured data, and good agreement is reported.     

Slotted waveguide directional coupler characteristics

A moment method (MoM) solution for slotted waveguide directional couplers which is sufficiently accurate for predicting the couplers' characteristics is demonstrated. The slot length in the waveguide directional couplers considered is about four wavelengths and the wall thickness is about 0.27 λ. To simplify the numerical computation, the formulation assumes a uniform field across the slot aperture and utilizes Galerkin's method with the entire domain sinusoidal basis. A self-consistent method taking the finite wall thickness into account avoids an additional matrix equation, as in other MoM formulations. The final solution forms the basis for an efficient computer code applicable to dielectric-loaded slotted waveguide directional couplers. The uniform field assumption restricts the present solution to narrow slots. Numerical results verify, by comparisons with published analytical and experimental data, that this solution is valid for slot lengths as long as 4λ. A detailed discussion of the characteristics of narrow-wall and broad-wall slotted waveguide directional couplers is presented