25 GHz polarization-insensitive electroabsorption modulators withtraveling-wave electrodes

Electroabsorption modulators with traveling-wave electrodes have been designed and fabricated using MOCVD grown InGaAsP-InGaAsP quantum wells. A modulation bandwidth of 25 GHz is achieved for a 2 μm-wide 30 μm-long device. Driving voltage of 1.20 V is achieved for an extinction ratio of 20 dB for operation at 1.55 μm     

Laser compatible waveguide electroabsorption modulator with high contrast and low operating voltage in GaAs/AlGaAs

The authors demonstrate a SQW-GRINSCH ridge-waveguide electroabsorption modulator in GaAs/Al/sub x/Ga/sub 1-x/As that has a very high contrast ratio and low operating voltage and also acts as a laser with relatively low threshold current. They achieve contrast ratios of 10 dB/100 mu m of cavity length with an operating voltage of less than -4 V. In addition, when operated as laser, the device exhibits a threshold current of 25 mA. The active layer has a capacitance of 205 pF/mm/sup 2/ which would allow the fabrication of a device with a modulation bandwidth of over 20 GHz. The laser operated at a wavelength only 2-3 nm shorter than the optimum modulation wavelength.<>     

High-speed electroabsorption modulator with strip-loaded GaInAsP planar waveguide

We describe fabrication and characterization of an electroabsorption (EA) light modulator (LM) with a strip-loaded GaInAsP planar waveguide. The EA LM's were fabricated from hydride vapor-phase-epitaxy (VPE) grown wafers. The electroabsorption, the insertion loss, the electrical properties, and the modulation characteristics were investigated for the EA LM's. The drive voltage at a 99-percent modulation depth has been noticeably reduced to 4.5 V by optimizing the thicknesses of the epitaxial layers. The total capacitance of 1.5 pF was obtained by inserting an insulating film under the wire-bonding pad and by improving the mount design. Consequently, a 3-dB bandwidth of 3.8 GHz has been achieved and a pulse modulation operation under 2 Gbit/s nonreturn-to-zero (NRZ) pseudorandom pattern has also been confirmed. Moreover, the dynamic spectra of the EA modulators were measured for the first time. A spectral broadening factor α has been determined to be 1-4 from a relative strength of the sideband to the carrier and it has been experimentally found to decrease with increasing the electric field inside the absorptive waveguide. As the other measures of merit for the EA LM's, the extinction ratio over 23 dB and the insertion loss of 10-14 dB including a coupling loss due to an end-fire method were obtained. As a whole, these results have exhibited that the EA LM is a promising external modulator which will be monolithically integrated into a gigabit per second optical source with a dynamic single-mode laser.     

25 to 300°C ultra-low-power voltage reference compatible withstandard SOI CMOS process

A new patented voltage reference is presented. The very simple architecture, which can be implemented in standard silicon-on-insulator CMOS processes, gives very low power consumption (from 1 pA at 25°C up to 50 nA at 300°C) and good voltage stability (about 200 ppm/°C) over the whole temperature range     

Two-section electroabsorption modulator with negative chirp at lowinsertion loss

A two-section electroabsorption modulator is proposed with an effective chirp parameter of -0.5 and an insertion loss of only 12.5 dB for a voltage swing of 1.2 V. These values are deduced from measured attenuation and phase characteristics for an SL InGaAsP-structure containing 15 quantum wells     

Peripheral-coupled-waveguide MQW electroabsorption modulator for near transparency and high spurious free dynamic range RF fiber-optic link

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-/spl mu/m wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V/sub /spl pi// simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of -3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB/spl middot/Hz/sup 2/3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz/sup 4/5/.     

Optimization design of an electroabsorption modulator integrated with spot-size converter

In the recent years ,the electroabsorption modulator(EAM) is attractive as anexternal modulator because ofits many features ,such as low power consumption,lowdrive voltage,small size,large bandwidth,polarization-intensity and potential for monolithic integration withother components[1-3].An optical device integrated witha spot-size converter(SSC) has been paid more attentionfor its direct couplingto an optical fiber without using amicro-lens or tapered fiber[4].EAMintegrated with anSSC(EA…     

Demonstration of negative chirp characteristics over wide wavelength range using monolithically integrated SG-DBR laser/electroabsorption modulator

For the first time negative large signal chirp characteristics from a widely-tunable laser/electroabsorption modulator transmitter are reported. This device employed an intermixed quantum well absorption region in the modulator. Large signal time resolved chirp measurements were made at wavelengths from 1542 to 1569 nm and were shown to exhibit negative characteristics at all wavelengths.     

High-temperature electrical characteristics of GaAs MESFETs(25-400°C)

The effects of elevated ambient and substrate temperatures (25°C up to 400°C) on the electrical characteristics of integrated GaAs MESFETs in a state-of-the-art commercial technology are reported. The focus is on the large- and small-signal parameters of the transistors. The existence of zero-temperature-coefficient drain currents is demonstrated analytically and experimentally for enhancement- and for depletion-mode GaAs MESFETs. The data show that, while GaAs MESFETs generally display degradation mechanisms similar to those of silicon MOSFETs with increasing temperature, they incur several additional effects, prominent among which are increased gate leakage currents, lowered Schottky-barrier height, decreased large- and small-signal (gate) input resistances, decreased sensitivity to sidegating and backgating up to approximately 200°C, and increased small-signal drain resistance     

Wide temperature (-20°C-95°C) operation of an uncooled2.5-Gb/s 1300-nm DFB laser

This letter describes a 2.5-Gb/s 1300-nm distributed feedback laser that can operate in a wide temperature range of -20°C to 95°C. We present RF and DC characteristics of the device and the statistical distribution of threshold current and slope efficiency at high temperature. Finally, we demonstrate the device performance in a 2.5-Gb/s small-form-factor module up to 85°C     

Continuous-fiber modulator with high-bandwidth coplanar strip electrodes

Operation of a continuous-fiber modulator based on coupling from a fiber side-polished beyond cut-off to a multimode planar waveguide has been demonstrated for the first time at gigahertz frequencies. The bandwidth of the modulator electrode structure was /spl sim/4 GHz while the optical insertion loss was measured at <0.5 dB. The device was used to produce mode-locked pulse trains in an erbium fiber laser at repetition rates of /spl sim/3 GHz.     

Small-chirp 40-Gbps electroabsorption modulator with novel tensile-strained asymmetric quantum-well absorption layer

A small-chirp 40-Gbps electroabsorption modulator (EAM) with a novel tensile-strained asymmetric quantum-well (QW) absorption layer has been demonstrated for the first time. The strain and the band line-up of the asymmetric QW structure were designed in order to obtain a small-chirp operation, a clear eye opening, and a high extinction ratio simultaneously. The chirp measured as /spl alpha/-parameter was reduced without any penalty of extinction ratio and eye opening. The measured /spl alpha/-parameter was smaller than 1.5 at any bias voltage from 0 to -2 V. The measured 3-dB bandwidth of a 75-/spl mu/m-long EAM exceeded 50 GHz at -1 V bias voltage. Under a 40-Gbps modulation, a clear eye opening was obtained, and the eye diagram showed no violation of the standard STM256/OC768 mask. The measured dynamic extinction ratio was over 11 dB.     

Design rules for a low-chirp integrated DFB laser with an electroabsorption modulator

Feedback from the front facet of an integrated DFB laser with an electroabsorption modulator generates additional chirp to the single modulator. The reduction of the sensitivity to that feedback is in tradeoff relation with the external differential quantum efficiency and the single-mode yield. We introduce a figure-of-merit for the feedback sensitivity. It is obtained from the modeling of the small signal frequency modulation (FM). It indicates design rules for low-chirp and high-efficiency devices.     

A wide range analog MMIC attenuator with integral 180° phaseshifter

A circuit topology is discussed for achieving a wide-range analog attenuator in MMIC form using enhancement mode FET's by combining it with a 90° phase shift network. By switching the phase shift network between a 90° phase lead high-pass structure and a 90° phase lag low-pass structure, a dual-purpose circuit is formed comprising both a variable attenuation and 180° phase shift function. The approach requires only a single control voltage for the attenuator and achieves an attenuation range of over 30 dB in L-band with less than 10° of phase imbalance over the range. In the low-loss state, the phase shifter achieves a 10° phase balance over a 250 MHz bandwidth with less than 0.3 dB of amplitude imbalance     

Single-loop ΔΣ modulator with extended dynamic range

A single-loop delta?sigma modulator with extended dynamic range is proposed. It employs an auxiliary quantiser to process the quantisation error of the main quantiser. This simple addition guarantees improved stability over a wider signal input range and also reduces the sensitivity to the front-end DAC nonlinearity. Simulation results are provided to verify the effectiveness of this structure.     

λ/4-shifted DFB laser/electroabsorption modulator integratedlight source for multigigabit transmission

High-speed, low-chirp, and low voltage driving characteristics of 1.55-μm λ/4-shifted distributed-feedback (DFB) laser/InGaAsP electroabsorption modulator integrated light sources are reported. By optimization of the composition and thickness of the modulator waveguide, the driving voltage for a 10-dB extinction ratio was reduced to 1.4-3 V, depending on the modulator length in the range of 240-125 μm. High-speed modulation up to 10-Gb/s NRZ modulation was achieved by the integrated device with a 125-μm modulator length. The linewidth enhancement factor of the integrated modulator was estimated to be 0.15-0.48     

Lossless electroabsorption modulator monolithically integrated with a semiconductor optical amplifier and a passive waveguide

We have developed a monolithic integrated device consisting of an electroabsorption modulator and a semiconductor optical amplifier (SOA) connected by a deep-ridge passive waveguide by means of butt-joint selective area growth. Lossless operation with a high extinction ratio of 32 dB and clear eye opening at 10 Gb/s are successfully achieved. We confirm that the optical injection should be from the SOA side of the device to obtain a wide error-free range of incident optical power from -20 to +10 dBm. Our device could lead to richly functional photonic integrated circuits comprising arrayed waveguide gratings (AWGs) for advanced wavelength-division-multiplexing networks, since the passive waveguide has the same structure as AWGs.     

High-power ultralow-chirp 10-Gb/s electroabsorption modulator integrated laser with ultrashort photocarrier lifetime

A high-power, ultralow-chirp electroabsorption modulator (EAM) integrated with a distributed-feedback laser diode (EML) having ultrashort lifetime of photogenerated holes in the EAM quantum-well (QW) structure is reported for the first time. A shallow QW structure having a small valence band offset to enhance the sweepout of photogenerated holes was employed as EAM absorption layer. The measured hole lifetimes were 7-11 ps, and the measured frequency chirp (/spl alpha/-parameter) was low or negative at low EAM reverse bias voltages even under high optical output power conditions. Successful 10-Gb/s 80-km normal-dispersion single-mode fiber transmission (chromatic dispersion D=1600 ps/nm) and the record average fiber optical output power (P/sub f/) of +5.3 dBm were achieved at 25/spl deg/C. In addition, semicooled operation of EML at enhanced bit rates has been demonstrated for application in small-form-factor protocol-agnostic optical transceivers. A 10.7-Gb/s 1600-ps/nm transmission was achieved at 45/spl deg/C and P/sub f/=+3.0 dBm.     

Lossless electroabsorption modulator monolithically integrated with a semiconductor optical amplifier and dual-waveguide spot-size converters

Semiconductor optical amplifier and electroabsorption modulator monolithically integrated with dual-waveguide spot-size converters at the input and output ports is demonstrated by means of selective area growth, quantum-well intermixing, and asymmetric twin waveguide technologies. At the wavelength range of 1550/spl sim/1600 nm, lossless operation with extinction ratios of 25-dB dc and 11.8-dB radio frequency and more than 10-GHz 3-dB modulation bandwidth is successfully achieved. The output beam divergence angles of the device in the horizontal and vertical directions are as small as 7.3/spl deg//spl times/10.6/spl deg/, respectively, resulting in 3.0-dB coupling loss with cleaved single-mode optical fiber.