Multiple Quantum-well Electroabsorption Modulator Research Articles

Ultra-flat broadband microwave frequency comb generation based on optical frequency comb with a multiple-quantum-well electro-absorption modulator in critical state

In this paper, we proposed a novel ultra-flat broadband microwave frequency comb (MFC) generation based on optical frequency comb (OFC) with a multiple-quantum-well electro-absorption modulator (MQW-EAM) in critical state. The scheme is simple and easy to adjust. The performance of the MFC generation scheme is investigated using software Optisystem. The results show that the comb spacing of MFC can be adjusted from 5 to 20 GHz by changing RF signal’s frequency and the MFC is almost independent on the linewidth of the tunable laser diode. The performance of the MFC can be improved by reasonably increasing the voltage of the RF, the small-signal gain of the Erbium-doped fiber amplifier (EDFA) and the responsivity of the photodetector. The MFC generated by this scheme has 300 GHz effective bandwidth with 15 comb lines, whose power variation is 0.02 dB, when the components’ parameters in the Optisystem are set as follows: the power of tunable laser diode (TLD) is 0 dBm, the wavelength is 1552.52 nm, and linewidth is 1 MHz; RF signal’s frequency is 20 GHz and the voltage is 10 V; the reverse bias voltage of MQW-EAM is 6.92 V; the small-signal gain of the EDFA is 40 dB; the responsivity of the photodetector (PD) is 1 A/W.

μ‐EXAFS, μ‐XRF, and μ‐PL Characterization of a Multi‐Quantum‐Well Electroabsorption Modulated Laser Realized via Selective Area Growth

In the past few years, strong efforts have been devoted to improving the frequency of optical-fiber communications. In particular, the use of a special kind of integrated optoelectronic device called an electroabsorption modulated laser (EML) allows communication at 10 Gb s(-1) or higher over long propagation spans (up to 80 km). Such devices are realized using the selective area growth (SAG) technique and are based on a multiple quantum well (MQW) distributed-feedback laser (DFB) monolithically integrated with a MQW electroabsorption modulator (EAM). Since the variation in the chemical composition between these two structures takes place on the micrometer scale, in order to study the spatial variation of the relevant parameters of the MQW EML structures, the X-ray microbeam available at the ESRF ID22 beamline is used. The effectiveness of the SAG technique in modulating the chemical composition of the quaternary alloy is proven by a micrometer-resolved X-ray fluorescence (μ-XRF) map. Here, reported micrometer-resolved extended X-ray absorption fine structure (μ-EXAFS) spectra represent the state of the art of μ-EXAFS achievable at third-generation synchrotron radiation sources. The results are in qualitative agreement with X-ray diffraction (XRD) and micrometer-resolved photoluminescence (μ-PL) data, but a technical improvement is still crucial in order to make μ-EXAFS really quantitative on such complex heterostructures.

Fiber-Optic 60-GHz Wireless Downlink Using Cross-Absorption Modulation in an EAM

We demonstrate the 60-GHz radio-over-fiber downlink adopting the fiber-optic upconversion process. The cross-absorption modulation (XAM) in the multiple-quantum-well electroabsorption modulator (MQW-EAM) is incorporated for the fiber-optic upconversion. Error-free transmission of the 1.25-Gb/s and 622.08-Mb/s pseudorandom bit sequence data is achieved without critical power penalties after the fiber transmission up to 34 km followed by 1-m wireless transmission between the base station and the customer unit. The system performance is dependent on the bias voltage asserted to the MQW-EAM due to the bias-dependent modulation characteristics of XAM and absorption changes. The optimum performance is obtained at the bias of -0.8 V.

Measurement-based model for MQW electroabsorption modulators

A model for a multiple-quantum-well (MQW) electroabsorption modulator is developed based on measurements of the escape time of photogenerated carriers, the dependence of the fiber-to-fiber loss on the applied voltage, the dependence of the /spl alpha/-parameter of the modulated signal on the applied voltage, and the intensity-modulation (IM) frequency response. The accuracy and computational efficiency of the model in describing the intensity- and phase-modulation properties of an optical signal make it suitable for computer simulations aimed at system design and performance evaluation.

Monolithic integration of an InGaAsP–InP strained DFB laser and an electroabsorption modulator by ultra-low-pressure selective-area-growth MOCVD

The design and basic characteristics of a strained InGaAsP–InP multiple-quantum-well (MQW) DFB laser monolithically integrated with an electroabsorption modulator (EAM) by ultra-low-pressure (22 mbar) selective-area-growth (SAG) MOCVD are presented. A fundamental study of the controllability and the applicability of band-gap energy by using the SAG method is performed. A large band-gap photoluminescence wavelength shift of 88 nm was obtained with a small mask width variation (0–30 µm). The technique is then applied to fabricate a high performance strained MQW EAM integrated with a DFB laser. The threshold current of 26 mA at CW operation of the device with DFB laser length of 300 µm and EAM length of 150 µm has been realized at a modulator bias of 0 V. The devices also exhibit 15 dB on/off ratio at an applied bias voltage of 5 V.

New Design of InGaAs–InGaAlAs MQW Electroabsorption Modulator for High-Speed All-Optical Wavelength Conversion

We have optimized the structure of InGaAlAs multiple quantum-well electroabsorption modulators for all-optical signal processing. As wavelength conversion is a key function for all-optical telecommunication network, we have based our optimization upon the main parameters of this function, namely, polarization insensitivity, exciton saturation, and photogenerated carrier sweep-out time. Four samples have been studied with different well tensile strain and barrier height. We find low polarization dependence over a range of applied bias. Less than 10-ps absorption-saturation recovery time at lower biases and smaller saturation power than in the literature are reported.

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-μm 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 xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> 5/.

A cat's eye multiple quantum-well modulating retro-reflector

A new kind of modulating retro-reflector using cat's eye optics and a multiple quantum-well electro-absorption modulator array is described. The device exhibits retro-reflection over a 30/spl deg/ field of view and can support data rates of up to 50 Mb/s using 1-mm pixels. The use of the device in free-space optical communication is discussed.

Heterodyne technique for measuring the amplitude and phase transfer functions of an optical modulator

We propose a technique based on heterodyne detection for accurately and simultaneously measuring the amplitude and phase transfer functions of an optical modulator. The technique is used to characterize an InGaAsP multiple quantum-well electroabsorption modulator. From the measurements we derive the small-signal /spl alpha/-parameter and the time-dependent chirp for different operation conditions.

Absorption Anisotropy for Lattice Matched GaAs/AlGaAs Multiple Quantum Well Structures under External Anisotropic Biaxial Strain: Compression along [110] and Tension along [1̄10

We report theoretical studies on the optical absorption anisotropy for excitonic transitions in lattice-matched GaAs/AlGaAs multiple quantum well (MQW) structures under simultaneous compression and tension applied along the [110] and [1̄10] directions of the MQW, respectively. The analyses are based on a model that includes both the 4×4 k·p Hamiltonian and the strain Hamiltonian. The wave functions, found by solving the eigenvalue equations, are used to calculate the dipole matrix elements for excitonic transitions and evaluate the anisotropic absorption properties. The effect of variation of parameters such as well width and barrier height on the performance of the strained GaAs/AlGaAs MQW electroabsorption modulators is discussed.

A Novel Linearization Method of Multiple Quantum Well (MQW) Electroabsorption Analog Modulator

A linearization method for a multiple quantum well (MQW) electroabsorption analog modulator is studied. We analyze the nonlinear characteristics of the light-voltage (L-V) transfer curve in a MQW electroabsorption modulator and estimate its intermodulation distortion (IMD). We propose a novel linearization method, the integration of twin MQW modulators with optical 3 dB couplers. This method can reduce IMD2 and IMD3 simultaneously by only adjusting the modulation depth and the bias voltage of each modulator. Results of simulations show that the method can suppress IMD2 and IMD3 to below -65 dBc at a modulation depth of 10% without any serious loss of optical signal power or increase in chirp.

Low-drive-voltage MQW electroabsorption modulator for optical short-pulse generation

This paper reports on InGaAsP-InGaAsP tensile strained MQW electroabsorption (EA) modulators with a high modulation efficiency of 35 GHz/V that generate optical short pulses. We studied and optimized the multiple-quantum-well (MQW) structural parameters, barrier height, and well number, thickness, and strain in the absorption layer to ensure high attenuation efficiency and generate low duty cycle pulses. Low TE/TM polarization sensitivity was obtained by controlling strain. Stable, nearly transform-limited optical pulse trains with a narrow pulsewidth of 3.6 ps are generated by applying a 20-GHz sinusoidal modulation voltage (6 V/sub pp/) to the EA modulator. This achieves a very small pulse duty cycle of 7.2%.

NRZ operation at 40 Gb/s of a compact module containing an MQW electroabsorption modulator integrated with a DFB laser

NRZ operation at 40 Gb/s has been successfully performed using a very compact module of a multiple-quantum-well (MQW) electroabsorption modulator integrated with a distributed-feedback (DFB) laser. While the DFB laser is injected with a constant current, the integrated MQW electroabsorption modulator is driven with a 10-Gb/s electrical NRZ signal. A clearly opened eye diagram has been observed in the modulated light from the modulator. And a receiver sensitivity of -27.2 dBm at 10/sup -9/ has been experimentally confirmed in the bit-error-rate (BER) performance.

Very high-speed light-source module up to 40 Gb/s containing an MQW electroabsorption modulator integrated with a DFB laser

A very high-speed integrated light source up to 40 Gb/s has been developed. The InGaAsP MQW integrated light source consists of an multiple-quantum-well (MQW) electroabsorption (EA) modulator and a distributed-feedback (DFB) laser. After optimizing the structure of the integrated modulator, the device is packaged in a compact module with a single-mode fiber (SMF). While the DFB laser is injected with a constant current, the integrated MQW electroabsorption modulator is driven with a 40-Gb/s electrical NRZ signal. A clearly-open eye diagram is observed in the modulated light from the modulator. Further, a receiver sensitivity of -27.2 dBm at 10/sup -9/ is experimentally confirmed in bit-error-rate (BER) performance. Highly resolved optical short pulse is also generated at a repetition rate of 40 GHz using the new light-source module.

Efficient harmonic generation using an electroabsorption modulator

A multiple quantum-well electroabsorption modulator has been assessed as a harmonic generator of millimeter-wave signals for radio-over-fiber systems. It is shown experimentally that the steep nonlinear absorption characteristics of electroabsorption modulators lead to efficient generation of high order harmonics when driven by a sinusoidal voltage. Photocurrent harmonic power levels generated using electroabsorption and Mach-Zehnder modulators are compared with theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optimizing driving conditions of a MQW EA modulator for soliton generation

A detailed analysis of the pulses generated with a multiple quantum well (MQW) electroabsorption (EA) modulator used as a soliton source is performed. The pulse temporal and spectral shape are simulated and a good agreement is obtained with the experimental results. An irregular holed spectrum shape is observed under certain operating conditions and its existence is attributed to parasitic phase modulation. This type of spectrum could be observed even for pulses having a time bandwidth /spl tau//spl Delta//spl nu/ product below 0.4 which makes them usually considered as nearly transform limited. However it is not the case. The influence of the pulse spectral shape on transmission performances is investigated by means of a realistic simulation of soliton pulse propagation at 10 Gb/s. It is shown that for 9000 km propagation distance and for pulses presenting this irregular spectral shape a signal degradation occurs as the timing jitter is above 10 ps and the quality factor Q is below 2, which results in an increase of the transmission bit error rate. In order to avoid the generation of this kind of pulses when operating a MQW modulator as a soliton source, a mapping is realized giving the adequate voltages to apply to the diode for acceptable soliton generation.

On the transmission performances and the chirp parameter of a multiple-quantum-well electroabsorption modulator

The chirp parameter of a multiple-quantum-well (MQW) electroabsorption modulator was measured with accuracy for several operating wavelengths in the 1.5 /spl mu/m window. It varied strongly with applied bias. Effective chirp parameter, defined as the ratio of phase change to transmission change between modulator on and off states, is about zero, or even negative. However, experimental transmission length on standard fiber at 10 Gb/s NRZ is much smaller than what is expected for such a low chirp parameter. It is demonstrated that the effective chirp parameter should not be computed from changes between on and off states, but from the average of the chirp parameter values in a 3 dB region of the most transparent states of the modulator. This simple rule allows us to predict transmission performances based on measurements of the chirp parameter, and can be used to optimize optical components without actually experimenting on a transmission system. The effective chirp parameter of the MQW electroabsorption modulator is found positive. This should be intrinsic to red-shift electroabsorption effects, such as the quantum confined Stark effect. >

High-extinction-ratio MQW electroabsorption-modulator integrated DFB laser fabricated by in-plane bandgap energy control technique

The local bandgap energy of an InGaAs/InGaAsP multiple quantum well (MQW) structure was precisely adjusted by in-plane Eg control in one-step selective area metalorganic chemical vapor deposition (MOCVD) growth. The technique was then applied to an MQW electroabsorption-modulator integrated distributed feedback (DFB) laser. Experimental results showed superior device characteristics, such as a high extinction ratio of 25 dB and low threshold current of 15 mA. >