Wavelength Detuning Research Articles

Simultaneous multichannel carrier-suppressed return-to-zero to non-return-to-zero format conversion using a fiber Bragg grating.

A novel multichannel carrier-suppressed return-to-zero (CSRZ) to non-return-to-zero (NRZ) format conversion scheme based on a single custom-designed fiber Bragg grating (FBG) with comb spectra is proposed. The spectral response of each channel is designed according to the algebraic difference between the CSRZ and NRZ spectra outlines. The tailored group delays are introduced to minimize the maximum refractive index modulation. Numerical results show that four-channel 200-GHz-spaced CSRZ signals at 40 Gbits/s can be converted into NRZ signals with high Q-factor and wide-range robustness. It is shown that our proposed FBG is robust to deviations of bandwidth and central wavelength detuning. Another important merit of this scheme is that the pattern effects are efficiently reduced owing to the well-designed spectra response.

Control over hysteresis curves and thresholds of optical bistability in different semiconductor double quantum wells**Project supported by the Lithuanian Research Council (Grant No. VP1-3.1-ŠM-01-V-03-001).

The effects of optical field on the phenomenon of optical bistability (OB) are investigated in a K-type semiconductor double quantum well (SDQW) under various parametric conditions. It is shown that the OB threshold can be manipulated by increasing the intensity of coupling field. The dependence of the shift of OB hysteresis curve on probe wavelength detuning is then explored. In order to demonstrate controllability of the OB in this SDQW, we compare the OB features of three different configurations which could arise in this SDQW scheme, i.e., K-type, Y-type, and inverted Y-type systems. The controllability of this semiconductor nanostructure medium makes the presented OB scheme more valuable for applications in all-optical switches, information storage, and logic circuits of all optical information processing.

Plasmon-Induced Transparency in Coupled Graphene Gratings

Wavelength-tunable plasmon-induced transparency (PIT) in coupled graphene gratings was theoretically investigated in mid-infrared region. Both direct and phase-coupled PITs were considered in the proposed structure. In both schemes, a proper wavelength detuning between two graphene gratings was required for PIT observations. The effect of graphene quality on the PIT was also investigated. Graphene quality of μ = 50,000 cm2/Vs was sufficient for achieving a distinct PIT peak while a weak PIT was observed for μ = 10,000 cm2/Vs. PIT peak amplitude modulation and tunability of operating wavelength were demonstrated by adjusting the Fermi level of graphene. Compared with previously studied graphene-based PITs, the proposed PIT based on the coupled graphene gratings is much easier to design and fabricate.

12 THz flat gain fiber optical parametric amplifiers with dispersion varying fibers.

We report a fiber-optic parametric amplifier with ultra-broad and flat gain band by using a longitudinally tailored optical fiber. The parametric amplifier has been designed from realistic numerical simulations combined with an inverse algorithm to obtain a flat and wide gain band through fiber dispersion management. We experimentally report ~12 THz gain bandwidth on the Stokes side of the pump with a gain ripple as low as 7 dB and a mean gain up to ~60 dB. Experimental results show good agreement with numerical predictions for different pump powers and wavelength detuning.

Plasmon-induced transparency effect in a single circular split-ring core ring resonator side-coupled to a metal-isolator-metal waveguide

We theoretically and numerically investigated the plasmon-induced transparency (PIT) effect in a single circular split-ring core ring resonator (CSRCRR) side coupled to a metal–isolator–metal waveguide, in which we can realize a single PIT effect window. The transmission line theory and the coupled mode theory are used. The results (transmission peak varies from 10% to 75%) show that the PIT window results from the destructive interference between the resonance modes in the CSRCRR. Then, the limit of wavelength detuning of the two modes in CSRCRR is studied. This work provides a new structure to realize the PIT effect and shows a new way to judge whether the phenomenon is the real PIT effect or not.

Circular polarization switching and bistability in an optically injected 1300 nm spin-vertical cavity surface emitting laser

We report the experimental observation of circular polarization switching (PS) and polarization bistability (PB) in a 1300 nm dilute nitride spin-vertical cavity surface emitting laser (VCSEL). We demonstrate that the circularly polarized optical signal at 1300 nm can gradually or abruptly switch the polarization ellipticity of the spin-VCSEL from right-to-left circular polarization and vice versa. Moreover, different forms of PS and PB between right- and left-circular polarizations are observed by controlling the injection strength and the initial wavelength detuning. These results obtained at the telecom wavelength of 1300 nm open the door for novel uses of spin-VCSELs in polarization sensitive applications in future optical systems.

A quintuple quantum dot system for electrical and optical control of multi/bistability in a telecommunication window

We propose a model for a quintuple coupled quantum dot system based on a GaAs/AlGaAs heterostructure. Then, we analyze the optical bistability (OB) and optical multistability (OM) behaviours and transition between the regimes at a wavelength of We take the benefit of consecutive and parallel interdot tunnelling and an incoherent pumping field for electrical and even optical control of the processes. It is shown that OB, OM and transition between them can be accomplished and controlled by adjusting the rate of the inter-dot tunnellings (electrical bias), probe wavelength detuning and rate of the optical incoherent pumping field. By proper choice of the controlling parameters, the bistable hysteresis loop becomes narrower, which makes it easier for the cavity field to reach saturation. We interpret the OB and OM behaviours by discussing the absorption of the active medium. We also investigate switching time between the two stable states when the output field jumps from a lower branch to an upper branch. Such a controllable OB/OM and transition between them in multiple QD molecules at a wavelength of 1.550 μm, may provide some new possibilities for technological applications in optoelectronics, solid-state quantum information science and systems dealing with signal processing.

Anomalous lasing of high-speed 850 nm InGaAlAs oxide-confined vertical-cavity surface-emitting lasers with a large negative gain-to-cavity wavelength detuning

The impact of a large negative quantum well gain-to-cavity etalon wavelength detuning on the static and dynamic characteristics of 850 nm InGaAlAs high-speed oxide-confined vertical-cavity surface-emitting lasers (VCSELs) was investigated. Three distinct lasing regimes were revealed in large square aperture (≥7 μm per side) devices with large detuning including: (1) an anomalous lasing via higher order Hermite–Gaussian modes at low forward bias current; (2) lasing via the lowest order Hermite–Gaussian modes at high bias current; and (3) simultaneous lasing via both types of transverse modes at intermediate bias currents. In contrast to conventional multimode VCSELs a two-resonance modulation response was observed for the case of co-lasing via multiple transverse modes with high spectral separation. The reduction in the oxide aperture area resulted in classical lasing via the lowest order modes with a conventional single-resonance frequency response.

Short-pulse controlled optical switch using external cavity based single mode Fabry-Pérot laser diode

We propose and demonstrate a novel scheme for short pulse controlled all-optical switch using external cavity based single mode Fabry- Pérot laser diode (SMFP-LD). The proposed scheme consists of control unit and switching unit as two essential blocks. The basic principle of the proposed scheme is the optical bistability property of SMFP-LD for the control unit and the suppression of the dominant beam of SMFP-LD with injection locking for the switching unit. We also present the analysis of hysteresis width and rising/falling time with change in wavelength detuning which helps to find the optimum wavelength detuning value and power of light beams at different stages of the proposed scheme that gives wide input dynamic power range, high ON/OFF contrast ratio, and low rising/falling time. Input data of 10 Gb/s Non Return to Zero (NRZ) signal is switched at output ports depending upon the control signal generated by the control unit, which comprises of optical SR latch. Output waveforms, clear eye diagrams with extinction ratio of about 11 dB, rising/falling time of about 30 ps and 40 ps, and bit error rate (BER) are measured to validate proposed scheme. No noise floor is observed at output ports up to BER of 10-(12) and the maximum power penalty recorded is about 1.7 dB at a BER of 10-(9) which shows good performance of the proposed short pulse controlled optical switch using SMFP-LDs.

Analysis of Hysteresis Width on Optical Bistability for the Realization of Optical SR Flip-Flop Using SMFP-LDs With Simultaneous Inverted and Non-Inverted Outputs

The width of hysteresis in optical bistability plays an important role on latching operation. The injected input optical power and wavelength detuning in single mode Fabry-Perot laser diode (SMFP-LD) are two parameters that can impact the width of hysteresis in bistability of dominant mode and injected mode. In this paper, we analyze the effect of wavelength detuning on width of the hysteresis loop, the dynamic power range for optical bistability, and the rising-falling time of output waveform. With this analysis, optical Set Reset flip-flop with simultaneous inverted and non-inverted output at the data rate of 8.5 Gb/s are obtained using SMFP-LDs. The principle is based on the optical bistability phenomena during injection-locking of the Fabry-Perot laser diode. The set and reset pulses are maintained in low power of about -14 and -6 dBm for the power effective configuration. The contrast ratios of more than 20 dB with simultaneous non-inverted and inverted output Q and Q are observed. Clear output spectrum domain results, waveforms, eye diagram with extinction ratio of more than 12 dB, a rising/falling time of about 40 ps, and bit error rate (BER) measurement without noise floor up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> are observed. The maximum power penalty is about 1.8 dB at BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> .

Single SOA based ultrafast all-optical wavelength conversion for PolSK signal

A novel ultrafast tunable all-optical wavelength conversion for polarization-shift-keying (PolSK) signal based on dual-pump four-wave mixing (FWM), including parallel dual-pump FWM and orthogonal dual-pump FWM, in a single semiconductor optical amplifier (SOA) is proposed. A comprehensive broad-band dynamic model of the all-optical wavelength converter based on parallel dual-pump FWM and orthogonal dual-pump FWM in SOA is developed, for the first time to our knowledge. By numerical simulation, the proposed all-optical wavelength conversion is realized at 40 Gbit/s. The effects of the powers of input waves and wavelength detuning on the conversion efficiency of the wavelength converter are theoretically investigated in detail. The results indicate that, due to using the PolSK modulation format, this scheme is free of pattern effect. In addition, a wide tuning range can be obtained. The proposed all-optical wavelength conversion for PolSK signal is robust and potential for applications in future optical networks in terms of simple implementation and high speed operation.

Widely Tunable Optical Decision Circuit Using a Monolithically Integrated SOA-SGDBR Laser

A widely tunable optical decision scheme using a monolithically integrated semiconductor optical amplifier-sampled-grating distributed Bragg reflector laser diode is proposed. Wavelength tunable optical decision is realized for both the cases of input wavelength detuning and output wavelength detuning. Within an input wavelength detuning range of 28 nm, or within an output wavelength detuning range of 24 nm, a maximum ON/OFF static contrast ratio of 42 dB over a 5-dB input power change is obtained. Dynamic performance up to 10 Gb/s is also demonstrated though numerical simulation using this scheme.

Characterization of Optomechanical RF frequency Mixing/Down-Conversion and its Application in Photonic RF Receivers

We have characterized the process of radio-frequency (RF) frequency mixing and signal down-conversion in radiation pressure driven optomechanical RF oscillators. We have studied the dependence of the optomechanical mixing process on RF frequency, optical pump power and wavelength detuning and verified the existence of a linear regime where down-converted power is proportional to the RF input power. These outcomes show that optomechanical oscillator (OMO) has the potential to be used as frequency down-converter in RF over fiber links and photonic RF receivers. We have verified the fidelity of the optomechanical down-conversion process and demonstrated the first optomechanical voice down-conversion from an RF carrier.

Design and Fabrication of Wide Wavelength Range 25.8-Gb/S, 1.3-μM, Push-Pull-Driven DMLs

We design and fabricate wide wavelength range directly modulated lasers (DMLs) on the same InP wafer to realize a large-capacity monolithically integrated light source array up to 1 Tb/s. We demonstrate a 25.8-Gb/s push-pull operation over a 30-nm wavelength range, which is conventionally about 14 nm for 100 GbE applications. To extend the operating wavelength range, we design the wavelength dependence of the differential gain (∂G/∂n) for an InGaAlAs multiple quantum well structure, and realize high frequency relaxation oscillation resulting from the high differential gain over a wide range. Next, we also design the wavelength detuning (Δλ) under an operating injection current condition by taking account of the thermal effect of the chip, because Δλ determines ∂G/∂n, and the threshold current of the laser diode (LD). In addition, to achieve a 25.8-Gb/s push-pull operation, we fabricate a ridge waveguide structure buried in benzocyclobutene (BCB) with a low parasitic capacitance, and electrically isolate the DML from the neighboring chip by etching off n-InP. By using this design and structure, we achieve a 3-dB-down frequency bandwidth of over 20 GHz from 1290 to 1320 nm. We also achieve a mean output power of 8.0 dBm, and a dynamic extinction ratio of 5 dB. We measure the 25.8-Gb/s transmission characteristics, and obtain clear eye openings for a back-to-back configuration. We also measure the bit-error-rate performance, and obtain error-free operation for a 30-nm operating wavelength range.

Excitation transfer between optically injected microdisk lasers

Recently, we have theoretically demonstrated that optically injected microdisk lasers can be tuned in a class I excitable regime, where they are sensitive to both inhibitory and excitatory external input pulses. In this paper, we propose, using simulations, a topology that allows the disks to react on excitations from other disks. Phase tuning of the intermediate connections allows to control the disk response. Additionally, we investigate the sensitivity of the disk circuit to deviations in driving current and locking signal wavelength detuning. Using state-of-the-art fabrication techniques for microdisk laser, the standard deviation of the lasing wavelength is still about one order of magnitude too large. Therefore, compensation techniques, such as wavelength tuning by heating, are necessary.

Thermo-optomechanical oscillations in high-Q ZBLAN microspheres

We report stable thermo-optomechanical oscillations in high-Q-spherical ZBLAN microcavities. The oscillations are manifested as a complex combination of fast and slow oscillation periods. This behavior appears to be a consequence of the interplay between the negative thermo-optic effect, thermal expansion, and the Kerr effect. We have characterized the oscillatory behavior and measured the corresponding frequencies as a function of input power, wavelength detuning, and loaded optical quality factor. Our analysis shows that, as a gas sensor in the mid-IR spectral region, this thermo-optomechanical oscillator is two orders of magnitude more sensitive than previously demonstrated hybrid microtoroidal oscillators operating in the near-IR spectral region.

Design Analysis and Performance Optimization of a Lyot Filter for Semiconductor Optical Amplifier Pattern Effect Suppression

In this paper, we analyze in detail, based on numerical modeling, the use of a Lyot filter to suppress the semiconductor optical amplifier (SOA) pattern effect. By formulating a robust design strategy, which is based on defining appropriate figures of merit and making the necessary tradeoffs between them, the filter performance can be optimized in terms of the wavelength spacing and detuning of its spectral response. The results obtained from this design procedure agree with experiment and enable us to accurately quantify to what degree the Lyot filter can resolve the SOA pattern effect problem.

Modeling of Seeded Reflective Modulators for DWDM Systems

We propose a theoretical model of reflective modulators for a seeded dense wavelength-division multiplexing (DWDM) system based on amplified spontaneous emission light. A travelling-wave amplifier model is modified to take into account the finite front-facet reflectivity. The net gain and phase shift are updated at every round trip of the cavity to have complex gain for the injected field. With the proposed model, we calculate side-mode suppression ratio, gain, relative intensity noise suppression as a function of injection power, and wavelength detuning for antireflection-coated Fabry-Perot laser diodes. We also investigate the performance of the seeded DWDM system by using the model. The simulation results match well with the experimental results.

A power and wavelength detuning-dependent hysteresis loop in a single mode Fabry—Pérot laser diode

In this paper, we observe experimentally the optical bistability induced by the side-mode injection power and wavelength detuning in a single mode Fabry—Pérot laser diode (SMFP-LD). Results show that the bistability characteristics of the dominant and injected modes are strongly dependent on the injected input optical power and wavelength detuning in an SMFP-LD. We observe three types of hysteresis loops: counterclockwise, clockwise, and butterfly hysteresis with various loop widths. In the case of a bistability loop caused by injection power, the transition from counterclockwise to clockwise in the hysteresis direction with the wavelength detuning from 0.028 nm to 0.112 nm is observed in a way of butterfly hysteresis for the dominant mode by increasing the wavelength detuning. The width of hysteresis loop, induced by wavelength detuning is also changed while the injection power is enhanced from −7 dBm to −5 dBm.

Optical bistability in side-mode injection locked dual-mode Fabry-Pérot laser diode

In this paper, optical bistability characteristics are demonstrated experimentally based on a dual-mode laser system comprising a multi-mode Fabry-Pérot laser diode (MMFP-LD) and a built-in feedback cavity formed by a fiber facet. The results show that two lasing modes with frequency separation of ∼0.58 THz and comparable peak powers can be achieved by judicious adjustment of the bias current and the operating temperature of the laser chip, which has a peak fluctuation of less than ∼1 dBm over a measurement period of one hour. A combination of appropriate external injection power and wavelength detuning can result in remarkable optical bistability in two oscillation modes, in which the resulting contrast ratio between the unlocked and locked states can be up to 30 dB, and the corresponding hysteresis loop width can be changed by controlling the side-mode injection power and the wavelength detuning.