Colorless monolithically integrated 120° downconverter

Abstract

We numerically demonstrate colorless reception of dense wavelength division multiplexed channels in the C-band for high-order QAM (16-64 QAM) signals on a 120° monolithically integrated downconverter, based on a 2x3 MMI with calibrated analog IQ recovery. It is shown that the proposed calibrated 120° downconverter can increase up to 80 the number of coincident channels in an efficient way, exhibiting good signal dynamic range and high fabrication yield. As this downconverter makes use of the minimum number of power outputs required for perfect recovery of IQ signals, it becomes an interesting alternative to conventional 90° based downconverters.

Colorless devices and reception techniques for polarization multiplexed communications

“…colorless operation), its performance is limited by an additive interfering baseband signal, arising from the self-beating of the adjacent channels [8], [9]. This interference is proportional to the power of the received signal (thereby limiting dynamic range), but is suppressed if the 90º hybrids exhibit a high common mode rejection ratio (CMRR>20dB).…”

Calibrated Monolithically Integrated 90 <named-content content-type="math" xlink:type="simple"> <inline-formula> <tex-math notation="TeX">$^{\circ} $</tex-math></inline-formula></named-content> Downconverter for Colorless Operation in the C+L Band

“…Therefore, a balanced 90 hybrid coherent receiver would require for colorless operation a high CMRR in the operation band and a high LO-to-signal power ratio. However, a wideband high CMRR demands stringent fabrication tolerance requirements (resulting in high cost and low fabrication yield) to reduce hardware imbalances [8]- [10]. Recently, to make the most of the available dynamic range of the 90 coherent receiver, it has been proposed to integrate in its signal path a monitor photodiode and a variable optical attenuator (VOA) to control and optimize input signal power level [4], [11].…”

“…The DSP (digital signal processing) block remains the same than in conventional downconverters with balanced detection. It is worth to note that coherent reception of QPSK/QAM modulated channels in a five-port phase diversity receiver from a calibrated analog circuit was reported in [10], [12] at optical frequencies and in [13] and [14] at microwaves frequencies. However, here we show for the first time that the same concept can also be applied to significantly increase the colorless operational bandwidth of an integrated six-port optical downconverter.…”

Polarization-beam-splitter-less integrated dual-polarization coherent receiver

“…To assure a realistic scenario, the ideal 90°hybrids are substituted by high-performance 2 × 4 MMI couplers designed using conventional InP/InGaAsP rib waveguides. These hybrids were already used in some of our previous work to characterize the sensitivity of a single-polarization coherent receiver to fabrication errors [11] and to implement a PBS-based dual-polarization coherent receiver with active tuning [8]. We will consider two different situations: (i) the nominal device, which is an optimum design that exhibits a maximum amplitude imbalance MAI 0.6 dB and a maximum phase imbalance MPI 0.4°within the C-band (1530-1570 nm); and (ii) a detuned design, which includes moderate fabrication errors, where the performance is degraded to a MAI 2.7 dB and a MPI 2°.…”

“…For each simulation case, the ASE noise level at the receiver input was adjusted to assure the optical signal-to-noise ratio (OSNR) required for a bit error rate BER 10 −3 . A more detailed description of the 90°hybrids and the simulation scenario can be found in [11]. In order to obtain a quantitative measurement of the performance degradation of the proposed approach when condition (4) is not perfectly fulfilled, we define the differential phase shift error ϵ ϕ ϕ Dist − 180°, and the receiver penalty PdB OSNR PBSless − OSNR conv: .…”