Solid Converter PDF 7.3 Build 1550 Portable ##VERIFIED##
Wei Spinks
LFC series are newest series of media converters. The LFC-100-SC20B is a 10/100Base-Tx to single strand single-mode fiber, simplex SC connector, T:1550/R:1310nm type B, 20Km BiDi WDM reach optical port. Media converter is un-managed but the RJ-45 copper port has auto-negotiation 10/100 and MDI/MDI-X features and DIP switch settings available for LFP function, converter-switch mode and speed and flow controls.
A BiDirectional type B media converter using Tx:1550nm/Rx:1310nm MUST be always paired with a type A media converter that has Tx:1310nm/1550nm optics for an operational link. This is required for operation over a single strand of fiber optic. Please make sure you have the complementary model required for proper fiber connectivity. For type B the counterpart media converter is LFC-10-100-SC20A.
LED indicators signal the power status of the converter, UTP port speed, UTP Link and FX port Link. Used with their compatible LFC-CH12 fiber optic chassis they can be aggregated up to 12 units in a 19" wide and only 1RU of height space only. This is the highest density attainable for unmanaged fiber media converters.
The LFC-100-SC20B Fast Ethernet converter also offers the optional wall mounting solution for individual converters named LFC-WMK.
Features
We demonstrate polarisation-preserving frequency conversion of single-photon-level light at 854 nm, resonant with a trapped-ion transition and qubit, to the 1550-nm telecom C band. A total photon in / fiber-coupled photon out efficiency of \(\sim\)30% is achieved, for a free-running photon noise rate of \(\sim\)60 Hz. This performance would enable telecom conversion of 854 nm polarisation qubits, produced in existing trapped-ion systems, with a signal-to-noise ratio greater than 1. In combination with near-future trapped-ion systems, our converter would enable the observation of entanglement between an ion and a photon that has travelled more than 100 km in optical fiber: three orders of magnitude further than the state-of-the-art.
Interfacing trapped ions with the telecom wavelengths of 1310 nm (O band) or 1550 nm (C band) is particularly appealing: these wavelengths suffer minimal transmission losses (0.32 and 0.18 dB/km, respectively, for SMF-28 Ultra fiber) through optical fibers and a broad range of established technologies and infrastructure for their manipulation and transmission exist. The telecom wavelengths are, therefore, an ideal choice for a universal standard for light-matter quantum networks, allowing similar and dissimilar quantum matter to interface over both short and long distances.
In this paper, we present experiments that demonstrate photon conversion from \(\lambda _s=\) 854 nm (\(s=\) signal) to \(\lambda _t=\) 1550 nm (\(t=\) target, Telecom C band), via difference-frequency generation (DFG) in a waveguide-integrated \(\chi ^2\) crystal, using a strong pump laser at \(\lambda _p=\) 1902 nm. The signal wavelength corresponds to the \(P_3/2\) to \(D_5/2\) dipole transition in singularly ionised atomic Ca\(^+\), which can be efficiently collected from the ion in a cavity quantum electrodynamic (CQED) setting. Our experiments use laser light, resonant with the ionic transition and attenuated to the single-photon level. We refer the reader to work studying conversion from 854 to 1310 nm [32].
The content of the paper is as follows. First, the importance of the 854-nm transition in Ca\(^+\) is briefly discussed and motivated. Section 2 presents a scheme that enables telecom conversion of one polarisation component of an 854-nm photon. Here, the limits on the efficiency and photon noise are presented. Section 3 presents a scheme that preserves the polarisation during conversion, allowing translation of a polarisation qubit from 854 to1550 nm with high fidelity. The achieved performance brings QFC experiments within reach of existing 854-nm trapped-ion photon sources.
From the perspective of achieving efficient, low-noise photon frequency conversion from a trapped-ion wavelength to telecom, the 854-nm transition in Ca\(^+\) represents an ideal choice. Transmission losses at this wavelength are low in non-linear conversion crystals and the required poling period to overcome the phase mismatch can be precisely manufactured, allowing for efficient first-order quasi phase matching and long interaction lengths. Furthermore, single-step conversion to 1550 nm requires a pump laser in the so-called long-pump-wavelength regime: the 1902-nm pump photons have lower energy than the target 1550-nm wavelength, such that spontaneous parametric down conversion (SPDC) of the pump cannot produce noise photons at 1550 nm [13]. The threshold input photon wavelength for this condition is \(\lambda>\) \(1550/2\,\mathrmnm =775\) nm (\(1310/2\,\mathrmnm =655\) nm), which can be found in very few ionic species and in each case is branching-ratio unfavored.
We perform frequency conversion by DFG using the \(\chi ^(2)\) nonlinearity in a LiNbO\(_3\) waveguide-integrated chip. Each chip is 48 mm long and contains ridge waveguides (LiNbO\(_3\) layer on LiTaO\(_3\) substrate) milled out along its length, with dimensions of approximately 11.0 \(\mu\)m by 12.1 \(\mu\)m (fabricated by NTT electronics). To achieve first-order quasi-phase matching, the guides are poled with a period of approximately 22 \(\mu\)m. While each chip has 12 individual waveguides, a single guide in any one chip is used for each experiment. The waveguides enable a continuous high spatial mode overlap between the three optical fields, are single mode for 1550 and 1902 nm, multimode for 854 nm and are anti-reflection coated for all those wavelengths on each facet (\(R\le 1\)%). The conversion process is phase-matched when all three optical fields have the same linear polarisation; the orthogonal polarisation is supported in the guide but remains unconverted.
QFC in a material with a \(\chi ^2\) nonlinearity is a three-wave mixing process in which the quantum states of light can be coherently interchanged between two frequencies \(\omega _1\) and \(\omega _2\) via the interaction with a strong (undepleted) pump field at frequency \(\omega _p\), where \(\omega _1+ \omega _p=\omega _2\). In our experiments, \(\omega _1\) and \(\omega _2\) are the frequencies of the 1550 and 854 nm photons, respectively. For QFC in a waveguide-integrated lossless material, and in the case of perfect phase matching, one can show that the efficiency of conversion for an interaction (waveguide) length L is given by [39] \(\eta = N_2/N_1 = \sin ^2(\sqrt\eta _\mathrmnorP_pL)\). Here, \(N_2\) is the number of output 1550 nm photons, \(N_1\) the number of input 854 nm photons, \(P_p\) is the pump power. The normalised efficiency \(\eta _\mathrmnor\) depends on the material nonlinear strength and the three-wave mode-overlap integrals. For a given waveguide length L, there is a pump power \(P_\mathrmmax\) that achieves complete conversion. For larger pump powers, conversion back to the initial frequency takes place.
At 200 mW, the pump photon flux in the waveguide is vast (\(2\times 10^18\) Hz) such that even extremely weak processes in the waveguide, through which pump photons are converted directly to telecom, can overwhelm the output. The key process through which this happens on propagation through the crystal is anti-Stokes Raman scattering, where pump photons receive energy from phonons in the crystal. Anti-stokes Raman spectra for similar ridge waveguides to ours are presented in [43] and show that the large spectral separation between our 1902 nm pump and 1550 nm target is far from any Raman resonance peaks. Nevertheless, significant photon noise has been observed at spectral separations well beyond that expected by theory [13], covering even the large spectral separation in our experiments.
We study the noise photons at the waveguide output for 200 mW input pump light only, using the single-photon analysis path at the waveguide output in Fig. 1. That analysis path consists of various removable filters and finally a single-mode-fiber-coupled, free-running InGaAs solid-state single photon detector (IDQuantique ID230 NIR). The detector is operated in a regime with the highest ratio of efficiency (10%, as specified) to dark counts (\(1.8\pm 0.1\) counts/s), achieved with a deadtime of 20 \(\mu\)s.
The NPR at the quasi-phase matching temperature is seen to reduce in proportion to the filtering bandwidth (Fig. 3), consistent with the noise source being broadband and white. Using our narrowest filtering bandwidth of 2 pm at 1550 nm (250 MHz bandwidth, transmission \(0.26\pm 0.01\) at 1550 nm), the NPR before detection is reduced to 4 \(\pm 2\) Hz. Note, in Section 3 we employ a few picometer filtering stage with a greatly improved transmission at 1550 nm.
Using calibrated neutral density filters, the input 854 nm light power in our setup is attenuated to a value corresponding to an average photon rate of 10 kHz (2 fW) before the input aspheric lens, to replicate a future trapped-ion source. Figure 4 presents the photon count rate of the 1550 nm detector as a function of pump power and for our 2 pm bandwidth telecom filter. At the peak conversion efficiency (again at around 200 mW pump) 136 \(\pm 3\) Hz counts are recorded, corresponding to a total detected conversion efficiency of 0.0136\(\pm 0.0004\). When removing the 0.10 efficiency of our detector this corresponds to a photon in/out conversion efficiency of \(\eta _out/in=0.136\): the probability that an incoming 854 nm photon is converted to a single-mode-fiber-coupled 1550 nm photon that has passed the filtering stage. This result is consistent with our classical light measurements, leading to an external waveguide conversion efficiency of \(0.62\pm 0.03\) when removing the filtering losses.
1550 nm noise photons produced directly by interaction of the strong pump with the waveguide. Plotted values are ten times the count rate of the single photon telecom detector, for 200 mW of pump light input into the waveguide alone (Fig. 1). The factor of ten accounts for the 10 % detector efficiency, yielding the total noise photons within the filtering bandwidth before detection. Rates are shown for three different filtering bandwidths centred at 1550 nm, as labelled, and for different temperatures of the waveguide. Filled points represent experimental data. Empty points show the count rate expected for the corresponding filtering bandwidth, when starting with the observed values for 12 nm bandwidth and assuming that the noise spectrum is white (points slightly shifted to the left for clarity). 12 nm (squares) and 15 pm (circles) filtering bandwidth values are normalised to total transmission efficiency of 2 pm bandwidth filtering stage (triangles), i. e. multiplied by factors 0.98 and 0.82, respectively, to allow for direct comparison. Solid line shows the fit by Boltzmann distribution (see the main text).
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