Modem | EPFL Graph Search

A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more carrier wave signals to encode digital information, while the receiver demodulates the signal to recreate the original digital information. The goal is to produce a signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 bit/s for asynchronous dial connections, 4,800 bit/s for synchronous lease

Preparation and Decay of a Single Quantum of Vibration at Ambient Conditions

Mitchell David Anderson, Christophe Marcel Georges Galland, Nils Kipfer, Kilian Robert Seibold, Vivishek Sudhir

A single quantum of excitation of a mechanical oscillator is a textbook example of the principles of quantum physics. But mechanical oscillators, despite their pervasive presence in nature and modem technology, do not genetically exist in an excited Fock state. In the past few years, careful isolation of gigahertz-frequency nanoscale oscillators has allowed experimenters to prepare such states at millikelvin temperatures. These developments illustrate the tension between the basic predictions of quantum mechanics-which should apply to all mechanical oscillators even at ambient conditions-and the extreme conditions required to observe those predictions. We resolve the tension by creating a single Fock state of a 40-THz vibrational mode in a crystal at room temperature and atmospheric pressure. After exciting a bulk diamond with a femtosecond laser pulse and detecting a Stokes-shifted photon, the Raman-active vibrational mode is prepared in the Fock state vertical bar 1 > with 98.5% probability. The vibrational state is then mapped onto the anti-Stokes sideband of a subsequent pulse, which when subjected to a Hanbury Brown-Twiss intensity correlation measurement reveals the sub-Poisson number statistics of the vibrational mode. By controlling the delay between the two pulses, we are able to witness the decay of the vibrational Fock state over its 3.9-ps lifetime at ambient conditions. Our technique is agnostic to specific selection rules, and should thus be applicable to any Raman-active medium, opening a new general approach to the experimental study of quantum effects related to vibrational degrees of freedom in molecules and solid-state systems.

2019

All-optical flip-flop based on dynamic Brillouin gratings

Andrey Denisov, Marcelo Alfonso Soto Hernandez, Luc Thévenaz

One of the most essential building blocks in modem electronics is the flip-flop. A flip-flop operates bi-stably between two states, remaining at a given output level (high or low level) until a specific input control signal changes. For many years, photonics has attempted to build all-optical flip-flops [1-3]; however, the success of these approaches has usually been limited by the dependence of the bi-stable operation on bit-rate and optical power [1, 2]. Furthermore, in most of the reported demonstrations, the storage time is inherently short. Typically, the figure-of-merit of these devices is measured by the time-bandwidth product, which is defined as the storage time of the device times the available bandwidth. State-of-the-art values are in the order of 10-100.This work proposes a method to generate all-optical flip-flops based on dynamic Brillouin gratings (DBGs) in polarisation maintaining fibres (PMF) [4]. Contrarily to existing approaches, this method can allow extremely long storage times and arbitrarily high bandwidth response. The technique relies on generating a very long, weak DBG along a PMF. The experimental setup here used as a proof-of-concept is shown in Fig. 1(a) (see ref. 4 for details). The DBG is generated by launching two continuous-wave pumps (Pump1 and Pump2) through the opposite sides of a 1 m-long Panda PMF. Both pumps are amplified by Erbium-doped fibre amplifiers (EDFAs) up to 25 dBm and aligned to the fast axis of the PMF. An electro-optic modulator is used to shift the optical frequency of one of the pumps, so that the frequencies fulfil the condition: fPump1 = fPump2 - QB, where QB (=10.8 GHz) is the Brillouin frequency along the fast axis of the PMF. The created DBG acts as the all-optical equivalent of an integrator [4]. To read the DBG, 300 ps pulses with controlled phase are generated (see lower branch in Fig. 1(a)) and launched along the slow axis of the PMF at the probe frequency fProbe = (nfast/nslow)fPump1, where nfast and nslow are the fibre refractive indexes along fast and slow axes. The output state of the flip-flop is changed (i.e. set and reset) using pulses with opposite phases. This flip-flop response is then observed at frequency.

IEEE2017

All-optical flip-flop based on dynamic Brillouin gratings

Andrey Denisov, Marcelo Alfonso Soto Hernandez, Luc Thévenaz

IEEE2017