Single Electro-optic Modulator Research Articles

Spatially resolved dual-comb sensing with a single electro-optic modulator

We demonstrate spatially resolved sensing by a novel approach that combines an infrared camera and a simplified dual-comb illumination arrangement. Specifically, our scheme employs a continuous-wave laser and only one electro-optic modulator to simultaneously create a pair of mutually coherent optical frequency combs, each one with a slightly different line spacing. The system operates by measuring this dual-comb spectrum from a sequence of acquired images, in order to recover the spectral response of every spatial point of a sample. Thanks to its excellent stability, our approach ensures integration times well in excess of 10 s. The result is an utterly simple multi-spectral imager, capable of resolving up to 127 independent comb lines (spectral channels) across 16 k individual spatial positions, with a digitization sampling rate close to 1 kHz. As a proof of concept, we measure spatial variations of the refractive index of a low-reflectivity etalon undergoing a heating process. This sensing unit has a great potential to work as a field-deployable system for the determination of the spatial distribution of external perturbations such as temperature or strain. We comprehensively discuss the current advantages and limitations of our sensing approach, as well as its further developments.

1064/1319 nm Dual-Wavelength Alternating Electro-Optic Q-Switched Laser Based on the Common Q-Switching Bias Voltage

A dual-wavelength alternating electro-optic (EO) Q-switched laser operating at 1064 and 1319 nm is designed, which takes the structure of double the gain crystals and a single EO modulator with the common Q-switching bias voltage (CQBV). The output characteristics of alternating dual-wavelength pulse lasers are studied via simulations and experiments. The results show that the energy ratio of the two lasing wavelengths can be controlled by changing the CQBV. This is because the CQBV affects the loss of two resonators, 1064 and 1319 nm, at the same time. The gain–loss relationship in the dual-wavelength laser resonators can be controlled by changing the CQBV in a certain range.

Time-resolved dual-comb spectroscopy with a single electro-optic modulator.

Time-resolved near-infrared absorption spectroscopy of single non-repeatable transient events is performed at high spectral resolution with a dual-comb interferometer using a continuous-wave laser followed by a single electro-optic amplitude modulator. By sharing high-speed electrical/optical components, our spectrometer greatly simplifies the implementation of dual-comb spectroscopy and offers a high mutual coherence time, measured up to 50 s, without any active stabilization system and/or data processing. The time resolution is as short as 100 µs in our experimental demonstration. For a span of 36 GHz, the mean signal-to-noise ratio of 80, at 100-MHz spectral resolution and 100-µs measurement time, enables precise determination of the parameters of rovibrational lines, including intensity or concentration.

Optical pulse generation by polarisation modulation and fibre dispersion

Optical pulse generation based on polarisation modulation and fibre dispersion is proposed that has the ability of generating multiform optical pulse trains by applying a single electro-optic modulator and a low frequency driving signal. In the experiment, using a 10 GHz RF source, the generation of a 20 GHz time and polarisation interleaved optical pulse train, a 10 GHz single-polarisation pulse train and a 20 GHz single-polarisation pulse train is demonstrated. By using differential group delay in a polarisation maintaining fibre to realise time-division-multiplexing, the repetition rate of the pulse train can be further increased. Based on this principle, the generation of a 40 GHz time and polarisation interleaved optical pulse train, and a 40 GHz single-polarisation pulse train is successfully implemented.

Interferometric length metrology for the dimensional control of ultra-stable ring laser gyroscopes

We present the experimental test of a method for controlling the absolute length of the diagonals of square ring laser gyroscopes. The purpose of this is to actively stabilize the ring cavity geometry and to enhance the rotation sensor stability in order to reach the requirements for the detection of the relativistic Lense–Thirring effect with a ground-based array of optical gyroscopes. The test apparatus consists of two optical cavities 1.32 m in length, reproducing the features of the ring cavity diagonal resonators of large-frame He–Ne ring laser gyroscopes. The proposed measurement technique is based on the use of a single diode laser, injection locked to a frequency stabilized He–Ne/iodine frequency standard, and a single electro-optic modulator. The laser is modulated with a combination of three frequencies, allowing us to lock the two cavities to the same resonance frequency and, at the same time, to determine the cavity free spectral range (FSR). We obtain a stable lock of the two cavities to the same optical frequency reference, providing a length stabilization at the level of 1 part in , and the determination of the two FSRs with a relative precision of ∼2 · 10−7. This is equivalent to an error of on the absolute length difference between the two cavities.

Power-efficient impulse radio ultrawideband pulse generator based on the linear sum of modified doublet pulses

We propose a new and power-efficient impulse radio ultawideband (IR-UWB) pulse design concept. The proposed concept is based on a linear sum of modified doublet pulses. The proposed concept is both simulated and experimentally demonstrated. The experimental demonstration employs a photonic scheme that generates the designed pulse using two main steps, mainly optical shaping and differential detection. The optical shaping is performed using a single electro-optic modulator biased in the nonlinear portion of its transfer function, and the differential detection is performed using a balanced photodetector. The generated IR-UWB pulse is fully Federal Communications Commission compliant, even in the highly power-restricted global positioning system band. The proposed optical scheme has potential to be integrated on a compact optical chip and thus suitable for reliable, low-cost, high-speed, short-range UWB wireless access, such as in-building networks.