Two-photon Absorption Detector Research Articles

Optical Autocorrelation Measurement for Ultrafast Pulses at NIR Wavelengths Using GaP, GaAsP, and Si Photoconductive Detectors

In this article, we report on an optical real-time autocorrelator readout with a 5 Hz refresh rate, equipped with a transimpedance amplified photodetector based on the two-photon absorption (TPA) of semiconductor photodiodes (PDs) for ultrashort (1 < ps) pulse measurement. By replacing the GaP PD of a commercial TPA detector with GaAsP and Si PD elements, we demonstrated that the spectral response based on the TPA of each photodetector followed the linear response of the corresponding semiconductor PD within accessible wavelength regions. The TPA spectral response of the GaAsP detector exhibited a peak at 1200 nm and a long wavelength limit near 1300 nm. The TPA spectral response of the Si detector exhibited a short wavelength limit near 1170 nm and a linear response up to 1300 nm. The two types of PD were compared with the characteristics of the GaP photodiode. These photoconductive detectors are efficient, compact, and robust sensors and can be used to diagnose the pulse characteristics of ultrafast fiber lasers and light sources near IR wavelengths.

Two-photon superbunching effect of broadband chaotic light at the femtosecond timescale based on a cascaded Michelson interferometer

It is challenging to observe the superbunching effect with true chaotic light. Here we propose and demonstrate a method to achieve the superbunching effect of ${g}^{(2)}(0)=2.42\ifmmode\pm\else\textpm\fi{}0.02$ with broadband stationary chaotic light based on a cascaded Michelson interferometer (CMI), exceeding the theoretical upper limit of 2 for the two-photon bunching effect of chaotic light. The superbunching correlation peak is measured with an ultrafast two-photon absorption detector whose full width at half-maximum reaches about 95 fs. Two-photon superbunching theory in a CMI is developed to interpret the effect and is in agreement with experimental results. The theory also predicts that the degree of second-order coherence can be much greater than 2 if chaotic light propagates $N$ times in a CMI. Finally, a type of weak signal detection setup that employs broadband chaotic light circulating in a CMI is proposed. Theoretically, it can increase the detection sensitivity of weak signals 79 times after the chaotic light circulates 100 times in the CMI.

Measuring Hanbury Brown and Twiss Effect of Multi-Spatial-Mode Thermal Light at Ultrashort Timescale by Two-Photon Absorption

Hanbury Brown and Twiss effect of multi-spatial-mode thermal light is obtained at ultrashort timescale by two-photon-absorption (TPA) in a semiconductor photon-counting module. A characteristic spectrum, due to the interference in multi-mode fiber, is observed directly in TPA detector for the first time. To analyze the output of such measurement, a theoretical model based on the Feynman's path-integral theory is built, which makes the contribution of related item and the corresponding spectral component match very well. In addition, by introducing an all-optical method into the current HBT apparatus, one can obtain the concerned second-order coherence spectrum directly without any postprocessing. This result may be helpful to develop ultrafast detection for the intensity interferometer with natural light. Meanwhile, the observation of HBT effect of multi-mode interference offers a new detection method for the optical fiber sensors.

Upconversion single-microbelt photodetector via two-photon absorption simultaneous

Single microbelt (MB) photodetectors with metal–semiconductor-metal structure have been demonstrated and characterized comprehensively. For single-photon absorption, the maximum responsivity of ZnO-MB photodetector can reach as high as 1.4 × 105 A W−1 at 20 V bias. The results about photoresponse of MB-detector reveals that two relaxation mechanisms contribute to the carrier decay time. Moreover, the two-photon absorption upconversion photoresponsivity in the single-MB detector has also been realized, which is the first report about the two-photon absorption detector to the best of our knowledge. The excellent two-photon absorption photoresponsivity characteristic of the MB device can be available not only for detector but also for solar cell and biomedical imaging. The above results present a significant step towards future fabrication of single micro/nano-structure based multiphoton excitation optoelectronic devices.

OSNR Monitoring for NRZ-PSK Signals Using Silicon Waveguide Two-Photon Absorption

We study the use of two-photon absorption (TPA) in a silicon optical waveguide for measuring the optical signal-to-noise ratio (OSNR) of a nonreturn to zero phase-shift keying (NRZ-PSK) signal. The average photocurrent generated in the silicon waveguide increased by 70 nA (from 375 to 445 nA) for a change in OSNR from 28 to 6 dB and a constant total input power of 10 dBm. The nonresonant nature of the silicon waveguide TPA detector enables the simple measurement of OSNR over a continuous wide (>; 10 nm) wavelength range. For a 10-Gb/s NRZ-PSK signal, we show that when the residual dispersion in the optical signal exceeds 425 ps/nm, further increases in dispersion have little effect on the photocurrent. Thus, this TPA-based OSNR monitor can be used in practical systems with large dispersion.

Pulse Width Stabilization for Ultrafast Laser Systems

In this report, we describe a method and the resultant performance data for precise and efficient laser pulse width stabilization in the ultrafast laser regime. The pulse quality feedback mechanism is based on a two-photon absorption detector, and the adjustments to system dispersion are executed by embedded software tuning the inter-grating distance in the pulse compressor. Relative pulse width variability of only 4% is demonstrated over 8hours despite changing ambient conditions. To our knowledge, this is the first ever ultrafast laser pulse autonomous stabilization scheme integrated into an industrial platform.

High fidelity femtosecond pulses from an ultrafast fiber laser system via adaptive amplitude and phase pre-shaping

The generation of high-fidelity femtosecond pulses is experimentally demonstrated in a fiber based chirped-pulse amplification (CPA) system through an adaptive amplitude and phase pre-shaping technique. A pulse shaper, based on a dual-layer liquid crystal spatial light modulator (LC-SLM), was implemented in the fiber CPA system for amplitude and phase shaping prior to amplification. The LC-SLM was controlled using a differential evolution algorithm, to maximize a two-photon absorption detector signal from the compressed fiber CPA output pulses. It is shown that this approach compensates for both accumulated phase from material dispersion and nonlinear phase modulation. A train of pulses was produced with an average power of 12.6W at a 50MHz repetition rate from our fiber CPA system, which were compressible to high fidelity pulses with a duration of 170 fs.

Chromatic Dispersion Monitoring of 80-Gb/s OTDM Data Signal via Two-Photon Absorption in a Semiconductor Microcavity

In this letter, a novel method of chromatic dispersion monitoring via two-photon absorption (TPA) is investigated. A specially designed semiconductor microcavity is employed as a TPA detector for monitoring data signals operating at rates up to 80Gb/s. As the microcavity has a wavelength-dependent response, a single device can be used to monitor multiple channels in a multiwavelength optical telecommunication system

Automatic Pulse Duration Control of Picosecond Laser using Two-Photon Absorption Detector

We have proposed and developed a new feedback control system to automatically minimize the pulse duration of an ultrafast laser using a two-photon absorption detector that has a Gires–Tournois interferometer (GTI) for compensating the positive group delay dispersion of the laser cavity. The signal of the two-photon detector is inversely proportional to the pulse duration when the average power, repetition rate, and pulse shape are maintained. The minimization of the pulse duration is accomplished by adjusting the voltage applied to the GTI to maximize the two-photon signal. We demonstrated the control of pulse duration minimization with the developed system.

Self-mode-locking effects in heavily doped single-clad Tm3+-doped silica fibre lasers

Self-mode-locking in single-clad Tm-doped silica fibre lasers operating at 1.92 µm is reported with 100% modulated mode-locked pulses observed for longer fibre lengths up to 6 m. The self-mode-locking was accompanied by self Q-switching. A mode-locked pulse duration of 191 ps has been measured using an autocorrelator based on a two-photon absorption detector for operation at 2 µm assembled for the purpose of this experiment. The experimental pulse train characteristics are found to be consistent with mode-locking theoretical analysis. The origin and properties of self-mode-locking in heavily Tm-doped fibre lasers are discussed.

Silicon waveguide two-photon absorption detector at 1.5 μm wavelength for autocorrelation measurements

We describe the use of a silicon waveguide for two-photon absorption measurements in an autocorrelator which achieved a peak-power average-power sensitivity of 1 (mW)2 at 1.56 μm wavelength and which was used to measure optical pulses generated by a mode-locked fiber ring laser. The experimental results agreed with a theoretical model of the two-photon-induced photocurrent generation inside the waveguide.