External Photodiode Research Articles

Surface plasmon resonance sensor with photodiode integrated beneath plasmonic layer

Surface plasmon resonance (SPR)-based sensors have demonstrated exceptional sensitivity in detecting changes in the refractive index (RI) occurring near the sensor surface due to variations in concentration within the medium, chemical reactions, analyte binding with its ligand, and similar factors. However, most conventional SPR sensors rely on an external photodiode system and a complex mechanical system to measure changes in both intensity and position of reflected light. This is the main limitation of typical SPR sensors, making them non-portable and challenging to apply in experiments beyond the laboratory. Here, we propose SPR sensor chips integrated with a photodiode that eliminates the disadvantage of conventional SPR sensors. The photodiode is based on an n-type Silicon (nSi)-intrinsic Silicon (iSi) junction, sandwiched between a transparent conductive oxide layer, specifically Indium Tin Oxide (ITO), and a plasmonic material, namely Gold (Au). The working principle of our photodiode-integrated SPR sensors was revealed, and the impact of nSi and iSi film thicknesses on sensor sensitivity was investigated. Our SPR sensors enhance the efficiency of SPR-based sensors across diverse applications and facilitate integration into completed electronic devices.

Laser diode driver on a programmable system on a chip.

A comprehensive solution of a laser diode (LD) driver with temperature control using a programmable system on a chip is proposed as an alternative to dedicated devices. A digital proportional integral differential controller is used for regulating the LD temperature. The light-current characteristics and frequency response of the LD are measured using an external photodiode and interrogated by an integrated transimpedance amplifier. The 0.084% stability, 2kHz bandwidth, and 0.11% full scale current error are demonstrated. The LD overshoot protection is digitally implemented, providing a soft start. While the circuit is initially optimized for a 3W infrared LD, instructions are provided for fine-tuning the design according to specific LD requirements.

High−Performance 4H−SiC UV p−i−n Photodiode: Numerical Simulations and Experimental Results

In this work, the optical response of a high−performance 4H−SiC−based p−i−n ultraviolet (UV) photodiode was studied by means of an ad hoc numerical model. The spectral responsivity and the corresponding external photodiode quantum efficiency were calculated under different reverse biases, up to 60 V, and in the wavelength range from λ = 190 to 400 nm. The responsivity peak is R = 0.168 A/W at λ = 292 nm at 0 V and improves as bias increases, reaching R = 0.212 A/W at 60 V and λ = 298 nm. The external quantum efficiency is about 71% and 88%. The good quality of the simulation setup was confirmed by comparison with experimental measurements performed on a p−i−n device fabricated starting from a commercial 4H−SiC wafer. The developed numerical model, together with the material electrical and optical parameters used in our simulations, can be therefore explored for the design of more complex 4H−SiC−based solid−state electronic and optoelectronic devices.

Systematic adjustment of the joining time in pulsed laser beam welding of aluminum-copper joints by means of a closed-loop control

Electric mobility has become increasingly important in recent years. For this purpose, the use of copper is essential due to its electrical properties. In order to save weight and costs, copper is replaced by aluminum in many electrical conductors.In this paper, the required joining time for pulsed laser beam welding of aluminum-copper joints is investigated to minimize the mixing of both materials. By using an external controller and photodiodes, it was possible to develop a real-time pulse control laser welding process based on process emissions. The spectral emission was used to detect when the lower joining partner is reached during the deep welding process. The control enables the adjustment of different joining times, on the one hand by a signal drop of the spectral emission, on the other hand by a specific time. The laser pulse was terminated between 500 – 800 µs after reaching this event. This led to differences in process conditions, resulting in significant changes in mechanical properties. In this way, a decisive influence was exerted on the resulting joining zone. The interaction duration and the work piece transition are of primary interest. By comparing the results with high-speed recordings in the half-section set-up, the resulting mechanisms can be identified. It could be shown that the breakup time have an high impact for the shear tensile force and the welding depth. A Change in the breakup time of 40 µs could lead to high changes in the tensile shear force.

Parameters of fast and high-yield InAs/GaAs quantum dot semiconductor scintillator

InAs quantum dots (QDs) embedded into a waveguiding GaAs semiconductor matrix may produce scintillation detectors with exceptional speed and yield, making them valuable for nuclear security, medical imaging, and high-energy physics applications. In this work, we developed thick (~ 25 μm) epitaxial heterostructures with high luminescence efficiency composed of self-assembled nano-engineered InAs QDs grown by molecular beam epitaxy. The bulk GaAs acts as a stopping material for incident particles and as a waveguide when layer-transferred onto a low-index substrate. Waveguiding and self-absorption (< 1 cm−1) were studied using photoluminescence with scanning laser excitation and modeled with ray optics approximation and geometrical coupling of high-index waveguide to a collection fiber. Scintillating signals from α-particles were analyzed with an external photodiode (PD) and an integrated PD which provided an improved optical coupling. The mean charge collected by the integrated PD corresponded to 3 × 104 photoelectrons per 1 MeV of deposited energy or ~ 13% of the theoretically achievable light yield. Combined with the previously measured QD scintillation time of 0.3–0.6 ns, this makes the InAs/GaAs QD heterostructures the fastest high-yield scintillation material reported.

Phosphor-Based InGaN/GaN White Light-Emitting Diodes With Monolithically Integrated Photodetectors

In this work, we report on the monolithic integrated photodetectors (PDs) in InGaN/GaN light-emitting diodes (LEDs) to monitor the fluctuation of LED intensity over time. The effect of PD position on the light-receiving performance is studied through ray-trace simulation. Three LED-PD devices with different PD positions are fabricated via standard microfabrication processes, and a series of experimental measurements are performed to examine their performances. The design of the PD located in the center of the LED exhibits a 58% increase in the detected photocurrent and has less influence on the emission profile of the LED, compared with the PD formed at the edge. The white light emission is demonstrated by encapsulating the LED-PD device with yellow phosphor and the on-chip PD shows highly similar sensing behaviors as the external Si-based photodiode. Compared with the traditional off-chip detection scheme, the optimal monolithic PD design can provide comparable sensing capabilities, higher compactness, insensitivity to ambient lighting, and less influence on the LED emission profile, making it highly suitable for real-time monitoring of LED intensity variations in various practical and scientific lighting applications.

The power spectral density of 1\f noise in a tunable diode laser at different temperatures

We present investigations of the 1/f noise fluctuations with the different setup temperatures of the tunable laser diode. The measurements are reported from the terminal of the external photodiode using LAB View Signal Express software. The fast Fourier transform method has been implemented, the power spectral density is evaluated at different operation temperatures of the diode laser. The amplitude A of 1/f noise at 1 kHz, and the relation between the frequency exponent factor α and temperatures has been demonstrated. The results show that the power spectral density of the 1/f noise, as well as the value of α decreases as the temperature, increase.

Detectorless measurements of the operational linewidth of NIR VCSELs by self-mixing interferometry.

Self-mixing based on vertical-cavity surface-emitting lasers (VCSELs) offers a compact and low-cost coherent detection scheme for interferometric accessible measurements. The direct detection of the change in the junction voltage, in contrast to the traditional optical detection method by means of an external photodiode, further simplifies the setup by adding detector-less capability. The linewidth of an NIR VCSEL was estimated by using the method based on the statistical analysis of the laser self-mixing fringe period in the moderate feedback regime. We investigate the junction voltage noise and optical power noise, simultaneously acquired, in order to establish the best operational condition for both detection schemes. When comparing the laser linewidth measured by the traditional optical power modulation with that of the detector-less voltage self-mixing signal, the agreement is within the experimental errors.

A 30–75 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\text{dB}\Omega$&lt;/tex-math&gt; &lt;/inline-formula&gt; 2.5 GHz 0.13-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu\text{m}$&lt;/tex-math&gt; &lt;/inline-formula&gt; CMOS Receiver Front-End With Large Input Capacitance Tolerance for Short-Range Optical Communication

This paper describes the design and implementation of a linear optical receiver front-end for short range optical communication applications in 0.13-μm CMOS technology. While conventional optical receivers are typically implemented using limiting amplifiers (LA), emerging optical systems are expected to employ advanced modulation schemes, which require preserving the signal envelope. The proposed linear optical receiver architecture utilizes super-Gm transimpedance amplification with common-mode restoration and constant settling time automatic gain control (AGC) with background illumination cancellation to preserve the signal linearity while tolerating capacitance up to 15 pF for large area photo-detectors. Linearity aware design of transimpedance amplifiers (TIA), variable gain control (VGA), and post amplifiers (PA) are discussed before introducing an exponential generator based on the parasitic BJTs available in the used technology. Consuming 40 mW from a 1.2 V supply in the presence of ~15 pF input capacitance, the circuit achieves a binary modulation data rate of 5 Gbps with an input sensitivity of ~ 65 μA maintaining a bit-error rate (BER) <; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> . S-parameter measurements show a constant -3 dB bandwidth of 2.5 GHz for a wide dynamic range of ~45 dB (30-75 dBΩ) with dB-linearity error better than ±1 dB. To demonstrate the optical functionality of the architecture, an external photodiode (PDCS70T-GS) is directly wirebonded to the chip. Optical measurements confirm a sensitivity of -9.5 dBm (BER <; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> ) at a highest data rate of 5 Gb/s (λ = 680 nm). The noise and linearity performance of the receiver is verified using input referred integrated noise and 1 dB-compression point measurements for different gain settings.

Single-Chip Receiver for 1.25 Gb/s Over 50-m SI-POF

This letter presents a single chip receiver for short-reach high-speed applications through low-cost plastic optical fiber. It compensates the limited bandwidth caused by the fiber and the external photodiode. The prototype contains a transimpedance amplifier, a continuous-time adaptive equalizer, a limiting amplifier, and a clock and data recovery circuit. Experimentally, we have obtained 1.25 Gb/s transmission for a simple nonreturn to zero modulation in an optical link composed of 50 m of step-index polymer optical fiber and a large area Si p-i-n photodetector. It achieves a power under 110 mW at only 1 V of supply voltage.

A Low-Power CMOS Receiver for 1.25 Gb/s Over 1- mm SI-POF Links

This paper presents an optical receiver for short-reach applications through low-cost plastic optical fiber. The limited bandwidth caused by the fiber and the external photodiode is compensated by a new adaptive equalizer based on the spectrum balancing technique. A clock and data recovery circuit is included that minimizes jitter and metastability using a new multilevel bang-bang architecture. The prototype, implemented in a standard 0.18-μm CMOS process, achieves 1.25 Gb/s with a power of 107 mW at only 1 V.

Optical Receiver Using Noise Cancelling With an Integrated Photodiode in 40 nm CMOS Technology

A transimpedance amplifier (TIA) based on an inverting voltage amplifier with a shunt feedback resistor using a noise cancelling technique is presented. The TIA is followed by two stages of differential limiting amplifiers and the last stage is a 50 Ω differential output driver to provide an interface to the measurement setup. The TIA shows a measured optical sensitivity of -20.7 dBm for a BER of 10-9 using an external photodiode (PD). Another chip with the same TIA and an integrated N+/Psub PD is also introduced. The optical receiver achieves a measured transimpedance gain of 78 dBΩ, 1.5 GHz bandwidth and a measured input referred noise current density of 7.2 pA/√Hz up to 1.5 GHz. The power consumption of the TIA is only 4.1 mW and the complete chip dissipates 12 mW for a single 1 V supply voltage.

Suspended microchannel resonators with piezoresistive sensors

Precision frequency detection has enabled the suspended microchannel resonator (SMR) to weigh single living cells, single nanoparticles, and adsorbed protein layers in fluid. To date, the SMR resonance frequency has been determined optically, which requires the use of an external laser and photodiode and cannot be easily arrayed for multiplexed measurements. Here we demonstrate the first electronic detection of SMR resonance frequency by fabricating piezoresistive sensors using ion implantation into single crystal silicon resonators. To validate the piezoresistive SMR, buoyant mass histograms of budding yeast cells and a mixture of 1.6, 2.0, 2.5, and 3.0 µm diameter polystyrene beads are measured. For SMRs designed to weigh micron-sized particles and cells, the mass resolution achieved with piezoresistive detection (∼3.4 fg in a 1 kHz bandwidth) is comparable to what can be achieved by the conventional optical-lever detector. Eliminating the need for expensive and delicate optical components will enable new uses for the SMR in both multiplexed and field deployable applications.

A 12.5-Gb/s Optical Transmitter Using an Auto-power and -modulation Control

In this paper, a 12.5-Gb/s optical transmitter is implemented using 0.13-<TEX>${\mu}m$</TEX> CMOS technology. The optical transmitter that we constructed compensates temperature effects of VCSEL (Vertical cavity surface emitting laser) using auto-power control (APC) and auto-modulation control (AMC). An external monitoring photodiode (MPD) detects optical power and modulation. The proposed APC and AMC demonstrate 5<TEX>$\sim$</TEX>20-mA of bias-current control and 5<TEX>$\sim$</TEX>20-mA of modulation-current control, respectively. To enhance the bandwidth of the optical transmitter, an active feedback amplifier with negative capacitance compensation is exploited. The whole chip consumes only 140.4-mW of DC power at a single 1.8-V supply under the maximum modulation and bias currents, and occupies the area of 1280-<TEX>${\mu}m$</TEX> by 330-<TEX>${\mu}m$</TEX> excluding bonding pads.

A Magnetically Actuated Resonant Mass Sensor With Integrated Optical Readout

Nickel cantilevers with integrated diffraction gratings are used as resonant mass sensors with a resolution of 500 femtograms. Their applicability to biosensing is demonstrated with human opioid receptors. The device is fabricated through a single-mask lithographic process. The microoptical readout provides a simple measurement platform with one external photodiode. Thanks to its AC operation principle, the device is immune to environmental noise and entails a high tolerance to fabrication defects. Obtained signal-to-noise ratio is comparable to that of a high-end Doppler vibrometer. The device with these aspects for systems integration and microarray technology is a candidate for low-cost portable sensors.

Frequency response of solid-state impact ionization multipliers

A study of the frequency response of solid-state impact ionization multipliers (SIMs) is presented that emphasizes the role of resistive and capacitive elements of the device to establish response limitations. SIMs are designed to amplify input currents from an external source through the impact ionization mechanism. An equivalent circuit model for the SIM is developed based on its current versus voltage characteristics, which is used to derive a frequency response model. Theoretical frequency response matches very closely to measured responses for first generation SIM devices constructed on p-type silicon epitaxial layers with nickel silicide Schottky contact injection points. Devices were measured using a photodiode as a current source under light intensities between 74nA and 7.4μA. These SIMs were shown to have a low frequency response that follows a KT∕I relationship. Using an external photodiode with an effective capacitance of 6.8pF, frequency response for a 1.8μA input current was limited to 100kHz. A large effective barrier resistance due to the Schottky contact and 12kΩ space charge resistance dependent on device geometry dominate the response. Future SIM designs with higher frequency response will have to significantly lower both the input barrier resistance and space charge resistance.

Self-mixing interferometry with a laser diode: experimental considerations for sensing applications

An investigation of the effects of external reflectance and pump current on the steady state current threshold and the output power of a laser diode are presented. Back-coupled external reflectance is achieved by placing a mirror in front of the laser diode cavity. Furthermore, by using a rotating wheel, the effect of external reflectance, pump current and combination of individual contributions to frequency shifting on the laser intensity power spectrum are explored. Feedback power ratios below 0.05 and pump currents up to 2Isth (Isth, solitary threshold current) are used in these experiments. The power emitted by the two laser facets are measured through an internal (built-in package) and an external photodiode; both observations are compared. Surprisingly, when evaluating the power–current (P–I) curve for the feedback and solitary cases, a cross over is noticed at ≈1.54Isth only through the external photodiode. Nonetheless, measurements obtained with the internal photodiode agree with the theoretical steady state analysis. Moreover, it is proved that a linear combination of the individual frequency shifts holds in the power spectrum; in addition, a modulation of the carrier density by frequency-shifted optical feedback is also observed. The results from these experiments provide a practical background that ensures a correct interpretation of measurements when using this system for sensing applications.

Effect of optical feedback on 60-GHz colliding-pulse semiconductor mode-locked lasers

We have experimentally investigated on the effects of optical feedback on the performance of monolithic colliding-pulse passively mode-locked semiconductor lasers operating at 60 GHz, designed to be efficient sources of millimeter-wave electrical signals. The characteristics of the optical-to-electrical converted signal are investigated for a long and a short external cavity by means of an external photodiode and by using the saturable absorber of the device as an intracavity photodetector. For a power feedback ratio larger than 10/sup -3/, the linewidth of the millimeter-wave signal is severely broadened with respect to the value of 230 kHz measured in unperturbed conditions. We also report that optical feedback causes central frequency shift and instability, and a reduction of the useful colliding-pulse mode-locked operating region in the biasing parameters of the device.

Optimisation and regime characterisation of monolithic semiconductor mode-locked lasers and colliding-pulse mode-locked lasers at microwave and millimetre-wave frequencies

The optimisation of the saturable absorber section length for mode-locked ridge waveguide lasers in GaAs/AlGaAs double quantum-well material is reported. Mode-locked lasers and colliding-pulse mode-locked lasers were fabricated using a simple self-alignment process. Regime analysis and signal characterisation are performed as a function of the laser cavity and saturable absorber section lengths. Device degradation is evaluated and compared in both configurations. Device performance in the frequency domain is assessed using both an external fast photodiode and the saturable absorber section, and the direct generation of millimetre-wave signal through the saturable section is discussed.

Characterization and use of deuterium lamps as transfer standards of spectral irradiance

Subcomparison CCPR-K1.b of the CCPR key comparison of spectral irradiance covering 200 nm to 400 nm will be carried out in 2002/03 piloted by the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. Deuterium arc lamps will be used as transfer standards of spectral irradiance, although they are known to have, in general, poor stability and reproducibility. PTB investigated a variety of deuterium lamps to test their capability (stability and reproducibility) for use as transfer standards. A measurement facility capable of characterizing up to three lamps at a time has been set up. Investigations of the spectral ageing pattern will help to interpolate between different reference measurements to markedly reduce the influence of ageing effects. The application of an external SiC photodiode as a monitor detector was tested. Spatial characterization of the irradiance of each lamp was also carried out. All this all helped us to find suitable types of lamp, producing reasonable irradiance homogeneously enough to be non-sensitive to small misalignments.