Monitor Photodiode Research Articles

Superluminescent diode integrated with monitor photodiode

Superluminescent diode integrated with monitor photodiode

Temperature measurement with photodiodes: Application to laser diode temperature monitoring

The temperature feedback of solid state laser diodes and various photovoltaic devices is critical for stable and reliable usage. We demonstrate that with a simple and passive electrical measurement process and optical calibration method the temperature of a photodiode can be determined, while keeping its original purpose. We present the idea with simulation and experiments, and provide an illumination-based parameter fitting method. The presented use case is a 5.6mm IR laser diode. We used its monitor photodiode to track the temperature inside the package with significantly better temporal resolution than the off-the-shelf external heat sink sensor provides. We reached a time resolution in the range of milliseconds and achieved precision of ±10mK with ±3K absolute, uncalibrated precision. The technique is not restricted to laser diodes, it is applicable to photovoltaic cells, photodiode arrays, organic diodes as well.

Constant Optical Power Operation of an Ultraviolet LED Controlled by a Smartphone.

Constant light power operation of an ultraviolet (UV) LED based on portable low-cost instrumentation and a monolithically integrated monitoring photodiode (MPD) has been reported for the first time. UV light irradiation has become one of the essential measures for disinfection and sterilization. Monitoring and maintaining a specified light power level is important to meet the criteria of sterilization. We built a module composed of a monolithically integrated UV LED and MPD, a transimpedance amplifier, an Arduino Uno card, a digital-to-analog converter and a Bluetooth transceiver. An Android App that we wrote remotely controlled the UV LED module via Bluetooth. The Arduino Uno card was programmed to receive demands from the smartphone, sent a driving voltage to the LED and returned the present MPD voltage to the smartphone. A feedback loop was used to adjust the LED voltage for maintaining a constant light output. We successfully demonstrated the functioning of remote control of the App, and the resultant UV LED measured power remained the same as the setting power. This setup can also be applied to visible or white LEDs for controlling/maintaining mixed light’s chromaticity coordinates or color temperature. With such controlling and internet capability, custom profiling and maintenance of precision lighting remotely would be possible.

Native signal self-mix interferometer has less than 1 nm noise equivalent displacement.

We demonstrate that the native configuration of a self-mixing interferometer attains a minimum detectable displacement of 0.72 nm or λ/1870 at the laser wavelength of 1310 nm, obtained by the bare laser diode package including a monitor photodiode, observed in the electrical domain by means of an oscilloscope and without any electronic processing of the signal.

Power Dither Technique for Measuring the RF Half-Wave Voltage of a Silicon Mach–Zehnder Modulator

A novel method to measure the radio frequency(RF) half-wave voltage of the silicon Mach-Zehnder modulator (SMZM) is presented based on a low-frequency power dither signal. In our method, the power dither is applied to the thermo-optic phase shifter built into the SMZM, and an RF modulation signal applied to the SMZM is produced by a pulse-code generator. Then, a low-frequency monitor photodiode is used to detect the output signal of the SMZM, and a pair of orthogonal trigonometric functions with the same frequency as the power dither signal is constructed. This performs the cross-correlation integral operations with the output signal of the SMZM. The aforementioned integral results versus different amplitude RF modulation signals are plotted as two third-order polynomial functions, and the intersection point of the third-order polynomial functions corresponding to the RF voltage is the half-wave modulation voltage. Compared with the conventional methods, this new method not only removes the electrical absorption effect and nonlinear electro-optic effect of the SMZM-induced measurement error but also improves measurement accuracy and reduces measurement complexity.

Selective laser melting of Ti-6Al-4V: Comparing μCT with in-situ process monitoring data

Additive Manufacturing (AM) is increasingly used for the fabrication of metallic components used in the medical device, aerospace and automotive industries. With the wider adoption of AM in these sectors, there is an increased demand for the in-situ process monitoring of the build process. This study investigates the performance of a photodiode based, co-axial in-situ process monitoring (PM) system, during the Selective laser melting (SLM) of Ti6Al4V alloy parts. The PM system measures the optical and thermal emissions created by the meltpool, as well as the intensity and stability of the laser during the SLM process. The process monitoring software then creates a 2D or 3D representation of the part, based on the signal intensity recorded.The Ti6Al4V alloy parts were manufactured containing internal cavities, with diameters/width’s in the range of 200–600μm, while varying the input energy between 32.9 and 131.6J/mm3. A close correlation was established between the laser monitoring photodiode signal intensity and the laser energy input. Along with this, an increase in signal intensity recorded, by the meltpool monitoring photodiode, was observed when the first capping layer above a cavity, was processed by the laser. Further to this, it was shown that only the first layer was influence by the overhang, with the signal generated by the layers directly above this remaining unaffected. In addition to providing data on the laser energy during the build process, the PM system also provided valuable information regarding the intensity of the meltpool. A comparison was made between the dimensional measurements obtained using PM software, with those obtained through CT scanning of the parts, post build. It was found that for the 600μm cavities that the measurements were, at best, within 1.7% of each other. This closeness of such measurements however decreased very significantly as the size of the cavities decreased, with a variation for example, of up to 32% been obtained, for 400μm cavities.

Towards Integrating True Random Number Generation in Coherent Optical Transceivers

The integration of quantum communication functions often requires dedicated opto-electronic components that do not bode well with the technology roadmaps of telecom systems. We investigate the capability of commercial coherent transceiver sub-systems to support quantum random number generation next to classical data transmission, and demonstrate how the quantum entropy source based on vacuum fluctuations can be potentially converted into a true random number generator for this purpose. We discuss two possible implementations, building on a receiver- and a transmitter-centric architecture. In the first scheme, balanced homodyne broadband detection in a coherent intradyne receiver is exploited to measure the vacuum state at the input of a 90-degree hybrid. In our proof-of-principle demonstration, a clearance of >2 dB between optical and electrical noise is obtained over a wide bandwidth of more than 11 GHz. In the second scheme, we propose and evaluate the re-use of monitoring photodiodes of a polarization-multiplexed inphase/quadrature modulator for the same purpose. Time-interleaved random number generation is demonstrated for 10 Gbaud polarization-multiplexed quadrature phase shift keyed data transmission. The availability of detailed models will allow to calculate the extractable entropy and we accordingly show randomness extraction for our two proof-of-principle experiments, employing a two-universal strong extractor.

A PM1, PM2.5, and PM10 Airborne Particle Detector With Laser Illumination Stabilized by Optical Feedback

This paper presents a read-out integrated circuit (ROIC) for PM1, PM2.5, and PM10 airborne particle detector with a laser diode. The ROIC has a monitoring photodiode, which provides negative feedback through an automatic power control circuit. This adjusts the driving current to the laser diode, and thus stabilizes the illumination level. Offset compensation circuit in analog front-end eliminates the large offset voltage introduced by stray light reaching the measuring photodiode. A digital back-end analyses each pulse to determine the corresponding particle size, and also linearizes the response, which would otherwise drop off for smaller particles. The ROIC was fabricated in a $0.18~\mu \text{m}$ CMOS process. It has an area of 6.27 mm2 and draws 10 mW at 5 V. The ROIC is incorporated in a particle detector which is tested against an aerosol spectrometer. For particle concentrations up to $100~\mu \text{g}/\text{m}^{{3}}$ , this detector was found to have an accuracy of $\pm ~10~\mu \text{g}/\text{m}^{{3}}$ for PM10 and PM2.5, and $\pm ~15~\mu \text{g}/\text{m}^{{3}}$ for PM1. At higher concentrations, up to $1000~\mu \text{g}/\text{m}^{{3}}$ , the corresponding accuracies are ± 5 % and ± 10 %. Within the temperature range of 0 °C to 50 °C, the effective resolution of the detector changes only from 8.78 bits to 8.97 bits.

On the Feasibility of Absolute Distance Measurement by Using Optical Feedback Into a Superluminescent Diode Cavity

The development of accurate absolute distance interferometers is a long-term research goal. The key impact of this article is the demonstration of an absolute distance interferometer based on the optical feedback (OF) into a superluminescent diode cavity. Due to the OF, we obtained huge interference fringes even with diffusive targets and without using high-sensitivity and low-noise detectors but directly exploiting the monitor photodiode enclosed in the same package of the optical source. The low coherence of the optical source makes the system robust to any stray light along the optical path and thus suitable to work in biological media and dusty industrial environments. The proposed signal processing exploits a zero-crossing approach to determine the absolute target position. Preliminary results show a 95% expanded uncertainty to measuring interval ratio of about 60 ppm over a measuring interval of 50 mm.

Automatic Initialization Methods for Photonic Components on a Silicon-Based Optical Switch

In this work we showed the optimization of the spectral response of several optical elements in a silicon-based optical switch. Integrated thermal resistors induced a local heating of the components. The temperature increase, in turn, caused a thermal shift of the optical response of the component. In this manner, we aligned interleavers and micro-ring resonators to the International Telecommunication Union (ITU) channels, by using a stochastic method named Globalized Bounded Nelder-Mead (GBNM) to determine the proper temperatures. The optimization engine relied on the optical feedback from on-chip monitor photodiodes to drive these photonic elements into the wanted functioning condition. This method is suited for restoring the spectral response of optical elements impaired by fabrication inaccuracies. In the same way, it can be applied to tune in resonance active components, whose transfer function has one or more local optima. We proved the reliability of the GBNM method for the optimization of an integrated optical switch, with more than thousand optical components, each one interfaced with a thermal resistor driven by a dedicated electronic circuit. On the one hand, the GBNM guaranteed the automatic alignment of all active components on the chip, over multiple instances. On the other hand, the method allowed for the proper working of such a complex device.

Characterization of photodetector temporal response for neutron time-of-flight (nToF) diagnostics at the National Ignition Facility.

The temporal response of a microchannel plate photomultiplier tube used in the suite of neutron time of flight (nToF) diagnostics at the National Ignition Facility has been characterized to reduce uncertainty in, and understanding of, shot parameters obtained from nTOF data. A short pulse laser, neutral density glass filters, and electrical attenuators were used to gather statistically significant samples of photodetector impulse response functions (IRF) in rapid succession. Individual components have been absolutely calibrated to minimize systematic uncertainties. The zeroth (collected charge), first (transit time), and second central moments (transit time spread) of the IRF were calculated as either the bias voltage or the amount of light incident on the detector was varied. Timing reference was provided by a monitor photodiode viewing a pickoff of the incident laser pulse. The primary sources of uncertainty are jitter in the monitor photodiode and the statistical variation across our measurement period. The spreads in the first moment, with respect to the timing photodiode, and the square root of the second central moment were found to be less than 50 ps and 150 ps, respectively.

Integrated Reconfigurable Silicon Photonics Switch Matrix in IRIS Project: Technological Achievements and Experimental Results

This paper reports the performances of a silicon photonics optical switch matrix fabricated by using large-scale three-dimensional (3-D) integration. The wavelength selective optical switch consists of a photonic integrated circuit (PIC), with 1398 circuit elements, interconnected in a 3-D stack with its control electronic integrated circuit (EIC). Each PIC element can be trimmed or reconfigured by using metallic heaters. The EIC is designed to drive the heaters and to read the signal of monitor photodiodes integrated into the PIC. Small footprint and high energy efficiency are achieved in the PIC and the EIC. Automatic wavelength alignment of the optical circuits in the PIC to the ITU grid and fine temperature tuning of each photonic element to optimize the switch insertion losses are obtained by an optimization routine. A fully packaged switch with input/output fibers is tested both for optical and electrical characteristics as well as for the system performances. Fiber-to-fiber insertion losses of about 20 dB and channel isolation of −35 dB are achieved. Bit error rate characteristics at 25 Gb/s are evaluated. Perspective applications of the optical switch in optical transport and intra-data center networks are discussed.

Control of Widely Tunable Lasers With High-Q Resonator as an Integral Part of the Cavity

We have designed and fabricated widely tunable semiconductor laser with a high- Q resonator as an integral part of the laser cavity. Wide tuning is realized by utilizing the Vernier effect of two rings with slightly different circumferences. A third ring with considerably larger circumference, and, consequently, higher Q is introduced inside the laser cavity. We study the control of such a laser and show that it is straightforward provided that the integrated laser has on-chip monitor photodiodes. This further shows the benefits of full integration as inclusion of additional monitor photodetectors is straightforward with no extra processing steps. As the complexity of photonic-integrated chips increases, the inclusion of more monitor photodetectors for control is necessary.

Single Channel Self-Mixing Interferometer Measures Simultaneously Displacement and Tilt and Yaw Angles of a Reflective Target

We show that a self-mixing interferometer can supply not only to the usual optical-phase signal cos 2ks( $t$ ) of the external reflector displacement $s(t)$ , but also the attitude signal $P(a$ ) because of the dependence of power from the angle a between wavevector k and normal n to the target reflective surface. By proper interrogation of $P(a$ ) along two orthogonal components of tilt and yaw, the two angles can be measured simultaneously, together with the displacement, in a single self-mixing interferometer channel implemented by a single-laser diode and monitor photodiode combination.

Effect of injection current and temperature on signal strength in a laser diode optical feedback interferometer.

We present a simple analytical model that describes the injection current and temperature dependence of optical feedback interferometry signal strength for a single-mode laser diode. The model is derived from the Lang and Kobayashi rate equations, and is developed both for signals acquired from the monitoring photodiode (proportional to the variations in optical power) and for those obtained by amplification of the corresponding variations in laser voltage. The model shows that both the photodiode and the voltage signal strengths are dependent on the laser slope efficiency, which itself is a function of the injection current and the temperature. Moreover, the model predicts that the photodiode and voltage signal strengths depend differently on injection current and temperature. This important model prediction was proven experimentally for a near-infrared distributed feedback laser by measuring both types of signals over a wide range of injection currents and temperatures. Therefore, this simple model provides important insight into the radically different biasing strategies required to achieve optimal sensor sensitivity for both interferometric signal acquisition schemes.

Laser Light Module with Integrated MEMS Mirror for Autostereoscopic Outdoor Displays

We have developed highly compact light modules to be used as pixels in multi-view autostereoscopic outdoor displays. Each light module consists of three laser diodes, associated monitor photodiodes, a cylindrical microlens, and an electromagnetic 1D MEMS mirror. The mirror deflects the collimated light beams to the left and right eyes of multiple viewers in a time- multiplexed manner. By synchronizing the MEMS mirror actuation with the three-dimensional image information, i.e. the laser diode driving signals, theoretically up to several thousand autostereoscopic views can be displayed.

On‐chip temperature compensation for optical transmitter modules

On-chip temperature compensation (TC) for optical transmitter (Tx) modules is reported. The TC block is integrated in common silicon (Si)-substrate with the Tx and demonstrates the ability to maintain a constant VCSEL output light power without an additional monitoring photodiode. Designed and fabricated in a 0.13 µm technology, the Tx with a TC block operates at up to 5 Gbit/s. A BER of less than 10− 12 is achieved at a received input power of − 3 dBm, with a 1.3 dBm variation of received power for a temperature increase of 20–100°C at 5 Gbit/s data rate. The percentage error of the temperature compensated Tx output light power is ± 3%. The Tx module consumes a power of 20 mW at 1.3 V, including the TC block.

Hybrid III–V/Si Distributed-Feedback Laser Based on Adhesive Bonding

A hybrid evanescently coupled III-V/silicon distributed-feedback laser with an integrated monitor photodiode, based on adhesive divinyl siloxane-benzocyclobutene bonding and emitting at 1310 nm, is presented. An output power of ~2.85 mW is obtained in a continuous wave regime at 10°C. The threshold current is 20 mA and a sidemode suppression ratio of 45 dB is demonstrated. Optical feedback is provided via corrugations on top of the silicon rib waveguide, while a specially developed bonding procedure yields 40-nm-thick adhesive bonding layers, enabling efficient evanescent coupling.

Transistor Laser Power Stabilization Using Direct Collector Current Feedback Control

An automatic laser power control scheme for the transistor laser has been developed and demonstrated using the transistor laser collector current output. The collector current enables an all-electrical feedback solution for laser power control, obviating the need for a hybrid integrated monitor photodiode. This control scheme enables the simple monolithic integration of the transistor laser and its power control circuits on a single die.

In Situ and Self-Restorable Injection-Locking Monitor by Integrated Photodiode for FPLD WDM Transmitter

A novel in situ self-restoration scheme to track real time the injection locking of a Fabry-Perot laser diode (FPLD) is demonstrated by a built-in integrated monitor photodiode (MPD). The variation in the received photocurrent of the integrated MPD was calculated by a microcontroller unit integrated with an analog-to-digital converter, which is employed to dynamically control the temperature of the FPLD via a thermal-electrical controller for wavelength stabilization. Such a scheme can be effectively implemented with a minimum amount of redundant network resources to achieve self-restoration within 50 s with Q factor >;8.2 and side-mode suppression ratio >;35 dB at 2.5 Gbit/s. The feasibility of the proposed self-restorable locker is suitable for most wavelength-locking FPLDs within high-speed wavelength-division multiplexing networks.