Input Optical Power Research Articles

Silicon-graphene conductive photodetector with ultra-high responsivity

Graphene is attractive for realizing optoelectronic devices, including photodetectors because of the unique advantages. It can easily co-work with other semiconductors to form a Schottky junction, in which the photo-carrier generated by light absorption in the semiconductor might be transported to the graphene layer efficiently by the build-in field. It changes the graphene conduction greatly and provides the possibility of realizing a graphene-based conductive-mode photodetector. Here we design and demonstrate a silicon-graphene conductive photodetector with improved responsivity and response speed. An electrical-circuit model is established and the graphene-sheet pattern is designed optimally for maximizing the responsivity. The fabricated silicon-graphene conductive photodetector shows a responsivity of up to ~105A/W at room temperature (27 °C) and the response time is as short as ~30 μs. The temperature dependence of the silicon-graphene conductive photodetector is studied for the first time. It is shown that the silicon-graphene conductive photodetector has ultra-high responsivity when operating at low temperature, which provides the possibility to detect extremely weak optical power. For example, the device can detect an input optical power as low as 6.2 pW with the responsivity as high as 2.4 × 107 A/W when operating at −25 °C in our experiment.

100 Gbps (4 × 25 Gbps) Optical Receiver Module Packaged in Chip-on-Board Based on Germanium Photodetector

100 Gbps (4 × 25 Gbps) optical receiver (Rx) module is demonstrated using Germanium (Ge) photodetector (PD) which is fabricated through Silicon-photonics process using 750 ohm-cm of high-resistivity silicon oxide insulator (SOI) wafer. Trans-impedance amplifier (TIA) and Ge PD are packaged with chip-on-board (COB) manner on a printed circuit board (PCB). High speed PCB for the assembly of both electronic and photonic devices in COB package is precisely designed from the material selection to the device footprint layout and transmission line design. The layout on PCB is optimized using high frequency simulation tool of HFSS to minimize RF loss happening in the transmission line and electrical interconnection points of bond wires. Electrical-optical (EO) S-parameter measurement for the Ge PD shows 22 GHz of transmittance (S21) 3dB bandwidth. Photocurrents of the photodetector induced by the optical input power are analyzed for signal integrity both TIA ON and OFF states. Photocurrent changes by the misalignment of the lensed optical fiber coupled to the edge coupler of the Ge PD shows that 3dB misalignment tolerances are 5.5 µm in the longitudinal and around +/-1 µm in the lateral directions. This COB packaging technique of optical Rx module can be applied for the integration and assembly of the optical module of higher data rate of 100 Gbps and beyond.

A Mobile-Based High Sensitivity On-Field Organophosphorus Compounds Detecting System for IoT-Based Food Safety Tracking

A mobile-based high sensitivity absorptiometer is presented to detect organophosphorus (OP) compounds for Internet-of-Things based food safety tracking. This instrument consists of a customized sensor front-end chip, LED-based light source, low power wireless link, and coin battery, along with a sample holder packaged in a recycled format. The sensor front-end integrates optical sensor, capacitive transimpedance amplifier, and a folded-reference pulse width modulator in a single chip fabricated in a 0.18 μm 1-poly 5-metal CMOS process and has input optical power dynamic range of 71 dB, sensitivity of 3.6 nW/cm2 (0.77 pA), and power consumption of 14.5 μW. Enabled by this high sensitivity sensor front-end chip, the proposed absorptiometer has a small size of 96 cm3, with features including on-field detection and wireless communication with a mobile. OP compound detection experiments of the handheld system demonstrate a limit of detection (LOD) of 0.4 μmol/L, comparable to that of a commercial spectrophotometer. Meanwhile, an android-based application (APP) is presented which makes the absorptiometer access to the Internet-of-Things (IoT).

High-Speed and High-Responsivity InP-Based Uni-Traveling-Carrier Photodiodes

In this paper, top-illuminated InP-based uni-traveling-carrier photodiodes (UTC-PDs) with dipole-doped structure which achieve both high speed and high responsivity simultaneously have been reported. With optimization of device size and layer structure, dipole-doped UTC-PDs have demonstrated a measured optical-to-electrical 3-dB bandwidth of over 40 GHz and a maximum responsivity of 0.6 A/W at optical input power of 100 mW. By using a semi-analytical equivalent circuit model, the 3-dB bandwidth was predicted to be 103 GHz. This high 3-dB bandwidth and responsivity yield a high figure-of-merit value of 61.8 A/ $\text{W}\cdot $ GHz.

Characterization of hexagonal ɛ-Ga1.8Sn0.2O3 thin films for solar-blind ultraviolet applications

Ga1.8Sn0.2O3 thin films were deposited on c-plane Al2O3 (0001) substrates by laser molecular beam epitaxy technology. Well crystallized (002) oriented ɛ-phase Ga1.8Sn0.2O3 thin films were obtained at the substrate temperature above 750 °C and the oxygen partial pressure more than 5 × 10−3 Pa. The band-gap slightly shrinks with Sn4+ ions incorporated into Ga3+ sites, showing an excellent solar-blind ultraviolet (UV) characteristic. The conductivity of hexagonal ɛ-Ga1.8Sn0.2O3 films is very low in the dark, and permitting the design and fabrication of solar-blind photodetector. The photodetector exhibits obvious photo-response under 254 nm UV light irradiation, and it increases in photocurrent with both the rise of applied bias and optical input power. The results suggest that ɛ-Ga1.8Sn0.2O3 thin film is a promising candidate for using in solar-blind photodetectors.

Integrated In-Band OSNR Monitor Based on Asymmetrical Parallel-MZIs for WDM signals

We propose a novel in-band optical signal-to-noise ratio (OSNR) monitor based on asymmetrical parallel Mach–Zehnder interferometers (A-PMZI). By exploiting two different lengths of delay arms in the A-PMZI, the monitor requires no prior knowledge of the noise-free coherence properties of the signal. The A-PMZI is fabricated on a SOI platform and demonstrated for OSNR monitoring of 4 × 28 GBd NRZ-QPSK WDM signals. Experimental results show that OSNR measurements from 7.7 to 24.8 dB within error of ±0.5 dB are achieved for all four channels. Due to the advantages of high fabrication tolerance and broad bandwidth of multimode interferometer couplers in the A-PMZI, the monitor works well in the whole C-band. Moreover, the monitor is insensitive to input optical power and chromatic dispersion.

High-photovoltage GaAs vertical epitaxial monolithic heterostructures with 20 thin p/n junctions and a conversion efficiency of 60%

Photovoltaic power converting III–V semiconductor devices based on the Vertical Epitaxial HeteroStructure Architecture (VEHSA) design have been achieved with up to 20 thin p/n junctions (PT20). Open circuit photovoltages in excess of 23 V are measured for a continuous wave monochromatic optical input power of ∼1 W tuned in the 750 nm–875 nm wavelength range. Conversion efficiencies greater than 60% are demonstrated when the PT20 devices are measured near the peak of their spectral response. Noticeably, the PT20 structure is implemented with its narrowest ultrathin base having a thickness of only 24 nm. In the present study, the spectral response of the PT20 peaks at external quantum efficiency (EQE) of 89%/20 for an input wavelength of 841 nm. We also performed a detailed analysis of the EQE dependence with temperature and for VEHSA structures realised with a varied number of p/n junctions. The systematic study reveals the correlations between the measured conversion efficiencies, the EQE behavior, and the small deviations in the implementation of the optimal designs. Furthermore, we modeled the photovoltage performance of devices designed with thinner bases. For example, we derive that the narrowest subcell of a PT60 structure would have a base as thin as 8 nm, it is expected to still generate an individual subcell photovoltage of 1.14 V, and it will begin to feature 2-dimensional quantum well effects.

Probabilistic 16-QAM Shaping in WDM Systems

This work proposes a probabilistic shaping scheme for optical WDM systems, where nonlinear interference noise depends on the input optical signal power distribution. With $16$ -QAM, a white Gaussian channel analysis shows that the shaped constellation is able to achieve a reach improvement of up to $7\%$ , while split-step Fourier method simulations suggest that even higher gains are possible in practice. An example system is developed for a transmission distance around $3280$ km. A constellation mapping and a low-density parity-check code are developed for this regime to show a reach improvement of $7.1\%$ . These shaping schemes can also be extended to $64$ -QAM, where a reach improvement of over $10\%$ is expected.

Multiple-Input Multiple-Output Enabled Large Bandwidth Density On-Chip Optical Interconnect

We propose to apply the multiple-input multiple-output (MIMO) from wireless communication to high density on-chip optical interconnect. MIMO makes it possible to reduce the waveguide pitch to subwavelength range and uses the crosstalk to improve system performance. The proposed N×N on-chip MIMO system consists of transmitter, high-density waveguides, homodyne coherent receivers, and electrical signal processing components. As an example, a 10×10 MIMO system with waveguide spacing of 250 nm is simulated. The possibility of data transmission at 10 Gb/s/channel from high-density waveguide array is numerically investigated. The minimum input optical power for the BER of 10−12 can reach −18.1 dBm. The BER is better than 10−12 when there is a phase shift of 73.5°. Compared to the conventional parallel waveguides with 2-μm pitch, the bandwidth density can be enhanced from 5 to 13.33 Gbit/μm/s at 10 Gb/s by using the MIMO techniques.

Performance evaluation of analog signal transmission in an integrated optical vortex emitter to 36-km few-mode fiber system

We experimentally demonstrate and evaluate the performance of an analog signal transmission system with photonic integrated optical vortex emitter and 3.6-km few-mode fiber (FMF) link using orbital angular momentum (OAM) modes. The fabricated photonic integrated device is capable of emitting vector optical vortices carrying well-defined and quantized OAM modes with topological charge l=-2 and 2. After propagating through 3.6-km FMF, we measure and assess the spurious free dynamic range of the second-order harmonic distortion. Moreover, we study the impact of nonlinearity-induced resonance wavelength shift of the optical vortex emitter on the analog link performance as increasing the input optical power.

High sensitivity SOA-PIN/TIA photoreceiver for 40 Gb/s applications and beyond

This paper reports a differential photoreceiver module designed for short reach applications such as access network and data center interconnect. It consists of a monolithically integrated semi-conductor optical amplifier with a PIN photodiode and a linear transimpedance amplifier (TIA) mounted on the same carrier. A matching circuit is placed between the PIN and the TIA in order to increase the cut-off frequency. The module shows a −3 dB bandwidth of 43 GHz, a single-ended conversion gain of 10 000 V/W for an optical input power of −25 dBm and a sensitivity at 40 Gb/s non-return-to-zero operation of −22.5 dBm for a bit error rate of 10−9.

Calibration Scheme for Large Kinetic Inductance Detector Arrays Based on Readout Frequency Response

Microwave kinetic inductance detector (MKID) provides a way to build large ground based sub-mm instruments such as NIKA and A-MKID. For such instruments, therefore, it is important to understand and characterize the response to ensure good linearity and calibration over wide dynamic range. We propose to use the MKID readout frequency response to determine the MKID responsivity to an input optical source power. A signal can be measured in a KID as a change in the phase of the readout signal with respect to the KID resonant circle. Fundamentally, this phase change is due to a shift in the KID resonance frequency, in turn due to a radiation induced change in the quasiparticle number in the superconducting resonator. We show that shift in resonant frequency can be determined from the phase shift by using KID phase versus frequency dependence using a previously measured resonant frequency. Working in this calculated resonant frequency, we gain near linearity and constant calibration to a constant optical signal applied in a wide range of operating points on the resonance and readout powers. This calibration method has three particular advantages: first, it is fast enough to be used to calibrate large arrays, with pixel counts in the thousand of pixels; second, it is based on data that are already necessary to determine KID positions; third, it can be done without applying any optical source in front of the array.

Self‐homodyne detection technique using extracted local oscillator light by GS‐SOA in optical coherent transmission

ABSTRACTA self‐homodyne coherent detection technique using gain‐saturated SOA (GS‐SOA) is proposed. In the proposed system, local oscillator (LO) for optical coherent detection is extracted from the optical signal which is sent from the transmitter using the fact that the modulated downlink data can be erased with SOA operation in saturation region. Therefore, carrier frequency offset noise does not occur because LO light which is extracted from the received optical signal has totally same wavelength with the optical signal. In order to operate SOA operates in deep saturation region, high optical input power is needed. The proposed scheme was experimentally demonstrated, and the feasibility was discussed with the experimental results. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:561–565, 2016

Shear Brillouin light scattering microscope.

Brillouin spectroscopy has been used to characterize shear acoustic phonons in materials. However, conventional instruments had slow acquisition times over 10 min per 1 mW of input optical power, and they required two objective lenses to form a 90° scattering geometry necessary for polarization coupling by shear phonons. Here, we demonstrate a confocal Brillouin microscope capable of detecting both shear and longitudinal phonons with improved speeds and with a single objective lens. Brillouin scattering spectra were measured from polycarbonate, fused quartz, and borosilicate in 1-10 s at an optical power level of 10 mW. The elastic constants, phonon mean free path and the ratio of the Pockels coefficients were determined at microscopic resolution.

Fiber Bragg grating sensing system using a TO-can–based compact optical module for wavelength demodulation

A combined scheme using the light source of a reflective semiconductor optical amplifier (RSOA) and an optical signal processing unit (OSPU) based on the compact TO-can package is fabricated and characterized for a fiber Bragg grating (FBG) sensing system. Due to the optical feedback behavior from the FBG sensor, the RSOA is self-injection locked and lasing occurs at the Bragg wavelength. Using the wavelength-dependent filter method, all of the components in the OSPU are compactly integrated on the TO-can package with a height of 17.6 mm and diameter of 6.0 mm. The wavelength demodulating output signals are based on the optical power difference, depending only on the wavelengths without the effect of input optical power variations. The sensitivity of the output signal to temperature shows 0.026 dB/°C . The entire FBG sensing system has an excellent linear response to temperatures controlled with an accuracy of ±0.3°C .

Optical links for the ATLAS Pixel Detector

With the expected increase in the instantaneous luminosity of the LHC in the next few years, the off-detector optical read-out system of the outer two layers of the Pixel Detector of the ATLAS experiment will reach its bandwidth limits. The bandwidth will be increased with new optical receivers, which had to be redesigned since commercial solutions could not be used. The new design allows for a wider operational range in terms of data frequency and input optical power to match the on-detector transmitters of the present Pixel Detector. We report on the design and testing of prototypes of these components and the plans for the installation in the Pixel Detector read-out chain in 2015.

Integrated optical deserialiser time sampling based SiGe photoreceiver.

A novel photoreceiver architecture enabling parallel processing in the electronic domain of a high-speed optical signal is demonstrated. This allows the electronics to operate at significantly lower frequency than the optical signal and hence reduce power consumption and the impact of parasitics. The photoreceiver performs optical time sampling with four integrated SiGe photodetectors connected in series by waveguide delay lines. Four variations of the optical time sampling receiver are designed and demonstrated which differ by the data rate (10 Gb/s and 20 Gb/s) and silicon delay waveguide loss (2.5 dB/cm and 0.2 dB/cm). The bit error rate performance of the photodetectors in the receiver was measured individually and reached a performance below 1 × 10⁻¹⁰ at an input optical power between 4.8 and 6.3 dBm through an off-chip 50 Ω load at the output. After O/E conversion, the electrical signal (one segment of 2¹⁵ - 1 PRBS data) from each of the photodetector is processed without errors at a quarter of the bit rate, leading to an overall more power efficient receiver front-end.

Semiconductor optical amplifiers and Raman amplification for 1310-nm dense wavelength division multiplexed transmission

We investigate the utilization of semiconductor optical amplifiers (SOAs) and quantum-dot laser-based Raman amplifiers in high-capacity dense wavelength division multiplexed (DWDM) 1310-nm transmission systems. Performed simulations showed that in a 10×40 Gbit/s system, the utilization of a single Raman amplifier in a back-propagation scheme can extend the maximum error-free (bit error rate <10−9) transmission distance by approximately 25 km in comparison with the same system utilizing only an SOA used as a preamplifier. We successfully applied a Raman amplifier in an 8×2×40 Gbit/s 1310-nm polarization multiplexed (PolMux) DWDM transmission over 25 km. Conducted experiments showed that the utilization of a Raman amplifier in this system leads to 4-dB improvement of the average channel sensitivity in comparison to the same system utilizing SOAs. This sensitivity improvement can be translated into a higher power budget. Moreover, lower input optical power in a system utilizing a Raman amplifier reduces the four-wave mixing interactions. The obtained results prove that Raman amplification can be successfully applied in 1310-nm high-capacity transmission systems, e.g., to extend the reach of 400G and 1T Ethernet systems.

Optical isolation in topological-edge-state photonic arrays.

We introduce a new type of optical isolator based on breaking time reversal symmetry in dissipative finite Su-Schrieffer-Heeger (SSH) waveguide arrays that support topological edge states at one end of the structure. In the forward propagation direction, light is launched into the edge waveguide to excite the localized topological midgap state. As a result, most of the input optical power is transmitted to the output port. On the other hand, backward reflected light encounters a propagation constant mismatch in that same channel which shifts the otherwise midgap state into one of the bands and hence becomes delocalized over the whole array. We show that under these conditions, a judicious spatial distribution of the optical dissipation across the structure can produce an isolation ratio of -50 dB. The required nonreciprocal phase shift is introduced by depositing a magnetic garnet film only on the edge waveguide and, thus, the required magnetic field can be generated by an integrated micromagnet. Similar concepts can also be applied to SSH arrays made from optical resonators.

All-optical NRZ-to-RZ format conversion at 10 Gbit/s with 1-to-4 wavelength multicasting exploiting cross-phase modulation & four-wave-mixing in single dispersion-flattened highly nonlinear photonic crystal fiber

All-optical NRZ-to-RZ format conversion with a function of wavelength multicasting is proposed in this paper, which is realized by exploiting cross-phase modulation (XPM) and four-wave-mixing (FWM) in a dispersion-flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF). The designed format converter is experimentally demonstrated, for which the 1-to-4 wavelength multicasting is achieved simultaneously by filtering out two FWM idler waves and both blue-chirped and red-chirped components of the broadened NRZ spectrum induced by XPM. Moreover, the wavelength tunability and dynamic characteristics of the proposed NRZ-to-RZ format converter are also exploited using the different central wavelengths of an optical clock signal and varying the input optical power at a DF-HNL-PCF in our experiment. It is shown that the designed format converter can possess a wide range of operational wavelength over 17 nm, an optimal extinction ratio of 11.6 dB, and a Q-factor of 7.1, respectively. Since the proposed scheme uses an optical fiber-based configuration and is easy for implementation, it can be very useful for future applications in advanced fiber-optic communication networks.