Uni-traveling Carrier Photodetector Research Articles

Automated intelligent design of modified uni-traveling carrier photodectors

This paper introduces an automatic intelligent design method for the modified uni-traveling carrier photodetector (MUTC-PD). The conventional photodetector design process often relies on the numerical solution of complex nonlinear partial differential equations to simulate and optimize device performance, which is not only computationally intensive but also inefficient. To overcome this challenge, we apply the charge control principle to calculate the photodetector bandwidth, which improves the computational speed by a factor of approximately 1800 compared to the numerical solution of nonlinear partial differential equations. To further optimize the structure of the photodetector, we incorporate the Velocity Varying Climbing Particle Swarm Optimization (VVCPSO) algorithm. This is an improved algorithm based on the traditional particle swarm algorithm, which is able to quickly find the optimal solution in a complex parameter space. By applying the VVCPSO algorithm, we successfully fine-tuned the photodetector structure and obtained structural parameters with optimal performance. Our thorough verification process confirms that the proposed method is consistent with the results of ATLAS simulation software. Automated design has resulted in a high-performance MUTC-PD with a responsivity of 0.52A/W and a bandwidth of 60 GHz (@-3 V) at a mesa diameter of 16µm. Compared to the pre-optimized device, the bandwidth is increased to three times the original. By reducing the mesa diameter to 4µm, the bandwidth can be further increased to 82 GHz (@-3 V). The proposed method's calculation speed is fast enough, enabling extensive parameter studies to optimize device performance.

High-Speed Mid-Wave Infrared Uni-Traveling Carrier Photodetector With Inductive Peaked Dewar Packaging

High-Speed Mid-Wave Infrared Uni-Traveling Carrier Photodetector With Inductive Peaked Dewar Packaging

Electrical feedback system for enhancing the RF power of photodetector.

In this paper, we propose a system for enhancing the RF output power of the photodetector, especially the power of fundamental tune and second-order harmonic, by feeding back part of the RF signal through an electrical feedback circuit. As a result of bias modulation and opto-electric mixing, the RF output power can be effectively enhanced. The structure of uni-traveling carrier photodetector (UTC-PD) is employed in this work. With the RF enhancement system, the power of fundamental tune and second-order harmonic improve by 6.4 dB and 9.9 dB respectively, under the condition of 26 dBm input optical power, 3 V bias voltage, and 14 GHz input optical signal. Further, it was observed that third-order harmonic appeared under the influence of this system.

Study of the Optoelectronic Mixer Based on Modified Uni-Traveling Carrier Photodetector for Efficient Harmonic Mixing

We report the measurements and characterizations of optoelectronic harmonic mixing in a modified uni-traveling carrier photodetector (MUTC-PD). A systematic study of the bias voltage-dependent properties of the output power under different input optical power levels has been made and the proper operating conditions for different mixing modes have been investigated. In addition to the fundamental mixing, the higher-order harmonic mixing and RF subharmonic mixing products were obtained. The harmonic mixing mechanism is mainly attributed to the nonlinearity of the dependence of the output power on the bias voltage. Flat intermediate responses over a wide RF signal frequency range were measured for the fundamental mixing and the high-order RF subharmonic mixing. The feasible harmonic optoelectronic mixing in MUTC-PD shows great application potential in the wireless multichannel communication system.

Cascade Uni-Traveling-Carrier Photodetector Array for Terahertz Applications

A cascade array structure and depleted layer thickness design method of uni-traveling-carrier photodetector (UTC-PD) for terahertz applications is proposed. The cascade array structure can increase the 3dB bandwidth from 203 GHz to 255 GHz compared to the high-speed single UTC-PD with a diameter of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3 ~\mu \text{m}$ </tex-math></inline-formula> by effectively reducing the overall device capacitance. The 3dB bandwidth can be further improved to 267 GHz by thickness optimization. The combination of cascade array structure and depleted layer thickness optimization can significantly improve the saturation output power of the device at 100, 200 and 300 GHz, which enables the design of cascade UTC-PD array to be applied in terahertz (THz) band.

High-Speed Photodetector With Simultaneous Electrical Power Generation

We demonstrate a novel 850 nm high-speed photodetector for simultaneous high-speed data acquisition and electrical power generation from the optical signal. The device is based on GaAs/AlGaAs modified uni-traveling carrier photodetector (MUTC-PD). Compared with the traditional p-i-n photodetector with the same absorber thickness, the MUTC device sustains a high 3 dB bandwidth of 11.9 GHz and a power conversion efficiency of 38.5% under a forward bias of +0.7 V. This outstanding performance is achieved by first adopting the MUTC structure on LPC devices. The device is expected to have applications for simultaneous lightwave information and power transfer. Our approach extends the high-speed detection to the forward bias region and may provide a potential solution for next-generation combined power and data transceiver modules.

High-Speed Mid-Wave Infrared InAs/InAsSb Superlattice Uni-Traveling Carrier Photodetectors With Different Absorber Doping

In this article, we studied two high-speed mid-wave infrared InAs/InAsSb type-II superlattice (T2SL) uni-traveling carrier (UTC) photodetectors (PDs) with different graded p-doping profiles in the absorber. It is found that the UTC device with higher absorber p-doping (hereafter referred to as Device A) has a larger 3-dB bandwidth than that of the device with lower absorber p-doping (hereafter referred to as Device B). However, Device A shows a higher dark current and lower responsivity performance than Device B. The peak responsivity of Devices A and B is about 0.9 and 1.2 A/W, respectively, under −1 V at room temperature. The performance comparisons of both devices are explored in detail. These results could contribute a further step toward developing high-speed InAs/InAsSb T2SL PDs.

Hybrid plasmonic uni-traveling carrier photodetector with periodic corrugated electrode

In this paper, a novel InP-based evanescently coupled hybrid plasmonic uni-traveling carrier photodetector (ECHP-UTC-PD) integrated with a hybrid plasmonic waveguide is proposed at 1.55 μm wavelength. It has been shown that the corrugated structure of nano-metals on the PD absorption layer highly increases the amount of light coupled from the input waveguide to the absorption layer and hence increases the PD responsivity. In order to achieve maximum responsivity, the structure of the PD has been optimized using the Particle Swarm Optimization (PSO) method. The frequency response of the proposed PD was determined using transit time simulation and output scattering parameter (S22) by extracting the small-signal equivalent circuit. Simulation results show that this PD has the responsivity of 0.8 A/W and the 3 dB-bandwidth of 200 GHz for a PD length of 12.5 μm, the width of 650 nm, and the InGaAs absorption layer thickness of 100 nm. The proposed PD can be monolithically integrated with generic InP-based devices.

The Optoelectronic Mixing Characterization of Uni-Traveling Carrier Photodetector

In this work, the optoelectronic mixing characteristics of the uni-traveling carrier photodetector (UTC-PD) were investigated. Three different types of optoelectronic mixing modes were analyzed, including fundamental mixing, harmonic mixing, and RF subharmonic mixing. The output power bias voltage-dependent behaviors of a 60-GHz optical sinusoidal wave and its harmonic signals were studied. The methods that can significantly improve the power of the optoelectronic mixing output signal were proposed. It is found that setting the peak-to-peak value of the RF signal at the bias end in the optimized bias voltage range where the RF output power can obtain a larger increment is the key to obtaining a high power mixing product. Increasing the power of the optical signal to make the output power increment in the same bias range further increased is also effective to enhance the mixing product. Taking the same techniques, the output power of the higher order harmonic mixing product can also be improved, which makes the higher order harmonic mixing application of the UTC-PD feasible.

Impact of nonlinearity including bleaching in MUTC photodetectors on RF-modulated electro-optic frequency combs.

We use the drift-diffusion equations to calculate the responsivity of a modified uni-traveling carrier (MUTC) photodetector (PD) with a frequency comb input that is generated by a series of short optical pulses. We first use experimental results for the responsivity of the MUTC PD to obtain an empirical model of bleaching in pulsed mode. We incorporate our empirical bleaching model into a drift-diffusion model to calculate the impact of nonlinearity in an MUTC PD on RF-modulated electro-optic frequency combs. We quantify the nonlinearity using the second- and third-order intermodulation distortion powers (IMD2 and IMD3), from which we calculate the second- and third-order output intercept points (OIP2 and OIP3). In contrast to a continuous wave (CW) input for which there is a single IMD2 and IMD3 and hence a single OIP2 and OIP3, each comb line n has its own IMD2n, IMD3n, OIP2n, and OIP3n associated with it. We determine the IMD2n, IMD3n, OIP2n, and OIP3n, and we compare the results with and without bleaching. We find that the impact of bleaching is complex and, somewhat surprisingly, not always detrimental. The principal effect of bleaching is to lower the responsivity, which decreases the nonlinearity due to space charge. While bleaching always reduces the OIP2n and OIP3n, we find that bleaching leads to a decreased distortion-to-signal ratio for large n.

Research on ultra-wideband and high saturation power uni-traveling carrier photodetectors (Invited)

Ultra-wideband uni-traveling carrier (UTC) photodetectors have broadband advantages over traditional PIN detectors, as only fast electrons are required to transport in UTC photodetectors. They will be one of the key optoelectronic devices in the sub-terahertz systems, such as 6G broadband wireless communications, terahertz imaging, ultra-wideband noise generators, etc. For the requirements of optoelectronic conversion in sub-terahertz frequency band, high-speed photo-generated carrier transport mechanics and inductive coplanar waveguide (CPW) structure were studied to improve the device bandwidth and saturation power of the photodetector. A dual-drift layer structure MUTC photodetector chip with bandwidth of 106 GHz, saturated output power of 7.3 dBm, and a CPW-optimized MUTC photodetector chip with bandwidth over 150 GHz were developed.

The Tunable Phase Shift of High-Speed PIN Photodetector and Modified Uni-Traveling Carrier Photodetector

We report the phase shift of two types of photodetectors for a variation of bias voltage and optical power. One type is PIN-PD and the other is a modified uni-traveling carrier photodetector (MUTC-PD). In PIN-PD, the phase change shows a photocurrent-dependent variation of about 15 degrees at 3 GHz. It exhibits good stability over a wide bandwidth as the bias voltage changes. By comparison, the phase shift of the MUTC-PD is more sensitive to the bias voltage and the photocurrent. The continuous tunable range of phase shift in MUTC-PD reaches 50 degrees at 10 GHz. It is demonstrated that the adjustable phase shift mainly results from the transit time and the impedance dynamic effects in response to the optical power and bias voltage.

High Speed Mid-Wave Infrared Uni-Traveling Carrier Photodetector

A mid-wave infrared (MWIR) frequency comb is expected to dramatically improve the precision and sensitivity of molecular spectroscopy. For high resolution applications, a high speed MWIR photodetector is one of the key components, however, commercially available high speed MWIR photodetectors only have sub-GHz bandwidth currently. In this paper, we demonstrate, for the first time to our knowledge, a high speed mid-wave infrared (MWIR) uni-traveling carrier photodetector based on InAs/GaSb type-II superlattice (T2SL) at room temperature. The device exhibits a cutoff wavelength of 5.6 μm and a 3dB bandwidth of 6.58 GHz for a 20μm diameter device at 300 K. These promising results show that the device has potential to be utilized in high speed applications such as frequency comb spectroscopy, free space communication and others. The limitations on the high frequency performance of the photodetectors are also discussed.

Uni-traveling-carrier photodetector with high-contrast grating focusing-reflection mirrors

A novel uni-traveling-carrier photodetector (UTC-PD) structure with an integrated focusing-reflection (FR) mirror realized by a non-periodic concentric circular high-contrast grating, referred to as FR-UTC-PD, is proposed to enhance responsivity in conventional UTC-PDs. The FR-UTC-PD allows us to improve the responsivity by 36.5% at a 1.55 μm wavelength as compared to a UTC-PD without integrated an FR mirror with 84.59% reflectivity. For 40 μm diameter PDs, the obtained 3 dB bandwidths are unaltered with values of 18 GHz at −3.0 V bias voltage. The radio-frequency output power and photocurrent are −1.77 dBm and 17.56 mA, respectively, at 10 GHz and the −6.0 V bias voltage.

Study of the operation optical power in modified uni-traveling carrier photodetector for low amplitude to phase conversion

The phase noise known as the amplitude to phase conversion (AM–PM) in modified uni-traveling carrier photodetector (MUTC-PD) is severely power-dependent. To achieve low AM–PM operation, applying proper injection optical power will be of crucial importance. For this purpose, the characterization of the phase change between the 60-GHz sinusoidal input and RF output of a MUTC-PD is analyzed under different incident optical power. Moreover, the equation of the phase change is deduced by applying an equivalent circuit model. The results demonstrate that the power-dependent nonlinear transit time plays a key role in the phase change. Besides, the absolute phase change is observed smallest when the differential capacitance equals to zero in a typical optical power. To the best of our knowledge, this is the first demonstration of the relationship between the differential capacitance and the phase change. When the differential capacitance equals to zero, the total capacitance of the MUTC exhibits a valley which could be a measurable feature of the optimum optical power for low phase noise operation.

Uni-Traveling-Carrier Photodetector With High-Reflectivity DBR Mirrors

A novel uni-traveling-carrier photodetector (UTC-PD), bonded to high-reflectivity (HR) distributed Bragg reflector (DBR) mirrors, referred to as HR-UTC-PD, is first developed to overcome the bandwidth-responsivity tradeoff in UTC-PDs at various wavelengths. Grubbs' test is adopted, for the first time, to measure the bonded thickness of random locations for evaluating the reflected light loss generated in the bonded region. Compared with a standard UTC-PD without HR DBR mirrors, the maximum improvement of HR-UTC-PD responsivity (0.88A/W at 1560 nm) is 24.4% under a bias voltage of 3 V. The obtained 3-dB bandwidth for a 40-μm-diameter PD, which is neither increased nor degraded with the HR DBR mirrors, is 13.87 GHz at a bias voltage of 6 V and a 1550 nm wavelength. The saturation current up to 50 mA at 1-dB compression point is obtained at the frequency of 10 GHz, under a 50-Ω load and a 6 V bias voltage.

High-Power, Aperture Coupled Photonic Antenna

A high-power charge-compensated modified uni-travelling carrier photodetector is directly integrated into an aperture coupled patch antenna. The coupling technique offers not only good isolation between feed and radiating patch substrates but also wide operational bandwidth. The antenna is developed to operate at 22 GHz with 3-dB relative bandwidth of ~20%, over which the measured effective isotropic radiated power approaches 31 dBm. The photonic antenna is integrated with a lightweight, low form factor fiber-optic feed that demonstrates potential for future wireless communications applications. The antenna's electrical and radiation characteristics are observed to be in good agreement with simulations.

Computational Study of Amplitude-to-Phase Conversion in a Modified Unitraveling Carrier Photodetector

We calculate the amplitude-to-phase (AM-to-PM) noise conversion in a modified unitraveling carrier photodetector. We obtained two nulls as measured in the experiments, and we explain their origin. The nulls appear due to the transit time variation when the average photocurrent varies, and the transit time variation is due to the change of electron velocity when the average photocurrent varies. We also show that the AM-to-PM conversion coefficient depends only on the pulse energy and is independent of the pulse duration when the duration is less than 500 fs. When the pulse duration is larger than 500 fs, the nulls of the AM-to-PM conversion coefficient shift to larger average photocurrents. This shift occurs because the increase in that pulse duration leads to a decrease in the peak photocurrent. The AM-to-PM noise conversion coefficient changes as the repetition rate varies. However, the repetition rate does not change the AM-to-PM conversion coefficient as a function of input optical pulse energy. The repetition rate changes the average photocurrent. We propose a design that would in theory improve the performance of the device.

Frequency dependent harmonic powers in a modified uni-traveling carrier photodetector.

We use a drift-diffusion model to study frequency dependent harmonic powers in a modified uni-traveling carrier (MUTC) phododetector. The model includes external loading, incomplete ionization, the Franz-Keldysh effect, and history-dependent impact ionization. In three-tone measurements, the bias voltage at which a null occurs (bias null) in the second-order intermodulation distortion (IMD2) is different for the sum frequency and difference frequency. We obtained agreement with the experimental results. The bias null that appears in the IMD2 is due to the Franz-Keldysh effect. The bias voltage at which the bias null is located depends on the electric field in the intrinsic region, and the difference in the location of the bias null for the sum frequency and difference frequency is due to the displacement current in the intrinsic region. When the frequency is large, the displacement current is large and has a large effect on the harmonic powers. We also found that the bias null depends on the recombination rate in the p-absorption region because the electric field decreases in the intrinsic region when the recombination rate in the p-region decreases.

High-bandwidth uni-traveling carrier waveguide photodetector on an InP-membrane-on-silicon platform.

A uni-traveling carrier photodetector (UTC-PD), heterogeneously integrated on silicon, is demonstrated. It is fabricated in an InP-based photonic membrane bonded on a silicon wafer, using a novel double-sided processing scheme. A very high 3 dB bandwidth of beyond 67 GHz is obtained, together with a responsivity of 0.7 A/W at 1.55 μm wavelength. In addition, open eye diagrams at 54 Gb/s are observed. These results promise high speed applications using a novel full-functionality photonic platform on silicon.