Near-ballistic Unitraveling-carrier Photodiode Research Articles

All-Optical Generation and Switching of Few-Cycle Millimeter-Wave Pulses

We conducted a comparative study of two schemes of photonic generation and switching of few-cycle sub-THz or millimeter wave (MMW) pulses by use of a photonic-transmitter-mixer (PTM) module with a broadband and high-power near-ballistic uni-traveling carrier photodiode (NBUTC-PD). In the first scheme, we performed all-optical ultra-fast switching (bias modulation) of the PTM injected with a 93 GHz optical local-oscillator signal. Sub-2-cycle short MMW pulses with central frequency at 93 GHz were generated. To compare, in scheme 2, we employed femtosecond optical short pulses to directly excite the PTM under a DC bias (optical modulation). The former approach is shown to be capable of providing much less signal distortion and much shorter pulse duration than the latter.

Design and demonstration of ultra-fast W-band photonic transmitter-mixer and detectors for 25 Gbits/sec error-free wireless linking

A 25 Gbits/s error-free on-off-keying (OOK) wireless link between an ultra high-speed W-band photonic transmitter-mixer (PTM) and a fast W-band envelope detector is demonstrated. At the transmission end, the high-speed PTM is developed with an active near-ballistic uni-traveling carrier photodiode (NBUTC-PD) integrated with broadband front-end circuitry via the flip-chip bonding technique. Compared to our previous work, the wireless data rate is significantly increased through the improvement on the bandwidth of the front-end circuitry together with the reduction of the intermediate-frequency (IF) driving voltage of the active NBUTC-PD. The demonstrated PTM has a record-wide IF modulation (DC-25 GHz) and optical-to-electrical fractional bandwidths (68-128 GHz, ~67%). At the receiver end, the demodulation is realized with an ultra-fast W-band envelope detector built with a zero-bias Schottky barrier diode with a record wide video bandwidth (37 GHz) and excellent sensitivity. The demonstrated PTM is expected to find applications in multi-gigabit short-range wireless communication.

Photonic Generation of Few-Cycle Millimeter-Wave Pulse Using a Waveguide-Based Photonic-Transmitter-Mixer

We demonstrate a novel technique for photonic generation of few-cycle millimeter-wave (MMW) pulse using a WR-10 waveguide and near-ballistic unitraveling carrier photodiode (NBUTC-PD)-based photonic-transmitter-mixer (PTM). A 2.5-cycle MMW pulse is generated by simultaneously exciting the PTM optical port with ~100-GHz optical MMW sinusoidal signal and the intermediate-frequency (IF) port with a 25-ps electrical short pulse, respectively. Compared to results using femtosecond optical short pulses to directly excite the PTM (without E-O signal mixing), our approach is capable of providing much less signal distortion, eliminating the ringing oscillation in the tail of response, a much shorter pulse duration, and a higher peak power.

10 Gb/s optical carrier distributed network with W-band (0.1 THz) short-reach wireless communication system

Millimeter-wave (mm-wave) operated in W-band (75GHz–0.11THz) is of particular interests, since this frequency band can carry signals at much higher data rates. We demonstrate a 10Gb/s optical carrier-distributed network with the wireless communication system. The mm-wave signal at carrier frequency of 0.1THz is generated by a high speed near-ballistic uni-traveling carrier photodiode (NBUTC-PD) based transmitter (Tx), which is optically excited by optical short pulses. The optical pulse source is produced from a self-developed photonic mm-wave waveform generator (PMWG), which allows spectral line-by-line pulse shaping. Hence these optical pulses have high tolerance to fiber chromatic dispersion. The W-band 10Gb/s wireless data is transmitted and received via a pair of horn antennas. The received 10Gb/s data is envelope-detected and then used to drive an optical modulator at the remote antenna unit (RAU) to produce the upstream signal sending back to the central office (CO). 20km single mode fiber (SMF) error free transmission is achieved. Analysis about the optimum repetition rate of the optical pulse source and the transmission performance of the upstream signal are also performed and discussed.

Design and Analysis of Ultra-High-Speed Near-Ballistic Uni-Traveling-Carrier Photodiodes Under a 50-$\Omega$ Load for High-Power Performance

We demonstrate a near-ballistic uni-traveling-carrier photodiode (NBUTC-PD) with a scaled-down epi-layer structure designed for high-power performance in the sub-THz frequency regime. Compared with UTC-PDs, NBUTC-PDs offer a higher optimum bias voltage for the near-ballistic transport of electrons, which leads to improvement in the output power performance. Furthermore, a small load resistance ( <; 50 Ω), which would sacrifice the output power for minimizing the output ac voltage swing on dc bias point, is not necessary. By scaling down the collector layer thickness and active area of the NBUTC-PDs, we achieve a large optical-to-electrical bandwidth (250 GHz) and a high saturation current (17 mA), which is close to the theoretical maximum, under a 50-Ω load and -2-V bias.

Remotely Up-Converted 20-Gbit/s Error-Free Wireless On–Off-Keying Data Transmission at W-Band Using an Ultra-Wideband Photonic Transmitter-Mixer

We demonstrate a remotely up-converted and distributed 20-Gbit/s wireless on-off-keying (OOK) data transmission link at the W-band that uses a near-ballistic uni-traveling-carrier photodiode (NBUTC-PD)-based photonic transmitter-mixer. This device consists of an active NBUTC-PD integrated with a planar passive circuit for feeding the intermediate-frequency (IF) modulation input and extracting the up-converted optical-to-electrical (O-E) output signals. An equivalent-circuit model is developed, which allows for the O-E and IF responses to be independently optimized. Accordingly, we can achieve both an ultra-wide O-E bandwidth (67-118 GHz) and IF modulation bandwidth (>;15 GHz) with a very-low coupling loss (<; 2 dB) from the NBUTC-PD to the WR-10 waveguide. We adopted a remotely distributed 1-ps optical pulse train source with a repetition rate at 93 GHz to serve as a high-performance photonic carrier, which is generated by a spectral line-by-line shaper utilizing the repetition-rate multiplication (RRM) technique. In contrast to lossy amplitude filtering, our RRM is based on applying periodic loss-less spectral phase filtering onto the 31-GHz comb lines. In comparison with the conventional 93-GHz sinusoidal carrier, the photogenerated millimeter-wave (MMW) power of this kind of carrier is 4 dB higher than that of PD under the same output photocurrent. In contrast to the traditional mode-locked laser, the fiber dispersion can be totally precompensated without additional dispersion compensation components. By use of such device and optical MMW source, we successfully demonstrate remotely distributed and up-converted 20-Gbit/s error-free OOK wireless data transmission link over a 25-km standard single-mode fiber.

Linear-Cascade Near-Ballistic Unitraveling-Carrier Photodiodes With an Extremely High Saturation Current–Bandwidth Product

Saturation current-bandwidth product (SCBP), the key of figure of merit in high-speed and high-power photodiodes (PDs), is mainly limited by the tradeoff between carrier drift time in depletion layer and RC-limited bandwidth of conventional PDs. Here, we present a revolutionary photodiode structure: linear-cascade photodiodes (LCPDs), designed to further improve the SCBP performance. Our demonstrated LCPD structure can greatly increase the SCBP without using a complex distributed structure of the traveling-wave PD or reducing the load resistance (output RF power). Two flip-chip bonding packaged near-ballistic unitraveling-carrier photodiode (NBUTC-PD) units are employed in our LCPD structure. It exhibits a great improvement in SCBP compared to that of the control device with a single NBUTC-PD. A two-port equivalent-circuit model is established for the LCPDs and the modeling results clearly indicate that the increase in SCBP can be attributed to the significant reduction in its total capacitance due to the serial connection. Furthermore, we find that only when each PD unit in the LCPD structure has the same amount of injected optical power and modulated frequency of optical signal, the whole structure exhibits a carrier transit time as short as that of a single PD. Under the proper optical excitation, we can achieve a record high SCBP (7500 mA·GHz and 100 GHz) for two-element LCPDs under a 50 Ω load.

Spectral Power Enhancement in a 100 GHz Photonic Millimeter-Wave Generator Enabled by Spectral Line-by-Line Pulse Shaping

We report generation of high-modulation-depth photonic millimeter-wave (MMW) waveforms by applying line-by-line pulse shaping on a phase-modulated continuous-wave frequency comb. The optimized 20 and 100 GHz optical waveforms are then converted into electrical MMW signals using a near-ballistic uni-traveling-carrier photodiode (NBUTC-PD). A 7.4 dB MMW power enhancement is experimentally achieved by using 2.6 ps optimized pulses at a 100 GHz repetition rate, as compared with excitation by a conventional sinusoidal signal for the NBUTC-PD operated at the same photocurrent. This is in qualitative agreement with a theoretical analysis of spectral power enhancement by optical short pulses comprised of equi-amplitude frequency lines over sinusoidal excitation.

100 GHz ultra-wideband (UWB) fiber-to-the-antenna (FTTA) system for in-building and in-home networks

Fiber-to-the-antenna (FTTA) system can be a cost-effective technique for distributing high frequency signals from the head-end office to a number of remote antenna units via passive optical splitter and propagating through low-loss and low-cost optical fibers. Here, we experimentally demonstrate an optical ultra-wideband (UWB) - impulse radio (IR) FTTA system for in-building and in-home applications. The optical UWB-IR wireless link is operated in the W-band (75 GHz - 110 GHz) using our developed near-ballistic unitraveling-carrier photodiode based photonic transmitter (PT) and a 10 GHz mode-locked laser. 2.5 Gb/s UWB-IR FTTA systems with 1,024 high split-ratio and transmission over 300 m optical fiber are demonstrated using direct PT modulation.

W-Band Wireless Data Transmission by the Integration of a Near-Ballistic Unitraveling-Carrier Photodiode With a Horn Antenna Fed by a Quasi-Yagi Radiator

We demonstrate a novel W-band photonic transmitter mixer, which is composed of a planar quasi-Yagi radiator for feeding a WR-10 waveguide-based horn antenna and a near-ballistic unitraveling-carrier photodiode. The module demonstrates reasonable coupling loss in terms of the millimeter-wave (MMW) power launched from the integrated radiator into the WR-10 waveguide. With the bias-modulation technique and an optical MMW source, we can successfully achieve a wireless data transmission of 2.5-Gb/s quadrature phase shift keying at a carrier wave frequency of 102.5 GHz with a transmission distance of over 2.3 m.

Near-Ballistic Unitraveling-Carrier Photodiode-Based V-band Optoelectronic Mixers With Low Upconversion Loss and High Operation Current Performance Under Optical IF Signal Injection

We demonstrate near-ballistic unitraveling-carrier photodiode (NBUTC-PD)-based V-band (50-75 GHz) optoelectronic (OE) mixers which can upconvert the V-band optical local-oscillator (LO) and intermediate-frequency (IF) signals. The optical LO and IF signals share a single erbium-doped optical fiber amplifier (EDFA) which means that the mixing performance of the device can be optimized by properly adjusting the ratio between the injected optical LO and IF power to the EDFA. The utilization of the strong nonlinearity of the ballistic transport of the electrons in the NBUTC-PD under a reverse bias regime means that our device achieves a low upconversion loss ( -6 dB) under a very high operating current (23 mA) in V-band (60 GHz). We are able to improve the operating current at the V-band over that previously reported for UTC-PD-based OE mixers. This is made possible by an increase in the optimum operating voltage from the near forward bias (0 V) to the reverse bias regime (-1.7 V).

A $W$-Band Photonic Transmitter/Mixer Based on High-Power Near-Ballistic Uni-Traveling-Carrier Photodiode (NBUTC-PD)

In this letter, we demonstrate a W-band photonic transmitter/mixer fabricated by the flip-chip bonding of a high-power back-illuminated near-ballistic uni-traveling-carrier photodiode (NBUTC-PD) and an end-fire quasi-Yagi antenna on an AlN substrate. This end-fire and directional antenna design eliminates the need for the integration of an additional Si-lens into the antenna for directional power transmission. The high bias dependent nonlinearity of the integrated NBUTC-PD means that the bias modulation technique can be used to directly up-convert the intermediate-frequency signal to a millimeter-wave signal at W-band without using a costly high-speed optical modulator. A reasonable detected power (-17 dBm at 106 GHz) can be achieved with the demonstrated device with a high-output photocurrent (30 mA) and a low internal-conversion loss (-2.4 dB) between the radio-frequency and local-oscillator signals at W-band.

Dynamic Analysis of High-Power and High-Speed Near-Ballistic Unitraveling Carrier Photodiodes at $W$-Band

In this letter, we demonstrate and analyze the high-speed and high-power performance of a back-illuminated near-ballistic unitraveling-carrier photodiode (PD) at TV-band. We utilize a three-port equivalent-circuit-modeling technique to show that the extracted average electron drift velocity in the whole epi-structure is around 5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s, which corresponds to an ultrahigh transit time limited bandwidth (~400 GHz). Such high internal bandwidth means that the demonstrated device can thus release the burden imposed on downscaling the device active area and epi-layer thickness for achieving ultrahigh-speed performance of PDs. With a collector thickness of 410 nm and an active area of 64 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , we can achieve a wide 3-dB bandwidth (120 GHz), and high saturation current bandwidth product performance (120 GHz, 24.6 mA, 2952 mAGHz) under 25 Omega loading at W-band.

Analytical modeling of a high-performance near-ballistic uni-traveling-carrier photodiode at a 1.55-/spl mu/m wavelength

We developed an analytical equivalent circuit model, which includes the resistance-capacitance-delay time and carrier transport time, to investigate the distinct dynamic performance of the near-ballistic uni-traveling-carrier photodiode (NBUTC-PD). This device, in which the structure of the collector of the UTC-PD is modified, can achieve excellent performance at a 1.55-μm wavelength. According to the measured frequency responses of the scattering (S) parameters of NBUTC-PD and detailed device-modeling, the observed significant reduction of the device capacitance and the enhancement of the net optical-to-electrical bandwidth under high-power operation can be attributed to the unique near-ballistic-transport property of the photogenerated electron, which has never been observed in the traditional high-speed high-power photodiode.