Balanced Photodiodes Research Articles

Balanced InP/InGaAs Photodiodes With 1.5-W Output Power

We report InP/InGaAs modified unitraveling-carrier balanced photodiodes (PDs). The back-illuminated PDs were flip-chip bonded on diamond submounts for enhanced heat sinking. The device demonstrated a 3-dB bandwidth of 8 GHz and a 30-dB common-mode rejection ratio at frequencies of 320 mA, maximum output power of 31.7 dBm (1.5 W) into a 50-Ω load, and good linearity with a third-order intercept point of up to 47 dBm were measured at the 3-dB bandwidth frequency of 8 GHz.

Monolithic InP receiver chip with a 90° hybrid and 56 GHz balanced photodiodes

We demonstrate a monolithically integrated quadrature coherent receiver photonic integrated circuit on an InP substrate with a 90° optical hybrid and two balanced 56 GHz pin-photodetectors on chip level and as a packaged device. The presented devices enable the use of 56/64 Gbaud dual polarisation 16-QAM signals either in the C-band or the L-band.

Design of coherent receiver optical front end for unamplified applications

Advanced modulation schemes together with coherent detection and digital signal processing has enabled the next generation high-bandwidth optical communication systems. One of the key advantages of coherent detection is its superior receiver sensitivity compared to direct detection receivers due to the gain provided by the local oscillator (LO). In unamplified applications, such as metro and edge networks, the ultimate receiver sensitivity is dictated by the amount of shot noise, thermal noise, and the residual beating of the local oscillator with relative intensity noise (LO-RIN). We show that the best sensitivity is achieved when the thermal noise is balanced with the residual LO-RIN beat noise, which results in an optimum LO power. The impact of thermal noise from the transimpedance amplifier (TIA), the RIN from the LO, and the common mode rejection ratio (CMRR) from a balanced photodiode are individually analyzed via analytical models and compared to numerical simulations. The analytical model results match well with those of the numerical simulations, providing a simplified method to quantify the impact of receiver design tradeoffs. For a practical 100 Gb/s integrated coherent receiver with 7% FEC overhead, we show that an optimum receiver sensitivity of -33 dBm can be achieved at GFEC cliff of 8.55E-5 if the LO power is optimized at 11 dBm. We also discuss a potential method to monitor the imperfections of a balanced and integrated coherent receiver.

The Performance of a Fiber-Optic Link Using Unbiased Balanced Photodiodes for Antenna Array Calibration

A quadrature-biased dual-output Mach-Zehnder modulator is used to drive unbiased balanced photodiodes for use in antenna array applications. The RF gain is measured as a function of frequency and photocurrent. Balanced photodiode two-tone measurements at 6 GHz are compared with those of a single photodiode to show 26-dB suppression of the second-order distortion. This results in a second-order limited spur-free dynamic-range improvement of 12 dB. The phase error introduced in unbiased photodiodes is compared to that of the biased case to demonstrate that it would have minimal effect on the performance of the antenna array system.

Monolithic InP Dual-Polarization and Dual-Quadrature Coherent Receiver

We realized a monolithic dual-polarization dual-quadrature coherent receiver with balanced detection on InP using a single epitaxial step. It monolithically integrates the polarization splitters, 90° hybrids, and balanced photodiodes in 4.1 mm2 . We demonstrate reception of 112-Gb/s polarization-division-multiplexed quadrature phase-shift keying with 17.3-dB optical signal-to-noise ratio at 10-3 bit-error rate.

InP/InGaAsP-Based Integrated 3-dB Trench Couplers for Ultra-Compact Coherent Receivers

We present the design, fabrication, and test results for ultra-compact 3-dB frustrated total internal reflection-based trench couplers in an InP/InGaAsP monolithic integration platform. The trench coupler is integrated with phase modulators and a balanced photodiode (BPD) pair to enable a 180° hybrid ultra-compact coherent receiver. Several trench splitter designs exhibit near 3-dB splitting with a loss of 3 dB. The BPD pair is used to characterize coherent mixing of two input optical signals into the trench splitter, and coherence efficiency of 75% is achieved.

Background-Free Arbitrary Waveform Generation via Polarization Pulse Shaping

A new technique for photonic synthesis of background-free arbitrary electrical waveforms is demonstrated. Optical intensity waveforms exhibiting complementary modulation are synthesized via polarization pulse shaping; balanced photodetection is then utilized to suppress the waveform pedestal in the electrical domain. This work demonstrates more than 25-dB suppression of unwanted low-frequency content which is within 5 dB of the limit set by the balanced photodiode.

Tb/s Coherent Optical OFDM Systems Enabled by Optical Frequency Combs

This paper discusses the realization of terabit per second high speed and high spectral-efficiency optical transmissions using much lower speed electronics and optoelectronics through parallel processing of coherent optical frequency combs at both the transmitter and receiver. The coherent and parallel processing enables electrical-to-optical and optical-to-electrical (E/O and O/E) conversion of wide-bandwidth optical signals which would otherwise exceeds the capability of conventional optoelectronics. In the first experiment, an optical frequency comb (OFC) generator provides 32 comb lines with less than 5-dB power variation. Subsequently, 1.008-Tb/s modulation capability is realized on 32 × 106 OFDM subcarriers with 16-QAM modulation in a 318-GHz seamless optical bandwidth. It demonstrates an effective way to generate an optical OFDM signal with tens of times wider optical bandwidth than that of analog-to-digital converters and digital-to-analog converters (ADC/DAC). The second experiment demonstrates simultaneous detection of multiple OFDM bands from a 32-band coherent optical OFDM signal using another optical frequency comb, a silica planar lightwave circuit (PLC) that implemented the major optical devices, and two pairs of balanced photodiodes. The experimental results indicate prospects for an optically integrated coherent optical OFDM system on a chip-scale platform.

Characterization of the common mode rejection ratio of amorphous silicon balanced photodiode

AbstractIn this work we report on the detailed characterization of an amorphous silicon/amorphous silicon carbide balanced photodiode structure suitable for differential photocurrent measurements. The device is a three‐terminal structure constituted by two series‐connected amorphous silicon p‐i‐n photodiodes. Two terminals are used to bias the two photodiodes at the same reverse voltage by the readout electronics. The output signal is the current difference between the two diodes, measured at the third terminal with a transimpedance circuit.Several devices have been fabricated with different areas and geometries utilizing four mask‐step process. The devices have been characterized by means of common mode rejection ratio (CMRR) measurements as a function of the radiation wavelength and intensity. The CMRR measured under white light illumination has been found to lie around 37 dB in the whole range of investigated radiation intensities. The decrease of the CMRR observed at shorter wavelengths has been ascribed to mismatches and inhomogeneities in the surface and in the p‐type window layer of the two hemi‐devices. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Compact optical 90° hybrid employing a tapered 2×4 MMI coupler serially connected by a 2×2 MMI coupler

We propose a novel optical 90 degrees hybrid employing a paired-interference-based tapered 2x4 multimode interference coupler and a 2x2 multimode interference coupler. It was experimentally shown that the proposed 90 degrees hybrid has very short device length of less than 227 mum and is never accompanied by any waveguide intersections for coupling to balanced photodiodes. The proposed device exhibited quadrature phase response with a common-mode rejection ratio of more than 20dB and a phase deviation of less than 5 degrees over C-band spectral range.

Monolithic Polarization and Phase Diversity Coherent Receiver in Silicon

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we realized a monolithic silicon photonic integrated circuit (PIC) for polarization and phase diversity coherent detection. The PIC includes two polarization beam splitters, two 90<formula formulatype="inline"> <tex Notation="TeX">$^{\circ}$</tex></formula> optical hybrids, and four pairs of balanced photodiodes implemented as integrated germanium detectors. We tested the PIC using polarization-division multiplexed quadrature phase-shift keyed signals at 43 and at 112 Gb/s. </para>

Optical 90° hybrid with broad operating bandwidth of 94 nm

We propose an optical 90 degree hybrid where no waveguide intersection in coupling to balanced photodiodes is required for coherent detection. The proposed device consisting of a paired-interference 2x4 multimode interference (MMI) coupler, a phase shifter, and a 2x2 MMI coupler exhibited quadrature phase response over a 94-nm-wide spectral range.

Amorphous silicon balanced photodiode for detection of ultraviolet radiation

In this work, we present a new amorphous silicon balanced photodiode, which takes advantage of the differential measurement to reveal very small variations of photocurrent in a large background current signal. The device has been fabricated with a four-mask process and characterized in dark and under 365 nm monochromatic ultraviolet radiation. Results have demonstrated the ability of the structure to detect differential currents three orders of magnitude lower than the current flowing in each sensor. Common mode rejection ratio (CMRR) values around 42 dB have been found comparable with those obtained in other crystalline differential diode structures. The CMRR resulted constant with both the reverse bias voltage and the radiation intensity.

Innovative Amorphous Silicon Balanced Ultraviolet Photodiode

An innovative balanced photodiode structure made in amorphous silicon/amorphous silicon carbide, suitable for detecting small current variations on a large background signal, is presented and characterized. The structure is a three-terminal device, constituted by two series-connected n-i-p photosensors, where the output signal is the difference between the currents flowing through the two diodes. The layer thickness and optical properties of the thin-film materials and the geometry of the structure have been optimized for the detection of ultraviolet radiation. Common mode rejection ratio (CMRR) values ranging between 30 dB at 254 nm and 42 dB at 365 nm have been measured, independent on the bias voltage. The decrease of the CMRR at lower wavelengths has been ascribed to differences in the surfaces of the two diodes exposed to the light.

A High Bandwidth Analog Heterodyne RF Optical Link With High Dynamic Range and Low Noise Figure

We demonstrate a 1.55-μm wavelength 5-GHz analog heterodyne optical link employing an integrated balanced photodiode (BPD) with a noise figure of (20/spl plusmn/1) dB and spurious-free dynamic range of (102/spl plusmn/2) dB/spl middot/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 3/. A wide-band rectifier narrow-band receiver architecture is employed to allow for phase noise cancellation. The advantage of BPD over a single photodiode is also explored.

A Monolithically Integrated Long-Wavelength Balanced Photodiode Using Asymmetric Twin-Waveguide Technology

We demonstrate a long-wavelength monolithically integrated photodiode pair balanced to within 0.4 dB. The (15/spl plusmn/1) GHz bandwidth balanced photodiode pair has minimum dark current of 5 nA, a responsivity of (0.32/spl plusmn/0.02) A/W at 1.55-/spl mu/m wavelength, linearity up to +3-dBm input optical power, and a common mode rejection ratio of (34/spl plusmn/2) dB. The asymmetric twin-waveguide architecture used makes it possible for integration of the detector pair with other optical components such as semiconductor optical amplifiers, lasers, modulators, and in-plane waveguide-filters.

Femtosecond coherence spectroscopy using spectrally selective differential photodetection

We present a novel, spectrally selective, detection scheme for pump–probe femtosecond coherence spectroscopy (FCS) that attenuates the non-oscillatory background signal so that the coherent oscillations are more clearly revealed. The method is based on spectral dispersion of the probe beam after it has traversed the sample, followed by detection of spectrally specific portions with a differential detector containing two balanced photodiodes. By appropriately choosing the spectral windows detected by each photodiode, we show how vibrational oscillations can be selectively enhanced or suppressed. Information about the phase behavior of the vibrational modes is also revealed using this detection scheme.

Precession dynamics in NiFe thin films, induced by short magnetic in-plane field pulses generated by a photoconductive switch.

Short magnetic in-plane field pulses were used to pull the magnetic spin system of a NiFe film out of its equilibrium state and to initiate coherent magnetisation dynamics. This field induced dynamics was investigated by means of a time-resolved pump-probe experiment, measuring the linear Kerr effect with a balanced photodiode scheme. Precession frequencies of several GHz and relaxation-times in the nanosecond range were observed. Emphasis is on the generation of the short magnetic in-plane field pulses. They were generated using an ultrafast photoconductive switch based on GaAs and launched by a waveguide to the sample. The waveguide and the photoswitch were designed to yield as large as possible magnetic field strengths. The field pulses used in this work had a rise time of 10-60ps, a decay time of 500-700ps and a maximum field strength of 9Oe.

Fabrication of a heterodyne receiver OEIC with optimized integration process using three MOVPE growth steps only

An optimized integration process is reported requiring only three epitaxial growth steps for the fabrication of an OEIC encompassing a single-mode laser, a waveguide element, and fast photodiodes. The process was applied to the fabrication of a heterodyne receiver including a semi-insulating buried heterostructure (SIBH)-DFB-laser with an output power of 14 mW and a side-mode suppression ratio greater than 40 dB, a 3-dB coupler, and high-speed balanced photodiodes with a bandwidth of 9 GHz. The laser can also be used as a transmitter laser exhibiting a modulation bandwidth of 11 GHz.

Instrumentation for multistep excitation of lithium atoms to Rydberg states

We have developed a diode laser apparatus to excite Li from its ground 2S state, through 2P and 3S, to its Rydberg states with three cw diode lasers operating at λ = 671 nm, 813 nm, and 630-635 nm. A He-Ne laser at λ = 633 is sometimes used in place of the 635-nm diode laser for the last step. The output power of each of these lasers was ~1 mW. We describe our technique of locking the first two lasers on Li resonance lines by obtaining a fluorescent signal from the second decay (3S ? 2P) that is normally overpowered by a strong background of fluorescent light from the first decay (2P ? 2S). We used two balanced photodiodes to reject the strong fluorescent light without loss of collection efficiency. A rejection ratio as high as 100 has been obtained.