The growing demand for bandwidth and energy efficiency requires new solutions for signal detection and processing. We demonstrate a concept for high-bandwidth signal detection with low-speed photodetectors and electronics. The method is based on the parallel optical sampling of a high-bandwidth signal with sinc-pulse sequences provided by a Mach-Zehnder modulator. For the electronic detection and processing this parallel sampling enables to divide the high-bandwidth optical signal with the bandwidth <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B$</tex-math></inline-formula> into <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> electrical signals with the baseband bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B/(\text{2}\,N)$</tex-math></inline-formula> . In proof-of-concept experiments with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N=3$</tex-math></inline-formula> , we present the detection of 24 GHz optical signals by detectors with a bandwidth of only 4 GHz. For ideal components, the sampling and bandwidth down-conversion does not add an excess error to the signals and even for the non-ideal components of our proof-of-concept setup, it is below 1%. Thus, the rms error for the measurement of the 24 GHz signal was reduced by a factor of about 3.4 and the effective number of bits were increased by 1.8. 

/pdf/high-bandwidth-arbitrary-signal-detection-using-low-speed-3defeqd1.pdf

High-Bandwidth Arbitrary Signal Detection Using Low-Speed Electronics

Low-power receivers use direct-detection receiver architecture for its design simplicity and its low power dissipation. However, the direct-detection based receivers suffer from co-channel interference which significantly degrades the communication reliability. Co-channel interference robustness can be improved by using a BPSK Barker code modulated Surface Acoustic Wave (SAW) correlator as a prior stage to the RF direct detection circuit. This paper reports in details the design, fabrication and measurements of a 2.45 GHz SAW correlator with 13 bits length Barker code. The device is fabricated on Lithium Niobate LiNbO3 substrate and it is composed of an input non-coded Inter Digital Transducers (IDT), a Piezoelectric substrate and an output coded IDT. The device wavelength λ is set to 1.6 µm, considering a phase velocity of the wave equal to 3970 m.s-1. Several configurations of the device were designed and fabricated, particularly varying the aperture and the non-coded IDT length to find out the optimal device configuration. All devices were found to operate with Insertion Loss (IL) ranging from 12 to 15 dB at 2.45 GHz with a tip probing measurement setup, while a packaged sample has an IL of 12.45 dB at 2.44 GHz mounted on a PCB with external 50 Ω LC matching network. Additionally, time-domain measurement for the packaged device shows that the output has a correlation peak with a peak-to-side-lobe (PSL) ratio of 4:1 for a −0.5 dBm input BPSK Barker code signal.

Design and Fabrication of Barker Coded Surface Acoustic Wave (SAW) Correlator at 2.45 GHz for Low-Power Wake-up Receivers

This article analyses the effect of noise and nonlinearity in optoelectronic phase-locked loops (OEPLLs). The OEPLL phase-locks a microwave oscillator on the envelope of the optical pulse train from a mode-locked laser (MLL). The phase detector of this type of OEPLL is called a balanced optical microwave phase detector (BOMPD) and operates in a mixed electro-optical domain. The main noise sources in a BOMPD, such as shot noise of photodiodes, generation-recombination noise of photodiodes, relative intensity noise of the laser, and noise of the bias voltage applied to the BOMPD. are discussed. The nonlinear behavior of the BOMPD with respect to the intensity of the optical field and the amplitude of the RF voltage is discussed. An OEPLL that can lock on the harmonics and interharmonics of the MLL repetition rate is demonstrated. The OEPLL has an in-band phase noise of below −150 dBc/Hz at 100-kHz offset frequency for a carrier frequency of 10 GHz. This phase noise level is 10–20 dB better than state-of-the-art commercial frequency synthesizers. 

/pdf/noise-processes-and-nonlinear-mechanisms-in-optoelectronic-34pf7xwx.pdf

Noise Processes and Nonlinear Mechanisms in Optoelectronic Phase-Locked Loop Using a Balanced Optical Microwave Phase Detector

This paper presents an ultralow phase noise 77 GHz frequency synthesizer for long range radar. The system consist of an optoelectronic phase-locked loop using a mode-locked laser as a reference clock and a frequency multiplier chip for the upconversion in the 77 GHz radar band. The presented system achieves a channel spacing of 1 GHz around the 77 GHz radar frequency with a phase noise better than -120 dBc/Hz at offset frequencies above 30 kHz.

A Low Phase Noise 77 GHz Frequency Synthesizer for Long Range Radar

This paper presents system level design and measurements of a novel 2. 4GHz low-power and low-data-rate receiver, which uses Barker-coded Binary Phase-shift keying (BPSK) along with Pulse Position Modulation (PPM) as a communication scheme. To achieve low-power dissipation levels, direct-detection receiver architecture is used in combination with a 13-bits Barker Code Surface Acoustic Wave (SAW) correlator to improve co-channel interference. Furthermore, in order to improve receiver sensitivity, the baseband bandwidth is reduced by means of an innovative Narrowband Correlator (NBC), which allows for scalable receiver sensitivity versus data-rate. The receiver can be used as a Wake-up Receiver (WuRx) in Wireless Sensor Networks (WSNs) to minimize the power dissipation and provide asynchronous and on-demand data communication. The receiver is designed using TSMC65n technology and achieves a power dissipation of 142 $\mu$W from 1. 2V supply source and sensitivity of −44 and −50dBm at a data-rate of 2Mbps and 600 kbps respectively.

Low-Power Low-Data-rate Wireless PPM Receiver Based on 13-Bits Barker Coded SAW Correlator with Scalable Data-rate and Sensitivity

This paper presents an ultra-wideband and ultra-low noise frequency synthesizer using a mode-locked laser as its reference. The frequency synthesizer can lock in the frequency range from 2 GHz to 20 GHz on any harmonic of a mode-locked laser optical pulse train. The integrated rms-jitter (1 kHz-100 MHz) of the synthesizer is less than 5 fs in the frequency range from 4 GHz to 20 GHz with a typical value of 4 fs and a minimum of 3 fs. This is the first reported wideband phase locked loop achieving sub-l0 fs rms-jitter for offset frequencies larger than 1 kHz.

Wide-Band Frequency Synthesizer with Ultra-Low Phase Noise Using an Optical Clock Source

Using direct-detection architecture in Radio Frequency (RF) receivers allows for ultra-low power dissipation and is often used in Wake-Up receivers. Unfortunately direct-detection receivers suffer from high sensitivity to co-channel interference which reduces the communication performance and reliability. In this paper, it is shown that co-channel interference robustness of direct-detection receivers is improved by using Binary Phase Shift Keying (BPSK) Barker code modulated Surface Acoustic Wave (SAW) correlator as a prior stage to the RF envelope detector. Replacing the band select filter with SAW correlator does not result in higher receiver hardware cost. In our receiver, the SAW correlator functions as a passive signal processor, providing gain for a BPSK Barker code modulated signal, while suppressing in-band interferers. This improves the co-channel interference robustness of the direct-detection receiver while preserving its advantage of power efficiency. The concept is verified by means of a direct-detection receiver with discrete components on an RF PCB including an SAW Barker Code correlator at a center frequency of 2.44 GHz fabricated on Lithium Niobate substrate. Measurements with WiFi signals demonstrate that the interference robustness is improved by more than 10 dB compared to a conventional direct-detection receiver.

Saeed Fard

Papers

Wide-Band Frequency Synthesizer with Ultra-Low Phase Noise Using an Optical Clock Source

Improving Co-Channel Interference Robustness In Direct Detection Receivers Using A Surface Acoustic Wave (SAW) Correlator