Optical phase lock loop as high-Q filter for optical frequency comb line selection

Broadband Access Communication Technologies XIII

Thakur

et al. 2019

In this paper we present two different techniques for photonic generation of millimeter and THz waves. Each of them tackles the phase noise problem associated with optical sources in a different way. The first one relays on the heterodyne down-conversion of two phase noise correlated optical tones. The correlation is achieved by generation of an optical frequency comb. To select one of the optical lines we use an optical phase lock loop, which besides enabling a frequency offset between output and input, can provide optical gain and is highly selective. The second one relays on the envelope detection of a single sideband-with carrier signal. In this approach the photonic remote antenna unit is implemented as monolithically integrated photonic chip.

Section: Opll Resultsmentioning

confidence: 99%

Photonic systems for tunable mm-wave and THz wireless communications

Gonzalez-Guerrero

Broadband Access Communication Technologies XIII

Thakur

et al. 2019

“…When the OPLL is active, the phase noise of the generated carrier is kept at the low level within the loop bandwidth until the power rise of the sideband peaks (which remains less than −55 dBm). The sideband peaks are measured to be 48 dB lower than the generated carrier at resolution bandwidth of 300 kHz, and can be reduced even further by adjusting the loop gain [31]. Furthermore, the phase noise of the heterodyne mixing of the OPLL output with an optical comb line spaced at 34 GHz, 231 GHz, 234 GHz, 236 GHz, and 244 GHz were measured using a Rohde&Schwarz FSU43 spectrum analyzer, and compared with the phase noise of the RF synthesizer (operating at 15 GHz) used to generate the comb lines, as shown in Fig.…”

Section: Frequency Tuneability Using Optical Phase Lock Loop (Opll)mentioning

confidence: 99%

Optical Frequency Tuning for Coherent THz Wireless Signals

Shams

Gonzalez-Guerrero

et al. 2018

J. Lightwave Technol.

THz wireless signals have become of interest for future broadband wireless communication. In a scenario where the wireless signals are distributed to many small remote antenna units, this will require systems which allow flexible frequency tuning of the generated THz carrier. In this paper, we demonstrate experimentally the implementation of two tuning methods using an optical frequency comb generator for coherent optical frequency tuning in THz wireless-over-fiber systems. The first method is based on using a photonic integrated circuit optical phase lock loop (OPLL) subsystem implemented as a high quality optical filter for single comb line selection and optical amplification. The OPLL generates an optical carrier, which is frequency and phase stabilized in reference to one of the optical comb lines with a frequency offset precisely selectable between 4 and 12 GHz. The second method is based on optical single sideband suppressed carrier (SSB-SC) modulation from the filtered comb line using an optical IQ modulator. With this technique, it is possible to suppress the other unwanted optical tones by more than 40 dB. This generated optical carrier is then heterodyned with another filtered optical comb line to generate a tuneable and stable THz carrier. The full system implementations for both methods are demonstrated by transmitting THz wireless signal over fiber with 20 Gb/s data in QPSK modulation. The system performance and the quality of the generated THz carrier are evaluated for both methods at different tuned THz carrier frequencies. The demonstrated methods confirm that a high quality tuneable THz carrier can easily be implemented in systems where dynamic frequency allocation is required.

“…8 demonstrates how varying the RF amplifier gain from 19 dB to 31 dB results in the loop bandwidth changing from approximately 20 MHz to 100 MHz. As defined in [33] and [34] the loop bandwidth is indicated by the offset of the side peaks from the heterodyne carrier. As the loop gain increases (as a result of increasing the gain of the RF amplifier), the phase noise close to the carrier frequency is suppressed, the offset frequency of the side peak increases and eventually the power of the side peaks rise [33], [34].…”

Section: Opll Locking and Tuneabilitymentioning

confidence: 99%

Optical Phase Lock Loop as High-Quality Tuneable Filter for Optical Frequency Comb Line Selection

Shams

Fice

et al. 2018

J. Lightwave Technol.

This paper describes an optical phase lock loop (OPLL) implemented as an ultraselective optical frequency comb line filter. The OPLL is based on a photonic integrated circuit (PIC) fabricated for the first time through a generic foundry approach. The PIC contains a distributed Bragg reflector (DBR) laser whose frequency and phase are stabilized by reference to an optical frequency comb generator. The OPLL output is a single-mode DBR laser line; other comb lines and noise at the output of the OPLL filter are attenuated by >58 dB below the peak power of the OPLLfilter output line. The OPLL bandwidth is up to 200 MHz, giving a filter quality factor greater than 1,000,000. The DBR laser can be tuned over 1 THz (8 nm), enabling different comb lines to be selected. Locking to a comb line with a frequency offset precisely selectable between 4 and 12 GHz is also possible. The coherence between the DBR laser and the comb lines is demonstrated by measurements of the heterodyne signal residual phase noise level, which is below −100 dBc/Hz at 5 kHz offset from the carrier. The OPLL-filter output can be up to 6 dB higher than the peak power of the comb line to be isolated by the filter. This optical gain is a unique characteristic which can significantly improve the SNR of communication or spectroscopy systems. This OPLL is envisaged to be used for high purity, tuneable microwave, millimetre-wave, and THz generation.