Optical Injection Phase-lock Loop Research Articles

Simultaneous BPSK classical communication and continuous variable quantum key distribution with a locally local oscillator regenerated by optical injection phase locked loop

This paper proposes a scheme for simultaneous classical communication and continuous variable quantum key distribution with a true local oscillator. In this scheme, the emitter’s laser, after binary phase-shift keying (BPSK) modulation, is multiplexed in polarization with the quantum signal and sent to the receiver. After BPSK demodulation and correction, this signal is used for local oscillator regeneration by an optical injection phase-locked loop method. Comparing the effective noise sources in this scheme with typical local local oscillator schemes revealed that continuous variable quantum key distribution (CV-QKD) with a true local oscillator based on the optical injection phase-locked loop encounters lower levels of noise in comparison to the pre-existing genuine local oscillator CV-QKDs.

Frequency Synchronization and Coherent Combining of Two Fiber Ring Cavities

Low noise synchronization of the frequency and phase of a DFB fiber laser and two fiber ring cavities was achieved based on a two-channel optical injection lock and phase lock loop. Two-channel modulation signals of different frequencies were adopted to extract the phase noise signals of the two fiber ring cavities. Finally, the lasers from the two fiber ring cavities were coherently combined in the closed loop of the control system owing to the synchronous frequency and phase. The power stability and polarization stability of the combined laser was improved under the optical injection lock and phase lock loop. The phase noise of the two cavities was $6.56 \times 10^{-7}$ rad/Hz1/2 and $1.34 \times 10^{-6}$ rad/Hz1/2 at 10 Hz; and $7.77 \times 10^{-8}$ rad/Hz1/2 and $1.35 \times 10^{-7}$ rad/Hz1/2 at 10 kHz. The total combined power was ~580 mW in the closed loop, and the entire system oscillated under a single frequency, providing excellent power scaling ability.

On the pull-in behavior of optical injection phase-lock loop

This paper presents a detailed study of the pull-in behavior of an optical injection phase-lock loop (OIPLL) neglecting the noise components of the loop. We provide formulas for pull-in voltage and pull-in range of OIPLL in terms of the loop propagation delay, line-width enhancement factor and other parameters of the loop. In addition, we give a compact expression for the frequency pulling time of OIPLL for low injection and high injection level in presence of loop-delay. The effects of loop-delay and optical injection on the pull-in performance of the OIPLL are studied for non-zero values of line-width enhancement factor. Analytical expression of the maximum allowable loop delay is presented to study the deterministic stability of the loop. From the stochastic stability of the loop, we provide formula for the maximum value of the laser line-width to achieve the desired tracking performance. The simulation results are given in partial support of the conclusions of the analysis.

High-Gain Optical Injection Locking Amplifier in Phase-Coherent Optical Frequency Transmission

Optical amplification, which is necessary for extending the distance of optical frequency transfer, has a significant impact on the transmission performance. In this paper, we propose a high-gain optical injection locking amplifier (OILA) with low phase noise based on an optical injection phase-locked loop for the phase-coherent optical frequency transmission. The high-gain OILA can provide more than 75-dB gain and ensure that the input carrier frequency fractional stability can reach 8.2 × 10 -20 at an averaging time of over 100 s. We then transfer a commercial narrow-linewidth laser over a 220-km fiber link with only one amplification step placed at the remote end. After eliminating the noise induced in the fiber link, the fractional frequency instability of the transferred frequency can reach 9.0 × 10 -16 at 1 s and 7.1 × 10 -20 at 20 000 s.

Relative stability analysis of optical injection phase-locked loop

In this paper, we analyze the relative stability of optical injection phase-locked loop (OIPLL) in terms of the phase margin considering loop-delay into account. Phase margin of first- and second-order OIPLL are calculated as a function of loop-delay, damping factor and other parameters of the loop. The effects of optical injection on damping factor and phase margin of the loop are shown. It is observed that the OIPLL has better stability than the conventional optical phase-locked loop (OPLL) in presence of loop-delay.

Optical injection locking-based amplification in phase-coherent transfer of optical frequencies.

We demonstrate the use of an optical injection phase locked loop (OIPLL) as a regenerative amplifier for optical frequency transfer applications. The optical injection locking provides high gain within a narrow bandwidth (<100 MHz) and is capable of preserving the fractional frequency stability of the incoming carrier to better than 10(-18) at 1000 s. The OIPLL was tested in the field as a mid-span amplifier for the transfer of an ultrastable optical carrier, stabilized to an optical frequency standard, over a 292 km long installed dark fiber link. The transferred frequency at the remote end reached a fractional frequency instability of less than 1×10(-19) at averaging time of 3200 s.

A Pilot-Carrier Coherent LEO-to-Ground Downlink System Using an Optical Injection Phase Lock Loop (OIPLL) Technique

A pilot-carrier coherent low-earth-orbit (LEO) satellite to ground (LEO-to-Ground) downlink system using an optical injection phase lock loop (OIPLL) technique is proposed and its feasibility under Doppler frequency shift conditions is demonstrated. A fiber-optic based experimental system is configured and it is demonstrated that a 10 Gbps BPSK transmission system based on the proposed configuration can successfully maintain stable frequency and phase locking status under simulated Doppler frequency shift conditions. It is demonstrated that the stable locking status is maintained over a 10.3 GHz (54 ppm) frequency offset with a maximum rate-of-change of up to 32.4 GHz/s (168 ppm/s), which is ample to meet the requirement for a coherent LEO-to-Ground downlink system. The locking capability of the experimental system for more rapidly changing Doppler frequency shift is investigated. It is shown that the OIPLL receiver remains locked for maximum rates of change of 2.6 THz/s (13 500 ppm/s) or more for peak-to-peak frequency offsets up to 2 GHz (10.7 ppm). The phase noise performance of the system is also investigated and phase noise power of less than -100 dBc/Hz at greater than 1 MHz offset frequency is achieved even if the received laser signal suffers from a simulated Doppler frequency shift with peak-to-peak frequency offset of 2.4 GHz (12.5 ppm) and maximum rate of change of 750 GHz/s (3 900 ppm/s).

Homodyne Coherent Optical Receiver Using an Optical Injection Phase-Lock Loop

We describe the operating principle, practical implementation, and experimental evaluation of a synchronous homodyne coherent optical receiver based on an optical phase-locking scheme that combines optical injection locking of the semiconductor laser local oscillator (LO) with low-speed electronic feedback to give both a large locking bandwidth and a wide tracking range. We demonstrate phase-error variance as low as 0.002 rad2 in 10-GHz bandwidth for locking to a continuous-wave (CW) signal for a combined signal and LO linewidth of 1.5 MHz (full-width at half-maximum), and robust phase locking to a 10-Gb/s binary amplitude-shift-keyed (ASK) signal, enabling synchronous back-to-back demodulation of the signal with low bit error ratio (BER <; 10- 10) and improved performance compared to direct detection at low optical SNR (OSNR). By locking to a low-power CW pilot carrier in the polarization orthogonal to the data signal, demodulation of binary phase-shift-keyed (BPSK) data has been achieved, with the required OSNR at BER = 10-3 reduced by 3 dB compared to demodulation of ASK data under the same conditions. The OSNR penalty after transmission of the ASK and BPSK signals over 40 km of standard single-mode fiber was 1-2 dB at BER = 10-3, indicating that the chromatic dispersion sensitivity of the coherent receiver is similar to that for direct detection, and verifying that the scheme for locking to the orthogonal pilot is applicable to transmission systems, provided that optical polarization tracking is employed. In addition, we demonstrate frequency-selective operation of the coherent receiver, demultiplexing and demodulating one of a pair of equal power, 10 Gb/s, ASK channels separated by 17.5 GHz, with OSNR penalty at BER = 10- 3 of 1.5 dB compared to single-channel operation.

Broadband access using wireless-over-fibre technologies

This paper describes a number of wireless-over-fibre technologies for broadband access which are being investigated in the Photonics Group at University College London (UCL). In particular, the paper will report the asymmetric Fabry-Perot modulator/detector (AFPM), functioning not only as an optical modulator in the uplink direction, but also as a conventional photodetector in the downlink direction in a single device. Compared to the existing waveguide type electro-absorption modulator, the AFPM is polarisation-insensitive to light, simpler to fabricate and uses only a single optical fibre for both uplink and downlink transmissions, and therefore has the potential to lower the costs of future picocell deployments. Direct modulation of a semiconductor laser is the simplest way to generate modulated optical signals. In the presence of multiple large modulation signals, however, intermodulation or inter-channel distortion can easily be generated in the semiconductor laser and affect other lower power neighbouring channels. A feed-forward linearisation technique for directly modulated semiconductor lasers, capable of operating at frequencies above 5 GHz, has been developed and will be described in detail in this paper. Most modern commercial buildings already have a multimode optical fibre (MMF) infrastructure for carrying the Ethernet data. To provide cost-effective and reliable indoor cellular and wireless local area network (WLAN) coverage without dependence on the radio penetration from outside base-stations, it is highly desirable that the same MMF infrastructure be used to carry these additional services between the equipment room and the remote antenna units around the building. Although not previously regarded as having sufficient bandwidth, it has now been shown that MMF can successfully carry microwave modulated optical signals, including GSM1800 and UMTS cellular radio. Use of MMF for multiservice, multioperator in-building radio coverage has been demonstrated in a collaboration between UCL and the University of Cambridge and will be described in this paper. As the number of cellular and broadband WLAN devices increases, the lower parts of the radio spectrum are becoming more and more congested. To meet the demand for ever higher data transmission rates, other parts of the radio spectrum are being considered for these applications, particularly the millimetre-wave region (30 GHz and above). One of the challenges facing such systems is the generation and delivery of a low phase noise precisely synchronised local oscillator signal. In this paper, a simple optical heterodyne source with two injection locked slave lasers and a more environmentally robust source using an optical injection phase lock loop will be described, together with signal distribution using a bidirectional semiconductor optical amplifier in a coarse wavelength division multiplex fibre ring architecture. Finally it will be argued in the conclusions that future broadband wireless-over-fibre access networks will be required to provide multiservice and multi-operator coverage for buildings, and having the required technologies at sufficiently low cost will be the key factor to success.

Nanosecond Channel-Switching Exact Optical Frequency Synthesizer Using an Optical Injection Phase-Locked Loop (OIPLL)

Experimental results are reported on an optical frequency synthesizer for use in dynamic dense wavelength-division-multiplexing networks, based on a tuneable laser in an optical injection phase-locked loop for rapid wavelength locking. The source combines high stability (<1-kHz channel frequency error over 5-K temperature change), with high output power (/spl sim/2dBm), wide tuning range (40 nm), high spurious suppression (>50 dB), narrow linewidth (10 MHz), and fast wavelength switching (<10 ns).

Generation and transmission of millimeter-wave data-modulated optical signals using an optical injection phase-lock loop

Generation and transmission of millimeter-wave data-modulated optical signals is presented using an optical injection phase-lock loop (OIPLL). Millimeter-wave signal generation is demonstrated with wide locking range, 30-GHz low phase noise level, -93 dBc/Hz, and a wide frequency tuning range, 4-60 GHz generation demonstrated using optical injection locking only, verified by using OIPLL in the 26-40 GHz range. The OIPLL is also used to transmit error-free 140-Mb/s amplitude shift keying and 68-Mb/s differential phase-shift keying (DPSK) modulated millimeter-wave signals over up to 65 km of uncompensated standard singlemode fiber. The DPSK system uses reference frequency modulation, eliminating the need for optical amplification.

A 65-km span unamplified transmission of 36-GHz radio-over-fiber signals using an optical injection phase-lock loop

We report generation and transmission of single side-band millimeter-wave modulated optical signals using a reference-modulated optical injection phase-lock loop. A 36-GHz 68-Mbit/s differential phase shift keyed signal is transmitted over a 65-km unamplified standard single-mode fiber using no dispersion compensation with a BER < 10/sup -9/.

36-GHz 140-Mb/s radio-over-fiber transmission using an optical injection phase-lock loop source

We report the first millimeter-wave radio-over-fiber transmission demonstration using optical phase-lock loop techniques. A 36-GHz 140-Mb/s ASK modulated carrier was transmitted through 65 km of standard single-mode fiber with a bit-error rate (BER) of <10/sup -9/, using an optical injection phase-lock loop based on fiber-pigtailed commercially available components.

Millimeter-wave modulated optical signal generation with high spectral purity and wide-locking bandwidth using a fiber-integrated optical injection phase-lock loop

We report the first experimental demonstration of millimeter-wave modulated optical signal generation by an optical injection phase-lock loop. A 36-GHz signal was generated by combining optical sideband injection locking with optical phase-lock loop techniques for two fiber-coupled DFB lasers. Single sideband noise spectral density of -92 dBc/Hz at 10 kHz offset, and phase-error variance lower than 0.005 rad/sup 2/ in a 100 MHz bandwidth were measured. The locking bandwidth exceeded 30 GHz.

High-performance phase locking of wide linewidth semiconductor lasers by combined use of optical injection locking and optical phase-lock loop

The requirement for narrow linewidth lasers or short-loop propagation delay makes the realization of optical phase-lock loops using semiconductor lasers difficult. Although optical injection locking can provide low phase error variance for wide linewidth lasers, the locking range is restricted by stability considerations. Theoretical and experimental results for a system which combines both techniques so as to overcome these limitations, the optical injection phase-lock loop (OIPLL), are reported. Phase error variance values as low as 0.006 rad/sup 2/ (500 MHz bandwidth) and locking ranges exceeding 26 GHz were achieved in homodyne OIPLL systems using DFB lasers of summed linewidth 36 MHz, loop propagation delay of 15 ns and injection ratio less than -30 dB. Phase error variance values as low as 0.003 rad/sup 2/ in a bandwidth of 100 MHz, a mean time to cycle slip of 3/spl times/10/sup 10/ s and SSB noise density of -94 dBc/Hz at 10 kHz offset were obtained for the same lasers in an heterodyne OIPLL configuration with loop propagation delay of 20 ns and injection ratio of -30 dB.

High-performance heterodyne optical injection phase-lock loop using wide linewidth semiconductor lasers

The requirements for narrow linewidth lasers or short-loop propagation delay limit optical phase-lock loop realizability with semiconductor lasers. Although optical injection locking can provide low-phase-error variance, its locking range is limited by stability considerations. The first experimental results for an heterodyne optical injection phase-lock loop are reported. Phase-error variance as low as 0.003 rad/sup 2/ in a bandwidth of 100 MHz, single-sideband (SSB) noise density of -94 dBc/Hz at 10-kHz offset and mean time to cycle slip of 3/spl times/10/sup 10/ s have been achieved using DFB lasers of 36-MHz summed linewidth, a loop propagation delay of 20 ns and an injection ratio of -30 dB.