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Diffractive optical elements are becoming increasingly popular due to their ability to provide a broad spectrum of design possibilities by manipulating Fresnel regions. These design capabilities enable the simultaneous accomplishment of various functions in electro-optical systems using a single optical element. This study presents novel dual-mode seeker design approaches incorporating squinted combined diffractive optical element (SCDOE) that allow us to combine two seeker types into one in a common aperture design. Multiple systems function in a multi-spectral detection and imaging manner combined with the usage of the SCDOE. The creation of the squinted diffractive lens, allows the seeker to operate in two modes simultaneously. In the first mode, the seeker functions as a traditional laser seeker, benefitting from enhanced measurement sensitivity and measurement range. In the second mode, with the aid of the squinted design of the SCDOE, the systems operate as imagers in the extended short-wave infrared (eSWIR) or long-wave infrared (LWIR) bands. The principle of operation of the seeker modes was simulated separately. The laser seeker simulation results were compared with the ideal lens having similar optical parameters. The imaging seekers (eSWIR, LWIR, and eSWIR/LWIR) were compared using fusion algorithms with the peak signal-to-noise ratio (PSNR), structural similarity index (SSIM) and system contrast transfer function (CTF). The assessment of the fusion algorithms in the eSWIR/LWIR seeker with the separated eSWIR and LWIR imagers indicates that the contrast pyramid algorithm (CP) gives the best result in target detection in terms of CTF. Besides this, the imaging capability of dual mode, a laser with imaging, gives superior measurement sensitivity, ± 0.6 mrad, in comparison with the laser seeker. As a result, the SCDOE in a dual-mode seeker combines the two electro-optical systems into one. The findings of this study make a substantial contribution to the progress of squinted combined diffractive lenses, enabling the simultaneous fulfillment of multiple modes and functions in electro-optical systems. [ABSTRACT FROM AUTHOR]

Recently, thin-film lithium niobate electro-optical modulators have developed rapidly and have become the core solution for the next generation of electro-optical problems. Compared with bulk lithium niobate modulators, these modulators not only retain the advantages of lithium niobate materials, such as low loss, high extinction ratio, high linear response and high optical power handling capabilities, but can also effectively improve some performance parameters, such as the voltage bandwidth performance of the modulator. Unfortunately, the extremely small electrode gap of thin-film lithium niobate EO (electro-optic) modulators causes metal absorption, resulting in higher microwave losses. The electro-optical performance of the modulator, thus, deteriorates at high frequencies. We designed traveling-wave electrodes with microstructures to overcome this limitation and achieve a 3 dB electro-optical bandwidth of 51.2 GHz. At the same time, we maintain low on-chip losses of <2 dB and a high extinction ratio of 15 dB. It is important to note that the devices we manufactured were metal-encapsulated and passed a series of reliability tests. The success of this modulator module marks a key step in the commercialization and application of thin-film lithium niobate modulation devices. [ABSTRACT FROM AUTHOR]

Through the use of diffractive optical elements (DOEs) in electro-optical systems, significant design freedoms have been achieved in these systems. Because of these design freedoms, a single DOE can perform several functions of an optical system. This provides considerable advantages in military and aerial applications. This paper presents a new combined diffractive optical element (CDOE) that increases a laser seeker's measurement sensitivity and maintains the linear measurement range almost the same as a conventional lens. The optical wave propagation method was applied to the CDOE in this study, and the simulation results were compared with a conventional refractive lens named the ideal refractive lens (IRL) in this article. The principle of operation of a laser seeker was analyzed by using MATLAB for IRL and CDOE. The analysis results indicate that the CDOE could increase the measurement sensitivity of the laser seeker while keeping the linear measurement range almost the same. Therefore, the new CDOE that provides many benefits would have better potential than conventional refractive lenses in laser seeker applications. This article will contribute to the development of combined lenses that simultaneously meet various parameters in an electro-optical system. [ABSTRACT FROM AUTHOR]

Recently, thin-film lithium niobate electro-optical modulators have developed rapidly and have become the core solution for the next generation of electro-optical problems. Compared with bulk lithium niobate modulators, these modulators not only retain the advantages of lithium niobate materials, such as low loss, high extinction ratio, high linear response and high optical power handling capabilities, but can also effectively improve some performance parameters, such as the voltage bandwidth performance of the modulator. Unfortunately, the extremely small electrode gap of thin-film lithium niobate EO (electro-optic) modulators causes metal absorption, resulting in higher microwave losses. The electro-optical performance of the modulator, thus, deteriorates at high frequencies. We designed traveling-wave electrodes with microstructures to overcome this limitation and achieve a 3 dB electro-optical bandwidth of 51.2 GHz. At the same time, we maintain low on-chip losses of

In this paper, we present a microwave photonic filter bandpass filter with narrow bandwidth and high quality (Q) factor is presented which with a bandwidth of 7.8 MHz, a gain response of 24 dB, and Q factor is 2412. This performance is achieved through tailoring one Brillouin gain spectrum by two Brillouin loss spectrums. By precise control of the individual pump power and frequency, a narrowed bandpass filter is generated. We achieve this performance through the mathematical formulation of the Stimulated Brillouin scattering (SBS) spectrum relative frequency shift and SBS pumps power ratio, resulting in precise parameters resolution of the narrowest filter bandwidth leading to experimentally demonstration. We further show the variation trend of the filter bandwidth and gain response, leading to exploit the general discipline of this technology.

This work describes the architecture and measured capabilities of an optical distance sensing application specific integrated circuit (ASIC) manufactured in 0.35 μm CMOS with a nominal supply voltage of 3.3 V for indirect time-of-flight. An integrated single-photon avalanche diode (SPAD) with an active diameter of 38 μm is used as detector with 6.6 V excess bias, active quenching and active resetting circuit. Phase measurement is performed using a digital correlation approach with digital counters. Due to the unmatched sensitivity of SPADs, sub-cm accuracy measurements can be performed with a received signal power in the pW range. Background light ratios up to 24.1 dB still allow sub-cm precision. Depending on the required accuracy and the received optical power, the measurement time can be adjusted freely up to several seconds only limited by digital counter depth. Compared to a pin-photodiode iTOF sensor in the same technology, this chip has a sensitivity improvement of 33.3 dB and 40.7 dB for a distance accuracy of 1 cm and 10 cm, respectively, while reducing the effective measurement time by 75% at the same time. The chip size is 1.4 mm × 1.4 mm including two correlator blocks, for simultaneous acquisition of two phase steps. The number of correlators is scalable allowing parallel measurements of phase correlations.

We present a detailed simulation study on plasmonic-organic hybrid electro-optic modulators based on coupled symmetric or asymmetric plasmonic slots. An electro-optic polymer is exploited as an active material, and the device is compatible with a silicon photonics platform. The proposed device operates at 1550 nm wavelength, typical of data center or long-haul telecommunication systems. The device performance in terms of area, plasmonic losses, optical bandwidth, intrinsic modulation bandwidth and energy dissipation are comparable to already proposed Mach-Zehnder solutions, but with potentially better extinction ratio, coupling losses due to photonic-plasmonic transitions, and flexibility in exploiting, without any performance penalty, asymmetric slots to shift the ON and OFF states bias. Finally, the bias dependence of the modulation chirp is investigated, comparing through and cross-coupling configurations.

We propose and experimentally demonstrate high-speed operation of random-channel cryptography (RCC) in multimode fibers. RCC is a key generation and distribution method based on the random channel state of a multimode fiber and multi-dimension to single-dimension projection. The reciprocal intensity transmittance of the channel shared between the two legitimate users is used to generate and distribute correlated keys. In previous work, RCC's key rate-distance product was limited by the speed of light. In this work, we show that adding a fast modulator at one end of the channel decouples the key rate and distance, resulting in a significant improvement in the key rate-distance product, limited only by the fiber's modal dispersion. Error-free transmission at a key rate-distance product of 64.7 Mbps × 12 km, which is seven orders of magnitude higher than the previous demonstration, was achieved. The proposed method's security arises from a fundamental asymmetry between the eavesdroppers' and legitimate users' measurement complexity.

In this work, a hybrid code division multiplexing (CDM) coding and digital filtering method for optical intensity modulation and direct detection (IM-DD) link is investigated to address multipath interference (MPI) and channel bandwidth limitation. CDM signaling already provides robustness to MPI through suppressing the unsynchronized paths by orthogonal (de)coding. As for digital filtering based on square root raised cosine (SRRC) waveforms, its advantage to IM-DD link includes robustness to channel bandwidth limitation due to pulse shaping. Additionally, matching filters achieve the best orthogonality only when they are synchronized well, thus robustness to MPI can be expected on the basis of CDM. We study the performance of such hybrid coding and filtering method over IM-DD link in the presence of MPI and bandwidth limitations through simulation. This is followed by experimental demonstrations of single point-to-point transmission with capacity at 112 Gbps. BER comparison between CDM only and hybrid filtering and coding method is performed by emulating MPI using a Mach-Zehnder interferometer. Furthermore, bidirectional transmission over a single fiber verifies its performance advantage and demonstrates potentials for reducing implementation costs of end-to-end optical communications.

In this work, we design, model, and characterize the Bragg grating modulator (BGM) on silicon-rich nitride and thin-film lithium niobate (SRN-TFLN) platform. In particular, the slow-light effect on the electro-optical modulation response is modeled and experimentally validated. The presented modulator shows a 3-dB electro-optical (E-O) bandwidth beyond 40 GHz, which agrees well with the simulation results. High-speed modulation up to 60 Gbps and 70 Gbps are experimentally obtained with extinction ratio (ER) of 4.7 dB and 2.7 dB, respectively. A measured modulation efficiency of 2.47 pm/V is also achieved. With optimized slow-light effect and proper design, the proposed BGM has great potential in high-speed data transmission.

In this paper, we present a novel transmission line architecture in thin-film lithium niobate (TFLN) platforms to improve the velocity match between the microwave and the optical wave. Compared to conventional coplanar waveguide (CPW), the microwave index ($n_m$) of the proposed slotted electrodes can be optimized from 2.1 to 3 while maintaining the high modulation efficiency and 50-$\Omega$ impedance match. Equivalent-circuit model analysis and finite-element simulation are performed. The simulated half-wave voltage (V$_\pi$) of 1.2 V and E-O modulation bandwidth greater than 80 GHz is obtained for a 2-cm-long modulator. By utilizing the slotted slow-wave electrode, TFLN Mach-Zehnder modulators with CMOS-compatible operating voltage and 3-dB modulation bandwidth greater than 100 GHz are potentialized.

We present a detailed simulation study on plasmonic-organic hybrid electro-optic modulators based on coupled symmetric or asymmetric plasmonic slots. An electro-optic polymer is exploited as an active material, and the device is compatible with a silicon photonics platform. The proposed device operates at 1550 nm wavelength, typical of data center or long-haul telecommunication systems. The device performance in terms of area, plasmonic losses, optical bandwidth, intrinsic modulation bandwidth and energy dissipation are comparable to already proposed Mach-Zehnder solutions, but with potentially better extinction ratio, coupling losses due to photonic-plasmonic transitions, and flexibility in exploiting, without any performance penalty, asymmetric slots to shift the ON and OFF states bias. Finally, the bias dependence of the modulation chirp is investigated, comparing through and cross-coupling configurations. [ABSTRACT FROM AUTHOR]

In this work, we design, model, and characterize the Bragg grating modulator (BGM) on silicon-rich nitride and thin-film lithium niobate (SRN-TFLN) platform. In particular, the slow-light effect on the electro-optical modulation response is modeled and experimentally validated. The presented modulator shows a 3-dB electro-optical (E-O) bandwidth beyond 40 GHz, which agrees well with the simulation results. High-speed modulation up to 60 Gbps and 70 Gbps are experimentally obtained with extinction ratio (ER) of 4.7 dB and 2.7 dB, respectively. A measured modulation efficiency of 2.47 pm/V is also achieved. With optimized slow-light effect and proper design, the proposed BGM has great potential in high-speed data transmission. [ABSTRACT FROM AUTHOR]

A novel nanocavity-based polymer-on-insulator (POI) electro-optic modulator (EOM) is proposed. It consists of a polymeric photonic-crystal nanobeam cavity (PCNC) with ultra-low index-contrast (ncavity/nbg = 1.17). Based on three-dimensional (3D) finite-difference time-domain (FDTD) method, the PCNC design and optimization are investigated theoretically. A high quality-factor (Q) of 3.4 × 104 and small mode-volume of 22.8 (λ/nSEO)3 can be achieved. In order to judge the efficiency of the cavity design for electro-optic (EO) modulation, the optical modes and the electric field distribution are computed using an electromagnetic finite-element solver. Benefiting from the fast and strong EO effect in polymers, the modulator shows an EO modulation efficiency of up to 16 pm/V, which is over an order of magnitude higher than that in lithium niobate (LN) PCNCs. Moreover, the device is only 80 μm in length, leading to a voltage-length product Vπ × L = 0.05 V·cm, which is much smaller than those of Mach-Zehnder modulators. To the best of our knowledge, this is the first on-chip POI-based EOM that features both ultra-compact size and high modulation efficiency. Hence, it is potentially an ideal platform for applications in optical communications, electric-field sensing, and tunable photonic circuits.

In this paper, we present a novel transmission line architecture in thin-film lithium niobate (TFLN) platforms to improve the velocity match between the microwave and the optical wave. Compared to conventional coplanar waveguide (CPW), the microwave index (nm) of the proposed slotted electrodes can be optimized from 2.1 to 3 while maintaining the high modulation efficiency and 50- Ω impedance match. Equivalent-circuit model analysis and finite-element simulation are performed. The simulated half-wave voltage (Vπ) of 1.2 V and E-O modulation bandwidth greater than 80 GHz is obtained for a 2-cm-long modulator. By utilizing the slotted slow-wave electrode, TFLN Mach-Zehnder modulators with CMOS-compatible operating voltage and 3-dB modulation bandwidth greater than 100 GHz are potentialized. [ABSTRACT FROM AUTHOR]

In this work, a hybrid code division multiplexing (CDM) coding and digital filtering method for optical intensity modulation and direct detection (IM-DD) link is investigated to address multipath interference (MPI) and channel bandwidth limitation. CDM signaling already provides robustness to MPI through suppressing the unsynchronized paths by orthogonal (de)coding. As for digital filtering based on square root raised cosine (SRRC) waveforms, its advantage to IM-DD link includes robustness to channel bandwidth limitation due to pulse shaping. Additionally, matching filters achieve the best orthogonality only when they are synchronized well, thus robustness to MPI can be expected on the basis of CDM. We study the performance of such hybrid coding and filtering method over IM-DD link in the presence of MPI and bandwidth limitations through simulation. This is followed by experimental demonstrations of single point-to-point transmission with capacity at 112 Gbps. BER comparison between CDM only and hybrid filtering and coding method is performed by emulating MPI using a Mach-Zehnder interferometer. Furthermore, bidirectional transmission over a single fiber verifies its performance advantage and demonstrates potentials for reducing implementation costs of end-to-end optical communications. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate high-speed operation of random-channel cryptography (RCC) in multimode fibers. RCC is a key generation and distribution method based on the random channel state of a multimode fiber and multi-dimension to single-dimension projection. The reciprocal intensity transmittance of the channel shared between the two legitimate users is used to generate and distribute correlated keys. In previous work, RCC's key rate-distance product was limited by the speed of light. In this work, we show that adding a fast modulator at one end of the channel decouples the key rate and distance, resulting in a significant improvement in the key rate-distance product, limited only by the fiber's modal dispersion. Error-free transmission at a key rate-distance product of 64.7 Mbps $ \times $ 12 km, which is seven orders of magnitude higher than the previous demonstration, was achieved. The proposed method's security arises from a fundamental asymmetry between the eavesdroppers’ and legitimate users’ measurement complexity. [ABSTRACT FROM AUTHOR]

We present a silicon photonic dual parallel multielectrode Mach-Zehnder modulator (MEMZM) based transmitter targeting 200 Gb/s four-level pulse amplitude modulation (PAM4) short reach transceivers. The MEMZMs have an average Vπ and electro-optic (EO) bandwidth of 5 V and 38 GHz, respectively. The transmitter is characterized versus receiver equalizer taps, received signal power, driving voltage swing, crosstalk voltage swing, bitrate, and reach. Results reveal that using only a three-tap equalizer at the receiver, 100 Gb/s PAM4 net rate per lane can be achieved at a bit error rate (BER) below the KP4 forward error correction (KP4-FEC) threshold of 2.4 × 10-4. Moreover, up to 128 Gb/s can be received at a BER below the KP4-FEC threshold using only 2 Vpp and 1 Vpp driving the MEMZM segments. Then, both MEMZMs are driven simultaneously to assess the crosstalk impact on the BER performance at parallel operation. Driven by four binary signals, we demonstrate 200 Gb/s PAM4 transmission over up to 10 km of single mode fiber at a BER below the KP4-FEC threshold.

This letter presents for the first time a systematic study of an atomic frequency standard based on coherent population trapping (CPT) effect in 87Rb vapour optically pumped with a multifrequency laser radiation formed with sidebands of a single-frequency laser whose injection current is modulated at a subharmonic frequency (1/2-1/6) relative to the frequency of hyperfine ground state splitting. Measured are the CPT resonance parameters and the atomic clock short-term stability at different subharmonic frequencies of microwave modulation. The possibility of CPT resonance light shift suppression is experimentally demonstrated at modulation frequencies between 1/3 and 1/5 of the resonant frequency for continuous wave optical pumping of the 87Rb vapour D1 line. Analyzed are the capabilities and potential of reduced energy consumption of atomic clocks when CPT resonance in rubidium vapour is excited at subharmonic modulation frequencies.

A novel nanocavity-based polymer-on-insulator (POI) electro-optic modulator (EOM) is proposed. It consists of a polymeric photonic-crystal nanobeam cavity (PCNC) with ultra-low index-contrast (n $_{\text{cavity}}$ /n $_{bg}$ = 1.17). Based on three-dimensional (3D) finite-difference time-domain (FDTD) method, the PCNC design and optimization are investigated theoretically. A high quality-factor (Q) of 3.4 $\,\times\, 10^4$ and small mode-volume of 22.8 ${({\lambda }/n_{SEO}})^{3}$ can be achieved. In order to judge the efficiency of the cavity design for electro-optic (EO) modulation, the optical modes and the electric field distribution are computed using an electromagnetic finite-element solver. Benefiting from the fast and strong EO effect in polymers, the modulator shows an EO modulation efficiency of up to 16 pm/V, which is over an order of magnitude higher than that in lithium niobate (LN) PCNCs. Moreover, the device is only 80  $\mu$ m in length, leading to a voltage-length product $V_{\pi }$ × L = 0.05 V $\cdot$ cm, which is much smaller than those of Mach-Zehnder modulators. To the best of our knowledge, this is the first on-chip POI-based EOM that features both ultra-compact size and high modulation efficiency. Hence, it is potentially an ideal platform for applications in optical communications, electric-field sensing, and tunable photonic circuits. [ABSTRACT FROM AUTHOR]

This study aims to demonstrate the development of multilayer antireflection (AR) coating on calcium fluoride (CaF2) optics. AR coating functions over ultra-broadband spectrum from 3.4 to 4.8 μm at mid-wave infrared (MWIR). The design of AR coating has five layers and a physical thickness less than 4 μm. Multilayer AR coating consists of aluminium oxide and germanium named as low and high refractive index materials respectively. Multilayer stack was coated by plasma-assisted e-beam evaporation with optimized process parameters. The results obtained in this study are found to be better ones exhibiting lower base reflectance values 0.05% and 0.025% at 3550 and 4450 nm respectively. Additionally, 0.121% average reflectance over 1400 nm width in MWIR also offers better spectral performance than the previous works reported. Besides high efficiency, the number of layers and overall thickness of design offer an efficient AR solution for CaF2 optical elements for electro-optical applications. [ABSTRACT FROM AUTHOR]

We derive compact equations describing the modification of amplified spontaneous emission signal beat noise arising from optical and electrical filtering in optically preamplified direct detection receivers. In particular, we show that this modification typically results in a further decrease of the signal quality factor. This is particularly pronounced in the presence of electrical filters with steep transfer functions such as, e.g., occurring when feeding the signal through an antialiasing filter prior to analog-to-digital conversion or in a real-time oscilloscope, in the latter case leading to counter-intuitive dependencies of the measured signal quality on the characteristics of the test setup. Predictions are exemplified in concrete system models and verified with experiments. While the modeling assumptions and the accuracy of the predictions are in line with models previously reported in the literature, derived expressions allow straightforwardly tying the modification of the level dependent noise to signal levels, baud rate, signal spectrum, and filter transfer functions.

• AR coating functions over ultra-broad band by 1400 nm spectral interval. • Resulting average transmission is more than 99.5%. • Design of AR coating consists of only 3 layers. • Overall AR coating thickness is less than 1 µm. • AR coating performance covers entire spectral response region of MWIR detectors. In this work, we describe an efficient design and fabrication process of anti-reflection (AR) coating over 1400 nm spectral interval from 3.4 μm to 4.8 μm at mid wave infrared (MWIR) on silicon optics with only 3 layers which have overall physical thickness less than 1 μm. Multi-layer AR coating consisting of aluminum oxide (Al 2 O 3) and germanium (Ge) layers as low (n L) and high (n H) index materials respectively are coated by plasma assisted e-beam evaporation on silicon substrates with well optimized process parameters. AR coating on silicon is the first one reported by exhibiting record average transmission more than 99.7% over 1400 nm broadband spectral interval in mid-wave infrared (MWIR) with minimum number of layers. Moreover, number of layers and overall thickness for our design enables a cost effective solution for low process cycle in mass production of AR coated silicon optics. [ABSTRACT FROM AUTHOR]

This letter presents for the first time a systematic study of an atomic frequency standard based on сoherent population trapping (CPT) effect in 87Rb vapour optically pumped with a multifrequency laser radiation formed with sidebands of a single-frequency laser whose injection current is modulated at a subharmonic frequency (1/2–1/6) relative to the frequency of hyperfine ground state splitting. Measured are the CPT resonance parameters and the atomic clock short-term stability at different subharmonic frequencies of microwave modulation. The possibility of CPT resonance light shift suppression is experimentally demonstrated at modulation frequencies between 1/3 and 1/5 of the resonant frequency for continuous wave optical pumping of the 87Rb vapour D1 line. Analyzed are the capabilities and potential of reduced energy consumption of atomic clocks when CPT resonance in rubidium vapour is excited at subharmonic modulation frequencies. [ABSTRACT FROM AUTHOR]

We present a silicon photonic dual parallel multielectrode Mach–Zehnder modulator (MEMZM) based transmitter targeting 200 Gb/s four-level pulse amplitude modulation (PAM4) short reach transceivers. The MEMZMs have an average $V_\pi$ and electro-optic (EO) bandwidth of 5 V and 38 GHz, respectively. The transmitter is characterized versus receiver equalizer taps, received signal power, driving voltage swing, crosstalk voltage swing, bitrate, and reach. Results reveal that using only a three-tap equalizer at the receiver, 100 Gb/s PAM4 net rate per lane can be achieved at a bit error rate (BER) below the KP4 forward error correction (KP4-FEC) threshold of $2.4 \times 10^{-4}$. Moreover, up to 128 Gb/s can be received at a BER below the KP4-FEC threshold using only 2 Vpp and 1 Vpp driving the MEMZM segments. Then, both MEMZMs are driven simultaneously to assess the crosstalk impact on the BER performance at parallel operation. Driven by four binary signals, we demonstrate 200 Gb/s PAM4 transmission over up to 10 km of single mode fiber at a BER below the KP4-FEC threshold. [ABSTRACT FROM AUTHOR]

A new optical frequency shifter is presented. It is based on a double sideband suppressed carrier radio-frequency (RF) modulated optical signal into a Brillouin-assisted filter, which is formed by a Brillouin medium between a pair of optical circulators. The frequency shifting operation is realized by utilizing multiple stimulated Brillouin scattering gain and loss spectra to amplify one of the third-order sidebands but attenuate the other sidebands. The frequency shifter has a simple structure and a high frequency shifted to unwanted frequency component ratio. It also has the ability to realize a very large frequency shift, which is three times the input electrical driving signal frequency. The frequency shifter is experimentally demonstrated with the results showing a 32.53 GHz optical frequency shift of a continuous wave light at 1551.016 nm with over 34 dB difference between the wanted frequency shifted and unwanted frequency components.

Here in this work, we study the electro-refractive modulation of CVD grown single layer graphene placed on top of a silicon microring resonator biased using a polymer electrolyte gate. A voltage length product for a phase shift of π, VπL = 2.7 Vmm has been extracted, which is better compared to silicon depletion horizontal and interleaved pn junction type phase modulators and competitive with Silicon-Insulator-Silicon Capacitor modulators.

We propose and demonstrate a novel method to narrow the linewidth of a laser diode at 1550 nm by an electronics-assisted feedforward path and weak locking to a femtosecond comb line simultaneously. By using a femtosecond comb as an ideal ultranarrow-linewidth optical reference, the laser diode is down converted, and its phase noise is “recorded” by the resulted intermediate frequency tone, which is filtered by a 40-MHz electronic filter. The consequentially introduced electronic delay is designed to match the optical delay, which is experienced by the same laser diode for upconversion. The delay match ensures that the phase noise of laser diode can be counteracted by its former “record” in upconversion and realizes linewidth reduction. As a result, the 20-dB linewidth of final radiation has been measured as 26 kHz, which is 1/35 of that of the laser diode.

We present a silicon photonic dual-parallel Mach-Zehnder modulator (MZM) operating near 1550 nm used for four-level pulse amplitude modulation (PAM-4). The differential and integral nonlinearities of the device are investigated. A driving scheme and a biasing method that improves the linearity and PAM operation of the device are presented. The measured second harmonic distortion and two-tone, third-order intermodulation spurious-free dynamic range are 75 dB · Hz1/2 and 86 dB · Hz3/2, respectively. We further investigate the performance of the device in a short-reach transmission system. We report a successful 50-Gbaud single-wavelength transmission of PAM-4 over 2 km of single-mode fiber (SMF) below hard decision pre forward error correction (pre-FEC) threshold of 4.4 × 10-3.

This work presents the design, fabrication, and characterization of a monolithic and complementary-metal-oxide-semiconductor (CMOS)-based integrated optical system, including the light emitter working in the visible range, waveguide, and photodetector. The presented system aims to be applied for the development of optochemical sensors. The work presents the proposed concept and the integration strategy, as well as the fabrication process. The individual elements of the system are theoretically evaluated to assure compatibility among them. Then, the fabrication and studies to the complete system are presented. The response of the light sensor is shown to be caused by optical stimulation of light originated in the integrated light source and transmitted through a dielectric waveguide, thus validating the integration procedure.

A six-channel wavelength-division-multiplexed optical transceiver with a compact footprint of 1.5 × 0.65 mm2 for off-chip and on-chip interconnects is demonstrated on a single silicon-on-insulator chip. An arrayed waveguide grating is used as the (de)multiplexer, and III-V electroabsorption sections fabricated by hybrid integration technology are used as both modulators and detectors, which also enable duplex links. The 30-Gb/s capacity for each of the six wavelength channels for the off-chip transceiver is demonstrated. For the on-chip interconnect, an electrical-to-electrical 3-dB bandwidth of 13 GHz and a data rate of 30 Gb/s per wavelength are achieved.

The frequency-dependent dispersion impairment of high-speed printed analog traces in next-generation pluggable modules is studied. This frequency dependence is considered for the first time in optical fiber communication systems. Transmission of ultra-broadband electrical signals over such traces dramatically enhances the frequency-dependent dispersion effect. Here, for the first time, an extended model of the ultrabroadband signal transmission that includes this frequency-dependent dispersion effect of the printed analog traces is proposed. Additionally, a novel approach to compensate for this frequency-dependent dispersion impairment is introduced. Inclusive analysis reveals that a significant performance improvement of up to 4 dB is achieved by using the proposed symbol-spaced sampling and reduced-complexity digital signal processing technique.

In process industries, an optical transmitting system has a great impact especially for long distance transmission through inflammable and hazardous areas. A combination of bellows and Mach-Zehnder Interferometer (MZI)-based pressure transmitting system has been proposed in this paper. This novel approach is capable to transmit pressure reading to a remote location using an electro-optic modulation in the MZI. The proposed system is the hybrid type and consists of two sections. First part is the electrical type which is responsible for transmission of measured information in an electrical domain (primary) and a second section is designed for transmission of measured information in an optical domain (secondary). Primary part is the combination of bellows, a Hall probe sensor, and a signal conditioning circuit, and the second part consists of the MZI with three electrodes. The pressure is directly applied to the bellows. The magnet is placed at the top of the Bellows and the variation of the magnet positions is sensed by the Hall probe sensor. The response of the Hall probe sensor, in terms of millivolt range, is not capable to perform the electro-optic modulation in the MZI, so it is further amplified by an instrumentation amplifier and a calibrating circuit. The output from the signal conditioning circuit is fed to the MZI so that the intensity of light which is propagating in the MZI is modulated due to the electro-optic effect. Transmission of the optical signal is very much beneficial for the inflammable industry to prevent the sparking like situation. The operation of the system has been explained with the help of derived theoretical equations. The experiment has been done and the performance of the system along with the experimental results is reported in this paper. The proposed system is linear and provides good repeatability with the applied pressure. [ABSTRACT FROM AUTHOR]

We derive compact equations describing the modification of amplified spontaneous emission signal beat noise arising from optical and electrical filtering in optically preamplified direct detection receivers. In particular, we show that this modification typically results in a further decrease of the signal quality factor. This is particularly pronounced in the presence of electrical filters with steep transfer functions such as, e.g., occurring when feeding the signal through an antialiasing filter prior to analog-to-digital conversion or in a real-time oscilloscope, in the latter case leading to counter-intuitive dependencies of the measured signal quality on the characteristics of the test setup. Predictions are exemplified in concrete system models and verified with experiments. While the modeling assumptions and the accuracy of the predictions are in line with models previously reported in the literature, derived expressions allow straightforwardly tying the modification of the level dependent noise to signal levels, baud rate, signal spectrum, and filter transfer functions. [ABSTRACT FROM AUTHOR]

We embody a miniature reflection-type optical displacement sensor tapping into a projected beam that features high structural tolerance. A code scale with periodic patterns spatially encrypts the projected beam, which is established by imaging a collimated beam from a vertical-cavity surface-emitting laser via an aspheric lens, and linearly expands it, so as to be decoded by a receiver that comprises four serially cascaded identical photodetector cells. For the modulated beam, we observe a pitch increase with a rate of 18 μm/mm along the propagation direction. The two quadrature signals Sig-A and Sig-B derived from the PD signals exhibit a 900 phase relationship. The proposed sensor has been designed via ray-optic simulations and embodied through passive alignment, combined with plastic injection mold. We achieve a positional resolution of 10 μm from either of Sig-A and Sig-B. By concurrently considering the two quadrature outputs, we efficiently enhance the resolution to 2.5 μm, with the discovered direction of displacement. Finally, we thoroughly investigate the crucial dependence of the sensor performance on the positional tolerance pertaining to the constituent elements, which is discovered to be as large as +/-100 μm, under a certain resolution.

The two-, three-, and four-channel mapping multiplexing technique (MMT) is demonstrated to increase the data capacity of multilevel intensity-modulated transmission formats to 2, 3, and 4 bits/symbol with a substantial reduction in power penalty. This paper outlines the N-channel MMT design metric consideration influence on the performance enhancement of higher order amplitude modulated systems in terms of power penalty, receiver sensitivity, and spectral efficiency. The signal space model has been developed for N-channel MMT, where the average electrical and optical power expressions are derived. Transmission of 2, 3, and 4 bits/symbol using MMT system shows better performance in terms of the average optical power penalty, in comparison with pulse amplitude modulation (M-PAM) formats, with respect to the information capacity. The proposed scheme can be considered as an alternative to M-PAM systems with enhanced power efficiency.

We present a silicon photonic traveling-wave Mach-Zehnder modulator operating near 1550 nm with a 3-dB bandwidth of 35 GHz. A detailed analysis of travelingwave electrode impedance, microwave loss, and phase velocity is presented. Small-and large-signal characterization of the device validates the design methodology. We further investigate the performance of the device in a short-reach transmission system. We report a successful 112-Gb/s transmission of four-level pulse amplitude modulation over 5 km of SMF using 2.2 Vp_p drive voltage. Digital signal processing is applied at the transmitter and receiver. 56-GBaud PAM-4 and 64-Gb/s PAM-2 transmission is demonstrated below a pre-FEC hard decision threshold of 4.4 x 10-3.

A simple optoelectronic regenerator for differential quadrature phase-shift keying (QPSK) signals is demonstrated. The regenerator consists of two parallel delay interferometers followed by balanced detectors, limiting and driving amplifiers, and a dual-parallel Mach-Zehnder modulator that regenerates noise-suppressed optical QPSK signals. We experimentally show that the regenerator improves the receiver sensitivity by about 8 dB at an input optical signal-to-noise ratio (OSNR) of 19 dB at a signal speed of 10 Gbaud. Numerical simulation is conducted for higher speed operation at 56 Gbaud to study the impact of the bandwidth of electrical circuits inside the regenerator on the regenerator performance. Electrical power consumption of the regenerator is assessed, and it is shown that the optoelectronic regenerator consumes a similar amount of electrical power as that consumed by an all-optical version of the regenerator using semiconductor optical amplifiers as a nonlinear element.

A reflective optical encoder has been proposed and realized capitalizing on a miniaturized sensing head, which integrates both a pair of index gratings and a beam router in a plastic smart frame. The index gratings play a role in selectively transmitting the incident beam carrying the periodic grating pattern of a code scale. The beam router, consisting of a collimating lens in conjunction with a prism, is used to collimate and steer the beam originating from a vertical-cavity surface-emitting laser (VCSEL) toward the code scale. The proposed encoder is rigorously designed by ray optic simulations and manufactured by passively aligning a smart frame, which is produced by plastic injection molding, with a VCSEL at λ = 850 nm and two semicircular photodetectors. The index grating is created by forming an Al grating pattern of a 10- μm pitch on a silica substrate. Two output signals provide sinusoidal signals, which are 90 ° out of phase from each other. The period of the signals is 4 μs at a frequency of 250 kHz, which is equivalent to a period of 10 μm. As expected, the relative phase relationship is reversed by altering the direction of rotation of the code scale. By examining either of the two output signals, we can simply demonstrate positional and angular resolutions of about 10 μm and 0.04 °, respectively. The attained resolutions can be readily enhanced to 2.5 μm and 0.01 °, by simultaneously taking into account the two signals with a distinct 90 ° phase difference.

We derive compact equations describing the modification of amplified spontaneous emission signal beat noise arising from optical and electrical filtering in optically preamplified direct detection receivers. In particular, we show that this modification typically results in a further decrease of the signal quality factor. This is particularly pronounced in the presence of electrical filters with steep transfer functions such as, e.g., occurring when feeding the signal through an antialiasing filter prior to analog-to-digital conversion or in a real-time oscilloscope, in the latter case leading to counter-intuitive dependencies of the measured signal quality on the characteristics of the test setup. Predictions are exemplified in concrete system models and verified with experiments. While the modeling assumptions and the accuracy of the predictions are in line with models previously reported in the literature, derived expressions allow straightforwardly tying the modification of the level dependent noise to signal levels, baud rate, signal spectrum and filter transfer functions. [ABSTRACT FROM AUTHOR]

A photonic approach to generate a frequency and bandwidth multiplying dual-chirp microwave waveform using a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and demonstrated. In the proposed scheme, an RF carrier is applied to one QPSK modulator and a baseband single-chirp waveform is applied to another. By setting the driving signals applied to the modulator and adjusting the dc bias phases in the modulator, high-order optical sidebands can be obtained with the optical carrier suppressed. After optical to electrical conversion, a frequency-doubling and bandwidth-quadrupling, or frequency-quadrupling and bandwidth-octupling dual-chirp microwave can be generated. The approach is verified by simulation. Dual-chirp microwave waveforms with 16-GHz central frequency, 2048-MHz bandwidth and 32-GHz central frequency, 4096-MHz bandwidth are generated through an 8-GHz RF carrier and 512-MHz bandwidth baseband signal. The generated dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution. [ABSTRACT FROM PUBLISHER]

By combining advanced fluid control technology with surface plasmonic resonance phenomenon, we could take advantage of various unique characteristics of plasmonics without changing the original structure to realize a tunable color filtering system. By modifying the wetting properties of solid surface with an electric field, electro-fluid control technology could tune the curvature of two-phase fluid interface continuously and, therefore, change the distributions of silver nanoparticles on the interface accordingly. Based on this fluidic optical design, we investigated the influencing factors of color filtering performance by modeling, finally got an optimized design to achieve broad spectrum filtering system. As the color filtering function is realized simply and rapidly by charging, and therefore, this design could improve the efficiency of the electro-optical systems and is a promising idea for many applications, such as the dynamic display devices. [ABSTRACT FROM PUBLISHER]

A new optical frequency shifter is presented. It is based on a double sideband suppressed carrier radio-frequency (RF) modulated optical signal into a Brillouin-assisted filter, which is formed by a Brillouin medium between a pair of optical circulators. The frequency shifting operation is realized by utilizing multiple stimulated Brillouin scattering gain and loss spectra to amplify one of the third-order sidebands but attenuate the other sidebands. The frequency shifter has a simple structure and a high frequency shifted to unwanted frequency component ratio. It also has the ability to realize a very large frequency shift, which is three times the input electrical driving signal frequency. The frequency shifter is experimentally demonstrated with the results showing a 32.53 GHz optical frequency shift of a continuous wave light at 1551.016 nm with over 34 dB difference between the wanted frequency shifted and unwanted frequency components. [ABSTRACT FROM PUBLISHER]

Here in this work, we study the electro-refractive modulation of CVD grown single layer graphene placed on top of a silicon microring resonator biased using a polymer electrolyte gate. A voltage length product for a phase shift of π, VπL = 2.7 Vmm has been extracted, which is better compared to silicon depletion horizontal and interleaved pn junction type phase modulators and competitive with Silicon-Insulator-Silicon Capacitor modulators. [ABSTRACT FROM PUBLISHER]

Fiber-optic research in signal processing for the first generation of coherent communication systems was dominated by receivers with blind adaptation. Next-generation systems will require a scalable and modular design for higher order modulation formats. Due to the nature of the fiber channel and the required parallelization in high-speed receivers, data-aided and blind algorithms call for a general reassessment when used in coherent optic receivers employing higher order modulation formats. In this paper, blind and data-aided receivers are compared for coherent single-carrier optical systems in terms of complexity, tracking ability, and convergence speed. Methods for equalization are discussed for time-domain- and frequency-domain-based receivers covering the most important algorithms. The general superiority of data-aided frequency-domain equalization is demonstrated.

An InP/InGaAsP integrated 1 times 8 optical phased-array switch is designed, fabricated, and characterized for high-throughput broadband wavelength-division multiplexed (WDM) optical packet switching application. With a single stage of phase shifters utilizing carrier-induced refractive index change, switching to the eight output ports is demonstrated successfully. The polarization-dependent loss is 2.2 dB in the worst case, and the wavelength-dependent loss is less than 2.5 dB across the entire C-band (1520-1580 nm) with the average extinction ratio of 17.7 dB. The measured reconfiguration time is shorter than 6 ns. Low-penalty transmission of a 40-Gb/s non-return-to-zero signal is also demonstrated for the first time. These features make the integrated phased-array switch an attractive candidate to be deployed in the future high-capacity optical packet switching networks.