Phase Control Section Research Articles

Photonic Generation of Frequency-Modulated Interrupted Continuous Waveforms

A frequency-modulated interrupted continuous waveform (FMICW) generator with an ultra-large bandwidth based on optical heterodyne detection is proposed and experimentally demonstrated. The FMICW generator is implemented through the heterodyne detection of a stable optical carrier and a gate-function-modulated frequency-chirped optical pulse. A stable sub-kHz optical fiber laser operates the optical carrier. The optical pulse is generated from a three-electrode distributed Bragg reflector (DBR) laser diode (LD), which is gate-function modulated by a current source via the passive phase control section. By beating the optical carrier and the optical pulse at a photodetector (PD), an FMICW is generated. The bandwidth of the FMICW is over 20 GHz, and the temporal duration is around 200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> . The compression ratio is obtained as large as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.78\times 10 ^{6}$ </tex-math></inline-formula> . Thanks to the tunability of the gate-function-modulated frequency-chirped optical pulse, the generated FMICW is fully tunable in terms of gate-function period and duty ratio.

16-channel tunable and 25-Gb/s EAM-integrated DBR-LD for WDM-based mobile front-haul networks.

We report a tunable distributed Bragg reflector-laser diode (DBR-LD) integrated with an electro-absorption-modulator (EAM) at an operating wavelength of 1.3 µm. This LD consists of gain, phase control (PC), DBR, and EAM sections, realized by using a butt-coupling technique in monolithically integrating the multiple quantum wells (MQWs) with the passive core and by applying an etched-mesa buried hetero-structure (EMBH) to the resonance cavity (i.e., gain to DBR section) and a deep-ridge type to the EAM section in fabricating the waveguide structure. Wavelength tuning of the LD is achieved by both applying a voltage to the heater metal of DBR section (coarse tuning) and injecting a current to the ohmic metal of PC section (fine tuning). From the work, the fabricated chips show a threshold current of about 13 mA, a side mode suppression ratio (SMSR) of more than 35 dB, and a tuning range of 15 nm within a heater voltage of 2 V. Dynamic tests for the EAM-integrated LD show the 3 dB bandwidth of more than 20 GHz and clear 25 Gb/s eye openings with a dynamic extinction ratio (DER) of over 7 dB for 16 channels spaced at the wavelength interval of 0.55 nm. Based on these results, we conclude that the EAM-integrated DBR-LD is capable of providing 16 channel operation at a data rate of 25 Gb/s and can be used as an effective light source for WDM-based mobile front-haul networks.

1.3-µm and 10-Gbps tunable DBR-LD for low-cost application of WDM-based mobile front haul networks.

We report a 1.3-µm and 10-Gbps tunable distributed Bragg reflector laser diode (DBR-LD) for the low-cost application of a wavelength division multiplex based mobile front-haul network. The device consists of gain, phase control, and DBR sections, implemented using a butt-coupling method through a monolithic integration and through the introduction of an etched mesa planar buried hetero-structure in a waveguide structure. From the work, a 560-µm long DBR-LD with a 220-µm long micro-heater DBR section has a threshold current of 10 mA ± 1 mA and a tuning range of more than 15 nm within a heater injection current of ∼100 mA. Spectral and dynamic tests for this LD show 16 channels spaced a wavelength grid of 0.8 nm with a side mode suppression ratio of greater 40 dB and clear eye openings with a dynamic extinction ratio of over 5.4 dB at an operating current of 60 mA.

Design and Simulation of Broadband Beam Splitter on a Silicon Nitride Platform for Optical Coherence Tomography

ABSTRACTIntegrated photonics enables the miniaturization of bulk optical components for biosensing applications such as optical coherence tomography (OCT) and is therefore promising for future lab-on-chip solutions. Here, we report the design and simulation of a compact low loss broadband beam splitter with arbitrary coupling ratios on silicon nitride platform for OCT systems. The reported coupler uses asymmetric waveguide-based phase control section for 10:90, 20:80, 30:70, 40:60, and 50:50 splitting ratios and is broadband over 100 nm with the central wavelength of 850 nm. The couplers are realized for transverse electric, transverse magnetic, and fully vectorial modes, and maximum excess loss for all mode types is reported to be less than 0.19 dB. The design tolerance of waveguide width and thickness of the designed coupler is further calculated and is within fabrication limit.

Low-Loss and Broadband &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$2 \times 2$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Polarization Beam Splitter Based on Silicon Nitride Platform

A low-loss and broadband $2 \times 2$ Mach–Zehnder interferometer-based polarization beam splitter (PBS) is proposed and experimentally demonstrated on the silicon nitride platform. The device is realized by using a 27.7- $\mu \text{m}$ -long phase control section, which consists of two arms with different widths to separate TE and TM polarized lights by providing different phase changes. Furthermore, a compact asymmetric 3-dB directional coupler with a parallel-coupling length of only 1.2 $\mu \text{m}$ is proposed to support polarization independent operation and reduce the device length. The measurement results show that the proposed PBS has a minimum insertion loss of 0.13 dB for the TE polarization and 0.34 dB for the TM polarization. The extinction ratio is over 20 dB throughout the measured band from 1530 to 1610 nm for the TE polarization, and it is higher than 20 dB over the entire $C$ -band for the TM polarization.

Broadband silicon photonic directional coupler using asymmetric-waveguide based phase control.

We design and demonstrate broadband directional couplers that use asymmetric-waveguide based phase control sections, on the silicon-on-insulator platform. Broadband directional couplers with various power splitting ratios, including 10%/90%, 20%/80%, 30%/70%, 40%/60% and 50%/50%, were realized for both transverse electric (TE) and transverse magnetic (TM) modes. Some of the devices exhitbit bandwidths in excess of 100 nm, and all in excess of 75 nm. The footprints of the TE mode couplers are 32 μm ×1.3 μm, or less, and those of the TM mode couplers are 13 μm ×1.3 μm, or less.

VPP Processed Variable Phase Controller for Array Antenna Scanning

An appropriate configuration of the magnetic bias geometry used in waveguide based phase control sections can help to reduce size, bulk and energy utilization. In this paper ferrite inserts for a toroidal phase controller are fabricated using a viscous plastic processing method. This technique has been exploited to produce a low reluctance magnetic geometry that avoids machining. The magnetostatic result for the bias geometry has been computed and used to analyze the phase control characteristics of a twin toroid phase controller. The microwave response in terms of S-Parameter over 8-12 GHz for various magnetization levels has been measured. The insertion loss of less than 1.1 dB has been achieved. The reflection coefficient (&lt;22 dB) has been experimentally verified.

Widely frequency tunable amplified feedback laser as 20 GHz optical microwave source

Optical microwave sources are required in optical signal processing. Amplified feedback laser (AFL) which can generate high frequency self-pulsation due to compound cavity modes beating are used as optical microwave sources. In this paper, we fabricate a four-section AFL consisted of a different distribute feedback (DFB) section, a phase control section, an amplifier section, and a transparent section. This AFL generate continuously tunable microwave in the range 19.87–26.30 GHz with 3 dB linewidth about 3 MHz. Microwave with narrow linewidth is obtained by injecting quarter frequency modulated light experimentally.

A Monolithic Wideband Wavelength-Tunable Laser Diode Integrated With a Ring/MZI Loop Filter

We propose a widely tunable and low insertion loss loop filter incorporating two ring resonators and an asymmetric Mach-Zehnder interferometer. A semiconductor optical amplifier, phase control section, and loop filter are monolithically integrated on one chip in the InP-InGaAsP material system. The tuning range of 39 nm with side-mode suppression ratio of over 30 dB was demonstrated. The maximum of the total heater power over the tuning range was 84 mW.

Time-Domain Analysis of Tunability and Modulation Characteristics in Coupled-Ring Reflector Laser Diode

The characteristics of a widely tunable coupled-ring reflector laser diode are studied using a time-domain modeling approach. The coupled-ring reflector is a planar waveguide reflector which does not require distributed Bragg gratings. Instead, the coupled-ring reflector consists of a bus waveguide and two coupled ring resonators coupled to the bus. It is shown that the tuning range can be a few tens of nanometers with a side mode suppression ratio exceeding 35 dB through the adjustment of currents into the phase control sections in the rings. The coupled-ring reflector laser diode has a long effective cavity compared with conventional laser diodes. Accordingly, a broad additional resonance peak in the amplitude modulation characteristics is observed between 20 to 30 GHz, implying the extension of amplitude modulation bandwidth.

이득 분산이 다중 영역 복소 결합 DFB 레이저의 Self-Pulsation 특성에 미치는 효과

이득 분산이 두 개의 복소 결합 DFB 영역과 위상조정 영역으로 구성되는 다중 영역 복소 결합 DFB 레이저에서 발진하는 두 모드의 비팅에 의한 self-pulsation (SP) 주파수와 출력 파워의 변조지수에 미치는 영향에 대하여 살펴보았다. 능동 영역의 이득이 최대가 되는 파장을 두 DFB 영역의 발진 모드의 파장 중심 또는 브래그 파장 중심에 위치시킨 경우가 특정 DFB 영역의 발진 모드의 파장 또는 브래그 파장에 위치시킨 경우에 비하여 두 DFB 영역의 브래그 파장 차이, <TEX>${\Dalta}{\lambda}_{B}$</TEX>, 증가에 따른 두 발진 모드가 받는 이득 차이가 적게 발생하여 최대 SP 주파수가 크고, 변조지수 특성도 좋음을 볼 수 있었다. 또한 능동 영역의 이득이 최대가 되는 파장을 두 DFB 영역의 브래그 파장 중심에 위치시키는 경우가 발진 모드의 파장 중심에 위치시키는 경우에 비하여 더 큰 최대 SP 주파수를 얻을 수 있었고 변조지수 특성도 더 우수함을 볼 수 있었다. The effect of gain dispersion on the self-pulsation (SP) characteristics due to the mode beating of two modes emitted in a multisection DFB laser composed of two complex-coupled DFB sections and a phase control section is investigated. When the peak wavelength, <TEX>${\lambda}_{p}$</TEX>, of the gain spectrum of the DFB section is positioned in the center of the lasing wavelengths or the Bragg wavelengths of the two DFB sections, the maximum SP frequencies are higher and the modulation index has better characteristics compared to those cases for <TEX>${\lambda}_{p}$</TEX> fixed at the lasing wavelength or Bragg wavelength of one DFB section, when the difference between the Bragg wavelengths of the two DFB sections, <TEX>${\Dalta}{\lambda}_{B}$</TEX>, is varied. When <TEX>${\lambda}_{p}$</TEX> is positioned in the renter of the Bragg wavelengths of the two DFB sections, the maximum SP frequency is higher and of the modulation index has better characteristics compared to those of the case for <TEX>${\lambda}_{p}$</TEX> positioned in the center of the lasing wavelengths of the two DFB sections.

결합 링 반사기 레이저 다이오드의 광대역 파장 가변 및 변조 특성 해석

본 논문에서는 기존의 DBR 격자 기반의 파장선택성 반사기를 대체시킬 수 있는 결합 링 반사기가 집적된 레이저 다이오드를 연산자 분리 시 영역 모델을 통해서 분석한다. 결합 링 반사기는 브래그 격자(Bragg grating) 필요로 하지 않는 평판 도파로 형태의 반사기이다. 결합 링 반사기는 하나의 직선 도파로와 두 개의 결합된 형태의 링 공진기가 하나의 직선 도파로에 결합되어 있다. 위상 조절 전류의 조절에 따른 파장 가변 범위는 수십 nm 정도가 되고, 파장 가변 과정에서 부모드 억압비도 35 dB 이상이 됨을 수치 해석을 통해 확인했다. 또한 결합 링 반사기 레이저 다이오드는 종래의 레이저 다이오드에 비해서 유효 공진기 길이(Effective Cavity Length)가 매우 길기 때문에 진폭 변조 시 20-30 GHz 주파수 영역에서 추가적인 공진 특성을 보이고, 이 특성으로 인해 진폭 변조 대역폭이 상당히 향상될 수 있으리라 기대된다. A time-domain modeling approach is used to study characteristics of a widely tunable coupled-ring reflector (CRR) laser diode(LD). The CRR consists of a bus waveguide and two coupled ring resonators coupled to the bus without resorting to distributed Bragg grating structure. The tuning range can be a few tens of nanometers with a side mode suppression ratio exceeding 35dB through the adjustment of currents into the phase control sections in the rings. The CRR laser diode has long effective cavity length compared to conventional laser diodes. Accordingly, a broad additional resonance peak in the amplitude modulation characteristics is observed between 20 to 30 GHz, implying the extension of amplitude modulation bandwidth.

Widely Tunable Grating Cavity Lasers

A widely tunable multi-channel grating cavity laser is proposed and experimentally demonstrated. The device is implemented in Littman configuration with an echelle grating based on Rowland circle construction and realized by monolithically integrating all elements in an InP substrate. Lasing wavelength is selected by turning on an amplifier and the appropriate channel element in the array, and it is tuned by controlling light deflection electrically. The 6-channel device exhibits a tuning range of about 50 nm with a side mode suppression ratio of more than 30 dB. This is accomplished by adjusting the applied current of the dispersive element and phase control section.

매우 넓은 영역의 Self-Pulsation 주파수와 높은 변조 지수를 가자는 다중 영역 복소 결합 DFB 레이저

We analyze the self-pulsation(SP) characteristics due to mode beating of two modes emitted in a multi-section complex-coupled (CC) DFB laser composed of two DFB sections and a phase control section between them. SP frequency due to mode beating of the two modes is determined by the difference of grating periods in the two CC DFB regions. As the difference of grating periods in the two CC DFB regions increases, the SP frequency increases from very low frequency to the THz region. In the case of a mode which is not located in the stop band of the other DFB region, the mode propagates into the other DFB region without a high reflection, so that output powers emitted in a multi-section CC DFB laser have high modulation indexes due to the large interaction between the two modes.

Self-pulsation in multisection laser diodes with a DFB reflector

A novel self-pulsation regime is observed in multisection laser diodes which consist of a loss-coupled distributed-feedback (DFB) section, a phase control section, and gain sections, where 10-GHz self-pulsation due to compound cavity mode beating has been reported with the DFB section operated as a single-mode laser. When the DFB section is below threshold current, the devices give the self-pulsation in a very wide operating range. We attribute the pulsation to passive mode-locking and also confirm that this structure is applicable to 40-GHz operation.

Monolithically integrated tunable external-cavity laser diode using InP-based planar waveguide collimating lens and optical deflector

A lensless tunable external-cavity laser diode monolithically integrated with InP-based planar waveguide parabolic-shaped collimating lens, optical deflector, and echelle grating is proposed and demonstrated in this work. The tunable laser exhibits a total wavelength tuning range of 9.3 nm with a side mode suppression ratio of about 35 dB by adjusting the applied current of optical deflectors and phase control section.

Monolithically integrated grating cavity tunable lasers

A novel grating cavity tunable laser is proposed and experimentally demonstrated. It is realized by monolithically integrating a semiconductor optical amplifier, a dispersive element, a phase-control section, and an etched diffraction grating in a single chip. Tuning operation is based on electrically controlled beam deflection provided by dispersive element and phase matching by phase-control section. With the electrical control, the wavelength tuning of 8.5 nm with a sidemode suppression ratio of about 35 dB has been successfully achieved.

Analysis of self-pulsating three-section DBR lasers

The characteristics of a three-section distributed Bragg reflector laser showing self-pulsation have been analyzed using a large signal time-domain traveling-wave simulator. The device dynamic properties have been investigated in all their complexity and analyzed as functions of the linewidth enhancement factor and of the injected current in the active and in the phase control sections. The simulation results have clearly shown the fundamental role of four wave mixing on the laser characteristics (output power, spectrum, etc.) and have been quantitatively correlated with the few available theoretical and experimental results. The considered self-pulsation operation frequencies around 40 GHz are of interest for practical applications.

Design and Analysis of a Widely Tunable Sampled Grating DFB Laser Diode with High Output Power

A widely tunable SG-DFB (Sampled Grating Distributed Feedback) laser diode is proposed and its feasibility is confirmed through simulation. The new SG-DFB laser diode is composed of a pair of sampled gratings, some parts of which are gain sections and the other parts of which are phase control sections. It is shown that a few tens of nanometers can be tuned through the adjustment of two currents into the phase control sections. Higher output power is expected compared with a SG-DBR laser diode with similar parameters. The dynamic single mode operation is also observed in the time-domain simulation.

Design and Analysis of Widely Tunable Sampled Grating DFB Laser Diode Integrated With Sampled Grating Distributed Bragg Reflector

A new widely tunable laser diode structure that requires only two tuning currents is proposed. The laser diode consists of a sampled grating distributed feedback (SGDFB) laser diode monolithically integrated with a sampled grating distributed Bragg reflector (SGDBR). The phase control sections are properly inserted between the grating bursts of the SGDBR and SGDFB sections for the discrete and continuous tuning. To confirm the feasibility of the new structure, the split-step time domain model is used. The simulation result for a particular design shows that the tuning range as wide as 27 nm is possible with side-mode suppression ratio exceeding 35 dB. Furthermore, the output power is larger than that from SGDBR laser diodes with similar parameters.